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We present a compact, fibre-coupled single photon source using gradient-index (GRIN) lenses and an InAsP semiconductor quantum dot embedded within an InP photonic nanowire waveguide. A GRIN lens assembly is used to collect photons close to the tip of the nanowire, coupling the light immediately into a single mode optical fibre. The system provides a stable, high brightness source of fibre-coupled single photons. Using pulsed excitation, we demonstrate on-demand operation with a single photon purity of 98.5% when exciting at saturation in a device with a source-fibre collection efficiency of 35% and an overall single photon collection efficiency of 10%. We also demonstrate “plug and play” operation using room temperature photoluminescence from the InP nanowire for room temperature alignment.

Among quantum devices based on 2D materials, gate-defined quantum confined 1D channels are much less explored, especially in the high mobility regime where many body interactions play an important role. We present results of measurements and theory of conductance quantization in a gate-defined one dimensional channel in a single layer of transition metal dichalcogenide material WSe2. In the quasi-ballistic regime of our high mobility sample, we report conductance quantization steps in units of e2/h for a wide range of carrier concentrations. Magnetic field measurements show that as the field is raised higher conductance plateaus move to accurate quantized values and then shift to lower conductance values while the e2/h plateau remains locked. Based on microscopic atomistic tight-binding theory, we show that in this material, valley and spin degeneracies result in 2 e2/h conductance steps for non-interacting holes, suggesting that symmetry breaking mechanisms such as valley polarization dominate the transport properties of such quantum structures.

We report on a platform for the production of single photon devices with a fabrication yield of 100%. The sources are based on InAsP quantum dots embedded within position-controlled bottom-up InP nanowires. Using optimized growth conditions, we produce large arrays of structures having highly uniform geometries. Collection efficiencies are as high as 83% and multiphoton emission probabilities as low as 0.6% with the distribution away from optimal values associated with the excitation of other charge complexes and re-excitation processes, respectively, inherent to the above-band excitation employed. Importantly, emission peak lineshapes have Lorentzian profiles indicating that linewidths are not limited by inhomogeneous broadening but rather pure dephasing, likely elastic carrier-phonon scattering due to a high phonon occupation. This work establishes nanowire-based devices as a viable route for the scalable fabrication of efficient single photon sources and provides a valuable resource for hybrid on-chip platforms currently being developed., Comment: 9 pages, 5 figures

Photonics-based quantum information technologies require efficient, high emission rate sources of single photons. Position-controlled quantum dots embedded within a broadband nanowire waveguide provide a fully scalable route to fabricating highly efficient single-photon sources. However, emission rates for single-photon devices are limited by radiative recombination lifetimes. Here, we demonstrate a multiplexed single-photon source based on a multidot nanowire. Using epitaxially grown nanowires, we incorporate multiple energy-tuned dots, each optimally positioned within the nanowire waveguide, providing single photons with high efficiency. This linear scaling of the single-photon emission rate with number of emitters is demonstrated using a five-dot nanowire with an average multiphoton emission probability of

Exoplanetary biosignatures, molecular compounds which indicate a likelihood of extraterrestrial life, can be detected by highly sensitive spectroscopy of starlight which passes through the atmospheres of exoplanets towards the Earth. Such sensitive measurements can only be accomplished with the next generation of telescopes, leading to a corresponding increase in cost and complexity spectrometers. Integrated astrophotonic instruments are well-suited to address these challenges through their low-cost fabrication and compact geometries. We propose and characterize an integrated photonic gas sensor which detects the correlation between the near-infrared quasi-periodic vibronic absorption line spectrum of a gas and a silicon waveguide ring resonator transmittance comb. This technique enables lock-in amplification detection for real-time detection of faint biosignatures for reduced observation timescales and rapid exoplanetary atmosphere surveys using highly compact instrumentation.

