U.S. patent application number 10/972955 was filed with the patent office on 2005-05-05 for radiation conditioning system.
This patent application is currently assigned to ACTUALITY SYSTEMS, INC.. Invention is credited to Favalora, Gregg E., Napoli, Joshua, Oliver, David-Henry.
Application Number | 20050094281 10/972955 |
Document ID | / |
Family ID | 26992721 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050094281 |
Kind Code |
A1 |
Favalora, Gregg E. ; et
al. |
May 5, 2005 |
Radiation conditioning system
Abstract
A radiation conditioning system is presented as comprising a
radiation source for generating radiation, a spatial light
modulator receptive of the radiation from the radiation source, a
control signal for addressing the spatial light modulator, and a
radiation conditioning device of the radiation field from the
spatial light modulator for conditioning the radiation field.
Inventors: |
Favalora, Gregg E.;
(Arlington, MA) ; Napoli, Joshua; (Winchester,
MA) ; Oliver, David-Henry; (Brookline, MA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Assignee: |
ACTUALITY SYSTEMS, INC.
Burlington
MA
|
Family ID: |
26992721 |
Appl. No.: |
10/972955 |
Filed: |
October 25, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10972955 |
Oct 25, 2004 |
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10324410 |
Dec 19, 2002 |
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60341901 |
Dec 19, 2001 |
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60407904 |
Sep 3, 2002 |
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Current U.S.
Class: |
359/619 |
Current CPC
Class: |
H04N 13/302 20180501;
G03H 2001/2292 20130101; G03H 2210/454 20130101; G02B 30/27
20200101; G02B 5/32 20130101; G03H 1/268 20130101; G03H 2225/31
20130101; G02B 26/106 20130101 |
Class at
Publication: |
359/619 |
International
Class: |
G02B 027/10 |
Claims
1-26. (canceled)
27. A radiation conditioning system comprising: a radiation source
for generating radiation; a spatial light modulator receptive of
the radiation from the radiation source and a control signal for
addressing the spatial light modulator, thereby projecting a
radiation field from the spatial light modulator; and a radiation
conditioning device receptive of the radiation field from the
spatial light modulator for conditioning the radiation field;
wherein the radiation conditioning device includes a plurality of
radiation conditioning regions.
28. The radiation conditioning system as set forth in claim 27
wherein the radiation conditioning device comprises a diffractive
optical element.
29. The radiation conditioning system as set forth in claim 28
wherein the diffractive optical element comprises a diffraction
grating.
30. The radiation conditioning system as set forth in claim 29
wherein the diffraction grating comprises a set of basis
fringes.
31. The radiation conditioning system as set forth in claim 29
wherein the diffraction grating comprises grating pattern having a
spatial frequency defined by the mathematical equation: f=A
sin(.theta.)+B wherein f is the spatial frequency of the grating
pattern, A is scaling factor that determines the ratio of maximum
to minimum diffraction grating frequencies, .theta. is a spatial
dimension and B is a carrier frequency offset factor.
32. The radiation conditioning system as set forth in claim 30
wherein the diffractive optical element comprises a disc.
33. The radiation conditioning system as set forth in claim 28
wherein the diffractive optical element comprises an acousto-optic
modulator.
34. The radiation conditioning system set forth in claim 27 wherein
the radiation conditioning device comprises a set of lenslets.
35. The radiation conditioning system set forth in claim 27 wherein
the set of lenslets comprise an array.
36. The radiation conditioning system set forth in claim 27 wherein
the set of lenslets are arranged in a rectangular host.
37. The radiation conditioning system set forth in claim 27 wherein
the rectangular host is in reciprocating motion.
38. The radiation conditioning system set forth in claim 27 wherein
the radiation conditioning device comprises a spatial light
modulator.
39. The radiation conditioning system set forth in claim 38 wherein
the spatial light modulator comprises an optically addressable
spatial light modulator.
40. The radiation conditioning system set forth in claim 39 wherein
the optically addressable spatial light modulator includes a
material having properties depending upon a first illumination
frequency and is read out at a second frequency.
41. A radiation conditioning device comprising: a diffractive
optical element including a diffraction grating comprising a set of
basis fringes.
