Comparison of III-V/Si on-chip lasers with etched facet reflectors.

Electrically pumped heterogeneously integrated III-V/SiO2 semiconductor on-chip lasers with different types of etched facet reflectors are designed and fabricated and their lasing performances are characterized and compared. The III-V quantum-well-based epitaxial layers are bonded on silica-on-silicon substrates and fabricated to form Fabry-Perot lasers with dry-etched rear facets. Three types of reflectors are demonstrated, which are etched facets terminated by air, benzocyclobutene, and metal with a thin layer of SiO2 insulator in-between. The laser devices are characterized and compared, including lasing threshold, external quantum efficiency, and output power, and show the impact of different types of etched facet reflectors on lasing performance.

Hetero-core III-V/Si microlaser.

We design and demonstrate optically pumped microlasers with a hetero-core cavity formed by III-V and silicon-on-insulator (SOI) materials. Hetero-core cavities with identical lateral dimension are fabricated. The cavity is formed by III-V layer with thickness of 210 nm on top of SOI layer with thickness of 300 nm via SiO2 interlayer wafer bonding. Continuous wave laser operation is achieved for a diameter down to 2 µm with a corresponding mode volume of 0.07λ3 and quality factor of 1.3×104. The architecture renders an alternative laser structure for heterogeneous laser-on-chip, with no dedicated vertical coupling mechanism needed between the two materials' layers.

Heterogeneously integrated III-V laser on thin SOI with compact optical vertical interconnect access.

A new heterogeneously integrated III-V/Si laser structure is reported in this report that consists of a III-V ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs), and silicon-on-insulator (SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300-nm-thick SOI layer through low temperature, plasma-assisted direct wafer-bonding and etched to form a III-V ridge waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in the same direction with a length of 50 µm for efficient coupling of light down to the 600 nm wide silicon nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous III-V/Si Fabry-Perot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold current of 65 mA at room temperature, and the slope efficiency from single facet is 144 mW/A. The maximal single facet emitting power is about 4.5 mW at a current of 100 mA, and the side-mode suppression ratio is ∼30 dB. This new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration with a sub-system on-chip for various applications.

Management of blunt traumatic thoracic aorta injuries with endovascular stent-grafts in a tertiary hospital in an urban Asian city.

BACKGROUND: Thoracic aortic injury from blunt trauma is a life-threatening condition with significant mortality and morbidity with open surgical repair. Endovascular means of treatment is emerging as an attractive and less invasive option. We report our experience with endovascular stent-graft repair for blunt traumatic thoracic aorta injury. METHODS: Between January 2003 and August 2009, six patients underwent endovascular repair of blunt traumatic thoracic aorta injury. Data from the medical records of these patients were analyzed. RESULTS: All patients had deceleration injury resulting in thoracic aorta pseudoaneurysm at the aortic isthmus just distal to the left subclavian artery. Four patients were motorcyclists who had been involved in road-traffic accidents and two had fallen from a height. The mean Injury Severity Score was 33.8 (range, 21-43). All procedures were performed within 48 hours of admission and technical success was 100%. Five patients (83.3%) had the left subclavian artery intentionally covered by the stent-graft to achieve adequate proximal landing zone. None of them had any left upper limb ischemic complications or cerebrovascular events after the procedure. One patient had preservation of the left subclavian artery because intraoperative vertebral angiogram showed a hypoplastic right vertebral artery. No other procedural complications, paraplegia, or deaths were reported. Mean follow-up was 18.8 months (range, 1.5-42 months). CONCLUSIONS: Our early experience of endovascular stent-grafting for blunt traumatic thoracic aorta injury suggests that this emerging technique is safe for treatment of such pathology in our inherently Asian population. Left subclavian artery may be sacrificed if adequate proximal landing zone is required for the stent-graft; and when vertebral angiogram was performed which did not show a dominant left vertebral artery.

Surgical management of infected pseudoaneurysms in intravenous drug abusers: single institution experience and a proposed algorithm.

