U.S. patent application number 17/249287 was filed with the patent office on 2021-08-19 for multiple-laser light source.
The applicant listed for this patent is MTT INNOVATION INCORPORATED. Invention is credited to Anders BALLESTAD, Gerwin DAMBERG, Eran ELIZUR, Eric Jan KOZAK, Raveen KUMARAN, Johannes MINOR, Gil ROSENFELD.
Application Number | 20210254797 17/249287 |
Document ID | / |
Family ID | 1000005564930 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210254797 |
Kind Code |
A1 |
MINOR; Johannes ; et
al. |
August 19, 2021 |
MULTIPLE-LASER LIGHT SOURCE
Abstract
A light source includes a plurality of laser diodes or other
light emitters. Beams of light from the light emitters are steered
to provide n array of parallel beams that illuminate a target area
with an array of patches of light. In some embodiments the parallel
beams are de-magnified to form the array of patches of light. Such
a light source has application in illuminating
dynamically-addressable focusing elements such as phase modulators,
deformable mirrors and dynamically addressable lenses. Light
projectors for a wide variety of applications may combine a light
source as described herein with a dynamically-addressable focusing
element to project defined patterns of light.
Inventors: |
MINOR; Johannes; (Vancouver,
CA) ; DAMBERG; Gerwin; (Vancouver, CA) ;
KUMARAN; Raveen; (Burnaby, CA) ; BALLESTAD;
Anders; (Vancouver, CA) ; KOZAK; Eric Jan;
(Burnaby, CA) ; ROSENFELD; Gil; (North Vancouver,
CA) ; ELIZUR; Eran; (Vancouver, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MTT INNOVATION INCORPORATED |
Vancouver |
|
CA |
|
|
Family ID: |
1000005564930 |
Appl. No.: |
17/249287 |
Filed: |
February 25, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16550090 |
Aug 23, 2019 |
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17249287 |
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15863717 |
Jan 5, 2018 |
10408390 |
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16550090 |
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15418505 |
Jan 27, 2017 |
9874319 |
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15863717 |
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PCT/CA2015/050778 |
Aug 14, 2015 |
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15418505 |
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62037543 |
Aug 14, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21V 29/90 20150115;
F21K 9/61 20160801; F21Y 2115/10 20160801; F21Y 2115/30 20160801;
F21K 9/60 20160801; G02B 26/0833 20130101 |
International
Class: |
F21K 9/60 20060101
F21K009/60; G02B 26/08 20060101 G02B026/08; F21V 29/90 20060101
F21V029/90; F21K 9/61 20060101 F21K009/61 |
Claims
1. (canceled)
2. A method for aligning an optical apparatus, the method
comprising: positioning a light emitter in approximate alignment
with a corresponding lens; applying a flat phase pattern to a
dynamic diffractive optical element in a path of a light beam
emitted by the light emitter and focusing the beam by moving the
light emitter relative to the dynamic diffractive optical element;
sampling a profile of the beam at plural distances along an optical
axis and adjusting a distance between the light emitter and the
lens until all the sampled profiles have equal widths; inserting a
polarizer into a light path of the beam and adjusting an angle of
the light emitter to maximize a brightness of the beam; applying an
alignment pattern to the dynamic diffractive element and adjusting
a position of the light emitter in one or more of XZ-plane
parallelism, YZ-plane parallelism, rotation about the X or Y axis
until the alignment pattern is registered.
3. A method for aligning a light source comprising a plurality of
lasers spaced in an arrangement, each of the lasers operable to
emit a beam of light, the method comprising: centering and
collimating each of the beams of light by positioning one or more
lenses in an optical path of the beam of light and fixing a
position of the one or more lenses; positioning mirrors to redirect
the beams of light to provide a closely spaced array of parallel
beams of light and fixing positions of the mirrors.
4. The method of claim 3 wherein positioning the mirrors comprises
reducing a spacing between adjacent ones of the beams of light
emitted from the plurality of lasers.
5. The method of claim 4 comprising positioning the mirrors to clip
edges of the beams of light emitted from the plurality of
lasers.
6. The method of claim 5 wherein the mirrors comprise a plurality
of knife-edge mirrors and each of the beams is reflected by two of
the plurality of knife-edge mirrors arranged at 90 degrees to one
another.
7. The method of claim 3 wherein positioning the mirrors comprises
adjusting an angle of each of the plurality of mirrors about a
corresponding pivot joint.
8. The method of claim 7 comprising, after each of the mirrors is
positioned, fixing the corresponding pivot joint with an
adhesive.
9. The method of claim 3 wherein positioning the mirrors comprises
mounting each of the plurality of mirrors on a flexible
structure.
10. The method of claim 9 comprising shimming the flexible
structure into place.
11. The method of claim 3 comprising applying a settable material
to fix the positions of the one or more lenses.
12. The method of claim 11 wherein the settable material comprises
epoxy, glue or solder.
13. The method of claim 3 comprising positioning a diffraction
grating in an optical path of the lasers to produce an alignment
pattern.
14. The method of claim 3 comprising controlling a dynamic optical
element positioned in an optical path of the lasers to display a
dynamically varying diffractive alignment pattern.
15. The method of claim 14 comprising controlling the dynamic
optical element to display progressively finer alignment
patterns.
16. The method of claim 3 comprising positioning one or more
additional lenses or mirrors to expand or contract the beam of
light emitted from a corresponding one of the lasers.
17. The method of claim 3 comprising equalize path lengths of the
beams of light by positioning one or more additional mirrors to
fold a light path of one or more of the beams of light.
18. The method of claim 3 comprising placing cooling elements
proximate to heat-generating elements of the light source.
19. The method of claim 3 comprising arranging the lasers in a
two-dimensional array that has a length and a width wherein the
length of the array is larger than a length of the closely spaced
array of parallel beams and the width of the array is larger than a
width of the closely spaced array of parallel beams.
20. The method of claim 3 wherein the lasers comprise laser
diodes.
21. The method of claim 20 wherein the laser diodes are provided by
at least one laser diode bar comprising a plurality of spaced-apart
laser diodes.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. application Ser.
No. 16/550,090 filed 23 Aug. 2019, which is a continuation of U.S.
application Ser. No. 15/863,717 filed 5 Jan. 2018 now issued as
U.S. patent Ser. No. 10/408,390, which is a continuation of U.S.
application Ser. No. 15/418,505 filed 27 Jan. 2017 now issued as
U.S. Pat. No. 9,874,319, which is a continuation of PCT
International Application No. PCT/CA2015/050778 filed 14 Aug. 2015
which is incorporated herein by reference for all purposes. PCT
International Application No. PCT/CA2015/050778 claims priority
from U.S. Application No. 62/037,543 filed 14 Aug. 2014. This
application claims the benefit under 35 U.S.C. .sctn. 119 of U.S.
Application No. 62/037,543 filed 14 Aug. 2014 and entitled
MULTIPLE-LASER LIGHT SOURCE, which is hereby incorporated herein by
reference for all purposes.
TECHNICAL FIELD
[0002] This invention relates to light projectors. Some embodiments
may be applied to project images for viewing. Other embodiments may
be applied to create structured light for illumination or other
purposes. Embodiments have example application in digital cinema,
TV and home theater, portable and personal projection (military,
mobile, etc.), indoor and outdoor personal and large screen
advertising and information dissemination,
signs/advertising/billboards/outdoor advertising, large-venue and
live performance, medical imaging, virtual reality, computer
gaming, office presentations and collaborative work, head-up
displays in cars and other vehicles, smart illumination such as
adaptive car head-lights, theatre spotlights,
security/architectural lighting, high contrast planetarium
projectors, indoor and outdoor general illumination systems,
street-lighting, road-lighting, aviation lighting systems,
high-contrast simulation displays such as flight simulators, and
small-scale structured lighting for 2D and 3D printing, and laser
micro-machining.
BACKGROUND
[0003] There are many situations where it is desired to create a
light field that has a specified luminance profile. Light
projection systems have a very wide range of applications from
architectural lighting to the display of lifelike images. The
projected light patterns can be dynamic (e.g. video), static (used
for static images or static applications like the beams of typical
car headlights projected through a lens onto the road, made by
arbitrarily shaped optical surfaces, etc.). Light may be projected
onto a wide range of screens and other surfaces which may be flat
or curved. Such surfaces may be fully reflective (like a canvas
used in a cinema, a wall or a building) or partially reflective
(such as the windshield of a vehicle). Screens may be low-gain or
high-gain, Lambertian or highly directional, high-contrast or lower
in contrast. Light may be projected onto solid objects or onto a
medium in a volume (such as fog).
[0004] Markets for and applications of light projectors include
digital cinema, in-door and out-door advertising, medical imaging
(both for display of images, as well as capture by a smart light
source), large venue and live events or performances, automotive
heads up displays, car head-lights and rear-lights, automotive
entertainment and information displays, home-theatre, portable
business projection, television and displays for consumer
applications, military applications, aviation applications (like
cockpit displays, smart landing-assistance, individual passenger
entertainment displays), structured light sources for industrial
applications, automotive headlights and other applications.
Structured light may also be used for high precision applications,
such as curing ink or other material for 2D or 3D printing, or
steering light for laser micro-machining.
[0005] Various devices may be used to spatially modulate light.
These may be called spatial light modulators (SLMs). Most SLMs
provide a 2D array of independently and individually addressable
pixels. Some examples of SLMs are reflective SLMs such as digital
micro-mirror devices (DMDs), liquid crystal on silicon (LCoS)
devices and transmissive SLMs such as LCD panels, transmissive LCD
chips such as high-temperature polysilicon (HTPS) or
low-temperature polysilicon (LTPS); and partially
reflective/partially transmissive SLMs such as
micro-electro-mechanical systems (MEMS) based systems in which some
of incident light is transmitted and some of incident light is
reflected. Most readily available spatial light modulation
technologies are subtractive. These SLM technologies operate by
absorbing or removing undesired light.
[0006] Other types of devices may controllably alter the nature
and/or distribution of light using techniques that are not
primarily subtractive. For example, the light redistributor may
exploit interference of electro-magnetic waves (light), to modulate
the distribution of light by controlling its phase characteristics
and/or modulate the frequency of the light in order to change the
apparent colour of light. Both of these examples show how light can
be changed without converting energy from the light into wasted
heat by absorbing the light.
[0007] Examples of dynamically-addressable focusing elements
include: transmissive 2D arrays of controllable liquid crystal
compartments with the property that the compartments can be
controlled to selectively retard the phase of light, effectively
causing a change in path-length. Devices that can controllably
adjust the phase of light of different areas are called Phase
Modulating Devices (PMD). PMDs may be transmissive or reflective.
Some PMDs can individually control phase in a 2D array made up of a
large number of pixels. A dynamically-addressable focusing element
may also affect the polarization of light. Some devices may alter
several light properties simultaneously.
[0008] Other types of dynamically-addressable focusing element
comprise one or more scanning mirrors, such as a 2D or 3D
microelectromechanical system (MEMS); and/or. one or more
deformable lenses or mirrors or other optical elements. A
dynamically-addressable focusing element may also or in the
alternative comprise one or more optical switches.
[0009] Various sources can be used for illuminating SLMs, PMDs,
imaging chips, or any other light re-distributing device, including
arc lamps, light-emitting diodes (LEDs), LEDs plus phosphor,
lasers, lasers plus phosphors. Each light source may emit light of
different shapes, intensities and profiles. Traditional approaches
to combining multiple light sources into a single higher-powered
source include coupling light into optical fibres, and knife edge
mirror beam combining, relaying into an integration rod, or some
other optical averaging device.
[0010] However, in some cases, the useful characteristics of
individual low-powered light sources are not preserved when
combined using the traditional approaches, and higher-powered
single-emitters are either not available, or have a prohibitively
high cost per watt of light. For example, when light from multiple
laser diodes is combined some of the characteristics affected are:
[0011] Coherence: When coupling light from multiple discrete laser
diodes or laser diode bars into a multi-mode fibre, or combining
multiple laser beams into a single beam using a knife edge mirror
array plus lens, coherence is lost. [0012] Polarization: The light
at the output of a multi-mode fibre is no longer polarized, so some
polarization recovery techniques must be used for applications that
require polarized light. There is a need for light sources and
projectors that effectively combine light from multiple light
sources. There is a particular need for cost-effective light
sources and projectors in which light from multiple light sources
can be manipulated to yield desired light patterns having desired
optical characteristics.
SUMMARY
[0013] This invention has a number of aspects. One aspect provides
light sources that combine light from a plurality of individual
lower-powered light emitters (which, in some non-limiting
embodiments comprise laser diodes or other laser light sources and
in other embodiments comprise non-laser light sources--which are
solid-state light sources in some embodiments). The light sources
may emit light in the form of arrays of discrete, collimated,
non-overlapping patches. In some embodiments, optical paths
provided by the light source cause the individual patches to have
desired optical characteristics such as desired polarizations
and/or coherence. Another aspect provides methods for illuminating
a dynamically-addressable focusing element. Another aspect provides
light projectors incorporating light sources as described
herein.
[0014] Further aspects and example embodiments are illustrated in
the accompanying drawings and/or described in the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings illustrate non-limiting example
embodiments of the invention.
[0016] FIGS. 1A and 1B illustrate a light source comprising a fixed
diode array with multiple mirrors.
[0017] FIGS. 2A and 2B illustrate a light source comprising a fibre
coupled diode array.
[0018] FIGS. 3A to 3C illustrates a light source comprising a
"Christmas Tree" mirror.
[0019] FIGS. 3D to 3F illustrates a light source comprising a
parabolic mirror.
[0020] FIGS. 4A and 4B illustrate light profile resizing.
[0021] FIGS. 5A and 5B illustrate combining arrays of light beams
from several light sources to yield a larger array of light
beams.
[0022] FIG. 6 illustrates an example optical arrangement for
collimating light beams from light emitters having a fast and a
slow axis.
[0023] FIG. 7 illustrates path length equalization with multiple
mirrors.
[0024] FIG. 8 illustrates a DMD control scheme.
[0025] FIGS. 9A and 9B illustrate a possible effect of asynchronous
modulation of a light source and operation of a DMD.
[0026] FIGS. 10A and 10B illustrate asynchronous modulation of a
light source and operation of a DMD in a case where the light
source is modulated at a high frequency relative to flip time of
the DMD.
[0027] FIG. 11 illustrates synchronous modulation of a light source
and operation of a DMD.
[0028] FIG. 12 is a block diagram of example apparatus for
generating a DMD sync signal by analyzing light dumped by the
DMD.
[0029] FIG. 13 illustrates an example staggered start of light
emitters relative to a DMD cycle.
[0030] FIGS. 14A and 14B schematically illustrate different
possible modes for controlling a dynamically-addressable focusing
element to display an image.
[0031] FIG. 15 is a block diagram illustrating an example
projector.
[0032] FIGS. 16A and 16B schematically illustrate possible color
imaging modes and ways to scale up or down optical power in a
projector.
[0033] FIG. 17 is a block diagram of an example system (light
efficient illuminator) at a high level.
[0034] FIG. 18 is a block diagram of the system of FIG. 17 at a
more detailed level showing basic components of a light efficient
illuminator.
[0035] FIG. 19 is a block diagram detailing the components within
the light module which is a component of the light efficient
illuminator shown in FIG. 18.
[0036] FIG. 20 details example optical components within the light
module of FIG. 3 and also depicts example light profiles at each
stage within the light module.
[0037] FIG. 21 is a block diagram of an example
dynamically-addressable light redistribution module.
[0038] FIG. 22 shows two examples (top and bottom) of light
profiles at the light module (left), at a dynamically-addressable
focusing element (center) and at the system output.
[0039] FIG. 23 illustrates example optics of a simple system that
does not require (but is compatible with) coherent light.
[0040] FIG. 24 illustrates example components of a system that
re-distributes light and utilizes a clean-up stage (e.g. an array
of integration rods) as well as showing example light profiles at
each component.
