U.S. patent application number 14/092769 was filed with the patent office on 2014-03-27 for method and device for 3-d display based on random constructive interference.
The applicant listed for this patent is Zhiyang Li. Invention is credited to Zhiyang Li.
Application Number | 20140085427 14/092769 |
Document ID | / |
Family ID | 39858399 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140085427 |
Kind Code |
A1 |
Li; Zhiyang |
March 27, 2014 |
Method and Device for 3-D Display Based on Random Constructive
Interference
Abstract
The present invention relates to a method and an apparatus for
3-D display based on random constructive interference. It produces
a number of discrete secondary light sources by using an
amplitude-phase-modulator-array, which helps to create 3-D images
by means of constructive interference. Next it employs a
random-secondary-light-source-generator-array to shift the position
of each secondary light source to a random place, eliminating
multiple images due to high order diffraction. It could be
constructed with low resolution liquid crystal screens to realize
large size real-time color 3-D display, which could widely be
applied to 3-D computer or TV screens, 3-D human-machine
interaction, machine vision, and so on.
Inventors: |
Li; Zhiyang; (Wuhan City,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Li; Zhiyang |
Wuhan City |
|
CN |
|
|
Family ID: |
39858399 |
Appl. No.: |
14/092769 |
Filed: |
November 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12865809 |
Aug 2, 2010 |
8624961 |
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PCT/CN2009/000112 |
Jan 23, 2009 |
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14092769 |
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Current U.S.
Class: |
348/46 |
Current CPC
Class: |
G03H 2225/60 20130101;
G03H 2223/19 20130101; H04N 13/32 20180501; G03H 1/2249 20130101;
G03H 1/2205 20130101; G03H 2210/30 20130101; G03H 2240/13 20130101;
G02B 30/25 20200101; G03H 2223/12 20130101; G03H 1/2294 20130101;
H04N 13/207 20180501; G03H 1/0808 20130101; G03H 2210/452 20130101;
H04N 13/189 20180501; G03B 35/24 20130101; H04N 13/239 20180501;
H04N 13/363 20180501 |
Class at
Publication: |
348/46 |
International
Class: |
H04N 13/04 20060101
H04N013/04; H04N 13/02 20060101 H04N013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2008 |
CN |
200810046861.8 |
Claims
1. A method for 3-D photography performed by a processor employing
a 3-D display method based on random constructive interference,
comprising following steps: A: Following the 3-D display method
based on random constructive interference, generate voxels in 3-D
space using a coherent point light source array in which the
positions of point light sources are of a uniform random
distribution; B: Read in an image from a conventional camera
focused on position of the voxels generated in step A; C: Repeat
step A through step B so that the voxels generated in step A scan
through a 3-D space, meanwhile analyze the images read in step B;
record positions of the voxels as local 3-D coordinates of a
surface when voxels' image sizes become minima; meanwhile record
colors and brightness of the image as colors and brightness of the
surface of an object.
2. The method of claim 1, where in step C: record positions of the
voxels as local 3-D coordinates of a surface when voxels' image
sizes become minima; meanwhile turn off the voxels generated in
step A, read in another image from the conventional camera and take
colors and brightness of the image as colors and brightness of the
surface of an object.
3. A method for 3-D human machine interaction performed by a
processor employing a 3-D display method based on random
constructive interference, comprising following steps: A: Following
the 3-D display method based on random constructive interference,
generate voxels in the air using a coherent point light source
array in which the positions of point light sources are of a
uniform random distribution; said voxels form up a number of
control elements in the air. B: Read in an image from a
conventional camera focused on the position of the voxels generated
in step A; C: Repeat step A through step B, meanwhile analyze the
images read in step B; when some voxels' image sizes become minima
issue a massage indicating a control element represented by the
voxels whose image sizes become minima is being touched.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/865,809, filed on Aug. 2, 2010, entitled "Method and Devices
for 3-D Display Based on Random Constructive Interference," which
is a filing under 35 U.S.C. 371 of International Application No.
PCT/CN2009/000112 filed Jan. 23, 2009, entitled "Three-Dimensional
Displaying Method and Apparatus Based on Random Constructive
Interference," which claims priority to Chinese Application No.
200810046861.8 filed on Feb. 3, 2008, which these applications are
incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to methods and apparatuses for
3-D display and 3-D photography based on random constructive
interference. The invention could be used as computer or TV
screens, for intelligent human-machine interaction and machine
vision etc., in such field as education, scientific research,
entertainment, advertisement and so on.
BACKGROUND OF THE PRESENT DISCLOSURE
[0003] Large size real-time 3-D display with wide viewing angle has
long been dreamed of. We may classify existing 3-D display
techniques roughly into two classes, pseudo 3-D display and true
3-D display. In pseudo 3D-display various means are employed to
present respectively to two eyes of an observer two pictures being
taken at slightly different angles. The observer combines the two
pictures and forms a virtual 3-D image in his/her mind. In true 3-D
display a real 3-D image is created in space, like what happens in
holographic display. To watch pseudo 3-D display one has to wear
some kind of auxiliary apparatuses like polarization spectacles, or
the eye position of an observer has to be tracked, limiting the
number of observers to one or a few more. For true 3-D display
observers need not wear any auxiliary apparatus and could watch a
displayed 3-D image conveniently as if they watch a real
object.
[0004] For the past decades with the development of liquid crystal
display (LCD), people tried to replace hologram plates with liquid
crystal panels and succeed in real-time holographic 3-D display for
very small objects. However even for projection type liquid crystal
panels the pixel pitch is usually more than ten micrometers, in
other words the space resolution is less than one hundred line
pairs per millimeter, which is nearly two orders lower than that of
a hologram plate. Therefore the holographic 3-D images generated so
far by using projection type liquid crystal panels were as small as
one centimeter so that very low density interference patterns were
involved. At the same time the created holographic 3-D images were
far away from the liquid crystal panels, yielding a very narrow
viewing angle.
[0005] For conventional liquid crystal computer screens the pixel
pitches increase to about 0.29 mm, which means the resolutions are
only several line pairs per millimeter. It is impossible to
generate 3-D holographic images with such low resolution liquid
crystal screens. In addition to produce a large size holographic
3-D image with wide viewing angle large space-bandwidth product is
necessary. At present, liquid crystal panels could only provide a
space-bandwidth product around 10.sup.6, several orders lower than
what is necessary. To make things worse with the increase of
space-bandwidth product huge data becomes inevitable, which puts a
great burden on real time data processing.
SUMMARY OF THE PRESENT INVENTION
[0006] The first aim of the present invention is to provide a
method based on random constructive interference for fast and
stable large size 3-D display using two-dimensional display devices
with low resolution and relatively low space-bandwidth product. The
second aim of the present invention is to provide a method for 3-D
photography which is capable of measuring and recording 3-D
positions and color information of real objects, and is widely
applicable to human-machine interaction, machine vision, and so
on.
[0007] The third aim of the present invention is to provide an
apparatus for large size and wide viewing angle real-time color 3-D
display for computer and TV screens, which could make use of
existing LCD technique and could shift between 3-D and 2-D display
easily.
[0008] For these purposes the present invention provided following
solutions.
