Search

As of 31 October 2023, there have been 771,795,258 confirmed cases of COVID-19 globally. Developing simple, portable, and reliable testing devices has become increasingly important. This paper presents a point-of-care testing (POCT) device for COVID-19 based on the dual-excitation fluorescence RT-LAMP method, which is derived from the principles of RT-LAMP-based COVID-19 detection kits available in the market. The key design solutions of the device were simulated and modeled. Key performance metrics such as detection repeatability and linearity were validated. Comparative experiments with the RT-qPCR detection method were conducted to verify the accuracy and reliability of the device. Additionally, the device's detection sensitivity and accuracy were assessed. Experimental results show that the repeatability coefficient of variation (CV) value is ≤0.09%; the linearity R2 for the FAM channel is 0.9977 and that for the HEX channel is 0.9899; it exhibits good anti-interference performance, with negligible cross-channel interference; the temperature stability is ±0.062 °C, the temperature accuracy is less than 0.2 °C, and there is no significant temperature overshoot during the heating process. Compared with the real-time quantitative PCR (RT-qPCR) instrument, the positive agreement rate is 100% and the negative agreement rate is 95.0%. This research provides a foundational basis for the development of equipment for the prevention of infectious diseases and clinical diagnostics. [ABSTRACT FROM AUTHOR]

Sulfonamides are auspicious chemosensors which are capable to bind with ionic species through various ways like complexation, charge transfer, proton transfer etc. and produce a detection signal in the form of an optical change either in visible or UV-light and for electronic as well as fluorimetric spectra. Sulfonamides have gained much attention of analytical chemists these days as these are inexpensive, robust, green in nature and some what sensitive and selective to many anionic and cationic species. Due to their promising versatility in sensing properties, these are under great consideration in forensic, environmental, analytical and biochemistry laboratories. This review narrates how sulfonamides are being used to optically sense ionic species. HIGHLIGHTS: Optical sensors are of great importance these days because of their optical detection properties rather using Hi-tech techniques. Optical sensors are economical, robust, selective, sensitive and green in nature. The color change, shifts in electronic spectra or alterations in fluorescence pattern may be attributed by interaction between species to be sensed and Sulfonamides by different mechanism i.e. electron transfer, fluorescence energy transfer, charge transfer, hydrogen bonding, etc. LOD data is a proof of their prodigious efficiency of Sulfonamides as optical sensors. [ABSTRACT FROM AUTHOR]

A spacing-adjustable and switchable multi-wavelength erbium-doped fiber laser is proposed and analyzed based on the polarization hole burning (PHB) effect. The comb filter consists of multimode fiber–polarization maintaining fiber–multimode fiber (MMF–PMF–MMF). Here the filter is used as the polarization-dependent element to induce the polarization hole burning (PHB) effect. The filter is placed in the laser cavity or embedded into the Sagnac loop. By adjusting the polarization controller (PC) in the cavity, when the filter is placed in the laser cavity, the output wavelengths can be switched from single-wavelength to sextuple-wavelength, and dual-, triple-, quad-, quintuple- and sextuple-wavelength with adjustable wavelength spacing can be obtained. The dual-wavelength has a substantial amount of wavelength spacing adjustability with the range of 3.32 nm to 30.16 nm. When the filter is embedded into the Sagnac loop, the wavelength tuning ranges for single-, dual-, triple- and quad-wavelength are 28.42 nm, 28.10 nm, 18.21 nm and 14.58 nm, respectively. The proposed erbium-doped fiber laser (EDFL) provides a wide range of wavelengths and adjustable spacing, which is suitable for a variety of applications such as optical communication, optical detection and optical signal processing. [ABSTRACT FROM AUTHOR]

Droplet microfluidics has emerged as a critical component of several high-throughput single-cell analysis techniques in biomedical research and diagnostics. Despite significant progress in the development of individual assays, multiparametric optical sensing of droplets and their encapsulated contents has been challenging. The current approaches, most commonly involving microscopy-based high-speed imaging of droplets, are technically complex and require expensive instrumentation, limiting their widespread adoption. To address these limitations, we developed the OptiDrop platform; this platform is a novel optofluidic setup that leverages the principles of flow cytometry. Our platform enables on-chip detection of the scatter and multiple fluorescence signals from the microfluidic droplets and their contents using optical fibers. The highly customizable on-chip optical fiber-based signal detection system enables simplified, miniaturized, low-cost, multiparametric sensing of optical signals with high sensitivity and single-cell resolution within each droplet. To demonstrate the ability of the OptiDrop platform, we conducted a differential expression analysis of the major histocompatibility complex (MHC) protein in response to IFNγ stimulation. Our results showed the platform's ability to sensitively detect cell surface biomarkers using fluorescently labeled antibodies. Thus, the OptiDrop platform combines the versatility of flow cytometry with the power of droplet microfluidics to provide wide-ranging, scalable optical sensing solutions for research and diagnostics. [ABSTRACT FROM AUTHOR]

