U.S. patent application number 11/269027 was filed with the patent office on 2006-03-16 for projection display systems for light valves.
Invention is credited to James M. Florence, Austin L. Huang, Jeffrey B. Sampsell.
Application Number | 20060055891 11/269027 |
Document ID | / |
Family ID | 34749062 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060055891 |
Kind Code |
A1 |
Florence; James M. ; et
al. |
March 16, 2006 |
Projection display systems for light valves
Abstract
Projection display systems for light valves such as liquid
crystal display panels, and in particular to the use of color
component rotators, such as retardation filters, to provide for
improved projection display architectures.
Inventors: |
Florence; James M.;
(Beaverton, OR) ; Sampsell; Jeffrey B.;
(Vancouver, WA) ; Huang; Austin L.; (Camas,
WA) |
Correspondence
Address: |
CHERNOFF, VILHAUER, MCCLUNG & STENZEL
1600 ODS TOWER
601 SW SECOND AVENUE
PORTLAND
OR
97204-3157
US
|
Family ID: |
34749062 |
Appl. No.: |
11/269027 |
Filed: |
November 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11044820 |
Jan 26, 2005 |
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11269027 |
Nov 7, 2005 |
|
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09539918 |
Mar 31, 2000 |
|
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11044820 |
Jan 26, 2005 |
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Current U.S.
Class: |
353/20 |
Current CPC
Class: |
G02B 27/283 20130101;
G03B 33/08 20130101; G03B 33/12 20130101; H04N 9/3105 20130101;
G03B 21/2073 20130101; G02B 27/1026 20130101; H04N 9/315 20130101;
G03B 21/14 20130101 |
Class at
Publication: |
353/020 |
International
Class: |
G03B 21/14 20060101
G03B021/14 |
Claims
1. A method for displaying an image, comprising: (a) providing
light comprised of a first color component, a second color
component, and a third color component; (b) converting said light
to a single polarization state; (c) separating said first color
component from said second and third color components while said
first, second, and third color components are in the same beam; (d)
mismatching said polarization states of said second and third color
components relative to each other while said second and third color
components are within the same beam; (e) separating said second
color component from said third color component while said second
and third color components are within the same beam; (f) generating
respective images from each of said first, second, and third color
components separated from one another into different beams; and (g)
projecting said images.
2. The method of claim 1, wherein said first, second and third
color components are green, blue, and red respectively.
3. The method of claim 1, wherein said first color component is
separated from said second and third color component using a
dichroic filter.
4. The method of claim 3, wherein said second color component is
separated from said third color component using a polarizing
beamsplitter.
5. The method of claim 1, wherein said polarization state of said
second color component is changed using a color component
rotator.
6. The method of claim 1, wherein said first, second and third
color components are reflected onto respective liquid crystal
display panels to generate said images.
7. The method of claim 6, wherein said first, second and third
color components are reflected onto respective liquid crystal
display panels using only two polarizing beamsplitters.
8. The method of claim 1, further comprising the step of changing
the polarization state of said first color component before
generating said image from said first color component.
9. The method of claim 8, further comprising the step of changing
the polarization state of said first color component again after
generating said image from said first color component.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/044,820 filed Jan. 25, 2005, which is a
divisional of U.S. patent application Ser. No. 09/539,918 filed
Mar. 31, 2000, to which it claims priority.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to projection display systems
for light valves such as liquid crystal display panels, and in
particular to the use of color component rotators, such as
retardation filters, to provide for improved projection display
architectures.
[0003] Projection systems for reflective liquid crystal displays
(LCDs) are generally characterized by their complexity and large
size relative to the systems implemented for transmissive LCDs.
FIG. 1A discloses a prior art configuration for a transmissive LCD
projector, while FIG. 1B shows a prior art reflective LCD projector
for comparison. Dichroic filters DF1 and DF2 separate the red,
green, and blue color components. The reflective LCDs require a
polarizing beamsplitter (PBS) to be placed in front of each LCD in
order to reflect light toward the reflective LCD, and then to
transmit the modulated light. These components add complexity to
the system and require the use of a larger distribution and
recombination optical system to divide the light into the three
color channels (i.e. the optical paths traveled by the three color
components such as red, green, and blue).
