Optical mode size control by MgO indiffusion in Ti:LiNbO3 waveguides

In this paper, the use of magnesium oxide (MgO) indiffusion in combination with Ti:LiNbO<sub>3</sub> through appropriate control of pre- and post-diffusion parameters is investigated as a way of controlling optical mode size. The co-diffusion of pre-patterned Ti with various patterned MgO films on LiNbO<sub>3</sub> has been compared experimentally. This method has been applied to study straight waveguides and couplers. The waveguides were optically characterized by near-field mode size and loss measurements methods at a wavelength of 1.55 μm. Reduction of inter-mode coupling between adjacent waveguides with the introduction of MgO has been observed

Using Coded Excitation to maintain Signal to Noise for FMC+TFM on Attenuating Materials

Ultrasonic Non-Destructive Evaluation using Full Matrix Capture (FMC) and Total Focusing Method (TFM) is used for high resolution imaging as every pixel is in optimal focus. FMC excites one element in turn, so operates with lower transmitted energy compared to phased array beamforming. The energy at a reflector is further reduced by the broad directivity pattern of the single element. The large number of Tx/Rx A-scans that contribute to each pixel recover the Signal-to-Noise Ratio (SNR) in the final TFM image. Maintaining this in the presence of attenuating materials is a challenge because relevant information in each A-scan signal is buried in the thermal noise, and the TFM process assumes no quantization effects in the Analogue-to-Digital Converters (ADCs) in each receiver. In-process inspection during Additive Manufacturing (AM) requires ultrasonic array sensors that can tolerate high temperatures, scan over rough surfaces and leave no residue. Dry-coupled wheel probes are a solution, but the tire rubbers are often highly attenuating, causing a problem for FMC+TFM needed to adapt the focus through the rough surface. Common approaches to maintain the SNR are to drop the frequency or to average over multiple transmissions, but these compromise resolution and acquisition rate respectively. In this paper, the application of coded excitation to maintain the SNR in the presence of high signal attenuation is explored

MIMO Visible Light Communications Using a Wide Field-of-View Fluorescent Concentrator

This letter reports a demonstration of a 2 x 2 multiple-input multiple-output (MIMO) indoor visible-light communication (VLC) system using a novel fluorescent optical concentrator-based receiver. This potentially allows a high degree of spatial multiplexing to be achieved using a simple receiver structure that can have a wide field-of-view. Details of a two-channel MIMO VLC system that operates at 32 Mb/s with a receiver acceptance angle of ±22.5° are given, and future directions are discussed.PostprintPeer reviewe

Barrierless slow dissociation of photogenerated charge pairs in high-performance polymer-fullerene solar cells

The work in St Andrews was supported by the Engineering and Physical Sciences Research Council (grants EP/L017008/1, EP/J009016/1 and EP/G03673X/1) and the European Research Council (grant 321305). The work in Vilnius was supported by the Research Council of Lithuania (project MIP-85/2015). I.D.W.S. acknowledges support from a Royal Society Wolfson Research Merit Award. D.A.V. is grateful to Supergen SuperSolar Hub for the travel grant. The research data supporting this publication can be accessed at http://dx.doi.org/10.17630/7ec84b4b-d2ab-493c-aaf6-5503a44c0eb5Broadband transient absorption spectroscopy is combined with ultrafast carrier drift measurements to study dissociation of photogenerated charge pairs in efficient photovoltaic blends of the electron donating polymer PTB7 with the acceptor PC71BM. A high ensemble-average mobility sum of electrons and holes is observed which is independent of applied electric field above 12 V/μm and indicates nearly barrier-less pair dissociation at room temperature on a picosecond time scale. High efficiency of pair dissociation in this material is achieved by a combination of high electron mobility in fullerene clusters and hole delocalization along the polymer chain which increases by 30% during dissociation. Our results suggest a predominantly diffusive charge pair dissociation mechanism which requires persistent mobility of both carriers and preferably some delocalization of at least one of them.PostprintPostprintPeer reviewe

Visible Light Communication Using a Blue GaN μLED and Fluorescent Polymer Color Converter

This letter presents a novel technique to achieve high-speed visible light communication (VLC) using white light generated by a blue GaN mu LED and a yellow fluorescent copolymer. We generated white light suitable for room illumination by optimizing the ratio between the blue electroluminescence of the mu LED and yellow photoluminescence of the copolymer color converter. Taking advantage of the components' high bandwidth, we demonstrated 1.68 Gb/s at a distance of 3 cm (at 240 lx illumination). To the best of our knowledge, this is the fastest white light VLC results using a single blue LED/color converter combination.PostprintPeer reviewe

