U.S. patent application number 10/444716 was filed with the patent office on 2003-11-27 for light recapture projection system.
Invention is credited to Huibers, Andrew G..
Application Number | 20030218726 10/444716 |
Document ID | / |
Family ID | 29553626 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030218726 |
Kind Code |
A1 |
Huibers, Andrew G. |
November 27, 2003 |
Light recapture projection system
Abstract
A projection system is disclosed comprising a light source, a
first reflector proximate the light source, a second reflector
proximate the light source, a light pipe, a color sequencing device
a spatial light modulator and a target. The color sequencing device
preferably directs three or more colors onto the spatial light
modulator at a time. Some light is reflected from the color
sequencing device back through the light pipe and is again
reflected at the reflector at the light source before returning to
the light pipe and color sequencing device. The brightness of the
projection system is thereby increased.
Inventors: |
Huibers, Andrew G.; (Palo
Alto, CA) |
Correspondence
Address: |
REFLECTIVITY, INC.
350 POTRERO AVENUE
SUNNYVALE
CA
94085
US
|
Family ID: |
29553626 |
Appl. No.: |
10/444716 |
Filed: |
May 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60383153 |
May 23, 2002 |
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Current U.S.
Class: |
353/84 ;
348/E9.027 |
Current CPC
Class: |
G03B 11/00 20130101;
H04N 9/315 20130101; G03B 21/14 20130101; G02B 26/008 20130101;
G03B 33/08 20130101; H04N 9/3114 20130101 |
Class at
Publication: |
353/84 |
International
Class: |
G03B 021/14 |
Claims
I claim:
1. A projection system, comprising: a point source of light and a
reflector proximate to the point source of light; a color
sequencer, wherein the point source of light, reflector and color
sequencer are arranged such that the light from the point source of
light is directed so as to be incident on the color sequencer, and
wherein at least 10% of the light that is reflected back from the
color sequencer impinges on the reflector proximate to the point
source of light and is reflected back so as to again be incident on
the color sequencer.
2. The projection system of claim 1, wherein at least 20% of the
light that is reflected back from the color sequencer impinges on
the reflector proximate to the point source of light and is
reflected back so as to again be incident on the color
sequencer.
3. The projection system of claim 2, wherein at least 30% of the
light that is reflected back from the color sequencer impinges on
the reflector proximate to the point source.
4. The projection system of claim 1, wherein the point source of
light is an arc lamp.
5. The projection system of claim 4, wherein the reflector is a
spherical reflector proximate the arc lamp.
6. The projection system of claim 5, wherein the spherical
reflector is a reflective coating on the glass bulb of the arc
lamp.
7. The projection system of claim 5, further comprising first
optics disposed between the arc lamp and the color sequencer,
wherein the first optics is positioned for focusing light from the
arc lamp and reflector proximate to the arc lamp onto the color
sequencer.
8. The projection system of claim 7, further comprising a light
pipe positioned between the first optics and the color
sequencer.
9. The projection system of claim 5, further comprising a light
valve disposed to receive multi colored light from the light
sequencer.
10. The projection system of claim 9, wherein the color sequencer
is capable of forming a spatial and temporal sequence of colors
that are incident on the light valve.
11. The projection system of claim 9, further comprising second
optics for focusing light from the color sequencer onto the light
valve.
12. The projection system of claim 9, further comprising third
optics for projection light from the light valve onto a target.
13. The projection system of claim 1, wherein the color sequencer
is a color wheel, drum, cone or color selective panel.
14. The projection system of claim 9, wherein the color sequencer
is a color wheel capable of passing multiple colors onto the light
valve at the same time.
15. The projection system of claim 1, wherein the light valve is a
micromirror array.
16. The projection system of claim 1, further comprising a second
reflector facing said reflector and disposed to direct light to the
color sequencer.
17. The projection system of claim 16, further comprising a light
pipe.
18. The projection system of claim 17, wherein said reflector is a
spherical reflector.
19. The projection system of claim 18, wherein the second reflector
is an elliptical reflector.
20. The projection system of claim 16, wherein light reflected from
the color sequencer is incident on both said reflector and said
second reflector so as to be again directed on the color
sequencer.
