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High-speed III-V based avalanche photodiodes for optical communicationsa??the forefront and expanding applications
摘要： Avalanche photodiodes (APDs), i.e., semiconductor devices, which convert and amplify optical signals into electrical signals, are used for optical communications and for imaging and medical applications. The major requirements for APDs in optical communications are high-speed operation for high data rates and high-sensitivity operation for extending the transmission reach. This paper overviews the achievements of high-speed APDs for 100-Gbit/s optical communications, focusing on III-V material systems, which are advantageous in terms of band engineering. The outlook for APDs in future optical communications is also described.
关键词： high-speed operation,high-sensitivity operation,III-V material systems,optical communications,Avalanche photodiodes
更新于2025-09-23 15:19:57
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Construction of Cr2O3:ZnO Nanostructured Thin Film Prepared by Pulsed Laser Deposition Technique for NO2 Gas Sensor
摘要： Rhombohedral structure of chromium oxide (Cr2O3) thin-film doped hexagonal zinc oxide (ZnO) nanoparticles have been prepared using pulsed laser deposition technique at a different weight percent of ZnO from 0 to 9 wt%. The results of X-ray diffraction analysis shown that the doped films are polycrystalline, and the average crystallite size of the synthesized thin films is found to be dependent on the ZnO concentration. The surface morphology of the prepared thin films was characterized by atomic force microscopy. The optical properties are investigated using ultraviolet–visible light (UV–Vis) absorption spectroscopy. The optical bandgap ranged from 2.45 to 2.68 eV, showing the shift towards longer-wavelength compared to bulk Cr2O3 (~ 3 eV). The sensitivity, response, and recovery times of the sensor towards nitrogen dioxide (NO2) gas were studied and discussed. The sensitivity increase with increasing the doping concentration, and started to decrease when ZnO concentrations reach 7 wt%. The optimal ZnO concentrations for NO2 gas sensitivity is 5 wt%, which attain maximum sensitivity of 87.5% at temperature of 523 K.
关键词： Cr2O3:ZnO nanostructure,Structural properties,Optical properties,Gas sensitivity,PLD technique
更新于2025-09-23 15:19:57
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Off-on fluorescent switching of boron-doped carbon quantum dots for ultrasensitive sensing of catechol and glutathione
摘要： A signal-off-on probe of B-doped carbon quantum dot (B-CQD) is developed for ultrasensitive detection of catechol (CC) by fluorescence quenching and glutathione (GSH) by fluorescence recovering without any auxiliary of biomolecules or labeled materials. In this sensing system, the B-CQDs with a high quantum yield of 42% are prepared via a facile hydrothermal method with precursors of citric acid as C source and sodium tetraphenylborate as B source. The microstructure and fluorescence stability of the B-CQDs are investigated. Under the optimum conditions, the B-CQDs are highly sensitive for detecting CC with a linear range of 1-50 nM and a detection limit of 0.25 nM under a typical signal-to-noise ratio of 3 to 1 (S/N=3), and for sensing GSH with a linear range of 2-100 nM and a detection limit of 0.5 nM (S/N=3). Meanwhile, the developed B-CQDs show a good selectivity for sensing CC and GSH under high concentrations of interfering substances, such as biological thiols and amino acids. The B-CQDs are successfully applied to determination of CC in river water and GSH in human serum, where the recoveries are 103.3%-106.0% and 99.8%-106.3% for CC and GSH sensing, respectively. The signal-off-on mechanisms of the B-CQDs sensor are discussed.