[0009] A 3-D display method based on random constructive
interference comprising following steps:
[0010] A: Decompose a 3-D image into discrete pixels;
[0011] B: Pick one of the pixels;
[0012] C: Select randomly coherent secondary light sources from a
coherent secondary light source array in which the positions of the
secondary light sources are of a uniform random distribution, the
number of randomly selected secondary light sources being
proportional to the intensity of the pixel picked up in step B;
[0013] D: For each coherent secondary light source selected in step
C calculate its distance to the pixel picked up in step B and the
related phase difference, and take the phase difference as the
phase adjustment that should be performed by the coherent secondary
light source to generate the said pixel;
[0014] E: For each coherent secondary light source selected in step
C set the amplitude adjustment it should make to generate the pixel
picked up in step B as a constant or proportional to the intensity
of the pixel;
[0015] F: For each discrete pixel obtained in step A, repeat step B
through step E, record the amplitude and phase adjustment that
should be made by each coherent secondary light source for each
discrete pixel; for each coherent secondary light source, in way of
complex-amplitude addition, sum up all the recorded amplitude and
phase adjustment it should make to generate the said pixels, and
take the amplitude and phase of resulting complex amplitude as the
total amplitude and phase adjustment it should make;
[0016] G: For each coherent secondary light source calculate its
final phase adjustment by subtracting its primary phase from the
total phase adjustment determined in step F and use the total
amplitude adjustment determined in step F as its final amplitude
adjustment; let each coherent secondary light source with random
position distribution produce the final phase and amplitude
adjustment.
[0017] A method for 3-D photography based on random constructive
interference, comprising following steps:
[0018] A: Following the 3-D display method based on random
constructive interference, generate light spots in 3-D space using
a coherent secondary light source array in which the positions of
secondary light sources are of a uniform random distribution.
[0019] B: Focus a conventional camera on the position of the light
spots generated in step A and record an image;
[0020] C: Repeat step A through step B so that the light spots
generated in step A scan through a 3-D space, meanwhile analyze the
images taken in step B; the positions of the light spots represent
the local 3-D coordinates of the surface when their image sizes
become minima; meanwhile the color and brightness of the surface of
the object being the same as recorded by the conventional
camera.
[0021] A 3-D display device based on random constructive
interference comprising: a coherent light source that emits
coherent light; an illuminating optic system disposed to receive
the coherent light and emit an expand coherent light beam; an
amplitude-phase-modulator-array disposed to receive the expand
coherent light beam and to produce a secondary light source array;
a random-secondary-light-source-generator-array disposed and
aligned with the amplitude-phase-modulator-array so that one
random-secondary-light-source-generator receives the light from one
amplitude-phase-modulator in the amplitude-phase-modulator-array
and creates a new coherent secondary light source array in which
the positions of the secondary light sources are of a uniform
random distribution.
[0022] The said amplitude-phase-modulator-array comprising: the
first polarizer disposed to receive the expanded light beam from
illuminating optic system and to emit a polarized light beam; the
first beam splitter disposed to receive the polarized light beam
and to split it into two equal light beams; two reflectors disposed
to receive the two equal light beams and reflect them normally onto
two transmission liquid crystal panels respectively; two
transmission liquid crystal panels together with the second beam
splitter disposed to form a Michelson interferometer with one
transmission liquid crystal panel placed at an angle of 45 degree
to the second beam splitter's half-reflect-half-transmit surface
and in mirror symmetry with another transmission liquid crystal
panel relative to the second beam splitter's
half-reflect-half-transmit surface; the second beam splitter
disposed to receive the light beams modulated by two transmission
liquid crystal panels and combine them to form an integrated light
beam; the second polarizer disposed in parallel with one of the two
liquid crystal panels to receive normally the integrated light beam
formed by the second beam splitter, the polarization directions of
the first and the second polarizer being arranged to set the two
transmission liquid crystal panels in phase-mostly mode; a
projection lens disposed to receive the polarized light emitted
from the second polarizer and form a magnified real image of the
two transmission liquid crystal panels.
[0023] The said random-secondary-light-source-generator-array being
disposed at the image plane of the liquid crystal panels generated
by the projection lens and comprising: a transparent scattering
screen or a reflective scattering screen or a micro-lens-array
disposed by or fabricated on a transparent plate covered with an
opaque film bearing transparent micro-holes whose positions are of
a uniform random distribution, the diameter of each micro-hole
being smaller than the size of the images of the pixels of the
liquid crystal panels, each micro-lens in the micro-lens-array
being aligned with each micro-hole on the opaque film so that the
optic axis of each micro-lens passes the center of the micro-hole
it aligned with.
[0024] The said illuminating optic system comprising: two convex
lenses with different focal lengths, the convex lens with smaller
focal length being disposed to receive the light, the convex lens
with larger focal length being disposed with its object focus at
the image focus of the convex lens with smaller focal length to
form a telescope and to emit an expanded light beam.
[0025] The said amplitude-phase-modulator-array comprising: the
first polarizer disposed to receive the expanded light beam from
illuminating optic system and to emit a polarized light beam; a
beam splitter disposed to receive the polarized light beam and to
split it into two equal light beams; two reflective liquid crystal
panels or liquid crystal light valves disposed to receive normally
the two equal light beams respectively and reflect them back, the
reflective liquid crystal panels or liquid crystal light valves
together with the beam splitter disposed to form a reflective
Michelson interferometer with one reflective liquid crystal panel
or one liquid crystal light valve placed at an angle of 45 degree
to the beam splitter's half-reflect-half-transmit surface and in
mirror symmetry with another reflective liquid crystal panel or
liquid crystal light valve relative to the beam splitter's
half-reflect-half-transmit surface, the beam splitter being
disposed also to receive the light beams modulated by the
reflective liquid crystal panels or liquid crystal light valves and
combine them to form an integrated light beam; the second polarizer
disposed in parallel with one of the two reflective liquid crystal
panels or liquid crystal light valves to receive normally the
integrated light beam formed by the beam splitter, the polarization
directions of the first and the second polarizer being arranged to
set two reflective liquid crystal panels or liquid crystal light
valves in phase-mostly mode; an projection lens disposed to receive
the polarized light emitted from the second polarizer and form a
magnified real image of two reflective liquid crystal panels or
liquid crystal light valves; two digital-mirror-devices disposed
behind two liquid crystal light valves to project two optic images
onto the back of two liquid crystal light valves respectively, the
optic image projected onto the back of one liquid crystal light
valve being in mirror symmetry with the optic image projected onto
the back of another liquid crystal light valve relative to the beam
splitter's half-reflect-half-transmit surface.
[0026] The said amplitude-phase-modulator-array comprising: a beam
splitter disposed to receive the expanded light beam from
illuminating optic system and to split it into two equal light
beams; two optically-addressed-electro-optic-phase-modulators
disposed to receive normally the two equal light beams with their
electro-optic material films and reflect them back, two
optically-addressed-electro-optic-phase-modulators together with
the beam splitter disposed to form a reflective Michelson
interferometer with one
optically-addressed-electro-optic-phase-modulator placed at an
angle of 45 degree to the beam splitter's
half-reflect-half-transmit surface and in mirror symmetry with
another optically-addressed-electro-optic-phase-modulator relative
to the beam splitter's half-reflect-half-transmit surface, the beam
splitter being disposed also to combine the light beams reflected
and modulated by two
optically-addressed-electro-optic-phase-modulators to form an
integrated light beam; an optic lens disposed to receive the
integrated light beam and form a magnified real image of two
optically-addressed-electro-optic-phase-modulators; two
digital-mirror-devices disposed behind two
optically-addressed-electro-optic-phase-modulators to project two
optic images onto the optic-sensitive films on the back of two
optically-addressed-electro-optic-phase-modulators respectively,
the optic image projected onto the back of one
optically-addressed-electro-optic-phase-modulator being in mirror
symmetry with the optic image projected onto the back of another
optically-addressed-electro-optic-phase-modulator relative to the
beam splitter's half-reflect-half-transmit surface.
