U.S. patent application number 10/885124 was filed with the patent office on 2004-12-02 for polarization recovery system for projection displays.
This patent application is currently assigned to Cogent Light Technologies, Inc.. Invention is credited to Li, Kenneth K..
Application Number | 20040240059 10/885124 |
Document ID | / |
Family ID | 27397711 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040240059 |
Kind Code |
A1 |
Li, Kenneth K. |
December 2, 2004 |
Polarization recovery system for projection displays
Abstract
A waveguide polarization recovery system both polarizes the
input light energy for use with an LCD imager and converts the
polarity of unusable light energy to add to the illumination of the
LCD imager. The compact polarization recovery waveguide system
generally includes: (1) an input waveguide that provides
non-polarized light energy into the system; (2) an output waveguide
that receives polarized light energy from the system; (3) a
polarized beam splitter that received the light energy from the
input waveguide and transmits lights energy of a first polarization
type and reflects light energy of a second polarization type, and
(4) a wave plate that modifies the polarization of either the
transmitted or reflected light energy. The polarization recovery
system also generally includes one or more mirrors that are
positioned as need to direct the transmitted and the reflected
light energy to the output waveguide. The input and output
waveguides may be shaped as needed by the projection system. For
example, either one or both of the input and output waveguides may
be tapered as needed to produce a desired image. In the waveguide
polarization recovery system, the input and output waveguides are
configured to have either an either a substantially parallel or a
substantially perpendicular orientation. In another embodiment, the
waveguide polarization recovery system further includes has one or
more "gaps" of optically clear material positioned between the
optical components to encourage the occurrence of total internal
reflection that minimizes the loss of the optical energy by the
system.
Inventors: |
Li, Kenneth K.; (Arcadia,
CA) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
Cogent Light Technologies,
Inc.
Santa Clarita
CA
|
Family ID: |
27397711 |
Appl. No.: |
10/885124 |
Filed: |
July 7, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10885124 |
Jul 7, 2004 |
|
|
|
10347522 |
Jan 21, 2003 |
|
|
|
10347522 |
Jan 21, 2003 |
|
|
|
09814970 |
Mar 23, 2001 |
|
|
|
6587269 |
|
|
|
|
60227312 |
Aug 24, 2000 |
|
|
|
60246583 |
Nov 8, 2000 |
|
|
|
Current U.S.
Class: |
359/489.11 ;
348/E5.141; 348/E9.027; 359/489.07 |
Current CPC
Class: |
H04N 5/7441 20130101;
G02B 27/283 20130101; G02B 27/285 20130101; G02B 27/145 20130101;
G02B 27/1033 20130101; G02B 27/149 20130101; H04N 9/3167 20130101;
G02B 6/4298 20130101; H04N 9/3152 20130101; G02B 27/286 20130101;
H04N 9/3102 20130101 |
Class at
Publication: |
359/497 |
International
Class: |
G02B 005/30; G02B
027/28 |
Claims
1-54 (Cancelled)
55. A light guide comprising at least first and second light guide
sections and at least one light coupling element between the light
guide sections, the light guide sections each having an entrance
aperture, an exit aperture and a guide wall defining a light
guiding direction, the light coupling element being composed of an
optically transparent material having an entrance face with a TIR
surface, and an exit face with a TIR surface, the entrance face
adjacent to the exit aperture of the first light guide section and
extending in the light guiding direction of the second light guide
section, and exit face adjacent to the entrance aperture of light
guide section and extending in the light guiding direction of the
first light guide section.
56. The light guide of claim 55 in which the light coupling element
is wedge-shaped and has an internally reflecting face extending
between the entrance face and the exit face.
57. The light guide of claim 56 in which the cross sections of the
light guide sections have the cross sectional shape of an
even-numbered polygon.
58. The light guide of claim 55 in which at least the first light
guide section is a solid element of an optically transparent
material, and the entrance face of light coupling element adjacent
to the exit aperture of the solid light guide section is spaced a
distance apart from the exit aperture of light guide section, to
form a space between the entrance face of light coupling element
and the exit aperture of the solid light guide section.
59. The light guide of claim 58 in which the second light guide
section is a solid element of an optically transparent material,
and the exit face of light coupling element adjacent to the
entrance aperture of the solid light guide section is spaced a
distance apart from the entrance aperture of light guide section,
to form a space between the exit face of light coupling element and
the entrance aperture of the solid light guide section.
60. The light guide of claim 58 in which the space is filled with
air.
61. The light guide of claim 58 in which the space is filled with
an optically transparent material having an index of refraction
less than that of the material of the light coupling element.
