Abstract: A relatively large scale low cost method of fabricating optical devices with associated coupling lenses comprises the following steps:(a) producing in one surface of a substrate (1) of suitable material(s) a predetermined array of planar diffused lenses (4);(b) forming or otherwise producing on the opposite surface of the substrate (1) remote from the planar lenses (4) but in predetermined positional relationship to the lenses in the general planar direction of the substrate an array or pattern of metallic bonding pads or other registration means co-operable with corresponding pads or other means provided on a multiplicity of optical devices (10) for the accurate registration of such devices relative to the optical lenses; and,(c) dividing the substrate (1) into a multiplicity of parts each of which comprises an optical device (10) having an associated planar lens (4).

Abstract: An optical sensing arrangement in which optical signals are transmitted along a plurality of discrete optical fibre paths of different lengths which are terminated in respective sensors adapted for sensing temperature, pressure or any other condition to be sensed at appropriate locations and in which optical signals reflected or otherwise caused to be transmitted back along the optical fibres of different lengths in response to the transmission of the optical signals along said fibres and in accordance with variations in conditions at the aforesaid locations are detected by optical time domain or frequency domain reflectometer means for determining the conditions at the sensor locations.

Abstract: An interpolator or decimator filter structure operable between two sampling rates (F.sub.s and 2F.sub.2), and in which two branches (21 and 23) of the structure are divided into low and high frequency sections by sampling switches (27 and 29). The high frequency section of one branch (21) incorporates a composite filter comprises of a nesting filter (1') and a nested filter 1. Each of these filters 1, 1' includes a digital coefficient multiplier (5,5'). The coefficient (K.sub.2) of the coefficient multiplier (5), part of the nested filter (1), is preset to a value such that 3 dB attenuation occurs at a point offset in frequency from one-half the lower sampling rate (F.sub.s).

Abstract: A spectral filtering optical sensor comprises a stationary zone plate and stationary co-terminous ends of input and output fibres with the interposition in the optical path between the zone plate and the optical fibre ends of a variable optical focussing arrangement the focussing characteristics of which change with changes in magnitude of the particular parameter being sensed and thereby vary the effective optical path length between the zone plate and the optical fibre ends and the wavelength of light impinging on the end of the output fibre.

Abstract: A frequency dividing arrangement 5 comprises a frequency divider 6 coupled to an active filler 7 which is operative to suppress output radiation from the frequency dividing arrangement. The arrangement 5 may be incorporated into a frequency synthesis loop 4 of a television tuner circuit in order to reduce interference between the loop 4 and a down conversion stage of the tuner circuit.

Abstract: The frequency synthesizer has a store which temporarily stores a data word for controlling a processor. A local oscillator provides a signal for the processor which drives an output interface to produce the required frequency. The output interface and processor are controlled by a control and decode circuit which also controls a reference divider. The output of the reference divider is compared with an output from the processor by a phase comparator and the signal generated is used to control the local oscillator. The reference divider is driven by a single reference oscillator.

Abstract: A simple and reliable method of recalibrating a LED print head comprises providing a photodetector array for detecting the intensity of illumination of each LED, comparing the actual intensity with a desired value and adjusting the level of current applied to the LED array until the actual and desired values correspond, at which time a memory storing the current levels to be applied to the diode array is updated. One or more reference diodes are provided and employed in an initial step in which the current applied to the reference diodes is adjusted until actual and desired current levels correspond, at which time all stored current values for all LED are updated.

Abstract: A reaction jet control system for a flying vehicle, the system comprising pairs (3, 4 and 5, 6) of jet reaction nozzles with associated gas flow supply ducts, the duct between two nozzles (3, 4) of any one pair including a first gas diverter valve (11B) and the duct between the pairs of nozzles including a second gas diverter valve (11A). This arrangement ensures accurate balancing of the gas flows between the nozzles and gives economy in use of the fuel supply.

Abstract: A biosensor includes an optically dense body provided with a coating sensitized to a specific assay species, and an input and output coupling structure. Light signal response is enhanced by incorporating a partially reflecting, partially transmitting medium between the coupling structure and the optically dense body having a lower refractive index. The thickness of such medium is chosen so that light may be coupled by frustrated total internal reflection and to enable the medium to serve as a resonant mirror.

Abstract: A differential delay optical coherent pulse generating arrangement, in which continuous wave light derived from a coherent light source is divided by beam splitting means into two optical paths, in which the light beam in one of said paths is delayed relative to the light beam in the other of said paths by differential delay means prior to the sequential selection of the light from the respective paths by optical switching means to produce two coherent pulses in predetermined time displaced relationship and in which a frequency difference may, if required, be produced between the frequencies of the two coherent pulses.

