Light valve projection system with non imaging optics for illumination

Page 1 — bibliographic record

Page 2

Drawing sheet — no readable text.

Page 3

Drawing sheet — no readable text.

Page 4

Drawing sheet — no readable text.

Page 5

Drawing sheet — no readable text.

Page 6

output of the lamp. In order to improve the eficiency of

LIGHT WALVE PROJECTION SYSTEM WITH the system as a whole, which is the luminous flux at the NON MAGING OPTICS FOR LLUMNATON projection screen as a percentage of lumen output of the

BACKGROUND OF THE INVENTION

lamp, it will also be necessary to keep the maximum 5 deviation angle of light emitted by the illumination

The present invention relates to high efficiency col system to a minimum. For a large aperture F/2.0 pro lection optics and more particularly to a projection jection lens, this maximum deviation angle would be system with a combination of a light source and a reflec 15. Finally, since rectangular light valves in the form of tor having a low maximum deviation angle, with re LCDs will be used and it would be desirable to have a spect to collimated light rays, to ensure collection by 10 100% fill factor, the illumination system should have a the rest of the optics in the system. rectangular output aperture corresponding to the shape The possibility of using liquid crystal displays in pro of the LCD.

jection television is well accepted, and several system have been proposed. In an article on pages 375-377 of SUMMARY OF THE INVENTION the 1986 issue of Society of Information Display Digest, 15 According to the invention, the illumination subsys Seiko Epson Corporation discloses a projection system tem includes a first non-imaging reflector having a rect including an illumination subsystem, a modulating de angular output aperture and a central Z axis. The light vice in the path of light emitted from the illumination source is positioned inside the reflector along the cen subsystem, and a projection lens for projecting the image of the modulating device. More specifically, an 20 tral axis for illuminating the modulating device at least substantially uniformly.

illumination subsystem in the form of a halogen lamp The use of non-imaging optics to efficiently collect and a spherical reflector projects light through the con sunlight in solar energy applications is well known. See, denser lens to a pair of dichroic mirrors which split the for example, "The Optics of Non Imaging Concentra light into its red, blue, and green components. Each beam component impinges a respective modulating 25 tors', Welford and Winston, Academic Press, 1978. A device in the form of a liquid crystal display (LCD); a typical non-imaging concentrator is a trough-shaped dichroic prism combines the three monochromatic im reflector with an input aperture and a pair of opposed ages into a single color image which the projection lens sidewalls which converge toward a closed end. The projects onto a screen. The article states that the system sidewalls are configured to concentrate incident energy offers the advantages of compactness, low cost, and 30 onto an energy receiver such as a photo-voltaic cell or brightness. Despite the latter claim, though, the overall a fluid carrying pipe positioned inside the reflector. light collection efficiency of the system is still less than Such a concentrator is discussed in U.S. Pat. No. 1%. That is, for a tungstenhalide lamp producing 8800 4,002,499, which teaches a concentrator configured for lumens, less than 60 lumens reach the projection screen. optimal concentration of radiant energy on a cylindrical This low efficiency is largely due to the fact that only a 35 absorber such as a pipe. The sidewalls ae symmetric and small percentage of the light rays is collected and di meet at a cusp which contacts the pipe. U.S. Pat. No. rected toward the modulating device and the entrance 4,230,095, which is hereby incorporated by reference, pupil of the projection lens. discloses the ideal profile for a trough-shaped concen A further discussion of conventional illumination trator with a gap between the absorber and the reflec systems will be helpful. It is well known that a parabolic 40 tor. This is the situation for a pipe concentrically lo reflector with a point light source at the focal point of cated within a transparent glazing, and utilizes symmet the parabola can provide collimated light beams, and thus offers a potentially high collection efficiency. ric sidewalls which meet at a cusp which contacts the glazing.