In-process calibration of a non-destructive testing system used for in-process inspection of multi-pass welding

In multi-pass welding, there is increasing motivation to move towards in-process defect detection to enable real-time repair; thus avoiding deposition of more layers over a defective weld pass. All defect detection techniques require a consistent and repeatable approach to calibration to ensure that measured defect sizing is accurate. Conventional approaches to calibration employ fixed test blocks with known defect sizes, however, this methodology can lead to incorrect sizing when considering complex geometries, materials with challenging microstructure, and the significant thermal gradients present in materials during the inter-pass inspection period. To circumvent these challenges, the authors present a novel approach to calibration and introduce the concept of in-process calibration applied to ultrasonic Non-Destructive Testing (NDT). The new concept is centred around the manufacturing of a second duplication sample, containing intentionally-embedded tungsten inclusions, with identical process parameters as the main sample. Both samples are then inspected using a high-temperature robotic NDT process to allow direct comparative measurements to be established between the real part and the calibration sample. It is demonstrated that in-process weld defect detection using the in-process calibration technique can more reliably identify defects in samples which would otherwise pass the acceptance test using a traditional calibration

Flexible Glass Hybridized Colloidal Quantum Dots for Gb/s Visible Light Communications

Color converting films of colloidal quantum dots (CQDs) encapsulated with flexible glass are integrated with microsize GaN LEDs (μLEDs) in order to form optical sources for high-speed visible light communications (VLC). VLC is an emerging technology that uses white and/or colored light from LEDs to combine illumination and display functions with the transmission of data. The flexible glass/CQD format addresses the issue of limited modulation speed of typical phosphor-converted LEDs while enhancing the photostability of the color converters and facilitating their integration with the μLEDs. These structures are less than 70 μm in total thickness and are directly placed in contact with the polished sapphire substrate of 450-nm-emitting μLEDs. Blue-to-green, blue-to-orange and blue-to-red conversion with respective forward optical power conversion efficiencies of 13%, 12% and 5.5% are reported. In turn, free-space optical communications up to 1.4 Gb/s VLC is demonstrated. Results show that CQD-converted LEDs pave the way for practical digital lighting/displays with multi-Gb/s capability

Impacts of Hurricanes Katrina and Rita on the microbial landscape of the New Orleans area

Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of National Academy of Sciences of the USA for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 104 (2007): 9029-9034, doi:10.1073/pnas.0610552104.Floodwaters in New Orleans from Hurricanes Katrina and Rita were observed to contain high levels of fecal indicator bacteria and microbial pathogens, generating concern about long-term impacts of these floodwaters on the sediment and water quality of the New Orleans area and Lake Pontchartrain. We show here that fecal indicator microbe concentrations in offshore waters from Lake Pontchartrain returned to prehurricane concentrations within 2 months of the flooding induced by these hurricanes. Vibrio and Legionella species within the lake were more abundant in samples collected shortly after the floodwaters had receded compared with samples taken within the subsequent 3 months; no evidence of a long-term hurricane-induced algal bloom was observed. Giardia and Cryptosporidium were detected in canal waters. Elevated levels of fecal indicator bacteria observed in sediment could not be solely attributed to impacts from floodwaters, as both flooded and nonflooded areas exhibited elevated levels of fecal indicator bacteria. Evidence from measurements of Bifidobacterium and bacterial diversity analysis suggest that the fecal indicator bacteria observed in the sediment were from human fecal sources. Epidemiologic studies are highly recommended to evaluate the human health effects of the sediments deposited by the floodwaters.This work was funded by NSF-NIEHS Oceans and Human Health Program (NSF OCE0432368, OCE0432479, OCE0430724 and NIEHS P50 ES12736, ES012740, ES012742), the NSF-SGER Program (OCE 0554402, OCE 0554674, OCE 0554850, OCE0600130), the NSF-REU Program, and by the Georgia Sea Grant College Program (NA04OAR170033)

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments:A review

The term “Total petroleum hydrocarbons” (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research. © 2021 Elsevier B.V

Ultra-wide coverage VLC system with alignment-free receiver

In this work we present an ultra-wide coverage visible light communication (VLC) system based on a mechanical beam steering system at the transmitter terminal and a fluorescent optical concentrator at the receiver. The transmitter and receiver full field of view (FFOV) are 100° and 120°, respectively. The coverage area of the transmitter system at 2m is 12.5m2 and a data link of 300Mbps has been achieved at this range.Postprin