Note: Descriptions are shown in the official language in which they were submitted.
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
POLARIZATION RECOVERY SYSTEM USING REDIRECTION
BACKGROUND OF THE INVENTION
Cross-reference to Related Applications:
[0001] This application claims priority to Provisional Application Serial Nos.
60/448,471, filed February 21, 2003, and 60/469,393, filed May 12, 2003, the
disclosures of which are incorporated by reference. This application is a
continuation-
in-part of co-pending Application Serial No. 10/347,522, filed January 21,
2003, which is
a continuation of Application Serial No. 09/814,970, filed March 23, 2001, now
U.S.
Patent No. 6,587,269.
Field of Invention:
[0002] This invention relates to the recovery of light that might otherwise be
unused in
projection systems.
Description of the Related Art:
[0003] Projection displays work by projecting light onto a screen. The light
is
arranged in patterns of colors or brightness and darkness or both. The
patterns are
viewed by a viewer who assimilates them by associating the patterns with
images with
which the viewer may already be familiar, such as characters or faces. The
patterns
may be formed in various ways. One way to form patterns is by modulating a
beam of
light wifih a stream of information.
[0004] Polarized light may be modulated by filtering it with polarized
filters. Polarized
filters will pass light, in general, if their polarization matches the
polarization of the
incident light. A liquid crystal display (LCD) imager may be used to perform
the
modulation in LCD-type projection displays. The LCD imager may include pixels
that
may be modulated by altering their polarization to either match or differ from
the
polarization of incident light. The light input to the LCD imager is polarized
such that
when the LCD pixels are modulated the polarization of the selected pixels is
changed,
and when the light output from the imager is analyzed by another polarizer,
the selected
pixels will be darkened. The pattern may be projected onto a screen as the
presence or
1
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
absence of light. If the polarization of the pixels is modulated with
information in a
pattern with which a viewer is familiar, the viewer may recognize the pattern
projected
onto the screen.
[0005] One way to polarize light for an LCD imager is with a polarizing beam
splitter
(PBS). Polarized light may be provided to an imaging system with an array of
lenses,
such as a fly's eye lens, and an array of polarizing beam splitters. A
parabolic reflector
may be used with a fly's-eye lens to focus light such that the light is nearly
parallel. The
beam is split into many sections by the lens array and each section is
refocused by
another lens array into the polarizing beam splitter array. A parabolic
reflector,
however, may reduce the brightness of a source of light, such as an arc.
Furthermore,
the efficiency of a fly's-eye lens recovery system depends critically on the
alignment of
the two lens arrays and the polarizing beam splitter array. Finally, a
polarization
recovery system comprised of a parabolic reflector and a fly's-eye lens may
not be
suited for sequential color single imager systems.
[0006] Elliptical reflectors may be used with a light pipe and a color wheel
to produce
sequential colors as well. Such a system, however, still requires a
polarization recovery
system and does not solve the intrinsic loss of brightness associated with
ellipsoidal
reflectors. The light output from the polarizing beam splitter array will then
be linearly
polarized and focused into the target. Each polarizing beam splitter divides
unpolarized
light into beams having disparate polarizations. Only one of the beams will be
of the
correct polarization to input to the LCD imager after the light is polarized.
The other
beam will be of an incorrect polarization and hence unusable direcfily.
[0007] Polarization recovery systems may be used to recover light of the
unused
polarization by converting it into usable light with the correct polarization.
Various
schemes have been developed to convert the incorrectly polarized light to the
correct
polarization so that it too may be used. One method, shown in Fig. 1, is to
transmit light
of a first polarization 102 from a polarizing beam splitter 104 directly to an
output 106
while reflecting light of a second polarization 108 at an angle to the output
106, such as
a 90° angle. The light of the second polarization 108 is then reflected
so it is parallel the
light of the first polarization 102, heading toward the output 106. A retarder
plate 110,
2
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
e.g. a quarter wave or half wave plate, is placed in the path of the light of
the second
polarization 108 to rotate it into light of the first polarization 102 such
the output consists
of light of only the first polarization 102.
