Electrooptical connector in an optical bus system

Abstract: An electrical apparatus having an electro-optical connector is described which permits the use of electrical circuit cards in a rack mounted system using an optical bus by converting optical signals to electrical signals and vice versa.

Description: This invention concerns connectors for interfacing between optical and electrical circuits and is particularly, but not exclusively concerned with the type of connector, generally termed a "back plane" connector whereinto an electrical circuit card may be plugged. The communication of signals and data by means of modulating optical beams transmitted via optical fibres or other optical waveguides offers the potential advantages of freedom from radio frequency interference (RFI) and very low propagation loss (fractions of dB per kilometer for single-mode fibres). In terms of equipment practise (i.e. designing and constructing racks of electronic equipment - each rack comprising a number of trays each containing a number of electronic printed circuit card assemblies), there is considerable, and growing, interest in realising so called "optical back-planes" to route and interconnect high-speed signals between cards, trays and using standardised back-planes containing a common optical waveguide "bus" which can be connected to optical waveguides on each card via a standard optical plug and socket arrangements akin to the ubiquitous edge-connector. In general however, while the equipment designer will be quite aware of the performance benefits that will accrue from the use of such optical back-planes, he will nevertheless prefer to be presented with straightforward electrical design tasks at the equipment level (i.e. he will prefer not to have to be expert at opto-electronic data communications in order to route and interconnect what are basically electrical signals). The present invention seeks to provide just such an interface by the use of connectors which emulate electrical interconnects, using opto-means. Prior art document WO-A-85 03179 (Hase) teaches a light conducting plate on which individual switching circuits are mounted and provides an alternative to more conventional electrical bus systems. The plate has a boundary layer of material with an index of refraction selected so as to retain light within the plate. Coupling of the switching circuits is achieved by arranging coupling windows in the boundary layer of material with electro-optical and opto-electrical transducers at both the transmit and receive windows. Light transmitted by a transmitter is refracted through the plate to a receiver via each of their respective windows. JP-A-58 012 450 (Nippon) teaches large capacity interconnection of packages, without complicated back wiring boards, by converting an electrical signal associated with each package into an optical signal using an electro-optic converting circuit and transmitting that signal along an optical fibre which interconnects a plurality of packages. A receiving package converts the received optical signal into an electrical signal using an electro-optic converting circuit. Therefore, from the prior art, it is known to provide an opto-electrical connector having a plurality of optical input and/or output paths operably connected to a transducer means and an associated plurality of electrical input and/or output paths also operably connected to the transducer means, the transducer means being operable to convert an optical signal on an optical input path into an electrical signal on an electrical output path and/or being operable to convert an electrical signal on an electrical input path into an optical signal on an optical output path. It is an object of the present invention to provide an improved connector wherein the aforesaid emulation is achieved. According to the present invention an opto-electrical connector is releasably connectable and comprises a first part arranged to carry the optical input and/or output paths and a second part to mate with the first part and to carry the electrical input and/or output paths. The first part of the connector may comprise a socket and the second part may comprise a plug. The transducer means are preferably located in the second part and each path in the first part of the connector may be entirely optical. Each input and output path of the first part advantageously couples directly or indirectly with an optical bus. Similarly, each electrical input and output path of the second part may be connected to an electrical bus. One or more of the paths through the connector may be bi-directional. The transducer means of each path through the connector may comprise an opto-electrical transducer and/or an electro-optical transducer. Each path may include amplifier means. Preferably, each amplifier means may be arranged to amplify an electrical input or electrical output signal. Each amplifier means may be a bi-directional buffer amplifier for conditioning electrical input and output signals. In a preferred embodiment, the first part of the connector may be in the form of a back plane connector of a rack-mounted electronic apparatus wherein data and/or signal paths may be carried by at least one optical bus and each second part of the connector is carried by a data processing card, such as a printed circuit card, and may be arranged to be plugged into the back plane connector with the first and second parts of the connector mating. Either the or some of the optical paths or the or some of the electrical paths may carry non-interfering signals using Wavelength Division Multiplexing (WDM) or a similar technique, the first or second part of the connector then including the necessary optical and/or electrical multiplexing