a2) United States Patent
`US 6,195,136 BL
`(10) Patent No.:
`Feb. 27, 2001
`(45) Date of Patent:
`Handschy etal.
`
`US006195136B1
`
`(54) OPTICS ARRANGEMENTINCLUDING
`LIGHT SOURCE ARRANGEMENTFOR AN
`ACTIVE MATRIX LIQUID CRYSTAL IMAGE
`GENERATOR
`
`(75)
`
`Inventors: Mark A. Handschy, Boulder; Michael
`R. Meadows, Nederland; Holden
`Chase, Lafayette, all of CO (US)
`
`(73) Assignee: Displaytech, Inc, Longmont, CO (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/422,815
`
`(22)
`
`Filed:
`
`Oct. 21, 1999
`
`Related U.S. Application Data
`
`(60) Continuation of application No. 09/046,898, filed on Mar.
`24, 1998, now Pat. No. 6,038,005, which is a division of
`application No. 08/362,234,filed on Dec. 22, 1994, now Pat.
`No. 5,808,800,
`
`Tint. C17 accccccscssessssssssssssnsssetnsssonnsseee G02F1/1335
`(SL)
`(52) US. C0.
`scessessssssssssssesssseenseee 349/5; 349/9; 359/631;
`359/629; 353/81
`(58) Field of Search .........c.c000 349/9, 5, 11; 359/631,
`359/639, 363, 629, 630, 487, 495, 638,
`640, 534; 353/33, 81, 30
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`10/1991 Hornbeck .
`5,061,049
`1/1992 Hornbeck .
`5,083,857
`3/1992 Hornbeck .
`5,096,279
`9/1992 Nelson viccsiciiaies 346/160
`5,151,718"
`1/1994 Hornbeck .
`5,280,277
`2/1995 Minoura et al... 353/20
`5,387,953 *
`11/1995 Lebbyet al. .
`5,467,215
`1/1996 Lebbyetal. .
`5,485,318
`4/1996 Nelson.
`
`....... 347/130
`5,504,514 *
`
` 5,539,554 * 7/1996 Lebby et al. w 359/83
`
`5,568,315 * 10/1996 SHUMAN srcccceceecesesersneess 359/487
`
`OTHER PUBLICATIONS
`
`Juris Upatnieks; “Edge—Illuminated Holograms”; Mar. LO,
`1992; Optics 31, (8) 1048.
`C. Carre and 8. Habraken and St. Roose; “Computer—Or-
`iginated Polarizing Holographic Optical Element Recorded
`in Photpolymerizable Layers”; May 1, 1993; Opt. Lett. 18,
`(9) 738.
`L.D. Dickson and R.D. Rallison and B.H. Yung; “Holo-
`graphic Polarization—Separation Elements”; Aug. 10, 1994;
`Apphed Optics 33, (23) 5378-5385.
`
`Primary Examiner—kenneth Parker
`(74) Attorney, Agent, or Firm—Steve Shear; Jay R Beyer
`
`(57)
`
`ABSTRACT
`
`is disclosed. The
`A system for producing modulated light
`system comprisesa spatial light modulator including a light
`modulating medium switchable between different states so
`as to act on light
`in ways which form overall patterns of
`modulated light. The system also includes an arrangement
`for switching the modulating medium between the different
`states In a controlled way and anillumination arrangement
`for producing a source oflight. The system further includes
`an optics arrangement for directing light from the source of
`light into the spatial light modulator and for directing light
`from the spatial light modulator through a predetermined
`source imaging area. The optics arrangement cooperates
`with the illumination arrangement and the spatial
`light
`modulator soas to produce a real image of the source oflight
`within the source imaging area such that an individualis able
`to view a virtual image of the overall patterns of modulated
`light from the source imaging area. A variety of novel optics
`arrangements are disclosed including specific combinations
`ofdifferent light sources, diffusing plates, polarizers, beam
`splitters, analyzers, lenses, mirrors, and holographic optical
`elements which allowthe overall optical arrangement to be
`miniaturized to the same degree and in coordination with the
`spatial light modulator. The different light sources include
`using a plurality of light sources, such as LEDs, to form an
`array of light sources, each ofthe light sources providing
`light to a corresponding portion of the spatial light modu-
`lator.
`
`(List continued on next page.)
`
`8 Claims, 10 Drawing Sheets
`
`ae
`+ 3
`‘
`‘
`.
`
`,
`;
`
`’
`
`’
`
`*
`‘ a94
`‘
`‘
`‘
`*
`36
`
`4
`'
`
`é
`
`‘
`
`'
`
`a
`
`
`
`‘
`
`'
`
`’
`
`=
`
`a
`
`7
`
`,
`
`*
`
`ss
`fo.
`*
`¥
`*
`
`%
`
`%*
`x
`*
`*
`
`‘84
`
`36
`
`AG
`
`VWGOoA EX1059
`VWGOAv. Spero
`IPR2023-00335
`
`VWGoA EX1059
`VWGoA v. Spero
`IPR2023-00335
`
`

