Applications Of Fiber Optic Sensors Research Articles

Multichannel Fiber Optic SPR Sensors: Realization Methods, Application Status, and Future Prospects

AbstractFiber optic sensors based on surface plasmon resonance (SPR) have demonstrated outstanding performance in biomedical, environmental monitoring, public safety, and other aspects, which provide powerful platforms for qualitative detection and quantitative analysis of molecular interactions. Among them, multichannel fiber optic SPR sensor has become a core tool in parallel detection scenarios due to the superiorities of compensating for nonspecific binding and environmental fluctuations and implementing multianalyte determination. The realization methods of multichannel sensing revolve around fiber microstructures, enhancement by materials, and hybrid fiber. The applications of multichannel fiber optic SPR sensors are demonstrated in sensing of liquid refractive index (RI), RI and temperature, biochemical molecules, and physical parameters. This review thoroughly analyzes and compares the structure, excitation effect, sensing performance, and the advantages and disadvantages of each type of multichannel fiber optic SPR sensor. Even though there are still some challenges, such as insufficient sensing channels and difficulty in fabrication, in their advancement, efforts in multidiscipline including developing high‐performance sensitive films and innovating micro–nano fabrication processes will overcome these bottlenecks. Lastly, the future development directions of multichannel fiber optic SPR sensors from principle, structure, and material aspects are discussed.

Brief Review on Optical Fiber Sensing for the Power Grid

In this work, a brief review on the application of fiber optic sensors on power grid apparatus is presented. Power transformers, which are the nodes between electrical transmission lines, are the most expensive, critical and one of the central units of this network. The failure of electrical machines compromises the whole grid leading to power outages and income losses. Thus, constant monitoring of structural health and operating conditions of core infrastructures is sought. With different types of sensors either on the market or in the literature, it is possible to measure physical parameters that make this equipment more reliable.

Temperature sensing of π-PSFBG with ITO film coated by PLD method

In this article the temperature sensing properties of π–phase-shifted fiber Bragg grating (π-PSFBG) were investigated. Surface coating is one of the commonly used modification methods for fiber gratings, which can improve its sensing performance and even enable it to sense more physical quantities. In this article, we aim to study the effect of coating on the temperature sensing performance of π-PSFBG. Indium tin oxide (ITO) films are widely used in the optoelectronics industry due to their unique combination of electrical conduction and optical transparency. In this paper, the ITO film was coated on the surface of π-PSFBG by pulsed laser deposition (PLD) method to improve its sensing performance. In the practical application of fiber optic sensors, multiple sensors are often used simultaneously, which leads to the mutual interference superposition between the spectra. In this case, the stable extraction of the sensing signal is a problem worth considering. The sensing stability of several interference optical paths and cascaded optical paths before and after π-PSFBG coating is investigated and compared. After the surface is coated with a layer of 0.19 µm thick ITO film, the temperature sensing sensitivity of π-PSFBG is increased by about 15%. It was found that the coating of ITO film enhanced the stability of π-PSFBG in various optical paths.

High-precision calibration for strain and temperature sensitivities of Rayleigh-scattering-based DOFS at cryogenic temperatures

Under extreme conditions such as cryogenic temperatures, the application of optical fiber sensors inevitably encounters significant challenges, which include the calibrations associated with the thermal problems of sensor placement and heat sinking and the nonlinear dependence of cryogenic temperatures. Thus, fundamental investigations involving high-precision calibrations of the strain and temperature at cryogenic temperatures are essential. To this end, in this study, the thermo-optic coefficient, temperature and strain sensitivity coefficients for a Rayleigh-scattering-based distributed optical fiber sensor (DOFS) were calibrated. This experiment was implemented using a self-built low-temperature test device, and the calibration study was conducted over a large cryogenic temperature range, from 77 K to room temperature. The results indicated that the strain sensitivity coefficient of the Rayleigh-scattering-based DOFS is temperature-independent, whereas the temperature sensitivity coefficient has a significantly nonlinear temperature dependence and is associated with the coating polymer layers of the fiber. The coefficients and fitting functions were obtained over a large range of cryogenic temperatures, which indicated the invaluable properties of optical fibers in practice. Furthermore, the strain and temperature of an aluminum beam under thermal and bending loads were measured. The results indicated good agreement between the optical fibers and strain gauges, which verified the availability and reliability of Rayleigh-scattering-based distributed optical fibers in cryogenic environments.