or demultiplexing means. The invention will be described further, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic representation of part of a rack mounted electronic apparatus; and Figure 2 is a diagrammatic representation of one form of a connector, in accordance with the present invention, used in the apparatus of Figure 1. As schematically shown in the drawings, an electronic apparatus may be in rack mounted form. Examples of such apparatus are well known and widespread. Computers from desk-top to mainframe generally have such form as do digital exchanges, radar apparatus, video signal processors etc. As is conventional, the apparatus comprises a frame indicated in the schematic by the reference numeral 10 which supports trays schematically shown at 12, each arranged to receive a plurality of cards schematically indicated by numeral 14. In the conventional form, the frame has an electrical bus which supplies tray buses with data and power lines. The cards are usually printed circuit cards adapted to be supported on the trays and to be connected to the tray bus via an electrical multipin or edge connector schematically shown at 16. Whilst the technology of optical data or other signal transmission is now well advanced, the cards themselves are still arranged for electrical data or signal processing. In accordance with the present invention, the connectors 16 are interface connectors and enable the use of optical frame and tray buses for carrying data or signals between the cards 14 whilst the cards themselves do not require hybrid circuitry and operate on electrical data or signals as heretofore. Thus, in the arrangement schematically shown in Figure 1, the frame 10 carries a rack optical bus 18 which in turn feeds intra-tray optical buses 20 whereto a first part of each connector 16 is connected. Each card 14 has secured thereto a second part of the connector 16 which second part has electrical outputs and electrical inputs. In accordance with the present invention, the connector 16 embodies all the necessary transducers and circuitry to interface between the electrical circuitry of the card and the optical circuitry of the tray and frame buses. Referring now to Figure 2, one form of connector 16 is shown. The intra-tray optical bus 20 is in the form of a plurality of optical waveguides 22. Each waveguide 22 provides a spur 23 into a first part 24 of the connector 16. At a mating interface 26 between the first part 24 and a second part 28 of the connector 16, optical connections 30 are provided whereby optical data or signals on the bus 20 are fed to the second part 28 of the connector 16. In the second part 28, each optical coupling at the interface 26 feeds a waveguide splitter/combiner 32 to provide an input 34 to a photodiode 36 and an output 38 from a laser or LED 40. The diode 36 is followed by an amplifier 42 and each laser or LED 40 is preceded by a driver amplifier 44 whereby incoming or outgoing optical signals are converted to or from matching electrical signals on a card 14 whereon the second part 28 of the connector 16 is mounted. The output of the amplifier 42 and the input to the driver amplifier 44 are connected via a control means 46 to provide a 1-bit input/output port 47 of, as shown, a 4-bit input/output port of the card 14. Power leads 48 from the card 14 provide power for the transducers and their amplifiers. The card 14 is, in this case, supplied with power, for example, via a flying lead and a further connector (not shown). It will be appreciated that power may be provided along the buses 18 and 20 and the connector 16 may include power feed paths to power the transducers (and the cards) if desired. The first and second parts 24, 28 of the connector 16 are arranged to mate in close tolerance register. In this way, the optical connections 30 may be simplified requiring only that the spurs 23 be brought into close adjacency with the inputs to the splitters/combiners 32 so that their evanescent fields interact. Similarly, the spurs 23 may be coupled to the waveguides 22 merely by interaction of the evanescent field of light conducted therealong. The invention is not confined to the precise details of the foregoing example and variations may be made thereto. For instance, the transducers 36 and 40, and/or amplifiers 42, 44 and/or the control means 46 may be provided in the first part of the connector 16. In such case, the combiner/splitters 32 may couple directly to the waveguides 22 whereby losses may be minimised. The path connections between the first and second parts 24, 28 of the connector 16 may then be provided by simple ohmic connections. The connector 16 has been described, for simplicity, in relation to a 4-bit bus. It will be appreciated that the invention is equally applicable to any size optical bus. Further, control paths have not been shown. The connector 16 may be "intelligent" and incorporate additional degrees of interface "smartness" whereby problems associated with intra-equipment communication protocols and electrical/optical signal multiplexing may be reduced. Further, wavelength division multiplexing may be employed to permit simultaneous transmission of more than one optical signal along each waveguide 22. In such case, multiplexing and de-multiplexing means are provided in the connector 16 and the number of electrical paths increased by the multiplexing factor. The electrical I/O control means 46 could itself provide MUX/DMUX to increase the number of effective electrical inputs and outputs. The connector 16 could be up-rated by the provision of application specific integrated circuits (ASICs) dedicated to a particular bus operating protocol. Other variations are possible within the scope of the present invention.

