Absence of UV-induced stress in Bragg gratings recorded by high-intensity 264 nm laser pulses in a hydrogenated standard telecom fiber

We report on photochemical two-photon Bragg grating preparation in hydrogenated fiber without any UV-induced stress in the core or cladding, leaving only the color-center model responsible for refractive index changes for UV femtosecond irradiation. Without hydrogen loading strong stress changes are observed in the core and in the cladding indicating glass compaction. The irradiation does not change the inelastic strains, in contrast to H2-loading.