Modeling and Optimization of Laser Cladding Fixation Process for Optical Fiber Sensors in Harsh Environments.

In order to overcome the shortcomings of the poor shear resistance of the bare optical fiber whose coating layer falls off due to harsh conditions, such as on aero-engines and the marine environment, the coaxial powder feeding laser cladding method (CPFLCM) is proposed to connect the optical fiber sensor and the substrate. The concentration field model of the powder flow is established in sections, the effective number model of particles and the corresponding laser attenuation rate are obtained. Through simulation, the influence of relevant parameters of laser cladding on the temperature field was analyzed, and the accurate parameters of laser cladding were optimized. Finally, the temperature rise trajectory of the substrate temperature field was verified by using the fiber grating temperature sensor. Through experiments, the quality of the molten pool and the optical transmission loss of the optical fiber sensor were analyzed, and the consistency of the simulation optimization parameters was verified. Through this paper, it can be concluded that the proposed CPFLCM can realize the effective connection of the optical fiber sensor to the substrate. It is of great significance in the application of optical fiber sensors in harsh environments of oceans and aerospace.

A Review on Current Technologies and Future Direction of Water Leakage Detection in Water Distribution Network

Water leakage in the supply system is a silent problem that costs billions of dollars yearly. As these supply pipes are mostly underground, this leakage remains undetected for a long time. In 2019, Liemberger and Wyatt estimated an annual loss of thirty-nine billion dollars due to water leakage in the supply pipe. In this systematic review, we have analyzed forty-seven articles about water leakage detection and location research. The aim is to find the new technology, trends, and possible direction in this research field. We have derived four research questions. The first question was about how the research evolved over time, and we have observed that researchers focus more on experimental data collection, ML algorithms, and IoT technology. The second question was about the sensor the researcher was using. The most popular sensors researchers have used are: vibration, acoustic, and flow sensors, as they are cheap and easy to install. We can also see some novel applications of image and optical fiber sensors. The third question was about the trend in the algorithm. ML and threshold-based algorithms are dominating the field. The fourth question was about the communication technology trend, and WIFI, cellular IoT, and LoRa technology are leading the space capturing 80% of the research.

Robust one-dimensional phase unwrapping algorithm based on LSTM network with reduced parameter number

For interferometric optical fiber sensor applications, one-dimensional (1D) phase unwrapping is one of the most intractable steps. It is generally more vulnerable to noise impact compared with two-dimensional (2D) phase unwrapping, since the data correlation for the 1D phase unwrapping is very limited. In a recent work, we proposed the 1D phase unwrapping algorithm by combining quasi-Gramian matrix and deep convolutional neural network (DCNN). The obtained result is very robust and can work very stably under low signal-to-noise ratio (SNR) level. But the required parameter amount is large being about 10⁷ making itself inadequate for resource limited computation platforms. In this work, a lightweight phase unwrapping algorithm based on long short-term memory (LSTM) network is proposed, which utilizes only 10⁶ parameter amounts, being 1 order smaller than the DCNN. Simulation results demonstrate that in the SNR range of 0 to 16 dB, the LSTM-based method shows comparable or better performance compared with the DCNN method, and for the very low SNR of -2 dB, only small performance decrease is observed. The generalization ability of the proposed method is also verified by using the experimental data collected from an actual phase-sensitive optical time domain reflectometry (ϕ-OTDR) system.

Questions of application of fiber-optic sensors for monitoring crack growth during rock deformations

The paper considers ways to solve the problem of developing a system for monitoring displacement in quarries, which are the main main cause of the collapse of boards and berms in quarries. To ensure safety and constant monitoring during work at the quarry, there are chiseled fiber-optic sensors. The fiber-optic sensor is made on the basis of a single-mode optical fiber, which makes it possible to measure the displacements of the mountain range at distances of about 30 km with high accuracy. Laboratory sample a fiber-optic sensor in its work uses a method for monitoring additional losses that occur during mechanical action on an optical fiber. The fiber-optic sensor was made to show a fairly high linearity and accuracy during measurements and can be used to control the deformation of the array after appropriate refinement of its design. This article is aimed at creating means of controlling the process of deformation and displacement of a mountain massif. Ultimately, the results of the study will help prevent accidents associated with the collapse of the sides. Since the growth of cracks in the rocks of the bort mountain massif leads to its sudden collapse and creates a significant danger for personnel, it also causes the failure of mining equipment.

