U.S. patent application number 09/836642 was filed with the patent office on 2001-10-25 for optical illumination apparatus.
This patent application is currently assigned to MINOLTA CO., LTD.. Invention is credited to Hayashi, Kohtaro.
Application Number | 20010033418 09/836642 |
Document ID | / |
Family ID | 18631262 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033418 |
Kind Code |
A1 |
Hayashi, Kohtaro |
October 25, 2001 |
Optical illumination apparatus
Abstract
An optical illumination apparatus has a polarization conversion
device for converting light from a light source into light
polarized uniformly in a predetermined manner and an optical
integrator system for illuminating a display panel with the light
polarized in the predetermined manner. The polarization conversion
device splits the light from the light source into a first light
beam and a second light beam in such a way that the first and
second light beams are polarized in different manners, and then
converts one of the first and second light beams into light
polarized in the identical manner as the other light beam.
Moreover, the first and second light beams pass through an
identical lens cell of a first lens array of the optical integrator
system and are imaged on an identical lens cell of a second lens
array of the optical integrator system.
Inventors: |
Hayashi, Kohtaro;
(Toyonaka-Shi, JP) |
Correspondence
Address: |
SIDLEY AUSTIN BROWN & WOOD
717 NORTH HARWOOD
SUITE 3400
DALLAS
TX
75201
US
|
Assignee: |
MINOLTA CO., LTD.
|
Family ID: |
18631262 |
Appl. No.: |
09/836642 |
Filed: |
April 17, 2001 |
Current U.S.
Class: |
359/485.07 ;
348/E5.141; 359/485.06; 359/487.02; 359/489.06; 359/489.07;
359/489.09; 359/489.17; 359/489.18; 359/489.19; 359/490.02;
359/491.01; 362/19 |
Current CPC
Class: |
G02B 27/283 20130101;
G02F 1/13362 20130101; G02B 27/285 20130101; H04N 5/7441
20130101 |
Class at
Publication: |
359/487 ;
359/497; 359/502; 362/19 |
International
Class: |
F21V 009/14; G02B
005/30; G02B 027/28 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2000 |
JP |
2000-120452 |
Claims
What is claimed is:
1. An optical illumination apparatus comprising: a polarization
conversion device for converting light from a light source into
light uniformly polarized in a predetermined manner; and an optical
integrator system for illuminating a display panel with the light
polarized in the predetermined manner, the optical integrator
system comprising a first lens array having a first lens cell, and
a second lens array having a second lens cell; wherein the
polarization conversion device is adapted to split the light from
the light source into a first light beam and a second light beam
such that the first and second light beams are polarized in
different manners, and to convert one of the first and second light
beams into light polarized in an identical manner as the other of
the first and second light beams; and wherein the first and second
light beams pass through the first lens cell and are imaged on the
second lens cell.
2. An optical illumination apparatus in accordance with claim 1,
wherein the light from the light source is split into the first and
second light beams in a direction corresponding to longer sides of
the display panel.
3. An optical illumination apparatus in accordance with claim 1,
wherein an optical relationship between the first and second light
beams is represented by a formula: 0.3<l.multidot.tan
.theta./d<0.75 wherein: .theta. represents an angle between the
first and second light beams; l represents an optical distance
between the first and second lens arrays; and d represents a size
of each lens cell, along longer sides of the second lens array.
4. An optical illumination apparatus in accordance with claim 1,
further comprising a color switching device disposed between the
polarization conversion device and the optical integrator system,
the color switching device adapted to time-divisionally switch
colors of the light polarized in the predetermined manner from one
color to another among a plurality of predetermined colors.
5. An optical illumination apparatus in accordance with claim 4,
wherein the color switching device is a cholesteric liquid crystal
device.
6. An optical illumination apparatus in accordance with claim 4,
wherein the color switching device is a hologram formed of a liquid
crystal polymer.
7. An optical illumination apparatus in accordance with claim 4,
wherein the color switching device comprises: a diffraction
grating; and a reflective light valve.
8. An optical illumination apparatus in accordance with claim 1,
wherein the first lens array comprises a plurality of lens cells,
the first and second light beams form a first group, the
polarization conversion device being adapted to further split the
light from the light source into a second group such that the first
and second groups travel in horizontally symmetric directions with
respect to a direction in which an image is displayed, and
individual lens cells of the first lens array are decentered in
horizontally symmetric directions with respect to the direction in
which the image is displayed.
9. An optical illumination apparatus in accordance with claim 1,
wherein the polarization conversion device comprises a plurality of
polarizing beam splitter prisms arranged in parallel.
10. An optical illumination apparatus in accordance with claim 1,
wherein the polarization conversion device comprises: a first
polarizing beam splitter prism; and a second polarizing beam
splitter prism; wherein the first polarizing beam splitter prism is
adapted to transmit light polarized in a first manner and to
reflect light polarized in a second manner to the second polarizing
beam splitter prism; and wherein the second polarizing beam
splitter prism is adapted to reflect the light polarized in the
second manner received from the first polarizing beam splitter
prism.
11. An optical illumination apparatus in accordance with claim 1,
wherein the first lens array comprises a plurality of the first
lens cells arranged in a rectangular grid array.
12. An optical illumination apparatus in accordance with claim 11,
wherein the rectangular grid array has an aspect ratio that is
substantially identical to an aspect ratio of the display
panel.
13. An optical illumination apparatus in accordance with claim 1,
wherein the second lens array comprises a plurality of the second
lens cells arranged in a rectangular grid array.
14. An optical illumination apparatus, comprising: a polarization
conversion device for splitting light from a light source into
first and second light beams polarized in first and second manners
and for converting one of first and second light beams into light
polarized in an identical manner as the other of the first and
second light beams; a cholesteric liquid crystal device for
switching colors of the first and second light beams on a
time-divisional basis; and an optical integrator system for
illuminating a display panel with the first and second light beams,
the optical integrator system comprising a first lens array having
a first lens cell, and a second lens array having a second lens
cell; wherein the first and second light beams pass through the
first lens cell and are imaged on the second lens cell.
15. An optical illumination apparatus in accordance with claim 14,
wherein the cholesteric liquid crystal device comprises: a layer of
cholesteric liquid crystal elements; and a controller for bringing
the layer into a first state wherein light of a particular
wavelength is reflected, and into a second state wherein all light
is transmitted through the layer.
16. An optical illumination apparatus in accordance with claim 14,
wherein the polarization conversion device comprises: a first
polarizing beam splitter prism adapted to transmit P-polarized
light and to reflect S-polarized light; a first quarter-wave plate
disposed behind the first polarizing beam splitter prism, adapted
to receive the P-polarized light therefrom and to convert the
P-polarized light to right-handed circularly polarized light; a
second polarizing beam splitter prism disposed parallel to the
first polarizing beam splitter prism, adapted to receive the
S-polarized light therefrom and to reflect the S-polarized light;
and a second quarter-wave plate disposed behind the second
polarizing beam splitter prism, adapted to receive the S-polarized
light therefrom and to convert the S-polarized light to
right-handed circularly polarized light.
