Abstract: In making bipolar transistors, an interfacial oxide layer (5) is formed over ther monocrystalline region (1), and polysilicon (6) is formed both thereon as an extrinsic emitter region. After doping the polysilicon a monocrystalline emitter region (4) is produced in the base region by diffusion from the extrinsic polysilicon emitter region. The oxide layer (5) acts as a diffusion barrier to ensure that excessive dopant does not reach the monocrystalline region.After the above operation, a thermal treatment is effected at a higher temperature, e.g. 1100.degree. C., for a few seconds, which breaks down the interfacial oxide layer referred to above. This temporary use of the interfacial oxide layer leads to better and more consistant transistor characteristics.

Abstract: In a pulsed plasma process for surface treatment of a substrate the containing reactor vessel (11) has an inner cross-section conforming to the substrate geometry so as to confine the intense plasma region to the substrate surface (12). Preferably this region should be within 15 to 20 mm of the surface. Advantageously the inner surface is provided by a demountable insert (13).

Abstract: A conferencing module, for conferencing two PCM words uses threshold detectors (7, 8) to assess whether the word represent signals above a preset threshold, plus a comparator (1) to determine the larger signal. One or other is switched by an electronic switch (5) to the output by control logic (4) as follows:(i) if only one PCM word is above the threshold it is switched to the output and the switch setting stored in a memory (6),(ii) if both PCM words are above the threshold, and one is larger than the other, that one is switched to the output and the switch setting noted in the memory,(iii) if neither PCM word is above the threshold, the switch is left as it is, and that fact noted in the memory,(iv) if both PCM words exceed the threshold, and are of equal size, the switch is left as it is, and that fail noted in the memory.

Abstract: A distributed optical fiber sensor cable, for sensing perturbations such as pressure, comprises a length of optical fiber (10) and means adapted, in response to the perturbation to be sensed, to mechanically deform separate portions of the length of the fiber at sensing elements (11,12,13) periodically along their length in order to cause optical power launched into a mode of propagation in the core (14) and guided thereby to be coupled to an unguided mode, for example a cladding (15) mode. The coupling is optical wavelength selective and the separate sensing elements are each addressed with a different wavelength (.lambda..sub.11, .lambda..sub.12, .lambda..sub.13) for spatial resolution along the length of the cable.

Abstract: To provide an adequate dc supply to the electronics of a telephone, when on hook or off hook, there is a transistor (T2) with its emitter-collector path in one line wire, and a storage capacitor (Cpsu) across the input to the telephones's circuits. This capacitor is charged up and maintains dc supply when the line voltage (at A) falls below a preset level. The base of this transistor is connected via another transistor (T1) to the other line wire. The speech output (V.sub.IN) is connected via an operational amplifier (A) to the base of the second transistor (T2). Hence the dc supply and the speech output are in parallel.

Abstract: The evolution of particulate material from the inner surface of a tubular zirconia susceptor while fibre is drawn from preform is inhibited by providing that surface with a glassy finish by laser-beam fusion.

Abstract: A fully self-aligned polycrystalline silicon emitter bipolar transistor. Self-alignment of the p.sup.+ base contact (12) is achieved by using oxidized 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 oxidized 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: An adaptive filter may be realized by weighting the outputs from a tapped delay line. This, however, allows nulls to corrupt a wanted signal spectral region. A fixed (non-adaptive) filter (2) coupled between the signal input and an input of means (3) for summing the weighted outputs serves to allow nulls only to be formed in the skirt region of the fixed filter response thus preserving a wanted signal.

Abstract: An optical signal pulse to be amplified and a pump signal pulse are launched consecutively into one end of an optical fiber, which may comprise a separate fibre or part of a transmission line. The pulses differ in wavelength by one or more Stokes shift and the order of launch is determined by the relative group velocities in the fibre. Owing to dispersion in the fibre the pulses overlap and overtake one another while they are transmitted along the fibre, the signal pulse being amplified as a result of Raman stimulated emission and compressed as a result of power depletion from the pump pulse, thus increasing the bandwidth of the transmission line.