[0041] FIG. 25 is a block diagram illustrating operation of an
optimization-based method for determining phase shifts to apply to
different areas of a dynamically-addressable focusing element to
create a target light field (or iterative program required to
operate the system in `exact mode`).
[0042] FIG. 26 is a block diagram illustrating a procedural method
for creating an approximation to a target light field.
[0043] FIG. 27 shows three examples of an optical setup for use
with coherent light.
[0044] FIG. 28 shows example optics for a variable laser scanning
approach.
[0045] FIG. 29 shows example optics of another variable laser
scanning approach (with dynamically focusable lenses or other
optics).
[0046] FIG. 30 is an example of an optical switch using MEMS (micro
electromechanical systems).
[0047] FIG. 31 is an example of how an optical switch or other
light re-distributor can be used in concert with a clean-up module
(e.g. an array of integrating rods).
[0048] FIG. 32 is a block diagram of a system including a
refinement module (e.g. a light efficient illuminator in
combination with a spatial light modulator (SLM).
[0049] FIG. 33 shows example optics of a system including a
refinement module. It also depicts example light profiles at the
output of the light efficient illuminator and at the input of the
imaging device (e.g. SLM).
[0050] FIG. 34 is a block diagram of an illumination system
including a clean-up stage and a refinement stage.
[0051] FIG. 35 shows example optics of a system including a
clean-up stage and a refinement stage. It also depicts example
light profiles at each stage.
[0052] FIG. 36 shows intensity-time and intensity-location plots of
a time-multiplexed or color field sequential system. Two example
methods use two different timing schemes.
DETAILED DESCRIPTION
[0053] Throughout the following description, specific details are
set forth in order to provide a more thorough understanding of the
invention. However, the invention may be practiced without these
particulars. In other instances, well known elements have not been
shown or described in detail to avoid unnecessarily obscuring the
invention. Accordingly, the specification and drawings are to be
regarded in an illustrative, rather than a restrictive sense.
[0054] Several novel approaches have been devised for tiling light
from multiple sources in a parallel, collimated fashion. It is
advantageous in some applications that the tiled light patches have
minimal overlap with one another. In any of these approaches the
light patches may be arrayed on a surface of a
dynamically-addressable focusing element such as a phase modulator
(PMD).
Adjustable Diode Array, Fixed Mirrors
[0055] A two-stage array of knife-edge mirrors can be used to tile
a two dimensional array of lower-powered light sources, such as
LEDs or laser diodes, to cover the active area of an imaging chip
with discrete, non-overlapping patches of light. Each discrete
laser diode (or other light emitter) is mounted in a holder with
built-in X, Y and angular adjustment, and a lens for capturing and
collimating the light. The holders each comprise a two-axis stage,
and a holder with a tip/tilt adjustment in some embodiments.
[0056] This limits the compactness of the light source arrangement,
so two arrays of knife edge mirrors are used, oriented 90 degrees
to each other. FIGS. 1A and 1B show an example light source 100
which applies this type of approach. Light source 100 includes
light emitters 102, lenses 103, knife-edge mirrors 104A and 104B.
Mirrors 104A and 104B are arranged at 90 degrees to one
another.
[0057] If space or design constraints force more complex geometry,
two knife edge arrays can be combined in other orientations to
achieve closely spaced parallel beams.
[0058] The knife edge mirrors serve to reduce the spacing of the
individual beams, and clip the edges to minimize overlap and
maximize coverage. Each beam may diverge slightly, and to different
degrees along the long and short axis, so the mirror assembly is
kept compact. The distance from the output of the mirror assembly
to the imaging chip is kept as small as is practical.
Fixed Diode Array with Adjustable Mirrors
[0059] In another example embodiment, a 2-dimensional grid of light
emitters (e.g. laser diodes) is fit into a fixed mount machined to
tight manufacturing tolerances, with inset collimating lenses.
Light beams emitted by the array of light emitters are directed at
a two-stage array of knife-edge mirrors. In this embodiment the
light emitters remain fixed and alignment is achieved by moving the
mirrors. Once alignment has been achieved the mirrors may be
permanently set, such that the output of the opto-mechanical system
is a two-dimensional array of discrete, non-overlapping patches of
light. This embodiment may otherwise be very similar or the same as
the embodiment illustrated in FIGS. 1A and 1B.
[0060] This adjustment can be achieved by mounting each mirror on a
pivot joint, which can be set with an adhesive once adjusted, or a
flexible structure that can be shimmed into place.
[0061] In some embodiments knife edge mirrors are split into
segments for each source, with individual tip-tilt control. This
facilitates de-coupling individual sources from a row or column.
Adjustable segments may be adjusted to apply any corrections to the
direction or divergence of the individual beams.
[0062] Some embodiments provide adjustments to the positions and/or
orientations of light emitters 102 as well as to the angles of
mirrors 104.
Fibre-Couple Each Diode
[0063] FIGS. 2A and 2B illustrate another embodiment wherein the
outputs of laser diodes 102 or other light emitters are guided by
optical fibers 203 to create a desired array of light patches. For
example, the light patches may be arrayed on a surface of a
dynamically-addressable focusing element such as a phase modulator
(PMD). In this design an array of light emitters 102 each has an
associated lens 103 that captures the emitted light, and couples it
into a single-mode optical fiber 203. Fibers 203 are bundled, and
the output of the bundle is relayed onto the imaging chip (e.g. a
PMD). This approach can be used to transform a source array into
any shape, spacing, or configuration. A single-mode fibre will
maintain polarization and coherence of laser light, but this same
approach can be implemented with multi-mode optical fibers, with
optimal diameter and geometry for increasing coupling efficiency
without significant losses in coherence or excessive
divergence.
"Christmas Tree" Mirror Mount
[0064] Instead of tiling patches in a rectangular pattern as shown,
for example, in FIGS. 1A and 2A, a radial pattern of light patches
can be achieved by using a mirror having a generally conical
"Christmas tree" design. One potential configuration 300 is
illustrated in FIGS. 3A to 3C. In this embodiment, light emitters
102 are mounted radially facing inward toward a Christmas tree
mirror 304. In the illustrated embodiment, mirror 304 comprises a
plurality of generally conical axially spaced-apart mirror surfaces
304A and 304B. The approach exemplified by FIGS. 3A to 3C can also
be expanded, by machining lens curvature into the mirror surfaces
304A and 304B to collimate the beams, reduce the spacing, and
aperture the beams in a single step.
[0065] A large source spacing may be used to improve alignment at
the expense of the overall size of the opto-mechanical system.
[0066] If consistent polarization is required, angles may be taken
into account to maintain consistent polarity in each beam as it
hits the imaging chip or other destination.
Parabolic Mirror for Combining Radial Beams
[0067] FIGS. 3D, 3E and 3F show an arrangement 300A which is
similar to arrangement 300 but uses a parabolic lens 304A to
deflect beams from a radial arrangement of light emitters 102A,
102B into a parallel, closely spaced arrangement. In the
illustrated embodiment, the emitters include light emitters 102A
which direct beams at mirror 304A at a first angle to the axis of
symmetry of mirror 304A and light emitters 102B which direct light
beams at mirror 304A at a second angle to the axis of symmetry of
mirror 304. This concept is similar to the "Christmas Tree"
approach illustrated in FIGS. 3A to 3C, but without the aperturing
effect of mirror edges.
De-Magnification of Over-Sized Beam Grid
[0068] The target illumination area, such as an imaging chip, SLM,
or PMD, may be small compared to an array of sources. Any of the
above approaches, including the knife-edge mirror approach
described with reference to FIGS. 1A and 1B can be used to create a
tiled pattern of non-overlapping patches of light (i.e. an array of
parallel light beams) on a scale that is larger than the target
area. In some embodiments, the scale of the patches of light is a
factor of 2 or more times larger than the target area (e.g. the
patches of light cover an area 4 or more times that of the target
area in some embodiments). An optical system can be used to reduce
the area of the resulting cluster of beams by demagnifying the
light beams such that the array of patches of light is adjusted to
the size required.
[0069] An example arrangement 400 is shown in FIGS. 4A and 4B. An
optical system 401 (for example any of the systems described above)
creates an array of beams 402. An optical system 404, in this
example comprising lenses 404A and 404B de magnifies the array of
beams.
[0070] Gaps may be maintained between the parallel beams, so
divergence or distortion in the de-magnified light profile may be
avoided.
Cascading Knife-Edge Mirror Stages
[0071] In some embodiments Individual modules each comprising a
plurality of light emitters as described above can be produced in
configurations which each yield an array of light patches (for
example a 3.times.3 or 3.times.2 configuration). Beams output by
two or more of such modules may be de-magnified as illustrated in
FIGS. 4A and 4B, and tiled using an adjustable mirror technique, as
described above (e.g. using arrays of tiltable mirrors arranged as
shown in FIG. 1A).
[0072] FIG. 5 illustrates an example system 500 in which light
output by three modules 401 is deflected by mirrors 502 to form an
array 503 of patches of light. Light from any suitable number of
modules 401 may be combined in this manner. Array 503 may combine
arrays from modules 401 in a linear manner, as shown, or may
combine arrays from modules 401 to yield an output array 503 that
is larger in each of two dimensions than the arrays of patches of
light from individual modules 401. For example, the arrays of
patches of light from modules 401 may be arranged to make a
composite array having plural rows and columns of arrays from
individual modules 401.
Light Emitters
[0073] Any of a wide variety of light emitters may be used in the
embodiments described above. for example, the light emitters may
comprise lasers. Solid state lasers such as laser diodes are
practical for a range of applications. Other examples of light
emitters include solid-state light emitters such as light emitting
diodes (LEDs); plasma light emitters; cold cathode light emitters;
lamps, etc. In some embodiments the light emitters emit coherent
light. In some embodiments the light emitters emit polarized
light.
[0074] Light emitters may be provided in the form of discrete
devices or may be packaged together in packages combining plural
light emitters. For example, light emitters in embodiments as
described above may be provided using systems comprising multiple
light emitters, such as diode bars, with appropriate emitter count
and spacing. Such embodiments may be advantageous for reducing the
number of separately-mounted components in a light source.
[0075] Some light emitters may emit light in a form which is
advantageously corrected to yield a beam with desired properties
(e.g. a beam that is well collimated and directed in a desired
direction). Custom optics may be provided for beam conditioning and
correction for beam path in some embodiments.
[0076] FIG. 6 shows an example apparatus 600 comprising an
edge-emitting diode array 602 which provides a plurality of
individual light emitters 102C. Each light emitter 102C has a fast
and slow axis. Apparatus 600 includes collimating optics 605 which
includes a lens 605A for collimating in one axis and a plurality of
lenses 605B for collimating in a second axis to yield a line of
collimated output light beams. Two or more sets of apparatus 600
may be stacked to provide a two dimensional array of emitters.
[0077] Especially where an off-the-shelf diode bar is used for
array 602, some conditioning and "smile correction" may be provided
in the optical system in the case that the line of emitters has
some curvature. An aperture, or reverse knife edging may be
provided to increase the separation between beams. This can
facilitate substantial elimination of overlap between adjacent
beams.
Dealing with Path Length and Divergence
[0078] Most light emitters do not emit perfectly collimated beams
of light. A beam of light from a light emitter will generally
exhibit some divergence. It is desirable to reduce the effect of
such divergence. In cases where divergence of the beams from
different emitters can be substantially eliminated, an output array
of patches of light may have the patches spaced very close to one
another without any significant overlap between the patches. Some
light emitters emit light that diverges differently in different
directions. A direction in which the divergence is large may be
called the fast axis. A direction in which divergence is smaller
may be called a slow axis. Where a light emitter has a fast and a
slow axis, a single symmetrical lens can approximately collimate a
beam from the light emitter along the fast or slow axis, but the
beam will continue to diverge in the other axis.
Pairs of Mirrors to Fix Path Length
[0079] Some embodiments equalize path length from the light
emitters to the corresponding patches at the target area. Making
path lengths equal for all beams is advantageous at least in part
because beam divergence can differ for different path lengths.
Where the path lengths are equal, divergence of all of the beams
may be approximately equal.
[0080] Mirrors can be used to fold the light path to equalize the
path length across all beams, as shown in apparatus 700 of FIG. 7.
Using multiple mirror stages, the path length for each beam can be
identical without complex geometry. Apparatus 7 includes light
emitters 102 that emit light beams 103-1, 103-2 and 103-3. Each
beam interacts with a pair of mirrors that fold its path. the
mirrors are spaced so that the path lengths from each light emitter
102 to output beams 703 are equal. Apparatus 700 includes mirror
pair 701A-1 and 701 B-1 which acts on beam 103-1; mirror pair
701A-2 and 701 B-2 which acts on beam 103-2; and mirror pair 701A-3
and 701B-3 which acts on beam 103-3.
Asymmetrical Lenses
[0081] Light profiles of source light beams may not be radially
symmetrical, either in terms of shape, or rate of divergence. For
example, the fast and slow axis of a laser diode have different
rates of divergence. This can be corrected by introducing a lens
that is not circularly symmetrical in the beam direction (e.g. a
cylindrical lens) in the light path.
[0082] Some embodiments provide an array of cylindrical lenses to
correct the divergence along the slow axis of beams from a
plurality of light emitters such as laser diodes. This approach is
well-suited for the case where diode bars or a diode bar stack
provide the light emitters. This approach may also be applied to an
array of discrete diodes or other light emitters. An example is
illustrated in FIG. 6.
[0083] Various possible optical arrangements to correct divergence
of beams having a fast and a slow axis include using pairs of
cylindrical lenses for each axis, using a single shared spherical
lens and a cylindrical lens for each axis and so on.
Long Geometry
[0084] As described above, the effects of divergence can be
mitigated by designing the source array such that distance from the
source array to the mirrors which guide the light into parallel
beams (e.g. knife edge mirrors as shown in FIG. 1A) is large,
relative to the distance between the knife-edge mirrors and the
target area (e.g. a dynamically addressable focusing element or
other imaging chip). In some embodiments the distance from the
light emitters to the mirrors is at least 3, 5, 10 or 18 times
larger than the distance from the mirrors to the imaging chip.
[0085] With this approach, increasing the distance from the light
emitters to the mirrors makes any relative differences in path
lengths for different beams smaller. The mirrors may be close
enough to the imaging chip that the amount of divergence between
the mirrors and the imaging chip is small, such that no undesirable
overlap occurs at the imaging chip.
Desired Light Source Characteristics for Freespace Laser Projector
Using Phase and Amplitude Modulation
[0086] In a traditional digital projector, it is important that the
amplitude SLM (DLP, LCD, LCoS) which is imaged onto the projection
screen via the projection lens is illuminated uniformly.
[0087] In some embodiments a light source illuminates a
dynamically-addressable focusing element non-uniformly. In such
embodiments dynamically-addressable focusing element (e.g. a phase
modulator) may be controlled to provide structured illumination
(which varies from location to location in a known way) on an
amplitude SLM. While it remains beneficial to illuminate the phase
modulator uniformly (even heat dissipation, uniform light profile
on SLM when a flat phase is addressed or in case the phase SLM
fails), intensity variation across the phase SLM can be accounted
for and the lensing pattern can be adjusted to `correct` for it
(for example to provide uniform illumination on the amplitude SLM
when desired).
Alignment Example
[0088] A light source for a particular application desirably
achieves specifications required by the application for beam
quality and stability in a package that is simple and compact.
Ideally the light source may be installed as a single module which
can be aligned at time of manufacture using adjustments that
facilitate rapid accurate alignment (e.g. orthogonal adjustments
such that adjustment of one beam property does not change other
beam properties).
[0089] In some embodiments alignment is performed in a `bottom-up`
approach in which light beams from individual light emitters are
centered and collimated, the light emitters are assembled into
banks, the alignment of the beams is adjusted, and then beam
shrinking optics are adjusted to deliver the output light to a
desired target area (in some embodiments the target area is a few
mm per side, for example 12.times.7 mm). After each alignment step
the adjustment may be fixed using a settable material such as a
suitable epoxy, glue, solder or the like.