17. An optical illumination apparatus in accordance with claim 16,
further comprising a quarter wave plate for converting circularly
polarized light into linearly polarized light, the quarter wave
plate being disposed between the cholesteric liquid crystal device
and the optical integrator system.
18. An optical illumination apparatus, comprising: a polarization
conversion device for splitting light from a light source into
first and second light beams polarized in different manners and for
converting one of first and second light beams into light polarized
in an identical manner as the other of the first and second light
beams; a liquid crystal hologram device for switching colors of the
first and second light beams on a time-divisional basis; and an
optical integrator system for illuminating a display panel with the
first and second light beams, the optical integrator system
comprising a first lens array having a first lens cell, and a
second lens array having a second lens cell; wherein the first and
second light beams pass through the first lens cell and are imaged
on the second lens cell.
19. An optical illumination apparatus in accordance with claim 18,
wherein the polarization conversion device comprises: a first
polarizing beam splitter prism adapted to transmit S-polarized
light and to reflect P-polarized light; a second polarizing beam
splitter prism, adapted to reflect the P-polarized light received
from the first polarizing beam splitter prism; and a half-wave
plate disposed behind the second polarizing beam splitter prism,
adapted to convert the P-polarized light therefrom to S-polarized
light.
20. An optical illumination apparatus in accordance with claim 18,
wherein the liquid crystal hologram device comprises: a layer of
liquid crystal hologram elements; and a controller for bringing the
layer into a first state wherein light of a particular wavelength
is reflected and diffracted, and into a transparent state wherein
all light is transmitted through the layer; wherein the light that
is reflected and diffracted exits from the liquid crystal hologram
device in a direction oblique to its surface.
21. An optical illumination apparatus, comprising: a polarization
conversion device for splitting light from a light source into
first and second light beams polarized in different manners and for
converting one of first and second light beams into light polarized
in an identical manner as the other of the first and second light
beams; a diffraction grating for separating colors of the first and
second light beams; a reflective light valve for switching the
colors of the first and second light beams on a time-divisional
basis; and an optical integrator system for illuminating a display
panel with the first and second light beams, the optical integrator
system comprising a first lens array having a first lens cell, and
a second lens array having a second lens cell; wherein the first
and second light beams pass through the first lens cell and are
imaged on the second lens cell.
22. An optical illumination apparatus in accordance with claim 21,
wherein the polarization conversion device comprises: a first
polarization separation mirror adapted to transmit light polarized
in a first manner and to reflect light polarized in a second
manner; a second polarization separation mirror disposed proximate
the first polarization separation mirror, adapted to reflect the
light polarized in the second manner received from the first
polarization separation mirror; and a half-wave plate disposed
behind the second polarization separation mirror, adapted to
receive the light polarized in the second manner therefrom and to
convert the light polarized in the second manner to light polarized
in the first manner.
23. An optical illumination apparatus in accordance with claim 21,
further comprising a fresnal lens disposed between the polarization
conversion device and the diffraction grating.
24. An optical illumination apparatus in accordance with claim 21,
further comprising a controller for separately driving each of red,
green, and blue regions of the reflective light valve.
Description
RELATED APPLICATIONS
[0001] This application is based on Japanese Patent Application No.
2000-120452 filed on Apr. 21, 2000, the contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an optical illumination
apparatus for use in an optical display apparatus employing a
display panel.
BACKGROUND OF THE INVENTION
[0003] Conventionally, as a means of displaying images,
projection-type optical display apparatuses such as projectors are
known. Such optical display apparatuses require an optical
illumination apparatus for efficiently and uniformly illuminating
the optical image formed on a display panel, such as a reflective
liquid crystal display panel. FIG. 10 is a diagram conceptually
showing an example of the construction of an optical display
apparatus employing a conventional optical illumination
apparatus.
[0004] In FIG. 10, reference numeral 101 represents a light source,
and reference numeral 102 represents a reflector disposed so as to
partially surround the light source 101. A PBS (polarizing beam
splitter) prism unit 103 is disposed immediately behind the
reflector 102, i.e., on the right side thereof in FIG. 10. The PBS
prism unit 103 includes a plurality of PBS prisms arranged parallel
to one another. The PBS prism unit 103 splits the light from the
light source 101 into two differently polarized types of light. Of
the individual PBS prisms 103a and 103b, those which let out
S-polarized light as described later have half-wave plates 104
disposed immediately behind them.
[0005] Behind the PBS prism unit 103 (i.e., on the right side
thereof in FIG. 10) are disposed, in order of arrangement, a first
lens array 105, then somewhat away therefrom, a second lens array
106, and a superimposing lens 107 immediately behind it. The first
lens array 105 has a plurality of lens cells 105a arranged in a
rectangular, grid-like array having an aspect ratio substantially
identical to that of a display panel 109 to be described later.
Similarly, the second lens array 106 also has a plurality of lens
cells 106a arranged in a rectangular, grid-like array. However, the
shape of the lens cells 106a of the second lens array 106 is not
necessarily geometrically similar to that of the lens cells
105a.
[0006] The images from the individual lens cells 105a of the first
lens array 105 are, by the second lens array 106 and the
superimposing lens 107 disposed immediately behind it, superimposed
on one another in the vicinity of the focal point of the
superimposing lens 107. The display panel 109 is disposed at the
focal point of the superimposing lens 107. The display panel 109 is
illuminated in a telecentric fashion by a condenser lens 108
disposed immediately in front of it. The components from the first
lens array 105 through the superimposing lens 107 mentioned above
together constitute an optical integrator system. It is to be noted
that, in all the diagrams referred to in the present specification,
irrespective of whether they relate to prior-art examples or to
embodiments of the present invention, light beams are represented
by their optical axes alone.
[0007] The light emitted from the light source 101 is reflected
from the reflector 102, and is thereby formed into a substantially
parallel beam and directed to the PBS prisms 103a of the PBS prism
unit 103. Here, P-polarized light, indicated by solid lines P, is
transmitted straight through the PBS prisms 103a. On the other
hand, S-polarized light, indicated by broken lines S, is reflected
inside the PBS prisms 103a so as to be directed to the outwardly
contiguous PBS prisms 103b, and is then reflected again inside the
PBS prisms 103b so as to exit therefrom, still as S-polarized
light. That is, by the PBS prism unit 103, the light from the light
source 101 is split into two differently polarized types of light
in the direction of the longer sides of the display panel 109,
i.e., in a vertical direction along the plane of the figure.
[0008] The S-polarized light exiting from the PBS prisms 103b is
transmitted through the half-wave plates 104 disposed immediately
behind the PBS prisms 103b and is thereby converted into
P-polarized light. That is, a portion of the light from the light
source 101 has its polarization converted first by the PBS prisms
103b of the PBS prism unit 103 and then by the half-wave plates
104, and eventually comes out as uniformly P-polarized light. This
arrangement constitutes a polarization conversion device. Here, the
type of light into which the light from the light source 101 is
converted does not necessarily have to be P-polarized light, but
can be of other polarizations. The arrangement described thus far,
starting with the light source 101 and ending immediately in front
of the display panel 109, constitutes an optical illumination
apparatus.
