Novel Sampled Grating Design for High Precision, Multiple Wavelength DFB Laser Arrays

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Laterally-Coupled Dual-Grating Distributed Feedback Lasers for Generating Mode-Beat Terahertz Signals

We present a laterally-coupled AlGaInAs/InP DFB laser emitting two longitudinal modes simultaneously within the same cavity and integrated with EAM. A stable 0.82 THz beating signal was observed over a wide range of bias parameters

Micromanipulation of InP lasers with optoelectronic tweezers for integration on a photonic platform

The integration of light sources on a photonic platform is a key aspect of the fabrication of self-contained photonic circuits with a small footprint that does not have a definitive solution yet. Several approaches are being actively researched for this purpose. In this work we propose optoelectronic tweezers for the manipulation and integration of light sources on a photonic platform and report the positional and angular accuracy of the micromanipulation of standard Fabry-Pérot InP semiconductor laser die. These lasers are over three orders of magnitude bigger in volume than any previously assembled with optofluidic techniques and the fact that they are industry standard lasers makes them significantly more useful than previously assembled microdisk lasers. We measure the accuracy to be 2.5 ± 1.4 µm and 1.4 ± 0.4° and conclude that optoelectronic tweezers are a promising technique for the micromanipulation and integration of optoelectronic components in general and semiconductor lasers in particular

A Low Cost Technique for Adding Microlasers to a Silicon Photonic Platform

In this paper we report the physical micromanipulation of standard InP telecommunications laser die in a liquid medium by means of optoelectronic tweezers. Optoelectronic tweezers have been shown to use much less optical power than optical tweezers, they do not require a coherent light source to function and the creation of multiple traps is straightforward. These properties make the technique a very good candidate for the massive parallel micromanipulation of optoelectronic components for assembly on a photonic platform. We discuss the positional and orientation accuracy of the optoelectronic tweezers in relation to the alignment requirements for low-loss coupling between the light sources and the other components in a photonic platform. Our experiments indicate that the accuracy is better than 2 µm and 2◦ for translations and rotations, respectively

Cross-sectional Nanoscale Resolution Mapping of Potential and Current Distribution in 3D Structure of Vertical Cavity Surface Emitting Laser iii-v Nanostructures

Vertical cavity surface emitting lasers (VCSELs) hold a major promise in the telecommunication and data interfacing due to their efficient manufacturing pathways and prospects of seamless integration with microelectronics components. VCSEL structures include multilayer Distributed Bragg Reflection (DBR) surrounding an active cavity that typically have multiple quantum wells (QWs) and in some devices quantum dots (QDs) layers [2]. The properties, morphology and quality of multiple buried layers and interfaces are crucial for the development of novel devices, improving device performance and optimization of production processes. Unfortunately, accessing these layers to explore these generally three-dimensional (3D) structures is often a laborious (e.g. via cross-sectional transmission or scanning electron microscopies, EMs) task. Significantly, the sample preparation can also change properties of the material and the device studied (e.g. Ga ion implantation during FIB milling) and usually allows to see only a very limited part of the wafer. Furthermore, the EM does not allow to access local physical properties of the device – such as local electric potential, current density and heat generation, all being extremely crucial to the device performance. Here we report for the first time the direct observation of local electric potential and conductance in the bulk of VCSEL stack by using combination of the Ar-ion beam exit cross-section polishing (BEXP) that creates an oblique section with sub-nm surface roughness through the VCSEL structure [2] combined with the material sensitive scanning probe microscopy (SPM). We used three different SPM measurement modes – nanomechanical local elastic moduli mapping via Ultrasonic Force Microscopy (UFM), surface potential mapping via Kelvin Probe Force Microscopy (KPFM) [3] and mapping of injected current (local conductivity) via Scanning Spreading Resistance Microscopy (SSRM). These allowed to observe the resulting geometry of the device, including active cavity MQW, and to obtain profiles of differential doping of the DBR stack, profile of electric potential in the active cavity, and spatial variation of current injection in the individual QW in MQW area. In conclusion, this approach opens unique novel possibility to directly explore the physical phenomena of operation of VCSELs and other iii-v devices, helping to advance the manufacturing of these these devices, as well as opening insight into the fundamental electronic and atomistic phenomena in these complex nanostructured materials [4]

