U.S. patent application number 10/749548 was filed with the patent office on 2004-07-22 for projector.
This patent application is currently assigned to Seiko Epson Corporation. Invention is credited to Itoh, Yoshitaka.
Application Number | 20040141153 10/749548 |
Document ID | / |
Family ID | 23937180 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040141153 |
Kind Code |
A1 |
Itoh, Yoshitaka |
July 22, 2004 |
Projector
Abstract
A projector 1 is mainly composed of a polarized light beam
illumination device, a collimating lens 170a, polarized beam
splitter, a reflection-type liquid crystal device, and a projection
optical system. The polarized light beam illumination device
includes a light source, a first optical element, and a second
optical element. Light emitted from the light source is divided
into a plurality of intermediate light beams by the first optical
element, and then converted into polarized light beams having
substantially one polarization direction by the second optical
element. The polarized light beams enter the collimating lens, are
transmitted by the polarized beam splitter, modulated by the
reflection-type liquid crystal device, reflected by the polarized
beam splitter, and then projected on a projection plane via the
projection optical system.
Inventors: |
Itoh, Yoshitaka; (Suwa-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Seiko Epson Corporation
Tokyo
JP
|
Family ID: |
23937180 |
Appl. No.: |
10/749548 |
Filed: |
January 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10749548 |
Jan 2, 2004 |
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10309164 |
Dec 4, 2002 |
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10309164 |
Dec 4, 2002 |
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09487806 |
Jan 20, 2000 |
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6497485 |
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09487806 |
Jan 20, 2000 |
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09011097 |
Jan 27, 1998 |
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6036318 |
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09011097 |
Jan 27, 1998 |
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PCT/JP97/01819 |
May 29, 1997 |
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Current U.S.
Class: |
353/20 ;
348/E5.141; 348/E9.027 |
Current CPC
Class: |
H04N 5/7441 20130101;
H04N 9/3167 20130101 |
Class at
Publication: |
353/020 |
International
Class: |
G03B 021/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 1996 |
JP |
8-135587 |
Claims
What is claimed is:
1. A projector comprising: a light source; a first optical element
that condenses a light beam from said light source and divides the
light beam into a plurality of intermediate light beams, the first
optical element having a light emitting side; a second optical
element placed on the light-emitting side of said first optical
element that converts said plurality of intermediate light beams
into one type of polarized light beams and superimposing the
polarized light beams on a reflection-type modulation device; only
one reflection-type modulation device that modulates light emitted
from said second optical element; a polarized light beam selection
element placed on an optical path between said second optical
element and said reflection-type modulation device that reflects or
transmits the light emitted from said second optical element to
allow the emitted light to reach said reflection-type modulation
device, and that transmits or reflects the light modulated by said
reflection-type modulation device to allow the modulated light to
reach a projection optical system; and a collimating lens placed
between said second optical element and said polarized light beam
selection element.
2. The projector according to claim 1, further comprising a
polarized light conversion element including: a polarized light
separation unit array in which a plurality of polarized light
separation units, each having a pair of a separation surface and a
reflection surface for polarized light, are aligned; and a
selective phase film in which .lambda./2 phase layers are regularly
formed.
3. The projector according to claim 2, further comprising a
light-shielding plate array that prevents the intermediate light
beams from directly entering portions of the reflection surfaces
placed on an incident side of the polarized light separation unit
array.
4. The projector according to claim 1, the one type of polarized
light beams emitted from the second optical element being a
p-polarized light beam type with respect to the polarized light
beam selection element.
5. The projector according to claim 1, further comprising a
polarizer provided on an optical path between the polarized light
beam selection element and the projection optical system.
6. A projector comprising: a light source; a first optical element
that condenses a light beam from the light source and divides the
light beam into a plurality of intermediate light beams, the first
optical element having a light-emitting side; a second optical
element placed on the light-emitting side of the first optical
element that converts the plurality of intermediate light beams
into one type of polarized light beams and superimposing the
polarized light beams a reflection-type modulation device; three
reflection-type modulation devices that modulate color light of
three colors; an optical color-light-separating-and-synthe- sizing
system that separates a light beam emitted from the second optical
element into color light of three colors, and synthesizes each
color light modulated by the three reflection-type modulation
devices; a polarized light beam selection element placed on an
optical path between the second optical element and the optical
color-light-separating-and-syn- thesizing system that reflects or
transmits the light emitted from the second optical element to
allow the emitted light to reach the optical
color-light-separating-and-synthesizing system, and transmits or
reflects light synthesized by the optical
color-light-separating-and-synthesizing system to allow the light
to reach a projection optical system; and a collimating lens placed
between the second optical element and the polarized light beam
selection element.
7. The projector according to claim 6, further comprising a
polarized light conversion element including: a polarized light
separation unit array in which a plurality of polarized light
separation units, each having a pair of a separation surface and a
reflection surface for polarized light, are aligned; and a
selective phase film in which .lambda./2 phase layers are regularly
formed.
8. The projector according to claim 7, further comprising a
light-shielding plate array that prevents the intermediate light
beams from directly entering the portions of the reflection
surfaces placed on an incident side of the polarized light
separation unit array.
9. The projector according to claim 6, the one type of polarized
light beams emitted from the second optical element being a
p-polarized light beam type with respect to the polarized light
beam selection element.
10. The projector according to claim 6, further comprising a
polarizer provided on an optical path between the polarized light
beam selection element and the projection optical system.
11. The projector according to claim 6, the optical
color-light-separating-and-synthesizing system including two
dichroic prisms.
12. The projector according to claim 6, the optical
color-light-separating-and-synthesizing system including one
cross-dichroic prism.
13. The projector according to claim 6, the optical
color-light-separating-and-synthesizing system including a
wedge-shaped dichroic prism.
14. A projector comprising: a light source; a first optical element
that condenses a light beam from the light source and divides the
light beam into a plurality of intermediate light beams, the first
optical element having a light-emitting side; a second optical
element placed on the light-emitting side of the first optical
element that converts the plurality of intermediate light beams
into one type of polarized light beams and superimposing the
polarized light beams on a modulation device; an optical
color-light-separating system that separates a light beam emitted
from the second optical element into color light of three colors;
three modulation devices that modulate each of the color light
separated by the optical color-light-separating system; an optical
color-light-synthesizing system that synthesizes the color light
modulated by the three modulation devices; three polarized light
beam selection elements placed on an optical path between the
optical color-light-separating system and the optical
color-light-synthesizing system that reflects or transmits the
light emitted from the optical color-light-separating system to
allow the emitted light to reach each of the three modulation
devices, and that transmits or reflects the light modulated by the
three modulation devices to allow the modulated light to reach the
optical color-light-synthesizing system; and three collimating
lenses, each placed between the optical color light-separating
system and a polarized light beam selection element.
15. The projector according to claim 14, further comprising a
polarized light conversion element including: a polarized light
separation unit array in which a plurality of polarized light
separation units, each having a pair of a separation surface and a
reflection surface for polarized light, are aligned; and a
selective phase film in which .lambda./2 phase layers are regularly
formed.
16. The projector according to claim 15, further comprising a
light-shielding plate array that prevents the intermediate light
beams from directly entering portions of the reflection surfaces
placed on an incident side of the polarized light separation unit
array.
17. The projector according to claim 14, the one type of polarized
light beams emitted from the second optical element being a
p-polarized light beam type with respect to at least one polarized
light beam selection element.
18. The projector according to claim 14, further comprising a
polarizer provided on an optical path between at least one
polarized light beam selection element and a projection optical
system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a projector for projecting
and displaying a display image formed by a reflection-type
modulation device, such as a reflection-type liquid crystal device,
on a projection plane.
[0003] 2. Description of Related Art
[0004] Nowadays, a projector using a transmissive liquid crystal
device as a light valve is well known as a method for displaying a
large screen image. As an example of such a projector, a typical
construction of a projector using three transmissive liquid crystal
devices is shown in FIG. 12.
[0005] A light source 110 is composed of a light source lamp 111
and a paraboloidal reflector 112, and light emitted from the light
source lamp 111 is reflected by the paraboloidal reflector 112 to
enter a dichroic mirror 401. The light is separated into red light,
green light, and blue light by two dichroic mirrors 401 and 402,
each having wavelength-selectivity, and then illuminates
transmissive liquid crystal devices 301R, 301G, and 301B
corresponding to each color light. The light transmitted by each of
the transmissive liquid crystal devices is synthesized by a
cross-dichroic prism 420, and is projected and displayed on a
projection plane 600 via a projection optical system 500.
Reflecting mirrors 403, 404, and 405 for reflecting light beams are
provided on an optical path of the red light and an optical path of
the blue light.
