We report third-order quasi-phase-matched (QPM) second harmonic generation (SHG) in a LiTaO3 channel waveguide. A deep domain-inverted region is first fabricated by a proton-exchange and heat treatment technique. Then a uniform and low-loss channel waveguide is fabricated by pyrophosphoric acid proton exchange. Consequently, 12 mW of blue light is obtained at 424 nm wavelength with a conversion efficiency of 6%. The observed FWHM temperature acceptance width for SHG power is 3.2°C and FWHM wavelength acceptance bandwidth for that is 0.2 nm. It is also shown that diffraction limited focusing of the generated blue light may be obtained.
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