Refractive index change in lithium niobate induced by focused femtosecond laser

Lithium Niobate is an important material in optical communication due to its special characteristics (high electrooptic coefficients and high optical transparency in the near infrared wavelengths). In this paper, we investigated the effects of 775-nm, femtosecond laser radiation on the Lithium Niobate crystal. By focusing the laser beam through a microscope objective, a certain refractive index change may be induced in Lithium Niobate substrate. Based on this effect, channel waveguides and other waveguide structures were fabricated. The output optical fields through them were measured, and the refractive index change of ~6×10^-4 was calculated with the Near-field Method. The properties of these waveguide structures were discussed. We also investigated the waveguides effect induced with different fabrication conditions. The experimental results revealed that different fabrication conditions affect the waveguide effect greatly.