Self-quasi-phase-matched second-harmonic generation in the proton-exchanged LiNbO3 optical waveguide with periodically domain-inverted regions

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Abstract
A self‐quasi‐phase matching technique for second‐harmonic generation (SHG) that uses a proton‐exchanged LiNbO3 optical waveguide with periodically domain‐inverted regions is proposed and demonstrated. The fundamental wave satisfying quasi‐phase‐matching (QPM) condition was generated by an InP/InGaAsP laser diode (LD) with antireflection coated facets which was optically connected to the LiNbO3 waveguide. As the domain‐inverted regions in the optical waveguide act as the distributed Bragg reflector (DBR), the LD is lased by the feedback waves from the DBR. We designed the period of domain‐inverted regions to satisfy the QPM conditions and the high‐reflectance conditions of the fundamental wave. We confirmed that the LD was lased at the wavelength satisfying the QPM conditions and SHG was observed simultaneously.