[0008] Retarder plates rotate light from one polarization to another by
slowing light in
one plane down while allowing light in the opposite plane to pass relatively
unimpeded.
The speed at which light propagates through a medium is, in general, related
to its
wavelength. The degree to which light is slowed down will thus also be related
to its
wavelength. Since retarder plates that are applied to broadband light must
pass light of
a range of wavelengths, some light will be retarded more than other light.
Retarder
plates are, in general, tuned to a particular wavelength. In particular,
wavelengths that
are longer or shorter than the tuned wavelength will not be completely rotated
from the
unusable polarization to the correct polarization. Thus some of the light of
wavelengths
longer or shorter than the tuned wavelength will be lost, or at least not
recovered.
Retarder plates, furthermore, are relatively expensive and often not reliable.
A retarder
plate makes a polarization recovery system itself expensive and unreliable.
[0009] Although these systems have been used commercially, the cost of the
components is high and they require critical alignments and optical designs.
As a
result, there is a need for a system to perform polarization conversion with
high
efficiency, simple configurations and lower costs.
Summary of the Invention:
[000] In a firsfi aspect of the invention a polarization recovery system may
include a
polarizing beam splitter transmitting a light of a useful polarization in an
output direction
and reflecting a light of a non-useful polarization in a first orthogonal
direction
substantially orthogonal to the output direction, an initial reflector
disposed reflectably to
the first orthogonal direction, the initial reflector reflecting the non-
useful polarization
light in a second orthogonal direction substantially orthogonal to the output
direction and
the first orthogonal direction, and a final reflector disposed reflectably to
the second
orthogonal direction, the final reflector reflecting the non-useful
polarization light in the
output direction, wherein the non-useful polarization light is rotated
substantially to light
3
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
of the useful polarization by the initial and final reflectors.
[0011] In a second aspect of the invention a method of polarization recovery
may
include polarizing substantially light into light of a useful polarization and
light of a non-
useful polarization, transmitting the useful polarization light in an output
direction,
reflecting the non-useful polarization light in a first orthogonal direction
substantially
orthogonal to the output direction, reflecting the non-useful polarization
light in a second
orthogonal direction substantially orthogonal to the output direction and the
first
orthogonal direction, and reflecting the non-useful polarization light in the
output
direction.
[0012] In a third aspect of the invention a system of polarization recovery
may include
means for polarizing substantially light into light of a useful polarization
and light of a
non-useful polarization, means for transmitting the useful light in an output
direction,
means for reflecting the non-useful light in a first orthogonal direction
substantially
orthogonal to the output direction, means for reflecting the non-useful light
in a second
orthogonal direction substantially orthogonal to the output direction and the
first
orthogonal direction, and means for reflecting the non-useful light in the
output direction.
Brief Description of the Several Views of the Drawings:
[0013] Fig. 1 shows a polarization recovery system;
Fig. 2 shows a schematic diagram of a polarization recovery system according
to an embodiment of the invention;
Fig. 3 shows a polarization recovery apparatus for use with an embodiment of
the invention;
Fig. 4 shows a polarization recovery apparatus for use with an embodiment of
the invention;
Fig. 5 shows a polarization recovery apparatus for use with an embodiment of
the invention;
Fig. 6 shows straight and tapered light pipes for use with an embodiment of
the invention;
Fig. 7 shows various cross-sections of light pipes for use with an embodiment
4
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
of the invention;
Fig. 8 shows various configurations of light pipes for use with an embodiment
of the invention; and
Fig. 9 shows a polarization recovery apparatus for use with an embodiment of
the invention.
Detailed Description of the Preferred Embodiments
[0014] It would be desirable if light of an unusable polarization could be
recovered
and used by converting its polarization to a correct, or useful, polarization.
Since a
retarder plate makes a polarization recovery system more expensive and less
reliable, it
would be desirable,for polarization recovery to be performed without resorting
to the use
of retarder plates. It would be desirable for polarization recovery to be
performed on
broadband radiation. It would be desirable for a polarization recovery system
to be
relatively simple to manufacture and assemble. It would be desirable for a
polarization
recovery system to allow the use of a color wheel in a single imager system.