62. The light guide of claim 58 in which the distance d between the
entrance face of light coupling element and the exit aperture of
the solid light guide section is substantially the same across the
width of the space.
63. The light guide of claim 55 in which at least the first light
guide section is a hollow conduit having a guide wall with an
interior reflective surface.
64. The light guide of claim 63 in which the second light guide
section is a hollow conduit having a guide wall with an interior
reflective surface.
65. The light guide of claim 55 in which the entrance and exit
faces of light coupling element form a right angle.
66. The light guide of claim 64 in which the guide walls form an
obtuse angle.
67. The light guide of claim 56 in which the reflective surface is
a polarizing surface, reflecting a first polarization direction and
transmitting a second one.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of application
Ser. No. 09/814,970, filed Mar. 23, 2001, which claims benefit of
U.S. Provisional Application No. 60/227,312, filed Aug. 24, 2000
and 60/246,583, filed Nov. 8, 2000.
FIELD OF INVENTION
[0002] The present invention relates an improved system and
methodology for substantially increasing the light output of a
polarized optical projection system through the recovery of optical
energy of an unused polarization.
BACKGROUND OF INVENTION
[0003] A liquid crystal display (hereafter "LCD") is a known device
used to control the transmission of polarized light energy. The LCD
may be either clear or opaque, depending on the current applied to
the LCD. Because of this functionality, projection systems commonly
use an array containing numerous LCDs to form an image source. In
particular, the projection system inputs high intensity, polarized
light energy to the LCD array (also called an imager), which
selectively transmits some of the inputted light energy to form a
projection of a desired image. Because a single LCD is relatively
small, numerous LCDs can be packed together into the array, thereby
forming an imager that can produce a high resolution image.
[0004] As suggested above, a projection system must first polarize
the light input to the LCD. However, light energy from a light
source, such as a bulb, may have either p-polarization or
s-polarization. Since this light input to the LCD imager must be in
one orientation (i.e., either p-polarization or s-polarization),
the LCD projector generally uses only half of the light energy from
the light source. However, it is desirable in projection systems to
maximize the brightness and intensity of the light output. In
response, various methodologies have been developed to capture the
light energy of unusable polarization, to convert the polarization
of this captured light energy, and then to redirect the converted
light energy toward the LCD imager. These known polarization
recovery methodologies involve creating an expanded beam of light
in which the unused portion of the light (of undesired polarity) is
sent through a half-wave plate to change the polarization and then
recombined with the original polarized beam. Unfortunately, the
implementation of these known methodologies requires complex, bulky
systems, which usually include 2-dimensional lense arrays and an
array of polarization beam splitters. Furthermore, the known
methodologies lose much of the light energy and, therefore,
compromise the projector's goal of producing a high intensity
output. As a result, there exists a current need for a simple, low
cost, and compact polarization recovery system that operates with
high efficiency.
SUMMARY OF THE INVENTION
[0005] In response to these needs, the present invention uses a
waveguide system to perform the polarization recovery function in
an LCD projection system. In particular, the present invention's
waveguide polarization recovery system both polarizes the input
light energy for use with an LCD imager and converts the polarity
of unusable light energy to add to the illumination of the LCD
imager. The compact polarization recovery waveguide system
generally includes the following optical components that are
integrated into a single unit: (1) an input waveguide that inputs
non-polarized light energy into the system; (2) an output waveguide
that removes polarized light energy from the system; (3) a
polarized beam splitter that receives the light energy from the
input waveguide and transmits light energy of a first polarization
type and reflects light energy of a second polarization type, and
(4) a wave plate that modifies the polarization of either the
transmitted or reflected light energy. The polarization recovery
system also generally includes one or more mirrors that are
positioned as needed to direct the transmitted and/or reflected
light energy to the output waveguide. The input and output
waveguides may be shaped as needed by the projection system. For
example, either one or both of the input and output waveguides may
be tapered as needed to produce a desired image.
[0006] In the waveguide polarization recovery system, the input and
output waveguides are configured to have either a substantially
parallel or a substantially perpendicular orientation. In
configurations in which the input and output waveguides are
substantially parallel, the output waveguide directly receives
light energy transmitted by the beam splitter. In this way, light
energy enters and exits the polarization recovery system in
substantially the same direction. Alternatively, the input and the
output waveguides may be positioned substantially perpendicular to
each other such that the light energy exits the polarization
recovery system at a right angle from the direction it enters. In
configurations having input and output waveguides of perpendicular
orientation, a mirror receives the light energy transmitted by the
polarized beam splitter and redirects this energy by 90.degree.
toward the output waveguide.
