Abstract: The moisture content of compressed air being supplied by a compressor 24 to propel an optical fibre line 18 along a duct is monitored by a dew point meter 22 and adjusted such that it is maintained within a predetermined range. The adjustment is carried out by passing the compressed air through two passages 30, 32 arranged in parallel with one passage 30 being provided with means 20 for increasing the moisture content of the air passing therethrough and adjusting the relative flow rates through the two passages.

Abstract: An installation 10 comprising a line 12 extending between and suspended from a plurality of spaced apart aerial suspension locations 14 defines a passage for an optical fiber unit. The line comprises a plurality of elongate tensile resistant tubes 18 connected end-to-end by respective connectors 20. The line is secured to each suspension location by respective securing means 22 which are secured to said line at two spaced apart locations 28, 30 thereon such that the portion 26 of said line between these locations is untensioned and includes a connector 20. The securing means 22 is adapted to allow tensioning of the portion 26 of said line when the tensile load on the line adjacent thereto on either side of said suspension location reaches a first predetermined amount, and the connector 20 is adapted to cause the end-to-end connection of the tensile resistant tubes 18 connected thereby to break when the tensile load on said portion reaches a second predetermined amount.

Abstract: An optical structure having two optical guidance paths between which coupling occurs in a band about one predetermined wavelength is manufactured by providing an optical structure having two optical guidance paths with respective propagation constants 12', 14' which vary differently with wavelength and coincide at one given wavelength .lambda.' arranged such that coupling occurs between said optical guidance paths in a band about said one given wavelength and subjecting the or at least one of the guidance paths which includes a radiation responsive refractive index changing dopant to radiation to change the propagation constant thereof until said one given wavelength equals said one predetermined wavelength .lambda.".

Abstract: A method of manufacturing a preform for drawing into an optical fibre comprises positioning a rod within a sleeving tube therefor to form an assembly in which there is an annular space between the rod and tube, and collapsing the tube onto the rod to form a solid cross-section preform. The collapsing step comprises sealingly closing the annular space at one end of the assembly and applying suction to the annular space from the other end of the assembly. The annular space at the one end is sealingly closed by locating the end of the tube at the one end on an annular rib of the rod and fusing the tube end to the rib.

Abstract: An apparatus for coating an optical fibre with a selected one of a plurality of different resins includes respective reservoirs for the resins, an applicator for applying a resin coating to the optical fibre and a distributor between the reservoirs and the applicator including a valve device which is operable for putting any selected one of the reservoirs in flow communication with the applicator. The valve device includes a first body defining a plurality of inlet passages each of which is interconnected to a respective reservoir by a respective inlet conduit and a second body defining an outlet passage which is interconnected to the applicator via an outlet conduit. A flow control device is disposed between the bodies and the bodies are relatively moveable for putting any selected one of the inlet passages in alignment with the outlet passage.

Abstract: A system for guiding optical fibres comprises a device which includes a plurality of units, each of which defines a row of ducts extending from a first end of the unit to a second end thereof for guiding optical fibres. The units are arranged successively in overlapping relationship with their first ends in substantial alignment at an end portion of the device and their second ends being spaced apart at successively increasing distances from the device end portion.

Abstract: Apparatus for use in interconnecting optical fibers comprises a shelf 12 slidably mounted between a retracted position (FIG. 2) and an extended position. Housings 48 for locating fiber interconnections are mounted on the shelf 12. A plurality of tubes 22 are connected to respective further tubes 26, which are connected to the housings 48, by tube connector 30. The tubes 22 and 26 guide optical fibers to the housings 48. Each tube 22 has a substantially helical configuration over a portion 24 of its extent located behind the shelf 12 to accommodate sliding movement of the shelf.

Abstract: An optical fibre assembly 10 for blown installation, comprises a fibre unit 12 having at least one optical fibre 14. The unit has a coating comprising an external layer 18 of a material containing hollow glass beads 22 at least some of which project from the outer surface 24 of the external layer. The coating also has an inner, buffer layer 16 of a material having a lower modulus of elasticity than that of the material of the external layer and an intermediate layer 20 of material disposed between the external and inner layers.

Abstract: In a method of forming a preform from which an optical fibre can be drawn, successive layers of matter (24, 28) are deposited by vapour deposition on a rotating cylindrical body (10) which is traversed by a heat source (15). For the deposition of at least two successive layers (24, 28), a rate of rotation of the body and/or a rate of traverse of the heat source is selected so as to generate in one of said layers a surface profile different to a surface profile generated in the other said layer.