[0015] In Fig. 2 is shown a polarization recovery system 200 according to a
first
embodiment of the invention. Polarization recovery system 200 may include a
polarizing beam splitter 202, such as a multi-layer coated or a wire-grid
polarizing beam
splitter. In one embodiment, light input to polarizing beam splitter 202 may
come
directly or indirectly from a source 212 of electro-magnetic radiation, i.e.
light. In one
embodiment, source 212 of electro-magnetic radiation may be an arc lamp, such
as a
xenon lamp, a metal halide lamp, a high intensity discharge (HID) lamp, or a
mercury
lamp. In another embodiment, source 212 may be a halogen lamp or a filament
lamp.
[0016] In one embodiment, polarization recovery system 200 may include an
input
light pipe 224, a supercube 268, and an output light pipe 232, as shown in
Figs. 2 and
5. In several embodiments, output light pipe 232 may be an homogenizer or an
integrator. The output of input light pipe 224 may be coupled into the prism
arrangement, i.e. supercube 268. Input light pipe 224 may use total internal
reflection
(TIR) to propagate light to supercube 268.
[0017] In several embodiments, input light pipe 224, output light pipe 232, or
both
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
input light and output light pipes 224 and 232 may be increasing taper light
pipes, as
shown in Fig. 6A, decreasing taper light pipes, as shown in Fig. 6B, or
straight light
pipes, as shown in Fig. 6C. In several embodiments, a cross-section of input
light pipe
224, output light pipe 232, or both input light and output light pipes 224 and
232 may be
rectangular, circular, triangular, rhomboid, trapezoidal, pentagonal,
hexagonal, or
octagonal, as shown in Figs. 7A-7H. In several embodiments, input light pipe
224,
output light pipe 232, or both input light and output light pipes 224 and 232
may be
comprised of an optical fiber, an optical fiber bundle, a fused fiber bundle,
a polygonal
waveguide, or a hollow light pipe, as shown in Figs. 8A-8E.
[0018] Several embodiments of polarization recovery system 200 are shown in
Figs. 3
and 4. Polarizing beam splitter 202 may separate unpolarized light from input
light pipe
224 into light of a useful polarization 204 having a polarization 270, as
shown in Figs.
3A and 4A, and light of non-useful polarization 208 having a polarization 272,
as shown
in Figs. 3B and 4B. Polarizing beam splitter 202 may transmit light of useful
polarization
204 in an output direction 206 and reflect light of non-useful polarization
208 in a first
orthogonal direction 210 substantially orthogonal to output direction 206. In
one
embodiment, polarization 270 may be substantially p-polarized, or horizontally
polarized, light, while polarization 272 is substantially s-polarized, or
vertically polarized,
light. In an alternative embodiment, the planes of polarization may be
reversed.
[0019] Light of useful polarization 204 may propagate through polarizing beam
splitter
202 and be redirected by first output reflector 220 and second output
reflector 222,
exiting second output reflector 222 with polarization 270 unchanged, as shown
in Figs.
3A and 4A. Light of non-useful polarization 208, on the other hand, may be
reflected by
an initial reflector 214 after exiting polarizing beam splitter 202, as shown
in Figs. 3B
and 4B. Initial reflector 214 may reflect light of non-useful polarization 208
about an
axis substantially orthogonal to the plane of polarization 272 of light of non-
useful
polarization 208, which is in this case the s or vertical plane. Final
reflector 218 may
then reflect light of non-useful polarization 208 in a direction parallel to
output direction
206. An inclined surface of initial reflector 214 may thus be rotated 90
° with respect to
final reflector 218. Although light of non-useful polarization 208 is still
labeled light of
6
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
non-useful polarization 208 for tracking purposes, it has become light of
useful
polarization, since the plane of polarization of light of non-useful
polarization 208 is now
horizontal, or p-polarized, to substantially match that of light of useful
polarization 204.
In one embodiment, both light of useful polarization 204 and light of non-
useful
polarization 208 may be coupled to output light pipe 232 and homogenized.