21. A projection system, comprising: an arc lamp; a spherical
reflector proximate to the arc lamp; a color sequencer; wherein the
arc lamp, spherical reflector and color sequencer are arranged in
the projection system such that the light from the arc lamp is
directed so as to be incident on the color sequencer, and wherein
at least a portion of light that is reflected back from the color
sequencer impinges on the spherical reflector so as to reflected
and again be incident on the color sequencer.
22. The projection system of claim 21, wherein at least 20% of the
light that is reflected back from the color sequencer impinges on
the spherical reflector proximate to the arc lamp and is reflected
back so as to again be incident on the color sequencer.
23. The projection system of claim 22, wherein at least 30% of the
light that is reflected back from the color sequencer impinges on
the spherical reflector proximate to the arc lamp.
24. The projection system of claim 21, wherein the arc lamp is a
UHP burner.
25. The projection system of claim 24, wherein the spherical
reflector is a reflective layer on the arc lamp.
26. The projection system of claim 25, wherein the spherical
reflector is a reflective coating on the glass bulb of the arc
lamp.
27. The projection system of claim 26, further comprising first
optics disposed between the arc lamp and the color sequencer,
wherein the first optics is positioned for focusing light from the
arc lamp and spherical reflector proximate to the arc lamp onto the
color sequencer.
28. The projection system of claim 27, further comprising a light
pipe positioned between the first optics and the color
sequencer.
29. The projection system of claim 25, further comprising a light
valve disposed to receive multi colored light from the light
sequencer.
30. The projection system of claim 29, wherein the color sequencer
is capable of forming a spatial and temporal sequence of colors
that are incident on the light valve.
31. The projection system of claim 29, further comprising second
optics for focusing light from the color sequencer onto the light
valve.
32. The projection system of claim 9, further comprising third
optics for projection light from the light valve onto a target.
33. The projection system of claim 21, wherein the color sequencer
is a color wheel, drum, cone or color selective panel.
34. The projection system of claim 29, wherein the color sequencer
is a color wheel capable of passing multiple colors onto the light
valve at the same time.
35. The projection system of claim 21, wherein the light valve is a
micromirror array.
36. The projection system of claim 21, further comprising a second
reflector facing said spherical reflector and disposed to direct
light to the color sequencer.
37. The projection system of claim 16, further comprising a light
pipe.
38. The projection system of claim 37, wherein said reflector is a
spherical mirror element disposed adjacent to the arc lamp.
39. The projection system of claim 38, wherein the second reflector
is an elliptical reflector.
40. The projection system of claim 36, wherein light reflected from
the color sequencer is incident on both said spherical reflector
and said second reflector so as to be again directed on the color
sequencer.
41. A projection system, comprising: a UHP lamp having a dichroic
coating; a color sequencer; wherein the UHP lamp with dichroic
coating and color sequencer are arranged in the projection system
such that the light from the UHP lamp is directed so as to be
incident on the color sequencer, and wherein at least a portion of
light that is reflected back from the color sequencer impinges on
the dichroic coating so as to reflected and again be incident on
the color sequencer.
42. The projection system of claim 41, wherein at least 10% of the
light that is reflected back from the color sequencer impinges on
the dichroic coating of the UHP lamp and is reflected back so as to
again be incident on the color sequencer.
43. The projection system of claim 42, wherein at least 30% of the
light that is reflected back from the color sequencer impinges on
the dichroic coating of the UHP lamp.
44. The projection system of claim 41, wherein the UHP lamp has an
arc gap of 1 mm or less.
45. The projection system of claim 44, wherein the dichroic coating
forms a spherical reflective surface.
46. The projection system of claim 45, wherein the spherical
reflector is a reflective coating on the glass bulb of the UHP
lamp.
47. The projection system of claim 46, further comprising first
optics disposed between the UHP lamp and the color sequencer,
wherein the first optics is positioned for focusing light from the
UHP lamp and spherical reflector proximate to the UHP lamp onto the
color sequencer.
48. The projection system of claim 47, further comprising a light
pipe positioned between the first optics and the color
sequencer.
49. The projection system of claim 45, further comprising a light
valve disposed to receive multi colored light from the light
sequencer.
50. The projection system of claim 49, wherein the color sequencer
is capable of forming a spatial and temporal sequence of colors
that are incident on the light valve.
51. The projection system of claim 49, further comprising second
optics for focusing light from the color sequencer onto the light
valve.
