Characteristics of periodically domain-inverted LiNbO3 and LiTaO3 waveguides for second harmonic generation

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Abstract
Characteristics of waveguides with periodically domain-inverted regions in LiNbO3 and LiTaO3 for quasi-phase-matched (QPM) second harmonic generation are investigated. The domain-inverted regions in LiNbO3 are formed by heat treatment using selective SiO2 mask and those in LiTaO3 are formed by heat treatment using selective proton exchange. The domain-inverted region in LiTaO3 is fabricated up to 2.7 μm depth, which is twice as deep as that in LiNbO3. The channel waveguides incorporating the regions are fabricated using proton exchange by pyrophosphoric acid. The propagation loss (0.9 dB/cm) of LiTaO3 waveguide is much lower than that of LiNbO3 waveguide (2.9 dB/cm). The second harmonic power generated in LiTaO3 waveguide by third-order QPM consequently has three time higher conversion efficiency, compared to that in LiNbO3 waveguide. In domain-inverted LiNbO3 waveguide, we have observed optical damage. On the other hand, in domain-inverted LiTaO3 waveguide, stable blue light (421 nm) has been obtained without optical damage.