Polarization properties of fibre Bragg gratings inscribed by high-intensity femtosecond 264Â nm pulses

We have investigated the polarization properties of Bragg gratings fabricated in hydrogen-free photosensitive Ge/B codoped PS1250/1500 and hydrogenated telecom SMF-28 fibres by high-intensity femtosecond UV pulses. We have shown that, under given experimental conditions, the Bragg grating inscription proceeds in these fibres differently, via single-photon (PS1250/1500) or two-photon (SMF-28) absorption mechanisms. In relation to that, in the first fibre both the polarization-dependent loss (PDL) and the differential group delay (DGD) grow linearly with the irradiation fluence, in the second one the PDL and DGD values show a linear dependence only up to fluence value of about 0.7 kJ/cm2 and then increase drastically. We found that PDL and DGD values for Bragg gratings recorded by high-intensity 264 nm pulses overcome significantly (by 2-4 and 4-10 times, respectively) the corresponding values obtained in the same fibres under low-intensity CW 244 nm irradiation.