[0009] The light thus converted into uniformly P-polarized light is
then directed through the above-mentioned optical integrator system
to the display panel 109. The display panel 109 modulates, pixel by
pixel, the light it is illuminated with according to the display
data fed thereto, and emits the modulated light. The light thus
emitted then enters an optical projection system 110. The display
data presented on the display panel 109 is projected, as an image,
onto a screen (not shown) through this optical projection system
110. Reference numeral 110a represents an aperture stop disposed in
the optical projection system 110.
[0010] FIG. 11 is a diagram conceptually showing another example of
the construction of an optical display apparatus employing a
conventional optical illumination apparatus. In this figure,
reference numeral 201 represents a light source, and reference
numeral 202 represents a reflector disposed so as to partially
surround the light source 201. Behind the reflector 202 (i.e., on
the right side thereof in FIG. 11) are disposed, in order of
arrangement, a first lens array 203 and, then somewhat away
therefrom, a second lens array 204. The first lens array 203 has a
plurality of lens cells 203a arranged in a rectangular, grid-like
array having an aspect ratio substantially identical to that of a
display panel 209 to be described later. Similarly, the second lens
array 204 also has a plurality of lens cells 204a arranged in a
rectangular, grid-like array. However, the shape of the lens cells
204a of the second lens array 204 is not necessarily geometrically
similar to that of the lens cells 203a.
[0011] A PBS (polarizing beam splitter) prism array 205 is disposed
immediately behind the second lens array 204. The PBS prism array
205 includes a plurality of PBS prisms arranged in an array. The
PBS prism array 205 splits the light from the light source 201 into
two differently polarized types of light. Of the individual PBS
prisms 205a and 205b, those which let out S-polarized light as
described later have half-wave plates 206 disposed immediately
behind them.
[0012] A superimposing lens 207 is disposed behind the PBS prism
array 205. The images of the individual lens cells 203a of the
first lens array 203 are, by the second lens array 204 and the
superimposing lens 207, superimposed on one another in the vicinity
of the focal point of the superimposing lens 207. The display panel
209 is disposed at the focal point of the superimposing lens 207.
The display panel 209 is illuminated in a telecentric fashion by a
condenser lens 208 disposed immediately in front of it. The first
lens array 203, the second lens array 204, and the superimposing
lens 207 mentioned above together constitute an optical integrator
system.
[0013] The light emitted from the light source 201 is reflected
from the reflector 202, and is thereby formed into a substantially
parallel beam and passed through the first lens array 203 and the
second lens array 204, so that the light exiting from the
individual lens cells 204a of the second lens array 204 enters
corresponding ones of the PBS prisms 205a of the PBS prism array
205. Here, P-polarized light, indicated by solid lines P, is
transmitted straight through the PBS prisms 205a. On the other
hand, S-polarized light, indicated by broken lines S, is reflected
inside the PBS prisms 205a so as to be directed to the contiguous
PBS prisms 205b, and is then reflected again inside the PBS prisms
205b so as to exit therefrom, still as S-polarized light.
[0014] The S-polarized light exiting from the PBS prisms 205b is
then transmitted through the half-wave plates 206 disposed
immediately behind the PBS prisms 205b and is thereby converted
into P-polarized light. That is, a portion of the light from the
light source 201 has its polarization converted first by the PBS
prisms 205b of the PBS prism array 205 and then by the half-wave
plates 206, and eventually comes out as uniformly P-polarized
light. This arrangement constitutes a polarization conversion
device. Here, the type of light into which the light from the light
source 201 is converted does not necessarily have to be P-polarized
light, but can be of other polarizations. The arrangement described
thus far, starting with the light source 201 and ending immediately
in front of the display panel 209, constitutes an optical
illumination apparatus.
[0015] The light thus converted into uniformly P-polarized light is
then directed through the superimposing lens 207 to the display
panel 209. The display panel 209 modulates, pixel by pixel, the
light it is illuminated with according to the display data fed
thereto, and emits the modulated light. The light thus emitted then
enters an optical projection system 210. The display data presented
on the display panel 209 is projected, as an image, onto a screen
(not shown) through this optical projection system 210. Reference
numeral 210a represents an aperture stop disposed in the optical
projection system 210.
[0016] In the conventional optical illumination apparatus
constructed as shown in FIG. 10, polarization conversion is
performed immediately behind the light source 101. Therefore, the
light emitted from the light source 101 and then reflected from the
reflector 102 has its beam diameter enlarged to about twice its
original beam diameter as a result of the polarization conversion.
This diminishes the f-number of the illumination light Ia that
strikes the display panel 109 and thus diminishes the f-number of
the projection light Ea that emanates from the display panel 109,
making the burden on the optical projection system 110 heavier.
[0017] On the other hand, in the conventional optical illumination
apparatus constructed as shown in FIG. 11, the light emitted from
the light source 201 and then reflected from the reflector 202
experiences no enlargement of its beam diameter. Therefore, no
diminishing occurs in the f-number of the illumination light Ib
that strikes the display panel 209 nor in the f-number of the
projection light Eb that emanates from the display panel 209. Thus,
no extra burden is placed on the optical projection system 210.
However, the light from the light source 201 is not converted into
uniformly polarized light until it has passed through the second
lens array 204. Therefore, in this optical illumination apparatus,
no space is available for inserting a polarization-dependent color
switching device such as those used in the embodiments of the
present invention to be described later. That is, this optical
illumination apparatus does not permit a so-called color sequential
illumination method using such a color switching device.
SUMMARY OF THE INVENTION
[0018] An object of the present invention is to provide an optical
illumination apparatus that causes no diminishing in the f-number
of illumination light so as to keep the burden on an optical
projection system minimal and that allows insertion of a
polarization-dependent color switching device.
[0019] To achieve the above object, according to one aspect of the
present invention, an optical illumination apparatus is provided,
including a polarization conversion device for converting light
from a light source into light uniformly polarized in a
predetermined manner and an optical integrator system for
illuminating a display panel with the light polarized in the
predetermined manner. The optical integrator includes a first lens
array having a first lens cell, and a second lens array having a
second lens cell. The polarization conversion device splits the
light from the light source into a first light beam and a second
light beam in such a way that the first and second light beams are
polarized in different manners, and then converts one of the first
and second light beams into light polarized in an identical manner
as the other of the first and second light beams. The first and
second light beams pass through the first lens cell of the first
lens array and are imaged on the second lens cell of the second
lens array.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] This and other objects and features of the present invention
will become clear from the following description, taken in
conjunction with the preferred embodiments with reference to the
accompanying drawings, in which:
[0021] FIG. 1 is a diagram conceptually showing an example of the
construction of an optical display apparatus employing an optical
illumination apparatus embodying the invention;
[0022] FIG. 2 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a first embodiment of the invention,
[0023] FIG. 3 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 2;
[0024] FIGS. 4A and 4B are sectional views schematically showing
the structure of a cholesteric liquid crystal element;
[0025] FIG. 5 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a second embodiment of the invention;
[0026] FIG. 6 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 5;
[0027] FIG. 7 is a sectional view schematically showing the
structure of a liquid crystal hologram element;
[0028] FIG. 8 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a third embodiment of the invention;
[0029] FIG. 9 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 8;
[0030] FIG. 10 is a diagram conceptually showing an example of the
construction of an optical display apparatus employing a
conventional optical illumination apparatus; and
[0031] FIG. 11 is a diagram conceptually showing another example of
the construction of an optical display apparatus employing a
conventional optical illumination apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Hereinafter, embodiments of the present invention will be
described with reference to the drawings. FIG. 1 is a diagram
conceptually showing an example of the construction of an optical
display apparatus employing an optical illumination apparatus
embodying the invention. In FIG. 1, reference numeral 1 represents
a light source, and reference numeral 2 represents a reflector
disposed so as to partially surround the light source 1. A PBS
(polarizing beam splitter) prism unit 3 is disposed immediately
behind the reflector 2, i.e., on the right side thereof in FIG. 1.
