Effect of boron concentration on the UV photosensitivity of silica glass film for planar lightwave circuit

The photosensitivity dynamics in SiO2 glass with a composition similar to that of silica planar lightwave circuit (PLC) devices was investigated as a fundamental study prior to device fabrication. Silica bulk glasses with similar composition to the core layer of PLC devices were prepared with various concentrations of B2O3. The photosensitivity in boron and germanium co-doped amorphous SiO2 yields a refractive index change Δn as high as 10−3 after irradiation with a KrF UV laser beam. The index modulation disappeared after thermal annealing. The result of annealing experiment and UV absorption/Raman spectra revealed that the molar volume change by UV irradiation is responsible for the index variation in the material.