Spectral characterisation of photoinduced high efficient Bragg gratings in standard telecommunication fibres

Abstract

High efficiency Bragg gratings were obtained in a standard telecommunication fibre with a germanium concentration of 3%. The best filter has a reflectivity of 94% and a bandwidth of 1.7nm. Its symmetric reflection spectrum with three side-lobes is in very good agreement with a theoretical calculation. A refractive index change of 1.2 × 10−3 and a length of 0.84mm were obtained by fitting a theoretical filter curve to the experiment data. Additionally, the transmission spectrum shows, on the short wavelength side of the resonance, a region with a maximum of 19% loss.