Laser-arc hybrid welding (LAHW), being a high-efficiency with excellent properties of high welding speed, deep penetration, and good bridging performance, has been paid close attention by domestic and overseas scholars. So far, the lack of suppression and detection of welding defects is still considered the critical technical obstacle that affects its welding quality, particularly for workpieces with industrial requirements. One vital method to conquer this challenging issue is the visual analysis technique with the combination of numerical simulation technique, which has been researched by abundant study outcomes. The primary target of detecting is to collect basic information and to understand the formation mechanism of welding defects. This review firstly describes welding defects online detection technology, such as high-speed image, electrical signal, acoustical signal, and optical signal detection technology. Then much emphasis has been placed on the internal mechanism of forming welding defects, including undercut, humping, porosity, and spatter defects. Particularly, the defect suppression methods are presented in order to restrain and address the welding defect problems. Finally, the current difficulties and potential remedies are discussed to supply an understanding on what still needs to be improved in the LAHW process. This comprehensive review is to offer guidance for those trying to reduce welding defects as they enhance the welding joints' quality. [ABSTRACT FROM AUTHOR]

Genetic engineering and directed evolution are effective methods for addressing the low yield and poor industrialization level of microbial target products. The current research focus is on how to efficiently and rapidly screen beneficial mutants from constructed large-scale mutation libraries. Traditional screening methods such as plate screening and well-plate screening are severely limited in their development and application due to their low efficiency and high costs. In the past decade, microfluidic technology has become an important high-throughput screening technology due to its fast speed, low cost, high automation, and high screening throughput, and it has developed rapidly. Droplet-based microfluidic high-throughput screening has been widely used in various fields, such as strain/enzyme activity screening, pathogen detection, single-cell analysis, drug discovery, and chemical synthesis, and has been widely applied in industries such as those involving materials, food, chemicals, textiles, and biomedicine. In particular, in the field of enzyme research, droplet-based microfluidic high-throughput screening has shown excellent performance in discovering enzymes with new functions as well as improved catalytic efficiency or stability, acid-base tolerance, etc. Currently, droplet-based microfluidic high-throughput screening technology has achieved the high-throughput screening of enzymes such as glycosidase, lipase, peroxidase, protease, amylase, oxidase, and transaminase as well as the high-throughput detection of products such as riboflavin, coumarin, 3-dehydroquinate, lactic acid, and ethanol. This article reviews the application of droplet-based microfluidics in high-throughput screening, with a focus on high-throughput screening strategies based on UV, visible, and fluorescence spectroscopy, including labeled optical signal detection screening, as well as label-free electrochemical detection, mass spectrometry, Raman spectroscopy, nuclear magnetic resonance, etc. Furthermore, the research progress and development trends of droplet-based microfluidic technology in enzyme modification and strain screening are also introduced. [ABSTRACT FROM AUTHOR]

As of 31 October 2023, there have been 771,795,258 confirmed cases of COVID-19 globally. Developing simple, portable, and reliable testing devices has become increasingly important. This paper presents a point-of-care testing (POCT) device for COVID-19 based on the dual-excitation fluorescence RT-LAMP method, which is derived from the principles of RT-LAMP-based COVID-19 detection kits available in the market. The key design solutions of the device were simulated and modeled. Key performance metrics such as detection repeatability and linearity were validated. Comparative experiments with the RT-qPCR detection method were conducted to verify the accuracy and reliability of the device. Additionally, the device’s detection sensitivity and accuracy were assessed. Experimental results show that the repeatability coefficient of variation (CV) value is ≤0.09%; the linearity R2 for the FAM channel is 0.9977 and that for the HEX channel is 0.9899; it exhibits good anti-interference performance, with negligible cross-channel interference; the temperature stability is ±0.062 °C, the temperature accuracy is less than 0.2 °C, and there is no significant temperature overshoot during the heating process. Compared with the real-time quantitative PCR (RT-qPCR) instrument, the positive agreement rate is 100% and the negative agreement rate is 95.0%. This research provides a foundational basis for the development of equipment for the prevention of infectious diseases and clinical diagnostics.

Lightning flashes are an important source of wildfires worldwide, contributing to the emission of trace gases to the atmosphere. Based on experiments and field observations, continuing currents in lightning have since a long time been proposed to play a significant role in the ignition of wildfires. However, simultaneous detections of optical and radio signals from fire‐igniting lightning confirming the role of continuing currents in igniting wildfires are rare. In this work, we first analyze the optical signal of the lightning‐ignited wildfires reported by the Geostationary Lightning Mapper over the Contiguous United States (CONUS) during the summer of 2018, and we then analyze the optical and the Extremely Low Frequency signal of a confirmed fire‐igniting lightning flash in the Swiss Alps. Despite data uncertainties, we found that the probability of ignition of a lightning flash with Continuing Current (CC) lasting more than 10 ms is higher than that of cloud‐to‐ground lightning in CONUS. Finally, we confirm the existence of a long CC (lasting about 400 ms) associated with a long‐lasting optical signal (lasting between 2 and 4 s) of a video‐recorded fire‐igniting lightning flash. Plain Language Summary: Lightning plays a significant role in causing natural fires. Previous studies have found that a specific type of lightning, known as continuing current lightning (CC), has a higher likelihood of igniting fires. CC lightning refers to a phenomenon where electrical charge continues to flow through the channel for extended periods of tens or hundreds of milliseconds, possibly leading to elevated vegetation temperatures. In our research, we used the optical lightning detections provided by the Geostationary Lightning Mapper to estimate the probability of wildfires associated with both normal lightning and CC lightning across the United States. To gain further insights, we employed a ground camera video and analyzed extremely low‐frequency radio signals to meticulously examine the duration of CC in a lightning strike that ignited a fire in the Alps. The findings of our study demonstrate that the probability of fire occurrence is higher when CC lightning is involved compared to typical lightning strikes. This highlights the importance of understanding the characteristics of lightning and its varying impacts on fire risk assessment. Key Points: The probability of wildfire ignition by cloud‐to‐ground lightning is larger for flashes with Continuing Current (CC)The variation of the lightning ignition efficiency of lightning with CC suggest a significant influence of other factorsThe analysis of one single lightning‐ignited fire in the Alps confirms the presence of a lightning with a long CC [ABSTRACT FROM AUTHOR]