`

`US 6,195,136 B1
`Page 2
`
`
`.
`6/1998 Kintz et al.
`5,771,124
`U.S. PATENT DOCUMENTS
`
`
`
`
`a FU ES=seewcreawewarasaanccwnee— poe n
`
`
`$580,156 * 12/1906 Swruikietal son/184 5,853,240 * 12/1998 Tanaka et al. sssccssssssossssosues 353/20
`
`
`
`
`
`sO,KmOwles.* 9D sccscscssssereuesesernec 359/63
`5,703,664
`12/1997 Jachimowiczet al.
`COURS
`“1eoNe Kanwles
`SHG
`
`sssssscisncsnctisone 359/631
`5,754,344 *
`$/1998 Fujiyarta.
`5,764,329
`6/1998 Chen etal. .
`
`* cited by examiner
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 1 of 10
`
`US 6,195,136 B1
`
`
`A
`
`32
`
`Figure 2A
`
`

`

`Sheet 2 of 10
`
`US 6,195,136 B1
`
`U.S. Patent
`
`Feb. 27, 2001
`
`aCU2S>LL
`
`

`

`U.S. Patent
`
`US 6,195,136 B1
`
`Feb. 27, 2001
`
`Sheet 3 of 10
`
`Figure 4
`
`geeeeoeoeesoeee
` Figure 5B
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 4 of 10
`
`US 6,195,136 B1
`
`Aw) 52
`
`Keathssebis,Gs
`
`mca
`
`eROY
`
`Figure 7A
`
`Figure 7B
`
`
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 5 of 10
`
`US 6,195,136 BI
`
`Figure 8
`* .
`
`e*-
`
`34
`
`eh
`
`*-
`
`"
`
`-*
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 6 of 10
`
`US 6,195,136 B1
`
`36
`
`100 )==—=it
` 5a®—a>LL
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 7 of 10
`
`US 6,195,136 BI
`
`2
`
`,
`
`ry
`
`‘ x
`‘,
`
`‘
`
`.
`38
`
`Fee
`Fd
`
`%
`*
`
`é
`
`e
`’
`
`s
`‘
`
`104
`
`36 Figure 12
`
`Figure 13
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 8 of 10
`
`US 6,195,136 B1
`
`
`Figure 14A
`
`Figure 14B
`
`Figure 15A
`
`Figure 15B
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 9 of 10
`
`US 6,195,136 BI
`
`Te hy
`
`
`Figure 17
`
`

`

`U.S. Patent
`
`Feb. 27, 2001
`
`Sheet 10of 10
`
`US 6,195,136 B1
`
`
`
`tes go
`164
`164
`
`166
`
`168
`
`1
`Figure 18B
`
`Figure 18C
`
`154
`
`A
`
`6s
`
`,
`t
`
`kL
`
`ia YS
`
`748
`
`178
`
`Figure 19
`
`