[0007] The polarization recovery waveguide system of the present
invention combines the above-enumerated list of optical components
into a single, compact unit. In one embodiment, the waveguide
polarization recovery system further includes one or more "gaps" of
optically clear material positioned between the optical components
to encourage the occurrence of total internal reflection that
minimizes the loss of the optical energy by the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other advantages of the present invention will be
described in detail with reference to the following drawings in
which like reference numbers refer to like elements:
[0009] FIGS. 1-4 and 6-10 are schematic diagrams that illustrate
various embodiments of the waveguide polarization recovery system
of the present invention; and
[0010] FIG. 5 is a schematic diagram that illustrates a compact
projection device that uses one embodiment of the polarization
recovery system of the present invention.
DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
[0011] As illustrated in FIGS. 1-4 and 6-10, the present invention
is a compact waveguide polarization recovery system 10 having an
input waveguide 20, a polarizing beam splitter ("PBS") 30, a wave
plate 40, which can be a half-wave plate, or a quarter-wave plate
depending on the configuration, and an output waveguide 50. The
waveguide polarization recovery system 10 generally further
includes mirrors 60 as needed to direct the light stream between
the input and output waveguides, 20 and 50. The following
discussion first summarizes several possible configurations for the
waveguide polarization recovery system 10 and then describes the
individual elements in greater detail.
[0012] FIGS. 1, 3, and 6 illustrate one configuration of the
waveguide polarization recovery system 10 in which the output light
energy is substantially parallel with the input light energy. In
this embodiment, the input waveguide 20 introduces unpolarized
input light at incidence to the PBS 30. The illustrated PBS 30
transmits p-polarized light, and so the p-polarized portion of the
input light energy continues through in the same direction as the
initial input while the s-polarized light is reflected in a
perpendicular direction to the initial direction of input. The
half-wave plate 40 is positioned to receive the reflected
s-polarized light and convert it to p-polarized. Subsequently,
mirror 60 redirects the converted energy from the half-wave plate
40 back to the initial direction of input. Both the transmitted
light energy from the PBS 30 and the converted light energy from
the half-wave plate 40 are recombined in the output waveguide and
mixed. As a result, the output light energy has a uniform intensity
profile and is polarized. It should be appreciated that an output
of the opposite polarization may be produced through the use of a
PBS 30 that only transmits s-polarized light.
[0013] FIGS. 2, 4, and 7-8 illustrate another embodiment of the
waveguide polarization recovery system 10 that has an alternative
configuration in which the output light energy is perpendicular to
the original input light energy. As in the embodiment of FIG. 1,
the input waveguide 20 introduces unpolarized input light at
incidence to the PBS 30. Furthermore, the PBS 30 performs the same
function of transmitting the p-polarized light, and so the
p-polarized portion of the input light energy continues through in
the same direction as the initial input while the s-polarized light
is reflected in a perpendicular direction to the initial direction
of input. However, in the configuration of FIG. 2, one mirror 60
redirects the transmitted p-polarized portion of the input light
energy by 90.degree. toward the output waveguide 50. Furthermore,
the reflected s-polarized light from the PBS 30 propagates once
through a quarter-wave plate 40', and a second mirror 60 then
returns the reflected light energy to the quarter-wave plate 40'
for another pass. The second pass is also in the direction of the
output waveguide 50. Because the reflected s-polarized light passes
twice through the quarter-wave plate 40', s-polarized light is
shifted by a half-wave to become p-polarized twice with the mirror
as shown. Again, both p-polarized outputs will be mixed in the
output waveguide, producing a uniform intensity output. The
embodiment of FIG. 2 requires only two optical sections: A first
section formed through the combination of the input waveguide 20,
the PBS 30, the quarter-wave plate 40' and a mirror 60; and a
second section formed through the combination of the output
waveguide 50 and a second mirror 60. Therefore, the system has a
simple design and a relatively low cost. Positioning the output
light energy perpendicular to the original input light energy also
has the advantage of allowing a more compact projection system, as
described in greater detail below.
[0014] In contrast to the above-described configuration in which
the wave plate 40 modifies the light energy reflected by the PBS
30, other configurations for the waveguide polarization recovery
system 10 position the wave plate to modify the light energy
transmitted by the PBS 30. For example, FIGS. 9 and 10 illustrate
configurations in which the half-wave plate 40 is positioned to
receive light energy transmitted by the PBS 30. In the
configuration of FIG. 9, the half-wave plate 40 is optically
positioned between a mirror 60 and the output waveguide 50. The
half-wave plate 40 receives transmitted light energy that has first
been redirected by a mirror 60. Similarly, in FIG. 10, the
half-wave plate 40 is placed between the PBS 30 and mirror 60. In
this way, the transmitted light energy from the PBS 30 is first
repolarized before being redirected toward the output waveguide 50.
