TAILORING OF OPTICAL PLANAR WAVE-GUIDES IN KNBO3 BY MEV HE ION-IMPLANTATION

In KNbO3 single crystals planar optical waveguides were fabricated by He ion implantation with doses from 2.5 . 10(14) cm-2 to 2 . 10(16) cm-2. The waveguides were analyzed by dark line spectroscopy at 633 nm and the detailed refractive index profiles were reconstructed with a dark mode reflectivity calculation method. We found a decrease of all three refractive indices n(a), n(b) and n(c) in a layer several mum below the crystal surface. At a dose of 10(16) cm-2 saturation of the index decrease of DELTAn(a) = -0.160, DELTAn(b) = -0.212 and DELTAn(c) = -0.048 occur indicating the formation of an optically isotropic layer with a refractive index of 2.119. In the surface close region of the waveguide an anomalous increase of the smallest index n(c) of DELTAn(c) = +0.013 was observed. The indices of KNbO3 are ten times more sensitive to radiation damage in comparison with LiNbO3.