Comparative results on the recording of Type IIA gratings in B-Ge optical fibres using femtosecond and picosecond 248nm laser radiation

Infrared and ultraviolet femtosecond radiation has been used for the inscription of Bragg or long period gratings in Ge-doped and all-silica optical fibres, with the refractive index changes induced being usually greater than 10^-4, even for glasses of low transparency at the illumination wavelength. We have recently presented for first time the recording of Type IIA Bragg gratings in B-Ge codoped optical fibres using 248 nm, 500 fs laser radiation. We extend our study here performing comparative exposures using the same laser wavelength and pulse durations of 5 ps and 120 fs.