42. The radiation conditioning device as set forth in claim 41
wherein the diffraction grating comprises grating pattern having a
spatial frequency defined by the mathematical equation: f=A
sin(.theta.)+B wherein f is the spatial frequency of the grating
pattern, A is scaling factor that determines the ratio of maximum
to minimum diffraction grating frequencies, .theta. is a spatial
dimension and B is a carrier frequency offset factor.
43. A method of conditioning a radiation field, the method
comprising: conditioning the radiation field by scanning the
radiation field with a radiation conditioning device comprising a
set of basis fringes.
44. The method as set forth in claim 43 further comprising
decomposing the radiation field into a set of components.
45. The method as set forth in claim 43 wherein the radiation
conditioning device comprises a diffractive optical element.
46. The method as set forth in claim 43 wherein conditioning the
radiation field comprises scanning the radiation field with a
diffraction grating having a grating pattern defined by the
mathematical equation: f=A sin(.theta.)+B wherein f is the spatial
frequency of the grating pattern, A is scaling factor that
determines the ratio of maximum to minimum diffraction grating
frequencies, .theta. is a spatial dimension and B is a carrier
frequency offset factor.
47. The method as set forth in claim 45 wherein scanning the
radiation field comprises rotating the radiation conditioning
device through a prescribed angular distance.
48. The method as set forth in claim 45 wherein scanning the
radiation field comprises rotating the diffraction grating through
a prescribed angular distance.
49. A method of conditioning a radiation field, the method
comprising: conditioning the radiation field by scanning the
radiation field with a radiation conditioning device having time
varying properties.
50. A radiation conditioning system comprising: a radiation
projector for projecting a radiation field; and a radiation
conditioning device receptive of the radiation field from the
radiation projector for conditioning the radiation field; wherein
the radiation conditioning device includes a plurality of radiation
conditioning regions.
51. The system as set forth in claim 50 wherein the radiation
conditioning device comprises a set of basis fringes.
52. A radiation conditioning device comprising: a diffractive
optical element comprising a diffraction grating comprising a set
of basis fringes; wherein the diffraction grating comprises a
grating pattern having a spatial frequency defined by the
mathematical equation: f=A sin(.theta.)+B and wherein f is the
spatial frequency of the grating pattern, A is a scaling factor
that determines a ratio of maximum to minimum diffraction grating
frequencies, .theta. is a spatial dimension and B is a carrier
frequency offset factor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/341,901, filed Dec. 19, 2001, which
is incorporated herein by reference thereto as if set forth at
length.
[0002] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/407,904, filed Sep. 3, 2002, which
is incorporated herein by reference thereto as if set forth at
length.
BACKGROUND
[0003] This disclosure relates generally to electronic display
technology and more specifically to multi-view three-dimensional
parallax displays.
[0004] It is known that it is possible to create a
three-dimensional image by approximating the wavefronts that
emanate from three-dimensional (3-D) scenes. One such class of
displays contains "parallax displays," which project the appearance
of a 3-D scene from multiple viewpoints. Parallax displays
generally allow a viewer to move his head horizontally and/or
vertically to inspect the 3-D scene from different viewpoints. FIG.
1 illustrates a generalized parallax display 10.
[0005] In FIG. 1, a 3-D image 20 is projected by the parallax
display 10 due to rays emerging from image plane (or hologram
plane) 40 which enter the eyes of a viewer at location A or B. In
general, an illumination source 50, which is typically a collimated
laser beam, a sequence of 2D bitmapped images, or a single 2D image
composed of interdigitated 2D views, passes light through a light
steering and shaping element 55.
[0006] There are several specific ways to construct parallax
displays. One approach utilizes a lens sheet, such as a lenticular
lens array or a holographic optical element of similar function, to
map a field of interdigitated images to their corresponding nearest
viewpoints. In this way, a user walking around the parallax display
will see a series of images that approximate the scene's appearance
from the corresponding viewpoints. In FIG. 2, a lenticular lens
sheet 52 includes an array of lenticular lenses 54 on at least one
of its surfaces. Lenticular lens sheet 52 enables the parallax
display 10 to project different imagery for different viewing
angles. If properly registered imagery is projected onto the
screen, or if the screen is overlaid on an image source such as a
liquid crystal display (LCD), the system will provide imagery that
provides correct perspective and parallax and also has variable
transparency so that objects may occlude each other. This requires
computing image data from several viewpoints for each projected
frame. Though lenticular lenses and lens arrays are well known in
the art, a brief description of how they work will be provided.
