Abstract: The working temperature range of a 2 .mu.m thick negative dielectric anisotropy smectic C phase filled ferroelectric liquid crystal cell that is addressed on a matrix basis with balanced bipolar data pulses and unipolar strobe pulses is extended by the inclusion of a temperature sensor to use the temperature of the cell to control the magnitudes of the data and strobe pulse waveforms and to provide, at least at high temperatures, a stabilization waveform with a frequency twice the fundamental frequency of the data pulse waveform.

Abstract: A fully self-aligned polycrystalline silicon emitter bipolar transistor. Self-alignment of the p.sup.+ base contact (12) is achieved by using oxidised sidewalls (8) (sidewall spacers) of the emitter mesa (7) as part of the p.sup.+ base contact implantation mask. Collector contact (13) alignment can be achieved using oxidised sidewalls (17) of polycrystalline silicon alignment mesas (14) defined in the same polysilicon as the emitter mesa (7) but deposited on oxide (2) rather than the implanted base region (5).

Abstract: A crush-resistant tube for a plastics packaged optical fibre (1, 2) is formed by helically stranding together five or more non-circular cross-section wires (3) which are created from circular cross-section wires during the stranding operation.

Abstract: An optical fibre star coupler in which the mixer element (11, 21, 45) exhibits optical gain. This allows the use of couplers having a relatively large number of outputs without the requirement for an excessive power level for any input signal.

Abstract: An optical detector comprises an array of PIN diodes each of which shows no photovoltaic output at zero bias but which can produce a photovoltaic output when correctly biased. A single amplifier is coupled to the array for amplifying produced photovoltaic voltages. When an optical signal incident on a particular PIN diode is required to be detected, that PIN diode is selectively and correctly biased by closure of an associated switch and the PIN diode output is amplified by the amplifier.

Abstract: A bipolar transistor structure (1) which can be used in an integrated circuit where bipolar (1) and CMOS transistors (2,3) are formed simultaneously on one substrate. In integrated circuit form the material, for example polycrystalline silicon, used for the gates (11,21) of the CMOS transistors is also used for the emitters (29) of the bipolar transistors, the collectors of the bipolar devices are comprised by doped wells (5) in the substrate (4) and the base contacts of the bipolar devices are comprised by regions (27,27a) equivalent to source and drain regions (17,18) of the n-well MOS transistors and bridged by base implants (28). The conventional CMOS processing is modified by the addition of two masking steps and one implant (base implant).

Abstract: A digital frequency up conversion arrangement comprising a source of fixed high speed clock pulses the frequency of which is near to the desired output frequency of the converter arrangement, a high frequency counter to which the clock pulses are applied to produce a repetitive fixed m-bit digital word in parallel output form, the sample rate of the m-bit word being equal to the high speed clock frequency, divider to which the high speed clock pulses are applied to form a slow clock pulse train, a slow frequency NCO to which the slow clock train is applied together with frequency control signals to produce m-bit words the sample rate of which is equal to the slow clock frequency, summing means to which the high sample rate and slow sample rate m-bit words are applied to produce resultant m-bit words which form a digital representation of a sine wave at the required output frequency, and digital-to-analog conversion means to which the resultant m-bit words are applied to produce an analog sine wave at the requ

Abstract: In order to eliminate the effect of water attack on silica optical fibres, the fibres are provided with a surface layer of silicon nitride or silicon oxynitride. The method proposed comprises direct nitridation. This may be achieved by adding a nitriding atmosphere to the drawing furnace gases, or to the reactive gases (TiCl.sub.4 and SiCl.sub.4) incorporated in the flame of an oxyhydrogen torch for the formation of a compressive silica/titania layer on an optical fibre by a glass soot deposition and sintering process.

Abstract: The system uses a 3B2T line code, i.e. one in which sets of three or triplets of binary digits are converted into pairs or duplets of ternary elements. All nine of the possible ternary duplets are used, in such a way that the same ternary duplet does not occur twice consecutively. This is done in one version by using the ninth duplet 00 as a repeat indicator, and in the other version by a conversion process in which each conversion operation takes into account the result of the preceding operation.

Abstract: A code correlation arrangement comprising clock means for sampling (11) an analogue input signal, means for generating a digital code sequence (14), means for clocking (15) the code generating means synchronously with the sampling of the analogue input signal, means for digitally multiplying (12) the code sequence with the sampled analogue signal, means for digitally filtering (13) the output of the multiplying means, and means for controlling the clock phase of the code generating means to maintain phase tracking of an incoming code phase in the analogue signal by the code generating means.

