Abstract: An optical fibre star coupler in which the mixer element (11, 21, 45) exhibits optical gain. This allows the use of couplers having a relatively large number of outputs without the requirement for an excessive power level for any input signal.

Abstract: A crush-resistant tube for a plastics packaged optical fibre (1, 2) is formed by helically stranding together five or more non-circular cross-section wires (3) which are created from circular cross-section wires during the stranding operation.

Abstract: A rod of silica 14 is inserted into a substrate tube 10 whose bore is lined with a layer 11 of material having a refractive index less than that of silica. This layer 11 is itself covered with a layer 12 of silica. The assembly of the rod and tube is drawn into fibre, or its components are fused together to form a solid cross-section optical fibre preform.

Abstract: A secure optical fibre consists of an inner waveguiding structure surrounded by an outer waveguiding structure and separated therefrom by an optical absorbing layer (3) rendered absorbing by irradiation. The inner waveguiding structure comprises a core (1) surrounded by a lower refractive index cladding layer (2). The outer waveguiding structure comprises an annular core layer (5) sandwiched between lower refractive index inner and outer cladding layers (4 and 6).

Abstract: An optical glass fiber is formed of an inner layer of germania doped glass within the bore of the outer cladding tube of silica. The tube with the higher index of refraction inner layer is rotated while being heated to collapse the bore to form an optical fiber preform. The preform is then drawn into fiber in a separate operation. A first silica layer can be deposited within the tube bore before the germania doped layer. The deposition of germania takes place under hydrogen free conditions. Appropriate heat treatment of the tube avoids excessive evaporation of germania and provides a graded transition of the refractive index in the boundary between core and cladding.

Abstract: Single mode optical fibre for operation in the wavelength range 1.5 to 1.7 microns is made by depositing a cladding glass layer and then a core glass layer upon the bore of a silica substrate tube. The bore of the coated tube is then collapsed to form a solid cross-section optical fibre preform. The cladding glass has an index matching that of silica and either contains no oxide of phosphorus or the minimal amount to provide a low enough deposition temperature and high enough deposition rate to provide an acceptably low diffusion of hydroxyl groups from the material of the substrate tube. Optionally the deposition of the cladding may be preceded by the deposition of a diffusion barrier layer which may contain a higher proportion of oxide of phosphorus.

Abstract: Single mode optical fibre for operation in the wavelength range 1.5 to 1.7 microns is made by first depositing an optically absorbing layer of silica doped with oxides of boron and/or phosphorus upon the bore of a silica substrate tube. The optical absorbing layer has a higher refractive index than silica, and on it is deposited a transparent optical cladding layer of matched index, and then a higher index optical core layer. The bore of the coated tube is then collapsed to form a solid cross-section optical fibre preform from which optical fibre can be drawn.

Abstract: A single mode optical fiber having a central core region of uniform composition and thickness and core end regions each having a core with a graded composition and increasing thickness towards the ends of the fiber. The fiber maintains a constant normalized frequency with a minimum bending loss. Methods are also provided for forming the fibers from a fiber optic preform.

Abstract: A method of making high purity glass by heating some of the glass ingredients in powder form to form a melt while adding other glass ingredients to the melt by chemical vapor deposition.

Abstract: A single mode optical fiber having a central core region of uniform composition and thickness and core end regions each having a core with a graded composition and increasing thickness. The fiber towards the ends of the fiber maintains a constant normalized frequency with a minimum bending loss. Methods are also provided for forming the fibers from a fiber optic preform.

Abstract: A device for measuring the proportion of a first liquid in a lower refractive index second liquid with which the first liquid is immiscible, such as oil in water. An unclad optical fiber, having an index of refraction between those of the two liquids but at least equal to and not more than ten percent greater than that of the first liquid. A light energy source and detector are connected by the immersed fiber and the light energy transmission measured to determine liquid proportions.