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.