Automatic quasiphase matching for second-harmonic generation in a periodically poled LiNbO3 waveguide

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Abstract
A novel technique is proposed and experimentally demonstrated to achieve a quasiphase matching (QPM) condition for second‐harmonic generation (SHG) in a nonlinear optical waveguide with a periodically poled LiNbO3 waveguide. The fundamental wave satisfying the QPM conditions is automatically generated when the laser diode (LD) and the optical waveguide are optically connected. Using the proton‐exchanged LiNbO3 waveguide with a periodically poled grating, which was fabricated by Ti diffusion and the InP/InGaAsP LD with antireflection‐coated facets, it was confirmed that the LD oscillated at the wavelength satisfying the QPM condition, and SHG was observed simultaneously. Using a Ti:sapphire laser, it was also confirmed that the SHG was realized at the third order of QPM condition, as was expected.