[0006] In the cross-dichroic prism 420 used as a
color-light-synthesizing unit, dichroic films are arranged in the
form of an X. The color-light-synthesizing unit of the projector
using three liquid crystal devices can be realized by arranging two
cross-dichroic mirrors in parallel with each other instead of the
cross-dichroic prism 420. The use of the cross-dichroic prism 420,
however, is characterized by providing a bright projected image
without using a large-aperture projection lens because the distance
between the liquid crystal devices 301R, 301G, and 301B and the
projection optical system 500 can be shortened as compared with a
case where the two dichroic mirrors are arranged in parallel with
each other.
[0007] In the conventional projector, however, while the optical
path can be shortened by the use of the cross-dichroic prism 420 in
a color-light-synchronization portion, the length of the optical
path is considerably long in a color-light-separation portion
because the dichroic mirrors 401 and 402, and the reflecting
mirrors 403, 404, and 405 are used. Therefore, in the conventional
projector, the light loss in a light separating process is large,
and characteristics of the cross-dichroic prism 420 cannot be
sufficiently utilized.
[0008] A light beam emitted from the light source 110 composed of
the light source lamp 111 and the paraboloidal reflector 112 has a
non-uniform light intensity distribution in a cross section of the
light beam, and has characteristics such that the light intensity
of illumination light near an optical axis of the light source is
high, and the light intensity of the illumination light decreases
with distance from the optical axis. Therefore, in the conventional
projector shown in FIG. 12, the light intensity of the illumination
light is non-uniformly distributed on the liquid crystal devices
301R, 301G, and 301B, which are areas to be illuminated, and
non-uniform brightness or color shading occurs in an image
projected on the projection plane 600.
[0009] Furthermore, when the brightness of the projected image is
to be considerably increased using a light source lamp having
extremely high optical output, light absorption is large in the
liquid crystal devices of the conventional projector using the
transmissive liquid crystal devices, and a large-scale cooling
device for cooling the liquid crystal devices is absolutely
required.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a
projector capable of obtaining a bright projected image without
using a large-aperture projection lens by shortening the length of
an optical path to prevent the loss of light.
[0011] In addition, it is an object to provide a projector which
reduces non-uniformity of light intensity distribution of
illumination light in an area to be illuminated, and which provides
uniform brightness and excellent image quality.
[0012] Furthermore, it is an object to provide a projector which
does not require a large-scale cooling device even if a light
source lamp having extremely high optical output is used.
[0013] A first projector of the present invention may consist of: a
light source, a first optical element for condensing a light beam
from the light source and dividing the light beam into a plurality
of intermediate light beams, a second optical element placed on the
light-emitting side of the first optical element for converting the
plurality of intermediate light beams into one type of polarized
light beams and superimposing the polarized light beams on a
reflection-type modulation device, only one reflection-type
modulation device for modulating light emitted from the second
optical element, a polarized light beam selection element placed on
an optical path between the second optical element and the
reflection-type modulation device for reflecting or transmitting
the light emitted from the second optical element to allow the
light to reach the reflection-type modulation device and for
transmitting or reflecting the light modulated by the
reflection-type modulation device to allow the light to reach a
projection optical system, and a collimating lens placed between
the second optical element and the polarized light beam selection
element.
[0014] According to the above construction of the first projector
of the present invention, the length of the optical path can be
extremely shortened, and the loss of light can be minimized.
Therefore, it is possible to obtain an extremely bright projected
image without using a large-aperture projection lens.
[0015] As the first optical element, a lens array having, for
example, a plurality of light beam-dividing lenses arranged in a
matrix may be used. By dividing the light beam from the light
source into a plurality of intermediate light beams with such a
lens array, and by superimposing the intermediate light beams on an
area to be illuminated, non-uniform luminance can be further
reduced than that of a single light beam. Therefore, even if the
light beam emitted from the light source has a non-uniform light
intensity distribution within a cross section of the light beam,
illumination light having uniform brightness can be obtained. In
particular, when the light intensity distribution of the light beam
is not random, but the light intensity distribution has a fixed
tendency as seen in a light beam emitted from a light source
composed of a light source lamp and a paraboloidal reflector, the
use of the above first optical element can make the light intensity
distribution and angular distribution of the illumination light on
the area to be illuminated extremely uniform.
[0016] The second optical element separates each of the
intermediate light beams into a p-polarized light beam and an
s-polarized light beam, aligns the polarization direction, and
finally superimposes the light beams on a single area to be
illuminated. In the conventional projector, only one of the
p-polarized light beam and the s-polarized light beam can be used
and the light loss is large in some polarized light beams. If the
second optical element of the present invention is used, however,
both of the polarized light beams can be used most efficiently.
Therefore, it is possible to obtain a bright image. Since the
plurality of divided intermediate light beams are finally
superimposed on the single area to be illuminated, the polarized
light beams having uniform brightness can be obtained as
illumination light even if the light beam emitted from the light
source has a non-uniform light intensity distribution within the
cross section of the light beam. In particular, even if the
intermediate light beams cannot be separated into the p-polarized
light beams and the s-polarized light beams with uniform light
intensity distribution or spectral characteristics, or even if the
light intensity or the spectral characteristics of one of the
p-polarized light beams is changed in a process of making the
polarization directions of both of the polarized light beams
uniform, polarized light beams having uniform brightness and less
color shading can be obtained as illumination light.
[0017] A second projector of the present invention may consist of:
a light source, a first optical element for condensing a light beam
from the light source and dividing the light beam into a plurality
of intermediate light beam, a second optical element placed on the
light-emitting side of the first optical element for converting the
plurality of intermediate light beam into one type of polarized
light beams and for superimposing the polarized light beams on a
reflection-type modulation device, an optical color-light-producing
system for producing a plurality of color light by time division
from light emitted from the second optical element, only one
reflection-type modulation device for modulating color light
produced by the optical color-light-producing system, a polarized
light beam selection element placed on an optical path between the
second optical element and the reflection-type modulation device
for reflecting or transmitting the light emitted from the second
optical element to allow the light to reach the reflection-type
modulation device and for transmitting or reflecting light
modulated by the reflection-type modulation device to allow the
light to reach a projection optical system, and a collimating lens
placed between the second optical element and the polarized light
beam selection element.
[0018] It is possible to obtain advantages similar to those of the
first projector by the second projector of the present invention.
Furthermore, since a color image can be displayed without
containing a color filter of large light loss in the
reflection-type modulation device, it is possible to prevent the
light loss and obtain a bright projected image.
[0019] A third projector of the present invention may consist of: a
light source, a first optical element for condensing a light beam
from the light source and dividing the light beam into a plurality
of intermediate light beams, a second optical element placed on the
light-emitting side of the first optical element for converting the
plurality of intermediate light beams into one type of polarized
light beams and for superimposing the polarized light beams on a
reflection-type modulation device, three reflection-type modulation
devices for modulating color light of three colors, an optical
color-light-separating-and-synthesizing system for separating a
light beam emitted from the second optical element into color light
of three colors and for synthesizing each color light modulated by
the three reflection-type modulation devices, a polarized light
beam selection element placed on an optical path between the second
optical element and the optical
color-light-separating-and-synthesizing system for reflecting or
transmitting the light emitted from the second optical element to
allow the light to reach the optical
color-light-separating-and-synthesizing system and for transmitting
or reflecting the light synthesized by the optical
color-light-separating-an- d-synthesizing system to allow the light
to reach a projection optical system, and a collimating lens placed
between the second optical element and the polarized light beam
selection element.
[0020] In the second projector of the present invention, since the
function of separating light and the function of synthesizing light
are achieved by the same unit, the necessity for placing dichroic
mirrors 401 and 402, or reflecting mirrors 403, 404, and 405, as in
the above-described conventional projector, is eliminated.
Therefore, the length of the optical path can be extremely
shortened, and the loss of light can be minimized. Therefore, an
extremely bright projected image can be obtained without using a
large-aperture projection lens.
[0021] As the first optical element, a lens array having, for
example, a plurality of light beam-dividing lenses arranged in a
matrix may be used. By dividing the light beam from the light
source into a plurality of intermediate light beams with such a
lens array, and by superimposing the intermediate light beams on an
area to be illuminated, non-uniform luminance can be further
reduced than that of a single light beam. Therefore, even if the
light beam emitted from the light source has a non-uniform light
intensity distribution within a cross section of the light beam,
illumination light having uniform brightness can be obtained. In
particular, when the light intensity distribution of the light beam
is not random, but the light intensity distribution has a fixed
tendency as seen in a light beam emitted from a light source
composed of a light source lamp and a paraboloidal reflector, the
use of the above first optical element can make the light intensity
distribution and angular distribution of the illumination light on
the area to be illuminated extremely uniform.
