Non-linear and photorefractive characterisation of highly confined LiNbO_3 waveguides prepared by high-energy, low-fluence ion irradiation

摘要

A preliminary characterisation is presented on the non-linear and photorefractive behavior of LiNbO_3 optical waveguides produced with a novel irradiation procedure. As described elsewhere, the method involves irradiation of the substrate with medium mass high-energy ions (F~(4+) at 20-22 MeV), whose electronic stopping power reaches a maximum value inside the crystal and not at the surface. Because a very low fluence is sufficient, the fabrication time is reduced about three orders of magnitude in comparison with similar guides prepared by conventional implantation. Thus, low-fluence irradiated guides seem serious candidate for massive cheap production in device applications. The guides show step-like, high-jump index profiles and support highly confined propagation modes. The fabrication process and the obtained index profiles have been described, and the second order nonlinear response and the recording and erasing of photorefractive gratings have been investigated in the paper. Results on the effect of the fluence (10~(14) at/cm~2) and annealing treatments (300°C, 1 h) on the non-linear optical waveguide behavior are also presented.