The PBS prism unit 3 includes a plurality of PBS prisms arranged
parallel to one another. The PBS prism unit 3 splits the light from
the light source 1 into two differently polarized types of light.
Of the individual PBS prisms 3a and 3b, those which let out
S-polarized light have half-wave plates 4 disposed immediately
behind them.
[0033] Behind the PBS prism unit 3 (i.e., on the right side thereof
in FIG. 1) are disposed, in order of arrangement, a first lens
array 5, then somewhat away therefrom, a second lens array 6, and a
superimposing lens 7 immediately behind the second lens array 6.
The first lens array 5 has a plurality of lens cells 5a arranged in
a rectangular, grid-like array, having an aspect ratio
substantially identical to that of a display panel 9 to be
described later. Similarly, the second lens array 6 also has a
plurality of lens cells 6a arranged in a rectangular, grid-like
array. However, the shape of the lens cells 6a of the second lens
array 6 is not necessarily geometrically similar to that of the
lens cells 5a.
[0034] The images from the individual lens cells 5a of the first
lens array 5 are, by the second lens array 6 and the superimposing
lens 7 disposed immediately behind it, superimposed on one another
in the vicinity of the focal point of the superimposing lens 7. The
display panel 9 is disposed at the focal point of the superimposing
lens 7. Here, the display panel 9 is of a single-panel type that
achieves color display with a single display panel. Moreover, the
display panel 9 is illuminated in a telecentric fashion by a
condenser lens 8 disposed immediately in front of it. The
components from the first lens array 5 through the superimposing
lens 7 constitute an optical integrator system.
[0035] The light emitted from the light source 1 is reflected from
the reflector 2, and is thereby formed into a substantially
parallel beam and directed to the PBS prisms 3a of the PBS prism
unit 3. Here, P-polarized light, indicated by solid lines P, is
transmitted straight through the PBS prisms 3a. On the other hand,
S-polarized light, indicated by broken lines S, is reflected inside
the PBS prisms 3a so as to be directed to the outwardly contiguous
PBS prisms 3b, and is then reflected again inside the PBS prisms 3b
so as to exit therefrom, still as S-polarized light. That is, by
the PBS prism unit 3, the light from the light source 1 is split
into two differently polarized types of light in the direction of
the longer sides of the display panel 9, i.e., in a vertical
direction along the plane of the figure.
[0036] The S-polarized light exiting from the PBS prisms 3b is
transmitted through the half-wave plates 4 disposed immediately
behind the PBS prisms 3b and is thereby converted into P-polarized
light. That is, a portion of the light from the light source 1 has
its polarization converted first by the PBS prisms 3b of the PBS
prism unit 3 and then by the half-wave plates 4, and eventually
comes out as uniformly P-polarized light. This arrangement
constitutes a polarization conversion device. Here, the type of
light into which the light from the light source 1 is converted
does not necessarily have to be P-polarized light, but can be of
other polarizations. The arrangement described thus far, starting
with the light source 1 and ending immediately in front of the
display panel 9, constitutes an optical illumination apparatus.
[0037] The light thus converted into uniformly P-polarized light is
then directed through the above-mentioned optical integrator system
to the display panel 9. The display panel 9 modulates, pixel by
pixel, the light it is illuminated with according to the display
data fed thereto, and emits the modulated light. The light thus
emitted then enters an optical projection system 10. The display
data presented on the display panel 9 is projected, as an image,
onto a screen (not shown) through this optical projection system
10. Reference numeral 10a represents an aperture stop disposed in
the optical projection system 10.
[0038] Here, the S-polarized light indicated by the broken lines S
is, when reflected inside the PBS prisms 3b, reflected inwardly
with respect to the optical illumination apparatus itself That is,
of the two types of differently polarized light split by the PBS
prism unit 3, the light Pb that is originally S-polarized and then
converted by the half-wave plates 4 into P-polarized light travels
along somewhat inwardly inclined paths and then passes through the
same lens cells 5a of the first lens array 5 as does the light Pa
that is P-polarized from the beginning.
[0039] The distance between the PBS prism unit 3 and the first lens
array 5 is represented by L. This is the space where a color
switching device, to be described later, is disposed. The lens
cells 5a are shaped like wedges and are arranged such that the
vertices of their curved surfaces are outwardly decentered. Thus,
the two types of light Pa and Pb, as they pass through the lens
cells 5a, are individually refracted so as to form two light source
images on identical lens cells 6a of the second lens array 6. The
polarization conversion device mentioned above splits the light
from the light source 1 into two groups of light in such a way that
the two groups of light travel in horizontally symmetric directions
with respect to the direction in which the projected image is
displayed. Accordingly, the lens cells 5a of the first lens array 5
are decentered in horizontally symmetric directions with respect to
the direction in which the projected image is displayed.
[0040] In the arrangement described above according to the present
invention, polarization conversion is performed immediately behind
the light source 1. Therefore, the light emitted from the light
source 1 and then reflected from the reflector 2 has its beam
diameter enlarged to about twice its original beam diameter as a
result of polarization conversion. In this respect, this
arrangement is the same as that of the conventional optical
illumination apparatus shown in FIG. 10. However, the arrangement
according to the present invention is so constructed that, as shown
in FIG. 1, the two types of light, although split so as to be
differently polarized, pass through identical lens cells 5a of the
first lens array 5 and form two light source images on identical
cells 6a of the second lens array 6. Therefore, no diminishing
occurs in the f-number of the illumination light I that strikes the
display panel 9 nor in the f-number of the projection light E that
emanates from the display panel 9. Thus, no extra burden is placed
on the optical projection system 10.
[0041] Here, as shown in FIG. 1, let the distance between the beam
centers of the P-polarized and the S-polarized light split by the
PBS prism unit 3 be D, and the angle between the directions in
which the beam centers of those two types of light point, i.e., the
angle between Pa and Pb, be .theta.. Moreover, let the optical
distance between the first lens array 5 and the second lens array 6
be l, and the size of each lens cell 6a of the second lens array 6,
along its longer sides, be d. Then, it is preferable that the
following conditional formula be fulfilled:
0.3<l.multidot.tan .theta./d<0.75
[0042] The optimum value of this conditional formula is 0.5,
because then the distance between the two light-source images
formed on an identical cell 6a of the second lens array 6 is equal
to 2/d, and thus the two images are formed in the best-balanced
position on the lens cell 6a.
