U.S. patent application number 13/008042 was filed with the patent office on 2011-08-04 for integrated photonics module for optical projection.
This patent application is currently assigned to PRIMESENSE LTD. Invention is credited to Mordehai Margalit, Zafrir Mor, Benny Pesach, Israel Petronius, Alexander Shpunt.
Application Number | 20110188054 13/008042 |
Document ID | / |
Family ID | 44341407 |
Filed Date | 2011-08-04 |
United States Patent
Application |
20110188054 |
Kind Code |
A1 |
Petronius; Israel ; et
al. |
August 4, 2011 |
INTEGRATED PHOTONICS MODULE FOR OPTICAL PROJECTION
Abstract
Optical apparatus includes a semiconductor substrate and an
edge-emitting radiation source, mounted on a surface of the
substrate so as to emit optical radiation along an axis that is
parallel to the surface. A reflector is fixed to the substrate in a
location on the axis and is configured to reflect the optical
radiation in a direction that is angled away from the surface. One
or more optical elements are mounted on the substrate so as to
receive and transmit the optical radiation reflected by the
reflector.
Inventors: |
Petronius; Israel; (Haifa,
IL) ; Mor; Zafrir; (Ein Habsor, IL) ;
Margalit; Mordehai; (Zichron Yaakov, IL) ; Pesach;
Benny; (Rosh HaAyin, IL) ; Shpunt; Alexander;
(Tel Aviv, IL) |
Assignee: |
PRIMESENSE LTD
Tel Aviv
IL
|
Family ID: |
44341407 |
Appl. No.: |
13/008042 |
Filed: |
January 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12762373 |
Apr 19, 2010 |
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13008042 |
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61300465 |
Feb 2, 2010 |
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Current U.S.
Class: |
356/610 ; 29/428;
359/205.1; 362/235; 362/236; 362/259; 362/307; 362/308 |
Current CPC
Class: |
F21V 13/04 20130101;
Y10T 29/49117 20150115; F21Y 2115/30 20160801; G01B 11/25 20130101;
F21V 5/007 20130101; G02B 26/105 20130101; B23P 11/00 20130101;
H04N 5/232 20130101; Y10T 29/49826 20150115; F21V 7/04 20130101;
G01B 11/2513 20130101; G02B 26/10 20130101; F21V 7/00 20130101 |
Class at
Publication: |
356/610 ;
362/307; 362/259; 362/308; 359/205.1; 362/235; 362/236; 29/428 |
International
Class: |
G01B 11/25 20060101
G01B011/25; F21V 7/00 20060101 F21V007/00; F21V 7/04 20060101
F21V007/04; F21V 13/04 20060101 F21V013/04; G02B 26/10 20060101
G02B026/10; B23P 11/00 20060101 B23P011/00 |
Claims
1. Optical apparatus, comprising: a semiconductor substrate; an
edge-emitting radiation source, mounted on a surface of the
substrate so as to emit optical radiation along an axis that is
parallel to the surface; a reflector, which is fixed to the
substrate in a location on the axis and is configured to reflect
the optical radiation in a direction that is angled away from the
surface; and one or more optical elements, which are mounted on the
substrate so as to receive and transmit the optical radiation
reflected by the reflector.
2. The apparatus according to claim 1, wherein the radiation source
comprises a laser diode.
3. The apparatus according to claim 2, wherein the laser diode has
a front surface, through which the optical radiation is emitted
toward the reflector, and a rear surface, and wherein the apparatus
comprises a radiation sensor mounted on the substrate adjacent to
the rear surface of the laser diode for monitoring an output of the
laser diode.
4. The apparatus according to claim 1, and comprising a cap, which
covers the radiation source, reflector and optical elements and
comprises: a transparent window through which the radiation exits
the apparatus; and a radiation sensor mounted in the cap adjacent
to the window for monitoring an output of the apparatus.
5. The apparatus according to claim 1, wherein the reflector
comprises a reflecting surface that is etched into the
substrate.
6. The apparatus according to claim 1, wherein the substrate
comprises a single crystal, and wherein the reflector comprises a
reflecting surface formed by cleaving the substrate along an axis
of the crystal.
7. The apparatus according to claim 1, wherein the reflector
comprises an optical surface having a profile selected to impart a
desired convergence or divergence to the radiation.
8. The apparatus according to claim 7, wherein the optical surface
comprises a concave reflecting surface for increasing an angular
spread of the radiation.
9. The apparatus according to claim 8, wherein the concave
reflecting surface is tilted relative to the axis, and wherein the
profile has a conical shape.
10. The apparatus according to claim 7, wherein the reflector
comprises a prism having an inner reflecting surface and having
entry and exit faces, such that at least one of the entry and exit
faces is curved.
11. The apparatus according to claim 1, wherein the one or more
optical elements comprise a lens.
12. The apparatus according to claim 1, wherein the one or more
optical elements comprise a patterned element.
13. The apparatus according to claim 12, wherein the patterned
element comprise a diffractive optical element.
14. The apparatus according to claim 1, wherein the reflector
comprises a scanning mirror, which is configured to scan the
reflected optical radiation over a predetermined angular range.
15. The apparatus according to claim 14, wherein the scanning
mirror comprises a micro-electrical mechanical system (MEMS)
driver, which is mounted on the substrate at a diagonal relative to
the surface on which the radiation source is mounted.
16. The apparatus according to claim 14, wherein the optical
radiation from the radiation source impinges on the scanning mirror
without other optics intervening between the radiation source and
the scanning mirror.