[0020] In one embodiment, a first output reflector 220 may be disposed
reflectably to
output direction 206. First output reflector 220 may reflect useful
polarization light 204
in second orthogonal direction 216. In several embodiments, first output
reflector 220
may be a mismatched impedance such as a prism, a right angle prism, or a
mirror. In
one embodiment, first output reflector 220 may have a coating that transmits a
pre-
determined portion of electro-magnetic radiation spectrum. This might be used
to
discard unusable non-visible light before it is coupled into an imager. In
several
embodiments, pre-determined portion of electro-magnetic radiation spectrum may
be
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or a combination thereof. In an alternative embodiment, the coating
may reflect
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or some combination thereof.
(0021] In one embodiment, shown in Fig. 3A, a second output reflector 222 may
be
disposed reflectably to second orthogonal direction 216. Second output
reflector 222
may reflect useful polarization light 204 in output direction 206. In another
embodiment,
shown in Fig. 4B, second output reflector 222 may be disposed reflectably to
output
direcfiion 206. Second output reflector 222 may reflect non-useful
polarization light 208
in second orthogonal direction 216. In several embodiments, second output
reflector
222 may be a mismatched impedance such as a prism, a right angle prism, or a
mirror.
In one embodiment, second output reflector 222 may have a coating that
transmits a
pre-determined portion of electro-magnetic radiation spectrum. This might be
used to
discard unusable non-visible light before it is coupled into an imager. In
several
embodiments, pre-determined portion of electro-magnetic radiation spectrum may
be
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or a combination thereof. In an alternative embodiment, the coating
may reflect
7
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or some combination thereof.
[0022] In one embodiment, initial reflector 214 may be disposed reflectably to
first
orthogonal direction 210. Initial reflector 214 may reflect non-useful
polarization light
208 in a second orthogonal direction 216 substantially orthogonal to output
direction
206 and first orthogonal direction 210. In several embodiments, initial
reflector 214 may
be a mismatched impedance such as a prism, a right angle prism, or a mirror. A
mismatched impedance may reflect a wave, such as an electro-magnetic wave, in
the
manner of an echo. A mismatched impedance, for example, may reflect part of a
wave,
or a range of wavelengths, while passing other parts of the wave, or other
wavelengths.
[0023] In one embodiment, initial reflector 214 may have a coating that
transmits a
pre-determined portion of electro-magnetic radiation spectrum. This might be
used to
discard unusable non-visible light before it is coupled into an imager. In
several
embodiments, pre-determined portion of electro-magnetic radiation spectrum may
be
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or a combination thereof. In an alternative embodiment, the coating
may reflect
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or some combination thereof.
[0024] In one embodiment, final reflector 218 may be disposed reflectably to
second
orthogonal direction 216. Final reflector 218 may reflect non-useful
polarization light
208 in output direction 206. In several embodiments, final reflector 218 may
be a
mismatched irvpedance such as a prism, a right angle prism, or a mirror. In
one
embodiment, final reflector 218 may have a coating that transmits a pre-
determined
portion of electro-magnetic radiation spectrum. This might be used to discard
unusable
non-visible light before it is coupled into an imager. In several embodiments,
pre-
determined portion of electro-magnetic radiation spectrum may be infrared
light, visible
light, a pre-determined band of wavelengths of light, a specific color of
light, or a
combination thereof. In an alternative embodiment, the coating may reflect
infrared light,
visible light, a pre-determined band of wavelengths of light, a specific color
of light, or
some combination thereof.
8
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
[0025] In one embodiment, polarization 272 of non-useful polarization light
208 may
be rotated substantially to match polarization 270 of light of useful
polarization 204 by
initial and final reflectors 214 and 218. In this embodiment, first orthogonal
direction
206 and second orthogonal direction 216 may lie substantially in a plane of
polarization
272 of light of non-useful polarization 208. This basic block may be used to
reflect and
redirect light of non-useful polarization 208 from polarizing beam splitter
202 as
described above such that polarization 272 of light of non-useful polarization
208 is
converted to polarization 270 of light of useful polarization 204 and
redirected to output
direction 206.
