United States Patent [191
`Beeson et a1.
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`[22]
`[51]
`[52]
`
`[53]
`
`[56]
`
`BACKLIGHTlNG APPARATUS EMPLOYING
`AN ARRAY 0F MICROPRISMS
`
`Inventors: Karl W. Beeson, Princeton; Scott M.
`Zimmerman, Basking Ridge; Paul M.
`Fem], Morristown, all of N_J_
`Assignee: AlliedSignal Inc., Morris Township,
`Moms County’ NJ"
`Appl' No’; 149,219
`
`Filed:
`
`Nov. 5, 1993
`
`1m. c1.6 ....................................... .. G02F 1/1335
`11.5.01. ...................................... .. 359/40- 359/48-
`’
`1
`359/251; 353/81
`Field of Search ..................... .. 359/40, 42, 48, 49,
`359/245, 246, 247, 251; 353/33, 81
`_
`References cued
`Us, PATENT DOCUMENTS
`
`llllllllllllllIIIIIIIIIIIIIIMIIllllllllllllllllllllllllllllllllllllll
`
`539635OA
`[11] Patent Number:
`[45] Date of Patent:
`
`5,396,350
`Mar. 7, 1995
`
`5,267,062 1l/ 1993 Bottorf ................................ .. 359/40
`5,267,063 11/1993 Ray ........... ..
`359/49
`5,276,538 1/1994 Monjiet al.
`359/40
`5,278,545 1/ 1994 Streck .................. ..
`345/102
`5,280,371 1/1994 McCartney, Jr. et a1.
`359/40
`5,295,048 3/ 1994 Park et a1. ........................... .. 362/26
`FOREIGN PATENT DOCUMENTS
`050096OA1 2/1992 European Pat. Off. .
`60-201326 10/1985 Japan .
`64-35416 2/1989 Japan .
`45505 2/ 1993 Japan .
`
`iapa" "
`apa“ '
`WO9400780 1/ 1994 WIPO .
`WO94/O6051 3/1994 WIPO .......................... .. GOZB 5/02
`w094/09395 4/1994 WIPO ,
`
`Primary Examiner—William L. Sikes
`Assistant Examiner—Huy Mai
`Attorney, Agent, or Firm—Verne E. Kreger, Jr.
`
`3,863,246 1/1975 Trcka et a1. ....................... .. 377/487
`4,043,636 8/1977 Eberhardt et a1. . . . . . .
`. . . .. 359/48
`
`[57]
`
`ABSTRACT
`
`4,330,813 5/1982 Deutsch . . . . . . . . . . . .
`4,365,869 12/1982 Hareng et a1.
`4,636,519 3/1987 YOShid? 6:1 a1
`
`. . . .. 359/48
`350/345
`340/701
`350/345
`4,726,662 2/ 1988 Cromack ----- ~
`512237333
`11333321551323 2?§5';1:"3:3j3....
`385/33
`5,O50’946 9/1991 Hathaway et a1.
`359 /48
`5,099,343 3/1992 Margemm et a1,
`358/241
`5,101,279 3/1992 Kurematsu et a1. ..
`5,126,882 6/1992 Oe et a1. ............................ .. 359/619
`5,128,783 7/1992 Abileah et a1.
`.............. .. 359/49
`
`359/40
`5,161,041 11/1992 Ab?eah et a1.
`. . . .. 359/70
`5,182,663 1/1993 Jones . . . . . . . . . . . . . .
`......... .. 385/146
`5,202,950 4/1993 Arego et a1.
`5,206,746 4/1993 0016i al. ................ ..
`359/40
`5,237,641 8/1993 lacqbson at al-
`" 385/146
`
`5,253,089 10/1993 Ima1 . . . . . . . . . . . . . . . . . . .
`
`5,253,151 10/1993 Mepharn et a1.
`5,262,880 11/1993 Abileah ............ ..