However, lamps have finite source sizes which result in The solar concentrators offer the advantage that all large deviation angles at the output aperture of a para 45 light within a predetermined angle of acceptance is bolic reflector. Even if a very small lamp is used, light focussed onto the energy absorber. The wider the angle displacements from the focal point can result in addi of acceptance, tional deviation. Further, when the light valve and thus wise, the angle oftheacceptance larger the absorber must be. Like is more narrowly confined the reflector are small, it may be impossible to center for a smaller absorber, resulting in greater light concen the lamp at the focal point due to the finite envelope 50 tration. Concentrators with small acceptance angles size. The most efficient refractive lens condensing sys require solar tracking to achieve absorption over more tems are not as efficient (typically less than 43% effi hours in a day.

ciency) and require expensive multi-element lenses to limit deviation angles. In these refractive lens condens The invention recognizes that non-imaging reflec ing systems, the envelope size of the lamp is not as 55 tors, heretofore used primarily in solar energy concen important. trators, are ideal for a light projection system having a Further, when either a parabolic reflector or a refrac collector with an output aperture which corresponds to tive lens condensing system used with a rectangular the input aperture of a concentrator and vice versa. The light valve such as an LCD for TV pictures, "fill fac deviation angle of the light at the output aperture of the tor' further diminishes efficiency. For example, for an collector in the form of a non-imaging reflector thus has LCD having a 4 to 3 aspect ratio, only 61% of a circum a well defined limit, just as the input in a concentrator scribing circle representing the light beam is filled by has a well defined field of acceptance. The collector the LCD. For a-5.33 to 3 aspect ratio as proposed for may thus be designed in conjunction with a given lamp high definition television, the fill factor is only 54%. to minimize deviation angle, making it possible to maxi From the foregoing it is apparent that it would be 65 mize efficiency when used in a projection system. When desirable to have a more highly efficient illumination the modulating device is a predetermined size, and if the system, that is, a system with far greater lumen output at modulating device is immediately adjacent the output the output of the reflector as a percentage of lumen aperture of the collector, the dimensions of the modu

Page 7

lating device and the maximum deviation angle will FIG.1b is a cross-section in the YZ plane of FIG. 1a; determine the shape of the collector. FIG. 1c is a cross-section in the XZ plane of FIG. 1a, According to a preferred embodiment the light FIG. 2 is an elevation view of a cylindrical light source is substantially cylindrical and is centered in the Source;

XY plane. The source includes an arc with a length FIG. 3 illustrates the mathematics of the collector along the Y-axis and a radius along the X-axis, and profile of FIG. 1c, further includes a cylindrical envelope concentric to the FIG. 4 is a plan view of a three lamp system with a art. The cross-section of the reflector in the XY plane is dichroic prism;

at least substantially rectangular, and the cross-section FIG. 5 is a plan view of a three lamp system with two in YZ plane comprises a compound parabola. The 10 dichroic filters;

cross-section in the XZ plane is trough-shaped, with FIG. 6 is a plan view of a single lamp system with two symmetric sidewalls which meet at a cusp in dichroic filters for color separation and a dichroic prism contact with the envelope, and has an ideal contour combining the images; and determined with respect to a virtual arc shape defined FIG. 7 is a plan view of a single lamp system with by the actual arc and two lines tangent thereto which 15 dichroic filters for color separation and dichroic filters intersect at the cusp.

According to a further preferred embodiment, the for combining the images.

modulating device is rectangular and is immediately DETAILED DESCRIPTION OF THE adjacent the output aperture. PREFERRED EMBODIMENTS The display system is especially useful in a projection 20 FIG. 1a depicts a cylindrical light source 2 in a col color television system having three illumination sub lector in the form of a non-imaging reflector 10 having systems according to the preferred embodiment, where a rectangular output aperture 20. For convenience in the respective lamps are spectrally tuned to the red, describing green, and blue wavelengths and the modulating de coordinate the reflector it is superposed on a rectangular system with the Z-axis extending centrally vices are liquid crystal displays (LCDs). Such a system 25 through the reflector and the light source centered in must further comprise means for combining the images of the LCDs for projection by the lens. Such means theReferring XY plane.

to FIG. 2, the light source 2 is an arc lamp could comprise a dichroic prism or a pair of dichroic such as a xenon arc lamp or a metal halide arc lamp filters.

having a pair

The display system could also find use in a television length L and radius

projection system with only a single illumination sub centrically r therebetween. The arc 5 is con system according to the preferred embodiment, and a having a radius r2 in theavicinity located in cylindrical glass envelope 6 of the arc 5. Referring pair of dichroic filters for separating the light into three to FIGS. 1a, 1b, and 1c, the length of the arc extends channels. Three LCDs would be located in the paths of light in respective channels, and combining means such 35 along the Y-axis and a radius extends along the X-axis. FIG. 1b shows the profile of the top and bottom as additional filters or a prism would be used to combine sidewalls 12 of the reflector, which profile is preferably the images for projection.