Absorption spectroscopy is widely used in sensing and astronomy to understand molecular compositions on microscopic to cosmological scales. However, typical dispersive spectroscopic techniques require multichannel detection, fundamentally limiting the ability to detect extremely weak signals when compared to direct photometric methods. We report the realization of direct spectral molecular detection using a silicon nanophotonic waveguide resonator, obviating dispersive spectral acquisition. We use a thermally tunable silicon ring resonator with a transmission spectrum matched and cross-correlated to the quasi-periodic vibronic absorption lines of hydrogen cyanide. We show that the correlation peak amplitude is proportional to the number of overlapping ring resonances and gas lines, and that molecular specificity is obtained from the phase of the correlation signal in a single detection channel. Our results demonstrate on-chip correlation spectroscopy that is less restricted by the signal-to-noise penalty of other spectroscopic approaches, enabling the detection of faint spectral signatures.

We present an integrated photonic correlation filter for the detection of remote HCN gas. We demonstrate sensing of absorption due to HCN using thermo-optic tuning of the drop port transmission spectrum in a silicon waveguide ring resonator., 2020 IEEE Photonics Conference (IPC), September 28 - October 1, 2020, Vancouver, BC, Canada

Subwavelength engineered metamaterial waveguides and devices are considered as fundamental building blocks for the next generation of integrated photonic circuits. Here we present an overview of recent advances in this surging field.

We present the design of integrated astrophotonic instruments for high background atmospheric gas detection. Such instruments can be fibre-coupled to long focal length space telescopes as compact, flexure-free, instruments., Conference on Lasers and Electro-Optics/Pacific Rim 2020, August 3-5, 2020, Sydney Australia

Subwavelength metamaterial structures in silicon waveguides open new degrees of freedom to control on-chip light propagation. They have been applied to many silicon photonic devices such as fiber-chip couplers, waveguide crossings, microspectrometers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators and colorless interference couplers [1]. Here we report a demonstration of a metamaterial coupler and an InAs-on-InP quantum dash buried heterostructure laser optimized for mutual integration by direct facet-to-facet coupling with -1.2 dB coupling efficiency, coupled laser relative intensity noise (RIN) of -150 dB/Hz and 152 kHz linewidth. We further demonstrate the design of multi-line spectral notch filters based on narrow linewidth metamaterial Bragg filters synthesized using the layer-peeling method., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, ON, Canada

Absorption spectroscopy is a powerful technique for characterizing remote gas composition where direct interaction with a target it not possible. While dispersive spectroscopy is typically used to acquire a spectrum with which the gas presence is determined, correlation spectroscopy can directly detect such spectral features in a single detection channel. Here we present a novel integrated photonics correlation technique on an integrated photonic platform which uses real-time spectral processing to generate a multiline gas specific detection signal., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, ON, Canada

In this work, the authors evaluated the access resistance of InP high electron mobility transistors (HEMTs) and their degradation during wafer processing. The transfer resistance, which was rarely separated from other components of the total access resistance of InP HEMTs in the literature, was found to be the dominant component of the access resistance. It was also found that the transfer resistance degraded during wafer processing. The selection of the ohmic metal stack and its impact on both the metal-cap contact resistance and the transfer resistance was also investigated. The observations in their experiments and relevant discussions in the report are expected to be useful in the identification of improvement opportunities in both material growth and wafer fabrication of InP HEMTs.

A compact, single-pass and low-power-consumption methane sensing system is presented and its sensitivity is investigated for a set of reference cells with pressures of 7.4, 74 and 740 Torr and the same methane concentration of 1351 ppm. A single-mode GaSb-based continuous-wave (CW) distributed feedback (DFB) tunable diode laser at 3270 nm and wavelength modulation spectroscopy were employed to collect 2f spectra in the ν₃,R₃ band of ¹²CH₄. A modulated Voigt line profile model was used to fit the collected 2f spectra. The best detectivity of 4 ppbm is obtained for the highest pressure cell using an Allan-Werle variance analysis., Quantum Sensing and Nano Electronics and Photonics XVII, February 1-6, 2020, San Francisco, US, Series: Proceedings of SPIE