[0027] The said optically-addressed-electro-optic-phase-modulator
comprising: the first film of optic-sensitive material, the second
film of opaque material, the third reflective film and the forth
film of electro-optic material, all of them being sandwiched
between two transparent conductive glasses in the given order.
[0028] The said random-secondary-light-source-generator-array
comprising: two identical opaque plates bearing transparent
micro-holes whose positions are of a uniform random distribution
disposed at the object plane of the projection lens, one opaque
plate being placed at an angle of 45 degree to the beam splitter's
half-reflect-half-transmit surface and in mirror symmetry with
another opaque plate relative to the beam splitter's
half-reflect-half-transmit surface.
[0029] The said amplitude-phase-modulator-array comprising: the
first polarizer; the first transmission liquid crystal panel
disposed by the first polarizer; the second polarizer disposed by
the first transmission liquid crystal panel; the second
transmission liquid crystal panel disposed by the second polarizer;
the third polarizer disposed by the second transmission liquid
crystal panel, the pixels on the first transmission liquid crystal
panel being aligned with the pixels on the second transmission
liquid crystal panel, the polarization directions of the three
polarizer being arranged to set one transmission liquid crystal
panel in phase-mostly mode and another transmission liquid crystal
panel in amplitude-mostly mode.
[0030] Position of pixels on the said two transmitted or reflective
liquid crystal panels are of an identical uniform random
distribution.
[0031] The said random-secondary-light-source-generator-array
comprising: the first micro-lens-array on which the micro-lens are
of a periodical distribution; the second micro-lens-array on which
the micro-lens are of a uniform random distribution being disposed
in parallel with the first micro-lens-array and aligned with the
first micro-lens-array so that the focused light emitted from each
micro-lens of the first micro-lens-array illuminates one micro-lens
of the second micro-lens-array and the image focus of each
micro-lens of the first micro-lens-array falls within one focal
length of one micro-lens of the second micro-lens-array.
[0032] The said random-secondary-light-source-generator-array
comprising: a bundle of optically isolated single-mode fibers
fabricated so that the single-mode fibers within the bundle are
glue together and polished at the first end and the spaces between
adjacent single-mode fibers are of a random distribution at the
second end; a micro-lens-array disposed to focus the light into the
cores of the single-mode fibers within the bundle at the first end,
one micro-lens in the micro-lens-array being aligned with one
single-mode fiber.
[0033] The present invention is based on the following two facts.
Firstly, a light spot, or a 3-D pixel, could be generated in free
space by constructive interference of a number of coherent discrete
secondary light sources. Lots of 3-D pixels make up a 3-D image.
Secondly, if the positions of above coherent discrete secondary
light sources are randomly located, high order diffraction could be
greatly depressed so that only one 3-D image is created. Detailed
explanation is given as follows.
[0034] Suppose N discrete secondary light sources are fixed on the
X-Y plane, whose amplitude and phases are adjustable. For
convenience of analysis, we further suppose the discrete secondary
light sources are point light sources. They emit spherical light
waves polarized along Y axis. Then the complex amplitude of the
optic field at any position r.sub.m is a summation of the N
spherical waves emitted by these N secondary point light sources
and the resulting electric field component along Y axis could be
described as,
U ( r m ) = j = 1 j = N A 0 j A c j , m cos ( .theta. j , m ) exp [
( .PHI. cj , m + .PHI. 0 j ) ] r m - R j exp [ - k j , m .cndot. (
r m - R j ) ] ( 1 ) ##EQU00001##
where vector R.sub.j, j=1, 2, . . . N stands for the coordinates of
N secondary point light sources, k.sub.j,m for the wave vector of
the light emitted from the j.sup.th secondary point light source
towards r.sub.m, .theta..sub.j,m for the angle between Y axis and
the electric component of the light field emitted from the j.sup.th
secondary point light source towards r.sub.m,
.theta..sub.j,m<90.degree., A.sub.0j and .PHI..sub.0j for
primary amplitude and phase of the j.sup.th secondary light source
respectively. A.sub.0j depends on the intensity of j.sup.th
secondary point light source and is also a function of direction.
A.sub.cj,m and .PHI..sub.cj,m stand for additional amplitude and
phase adjustment made by the j.sup.th secondary light source under
electrical control. Both A.sub.0j and A.sub.cj,m are positive. To
ensure constructive interference at position r.sub.m it is
necessary to digitally set the phase .PHI..sub.cj,m of each
secondary point light source so that,
.PHI..sub.cj,m+.PHI..sub.0j-k.sub.j,m(r.sub.m-R.sub.j)=2n.pi.
(2)
Where n is an integer. When Eq. (2) is satisfied, Eq. (1)
becomes,
U ( r m ) = j = 1 j = N A 0 j A cj , m cos ( .theta. j , m ) r m -
R j ( 3 ) ##EQU00002##
[0035] Therefore the light field at position r.sub.m reaches a
maximum, creating a light spot, or a 3-D pixel, in free space. The
larger the number N is, the brighter and sharper the 3-D pixel is.
Away from the position of r.sub.m, the intensity of the light field
decreases dramatically.
[0036] From Eq. (3) it could be seen that the intensities of the
generated 3-D pixels depend on both the number N and the amplitude
A.sub.cj,m of the secondary point light sources. When both N and
A.sub.cj,m keep constant, according to Eq. (3), the intensity of a
3-D pixel is roughly in inverse proportion to the square of
|r.sub.m-R.sub.j|. That means the larger the distance
|r.sub.m-R.sub.j| of the generated 3-D pixel from secondary point
light sources is, the lower the intensity is. Since an observer
stands at opposite side and faces the secondary point light
sources, above fact implies that the closer the generated 3-D pixel
towards the observer, the lower its intensity. However it should be
noticed that the intensity calculated by Eq. (3) does not precisely
represent the brightness of the generated 3-D pixel seen by the
observer since not all the light emitted by N secondary point light
sources could come into the eyes of an observer. To estimate how
many lights could enter the eye of an observer, we may draw a cone
taking observer's pupil as the bottom and the 3-D pixel as the apex
and stretch the cone in opposite direction towards the secondary
point light sources. It is easy to see that only the light emitted
by the secondary light sources located within the cone could reach
the pupil of the observer and contribute to the brightness of the
3-D pixel. Suppose the distance between the generated 3-D pixel and
the observer is d, it could be find from their geometrical relation
that the number N.sub.eff of the secondary point light sources
located within the cone is in inverse proportion to the square of d
and in proportion to the square of |r.sub.m-R.sub.j|. Replace N
with N.sub.eff in Eq. (3), one could find that now the brightness
of the generated 3-D pixel seen by the observer is roughly in
inverse proportion to the square of d. In other words, the closer
the 3-D pixel towards the observer, the brighter it appeared to the
observer, which is in good agreement with our common sense.
Furthermore, A.sub.cj,m could be adjusted to compensate for the
influence of the primary amplitude A.sub.0j and the angle
.theta..sub.j,m on the intensity of the generated 3-D pixel, so
that it appears with the same intensity when looked from different
angle.