Abstract: An Ar.sup.+ ion laser pumped optical fibre amplifier is provided with an optical fibre having a core which has been solution doped using a solution of an aluminum and an erbium salt.

Abstract: A polyol-water mixture is applied over the polymeric insulation of the or each conductor core of an electrical cable prior to extruding the polymeric sheath of the cable thereover such that the polymeric sheath is prevented from adhering to the polymeric insulation.

Abstract: An apparatus for forming metal tubes is shown in which a metal strip 2 is passed through the apparatus and is formed by a combination of rollers 17, 17', 19, and dies 15, 24 into a shape defining a tube. Prior to the completion of the formation of the metal strip 2 into a shape defining a tube, a brazing wire 1 is supplied through rollers 8 onto the metal strip 2 between two edge portions thereof to be bonded together. The edge portions are bonded together by means of a frictional wheel 27 rotating at high speed.

Abstract: An apparatus for forming metal tubes is shown in which a metal strip 2' having a brazing wire 1 bonded to an edge portion thereof passes through the apparatus and is formed by a combination of rollers 17, 17', 19, 19' and dies 15, 24 into a shape defining a tube. A frictional wheel 27 bonds together the two edge portions of the shape defining a tube.

Abstract: A polyol-water mixture is applied over the polymeric insulation of the or each conductor core of an electrical cable prior to extruding the polymeric sheath of the cable thereover such that the polymeric sheath is prevented from adhering to the polymeric insulation.

Abstract: An extra-high-voltage power cable is provided with extruded insulation 3 over a conductor 1 thereof. The insulation comprises an inner layer 5 of an unfilled high density polyethylene or polypropylene material having a higher electric strength than the material of the insulation adjacent thereto in an outer layer 6 thereof.

Abstract: The wave guide has an annular core region divided into an integral number times eight annular sectors. Respective alternate sectors are of a first type 5 having a substantially constant refractive index and a second type 6 having a refractive index which varies substantially in inverse proportion to the square of the distance from the longitudinal axis 3 of the wave guide. The wave guide is twisted about the axis 3 such that the sectors 5, 6 extend helically. The circular birefringence of the wave guide is improved by the sectors 6 having a different elasto-optic coefficient under torsional stresses to that of the sectors 5.

Abstract: Graft polymers are produced by grafting amine or acyl groups onto the imide groups of silicone polyimides or polyetherimides; the graft polymers can be moulded onto wires and cross-linked by electron beam irradiation to form insulation having improved properties.

Abstract: An optical fibre structure usable in amplifying optical signals, comprising a length of optical fibre (1) which includes two uniformally spaced monomode optical cores (2,4) located within a common cladding (6) so as to provide two optical guidance paths, the optical characteristics of at least the cores being different such as to give the two guidance paths different propagation constants the values of which coincide for a predetermined coupling wavelength, one of the cores including a fluorescent material capable of producing stimulated emission. There is also disclosed a method of amplifying an optical signal using such an optical fibre structure, comprising arranging for the wavelength (.lambda..sub.s) of the optical signal, the fluorescent wavelength of said material in said one core, and said predetermined coupling wavelength all to be substantially the same, launching optical pump energy having a different wavelength (.lambda..sub.

Abstract: An electrically tunable optical fibre structure comprising a length of optical fibre which includes two uniformly spaced monomode optical cores (1,2) located within a common cladding (4) so as to provide two optical guidance paths, the optical characteristics of at least the cores being different such as to give the two guidance paths different propagation constants the values of which coincide for a predetermined wavelength, so that optical energy at said wavelength will repeatedly transfer from one core to the other, characterized in that two electrodes (6,8,20) are provided within the cladding and are located with at least one core between them for applying an electrical field to that core whereby to alter its propagation constant by the electro-optic effect and hence to alter said wavelength, the structure thereby being tunable. Methods of making such a structure are also disclosed.

Abstract: An attenuating device 10 for use with signal carrying optical fibres 14 comprises a length 18 of optical fibre coiled within a casing 16. The optical fibre length 18 is of higher attenuation per unit length than the optical fibres 14 and the device comprises means, for example optical fibre tails 22,24 fusion spliced at 20,22 to the opposite ends of the length 18 for optically connecting those ends to the fibres 14.