U.S. patent application number 15/965288 was filed with the patent office on 2019-05-23 for concurrent scan of multiple pixels in a lidar system equipped with a polygon mirror.
The applicant listed for this patent is LUMINAR TECHNOLOGIES, INC.. Invention is credited to Scott R. Campbell, Jason M. Eichenholz, Lane A. Martin, Matthew D. Weed.
Application Number | 20190154802 15/965288 |
Document ID | / |
Family ID | 66532279 |
Filed Date | 2019-05-23 |
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United States Patent
Application |
20190154802 |
Kind Code |
A1 |
Campbell; Scott R. ; et
al. |
May 23, 2019 |
CONCURRENT SCAN OF MULTIPLE PIXELS IN A LIDAR SYSTEM EQUIPPED WITH
A POLYGON MIRROR
Abstract
A lidar system includes one or more light sources configured to
generate a first and second beams of light, a scanner configured to
synchronously scan a field of regard of the lidar system using the
two beams, and a receiver configured to detect light of the two
beams scattered by one or more remote targets. The scanner includes
a rotatable polygon mirror having a block having a first wall, a
second wall, and reflective surfaces extending between the first
and second walls, the reflective surfaces being angularly offset
from one another along a periphery of the block; a polygon mirror
axle extending into the block, about which the block rotates;
optical elements configured to direct the first and second beams of
light respectively to two adjacent reflective surfaces of the
rotatable polygon mirror; and a second mirror pivotable along an
axis orthogonal to the polygon mirror axle.
Inventors: |
Campbell; Scott R.;
(Sanford, FL) ; Eichenholz; Jason M.; (Orlando,
FL) ; Weed; Matthew D.; (Winter Park, FL) ;
Martin; Lane A.; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LUMINAR TECHNOLOGIES, INC. |
Orlando |
FL |
US |
|
|
Family ID: |
66532279 |
Appl. No.: |
15/965288 |
Filed: |
April 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62590235 |
Nov 22, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 5/09 20130101; G01S
17/42 20130101; H01L 27/14694 20130101; G01S 17/89 20130101; G02B
26/105 20130101; G02B 26/123 20130101; G01S 7/4817 20130101; G02B
27/30 20130101; H01L 27/14643 20130101; G01S 17/08 20130101; G02B
26/101 20130101; G01S 7/4813 20130101; G02B 5/1857 20130101; G02B
26/125 20130101; G01S 17/87 20130101; G01S 17/931 20200101; G02B
27/0955 20130101; G02B 7/1821 20130101; G02B 5/22 20130101; H01L
27/14647 20130101; G02B 27/1086 20130101; H01L 25/167 20130101;
G02B 5/0841 20130101; G02B 27/0977 20130101 |
International
Class: |
G01S 7/481 20060101
G01S007/481; G02B 26/10 20060101 G02B026/10 |
Claims
1. A lidar system comprising: one or more light sources configured
to generate a first beam of light and a second beam of light; a
scanner configured to synchronously scan a field of regard of the
lidar system using the first beam of light and the second beam of
light, the scanner including: a rotatable polygon mirror having a
block having a first wall, a second wall, and a plurality of
reflective surfaces extending between the first and second walls,
the reflective surfaces being angularly offset from one another
along a periphery of the block, a polygon mirror axle extending
into the block through at least one of the first and second walls,
about which the block rotates, a plurality of optical elements
configured to direct the first and second beams of light
respectively to two adjacent reflective surfaces of the rotatable
polygon mirror, and a second mirror pivotable along an axis
orthogonal to the polygon mirror axle, wherein the first and second
beams of light are incident on the second mirror; and a receiver
configured to detect the first beam of light and the second beam of
light scattered by one or more remote targets.
2. The lidar system of claim 1, wherein each optical element
comprises a fiber-optic cable, a fiber-optic collimator, a lens, or
a mirror.
3. The lidar system of claim 1, wherein each optical element
comprises: a fiber-optic cable to convey light from the light
source to the scanner, a collimator or lens at a terminal end of
the fiber-optic cable to produce a collimated free-space output
beam directed at the polygon mirror.
4. The lidar system of claim 1, wherein: the first beam of light
and the second beam of light are scanned by the scanner to define a
first field of regard and a second field of regard, respectively,
the first field of regard and the second field of regard in
combination define the field of regard of the lidar system, and the
first field of regard and the second field of regard partially
overlap to define an overlap region within the field of regard of
the lidar system.
5. The lidar system of claim 4, wherein a width of the overlap
region is less than or equal to one-third of a width of the first
or second field of regard.
6. The lidar system of claim 4, wherein a width of the overlap
region is between 20 and 40 degrees.
7. The lidar system of claim 4, wherein each of the first beam of
light and the second beam of light scans the respective field of
regard according to a scan pattern that defines horizontal or
vertical scan lines, and wherein the scan lines of the first field
of regard are offset relative to the scan lines of the second field
of regard by approximately one half of a scan line to yield double
pixel density within the overlap region.
8. The lidar system of claim 4, wherein the overlap region is
oriented in a direction of travel of a vehicle on which the lidar
system is deployed.
9. The lidar system of claim 1, wherein each of the first beam of
light and the second beam of light are scanned by the scanner to
define a respective field of regard approximately 60 degrees
wide.
10. The lidar system of claim 1, further comprising: one or more
power splitters to split each of the first beam of light and the
second beam of light into a pair of beams; four fiber-optic cables
to separately convey each of the split beams to the scanner,
wherein the scanner mechanically aims each of the split beams to
produce angular separation between the split beams of the first
beam of light and the split beams of the second beam of light;
wherein the receiver includes: a first pair of detectors for the
pair of angularly offset beams corresponding to the first beam of
light, and a second pair of detectors for the pair of angularly
offset beams corresponding to the second beam of light.
11. The lidar system of claim 10, wherein: each detector defines a
respective pixel within a scan pattern, and each of the first pair
of detectors and the second pair of detectors defines an even pixel
and an odd pixel separated by N detector field-of-view (FOV) areas
to reduce cross-talk, wherein N is larger than two.
12. The lidar system of claim 10, wherein: each detector defines a
respective pixel within a scan pattern, and each of the first pair
of detectors and the second pair of detectors define non-integer
separation between pixels in a corresponding row or column.
13. The lidar system of claim 10, wherein the splitters include at
least one of (i) a diffractive optical element, (ii) a fiber-optic
power splitter, or (iii) a free-space power splitter.
14. The lidar system of claim 1, wherein: a first input beam
includes light of the first beam of light scattered by one or more
remote targets, a second input beam includes light of the second
beam of light scattered by one or more remote targets, and the
rotatable polygon mirror and the second mirror reflect each of the
first input beam and the second input beam to direct the first
input beam and the second input beam toward respective detectors of
the receiver.
15. The lidar system of claim 14, wherein for each detector of the
receiver and a corresponding outbound beam of light associated with
a respective light source: an instantaneous field of view (FOV) of
the light source is at least partially outside and ahead of a FOV
of the detector along a scan direction, at a time when a light
pulse associated with the outbound beam is emitted, and the FOV of
the detectors is coincident with or overlaps the instantaneous FOV
of the light source after a time T during which the light pulse
traverses a maximum distance D and returns to the detector, after
being scattered by one or more targets.
16. A method in a lidar system for scanning a field of regard, the
method comprising: directing, within a single ranging event, a
first pulse of light at a first reflective surface of a polygon
mirror and a second pulse of light at a second reflective surface
of the polygon mirror, wherein the polygon mirror rotates about a
polygon mirror axis; directing, with the polygon mirror within the
single ranging event, the first pulse of light and the second pulse
of light to respective locations on a reflective surface of a
second mirror that pivots along an axis orthogonal to the polygon
mirror axis; directing, with the second mirror, the first pulse of
light and the second pulse of light along a scan direction to
illuminate a first instantaneous light-source field of view (FOV)
corresponding to a first pixel and a second instantaneous
light-source FOV corresponding to a second pixel, respectively;
detecting, within a single ranging event, the first beam of light
scattered by one or more remote targets using a first detector and
the second beam of light scattered by the one or more remote
targets using a second detector, to generate values for the first
pixel and the second pixel.
17. The method of claim 16, wherein the first pulse of light is
associated with a first beam and the second pulse of light is
associated with a second beam, the method further comprising:
scanning, using the polygon mirror and the second mirror, the first
beam and the second beam to define a first field of regard and a
second field of regard, respectively, wherein the first field of
regard and the second field of regard in combination define the
field of regard of the lidar system, and wherein the first field of
regard and the second field of regard partially overlap to define
an overlap region within the field of regard of the lidar
system.
18. The method of claim 17, wherein a width of the overlap region
is less than or equal to one-third of a width of the first or
second field of regard.
19. The method of claim 17, further comprising scanning the first
beam and the second beam across the respective field of regard
according to a scan pattern that defines horizontal or vertical
scan lines, wherein the scan lines of the first field of regard are
offset relative to the scan lines of the second field of regard by
approximately one half of a scan line to yield double pixel density
within the overlap region.
20. The method of claim 16, further comprising splitting each of
the first pulse of light and the second pulse of light into a
respective pair of angularly separated pulses corresponding to two
different pixels within a same scan line.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to provisional U.S.
application Ser. No. 62/590,235, filed on Nov. 22, 2017, titled
"Low Profile Lidar Scanner with Polygon Mirror," the entire
disclosure of which is hereby expressly incorporated by reference
herein.
FIELD OF TECHNOLOGY
[0002] This disclosure relates generally to lidar sensor heads and,
more specifically, to multi-mirror lidar sensor heads having a
compact construction so as to occupy minimal area when deployed on
a vehicle.
BACKGROUND
[0003] The background description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent it is described in
this background section, as well as aspects of the description that
may not otherwise qualify as prior art at the time of filing, are
neither expressly nor impliedly admitted as prior art against the
present disclosure.
[0004] Light detection and ranging (lidar) is a technology that can
be used to measure distances to remote targets. Typically, a lidar
system includes a light source and an optical receiver. The light
source can be, for example, a laser which emits light having a
particular operating wavelength. The operating wavelength of a
lidar system may lie, for example, in the infrared, visible, or
ultraviolet portions of the electromagnetic spectrum. The light
source emits light toward a target which then scatters the light.
Some of the scattered light is received back at the receiver. The
system determines the distance to the target based on one or more
characteristics associated with the returned light. For example,
the system may determine the distance to the target based on the
time of flight of a returned light pulse.
[0005] While the precision and efficacy of lidar scanners have
continually improved, the power requirements, heat dissipation, and
physical dimensions of existing lidar scanners have posed obstacles
to designers of lidar systems. With the increasing prevalence of
the use of lidar systems in vehicles, such considerations are of
increased concern to designers of lidar systems.
SUMMARY
[0006] A lidar system including a light emitting light source
(i.e., a laser), a scanner configured to direct the embedded light
to scan a field of regard (FOR) of the lidar system in accordance
with a scan pattern, a receiver that detects light scattered by one
or more remote targets, and a controller to control one or more
mirrors of the scanner, is provided. The scanner includes both a
polygon mirror and a planar mirror. The polygon mirror may be in
the form of a rotatable block having a first wall, a second wall
spaced away from and parallel to the first wall, and a plurality of
reflective surfaces extending between the first and second walls,
the reflective surfaces being angularly offset from one another
along a periphery of the block. The planar mirror rotates about an
axis orthogonal to an axis of rotation of the polygon mirror, and
is thereby considered a pivotable oscillating planar mirror. At
least the scanner and the receiver may be disposed inside a housing
of a lidar sensor unit (or "sensor head"), and the lidar system can
include one or several lidar sensor units.
[0007] The polygon mirror may also be provided with a motor to
power its rotation that is disposed at least partially, but
preferably substantially or entirely, within the rotatable block.
By arranging the motor for the polygon mirror within the rotatable
block of the polygon mirror, the overall three dimensional
footprint of the scanner can be further reduced.
[0008] The polygon mirror may be provided with one or more tabs
that pass through a stationary photo-interrupter as the polygon
mirror rotates. The photo-interrupter provides feedback data
indicative of the rotational speed of the polygon mirror, which
feedback data can then be processed by a controller associated with
the motor of the polygon mirror to regulate, stabilize, or adjust
the rotational speed of the polygon mirror as needed.
[0009] The scanner of the lidar sensor unit is provided with a low
profile when compared to conventional multi-mirror lidar systems.
Certain structural and operational features of the lidar sensor
units of the present disclosure may be employed, individually or
collectively, to not only minimize the three-dimensional footprint
or volume of space occupied by the lidar scanner, but also serve to
improve aerodynamic performance (both internally and externally),
reduce audible noise, reduce heat, and improve resistance to
vibration, acceleration, deceleration, or other environmental
factors that might otherwise negatively affect scanner accuracy and
performance.
[0010] The orientation of the scanner, and specifically, the
orientation of the axis of rotation of the polygon mirror, may be
selected so as to align with an orientation of a vehicle in which
the lidar sensor unit operates. In some implementations, however, a
lidar system operating in a vehicle includes multiple lidar sensor
units, with at least some of the lidar sensor units oriented
differently from each other.
[0011] The planar mirror of the scanner may be provided with an
optimized geometry to enhance durability and service life. For
instance, the planar mirror may have a center of gravity closer to
its reflective surface than conventional planar mirrors of lidar
scanners. This may be effected by constructing a pivotable backing
or support surface for the reflective surface of the planar mirror
of a honeycomb structure or other ribbed structure, with material
arranged such that the center of gravity of the planar mirror is
closer to the reflective surface than to an edge of the ribbed or
honeycomb structure opposite the reflective surface.
[0012] The speed of oscillation of the planar mirror may be
controlled so as to dynamically vary distances between scan lines.
In general, a scan line can have a horizontal orientation, vertical
orientation, or any other suitable orientation. In at least some of
the embodiments discussed herein, each scan line corresponds to a
reflection of the emitted light from one of the reflective surfaces
of the rotating polygon mirror. The distances between scan lines
can vary on a frame-by-frame basis, and can vary in different
portions of the field of regard. A drive signal of a motor driving
the speed of oscillation of the planar mirror can be shaped as a
Gaussian to optimally space scan lines apart. For example, the
Y-scan mirror can be driven with a Gaussian-type function so that
the mirror has a relatively high scan speed at the ends of its
motion and a relatively low scan speed near the middle of its
motion. This type of Gaussian scan produces a higher density of
scan lines near the middle region of the FOR and a lower density of
scan lines at the upper and lower ends of the FOR.
[0013] The width of the planar mirror can determine the horizontal
scan range, also referred to below as the horizontal dimension of
the field of regard (FOR.sub.H). For a given polygon mirror,
FOR.sub.H can be increased by selecting a wider planar mirror. The
lidar sensor unit can support modular optical assembly, so that
planar mirrors of different widths can be compatible with the same
remaining opto-mechanics of the lidar sensor unit. Thus, by
providing an oscillating planar mirror of a significantly greater
width than the reflective surfaces of the rotating polygon mirror,
not only can the oscillating planar mirror achieve desired field of
regard along the vertical dimension (FOR.sub.V), but the
oscillating planar mirror, in concert with the polygon mirror, can
also advantageously increase the FOR.sub.H, all while reducing the
overall three dimensional footprint of the lidar sensor unit.
[0014] The planar mirror preferably has a range of motion that
exceeds the vertical dimension of the FOR. For instance, if the FOR
is 30.degree. vertically by 120.degree. horizontally, the range of
motion for the planar mirror (which, for the sake of convenience,
is also referred to herein as a Y-scan mirror) can be 60.degree.
vertically, to accommodate a 30.degree. vertical component of the
FOR in various ranges. This enables a lidar sensor head to scan a
greater range of vertical area, such as when a vehicle on which the
lidar sensor is mounted approaches an incline.
[0015] As explained in more detail in the following detailed
description, the polygon mirror, at any given time during its
rotation, includes at least two active, adjacent reflective
surfaces. This enables the lidar sensor unit to direct pulses
toward different sections of a scan line so as to process at least
two distinct return pulses within the time of a single ranging
event. The outbound pulses can scatter from the same remote target
or different remote targets. Using two beams of light with two
facets of the polygon mirror thus increases the FOR.sub.H of the
lidar sensor unit without increasing the time it takes to scan one
line.
[0016] The adjacent reflective surfaces direct the output beams
toward different portions of the planar mirror. Thus, the lidar
sensor unit can have two active "eyes" that share both the polygon
mirror and the planar mirror, thereby providing both a cost
reduction and a size reduction. The beams are incident on the
respective surfaces in such a manner that provides a large angular
separation between the outbound beams, so as to reduce the
probability of cross-talk detection. In one example, two beams can
be offset along the x-axis by half a pixel to produce two times the
pixel density in the overlap region (e.g., for a pair of adjacent
pixels generated using one beam, another pixel centered at the
midpoint between the pair of pixels can be generated using the
other beam). In another example, two beams can be offset along the
y-axis by half a line to produce two times the pixel density in the
overlap region (e.g., for a pair of adjacent scan lines generated
using one beam, another scan line centered between the pair of
adjacent scan lines can be generated using the other beam). The
first approach involves offsetting the pixels along the x-axis so
that, in the overlap region, the pixels from one beam are
interleaved along the x-axis with pixels from the other beam. The
second approach involves offsetting the scan lines along the y-axis
so that the scan lines are interleaved in the overlap region. These
two approaches (interleaving pixels and interleaving scan lines)
are independent of each other and can be implemented separately or
together.
[0017] By having two adjacent active surfaces, and at least two
inactive surfaces of the rotating polygon mirror at any one time, a
baffle or shroud can be provided around the inactive surfaces so as
to further reduce aerodynamic drag and aid in air circulation of
the polygon mirror. The use of such a baffle or shroud is not
possible with a 360.degree. scanner, as such a shroud would block
active reflective surfaces of the mirror.
[0018] Input and output beams can be incident on the same mirror
operating in a lidar scanner, or the same multi-mirror assembly
including a mirror to generate scan lines (e.g., a polygon mirror)
and another mirror to distribute these scan lines along the other
dimension (e.g., a planar mirror). The fields of view (FOVs) of the
beams can be arranged to minimize the overall surface area. In
another aspect of the present disclosure, the fields of view of two
output beams define relatively small circles, whereas the field of
view of the input beams defines a relatively large circle. The
smaller circles are arranged adjacent to the larger circle, with
little or no overlap, and with the imaginary line segment
connecting the centers of the smaller circles displaced relative to
the diameter of the larger circle. This more compact arrangement
facilitates minimization of the overall three dimensional footprint
of the scanner.
[0019] The lidar scanner of the present disclosure preferably
employs a single lens with off-axis illumination for two detectors,
which are placed in the same optical path. The displacement of the
transit beam relative to the center of the lens allows the
detectors to be placed adjacent one another and off-center, thereby
further facilitating a minimized overall profile. The detector
diameter is approximately 50-150 microns, and the detector
separation distance is approximately 0.5-2 mm.
[0020] The use of off-axis illumination eliminates the need to use
an overlap mirror with a center hole, which sometimes is referred
to as a "doughnut mirror." In particular, the beams are coupled
into the scanner by the side of an overlap mirror that reflects
input light to the detector. The output beam(s) and the input
beam(s) thus are not entirely coaxial, as discussed in more detail
below. The output beam(s) and the input beam(s) are offset relative
to each other spatially and angularly. In other implementations,
however, a doughnut mirror can be used with the polygon mirror and
the planar mirror of this disclosure.