[0007] A widely known embodiment of a lenticular lens array is a
lenticular lens sheet. It includes a sheet with a plurality of
adjacent, parallel, elongated, and partially cylindrical lenses and
multiple (e.g. two) interleaved lenses on the sheet. In general,
the plurality of lenses enables the multiple interleaved images to
be displayed on the underlying sheet but only one of the images
will be visible from any given vantage point above the sheet.
[0008] The underlying principle which explains this is illustrated
in FIG. 2, which presents a schematic side view of a lenticular
lens sheet 52 with a plurality of lens elements 54(1-3). The image
on the underlying sheet is represented by pixels 56-58. In this
example, three image pixels, identified by suffixes "a", "b", and
"c", respectively, are shown under each lens element 54. Thus, for
example, under lens element 54(1) there are three associated
pixels, namely 56a, 56b, and 56c.
[0009] If a person views the sheet from location "A", lens element
54(1), because of its focusing ability, allows that person to see
light from pixel 56a. That is, of the light which lens element
54(1) collects, it only sends toward the person at location "A"
that light which is collected from pixel element 56a. The rest of
the light which lens element 54(1) collects from other locations
under the lens is sent off in other directions and will not be seen
by a person at location "A". For similar reasons, a person at
location "B" only sees light emanating from pixel 56b, but does not
see light emanating from other locations under lens element
54(1).
[0010] In U.S. Pat. No. 5,172,251, Benton and Kollin disclose a
three dimensional display system. More recently, Eichenlaub et al
(Proc. SPIE, 3639, p. 110-121, 1999) disclosed a discrete light
field display, which produces up to 24 discrete viewing zones, each
with a different or pre-stored image. As each of the observer's
eyes transitions from one zone to another, the image appears to
jump to the next zone.
[0011] In practice, parallax displays are problematic. In general,
there is significant noticeable light emitted in inappropriate
directions, causing imagery from wrong viewpoints to be visible.
Furthermore, image realism is reduced because practical constraints
limit the number of views that can be handled by each lens element.
For example, the pixel density and the number of viewpoints are
bounded by diffraction effects and brightness requirements. Also,
many known lenticular sheet parallax displays produce undesirable
dark bands as the viewer transitions between viewpoints. Therefore
a parallax display with a large (i.e., 100+) number of viewpoints,
high resolution, high brightness, and smooth transition between
view zones is desired.
[0012] It is necessary to more closely approximate the light field
generated by a 3D scene than by using lenticular sheets. A subset
of the parallax display set contains holographic displays and
holographic stereograms. A holographic video ("holovideo") system
creates 3D imagery that looks realistic, appears to float inside or
outside of a viewing zone or panel, and exhibits motion parallax.
Holovideo provides the monocular and binocular depth cues of
shading, motion parallax, and viewer-position-dependent reflection
and hidden-surface removal.
[0013] One group of systems was created at the Massachusetts
Institute of Technology (MIT) Media Laboratory that in general
creates holographic video by scanning the image of an acousto-optic
scanner over a vertical diffuser. This is illustrated in FIG.
3.
[0014] An idealized holographic stereogram emits light from each
holographic pixel (or "hogel") in a way that allows a
horizontally-moving viewer to see a continuous range of
perspectives. See FIG. 5A. Here, the hologram plane 340 is
decomposed into hogels such as hogel 341. A continuous range of
viewer locations is shown.
[0015] Existing synthetic holographic stereograms sample the
parallax views. Sampled parallax is shown in FIG. 5B. Scene
parallax is captured from a finite set of directions, and is then
re-projected back in those same capture directions. In order to
prevent gaps between parallax views in the view zone, each view is
uniformly horizontally diffused over a small angular extent.
[0016] Two things are needed to generate a holographic stereogram
in this fashion: a set of N images that describe scene parallax,
and a diffraction pattern that relays them in N different
directions. In the case of the MIT Media Laboratory's holographic
video system, a set of N diffractive elements, called basis
fringes, are computed. When illuminated, these fringes redirect
light into the view zone as shown in FIG. 6. These diffractive
elements are independent of any image information, but when one is
combined with an image pixel value, it directs that pixel
information to a designated span in the view zone. FIG. 6 shows
three basis fringes, 355, 360, and 365 for three spatial
frequencies. To the right of each basis fringe is shown an example
of repeating that basis fringe across a hologram line. Basis fringe
355 is repeated across a hologram line 342 and is illuminated by
illumination 350, resulting in output 356 with a trajectory
determined by basis fringe 355. Likewise, basis fringe 360 of
higher frequency is repeated across a hologram line 343 and is
illuminated by illumination 350, resulting in output 361 with a
different trajectory and similarly for 365.
