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.

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.

Second-harmonic generation using the type-II polarization configuration is demonstrated in quasi-phase-matched GaAs radicalAlGaAs superlattice waveguides. Phase-matching wavelengths and conversion efficiencies were determined for several quasi-phase-matching periods using 1.9 ps pulses. Saturation effects at high input power were concluded to be the result of third-order nonlinear effects.

Abstract-The optical Kerr effect was measured by observing self-phase modulation in GaAs-AlGaAs superlattice-core waveguides modified by ion-implantation quantum-well intermixing. The band-gap energy was shifted by 68 nm for an implantation dose of 0 5 10 13 cm 2 and annealing temperature of 775 C. The Kerr effect was suppressed by up to 71% in the transverse-electric polarization after intermixing. A reduced polarization dependence of the self-phase modulation was observed after intermixing.Index Terms-Nonlinear optics, optical Kerr effect, quantumwell intermixing (QWI), semiconductor superlattice. COMPOUND semiconductors have led the way towards monolithically integrated all-optical signal processing devices. Mature fabrication technologies have allowed the development of low-loss waveguides and advanced structures such as Bragg reflection waveguides [1], passive mode converters [2], and cascaded microring resonators [3]. AlGaAs is of particular interest since the optical Kerr effect, a third-order nonlinearity, has been shown to be 500 times stronger than in silica [4]. These nonlinearities are nonresonant and do not rely on free-carrier plasma dispersion effects since the operating wavelengths are typically below the half-band-gap energy. This has opened the possibility of all-optical switching devices such as nonlinear directional couplers (NLDCs) [5] and nonlinear Mach-Zehnder interferometers (NLMZIs) [6] with ultrafast response times necessary for ultrahigh-speed communications systems and signal processing. Multiple quantum-well (MQW) structures based on AlGaAs permit greater flexibility to tailor the band-gap energy to suit the optical properties required for particular applications. Furthermore, the band-gap energy of MQWs can be modified after wafer growth by quantum-well intermixing (QWI) techniques [7]. This cost-effective approach allows selective control , which is a requirement for devices such as QPM gratings. Deep-well semiconductor superlattices have attracted attention as the greater fill-factor and large band discontinuity in comparison to conventional quantum-well structures potentially provides a larger modification to nonresonant optical properties such as the refractive index and nonlinear optical susceptibilities in the transparency window for the complete structure. Thus, shorter and more efficient devices that require less power to operate are possible. In this letter, we demonstrate large modifications of the optical Kerr effect in GaAs-AlGaAs superlattice-core waveguides induced by ionimplantation QWI at wavelengths near the half-band-gap. We have previously reported on the large polarization dependence of the Kerr coefficient in GaAs-AlAs superlattice waveguides [12]. However, measurements indicated the presence of parasitic two-photon absorption (TPA) resonances due to the reduced barrier resulting in asymmetric quantum wells (ASQW) found on either side of the superlattice waveguide core. In the present study, we modified the waveguide structure with several improvements. The new ...

We report on the development of Germanium-on-SOI waveguides for mid-infrared wavelengths. The strip waveguides have been formed in 0.85 and 2 μm thick Ge grown on SOI substrate with 220 nm thick Si overlayer. The propagation loss for various waveguide widths has been measured using the Fabry-Perot method with temperature tuning. The minimum loss of ~8 dB/cm has been achieved for 0.85 μm thick Ge core using 3.682 μm laser excitation. The transparency of these waveguides has been measured up to at least 3.82 μm.

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Silicon-on-insulator is an attractive choice for developing mid-infrared photonic integrated circuits. It benefits from mature fabrication technologies and integration with on-chip electronics. We report the development of SOI channel and rib waveguides for mid-infrared wavelengths centered at 3.7 μm. Propagation loss of ∼1.44 dB/cm and ∼1.2 dB/cm has been measured for TE and TM polarizations in channel waveguides, respectively. Similarly, propagation loss of ∼1.39 dB/cm and ∼2.82 dB/cm has been measured for TE and TM polarized light in rib waveguides. The propagation loss is consistent with the measurements obtained using a different characterization setup and for the same waveguide structures on a different chip. Given the tightly confined single-mode in our 400 nm thick Si core, this propagation loss is among the lowest losses reported in literature. We also report the development of Ge-on-SOI strip waveguides for mid-infrared wavelengths centered at 3.7 μm. Minimum propagation loss of ∼8 dB/cm has been measured which commensurate with that required for high power midinfrared sensing. Ge-on-SOI waveguides provide an opportunity to realize monolithically integrated circuit with on-chip light source and photodetector.

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