Distributed Optical Fiber Sensor Applications in Geotechnical Monitoring.

We report the experimental application of distributed optical fiber sensors, based on stimulated Brillouin scattering (SBS), to the monitoring of a small-scale granular slope reconstituted in an instrumented flume and subjected to artificial rainfall until failure, and to the monitoring of a volcanic rock slope. The experiments demonstrate the sensors’ ability to reveal the sudden increase in soil strain that foreruns the failure in a debris flow phenomenon, as well as to monitor the fractures in the tuff rocks. This study offers an important perspective on the use of distributed optical fiber sensors in the setting up of early warning systems for landslides in both rock and unconsolidated materials.

High-Stability PGC Demodulation Algorithm Based On a Reference Fiber-Optic Interferometer With Insensitivity to Phase Modulation Depth

An ameliorated phase generated carrier demodulation algorithm based on a reference interferometer is proposed. It is theoretically analyzed, numerically simulated, and experimentally verified in this paper. The method of matching the amplitude of the quadrature signal in the reference interferometer algorithm eliminates the harmonic distortion caused by modulation depth fluctuations, suppresses system noise, and improves system stability. In experiments, where the sensed signal amplitude is 0.68 rad, the frequency is 1 kHz, and the modulation depth ranges from 1.5 to 3.5 rad, the ameliorated algorithm has SINAD that reaches 24.5 dB, which is an average improvement of 7.9 dB over the PGC-DCM algorithm based on a reference interferometer and an average improvement of 3 dB over the PGC-Arctan algorithm based on a reference interferometer. The ameliorated algorithm achieves a THD of 0.451%, which consistently maintains the best level of the traditional PGC algorithm based on a reference interferometer. The method provides an effective reference for signal processing in practical applications of fiber-optic sensors.

Detection limit enhancement of fiber optic localized surface plasmon resonance biosensor by increased scattering efficiency and reduced background signal

To reduce the limit of detection (LOD) in fiber optic localized surface plasmon resonance (FO LSPR) sensors, design strategies with high scattering efficiency and low background signal are proposed. Despite the cost effectiveness of fabrication, miniaturization capabilities, and high portability of optic fibers, the LOD is a limiting factor for fiber optic sensor applications. To overcome this limitation, we propose methods to increase the scattering efficiency and reduce background signal using gold capping and reactive-ion etching (RIE). Specifically, three strategies are implemented. First, the effective coverage for detection is selected by analyzing the sensor output according to the density of gold nanoparticles (AuNPs), which have been immobilized on the cross-section of the optical fiber. Next, the sensitivity is studied by examining changes in scattering efficiency of the AuNPs grown with different capping times. Third, RIE is performed on the fiber optic surface to reduce the reflectance in areas where the AuNPs are not fixed, thereby decreasing the background signal. Thyroglobulin, amyloid beta monomer, and oligomer are measured using the thus-fabricated FO LSPR sensor. The results are compared with those obtained with a sensor fabricated without using these strategies. The former showed the lower LOD and higher accuracy for biomarkers of the two. • The effective coverage of AuNPs is selected on the optical fiber. • For improvement of scattering efficiency, AuNPs are directly grown on fiber optic surface. • Surface etching is executed for reduction of background in bare surface. • The enhancement of the LODs is evaluated for several biomarkers.

