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

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.