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Full-Text Articles in Physics
Study Of The Effects Of Cavity Mode Spacing On Mode-Hopping In Iii–V/Si Hybrid Photonic Crystal Lasers, Praveen K.J. Singaravelu, Sharon M. Butler, Robert N. Sheehan, Alexandros A. Liles, Stephen P. Hegarty, Liam O'Faolain
Study Of The Effects Of Cavity Mode Spacing On Mode-Hopping In Iii–V/Si Hybrid Photonic Crystal Lasers, Praveen K.J. Singaravelu, Sharon M. Butler, Robert N. Sheehan, Alexandros A. Liles, Stephen P. Hegarty, Liam O'Faolain
Cappa Publications
We present a design methodology for hybrid lasers to realise mode-hop free operation by controlling the cavity mode spacing. In this study, a compact hybrid photonic crystal laser (H-PhCL) was employed which allowed a reduction of the Fabry–Perot length of the laser cavity and eliminated the need for an active mode stabilisation mechanism in order to realise mode-hop free operation. The H-PhCL was formed by butt-coupling a reflective semiconductor optical amplifier (RSOA) with a two-dimensional silicon (Si) photonic crystal (PhC) cavity. Continuous stable single frequency operation with >40 dB side-mode suppression ratio (SMSR) of the laser was achieved for gain …
Investigating The Use Of Ultraviolet Light Emitting Diodes (Uv-Leds) For The Inactivation Of Bacteria In Powdered Food Ingredients, Laura Nyhan, Milosz Przyjalgowski, Liam O'Faolain, Máire Begley, Michael Callanan
Investigating The Use Of Ultraviolet Light Emitting Diodes (Uv-Leds) For The Inactivation Of Bacteria In Powdered Food Ingredients, Laura Nyhan, Milosz Przyjalgowski, Liam O'Faolain, Máire Begley, Michael Callanan
Cappa Publications
The addition of contaminated powdered spices and seasonings to finished products which do not undergo further processing represents a significant concern for food manufacturers. To reduce the incidence of bacterial contamination, seasoning ingredients should be subjected to a decontamination process. Ultraviolet light emitting diodes (UV-LEDs) have been suggested as an alternative to UV lamps for reducing the microbial load of foods, due to their increasing efficiency, robustness and decreasing cost. In this study, we investigated the efficacy of UV-LED devices for the inactivation of four bacteria (Listeria monocytogenes, Escherichia coli, Bacillus subtilis and Salmonella Typhimurium) on a plastic surface and …
Excitable Interplay Between Lasing Quantum Dot States, Michael Dillane, I. Dubinkin, N. Fedorov, T. Erneux, David Goulding, B. Kelleher, E.A. Viktorov
Excitable Interplay Between Lasing Quantum Dot States, Michael Dillane, I. Dubinkin, N. Fedorov, T. Erneux, David Goulding, B. Kelleher, E.A. Viktorov
Cappa Publications
The optically injected semiconductor laser system has proven to be an excellent source of experimental nonlinear dynamics, particularly regarding the generation of excitable pulses. Typically for low-injection strengths, these pulses are the result of a small above-threshold perturbation of a stable steady state, the underlying physics is well described by the Adler phase equation, and each laser intensity pulse is accompanied by a 2π phase rotation. In this article, we show how, with a dual-state quantum dot laser, a variation of type I excitability is possible that cannot be described by the Adler model. The laser is operated so that …
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
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
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
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 …
Subwavelength Grating-Based Spiral Metalens For Tight Focusing Of Laser Light, Victor V. Kotlyar, Sergey S. Stafeev, Anton G. Nalimov, Liam O'Faolain
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 …
Thermally Stable Hybrid Cavity Laser Based On Silicon Nitride Gratings, Simone Iadanza, Andrei P. Bakoz, Praveen K. J. Singaravelu, Danilo Panettieri, Stefan Schulz, Ganga Chinna Rao Devarapu, Sylvain Guerber, Charles Baudot, Frédéric Boeuf, Stephen Hegarty, Liam O'Faolain
Thermally Stable Hybrid Cavity Laser Based On Silicon Nitride Gratings, Simone Iadanza, Andrei P. Bakoz, Praveen K. J. Singaravelu, Danilo Panettieri, Stefan Schulz, Ganga Chinna Rao Devarapu, Sylvain Guerber, Charles Baudot, Frédéric Boeuf, Stephen Hegarty, Liam O'Faolain
Cappa Publications
In this paper, we show the experimental results of a thermally stable Si3N4 external cavity (SiN EC) laser with high power output and the lowest SiN EC laser threshold to our knowledge. The device consists of a 250 μm sized reflective semiconductor optical amplifier butt-coupled to a passive chip based on a series of Si3N4 Bragg gratings acting as narrow reflectors. A threshold of 12 mA has been achieved, with a typical side-mode suppression ratio of 45 dB and measured power output higher than 3 mW. Furthermore, we achieved a mode-hop free-lasing regime in the range of 15–62 mA and …
Rotation Of Two-Petal Laser Beams In The Near Field Of A Spiral Microaxicon, S. S. Stafeev, Liam O'Faolain, M. V. Kotlyar
Rotation Of Two-Petal Laser Beams In The Near Field Of A Spiral Microaxicon, S. S. Stafeev, Liam O'Faolain, M. V. Kotlyar
Cappa Publications
Using a spiral microaxicon with the topological charge 2 and NA = 0.6 operating at a 532-nm wavelength and fabricated by electron-beam lithography, we experimentally demonstrate the rotation of a two-petal laser beam in the near field (several micrometers away from the axicon surface). The estimated rotation rate is 55 °/mm and linearly dependent on the on-axis distance, with the theoretical rotation rate being 53 °/mm. The experimentally measured rotation rate is found to be linear and coincident with the simulation results only on the on-axis segment from 1.5 to 3 mm. The experimentally measured rotation rate is 66 °/mm …
Tunable Optical Buffer Through An Analogue To Electro-Magnetically Induced Transparency In Coupled Photonic Crystal Cavities, Changyu Hu, Sebastian A. Schulz, Alexandros A. Liles, Liam O'Faolain
Tunable Optical Buffer Through An Analogue To Electro-Magnetically Induced Transparency In Coupled Photonic Crystal Cavities, Changyu Hu, Sebastian A. Schulz, Alexandros A. Liles, Liam O'Faolain
Cappa Publications
Tunable on-chip optical delay has long been a key target for the research community, as it is the enabling technology behind delay lines, signal re-timing and other applications vital to optical signal processing. To date the field has been limited by high optical losses associated with slow light or delay structures. Here, we present a novel tunable delay line, based on a coupled cavity system exhibiting an Electromagnetically Induced Transparency-like transmission spectrum, with record low loss, around 15dB/ns. By tuning a single cavity the delay of the complete structure can be tuned over 120ps, with the maximum delay approaching 300ps.