[0022] The second optical element separates each of the
intermediate light beams into a p-polarized light beam and an
s-polarized light beam, aligns the polarization direction of one of
the polarized light beams with that of the other one of polarized
light beams, and finally superimposes the light beams on a single
area to be illuminated. In the conventional projector, only one of
the p-polarized light beams and the s-polarized light beams can be
used, and the light loss is large in some polarized light beams. If
the second optical element of the present invention is used,
however, both of the polarized light beams can be used most
efficiently. Therefore, it is possible to obtain a bright image.
Since the plurality of divided intermediate light beams are finally
superimposed on the single area to be illuminated, the polarized
light beams having uniform brightness can be obtained as
illumination light even if the light beam emitted from the light
source has a non-uniform light intensity distribution within the
cross section of the light beam. In particular, even if the
intermediate light beams cannot be separated into the p-polarized
light beams and the s-polarized light beams with uniform light
intensity distribution or spectral characteristics, or even if the
light intensity or the spectral characteristics of one of the
p-polarized light beams is changed in a process of aligning the
polarization directions of both of the polarized light beams,
polarized light beams having uniform brightness and less color
shading can be obtained as illumination light.
[0023] In the third projector, one of constructions including two
dichroic prisms, including one cross-dichroic prism, and including
a wedge-like prism can be used as the
color-light-separating-and-synthesizing optical system.
[0024] A fourth projector of the present invention may consist of:
a light source, a first optical element for condensing a light beam
from the light source and dividing the light beam into a plurality
of intermediate light beams, a second optical element placed on the
light-emitting side of the first optical element for converting the
plurality of intermediate light beams into one type of polarized
light beams and for superimposing the polarized light beams on a
reflection-type modulation device, an optical
color-light-separating system for separating a light beam emitted
from the second optical element into color light of three colors,
three modulation devices for modulating each of the color light
separated by the optical color-light-separating system, an optical
color-light-synthesizing system for synthesizing the color light
modulated by the three modulation devices, three polarized light
beam selection elements placed on an optical path between the
optical color-light-separating system and the optical
color-light-synthesizing system for reflecting or transmitting the
light emitted from the optical color-light-separating system to
allow the light to reach each of the modulation devices, and for
transmitting or reflecting the light modulated by the modulation
devices to allow the light to reach the optical
color-light-synthesizing system, and three collimating lenses, each
placed between the optical color light-separating system and the
polarized light beam selection element.
[0025] As the first optical element, a lens array having, for
example, a plurality of light beam-dividing lenses arranged in a
matrix may be used. By dividing the light beam from the light
source into a plurality of intermediate light beams with such a
lens array, and by superimposing the intermediate light beams on an
area to be illuminated, non-uniform luminance can be further
reduced than that of a single light beam. Therefore, even if the
light beam emitted from the light source has a non-uniform light
intensity distribution within a cross section of the light beam,
illumination light having uniform brightness can be obtained. In
particular, when the light intensity distribution of the light beam
is not random, but the light intensity distribution has a fixed
tendency as seen in a light beam emitted from a light source
composed of a light source lamp and a paraboloidal reflector, the
use of the above first optical element can make the light intensity
distribution and angular distribution of the illumination light on
the area to be illuminated extremely uniform.
[0026] The second optical element separates each of the
intermediate light beams into a p-polarized light beam and an
s-polarized light beam, aligns the polarization direction of one of
the polarized light beams with that of the other one of polarized
light beams, and finally superimposes the light beams on a single
area to be illuminated. In the conventional projector, only one of
the p-polarized light beam and the s-polarized light beam can be
used and the light loss is large in some polarized light beams. If
the second optical element of the present invention is used,
however, both of the polarized light beams can be used most
efficiently. Therefore, it is possible to obtain a bright image.
Since the plurality of divided intermediate light beams are finally
superimposed on the single area to be illuminated, the polarized
light beams having uniform brightness can be obtained as
illumination light even if the light beam emitted from the light
source has a non-uniform light intensity distribution within the
cross section of the light beam. In particular, even if the
intermediate light beams cannot be separated into the p-polarized
light beams and the s-polarized light beams with uniform light
intensity distribution or spectral characteristics, or even if the
light intensity or the spectral characteristics of one of the
p-polarized light beams is changed in a process of aligning the
polarization directions of both of the polarized light beams,
polarized light beams having uniform brightness and less color
shading can be obtained as illumination light.
[0027] In the fourth projector, since the three polarized light
beam selection elements corresponding to each of color light are
used, the wavelength range of the polarized light beam selection
elements can be restricted, and both an increase in performance and
a cost reduction can be relatively easily achieved. Therefore, it
is possible to realize a brighter projected image having a wider
range of colors.
[0028] As a polarized light conversion element of the second
optical element in the above first to fourth projectors, a
plate-like polarized light conversion element can be employed which
includes a polarized light separation unit array in which a
plurality of polarized light separation units each having a pair of
a separation surface and a reflection surface for polarized light
are aligned and a selective phase film in which .lambda./2 phase
layers are regularly formed. By employing such a polarized light
conversion element, polarized light conversion can be performed
with a small space and without extending the width of the light
beam emitted from the light source.
[0029] In this case, it is preferable that a light-shielding plate
array for preventing the intermediate light beams from directly
entering the portions of the reflection surfaces be placed on the
incident side of the polarized light separation unit array. If such
a light-shielding plate array is placed, a degree of polarization
of the polarized light beams emitted from the second optical
element can be further increased.
[0030] In the above first to fourth projectors, it is preferable
that the one type of polarized light beams emitted from the second
optical element be p-polarized light beams with respect to the
polarized light beam selection element. With this construction, a
projected image having high contrast can be easily obtained.
[0031] In the above first to fourth projectors, a polarizer may
preferably be provided on an optical path between the polarized
light beam selection element and the projection optical system.
With this construction, a degree of polarization of the polarized
light emitted from the polarized light beam selection element.
Accordingly, an image projected on a display plane or a projection
plane via the projection optical system can be increased.
Therefore, by placing the polarizer in this way, the contrast of
the projected image can be increased, and the extreme high-quality
projected image can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 schematically shows the construction of a principal
part of a projector 1 of a first embodiment.
[0033] FIG. 2 is a perspective view showing the construction of a
first optical element 120 in a polarized light beam illumination
device 100.
[0034] FIG. 3 is a view for the explanation of the function of a
second optical element 130 in the polarized light beam illumination
device 100.
[0035] FIG. 4(A) is a perspective view showing the construction of
a polarized light separation unit array 141 in the polarized light
beam illumination device 100; and FIG. 4(B) is a perspective view
showing the construction of a selective phase film 147.
[0036] FIG. 5 is a schematic sectional view showing an example of a
reflection-type liquid crystal device.
[0037] FIG. 6 schematically shows the construction of a principal
part of a projector 2 of a second embodiment.
[0038] FIG. 7 is an external view of a rotary color filter used in
the projector 2 of the second embodiment.
[0039] FIG. 8 schematically shows the construction of a principal
part of a projector 3 of a third embodiment.
[0040] FIG. 9 schematically shows the construction of a principal
part of a projector 4 of a fourth embodiment.
[0041] FIG. 10 schematically shows the construction of a principal
part of a projector 5 of a fifth embodiment.
[0042] FIG. 11 schematically shows the construction of a principal
part of a projector 6 of a sixth embodiment.
[0043] FIG. 12 schematically shows the construction of a principal
part of a conventional projector.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0044] Embodiments of the present invention will now be described
with reference to the drawings. In the following embodiments, three
directions which are perpendicular to each other are conveniently
referred to as the X direction, the Y-axis direction, and the
Z-axis direction, and the Z-axis direction is referred to as the
direction of light propagation.
[0045] (First Embodiment)
[0046] FIG. 1 includes a schematic plan view showing the
construction of a principal part of a projector 1 of the first
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120 to be described
hereinbelow.
[0047] The projector 1 of this embodiment is mainly composed of a
polarized light beam illumination device 100 which is mainly
composed of a light source 110 placed along two system optical axes
L1 and L2 which are perpendicular to each other, a first optical
element 120, and a second optical element 130; a reflection-type
liquid crystal device 300 for optically modulating polarized light
beams from the polarized light beam illumination device 100
according to external image information (not shown) to produce a
modulated light beam; an projection optical system 500 for
projecting the light beam modulated by the reflection-type liquid
crystal device 300 on a projection plane 600; a polarized light
beam selection element 200 placed between the reflection-type
liquid crystal device 300 and the polarized light beam illumination
device 100, transmitting the polarized light beams from the
polarized light beam illumination device 100 and allowing the
polarized light beams to reach the reflection-type liquid crystal
device 300, and reflecting the light beam modulated by the
reflection-type liquid crystal device 300 and allowing the
modulated luminous flux to reach the projection optical system 500;
a collimating lens 170 placed between the polarized light beam
illumination device 100 and the polarized light beam selection
element 200; and a polarizer 180 placed between the polarized light
beam selection element 200 and the projection optical system
500.