[0026] In an alternative embodiment, shown in Fig. 9, initial reflector 214
may reflect
light of non-useful polarization 208 about an axis in the plane of
polarization 272 while
final reflector 218 reflects light of non-useful polarization 208 about an
axis substantially
orthogonal to plane of polarization 272, thereby also causing light of non-
useful
polarization 208 to assume polarization 270. The light from final reflector
218 may pass
through a spacer 246 so that now-horizontally polarized light of non-useful
polarization
208 may exit at the same plane as light of useful polarization 204. The two
outputs may
be coupled into output light pipe 232 to be homogenized and to have their
shape and
NA converted to the shape and numerical aperture desired at the output face.
In one
embodiment, output light pipe 232 may also use total internal reflection to
propagate
light to its output.
[0027] In one embodiment, light of useful polarization 204 may exit polarizing
beam
splitter 202 in a different direction than that of light of non-useful
polarization 208 after it
has been redirected to output direction 206 by final reflector 218. In one
embodiment,
shown in Fig. 3A, first output reflector 220 and second output reflector 222
may be used
to redirect light of useful polarization 204 in the same direction as light of
non-useful
polarization 208. In an alternative embodiment, first output reflector 220,
shown in Fig.
4A, redirects light of useful polarization 204 while second output reflector
222, shown in
Fig. 4B, redirects light of non-useful polarization 208 in the same direction
as light of
useful polarization 204. A spacer 246 may be used in either case to allow
light of useful
polarization 204 to exit at the same surface as light of non-useful
polarization 208. This
9
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
may be useful in order to couple light of useful polarization 204 and light of
non-useful
polarization 208 into output light pipe 232.
[0028] In one embodiment, supercube 268 may consist of polarizing beam
splitter 202
and reflectors 214, 218, 220 and 222. Light may be propagated through these
optical
components via total internal reflection. The surfaces of the optical
components may be
optically polished to promote total internal reflection. In one embodiment the
optical
material used for reflectors 214, 218, 220 and 222 may have a high index of
refraction
to promote total internal reflection of skew rays. In one embodiment, the
input and
output faces of the optical components may be coated with an anti-reflective
(AR)
coating to minimize Fresnel reflection losses.
[0029] In one embodiment, reflectors 214, 218, 220 and 222 may be produced
from
an optical glass such as SF11 (n = 1.785). In another embodiment, reflectors
214, 218,
220 and 222 may be produced from an optical glass such as BK7 (n = 1.517). In
this
embodiment, however, the rays may start to leak out from the walls,
particularly on the
diagonal walls of reflectors 214, 218, 220 and 222.
[0030] In one embodiment, a spacer 246 may be used in conjunction with
reflectors
214, 218, 220 and 222 to form a large cubic shape for ease of packaging. In
one
embodiment, spacer 246 may be a cube. In one embodiment, each of reflectors
214,
218, 220 and 222 may be combined with a complementary spacer 246, such as a
right
angle spacer, to form a little cube. In one embodiment, eight little cubes may
form a
supercube 268. In one embodiment, reflectors 214, 218, 220 and 222 and spacers
272
are stacked togefiher to form supercube 268. In one embodiment, the components
may
be glued together by an adhesive material. In another embodiment, the
components
may be held together by means of a mechanical holder. This construction may be
rugged and may have minimal loss.
[0031] In several embodiments, gaps may be introduced between any two of input
and output light pipes 224 and 232, reflectors 214, 218, 220 and 222, or
polarizing
beam splitter 202 to promote total internal reflection and to reduce losses.
In one
embodiment, input light pipe 224, reflectors 214, 218, 220 and 222, and output
light pipe
232 may be separated by small air gaps.
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
[0032] In one embodiment, shown in Fig. 5, supercube 268 may be made up of
individual components. In one embodiment, some of the components may be
combined
into single unit. In one embodiment, for example, two prisms may be combined
into a
single prism. In this embodiment, a pair of reflectors 214, 218, 220 or 222
may be
combined during the manufacturing process, such as during a glass molding
process.
In an alternative embodiment, two prisms may be glued together to form a
single unit. In
one embodiment, two prisms may be combined with half of polarizing beam
splitter 202
to form a single unit. In this embodiment, the full PCS system may be made
with two
components together with the spacer 246. In another embodiment, a prism may be
combined with a spacer 246. In one embodiment, the system may be made in two
components with the separation at polarizing beam splitter 202. In this
embodiment,
cost may be minimized.
