Optical Current Sensor Research Articles

Sensitivity-improved fiber optic current sensor based on an optoelectronic oscillator utilizing a dispersion induced microwave photonic filter.

An optoelectronic oscillator (OEO)-based fiber optic current sensor (FOCS) with greatly improved sensitivity is proposed and experimentally demonstrated. A microwave photonic filter (MPF) induced by the dispersion effect of a linearly chirped fiber Bragg grating (LCFBG) is used to select the frequency of the OEO oscillating signal. A two-tap MPF formed by a polarization multiplexed composite cavity is cascaded to achieve a stable single mode oscillation. When the current changes, the magneto-optic phase shift induced by Faraday effect will be introduced between the left and right circularly polarized lights transmitted in the reflective sensing unit. The magneto-optic phase shift is converted to the phase difference between the optical carrier and sidebands through a LiNbO3 Mach-Zehnder modulator. This phase difference is the decisive factor for the center frequency of the cascaded MPF as well as the oscillating frequency. Therefore, the current can be measured in the microwave frequency domain, which can improve the interrogation speed and accuracy to a large extent. The experimental results show that the oscillating frequency shifts up to 407.9 MHz as the current increases by 1 A.

Simulation analysis of temperature effects on all-fiber optic current sensor

Temperature is the main factor restricting the application of all-fiber current sensors. To comprehensively analyze temperature influences, the influences of temperature on Verdet constant, birefringence, and phase delay of the quarter-wave plate are modeled and simulated by the Jones matrix and Matlab. Basing on the normalized scale coefficient, the relationship between the normalized ratio coefficient and temperature is discussed. Finally, we get the conclusion that the normalized proportional coefficient of feedback phase shift fluctuates on both sides of the reference temperature. Keeping the temperature in a narrow range is a practical scheme to improve the system performance.

Low error of garnet optical sensor induced by spin Hall effect

The Polarization properties of a linearly polarized laser beam reflected from garnet/Au, Ta/Nd2Fe14B/Ta/garnet/Au are studied by a Thorlabs PAX 5710 IR3 polarimeter undser external magnetic and direct current (DC) electric fields. The Nd2Fe14B, Ta and Au films are prepared by a DC magnetron sputtering method. The magnetic domains of the garnet films are obtained by a polarized light microscope. The magnetic domains in different garnet films show different distributions. The error of the Stokes parameter S1 is used to characterize the results. The S1 of the linearly polarized laser beam reflected from garnet/Au and Ta/Nd2Fe14B/Ta/garnet/Au shows different trends with the magnetic and electric fields. The maximum error S1 of garnet/Au is 0.005%, while the maximum error S1 of Ta/Nd2Fe14B/Ta/garnet/Au is 0.003%, when the external DC voltage increases from 0 to 2.5V, and the magnetic field increases from 0 to 100Oe. The low error may be induced by the spin Hall effect of garnet and Au. It is very important for the manufacture and design of optical current and voltage sensors.

Highly Stable and Precise Demodulation of an FBG-Based Optical Current Sensor Using a Dual-Loop Optoelectronic Oscillator

Electrical current monitoring plays an important role in power transmission system, electric instruments, etc. The stability of the monitoring system is highly demanded. In this paper, a new interrogation scheme for a fiber Bragg grating (FBG) current sensor based on a dual-loop optoelectronic oscillator (OEO) with high stability, high precision and simple structure is proposed and experimentally demonstrated. The wavelength shift of the FBG, which is bonded on a magnetostrictive alloy-strip, is converted into the frequency shift of the microwave signal through the OEO system utilizing the wavelength to frequency mapping mechanism. Different from previous single-loop OEO schemes, a length of ∼1 km single mode fiber is used to form the second loop in the OEO-cavity, which can enhance the mode-selection ability and reduce the total gain requirement of the system. In addition, a fiber-ring-laser (FRL) cavity is adopted by integrating the sensing FBG-head as the wavelength-selective component to improve the quality of the optical carrier signal. The measured side-mode suppression ratio (SMSR) is up to 62.59 dB and the free spectral range (FSR) is five times larger than the single-loop structure, resulting in highly-enhanced stability and so the precision. Most importantly, the frequency fluctuation is as low as 0.277 ppm, which is the minimum to the best of our knowledge. Compensating methods for the influence of the temperature and the hysteresis are also discussed. The proposed scheme provides a feasible solution to promoting the development of OEO-based interrogation technology and its commercial applications.