[0090] Table I provides three sets of example design
specifications. Some of these specifications are achieved in some
embodiments. One or more of these sets of specifications are
achieved in some embodiments.
TABLE-US-00001 TABLE I Example Design Specifications Good Better
Best Priority Feature specs specs specs Unit Comments/Metrics 1
Z-Parallelism 500 210 0.5 arc sec Fast axis, measure on optical
axis at .1 m, .5 m and 5 m distance 6.4 um resolution, 300 mm away
2 XY 15 2 0.5 Degrees Parallelism 3 XY-Shifting 50 10 0.1 px
(tiling) (LETO) 4 Divergence mrad (fast axis) Divergence mrad (slow
axis) 5 Fill-factor on 40 95 99 % LETO Fill factor is a LETO area
function of beam size and diode count. Need to modify one or the
other 6 Intensity 40 75 95 % uniformity on relative LETO to peak 7
Measurement absent Present, absent port removable 8 Beam unknown
quantified constrained % Meet 1, 2, 3 after 1 h, stability over
variation 6 h, 24 h time 9 Beam unknown quantified constrained Meet
1, 2, 3 after stability over 20 C., 40 C., 60 C. temperature 10
Beam unknown quantified constrained (Profile, Centre stability over
Location, Intensity) power Consistency & predictability over
various modulation approaches, PWM, current control, etc. 11
Throughput 60 75 90 %
Example Light Source Block
[0091] In this example, eight laser diodes, each with a
corresponding collimating lens, are positioned in an array, with 10
mm separation distance. Each diode is pressed into a copper block
with integrated cooling fins, and attachment features. Eight lenses
are mounted in a fixed block with 10 mm spacing. A jig holds the
fixed lens array stationary relative to an alignment pattern some
arbitrarily large distance away, in the far field. This alignment
pattern includes reference lines indicating desired beam positions,
with 10 mm spacing.
[0092] A single diode block is held in a three-, four-, five-, or
six-axis positioning stage, and positioned such that the emitter is
centered with respect to the corresponding lens, the output beam is
collimated (neither diverging or converging in the far-field),
oriented so that the polarization is consistent with the light
source specification, and directed such that the beam is coincident
with the corresponding position indicated on the alignment
pattern.
[0093] The z-axis position of the diode emitter (parallel to the
beam direction) controls the divergence of the beam. The x- and
y-axis position of the diode emitter control the x- and y-location
of the laser spot on the alignment pattern. Rotation about the
z-axis controls the polarization orientation. The x- and y-axis
position of the diode emitter can be adjusted to correct for
distortions in the beam shape.
[0094] When the diode is suitably positioned, it is fixed to the
lens block. This mechanical connection can be achieved in a number
of ways such as: [0095] 1. The diode block has tabs that are
soldered to pads on the lens block [0096] 2. The diode block
remains in the jig, and an adhesive such as epoxy or a suitable
UV-curing adhesive or a suitable thermal curing adhesive is applied
to fix the diode position, [0097] 3. The diode block is spot welded
to lens block, [0098] 4. The diode block is initially aligned
coarsely and is precisely deformed in the jig for fine
alignment.
Techniques for Improving Alignment Precision
[0099] With a printed alignment mask on the example system
described, collimation and parallelism accuracy is limited to on
the order of +/-1 mm at a distance of 3 m, or 0.015 degrees.
[0100] For improved accuracy, more advanced techniques can be
implemented. Some examples are: [0101] 1. A diffraction grating can
be positioned in the light path, to produce larger alignment
patterns with diffractive imaging, and magnified for increased
measurement accuracy. [0102] The collimation can be adjusted to
achieve the optimal point spread function to a much higher
precision. [0103] The parallel beam alignment precision can be
improved by registering two alignment patterns rather than
attempting to centre an amorphous beam dot on an alignment grid
visually. [0104] 2. A dynamic diffractive optical element, such as
a phase-only Spatial Light Modulator, can also be used to improve
alignment precision, by dynamically changing the diffractive
alignment pattern for a multi-step alignment approach. [0105] Sets
of alignment patterns can be generated, starting with coarse
patterns, and moving to progressively finer alignment. [0106]
Different patterns may be better suited to achieving different
aspects of alignment. For example, horizontal lines for XZ-plane
alignment, vertical lines for YZ-plane alignment, a suitable
horizontally and vertically symmetrical pattern for collimation
adjustment, or for optimizing the beam angle about the optical axis
etc.
Automation of Light Source Alignment
[0107] The alignment process can be automated, diode-by-diode,
using computer-controlled 4-, 5-, or 6-axis alignment stages, and
either a machine vision camera directed at a screen, or by relaying
the output beams onto an optical sensor, such as a CCD, or CMOS.
The following is an example algorithm that may be applied for
automated or semi-automated alignment. The algorithm begins with a
fixed block of lenses, mounted to an alignment jig. For the
duration of the alignment procedure, the lens array may remain
fixed relative to the all other elements, excluding the diodes. The
alignment jig holds the lens array block, pointed at a dynamic
diffractive optical element (e.g. a phase modulator). Light output
from the phase modulator is resized using standard optics, and
relayed onto an optical sensor, or projected onto a screen and
captured by a machine vision camera. The diffractive optical
element and screen or optical sensor are placed at a distance that
is very large compared to the focal length of the lenses in the
fixed array. [0108] 1. Begin [0109] 2. Position the light emitter
(e.g. a laser diode) in approximate alignment with the
corresponding lens and clamp the laser emitter in a jig, providing
4-, 5-, or 6-axis micro-positioning. The jig may comprise a stage,
and a holding device. [0110] 3. Proceed with the automated
alignment procedure: [0111] a. Apply a flat phase pattern to the
dynamic diffractive optical element, and adjust the focus by moving
the light emitter so that the beam neither converges nor diverges.
This can be achieved by sampling the beam profile at several
distances along the optical axis and adjusting the distance between
the laser diode and the lens until all samples are the same width.
This can also be achieved using a beam splitter and a phase sensor,
and adjusting the position of the laser emitter until the beam
profile is maximally flat. [0112] b. Insert a polarizer into the
light path (if the dynamic diffractive optical element is not
polarized, or if it is not polarized in the desired direction).
Adjust the angle of the light emitter about the optical axis,
holding all other adjustments constant, until the beam reaches
maximum brightness. [0113] c. Apply alignment patterns to the
dynamic diffractive element and adjust the position of the light
emitter position until the patterns are registered optimally. This
process can be repeated for various aspects of alignment, including
XZ-plane parallelism, YZ-plane parallelism, rotations about the X
or Y axes. [0114] d. This alignment procedure can be repeated in
multiple steps, from coarse to fine alignment [0115] 4. When
sufficiently precise alignment is achieved for the light
emitter-lens pair, fix the light emitter to the lens block using
one of the methods described above. [0116] 5. Repeat the above
steps for each additional light emitter adjusting for beam
characteristics as above and also ensuring that the beam is
parallel to the beams of previously-aligned light emitters added to
the block.
Combined System
[0117] Once a block of light-emitter-lens pairs has been aligned to
yield collimated, parallel beams, with identical polarization
orientation the block may be combined with other elements which
function to create a more compact beam array, and to shape and
resize the combined light profile to cover an imaging chip. Such a
system might comprise: [0118] a mount to hold the array of
diode-lens pairs; [0119] an array of knife-edged mirrors arranged
to decrease the spacing between adjacent beams; [0120] one or more
lenses or mirrors for expanding or contracting the beam to suit the
desired application; [0121] mirrors for folding the light path to
achieve a compact footprint and/or to equalize path lengths or
different beams; [0122] cooling for the heat-generating elements
(e.g. suitable heat sinks and/or active coolers such as Peltier
elements); and [0123] control electronics for the light
emitters.
[0124] Some embodiments also include monitoring sensors such as
temperature sensors attached to measure operating temperatures of
the light emitters and/or other elements and/or measurement ports
at which beam profiles may be evaluated.
[0125] In an example embodiment the light emitters comprise 500 mW
lase diodes such as the model ML501P73 laser diodes available from
Mitsubishi electric. these laser diodes output light at 638 nm. An
example display includes 6 to 20 such laser diodes.
Control Electronics
[0126] It is not always desired to have light emitters running at
full brightness at all times due to the fact that some images do
not contain much light. It is possible to steer unneeded light into
a dump area (e.g. through suitable control of a
dynamically-addressable focusing element), but it would be more
ideal to reduce the light output of the light emitters and reduce
energy consumption and heat output. Reducing the output of the
light emitters for darker images may also improve black level by
reducing scattered light.
[0127] Laser diodes can be dimmed by reducing the amount of current
passing through them and or turning them off and on at a
sufficiently rapid speed to not be noticeable by a human
observer--known as pulse width modulation (PWM). It is more
difficult to achieve precise intensity control by controlling the
current than by PWM.
[0128] When using PWM control a duty cycle (% of the time that a
light emitter is ON) can be thought of as controlling the output
light intensity. For example one way to implement 8 bit control
over light intensity is to clock a counter at 256xx the PWM
frequency such that an output is held in a state corresponding to
the light emitter being ON until the counter value reaches the 8
bit intensity value. The output would be in a state corresponding
to the light emitter being OFF at other times during each PWM
cycle.
[0129] In some projectors Digital Light Processing (DLP) devices
are used to create the final image. It is desirable to provide a
light source as described herein which is compatible with
downstream DLP devices. In a DLP device a binary modulator flips a
micro mirror back and forth between an "on" state where it sends
light to the screen and an "off" state where it sends light to a
"dump" area. Each pixel has a corresponding micro mirror. The DLP
creates greyscale by flipping the micro-mirror back and forth
rapidly. The micro mirror is controlled to spend more time in the
"on" state to make a brighter pixel or more time in the "off" state
to make the pixel dimmer.
[0130] In an example DLP driving scheme, each pixel has an 8 bit
(or more) greyscale drive value per frame of video (usually 60
fps), these are translated into 8 mirror flip periods, with one
period for each bit. The period corresponding to the least
significant bit is short. The period doubles for each bit and is
longest for the most significant bit.
[0131] Whether a bit is set to 0 or a 1 determines whether the
mirror is flipped to the "on" or the "off" position for the
corresponding period. FIG. 8 shows that the shortest period that
the mirror may be in the "on" or "off" state is for the
lowest-order bit (b0). This shortest period may be called the "flip
period".
Asynchronous Light Pulses
[0132] If a pulsed light source is used (for example to produce
light at 50% of the maximum level), flickering will occur if the
"off" and "on" pulses of the light emitter are asynchronous to the
mirror flipping and the periods of "off" and "on" significantly
differ from frame to frame on a static image due to a low pulse
frequency for the light state.
Slow Asynchronous Light Pulses
[0133] This is illustrated in FIGS. 9A and 9B. In frame 1 of FIG.
9A the viewer perceives two light pulses during the time the DMD
transmits light. In frame 2 of FIG. 9B the viewer perceives three
light pulses during the same DMD open period. This 50% change in
light intensity is due to the light pulses being asynchronous to
the mirror flips.
Fast Asynchronous Light Pulses
[0134] If the "off" and "on" light source periods are short
relative to the "mirror flip" period, the difference between "off"
and "on" periods between static frames should be drastically
reduced and be imperceptible to the human eye. For example, FIGS.
10A and 10B show an example in which the light emitter is modulated
significantly faster than the DLP flip period.
[0135] In FIGS. 10A and 10B only a single minimum width mirror flip
is shown depicting a drive value of 1. The viewer perceives a light
intensity corresponding to 27/54 in FIG. 10A and to 28/54 in FIG.
10B. A disadvantage of this solution is that a large amount of
electromagnetic interference (EMI) can be produced by switching
powerful lasers off and on very quickly. Also, tighter timing
tolerances are required by the circuitry to minimize duty cycle
distortion between lasers.
Synchronous Light Pulses
[0136] If the light emitter "off" and "on" periods are synchronous
to mirror flips, there should be practically no difference between
static frames and the light source pulse generator need only run at
the period of the mirror flips, drastically reducing generated EMI
and allowing for slacker timing considerations. FIG. 11 illustrates
an example embodiment in which light output from a light emitter is
synchronized to DLP flip cycles.
[0137] When a new frame arrives, the mirror flip logic for all
pixels can be updated simultaneously via a double buffering scheme
(or in blocks from top to bottom if desired).
Synchronizing the Light Source to the DLP
[0138] Some DLP driver chips provide a "trigger out" pin that
indicates the start of a mirror flip cycle. In absence of this an
independent "mirror timing recovery" circuit can be constructed.
When the mirror is in the "off" state it sends light to a "dump"
area. Placing a photoreceptor in the dump area will send a voltage
back to the circuit when a mirror flips to the "off" state. During
a "training mode" the lasers are constantly on and the DLP sends
only the least significant bit to the dump area (i.e. drive level
254 for a DLP with 8 bit control). Using a high speed reference
clock and counters the period of the shortest mirror flip can be
determined and the timing of subsequent mirror flips can be
predicted. Similar methods are employed in telecom applications for
clock and data recovery from a single wire serial data stream. A
jitter attenuator may be provided depending on the amount of error
in the recovery system.
[0139] With the recovered mirror flip period, the light source can
synchronize PWM for the light emitters to the mirror flip periods
such that a deterministic light intensity can be produced for the
shortest mirror flip period (and all longer periods). During longer
mirror flip periods the PWM cycle could simply repeat (twice for
bit 1, four times for bit 2, 8 times for bit 3 etc.), or to further
reduce EMI the PWM cycle period could lengthen for each bit.
[0140] FIG. 12 illustrates an example system 1200 in which a light
source 102 illuminates a PMD 1204 by way of an optical system
(which may, for example, be as described in any embodiment
discussed herein), Light 1205 is steered by PMD 1204 to illuminate
an active area of a DMD (or DLP) 1206. Pixels of DMD 1206 are
operable to direct light to a screen 1208 or a light dump 1210. A
photo receptor 1212 measures the light incident at light dump 1210.
Since this light is turned on and off at the times that
micromirrors of the DMD 1206 flip, the output signal of
photoreceptor 1212 is modulated. The output signal of photoreceptor
1212 is provided to a timing recovery circuit 1214 which also
receives a reference clock signal 1214A. Timing recovery circuit
determines the timing of the DMD mirror flip cycle through analysis
of the signal from photoreceptor 1212 and generates a sync signal
1215 which is provided to PWM generator 1218. PWM generator 1218
receives light emitter drive values 1219 and generates PWM signals
to cause light emitter driver 1220 to drive light sources 102 at
appropriate levels. PWM generator 1218 synchronizes the PWM signals
to sync signal 1215.
[0141] A further enhancement that may be added to reduce the
maximum current draw from the laser power supply and somewhat
reduce EMI is to shorten the PWM period slightly and stagger the
turn on times for different light emitters.
[0142] Staggering the laser turn on times requires less maximum
current capacity from the laser power supply because only one laser
turns on at any given time. This should also reduce EMI produced by
the power supply. FIG. 13 illustrates staggered laser turn on times
synchronized to a DMD mirror flip.
Light Emitter Temperature Control
[0143] The temperature of a laser diode affects the wavelength
produced and the efficiency (lumens per watt). If laser output is
attenuated to a low level for an extended period the laser may cool
excessively and lumens output may deteriorate. Worse, the light
output may become non-deterministic relative to the PWM drive
level. To correct for this condition, the light source may be
configured to drive the lasers harder when they are cool and to
steer the excess light to a dump area to warm the lasers up.
Alternatively, a Peltier element (and or another heater) can be
used to warm or cool a laser that is operating outside of a desired
temperature range. An optical feedback path can be implemented to
detect light intensity in part of the beam to measure accuracy of
lumens output in relation to laser drive levels and
temperature.
