CHARACTERISTICS OF PERIODICALLY DOMAIN-INVERTED LINBO3 AND LITAO3 WAVE-GUIDES FOR 2ND HARMONIC-GENERATION

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-mu-m 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.