Measurement Of Optical Signals Research Articles

Real‐Time Measurements of Photonic Microchips with Femtometer‐Scale Spectral Precision and Ultrahigh Sensitivity

AbstractPhotonic integrated circuits (PICs) are enabling breakthroughs in several areas, including quantum computing, neuromorphic processors, wearable devices, and more. Nevertheless, existing PIC measurement methods lack the spectral precision, speed, and sensitivity required for refining current applications and exploring new frontiers such as point‐of‐care or wearable biosensors. Here, the “sweeping optical frequency mixing method (SOHO)” is presented, surpassing traditional PIC measurement methods with real‐time operation, 30 dB higher sensitivity, and over 100 times better spectral resolution. Leveraging the frequency mixing process with a sweeping laser, SOHO excels in simplicity, eliminating the need for advanced optical components and additional calibration procedures. Its superior performance is demonstrated on ultrahigh‐quality factor (Q) fiber‐loop resonators (Q = 46 × 106), as well as microresonators, realized on a new optical waveguide platform. An experimental spectral resolution of 19.1 femtometers is demonstrated using an 85‐meter‐long unbalanced fiber Mach Zehnder Interferometer, constrained by noise resulting from the extended fiber length, while the theoretical resolution is calculated to be 6.2 femtometers, limited by the linewidth of the reference laser. With its excellent performance metrics, SOHO has the potential to become a vital measurement tool in photonics, excelling in high‐speed and high‐resolution measurements of weak optical signals.

Bidirectional single-multicore-fiber spatial channel network based on a spatial cross-connect and multicore EDFA that efficiently accommodates asymmetric data traffic

In current wavelength division multiplexed (WDM) networks, capacity is deployed in a symmetrical manner, in which wavelength channels provide the same capacity in both directions. However, real data traffic in metro and backbone networks is observed to be considerably asymmetric resulting in wasted capacity in an under-loaded direction. This data traffic asymmetry is expected to increase further in the forthcoming Beyond 5G era due to newly emerging bandwidth-hungry services based on cloud computing. In such a situation, the wasted link capacity in the under-loaded direction can no longer be overlooked. In this paper, we propose a single-multicore-fiber (MCF) bidirectional spatial channel network (SCN) architecture that efficiently accommodates up and down asymmetric traffic. We present a proof-of-concept demonstration of the asymmetric bandwidth allocation in a single-MCF SCN by constructing a single-MCF bidirectional ring network testbed that comprises two spatial cross-connects based on 19-core fiber core selective switches with an M×N wavelength-selective switch and a bidirectional 7-core erbium-doped fiber amplifier with reversible optical isolators. Experimental results for bit error rate measurements of WDM optical signals traveling through different cores in different directions show there is almost no optical signal-to-noise ratio penalty for transmission through the single-MCF bidirectional ring network testbed.

