Abstract: An active optical fibre star coupler having a length of amplifying optical fibre (1) optically connected at one end to a wavelength combining coupler (2) and at the other end to via a beam expanding element (3) to a set of output optical fibres.

Abstract: A fused tapered optical fibre directional coupler for use in a polarisation-preserving fibre system has a short stub length of non-polarisation-preserving fibre spliced into each fibre from which the coupler is made. The reduced diameter and tapered portions of the coupler are confined to the stub lengths since it is found that low loss coupling is not achieved if these portions are fabricated in fibre with a polarisation-preserving structure.

Abstract: Polarization beam splitters/combiners or polarization insensitive beam splitters/combiners are manufactured from low or zero birefringence single mode optical fibre, rather than high birefringence fibre, by using a differential pulling technique to induce the appropriate amount of form birefringence, the fibres being stretched further than hitherto.

Abstract: A hermetically sealed injection laser package is made by first forming a sub-assembly of a monitoring photodiode (50) on a metal support member (53) and welding it to a heat sink (30) on which the laser (31) is mounted. The heat sink is secured inside the package housing (10) and then a further sub-assembly, comprising a plastics packaged optical fiber (60) hermetically sealed in a fiber support tube (61), is introduced through an aperture in one wall of the housing. Anchorage means (70) is laser beam welded to this tube and to the heat sink to secure the inner end in position for optimum optical coupling between the laser and the fiber.

Abstract: A method of making a single mode optical fibre directional coupler in which a pair of fibres (30,31) in side-by-side contact is subjected to a succession of drawing operations produced by traversing the fibres longitudinally through a flame (34) while stretching them between a pair of carriages (32,33) driven at slightly different speeds.

Abstract: An optical fibre directional coupler has first and second optical fibres clamped together by a piece of low index heat-shrunk tubing 12. The first fibre consists solely of a core 10 and cladding 11 while the second has a core 13 a primary cladding 14 whose cross-sectional area is larger than that of the core, and a secondary cladding 15. The outermost layer of each fibre is absent over a portion of its length within the tubing 12 so that the core 10 of the first is in intimate contact with the primary cladding 14 of the second. The second fibre may have a mode stripper 45 to strip modes guided by the primary/secondary cladding interface. Fibre break detection apparatus and a single-fibre two-way transmission system are described which use such directional couplers.

Abstract: When a pair of plastics sheathed glass optical fibres (1, 2) is joined by a fusion splice there is a length of bare fibre between where the original sheathing of one fibre terminates and where that of the other begins. This gap is filled with reinstatement sheathing (5, 5b) which is fused to the original sheathing using a length (4) of heat-shrink tubing as a mould. The heat-shrink tubing is then removed to leave a smooth profile for the spliced fibre.