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: 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: An optical repeater for an undersea telecommunications system has a tubular casing (1) closed by a bulkhead (2) with a tail cable gland (2a) providing a common feed through for electrical power conductor (39) to power the regenerator and for optical fibres (28) for optical intelligence signals. Then the electrical power conductor and optical conductor are fed through separate glands ((40) and (32)) which facilitates manufacture and individual pressure testing prior to assembly in the regenerator.

Abstract: In a telecommunication system with a number of units (Ula-Una, Ulb-Unb) for control purposes and also for subscriber facilities, each such unit is duplicated, as is the system controller (SCa, Scb). There are two local area networks (1,3), each of which interconnects one system controller and one unit of each pair of units. When one network is to be isolated, e.g. for servicing or when a fault occurs, its controller detects that condition, and isolates that network by relay circuitry in the termination (T2, T3) of the bus. Another version of the system uses local area networks of the closed ring type. In certain cases the units, etc., may be triplicated.

Abstract: A dielectric composition comprising a ternary system of non-stoichiometric lead magnesium niobate, non-stoichiometric lead zinc niobate and non-stoichiometric lead iron niobate up to 10 wt % PbO may be added to the ternary mix. Compositions with firing temperatures in the range 950.degree. to 1040.degree. C., have dielectric constants in the range 13,900-22,100 making the composition particularly suitable for high silver content multilayer ceramic capacitors.

Abstract: A cable comprises a central electrically insulating composite string, including a relatively hard strength member filament (8) with a relatively soft layer (9) thereon. Four, in the case of a quad, electrical or optical conductors (10) are at least partially embedded in the softer layer (9) and may abut the filament (8). A polyethylene sheath (11) is extruded over the string. The quad may be made by pressing the conductors against the outer periphery of the string whereby to deform it without heating it, and may involve the use of a die arrangement (FIGS. 3 and 4) which ensures the desired spacing and configuration of the conductors relative to one another, necessary for high quality quads of electrical conductors in order to have low crosstalk, is obtained. The cable construction, which facilitates miniature quad manufacture, is such that cable can be manufactured with a minimum of process stages at high throughput speeds.