Example Applications
[0144] Embodiments of this invention can be used to provide
illumination for any of the applications or markets described
above. A light profile made up of tiled, substantially
non-overlapping patches of coherent, polarized laser light has
multiple potential applications. An example application is
providing illumination for creating a light field using a phase
modulating device (PMD). Outputs of the lasers may be individually
modulated if desired. In some embodiments, polarizations of the
light patches is oriented to match a polarization preferentially
passed by the PMD.
[0145] Example phase modulation devices include: [0146] Spatial
light modulators (SLM), for example a 1D or 2D array of pixels, in
which the drive level addressed at a pixel correlates to the phase
delay applied to the light impinging on that pixel, for example the
drive levels between 0 and 65535 may correspond to the range of
phase delay between 0 and 2.pi. radians (one cycle of the
wavelength of the light). [0147] Such a spatial modulator can
simultaneously change the state of polarization of the light (an
example is a transmissive liquid-crystal display, or a reflective
liquid crystal-on-Silicon display (LCoS)). Alternatively, such an
SLM can be designed to affect the phase delay of that pixel, but
not its polarization. [0148] An acousto-optical modulator (AOM;
also called a Bragg cell) can affect deflection angle of the
incoming light, its phase, frequency and polarization
characteristics. [0149] A grating light valve (GLV); currently,
these devices are 1D addressable arrays where each pixel or element
can vary the phase of the impinging light by mechanically varying
the path length. [0150] Deformable Mirrors; using either
continuously deformable mirror surface with an array of control
points, or arrays of discrete, individually modulated reflective
pixels.
[0151] A phase modulation device can be used to create a desired
light field. A lens in the classical sense is a variable thickness
piece of transparent material such as glass that retards the phase
of the incident light differently across the lens surface,
resulting in a focused or de-focused spot of light depending on the
curvature or shape of the lens. A similar effect can be achieved by
retarding the phase of the incoming light beam using a phase
modulating device (PMD). For example, the effect of a lens can be
achieved by addressing a varying phase pattern on the PMD, with for
example 2.pi. phase retardation in the centre of the PMD, falling
off to 0 phase retardation on the edges of the PMD. Stronger lenses
(lenses with a shorter focal distance) can be achieved by
controlling the PMD to provide phase modulation in a pattern like
that of a Fresnel-lens (i.e. by phase wrapping the values applied
to drive the PMD pixels).
[0152] A PMD may be controlled to simulate the effects of other
optical elements, such as prisms and gratings in a similar fashion,
for example by applying a slowly varying amount of phase delay in
one direction on the PMD.
[0153] Different effects may be combined on the PMD. An example is
a phase-pattern that both focuses and shifts the incoming light
profile. This may be achieved by controlling the PMD to alter the
phases of light in a pattern that superimposes (adds) the
respective phase delay patterns for a lens and a prism.
[0154] Several lenses side-by-side or super-imposed on the PMD can
coarsely approximate an image. By suitably controlling a PMD to
emulate the action of a number of lenses one can create a situation
where an image or parts of an image are in focus anywhere along the
direction of light propagation, for example in several planes.
[0155] A PMD may be controlled to create any of an exceedingly
broad range of output light fields. Determining what data to use to
drive the PMD to yield a specific desired output light field may be
done in a number of ways. In a more-computationally expensive but
more exact mode one can apply a mathematical model of the inverse
transformation provided by the entire optical system (including the
PMD) to start with the desired output light field and calculate the
PMD pixel settings corresponding to the desired output light field.
A less-computationally intensive but less exact mode includes
setting parameters for one or more discrete optical elements
(lenses, prisms, etc.) that can be emulated by the PMD to yield an
output light pattern that approximates the target light pattern.
The parameters may, for example, include sizes, locations and
optical strength.
[0156] Various approaches to controlling a PMD to cause a desired
image or other light pattern to be displayed are described in
PCTCA2014051013 published as WO2015054797 (reproduced below with
figure numbers changed); PCTCA2015000324; PCTCA2015050515; and
PCTCA2015050730; the disclosures of all of which are hereby
incorporated herein by reference for all purposes.
TECHNICAL FIELD
[0157] This invention relates to light projectors. Some embodiments
may be applied to project images for viewing. Other embodiments may
be applied to create structured light for illumination or other
purposes. Embodiments have example application in markets such as
digital cinema, TV and home theater, portable and personal
projection (military, mobile, etc.), indoor and outdoor personal
and large screen advertising and information dissemination,
signs/advertising/billboards/outdoor advertising, large-venue and
live performance, medical imaging, virtual reality, computer
gaming, office presentations and collaborative work, head-up
displays in cars and other vehicles, smart illumination such as
adaptive car head-lights, theatre spotlights,
security/architectural lighting, high contrast planetarium
projectors, indoor and outdoor general illumination systems,
street-lighting, road-lighting, aviation lighting systems, and
high-contrast simulation displays such as flight simulators
BACKGROUND
[0158] There are many situations where it is desired to create a
light field that has a specified luminance profile. Light
projection systems have a very wide range of applications from
architectural lighting to the display of lifelike images. The
projected light patterns can be dynamic (e.g. video), static (used
for static images or static applications like the beams of typical
car headlights projected through a lens onto the road, made by
arbitrarily shaped optical surfaces, etc.). Light may be projected
onto a wide range of screens and other surfaces which may be flat
or curved. Such surfaces may be fully reflective (like a canvas
used in a cinema, a wall or a building) or partially reflective
(such as the windshield of a vehicle). Screens may be low-gain or
high-gain, Lambertian or highly directional, high-contrast or lower
in contrast. Light may be projected onto solid objects or onto a
medium in a volume (such as fog).
[0159] Markets for and applications of light projectors include
digital cinema, in-door and out-door advertising, medical imaging
(both for display of images, as well as capture by a smart light
source), large venue and live events or performances, automotive
heads up displays, car head-lights and rear-lights, automotive
entertainment and information displays, home-theatre, portable
business projection, television and displays for consumer
applications, military applications, aviation applications (like
cockpit displays, smart landing-assistance, individual passenger
entertainment displays), structured light sources for industrial
applications, automotive headlights and other applications.
[0160] Various devices may be used to spatially modulate light.
These may be called spatial light modulators (SLMs). Most SLMs
provide a 2D array of independently and individually addressable
pixels. Some examples of SLMs are reflective SLMs such as digital
micro-mirror devices (DMDs), liquid crystal on silicon (LCoS)
devices and transmissive SLMs such as LCD panels, transmissive LCD
chips such as high-temperature polysilicon (HTPS) or
low-temperature polysilicon (LTPS); and partially
reflective/partially transmissive SLMs such as
micro-electro-mechanical systems (MEMS) based systems in which some
of incident light is transmitted and some of incident light is
reflected. One problem is that most readily available spatial light
modulation technologies are subtractive. These SLM technologies
operate by absorbing or removing undesired light. This contributes
to the more general problem that light projection and often general
illumination technologies tend to have undesirably high energy
consumption and may also have an undesirably limited peak
luminance.
[0161] Additional considerations apply to light projectors that are
applied to project images. For example, in such projectors raised
black-levels, undesirably low contrast and limited
colour-saturation can be concerns.
[0162] These limitations can mean that a dark viewing environment
such as a cinema, a dark living room, or some other
lighting-controlled environment, is needed to get the best out of
projected imagery. This limits the possible applications for
projectors.
[0163] In all fields of technology including light projection
achieving a desired level of performance at a competitive cost can
be an issue.
[0164] There is a general need for light projection systems that
ameliorate one or more of the above-noted problems.
SUMMARY
[0165] This invention relates to systems that re-distribute light
dynamically from a single or multiple light sources in order to
achieve a desired light field (which may or may not comprise an
image depending on the application) efficiently. Re-distribution of
light involves taking light from one area within a light field and
directing the light to another area within the light field. Some
embodiments provide a controllable illumination system that can be
used as a component in any of a wide range of lighting
applications. Other aspects of the invention provide methods for
creating light fields and light projectors which apply such
methods.
[0166] A light field projection system according to some
embodiments comprises a data processor, a computer software
program, one or more light sources and a light control mechanism
that includes one or more dynamically-addressable optical elements.
The light control mechanism may also include one or more static
optical elements such as lenses, mirrors, gaps, optical fibers,
light guides and the like in an optical path. The software program,
when executed by the processor may process data specifying one or
more desired target light fields (which may, for example, comprise
anything from desired headlight patterns to image frames in a
movie) and may cause the one or more dynamically-addressable
optical elements to redirect light to achieve the desired light
fields.
[0167] Example embodiments of the invention provide light
projectors, projection displays, methods for operating projection
displays, media containing computer readable constructions which,
when executed by a data processor, cause the data processor to
execute a method according to the invention, methods for displaying
images, methods for processing image data for display, methods for
processing sequences of image data for display, among others.
[0168] Further aspects of the invention and features of an
illustrative set of example embodiments are illustrated in the
accompanying drawings and/or described in the following
description.
DETAILED DESCRIPTION
[0169] Throughout the following description specific details are
set forth in order to provide a more thorough understanding to
persons skilled in the art. However, well known elements may not
have been shown or described in detail to avoid unnecessarily
obscuring the disclosure. The following description of examples of
the technology is not intended to be exhaustive or to limit the
system to the precise forms of any example embodiment. Accordingly,
the description and drawings are to be regarded in an illustrative,
rather than a restrictive, sense.
[0170] FIG. 17 illustrates schematically an example system for
generating a light field according to an example embodiment. The
system is configured to receive data describing a target light
field and to produce an output light field that closely matches the
desired target light field by redirecting light. In some cases the
output light field may require further optical or other treatment
to produce the desired target output light field. Such treatment
may be provided by one or more refinement stages as described
herein. As described in more detail below, the system does this in
an optically efficient manner, in which little light is wasted. The
system includes one or more light generators (light sources) that
can be operated to create light. In some embodiments the system
operates the light generators to output light and then redirects
the light to provide the output light field. The output of the
light generators may be controlled to match the amount of output
light to the amount of light required for the output light field.
Most of the light generated by the light generator(s) may end up in
the output light field.
[0171] FIG. 18 depicts an example dynamic light-efficient
illuminator in more detail. A program is executed on a data
processor. The program receives data describing the target light
field and computes a light redistribution scheme to be applied by a
dynamically-addressable light re-distributor. The program also
computes data describing the intensities for one or more light
sources that generate light supplied to the light
redistributor.
[0172] A data processor is not required in all embodiments. In some
embodiments light redistribution schemes for a predetermined set of
light fields are determined in advance. In such embodiments data
defining the light redistribution schemes corresponding to the
light fields may be stored, embodied in fixed or configurable logic
circuits or the like. Appropriate data can then be applied to
control the light redistributor to generate a desired one of the
light fields without the necessity for any computation.
[0173] The light module (comprising the light sources and light
redistributor and associated optics) receives power, as well as
data describing the intensities of one or several light sources and
generates a light field having a desired light profile. An example
light module is further illustrated in FIG. 19.
[0174] FIG. 19 is a more detailed schematic view of an example
light module. The light module comprises a data processor, a power
regulator, one or many light sources, and a light combining and
beam-shaping module.
[0175] The data processor receives data describing the intensity
for the light source(s) and produces a control signal for the power
regulator that in turn controls the amount and/or timing of power
distributed to each light source. The power regulator may include a
plurality of separate outputs and/or may include a plurality of
independent power regulation circuits.
[0176] The light sources may be of any of a wide variety of types.
One light module may optionally include light sources of a
plurality of types. Some examples of light sources are: lasers,
arc-lamps, LEDs, high-intensity lamps, etc.
[0177] Each light source may emit light of different shapes,
intensities and profiles. An example light profile produced by a
light source could be a uniform, rectangular intensity profile
which could be produced using integrating rods or other optics.
Another example of a light profile has a Gaussian or sum of
Gaussians intensity profile. Another example is an array of
rectangular uniform profiles (blocks) with different intensities.
In another example, the light profile produced by the light module
can take any desired shape.
[0178] The light from the light source(s) is then coupled to the
input of the light redistributor. The coupling may involve
spatially combining light from a plurality of light sources and/or
shaping the light optically to yield light having the desired light
profile for input to the dynamically-addressable light
redistributor. The light combination and beam shaping may be done
using common optical elements such as beam-splitters, polarizers,
wave plates, multi-layer thin films, beam-combiners, micro-lens
arrays, lenses, apertures and/or mirrors. These elements can be
optimized for the nature of the light emitted by the light sources
(e.g. narrow-band or broad-band light sources).
[0179] In one preferred embodiment, light from a plurality of light
sources is coupled into a common optical fibre and at the output of
the fiber the light is collimated using a set of lenses.
[0180] Data present within the system, for example the control
signal or data describing the light profile incident on the
Dynamically-addressable Light Re-Distributor may be provided to
external components or systems, for example in the form of
metadata.
[0181] FIG. 20 shows example light profiles at various stages
through the system illustrated in FIG. 19.
[0182] The light redistributor may controllably alter the nature
and/or distribution of light using techniques that are not
primarily subtractive. For example, the light redistributor may
exploit interference of electro-magnetic waves (light), to modulate
the distribution of light by controlling its phase characteristics
and/or modulate the frequency of the light in order to change the
apparent colour of light. Both of these examples show how light can
be changed without converting energy from the light into wasted
heat by absorbing the light.
[0183] In one embodiment one or more light sources LS 1 to LSn are
coupled into one or more optical fibres 2008, for example using
focusing lenses 2009. 2005 shows an example light profile of the
.eta.{dot over (.omega.)} light source. The combined output from
the optical fibres 2008 are relayed onto the
dynamically-addressable light redistributor 2007, for example using
relay lens system 2000, comprising, for example, two focusing
lenses 2001 and 2002. The combined effect of the two lenses 2001
and 2002 in 2000 may be to asymmetrically magnify the output
profile from the optical fibres 2008. 2003 shows two example plots:
at top the combined intensity across one spatial dimension of 2007
and at bottom contours of the light profile present on 2007 in two
dimensions. 2004 shows an example of the same type of plots of the
intensity and contours present at the output of 2008. Furthermore
the top plot in 404 illustrates how the total intensity of the
light profile may be made up from a plurality of light profiles for
example 2006 from each light source LS1 to LSn.
[0184] FIG. 21 schematically illustrates one type of
dynamically-addressable light redistributor. The
dynamically-addressable light redistributor comprises receiving
optics, and a dynamically-addressable focusing element.
[0185] Examples of devices suitable for use as
dynamically-addressable focusing elements in different embodiments
include: transmissive 2D arrays of controllable liquid crystal
compartments with the property that the compartments can be
controlled to selectively retard the phase of light, effectively
causing a change in path-length. The same type of device could be
implemented in a reflective manner. A dynamically-addressable
focusing element may also affect the polarization of light. Some
devices may alter several light properties simultaneously.
[0186] In some other embodiments a dynamically-addressable focusing
element comprises one or more scanning mirrors, such as a 2D or 3D
microelectromechanical system (MEMS); and/or one or more deformable
lenses or mirrors or other optical elements. A
dynamically-addressable focusing element may also or in the
alternative comprise one or more optical switches.
[0187] The receiving optics transforms an incoming light profile
from the light module into an illumination light field that matches
or approximately matches the size, shape and angular acceptance
range of the dynamically-addressable focusing element. The
receiving optics could, for example, comprise one or more of: a
prism system, a lens, a free space optical path, an integrating rod
or waveguide.
[0188] The dynamically-addressable focusing element is controlled
by data that corresponds to a light re-distribution scheme. The
data may describe a variation in light path-length across the
device which, when implemented by or executed on the
dynamically-addressable focusing element causes the formation of
the desired output light-field.
[0189] FIG. 22 shows some examples of light profiles created in the
light module and an example final system output light profile. FIG.
22 includes two examples of what the light fields may be at three
stages of FIG. 21: an incoming light profile from the light module,
the illumination light field present at the dynamically-addressable
focusing element, and the light field going to the output optics.
Example 1 illustrates the case where a fairly uniform input light
field is transformed into an arbitrary and desired output light
field. Example 2 illustrates the case where a non-uniform input
light profile made up with light from an array of independent light
sources is transformed into a uniform light field at the
output.
