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We propose herein a novel optical sensing technology using liquid crystal based transducers to measure simultaneously voltage and current from overhead power lines in real time. Doing so, we implemented a proof-of-principle system based on this approach and we demonstrated not only good accuracy, but also small phase shift and adequate bandwidth for power quality and fault monitoring applications. This is supported by experimental results for current, voltage and power monitoring, which include transient measurements and show excellent agreement with commercial reference probes. The system presented in this paper has been developed for single wire earth return (SWER) lines operating at 12.7 kV or 19.1 kV, but can be adapted to work at higher or lower voltages with appropriate modifications. We conclude by discussing the calibration process improvements that would be required for the technology to meet industry standards. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a fiber optic multi-point bending measurement system that uses Bragg gratings inscribed along a multi-core fiber (MCF) and a silicon avalanche photodiode (Si-APD) that produces two-photon absorption (TPA) photocurrent for 1.55- $\mu \text{m}$ light. Because the TPA photocurrent from the Si-APD is proportional to the mean square of the optical intensity, the intensity correlation between 1.55- $\mu \text{m}$ probe and reference beams is measured from it without using complex electrical circuits. The proposed system has different lengths of optical fibers between each core of MCF and input/output ends of a single mode fiber optic system, which makes different the correlation signal between the reference beam and the probe beam reflected from different Bragg gratings in MCF. That enables the reflection spectra of all the Bragg gratings in MCF to be separately measured even when they are overlapped in the wavelength domain. As a result, the bending radius and its direction are measured without using multiple detectors or optical switching devices. We conducted proof-of-concept experiments by using a 7-core MCF with almost the same Bragg gratings inscribed in each core at three points along the fiber. We also demonstrated an example of application to shape measurement. [ABSTRACT FROM AUTHOR]

A novel fast measurement method based on Brillouin gain spectrum (BGS) and Brillouin beat spectrum (BBS) in a complex index profile fiber has been proposed to realize simultaneous measurement of distributed temperature and strain. An interesting phenomenon that the temperature/strain sensitivities of the power on the BGS slope and the power on the BBS peak are very different has been discovered and utilized for temperature and strain sensing. By means of only measuring the power trace of the BGS slope and the power trace of one BBS peak along the sensing fiber, the distributed temperature and strain can be measured by using the Brillouin optical time-domain reflectometry (BOTDR) without scanning the Brillouin spectrum. The temperature and strain measurement uncertainties of the proposed method are one order of magnitude lower than that of the BBS-based measurement method. In a proof-of- concept experiment, the temperature and strain of the 2 km large effective area fiber (LEAF) are measured at a spatial resolution of 3 m within 18 s. [ABSTRACT FROM AUTHOR]

Optical sinc-shaped Nyquist pulses are promising in photonic signal processing and high-speed optical data transmission due to their orthogonality and inter-symbol interference (ISI) free characteristics. Nonetheless, the presence of non-idealities results in a deteriorated system performance, especially for the metrological assessment of sampling precision. In this work, we explore the impact of the optical filter roll-off factor on Nyquist pulses for a three-line comb with a frequency spacing of 8.4 GHz using a wideband on-chip silicon Mach-Zehnder modulator. Furthermore, we characterize the integrated modulator and compare the sinc-shaped Nyquist pulse quality with the recently reported works. [ABSTRACT FROM AUTHOR]

Distributed vibration sensing (DVS) utilizes an optical fiber as an array of virtual strain sensors. It can reveal dynamic strain distributions such as seismic events and car traffic, thus giving a new function to existing optical communication fibers. In this work, we use optical frequency domain reflectometry (OFDR) to investigate the dynamic strain distribution along an optical fiber implemented in a deployed aerial optical fiber cable that vibrates with the wind. The OFDR setup is customized for distant location interrogation with a high repetition rate of the probe light and overcomes the OFDR drawbacks of short measurement range and low repetition rate, thus enabling application to the investigation of dynamic strain along a range of telecommunications outside a plant. Sub-1-m spatial resolution measurements revealed that dynamic strain along the optical fiber in an aerial cable depends on the deployment condition. It also provides the deployed optical telecommunication fiber with a function for visualizing the deployment conditions of the telecommunications outside plants. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a notch filter on a silicon chip and apply it to a photonic microwave frequency measurement system with high precision and adjustable wide measurement range. The on-chip notch filter is implemented by embedding a serially coupled double microring resonator in a Fabry-Perot cavity consisting of two circular Bragg gratings with high reflectivity. The notch filtering with high quality factor and high rejection ratio is obtained by reconstructing the power transmission spectrum of the double microring resonator through the coherent interference within the Fabry-Perot cavity. The proposed notch filter is fabricated on a silicon-on-insulator wafer and the rejection ratio of the notch filter is measured to be 33.54 dB and the quality factor is 3.93×104. Based on the notch filter, a photonic microwave frequency measurement system is presented where the unknown radio frequency signal is detected by the variation of the output optical power from the notch filter through sweeping reference frequency. The measurement bandwidth of the system can be flexibly adjusted by tuning the output wavelength of the laser source. Broad measurement range of 0-26.62 GHz with a low error of ±0.25 GHz are obtained in a proof-of-concept experiment. [ABSTRACT FROM AUTHOR]

Scanning probes on the micro/nano-coordinate measuring machines (micro/nano-CMMs) can produce on/off signals and achieve 3D measurement ability within a specific range. The authors have developed several scanning probes based on a 2D angle sensor and a miniature Michelson interferometer that can work within ± $10~\mu \text{m}$. When the probe’s lateral displacement is greater than $10~\mu \text{m}$ , the interferometer signal is easy to break, limiting the measurement range of these probes. A 2D angle fine-tuning stage using piezoelectric stack actuators is designed to adjust the reference mirror in real-time to solve signal separation between the reference beam and the measuring beam of the miniature Michelson interferometer. The coupling of the 2D angle fine-tuning stage in the x and y directions is analyzed, and the coupling model is established for a relatively precise compensation. Experimental results show that through the proposed 2D angle fine-tuning stage, the measurement range of the probe can be extended to ± $30~\mu \text{m}$ , and the interference signal can still remain stable and uninterrupted. [ABSTRACT FROM AUTHOR]