[0021] Methods of manufacture of a suitable polygon mirror are also
disclosed herein. To obtain optimal balance of the polygon mirror,
and ensure the field of regard is accurately scanned, high-energy
laser pulses are used to remove matter at precise locations of the
rotating polygon mirror. This can be combined with initial drilling
for coarse balancing (so as to achieve both coarse and fine
balancing). More particularly, a coarse balancing procedure using a
drill or another suitable equipment can be used to form a
relatively well-balanced block, and the surfaces can be made
reflective (as explained in greater detail below). The block then
can be mated to a motor in an assembly to be used in a scanner
(rather than using an assembly specifically set up for
manufacturing or testing). Once mated to the motor, the block can
be rotated, and high-energy laser pulses can remove excess material
from the block to achieve a high degree of balancing.
[0022] The polygon mirror is preferably manufactured by surface
replication. In embodiments where the polygon mirror includes an
even number of facets, pairs of opposite facets may be serviced
simultaneously. While a four-sided polygon mirror will be disclosed
as the preferred embodiment, the specification will explain that
other numbers of sides are possible, with the understanding that
the more facets of the polygon mirror, the closer the overall
polygon mirror resembles a circle.
[0023] The lidar scanner can be implemented in a manner that
directs two angularly separated pulses toward different sections of
the scan line and processes the return pulses within the time of a
single ranging event, where the two pulses reflect from the same
reflective surface of the polygon mirror. Thus, according to some
implementations, a single sensor head includes a total of four
beams and four detectors: each pair of beams includes two angularly
separated beams that reflect from the same surface of the polygon
mirror. The lidar system can process return pulses corresponding to
a non-integer separation in pixels (for example, an angular
separation corresponding to 51/2 or 111/2 pixels). In this manner,
the system can superimpose the return values to more accurately
determine the values of pixels 1, 2, 3, . . . , N of the scan line.
Otherwise, the lidar system receives duplicate readings for many of
the pixels. Additionally, separating the two beams by a significant
number of pixels (e.g., approximately 9-13 pixels rather than 3-5
pixels) mitigates problems with defocusing of the beam received at
the detectors. The separation distance between the detectors (e.g.,
0.8-1.2 mm) corresponds to the angular separation of the beams
(e.g., 2-3 degrees). Since the two detectors are separated by a
certain distance, if the beams become defocused, there will not be
a problem with cross-talk where light from one beam spills over to
the other detector.
[0024] Alternately, the beams are interleaved/offset by 1/2-pixel
so that one beam provides information about pixels 1, 2, 3, etc.,
and the other beam provides information about pixels 11/2, 21/2,
31/2, etc. Since the pixels can be numbered in any fashion, this
can also be expressed as the beams being offset by 1 pixel (e.g.,
one beam samples the odd pixels and the other beam samples the even
pixels), where adjacent pixels may have some amount of overlap.
[0025] In some implementations, diffractive optical elements (DOEs)
can be used to produce angularly separated beams. In other
implementations, however, the lidar system uses fiber-optic power
splitters and mechanical positioning/aiming to produce the
angularly separated beams. For example, the output from the light
source is split four ways (e.g., with a 4.times.1 power splitter,
or with 3 2.times.1 power splitters) into four fiber-optic cables.
Then, each of the four fiber-optic cables is terminated by a
collimator (essentially, a lens that is rigidly coupled to the end
of a fiber) to form a collimated free-space output beam. For each
"eye" of the sensor head, two collimators can be positioned and
aimed to form two angularly offset output beams (e.g., with a
2-degree angle between the beams). These two beams are directed so
that together they reflect off of one face at a time of the
rotating polygon mirror.
[0026] Further, the splitters can also be fiber-optic power
splitters or free-space power splitters. The fiber-optic power
splitters can be considered to be part of the light source or part
of the optical elements.
[0027] The low-profile lidar scanner head can be provided as a
box-like protrusion on each corner of the roof of a vehicle,
preferably at 45.degree. relative to each of the edges. In a
particularly preferred embodiment, the lidar scanner head may be
partially embedded in the vehicle roof or other vehicle body part
so only a window of the unit protrudes prominently from the roof
(or hood, side mirror, rear-view mirror, windshield, bumper, grill,
or other body part surface in which the lidar scanner head is
disposed).
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a front perspective view of a lidar sensor unit of
the present disclosure;
[0029] FIG. 2 is a top, front perspective view of the lidar sensor
unit of FIG. 1;
[0030] FIG. 3 is a front perspective view of the lidar sensor unit
of FIG. 1, with the housing removed for clarity;
[0031] FIG. 4 is a right, rear perspective view of the lidar sensor
unit of FIG. 1;
[0032] FIG. 5 is a right, front perspective view of the lidar
sensor unit of FIG. 1;
[0033] FIG. 6 is a right, front perspective view of a polygon
mirror and motor assembly of the lidar sensor unit of FIG. 1;
[0034] FIG. 7 is a rear perspective view of the polygon mirror and
motor assembly of the lidar sensor unit of FIG. 1;
[0035] FIG. 8 is a left rear perspective view of the polygon mirror
and motor assembly of the lidar sensor unit of FIG. 1;
[0036] FIG. 9 is a rear perspective view of the polygon mirror and
motor assembly of the lidar sensor unit of FIG. 1;
[0037] FIG. 10 is a top perspective view of a polygon mirror of the
lidar sensor unit of FIG. 1;
[0038] FIG. 11 is a rear, top perspective view of the polygon
mirror of the lidar sensor unit of FIG. 1;
[0039] FIG. 12 is a right, rear perspective view of the polygon
mirror of the lidar sensor unit of FIG. 1;
[0040] FIG. 13 is a rear elevation view of the polygon mirror of
the lidar sensor unit of FIG. 1;
[0041] FIG. 14 is a front elevation view of the polygon mirror of
the lidar sensor unit of FIG. 1;
[0042] FIG. 15 is a front perspective view of the planar mirror and
motor assembly of the lidar sensor unit of FIG. 1;
[0043] FIG. 16 is a front, right perspective view of the planar
mirror and motor assembly of the lidar sensor unit of FIG. 1;
[0044] FIG. 17 is a left, front perspective view of just the
polygon mirror and the planar mirror of the lidar sensor unit of
FIG. 1;
[0045] FIG. 18 is a left elevation view of just the polygon mirror
and the planar mirror of the lidar sensor unit of FIG. 1;
[0046] FIG. 19 is a front perspective view of just the polygon
mirror and the planar mirror of the lidar sensor unit of FIG.
1;
[0047] FIG. 20 is a rear perspective view of just the polygon
mirror and the planar mirror of the lidar sensor unit of FIG.
1;
[0048] FIG. 21 is a perspective view of the optical base of the
lidar sensor unit of FIG. 1, enclosing a lens and a receiver;
[0049] FIG. 22 is a perspective view of several components of the
lidar sensor unit of FIG. 1 in an example implementation that
includes an overlap "doughnut mirror," along with a schematic
representation of example paths of beams;
[0050] FIG. 23 is a perspective view of several components of the
lidar sensor unit of FIG. 1 in an example implementation free of an
overlap doughnut mirror;
[0051] FIG. 24 is a perspective view of a path of an input beam
relative to the polygon mirror and the planar mirror of the lidar
sensor unit of FIG. 1;
[0052] FIG. 25 is a perspective view of paths of an input beam and
output beams relative to the polygon mirror and the planar mirror
of the lidar sensor unit of FIG. 1;
[0053] FIG. 26A is a block diagram of an example lidar system in
which the lidar sensor unit of FIG. 1 can operate in a single-eye
configuration;
[0054] FIG. 26B is a block diagram of an example lidar system in
which the lidar sensor unit of FIG. 1 can operate in a two-eye
configuration;
[0055] FIG. 27 illustrates an example InGaAs avalanche photodiode
which can operate in the lidar system of FIG. 26A or FIG. 26B;
[0056] FIG. 28 illustrates an example photodiode coupled to a
pulse-detection circuit, which can operate in the lidar system of
FIG. 26A or 26B;
[0057] FIG. 29 is a perspective view of a housing of a lidar sensor
unit, such as the lidar sensor of FIG. 1, protruding from a surface
of a vehicle;
[0058] FIG. 30 is perspective view of several components of the
lidar system of FIG. 26A or 26B, disposed on a vehicle so that the
axis of rotation of the polygon mirror aligns with an orientation
of the vehicle;
[0059] FIG. 31 is a perspective view of a roof of a vehicle, on
which four sensor head unit are arranged at respective corners;
[0060] FIG. 32 illustrates an example vehicle in which one
implementation of the lidar system of FIG. 26a or 26B can
operate;
[0061] FIG. 33 illustrates an example vehicle in which another
implementation of the lidar system of FIG. 26a or 26B can
operate;
[0062] FIG. 34 is a flow diagram of an example method for
manufacturing a highly balanced rotatable polygon mirror that can
be used in the lidar sensor unit of FIG. 1;
[0063] FIG. 35 schematically illustrates fields of view (FOVs) of a
light source and a detector that can operate in the lidar sensor
unit of FIG. 1;
[0064] FIG. 36 schematically illustrates the operational vertical
field of regard FOR.sub.V of the lidar sensor unit of FIG. 1
relative to the available FOR.sub.V-AVAIL of the lidar sensor unit,
within which the operational FOR.sub.V can be adjusted;
[0065] FIG. 37 schematically illustrates non-equal distribution of
scan lines within a vertical field of regard FOR.sub.V of the lidar
sensor unit of FIG. 1, in a certain operational mode of the lidar
sensor unit;
[0066] FIG. 38 is a flow diagram of an example method for
repositioning the vertical field of regard FOR.sub.V within the
available FOR.sub.V-AVAIL by adjusting the oscillation of the
planar mirror of the lidar sensor unit of FIG. 1;
[0067] FIGS. 39A and 39B schematically illustrate adjusting the
vertical field of regard FOR.sub.V based on detected changes in the
grade of the road, which can be implemented in the lidar sensor
unit of FIG. 1;
[0068] FIG. 40 is a diagram of an example detector array with two
detectors configured to detect return pulses associated with
different respective output beams, which can be implemented in the
lidar system of FIG. 26A or 26B;
[0069] FIG. 41 illustrates an example forward scan of a pair of
spaced-apart pixels based on the detector array of FIG. 40;
[0070] FIG. 42 illustrates an example interleave of scan lines in
an overlap region, which the lidar system of FIG. 26A or 26B can
generate;
[0071] FIG. 43 illustrates an example scan using output beams with
non-integer pixel separation, which the lidar system of FIG. 26A or
26B can generate; and
[0072] FIG. 44 is a flow diagram of an example method for
generating pixel values using output beams with non-integer pixel
separation.
DETAILED DESCRIPTION
[0073] A lidar sensor unit and various techniques for operating the
lidar sensor unit are discussed below, in particular: (i) an
example assembly of a lidar sensor unit, and particularly a scanner
of the lidar sensor unit, is discussed with reference to FIGS.
1-21; (ii) propagation of light through the lidar sensor unit in
example scenarios is considered in connection with FIGS. 22-25;
(iii) example operation of the lidar sensor unit as part of a lidar
system is considered with respect to the block diagrams of FIGS.
26A-28; (iv) example placement of a lidar sensor unit on a body of
a vehicle is discussed with reference to FIGS. 29-33; (v) an
example method of manufacturing a polygon mirror for use in the
lidar sensor unit is discussed with reference to FIG. 34; (vi)
example modifications to the scan pattern of the lidar sensor unit
are discussed with reference to FIGS. 35-39B; and (vii) example
generating of pixels is considered in connection with FIGS.
40-44.
I. Lidar Sensor Unit Equipped with a Scanner having a Planar and
Polygon Mirrors
[0074] Referring to FIGS. 1-5, a lidar sensor unit 10 of the
present disclosure includes a scanner 11 with a rotatable polygon
mirror 12 and a pivotable planar mirror 14 that cooperates with the
rotatable polygon mirror 12 to perform a scan of a field of regard
(FOR) of the lidar sensor unit 10. The pivotable planar mirror 14
may be referred to herein as a Y-scan mirror, but it is understood
that depending on the orientation of the rotatable polygon mirror
12 and the pivotable planar mirror 14, the scanning range achieved
by the pivotable mirror 14 may be in any of the X- Y- or Z-planes.
The rotatable polygon mirror 12 includes a block 16 having a
plurality of (preferably at least four) finished reflective
surfaces 18, 20, 22, 24. It is possible, however, to a use a
triangle-shaped rotatable polygon mirror with three reflective
surfaces. In another implementation, not every surface of the
rotatable polygon mirror oriented toward the planar mirror 14 is
reflective (e.g., the rotatable polygon mirror can be a flat
substrate with reflective surfaces on the front and back sides).
More generally, the rotatable polygon mirror 12 may have any
suitable number of reflective surfaces, such as for example 2, 3,
4, 5, 6, 7, or 8 reflective surfaces. The polygon mirror 12 may be
made from any suitable material, such as for example, glass,
plastic (e.g., polycarbonate), metal (e.g., aluminum or beryllium),
metal foam, carbon fiber, ceramic, or any suitable combination
thereof.
[0075] The rotatable polygon mirror 12 further includes a first
wall 26 and a second wall 28. Each of the plurality of reflective
surfaces 18, 20, 22, 24 extends between the first and second walls
26, 28. The reflective surfaces 18-24 are angularly offset from one
another along a periphery of the block 16.
[0076] Generally speaking, as the polygon mirror 12 rotates, the
scanner 11 produces one scan line for each reflective surface of
the polygon mirror 12, and the planar mirror 14 pivots to
distribute the scan lines across the FOR. Thus, if the scan lines
are directed horizontally, the polygon mirror 12 is responsible
primarily for the horizontal dimension of the field of regard
(FOR.sub.H), and the planar mirror 14 accordingly is responsible
for vertical dimension of the field of regard (FOR.sub.V).
[0077] Adjacent reflective surfaces 18-24 of the block are
preferably joined to one another along a drag-reducing, non-sharp
edge to promote aerodynamic efficiency and reduce audible noise. As
an example, the block may include rounded or chamfered edges or
corners. As another example, the block may include edges with
texturing, grooves, riblets, or a sawtooth pattern.
[0078] As best illustrated in FIGS. 6-9, the rotatable polygon
mirror 12 is mounted in a bracket or mount 29 on a polygon mirror
axle 30, which polygon mirror axle 30 extends through at least one
of the first and second walls 26, 28. A motor 32 drives the polygon
mirror axle 30, thereby imparting rotational oscillation to the
rotatable polygon mirror 12. The motor 32 may be a synchronous
brushless DC motor in driving relationship with the axle 30 and may
be external to the block 16. Alternately, the block 16 may
accommodate an internal motor, or enable a motor 32 to be at least
partially embedded within the block 16, such as where a rotor of
the motor 32 is disposed within the block 16, reducing the overall
size of the lidar sensor unit 10. The motor 32 may drive rotation
of the rotatable polygon mirror 12 in an open-loop or closed-loop
fashion. In general, the motor 32 can be any actuator or mechanism
suitable for rotating the polygon mirror 12.
[0079] The rotatable polygon mirror 12 may additionally employ an
optical beam, the presence or absence of which is detectable by a
stationary photo-interrupter, to collect data indicative of the
rotational speed of the rotatable polygon mirror 12. One or more
tabs may be provided on the axis of rotation of the polygon mirror
12 or an interior surface of the block 16, which tab(s) pass
through the stationary photo-interrupter during rotation of the
polygon mirror 12. Upon receiving from the photo-interrupter
feedback data indicative of the rotational speed of the polygon
mirror 12, the feedback data can then be processed by a controller
associated with the motor 32 of the polygon mirror 12 to make any
necessary adjustments to the rotational speed of the polygon mirror
12, for example. The controller may regulate or stabilize the
rotational speed of the polygon mirror 12 so that the rotational
speed is substantially constant. For example, the polygon mirror 12
may be rotated at a rotational speed of approximately 150 Hz (150
revolutions per second), and the rotational speed may be stabilized
so that it varies by less than or equal to 1% (e.g., 150 Hz .+-.1.5
Hz), 0.1%, 0.05%, 0.01%, or 0.005%.
[0080] The planar mirror 14 is pivotally mounted along a planar
support shaft 34 that extends orthogonal to the polygon mirror axle
30. The planar mirror 14 preferably has a body 50 defined by a
plurality of rib-like members 52 that form a honeycomb-like
structure, supporting a finished planar reflective surface 54 (see
FIG. 20). The center of gravity of the planar mirror 14 is closer
to the reflective surface 54 than to an edge of the ribbed or
honeycomb body 50 opposite the reflective surface 54. The planar
mirror 14 may be made from any suitable material, such as for
example, metal (e.g., aluminum), ceramic polymer, or carbon
fiber.
[0081] The reflective surface 54 of the planar mirror 14 preferably
has a width that is greater than a width of each of the reflective
surfaces 18-24 of the rotatable polygon mirror 12, measured along a
common axis. In the embodiment illustrated in FIGS. 1-25, the width
of the planar mirror 14 is measured in the horizontal dimension,
i.e., along a scan line (see FIG. 19). The width of each surface of
the polygon mirror 12 can be measured along an axis that is
parallel to the pivot axis of the planar mirror 14 in a certain
orientation of the polygon mirror 12. The width of the planar
mirror 14 effectively determines the horizontal range, i.e.,
FOR.sub.H.
[0082] For the same polygon mirror 12, the FOR.sub.H of the sensor
unit 10 can be increased by selecting a wider planar mirror. For
example, the planar mirror of width 5.3 inches can provide a
FOR.sub.H of about 100 degrees. As a more specific example, the
lidar sensor unit 10 can have two eyes, each with an FOR.sub.H of
52 degrees, and a two-degree overlap between the eyes. The planar
mirror of width 8.1 inches can provide a FOR.sub.H of about 130
degrees. The possibility of increasing the FOR.sub.H of the lidar
sensor unit 10 by selecting a planar mirror of a different width
for the same polygon mirror provides for a modular optical
design.
[0083] As illustrated in FIG. 14, the first wall 26 of rotatable
polygon mirror 12 has a major diameter D1 that extends from the
corner of two adjacent finished reflective surfaces 18, 20 to a
corner of two opposite finished reflective surfaces 22, 24, and a
minor diameter D2 that extends from a center of one of the finished
reflective surfaces 18 to a center of an opposite one of the
finished reflective surfaces 22. A limiting factor in optimizing
the minimal height and width of the lidar sensor unit 10 is the
necessary spacing between the finished reflective surfaces 18-24 of
the rotatable polygon mirror 12 and the planar mirror 14. By
strategically removing portions of material from the block 16, it
is found that the dimensional difference between the major diameter
D1 and the minor diameter D2 need not serve as a constraint to the
dimensioning of the overall lidar sensor unit 10. As illustrated in
FIGS. 10-12, a plurality of chamfers 36, 38, 40, 42 are formed in
the block 16, each of the chamfers being bounded by a pair of
adjacent reflective surfaces 18-24 and the second wall 28. Each of
these chamfers 36-42 is preferably cut at an angle of 45.degree. to
the adjacent finished reflective surfaces and second wall 28.
However, the chamfers may be formed at a different angle to these
adjacent surfaces.
[0084] The planar mirror 14 is located on the side of the rotatable
polygon mirror 12 closest to the second wall 28. The chamfers 36-42
effectively reduce the major diameter of the rotatable polygon
mirror 12 to a maximum dimension D1' (see FIG. 13) that is less
than D1, such that a minimum distance between the rotatable polygon
mirror 12 and the planar mirror 14 can be maintained while still
minimizing the overall height and width dimensions of the lidar
sensor unit 10. The reflective surfaces 18-24 of the polygon mirror
12 can be manufactured using surface replication techniques, and
coarse as well as fine balancing techniques can be applied to the
polygon mirror 12, as discussed below.
