James F. McMillan

Regenerative oscillation and four-wave mixing in graphene optoelectronics

We demonstrate the exceptionally-high third-order nonlinearity of integrated mono-layer graphene-silicon hybrid optoelectronics, enabling ultralow power resonant optical bistability, self-induced regenerative oscillations, and coherent four-wave mixing, all at few femto-joule cavity recirculating energies.

Observation of four-wave mixing in slow-light silicon photonic crystal waveguides

Four-wave mixing is observed in a silicon W1 photonic crystal waveguide. The dispersion dependence of the idler conversion efficiency is measured and shown to be enhanced at wavelengths exhibiting slow group velocities. A 12-dB increase in the conversion efficiency is observed. Concurrently, a decrease in the conversion bandwidth is observed due to the increase in group velocity dispersion in the slow-light regime. The experimentally observed conversion efficiencies agree with the numerically modeled results.

Demonstration of an Air-Slot Mode-Gap Confined Photonic Crystal Slab Nanocavity with Ultrasmall Mode Volumes

We demonstrate experimentally an air-slot mode-gap photonic crystal cavity with quality factor of 104 and modal volume of 0.02 cubic wavelengths, based on the design of an air-slot in a width-modulated line-defect in a photonic crystal slab. The origin of the high Q air-slot cavity mode is the mode-gap effect from the slotted PhCWG mode with negative dispersion. The high Q cavities with ultrasmall mode volume are important for applications such as cavity quantum electrodynamics, nonlinear optics, and optical sensing.

Temperature-Tuning of Near-Infrared Monodisperse Quantum Dot Solids at 1.5 µm for Controllable Förster Energy Transfer

We present the first time-resolved cryogenic observations of Forster energy transfer in large, monodisperse lead sulfide quantum dots with ground-state transitions near 1.5 microm (0.8 eV), in environments from 160 K to room temperature. The observed temperature-dependent dipole-dipole transfer rate occurs in the range of (30-50 ns) (-1), measured with our confocal single-photon counting setup at 1.5 microm wavelengths. By temperature-tuning the dots, 94% efficiency of resonant energy transfer can be achieved for donor dots. The resonant transfer rates match well with proposed theoretical models.

Observation of zeroth-order band gaps in negative-refraction photonic crystal superlattices at near-infrared frequencies.

We present the first observations of zero-n bandgaps in photonic crystal superlattices consisting of alternating stacks of negative index photonic crystals and positive index dielectric materials in the near-infrared. Guided by ab initio three-dimensional numerical simulations, the fabricated nanostructured superlattices demonstrate the presence of zero-order gaps in remarkable agreement with theoretical predictions across a range of different superlattice periods and unit cell variations. These volume-averaged zero-index superlattice structures present a new type of photonic band gap, with potential for complete wavefront control for arbitrary phase delay lines and open cavity resonances.

Theoretical Analysis of Pulse Dynamics in Silicon Photonic Crystal Wire Waveguides

In this paper, we present a comprehensive theoretical description of the propagation of optical pulses in 1-D waveguides consisting of a line defect in a photonic crystal (PhC) slab waveguide made of silicon. We incorporate in our analysis linear optical effects, such as group-velocity dispersion and optical losses, as well as nonlinear effects induced by the Kerr nonlinearity of the PhC. We also include in our model the free-carrier (FC) dispersion and FC-induced optical losses, and thus study the influence of FCs generated through two-photon absorption on the pulse dynamics. Our analysis reveals that important quantities, such as the pulse group velocity, dispersion coefficients, or the waveguide nonlinear coefficient are strongly affected by the periodic nature of the guiding structure. Finally, we demonstrate that both linear and nonlinear effects are stronger in the case of slow-light modes, with the nonlinear effects being enhanced more as compared to the linear ones.

Observation of spontaneous Raman scattering in silicon slow-light photonic crystal waveguides

We report on the observation of spontaneous Raman scattering in silicon photonic crystal waveguides. Continuous-wave measurements of both forward scattered and backscattered Stokes emissions are reported in single line-defect waveguides in hexagonal lattice photonic crystal silicon membranes. By utilizing the Bragg gap edge dispersion of the TM-like mode for pump enhancement and the TE-like fundamental mode onset for Stokes enhancement, the spontaneous Raman scattering coefficient was observed to increase by up to six times in the region of slow group velocity. The results show explicit nonlinear enhancement in a silicon photonic crystal slow-light waveguide device.

Enhanced four-wave mixing in graphene-silicon slow-light photonic crystal waveguides

We demonstrate the enhanced four-wave mixing of monolayer graphene on slow-light silicon photonic crystal waveguides. 200-μm interaction length, a four-wave mixing conversion efficiency of −23 dB is achieved in the graphene-silicon slow-light hybrid, with an enhanced 3-dB conversion bandwidth of about 17 nm. Our measurements match well with nonlinear coupled-mode theory simulations based on the measured waveguide dispersion, and provide an effective way for all-optical signal processing in chip-scale integrated optics.

Photon transport enhanced by transverse Anderson localization in disordered superlattices

Photonic-crystal waveguides can control light propagation on subwavelength scales, but structural disorder typically causes scattering and broadening. It is now shown that disorder can enhance light collimation beyond conventional limits.

Selective tuning of high-Q silicon photonic crystal nanocavities via laser-assisted local oxidation

We examine the cavity resonance tuning of high-Q silicon photonic crystal heterostructures by localized laser-assisted thermal oxidation using a 532 nm continuous wave laser focused to a 2.5 μm radius spot-size. The total shift is consistent with the parabolic rate law. A tuning range of up to 8.7 nm is achieved with ∼ 30 mW laser powers. Over this tuning range, the cavity Qs decreases from 3.2×10(5) to 1.2×10(5). Numerical simulations model the temperature distributions in the silicon photonic crystal membrane and the cavity resonance shift from oxidation.