Abstract:
Provided is an optical backplane interconnect system, one embodiment of which features transceiver subsystems employing holographic optical elements (HOEs) that define, and discriminate between, differing optical channels of communication. The HOEs employ a holograph transform to concurrently refract and filter optical energy to remove optical energy having unwanted characteristics. To that end, the transceiver subsystem is mounted to an expansion card and includes a source of optical energy and an optical detector. The HOE need not be mounted to the expansion card. In one embodiment, however, the HOE is mounted to the expansion card and in optical communication with either the source of optical energy, the optical detector or both.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     The present patent, application claims priority from U.S. Provisional patent application No. 60/261,042 filed Jan. 11, 2001 entitled COMPUTER BACKPLANE EMPLOYING FREE SPACE OPTICAL INTERCONNECT and listing Robert Mays, Jr. as inventor, which is incorporated herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an optical free space interconnect of circuitry. Particularly, the present invention concerns optical interconnection employed in computers. 
     Expansion slots greatly increase operational characteristics of personal computers (PCs). The expansion slots are connected to various PC circuitry, such as a microprocessor, through a bus and allow the PC to communicate with peripheral devices, such as modems, digital cameras, tape drives and the like. To that end, electrical interface circuitry, referred to as adapters or expansion cards, are inserted in the expansion slots to facilitate communication between the PC circuitry and the peripheral devices. The combination of expansion slots, expansion cards and bus system is commonly referred to as a backplane interconnect system. The bus system associated with the backplane interconnect system connects power, data and control lines to the expansion cards and facilitates communication between the expansion cards and other PC circuitry. The bus system cooperates with a protocol to, among other things, prevent two or more expansions cards from concurrently communicating on a common bus line. 
     Referring to FIG. 1, an example of a prior art backplane interconnect system  10  includes expansion slots  12  mounted on a motherboard  14 . The expansion slots  12  are wired together with one or more busses  16  disposed on the motherboard  14 . Each bus  16  normally has multiple lines with terminations  18  at opposing ends of each line. The expansion card  22  has a mating connector  20  that is adapted to be received into the expansion slot  12 . Each expansion card  22  may contain numerous circuits and components  24  to perform desired functions. The circuits and components  24  are in electrical communication with conductive traces  26  on the mating connector  20  through bus transceivers  28 . Bus transceivers  28  facilitate communication between components  24  of the various expansion cards  22  in backplane interconnect system  10  by driving and detecting signals on the bus lines  16 . 
     As the operational speed of PCs increases, the need to increase the data transfer rate over the backplane interconnect system becomes manifest. Conventionally, increases in data transfer rate have been achieved by either increasing the operational frequency of the individual expansion boards or by increasing the number of lines associated with a bus. Increases in data transfer rates of backplane interconnect systems have been inhibited by crosstalk, noise, degradation in signal integrity and the operational limitations of connectors. One attempt to increase the data transfer rates of a backplane interconnect system has been directed to controlling the impedance associated with the bus lines, as discussed in U.S. Pat. No. 6,081,430 to La Rue. However, it has been recognized that optical backplanes have been successful in increasing the data transfer rates of backplane interconnect systems. 
     U.S. Pat. No. 6,055,099 to Webb discloses an optical backplane having an array of lasers in optical communication with a lens relay system. The lens relay includes a series of coaxially aligned lenses. The lenses are spaced apart along a planar substrate and form repeated images of an optical array at the input to an interconnect. Output ports are located at different points along the interconnect. Each pair of lenses encloses one of the repeated images and is formed as a single physically integral member. The integral member may take the form of a transparent rod having spherical end surfaces. Each of the spherical end surfaces then provided one of the pair of lenses. 
     U.S. Pat. No. 5,832,147 to Yeh et al. discloses an optical backplane interconnect system employing holographic optical elements (HOEs). The backplane interconnect system facilitates communication with a plurality of circuit boards (CBs) and a plurality of integrated circuit chips. Each CB has at least an optically transparent substrate (OTS) mate parallel to the CB and extending outside a CB holder. On another OTS mate, two HOEs are utilized to receive and direct, at least part of, a light beam received to a detector on a corresponding CB via free space within the circuit board holder or reflection within the OTS mate. A drawback with the prior art optical backplane interconnect system is that the number of optical channels that may be provided is limited due to the difficulty in achieving discrimination between optical free space signals. 