In its broadest aspect the present invention relates to a compound parabola to minimize the deviation angle an illumination system used as the illumination subsys 0, where 0 is the maximum angle between the Z-axis tem in the display system so far described. That is, an and light rays exiting from output aperture 20. As de illumination system having a light source used with a scribed in companion U.S. application Ser. No. 137,049, non-imaging reflector having a rectangular output aper entitled "Light Valve Projection System with Im ture and a central Z axis. The non-imaging reflector this proved Illumination', which is filed concurrently with cooperates with the light source to illuminate the output application and is hereby incorporated by refer aperture, and thus the modulating device, at least sub 45 ence, a compound parabola is achieved by rotating a stantially uniformly. According to a preferred embodi parabolic shape 180' with its axis along line 25 about the ment the light source is cylindrical, and the reflector is reflector axis 26 (herein the Z-axis). This is the ideal as described for a cylindrical light source in a display reflector profile in the YZ plane and planes parallel system according to the invention. thereto when the arc 5 extends from one sidewall 12 to Other shapes of light sources and other forms of 50 the other. The ideal reflector profile parallel to the axis non-imaging reflectors than those described may be of a cylindrical light source is thus the same as the pro used to achieve substantially uniform illumination of the file for a planar source as described in the companion modulating device. Each form of non-imaging reflector case, wherein a light source outside the reflector is has its own characteristics. For example, the compound considered as a planar source at the input aperture of parabolic shape is especially suitable when uniform 55 the collector.

illumination of the output aperture is desired. This is the It can be shown that:

case when the modulating device is at the output aper ture. However, some non-imaging reflectors can pro y = -- Z cos0y siney + L(1 + sin8) -- vide substantially homogeneous illumination in more 2 cos’0, remote planes. A compound elliptical reflector, for 60 example, can illuminate a plane remote from the output aperture substantially homogeneously. Thus, it maybe N to snoozcoso, a . sing suitable where the modulating device is remote from 2A.

the output aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

65 Referring to FIG. 1c, the cross-section of the collec tor in the XZ plane and planes parallel thereto is

FIG. 1a is a perspective of a non-imaging collector bounded by vertical sidewalls 17. The sidewalls 17 are with a cylindrical light source; symmetric and meet at a cusp in contact with the lamp

Page 8

envelope 6. From a mathematical standpoint, each side X=ri sin 0-p cos 0 wall 17 has three segments which define the ideal con Z=ricos 0-p sin 0 tour with respect to a virtual arc shape defined by lines Based on the foregoing, it can be shown that for an tangent to the arc which intersect at the cusp. The first output aperture 50 mm by 67 mm and a source with an segment 15 of each sidewall is the involute of the virtual 5 arc length L of 6 mm, an arc radius of r1 of 0.5 mm and arc extending from the cusp to the line formed by a ray an envelope radius of 5 mm, 0=9.9 and 0=6.9. along line 28 as shown. The second or intermediate Note that the above mathematics are found in the segment 16 follows the rule that rays emitted tangent to prior art, e.g. Winston and Welford, supra, and are the virtual arc will have a maximum angle of 6 with the given here solely for convenience. Note also that other Z-axis. This segment extends to the intersection of line 10 non-imaging reflectors such as compound elliptical and 29 and the reflector. The segments 15 and 16 corre compound hyperbolic concentrators can be used to spond to the shape of a reflector for a glazed cylindrical achieve substantially uniform illumination of an output absorber as described in U.S. Pat. No. 4,230,095, incor aperture where limiting the deviation angle of light porated herein by reference. The third segment 17 is emitted. Further, some reflectors such as the compound rectilinear in cross-section (planar in the reflector) and 15 elliptical reflector are known to provide substantially parallels the opposed segment 17 of the other sidewall uniform illumination of a plane remote from the output 14. The segments 17 merely reflect light without in aperture. See, inter alia, Welford and Winston, Supra; creasing 6, and are necessary to extend the ideal reflec Eichhorn, "Designing generalized conic concentrators tor profile in the XZ plane to the output aperture. for conventional optical systems'. Applied Optics, Vol. Where a longer reflector is desired without increasing 20 24, No. 8; U.S. Pat. No. 3,957,031. Note also that other the size of output aperture 20 the sidewalls 12 may shaped sources could likewise be used to illuminate a likewise be extended in parallel, essentially forming a rectangular output aperture. With a point or spherical light pipe. source, for example, a cusp would be formed in both the FIG. 3 shows the section through the XZ plane in 25 XZ and the YZ planes.