[0085] By way of example only, and referring back to FIG. 1, the
lidar sensor unit 10 may be provided in a housing that includes a
shell roof 56, a first shell side wall 58, a second shell side wall
60, and a shell floor 62. Depending on where the lidar sensor unit
10 is mounted on a vehicle, one or more of the surfaces of the
housing could coincide with an external or interior surface of a
vehicle, as discussed below.
[0086] The housing of the lidar sensor unit 10 is configured so
that rotation of the polygon mirror 12 imparts a flow of air
through the housing to provide cooling to components enclosed
within the housing. The air flow may be a laminar flow, a turbulent
flow, or any suitable combination thereof. Such cooling need not be
the exclusive means of cooling of the interior components of the
lidar sensor unit 10. For instance, one or more of a fan, cooling
fins, or a heat exchanger can be used to moderate the temperature
of the components of the lidar sensor unit 10. However, the air
flow within the housing and the aerodynamic construction of the
components of the polygon mirror 12 of the lidar sensor unit 10
preferably account for a substantial portion of the temperature
mitigation of the lidar sensor unit 10, even when any one or more
of a fan, cooling fins, or a heat exchanger are additionally
provided in the housing to supplement cooling. A substantial
portion of the temperature mitigation of the lidar sensor unit 10
may be a majority of the cooling, at least 75% of the cooling, at
least 80% of the cooling, at least 85% of the cooling, at least 90%
of the cooling, at least 95% of the cooling, at least 98% of the
cooling, or at least 99% of the cooling. Alternatively, the air
flow within the housing and the aerodynamic construction of the
components of the polygon mirror 12 of the lidar sensor unit 10 may
be relied upon to supply all of the cooling when at least one of
the temperature within the housing of the lidar sensor unit 10 or
the ambient temperature is below a certain predefined temperature,
and if the at least one of the temperature within the housing of
the lidar sensor unit 10 or the ambient temperature exceeds the
predefined temperature, the air flow within the housing and the
aerodynamic construction of the components of the polygon mirror 12
of the lidar sensor unit 10 may be supplemented by at least one or
more of a fan, cooling fins, or a heat exchanger to provide
cooling. In some implementations, the polygon mirror 12 may be at
least partially surrounded or enclosed by a shroud that may act to
aid or direct the air circulation provided by the polygon mirror
12. The shroud may include a dust collector (e.g., a filter)
configured to remove dust from circulating air.
[0087] The planar mirror 14 is actuated by a drive system such as
that illustrated in FIG. 15. The drive system includes a drive
motor 64, which, by way of example, may be a brushless FAULHABER
(trademark) drive motor, a plurality of pulleys 66, 68, 70, one of
the pulleys 68 axially aligned with an encoder 72, and a drive belt
74 translating rotational motion of one of the pulleys 68 driven
directly by the drive motor 64 to the other two pulleys 68, 70. The
drive motor 64 may be secured to the shell roof 56 by a shell roof
motor mount 76.
[0088] As discussed in more detail below, the lidar sensor unit 10
according to some implementations includes optical elements
configured to receive light signals such as intermittent pulses or
continuous beams from a laser, and direct the light signals toward
the active reflective surface(s) of the rotatable polygon mirror
12. The optical elements can include a fiber-optic cable via which
the lidar sensor unit 10 is coupled to the laser, and a collimator
or a lens to produce a collimated free-space output beam. Referring
to FIG. 1, one or several output collimators 77 in an example
implementation direct light pulses of respective output beams
toward the rotatable polygon mirror 12 via apertures of the overlap
doughnut mirror 79. However, in other implementations considered in
more detail with reference to FIGS. 23-25, output collimators of
the lidar sensor unit 10 and an aperture-free overlap mirror
implement an off-axis illumination technique. The mirror 79, or an
aperture-free mirror oriented similar to the mirror 79, also can be
referred to as a superposition mirror or beam-combiner mirror.
[0089] If desired, the housing of the lidar sensor unit 10 can
enclose a laser or multiple lasers configured to generate output
beams with different wavelengths. Further, a diffractive optical
element (DOE) beam splitter 46 can be used to split a beam output
by the laser (or the beam received from a remote laser via a
fiber-optic cable) into at least two beams. The beams may have
distinct wavelengths from one another. The beam splitter 46 in
general can be any suitable holographic element, a pixelator,
diffractive element, etc.
[0090] In any case, the one or several collimators 77 direct pulses
of light at the reflective surfaces of the rotatable polygon mirror
12, which in turn reflect the pulses toward the planar reflective
surface 54. The rotation of the rotatable polygon mirror 12 and the
planar mirror 14 achieve the horizontal and vertical scan effect of
the lidar sensor unit 10.
[0091] An optic base 44 (see FIGS. 1 & 2) can enclose a
receiver with one or more detectors. Depending on whether the
scanner 11 utilizes a single reflective surface of the polygon
mirror 12 or two reflective surfaces, the sensor unit 10 can
include a single optic base 44 or two optic bases 44. As
illustrated in FIG. 21, the optic base 44 can enclose a lens 80 to
focus an input beam onto an assembly 81 including an optical filter
and a detector, discussed in more detail below.
[0092] The axis of rotation of the polygon mirror 12 may be aligned
with an orientation of predominant motion of the vehicle in which
the lidar system 10 operates. For instance, a front-facing lidar
system 10 may be oriented such that the axis of rotation of the
polygon mirror 12 is aligned with a longitudinal axis of the
vehicle. Such an orientation may serve to reduce adverse effects of
vibration, acceleration, and deceleration. These techniques are
illustrated in FIG. 30.
[0093] The planar mirror 14 may be configured so as to pivot over a
range of allowable motion larger than a range corresponding to the
vertical angular dimension of the field of regard, so as to define
a maximum range of allowable motion larger than a range within
which the planar mirror 14 pivots during a scan. A controller
associated with the planar mirror 14 selects different portions of
the maximum range of allowable motion as the range within which the
second mirror pivots, in accordance with modifications of the scan
pattern. In particular, to modify at least one of a scan pattern or
a scan rate, a controller associated with the motor 32 of the
polygon mirror 12 can be configured to cause the motor 32 to vary
the speed of rotation of the polygon mirror 12, cause the drive
motor 64 to vary the vary the oscillation of the planar mirror 14,
or both. The controller can be associated with both the polygon
mirror 12 and the planar mirror 14. The controller may be
configured to modify the scan pattern on a frame-by-frame basis,
each frame corresponding to a complete scan of the field of regard
of the lidar system 10. In some implementations, the oscillation of
the planar mirror 14 may be varied (e.g., to change the vertical
angular dimension of the field of regard), and the rotational speed
of the polygon mirror 12 may be regulated or stabilized so that the
polygon mirror 12 rotates at a substantially constant speed.
[0094] With reference to FIGS. 1-5, the polygon mirror 12 in some
implementations can be disposed between a third of the way from a
first edge of the y-scan mirror 14 and a third of the way from a
second edge of the y-scan mirror 14. In a particular embodiment,
the polygon mirror axis bisects a length of the y-scan mirror
14.
[0095] Besides the lidar sensor unit 10, the scanner 11 can operate
in any suitable optical system to scan the FOR. The scanner 11 in
an embodiment includes the polygon mirror 12 rotatable about a
polygon mirror axis to scan the FOR of the optical system along a
horizontal dimension, the polygon mirror 12 including a plurality
of reflective surfaces 18-24 being angularly offset from one
another along a periphery of the block 16; and a y-scan mirror 14
pivotable along a pivot axis orthogonal to the polygon mirror axis
to scan the FOR of the optical system along a vertical dimension.
The width of the y-scan mirror 14 is larger than the width of each
of the reflective surfaces 18-24 of the polygon mirror 12. The
polygon mirror 12 reflects light incident on one of the reflective
surfaces toward the y-scan mirror 14. The width of the y-scan
mirror 14 ultimately determines the scan range along the horizontal
dimension.
II. Propagation of Input and Output Light Beams Through the Lidar
Sensor Unit
[0096] FIG. 22 schematically depicts an example implementation of
the lidar sensor unit 10 that includes the doughnut overlap mirror
79 discussed above. In this implementation, an output beam 82
travels from the output collimator 77 through an aperture of the
overlap mirror 79 and impinges on one of the reflective surfaces of
the polygon mirror 12. The reflective surface of the polygon mirror
12 reflects the output beam 82 to a location on the planar mirror
14 that depends on the current orientation of the polygon mirror
12, thereby defining the current angle within the FOR.sub.H. The
planar mirror 14 then directs the output beam 82 out of the lidar
sensor unit 10 at a vertical angle that depends on the current
orientation of planar mirror 14, thereby defining the current angle
within the FOR.sub.V. In this manner, the scanner 11 can disperse
light pulses of the output beam 82 across the FOR of the lidar
sensor unit 10. An input beam 83 travels to the planar mirror 14,
which directs the input beam 83 to the polygon mirror 12, which in
turn directs the input beam 83 to the overlap mirror 79.
[0097] Now referring to FIG. 23, an assembly 86 is generally
similar to the assembly of FIG. 22. However, unlike the overlap
doughnut mirror 79, an overlap mirror 90A does not include an
aperture, and an output collimator 92A directs an output beam by
the side of the overlap mirror 90A toward a reflective surface 12-1
of the polygon mirror 12. An output collimator 94A can direct
another output beam by the side of the overlap mirror 90A toward
the same reflective surface 12-1 of the polygon mirror 12. The
output collimators 92A and 94A can be configured to emit pulses
having different wavelengths, and two respective detectors can be
configured to detect the corresponding return pulses in a shared
input beam reflected by the surface 12-1. In this manner, a lidar
sensor unit that includes the assembly 86 can generate values for
two pixels in a certain scan line within a same ranging event.
Alternatively, the output collimators 92A and 94A can launch the
output beams with a particular spatial or angular offset, and the
two input beams have a corresponding spatial or angular offset,
with the wavelength of the pulses emitted b the output collimators
92A and 94A being the same.
[0098] Further, in the example implementation of FIG. 23, the
assembly 86 includes output collimators 92B and 94B mechanically
aimed at a surface 12-2 of the polygon mirror 12. The output
collimators 92B and 94B also direct output beams by the side of the
corresponding overlap mirror 90B. Similar to the overlap mirror
90A, the overlap mirror 90B does not include an aperture.
[0099] The input beam which the reflective surface 12-1 directs to
the overlap mirror 90A can be regarded as the first eye of the
lidar sensor unit, and the input beam which the reflective surface
12-2 directs to the overlap mirror 90B can be regarded as the
second eye of the lidar sensor unit. The assembly 86 thus
implements off-axis illumination for both eyes of the lidar sensor
unit.
[0100] For further clarity, FIGS. 24 and 25 illustrate example
paths along which input and output beams travel in the sensor unit
10 and, in particular, the scanner 11. As discussed in more detail
below, an input beam typically contains only a relatively small
portion of the energy of an output beam. A receiver field of view
(FOV) may define a larger angular cone over which the receiver
detects light as compared to the light-source FOV, or the angular
cone illuminated by the light source. Accordingly, FIGS. 24 and 25
illustrate input and output beams of as cones of different sizes,
but neither the sizes of the cones nor the degrees of divergence of
these cones are drawn to scale.
[0101] In the scenario of FIG. 24, the input beam 102A first
impinges on the reflective surface of the planar mirror 14, which
reflects the input beam 102A toward the reflective surface of the
polygon mirror 12, which in turn reflects the input beam 102B
toward the overlap mirror 90A. The overlap mirror 90A then directs
the input beam 102A toward a lens 104A, which focuses the input
beam 102A on an active region 106A of a receiver 108A. For a given
operational state, the current orientation of the polygon mirror 12
defines the horizontal position of the receiver field of view
FOV.sub.A within the FOR of the sensor unit 10, and the current
orientation of the planar mirror 14 defines the vertical position
of the FOV.sub.A within the FOR. An input beam 102B in meantime
impinges on the planar mirror 14 at a different location. The
planar mirror 14 directs the input beam 102B to a different surface
of the polygon mirror 12, which in turn directs the input beam 102B
to an assembly including an overlap mirror, a lens, an active
region of a receiver, etc. (not illustrated to avoid clutter)
disposed on the opposite side of the polygon mirror 12 from the
components 90A, 104A, etc.
[0102] The output beams according to these implementations are
scanned synchronously because these beams reflect off the same
mirrors 12 and 14. In other words, the output beams are scanned at
approximately the same scanning rate across the field of regard,
and the input beams maintain approximately the same angular
separation. For example, both output beams may scan horizontally
across the field of regard at approximately 600 radians/sec, and
the two output beams may have a substantially fixed angular
separation of approximately 20 degrees. In addition to the two
output beams being scanned synchronously with respect to each
other, each receiver FOV is also scanned synchronously with its
respective light-source FOV.
[0103] As discussed in more detail below, a lidar system can use
the input beams 102A and 102B to generate two pixels during the
same ranging event, with an integer or non-integer separation
between the pixels. Further, in some implementations, each of the
input beams 102A and 102B is made up of two beams of light
corresponding to two output beams of different wavelengths,
.lamda..sub.1 and .lamda..sub.2, and accordingly can be used to
produce two pixels (e.g., an odd pixel and an even pixel) rather
than a single pixel during a single ranging event. The lidar sensor
unit 10 thus can produce the total of four pixels per ranging
event. As a more specific example, a DOE or another suitable
element can impart to a pulse of light a relatively small angular
separation into pulses of wavelengths .lamda..sub.1 and
.lamda..sub.2, so that the distance between the light pulses of
wavelengths .lamda..sub.1 and .lamda..sub.2 at the maximum range of
the lidar system corresponds to the width of multiple pixels. The
DOE may split the pulse before directing the resulting output beams
to the polygon mirror, or the DOE may be disposed downrange of the
mirrors 12 and 14 and split a pulse after propagation through the
scanner.
[0104] In another example implementation, the input beam 102A
includes two component input beams of the same wavelength, which
are substantially overlapped spatially but have a small angular
offset (e.g., between approximately 0.1 and 2 degrees) with respect
to one another. When the two component input beams pass through the
lens 104A, the angular offset results in the two beams being
focused on two separate spots, which may be separated by
approximately 0.4 to 2 mm. In this manner, the angular offset
between the beams results in a spatial separation after passing
through the lens.
[0105] FIG. 25 illustrates an example spatial arrangement of the
fields of view of the input beam 102A and output beams 110A and
110B. The beams 102A, 110A, and 110B are mechanically aimed so as
to minimize the resulting "footprints" on the mirrors 14 and 12.
Thus, the beams are adjacent to each other on the reflective
surfaces of the mirrors 12 and 14. Further, in accordance with
off-axis illumination techniques, the output beams 110A and 11B are
directed at a reflective surface of the polygon mirror 12 so as to
be not entirely coaxial with the input beam 102A (illustrated in
FIG. 25 in an exaggerated manner).
[0106] In contrast to the implementation of FIGS. 23-25, the output
beam 82 and the input beam 83 in FIG. 22 are more aligned with each
other, and may be substantially coaxial. The output beam 82 and
input beam 83 may at least partially overlap or share a common
propagation axis, so that the output beam 82 and input beam 83
travel along substantially the same optical path (albeit in
opposite directions). As the lidar system scans the output beam 82
across a field of regard, the input beam 83 may follow along with
the output beam 82, so that the coaxial relationship between the
two beams is maintained.
[0107] Referring again to FIG. 25, the output beams of light 110A
and 110B emitted by the light source (such as a light source 122A,
discussed below with reference to FIGS. 26A and 26B) is a
collimated optical beam with any suitable beam divergence, such as
a divergence of approximately 0.1 to 3.0 milliradian (mrad).
Divergence of the output beams 110A and 110B may refer to an
angular measure of an increase in beam size (e.g., a beam radius or
beam diameter) as the output beams 110A and 110B travel away from
the lidar system. The output beams 110A and 110B may have a
substantially circular cross section with a beam divergence
characterized by a single divergence value. For example, the output
beams 110A and 110B with a circular cross section and a divergence
of 1 mrad may have a beam diameter or spot size of approximately 10
cm at a distance of 100 m from the lidar system. In some
implementations, the output beams 110A and 110B may be an
astigmatic beam or may have a substantially elliptical cross
section and may be characterized by two divergence values. As an
example, the output beams 110A and 110B may have a fast axis and a
slow axis, where the fast-axis divergence is greater than the
slow-axis divergence. As another example, the output output beams
110A and 110B may be an astigmatic beam with a fast-axis divergence
of 2 mrad and a slow-axis divergence of 0.5 mrad.
[0108] The output beams 110A and 110B may be unpolarized or
randomly polarized, may have no specific or fixed polarization
(e.g., the polarization may vary with time), or may have a
particular polarization (e.g., the output beams 110A and 110B may
be linearly polarized, elliptically polarized, or circularly
polarized). As an example, the light source may produce linearly
polarized light, and the lidar system may include a quarter-wave
plate that converts this linearly polarized light into circularly
polarized light. The lidar system may transmit the circularly
polarized light as the output beams 110A and 110B, and receive the
input beam(s) 102A, which may be substantially or at least
partially circularly polarized in the same manner as the output
beams 110A and 110B (e.g., if the output beams 110A and 110B are
right-hand circularly polarized, then the input beam 102A may also
be right-hand circularly polarized). The input beam 102A may pass
through the same quarter-wave plate (or a different quarter-wave
plate), resulting in the input beam 102A being converted to
linearly polarized light which is orthogonally polarized (e.g.,
polarized at a right angle) with respect to the linearly polarized
light produced by light source 110. As another example, the lidar
system may employ polarization-diversity detection where two
polarization components are detected separately. The output beams
110A and 110B may be linearly polarized, and the lidar system may
split the input beam 102A into two polarization components (e.g.,
s-polarization and p-polarization) which are detected separately by
two photodiodes (e.g., a balanced photoreceiver that includes two
photodiodes).
[0109] The scanner 11 can scan each of the first beam of light and
the second beam of light so as to define a respective field of
regard approximately 60 degrees wide. Depending on the
implementation, the fields of regard can have a relatively large
overlap (e.g., 20 degrees, 30 degrees, 40 degrees), a relatively
small overlap (e.g., one degree, two degrees, three degrees, four
degrees, five degrees), or no overlap. Dynamic modifications to the
fields of regard are discussed in more detail below. The overlap
region may be oriented in a direction of travel of a vehicle on
which the lidar system 10 is deployed.
[0110] III. Operation of a Lidar System
[0111] Next, FIG. 26A illustrates an example lidar system 120A in
which all or some of the components of lidar sensor unit 10 can be
implemented according to a single-eye configuration. The lidar
system 120A may be referred to as a laser ranging system, a laser
radar system, a LIDAR system, a lidar sensor, or a laser detection
and ranging (LADAR or ladar) system. The lidar system 120A may
include a light source 122A, a mirror 124A (referred to as overlap
mirror, superposition mirror, or beam-combiner mirror), a scanner
11, a receiver 128A, and a controller 130 equipped with a memory
unit 132. In some implementations, the lidar system 120A also can
include one or more sensors 134 such as a temperature sensor, a
moisture sensor, etc.
[0112] The scanner 11 may be referred to as a beam scanner, optical
scanner, or laser scanner. The scanner 11 may be implemented as
discussed above with reference to FIGS. 1-25 and include a polygon
mirror 12, a planar mirror 14, and corresponding motors to drive
the rotation of the polygon mirror 12 and the oscillation of the
planar mirror 14.