`

`US 6,195,136 B1
`
`1
`OPTICS ARRANGEMENT INCLUDING
`LIGHT SOURCE ARRANGEMENTFOR AN
`ACTIVE MATRIX LIQUID CRYSTAL IMAGE
`GENERATOR
`
`This application is a continuation of Ser. No, 09/046,898
`filed Mar, 24, 1998, U.S, Pat. No. 6,038,005 which is a
`Division of Ser. No. 08/362,234 filed Dec. 22, 1994, US.
`Pal. No. 5,808,800.
`
`GOVERNMENTCONTRACT CLAUSE
`
`This invention was made with Government support under
`contracts NAS9-18858 and NAS9-19102 awarded by the
`National Aeronautics and Space Administration and con-
`tracts DAA-HO01-92-C-R275 and DAA-H01-94-C-R154
`
`15
`
`awarded by the Advanced Research Projects Agency. The
`Government has certain rights in this invention.
`BACKGROUND OF THE INVENTION
`
`The present invention relates generally to image gener-
`ating systems, and more particularly to optics arrangements
`and light source arrangements especially suitable for min-
`lalurized image generating systems such as the miniaturized
`image generator disclosed in copending U.S. patent appli-
`cation Ser. No. 08/362,665, now U.S. Pat. No. 5,748,164
`Attorney Docket Number DIS1P003 entitled ACTIVE
`MATRIX LIQUID CRYSTAL IMAGE GENERATOR and
`copending U.S. patent application Ser. No. 08/361,775, now
`abandoned, Attorney Docket Number DIS1P006 entitled DC
`FIELD-BALANCING TECHNIQUE FOR AN ACTIVE
`MATRIX LIQUID CRYSTAL IMAGE GENERATORfiled
`cotemperaneously herewith, which applications are incor-
`porated herein by reference.
`One of the ongoing challenges facing the manufacture of
`miniature image generating systemsis providing smaller and
`smaller systems. Miniature image generating systems which
`are small enough to be mounted onto a helmet or small
`enough to be supported by a pair of eyeglasses will find a
`wide variety of uses if they can provide adequate resolution
`and brightness in a small, low-power package at a low cost.
`Conventional
`technologies such as CRTs are difficult
`to
`miniaturize and therefore do not hold much promise in this
`field. Alternatively, new systems based on VLSI integrated
`circuits are currently being developed which provide much
`smaller spatial light modulators for use in a miniaturized
`image generaling systems. However, one of the problems in
`this field is providing optics and illuminating arrangements
`which may be sealed down in coordination with the minia-
`turized spatial light modulator in order to provide an overall
`image generating system which is practical and compact
`enough to be mounted onto a helmet or supported by a pair
`of glasses. Another problem in this field is providing an
`illuminating arrangement which requires aslittle power as
`possible in order to make the overall system more portable.
`Referring to FIG. 1, a prior art miniature image generator
`system generally designated by reference numeral 10 will be
`described. System LO includes a transmissive spatial light
`modulator 12 which modulates light from a light source 14
`positioned immediately adjacent to spatial light modulator
`12 by selectively changing the polarization of light passing
`through the spatial light modulator. A polarizer L6 is posi-
`tioned between light source 14 and spatial light modulator
`12 which allows light of one polarization from light source
`14 to enter spatial light modulator 12. An analyzer 18 is
`positioned adjacent to the opposite side of spatial light 12
`which allows light of a particular polarization to pass
`
`25
`
`30
`
`35
`
`40
`
`45
`
`$0
`
`55
`
`60
`
`65
`
`2
`through analyzer 18. An eyepiece lens 20 having a focal
`length F1 is positioned approximately one focal length F1