关键词： Glutathione,B-doped carbon quantum dot,Sensitivity,Fluorescent sensing,Catechol
更新于2025-09-23 15:19:57
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - An Efficient Algorithm of Explicit Sensitivity Matrix in 3D Marine Controlled-source Electromagnetic Imaging
摘要： In this paper, we set up an e?cient algorithm of the 3D synthetic response and explicit sensitivity matrix of 3D mCSEM inversion in the two di?erent model spaces: block model and pixel model. The Helmholtz equations of coupled electrical scalar-vector potentials with Coulomb gauge is discretized by 3D ?nite volume method at Yee’s staggered girds to form a large, sparse and complex linear system with multi-transmitters. A direct solver PARDISO is used to stably and accurately solve the system. Furthermore, the scattered EM ?elds caused by the conductivity perturbation are also solved by the 3D ?nite volume method based on the scattered scalar-vector potentials at the same Yee’s staggered girds. In order to further enhance the whole computation e?ciency, the interpolation operator and projection operator are advanced to realize directly and fast transformation of the terms on right hands side of discrete systems to the EM ?elds at arbitrary position because the number of receivers is greatly less than that of scattering sources and transmitters. The explicit EM sensitivity matrix in the two di?erent model space will be set up by only addition of a two-matrix multiple. Finally, we investigate the distributing disciplinarian and response characteristics of explicit sensitivity matrix in two di?erent cases for block and pixel inversion.
关键词： finite volume method,block model,pixel model,explicit sensitivity matrix,3D marine controlled-source electromagnetic imaging,PARDISO
更新于2025-09-23 15:19:57
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Method for Measuring the Absolute Spectral Response of Infrared Photodetector Arrays
摘要： Physical and technical aspects of the implementation of an alternative method for measuring the absolute spectral response of infrared photodetector arrays (IR PDA) (current sensitivity spectrum, voltage sensitivity, and quantum efficiency) without the use of spectral instruments are considered. The method is based on multiple measurements of the output signal of all IR array’s photosensitive elements (PSEs) generated by modulated black-body radiation at different temperatures of the black body (BB). The signal is measured against the sum of constant signals from the background radiation, the detector input optical window, the BB radiation modulator, the PSE dark current, and the constant signal of the LSI multiplexer. A system of Fredholm integral equations of the first kind is constructed based on the measured PSE signals. Its left side includes measured BB signals and, the right side, analytical expressions describing these signals. The solution of the system are the absolute values of the above-mentioned spectral components of all PSEs of PDAs. The block diagram of the measurement setup is considered, functional features of its operation are analyzed, and requirements for its blocks are substantiated. Additional advantages of the new method in comparison with the existing methods are presented.
关键词： useful and stray irradiation,current and voltage sensitivity spectra,PSE red boundary histogram,PSE red boundary distribution on IR array area,BB radiation modulation,IR PDA output signal,quantum efficiency spectrum
更新于2025-09-23 15:19:57
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A Procedure for Mitigating the Light Flicker in Office LED Lighting Caused by Voltage Fluctuations
摘要： Progress in the development of LED technologies has reached a state which justifies the replacement of lighting with traditional light sources, not only in new buildings but also in existing, older ones. One of such replacements was used as an example of a lighting flicker study presented in this paper. The results of initial measurements indicated that Rapid Voltage Changes (RVCs) are the cause of light flicker. The procedure was introduced and described in this paper to provide the necessary actions to mitigate the light flicker in LED lighting. In order to fulfil this task, the source of locally induced voltage fluctuations has to be identified. A method of identification was developed and a multi-function office printer was identified as the source of RVCs. Using a less sensitive LED driver, changing the connection point of the interfering device, and improving the electrical installation were considered as a set of possible solutions. Laboratory measurements have shown significant sensitivity of the LED driver to RVCs. The identified source of voltage disturbances was confirmed by a simulation of supply voltage variation in the presence of such device in Matlab Simulink with the use of digital flickermeter.
关键词： voltage fluctuations,light flicker,sensitivity of LED drivers,digital flickermeter,power control with zero voltage crossing
更新于2025-09-23 15:19:57
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Theoretical analysis on SPR based optical fiber refractive index sensor with resonance wavelength covering communication C+L band
摘要： Surface plasmon resonance (SPR) based optical fiber refractive index sensor with resonance wavelength covering communication C+L band with high sensitivity. When the thicknesses of MgO, TeO2 and TiO2 are set at 80nm, 45nm and 40nm respectively, the sensitivity are all larger than 9000nm/RIU, meanwhile the resonance wavelength covers communication C+L band(1530nm-1625nm).