We adopted TiO2 seed layers for thin-film growth of anatase Ti0.95Co0.05O2−δ, a room-temperature ferromagnetic semiconductor, on rigid and flexible (ultrathin) glass substrates. The Ti0.95Co0.05O2−δ thin films with preferred (101) orientation and large crystallographic domains around 50 μm in lateral size showed clear ferromagnetic hysteresis loops in the magnetization curves at 300 K. In addition, their high electrical conductivity and transparency allowed electrical and optical detection of the ferromagnetic signal via the anomalous Hall effect and magneto-optical effect, respectively. Intriguingly, flatter thin films with larger domains were obtained on flexible glass substrates, which were beneficial to achieve higher conductivity and larger anomalous Hall signals, comparable to those in epitaxial thin films. [ABSTRACT FROM AUTHOR]

This paper presents a study of the performances of different Mach–Zehnder modulation technologies with applications in microwave polarimeters based on a near-infrared (NIR) frequency up-conversion stage, allowing for optical correlation and signal detection at a wavelength of 1550 nm. Commercial Mach–Zehnder modulators (MZMs) are traditionally implemented using LiNbO3 technology, which does not enable integration for the fabrication of MZMs. In this work, we propose the use of an alternative technology based on InP, which allows for integration in the fabrication process. In this way, it is possible to obtain advantages in terms of bandwidth, cost, and size reductions, which yield results that are very interesting for wide-band applications such as microwave instrumentation for the study of the cosmic microwave background (CMB). Here, we describe and compare the modulation performances of different MZMs, with one commercial unit presenting a higher bandwidth than those in previous works, and another three InP integrated units provided by the Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institute (HHI). Then, these modulators were coupled to a microwave polarimeter demonstrator, which has also been presented previously, to compare the polarization measurement performances of each of the MZMs. [ABSTRACT FROM AUTHOR]

Accurate detection of weak optical signals is a key function for a wide range of applications. A key performance parameter is the receiver signal-to-noise ratio, which depends on the noise of the photodetector and the following electrical circuitry. The circuit noise is typically larger than the noise of photodetectors that do not have internal gain. As a result, a detector that provides signal gain can achieve higher sensitivity. This is accomplished by increasing the photodetector gain until the noise associated with the gain mechanism is comparable to that of the output electrical circuit. For avalanche photodiodes (APDs), the noise that arises from the gain mechanism, impact ionization, increases with gain and depends on the material from which the APD is fabricated. Si APDs have established the state-of-the-art for low-noise gain for the past five decades. Recently, APDs fabricated from two Sb-based III-V compound quaternary materials, AlxIn1-xAsySb1-y and AlxGa1-xAsySb1-y, have achieved noise characteristics comparable to those of Si APDs with the added benefit that they can operate in the short-wave infrared (SWIR) and extended SWIR spectral regions. This paper describes the materials and device characteristics of these APDs and their performance in different spectral regions. [ABSTRACT FROM AUTHOR]

A concept of a microfluidic fluorescent chemical sensing system is presented and demonstrated as a sensor for measurement of dissolved oxygen in water. The system utilizes on-line mixing of a fluorescent reagent with the analyzed sample, while it measures the fluorescence decay time of the mixture. The system is built entirely out of silica capillaries and optical fibers, and allows for very low consumption of the reagent (of the order of mL/month) and the analyzed sample (of the order of L/month). The proposed system can, thus, be applied to continuous on-line measurements, while utilizing a broad variety of different and proven fluorescent reagents or dyes. The proposed system allows for the use of relatively high-excitation light powers, as the flow-through concept of the system reduces the probability of the appearance of bleaching, heating, or other unwanted effects on the fluorescent dye/reagent caused significantly by the excitation light. The high amplitudes of fluorescent optical signals captured by an optical fiber allow for low-noise and high-bandwidth optical signal detection, and, consequently, the possibility for utilization of reagents with nanosecond fluorescent lifetimes. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) has been widely recognized as a promising technology to improve the transmission capacity of wireless optical communication systems. NOMA considers the principle of successive interference cancellation (SIC) to separate a user's signal at the receiver side. To improve the ability of optical signal detection, we developed a quantum dot (QD) fluorescent concentrator incorporated with multiple-input and single-output (MISO) to realize an uplink NOMA-based optical wireless system. However, inaccurate interference assessment of multiple users using the SIC detection algorithm at the receiver side may lead to more prominent error propagation problems and affect the bit error rate (BER) performance of the system. This research aims to propose a novel recurrent neural network-based guided frequency interference coefficient estimation algorithm in a NOMA visible light communication (VLC) system. This algorithm can improve the accuracy of interference estimation compared with the traditional SIC detection algorithm by introducing interference coefficients. It provides a more accurate reconstruction possibility for level-by-level interference cancellation and weakens the influence of error propagation. In addition, we designed uplink and downlink NOMA-VLC communication systems for experimental validation. When the power allocation ratio was in the range of 0.8 to 0.97, the experimental results of the downlink validated that the BER performance of both users satisfied the forward error correction (FEC) limit with the least squares (LS)-SIC and the long short-term memory recurrent neural networks (LSTM)-SIC detection strategy. Moreover, the BER performance of the LSTM-SIC algorithm was better than that of the LS-SIC algorithm for all users when the power allocation ratio was in the range of 0.92 to 0.93. In particular, our proposed system offered a large detection area of 2 cm2 and corresponding aggregate data rate up to 40 Mbps over 1.5 m of free space by using QDs, and we successfully achieved a mean bit error rate (BER) of 2.3 × 10−3 for the two users. [ABSTRACT FROM AUTHOR]

Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Photonic synapses with the dual function of optical signal detection and information processing can simulate human visual system. However, photonic synapses with selective detection of short‐wavelength infrared (SWIR) light have never been reported, which can not only broaden the human vision region but also integrate neuromorphic computation and infrared optical communication. Here, organic photonic synapses based on a new donor‐acceptor copolymer P1 are fabricated, which exhibit excellent synaptic characteristics with selective detection for SWIR and extremely low energy consumption (2.85 fJ). The working mechanism is rooted in energy level barriers and unbalanced charge transportation. Moreover, these photonic synapses demonstrate excellent performance in multi‐signal logic editing, letter imaging and memory with noise reduction function. This contribution provides ideas of constructing selective‐response synapses for artificial visual system and neuromorphic computing. [ABSTRACT FROM AUTHOR]

Both the possibility of improving biosensor signaling using gene engineering and the availability of effective methods for cell immobilization are the valuable properties of cell-based biosensors [[6]]. In contrast to molecular-based devices, biosensors containing native or recombinant living cells, pieces of tissue, organelles, biomembranes, liposomes or receptors, have some important advantages, including easy isolation and a broad specificity to the studied analytes. Such materials are necessary for the fabrication of traditional devices with improved analytical characteristics, as well as the design and generation of new high-tech biosensors, including piezoelectric, mass-based and nanomechanical sensors amongst other types [[9]]. The broad definition of the term biosensing relates to practically all processes of molecular recognition. [Extracted from the article]

Nonlinear optical imaging is a versatile tool that has been proven to be exceptionally useful in various research fields. However, due to the use of photomultiplier tubes (PMTs), the wide application of nonlinear optical imaging is limited by the incapability of imaging under ambient light. In this paper, we propose and demonstrate a new optical imaging detection method based on optical parametric amplification (OPA). As a nonlinear optical process, OPA intrinsically rejects ambient light photons by coherence gating. Periodical poled lithium niobate (PPLN) crystals are used in this study as the media for OPA. Compared to bulk nonlinear optical crystals, PPLN crystals support the generation of OPA signal with lower pump power. Therefore, this characteristic of PPLN crystals is particularly beneficial when using high-repetition-rate lasers, which facilitate high-speed optical signal detection, such as in spectroscopy and imaging. A PPLN-based OPA system was built to amplify the emitted imaging signal from second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy imaging, and the amplified optical signal was strong enough to be detected by a biased photodiode under ordinary room light conditions. With OPA detection, ambient-light-on SHG and CARS imaging becomes possible, and achieves a similar result as PMT detection under strictly dark environments. These results demonstrate that OPA can be used as a substitute for PMTs in nonlinear optical imaging to adapt it to various applications with complex lighting conditions. [ABSTRACT FROM AUTHOR]

This paper presents a polarization calibration method applied to a microwave polarimeter demonstrator based on a near-infrared (NIR) frequency up-conversion stage that allows both optical correlation and signal detection at a wavelength of 1550 nm. The instrument was designed to measure the polarization of cosmic microwave background (CMB) radiation from the sky, obtaining the Stokes parameters of the incoming signal simultaneously, in a frequency range from 10 to 20 GHz. A linearly polarized input signal with a variable polarization angle is used as excitation in the polarimeter calibration setup mounted in the laboratory. The polarimeter systematic errors can be corrected with the proposed calibration procedure, achieving high levels of polarization efficiency (low polarization percentage errors) and low polarization angle errors. The calibration method is based on the fitting of polarization errors by means of sinusoidal functions composed of additive or multiplicative terms. The accuracy of the fitting increases with the number of terms in such a way that the typical error levels required in low-frequency CMB experiments can be achieved with only a few terms in the fitting functions. On the other hand, assuming that the calibration signal is known with the required accuracy, additional terms can be calculated to reach the error levels needed in ultrasensitive B-mode polarization CMB experiments. [ABSTRACT FROM AUTHOR]