[0048] The light source 110 is mainly composed of a light source
lamp 111 and a paraboloidal reflector 112. Light emitted from the
light source lamp 111 is reflected by the paraboloidal reflector
112 in one direction, and becomes substantially a parallel light
beam which enters the first optical element 120. A metal halide
lamp, a xenon lamp, a high-pressure mercury lamp, or a halogen lamp
can be used as the light source lamp 111, and an ellipsoidal
reflector or a spherical reflector can be used as the reflector in
addition to the paraboloidal reflector, described in this
embodiment.
[0049] The first optical element 120, as the appearance thereof is
shown in FIG. 2, is a lens array including a plurality of
rectangular light beam-dividing lenses 121 arranged in the form of
a matrix. The positional relationship between the light source 110
and the first optical element 120 is set so that a light source
optical axis R is placed substantially in the center of the first
optical element 120. The light incident on the first optical
element 120 is divided into a plurality of intermediate light beams
by the light beam-dividing lenses 121, and at the same time, by a
condensing operation of the light beam-dividing lenses, as many
focal images 123 as the number of light beam-dividing lenses are
formed at positions within a plane perpendicular to the system
optical axis L1 (the XY plane in FIG. 1) where the intermediate
light beams converge. Hereinafter, a plane on which these focal
images 123 are formed is referred to as a virtual plane Q. The
shape of the cross section of each light beam-dividing lens 121 may
be designed so as to be nearly similar to the shape of a display
area (area to be illuminated) of the reflection-type liquid crystal
device 300. In this embodiment, the display area is assumed to have
a rectangular area on the XY plane to be illuminated that is longer
in the X direction, thus the cross section of each light
beam-dividing lens 121 also has a rectangular shape that is longer
in the X direction.
[0050] The function of the second optical element 130 will now be
described with reference to FIG. 3.
[0051] The second optical element 130 is a composite element which
is placed on or near the virtual plane Q, and is generally
consisted of a condenser lens array 131, a light-shielding plate
array 135, a plate-like polarized light conversion element 140
comprising a polarized light separation unit array 141 and a
selective phase film 147, and a superimposing lens 150 for
superimposing intermediate light beams 122 emitted from the
polarized light conversion element 140 on a predetermined area 160
to be illuminated. The second optical element 130 has the function
of separating each of the intermediate light beams 122 into a
p-polarized light beam and an s-polarized light beam, of converting
the beams into one type of polarized light beams, and of
superimposing the polarized light beams on one area 160 to be
illuminated.
[0052] A placement pattern of the condenser lens array 131, the
polarized light conversion element 140 and the superimposing lens
150 which constitute the second optical element 130 is not limited
to one pattern, but various placement patterns can be employed.
More specifically, the following three patterns can be used, each
including the placement order from the light source 110. Pattern 1:
the condenser lens array 131, the polarized light conversion
element 140, and the superimposing lens 150; Pattern 2: the
polarized light conversion element 140, the condenser lens array
131, and the superimposing lens 150; and Pattern 3: the condenser
lens array 131, the superimposing lens 150, and the polarized light
conversion element 140. Pattern 1 is easily employed when attaching
importance to light utilization factor in the polarized light
conversion element 140, and Pattern 1 is employed in this
embodiment.
[0053] The condenser lens array 131 is constructed, in a manner
similar to the first optical element 120, by aligning a plurality
of condenser lenses 132, as many as the light beam-dividing lenses
constituting the first optical element 120, in a matrix. There is
no restriction in the external shape of each condenser lens 132 on
the XY plane. However, if a shape can be arrayed easily, such as a
rectangular or hexagonal shape, the cost of manufacturing the
condenser lens array 131 can be reduced. Therefore, in this
embodiment, the condenser lens array 131 is constructed using
condenser lenses each having a shape substantially similar to that
of the light beam-dividing lenses 121 constituting the first
optical element 120. The condenser lens array 131 has the function
of transmitting images formed on the light beam-dividing lenses 121
of the first optical element 120 on the single area 160 to be
illuminated via the polarized light separation unit array 141 and
the superimposing lens 150. In addition, in this embodiment, since
the condenser lens array 131 is placed on the incident side of the
polarized light conversion element 140, the condenser lens array
131 has the function of introducing the intermediate light beams
122 from the first optical element 120 into a specific incident end
surface of the polarized light conversion element 140, and of
converting the intermediate light beams so that central axes of the
intermediate light beams are substantially parallel to the system
optical axis L1. In general, in order to increase polarization
convertibility of the polarized light conversion element 140, the
intermediate light beams 122 are preferably incident on polarized
beam separation surfaces 143 to be described hereinbelow at an
incident angle of 45 degrees, that is, incident on the incident end
surface of the polarized light conversion element 140 at an
incident angle of 0 degree. Therefore, lens characteristics of the
condenser lenses 132 are set according to the characteristics of
the intermediate light beams 122 divided by the first optical
element 120. With regard to the placement pattern of the condenser
lens array 131, the polarized light conversion element 140, and the
superimposing lens 150, the placement Patterns 2 and 3 can be
employed as described above. In particular, these patterns are
suitable when the light beams emitted from the light source 110
have excellent parallelism. In the above two patterns, since the
condenser lens array 131 is adjacent to the superimposing lens 150,
the cost of the illumination device can be reduced by allowing the
condenser lens array 131 to also have the function of the
superimposing lens 150, thereby allowing the superimposing lens 150
to be omitted. In these patterns, however, since the incident angle
of the intermediate light beams incident on the polarized beam
separation surfaces 143 of the polarized light conversion element
140 varies for each polarized light separation unit 142 to be
described hereinbelow, it is preferable that optical
characteristics of the polarized beam separation surfaces 143 be
set for each polarized light separation unit 142.
[0054] As shown in FIG. 4(A), the polarized light separation unit
array 141 is composed of a plurality of polarized light separation
units 142 aligned in the X-axis direction. Each of the polarized
light separation units 142 is a square rod-like structure including
the polarized beam separation surface 143 and a reflection surface
144 as a pair within a prism formed of optical glass, and has the
function of separating each of incident intermediate light beams
into a p-polarized light beam and an s-polarized light beam,
respectively. The polarized beam separation surfaces 143 and the
reflection surfaces 144 are arranged so that they are alternately
aligned in the X-axis direction while keeping them substantially
parallel, and they are inclined about 45 degrees with respect to
the system optical axis L1. In addition, the polarized beam
separation surfaces 143 and the reflection surfaces 144 are
arranged so as not to overlap, and therefore, an area of each
polarized beam separation surface 143 projected on the XY plane is
equal to an area of each reflection surface 144 projected on the XY
plane. Each of the polarized beam separation surfaces 143 can be
formed by a dielectric multilayer film and the like, and each of
the reflection surfaces 144 can be formed by a dielectric
multilayer film or an aluminum film. The polarized light separation
unit array 141 may have a structure including therein a plurality
of pairs of the polarized beam separation surfaces 143 and the
reflection surfaces 144, and is not necessarily composed of a
plurality of the polarized light separation units 142. The idea of
the polarized light separation unit 142 is merely introduced for
easy explanation of the function of the polarized light separation
unit array 141. Furthermore, all of the polarized light separation
units 142 are not necessarily aligned in the same direction. For
example, each of the polarized light separation units 142 may be
placed so that each polarized beam separation surface 143 can be
folded and positioned using the YZ plane as a plane of symmetry.
The alignment direction of the polarized light separation units 142
is not limited to one direction. For example, the polarized light
separation unit array 141 may be composed of the polarized light
separation units 142 aligned in the X-axis direction and the
polarized light separation units. 142 aligned in the Y-axis
direction. In short, it is preferable that the method of alignment
of the polarized light separation units 142 be determined so that
the intermediate light beams 122 can be efficiently incident on the
polarized beam separation surfaces 143. Furthermore, the placement
distance (plane distance) between each polarized beam separation
surface 143 and each reflection surface 144 is equally set for all
the polarized light separation units 142, and the distance may be
different for each polarized light separation unit 142.
[0055] Light incident on the polarized light separation unit 142 is
separated into p-polarized light beams transmitted by the polarized
beam separation surfaces 143 and s-polarized light beams reflected
by the polarized beam separation surfaces 143 to change the
direction of travel toward the reflection surfaces 144. The
p-polarized light beams are emitted from a p-polarized light-beam
emitting surface 145 of the polarized light separation unit 142. On
the other hand, the s-polarized light beams are reflected by the
reflection surfaces 144 and become substantially parallel to the
p-polarized light beams to be emitted from an s-polarized
light-beam emitting surface 146 of the polarized light separation
unit 142. That is, the intermediate light beams 122 incident on the
polarized light separation unit 142 and having random polarization
directions are separated by the polarized light separation unit 142
into p-polarized light beams and s-polarized light beams, and are
emitted from the p-polarized light-beam emitting surface 145 and
the s-polarized light beam-emitting surface 146 in substantially
the same direction. There is some way to construct polarized beam
separation surfaces that reflect the p-polarized light beams and
transmit the s-polarized light beams, and such polarized beam
separation surfaces may be used in the polarized light separation
unit 142 of the present invention.