`
`. . . .. 359/49
`
`.. 362/216
`359/40
`
`An improved backlighting apparatus comp?'sing a Slab
`waveguide that accepts light rays generated by a light
`source and transmits the light rays via total internal
`re?ection. Attached on one face of the slab waveguide
`15 an my efmicmprisms’ with each "1190mm hav
`ing an light input surface parallel to a light output sur
`face and at least one sidewall tilted at an angle from the
`direction normal to the surface of the waveguide such
`that light rays escape from the slab waveguide, re?ect
`Off the tilted sidewall and emerge from the microprism
`as a light source substantially perpendicular to the light
`output surface. An array of microlenses may be posi
`tioned to accept the Output of the microprisms 80 that
`the light exiting from the microlenses is substantially
`more perpendicular_ The backlight apparatus is advan
`tageously used as a backlighting means for ?at panel
`
`electronic displays
`
`'
`
`5,262,928 ll/ 1993 Kashima et a]. . . . . . . .
`
`. . . .. 362/31
`
`19 Claims, 10 Drawing Sheets
`
`94
`1
`/
`
`1
`
`492
`
`11
`/l \
`l
`\ /
`
`11
`f
`/
`
`\
`
`"2 "0
`l
`l
`/
`r
`/
`
`W4
`
`illllliii;
`
`6
`
`7A 4A
`
`LGE_001239
`
`LG Electronics Ex. 1038
`
`

`
`U.S. Patent
`
`Mar. 7, 1995
`
`Sheet 1 of 10
`
`5,396,350
`
`
`
`
`11111:}8
`—Jf
`
`V//I///IIIIIJ to
`
`FIG‘. I
`
`
`
`LGE_001240
`
`LGE_001240
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 2 of 10
`
`5,396,350
`
`as]
`28
`4o
`171’.
`if
`' [l
`17
`~27
`1/
`~11"
`1,; My
`15/1
`'51’
`
`.
`. I11
`
`FIG. 3.4
`
`gm 8
`mmmmm m UUUUU H
`
`UUUUUYm
`
`F
`
`.lllllllnllllI-Illl
`
`LGE_001241
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 3 of 10
`
`5,396,350
`
`3?
`
`4
`\ /
`
`42
`(
`
`44
`
`inhi?in
`FIG‘. 4
`
`.
`/
`6
`
`LGE_001242
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 4 of 10
`
`5,396,350
`
`32
`
`A
`
`28
`
`33
`72
`
`30
`
`J_
`
`70
`
`66
`
`68
`
`*HHW’“
`
`mm!!!
`
`56
`
`6O
`
`64
`
`62
`
`58
`
`hlllliilinin
`6)
`
`iii
`FIG‘. 6
`
`{Ll iinii
`
`LGE_001243
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 5 of 10
`
`5,396,350
`
`\H/Ké
`
`--m
`
`2::
`
`8.
`
`::=
`
`III
`
`: 0-0
`
`z; ¢
`
`mm
`Fom
`
`wit;
`
`. <\
`
`
`
`. L’ 7
`
`’
`
`LGE_001244
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 6 of 10
`
`5,396,350
`
`LGE_001245
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 7 0f 10
`
`5,396,350
`
`I24 -/
`
`I26
`
`iihiniim
`
`LGE_001246
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 8 of 10
`
`5,396,350
`
`LGE_001247
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 9 0f 10
`
`5,396,350
`
`|
`
`1'
`
`LGE_001248
`
`

`
`US. Patent
`
`Mar. 7, 1995
`
`Sheet 10 of 10
`
`5,396,350
`
`24
`26
`I84
`I86
`
`24
`26
`I84
`I86
`
`I52
`I84
`I86
`
`I80
`28
`'82
`
`FIG‘. /.9A
`
`\ / \ / \ f/IQO
`I80
`90
`'82
`
`F/G'. I95
`
`I
`I, \\
`
`L
`I \
`
`I
`r’
`‘a
`
`A
`/ \
`
`H92
`LI \\
`
`A
`I \
`
`1
`
`|80
`
`I30
`"'82
`
`FIG. L96‘
`
`LGE_001249
`
`

`
`BACKLIGHTING APPARATUS EMPLOYING AN
`ARRAY OF MICROPRISMS
`
`BACKGROUND OF THE INVENTION
`
`5
`
`a. Field of the Invention
`This invention relates generally to ?at panel elec
`tronic displays, and more particularly, relates to an
`apparatus for collimating light as applied advanta
`geously as a backlighting means that provides for rela
`tively high light transmission for liquid crystal displays
`or the like.