When the high aspect ratio contact, called as HARC, hole dry etching process with a high degree of difficulty is carried out in the high performance memory manufacturing process, there is a problem that the sensitivity of the optical signal detection is low due to the small open ratio and the high aspect ratio of the hole when detecting the etching end point signal using the plasma light emission. In particular, due to the fluorocarbon polymer characteristics of fluorocarbon gas, such as C4F6, C4F8, C3F8, and CH2F2, which is mainly used in the HARC hole dry etching process, the viewport, which is a part to which the optical lens is connected to measure the plasma light emitting signal with optical emission spectroscopy, called as OES, can be contaminated with the fluorocarbon polymer coating. As a result of this viewport clogging phenomenon, the intensity of the optical signal collected gradually decreases during the process (∼4%), and thus the sensitivity of the etching end point signal indicating that the etching process is terminated gradually decreases. In this study, a xenon flashlamp for optical signal compensation was additionally applied to the existing OES structure to improve the detection of the etching end point during the HARC hole dry etching process. This can improve the detection sensitivity of the OES etching end point by monitoring the viewport clogging phenomenon in real time and compensating for the reduction of the collected OES signal. The pattern wafer for testing used to verify the effect of the etching end point consists of a structure in which a mold layer sequentially stacked with Si3N4, SiO2, and SiO2 are mixed as a single layer, and as a result of the experiment, it was confirmed that the detection sensitivity of the etching end point applied with the optical signal compensation method was 18% improved from the signal measured only by the existing OES. The method is expected to improve the detection sensitivity of etching end point during the next generation high difficulty HARC hole etching process to improve the plasma etching process control method. [ABSTRACT FROM AUTHOR]

The use of coherent optical signal processing in long-distance optical communication systems has dramatically increased data capacity enabling encoding of multiple-bit information in the phase of a light beam. Direct detection of phase information of a high-speed modulated light remains challenging and requires an external, local oscillator for referencing, which is expensive for short-reach optical communications, for example, in data centers. The availability of less-complex integrated photonics devices for coherent signal detection will alleviate this bottleneck. On the other hand, phase information of coherent, orthogonally polarized light beams can be extracted from their polarization states, and it is, therefore, possible to achieve phase measurements via fast polarization detection. Here, an on-chip nanodisk device is demonstrated for high-speed coherent optical signal detection enabled by spin–orbit coupling in Si-photonics circuitry. In a coherent communication experiment with up to 32 GBaud rate, the high-speed phase-shift keying and quadrature amplitude modulation signals detected by a Si nanodisk based polarization measurements at multiple wavelengths in the C-band are recovered with a bit error rate below the forward error correction threshold. The proposed on-chip nanodisk device shows promise in high-speed coherent optical communication applications where phase detection is required at low cost and small footprint. [ABSTRACT FROM AUTHOR]

The continuing drive towards broadband access necessitates cost-effective optical access and mobile fronthaul solutions. While the fixed-mobile convergence motivates high-speeds for the antenna remoting through broadband digitized radio-over-fiber, the access segment still uses time division multiplexed access equipment. Although the steadily increasing line rates call for 50 Gb/s solutions, the unshared per-user rate remains in the 1-Gb/s range. It is a question whether such data rate can be facilitated without high-speed components, at the same time supporting higher passive splits for the optical distribution networks. We experimentally demonstrate a simplified receiver based on an electro-absorption modulated laser, co-integrated on a die-level with a transimpedance amplifier. We investigate its sensitivity for the phase-agnostic coherent heterodyne downstream detection of data signals in a passive optical network scenario. We will show that despite the omission of a high-performance local oscillator, balanced detection and digital signal processing, the proposed receiver accomplishes reception of 1 Gb/s phase-modulated signals over a link reach of 57 km and an optical budget of 48 dB, thus enabling high passive splits of 1:128. We study the implications raised by this single-ended coherent receiver architecture under multi-channel transmission and investigate the susceptibility of its integrated local oscillator to optical feedback. [ABSTRACT FROM AUTHOR]

Ultraviolet-visible absorption spectroscopy is widely used to monitor water quality, and rapid optical signal detection is a key technology in the process of spectrum measurement. In this paper, an ultrafast spectrophotometer system that can achieve spectrum data acquisition in a single flash of the xenon lamp (within 200 ns) is introduced, and a real-time denoising method for the spectrum is implemented on a field programmable gate array (FPGA) to work cooperatively with the nanosecond spectrum acquisition system, in order to guarantee the quality of the spectrum signals without losing running speed. The hardware of the data acquisition and processing system are constructed on a Xilinx Spartan 6 FPGA chip and its peripheral circuit, including an analog to digital converter and a complementary metal-oxide-semiconductor transistor (CMOS) sensor's diver circuit. An oversampling method that is suitable for the CMOS sensor's output is proposed, which works on the CMOS sensor's dark current noise and readout noise. Another moving-average filter method is designed adaptively, which works on the low-frequency component to filter out the residual spectrum noise of the spectrum signal. The implementation of the filter on the FPGA has been optimized by using a pipelined structure and dual high-speed random-access memory (RAM). As a result, the CMOS linear image sensor successfully captured the spectrum of xenon flash light at the readout clock frequency of 500 kHz and the processing manipulation to the full UV-Vis spectrum data was accomplished at a sub-microsecond speed performance. After the digital filter and oversampling technology were implemented, the coefficient of variation of the measurements reduced from 9.57% to 1.74%, while the signal noise ratio (SNR) of the absorption spectrum increased nine times, compared to the raw data of the CMOS sensor's output. The tests towards different analyte samples were conducted, and the system shows good performance on distinguishing different concentrations of different analyte solutions on both ultra-violet and visible spectrum bands. The present work showcases the potential of the CMOS sensor's technique for the fast detection of contaminated water containing nitrate and organic compounds. [ABSTRACT FROM AUTHOR]

