Abstract: In order accurately to align an array of optical fibres (10) with optical components such as waveguides (14) in a block of insulative material (12) on a substrate (2) both in the plane of the substrate and in a height dimension normal to the substrate, the fibres are fixed in accurately formed V-grooves (8), and the block (12) has an array of accurately formed solder pads (16) in one to one correspondence with an array of solder pads (4) on the surface of the substrate (2) the array of solder pads (4, 16) being secured to one another by solder drops (6) containing controlled amounts of solder and thus being precisely dimensioned. The fibres (10) may be secured in V-grooves (8) with solder. Some of the solder pads (4) may be formed as conductive tracks electrically interconnecting with electrical components formed in block (12) and integrated circuits formed in substrate (2).

Abstract: A device for measuring the liquid content of a gas, as for example measuring the liquid water content in the atmosphere. The device employs a probe fabricated in part from a material which is thermally self-stabilizing and which preferably has a positive temperature coefficient. In use the probe is electrically heated and disposed in a flowing gas or is adapted for movement through a static gas so that droplets of liquid are deposited on the surface of the probe. Means is provided for detecting a change in the electrical resistance of the probe in response to a change in the heat loss rate due to the integrated evaporation of droplets of liquid from the surface of the probe. The temperature of the gas, the degree of relative movement between the probe and the gas, and the gas pressure are also sensed so that when their measurements are processed with a measurement dependent on the change in the electrical resistance of the probe a measurement is obtained of the liquid droplet content in the gas.

Abstract: The Troposcatter Modem Receiver includes a combiner, demodulator, baseband filter, a complex coefficient forward equalizer, a detector and a feedback circuit. The combiner is a linear maximal-ratio combiner and receives a plurality of input signals at an intermediate frequency and generates a combined output signal for presentation to the demodulator. The demodulator produces a demodulated signal which is filtered by the baseband filter prior to being presented to a first input of the equalizer. The output of the equalizer is forwarded to the detector which produces an output signal. The signal is fed back by way of the feedback circuit to a second input of the equalizer to modify the output signal.

Abstract: A two-wavelength referencing optical sensing arrangement comprises two laser sources for producing simultaneous optical pulse signals of two different wavelengths for transmission over a plurality of discrete optical fibre paths to the sensors terminating such paths. Time-displaced return signals of different wavelengths received over the optical paths from sensors are fed into a single receiver which uses the intensity of signals of one wavelength in order to compensate for unknown losses in the system when indicating measurement of conditions sensed at the locations of the optical sensors.

Abstract: A linear to rotary transducer comprising a linearly movable input structure restrained against rotation by a rotation restraining arrangement and a rotatable output structure, in which a permanently biased torsion spring having the rotatable output structure integral with it is fixed at one end relative to the rotation restraining arrangement and provides at its other end an elongate torsion spring strip along which a linearly movble connection is provided between the linearly movable input structure and the torsion spring strip so that as the input structure and thus the linearly movable connection move towards or away from the rotatable structure the effective location of the rotatable output structure within the active part of the torsion spring is varied in order to produce proportional rotation of the rotatable output structure.

Abstract: A variable bandwidth filter comprises a transistor long-tailed pair. One of the transistors of the pair has a field effect transistor which is connected in the collector circuit of the transistor and which is used as a variable collector load resistor. The field effect transistor is shunted by a capacitor and the gate of the field effect transistor is fed with a control voltage via a feed-back control loop arrangement which serves to maintain constant the d.c. voltage across the field effect transistor whereby the effective bandwidth of a filter circuit defined between the base of the said one transistor is arranged to be controllable in dependence upon the current in the common tail of the pair as determined by a variable current source connected in the tail.

Abstract: A power supply for a laser diode comprising optical detector means coupled for monitoring the intensity of light emitted by the diode, the optical detector means being coupled, via capacitive means, for integrating the signal from the detector means, to the gate of a field effect transistor, the field effect transistor being coupled to the control electrode of a transistor means to control the main current path thereof, the transistor means being arranged to regulate the power supply to the laser diode, whereby the power output of the laser diode is stabilised. The power supply is incorporated with the diode in a module for connection to a printed circuit board for coupling to an optical fibre in a local area network.

Abstract: An optical fiber sensing system for measuring the location and/or magnitude of an external parameter acting at a single point along an optical fiber loop sensor. The system comprises light source means for producing light for propagation in opposite directions around the loop sensor and directional coupler means for coupling the light source means and detector means to the loop sensor and to other optical fiber interfering paths of the system. The detector means are arranged for measuring a phase change (x) between interfering light signals propagating around the sensor loop in opposite directions and for simultaneously measuring a phase change (y) experienced by the light propagating around the loop sensor in one direction. By computation or otherwise, the rate of change of the phase change (x) can be derived and by the use of an algorithm the location and/or magnitude of the applied parameter can be determined.

Abstract: A liquid fuel pump arrangement for delivering fuel to an engine comprises a liquid-ring pump including a motor driven bladed impeller rotor which is located eccentrically within a cylindrical bore of a chamber forming part of a hollow pump body structure. The hollow pump body structure also accommodates a motor-driven prime pump impeller which pumps fuel within the pump body structure to an aircraft or other engine. An inner end wall of the liquid ring pump provides the liquid ring with access to the liquid fuel within the pump body structure while an outer end wall of the liquid ring pump has an air/vapor inlet port through which the bladed impeller of the liquid ring pump during rotation thereof draws air/vapor and an air/vapor outlet port the flow of air/vapor expelled therefrom by compression of the air/vapor within the liquid ring in response to rotation of the bladed impeller being restricted by flow restriction means.

