Second Harmonic Generation in Nb₂O₅ Thin-Film Optical Waveguide Deposited on LiTaO₃ Substrate by RF Magnetron Sputtering

The first experimental observation of Cerenkov-type second harmonic generation (SHG) in an amorphous Nb₂O₅ thin-film optical waveguide on (0001) LiTaO₃ substrate is reported. The Nb₂O₅ thin films were deposited by rf magnetron sputtering on LiTaO₃ substrate. A Nd:YAG laser at 1064 nm wavelength was used as the pumping source for the SHG experiments. The conversions occurred between the fundamental (1064 nm) TE₀ guided mode and the harmonic (532 nm) TM radiation mode, and between the TM₀ guided mode and the TM radiation mode. The efficiency of both conversions was about 10^-8 for a sample with a film thickness of 788 nm. These SHG results were in good agreement with the coupled-mode theory, and the theoretical calculation revealed that the low conversion efficiencies were due to the unsuitable film thickness. It was predicted that the efficiencies could be raised to a much higher level.