In recent years, nitrogen vacancy (NV) centers have shown great potential for application in quantum sensor research due to their high sensitivity to magnetic fields and excellent spatial resolution. However, in practical applications, it is necessary to eliminate environmental requirements and bulky instruments brought by the optical detection of magnetic resonance (ODMR) measurement method.. In this paper, we propose an efficient portable magnetometer with a miniature confocal system (CSPM) to resist background noise and improve integration. The confocal system can automatically focus, and the volume is limited to 11 cm3. Moreover, a fiber optic flange, an antenna and a homemade integrated photodetector are integrated in the magnetometer to achieve the actual sensitivity of sub-40 nT/Hz1/2. In the experimental process of optimizing system parameters, we discovered the important influence of beam focusing or microwave uniform operation on the detection signal and proposed specific optimization methods, which have guiding significance for future integrated design. Through comparative experiments with an integration scheme that does not use uniform operation, we found that the CSPM reduces the system noise by 4.2 times and that the signal-to-noise ratio (SNR) increases by 6.2 dB. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel optical BioNEMS (Biological-Nano-Electro-Mechanical Systems) sensor based on a 1D photonic crystal (PhC) structure in order to develop a label free biosensing platform. The proposed biosensor consists of a BioNEMS cantilever as the tunable defect of the PhC detection part. This optical sensing system is a finite air hole photonic crystal with a nano air gap in the center of the structure so that the NEMS movable part can be freely displaced. Biomolecular interactions induce a surface stress on the functionalized surface of the movable structure. As a consequence, a nanomechanical bending occurs in the NEMS cantilever because of the released energy of binding events. This can change the defect of the proposed PhC which causes shifts in the transmitted wavelength for various concentrations of biomarkers. By analyzing the proposed device using numerical and analytical approaches, the functional characteristics of the present BioNEMS sensor are obtained as follows: optical sensitivity of 13452 nm/RIU, FOM of 7912 RIU−1, mechanical sensitivity of $4.6~\mu \text{m}$ /Nm−1 and resonant frequency of 33.3 kHz. According to the results, this ultra-high sensitive sensor can be a promising choice to realize efficient label-free biosensors for early diagnoses of diseases in Point-of-Care Testing (POCT). [ABSTRACT FROM AUTHOR]

This paper introduces an under-sampling E-field measurement system involving three femtosecond pulse lasers, which can be used to measure a multi-frequency electric field (E-field) in a wide frequency range. Optical under-sampling technology utilizes femtosecond laser pulses to sample the electrical signals and convert the high-frequency signal down to the first pulse repetition frequency (RPF) intervals for measurement, i.e., tens to hundreds of MHz. However, previous work rarely studied the measurement of multi-frequency signals. Therefore, in this work, we use three RPFs and propose the Remainder Matching (RM) method of three RPFs to eliminate false-alarm-triggered frequencies. Moreover, to solve the challenging problem of grouping the down-conversion components of each measured frequency, we suggest the Eigenvalue Matching of Remainder’s Difference (EMRD) method to obtain the correct group accurately. Hence, this work combines the RM and EMRD methods to improve the system’s measurement accuracy. To evaluate the suggested measurement technique, detailed theoretical analysis and simulation are performed to demonstrate the universality of our method that can effectively guide the design of E-field measuring systems using optical under-sampling technology. The proposed scheme manages an error rate less than 0.1% without any measurement error of the down-converted components when six frequencies exist simultaneously and is less than 5% when the measured frequency deviation is ±25kHz. Finally, the proposed system is challenged on noise perturbations, with the results demonstrating that the suggested combined RM and RDEM scheme attains an appealing performance. [ABSTRACT FROM AUTHOR]

This paper describes a novel cantilever type accelerometer using a mirror-terminated hetero-core optical fiber for fault diagnosis of machinery. Hetero-core optical fiber sensors are suitable for long-term measurement in on-site fields with attractive advantages of robustness to environmental disturbances such as electromagnetic interference, chemical corrosion, and temperature fluctuation. Moreover, the proposed sensor contained a mirror termination on the hetero-core fiber in order to form a compact and cantilever-shaped structure. It was experimentally found that the mirror-terminated hetero-core fiber worked as Mach-Zehnder interferometry having interference fringes in transmission spectrum, in which linear changes in peak intensities enabled to detect the deflection of fiber beam using a cost-effective LED/PD measurement instrument. For the vibration response characteristics, the sensor reproduced the waveforms of input vibrations to optical loss changes when sinusoidal vibration was applied. Furthermore, the sensitivities were stable in the range of $5.4\times10^{3}$ to $2.3\times10^{2}$ dB/g for the frequency ranges less than 620–130 Hz, when setting a fiber beam length by 6–13 mm. Additionally, finite element simulations indicated that the frequency response characteristics were well correlated with the vibration characteristics of the cantilever-shaped fiber beam, which implied that the sensor performance can be optimized with respects to the sensitivity and the measurable frequency range by changing the fiber beam length. [ABSTRACT FROM AUTHOR]