Influence of polarization, multi-valences and multi-coordination of cobalt: Third-order nonlinear, dielectric and Faraday properties of Bi0.5Co1.5S3/high optical basicity glass

In this study, we have successfully grown Co doped Bi0.5Co1.5S3 nanocrystals inside heavy metal oxide diamagnetic 42PbO-48TeO2-10B2O3 glass whose morphology, structure and properties were characterized using various techniques. The optimum parameters for Bi0.5Co1.5S3 nanocrystals formation is 380°C for 10hours. Glasses having different amounts of Bi0.5Co1.5S3presented colors from light yellow to green and pure blue due to the different optical absorption of Co2+ ions in octahedral and tetrahedral coordination units. X-ray diffraction pattern revealed the formation of orthorhombic Bi2S3 nanocrystals in glass and Raman spectra demonstrated modification on structure such as TeO4 → TeO3 and BO → NBO conversion. The red shift in transmission cutoff edge of glasses showed experimental evidence of quantum confinement effect. Due to the high optical basicity system, X-ray photoelectron spectra studies confirmed the co-existence of Co2+, Co3+ and Co4+ which presented characteristic absorption in ultraviolet-visible spectra. The introduction of Bi0.5Co1.5S3 greatly increased the polarizability of glass, resulting in significant improvement on third-order nonlinearity, AC conductivity and dielectric constant. 1% Bi0.5Co1.5S3 doped glass presents giant Verdet constant of 62 rad/T.m at 633nm, promising nonlinear refractive index (5.662 × 10−11 esu) and large dielectric constant (78). This result proved that the synthesis of multivalence states of Co doped Bi2S3 in glass is an efficient method to improve the optical, dielectric and magneto optical performance of glass. Such dilute magnetic semiconductor nanocrystals-glass system has great potential applications in nonlinear, dielectric and magneto optical current sensors and isolators devices.

Applications of magneto-strictive, magneto-optical, magnetic fluid materials in optical fiber current sensors and optical fiber magnetic field sensors: A review

Currently, electromagnetic current and magnetic field sensors are suffering from disadvantages of a complex insulating structure, high cost, easily explosive and difficult to digitized. Optical fiber current sensors and optical fiber magnetic field sensors are promising methods to overcome these risks due to these features of the optical fiber itself insulating, light weight, digitizable. Moreover, it is more potential to transform them from lab to application. This review focus on the optical fiber current sensors and optical fiber magnetic field sensors based on magnetically sensitive materials. According to the different magnetically sensitive materials to be coated, the optical fiber current sensors and optical fiber magnetic field sensors based on magneto-strictive materials, magneto-optical (MO) materials and magnetic fluid (MF) materials are discussed in detail. The sensing mechanism of three magnetically sensitive materials are studied. And the optical fiber current sensors and optical fiber magnetic field sensors are researched about the sensing principle, characterization, structure, and performance of the sensors. The future development direction is prospected about optical fiber current sensors and optical fiber magnetic field sensors based on magnetically sensitive materials, and then the future development prospects and challenges of three magnetically sensitive materials are analyzed in detail.

