Abstract: A multi-layer Langmuir-Blodgett film having non-linear optical properties is described. Alternate layers of the film are composed of first and second elongate chromophore molecules extending transverse to the plane of the film in a Y-configuration. The molecules are sythesised so that when deposited in a Y-configuration they are non-centrosymmetric and therefore exhibit significant optical nonlinearity.

Abstract: A multi-input/output optical switch structure comprises a pair of parallel, inwardly facing main mirror elements 24, 25 and mounted equidistant between the main mirror elements is a co-linear array of optical switching units 40. To provide the multi-switching function and to compensate for the fact that the switch units are in a colinear array there are a plurality of additional mirror elements (41,42,43,44) mounted between the linear array and one main mirror element.

Abstract: Flexible electrical connectors are employed to connect rigid members, such as plugs and printed circuit boards. Such connectors have a tendency to tear, especially in the region near the rigid member, and this can prove expensive to remedy. The invention provides reinforcing thread members, for example, along the connector which prevent any tear which may develop from growing further.

Abstract: A charge coupled device (CCD) image sensor for producing a video output for a given TV line standard wherein the image section (9) has a number of CCD elements appropriate to the given line standard and the store section (11) has a number of CCD elements appropriate to a second, higher line standard. The electronic package required to drive the sensor is then not very different from an electronic package required to drive a sensor for the higher line standard, thus making it practicable to use in the sensor an electronic package capable of use in sensors for either standard.

Abstract: Infra-red from a field of view is periodically interrupted before being incident on a mechanically resonant detector. Resonation of this caused by the photo-acoustic effect is detected by an optical beam.

Abstract: A Gunn effect oscillator comprises a body of semiconductor material in which electrons are injected from one region to another region via a very thin intervening system. The thin region has a thickness which is less than the mean free electron path length and is typically of the order of 100 .ANG., which results in hot electrons being transferred from the injection region into the other region in which electron bunches form.

Abstract: By placing a mirror in the field of view of an infrared imager it is caused to produce an image of its own detector assembly which is correctly focussed when the lens system is focussed at infinity. This phenomenon is used either manually or automatically to focus the system.

Abstract: The output of a laser diode or L.E.D. is amplitude modulated by varying the forward current through it. This is done by applying a dc current component from a first current source and an ac current component from another part of the circuit. The ac current component is applied to the laser diode or L.E.D. via an ideal impedance matching transformer which includes the internal capacitance of the laser diode or L.E.D, such that when the frequency of the modulating signal is varied, and hence the response of the laser diode or L.E.D varies, ideal matching is still obtained since the internal capacitance enables compensation to be made.

Abstract: In a radar receiver signals at IF are converted to digital form at 22 and the real and imaginary components are separated at 24 and 25 before passing to respective digital low-pass filters 28 and 29. These filters operate by adding samples within blocks of a given number of samples. In order to reduce the response of these filters at the sum frequency the first and last member of each blocks of samples taken by the filter is weighted so as to reduce its value relative to the center values of the batch which are left unchanged relative to each other.

Abstract: A thermal imaging device uses a compensated cholesteric liquid crystal mixture as its thermo-optic conversion element. The mixture is obtained by mixing two cholesteric liquid crystals, one with a left-handed twist and the other with a right-handed twist. The twists cancel at a compensation temperature, the mixture thus having infinite twist at this temperature. The device is designed to operate with the mixture held in the region of the compensation temperature.

Abstract: A self-excited induction motor variable speed drive using a known self-excitation method in which a capacitor is connected in parallel with the motor. Power is supplied by a supply convertor, a D.C. link and a motor convertor, the latter running at the motor frequency. The motor convertor includes a current bypass switching circuit comprising a capacitor bank connected to the motor terminals and to a neutral point between a pair of thyristors connected across the D.C. link.

Abstract: A terminal for a telephone system and for receiving digital data in the form of a time multiplexed (TDM) data stream incorporating frames appearing at a predetermined frame period and each frame incorporating a frame word. The terminal comprises a frame word detecting circuit (52) for detecting frame words; an alignment detecting circuit (53, 55, 56) for determining whether a received TDM data stream is in alignment or not; a search circuit (53, 55, 56, 57, 59, 60) for initiating a bit-by-bit search of the incoming data stream for the sequence of bits forming the frame word when an "out-of-alignment " condition has been detected by the said alignment detecting circuit; and a delay circuit (58) for delaying the start of the bit-by-bit search after an "out-of-alignment" condition has been detected.

Abstract: A fibre-optic coupler has the claddings of two or more optical fibres partially fused together over a coupling region, and a body of light-transmissive material, having a variable refractive index, contacts the claddings at the coupling region, such that by varying the refractive index of said body light transmitted along one fibre is split between the fibres in a varying ratio.

Abstract: The present invention enables compression of digitized pictorial data to be achieved by comparing a data block of a predetermined size with a group of patterns relevant to that size held in a library. If a match is found the data block is represented by a code identifying the pattern on an output signal by a code identifying the pattern. If no match is found, the data block is sub-divided into smaller blocks which are compared with another group of patterns relating to the smaller block size. This sub-division process continues until the data is matched or a predetermined minimum size of data block is reached, in which case the data itself is applied to the output signal. The compressed data may be reconstituted and displayed or used to monitor the progress of a vehicle, for example.

Abstract: A temperature sensing and measuring system in which a luminescent material is excited using a light source. The luminescence emitted decays with time, the decay time being dependent on temperature. Thus by monitoring the excitation and luminescence transmitted to and from the material via an optical fibre, the decay time constant and thus the temperature can be determined.

Abstract: An electric power measuring device wherein input analogue signals representative of instantaneous values of current and voltage are applied to a multiplier (23) and the resulting product signal is applied to a converter (35, 37, 41, 43, 45, 47) to provide a pulse output signal having a pulse rate representative of the product, and hence of the level of power consumption. The converter is of the kind including a capacitor (35) which is charged during successive periods of equal duration by the product signal and a much larger reference signal which reverses at the end of each capacitor charging period until the capacitor charge does not reverse in polarity during a charging period, so that reversal of charge on the capacitor is assured during the next charging period, whereafter the direction of the reference signal is again reversed at the end of each charging period.

Abstract: A sensor comprises a beam, e.g. of silicon, which resonates at a frequency dependent on the force imposed on the beam. Light on a line induces resonance of the beam by means of the photothermal effect. The light reflected from the beam is amplitude modulated at the resonance frequency, and returns along the line. It is reflected by a semi-reflecting plane mirror onto a lens which focusses it onto a photodetector. The photodetector produces an output voltage modulated at the oscillation frequency, and is thus representative of the force imposed on beam 1.

Abstract: A folding antenna for use in a satellite communication system comprises a box having a base (1) which forms the supporting structure for the antenna. A main reflector (16) is mounted on a platform (11) to which it is pivotted about a first axis (14). A sub-reflector (26) is pivotted to the main reflector about a second axis (21). By pivotting the sub-reflector and the main reflector downwardly they can be stowed into a position close to the base (1) and the lids (8) of the box closed to protect the system during transportation.

Abstract: A device for removing a component from a substrate to which it is secured by solder. The device has a moveable member which defines a space to which suction can be applied. The space has an opening which can be positioned against the component so as to hold the latter to the moveable member by suction. Provision is made for applying heat to the solder to soften it. The moveable member is arranged such that the suction causes it to pull the component so as to remove it from the substrate when the solder is molten.