Techniques used to assist phase matching of second-order nonlinearities in semiconductor waveguides are reviewed. The salient points of each method are highlighted, with their strengths and weaknesses with regard to various key applications discussed. Recent progress in these techniques is also reviewed. Emphasis is placed on two techniques, namely quasi-phase matching via domain disordering utilizing quantum well intermixing, and exact phase matching using Bragg reflection waveguides.The figure shows (a) An optical microscope image of an ion implantation mask used to fabricate gratings used for quasiphase matching, (b) a scanning electron micrograph of an ion implantation mask, (c) a scanning electron micrograph of a semiconductor ridge waveguide structure, and (d) an optical microscope image of group monolithic ring lasers designed for integration with quasiphase matched structures.

We experimentally demonstrate a transverse electric (TE)-pass polarizer using the recently proposed hybrid plasmonic waveguide. The device consists of a silicon film separated from a chromium layer by a silica spacer. The device was characterized using a tunable laser in the 1.52-1.58 μm wavelength range. For a 30 μm long polarizer, the extinction ratio in this wavelength range varies from 23 to 28 dB and the insertion loss for the TE mode is 2-3 dB. The device is compact; its fabrication is completely compatible with silicon-on-insulator technology, and its performance compares favorably against previously reported silicon-based integrated optic TE-pass polarizers.

We review our recent progresses on frequency conversion in integrated devices, focusing primarily on experiments based on strip-loaded and quantum-well intermixed AlGaAs waveguides, and on CMOS-compatible high-index doped silica glass waveguides. The former includes both second-and third-order interactions, demonstrating wavelength 2 conversion by tunable difference-frequency generation over a bandwidth of more than 100 nm, as well as broadband self-phase modulation and tunable four-wave mixing. The latter includes four-wave mixing using low-power continuous-wave light in microring resonators as well as hyper-parametric oscillation in a high quality factor resonator, towards the realization of an integrated multiple wavelength source with important applications for telecommunications, spectroscopy, and metrology.

Second-harmonic generation in domain-disordered quasi-phase-matched GaAs/AlGaAs superlattice-core waveguides was demonstrated using a continuous wave fundamental source. Output second-harmonic powers of up to 1.6 W were measured when on a Fabry-Pérot resonance peak. Temperature-related bistable behavior was observed in both the fundamental and second-harmonic output when tuning either the input power or input wavelength.

Abstract-Wavelength conversion by difference frequency generation is demonstrated in domain-disordered quasi-phase matched waveguides. The waveguide structure consisted of a GaAs/AlGaAs superlattice core that was periodically intermixed by ion-implantation. For quasi-phase matching periods of 3.0-3.8 µm, degeneracy pump wavelengths were found by secondharmonic generation experiments for fundamental wavelengths between 1520-1620 nm in both type-I and type-II configurations. In the difference frequency generation experiments, output powers up to 8.7 nW were generated for the type-I phase matching interaction, and 1.9 nW for the type-II interaction. The conversion bandwidth was measured to be over 100 nm covering the C, L, and U optical communications bands, which agrees with predictions.