CHARACTERIZATION OF PROTON EXCHANGED PLANAR OPTICAL WAVEGUIDES IN ZNO:LINBO3 CRYSTALS

Abstract

In this thesis, we repon the systematic study of proton exchanged planar optical waveguides in x-cut, y-cut, and z-cut 6mol%, ZnO-doped lithium niobate crystals (ZnO:LiNbO3) using adipic acid as proton source for the first time. The diffusion properties m1d optical features of the waveguides were optically characterised using the prism coupling method. Surface damage was found in multimode y-cut waveguides. The structural properties in the waveguide layers were investigated using the double-crystal X-ray diffraction and infrared absorption techniques. The OH infrared absorption was carried out to identify the proton positions in the waveguide lattices. Based on strain data measured, a mechanism was proposed to explain the extraordinary refractive index increase caused by proton exchange reaction with LiNbO3 crystal. Annealing properties of z-cut waveguides were systematically studied, and a two-stage annealing process was identified from the distribution of m-lines of the annealed waveguide. A modified Fermi function was used to describe the annealed index profiles of z-cut multimode waveguides. Annealed Li+ concentration profile was obtained by solving a standard thermal diffusion equation. This annealed lithium ion concentration profile was found to reasonably fit the annealed index profiles for a single waveguide.