`from spatial light modulator 12 such that a viewer may see
`a virtual image of the pattern of modulated light formed by
`spatial light modulator 12 when the viewer’s eye is posi-
`tioned in an appropriate location. As shown in FIG, 1, this
`arrangement results in a viewing region indicated by refer-
`ence numeral 22 from which a viewer may view the entire
`virtual image of the pattern of modulated light produced by
`the spatial light modulator display.
`In the above described arrangement, since light source 14
`is positioned adjacent
`to spatial light modulator 12, light
`source 14 must have a light emitting surface with essentially
`the same surface area as spatial light modulator 12. Also, in
`order for the optics to perform properly, the light source is
`a diffuse light source. However, these requirements causes
`two major problems. First, a large diffuse light source as
`described above is substantially more expensive than other
`types oflight sources. Second, because light source 14 is
`diffuse, a large percentage of the light generated by light
`source 14, indicated by lines 24,is directed to areas which
`are not within viewing region 22 including areas in which
`the light does not pass through eyepiece lens 20. This wastes
`a large percentage of the light produced by light source 14
`and requires much more light to be produced than would be
`necessary if substantially all of the available light were
`directed into viewing region 22. This wastage of light
`significantly increases the power requirements of the overall
`system. As will be seen hereinafter, the present invention
`provides a variety of novel optics arrangements including
`novel
`light source arrangements which, when combined
`with miniaturized spatial light modulators, are capable of
`providing low power, compact miniaturized image generat-
`ing systems that may be used to produce a direct view
`miniature display.
`
`SUMMARY OF THE INVENTION
`
`As will be described in more detail hereinafter, a system
`for producing modulated light
`is disclosed. The system
`comprises a spatial light modulator including a light modu-
`lating medium switchable between different states so as to
`act on light in ways which form overall patterns of modu-
`lated light. The system also includes means for switching the
`modulating medium between the different states in a con-
`trolled way and illumination means for producing a source
`of light. The system further
`includes optics means for
`directing light from the source oflight into the spatial light
`modulator and for directing light from the spatial
`light
`modulator through a predetermined source imaging area.
`The optics means cooperates with the illumination means
`and the spatial light modulatorso as to produce a real image
`of the source of light within the source imaging area such
`that an individual is able to view a virtual image of the
`overall patterns of modulated light from the source imaging
`area.
`
`In one preferred embodiment ofthe present invention the
`spatial
`light modulator
`is a reflective type spatial
`light
`modulator and the optics means cooperate with said illumi-
`nation meansandsaid spatial light modulator such that some
`of the light passing from the illumination means to the
`spatial
`light modulator overlaps with some of the light
`passing from the spatial
`light modulator to the source
`imaging area.
`In another embodiment of the present invention, the light
`source is provided by means of an array of light emitting
`sources such as LEDs(light emitting diodes) spaced apart by
`
`

