Search

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.

Intensive agriculture, as is typical of corn and soybean production, may be responsible for declines in the abundance and diversity of farmland birds. In Quebec, the transition to intensive crops is evidenced by marked increases of corn and soybean fields. From 2008 to 2010, we used satellite telemetry to study use of corn (Zea mays) and soybean (Glycine max) fields, other farmlands, wetlands, urban areas, and other habitats by 10 female Peregrine Falcons (Falco peregrinus) of the anatum—tundrius complex, a taxon of “special concern” in Canada. We monitored females during the nesting season, from hatching of eggs to independence of young, but before the young dispersed away from the nest site. Adult females were less likely to use corn and soybean fields than the “other farmlands” and “other habitats” categories during the nestling stage and the first month after young fledged. Once young fledged, other farmlands and urban areas were more likely to be used than the “other habitats” category when...

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.

Photoluminescence from individual InAs/InP quantum dots embedded within a planar n–i structure is studied as a function of vertical electric field. We demonstrate control of the electron number and determine the Stark shift and built-in dipole at zero electric field. In contrast to the well studied InAs/GaAs quantum dot material system, we obtain a built-in dipole which indicates that the electron lies above the hole at zero electric field. The magnitude and direction of the measured dipole suggests a uniform quantum dot composition. The gating principles we demonstrate can be applied to pre-positioned InAs/InP quantum dots, such that arrays of initialized single spins can be employed for quantum information applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

A crucial pre-requisite for quantum information applications is the ability to produce a scalable quantum system that can be controllably manipulated. We present a technique that promises the practical realization of a scalable system with arrays of gated quantum dots (QDs) emitting at wavelengths suitable for fibre based quantum cryptography. We show how the random nature of the nucleation site for self-assembled QDs can be overcome by a nanotemplate deposition technique such that further processing around these dots can be performed. By knowing exactly where the QD is, we position electrostatic gates around the dot with better than 30 nm accuracy. With these gates and a Si n-doped back gate, we demonstrate from both simulation and experiment that we can control the electron number of the dot via vertical electric fields.

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

Contains fulltext : 152344.pdf (Publisher’s version ) (Open Access) BACKGROUND: Trauma is the most common cause of mortality among people between the ages of 1 and 45 years, costing Canadians 19.8 billion dollars a year (2004 data), yet half of all patients with major traumatic injuries do not receive evidence-based care, and significant regional variation in the quality of care across Canada exists. Accordingly, our goal is to lead a research project in which stakeholders themselves will adapt evidence-based trauma care knowledge tools to their own varied institutional contexts and cultures. We will do this by developing and assessing the combined impact of WikiTrauma, a free collaborative database of clinical decision support tools, and Wiki101, a training course teaching participants how to use WikiTrauma. WikiTrauma has the potential to ensure that all stakeholders (eg, patients, clinicians, and decision makers) can all contribute to, and benefit from, evidence-based clinical knowledge about trauma care that is tailored to their own needs and clinical setting. OBJECTIVE: Our main objective will be to study the combined effect of WikiTrauma and Wiki101 on the quality of care in four trauma centers in Quebec. METHODS: First, we will pilot-test the wiki with potential users to create a version ready to test in practice. A rapid, iterative prototyping process with 15 health professionals from nonparticipating centers will allow us to identify and resolve usability issues prior to finalizing the definitive version for the interrupted time series. Second, we will conduct an interrupted time series to measure the impact of our combined intervention on the quality of care in four trauma centers that will be selected-one level I, one level II, and two level III centers. Participants will be health care professionals working in the selected trauma centers. Also, five patient representatives will be recruited to participate in the creation of knowledge tools destined for their use (eg, handouts). All participants will be invited to complete the Wiki101 training and then use, and contribute to, WikiTrauma for 12 months. The primary outcome will be the change over time of a validated, composite, performance indicator score based on 15 process performance indicators found in the Quebec Trauma Registry. RESULTS: This project was funded in November 2014 by the Canadian Medical Protective Association. We expect to start this trial in early 2015 and preliminary results should be available in June 2016. Two trauma centers have already agreed to participate and two more will be recruited in the next months. CONCLUSIONS: We expect that this study will add important and unique evidence about the effectiveness, safety, and cost savings of using collaborative platforms to adapt knowledge implementation tools across jurisdictions.

