U.S. patent application number 10/151698 was filed with the patent office on 2003-11-20 for projection display system.
Invention is credited to Aastuen, David J.W., Ma, Jiaying, Mahmoodi, Abolghassem B..
Application Number | 20030214632 10/151698 |
Document ID | / |
Family ID | 29419498 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030214632 |
Kind Code |
A1 |
Ma, Jiaying ; et
al. |
November 20, 2003 |
Projection display system
Abstract
In one embodiment, a projection screen includes a diffuse
reflecting polarizer that diffusively reflects light polarized in a
first direction and transmits light polarized in a second
direction. The projection screen may also include a second
polarizer adjacent a back side of the diffuse reflecting polarizer,
wherein the second polarizer is oriented to transmit light
polarized in the second direction. The projection screen may appear
substantially diffuse when viewed from a front side and
substantially transparent when viewed from a back side.
Inventors: |
Ma, Jiaying; (Maplewood,
MN) ; Aastuen, David J.W.; (Shoreview, MN) ;
Mahmoodi, Abolghassem B.; (St. Paul, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
29419498 |
Appl. No.: |
10/151698 |
Filed: |
May 16, 2002 |
Current U.S.
Class: |
353/31 |
Current CPC
Class: |
G03B 21/604 20130101;
G03B 21/60 20130101 |
Class at
Publication: |
353/31 |
International
Class: |
G03B 021/00 |
Claims
1. An apparatus comprising: a diffuse reflecting polarizer that
diffusively reflects light polarized in a first direction and
transmits light polarized in a second direction; and a second
polarizer adjacent a back side of the diffuse reflecting polarizer,
wherein the second polarizer is oriented to transmit light
polarized in the second direction.
2. The apparatus of claim 1, wherein the second polarizer includes
a reflective polarizer that reflects light polarized in the first
direction.
3. The apparatus of claim 1, wherein the second polarizer includes
an absorption polarizer that absorbs light polarized in the first
direction.
4. The apparatus of claim 1, wherein the second polarizer includes
a non-diffuse polarizer.
5. The apparatus of claim 1,wherein the first direction is
substantially perpendicular to the second direction.
6. The apparatus of claim 1, wherein the apparatus appears
substantially transparent when viewed from a back side of the
apparatus corresponding to a light incident side of the second
polarizer and appears substantially diffuse when viewed from a
front side of the apparatus corresponding to a light incident side
of the diffuse reflecting polarizer.
7. The apparatus of claim 6, wherein the apparatus transmits at
least 20% of randomly polarized light incident the front side of
the apparatus.
8. The apparatus of claim 7, wherein the apparatus transmits at
least 35% of randomly polarized light incident the front side of
the apparatus.
9. The apparatus of claim 7, wherein the apparatus transmits
approximately 50% of randomly polarized light incident the front
side of the apparatus.
10. The apparatus of claim 6, wherein the apparatus diffusely
reflects greater than approximately 20% of randomly polarized light
incident the front side of the apparatus.
11. The apparatus of claim 10, wherein the apparatus diffusely
reflects greater than approximately 35% of randomly polarized light
incident the front side of the apparatus.
12. The apparatus of claim 10, wherein the apparatus diffusely
reflects approximately 50% of randomly polarized light incident the
front side of the apparatus.
13. The apparatus of claim 1, wherein the apparatus reflects
greater than approximately 70% of light polarized in the first
direction incident the diffuse reflecting polarizer.
14. The apparatus of claim 13, wherein the apparatus reflects
greater than approximately 80% of light polarized in the first
direction incident the diffuse reflecting polarizer.
15. The apparatus of claim 13, wherein the apparatus reflects
greater than approximately 90% of light polarized in the first
direction incident the diffuse reflecting polarizer.
16. The apparatus of claim 1, further comprising a
glare-suppressing element adjacent a front side of the diffuse
reflecting polarizer to suppress glare.
17. A system comprising: a multi-color transmissive projector that
emits light in which all colors are substantially polarized in a
common direction; and a diffuse reflecting projection screen that
reflects light polarized in a same direction as the light emitted
from the projector, and transmits light polarized in a different
direction as the light emitted from the projector.