Claims: An opto-electrical connector (16) having a plurality of optical input/or output paths (23) operably connected to a transducer means (36, 40) and an associated plurality of electrical input and/or output paths (47) also operably connected to the transducer means (36, 40), the transducer means being operable to convert an optical signal on an optical input path (23) into an electrical signal on an electrical output path (47) and/or being operable to convert an electrical signal on an electrical input path (47) into an optical signal on an optical output path (23), characterised in that the opto-electrical connector (16) is releasably connectable and comprises a first part (24) arranged to carry the optical input and/or output paths (23) and a second part (28) arranged to mate with the first part (24) and to carry the electrical input and/or output paths (47). An opto-electrical connector (16), as in Claim 1, wherein the first part (24) of the connector (16) comprises a socket and the second part (28) comprises a plug. An opto-electrical connector (16), as in Claim 1 or 2, wherein the transducer means (36, 40) is located in the second part and each path (23) in the first part (24) of the connector (16) is entirely optical. An opto-electrical connector (16), as in any preceding claim, wherein each input and output path (23) of the first part (24) couples directly or indirectly with an optical bus (20). An opto-electrical connector (16), as in any preceding claim, wherein each electrical input and output path (47) of the second part (48) are connected to an electrical bus. An opto-electrical connector (16), as in any preceding claim, wherein one or more of the paths (23, 47) through the connector (16) is bi-directional. An opto-electrical connector (16), as in any preceding claim, wherein the transducer means (36, 40) of each path through the connector (16) comprises an opto-electric transducer (36) and/or an electro-optic transducer (40). An opto-electrical connector (16), as claimed in any preceding claim, wherein each path (23, 47) includes amplifier means (42, 44). An opto-electrical connector (16), as in Claim 8, wherein each amplifier means (42, 44) is arranged to amplify an electrical input or electrical output signal. An opto-electrical connector (16), as in Claim 8 or 9, wherein each amplifier means (42, 44) is a bi-directional buffer amplifier for conditioning electrical input and output signals. An opto-electrical connector (16), as in any preceding claim, wherein the first part (24) of the connector (16) is in the form of a back plane connector of a rack mounted electronic apparatus wherein data and/or signal paths are carried by the at least one optical bus (18), each second part (28) of the connector (16) is carried by a data processing card, and are arranged to be plugged into the back plane connector with the first and second parts (24, 28) of the connector mating. An opto-electrical connector (16), as in any preceding claim, wherein at least one of the optical paths (23) or at least one of the electrical paths (47) carries non-interfering signals using Wavelength Division Multiplexing (WDM) or a similar technique, the first or second part (24 or 28) of the connector (16) then including optical and/or electrical multiplexing or demultiplexing means.

Inventors: WISBEY PHILIP HENRY, WISBEY, PHILIP HENRY
Applicants: MARCONI GEC LTD, GEC-MARCONI LIMITED
Application year: 1993
Main classification: H04B10
IPC codes: H04B10, G02B6