Abstract:
Systems and methods for embedding optical elements in an optical device are described. A method includes: providing a resin layer with a replica surface topography; cutting the resin layer to form an optical element layer that includes the replica surface topography; coating the replica surface topography with a layer; providing a substrate having a substrate refractive index; and connecting the layer to the substrate with an index matching material having a matching refractive index that is substantially equal to the substrate refractive index. The systems and methods provide advantages in that surface topography is replicated with enhanced overall cost effectiveness.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to the field of making laminated components. More particularly, the present invention relates to a method of making laminated optical components having embedded optical elements. Specifically, a preferred embodiment of the present invention relates to a method of making the collimating backlight of a liquid crystal display system by replicating a plurality of optical elements in a layer of material and then laminating the replication side of the layer to a substrate with an index of refraction matching material, thereby embedding the optical elements within the collimating backlight. The present invention thus relates to a method of making optical components of the type that can be termed lamination embedding. 
     2. Discussion of the Related Art 
     Within this application several publications are referenced by arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art. 
     Historically, it was known in the prior art to replicate structural features in various polymeric materials.sup.(1). As is known to those skilled in the art, a master topography can be machined into a material, such as, for example aluminum or copper. Replicas can then be made from the master by pressing the master topography into a polymeric material. In the past, this replication process has been inefficient because the replicas were made individually. Thus, a previously recognized problem has been that large amounts of time are consumed in making a large number of replicas, resulting in a high per unit cost which did not decrease as the number of replicas made increased. 
     Needless to say, it is desirable to provide a method of mass producing replicas with higher efficiency. However, merely enhancing the efficiency of the replication step without considering any attendant increase in overall costs is not an adequate solution because the way in which the replication step is improved may involve more time, expense and/or energy than is saved due to improvements in the replication step. 
     For example, one unsatisfactory previous approach involves machining the master topography into an outer surface of a cylindrical unitary metal drum. The use of such a unitary metal drum might permit the replicas to be made continuously, thereby enhancing efficiency and quality. However, a disadvantage of this previously recognized approach is that such a metal drum is a single purpose tool. When there is no longer any demand for a particular replica, the metal drum cannot be adapted for another use because the master topography is an integral part of the drum itself. 
     Moreover, this previously recognized solution also has the significant disadvantage of high initial cost. The cost of machining the metal drum can easily be more than the savings incurred from the use of a continuous replication step, especially where a moderate number of replicas will be made, or where the replication features to be machined into the surface of the drum are numerous and/or very small. From a business point of view, the decision of whether or not to invest in such a unitary metal drum can be problematic where the individual orders in-hand for a particular type of replica do not justify the cost of machining a unitary metal drum. Therefore, what is needed is a method that replicates a surface topography with enhanced overall cost effectiveness, where the number of replicas to be made is, at best, uncertain. 
     The manufacture and sale of replicas is a competitive business. A preferred solution will be seen by the end-user as being cost effective. A solution is cost effective when it is seen by the end-user as compelling when compared with other potential uses that the end-user could make of limited resources. 
     Liquid crystal displays of the type hereunder consideration, sometimes called LCDs, are well-known to those skilled in the art.sup.(2,3). An LCD can be illuminated from the back so that the LCD can be viewed under conditions of low ambient lighting. For example, a backlight that includes one or more fluorescent light bulbs can be located behind the LCD. 
     A previously recognized problem has been that the light from the backlight must be polarized in order for the LCD to function properly. One approach, in an attempt to solve this polarization problem, involves providing a polarizing sheet between the backlight and the LCD. However, a major disadvantage of this approach is that a large amount of the available light from the backlight is not transmitted through the polarizing sheet, thereby resulting in decreased brightness. 
     To address the decreased brightness disadvantage discussed above, one approach has been to provide a plurality of optical elements in the bottom surface of the backlight. The purpose of these optical elements is to condition the light from the backlight before it reaches the polarizing sheet. By providing these optical elements, less power is lost when the collimated light passes through the polarizing sheet and the brightness of the LCD is enhanced. 
     However, this approach has the significant disadvantage of relatively high cost. Specifically, the cost of providing the optical elements on the bottom surface of the backlight is too high. For example, injection molding such a backlight requires expensive tooling and several minutes of production time for each molding. Further, the cost of tooling is even higher where a large number of optical elements are to be formed on each backlight or where the size of each of the optical elements is small. Therefore, what is also needed is a method of mass producing optical elements in an LCD backlight with enhanced overall cost effectiveness. Heretofore the above-discussed requirements have not been fully met. 
