Abstract:
A circuit board has optical fibers embedded in at least one layer for optical transmission of data at high speed, digital signal rates and electrically conductive strips in other layers to provide for conventional data signals and power for optoelectronic and electronic integrated circuits (IC). Optical fibers connect to optoelectronic IC&#39;s, off board IC&#39;s, circuit boards and conductors to reduce high speed digital signal latency and increase signal bandwidth/throughput. Optical fibers are used within printed circuit boards, integrated circuits, circuit board connectors, and backplane connectors to interface printed circuit boards and backplane.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     Contemporary printed circuit boards have embedded circuits or patterned traces made from layers of copper. The traces typically connect electrical components, cables, and other printed circuit boards through electrical connectors, and create functional circuits transmitting data as electrical signals. These traces and the circuits and connections they create do not, of course, pass optical data signals. A main limitation of this transmission method is that electrical signals experience a phenomenon known as “propagation delay,” which is the length of time it takes for a signal to travel from its starting location to its final location. 
     Consequently, current technology is limited to such an extent that modem Central Processing Units (CPUs) are placing more components directly on the CPU itself, because the propagation delay is limiting the CPU speed to unacceptably slow rates. As a result, internal CPU backplanes are required to allow for increases in CPU power and efficiency. Circuit card backplanes having various printed circuit boards that plug into a central circuit board for inter-circuit board communication are also reaching their maximum speeds, and require special cables and alternate signal routes to bypass the backplanes. 
     In addition, data transmissions via conventional electrical signals also reach bandwidth limitations, which are maximum amounts of data that can be carried over a particular signal path, cable, or electrical bus. Furthermore, many conventional electrical transmissions are fed through electrical connectors that may experience “contact corrosion resistance,” which is the increased electrical resistance due to corrosion that can form at connection points. Although gold-plated contacts reduce this, they are not totally impervious to its occurrence. 
     Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a circuit board that utilizes copper or other metallic strips for conventional data and power signals and embedded fiber optic conductors for optical transmission of data at high speed, digital signal rates to reduce signal latency and increase signal bandwidth/throughput. 
     SUMMARY OF THE INVENTION 
     The present invention provides a printed circuit board that has embedded optical fibers to transmit optical data signals between optoelectronic components in interfacing integrated circuits and further has interfacing electrical conductors to transmit electrical data signals and power. 
     An object of the invention is to utilize optical fibers directly within printed circuit boards and integrated circuits that interface with printed circuit boards. 
     Another object of the invention is to provide embedded optical fibers in printed circuit boards, integrated circuits, and connectors/sockets for printed circuit boards and integrated circuits. 
     Another object of the invention is to provide optic fibers directly within printed circuit boards to transmit digital optic (light) signals between electrical components that are capable of emitting and receiving these signals. 
     Another object of the invention is to provide printed circuit boards utilizing optical connections to other circuit boards, cables, and individual components that do not require optical-to-electrical conversion and coupling to standard electrical conductors. 
     Another object of the invention is to utilize fiber optics directly within printed circuit boards and integrated circuits that have onboard converters from electrical to optic signals, and vice versa. 
     Another object of the invention is to provide embedded optical fibers in printed circuit boards and integrated circuits to improve speed of transmission of digital data signals. 
     Another object of the invention is to provide embedded optical fibers in printed circuit boards and integrated circuits to decrease propagation delay of digital data signals. 
     Another object of the invention is to provide embedded optical fibers in printed circuit boards and integrated circuits to increase bandwidths of signal transmission. 
     Another object of the invention is to provide embedded optical fibers in printed circuit boards and integrated circuits to eliminate the problems associated with poor electrical connections between electrical connector contacts due to corrosion of the contacts. 
     These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway view of a circuit board having different layers of embedded optical fibers for optical data transmission and electrical conductors for circuit power and electrical data signal transmission that allow the optical fibers and electrical conductors access to the top and bottom surface areas of the printed circuit board. 