[0113] Depending on the implementation, the controller 130 may
include one or more processors, an application-specific integrated
circuit (ASIC), a field-programmable gate array (FPGA), and/or
other suitable circuitry. The non-transitory computer-readable
memory 132 of the controller 130 can be configured to store
instructions executable by the controller 130 as well as data which
the controller 130 can produce based on the signals from the
components of the system 120A and/or provide to these components.
The memory 132 can include volatile (e.g., RAM) and/or non-volatile
(e.g., flash memory, a hard disk) components. The data the
controller 130 generates during operation and stores in the memory
132 can include pixel data and other results of analyzing
characteristics of the target 160, alarm data (e.g., readings from
the sensors 134 that exceed certain predefined thresholds), and the
configuration data the controller 130 can retrieve from the memory
132 during operation can include definitions of various scan
patterns, for example. Alternatively or additionally to the memory
132, the controller 130 can be configured to access memory disposed
remotely relative to the lidar system 120A in the vehicle
controller (see below) or even memory disposed remotely relative to
the vehicle, such as on a network server. In addition to collecting
data from receiver 128A, the controller 130 can provide control
signals to and, in some implementations, receive diagnostics data
from, the light source 122A, the one or more sensors 134, and the
scanner 11 via communication links 136.
[0114] In some implementations, the light source 122A can be an
output collimator similar to the output collimator(s) 77 discussed
above, e.g., a lens rigidly coupled to an end of a fiber-optic
cable, with the other end of the fiber-optic cable coupled to a
laser disposed remotely relative to the scanner 11. Examples of
such configurations are discussed in more detail below with
reference to FIGS. 32 and 33. In other implementations, the light
source 122A can be an assembly that includes a laser.
[0115] The light source 122A thus may include, or be optically
coupled to, a laser which emits light having a particular operating
wavelength in the infrared, visible, or ultraviolet portions of the
electromagnetic spectrum. As a more specific example, the light
source 122A may include a laser with an operating wavelength
between approximately 1.2 .mu.m and 1.7 .mu.m.
[0116] In operation, the light source 122A emits an output beam of
light 150A which may be continuous-wave, pulsed, or modulated in
any suitable manner for a given application. The output beam of
light 150A is directed downrange toward a remote target 160 located
a distance D from the lidar system 120A and at least partially
contained within a field of regard of the system 120A. Depending on
the scenario and/or the implementation of the lidar system 120A,
the distance D can be between 1 m and 1 km, for example.
[0117] Once the output beam 150A reaches the downrange target 160,
the target 160 may scatter or, in some cases, reflect at least a
portion of light from the output beam 150A, and some of the
scattered or reflected light may return toward the lidar system
120A. In the example of FIG. 26A, the scattered or reflected light
is represented by input beam 164A, which passes through the scanner
11. The input beam 164A passes through the scanner 11 to the mirror
124A. The mirror 124A in turn directs the input beam 164A to the
receiver 128A. The input beam 164A may contain only a relatively
small fraction of the light from the output beam 150A. For example,
the ratio of average power, peak power, or pulse energy of the
input beam 164A to average power, peak power, or pulse energy of
the output beam 150A may be approximately 10.sup.-1, 10.sup.-2,
10.sup.-3, 10.sup.-4, 10.sup.-5, 10.sup.-6, 10.sup.-7, 10.sup.-8,
10.sup.-9, 10.sup.-10, 10.sup.-11, or 10.sup.-12. As another
example, if a pulse of the output beam 150A has a pulse energy of 1
microjoule (.mu.J), then the pulse energy of a corresponding pulse
of the input beam 164A may have a pulse energy of approximately 10
nanojoules (nJ), 1 nJ, 100 picojoules (pJ), 10 pJ, 1 pJ, 100
femtojoules (fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10 aJ, or 1
aJ.
[0118] The output beam 150A may be referred to as a laser beam,
light beam, optical beam, emitted beam, or just beam; and the input
beam 164A may be referred to as a return beam, received beam,
return light, received light, input light, scattered light, or
reflected light. As used herein, scattered light may refer to light
that is scattered or reflected by the target 160. The input beam
164A may include light from the output beam 150A that is scattered
by the target 160, light from the output beam 150A that is
reflected by the target 160, or a combination of scattered and
reflected light from target 160A. The input beam 164A also can
include "passive" light signals, or light from various other
sources and of various wavelengths scattered by the target 160.
[0119] The operating wavelength of a lidar system 120A may lie, for
example, in the infrared, visible, or ultraviolet portions of the
electromagnetic spectrum. The Sun also produces light in these
wavelength ranges, and thus sunlight can act as background noise
which can obscure signal light detected by the lidar system 120A.
This solar background noise can result in false-positive detections
or can otherwise corrupt measurements of the lidar system 120A,
especially when the receiver 128A includes SPAD detectors (which
can be highly sensitive).
[0120] Generally speaking, the light from the Sun that passes
through the Earth's atmosphere and reaches a terrestrial-based
lidar system such as the system 120A can establish an optical
background noise floor for this system. Thus, in order for a signal
from the lidar system 120A to be detectable, the signal must rise
above the background noise floor. It is generally possible to
increase the signal-to-noise (SNR) ratio of the lidar system 120A
by raising the power level of the output beam 150A, but in some
situations it may be desirable to keep the power level of the
output beam 150A relatively low. For example, increasing transmit
power levels of the output beam 150A can result in the lidar system
120A not being eye-safe.
[0121] In some implementations, the lidar system 120A operates at
one or more wavelengths between approximately 1400 nm and
approximately 1600 nm. For example, the light source 122A may
produce light at approximately 1550 nm.
[0122] In some implementations, the lidar system 120A operates at
frequencies at which atmospheric absorption is relatively low. For
example, the lidar system 120A can operate at wavelengths in the
approximate ranges from 980 nm to 1110 nm or from 1165 nm to 1400
nm.
[0123] In other implementations, the lidar system 120A operates at
frequencies at which atmospheric absorption is high. For example,
the lidar system 120A can operate at wavelengths in the approximate
ranges from 930 nm to 980 nm, from 1100 nm to 1165 nm, or from 1400
nm to 1460 nm.
[0124] According to some implementations, the lidar system 120A can
include an eye-safe laser, or the lidar system 120A can be
classified as an eye-safe laser system or laser product. An
eye-safe laser, laser system, or laser product may refer to a
system with an emission wavelength, average power, peak power, peak
intensity, pulse energy, beam size, beam divergence, exposure time,
or scanned output beam such that emitted light from the system
presents little or no possibility of causing damage to a person's
eyes. For example, the light source 122A or the lidar system 120A
may be classified as a Class 1 laser product (as specified by the
60825-1 standard of the International Electrotechnical Commission
(IEC)) or a Class I laser product (as specified by Title 21,
Section 1040.10 of the United States Code of Federal Regulations
(CFR)) that is safe under all conditions of normal use. In some
implementations, the lidar system 120A may be classified as an
eye-safe laser product (e.g., with a Class 1 or Class I
classification) configured to operate at any suitable wavelength
between approximately 1400 nm and approximately 2100 nm. In some
implementations, the light source 122A may include a laser with an
operating wavelength between approximately 1400 nm and
approximately 1600 nm, and the lidar system 120A may be operated in
an eye-safe manner. In some implementations, the light source 122A
or the lidar system 120A may be an eye-safe laser product that
includes a scanned laser with an operating wavelength between
approximately 1530 nm and approximately 1560 nm. In some
implementations, the lidar system 120A may be a Class 1 or Class I
laser product that includes a fiber laser or solid-state laser with
an operating wavelength between approximately 1400 nm and
approximately 1600 nm.
[0125] The receiver 128A may receive or detect photons from the
input beam 164A and generate one or more representative signals.
For example, the receiver 128A may generate an output electrical
signal 145A that is representative of the input beam 164. The
receiver 128A may send the electrical signal to the controller 130.
The controller 130 can be configured to analyze one or more
characteristics of the electrical signal 145A to determine one or
more characteristics of the target 160, such as its distance
downrange from the lidar system 120A. More particularly, the
controller 130 may analyze the time of flight or phase modulation
for the beam of light 150A transmitted by the light source 122A. If
the lidar system 120A measures a time of flight of T (e.g., T
represents a round-trip time of flight for an emitted pulse of
light to travel from the lidar system 120A to the target 160 and
back to the lidar system 120A), then the distance D from the target
160 to the lidar system 120A may be expressed as D=cT/2, where c is
the speed of light (approximately 3.0.times.10.sup.8 m/s).
[0126] As a more specific example, if the lidar system 120A
measures the time of flight to be T=300 ns, then the lidar system
120A can determine the distance from the target 160 to the lidar
system 120A to be approximately D=45.0 m. As another example, the
lidar system 120A measures the time of flight to be T=1.33 .mu.s
and accordingly determines that the distance from the target 160 to
the lidar system 120A is approximately D=199.5 m. The distance D
from lidar system 120A to the target 160 may be referred to as a
distance, depth, or range of the target 160. As used herein, the
speed of light c refers to the speed of light in any suitable
medium, such as for example in air, water, or vacuum. The speed of
light in vacuum is approximately 2.9979.times.10.sup.8 m/s, and the
speed of light in air (which has a refractive index of
approximately 1.0003) is approximately 2.9970.times.10.sup.8
m/s.
[0127] The target 160 may be located a distance D from the lidar
system 120A that is less than or equal to a maximum range R.sub.MAX
of the lidar system 120A. The maximum range R.sub.MAX (which also
may be referred to as a maximum distance) of a lidar system 120A
may correspond to the maximum distance over which the lidar system
120A is configured to sense or identify targets that appear in a
field of regard of the lidar system 120A. The maximum range of
lidar system 120A may be any suitable distance, such as for
example, 25 m, 50 m, 100 m, 200 m, 500 m, or 1 km. As a specific
example, a lidar system with a 200-m maximum range may be
configured to sense or identify various targets located up to 200 m
away. For a lidar system with a 200-m maximum range (R.sub.MAX=200
m), the time of flight corresponding to the maximum range is
approximately 2R.sub.MAX/c.apprxeq.1.33 .mu.s.
[0128] In some implementations, the light source 122A, the scanner
11, and the receiver 128A are packaged together within a single
housing 165, which may be a box, case, or enclosure that holds or
contains all or part of a lidar system 120A. The housing 165 can
include at least some of the housing components (the shell roof 56,
the shell side wall 58, etc.) discussed above. In the example of
FIG. 26A, the housing 165 includes a window 167 through which the
beams 150A and 164A pass. In one example implementation, the
lidar-system housing 165 contains the light source 122A, the
overlap mirror 124A, the scanner 11, and the receiver 128A of the
lidar system 120A. The controller 130 may reside within the same
housing 165 as the components 122A, 11, 128A or the controller 130
may reside remotely from the housing 165.
[0129] Moreover, in some implementations, the housing 165 includes
multiple lidar sensor units, each including a respective scanner
and a receiver. Depending on the particular implementation, each of
the multiple lidar sensor units can include a separate light source
or a common light source. The multiple lidar sensor units can be
configured to cover non-overlapping adjacent fields of regard or
partially overlapping fields of regard, depending on the
implementation.
[0130] The housing 165 may be an airtight or watertight structure
that prevents water vapor, liquid water, dirt, dust, or other
contaminants from getting inside the housing 165. The housing 165
may be filled with a dry or inert gas, such as for example dry air,
nitrogen, or argon. The housing 165 may include one or more
electrical connections for conveying electrical power or electrical
signals to and/or from the housing.
[0131] The window 167 may be made from any suitable substrate
material, such as for example, glass or plastic (e.g.,
polycarbonate, acrylic, cyclic-olefin polymer, or cyclic-olefin
copolymer). The window 167 may include an interior surface (surface
A) and an exterior surface (surface B), and surface A or surface B
may include a dielectric coating having particular reflectivity
values at particular wavelengths. A dielectric coating (which may
be referred to as a thin-film coating, interference coating, or
coating) may include one or more thin-film layers of dielectric
materials (e.g., SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3,
Ta.sub.2O.sub.5, MgF.sub.2, LaF.sub.3, or AlF.sub.3) having
particular thicknesses (e.g., thickness less than 1 .mu.m) and
particular refractive indices. A dielectric coating may be
deposited onto surface A or surface B of the window 167 using any
suitable deposition technique, such as for example, sputtering or
electron-beam deposition.
[0132] The dielectric coating may have a high reflectivity at a
particular wavelength or a low reflectivity at a particular
wavelength. A high-reflectivity (HR) dielectric coating may have
any suitable reflectivity value (e.g., a reflectivity greater than
or equal to 80%, 90%, 95%, or 99%) at any suitable wavelength or
combination of wavelengths. A low-reflectivity dielectric coating
(which may be referred to as an anti-reflection (AR) coating) may
have any suitable reflectivity value (e.g., a reflectivity less
than or equal to 5%, 2%, 1%, 0.5%, or 0.2%) at any suitable
wavelength or combination of wavelengths. In particular
embodiments, a dielectric coating may be a dichroic coating with a
particular combination of high or low reflectivity values at
particular wavelengths. For example, a dichroic coating may have a
reflectivity of less than or equal to 0.5% at approximately
1550-1560 nm and a reflectivity of greater than or equal to 90% at
approximately 800-1500 nm.
[0133] In some implementations, surface A or surface B has a
dielectric coating that is anti-reflecting at an operating
wavelength of one or more light sources 122A contained within
enclosure 165. An AR coating on surface A and surface B may
increase the amount of light at an operating wavelength of light
source 122A that is transmitted through the window 167.
Additionally, an AR coating at an operating wavelength of the light
source 120A may reduce the amount of incident light from output
beam 150A that is reflected by the window 167 back into the housing
165. In an example implementation, each of surface A and surface B
has an AR coating with reflectivity less than 0.5% at an operating
wavelength of light source 122A. As an example, if the light source
122A has an operating wavelength of approximately 1550 nm, then
surface A and surface B may each have an AR coating with a
reflectivity that is less than 0.5% from approximately 1547 nm to
approximately 1553 nm. In another implementation, each of surface A
and surface B has an AR coating with reflectivity less than 1% at
the operating wavelengths of the light source 110. For example, if
the housing 165 encloses two sensor heads with respective light
sources, the first light source emits pulses at a wavelength of
approximately 1535 nm and the second light source emits pulses at a
wavelength of approximately 1540 nm, then surface A and surface B
may each have an AR coating with reflectivity less than 1% from
approximately 1530 nm to approximately 1545 nm.
[0134] The window 167 may have an optical transmission that is
greater than any suitable value for one or more wavelengths of one
or more light sources 122A contained within the housing 165. As an
example, the window 167 may have an optical transmission of greater
than or equal to 70%, 80%, 90%, 95%, or 99% at a wavelength of
light source 122A. In one example implementation, the window 167
can transmit greater than or equal to 95% of light at an operating
wavelength of the light source 122A. In another implementation, the
window 167 transmits greater than or equal to 90% of light at the
operating wavelengths of the light sources enclosed within the
housing 165.
[0135] Surface A or surface B may have a dichroic coating that is
anti-reflecting at one or more operating wavelengths of one or more
light sources 122A and high-reflecting at wavelengths away from the
one or more operating wavelengths. For example, surface A may have
an AR coating for an operating wavelength of the light source 122A,
and surface B may have a dichroic coating that is AR at the
light-source operating wavelength and HR for wavelengths away from
the operating wavelength. A coating that is HR for wavelengths away
from a light-source operating wavelength may prevent most incoming
light at unwanted wavelengths from being transmitted through the
window 167. In one implementation, if light source 122A emits
optical pulses with a wavelength of approximately 1550 nm, then
surface A may have an AR coating with a reflectivity of less than
or equal to 0.5% from approximately 1546 nm to approximately 1554
nm. Additionally, surface B may have a dichroic coating that is AR
at approximately 1546-1554 nm and HR (e.g., reflectivity of greater
than or equal to 90%) at approximately 800-1530 nm and
approximately 1570-1700 nm.
[0136] Surface B of the window 167 may include a coating that is
oleophobic, hydrophobic, or hydrophilic. A coating that is
oleophobic (or, lipophobic) may repel oils (e.g., fingerprint oil
or other non-polar material) from the exterior surface (surface B)
of the window 167. A coating that is hydrophobic may repel water
from the exterior surface. For example, surface B may be coated
with a material that is both oleophobic and hydrophobic. A coating
that is hydrophilic attracts water so that water may tend to wet
and form a film on the hydrophilic surface (rather than forming
beads of water as may occur on a hydrophobic surface). If surface B
has a hydrophilic coating, then water (e.g., from rain) that lands
on surface B may form a film on the surface. The surface film of
water may result in less distortion, deflection, or occlusion of an
output beam 150A than a surface with a non-hydrophilic coating or a
hydrophobic coating.
[0137] With continued reference to FIG. 26A, the light source 122A
may include a pulsed laser configured to produce or emit pulses of
light with a certain pulse duration. In an example implementation,
the pulse duration or pulse width of the pulsed laser is
approximately 10 picoseconds (ps) to 20 nanoseconds (ns). In
another implementation, the light source 122A is a pulsed laser
that produces pulses with a pulse duration of approximately 1-4 ns.
In yet another implementation, the light source 122A is a pulsed
laser that produces pulses at a pulse repetition frequency of
approximately 100 kHz to 5 MHz or a pulse period (e.g., a time
between consecutive pulses) of approximately 200 ns to 10 .mu.s.
The light source 122A may have a substantially constant or a
variable pulse repetition frequency, depending on the
implementation. As an example, the light source 122A may be a
pulsed laser that produces pulses at a substantially constant pulse
repetition frequency of approximately 640 kHz (e.g., 640,000 pulses
per second), corresponding to a pulse period of approximately 1.56
.mu.s. As another example, the light source 122A may have a pulse
repetition frequency that can be varied from approximately 500 kHz
to 3 MHz. As used herein, a pulse of light may be referred to as an
optical pulse, a light pulse, or a pulse, and a pulse repetition
frequency may be referred to as a pulse rate.
[0138] In general, the output beam 150A may have any suitable
average optical power, and the output beam 150A may include optical
pulses with any suitable pulse energy or peak optical power. Some
examples of the average power of the output beam 150A include the
approximate values of 1 mW, 10 mW, 100 mW, 1 W, and 10 W. Example
values of pulse energy of the output beam 150 include the
approximate values of 0.1 .mu.J, 1 .mu.J, 10 .mu.J, 100 .mu.J, and
1 mJ. Examples of peak power values of pulses included in the
output beam 150A are the approximate values of 10 W, 100 W, 1 kW, 5
kW, 10 kW. An example optical pulse with a duration of 1 ns and a
pulse energy of 1 .mu.J has a peak power of approximately 1 kW. If
the pulse repetition frequency is 500 kHz, then the average power
of the output beam 150 with 1-.mu.J pulses is approximately 0.5 W,
in this example.
[0139] The light source 122A may include a laser diode, such as a
Fabry-Perot laser diode, a quantum well laser, a distributed Bragg
reflector (DBR) laser, a distributed feedback (DFB) laser, or a
vertical-cavity surface-emitting laser (VCSEL). The laser diode
operating in the light source 122A may be an
aluminum-gallium-arsenide (AlGaAs) laser diode, an
indium-gallium-arsenide (InGaAs) laser diode, or an
indium-gallium-arsenide-phosphide (InGaAsP) laser diode, or any
other suitable diode. In some implementations, the light source
122A includes a pulsed laser diode with a peak emission wavelength
of approximately 1400-1600 nm. Further, the light source 122A may
include a laser diode that is current-modulated to produce optical
pulses.
