Frequency doubling: blue light and UV generation in periodically poled LiTaO3/ LiNbO3

A novel structure for a quasi-phase-matched-second harmonic generation (QPM-SHG) device with a high-index-clad waveguide is shown. The periodic domain inversion was fabricated in LiTaO₃ using selective proton-exchange followed by quick heat treatment, which has advantages of uniform periodicity over large area, and is a good combination with a low loss proton-exchanged waveguide. To achieve strong confinement and efficient overlap between fundamental and SH wave, we have proposed a high-index-clad waveguide, Using a Nb₂ O₅ film as the clad layer, harmonic blue light of 10 mW at a wavelength of 425 nm was obtained for a conversion efficiency of 280% W. Recently, to achieve further improvement in conversion efficiency and output power, we focused our attention on X-cut MgO:LiNbO ₃, which has advantages of larger nonlinear coefficient, higher damage threshold, and potential to achieve low-loss coupling with the laser diode of transverse-electric mode oscillation. We have succeeded in fabricating a first-order QPM waveguide in X-cut MgO:LiNbO ₃ utilizing two-dimensional high-voltage application that produces deep domains with uniform periodicity over long interaction length. Using this domain structure with the high-index-clad proton-exchanged waveguide, efficient harmonic blue light of 5.5 mW at 434 nm wavelength was generated for a normalized conversion efficiency of 1200% W.cm²