An optical backplane

Abstract: The present invention relates to an optical backplane (10) for use in a switching system or computer for interconnecting a plurality of associated circuit modules. The backplane comprises a switch (13) which is interconnected to each of the associated circuit modules (11) by a separate multifiber ribbon (12), each ribbon including (1) a plurality of transmit (37) and receive (38) optical fibers, and (2) an optical fiber (39) for providing concurrent synchronization signals to each of the associated circuit modules. The switch includes a switching block (31) for coupling parallel optical signals received from the plurality of receive optical fibers in any multifiber ribbon, transmitted by a sending module, to the transmit fibers of each of the multifiber ribbons for transmission to all of the modules associated with the optical backplane. The switch also includes a timing generation block (32) which generates an optical timing signal that is simultaneously distributed to the separate optical fibers in each of the multifiber ribbons in order to concurrently synchronize all of the associated modules. Each of the associated modules is connected to the backplane via the separate associated optical multifiber ribbon, and includes (1) an interface logic block (21) for interfacing an associated user circuit to the optical backplane, and (2) a means (22) for permitting the module to contend for access to the optical backplane.

Description: Technical Field The present invention relates to an optical backplane architecture and, more particularly, an optical backplane comprised of active and passive optical components that provide optical interconnects between a plurality of circuit modules. Description of the Prior Art The number of computers being used in society is continuously expanding as more people acquire computer expertise and the cost of computer hardware declines. This expansion in the use of computers in the office and home has decentralized computer resources and has created a need for improved interconnects and networking between computers. In addition to this decentralization, the speeds at which computers operate and communicate with each other and terminals have also increased. This, in turn, is creating a demand upon networking and backplane technology to provide not only higher speed networks but higher speed nodes, or switching systems and computers, within these networks. For example, networking technology has attempted to responded to the demand caused by the expansion and decentralization in computer use by providing a number of networking systems having relatively high speeds. However, a problem that is common among high speed switching systems is their limitation on internal, or intranode, data rates due to their electrical backplanes. Electrical backplanes currently used to interconnect the circuit modules within a switching node limit the data bandwidth through the switching node. The bandwidth limitations of electrical backplanes result from the increase in their system parasitics at higher data rates and their susceptibility to electromagnetic radiation. As the demand for higher speed switching systems increases, electrical backplanes will be an even greater obstacle to providing higher speed networks. Finding alternate approaches to designing and constructing higher speed backplanes for switching systems is imperative. Fiber optic technology has penetrated the long distance communications market as a point-to-point transmission media and has been implemented to provide higher speed communications between nodes in local-area networks. U.S. patent 4,654,889 issued to H.B. Shutterley on March 31, 1987 describes a multi-star fiber optic communication network having subnetworks of terminals with access control being localised to each individual subnetwork, and communication between subnetworks being conducted over a bus via non-interfering optical channels by using light sources having different wavelengths or by modulating light at different channel frequencies. An optical configuration for interconnecting a network of terminals is disclosed in U.S. patent 4,457,581 issued to D.C. Johnson et al. on July 3, 1984 and comprises hybrid transmission-reflection star couplers that are interconnected by their transmission ports with the terminals being connected to the reflection ports of the hybrid couplers. In addition, U.S. patent 4,417,334 issued to R.O. Gunderson et al. on November 22,1983 describes a data processing system having a plurality of stations grouped into subsystems and interconnected by two optical channels with each channel including a star coupler. These references are all directed to point-to-point long distance and local-area optical fiber networks. As optical fiber continues to be the technology of choice in the design of these networks, and