`b. Description of Related Art
`There has been an extensive ongoing effort to pro
`vide large, full color display systems which do not rely
`upon the conventional cathode ray tube. See, for exam
`ple, “Flat-Panel Displays,” Scientific American, March
`1993, pages 90—97. In systems such as television receiv
`ers, computer monitors, avionics displays, aerospace
`displays and military-related displays, the elimination of
`cathode ray tube technology is desirable. See US. Pat.
`Nos. 4,843,381, 5,128,783 and, 5,161,041 for a discussion
`of the disadvantages of cathode ray tube technology.
`Display devices, as for example, projection display
`devices, off screen display devices and direct-view dis
`plays are known. See for example, EPO 0 525 755 Al;
`US Pat. Nos. 4,659,185, 5,132,830 and 5,159,478; and
`Japanese Publication Nos. 245106 and 42241. Such dis
`plays are used in a wide range of applications including
`televisions, computer monitors, avionics displays, aero
`space displays, automotive instrument panels and other
`devices that provide text, graphics or video informa
`tion. These types of displays can replace conventional
`cathode ray tube displays and offer advantages such as
`lower pro?le, reduced weight and lower power con
`sumption.
`One display which can eliminate the shortcomings of
`a cathode ray tube is the ?at panel liquid crystal display
`(LCD). LCDs are typically either re?ective or trans
`missive. A re?ective display is one which depends upon
`ambient light conditions in order to view the display. A
`transmissive LCD requires an illuminating means or
`backlight to ensure that the display image is as bright as
`possible. LCDs suffer from a number of inherent disad
`vantages. For example, at high viewing angles (large
`angles from the direction normal to the surface of the
`display), LCDs exhibit low contrast and changes in
`visual chromaticity as the viewing angle changes.
`The characteristics of the backlighting apparatus are
`very important to both the quality of the image dis
`played by the matrix array of picture elements of the
`LCD and the pro?le of the display. See US. Pat. Nos.
`5,128,783 and 5,161,041 for a discussion of the de?cien
`cies in past backlighting con?gurations.
`Additionally, current backlighting systems, in appli
`cations such as laptop computers, are inefficient with
`regard to the amount of light that the viewer sees versus
`the light produced by the source. Only about ten to
`twenty percent of the light generated by the light
`source ends up being usefully transmitted through the
`computer display. Any increase in the light throughput
`will positively impact power consumption and ulti
`mately increase the battery life of a portable computer.
`Accordingly, there exists a need in the ?at panel
`electronic display art to provide a backlight assembly
`that provides an energy ef?cient and uniform light
`
`25
`
`45
`
`55
`
`65
`
`1
`
`5,396,350
`
`2
`source for the electronic display while maintaining a
`narrow pro?le.
`
`SUMMARY OF THE INVENTION
`The present invention is directed to direct-view ?at
`panel displays, and speci?cally to a liquid crystal dis
`play, having an improved backlight assembly which
`provides an energy ef?cient and uniform light source.
`Additionally, this invention is directed to any lighting
`application that requires a low pro?le, substantially
`collimated light source.
`The ?at panel electronic display comprises: a modu
`lating means that is capable of projecting an image to a
`remotely positioned observer, the modulating means
`spacedly disposed from an improved backlit assembly
`comprising a light source in close proximity to a light
`transmitting means, the light source being positioned so
`that the light rays travel through the light transmitting
`means in a direction substantially parallel to the plane of
`the modulating means; and a re?ecting means for colli
`mating the light rays emanating from the light source,
`said re?ecting means operatively disposed between and
`in close proximity to said light transmitting means and
`said modulating means. The improvement in the display
`through the use of the present invention is that the
`re?ecting means provide an energy efficient, bright and
`uniform distribution of light that is provided in a low
`pro?le assembly.