     What is needed, therefore, is an optical backplane interconnect system that increases the number of optical channels while avoiding crosstalk in optical signals propagating along the optical channels. 
     SUMMARY OF THE INVENTION 
     Provided is an optical backplane interconnect system, one embodiment of which features transceiver subsystems employing holographic optical elements (HOEs) that define, and discriminate between, differing optical channels of communication. The HOEs employ a holograph transform to concurrently refract and filter optical energy having unwanted characteristics. To that end, the transceiver subsystem is mounted to an expansion card and includes a source of optical energy and an optical detector. The HOE need not be mounted to the expansion card. In one embodiment, however, the HOE is mounted to the expansion card and in optical communication with either the source of optical energy, the optical detector or both. 
     The expansion card is in optical communication with an additional expansion card associated with the interconnect system that also includes the transceiver subsystem and HOE discussed above. The source of optical energy is positioned so that the optical detector associated with the additional expansion card senses the optical energy produced by the source, defining a first source/detector pair. A first HOE is disposed between the source and the detector of the first source/detector pair. A second HOE is disposed between a second source/detector pair that includes the optical detector of the expansion card positioned to sense optical energy produced by the optical source of the additional expansion card. The first and second HOEs are formed to limit the optical energy passing therethrough, attenuating all optical energy that impinges thereupon and having unwanted characteristics. In this example, optical energy of the type that is attenuated by the first HOE may propagate through the second HOE, and optical energy of the type attenuated by the second HOE may propagate through the first HOE. In this manner, the first and second HOEs may define differing optical channels by selectively allowing optical energy to pass therethrough. To that end, the first HOE is placed in close proximity with the optical detector of the additional expansion card, and the second HOE is placed in close proximity to the optical detector of the expansion card. Each of the two aforementioned optical detectors would sense only optical energy having desired characteristics. Hence, two discrete optical channels are defined, each of which may be in communication with one or both of the two sources of optical energy. 
     In another exemplary embodiment, each of the aforementioned optical channels may be uniquely associated with one of the optical detectors and one of the sources of optical energy. To that end, two or more pairs of HOEs are employed. Each HOE of one of the two pairs is associated with a source/detector pair and has holographic transforms that is substantially similar, if not identical, to the holographic transform associated with the remaining HOE of the pair. However, the holographic transform associated with one of the pairs of HOEs differs from the holographic transform associated with the remaining pair of HOEs. In this manner, two optical channels may be defined with crosstalk between the channels being substantially reduced, if not eliminated. With this configuration, the number of optical channels may be increased so that hundreds of optical channels may facilitate communication between two expansion cards, with some of the optical channels being redundant to increase the operational life of the optical backplane interconnect system. These and other embodiments are described more fully below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a backplane interconnect system in accordance with the prior art; 
     FIG. 2 is a simplified plan view of a computer system employing an optical backplane interconnect system in accordance with the present invention; 
     FIG. 3 is a simplified plan view of a source of optical energy mounted to a first expansion card and optical detector mounted to a second expansion card spaced apart from the first expansion card; 
     FIG. 4 is a cross-sectional view of a lens employed in the backplane interconnect system shown above in FIG. 2, in accordance with the present invention; 
     FIG. 5 is a cross-sectional view of the lens shown above in FIG. 4 in accordance with an alternate emb the present invention; 
     FIG. 6 is a cross-sectional view of the lens shown above in FIG. 4 in accordance with a second alternate embodiment of the present invention; 
     FIGS. 7A-7B are perspective views of an optical communication system employed in the backplane interconnect system shown above in FIG. 2, in accordance with an alternate embodiment; 
     FIG. 8 is perspective view of an array of the lenses fabricated on a photo-sheet shown above in FIGS. 7A-7B, 
     FIG. 9 is a cross-sectional plan view of the optical communication system shown above in FIGS. 7A-7B, in accordance with the present invention; 
     FIG. 10 is a cross-sectional plan view of the optical communication system shown above in FIG. 9, in accordance with an alternate embodiment of the present invention; 