[0043] A color switching device, to be described later, exhibits
dependence on polarization. In view of this, one might consider
that, in the conventional optical illumination apparatus
constructed as shown in FIG. 11, it is possible to dispose the
color switching device between the superimposing lens 207 and the
condenser lens 208, where the illumination light Ib is uniformly
polarized. However, if the color switching device is disposed in
this position, the color switching device receives incident rays
from so wide a range of angles that its dependence on angle of
incidence exerts an undesirable effect. Thus, this position is
unfit for the placement of the color switching device.
[0044] Specifically, although the f-number is not small, the
illumination light Ib is a divergent beam that fans out in a range
of angles of about .+-.10 degrees, thus causing the undesirable
effect mentioned above. In contrast, according to the present
invention, a color switching device is disposed between the PBS
prism unit 3 and the first lens array 5, where the
previously-mentioned angle .theta., which corresponds to the range
of angles of incident rays, is 4 to 5 degrees at the very most.
Therefore, the effect resulting from the dependence of the color
switching device on the angle of incidence is negligible.
[0045] Hereinafter, optical illumination apparatuses embodying the
present invention and employing various types of color switching
device will be described. An optical display apparatus of a
single-panel type that achieves color, i.e., RGB, display with a
single display panel adopts a so-called color sequential (color
time-divisional) illumination method. More specifically, in such a
case, it has been customary to adopt, for example, a color wheel
time-divisional method.
[0046] The color wheel used in such a method has the shape of a
disk, and has three color filters, which respectively transmit R
(red), G (green), and B (blue) colors. The filters are arranged in
three regions around a rotational axis that runs through the center
of the color wheel. As those color filters rotate at high speed
about the axis of rotation, the illumination light passing
therethrough has its color switched at high speed from one color to
another.
[0047] However, a color wheel time-divisional method involves
mechanical rotation of a color wheel and is thus not entirely
satisfactory in terms of reliability and operating life. For this
reason, according to the present invention, the switching of the
color of illumination light from one color to another is achieved
electrically by the use of a color switching device such as those
used in the individual embodiments of the invention described
below.
[0048] FIG. 2 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a first embodiment of the invention. In FIG. 2,
reference numeral 1 represents a light source, and reference
numeral 2 represents a reflector disposed so as to partially
surround the light source 1. A PBS (polarizing beam splitter) prism
unit 3 is disposed immediately behind the reflector 2, i.e., on the
right side thereof in FIG. 2. The PBS prism unit 3 includes a
plurality of PBS prisms arranged parallel to one another. The PBS
prism unit 3 splits the light from the light source 1 into two
differently polarized types of light.
[0049] Quarter-wave plates 18 are disposed immediately behind the
PBS prism unit 3. More specifically, of the individual PBS prisms
3a and 3b of the PBS prism unit 3, those PBS prisms 3a which let
out P-polarized light as described later have quarter-wave plates
18a disposed immediately behind them that have their principal axes
oriented at -45 degrees, and those PBS prisms 3b which let out
S-polarized light have quarter-wave plates 18b disposed immediately
behind them that have their principal axes oriented at +45
degrees.
[0050] Behind the quarter-wave plates 18 (i.e., on the right side
thereof in FIG. 2) are disposed, in order of arrangement, a
cholesteric liquid crystal device 11, a quarter-wave plate 19, then
a first lens array 5 immediately behind it, then somewhat away
therefrom, a second lens array 6, and a superimposing lens 7
immediately behind it. The first lens array 5 has a plurality of
lens cells 5a arranged in a rectangular, grid-like array having an
aspect ratio substantially identical to that of a display panel 9
to be described later. Similarly, the second lens array 6 also has
a plurality of lens cells 6a arranged in a rectangular, grid-like
array. However, the shape of the lens cells 6a is not necessarily
geometrically similar to that of the lens cells 5a.
[0051] The cholesteric liquid crystal device 11 is one type of
color switching device that electrically switches the color of
illumination light on a time-divisional basis from one color to
another among R, G, and B colors. How this is achieved will be
described in detail later. The images from the individual lens
cells 5a of the first lens array 5 are, by the second lens array 6
and the superimposing lens 7 disposed immediately behind it,
superimposed on one another in the vicinity of the focal point of
the superimposing lens 7.
[0052] The components from the first lens array 5 through the
superimposing lens 7 constitute an optical integrator system. The
display panel 9 is disposed at the focal point of the superimposing
lens 7. The display panel 9 is illuminated in a telecentric fashion
by a condenser lens 8 disposed immediately in front of it. A PBS
prism 12 is disposed between the condenser lens 8 and the display
panel 9. Illumination light from the optical illumination apparatus
is converted into projection light by the display panel 9 and
transmitted, via the PBS prism 12, to the optical projection system
10. Projection light is considered to include the image information
from the display panel 9.
[0053] The light emitted from the light source 1 is reflected from
the reflector 2, and is thereby formed into a substantially
parallel beam and directed to the PBS prisms 3a of the PBS prism
unit 3. Here, P-polarized light, indicated by solid lines P, is
transmitted straight through the PBS prisms 3a. On the other hand,
S-polarized light, indicated by broken lines S, is reflected inside
the PBS prisms 3a so as to be directed to the outwardly contiguous
PBS prisms 3b, and is then reflected again inside the PBS prisms 3b
so as to exit therefrom, still as S-polarized light. That is, by
the PBS prism unit 3, the light from the light source 1 is split
into two differently polarized types of light in the direction of
the longer sides of the display panel 9, i.e., in a vertical
direction along the plane of the figure.
[0054] The P-polarized light exiting from the PBS prisms 3a is
converted into right-handed circularly polarized light by being
transmitted through the quarter-wave plates 18a disposed
immediately behind the PBS prisms 3a. Similarly, the S-polarized
light exiting from the PBS prisms 3b is also converted into
right-handed circularly polarized light by being transmitted
through the quarter-wave plates 18b disposed immediately behind the
PBS prisms 3b. That is, the light from the light source 1 has its
polarization converted first by the PBS prism unit 3 and then by
the quarter-wave plates 18, and eventually comes out as uniformly
right-handed circularly polarized light. This arrangement
constitutes a polarization conversion device. Here, the type of
light into which the light from the light source 1 is converted
does not necessarily have to be right-handed circularly polarized
light, but can be of other polarizations. The arrangement described
thus far, starting with the light source 1 and ending immediately
in front of the display panel 9, constitutes an optical
illumination apparatus.
[0055] The light thus converted into uniformly right-handed
circularly polarized light has its color switched by the
cholesteric liquid crystal device 11, is converted into linearly
polarized light by the quarter-wave plate 19, passes through the
above-mentioned optical integrator system, and eventually strikes
the display panel 9. The display panel 9 modulates, pixel by pixel,
the light it is illuminated with according to the display data of
R, G, and B colors fed thereto, and emits the modulated light. The
light thus emitted then enters an optical projection system 10. The
display data presented on the display panel 9 is projected, as an
image, onto a screen (not shown) through this optical projection
system 10. Reference numeral 10a represents an aperture stop
disposed in the optical projection system 10.