[0037] It could be seem from Eq. (1) that such a 3-D display system
is a linear system. Therefore a number of 3-D pixels could be
created in free space to form a discrete 3-D image. Following above
method we may indeed carry out 3-D display by utilizing each pixel
of a 2-D liquid crystal screen as a discrete secondary light
source. However there exists a serious problem. Along the
directions of .+-.1, .+-.2 . . . order diffractions, multiple
images would be generated at the same time due to periodical
arrangement of the pixels. Near the screen these images overlap
with each other, decreasing the image quality. Away from the screen
the images make a small angle with the screen yielding a very
narrow viewing angle, although they are separated from each
other.
[0038] To avoid the creation of multiple images, present invention
let the discrete secondary light sources locate at random
positions. The images at .+-.1, .+-.2 . . . order diffraction
directions disappear due to the loss of the periodicity of the
positions of the secondary light sources and only one 3-D image is
formed. Near the screen the image makes a very large angle with the
screen yielding a very wide viewing angle.
[0039] When coherent secondary point light sources with random
distribution are employed, it could be revealed using Eq. (1) that
a single 3-D pixel might be created at position r.sub.m. If a total
of M discrete 3-D pixels need be created, denote the amplitude and
phase adjustment made by the j.sup.th secondary light point source
to create the m.sup.th 3-D pixel as A.sub.cj,m and .PHI..sub.cj,m,
the total complex amplitude adjustment that should be carried out
by j.sup.th secondary light source should be,
A j = m = 1 m = M A cj , m exp ( .PHI. cj , m ) ( 4 )
##EQU00003##
[0040] According to Eq. (1-4), Eq. (1) reaches maxima when and only
when r=r.sub.m, m=1, 2, . . . M, since at these locations Eq. (2)
is satisfied. All the 3-D pixels generated as such make up a 3-D
image.
[0041] From the simulation based on Eq. (1), (2) and (4) it was
found that multiple 3-D images were indeed inevitable when periodic
secondary light sources were used. However, when the secondary
point light sources shift randomly within a certain range around
their initial periodic positions, high order diffraction images
disappear gradually as the range of shift becomes large. When the
range of shift reaches 90% of the initial period high order
diffraction images disappear completely and only a zero order 3-D
image remains. For uniform random distribution a secondary light
source has the same probability to locate at any position and the
periodicity could be destroyed completely. Other type of random
distribution could also be adopted if high order diffraction images
could be depressed.
[0042] In above analyses the secondary light sources are assumed to
be point light sources. For secondary light sources with a certain
size the same conclusion could be reached although the calculation
becomes more complicated since the contribution of each secondary
light source need be calculated by integration. It is also worth to
point out that above 3-D display method is very robust. For
example, if a small fraction of secondary light sources go wrong,
the intensity of generated 3-D pixels would change only slightly.
This is due to the fact that each 3-D pixel being a result of
constructive interference of hundreds and thousands of secondary
light sources. If Eq. (2) was not strictly satisfied, that is, the
phase difference between two light waves arriving at a given
position was not exactly multiple of 2.pi., but with an error less
than .pi./2, the intensity of resulting light field still become
larger than individual light field. Of course the maxima are
reached only when Eq. (2) is strictly satisfied. In a word, the
intensity of created 3-D pixels might change slightly due to a
small decrease of the number of secondary light sources, or small
errors in carrying out phase and amplitude adjustment. However the
position and the number of pixels of created 3-D images would not
change. In contrast when a pixel in a 2-D screen goes wrong it
become inaccessible forever, making the displayed scene
incomplete.
[0043] A 3-D display device based on above principle comprises
mainly four components, namely, an amplitude-phase-modulator-array,
a random-secondary-light-source-generator-array, a coherent light
source and an illuminating optic system. Detailed description is
given below.
[0044] The amplitude-phase-modulator-array is responsible for
producing discrete secondary light sources and carrying out
independent amplitude and phase modulation for each secondary light
source. An amplitude-phase-modulator-array might be constructed
using liquid crystal panels. Each pixel of a liquid crystal panel
acts as a secondary light source. It is known that for a single SN
or other type liquid crystal panel, the amplitude adjustment and
phase adjustment are usually correlated with each other. However,
if the polarizer on its two sides are set to proper polarization
directions a single liquid crystal panel might work in phase-mostly
mode or amplitude-mostly mode. Based on this fact, simultaneous
independent amplitude and phase modulation might be performed by a
combination of two liquid crystal panels. One way to combine two
liquid crystal panels is to place them in an order so that the
illuminating light passing them in sequence. The total modulation
is a vector production of the modulations made by each liquid
crystal panel. Another way to combine two liquid crystal panels is
to place them on the two arms of a Michelson interferometer so that
the illuminating light passing them respectively and then combine
together. The total modulation is a vector addition of the
modulations made by each liquid crystal panel. Which way should be
adopted depends on what type and what size of liquid crystal panels
are used. Besides liquid crystal panels, there are also other
devices to create discrete secondary light sources. For example,
optically-addressed-electro-optic-phase-modulators proposed by
present invention might be utilized for the purpose.
[0045] The random-secondary-light-source-generator-array is
responsible for transforming the discrete secondary light sources
produced by amplitude-phase-modulator-array into new secondary
light sources whose positions are of a random distribution. There
are various ways to create randomly located secondary light
sources. A direct way is to randomly arrange the pixels when
designing a liquid crystal panel. In this case, no additional
random-secondary-light-source-generator-array is necessary, or the
liquid crystal panel itself is a combination of an
amplitude-phase-modulator-array and a
random-secondary-light-source-generator-array. For existing
commercial liquid crystal panels, additional
random-secondary-light-source-generator-arrays have to be employed
since their pixels are periodically arranged. A
random-secondary-light-source-generator-array may be built with an
opaque plate bearing a number of transparent holes whose positions
are randomly located, or with a micro-lens-array in which the
positions of the micro-lenses are randomly located, or with a
micro-prism array in which the directions of the micro-prisms are
randomly arranged, or a combination of them. A
random-secondary-light-source-generator-array may also be built in
other ways, for example by means of a bundle of fibers as proposed
by present invention.
[0046] As a coherent imaging system, a 3-D display device based on
random constructive interference needs a coherent laser, whose
coherent length should be larger than the possible maximum optic
path difference between any two secondary light sources to any 3-D
pixel. The brightness and contrast of a 3-D image depends on the
power of the laser. In order to display color 3-D images, lasers
with different wavelengths should also be employed. When black and
white liquid crystal panels are used, lasers for basic colors may
be turned on and off in sequence to display color 3-D images based
on persistence of vision. When color liquid crystal panels are
used, all the basic colors may be turned on at the same time.
Pixels covered with different color filters perform amplitude-phase
modulations for different wavelengths. Therefore all the basic
color images could be created at the same position and make up a
true 3-D color image. For 3-D measurement and human-machine
interaction, near infrared lasers might be used to avoid
disturbances to the observer. Since the diameter of a primary laser
beam is usually very small, an optic illuminating system is
necessary to expand the laser beam. An optic illuminating system
should also be thin and light for portable devices.
[0047] To improve the quality of 3-D images generated by above 3-D
display devices based on random constructive interference, some
auxiliary optic elements may be used. For example, a Fresnel lens
may be employed to magnify a 3-D image and separate the image away
from the bright secondary light sources to avoid the interference
of background light to the observer.