An InAs-on-InP quantum dash buried heterostructure laser and silicon chip optimized for mutual integration by direct facet-to-facet coupling have achieved -1.2 dB coupling efficiency, with coupled laser RIN of -150 dB/Hz and 152 kHz linewidth., 2020 22nd International Conference on Transparent Optical Networks (ICTON), July 19-23, 2020, Bari, Italy

An accurate model for the silicon refractive index including its temperature and wavelength dependence is critically important for many disciplines of science and technology. Currently, such a model for temperatures above 22°C in the optical communication bands is not available. The temperature dependence in the spectral response of integrated echelle grating filters made in silicon-on-insulator is solely determined by the optical properties of the slab waveguide, making it largely immune to dimensional uncertainties. This feature renders the echelle filters a reliable tool to evaluate the thermo-optic properties of silicon. Here we investigate the temperature dependence of silicon echelle filters for the wavelength range of both O and C bands, measured between 22°C to 80°C. We show that if a constant thermo-optic coefficient of silicon is assumed for each band, as is common in the literature, the predictions show an underestimate of up to 10% in the temperature-induced channel wavelength shift. We propose and assess a model of silicon refractive index that encompasses both the wavelength and temperature dependence of its thermo-optic coefficients. We start from literature data for bulk silicon and further refine the model using the echelle filter measurement results. This model is validated through accurate predictions of device channel wavelengths and their temperature dependence, including the quadratic term, over a wide wavelength and temperature range. This work also demonstrates a new high-precision method for characterizing the optical properties of a variety of materials.

Metamaterial engineered waveguide structures are emerging as fundamental building blocks for integrated photonics. Here we present an overview of our recent advances in this field, including fiber-chip couplers, ultra-broadband beam splitters, nanophotonic waveguides with engineered anisotropy and integrated Bragg filters., 2019 IEEE Photonics Conference (IPC), September 29 - October 3, 2019, San Antonio, TX, USA

Astronomical instrumentation is traditionally costly, large, and alignment-sensitive owing to the use of bulk optics. The use of integrated photonic devices in astronomical instrumentation can mitigate such drawbacks in certain applications where high light throughput and spectral bandwidth are less crucial. In this work, we present an ultra-compact carbon dioxide detection scheme using a single silicon waveguide ring resonator. The comb-like absorption line spectrum of CO2 around 1580 nm wavelength can closely match the comb spectrum of an appropriately designed ring resonator. By actively correlating such a ring spectrum with the CO2 absorption lines, a specific detection signal can be generated. We design the free spectral range of a ring resonator to match the absorption line spacing of carbon dioxide lines in the range from 1575 to 1585 nm. Using thermo-optic modulation, the ring resonator drop or through port transmission spectrum can be shifted back and forth across the incoming CO2 light spectrum, resulting in a modulated signal with an amplitude proportional to the CO2 absorption line strength. Furthermore, high frequency modulation and lock-in detection can result in a significant improvement in the signal to noise ratio. We demonstrate that such a device can provide real-time carbon dioxide detection for applications in ground- and satellite-based astronomy, as well as remote atmospheric sensing, in a compact package. In future work, such a sensor can be adapted to a range of gases and used to determine radial velocities and compositional maps of astronomical objects.

We report on the design of an ultra-compact integrated wavelength demultiplexer in echelle configuration for the optical O-band realized on silicon-on-insulator technology. The device has four channels with channel spacing of 800 GHz and a small footprint of 260 &times, 83 &mu, m2. Channel crosstalk lower than &minus, 28 dB across the four channels is experimentally demonstrated along with insertion losses of &minus, 1.5 dB.