Coulomb blockade studies of lateral quantum dots and measurements of the quantised conductance of quantum point contacts, in high magnetic fields, reveal novel features which are hysteretic in magnetic-field sweep direction. These features are associated with long-lived eddy currents, induced in the 2D electron gas leads in these devices as the magnetic field sweeps and the 2DEG enters the quantum Hall effect state. Torsion-balance magnetometry measurements confirm the presence of these induced currents, and their influence on the nanostructures. The decay of the eddy currents, after the magnetic field sweep is stopped, exhibits two distinct regimes: a fast initial exponential decay followed by a much longer power-law decay in which the size of the eddy current falls typically to 60% of its original value in one day. The interpretation of these observations is that the Coulomb blockade and quantum point contact devices are influenced by the local Hall potential at the edges of the 2DEG leads. The Hall potential changes the local chemical potential of the leads, and hence the properties of the devices, in a manner which reverses when the field sweep direction is reversed.

The electrodes in a carrier-injection-based digital optical switch are separated by a gap of less than 1μm. Good switch performance requires minimal current spreading and effective electrical isolation of these two electrodes without perturbing the underlying guided optical fields. Two methods of such isolation are modeled and experimentally compared. One is the etching of an e-beam-defined 0.5-μm-wide trench down to an etch stop layer, and the other is the implanting of oxygen ions using the electrodes as a shadow mask. Electrical simulation results suggest that injected current magnitudes and carrier concentration profiles are similar with both the trench and the ion implant, and so they should be equally effective in preventing current flow between the two branches. However, experimental results show that ion implantation produces better switching contrasts of greater than 20dB. We attribute this to the fact that implantation using the electrodes as a shadow mask results in an injected carrier distribution that more accurately reproduces the shape of the overlying electrode.The electrodes in a carrier-injection-based digital optical switch are separated by a gap of less than 1μm. Good switch performance requires minimal current spreading and effective electrical isolation of these two electrodes without perturbing the underlying guided optical fields. Two methods of such isolation are modeled and experimentally compared. One is the etching of an e-beam-defined 0.5-μm-wide trench down to an etch stop layer, and the other is the implanting of oxygen ions using the electrodes as a shadow mask. Electrical simulation results suggest that injected current magnitudes and carrier concentration profiles are similar with both the trench and the ion implant, and so they should be equally effective in preventing current flow between the two branches. However, experimental results show that ion implantation produces better switching contrasts of greater than 20dB. We attribute this to the fact that implantation using the electrodes as a shadow mask results in an injected carrier distribu...

Hexagonal lattice photonic crystal microcavities with modified single missing air-hole defects were fabricated in suspended InAs∕InP quantum dot membranes. The cavity modes predicted from finite-difference time-domain simulations are observed in photoluminescence measurements. The resonant energies of the defect modes are tuned across the band gap of the photonic crystal through modifications of the size and position of the inner ring holes surrounding the defect. Up to a 20-fold enhancement of the quality factor of the modes are observed as they are tuned across the band gap, with measured Q values of up to 6000.

Grating couplers are key elements enabling the coupling of light between planar waveguide circuits and optical fibers. In this work, it is demonstrated 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 structure, allowing straightforward apodization and single etch step fabrication. The design has been implemented using Fourier-eigenmode expansion and finite difference time domain methods. The measured coupling loss of a continuously apodized grating is -2.16 dB with a 3 dB bandwidth of 64 nm, therefore opening promising prospects for low-cost and high-volume fabrication using 193 nm deep-ultraviolet lithography. It is also shown by simulations that a coupling loss as low as -0.42 dB is predicted for a modified coupler structure with bottom mirror.

Periodic structures with a sub-wavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves. While the use of these structures in waveguide optics was proposed in the 1990s, it has been with the more recent developments of silicon photonics and high-precision lithography techniques that sub-wavelength structures have found widespread application in the field of pho- tonics. This review first provides an introduction to the physics of sub-wavelength structures. An overview of the applications of sub-wavelength structures is then given including: anti-reflective coatings, polarization rotators, high-efficiency fiber-chip cou- plers, spectrometers, high-reflectivity mirrors, athermal waveg- uides, multimode interference couplers, and dispersion engi- neered, ultra-broadband waveguide couplers among others. Particular attention is paid to providing insight into the design strategies for these devices. The concluding remarks provide an outlook on the future development of sub-wavelength structures and their impact in photonics.