A PORTABLE OPTO-ACOUSTIC SURVEY SOLUTION FOR MAPPING OF UNDERWATER TARGETS

Abstract. During underwater investigations, whatever the mission objective and the type of vehicle, obstacles detection and avoidance are essential tasks. They can either represent a target of interest that is the object of the mission or, on the contrary, represent obstacles that can hinder or affect the navigation of the vehicle. The underwater optical cameras that are usually fitted to underwater vehicles only offer a narrow field of view. The absorption of electromagnetic waves in the first few meters and the diffusion of light by the particles limit the use of these sensors to only a few meters range. The use of acoustic sensors, such as the forward looking sonar (FLS), is then necessary to enlarge the volume in which a target can be detected during the progression of the vehicle. Traditionally, sonars featured mechanical rotating parts, but lately bidirectional forward looking sonar, which directly produces a 2D image of the area, are becoming more and more common. Although these sonars can operate at frequency higher than 1MHz, their spatial resolution remains much lower if compared to current optical sensors and can be insufficient to identify and characterize a target. The combination of these two sensors in an operational scenario is essential to take advantage of each technology. In this paper we describe a low cost, multi-sensor, underwater survey solution for the identification, tracking, and 3D mapping of targets. After a description of the architecture of the opto-acoustics data acquisition and processing platform, we will focus on the calibration of the rigid transformation between the two sensors.

Current sensing characteristics of the helical long-period fiber grating written in polarization maintaining fiber

An optical fiber current sensor based on helical long-period fiber grating (HLPG) inscribed in polarization-maintaining fiber (PMF) by CO2 laser has been proposed. The PMF-HLPG is put into the solenoids with a direct current (DC) current source, and the value of applied current can be measured by monitoring the rotation angle of the input elliptical polarized light due to the changes of the magnetic field along the grating. The main factors that affect the rotation angle have been investigated experimentally. The experimental results show a good linear relationship between the rotation angle and the applied current, which indicate that the PMF-HLPG can be used as all fiber current sensor. The maximum sensitivity of the current measurement can be achieved by adjusting the parameters of the input elliptical polarized light. The current sensor based on the PMF-HLPG exhibits high sensitivity even for the detection of small electric current.

Passively biased inline Sagnac interferometer-optical current sensor: theoretical review

A full theoretical analysis of the performance of passive inline Sagnac interferometric optical current sensor with component errors has been completed. A mathematical model was developed to show how nonideal components affect the overall performance of the sensor. The Faraday rotator element is a critical component in this passively biased optical current sensor. The analysis indicates that errors in the rotation element in the assembly can cause a ∼10 % / deg nonlinear error with current. Another source of nonlinearity in the response of the sensor is the 45-deg splices to the polarization maintaining fiber (PMF) link between the rotator element and the sensing head assembly. The analysis indicates a ∼0.2 % / deg error for the splice between the rotator and PMF link to the sensing head and a ∼0.1 % / deg error for the splice between the PMF and the quarter waveplate fiber at the sensing head. All quarter waveplate errors in the rotator assembly have linear effects to the sensor response function which can be calibrated out of the final sensor assembly. Temperature response data are presented for an uncompensated sensor over the +40 ° C to −30 ° C temperature range and the sensor shows a ±1.5 % accuracy.

Digital Optical CT Application to HVDC Earthing Line Fault Measurements

A digital optical current transducer designed for the measurement of small alternating currents is applied to current measurements for an HVDC earthing line. A novel scanning band pass filter was used to make experimental measurements of small high frequency currents. Currents from 1 kHz to 5 kHz and 0.2 A to 2 A in the presence of 20 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> have been experimentally made. With accuracies of less than 0.4% for the 2 A measurement. The optical current transducers can measure currents remotely up to 20 km from the converter station. This new optical current sensor measurement method can allow the location of faults on HVDC earthing lines.

The effect analysis of impact on a fiber optic current sensor

Nowadays, the fiber optic current sensor (FOCS) has been massively used on the warships. However, the performance of the FOCS will be greatly affected by the impact on warships, since the stress field caused by the impact will introduce an elastic-optic effect-induced bias error to the FOCS. To improve the performance of FOCS applied in warships, the accurate model of elastic-optic effect-induced bias error is necessary for its practical applications. In this paper, we analyze the mechanical stress on an in-line Sagnac fiber optic current sensor during the impact and find that the bias error is mainly caused by the stress acting on the delay coil. Then we present a mathematical model of non-anisotropic phase error caused by impact on delay coil from the perspective of the three-dimensional model and theoretical results are obtained by simulation. Finally, experiments are carried out according to the test methods specified in national standards. The correctness of the error mathematical model is verified by experiments that the differences between simulation and experiment are within 10%.