We present a correlation spectrometer using a silicon waveguide ring resonator for the identification of molecules in stellar and planetary atmospheres. We tailor the free spectral range of a ring resonator to the vibronic overtones of carbon dioxide in the near infrared. The ring resonator spectrum is modulated via the thermo-optic effect and produces a detection signal unique to carbon dioxide. This spectrometer can be used for real-time remote gas detection and radial velocities of exoplanets in a narrow spectral band., 2019 Photonics North (PN), May 21-23, 2019, Quebec City, QC, Canada

We report on the site-selected growth of bright single InAsP quantum dots embedded within InP photonic nanowire waveguides emitting at telecom wavelengths. We demonstrate a dramatic dependence of the emission rate on both the emission wavelength and the nanowire diameter. With an appropriately designed waveguide, tailored to the emission wavelength of the dot, an increase in the count rate by nearly 2 orders of magnitude (0.4 to 35 kcps) is obtained for quantum dots emitting in the telecom O-band, showing high single-photon purity with multiphoton emission probabilities down to 2%. Using emission-wavelength-optimized waveguides, we demonstrate bright, narrow-line-width emission from single InAsP quantum dots with an unprecedented tuning range of 880 to 1550 nm. These results pave the way toward efficient single-photon sources at telecom wavelengths using deterministically grown InAsP/InP nanowire quantum dots.

Subwavelength grating (metamaterial) waveguide devices are becoming established as key building blocks for advanced integrated photonic circuits. In this talk we will present an overview of our recent advances in this surging field.

We demonstrate an in-situ technique to tune the emission energy of semiconductor quantum dots. The technique is based on laser-induced atomic intermixing applied to nanowire quantum dots grown using a site-selective process that allows for the deterministic tuning of individual emitters. A tuning range of up to 15 meV is obtained with a precision limited by the laser exposure time. A distinct saturation of the energy shift is observed, which suggests an intermixing mechanism relying on grown-in defects that are subsequently removed from the semiconductor material during annealing. The ability to tune different emitters into resonance with each other will be required for fabricating remote quantum dot-based sources of indistinguishable photons for secure quantum networks.

We present a quantum optics theory, numerical calculations, and experiments on coupled quantumdots in semiconductor nanowire waveguides. We first present an analytical Green function theory tocompute the emitted spectra of two coupled quantum dots, treated as point dipoles, fully accountingfor retardation effects, and demonstrate the signatures of coherent and incoherent coupling througha pronounced splitting of the uncoupled quantum dot resonances and modified spectral broadening.In the weak excitation regime, the classical Green functions used in models are verified and justifiedthrough full 3D solutions of Maxwell equations for nanowire waveguides, specifically using finite-difference time-domain techniques, showing how both waveguide modes and near-field evanescentmode coupling is important. The theory exploits an ensemble-based quantum description, and andan intuitive eigenmode-expansion based Maxwell theory. We then demonstrate how the molecularresonances (in the presence of coupling) take on the form of bright and dark (or quasi-dark) reso-nances, and study how these depend on the excitation and detection conditions. To go beyond theweak excitation regime, we also introduce a quantum master equation approach to model the non-linear spectra from an increasing incoherent pump field, which shows the role of the pump field onthe oscillator strengths and broadening of the molecular resonances, with and without pure dephas-ing. Next, we present experimental photoluminescence spectra for spatially-separated quantum dotmolecules (InAsP) in InP nanowires, which show clear signatures of pronounced splittings, thoughthey also highlight additional mechanisms that are not accounted for in the dipole-dipole couplingmodel. Two different approaches are taken to control the spatial separation of the quantum dotmolecules, and we discuss the advantages and disadvantages of each., Comment: 20 pages, 16 figures

Few data are available on population-based access to specialised trauma care and its influence on patient outcomes in an integrated trauma system. We aimed to evaluate the influence of access to an integrate trauma system on in-hospital mortality and length of stay (LOS).All adults admitted to acute care hospitals for major trauma [International Classification of Diseases Injury Severity Score (ICISS0.85)] in a Canadian province with an integrated trauma system between 2006 and 2011 were included using an administrative hospital discharge database. The influence of access to an integrated trauma system on in-hospital mortality and LOS was assessed globally and for critically injured patients (ICISS0.75), according to the type of injury [traumatic brain injury (TBI), abdominal/thoracic, spine, orthopaedic] using logistic and linear multivariable regression models.We identified 22,749 injury admissions. In-hospital mortality was 7% and median LOS was 9 days for all injuries. Overall, 92% of patients were treated within the trauma system. Globally, patients who did not have access had similar mortality and LOS compared to patients who had access. However, we observed a 62% reduction in mortality for critical abdominal/thoracic injuries (odds ratio=0.38; 95% CI, 0.16-0.92) and an 8% increase in LOS for TBI patients (geometric mean ratio=1.08; 95% CI, 1.02-1.14) treated within the trauma system.Results provides evidence that in a health system with an integrated mature trauma system, access to specialised trauma care is high and the small proportion of patients treated outside the system, have similar mortality and LOS compared to patients treated within the system. This study suggests that the Québec trauma system performs well in its mandate to offer appropriate treatment to victims of injury that require specialised care.