[0017] There are several ways to infer what basis fringes are
required to generate a 3D scene. A typical method is to capture a
scene using computer-graphic methods from N different directions.
This method is illustrated in FIG. 7. In FIG. 7, to capture or
render scene parallax information, cameras are positioned along a
linear track, with the view also normal to the capture plane. N
views are generated from locations along the track that correspond
with center output directions of the basis fringes. In this type of
horizontal parallax only (HPO) computed stereogram, correct capture
cameras employ a hybrid projection--perspective in the vertical
direction and orthographic in the horizontal. A desired 3D scene 2
is positioned near a capture plane 4. A set of cameras, C.sub.0,
C.sub.1, and C.sub.N-1, are illustrated taking snapshots of the
scene 2 from a series of viewpoints.
[0018] Once N parallax views have been generated, the MIT group
combines them with the N pre-computed basis fringes to assemble a
holographic stereogram. In practice, this scene reconstruction is
achieved using the apparatus illustrated in FIG. 3. The
acousto-optical modulators (AOM) produce a stream of weighted
linear combinations of basis vectors, as a function of the data
compiled from the step illustrated in FIG. 7.
[0019] As described, the handful of existing systems decompose a
synthetic hologram plane into spectrally-homogenous regions called
hogels, each of which is "projected" in its entirety by a spatial
light modulator (SLM) or acousto-optical modulator. An
acousto-optical modulator is a device which, in one mode of
operation, can diffract light when an ultrasonic sound wave
propagates through it. Because holograms may require 1000 line
pairs per millimeter, the imagery is usually small, or of low
resolution.
[0020] It is well known that computational techniques enable the
creation of synthetic holograms. Typical holograms require roughly
300 to 2000 lines per mm (ten million samples per square
millimeter) for practical diffraction of visible light. This has
been a difficult obstacle.
[0021] It is computationally difficult to generate the AOM inputs
that result in the desired light field. Furthermore, the system
uses components such as acousto-optic scanners and galvanometric
scanners which are financially prohibitive. This type of system is
shown in FIG. 3. A laser 150 illuminates a back of AOMs 154. The
AOMs operate in a mode that diffracts the laser light horizontally,
generating the constituent "hogels" of the final holographic image.
Vertical and horizontal scanners throw the diffracted light to a
vertical diffuser 159. An image volume 30 straddles the vertical
diffuser 159. The 3D light field is visible by a viewer.
[0022] Another method of holographic video uses groups of SLM
pixels as holographic fringes. One embodiment of this is described
in C. Slinger, B. Bannister, C. Cameron, S. Coomber, I. Cresswell,
P. Hallett, J. Hughes, V. Hui, C. Jones, R. Miller, V. Minter, D.
Pain, D. Scattergood, D. Sheerin, M. Smith, and M. Stanley,
"Progress and prospects for practical electro-holography systems,"
in Practical Holography XV and Holographic Materials VII, Stephen
A. Benton, Sylvia H. Stevenson, and T. John Trout, eds.,
Proceedings of SPIE v. 4296 (2001). This is depicted in FIG. 4. A
laser 250 illuminates an electrically-addressable spatial light
modulator (EASLM) 251. An optically addressable spatial light
modulator (OASLM) 253 is addressed by a time series of images from
EASLM 251 by a replication/relay stage 252. In this way, the speed
of the EASLM is traded-off for spatial resolution on the surface of
the OASLM. The imagery projected onto the OASLM is a hologram. Each
pixel of the EASLM and OASLM are used as constituents of the
underlying diffraction patterns. Electrically-addressable SLMs and
replication optics project computer-generated hologram image
segments onto an optically-addressable SLM (OASLM) for readout. The
system requires a high-powered laser and generates low-resolution
imagery because each SLM pixel is used within holographic
fringes.
