Planar waveguide in beta barium borate formed by proton implantation and optical properties in visible and near-infrared band

•Waveguide structure on β-BBO crystal has been fabricated at near-infrared band.•The near-field light intensity distributions have been measured on β-BBO waveguide structure.•Annealing process has been carried out prior to the implantation process.•The process of proton implantation has not influence the microstructure of the β-BBO crystal.

β-BaB2O4 is nonlinear crystal that provides attractive features for various nonlinear optical application. We report on z-cut β-BaB2O4 planar waveguide produced by multi-energy proton implantation in total of 3 × 1016 ion/cm2 at room temperature. The refractive index profile is a barrier-confined distribution, which is reconstructed according to the dark mode spectroscopy at the wavelength of 633 nm. The near-field light intensity profiles in the visible (633 nm) and near-infrared band are measured by end-face coupling method. The absorption spectra recorded over the wavelength range 185–2500 nm shows there is hardly change after proton implantation. The investigation results of the Raman spectra demonstrate that the positions and widths of all the peaks are very similar in the β-BaB2O4 crystal and waveguide layer.