Linear and Nonlinear Optical Properties of Annealed Proton Exchanged LiNbO3 Waveguides

Abstract

Quasi-phasematched frequency conversion in LiNbO3 waveguides is an efficient method for the generation of short wavelength radiation from infrared laser diodes. While many techniques are used to form the ferroelectric domain grating necessary for quasi-phasematching, waveguide confinement is usually provided by the annealed proton exchange (APE) process. The optical properties of APE waveguides are not well understood and accurate models relating the modes of the waveguide to processing parameters are not available. Also, effects of the APE process on the nonlinear optical properties of LiNbO3 have yet to be understood. In this presentation we discuss two sets of experiments. First, we report a nonlinear diffusion coefficient for protons in LiNbO3 and the relationship between concentration and index change, which allow a quantitative prediction of the modes of APE waveguides.1 Second, we report depth profiling of the d33 nonlinear coefficient in proton exchanged (PE)2 and APE waveguides which, in conjunction with the optical modes, allows accurate calculation of the overlap integrals and normalized conversion efficiencies for guided wave nonlinear optical interactions. These models make possible the optimization of APE waveguides for maximum normalized conversion efficiency, noncritical phasematching, or efficient coupling to a laser diode for any guided wave nonlinear optical interaction.