18. The system of claim 17, wherein the diffuse reflecting
projection screen comprises a diffuse reflecting polarizer that
diffusively reflects light polarized in a first direction and
transmits light polarized in a second direction.
19. The system of claim 18, wherein the diffuse reflecting
projection screen further includes a second polarizer adjacent a
back side of the diffuse reflecting polarizer, wherein the second
polarizer is oriented to transmit light polarized in the second
direction.
20. The system of claim 19, wherein the second polarizer comprises
a polarizer selected from the following group: an absorbing
polarizer and a reflecting polarizer.
21. The system of claim 17, wherein the diffuse reflecting
projection screen is a two-sided screen comprising: a first diffuse
reflecting polarizer that diffusely reflects light polarized in a
first direction and transmits light polarized in a second direction
a second diffuse reflecting polarizer that reflects light polarized
in the first direction and transmits light polarized in the second
direction; and a third polarizer, between the first and second
diffuse reflecting polarizers.
23. The system of claim 21, further including a second projector to
project an image on a second side of the projection screen, wherein
the second side is a light incident side of the second diffuse
reflecting polarizer.
24. The system of claim 21, wherein the projector is a dual image
projector that simultaneously projects an image onto both sides of
the screen.
25. The system of claim 17, wherein the multi-color transmissive
projector is a liquid crystal display projector.
26. The system of claim 17, wherein the projector includes a
rotator to rotate polarization of at least some of the light
emitted from the projector such that all the colors are polarized
in the common direction.
27. The system of claim 17, wherein the projector includes a color
combiner that combines the colors.
28. The system of claim 17, further including a mirror to reflect
light emitted from the projector onto the projection screen.
29. A system comprising: a multi-color transmissive projector that
emits light; a rotator to rotate polarization of at least some of
the light emitted from the projector such that all colors of light
are polarized in a common direction; and a projection screen onto
which the light emitted from the projector is diffusely reflected,
wherein the projection screen appears substantially diffuse when
observed from one side of the screen and appears substantially
transparent when observed from an opposite side of the screen.
30. The system of claim 29, wherein the projection screen
comprises: a diffuse reflecting polarizer that diffusively reflects
light polarized in a first direction and transmits light polarized
in a second direction; and a second polarizer adjacent a back side
of the diffuse reflecting polarizer, wherein the polarizer is
oriented to transmit light polarized in the second direction.
31. A method comprising: combining multiple colors of light such
that all of the colors of light are substantially polarized in a
first direction; and projecting the combined colored light onto a
display screen that diffusely reflects light polarized in the first
direction and transmits light polarized in a second direction.
32. A method comprising: combining multiple colors of light such
that all of the colors of light are substantially polarized in a
first direction; and projecting the combined colored light onto a
display screen that reflects light polarized in the first direction
and absorb light polarized in the second direction.
33. An apparatus comprising: a diffuse reflecting polarizer that
diffusively reflects light polarized in a first direction and
transmits light polarized in a second direction; and a reflecting
polarizer adjacent a back side of the diffuse reflecting polarizer,
wherein the reflective polarizer is oriented to reflect light
polarized in the first direction and transmit light polarized in
the second direction such that the apparatus appears substantially
transparent when viewed from a back side of the apparatus
corresponding to a light incident side of the reflecting polarizer
and appears substantially diffuse when viewed from a front side of
the apparatus corresponding to a light incident side of the diffuse
reflecting polarizer.
34. An apparatus comprising: a diffuse reflecting polarizer that
diffusively reflects light polarized in a first direction and
transmits light polarized in a second direction; and an absorbing
polarizer adjacent a back side of the diffuse reflecting polarizer,
wherein the absorbing polarizer is oriented to absorb light
polarized in the first direction and transmit light polarized in
the second direction such that the apparatus appears substantially
transparent when viewed from a back side of the apparatus
corresponding to a light incident side of the absorbing polarizer
and appears substantially diffuse when viewed from a front side of
the apparatus corresponding to a light incident side of the diffuse
reflecting polarizer.
35. An apparatus comprising: a means for combining multiple colors
of light such that all of the colors of light are substantially
polarized in a common direction; a means for projecting the
combined colors of light; and a means for diffusely reflecting the
projected combined colors of light, wherein the means for diffusely
reflecting substantially transmits light that is not polarized in
the common direction.