[0004] An alternative system for reflective LCDs divides the
illumination into the three color channels and recombines the
output distributions into a smaller and less complex system. The
basic configuration is shown in FIG. 2. However, the illumination
input to this system must have a very specific distribution of
color components and polarizations in which two of the color
components (green and blue) are polarized in one direction, and the
other color component (red) is polarized orthogonally to the other
two. In order to produce that combination of color components and
polarizations, a complicated prefiltering system is needed.
[0005] One such system is shown in FIG. 2, and indicates that
considerable complexity is added back to the system in order to
implement the prefiltering. In the system shown in FIG. 2, only
one-half of the light is used, since the unwanted polarization
state of each color component is simply discarded. In order to
increase brightness of the system, a more complex prefiltering
system is required that recycles the polarized light.
[0006] Various architectures have been proposed for projection
display systems. Ledebuhr, U.S. Pat. No. 4,687,301, and Ledebuhr,
U.S. Pat. No. 4,836,649, both describe projection systems for
liquid crystal light valve (LCLV). The LCLV is an optically
addressed reflective LC modulator and the systems described in
these patents show optics to split a light source into separate
colors paths and then individually illuminate and project the three
LCLV devices. Both of these systems use only one-half of the
illumination light since the unwanted polarization state is
initially discarded. Ledebuhr, U.S. Pat. No. 4,687,301, uses a
complicated color separating system to direct the color components
to the LCLVs. Ledebuhr, U.S. Pat. No. 4,836,649 uses simpler but
more numerous elements resulting in a large projection system.
[0007] Doany, et al. U.S. Pat. No. 5,621,486, and Dove, U.S. Pat.
No. 5,658,060, both describe architectures that use Philips type
prisms to control the three separate color channels. Doany, et al.
U.S. Pat. No. 5,621,486, uses a single PBS prism to control the
light into and out of all three LCIs) and a Philips prism to both
split up and recombine the color channels. This arrangement appears
simple, but the control of color in a Philips prism for
p-polarization on the input and s-polarization on the output is
extremely difficult, and no successful implementation of this type
of system exists. Dove, U.S. Pat. No. 5,658,060, places a P13S
prism in front of each LCD and uses the Philips prism only to
recombine the color channels. This requires a second optical
arrangement to split up the color distributions and leads to a
larger, more complicated system overall.
[0008] Ooi et al., U.S. Pat. No. 5,648,860, uses an offset
illumination and projection scheme. The system does not use a PBS
prism, but instead relies on the offset to separate the input and
output light distributions. The color splitting and recombination
is accomplished by tilted dichroics that perform essentially the
same as the dichroics in a Philips prism, with the same
polarization related problems.
[0009] Hattori et al., U.S. Pat. No. 5,798,819, and Ueda, U.S. Pat.
No. 5,918,961, both describe minor variations of the typical
reflective LCD projector of FIG. 1B. These systems use a crossed
dichroic prism to recombine light from the three LCDs and a
separate crossed dichroic arrangement to perform the color
splitting from the illumination system.
[0010] Sharp, U.S. Pat. No. 5,751,384, describes techniques for
making waveband-specific retardation filters. This patent also
describes a single panel LCD projector using the retardation
filters in an active color shutter to gate the three colors onto
the LCD for color field sequential projection.
[0011] Nevertheless, there remains a need for a bright projection
display system, preferably for reflective LCD panels that utilize a
small architecture. What is therefore desired is a projection
display that is as small as or smaller than conventional projection
displays, is capable of utilizing reflective LCD panels, uses
readily available optical elements that perform well, uses
conventional polarization converters, and provides good contrast
without sacrificing brightness.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention overcomes the drawbacks of the prior
art by providing in a first aspect of the invention a projection
display system having a light source, a polarization converter, at
least one polarizing beamsplitter, at least one liquid crystal
display panel for generating an image, a projection source for
projecting the image, and a color component rotator located between
the polarization converter and the projection source.
[0013] In a second separate aspect of the invention, a projection
display system has a light source, a polarization converter, at
least two polarizing beamsplitters, at least three liquid crystal
display panels, each for generating a respective image, a
projection source for projecting the images, and at least two color
component rotators, each of the color component rotators located
between the polarization converter and the projection source.