greater detail, with the reflector profile defined in terms Thus it is not the geometry of non-imaging reflectors of p and 6, where p is the length of a line tangent to the but the recognition of their usefulness in conjunction light source measured from the source to the collector, with internal light sources and projection systems and 6 is the angle between the normal to the tangentline which constitutes the invention. The beam of light emit and the -Z-axis. Note that: ted by an illumination system comprising a source with 30 a non-imaging reflector yields sufficiently low deviation angles with respect to collimated light that a projection television system utilizing LCDs is feasible to manufac ture. Several examples of such projection systems fol low.

35 FIG. 4 shows three lamps 24, 30, and 36 which are spectrally tuned to the red, green, and blue portions of the visible spectrum. These are used in conjunction with respective non-imaging reflectors 26, 32, 38 to illumi nate the LCDs 28, 34, 40. The red, green, and blue

Angles 6B and 6s, measured with respect to the -Z- images on the LCDs are then combined by dichroic axis, defined the start and end of segment 15 and 0L prism 42 for projection by lens 44. FIG. 5 is another defines to the end of the segment 16. Similarly, pp and three lamp system wherein the images of LCDs 28 and ps are the length of the tangent lines which define the 34 are combined by dichroic filter 46 then further com beginning and end of involute segment 15. p is the 45 bined with the image of LCD 40 by dichroic filter 48 for length of the line which defines the end of segment 16. projection by lens 44.

Here the light ray represented by px would exit the FIG. 6 shows a source of white light 50 which is reflector were it not for the planar sections 17 (FIG.1c). divided into red, green, and blue channels by dichroic Thus the first or involute section 15 may be defined by filters 52, 55 and reflected via mirrors 53 toward respec tive LCDs 54, 56, 57 then combined by prism 60 for p =(0-4-0D)r for 6BC6C0s 50 projection by lens 61. Lenses 62 and 63 are used to image the output aperture of the non-imaging reflector where 6D is the overlap angle, i.e., the increment over to the LCDs. FIG. 7 again shows a white light source 6B which when added thereto would subtend an arc of 50 and dichroic filters 52, 55 to image the three chaan length pp. 6D is given by - nels onto respective LCDs but dichroic filters 58,59 are 55 used to combine the images for projection by lens 61.

The foregoing is exemplary and not intended to limit 2 the scope of the claims which follow.

1. A display system of the type comprising an illumi 60 nation subsystem including a light source, said subsys

The second or intermediate segment 16 is defined by tem being disposed within a spatial coordinate system having orthogonal X, Y, and Z axes, and comprising a first non-imaging reflector having a rectangular output

aperture disposed centrally about said Z axis, said light 65 Source being positioned inside said reflector along said

Z axis for illuminating said output aperture, said non

In x,z coordinates this becomes imaging reflector having sidewalls extending from said light source in the direction of said Z-axis, said sidewalls

