Behaviors of spectral transmissions of photorefractive filters written in germania-doped fibers: writing and erasing experiments

摘要

Photoinscriptions of Bragg gratings have been carried out within several germanosilicate fibers via UV side writing near 243 nm. Real-time measurements of the spectral transmission, of the FWHM bandwidth and of the resonance wavelengths of the Bragg gratings lead to noteworthy observations when long irradiation times are used. Thus, second order diffraction efficiency has been observed from Bragg gratings written within some fibers. Second order diffraction can be detected once the first order grating reflectivity has begun to saturate. Whereas the dynamics of the UV induced excess losses may vary from one sample to another, no obvious direct correlation can be established between the dynamical evolutions of the loss spectra and the features of the grating growth.