[0140] In some implementation, the light source 122A includes a
pulsed laser diode followed by one or more optical-amplification
stages. For example, the light source 122A may be a fiber-laser
module that includes a current-modulated laser diode with a peak
wavelength of approximately 1550 nm, followed by a single-stage or
a multi-stage erbium-doped fiber amplifier (EDFA) or
erbium/ytterbium-doped fiber amplifier (EYDFA). As another example,
the light source 122A may include a continuous-wave (CW) or
quasi-CW laser diode followed by an external optical modulator
(e.g., an electro-optic modulator), and the output of the modulator
may be fed into an optical amplifier. In yet other implementations,
the light source 122A may include a pulsed solid-state laser or a
pulsed fiber laser.
[0141] The lidar system 120A also may include one or more optical
components configured to condition, shape, filter, modify, steer,
or direct the output beam 150A and/or the input beam 164. For
example, lidar system 120A may include one or more lenses, mirrors,
filters (e.g., bandpass or interference filters), beam splitters,
polarizers, polarizing beam splitters, wave plates (e.g., half-wave
or quarter-wave plates), diffractive elements, or holographic
elements. In some implementations, the lidar system 120A includes a
telescope, one or more lenses, or one or more mirrors to expand,
focus, or collimate the output beam 150A or the input beam 164A to
a desired beam diameter or divergence. As an example, the lidar
system 120A may include one or more lenses to focus the input beam
164A onto an active region of the receiver 128A. As another
example, the lidar system 120A may include one or more flat mirrors
or curved mirrors (e.g., concave, convex, or parabolic mirrors) to
steer or focus the output beam 150A or the input beam 164A. For
example, the lidar system 120A may include an off-axis parabolic
mirror to focus the input beam 164A onto an active region of
receiver 128A.
[0142] In operation, the light source 122A may emit pulses of light
which the scanner 11 scans across a FOR of lidar system 120A. The
target 160 may scatter one or more of the emitted pulses, and the
receiver 128A may detect at least a portion of the pulses of light
scattered by the target 160. Example techniques for selecting and
dynamically modifying the FOR using the lidar sensor unit of this
disclosure are discussed in more detail below with reference to
FIGS. 35-40.
[0143] The receiver 128A may be referred to as (or may include) a
photoreceiver, optical receiver, optical sensor, detector,
photodetector, or optical detector. The receiver 128A in some
implementations receives or detects at least a portion of the input
beam 164A and produces an electrical signal that corresponds to the
input beam 164A. For example, if the input beam 164A includes an
optical pulse, then the receiver 128A may produce an electrical
current or voltage pulse that corresponds to the optical pulse
detected by the receiver 128A. In an example implementation, the
receiver 128A includes one or more avalanche photodiodes (APDs) or
one or more single-photon avalanche diodes (SPADs). In another
implementation, the receiver 128A includes one or more PN
photodiodes (e.g., a photodiode structure formed by a p-type
semiconductor and a n-type semiconductor) or one or more PIN
photodiodes (e.g., a photodiode structure formed by an undoped
intrinsic semiconductor region located between p-type and n-type
regions).
[0144] The receiver 128A may have an active region or an
avalanche-multiplication region that includes silicon, germanium,
or InGaAs. The active region of receiver 128A may have any suitable
size, such as for example, a diameter or width of approximately
50-500 .mu.m. The receiver 128 may include circuitry that performs
signal amplification, sampling, filtering, signal conditioning,
analog-to-digital conversion, time-to-digital conversion, pulse
detection, threshold detection, rising-edge detection, or
falling-edge detection. For example, the receiver 128A may include
a transimpedance amplifier that converts a received photocurrent
(e.g., a current produced by an APD in response to a received
optical signal) into a voltage signal. The receiver 128A may direct
the voltage signal to pulse-detection circuitry that produces an
analog or digital output signal 145A that corresponds to one or
more characteristics (e.g., rising edge, falling edge, amplitude,
or duration) of a received optical pulse. For example, the
pulse-detection circuitry may perform a time-to-digital conversion
to produce the digital output signal 145A. The receiver 128A may
send the electrical output signal 145A to the controller 130 for
processing or analysis, e.g., to determine a time-of-flight value
corresponding to a received optical pulse.
[0145] The controller 130 may be electrically coupled or otherwise
communicatively coupled to one or more of the light source 122A,
the scanner 11, and the receiver 128A. The controller 130 may
receive electrical trigger pulses or edges from the light source
122A, where each pulse or edge corresponds to the emission of an
optical pulse by the light source 122A. The controller 130 may
provide instructions, a control signal, or a trigger signal to the
light source 122A indicating when the light source 122A should
produce optical pulses. For example, the controller 130 may send an
electrical trigger signal that includes electrical pulses, where
the light source 122A emits an optical pulse in response to each
electrical pulse. Further, the controller 130 may cause the light
source 122A to adjust one or more of the frequency, period,
duration, pulse energy, peak power, average power, or wavelength of
the optical pulses produced by the light source 122A.
[0146] The controller 130 may determine a time-of-flight value for
an optical pulse based on timing information associated with when
the pulse was emitted by the light source 122A and when a portion
of the pulse (e.g., the input beam 164A) was detected or received
by the receiver 128A. The controller 130 may include circuitry that
performs signal amplification, sampling, filtering, signal
conditioning, analog-to-digital conversion, time-to-digital
conversion, pulse detection, threshold detection, rising-edge
detection, or falling-edge detection.
[0147] As indicated above, the lidar system 120A may be used to
determine the distance to one or more downrange targets 160. By
scanning the output beam 150A across a field of regard, the lidar
system 120A can be used to map the distance to a number of points
within the field of regard. Each of these depth-mapped points may
be referred to as a pixel or a voxel. A collection of pixels
captured in succession (which may be referred to as a depth map, a
point cloud, or a frame) may be rendered as an image or may be
analyzed to identify or detect objects or to determine a shape or
distance of objects within the FOR. For example, a depth map may
cover a field of regard that extends 60.degree. horizontally and
15.degree. vertically, and the depth map may include a frame of
100-2000 pixels in the horizontal direction by 4-400 pixels in the
vertical direction.
[0148] The lidar system 120A may be configured to repeatedly
capture or generate point clouds of a field of regard at any
suitable frame rate between approximately 0.1 frames per second
(FPS) and approximately 1,000 FPS. For example, the lidar system
120A may generate point clouds at a frame rate of approximately 0.1
FPS, 0.5 FPS, 1 FPS, 2 FPS, 5 FPS, 10 FPS, 20 FPS, 100 FPS, 500
FPS, or 1,000 FPS. In an example implementation, the lidar system
120A is configured to produce optical pulses at a rate of
5.times.10.sup.5 pulses/second (e.g., the system may determine
500,000 pixel distances per second) and scan a frame of
1000.times.50 pixels (e.g., 50,000 pixels/frame), which corresponds
to a point-cloud frame rate of 10 frames per second (e.g., 10 point
clouds per second). The point-cloud frame rate may be substantially
fixed or dynamically adjustable, depending on the implementation.
For example, the lidar system 120A may capture one or more point
clouds at a particular frame rate (e.g., 1 Hz) and then switch to
capture one or more point clouds at a different frame rate (e.g.,
10 Hz). In general, the lidar system can use a slower frame rate
(e.g., 1 Hz) to capture one or more high-resolution point clouds,
and use a faster frame rate (e.g., 10 Hz) to rapidly capture
multiple lower-resolution point clouds.
[0149] The field of regard of the lidar system 120A can overlap,
encompass, or enclose at least a portion of the target 160, which
may include all or part of an object that is moving or stationary
relative to lidar system 120A. For example, the target 160 may
include all or a portion of a person, vehicle, motorcycle, truck,
train, bicycle, wheelchair, pedestrian, animal, road sign, traffic
light, lane marking, road-surface marking, parking space, pylon,
guard rail, traffic barrier, pothole, railroad crossing, obstacle
in or near a road, curb, stopped vehicle on or beside a road,
utility pole, house, building, trash can, mailbox, tree, any other
suitable object, or any suitable combination of all or part of two
or more objects.
[0150] With continued reference to FIG. 26A, the input beam 164A
may pass through the lens 170A which focuses the beam onto an
active region 176A of the receiver 128A. The active region 176A may
refer to an area over which receiver 128A may receive or detect
input light. The active region 176A may have any suitable size or
diameter d, such as for example, a diameter of approximately 25
.mu.m, 50 .mu.m, 80 .mu.m, 100 .mu.m, 200 .mu.m, 500 .mu.m, 1 mm, 2
mm, or 5 mm. The overlap mirror 124A may have a reflecting surface
174 that is substantially flat or the reflecting surface 174 may be
curved (e.g., the mirror 124 may be an off-axis parabolic mirror
configured to focus the input beam 164 onto an active region of the
receiver 128A).
[0151] Next, FIG. 26B illustrates a lidar system 120B in which the
lidar sensor 10 discussed can be implemented. The lidar system 120B
is generally similar to the lidar system 120A, but the lidar system
120B uses two eyes to scan a combined FOR rather than a single eye.
The scanner 11 in this configuration uses two different reflective
surfaces of the polygon mirror 12 to direct output beams 150A and
150B toward the target 160 and concurrently receives and processes
input beams 164A and 164B. The output beams 150A and 150B are
generated by different light sources 122A and 122B, which can
operate at a same wavelength or different wavelength. In some
implementations, the lidar system 120B is equipped with two lasers,
while in other implementations the light sources 122A and 122B
receive laser pulses from a shared laser inside or outside the
housing of the lidar system 120B.
[0152] Similar to the examples above, each of the output beams 150A
and 150B can be further split to generate odd and even pixels, for
example. The input beams 164A and 164B can follow different
respective paths toward the receivers 128A and 128B, respectively.
More particularly, the input beam 164A can travel via an overlap
mirror 124A toward a lens 170A, which focusses the light on the
active region 176A of the receiver 128A, while the input beam 164B
can travel via an overlap mirror 124B toward a lens 170B, which
focusses the light on the active region 176AB of the receiver 128B.
The lidar system 120B can provide a relatively large angular
separation between the outbound beams 150A and 150B, so as to
reduce the probability of cross-talk detection.
[0153] The controller 130 in the configuration of FIG. 26B can
receive electrical signals 145A and 145B from the receivers 128A
and 128B, respectively, to determine one or more characteristics of
the target 160. The controller 130 can exchange control data with
the light sources 122A and 122B, the scanner 11, and the sensors
134.
[0154] FIG. 27 illustrates an example InGaAs avalanche photodiode
(APD) 200. Referring back to FIGS. 26A and 26B, the receiver 128
may include one or more APDs 200 configured to receive and detect
light from input light such as the beam 164A or 164B. More
generally, the APD 200 can operate in any suitable receiver of
input light. The APD 200 may be configured to detect a portion of
pulses of light which are scattered by a target located downrange
from the lidar system in which the APD 200 operates. For example,
the APD 200 may receive a portion of a pulse of light scattered by
the target 160 depicted in FIGS. 26A and 26B, and generate an
electrical-current signal corresponding to the received pulse of
light.
[0155] The APD 200 may include doped or undoped layers of any
suitable semiconductor material, such as for example, silicon,
germanium, InGaAs, InGaAsP, or indium phosphide (InP).
Additionally, the APD 200 may include an upper electrode 202 and a
lower electrode 206 for coupling the ADP 200 to an electrical
circuit. The APD 200 for example may be electrically coupled to a
voltage source that supplies a reverse-bias voltage V to the APD
200. Additionally, the APD 200 may be electrically coupled to a
transimpedance amplifier which receives electrical current
generated by the APD 200 and produces an output voltage signal that
corresponds to the received current. The upper electrode 202 or
lower electrode 206 may include any suitable electrically
conductive material, such as for example a metal (e.g., gold,
copper, silver, or aluminum), a transparent conductive oxide (e.g.,
indium tin oxide), a carbon-nanotube material, or polysilicon. In
some implementations, the upper electrode 202 is partially
transparent or has an opening to allow input light 210 to pass
through to the active region of the APD 200. In FIG. 27, the upper
electrode 202 may have a ring shape that at least partially
surrounds the active region of the APD 200, where the active region
refers to an area over which the APD 200 may receive and detect the
input light 210. The active region may have any suitable size or
diameter d, such as for example, a diameter of approximately 25
.mu.m, 50 .mu.m, 80 .mu.m, 100 .mu.m, 200 .mu.m, 500 .mu.m, 1 mm, 2
mm, or 5 mm.
[0156] The APD 200 may include any suitable combination of any
suitable semiconductor layers having any suitable doping (e.g.,
n-doped, p-doped, or intrinsic undoped material). In the example of
FIG. 27, the InGaAs APD 200 includes a p-doped InP layer 220, an
InP avalanche layer 222, an absorption layer 224 with n-doped
InGaAs or InGaAsP, and an n-doped InP substrate layer 226.
Depending on the implementation, the APD 200 may include separate
absorption and avalanche layers, or a single layer may act as both
an absorption and avalanche region. The APD 200 may operate
electrically as a PN diode or a PIN diode, and, during operation,
the APD 200 may be reverse-biased with a positive voltage V applied
to the lower electrode 206 with respect to the upper electrode 202.
The applied reverse-bias voltage V may have any suitable value,
such as for example approximately 5 V, 10 V, 20 V, 30 V, 50 V, 75
V, 100 V, or 200 V.
[0157] In FIG. 27, photons of the input light 210 may be absorbed
primarily in the absorption layer 224, resulting in the generation
of electron-hole pairs (which may be referred to as photo-generated
carriers). For example, the absorption layer 224 may be configured
to absorb photons corresponding to the operating wavelength of the
lidar system 120A or 120B (e.g., any suitable wavelength between
approximately 1200 nm and approximately 1600 nm). In the avalanche
layer 222, an avalanche-multiplication process occurs where
carriers (e.g., electrons or holes) generated in the absorption
layer 224 collide with the semiconductor lattice of the absorption
layer 224, and produce additional carriers through impact
ionization. This avalanche process can repeat numerous times so
that one photo-generated carrier may result in the generation of
multiple carriers. As an example, a single photon absorbed in the
absorption layer 224 may lead to the generation of approximately
10, 50, 100, 200, 500, 1000, 10,000, or any other suitable number
of carriers through an avalanche-multiplication process. The
carriers generated in an APD 200 may produce an electrical current
that is coupled to an electrical circuit which may perform signal
amplification, sampling, filtering, signal conditioning,
analog-to-digital conversion, time-to-digital conversion, pulse
detection, threshold detection, rising-edge detection, or
falling-edge detection.
[0158] The number of carriers generated from a single
photo-generated carrier may increase as the applied reverse bias V
is increased. If the applied reverse bias V is increased above a
particular value referred to as the APD breakdown voltage, then a
single carrier can trigger a self-sustaining avalanche process
(e.g., the output of the APD 200 is saturated regardless of the
input light level). The APD 200 that is operated at or above a
breakdown voltage may be referred to as a single-photon avalanche
diode (SPAD) and may be referred to as operating in a Geiger mode
or a photon-counting mode. The APD 200 that is operated below a
breakdown voltage may be referred to as a linear APD, and the
output current generated by the APD 200 may be sent to an amplifier
circuit (e.g., a transimpedance amplifier). The receiver 128A or
128B (see FIGS. 26A and 26B) may include an APD configured to
operate as a SPAD and a quenching circuit configured to reduce a
reverse-bias voltage applied to the SPAD when an avalanche event
occurs in the SPAD. The APD 200 configured to operate as a SPAD may
be coupled to an electronic quenching circuit that reduces the
applied voltage V below the breakdown voltage when an
avalanche-detection event occurs. Reducing the applied voltage may
halt the avalanche process, and the applied reverse-bias voltage
may then be re-set to await a subsequent avalanche event.
Additionally, the APD 200 may be coupled to a circuit that
generates an electrical output pulse or edge when an avalanche
event occurs.
[0159] In some implementations, the APD 200 or the APD 200 along
with transimpedance amplifier have a noise-equivalent power (NEP)
that is less than or equal to 100 photons, 50 photons, 30 photons,
20 photons, or 10 photons. For example, the APD 200 may be operated
as a SPAD and may have a NEP of less than or equal to 20 photons.
As another example, the APD 200 may be coupled to a transimpedance
amplifier that produces an output voltage signal with a NEP of less
than or equal to 50 photons. The NEP of the APD 200 is a metric
that quantifies the sensitivity of the APD 200 in terms of a
minimum signal (or a minimum number of photons) that the APD 200
can detect. The NEP may correspond to an optical power (or to a
number of photons) that results in a signal-to-noise ratio of 1, or
the NEP may represent a threshold number of photons above which an
optical signal may be detected. For example, if the APD 200 has a
NEP of 20 photons, then an input beam with 20 photons may be
detected with a signal-to-noise ratio of approximately 1 (e.g., the
APD 200 may receive 20 photons from the input beam 210 and generate
an electrical signal representing the input beam 210 that has a
signal-to-noise ratio of approximately 1). Similarly, an input beam
with 100 photons may be detected with a signal-to-noise ratio of
approximately 5. In some implementations, the lidar system 120A or
120B with the APD 200 (or a combination of the APD 200 and
transimpedance amplifier) having a NEP of less than or equal to 100
photons, 50 photons, 30 photons, 20 photons, or 10 photons offers
improved detection sensitivity with respect to a conventional lidar
system that uses a PN or PIN photodiode. For example, an InGaAs PIN
photodiode used in a conventional lidar system may have a NEP of
approximately 10.sup.4 to 10.sup.5 photons, and the noise level in
a lidar system with an InGaAs PIN photodiode may be 10.sup.3 to
10.sup.4 times greater than the noise level in a lidar system 120A
or 120B with the InGaAs APD detector 200.
[0160] Referring back to FIGS. 26A and 26B, an optical filter may
be located in front of the receiver 128A or 128B and configured to
transmit light at one or more operating wavelengths of the light
source 122A or 122B and attenuate light at surrounding wavelengths.
For example, an optical filter may be a free-space spectral filter
located in front of APD 200 of FIG. 27. This spectral filter may
transmit light at the operating wavelength of the light source 122A
or 122B (e.g., between approximately 1530 nm and 1560 nm) and
attenuate light outside that wavelength range. As a more specific
example, light with wavelengths of approximately 200-1530 nm or
1560-2000 nm may be attenuated by any suitable amount, such as for
example, by at least 5 dB, 10 dB, 20 dB, 30 dB, or 40 dB.
[0161] Next, FIG. 28 illustrates an APD 250 coupled to an example
pulse-detection circuit 254. The APD 250 can be similar to the APD
200 discussed above, or can be any other suitable detector. The
pulse-detection circuit 254 can operate in the lidar system of FIG.
26A or 26B as part of the receiver 128. Further, the
pulse-detection circuit 254 can operate in the receiver 128 of FIG.
26A, the receiver 128A of FIG. 26B, or any other suitable receiver.
The pulse-detection circuit 254 alternatively can be implemented in
the controller 130 or another suitable controller. In some
implementations, parts of the pulse-detection circuit 254 can
operate in a receiver and other parts of the pulse-detection
circuit 254 can operate in a controller. For example, components
256 and 258 may be a part of the receiver 140, and components 260
and 262 may be a part of the controller 130.
