Grating inscription in optical fibres using 213 nm picosecond radiation: a new route in silicate glass photosensitivity

The use of 213 nm, 150 ps Nd:YAG radiation for the inscription of Bragg grating structures in Ge-doped optical fibres is presented. Commercially available low-Ge-content and B/Ge-codoped optical fibres are exposed to 213 nm radiation, using an elliptical Talbot interferometer. Type I recording mechanism is observed for gratings inscribed in low Ge-content fibres; while Type IIA recording mechanism applies for the case of B/Ge-codoped fibres. The use of a high-energy photon (5.8 eV)-such that of 213 nm wavelength-in combination with short pulse duration enhances non-linear phenomena in the Ge-doped fibre core, leading to photosensitivity mechanisms that are not directly dependent on concentration of specific defects. Significant index changes greater than 10^-3 have been observed in both of the fibres exposed. Refractive index change evolution figures, grating spectra and annealing data will be presented in accordance with a detailed discussion regarding the photosensitivity mechanism for each of the fibres exposed.