British Telecommunications Corporation

British Telecommunications Public Limited Company

Susan P Craig

Benjamin J Ainslie

Jonathan R Armitage

Steven T Davey

Glass fibre suitable for use as the core in fibre lasers and/or amplifiers has a core which consists of a continuous glass phase and a dispersed phase of crystallites. The preferred crystallites are the oxides and phosphates of rare earth metals, e.g. Nd.sub.2 O.sub.3 and NdP.sub.5 O.sub.14. The small size concentration and distribution of the crystallites keeps the attenuation down to acceptable levels.

Optical wave guides

An optical fibre for use in fibre lasers has the lasing additive eg Er.sup.3+, concentrated in center of the core. Preferably the core has an inner region which contains the additive and an outer region which is dopant free. The concentration of the dopant reduces the pump threshold for a laser and improves the gain performance for a given pump power. The fibre is conveniently made in MCVD. The use of Al.sub.2 O.sub.3 in the inner zone appears to reduce loss of dopant during tube collapse.

Optical fibre with fluorescent additive

Rare earth elements, e.g. Nd, are introduced into optical glass fibre for telecommunications by evaporating a suitable salt, e.g. NdCl.sub.3, from a glass sponge into the gas stream used to deposit core material. Preferred sponges are in the form of tubes having an outer impervious layer and an inner porous layer. These sponges are conveniently made by MCVD and the impregnation is preferably carried out using an alcoholic solution of the impregnant.

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Ipswich, United Kingdom

Susan P Craig