Abstract: A cable (C) is laid in a pipeline (10) by pushing the cable and (C') through a hydraulically variable diaphragm in an inlet tube (11). The end (C') of the cable has collapsible moulded cups (20) attached which can be pushed through the diaphragm and which erect themselves to act as a drag inducing device so that flowed liquid in the pipeline can be used to pull the cable and (C') towards an exit tube (12) downstream. A cable pusher (13) pushes the cable through the inlet (11). The cable has a specific gravity less than the liquid, preferably 0.7, which is substantially pressure independent.

Abstract: An interface arrangement (2) comprising interface circuits (5,7) and processor (14) allows a personal computer (10) to operate in conjunction with a telephone subset (1) associated with a main switch system (9) in which the signalling systems used by the telephone subset and the computer differ. The interface arrangement allows the subset and the computer to be connected to the subsets switching system to permit at least some of the subsets signalling functions to be performed by the computer.

Abstract: A protection device is provided for a telephone having a two wire subscriber line and an earth line. The protection device comprises a single surge protection device connected between a bridge rectifier polarity guard and the remainder of the telephone circuitry, which is connected to the output of the polarity guard. Three diodes are used to interconnect the earth line and the pair of output lines from the polarity guard to the surge protection device in such a way as to prevent surges from being fed to the remainder of the telephone circuitry. The surge paths including one or two arms of the polarity guard.

Abstract: A device for the controlled release of an active material into an aqueous medium comprises a water soluble capillary tube (11) the bore (12) of which contains an active material (13). Dissolution of the active material is diffusion limited during a delay period while the capillary is dissolving. When dissolution of the tube is complete rapid dissolution of the remaining active material then takes place.

Abstract: In a pulsed radio frequency plasma deposition process the pulse repetition frequency is matched to the gas exchange rate. This is achieved by using a pulse width of 50 to 500 microseconds and a pulse repetition rate corresponding to the time within which gas is exchanged in the reaction region.

Abstract: An optical fibre is provided with a coating by coating the fibre (1) with a coating material (4) on-line with the fibre drawing process (2) and employing a laser beam (6) to locally heat the coating material whereby to change its physical or chemical properties. Metallic glass coated fibres, useful for hermeticity and sensor applications, can thus be achieved in multikilometer lengths by fusing metallic glass forming alloy coatings to a fibre. Alternatively, polymer coatings may be cured by laser beam local heating.

Abstract: Voice and data signals can be transmitted simultaneously yet independently over a subscriber telephone line. The speech and data use the same cable pair as far as the local exchange but thereafter they may be routed to the same destination or to different destinations, as desired. Each terminal unit (A or B) has a low pass filter (2) to isolate the voice and data. A data switch (5) switches an oscillator (6) by FSK. Switch (7) locks onto the Data Ready Interface (8). Bandpass filter (9) feeds the signal to the telephone line. A loop back switch LBS provides for testing from the exchange.

Abstract: A device for the controlled release of an active material into an aqueous medium, e.g. body fluids, comprises a water soluble glass container in which the active material is sealed. The container wall has a region of reduced thickness which region dissolves before the remainder of the container wall to release the active material.

Abstract: In an optical fibre submarine cable the ingress of hydrogen ions is reduced if not eliminated by at least one envelope which provides a barrier to hydrogen ions.In one embodiment a copper tape (L) is folded longitudinally around the cable core comprising strength member wires (G,H) split aluminium or coppr tube (E) and optical fibre package (A). The abutting edges (L') are seam welded with less than 0.1% skips. Preferably the folded copper tape is longitudinally welded while a loose fit and subsequently reduced in diameter to leave an accurately determined small annular gap between tubes E and F which is filled with a water blocking material that is highly viscose at ambient temperature and effectively glues the tubes together.

Abstract: In a digital optical submersible repeater the electronic and opto-electronic components are housed in an hermetically sealed modular assembly (20, 60, 70) of a first regenerator module (20) for one fibre (7, 6a), a second regenerator module (60) for the second fibre (6, 7a) of the pair of fibres, and a power module (70) for extracting power from the power feed conductor of the cable. In each regenerator module (20) the transmit laser (8) and the receive PINFET diode are on diametrically opposed faces, and power feed and optical signal feed are disposed in spaces between the modules and the inside surface of the repeater housing (1). The modular assembly is resiliently secured to the bulkhead (2).

