Search

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.

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.

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.

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.

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.

We report our advances in development of subwavelength engineered structures for integrated photonics, specifically high-efficiency fiber-chip couplers, broadband surface grating couplers and ultra-broadband nanophotonic beam splitters.

In 2000, more than 50 million Americans were treated in hospitals following injury, with costs estimated at $80 billion, yet no performance indicator based on costs has been developed and validated specifically for acute trauma care. This study aimed to describe how data on costs have been used to evaluate the performance of acute trauma care hospitals.A systematic review using MEDLINE, EMBASE, Web of Science, The Cochrane Library, CINAHL, TRIP, and ProQuest was performed in December 2012. Cohort studies evaluating hospital performance for the treatment of injury inpatients in terms of costs were considered eligible. Two authors conducted the screening and the data abstraction independently using a piloted electronic data abstraction form. Methodological quality was evaluated using seven criteria from the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement and the Downs and Black tool.The search retrieved 6,635 studies, of which 10 were eligible for inclusion. Nine studies were conducted in the United States and one in Europe. Six studies used patient charges as a proxy for patient costs, of which four used cost-to-charge ratios. One study estimated costs using average unit costs, and three studies were based on the real costs obtained from a hospital accounting system. Average costs per patient in 2013 US dollar varied between 2,568 and 74,435. Four studies (40%) were considered to be of good methodological quality.Studies evaluating the performance of trauma hospitals in terms of costs are rare. Most are based on charges rather than costs, and they have low methodological quality. Further research is needed to develop and validate a performance indicator based on inpatient costs that will enable us to monitor trauma centers in terms of resource use.Systematic review, evidence, level III.

A single-pass, compact, and low-power-consumption methane sensing system is presented, and its sensitivity is examined for a set of reference cells with pressures of 7.4, 74, and 740 Torr and the same methane concentration at laboratory temperature of 23°C. A GaSb-based continuous-wave distributed feedback tunable diode laser at 3270 nm and wavelength modulation spectroscopy were employed to collect 2f spectra in the 𝜈₃, R₃ band of ¹²CH₄. The collected 2f spectra were fitted to a modulated Voigt line profile model. An Allan–Werle variance analysis shows that the best detectivity, 4 ppbm, is obtained for the highest pressure cell. At pressures of 74 and 7.4 Torr the detectivities are 16 and 28 ppbm, respectively. For these low-pressure cells, further sensitivity improvements were achieved using a large modulation depth (𝑚>2.2) at the expense of spectral resolution.

A method to integrate nanowire-based quantum dot single photon sources on-chip using evanescent coupling is demonstrated. By deterministically placing an appropriately tapered III-V nanowire, containing a single quantum dot, on top of a silicon-based ridge waveguide, the quantum dot emission directed toward the taper can be transferred to the ridge waveguide with calculated efficiencies close to 100%. As the evanescent coupling is bidirectional, the source can be optically pumped in both free-space and through the ridge waveguide. The latter configuration paves the way toward a self-contained, all-fiber, plug-and-play solution for applications requiring a bright on-demand single photon source. Using InAsP quantum dots embedded in InP nanowire waveguides, coupling efficiencies to a SiN ridge waveguide of 74% with a single photon purity of 97% are demonstrated. The technique to demonstrate deterministic placement of single quantum emitters onto pre-fabricated waveguides is used, an important step toward the fabrication of complex quantum photonic circuits.

Bragg gratings are fundamental building blocks for integrated photonic circuits. In the high-index contrast silicon-on-insulator material platform, it is challenging to accurately control the grating strength and achieve narrow spectral bandwidths. Here we demonstrate a novel Bragg grating geometry utilizing a silicon subwavelength grating (SWG) waveguide with evanescently coupled periodic Bragg loading segments placed outside the SWG core. We report experimental 3 dB filter bandwidths in a range from 8 nm to 150 pm by adjusting the distance of the Bragg loading segments from the core and the relative phase shift of the segments on the two sides of the waveguide, with a structure that has a minimum feature size of 100 nm.

A planar waveguide Fourier-transform spectrometer with densely arrayed Mach-Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach-Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free-spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of -25 to -30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements.

Multimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two-fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 × 2 MMI fabricated on a commercial silicon-on-insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in-house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 μm x 23 μm and it exhibits a measured extinction ratio better than 15 dB within the full C-band (1530 nm‒1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance.