Abstract: A method of addressing a matrix addressed ferroelectric liquid crystal cell is described that uses parallel entry of balanced bipolar data pulses on one set of electrodes to co-operate with serial entry of unipolar strobe pulses on the other set of electrodes. The polarity of the strobe pulses is periodically reversed to maintain charge balance in the long term.

Abstract: A method of making very long length e.g. 50 km of optical fibre submarine cable in which acrylate-coated fibres (5) are guided by a fixed lay plate (10) and embedded by a fixed trumpet shaped die (7) in a relatively soft thermoplastic polymer coating (3) (e.g. Hytrel-RTM) with a zero lay angle. The coating (3) is heat softened and carried on a kingwire (2). The partially-embedded fibres are encased in a second coating (12) of the polymer by conventional extrusion. The element is coated with a water blocking material as the element is encased in a tubular strength member comprising a conductive tube of copper or aluminium surrounded by two layers (24,25) of high tensile strength wires. A dielectric sheath of e.g. natural polyethelene is extruded over the wires. The structure of the cable limits the bending of the fibres to e.g. 0.6 m, so that very low losses can be achieved.

Abstract: A ribbed structure (60a), co-operating with an unribbed surface of a coupling element 64, is employed to introduce microbending in an optical fibre (51) intermediate its two ends with a periodicity which couples the fundamental bound mode of the fibre into a cladding mode from which optical power is tapped into the optical coupling element (64) provided with a conical reflecting surface (63a) for collimating the extracted light. Light injection is achieved by a reciprocal process using a ribbed structure (60b) and a conical reflecting surface 63b.

Abstract: A non-circularly-symmetric intensity distribution is formed on a quadrant photodetector by coherently mixing two optical signals propagating in selected modes of different order. These modes are chosen either such that a change in relative phase of the two signals produces solely a rotation of the orientation of that intensity distribution, or such that a change in relative states of polarization produces this rotation.

Abstract: A drive circuit for a liquid crystal display uses a sampling technique to derive drive signals from a pair of input waveforms. The waveforms comprise positive going and negative going trapezoidal pulses. By sampling the waveforms at appropriate points, single cycle AC signals and zero voltage signals can be provided. The technique subjects the drive circuit to a voltage stress that is lower than that provided by conventional techniques.

Abstract: An optically addressed optical fiber sensor system in which light is employed to excite an optical fiber cantilever (6) into mechanical oscillation at a frequency f.sub.o. This oscillation modulates the amplitude of the light launched into the cantilever. The sensed parameter controls the displacement of the free end of the cantilever with respect to the end of the fiber (2) from which light is launched into the cantilever. The magnitude of this displacement affects the magnitudes of the components of modulated light at frequencies f.sub.o and 2f.sub.o. From an analysis of these components a measure of the displacement is obtained, and also a measure of the magnitude of the sensed parameter.

Abstract: In a semi-custom integrated circuit, e.g. a bipolar analogue array, underpass areas are so configured as to permit operation as capacitors by suitable configuration of a user determined interconnection pattern. Typically each underpass comprises a highly doped region disposed over a buried layer. A thin oxide layer is applied to the surface of the underpass. Suitable configuration of polysilicon and metal masks provides either a cross-over or a capacitor.

Abstract: A polysilicon layer or a single crystal silicon substrate is plasma etched in a two staged process. The first stage was a non-selective anisotropic etch to define a desired pattern by etching part way through the polysilicon. The second stage was a selective etch to secure remaining polysilicon and expose the substrate.

Abstract: A pressure sensor includes a resonator element (14) mounted on an optical fibre ferrule (11) whereby light signals for maintaining the resonator in a state of oscillation and for returning a modulated signal to a remote station are coupled to the resonator. The resonator is located in an evacuated cavity and is mounted on a flexible diaphragm whereby pressure changes may be detected as changes in the resonant frequency.

Abstract: A ferroelectric liquid crystal cell is provided with one alignment layer (14) constituted by rubbed nylon which promotes planar alignment in a specific azimuthal direction and the other alignment layer (15) constituted by a polymer with flexible side chains which promotes planar alignment without any preferred azimuthal direction.