Characteristics of pyrophosphoric acid proton-exchanged waveguides in LiNbO3

Abstract
The characteristics of proton‐exchanged LiNbO3 waveguides fabricated using pyrophosphoric acid process are reported. Using this process, high index change waveguides with step profile have been realized. Low‐loss (0.7 dB/cm) channel waveguides have been also obtained by pyrophosphoric acid process. The loss is much lower than that given by conventional benzoic acid process. We show that the reason for low‐loss waveguide fabrication is due to the uniform proton‐exchange formed by this process, compared with the benzoic acid process.