Interface pressure between cable and accessory is the key to ensure the long-term reliable operation of cable accessories. The traditional measurement method of interface pressure is off-line measurement through a built-in piezoelectric sensor. However, this method is difficult to operate and damages the interface structure. In addition, the offline measurement cannot reflect the real-time dynamic change of interface pressure during the operation of cable accessories. Therefore, this paper proposes a new method for the on-line measurement of interface pressure between cable and accessory by means of an exterior optical fibre curvature sensor, whose design mechanism is based on the pure bending theory of optical fibre. Then the relationship model involving the exterior curvature of the cable accessory, the radial displacement and the inner interface pressure is established. Finally, interface pressures of the 8.7/10 kV cable accessory under different expansion ratios are measured by the calibrated optical fibre curvature sensor. The measurement results show that the optical fibre curvature sensor measures the exterior curvature of the accessory accurately; the average sensitivity reaches 7.679 nm/mm−1, and the measurable curvature ranges from 0.03 to 0.05 mm−1. The conversion results of interface pressure are basically consistent with the results measured directly by a traditional piezoelectric sensor or simulated mechanically by finite element software. Therefore, the exterior optical fibre sensing technology proposed in this paper is expected to be used for the on-line measurement of the interface pressure between cable and accessory. [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication and characterization of a miniature GaN chip with a size of $1.1\times 1.1\times0.21$ mm3 for surface roughness measurement. Unlike conventional optical metrology that requires external components for the optical coupling between light source and detector, a monolithic GaN-on-sapphire chip fabricated through wafer-scale processes provides light emission and photodetection functions and is capable of sensing a range of average surface roughness from 0.025 to $1.6~\mu \text{m}$. The sensing performances are compared with fiber-optic metrology, and the ability to real-time monitor the roughness of the moving surface is demonstrated. The novel chip offers the advantage of non-contact and non-destructive, compact structure, simple operation, and in situ measurement capability, which is highly valuable for various practical and industrial surface metrology applications. [ABSTRACT FROM AUTHOR]

Lidar is considered to play an essential role on the road towards fully autonomous driving. In this context, coherent lidar systems hold the potential for lean, efficient and inexpensive sensors, but their performance depends significantly on suitable modulation and signal processing methods that can handle high Doppler shifts and enable high measurement rates at low computational complexities. This paper presents four novel phase-modulation-based approaches that utilize pseudo-random binary sequences to estimate target distances up to 180 m and the absolute value of target velocities up to 80 m/s. The corresponding system setup is lean, as it is based on only one phase modulator and one non-quadrature demodulator. The proposed methods are assessed analytically and by simulations and are compared in terms of computational complexity, detection performance, measurement rate and accuracy. The results demonstrate that while each approach has individual advantages and limitations, the proposed methods offer essential advancements in terms of measurement rate, multiplexing potential and multi-target capability, compared to already known methods. The feasibility of all presented approaches is validated by measurements. [ABSTRACT FROM AUTHOR]

A method to carry out a priori simulations of pulsed-laser-induced single-event effects experiments is reported. Nonlinear optical simulations are conducted to model the 3-D distributions of charge from a laser pulse. These pulsed-laser-induced charge distributions are then incorporated into a charge transport solver to model the movement of charge as the device returns to a steady state. The output of the simulation infrastructure is a current transient from which collected charge and the temporal characteristics of the transient can be determined. This complete approach to modeling, which includes full device structure information, nonlinear optical energy deposition, and the subsequent movement of optically generated charge in a device and measurement circuit, allows for direct comparison between experimental and simulated current transients. A large-area silicon diode was used as the test vehicle, and good agreement was found between simulations and experiments in both total injected charge as well as temporal characteristics. Importantly, the a priori simulation approach does not require knowledge from prior heavy-ion testing, making it a predictive tool with broad versatility and minimal reliance on approximations. [ABSTRACT FROM AUTHOR]

We experimentally and numerically propose a deep ultraviolet light-emitting diode (DUV LED) possessing the quantum barriers (QBs) with the gradually reduced Al composition along the [0001] orientation. The induced negative polarization bulk charges in the graded QBs can screen the positive polarization sheet charges at the QB/quantum well (QW) interface, i.e., generating the polarization self-screening effect, which weakens the electric field in the QWs. The polarization self-screened feature is important in enhancing the overlap level of the electron and hole wave functions within the active region and increasing the hole injection, thus improving the electroluminescence intensity and the optical power. [ABSTRACT FROM AUTHOR]

Globally accurate manipulation and localization of the terminal of a mobile robot arm within a large workspace has always been a bottleneck problem. In this article, a planar-laser-guided solution is proposed for this issue. The core of this solution is using three movable planar lasers to designate a unique reference point with orientation information within the workspace, and designing a sensor module mounted on the terminal of the robot arm with photoelectric position sensitive devices (PSDs) to measure the relative pose between the terminal and the reference point. Thus, the terminal of the robot can be guided by this relative pose to the target in a given orientation. According to this concept, a parameterized model of the moveable planar lasers and the poses of the PSDs, as well as an expression of their geometric relationship, were derived. The manipulation strategy of the robot arm was further investigated through the model, and an error compensation method to improve the manipulation accuracy was proposed. Finally, a reduced-scale prototype system, based on this solution, was built, on which tracking and positioning experiments of the robot arm were carried out to verify the feasibility of the solution. It has been shown that this laser-guided solution is not sensitive to the blockage (occlusion) of several laser transmitters, which could be an advantage for its application in future autonomous settings. [ABSTRACT FROM AUTHOR]

In this article, the investigation has been carried out for the characterization of the proposed tapered geometry of dielectric barrier discharge (DBD)-based cold atmospheric pressure plasma jet (C-APPJ) on the basis of optical emission spectroscopy (OES) and imaging for different operating parameters, such as argon gas flow rates, applied voltages, and frequencies. The detailed characteristics for the formation of the plasma plume using argon as a working gas have been presented for a wide range of flow rates [1–3 standard liter per minute (SLM)] and frequencies (15–25 kHz). Increasing the pulse frequency, the length and the diameter of the plasma plume increase, while the length of the plasma plume increases when increasing the gas flow rate up to 2 SLM. Time-integrated images have been captured using the intensified charge couple device (ICCD) camera, which illustrates that the plasma plume comprises different emission layers of definite patterns. The propagation dynamics and formation of different emission layers of the plasma plume have also been investigated using the COMSOL Multiphysics simulation. It has been observed that the local electric field of 6 kV/cm is responsible for the propagation of the plasma bullet and the generation of the electron with an average energy of ~9 eV. OES has also been performed to understand the plasma chemistry and identify the reactive species in the C-APPJ. The discharge analysis and characteristics performed through experiment and simulation would certainly be helpful for the design and development of C-APPJ sources. [ABSTRACT FROM AUTHOR]

