Relief Bragg gratings were imprinted by 248 nm interferometric excimer laser ablation on potassium ion-exchanged channel waveguides in BK-7 glass overlaid with a thin high-index InOx film. Using five pulses of energy density 60 mJ/cm2, a spectral transmittance notch of depth 66% and FWHM<0.1 nm was obtained at 1547 nm in the TE polarization for a waveguide having a nominal width of 8 µm and a 135-nm-thick InOx overlayer. In waveguides coated with 100 nm InOx, with widths increasing from 3 to 8 µm, the reflection wavelength shifted by 0.12 nm/µm and the reflectivity increased monotonically.