Preface

The 2023 5th International Conference on Wireless Communications and Smart Grid (ICWCSG 2023) supported by South China University of Technology was successfully held in Sipsongpanna, China from June 30th to July 2nd, 2023 (hybrid event). This Conference was the fifth in a series of topical meetings, which began with the Guilin meeting in 2019. ICWCSG 2023 was attended by about 60 participants from different countries and regions.For this fifth meeting we chose Sipsongpanna as our Conference venue and met with our old and new friends. While the location of the conferences has been changed, what remained invariant is the aim of these conferences, which is to discuss recent advances and new perspectives in wireless communications and smart grid in a pleasant and friendly atmosphere. At this meeting we had a comprehensive overview of this fascinating field and of future scenarios thanks to the participation of leaders of the most important projects.The Conference presented an outstanding paper volume covering the most recent advances in wireless communications and smart grid, including Computer Vision and Audition, Optical Modulation and Signal Processing, Antenna Modeling and Measurements, Smart Grid Interoperability and Standards, etc. The papers in this Proceedings published by Journal of Physics: Conference Series represent a collection of plenary talks, invited keynote speeches and other contributions.The Conference program consisted of four keynote speeches presented in plenary sessions, including four “hot topic” speeches highlighting the most recent advances in the fields, and various oral and poster presentations. Among them, Professor Wenjie Feng from South China University of Technology, China performed a keynote speech on Research on Millimeter-wave Circuits Based on Gap Waveguide (GWG). In this research, the microstrip transitions were introduced here for system integration between the antenna and the passive/active components. The theory background and the evolution of gap waveguide proposed by Prof. P. S. Kildal, were also described simply. Finally, the future development of the gap waveguide based on the Micro-Electromechanical System (MEMS) technology was discussed. This overview study aimed to provide a solution for the millimeter-wave circuits, especially in the W-band.We would like to thank the participants, especially those who contributed speeches, posters and manuscripts, for making ICWCSG 2023 such an exciting and memorable Conference. We thank the International Technical Program Committee for putting together the outstanding program and the Organizing Committee for their tireless efforts in the organization of the Conference. Finally, we extend our gratitude to the members of Journal of Physics: Conference Series whose friendly and efficient work contributed much to the successful publication of this volume.The Committee of ICWCSG 2023List of Committee Member is available in this pdf.

Optical frequency divider: Capable of measuring optical frequency ratio in 22 digits

Recent advances in optical frequency standards and optical frequency combs (OFCs) have drawn wide attention since by transforming other quantities into frequency metrology, a higher measurement sensitivity or accuracy can be achieved. Among them, the search for dark matter, tests of relativity, and detection of gravitational wave anticipate even more precise frequency ratio measurement of optical signals, which challenges the state-of-the-art optical frequency standards and OFCs. Here, we report an optical frequency divider (OFD) based on a Ti:sapphire mode-locked laser, which can realize ultraprecise optical frequency ratio measurements and optical frequency division to other desired frequencies. The OFD is based on an OFC frequency-stabilized to a hydrogen maser, whose frequency noise in optical frequency division is subtracted via the transfer oscillator scheme. An optically referenced radio frequency time-base is introduced for the fine-tuning of the divisor and the reduction in division noise. Using the OFD, the frequency ratio between the fundamental and its second harmonic of a 1064 nm laser is measured with a fractional uncertainty of 3 × 10−22, nearly five times better than previous results. Meanwhile, we also report the ability to transport between laboratories, the long-term operation, and the multi-channel division of the OFD.

Quantitative Analysis of Bioluminescence Optical Signal.

Bioluminescence is light emission based on the luciferin-luciferase enzymatic reaction in living organisms. Optical signals from bioluminescence (BL) reactions are available for bioanalysis and bioreporters for gene expression, in vitro, in vivo, and ex vivo bioimaging, immunoassay, and other applications. Although there are numerous bioanalysis methods based on BL signal measurements, the BL signal is measured as a relative value, and not as an absolute value. Recently, some approaches have been established to completely quantify the BL signal, resulting in, for instance, the redetermination of the quantum yield of the BL reaction and counting the photon number of the BL signal at the single-cell level. Reliable and reproducible understanding of biological events in the bioanalysis and bioreporter fields can be achieved by means of standardized absolute optical signal measurements, which is described in an International Organization for Standardization (ISO) document.

Analysis and optimization of acceleration model in coaxial plasma gun in pre-fill mode