The configurations of FIGS. 9-10 are advantageous because the input
light energy only passes through the polarization layer of the PBS
30 once, thus reducing the loss of optical energy in the system 10.
In contrast, the above-described configuration of the FIGS. 2, 4,
and 7-8 requires some of the input light energy to pass through the
PBS 30 twice.
[0015] Elements of the Waveguide Polarization Recovery System
[0016] The various configurations of the waveguide polarization
recovery system 10 use the same elements, which are now described
in greater detail.
[0017] The input waveguide 20 is typically an integrator that
collects the light from a light source, such as an arc lamp, and
mixes the light through multiple reflections to produce a more
uniform intensity profile into the waveguide polarization recovery
system 10. Likewise, the output waveguide 50 is typically an
integrator that collects the light from the waveguide polarization
recovery system 10 and mixes the light through multiple reflections
to produce a more uniform intensity profile for illumination of the
imager. The input waveguide 20 and the output waveguide 50 may be,
for example, single core optic fibers, fused bundles of optic
fibers, fiber bundles, solid or hollow square or rectangular light
pipes, or homogenizers, which can be tapered or un-tapered. In
optical projection systems, the input waveguide 20 and the output
waveguide 50 are typically rectangular in cross-section to
correspond with the shape of the imager and the final projected
image. The input waveguide 20 and the output waveguide 50 wave can
be made from glass, quartz, or plastic depending on the
power-handling requirement.
[0018] Either one or both of the input waveguide 20 and the output
waveguide 50 can have an increasing or decreasing taper as needed
for the projection system. For example, FIG. 3-4 and 6-10
illustrate embodiments of the waveguide polarization recovery
system 10 in which the input waveguide 20' is a tapered rod with
the input cross-section matched to the area of the light source and
the output cross-section related to the dimensions of a LCD imager.
The final dimensions for the input waveguide 20 may vary as needed
to minimize stray light loss in the optical projection system.
Similarly, FIG. 8 illustrates an embodiment of the waveguide
polarization recovery system 10 in which the output waveguide 50'
is also tapered. Tapering of the output waveguide 50' is
advantageous because, depending on the performance parameters of
the PBS 30, the wave plate 40, and the output requirements for the
projection system, polarization recovery may not always be done at
the same numerical aperture as the output aperture. The
performances of the PBS 30 and the wave plate 40 are better at
smaller numerical apertures, and as a result, advantageous
increases in performance are achieved by transforming the input
light energy into a larger area with a small numerical aperture and
then transforming the light energy back into larger numerical
apertures at the output of the output waveguide 50'. Overall, the
tapering of the input wave guide 20 and the output waveguide 50 can
be selected to match the overall performance requirements of the
projection system, and similarly, the input and output waveguides
can be tapered in either direction.
[0019] The waveguide polarization recovery system 10 further
includes PBS 30. The PBS 30 is a well-known optical element that
transmits light energy of one polarization while reflecting light
energy of a different polarization. Typically, the PBS 30 is a
rectangular prism of optically clear material, such as plastic or
glass, that has a polarizing coating applied to the diagonal
surface. Alternatively, the PBS 30 may be composed of a material
that selectively transmit light energy depending on the
polarization of the light energy. However, it should be appreciated
that there exist numerous alternative designs and types of PBS, and
any of these alternative PBS's may be employed in the waveguide
polarization recovery system 10 of the present invention. Because
the PBS 30 is a well known and commercially available item, it is
not discussed further.
[0020] Another element of the waveguide polarization recovery
system 10 is the wave plate 40. The wave plate 40 is an optically
transparent component that modifies the polarization of light
energy that passes through the wave plate 40. The wave plate 40
typically changes the propagating of light in one oaxis, thus
changes the polarization. The wave plate 40 may be either a
half-wave or quarter-wave as needed by the specific configuration
of the waveguide polarization recovery system 10. Overall, the wave
plate 40 is a well known and commonly available item and will not
be discussed further.
[0021] The waveguide polarization recovery system 10 may further
include one or more mirrors 60 as needed to direct the light energy
through the waveguide polarization recovery system 10. While
mirrors are commonly known to be metal-coated glass surfaces or
polished metal, the mirrors 60 should not be limited to this common
definition for the purpose of this invention. Instead, mirrors 60
should be considered any optical component capable of reflecting or
redirecting light energy. For example, mirrors 60 may be prisms
that use the angle of incidence to capture and redirect light
energy. For example, FIGS. 9 and 10 illustrate a waveguide
polarization recovery system 10 that has a prism to redirect light
energy transmitted by the PBS 30 toward the output waveguide 50.