17. The apparatus according to claim 1, wherein the radiation
source comprises a plurality of edge-emitting radiation sources
which are arranged together on the substrate to emit the optical
radiation along multiple, respective axes.
18. Optical apparatus, comprising: a semiconductor substrate; a
first array of surface-emitting radiation sources, which are
mounted on a surface of the substrate so as to emit optical
radiation along respective axes that are perpendicular to the
surface; and a second array of optical elements, which are mounted
over the first array and aligned with the respective axes so that
each optical element receives and transmits the optical radiation
emitted by a respective radiation source.
19. An imaging system, comprising: an illumination assembly, which
is configured to project a pattern of optical radiation onto an
object, and which comprises: a semiconductor substrate; at least
one radiation source, mounted on a surface of the substrate so as
to emit optical radiation along an axis; and optical elements,
which are mounted on the substrate in alignment with the axis so as
to receive and transmit the optical radiation toward the object; an
imaging assembly, which is configured to capture an image of the
pattern on the object; and a processor, which is configured to
process the image so as to generate a depth map of the object.
20. A method for producing a photonics module, comprising: mounting
an edge-emitting radiation source on a surface of a semiconductor
substrate so that the source emits optical radiation along an axis
that is parallel to the surface; fixing a reflector to the
substrate in a location on the axis so as to reflect the optical
radiation is a direction that is angled away from the surface; and
mounting one or more optical elements on the substrate so as to
receive and transmit the optical radiation reflected by the
reflector.
21. The method according to claim 20, wherein the radiation source
comprises a laser diode.
22. The method according to claim 21, wherein the laser diode has a
front surface, through which the optical radiation is emitted
toward the reflector, and a rear surface, and wherein the method
comprises mounting a radiation sensor on the substrate adjacent to
the rear surface of the laser diode for monitoring an output of the
laser diode.
23. The method according to claim 20, and comprising: fitting a cap
over the radiation source, reflector and optical elements, the cap
comprising a transparent window through which the radiation exits
the module; and mounting a radiation sensor in the cap adjacent to
the window for monitoring an output of the method.
24. The method according to claim 20, wherein fixing the reflector
comprises etching a reflecting surface into the substrate.
25. The method according to claim 20, wherein the substrate
comprises a single crystal, and wherein fixing the reflector
comprises forming a reflecting surface by cleaving the substrate
along an axis of the crystal.
26. The method according to claim 20, wherein the reflector
comprises an optical surface having a profile selected to impart a
desired convergence or divergence to the radiation.
27. The method according to claim 20, wherein the one or more
optical elements comprise a lens.
28. The method according to claim 20, wherein the one or more
optical elements comprise a patterned element.
29. The method according to claim 20, wherein mounting the
edge-emitting radiation source and fixing the reflector comprises
producing multiple optoelectronic sub-modules, comprising
respective radiation sources and reflectors, on a semiconductor
wafer, and wherein mounting the one or more optical elements
comprises overlaying a wafer-level array of the optical elements on
the optoelectronic sub-modules.
30. The method according to claim 29, and comprising, after
overlaying the wafer-level array, dicing the wafer and the array
together to produce multiple integrated photonics modules.
31. The method according to claim 20, wherein fixing the reflector
comprises mounting a scanning mirror on the substrate, and driving
the mirror to scan the reflected optical radiation over a
predetermined angular range.
32. The method according to claim 20, wherein mounting the
radiation source comprises mounting a plurality of edge-emitting
radiation together on the substrate so as to emit the optical
radiation along multiple, respective axes.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/762,373, filed Apr. 19, 2010, and claims
the benefit of U.S. Provisional Patent Application 61/300,465,
filed Feb. 2, 2010. Both of these related applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to optoelectronic
devices, and specifically to integrated projection devices.
BACKGROUND
[0003] Miniature optical projectors are used in a variety of
applications. For example, such projectors may be used to cast a
pattern of coded or structured light onto an object for purposes of
3D mapping (also known as depth mapping). In this regard, U.S.
Patent Application Publication 2008/0240502, whose disclosure is
incorporated herein by reference, describes an illumination
assembly in which a light source, such as a laser diode or LED,
transilluminates a transparency with optical radiation so as to
project a pattern onto the object. (The terms "optical" and "light"
as used herein refer generally to any of visible, infrared, and
ultraviolet radiation.) An image capture assembly captures an image
of the pattern that is projected onto the object, and a processor
processes the image so as to reconstruct a three-dimensional (3D)
map of the object.
[0004] PCT International Publication WO 2008/120217, whose
disclosure is incorporated herein by reference, describes further
aspects of the sorts of illumination assemblies that are shown in
the above-mentioned US 2008/0240502. In one embodiment, the
transparency comprises an array of micro-lenses arranged in a
non-uniform pattern. The micro-lenses generate a corresponding
pattern of focal spots, which is projected onto the object.
[0005] Optical projectors may, in some applications, project light
through one or more diffractive optical elements (DOEs). For
example, U.S. Patent Application Publication 2009/0185274, whose
disclosure is incorporated herein by reference, describes apparatus
for projecting a pattern that includes two DOEs that are together
configured to diffract an input beam so as to at least partially
cover a surface. The combination of DOEs reduces the energy in the
zero-order (undiffracted) beam. In one embodiment, the first DOE
generates a pattern of multiple beams, and the second DOE serves as
a pattern generator to form a diffraction pattern on each of the
beams.
SUMMARY
[0006] Embodiments of the present invention that are described
hereinbelow provide photonics modules that include optoelectronic
components and optical elements in a single integrated package.
