Long-period grating inscription in hydrogen-free SMF-28 fiber by high-repetition-rate femtosecond UV pulses

Abstract Using femtosecond UV (258 nm) pulses, generated at high-repetition-rate (50 kHz), we managed to record high-quality long-period gratings in a number of fibers, including a standard telecommunication one, SMF-28. Along with the main grating, connected to the refractive index change in the fiber core, at the relatively high intensity of the inscribing UV radiation, I  ∼ 1.5 TW/cm 2 , we recorded the formation of an additional long-period grating, based on the refractive index change induced in the fiber cladding. We have compared the temperature sensitivity and the thermal stability of both gratings.