Recent advancements in radio communication networks and the extensive use of fiber-optic technologies have escalated the demand for efficient photodetectors capable of handling high-frequency optical signals. A primary challenge in this domain is the effective reception and conversion of high-frequency optical signals into electrical signals [1]. To address this issue, this study proposes the development of photodetectors based on gallium-boron-selenium (Ga1-xBxSe) compounds. These photodetectors exhibit photosensitivity in the near-infrared and visible spectra [2], with an anticipated photosignal relaxation time on the order of nanoseconds. Such properties suggest their capability to handle optical signals with frequencies up to 10 THz, converting them effectively into electrical signals. Figure 1 presents the photocurrent kinetics of a Ga0.95B0.05Se crystal under conditions of high optical excitation. The analysis of the photocurrent kinetics reveals that the relaxation time for quasi-equilibrium charge carriers in the Ga0.95B0.05Se crystal is approximately 12 ns. The rapid relaxation is attributed to a recombination portential with a localization depth of 0.9 eV observed within the crystal. This characteristic makes Ga0.95B0.05Se a promising candidate for developing photodetectors capable of operating at gigahertz frequencies. Unlike alternative materials used in photodetector fabrication, Ga1-xBxSe demonstrates a notable resistance to signal distortions during the reception and conversion processes. This material's intrinsic properties extend the high-frequency operational range of the detector into the terahertz spectrum. Consequently, the implementation of Ga1-xBxSe - based photodetectors has the potential to enhance the speed of information transmission across extensive distances, thereby benefiting modern information technology. [ABSTRACT FROM AUTHOR]

In this article, a multifunctional optical processing unit for differential eight phase‐shift‐keying (D8PSK) and differential quadrature phase‐shift‐keying (DQPSK) based on four‐wave mixing (FWM) effects in semiconductor optical amplifier (SOA) is proposed. All‐optical wavelength conversion, D8PSK‐to‐DQPSK format conversion and signal encryption of 10‐Gbaud DQPSK and D8PSK optical signals are achieved simultaneously by simulation. Detailed theoretical analysis and simulation results are conducted to verify the feasibility of the scheme. The Q factor of the electrical signals and the bit error rate recovered from wavelength and format converted components are approximated to be around 6, and 10−9, which indicates the feasibility of the scheme. For the encrypted signal, the FWM effect of another SOA is utilized to decrypt the encrypted signal, and the encryption function of 10‐Gbaud DQPSK and D8PSK optical signals is also verified. [ABSTRACT FROM AUTHOR]

With on-chip integration enabled, resonant integrated optical gyroscope (RIOG) is a promising choice of rotation rate sensor in the novel micro inertial navigation systems. However, various optical errors, especially the backward-light-related errors including backscattering error and back-reflection error caused by the manufacturing process and heterogeneous materials in the optical elements, limit the performance of RIOG. Here, we propose the frequency spectrum separation method to suppress the backward-light-related errors for improving the detection precision of RIOG. The method can separate the angular velocity signal from the backward-light-related errors in the frequency domain. And, we investigate the optimal strategy of modulation frequencies to obtain maximum spectrum gaps of clockwise and counter-clockwise light for suppressing the backward-light-related errors, and simultaneously maintain maximum demodulation gain and minimum nonlinearity of optical effect for improving detection sensitivity. With the frequency spectrum separation method, the long-term bias stability of RIOG achieves 0.3°/h based on Allan deviation, which is the best reported result to the best of our knowledge. The proposed method of backward-light-related errors suppression can significantly improve the detection precision of RIOG based on a photonic chip, which contributes to the application of RIOG in the novel micro inertial navigation field such as cluster unmanned aerial vehicles and micro-nano satellites. [ABSTRACT FROM AUTHOR]

Pulsed laser systems for long range target detection process multiple pulses to increase signal-to-noise ratio SNR from that of a single pulse. Unipolar on–off keying (OOK) periodic pulse modulation codes are appropriate for an incoherent system. Mismatched filters for cross-correlation with codes are solutions to exactly determined linear equations, so all zero sidelobes are realized for any nonsingular set of equations and codes that are not all zeros. Therefore, maximum SNR is proposed as the criterion for code-filter pair adoption at a given code length. The fast solution of the mismatched filtering circulant equations allows all codes for a set of balancing values [differences of numbers of on (ones) and off (zeros)] to be tested for odd code lengths up through 33. M-sequences and Legendre codes of prime lengths one less than a multiple of four and an excess of one more on than off lead to optimal SNR code-filter pairs. These Legendre codes are suggested for longer codes since they are easily constructed. Code-filter pairs that optimize SNR for a given code length and balancing values of ±1, ±3, ±5, and ±7 are reported. For a balancing value of –1, a new set of codes with corresponding two-value filters is found. [ABSTRACT FROM AUTHOR]

Taking advantage of the photoelectric characteristics of LED other than the light‐emitting function, this paper proposes a light sensing detection method and system without adding additional sensors to the LED screen. A two‐pole detection structure with a function of detecting positive and negative voltage is introduced to the LED drive circuit, which ensures the high‐speed characteristics during detection. What's more, the LED is controlled to work in photoconductive mode to obtain high voltage sensitivity when the intensity of incident light changes. The proposed module can reach an optical signal response rate of 19.1 μs with a detection rate of 23.5 Hz without affecting the original display function. The optical signal detection can reach a voltage sensitivity of 3.02 mV per lx. To verify the photoelectric detection capability of the method presented in this paper, a brand‐new screen object recognition system is built and tested. An 8 × 8 LED display module is used in experiment, and the scale of LED screen can be expanded easily and flexibly. In an ideal environment, a recognition accuracy of 99.25% can be achieved, while the recognition accuracy can still reach over 96.5% in a complex light environment. Therefore, this work has further application possibilities for light interaction and fast object recognition in large screens. [ABSTRACT FROM AUTHOR]

