Advance and Applications of Fiber Optic Measurement

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Automation automation	-	-	2020	26.3 Days	CHF 1000
Fibers fibers	3.9	7.0	2013	24.1 Days	CHF 2000
Metrology metrology	-	-	2021	28.6 Days	CHF 1000
Photonics photonics	2.4	2.3	2014	15.5 Days	CHF 2400
Sensors sensors	3.9	6.8	2001	17 Days	CHF 2600

15 pages, 23625 KiB

Open AccessArticle

Fiber-Optic Telecommunication Network Wells Monitoring by Phase-Sensitive Optical Time-Domain Reflectometer with Disturbance Recognition

by Andrey A. Zhirnov, German Y. Chesnokov, Konstantin V. Stepanov, Tatyana V. Gritsenko, Roman I. Khan, Kirill I. Koshelev, Anton O. Chernutsky, Cesare Svelto, Alexey B. Pnev and Olga V. Valba

Sensors 2023, 23(10), 4978; https://doi.org/10.3390/s23104978 - 22 May 2023

Cited by 7 | Viewed by 1873

Abstract

The paper presents the application of a phase-sensitive optical time-domain reflectometer (phi-OTDR) in the field of urban infrastructure monitoring. In particular, the branched structure of the urban network of telecommunication wells. The encountered tasks and difficulties are described. The possibilities of usage are [...] Read more.

The paper presents the application of a phase-sensitive optical time-domain reflectometer (phi-OTDR) in the field of urban infrastructure monitoring. In particular, the branched structure of the urban network of telecommunication wells. The encountered tasks and difficulties are described. The possibilities of usage are substantiated, and the numerical values of the event quality classification algorithms applied to experimental data are calculated using machine learning methods. Among the considered methods, the best results were shown by convolutional neural networks, with a probability of correct classification as high as 98.55%. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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16 pages, 22475 KiB

Open AccessArticle

Young’s Modulus-Independent Determination of Fibre Parameters for Rayleigh-Based Optical Frequency Domain Reflectometry from Cryogenic Temperatures up to 353 K

by Caroline Girmen, Clemens Dittmar, Thorsten Siedenburg, Markus Gastens, Michael Wlochal, Niels König, Kai-Uwe Schröder, Stefan Schael and Robert H. Schmitt

Sensors 2023, 23(10), 4607; https://doi.org/10.3390/s23104607 - 09 May 2023

Viewed by 1384

Abstract

The magnetic spectrometer AMS-100, which includes a superconducting coil, is designed to measure cosmic rays and detect cosmic antimatter in space. This extreme environment requires a suitable sensing solution to monitor critical changes in the structure such as the beginning of a quench [...] Read more.

The magnetic spectrometer AMS-100, which includes a superconducting coil, is designed to measure cosmic rays and detect cosmic antimatter in space. This extreme environment requires a suitable sensing solution to monitor critical changes in the structure such as the beginning of a quench in the superconducting coil. Rayleigh-scattering-based distributed optical fibre sensors (DOFS) fulfil the high requirements for these extreme conditions but require precise calibration of the temperature and strain coefficients of the optical fibre. Therefore, the fibre-dependent strain and temperature coefficients

K_{T}

and

K_{ϵ}

for the temperature range from 77 K to 353 K were investigated in this study. The fibre was integrated into an aluminium tensile test sample with well-calibrated strain gauges to determine the fibre’s

K_{ϵ}

independently of its Young’s modulus. Simulations were used to validate that the strain caused by changes in temperature or mechanical conditions was the same in the optical fibre as in the aluminium test sample. The results indicated a linear temperature dependence of

K_{ϵ}

and a non-linear temperature dependence of

K_{T}

. With the parameters presented in this work, it was possible to accurately determine the strain or temperature of an aluminium structure over the entire temperature range from 77 K to 353 K using the DOFS. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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15 pages, 2529 KiB

Open AccessArticle

Linewidth Narrowing of a Dual Wavelength-Selectable, Ring Cavity Erbium-Doped Fiber Laser Using a Saturable Absorber

by Ebuka E. Okafor, Frank N. Igboamalu, Khmaies Ouahada and Habib Hamam

Photonics 2023, 10(5), 522; https://doi.org/10.3390/photonics10050522 - 02 May 2023

Viewed by 1323

Abstract

The narrow linewidth fiber laser is useful in applications such as fiber sensing, optical communications, and spectroscopy. This paper presents an investigation of the model and an experiment of a stable, wavelength-selective, narrow linewidth, ring cavity erbium-doped fiber laser incorporating two fiber Bragg [...] Read more.