[0014] In a third separate aspect of the invention, a method of
displaying an image is provided. First, light comprised of at least
a first, second, and third color component is provided. The light
is converted to polarized light having a single polarization state.
The first color component is separated from the second and third
color components. The polarization state of the second color
component is changed relative to the third color component. The
second color component is separated from the third color component.
Respective images are generated from each of the three color
components. The images are then combined and projected.
[0015] The various aspects of the present invention each have one
or more of the following advantages. The systems achieve their
advantages through the use of color component rotators, or
wavelength-specific retardation filters, located within the optical
systems to control the polarization orientation of one of the color
components in the system relative to the other two. The use of a
color component rotator allows the polarization orientation of the
three color components to be controlled within the main color
distribution and recombination portion of the system rather than in
a prefiltering system included within the illumination optics. This
allows the use of conventional polarization converters rather than
complicated prefiltering systems.
[0016] In addition, the use of color component rotators enables
smaller distribution and recombination systems than conventional
reflective projection display systems and, in one case, smaller
even than typical transmissive projection display systems. Thus,
the projection display systems and methods of the present invention
reduce the overall projection display system size and complexity.
The systems provide these advantages while achieving good contrast
and without sacrificing brightness.
[0017] The foregoing and other objectives, features, and advantages
of the invention will be more readily understood upon consideration
of the following detailed description of the invention, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0018] FIG. 1A is a schematic diagram of a prior art transmissive
LCD projector.
[0019] FIG. 1B is a schematic diagram of a prior art reflective LCD
projector.
[0020] FIG. 2 is a schematic diagram of a projection display system
that utilizes a prefiltering system.
[0021] FIG. 3 is a schematic diagram of one embodiment of a
projection display system of the present invention.
[0022] FIG. 4A is a second embodiment of a projection display
system of the present invention.
[0023] FIG. 4B is a detail view of the distribution and
recombination portion of the display of FIG. 4A.
[0024] FIG. 5 is a third embodiment of a projection display system
of the present invention.
[0025] FIG. 6 is a fourth embodiment of a projection display system
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0026] Referring now to the figures, wherein like numerals refer to
like elements, FIG. 3 shows an exemplary projection display 10
having an illumination portion 11 and distribution and
recombination portion 22. Distribution and recombination portion 22
includes three reflective liquid crystal display (LCD) panels 14,
16, and 18, also referred to as liquid crystal light valves.
[0027] Illumination portion 11 includes a light source 12 for
producing white light, which may be separated into different color
components of different bandwidths, such as a red color component,
blue color component, and green color component. The white light
from light source 12 passes through a polarization converter shown
generally at 20. Polarization converter 20 may take the form of any
conventional polarization converter, so that the randomly polarized
light from light source 12 is converted into a single polarization
state. In the embodiment shown in FIG. 3, the polarization
converter 20 converts the white light from randomly polarized light
into light that is polarized in the S direction. Polarization
converter 20 is a conventional polarization converter structure
comprised of fly's-eye lens plates 24, 26 and polarization
converter prism array 28. Other polarization converters may also be
used. While not preferred, the present invention could be used with
a polarizing filter to produce uniformly polarized light; however,
only half the light from light source 12 would be used. The
polarized light is directed from the polarization converter 20
toward a mirror 30, which reflects the light through a lens 32.
[0028] The now S-polarized light exits the illumination portion 11
of the display 10 and enters the distribution and recombination
portion 22. The white light encounters dichroic filter 34, which
separates the red color component from the blue and green color
components. In general, dichroic filters transmit light of a
certain bandwidth, and reflect light of another band width. In
display 10, dichroic filter 34 transmits the red color component
while reflecting the blue and green color components.
[0029] Referring now to the blue and green channels, after
reflecting from dichroic filter 34 the blue and green light
components pass through a field lens 36, which in combination with
other elements controls the size of the light projected on the LCD
panel. The blue and green color components then pass through a
polarizer 38 that transmits only S-polarized light. The polarizer
38 improves contrast by filtering out P-polarized light that
otherwise may leak through to the LCD panels 16 and 18.