     FIG. 2 shows an integrated circuit to be fitted and seated within an integrated circuit socket to interface a circuit board, and the integrated circuit is above the socket and rotated 90 degrees to show ends of electrical conductors and optical fibers on its bottom to electrically and optically couple with correspondingly disposed ends of electrical conductors and optical fibers embedded in the circuit board. 
     FIG. 3 shows a circuit board for a fiber optic backplane that has a circuit board connector interfacing a backplane connector and/or optical fibers directly terminating at the edge of the circuit board to interface the fibers of the circuit board with fibers in the backplane. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Printed circuit boards have patterns of conductive strips deposited, printed, or etched onto an insulating board. Several boards may be grouped into assemblies that include many printed components and integrated circuits to electronically process data. However, because of the time and bandwidth needed to transmit electric signals on conductive strips, the design of these conventional integrated circuit board assemblies appears to have reached practical limits. 
     Many limitations of conventional circuit boards using conductive strips for electronic data transmission are overcome by this invention including optical fibers and other waveguides in layers of the printed circuit boards. Optical fibers allow transmission of data signals as light in circuit boards and associated components in much larger bandwidths at the speed of light (about 2.997925 meters per second) to allow interfacing of components with optical fibers carrying high bandwidth, multiplexed optical data signals over long distances. 
     Referring to FIG. 1, circuit board  10  has a plurality of insulating layers  11  mounting electrically conductive strips  12  that may be arranged in patterns to transmit electrical power and electrical data signals from sources  12   a  and  12   b  to interconnected components, (not shown) and to at least one output  12   c . Insulating layers  15  are disposed adjacent to or interleaved with layers  11  to transmit optical data signals through optical fibers, or waveguides,  16  to optoelectronic and/or electronic integrated circuits (not shown), at least one optical data source  19 , optical output terminal  20 , optical circuit board connector  21 , and/or backplane connector  22 . 
     The side cutaway view of juxtaposed insulating layers  11  and  16  in circuit board  10 , shows optical fibers  16  in insulating layers  15  that have the capability to bidirectionally transmit different optical signals simultaneously without any mutual interference, and standard electrical conductors, or electrically conductive strips  12  in adjacent layers  11  that have the capability to simultaneously, bidirectionally transmit circuit power and multiple electrical data signals. Optical fibers  16  in different layers  15  are provided with optically transmitting portions  17  and  18  that extend in substantially right angles from individual fibers  16  to ends  17   a  and  18   a  flush with top and bottom surfaces  10   a  and  10   b  of circuit board  10 , respectively. Conductive strips  12  in different layers  11  have electrically conducting portions  13  and  14  that extend in substantially right angles from individual conductive strips  12  to ends  13   a  and  14   a  flush with top and bottom surfaces  10   a  and  10   b  of circuit board  10 , respectively. 
     Portions  17  and  18  from layers  15  and portions  13  and  14  from layers  11  allow optical fibers  16  and conductive strips  12  to separately access discreet areas of the top and bottom surfaces of printed circuit board  10 . Some of ends  17   a ,  18   a  and ends  13   a ,  14   a  are shown at or near the edge of circuit board  10 , and other ones of ends  17   a  and  13   a  extend through top surface  10   a  inside of the edges of circuit board  10  to interface with other electronic and optoelectronic components through, for example, integrated circuit sockets, as will be explained below. Although not shown in the drawings, it is to be understood that other ones of ends  18   a  and  14   a  may extend to bottom surface  10   b  at or near the edges of circuit board  10  and/or inside of the edges of circuit board  10  and be operatively coupled to other integrated circuits that are to be joined to the bottom of circuit board  10 . Furthermore, circuit board  10 ′ in FIG. 3 shows ends  16 ′ of optical fibers  16  and ends  12 ′ of conductive strips  12  that may interface directly with optical connectors  50   a  and electrical connectors  50   b  of backplane  50 . More such direct connections between  10 ′ and  50  can be made across the thickness of circuit board  10 . 