Although the disclosed embodiments relate specifically to modules
that are used in projecting patterned light, the principles of
these embodiments may similarly be applied in other sorts of
systems.
[0007] There is therefore provided, in accordance with an
embodiment of the present invention, optical apparatus, including a
semiconductor substrate and an edge-emitting radiation source,
mounted on a surface of the substrate so as to emit optical
radiation along an axis that is parallel to the surface. A
reflector is fixed to the substrate in a location on the axis and
is configured to reflect the optical radiation in a direction that
is angled away from the surface. One or more optical elements are
mounted on the substrate so as to receive and transmit the optical
radiation reflected by the reflector.
[0008] In some embodiments, the radiation source includes a laser
diode, which has a front surface, through which the optical
radiation is emitted toward the reflector, and a rear surface. The
apparatus may include a radiation sensor mounted on the substrate
adjacent to the rear surface of the laser diode for monitoring an
output of the laser diode.
[0009] In one embodiment, the apparatus includes a cap, which
covers the radiation source, reflector and optical elements, and
which includes a transparent window through which the radiation
exits the apparatus. A radiation sensor is mounted in the cap
adjacent to the window for monitoring an output of the
apparatus.
[0010] The reflector may include a reflecting surface that is
etched into the substrate. Alternatively, when the substrate
includes a single crystal, the reflector may include a reflecting
surface formed by cleaving the substrate along an axis of the
crystal.
[0011] In some embodiments, the reflector includes an optical
surface having a profile selected to impart a desired convergence
or divergence to the radiation. The optical surface may include a
concave reflecting surface for increasing an angular spread of the
radiation. The concave reflecting surface may be tilted relative to
the axis, and wherein the profile has a conical shape.
Alternatively, the reflector may include a prism having an inner
reflecting surface and having entry and exit faces, such that at
least one of the entry and exit faces is curved.
[0012] The one or more optical elements may include a lens.
Alternatively or additionally, the one or more optical elements may
include a patterned element, such as a diffractive optical
element.
[0013] In one embodiment, the reflector includes a scanning mirror,
which is configured to scan the reflected optical radiation over a
predetermined angular range. The scanning mirror may include a
micro-electrical mechanical system (MEMS) driver, which is mounted
on the substrate at a diagonal relative to the surface on which the
radiation source is mounted. Typically, the optical radiation from
the radiation source impinges on the scanning mirror without other
optics intervening between the radiation source and the scanning
mirror.
[0014] In another embodiment, the radiation source includes a
plurality of edge-emitting radiation sources which are arranged
together on the substrate to emit the optical radiation along
multiple, respective axes.
[0015] There is also provided, in accordance with an embodiment of
the present invention, optical apparatus, including a semiconductor
substrate and a first array of surface-emitting radiation sources,
which are mounted on a surface of the substrate so as to emit
optical radiation along respective axes that are perpendicular to
the surface. A second array of optical elements are mounted over
the first array and aligned with the respective axes so that each
optical element receives and transmits the optical radiation
emitted by a respective radiation source.
[0016] There is additionally provided, in accordance with an
embodiment of the present invention, an imaging system, including
an illumination assembly, which is configured to project a pattern
of optical radiation onto an object, as described above. An imaging
assembly is configured to capture an image of the pattern on the
object, and a processor is configured to process the image so as to
generate a depth map of the object.
[0017] There is further provided, in accordance with an embodiment
of the present invention, a method for producing a photonics
module, including mounting an edge-emitting radiation source on a
surface of a semiconductor substrate so that the source emits
optical radiation along an axis that is parallel to the surface. A
reflector is fixed to the substrate in a location on the axis so as
to reflect the optical radiation is a direction that is angled away
from the surface. One or more optical elements are mounted on the
substrate so as to receive and transmit the optical radiation
reflected by the reflector.
[0018] The present invention will be more fully understood from the
following detailed description of the embodiments thereof, taken
together with the drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic side view of an imaging system, in
accordance with an embodiment of the present invention;
[0020] FIGS. 2A and 2B are schematic sectional views of a
projection subassembly, in accordance with an embodiment of the
present invention;
[0021] FIG. 3 is a schematic sectional view of an integrated
photonics module (IPM), in accordance with an embodiment of the
present invention;
[0022] FIG. 4 is a schematic sectional view of an IPM, in
accordance with an alternative embodiment of the present
invention;
[0023] FIG. 5 is a schematic pictorial illustration showing
multiple IPMs on a silicon wafer, in accordance with an embodiment
of the present invention;
[0024] FIG. 6 is a flow chart that schematically illustrates a
method for production of IPMs, in accordance with an embodiment of
the present invention;
[0025] FIGS. 7A-7G are a sequence of schematic sectional views
showing stages in the production of an IPM, in accordance with an
embodiment of the present invention;
[0026] FIG. 8 is a schematic top view of an optoelectronic
sub-module used in an IPM, in accordance with an embodiment of the
present invention;
[0027] FIGS. 9 and 10 are schematic pictorial views of reflectors
for use in an IPM, in accordance with embodiments of the present
invention;
[0028] FIG. 11 is a schematic side view of an IPM, in accordance
with another embodiment of the present invention; and
[0029] FIG. 12 is a schematic sectional view of an IPM, in
accordance with yet another embodiment of the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
Overview and System Description
[0030] Embodiments of the present invention that are described
hereinbelow provide photonics modules that include optoelectronic
components and optical elements (refractive and/or patterned) in a
single integrated package. These modules can be produced in large
quantities at low cost, while offering good optical quality and
high reliability. They are useful as projectors of patterned light,
for example in 3D mapping applications as described above, but they
may also be used in various other applications that use optical
projection and sensing, including free-space optical
communications.
