Development Of Fiber Optic Sensor Research Articles

Fiber-Optic Sensors and Their Practical Research in the Internet of Things

With the rapid development of the Internet of Things (IoT) technology, fiber-optic sensors, as a kind of high-precision and high-sensitivity measurement tool, are increasingly widely used in the field of IoT. This paper outlines the advantages of fiber-optic sensors over traditional sensors, such as high precision, strong resistance to electromagnetic interference, and long transmission distance. On this basis, the paper discusses the application scenarios of fiber-optic sensors in the Internet of Things, including environmental monitoring, intelligent industry, medical and health care, intelligent transportation, and other fields. It is hoped that this study can provide theoretical support and practical guidance for the further development of fiber-optic sensors in the field of the Internet of Things, as well as promote the innovation and application of IoT.

A high-sensitivity balloon-type optical fiber sensor enables wide-range strain sensing with the assistance of CNN

A balloon-type optical fiber sensor (OFS) for strain measurement was proposed, and the measurement range was significantly increased with the assistance of convolutional neural networks (CNN). The presented OFS was prepared by bending a Mach-Zehnder structure based on polarization-maintaining fibers into a balloon-type, which exhibits a sensitivity of 26.3 pm/με under the strain range from 0 to 300 με. The CNN-based signal analysis method can effectively extract the data information in the spectral, and the strain range that can be measured is greatly enlarged to 0–2000 με, while the accuracy of the measurement can be guaranteed. Further, the temperature sensitivity of the OFS is −0.0252 nm/°C; the lower temperature sensitivity can effectively suppress the crosstalk problem caused by temperature changes during strain measurement. The proposed method remarkably increases the strain measurement range of OFS, which is conducive to the application and development of OFSs.

Multiparameter sensor based on long-period grating in few-mode ring-core fiber for vector curvature and torsion measurement

With the rapid development of optical fiber sensor in physical measurement, it is of practical significant to realize multi-parameter measurement. In this work, we proposed and demonstrated a multiparameter sensor for curvature, torsion and temperature. The sensor is formed from CO2 laser-inscribed long-period grating (LPG) in few-mode ring-core fiber (RCF), which can convert fundamental mode to LP11 mode. One-side inscription enhances asymmetric index modulation in fiber, resulting in directionally sensitive to bend by intensity interrogation. The curvature sensitivities in various bending directions perform linearity in curvature range of 5–9.466 m−1. Curvature sensitivities are related to the bending directions. The intensity sensitivity achieves − 0.584 dB/m−1, 0.879 dB/m−1, and − 0.735 dB/m−1, respectively. And torsion sensitivity from -6.98 rad/m to 6.98 rad/m displays linearity with −0.554 dB/(rad/m). The measured influence of temperature can be negligible. The proposed RCF-LPG could not only be used as high-efficiency mode converter in mode division multiplexing systems but also be potential in few-mode fiber based multiparameter sensing fields.

Probe-Type Multi-Core Fiber Optic Sensor for Simultaneous Measurement of Seawater Salinity, Pressure, and Temperature.

In this article, we propose and demonstrate a probe-type multi-core fiber (MCF) sensor for the multi-parameter measurement of seawater. The sensor comprises an MCF and two capillary optical fibers (COFs) with distinct inner diameters, in which a 45° symmetric core reflection (SCR) structure and a step-like inner diameter capillary (SIDC) structure filled with polydimethylsiloxane (PDMS) are fabricated at the fiber end. The sensor is equipped with three channels for different measurements. The surface plasmon resonance (SPR) channel (CHSPR) based on the side-polished MCF is utilized for salinity measurement. The fiber end air cavity, forming the Fabry-Pérot interference (FPI) channel (CHFPI), is utilized for pressure and temperature measurement. Additionally, the fiber Bragg grating (FBG) channel (CHFBG), which is inscribed in the central core, serves as temperature compensation for the measurement results. By combining three sensing principles with space division multiplexing (SDM) technology, the sensor overcomes the common challenges faced by multi-parameter sensors, such as channel crosstalk and signal demodulation difficulties. The experimental results indicate that the sensor has sensitivities of 0.36 nm/‱, -10.62 nm/MPa, and -0.19 nm/°C for salinity, pressure, and temperature, respectively. As a highly integrated and easily demodulated probe-type optical fiber sensor, it can serve as a valuable reference for the development of multi-parameter fiber optic sensors.

