Optical fibre with fluorescent additive

摘要

An optical fibre for use in fibre lasers has the lasing additive, eg Er<3><+>, concentrated in centre (13) of the core (14). Preferably the core (14) has an inner region (13) which contains the additive and an outer region (12) 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 by MCVD. The use of Al2O3 in the inner zone appears to reduce loss of dopant during tube collapse.