Thermal hypersensitisation and grating evolution in Ge-doped optical fibre

Low temperature (sub 1000°C) thermal hypersensitisation is reported in germanosilicate optical waveguides. Gratings are written using a CW 266nm laser source. In contrast to laser hypersensitisation, thermal excitation is generally dispersive involving a range of specific glass sites. More complex grating profiles presenting evidence of solid-state autocatalysis and bistability at increasingly high sensitisation temperatures are observed. More specifically, at 500°C, a behaviour resembling type IIA grating response is observed.