     The below-referenced U.S. patents disclose embodiments that were at least in-part satisfactory for the purposes for which they were intended. The disclosures of all the below-referenced prior United States patents in their entireties are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art. 
     U.S. Pat. No. 5,396,350 discloses a backlighting apparatus employing an array of microprisms. U.S. Pat. No. 5,390,276 discloses a backlighting assembly utilizing microprisms. U.S. Pat. No. 5,371,618 discloses a color liquid crystal display employing dual cells. U.S. Pat. No. 5,359,691 discloses a backlighting system with a multi-reflection light injection system. U.S. Pat. No. 5,056,892 discloses a totally internally reflecting thin flexible film. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     By way of summary, an effect of the present invention is to make the collimating backlight of a liquid crystal display system by replicating a plurality of optical elements in a layer of material and then laminating the replication side of the layer of material to a substrate with an index of refraction matching material, thereby embedding the optical elements within the collimating backlight. The replication side can be coated with a reflective layer before lamination. 
     A primary object of the invention is to provide an apparatus for producing replicas of a surface topography with enhanced overall cost effectiveness. It is another object of the invention is to provide an apparatus that is rugged and reliable, thereby decreasing down time and operating costs. It is yet another object of the invention to provide an apparatus that has one or more of the characteristics discussed above but which is relatively simple to operate using a minimum of equipment and relatively simple to setup and operate using relatively low skilled workers. 
     In accordance with a first aspect of the invention, these objects are achieved by providing an apparatus comprising: a carrier sheet; a source of a resin; a coater for coating said carrier sheet with said resin; and a drum for replicating a topography in said resin. In one embodiment, said drum includes a plurality of submasters, each of said plurality of submaster having said topography. 
     Another object of the invention is to provide a method of producing replicas of optical elements that are to be embedded in an optical component. Another object of the invention is to provide a method that is predictable and reproducible, thereby decreasing variance and operating costs. It is yet another object of the invention to provide a method that has one or more of the characteristics discussed above but which is relatively simple to practice using relatively low skilled workers. 
     In accordance with a second aspect of the invention, these objects are achieved by providing a method comprising: providing a master surface topography with a plurality of optical elements; providing a plurality of submaster blanks, each of said plurality of submaster blanks having a) a first submaster surface and b) a second submaster surface; pressing said master surface topography against said first submaster surface of each of said plurality of submaster blanks; replicating said master surface topography in said first submaster surface of each of said plurality of submaster blanks as a submaster surface topography; providing a drum with an external surface; connecting said second submaster surface of each of said plurality of said submaster blanks to said external surface of said drum; providing a resin layer having a) a viscosity, b) a first resin surface and c) a second resin surface; 1) pressing said first submaster surface of one of said plurality of submaster blanks against said first resin surface; 2) replicating said submaster surface topography of said one of said plurality of submaster blanks in said first resin surface of said resin layer as a replica surface topography, said replica surface topography including replicas of said plurality of optical elements; 3) releasing said first submaster surface of said one of said plurality of submaster blanks from said first resin surface; increasing said viscosity of said resin layer; cutting said resin layer to form an optical element layer that includes said replica surface topography; coating said replica surface topography with a layer; providing a substrate having a substrate refractive index; and connecting said layer to said substrate with an index matching material having a matching refractive index that is substantially equal to said substrate refractive index. One embodiment of the invention further comprises repeating continuously steps 1), 2) and 3). 
     These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A clear conception of the advantages and features constituting the present invention, and of the construction and operation of typical mechanisms provided with the present invention, will become more readily apparent by referring to the exemplary, and therefore nonlimiting, embodiments illustrated in the drawings accompanying and forming a part of this specification, wherein like reference numerals designate the same elements in the several views, and in which: 
     FIGS. 1A-1F illustrate a schematic sequence of method steps according to the present invention; 
     FIG. 2 illustrates a schematic elevational view of an apparatus for carrying out a method according to the present invention; 
     FIG. 3 illustrates a schematic elevation view of a first embodiment of a drum according to the present invention; and 
     FIG. 4 illustrates a schematic elevation view of a second embodiment of a drum according to the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention and the various features and advantageous details thereof are explained more fully with reference to the nonlimiting embodiments described in detail in the following description. 
