US006158245A
`6,158,245
`(114) Patent Number:
`United States Patent 55
`
` Savant [45] Date of Patent: Dec. 12, 2000
`
`
`[54] HIGH EFFICIENCY MONOLITHIC GLASS
`LIGHT SHAPING DIFFUSER AND METHOD
`OF MAKING
`
`[75]
`
`Inventor: Gajendra D. Savant, Torrance, Calif.
`
`[73] Assignee: Physical Optics Corporation,
`Torrance, Calif.
`
`[21] Appl. No.: 09/139,379
`.
`Filed:
`
`Aug.25, 1998
`
`[22]
`
`oo,
`Related U.S. Application Data
`[63] Continuation-in-part of application No. 08/902,415, Jul. 29,
`1997.
`Tent, Cdn ceceeccceeeeescesnneeeceestneeesnnesees C03B 8/02
`SL]
`[52] US. Che eee cecceeeessessecseeseeseeseeseenceneeneensensente 65/17.2
`[58] Field of Search o....cseccsesssssssssssssseeseseneeeeee 65/17.2
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`8/1971 Schroderet al. ween 501/12
`3,597,252
`65/134
`2/1972 Leveneetal. .....
`3,640,093
`.. 423/338
`11/1993 Wang et al.
`.......
`5,264,197
`.. 427/226
`11/1994 Hoshinoetal. ...
`5,368,887
`besees 342/4
`1/1995 Myers etal. .......
`5,384,571
`7/1996 Petersen et al.
`...
`5,534,386
`.. 430/320
`7/1996 Nisperetal. ......
`5,538,674
`. 264/1.31
`3/1997 Petersen et al.
`5,609,939
`428/141
`...
`»» 427/226
`6/1998 Schmidtet al.
`5,766,680
`1/1999 Choquette et al. oe 2604/1.24
`5,861,113
`FOREIGN PATENT DOCUMENTS
`61-68314
`4/1986
`Japan .
`
`...
`
`materials”, Optics Letters, vol. 8, No. 10, pp. 537-539, Oct.
`1983.
`Shagam, R.N., Ph.D., “Light Shaping Diffusers™ Simplify
`Aircraft Inspection,” Photonics Spectra, Nov. 1994.
`Dusinberre, B., “Light Shaping Diffusers Enhance Depth—
`Finder Performance,” Laser Focus World, Jun. 1995.
`Szezesniak, S., & Shie, R., “Machine Vision for Semicon-
`ductor Manufacture,” Photonics Spectra, Nov. 1995.
`“Directional Turning Film™”, Physical Optics Corporation,
`1996, Brochure (No Month Available).
`Giancola, S., “Hologrpahic Diffuser Makes Light Work of
`Screen Tests,” Photonics Spectra, Aug. 1996.
`Laine, J., “Mini Display,” Design News, Dec. 15, 1997.
`“Light Shaping Diffusers® Technical Data Sheet,” Physical
`Optics Corporation, Jul. 1, 1998.
`“Light Shaping Diffuser® Transmissive Thin Film Price
`List,” Physical Optics Corporation, May 1, 1998.
`“Light Shaping Diffuser® Transmission Kits Price List,”
`Physical Optics Corporation, May 1, 1998.
`“Light Shaping Diffuser® Transmission Sheet Price List,”
`Physical Optics Corporation, May 1, 1998.
`Primary Examiner—Sean Vincent
`Attorney, Agent, or Firm—Nilles & Nilles, S.C.
`(57]
`ABSTRACT
`
`A surface light shaping diffuser (LSD) is formed from a
`monolithic glass material by recording light shaping struc-
`tures on a surface of the material during its formation. A
`surface LSD is produced by embossing or molding light
`shaping structures onto a high quality optical glass or by
`embossing light shaping structures on a glass film layer
`coated onto a substrate. A rubber submaster carrying the
`light shaping structures is used as the master in such
`diffusers control
`the angular spread of transmitted light
`while homogenizing otherwise spatially noisy light sources
`such as LCDs and filamented light sources and while
`maintaining damage thresholds consistent with any glass
`optical element. The surface LSD has a transmission effi-
`ciency of over 90% from the Ultraviolet wavelengths
`through the
`physical
`t
`d into
`th
`-infrared.