D-shape Optical Fiber Development and Enhancement as a Refractive Indices Sensor Using Surface Plasmon Resonance

This article showcases the development and utilization of a side-polished fiber optic sensor that can identify altered refractive index levels within a glucose solution through the investigation of the surface Plasmon resonance (SPR) effect. The aim was to enhance efficiency by means of the placement of a 50 nm-thick layer of gold at the D-shape fiber sensing area. The detector was fabricated by utilizing a silica optical fiber (SOF), which underwent a cladding stripping process that resulted in three distinct lengths, followed by a polishing method to remove a portion of the fiber diameter and produce a cross-sectional D-shape. During experimentation with glucose solution, the side-polished fiber optic sensor revealed an adept detection sensitivity of 0.2015 au. /RIU. In order to improve sensitivity, a recent sensor was subjected to a coating process utilizing a thin film layer of gold (Au) measuring a thickness of 50 nm. The sensor was subsequently subjected to a series of tests utilizing the same glucose solutions as in previous experiments. A notable enhancement in sensitivity was observed when utilizing gold as the sensing material, with an equivalent maximum sensitivity of 3.101 au. /RIU.

Development of Optical Fiber Sensor for Water Salinity Detection

Development of Optical Fiber Sensor for Water Salinity Detection

Low-Cost Online Monitoring System for the Etching Process in Fiber Optic Sensors by Computer Vision.

The present research exposes a novel methodology to manufacture fiber optic sensors following the etching process by Hydrofluoric Acid deposition through a real-time monitoring diameter measurement by computer vision. This is based on virtual instrumentation developed with the National Instruments® technology and a conventional digital microscope. Here, the system has been tested proving its feasibility by the SMS structure diameter reduction from its original diameter of 125 μ until approximately 42.5 μm. The results obtained have allowed us to demonstrate a stable state behavior of the developed system during the etching process through diameter measurement at three different structure sections. Therefore, this proposal will contribute to the etched fiber optic sensor development that requires reaching an enhanced sensitivity. Finally, to demonstrate the previously mentioned SMS without chemical corrosion, and the etched manufactured SMS, both have been applied as glucose concentration sensors.

Mirror-Assisted Radioluminescent Optical Fibers for X-Ray Beam Monitoring

In the framework of the current development of optical fiber sensors for dosimetry or beam monitoring applications based on radioluminescence (RL), we propose a method to enhance their radiation-induced light collection efficiency. This method consists in the deposition of a thin metallic layer, acting as a mirror, at the free output extremity of a radioluminescent optical fiber. Emitted visible photons guided in both directions along the optical fiber core can be collected by a single-ended detection system such as a photomultiplier tube. We characterize the impact of depositing two different types of metallic mirrors (Al and Au) on the performances of a RL based dosimeter, constituted by a Nitrogen-doped multimode optical fiber: its sensitivity has been calibrated with 40 keV X-rays at room temperature for dose rates from 0.05 to ~4 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s. Also, investigation about the total ionizing dose effects on the mirror has been carried out to understand the evolution of the reflectance of the mirror under radiation exposure. This architecture of sensors appears as very promising, especially for the monitoring of low photon flux.

Study and Realization of Environmental Health Diagnosis by Using Nanomaterial Based Fiber Optic Sensor–A Review

In these days, the significance of fiber optic sensors has exceptionally increased due to technological advances in modern society. Nowadays, researchers are attracted toward the development of a sensor that possesses the integration of both fiber optic sensors and nanocomposite thin film to improve the sensor’s performance. Thin-film nanomaterial based optical fiber sensors have great potential applications, namely, gas sensing, chemical sensing, biomolecules, food plant, industrial hazards, safety issues, drug monitoring, and heavy metal detections. There are various techniques, namely, evanescent field absorption spectroscopy, fiber Bragg grating (FBG), long-period grating (LPG), ringdown spectroscopy, surface plasmon resonance (SPR), Mach–Zehnder interferometer (MZI) techniques, and so on, which are used for the development of fiber optic sensors that are majorly emphasized in the current article. Numerous scientific researchers have demonstrated that functionalized fiber optic sensors are found more beneficial in terms of improvement of the sensing performance, such as sensitivity, repeatability, response time, specificity, recovery time, and repeatability. Henceforth, in this review article, we have focused on these requisite sensing parameters in detail. Furthermore, to keep human beings healthy, it is our responsibility to develop a sensor that can monitor the optimum toxic concentrations accurately. Thus, the monitoring of industrial environmental pollutants, such as NH3, ethylenediamine, alcohol, and acetone, is immensely important to save human lives on Earth. In the report, all the details of the target analytes, such as optimum concentrations, adverse effects on human beings, and monitoring techniques, are discussed.