52. The projection system of claim 9, further comprising third
optics for projection light from the light valve onto a target.
53. The projection system of claim 41, wherein the color sequencer
is a color wheel, drum, cone or color selective panel.
54. The projection system of claim 49, wherein the color sequencer
is a color wheel capable of passing multiple colors onto the light
valve at the same time.
55. The projection system of claim 41, wherein the light valve is a
micromirror array.
56. The projection system of claim 41, further comprising a second
reflector facing said spherical reflector and disposed to direct
light to the color sequencer.
57. The projection system of claim 56, further comprising a light
pipe.
58. The projection system of claim 57, wherein said reflector is a
spherical mirror element disposed adjacent to the UHP lamp.
59. The projection system of claim 58, wherein the second reflector
is an elliptical reflector.
60. The projection system of claim 56, wherein light reflected from
the color sequencer is incident on both said spherical reflector
and said second reflector so as to be again directed on the color
sequencer.
61. A light collecting system comprising a color filter element;
and a concentrated light source illuminating a color filter
element; wherein a substantial portion of light that does not pass
through said color filter element is reflected back to said light
source, and subsequently is reflected back to said color filter
element and then passes through a different location of said color
filter element with a 10% or less change in the etendue of the
system.
62. The light collecting system of claim 61, wherein the light
source is a high temperature gas plasma.
63. An optical system comprising: a multi spectral light source; a
reflector at the light source for reflecting light from the light
source; a color sequencing device disposed to receive light from
the reflector and that spatially passes some colors and reflects
others back to the reflector, wherein at least 60% of the light
that is reflected from the color sequencing device is directed back
onto the reflector at the light source.
64. The optical system of claim 63, wherein a light tunnel is
provided between the light source and color sequencing device.
65. The optical system of claim 64, further comprising a second
reflector disposed to reflect light from the light source back
through the light source and to the color sequencing device via the
reflector.
66. The optical system of claim 65, wherein the second reflector
lowers the etendue of the optical system.
67. The optical system of claim 63, wherein the reflector is an
elliptical reflector.
68. The optical system of claim 65, wherein the second reflector is
spherical reflector.
69. The optical system of claim 68, wherein the second reflector is
a coating on the light source, the light source being an arc
lamp.
70. The optical system of claim 65, wherein the second reflector is
an elliptical reflector.
71. The optical system of claim 63, wherein the light source is an
arc lamp having an arc length of 1 mm or less.
72. The optical system of claim 63, wherein the reflector is a
spherical reflector.
73. The optical system of claim 65, further comprising a third
reflector that reflect light into the light tunnel that exits the
light tunnel but is not directed to said reflector.
74. The optical system of claim 65, wherein the light tunnel does
not have a restricted opening.
75. The optical system of claim 65, wherein light is recycled back
to the reflector while conserving etendue.
76. The optical system of claim 63, further comprising focusing
optics for focusing light from the color sequencing device on the
light valve.
77. The optical system of claim 76, further comprising projection
optics for projecting an image from the light valve onto a
target.
78. The optical system of claim 63, wherein at least 70% of the
light that is reflected from the color sequencing device is
directed back onto the reflector at the light source.
79. The optical system of claim 78, wherein at least 80% of the
light that is reflected from the color sequencing device is
directed back onto the reflector at the light source.
80. A projection system, comprising: a light source and a reflector
proximate to the light source; a color sequencer, wherein the light
source, reflector and color sequencer are arranged such that the
light from the light source is directed so as to be incident on the
color sequencer, and wherein at least 10% of the light that is
reflected back from the color sequencer is recycled via the light
source by being incident on the reflector proximate to the light
source and is reflected back so as to again be incident on the
color sequencer, and wherein the etendue of the projection system
is less than 20% different from a system without light being
recycled via the light source.
81. The projection system of claim 80, wherein the etendue is less
than 10% different from a system without light being recycled via
the light source.
82. A projection system, comprising: a light source and a reflector
proximate to the light source; a spatial light modulator; a color
sequencer that provides three or more different colors onto the
spatial light modulator at the same time; wherein the light source,
reflector and color sequencer are arranged such that the light from
the light source is directed so as to be incident on the color
sequencer, and wherein at least 60% of the light that is reflected
back from the color sequencer to be incident on the reflector
proximate to the light source and is reflected back so as to again
be incident on the color sequencer.