[0190] FIG. 22 shows two example sets of light profiles at various
stages of the Light Efficient Illuminator. In 2210, an application
is shown in which the light profile 2211 at the output of the light
module is transformed into an arbitrary light profile 2213 at the
output of the light efficient illuminator. The arbitrary light
profile 2213 may directly represent the target light field or
target image. The light profile 2212 shows the light profile 2211
relayed and magnified onto the dynamically-addressable focusing
element. MI and M2 represent the magnification of the optical
system, resulting in the intensity scale factors NI and N2,
respectively.
[0191] In 2220, an application is shown in which the light profile
2221 at the output of the light module is transformed into a
uniform light profile 2223 at the output of the light efficient
illuminator. The light profile 2222 shows the light profile 2221
relayed and magnified onto the dynamically-addressable focusing
element. MI and M2 represent the magnification of the optical
system, resulting in the intensity scale factors NI and N2,
respectively.
[0192] Providing a module capable of yielding a wide range of
output light fields is advantageous as such modules may be
optimized for optical efficiency and may be applied in any of a
wide range of applications as described above. Apparatus according
to the invention may also be integrated directly into projectors,
displays, lights etc.
Explanation of how to Use a Phase Modulator to Create a Desired
Light Field, Description of Basic Arrangement.
[0193] Example phase modulation devices include: [0194] Spatial
light modulators (SLM), for example a ID or 2D array of pixels, in
which the drive level addressed at a pixel correlates to the phase
delay applied to the light impinging on that pixel, for example the
drive levels between 0 and 65535 may correspond to the range of
phase delay between 0 and 2.pi. radians (one cycle of the
wavelength of the light). [0195] Such a spatial modulator can
simultaneously change the state of polarization of the light (an
example is a transmissive liquid-crystal display, or a reflective
liquid crystal-on-Silicon display (LCoS)). Alternatively, such an
SLM can be designed ONLY to affect the phase delay of that pixel,
but not its polarization. [0196] An acousto-optical modulator (AOM;
also called a Bragg cell) can affect deflection angle of the
incoming light, its phase, frequency and polarization
characteristics. [0197] A grating light valve (GLV); currently,
these devices are ID addressable arrays where each pixel or element
can vary the phase of the impinging light by mechanically varying
the path length.
How to Use a Phase Modulator to Create a Desired Light Field:
[0198] A lens in the classical sense is a variable thickness piece
of glass that retards the phase of the incident light differently
across the lens surface, resulting in a focused or de-focused spot
of light depending on the curvature or shape of the lens. A similar
effect can be achieved by retarding the phase of the incoming light
beam using a phase modulating device (PMD). For example, the effect
of a lens can be achieved by addressing a varying phase pattern on
the PMD, with for example 2.pi. phase retardation in the centre of
the PMD, falling off to 0 phase retardation on the edges of the
PMD. Stronger lenses (lenses with a shorter focal distance) can be
achieved by controlling the PMD to provide phase modulation in a
pattern like that of a Fresnel-lens.
[0199] A PMD may be controlled to simulate the effects of other
optical elements, such as prisms and gratings in a similar fashion,
for example by applying a slowly varying amount of phase delay in
one direction on the PMD.
[0200] Different effects may be combined on the PMD. An example is
a phase-pattern that both focuses and shifts the incoming light
profile. This may be achieved by controlling the PMD to alter the
phases of light in a pattern that superimposes (adds) the
respective phase delay patterns for a lens and a prism.
[0201] Several lenses side-by-side or super-imposed on the PMD can
coarsely approximate an image. By suitably controlling a PMD to
emulate the action of a number of lenses one can create a situation
where an image or parts of an image are in focus anywhere along the
direction of light propagation, for example in several planes.
[0202] More complex images or illumination profiles can be achieved
by controlling the PMD to present a phase adjustment that is
continuously-varying over the area of the PMD as opposed to
controlling the PMD to emulate a combination of discrete optical
surfaces such as lenses and/or prisms.
Example Arrangements for Light Sources
Types of Light Sources:
[0203] The light source for the system can for example be one or
more lasers, arc-lamps, LEDs, or even the sun. The specific
characteristics of a light-source can make it more desirable than
others. For example, a laser might be preferable over a broad-band
lamp due to its small beam size, limited optical spread (resulting
in a very high intensity), limited etendue, its narrow
spectral-band frequency distribution (and thereby pure colour), its
polarization-, lifetime-, decay-, efficiency-, coherence and
collimation characteristics.
Example Optics to Bring Light to/from Phase Modulation Device:
[0204] Light needs to be transported to and from the phase
modulating device (PMD). It may also be desirable to have one or
several of its characteristics changed, like its illumination
profile, its magnification and shape, its polarization or
frequency. It is sometimes preferable to have the incoming light
profile match the shape of the PMD. Examples of elements or devices
that can be used to achieve this include but are not limited to:
[0205] Beam expanders consisting of one or several physical lenses;
[0206] Single or bundled optical fibres; [0207] Prisms; [0208]
Cylindrical lenses; [0209] Micro-lens arrays; [0210] Gratings;
[0211] Diffusers; [0212] Polarization filters; [0213] Apertures;
[0214] Wave-plates; [0215] Integrating rods.
Different Light Sources Illuminating Different Areas of
Modulator
[0216] In the case that several light sources are used to
illuminate the PMD, the light profiles from these separate sources
may overlap, partially overlap, or not overlap on the PMD.
[0217] It might be desirable to achieve a uniform combined light
profile on the PMD. In that case, optical elements such as
integration rods, micro-lens arrays, diffusers, or other
light-shaping devices may be included to uniformly illuminate the
PMD.
[0218] The intensity of one or more of these light sources may be
independently adjusted in order to achieve a desired combined light
profile on the PMD. As an example, one might want to have the
incident light profile be brighter in the centre of the PMD than on
its edges.
[0219] Alternatively, the total amount of light from one or more
light sources incident on a region on the PMD over a fixed period
of time can be adjusted by turning the light-sources on and off
(pulse-width modulation, PWM) instead of adjusting the intensity of
the light sources. The on-time relative to the off-time determines
the overall amount of light incident on the PMD over a period of
time. The duration of the on-pulses in the time period may vary,
and they may be periodic, non-periodic or random; the total on-time
may be more relevant to perceived brightness or colour by an
observer.
[0220] The pulsed PWM approach may require a synchronization
between the incident light sources and other elements in this
optical system.
Example Projection Arrangements
[0221] The most simple projection system comprises a light source,
some beam-shaping optics to partially or fully illuminate the PMD,
and a phase-retardation pattern on the PMD.
[0222] In another embodiment, a plurality of light sources may
illuminate the PMD.
[0223] In another embodiment, the output light field from the PMD
may be relayed onto a spatial light modulator (SLM) for further
refinement, for example by amplitude modulation.
[0224] In another embodiment, the output light field from the PMD
may be presented onto one or more integration rods, each of which
integrates all the light incident on it into a uniform output. This
output in turn may be relayed onto different regions of the SLM for
further refinement.
[0225] In some embodiments, it may be desirable to relay the output
light-field from any of these system arrangements onto a projection
screen or surface.
Different Focusing Arrangements
[0226] In one common application, it is desirable that the
projection system form an image on a flat, a near-flat, or at most
slightly curved surface. In other applications, it may be desirable
to project onto one or several non-flat surfaces or screens, for
example a curved screen or a rough surface like a brick-wall, or a
building. In another application, one might wish to project onto a
moving object, like a person or animal, or a vehicle moving either
on land, in the air, on water or submerged under water. Such an
application may require the synchronized capture and detection of
that moving object. It may also be desirable to project images or
patterns onto different objects within a volume, or to different
points in a volume. For example, in a car head-light application,
one may wish to illuminate an upcoming stop-sign very brightly, but
an approaching vehicle with reduced intensity.
[0227] A phase-pattern present on a PMD can be arranged in such a
way as to focus at different depths or with different effective
focal lengths. The corresponding light field can include images or
features that are in focus at one plane or point, and other images
or features that are simultaneously or time-delayed in focus at
another plane or point. In some embodiments, one can arrange the
phase-pattern on the PMD so that the system is focus-free, or in
focus at any distance.
[0228] Focus at any of these points or planes can be achieved using
a phase pattern on the PMD exclusively ("dynamic lenses"), rather
than with physical lenses. It can also be achieved using a
combination of dynamic lenses on the PMD and physical lenses. It
can also be achieved using only physical lenses.
How to Image in Colour.
[0229] In one embodiment, colour images are formed by mixing
appropriate ratios of light of three differently perceived colours,
for example red, green and blue everywhere in the target image. For
example, in an image described by a pixellated 2D array, each pixel
may have different amounts of red, green and blue contributions. In
another embodiment, light of four or more differently perceived
colours may be mixed for a similar effect.
[0230] In one application, the different colours can be supplied
simultaneously but in parallel, for example by shining each of the
primary colours onto its own SLM or PMD, and then recombining the
different colours using a colour re-combiner, for example a cube
made up from dichroic mirrors (a so-called "X-cube")--In another
application, the three (or more) light sources may illuminate
different areas of one PMD. Because of the steering-capability of
the PMD(s), these three (or more) regions may be combined
downstream in the optical system by applying the appropriate phase
pattern on the PMD(s). The phase-patterns for the differently
coloured regions will be determined individually in order to ensure
that when they are combined, they form a colour-image as close as
possible to the target-image.
[0231] In another application, each frame of the video is broken
down into its separate colour channels, for example red, green and
blue. The differently coloured light sources may illuminate one
image-forming device (such as the PMD, or a conventional
amplitude-modulating SLM) in sequence (so-called
time-multiplexing). It is desirable for these sequential colour
fields to be presented in fast succession, so that the human visual
system perceives the resulting colour image without colour break-up
or flicker. An example is to show a red colour field for the first
image of a video sequence for I/72th of a second, followed by the
green colour field for the first image for the next I/72th of a
second, followed by the blue colour field for the first image for
the third I/72th of a second for an effective frame-rate of 24 Hz
or 24 frames per second. This process is then repeated for the
ensuing frames of the video or image sequence.
[0232] In one embodiment, time-multiplexing may be combined with
beam-steering in the following manner. In the case of a
three-primary imaging system (for example R, G, and B), each of the
three colours may be time-multiplexed by different amounts,
providing a different amount of integrated intensity of R, G, and B
onto the display screen. For example, within one complete
frame-duration, the on-time of the red colour field may be a much
larger fraction of the total frame-duration than the green colour
field on-time. This can be extended to a higher number of primary
colour light sources.
[0233] In another embodiment, the different colours may be provided
simultaneously off one imaging device per colour channel. Dimming
of each colour channel independently may be achieved by
multiplexing each colour channel.
[0234] In another application, broadband light or several combined
narrowband light sources may be split apart using a diffraction
grating or a prism (for static deflection), or a PMD (for dynamic
deflection). The chromatically split light may be relayed onto a
(second) PMD where several bands of colour may be processed
independently in order to form a final colour image at the display
screen.
[0235] In one or all of the above-mentioned applications, one might
use integration rods to make the intensity profile of different
regions more uniform before further processing.
Control Modalities
Examples of Control System Hardware
[0236] The control system hardware may comprise a data processor
and computer readable data representing the sequence of light
fields ("target images"). In some embodiments, it may be preferable
to process the data in real-time, and in other embodiments the data
may be pre-processed and stored on computer-readable media. In some
applications, the data processing may be executed on a
field-programmable gate-array (FPGA), an application-specific
integrated circuit, or a general purpose possibly CPU-optimized or
possibly GPU-optimized computer.
[0237] A PMD may be controlled to create any of an exceedingly
broad range of output light fields. Determining what data to use to
drive the PMD to yield a specific desired output light field may be
done in a number of ways. In a more-computationally expensive but
more exact mode one can apply a mathematical model of the inverse
transformation provided by the entire optical system (including the
PMD) to start with the desired output light field and calculate the
PMD pixel settings corresponding to the desired output light field.
A less-computationally intensive but less exact mode includes
setting parameters for one or more optical elements (lenses,
prisms, etc) that can be emulated by the PMD to yield an output
light pattern that approximates the target light pattern. The
parameters may, for example, include sizes, locations and optical
strength.
[0238] In one embodiment, the applied phase pattern on the PMD is
determined so that given the particular optical layout of this
imaging system and a matching model of this system, the light
applied to it will result in an image on the display screen that
very closely matches the desired light-field (the "target-image")
provided by the content-device (for example from a TV network, a
DVD, a Blu-Ray disk, or from a streaming internet source). Such a
phase-pattern can be achieved by an iterative optimization
approach, where the difference between the current solution and the
target-image is iteratively minimized until a completion criterion
is satisfied.
[0239] In another embodiment, the applied phase pattern on the PMD
is determined so that the resulting light-field output from the PMD
only partially matches the target-image or target light-field. As
an example, an approximation of the target-image may be formed by
summing up a number of similar or dissimilar features each
described by a set of feature parameters. The features can for
example be a set of Gaussian intensity profiles placed at different
positions, with different amplitudes and different full-width
half-maxima. This may result in a low-pass filtered or blurred
version of the target-image, but may also be executed at reduced
computational cost. In this embodiment, a "refinement-stage" may be
required, and the output light-field of this system may be relayed
onto for example a secondary amplitude modulating spatial light
modulator or another PMD. The purpose of the refinement stage in
this situation would be to restore the finer details of the target
image or light-field.
[0240] In another embodiment, one could simulate basic
physical-optics devices such as lenses and prisms on the PMD in
order to scale and translate regions or parts of an image. Scaling
of a particular input light intensity profile may be obtained by
simulating a lens on the PMD. This lens may have a circular or a
two-dimensional cylindrical symmetry. Translating a particular
input light intensity profile may be achieved by simulating a prism
on the PMD, for example by gradually varying the phase delay across
the PMD. A lens may be described simply by its curvature, and a
prism may be described by its tilt relative to the optical axis.
The result of applying a uniform light distribution onto a lens is
to focus, or de-focus it. If the display screen is not positioned
exactly at the focal distance of said lens, a round shape of
uniform light is created if the lens has circular symmetry, and a
rectangle is created if the lens has a cylindrical shape.
[0241] In some embodiments, one might wish to simultaneously scale
and translate a region of the image. This can be achieved by
superimposing the simulated patterns for a lens and a prism.
[0242] Should the desired lens or prism require an amount of phase
retardation that the PMD is unable to provide, then one could
utilize a Fresnel approach where an integer multiple of 2.pi. is
subtracted from the desired value. For example, a phase retardation
of "if" can have the same effect on the light-steering capabilities
of a PMD as can a phase retardation value of 5.pi.. The equivalent
mathematical function may be the modulus; in this example modulus
(5ji, 2.pi.)=.pi..
Ways to Determine Areas;
[0243] In one embodiment, the light redistribution scheme describes
a method to determine how one or more regions of light entering a
light redistributor could be mapped to other regions in the light
exiting the light redistributor. As an example, the scheme may
describe how the light incident on a 10.times.10 pixel region could
be redirected to a 30.times.5 pixel region, possibly translated to
another part of the image. In this particular example, the incident
light used to be illuminating only 100 pixels (10.times.10), but
after the mapping illuminates 150 pixels (30.times.5). Since the
illuminated area in this example has been increased by 50%, the
resulting intensity has been reduced by one-third. The light
redistribution scheme may analyze the target-image in order to
arrive at how a particular region is to be mapped.
[0244] In another embodiment, a number of equally sized regions
gets mapped to the same number of regions, but these regions may
all be of different sizes. Such an approach can be utilized to
create a low-resolution version of the target image or light-field.
The high-resolution parts of the image will now have to be restored
in a downstream modulation or "refinement" stage, for example by an
amplitude modulating SLM.
[0245] In some embodiments, the amount of scaling and shifting that
gets applied to the equally sized regions of the image correlates
in a direct or indirect way to the total intensity of light
required by the target image or light-field in that region.