Snowplow model is the main method to describe the acceleration process of coaxial plasma gun in the pre-fill mode, which can directly give the analytical expression of plasma velocity versus time. So it has become an important reference in designing the device structures satisfying the requirements for different applications. Through measuring the current, magnetic and optical signals, the characteristics of current during the discharge and the motion of plasmoid are investigated. The variation of discharge current with time is close to the damping sine curve, which is an underdamping solution of RLC equivalent discharge circuit. The measured current in lieu of the sine one is used to calculate the theoretical velocity so as to eliminate the error of magnetic pressure. The variation of plasma velocity with discharge voltage and chamber pressure are consistent with those obtained by solving the equation of plasma motion under snow plough model, but the acceleration process is another story. At the initial stage of the discharge, owing to the low sweep efficiency, the plasma is accelerated to a higher velocity than the predicted one, the increase of voltage and the decrease of pressure further enhance the effect. With the extension of the acceleration distance, owing to the friction resistance between plasma and electrodes, the acceleration slows down and the velocity starts to fall below the predicated value, the saturation of plasma velocity at the nozzle is found. The friction resistance term is added to the equation of plasma motion. Compared with the deviation range of 26.8%–53.6% of the existing model, the differences between the theoretical speed and the measured speed under different voltages and pressures are in a range of 3.1%–8.4% after adding the friction resistance term into the equation of plasma motion. The optimization of snow plow model greatly improves the accuracy of velocity prediction, which can provide an effective reference for designing device structure and calculating energy efficiency.

Mixed Event-Frame Vision System for Daytime Preceding Vehicle Taillight Signal Measurement Using Event-Based Neuromorphic Vision Sensor

An important aspect of the perception system for intelligent vehicles is the detection and signal measurement of vehicle taillights. In this work, we present a novel vision-based measurement (VBM) system, using an event-based neuromorphic vision sensor, which is able to detect and measure the vehicle taillight signal robustly. To the best of our knowledge, it is for the first time the neuromorphic vision sensor is paid attention to for utilizing in the field of vehicle taillight signal measurement. The event-based neuromorphic vision sensor is a bioinspired sensor that records pixel-level intensity changes, called events, as well as the whole picture of the scene. The events naturally respond to illumination changes (such as the ON and OFF state of taillights) in the scene with very low latency. Moreover, the property of a higher dynamic range increases the sensor sensitivity and performance in poor lighting conditions. In this paper, we consider an event-driven solution to measure vehicle taillight signals. In contrast to most existing work that relies purely on standard frame-based cameras for the taillight signal measurement, the presented mixed event/frame system extracts the frequency domain features from the spatial and temporal signal of each taillight region and measures the taillight signal by combining the active-pixel sensor (APS) frames and dynamic vision sensor (DVS) events. A thresholding algorithm and a learned classifier are proposed to jointly achieve the brake-light and turn-light signal measurement. Experiments with real traffic scenes demonstrate the performance of measuring taillight signals under different traffic conditions with a single event-based neuromorphic vision sensor. The results show the high potential of the event-based neuromorphic vision sensor being used for optical signal measurement applications, especially in dynamic environments.

Vacuum Based Gas Sensing Material Characterization System for Precise and Simultaneous Measurement of Optical and Electrical Responses.

Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.

Behavioral Model of Silicon Photo-Multipliers Suitable for Transistor-Level Circuit Simulation

Silicon Photomultipliers (SiPMs) are photo-electronic devices able to detect single photons and permit the measurement of weak optical signals. Single-photon detection is accomplished through high-performance read-out front-end electronics whose design needs accurate modeling of the photomultiplier device. In the past, a useful model was developed, but it is limited to the device electrical characteristic and its parameter extraction procedure requires several measurement steps. A new silicon photomultiplier model is proposed in this paper. It exploits the Verilog-a behavioral language and is appropriate to transistor-level circuit simulations. The photon detection of a single cell is modeled using the traditional electrical model. A statistical model is included to describe the silicon photomultiplier noise caused by dark-count or after-pulsing effects. The paper also includes a procedure for the extraction of the model parameters through measurements. The Verilog-a model and the extraction procedure are validated by comparing simulations to experimental results.