Description
TECHNICAL FIELD
[0001] The invention relates to projection display systems and
display screens for LCD projectors.
BACKGROUND
[0002] Projection display systems typically include a projector and
a projection display screen. The projector may be a three-color
liquid crystal display projector that combines polarized light from
different liquid crystal displays and emits combined light to form
images. The projector can project the images on the display screen
for presentation to viewers. The display screen may provide a
diffuse surface to improve the image quality seen by viewers.
[0003] Projectors capable of emitting polarized light may be most
efficient when the directions of polarization vary for the
different colored lights that are combined. For instance, light
polarized in one direction may be more efficient for reflecting,
while light polarized in another direction may be more efficient
for transmission. Therefore, the light output from the projector
may contain some colored light that is reflected within the
projector and is polarized in one direction, and may contain other
colored light that only transmits through the projector and is
polarized in the other direction.
[0004] Projection screens typically include particles held in a
transparent medium and a reflective material located behind the
particles. Conventional projection screens may reflect
substantially all of the incident light, including both the light
from the imaging source and the ambient light. The reflection of
the ambient light towards the viewers may result in reduced
contrast of the image, particularly in areas that receive
relatively high levels of ambient light. Such reductions in
contrast, however, are generally undesirable.
[0005] Improving the projection screen and/or the projector can
improve the image quality presented to viewers. Furthermore,
improvements to the screen and/or the projector may allow the
system to be used in non-conventional settings. For theses and
other reasons it is highly desirable to improve projectors and
projection screens.
SUMMARY
[0006] In general, the invention is directed to projectors,
projection screens, and projection systems that include a projector
that projects images on a projection screen. As described in
greater detail below, light polarization can be manipulated and
exploited in order to improve the display of images to viewers. In
addition, the techniques and structures described below may allow
projection systems to be used in non-conventional settings. In one
example, a projection screen is described that allows viewers on
the side where the image is projected, i.e the front side, to see
improved image quality. In addition, viewers on the other side,
i.e. the back side of the screen, may be able to see through the
projection screen. In particular, the screen may appear
substantially diffuse when viewed from the front side of the screen
and substantially transparent and non-diffuse when viewed from the
back side of the screen.
[0007] In another embodiment, the invention may be directed to a
system comprising a multi-color transmissive projector that emits
light in which all colors are polarized in a common direction. The
system may further include a diffuse projection screen that
reflects light of the same polarization as the light emitted from
the projector, and transmits light of a different polarization as
the light emitted from the projector. The diffuse projection screen
may comprise a diffuse reflecting polarizer that diffusively
reflects light polarized in a first direction and transmits light
polarized in a second direction. The projection screen may also
include a second polarizer adjacent a back side of the diffuse
reflecting polarizer. Like the diffuse reflective polarizer, the
second polarizer may be oriented to transmit light polarized in the
second direction. For example, the second polarizer may comprise a
reflecting polarizer or an absorbing polarizer. The combination of
the diffuse reflective polarizer and the second polarizer may
result in a projection screen which appears substantially
transparent when viewed from the back side, and substantially
diffuse when observed from the front side.
[0008] Additional details of various embodiments of the invention
are set forth in the accompanying drawings and the description
below. Other features, objects, and advantages of the invention
will be apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a cross-sectional side view illustrating an
exemplary projection system in accordance with the principles of
the invention.
[0010] FIG. 2 is another cross-sectional side view illustrating an
exemplary projection system in accordance with the principles of
the invention.
[0011] FIG. 3 is a cross-sectional side view illustrating an
exemplary embodiment of a projection screen incorporating a diffuse
reflecting polarizer adjacent a reflecting polarizer.
[0012] FIG. 4 is cross-sectional side view illustrating an
exemplary embodiment of a projection screen incorporating a diffuse
reflecting polarizer adjacent an absorbing polarizer.
[0013] FIG. 5 is cross-sectional top view illustrating an exemplary
projection system that includes a multi-color transmissive LCD
projector and a projection screen.
[0014] FIG. 6 is a cross-sectional side view illustrating an
exemplary projection system having a two-sided projection
screen.
