Abstract: An omnidirectional antenna comprises a ring-shaped subreflector surrounding an omnidirectional feed and a ring-shaped main reflector for redirecting radiation from the subsidiary reflector to the target zone. The feed has a focal ring and a hollow centre to accommodate supports, feeders etc which facilitates stacking of antennas.

Abstract: A node of an optical transmission network, for example a local area network, has a combined by-pass switch and optical modulator. The by-pass switch and modulator (45) comprises an optical switching matrix with two non-intersecting waveguides (W1, W2) connected by a further waveguide (W3). The junctions between the non-intersecting waveguides and the further waveguide perform both modulation of an optical carrier signal and re-routeing of the transmission path along the network.

Abstract: A method and apparatus for monitoring and/or controlling the frequency of a beam of coherent radiation. The apparatus comprises a reference source (1) which is controlled to generate reference radiation beam with a frequency which is repeatedly swept through a range of operating frequencies. This reference beam is combined with a beam of coherent radiation from a test source and the combined beams are fed to a photodiode (9). The output of the photodiode (9) can be displayed so that the upper and lower beat frequencies can be determined enabling the variation of the average of the upper and lower beat frequencies with time to be monitored. Alternatively, the average beat frequency can be fed back as a control signal to control the test beam source (8). In this latter case, the frequency of the test beam will be locked.

Abstract: An optical communication system is disclosed comprising a transmission assembly including a semiconductor laser amplifier. The laser amplifier superimposes onto an amplitude modulated signal a phase modulation corresponding to the amplitude modulation. The optical communication system may further include a separation device for filtering out the amplitude modulation. A receiving assembly is provided for detecting the phase modulation of a transmitted signal.

Abstract: A communication network comprises a number of slotted rings which interconnect nodes so that information is carried between nodes in the form of slot sized packets on each ring. Each node includes controller for controlling the maximum acces delay experienced by packets belonging to the synchronous services, and selector for allowing any synchronous connection to utilize the first available ring for transmission of packets.

Abstract: A submarine telecommunications cable includes a plurality of optical fibers in the bore of an orientated plastics strength member. The cable may have an average density of 0.9 to 4.0 and preferably a neutral buoyancy whereby most of the weight of the cable is carried by the sea. This reduces tension in the cable during laying. The bore of a submarine cable is filled with a solid elastomeric embedding medium which occupies the space between the fibers. This gives a void-free structure which assumes ambient pressure. The strength member may be made from orientated polyethylene. The cable is preferably buried in the sea bed during use.

Abstract: A semiconductor device is disclosed that comprises a base semiconductor portion and, thereon, first and second elevated semiconductor portions separated by a channel. The uppermost surface of the first elevated semiconductor portion carries a metal electrical contact layer and the uppermost of the second a dielectric layer. The surfaces defining the channel are substantially free of metal and dielectric. The structure can be used in a ridge waveguide laser, the first elevated semiconductor portion constituting the ridge. Distributed feedback corrugations may be incorporated in such devices or in other ridge waveguide structures.

Abstract: Rare earth elements, e.g. Nd, are introduced into optical glass fibre for telecommunications by evaporating a suitable salt, e.g. NdCl.sub.3, from a glass sponge into the gas stream used to deposit core material. Preferred sponges are in the form of tubes having an outer impervious layer and an inner porous layer. These sponges are conveniently made by MCVD and the impregnation is preferably carried out using an alcoholic solution of the impregnant.

Abstract: A fused optical fibre coupler in which one of the fibres has a propagation constant which in the coupling region is slightly different from that of the other. The propagation constant difference can be arranged to provide selected splitting ratios over a relatively wide wavelength range.

Abstract: An improved technique for mounting optical components on a substrate comprises providing each component with a dedicated heating element on the component itself to permit controlled and well-localized heating of solder on the substrate during fixing. In the example illustrated the optical component is an optical fibre carrier comprising fibre (10), carrier plate (12) and heating element (20), which itself comprises an ink film resistor (22) deposited on a ceramic chip (21) having metallized electrical contacts (23).