Abstract: A Manchester code clock and data recovery system comprises an input means which receives an encoded input signal. Data integration and error integration devices are provided which receive modified versions of the input signal and produce signals for presentation to an error modulator. The modulator generates an error signal for controlling a phase lock loop circuit having a voltage controlled oscillator.A first output of the oscillator generates signals for controlling the data integration device over a full bit period, and for controlling the error integration device over a half bit period, in a manner that permits the clock signal to be recovered from the first output of the oscillator, and the data to be recovered from the data integration device which is arranged to generate a Manchester biphase coded signal.

Abstract: An optical fibre sensing system for monitoring and/or measuring temperatures or pressures distributed around an optical fibre sensing loop. Light source and coupler are provided for applying continuous wave light to the loop so that the light propagates simultaneously in opposite directions around the loop with the resultant light output from the loop being detected by a detector. Light pulse generating source and coupler cause light pulses to propagate in one direction only around the loop and by so doing produce transient variations in the propagation constant along the looped fibre in dependence upon the distributed temperature or pressure around the loop. The detector detects the phase changes occurring in the continuous wave light received from the sensing loop due to variations in temperature or pressure around the loop.

Abstract: The invention provides a phase-shifting device for inclusion into a microwave transmission line to effect a predetermined, constant, broadband shift in phase of transmitted signals. The device comprises, in its preferred form, two Gallium Arsenide field effect transistors, connected in parallel, serially included in the line, and means for switching the transistors between alternate states to effect the phase shift.

Abstract: An optical transmission system comprises a plurality of transducers located at intervals along a continuous optical fibre data transmission path. Data signals are derived from respective transmitters associated with the transducers and are applied to the transducers to produce mechanical stressing or deformation of the data transmission path optical fibre for imparting corresponding modulation of the polarization state of light being propagated along the optical fibre. A receiver connected to the far end of the transmission path includes means for determining the exact state of polarization of the received light and for extracting the modulation information and hence transmitted data therefrom.

Abstract: A gain control circuit arrangement comprises a transistor amplifier (A) for providing an output signal (OP) in response to a received input signal (IP). The gain of the transistor amplifier (A) is controlled by means of a field effect transistor (TF) connected in the emitter circuit of the amplifier and included in a feedback control loop to which a gain control signal (Ref A) is applied in operation of the gain control arrangement. A collector load of the amplifier comprises a potential divider (R1 and R2) one portion of which is shunted by a control loop which serves to maintain constant the collector current passing through the transistor amplifier.

Abstract: A thermal detector of the type comprising an array of discrete detector elements each of which is supported by a common supportive layer, each of which is provided in thermal contact with a corresponding collector of radiation absorbent material, the area of each collector being larger than the area of the corresponding detector element, characterized in that contact between each collector and the supportive layer is restricted to an area lying substantially within and displaced from the edge periphery of said collector.

Abstract: A method (FIG. 3) for producing MOS transistors of the type having shallow, lightly doped, source/drain structure. In this method sidewall fillets (7) of n-type doped dielectric material are defined adjacent to the sides of the oxide (1) and metal electrode (3) features. These fillets (7) are then employed to provide self aligned masking during implantation of heavy dopant of either n- or p- type (9; 13). In a subsequent rapid anneal step, the implant dopant is activated and n-type dopant diffused into the substrate (5) from the fillets (7) to provide lightly doped source/drain structures (11; 15).Examples of this method are described for producing phosphorus-arsenic n.sup.- /n.sup.+ are phosphorus-boron p.sup.- /p.sup.+ source/drain structures.

Abstract: An optical connecting arrangement is provided between an optical device and an optical fibre in which the optical device is mounted with positional precision on a substrate which is fabricated for locating one end of a so-called grin rod lens in precise optical alignment with the active surface of the optical device and in which the other end of the same grin rod lens or the corresponding end of a further grin rod lens coupled to it has the optical fibre optically coupled thereto in optical alignment.

Abstract: An optical resonant assembly which has at least two stable light transmittance values dependent on incident light beams. The assembly consists of a pair of parallel partially transmission mirrors with a photochromic layer placed therebetween which has a refractive index dependent upon the intensity of incident light beams. The parallel mirrors constitute a Fabry-Perot type resonator. The incident light beams have the effect of "couloring" or "bleaching" the photochromatic material.

Abstract: A bias circuit (FIG. 5) of the type comprising a bias transistor (T1) having a pair of resistors (R1, R2) in its collector path, the junction of these two resistors (R1 and R2) being connected to the transistor base. The base of a drive transistor (T2), of like polarity type, is connected to the collector of the bias transistor (T1), this serving as current source or sink. To provide and increase extended operation, operation at supply voltages lower than usual and current regulation from low supply voltage (0.9V) to much high voltage, this circuit is modified by the provision of a third resistor (R3) in the collector path and a diode shunt (T3) between the base of the drive transistor T2 and the junction of the third and first resistors (R3 and R1). The polarity inverse of this modified circuit is also effective and may be combined, in cascade or in ring feedback loop configuration, with the aforementioned modified circuit. These latter combinations serve to provide yet higher order current regulation.