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.