[0033] In one embodiment, polarizing beam splitter 202 and reflectors 214,
218, 220
and 222 may be substantially cubical. In one embodiment, polarizing beam
splitter 202
and reflectors 214, 218, 220 and 222 may have all sides with the substantially
similar
dimensions, except for the hypotenuses of the reflectors. In this embodiment,
the
output of input light pipe 224 may be square, and the input of output light
pipe 232 may
be rectangular with an aspect ratio of 2:1. Non-cube configurations may also
be
implemented such that output light pipe 232 input has an aspect ratio other
than 2:1,
albeit with possibly larger coupling losses.
[0034] In several embodiments, input and output light pipes 224 and 232,
reflectors
214, 218, 220 and 222, or polarizing beam splitter 202 may be coated with an
anti-
reflection (AR) coating in order to increase efficiency. In several
embodiments, input
and output light pipes 224 and 232 may be tapered in an increasing or
decreasing
manner as required by the application. Reflectors 214, 218, 220 and 222 may be
reflection coated as appropriate for high angle light. Supercube 268 may be
used in
various configuration besides the one described.
[0035] In one embodiment, an input light pipe 224 may be placed proximate to
an
input 226 of polarizing beam splitter 202. In one embodiment, input light pipe
224 may
have an input surface 228 and an output surface 230. In several embodiments,
input
11
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
light pipe 224 may be made of quartz, glass, plastic, or acrylic. In several
embodiments, input light pipe 224 may be a tapered light pipe (TLP) or a
straight light
pipe (SLP). In several embodiments, a shape of input surface 228 may be flat,
convex,
concave, toroidal, or spherical. A surface of input light pipe 224 may be
coated such
that the total internal reflection preserves the polarization. The dimensions
of input
surface 228 and output surface 230 may be selected such that the output
numerical
aperture (NA) is matched to a device receiving light from input light pipe
224.
[0036] In one embodiment, output surface 230 may be disposed proximate to
input
226 of polarizing beam splitter 202. In several embodiments, a shape of output
surface
230 may be flat, convex, concave, toroidal, or spherical. In one embodiment,
input light
pipe 224 may receive substantially un-polarized light at input surface 228 and
transmit
un-polarized light at output surface 230 to polarizing beam splitter 202.
[0037] In one embodiment, input light pipe 224 may be hollow. Output surface
230
may be a piano-convex lens. A convex surface of output surface 230 may be
spherical
or cylindrical depending on the final configuration and cost of the
components. A power
of output surface 230 may be designed such that the light from output surface
230 is
imaged onto polarizing beam splitter 202. An inner surface of input light pipe
224 may
be coated with a polarization preserving material.
[0038] In one embodiment, an output light pipe 232 may be placed proximate to
an
output 234 of supercube 268. In one embodiment, output light pipe 232 may have
an
input surface 236 that is disposed proximate to output direction 206 and an
output
surface 238. Output light pipe 232 may receive useful polarization light 204
and non-
useful polarization light 208 at input surface 236 and may transmit useful
polarization
light 204 and non-useful polarization light 208 at output surface 238.
[0039] In several embodiments, a shape of input surface 236 may be flat,
convex,
concave, toroidal, or spherical. In several embodiments, a shape of output
surface 238
may be flat, convex, concave, toroidal, or spherical. In several embodiments,
output
light pipe 232 may be comprised of a material selected from group consisting
of quartz,
glass, plastic, or acrylic. In several embodiments, output light pipe 232 may
be a
tapered light pipe (TLP) or a straight light pipe (SLP). A surface of output
light pipe 232
12
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
may be coated such that the total internal reflection preserves the
polarization. The
dimensions of input surface 236 and output surface 238 may be selected such
that the
output numerical aperture (NA) is matched to a device receiving light from
output light
pipe 232.
