Sean J. Wagner

Experimental demonstration of a hybrid plasmonic transverse electric pass polarizer for a silicon-on-insulator platform

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.

Continuous wave second-harmonic generation using domain-disordered quasi-phase matching waveguides

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 μW were measured when on a Fabry-Perot 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.

Difference Frequency Generation by Quasi-Phase Matching in Periodically Intermixed Semiconductor Superlattice Waveguides

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 second-harmonic generation experiments for fundamental wavelengths between 1520 and 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.

Modeling and Optimization of Quasi-Phase Matching Via Domain-Disordering

Second-harmonic generation in a quasi-phase matched waveguide produced using a domain-disordered GaAs-AlAs superlattice is modeled including the effects of group velocity mismatch, nonlinear refraction, two-photon absorption, and linear loss. The model predicts our experimentally observed second-harmonic powers within an order of magnitude. Self-phase modulation and two-photon absorption led to reduced conversion efficiencies of up to 33% at input peak powers >50 W. Group velocity mismatch results in a reduction of 23% in conversion efficiency using estimated group velocities calculated from the measured effective refractive index. The modeling also shows that the conversion efficiency peaks at propagation lengths longer than the pulse walk off length and that duty cycle variations induced shifts in the tuning curves. Group velocity mismatch also increased the conversion bandwidth by ~ 30%. Incomplete modulation of chi(2) in disordered regions reduced the output conversion efficiency by up to two orders of magnitude. Grating-assisted phase matching led to a 7% efficiency drop for a Deltan of 0.045 at the second-harmonic and 0.01 at the fundamental. This model serves as a valuable tool to provide insight into the optimization of these devices.

Controlling Third-Order Nonlinearities by Ion-Implantation Quantum-Well Intermixing

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 0.5times1013 cm-2 and annealing temperature of 775degC. 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.

Type-II quasi phase matching in periodically intermixed semiconductor superlattice waveguides

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.

Optical frequency conversion in integrated devices

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 conversion by tunable difference-frequency generation over a bandwidth of more than 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.

Optical frequency conversion in integrated devices [Invited]

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 conversion by tunable difference-frequency generation over a bandwidth of more than 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.

Performance and Limitations of Quasi-Phase Matching Semiconductor Waveguides with Picosecond Pulses

Quasi-phase matched (QPM) second-order nonlinear optical processes in compound semiconductors are attractive for frequency conversion because of their large nonlinear susceptibilities and their mature fabrication processes that permit monolithic integration with pump lasers and other optical elements. Using quantum well intermixing (QWI), we have fabricated domain-disordered QPM (DD-QPM) waveguides in GaAs/AlGaAs superlattices and have previously demonstrated continuous-wave (CW) Type-I second-harmonic generation (SHG) and pulsed Type-II SHG. CW experiments were complicated by Fabry-Perot resonances and thermal bistability. Experiments using a 2-ps pulsed system were affected by third-order nonlinear effects, group-velocity mismatch (GVM), and poor spectral overlap with the conversion bandwidth. A better evaluation of the conversion efficiency may, however, be determined by using longer pulses in order to avoid these complications. By this, the effective CW conversion efficiency and χ(2) modulation can be ascertained. In this paper, we demonstrate SHG in DD-QPM waveguides with reduced parasitic effects by using 20 ps pulses. The waveguide structure consisted of a core layer of GaAs/Al0.85Ga0.15As superlattice into which QPM gratings with a period of 3.8 μm were formed using QWI by As2+ ion implantation. For a Type-I phase matching wavelength of 1583.4 nm, average second-harmonic (SH) powers produced were as high as 2.5 μW for 2 ps pulses and 3.5 μW for 20-ps pulses. At low input powers, the SHG average power conversion efficiency of the 2-ps system was more than 10 times larger than the 20 ps system. As power was increased, the SH power saturated and conversion efficiency decreased to nearly equal to the 20-ps system which remained consistent over the same power range. This is attributed to a reduction in third-order nonlinear effects, a smaller pulse spectral width that overlaps better with the conversion bandwidth, and less pulse walkoff for the 20-ps pulses. Thus, by using 20-ps pulses over 2-ps pulses, we achieved similar output SH powers and potentially higher SH powers are possible since there was no observed saturation at high input power.

Type-II quasi-phase-matched second-harmonic generation in domain-disordered semiconductor waveguides

Second-harmonic generation is demonstrated in periodically intermixed GaAs/AlGaAs superlattice waveguides by Type-II phase matching. Second-harmonic powers of 2.0 µW were generated at fundamental phase matching wavelength of 1577.4 nm.