A correlation optical time-domain reflectometry (C-OTDR) method is presented, which measures the propagation delay with an accuracy of a few picoseconds. This accuracy is achieved using a test signal data rate of 10 Gbit/s and employing cross-correlation and pulse fitting techniques. In this paper we introduce and evaluate the basic signal processing steps, investigate the measurement accuracy, and discuss applications for monitoring link delay and chromatic dispersion of long fiber spans as well as temperature sensing applications. [ABSTRACT FROM AUTHOR]

Distributed optical fiber sensors using Brillouin scattering have already demonstrated their ability to measure changes in strain and temperature over long distance. However, the simultaneous sensitivity of the Brillouin scattering to these two parameters is a real disadvantage during the instrumentation and monitoring of structures, such as for civil engineering, oil industry applications (i.e. instrumentation of pipelines or wells) or electrical power cables monitoring. In this article, we present a new instrument enabling independently measurement of temperature or strain using a unique fiber in a single measurement. This method, which we will call B-OTDR DSTS for “Distributed Strain and Temperature Sensing”, is based on the measurement of frequency (as a standard BOTDR) but also intensity of Brillouin scattering. However, as the measurement of the latter requires an accurate measurement of power levels along the fiber, it is necessary to correct the losses by a Rayleigh OTDR measurement. The architecture of the BOTDR-DSTS allows simultaneous measurement of the Brillouin and Rayleigh backscatters. We will detail the validation results of this new device and show the interest of such a measurement on the instrumentation of a cable into a 2 km deep observation well. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotube encapsulated in boron nitrite nanotube (SWCNT@BNNT) is a novel nanomaterial with a one-dimensional van der Waals (1D-vdW) heterostructure. In this paper, we demonstrated that the SWCNT@BNNT has an enhanced optical power tolerance compared to that of the pristine SWCNT while preserving the ultrafast optical saturable absorption properties. The thermal damage threshold of SWCNT@BNNT is 2 dB higher than that of the pristine SWCNT, resulting in 9 times longer lifetime for 1 dB degradation and 214 times longer lifetime for 3 dB degradation under optical power intensity of 6.8 kW/cm2. The high optical power tolerance of SWCNT@BNNT is further confirmed in a short-cavity mode-locked laser with a high repetition rate of 1 GHz with a high optical power intensity. We have shown the potential of using 1D-vdW heterostructure fabrication technique to modify and enhance the optical properties of the encapsulated nanomaterials [CE: Please check aff. we have deleted addrline mater and table 1 missing in source file we have capture in pdf. Please need to proof reading.]. [ABSTRACT FROM AUTHOR]

Networked optical wireless communication, also denoted as LiFi, is expected to play an important role in so-called smart hospitals. In this paper, we present the first experimental study of LiFi in an operating room at Motol University Hospital in Prague, Czech Republic. First, we perform one-to-one measurements using an optical transmitter (Tx) and receiver (Rx) and observe that channels with a free LOS provide sufficient signal strength for mobile communication inside the operating room. Then we combine the individual LOS links into a multiple-input multiple-output (MIMO) link using four distributed transmitters representing a wireless infrastructure, and six distributed receivers representing medical devices. In this configuration, at least two strong singular values of the MIMO channel matrix are observed which allow spatial multiplexing. By appropriately clustering the transmitters and selecting the users, mobile devices can be served in parallel. For data transmission, several multiplexing schemes such as time-division multiple access (TDMA) with one and two best links, TDMA with spatial reuse, space-division multiple access (SDMA) with two best links with and without zero forcing (ZF) are considered. Results show that SDMA with ZF increases the data rate by 2.7 times compared to baseline TDMA, resulting in a total data rate of 600 Mbit/s. [ABSTRACT FROM AUTHOR]

A novel technique was designed to measure the meniscus height (MH) of liquids on a standard single mode fiber (SMF) using fiber optics. Once the MH is known, the contact angle could be calculated, and the surface tension of liquids can be determined. In this paper, the MH is measured using a cleaved and side polished optical fiber attached to a SMF with a known separation distance between their fiber tips. When the liquid reaches the SMF, the liquid meniscus rises on the vertical wall of the SMF, which also causes a variation in mass (measured by a $\mu \text{g}$ scale). At this point, the liquid moves upwards until the liquid meniscus touches the side polished fiber, which registers a variation of the reflected optical power. The MH seems to increase as the surface tension decreases, and the variation of the mass measured by the scale increase with the increase of the surface tension. This sensor was also used to measure the interfacial surface tension of the air-liquid and liquid-liquid interface since the contact angle could be measured. In addition, the small dimension of the sensor is adequate for applications where using small amounts of liquid is critical, i.e., biomedical applications. [ABSTRACT FROM AUTHOR]

The nondispersive per-sample channel model for the optical fiber channel is considered. Under certain smoothness assumptions, the problem of finding the minimum amount of noise energy that can render two different input points indistinguishable is formulated. This minimum noise energy is then taken as a measure of distance between the points in the input alphabet. Using the machinery of optimal control theory, necessary conditions that describe the minimum-energy noise trajectories are stated as a system of nonlinear differential equations. It is shown how to find the distance between two input points by solving this system of differential equations. The problem of designing signal constellations with the largest minimum distance subject to a peak power constraint is formulated as a clique-finding problem. As an example, a 16-point constellation is designed and compared with conventional quadrature amplitude modulation. A computationally efficient approximation for the proposed distance measure is provided. It is shown how to use this approximation to design large constellations with large minimum distances. Based on the control-theoretic viewpoint of this paper, a new decoding scheme for such nonlinear channels is proposed. [ABSTRACT FROM AUTHOR]

