Abstract: A data packet switching arrangement wherein data packets are switched into a transmission pathway according to their priority. Data packet priority is consequently determined in a ring and a priority token attributed thereto. A high priority token ensures its data packet is switched into the transmission pathway when next available. Lower priority tokens are held by respective packets until all data packet priorities have been determined and no higher priority tokens attributed, whereupon the respective data packet is switched into the transmission pathway when next determined.

Abstract: An optical scanning arrangement for gas sensing, in which scanned light source means produces a spectrum of regularly spaced wavelengths or lines which correspond as regards spacing to the absorption line spectrum of a gas to be monitored and in which the multi-line output from the light source means propagates through a region to be sensed for gas and means for determining the light output from the region for detecting the attenuation of the components of the multi-line output from the light source means due to absorption by said gas being monitored.

Abstract: The contrast and sharpness of photoresist images is enhanced by depositing a layer of a photobleachable compound onto the photoresist layer. The photobleachable layer is sensitive to the light used to expose the photoresist and forms a contrast enhancement layer (CEL) on the photoresist layer. Fulgides and photochromic butyrolactones are selected for forming the photobleachable layer. Such compounds can be deposited from a hydrocarbon solution, such as toluene, and are soluble in the standard alkali, photoresist developers. The process is particularly advantageous for producing integrated circuits.

Abstract: A circuit for recovering clock information from an incoming data signal preferably in NRZ1 form, the circuit including a VCO (18) providing a clock signal (CK) to four integrate/hold circuits (I1to I4) which receive an incoming data signal, the integrate/hold circuits providing an error signal to the VCO (18) for adjusting the phase thereof to that of the incoming data signal, the integrate/hold circuits being sequenced by logic (10) to provide within each period of the clock signal three functions: (1) an integration of the incoming data signal in every bit period in which a voltage transition occurs, (2) a holding of the integrated value within a subsequent bit period or periods, and (3) a resetting of the integrated value following the next voltage transition in the incoming data signal, whereby the held integrated value, whose magnitude is dependent of the phase of the clock signal relative to the phase of the incoming data signal, provides said error signal.

Abstract: A data transmission system comprising a plurality of radio stations, each station including a transceiver with associated encoding/decoding means for transmitting/receiving data, wherein data signals are transmitted as packets including one or more blocks of data encoded with an error correcting code, wherein each station is arranged automatically to issue a request for repeat of a packet of data should it receive a packet containing errors which cannot be corrected, and wherein should the error rate in received packets be more than a predetermined amount over a predetermined interval of data transmission, the system is arranged automatically to reduce the rate of data transmission within each packet and/or change the channel frequency.

Abstract: A method of marking an article or substrate with a mark or device which is made visible or is enhanced on exposure to U.V. light which comprises printing onto the article or substrate a photochromic ink containing a photochromic compound which is reversibly converted to a colored form on exposure to U.V. light and reverts to a substantially colorless form in the absence of U.V. light and applying a superficial protective layer to said mark or device which protects the phototochromic compound against degradation by atmospheric moisture and oxygen. In addition the invention includes a security device in the form of a label, document or card which incorporates a mark or device which is partially or wholly invisible in light which does not contain a U.V.

Abstract: The invention provides an amplifier having a feed-back path into which either of two different value resistances may be switched in dependance upon the level of the amplifier output.

Abstract: Apparatus of the type comprising an optical assembly and reflection grating--for collimating light emitted by a laser and for refocussing the same onto an output waveguide. The waveguide is modified to enhance reflection of the refocussed light, which in turn dominates the resonant response of the laser. Laser resonance thus depends on geometrical factors--the relative positions of laser and waveguide and the dispersion properties of the assembly. Wavelength selectivity is improved by confining reflection to the core of the waveguide e.g. by using an embedded reflector, or further still by using an etalon pair. The laser may be used in conjunction with other lasers and/or detectors, or with retroreflectors. A multi-laser input multiplexer and single channel drop-and-add devices are described.

Abstract: A phase shift arrangement comprising bi-stable devices arranged to provide phase shifted output signals triggered by a clock pulse level. The bi-stable devices including biasing means such that the clock pulse level at which the bi-stable devices are triggered is adjusted. The adjustment of the triggering level providing an offset for the degree of phase shift between output signals.

Abstract: In the present invention a switchable synthesizer is disclosed wherein a single loop is used to lock any one of a plurality of control signals by multiplexing the frequencies into and control signals out of the specific frequencies loop to control the frequency generators.

Abstract: A thin film deposition process comprises the steps of providing a first target area on a magnetron electrode, sputtering particles from said area so that they fall onto a heated substrate body for forming the required deposit, simultaneously operating a sputtering gun such that further particles are dislodged from a second target area and directed towards the substrate, the two resulting particle plasmas mixing at the substrate surface such that a deposit of a predetermined chemical composition is produced.This allows a multicomponent material such as a PLZT ceramic to be deposited without a change in composition due to different volatilities etc. of the components.