Heat treatment and polymer coating effect on Rayleigh scattering based fiber optic temperature measurement

This study experimentally investigates the effect of heat treatment on Rayleigh scattering based distributed single-mode fiber optic temperature measurement. A finite element model was established to investigate the effect of thermal expansion of coatings on the optical fiber core strains and thus, temperature sensitivity before the coatings soften and melt away. A theoretical derivation for the fiber core strains, using Lame equations, was performed to validate the accuracy of the finite element model. It was found that the one-time heat treatment eliminates the hysteresis effect and stabilizes the Rayleigh scattering based fiber optic temperature measurement up to 1000 °C. The typical dual-layer coating effect on the temperature sensitivity of the Rayleigh frequency shift can be neglected at high temperatures in civil engineering application. Numerical parametric studies are performed to design coatings of fiber optic temperature sensors. The present study is promoting distributed fiber optic temperature sensor development and application.

Recent Advances in Lossy Mode Resonance-Based Fiber Optic Sensors: A Review.

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which mainly utilizes the thin film of metals, a wide range of materials such as conducting metal oxides and polymers support LMR. The past several years have witnessed a remarkable development in the field of LMR-based fiber optic sensors; through this review, we have tried to summarize the overall development of LMR-based fiber optic sensors. This review article not only provides the fundamental understanding and detailed explanation of LMR generation but also sheds light on the setup/configuration required to excite the lossy modes. Several geometries explored in the literature so far have also been addressed. In addition, this review includes a survey of the different materials capable of supporting lossy modes and explores new possible LMR supporting materials and their potential applications in sensing.

Investigating key factors for optimizing FBG inscribed by femtosecond laser

As the key device of optical fiber sensor, the manufacturing methods of FBG have attracted much attention. Point by point inscribing method using femtosecond laser has some great advantages of modulating the central wavelength, grating pitch and length according to the needs of sensing information. However, the relationship between the spectrum and the characteristic structure of FBG has not been completely clear. Among them, the key factors related to process implementation and their influencing laws are a very important part. Facing the current dilemma, the key factors for optimizing FBG inscribed by femtosecond laser are investigated in this paper, such as power, fiber type, polarization effect, and grating length. The direct relationship between different influencing factors is explored through experimental analysis and a method to optimize the polarization effect is proposed by increasing rotational degrees of freedom. At the optimal power with the grating length of 5 mm, cascaded FBGs on ordinary single-mode fiber with a reflection peak height of more than 20 dB and 3 dB bandwidth of less than 0.3 has been manufactured. This research is an improvement of the point by point method for obtaining FBG with optimized performance and spectra, which provides a good support for the development of optical fiber sensor with FBG as sensitive device.

Temperature Sensors Based on Polymer Fiber Optic Interferometer

Temperature measurements are of great importance in many fields of human activities, including industry, technology, and science. For example, obtaining a certain temperature value or a sudden change in it can be the primary control marker of a chemical process. Fiber optic sensors have remarkable properties giving a broad range of applications. They enable continuous real-time temperature control in difficult-to-reach areas, in hazardous working environments (air pollution, chemical or ionizing contamination), and in the presence of electromagnetic disturbances. The use of fiber optic temperature sensors in polymer technology can significantly reduce the cost of their production. Moreover, the installation process and usage would be simplified. As a result, these types of sensors would become increasingly popular in industrial solutions. This review provides a critical overview of the latest development of fiber optic temperature sensors based on Fabry–Pérot interferometer made with polymer technology.

Distributed Polarization Characteristic Testing for Optical Closed Loop of Sagnac Interferometer

Distributed polarization characteristic of Sagnac optical closed loop that composed of two polarizing devices– polarization maintaining fiber coil and Y-waveguide, can directly affect the performance of fiber optic sensors. Several existing methods are applicable for only one device testing at a time, the efficiency is therefore relatively low and the connection quality between devices is unavailable. In this paper, the Sagnac optical closed loop is split into semi-closed loop (SCL) and full-closed loop (FCL) structures. The transmission behavior of polarized optical signal is fully analyzed, and the information of polarization mode crosstalk is positioned and extracted accurately. By conducting one test of SCL and FCL respectively utilizing white light interferometry, the distributed polarization characteristic of both optical devices and connection points can be entirely obtained. The testing results of optical closed loop are highly consistent with single device test and the difference is less than 0.2dB. A good testing stability is demonstrated through ten repeat measurements and the fluctuation is almost around 0.1dB. We believe that the proposed testing method is capable of promoting the assembly of high-performance Sagnac interferometer and the development of fiber optic sensors.

Single- and Double-Comb Tilted Fibre Bragg Grating Refractive Index Demodulation Methods with Fourier Transform Pre-Processing.