[0040] In one embodiment, output light pipe 232 maybe hollow. Output surface
238
may be convex in shape. A convex surface of output surface 238 may be
spherical or
cylindrical depending on the final configuration and cost of the components. A
power of
output surface 238 may be designed such that the light from output surface 238
is
imaged onto an image projection system. An inner surface of output light pipe
232 may
be coated with a polarization preserving material.
(0041] In one embodiment, a shell reflector 240 may reflect light from source
212 to
polarizing beam splitter 202. In one embodiment, shell reflector 240 may have
a
coating that transmits a pre-determined portion of electro-magnetic radiation
spectrum.
This might be used to discard unusable non-visible light before it is coupled
into an
imager. In several embodiments, pre-determined portion of electro-magnetic
radiation
spectrum may be infrared light, visible light, a pre-determined band of
wavelengths of
light, a specific color of light, or a combination thereof. In an alternative
embodiment, the
coating may reflect infrared light, visible light, a pre-determined band of
wavelengths of
light, a specific color of light, or some combination thereof.
(0042] In one embodiment, shell reflector 240 may have a first and a second
focal
points 242 and 244. In one embodiment, source 212 of electro-magnetic
radiation may
be disposed substanfiially proximate to firsfi focal point 242 of shell
reflecfior 240 to emit
rays of light that reflect from shell reflector 240 and converge substantially
at second
focal point 244. In one embodiment, input surface 228 may be disposed
proximate to
second focal point 244 to collect and transmit substantially all of light. In
another
embodiment, input 226 of polarizing beam splitter 202 may be disposed
proximate to
second focal point 244 to collect and transmit substantially all of light. In
several
embodiments, shell reflector 240 may be at least a portion of a substantially
elliptical
surface of revolution, a substantially spherical surface of revolution, or a
substantially
toric surface of revolution.
13
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
[0043] In one embodiment, shell reflector 240 may include a primary reflector
250 with
a first optical axis 252, and first focal point 242 may be a focal point of
primary reflector
250. In this embodiment, shell reflector 240 may also include a secondary
reflector 254
having a second optical axis 256 placed substantially symmetrically to primary
reflector
250 such that first and second optical axes 252 and 256 are substantially
collinear. In
this embodiment, second focal point 244 may be a focal point of secondary
reflector
254, and rays of light may reflect from primary reflector 250 toward secondary
reflector
254 and converge substantially at second focal point 244. In several
embodiments,
primary and secondary reflectors 250 and 254 each may be a substantially
elliptical
surface of revolution, or a substantially parabolic surface of revolution.
[0044] In one embodiment, primary reflector 250 may be at least a portion of a
substantially elliptical surface of revolution, and secondary reflector 254
may be at least
a portion of a substantially hyperbolic surface of revolution. In another
embodiment,
primary reflector 250 may be at least a portion of a substantially hyperbolic
surface of
revolution, and secondary reflector 254 may be at least a portion of a
substantially
elliptical surface of revolution.
[0045] Source 212 may be placed at first focal point 242 of primary reflector
250 to
collimate the collected light and direct it towards secondary reflector 254.
The output at
input surface 223 may be directed into an input light pipe 224. In one
embodiment,
input light pipe 224 may be a tapered light pipe (TLP). Input light pipe 224
may be
useful to transform a cross-sectional area or a numerical aperture of the
image of
source 212. The light may be directed into a supercube polarization recovery
system to
obtain linearly polarized light at output light pipe 232. Linearly polarized
light may be
suitable for illumination of LCD-based imager chips that require polarized
light.
[0046] The degree of collimation may depend on the size of source 212.
Secondary
reflector 254 may be positioned symmetrically with respect to primary
reflector 250 such
that they share common optical axes. The beam entering secondary reflector 254
converges to second focal point 244 where a target, i.e., input light pipe
224, is placed.
Input light pipe 224 may couple light from second focal point 244 of secondary
reflector
254. In one embodiment, source 212 may be imaged onto a target in a 1:1 ratio
such
14
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
that the brightness of source 212 is essentially preserved. The image of
source 212 at
input surface 228 may be exactly the same as source 212 with unit
magnification, due
to the 1:1 symmetry of the system.