`

`US 6,195,136 B1
`
`15
`
`20
`
`25
`
`30
`
`40
`
`3
`a predetermined distance. These spaced apart light sources,
`in combination with the optical components, produce an
`equal plurality of images at the source imaging area which
`are spaced apart
`from one another by a predetermined
`distance. The optical components of this embodiment may
`include a single collimating lens disposed optically between
`the light sources and the spatial
`light modulator, or
`alternatively, may include a plurality of collimating lenses,
`each of which is disposed optically between an associate
`done of the light sources and the spatial light modulator so
`as to direct
`light
`from its associated light source to a
`corresponding portion of the spatial light modulator,
`In the case of a plurality of collimating lenses, the optical
`components also include a single eyepiece lens which is
`disposed optically between the spatial light modulator and
`the source imaging area and which defines a much greater
`focal length than the focal length of each ofthe individual
`collimating lenses. Also, the light sources may be disposed
`optically approximately a focal
`length away from their
`associated collimating lens, suchthatthe plurality of images
`produced at the source imaging area are substantially larger
`than their respective light sources. Alternatively,
`in this
`arrangement, the light sources are disposedoptically slightly
`closer to their associated collimating lens than one focal
`length so as to cause each collimating lens to direct light
`from its associatedlight source tothe spatial light modulator
`in a slightly diverging manner. The spatial
`relationship
`between the light sources and the divergence of the light
`from the collimating lenses are such that
`the plurality of
`images produced at the source imaging area overlap one
`another in a predetermined way.
`The plurality of light sources may be providedin a variety
`of arrangements.
`In a first arrangement, the arrangement
`includes a single dielectric substrate having on one surface
`a pattern of electrically conductive leads adapted for con- ;
`nection to a source of electric power. A plurality of LEDs are
`individually attached to the substrate and electrically con-
`nected with the pattern of leads. An equal plurality of
`individual collimating lenses are attached to the substrate
`and disposedoptically over associated ones of the LEDs.In
`a second arrangement, the arrangement includes a single
`LED wafer having on one surface a pattern of electrically
`conductive leads adapted for connection to a source of
`electric power. The pattern ofleads divides the wafer into the
`plurality of LEDs. An equal plurality of individual collimat-
`ing lenses may be attached to the wafer and disposed
`optically over associated ones of the LEDs. Alternatively,
`the arrangement includes a single substrate which is attached
`to the LED wafer and which is integrally formed to define
`an associated collimating lens for each of the LEDs. In a
`third arrangement which may be any combination ofthefirst
`and second arrangement,
`the plurality of LEDs include
`LEDsof different colors thereby providing a color version of
`the miniaturized assembly.
`the light
`invention,
`In a color version of the present
`sources include different color light sources, such as LEDs,
`which are spaced apart a predetermined distance d and
`which emit light outwardly at a maximum angle A. A light
`diffusing plate is spaced from the light sourcesa distance L.
`Thus, the positional relationship between the light sources
`and the diffusing plate is such that Lis at least approximately
`equal to d/A. In this way, as will be seen, it is possible to
`obtain proper registration ofthe different color images even
`though the light sources are spaced apart from one another.
`Aswill be described in more detail hereinafter, a variety
`of specific arrangements for the optical components of the
`system for producing modulated light are also disclosed.
`
`$0
`
`55
`
`60
`
`65
`
`4
`These arrangements include specific combinations of a
`variety of light sources, polarizers, beam splitters, analyzers,
`lenses, mirrors, and holographic optical elements arranged
`to direct the light from the light source into the spatial light
`modulator and from the spatial light modulator to the source
`imaging area.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features of the present invention may best be under-
`stood by reference to the following description of the
`presently preferred embodiments together with the accom-
`panying drawings in which:
`FIG, 1 is a diagrammatic side view of a prior art minia-
`turized image generating system;
`FIG, 2A is a diagrammatic side view of a miniature image
`generating system designed in accordance with the present
`invention having a light source positioned away from the
`spatial light modulator and including optical elements which
`form a real imageof the light source al a source imaging area
`and allow a viewer to view a virtual image of a pattern of
`modulated light formed by a spatial light modulator when
`the pupil of the viewer's eye is positioned in the source
`imaging area;
`FIG. 2B is a diagrammatic side view ofa basic reflective
`type miniaturized image generating system designed in
`accordance with the present invention whichillustrates all of
`the elements of a particular optical system for the miniatur-
`ized image generator including a light source, a spatial light
`modulator, an eyepiece, a source imaging area, and a polar-
`izing beam splitting cube for directing one polarization of
`light from the light source into the spatial light modulator
`and for directing the opposite polarization of light from the
`spatial
`light modulator to the eyepiece which directs the
`light to the source imaging area forming a real image of the
`light source within the source imaging area;
`FIG. 3 is a diagrammatic side view of one embodiment of
`a miniaturized image generating system designed in accor-
`dance with the present invention including a plurality of
`light sources which,
`in combination with the other optics
`components, produce a corresponding real
`image of the
`plurality of light sources at the source imaging area;
`FIG, 4 is a diagrammatic side view of second embodiment
`of a miniaturized image generating system designed in
`accordance with the present invention including a plurality
`oflight sources and a plurality of collimating lenses each of
`which is associated with a corresponding light source,
`which,
`in combination with the other optics components,
`produce a corresponding real imageof the plurality of light
`sources at the source imaging area;
`FIGS. 5A and 3B are diagrammatic side viewsillustrating
`the optical relationship between the collimating lenses and
`the eyepiece lenses of FIG. 2 and FIG. 4;
`FIG, 6 is a diagrammaticside view of the image generator
`of FIG. 4 in which the light sources are positioned slightly
`closer to their associated collimating lens than one focal
`length so as to cause each collimating lens to direct light
`from its associatedlight source to the spatial light modulator
`in a slightly diverging manner.
`FIGS. 7A and 7B are diagrammatic perspective views of
`light source arrangements designed in accordance with the
`present
`invention for use in, for instance,
`the miniature
`image generator of FIG. 4;
`FIG. 8 is a diagrammatic side view ofa third embodiment
`of a miniaturized image generating system designed in
`accordance with the present invention including an auxiliary
`
`