关键词： Oxide,Optical fiber sensor,Sensitivity,Surface plasmon resonance (SPR),Communication C+L band
更新于2025-09-23 15:19:57
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Estimation of power loss spectra in slightly flattened distorted Bragg fiber waveguide
摘要： Dispersion characteristic and fiber loss spectra of a Bragg fiber waveguide having slightly flattened distortion are estimated for sensing applications. The characteristic and optical power loss equations of waveguide are obtained by matching the fields at various boundaries under quarter wave stack conditions. It is found that the optimum power loss is inversely proportional to the ninth power of distortion coefficient. The obtained results show that optimum fiber loss decreases with decrease of refractive index of cladding layer ′ ′b (low refractive index layer) and increase of refractive index of cladding layer ′ ′a (high refractive index layer). Also, fiber losses are estimated with increase of the high and low refractive index cladding layer losses. This loss spectrum of fiber can be considered as sensing signal. Since obtained fiber losses in distorted Bragg fiber are higher than standard Bragg fiber therefore, the sensitivity of proposed structure is higher than the standard Bragg fiber. Also, the sensitivity increases with the increase of refractive index of core medium. These results would be helpful to design a novel highly sensitive sensor based on hollow core distorted Bragg fiber.
关键词： Power losses,Distorted Bragg fiber,Dispersion curve,Sensitivity
更新于2025-09-23 15:19:57
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Device performance of standard strip, slot and hybrid plasmonic ??-ring resonator: a comparative study
摘要： In this paper, we presented three μ-ring resonator structures based on the standard strip, slot and hybrid plasmonic waveguides based on the SOI platform. A standard strip waveguide is formed by depositing a silicon core on a silica substrate. Whereas the slot waveguide is tailored by keeping a narrow air gap between two silicon strip waveguides. Finally, the hybrid plasmonic waveguide is composed of Metal-Air-Silicon structure, where the E-field is significantly enhanced in the narrow air gap. The ring radius is kept at 1.5 μm for the three designs. The transmission spectrum and E-field distribution of these structures are simulated using the finite element method (FEM). Silicon strip waveguide-based ring resonators are easy to fabricate but their sensitivity is quite low as compared to the other two designs. μ-ring resonator based on hybrid plasmonic waveguide shows the best sensitivity of 333.3 nm/RIU. While, slot waveguide based μ-ring resonator showed the best performance in the quality factor, the figure of merits and limit of detection. We believe that this comparative study will facilitate the researchers to choose the suitable waveguide design for ring resonators depending on their preferred application and fabrication technology available.
关键词： Conventional ring resonator,hybrid plasmonic ring resonator,sensitivity,figure of merit,limit of detection,Q-factor,slot ring resonator
更新于2025-09-23 15:19:57
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Investigation into effect of coupled resonance phenomenon towards sensitivity enhancement of SAW conductivity sensors integrated with ZnO nanorods
摘要： In this work, FEM simulation was used to investigate the sensitivity of a one-port surface acoustic wave (SAW) resonator sensor to changes in electrical conductivity of the sensing medium composed of ZnO nanorods offering elastic loading on the surface of the resonator. A system of coupled resonators was formed when the height of the ZnO nanorods attached to the surface of the resonator was adjusted such that the resonant frequency of the nanorod approached the original resonant frequency of the SAW resonator. It was observed that the use of ZnO nanorods of resonant dimensions as sensing medium could enhance the sensitivity of the composite SAW sensor to changes in electrical conductivity of the sensing medium by up to 79 times. The comparatively higher sensitivity of the SAW conductivity sensor utilizing ZnO nanorods at resonant dimensions as sensing medium was attributed to the fact that the system of coupled resonators thus formed operates at a state of high sensitivity to changes induced in piezoelectric stiffening of the substrate during SAW propagation. The observations from FEM simulation conducted in the present work suggests strong prospects for the use of coupled resonance phenomenon at nanoscale for enhancing the sensitivity of conductivity-based SAW gas sensors and UV detectors employing 1-D ZnO nanostructures as sensing medium.
关键词： ZnO nanorods,sensitivity enhancement,SAW resonator,coupled resonance,FEM simulation
更新于2025-09-23 15:19:57