Abstract: A single mode optical fibre preset attenuator is made by forming a fusion splice (2) between a length of silica fibre possessing no internal waveguiding structure to a length (1) of single mode optical fibre. Then the silica fibre is cut to a predetermined length to form a short stub (3) which is fusion spliced to a second length (4) of single mode fibre. The fusion splicing equipment may subsequently be used to heat soften the central region of the stub to enable it to be shortened or lengthened to fine tune the attenuation provided.

Abstract: Use is made of stimulated Raman emission to induce gain in an optical signal (13) of a first wavelength. The optical signal (13) and a pump signal (14) are synchronously coupled to a length of optical fibre (15). The pump signal is at a second wavelength. The first wavelength corresponds to one Stokes shift from the pump signal. The pump signal is generated by a semiconductor laser (11) and thus only relatively low pump powers are involved in comparison with the conventional use of YAG lasers as the pumps, however significant gain is achieved despite the low pump powers. Preferably the optical fibre (15) has a high Raman cross-section and a low transmission loss, for example GeO.sub.2 doped SiO.sub.2 or pure GeO.sub.2.

Abstract: A mass transport process for use in the manufacture of semiconductor devices, particularly but not exclusively low threshold semiconductor lasers in the InP/InGaAsP system, involves the arrangement of a cover wafer (18) of the material to be grown adjacent to a semiconductor wafer (15) on which the material is to be grown, their disposition together with a crystalline alkali halide (20) in a crucible (16), and heating the crucible, which is almost but not completely sealed, in a hydrogen stream.For the manufacture of InP/InGaAsP lasers and the growth of InP, the alkali halide may comprise KI, RbI or CsI and a controlled amount of In metal (21) may be optionally contained in the crucible (16) to control the balance between growth of InP for defining the laser active region and erosion of InP from other areas of the wafer. Growth is achieved at temperatures comparable with liquid phase epitaxy processing temperatures.

Abstract: A temperature sensor for a motor vehicle comprises a composite of PTC and NTC thermistors (1, 2, 3) whose overall temperature characteristic (c) is negative with a plateau (P) centered on the normal working temperature (88.degree. C.) to be sensed, so that tolerances in the sensing system and normal fluctuations of the working temperature will tend not to be registered by the vehicle temperature gauge. Thus only abnormal variations in temperature caused by a fault or overload condition will be indicated.

Abstract: An associative (content addressable) optical memory system is comprised by a matched optical holographic filter (10, 18, 21, L1, L2) coupled to a digital computing system (14, 15, 16) having a memory (15, 16). In order to search the computing system memory for occurrences of an item, a hologram of a binary representation of the item is formed in the Fourier transform plane (18) employing laser (11) as the light source. A page of the memory to be searched is subsequently displayed at the input plane (10), which for example is comprised by a liquid crystal over silicon display, and illuminated by the laser (11). The light is filtered at the Fourier transform plane (18). Any occurrences in the input plane display of the item result in a respective correlation spot at the output plane, which spot output is decoded and supplied to the processor (14), thus providing correlation information to the computing system as to the location in its memory of the occurrences of the item.

Abstract: A laser beam addressed smectic display in which the laser beam is used to write clear tracks in an optically scattering field employs an anisotropic conductivity dopant in the liquid crystal filling so that the cell can be electrically set into the scattering state by means of dynamic scattering effects. This requires the use of a laser light absorbing dye that is not only photochemically stable, but also stable against the effects of the relatively high fields and currents present when the cell is being set into the scattering state.

Abstract: Amorphous metallic material in ribbon form is employed to provide hermeticity of cable elements, particularly optical fibres. The metallic glass CuZr has a low permeability for hydrogen, particularly when erbium is included. Thus sealing optical fibres (1) in amorphous metal tubes (3) will prevent increase in attenuation of such fibres when used in submarine cables by preventing contact with hydrogen generated in such cables during use thereof.