3D mapping of nanoscale physical properties of VCSEL devices

There is clear lack of methods that allows studies of the nanoscale structure of the VCSEL devices1 that are mainly focused on the roughness of the DBR, or using FIB cross-sectioning and TEM analysis of failed devices to observe the mechanism of the degradation. Here we present a recently developed advanced approach that combines Ar-ion nano-cross-sectioning with material sensitive SPM2 to reveal the internal structure of the VCSEL across the whole stack of top and bottom DBR including active area. We report for the first time the direct observation of local mechanical properties, electric potential and conductance through the 3D VCSEL stack. In order to achieve this, we use beam exit cross-section polishing that creates an oblique section with sub-nm surface roughness through the whole VCSEL structure that is fully suitable for the subsequent cross-sectional SPM (xSPM) studies. We used three different SPM measurement modes – nanomechanical local elastic moduli mapping via Ultrasonic Force Microscopy (UFM) 3, surface potential mapping via Kelvin Probe Force Microscopy (KPFM) and mapping of injected current (local conductivity) via Scanning Spreading Resistance Microscopy (SSRM). xSPM allowed to observe the resulting geometry of the whole device, including active cavity multiple quantum wells (MQW), to obtain profiles of differential doping of the DBR stack, profile of electric potential in the active cavity, and spatial variation of current injection in the individual QW in MQW area. Moreover, by applying forward bias to the VCSEL to initiate laser emission, we were able to observe distribution of the potential in the working regime, paving the way to understanding the 3D current flow in the complete device. Finally, we use finite element modelling (FEM) that confirm the experimental results that of the measurements of the local doping profiles and charge distribution in the active area of the VCSEL around the oxide current confinement aperture. While we show that the new xSPM methodology allowed advanced in-situ studies of VCSELs, it establishes a highly efficient characterisation platform for much broader area of compound semiconductor materials and devices. REFERENCES. 1. D. T. Mathes, R. Hull, K. Choquette, K. Geib, A. Allerman, J. Guenter, B. Hawkins and B. Hawthorne, in Vertical-Cavity Surface-Emitting Lasers Vii, edited by C. Lei and S. P. Kilcoyne (2003), Vol. 4994, pp. 67-82. 2. A. J. Robson, I. Grishin, R. J. Young, A. M. Sanchez, O. V. Kolosov and M. Hayne, Acs Applied Materials & Interfaces 5 (8), 3241-3245 (2013). 3. J. L. Bosse, P. D. Tovee, B. D. Huey and O. V. Kolosov, Journal of Applied Physics 115 (14), 144304 (2014)

COVID 19:Seroprevalence and vaccine responses in UK dental care professionals

Dental care professionals (DCPs) are thought to be at enhanced risk of occupational exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, robust data to support this from large-scale seroepidemiological studies are lacking. We report a longitudinal seroprevalence analysis of antibodies to SARS-CoV-2 spike glycoprotein, with baseline sampling prior to large-scale practice reopening in July 2020 and follow-up postimplementation of new public health guidance on infection prevention control (IPC) and enhanced personal protective equipment (PPE). In total, 1,507 West Midlands DCPs were recruited into this study in June 2020. Baseline seroprevalence was determined using a combined IgGAM enzyme-linked immunosorbent assay and the cohort followed longitudinally for 6 mo until January/February 2021 through the second wave of the coronavirus disease 2019 pandemic in the United Kingdom and vaccination commencement. Baseline seroprevalence was 16.3%, compared to estimates in the regional population of 6% to 7%. Seropositivity was retained in over 70% of participants at 3- and 6-mo follow-up and conferred a 75% reduced risk of infection. Nonwhite ethnicity and living in areas of greater deprivation were associated with increased baseline seroprevalence. During follow-up, no polymerase chain reaction–proven infections occurred in individuals with a baseline anti–SARS-CoV-2 IgG level greater than 147.6 IU/ml with respect to the World Health Organization international standard 20-136. After vaccination, antibody responses were more rapid and of higher magnitude in those individuals who were seropositive at baseline. Natural infection with SARS-CoV-2 prior to enhanced PPE was significantly higher in DCPs than the regional population. Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 mo after initial sampling and 9 mo from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech 162b vaccine is associated with an antibody response indicative of immunological memory

Adaptive optical interconnects: The ADDAPT project

Existing optical networks are driven by dynamic user and application demands but operate statically at their maximum performance. Thus, optical links do not offer much adaptability and are not very energy-effcient. In this paper a novel approach of implementing performance and power adaptivity from system down to optical device, electrical circuit and transistor level is proposed. Depending on the actual data load, the number of activated link paths and individual device parameters like bandwidth, clock rate, modulation format and gain are adapted to enable lowering the components supply power. This enables exible energy-efficient optical transmission links which pave the way for massive reductions of CO2 emission and operating costs in data center and high performance computing applications. Within the FP7 research project Adaptive Data and Power Aware Transceivers for Optical Communications (ADDAPT) dynamic high-speed energy-efficent transceiver subsystems are developed for short-range optical interconnects taking up new adaptive technologies and methods. The research of eight partners from industry, research and education spanning seven European countries includes the investigation of several adaptive control types and algorithms, the development of a full transceiver system, the design and fabrication of optical components and integrated circuits as well as the development of high-speed, low-loss packaging solutions. This paper describes and discusses the idea of ADDAPT and provides an overview about the latest research results in this field

A realist evaluation of an enhanced court‐based liaison and diversion service for defendants with neurodevelopmental disorders

Background: In England, court‐based mental health liaison and diversion (L&D) services work across courts and police stations to support those with severe mental illness and other vulnerabilities. However, the evidence around how such services support those with neurodevelopmental disorders (NDs) is limited. Aims: This study aimed to evaluate, through the lens of court and clinical staff, the introduction of a L&D service for defendants with NDs, designed to complement the existing L&D service. Methods: A realist evaluation was undertaken involving multiple agencies based within an inner‐city Magistrates' Court in London, England. We developed a logic model based on the initial programme theory focusing on component parts of the new enhanced service, specifically training, screening, signposting and interventions. We conducted semi‐structured interviews with the court staff, judiciary and clinicians from the L&D service. Results: The L&D service for defendants with NDs was successful in identifying and supporting the needs of those defendants. Benefits of this service included knowledge sharing, awareness raising and promoting good practice such as making reasonable adjustments. However, there were challenges for the court practitioners and clinicians in finding and accessing local specialist community services. Conclusion: A L&D service developed for defendants with NDs is feasible and beneficial to staff and clinicians who worked in the court setting leading to good practice being in place for the defendants. Going forward, a local care pathway would need to be agreed between commissioners and stakeholders including the judiciary to ensure timely and equitable access to local services by both defendants and practitioners working across diversion services for individuals with NDs