more and more nodes within these networks are interconnected using optical fiber, the problem of bandwidth limitations due to the electrical backplanes within each node will become even more evident. The prior art appears to provide novel approaches or improvements to the design and topology of networks. However, advances in the design of the optical backplane has not kept pace with improvements in the topology of networks. For example, Electronic Letters, Vol. 22, No. 23, 6th November 1986, pages 1218-1219, IEEE, Stevenage, GB; P.R. Prucal et al: "TDMA Fibre-Optic Network With Optical Processing"; discloses one approach in the design of an optical backplane, in which each user station connecting to the backplane is assigned a time slot during which the user can receive a bit of information. The backplane employs delay lines the number of which is selected by a station that needs to transmit data to another station. That is, the transmitting station chooses a delay length corresponding to the slot position of the intended receiving station. If the receiving station is assigned to the kth time slot, then the receiver has to delay the system clock signal by k(tau) to optically sample its assigned time slot, and adds the delay incoherently to the incoming signal. This results in the correct signal riding on top of the clock signal. Such a backplane is not only inefficient, but also complex from the standpoint that it requires a receiving station to calculate a delay and add the delay to the system clock signal so that the receiver can sample the system backplane bus at the appropriate time. The prior art does not address the problems associated with and caused by the use of electrical backplanes within the nodes of a network. The problem remaining in the prior art is to provide a high speed backplane for interconnecting circuit modules within the nodes of a network or within any other computer systems that require high bandwidth and data rates between circuit modules. According to the present invention there is provided a backplane as defined in claim 1. The foregoing problem in the prior art has been solved in accordance with an embodiment of the present invention which relates to an optical backplane architecture for a switching system or computer, wherein the optical backplane comprises active and passive optical components that provide optical interconnects between a plurality of N circuit modules associated with the optical backplane. More particularly, the optical backplane comprises a switch that includes at least one optical coupler for optically coupling a plurality of transmit ports on one of the N modules to a plurality of receive ports on all of the N modules connected to the backplane. There is at least one coupler in the backplane for each type of information signal to be transmitted on the backplane. All of the transmit ports on the N modules corresponding to the same type of information signal are optically connected to the input side of a corresponding coupler in the switch and the output side of the coupler is optically connected to all of the receive ports on the N modules corresponding to that type of information signal. Additionally, the switch includes a means for synchronizing all of the N circuit modules. Brief Description of the Drawings FIG. 1 is a simplified block diagram in perspective of an optical backplane in accordance with the present invention; FIG. 2 is a block diagram in perspective of a module shown in the optical backplane of FIG. 1; FIG. 3 is a block diagram in perspective illustrating in greater detail a switch shown in the optical backplane of FIG. 1; FIG. 4 is a block diagram in perspective illustrating an alternative embodiment for a switch shown in the optical backplane of FIG. 1; and FIG. 5 is a block diagram in perspective of a N-to-N active coupler. Detailed Description FIG. 1 shows a simplified block diagram of a preferred embodiment of an optical backplane 10 in accordance with the present invention. Optical backplane 10 comprises a switch 13 which functions to permit interconnection thereto of up to a plurality of N modules 11₁-11 N which are to be associated with backplane 10. For purposes of explanation hereinafter, it will be considered that a full compliment of N modules 11₁-11 N are present and associated with backplane 10, but it should be understood that a lesser amount of modules 11 could be associated with backplane 10 depending on the present need of the system. Switch 13 includes a plurality of N exemplary multifiber connectors 14₁-14 N , with each multifiber connector 14 i being connected via an exemplary separate multifiber ribbon 12 i to a similar multifiber connector 14 i on an associated correspondingly numbered module 11 i , when that module is present. Each of the N possible multifiber ribbons 12₁-12 N comprises a plurality of optical fibers, each