IMPROVEMENTS IN AND RELATING TO GLASS FIBRES FOR OPTICAL COMMUNICATION

摘要

A glass fibre for optical communication is formed by a vapour deposition process on the inside surface of pure silica substrate tube. The substrate forms the outer cladding whilst the inner and core are formed by the deposited layers. An intermediate layer of the cladding has a refractive-index similar to pure silica but due to compensating dopants. Thus deposition and sintering temperature is reduced. The inner layer of the cladding is however undoped pure silica, thus reducing absorbtion losses in this important region. The inner layer is described as having an outer radius of 1.5 to 2 times the radius of the core. A step in a process for making optical fibres comprising collapsing a tubular substrate to provide a preform is carried out in a stream of pure chlorine vapour acting as a drying agent.