[0162] The pulse-detection circuit 254 may include circuitry that
receives a signal from a detector (e.g., an electrical current from
the APD 250) and performs current-to-voltage conversion, signal
amplification, sampling, filtering, signal conditioning,
analog-to-digital conversion, time-to-digital conversion, pulse
detection, threshold detection, rising-edge detection, or
falling-edge detection. The pulse-detection circuit 254 may
determine whether an optical pulse has been received by the APD 250
or may determine a time associated with receipt of an optical pulse
by the APD 250. Additionally, the pulse-detection circuit 254 may
determine a duration of a received optical pulse. In an example
implementation, the pulse-detection circuit 254 includes a
transimpedance amplifier (TIA) 256, a gain circuit 258, a
comparator 260, and a time-to-digital converter (TDC) 262.
[0163] The TIA 256 may be configured to receive an
electrical-current signal from the APD 250 and produce a voltage
signal that corresponds to the received electrical-current signal.
For example, in response to a received optical pulse, the APD 250
may produce a current pulse corresponding to the optical pulse. The
TIA 256 may receive the current pulse from the APD 250 and produce
a voltage pulse that corresponds to the received current pulse. The
TIA 256 may also act as an electronic filter. For example, the TIA
256 may be configured as a low-pass filter that removes or
attenuates high-frequency electrical noise by attenuating signals
above a particular frequency (e.g., above 1 MHz, 10 MHz, 20 MHz, 50
MHz, 100 MHz, 200 MHz, or any other suitable frequency).
[0164] The gain circuit 258 may be configured to amplify a voltage
signal. As an example, the gain circuit 258 may include one or more
voltage-amplification stages that amplify a voltage signal received
from the TIA 256. For example, the gain circuit 258 may receive a
voltage pulse from the TIA 256, and the gain circuit 258 may
amplify the voltage pulse by any suitable amount, such as for
example, by a gain of approximately 3 dB, 10 dB, 20 dB, 30 dB, 40
dB, or 50 dB. Additionally, the gain circuit 258 may also act as an
electronic filter configured to remove or attenuate electrical
noise.
[0165] The comparator 260 may be configured to receive a voltage
signal from the TIA 256 or the gain circuit 258 and produce an
electrical-edge signal (e.g., a rising edge or a falling edge) when
the received voltage signal rises above or falls below a particular
threshold voltage V.sub.T. As an example, when a received voltage
rises above V.sub.T, the comparator 260 may produce a rising-edge
digital-voltage signal (e.g., a signal that steps from
approximately 0 V to approximately 2.5 V, 3.3 V, 5 V, or any other
suitable digital-high level). As another example, when a received
voltage falls below V.sub.T, the comparator 260 may produce a
falling-edge digital-voltage signal (e.g., a signal that steps down
from approximately 2.5 V, 3.3 V, 5 V, or any other suitable
digital-high level to approximately 0 V). The voltage signal
received by the comparator 260 may be received from the TIA 256 or
the gain circuit 258 and may correspond to an electrical-current
signal generated by the APD 250. For example, the voltage signal
received by the comparator 260 may include a voltage pulse that
corresponds to an electrical-current pulse produced by the APD 250
in response to receiving an optical pulse. The voltage signal
received by the comparator 260 may be an analog signal, and an
electrical-edge signal produced by the comparator 260 may be a
digital signal.
[0166] The time-to-digital converter (TDC) 262 may be configured to
receive an electrical-edge signal from the comparator 260 and
determine an interval of time between emission of a pulse of light
by the light source and receipt of the electrical-edge signal. The
output of the TDC 262 may be a numerical value that corresponds to
the time interval determined by the TDC 262. In some
implementations, the TDC 262 has an internal counter or clock with
any suitable period, such as for example, 5 ps, 10 ps, 15 ps, 20
ps, 30 ps, 50 ps, 100 ps, 0.5 ns, 1 ns, 2 ns, 5 ns, or 10 ns. The
TDC 262 for example may have an internal counter or clock with a 20
ps period, and the TDC 262 may determine that an interval of time
between emission and receipt of a pulse is equal to 25,000 time
periods, which corresponds to a time interval of approximately 0.5
microseconds. The TDC 262 may send the numerical value "25000" to a
processor or controller 130 of the lidar system 120A or 120B, which
may include a processor configured to determine a distance from the
lidar system 120A or 120B to the target 160 based at least in part
on an interval of time determined by a TDC 262. The processor may
receive a numerical value (e.g., "25000") from the TDC 262 and,
based on the received value, the processor may determine the
distance from the lidar system 120A or 120B to the target 160.
IV. Placement and Operation of a Lidar Sensor Unit in a Vehicle
[0167] Depending on where a lidar sensor unit is mounted on a
vehicle, one or more of the surfaces of the housing could coincide
with an external or interior surface of a vehicle. Example surfaces
include a hood, a quarter-panel, a sideview mirror housing, a trunk
lid, grill, headlamp or tail light housing, dashboard, vehicle
roof, front bumper, rear bumper, or other vehicle body part
surface. When provided in a vulnerable location of a vehicle, such
as a front or rear bumper, the front or rear bumper may be
fortified or reinforced with additional force resistance or force
dampening features to protect sensitive components of the lidar
sensor unit 10 from damage. The low profile of the lidar sensor
unit 10 lends itself to being strategically located at optimal
locations of a vehicle body without detracting from the aesthetic
appearance of the vehicle. For example, a plurality of the lidar
sensor units 10 may be disposed one at each front corner, or even
one at each of all four corners, of a vehicle roof, with the
majority of the volume occupied by the lidar sensor units 10
embedded within the roof, so that only a window of the unit
protrudes prominently of the vehicle roof (or other vehicle surface
in which the lidar sensor unit 10 is embedded).
[0168] The components of the lidar sensor unit 10 may be configured
so that at least a portion of the planar mirror 14 extends above
the rotatable polygon mirror 12, and only a region extending from a
lower edge of the planar mirror 14 to a top of the housing projects
prominently from a surface of a body of a vehicle on which the
lidar sensor unit 10 is deployed.
[0169] More particularly, as illustrated in FIG. 29, a housing 302
may enclose a lidar sensor unit. Some or all of the enclosed
components can be the components of the lidar sensor unit 10. The
housing 302 is placed in an opening in a surface 300, which may
correspond to a section of a vehicle roof or another suitable
surface of a vehicle. A portion 306 protrudes prominently above the
surface 300, and a portion is 304 is "submerged" under the surface
300. The portion 306 includes a window 308 through which input and
output beams of light travel. The size of the submerged portion of
304 is larger than the protruding portion 306, in at least some of
the implementations, to reduce aerodynamic drag. Although the
window 308 is illustrated in FIG. 29 as a vertical surface
perpendicular to the surface 300, in general the window 308 may be
sloped, curved, or otherwise configured to direct a flow of air
around the protruding portion 306. In an example implementation,
the size of the window 308 corresponds approximately to the size of
the planar mirror 14. The window 308 may be the same or similar to
the window 167 depicted in FIGS. 26A and 26B.
[0170] Referring to FIG. 30, the housing 302 may be embedded in the
roof of a vehicle 320, with the window 308 oriented similar to the
windshield of the vehicle 320. The housing 302 encloses the lidar
sensor unit 10, oriented so that the axis of rotation 324 of the
polygon mirror 12 is aligned with a longitudinal axis of the
vehicle 326. This orientation may serve to reduce adverse effects
of vibration, acceleration, and deceleration. Thus, when the
vehicle 320 accelerates quickly, the polygon mirror enclosed in the
housing 302 may be displaced along the axis 324, and the input and
output beams impinge on the surface of the polygon mirror on the
same plane as in the configuration prior to the displacement, which
does not result in the scan lines being misaligned to displaced
(i.e., the beams may strike different portions of the reflective
surface, but the reflection imparted by these portions of the
reflective surface is the same as in the original configuration).
Similarly, when the vehicle 320 decelerates quickly, the potential
displacement of the polygon mirror along the axis 324 does not
adversely affect the scan lines. In contrast to these scenarios,
when axis 324 is perpendicular to the orientation of the vehicle
320, the displacement of the polygon mirror may result in the
FOR.sub.H shifting right or left, which in turn results in scan
errors.
[0171] In general, any suitable number of lidar sensor units 10 may
be integrated into a vehicle. In one example implementation,
multiple lidar sensor units 10, operating in a lidar system similar
to the system 120B, may be integrated into a car to provide a
complete 360-degree horizontal FOR around the car. As another
example, 4-10 lidar sensor units 10, each system having a 45-degree
to 90-degree horizontal FOR, may be combined together to form a
sensing system that provides a point cloud covering a 360-degree
horizontal FOR. The lidar sensor units 10 may be oriented so that
adjacent FORs have an amount of spatial or angular overlap to allow
data from the multiple lidar sensor units 10 to be combined or
stitched together to form a single or continuous 360-degree point
cloud. As an example, the FOR of each lidar sensor unit 10 may have
approximately 1-15 degrees of overlap with an adjacent FOR. In
particular embodiments, a vehicle may refer to a mobile machine
configured to transport people or cargo. For example, a vehicle may
include, may take the form of, or may be referred to as a car,
automobile, motor vehicle, truck, bus, van, trailer, off-road
vehicle, farm vehicle, lawn mower, construction equipment, golf
cart, motorhome, taxi, motorcycle, scooter, bicycle, skateboard,
train, snowmobile, watercraft (e.g., a ship or boat), aircraft
(e.g., a fixed-wing aircraft, helicopter, or dirigible), or
spacecraft. In particular embodiments, a vehicle may include an
internal combustion engine or an electric motor that provides
propulsion for the vehicle.
[0172] Referring to FIG. 31, lidar sensor units 322A-D are
installed in the roof of a vehicle 320, in an example
implementation. Each of the lidar sensor units 322A-D is
approximately at 45.degree. relative to one of the edges of the
roof. The lidar sensor units 322A-D thus are oriented so that the
FOR of the lidar sensor unit 322A covers an area in front of the
vehicle and to the right of the vehicle, the FOR of the lidar
sensor unit 322B covers an area behind the vehicle and to the right
of the vehicle, the FOR of the lidar sensor unit 322C covers an
area behind the vehicle and to the left of the vehicle, and the FOR
of the lidar sensor unit 322D covers an area in front of the
vehicle and to the left of the vehicle. The FORs of the lidar
sensor units 322A and 322D have an angular overlap (e.g., five
degrees) directly in front of the vehicle, in an example
implementation. Further, in an example implementation, the FORs of
the lidar sensor units 322A and 322B have no angular overlap or
little angular overlap.
[0173] In some implementations, one or more lidar sensor units 10
are included in a vehicle as part of an advanced driver assistance
system (ADAS) to assist a driver of the vehicle in the driving
process. For example, a lidar sensor units 10 may be part of an
ADAS that provides information or feedback to a driver (e.g., to
alert the driver to potential problems or hazards) or that
automatically takes control of part of a vehicle (e.g., a braking
system or a steering system) to avoid collisions or accidents. The
lidar sensor units 10 may be part of a vehicle ADAS that provides
adaptive cruise control, automated braking, automated parking,
collision avoidance, alerts the driver to hazards or other
vehicles, maintains the vehicle in the correct lane, or provides a
warning if an object or another vehicle is in a blind spot.
[0174] In some cases, one or more lidar sensor units 10 are
integrated into a vehicle as part of an autonomous-vehicle driving
system. In an example implementation, the lidar sensor units 10
provides information about the surrounding environment to a driving
system of an autonomous vehicle. An autonomous-vehicle driving
system may include one or more computing systems that receive
information from the lidar sensor units 10 about the surrounding
environment, analyze the received information, and provide control
signals to the vehicle's driving systems (e.g., steering wheel,
accelerator, brake, or turn signal). For example, the lidar sensor
units 10 integrated into an autonomous vehicle may provide an
autonomous-vehicle driving system with a point cloud every 0.1
seconds (e.g., the point cloud has a 10 Hz update rate,
representing 10 frames per second). The autonomous-vehicle driving
system may analyze the received point clouds to sense or identify
targets 160 (see FIGS. 26A and 26B) and their respective locations,
distances, or speeds, and the autonomous-vehicle driving system may
update control signals based on this information. As an example, if
the lidar sensor unit 10 detects a vehicle ahead that is slowing
down or stopping, the autonomous-vehicle driving system may send
instructions to release the accelerator and apply the brakes.
[0175] An autonomous vehicle may be referred to as an autonomous
car, driverless car, self-driving car, robotic car, or unmanned
vehicle. An autonomous vehicle may be a vehicle configured to sense
its environment and navigate or drive with little or no human
input. For example, an autonomous vehicle may be configured to
drive to any suitable location and control or perform all
safety-critical functions (e.g., driving, steering, braking,
parking) for the entire trip, with the driver not expected to
control the vehicle at any time. As another example, an autonomous
vehicle may allow a driver to safely turn their attention away from
driving tasks in particular environments (e.g., on freeways), or an
autonomous vehicle may provide control of a vehicle in all but a
few environments, requiring little or no input or attention from
the driver.
[0176] An autonomous vehicle may be configured to drive with a
driver present in the vehicle, or an autonomous vehicle may be
configured to operate the vehicle with no driver present. As an
example, an autonomous vehicle may include a driver's seat with
associated controls (e.g., steering wheel, accelerator pedal, and
brake pedal), and the vehicle may be configured to drive with no
one seated in the driver's seat or with little or no input from a
person seated in the driver's seat. As another example, an
autonomous vehicle may not include any driver's seat or associated
driver's controls, and the vehicle may perform substantially all
driving functions (e.g., driving, steering, braking, parking, and
navigating) without human input. As another example, an autonomous
vehicle may be configured to operate without a driver (e.g., the
vehicle may be configured to transport human passengers or cargo
without a driver present in the vehicle). As another example, an
autonomous vehicle may be configured to operate without any human
passengers (e.g., the vehicle may be configured for transportation
of cargo without having any human passengers onboard the
vehicle).
[0177] As indicated above, a light source of the lidar sensor unit
10 can be located remotely from some of the other components of the
lidar sensor unit 10 (such as the scanner 11 and the receiver 128A
or 128B). Moreover, a lidar system implemented in a vehicle may
include fewer light sources than scanners and receivers.
[0178] FIG. 32 illustrates an example vehicle 350 with a lidar
system 351 that includes a laser 353 with multiple sensor heads 352
coupled to the laser 353 via multiple laser-sensor links 370. Each
of the sensor heads 352 can be implemented similar to the lidar
sensor unit 10.
[0179] Each of the laser-sensor links 370 may include one or more
optical links and/or one or more electrical links. The sensor heads
352 in FIG. 32 are positioned or oriented to provide a greater than
30-degree view of an environment around the vehicle. More
generally, a lidar system with multiple sensor heads may provide a
horizontal field of regard around a vehicle of approximately
30.degree., 45.degree., 60.degree., 90.degree., 120.degree.,
180.degree., 270.degree., or 360.degree.. Each of the sensor heads
352 may be attached to or incorporated into a bumper, fender,
grill, side panel, spoiler, roof, headlight assembly, taillight
assembly, rear-view mirror assembly, hood, trunk, window, or any
other suitable part of the vehicle.
[0180] In the example of FIG. 32, four sensor heads 352 are
positioned at or near the four corners of the roof of the vehicle,
and the laser 353 may be located within the vehicle (e.g., in or
near the trunk). The four sensor heads 352 may each provide a
90.degree. to 120.degree. horizontal field of regard (FOR), and the
four sensor heads 352 may be oriented so that together they provide
a complete 360-degree view around the vehicle. As another example,
the lidar system 351 may include six sensor heads 352 positioned on
or around a vehicle, where each of the sensor heads 352 provides a
60.degree. to 90.degree. horizontal FOR. As another example, the
lidar system 351 may include eight sensor heads 352, and each of
the sensor heads 352 may provide a 45.degree. to 60.degree.
horizontal FOR. As yet another example, the lidar system 351 may
include six sensor heads 352, where each of the sensor heads 352
provides a 70.degree. horizontal FOR with an overlap between
adjacent FORs of approximately 10.degree.. As another example, the
lidar system 351 may include two sensor heads 352 which together
provide a forward-facing horizontal FOR of greater than or equal to
30.degree..
[0181] Data from each of the sensor heads 352 may be combined or
stitched together to generate a point cloud that covers a greater
than or equal to 30-degree horizontal view around a vehicle. For
example, the laser 353 may include a controller or processor that
receives data from each of the sensor heads 352 (e.g., via a
corresponding electrical link 370) and processes the received data
to construct a point cloud covering a 360-degree horizontal view
around a vehicle or to determine distances to one or more targets.
The point cloud or information from the point cloud may be provided
to a vehicle controller 372 via a corresponding electrical,
optical, or radio link 370. In some implementations, the point
cloud is generated by combining data from each of the multiple
sensor heads 352 at a controller included within the laser 353 and
provided to the vehicle controller 372. In other implementations,
each of the sensor heads 352 includes a controller or process that
constructs a point cloud for a portion of the 360-degree horizontal
view around the vehicle and provides the respective point cloud to
the vehicle controller 372. The vehicle controller 372 then
combines or stitches together the points clouds from the respective
sensor heads 352 to construct a combined point cloud covering a
360-degree horizontal view. Still further, the vehicle controller
372 in some implementations communicates with a remote server to
process point cloud data.
[0182] In any event, the vehicle 350 may be an autonomous vehicle
where the vehicle controller 372 provides control signals to
various components 390 within the vehicle 350 to maneuver and
otherwise control operation of the vehicle 350. The components 390
are depicted in an expanded view in FIG. 32 for ease of
illustration only. The components 390 may include an accelerator
374, brakes 376, a vehicle engine 378, a steering mechanism 380,
lights 382 such as brake lights, head lights, reverse lights,
emergency lights, etc., a gear selector 384, and/or other suitable
components that effectuate and control movement of the vehicle 350.
The gear selector 384 may include the park, reverse, neutral, drive
gears, etc. Each of the components 390 may include an interface via
which the component receives commands from the vehicle controller
372 such as "increase speed," "decrease speed," "turn left 5
degrees," "activate left turn signal," etc. and, in some cases,
provides feedback to the vehicle controller 372.
[0183] In some implementations, the vehicle controller 372 receives
point cloud data from the sensor heads 352 via the link 373 and
analyzes the received point cloud data to sense or identify targets
130 and their respective locations, distances, speeds, shapes,
sizes, type of target (e.g., vehicle, human, tree, animal), etc.
The vehicle controller 372 then provides control signals via the
link 373 to the components 390 to control operation of the vehicle
based on the analyzed information. For example, the vehicle
controller 372 may identify an intersection based on the point
cloud data and determine that the intersection is the appropriate
location at which to make a left turn. Accordingly, the vehicle
controller 372 may provide control signals to the steering
mechanism 380, the accelerator 374, and brakes 376 for making a
proper left turn. In another example, the vehicle controller 372
may identify a traffic light based on the point cloud data and
determine that the vehicle 350 needs to come to a stop. As a
result, the vehicle controller 372 may provide control signals to
release the accelerator 374 and apply the brakes 376.
[0184] As another example, FIG. 33 illustrates a vehicle 400 in
which a laser 404 is optically coupled to six sensor heads 402,
each of which can be implemented as the lidar sensor unit 10. The
sensor heads 402A and 402G are disposed at the front of the vehicle
400, the sensor heads 402B and 402F are disposed in the side view
mirrors, and the sensor heads 402C-E are disposed on the trunk. In
particular, the sensor head 402D is oriented to face backward
relative to the orientation of the vehicle 400, and the sensor
heads 402E and 402C are oriented at approximately 45 degrees
relative to the axis of orientation of the sensor head 402D.