Improving the computational efficiency of birefringent model based on equivalent matrix and modified permittivity

Taking advantage of optical birefringence is a promising method for manufacturing many useful devices. However, due to the multiple causes of birefringence or the large size of the birefringent devices, the numerical simulation of equal-ratio-size birefringent devices is highly inefficient. In this paper, a new method for improving the calculation efficiency of birefringent model based on equivalent matrix and modified permittivity is proposed. By calculating the equivalent matrix with scaling factor a and then modifying the permittivity, complex and large size structures are equivalent to a simple model in the simulation software. Considering the power transmittance and the authenticity of the model, the value range of a has been fully discussed. With the proposed method, simulation time and memory requirement are greatly optimized in proportion to a. We use fiber optics current sensor as an example to verify our model, and the numerical results are in close agreement with the analytical calculation.

Performance assessment of plasma current measurement at JET using fibre optics current sensor

The Fibre Optic Current Sensor (FOCS) is a diagnostic system to be installed in ITER to perform plasma current measurements during long plasma discharges under intense nuclear radiation. The sensor performance must be experimentally assessed at ITER representative conditions. JET is a unique machine where this task can be performed. We have installed polarisation detection based FOCS systems at JET and performed measurements in various machine operating scenarios at currents up to 3.5 MA. The frequency analysis of the data was performed to investigate the sensitivity of FOCS to mechanical perturbations. A significant part of the noise originates from the optical link between the sensing fibre and the polarisation analyser. Operation with a Faraday mirror reduces this effect. It is confirmed that the FOCS system has performance characteristics compatible with the ITER requirements.

Design of Polarimetric-Based Optical Current Sensor for Electric Power System Application

Many problems arise in the electric power protection system due to applying a ferrous core current transformer (CT). One of the most crucial problems is a magnetic saturation issue, which tends to cause a measurement error on the secondary side of the CT and could reduce the performance of the protection system. An alternative solution to this issue is the needs to develop an electric current sensor utilizing optical materials. A polarimetric-based optical current sensor (OCS) is a technique considered to be compatible with the future smart grid environment. The OCS principles are based on the magneto-optic Faraday effect that could produce optical rotation in the optical media when a polarized light propagates in those materials. Due to the linear and circular birefringences effect in optical fiber medium are exist, therefore, in this paper the OCS and its associated elements are modelled by considering the birefringence effect in the optical sensor system including optical fiber links. Then, the OCS model is translated to a computer simulation program using a computer application software. Orientation of the second polarizer (analyzer) to the first polarizer in the simulation were conducted using two different angles which are angle α of 45° and 90°. Performance assessment of the OCS model is presented using two various electric current of the power system test to investigate the presence or absence of the saturation effect that may arise in the polarimetric-based optical current sensor model. The simulation results have provided that the saturation effect disappear in the simulation and the analyzer orientation angle α of 45° gives better performances of optical power modulation than the other angle.

Influence of structure parameters of optical current sensor with iron core on temperature distribution

The accuracy of optical current sensors in power systems will be affected by the interference of the external environment. Among them, temperature has a significant influence on the accuracy of optical current sensors, which is one of the main factors that restrict the practicality of optical current sensors. In this paper, the temperature field distribution of the optical current sensor with iron core is calculated by simulation. The influence of its structural parameters on the temperature field distribution is studied. It is compared with the temperature field distribution of the optical current sensor of the commonly used magnetic ring structure. It is found that under the same current, the temperature of the magneto-optical material with the core optical current sensor is much lower than the optical current mutual inductance of the common magnetic ring structure. The geometric structure parameters of the optical current sensor with iron core have a great influence on its temperature field distribution. The temperature field distribution can be improved by optimizing the structure parameters, thereby improving the measurement accuracy. This article can provide a basis for the design optimization of optical current sensors.