Series of Photovoltaic Converters Based on Semiconductors with Intrinsic Photoconductivity

One of the ways to solve multiple problems of optical diagnostics is to use photovoltaic converters based on semiconductors with intrinsic photoconductivity slightly doped with deep impurities which form several energy levels with different charge states within the semiconductor′s bandgap. Peculiarities of physical processes of recharging these levels make it possible to construct photodetectors with different functionality based on a range of simple device structures.The aim of this work is to analyze peculiarities of conversion characteristics of single-element photovoltaic converters based on semiconductors with intrinsic photoconductivity, to systematize their properties and to represent structures of photovoltaic convertors as a device structures suitable for implementation in measurement transducers of optical diagnostics systems.Based on the analysis of the characteristics of the conversion characteristics of single-element photovoltaic converters based on semiconductors with intrinsic photoconductivity and the requirements for their design, a dash series of photovoltaic converters was developed for use in the measuring transducers of optical diagnostics systems. The possibility of constructing functional measuring transducers for multiparameter measurements of optical signals is shown.

Rapid Molecular Diagnostic Sensor Based on Ball-Lensed Optical Fibers.

Given the fatal health conditions caused by emerging infectious pathogens, such as severe acute respiratory syndrome coronavirus 2, their rapid diagnosis is required for preventing secondary infections and guiding correct treatments. Although various molecular diagnostic methods based on nucleic acid amplification have been suggested as gold standards for identifying different species, these methods are not suitable for the rapid diagnosis of pathogens owing to their long result acquisition times and complexity. In this study, we developed a rapid bio-optical sensor that uses a ball-lensed optical fiber (BLOF) probe and an automatic analysis platform to precisely diagnose infectious pathogens. The BLOF probe is easy to align and has a high optical sensing sensitivity (1.5-fold) and a large detection range (1.2-fold) for an automatic optical sensing system. Automatic signal processing of up to 250 copies/reaction of DNA of Q-fever-causing Coxiella burnetii was achieved within 8 min. The clinical utility of this system was demonstrated with 18 clinical specimens (9 Q-fever and 9 other febrile disease samples) by measuring the resonant wavelength shift of positive or negative samples for Coxiella burnetii DNA. The results from the system revealed the stable and automatic optical signal measurement of DNA with 100% accuracy. We envision that this BLOF probe-based sensor would be a practical tool for the rapid, simple, and sensitive diagnosis of emerging infectious pathogens.

High-Pressure Optical Measurements of Temperature at Turbine Rotor Inlet Conditions

Abstract In gas turbine engines, the measurement of the rotor inlet temperature remains particularly challenging because of harsh operating conditions and limited access. The integrated spectral band ratio (ISBR) method is a nonintrusive optical emission gas temperature measurement technique suitable for this application. Optical fibers made of sapphire were used to transmit the radiative signal from the postcombustion zone to a Fourier transform infrared (FTIR) spectrometer. The ratio of spectral bands of H2O, nominally 100 cm−1 wide between 4600 and 6200 cm−1, was used to infer temperature. ISBR and thermocouple measurements were obtained during two temperature sweeps: one at high load and one at low load (pressures of 1.2 and 0.7 MPa, respectively). The average of three thermocouples 76 mm downstream of the ISBR measurements was on the order of 200 K lower than the ISBR temperatures, consistent with a radiative correction and the heat loss between the two measurements. The change in ISBR temperature (95 K) during the sweep was similar to the change in average thermocouple temperature (89 K). Repeatability of the optical measurement at a given operating condition was on the order of ±15 K and the absolute uncertainty of a single ISBR temperature measurement was estimated to be ±61 K. A linear correlation with an R2 value of 0.97 was also found between raw optical signal and thermocouple measurements, suggesting that once a calibrated measurement is obtained.

