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Dynamic behaviour of a Bragg grating spectrum produced by single UV-writing pulses

Transient Bragg wavelength changes as large as 2 nm and increases of the reflectivity of about 25% are observed in a hydrogen-loaded standard telecommunications fibre during and directly after 20 ns irradiating UV-pulses. We present here an experiment aimed at obtaining an estimation of the temperature increase directly after a UV writing pulse. It consists of time-resolved measurements of the reflection and transmission changes of a CW DBR laser launched into the irradiated fibre whose wavelength is tuned to different positions with regard to the grating spectrum.