Abstract

Parametric wave mixing in quadratic (or χ⁽²⁾) nonlinear materials has attracted a growing attention because of its perspectives for all-optical switching devices [1]. Many of the theoretically predicted effects, such as large nonlinear phase-shifts and dichromatic spatial solitons (mutually trapped fundamental and second harmonic beams), have already been observed experimentally in bulk crystals and slab waveguides [1]. Switching devices based on the non linear phase shift in quadratic materials such as integrated Mach-Zehnder interferometers and directional couplers have also been experimentally demonstrated [2]. However, most of the switching effects require a small wave vector mismatch between fundamental wave (FW) and second harmonic (SH). Quasi-phase matching (QPM) is a promising technique, since it allows, at least potentially, to achieve phase-matching in any material over a wide range of wavelengths [3]. As a consequence the largest component of the second-order susceptibility tensor can be used, allowing for a decrease in operating power. The idea of QPM is to periodically modulate the χ⁽²⁾ coefficient where the pertinent grating vector can compensate the mismatch. Although the physics of QPM has been known since 1962 [4] technological difficulties have been overcome only recently and stable QPM structures have been developed [5].

© 1998 Optical Society of America