Abstract

Annealed proton exchange (APE) is an important technique for the fabrication of waveguides in LiNbO₃ for electrooptic and nonlinear optical applications. Unannealed proton exchanged (PE) waveguides have step-like refractive index profiles and large extraordinary refractive index changes, but suffer from reduced electrooptic and nonlinear coefficients. Post-exchange annealing is necessary to produce single mode waveguides that exhibit electrooptic and nonlinear optical properties comparable to bulk LiNbO₃ and low insertion loss in fiber optic applications.¹ While the PE process is well-characterized, quantitative modeling of APE waveguides is much less well developed. In this paper we present measurements of the effective mode indices and fundamental mode profiles for APE waveguides subjected to a variety of exchange and annealing conditions in both X- and z-cut substrates, along with empirical models for the concentration-dependent diffusion coefficient and dispersion that allow accurate calculation of the refractive index profile for APE waveguides as a function of exchange depth and anneal time for wavelengths between 0.4 and 1.1 μm. The reduction of the nonlinear susceptibility in PE waveguides, measured by a reflected second harmonic generation technique, is also discussed.

© 1992 Optical Society of America