Abstract: An optical fibre transmission line is installed by first installing a conduit having one or more bores and subsequently inserting flexible, lightweight optical fibre members containing the optical fibres into the bores.The optical fibre members are propelled by employing the fluid drag of air, or another suitable gas, passed at high velocity through the bores.

Abstract: A SAW device is formed by applying metallized areas (11) to a surface of a SAW substrate (10) and attaching conductive leads (18) to the metallized areas. The substrate is inverted and located on a hybrid circuit so that the leads (18) contact and are supported on conductive areas (30) of the circuit. This mounting arrangement minimizes the stresses which occur in the substrate in its operational life. A novel shape for the device is also disclosed.

Abstract: The present invention provides an apparatus for selectively connecting one of a plurality of data units (21,22,23) (for example modems) to a telephone line (20). The apparatus comprises a plurality of interface circuits (24) each having a respective data unit connected thereto. Also connected to each interface unit, and thereby connecting the interface units together, is a common dialing device (28), a telephone line, a dial request bus and a line occupied bus. Each interface circuit has a dial connect switch and a line connect switch, a first switching means for connecting the telephone line to the common dialing device, on operation of the dial connect switch, and a second switching means for disconnecting the telephone line from the common dialing device and connecting the telephone line to a data unit on operation of the line connect switch.

Abstract: An electronic adaptive recognizing device which includes an input store having a number of storage locations for receiving an input signal, and a number of addressable stores each having one or more address lines connected to a number of the input store locations in either a random way or one determined by the input signal. The contents of the input store specify addressable store locations at which words of at least one bit are stored. Structure is provided for deriving a common value based on the words stored at the specified addressable store locations and for calculating a corrected value based on a received value and the common value. An updated value is applied, dependent on the corrected value, to each of the specified addressable store locations so that the common value is adapted to changes in the dependence of the received value on the input signal and so that the device can output an appropriate corrected value for a given input signal.

Abstract: A broadband digital transmission system is disclosed which enables high bit rate data streams to be transmitted over low bit rate telephone networks. A high bit rate stream of data from a source is distributed by a distributor into six separate streams to provide six low bit rate streams of data. A call unit establishes six channel communication with a receiver and the six data streams are fed in parallel along six channels. A reassembler receives the six low bit rate streams and reconstructs them to produce the original high bit rate stream of data.

Abstract: A transversal finite impulse response, adaptive digital filter comprises three stages (10, 11, 12). The stage (10) is a memory stage which stores input samples x and coefficients. The second stage (11) is an arithmetic stage which forms convolution products and accumulates the product to provide an output. The third stage (12) forms update values for updating the coefficients according to a predetermined algorithm. The stages are coupled by buses (14, 15) and data transfer between the stages via the buses is controlled by a control unit (18). The filter operates so that convolution products are formed during a first part of each sample period and update values are formed during a second part of each sample period for use in the subsequent sample period.

Abstract: An optical fibre Michelson interferometer has mirrors of highly reflective coatings deposited on the ends of the fibres forming the free arms of the interferometer. The interferometer preferably comprises single mode fibres, and is operated by a frequency swept laser.The interferometer has applications in the optical fibre interferometer sensing field.

Abstract: A series of electrical connector assemblies each comprising plugs and corresponding sockets which are of a number of different widths. Narrower plugs of the series are prevented from insertion into wider sockets of the series by the variation of the height of the plugs and sockets and or the cross-sectional dimensions of a key and keyway provided on the plugs and sockets. Further differentiation, between plugs and sockets of the same width, is achieved by variation of the location of the key and keyway on the plug and socket sidewalls and or the cross-sectional dimensions of the keys and keyways.

Abstract: The antenna (e.g., a transportable, lightweight and cheap antenna for temporary earth stations) is constructed out of three components. The center component is a circular/parabolic dish. The side components extend the dish to give the composite a major diameter and a minor diameter. In use the antenna is aligned so that the major diameter is aligned with the direction of the geostationary arc.

Abstract: A regenerator 10 is provided with a tuning recovery facility 15 which has a multiple passband capability. The regenerator can operate with several line bit rates each corresponding to one of the passbands.