`aoc eeeeeeCO ING CAIUS
`23 Claims, 8 Drawing Sheets
`
`OTHER PUBLICATIONS
`Lukosz et al, “Embossing technique for fabricating inte-
`grated optical components in hard inorganic waveguiding
`PROCESSFOR CASTING PHOTOSENSITIVE GLASS LSDs
`
`30 ——~| Si(OEt)4+ EtOH + HO +HCl + PHOTOSENSITIZER| Sol-Gel Solution
`
`
`
`32——_| MIXING ATROOM|49.499 om
`
`TEMPERATURE|20120 mins.
`
`
`
`
`
`
`
`
`
`34—~|castine wirr| 1-2 hrs.
`RUBBER MOLD OR
`Seat
`Y
`S6-—~| GELLINGIAGING|2-4 weeks
`
`
`y
`
`FIXING LSD“| PATTERN HEAT
`TREATMENT
`
`y
`CONSOLIDATE LSD
`— GLASS
`
`40
`
`42
`
`1-12 hrs.
`
`24-48 hrs.
`s
`
`1
`
`APPLE 1012
`
`APPLE 1012
`
`1
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 1 of 8
`
`6,158,245
`
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`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 2 of 8
`
`6,158,245
`
`FO
`
`/00%TKANSIVIES/ON A§
`
`x a S
`
`00 FAS 690 295 HE0O 1475 [670 /U5
`WAVELENGTH (rra)
`
`FIG. 3
`
`3
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 3 of 8
`
`6,158,245
`
`RECORD MASTER
`DIFFUSER SURFACE
`
`POUR RUBBER OVER
`MASTER SURFACE
`
`CURE RUBBER
`MATERIAL
`
`- 200
`
`- 202
`
`- 204
`
`SEPARATE RUBBER MATERIAL
`LAYER FROM MASTER
`
`- 206
`
`FIG. 4
`
`4
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 4 of 8
`
`6,158,245
`
`COATING PROCESS FOR GLASS LSDs
`
`
`
`70 Si(OEt)4+ EtOH + H20 +HCI|Sol-Gel Solution
`
`
`
`72
`MIXING AT ROOM
`TEMPERATURE|°°120 min.
`
`74
`COATING
`SPINNING/DIPPING|210 mI.
`
`GELLING
`
`
`
`
`
`PRESS LSD RUBBER|
`
`SUBMASTER PATTERN
`
`16
`
`78
`
`79
`
`
`
`
` FIXING LSD
`
`«40 ming
`
`1-5 hrs.
`
`24-48hrs.
`
`REMOVE LSD MASTER
`
`PATTERN HEAT
`TREATMENT
`
`
`
`CONSOLIDATE
`LSD GLASS
`
`FIG. 5
`
`5
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 5 of 8
`
`6,158,245
`
`PROCESS FOR CASTING PHOTOSENSITIVE GLASS LSDs
`
`Si(OEt)4+ EtOH + HoO0 +HCl + PHOTOSENSITIZER Sol-Gel Solution
`
`30
`
`
`32
`MIXING AT ROOM
`TEMPERATURE|20120 mins.
`
`
`34
`
`CASTING WITH
`RUBBER MOLD OR
`MOLD INSER
`
`
`1-2 hrs.
`
`36
`
`GELLING/AGING
`
`2-4 weeks
`
`
`
`
`
`
`FIXING LSD
`
`PATTERN HEAT
`TREATMENT
`
`CONSOLIDATE LSD
`GLASS
`
`
`
`
`FIG. 6
`
`40
`
`42
`
`4-12 hrs.
`
`24-48 hrs.