[0048] If above 3-D display device stops amplitude and phase
modulation following above random constructive interference
principle, and changes mainly the intensities of secondary light
sources by amplitude, 2-D images could then be displayed. In other
words, a 3-D image device based on random constructive interference
may shift freely between a 3-D display device and a 2-D display
device under the control of software.
[0049] With the aid of a conventional camera, above 3-D display
method could also be used to take 3-D images and carry out 3-D
measurements. To do so one may display an array of light spots or
lines in free space and let them scan in space repeatedly,
meanwhile monitor where the light spots or lines touch the surface
of an object with a conventional camera. The pre-known positions of
the light spots or lines help to determine the coordinates of the
surface of an object. Furthermore the moving direction and speed of
the object could be calculated. Similarly, if we display a 3-D
button in space and monitor when a finger touches the button, 3-D
human machine interaction could be performed.
[0050] Present invention has following advantages compared with
existing techniques:
[0051] Firstly, true 3-D images are displayed in free space.
Observers may watch the image as if watching a real object without
bearing any auxiliary apparatus. There is no need to track the eye
position of an observer. Many observers may watch the image at the
same time and change their positions as they like. Secondly, large
size real-time color 3-D images could be created with wide viewing
angle. Thirdly, since it is based on a principle totally different
from traditional holography, no reference light is necessary and
there is also no need to record high density interference patterns.
As a result, it does not require dense secondary light sources and
existing LCD techniques could be used. Fourthly, it is very robust.
The intensity of created 3-D pixels might change slightly due to
small decrease of the number of secondary light sources, or small
errors in carrying out phase and amplitude adjustment. However, the
positions and the number of created 3-D pixels would not change.
Fifthly, it could easily shift between 2-D display and 3-D display
under the control of software without any hardware change. Sixthly,
it could carry out 3-D measurement and 3-D human machine
interaction when cooperated with a conventional camera.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is a schematic diagram of an embodiment of present
invention using two small-size TFT-ST projection type liquid
crystal panels.
[0053] FIG. 2 is a schematic diagram of an embodiment of
random-secondary-light-source-generator-array using an opaque plate
bearing holes whose positions are of a random distribution.
[0054] FIG. 3 is a schematic diagram of an embodiment of present
invention using two reflective liquid crystal panels.
[0055] FIG. 4 is a schematic diagram of an embodiment of present
invention using two liquid crystal light valves.
[0056] FIG. 5 is a schematic diagram of an embodiment of present
invention using two
optically-addressed-electro-optic-phase-modulators.
[0057] FIG. 6 is a schematic diagram of an
optically-addressed-electro-optic-phase-modulator.
[0058] FIG. 7 is a schematic diagram of an embodiment of present
invention using two large-size TFT-ST liquid crystal panels.
[0059] FIG. 8 is a schematic diagram of an embodiment of
random-secondary-light-source-generator-array using two
micro-lens-arrays.
[0060] FIG. 9 is a schematic diagram of an embodiment of
random-secondary-light-source-generator-array using a bundle of
single-mode fibers.
DETAILED DESCRIPTION
[0061] FIG. 1 is a schematic diagram of a 3-D display device based
on random constructive interference using two small-sized TFT-ST
projection type liquid crystal panels. It comprises an
amplitude-phase-modulator-array 1, a
random-secondary-light-source-generator-array 2, a coherent light
source 3 and an illuminating optic system 4. The
amplitude-phase-modulator-array comprises two transmission liquid
crystal panels 5,6, two polarizer 7, 8, two beam splitters 9, 10,
two reflectors 11,12 and a projection lens 13. Two beam splitters
9,10 and two reflectors 11,12 are disposed to form a Michelson
interferometer with two transmission liquid crystal panels 5,6
placed on the interferometer's two arms respectively. The first
transmission liquid crystal panels 5 seats at an angle of 45 degree
to half-reflect-half-transmit surface A1-A2 of the second beam
splitter 9 and in mirror symmetry with the second transmission
liquid crystal panel 6 relative to the second beam splitter 9's
half-reflect-half-transmit surface A1-A2. Both transmission liquid
crystal panels 5 and 6 are at a distance of one to two focal
lengths away from the projection lens 13. The first polarizer 7 is
placed at the entrance port of the Michelson interferometer to
receive light and in parallel with the second transmission liquid
crystal panel 6. The second polarizer 8 is placed at the exit port
of the Michelson interferometer and in parallel with the first
transmission liquid crystal panel 5. The polarization directions of
the first and the second polarizer 7,8 are arranged to set the two
transmission liquid crystal panels 5,6 in phase-mostly mode, to do
so the polarization direction of polarizer 7 is rotated at an angle
of 45 degree with the polarization direction of polarizer 8
(different polarization direction may be required for different
type of liquid crystal panels).
[0062] The illuminating optic system 4 comprises the first optic
lens 16 with smaller focal length disposed to receive the light;
the second optic lens 17 with larger focal length disposed with its
object focus at the image focus of the first optic lens 16 to form
a telescope and to emit an expanded light beam. If a compact
illuminating optic system is required, the first convex optic
lenses 16 may be replaced by a concave optic lens with its object
focus placed at the second optic lens 17's object focus. The
parallel laser beam emitted from coherent light source 3 is first
focused by the first optic lens 16 and transformed into parallel
laser beam again but with larger diameter by the second optic lens
17. The expanded laser beam penetrates normally the first polarizer
7 and gets split by the first beam splitter 10 into two equal
beams. After being reflected by two reflectors 11 and 12, the two
equal beams penetrate normally the two transmission liquid crystal
panels 5 and 6 respectively and get combined by the second beam
splitter 9 to form an integrated laser beam. The integrated laser
beam penetrates normally the second polarizer 8 and gets projected
by the projection lens 13. Since the pixels on both transmission
liquid crystal panels 5 and 6 are aligned accurately with each
other and within a range of one to two focal lengths from the
projection lens 13, they form enlarged real images on opaque plate
14, which bears quantities of transparent micro-holes. These
overlapped images produce a secondary light source array with
variable amplitude and phase in way of vector addition.
[0063] The random-secondary-light-source-generator-array 2 in FIG.
1 comprises a micro-lens-array 15 fabricated on an opaque plate 14
bearing transparent micro-holes that are of a uniform random
distribution. Each micro-lens in the micro-lens-array 15 is aligned
with each micro-hole on the opaque plate 14 so that the optic axis
of each micro-lens 15 passes the center of the micro-hole it
aligned with. As illustrated in FIG. 2, opaque plate 14 is made by
covering a transparent plate with an opaque film. The transparent
micro-holes are produced by etching through the opaque film, one
micro-hole for one pixel of the transmission liquid crystal panel 5
or 6. The diameter of each micro-hole is made smaller than the size
of the image of the pixels of the transmission liquid crystal
panels 5 or 6 (as illustrated by broken line) so that a micro-hole
could move around within a certain range. The smaller the diameter
of each micro-hole is, the larger the range of free movement and
the larger the optic energy loss. Although the pixels of
transmission liquid crystal panel 5 or 6 and their image on opaque
plate 14 are of a periodic distribution, the new secondary light
sources generated by micro-lens-array 15 are of a random
distribution. This is because the micro-holes on opaque plate 14
are of a random distribution. The advantage to form a coherent
secondary light source array by projection is that it may cover a
large area which is essential for creation of large size 3-D
images.