Subwavelength grating structures with a pitch smaller than the Bragg resonance length can be used for engineering the refractive index in silicon photonic waveguides. We discuss the principles, design, fabrication and applications of subwavelength nanostructures in silicon photonics and review our recent results on fiber-chip coupling structures, surface grating couplers, waveguide crossings, and athermal waveguides with a polymersilicon hybrid core., 16th International Conference on Transparent Optical Networks, ICTON 2014, 6 July 2014 through 10 July 2014, Graz

Unplanned readmissions represent 20% of all admissions and cost $12 billion annually in the United States. Despite the burden of injuries for the health care system, no quality indicator (QI) based on readmissions is available to evaluate trauma care. The objective of this study was to derive and internally validate a QI for a 30-day unplanned hospital readmission to evaluate trauma care.We performed a multicenter retrospective cohort study in a Canadian integrated provincial trauma system. We included adults admitted to any of the 57 provincial trauma centers between 2005 and 2010 (n = 57,524). Data were abstracted from the provincial trauma registry and linked to the hospital discharge database. The primary outcome was unplanned readmission to an acute care hospital within 30 days of discharge. Candidate risk factors were identified by expert consensus and selected for derivation of the risk adjustment model using bootstrap resampling. The validity of the QI was evaluated in terms of interhospital discrimination, construct validity, and forecasting.The risk adjustment model includes patient age, sex, the Injury Severity Score (ISS), region of the most severe injury, and 11 comorbid conditions. The QI discriminates well across trauma centers (coefficient of variation, 0.02) and is correlated with QIs that measure hospital performance in terms of clinical processes (r = -0.38), risk-adjusted mortality (r = 0.32), and complication rates (r = 0.38). In addition, performance in 2005 to 2007 was predictive of performance in 2008 to 2010 (r = 0.59).We have developed a QI based on risk-adjusted 30-day rates of unplanned readmission, which can be used to evaluate trauma care with routinely collected data. The QI is based on a comprehensive risk adjustment model with good internal and temporal validity and demonstrates good properties in terms of discrimination, construct validity, and forecasting. This research represents an essential step toward reducing unplanned readmission rates to improve resource use and patient outcomes following injury.Prognostic study, level III.

OBJECTIVE To describe acute care length of stay (LOS) over all consecutive hospitalizations for the injury and according to level of care [intensive care unit (ICU), intermediate care, general ward], compare observed and expected LOS, and identify predictors of LOS. BACKGROUND Prolonged LOS has important consequences in terms of costs and outcome, yet detailed information on LOS after trauma is lacking. METHODS This multicenter retrospective cohort study was based on adults discharged alive from a Canadian trauma system (1999-2010; n = 126,513). Registry data were used to calculate index LOS (LOS in trauma center with highest designation level) and were linked to hospital discharge data to calculate total LOS (all consecutive hospitalizations for the injury). Expected LOS was obtained by matching general provincial discharge statistics to study data by year, age, and sex. Potential predictors of LOS were evaluated using linear regression. RESULTS Mean index and total LOS were 8.6 and 9.4 days, respectively. ICU, intermediate care unit, and general ward care constituted 8.9%, 2.5%, and 88.6% of total hospital days. Observed mean index and ICU LOS in our trauma patients were 2.9 and 1.3 days longer than expected LOS (P < 0.0001). The strongest determinants of index LOS were discharge destination, age, transfer status, and injury severity. CONCLUSIONS Results suggest that acute care LOS after injury is underestimated when only information on the index hospitalization is used and that ICU or intermediate care constitute an important part of LOS. This information should be used to inform the development of an informative and actionable quality indicator.

As most integrated optics platforms, silicon offers only a fixed set of material refractive indices for designing devices. The ability of sub-wavelength patterned structures to synthesize arbitrary equivalent index values between nSi ~ 3.5 and nair=1 has thus enabled completely new design approaches that have led to silicon waveguide devices with breakthrough performance. This review covers the latest advances in sub-wavelength structured fiber-to-chip grating couplers and multimode interference couplers. We discuss, among others, single-etch grating couplers with high coupling efficiency ( -1.8 dB), and broad bandwidth ( 115 nm at 3 dB), as well as ultra-short, high performance multi-mode interference couplers. We furthermore introduce the concept of dispersion engineering with sub-wavelength structures, showing its potential to increase the bandwidth of waveguide devices, including multi-mode interference couplers covering a 450 nm wavelength span.