     1. System Overview 
     The above-mentioned requirements are mutually contradicting and cannot be satisfied simultaneously in the case of a machined cylindrical unitary metal drum. However, it is rendered possible to simultaneously satisfy these requirements to a certain extent by employing a drum that includes a plurality of submasters in consideration of the fact that the submasters can themselves be replicas. 
     2. Detailed Description of Preferred Embodiments 
     Referring to the drawings, especially FIGS. 2-4, it can be seen that a surface topography can be replicated on a continuous basis using a drum that includes a plurality of submasters. Pursuant to the present invention, complex surface topographies that include a large number of very small features can be efficiently replicated and then embedded within an optical element. 
     Referring to FIG. 1A, submaster 10 includes a surface topography that defines a plurality of optical elements 20. Although submaster 10 can be metal, or an electrodeless plated replication, submaster 10 does not need to include any metal and can be made of any material that is capable of holding and transferring the surface topography, such as, for example, polymethylmethacrylate (PMMA). 
     Resin layer 30 is located near but not initially touching submaster 10. Resin layer 30 can be any material capable of being impressed with the surface topography, and, with or without subsequent processing, holding the surface topography. For example, in an extrusion replication process, resin layer 30 can be a polycarbonate thermoplastic that is coated on carrier 35 as a continuous film. Carrier 35 can be a film of polyester or polycarbonate and can be any thickness. Resin layer 30 is chilled after the surface topography is transferred. Alternatively, in a printing replication process, resin layer 30 can be a polymethylmethacrylate that is coated on carrier 35 as a continuous film and then cured by exposure to ultraviolet radiation after the surface topography is transferred and before the submaster 10 is removed from resin layer 30. 
     It should be noted that the surface topography is represented in FIG. 1A as a periodic series of isosceles triangular prisms for improved clarity. Although the preferred embodiment shown in FIG. 1A includes the periodic series of isosceles triangular prisms, it is within the level of ordinary skill in the art after having knowledge of the invention disclosed herein to substitute any other type of surface topography. The depth of the surface topography can be any depth that can be stabilized in the resin layer, preferably from approximately 0.2 μm to approximately 200 μm, more preferably from approximately 1 μm to approximately 100 μm. The aspect ratio of individual features that optionally compose an optical element can be any aspect ratio that can be stabilized in the resin layer. The width ratio of adjacent individual features can be any width ratio that can be stabilized in the resin layer, preferably at least approximately 2. The width of the individual optical elements can be any width that can be stabilized in the resin layer, preferably at least approximately 0.1 μm, more preferably at least approximately 10 μm. The width of any bottom plateau that optionally composes an optical element can be any width that can be stabilized in the resin layer, preferably at least approximately 0.1 μm, more preferably at least approximately 10 μm. 
     While the individual features shown in FIG. 1A are the flat sides of isosceles prisms, the individual features can be curved. For example, the individual features can be convex with respect to the resin layer 30, thereby creating a concave replica feature. 
     Referring now to FIG. 1B, the next step in the sequence of procedures is to contact resin layer 30 with submaster 10. When submaster 10 is in full contact with resin layer 30, the plurality of optical elements 20 is expressed in resin 30 as a replica. Submaster 10 should be in contact with resin 30 for a period of time sufficient to transfer the surface topography. Assuming that resin layer 30 includes a thermoplastic, it can be advantageous to cool resin layer 30 while it is in contact with submaster 10 to stabilize the surface topography. Similarly, assuming that resin layer 30 includes an ultraviolet curing polymer, it can be advantageous to expose resin layer 30 to UV radiation while it is in contact with submaster 10 to stabilize the surface topography. 
     Referring now to FIG. 1C, the next step in the sequence of procedures is to separate submaster 10 from resin layer 30 so as to obtain the release of the submaster surface topography from the replicated surface topography. After the release, resin layer 30 can be cooled and/or cured to stabilize the surface topography. 