The narrow linewidth fiber laser is useful in applications such as fiber sensing, optical communications, and spectroscopy. This paper presents an investigation of the model and an experiment of a stable, wavelength-selective, narrow linewidth, ring cavity erbium-doped fiber laser incorporating two fiber Bragg gratings (FBG) at 1530.18 nm and 1550.08 nm, respectively. An F-P tunable filter was used to select a specific wavelength after optimizing the spectral output from the two FBGs to measure their respective linewidths. The erbium-doped ring fiber laser was optimized by adjusting the optical cavity loss using a variable optical coupler at a coupling ratio of 95%. The variable coupler was set to an optimal coupling ratio of 95%, where the spectral output powers of 3.4 mW at 1530.18 nm and 3.1 mW at 1550.08 nm were achieved as the optimal fiber laser output powers. The balanced output power had an optical signal-to-noise ratio of (OSNR) of 61 dB for each wavelength. The linewidth was measured for both wavelengths without saturable absorbers, and 27.7 kHz and 28.3 kHz for 1530.18 nm and 1550.08 nm were obtained. Using the saturable absorber, the linewidths were narrowed to 25.3 KHz and 21.1 kHz for 1530.18 nm and 1550.08 nm, respectively. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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10 pages, 7007 KiB

Open AccessCommunication

Application of Crossed Polarizer Method in the Measurement of Differential Group Delay of Optical Fibers

by Cheng Wu, Fei Yu, Suya Feng, Chunlei Yu, Lixin Xu, Ruizhan Zhai, Zhongqing Jia and Lili Hu

Photonics 2023, 10(5), 518; https://doi.org/10.3390/photonics10050518 - 01 May 2023

Viewed by 993

Abstract

In this paper, we report the use of crossed polarizer technique to measure the differential group delay (DGD) of few-mode optical fiber (FMF). The windowed Fourier transform (WFT) is applied in the analysis of beat length measurement in the spectral domain to obtain [...] Read more.

In this paper, we report the use of crossed polarizer technique to measure the differential group delay (DGD) of few-mode optical fiber (FMF). The windowed Fourier transform (WFT) is applied in the analysis of beat length measurement in the spectral domain to obtain the dependence of DGD as a function of wavelength. The birefringence of polarization-maintaining fiber (PMF) and the DGD of FMF are measured by applying our method. We discuss the noise background, the width of DGD peaks, and the possible errors introduced in the optical path in the modified crossed polarizer technique. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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13 pages, 10423 KiB

Open AccessCommunication

New Method for Measuring the Scattering Phase Function of Micron/Nano Particles

by Xingcan Li, Li Lin, Hongyang Wang, Zeguo Shang, Jinyuan Lv and Yi Hao

Photonics 2023, 10(5), 511; https://doi.org/10.3390/photonics10050511 - 28 Apr 2023

Viewed by 1125

Abstract

The scattering phase function is crucial to analyze the light transport in the micron/nano particle suspensions. A new method including a liquid–particle system and reference system is proposed to measure the scattering phase function of the liquid–particle suspensions. In this method, a reference [...] Read more.

The scattering phase function is crucial to analyze the light transport in the micron/nano particle suspensions. A new method including a liquid–particle system and reference system is proposed to measure the scattering phase function of the liquid–particle suspensions. In this method, a reference system of a standard particle is used to obtain the correction factor to compensate for the influence of the cuvette. Experimental validation was conducted for monodisperse silicon dioxide microspheres and monodisperse polystyrene microspheres. By considering the influence of the cuvette, both theoretical and experimental analyses prove that the proposed method can achieve a good result in the measurement of the scattering phase function of liquid–particle suspensions for particles with unknown size parameters and optical constants, especially when the size parameter of the particle is larger than 10. The correction factors of scattering light distribution of silicon dioxide microsphere suspensions with various mean particle sizes were obtained and analyzed. This method provides an alternative and simple way of measuring the scattering phase function of micron/nano particle suspensions. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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11 pages, 3160 KiB

Open AccessArticle

Distributed Refractive Index Sensing Based on Etched Ge-Doped SMF in Optical Frequency Domain Reflectometry

by Cailing Fu, Ronglong Sui, Zhenwei Peng, Yanjie Meng, Huajian Zhong, Mingquan Li, Xiaoyu Yin and Yiping Wang

Sensors 2023, 23(9), 4361; https://doi.org/10.3390/s23094361 - 28 Apr 2023

Cited by 5 | Viewed by 1311

Abstract

A distributed optical fiber refractive index sensor based on etched Ge-doped SMF in optical frequency domain reflection (OFDR) was proposed and demonstrated. The etched Ge-doped SMF was obtained by only using wet-etching, i.e., hydrofluoric acid solution. The distributed refractive index sensing is achieved [...] Read more.

