Theoretical analysis of phase-matched second-harmonic generation and optical parametric oscillation in birefringent semiconductor waveguides

We analyze the phase-matching conditions for second-harmonic generation (SH G) and optical parametric oscillation (OPO) in birefringent nonlinear semic onductor waveguides and apply these results to the model system of ZnGeP2 o n a GaP substrate. The analyses and numerical results show that phase match ing can be achieved for OPO and SHG for reasonable guide thicknesses throug hout much of the infrared, indicating significant potential applications fo r nonlinear birefringent waveguides. For the fundamental mode of a relative ly thick guide the region of phase matching and the phase-matching angles a re similar to those in bulk material. However, the waveguide has the added flexibility that phase-matched coupling can occur between the various modes of the guide. For example, the phase-matching region for SHG can be consid erably extended by coupling the pump into the guide in the fundamental, m = 0, mode and phase matching to the m = 2 mode of the second harmonic. Signi ficantly, the results indicate, among other things, that ZnGeP2 waveguides with harmonic output in the m = 2 mode can be used for efficient SHG from i nput radiation in the 9.6-10.6-mum region where bulk efficiencies in this w avelength range are too small to be useful. (C) 2001 Optical Society of Ame rica.