     FIG. 2 shows circuit board  10  adapted to interface with integrated circuit  25  which may include many optoelectronic and/or electronic components to perform a wide variety of optical and/or electronic processing. Integrated circuit  25  is depicted as removed from cavity  30 ′ of integrated circuit socket  30  and rotated about ninety degrees to show ends  26   a  and  27   a  of its fiber optics  26  and lengths of electrical conductors  27 . Fiber optics  26  extend from optoelectronic components in integrated circuit  25  and terminate in ends  26   a  that may be flush with the bottom of integrated circuit  25 . When integrated circuit  25  is fitted, seated, and properly retained in cavity  30 ′ in integrated circuit socket  30  that is mounted on surface  10   a  of circuit board  10 , ends  26   a  of fiber optics  26  are aligned to abut with correspondingly disposed ends  17   a  of optical fiber portions  17  or small lengths of interfacing optical fibers  30   a  built into span  30 ″ across socket  30 . These butt-type joints transmit optic data signals to and from circuit board  10 . An optical gel, or other suitable optical coupling can be used to enhance transmission. 
     Integrated circuit  25  also has ends  27   a  of lengths of electrical conductors  27  that spatially correspond with certain ones of ends  13   a  of electrically conductive portions  13  on surface  10   a  of circuit board  10 . When integrated circuit  25  is fitted, seated and properly retained in cavity  30 ′ of integrated circuit socket  30  on surface  10   a  of circuit board  10 , ends  27   a  of electrically conductive strips  27  are aligned to contact correspondingly disposed ends  13   a  of electrically conductive portions  13 . Electrical contact is assured since ends  27   a  are flush with the bottom of integrated circuit  25  or they may bulge slightly outwardly from it. Integrated circuit socket  30  may have small lengths of interfacing electrical conductor  30   b  built into span  30 ″ across socket  30  to further assure electrical interconnection between integrated circuit  25  and circuit board  10 . A suitable conductive compound can be applied at points of contact to aid electrical contact. 
     Thus, socket  30  provides for both electrical and optic connections, so that both types of signals (as well as electrical power for the integrated circuit) can be transmitted. Couplers  60  can be included at the junction of circuit board  10  and socket  30  and at the junction of socket  30  and integrated circuit  25  to mechanically hold them together to ensure optical and electrical connections. Other ones of ends  14   a  of electrically conductive portions  14  and ends  18   a  of optically transmitting portions  18  of optical fibers  16  in circuit board  10  may extend to bottom surface  10   b  inside of the edges of circuit board  10  and be operatively coupled to other integrated circuits, such as integrated circuit  25 ′ on the bottom of circuit board  10 . 
     FIG. 3 shows circuit board  10  provided with circuit board connector  35 . Circuit board connector  35  has embedded electrical and/or optical fibers appropriately arranged to interface with circuit board  10  and transmit and receive electrical and optical signals to and from it. Circuit board connector  35  has an arrangement of ends  36   a  of electrically conductive strips  36  and ends  37   a  of connector optical fibers  37  that correspond to interface and interconnect with some electrically conductive ends  13   a  and some of optical fiber ends  17   a  on surface  10   a  of circuit board  10 . Electrically conductive conductor strips  36  and connector optical fibers  37  embedded in circuit board connector  35  make an essentially right-angled turn and respectively terminate in ends  36   b  and  37   b  at the back surface of circuit board connector  35 . Ends  36   b  and  37   b  are flush with, or, in the case of electrically conductive ends  36   b , are slightly bulging above the back surface of circuit board connector  35 . 
     Backplane connector  40  has backplane connector electrical conductors  41  and/or backplane connector optical fibers  42  at or near its surfaces or further embedded therein that reach from ends  41   a  of electrical conductors  41  and ends  42   a  of optical fibers  42  at the front surface of backplane connector  40  to ends  41   b  and  42   b  at its back surface. Ends  41   a  and  42   a  are flush with, or, in the case of electrically conductive ends  41   b , may be slightly bulging above the back surface of backplane connector  40  and arranged to bidirectionally conduct optical and electrical data signals through appropriately disposed abutting ends  36   b  and  37   b  of circuit board connector  35 . Ends  41   b  and  42   b  are flush with, or, in the case of electrically conductive ends  41   b , may be bulging above the back surface of backplane connector  40  to abut the front surface of backplane  50 . 