A distributed optical fiber refractive index sensor based on etched Ge-doped SMF in optical frequency domain reflection (OFDR) was proposed and demonstrated. The etched Ge-doped SMF was obtained by only using wet-etching, i.e., hydrofluoric acid solution. The distributed refractive index sensing is achieved by measuring the spectral shift of the local RBS spectra using OFDR. The sensing length of 10 cm and the spatial resolution of 5.25 mm are achieved in the experiment. The refractive index sensing range is as wide as 1.33–1.44 refractive index units (RIU), where the average sensitivity was about 757 GHz/RIU. Moreover, the maximum sensitivity of 2396.9 GHZ/RIU is obtained between 1.43 and 1.44 RIU. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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13 pages, 3453 KiB

Open AccessArticle

A Novel Fiber-Optic Ice Sensor to Identify Ice Types Based on Total Reflection

by Chi Zhang, Chunhua Xiao, Shaorong Li, Xiaowei Guo, Qi Wang, Yizhou He, Huiyan Lv, Hongkai Yan and Dongan Liu

Sensors 2023, 23(8), 3996; https://doi.org/10.3390/s23083996 - 14 Apr 2023

Cited by 2 | Viewed by 1601

Abstract

To address the issues of not accurately identifying ice types and thickness in current fiber-optic ice sensors, in this paper, we design a novel fiber-optic ice sensor based on the reflected light intensity modulation method and total reflection principle. The performance of the [...] Read more.

To address the issues of not accurately identifying ice types and thickness in current fiber-optic ice sensors, in this paper, we design a novel fiber-optic ice sensor based on the reflected light intensity modulation method and total reflection principle. The performance of the fiber-optic ice sensor was simulated by ray tracing. The low-temperature icing tests validated the performance of the fiber-optic ice sensor. It is shown that the ice sensor can detect different ice types and the thickness from 0.5 to 5 mm at temperatures of −5 °C, −20 °C, and −40 °C. The maximum measurement error is 0.283 mm. The proposed ice sensor provides promising applications in aircraft and wind turbine icing detection. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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20 pages, 6011 KiB

Open AccessArticle

Depolarization Measurement through a Single-Mode Fiber-Based Endoscope for Full Mueller Endoscopic Polarimetric Imaging

by Colman Buckley, Marc Fabert and Dominique Pagnoux

Photonics 2023, 10(4), 387; https://doi.org/10.3390/photonics10040387 - 31 Mar 2023

Viewed by 1495

Abstract

Coupled to endoscopic techniques, Mueller polarimetry has been proven to be promising for early detection of certain diseases which affect biological tissues of inner organs. However, the depolarization power which is one of the most informative polarimetric characteristics cannot be directly measured through [...] Read more.

Coupled to endoscopic techniques, Mueller polarimetry has been proven to be promising for early detection of certain diseases which affect biological tissues of inner organs. However, the depolarization power which is one of the most informative polarimetric characteristics cannot be directly measured through a fiber endoscope. For evaluating this quantity, we propose a method based on the Lu–Chipman decomposition of the averaged sum of the Mueller matrices of neighboring pixels. The principle is well supported by numerical simulations. Depolarization powers of Spectralon and of different areas of a biological sample are also successfully evaluated. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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13 pages, 6300 KiB

Open AccessArticle

Optical Fiber Fabry–Pérot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method

by Shengnan Wu, Nanfei Lv, Yuhang Geng, Xiaolu Chen, Gaoxuan Wang and Sailing He

Sensors 2023, 23(6), 3198; https://doi.org/10.3390/s23063198 - 16 Mar 2023

Viewed by 1465

Abstract

In this paper, an optical fiber Fabry–Pérot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side [...] Read more.

In this paper, an optical fiber Fabry–Pérot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side illuminated by another single mode fiber (SMF). The CF acts as a naturally microfluidic channel, which can be served as a potential microfluidic solution concentration sensor. Moreover, the FP cavity formed by silica wall is insensitive to ambient solution refractive index but sensitive to the temperature. Thus, the HFP sensor can simultaneously measure microfluidic refractive index (RI) and temperature by cross-sensitivity matrix method. Three sensors with different inner air hole diameters were selected to fabricate and characterize the sensing performance. The interference spectra corresponding to each cavity length can be separated from each amplitude peak in the FFT spectra with a proper bandpass filter. Experimental results indicate that the proposed sensor with excellent sensing performance of temperature compensation is low-cost and easy to build, which is suitable for in situ monitoring and high-precision sensing of drug concentration and the optical constants of micro-specimens in the biomedical and biochemical fields. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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13 pages, 3788 KiB

Open AccessCommunication

FPGA-Based Hardware Implementation of Homodyne Demodulation for Optical Fiber Sensors

by Abimael Jiménez, Ángel Sauceda, Antonio Muñoz, José Duarte and José Mireles, Jr.