[0031] FIG. 1 is a schematic side view of an imaging system 20, in
accordance with an embodiment of the present invention. A set of
X-Y-Z axes is used in this figure and throughout the description
that follows to aid in understanding the orientation of the
figures, wherein the X-Y plane is the frontal plane of system 20,
and the Z-axis extends perpendicularly from this plane toward the
scene that is to be imaged. The choice of axes, however, is
arbitrary and is made solely for the sake of convenience in
describing embodiments of the invention.
[0032] An illumination assembly 22 projects a patterned radiation
field 24 onto an object 26 (in this case a hand of a user of the
system) in a scene. An imaging assembly 28 captures an image of the
scene within a field of view 30. A controller 31 or other
electronic processor processes the image in order to generate a 3D
depth map of object 26. Further details of this sort of mapping
process are described, for example, in the above-mentioned US
2008/0240502 and in PCT International Publication WO 2007/105205,
whose disclosure is also incorporated herein by reference. The 3D
map of the user's hand (and/or other parts of the user's body) may
be used in a gesture-based computer interface, but this sort of
functionality is beyond the scope of the present patent
application.
[0033] Imaging assembly 28 comprises objective optics 36, which
form an optical image of the scene containing object 26 on an image
sensor 38, such as a CMOS integrated circuit image sensor. The
image sensor comprises an array of sensor elements 40, arranged in
multiple rows. The sensor elements generate respective signals in
response to the radiation focused onto them by optics 36, wherein
the pixel value of each pixel in the electronic images output by
image sensor 38 corresponds to the signal from a respective sensor
element 40.
[0034] Illumination assembly 22 comprises a projection subassembly
32, which generates a beam of patterned light, and projection
optics 34, which project the beam onto field 24. The design,
production and operation of subassembly 32 are described in detail
hereinbelow. Subassemblies of this sort may be used in the sorts of
pattern projectors that are described in the above-mentioned US
2008/0240502 and WO 2008/120217 publications, for example, as well
as in pattern projectors based on diffractive optical elements
(DOEs), such as those described in U.S. Patent Application
Publication 2010/0284082, whose disclosure is incorporated herein
by reference. Alternatively, as noted earlier, subassemblies of
this sort may be configured for other applications.
[0035] FIGS. 2A and 2B show schematic sectional views of projection
subassembly 32 in two orthogonal planes, in accordance with an
embodiment of the present invention. Subassembly 32 comprises an
integrated photonics module (IPM) 42, which is shown in detail, in
various different embodiments, in the figures that follow. Briefly
put, IPM 42 comprises an optoelectronic light source, such as a
laser diode or light-emitting diode (LED), with optics for
directing light upward (the Z-direction in the frame of reference
shown in the figures). The light source is mounted on a
semiconductor substrate, such as a silicon wafer, which serves as
an optical bench. A focusing component, such as a lens, collects
and directs the light through a patterned element, such as a DOE or
micro-lens array (MLA). Projection optics 34 outside subassembly 32
(at the right of assembly 22 in the view shown in FIG. 1, or above
subassembly 32 in the views of FIGS. 2A and 2B) may be used to cast
the pattern onto object 26.
[0036] Electrical conductors on the substrate of IPM 42 are
connected to an electrical interface, which in this embodiment has
the form of a flexible printed circuit 44, for coupling to power
and control circuits. The connection between the IPM substrate and
FPC 44 may be via any suitable type of interconnect, such as
terminals 46 of a ball-grid array.
[0037] IPM 42 may be mounted on a thermo-electric cooler (TEC) 52,
which holds the IPM at a constant temperature and thus reduces
frequency variations of the light source due to temperature change.
The TEC can also help in extending the life of the light source.
The semiconductor surface that contacts the TEC is typically
metalized (not shown) and flat for good thermal contact.
Subassembly 32 may also comprise a temperature sensor, such as a
thermistor or thermocouple (not shown), which provides a
temperature signal for use in controlling the operation of TEC 52
to maintain a constant temperature.
[0038] A cap 48 covers and attaches IPM 42 to TEC 52, and attaches
both of them to an underlying chassis (not shown), with good
thermal conductivity. The gaps between the cover cap and the IPM
may be filled with a suitable glue. The cover cap has a transparent
window 50 through which the patterned beam from IPM 42 exits
subassembly 32. The IPM and cap in this embodiment are not
cylindrically symmetrical (having a greater width in the plane of
FIG. 2A than that of FIG. 2B) because the beam output by the IPM is
similarly non-symmetrical. In this embodiment, for example,
projection subassembly 32 may project a light pattern with a field
of view of 63.1.degree..times.48.35.degree..
[0039] A radiation sensor, such as a monitoring photodiode (MPD)
54, may be incorporated into projection subassembly in order to
monitor the output light intensity from the light source. Such
sensors are useful both in maintaining the power level of IPM 42
within desired limits and verifying eye-safe operation. These
functions of MPD 54, as well as alternative modes of implementation
of the light sensor, are described in detail in U.S. patent
application Ser. No. 12/945,908, filed Nov. 15, 2010, whose
disclosure is incorporated herein by reference. In the embodiment
shown in FIG. 2, MPD 54 is located at the side of transparent
window 50 in order to measure the light intensity in an unused part
of the pattern (such as an unused diffraction lobe) projected by
the patterned element in IPM 42. If the MPD senses light intensity
in excess of a predetermined threshold, controller 31 may
automatically switch off or reduce the power to the IPM.