BACKGROUND: Vascular complications from intravenous drug abuse pose significant challenges to vascular surgeons. No formalized policies have been reached on surgical management of the resultant infected pseudoaneurysm. METHODS: A retrospective review of all patients who underwent surgery for pseudoaneurysms due to chronic intravenous drug abuse from July 2005 to February 2008 was performed. RESULTS: A total of 15 patients with infected pseudoaneurysms from chronic intravenous drug abuse were operated on during the study period. The sites of involvement were restricted to the femoral (86.7%) and brachial (13.3%) areas. The drug involved was buprenorphine (Subutex) in all cases. Pain over the limb swelling (100%), pulsatility (60%), and symptoms suggestive of septicemia (46.7%) were the most common symptoms. Staphylococcus aureus was present in 93.3%. Diagnosis was achieved clinically in 26.7%, by duplex ultrasonography in 60.0%, and by computed tomography (CT) angiography in 13.3%. In the two patients with brachial pseudoaneurysms, the brachial artery was ligated in one, and a basilic vein patch was used in the other. In the 13 patients with femoral pseudoaneurysms, the pseudoaneurysm was ligated and excised in 8 (61.5%), and immediate reconstructive bypass surgery was performed in 5 (38.5%). Two patients had critical ischemia after ligation and required reconstructive bypass surgery a few weeks later. Postoperative complications included claudication, digital gangrene, localized wound infection, and rebleeding. There was no associated mortality. CONCLUSIONS: Pseudoaneurysm from intravenous drug abuse continues to pose significant challenges to surgeons worldwide, ranging from an accurate diagnosis to the choice of surgery. The aims of surgery must be to achieve adequate débridement and control infection and hemorrhage. Any associated postoperative complications must be identified and dealt with.

An Overview of Maxillofacial Trauma in Oral and Maxillofacial Tertiary Trauma Centre, Queen Elizabeth Hospital, Kota Kinabalu, Sabah.

The aims of this study were to provide an overview of maxillofacial trauma and its relationship to patient's demographic data and alcohol consumption within the state of Sabah. It was a retrospective study of maxillofacial trauma cases treated by Oral and Maxillofacial Surgery Department, Queen Elizabeth Hospital, Kota Kinabalu, Sabah, from January 1, 2009, until December 31, 2013. A total of 630 maxillofacial trauma cases were included. Details of the trauma were collected from patients' record, including patients' cause of injuries, injuries suffered, treatment indications, and treatment received. Patients' demographic data (age, gender), alcohol consumption in relation to causes, and type of maxillofacial injury were analyzed. There were 538 male (85.4%) and 92 female (14.6%) patients (ratio: 5.8:1), with mean age of 31.0 years. Most common causes of maxillofacial injury were motor vehicle accident (MVA; 66.3%), followed by fall (12.4%) and assault (11.6%). Motorcyclists made up more than half of the total cases (53.1%). Cases referred were primarily due to soft-tissue injury (458 cases). Other cases were dentoalveolar and maxillofacial bone fractures. Treatment provided for the fractures included open reduction and internal fixation (22.9%), closed reduction (28.7%), and conservative management (48.4%). Toilet and suturing were done for all patients with soft-tissue injury. Maxillofacial trauma is a major problem in Sabah. It affects mostly males in the age group of 21 to 30 years. Most of the MVA patients were motorcyclists. Mandibular fracture with parasymphysis involvement recorded the highest number. Most of the patients preferred conservative management, probably due to financial and logistic issue.

Polarization-independent vertical coupler for photonics integration.

We present the first systematic design approach for compact polarization-independent mode-size transformers based on tapered resonant vertical couplers with transfer efficiencies greater than 90%. Resonant coupling occurs at a critical taper width having equal TE and TM effective index. Being polarization-independent broadens the usefulness of vertical coupler as a building block for minimizing insertion loss in photonic integrated circuits.

Transformation between directional couplers and multi-mode interferometers based on ridge waveguides.

We present a unique comparison of ridge-type directional couplers (DC) and multi-mode interferometers (MMI) in terms of their transformational relationship. The two devices are intimately related as the MMI is derived from the DC. We show for the first time the continuous evolution from the two-mode coupling characteristic of DC to the multimode mixing and interference characteristic of MMI, as the DC is structurally transformed into the MMI. We also show that DC can be designed to have the MMI features of compactness and polarization-insensitivity, two traits that reflect their shared lineage. However, the design of DC requires careful control of a large set of design parameters, while the MMI design is more robust and involves fewer design variables.