[0056] In the polarized light beam illumination device 100 of the
present invention, it is necessary to guide the intermediate light
beams into the polarized beam separation surfaces 143 of the
polarized light separation unit 142. Therefore, in this embodiment,
the condenser lens array 131 is placed in a state of being shifted
in the X-axis direction with respect to the polarized light
separation unit array 141 by a distance D equivalent to 1/4 of the
width W of the polarized light separation unit 142 so that the
intermediate light beams 123 are condensed at the center portions
of the polarized beam separation surfaces 143. The first optical
element 120 and the light source 110 are similarly placed in a
state of being shifted in parallel (see FIG. 3).
[0057] On the incident side of the polarized light separation unit
array 141, the light-shielding plate array 135 is placed for
allowing the intermediate light beams 122 to be incident only on
the polarized beam separation surfaces 143 and preventing the
intermediate light beams 122 from being directly incident on the
reflection surfaces 144. The light-shielding plate array 135 has
openings 136 and light-shielding portions 137 arrayed corresponding
to the polarized beam separation surfaces 143 and the reflection
surfaces 144 of the polarized light separation unit array 141. A
light-shielding plate array in which light-shielding plates, such
as metal plates, are arrayed or conversely, a light-shielding plate
in which openings are arrayed in a light-shielding flat plate can
be used. The placement of such a light-shielding plate array can
decrease light beams incident on the reflection surfaces 144 and
emitted from the polarization beam separation surfaces 143 of the
polarized light separation unit array 141, so that a degree of
polarization of the polarized light beams emitted from the
polarized light conversion element 140 can be further increased,
and this is suitable for obtaining polarized light beams incident
on the reflection-type liquid crystal device 300. The position of
the light-shielding plate array 135 is not limited to the incident
side of the polarized light separation unit array 141, and it may
be placed on the incident side of the condenser lens array 131. The
light-shielding plate array 135 may be an optical element that does
not have complete light-shielding properties, such as a
light-scattering element, as long as it does not lose the essence
of the function thereof. Furthermore, when the parallelism of the
light beams emitted from the light source 110 is high, very small
focal images can be formed by the light beam-dividing lenses 121.
In this case, the light-shielding plate array 135 may be
omitted.
[0058] On the side of the light emitting surface of the polarized
light separation unit array 141, the selective phase film 147 is
placed in which .lambda./2 phase layers 148 are regularly formed.
FIG. 4(B) shows an example of the selective phase film 147. The
selective phase film 147 is an optical element in which the
.lambda./2 phase layers 148 are formed only on the s-polarized
light-beam emitting surface 146, and the .lambda./2 phase layers
148 are not formed on the p-polarized light beam-emitting surface
145. Therefore, the s-polarized light beams emitted from the
polarized light separation unit 142 are rotated by the .lambda./2
phase layers 148 in the polarization direction when passing through
the selective phase film 147, and are converted into the
p-polarized light beams. On the other hand, since the .lambda./2
phase layers 148 are not formed on the p-polarized light-beam
emitting surface 145, the p-polarized light beams emitted from the
p-polarized light-beam emitting surface 145 of the polarized light
separation unit 142 pass through the selective phase film 147 as
they are.
[0059] That is, the intermediate light beams 122 emitted from the
first optical element 120 and having random polarization directions
are separated by the polarized light separation unit array 141 into
p-polarized light beams and s-polarized light beams, and are
converted by the selective phase film-147 into one type of
polarized light beams (in this embodiment, p-polarized light beams)
having a uniform polarization direction.
[0060] The superimposing lens 150 (FIG. 3) placed on the side of
light emitting surface of the polarized light conversion element
140 functions as a superimposing element for superimposing the
intermediate light beams 122 converted by the polarized light
conversion element 140 into the p-polarized light beams on the area
160 to be illuminated (display area of the reflection-type liquid
crystal device 300). That is, each of the intermediate light beams
122 (in other words, image surfaces cut out by the light
beam-dividing lenses 121) is converted by the polarized light
conversion element 140 into one type of polarized light beams
having a uniform polarization direction, and is superimposed by the
superimposing lens 150 on the single area 160 to be illuminated. In
this case, since the light intensity is averaged in the process of
superimposing the plurality of divided intermediate light beams
even if the light intensity distribution of each light beam
incident on the first optical element is not uniform within its
incident cross section, the light intensity distribution of the
illumination light on the area to be illuminated is nearly uniform.
Therefore, one type of polarized light beams can nearly uniformly
illuminate the area 160 to be illuminated. The superimposing lens
150 is not necessarily a single lens element, and may be a lens
array composed of a plurality of lenses like the first optical
element 120.
[0061] In summary, illumination light having uniform brightness and
a substantially aligned polarization direction can be obtained by
the polarized light beam illumination device 100. In the polarized
light beam illumination device 100, a plurality of very small focal
images 123 are formed by the first optical element 120, and spaces
generated in the formation process of the focal images where light
does not exit are well utilized, and the reflection surfaces 144 of
the polarized light separation unit 142 are placed in the spaces.
Therefore, the polarized light beam illumination device 100 is
characterized in that widening of the light beam occurs when
separating light beams emitted from the light source into two types
of polarized light beams can be restricted and polarized light
conversion can be effected with a small space. The shape of the
cross section of each of the light beam-dividing lenses 121
constituting the first optical element 120 is formed in the
rectangular shape elongated in the X-axis direction in accordance
with the rectangular shape of the area 160 to be illuminated, which
is elongated in the X-axis direction, and the polarized-beam
separation direction in the polarized light separation unit 142 is
set to the X-axis direction so that two types of polarized light
beams emitted from the polarized light separation unit array 141
are aligned in the X-axis direction. Therefore, the incident angle
of each of the light beams incident on the area 160 to be
illuminated can be decreased, whereby light utilizing efficiency in
the area 160 to be illuminated is increased.
[0062] The condenser lens array 131, the polarized light separation
unit array 141, the selective phase film 147, and the superimposing
lens 150, which constitute the second optical element, are
optically integrated so as to reduce the light loss generated at
the interfaces thereof and further increase light utilization
factor. These optical devices, however, are not necessarily
optically integrated.
[0063] A description will be given returning to FIG. 1 again. The
collimating lens 170 is placed on the incident side of the
polarized light beam selection element 200, and has the function of
converting the plurality of intermediate light beams 122 incident
on the polarized light beam selection element 200 into light beams
substatially parallel to the central axes thereof. In general,
since polarized-beam selecting performance of the polarized light
beam selection element 200 and display performance of the
reflection-type liquid crystal device 300 have great angular
dependency with respect to the incident light beam, it is
preferable that the collimating lens 170 be placed on the incident
side of the polarized light beam selection element 200 to decrease
the incident angle of the light beams incident on the polarized
light beam selection element 200 or the reflection-type liquid
crystal device 300. Therefore, the collimating lens 170 may be
placed between the polarized light beam selection element 200 and
the reflection-type liquid crystal device 300, or the collimating
lens 170 may be omitted according to the optical characteristics of
the polarized light beam selection element 200 or the
reflection-type liquid crystal device 300. Optical integration of
the collimating lens 170 and the polarized light beam selection
element 200 is effective for increasing light utilization factor
because the light loss generated at the interfaces of the
collimating lens 170 and the polarized light beam selection element
200 can be reduced.
[0064] The polarized light beam selection element 200 has a
polarized light beam selection film 201 formed on mating faces of
two prism parts 202 and 203. The polarized light beam selection
film 201 is composed of a dielectric multilayer film or the like,
which reflects s-polarized light beams, and transmits p-polarized
light beams. As described previously, since almost all of the light
beams emitted from the polarized light beam illumination device 100
are converted into one type of polarized light beams, almost all of
the light beams emitted from the polarized light beam illumination
device 100 will be transmitted or reflected by the polarized light
beam selection film 201. In this embodiment, since almost all of
the light beams emitted from the second optical element 130 are
p-polarized light beams, almost all of the light beams incident on
the polarized light beam selection element 200 are transmitted by
the polarized light beam selection film 201 to reach the
reflection-type liquid crystal device 300.
[0065] When the light beams emitted from the second optical element
130 are s-polarized light beams, the light beams incident on the
polarized light beam selection element 200 are reflected by the
polarized light beam selection film 201. Therefore, in such a case,
the reflection-type liquid crystal device 300 may be placed so as
to oppose the optical projection system 500 across the polarized
light beam selection element 200. In addition, a polarized light
beam selection film for reflecting the p-polarized light beams and
transmitting the s-polarized light beams can be realized according
to the construction of the polarized light beam selection film 201
of the polarized light beam selection element 200, and such a
polarized light beam selection film may be used in the polarized
light beam selection element 200 of the present invention.