Additionally or alternatively, one or more MPDs may be positioned
and calibrated to sense the projected power distribution (and not
only the total power), and controller 31 may turn off or otherwise
modify the operation of the IPM if an undesired change in the
distribution occurs.
IPM Embodiments with a Single Light Source
[0040] FIG. 3 is a schematic sectional view showing details of IPM
42, in accordance with an embodiment of the present invention. IPM
42 as shown in this figure comprises an edge-emitting radiation
source, such as a laser diode 62, on a substrate in the form of a
silicon optical bench 60. Laser diode 62 may comprise, for example,
a GaAs laser diode, which is electrically and mechanically bonded
to optical bench 60 and emits radiation in the near-infrared range
(for example, at 828 nm) along an axis that is parallel to the
optical bench. ("Parallel" in this case may be an approximate term,
since the laser beam typically has a divergence of at least several
degrees.) Alternatively, other types of coherent or non-coherent
solid-state emitters may be used. A reflector is fixed to optical
bench 60 in the form of a mirror surface 64 etched into the bench
at a 45.degree. angle, which is coated so as to reflect the laser
radiation upward, at an angle (in this case 90.degree.) relative to
the surface of the optical bench.
[0041] A lens 66 collects and collimates light from laser diode 62
that has been reflected from mirror surface 64, directing the light
through a pair of DOEs 68 and 70. These two DOEs may be configured
as described in the above-mentioned US 2009/0185274 or US
2010/0284082, and may thus serve as an eye-safe pattern projector
for 3D mapping. Alternatively, the two DOEs may be replaced by one
or more patterned elements of another type, such as a MLA, or by an
active element that can creates a variable pattern, such as a
spatial light modulator (SLM) with suitable control circuits. The
optical elements (lens 66 and DOEs 68 and 70) that receive and
transmit the light from laser diode 62 are mounted on bench 60 by
means of spacers 72.
[0042] In addition, IPM 42 may comprise other components not shown
in the figure, such as a thermistor (or other temperature sensor)
and/or a MPD. The MPD may be adjacent to the rear face of laser
diode 62, as shown below in FIG. 4, or in any other suitable
location.
[0043] Laser diode 62 may, in this embodiment, comprise end
reflectors configured to define a Fabry-Perot cavity.
Alternatively, the laser diode may comprise a reflector in the form
of a volume Bragg grating (VBG). (Because the VBG is applied
externally to the laser, in order to reflect the desired wavelength
back into the cavity, high accuracy is required in placement of the
VBG. The micron-level accuracy of the silicon optical bench in the
present design supports the use of a VBG without substantial added
complexity or cost.) Further alternatively, the laser diode may
comprise a distributed feedback (DFB) grating. These latter
configurations are advantageous in maintaining wavelength stability
and may alleviate the need for TEC 52.
[0044] FIG. 4 is a schematic sectional view showing details of an
IPM 80, in accordance with an alternative embodiment of the present
invention. IPM 80 may be used in place of IPM 42 in projection
subassembly 32, as well as in other applications. In the embodiment
of FIG. 4, a silicon optical bench 82 is made from a single-crystal
silicon wafer, which is oriented in the 100 crystal plane (in
accordance with common practice in semiconductor device
fabrication). An edge-emitting laser diode 84 is mounted parallel
to this plane. A MPD 94 may be placed adjacent to the rear
reflector of the laser diode in order to measure the laser output
power.
[0045] A mirror 86 is cleaved in the 111 crystal plane, which is
naturally oriented at an angle .alpha.=54.7.degree. relative to the
100 plane. This sort of mirror implementation is advantageous in
avoiding the need to etch the mirror at an angle, but it means that
the mirror reflects the beam from laser diode 84 diagonally, rather
than perpendicularly upward as in FIG. 3. To alleviate this
problem, the light from laser diode 84 is collected by an eccentric
lens 88, as shown in FIG. 4.
[0046] In this embodiment, IPM 80 comprises only a single patterned
element 90. As noted earlier, this element may be a MLA, or it may
be a dual-DOE, with patterns on both the inner and outer surfaces.
A cover 92 may be placed over the IPM to protect the outer DOE
surface.
[0047] As a further alternative (not shown in the figures), the
optical bench of the IPM may be flat, without etching or cleaving
of a diagonal surface as in FIGS. 3 and 4. In this case, the
diagonal mirror surface (at 45.degree. or any other desired angle)
may be produced by gluing or otherwise attaching a suitable prism
with a reflective coating onto the bench in front of the laser
diode.
[0048] Further alternatively or additionally, the reflector that
reflects the laser output may comprise an optical surface that is
not flat, but rather has a profile selected to impart a desired
convergence or divergence to the radiation. For example, the
reflector may be curved in order to correct the astigmatism or
otherwise shape the beam of the laser or lasers that are used.
Curved mirror and prism configurations of this sort are shown in
FIGS. 8, 9 and 10. With appropriate curvature of an optical surface
of the mirror or prism, it may be possible in some applications to
alleviate the need for a refractive element (such as lens 66 or 88)
to collect and direct light from the laser diode through the
patterned optical element.