     Referring now to FIG. 1D, the next step in the sequence of procedures is to coat the replica surface topography. Coating 40 can be a reflective, or merely refractive, coating. If coating 40 is a reflective coating, then it is preferred that coating 40 comprise at least one element selected from the group consisting of aluminum and silver. However, the reflective coating material can contain any components so long as the coating as a whole retains its reflective character. Coating 40 can be a chemical vapor deposited thin film or a sputtered thin film. 
     Referring now to FIG. 1E, the next step in the sequence of procedures is to deposit an index matching fluid 50 on top of coating 40. Index matching fluid 50 can be any material that is at least partially transmissive. For example, index matching fluid 50 can be an acrylic based epoxy for the purpose of providing clarity. Index matching fluid 50 can be a mixture of two or more components. It is preferred that the index matching fluid 50 be a UV curable fluid. 
     Referring now to FIG. 1F, the next step in the sequence of procedures is to contact index matching fluid 50 with substrate 60. Index matching fluid 50 is thereby sandwiched between substrate 60 and coating 40. It is preferred that if index matching fluid 50 is a UV curable composition, then the curing be delayed until after substrate 60 is in contact with index matching fluid 50. 
     Alternatively, the index matching fluid 50 can be coated on substrate 60. In this alternative embodiment, the index matching fluid would then be contacted with coating 40. The elements shown in FIGS. 1A-1F are not necessarily drawn to scale. 
     It can be seen from FIG. 1F that the effect of the invention is to replicate and embed a surface topography in an optical element. FIG. 1F demonstrates substantially improved results that are unexpected. Specifically, the result of transferring, coating and embedding demonstrates the unexpected advantageous result that when a surface topography is replicated and then coated with a reflective coating, a reflective topography can be accurately and precisely geometrically located with respect to the balance of an optical component or device, (i.e., substrate 60). Further, by embedding the coating, the reflective surface is unexpectedly advantageously efficiently optically coupled to the balance of the optical component or device. Furthermore, by embedding the coating, the reflective surface is protected. Therefore, this inventive choice of design provides energetic and economic efficiencies. 
     Referring now to FIG. 2, an apparatus for carrying out the method of the presently claimed invention is depicted. Supply of carrier 70 can be a large roll of sheet material. Carrier 80 is drawn from supply of carrier 70. Carrier 80 can be any suitable substrate that is capable of providing a sufficient backing for the replication process. For example, carrier 80 can be polyester, polycarbonate, polyvinylchloride, or even paper. 
     Coater 90 can be located near and above carrier 80. Coater 90 deposits a coating 100 on carrier 80. Coater 90 can be a tape casting unit with a doctor blade or any other device capable of depositing a suitable layer of coating 100. Coating can include a thermoplastic material and/or a photopolymerizable material. 
     As carrier 80 is drawn downstream, coating 100 is pressed against drum 110. Drum 110 includes a surface topography that is transferred to coating 100. Drum 110 can include a heater and/or a chiller so as to transfer thermal energy to or away from carrier 80 and coating 100. Drum 110 can be transparent and include an ultraviolet light source. 
     If coating 100 includes a photopolymerizable material, ultraviolet light source 140 is located near drum 110 and opposite coating 100 and carrier 80. Ultraviolet light source should be capable of causing coating 100 to cure, at least partially, while coating 100 is still in contact with the surface topography of drum 110. 
     If coating 100 includes a thermoplastic material, heater 105 is located near drum 110 and opposite coating 100 and carrier. Heater 105 should be capable of supplying sufficient thermal energy to coating 100 before coating 100 contacts drum 110 such that the viscosity of coating 100 is suitable for replication of the surface topography of drum 110. 
     As carrier 80 is drawn further downstream, coating 100 is released from, and pulled away from drum 110. The pressing processes can be described as rolling because carrier 80 carries coating 100 away from drum 110 so that coating 100 does not drag. Coating 100 and its carrier 80 emerges from drum 110 as a replicated structure 130. 
     Replicated structure 130 can then pass under device 141. Device 141 can be an ultraviolet light source, a chiller or analogous device depending on whether the replication process is one of UV cured printing or thermoplastic extrusion, respectively. Device 141 can be serially duplicated, or entirely omitted. As a given section of replicated structure 130 passes beneath device 141, the carrier 80 side of replicated structure 130 can simultaneously pass above device 151. Device 151 can be an ultraviolet light source, a chiller or analogous device depending on whether the replication process is one of UV cured printing or thermoplastic extrusion, respectively. The use of device 141 and/or device 151 can ensure that coating 100 is fully cured and/or improve the adhesion of coating 100 to carrier 80. 