[0066] The light beams incident on the reflection-type liquid
crystal device 300 change the polarization state based on external
image information (not shown), and become modulated light beams
including the image information.
[0067] An example of the reflection-type liquid crystal device 300
is shown in FIG. 5. The reflection-type liquid crystal device 300
is an active-matrix-type liquid crystal device in which switching
elements consisting of thin-film transistors are connected to
reflective pixel electrodes 319 arranged in a matrix, and has a
structure in which a liquid crystal layer 320 is sandwiched between
a pair of substrates 310 and 330. The substrate 310 is made of
silicon, and sources 311 and drains 316 are formed on a part
thereof. A source electrode 312 and a drain electrode 317 each made
of aluminum, a channel 313 made of silicon dioxide, a gate
electrode including a silicon layer 314 and a tantalum layer 315,
an interlayer insulating film 318, and the reflective pixel
electrodes 319 made of aluminum are formed on the substrate 310,
and the drain electrode 317 and the reflective pixel electrode 319
are electrically connected via a contact hole H. Since the
reflective pixel electrodes 319 are opaque, they can be deposited
on the gate electrode, the source electrode 312, and the drain
electrode 317 via the interlayer insulating film 318. Therefore,
the distance X between the adjacent reflective pixel electrodes 319
can be considerably shortened, and a large aperture ratio can be
obtained. In this embodiment, a holding capacitor section is
composed of the drain 316, a silicon dioxide layer 340, a silicon
layer 341, and a tantalum layer 342.
[0068] On the other hand, the opposing substrate 330 has a counter
electrode 331 made of ITO which is formed on the surface of the
liquid crystal layer 320, and a reflection-preventing layer 332
formed on the other surface. A voltage is applied between the
counter electrode 331 and each of the pixel electrodes 319, whereby
the liquid crystal layer 320 is driven.
[0069] The liquid crystal layer 320 is of a super-homeotropic type
in which liquid crystal molecules are vertically aligned when a
voltage is not applied (OFF), and the liquid crystal molecules are
twisted by 90 degrees when the voltage is applied (ON). As shown in
FIG. 5, p-polarized light beams incident on the reflection-type
liquid crystal device 300 from the polarized light beam selection
element 200 when the voltage is not applied (OFF) are emitted from
the reflection-type liquid crystal device 300 without changing the
polarization directions thereof, transmitted by the polarized light
beam selection element 200, and returned to the polarized light
beam illumination device 100. Therefore, the p-polarized light
beams do not enter the projection optical system 500. On the other
hand, the polarization direction of the p-polarized light beams
incident on the reflection-type liquid crystal device 300 from the
polarized light beam selection element 200 when the voltage is
applied (ON) is changed by twisting of the liquid crystal molecules
321, and the p-polarized light beams are converted into s-polarized
light beams, reflected by the polarized light beam selection film
201, and then enter the projection optical system 500 to be guided
to the projection plane 600.
[0070] The polarizer 180 is placed between the polarized light beam
selection element 200 and the projection optical system 500 to
perform the function of increasing display quality of the projected
image by removing undesired polarization present in the polarized
light beams emitted from the polarized light beam selection element
200 and increasing the degree of polarization of the light beams
incident on the projection optical system 500. Therefore, the
polarizer 180 can be omitted according to the optical
characteristics of the polarized light beam selection element
200.
[0071] As described above, in the projector 1 of this embodiment,
the length of the optical path between the reflection-type liquid
crystal device 300 and the projection optical system 500 is
extremely short. In addition, since the aperture ratio of the
liquid crystal device can be increased, the loss of light can be
prevented to the fullest extent. Therefore, it is possible to
obtain an extremely bright projected image without using a
large-aperture projection lens (projection optical system) having a
small F-number.
[0072] In addition, the first optical element 120 and the second
optical element 130 are used, whereby polarized light beams having
uniform brightness can be obtained as illumination light.
Therefore, it is possible to obtain an extremely bright projected
image without non-uniform brightness or color shading on the entire
display plane or projection plane.
[0073] Furthermore, since the reflection-type liquid crystal device
of smaller light absorption is used, the brightness of the
projected image can be considerably increased without necessitating
a large-scale cooling device, even if a light source lamp having
extremely high optical output is used.
[0074] Still furthermore, illumination light beams incident on the
polarized light beam selection element 200 from the polarized light
beam illumination device 100 are p-polarized light beams, and
projected light beams emitted from the reflection-type liquid
crystal device on the projection plane 600 are s-polarized light
beams. In general, the polarized light beam selection film 201 of
the polarized light beam selection element 200 formed of a
dielectric multilayer film or the like can relatively easily
increase s-polarized light beam reflectance as compared with
p-polarized light beam transmittance. Therefore, with the
construction of this embodiment, a projected image having high
contrast can be easily obtained.
[0075] The structure of the reflection-type liquid crystal device
300, materials of the components thereof, and an operation mode of
the liquid crystal layer 320 are not limited to those in the
above-described examples. For example, a TN liquid crystal, an SH
liquid crystal and the like can be used as the liquid crystal. In
addition, it is possible to use a reflection-type liquid crystal
device using a two-terminal nonlinear element, such as a TFD
(Thin-Filmed-Diode), as the switching element.
[0076] While the above-described reflection-type liquid crystal
device 300 is used for displaying a monochrome image, it can
display a color image if a color filter is placed inside the
reflection-type liquid crystal device 300, or an optical
color-light-producing system utilizing a rotary filter or a
transmitted wavelength selective element is provided between the
light source 110 and the projection optical system 500.
[0077] (Second Embodiment)
[0078] FIG. 6 includes a schematic plan view showing the
construction of a principal part of a projector 2 of the second
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120. In projectors to be
described hereinbelow including a projector of this embodiment,
components similar to the explained components for the projector 1
(first embodiment) are indicated by the same reference numerals as
those used in FIGS. 1 to 5, and a detailed description thereof will
be omitted.
[0079] In the projector 2 of this embodiment, projecting and
displaying of a color image are realized based on the
above-described projector 1 of the first embodiment with a
construction in which an optical color-light-producing system
including a rotary color filter 190 is placed on the incident side
of a collimating lens 170, and a time-division-driving-type
reflective liquid crystal device 300T is provided instead of the
reflection-type liquid crystal device 300. In this embodiment, the
collimating lens 170 is also placed on the incident side of a
polarized light beam selection element 200, and a polarizer 180 is
placed between the polarized light beam selection element 200 and
an projection optical system 500, and the functions thereof are
similar to those of the first embodiment.
[0080] The rotary color filter 190, as the appearance thereof shown
in FIG. 7, is formed by dividing a disc-like transparent substrate
(for example, glass substrate) into at least three areas, and
forming a red-light-transmitting filter 191R, a
green-light-transmitting filter 191G, and a blue-light-transmitting
filter 191B on the areas, and is rotated by a motor or the like
(not shown) using a central axis 192 of the rotary color filter 190
as a rotation axis. Therefore, a light beam emitted from a
polarized light beam illumination device 100 becomes time-divided
color light by being transmitted by the rotary color filter 190,
and enters the time-division-driving-type reflective liquid crystal
device 300T. The transmitting filters 191R, 191G, and 191B are
formed of a dielectric multilayer film or the like.
[0081] The color light incident on the time-division-driving-type
reflective liquid crystal device 300T is optically modulated
according to external image information (not shown) to produce
modulated light beams according to the color light transmitted by
the rotary color filter 190, and is then projected on a projection
plane 600 by the projection optical system 500. Therefore, the
rotation of the rotary color filter 190 is in synchronism with the
transmission of the image information to the reflective liquid
crystal device 300T by a driver circuit (not shown). Since the
modulated light beams according to each of the color light are
successively projected on the projection plane 600 for every very
short period in this way, the projected images thereof can be
recognized as a color image if the projected images are
successively seen.
[0082] According to the construction as described above, since the
projector 2 of this embodiment can display the color image without
containing a color filter of a large light loss in the
reflection-type liquid crystal device, it is possible to prevent
the light loss and obtain a bright projected image.
[0083] Furthermore, the first optical element and the second
optical element are used, whereby polarized light beams having
uniform brightness can be obtained as illumination light.
Therefore, it is possible to obtain an extremely bright projected
image without non-uniform brightness or color shading on the entire
display plane or projection plane.
[0084] Although the transmitting filters 191R, 191G, and 191B
formed of the dielectric multilayer film have a high light
transmittance, they have a drawback that the color tones thereof
tend to deviate from desired values with respect to the luminous
flux incident thereon at a high angle. In the projector 2 of this
embodiment, however, even though polarized light conversion is
being performed, it is difficult for color shift to occur in color
light produced by the rotary color filter 190 because a divergent
angle of the polarized light beams emitted from the polarized light
beam illumination device 100 is restricted. Therefore, it is
possible to project and display a color image having a wider range
of colors.