[0030] The blue and green color components then pass through a
selective color component rotator 40, which rotates one of the
color components (e.g., the blue color component) from one
polarization state (e.g., the S-polarization state) to another
polarization state (e.g., the P-polarization state). The color
component rotator is a waveband specific retardation filter. It is
a specially designed stack of retardation films in which the amount
of retardation imparted to different wavebands can be selectively
controlled by the orientation and number of retardation films used.
The details of the design and operation of such color component
rotators are described in Sharp, U.S. Pat. No. 5,751,384. A
retardation filter can be made to act like a half waveplate for one
bandwidth of light while leaving light of all other colors or
bandwidths unaffected. Such color component rotators may be
obtained from Color Link in Boulder, Colo., or Cambridge Research
& Instrumentation in Cambridge, Massachusetts. In the
projection display 10, color component rotator 40 acts as a half
waveplate for the blue color component, thus rotating the blue
color component 90.degree., but leaving the green color component
unaffected. Accordingly, the color component rotator 40 rotates the
blue color component from the S to P-polarization state, while the
green color component remains in the S-polarization state.
[0031] The blue and green color components then enter a polarizing
beamsplitter 41 having different polarization states (e.g., S and
P, respectively). The polarizing beamsplitter reflects the
S-polarized green color component while transmitting the
P-polarized blue color component. The green color component
reflecting off the polarizing beamsplitter 41 is imaged using green
LCD panel 16. The green image reflected by the modulated LCD panel
16 is in the P-polarization state and is transmitted through
polarizing beamsplitter 41 and into the crossed dichroic prism
42.
[0032] Returning to the blue channel, the blue color component
transmitted through the polarizing beamsplitter 41 is transmitted
through relay lens 44, reflected off mirror 46 and transmitted
through a second relay lens 48. The blue color component passes
through another selective color component rotator 50, which rotates
the polarization of the blue color component back to the
S-polarization state. The now S-polarized blue color component then
passes through a polarizer 51 which transmits S-polarized light.
The S-polarized blue color component then enters a third polarizing
beamsplitter 52, which reflects the S-polarized blue color
component onto the blue LCD panel 18. The blue image reflected by
blue LCD panel 18 is in the P-polarization state and is transmitted
through polarizing beamsplitter 52 into the crossed dichroic prism
42. The relay lenses 44 and 48 are used to compensate for the
longer path length of the blue channel relative to the green and
red channels.
[0033] Returning to the red channel, the red color component is
transmitted by dichroic filter 34 and is focused by a field lens
54. The red color component then passes through polarizer 56, which
is oriented to transmit S-polarized light. The polarizer 56
improves contrast by eliminating P-polarized light that might
otherwise leak through to LCD panel 14. The red color component
then enters polarizing beamsplitter 58 which reflects the
S-polarized light into the red LCD panel 14. The modulated LCD
panel 14 generates a red image. The reflected red image (in the
P-polarization state) passes through the beamsplitter 58 and into
the crossed dichroic prism 42.
[0034] The three color components reflected from the three LCD
panels 14, 16, and 18 pass through their respective polarizing
beamsplitters and into the crossed dichroic prism 42, which
combines the reflected images. The projection lens 62 then projects
the converged images from all three LCD panels onto a projection
screen (not shown).
[0035] The projection system of FIG. 3 retains the configuration of
polarizing beamsplitters and crossed dichroic prism of the
conventional reflective LCD projector shown in FIG. 1B. However,
this projector significantly reduces the size of the optics
required to distribute the illumination light into the three color
channels. The key to this reduction is the use of the color
component rotator 40, in this case a blue color component rotator,
which allows the single polarizing beamsplitter 41 to perform the
dual function of separating the green and blue color components and
also to control the operation of green LCD panel 16. Thus, the
system 10 has significantly reduced the size and complexity of the
optics required.
[0036] An alternative projection display system 10A is shown in
FIGS. 4A and 4B. Like system 10 shown in FIG. 3, system 10A shown
in FIG. 4A has a light source 12, red LCD panel 14, green LCD panel
16, and blue LCD panel 18. The system 10A utilizes the same
illumination portion 11. A polarization converter 20 comprised of
fly's-eye lens plates 24, 26 and prism array 28 provide light
consisting of all three color components polarized in the S
direction. Mirror 30 reflects light through lens 32 into the
distribution and recombination portion 22A of the system.