[0049] The IPM configurations shown in the figures above are
illustrated and described here only by way of example, and other
configurations are possible. For example, the beam characteristics
of the laser diodes in these figures are characteristic of
single-mode lasers. In an alternative embodiment, a multi-mode
laser may be used, possibly with the addition of a suitable
refractive element to correct the astigmatism of the multi-mode
laser beam. As yet another alternative, the IPM may comprise one or
more surface-emitting devices, such as a light-emitting diode (LED)
or vertical-cavity surface-emitting laser (VCSEL) diodes, which
emit radiation directly into the Z-direction, so that a turning
mirror is not required. (An embodiment based on a VCSEL array is
shown in FIG. 11.)
Fabrication Processes
[0050] FIG. 5 is a schematic pictorial illustration showing
multiple IPMs 100 on a silicon wafer 102, in accordance with an
embodiment of the present invention. Wafer-scale manufacturing
makes it possible to produce large numbers of IPMs together at low
cost. In this figure, IPMs 100 are shown on the wafer as separate
cubes. Each IPM contains optoelectronic components 104 (such as the
laser diode and MPD) on an indented silicon optical bench. A lens
106 and a patterned optical element 108 are assembled and aligned
on each IPM individually.
[0051] Alternatively, the IPMs may be produced by overlaying and
bonding to the wafer complete, wafer-size layers of refractive and
patterned elements (made from glass or plastic, for example), in
alignment with the silicon optical benches holding the
optoelectronic components. After the layers have been bonded
together, they are diced to produce the individual IPMs.
[0052] Reference is now made to FIGS. 6 and 7A-G, which
schematically illustrate a method for production of IPMs, in
accordance with an embodiment of the present invention. FIG. 6 is a
flow chart, while FIGS. 7A-G are a sequence of sectional views
showing stages in the production of an IPM.
[0053] According to this method, a silicon substrate 112 of the
silicon optical benches is prepared, at a wafer manufacturing step
110. In this step, substrate 112 is etched or cleaved to create a
suitable recess 113 and thus provide the diagonal surface for the
mirror (unless a separate prism is used, as mentioned above). Metal
layers are then added, with pads (not shown) for attachment of the
optoelectronic components (laser diode and MPD) and conductors for
the necessary electrical connections. A mirror surface 114 may also
be coated with metal at this stage.
[0054] Optoelectronic components 118, 120 are then bonded,
mechanically and electrically, to the pads on the silicon optical
bench, at a substrate population step 116. Electrical connections
may be made by wire bonding, for example, or by any other suitable
technique, at a bonding step 124. High accuracy is desirable in
steps 116 and 124, with placement error typically no greater than
.+-.1 .mu.m, and rotation error no more than 0.5.degree.. This sort
of micro-assembly, with accurate alignment of components, can be
carried out by various service providers, such as Luxtera
(Carlsbad, Calif.), Avago Technologies (San Jose, Calif.), and
EZconn Czech a.s. (Trutnov, Czech Republic). After micro-assembly,
the optoelectronics may optionally be covered by a transparent lid
122, creating an optoelectronic sub-module 126. This sub-module may
itself be used as an accurate, low-cost laser source even without
the refractive and patterned optical elements that are described
herein.
[0055] The optoelectronic components on each of sub-modules 126 are
tested, at a populated substrate testing step 132, in order to
identify and reject components that are non-functional or otherwise
faulty. The individual sub-modules 126 are then diced apart, and
the rejected units are discarded. This step enhances the ultimate
production yield of IPMs.
[0056] The acceptable sub-modules 126 are bonded mechanically to an
underlying wafer substrate 128. A large number of individual IPMs
may be assembled in this manner on a single wafer (typically
500-1000 units per 8'' wafer). At this stage, the entire
optoelectronic sub-module of each IPM is aligned as a unit relative
to the wafer substrate. The optoelectronic sub-module may, for
example, be attached to the wafer substrate by a malleable glue,
which is then cured after the package has been adjusted to the
proper alignment. This alignment may be active--based on energizing
the laser diodes and then adjusting the beam direction, or
passive--based on geometrical considerations without energizing the
laser diodes.
[0057] Alternatively, wafer substrate 128 may itself serve as the
optical bench, with sub-modules 126 formed directly on this
substrate. In this case, the IPMs may be individually aligned after
substrate population, if necessary, by adjustment of the refractive
and/or patterned optical elements in each IPM.
[0058] In addition to mechanical bonding of each sub-module 126 to
the underlying wafer substrate 128, the electrical conductors on
the silicon optical bench are coupled to corresponding conductors
(not shown) on substrate 128. This step may be carried out by
conventional methods, such as wire bonding. Alternatively, the
silicon optical bench may contain conductive vias (not shown),
which serve as electrical feed-throughs to make contact between the
components on the upper side of the bench and conducting pads on
wafer substrate 128. For example, the vias may connect to terminals
130 of a ball-grid array (BGA) or any other suitable type of
interconnect that is known in the art. Once the mechanical and
electrical bonding steps have been completed, the optoelectronic
packages on the wafer substrate may be tested.
[0059] In parallel with the above electrical manufacturing steps, a
wafer-size array of lenses 140 is produced, at a wafer-level lens
(WLL) manufacturing step 134. This lens array is overlaid with one
or more wafer-size arrays of patterned optical elements 142, such
as DOEs, at an WLL overlay step 136. The optical layers of lenses
and patterned elements may be produced, for example, by molding
suitable glass or plastic wafers. The wafer-size optical array is
precisely manufactured and has fiducial marks to enable exact
alignment with the beams emitted by the optoelectronic components
on the wafer substrate 128 (typically to an accuracy of .+-.5
.mu.m).
[0060] The optical array is then overlaid on and aligned with the
array of optoelectronic packages, in a WLL attachment step 138.