[0023] In summary, many existing holographic video systems can be
schematically illustrated as shown in FIG. 10. A set of basis
fringes 355, 360, and 365 are weighted using known techniques after
scene generation by a "hogel vector" to form a stream of hogels
370. A "hogel vector" is a sampled hogel spectrum, specifying the
diffractive purpose of a hogel. A scanning or tiling system, 154,
scans this over hologram plane 340 to generate an image volume
30.
[0024] The systems described above suffer from low resolution,
demanding computational requirements, and the utilization of costly
optical and mechanical components. A system made of
volume-reproducable components and existing computational
infrastructure is desired which is capable of high-resolution
imagery and the ability to better approximate 3D light fields.
SUMMARY OF THE INVENTION
[0025] The system described here exploits human persistence of
vision in a different way than other known systems. Here, we
previously encode a set of basis fringes into a rotating
diffractive optical element (DOE). A basis fringe is an elemental
fringe pattern computed to contain a particular spectral profile.
Linear summations of basis fringes are used to diffract light. This
name is analogous to mathematical basis functions. The DOE is
addressed optically by a 2D SLM at the appropriate times. As a
result, over a time window of about 0.05 sec, the holographic plane
is formed by summation over time.
[0026] A multi-view parallax display according to this disclosure
utilizes a high-resolution 2D image generator (SLM) in which each
directional field is generated in its entirety, allowing the
resolution of the hologram plane to theoretically equal the SLM
resolution. A periodic image scanner, such as a rotating
holographic optical element, scans a sequence of directional fields
across a range of exit angles. Therefore, a 3D light field is
synthesized at high spatial and angular resolution using what is
termed spectral multiplexing, since a sequence of angular (or
spectral) components is projected in time sequence. Human
persistence of vision integrates the sequence of spectral
components into a visible image. The system engineer is given
flexibility in using the sequence of directional fields as a set of
distinct viewpoints, or as components of a more precisely-computed
generalized light field using known techniques.
[0027] In general, the approach occurs in several steps:
[0028] 1. Spectral decomposition of the scene: a database of ray
trajectories (e.g. point of origin, the angle of the trajectory,
the intensity and color) that exit a hologram plane is generated.
One method renders or records the scene from multiple viewpoints,
such as from a camera moving along a horizontal track, and assigns
each snapshot to a different projection time. Another method
examines the light field of a 3-D scene and computes the
trajectories of the constituent rays that would exit the hologram
plane to generate that light field. This is illustrated in FIGS. 8A
and 8B. A point source image 2 is positioned near a capture plane 4
which is intended to be visible from viewer position A to viewer
position B. The top view of hologram line 4a is illustrated in FIG.
8B. Here, the ray trajectories exiting the point source image 2 are
traced back to the hologram line 4a. For hogels i through i+3, beam
exit angles are shown. More complex scenes are constructed by
summing the contributions of each element of the 3D scene. A hogel
(holographic element) is a small functionally diffractive piece of
a hologram representing a spatial sample of the fringe pattern and
possessing a homogeneous spectrum.
[0029] 2. Elemental image projection. A high-speed 2D projector
projects the spectrally-classified (sorted by ray angle) data in a
rapid sequence of 5,000-10,000 frames per second. Typically, the
holographic video refresh rate equals this projector rate divided
by the total number of ray angles (or, equivalently, the number of
perspective viewpoints.) The imagery is projected on or through a
scanning element, preferably a rotating diffractive optical element
(DOE).
[0030] 3. View zone scanning. In FIG. 9 a rotating DOE 455 scans
the sequence of views across the viewing zone. The DOE is encoded
with a varying spatial frequency or a set of spatial frequencies
and focusing characteristics. The spatial frequency is a sinusoidal
function of the angle on the surface of the DOE. The DOE 455
directs light from the 2D projector at different angels through the
hologram plane, resulting in the creation of a visible 3D image.
Alternatively, the DOE can scan zero-, one- or two-dimensional
light and is also a physical embodiment of basis fringes.