We present a portable Rydberg-atom-based radio frequency (RF) electric ($E$) field measurement instrument (Rydberg field measurement system or RFMS). The RFMS comprises an atomic RF field probe (RFP) connected by a ruggedized fiber-optic patch cord to a portable mainframe control unit. The unit includes a software interface providing self-calibrated SI-traceable RF measurement and analysis, including real-time field and measurement uncertainty readout and spectral RF waveform visualization. We characterize the RFP and measure polar field and polarization patterns along primary axes of the RFP at 12.6 GHz, obtained by rotations of the RFP in the far-field of a standard gain horn antenna. Field pattern measurements at 2.5 GHz are also presented. The measured field patterns are in good agreement with finite-element simulations of the RFP, establishing that the atom-based RF $E$ -field probe is well-suited for SI-traceable RF measurements over multiple bands. A one-time calibration procedure and an uncertainty analysis are introduced and implemented, as required for practical atomic probe designs to realize absolute-standard SI-traceable measurement capability. This includes uncertainty contributions from the atomic-spectroscopy measurement method and analysis and from the material, geometry, and hardware design. Simultaneous RF field and polarization measurements are demonstrated. RF waveform measurement is demonstrated using example pulsed and modulated RF signals. [ABSTRACT FROM AUTHOR]

We developed a high spatial resolution and sensitive detector particularly suitable for radiation dose measurements in radiotherapy at small fields and X-ray imaging applications. The detector is based on a silica optical fiber whose sensitive terminal is functionalized by grafting Ag-doped ZnS scintillating materials that emit blue luminescence under X-ray irradiation. Due to the small scintillating head of the detector, the acquisition signal is quite low, and it is measured by a sensitive photon counter plugged at the other terminal of the fiber. The weaker signal can be enhanced significantly by adding a metal coating over the scintillator. Therefore, this study presents the effect of metal thickness and density on the signal amplification at high irradiation energies of 6 MeV and 15 MeV using a Linear Accelerator (LINAC). In addition, the stem effect was characterized for regular to small field beam size and shows that the detector is almost free from stem contribution during high energy irradiation. [ABSTRACT FROM AUTHOR]

This work develops a new optical photodiode array sensor for flow pattern identification of gas-liquid two-phase flow in minichannel. The array sensor is developed by the following steps to acquire comprehensive information of the flow and maintain a simple structure: 1) optical signals of the flow are acquired by a matrix array sensor with 60 sensing elements; 2) the signals are preprocessed and divided into 5 clusters by hierarchical clustering; 3) one typical sensing element from each cluster is selected; 4) the selected elements of four typical flow patterns are combined and the final sensor structure with 7 elements is determined. Experiments of flow pattern identification based on support vector machine (SVM) is carried out to verify the feasibility of the developed sensor in a 4.04 mm diameter channel. In addition, three types of feature vectors are built, including mean value, standard deviation and frequency, and their performance on the identification is investigated. The flowrate of liquid and gas phase range from 55~332 mm/s and 8~41468 mm/s, respectively. The investigated flow patterns include bubble flow, slug flow, stratified flow and annular flow. Results verifies the feasibility of the optical sensor. Among the three types of feature vectors, the standard deviation has the best performance, while the frequency has the worst. Meanwhile, the results also demonstrate that the combination of some specific feature vectors is an effective way to improve the identification performance. [ABSTRACT FROM AUTHOR]

The principle and procedure of coding a convolutional neural network (CNN) in terms of the spectral transmittance of a programmable optical filter are proposed and discussed. They exhibit an intrinsic link between the CNNs and the optical filters, which leads to a methodology by which optical imaging through such spectral transmittance can be seen as equivalent to the results of hyperspectral data numerically postprocessed by the CNN. In such a manner, hyperspectral data acquisition and CNN postprocessing can be implemented simultaneously by the physical process of optical imaging in a snapshot; thus, more intelligent, informative, and real-time optical detection and sensing in the remote sensing applications can be achieved. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles. [ABSTRACT FROM AUTHOR]

In this study, quantum dot light-emitting diodes with a side-pumping structure were designed for efficient heat management. The COMSOL Multiphysics software suite was used to conduct numerical evaluations. The electrical and optical field distributions and the heat distribution capability of the aforementioned structure were investigated. The side-pumping package was found to be capable of effectively dissipating heat and significantly reducing the areal temperature from 32.1 °C (in-chip) to 28.9 °C with an operating current of 35 mA. The integrated intensities of the perovskite quantum dot photons of the in-chip and side-pumping devices were approximately identical (1.23:1). However, the side-pumping device required 58.3% less filling material than the in-chip device. Optical and thermal modeling and measurements indicated that the side-pumping architecture can not only enhance thermal dissipation but also reduce the usage of quantum dot material. The findings of this study provide useful information for the incorporation of quantum dots in photonic devices. [ABSTRACT FROM AUTHOR]

All-silicon highly-doped PN junction-based photodetectors, for photonic integrated circuit (PIC) calibration and power monitoring, are designed and fabricated in the C-band. The photodetector response is measured for different doping conditions. The photodetectors are integrated with an interferometric based phase-interrogator structure for a test calibration circuit. The measured devices show high responsivity (12 A/W) obtained under avalanche condition at 5.7 V reverse bias and reasonable dark current ($1~\mu \text{A}$) due to photon assisted tunneling effect and are therefore, proved to be an ideal candidate for power monitoring and phase calibration of PICs. [ABSTRACT FROM AUTHOR]