Overview of Fibre Optic Sensing Technology in the Field of Physical Ocean Observation

Fiber optic sensors are expected to be an auxiliary measurement tool in the field of ocean observation due to their small size, easy networking, intrinsic immunity to electromagnetic interference, and many other advantages. In recent years, the research around fiber optic sensing technology in the field of physical ocean observation has received increasing attention from researchers. According to the different measurement objects and measurement principles, the focus is on the seawater temperature sensor based on fiber grating, seawater salinity sensor, seawater pressure sensor, seawater salinity sensor based on multi-core optical fiber, seawater salinity sensor based on Michelson and Mach-Zehnder interferometry, seawater pressure sensor based on Fabry-Perot cavity, fiber optic temperature salinity and depth sensors based on resonant and coupling technology, flow velocity sensor based on multi-core optical fiber and fiber optic turbulence sensors based on thermal dissipation and turbulent kinetic energy dissipation. The test methods and test results of various sensors are analyzed, and the advantages and disadvantages of the technologies are pointed out. Prospects for the application of fiber optic sensors in physical ocean observation are presented.

Recent Advances in Machine Learning for Fiber Optic Sensor Applications

Over the last three decades, fiber optic sensors (FOS) have gained a lot of attention for their wide range of monitoring applications across many industries, including aerospace, defense, security, civil engineering, and energy. FOS technologies hold great promise to form the backbone for next‐generation intelligent sensing platforms that offer long‐distance, high‐accuracy, distributed measurement capabilities and multiparametric monitoring with resilience to harsh environmental conditions. The major limitations posed by FOS are 1) cross‐sensitivity, 2) enormous volume and large data generation, 3) low data processing speed, 4) degradation of signal‐to‐noise ratio over the fiber length, and 5) overall cost of sensor and interrogator systems. These challenges can be overcome by building advanced data analytics engines enabled by recent breakthroughs in machine learning (ML) and artificial intelligence (AI). This article presents a comprehensive review of recent studies that integrate ML and AI algorithms with FOS technologies. This review also highlights several FOS technology development directions that promise a significant impact on widespread use for several industrial applications, with an emphasis on energy systems monitoring. A perspective on future directions for further research development is also provided.

Low effective Poisson’s ratio and confinement loss photonic crystal fibers using negative Poisson’s ratio air holes structure

The additional confinement loss caused by external loads has so far restricted the wide applications of photonic crystal fibers (PCFs). With the rapid development of metamaterials, there is an increasing interest in negative Poisson’s ratio (NPR) composite structure due to its outstanding advances in energy and vibration absorption capabilities. In this paper, a novel design concept of PCF with NPR air holes composite structure is proposed. The feasibility of this novel PCF structure is verified by photo-elastic theory and finite element method under compression and impact loads to test the mechanical and optical properties of the fiber. The results show that the PCF with NPR air holes structure effectively suppresses the fiber deformation caused by external loads, thereby reducing the additional fiber confinement loss. Meanwhile, this novel concept displays structural diversity. The macro effective Poisson’s ratio of the fiber can still be reduced by maintaining the generalized NPR holes cladding structure, which provides support for the flexible core layer design of PCF under different application requirements. In sum, this design concept subverts the traditional design method of photonic crystal fibers with complex structures and looks promising for future applications in optical fiber sensors.

High extinction ratio elliptical core Panda-type polarization-maintaining fiber coil.

The polarization-maintaining performance of the traditional Panda-type polarization-maintaining fiber (PMF) coil is significantly affected by winding stress and temperature. Here, we present an elliptical core Panda-type PMF coil based on a fiber that employs both geometric and stress birefringence. The extinction ratio of the elliptical core PMF coil was found to be 20.13 dB at a temperature of 20°C, corresponding to an increase of 3.71 dB compared to the traditional Panda-type PMF coil. In addition, results from distributed polarization cross talk and gyroscope output tests also revealed a low sensitivity of the fiber to stress caused by the winding process and temperature. In summary, the proposed fiber coil has better polarization-maintaining ability compared to conventional coil and is promising for applications in high-precision optical fiber sensors.