`

`US 6,195,136 B1
`
`5
`polarizer positioned optically between the light source and
`the spatial light modulator;
`FIG. 9 is a diagrammatic side view of the miniaturized
`image generating system of FIG. 8 including an auxiliary
`analyzer positioned optically between the spatial
`light
`modulator and the source imaging area;
`FIG. 10 is a diagrammatic side view of a fourth embodi-
`ment of a miniaturized image generating system designedin
`accordance with the present invention including an polarizer
`positioned optically between the light source and the spatial
`light modulator, an analyzer positioned between the spatial
`light modulator and the source imaging area, and a curved
`surface arrangement for directing the light from the light
`source to the spatial light modulator and transmitting the
`light from the spatial light modulator to the eyepiece which
`directs the light to the source imaging area;
`FIG. 11 is a diagrammatic side view of the miniaturized
`image generating system illustrated in FIG. 10 in which the
`polarizer and analyzer are formed as part of the curved
`surface arrangement;
`FIG, 12 is a diagrammaticside view of a fifth embodiment
`of a miniaturized image generating system designed in
`accordance with the present
`invention including a holo-
`graphic polarizing beam splitter positioned optically
`between the light source and the spatial light modulator and
`between the spatial light modulator and the source imaging
`area;
`
`FIG, 13 is a diagrammatic side view of a sixth embodi-
`ment of a miniaturized image generating system designed in
`accordance with the present
`invention including an edge-
`illuminated holographic illuminator;
`FIGS. 14A and 14B are diagrammatic side views of a
`seventh embodiment of a miniaturized image generating
`system designed in accordance with the present invention in
`which the spatial light modulatoris directly illuminated by
`the light source without other optics components for direct-
`ing the light into the spatial light modulator;
`FIGS. 15A and 15B are diagrammatic side views of an
`eighth embodiment of a miniaturized image generating
`system designed in accordance with the present invention in
`which the spatial light modulator is directly illuminated by
`the light source without other optics components for direct-
`ing the light into the spatial light modulator and the light
`source is positioned between the spatial light modulator and
`the eyepiece lens;
`FIG. 16 is a diagrammatic side view ofa ninth embodi-
`ment of a miniaturized image generating system designed in
`accordance with the present invention including an arrange-
`ment for converting light which is not directed into the
`spatial light modulator by the polarizing beam splitting cube
`to the opposite polarization and redirecting it back into the
`polarizing beam splitting cube;
`FIG. 17 is a diagrammatic side view of a tenth embodi-
`ment of a miniaturized image generating system designedin
`accordance with the present invention including a arrange-
`ment for converting light which is not directed into a first
`portion of the spatial light modulator by a first polarizing
`beam splitting cube to the opposite polarization and direct-
`ing it into a second polarizing beam splitting cube associated
`with a second portion of the spatial light modulator.
`FIGS, 18A-18C are diagrammatic views of an eleventh
`embodiment of a miniaturized image generating system
`designed in accordance with the present invention; and
`FIG. 19 is a diagrammatic side view of a portion of a
`miniaturized image generating system illustrating a plurality
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`$0
`
`55
`
`60
`
`6
`of light sources of three different colors, a collimating lens,