We report our advances in development of subwavelength engineered structures for integrated photonics. This unique technology allows synthesis of an effective photonic medium with an unprecedented control of material properties, constituting a powerful tool for a designer of photonic integrated circuits. By locally engineering the refractive index of silicon by forming a pattern of holes at the subwavelength scale it is possible to manipulate the flow of light in silicon photonic waveguides. We have demonstrated a number of subwavelength engineered devices operating at telecom wavelengths, including fiber-chip couplers, waveguide crossings, WDM multiplexers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators, transceiver hybrids and colorless interference couplers. The subwavelength metamaterial concept has been adopted by industry (IBM) for fiber-chip coupling and subwavelength engineered structures are likely to become key building blocks for the next generation of integrated photonic circuits. We present an overview of different implementations of these structures in silicon photonic integrated circuits, such as high-efficiency fiber-chip couplers, wavelength multiplexers, microspectrometers, waveguide crossovers, ultra-broadband splitters and mid-infrared waveguide components, to name a few., 2016 Progress in Electromagnetic Research Symposium (PIERS), August 8-11, 2016, Shanghai, China

Subwavelength engineering in silicon photonic integrated circuits is a powerful design tool that allows one to synthesize an effective photonic medium with adjustable refractive index. This creates a new degree of freedom in photonic circuit design. We present an overview of the fundamental concept and its application to address several important practical challenges in the implementation of silicon photonics as a next generation photonics platform for telecom, datacom and sensing. In particular, we report our results in developing highly efficient and broadband fiber-chip couplers for silicon photonic wire waveguides using subwavelength engineered edge coupling structures. We experimentally demonstrate a coupling efficiency of -0.4 dB and polarization independent operation for a broad spectral range exceeding 100 nm for optical fiber with a core diameter of 3.2 μm. For coupling to standard SMF-28 fiber with 10.4 μm mode field diameter we numerically demonstrate a subwavelength engineered overlayer structure composed of SiO2 and Si3N4 which exhibits an overall coupling efficiency exceeding 90%. We have also used our subwavelength structure for coupling experiments with a conventional InGaAsP/InP buried heterostructure laser at λ = 1.3 μm with a measured near field mode size of 2.1 μm×2.8 μm. Peak coupling efficiency is 1.5 dB with 1-dB alignment tolerance of approximately ±1.2 μm horizontally and ±0.8 μm vertically. We further present subwavelength engineered grating couplers fabricated in a single-etch step for the telecom (1.55 μm) and datacom (1.3 μm) wavelengths with efficiencies exceeding -0.5 dB. Further applications that will be discussed include waveguide crossings, microspectrometers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators and colorless interference couplers., 2016 Progress in Electromagnetic Research Symposium (PIERS), August 8-11, 2016, Shanghai, China

Key aspects of the growth of site selected InP nanowires will be discussed, focussing on those relevant to quantum information processing. Parameters including high brightness, narrow linewidth and single photon purity, and a route to integration into planar optical circuits will be discussed., 2016 IEEE Photonics Society Summer Topical Meeting Series (SUM), July 11-13, Newport Beach, CA, USA

We report our recent advances in development of subwavelength engineered dielectric metamaterial structures for integrated photonics., 18th International Conference on Transparent Optical Networks (ICTON), July 10 -14, 2016, Trento, Italy

International audience; We report, for the first time, on the design and experimental demonstration of fiber-chip surface grating couplers based on subwavelength grating engineered nanostructure operating in the low fiber chromatic dispersion window (around 1.3 μm wavelengths), which is of great interest for short-reach data communication applications. Our coupler designs meet the minimum feature size requirements of large-volume deep-ultraviolet stepper lithography processes. The fiber-chip couplers are implemented in a standard 220-nm-thick silicon-on-insulator (SOI) platform and are fabricated by using a single etch process. Several types of couplers are presented, specifically the uniform, the apodized, and the focusing designs. The measured peak coupling efficiency is −2.5 dB (56%) near the central wavelength of 1.3 μm. In addition, by utilizing the technique of the backside substrate metallization underneath the grating couplers, the coupling efficiency of up to −0.5 dB (89%) is predicted by Finite Difference Time Domain (FDTD) calculations.