Low-cost high-performance temperature sensor based on unsymmetrical U-shaped microfiber

A novel temperature sensor based on microfiber (MF) interferometer with low-cost, long-term reliability and high repeatability was developed. The experimental results indicate that the unsymmetrical U-shaped MF has particularly advantages of a thinner waist diameter and better sensing stability compared with symmetrical U-shaped MF in terms of structure and spectrum. The air temperature sensitivity of 10 pm/°C was observed by the sensor with a diameter of 4.26 μm. In order to study the relationship between the structure parameters of transition region and the performance of temperature sensor, we fabricated another MF with a larger taper angle of transition region. The new sensor fabricated with this MF obtained a higher temperature sensitivity of 16.7 pm/°C. Considering the impact force from the temperature measurement environment (such as air and liquid environment), the MF interferometer was packaged in a special glass tube to enhance its impact resistance. After that this proposed sensing structure was applied to the measurement of liquid temperature. Results show that its temperature sensitivity is about 349.5 pm/°C when the liquid temperature changes from 18 °C to 30 °C. The sensor designed in this paper has the advantages of good resistance to liquid impact and high sensitivity. It is of great significance to the application of optical fiber sensor in the detection of liquid and atmospheric environment.

Application of Optical Fiber Sensors for Crack Monitoring in a Masonry Structure during Geotechnical Foundation Remediation

Application of Optical Fiber Sensors for Crack Monitoring in a Masonry Structure during Geotechnical Foundation Remediation

Application of U-Shaped hybrid fiber optic sensor to determine the temperature dependent variation of refractive index of binary liquids

The study of refractive index of liquids becoming increasingly popular in diverse areas to monitor chemical, pharmaceutical, food, scientific, biochemical, medical, etc. processes and procedures. In the present paper a low cost, simple, compact, reliable, robust, miniaturized and sturdy Refractive Index sensor is reported. It is configured by using a set of two multimode PCS fiber of 50 cm length in each, connected one to the source of wavelength 660 nm and other to a light detector. A glass rod drawn in the form of ‘U’, of compatible dimensions to that of two multimode fibers, was connected between source and detector by jointing to the remaining ends of the fibers, thus creating a sensing zone. Maintaining the binary liquids of Toluene and t-Butanol at the sensing zone at various temperatures, the light launched from source was monitored in the detector at the detector end. By forming relationship between index of refraction and power output at the temperature range of 10 °C to 60 °C, the sensor expected to be used to detect the index of refraction of liquids with maximum resolution of the order of 10-5 in the operating range from 1.36312nD to 1.50915nD.

Review of fiber optic sensors for corrosion monitoring in reinforced concrete

Monitoring corrosion in reinforced concrete is critical to assess the health condition of structures at an early stage and enable effective and efficient asset management. Various novel fiber optic sensors have been developed and demonstrated many advantages in monitoring corrosion in reinforced concrete under different conditions. However, currently, there is a gap between sensor technology innovation and engineering practices, and the gap hinders further development and wide applications of fiber optic sensors. This paper reviews representative types of fiber optic sensors for monitoring corrosion in reinforced concrete. The reviewed types of sensors include grating sensors, interferometer sensors, distributed sensors, and reflectometer sensors. For each type of sensors, the reviewed contents include the sensing principle and key features of applications, such as sensor design and installation, sensitivity, resolution, and sensor life. Emphasis is placed on discussing the functions and performance of the sensors in different corrosion stages. Based on the review, technical challenges and future research needs are identified and discussed. This review is expected to advance sensor development and promote effective applications of fiber optic sensors for intelligent structures and asset management.

Effect of temperature and wavelength on the refractive index of water: a fiber-optic sensor application

The refractive index \(n(\lambda ,T\)) is a basic optical property of materials. The refractive index and the thermo-optic coefficient (\({\mathrm{d}}n/{\mathrm{d}}T\)) are significant parameters of liquids for optically controlled systems, such as the direct measurement of liquid solution concentrations and optical paths. In this study, the variation in the refractive index of water in the liquid phase with temperature was measured with our self-designed fiber optic-based refractive index sensor and \({\mathrm{d}}n/{\mathrm{d}}T\) values were obtained with a full-width half-maximum method at wavelengths of 980, 1426, and 1550 nm, respectively. Water is the most abundant and life-critical substance in the world, and its optical properties pose challenging scientific problems that require knowledge of the refractive index to be resolved. The results indicate that the experimental refractive index values are compatible with both the theoretical and experimental data in the literature. We also tested the refraction index results with two theoretical models and obtained good agreement between the calculated and experimental values. The resolution of the fiber optic-based refractive index sensor was 10\(^{-5}\). Our designed sensor could measure the refractive index of liquids with temperature with accuracy.