Effect of length of outer electrode on plasma characteristics in coaxial gun

The dense plasma produced by a coaxial gun possesses an extremely high velocity (~100 km/s), electron density (~10<sup>16</sup> cm<sup>–3</sup>) and energy density (~1 MJ/m<sup>2</sup>), which has great potential applications in fusion energy, astrophysics and aerospace physics. Through the measurements of electrical and optical signals, as well as the temporal and spatial evolution of the ejected plasma, the plasma characteristics of two different outer electrodes in length are investigated. As the outer electrode is lengthened, the axial velocity, the collimation and the propagation distance of plasma are all enhanced while the electron density and the optical intensity decrease, this can be ascribed to the extension of plasma column formed by <i>Z</i>-pinch on the central electrode during the discharge. When moving across the end of the inner electrode, the plasma sheet can be stretched into a bow shape due to the Coulomb and Lorentz force. With the appearance of axial current, part of the plasma sheet near the head of the inner electrode converges toward the center, and then generates a plasma column with much higher electron density and temperature. On the one hand, the extending of the plasma column can match the outer electrode in length and therefore the plasma column gains longer accelerating time in the coaxial gun resulting in the growing of ejected velocity. On the other hand, it also brings higher losses of the charged particles and recombination rates between the plasma and the wall of electrodes, resulting in the decrease of electron density and optical intensity. Moreover, the axial kinetic energy, the electron density and the radial Lorentz force of ejected plasma are jointly responsible for the collimation and the attenuation characteristics in its propagation. As the axial velocity and electron density increase, the axial kinetic energy of ejected plasma increases, which induces a longer propagating distance. In contrast, with the electron density and radial Lorentz force growing, the density gradient and thermal expansion of ejected plasma are enhanced correspondingly, leading the energy density to decrease and finally the propagating distance to shorten. In conclusion, a high collimation plasma jet trends to generate in a high axial velocity, electron density and with a relatively long outer electrode.

Фотоприймальний пристрій, стійкий до фонової засвітки, з розширеним динамічним діапазоном вхідних сигналів

Measurement of periodic optical information signals in the background light noise with a photodetector with extended dynamic range is an urgent task of modern electronics and thus has become the aim of this study. To increase the dynamic range of the photodetector, a new version of the automatic gain control (AGC) circuit has been developed, which consists of an AGC controller, an output photodetector amplifier and an AGC detector. The authors measured the dynamic range of the photodetector when receiving optical radiation with a wavelength of 1064 nm in the power range from 2.10–8 to 2.10–5 W at a modulation frequency of 20 kHz with the AGC on. Under these conditions, the dynamic range of the photodetector was found to be up to 67 dB. If the AGC was off, the dynamic range did not exceed 30 dB. Thus, the study made it possible to create a photodetector with an extended dynamic range up to 67 dB based on a new version of the AGC circuit. The design of the photodetector allowed choosing a useful signal of a particular modulation frequency in the frequency range from 3 to 45 kHz and effectively suppresses the frequencies caused by optical interference in the low frequency range from the frequency of the input signal of constant amplitude up to 3 kHz inclusive. This compensates the current up to 15 mA, which is equivalent to the power of light interference of about 15 mW. Further research should address the issues of reliability of the proposed photodetector design and optimization of its optical system. The photodetector can be used in geodesy and ambient air quality monitoring.

Measuring complex field waveforms of quadrature amplitude modulation optical signals using a spectrally slicing-and-synthesizing coherent optical spectrum analyzer.

We propose a spectrally slicing-and-synthesizing coherent optical spectrum analyzer to measure complex field waveforms of quadrature amplitude modulation (QAM) optical signals with ultralong periods. The optical spectrum of a measured optical signal is divided into multiple narrowband spectral components, called slices. The slices are sequentially measured using low-speed coherent detection. After phase noise suppression and frequency fluctuation compensation on each slice, the measured slices are synthesized to recover the original signal spectrum. Our numerical and experimental results confirm that the proposed method can overcome the limitation of the measurement bandwidth because the signal spectrum can synthesize more than 100 slices. We experimentally demonstrate complex field measurements of 16QAM optical signals. Our method can measure high-speed optical complex field waveforms with no bandwidth limitation.