`
`6
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 6 of8
`
`6,158,245
`
`SYdeg = 0.05CIES |
`
`10.00
`000
`-1000
`DEGREE FROM CENTER
`FIG. ‘|
`
`"2390.00 -2000
`
`£0.00
`
`30.00
`
`7
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 7 of 8
`
`6,158,245
`
`400
`IF FWHIA=0.7/
`
`1deg. =1BLFUN1
`
`"-200
`
`SKF
`
`067
`OO
`-067
`DEGREE FROM CENTER
`FIG. &
`
`"PF
`
`200
`
`8
`
`

`

`U.S. Patent
`
`Dec. 12, 2000
`
`Sheet 8 of 8
`
`6,158,245
`
`FWHIA= 211
`
`Pldeg =0.707899 00
`
`-700
`
`-467
`
`FF A067
`200
`-fFF
`LIEGREE FROIE CENTER
`FIG. 9
`
`7.00
`
`9
`
`

`

`6,158,245
`
`1
`HIGH EFFICIENCY MONOLITHIC GLASS
`LIGHT SHAPING DIFFUSER AND METHOD
`OF MAKING
`
`This application is a continuation-in-part of Liebermanet
`al. U.S. application Ser. No. 08/902,415,filed Jul. 29, 1997,
`and assigned to the assignee of the present invention.
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`2
`The light shaping structures in volume LSDsare recorded
`using a coherent light recording system similar to a holo-
`graphic recording system. Coherent light passed through a
`master diffuser is incident upon a volumetric photosensitive
`medium (such as dichromated gelatin DCG or another
`volumerecording material). The speckle pattern in the light
`incident the medium is rendered in the medium byaltering
`the refractive index of the medium. Where the speckle
`pattern is bright, the medium is hardened andthe refractive
`index of the medium is increased. Where the speckle pattern
`is dark,
`the refractive index remains substantially
`The invention relates generally to light shaping diffusers,
`unchanged. Upon development,
`these variations in the
`and more particularly, to a surface light shaping diffuser
`refractive index are rendered essentially permanent.
`formed from a monolithic glass material and also to a
`Alternatively, the speckle pattern may be generated using an
`method of forming the surface light shaping diffuser.
`incoherent light source and a speckle-imitating mask in a
`2. Description of the Related Art
`process akin to a printing process. Light passed through the
`A Light Shaping Diffuser™ (LSD®), sometimes known
`mask is incident upon the volumetric medium and the
`as a light shaping homogenizer or simply a diffuser, is a type
`speckle pattern generates variationsin the refractive index of
`of diffuser used in a variety of illuminating, imaging, and
`the material essentially as before.
`light projecting applications. A LSD is a transparent or
`Surface LSDs are produced in similar fashion as well as
`translucent structure having an entrance surface, an exit
`in alternative ways. Recording set ups similar to those
`surface, and light shaping structures formed on its entrance
`described above are used with the exception that a nonvol-
`surface and/or in its interior. These light shaping structures
`ume recording medium suchas standard photoresist is used
`are random,disordered, and non-planar microsculpted struc-
`in place of a volume medium such as DCG. During
`tures. These structures are created during recording of the
`development,
`the areas having increased refractive index
`medium by illuminating the medium with a speckle pattern
`due to hardening remain while the softer, lower index areas
`are washed away. This process leaves microstructures hav-
`produced in conjunction with coherent light or the combi-
`ing light shaping properties at the surface of the medium.
`nation of incoherent light and a computer-generated mask
`These structures are then replicated in any number of
`which simulates speckle. The speckle produce changes in
`materials including plastics using various replication tech-
`the refractive index of the medium which, when developed,
`niques such as embossing, injection molding, and epoxy
`are the micro-sculpted structures. These light shaping struc-
`replication.
`tures diffract light passing through the LSD so that the beam
`LSDproductionis disclosed in U.S. Pat. No. 5,365,354 to
`of light emitted from the LSD’s exit surface exhibits a
`Jannsonetal. (the 354 patent), U.S. Pat. No. 5,609,939 to
`precisely controlled energy distribution along horizontal and
`Petersen etal. (the 939 patent), and U.S. Pat. No. 5,534,386
`vertical axes. LSDs can be used to shape a light beam so that
`to Petersenetal. (the ’386 patent). The ’354 patent, the ’386
`over 90% (and up to 95%—98%) of the light beam entering
`patent, and the 939 patent hereby are incorporated by
`the LSD is directed towards and into contact with a target
`located downstream of the LSD. A LSD can be made to
`reference for their disclosure of the production of a LSD.
`collect incoming light and either (1) distribute it over a
`Commonly assigned U.S. patent application Ser. No.
