UV-Induced Refractive Index Changes in Germanosilicate Fibres

Abstract

Photorefractivity in germanosilicate fibres was first reported by Hill and co-workers over a decade ago1. They were able to produce holographic gratings 60 cm long by interfering counterpropagating modes at 488 and 514.5 nm. Further measurements by Lam and Garside2 indicated that reflection efficiencies approached 100% for interaction lengths of l-2cm implying refractive index modulations of the order of 10-5. They were unable to estimate the spectral variation of the index change Δn(λ) because the reflection band was restricted to the recording wavelength. It is clear that, for distributed reflectors at communications wavelengths, the effect is only useful if i) a substantial index change, extends out to beyond 1 μm and ii) a satisfactory method of side-writing gratings can be found.