[0056] FIG. 3 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 2. While FIG. 2 illustrates a conceptual view wherein the
optical system is formed along a straight line, an optical axis of
the optical system is preferably bent at a reflecting surface as
shown in FIG. 3.
[0057] With reference to FIG. 3, the paths of rays in this
embodiment will be described once again below. The light emitted
from the light source 1 is reflected from the reflector 2, and is
thereby formed into a substantially parallel beam and directed to
the PBS prism unit 3. The light has its polarization converted by
this PBS prism unit 3 and the quarter-wave plates 18 disposed
immediately behind it, and eventually comes out as uniformly
right-handed circularly polarized light. The light thus converted
into uniformly right-handed circularly polarized light then strikes
the surface of the cholesteric liquid crystal device 11.
[0058] The cholesteric liquid crystal device 11 is composed of, for
example, a total of three layers of cholesteric liquid crystal
elements that are laid over one another, one layer for each of R,
G, and B colors. These cholesteric liquid crystal elements exhibit
dependence on polarization; that is, they reflect only right-handed
circularly polarized light. Here, the individual cholesteric liquid
crystal elements are driven by a controller 15, shown as a block in
FIG. 3, on a color-sequential basis in such a way as to be turned
on and off one after another at a high speed. As a result, light of
R, G, and B colors, which are contained in the white light from the
light source, is reflected one after another on a time-divisional
basis. The light of the colors that are not reflected is
transmitted through the cholesteric liquid crystal device 11. An
example of the structure of each cholesteric liquid crystal element
will be described later.
[0059] The light exiting from the cholesteric liquid crystal device
11 after having its color switched is still right-handed circularly
polarized light. The quarter-wave plate 19 then converts the light
into linearly polarized light, for example, S-polarized light. The
light then passes through the above-mentioned optical integrator
system, enters the PBS prism 12, and is then reflected inside it so
as to strike the display panel 9. The display panel 9 is realized
with, for example, a reflective liquid crystal display panel. The
display panel 9 reflects, pixel by pixel, the light it is
illuminated with by rotating (when "on") or not rotating (when
"off") the polarization plane of the light according to the display
data of R, G, and B colors fed thereto.
[0060] Here, the light reflected by the "off" pixels returns to the
PBS prism 12, and, since this light is S-polarized light, it is
reflected from the PBS prism 12 so as to be directed back to the
light source 1. On the other hand, the light reflected by the "on"
pixels, which has thereby been converted into P-polarized light, is
transmitted through the PBS prism 12 so as to reach the optical
projection system 10. The display data presented on the display
panel 9 is projected, as an image, onto a screen (not shown)
through this optical projection system 10.
[0061] FIGS. 4A and 4B are sectional views schematically showing
the structure of each cholesteric liquid crystal element. As shown
in these figures, the cholesteric liquid crystal element has
cholesteric liquid crystal material 35 sandwiched between ITO films
(transparent electrodes) 32 formed over the inner surfaces of a
pair of glass substrates (or transparent film substrates) 31, which
are arranged so as to face each other. When a high voltage pulse
from a voltage pulse source 36 is applied between the ITO films 32,
as shown in FIG. 4A, the liquid crystal molecules 35a are brought
into a so-called planar orientation and thus into an opaque state.
Here, let the so-called twist pitch of the liquid crystal molecules
35a be p, and let the average refractive index of the cholesteric
liquid crystal 35 be n.sub.a, then the wavelength of the light
reflected is given by .lambda.=n.sub.ap.
[0062] As shown in FIG. 4A, the light incident on the cholesteric
liquid crystal 35 is indicated by arrow A. In the opaque state,
light of a particular wavelength is reflected as indicated by arrow
B, and light of other wavelengths is transmitted as indicated by
arrows C. In contrast, when a lower voltage pulse from the pulse
voltage source 36 is applied between the ITO films 32 as shown in
FIG. 4B, the liquid crystal molecules 35a are brought into a
so-called focal conic orientation and thus into a transparent
state. In this state, all the light incident on the cholesteric
liquid crystal 35 is transmitted, as indicated by arrows D.
[0063] Thus, by switching the voltage of the pulse applied to the
ITO films 32 between a high voltage pulse and a low voltage pulse,
it is possible to switch the cholesteric liquid crystal 35 between
an opaque state and a transparent state at high speed. That is, by
preparing different types of cholesteric liquid crystal materials
35 that act on light of different wavelength ranges, for example
the wavelength ranges of R, G, and B colors, and laying cholesteric
liquid crystal elements having such different types of cholesteric
liquid crystal one over another, it is possible, as described
above, to reflect light of R, G, and B colors one after another on
a time-divisional basis by switching on and off the individual
cholesteric liquid crystal elements one after another at high speed
through pulse control.
[0064] FIG. 5 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a second embodiment of the invention. In FIG. 5,
reference numeral 1 represents a light source, and reference
numeral 2 represents a reflector disposed so as to partially
surround the light source 1. A PBS (polarizing beam splitter) prism
unit 3 is disposed immediately behind the reflector 2, i.e., on the
right side thereof in FIG. 5. The PBS prism unit 3 includes a
plurality of PBS prisms arranged parallel to one another. The PBS
prism unit 3 splits the light from the light source 1 into two
differently polarized types of light. Of the individual PBS prisms
3a and 3b, those which let out P-polarized light have half-wave
plates 4 disposed immediately behind them.
[0065] Behind the PBS prism unit 3 (i.e., on the right side thereof
in FIG. 5) are disposed, in order of arrangement, a liquid crystal
hologram device 13, a first lens array 5, a second lens array 6,
and a superimposing lens 7 immediately behind it. The first lens
array 5 has a plurality of lens cells 5a arranged in a rectangular,
grid-like array, having an aspect ratio substantially identical to
that of a display panel 9 to be described later. Similarly, the
second lens array 6 also has a plurality of lens cells 6a arranged
in a rectangular, grid-like array. However, the shape of the lens
cells 6a of the second lens array 6 is not necessarily
geometrically similar to that of the lens cells 5a.
[0066] The liquid crystal hologram device 13 is one type of a color
switching device that electrically switches the color of
illumination light on a time-divisional basis from one color to
another among R, G, and B colors. How this is achieved will be
described in detail later. The images from the individual lens
cells 5a of the first lens array 5 are, by the second lens array 6
and the superimposing lens 7 disposed immediately behind it,
superimposed on one another in the vicinity of the focal point of
the superimposing lens 7.
[0067] The components from the first lens array 5 through the
superimposing lens 7 constitute an optical integrator system. The
display panel 9 is disposed at the focal point of the superimposing
lens 7. The display panel 9 is illuminated in a telecentric fashion
by a condenser lens 8 disposed immediately in front of it. A PBS
prism 12 is disposed between the condenser lens 8 and the display
panel 9. Illumination light from the optical illumination apparatus
is converted into projection light by the display panel 9 and
transmitted, via the PBS prism 12, to the optical projection system
10. Projection light is considered to include the image information
from the display panel 9.