optical fiber of a multifiber ribbon 12 i being used for propagating a separate optical information signal between switch 13 and the associated module 11 i being interconnected to backplane 10. Optical backplane 10, in its preferred form, is an interfacing system used to interconnect, in a closely coupled hardware configuration, a plurality of N modules 11₁- 11 N , with each separate module 11 i providing an interface between the optical backplane 10 and a separate associated user circuit 26 (shown in FIG. 2). Optical backplane 10 in FIG. 1 can have an exemplary actual physical embodiment of a conventional card mounting frame commonly used to both mount and electrically interconnect circuit cards. However, in accordance with the present invention the circuit cards or modules 11₁-11 N are interconnected optically rather than electrically. In FIG. 2, a block diagram in perspective of an exemplary module 11 i is shown, wherein module 11₁ comprises a multifiber connector 14 i and a backplane interface logic block 21. Backplane interface logic block 21 is shown as comprising a plurality of K transmit ports 23₁-23 K , a plurality of K receive ports 24₁-24 K , a timing port 25, and an optional addressing and/or contention mechanism 22. Each of the transmit ports 23₁-23 K and receive ports 24₁-24 K on module 11 i are optically connected by the multifiber connector 14 i to a separate preassigned optical fiber 37₁-37 K and 38₁-38 K , respectively, in multifiber ribbon 12 i which terminates at the other end at switch 13. The transmit ports 23₁-23 K provide two functions: (1) they concurrently convert the associated electrical signals received from addressing and/or contention mechanism 22 into optical signals, and (2) they transmit these optical signals forming a transmission in parallel through their preassigned optical fibers 37₁-37 K in multifiber ribbon 12 i to switch 13. The receive ports 24₁-24 K do the converse of the transmit ports 23, and receive the optical signals forming a transmission in parallel from their preassigned optical fibers 38₁-38 K and concurrently convert these received parallel optical signals into electrical signals. The electrical signals from receive ports 24₁-24 K are then sent to addressing and/or contention mechanism 22 which then sends them to an associated user circuit 26. The operation of timing port 25 is similar to that of receive ports 24, in that timing port 25 receives an optical timing signal (TS o ) from an optical fiber 39 i , preassigned to carry the optical timing signal (TS o ), in multifiber ribbon 12 i and converts that optical timing signal (TS o ) into an electrical timing signal (TS e ) that is then electrically distributed to the associated user circuit 26 via contention mechanism 22 and a timing signal line 29. The optical timing signal (TS o ) is generated in switch 13 and distributed concurrently to each of the N modules 11₁-11 N to synchronize the modules 11₁-11 N and insure that each module 11 i has a timing signal which is within several nanoseconds of all of the other modules. User circuit 26 is electrically connected to optional addressing and/or contention mechanism 22 by a plurality of K receive lines 28₁-28 K , a plurality of K transmit lines 27₁-27 K , and a timing signal line 29 (TS e ). Mechanism 22 is transparent to user circuit 26 when user circuit 26 is receiving data from backplane 10 via the receive lines 28₁-28 K , but not when user circuit 26 attempts to transmit onto backplane 10. When the associated user circuit 26, of a sending module 11 i , needs to transmit through backplane 10 to a user circuit 26 on another module 11 j , the contention circuit of mechanism 22 of the sending module 11 i determines when its module 11 i is allowed to access backplane 10. When the contention circuit of mechanism 22 determines that its module 11 i is allowed to have access to backplane 10, user circuit 26 then sends electrical data signals in parallel over the transmit lines 27₁-27 K to the backplane interface logic block 21 of module 11 i . The addressing circuit of mechanism 22 (1) when transmitting associates the electrical data signal with a destination user circuit 26 on one or more modules 11 associated with backplane 10, and (2) when receiving it identifies whether the electrical data signal is destined for its associated user circuit 26. The plurality of transmit ports 23₁-23 K within backplane interface logic block 21 then convert the received parallel electrical signals to optical signals and transmit these optical signals in parallel via the K optical fibers 37₁-37 K in multifiber ribbon 12 i to backplane 10. The parallel optical signals are distributed by backplane 10 via multifiber ribbons 12₁-12 N to each module 11₁-11 N connected to backplane 10. In each of the modules 11₁-11 N the parallel optical signals are received on the K optical