Temporal Imaging Using Dispersive Gradient-Index Time Lenses

We study the temporal imaging with a gradient-index (GRIN) time lens in which both dispersion and time-varying quadratic phase modulation are introduced. The lens is built by using cross-phase modulation between a signal and a parabolic pump pulse in the nonlinear optical fiber with group velocity dispersion. A general theoretical analysis of temporal imaging by the GRIN time lens is performed in detail. Compared to thin lens in previous studies, the introduction of dispersion, benefits periodic self-imaging of both time waveform and frequency spectrum for optical pulses. Interestingly, the temporal and spectral profiles of the input can be exchanged with each other periodically in the GRIN time lens. By combining the GRIN time lens with dispersive elements on both sides, the temporal waveforms of incident optical pulses can be stretched and compressed. For an input signal composed of multiple pulses experiencing different dispersions, the temporal depth imaging of the signal is realized by scanning the timing of the pump pulse applied on the lens. The study may find great applications in ultrafast optical signal processing and measurement.

Dynamic, surface displacement measurements using a proximate, radiating electric dipole

Expressions for the optical power radiated by a vertically oriented, electric dipole are developed to understand the dependence of this power on the distance between the dipole and a nearby surface, especially when this distance is varying with time. Results of this analysis assess the conditions under which the power depends linearly on displacement amplitude when this distance has a sinusoidal, time-varying component of fixed amplitude combined with a mean dipole-to-surface distance. The variation in the radiated power with this mean distance is also examined so that comparisons can be made to experimental measurements of near-field optical signals.

Channel Measurements for Free Space Optical Communication

This article presents and analyzes fading measurements of optical signal in a terrestrial free space optical communication link using a commercial system. Unlike previous work, the link distance is very short (around 91 meters). Still, it was possible to observe significant scintillation index variations over a day. This behaviour agrees with previous results obtained in the literature for much longer links.

Imaging of Neuronal Activity in Awake Mice by Measurements of Flavoprotein Autofluorescence Corrected for Cerebral Blood Flow.

Green fluorescence imaging (e.g., flavoprotein autofluorescence imaging, FAI) can be used to measure neuronal activity and oxygen metabolism in living brains without expressing fluorescence proteins. It is useful for understanding the mechanism of various brain functions and their abnormalities in age-related brain diseases. However, hemoglobin in cerebral blood vessels absorbs green fluorescence, hampering accurate assessments of brain function in animal models with cerebral blood vessel dysfunctions and subsequent cerebral blood flow (CBF) alterations. In the present study, we developed a new method to correct FAI signals for hemoglobin-dependent green fluorescence reductions by simultaneous measurements of green fluorescence and intrinsic optical signals. Intrinsic optical imaging enabled evaluations of light absorption and scatters by hemoglobin, which could then be applied to corrections of green fluorescence intensities. Using this method, enhanced flavoprotein autofluorescence by sensory stimuli was successfully detected in the brains of awake mice, despite increases of CBF, and hemoglobin interference. Moreover, flavoprotein autofluorescence could be properly quantified in a resting state and during sensory stimulation by a CO2 inhalation challenge, which modified vascular responses without overtly affecting neuronal activities. The flavoprotein autofluorescence signal data obtained here were in good agreement with the previous findings from a condition with drug-induced blockade of cerebral vasodilation, justifying the current assaying methodology. Application of this technology to studies on animal models of brain diseases with possible changes of CBF, including age-related neurological disorders, would provide better understanding of the mechanisms of neurovascular coupling in pathological circumstances.

Models of WOx films growth during pulsed laser deposition at elevated pressures of reactive gas

The films of tungsten oxides were prepared by pulsed laser ablation of W target in a reactive gas atmosphere (air of laboratory humidity). Optical analysis and ion signal measurements for the laser plume allowed to recognise a threshold gas pressure that suppresses the deposition of non-scattered atomic flux from the plume. When the pressure exceeds about 40 Pa, the films grow due to the deposition of species that could be formed in collisions of W atoms with reactive molecules (e.g., O2). Kinetic Monte Carlo method was used for modelling film growth. Comparison of the model structures with the experimentally prepared films has shown that the growth mechanism of ballistic deposition at a pressure of 40 Pa could be changed on the diffusion limited aggregation at a pressure of ~100 Pa. Thus, a cauliflower structure of the film transformed to a web-like structure. For good correlation of experimental and model structures of WOx, a dimension of structural elements in the model should coincide with W-O cluster size.