Physics Commons^™

Monolayer Doping Of Silicon-Germanium Alloys: A Balancing Act Between Phosphorus Incorporation And Strain Relaxation, Noel Kennedy, Ray Duffy, Gioele Mirabelli, Luke Eaton, Nikolay Petkov, Justin D. Holmes, Chris Hatem, Lee Walsh, Brenda Long

Cappa Publications

This paper presents the application of monolayer doping (MLD) to silicon-germanium (SiGe). This study was carried out for phosphorus dopants on wafers of epitaxially grown thin films of strained SiGe on silicon with varying concentrations of Ge (18%, 30%, and 60%). The challenge presented here is achieving dopant incorporation while minimizing strain relaxation. The impact of high temperature annealing on the formation of defects due to strain relaxation of these layers was qualitatively monitored by cross-sectional transmission electron microscopy and atomic force microscopy prior to choosing an anneal temperature for the MLD drive-in. Though the bulk SiGe wafers provided are …

Slow Light With Interleaved P-N Junction To Enhance Performance Of Integrated Mach-Zehnder Silicon Modulators, Marco Passoni, Dario Gerace, Liam O'Faolain, Lucio Claudio Andreani

Cappa Publications

Slow light is a very important concept in nanophotonics, especially in the context of photonic crystals. In this work, we apply our previous design of band-edge slow light in silicon waveguide gratings [M. Passoni et al, Opt. Express 26, 8470 (2018)] to Mach-Zehnder modulators based on the plasma dispersion effect. The key idea is to employ an interleaved p-n junction with the same periodicity as the grating, in order to achieve optimal matching between the electromagnetic field profile and the depletion regions of the p-n junction. The resulting modulation efficiency is strongly improved as compared to common modulators based on …

Single Metalens For Generating Polarization And Phase Singularities Leading To A Reverse Flow Of Energy, Victor V. Kotlyar, Anton G. Nalimov, Sergey S. Stafeev, Liam O'Faolain

Cappa Publications

Using Jones matrices and vectors, we show that a metasurface-based optical element composed of a set of subwavelength diffraction gratings, whose anisotropic transmittance is described by a matrix of polarization rotation by angle m, where is the polar angle, generate an mth order azimuthally or radially polarized beam, when illuminated by linearly polarized light, or an optical vortex with topological charge m, when illuminated by circularly polarized light. Such a converter performs a spin–orbit transformation, acting similarly to a liquid-crystal half-wave plate. Using the FDTD-aided numerical simulation, we show that uniform linearly or circularly polarized light passing through the …

Frequency Modulated Hybrid Photonic Crystal Laser By Thermal Tuning, Sharon M. Butler, Andrei P. Bakoz, Praveen K.J. Singaravelu, A. A. Liles, Ben O’Shaughnessy, E. A. Viktorov, Liam O'Faolain, Stephen P. Hegarty

Cappa Publications

We demonstrate frequency modulation (FM) in an external cavity (EC) III-V/silicon laser, comprising a reflective semiconductor optical amplifier (RSOA) and a silicon nitride (SiN) waveguide vertically coupled to a 2D silicon photonic crystal (PhC) cavity. The PhC cavity acts as a tunable narrowband reflector giving wavelength selectivity. The FM was achieved by thermo-optical modulation of the reflector via a p-n junction. Single-mode operation was ensured by the short cavity length, overlapping only one longitudinal laser mode with the reflector. We investigate the effect of reflector modulation theoretically and experimentally and predict a substantial tracking of the resonator by the laser …

Subwavelength Grating-Based Spiral Metalens For Tight Focusing Of Laser Light, Victor V. Kotlyar, Sergey S. Stafeev, Anton G. Nalimov, Liam O'Faolain

Cappa Publications

In this paper, we investigate a 16-sector spiral metalens fabricated on a thin film (130 nm) of amorphous silicon, consisting of a set of subwavelength binary diffractive gratings and with a numerical aperture that is close to unity. The metalens converts linearly polarized incident light into an azimuthally polarized optical vortex and focuses it at a distance approximately equal to the wavelength of the incident light, k ¼ 633 nm. Using a scanning near-field optical microscope, it is shown experimentally that the metalens forms an elliptical focal spot with diameters smaller than the diffraction limit: FWHMx ¼ 0.32k (60.03k) and …

Development Of Uv Led Based Lamps With Modular Optical Heads, Ciara O'Hara

Theses

This project was centred around the development of the optical components, and the optimisation of the optical performance, of ProPhotonix Ltd’s Cobra Cure FX series of products. These are high irradiance, high dose, UVA (primarily 395 nm and 365 nm) Light Emitting Diode (LED) lamps designed for curing applications. An initial prototype developed by ProPhotonix, the smallest in the series, the FX1, underwent significant redesign throughout the project, and the two larger lamps, the FX2 and the FX3 were developed during the course of the project. This work primarily consisted in characterising, accurately modelling, and thereby refining, the optical reflector …

Dynamics Of Swept Source Lasers, Ben O'Shaughnessy

Theses

The aim of this thesis is to investigate the dynamics of two kinds of swept source lasers for optical coherence tomography. A mathematical model consisting of a pair of coupled delay differential equations was adapted to study Fourier Domain Mode-Locked (FDML) lasers and short cavity swept source lasers, and to explain experimental observations of these lasers.

The short cavity laser is experimentally observed to produce pulses during the frequency sweep. This ‘sliding frequency mode-locking’ behaviour is reproduced by simulation, which is then used to establish simple relationships between the key parameters of sweep speed, linewidth and output power.

The FDML …