US20020089709A1

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Publication number: US20020089709A1
Application number: US09/884,459
Authority: US
Inventors: Robert Mays
Original assignee: R&DM FOUNDATION Inc
Current assignee: R&DM FOUNDATION Inc
Priority date: 2001-01-11
Filing date: 2001-06-19
Publication date: 2002-07-11
Anticipated expiration: 2021-06-19
Also published as: US6452700B1

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 cared. 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 entitled COMPUTER BACKPLANE EMPLOYING FREE SPACE OPTICAL INTERCONNECT and listing Robert Mays, Jr. as inventor, which is incorporated herein in its entirety.[0001]

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.[0002]

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.[0003]

Referring to FIG. 1, an example of a prior art[0004]

backplane interconnect system

10 includesexpansion slots12 mounted on amotherboard14. Theexpansion slots12 are wired together with one ormore busses16 disposed on themotherboard14. Eachbus16 normally has multiple lines withterminations18 at opposing ends of each line. The expansion card22 has amating connector20 that is adapted to be received into theexpansion slot12. Each expansion card22 may contain numerous circuits andcomponents24 to perform desired functions. The circuits andcomponents24 are in electrical communication withconductive traces26 on themating connector20 throughbus transceivers28.Bus transceivers28 facilitate communication betweencomponents24 of the various expansion cards22 inbackplane interconnect system10 by driving and detecting signals on thebus lines16.

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 has 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 backplanes interconnect systems has 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.[0005]

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.[0006]

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 systems 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.[0007]

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.[0008]

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.[0009]

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 an 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.[0010]

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 in 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.[0011]

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a backplane interconnect system in accordance with the prior art;[0012]

FIG. 2 is a simplified plan view of a computer system employing an optical backplane interconnect system in accordance with the present invention;[0013]

FIG. 3 is a simplified plan view of a source of optical energy mounted to a first expansion card and an optical detector mounted to a second expansion card spaced apart from the first expansion card;[0014]

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;[0015]

FIG. 5 is a cross-sectional view of the lens shown above in FIG. 4 in accordance with an alternate embodiment of the present invention;[0016]

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;[0017]

FIG. 7 is perspective view of an optical communication system employed in the backplane interconnect system shown above in FIG. 2, in accordance with an alternate embodiment;[0018]

FIG. 8 is perspective view of an array of the lenses fabricated on a photo-sheet shown above in FIG. 7;[0019]

FIG. 9 is a cross-sectional plan view of the optical communication system shown above in FIG. 7, in accordance with the present invention;[0020]

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;[0021]

FIG. 11 is a simplified plan view showing an apparatus for fabricating the lenses shown above in FIGS.[0022]4-6 and8, 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.[0023]4-6 and8 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;[0024]

FIG. 14 is a cross-sectional view of the substrate, shown above in FIG. 13, under going processing showing a photoresist layer being patterned;[0025]

FIG. 15 is a cross-sectional view of the substrate, shown above in FIG. 14, under going processing after a first etch step; and[0026]

FIG. 16 is a cross-sectional view of the substrate, shown above in FIG. 15, under going processing after a second etch step.[0027]

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 2, shown is an[0028]

exemplary computer system

30, such as a personal computer that includes apower supply32, aprocessor34, input/output device controller and associated memory (I/O controller)36,main memory38,expansion slots40 and

expansion cards

40a,40b,40cand40d. Theexpansion slots40 are in electrical communication with thepower supply32 over apower bus42. Thepower bus42 includes multiple lines, each of which is dedicated to carrying a single voltage level. A mainsystem data bus44 is in data communication withprocessor34,expansion slots40 andmain memory38.Main data bus44 includes eight to sixty-four different lines, depending upon the data transfer protocol supported by thesystem30, e.g., ISA, EISA, or MCA protocols and the like.Main data bus44 carries data transferred betweenprocessor34,main memory38 andexpansion slots40. Anaddress bus46 comprising, for example, twenty lines is in data communication withmain memory38,processor34 andexpansion slots40.Address bus46 carries information that specifies the address from, or to, data is to be moved. To facilitate data transfers, acontrol bus48 is included that has a plurality of lines placingmain memory38 andexpansion slots40 in data communication with I/O controller36.