For systems with small numerical apertures, total internal
reflection at the prism can be used, and as a result, the coating
is not necessary.
[0022] In another preferred embodiment of the present invention,
illustrated in FIGS. 6-10, the waveguide polarization recovery
system 10 further includes one or more optically clear areas, or
"gaps," 70 between the other optical elements. The gaps 70 may be
pockets of air left between the optical components. The gap 70 can
also be filled with low index epoxy or other transparent material
such that the total internal reflection still occurs, but the
assembly of the components will be simplified. For example, FIG. 6
illustrates a configuration having gap 70 between the input
waveguide 20 and the PBS 30. This gap 70 ensures that light energy
reflected by the diagonal PBS 30 is turned by 90.degree. toward the
quarter-wave plate 40' because total internal reflection from the
interface between the PBS 30 and the gap 70 prevents the light
energy from returning instead to the input waveguide 20 and exiting
as a loss. The waveguide polarization recovery system 10 in FIG. 6
also has other gaps 70 to promote total internal reflection between
the different optical elements. Similarly, FIG. 7 illustrates a
waveguide polarization recovery system 10 in which gaps 70 have
been added to a polarization recovery system with a tapered input
waveguide 20 and perpendicularly configured output waveguide 50
illustrated in FIG. 4. Again these gaps 70 increase the efficiency
by encouraging total internal reflection between the optical
components. As illustrated in FIGS. 6-7, the gaps 70, while
increasing the efficiency of the system, cause the waveguide
polarization recovery system 10 to become more complex with an
increased number of discrete parts.
[0023] In the above-described configurations of FIG. 9-10, the gaps
70 further serve the purpose of improving the performance of the
prism 60' that serves as a mirror to direct the light energy toward
the output waveguide 50. In particular, the gap 70 is needed
between the PBS 30 and the prism 60' such that the light reflected
from the hypotenuse of the prism 60', back toward the PBS 30, hits
this interface of the gap 70 and is internally reflected toward the
output waveguide 50. In this way, efficiency of the system is
improved by minimizing loss.
[0024] The performance advantages of the gaps 70 may be further
increased through the use of anti-reflection coating on both
surfaces such that the transmitted light suffers minimal loss.
[0025] FIG. 5 illustrates a projector 100 that employs the
waveguide polarization recovery system 10. The projector 100
consists of a light collecting system 110, which in this
illustrated example has two paraboloid reflectors and a
retro-reflector that increase the output by reflecting the light
from a light source 120 back into itself. The arc of the light
source 120 is placed at a focus of the first paraboloid reflector
and the proximal end of the input waveguide 20 is at the focus of
the second paraboloid reflector. It should be appreciated that this
light collection system 110 is provided merely for illustration,
and many other light collection systems are known and may be used.
Likewise, the light source 120 may be an arc lamp, such as xenon,
metal-halide lamp, HID, or mercury lamps, or a filament lamp, such
as a halogen lamp, provided that the system is modified to
accommodate the non-opaque filaments of the lamp.
[0026] Within the illustrated projector 100, the input waveguide 20
is a tapered light pipe that is designed to match the light input
collected from the light collecting system 110 to the optical needs
of an LCD imager 150. As described above in FIG. 4, the light
output of the input waveguide 20 is polarized by the PBS 30 and the
other polarization is recovered by the quarter-wave plate 40'. The
output waveguide 50 then directs the polarized optical energy
toward the LCD imager 150. In this case, the light output in the
output waveguide 50 is then incident into a second PBS 130 whose
orientation is matched to the polarization of the incident light to
minimize the loss. A color wheel 140, or other type of color
selection system, and the reflective LCD imager 150 create the
projected image by the projection lenses 160 in a traditional
manner. As shown in FIG. 5, the number of optical elements is
minimal and, as the result, the cost for the projector is
relatively low.
[0027] It should be appreciated that the waveguide polarization
recovery system 10 may be used in other types of projection
systems. For example, the projector may also use two or three
imagers 150 to define the projected image. The imager 150 may also
be a reflective display using liquid crystal on silicon ("LCOS")
technology, or any other type of systems that requires polarized
light. Similarly, the color wheel 140 can also be replaced by
electrically switchable color system without moving parts or other
known color projection systems.
[0028] While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth, and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
* * * * *