Characterization of proton-exchange slab optical waveguides in z-cut LiNbO3

We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.