[0037] Referring now to the distribution and recombination portion
22A shown in more detail in FIG. 4B, dichroic filter 134 separates
the white light by transmitting the green color component while
reflecting the red and blue color components. Referring to the
green channel, the green color component passes through polarizer
156 which transmits light polarized in the S direction. The green
color component then enters polarizing beamsplitter 158 which
reflects the S-polarized light onto the green LCD panel 16. The
reflected image (now in the P-polarization state) passes through
the beamsplitter 158 and through analyzer 160, which transmits
light in the P-polarization state. Analyzer 160 improves contrast
by eliminating S-polarized light that has leaked through the green
channel. The green color component is then reflected by dichroic
filter 164, and then transmitted through projection lens 62.
[0038] Turning to the red and blue channels, the red and blue color
components are reflected by dichroic filter 134 and passed through
polarizer 136, which transmits only S-polarized light. The red and
blue color components then pass through a selective color component
rotator 138, that acts as a half waveplate for the blue color
component. Thus, the blue color component is rotated from the
S-polarization state to the P-polarization state, while the red
color component remains unaffected. Thus, the two color components
(red and blue) entering the polarizing beamsplitter 140 have
different polarization states (e.g. S and P respectively). The
polarizing beamsplitter 140 reflects the red color component and
transmits the blue color component. The polarizing beamsplitter 140
reflects the S-polarized red color component onto the modulated red
LCD panel 14, which generates a red image now in the P-polarization
state. Similarly, the blue color component transmitted by the
polarizing beamsplitter 140 is reflected off the modulated blue LCD
panel 18, which generates a blue image in the S-polarization state.
The red image reflected by LCD panel 14 is transmitted through
polarizing beamsplitter 140 while the blue image reflected by LCD
panel 18 is reflected by the polarizing beamsplitter 140. Both the
red and blue color components pass through another selective color
component rotator 150, which selectively rotates the blue color
component from the S to the P-polarization state, so that the two
color components again have the same polarization state. The red
and blue color components then pass through an analyzer 152 which
transmits only light that is P-polarized. The blue and red color
components then pass through dichroic filter 164, where they are
combined with the green color component and projected through
projection lens 62.
[0039] The analyzer 152 and the second selective color component
rotator 150 are introduced to control a practical implementation
problem that arises due to the non-ideal operation of the
polarizing beamsplitter 140. Ideally, a polarizing beamsplitter
will reflect all S-polarized light that enters and transmit all
P-polarized light. However, a typical practical polarizing
beamsplitter has extremely high reflectivity for S-polarized light
with virtually no S-polarized light transmitted. The transmitted
light is therefore a highly pure, P-polarized distribution.
However, the practical polarizing beamsplitter also reflects a
small portion of the P-polarized light, sometimes as much as 10
percent, giving a reflected distribution that is a mixture of
predominantly S-polarized light and a small portion of P-polarized
light.
[0040] Turning now to the projection display system shown in FIG.
4B, the selective color component rotator 138 rotates the blue
color component from the S to P-polarization state, leaving the red
color component S-polarized. The light transmitted through
polarizing beamsplitter 140 will be just the blue color component
with the P-polarization, but the reflected light will be the
S-polarized red color component and a small portion of the
P-polarized blue color component. Accordingly, a portion of the
blue color component leaks into the red channel and illuminates the
red LCD panel 14. If the blue color component reflects off the red
LCD panel 14 without modulation, it will re-enter polarizing
beamsplitter 140 as P-polarized light and transmit through the
polarizing beamsplitter 140, through the dichroic filter 164, and
through the projection lens 62. This undesired light will
significantly reduce the contrast in the blue color component.
[0041] However, by introducing the second selective color component
rotator 150, also designed like the color component rotator 138 to
be a half waveplate for the blue color component, the unwanted
P-polarized blue color component from the red channel will be
rotated to be S-polarized. The desired output blue color component
from the blue channel will reflect out of the polarizing
beamsplitter 140, as S-polarized and will be rotated to the
P-polarization state by the selective color component rotator 150.