[0031] The system described here utilizes the viewer's persistence
of vision to sum the basis fringes. Also, it uses the concept of
"spectral multiplexing" which gives the system engineer flexibility
in how the view zone is scanned, decreases the cost and complexity
of fringe generation, and greatly increases system resolution by
densely mapping individual projector pixels to hologram plane
regions. This is illustrated in FIG. 11. A database is generated of
hogel fringe components. An image 20 in image volume 30 is
projected from hologram plane 440 by a stream of 2D bitmaps
projected by a radiation projector 451 such as a spatial light
modulator (SLM), an LED array or other device capable of projecting
zero-, one-, two- or three-dimensional radiation through rotating
DOE 455. In this way, each pixel of the 2D SLM is mapped to a
region in the hologram plane, and its trajectory is generally
determined as a function of time (which relates to the scan angle
of the DOE.)
[0032] Other features and advantages of the invention will be
apparent from the following detailed description, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A show a top view of the components of a generalized
parallax display;
[0034] FIG. 1B show a side view of the components of a generalized
parallax display;
[0035] FIG. 2 is a schematic representation of a lenticular
screen;
[0036] FIG. 3 shows a holographic video system using the scanned
image of acousto-optical modulators onto a vertical diffuser;
[0037] FIG. 4 shows a holographic video system using optical
tiling;
[0038] FIG. 5A shows continuous parallax sampling;
[0039] FIG. 5B shows discrete parallax sampling;
[0040] FIG. 6 shows basis fringes and their diffractive
effects;
[0041] FIG. 7 shows image capture by a set of cameras on a
horizontal track;
[0042] FIG. 8A shows a cross section of a hologram plane for a
point source image;
[0043] FIG. 8B shows a top view of a cross section of a hologram
plane for a point source image;
[0044] FIG. 9A illustrates a disc-shaped diffractive optical
element (DOE);
[0045] FIG. 9B illustrates a rectangular shaped diffractive optical
element (DOE);
[0046] FIG. 9C illustrates a top view of the disc-shaped and
rectangular diffractive optical elements (DOE) of FIGS. 9A and
9B;
[0047] FIG. 10 illustrates the data and optical flow of scanned- or
tiled-hogel techniques;
[0048] FIG. 11 illustrates the data and optical flow of spectral
multiplexing;
[0049] FIG. 12A illustrates one hologram plane line for a point
source image;
[0050] FIG. 12B illustrates the temporal evolution of the hologram
plane line for a point source image of FIG. 12A;
[0051] FIG. 13A illustrates a top view of a spectrally-multiplexed
display device;
[0052] FIG. 13B illustrates a side view of a spectrally-multiplexed
display device; and
[0053] FIG. 14 illustrates a data base of FIG. 13 connected to a
communication network.
DETAILED DESCRIPTION OF THE INVENTION
[0054] Holographic video requires the generation of arbitrary
three-dimensional (3D) light fields. A 3D light field can be
generated by decomposing the field computationally into
components--such as an ensemble of beams with various trajectories
and profiles--and projecting these components by a projector whose
light is modulated by a multi-region light-shaping element with
time-varying properties.
[0055] In FIG. 11, a 3D image 20 is generated in image volume 30
when the appropriate set of rays exit hologram plane 440. A
diffractive optical element (DOE) 455, physically encoded with a
diffraction pattern whose frequency is a sinusoidal function of
angle, scans a time series of 2D bitmaps that exit a radiation
projector 451 such as a spatial light modulator (SLM), an LED array
or other device capable of projecting zero-, one-, two- or
three-dimensional radiation. The SLM is controlled by a 3D data
stream or control signal 435. The data stream 435 comprises a time
division multiplexed set of hogel vectors.
[0056] First, a database of ray origins and trajectories is
created. That is, the output of each hogel can correspond to the
images taken by a set of cameras arranged on a line, or can be
inferred by backwards ray-tracing from each element of a 3D
scene.
[0057] See FIG. 12. Once the image database has been created, a
data stream 435 activates a 2D SLM 451, such as a ferroelectric
liquid crystal display (FELCD) or microelectromechanical system
(MEMS) device such as the Texas Instruments Digital Micromirror
Device.TM.. Digital (or "deformable") Mirror Device is a trade name
of a MEMS-based microdisplay manufactured by Texas Instruments,
Inc. A typical DMD is an array of 1024.times.768 13.7 um mirrors
that are electronically addressable. Each mirror is in an "on" or
"off" state, tilting 10-12 degrees. For a point source image 2
located in front of the image plane, we illustrate the activation
sequence in time for a single line C of the 2D SLM. In the first
time slot, t.sub.0, SLM pixel i is activated, so that after beam
steering occurs (described below), a ray of light will pass from
pixel i through point source 2. In a subsequent time slot, t.sub.1,
SLM pixel i+2 is activated such that light passes in a direction
normal to the hologram plane. In time slot, t.sub.2, SLM pixel i+4
is activated such that light exiting it will be steered by a
steering component in a direction that again intersects point
source 2.