Page 9

having a profile which is a regularly curved contour 14. A display system as in claim 9 wherein said means along at least a portion of the distance between said for combining said images comprises a pair of dichroic light source and said output aperture to provide light filters, one of said filters combining the images of re rays having a low angle of deviation exiting from said spective first and second modulating devices, the other output aperture, a first substantially rectangular modu said filter combining the combined images of the first lating device in the path of light emitted by said illumi and second modulating devices with the image of the nation subsystem, said reflector cooperating with said third modulating device for projection by said lens. light source to illuminate said modulating device sub 15. A display system as in claim 1 wherein said first stantially uniformly in a rectangular pattern; and a pro light source is a white light source, said system further jection lens for projecting the substantially rectangular 10 comprising image of said modulating device to form at least a por a pair of dichroic filters which separate the light from tion of a display. said source into three channels, 2. A display system as in claim 1 wherein said light second and third modulating devices, each of said source is substantially cylindrical and is centered in the modulating devices receiving one of said channels, XY plane, said light source having an arc with a length 15 and along the Y-axis and a radius along the X-axis, said means for combining the images of said modulating source further comprising a cylindrical envelope con devices for projection by said projection lens. centric to said arc. 16. A display system as in claim 15 wherein said 3. A display system as in claim 2, wherein the cross means for combining said images comprises a dichroic section of said reflector in the XY plane is at least sub 20 prism.

stantially rectangular. 17. A display system as in claim 15 wherein said 4. A display system as in claim 3 wherein a cross-sec means for combining said images comprises a second tion of said reflector in the YZ plane comprises a com pair of dichroic filters.

pound parabola. 18. An illumination system disposed within a spatial 5. A display system as in claim 3 wherein a cross-sec 25 coordinate system having orthogonal X, Y and Z axes tion of said reflector in the XZ plane is trough shaped and being of the type comprising a light source and a and comprises two symmetric sidewalls which meet at a collector having an output aperture, characterized in cusp in contact with the envelope, said cross-section in that said collector is a non-imaging reflector having a the XZ plane having an ideal contour determined with rectangular output aperture disposed along a central respect to a virtual arc shape defined by the actual arc 30 Z-axis, said light source being substantially cylindrical and two tangents thereto which intersect at the cusp. and centered in the XY plane, said light source having 6. A display system as in claim 5 wherein said side an arc with a length along the Y-axis and a radius along walls comprise parallel bounding surfaces adjacent said the X-axis, said source further comprising a cylindrical output aperture. envelope concentric to said arc and being positioned 7. A display system as in claim 1 wherein said modu 35 inside said reflector along said central axis for illuminat lating device is a liquid crystal display. ing said output aperture, said non-imaging reflector 8. A display system as in claim 1 wherein said first having sidewalls extending from said light source in the modulating device is a liquid crystal display immedi direction of said Z-axis, said sidewalls having a profile ately adjacent said output aperture. which is a regularly curved contour along at least a 9. A display system as in claim 1 further comprising portion of the distance between said light source and second and third non-imaging reflectors having re said output aperture to provide light rays having a low spective output apertures, angle of deviation exiting from said output aperture, second and third light sources in respective second said non-imaging reflector cooperating with said light and third concentrators, source to illuminate said output aperture substantially second and third modulating devices in the path of 45 uniformly in a substantially rectangular pattern. light emitted from the respective output apertures, 19. An illumination system as in claim 18 wherein the means for combining the images of said modulating cross-section of said reflector is the XY plane is at least devices for projection by said projection lens. substantially rectangular.

10. A display system as in claim 9 wherein said modu 20. An illumination system as in claim 18 wherein a lating devices are immediately adjacent respective out 50 cross-section of said reflector in the yz plane comprises put apertures. a compound parabola.

11. A display system as in claim 9 wherein the output 21. An illumination system as in claim 19 wherein a apertures of the first, second, and third reflectors are cross-section of said reflector in the XZ plane is trough rectangular, said modulating devices likewise being shaped and comprises two symmetric sidewalls which rectangular and of substantially the same shape as re 55 meet at a cusp in contact with the envelope, said cross spective output apertures. section in the XZ plane having an ideal contour deter 12. A display system as in claim 9 wherein said light mined with respect to a virtual arc shape defined by the sources are lamps which are respectively spectrally actual arc and two tangents thereto which intersect at tuned to the red, blue and green portions of the visible the cusp.

spectrum. 22. An illumination system as in claim 21 wherein said 13. A display system as in claim 9 wherein said means sidewalls comprise parallel bounding surfaces adjacent for combining said images comprises a dichroic prism said output aperture.

system. xk k