[0085] Furthermore, since a light-absorbing-type color filter is
not used in the time-division-driving-type reflective liquid
crystal device 300T of this embodiment, the brightness of the
projected image can be considerably increased without necessitating
a large-scale cooling device, even if a light source lamp having
extremely high optical output is used.
[0086] A liquid crystal tunable filter capable of switching
transmitted wavelength regions at high speed without using a
dynamic part may be used instead of the rotary color filter 190. In
such a color-light-producing filter, spectral characteristics also
have great incident angle dependency. The polarized light beam
illumination device of this embodiment is suitable for such an
optical element having great incident angle dependency since it can
obtain high optical output by performing polarized light conversion
without taking a high illumination angle.
[0087] (Third Embodiment)
[0088] FIG. 8 includes a schematic plan view showing the
construction of a principal part of a projector 3 of the third
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120.
[0089] The projector 3 of this embodiment is mainly composed of a
polarized light beam illumination device 100 placed along a system
optical axis L1, a polarized light beam selection element 200,
three reflection-type liquid crystal devices 300R, 300G, and 300B
respectively corresponding to red light R, green light G, and blue
light B, which perform optical modulation according to external
image information (not shown) to produce modulated light beams, an
optical color-light-separating-and-synthesizing system 410 placed
between the polarized light beam selection element 200 and the
three reflection-type liquid crystal devices 300R, 300G, and 300B,
for separating a light beam from the polarized light beam
illumination device 100 into three types of color light, and for
synthesizing each of the color light from the three reflection-type
liquid crystal devices 300R, 300G, and 300B in one color light, and
a projection optical system 500 placed along a system optical
system L2 for projecting light beams modulated by the three
reflection-type liquid crystal devices 300R, 300G, and 300B on a
projection plane 600. In this embodiment, a collimating lens 170 is
also placed on the incident side of the polarized light beam
selection element 200, and a polarizer 180 is placed between the
polarized light beam selection element 200 and the projection
optical system 500, and functions thereof are similar to those of
the first embodiment.
[0090] In the projector 3 of this embodiment, the polarized light
beam illumination device 100 having exactly the same construction
as the first embodiment is used. As described in the first
embodiment, in the polarized light beam illumination device 100,
random polarized light beams emitted from a light source 110 are
divided into a plurality of intermediate light beams by the first
optical element 120, are converted into one type of polarized light
beams (in this embodiment, p-polarized light beams) having a
substantially uniform polarization direction, and enter the
polarized light beam selection element 200.
[0091] The p-polarized light beams incident on the polarized light
beam selection element 200 are transmitted by a polarized light
beam selection film 201, enters the optical
color-light-separating-and-synthesizing system 410, and are
separated into red light R, green light G, and blue light B by a
first dichroic prism 411 and a second dichroic prism 412.
[0092] The first dichroic prism 411 has a red-light-reflecting
dichroic film 418, which is made of a dielectric multilayer film or
the like, formed on mating faces of two prism parts 414 and 415. Of
the p-polarized light beams transmitted by the polarized light beam
selection film 201, the red light R is reflected by the
red-light-reflecting dichroic film 418, enters the reflection-type
liquid crystal device 300R for the red light via a light guide
prism 413, and is optically modulated based on external image
information (not shown). The light guide prism 413 may be omitted
since it is used for equalizing the length of an optical path of
the red light R to the length of optical paths of other color
lights.
[0093] The second dichroic prism 412 has a green-light-reflecting
dichroic film 419, which is made of a dielectric multilayer film or
the like, formed on mating faces of two prism parts 416 and 417. Of
the color light transmitted by the red-light-reflecting dichroic
film 418 of the first dichroic prism 411, the green light G is
reflected by the green-light-reflecting dichroic film 419, enters
the reflection-type liquid crystal device 300G for the green light,
and is optically modulated based on external image information (not
shown). Furthermore, the blue light B transmitted by the
green-light-reflecting dichroic film 419 of the second dichroic
prism 412 enters the reflection-type liquid crystal device 300B for
the blue light, and is optically modulated based on external image
information (not shown).
[0094] The red light R, the green light G, and the blue light B
modulated by the reflection-type liquid crystal devices 300R, 300G,
and 300B are synthesized by the optical
color-light-separating-and-synthesizing system 410, are reflected
by the polarized light beam selection film 201 of the polarized
light beam selection element 200 since they are partially changed
to s-polarized light beams, and are projected on the projection
plane 600 via the projection optical system 500.
[0095] According to the above construction, the projector 3 of this
embodiment can also prevent the loss of light to the fullest extent
since the opening ratio of the liquid crystal devices is high in a
manner similar to the above-described projector 1. Therefore, it is
possible to obtain an extremely bright projected image.
[0096] Furthermore, the first optical element and the second
optical element are used, whereby polarized light beams having
uniform brightness can be obtained as illumination light.
Therefore, it is possible to obtain an extremely bright projected
image without non-uniform brightness or color shading on the entire
display plane or projection plane.
[0097] Still furthermore, since three sheets of reflection-type
liquid crystal devices are used, light absorption per one sheet of
reflection-type liquid crystal device is smaller than that of the
projectors 1 and 2 of the above-described first and second
embodiments. Therefore, even if a light source lamp having
extremely high optical output is used, the brightness of the
projected image can be considerably increased without necessitating
a large-scale cooling device.
[0098] In the projector 3 of this embodiment, it is possible to
optically incorporate the prism part 202 constituting the polarized
light beam selection element 200 and the collimating lens 170.
Similarly, it is also possible to constitute the prism part 203 and
the prism part 414, the prism part 415 and the prism part 416, and
the prism part 414 and the light guide prism 413 as integrated
prisms. By integrating these prism parts, the light loss generated
at boundaries of the lens and the prism and at boundaries of the
prisms can be prevented, light utilizing efficiency is further
increased, and a bright projected image can be realized.
[0099] For the purpose of complementing separation efficiency of
color light in the above optical
color-light-separating-and-synthesizing system 410, a color filter
for controlling the transmittance of a specific color light can be
placed at least one place between the polarized light beam
selection element 200 and the three reflection-type liquid crystal
devices 300R, 300G, and 300B. Since the polarized light conversion
characteristics of the second optical element 130 placed in the
polarized light beam illumination device 100 have wavelength
dependency, and the color light separating and synthesizing
characteristics of the two dichroic prisms 411 and 412 placed in
the optical color-light-separating-- and-synthesizing element 410
have polarization dependency, color purity of the color light is
apt to be influenced by passing through the optical elements.
Therefore, the application of the above construction can increase
the color purity of the projected image, and the color range is
effectively extended.
[0100] Furthermore, a dichroic mirror in which a
red-light-reflecting dichroic film and a green-light-reflecting
dichroic film are formed on a plate-like transparent glass plate
may be used instead of the first and second dichroic prisms 411 and
412. The application of the dichroic mirror effectively reduces the
weight and cost of the projector 3.
[0101] (Fourth Embodiment)
[0102] In the projector 3 of the above described third embodiment,
the two dichroic prisms 411 and 412 are used as the optical
color-light-separating-and-synthesizing system 410, and the light
guide prism 413 is provided on the optical path of the red light in
order to equalize the length thereof to the optical paths of other
color lights. However, the optical
color-light-separating-and-synthesizing system 410 can be
constituted by one cross-dichroic prism. An example of such a
projector is shown in FIG. 9.
[0103] FIG. 9 includes a schematic plan view showing the
construction of a principal part of a projector 4 of the fourth
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120. Instead of the first and
second dichroic prisms 411 and 412 constituting the optical
color-light-separating-and-synthesizing system of the
above-described projector 3, the projector 4 of this embodiment
uses a cross-dichroic prism 420 in which red-light-reflecting
dichroic films 425 and 426 and blue-light-reflecting dichroic films
427 and 428 are arranged in the form of an X between four prism
parts 421, 422, 423, and 424. The use of the cross-dichroic prism
420 can extremely shorten the length of an optical path and
consequently, an extremely bright projected image can be obtained
without using an expensive large-aperture projection lens having a
small F-number.
[0104] In the projector 4 of this embodiment, it is possible to
optically integrate a prism part 202 constituting a polarized light
beam selection element 200 and a collimating lens 170. Similarly,
it is also possible to integrate a prism part 203 and the prism
part 421. With such an integrated construction, the light loss
generated at boundaries of the lens and the prism and at boundaries
of the prisms can be prevented, light utilizing efficiency is
further increased, and a bright projected image can be
realized.
[0105] Other advantages of the projector 4 of this embodiment are
similar to those of the above-described projector 3.