Polarimetry has been demonstrated essential in various disciplines, such as optical communications, imaging, and astronomy. On-chip nanostructures for polarization measurements are most expected to replace the conventional bulk elements, and hence minimize the polarimeter for integrated applications. Some on-chip nanophotonic polarimeter via polarization detection has been implemented, in which the separation of two spin polarized states is needed. However, due to the relatively low coupling efficiency or complicated photonic silicon circuits, on-chip polarimetry using a single device still remains challenging. Here, we introduce and investigate an on-chip polarimeter with nanostructures using the inverse design method. The developed device shows the ability to detect the four polarization components of light, two of which are the spin polarizations, and the other two are the linear polarizations. The retrieved Stokes parameters with experimentally tested data are in close agreement with the numerical results. We also show the proof of concept demonstration for high-speed Stokes vector optical signals detection. In the high-speed communication experiment with data rate up to 16 GBd, the detected optical signals via polarization measurements at multiple wavelengths in the C-band were recovered with the bit error rate below the 20% forward error correction threshold. The proposed on-chip polarimeter shows promising performance both in Stokes polarimetry and high-speed optical communication applications. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide and biothiol molecules such as Cys and GSH acted important roles in many physiological processes. To simultaneously detect and distinguish them was quite necessary by a suitable fluorescent probe. A novel chemosensor 4-(4-(benzo[d]thiazol-2-yl)-2-methoxyphenoxy)-7-nitrobenzo[c][1,2,5]oxadiazole (BMNO) was designed to detect H2S/Cys/GSH using the combination of nitrobenzofurazan (NBD) and benzothiazole fluorophores linked by a facile ether bond. The probe BMNO was developed for simultaneous identification of H2S, Cys and GSH. Noticeably, the color changes (from colorless to light purple, light orange and light yellow) of probe BMNO solutions for sensing H2S, Cys and GSH could be observed by naked eyes, respectively. The probe BMNO exhibited high selectivity and sensitivity for H2S, Cys and GSH showing distinct optical signal with detection limit as low as 0.15 μM, 0.03 μM and 0.14 μM, respectively. The sensing mechanism was clarified by spectrum analysis and some controlled experiments. In addition, these outstanding properties of probe BMNO enabled its practical applications in detection H2S in beer, and in cell imaging for Cys and GSH as well. [ABSTRACT FROM AUTHOR]

The bandwidth and latency demands driven by 5G wireless networks are putting a focus on analog radio-over-fiber techniques as a promising candidate for broadband optical fronthauling. In contrast to intensity modulation / direct detection systems, as they are commonly adopted for mobile fronthaul links due to their simplicity, we are exploring a migration option towards coherent radio-over-fiber transmission. A simplified coherent homodyne receiver based on an electro-absorption modulated laser is co-integrated at the die-level with a transimpedance amplifier and evaluated for analogue coherent radio-over-fiber transmission. This low-complexity homodyne receiver can unlock channel selectivity and high receiver sensitivity inherent to coherent detection, but without the need for digital signal processing. We will demonstrate a sensitivity that allows for an optical budget of 42 dB, and thus eases the fixed-mobile convergence in power-splitting fiber plants. We further show filterless radio signal reception in presence of modulated adjacent channels. Signal integrity is confirmed through transmission of orthogonally frequency multiplexed radio signals with 16-point quadrature amplitude modulated formats, with an error vector magnitude below the corresponding antenna limit. [ABSTRACT FROM AUTHOR]

The full solid‐state, intrinsic cutoff solar‐blind UV photodetectors are widely used in the military and civilian fields. Herein, to achieve real‐time solar‐blind UV signal detection for application in portable equipment, the material epitaxy, device fabrication, and performance characterization of high‐performance back‐illuminated AlGaN‐based solar‐blind UV photodetectors are conducted at first. Based on the photodetector, a discrete signal amplifier circuit is subsequently designed and prepared to fulfill the weak solar‐blind signal detection. Through assembling the amplifier circuit with the AlGaN‐based solar‐blind UV photodetector, it can output real‐time voltage signal with different amplitude according to the intensity of the incident UV light signal. This study is of great significance for developing a portable solar‐blind UV detection system. [ABSTRACT FROM AUTHOR]

We present a mobile fronthaul methodology for the analogue optical transmission of native radio signals with integrated photonic true-time delay for the beam steering of phased-array antennas. Laser-based coherent homodyne detectors and the delay dissemination through ultra-dense wavelength division multiplexing ensure a low complexity at the optical layer. We experimentally demonstrate beamsteering for a linear phased-array antenna with a 1 × 3 configuration at 3.5 GHz carrier frequency and prove native radio signal transmission over the 14.3-km reach coherent optical fronthaul at a low end-to-end error vector magnitude of 3.3%. Experimental results are found to stand in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