83. The projection system of claim 82, wherein at least 70% of the
light that is reflected back from the color sequencer to be
incident on the reflector proximate to the light source and is
reflected back so as to again be incident on the color
sequencer.
84. The projection system of claim 83, wherein at least 80% of the
light that is reflected back from the color sequencer to be
incident on the reflector proximate to the light source and is
reflected back so as to again be incident on the color
sequencer
85. A projection system, comprising: a light source and a reflector
proximate to the light source; a spatial light modulator; a color
sequencer that provides three or more different colors onto the
spatial light modulator at the same time; wherein the light source,
reflector and color sequencer are arranged such that the light from
the light source is directed so as to be incident on the color
sequencer and has a first etendue, and wherein light reflected back
from the color sequencer is incident on the reflector proximate to
the light source and is reflected back so as to again be incident
on the color sequencer with a second etendue less than 20%
different from the first etendue.
86. The projection system of claim 85, wherein the second etendue
less than 10% different from the first etendue.
Description
[0001] This application claims priority to U.S. provisional
application 60/383,153 to Huibers filed May 23, 2002, the subject
matter of which is incorporated herein by reference.
[0002] The present invention is in the field projection systems,
and in particular in the field of projection systems with
sequential color illumination of a spatial light modulator--that
forms a color image on a target. More particularly, the present
invention is directed to increasing light throughput in such
sequential color projection systems, and in particular utilizing
scrolling color and light recapture via recycling through the light
source.
SUMMARY OF THE INVENTION
[0003] In accordance with one embodiment of the invention a
projection system is disclosed, comprising: a point source of light
and a reflector proximate to the point source of light; a color
sequencer, wherein the point source of light, reflector and color
sequencer are arranged such that the light from the point source of
light is directed so as to be incident on the color sequencer, and
wherein at least 10% of the light that is reflected back from the
color sequencer impinges on the reflector proximate to the point
source of light and is reflected back so as to again be incident on
the color sequencer.
[0004] In accordance with another aspect of the invention, a
projection system is disclosed, comprising: an arc lamp; a
spherical reflector proximate to the arc lamp; a color sequencer;
wherein the arc lamp, spherical reflector and color sequencer are
arranged in the projection system such that the light from the arc
lamp is directed so as to be incident on the color sequencer, and
wherein at least a portion of light that is reflected back from the
color sequencer impinges on the spherical reflector so as to
reflected and again be incident on the color sequencer.
[0005] In accordance with a further aspect of the invention, a
projection system is disclosed, comprising: a UHP lamp having a
dichroic coating; a color sequencer; wherein the UHP lamp with
dichroic coating and color sequencer are arranged in the projection
system such that the light from the UHP lamp is directed so as to
be incident on the color sequencer, and wherein at least a portion
of light that is reflected back from the color sequencer impinges
on the dichroic coating so as to reflected and again be incident on
the color sequencer.
[0006] In accordance with a still further aspect of the invention,
a light collecting system is disclosed comprising a color filter
element; and a concentrated light source illuminating a color
filter element; wherein a substantial portion of light that does
not pass through said color filter element is reflected back to
said light source, and subsequently is reflected back to said color
filter element and then passes through a different location of said
color filter element.
[0007] In accordance with yet another aspect of the invention, an
optical system is disclosed comprising: a multi spectral light
source; a reflector at the light source for reflecting light from
the light source; a color sequencing device disposed to receive
light from the reflector and that spatially passes some colors and
reflects others back to the reflector, wherein at least 60% of the
light that is reflected from the color sequencing device is
directed back onto the reflector at the light source.
[0008] In accordance with yet another aspect of the invention, a
projection system is disclosed comprising: a light source and a
reflector proximate to the light source; a spatial light modulator;
a color sequencer that provides three or more different colors onto
the spatial light modulator at the same time; wherein the light
source, reflector and color sequencer are arranged such that the
light from the light source is directed so as to be incident on the
color sequencer and has a first etendue, and wherein light
reflected back from the color sequencer is incident on the
reflector proximate to the light source and is reflected back so as
to again be incident on the color sequencer with a second etendue
less than 20% different from the first etendue.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an illustration of a projection system in
accordance with one embodiment of the invention;
[0010] FIG. 2 is an illustration of a projection system in
accordance with a second embodiment of the invention;
[0011] FIG. 3 is an illustration of a projection system in
accordance with a third embodiment of the invention;
[0012] FIG. 4 is an illustration of a projection system in
accordance with a fourth embodiment of the invention;
[0013] FIG. 5 is another embodiment of the invention where a
spherical reflector is used; and
[0014] FIG. 6 is an illustration of the light pipe superimposed on
the color wheel.