Light extraction--a practical consideration for a plasmonic nano-ring laser.

An integrated semiconductor plasmonic nano-ring laser with a connecting output plasmonic waveguide for light extraction is proposed, designed and demonstrated numerically. The maximum light extraction efficiency can be up to 56%. The design was optimized with 2D FDTD and verified with 3D FDTD methods, where close agreement is shown between the two.

New hope for an old cure: a pilot animal study on selective venesection in attenuating the systemic effects of ischaemic-reperfusion injury.

INTRODUCTION: Reperfusion of acutely ischaemic tissue may, paradoxically, lead to systemic complications. This phenomenon is believed to be initiated by humoral factors that have accumulated in the ischaemic tissue. The ancient art of venesection may reduce the load of these mediators at the point of reperfusion. The aim of this study is to test if selective venesection, by removing the initial venous return from the ischaemic tissue, can attenuate the systemic effects of the ischaemic-reperfusion injury using a porcine model of acute limb ischaemia. MATERIALS AND METHODS: The right femoral arteries of anaesthetised female pigs were clamped. Twelve pigs were divided into 2 groups (n = 6 per group). In the treatment group, 5% of blood volume was venesected from the ipsilateral femoral vein upon reperfusion; the other arm served as control. The animals were sacrifi ced after 4 days for histological examination. A pathologist, blinded to the experimental groups, graded the degree of microscopic injury. RESULTS: For the control group, the kidneys showed glomeruli and tubular damage. The livers demonstrated architectural distortion with cellular oedema. There was pulmonary oedema as well as extensive capillary congestion and neutrophil infiltration. Such findings were absent or reduced in the venesected animals. Consequently, the injury scores for the kidney, lung, liver and heart were significantly less for the venesected animals. CONCLUSION: Selective venesection reduces the remote organ injuries of the ischaemic-reperfusion phenomenon.

Argon-plasma-induced InAs/InGaAs/InP quantum dot intermixing.

We report the first study of argon (Ar)-plasma-enhanced intermixing of InAs/InGaAs/InP self-assembled quantum dots (QDs) in an inductively coupled plasma reactive ion etch system. The Ar-plasma exposure creates point defects, which propagate into the QD structure and enhance the intermixing between the QDs and their barrier layers, hence tuning the energy bandgap of the QDs. By optimizing the plasma exposure time and the annealing temperature, we observe (i) a blueshift of 160 nm and an increase in the photoluminescence (PL) intensity of the QD samples immediately after Ar-plasma exposure for 90 s, and (ii) a further increase in the blueshift of 330 nm, accompanied by 2.5-times increase in the PL intensity and 37 nm narrowing in the PL linewidth after subsequent rapid thermal annealing at 720 °C. The ability to generate a large blueshift without degrading the material quality shows that Ar-plasma exposure is an efficient post-growth technique for tuning the energy bandgap of QD structures.

High-index-contrast waveguides and devices.

We present a theoretical and experimental study of high-index-contrast waveguides and basic (passive) devices built from them. Several new results are reported, but to be more comprehensive we also review some of our previous results. We focus on a ridge waveguide, whose strong lateral confinement gives it unique properties fundamentally different from the conventional weakly guiding rib waveguides. The ridge waveguides have distinct characteristics in the single-mode and the multimode regimes. The salient features of the single-mode waveguides are their subwavelength width, strong birefringence, relatively high propagation loss, and high sensitivity to wavelength as well as waveguide width, all of which may limit device performance yet provide new opportunities for novel device applications. On the other hand, wider multimode waveguides are low loss and robust. In addition, they have a critical width where the birefringence is minimal or zero, giving rise to the possibility of realizing intrinsically polarization-independent devices. They can be made effectively single mode by employing differential leakage loss (with an appropriate etch depth) or lateral mode filtering (with a taper waveguide). Together these waveguides provide the photonic wire for interconnections and the backbone to build a broad range of compact devices. We discuss basic single-mode devices (based on directional couplers) and multimode devices (multimode interferometers) and indicate their underlying relationship.