[0068] The light emitted from the light source 1 is reflected from
the reflector 2, and is thereby formed into a substantially
parallel beam and directed to the PBS prisms 3a of the PBS prism
unit 3. Here, S-polarized light, indicated by solid lines S, is
transmitted straight through the PBS prisms 3a. On the other hand,
P-polarized light, indicated by broken lines P, is reflected inside
the PBS prisms 3a so as to be directed to the outwardly contiguous
PBS prisms 3b, and is then reflected again inside the PBS prisms 3b
so as to exit therefrom still as P-polarized light. That is, by the
PBS prism unit 3, the light from the light source 1 is split into
two differently polarized types of light in the direction of the
longer sides of the display panel 9, i.e., in a vertical direction
along the plane of the figure.
[0069] The P-polarized light exiting from the PBS prisms 3b is
converted into S-polarized light by being transmitted through the
half-wave plates 4 disposed immediately behind the PBS prisms 3b.
That is, a portion of the light from the light source 1 has its
polarization converted first by the PBS prism unit 3, and then by
the half-wave plates 4, and eventually comes out as uniformly
S-polarized light. This arrangement constitutes a polarization
conversion device. Here, the type of light into which the light
from the light source 1 is converted does not necessarily have to
be S-polarized light, but can be of other polarizations. The
arrangement described thus far, starting with the light source 1
and ending immediately in front of the display panel 9, constitutes
an optical illumination apparatus.
[0070] The light thus converted into uniformly S-polarized light
has its color switched by the liquid crystal hologram device 13,
passes through the above-mentioned optical integrator system, and
eventually strikes the display panel 9. The display panel 9
modulates, pixel by pixel, the light it is illuminated with
according to the display data of R, G, and B colors fed thereto,
and emits the modulated light. The light thus emitted then enters
an optical projection system 10. The display data presented on the
display panel 9 is projected, as an image, onto a screen (not
shown) through this optical projection system 10. Reference numeral
10a represents an aperture stop disposed in the optical projection
system 10.
[0071] FIG. 6 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 5. While FIG. 5 illustrates a conceptual view wherein the
optical system is formed along a straight line, an optical axis of
the optical system is preferably bent at a reflecting surface as
shown in FIG. 6.
[0072] With reference to FIG. 6, the paths of rays in this
embodiment will be described once again below. The light emitted
from the light source 1 is reflected from the reflector 2, and is
thereby formed into a substantially parallel beam and directed to
the PBS prism unit 3. The light has its polarization converted by
this PBS prism unit 3 and the half-wave plates 4 disposed
immediately behind it, and eventually comes out as uniformly
S-polarized light. The light thus converted into uniformly
S-polarized light then strikes the surface of the liquid crystal
hologram device 13 from a direction substantially perpendicular
thereto.
[0073] The liquid crystal hologram device 13 is composed of, for
example, a total of three layers of liquid crystal hologram
elements that are laid over one another, one layer for each of R,
G, and B colors. These liquid crystal hologram elements exhibit
dependence on polarization and on the angle of incidence. Here, the
individual liquid crystal hologram elements are driven by a
controller 16, shown as a block in FIG. 6, on a color-sequential
basis in such a way as to be turned on and off one after another at
a high speed. As a result, light of R, G, and B colors, which are
contained in the white light from the light source 1 is reflected
and diffracted one after another on a time-divisional basis and
exits from the liquid crystal hologram device 13 in a direction
oblique to its surface. The light of the colors that have not been
reflected and diffracted is transmitted through the liquid crystal
hologram device 13. An example of the structure of each liquid
crystal hologram element will be described later.
[0074] The light exiting from the liquid crystal hologram device 13
after having its color switched passes through the above-mentioned
optical integrator system, then enters, as S-polarized light, the
PBS prism 12, and is then reflected inside it so as to strike the
display panel 9. The display panel 9 is realized with, for example,
a reflective liquid crystal display panel. The display panel 9
reflects, pixel by pixel, the light it is illuminated with by
rotating (when "on") or not rotating (when "off") the polarization
plane of the light according to the display data of R, G, and B
colors fed thereto.
[0075] Here, the light reflected by the "off" pixels returns to the
PBS prism 12 and, since this light is S-polarized light, it is
reflected from the PBS prism 12 so as to be directed back to the
light source. On the other hand, the light reflected by the "on"
pixels, which has thereby been converted into P-polarized light, is
transmitted through the PBS prism 12 so as to reach the optical
projection system 10. The display data presented on the display
panel 9 is projected, as an image, onto a screen (not shown)
through this optical projection system 10.
[0076] FIG. 7 is a sectional view schematically showing the
structure of each liquid crystal hologram element. As shown in this
figure, the liquid crystal hologram element has a hologram 33
sandwiched between ITO films (transparent electrodes) 32 formed
over the inner surfaces of a pair of glass substrates (or
transparent film substrates) 31 arranged so as to face each other.
The hologram 33 is produced by irradiating a liquid crystal polymer
with two light beams that intersect each other on the liquid
crystal polymer so as to form interference fringes thereon and then
setting the liquid crystal polymer. Specifically, layers of a
polymer 33a and layers containing clusters of liquid crystal
molecules 33b in the form of minuscule droplets are alternately
laid over one another, with those layers inclined with respect to
the glass substrates 31.
[0077] In a normal state, the refractive index of the liquid
crystal molecules 33b is higher than that of the polymer 33a. In
this state, the hologram 33 reflects and diffracts light of a
particular wavelength range and transmits light of other wavelength
ranges. When an alternating-current or direct-current voltage from
a voltage source 34 is applied between the ITO films 32 so as to
produce an electric field in the hologram 33, the refractive index
of the liquid crystal molecules 33b lowers and becomes
substantially equal to that of the polymer 33a. In this state, the
hologram 33 almost entirely loses its properties as a hologram, and
functions substantially as a transparent plate.
[0078] Thus, by turning the voltage applied to the ITO films 32 on
and off, it is possible to switch the hologram 33 at high speed
between a state in which it functions as a hologram and a state in
which it functions as a transparent plate. That is, by preparing
different types of holograms 33 that act on light of different
wavelength ranges (for example the wavelength ranges of R, G, and B
colors) and laying the liquid crystal hologram elements having such
different types of holograms 33 over one another, it is possible to
reflect and diffract light of R, G, and B colors one after another
on a time-divisional basis by switching on and off the individual
liquid crystal hologram elements one after another at high
speed.
[0079] Now, suppose that, with no voltage applied to the ITO films
32, S-polarized light L is incident to the surface of the glass
substrate 31 from a direction substantially perpendicular thereto.
The hologram 33 lets light of a particular wavelength range emit
therefrom in a direction oblique to the surface of the glass
substrate 31. The angle of emergence .theta. depends on the
inclination of the layers of the polymer 33a and the layers of the
liquid crystal molecules 33b that are laid on one another. In this
embodiment, holograms that provide an angle of emergence .theta. of
about 30 to 40 degrees are used.
[0080] FIG. 8 is a diagram conceptually showing the construction of
an optical display apparatus employing an optical illumination
apparatus of a third embodiment of the invention. In FIG. 8,
reference numeral 1 represents a light source, and reference
numeral 2 represents a reflector disposed so as to partially
surround the light source 1. A set of polarization separation
mirrors 20 are disposed immediately behind the reflector 2, i.e.,
on the right side thereof in FIG. 8. The set of polarization
separation mirrors 20 splits the light from the light source 1 into
two differently polarized types of light. Of the individual
polarization separation mirrors 20a and 20b, those which let out
S-polarized light have half-wave plates 4 disposed immediately
behind them.