Currently, the breast cancer diagnosis is performed by microscopic examination of thin slices of ex-vivo biopsy tissue by the pathologist. In this paper, a robust and affordable LED-based time-domain near-infrared spectroscopy system (Spectro-IRTDx) is proposed to further aid the pathologist for rapid and accurate breast cancer diagnosis. The measurements are performed on formalin-fixed cancerous tissues (invasive ductal carcinoma) and their adjacent normal tissues obtained from N = 6 patients. The mean effective attenuation coefficient (${\mu }_{\textit {eff}}$) for cancerous tissue is found to be 5.41 and 2.41 times higher than adjacent normal tissue, with good statistical significance (p = 0.00216) while operating at 850 nm and 940 nm, respectively. The average detected peak voltage (DPV) for adjacent normal tissue is found to be 3.44 and 4.16 times higher than cancerous tissue, with good statistical significance (p = 0.00216) while operating at 850 nm and 940 nm, respectively. The mean time of flight for cancerous tissue was 46 ns and 4 ns higher than the adjacent normal tissue while operating at 850 nm and 940 nm, respectively, with good statistical significance (p = 0.00216) at 850 nm. The obtained results establish the proof-of-concept of the time-domain near-infrared spectroscopy for rapid diagnosis of core biopsy tissues. [ABSTRACT FROM AUTHOR]

Deep learning has been widely used in various sensor detection fields to realize intelligent detection tasks. However, there are always restrictions on how these functions can be integrated into embedded devices to complete mobile and convenient sensing detection tasks. Therefore, the MobileNet_SSD, A lightweight model after simplification and optimization, is used in this paper to design a portable visual sensor system for the detection of spray droplet deposition in drone applications. The sensing system includes a droplet deposition image loop acquisition device and a supporting host computer interactive platform. It introduces the Sarsa algorithm to establish an adaptive model of light intensity to enhance the robustness and combines Deep Neural Networks and image processing technology to achieve rapid loop detection of droplet deposition parameters on the mobile terminal. Experimental results indicate that the proposed sensor can adapt to light changes in complex environments, and accurately measure the deposition parameters of different droplet density images. Furthermore, it is of great significance to detect the quality of drone sprays, master the rules of droplet deposition, and understand the effects of pesticide spraying. [ABSTRACT FROM AUTHOR]

In this study, lightning-induced currents due to a triggered lightning with a strike distance of 8 m were measured at an unenergized 200-m overhead line. The characteristics of the coupling current excited by four return strokes were analyzed in time and frequency domains, respectively. Moreover, a 3-D finite-difference time-domain (3-D FDTD) model was built to calculate the coupling current, which was verified by comparing the simulation results against the recorded data. The influence of the constant return stroke velocity and the variable velocity on the coupling current was analyzed by using the 3-D FDTD model. The results indicate that the lightning-induced currents on the overhead line are significantly affected by the nonmonotonically variable return stroke velocity. [ABSTRACT FROM AUTHOR]

Silicon photonics realized in CMOS processes has transformed computing, communications, sensing, and imaging. Although silicon is an indirect bandgap material prohibiting efficient light generation, considerable work has been conducted in the field of silicon p-n junctions emitting broadband visible light when operating in the high-voltage reverse breakdown avalanching mode. Here, we demonstrate high-brightness near-infrared (NIR) light emission for forward-biased silicon micro-light emitting diodes (micro-LEDs) realized in an open-foundry microelectronic CMOS process—55 BCDLite—with zero modification. Under room-temperature continuous-wave operation, the external light emission intensity of over 40 mW/cm $^{{2}}$ at a central wavelength of 1020 nm is achieved for a 4- $\mu \text {m}$ -diameter device at below 2.5 V. This is realized by adopting a deep vertical junction with guard ring designs that ensure carrier transport away from the device surface and material interfaces where nonradiative recombination usually dominates. Here, we also demonstrate a complete chip-to-chip communication link using only standard multimode fiber and monolithically integrated CMOS micro-LEDs and detectors. [ABSTRACT FROM AUTHOR]

We calculate numerically the capacity of a lossy photon channel assuming photon number resolving detection at the output. We consider scenarios of input Fock and coherent states ensembles and show that the latter always exhibits worse performance than the former. We obtain capacity of a discrete-time Poisson channel as a limiting behavior of the Fock states ensemble capacity. We show also that in the regime of a moderate number of photons and low losses the Fock states ensemble with direct detection is beneficial with respect to capacity limits achievable with quadrature detection. [ABSTRACT FROM AUTHOR]

Water leakages in water distribution systems due aging of pipes is a problem affecting most countries around the world. Official reports from government-commissioned surveys indicate that water losses are estimated to amount to an average of around 30% in most countries, with peaks up to 60% [1]–[3]. Such amounts increase in urban areas, reaching 70 to 80% in some cities. From an economic point of view, these losses have a cost that has been estimated for the European region to an overall of 8 billion a year [1]. [ABSTRACT FROM AUTHOR]

The whole world experienced in the last decades a continuous change in the age pyramid related to the population aging, where there is an increase in the elderly population (over 65 years) when compared with other age groups [1]. Such demographic change is not essentially an issue, since it demonstrates that the life expectancy is increasing, directly related to many advances in medicine, public health and biotechnology as well as social and economic developments that allow access for the general population to health treatments [1]. The population aging in conjunction with chronic diseases, where some of them are also age-related, leads to some clinical conditions that can affect human health such as osteoarthritis, rheumatoid arthritis, Alzheimer's disease, Parkinson's disease and weakness of the skeletal muscles [2]. These clinical conditions can lead to different types of disabilities, and the most common type is locomotion impairment, which occurs with nearly 14% of the world population [3] and represents around 1 billion people. As locomotor impairment harms work performance, activities of daily living and independence in the community, there is a necessity for continuous treatment of the different conditions that result in locomotor impairments. [ABSTRACT FROM AUTHOR]