DETAILED DESCRIPTION
[0015] The invention is described herein in relation to specific
embodiments. Nevertheless, persons familiar with the field will
appreciate that many variations exist in light of the embodiments
described herein.
[0016] Sequential color systems (either full frame, partial frame,
line or pixel based systems) are useful because the same physical
pixels can be used to achieve all colors. By using an array of such
pixels with a color sequencer that sequences light into colors, it
is possible to use a single pixel array and achieve a color image
on a target. In these systems a detector (e.g. the human eye)
serves to integrate the sequential light coming zfrom the display
pixel elements, provided that the colors are shown in sequence
faster than the response time of the detector. Thus, a sequence of
red, green and blue light onto a pixel array (or a sequence of a
spatial combination of red, green and blue light), when
sufficiently fast, will result in a full color image. Such a
projected image may be a still image (office or conference
presentation) or a moving image (home theater).
[0017] In some sequential systems, a color wheel having red, green
and blue segments is rotated through a white light beam resulting
in consecutive red, green and blue images on a light valve. The
light valve can be, for example, a liquid crystal light valve
(transmissive or reflective) or a MEMS (micro electromechanical
systems) type light valve (diffraction grating or micromirror
array). In some sequential color systems, such as the Philips
rotating prism based color system (Jeffrey Shimizu, Information
Display, "Philips Scrolling-Color LCoS Engine for HDTV Rear
Projection", November 2001, pp. 14-19), the three colors are
separated and then directed at a light valve (display panel) all at
the same time with different colors being incident on different
areas of the light valve. This has the advantage of using all of
the light energy available (all of the red, green or blue light is
potentially used all of the time). However, with the separate
beams, the required panel size becomes quite large. In other words,
the etendue (optical extent, which is the minimum area multiplied
by the solid angle) of the illumination beam in the light valve
illumination system is made bigger. Because of this, this type of
system uses a very large light valve (larger than 1.1 inch
diagonal), which increases both the light valve cost and the costs
of the associated illumination and projection optics.
[0018] In another system, sequential color recapture (such as set
forth in U.S. patent application Ser. Nos. 2002/0,005,914 to Tew,
2002/0,135,862 to Dewald, and 2001/0,008,470 to Dewald, the subject
matter of each being incorporated herein by reference), a light
pipe (also referred to as a light tunnel) has a mirrored internal
surface with an aperture at one end (where light from the light
source enters) and a color wheel having spiral bands of color
disposed proximate to the other end. When white light passes
through the light pipe and is incident on a particular band of the
spiral color wheel (e.g. a red band), a color is transmitted (e.g.
red light) with the remainder of the light (e.g. green and blue)
being reflected back into the light pipe. Such reflected light is
incident on the reflective surface (around the above mentioned
aperture) at the other end of the light pipe and is again incident
on the color wheel, with some of the green light that had been
reflected now passing through a green band, some of the blue light
now passing through a blue band. With multiple instantaneous
reflections, much of the light that does not pass through the color
wheel the first time will pass through adjacent bands after being
reflected back into the light pipe. Though more light passes
through the color wheel in such a system, because the exit of the
light pipe is significantly larger than the entrance (due to the
aperture at the light pipe entrance), the etendue is increased, yet
the light recycling is incomplete, offering a compromised
advantage.
[0019] Thus there is a need for a system that can recycle color
without increasing beam size (and illumination light bundle
etendue), and without significantly increasing system
complexity.
[0020] This invention accomplishes color recycling by recycling
light that is reflected from a changing color filter, such as a
color wheel, drum, cone, or color selective panel (such as a
Colorlink device), and directing back through the arc.
[0021] A first embodiment of the invention is illustrated in FIG.
1. Illustrated are a light source 1, such as an arc lamp, a first
reflector 3, a second reflector 5, and a light pipe or tunnel 7.