[0064] As could be seen in FIG. 1, there is an auxiliary optic
element, the Fresnel lens 19, placed in front opaque plate 14. Its
function is to transform divergent light into parallel light before
it's incidence on opaque plate 14. As a result the focused new
secondary light sources by micro-lens 15 emit symmetric divergent
light, providing a better 3-D image quality for observers seating
right before the device. Without Fresnel lens 19 the secondary
light sources would emit asymmetric divergent light, making the 3-D
image appears darker for observers seating right before the device
and brighter for observers seating at a large angle with the
device. Any way Fresnel lens 19 has a limited auxiliary function to
improve image quality. In addition, the entrance and exit surfaces
of beam splitter 9,10 and other related surfaces that may cause
reflection may be evaporated with a thin anti-reflection film to
depress the interference of reflected light.
[0065] Referring to the device illustrated in FIG. 1, the 3-D
display method based on random constructive interference put forth
by present invention may be carried out as follows. It comprises
seven steps:
[0066] A: Decompose a 3-D image 18 to be displayed into M discrete
pixels;
[0067] B: Pick up one pixel m from the pixels obtained in step
A;
[0068] C: Select randomly N coherent secondary light sources from a
coherent secondary light source array in which the positions of the
secondary light sources are of a uniform random distribution, the
number N depends on the intensity of the pixel m picked up in step
B; The higher the intensity is, the larger the number N is;
[0069] D: For each coherent secondary light source j selected in
step C, calculate its distance to the pixel m picked up in step B
and the related phase difference
.PHI..sub.cj,m=k.sub.j,m(r.sub.m-R.sub.j), and take the phase
difference .PHI..sub.cj,m as the phase adjustment that should be
performed by the coherent secondary light source j to generate the
said pixel m;
[0070] E: For each coherent secondary light source j selected in
step C, set the amplitude adjustment A.sub.cj,m it should be made
as a constant or proportional to the intensity of the pixel m
picked up in step B;
[0071] F: For all the M discrete pixels in step A, repeat step B
through step E, record the amplitude and phase adjustment
.PHI..sub.cj,m A.sub.cj,m, that should be made by each coherent
secondary light source j for each discrete pixel m; for each
coherent secondary light source j, in way of complex-amplitude
addition, sum up all the recorded amplitude A.sub.cj,m and phase
adjustment .PHI..sub.cj,m,
A j = m = 1 m = M A cj , m exp ( .PHI. cj , m ) = A cj exp ( .PHI.
cj ) ##EQU00004##
and take the amplitude and phase A.sub.cj, .PHI..sub.cj of
resulting complex amplitude as the total amplitude and phase
adjustment it should make.
[0072] G: For each coherent secondary light source j, calculate its
final phase adjustment by subtracting its primary phase
.PHI..sub.0j from the total phase adjustment .PHI..sub.cj
determined in step F. Of course multiples of 2.pi. phase adjustment
should be cut off. Meanwhile use the total amplitude adjustment
A.sub.cj determined in step F as its final amplitude adjustment. Or
divide the total amplitude adjustment A.sub.cj determined in step F
by the primary amplitude A.sub.0j of coherent secondary light
source j and multiply the result with a constant c.sub.1, then use
c.sub.1A.sub.cj/A.sub.0j as the final amplitude adjustment to
compensate for the primary amplitude A.sub.0j of coherent secondary
light source j so that the contribution of every secondary light
source become equal. Lastly drive the transmission liquid crystal
panels 5 and 6 to make each coherent secondary light source j
produce above final phase and amplitude adjustment.
[0073] According to the principle of coherent interference as
represented by Eq. (1-4), a primary 3-D image 18 might be created
following steps A through G. There is only one 3-D image 18
generated because the positions of secondary light sources are of a
random distribution.
[0074] In FIG. 1, suppose the transmission liquid crystal panels 5
and 6 each contains a total of 1920.times.1080 pixels and the
amplitude adjustment A.sub.cj,m=1 in step E for each secondary
light source in creation of one 3-D pixel. 3-D pixels with 256 gray
levels might be created by changing the number N of randomly
selected coherent secondary light sources in step C. Suppose we
chose N=400 for the darkest 3-D pixel. When N increases by 16 times
to reach N=6400, the intensity of the 3-D pixel would increase by
256 times. For average intensity we have N.apprxeq.4800. That means
roughly 1920.times.1080/4800=432 groups of pixels might be randomly
selected from a total of 920.times.1080 pixels. If transmission
liquid crystal panels 5,6 are driving with 8-bit D/As, or the
maximum gray level of each pixel, also maximum value of A.sub.cj,m
is 256, then each group of pixels could create about 256 3-D pixels
and a total of about 432.times.256 discrete 3-D pixels might be
generated. The absolute intensity of each 3-D pixel depends on the
power of the laser. Very bright 3-D images may be created using
high power lasers. From above estimation it could be seen that
10.sup.6 3-D pixels might be generated with a space
bandwidth-product of about 10.sup.7.about.10.sup.8.
[0075] To display an extremely large 3-D scene, several 3-D display
devices based on random constructive interference as illustrated in
FIG. 1 might be incorporated, each creating a small part of the
scene. The interfaces between each part might be made
indistinguishable since they are displayed in free space away from
the device.
[0076] In cooperation with a conventional camera, the device
illustrated in FIG. 1 might be employed to take 3-D images and
carry out 3-D measurement following the steps given below.
[0077] A: Following the 3-D display method based on random
constructive interference, display light spots in 3-D space using a
random coherent secondary light source array produced by a device
as illustrated in FIG. 1;
[0078] B: Focus a conventional camera at the position of the light
spots generated in step A and record an image;
[0079] C: Repeat step A through step B so that the light spots
generated in step A scan through a 3-D space, meanwhile analyze the
recorded images in step B; the positions of the light spots
represent the local 3-D coordinates of the surface when their image
sizes become minima; meanwhile the color and brightness of the
surface of the object being the same as recorded by the
conventional camera.
[0080] 3-D coordinates of the entire surface of an object could be
determined following above steps A-C. If large scan steps are
adopted in scanning 3-D space in step A, very fast 3-D measurement
speed might be achieved, while an high accuracy might be obtained
if very small scan steps are adopted. If large scan steps are
adopted away from the surface of an object and small scan steps are
adopted near the surface by using the known information from
previous scan, then both high accuracy and high speed could be
attained. Above real-time 3-D measurement method might widely be
applied to 3-D human-machine interaction and machine vision.
[0081] FIG. 3 is a schematic diagram of a 3-D display device based
on random constructive interference using two reflective liquid
crystal panels. It comprises an amplitude-phase-modulator-array 1,
a random-secondary-light-source-generator-array 2, a coherent light
source 3 and an illuminating optic system 4. The
amplitude-phase-modulator-array 1 comprises a splitter 9, two
polarizer 7, 8, a projection lens 13 and two reflective liquid
crystal panels, namely liquid crystal on silicon (LCOS) 20,21. Two
LCOS 20,21 together with the beam splitter 9 are disposed to form a
reflective Michelson interferometer with two LCOS 20,21 at its two
arms acting as the reflectors. The first reflective liquid crystal
panel 20 is placed at an angle of 45 degree to beam splitter 9's
half-reflect-half-transmit surface A1-A2 and in mirror symmetry
with the second reflective liquid crystal panel 21 relative to beam
splitter 9's half-reflect-half-transmit surface A1-A2. The device
illustrated in FIG. 3 works in a similar way as the device in FIG.