     FIG. 11 is a simplified plan view showing an apparatus for fabricating the lenses shown above in FIGS. 4-6 and  8 , in accordance with the present invention; 
     FIG. 12 is a cross-sectional view of a substrate on which the lenses discussed above with respect to FIGS. 4-6 and  8  are fabricated; 
     FIG. 13 is a cross-sectional view of the substrate, shown above in FIG. 12, under going processing showing a photoresist layer disposed thereon; 
     FIG. 14 is a cross-sectional view of the substrate, shown above in FIG. 13, under going processing showing a photoresist layer being patterned; 
     FIG. 15 is cross-sectional view of the substrate, shown above in FIG. 14, under going processing after a first etch step; and 
     FIG. 16 is a cross-sectional view of the substrate, shown above in FIG. 15, under going processing after a second etch step. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, shown is an exemplary computer system  30 , such as a personal computer that includes a power supply  32 , a processor  34 , input/output device controller and associated memory (I/O controller)  36 , main memory  38 , expansion slots  40  and expansion cards  40   a,    40   b,    40   c  and  40   d.  The expansion slots  40  are in electrical communication with the power supply  32  over a power bus  42 . The power bus  42  includes multiple lines, each of which is dedicated to carrying a single voltage level. A main system data bus  44  is in data communication with processor  34 , expansion slots  40  and main memory  38 . Main data bus  44  includes eight to sixty-four different lines, depending upon the data transfer protocol supported by the system  30 , e.g., ISA, EISA, or MCA protocols and the like. Main data bus  44  carries data transferred between processor  34 , main memory  38  and expansion slots  40 . An address bus  46  comprising, for example, twenty lines is in data communication with main memory  38 , processor  34  and expansion slots  40 . Address bus  46  carries information that specifies the address from, or to, data that is to be moved. To facilitate data transfers, a control bus  48  is included that has a plurality of lines placing main memory  38  and expansion slots  40  in data communication with I/O controller  36 . 
     Referring to both FIGS. 2 and 3, as mentioned above, each of the expansion slots  40  is adapted to receive an expansion card  40   a,    40   b,    40   c  and  40   d.  One or more optical channels facilitate communication between two or more of the expansion cards  40   a,    40   b,    40   c  and  40   d.  One optical channel includes one or more sources of optical energy  48   a  mounted to expansion card  40   a,  and one or more optical detectors  50   a  mounted to expansion card  40   b  and in data communication with the source of optical energy  48   a.  A HOE  52   a  is disposed between the source of optical energy  48   a  and the detector  50   a.  A second optical channel includes one or more sources of optical energy  48   b  mounted to expansion card  40   b,  and one or more optical detectors  50   b  mounted to expansion card  40   a  and in data communication with the source of optical energy  48   b.  A HOE  52   b  is disposed between the source of optical energy  48   b  and the detector  50   b.    
     Source of optical energy  48   a  directs optical energy  54   a  along a path  56   a  in which the detector  50   a  lies. The HOE  52   a  is disposed in the optical path  56   a.  Source of optical energy  48   b  directs optical energy  54   b  along a path  56   b  in which the detector  50   b  lies. The HOE  52   b  is disposed in the optical path  56   b.  Each of the HOEs  52   a  and  52   b  has both a refractory function and a holographic transform function enabling the HOEs  52   a  and  52   b  to concurrently filter and refract the optical energy propagating therethrough. In this manner, the HOEs  52   a  and  52   b  filter the optical energy  54   a  and  54   b,  respectively so that the optical energy passing therethrough to impinge upon the optical detectors  50   a  and  50   b,  respectively, have desired characteristics. 
     HOE  52   a  and  52   b  are identical in construction and, therefore, only HOE  52   a  will be discussed, but it should be borne in mind that the discussion with respect to HOE  52   a  applies with equal weight to HOE  52   b.  HOE  52   a  is a refractory lens having a bulk hologram recorded therein that defines a holographic transform function. The bulk hologram facilitates characterizing the optical energy  54   a  to have desired characteristics that may improve detection, by the optical detector  50   a,  of information contained in the optical energy  54   a.  For example, the transform function may allow a specific wavelength to pass through the lens, diffracting all other wavelengths to deflect away from the optical detector  50   a.  Alternatively, the transform function may allow only a certain polarization of the optical energy  54   a  to propagate therethrough, diffracting all other polarizations away from the optical detector  50   a.    