[0058] The beam steering is performed by a diffractive optical
element (DOE) which may be linear (rectangular) or circular. A
typical DOE for this purpose is the spinning-disc diffractive
optical element illustrated in FIG. 9. The DOE 455 includes the
basis fringes and is etched with a diffraction grating that varies
according to Equation 1:
f=A sin(theta)+B, (1)
[0059] where f is the spatial frequency of the diffraction grating,
A is a scaling factor that determines the ratio of maximum to
minimum diffraction grating frequencies 465 and 454, theta is an
angular dimension and B is an offset which may be considered to be
an angular carrier frequency. The purpose of the disc-shaped DOE
455 is that it causes incident light, such as a laser beam 450, to
sweep back-and-forth through a variety of exit angles if the DOE is
rotated about the axis that is normal to the plane of the DOE and
intersects the center of the DOE. The rotation of the DOE thus
provides for a time varying property in the DOE. The coefficients A
and B are chosen such that visible light is able to make a maximum
excursion of 30.degree. from the angle of incidence. Here theta is
a rotational angle measured from a reference angle in the plane of
the DOE.
[0060] FIG. 9A shows a schematic DOE 455 with angularly increasing
and decreasing diffraction grating frequencies. The top view (FIG.
9C) shows how the first order diffraction of incident illumination
450 is steered to a trajectory 456 by DOE region 454. It also
illustrates how DOE region 460 steers illumination 450 in direction
461, and likewise DOE region 465 steers the illumination 450 to
direction 466. Therefore, when the DOE 455 is spun or rotated about
the direction normal to the plane of the DOE, incident light will
be scanned in a back-and-forth manner. FIG. 9B shows a schematic
DOE 455 with rectilinearly increasing and decreasing diffraction
grating frequencies. Therefore, when the DOE 455 is moved back and
forth in the "y" direction in the plane of the DOE 455, incident
light will be scanned in a back-and-forth or time varying
manner.
[0061] The DOE 455 allows spectral multiplexing to occur. The DOE
455 acts as the optical equivalent to a lookup table, a device
which is typically used in computer programs or electronics in
order to speed up calculation. Here, an optical device (the DOE) is
encoded with a set of fringes that can be optically addressed when
needed. This is better than other techniques (described earlier) in
which the illumination source is modulated to create diffraction
patterns, wasting resolution. In our case, we modulate the
illumination source to address diffraction patterns. The
diffraction patterns (the optical lookup table) can take any of a
number of forms. It can be previously encoded on a DOE, or can be a
predictable set of inputs to an AOM, or can be a galvanometric
mirror sweeping back and forth.
[0062] Please see FIG. 13. A laser provides illumination 450 to
beam-expansion optics that illuminate the 2D SLM 451. As discussed,
the SLM 451 is addressed to activate the time series of pixels that
correspond to the desired database of beam origins and
trajectories. The SLM modulates the illumination 450 which is
steered by rotating DOE 455. For a horizontal parallax only (HPO)
holographic video image, the DOE only steers the light in the
horizontal plane, as illustrated. Horizontal parallax only
describes 3D display systems that provide only horizontal motion
parallax. The steered beams are optionally magnified by
magnification optics 438 so that the SLM is imaged onto a vertical
diffuser 439 which is typically positioned at the hologram plane
440. The vertical diffuser permits an observer to move his head
vertically and still see the 3D image 20.