`circular area fromafraction of a degree to over 100°, or (2)
`08/902,415, to Lieberman entitled “Monolithic Glass Light
`40
`Shaping Diffuser and Method for its Production” (the ’415
`send it into an almost unlimited range ofelliptical angles.
`application) discloses several methods for fabricating dif-
`For example, a 0.2°x50° LSD will produce a line when
`illuminated by a LED orlaser and a 35°x90° LSD will form
`fusers from a sol-gel glass composition from a plastic or
`a narrow field, high resolution rear projection screen when
`epoxy submaster for high temperature uses. The *415 appli-
`illuminated by the same light source.
`cation is also incorporated herein by reference for its dis-
`closure of LSD production. Other related U.S. patent appli-
`Rather than exploiting a property of monochromatic laser
`cations include “Non-Lambertian Glass Diffuser and
`light known as coherence that requires that the finished
`holographic element be used only at the laser’s wavelength,
`a LSD operates perfectly in white light. LSDs therefore
`exhibit a high degree of versatility because they may be
`employed with light from almost any source,
`including
`LEDs, daylight, a tungsten halogen lamp, or an arc lamp.
`Two types of LSDs are currently available, namely a
`“volume LSD”and a “surface LSD.” A volume LSDis a
`volumetric optical element primarily characterized by the
`incorporation of light shaping structures within its body and
`which diffract light passing therethrough. A surface LSD is
`a surface relief optical element primarily characterized by
`the incorporation of light shaping structures on its surface
`and whichdiffract light passing therethrough. A surface LSD
`in addition to being produced optically may also be created
`by mechanical manipulation of the surface of the medium.
`See below for a list of some pending applications and issued
`patents related to each. Volume LSDsand surface LSDsare
`interchangeable in most applications. There are some lim-
`ited applications, however,
`in which volume LSDs are
`preferred, such as applications in which the LSD is sub-
`merged in a liquid.
`
`Method of Making,” filed Aug. 20, 1998, “Diffuser Master
`and Method of Manufacture,” filed Aug. 20, 1998, “High
`Efficiency Monolithic Glass Light Shaping Diffuser and
`Method of Making,” filed Aug. 25, 1998, “Optical Element
`Having an Integral Surface Diffuser,” filed Aug. 25, 1998,
`“Vehicle Light Assembly Including a Diffuser Surface
`Structure,” filed Aug. 25, 1998, “Apparatus Having a Light
`Source and a Sol-Gel Monolithic Diffuser,” filed Aug. 25,
`1998, “Passive Matrix Liquid Crystal Display,” filed Aug.
`25, 1998, and “Device Including an Optical Element With a
`Diffuser,” filed Aug. 25, 1998. These applications are also
`incorporated by reference herein.
`LSDsheretofore were formed solely from plastics such as
`acrylic or polycarbonate plastics because only these mate-
`rials were sufficiently deformable (under conditions suitable
`for interaction with a submaster) to accept the light shaping
`structures. Limitations resulting from the physical properties
`of these plastics restrict the applicable range of LSD opera-
`tion.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`10
`
`For instance, the plastics from which LSDs are formed
`typically have a glass transition temperature of below about
`
`10
`
`

`

`6,158,245
`
`3
`150° C. and often below about 100° C. Conventional plastic
`LSDstherefore cannot be used in applications in which the
`LSD may besubjected to sufficient heat to raise the tem-
`perature of the LSD to abovethis glass transition tempera-
`ture. This heat may be received directly from a light source
`such as an arc lamp or may be absorbed in the form of UV
`or infrared radiation. Plastic LSDs therefore generally can-
`not be used in heat lamps, liquid crystal display projectors,
`projector lamps, track lighting, or other light sources that
`generate significant heat near the location of the LSD.
`Plastic LSDs also are not widely usable with light sources
`operating in the ultraviolet range or infrared range which
`emit radiation that is absorbed bytheplastic.
`One limitation of plastic LSDs is that they cannot be
`subject to a hot coating operation. It is often desirable to coat
`a diffuser with a layer of an anti-reflective (AR) coating in
`order to raise the efficiency of the diffuser. Many coatings,
`including many AR coatings, can be applied only at tem-
`peratures above the glass transition temperature of plastics
`commonly used in LSDs. Conventional LSDsare not usable
`with these coatings.