Appropriate spacers may be included between lenses 140, patterned
elements 142, and optoelectronic sub-modules 126, as shown in FIGS.
3 and 4, for example. Thus, the optical emitter in each sub-module
126 is precisely aligned with corresponding refractive and
patterned optical elements 140 and 142, all of which are mounted on
substrate 128.
[0061] The complete wafer-size assembly may be tested at this
stage, at a functional testing step 144. The individual IPMs are
then separated by dicing substrate 128 and the overlying optical
layers, at a dicing step 146. The IPMs are packaged to form the
type of projection sub-assemblies 32 that is shown in FIG. 2, at a
projector packaging step 148.
Multi-Emitter Modules and Curved Reflectors
[0062] FIG. 8 is a schematic top view of an optoelectronic
sub-module used in an IPM, in accordance with an embodiment of the
present invention. This sort of sub-module may be used, for
example, in IPMs of the general design shown in FIG. 3 or FIG. 4.
In the embodiment of FIG. 8, however, instead of a single light
source, the pictured sub-module comprises a row of edge-emitting
optoelectronic elements 154, such as laser diodes, which are formed
on a substrate 156, such as a silicon wafer. Elements 154 emit
radiation in a direction parallel to the substrate.
[0063] A reflector 150 on the substrate turns the radiation emitted
by elements 154 away from the substrate, which is oriented in the
X-Y plane, toward the Z-axis. The reflector may be integrally
formed in substrate 156, as shown in FIG. 3, or it may
alternatively comprise a separate element, which is positioned on
the substrate and aligned with optoelectronic elements 154.
Although reflector 150 could simply comprise a flat reflecting
surface, in the pictured embodiment the reflector comprises a
convex reflective surface 152, made up of one or more curved
surfaces or multiple flat surfaces which spread the radiation beams
emitted by elements 154. In an alternative embodiment (not shown in
the figures), reflective surface 152 may be configured to
concentrate the beams from elements 154 into a narrower output
beam. Generally speaking, the reflector may comprise a surface that
is non-flat with any suitable profile to impart a desired
convergence or divergence to the beam or beams.
[0064] Each of optoelectronic elements 154 emits radiation that
forms a respective stripe 158. (Although FIG. 8 shows six such
elements and respective stripes, a larger or smaller number of
elements and stripes may be used, depending on application
requirements.) Convex surface 152 of reflector 150 causes stripes
158 to spread over a relatively wide area and overlap the adjacent
stripes at their edges. Controller 31 (FIG. 1) may activates
elements 154 to emit radiation sequentially, in synchronization
with a rolling shutter of image sensor 38 during each image frame
captured by imaging assembly 28, as described in the
above-mentioned U.S. patent application Ser. No. 12/762,373.
Alternatively, elements 154 may be activated concurrently, in
either pulsed or continuous-wave (CW) mode.
[0065] In embodiments in which the patterned element (or elements)
in the IPM comprises a MLA or other transparency, each stripe 158
passes through a different, respective region of the transparency,
and thus creates a respective part of the overall illumination
pattern corresponding to the pattern embedded in the transparency.
Projection optics 34 project this pattern onto the object.
[0066] On the other hand, in embodiments in which the patterned
element comprises a DOE, either the collecting lens in the IPM or
one of the patterned elements (or the geometry of optoelectronic
elements 154 themselves) is typically configured to create an
appropriate "carrier" angle for the beam emitted by each of the
optoelectronic elements. In such embodiments, the beams emitted by
the different optoelectronic elements use different parts of the
collecting lens, which may therefore be designed so that the
collimated beams created by the lens exit at respective angles
corresponding to the desired fan-out of stripes 158. Alternatively,
reflector 150 may comprise some other type of optics, such as a
blazed grating with as many different zones as there are
optoelectronic elements.
[0067] FIG. 9 is a schematic pictorial view of a reflector 160 for
use in an IPM, in accordance with an alternative embodiment of the
present invention. This prism-shaped reflector may be used in the
optoelectronic sub-module of FIG. 8 in place of reflector 150. In
this case, radiation emitted by elements 154 is reflected
internally from a diagonal interior surface 166 (typically with a
suitable reflective coating) of reflector 160. The radiation from
elements 154 enters reflector 160 via a curved entry surface 164 of
a front face 162 of the prism and exits via a flat exit surface
168. (Alternatively, the exit surface may be curved, in addition to
or instead of the entry surface.) As a result, the respective beams
generated by elements 154 spread apart and overlap partially with
the adjacent beams.
[0068] FIG. 10 is a schematic pictorial view of a reflector 170 for
use in an IPM, in accordance with yet another embodiment of the
present invention. Reflector 170 has a curved reflective surface
172 and may be used in an IPM in place of reflector 150 or
reflector 160. Alternatively, reflector 170 (as well as reflectors
150 and 160) may be used to shape the beam of a single laser diode
or other optoelectronic element, as in the embodiments of FIGS. 3
and 4. Curved surface 172 may be shaped, for example, to widen the
slow axis (i.e., the narrower beam dimension in a non-symmetrical
laser output) of the laser output in order to illuminate a wider
area of the patterned element in the IPM. Alternatively or
additionally, the curved surface may be configured to shape the
Gaussian distribution that is typical of the laser fast axis into a
flat-topped beam profile in order to illuminate the patterned
element more uniformly.