[0063] The system that generates the 3D light fields can be used to
serve purposes other than visual display. For example, it may be
desired to illuminate a moving target. Existing algorithms in the
field of computer vision are able to detect the three-dimensional
position of a target. One approach of illuminating the target would
be to use a spotlight under mechanical control, as directed by the
computer vision algorithm. However, it may be undesirable to have
large mechanical components, such as a set of two galvanometric
scanning mirrors. The system disclosed in this application can be
used to replace the spotlight's mechanical mirrors. Given the
target's location, an SLM will allow light to pass through the
regions of a DOE which result in steering the output beam to
illuminate the target. As the target moves, the SLM will again
couple the input illumination to the appropriate region of the DOE
to illuminate the target. For example, FIG. 12A and FIG. 12B can be
interpreted to be illuminating the point 2. As noted above,
beam-shaping elements are capable of focusing, as well. Also, as
noted elsewhere, the regions of the radiation-shaping element 455
can be diffractive (for beam steering, focusing,
wavelength-splitting, etc.) or operate chiefly under geometrical
optics (as macroscopic mirrors, lenses, diffusers, etc.). Rather
than imposing a set of diffraction gratings on element 455, the
element can contain a series of lenslets with varying focal
planes.
[0064] Therefore, the system disclosed here can also be used as a
varifocal projector. Assume the radiation-shaping element 455
contains a series of lenslets with different focal lengths. For
example, it is able to focus 2D imagery onto a surface whose
distance varies with time. This might be useful as an office
projector that is self-focusing. After well-known circuitry detects
the distance of a projection screen, a 2D SLM projects a 2D image
through the radiation-shaping element at only those times in which
the appropriate lenslet is in the beam path from the SLM to the
projection screen.
[0065] As seen in FIG. 14, the data base of FIG. 13 which may
reside in a personal computer (PC) or server, may be in
communication with a network 500 such as a distributed computer or
communications network, such as a local area network (LAN) or a
wide area network (WAN), a global network (e.g. the Internet) or an
intranet 502. The computer network 500 includes at least one
personal computer 412 or display device connected to a server from
remote geographical locations by wired or wireless connections, by
radio based communications, by telephony based communications, or
by other network-based communications. The computer 412 or display
device may also be connected directly to other like computers or
display devices. The computer 412 is in turn similarly connected to
other computers 412, display devices or networks through the
Internet 502. The computers 412, display devices and other
electronic media devices of the networks may be configured to
execute computer program software, that allows them to send,
receive, record, store and process commands or algorithms between
and amongst themselves via the networks and the Internet 502 to
read and process the data stored in the data base 435. Such
processing of the commands or algorithms includes, for example,
various types of encryption, decryption, image compression and
decompression algorithms, as well as other types of filtering,
contrast enhancement, image sharpening, noise removal and
correlation for image classification.
[0066] Other DOE patterns are possible to optimize, for example,
resolution in a particular zone, or the range of viewing angles.
The diffraction frequency of a disc-shaped DOE is mapped directly
to its rotational angle. The DOE can alternatively incorporate a
different scanning function than sin theta; can include a focusing
or diffusing capability; or can utilize a scan angle that is a
function of both radius and angle, which may reduce the perception
of image flicker. The DOE or scanning element can contain vertical
or horizontal diffusing capability. It is usually desirable to
incorporate some horizontal diffusion into the DOE so that the
viewer sees a continuous transition between view zones (beam
trajectories.) The optical-lookup table can be implemented by a
scanning mirror, AOM with periodic input, or other elements. Color
imagery may be created by using colored illumination, such as red,
green, and blue components from a standard projector engine.
Dispersion compensation can be performed computationally.
Furthermore, animated imagery can be created by software.
[0067] For the purposes of this document, "radiation-shaping" or
"radiation conditioning" and "light-shaping" or "light
conditioning" should be defined to include radiation--(and thus
light-) shaping, steering, profile-shaping, focusing, diffusion,
and all other types of modulating radiation.
[0068] Any reference to first, second, etc., or front or back,
right or left, top or bottom, upper or lower, horizontal or
vertical, or any other phrase indicating the relative position of
one object, quantity or variable with respect to another is, unless
otherwise noted, intended for the convenience of description, and
does not limit the present invention or its components to any one
positional, spatial or temporal orientation. All dimensions of the
components in the attached Figures can vary with a potential design
and the intended use of an embodiment without departing from the
scope of the invention.
[0069] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this disclosure belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice or testing of the
present disclosure, suitable methods and materials are described
below. All publications, patent applications, patents, and other
references mentioned herein are incorporated by reference thereto
in their entirety. In case of conflict, the present specification,
including definitions, will control. In addition, the materials,
methods, and examples are illustrative only and not intended to be
limiting.
[0070] While the invention has been described with reference to
several embodiments thereof, it will be understood by those skilled
in the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiments disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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