Long wavelength mid-infrared multi-gases spectroscopy using tunable single-mode slot waveguide quantum cascade laser.

Single-mode tunable quantum cascade lasers (QCLs) are promising for high-resolution and highly sensitive trace gases sensing across the mid-infrared (MIR) region. We report on the development of a tunable single-mode slot waveguide QCL array in the long wavelength part of the MIR regime (>12 µm). This laser array exhibits a tuning range of around 12 cm-1, from 735.3 to 747.3 cm-1. Using this developed single-mode tunable QCL, we demonstrate individual gas sensing, yielding the detection limit of 940 ppb and 470 ppb for acetylene and o-xylene, respectively. To verify the potential of the developed QCL array in multi-species gas detection, laser absorption measurements of two mixed gases of acetylene and o-xylene were conducted, showing the absorption features of the corresponding gases agree well with the theoretical predictions.

Widely tunable single-mode slot waveguide quantum cascade laser array.

We report designs and experimental demonstrations of a widely tunable single-mode quantum cascade laser array based on slot waveguide structures in the mid-infrared region. The laser array device realized a continuous tuning range of 71 cm-1 from 9.66 µm to 10.37 µm at 300 K only using the current tuning without any external heatsink temperature adjustments, in good agreement with the design. Stable single-mode operations free of undesired mode-hops have been obtained over the whole tuning range. Another slot waveguide QCL array with a 41 cm-1 continuous tuning range around 7.3 µm has also been realized with the same design principle, demonstrating the universal applicability of the array design. The broadly continuous tuning with simple processing makes the array device a suitable candidate for mid-infrared sensing and spectroscopy application.

Beam combining of a broadly and continuously tunable quantum cascade laser.

We report a cost-efficient method to demonstrate the beam combining of five laser elements in an array of tunable slot waveguide quantum cascade lasers in the mid-infrared region at around 10 µm. An aspherical lens with five fine-tuned mini mirrors was employed to collimate the individual beams from the laser array. To verify the feasibility of this beam combining approach, the combined beams were coupled into a hollow-core fiber gas cell with a low numerical aperture (N.A.) of 0.03 and a coupling efficiency >= 0.82, for gas sensing of binary compound gases of ammonia and ethylene simultaneously.

Integration of an InSb photodetector on Si via heteroepitaxy for the mid-infrared wavelength region.

In this study, InSb p-i-n photodetectors with In0.82Al0.18Sb barrier layers were grown on a (100) 6° offcut Si substrate by heteroepitaxy via an AlSb/GaSb buffer. Based on an interfacial misfit array growth mode, the dislocations at the GaSb/Si and InSb/AlSb interfaces accommodated the lattice mismatch. The In0.82Al0.18Sb barrier layer increased the 77 K R0A of the detector. From 180 K to 300 K, the generation-recombination mechanism dominated the dark current generation in the detector and surface leakage became dominant below 120 K. The detector exhibited a 77 K responsivity of 0.475 A/W and a Johnson-noise-limited detectivity of 3.08 × 109 cmHz1/2W-1 at 5.3 µm.

Integration of InGaAs MOSFETs and GaAs/ AlGaAs lasers on Si Substrate for advanced opto-electronic integrated circuits (OEICs).

Lasers monolithically integrated with high speed MOSFETs on the silicon (Si) substrate could be a key to realize low cost, low power, and high speed opto-electronic integrated circuits (OEICs). In this paper, we report the monolithic integration of InGaAs channel transistors with electrically pumped GaAs/AlGaAs lasers on the Si substrate for future advanced OEICs. The laser and transistor layers were grown on the Si substrate by molecular beam epitaxy (MBE) using direct epitaxial growth. InGaAs n-FETs with an ION/IOFF ratio of more than 106 with very low off-state leakage and a low subthreshold swing with a minimum of 82 mV/decade were realized. Electrically pumped GaAs/AlGaAs quantum well (QW) lasers with a lasing wavelength of 795 nm at room temperature were demonstrated. The overall fabrication process has a low thermal budget of no more than 400 °C.

Monolithic integration of InGaAs n-FETs and lasers on Ge substrate.

We report the first monolithic integration of InGaAs channel field-effect transistors with InGaAs/GaAs multiple quantum wells (MQWs) lasers on a common platform, achieving a milestone in the path of enabling low power and high speed opto-electronic integrated circuits (OEICs). The III-V layers used for realizing transistors and lasers were grown epitaxially on the Ge substrate using molecular beam epitaxy (MBE). A Si-CMOS compatible process was developed to realize InGaAs n-FETs with subthreshold swing SS of 93 mV/decade, ION/IOFF ratio of more than 4 orders of magnitude with very low off-state leakage current, and a peak effective mobility of more than 2000 cm2/V·s. In addition, fabrication process uses a low overall processing temperature (≤ 400 °C) to maintain the high quality of the InGaAs/GaAs MQWs for the laser. Room temperature electrically-pumped lasers with a lasing wavelength of 1.03 µm and a linewidth of less than 1.7 nm were realized.

Epidemiology of paediatric poisoning presenting to a children's emergency department in Singapore over a five-year period.

INTRODUCTION: Paediatric poisoning accounts for 1% of daily emergency department presentations. The aim of this study was to review the characteristics and outcomes of paediatric patients who presented with drug overdose over a five-year period. METHODS: We performed a retrospective review of paediatric poisoning cases at KK Women's and Children's Hospital (KKH), the largest children's public hospital in Singapore, from 1 January 2009 to 31 December 2013. RESULTS: A total of 1,208 cases of poisoning were seen in KKH's Department of Children's Emergency during the study period. The gender distribution was about equal, with a slight male predominance. The majority of the poisoning cases were accidental. Slightly more than half of the intentional ingestions were of paracetamol and the majority were female patients belonging to the 12-16 year age group. The bulk of poisonings occurred in children aged 1-4 via the oral route, slightly more than half of the oral ingestions consisted of oral medications and a sizeable portion were of household liquids. Mothballs and silica gels accounted for almost a quarter of the solid household products ingested. Slightly less than half of the patients required admission and only a small portion of the admitted patients required intensive or high dependency care. CONCLUSION: The prognosis of paediatric patients who presented with poisoning in our study was good, with a short median length of stay for those admitted and no fatalities being reported across the span of five years.