`and a polarizing beam splitting cube tunedtoa first one of
`the three different colors of light, and in which the light
`sources of the other two colors are positioned to cooperate
`with the collimating lens to direct their light to the polarizing
`beam splitting cube at angles which improve the efficiency
`at which the polarizing beam splitting cube acts upon the
`light of the two other colors.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Turning to FIGS. 2-18, wherein like components are
`designated by like reference numerals throughout the vari-
`ous Figures, attention is initially directed to FIG. 2A. This
`Figure illustrates the general optical elements of an optical
`system, designed in accordance with the present invention,
`for an image generating system, or miniaturized assembly
`for producing modulated light,
`including a spatial
`light
`modulator. In this case, the system is a miniature display
`system generally indicated by reference numeral 26. As
`shown in FIG. 2A, a suitable and readily providable light
`source 28 is positioned away from a transmissive spatial
`light modulator 30 having an writing arrangement 32 for
`controlling the light modulating states of spatial light modu-
`lator 30, Writing arrangement 32 may also switchably con-
`trol light source 28. Spatial light modulator 30 modulates
`light
`from light source 28 by selectively changing the
`polarization of the light passing through the spatial
`light
`modulator in response to data signal from writing arrange-
`ment 32. A collimating lens 34 is positioned between light
`source 28 and spatial light modulator 30 and an eye piece
`lens 36 is positioned between spatial light modulator 30 and
`a source imaging area 38 such that substantially all of the
`light generated by light source 28 is directed through source
`imaging area 38 except for any light which is specifically
`absorbed by or directed away from source imaging area 38
`by other optical elements positioned within the optical path
`between light source 28 and source imaging area 38 such as,
`for example a polarizer 40 or an analyzer 41. Eyepiece lens
`36 having a focal length F2 is positioned one focal length F2
`from spatial light modulator 30 and cooperates with light
`source 28, collimating lens 34, and spatial light modulator
`30 to form a real image of light source 28 at source imaging
`area 38 such that a virtual imageof the pattern of modulated
`light from spatial light modulator 30 is directly visible by a
`viewer from a viewing region 42. The real image of light
`source 28 is formed at source imaging area 38 because light
`source 28 is positioned a distance more than F2, the focal
`length of eyepiece lens 36, from eyepiece lens 36.
`The above described arrangement illustrated in FIG. 2A
`has the advantage over the prior art of directing a much
`greater percentage ofthe light from light source 28 through
`source imaging area 38 and into viewing region 42. This
`significantly reduces the power requirement for the light
`source since the wastage of light described above for the
`prior art arrangement is significantly reduced if not elimi-
`nated. Also, a system designed in accordance with the
`present invention allows a wide variety oflight sources to be
`used including light sources which are substantially less
`expensive than the large diffuse light source 14 used in the
`prior art system. However,
`this particular arrangement
`shown in FIG. 2A substantially increases the overall length
`of the system and therefore is not practical when miniatur-
`ization of the overall system is important.
`Referring now to FIG. 2B, an alternative basic configu-
`ration of an overall display system designed in accordance
`with the present
`invention and generally designated by
`
`