Referring to both FIGS. 2 and 3, as mentioned above, each of the[0029]

expansion slots

40 is adapted to receive an

expansion card

40a,40b,40cand40d. One or more optical channels facilitate communication between two or more of the

expansion cards

40a,40b,40cand40d. One optical channel includes one or more sources ofoptical energy48amounted toexpansion card40a, and one or moreoptical detectors50amounted toexpansion card40band in data communication with the source ofoptical energy48a. AHOE52ais disposed between the source ofoptical energy48aand thedetector50a. A second optical channel includes one or more sources ofoptical energy48bmounted toexpansion card40b, and one or moreoptical detectors50bmounted toexpansion card40aand in data communication with the source ofoptical energy48b. AHOE52bis disposed between the source ofoptical energy48band thedetector50b.

Source of[0030]

optical energy

48adirectsoptical energy54aalong apath56ain which thedetector50alies. TheHOE52ais disposed in theoptical path56a. Source ofoptical energy48bdirectsoptical energy54balong apath56bin which thedetector50blies. TheHOE52bis disposed in theoptical path56b. each of the

HOEs

52aand52bhas both a refractory function and a holographic transform function enabling the

HOEs

52aand52bto concurrently filter and refract the optical energy propagating therethrough. In this manner, the

HOEs

52aand52bfilters the

optical energy

54aand54b, respectively so that the optical energy passing therethrough to impinge upon the

optical detectors

50aand50b, respectively, having desired characteristics.

[0031]

HOE

52aand52bare identical in construction and, therefore, only HOE52awill be discussed, but it should be borne in mind that the discussion with respect to HOE52aapplies with equal weight to HOE52b.HOE52ais a refractory lens having a bulk hologram recorded therein that defines a holographic transform function. The bulk hologram facilitates characterizing theoptical energy54ato have desired characteristics that may improve detection, by theoptical detector50a, of information contained in theoptical energy54a. For example, the transform function may allow a specific wavelength to pass through the lens, diffracting all other wavelengths to deflect away from theoptical detector50a. Alternatively, the transform function may allow only a certain polarization of theoptical energy54ato propagate therethrough, diffracting all other polarizations away from theoptical detector50a.

The refractory function of the[0032]

HOE

52afacilitates impingement of theoptical energy54aonto theoptical detector50a. In this manner, the precise alignment of theoptical detector50awith respect to thesource48aand, therefore, thepath56amay be relaxed. This is beneficial when facilitating communication between expansion cards, such as40aand40b, because the mechanical coupling of the

expansion cards

40aand40bto therespective slots40 would typically make difficult precisely aligningsource48awith thedetector50a.

Referring to FIG. 4, the[0033]

HOE

52ais alens58 having anarcuate surface60, e.g., cylindrical, spherical and the like with a bulk holographic transform function formed therein. The bulk holographic transform function is shown graphically asperiodic lines62 for simplicity. The bulkholographic transform function62 is recorded in substantially the entire volume of thelens58 through which optical energy will propagate. Thetransform function62 is a periodic arrangement of the space-charge field of the material from which thelens58 is fabricated. To that end, thelens58 may be formed from any suitable photo-responsive material, such as silver halide or other photopolymers. In this manner, thelens58 and the bulkholographic transform function62 are integrally formed in a manner described more fully below. Although thesurface64 of thelens58 disposed opposite to the sphericalarcuate surface60 is shown as being planar, thesurface64 may also be arcuate as shown insurface164 oflens158 in FIG. 5.

Referring to both FIGS. 3 and 4, were it desired to further control the shape of optical energy propagating through[0034]

lens

58, aFresnel lens258 may be formed opposite to thespherical surface260. To that end, theFresnel lens258 includes a plurality of concentric grooves, shown as recesses258a258band258cthat are radially symmetrically disposed about acommon axis256. Thus, thelens258 may have three optical functions integrally formed in a common element, when providing the bulk holographic transform function262 therein, which facilitates creation of a well defined optical channels between

expansion cards

40aand40b.

Facilitating communication between[0035]

expansion cards

40aand40bover optical channels increase the bandwidth of thecomputer system30's bus systems. Specifically, the transfer of power and data between the

expansion cards

40aand40band thecomputer system30 is bifurcated. The power to the

expansion cards

40aand40bis transferred overpower bus42 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

40aand40bare made backwards compatible with existing technology. This is shown by the implementation of

standard expansion cards

40cand40dalong with

expansion cards

40aand40b, as well as the compatibility of

expansion cards

40aand40bwithstandard expansion slots40. The presence of the optical channels, however, reduces the need to transfer information between the

expansion cards

40aand40bover themain data bus44, as well the need to transfer information over theaddress bus46 or thecontrol bus48, were appropriate control circuitry included on the

expansion cards

40aand40b. Thus, employing the optical channels as described above, thecomputer system30 bus bandwidth may be increased.