`Yet another problem associated with a conventional plas-
`tic LSD is that it is difficult or impossible to form a high
`quality three-dimensional
`lens on its exit surface.
`It
`is
`desirable in a variety of diffuser applicationsto place a lens
`on the exit surface of the diffuser. Conventional plastic LSDs
`cannot be ground, polished, or molded into high quality
`lenses. High quality lenses can be produced on the exit
`surface of a LSD only by laminating or otherwise attaching
`a Fresnel lens on it. As is well known in the art, a Fresnel
`lens is one having a planar or two-dimensional surface that
`in use creates an effect that 1s designed to approximate the
`effect of a three-dimensional curved lens. Mounting a sepa-
`rate Fresnel
`lens onto the exit surface of a diffuser is
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`4
`submaster from which the surface relief structures are
`recorded is formed from a substantially rigid and hard
`plastic material whichis very stiff and inflexible. In order for
`the surface relief structures to be completely and properly
`recorded into the sol-gel material, the sol-gel material must
`be sustained in a containing space, coated onto a base
`substrate or inserted into a mold at a precisely controlled
`viscosity. If the viscosity varies even slightly less or slightly
`greater than desired,
`the sol-gel material may not flow
`properly and completely contact the surface relief structure
`of the master. Additionally, the sol-gel material may not flow
`completely into all of the surface relief spacesif at a slightly
`undesirable viscosity. The hard plastic material of the master
`or submaster does not yield, bend or flex at all to aid in
`having the sol-gel material flow properly. Hence, if the
`viscosity is not precisely as desired,all of the surface relief
`structures may not be recorded into the sol-gel material or
`may be recorded inaccurately.
`An additional problem with these present processes is that
`each time a submaster copy of a particular original master
`surface relief structure is recorded it
`loses some of its
`resolution and therefore providesslightly altered light shap-
`ing characteristics. For example, a master photoresist mate-
`rial is typically provided having the surface relief structures
`recorded therein from which a second generation submaster
`is created having the features subsequently recorded therein.
`A third generation submasteris then created from the second
`submaster having the features subsequently recorded therein
`as well. Sometimes, other additional submasters are created
`between the original master and the final diffuser product.
`Each subsequent formation of the surface relief structures in
`a subsequently produced submaster creates lower resolution
`and hence lower quality light shaping characteristics, and
`thus it would be beneficial to be able to eliminate one of
`
`these submastersteps.
`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`substantially more difficult and expensive than simply grind-
`ing or otherwise forming a conventional curved lens on the
`exit surface and may produce a lower quality lens.
`Manyof the above-identified disadvantages of a plastic
`LSD could be avoided if the LSD were to be formed from
`glass rather than a plastic. However,light shaping structures
`cannot be embossed on or otherwise recorded in a conven-
`tional glass structure during its production process because
`the high temperatures accompanying formation of conven-
`tional glass (on the order of 1,800° C.) would destroy the
`master or submaster bearing the light shaping structures.
`The °415 application noted above discloses a monolithic
`glass light shaping diffuser construction and a method of
`making the diffuser from a glass composition known as
`sol-gel. The *415 application discloses a volume LSD and a
`method of making the volumediffuser. It also discloses a
`surface LSD and methods of making the surface diffuser.
`The surface LSD is formed by a casting process wherein the
`sol-gel composition is cast in a plastic mold which bears the
`light shaping structures on an inner surface of the mold.
`Another method for forming a surface LSD is disclosed in
`the °415 application whereby a coating or layerof the sol-gel
`composition forms a film layer on a substrate. A submaster
`or master diffuser which bears the light shaping relief
`structures contacts the film layer so that the surface struc-
`A still further object of the invention is to provide a
`tures are recorded in the film layer after the sol-gel layer
`method of making a surface glass LSD which is more
`undergoes a glass transition, an aging and a heat treating
`tolerant of varying viscosity in the glass material during
`fabrication of the LSD.
`process. The master or submaster which bears the surface
`relief structures is disclosed as being made fromaplastic
`These objects are achieved in a remarkably simple and
`material.