1. The first polarizer 7 is placed at the entrance port of the
reflective Michelson interferometer to receive light and in
parallel with the first reflective liquid crystal panel 20. The
second polarizer 8 is placed at the exit port of the reflective
Michelson interferometer and in parallel with the second reflective
liquid crystal panel 21. The polarization directions of the first
and the second polarizer 7,8 are arranged to set the two reflective
liquid crystal panel 20 and 21 in phase-mostly mode, to do so the
polarization direction of polarizer 7 is rotated at an angle of 45
degree with the polarization direction of polarizer 8 (different
polarization direction may be required for different type of
reflective liquid crystal panels). The expanded laser beam emitted
from illuminating optical system 4 penetrates normally the first
polarizer 7, becomes polarized laser beam and gets split by the
beam splitter 9 into two equal beams. The two equal beams incident
normally on the liquid crystal layers of the two reflective liquid
crystal panels 20 and 21 respectively. After reflection the two
equal beams get combined by the same beam splitter 9 to form an
integrated laser beam. The integrated laser beam penetrates
normally the second polarizer 8 and gets projected by the
projection lens 13. Since the pixels on both reflective liquid
crystal panels 20 and 21 are aligned accurately with each other and
within a range of one to two focal lengths from the projection lens
13, they form enlarged real images on opaque plate 14, which bears
quantities of transparent micro-holes. These overlapped images
produce a secondary light source array with variable amplitude and
phase in way of vector addition. Next the secondary light source
array is transformed into a new secondary light source array with
uniform random distribution by
random-secondary-light-source-generator-array 2, which is made up
with a transparent scattering screen 22 covered with an opaque
plate 14 bearing micro-holes of uniform random distribution. The
function of transparent scattering screen 22 is to make the light
emitted by secondary light sources diverge greatly so that each
discrete 3-D pixel is built up with lights coming from a wide range
of direction and therefore could be seen from a wide range of
direction, providing a wide viewing angle. The roughness of
scattering screen 22 should be controlled within a proper range so
that the phase difference of lights coming from different parts of
the same secondary light source is very small. Otherwise they would
cancel with each other, lowering the intensity of created 3-D
pixels.
[0082] FIG. 4 is a schematic diagram of a 3-D display device based
on random constructive interference using two liquid crystal light
valves. It adopted the same optic configuration as illustrated in
FIG. 3 except that two LCOS 20, 21 are now replaced by two liquid
crystal light valves 23, 24 together with two digital light
processors (DLP) 26. A DLP 26 comprises a light source 27, a
digital micro-mirror-device 28 and an optic lens 29. The light
emitted from light source 27 is reflected by digital
micro-mirror-device 28 and projected onto the back of liquid
crystal light valve 23 or 24 by optic lens 29 to form an image with
specific intensity distribution. If only one DLP is used, a color
filter is necessary to project images with different colors onto
the back of liquid crystal light valves 23 and 24 respectively.
[0083] A liquid crystal light valve comprises mainly an
optic-sensitive film and a liquid-crystal film. Between them there
is an opaque film and a multilayer reflector. A driving voltage is
applied on these films in sequence. When an optic image is
projected onto the optic-sensitive film, it changes the resistance
of the optic-sensitive film, which in turn changes the voltage
falling on the liquid crystal film. Since the illuminating light
first penetrates the liquid-crystal film, then reflected by the
multilayer reflector and penetrates the liquid-crystal film again,
its phase become modulated by the optic image projected on the
optic-sensitive film. As the optic image consists of quantities of
discrete pixels of different intensity, different parts of the
liquid crystal film under different pixels receive different
voltages and carry out different phase modulations. The liquid
crystal film appears therefore divided into quantities of discrete
pixels with the same pixel size as that of the optical image,
although it is not physically divided into individual pixels in
structure.
[0084] In FIG. 4, two identical DLPs 26 projects two optic images
for phase modulation onto the optic-sensitive films on the back of
two liquid crystal light valves 23, 24 respectively. The
polarization direction of polarizer 7 is rotated at an angle of 45
degree with the polarization direction of polarizer 8 to set the
liquid crystal light valves 23, 24 in phase-mostly mode (different
polarization direction may be required for different type of liquid
crystal light valves). Since two optic images projected onto the
back of two liquid crystal light valves 23, 24 are in mirror
symmetry with each other relative to beam splitter 9's
half-reflect-half-transmit surface A1-A2, secondary light sources
with desired amplitudes and phases are produced by vector addition
on random-secondary-light-source-generator-array 2. The
random-secondary-light-source-generator-array 2 is made up with a
reflective scattering screen 25 covered with an opaque plate 14
bearing micro-holes with uniform random distribution. The advantage
to use a liquid crystal light valve is that more gray levels and
higher display frequency may be obtained with the help of DLPs so
as to increase stability of color display. In addition the
brightness of a 3-D image could be greatly increased by using very
high power laser.
[0085] FIG. 5 is a schematic diagram of a 3-D display device based
on random constructive interference using two
optically-addressed-electro-optic-phase-modulators. Its optic
configuration is the same as that in FIG. 4 except that two liquid
crystal light valves 23, 24 are now replaced by two
optic-addressed-electro-optic-phase-modulators 30, 31. In addition,
the polarizer 7, 8 are taken away. As illustrated in FIG. 6, an
optic-addressed-electro-optic-phase-modulator has similar structure
as a liquid crystal light valve except that liquid crystal is
replaced by electro-optic material. It comprises the first film 35
of optic-sensitive material, the second film 36 of opaque material,
the third reflective film 37 and the forth film 38 of electro-optic
material, all of them being sandwiched between two transparent
conductive glasses 34, 39 in the given order. A driving voltage V
is applied on optic-sensitive material film 35 and electro-optic
material film 38 via two transparent conductive glasses 34, 39.
When an optic image is projected onto the optic-sensitive film 35,
it changes the resistance of the optic-sensitive film 35, which in
turn changes the voltage falling on electro-optic material film 38.
As a result the refractive index of the electro-optic material film
38 changes due to electro-optic effect. Since the illuminating
light first penetrates electro-optic material film 38, then
reflected by the reflective film 37 and penetrates the
electro-optic material film 38 again, its phase becomes modulated
by electro-optic material film 38. The quantity of phase modulation
depends on the optic image projected on the optic-sensitive film
35. Since the voltage V is fixed and need not change precisely from
time to time, very high voltage V could be applied on
optic-sensitive material film 35 and electro-optic material film 38
to generate a phase change as large as .pi.. To perform fast and
accurate modulation, the respond time of optic-sensitive film 35
and its resistance relative to that of electro-optic material film
38 should be properly designed. If another reflective film were
fabricated over transparent conductive glass 39, together with
existing reflective film 37, a Fabry-Perot interferometer could be
constructed, which is capable of carrying out amplitude modulation.
Replacing liquid crystal with electro-optic material makes
polarizer unnecessary and increases energy efficiency by twofold.
In addition, 3-D display frequency might reach very high, because
the responds time of electro-optic material may reach as short as
nano-seconds.
[0086] The random-secondary-light-source-generator-array in FIG. 5
is made up with two identical opaque plates 32, 33 bearing
transparent micro-holes that are of a uniform random distribution.
The plates are placed on the front surfaces of the two
optic-addressed-electro-optic-phase-modulators 30, 31, that is,
placed on the surface facing the projection lens 13. The opaque
plate 32 is placed at an angle of 45 degree to beam splitter 9's
half-reflect-half-transmit surface A1-A2 and in mirror symmetry
with the opaque plate 33 relative to beam splitter 9's
half-reflect-half-transmit surface A1-A2. Therefore their images
projected on transparent scattering screen 22 overlap and creates a
random coherent secondary light source array by vector addition.
