Recording of Type IIA Gratings in B-Ge codoped Optical Fibres Using 248nm Femtosecond and Picosecond Laser Radiation

Recent results on the recording of type IIA, negative index change gratings in B-Ge and high-Ge optical fibres by using 248 nm 500 fs and 5 ps laser radiation, will be reviewed here. Refractive index evolution curves for both average and modulated index changes are presented. Index changes of the order of 10^-3 are obtained for the fibers exposed, under accumulated energy density of few kJ/cm². The results presented reveal the non-linear underlying mechanism of the type IIA photosensitivity, which is directly dependent on pulse duration. For comparative purposes grating exposures in the same fibres using 248 nm nanosecond excimer laser radiation are also appended. Thermal annealing studies performed for all gratings fabricated, revealed that type IIA negative index gratings inscribed using femtosecond pulses exhibit enhanced thermal stability, enduring temperatures up to 650degC