Access to specialised trauma care is an important measure of trauma system efficiency. However, few data are available on access to integrated trauma systems. We aimed to describe access to trauma centres (TCs) in an integrated Canadian trauma system and identify its determinants.We conducted a population-based cohort study including all injured adults admitted to acute care hospitals in the province of Québec between 2006 and 2011. Proportions of injured patients transported directly or transferred to TCs were assessed. Determinants of access were identified through a modified Poisson regression model and a relative importance analysis was used to determine the contribution of each independent variable to predicting access.Of the 135,653 injury admissions selected, 75% were treated within the trauma system. Among 25,522 patients with major injuries [International Classification of diseases Injury Severity Score (ICISS0.85)], 90% had access to TCs. Access was higher for patients aged under 65, men and among patients living in more remote areas (p-value0.001). The region of residence followed by injury mechanism, number of trauma diagnoses, injury severity and age were the most important determinants of access to trauma care.In an integrated, mature trauma system, we observed high access to TCs. However, problems in access were observed for the elderly, women and in urban areas where there are many non-designated hospitals. Access to trauma care should be monitored as part of quality of care improvement activities and pre-hospital guidelines for trauma patients should be applied uniformly throughout the province.

Le Québec offre un potentiel considérable pour le développement de l’industrie éolienne. Cette industrie peut être à l’origine de mortalités chez les rapaces et pourrait affecter certaines espèces vulnérables comme le faucon pèlerin. De 2008 à 2010, nous avons comparé l’utilisation de 5 types de milieux par 10 femelles nicheuses de faucon pèlerin dans le Québec méridional, afin de déterminer ceux à favoriser pour l’implantation de parcs éoliens. Les milieux les moins utilisés par les femelles étaient ceux considérés comme diminuant les risques de collision avec les éoliennes. Après l’envol des fauconneaux, les femelles parcouraient de plus grandes distances que lorsque les fauconneaux étaient confinés au nid. À cette période, 90 % des localisations télémétriques dans les cultures de maïs et de soya ont été enregistrées à l’intérieur d’un rayon de 8,3 km d’un nid, comparativement à un rayon de 15,9 km dans les autres cultures. Aussi, les femelles avaient moins de chances d’utiliser les cultures de maïs et de soya que les autres cultures et les milieux non propices pour la chasse. Nos résultats permettent de faire des recommandations quant à la localisation de projets éoliens, en termes de milieux à favoriser et de distances à respecter, afin de minimiser les risques de collision du faucon pèlerin., The province of Québec has considerable potential for the continued expansion of its wind power industry. Wind farms may be a cause of mortality for birds of prey and could have a particularly negative affect on certain vulnerable species, such as the peregrine falcon. To help determine the types of sites to favour for the establishment of new wind farms, we compared the use of 5 environments by 10 female peregrine falcons nesting in southern Québec during the period from 2008 to 2010. To minimize potential collision risks with wind turbines, the environments least used by females peregrine falcons should be preferentially chosen for locating wind farms. Once the young had fledged, females traveled farther afield than when the chicks were flightless. During this period, 90 % of the telemetry locations in corn and soybean fields were recorded within an 8.3-km radius of the nest, compared to a 15.9-km radius for other crops. Also, females were less likely to use corn and soybean fields, than other crops and environments that were not suitable for hunting. Our results lead to recommendations regarding the environments to favour for the location of future wind farms, and the minimal distances that should be respected between wind farms and peregrine falcon nests sites to minimize collision risks.