[0081] Behind the set of polarization separation mirrors 20 (i.e.,
on the right side thereof in FIG. 8) are disposed, in order of
arrangement, a diffraction grating 14, a first lens array 5, a
second lens array 6, and a superimposing lens 7 immediately behind
it. Although not illustrated here, the light incident on the
diffraction grating 14 is directed along a separately provided
optical path so as to be subjected to color switching. How this is
achieved will be described in detail later. The first lens array 5
has a plurality of lens cells 5a arranged in a rectangular,
grid-like array, having an aspect ratio substantially identical to
that of a display panel 9 to be described later. Similarly, the
second lens array 6 also has a plurality of lens cells 6a arranged
in a rectangular, grid-like array. However, the shape of the lens
cells 6a is not necessarily geometrically similar to that of the
lens cells 5a.
[0082] The diffraction grating 14, in combination with a reflective
light valve to be described later, functions as one type of color
switching device that electrically switches the color of
illumination light on time-divisional basis from one color to
another among R, G, and B colors. How this is achieved will be
described in detail later. The images from the individual lens
cells 5a of the first lens array 5 are, by the second lens array 6
and the superimposing lens 7 disposed immediately behind it,
superimposed on one another in the vicinity of the focal point of
the superimposing lens 7.
[0083] The components from the first lens array 5 through the
superimposing lens 7 constitute an optical integrator system. A
display panel 9 is disposed at the focal point of the superimposing
lens 7. The display panel 9 is illuminated in a telecentric fashion
by a condenser lens 8 disposed immediately in front of it. A PBS
prism 12 is disposed between the condenser lens 8 and the display
panel 9. Illumination light from the optical illumination apparatus
is converted into projection light by the display panel 9 and
transmitted, via the PBS prism 12, to the optical projection system
10. Projection light is considered to include the image information
from the display panel 9.
[0084] The light emitted from the light source 1 is reflected from
the reflector 2, and is thereby formed into a substantially
parallel beam and directed to the polarization separation mirrors
20a of the set of polarization separation mirrors 20. Here,
P-polarized light, indicated by solid lines P, is transmitted
straight through the polarization separation mirrors 20a. On the
other hand, S-polarized light, indicated by broken lines S, is
reflected from the polarization separation mirrors 20a on which it
is incident, directed to the outwardly contiguous polarization
separation mirrors 20b, and is then reflected again from those
polarization separation mirrors 20b. That is, by the set of
polarization separation mirrors 20, the light from the light source
1 is split into two differently polarized types of light in the
direction of the longer sides of the display panel 9 (i.e., in a
vertical direction along the plane of the figure).
[0085] The S-polarized light exiting from the polarization
separation mirrors 20b is converted into P-polarized light by the
half-wave plates 4 disposed immediately behind the polarization
separation mirrors 20b. That is, a portion of the light from the
light source 1 has its polarization converted first by the set 20
of polarization separation mirrors and then by the half-wave plates
4, and eventually comes out as uniformly P-polarized light. This
arrangement constitutes a polarization conversion device. Here, the
type of light into which the light from the light source 1 is
converted does not necessarily have to be P-polarized light, but
can be of other polarizations.
[0086] The arrangement described thus far, starting with the light
source 1 and ending immediately in front of the display panel 9,
constitutes an optical illumination apparatus. As described
previously, the light thus converted into uniformly P-polarized
light then has its color switched by the function of the
diffraction grating 14 and other components, passes through the
above-mentioned optical integrator system, and eventually strikes
the display panel 9. The display panel 9 modulates, pixel by pixel,
the light it is illuminated with according to the display data of
R, G, and B colors fed thereto, and emits the modulated light. The
light thus emitted then enters an optical projection system 10. The
display data presented on the display panel 9 is projected, as an
image, onto a screen (not shown) through this optical projection
system 10. Reference numeral 10a represents an aperture stop
disposed in the optical projection system 10.
[0087] FIG. 9 is a diagram schematically showing an example of a
practical construction of the optical display apparatus shown in
FIG. 8. While FIG. 8 illustrates a conceptual view wherein the
optical system is formed along a straight line, an optical axis of
the optical system is preferably bent at a reflecting surface as
shown in FIG. 9.
[0088] With reference to FIG. 9, the paths of rays in this
embodiment will be described once again below. The light emitted
from the light source 1 is reflected from the reflector 2, and is
thereby formed into a substantially parallel beam and directed to
the set of polarization separation mirrors 20. The light has its
polarization converted by this set of polarization separation
mirrors 20 and the half-wave plates 4 disposed immediately behind
it, and eventually comes out as uniformly P-polarized light. The
light thus converted into uniformly P-polarized light then passes
through a Fresnel lens 21 and then enters the diffraction grating
14. Here, instead of the Fresnel lens 21, it is also possible to
use an ordinary lens.
[0089] The light that has passed through the Fresnel lens 21 and
entered the diffraction grating 14 is preferably polarized in a
direction perpendicular to the plane of the figure. The different
wavelength ranges (i.e., the wavelength ranges of R, G, and B
colors) contained in this light is diffracted at different angles
relative to the plane of the figure (i.e., separated so as to
travel in different directions), passes through a condenser lens
22, and then strikes different regions on a reflective light valve
23 that respectively correspond to the R, G, and B colors. Here,
those regions are individually driven by a controller 17, shown as
a block in FIG. 9, on a color-sequential basis in such a way as to
be turned on and off one after another at a high speed. As a
result, the light of R, G, and B colors is reflected one after
another on a time-divisional basis.
[0090] The light exiting from the reflective light valve 23 after
having its color switched then enters the diffraction grating 14
again so as to be integrated into light that travels in an
identical direction, and then passes through the Fresnel lens 21
again. The light then passes through the above-mentioned optical
integrator system, enters the PBS prism 12 as S-polarized light,
and is then reflected inside it so as to strike the display panel
9. The display panel 9 is realized with, for example, a reflective
liquid crystal display panel. The display panel 9 reflects, pixel
by pixel, the light it is illuminated with by rotating (when "on")
or not rotating (when "off") the polarization plane of the light
according to the display data of R, G, and B colors fed
thereto.
[0091] Here, the light reflected by the "off" pixels returns to the
PBS prism 12, and, since this light is S-polarized light, it is
reflected from the PBS prism 12 so as to be directed back to the
light source 1. On the other hand, the light reflected by the "on"
pixels, which has thereby been converted into P-polarized light, is
transmitted through the PBS prism 12 so as to reach the optical
projection system 10. The display data presented on the display
panel 9 is projected, as an image, onto a screen (not shown)
through this optical projection system 10.
[0092] Although the present invention has been fully described by
way of examples and with reference to the accompanying drawings, it
is to be understood that various changes and modifications will be
apparent to those skilled in the art without departing from the
spirit and scope of the invention. Therefore, unless such changes
and modifications depart from the scope of the present invention,
they should be construed as being included therein.
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