     The refractory function of the HOE  52   a  facilitates impingement of the optical energy  54   a  onto the optical detector  50   a.  In this manner, the precise alignment of the optical detector  50   a  with respect to the source  48   a  and, therefore, the path  56   a  may be relaxed. This is beneficial when facilitating communication between expansion cards, such as  40   a  and  40   b,  because the mechanical coupling of the expansion cards  40   a  and  40   b  to the respective slots  40  would typically make difficult precisely aligning source  48   a  with the detector  50   a.    
     Referring to FIG. 4, the HOE  52   a  is a lens  58  having an arcuate surface  60 , e.g., cylindrical, spherical and the like with a bulk holographic transform function formed therein. The bulk holographic transform function is shown graphically as periodic lines  62  for simplicity. The bulk holographic transform function  62  is recorded in substantially the entire volume of the lens  58  through which optical energy will propagate. The transform function  62  is a periodic arrangement of the space-charge field of the material from which the lens  58  is fabricated. To that end, the lens  58  may be formed from any suitable photo-responsive material, such as silver halide or other photopolymers. In this manner, the lens  58  and the bulk holographic transform function  62  are integrally formed in a manner described more fully below. Although the surface  64  of the lens  58  disposed opposite to the spherical arcuate surface  60  is shown as being planar, the surface  64  may also be arcuate as shown in surface  164  of lens  158  in FIG.  5 . 
     Referring to both FIGS. 4 and 5, were it desired to further control the shape of optical energy propagating through lens  58 , a Fresnel lens  258  may be formed opposite to the spherical surface  260 . To that end, the Fresnel lens  258  includes a plurality of concentric grooves, shown as recesses  258   a,    258   b  and  258   c  that are radially symmetrically disposed about a common axis  256 . Thus, the lens  258  may have three optical functions integrally formed in a common element, when providing the bulk holographic transform function  262  therein, which facilitates creation of well defined optical channels between expansion cards  40   a  and  40   b  shown in FIG.  3 . 
     In FIG. 2, facilitating communication between expansion cards  40   a  and  40   b  over optical channels increase the bandwidth of the computer system  30 &#39;s bus systems. Specifically, the transfer of power and data between the expansion cards  40   a  and  40   b  and the computer system  30  is bifurcated. The power to the expansion cards  40   a  and  40   b  is transferred over power bus  42  and the data transfer between two or more expansion cards may be achieved over one or more optical channels. To that end, the expansion cards  40   a  and  40   b  are made backwards compatible with existing technology. This is shown by the implementation of standard expansion cards  40   c  and  40   d  along with expansion cards  40   a  and  40   b,  as well as the compatibility of expansion cards  40   a  and  40   b  with standard expansion slots  40 . The presence of the optical channels, however, reduces the need to transfer information between the expansion cards  40   a  and  40   b  over the main data bus  44 , as well as the need to transfer information over the address bus  46  or the control bus  48 , were appropriate control circuitry included on the expansion cards  40   a  and  40   b.  Thus, employing the optical channels as described above, the computer system  30  bus bandwidth may be increased. 
     Referring to FIGS.  2  and  7 A- 7 B, as mentioned above the expansion cards  40   a  and  40   b  may each include multiple sources of optical energy  48   a  and multiple detectors  50   a.  To that end provided are an array of sources of optical energy  348 , shown generally as optical emitters  348   a - 348   p,  and an array of optical detectors  350 , shown generally as optical receivers  350   a - 350   p.  The optical emitters  348   a - 348   p  generate optical energy to propagate along a plurality of axes, and the optical receivers  350   a - 350   p  are positioned to sense optical energy propagating along one of the plurality of optical axes. Specifically, the array  348  is an (X×Y) array of semiconductor lasers that produce a beam that may be modulated to contain information. The array  350  may comprise of virtually any optical receiver known, such a charged coupled devices (CCD) or charge injection detectors (CID). In the present example, the array  350  comprises of CIDs arranged in an (M×N) array of discrete elements. The optical beam from the each of the individual emitters  348   a - 348   p  may expand to impinge upon each of the receivers  350   a - 350   p  of the array  350  if desired. Alternatively, the optical beam from each of the individual emitters  348   a - 348   p  may be focused to impinge upon any subportion of the receivers  350   a - 350   p  of the array  350 . In this fashion, a beam sensed by one of the receivers  350   a - 350   p  of the array  350  may differ from the beam sensed upon the remaining receivers  350   a - 350   p  of the array  350 . To control the wavefront of the optical energy produced by the emitters  348   a - 348   p,  the HOE  52   a - 52   b,  discussed above with respect to FIGS. 3-6 may be employed as an array of the lenses, shown more clearly in FIG. 8 as array  400 . 