Forward light (light that is emitted by the arc lamp 1 in the
direction going to the right in the figure) is reflected by the
first reflector 3 back to the second reflector 5 via the arc lamp,
and on to light pipe 7. First reflector 3 can be a spherical
reflector as shown, or an elliptical or other reflector. The second
reflector 5 can be an elliptical reflector as shown, or other
suitable reflector (including a spherical or other reflector).
Backward light from the light source 1 (light directed from the arc
lamp to the left in the drawing) is focused first on the second
reflector 2 and then enters light pipe 7. The light that is
reflected by reflector 3 back through the arc lamp has been
observed to be about 70% efficient because some parts of the arc
plasma re-absorb the light. Reflector 3 can be a reflector disposed
adjacent the arc lamp, or it can be a reflective coating coated
directly on the side of the lamp.
[0022] After light is reflected from the second reflector 5, it
enters the light pipe 7, passes therethrough and is incident on the
color selective element 10--in this case a color wheel. The color
selective element could be one of many types of optical elements
that divide white light from the light source into individual color
bands--either a moving part (cone, wheel, drum) or some other type
of color selective device, for example one based on liquid crystals
or MEMS. As mentioned above with respect to prior art color wheels,
not all light will pass through the color selective element--some
will be reflected back into the light pipe. In the present
invention, this reflected light is reflected back through light
pipe 7, is reflected from second reflector 5, through light source
1 and is finally incident on first reflector 3. Once incident on
first reflector 3, the light is effectively "recycled" by being
passed once again though the light source 1, via the second
reflector 5 back into light pipe 7. This "recycled" light is once
again incident on the color selective element with more passing
through the second time (and third and fourth, etc.).
[0023] Light which passes the color selective element 10 is
incident on the light valve 12. Light valve 12 is an array of
pixels that are selectively actuated in analog or digital mode to
direct light to target 14 (e.g. a viewing screen). Light valve 12
can be an array of for example liquid crystal cells or
micromirrors. Also shown in FIG. 1 are condensing optics 16 (for
focusing the light toward the light valve 12, projection optics 17,
and TIR (total internal reflection) prisms 18. These optical
elements can of course be of various designs (e.g. omit the TIR
prisms 18, multiple lenses for either optics 16 or optics 17,
etc.). As will be seen better in FIG. 6, multiple colors from the
color sequencing element are incident on the light valve at the
same time but in different areas of the light valve. As such, the
filter wheel image is focused onto the light valve so that there
are sharp transitions between colors, and the illumination colors
at the valve correspond to the colors at the color filter
element.
[0024] An alternative approach is shown in FIG. 2. As can be seen
in this figure, an additional lens (or group of lenses) 20 is used
to image the end of the light pipe onto the color wheel/filter. One
practical issue with the color wheel is that it is difficult to get
it close to the end of the light pipe. If it is spaced away from
the light pipe, then some light will leak out at the edges. That
is, some light which exit the light pipe at an angle and is located
at the very edge of the light pipe (in FIG. 1) could reflect from
the color wheel and not re-enter the light pipe. The extra lens of
FIG. 2 allows the image of the light pipe exit exactly focus at the
color wheel, so less light is lost. Also illustrated in FIG. 2 is a
third reflector 22 at the light source. This third reflector
reflects light coming back from light pipe 7 that does not pass
around the light source toward reflector 5, but is incident on a
back side of the light source. This third reflector, whether part
of the light source or a separate reflective element, can be curved
or planar and aids in the light recycling and thus overall
brightness of the display.
[0025] FIGS. 3 and 4 are similar to FIGS. 1 and 2, respectively,
but are embodiments where the first reflector 3 from FIGS. 1 and 2
is absent. FIG. 5 shows an embodiment in which a spherical lens is
used to couple light to the light pipe. Reflector 5 in this
embodiment is a spherical reflector.
[0026] Etendue (the extent of the beam) is not increased in the
approach of this invention. Light that is not selected by a color
filter element is sent back to the arc lamp which is configured so
that the light will be reflected back into the illumination system.
In an embodiment of the invention, any change in etendue is less
than 20%; preferably less than 10%. This enables the valve size to
remain small.
[0027] FIG. 6 shows what one type of color sequencing device--in
this case a color wheel with thin "pie wedges" of different colors
(e.g. red, green and blue--or red, green, blue and white or another
less saturated light boost color) that could be placed at the end
of the light pipe, a color wheel, will look like. A color wheel
with spiral color bands could be used as mentioned above, or
another design--though whatever design is selected more than one
color (preferably three or more colors) should "overlap" the end of
the light pipe at a time so as to take advantage of the color
recycling (or at least allow more than one color--preferably three
or more colors to be incident on the light valve at any one time).
In. FIG. 6, approximately 3 spokes, separating three colors, are
shown superimposed on the light valve exit.
[0028] FIGS. 7a and 7b are illustrations of the end of the light
pipe that faces towards the light source. FIG. 7a is an
illustration of a prior art light pipe that comprises a closed end
except for an aperture through which a beam of light from the light
source enters into the light pipe. Light pipes with both types of
openings facing the light source are known--however, till now, the
opening of FIG. 7a was used with a color recycling type color
sequencer (one that allows for multiple colors to be incident on a
light valve at any one time), whereas the opening of FIG. 7b has
been always used with a light valve where, except at color
transitions, a single color is directed at the light pipe at any
one time--and never three colors at any one time. The light pipe of
FIG. 7b is used in the embodiments of the present invention. Though
the opening need not be fully open as in FIG. 7b, no more than 50%
of the area of the opening should be covered--preferably no more
than 25%, and more preferably no covering at all, such as
illustrated in this figure. By removing the restricted opening at
the end of the light pipe, almost all of the light reflected from
the color sequencing device back into the light pipe--passes out of
the light pipe back to the light source. It is preferred that, if
the opening is partly restricted, the restriction is not great--and
at least 60% (preferably at least 70%, at least 80% or 90% or more)
of the light that is reflected off of the color sequencing device
will pass out of the light pipe to the light source though a lower
percentage of light can reach the light source (10% or more, 20% or
more, or 30% or more), the higher percentages are preferred. Also,
the light pipe can have different entrance and exit shapes with a
preferably smooth transition between the differently shaped ends of
the pipe.
[0029] In the present invention, a highly reflective reflector can
be positioned very close to the arc lamp burner. In one example of
the invention, the light source is a UHP lamp with a reflective
coating directly on the lamp. The reflective coating can be a
dichroic coating--preferably one that reflects visible light but
transmits light of other wavelengths. The coating or separate
reflector 3 allows for the reflector 5 to focus light inside an
angle of 20 degrees or less, or even 16 degrees or less. The arc
length can be 1.3 mm or less, or even 1.0 mm or less. If a very
short arc length is desired, an around 0.7 mm arc length can be
used. A short arc length, combined with the reflector (or
reflective coating) that redirects light back through the lamp, and
combined with the color sequencing device as disclosed herein,
results in a bright light beam incident on the light valve, which,
due to the lower etendue of the system, allows for a small light
valve thus increasing the brightness of the projected image. The
light valve can have a diameter of around 0.5 cm or less, or even
around 0.4 cm or less, depending upon the optical system components
selected.
[0030] There are many variations possible.
[0031] The light pipe or illumination system can be anamorphic.
[0032] This system can be used for either MEMS or LC devices, and
in either transmissive or reflective mode.
[0033] The arc lamp could be rotated so that the arc lamp axis is
perpendicular to the illumination optical system axis.
[0034] A parabolic arc lamp reflector could be used.
[0035] An illumination configuration similar to that used in liquid
crystal display projection systems--with two sets of fly's eye
lenses and/or polarization conversion being used (not illustrated).
In such an embodiment, there is a color selective filter element
that is imaged onto the valve, and which reflects unwanted light
back into an arc lamp with high retro-reflection capability.
[0036] More than three colors (Red, Green, Blue) could be used to
increase the color gamut (red, green, blue, magenta and yellow, for
example).
[0037] Because the light coming back out the light pipe is spread
out, it will more efficiently make its way through and back out of
the arc, since it will not focus on the "hot spots".
[0038] The illumination system does not need to use a TIR prism. An
approach using a field lens in front of the light valve, or light
that converges onto the light valve, can also be used. Many known
projection system configurations could be used with the present
invention.
[0039] The invention disclosed herein is presented in preferred
embodiments of projection system design to exemplify the inventive
features, but the scope of the invention is much broader than
illustrated with these preferred embodiments. The scope of the
invention is intended to be broadly interpreted to cover the
general field of projector design.
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