Low-Loss Channel Waveguides in MgO:LiNbO₃ and LiTaO₃ by Pyrophosphoric Acid Proton Exchange

The characteristics of proton-exchanged MgO-doped LiNbO₃ (MgO:LiNbO₃) and LiTaO₃ waveguides fabricated by the pyrophosphoric acid process are reported. Using this process, low-loss (0.4 dB/cm) channel waveguides in MgO:LiNbO₃ have been realized at 633 nm without annealing. The optical damage in MgO:LiNbO₃ waveguides at 441.6 nm wavelength is lower than that obtained in LiNbO₃. For LiTaO₃, by annealing, low-loss (0.3 dB/cm) channel waveguides can be fabricated by pyrophosphoric acid proton exchange. No optical damage was observed in the LiTaO₃ waveguides even when the incident power was above 1 mW at 442 nm.