A refractometric sensor was applied to measure in real-time the concentration of Active Pharmaceutical Ingredients (APIs) in crystallization experiments. Paracetamol was used as a model system due to the extensive literature available for this API. The refractometric sensor was fabricated by a simple and inexpensive method that consisted in splicing a short section of a multimode fiber to a single mode fiber. The compact geometry of this sensor, with an external diameter of just 125 μm, allowed it to measure the concentration of paracetamol, both in a stirred tank crystallizer operating in batch and in an oscillatory flow crystallizer operating continuously. The proposed technique shows the potential to monitor the concentration of APIs in crystallizers of different sizes and geometries as an alternative to more expensive and complex analysis equipment. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate digitally programmable optical frequency combs (OFCs), featured by binary phase distribution and flat power envelope among comb lines for the first time. In the proposed simple generation scheme, a programmable optimized binary sequence is generated and applied to phase modulate a CW lightwave, creating an OFC with joint manipulation of both binary phase distribution and flat power envelope. Moreover, by digitally programing of the binary sequence, the generated OFC shows high tunability on comb spacing and comb-line number. In the experiments, tunable comb spacing of 20, 10, 5, 2 MHz and tunable comb-line number of 21, 51, 101 are demonstrated, while retaining excellent binary phase and flat power envelope. Such an agile joint manipulation of both phase and power paves a new way for promising phase-correlated applications of OFCs, such as the covert communications and weak signal detection. [ABSTRACT FROM AUTHOR]

We demonstrate a technique of evaluating optical signal to noise ratio (OSNR) associated with an optical carrier in a fiber-optic system using a commercial coherent optical transceiver equipped with digital signal processing capability. The procedure of measuring noises caused by the transmitter and the receiver is outlined, and these transceiver-related noises need to be taken into account in order to accurately evaluate the system OSNR. Through digital polarization-demultiplexing and polarization nulling in the receiver, it is possible to extract the noise underneath the optical signal, and to measure the tilt of the ASE noise spectrum within the optical signal bandwidth. [ABSTRACT FROM AUTHOR]

Dual-wavelength light source assisted frequency response measurement of photodetectors based on double-sideband suppressed-carrier modulation is proposed in this letter. In this method, a directly modulated laser with a modulation frequency of ƒ1 combined with an optical tunable filter is used to generate a dual-wavelength carrier, which can be highly stable since only one light source is introduced. The dual-wavelength carrier generates two pairs of first-order sidebands under double-sideband suppressed-carrier modulation of the Mach-Zehnder modulator at frequency ƒm. Afterwards, the modulated signal is injected into the photodetector under test, and the frequency response of the photodetector can be extracted by recording the electric power at specific frequencies. Based on this method, we used a 35-GHz modulator to measure the frequency response of photodetectors with bandwidth of 15 GHz and 43.5 GHz respectively. Moreover, a comparison of the results is performed between our method, the swept frequency method, and electro-absorption modulator deduction method. The results show that the new method extends the frequency response measurement range from ƒm to ƒ1 + 2ƒm, and the influence of the modulator on the frequency response measurement results is reduced simultaneously. [ABSTRACT FROM AUTHOR]

A low-frequency angular acceleration rotary table (LFAART) is capable of sinusoidal motion around a fixed position and essential to verify dynamic characteristics of a gyroscope device. The table’s performance at different swinging frequencies and amplitudes needs to be calibrated to realize traceability. However, there has been little research on the LFAART calibration. Besides, the existing measurement methods of sinusoidal angular motion parameters are not adequate for the needs of the LFAART calibration in terms of measurement range, precision, and feasibility. This article presents a calibration scheme combining an optical shaft encoder and a laser triangulation sensor. When the rotation amplitude covers sufficient slots of the scale grating, the optical shaft encoder is applied, while the laser triangulation sensor is used for a tiny amplitude motion. An algorithm is proposed to accurately calculate the angular acceleration amplitude and frequency of the rotation utilizing sinusoidal phase-modulated signals of the optical shaft encoder output. Singular zero-crossings of the series are discarded, and intervals of reversing moments are recognized according to the signal derivative’s sign at remaining zero-crossings. Then intervals are divided into subintervals to obtain accurate reversing moments. Finally, angular displacements between two adjacent reversing moments are estimated based on the fringe counting method, and the amplitude and frequency are calculated. The measurement uncertainty analysis and experiment demonstrate that the calibration scheme, including the algorithm, possesses high accuracy and resolution, wide range, and good operability, which perfectly solves the rotation’s angular acceleration amplitude and frequency. [ABSTRACT FROM AUTHOR]

We here demonstrate the potentialities of pigtailed electrooptic probes to perform vectorial electric field characterizations of dielectric barrier discharges (DBDs). The analysis leads to the accurate determination of the breakdown voltage and the associated electric field in the vicinity of the discharge. A polarimetric analysis of the DBDs is proposed due to real-time measurement of longitudinal and radial components of the electric field vector. Moreover, the transition from capacitive to resistive behavior is characterized at the breakdown field. [ABSTRACT FROM AUTHOR]

Remote photoplethysmography (rPPG) enables noncontact heart rate (HR) estimation using facial videos and exhibits significant convenience over traditional contact-based HR measurement approaches. However, its effectiveness depends mainly on the number of pixels of the facial region; thus, the estimation accuracy is easily degraded due to missing rPPG information when the resolution of facial images is low. Given that, in most real application scenarios, such as group-oriented and long-distance vital signs measurement, only low-resolution facial videos are available, finding a solution to recover rPPG information is a key to improve the performance of noncontact HR measurement. In this article, we propose a two-stage deep learning scheme to achieve accurate HR measurement from low-resolution facial videos. In the first stage, an rPPG information recovery network is proposed to recover the rPPG information during video super-resolution (SR) processing. The up-scaled images are then fed into a temporally aware HR measurement network in the second stage. An attention mechanism that reassigns the weights of the temporal information in each feature channel is designed to improve the measurement accuracy. The mean absolute percentage error achieves 3.320 and 4.231, while Pearson’s correlation coefficient reaches 0.930 and 0.892 on two datasets, respectively. Experimental results show that rPPG information could be effectively recovered through SR processing. Compared with the state-of-the-art approaches that treat high-resolution images as the input, the proposed method achieved closely comparable measurement performance using merely low-resolution images. [ABSTRACT FROM AUTHOR]