`

`US 6,195,136 B1
`
`7
`reference numeral 44 will be described. Display system 44
`includes light source 28, collimating lens 34, eyepiece lens
`36, and source imaging area 38 as describe above for FIG.
`2A. However, in this embodiment ofthe present invention,
`a reflective type spatial light modulator 46 controlled by
`writing arrangement 32 is used instead of a transmissive
`spatial light modulator. As shown in FIG, 2B, a suitable and
`readily providable polarizing beam splitting cube 48 is
`positioned between spatial light modulator 46 and eyepiece
`lens 36. Also, light source 28 and collimating lens 34 are
`positioned to one side of polarizing beam splitting cube 48.
`During the operationofbasic display system 44 described
`above, light from light source 28, indicated by lines 49,is
`collected by collimating lens 34 and directed into polarizing
`beam splitting cube 48. The polarizing beam splitting cube
`reflects light of one polarization, for example S-polarized
`light, into spatial ight modulator 46 and wastes light of the
`opposite polarization, for example P-polarizedlight, allow-
`ing it to pass through polarizing beam splitting cube 48.
`Spatial light modulator 46, controlled by writing arrange-
`ment 32, acts on the light of the one polarization
`(S-polarized light) directed into the modulator by converting
`certain portions of the light of the one polarization
`(S-polarized light)
`to light of the opposite polarization
`(P-polarized light) forming an overall pattern of modulated
`light
`that
`is reflected back into polarizing beam splitting
`cube 48. The polarizing beam splitting cube wastes light of
`the one polarization (S-polarized light) by reflecting it back
`toward light source 28 and allows the converted light of the
`opposite polarization (P-polarized light) to pass through
`polarizing beam splitting cube 48 into eyepiece lens 36
`forming a real image of light source 28 at source imaging
`area 38. As described above, the real image of light source
`28 is formed at source imaging area 38 because light source
`28is positioned optically a distance greater than one focal
`length of eyepiece lens 36 from eyepiece lens 36. This
`arrangement also produces a virtual image of the pattern of
`modulated light that is viewable from the source imaging
`area and viewing region 42. One specific novel arrangement
`for spatial light modulator 46 and writing arrangement 32 is
`disclosed in copending U.S. patent application Ser. No.
`08/362,665 Attorney Docket Number DIS1P003 entitled
`ACTIVE MATRIX LIQUID CRYSTAL IMAGE GENERA-
`TOR field cotemperaneously herewith.
`As illustrated by FIG. 2B,
`the above described
`arrangement, which includes a reflective type spatial light
`modulator such as spatial light modulator 46, allows light
`source 28 to be moved away from spatial light modulator 46
`without increasing the front to back length of the overall
`system as was shown in FIG. 2A. This system, designed in
`accordance with the present invention,folds the optical path
`such that the portion of the optical path in which light from
`the light source is directed into the spatial light modulator
`overlaps the portion of the optical path in which the light is
`directed from the spatial light modulator to the eyepiece
`lens. By overlapping the optical path as described, the same
`physical space is used for both of these purposes and
`therefore the length of the system is not increasedrelative to
`the prior art system described above and shownin FIG. 1. In
`the embodiment illustrated in FIG. 2B, this folding of the
`optical path is accomplished by positioning polarizing beam
`splitting cube 48 in the space between spatial light modu-
`lator 46 and eyepiece 36, Again, this does not increase the
`length of the system because, as shown in FIGS. 1 and 2A,
`the eyepiece lens must be positioned approximately one
`focal length of the eyepiece lens away from the spatial light
`modulator which provides sufficient space for the polarizing
`beam splitting cube.
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`$0
`
`55
`
`60
`
`8
`By moving light source 28 away from the spatial light
`modulator as specified by the present invention in order to
`forma real imageof light source 28 at source imaging area
`38, optical elements may be added to the system which
`direct the light from source 28 into spatial light modulator 46
`in a controlled way. A variety of optical elements, which will
`be described in more detail hereinafter, may be usedto direct
`the light from source 28 into the spatial light modulator and
`from the spatial light modulator so as to form a real image
`of light source 28 at source imaging area 38. As described
`above, these optical elements may also be arranged to allow
`a virtual
`image of the overall pattern of modulated light
`produced by the spatial light modulator,
`in other words a
`virtual
`image of the display, to be visible from source
`imaging area 38 and viewing region 42. Also as mentioned
`above, this arrangement of the present invention provides
`the substantial benefit of being able to direct a much larger
`percentage of the light generated by light source 28 into
`source imaging area 38 when compared with prior art
`systems. This avoids wasting light by directing light into
`regions other than viewing region 42, or in other words,
`regions from which a viewer viewing the display would not
`be able to view the entire virtual image of the pattern of
`modulated light produced by the spatial light modulator.
`Therefore, a system designed in accordance with the present
`invention more efficiently uses the ligh