Second-harmonic generation with a high-index-clad waveguide

Theoretical and experimental analyses of second-harmonic generation (SHG) with a high-index-clad waveguide are reported. It was found that confinement of the propagation modes and the overlap between the fields of fundamental and second-harmonic waves could be increased in this waveguide. This structure was achieved in an $x$-cut MgO:LiNbO ₃ quasi-phase-matched (QPM) waveguide by use of Nb₂O₅ as a cladding layer. With the QPM SHG device, harmonic blue light of 5.5 mW at the 434-nm wavelength was generated with a normalized conversion efficiency of $1200\%/{\mathrm{W cm}}^2$.