Abstract: A dual wavelength reflectometer for single mode fibre is provided with separate lasers (5, 6) with emission wavelengths at 1300 and 1550 nm whose outputs are combined using a single mode optical fibre wavelength multiplexer (7) of tapered coupler format. The combined output is fed to a single mode optical fibre beam splitter (9), also of tapered coupler format, which is constructed to act as a 3 dB splitter for both wavelengths. This beam splitter directs light from the lasers into the fibre under test (10) and back-scattered light from the test fibre n to a photodetector (11).

Abstract: A single mode fiber expanded beam termination is formed by fusion splicing an undoped (pure) silica rod to a single mode fiber. The length of the rod controls the expanded beam diameter, and forms a lens on the free end of the undoped silica rod to collimate an output beam.

Abstract: In an inside tube vapor phase deposition process for the production of doped silica glass by an oxidation reaction for optical fibre manufacture, in particular fluorine doped silica, the oxidation reaction is prevented from occurring until the reactant material, for example silicon tetrachloride and a fluorinating reagent, has been heated to a temperature above that required for the oxidation reaction. This preheating of the reactant material results in the oxidation reaction producing compositions of glasses which are not allowed from thermodynamic considerations at the lower temperature usually employed for the oxidation reaction, for example silica more highly doped with fluorine than hitherto achieved.

Abstract: A regenerator for an undersea optical transmission system has a timing extraction circuit for extracting the clock signal from an NRZ PCM signal. The circuit comprises a surface acoustic wave filter (F) which feeds an amplifier which comprises a number of similar cascaded amplifier sections provided by an integrated circuit. The first stage is a grounded base stage (stage 1) and the following sections each include a balanced emitter-follower buffer stage (stage 2) and a balanced long-tailed pair stage (stage 3). Any base and emitter voltages in an amplifier section are minimised if not eliminated by the long-tailed pair having equal emitter and collector loads.

Abstract: A microprogrammed processor in which instructions have alternative fast and slow microprogram sequences. The fast sequences are designed for speed, and can detect exception conditions but do not resolve them. The slow sequences perform all the necessary tests to resolve these conditions. When a fast sequence detects an exception, that sequence is abandoned, and the corresponding slow sequence is run.

Abstract: A receiver for modulated optical signals including a multiport optical fibre coupler arrangement (10) to one input port of which the modulated optical signals are applied and to another input port of which a local oscillator optical signal of substantially the same optical frequency as the modulated optical signal is applied whereby the output ports of the coupler give separate output signals that are differentially related to the optical frequency phase difference between the modulated input signal and the local oscillator signal, means for individually demodulating (12a-12c) the output signals and means for summing the demodulated output signals.

Abstract: A multi-mode radio transceiver comprising a sequence of bi-directional circuit modules including a radio frequency input/output amplifier module (1), a radio frequency/baseband I and Q quadrature channel conversion module (2), an analogue/digital conversion module (3), a digital signal processor (4,5), and a digital signal input/output interface (6), with a control means (7) whereby for transmission a radio frequency signal is formed from analogue quadrature I and Q channel components of a digitized signal at baseband and translated to the radio transmission frequency and for reception the radio frequency signals are transformed into I and Q quadrature analogue components at baseband and subsequently digitized.

Abstract: A sawn cavity single heterostructure laser chip is provided with secondary saw cuts to produce an inverted Tee shaped cross-section in order to limit the width of emission to less than the full width of the chip. The depth of the secondary cuts is arranged to terminate just short of the active region (3).

Abstract: A bit-line load for a static random access memory incorporates a load comprising a diode, and current limiting means in series with the diode, the diode/limiter assembly being shunted by a current source. This overcomes both the V.sub.dd drop problem and the high write cycle current flow experienced with conventional bit line loads.

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. Data entry is preceded with blanking (erasing) pulses applied to the strobe lines. The polarity of the strobing and blanking pulses is periodically reversed to maintain charge balance in the long term.

Abstract: An analogue-to-digital converter arrangement including a signal de-emphasis network 10.sub.I, 10.sub.Q which attenuates higher frequency analogue signals relative to lower frequency analogue signals, an A/D converter 11.sub.I, 11.sub.Q to which the de-emphasised signals are applied, and a pre-emphasis network 12.sub.I, 12.sub.Q substantially complementary to the de-emphasis network to which the digitised signals are applied.