Christopher G. Poulton

Nonlinear silicon-on-insulator waveguides for all-optical signal processing

Values up to gamma=7 x 10(6)/(W km) for the nonlinear parameter are feasible if silicon-on-insulator based strip and slot waveguides are properly designed. This is more than three orders of magnitude larger than for state-of-the-art highly nonlinear fibers, and it enables ultrafast all-optical signal processing with nonresonant compact devices. At lambda=1.55 microm we provide universal design curves for strip and slot waveguides which are covered with different linear and nonlinear materials, and we calculate the resulting maximum gamma.

Waveguiding and plasmon resonances in two-dimensional photonic lattices of gold and silver nanowires

We report the fabrication of triangular lattices of parallel gold and silver nanowires of high optical quality, with diameters down to

Inducing and harnessing stimulated Brillouin scattering in photonic integrated circuits

500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

Models for guidance in kagome-structured hollow-core photonic crystal fibres

and length-to-diameter ratios as high as 100 000. The nanowires are supported by a silica glass matrix and are disposed around a central solid glass core, i.e., a missing nanowire. These centimeter-long structures make it possible to trap light within an array of nanowires and characterize the plasmon resonances that form at specific optical frequencies. Such nanowire arrays have many potential applications, e.g., imaging on the subwavelength scale.

Modal analysis of enhanced absorption in silicon nanowire arrays

We review recent progress in inducing and harnessing stimulated Brillouin scattering (SBS) in integrated photonic circuits. Exciting SBS in a chip-scale device is challenging due to the stringent requirements on materials and device geometry. We discuss these requirements, which include material parameters, such as optical refractive index and acoustic velocity, and device properties, such as acousto-optic confinement. Recent work on SBS in nano-photonic waveguides and micro-resonators is presented, with special attention paid to photonic integration of applications such as narrow-linewidth lasers, slow- and fast-light, microwave signal processing, Brillouin dynamic gratings, and nonreciprocal devices.

Photonic chip based tunable and reconfigurable narrowband microwave photonic filter using stimulated Brillouin scattering

We demonstrate by numerical simulation that the general features of the loss spectrum of photonic crystal fibres (PCF) with a kagome structure can be explained by simple models consisting of thin concentric hexagons or rings of glass in air. These easily analysed models provide increased understanding of the mechanism of guidance in kagome PCF, and suggest ways in which the high-loss resonances in the loss spectrum may be shifted.

Radiation Modes and Roughness Loss in High Index-Contrast Waveguides

We analyze the absorption of solar radiation by silicon nanowire arrays, which are being considered for photovoltaic applications. These structures have been shown to have enhanced absorption compared with thin films, however the mechanism responsible for this is not understood. Using a new, semi-analytic model, we show that the enhanced absorption can be attributed to a few modes of the array, which couple well to incident light, overlap well with the nanowires, and exhibit strong Fabry-Pérot resonances. For some wavelengths the absorption is further enhanced by slow light effects. We study the evolution of these modes with wavelength to explain the various features of the absorption spectra, focusing first on a dilute array at normal incidence, before generalizing to a dense array and off-normal angles of incidence. The understanding developed will allow for optimization of simple SiNW arrays, as well as the development of more advanced designs.

Eigenvalue problems for doubly periodic elastic structures and phononic band gaps

We report the first demonstration of a photonic chip based dynamically reconfigurable, widely tunable, narrow pass-band, high Q microwave photonic filter (MPF). We exploit stimulated Brillouin scattering (SBS) in a 6.5 cm long chalcogenide (As2S3) photonic chip to demonstrate a MPF that exhibited a high quality factor of ~520 and narrow bandwidth and was dynamically reconfigurable and widely tunable. It maintained a stable 3 dB bandwidth of 23 ± 2MHz and amplitude of 20 ± 2 dB over a large frequency tuning range of 2-12 GHz. By tailoring the pump spectrum, we reconfigured the 3 dB bandwidth of the MPF from ~20 MHz to ~40 MHz and tuned the shape factor from 3.5 to 2 resulting in a nearly flat-topped filter profile. This demonstration represents a significant advance in integrated microwave photonics with potential applications in on-chip microwave signal processing for RADAR and analogue communications.

Design for broadband on-chip isolator using stimulated Brillouin scattering in dispersion-engineered chalcogenide waveguides

We predict the scattering loss in rectangular high index-contrast waveguides, using a new variation of the classical approach of coupled-mode theory. The loss predicted by this three-dimensional (3-D) model is considerably larger than that calculated using previous treatments that approximate the true 3-D radiation modes with their two-dimensional counterparts. The 3-D radiation modes of the ideal waveguide are expanded in a series of cylindrical harmonics, and the coupling between the guided and radiation modes due to the sidewall perturbation is computed. The waveguide attenuation can then be calculated semianalytically. It is found that the dominant loss mechanism is radiation rather than reflection, and that the transverse electric polarization exhibits much larger attenuation than transverse magnetic polarization. The method also gives simple rules that can be used in the design of low-loss optical waveguides. The structural properties of sidewall roughness of an InGaAs/InP pedestal waveguide are measured using atomic force microscopy, and the measured attenuation is found to compare well with that predicted by the model

Temporal Dynamics of the Alpha Factor in Semiconductor Optical Amplifiers

We consider the problem of elastic waves propagating in a two–dimensional array of circular cavities, taking rigorous account of coupling between shear and dilational waves. A technique, originally due to Rayleigh, is derived that involves an elegant identity between the singular and non–singular components of the stress fields in the array. This leads to an infinite linear system which can be truncated and solved in order to determine the complete structure of the propagating modes. Of particular interest is the possibility of exhibiting phononic band gaps, i.e. domains of frequency for which all propagating vibration in the material is suppressed.