`65
`effective manner by forming a LSD in a glass material which
`assumes a state during one or more phasesofits formation
`process in which the desired light shaping structures can be
`
`40
`
`45
`
`A principle object of the present invention is to provide a
`monolithic glass surface LSD that has a wider operating
`range in terms of temperature and/or wavelength than cur-
`rently available plastic LSDs.
`Another object of the invention is to provide a surface
`LSD capable of having a high quality curved lens formed on
`its exit surface.
`
`Still another object of the inventionis to provide a method
`of making a surface glass LSD from a monolithic glass
`material which, when formed, meets some orall of the
`foregoing objects.
`An additional object of the invention is to provide a high
`efficiency glass surface LSD that has a high resolution of the
`surface relief structures originally formed in the original or
`first master diffuser, therefore providing more accurately
`recorded light shaping characteristics.
`Another object of the invention is to provide a method of
`making such a high efficiency surface LSD which reduces
`the number of subsequent recordings from the original
`master surface to the surface of the LSD.
`
`50
`
`55
`
`60
`
`Depending uponthe process utilized to form the sol-gel
`glass LSD disclosed in the °415 application, the master or
`
`11
`
`11
`
`

`

`6,158,245
`
`6
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`1. Introduction
`
`5
`embossed on or otherwise recorded into the surface of the
`glass material under conditions hospitable to the master or
`submaster. Preferably, the light shaping structures are pro-
`duced during formation of a so-called “sol-gel” glass either
`by a casting or molding technique or by an embossing or
`Pursuant to the invention, a method is provided of form-
`pressing technique thereby forming a surface LSD.
`ing a surface light shaping diffuser (LSD) from a monolithic
`Surface LSDs can be produced from castable sol-gel
`glass material by recording light shaping structures in the
`glasses simply by casting the solutioninarelatively flexible
`glass material during its formation. A surface LSD can be
`mold formed of a rubber material wherein the mold bears the
`10
`produced by adding the sol-gel material
`to a relatively
`light shaping structures on an inner surface. The light
`flexible mold having the surface relief shaping structure on
`shaping structures are embossed on the sol-gel material
`an interior mold surface, or by embossing the surface relief
`during the molding process.
`light shaping structures onto a high quality optical glass
`Surface LSDscan also be produced from coatable sol-gel
`from a rubbersubstrate, or by embossing the light shaping
`glasses by coating a layer of the sol-gel solution onto a base
`structures from a rubber substrate onto a glass film layer
`substrate to produce a film layer on the substrate, causing the
`coated onto a base substrate. Such LSD’s control the angular
`film layer to undergo a sol-to-gel transition, recording light
`spread of transmitted light and homogenize otherwise spa-
`shaping structures in at least a portion of the film layer by
`tially noisy light sources such as liquid crystal displays and
`contacting the film layer with a rubber submaster, and aging
`filamented light sources, both while maintaining damage
`the gel to form a porousglass. The final step in the preferred
`thresholds consistent with any glass optical element. The
`processis to heat treat the glass to its sintering temperature
`LSD has a transmission efficiency of over 90% from the
`to produce a non-porous glass. The process may be
`Ultraviolet wavelengths through the visible spectrum and
`enhanced by pressing the rubber master bearing the light
`into the near-infrared. Moreover, because the LSD is a true
`shaping structures into contact with the film layer.
`glass, it is capable of withstanding temperatures well beyond
`These and other objects, features and advantages of the
`glass transition temperatures of plastic LSDs, can be formed
`invention will become apparent to those skilled in the art
`in a convex or concave surface through conventional
`from the following detailed description and the accompa-
`molding, grinding, or polishing techniques, and can be
`nying drawings. It should be understood, however, that the
`coated by hot-coating techniques. The LSD also has a very
`detailed description and the specific examples, while indi-
`high laser power threshold.
`cating preferred embodiments of the present invention, are
`2. Process Overview
`given by way of illustration and not of limitation. Many
`changes and modifications may be made within the scope of
`the present invention and without departing from the spirit
`thereof, and the invention includes all such modifications.