`In one preferred embodiment, the light source is posi
`tioned adjacent to a light accepting surface of the light
`transmitting means so that the light rays emanating
`from the light source travel in a direction substantially
`parallel to the plane of the modulating means. The light
`transmitting means may be any structure that transmits
`light rays via re?ection, such as a light pipe, light
`wedge, slab waveguide or any other structure known to
`those skilled in the art. Preferably the light transmitting
`means comprises a slab waveguide that accepts the light
`rays generated by the light source and transports the
`light via total internal re?ection (TIR). Attached on
`one face of the slab waveguide is an array of micro
`prisms. The microprisms comprise a light input surface
`adjacent to the slab waveguide and a light output sur
`face distal to and parallel with the light input surface.
`Preferably the microprisms further comprise a tilted
`sidewall angled in such a way that light rays escape
`from the slab waveguide, re?ect through the micro
`prisms via TIR and emerge from the microprisms as a
`substantially collimated light source in a direction sub
`stantially perpendicular to the modulating means.
`In another preferred embodiment two light sources
`are positioned adjacent to oppositely disposed light
`accepting surfaces of the light transmitting means. The
`light transmitting means comprises a slab waveguide
`that accepts the light rays generated by both light
`sources and transports the light rays via TIR. Attached
`on one face of the slab waveguide is an array of micro
`prisms. The microprisms comprise oppositely disposed
`tilted side walls that are angled in such a way that light
`rays traveling in two directions along the slab wave
`guide escape from the slab waveguide and re?ect
`through the microprisms via TIR and emerge from the
`microprisms as a substantially collimated light source in
`a direction substantially perpendicular to the modulat
`ing means.
`In still a further embodiment, four light sources are
`positioned adjacent to separate light accepting surfaces
`of a slab waveguide that accepts the light rays gener
`
`LGE_001250
`
`

`
`5,396,350
`3
`4
`ated by all four light sources and transports the light
`FIG. 14 is a perspective view of a alternate embodi
`ment of the present invention using four light sources;
`rays via TIR. Attached on one face of the slab wave
`guide is an array of microprisms. The microprisms com
`FIG. 15 is an alternate embodiment of the embodi
`prise four tilted side walls that are angled in such a way
`ment shown in FIG. 14;
`that light rays traveling in four directions along the slab
`FIG. 16 is a perspective view of a single microprism
`having four angled sides;
`waveguide escape from the waveguide and re?ect
`through the microprisms and emerge as a substantially
`FIG. 17 is a sectional view of a single microprism
`shown in FIG. 16;
`, collimated light source in a direction substantially per~
`pendicular to the modulating means.
`FIG. 18 is another sectional view of a single micro
`prism shown in FIG. 16;
`In still another preferred embodiment, the present
`invention further comprises microlenses disposed be
`FIG. 19A illustrates a method for fabricating the
`embodiment of FIGS. 1-5;
`tween the microprisms and the modulating means. The
`microlenses are formed and positioned at the proper
`FIG. 19B illustrates a method for fabricating the
`focal length so that the substantially collimated light
`embodiment of FIGS. 10-13; and
`emanating from each microprism is directed to a corre
`FIG. 19C illustrates a method for fabricating the
`sponding microlens. The light transmits through the
`embodiment of FIGS. 14-18.
`microlenses and emerges as a substantially more colli
`mated light source for the modulating means.
`Additional objects, advantages and novel features of
`the invention will be set forth in part in the description
`20
`which follows, and in part will become apparent to
`those skilled in the art upon examination of the follow
`ing or may be learned by practice of the invention. The
`objects and advantages of the invention may be realized
`and attained by means of the instrumentalities and com
`binations particularly pointed out in the claims.
`
`25
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The preferred embodiments of the present invention
`will be better understood by those skilled in the art by
`reference to the above ?gures. The preferred embodi
`ments of this invention illustrated in the ?gures are not
`intended to be exhaustive or to limit the invention to the
`precise form disclosed. They are chosen to describe or
`to best explain the principles of the invention and its
`applicable and practical use to thereby enable others
`skilled in the art to best utilize the invention.
`One preferred application of the present invention is
`a backlighting means for a flat panel display, such as a
`liquid crystal display shown in FIG. 1, represented by
`the number 2. The display is composed of a light gener
`ating means 4, a slab waveguide 6 having a light accept
`ing surface 7, a transparent re?ecting means 8 in contact
`with slab waveguide 6, an optional input light polariz
`ing means 10, a modulating means 12, an optional out
`put light polarizing means 14 and a display means 16. It
`is understood that the representation of the present
`invention in FIG. 1 and throughout is for illustrative
`purposes only and is not meant to convey size or limit
`possible con?gurations of the microprisms.