Azobenzene dyes have large refractive index near their main resonance, but the poor figure of merit (FOM) limits their potential for all-optical applications. To improve this situation, disperse red 1 (DR1) molecules were dispersed in a sol-gel germanium/Ormosil organic-inorganic hybrid matrix. Z-scan measurement results showed a good compatibility between the dopant and the matrix, and also, an improved FOM was obtained as compared to the DR1/polymer films reported previously. To demonstrate the all-optical signal processing effect, a cw Nd:YAG laser emitting at 532 nm and a He-Ne laser emitting at 632.8 nm were used as pump and probe beams, respectively. DR1 acts as an initiator of the photo-induced transient holographic grating, which is attributed to the trans-cis-trans photoisomerization. Thus, a three inputs AND all-optical logic gate was achieved by using choppers with different frequencies. The detailed mechanism of operation is discussed. These results indicate that the DR1 doped germanium/Ormosil organic-inorganic hybrid film with an improved FOM has a great potential in all-optical devices around its main resonance. [ABSTRACT FROM AUTHOR]

Optically controllable signals are fundamental to various applications from communication to super-resolution imaging. However, literature on non-fluorescent, nonlinear optical signals that can be reversibly turned on/off on a sub-micrometer scale is scant. In this work, we experimentally demonstrate a scheme for the reversible suppression of second harmonic generation (SHG) based on dye-doped nematic liquid crystal molecules. Under a pump (suppressing SHG) and probe (generating SHG) setup with a tightly focusing microscope and a time-gated detection, outstanding modulation depth (>80%) has been realized. Surprisingly, the mechanism of liquid crystal SHG switch on a sub-micrometer scale was found to be light-induced thermal phase transition as against optical Frederick's transition. Quantitative analysis of the optical nonlinearity vχ(2) versus local heating shows an excellent agreement of SHG signal suppression as well as its dependence on the liquid crystal molecular order and phase change. Our work provides an innovative example of applying nonlinear optical properties of soft materials, and can be further optimized for all-optical modulation applications. [ABSTRACT FROM AUTHOR]

Symmetry breaking caused by geometric fluctuations can enable processes that are otherwise forbidden. An example is a perylene bisimide dyad whose dipole moments are perpendicular to each other. Förster-type energy transfer is thus forbidden at the equilibrium geometry since the dipolar coupling vanishes. Yet, fluctuations of the geometric arrangement have been shown to induce finite energy transfer that depends on the dipole variance, rather than the mean. We demonstrate an analogous effect associated with chirality symmetry breaking. In its equilibrium geometry, this dimer is nonchiral. The linear chiral response which depends on the average geometry thus vanishes. However, we show that certain 2D chiral optical signals are finite due to geometric fluctuations. Furthermore, the correlation time of these fluctuations can be experimentally revealed by the waiting time dependence of the 2D signal. [ABSTRACT FROM AUTHOR]

The quantum positioning system (QPS) takes advantage of the entanglement property of the quantum system itself, and it is possible to breakthrough the limitation of the positioning accuracy due to signal bandwidth and power limitation in classical radio-based global positioning system (GPS), and improve the positioning performance. In this paper, a comprehensive survey of the research status of QPS and its several key components are presented, including the quantum entanglement states preparation, the quantum satellite technique, the optical signal acquisition, tracking and pointing (ATP) system, and the quantum positioning and clock synchronization technique. We also discuss the current challenges and future research directions at the end of the paper. [ABSTRACT FROM AUTHOR]

Motivated by modern applications of light detection and ranging (LIDAR), we study the model of an optical receiver based on an avalanche photo-diode (APD), followed by electronic circuitry for detection of reflected optical signals and estimation of their delay. This model is known to be quite complicated as it consists of at least three different types of noise: thermal noise, shot noise, and multiplicative noise (excess noise) that stems from the random gain associated with the photo-multiplication of the APD. Consequently, the derivation of the optimal likelihood ratio test (LRT) associated with signal detection is a non–trivial task, which has no apparent exact closed–form solution. We consider instead a class of relatively simple detectors, that are based on correlating the noisy received signal with a given deterministic waveform, and our purpose is to characterize the optimal waveform in the sense of the best tradeoff between the false–alarm (FA) error exponent and the missed–detection (MD) error exponent. In the same spirit, we also study the problem of estimating the delay on the basis of maximizing the correlation between the received signal and a time–shifted waveform, as a function of this time shift. We characterize the optimal correlator waveform that minimizes the mean square error (MSE) in the regime of high signal–to–noise ratio (SNR). The optimal correlator waveforms for detection and for estimation turn out to be different, but their limiting behavior is the same: when the thermal Gaussian noise is dominant, the optimal correlator waveform becomes proportional to the clean signal, but when the thermal noise is negligible compared to the other noises, then it becomes a logarithmic function of the clean signal, as expected. [ABSTRACT FROM AUTHOR]

Silicon photonics is the leading candidate technology for high-speed and low-energy-consumption networks. Thermal and process variations are the two main challenges of achieving high-reliability photonic networks. Thermal variation is due to the heat issues created by application, floorplan, and environment, while process variation is caused by fabrication variability in the deposition, masking, exposition, etching, and doping. Tuning techniques are then required to overcome the impact of the variations and efficiently stabilize the performance of silicon photonic networks. We extend our previous optical switch integration model, BOSIM, to support the variation and thermal analyses. Based on device properties, we propose indirect feedback tuning (IFT) to simultaneously alleviate thermal and process variations. IFT can improve the BER of silicon photonic networks to 10−9 under different variation situations. Compared to state-of-the-art techniques, IFT can achieve an up to 1.52 × 108 times bit-error-rate improvement and 4.11X better heater energy efficiency. Indirect feedback does not require high-speed optical signal detection, and thus, the circuit design of IFT saves up to 61.4% of the power and 51.2% of the area compared to state-of-the-art designs. [ABSTRACT FROM AUTHOR]