Abstract: A high power monomode laser arrangement is able to manipulate the output from a high power laser diode array pump source using a computer-generated hologram to launch a high proportion of the pump source light into a multimode fibre portion including input reflector. A monomode fibre portion with the same fundamental-mode spot size as the multimode fibre portion is optically coupled to the multimode fibre portion and includes a reflector which reflects only the fundamental mode of the multimode and monomode fibre portions. The fundamental mode reflection forced by the monomode fibre portion provides the feedback necessary to force predominantly fundamental mode oscillation which enables stimulated emission in only the fundamental mode.

Abstract: A fault signalling system for an optical fiber-based communications link having erbium doped fiber amplifier repeaters comprises a broadband optical source for generating a fault signal in the event of a fault occurring. Each repeater includes such a broadband source, which will output a characteristic fault signal onto the link for transmission to a receiving station, in the event of a fault being detected at that repeater. Advantageously, a control circuit which enables the source to emit its fault signal when appropriate is also used as part of an automatic gain control for the output of the amplifier repeater in normal operation.

Abstract: A switched telecommunications network includes different types of traffic, such as audio data, including voice data, fax and modem originated data, digital computer originated data and video data. A communications link connects a user's site to the network, and a bandwidth manager is provided to multiplex traffic of different types for transmission over the link. After transmission over the link, a complementary bandwidth manager is arranged to de-multiplex the traffic for application to the respective switch. The bandwidth manager is arranged to dynamically allocate bandwidth to the different types of traffic, thereby optimizing the available bandwidth provided by the communications link.

Abstract: An optical code recognition unit (OCRU) for recognizing a predetermined n-bit optical code has an n-way splitter having an input and n parallel outputs. A plurality of combiners are associated with the splitter outputs, and a respective gate is controlled by the output of each of the combiners. Each of the splitter outputs is subject to a different delay of from 0 to (n-1) bit periods, and each combiner receives an input from at least one of the splitter outputs. The OCRU is such that all the gates are turned on if a predetermined optical code is applied to the splitter input.

Abstract: A system for installation of optical fibre transmission lines into ducts by feeding coiled optical fibre packages from a container with an annular configuration. The optical fibre package comprises filamentary material coiled into a series of turns each offset from preceeding turns and containing 360 degrees of torsion.

Abstract: The resistance of a resistive memory element, e.g. a synaptic element is programmed, e.g. adjusted to a target value, by pulses of a constant height and variable width. One polarity gives an increase in resistance; the other polarity gives a decrease. A short pulse applied after a longer pulse appears to have no effect. After each polarity change short pulses can again be used to make small adjustments. In a preferred embodiment longer and longer pulses are used until the resistance overshoots the target value. After overshooting the polarity is reversed and a second series of pulses is used to obtain a closer approach to the target. The resistive element comprises a resistive layer located between two electrodes, e.g. a matrix of amorphous silicon doped with boron containing V. One electrode is Cr and the other is V.

Abstract: A service node is used in an intelligent communications network to provide services for customers. The node includes a service defining sub-system arranged to define a plurality of services. A first resource has a memory for storing speech segments, each segment having a corresponding identity, and a resource controller is arranged to convert a received command signal to a corresponding succession of speech segment identities for a speech announcement corresponding to the command signal. The first resource accesses the memory storing speech segments in accordance with the speech segment identities, to generate the corresponding speech segments for the speech announcement and provides an "announcement finished" signal when a last speech segment of the announcement has been generated. A switch is arranged to connect the first resource to an incoming call routed by the network to the service node.

Abstract: An optical memory for storing optical signals of a first wavelength comprises a first non-linear loop mirror switch having first and second optical ports, an optical delay line having one end coupled to one port of the first switch and its other end coupled to a reflector. The delay line includes an optical amplifier for providing gain at the first wavelength.

Abstract: A planar waveguiding device has the cores of fibre tails directly connected to the path regions of the waveguiding structure. The devices are produced by attaching the fibre tails before the path layer is deposited. The direct connections are produced when the path layer is sintered.

Abstract: The present invention is based on the use of a plurality of gratings recorded in an optical waveguide, the gratings having different Bragg wavelengths selected to store individual bits of data. The invention has particular application to optical fiber communications networks.

Abstract: An optical network having a spatially-multiplexed plurality N of optical waveguides is employed in conjunction with another, non-spatial signal multiplexing technique (e.g., frequency multiplexing) defining a plurality M of further optical signal channels thereby providing an enhanced number N.times.M of optical signal channels that can be selectively coupled to by optical signal processors.

Abstract: A telecommunications system comprising first and second nodes interconnected by a network transmission line. The first node comprises an optical data generator for producing an optical data signal at a first wavelength, an optical header generator for producing an optical control signal at a second wavelength, and means for multiplexing the data and control signals onto the transmission line. The second node comprises a switch and a controller responsive to signals at the second wavelength for controlling the routing of optical signals through the switch. A delay unit and associated control means are provided to ensure that sufficient delay occurs between the transmission start times of the control and data signals that the control signal completely overlaps the data signal at the second node.