Referring to both FIGS. 2 and 7, as mentioned above the[0036]

expansion cards

40aand40bmay each include multiple sources ofoptical energy48aandmultiple detectors50a. To that end provided are an array of sources ofoptical energy348, shown generally asoptical emitters348a-348p, and an array ofoptical detectors350, shown generally asoptical receivers350a-350p. Theoptical emitters348a-348pgenerate optical energy to propagate along a plurality of axes, and theoptical receivers350a-350pare positioned to sense optical energy propagating along one of the plurality of optical axes. Specifically, thearray348 is an (XxY) array of semiconductor lasers that produce a beam that may be modulated to contain information. Thearray350 may comprise of virtually any optical detector known, such a charged coupled devices (CCD) or charge injection detectors (CID). In the present example, thearray350 comprises of CIDs arranged in an (MxN) array of discrete elements. The optical beam from the each of theindividual emitters348a-348pmay expand to impinge upon each of thedetectors350a-350pof thearray350 if desired. Alternatively, the optical beam from each of theindividual emitters348a-348pmay be focused to impinge upon any subportion of thedetectors350a-350pof thearray350. In this fashion, a beam sensed by one of thedetectors350a-350pof thearray350 may differ from the beam sensed upon the remainingdetectors350a-350pof thearray350. To control the wavefront of the optical energy produced by thetransmitters348a-348p, the HOE52, discussed above with respect to FIGS.3-6 may be employed as an array of the lenses252, shown more clearly in FIG. 8 asarray400.

Specifically, referring to FIGS. 5 and 7, the[0037]

individual lenses

458 of the array are arranged to be at the same pitch and sizing of thearray348. The numerical aperture of each of thelenses458 of thearray400 is of sufficient size to collect substantially all of the optical energy produced by theemitters348a-348pcorresponding thereto. In one example, thearray400 is attached to thearray348 with each lens resting adjacent to one of theemitters348a-348p. To provide the necessary functions, each of the lenses of thearray400 may be fabricated to include the features mentioned above in FIGS.2-4. As a result, each of thelenses458 of the array may be formed to having functional characteristics that differ from the remaininglenses458 of the array. In this manner, each beam produced by thearray348 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 system310.

Specifically, an additional array of[0038]

lenses

400bthat match the pitch of theindividual receivers350a-350pof thearray350, shown more clearly in FIG. 10. The lenses may be fabricated to provide the same features as discussed above with respect toarray400, shown in FIG. 8.

Referring to FIGS. 7, 8 and[0039]10 each of theemitters348a-348pof thearray348 would then be uniquely associated to communicate with only one of thedetectors350a-350pof thearray350. In this manner, theemitter348a-348pof thearray348 that is in data communication with one of the one of thereceivers350a-350pof thearray350 would differ from theemitters348a-348pin data communication with remainingreceivers350a-350pof thearray350. This emitter/receiver pair that were in optical communication is achieved by having the properties of thelens458 inarray400 match the properties of thelens458binarray400b. It should be understood, however that one of theemitters348a-348pmay be in data communication with any number of thereceivers350a-350pbymultiple lenses458bmatching the properties of one of thelenses458. Similarly, one of themultiple emitters348a-348pmay be in optical communication with one or more of thedetectors350a-350pby appropriately matching thelenses458 to thelenses458b.

In one example, superior performance was found by having the[0040]

array

350 sectioned into (mxn) bins, with each bin corresponding to a particular polarization and/or wavelength that matched a particular polarization and/or wavelength corresponding to aemitter348a-348p. Thus, were a beam from one or more of theemitters348a-348pto flood the entire (MxN)array350 or multiple (mxn) bins, only theappropriate detectors350a-350psense information with a very high signal-to-noise ratio and discrimination capability. It will be noted that the (mxn) bins can also be effectively comprised of a single sensing pixel (element) to exactly match the (XxY) array.

Additional beam-sensor discrimination may be achieved by employing[0041]

emitters

348a-348phaving different wavelengths or by incorporating up-conversion processes that include optical coatings applied to theindividual emitters348a-348por 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[0042]11, thesystem500 employed to fabricate thelens58 and the

lens arrays

400aand400bincludes abeam source502 that directs abeam504aintowave manipulation optics506 such as a ¼ waveplate508 so that thebeam504bis circularly polarized. Thebeam504bimpinges uponpolarizer510 so that thebeam504cpropagating therethrough is linearly polarized. Thebeam504cimpinges upon aFaraday rotator512 that changes birefringence properties to selectively filter unwanted polarizations from thebeam504c. In this manner, thebeam504degressing from therotator512 is linearly polarized. Thebeam504dimpinges upon abeam splitter514 that directs afirst subportion504eofbeam504donto aplanar mirror516. Asecond subportion504fof thebeam504dpass through thesplitter514. The first and