The advantage to place opaque plates 32, 33 at the object plane of
projection lens 13 is that the magnification ratio of projection
lens 13 may change at any time without changing the size and the
structure of the opaque plates. The larger the magnification ratio
of projection lens 13, the larger the size of obtained coherent
secondary light source array and the larger the possible size of
displayed 3-D image. On the other hand, if opaque plates are placed
at the image plane of projection lens 13 like what happened in
FIGS. 1, 3 and 4, the size and the location of these opaque plates
have to be fixed very accurately. When building a rear-projection
3-D TV, opaque plates may be placed at the image plane of
projection lens 13 as shown in FIGS. 1, 3 and 4. However, when
magnification ratio of projection lens 13 need change constantly,
it is preferable to put the opaque plates at the object plane of
projection lens 13 as shown in FIG. 5.
[0087] FIG. 7 is a schematic diagram of a 3-D display device based
on random constructive interference using two large-size TFT-ST
liquid crystal panels. It mainly comprises an
amplitude-phase-modulator-array 1, a coherent light source 3 and an
illuminating optic system 4. The amplitude-phase-modulator-array 1
comprises the first polarizer 42; the first transmission liquid
crystal panel 40 disposed by the first polarizer 42; the second
polarizer 43 disposed by the first transmission liquid crystal
panel 40; the second transmission liquid crystal panel 41 disposed
by the second polarizer 43; and the third polarizer 44 disposed by
the second transmission liquid crystal panel 41. The first
transmission liquid crystal panel 40 and the second transmission
liquid crystal panel 41 are identical and their pixels are of a
uniform random distribution. Therefore they play the functions of
an amplitude-phase-modulator-array and a
random-secondary-light-source-generator-array at the same time. The
polarization direction of the three polarizer 42, 43, 44 are
arranged to set the first transmission liquid crystal panel 40 in
phase-mostly mode and the second transmission liquid crystal panel
41 in amplitude-mostly mode. In the device illustrated in FIG. 7
this was achieved by rotate the polarization direction of the first
polarizer 42 at an angle of 45 degree relative to that of the
second polarizer 43 and rotate the polarization direction of the
third polarizer 44 at an angle of 90 degree relative to that of the
second polarizer 43. For different liquid crystal panels different
polarization directions should be chosen. In addition if a
polarized laser beam is used, the first polarizer 42 may be
omitted. In general an illuminating optic system uses two optic
lenses to expand a laser beam. To obtain a compact size the
illuminating optic system 4 in FIG. 7 used a stack of beam
splitters instead. Along the optic path, the reflectivity of the
beam splitters increase gradually, the reflectivity of the next
beam splitter being the ratio of the reflectivity to the
transmittance of the previous beam splitter, so that the emitted
laser beams from different beam splitters are of equal intensity.
The wide laser beam produced in this way penetrates the first
polarizer 42, the first transmission liquid crystal panel 40, the
second polarizer 43, the second transmission liquid crystal panel
and the third polarizer 44 in the given order, creating a secondary
light source array with uniform random distribution. A primary 3-D
image 18 may then be generated by adjusting the amplitudes and
phases of these secondary light sources. In FIG. 7 the liquid
crystal panels 40,41 may adopt a very large size, for example, as
large as 19 inches or more. When 19 inches liquid screen is used,
the pixel pitch is about 0.29 mm and diffraction effect becomes
negligible within a short distance. The light passing through one
pixel of the first liquid crystal panel 40 would incident on the
corresponding pixel of the second liquid crystal panel 41 without
interfering with the adjacent pixels. However when the pixel pitch
decreases, diffraction effect might grow and a 1:1 optic system or
a micro-lens-array should be utilized to project the pixels of the
first liquid crystal panel 40 onto the second liquid crystal panel
41.
[0088] As could be seen in FIG. 7 there is an auxiliary optic
element, a Fresnel lens 19, placed on the right side of primary 3-D
image 18. The primary 3-D image 18 is within one focal length of
Fresnel lens 19, while the secondary light source array generated
on the right surface of the second liquid crystal panel 41 is more
than double focal lengths away from Fresnel lens 19. As a result a
magnified virtual image of the primary 3-D image 18 is produced on
the left side of Fresnel lens 19 and a real shrunk image of
secondary light source array is created on the right side of
Fresnel lens 19. The separation of the final 3-D image from the
bright secondary light source array may greatly depress the
disturbance of the bright secondary light source array to the
observer and increase the contrast of the final 3-D image.
[0089] In FIGS. 1, 3, 4 and 5, the secondary light sources are
generated by vector addition. Assuming the amplitude of the
illuminating laser beam for each phase-modulator being 1 unit, the
maximum amplitude of the secondary light source generated by vector
addition may reach 2 units, yielding an intensity of 4 units. While
in FIG. 7 the secondary light sources are generated by vector
production. Again assuming the amplitude of the illuminating laser
beam being 1 unit, the maximum amplitude of the secondary light
source generated by vector production may reach 1 unit, yielding an
intensity of 1 unit. In other words, a 3-D image displayed by
vector addition might be four times bright than the same 3-D image
displayed by vector production.
[0090] FIG. 8 is a schematic diagram of a
random-secondary-light-source-generator-array using two
micro-lens-arrays. It comprises the first micro-lens-array 45 on
which the micro-lens are of a periodical distribution; the second
micro-lens-array 46 on which the micro-lens are of a uniform random
distribution disposed in parallel with the first micro-lens-array
45 and aligned with the first micro-lens-array 45 so that the
focused beam created by each micro-lens of the first
micro-lens-array 45 illuminates one micro-lens of the second
micro-lens-array 46 and the image focus of each micro-lens of the
first micro-lens-array 45 falls within one focal length of the
micro-lens of the second micro-lens-array 46. A parallel light beam
incident on micro-lens-array 45 is first focused at the focus of
each micro-lens of micro-lens-array 45. Next it is magnified by
each micro-lens of micro-lens-array 46. The vertical magnification
ratio is of a random distribution since the optic axis of each
micro-lens of micro-lens-array 46 is randomly distributed relative
to the optic axis of each micro-lens of the first micro-lens-array
45. The new secondary light sources obtained is therefore of a
random distribution. The micro-lens-arrays 45 and 46 may be
fabricated on the opposite sides of the same plate to avoid later
tedious assembling work. The
random-secondary-light-source-generator-array 2 illustrated in FIG.
8 might also be used to couple two liquid crystal panels to
eliminate possible interferences of adjacent pixels due to
diffraction.
[0091] FIG. 9 is a schematic diagram of a
random-secondary-light-source-generator-array 2 using a bundle of
single-mode fibers. It comprises a bundle of single-mode fibers 47
and a micro-lens-array 48. The single-mode fibers within the bundle
47 are optically isolated from each other. They are glue together
and polished at the left end. A micro-lens-array 48 is disposed to
focus the light from illuminating optic system into the cores of
the single-mode fibers within the bundle 47 at the left end. One
micro-lens in the micro-lens-array 48 is aligned with one
single-mode fiber. The light exit from the right ends of the
single-mode fibers and propagate towards 3-D image 18. At the right
end the spaces between adjacent single-mode fibers are of a random
distribution.
* * * * *