DETAILED DESCRIPTION
[0015] FIG. 1 is a cross-sectional side view illustrating an
exemplary projection system 10 in accordance with the principles of
the invention. Projection system 10 comprises a projector 12 and a
projection screen 14. Projection screen 14 includes a diffuse
reflecting polarizer 16 that diffusely reflects light polarized in
a first direction and transmits light polarized in a second
direction. The first and second directions of polarization may be
perpendicular to one another, although the invention is not
necessarily limited in that respect.
[0016] Projection screen 14 also includes a second polarizer 18
adjacent the back side of diffuse reflecting polarizer 16. The
orientation of polarizer 18 with respect to diffuse reflecting
polarizer 16 is such that polarizer 18 transmits light polarized in
the second direction. In other words, the diffuse reflecting
polarizer 16 and the second polarizer 18 are aligned such that both
polarizers transmit light polarized in the second direction. By way
of example, polarizer 18 may be a reflecting polarizer or an
absorbing polarizer. Alternatively, polarizer 18 may be another
diffuse reflecting polarizer.
[0017] When polarizer 18 comprises a reflecting polarizer or an
absorbing polarizer, advantages can be realized. In those cases,
projection screen 14 may appear substantially diffuse when
observing from a front side, i.e., the side illuminated by
projector 12. At the same time, projection screen 14 may appear
substantially transparent when viewed from the back side, i.e., the
side not illuminated by projector 12. In other words, the back side
corresponds to a light incident side of the second polarizer 18 and
the front side corresponds to a light incident side of the diffuse
reflecting polarizer 16.
[0018] Because projection screen 14 appears substantially diffuse
when viewed from the front side and substantially transparent when
viewed from the back side, it may be particularly useful in
non-traditional settings. For example, projection screen 14 may be
used in a window, allowing images to be viewed by people outside,
while simultaneously allowing people inside to see outward, through
the window. Such applications may find use in a variety of window
applications, including for example, commercial business settings
and restaurants that display advertisements to persons passing by
the storefront. In those cases, customers inside the store may be
able to see out through the screen 14, and potential customers
outside the store may be lured into the store by the displayed
advertisements.
[0019] As mentioned, the front side of screen 14 may appear
substantially diffuse and the back side of screen 14 may appear
substantially transparent. At the same time screen 14 may help
reduce the amount of external light, such as sunlight, allowed
through screen, much like tinted glass. Thus, when viewed from the
back side, screen 14 may appear tinted, blocking some light, but
remaining substantially transparent such that objects can be viewed
through the screen 14.
[0020] Projection screen 14 may further include a glare-suppressing
element 19 to suppress glare from the front surface of projection
screen 14. Glare from the front surface of projection screen 14 may
occur due to the interface between diffuse reflecting polarizer 16
and air. Glare suppressing element 19 may be a coating of an
antireflective material that reduces the intensity of glare by
controlling the refractive index differences between the air and
diffuse reflecting polarizer 16. Alternatively, glare suppressing
element 19 may be an optically rough surface that distributes the
light reflected from the interface between the air and diffuse
reflecting polarizer 16 into a wide variety of angles. The
diffusion of the reflected light by glare-suppressing element 19
may be random, ordered, or partially ordered. Optically rough
surfaces may include a matte finish, a structured surface, a
microstructured surface, an abraded surface, or the like.
Furthermore, glare-suppressing element 19 may be a combination of
an antireflective material and an optically rough surface.
[0021] Projector 12 is capable of projecting polarized light
towards projection screen 14 to form a reflected image thereon. For
example, projector 12 may project images on to projection screen 14
for presentation to viewers. Projector 12 may be any projector that
produces images using polarized light, such as a liquid crystal
display (LCD) projector. Light from projector 12 can be polarized
in the same direction as the light reflected by screen 14. Thus,
projection screen 14 may reflect a substantial portion of the
polarized light transmitted by projector 12. A smaller percentage
of ambient light, however, may be reflected off screen 14, which
may improve image quality in terms of contrast. Projection screen
14 may reflect a substantial portion of an incident wave of
polarized light 20 into a variety of directions, as is illustrated
by reflected waves 22 and 24. Polarized light from projector 12 may
be directly incident on the front side of projection screen 14, as
shown in embodiment of FIG. 1.