     As carrier 80 is pulled further downstream, carrier 80 is run up and over traction roller 120. Although traction roller 120 is depicted in FIG. 2 as having the same diameter as drum 110, traction roller 120 can have any relative diameter. Traction roller 120 can include a heater and/or a chiller. Traction roller 120 can be transparent and include an ultraviolet light source. Although traction roller 120 is depicted in FIG. 2 as being positioned relative to drum 110 so as to pull replicated structure up and away from the centerline of drum 110, traction roller 120 can be located so at to pull replicated structure straight up, or even up and toward the centerline of drum 110. 
     The post rolling processing can be continued by passing replicated structure 130 beneath device 142. Device 142 can be the same type of device as device 141 or a different type of device, such as, for example, a surface conditioner for coating 100. Device 142 can be serially duplicated, or entirely omitted. As a given section of replicated structure 130 passes beneath device 142, the carrier 80 side of replicated structure 130 simultaneously passes above device 152. Device 152 can be the same type of device as device 151 or a different type of device, such as, for example, a delaminating structure for separating carrier 80 from coating 100. Of course, device 152 can be serially duplicated, or entirely omitted. 
     Replicated structure 130 then passes to subsequent processing assembly 160. Assembly 160 can include further viscosity changing devices 163. Assembly 160 can include a coating system 165 such as, for example, a chemical vapor deposition (CVD) reactor or a sputtering chamber for deposition of coating 40. Such a coating system can be a continuous differentially pumped coating system. Assembly 160 can include a dynamic shearing mechanism 167 that cuts replicated structure 130 perpendicular to its drawn axis, thereby slicing sheets of replicated structures 130. Assembly 160 can also include pick and place robots that move sheared segments of replicated structure 130 to different positions for addition of the index matching fluid 50. Assembly 160 can also include pick and place robots that join sheared segments of replicated structure 130 with substrate 60. (It should be noted that the assembly 160 is represented in FIG. 2 schematically for improved clarity.) Although the preferred embodiment shown in FIG. 2 includes the shearing mechanism, it is within the level of ordinary skill in the art after having knowledge of the invention disclosed herein to provide any type of post processing device as part of assembly 160. 
     Referring now to FIG. 3, a drum 210 with a plurality of submasters 220 is depicted. Drum 210 in FIG. 3 is analogous to drum 110 in FIG. 2. A plurality of submasters 220 can be attached to the exterior surface of drum 210 with a pressure sensitive adhesive. Drum 210 can be transparent and an ultraviolet light source can be located therein. (It should be noted that the submasters 220 represented in FIG. 3 as twelve relatively short thick strips are not drawn to scale and are depicted schematically for improved clarity.) Although the preferred embodiment shown in FIG. 3 includes twelve submasters, it is within the level of ordinary skill in the art after having knowledge of the invention disclosed herein to attach any number of submasters to the exterior surface of drum 210. 
     Referring now to FIG. 4, a drum 310 is shown with its surface topography provided directly on the exterior surface thereof. Drum 310 in FIG. 4 is analogous to drum 210 in FIG. 3 and drum 110 in FIG. 2. Drum 310 can be made of any transparent material, such as, for example, polymethylmethacrylate (i.e., PLEXIGLASS™). An ultraviolet light source 320 is shown located within the interior of drum 310. Ultraviolet light source 320 can be located angularly with respect to the axis of drum 310 so as to provide ultraviolet radiation to a portion or all of the exterior surface of drum 310. (It should be noted that the ultraviolet light source is represented in FIG. 4 as a schematic for improved clarity.) Although the preferred embodiment shown in FIG. 4 includes an ultraviolet light source that directs ultraviolet light toward and through the drum 310 directly after the rolling operation, along an arc of the drum beginning at approximately π radian and ending at approximately 2π/3 radian, it is within the level of ordinary skill in the art after having knowledge of the invention disclosed herein to provide any type of light source directing any type of light toward and through any portion, or all, of the drum 310. 