Abstract: A method of alignment of monolithic chips of arrays of light emitting diodes to form part of a print head, the method comprising placing microscopically visible alignment marks on each chip in predetermined positions relative to the diode array carried on the chip, positioning two chips adjacent to one another in desired relative positions, and viewing the two chips through a microscope having a graticule, whereby the alignment marks of the two chips are positioned on the cross wires of the graticule whereby the chips are aligned with their respective diode arrays in a correct spacing and orientation relative to one another.

Abstract: A circuit board (10) is described in which VMEbus connectors (15), wedge-lock clamping means (19), and a heat management layer (13) are mounted on the same side of the board as that whereon the components are mounted and wherein edge guides, are provided in thermal contact with the heat management layer but present heat dissipating surfaces at the opposite side of the board.

Abstract: A method of fabricating a piezoelectric composite comprising an array of piezoelectric elements and a reinforcement structure embedded in a material. The method includes the step of forming the reinforcement structure prior to assembly with the piezoelectric elements, the reinforcement structure defining an array of holes for receiving the piezoelectric elements.

Abstract: An FM interference suppressor comprises two FM demodulators, one of which is fed with an input signal via an envelope detector and is arranged to feed a zero frequency detector and a phase inverter to produce a baseband composite signal comprising wanted and unwanted modulation. The other FM demodulator is fed directly with an input signal directly to produce a baseband signal comprising the unwanted modulation alone. A combiner is provided for subtractively combining the baseband signal and the baseband composite signal to produce the wanted modulation signal.

Abstract: A rotary pump system for pumping a liquid which is delivered under pressure from a backing pump 8, in which a rotary pump 1 has a pump body which is required to be drained of liquid at times when the pump 1 is inoperative, wherein the backing pump 8 has a by-pass circuit between its inlet and outlet ports, the by-pass circuit comprisng a multiphase pump 13 which has a suction inlet 14 connected to a drain point 16 on the pump 1 body and a vortex chamber 17 through which liquid passes from the pump 13 outlet to the backing pump 8 inlet, a central outlet 18 of said vortex chamber being connected to an inlet port 6 of said pump 1. This allows automatic draining of the pump 1 body when use of this pump is not required.

Abstract: An optical assay apparatus of the type comprising an optic waveguide and a coating sensitized to a specific assay species. The light signal response of the apparatus is enhanced by coupling a resonant metallic medium to the waveguide and to the sensitized coating. To this end, a metal coated transparent buffer layer may be interposed between the waveguide and the sensitized coating. Alternatively, a metallized optically matched grating can be used in place of the buffer layer or the metallic medium can be of particulate form, with each particle having a sensitized coating.In using the optical assay apparatus, the sensitized coating is exposed to a fluid assay sample. A light beam is directed onto the sensitized coating and reflected onto a detector. The detected light is monitored for any change indicating the presence of the specific assay species in the fluid sample.

Abstract: A pyroelectric ceramic having the composition: ##EQU1## where .phi. is U (uranium) or Mn (manganese) and in which .alpha. is a number substantially within the range 0.01 to 0.10; x is a number substantially within the range 0.10 to 0.25; y is a number substantially within the range 0 to 0.4; z is a number substantially within the range 0 to 0.05 and .delta. is a number substantially within the range 0 to 0.06. Methods of fabricating the pyroelectric ceramic are also described.

Abstract: A subranging analogue to digital converter comprising a first analogue to digital converter for receiving an analogue input signal to be converted, a digital to analogue converter the input of which is coupled in series to the output of the first analogue to digital converter and a second analogue to digital converter the input of which is coupled in series to the output of the digital to analogue converter. The improvement lies in the provision of a circuit arrangement, in parallel with the first analogue to digital converter and the digital to analogue converter, for inverting the analogue input signal to provide an inverted analogue signal and summing means for combining the inverted analogue signal with the output signal from the digital to analogue converter to provide an input signal for the second analogue to digital converter.

Abstract: A gas handling manifold for use in metal-organic chemical vapor deposition systems, the manifold having a radial configuration with each vent/run valve equidistant from the center. Ensuring that gases switched simultaneously arrive in a reactor vessel substantially simultaneously, alleviating problems caused by intermediate reactions in the manifold. The manifold has minimal unflushed area (dead volumes) allowing incompatible materials to be handled in tandem.

Abstract: A modulator of the type including an array of light modulating elements. To afford fast response and thus greater modulation bandwidth these elements, each comprising a pair of electrodes and a reflector, are defined in a sheet layer of electro-optic solids material. In particular, this material may be of PLZT ceramics material or of a similar ceramic having a high electro-optic coefficient (quadratic). To advantage, the electrodes may be embedded in the sheet layer. Each modulating element is aligned with and connected to a corresponding drive circuit, part of an integrated circuit structure. Conveniently, solder bumps are used to this end.Light is directed onto the array of modulating elements by an optical interface. This may comprise an array of micro-lenses which too may be aligned by solder bumps. A second reflector may be added to each modulating element, each then being optically resonant.