We experimentally demonstrate a subwavelength refractive index engineered nanostructure for edge coupling, enabling a coupling efficiency of -0.4 dB and polarization independent operation for a broad spectral range exceeding 100 nm., Optical Fiber Communication Conference, March 20-24, 2016, Anaheim, CA USA

37th PIERS, Progress In Electromagnetics Research Symposium, PIERS 2016 in Shanghai, China, 8 August - 11 September, 2016 ; http://piers.org/piers2016Shanghai/, We present some of the latest developments in silicon-based Fourier-transform microspectrometers for the near and mid-infrared. The devices comprise waveguide arrays of Mach-Zehnder interferometers with linearly increasing optical path differences, enabling scan-less spectral retrieval with large radiant throughput. Resolutions down to 40pm are experimentally demonstrated. Spatial heterodyne Fourier-transform (SHFT) spectrometry is an interferometric technique which circumvents the need of moving elements and provides an increased έtendue. The SHFT scheme can be implemented with a waveguide array of Mach-Zehnder interferometers (MZI) with linearly increasing optical path differences. The high refractive index contrast of the SOI platform and the waveguide bend radius of ~ 5 μm readily allow achieving high resolutions in a reduced footprint. We report three alternative implementations of the SHFT principle in SOI waveguides. Firstly, a SHFT chip with Si-wire microphotonic spirals, reaching a resolution of 40 pm at a central wavelength near 1.5 μm. Secondly, a SHFT micro-spectrometer with subwavelength gratings for refractive index engineering of the optical delay lines. Finally, an extension of the SHFT scheme to the mid-infrared, addressing specific challenges of this spectral region such as efficient coupling and power splitting structures, and robust performance over a substantially broader free spectral range. SHFT spectrometers are promising for a wide range of applications, including chemical and biological sensing, astronomy, communications, hand-held spectroscopy, and sensing from satellites or planetary rowers. Furthermore, the resolution of these devices can be readily scaled up to very long optical delays, opening a new pathway toward possibly overcoming current resolution limits of state-of-the-art spectroscopic instruments.

In this review, we summarize and discuss our recent studies of subwavelength grating (SWG) structures for engineering the refractive index of silicon microphotonic waveguides. The SWG effect allows control of the effective refractive index of a waveguide core over a range spanning the values of the cladding material and silicon by lithographic patterning. We demonstrate this effect with the example of segmented photonic wire waveguides, which are shown to exhibit low propagation loss, and can be used to make highly efficient waveguide crossings and in-plane fiber-chip coupling structures. Other applications of SWG structures in silicon photonic waveguide devices include surface grating couplers with enhanced performance and simplified fabrication requirements, as well as a novel curved waveguide sidewall grating micro-spectrometer, in which an SWG structure fulfills a dual purpose by acting as an effective slab waveguide for diffracted light and as a lateral cladding for a channel waveguide.

First implementations of subwavelength gratings (SWGs) in silicon-on-insulator (SOI) waveguides are discussed and demonstrated by experiment and simulations. The subwavelength effect is exploited for making antireflective and highly reflective waveguide facets as well as efficient fiber-chip coupling structures. We demonstrate experimentally that by etching triangular SWGs into SOI waveguide facets, the facet power reflectivity can be reduced from 31% to 94% facet reflectivity can be achieved with square SWGs for 5 μm thick SOI waveguides. Finally, SWG fiber-chip couplers for SOI photonic wire waveguides are introduced, including design, simulation, and first experimental results.

We present the first experimental demonstration of a new fiber-chip grating coupler concept that exploits the blazing effect by interleaving the standard full (220 nm) and shallow etch (70 nm) trenches in a 220 nm thick silicon layer. The high directionality is obtained by controlling the separation between the deep and shallow trenches to achieve constructive interference in the upward direction and destructive interference toward the silicon substrate. Utilizing this concept, the grating directionality can be maximized independent of the bottom oxide thickness. The coupler also includes a subwavelength-engineered index-matching region, designed to reduce the reflectivity at the interface between the injection waveguide and the grating. We report a measured fiber-chip coupling efficiency of −1.3 dB , the highest coupling efficiency achieved to date for a surface grating coupler in a 220 nm silicon-on-insulator platform fabricated in a conventional dual-etch process without high-index overlays or bottom mirrors.

Surface grating couplers are fundamental components in chip-based photonic devices to couple light between photonic integrated circuits and optical fibers. In this work, we report on a grating coupler with sub-decibel experimental coupling efficiency using a single etch process in a standard 220-nm silicon-on-insulator (SOI) platform. We specifically demonstrate a subwavelength metamaterial refractive index engineered nanostructure with backside metal reflector, with the measured peak fiber-chip coupling efficiency of -0.69 dB (85.3%) and 3 dB bandwidth of 60 nm. This is the highest coupling efficiency hitherto experimentally achieved for a surface grating coupler implemented in 220-nm SOI platform.

