Waveguides produced by ultra-short laser pulses inside lithium niobate

Abstract

Lithium Niobate is widely used in optical communication due to its high electrooptic coefficients and high optical transparency in the near infrared wavelengths. In this thesis, a novel technology of writing waveguide structures in the Lithium Niobate crystal with femtosecond laser was investigated. By focusing the laser beam in the substrate through a microscope objective, a certain refractive index change may be induced in the focal volume. In this project, channel waveguides were fabricated, and the properties of these waveguides were characterized. Maximum refractive index change of ~6??10-4 and the propagation loss of ~1dB/cm have been obtained in these channel waveguides. The waveguide effect induced with different fabrication conditions was investigated. The experimental results revealed that different fabrication conditions affect the waveguide effect greatly. In addition, some functional waveguide structures such as Y-splitters and Mach-Zehnder structures were fabricated, and their properties were characterized. Finally, plenty of simulations of different waveguide structures were discussed to validate qualitatively the properties of those fabricated waveguides and instruct the further work.