second subportions

504eand504fintersect atregion520 forming an optical interference pattern that is unique in both time and space. Aphotosensitive sheet558 is disposed in the region so as to be exposed to the optical interference pattern. The interference pattern permeates thephotosensitive sheet558 and modulates the refractive index and charge distribution throughout the volume thereof. The modulation that is induced throughout the volume of thephotosensitive sheet558 is in strict accordance with the modulation properties of the first and

second subportions

504eand504f. 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[0043]

photosensitive sheet

558 by adhering aphotosensitive layer600 to asacrificial support602, such as glass, plastic and the like to form aphotosensitive substrate604. Typically, thephotosensitive layer600 is tens of microns thick. As shown in FIG. 13, a photo resistlayer606 is deposited onto thephotosensitive layer600 and then is patterned to leave predetermined areas exposed, shown as608 in FIG. 14, defining apatterned substrate610. Located between the exposedareas608 are photo resistislands612. The patternedsubstrate610 is exposed to a light source, such as ultraviolet light. This ultraviolet light darkens the volume of the photo resistlayer600 that is coextensive with the exposedareas608 being darkened, i.e., become opaque to optical energy. The volume of thephotosensitive layer600 that are coextensive with the photo resistislands612 are not darkened by the ultraviolet light, i.e., remaining transparent to optical energy. Thereafter, the photo resistislands612 are removed using standard etch techniques, leaving etchedsubstrate614, shown in FIG. 15.

The etched[0044]

substrate

614 has twoarcuate regions616 that are located in areas of thephotosensitive layer600 disposed adjacent to theislands612, shown in FIG. 14. Thearcuate regions616 of FIG. 15 result from the difference in exposure time to the etch process of the differing regions of thephotosensitive layer600.

Referring to FIGS. 10 and 16, a subsequent etch process is performed to form[0045]

array

400. During this etch process the support is removed as well as nearly 50% of thephotosensitive layer600 to form a very thin array. Thearray400 is then placed in theapparatus500 and the bulk holographic transform functions are recorded in thearcuate regions616 that define thelenses458, as discussed above. A Fresnel lens may also be formed on thelenses458 of the array using conventional semiconductor techniques. Thereafter, the lenses may be segmented from the photo resistive sheet or MxN subarrays of lenses may be segmented therefrom.

Lenses with differing transform functions are formed on differing[0046]

photosensitive sheets

558. Specifically, the transform function is defined by the interference pattern formed by the first and

second subportions

504eand504fintersecting atregion520. This interference pattern is unique in both time and space. As a result, each of the lenses formed on thesheet558 would have substantially identical holographic transform functions. To create lenses with differing transform functions, an additionalphotosensitive sheet558 would be employed and, for example, theFaraday rotator512 may be rotated to provide the lenses formed on thephotosensitive sheet558 with a holographic transform function that differs from the holographic transform function associated with the lenses formed on a previousphotosensitive sheet558. Therefore,lenses458aassociated with thefirst array458 would come from differingsheets558 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[0047]

arcuate regions

616 using standard etch techniques, the same may be formed by exposing thesubstrate610, shown in FIG. 12, to thermal energy. In one example, thesubstrate610 is convectionally heated, and the photo resistlayer606 is patterned to control the regions of thephotosensitive layer600 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 thephotosensitive layer600 where lens are to be formed. The thermal energy from the laser beam causes thephotosensitive layer600 to bubble, formingarcuate regions616 thereon shown in FIG. 13. 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.

Claims

What is claimed is:

1. A backplane interconnect system comprising:

an expansion slot;

an expansion card in electrical communication with said expansion slot, said expansion card having a source of optical energy to propagate optical energy along an optical path;

a detector positioned in the optical path; and

a holographic optical element having an arcuate surface and a holographic transform function, with said optical element being disposed to filter the optical energy in accordance with properties of the holographic transform function to remove optical energy having unwanted characteristics, defining transformed optical energy, and refract the transformed energy in accordance with properties of said arcuate surface to impinge upon said detector.

2. The system as recited inclaim 1 further including an additional expansion slot and an additional expansion card in electrical communication with said additional expansion slot, with said detector being mounted to said additional expansion card to facilitate data communication between said expansion cards.

3. The system as recited inclaim 1 further including an additional expansion slot and an additional expansion card, in electrical communication with said additional expansion slot, said detector being mounted to said additional expansion card, and said source of optical energy including an array of optical emitters to generate optical energy to propagate along a plurality of axes and said detector including an array of optical receivers, each of which is positioned to sense optical energy propagating along one of the plurality of optical axes, with said holographic optical element including an array of lenses, each of which is disposed in one of the plurality of axes and includes the arcuate surface with the holographic transform being disposed within a volume of the array of lenses.