Coupling of light to and from integrated optical circuits has been recognized as a major practical challenge since the early years of photonics. The coupling is particularly difficult for high index contrast waveguides such as silicon-on-insulator, since the cross-sectional area of silicon wire waveguides is more than two orders of magnitude smaller than that of a standard single-mode fiber. Here, we experimentally demonstrate unprecedented control over the light coupling between the optical fiber and silicon chip by constructing the nanophotonic coupler with ultra-high coupling efficiency simultaneously for both transverse electric and transverse magnetic polarizations. We specifically demonstrate a subwavelength refractive index engineered nanostructure to mitigate loss and wavelength resonances by suppressing diffraction effects, enabling a coupling efficiency over 92% (0.32 dB) and polarization independent operation for a broad spectral range exceeding 100 nm.

According to Donabedian's health care quality model, improvements in the structure of care should lead to improvements in clinical processes that should in turn improve patient outcome. This model has been widely adopted by the trauma community but has not yet been validated in a trauma system. The objective of this study was to assess the performance of an integrated trauma system in terms of structure, process, and outcome and evaluate the correlation between quality domains.Quality of care was evaluated for patients treated in a Canadian provincial trauma system (2005-2010; 57 centers, n = 63,971) using quality indicators (QIs) developed and validated previously. Structural performance was measured by transposing on-site accreditation visit reports onto an evaluation grid according to American College of Surgeons criteria. The composite process QI was calculated as the average sum of proportions of conformity to 15 process QIs derived from literature review and expert opinion. Outcome performance was measured using risk-adjusted rates of mortality, complications, and readmission as well as hospital length of stay (LOS). Correlation was assessed with Pearson's correlation coefficients.Statistically significant correlations were observed between structure and process QIs (r = 0.33), and process and outcome QIs (r = -0.33 for readmission, r = -0.27 for LOS). Significant positive correlations were also observed between outcome QIs (r = 0.37 for mortality-readmission; r = 0.39 for mortality-LOS and readmission-LOS; r = 0.45 for mortality-complications; r = 0.34 for readmission-complications; 0.63 for complications-LOS).Significant correlations between quality domains observed in this study suggest that Donabedian's structure-process-outcome model is a valid model for evaluating trauma care. Trauma centers that perform well in terms of structure also tend to perform well in terms of clinical processes, which in turn has a favorable influence on patient outcomes.Prognostic study, level III.

Surface grating couplers are key components to couple light between planar waveguide circuits in silicon-on-insulator (SOI) platform and optical fibers. Here, we demonstrate by using simulations and experiments that a high coupling efficiency can be achieved for an arbitrary buried oxide thickness by judicious adjustment of the grating radiation angle. The coupler strength is engineered by subwavelength structures, which have pitch and feature sizes smaller than the wavelength of light propagating through it, thereby frustrating diffraction effects and behaving as a homogeneous media with an adjustable equivalent refractive index. This makes it possible to apodize the grating coupler with a preferred single etch fabrication process. The coupling efficiency of the grating coupler is optimized for operating with the transverse electric (TE) polarization state at the wavelengths near 1.3 μm and 1.55 μm, which are the bands relevant for datacom and telecom interconnects applications, respectively. The design and analysis of the grating coupler is carried out using two-dimensional (2-D) Fourier-eigenmode expansion method (F-EEM) and finite difference time domain (FDTD) method. The simulations show a peak fiber-chip coupling efficiency of -1:61 dB and - 1:97 dB at 1.3 μm and 1.55 μm wavelengths, respectively, with a minimum feature size of 100 nm, compatible with 193 nm deep-ultraviolet (DUV) lithography. The measurements of our fabricated continuously apodized grating coupler demonstrate fiber-chip coupling efficiency of - 2:16 dB at a wavelength near 1.55 μm with a 3 dB bandwidth of 64 nm. These results open promising prospects for low-cost and high-volume fabrication of surface grating couplers in SOI using 193 nm DUV lithography, which is now used in several silicon photonics foundries. It is also predicted that a coupling efficiency as high as - 0:42 dB can be achieved for the coupler structure with a bottom dielectric mirror., SPIE Optics + Optoelectronics, April 13-15, 2015, Prague, Czech Republic, Series: Proceedings of SPIE; no. 9516