Properties of buried waveguides produced by He-irradiation in KTP and Rb:KTP

Abstract

Buried waveguides were produced by He +-irradiation with energies between 1 and 3 MeV and ion fluences, which are sufficient to generate multiple buried amorphous layers in KTP and Rb:KTP, respectively. Within these layers the refractive index is decreased and they act as barriers for light guiding. The irradiation causes the formation of defects within the waveguide, reducing the optical transmittance. By post-irradiation thermal annealing light scattering and absorption inside the waveguides can be significantly reduced. In the case of Rb:KTP rapid thermal annealing up to temperatures of 500 °C was found to be suitable to abolish point defects and to prevent the Rb-diffusion at the same time. Due to adjacent regions of different refractive indexes non-symmetrical electric field distributions are obtained within the waveguide. For the completely irradiated waveguides the homogeneous refractive indexes around the waveguide cause fibre-like symmetrical electric field distributions in a single-mode waveguide undisturbed of surface effects. The samples were analysed by means of various complementary methods (Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, m-line spectroscopy). The near-field pattern and the attenuation of the waveguides were measured.