Wavelength shift of planar waveguide Bragg gratings under the UV-laser irradiation of polymer cladding

The UV laser trimming is a useful technology for adjusting the effective refractive index of planar waveguide and to achieve accurate specifications of the passive devices. The change in the refractive index of polymer overcladding layer under the irradiation of UV light results in the change of the effective refractive index of waveguides, which can be measured from the shift of transmission spectrum of Bragg gratings fabricated on the silica core beforehand. Saturated effective refractive index change of 7.5 times 10^-5 was obtained for a 26 mum thick overcladding irradiated by UV laser of fluence 41 J/cm .