Large Photo-Induced Index Changes in Sn-codoped Germanosilicate Fibres

Abstract

There has been a surge of interests in photosensitive fibre gratings in recent years chiefly due to their ease of fabrication and numerous application. Although very large photo-induced index changes have been achieved in pure germanosilicate fibres, an enhanced photosensitivity is desirable to enable gratings to be written with ease and with much cheaper laser source. Stronger photosensitivity also opens up many new applications. Boron-codoping in germanosilicate fibres has been reported to give a much enhanced photosensitivity comparing to that in pure germanosilicate fibres [1], but gratings in those fibres have a much poorer high temperature stability and the B-codoping can also give rise to excessive loss at the important telecommunication window of 1.55 μm. Some post-fabrication techniques have also been devised, i.e. H2/O2 flame-brushing of a germanium doped fibre [2] and Low-temperature hydrogen loading [3], but they are very time-consuming and there are also large induced losses [3]. In this paper, we report on enhanced photosensitivity in Sn-codoped germanosilicate fibres. The gratings in the Sn-doped fibres also have a much improved high temperature stability than those in B-codoped fibres. Unlike B-codoping, Sn- codoping does not introduce significant loss at the important telecommunication window of 1.55 μm.