     While not being limited to any particular theory, it is believed that the replicated topography changes during the removal of the submaster from the resin. This relationship may be due to adhesion and/or surface tension on the resin. For example, replicated features of a concave nature are believed to change into features that are more nearly flat (or convex). By using an ultraviolet curing resin together with a drum that is transparent in the ultraviolet spectrum, the interior of which is equipped with an ultraviolet light source, it is believed that the topography of the resin can be stabilized before and/or shortly after the submaster topography is removed from the resin. 
     Such a transparent drum can have the master topography directly replicated in its exterior surface. Alternatively, such a transparent drum can include a plurality of transparent submasters. 
     The disclosed embodiments show a drum as the structure for performing the function of transferring the surface topography, but the structure for transferring the surface topography can be any other structure capable of performing the function of transferring the topography, including, by way of example a continuous belt, a disc or even a torus. 
     The particular manufacturing process used for replicating the surface topography should be reliable and predictable. Conveniently, the replication of the present invention can be carried out by using any impressing method. It is preferred that the process be pressing. For the manufacturing operation, it is moreover an advantage to employ a rolling method. 
     However, the particular manufacturing process is not essential to the present invention as long as it provides the described transformation. Normally the manufacturers of this product will select the manufacturing process as a matter of design choice based upon tooling and energy requirements, in view of the expected application requirements of the final product and the demands of the overall manufacturing process. 
     The particular material used for the resin layer should be capable of stabilizing a high resolution surface topography. Conveniently, the resin layer of the present invention can be made of any plastic material. It is preferred that the material be an ultraviolet curing polymer resin. For the manufacturing operation, it is moreover an advantage to employ a polymethylmethacrylate material. 
     However, the particular material selected is not essential to the present invention, so long as it provides the described function. Normally, the manufacturers of this product will select the best commercially available material as a matter of design choice based upon the economics of cost and availability, in view of the expected application requirements of the final product and the demands of the overall manufacturing process. 
     Preferred embodiments of the present invention can be identified one at a time by testing for the presence of accurate and precise replication. The test for the presence of accurate and precise replication can be carried out without undue experimentation by the use of simple and conventional profile metering instrumentation. Among the other ways in which to seek embodiments having the attribute of accurate and precise replication, guidance toward the next preferred embodiment can be based on the presence of easy, clean and complete submaster release. 
     A practical application of the present invention which has value within the technological arts is transferring a surface topography, such as, for example, a collimating array of microprisms, a surface diffuser, or even a diffraction grating. Further, all the disclosed embodiments of the present invention are useful in conjunction with transferring surface topography patterns such as are used for the purpose of decoration, or the like. There are virtually innumerable uses for the present invention described herein, all of which need not be detailed here. 
     The present invention described herein provides substantially improved results that are unexpected. The present invention described herein can be practiced without undue experimentation. The entirety of everything cited above or below is hereby expressly incorporated by reference. 
     Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the features of the present invention may be made without deviating from the spirit and scope of the underlying inventive concept. 
     For example, the process could be enhanced by providing a multi-layer resin layer. Similarly, although a supply roll of carrier material is preferred, any supply of carrier material could be used in its place. In addition, the individual components need not be fabricated from the disclosed materials, but could be fabricated from virtually any suitable materials. 
     Moreover, the individual components need not be formed in the disclosed shapes, or assembled in the disclosed configuration, but could be provided in virtually any shape, and assembled in virtually any configuration, which replicate a surface topography so as to provide a useful product. Further, although the assembly shown in FIG. 1F is described herein as physically separate module, it will be manifest that the assembly may be integrated into the apparatus with which it is associated. Furthermore, all the disclosed features of each disclosed embodiment can be combined with, or substituted for, the disclosed features of every other disclosed embodiment except where such features are mutually exclusive. 
     It is intended that the appended claims cover all such additions, modifications and rearrangements. Expedient embodiments of the present invention are differentiated by the appended subclaims. 
     REFERENCES 
     1. Joel R. Fried, Polymer Science and Technology, Prentice Hall PTR, (1995). 
     2. Bahaa E. A. Saleh &amp; Malvin C. Teich, Fundamentals of Photonics, John Wiley &amp; Sons, (1991). 
     3. Handbook of Optics, 2nd ed., Vols. I-II, McGraw Hill, (Michael Bass et al. eds., 1995). 
     4. Van Nostrand&#39;s Scientific Encyclopedia, 8th ed., Van Nostrand Reinhold, (Douglas M. Considine et al. eds., 1995).