[0246] In other embodiments, the target image is analyzed and a
number of differently sized regions are mapped to the same number
of equally sized regions. The output of this approach may be
incident on an array of integration rods matching the size and
shape of each region.
[0247] In another embodiment, differently sized areas may be mapped
to another set of differently sized areas.
[0248] In another embodiment, one number of regions may be mapped
to a different number of regions.
[0249] In some embodiments, it may be desirable to ensure that
neighbouring regions on the input side are still neighbours on the
output side, so as to avoid gaps of illumination between two or
more regions and therefore incorrectly reduce or increase the
luminance or brightness in that gap between the two regions. As an
example, if the light distribution scheme dictates that one region
be translated away from its neighbouring region, then it should
also dictate that the neighbouring region be translated along with
it, either by pure translation, or by scaling, or by a combination
of the two.
[0250] In an example embodiment, light incident on each of a
plurality of areas on a PMD is scaled and/or translated by causing
the area of the PMD to emulate a lens, a prism, or a combination
thereof. The output light field is made up of the scaled/translated
light.
[0251] Some embodiments may include optical switches that may be
operated to selectively direct light from one area of the image or
light-field to a different area or a number of different areas of
the image or light-field. Such optical switches may augment a PMD
or replace a PMD in some embodiments. For example, optical switches
may be applied to selectively direct light from a light source into
one of a plurality of integrating rods or optical fibers. The
intensity of light being carried in the integrating rods or optical
fibers may be adjusted by setting optical switches to change which
integrating rods or optical fibers carry light from which light
sources.
[0252] Another embodiment uses one or more scanning lasers to
provide a desired light field. For example, a laser beam can be
scanned rapidly across an area, leaving the viewer with the
impression that the whole area is illuminated with equal intensity.
If the laser beam is a spot, a 2-or-more axis scan may be
performed. If the laser beam has the shape of a line, a 1-or more
axis scan may be performed. The beam may be widened by using for
example a motorized focusing lens. The power density or light
intensity of various regions of the image can be controlled by
varying one or more of for example the scanning speed, the size of
the area to be scanned, or the density of the scanning pattern.
Application Classes: Display, Projection, Illumination
[0253] Several classes of applications may apply the approaches
described herein. These application classes include, but are not
limited to light projectors that utilize a projector and a screen
to form an image on a projection screen, displays such as
televisions and control monitors and general illumination devices
such as smart lamps and lighting. All applications share, that it
is desirable to efficiently illuminate an object or form an image.
Some applications might be static, but others can dynamically
change the light pattern formed.
Display
[0254] Displays can include a projector that is mounted fixed to a
surface to be illuminated. The projector can be controlled in such
as way as to form an image on the surface by illuminating a
reflective or partially reflective surface from the front. It can
also be controlled as to form an image by rear-projecting onto a
transmissive or partially transmissive surface from the rear.
Additional optics can be used to allow varying the distance and
angle between the screen and the projector, for example folding
mirrors may be used to fold the optical path and place the
projector very close to the screen. Lenses may be used to magnify,
focus and/or distort the image to match the properties of the
projection screen such as dimensions, curvature and surface
properties.
Display--TV
[0255] Example use cases of such a display include a system to
replace televisions and other displays. For example, a light
efficient illuminator may be mounted to a retractable or fixed
screen using optics that allow very close placement of the
projector and screen. The entire system may be mounted to a wall,
like a TV. The light efficient illuminator may be mounted at the
bottom relative to the screen or at the top relative to the screen.
The screen maybe flexible, retractable or solid. It maybe
incorporated into a building structure, such as a ceiling or a
wall.
Display--Billboards
[0256] Billboard displays, digital and static signs and advertising
displays are other example display systems that may apply the
invention. An example of a billboard is a digital display used to
display a sequence of advertising patterns on the shoulder of a
highway. The viewing angle of such a display may be optimized in a
way that all or most of the light is reflected in the direction of
oncoming traffic and not in other directions. A system replacing or
upgrading existing paper-based billboards to display digital
content may be desirable.
Display--Flight Simulators
[0257] Another example of display systems that may apply this
invention are flight simulators, used for on ground flight training
of airplane pilots. In such an application it may be desirable to
achieve efficient image formation on a flat or curved screen or
display features that are in focus on a volume rather than on a
plane.
Projection Systems:
[0258] Projection systems a may include a projector and a screen
that are aligned so that the projector forms an image on the
screen. The screen maybe flat, curved or of arbitrary shape. The
screen may have certain reflectance properties, such as a
lambertian reflectance profile or a somewhat directional
reflectance profile. The screen might be transparent, or partially
transparent. It may also be perforated to allow air and other media
to pass through it.
Projection Systems: Cinema and Home Cinema
[0259] An example of a projection system that may apply this
invention are cinema projectors in which a projector mounted above
and behind the audience forms an image on a flat or curved large
front projection screen. In such a system it might be desirable to
achieve very high peak brightness levels (luminance) for some or
all parts of the image. An example of a high peak brightness might
be a level above 48 cd/m.sup.2. Another example of a high peak
brightness might be a level above 200 cd/m.sup.2. Another example
of a very high peak brightness might be 1000 to 10000 cd/m.sup.2.
Generally a high peak brightness is significantly brighter that the
level that a viewer might be adapted to in the viewing environment.
In such a system it might also be desirable to achieve high
contrast levels (dark compared to bright features). It might be
desirable to achieve such contrast levels either sequentially or
simultaneously. In such a system it might also be desirable to
achieve very pure colours.
[0260] An example of a system with similar requirements is a home
theatre projector for use in a non-public space and for a smaller
audience.
Projection Systems: Planetariums
[0261] Another example of a projection system that may apply this
invention is a projector in a planetarium. A desirable property of
such a system might be that it produces very small and very bright
highlights, such as stars within an overall dark or dim scene (the
night sky). Another desirable property of such a system might be
that the black level is close to or identical to pure black, which
means that no or little light is present in dark areas of the
scene. Another property of such a system might be that the image is
in focus on a non-flat surface, such as the dome inside a
planetarium.
Projection Systems: Portable and Personal Projection (Military,
Mobile, Etc.)
[0262] Another example of a projection system that may apply this
invention are portable, mobile or personal projectors. One
desirable property of such a system might be that it is small in
size and/or light in weight. Another desirable property of such a
system might be that it uses little power and/or is an efficient
system. Another desirable property of such a system might be that
it can be operated from a portable power source such as a battery
pack or a fuel cell or another type of small generator. Another
desirable property of such a system might be that it does not need
a well controlled environment, for example that it can form clearly
readable images in a bright environment such as in sun lights.
Another desirable property of such as system is that it is easy to
setup, which might include that the systems turns on near
instantly, that is it in focus on non-flat surfaces or that it
undistorts the image, even if no calibrated projection screen is
present. Another example of such a system overlays information on
physical objects, for example instructions and locations of parts
in a machine that requires fixing.
Projection Systems: Head-Up Display
[0263] Another example of a projection system that may apply this
invention is a head-up display, a display that presents additional
information within the field of view of a user, for example on a
windshield in a car or on the windows of an airplane. In such a
system it is desirable to be able to form an image that is clearly
viewable in many viewing environments. For example a desirable
property of such a system might be that it is not too bright
(blinding) when driving at night, but bright enough to be visible
during sunlight. Another desirable property of such a system might
be that it is in focus on a non-flat surface. Another desirable
property of such a system might be that the image projected by it
may be of high quality such that artifacts (e.g. raised black
level) related to the image projection do not interfere with the
field of view it is overlaying.
Projection Systems: Architectural Structured Illumination and Large
Venue Shows
[0264] Another example of a projection system that may apply this
invention is a projector that forms an image on a building or on a
different structure as part of an artistic light show. Another
example is the projection onto a stadium floor and/or ceiling. In
such a system it might be desirable to be able to form very bright
highlights, that are significantly brighter that the surrounding
light levels and therefore stick out. It might also be desirable
for the system to be very efficient to lower cost of the
installation, setup time and cooling requirement. It might also be
desirable for such a system to be able to dynamically focus parts
of an image or light field onto different planes or objects within
a volume.
Illumination and Lighting
[0265] Illumination and lighting systems that may apply this
invention can be used in applications in which it is desirable to
statically or dynamically illuminate objects and not illuminate
other objects. In some applications it might be desirable to use an
illumination system with the capability to illuminate an entire
scene or only parts of a scene simultaneously. Another desirable
property of such a system might be that the illumination system
closely or approximately resembles the spectral reflectance
properties of the objects that are to be illuminated. In some
applications the scene to be illuminated may first be analyzed by a
camera or other imaging device.
Illumination and Lighting: Automotive
[0266] An example of a system that may apply this invention is
dynamic or smart automotive headlights. It might be desirable to
illuminate an upcoming road sign and the road itself brightly, but
at the same time not blind upcoming traffic. It might also be
desirable to illuminate the road ahead efficiently. Such a system
could work in concert with a camera that analyses the scene ahead
and provides a target light profile to the illumination system.
Another desirable property of such a system might be that the
illumination system closely or approximately resembles the spectral
reflectance properties of the objects that are to be
illuminated.
Illumination and Lighting: Theater Lighting
[0267] Another example of an illumination system based on this
invention is a theater spot light. Commonly such spotlights create
a bright spot that can be manually or automatically moved to follow
for example an actor on a theater stage. It might be desirable to
replace such a system with an illumination system that can
illuminate the entire stage and create local spot lights
dynamically. A desirable property of such a system might be that it
efficiently illuminates one or more objects within the scene. A
common data projector is an example of a system that can illuminate
a large scene, but is not very efficient when illuminating only a
partial scene or object, because light is blocked in regions in
which illumination is not required. A system based on this
invention may present an efficient alternative. Another desirable
property of such a system might be the ability to focus light on
objects that are at different distances from the illumination
system.
[0268] Some light sources, such as lasers light sources, can
produce coherent light, which is a desirable property in some
embodiments. However, depending on the brightness requirement of
the final system output light field, one might require several
independent light sources inside the light module or a different
type of light source, such as an LED or a broadband lamp. This
might result in a non-coherent light profile impinging on a
dynamically-addressable light redistributor.
[0269] FIG. 23 shows an example of a system that does not require
coherent light. The output from light module 2304 is shaped and
relayed onto a dynamically-addressable light redistributor 2303
using for example an optical module 2300 comprising for example two
focusing lenses 2301 and 2302. The objective may be to form an
image in the plane 2305, which might be a projection screen.
Dynamically-addressable light redistributor 2303 may be configured,
for example with a pre-determined phase pattern, to produce the
desired light field at 2305.
[0270] In some embodiments an output light field may be required
with higher uniformity than can be achieved with the available
optics including the dynamically-addressable focusing element. In
this case additional optics (such as integration rods, integrating
chambers, optical fibres, etc.) may be provided to homogenize the
intensity profile in one or more subsections of the light field. A
coarse initial light field may be produced by the system (by an
approach using coherent light or non-coherent light) and presented
upon the input port of such additional optics.
[0271] FIG. 24 shows an example case in which a plurality of light
sources are arranged to illuminate a dynamically-addressable
focusing element 2401. The light re-distribution scheme driving the
dynamically-addressable focusing element causes the
dynamically-addressable focusing element to distribute an initial
light field onto an array of integration rods. The output light
field of the integration rod array is made up of uniform
rectangular fields having intensities at least approximately equal
to the total light present at the input port of each integration
rod divided by the cross section area of the integrating rod.
[0272] For the sake of illustration dynamically-addressable
focusing element 2401 has been sub-divided into two equally sized
regions RI and R2. 2410, 2420 and 2430 illustrate example light
profiles at various stages of this optical system. 2410 depicts
light profiles 2411, 2412, 2413 and 2414 from LS1 to LS4. 2411 and
2412 are incident on RI, 2413 and 2414 are incident on R2. Region
RI may be present on integration rod IRI and region R2 may be
present on integration rod IR2. Dynamically-addressable focusing
element 2401 re-distributes the incident light.
[0273] In this example the light from LS2 is re-distributed to
integration rod IR2 along with the light from LS3 and LS4. The
light from LS1 is present on integration rod IRI. 2420 depicts the
light profile incident on IRI and IR2. 2421 is present on IRI and
stems from LS1, 2422 is present on IR2 and stems from LS2 and LS3
and 2423 is present on IR2 and stems from LS4. 2430 shows the
output light profile from the integration rod array, where 2431
shows the output from IRI and 2432 shows the output from IR2.
[0274] FIG. 25 depicts an example framework of a program to be
executed on the system processor. Its purpose is to compute a light
re-distribution scheme (for example in form of a 2D array of phase
retardation values) that, then be addressed onto the
dynamically-addressable focusing element to, in combination with
the input illumination profile and system optics cause an output
light profile that closely matches the target light field.
[0275] FIG. 25 illustrates an iterative method to finding a
solution using a minimization or optimization approach based on a
forward model and its inverse. This example shows an iterative
method "the optimizer" that finds a solution using a minimization
or optimization approach based on a forward model and its inverse.
An initial guess of the light re-distribution scheme as well as
regularization terms may be utilized to converge towards a suitable
solution in fewer iterations. System constraints may also be
supplied. An exit metric, for example the maximum number of
iterations, a residual, or a perceptual metric, determines when the
program stops and outputs the current solution in form of a light
re-distribution scheme.
[0276] In alternative embodiments a metric may determine when the
current solution is ready to be applied to drive a PMD. After this
occurs, the program may continue iterating to find a better
solution. As better solutions are obtained they may be applied to
drive the PMD. In an example embodiment, after a set number of
iterations (e.g. 3, 4, 10, a few iterations) the current best phase
pattern solution may be applied to the PMD while the
computer/algorithm continues to calculate better solutions. After
another few iterations a new (and better) solution may be available
and can be addressed on the PMD. All this can happen within
fractions of a frame of a video.
[0277] An example of a pair of a forward model and its inverse
model is a two-dimensional Fourier transformation and a
two-dimensional inverse Fourier transformation, which could be used
as an approximate model for a coherent, collimated beam of light
passing through a lens.
[0278] In another example, the forward model may describe the
amount of deflection caused by a difference in phases or light path
lengths of neighbouring regions on the PMD when illuminated by
light, as well as the resulting intensity profile. Although an
exact inverse system model may not exist, an iterative optimization
approach may be used to solve for an approximate solution of the
phase pattern to be addressed on the PMD.
[0279] FIG. 26 depicts another example framework of a program that
may be executed on the system processor. Its purpose is to compute
a light re-distribution scheme (for example in the form of a 2D
array of phase retardation values) that, when addressed onto the
dynamically-addressable focusing element will, in combination with
the input illumination profile and system optics cause an output
light profile that closely matches the target light field or an
output light field that may require further optical or other
treatment to produce the desired target output light field.
[0280] The method of FIG. 26 creates an approximation of the full
target light field using a number of component light fields that
may be added together. Examples of such components may be
rectangular shaped uniform light fields or Gaussian light
fields.
[0281] This example shows a procedural approach (non-iterative)
that has access to a set of features, such as virtual optical
elements (described by for example their shapes, sizes and
positions on a PMD and its resulting light field which can be
either pre-computed or provided in functional form as well as
description of parameters that may be varied by the program). Each
such feature, when applied to the PMD results in a related output
component light field. A light field analyzer compares such
features, in particular the resulting output light fields to the
target light fields and determines a set of feature parameters for
a plurality of features. These are combined into a final light
re-distributing scheme in the pattern building block.
[0282] As an example, one virtual optical element may produce a
Gaussian intensity profile as its output. The peak-intensity and
full-width half-maximum may be described directly when the virtual
optical element is formed on the PMD. A superimposed set of such
Gaussians may resemble the target light-field when relayed on a
display screen.