     Specifically, referring to FIGS. 7A-7B and  9 , the individual lenses  458  of the array are arranged to be at the same pitch and sizing of the array  348 . The numerical aperture of each of the lenses  458  of the array  400  is of sufficient size to collect substantially all of the optical energy produced by the emitters  348   a - 348   p  corresponding thereto. In one example, the array  400  is attached to the array  348  with each lens resting adjacent to one of the emitters  348   a - 348   p.  To provide the necessary functions, each of the lenses of the array  400  may be fabricated to include the features mentioned above in FIGS. 4-6. As a result, each of the lenses  458  of the array  400  may be formed to have functional characteristics that differ from the remaining lenses  458  of the array  400 . In this manner, each beam produced by the array  348  may be provided with a unique wavelength, polarization or both. This facilitates reducing cross-talk and improving signal-to-noise ratio in the optical communication system. 
     Specifically, an additional array of lenses  400   b  that match the pitch of the individual receivers  350   a - 350   p  of the array  350 , is shown more clearly in FIG.  10 . The lenses may be fabricated to provide the same features as discussed above with respect to array  400 , shown in FIG.  8 . 
     Referring to FIGS. 7A-7B,  8  and  10  each of the emitters  348   a - 348   p  of the array  348  would then be uniquely associated to communicate with only one of the receivers  350   a - 350   p  of the array  350 . In this manner, the emitter  348   a - 348   p  of the array  348  that is in data communication with one of the receivers  350   a - 350   p  of the array  350  would differ from the emitters  348   a - 348   p  in data communication with remaining receivers  350   a - 350   p  of the array  350 . This emitter/receiver pair that were in optical communication is achieved by having the properties of the lens  458   a  in array  400   a  match the properties of the lens  458   b  in array  400   b . It should be understood, however that one of the emitters  348   a - 348   p  may be in data communication with any number of the receivers  350   a - 350   p  by multiple lenses  458   b  matching the properties of one of the lenses  458   a . Similarly, one of the multiple emitters  348   a - 348   p  may be in optical communication with one or more of the receivers  350   a - 350   p  by appropriately matching the lenses  458   a  to the lenses  458   b.    
     In one example, superior performance was found by having the array  350  sectioned into (m×n) bins, with each bin corresponding to a particular polarization and/or wavelength that matched a particular polarization and/or wavelength corresponding to a emitter  348   a - 348   p . Thus, were a beam from one or more of the emitters  348   a - 348   p  to flood the entire (M×N) array  350  or multiple (m×n) bins, only the appropriate receivers  350   a - 350   p  sense information with a very high signal-to-noise ratio and discrimination capability. It will be noted that the (m×n) bins can also be effectively comprised of a single sensing pixel (element) to exactly match the (X×Y) array. 
     Additional beam-sensor discrimination may be achieved by employing emitters  348   a - 348   p  having different wavelengths or by incorporating up-conversion processes that include optical coatings applied to the individual emitters  348   a - 348   p  or made integral therewith. One such up-conversion process is described by F. E. Auzel in “Materials and Devices Using Double-Pumped Phosphors With Energy Transfer”, Proc. of IEEE, vol. 61. no. 6, June 1973. 