The growth of GaN/AIGaN high electron mobility transistor structures (HEMT) on 4H-SiC by ammonia molecular beam epitaxy (a-MBE) is reported. Structures were grown using a magnetron sputter epitaxy deposited AlN buffer layer prior to the MBE growth of a carbon-doped insulating GaN isolation layer, undoped GaN channel layer and AIGaN cap layer. No ex-situ or in-situ high temperature pre-treatment of the SiC substrate was used. The electrical characteristics of the layers was excellent with RT mobilities of >1100 cm 2 /Vs for a sheet carrier density of >1 x 10 13 cm -2 . 2 HEMTs fabricated from layers gave an f t and f max of 36 and 80 GHz, respectively with a maximum saturated drain current of 450 mA/mm and transconductance of 160 mS/mm for a gate length of 0.3 μm.

Magnetoresistance data in p-SiGe samples is analysed using the Renormalisation Group theories of Finkel'stein and Castellani et al. The interaction parameter, γ 2 is found to be of order one or larger than one, sufficient to explain the metallic behaviour in terms of delocalising Coulomb interaction corrections.

Quantum dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular beam epitaxy. At 77 K, we tune the lasers from the first to the fourth excited state of the QDs by varying the cavity length, this covers a wavelength range from 869 to 963 nm. At room temperature, we obtain lasing from the second to the fourth excited state covering the 938 to 984 nm wavelength range. For high injection currents, a large part of the QD ensemble contributes at once to the stimulated emission yielding a lasing emission linewidth having a full width at half maximum of 25 nm. By increasing the energy spacing between the QD energy level contributing to the lasing and the wetting layer energy levels, improved thresholds at higher temperatures are observed, leading to lasing below 100 A/cm2 at room temperature.Quantum dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular beam epitaxy. At 77 K, we tune the lasers from the first to the fourth excited state of the QDs by varying the cavity length, this covers a wavelength range from 869 to 963 nm. At room temperature, we obtain lasing from the second to the fourth excited state covering the 938 to 984 nm wavelength range. For high injection currents, a large part of the QD ensemble contributes at once to the stimulated emission yielding a lasing emission linewidth having a full width at half maximum of 25 nm. By increasing the energy spacing between the QD energy level contributing to the lasing and the wetting layer energy levels, improved thresholds at higher temperatures are observed, leading to lasing below 100 A/cm2 at room temperature.

An airbridge technique was developed and subsequently employed to fabricate mesoscopic devices, such as parallel quantum point contacts. The airbridge technique mainly involves two different electron sensitive polymers, polymethylglutarimide and polymethyl methacrylate. The airbridge was patterned by electron beam lithography and metal lift-off with bilayer resist. Conductance measurements were performed on the devices at low magnetic fields. The results confirmed both the presence of the elliptical antidot as a negative voltage was applied to the center gate, as well as the nonintrusive nature of the airbridge technique.

High-resolution spectroscopy was used to examine gain characteristics of Cr-grating complex-coupled distributed-feedback (DFB) lasers near 2.4 $\mu$ m. The single-mode lasers contain InGaAsSb–AlGaAsSb active regions grown by molecular beam epitaxy on GaSb. Modal gain was extracted from the measured amplified spontaneous emission spectra and compared with reference Fabry–PErot lasers. The material gain is similar in both cases, having a value near 1300 cm $^{-1}$ , while the internal losses are quite different. The DFBs have an additional loss, approximately equal to the lateral Cr grating coupling coefficient. This indicates a fundamental performance limitation for complex-coupled DFBs.

We report a spatial heterodyne Fourier-transform spectrometer implemented with an array of optical fiber interferometers. This configuration generates a wavelength-dependent stationary interferogram from which the input spectrum is retrieved in a single shot without scanning elements. Furthermore, fabrication and experimental deviations from the ideal behavior of the device are corrected by spectral inversion algorithms. The spectral resolution of our system can be readily scaled up by incorporating longer optical fiber delays, providing a pathway toward surpassing current spectroscopy resolution limits. © 2013 Optical Society of America.

