Leaky-waveguide configuration for quasi-phase-matched second-harmonic generation

We consider quasi-phase-matched (QPM) second-harmonic generation in a leaky-waveguide structure in which the fundamental is a guided mode and the second harmonic is radiated into the substrate. Under a no-pump-depletion approximation and using the coupled-mode theory, we show through numerical calculations that by an appropriate choice of the thickness of the index depression region of the leaky waveguide one can achieve conversion efficiencies and tolerance values that are intermediate between QPM and QPM Cerenkov configurations. The proposed configuration thus possesses the advantages of both QPM guided-to-guided and Cerenkov configurations and hence should be of interest in the realization of short-wavelength light sources. (C) 1998 Optical Society of America.