fibers 38₁-38 K by a plurality of receive ports 24₁-24 K . The receive ports 24₁-24 K in each module 11₁-11 N concurrently (1) convert the parallel received optical signals to electrical signals, and (2) transmit the parallel electrical signals to their associated user circuit 26 via addressing and/or contention mechanism 22 and receive lines 28₁-28 K . When the functions of the optional address and contention circuits in mechanism 22 are placed alternatively in user circuit 26, the above described functions of these circuits will be performed in user circuit 26. It is to be understood that module 11 i , as shown in FIG. 2, is for purposes of illustration and not for purposes of limitation, and that module 11 i could include (1) any conventional means for providing a suitable contention mechanism 22 with the above characteristics, and (2) any suitable and commonly available optical devices to implement the functions of the transmit ports 23, receive ports 24, and timing port 25. For example, as shown in FIG. 2 by the dashed line 19, the contention circuit of mechanism 22 can be electrically interconnected to all other contention circuits of backplane 10. In addition, the functionality of the user circuit 26 is not intended to be a limitation or part of the present invention. User circuit 26 is simply representative of a source and destination for the electrical signals to and from backplane 10 and could reside either on or external to module 11 i . User circuit 26 could comprise data processing, data storage, and/or peripheral control devices. FIG. 3 is a block diagram illustrating switch 13 in greater detail. Switch 13 is shown as comprising a switching block 31, an exemplary timing generation block 32, and a plurality of N multifiber connectors 14₁-14 N . Switch 13 is responsible for receiving K parallel optical signals from any sending module 11 i during a predetermined period of time and then forwarding these K parallel optical signals to all of the N modules 11₁-11 N connected thereto. Each of the N multifiber connectors 14₁-14 N connects both the set of K optical fibers 37₁-37 K and the set of K optical fibers 38₁-38 K from a corresponding multifiber ribbon 12₁-12 N to one of N sets of internal receive optical fibers 47₁-47 N and one of N sets of internal transmit optical fibers 48₁-48 N , respectively. The set of K optical fibers 37₁-37 K carries optical signals from a separate one of modules 11₁-11 N to switch 13 and the set of K optical fibers 38₁-38 K carries optical signals from switch 13 to a separate one of modules 11₁-11 N . Each set of internal receive optical fibers 47 i comprises a plurality of K individual optical fibers, with each optical fiber corresponding to one of the K optical fibers 37₁-37 K in multifiber ribbon 12 i . Similarly, each set of internal transmit optical fibers 48 i comprises a plurality of K individual optical fibers, with each optical fiber corresponding to one of the K optical fibers 38₁-38 K in multifiber ribbon 12 i . The other end of both sets of internal optical fibers, 47 i and 48 i , are connected to opposite sides of a plurality of K passive optical star couplers 36₁-36 K within switching block 31. Switching block 31 comprises a plurality of K passive optical star couplers 36₁-36 K , a separate passive optical coupler 36 i for each of the plurality of K optical information signals in either one of the sets of internal optical fibers, 47 i and 48 i . Switching block 31 receives a plurality of K parallel optical signals from one of the N sets of the internal receive optical fibers 47₁-47 N , and couples these K parallel optical signals via couplers 36₁-36 K to each of the N sets of the internal transmit optical fibers 48₁-48 N going to each of the multifiber connectors 14₁-14 N . Each of the passive optical couplers 36 i includes N input ports and N output ports for coupling an optical signal received on any of the N input ports to all of the N output ports. Each of the N input ports of each optical coupler 36 is connected to a separate correspondingly numbered optical fiber within each set of internal receive optical fibers 47₁-47 N coming from each of the N multifiber connectors 14₁-14 N , and each of the N output ports of each optical coupler 36 is connected to a separate correspondingly numbered optical fiber within each set of internal transmit optical fibers 48₁-48 N going to each of the N multifiber connectors 14₁-14 N . It is to be understood that the present backplane could also operate with modules 11 i that may only require to transmit information to other modules 11 i and not receive information from other modules 11 i , as may be found for modules that provide broadcast messages on the backplane. Alternatively, the present backplane could also operate with modules 11 i that may only require to receive information from other modules 11 i and not