[0022] FIG. 2 illustrates an alternative configuration of system
10B, in which polarized light from projector 12 reflects off one or
more mirrors 26 before projecting incident on the front side of
projection screen 14. In particular, the use of one or more mirrors
26 to reflect images produce by projector 12 onto projection screen
14 may allow system 10 to assume a more compact arrangement.
[0023] FIG. 3 is a cross-sectional side view illustrating an
exemplary embodiment of a projection screen 33 that may be used in
a system similar to system 10 or system 10B. Projection screen 33
comprises a diffuse reflecting polarizer 16 that diffusely reflects
light polarized in a first direction and transmits light polarized
in a second polarization. Projection screen 33 also includes a
reflecting polarizer 34 adjacent the back side of diffuse
reflecting polarizer 16. The orientation of reflecting polarizer 34
with respect to diffuse reflecting polarizer 16 is such that
reflecting polarizer 34 reflects light of the first polarization
and transmits light of the second polarization. In other words, the
transmissive and reflective properties associated with diffuse
reflecting polarizer 16 and reflecting polarizer 34 are
substantially aligned. Thus, light that is able to pass though
diffuse reflecting polarizer 16 can also pass through reflecting
polarizer 34
[0024] Diffuse reflecting polarizer 16 reflects a substantial
portion of incident polarized light that is polarized in the same
direction as the light reflected by diffuse reflecting polarizer
16. A substantial portion of incident polarized light refers to
greater than approximately 70 percent, and preferably greater than
approximately 80 percent, and still more preferably greater than
approximately 90 percent of the incident polarized light. In that
case, diffuse reflecting polarizer 16 transmits approximately 10 to
30 percent of the incident polarized light due to inefficiency. For
example, diffuse reflecting polarizer 16 may diffusely reflect a
substantial proportion of an incident polarized light wave 36, when
polarized light wave 36 is polarized in the same direction as the
light reflected by diffuse reflecting polarizer 16, as shown by
reflected light waves 38 and 40. Diffuse reflecting polarizer 16
may transmit the portion of polarized light wave 36 that is not
reflected, illustrated by transmitted light wave 42, when diffuse
reflecting polarizer 16 is not a "perfect" diffuse reflecting
polarizer. In theory, a perfect diffuse reflecting polarizer may
diffusely reflect all incoming light polarized in the same
direction as the light reflected by the perfect diffuse reflecting
polarizer.
[0025] Reflecting polarizer 34 may reflect a substantial portion of
transmitted light wave 42 as shown by reflected wave 44. Thus,
reflecting polarizer 34 adjacent to the back side of diffuse
reflecting polarizer 16 may increase the brightness of the
projected image to an observer 47 viewing from the front side of
screen 33. Furthermore, reflecting polarizer 34 may help prevent
observer 46 from viewing a faint image on the back side of
projection screen 33. However, due to inefficiencies, a small
portion of polarized light wave 36 may still transmit through both
diffuse reflecting polarizer 16 and reflecting polarizer 34.
[0026] Ambient light may also be incident on projection screen 33.
Ambient light has a generally random polarization. Therefore,
diffuse reflecting polarizer 34 may reflect approximately half of
the ambient light and transmit the rest. The amount of ambient
light that is reflected may vary, however, depending on the quality
and efficiency associated with diffuse reflecting polarizer 34.
Ambient light may come from sources such as artificial lighting in
a room, the sun, or the like. For example, an ambient light wave 48
may be incident on projection screen 14 and, more particularly,
incident on diffuse reflecting polarizer 16. Since ambient light
wave 48 is polarized in a random fashion, diffuse reflecting
polarizer 16 diffusely reflects approximately half of ambient light
wave 48, as illustrated by reflected light waves 49 and 50. Because
diffuse reflecting polarizer 16 diffusely reflects approximately
half of ambient light wave 48, from the perspective of observer 47,
display screen 33 may appear substantially diffuse, i.e. may appear
white. As used herein the phrase "substantially diffuse" refers to
a display screen that diffusely reflects greater than 20 percent,
more preferably greater than 35 percent, and still, even more
preferably approximately 50 percent of randomly polarized
light.