[0283] FIG. 27 shows three examples of optics and the light field
that may be used where coherent light is present on the
dynamically-addressable focusing element and a system transfer
function (forward model), such as can be described by a two
dimensional Fourier transformation is desired. Example a) uses
coherent and collimated light present on the
dynamically-addressable focusing element followed by a field lens
to focus light. Example b) achieves a similar result, however the
field lens is represented as a path length varying pattern that can
be superimposed with the desired light redistribution scheme.
Example c) provides similar results, utilizing a slightly
converging beam.
[0284] Common for all three implementations is that coherent or
partially coherent light from a light module 2701 is expanded using
expansion and beam shaping optics 1102 and the light is incident on
the PMD 2705. 2702 may comprise two or more focusing elements 1103
and 1104. In 1110, the light incident on 2705 is collimated. The
output light from 1105 is focused by focusing lens 2706 onto 2707
in the case when 2705 does not change phase or changes phase
uniformly across the device.
[0285] In 2720, the light incident on 2705 is collimated. The
output light from 2705 is focused onto 2707 in the case when the
phase retardation pattern on 2705 resembles a lens or an
approximation thereof.
[0286] In 2730, the light incident on 2705 is not collimated, but
converging to focus at 2707 in the case when 2705 does not change
phase or changes phase uniformly across the device.
[0287] In all three implementations, 2705 is configured in such a
way as to produce an approximation of a desired target light field
at 2707, for example at a projection screen.
[0288] FIG. 28 shows an example of variable scanning optics in
which two laser beams or other light beams collectively scan an
area. This scheme may be expended to any suitable number of light
beams. Each light beam scans a region within the area. By altering
the sizes of the scanned regions the luminance within each region
may be varied. The dimensions of the scanned regions may be
changed, for example, the scanned regions may be rectangular and
the lengths and widths of the scanned regions may be changed,
thereby altering the areas of the scanned regions. The scanning
speed and pattern may remain fixed as the size and/or shape of a
scanned region is changed or may be altered. For example, scanning
speed may be reduced when the scanned region is smaller and
increased when the scanned region is larger.
[0289] In the example implementation illustrated in FIG. 28 a
plurality of light sources such as lasers LS1 and LS2 are used in
conjunction with for example steerable MEMS mirrors that allow the
beams to be scanned across different areas. In this example LS1
illuminates Area 1 and LS2 illuminates Area 2. Together, LS1 and
LS2 illuminate the entire imaging area 1201.
[0290] LS1 provides a beam of light incident on a two-axis scanning
mirror 1204 that scans the beam 2803 over Area 1. LS2 provides a
beam of light incident on a two-axis scanning mirror 2805 that
scans the beam 2802 over Area 2. The beams 2803 and 2802 may be
scanned over the respective areas in a line-by-line fashion or any
other desired path. In this example Area 1 is of a different size
than Area 2. Therefore the scanning speed of 2802 maybe increased
order to scan over Area 2 in the same time required for 2803 to
scan Area 1. Provided that LS1 and LS2 are of same or similar
intensities, the resulting average intensity of Area 1 may be
higher than that of Area2. Other scanning patterns, scan speeds,
pattern densities, light source modulation or intensities may be
utilized to achieve a similar effect.
[0291] In some embodiments, an image data processor divides the
image into equal area sections, each section being illuminated by
one light source each with a modulated amplitude according the
requirements of the individual areas.
[0292] In some embodiments, the illumination comes in the form of a
uniform field that covers its whole subsection. In some
embodiments, the image sections comprise differently sized areas of
equal light energy of one or more of the present frequencies in the
image (colours), so that each sub-section and frequency may reach
different peak amplitudes.
[0293] In some embodiments, the illumination comes in the form of a
spot light source which is scanned across its subsection of the
screen, for example using a laser and a mirror mounted on a
rotational 2-axis mirror.
[0294] In some embodiments, the illumination comes in the form of a
line light source which is scanned across its subsection of the
screen, for example using a laser and a mirrors mounted on a
rotational 1-axis mirror.
[0295] In some embodiments, each image subsection is illuminated
with a sequence of random illumination patterns, each generated by
an image data processor that ensures that the resulting image is in
accordance with the input image data.
[0296] In some embodiments, the projection system comprises
differently sized areas of equal light energy of one or more of the
present frequencies in the image (colours). Each subsection goes
through spatial light amplitude modulation, for example by an
SLM.
[0297] In some embodiments, the projection system comprises
differently sized areas of equal light energy of one or more of the
present frequencies in the image (colours). Within each subsection,
the scanning is done at variable speed, but with a constant
intensity, so that the perceived subsection varies in intensity. A
controller may be configured to ensure that each subsection while
scanned at variable speeds within each subsection still completes
to total subsections in the same amount of time.
[0298] In some embodiments the required scanning speed is high and
instead of a motorized mirror, diffractive dynamic elements such as
acousto-optical modulator or acousto-optical deflectors are applied
to scan the light used.
[0299] FIG. 29 shows example variable laser scanning optics which
is an alternative to the implementation depicted in FIG. 12. In
FIG. 13, each light source is relayed onto a respective area not as
a scanning beam, but as a complete field expanded using beam
shaping and expansion optics.
[0300] Beam LS1 is shaped and expanded using the asymmetric beam
expander ABEL The expanded light profile is then steered using a
two-axis scanning mirror 1302 onto Area 1 of the image. Similarly,
LS2 is shaped and expanded using the asymmetric beam expander ABE2.
The expanded light profile is then steered using a two-axis
scanning mirror 1301 onto Area 2 of the image.
[0301] Asymmetric beam expander ABE2 is explained in 2910 and 2920.
2910 shows how the incident beam is expanded by different amounts
in two perpendicular directions using the cylindrical lenses 2911
and 2912. In its default configuration, the input beam profile
which may be in the form of a focused spot, will result in the
output light profile being a square and uniform intensity beam. If
a rectangular shape is required, one or both of the cylindrical
lenses 2911 or 2912 may be moved by for example a motor along the
optical axis of this system. Moving 2911 will change the square
shape 2921 into shape 2922. Likewise, moving 2912 will change the
square shape 2923 into shape 2924. If both lenses 2911 and 2912 are
moved, the output light profile may be as depicted in 2925. In
addition to shaping the individual beams, the output light profiles
from ABE1 and ABE2 may be steered by 2901 and 2902 so that their
combined illumination from 2900 and 2903 fills the complete
image.
[0302] FIG. 30 shows an example application of optical switches to
remove light from a first area and direct that light to a second
area. The first area becomes dimmer and the second area becomes
brighter as a result.
[0303] In FIG. 30, a plurality of light sources LS1 to LSn provide
input beams onto an array of input ports 3000, for example via
optical fibres. The light from each input port is present on device
3003 comprising one or more elements such as 3005 that steers the
light. 3005 could for example be a two-axis controllable mirror.
This light can furthermore be relayed off a secondary device 3004
comprising one or more elements such as 3006 that steers the light
towards an output array of output ports. In one embodiment, the
input light beams provided by the light sources are collimated and
remain collimated at the output port 3001.
[0304] FIG. 31 depicts an implementation of a light-efficient
illuminator using optical switches and a clean-up module such as an
array of integrating rods IR1, . . . , IRn 3110, a plurality of
light sources LS1 to LSn provide input beams onto an array of input
ports 3100, for example via optical fibres. These beams are further
directed onto a clean-up module, for example an array of
integration rods IRI to IRn. In this example, LS1 and LS2 are
incident on IR1, LS3 and LS4 are incident on IR2 and so forth. 3111
shows the incident light profile on IR1 and IR2. 3113 is the light
stemming from LS1. 3114 is the light stemming from LS2. 3115 is the
light stemming from LS3. 3115 is the light stemming from LS4. The
remaining integrating rods in this system can be described in a
similar matter. 3112 shows the output light profile from
integration rods IR1 and IR2, and illustrates how the non-uniform
input profiles have been made uniform. The average intensity of
1517 is approximately that of the average intensity of 3113 and
3114 combined or integrated. The average intensity of 1518 is
approximately that of the average intensity of 3115 and 3116
combined or integrated.
[0305] In 3120 shows the same system with steering. In this
example, LS2 is steered away from IR1 and into IR2, thereby
reducing the intensity output from IR1 and increasing that of IR2.
3121 shows the input light profiles onto IR1 and IR2. 3123 shows
the input light profile from LS1 onto IR1. 3124 shows the combined
light input from LS2, LS3 and LS4 onto IR2.
[0306] 3122 shows the output light profile from integration rods
IR1 and IR2. The average intensity of 3125 is approximately that of
the average intensity of 3123. The average intensity of 3126 is
approximately that of the average intensity of 3124 combined or
integrated.
[0307] FIG. 32 illustrates an embodiment which applies a refinement
module (for example a DMD) to fine tune a light field.
[0308] The output light field of a device as described herein may
be used as a controllable light source to illuminate a refinement
stage which may include an imaging device, like a DMD, an LCD, or
an LCoS. The imaging device may comprise an amplitude modulating
SLM, a PMD, a diffusive device, like a DMD, an LCD, or an LCoS.
Refinement may provide a refined output that may improve the
quality of the output light-field of the complete system. The
refinement module may comprise a de-speckling module, a
polarization-varying device, a colour-enhancing device etc.
[0309] The refined output light-field may be imaged or relayed onto
a projection screen or the like in the usual manner. As shown in
FIG. 32, a light-efficient illuminator may be combined with one or
several refinement modules which may be arranged in serial and/or
parallel configurations.
[0310] For example, the refinement module may provide high spatial
frequency detail to the final light-field that can now be imaged or
relayed onto a projection screen or the like on top of the output
light-field from the light efficient illuminator.
[0311] Another use of the refinement module is to minimize visual
artifacts introduced by the light efficient illuminator. In some
implementations, these improvements may be executed in accordance
with analysis of the light efficient illuminator output as well as
models of the human visual system such as colour appearance models,
visual difference predictors or other models.
[0312] In a preferred embodiment, the dynamic light efficient
illuminator provides a first low quality version of the target
light field, for example low spatial resolution colour image, as
input to the refinement module. The refinement module may comprise
a single spatial amplitude modulator of high spatial resolution
relative to the colour image and provide luminance modulation only.
The combined output may be different from the target light field in
an absolute sense, but perceptually comparable.
[0313] FIG. 33 depicts an example optical implementation as well as
light profiles present at various stages of a light efficient
illuminator with a refinement module. The output light field 3300
from the light efficient illuminator is relayed onto the refinement
module 3303 via for example a relay lens system 3301. 3304 shows an
example output light profile produced by the light efficient
illuminator. 3305 shows an example light profile incident on the
refinement module 3303. In some embodiments it may be preferable
not to focus the output of 3300 exactly onto 3303, but instead blur
or spatially low-pass filter 3304 by moving 3303 by an amount
3302.
[0314] FIG. 34: illustrates an embodiment comprising a refinement
module (for example a DMD) and a clean-up module (for example an
integration rod array).
[0315] Certain applications may require that the output light field
be of high fidelity, uniformity, or predictability. In some cases
an output light field may include undesirable sharp spikes or other
optical noise not specified for the target light field. One could
reduce these issues by providing an array of homogenizing elements
such as an array of independent integrating rods or a bundle of
fibers or a number of optical waveguides between the illuminator
and the refinement module. The spatially-varying output light-field
is then reduced to a number of known intensity profile regions
matching the number of homogenizing elements (e.g. fibers or
integrating rods) used. The benefits of steering light into a
number of integrating rods, fibres or regions may include enhanced
contrast, improved black-levels, higher peak-intensities, and/or
improved predictability of the output light profile. Additionally,
as light that would otherwise pass through one homogenizing element
can be redirected into another homogenizing element, the resulting
peak luminance can in the best case be increased by approximately
the number of regions (e.g. all or most of the light could be
directed into one of the homogenizing elements). By contrast, in a
system that does not redirect light but merely attenuates light to
achieve desired luminance levels, the peak luminance is limited to
the global luminance level that the system's light module can
provide.
[0316] FIG. 35 depicts an example implementation of a
light-efficient illuminator combined with a clean-up module and a
refinement module. The output of the light-efficient illuminator
3500 is relayed using for example a lens 3501 onto an array of
integration rods 3502, IR1, IR2, IR3 and IR4. The output 3503 of
the array of integration rods is further relayed onto 3505 using
for example a lens 3504. 3505 represents the refinement module, for
example in the form of an amplitude-modulating SLM. The output of
3505 is relayed onto for example a projection screen 3512 using for
example a lens 3511. An example output light-field from 3500 is
depicted in 3507. The light profile incident on 3505 may be blurred
using a small offset 3506, turning the light profile 3508 at 3503
into 3509 at 3505. 3510 shows the final output light-field from the
complete system, where 3513 represents a relayed version of 3509
modulated to 3514 by 3512.
[0317] Projection systems as described herein may comprise multiple
stages of modulation. One or more stages may modulate phase of the
light, and/or one or more other stages modulate the light's
amplitude, and/or one or more other stages modulate the light's
frequency, and/or one or more other stages modulate the light's
polarization. For example, one projection system could have two
spatial amplitude modulators, and one spatial phase modulator.
[0318] Such stages may be arranged to process light in a serial or
parallel fashion, or a mix thereof. In the parallel case, different
light fields can be combined by a beam-splitter or beam-combiner,
for example a dichroic mirror in order to combine light of
different frequencies, or a polarizing beam-splitter in order to
combine light with different polarizations. For the serial case,
the output of one stage is used as the input for the next stage.
For example, one system can use a frequency modulator in parallel
with a phase modulator, both of which are placed in series with a
spatial amplitude modulator. The two parallel stages can be
combined by a beam-combiner before they are relayed onto the
spatial amplitude modulator which is placed in series with the
parallel stage.
[0319] FIG. 36 shows intensity-time and intensity-location plots in
a system employing a color field sequential scheme. 3610 indicates
an example of a desired spatial cross-sectional light profile in a
three-primary light-efficient illuminator made up from a red
(3611), a green (3612) and a blue (3613) channel. Since the
light-efficient illuminator achieves its target light profile by
re-distributing light rather than exclusively amplitude-modulating
light (by attenuation), the total amount of light required by each
light source is proportional to the integrated light of each colour
channel light profile, 3611, 3612, and 3613 respectively for R, G,
and B. In this particular example, one can inspect the light
profiles 3611, 3612 and 3613 and deduce that a lesser amount of
green light is required, an intermediate amount of red light is
required, and a largest amount of blue light is required.
[0320] The total amount of light for each color within one video
frame in a color field sequential drive scheme can either be
modulated at the source by reducing the intensity of individual
light sources over a fixed period of time as depicted in 3600, or
by a fixed intensity over varying amounts of time as depicted in
3620 or by a combination of these two schemes, not depicted here.
In 3600 the intensity modulating approach is depicted for red by
3601, green by 3602 and blue by 3603. In 3620 the time modulating
approach is depicted for red by 3621, green by 3622 and blue by
3623.
Interpretation of Terms
[0321] Unless the context clearly requires otherwise, throughout
the description and the claims: [0322] "comprise", "comprising",
and the like are to be construed in an inclusive sense, as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to"; [0323] "connected", "coupled",
or any variant thereof, means any connection or coupling, either
direct or indirect, between two or more elements; the coupling or
connection between the elements can be physical, logical, or a
combination thereof; [0324] "herein", "above", "below", and words
of similar import, when used to describe this specification, shall
refer to this specification as a whole, and not to any particular
portions of this specification; [0325] "or", in reference to a list
of two or more items, covers all of the following interpretations
of the word: any of the items in the list, all of the items in the
list, and any combination of the items in the list; [0326] the
singular forms "a", "an", and "the" also include the meaning of any
appropriate plural forms.
[0327] Words that indicate directions such as "vertical",
"transverse", "horizontal", "upward", "downward", "forward",
"backward", "inward", "outward", "vertical", "transverse", "left",
"right", "front", "back", "top", "bottom", "below", "above",
"under", and the like, used in this description and any
accompanying claims (where present), depend on the specific
orientation of the apparatus described and illustrated. The subject
matter described herein may assume various alternative
orientations. Accordingly, these directional terms are not strictly
defined and should not be interpreted narrowly.