transmit information to other modules 11 i , as may be found for modules functioning as monitors on the backplane. Under such conditions, when using the exemplary optical couplers 36₁-36 N with an equal number of N input ports and N output ports, a transmit only module would only use optical fibers 37₁-37 K in multifiber ribbon 12 i to transmit information to backplane 10; and a receive only module 11 i would only use optical fibers 38₁-38 K in multifiber ribbon 12 i to receive information from backplane 10. It is to be understood, however, that the exemplary use in FIG. 3 of optical star couplers 36₁-36 K with an equal number of N input ports and N output ports is not to be a limitation on the present invention. Any suitable optical coupler with the above described characteristics could be used and still remain within the spirit and scope of the present invention. FIG. 4 shows an alternative embodiment of switch 13 that includes a plurality of K optical star couplers 36₁-36 K with L input ports and M output ports, where L and M are equal to or less than N and where L can be equal to or different from M. In FIG. 4, multifiber ribbon 12 N-1 is connected to multifiber connector 14 N-1 and at the distant end to a transmit only module 11 N-1 . Multifiber connector 14 N-1 only connects (1) the K optical fibers 37₁-37 K from multifiber ribbon 12 N-1 to switching block 31 via the set of internal receive optical fibers 47 L , and (2) the timing generation block 32 to optical timing fiber 39 N-1 . Optical fibers 38₁-38 K in multifiber ribbon 12 N-1 are not connected to switching block 31 since they are not required by the distant transmit only module 11 N-1 . A similar arrangement is obtained when connecting a distant receive only module 11 N to multifiber connector 14 N on switch 13 via multifiber ribbon 12 N . However, with this arrangement, multifiber connector 14 N only connects (1) switching block 31 to the K optical fibers 38₁-38 K in multifiber ribbon 12 N via a set of internal transmit optical fibers 48 M , and (2) timing generation block 32 to optical timing fiber 39 N . Optical fibers 37₁-37 K in multifiber ribbon 12 N are not connected to switching block 31 since they are not required by the distant receive only module 11 N . It is to be understood that in FIG. 4 each of the internal optical fibers 47₁-47 L and 48₁-48 M may have one or up to K optical fibers dependent on the type of signal being received or transmitted respectively over that internal optical fiber. It is to be further understood that the number of L input ports and the number of M output ports of each coupler 36₁-36 K can be different for each coupler 36 dependent on the signals received from the associated one or more internal optical fibers 47₁-47 L and transmitted to internal optical fibers 48₁-48 M . For example, a signal from module 11₁ can comprise a video signal requiring K optical fibers whereas a signal from module 11₂ can comprise a voice signal requiring only one optical fiber. The exemplary timing generation block 32, shown in both FIG. 3 and FIG. 4, provides an optical timing signal (TS o ) to optical backplane 10 to synchronize all of the associated N modules 11₁-11 N and the user circuits 26 connected thereto. Timing generation block 32 includes an exemplary single crystal oscillator 33 for generating an electrical timing signal (TS e ), an optical transmit port 34 for converting the electrical timing signal (TS e ) into an optical timing signal (TS o ), and a 1-to-N optical splitter 35 to split the optical timing signal (TS o ) for distribution to each of the N modules 11₁-11 N . Each of the associated N optical outputs from optical splitter 35 is connected via the N multifiber connectors 14₁-14 N to the corresponding optical fiber 39 i assigned to carry the optical timing signal (TS o ) in each of the N multifiber ribbons 12₁-12 N to the separate one of the associated modules 11₁-11 N connected to the other end of each multifiber ribbon 12₁-12 N . Alternatively, it is to be understood, the timing signal can be distributed electrically to each module or broadcast by free-space electromagnetic radiation to each module. Other suitable variations and modifications could be made to either one or all of optical backplane 10 in FIG. 1, module 11 i in FIG. 2, or switch 13 in FIG. 3 and FIG. 4. For example, an alternative to using the K passive optical couplers 36₁-36 K , shown in FIG. 3, is to implement the switching block using one or up to K active couplers. More particularly, the N-to-N passive optical couplers 36₁-36 K would be replaced with an N-to-N active coupler 50 like that shown in FIG. 5. Such exemplary N-to-N active coupler 50 can comprise an N-to-1 passive coupler 51, followed by an optical-to-electrical receiving means 54, an electrical-to-optical transmitting means 55, and then a 1-to-N passive optical splitter 53.