[0027] Diffuse reflecting polarizer 16 transmits the portion of
ambient light wave 48 that is not reflected, as shown by
transmitted light wave 52. Reflecting polarizer 34 may also
transmit transmitted light wave 52. Because diffuse reflecting
polarizer 16 transmits approximately half of incident ambient light
wave 48 and reflecting polarizer 34 transmits substantially all of
transmitted light wave 52, display screen 33, as viewed by observer
46, may be substantially transparent. As used herein the phrase
"substantially transparent" refers to a display screen that
transmits greater than 20 percent, more preferably greater than 35
percent, and even more preferably approximately 50 percent of
randomly polarized light. Furthermore, because display screen 33
transmits approximately half of ambient light wave 48 there may be
less ambient light interference to viewer 47, which may increase
the contrast of the projected image and improve image quality of
images viewed by viewer 47. Display screen 33 illustrated in FIG. 3
may be particularly useful in an environment in which the amount of
ambient light is relatively low on the back side of display screen
33 relative to the ambient light on the front side of display
screen 33.
[0028] One suitable diffuse reflecting polarizer 16 is diffuse
reflecting polarizer film (DRPF.TM. film) commercially available
from Minnesota Mining and Manufacturing Company, of St. Paul, Minn.
(hereafter 3M). One suitable reflecting polarizer 34 is dual
brightness enhancing film (DBEF.TM. film) commercially available
from 3M. These or similar optical films may be used to realize
display screen 33.
[0029] FIG. 4 is a cross-sectional side view illustrating another
exemplary embodiment of a projection screen 54. Projection screen
54 conforms substantially to projection screen 33 illustrated in
FIG. 3, but incorporates an absorbing polarizer 56 instead of a
reflecting polarizer 34. Like the configuration in FIG. 3,
absorbing polarizer 56 and diffuse reflecting polarizer 16 are
aligned such that polarized light that is able to transmit through
diffuse reflecting polarizer 16 is also able to transmit through
absorbing polarizer 56. Absorbing polarizer 56 may absorb a
significant portion of transmitted light wave 42, which may pass
through diffuse reflecting polarizer 16 because of inefficiency. In
addition, absorbing polarizer 56 may prevent an observer 46 from
observing a reflection on the back side of projection screen
54.
[0030] Projection screen 54 allows approximately half of the
randomly polarized light to transmit from the front side of screen
54 to the back side. This is conceptually illustrated by the
portions 49 and 50 of incident light 48 being diffusely reflected,
and the portion 52 being transmitted. In a similar manner,
absorbing polarizer 56 also absorbs or transmits ambient light
incident from the back side of projection screen 54. By way of
example, absorbing polarizer 56 may absorb approximately half of
ambient light incident the back side of screen 54 and may transmit
the rest. Therefore, little or no ambient light incident the back
side of screen 54 may be reflected. Furthermore, since little or no
ambient light reflects toward observer 46, observer 46 may not
observe any low contrast images of objects located near the back
side of screen 54. In particular, observer 46 may not be able to
see a reflection on the back side of screen 54.
[0031] Screen 54 may be more suitable for an environment in which
the amount of ambient light on the back side of display screen 54
is relatively high in comparison with the amount of ambient light
on the front side of display screen 54. For example, screen 54 may
be preferred for window displays illuminated during the evening
because internal lighting may result in a larger amount of ambient
light on the back side of display screen 54. In contrast, screen 33
(FIG. 3) may be preferred for window displays illuminated by a
projector during the day, particularly when the window displays are
facing the sun.
[0032] One suitable absorbing polarizer 56 is product number
SG-1852A, commercially available from Sumitomo Chemical Company
Ltd. of Japan. Another suitable absorbing polarizer 56 is product
number LLC2-8218, commercially available from Sanritz Company of
Japan. These or similar optical films may be used to realize
display screen 54.