     Referring to FIGS. 3,  10  and  11 , the system  500  employed to fabricate the lens  58  and the lens arrays  400   a  and  400   b  includes a beam source  502  that directs a beam  504   a  into wave manipulation optics  506  such as a ¼ waveplate  508  so that the beam  504   b  is circularly polarized. The beam  504   b  impinges upon polarizer  510  so that the beam  504   c  propagating therethrough is linearly polarized. The beam  504   c  impinges upon a Faraday rotator  512  that changes birefringence properties to selectively filter unwanted polarizations from the beam  504   c . In this manner, the beam  504  degressing from the rotator  512  is linearly polarized. The beam  504   d  impinges upon a beam splitter  514  that directs a first subportion  504   e  of beam  504   d  onto a planar mirror  516 . A second subportion  504   f  of the beam  504   d  pass through the splitter  514 . The first and second subportions  504   e  and  504   f  intersect at region  520  forming an optical interference pattern that is unique in both time and space. A photosensitive sheet  558  is disposed in the region  520  so as to be exposed to the optical interference pattern. The interference pattern permeates the photosensitive sheet  558  and modulates the refractive index and charge distribution throughout the volume thereof. The modulation that is induced throughout the volume of the photosensitive sheet  558  is in strict accordance with the modulation properties of the first and second subportions  504   e  and  504   f . Depending upon the photosensitive material employed, the holographic transform function may be set via thermal baking. 
     Referring to FIGS. 11 and 12, an arcuate surface is formed in the photosensitive sheet  558  by adhering a photosensitive layer  600  to a sacrificial support  602 , such as glass, plastic and the like to form a photosensitive substrate  604 . Typically, the photosensitive layer  600  is tens of microns thick. As shown in FIG. 13, a photo resist layer  606  is deposited onto the photosensitive layer  600  and then is patterned to leave predetermined areas exposed, shown as  608  in FIG. 14, defining a patterned substrate  610 . Located between the exposed areas  608  are photo resist islands  612 . The patterned substrate  610  is exposed to a light source, such as ultraviolet light. This ultraviolet light darkens the volume of the photosensitive layer  600  that is coextensive with the exposed areas  608  being darkened, i.e., become opaque to optical energy. The volume of the photosensitive layer  600  that are coextensive with the photo resist islands  612  are not darkened by the ultraviolet light, i.e., remaining transparent to optical energy. Thereafter, the photo resist islands  612  are removed using standard etch techniques, leaving etched substrate  614 , shown in FIG.  15 . 
     The etched substrate  614  has two arcuate regions  616  that are located in areas of the photosensitive layer  600  disposed adjacent to the islands  612 , shown in FIG.  14 . The arcuate regions  616  of FIG. 15 result from the difference in exposure time to the etch process of the differing regions of the photosensitive layer  600 . 
     Referring to FIGS. 10 and 16, a subsequent etch process is performed to form array  400 . During this etch process the support is removed as well as nearly 50% of the photosensitive layer  600  to form a very thin array. The array  400  is then placed in the system  500 , shown in FIG. 11, and the bulk holographic transform functions are recorded in the arcuate regions  616  that define the lenses  458 , as discussed above. A Fresnel lens may also be formed on the lenses  458   a  and  458   b  of the array  400  using conventional semiconductor techniques. Thereafter, the lenses may be segmented from the photo resistive sheet or M×N subarrays of lenses may be segmented therefrom. 
     Lenses with differing transform functions are formed on differing photosensitive sheets  558 . Specifically, the transform function is defined by the interference pattern formed by the first and second subportions  504   e  and  504   f  intersecting at region  520 . This interference pattern is unique in both time and space. As a result, each of the lenses formed on the sheet  558  would have substantially identical holographic transform functions. To create lenses with differing transform functions, an additional photosensitive sheet  558  would be employed and, for example, the Faraday rotator  512  may be rotated to provide the lenses formed on the photosensitive sheet  558  with a holographic transform flnction that differs from the holographic transform function associated with the lenses formed on a previous photosensitive sheet  558 . Therefore, lenses  458   a  associated with the first array  458  would come from differing sheets  558  if the lenses were to have differing holographic transform functions. 
     Although the invention has been described in terms of specific embodiments, one skilled in the art will recognize that various changes to the invention may be performed, and are meant to be included herein. For example, instead of forming the arcuate regions  616 , shown in FIG,  15 , using standard etch techniques, the same may be formed by exposing the substrate  610 , shown in FIG. 14, to thermal energy. In one example, the substrate  610  is convectionally heated, and the photo resist layer  606  is patterned to control the regions of the photosensitive layer  600  that may expand. In another example, the photosensitive layer is heated by conduction employing laser ablation/shaping. Specifically, a laser beam impinges upon areas of the photosensitive layer  600  where lenses are to be formed. The thermal energy from the laser beam causes the photosensitive layer  600  to bubble, forming arcuate regions  616  thereon shown in FIG.  15 . Therefore, the scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof.