Engineering the Second-order Optical Nonlinearity in Semiconductors

Abstract

Quasi-phase matching techniques have revolutionized the field of nonlinear optical frequency mixing. Nonlinear crystals for conventional second-harmonic (SH) generation require anisotropic linear optical properties to permit the phase matching of the the pump and SH beams. This requirement severely limits useable materials and geometries. The mismatch between pump and SH beams can be compensated by periodically modulating the optical properties of a material, resulting in a quasi-phase matched (QPM) geometry with efficiencies approaching that of conventional phase matched geometries. Although the concept of QPM has been known for more than thirty years, only in the last decade has QPM been widely implemented for a variety of applications1. For example, QPM SH generation with very high efficiencies has been achieved in LiNbO3 and KTP waveguides1, and optical parametric oscillators (OPO) employing QPM structures have been demonstrated2. The advent of QPM has important implications for optical materials science. Virtually any material with a non-zero second-order susceptibility, χ(2) may be useful for nonlinear devices, and so it has become increasingly important to understand and learn how to control the optical nonlinearities in a wide variety of materials.