[0069] The design of surface 172 that is illustrated in FIG. 10 is
useful particularly in widening the slow axis of the beam. Surface
172 is shaped as a part of a cone, tilted at 45.degree.. In
principle, if the reflecting surface were not tilted, a cylindrical
mirror would be sufficient to widen the slow axis. Since reflector
170 is used to divert the laser beam by 90.degree., however,
surface 172 has a different distance from the laser aperture for
each section along the fast axis of the laser, and therefore
requires a varying radius of curvature to widen the slow axis
uniformly. Thus, as shown in FIG. 10, the radius of curvature of
surface 172 grows with distance from the laser aperture. A good
approximation to the required shape is a cone. The mirror shape can
be further optimized to improve the uniformity of illumination of
the patterned element.
[0070] FIG. 11 is a schematic side view of an IPM 180, in
accordance with another embodiment of the present invention. IPM
180 may be used in system 20 in place of illumination assembly 22,
for example. IPM 180 comprises radiation sources in the form of a
two-dimensional matrix of optoelectronic elements 182, which are
arranged on a substrate 184 and emit radiation in a direction
perpendicular to the substrate. Although FIG. 11 shows only a
single row of elements 182 arrayed along the X-axis, IPM 180
typically comprises multiple, parallel rows of this sort, forming a
grid in the X-Y plane. FIG. 11 illustrates a grid with eight
columns of elements 182, but larger or smaller matrices, not
necessarily square or rectilinear, may alternatively be used.
[0071] In contrast to the preceding embodiments, elements 182
comprise surface-emitting devices, such as light-emitting diodes
(LEDs) or vertical-cavity surface-emitting laser (VCSEL) diodes,
which emit radiation directly into the Z-direction. An array of
microlenses 186 (or other suitable micro-optics, such as total
internal reflection-based micro-structures) is aligned with
elements 182, so that a respective microlens collects the radiation
from each element and directs it into an optical module. The
optical module comprises, inter alia, a suitable patterned element
188, as described above, and a projection lens 190, which projects
the resulting pattern onto the scene.
IPM with Scanning Mirror
[0072] FIG. 12 is a schematic sectional view of an IPM 200, in
accordance with yet another embodiment of the present invention.
Some elements of this embodiment are similar to those of IPM 80
(shown in FIG. 4) and are therefore marked with the same numbers.
In IPM 200, however, the stationary mirror of the preceding
embodiments is replaced by a scanning mirror 202. This mirror is
mounted on a suitable driver, such as on a micro-electrical
mechanical system (MEMS) driver chip 204, which typically provides
an angular scan range on the order of .+-.5.degree. in one or two
scan dimensions (X and Y). Chip 204 is fixed to a diagonal surface
of silicon optical bench 82. This diagonal surface may be produced
by cleaving a single-crystal silicon wafer in the 111 crystal
plane, as described above in reference to IPM 80. In the pictured
embodiment, mirror 202 may receive and scan the beam from laser
diode 84 directly, without intervening optics (for collimation, for
example), thus reducing the width of IPM 200 and simplifying the
alignment of optical bench 82. Laser diode 84 and mirror 202
themselves can be placed in alignment on bench 82 with high
accuracy, typically to within a few microns.
[0073] IPM 200 comprises an optical stack 206, comprising one or
more optical elements that typically collimate the scanned beam
reflected by mirror 202 and may also adjust the beam angles.
Optical stack 206 may comprise a refractive and/or diffractive
optical element, which enlarges the angular range of the output
beam from IPM 200. A larger range of this sort is desirable in
applications, such as system 20, in which the field of view is
larger than the limited scan range of mirror 202. Additionally or
alternatively, the optical stack may comprise an eccentric lens, of
the type shown in FIG. 4.
[0074] Further additionally or alternatively, IPM 200 may comprise
additional components (as part of optical stack 206 or as separate
components, not shown in the figure) for controlling and monitoring
the scanned beam, as described, for example, in U.S. Provisional
Patent Application 61/425,788, filed Dec. 22, 2010, which is
incorporated herein by reference. In one embodiment, optical stack
206 may comprise a patterned element, such as a diffractive optical
element (DOE), and driver chip 204 may direct the beam from laser
84 through the DOE at different angles in order to tile the field
of view of IPM 200 with multiple instance of the pattern, as
described in this provisional patent application.
[0075] The sort of scanning arrangement that is implemented in IPM
200 can be used for various purposes. For example, the scan may be
synchronized with the rolling shutter of image sensor 38, as is
described generally in the above-mentioned U.S. patent application
Ser. No. 12/762,373. Alternatively or additionally, IPM 200 can be
used to create patterned illumination without the use of a
patterned element (which may thus be eliminated from the IPM) by
pulsing laser diode 84 on and off in synchronization with the scan
of mirror 202. This sort of patterned illumination can be used in
pattern-based depth mapping schemes, such as those described above,
including schemes based on time-coded illumination, such as those
described in U.S. Provisional Patent Application 61/415,352, filed
Nov. 19, 2010, which is incorporated herein by reference.
Alternatively, modules based on the principles of IPM 200 may be
used in a variety of other scanned-beam applications that can
benefit for a very small, low-cost scanner.
[0076] Thus, although the embodiments described above relate mainly
to depth mapping, the principles of the IPMs in these embodiments
may likewise be used in other applications that involve projection
of a patterned beam. It will therefore be appreciated that the
embodiments described above are cited by way of example, and that
the present invention is not limited to what has been particularly
shown and described hereinabove. Rather, the scope of the present
invention includes both combinations and subcombinations of the
various features described hereinabove, as well as variations and
modifications thereof which would occur to persons skilled in the
art upon reading the foregoing description and which are not
disclosed in the prior art.
* * * * *