[0106] (Fifth Embodiment)
[0107] When the cross-dichroic prism 420 is used as the optical
color-light-separating-and-synthesizing system as in the projector
4 of the fourth embodiment, a portion in which dichroic films
perpendicularly intersect each other may exist in the center of the
prism, and the portion may appear as a shadow on the projected
image. If a dichroic prism 430 using a wedge-shaped prism shown in
FIG. 10 is employed instead of the cross-dichroic prism 420, this
phenomenon can be completely prevented.
[0108] FIG. 10 includes a schematic plan view showing the
construction of a principal part of a projector 5 of the fifth
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120. In the projector 5 of
this embodiment, the cross-dichroic prism 420 serving as the
optical color-light-separating-an- d-synthesizing system of the
projector 4 of the fourth embodiment is replaced with the dichroic
prism 430 in which two dichroic films are arranged at different
angles with respect to the optical axes thereof.
[0109] The dichroic prism 430 is composed of three wedge-shaped
prisms 431, 432 and 433 having different shapes in combination. The
wedge-shaped prism 431 is formed in the columnar shape having a
triangular cross section, and a blue-light-reflecting dichroic film
434 for reflecting blue light and transmitting other color light is
formed on a surface thereof adjacent to the wedge-shaped prism 432
to be described hereinbelow. The wedge-shaped prism 432 is also
formed in the columnar shape having a triangular cross section, and
a red-light-reflecting dichroic film 435 for reflecting red light
and transmitting other color light is formed on a plane thereof
contacting the wedge-shaped prism 433 to be described hereinbelow.
The wedge-shaped prism 433 is formed in substantially a trapezoidal
shape in which each side is formed as an oblique line, and is
placed by allowing a plane equivalent to an inclined plane to abut
against the red-light-reflecting dichroic film 435 of the
wedge-shaped prism 432. The wedge-shaped prism 432 is placed while
keeping a very small clearance between the wedge-shaped prism 432
and the wedge-shaped prism 431.
[0110] As described above, when the dichroic prism 430 having the
wedge-shaped prisms is used as the optical
color-light-separating-and-syn- thesizing system, since it does not
have a localized cut portion, the portion does not appear as a
shadow on the projected image. Since the incident angle of the
light incident on the blue-light-reflecting dichroic film 434 or
the red-light-reflecting dichroic film 435 can be decreased as
compared with the cross-dichroic prism 420, the polarization
dependency of the color-light-separating-and-synthesizing
characteristics of the dichroic films can be restricted. Therefore,
a bright projected image having high color purity and a wider range
of colors can be obtained.
[0111] Other advantages of the projector 5 of this embodiment are
similar to those of the above-described projector 3.
[0112] (Sixth Embodiment)
[0113] 101051 FIG. 11 includes a schematic plan view showing the
construction of a principal part of a projector 6 of the sixth
embodiment, and a sectional view in the XZ plane passing through
the center of a first optical element 120. While the
color-light-separating-a- nd-synthesizing optical system 410 having
both the function of separating and the function of synthesizing
color light is used in the projector 3 to 5 of the above-described
third to fifth embodiments, the projector 6 of this embodiment
differs from the above projectors in that the function of
separating the color light and the function of synthesizing the
color light are separated, a color-light-separating optical system
is placed between a polarized light beam illumination device and a
reflection-type liquid crystal device, and a
color-light-synthesizing optical system is placed between the
reflection-type liquid crystal device and a projection optical
device.
[0114] A polarized light beam illumination device 100A used in this
embodiment is basically the same as the above-described polarized
light beam illumination device 100, but a folding mirror 101 is
placed between the first optical element 120 and a second optical
element 130 to achieve a reduction in the depth of the projector 6.
Furthermore, if the function of reflecting only visible light and
transmitting infrared rays or ultraviolet rays is given to the
folding mirror 101, optical elements subsequent to the folding
mirror 101 can be prevented from being deteriorated by the infrared
rays or the ultraviolet rays.
[0115] Polarized light beams (in this embodiment, p-polarized light
beams) emitted from the polarized light beam illumination device
100A enter a first optical color-light-separating system 510 (first
color-light-separating element) having red-light-reflecting
dichroic mirrors 511 and green and blue-light-reflecting dichroic
mirrors 512 arranged in the shape of an X, and are separated into
two types of light beams of red light R, and green light G and blue
light B. The red light R separated by the first
color-light-separating element 510 enters a polarized light beam
selection element 200R for the red light, to be described
hereinbelow, via a folding mirror 530 and a collimating lens 170.
On the other hand, the green light G and the blue light B separated
by the first color-light-separating element 510 enter a
green-light-reflecting dichroic mirror 513 serving as a second
color-light-separating element 520 to be separated into green light
G (reflected light) and blue light B (transmitted light), and then
enter a polarized light beam selection element 200G for the green
light and a polarized light beam selection element 200B for the
blue light, to be described hereinbelow, via corresponding
collimating lenses 170.
[0116] Each of the color light (p-polarized light beams) incident
on the three polarized light beam selection elements 200R, 200G,
and 200B, which are independently placed for each color light, is
optically modulated based on external image information (not shown)
so as to change the polarization condition into s-polarized light.
Each of the color light changed into an s-polarized light beam
including the image information is reflected by the polarized light
beam selection films 201R, 201G, and 201B, enters a cross-dichroic
prism 420 constituting the color-light-synthesizing optical system,
to be synthesized, and is then projected and displayed as a color
image on a projection plane 600 via a projection optical system
500. Polarizers 180R, 180G, and 180B are placed between the three
polarized light beam selection elements 200R, 200G, and 200B and
the cross-dichroic prism 420.
[0117] According to the construction as described above, the loss
of light can be prevented to the fullest extent since the projector
6 of this embodiment has a large aperture ratio of the liquid
crystal device in a manner similar to the above-described projector
1. Therefore, it is possible to obtain an extremely bright
projected image.
[0118] Furthermore, the first optical element and the second
optical element are used, whereby polarized light beams having
uniform brightness can be obtained as illumination light.
Therefore, it is possible to obtain an extremely bright projected
image without non-uniform brightness or color shading on the entire
display plane or projection plane.
[0119] In general, since the polarized light selecting
characteristics of the polarized light beam selection film have
great wavelength dependency, it is difficult to realize excellent
characteristics across the visible range, and such a polarized
light beam selection element is very expensive. In the projector 6
of this embodiment, however, since the three polarized light beam
selection elements 200R, 200G, and 200B corresponding to each color
light are used, the wavelength ranges for the polarized light beam
selection films 201R, 201G, and 201B can be restricted, and both an
increase in performance and a cost reduction can be achieved
relatively easily. Therefore, it is possible to realize a bright
projected image having a wider range of colors as compared with the
above-described projectors 3 to 5.
[0120] Since the polarizers 180R, 180G, and 180B corresponding to
each color light are placed on the emitting side of each of the
polarized light beam selection elements 200R, 200G, and 200B,
polarization characteristics of the polarizers 180R, 180G, and 180B
can be easily increased, whereby a degree of polarization of the
light beam incident on the cross-dichroic prism 420 can be further
increased, and a projected image having high contrast ratio can be
obtained.
[0121] In this embodiment, while the polarization conditions of all
of the color lights synthesized by the cross-dichroic prism 420 are
equally set, a polarization condition of a color light transmitted
by the cross-dichroic prism 420 (in this embodiment, green light G)
may be set so as to different from that of other color lights. For
example, this can be realized by placing a .lambda./2 phase plate
(not shown) between the polarized light beam selection element 200G
and the cross-dichroic prism 420. This construction allows both a
cost reduction and color-synthesizing characteristics of the
cross-dichroic prism 420 to be achieved, and is effective for
increasing the brightness and reducing the cost of the projector
6.
[0122] (Others)
[0123] While the p-polarized light beams are obtained in the
polarized light beam illumination device in all of the
above-described embodiments, s-polarized light beams may be
obtained. In this case, the .lambda./2 phase layer 148 of the
selective phase film 147 may be formed on the p-polarized
light-beam emitting surface 145 of the polarized light separation
unit array 141.
[0124] The projectors include a front type in which a projected
image is viewed from the projection plane 600 on the side of the
projection optical system 500, and a rear type in which the
projected image is viewed from the plane on the opposite side of
the projection optical system 500, and the present invention is
optical applicable to either of the types.
[0125] As described above, according to the projector of the
present invention, it is possible to obtain a bright projected
image without using a large-aperture projection lens since the
length of an optical path can be shortened as compared with a
conventional projector. In addition, it is possible to decrease
non-uniform illuminance of an area to be illuminated, and it is
possible to obtain an extremely uniform and bright projected image
on the entire display plane or projection plane. Furthermore, since
the reflection-type liquid crystal device of small light absorption
is used, brightness of a projected image can be considerably
increased without necessitating a large-scale cooling device, even
if a light source lamp having extremely high optical output is
used.
* * * * *