The blue output distribution then has the same P-polarized
orientation as the desired red output distribution. The analyzer
152, oriented in the P direction, transmits the desired red and
blue color components in the P-polarization state, but absorbs and
eliminates the unwanted blue color component in the P-polarization
state that leaked into the red channel and reflected off the red
LCD panel 14 through polarizing beamsplitter 140. Some portion of
the blue color component that leaks into the red channel may be
modulated by the red LCD panel 14 and re-enter the polarizing
beamsplitter 140 as S-polarized light. If this occurs, the
polarizing beamsplitter 140 has strong S-polarized reflection and
virtually no S-polarized transmittance. The modulated portion of
the blue leakage color component will then be reflected back toward
the illumination optics and will not pass through to the projection
lens. This particular configuration of using two selective color
component rotators 138, 150 and an analyzer 152 is essential to
enable the high contrast operation of two LCD panels with a single
PBS prism.
[0042] Another alternative projection display system is shown in
FIG. 5. The system again begins with a conventional illumination
system as described previously for the embodiments of FIGS. 3 and
4A and 4B. The input color components, all S-polarized, enter the
color distribution and recombination portion 22B of the system 10B.
A green transmitting dichroic filter 134 reflects the blue and red
color components up to the polarizing beamsplitter 140. The
polarizer 136 and analyzer 152, the selective color component
rotators 138 and 150, and the polarizing beamsplitter 140 control
the operation of splitting and recombining the red and blue color
components in exactly the same fashion as in the system 10A of
FIGS. 4A and 4B.
[0043] The alternative arrangement is contained within the green
channel. The S-polarized green color component is passed through
lens 200 and is reflected by mirror 202. The green color component
then is passed through lens 204 and polarizer 206. The polarizer
206 removes any residual P-polarized light. The green color
component then passes through a selective color component rotator
208, which is designed and oriented to rotate green light
polarization by 90 degrees, so as to rotate the green color
component to the P-polarization state. The green color component
passes through polarizing beamsplitter 216 to the green LCD panel
16. The relay lenses 200 and 204 are used to compensate for the
longer path length of the green channel relative to the red or blue
channels. A block of glass 212 is introduced to provide the same
optical path length for the green channel as the red and blue
channels between the LCD panels and the projection lens. The
modulated LCD panel 16 generates a green image, which is reflected
in the S-polarization state. The green image reflects off the
polarizing beamsplitter 216 and into a color component rotator 210.
This color component rotator 210 selectively rotates the
polarization of the green color component from the S to the P
state. The analyzer 214 eliminates any green light that might have
been reflected into the red or blue channel from polarizing
beamsplitter 216 and maintains high contrast performance for the
green channel.
[0044] While exemplary projection displays have been described,
other projection display configurations that utilize LCD panels
(either reflective, transmissive, or a combination thereof) and
polarizing devices such as polarization converters may find utility
with the present invention. Moreover, other color components,
wavelength ranges, and polarization states may be used as
desired.
[0045] Other alternative system architectures are also possible. In
the system shown in FIG. 4B, dichroic filter 134 may instead
transmit the red or blue color component. Alternatively, the output
dichroic filter 164 could be changed to a green transmitting filter
164A, rather than a green reflecting filter. The resulting system
configuration is shown in FIG. 6. The projection lens 62 is moved
to capture the output and send the projected image up, rather than
to the right, and may be considered for overall system packaging
considerations.
[0046] With respect to the embodiment shown in FIG. 3, it may be
possible to switch the red reflecting dichroic in the crossed
dichroic prism 42 to a green reflecting dichroic. Then, by changing
the input dichroic filter 34 to a green transmitting filter, the
LCD panels 14 and 16 may be substituted for each other, so that the
green color component would enter from the bottom as shown in FIG.
3 while the red color component would enter the crossed dichroic
prism 42 from the left as shown in FIG. 3.
[0047] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention, in the use of
such terms and expressions, of excluding equivalents of the
features shown and described or portions thereof, it being
recognized that the scope of the invention is defined and limited
only by the claims which follow.
* * * * *