Research on Measurement Technology of Ship Leakage Current by All-Fiber Optic Current Sensor

Research on Measurement Technology of Ship Leakage Current by All-Fiber Optic Current Sensor

Optical Fiber Current Sensors Based on FBG and Magnetostrictive Composite Materials

Optical fiber current sensors are widely used in the online monitoring of a new generation power system because of their high electrical insulation, wide dynamic range, and strong anti-electromagnetic interference ability. Current sensors, based on fiber Bragg grating (FBG) and giant magnetostrictive material, have the advantages of high reliability of FBG and high magnetostrictive coefficient of giant magnetostrictive material, which can meet the monitoring requirements of digital power systems. However, giant magnetostrictive materials are expensive, fragile, and difficult to mold, so giant magnetostrictive composite materials have replaced giant magnetostrictive materials as the sensitive elements of sensors. High sensitivity, high precision, wide working range, low response time, and low-cost optical fiber current sensors based on magnetostrictive composites have become a research hotspot. In this paper, the working principle of the sensor, the structure of the sensor, and the improvement of magnetostrictive composite materials are mainly discussed. At the same time, this paper points out improvements for the sensor.

Self-Compensative Fiber Optic Current Sensor

The measurement accuracy of fiber optic current sensors (FOCS) is closely related to the stability of Verdet constant and the polarization characteristic of the sensing coils, which are easily influenced by environmental disturbance. In this article, a self-compensative fiber optic current sensor (SFOCS) with two sensing heads made of single mode fibers is designed and demonstrated. Utilizing sensing and compensative unit as well as a close-loop system, variation of Verdet constant and birefringence is compensated. We numerically calculate the output signal of SFOCS with temperature varying from $-\text{30}^{\circ }$C to 75 $^{\circ }$C and simulate the situation where SFOCS is affected by the circular and linear birefringence from the environment, and the results confirm that well designed SFOCS is completely temperature- and vibration-independent. Additionally, in order to achieve the ideal compensation, $\mathcal {H}$ function of SFOCS related to birefringence and the current to be measured is introduced and deeply studied. Moreover, we discuss the measurement errors of SFOCS caused by the difference between two sensing heads such as the coupling ratio, the linear and circular birefringence, and we calculate the acceptable error range, within which SFOCS can meet the class 0.2 standard.

Research on the Methods and Algorithms Improving the Measurements Precision and Market Competitive Advantages of Fiber Optic Current Sensors.

An electromagnetic instrument transformer is a common device used to measure large current values in high-voltage electrical networks; it has been in use for more than a century. However, the optical current transformer, a promising technology also known as a fiber optic current sensor (FOCS), offers increased safety and ease of operation, as well as the absence of errors caused by the magnetic circuit of legacy transformers. Although the FOCS scheme is well known and has been actively developed for over a quarter century, it has certain disadvantages that limit its use. This paper describes the authors’ efforts to solve these problems in order to make FOCS technology competitive and widely adopted. We upgraded the FOCS optical circuit, expanded the frequency band of the captured current signal, and reduced the solution’s cost. We designed new signal processing algorithms to compensate for errors caused by internal factors in the measurement circuit, as well as those caused by environmental influences. We developed an FOCS computer model based on the Jones matrix formalism to enhance the experimental debugging. It allowed us to define the requirements for elements of the optical circuit and its production accuracy.

High sensitivity demodulation of a reflective interferometer-based optical current sensor using an optoelectronic oscillator.

A novel, to the best of our knowledge, interrogation scheme based on an optoelectronic oscillator (OEO) with high sensitivity and high speed response for a fiber optical current sensor utilizing a reflective interferometer is proposed and experimentally demonstrated. Due to the Faraday effect, a magneto-optic phase shift induced by current variation is generated between two orthogonal light waves. The polarization-dependent properties of the Mach-Zehnder modulator are used to convert the magneto-optic phase shift into the phase difference between the optical carrier and sideband, which is then mapped to the oscillating frequency shift by closing an OEO loop. A high current sensitivity of 152.5 kHz/A with a range of 0-2.5 A is obtained in the experiment.