David Duchesne

Low power four wave mixing in an integrated, micro-ring resonator with Q = 1.2 million

We demonstrate efficient, low power, continuous-wave four-wave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20 nm. We show theoretically that the characteristic low dispersion enables phase-matching over a tuning range > 160 nm.We demonstrate efficient, low power, continuous-wave fourwave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20nm. We show theoretically that the characteristic low dispersion enables phasematching over a bandwidth > 160nm.

Efficient self-phase modulation in low loss, high index doped silica glass integrated waveguides

We demonstrate efficient self phase modulation, as well as negligible nonlinear absorption, in low loss (<0.06 dB/cm), high index silica glass-based waveguides. Using approximately 1 ps pulses near 1560 nm we achieve a 1.5pi nonlinear phase shift in an integrated 45 cm long spiral waveguide with <60 W of peak input power, corresponding to a large nonlinearity (gamma) of 220 W(-1)km(-1). Further, we observe negligible nonlinear absorption for input intensities > 25 GW/cm(2). The high nonlinearity and low linear and nonlinear losses of these waveguides make them promising for nonlinear all-optical signal processing applications.

Self-locked optical parametric oscillation in a CMOS compatible microring resonator: A route to robust optical frequency comb generation on a chip

We report a novel geometry for OPOs based on nonlinear microcavity resonators. This approach relies on a self-locked scheme that enables OPO emission without the need for thermal locking of the pump laser to the microcavity resonance. By exploiting a CMOS-compatible microring resonator, we achieve oscillation with a complete absence of shutting down, or self-terminating behavior, a very common occurrence in externally pumped OPOs. Further, this scheme consistently produces very wide bandwidth (>300nm, limited by our experimental set-up) combs that oscillate at a spacing of the FSR of the micro cavity resonance.

Supercontinuum generation in a high index doped silica glass spiral waveguide

We demonstrate supercontinuum (SC) generation at both 1550 nm and 1288 nm in a compact (< 5mm(2)) 45 cm spiral waveguide composed of CMOS-compatible doped high-index glass. While both wavelengths have weak dispersion and are near zero dispersion points, they present different symmetries. At 1550 nm, the normal dispersion regime takes place at longer wavelengths, whereas at 1290 nm it is at shorter wavelengths, and we observe features in the SC spectra that clearly reflect this. In particular, the spectrum at 1550 nm is more than 300 nm wide (limited by detection) and is well reproduced by simulations based on the measured dispersion. This work represents a practical on-chip broadband wavelength source with potential use in many important applications.

Extremely high aspect ratio GaAs and GaAs/AlGaAs nanowaveguides fabricated using chlorine ICP etching with N2-promoted passivation

Semiconductor nanowaveguides are the key structure for light-guiding nanophotonics applications. Efficient guiding and confinement of single-mode light in these waveguides require high aspect ratio geometries. In these conditions, sidewall verticality becomes crucial. We fabricated such structures using a top-down process combining electron beam lithography and inductively coupled plasma (ICP) etching of hard masks and GaAs/AlGaAs semiconductors with Al concentrations varying from 0 to 100%. The GaAs/AlGaAs plasma etching was a single-step process using a Cl(2)/BCl(3)/Ar gas mixture with various fractions of N(2). Scanning electron microscope (SEM) observations showed that the presence of nitrogen generated the deposition of a passivation layer, which had a significant effect on sidewall slope. Near-ideal vertical sidewalls were obtained over a very narrow range of N(2), allowing the production of extremely high aspect ratios (>32) for 80 nm wide nanowaveguides.

High-efficiency second-harmonic generation in doubly-resonant χ (2) microring resonators

By directly simulating Maxwells equations via the finite-difference time-domain (FDTD) method, we numerically demonstrate the possibility of achieving high-efficiency second harmonic generation (SHG) in a structure consisting of a microscale doubly-resonant ring resonator side-coupled to two adjacent waveguides. We find that ≳ 94% conversion efficiency can be attained at telecom wavelengths, for incident powers in the milliwatts, and for reasonably large bandwidths (Q ∼ 1000s). We demonstrate that in this high efficiency regime, the system also exhibits limit-cycle or bistable behavior for light incident above a threshold power. Our numerical results agree to within a few percent with the predictions of a simple but rigorous coupled-mode theory framework.

Ultrafast all-optical temporal differentiators based on CMOS-compatible integrated-waveguide Bragg gratings

We report the first realization of integrated, all-optical first- and higher-order photonic differentiators operating at terahertz (THz) processing speeds. This is accomplished in a Silicon-on-Insulator (SOI) CMOS-compatible platform using a simple integrated geometry based on (π-)phase-shifted Bragg gratings. Moreover, we achieve on-chip generation of sub-picosecond Hermite-Gaussian pulse waveforms, which are noteworthy for applications in next-generation optical telecommunications.

Second harmonic generation in AlGaAs photonic wires using low power continuous wave light

We report modal phase matched (MPM) second harmonic generation (SHG) in high-index contrast AlGaAs sub-micron ridge waveguides, by way of sub-mW continuous wave powers at telecommunication wavelengths. We achieve an experimental normalized conversion efficiency of ~14%/W/cm2, obtained through a careful sub-wavelength design supporting both the phase matching requirement and a significant overlap efficiency. Furthermore, the weak anomalous dispersion, robust fabrication technology and possible geometrical and thermal tuning of the device functionality enable a fully integrated multi-functional chip for several critical areas in telecommunications, including wavelength (time) division multiplexing and quantum entanglement.

Picosecond linear optical pulse shapers based on integrated waveguide Bragg gratings

We demonstrate a general linear pulse-shaping technique based on integrated III-V Bragg gratings (BGs). Such a technique allows for the synthesizing of complex waveforms with picosecond resolution using a compact single-waveguide design. This approach is experimentally demonstrated by fabricating and testing a series of integrated ultrafast optical pulse shapers based on BG geometries acting as time-domain code generators operating at 500 Gbits/s.

Group-index birefringence and loss measurements in silicon-on-insulator photonic wire waveguides

Group-index birefringence in silicon-on-insulator photonic wire waveguides is determined through a polarization beating technique and a Fabry-Perot resonance method. A large group-index birefringence, up to 0.67, is obtained as a result of the structural asymmetry and high field confinement of our waveguides. The group index and linear propagation loss are also determined. In particular, the group index is found to be as large as 4.45 due to the significant change in the effective mode index of the waveguide as a function of the wavelength. The effects of structure size on the measured losses and group indices are analyzed. Our experimental results are in good agreement with our simulations, and the method employed is found to be effective in analyzing the linear properties of submicrometer optical waveguide structures.