`The exact features of light generating means 4, modu
`lating means 12, polarizing means 10 and 14 and display
`means 16 are not critical and can vary widely, and any
`such elements conventionally used in the art of ?at
`panel displays may be employed in the practice of this
`invention. Illustrative of useful light generating means 4
`are lasers, ?uorescent tubes, light emitting diodes, in
`candescent lights, sunlight and the like. Preferred mod
`ulating means 12 for use in the practice of this invention
`are liquid crystal cells. The liquid crystal material in
`liquid crystal cell 12 can vary widely and can be one of
`several types including, but not limited to, twisted ne
`matic (TN) material, super-twisted nematic (STN) ma
`terial and polymer dispersed liquid crystal (PDLC)
`material. Such liquid crystal material is arranged as
`known in the art in a matrix array of rows and columns.
`Exemplary of useful input light polarizing means 10 and
`output light polarizing means 14 are plastic sheet polar
`oid material and the like. The preferred display means
`16 is the display means as disclosed in copending US.
`patent application Ser. No. 08/086,414, assigned to the
`assignee of the present application, the disclosure of
`which is incorporated herein by reference.
`In FIG. 1, light generating means 4 is in close proxim
`ity to slab waveguide 6, and re?ecting means 8 is in
`close proximity to polarizing means 10 which itself is in
`proximity to modulating means 12. As used herein,
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The above and other objects and advantages of this
`invention will be apparent on consideration of the fol
`lowing detailed description, taken in conjunction with
`the accompanying drawings, in which like reference
`characters refer to like parts throughout, and in which:
`FIG. 1 is a cross-sectional view of an embodiment of
`a liquid crystal display constructed in accordance with
`the present invention;
`FIG. 2 is an exploded elevation view of one embodi
`ment of the backlight assembly in accordance with the
`present invention;
`FIG. 3A is a perspective view of one embodiment of
`40
`the present invention;
`FIG. 3B is a plan view of a rectangular arrangement
`of the microprisms on the slab waveguide;
`FIG. 3C is a plan view of a hexagonal arrangement of
`the microprisms on the slab waveguide;
`45
`FIG. 3D is a plan view of a still further alternate
`arrangement of the microprisms on the slab waveguide;
`FIG. 4 is an exploded elevation view of an alternate
`embodiment of the present invention;
`FIG. 5 is a perspective view of a single microprism;
`FIG. 6 is an exploded view of a single microprism on
`a slab waveguide illustrating directions of light rays
`traveling through the slab waveguide;
`FIG. 7 is a cross-sectional view of a alternate embodi
`ment of the re?ecting means having an array of micro
`lenses;
`FIG. 8 is a perspective view of the alternate embodi
`ment shown in FIG. 7;
`FIG. 9 is a sectional view of a single microlens;
`FIG. 10 is a cross-sectional view of a alternate em
`bodiment of the present invention using two light
`sources;
`FIG. 11 is a perspective view of the embodiment
`shown in FIG. 10;
`FIG. 12 is an alternate embodiment of the embodi
`ment shown in FIG. 10;
`FIG. 13 is a sectional view of a single microprism
`having two angled sides;
`
`65
`
`55
`
`60
`
`LGE_001251
`
`

`
`5
`“proximity” means in intimate physical contact or
`closely positioned, preferably within about 1 inch, more
`preferably within about 0.75 inch, most preferably
`within about 0.5 inch, and within about 0.25 inch in the
`embodiments of choice, so that light does not have to be
`“projected” from one element to the next.