Bounded Phase Phenomena In The Optically Injected Laser, Bryan Kelleher, David Goulding, B. Baselga Pascual, Stephen P. Hegarty, Guillaume Huyet
Bounded Phase Phenomena In The Optically Injected Laser, Bryan Kelleher, David Goulding, B. Baselga Pascual, Stephen P. Hegarty, Guillaume Huyet
Cappa Publications
Two routes to phase-locking in the optically injected laser system are investigated both involving limit cycles where the phase of the slave laser is unlocked but is nevertheless bounded. We use an experimental phase-resolving technique to unambiguously demonstrate the phenomenon via explicit phasors for the slave laser electric field. Theoretical considerations show that for locking mechanisms involving Hopf bifurcations, such limit cycles of bounded phase are generic. For weakly damped devices, such as quantum well lasers, this can involve an excited resonance at the relaxation oscillation frequency. For highly damped devices there is no such excitation but the bounded phase …
Coulomb-Induced Emission Dynamics And Self-Consistent Calculations Of Type-Ii Sb-Containing Quantum Dot Systems, Kamil Gradkowski, Tomasz J. Ochalski, N. Pavarelli, H. Y. Liu, J. Tatebayashi, D. B. Williams, Guillaume Huyet, D. L. Huffaker
Coulomb-Induced Emission Dynamics And Self-Consistent Calculations Of Type-Ii Sb-Containing Quantum Dot Systems, Kamil Gradkowski, Tomasz J. Ochalski, N. Pavarelli, H. Y. Liu, J. Tatebayashi, D. B. Williams, Guillaume Huyet, D. L. Huffaker
Cappa Publications
This paper investigates the effects of Coulomb interactions on the emission dynamics of Sb-containing quantum dot (QD) systems under high excitation densities. Two different type-II confinements are studied: confined electrons with unconfined holes using InAs/GaAs QDs capped with a GaAsSb quantum well (type-IIa), and confined holes with unconfined electrons using GaSb/GaAs QDs capped with an InGaAs quantum well (type-IIb). Time-resolved photoluminescence experiments are compared with self-consistent numerical calculations using an 8-band k·p model. In both structures, we observe a significant blueshift of emission and wavelength-dependent radiative lifetimes, but with marked quantitative differences between the two systems: in the type-IIa, the …
Wettability And “Petal Effect” Of Gaas Native Oxides, A. Gocalinska, Kamil Gradkowski, V. Dimastrodonato, L. O. Mereni, G. Juska, Guillaume Huyet, E. Pelucchi
Wettability And “Petal Effect” Of Gaas Native Oxides, A. Gocalinska, Kamil Gradkowski, V. Dimastrodonato, L. O. Mereni, G. Juska, Guillaume Huyet, E. Pelucchi
Cappa Publications
We discuss unreported transitions of oxidised GaAs surfaces between (super)hydrophilic and hydrophobic states when stored in ambient conditions. Contact angles higher than 90° and high adhesive force were observed for several air-aged epitaxial samples grown under different conditions, as well as on epi-ready wafers. Regardless of the morphologies of the surface, superhydrophilicity of oxygen-plasma treated samples was observed, an effect disappearing with storage time. Reproducible hydrophobicity was likewise observed, as expected, after standard HCl surface etching. The relation between surface oxides and hydrophobic/hydrophilic behaviour is discussed.
Excitability In Optically Injected Semiconductor Lasers: Contrasting Quantum- Well- And Quantum-Dot-Based Devices, Bryan Kelleher, C. Bonatto, Guillaume Huyet, Stephen P. Hegarty
Excitability In Optically Injected Semiconductor Lasers: Contrasting Quantum- Well- And Quantum-Dot-Based Devices, Bryan Kelleher, C. Bonatto, Guillaume Huyet, Stephen P. Hegarty
Cappa Publications
Excitability is a generic prediction for an optically injected semiconductor laser. However, the details of the phenomenon differ depending on the type of device in question. For quantum-well lasers very complicated multipulse trajectories can be found, while for quantum-dot lasers the situation is much simpler. Experimental observations show the marked differences in the pulse shapes while theoretical considerations reveal the underlying mechanism responsible for the contrast, identifying the increased stability of quantum-dot lasers to perturbations as the root.