Nonlinear optical properties of proton-exchanged waveguides in z-cut LiTaO3

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Abstract
Reflection second‐harmonic generation from the polished waveguide end face is used to investigate the second‐order nonlinear optical properties of as‐exchanged and annealed proton‐exchanged waveguides in z‐cut LiTaO3. It is found that proton exchange results in a strongly reduced nonlinearity which, however, can be restored by thermal annealing. Selective etching is used as a method to further investigate the structural changes following proton exchange and annealing. A correlation is found between the etching properties and the nonlinear optical properties. The results are discussed and related to the hydrogen concentration profile using a linear diffusion model for the anneal process.