For the purpose of monitoring seawater temperature, a novel Mach–Zehnder (MZ) temperature-sensing structure with a wedge-shaped open cavity is presented and experimentally studied in this article. The open-cavity structure realizes the direct contact between the sensing optical path and the external environment, and ensures the high sensitivity of the structure. At the same time, it achieves not only low loss by direct fusion splicing instead of dislocation fusion splicing, but also low cost by hydrofluoric (HF) etching instead of femtosecond processing. In addition, the temperature sensitivity of the sensor structure proposed in this article can reach 1.5 nm/°C without temperature-sensitive material filled, and 6 nm/°C with silicone oil filled. Moreover, the resolution of the sensing structure is 0.24 °C based on the criterion of $3\sigma $. [ABSTRACT FROM AUTHOR]

For many industrial applications, corrosion is a life-limiting phenomenon and therefore requires careful consideration and rigorous experimental testing before structural materials can be reliably deployed, particularly in harsh chemical environments. The traditional approach to measuring corrosion requires exposing many samples to the intended environment and then extracting them individually at discrete intervals for postexposure characterization. This approach does not provide a high degree of temporal resolution, nor does it provide any real-time information regarding dynamic changes in corrosion rates. Developing an online corrosion monitor capable of surviving harsh chemical environments could provide valuable information regarding the structural health of components and changing process conditions that could accelerate corrosion. To this end, a corrosion sensor was developed based on a pressure-driven Fabry-Pérot cavity (FPC). This sensor uses a pressure control system to internally pressurize the FPC formed between the sensor’s housing and a metal-embedded singlemode optical fiber. Simultaneous measurement of the change in FPC length using low-coherence interferometry and the applied pressure enables the calculation of the relative changes in the sensor’s diaphragm thickness due to corrosion on its outer surface. Measurements were made in situ while actively corroding the sensor and were validated against surveillance specimens that were corroded simultaneously. The uncertainties in the measured corrosion were analyzed using error propagation of the uncertainties in the measured pressures and displacements and were found to be <1% of the initial diaphragm thickness. [ABSTRACT FROM AUTHOR]

This article demonstrates a spectroscopic diffuse optical tomography (DOT) system for the noninvasive continuous imaging of tissue. The system was built on an embedded system architecture along with an algorithm that performs entire system control, data acquisition, noise-free lock-in detection, and wireless data transmission to a host computer, equipped with a graphics processing unit (GPU). The GPU system executes a fast 3-D DOT spectroscopic image reconstruction algorithm. The algorithm computes Jacobians and solves four different depth-sensitive inverse problems of image reconstruction. The host computer sends commands to the DOT server system and collects data, and simultaneously performs high-speed 3-D spectroscopic image reconstruction to display images in real-time. We designed a configurable optical fiber patch to collect depth-resolved diffused light exiting the imaging media by placing the patch on the surface. The simulation and experimental results from two setups showed the spectroscopic imaging capability of the system to map the concentration of oxyhemoglobin, deoxyhemoglobin, and water, and to characterize the tumor located deep inside the tissue. The proposed system uses low-cost LEDs, photodiode detectors, embedded system, and algorithms to perform high-speed 3-D functional imaging and can be further miniaturized. Our promising results pave the way for the development of a low-cost hand-held spectroscopic DOT system for the real-time onsite functional imaging of biological tissue. [ABSTRACT FROM AUTHOR]

A broadband optoelectronic (O/E) frequency response measurement method utilizing photonics-based frequency conversion is proposed and experimentally demonstrated. It is characterized by a sub-kilohertz frequency resolution and a doubled measurement bandwidth compared with the RF frequency sweeping range and the working bandwidth. A carrier-frequency-shifted optical double-sideband (ODSB) signal is produced by employing a dual-drive Mach-Zehnder modulator (DD-MZM) and stimulated Brillouin scattering (SBS). Then, a photodetector (PD) under test receives and converts the optical signal into a photocurrent. By detecting the frequency up- and down-conversion components generated by the two first-order sidebands and the optical carrier, the O/E frequency responses in the low- and high-frequency regions are achieved. After stitching the two measured responses together, an O/E frequency response with a frequency range that is twice the bandwidth of the input microwave signal is obtained. In an experiment, the O/E frequency response of a commercial high-speed PD is precisely characterized with a frequency resolution up to 5.55 MHz. A frequency bandwidth of 66.8 GHz (0.1–66.9 GHz) is achieved by using a 25-GHz DD-MZM. The measured O/E frequency response is coincident with that measured by a commercial instrument. [ABSTRACT FROM AUTHOR]

Obtaining a continuous relationship between input and output is essential during sensor characteristic determination. However, it is a little challenging for complicated input data, for example, image data. In this article, a sensor characteristic determining method using deep learning Compact yet Efficient Cascade Context-based Estimation (C3E) network, which can establish the continuous relationship between the input and the output, was proposed. A UV sensing system based on this C3E method was presented. The sensor after algorithm optimization has a sensitivity of $1~\mu \text{W}$ /cm2. The limit of detection is $9~\mu \text{W}$ /cm2. The network test time is close to 3 s, and the error rate is 5%, which is very suitable to transplant to the embedded platform and provides solutions for compact instruments. [ABSTRACT FROM AUTHOR]