4. The system as recited inclaim 1 further including an additional expansion slot and an additional expansion card, in electrical communication with said additional expansion slot, with said detector being mounted to said additional expansion card, said source of optical energy including an array of optical emitters to generate optical energy to propagate along a plurality of axes and the detector includes an array of optical receivers, each of which is positioned to sense optical energy propagating along one of the plurality of optical axes, said holographic optical element including a plurality of lenses having the arcuate surface, with said holographic transform function being disposed within a volume thereof, with said plurality of lenses being arranged in first and second arrays, said first array being disposed between said array of optical emitters and said array of optical receivers and said second array being disposed between said first array and the optical receivers.

5. The system as recited inclaim 4 wherein the holographic transform function associated with a subgroup of the lenses of the first array differs from the holographic transform function associated with the remaining lenses of the first array of lenses, and the holographic transform function associated with a subset of the lenses of the second array matching the transfer function.

6. The system as recited inclaim 1 wherein said source includes semiconductor lasers.

7. The system as recited inclaim 1 wherein said detector comprises charge injection devices.

8. The system as recited inclaim 1 wherein said holographic optical element further includes a telecentric lens having a bulk hologram recorded therein.

9. The system as recited inclaim 1 wherein said holographic optical element further includes a converging lens having a bulk hologram recorded therein.

10. The system as recited inclaim 1 further including a processor in data communication with said expansion card slot over a bus with said source producing modulated optical energy in accordance with instructions received from said processor.

11. A backplane interconnect system comprising:

first and second expansion slots;

a first expansion card in electrical communication with said first expansion slot, said first expansion card having a first array of optical emitters to generate optical energy to propagate along a plurality of axes and a first array of optical receivers;

a second expansion card in electrical communication with said second expansion slot, said second expansion card having a second array of optical emitters to generate optical energy to propagate along a plurality of paths, and a second array of optical receivers, each of which is positioned to sense optical energy propagating along one of the plurality of optical axes, with the optical receivers of said first optical array positioned to sense optical energy propagating along said plurality of paths; and

a holographic optical element including a plurality of lens elements, each of which has a holographic transform function recorded therein, defining a plurality of holographic transform functions, each of said plurality of detectors being associated with one of said plurality of holographic transform functions, with the holographic transform function associated with one of said plurality of detectors differing from the holographic transform functions associated with the remaining detectors of said plurality of detectors.

12. The system as recited inclaim 11 wherein each of the optical emitters of said first and second arrays comprises semiconductor lasers.

13. The systems as recited inclaim 11 wherein each of the optical receivers of said first and second array comprises charge injection devices.

14. The system as recited inclaim 11 wherein a subset of said plurality of lens elements comprise telecentric lenses having a bulk hologram recorded therein.

15. The system as recited inclaim 11 wherein a subset of said plurality of lens elements comprise converging lenses having a bulk hologram recorded therein.

16. The system as recited inclaim 11 further including a processor in data communication with said first and second expansion card slots over a bus with the optical emitters of said first and second arrays adapted to produce modulated optical energy in accordance with instructions received from said processor.

17. A backplane interconnect system comprising:

first and second expansion slots;

a second expansion card in electrical communication with said second expansion slot, said second expansion card having a second array of optical emitters to generate optical energy to propagate along a plurality of paths, and a second array of optical receivers, each of which is positioned to sense optical energy propagating along one of the plurality of optical axes, with the optical receivers of said first optical array positioned to sense optical energy propagating along said plurality of paths, with the optical emitters of said first and second arrays comprising semiconductor lasers and the optical receivers of said first and second array comprising charge injection devices; and

a holographic optical element including a plurality of lens elements, each of which has a bulk holographic transform function recorded throughout a volume thereof, defining a plurality of holographic transform functions, each of said plurality of detectors being associated with one of said plurality of holographic transform functions, with the holographic transform function associated with one of said plurality of detectors differing from the holographic transform functions associated with the remaining detector of said plurality of detectors.

18. The system as recited inclaim 17 wherein a subset of said plurality of lens elements comprise telecentric lenses.

19. The system as recited inclaim 17 wherein a subset of said plurality of lens elements comprise converging lenses.

20. The system as recited inclaim 1 further including a processor in data communication with said first and second expansion card slots over a bus with said optical emitters of said first and second arrays adapted to produce modulated optical energy in accordance with instructions received from said processor.