[0328] Embodiments of the invention may be implemented using
specifically designed hardware, configurable hardware, programmable
data processors configured by the provision of software (which may
optionally comprise "firmware") capable of executing on the data
processors, special purpose computers or data processors that are
specifically programmed, configured, or constructed to perform one
or more steps in a method as explained in detail herein and/or
combinations of two or more of these. Examples of specifically
designed hardware are: logic circuits, application-specific
integrated circuits ("ASICs"), large scale integrated circuits
("LSIs"), very large scale integrated circuits ("VLSIs"), and the
like. Examples of configurable hardware are: one or more
programmable logic devices such as programmable array logic
("PALs"), programmable logic arrays ("PLAs"), and field
programmable gate arrays ("FPGAs")). Examples of programmable data
processors are: microprocessors, digital signal processors
("DSPs"), embedded processors, graphics processors, math
co-processors, general purpose computers, server computers, cloud
computers, mainframe computers, computer workstations, and the
like. For example, one or more data processors in a control circuit
for a device may implement methods as described herein by executing
software instructions in a program memory accessible to the
processors.
[0329] Processing may be centralized or distributed. Where
processing is distributed, information including software and/or
data may be kept centrally or distributed. Such information may be
exchanged between different functional units by way of a
communications network, such as a Local Area Network (LAN), Wide
Area Network (WAN), or the Internet, wired or wireless data links,
electromagnetic signals, or other data communication channel.
[0330] For example, while processes or blocks are presented in a
given order, alternative examples may perform routines having
steps, or employ systems having blocks, in a different order, and
some processes or blocks may be deleted, moved, added, subdivided,
combined, and/or modified to provide alternative or
subcombinations. Each of these processes or blocks may be
implemented in a variety of different ways. Also, while processes
or blocks are at times shown as being performed in series, these
processes or blocks may instead be performed in parallel, or may be
performed at different times.
[0331] In addition, while elements are at times shown as being
performed sequentially, they may instead be performed
simultaneously or in different sequences. It is therefore intended
that the following claims are interpreted to include all such
variations as are within their intended scope.
[0332] Software and other modules may reside on servers,
workstations, personal computers, tablet computers, image data
encoders, image data decoders, PDAs, video projectors, displays
(such as televisions), digital cinema projectors, media players,
and other devices suitable for the purposes described herein.
[0333] The invention may also be provided in the form of a program
product. The program product may comprise any non-transitory medium
which carries a set of computer-readable instructions which, when
executed by a data processor, cause the data processor to execute a
method of the invention. Program products according to the
invention may be in any of a wide variety of forms. The program
product may comprise, for example, non-transitory media such as
magnetic data storage media including floppy diskettes, hard disk
drives, optical data storage media including CD ROMs, DVDs,
electronic data storage media including ROMs, flash RAM, EPROMs,
hardwired or preprogrammed chips (e.g., EEPROM semiconductor
chips), nanotechnology memory, or the like. The computer-readable
signals on the program product may optionally be compressed or
encrypted.
[0334] In some embodiments, the invention may be implemented in
software. For greater clarity, "software" includes any instructions
executed on a processor, and may include (but is not limited to)
firmware, resident software, microcode, and the like. Both
processing hardware and software may be centralized or distributed
(or a combination thereof), in whole or in part, as known to those
skilled in the art. For example, software and other modules may be
accessible via local memory, via a network, via a browser or other
application in a distributed computing context, or via other means
suitable for the purposes described above.
[0335] Where a component (e.g. a software module, processor,
assembly, device, circuit, etc.) is referred to above, unless
otherwise indicated, reference to that component (including a
reference to a "means") should be interpreted as including as
equivalents of that component any component which performs the
function of the described component (i.e., that is functionally
equivalent), including components which are not structurally
equivalent to the disclosed structure which performs the function
in the illustrated exemplary embodiments of the invention.
[0336] Specific examples of systems, methods and apparatus have
been described herein for purposes of illustration. These are only
examples. The technology provided herein can be applied to systems
other than the example systems described above. Many alterations,
modifications, additions, omissions, and permutations are possible
within the practice of this invention. This invention includes
variations on described embodiments that would be apparent to the
skilled addressee, including variations obtained by: replacing
features, elements and/or acts with equivalent features, elements
and/or acts; mixing and matching of features, elements and/or acts
from different embodiments; combining features, elements and/or
acts from embodiments as described herein with features, elements
and/or acts of other technology; and/or omitting combining
features, elements and/or acts from described embodiments.
[0337] It is therefore intended that the following appended claims
and claims hereafter introduced are interpreted to include all such
modifications, permutations, additions, omissions, and
sub-combinations as may reasonably be inferred. The scope of the
claims should not be limited by the preferred embodiments set forth
in the examples, but should be given the broadest interpretation
consistent with the description as a whole.
Hybrid GS-Based Imaging:
[0338] In an example embodiment, an adaptation of the
Gerchberg-Saxton algorithm is used to generate a pattern on a PMD
to produce an image in the far field. The Gerchberg-Saxton
algorithm is an iterative approach to retrieving the phase of a
pair of light fields. Given some target illumination profile, and a
well-characterized input light profile, an iterative approach can
be used to converge on a phase pattern that, when applied to the
PMD, will approximate the target profile in the far field.
[0339] An array of parallel beams is relayed onto an active area of
the PMD, each covering a segment of the active area, and supplying
light to form a sub-image in the far-field. This is illustrated in
FIG. 14A. Misalignment caused by imperfect parallelism of the light
beams may be corrected by superimposing a prism on the modulation
pattern applied to a corresponding area of the PMD to shift a
sub-image corresponding to that area into alignment so that each
sub-image is overlaid correctly at the image location.
Segmented Approach
[0340] In this approach, a phase pattern is calculated for the PMD
with the image divided up into segments, corresponding to incoming
beams. This pattern can be calculated using a similar approach to
the one described above. In this approach, light field
re-distribution using a PMD is restricted to local redistribution
within the image segment, such that light from a single beam is
only re-directed within the corresponding image segment, as
illustrated in FIG. 14B. As described above, a prism may be
superimposed on the phase pattern in each image segment as
required, for fine alignment adjustment.
Lensing
[0341] A PMD may be controlled to simulate the effects of other
optical elements, such as prisms and gratings in a similar fashion,
for example a prism may be provided by applying a slowly varying
amount of phase delay in one direction on the PMD.
[0342] Different effects may be combined on the PMD. An example is
a phase-pattern that both focuses and shifts the incoming light
profile. This may be achieved by controlling the PMD to alter the
phases of light in a pattern that superimposes (adds) the
respective phase delay patterns for a lens and a prism.
[0343] This approach can be used to in conjunction with an input
light field made up of tiled, non-overlapping patches of light, to
shift and scale individual light patches, or small sections of
patches to approximate an image.
Free-Form Lensing
[0344] Several lenses side-by-side or super-imposed on the PMD can
coarsely approximate an image. More complex images or illumination
profiles can be achieved by controlling the PMD to present a phase
adjustment that is continuously-varying over the area of the PMD.
Such a phase-pattern can be achieved by an iterative optimization
approach, where the difference between the current solution and the
target-image is iteratively minimized until a completion criterion
is satisfied.
[0345] The optimizer finds a solution using a minimization or
optimization approach based on a forward model and its inverse. An
initial guess of the light re-distribution scheme as well as
regularization terms may be utilized to converge towards a suitable
solution in fewer iterations. System constraints may also be
supplied. An exit metric, for example the maximum number of
iterations, a residual, or a perceptual metric, determines when the
program stops and outputs the current solution in form of a light
re-distribution scheme.
[0346] An optimization approach can be applied where the incoming
light is in the form of a 2D array of parallel beams. The input
light distribution may be characterized and provided as input to
the algorithm, and a lens surface must be calculated that
transforms the input light distribution into the desired image in
the focal plane.
Lensless Algorithms
[0347] Another approach calculates a phase pattern that produces a
target light field in a specified focal plane some distance from
the PMD, instead of in the far-field. This algorithm can yield a
desired output light pattern without additional lenses in the light
path. Such lensless algorithms can be used with a
well-characterized tiled array of non-overlapping beams. The phase
pattern to be provided on a PMD may be generated based on the
incoming light distribution.
Shifting to Dump for Local Dimming
[0348] Dynamic dimming of some light sources, including laser
diodes or LEDs, whether by pulsing or by dynamically varying
current, can adversely affect light source stability and lifetime.
The dynamic shifting approach used to algorithmically correct beam
alignment can be used to shift an entire beam into a beam dump to
achieve a global dimming effect if the scene calls for it, without
pulsing or modifying source input power.
Diode Property Diversity for Artifact Mitigation
[0349] Strategically combining light sources with different
properties can be used for minimizing the appearance of certain
undesirable artifacts. Artifacts such as speckle can occur for
example, when using coherent, monochromatic light to display an
image. Combining multiple beams form an overall image can result in
a reduction in algorithm noise, image speckle, and screen speckle
when compared to imaging with a single source. Furthermore, if
light sources are selected to have slightly different wavelengths,
or configured for varying input angles, an averaging effect may
minimize the appearance of certain image artifacts.
Example Application in a Projection System
[0350] FIG. 15 shows a light projection system 1500 according to an
example embodiment. Light beams from an array of light sources 102
are combined at 1502 into a 2D array of non-overlapping, parallel,
collimated beams, and relayed by relay optics 1504 onto a spatial
light modulator 1505. A computer sends a control signal to the
spatial light modulator, which alters the incoming light field to
achieve a target illumination profile. The output of this spatial
light modulator is then relayed through projection optics 1506, and
focused onto a surface, in this case, a projection screen 1507.
Example Application to Stereolithography
[0351] Stereolithography 3D printers use UV, IR or visible light to
cure a resin. Such systems may include a resin bath and a 2D
scanning laser beam that cures one layer (Z-Axis) at a time. Upon
completion of each layer the partially completed model is lowered
by one step into the bath and the next layer is "written". This
process typically takes some time to complete, for example 10
minutes per layer or 6 hours for an entire 3D model.
[0352] Some approaches replace the visible light source within a
projection system with a UV light source, and then, instead of
scanning in a 2D fashion to create a layer, expose the entire layer
at once. There are two limitations using this technique: first the
intensity that a typical projector can create is limited, and hence
the layer needs to be exposed for a longer time, secondly, the
contrast of a typical projector is limited, and as such areas in
which resin is not supposed to be cured, will receive a small
amount of light, which may be enough to cure resign and effectively
limit the resolution at which a model can be printed.
[0353] Using a light re-direction projection approach, for example
as discussed herein, to project light to imagewise expose a layer
in a 3D printer can result in improvements in both higher printing
speed (because local intensity is higher) and higher accuracy
(because there is limited or no light leakage).
Example Embodiment
[0354] FIGS. 16A and 16B provide illustrations of how embodiments
as described herein may be applied to display color images or other
light patterns and also how optical power may be scaled up (either
by changing modes within one projector or between different
projectors). Some embodiments perform color imaging by generating
and modulating light of three colors (e.g. red, green and blue).
These colors may be generated and modulated in parallel (e.g. using
different PMDs) or displayed in a time-multiplexed manner (e.g. the
same PMD may modulate different colors of light in different time
periods).
[0355] Light emitters of different colors may have different
optical power outputs. also, certain imaging or illumination
applications may need different optical power levels for different
colors. The desire to use light emitters of different colors that
may have different optical power outputs and or the need for
different optical power levels in different colors for certain
applications may be accommodated in various ways. In some
embodiments the number of light emitters of different colors is
different. An optical system for each color may tile the active
area of a PMD or other dynamically-addressable focusing element
with a number of light patches corresponding to the number of light
sources being used for that color. Additionally, the arrangement of
patches of light may differ among different colors. For example,
for some colors the active area of a PMD may be covered by a single
row or column of patches of light while for other colors the active
area of the PMD may be covered by an array or patches of light
having plural rows and plural columns.
[0356] Furthermore, the overall optical power available may be
increased by increasing the number of light emitters. This may be
done for a single-color projector or for any one or more colors in
a multi-color projector. FIGS. 16A and 16B illustrate two possible
arrangements one (FIG. 16A) for a lower power projector and another
(FIG. 16B) for a higher power projector. In this non-limiting
example embodiment the number of red and green light emitters is
doubled in FIG. 16B. The same number of blue light emitters
provides adequate optical power in both embodiments (of course the
number of blue light emitters could also be increased if desired).
FIGS. 16A and 16B could represent different projectors or different
operating modes of a single projector.
[0357] In some example embodiments like FIGS. 16A and 16B light is
supplied by laser diodes, the fast axis of the laser diodes are
collimated. The beams diverges along the slow axis in order to fill
the active area of a PMD. In other embodiments, the patches of
light that collectively illuminate the active area of the PMD may
be of different shapes or may be arranged to provide different
tilings of the PMD active area.
Interpretation of Terms
[0358] Unless the context clearly requires otherwise, throughout
the description and the claims: [0359] "comprise", "comprising",
and the like are to be construed in an inclusive sense, as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to"; [0360] "connected", "coupled",
or any variant thereof, means any connection or coupling, either
direct or indirect, between two or more elements; the coupling or
connection between the elements can be physical, logical, or a
combination thereof; [0361] "herein", "above", "below", and words
of similar import, when used to describe this specification, shall
refer to this specification as a whole, and not to any particular
portions of this specification; [0362] "or", in reference to a list
of two or more items, covers all of the following interpretations
of the word: any of the items in the list, all of the items in the
list, and any combination of the items in the list; [0363] the
singular forms "a", "an", and "the" also include the meaning of any
appropriate plural forms.
[0364] Words that indicate directions such as "vertical",
"transverse", "horizontal", "upward", "downward", "forward",
"backward", "inward", "outward", "vertical", "transverse", "left",
"right", "front", "back", "top", "bottom", "below", "above",
"under", and the like, used in this description and any
accompanying claims (where present), depend on the specific
orientation of the apparatus described and illustrated. The subject
matter described herein may assume various alternative
orientations. Accordingly, these directional terms are not strictly
defined and should not be interpreted narrowly.
[0365] While processes or blocks are presented in a given order,
alternative examples may perform routines having steps, or employ
systems having blocks, in a different order, and some processes or
blocks may be deleted, moved, added, subdivided, combined, and/or
modified to provide alternative or subcombinations. Each of these
processes or blocks may be implemented in a variety of different
ways. Also, while processes or blocks are at times shown as being
performed sequentially (in series), these processes or blocks may
instead be performed in parallel, or may be performed at different
times.
[0366] Where a component (e.g. a light emitter, mirror, lens,
assembly, device, circuit, etc.) is referred to above, unless
otherwise indicated, reference to that component (including a
reference to a "means") should be interpreted as including as
equivalents of that component any component which performs the
function of the described component (i.e., that is functionally
equivalent), including components which are not structurally
equivalent to the disclosed structure which performs the function
in the illustrated exemplary embodiments of the invention.
[0367] Specific examples of systems, methods and apparatus have
been described herein for purposes of illustration. These are only
examples. The technology provided herein can be applied to systems
other than the example systems described above. Many alterations,
modifications, additions, omissions, and permutations are possible
within the practice of this invention. This invention includes
variations on described embodiments that would be apparent to the
skilled addressee, including variations obtained by: replacing
features, elements and/or acts with equivalent features, elements
and/or acts; mixing and matching of features, elements and/or acts
from different embodiments; combining features, elements and/or
acts from embodiments as described herein with features, elements
and/or acts of other technology; and/or omitting combining
features, elements and/or acts from described embodiments.
[0368] It is therefore intended that the following appended claims
and claims hereafter introduced are interpreted to include all such
modifications, permutations, additions, omissions, and
sub-combinations as may reasonably be inferred. The scope of the
claims should not be limited by the preferred embodiments set forth
in the examples, but should be given the broadest interpretation
consistent with the description as a whole.
* * * * *