[0033] FIG. 5 is a cross sectional top view illustrating an
exemplary embodiment of a projection system 58 that includes a
multi-color transmissive LCD projector 60 that emits light in which
all colors are polarized in a common direction. System 58 also
includes a projection screen 69 that diffusely reflects light
polarized in one direction and transmits light polarized in another
direction. By aligning the polarization of light emitted from
projector 60 with the diffuse characteristics of screen 69,
improved image quality can be achieved. In particular, a higher
percentage of light emitted from projector 60 may be diffusely
reflected by screen 69, relative to randomly oriented ambient
light. Thus, image quality in terms of contrast may be greatly
improved, particularly when system 58 is used in settings where
large amounts of ambient light is incident the projection surface
of screen 69.
[0034] Projector 60 is a three-color projector, although the same
principles may be extended to hi-fidelity displays that incorporate
additional LCDs and additional colors. LCD projector 60 may include
light sources 62A to 62C, collectively referred to as light sources
62. Light sources 62, for example, may be a blue light source 62A,
a green light source 62B, and a red light source 62C. However, as
mentioned, the number of light sources is not limited to three. For
example, LCD projector 60 may have fewer than three light sources
or more than three light sources.
[0035] Light sources 62 emit colored light waves 64A-64C
(collectively colored lights 64). Colored lights 64 may pass
through a respective one of polarizers 66A to 66C (collectively
polarizers 66), which transmit light polarized in a first
direction. Liquid crystal displays (LCDs) 68A to 68C (collectively
LCDs 68) may selectively transmit colored lights 64 possibly
changing the polarization as the light passes through LCDs 68 as is
well known in the art. For example, voltages can be selectively
applied across any of LCDs 68 to selectively cause LCDs 68 to
change the polarization of one or more of colored lights 64. For
example, LCD projector 60 may apply an appropriate voltages across
LCDs 68 to selectively rotate the polarization of colored lights 64
as the lights pass through LCDs 68.
[0036] Colored lights 64 then become incident on a respective one
of anlyzers 70A-70C (collectively analyzers 70). Analyzers 70 may
be aligned to transmit light polarized in the same direction as
light transmitted by polarizer 66, or aligned to transmit light
polarized in the opposite direction as light transmitted by
polarizer 66. In some cases, analyzer 70 and polarizer 66 may be
substantially similar components.
[0037] Each of the colored lights 64 that transmit through analyzer
70 enters a color combiner 72. Color combiner 72 may reflect
colored lights 64, such as by using mirrors 74A and 74C. However,
color combiner 72 may not reflect all colored lights 64 but,
instead may project colored light 64B without reflection. Color
combiner 72 combines each of colored lights 64 to create full color
images. One or more lenses 78 may be used to expand the combined
image for display on screen 69.
[0038] Light polarized in one direction may be more efficient for
reflection whereas light polarized in another direction may be more
efficient for transmission. Therefore, to make LCD projector 60 as
efficient as possible, it is desirable to cause some of colored
light to be polarized in a direction that is more efficient for
reflection, and to cause other colored lights to be polarized in a
direction that is more efficient for transmission. For example, in
the embodiment shown in FIG. 5, colored lights 64A and 64C may be
polarized in the direction that is more efficient for reflection,
whereas colored light 64B may be polarized in the direction that is
more efficient for transmission.
[0039] In accordance with one embodiment of the invention, a
rotator 76 may be used to rotate the polarization of one or more
colored lights 64 emitted from projector 60 in order to align all
the polarizations in a common direction. Rotator 76 may be viewed
as a part of projector 60, or a separate component to system 58. In
any case, it may be highly desirable to have emitted light
polarized in a common direction so that all of the colors of the
projected light are diffusely reflected off of projection screen
69. To achieve common polarization for all colored light 64,
rotator 76 may rotate the polarization of green light 64B, aligning
it with the polarizations of blue light 64A and red light 64C. As
illustrated in FIG. 5, rotator 76 may be positioned outside of
projector 60 to achieve this effect. Alternatively, rotator 76 may
be positioned within projector 60, possibly located to rotate the
polarization of light before or after it is refracted by lens 78.
In any case, by causing the emitted light to be polarized in a
single direction, advantages may be realized. For example, the
color contrast associated with images displayed on a display screen
implementing a diffuse reflective polarizer can be improved.
[0040] Rotator 76 may also be used not only to align the
polarizations of the various colored light but also, to
collectively rotate all of the colored light. For example, rotator
76 may be used to ensure that all of the colored light is properly
polarized for display on projection screen 69.
