Spatial-Mode Discrimination in Guided and Antiguided Arrays of Long-Wavelength VCSELs

Three means of optical confinement imposed on InAlGaAs/InP 1.3 mu m VCSEL arrays are investigated with self-consistent numerical model of laser operation. Laterally patterned tunnel junction (TJ), in-build guiding realized with air-gap patterning, and antiguiding schemes are investigated and optimized to achieve single-mode operation. The analysis shows that mode discrimination in laterally patterned TJ is very responsive to the injected current, the air-gap patterning reduces influence of the working conditions and supports multimode operation, and finally, antiguiding schemes provide single-mode operation for prescribed geometrical design

Nearly total optical transmission of linearly polarized light through transparent electrode composed of GaSb monolithic high-contrast grating integrated with gold

Achieving high transmission of light through a highly conductive structure implemented on a semiconductor remains a challenge in optoelectronics as the transmission is inevitably deteriorated by absorption and Fresnel reflection. There have been numerous efforts to design structures with near-unity transmission, yet they are typically constrained by a trade-off between conductivity and optical transmission. To address this problem, we propose and demonstrate a transmission mechanism enabled by a monolithic GaSb subwavelength grating integrated with Au stripes (metalMHCG). Near-unity transmission of polarized light is achieved by inducing low-quality factor resonance in the air gaps between the semiconductor grating stripes, which eliminates light absorption and reflection by the metal. Our numerical simulation shows 97% transmission of transverse magnetic polarized light and sheet resistance of 2.2 ωSq-1. The metalMHCG structure was realized via multiple nanopatterning and dry etching, with the largest transmission yet reported of ∼90% at a wavelength of 4.5 μm and above 75% transmission in the wavelength range from 4 to 10 μm and sheet resistance at the level of 26 ωSq-1. High optical transmission is readily achievable using any high refractive index materials employed in optoelectronics. The design of the metalMHCG is applicable in a wide electromagnetic spectrum from near ultraviolet to infrared.Agency for Science, Technology and Research (A*STAR)Published versionThis work is supported by A*STAR (SERC 1720700038 and A1883c0002), Singapore, Narodowe Centrum Badań i Rozwoju (NCBR) (HybNanoSens no. DZP/ POL-SINIV/283/2017) and Narodowe Centrum Nauki (OPUS 018/29/B/ST7/01927)

Vertical cavity surface emitting laser cavity with low thermal impedance

The present invention concerns new designs of VCLs with high contrast gratings (HCG) combined with diamond layer as a bottom mirror. They can be realized either with a classical V-shaped pumping scenario, or through the introduction of the pumping beam from the bottom direction, through the HCG that can be designed to be transparent at the wavelength of the pumping light. They can also be completed by a HCG combined with diamond layer as top mirror, reflecting the pump diode laser and transparent to the VCL emission in the case the pumped and emitted beams are collinear

Electrically Pumped Vertical-External-Cavity Surface-Emitting Lasers With Patterned Tunnel Junction for Single Transversal-Mode Emission

This paper reports on a numerical analysis of methods for current injection into AlInGaAs/InP tunnel-junction electrically pumped vertical-external-cavity surface-emitting lasers. The tunnel junction is patterned to minimize the current crowding effect and support the fundamental transverse modes. Optimization of the tunnel junction radius predicts 9-mW emission and 4% wall-plug efficiency in the single-mode regime. Additional patterning of the tunnel junction in the form of a coaxial ring, without modifying its total radius but reducing its area, maintains or improves the emitted power and in addition enhances wall-plug efficiency by around 60%. A design of E-VECSEL is proposed which offers five times larger emitted power and wall-plug efficiency in the single-mode regime in comparison to recently reported experimental devices

Standard B presentation vs. contrast-enhanced ultrasound (US-CE) : a comparison of usefulness of different ultrasonographic techniques in the evaluation of the echo structure and size of haematomas in post-renal transplant patients : a preliminary report

Background: During routine ultrasonographic examination in B presentation, performed as a standard diagnostic procedure during the early post-operative period, the most important problem with the interpretation of the images of perirenal haematoma is their ability to change in time. The aim of this work was to assess the echogenicity and the size of perirenal haematomas in patients after kidney transplant during routine examinations in B presentation and during examinations enhanced with a contrast medium (CE-US). Material/Methods: Thirty-seven patients after kidney transplant were examined using standard examination in B presentation. Sixteen patients (7 women and 9 men) with isoechogenic and hypoechogenic areas visualized within the renal parenchyma, who were suspected of perirenal haematoma, underwent a CE-US examination after intravenous administration of sculpture hexafluoride (dose: 2.4 ml/ examination). Using time-intensity curves (TIC), changes in the values were analysed for two areas of interest (ROI): in the renal parenchyma and in the areas identified during standard US as haematomas. Identical examination protocols and dynamic data loops allowed the acquisition of identical kidney cross-sections and enabled measuring the echogenicity and thickness of the abnormalities at the same location. Results: During the routine B presentation examination, the average difference between haematoma and the renal cortex was 5 dB. When performing US-CE examination, a significantly greater difference in echogenicity was observed and reached 31 dB. In six patients, the size of haematomas was comparable using both techniques, whereas in ten patients lesions visualized in B presentation were smaller than in the US-CE examination. Conclusions: The US-CE examination demonstrated a greater, statistically significant, difference in the echogenicity of perirenal haematomas compared to the routine examination in B presentation. This method enabled a more detailed assessment of the size of haematomas in the perirenal space that appeared during early post-operative period

Low temperature Raman spectra of cyanobutadiyne (HC5N)

WOS:000308855000037International audienceLow temperature Raman scattering spectra of cyanobutadiyne, either condensed from the vapour as a solid film, or isolated in a cryogenic argon matrix, have been measured - leading to the identification of all vibrational fundamentals, together with several overtones and combination modes. The analysis is based on previous experimental data, including the vibrationally resolved phosphorescence spectra, and on the comparison to available theoretical predictions. (C) 2012 Elsevier B.V. All rights reserved