Abstract: A Sagnac interferometer (19) is defined by four port, 50:50 optical fiber coupler (20), two output ports (38, 40) of which are coupled together by a non-linear semiconductor laser amplifier (3) in series between a pair of optical fibres (22, 24). The coupling losses between the ports (38, 40) and the amplifier (30) are different. An input pulse coupled to port (34) of the coupler (20) is split into two portions which counterpropagate from one of the output ports (38, 40) to the other. The portions return to the coupler (20) with an intensity dependent relative phase shift. This provides switching of an input pulse at the input port (34) between the input ports (34 and 36) dependant on the intensity of the input pulse. The device can provide intensity dependent switching at optical power levels of less than 250 .mu.W.

Abstract: A public telecommunications system includes a local exchange 10, an element manger 11 for managing the exchange 10 and a configuration manager 12 for managing the element manager 11. The element manager 11 is located with the exchange 10 and the configuration manger 12 is situated at a distant location. The exchange 10, element manager 11 and configuration manager 12 are connected by communication links 18, 19. In order to provide a new or existing customer with basic telephony services or one or more supplementary services such as call forwarding, the configuration manager 12 sends an appropriate set of requests to the element manager 11. If one or more of the requests are not successfully performed in the element manager 11, the configuration manger 12 sends further requests to the element manager 11 to cancel the requests which have been successfully performed and thereby return the element manager 11 to its original configuration.

Abstract: An optical transmission system including an interferometer and a source of optical signals. The interferometer comprises a four-pod optical coupler having first and second input ports and first and second output pods, a silica optical fiber coupling the first and second output pods which exhibits the Kerr optical non-linearity, and an erbium fiber optical amplifier situated asymmetrically between the output ports. The source of optical signals is coupled to the first input port of the interferometer. The system is operated in a regime in which the optical signals saturate the amplifier thereby suppressing any oscillatory output, and their power is sufficient to switch an input signal coupled to the first input pod to the second input pod. This provides pulse shaping and amplification characteristics which are relatively insensitive to the input power of the optical signals from the optical source.

Abstract: An optical switch comprises an optical fibre Sagnac loop interferometer having an input port and an output port. A source of optical signals at 1.53 .mu.m is coupled to the input port and a source of control optical signals of wavelengths 1.30 .mu.m and 1.31 .mu.m are coupled to the interferometer by a dichroic coupler. The coupler splits the 1.53 .mu.m input optical signal into two signal portions which counterpropagate round the loop and couples the control signal to propagate in one direction only round the loop. The phase difference between the signal portions at the output port is dependent on the intensity of the control optical signal when they recombine at the coupler. The optical control signals are formed by combining at least two optical pulse streams, the pulses of distinct optical pulse streams being non-interferometric, to provide a logical AND gate.

Abstract: A planar waveguiding device has the cores of the fibre tails directly connected to the path regions of the waveguiding structure. The devices are produced by attaching the fibre tails before the path layer is deposited. The direct connections are produced when the path layer is sintered.

Abstract: An optical code recognition unit (OCRU) for recognising a predetermined n-bit optical code sequence coded using the Manchester code format, has an n-way splitter (7) having an input and n parallel outputs (7a). A plurality of gates (9a, 9b, 9c, 9d) are associated with the splitter outputs (7a), respective pairs of splitter outputs leading to each of the gates ( 9a, 9b, 9c) via a respective optical combiner (8a, 8b, 8c), and any remaining single splitter output leading directly to its gate (9d). Each of the splitter outputs (7a) is subject to a different delay of m half bit periods, where m=0 to 2(n-1), the values of m being chosen such that, if a predetermined optical code sequence is applied to the splitter input, the `1`s in the outputs of each of the pairs of splitter outputs (7a) reach the associated AND gates (9a, 9b, 9c) and the `1` in any remaining single splitter output (7a) reaches its AND gate (9d) at predetermined times such that all the gates are turned on.

Abstract: A method of multipoint communications utilizes a protocol in which data messages (10) sent by a primary source are multicast to a plurality of secondary receiving stations (S.sub.1 . . . S.sub.n). Each message packet contains a control field comprising a station identifier code (14) and an instruction for the specified station to acknowledge a predetermined number of messages. Each successive message packet comprises a station identifier code which differs in an alterable set cyclical sequence. Thus, acknowledgements of correct receipt of data are taken in a cycle of length L such that in a space of L messages each receiver must acknowledge at least once. In this way the primary source need only keep the L latest messages because all the stations have acknowledged correct receipt of at least up to the current message minus L. The multipoint communications method uses a protocol which can be applied to existing communications networks.

Abstract: An optical fibre amplifier comprises a thulium-doped optical fibre pumped at 790 nm by a semi-conductor diode laser coupled to the fibre via optical fibre coupler. The amplifier is optically coupled in series to a pair of systems fibres to provide amplification to optical signals.