Abstract: A LOCOS process, a process of the type wherein a capped recessed mesa structure (1,3) is defined in single crystal, semiconductor grade, silicon and thereafter, and in the presence of the capping layers (5,7), local oxide (13) is thermally grown to provide an isolation structure. This process is modified (FIG. 3) by introducing a layer (11) of passive oxide deposit to cover the substrate (3), mesa (1) and upper capping layer (7) prior to the thermal growth of further oxide (13). The resulting oxide (13) is then etched back to remove excess material. This modification results in reduced bird's head height non-planarity and also in reduced bird's beak encroachment into the active area of the silicon device (3). Re-entrancy at the base of the bird's head (13) is also eliminated.

Abstract: A fibre laser (1) of the type comprising a doped single-mode optical fibre (3) arranged between reflectors (5,7), and which is coupled (11) to an optical pumping source (9). For the given reflection efficiency of the reflectors (5,7), the length of the optical fibre (3) is chosen such that it exceeds that affording saturation and provides at its end a region for absorption (FIG. 1). The resultant hysteretic behavior of this bistable device may be utilized for logic memory (bistable), and regenerative amplification applications. To this end a second source (9') can be coupled (11',19) to the laser fibre (3).

Abstract: A quadrature signal generator is provided which includes a voltage dependent resistance capacitance phase-shifting network (12) and a phase detector (26) for detecting any difference, from 90.degree., between the phases of the in-phase and quadrature phase signals (2, 24) generated by the network (12) and for producing a control signal in dependence upon such difference. The control signal is applied to the network (12) to vary the phase-shifting characteristic thereof to restore and maintain the 90.degree. phase difference.

Abstract: A filter structure including a notch filter is designed to have a transmission zero at a frequency slightly displaced from one half of the lower sampling rate of the interpolator/decimator, and thus providing increase in attenuation at the half-rate frequency. The notch filter is comprised of two like all-pass-network filters and has feed forward and feedback connections, the latter connection including a coefficient multiplier. The feedback connection is made between a tapped output of the second of the network filters and an input node. The tapped filter is characterized by throughput and a tapped output transform functions X(Z) and Y(Z) given by the following expressions:X(Z)=[Z.sup.-1 -K]/[1-KZ.sup.-1 ; and,Y(Z)=.alpha.Z.sup.-1 /[1-KZ.sup.-1 ;where Z.sup.-1 is the unit delay operator, K the multiplier coefficient and, .alpha., a structure dependant constant.

Abstract: An optical time domain reflectometry system in which laser level reference signals are derived from the respective laser outputs from the laser sources and fed into a single receiver provided for receiving the back-scattered or returned light along an optical fibre. The receiver is thus continuously calibrated in accordance with the relative intensities of the optical signals at different frequencies being launched into the optical fibre so that the receiver provides an accurate measurement of temperature or other parameter being measured by the system.

Abstract: The minehunting system includes a remotely operated vehicle which is driven ahead of a vessel. The vehicle is equipped with a sonar system for detecting, classifying and disposing of a mine.The sonar system comprises an acoustic mirror sonar which includes a dual field-of-view reflector, a height finding element and a dual frequency classifier.The vehicle has a autopilot which, is conjunction with control algorithms in a shipborne tactical computer on the vessel provides navigation and manoeuvering commands.

Abstract: An interpolating converter for digitizing an analogue signal, the converter in which comprises combiner means for receiving an analogue signal, one step digital quantizer means for receiving an input signal dependent upon an output signal from the combiner means, means for identifying the quantization error of the digital quantizer means, and feedback means for affording a signal dependent upon the quantization error of the digital quantizer means to the combiner means.

Abstract: A Fabry-Perot pressure or displacement sensor comprises an optical fibre which serves to transmit a light beam to the mirrors of the sensor and to receive light which is reflected back from the mirrors. The light beam and the reflected light comprise light at a plurality of wavelengths. The wavelength components of the transmitted light and the wavelength components of the received light are range rated in range gates and are compared in comparators to provide respective ratios of transmitted intensities and received intensities. These ratios are in turn compared in comparator to provide a ratio dependent upon the displacement of the mirrors of sensor due to pressure applied thereto but independent of any changes in the intensities of transmitted light due to reflections from optical components in the pressure or displacement monitoring arrangement.

Abstract: An MOCVD deposition technique wherein the pressure of reagent vapors within the reaction vessel (1) is maintained at a reduced pressure in the range 10.sup.-2 to .about.10 millibars and contained mounted substrates (15) are heated non-inductively e.g. by an electric resistance circumferential furnace (5). In the above pressure range, high diffusivity of the reagent vapors ensures exposure of the substrates (15) to a uniform reagent mixture. A large number of substrates (15) may be processed simultaneously. As heating is non-inductive, an inert mounting (17) can be utilized avoiding the introduction of contaminants (e.g. carbon) into the deposited film.