Suppression of discrete cladding mode resonances in fibre slanted Bragg gratings for gain equalisation.

In a slanted Bragg grating, coupling between the fundamental guided mode and the counterpropagative cladding modes result in discrete resonances in the transmission spectrum. These resonances are a drawback when Slanted Bragg Gratings are used for gain flattening of fibres amplifiers. A new method based on a chemical etching of the cladding is proposed leading to an overlap of the resonances and a reduction of the amplitude of the modulation. This method can be applied for any value of photo induced modulation amplitude in the SBG.

Thermal stability of the 248-nm-induced presensitization process in standard H2-loaded germanosilicate fibers.

Grating growths through exposure of presensitized standard fibers to KrF light were recorded in various experimental condition. It is shown that there exists an optimum sensitization fluence at which the efficiency of the sensitization process is higher. Isochronal thermal annealing of pre-exposed fibers led to a decrease in the sensitization-induced enhancement of photosensitivity. IR-absorption spectroscopy was carried out in fibers or preform plates to monitor the attenuation ascribed to H-bearing species in the same samples. The annealing-induced decay in photosensitivity cannot be correlated with those of the H-bearing species in the whole temperature range (110 degrees C-800 degrees C). This indicates that the enhancement of photosensitivity comes from the transformation of more than one species.