`
`At the heart of the invention is the discovery that a LSD
`can be produced by recording light shaping structures
`(sometimes known collectively as “speckle,” particularly
`whenthe structures extend into the interior of the diffuser)
`in a monolithic glass material during material formation if
`the glass material is one which is formed under conditions
`hospitable to the master or submaster bearing the light
`shaping structures. The currently-preferred technique for
`carrying out the present invention involves recording the
`light shaping structures in the material during a so-called
`FIG. 1 is a ternary phase diagram for the TEOS-Water-
`“sol-gel” process. As is knownto those skilled in the art of
`ethanol sol-gel solution with compositions plotted in mole
`making sol-gel glass,
`the sol-gel process is a low-
`percent;
`temperature approachto the production of oxide glasses. An
`FIG. 2 is a flow chart schematically representing a process
`oxide network is obtained via hydrolization and inorganic
`for preparing a sol-gel monolithic glass from a TEOS
`polymerization reactionsstarting with molecular precursors.
`precursor solution;
`The sol-gel process offers several advantages when com-
`pared to the production of glasses by conventional melting
`FIG. 3 is a graph plotting wavelength versus transmission
`techniques including (1) the formation of a higher optical
`percentage for a sol-gel monolithic glass with which the
`quality metal oxide glass,
`(2)
`the ready obtainment of
`present invention is applicable;
`homogeneous multi-component glasses by mixing molecu-
`FIG. 4 is a flow chart schematically representing a process
`lar precursorsolutions, (3) the obtainment of higher purity
`for forming a rubber submaster incorporating an optical
`and lower processing temperatures, and (4) the ability to
`surface relief structure recorded from a master;
`form fibers, films, monoliths, or compositions by techniques
`FIG. 5 is a flow chart schematically representingafirst
`55
`such as fiber drawing, spinning, dipping, casting and
`process for forming a monolithic glass LSD by coating;
`impregnation due to the rheological properties of the sols or
`FIG. 6 is a flow chart schematically representingafirst
`gels. Properties of sol-gel glasses rendering them well-suited
`for use as LSDs are summarized in Table 1:
`process for forming a monolithic glass LSD by casting or
`molding;
`FIG. 7 is a graph plotting the light diffusing angular
`distribution of a cast sol-gel monolithic glass LSD;
`FIG. 8 is a graph plotting angular light spatial distribution
`of a narrow angle sol-gel monolithic glass LSD in which the
`glass is a porous glass; and
`FIG. 9 is a graph plotting angular light spatial distribution
`of a narrow angle sol-gel monolithic glass LSD in which the
`glass is a sintered glass.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Preferred exemplary embodiments of the invention are
`illustrated in the accompanying drawings in which like
`reference numerals represent like parts throughout, and in
`which:
`
`5
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`15
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`25
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`30
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`35
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`40
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`45
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`50
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`60
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`TABLE1
`
`Material Properties of Sol-Gel Derived Silica Glasses
`
`Young Modulus
`Hardness
`Strength
`Thermal Expansion Coefficient
`Thermal Conductivity
`
`73 GPa
`6.2 GPa
`5.5 GPa
`5.5 x 107° Ct
`3.3 x 1073 cal seem? ° Ct
`
`12
`
`12
`
`

`

`6,158,245
`
`7
`
`TABLE 1-continued
`
`Material Properties of Sol-Gel Derived Silica Glasses
`1-5 Joules cm~?
`High (moisture acid and base)
`
`Laser Damage Threshold
`Chemical Resistance
`
`The typical sol-gel process includes first preparing a
`solution of a metal alkyl oxide, water, and a suitable solvent
`such as ethanol, then causing or permitting the solution to
`undergo a sol-to-gel transition to form a gel, and then aging
`the gel to form a porous hydrated glass. The hydrated glass
`is then heat treated to reduce its porosity by consolidation.
`A common example of the process uses a mixture of
`tetraethylorthosilicate (TEOS), water, and ethanol to pro-
`duce fused silica glass. Other examples include the use of
`aluminumtert-buitoxide [Al(OBu),] for alumina gels and
`tetraorthoethyltitanate (TET) fortitania gels. Depending on
`the optical properties of the glass material desired, multi-
`component reagents are often mixed into the solution to
`produce glasses with special characteristics such as high
`indices of refraction, high strength, high temperature, non-
`linear properties, and conduction properties.