Non-classical light sources that can produce streams of correlated on-demand photons are a central building block for optics based quantum information technologies. There are numerous possible approaches for producing such a light source. One of the most promising is the solid-state single photon source based on a single quantum dot in III-V semiconductors. Utilizing a single InAs quantum dot in an InP nanowire, we previously demonstrated a bright and efficient source for single photons [1] and entangled photon pairs [2] that emits around 950 nm. In order to interface with telecom systems, single photon sources emitting at longer wavelengths are required. A few works have extended the emission to the telecom band using a single InAs/InP quantum dot in a micro-cavity [3-4]. However, improving the source brightness and the extraction efficiency remains a challenging task. In this contribution, by modifying the growth conditions and the pre-growth pattern for an InAs dot in an InP nanowire, we demonstrate a bright light source that emits in the telecom O-band, an important step towards the demonstration of a single photon source.

Subwavelength gratings (SWGs) are periodic structures with a pitch (Λ) smaller than the wavelength of the propagating wave (λ), so that diffraction effects are suppressed. These structures thus behave as artificial metamaterials where the refractive index and the dispersion profile can be controlled with a proper design of the geometry of the structure. SWG waveguides have found extensive applications in the field of integrated optics, such as efficient fiber-chip couplers, broadband multimode interference (MMI) couplers, polarization beam splitters or evanescent field sensors, among others. From the point of view of nano-fabrication, the subwavelength condition (Λ << λ) is much easier to meet for long, mid-infrared wavelengths than for the comparatively short near-infrared wavelengths. Since most of the integrated devices based on SWGs have been proposed for the near-infrared, the true potential of subwavelength structures has not yet been completely exploited. In this talk we summarize some valuable guidelines for the design of high performance SWG integrated devices. We will start describing some practical aspects of the design, such as the range of application of semi-analytical methods, the rigorous electromagnetic simulation of Floquet modes, the relevance of substrate leakage losses and the effects of the random jitter, inherent to any fabrication process, on the performance of SWG structures. Finally, we will show the possibilities of the design of SWG structures with two different state-of-the-art applications: i) ultra-broadband MMI beam splitters with an operation bandwidth greater than 300nm for telecom wavelengths and ii) a set of suspended waveguides with SWG lateral cladding for mid-infrared applications, including low loss waveguides, MMI couplers and Mach-Zehnder interferometers.

Producing advanced quantum states of light is a priority in quantum information technologies. While remarkable progress has been made on single photons and photon pairs, multipartite correlated photon states are usually produced in purely optical systems by post-selection or cascading, with extremely low efficiency and exponentially poor scaling. Multipartite states enable improved tests of the foundations of quantum mechanics as well as implementations of complex quantum optical networks and protocols. It would be favorable to directly generate these states using solid state systems, for better scaling, simpler handling, and the promise of reversible transfer of quantum information between stationary and flying qubits. Here we use the ground states of two optically active coupled quantum dots to directly produce photon triplets. The wavefunctions of photogenerated excitons localized in these ground states are correlated via molecular hybridization and Coulomb interactions. The formation of a triexciton leads to a triple cascade recombination and sequential emission of three photons with strong correlations. The quantum dot molecule is embedded in an epitaxially grown nanowire engineered for single-mode waveguiding and improved extraction efficiency at the emission wavelength. We record 65.62 photon triplets per minute, surpassing rates of all earlier reported sources, in spite of the moderate efficiency of our detectors. Our structure and data represent a breakthrough towards implementing multipartite photon entanglement and multi-qubit readout schemes in solid state devices, suitable for integrated quantum information processing., Comment: 27 pages, 3 figures