The development of fibre optic sensors for measuring the refractive index is related to the creation of new periodic structures and demodulation algorithms for the measured spectrum. Recently, we proposed a double-comb Tilted fibre Bragg grating (DCTFBG) structure. In this article, we analyse such a structure for measuring the refractive index in comparison to a single classical structure. Increasing the number of modes causes a significant change in the Fourier spectrum of optical spectra. For the purpose of data pre-processing, we propose the Fourier Transform as a filtering method in the frequency domain. Then, we analyse separately the band-filtered optical spectra for several frequency ranges. For quantitative analysis, we use algorithms that use quantitative changes in the transmission, i.e., the method of the envelope and the length of the spectrum contour. We propose the use of the Hilbert transform as the envelope method. The second type of algorithms used are methods determining the shift of spectrum features along the wavelength axis. The method of determining the centre of gravity of the area bounded by the envelope and the maximum of the second derivative of the smoothed cumulative spectrum contour length is proposed here. Using the developed methods, the measurement resolution was achieved at the level of 2 × 10−5 refractive index unit.

Sweep frequency method with variance weight probability for temperature extraction of the Brillouin gain spectrum based on an artificial neural network.

The development of optical fiber sensors has led to the possibility of accumulating vast, real-time databases of acoustic and other measurements throughout fiber networks, which brings even more widespread concern on improving the sampling effectiveness. In this paper, we present two kinds of sweep frequency methods based on using a neural network to extract temperature from the Brillouin gain spectrum (BGS). Gauss centralization and variance weight probability methods are proposed to compare with the uniform sweep frequency method. By analyzing formulas of the ideal BGS model, we find the gain near the peak of Brillouin gain spectrum has greater correlation with temperature extraction than other positions. Therefore, the Gaussian centralized sweep method is proposed. We further investigate the variation of the weights in the neural network and Brillouin data distribution in different positions and find that the variance is positively correlated with the weights in hidden layers. So, we propose the sweep frequency method based on variance weight probability and make a complement to interpret the rationality of this method in neural network. In all the aforementioned approaches, 281 points are obtained between the 9.07 GHz to 9.35 GHz range under the same condition. The data of each method is trained ten times and tested through the same neural network structure. All the RMSE of each test stage covers all data collecting the passage. The result shows that the RMSE of variance weight probability sweep frequency method is 0.5277, which is superior to the Gauss centralization sweep frequency method that was 0.6864 and the uniform sweep frequency method that was 0.9140.

Temperature Sensor Using Fiber Ring Laser Based On a Core-Offset Mach-Zehnder Interferometer

The development of fiber optic sensors receives special interest since they can be used in multiple applications. As a result, fiber optic laser-sensor schemes had emerged as a reliable device, due to its characteristics such as: high power, low threshold, and high stability. In this work, it is proposed a fiber laser-sensor based on a ring cavity configuration. The cavity is operated by a core-offset Mach-Zehnder interferometer, which is used as a wave selection filter and temperature detection device. Here, the proposed fiber laser-sensor exhibits sensing properties such as sensitivity of 0.03119 pm/°C , dynamic range of 90ºC and a signal to noise ratio of 52 dB

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.

Design and development of fiber optic sensor for measurement of purity of ethanol

Pure alcohol (ethanol) has number of applications in automobile, chemical and pharmaceutical industries. Fiber optic sensor has widespread use due to its non contact type measurement in retro reflective configuration. This paper proposes non contact type refractometric fiber optic sensor for measurement of purity of alcohol manufactured in distilleries. This refractometric based sensor shows variation in the received light intensity with variation in water content of ethanol i.e. purity of alcohol. The sensor is studied and analyzed by performing simulation based on mathematical model developed using ray tracing technique. The sensor is fabricated and tested by preparing samples in the laboratory. The refractive indices are later measured using Abbe’s refractometer having the resolution of 0.001 in white light. Field tests are also carried out at the local distilleries. Experimental results show good agreement with the simulated results as well as with the conventional methods used in industry for measurement of the purity of alcohol. The sensor shows linear variation in the output voltage with the variation in alcohol purity of alcohol from 90% to 99%. The repeatability of the sensor is checked by repeating the experiment 60 times for each value of purity.

NTE material employment in temperature resistive high sensitive fiber optic strain sensor development

In this paper, an optical strain sensor with automatic temperature compensation is presented. The strain sensitivity is 198.547 pm/με, which is nearly 2.8 times that of the latest generation multilayer optical fiber strain sensor based on mode field diameter (70.77 pm/με). This increase in sensitivity is due to the particular structure within which the optical fiber sensor is installed. This structure amplifies the applied strain and transfers it to the optical fiber. In order to compensate for the temperature effects, employing a negative temperature expansion (NTE) element is essential. In addition, applying an initial strain is required to adjust the system performance. As a result, the entire sensor system is automatically compensated for the temperature with less than 1 percent error.