Writing of refractive-index gratings in germanosilicate fibres by near-UV radiation

A refractive-index grating was formed for the first time in a germanosilicate fibre by cw Ar⁺ laser radiation in the near-UV range (333—364 nm). The refractive index change induced in a fibre with 10 mol.% GeO₂ in the core was 1.9 × 10^-4 when the radiation power density was 1.7 × 10⁵ W cm^-2. The gratings formed in this way were as therma lly stable as those formed by KrF laser (248 nm) radiation.