`FIG. 2 shows an exploded view of slab waveguide 6
`and the re?ecting means 8. The slab waveguide 6 is
`made from any transparent material such as glass or
`polymer. The re?ecting means 8 is composed of an
`adhesion promoting layer 22, a substrate 24, a second
`adhesion promoting layer 26 and an array of micro
`prism waveguides 28. The microprisms 28 are con
`structed to form a six-sided geometrical shape having a
`light input surface 30 parallel with a light output surface
`32 and sidewalls 33 and 34. Only sidewall 33 is effective
`in reflecting the light rays which are propagating
`through waveguide 6. Preferably, the intersection of
`sidewall 33 with substrate 24, or adhesion layer 26
`thereon, forms a line that is perpendicular to the aver
`age direction of the light rays. For example, as shown in
`FIG. 3A, for a rectangular slab waveguide 6, the inter
`section of sidewall 33 with substrate 24 forms a line
`parallel to the light accepting surface 7 and is therefore
`perpendicular to the average direction of the light rays
`traveling through the slab waveguide 24. Although
`sidewall 34 is shown as parallel to sidewall 33, the orien
`tation of side 34 is not critical. Microprisms 28 are sepa
`rated by interstitial regions 36 that have a lower refrac
`tive index than the refractive index of the microprism
`28. Light rays re?ect through waveguide 6 via TIP, and
`enter each microprism 28 by way of light input surface
`30, reflect off sidewall 33 and exit the microprism 28
`through the light output surface 32 in a direction sub
`stantially perpendicular to the modulating means.
`Slab waveguide 6 and substrate 24 are transparent to
`light within the wavelength range from about 400 to
`about 700 nm. In the preferred method of fabrication, as
`described below, the substrate 24 is also transparent to
`ultraviolet (UV) light in the range from about 250 to
`about 400 nm. This range allows the microprisms to be
`formed by photopolymerization of reactive monomers
`initiated by UV light. The index of refraction of both
`are equal or substantially equal and may range from
`about 1.45 to about 1.65. The most preferred index of
`45
`refraction is from about 1.50 to about 1.60. The slab
`waveguide 6 and substrate 24 may be made from any
`transparent solid material. Preferred materials include
`transparent polymers, glass and fused silica. Desired
`characteristics of these materials include mechanical
`50
`and optical stability at typical operation temperatures of
`the device. Most preferred materials are glass, acrylic,
`polycarbonate and polyester.
`Microprisms 28 can be constructed from any trans
`parent solid polymer material. Preferred materials have
`an index of refraction equal to or substantially equal to
`substrate 24 of between about 1.45 and about 1.65 and
`include polymethylmethacrylate, polycarbonate, poly
`ester, polystryrene and polymers formed by photopo
`lymerization of acrylate monomers. More preferred
`materials have an index of refraction between abut 1.50
`and about 1.60 and include polymers formed by photo
`polymerization of acrylate monomer mixtures com
`posed of urethane acrylates and methacrylates, ester
`acrylates and methacrylates, epoxy acrylates and meth
`acrylates, (poly) ethylene glycol acrylates and methac
`rylates and vinyl containing organic monomers. Useful
`monomers include methyl methacrylate, n-butyl acry
`
`5,396,350
`6
`late, Z-ethylhexyl acrylate, isodecyl acrylate, Z-hydrox
`yethyl acrylate, Z-hydroxypropyl acrylate, cyclohexyl
`acrylate, 1,4-butanediol diacrylate, ethoxylated bisphe
`nol A diacrylate, neopentylglycol diaerylate, diethyl
`eneglycol diacrylate, diethylene glycol dimethacrylate,
`1,6-hexanediol diacrylate, trimethylol propane triacryl
`ate, pentaerythritol triacrylate and pentaerythritol tet
`ra-acrylate. Especially useful are mixtures wherein at
`least one monomer is a multifunctional monomer such
`as diacrylate or triacrylate, as these will produce a net
`work of crosslinks within the reacted photopolymer.
`The most preferred materials for use in the method of
`the invention are crosslinked polymers formed by
`photopolymerizing mixtures of ethoxylated bisphenol
`A diacrylate and trimethylol propane triacrylate. The
`index of refraction of the most preferred materials
`ranges from about 1.53 to about 1.56.
`In order that modulating means 12 and display means
`16 (FIG. 1 ) have high overall light output, it is pre
`ferred that the sum of the areas for all microprism wave
`guide input surfaces 30 be greater than 20 percent of the
`total area of substrate 24. It is more preferred that the
`sum of the areas for all microprism waveguide input
`surfaces 30 be greater than 35 percent of the total area
`of substrate 24. It is most preferred that the sum of the
`areas for all microprism waveguide input surfaces 30 be
`greater than 50 percent of the total area of substrate 24.