V. Manufacturing a Highly Balanced Polygon Mirror
[0185] The reflective surfaces 18-24 of the polygon mirror 12 may
be manufactured using surface replication techniques. Coarse and
fine balancing techniques, including (by way of example only) the
use of drilling, milling, etching, and polishing, can be employed
prior to mounting the polygon mirror 12 to a motor 32, and
subsequent to mounting, high-energy laser pulses can be utilized to
remove matter at precise locations on the polygon mirror 12. The
coarse balancing techniques employed may include utilizing a
shaft-balancing machine. Further, in forming the block 16, a
hollowed-out substrate may be used to reduce the weight of the
block.
[0186] More particularly, FIG. 34 depicts a flow diagram of an
example method 500 for manufacturing a highly balanced rotatable
polygon mirror that can be used as the polygon mirror 12 in the
lidar sensor unit 10.
[0187] First, a block for a polygon mirror is formed (502). A glass
substrate is used in an example implementation. In general, any
suitable material such as a plastic, a polycarbonate, a composite
material, metal, carbon fiber, or a ceramic can be used. It is also
possible to use a metal frame with inserts of material susceptible
to ablation by high-powered lasers. For example, a metal frame can
contain glass or plastic cylinders at or near the corners of the
block.
[0188] Next, a coarse balancing procedure is used (504) to obtain a
relatively balanced block. The coarse balancing procedure can
involve one or more of drilling, milling, etching, polishing, or
any other suitable technique. Balancing machines available today
from various manufacturers can be used during coarse balancing.
However, many balancing machines, even small-part balancing
machines, cannot provide precise balancing desirable in the lidar
sensor unit 10. Small deviations in weight distribution can result
in non-uniform angular velocity when the polygon mirror 12 rotates
at a high rate, which in turn can result in distortion of scan
lines (e.g., wrong distances between adjacent pixels).
[0189] Further, one or more surfaces of the block formed at block
502 can be made reflective (506). Referring to FIGS. 10-12, for
example, all four surfaces of the polygon mirror block 12 can be
made reflective, but in other implementations of the scanner only
one of the surfaces can be made reflective, or two non-adjacent
surfaces can be made reflective. In one implementation of the
method 500, the one or more surfaces of the block are made
reflective using surface replication, e.g., by creating a thin
reflective film and applying the film to the surfaces of the block.
Surface replication can be applied to two opposite sides of the
block at the same time to accelerate the process of manufacturing a
highly balanced mirror. Other coating (e.g., sputtering) and
non-coating techniques also can be used to make the surfaces
reflective, preferably those techniques that reduce the probability
of damaging the reflective surfaces during the fine balancing
procedure. In some implementations, the order of execution of
procedures 504 and 506 can be reversed (i.e., coarse balancing can
occur before making the surfaces reflective or after making the
surfaces reflective).
[0190] Once the block acquires one or more reflective surfaces and
is approximately balanced, the block is mated to a motor (508). To
reduce the probability of subsequently damaging a precisely
balanced block, the block is mated to the motor in the
corresponding assembly of the lidar sensor unit 10. As a more
specific example, the polygon mirror axle 30 is inserted through or
attached to a coarsely balanced polygon mirror 12, and the coarsely
balanced polygon mirror 12 is installed on the bracket 29 and mated
to the motor 32 (see FIGS. 1 and 2). After the polygon mirror 12 is
precisely balanced as discussed below, the assembly including the
components 12, 29, 30, and 32 is used in the lidar sensor unit 10
as a single unit, i.e., is not disassembled into the individual
components.
[0191] To balance the block more precisely, rotation is imparted to
the block (510) and material is removed from the block using
high-energy laser pulses or a continuous laser beam (512). The
removal of the material can be optimized by selecting a laser
having an appropriate operating wavelength based on the material
from which the block is made. For example, a laser operating in the
ultraviolet wavelength range (e.g., an excimer laser) may be used
to ablate material from a block made of glass or plastic. As
another example, a laser operating in the infrared wavelength range
(e.g., a neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser
operating at a wavelength of approximately 1.06 .mu.m or a CO.sub.2
laser operating at 9.4-10.6 .mu.m) may be used to ablate material
from a block made of metal. To continue with the example above, the
motor 32 can impart rotation to the polygon mirror 12, and a
high-power laser can aim at the wall 26 (best illustrated in FIGS.
2 and 3). The laser can be aimed at the regions close to the
corners, where the impact on angular velocity due to torque is the
greatest, due to the vertical orientation of the polygon mirror 12.
In some implementations, material may be removed from the axle or
shaft attached to the polygon mirror 12 and about which the polygon
mirror 12 rotates.
[0192] As the block rotates and ablation is carried out, the
changes in balancing can be monitored by, for example, determining
rotational speed of the block and determining the differences
between the speed of individual facets. To this end, a stationary
photo-interrupter can be used, with tabs corresponding to each
facet provided on the axis of rotation of the block (or on the
block itself). As the tabs pass through the stationary
photo-interrupter, the rate each facet is traveling can be
measured. Thus, if for a block with four facets, the time between
the first tab and the second tab traveling past the
photo-interrupter is t, the time between the second tab and the
third tab traveling past the photo-interrupter is t+e, the time
between the third tab and the fourth tab traveling past the
photo-interrupter is t+e', and the time between the third tab and
the fourth tab traveling past the photo-interrupter is t+e''.
Ablation can be applied to the block so as to make these
measurements as close to each other as practically possible. After
the procedure of rotation and material removal (510,512) is
completed, the time between each pair of adjacent tab traveling
past the photo-interrupter is as close to t as possible. A
controller, a workstation, or any suitable computing device can be
used to control the high-powered laser used in ablation in view of
the data from the photo-interrupter. The controller also can
determine the changes in time between pairs of adjacent tabs
traveling past the photo-interrupter and generate an appropriate
notification for the operator to indicate when the process is
complete, or automatically complete the method 500, depending on
the implementation.
[0193] In another implementation, a light source (not necessarily a
laser) can be used to direct a light at the block, with a temporary
detector being in a fixed position relative to the block, so as to
determine the rate at which each facet is moving. The light source
can direct a beam of light at the block, which reflects the beam of
light along a scan line. The temporary detector can be placed at a
point on the scan line, in the path of the beam of light. The
controller can measure the times at which the temporary detector
detects the beam of light and derive the appropriate measurements
of t+e, t+e', etc., similar to the example above. Similar to the
example above, the controller then can automatically shut down the
laser emitting high-energy pulses and/or provide a notification to
the operator.
[0194] In yet another implementation, a balancing machine can be
used along with a high-energy laser for the fine-balancing
process.
[0195] In some implementations, all or part of a method for
manufacturing a highly balanced rotatable polygon mirror as
described herein may be applied to any suitable rotating object.
For example, material removal by a laser source to form a
high-balanced rotatable object may be applied to a high-speed
motor, dental drill, or hard disk drive.
VI. Scan Patterns and Scan Pattern Modifications in a Lidar Sensor
Unit
[0196] FIG. 35 illustrates an example light-source field of view
(FOV.sub.L) and receiver field of view (FOV.sub.R) for the lidar
sensor unit 10 and/or the lidar system 120A or 120B, as well as a
scan pattern 520 which the lidar sensor unit 10 and/or the lidar
system 120 can produce.
[0197] The scan pattern 520 corresponds to a scan across any
suitable field of regard (FOR) having any suitable horizontal FOR
(FOR.sub.H) and any suitable vertical FOR (FOR.sub.V). For example,
a certain scan pattern may have a field of regard represented by
angular dimensions (e.g., FOR.sub.H.times.FOR.sub.V)
40.degree..times.30.degree., 90.degree..times.40.degree., or
60.degree..times.15.degree.. As another example, a certain scan
pattern may have a FOR.sub.H greater than or equal to 10.degree.,
25.degree., 30.degree., 40.degree., 60.degree., 90.degree., or
120.degree.. As yet another example, a certain scan pattern may
have a FOR.sub.V greater than or equal to 2.degree., 5.degree.,
10.degree., 15.degree., 20.degree., 30.degree., or 45.degree.. In
the example of FIG. 35, a reference line 522 represents a center of
the field of regard of the scan pattern 520. The reference line 522
may have any suitable orientation, such as, a horizontal angle of
0.degree. (e.g., reference line 522 may be oriented straight ahead)
and a vertical angle of 0.degree. (e.g., reference line 522 may
have an inclination of) 0.degree., or the reference line 522 may
have a nonzero horizontal angle or a nonzero inclination (e.g., a
vertical angle of +10.degree. or) -10.degree.. In FIG. 35, if the
scan pattern 520 has a 60.degree..times.15.degree. field of regard,
then the scan pattern 520 covers a .+-.30.degree. horizontal range
with respect to reference line 522 and a .+-.7.5.degree. vertical
range with respect to reference line 522. Additionally, an optical
beam 532 in FIG. 35 has an orientation of approximately -15.degree.
horizontal and +3.degree. vertical with respect to reference line
522. The beam 532 may be referred to as having an azimuth of
-15.degree. and an altitude of +3.degree. relative to the reference
line 246. An azimuth (which may be referred to as an azimuth angle)
may represent a horizontal angle with respect to the reference line
522, and an altitude (which may be referred to as an altitude
angle, elevation, or elevation angle) may represent a vertical
angle with respect to the reference line 522.
[0198] The scan pattern 520 may include multiple pixels along scan
lines 524, each pixel corresponding to instantaneous light-source
FOV.sub.L. Each pixel may be associated with one or more laser
pulses and one or more corresponding distance measurements. A cycle
of the scan pattern 520 may include a total of
P.sub.x.times.P.sub.y pixels (e.g., a two-dimensional distribution
of P.sub.x, by P.sub.y pixels). For example, the scan pattern 520
may include a distribution with dimensions of approximately
100-2,000 pixels along a horizontal direction and approximately
4-200 pixels along a vertical direction. As another example, the
scan pattern 520 may include a distribution of 1,000 pixels along
the horizontal direction by 64 pixels along the vertical direction
(e.g., the frame size is 1000.times.64 pixels) for a total of
64,000 pixels per cycle of scan pattern 520. The number of pixels
along a horizontal direction may be referred to as a horizontal
resolution of the scan pattern 520, and the number of pixels along
a vertical direction may be referred to as a vertical resolution of
the scan pattern 520. As an example, the scan pattern 520 may have
a horizontal resolution of greater than or equal to 100 pixels and
a vertical resolution of greater than or equal to 4 pixels. As
another example, the scan pattern 520 may have a horizontal
resolution of 100-2,000 pixels and a vertical resolution of 4-400
pixels.
[0199] Each pixel may be associated with a distance (e.g., a
distance to a portion of a target 160 from which the corresponding
laser pulse was scattered) or one or more angular values. As an
example, the pixel may be associated with a distance value and two
angular values (e.g., an azimuth and altitude) that represent the
angular location of the pixel with respect to the lidar system 120A
or 120B. A distance to a portion of the target 160 may be
determined based at least in part on a time-of-flight measurement
for a corresponding pulse. An angular value (e.g., an azimuth or
altitude) may correspond to an angle (e.g., relative to reference
line 522) of the output beam 532 (e.g., when a corresponding pulse
is emitted from the lidar sensor unit 10 or the lidar system 120)
or an angle of the input beam 534 (e.g., when an input signal is
received by the lidar sensor unit 10 or the lidar system 120A or
120B). In some implementations, the lidar sensor unit 10 or the
lidar system 120A or 120B determines an angular value based at
least in part on a position of a component of the scanner 11. For
example, an azimuth or altitude value associated with the pixel may
be determined from an angular position of one or more corresponding
scanning mirrors of the scanner 11.
[0200] The light source 122A or 122B may emit pulses of light as
the FOV.sub.L and FOV.sub.R are scanned by the scanner 11 across
the FOR. The light-source field of view may refer to an angular
cone illuminated by the light source 122A or 122B at a particular
instant of time or an angular cone that would be illuminated by the
light source 122A or 122B at a particular instant of time if the
light source 122A or 122B were to emit light at that instant of
time. For example, when the light source 122A or 122B operates in a
pulsed mode, the light source 122A or 122B may continuously change
its orientation relative to the external world but actively
illuminate corresponding regions only during the duty cycle.
[0201] Similarly, a receiver field of view may refer to an angular
cone over which the receiver 128A or 128B may receive or detect
light at a particular instant of time, and any light outside the
receiver field of view may not be received or detected. For
example, as the scanner 11 scans the light-source field of view
across a field of regard, the lidar sensor unit 10 or the lidar
system 120A or 120B may send the pulse of light in the direction
the FOV.sub.L is pointing at the time the light source 122A or 122B
emits the pulse. The pulse of light may scatter off the target 160,
and the receiver 128A or 128B may receive and detect a portion of
the scattered light that is directed along or contained within the
FOV.sub.R.
[0202] An instantaneous FOV may refer to an angular cone being
illuminated by a pulse directed along the direction the
light-source FOV is pointing at the instant the pulse of light is
emitted. Thus, while the light-source FOV and the detector FOV are
scanned together in a synchronous manner (e.g., the scanner 11
scans both the light-source FOV and the detector FOV across the
field of regard along the same scan direction and at the same scan
speed, maintaining the same relative position to each other), the
instantaneous FOV remains "stationary," and the detector FOV
effectively moves relative to the instantaneous FOV. More
particularly, when a pulse of light is emitted, the scanner 11
directs the pulse along the direction in which the light-source FOV
currently is pointing. Each instantaneous FOV (IFOV) corresponds to
a pixel. Thus, each time a pulse is emitted, the lidar sensor unit
10 or the lidar system 120A or 120B produces or defines an IFOV (or
pixel) that is fixed in place and corresponds to the light-source
FOV at the time when the pulse is emitted. During operation of the
scanner 11, the detector FOV moves relative to the light-source
IFOV but does not move relative to the light-source FOV.
[0203] In some implementations, the scanner 11 is configured to
scan both a light-source field of view and a receiver field of view
across a field of regard of the lidar system 120A or 120B. The
lidar system 120A or 120B may emit and detect multiple pulses of
light as the scanner 11 scans the FOV.sub.L and FOV.sub.R across
the field of regard while tracing out the scan pattern 520. The
scanner 11 in some implementations scans the light-source field of
view and the receiver field of view synchronously with respect to
one another. In this case, as the scanner 11 scans FOV.sub.L across
a scan pattern 520, the FOV.sub.R follows substantially the same
path at the same scanning speed. Additionally, the FOV.sub.L and
FOV.sub.R may maintain the same relative position to one another as
the scanner 11 scans FOV.sub.L and FOV.sub.R across the field of
regard. For example, the FOV.sub.L may be substantially overlapped
with or centered inside the FOV.sub.R, and the scanner 11 may
maintain this relative positioning between FOV.sub.L and FOV.sub.R
throughout a scan. As another example, the FOV.sub.R may lag behind
the FOV.sub.L by a particular, fixed amount throughout a scan
(e.g., the FOV.sub.R may be offset from the FOV.sub.L in a
direction opposite the scan direction). As yet another example,
during a time between the instant when a pulse is emitted and prior
to the time when the pulse can return from a target located at the
maximum distance R.sub.MAX, FOV.sub.R may move relative to the IFOV
or pixel to define different amounts of overlap, as discussed in
more detail below.
[0204] The FOV.sub.L may have an angular size or extent
.THETA..sub.L that is substantially the same as or that corresponds
to the divergence of the output beam 532, and the FOV.sub.R may
have an angular size or extent .THETA..sub.R that corresponds to an
angle over which the receiver 128 may receive and detect light. The
receiver field of view may be any suitable size relative to the
light-source field of view. For example, the receiver field of view
may be smaller than, substantially the same size as, or larger than
the angular extent of the light-source field of view. In some
implementations, the light-source field of view has an angular
extent of less than or equal to 50 milliradians, and the receiver
field of view has an angular extent of less than or equal to 50
milliradians. The FOV.sub.L may have any suitable angular extent
.THETA..sub.L, such as for example, approximately 0.1 mrad, 0.2
mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3 mrad, 5 mrad, 10 mrad,
20 mrad, 40 mrad, or 50 mrad. Similarly, the FOV.sub.R may have any
suitable angular extent .THETA..sub.R, such as for example,
approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2
mrad, 3 mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. The
light-source field of view and the receiver field of view may have
approximately equal angular extents. As an example, .THETA..sub.L
and .THETA..sub.R may both be approximately equal to 1 mrad, 2
mrad, or 3 mrad. In some implementations, the receiver field of
view is larger than the light-source field of view, or the
light-source field of view is larger than the receiver field of
view. For example, .THETA..sub.L may be approximately equal to 1.5
mrad, and .THETA..sub.R may be approximately equal to 3 mrad. As
another example, .THETA..sub.R may be approximately L times larger
than .THETA..sub.L, where L is any suitable factor, such as for
example, 1.1, 1.2, 1.5, 2, 3, 5, or 10.
[0205] As indicated above, a pixel may represent or correspond to
an instantaneous light-source FOV. As the output beam 532
propagates from the light source 122A or 122B, the diameter of the
output beam 532 (as well as the size of the corresponding pixel)
may increase according to the beam divergence .THETA..sub.L. As an
example, if the output beam 532 has a .THETA..sub.L of 2 mrad, then
at a distance of 100 m from the lidar system 120A or 120B, the
output beam 532 may have a size or diameter of approximately 20 cm,
and a corresponding pixel may also have a corresponding size or
diameter of approximately 20 cm. At a distance of 200 m from the
lidar system 120, the output beam 532 and the corresponding pixel
may each have a diameter of approximately 40 cm.
[0206] The scanner 11 may be configured to scan the output beam 532
over a 5-degree angular range, 20-degree angular range, 30-degree
angular range, 60-degree angular range, or any other suitable
angular range. The FOR of the lidar system 120A or 120B may refer
to an area, region, or angular range over which the lidar system
120A or 120B may be configured to scan or capture distance
information. When the lidar system 120 scans the output beam 532
within a 30-degree scanning range, the lidar system 120A or 120B
may be referred to as having a 30-degree angular field of regard.
In various implementations, the lidar system 120A or 120B may have
a FOR of approximately 10.degree., 20.degree., 40.degree.,
60.degree., 120.degree., or any other suitable FOR. The FOR also
may be referred to as a scan region.
[0207] The scanner 11 is configured to scan the output beam 532
horizontally, with each reflective surface of the polygon mirror 12
defining a respective scan line 524, and vertically, where the
oscillation of the planar mirror 14 moves the scan lines 524 upward
or downward. The lidar system 120 may have a particular FOR along
the horizontal direction and another particular FOR along the
vertical direction. For example, the lidar system 120 may have a
horizontal FOR of 10.degree. to 120.degree. and a vertical FOR of
2.degree. to 45.degree..
[0208] Referring back to FIGS. 1 and 26A/26B, the controller 130 in
one implementation generates and dynamically modifies the drive
signal for the motor 64 which oscillates the planar mirror 14. The
motor 32 driving rotation of the polygon mirror 12 may operate in
an open-loop mode, without relying on control signals from the
controller 130. In this implementation, the motor 32 driving the
polygon mirror 12 may rotate at a constant speed to generate
similar scan lines, while variations in the speed at which the
planar mirror 14 moves relative to the axis of oscillation can
result in some scan lines being farther apart, some scan lines
being closer together, etc. Further, the controller 130 can modify
the drive signal for the motor 64 to reposition the entire
operational FOR of the lidar sensor unit 10 within the larger range
motion available to the planar mirror 14. Still further, the
controller 130 can modify the drive signal for the motor 64 to
"stretch" the FOR of the operational FOR of the lidar sensor unit
10 so as to encompass the entire available FOR. In some
implementations, the motor 32 driving rotation of the polygon
mirror 12 may operate in a closed-loop mode, where the motor 32
receives a control signal that regulates, stabilizes, or adjusts
the rotational speed of the polygon mirror 12. For example, the
polygon mirror 12 may be provided with a tab that passes through
one or more stationary photo-interrupters as the polygon mirror 12
rotates. The signals from the photo-interrupters may be sent to the
controller 130, and the controller 130 may provide a control signal
to the motor 32 to maintain the rotation speed of the polygon
mirror 12 at a substantially constant value.
