Behaviour of spectral transmissions of Bragg gratings written in germania-doped fibres: writing and erasing experiments using pulsed or cw uv exposure

Abstract Photoinscriptions of Bragg gratings have been carried out within several germanosilicate fibres via uv side writing near 244 nm. The gratings have been written with a pulsed or a continuous-wave (cw) laser. It has been observed that the refractive index changes were strongly non linear as a function of the exposure time whatever the nature of the source may be. Uv pulsed or cw photobleaching experiments have been performed using gratings written under various conditions in fibres for which complex evolutions of spectra could be observed. Uv fringeless illumination of a grating firstly can erase the first order transmission spectrum and then build a new spectrum. Results of thermal annealing of gratings written using pulsed exposure or using cw light are analysed. We render a phenomenological account of the experimental results by assuming that, at least, two photorefractive effects are responsible for the grating formation or erasure.

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