Fibre-Bragg-grating writing in single-mode optical fibres by UV femtosecond pulses

Fibre-Bragg-grating writing in single-mode optical fibres by the phase-mask method using 220-fs, 264-nm UV pulses of intensity 31 – 77 GW cm^-2 is reported for the first time. The achieved degree of modulation of the photoinduced refractive index was 1.9 × 10^-3 in an H₂-loaded SMF-28 telecommunication fibre and 1.1 × 10^-3 in a H₂-free Nufern GF1 fibre. The dependence of the induced refractive index on the intensity for the same irradiation fluences in the case of the H₂-loaded SMF-28 fibre shows that the refractive index is induced due to nonlinear absorption.