`The index of refraction of interstitial regions 36 be
`tween the microprism waveguides 28 must be less than
`the index of refraction of the microprism waveguides
`28. Preferred materials for interstitial regions include
`air, with an index of refraction of 1.00 and ?uoropoly
`mer materials with an index of refraction ranging from
`about 1.16 to about 1.35. The most preferred material is
`air.
`The adhesion promoting layers 22 and 26 shown in
`FIG. 2 are an organic material that is light transmissive
`and that causes the waveguides 28, especially wave
`guides forrned from polymers, as for example photo
`crosslinked acrylate monomer materials, to adhere
`strongly to the substrate 24. Such materials are well
`known to those skilled in the art. The thickness of adhe
`sion promoting layers 22 and 26 is not critical and can
`vary widely. In the preferred embodiment of the inven
`tion, adhesion layers 22 and 26 are less than about 10
`micrometers thick.
`FIG. 3A shows an exploded perspective view of light
`generating means 4, slab waveguide 6, substrate 24,
`adhesion promoting layers 22 and 26, and an array of
`microprisms 28. In this illustration, the microprisms 34
`are arranged in a square or rectangular array, as shown
`in FIG. 3B, although other arrangements such as a
`hexagonal pattern are possible, as shown in FIG. 3C.
`The microprisms have a repeat distance 38 in the direc
`tion perpendicular to light generating means 4 and re
`peat distance 40 in the direction parallel to light gener
`ating means 4. Repeat distances 38 and 40 may be equal
`or unequal and may vary widely depending on the reso
`lution and dimensions of the display. In addition, the
`repeat distances 38 and 40 may vary across the surface
`of the light re?ecting means 8 in order to compensate
`for a lowering of the light intensity inside waveguide 6
`as the distance from light generating means 4 increases.
`This lowering of the light intensity is due to light re
`moval by the other microprisms of the array. Desired
`values of the repeat distances 38 and 40 range from
`about 10 microns to about 40 millimeters. More pre
`ferred values of the repeat distances 38 and 40 range
`
`55
`
`65
`
`25
`
`35
`
`40
`
`LGE_001252
`
`

`
`5,396,350
`7
`8
`lated from Snell’s Law, then the total angular spread for
`from about 50 microns to about 10 millimeters. Most
`preferred values of the repeat distances 38 and 40 range
`light which can propagate in waveguide 6 is the sum of
`from about 100 microns to about 2 millimeters.
`angles 60 and 62 where angles 60 and 62 are each equal
`FIG. 4 illustrates an alternate embodiment of the
`to 90°-0C. Only 50 percent of the light, the light rays
`present invention shown in FIGS. 2 and 3. The light
`with propagation angles ranging from approximately
`input surface 30 of microprisms 28 is attached to slab
`zero (parallel to the plane of the slab waveguide) up to
`waveguide 6 via an adhesion layer 46. Attached to the
`angle 60, have a chance of being removed from the slab
`light output surface 32 is a substrate layer 42 via an
`waveguide by encountering the light input surface 30 of
`adhesion layer 44.
`microprism 28. Light rays with angles from approxi
`A single microprism waveguide 28 is shown in FIG.
`mately zero to angle 62 will be reflected off the bottom
`5. The desired values of tilt angle 72 range from about
`surface of waveguide 6 by total internal re?ection and
`25 degrees to about 40 degrees. More preferred values
`will then be directed toward the top surface of wave
`for tilt angle 72 range from about 28 degrees to about 37
`guide 6 where they have a chance of being removed
`degrees. Most preferred values for tilt angle 72 are from
`from waveguide 6 by other microprisms 28 farther
`about 30 degrees to about 35 degrees. A method for
`down the waveguide.
`estimating the desired value of tilt angle 72 is discussed
`For optimum functioning of microprism 28, surface
`below.