[0041] As mentioned, projection screen 69 includes a diffuse
reflecting polarizer aligned to diffuse light polarized in the
direction corresponding to the common direction of polarized light
emitted from projector 60. Again, by aligning the polarization of
light emitted from projector 60 with the diffuse characteristics of
screen 69, improved image quality can be achieved. For example,
approximately 50 percent randomly oriented ambient light may be
reflected. However, a much larger percentage of the polarized light
emitted from projector 60 can be diffusely reflected. Therefore,
image quality in terms of contrast may be greatly improved,
particularly when system 58 is used in settings where large amounts
of ambient light is incident the projection surface of screen 69.
Screen 69 may further include various other components as outlined
in greater detail above, including for example, a second polarizer
adjacent a back side of the diffuse reflecting polarizer, and a
glare suppressing element, if desired.
[0042] FIG. 6 is a cross-sectional side view illustrating an
exemplary projection system 77. Projection system 77 includes
projectors 60A and 60B (collectively projectors 60), and a
projection screen 78. Projection screen 78 comprises a diffuse
reflecting polarizer 80 that diffusely reflects light polarized in
a first direction and transmits light polarized in a second
direction. Projectors 60 may project images onto each side of
display screen 78 simultaneously.
[0043] Projection screen 78 may also comprise a second diffuse
reflecting polarizer 82 oriented to have the same polarization
characteristic as diffuse reflecting polarizer 80, i.e. oriented to
reflect light polarized in the first direction and transmit light
polarized in the second direction. A polarizer 84 may also be
placed between diffuse reflecting polarizer 80 and diffuse
reflecting polarizer 82. The orientation of polarizer 84 with
respect to diffuse reflecting polarizers 80, 82 may be such that
polarizer 84 transmits light polarized in the second direction. In
other words, diffuse reflecting polarizer 80, diffuse reflecting
polarizer 82, and polarizer 84 are aligned such that all three
polarizers transmit light polarized in the same direction.
Alternatively, polarizer 84 may be oriented to reflect or absorb
light that is transmitted through diffuse reflecting polarizers 80
and 82. By way of example, polarizer 84 may be a reflecting
polarizer or an absorbing polarizer.
[0044] Diffuse reflecting polarizers 80, 82 may transmit a portion
of the polarized light from respective projectors 60, due to
inefficiencies. Polarizer 84 may reflect or absorb a substantial
portion of the transmitted polarized light depending on whether
polarizer 84 is a reflecting polarizer or absorbing polarizer,
respectively. Further, polarizer 84 may reduce the amount of
polarized light that transmits through projection screen 78,
reducing the amount of image interference. Improved contrast may be
achieved because approximately one-half of ambient light is
respectively transmitted through diffuse reflecting polarizers 80,
82. However, if polarizer 84 is aligned with diffuse reflecting
polarizers 80, 82, the ambient light that transmits through screen
78 may affect image quality of images displayed on the opposing
side.
[0045] Projectors 60 may capable of projecting polarized light
towards one or both sides of projection screen 78 to form a
reflected image thereon. For example, one projector 60A may project
images onto one side of projection screen 78 for presentation to
viewers. At the same time, the other of projector 60B may project
images onto the other side of projection screen 78. For example,
projector 60A may project images on a first side of screen 78,
while projector 60B simultaneously projects images on the opposite
side. Alternatively, one of projectors 60 may project images onto
both sides of projection screen 78 for presentation to viewers. For
example, projector 60A may be a dual image projector that projects
an image on a first side of screen 78 and projects another image on
the opposite side of screen 78 using one or more mirrors. In that
case, the additional projector 60B may be removed from the
system.
[0046] A number of embodiments of the present invention have been
described. For example, various techniques of manipulating and
exploiting light polarization have been described that can improve
the display of images to viewers. In addition, the techniques and
structures described above may improve projection systems for use
in non-conventional settings such as storefront window displays, or
settings where large amounts of ambient light is present.
Projection screens have also been described that allow viewers
viewing the front side of the screen to see improved image quality,
while viewers on the back side of the screen are able to see
through the screen. These and other embodiments are within the
scope of the following claims.
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