[0047] Polarization recovery system 200 may be able to conserve etendue
throughout
the source collector components of polarization recovery system 200. The full
angle of
light at input surface 228 may be approximately 180° about an axis of
source 212 and
90° about an axis normal to the axis of source 212, due to the extent
of the reflectors.
These angles may be too large for applications such as micro displays. In one
embodiment, input light pipe 224 may be a tapered light pipe (TLP) to
transform a high
input numerical aperture (NA) and small input area into a lower NA and larger
output
area without a loss of brightness, thus reducing the angles.
[0048] In one embodiment, source 212 may not be circular. In several
embodiments,
the input of input light pipe 224 may be designed to be of rectangular,
elliptical,
octagonal, or other cross-sectional shape to match the shape of the image of
source
212. An input matched to the image of source 212 may prevent or reduce
degradation
of system etendue due to shape mismatches. The output dimensions and aspect
ratios
of input light pipe 224 may be designed to match a size and an aspect ratio of
an
imager panel, but with a super cube-based configuration they may be relatively
arbitrary.
[0049] Primary and secondary reflectors 250 and 254 may cover substantially a
rotational arc extent of 180° to maximize the collection efficiency,
i.e., primary reflector
250 will collect approximately one half of the light emitfied from source 212.
A retro-
reflector 258 may be placed on the opposite side of primary reflector 250 to
collect the
other half of the emitted light. In one embodiment, retro-reflector 258 may be
a
hemispherical retro-reflector. In one embodiment, a center of curvature of
retro-reflector
258 may be placed near source 212 of the lamp. In this embodiment, nearly all
of the
light may be reflected back through source 212 to be collected by primary
reflector 250
and subsequently focused into the light pipe. In practice, the efficiency of
retro-reflector
258 may be reduced as much as 60% to 80% by reflectivity losses, Fresnel
reflection
losses, and distortion losses from the envelope of source 212.
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
[0050] In one embodiment, a retro-reflector 258 may be disposed on a side of
source
212 opposite shell reflector 240. In one embodiment, retro-reflector 258 may
be a
spherical retro-reflector. In one embodiment, retro-reflector 258 may be
integral to shell
reflector 240. In one embodiment, retro-reflector 258 may have a coating that
transmits
a pre-determined portion of electro-magnetic radiation spectrum. This might be
used to
discard unusable non-visible light before it is coupled into an imager. In
several
embodiments, pre-determined portion of electro-magnetic radiation spectrum may
be
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or a combination thereof. In an alternative embodiment, the coating
may reflect
infrared light, visible light, a pre-determined band of wavelengths of light,
a specific color
of light, or some combination thereof.
[0051] In one embodiment of the invention an image projection system 260 may
be
disposed proximate to output direction 206 to collect substantially all of
useful
polarization light 204. In several embodiments, image projection system 260
may be a
liquid crystal on silicon (LCOS) imager, a digital micromirror device (DMD)
chip, or a
transmissive liquid crystal display (LCD) panel.
[0052] In one embodiment of the invention a focusing lens 262 may be disposed
proximate to output direction 206, with image projection system 260 disposed
proximate
to an output side 264 of focusing lens 262. An image 266 illuminated by useful
polarization light 204 collected and focused at focusing lens 262 will be
released by the
projection system 260 to display the image 266.
[005] In one embodiment of the invention, a method of polarization recovery
may
include the steps of polarizing substantially light into light of useful
polarization 204 and
light of non-useful polarization 208, transmitting useful polarization light
204 in an output
direction 206, reflecting non-useful polarization light 208 in a first
orthogonal direction
210 substantially orthogonal to output direction 206, reflecting non-useful
polarization
light 208 in a~ second orthogonal direction 216 substantially orthogonal to
output
direction 206 and first orthogonal direction 210, and reflecting non-useful
polarization
light 208 in output direction 206.
[0054] While the invention has been described in detail above, the invention
is not
16
CA 02515141 2005-08-03
WO 2004/077102 PCT/US2004/004866
intended to be limited to the specific embodiments as described. It is evident
that those
skilled in the art may now make numerous uses and modifications of and
departures
from the specific embodiments described herein without departing from the
inventive
concepts.
17