`33 should be at angle 72 such that the midpoint of the
`The height of microprism waveguide 28 in FIG. 5 has
`light distribution represented by angle 60 will be di
`dimension 50. Height 50 may vary widely depending on
`rected through output surface 32 of microprism 28 at an
`the dimensions and resolution of the display. That is,
`angle perpendicular to the plane of waveguide 6. The
`smaller displays, such as laptop computer displays and
`midpoint of angle 60 is angle 64 which can be expressed
`avionics displays would have greatly reduced dimen
`as either (90°—0¢)/2 or (45°—6c/2). Angle 66 is then
`sions versus larger displays such as large screen, ?at
`equal to (90°-angle 64) or 45+0c/2. The proper direc
`panel televisions. Desired values of the dimension 50
`tionality for light in microprism 28 will occur if angle 72
`range from about 10 microns to about 40 millimeters.
`equals angle 70 which in turn equals one-half of angle
`More preferred values of the dimension 50 range from
`66. As a result, angle 72 equals 22.5°+0¢/4. For exam
`about 50 microns to about 10 millimeters. Most pre
`ple, if the index of refraction of the waveguide 6 and
`ferred values of dimension 50 range from about 100
`microprism 28 is 1.55 and the waveguide and micro
`microns to about 2 millimeters. The length of micro
`prism are surrounded by air with an index of refraction
`prism waveguide 28 has dimension 52. Length 52 may
`of 1.00, then 0c=40° and angle 72 is 32.5°.
`vary widely depending on the dimensions and resolu
`A further embodiment of the present invention is
`tion of the display. In addition, the length 52 may vary
`illustrated in FIGS. 7 and 8. Re?ecting means 8 further
`across the surface of the light re?ecting means 8 in
`comprises an array of microlenses 80. In this embodi
`order to compensate for a lowering of the light intensity
`ment, the microlenses 80 are disposed between and in
`inside waveguide 6 as the distance from light generating
`close proximity to the microprisms 28 and modulating
`means 4 increases. This lowering of the light intensity is
`means 12 (not shown). The microlenses 80 are prefera
`due to light removal by the other microprisms of the
`bly made from the same monomers as those previously
`array. The maximum value for the length 52 is less than
`disclosed for the microprisms 28 and have a index of
`the repeat distance 38. Desired values of the dimension
`refraction equal to or substantially equal to the index of
`52 range from about 10 microns to less than about 40
`refraction of the microprisms 28. However, any trans
`millimeters. More preferred values of the dimension 52
`parent material may be used, as for example, those mate
`range from about 50 microns to less than about 10 milli
`rials previously discussed.
`meters. Most preferred values of dimension 52 range
`In FIG. 7, the substrate 82 for the microlenses 80 also
`from about 100 microns to less than about 2 millimeters.
`serves as a spacer between the microlenses 80 and the
`The width of microprism 28 has dimension 54. Width 54
`45
`microprisms 28. The thickness of substrate 82 is opti
`may vary widely depending on the dimensions and
`mized to cause light from microprisms 28 to be colli
`resolution of the display. In addition, the width 54 may
`mated by microlenses 80. Substrate 82 may be made
`vary across the surface of the light re?ecting means 8 in
`from any transparent solid material. Preferred materials
`order to compensate for a lowering of the light intensity
`include transparent polymers, glass and fused silica.
`inside waveguide 6 as the distance from light generating
`Desired characteristics of these materials include me
`means 4 increases. This lowering of the light intensity is
`chanical and optical stability at typical operation tem
`due to light removal by the other microprisms of the
`peratures of the device. Most preferred materials are
`array. The maximum value for the width 54 is the repeat
`glass, acrylic, polycarbonate and polyester.
`distance 40. That is, when width 54 equals repeat dis
`An exploded perspective view of the microprism
`tance 40, the microprisms are contiguous across the
`55
`array and the microlens array 80 is shown in FIG. 8.
`substrate width as shown in FIG. 3D. Desired values of
`The microlens array is shown as a square or rectangular
`the dimension 54 range from about 10 microns to about
`array although other arrangements such as a hexagonal
`40 millimeters. More preferred values of the dimension
`pattern are possible. The center-to-center distance be
`54 range from about 50 microns to about 10 millimeters.
`tween microlenses directly correlates to the repeat dis
`Most preferred values of dimension 54 range from about
`tances 38 and 40