[0209] In other implementations, however, the controller 130
modifies the drive signal supplied to the motor 32 to thereby
adjust the rotation of the polygon mirror 12. For example, the
controller 130 may slow down the rotation of the polygon mirror 12
when the output beam (or a pair of output beams associated with the
same eye) traverses the middle of the scan line, so that pixel
density near the center of the FOR.sub.H is higher than at the
periphery of the FOR.sub.H.
[0210] The controller may modify the drive signal for the motor 32
and/or the drive signal for the motor 64 dynamically in response to
various triggering events. In addition to detection of an upward or
downward slope, as discussed in more detail below, examples of
suitable triggering events include detection of a particular object
in a certain direction relative to the vehicle (e.g., if an object
is moving quickly across the path of the vehicle, the lidar system
120A and 120B may modify the scan pattern to obtain a higher
density rate where the object is detected to be able to better
respond to the potential threat of collision), a sound detected at
in a certain direction relative to the vehicle, a heat signature
detected at in a certain direction relative to the vehicle,
etc.
[0211] FIG. 36 depicts an example range 600 within which the lidar
system 120 can set the operational FOR 602. In the lidar system
120A or 120B, the range of motion for the planar mirror 14 can
define a vertical dimension of the available FOR.sub.V-AVAIL (e.g.,
90.degree., 100.degree., 110.degree., 120.degree. that exceeds the
vertical dimension of the operational FOR.sub.V-OPER (e.g.,
60.degree.). The controller 130 can adjust the drive signal for the
motor 64 so as to move the FOR 602 upward or downward relative to
the center of the available FOR 600.
[0212] In some implementations or scenarios, the controller 130
adjusts the drive signal for the motor 64 so that the
FOR.sub.V-OPER "stretches" out to cover a larger portion of the
FOR.sub.V-AVAIL. For example, the controller 130 may cause the
FOR.sub.V-OPER to temporarily change from
60.degree..times.30.degree. to 60.degree..times.40.degree. or
60.degree..times.30.degree. to 60.degree..times.50.degree.. The
controller may modify the drive signal for the motor 64 without
modifying the operation of the motor 32 driving the polygon mirror
and, as a result, the modification of the FOR.sub.V-OPER from
60.degree..times.30.degree. to 60.degree..times.40.degree. results
in changes in distances between at least some of the scan lines.
The controller 130 may cause these changes to be uniform or
non-uniform (e.g., separate the scan lines near the edges of the
FOR.sub.V by a larger amount).
[0213] Further, the lidar system 120A or 120B can modify the drive
signal for the motor 64 to adjust distances between scan lines. As
illustrated in FIG. 37, the distance between the scan lines 524A
and 524B is greater than the distance between the scan lines 524B
and 524C in the example FOR 620. The controller 130 generates a
drive signal such that the planar mirror 14 slows down near the
middle of the FOR.sub.V, and speeds up near the fringes of the
FOR.sub.V. The lidar system 120A and 120B can adjust this distance
temporarily in view of certain triggering conditions, in some
implementations.
[0214] The controller 130 can be configured to modify the one or
both drive signals for the motors 32, 64 on a frame-by-frame basis,
with each frame corresponding to a complete scan of the field of
regard of the lidar system 120A or 120B. In other implementations
or scenarios, the controller 130 modifies the scan pattern for a
certain pre-configured time interval (e.g., 10 milliseconds, 100
milliseconds, one second, two seconds, four seconds). In yet other
implementations or scenarios, the controller 130 modifies the scan
pattern in response to a triggering event and restores the default
configuration in response to another triggering event.
[0215] FIG. 38 is a flow diagram of an example method 700 for
modifying the FOR. The method 38 can be implemented in the
controller 130, for example, as a set of instructions. The method
700 begins at block 702, where the initial operational FOR for the
scanner is selected. The centerline of the FOR.sub.V-OPER initially
can coincide with the centerline of the FOR.sub.V-AVAIL. Referring
back to FIGS. 1-20, the planar mirror 14 at block 702 oscillates
near the middle of its available range of motion.
[0216] At block 704, an upcoming road segment with a grade is
detected. Referring to FIG. 39A, for example, a vehicle 750 can
detect a downward slope using the lidar sensor unit 10 and/or other
sensors. In the scenario illustrated in FIG. 39B, on the other
hand, the vehicle detects an upward slope. At block 706, the
operational FOV is moved upward or downward. The lidar sensor unit
10 accordingly moves FOR.sub.V-OPER downward or upward,
respectively, to better "see" along the surface of the road. To
this end, the controller 130 can adjust the drive signal for the
motor 64. At block 708, the default position of the FOR.sub.V-OPER
within the FOR.sub.V-AVAIL is restored when the vehicle 750 detects
that the road again is level. The controller 130 again can provide
the corresponding drive signals to the motor 64.
VII. Generating Pixels with Non-Integer Separation in a Lidar
Sensor Unit
[0217] The lidar sensor unit 10 in a two-eye configuration directs
output beams on two reflective surfaces of the polygon mirror 12.
Moreover, the lidar sensor unit 10 can angularly separate each of
the output beams into two output beams (see FIG. 25). The two
output beams of the same eye may have different wavelengths. The
lidar sensor unit 10 can use the two output beams to scan different
pixels in a same scan line during a single ranging event. The
pixels can have non-integer separation such as 5.5 pixels or 9.5
pixels, for example. Further, the two eyes of the sensor unit 10
can define an overlap region in which the interleave between pixels
and/or lines does not correspond to an integer value. Measured
angularly, the width of the overlap region may have any suitable
value such as 1, 2, 5, 10, 20, 30, or 40 degrees. The width of the
overlap region may be determined, at least in part, by the angle of
incidence at which the two output beams which are directed onto the
two reflective surfaces of the polygon mirror 12. Interleaving
pixels and interleaving scan lines in this manner can be
implemented separately or together in a lidar system.
[0218] To detect two pulses within a ranging event for the same
eye, the lidar sensor unit 10 can include two detectors for each
optical path. FIG. 40 is a diagram of a detector array 800 which
includes two detector sites 802A, 802B, which can be used in the
lidar system 120A or 120B, for example, or another suitable lidar
system. Each of the detector sites 802A and 802B may include a
single detector or a cluster of individual detectors (APDs, SPADs,
etc.) to mitigate potential registration, tolerance, and
capacitance issues. The two detector sites 802A and 802B may be
offset from one another along a direction corresponding to the
scanning direction of the light source. The lidar system 120A or
120B may use the detector site 802A to scan even pixels and the
detector site 802B to scan odd pixels. For convenience, detector
sites such as the sites 802A and 802B are referred to herein simply
as detectors.
[0219] In one implementation, a DOE or a free-space splitter
disposed in the path of an output beam may separate pulses by any
suitable angle .THETA., such as for example, 1 mrad, 2 mrad, 5
mrad, 10 mrad, 20 mrad, or 50 mrad. As an example, the splitter may
split an emitted pulse into two pulses of angularly separated light
(e.g., a first pulse and a second pulse). In another
implementation, a pair of collimators may be used to produce any
suitable angle .THETA. between two pulses. As an example, an
emitted pulse may be split into two pulses by a fiber-optic
splitter, and two collimators (e.g., collimators 92A and 94A in
FIG. 23) may be arranged to produce an angle of approximately 20
mrad between the two pulses. The scanner 11 may scan these pulses
of light along a scanning direction across pixels located downrange
from the lidar system 120A or 120B. The detectors 802A and 802B in
this implementation may be separated by a detector-separation
distance along a direction corresponding to the scanning direction
of the light pulses. The detector 802A may be configured to detect
scattered light from the first pulse of light, and the detector
802B may be configured to detect scattered light from the second
pulse of light. The controller 130 is configured to determine one
or more distances to one or more targets based at least in part on
a time of flight of the first pulse of light or a time of flight of
the second pulse of light. A respective splitter, DOE, or pair of
collimators can be used with each of the two eyes of the lidar
sensor unit 10.
[0220] Referring to FIG. 41, the output beams can be aimed so that
the detector FOV 812A of the detector 802A and the detector FOV
812B of the detector 802B initially have little or no overlap
(e.g., less than 10% overlap) with the corresponding instantaneous
light-source FOVs, or pixel #i or #j. The scanner 11 can be
configured so that after the round-trip time corresponding to the
maximum range of the lidar system 120A or 120B has elapsed, the
detector FOV 812A has moved so as to coincide with pixel #i, and
the detector FOV 812B has moved so as to coincide with pixel #j. In
other words, when a scattered pulse of light returns from a target
at maximum operational distance of the lidar system 120, e.g.,
R.sub.MAX, the instantaneous light-source FOV is located in the
detector FOV 812A or 812B. If a light pulse returns from a location
beyond the maximum range R.sub.MAX (if the target is highly
cooperative, for example), the detector 802A and 802B generates a
weaker signal, which the lidar system 120 can ignore, because the
FOV 812A or 812B overlaps pixel #i or #j only partially.
[0221] In one implementation, pulses of light in each output beam
are angularly separated so as to scan two lines in parallel. Thus,
a pulse of light P can be split into pulse P' and P'' to generate
pixels in scan lines L.sub.i and L.sub.i+1 , so that the planar
mirror then can be repositioned to scan lines L.sub.i+2 and
L.sub.i+3 in the next instance. In another implementation, pulses
of light in each output beam are angularly and/or spatially
separated and directed toward different sections of a same scan
line, so as to produce two pixels within the time of a single
ranging event. The two beams in this implementation can be
separated by a non-integer number of pixels (e.g., 3.5, 5.5, 7.5,
10.5) so as improve the resulting pixel quality. More particularly,
for a pair of adjacent pixels generated using one beam, another
pixel centered at the midpoint between the pair of pixels can be
generated using the other beam, and the two adjacent pixels can be
corrected as necessary using the midpoint pixel.
[0222] FIG. 42 illustrates an example combined scan pattern 850
according to which the lidar system 120 can scan the combined FOR
of the lidar sensor unit 10. The combined scan pattern 850 includes
a scan pattern 852A of the first eye of the lidar sensor unit 10
and a scan pattern 852B of the second eye of the lidar sensor unit
10. Referring back to FIG. 26B, the scan pattern 852A can
correspond to the first eye corresponding to the receiver 128A, and
the scan pattern 852B can correspond to the second eye
corresponding to the receiver 128B. The scan patterns 852A and 852B
overlap in a region 860. In the region 860, the scan lines in the
scan pattern 852A are offset relative to scan lines of the scan
pattern 852B by approximately one half of a scan line to yield
double pixel density within the overlap region 860. In the forward
orientation of the lidar sensor unit 10, the overlap region 860
corresponds to the area directly ahead of the vehicle. The
controller 130 or the vehicle controller 372 can use the increased
pixel density to more accurately identify objects within overlap
region 860.
[0223] FIG. 43 schematically illustrates a technique for scanning
pixels with non-integer separation. In an example scenario 900,
pulses of light in each output beam are directed toward different
sections of a same scan line, so as to produce two pixels within
the time of a single ranging event. For example, referring back to
FIGS. 25, the lidar sensor unit 10 during a first ranging event can
direct the output beams 110A and 110B at pixels 1 and 7.5,
respectively. In the next ranging event, the lidar sensor unit 10
can direct the output beams 110A and 110B at pixels 2 and 8.5,
respectively, and during the third ranging event the output beams
110A and 110B can be aimed at pixels 3 and 9.5. When the controller
130 and/or the vehicle controller 372 processes data from the
receiver 128A of 128B, the values corresponding to pixels with
fractional indices (7.5, 8.5, 9.5, etc.) can be used to more
accurately determine the values of pixels with neighboring integer
indices (7, 8, 9, 10, etc.), as illustrated in FIG. 43.
[0224] Thus, the lidar sensor unit 10 in this example configuration
concurrently scans pixels with a separation of 6.5 using two output
beams of the same eye. More generally, the lidar sensor unit 10 can
apply non-integer separation of pixels to beams associated with the
same eye or two different eyes. Also, as discussed above, the lidar
sensor unit 10 also can apply non-integer separation of pixels to
beams associated with different eyes.
[0225] FIG. 44 is a flow diagram of an example method 950 for
generating pixel values using output beams with non-integer pixel
separation, which can be implemented in the controller 130 of the
lidar system 120A or 120B and/or vehicle controller 372.
[0226] At block 952, pixels N, N+1, vand N+2 are scanned using a
first output beam. Pixels N, separated by a non-integer offset, are
scanned at block 954 to generate pixels N+integer offset+0.5,
pixels N+integer offset+1.5, pixels N+integer offset+2.5, etc. The
blocks 954 and 956 are executed concurrently. At block 956, the
values of pixels are calculated using the data generated by
scanning the FOR with the first beam and the second beam. For
example, the value of pixel #27 can be calculated using the result
of scanning pixel #27 using the first output beam as well as the
result of scanning pixels #26.5 and 27.5 using the second output
beam. Block 956 can be implemented in the controller 130, for
example.
VIII. General Considerations
[0227] In some cases, a computing device may be used to implement
various modules, circuits, systems, methods, or algorithm steps
disclosed herein. As an example, all or part of a module, circuit,
system, method, or algorithm disclosed herein may be implemented or
performed by a general-purpose single- or multi-chip processor, a
digital signal processor (DSP), an ASIC, a FPGA, any other suitable
programmable-logic device, discrete gate or transistor logic,
discrete hardware components, or any suitable combination thereof.
A general-purpose processor may be a microprocessor, or, any
conventional processor, controller, microcontroller, or state
machine. A processor may also be implemented as a combination of
computing devices, e.g., a combination of a DSP and a
microprocessor, a plurality of microprocessors, one or more
microprocessors in conjunction with a DSP core, or any other such
configuration.
[0228] In particular embodiments, one or more implementations of
the subject matter described herein may be implemented as one or
more computer programs (e.g., one or more modules of
computer-program instructions encoded or stored on a
computer-readable non-transitory storage medium). As an example,
the steps of a method or algorithm disclosed herein may be
implemented in a processor-executable software module which may
reside on a computer-readable non-transitory storage medium. In
particular embodiments, a computer-readable non-transitory storage
medium may include any suitable storage medium that may be used to
store or transfer computer software and that may be accessed by a
computer system. Herein, a computer-readable non-transitory storage
medium or media may include one or more semiconductor-based or
other integrated circuits (ICs) (such, as for example,
field-programmable gate arrays (FPGAs) or application-specific ICs
(ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs),
optical discs (e.g., compact discs (CDs), CD-ROM, digital versatile
discs (DVDs), blue-ray discs, or laser discs), optical disc drives
(ODDs), magneto-optical discs, magneto-optical drives, floppy
diskettes, floppy disk drives (FDDs), magnetic tapes, flash
memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECURE
DIGITAL cards or drives, any other suitable computer-readable
non-transitory storage media, or any suitable combination of two or
more of these, where appropriate. A computer-readable
non-transitory storage medium may be volatile, non-volatile, or a
combination of volatile and non-volatile, where appropriate.
[0229] In some cases, certain features described herein in the
context of separate implementations may also be combined and
implemented in a single implementation. Conversely, various
features that are described in the context of a single
implementation may also be implemented in multiple implementations
separately or in any suitable sub-combination. Moreover, although
features may be described above as acting in certain combinations
and even initially claimed as such, one or more features from a
claimed combination may in some cases be excised from the
combination, and the claimed combination may be directed to a
sub-combination or variation of a sub-combination.
[0230] While operations may be depicted in the drawings as
occurring in a particular order, this should not be understood as
requiring that such operations be performed in the particular order
shown or in sequential order, or that all operations be performed.
Further, the drawings may schematically depict one more example
processes or methods in the form of a flow diagram or a sequence
diagram. However, other operations that are not depicted may be
incorporated in the example processes or methods that are
schematically illustrated. For example, one or more additional
operations may be performed before, after, simultaneously with, or
between any of the illustrated operations. Moreover, one or more
operations depicted in a diagram may be repeated, where
appropriate. Additionally, operations depicted in a diagram may be
performed in any suitable order. Furthermore, although particular
components, devices, or systems are described herein as carrying
out particular operations, any suitable combination of any suitable
components, devices, or systems may be used to carry out any
suitable operation or combination of operations. In certain
circumstances, multitasking or parallel processing operations may
be performed. Moreover, the separation of various system components
in the implementations described herein should not be understood as
requiring such separation in all implementations, and it should be
understood that the described program components and systems may be
integrated together in a single software product or packaged into
multiple software products.
[0231] Various implementations have been described in connection
with the accompanying drawings. However, it should be understood
that the figures may not necessarily be drawn to scale. As an
example, distances or angles depicted in the figures are
illustrative and may not necessarily bear an exact relationship to
actual dimensions or layout of the devices illustrated.
[0232] The scope of this disclosure encompasses all changes,
substitutions, variations, alterations, and modifications to the
example embodiments described or illustrated herein that a person
having ordinary skill in the art would comprehend. The scope of
this disclosure is not limited to the example embodiments described
or illustrated herein. Moreover, although this disclosure describes
or illustrates respective embodiments herein as including
particular components, elements, functions, operations, or steps,
any of these embodiments may include any combination or permutation
of any of the components, elements, functions, operations, or steps
described or illustrated anywhere herein that a person having
ordinary skill in the art would comprehend.
[0233] The term "or" as used herein is to be interpreted as an
inclusive or meaning any one or any combination, unless expressly
indicated otherwise or indicated otherwise by context. Therefore,
herein, the expression "A or B" means "A, B, or both A and B." As
another example, herein, "A, B or C" means at least one of the
following: A; B; C; A and B; A and C; B and C; A, B and C. An
exception to this definition will occur if a combination of
elements, devices, steps, or operations is in some way inherently
mutually exclusive.
[0234] As used herein, words of approximation such as, without
limitation, "approximately, "substantially," or "about" refer to a
condition that when so modified is understood to not necessarily be
absolute or perfect but would be considered close enough to those
of ordinary skill in the art to warrant designating the condition
as being present. The extent to which the description may vary will
depend on how great a change can be instituted and still have one
of ordinary skill in the art recognize the modified feature as
having the required characteristics or capabilities of the
unmodified feature. In general, but subject to the preceding
discussion, a numerical value herein that is modified by a word of
approximation such as "approximately" may vary from the stated
value by .+-.0.5%, .+-.1%, .+-.2%, .+-.3%, .+-.4%, .+-.5%, .+-.10%,
.+-.12%, or .+-.15%.
[0235] As used herein, the terms "first," "second," "third," etc.
may be used as labels for nouns that they precede, and these terms
may not necessarily imply a particular ordering (e.g., a particular
spatial, temporal, or logical ordering). As an example, a system
may be described as determining a "first result" and a "second
result," and the terms "first" and "second" may not necessarily
imply that the first result is determined before the second
result.
[0236] As used herein, the terms "based on" and "based at least in
part on" may be used to describe or present one or more factors
that affect a determination, and these terms may not exclude
additional factors that may affect a determination. A determination
may be based solely on those factors which are presented or may be
based at least in part on those factors. The phrase "determine A
based on B" indicates that B is a factor that affects the
determination of A. In some instances, other factors may also
contribute to the determination of A. In other instances, A may be
determined based solely on B.
* * * * *