`The chemistry of the sol-gel process is based on the
`hydroxylation and condensation reactions of organometallic
`molecular precursors. Metal alkoxides are the most versatile
`precursors for the sol-gel synthesis of oxides because they
`are very reactive towards nucleophilic reagents such as
`water. Hydrolysis occurs when a metal alkoxide and water
`are mixed in a mutual solvent, usually an alcohol. Sol-gel
`matrices for silica LSDs can be divided into spinnable,
`coatable, and castable solutions. Empirical miscibility for-
`mulations for TEOS-water-ethanol solutions at room tem-
`
`perature are plotted on the triangular phase diagram of FIG.
`1 in mole percent. As can be seen from this Figure, sol-gel
`solutions are spinnable with less than 40 mole percent water,
`are coatable with between 40 and 70 mole percent water, and
`are castable with more than 70 mole percent water.
`A typical sol-gel process will now be described to facili-
`tate an understanding of how light shaping structures
`(speckle) can be recorded in a monolithic glass structure at
`low temperatures hospitable to the master or submaster.
`Referring now to FIG. 2, a process for producing a high
`optical quality monolithic silica glass by casting begins by
`preparing a solution of TEOS in ethanol and then partially
`hydrolyzing the solution with water as seen in Step 20. The
`solution subject to mixing typically will contain about 45%
`by volume TEOS, 45% by volume ethanol, and 10% by
`volume water which if desired may include approximately
`1% by volumeof a suitable acid such as HCI to lower the pH
`of the finished glass product so as to increase its durability.
`Theratios of TEOS, ethanol, and water can be varied so long
`as the relative ratios of all three of these components are
`retained in the portion of the triangular construction of FIG.
`2 that results in a castable solution.
`
`The solution is then mixed in Step 22 to increase its
`viscosity by the hydrolyzation of TEOSandthe evaporation
`of ethanol. This mixing preferably takes place at room
`temperature and usually continues for 30-120 minutes with
`a 60 minute or one hour mixing period being the preferred
`minimum period to obtain a preferred viscosity of approxi-
`mately 100 Cts. The process can be accelerated by mixing at
`higher temperatures (up to about 70° C.) to increase the rate
`of ethanol evaporation or can be decelerated by mixing at
`lower temperatures (down to about 0° C.) to decrease the
`rate of ethanol evaporation.
`
`10
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`15
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`20
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`25
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`30
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`8
`Next, the viscous solution formed by the mixing step is
`cast in a suitable casting mold in Step 24. The cast solution
`then undergoes a gelling/aging process in Step 26 charac-
`terized by transition of the viscous solution to a gelatinous
`phase followed by transition of the gel to a porous glass
`phase. For monoliths, this process typically takes about 2 to
`4 weeks (and sometimes longer) depending upon the initial
`viscosity of the solution,
`the volume of solution in the
`casting mold, and the environmental conditions under which
`the process occurs. High quality glass can be obtained most
`assuredly by aging under conditions of controlled tempera-
`ture and humidity. The aging process terminates with a
`baking operation in which the glass is heated in the mold at
`a relatively low temperature (preferably on the order of
`about 70° C. to 120° C.) for a sufficient period of time to
`harden the glass sufficiently to permit its removal from the
`mold and subsequent handling. The length of the baking
`period varies from application to application, ranging from
`as little as a few hours to as long as two days.
`A true monolithic glass material is formed during the
`aging process. However,
`this glass is very porous and
`relatively brittle. The glass preferably is heat treated in Step
`28 to consolidate the glass (i.e., to collapse the pores into a
`solid glass structure) by sintering and thereby to increaseits
`rigidity and durability. The typical heat treatment process
`lasts about 24-48 hours in a cycle in which the temperature
`ramps upward from about 25° C. to about 1000° C. to about
`1050° C. at a rate of 0.1° C. per minute (with the temperature
`being held at plateaus for periods of about 2 hours at
`increments of about 100° C.), and then ramps back down
`again.
`The result of the process of FIG. 2 is a high quality silica
`glass monolith with high durability and other beneficial
`qualities discussed above in conjunctio