We report a spatial heterodyne Fourier-transform spectrometer consisting of an array of Mach-Zehnder interferometers (MZI) implemented in silicon microphotonics. Optical path differences between the MZI arms increase linearly along the array, generating a wavelength-dependent interferogram which enables the retrieval of the source spectrum with a single measurement. Optical delays were implemented with Si-wire waveguides arranged in tightly coiled spirals to achieve a high resolution in a reduced footprint. Our spectral retrieval algorithm compensates phase and amplitude errors arising from fabrication imperfections by using a transformation matrix based on the calibration data. A wavelength resolution of 40 pm within a free spectral range of 0.75 nm is demonstrated., 15th International Conference on Transparent Optical Networks, ICTON 2013, June 23-27, 2013, Cartagena, Spain, Series: International Conference on Transparent Optical Networks : [proceedings]

Recently developed subwavelength structures in silicon waveguides are presented. Subwavelength grating photonic structures are discussed along with emerging practical components that exploit the principle of subwavelength refractive index engineering, including polarization-independent athermal silicon waveguides, ultra-broadband and compact multimode interference couplers, fabrication tolerant polarization rotators and interferometer arrays with subwavelength optical delay lines.

BACKGROUND: Process performance indicators that evaluate trauma centers in clinical case management provide information essential to the improvement of trauma care. However, multiple indicators are needed to adequately evaluate process performance, which renders comparisons cumbersome. Several methods are available for generating composite indicators that measure global performance. The goal of this study was to compare three composite methods that are widely used in other health care domains to identify the most appropriate for trauma care process performance evaluation. METHODS: In this retrospective, multicenter cohort study, 15 process performance indicators were implemented using data from a Canadian provincial trauma registry (19,853 patients; 59 centers) on patients with an Injury Severity Score (ISS) greater than 15. Composite scores were derived using three methods as follows: the indicator average, the opportunity model, and a latent variable model. Composite scores were evaluated in terms of discrimination, construct validity (association with an indicator of trauma center structural performance), criterion predictive validity (association with clinical outcomes), and forecasting (correlation over time). RESULTS: All composite scores discriminated well between trauma centers. Only the average indicator score was correlated with improved structure (r = 0.29; 95% confidence interval [CI], 0.07Y0.53), lower risk-adjusted mortality (r = j0.22; 95% CI, j0.46 to 0.04), and lower risk-adjusted complication rate (r = j0.48; 95% CI, j0.65 to j0.25). Composite scores calculated with 1999 to 2002 data all correlated with those calculated with 2003 to 2006 data (r = 0.49, 0.87, and 0.84 for the indicator average, the opportunity model, and the latent variable model, respectively). CONCLUSION: Results suggest that of the three composite scores evaluated, only the indicator average demonstrates content and predictive criterion validity, discriminates between centers, and has good forecasting properties. In addition, this score is simple and intuitive and not subject to variation in weights over trauma systems and time. The observed association between higher indicator average scores and lower risk-adjusted mortality and complication rates suggests that improving process performance may improve patient outcome. (J Trauma Acute Care Surg. 2013;74: 1344Y1350. Copyright * 2013 by Lippincott Williams & Wilkins)

A lateral etched-grating process was used to produce singlemode distributed feedback laser diodes at 3.23 μm. The devices are based on InGaAsSb/AlInGaAsSb type-I quantum well active regions grown on GaSb substrates by molecular beam epitaxy. The lasers were used in high-resolution spectroscopy of methane gas near the v 3 , R 7 vibrational absorption transitions.

Normally, the larger refractive index contrast of silicon-on-insulator (SOI) photonics used for transporting highly confined optical modes is not available in compound semiconductor systems because the optically active layer rests upon an epitaxial support layer having a similar refractive index. Here, a semiconductor-under-insulator (SUI) technology for compound semiconductor membrane photonic circuitry is presented. It will be shown that such a technology can facilitate the transport of highly confined optical modes in compound semiconductor systems and is anticipated to be a critical part of future scalable quantum photonics applications. © 2013 Copyright SPIE., Advanced Fabrication Technologies for Micro/Nano Optics and Photonics VI, 5 February 2013 through 6 February 2013, San Francisco, CA, Series: Proceedings of SPIE

Subwavelenth structures offer exciting new opportunities for integrated optics. Effective refractive index can be chosen from a broad range by lithographic patterning using just two materials. Many practical subwavelength engineered devices already demonstrated, with superior performance compared to their conventional counterparts and likely many more to come.

We review our recent results on subwavelength grating structures for engineering the refractive index of silicon waveguides. Various applications are presented, such as fiber-chip coupling, waveguide crossings and athermal waveguides with a polymer-silicon hybrid core.