Background Collaborative writing applications (CWAs), such as wikis and Google Documents, hold the potential to improve the use of evidence in both public health and healthcare. Although a growing body of literature indicates that CWAs could have positive effects on healthcare, such as improved collaboration, behavioural change, learning, knowledge management, and adaptation of knowledge to local context, this has never been assessed systematically. Moreover, several questions regarding safety, reliability, and legal aspects exist. Objectives The objectives of this review were to (1) assess the effects of the use of CWAs on process (including the behaviour of healthcare professionals) and patient outcomes, (2) critically appraise and summarise current evidence on the use of resources, costs, and cost-effectiveness associated with CWAs to improve professional practices and patient outcomes, and (3) explore the effects of different CWA features (e.g. open versus closed) and different implementation factors (e.g. the presence of a moderator) on process and patient outcomes. Search methods We searched CENTRAL, MEDLINE, Embase, and 11 other electronic databases. We searched the grey literature, two trial registries, CWA websites, individual journals, and conference proceedings. We also contacted authors and experts in the field. We did not apply date or language limits. We searched for published literature to August 2016, and grey literature to September 2015. Selection criteria We included randomised controlled trials (RCTs), non-randomised controlled trials (NRCTs), controlled before-and-after (CBA) studies, interrupted time series (ITS) studies, and repeated measures studies (RMS), in which CWAs were used as an intervention to improve the process of care, patient outcomes, or healthcare costs. Data collection and analysis Teams of two review authors independently assessed the eligibility of studies. Disagreements were resolved by discussion, and when consensus was not reached, a third review author was consulted. Main results We screened 11,993 studies identified from the electronic database searches and 346 studies from grey literature sources. We analysed the full text of 99 studies. None of the studies met the eligibility criteria; two potentially relevant studies are ongoing. Authors' conclusions While there is a high number of published studies about CWAs, indicating that this is an active field of research, additional studies using rigorous experimental designs are needed to assess their impact and cost-effectiveness on process and patient outcomes.

GaSb-based tunable single-mode diode lasers can enable rapid, highly-selective and highly-sensitive absorption spectroscopy systems for gas sensing. In this work, single-mode distributed feedback (DFB) laser diodes were developed for the detection of various trace gases in the 2-3.3um range, including CO2, CO, HF, H2S, H2O and CH4. The lasers were fabricated using an index-coupled grating process without epitaxial regrowth, making the process significantly less expensive than conventional DFB fabrication. The devices are based on InGaAsSb/AlGaAsSb separate confinement heterostructures grown on GaSb by molecular beam epitaxy. DFB lasers were produced using a two step etch process. Narrow ridge waveguides were first defined by optical lithography and etched into the semiconductor. Lateral gratings were then defined on both sides of the ridge using electron-beam lithography and etched to produce the index-grating. Effective index modeling was used to optimize the ridge width, etch depths and the grating pitch to ensure single-lateral-mode operation and adequate coupling strength. The effective index method was further used to simulate the DFB laser emission spectrum, based on a transfer matrix model for light transmission through the periodic structure. The fabricated lasers exhibit single-mode operation which is tunable through the absorption features of the various target gases by adjustment of the drive current. In addition to the established open-path sensing applications, these devices have great potential for optoelectronic integrated gas sensors, making use of integrated photodetectors and possibly on-chip Si photonics waveguide structures.

Waveguides structured at the subwavelength scale frustrate diffraction and behave as optical metamaterials with controllable refractive index. These structures have found widespread applications in silicon photonics, ranging from sub-decibel efficiency fibre-chip couplers to spectrometers and polarization rotators. Here, we briey describe the design foundations for sub-wavelength waveguide devices, both in terms of analytic effective medium approximations, as well as through rigorous Floch-Bloquet mode simulation. We then focus on two novel structures that exemplify the use of subwavelength waveguides: mid-infrared waveguides and ultra-broadband beamsplitters., SPIE OPTO, 28 January 2017, San Francisco, CA, USA, Series: Proceedings of SPIE; no. 10107

This tutorial will cover the principles, design, fabrication and applications of subwavelength metamaterial structures in integrated optics, including a comprehensive overview of recent advances in implementations of these structures in silicon photonics.