     Backplane  50  has electrical conductors  51  and/or optical fibers  52  embedded therein to extend to other interfacing structure or remote networks. Ends  51   a  and  52   a  of electrical conductors  51  and optical fibers  52  are flush with, or, in the case of electrically conductive ends  51   a , may be slightly raised above the front surface of backplane  50  to transmit and receive optical and electric data signals via abutting ends  41   b  of electrical conductors  41  and ends  42   a  of optical fibers  42  in backplane connector  40 . Circuit board  10  and circuit board connector  35 , circuit board connector  35  and backplane connector  40 , and backplane connector  40  and backplane  50  may be securely held together in their abutting relationships along their junctions by one or more couplers  60 , such as well known bolt-and-socket types. Details of couplers  60  to secure the circuit boards, connectors, and backplane are not shown since many current standards in this area are well known. These connections assure that electrical and optical data signals can bidirectionally pass among elements  10 ,  35 ,  40 ,  50 , and other circuits. 
     Only a few of ends  13   a ,  17   a ,  26   a ,  27   a ,  26   b ,  27   b ,  50   a , and  50   b  that might be along the edges of circuit board  10 , circuit board connector  35 , backplane connector  40 , and backplane  50  are shown. Many additional ends of embedded electrical and optical data conductors may be disposed across abutting surfaces of circuit board  10 , circuit board connector  35 , backplane connector  40 , and backplane  50  to transmit optical and electrical data signals, and electrical power. Elements  10 ,  35 ,  40 , and  50  may also have integrated circuits for more optoelectronic and/or electronic processing capabilities. 
     This interface between circuit board  10 , circuit board connector  35 , backplane connector  40 , and backplane  50  permits direct coupling from circuit board  10  to fiber optic waveguides  51  embedded in backplane  50  and helps reduce “rats-nest” like interconnections that are common in many conventional backplane interconnections. Optionally, if backplane connector  40  is not needed, ends  37   b  of optical fibers  37  and ends  36   b  of electrical conductors  36  of circuit board connector  35  could be directly interfaced with matingfibers  51   a  and conductors  52   a  on  50 . 
     Embedded fiber optics in circuit boards  10  and integrated circuits  25  improve speed of transmission of data signals, decrease propagation delay of digital signals, increase bandwidths of data signal transmission, and eliminate poor contacts at connectors due to increased resistance attributed to corrosion of contacts. Optical fibers are embedded directly into circuit boards, integrated circuits, and connectors/sockets for improved operation by reducing signal latency and increasing signal bandwidth/throughput. 
     The disclosed components and their arrangements as disclosed herein all contribute to the novel features of this invention. Many diverse patterns of optical fibers and electrical conductors on one or more layers might be adapted to support a host of different integrated components performing widely diverse functions from data storage to mechanical operations without departing from the scope of this invention. In addition to the disclosed optical and electrical ends that abut for optical and electrical connections, other known optical and electrical couplers could be used within the scope of this invention. For examples, extensions of the optical fibers and electrical conductors could fit into mating optically or electrically conducting bores, or mating plug-and-socket assemblies might be used, or connectors or pin-and-receptacle connectors might by employed at surfaces of elements  10 ,  25 ,  35 ,  40 , and  50 . 
     Having the teachings of this invention in mind, modifications and alternate embodiments of this invention may be adapted to many other data processing applications. Therefore, the invention as disclosed herein is not to be construed as limiting, but rather, is intended to be demonstrative of this inventive concept. 
     It should be readily understood that many modifications and variations of the present invention are possible within the purview of the claimed invention. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.