Claims: A backplane (10) for interconnecting a plurality of N associated user circuits comprising means (32) for transmitting a timing signal concurrently to each of N associated user circuits for synchronizing the N user circuits, and CHARACTERIZED IN THAT the backplane comprises a switch (13) including: a plurality of K optical couplers (36), where K>1 and each of the optical couplers includes a plurality of L input ports and a plurality of M output ports, where (1) a signal received at any one of the L input ports is distributed to each of the M output ports, (2) L is different from M, and (3) L and M can be equal to or less than N, and each of the corresponding ones of the L input ports of the plurality of K optical couplers being both associated with a separate one of the N associated user circuits and capable of receiving a separate one of K parallel signals forming a transmission signal from the associated user circuit, and each of the corresponding ones of the M output ports of the plurality of K optical couplers being both associated with a separate one of the N associated user circuits (26) and capable of transmitting a separate one of K parallel signals forming a transmission signal to the associated user circuit. A backplane according to claim 1 CHARACTERIZED IN THAT the timing signal transmitting means comprises: an optical timing source (33,34) for generating an optical timing signal; and a 1-to-N optical splitter (35) including a single input port and a plurality of N output ports, said input port being connected to the optical timing source for receiving the optical timing signal and each of the N output ports being arranged for optical connection to a separate one of the N user circuits for distributing the optical timing signal to each of the N user circuits. A backplane according to claim 2 CHARACTERIZED IN THAT the optical timing source comprises: means (33) for generating an electrical timing signal; and an optical transmit port (34) for converting the electrical timing signal into the optical timing signal. A backplane according to claim 1 or 2 CHARACTERIZED IN THAT the backplane further comprising a plurality of N modules (11) for interfacing each of the N user circuits to the plurality of K optical couplers, each of the N modules being connected to a separate user circuit on one side and to the plurality of K optical couplers on the other side, wherein each of the N modules includes a plurality of K optical transmit ports (23), each optical transmit port being responsible for sending a separate one of K parallel signals to the associated corresponding one of the L input ports of the plurality of K optical couplers associated with said transmitted signals, and a plurality of K optical receive ports (24), each optical receive port being responsible for receiving a separate one of the K parallel signals from the associated corresponding one of the M output ports of the plurality of K optical couplers associated with said received signals. A backplane according to claim 4 CHARACTERIZED IN THAT each of the N modules includes a timing port for converting the timing signal, received from the timing signal transmitting means, into an electrical timing signal that is distributed to the user circuit connected to each module. A backplane according to claim 5 CHARACTERIZED IN THAT each of the N modules includes a contention circuit (22) for determining an instant in time when the associated module will be permitted to transmit the plurality of K parallel signals from its plurality of K optical transmit ports. A backplane according to claim 4 CHARACTERIZED IN THAT each of the N modules includes a contention circuit for determining an instant in time when the associated module will be permitted to transmit the plurality of K parallel signals from its plurality of K optical transmit ports. A backplane according to claim 5 CHARACTERIZED IN THAT each of the N modules includes an addressing circuit (22) for (1) associating the plurality of K parallel signals being transmitted from the associated module with a destination user circuit on another module, and (2) identifying whether the plurality of K parallel signals being received by the associated module are destined for its associated user circuit. A backplane according to claim 4 CHARACTERIZED IN THAT each of the N modules includes an addressing circuit for (1) associating the plurality of K parallel signals being transmitted from the associated module with a destination user circuit on another module, and (2) identifying whether the plurality of K parallel signals being received by the associated module are destined for its associated user circuit. A backplane according to claim 1 CHARACTERIZED IN THAT each of the optical couplers comprises: an N-to-1 optical coupler (51) including a plurality of N input ports and a single output port for coupling optical signals received on the N input ports to the output port; receiving means (54) for converting the optical signal received from the output port of the N-to-1 optical coupler into a representative electrical output signal; transmitting means (55) for converting the representative electrical output signal from the receiving means into a representative optical output signal; and a 1-to-N optical splitter (53) including a single input port and a plurality of N output ports for distributing the representative optical output signal from the transmitting means to each of the N output ports.

Inventors: FOLLETT DAVID RHODES, SOBIN DAVID L, FOLLETT, DAVID RHODES, SOBIN, DAVID L.
Applicants: AT & T CORP, AT&T CORP.
Application year: 1988
Main classification: H04Q3
IPC codes: G06F3, H04Q1, H04B10, H04Q3