Photonics 2023, 10(3), 258; https://doi.org/10.3390/photonics10030258 - 28 Feb 2023

Viewed by 1936

Abstract

Homodyne demodulation is a convenient technique for signal detection in interferometric sensors. The demodulation process is typically developed using analog circuits. However, to improve the performance of the demodulator, a digital system must be employed. In this study, we developed an optical fiber [...] Read more.

Homodyne demodulation is a convenient technique for signal detection in interferometric sensors. The demodulation process is typically developed using analog circuits. However, to improve the performance of the demodulator, a digital system must be employed. In this study, we developed an optical fiber sensor by combining: (a) a Michelson interferometer, (b) a micro-electro-mechanical system (MEMS) device, and (c) a field-programmable gate array (FPGA)-based interrogator. Signal processing was integrated into the FPGA-embedded system. The homodyne demodulation algorithm was implemented with hardware modules developed in the hardware description language (HDL) to provide a portable, low-cost, and scalable digital system. The present study successfully demonstrates the development and validation of an FPGA-based interrogator capable of processing interferograms through a homodyne demodulation scheme. The experimental results reveal proper displacement measurements of the proof-mass MEMS and the low amount of hardware resources used. The displacement measurements obtained from the system matched those obtained from a certified characterization system. As the system can be easily reconfigured to the required measured signal, a similar measurement methodology can be developed using other demodulation schemes and optical fiber sensors. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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13 pages, 4541 KiB

Open AccessArticle

An All-Fiber Fabry–Pérot Sensor for Emulsion Concentration Measurements

by Simon Pevec, Janez Kunavar, Vedran Budinski, Matej Njegovec and Denis Donlagic

Sensors 2023, 23(4), 1905; https://doi.org/10.3390/s23041905 - 08 Feb 2023

Cited by 2 | Viewed by 2301

Abstract

This paper describes a Fabry–Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under [...] Read more.

This paper describes a Fabry–Pérot sensor-based measuring system for measuring fluid composition in demanding industrial applications. The design of the sensor is based on a two-parametric sensor, which enables the simultaneous measurement of temperature and refractive index (RI). The system was tested under real industrial conditions, and enables temperature-compensated online measurement of emulsion concentration with a high resolution of 0.03 Brix. The measuring system was equipped with filtering of the emulsion and automatic cleaning of the sensor, which proved to be essential for successful implementation of a fiber optic RI sensor in machining emulsion monitoring applications. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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11 pages, 2190 KiB

Open AccessCommunication

Design of a Flexible Weight Sensor Using Optical Fibre Macrobending

by Adam C. Funnell and Peter James Thomas

Sensors 2023, 23(2), 912; https://doi.org/10.3390/s23020912 - 12 Jan 2023

Cited by 4 | Viewed by 2094

Abstract

A flexible weight sensor based on optical fibre macrobending loss, using 1550 nm wavelength light and small fibre bending path lengths is presented. An applied load depresses an impactor layer of cylindrical protrusions into a soft mat covered with optical fibre, causing the [...] Read more.

A flexible weight sensor based on optical fibre macrobending loss, using 1550 nm wavelength light and small fibre bending path lengths is presented. An applied load depresses an impactor layer of cylindrical protrusions into a soft mat covered with optical fibre, causing the optical loss of the fibre to increase. An experimental study of two fibre types, two impactor materials, two impactor designs and a range of protrusion bend radii from 3 mm to 10 mm is shown. For weights greater than 2 kg, a linear response in optical loss (dB) is observed for an applied weight load in kg. The proportionality constant between loss and load, and thus the total amount of optical loss for up to 10 kg of weight load, can be tuned by changing the sensor physical parameters, shown here in ranges from 0.5 dB up to 25 dB. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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12 pages, 3116 KiB

Open AccessArticle

Ratiometric Temperature Sensing Using Highly Coupled Seven-Core Fibers

by Daniel A. May-Arrioja, Miguel A. Fuentes-Fuentes, Iván Hernández-Romano, Rodolfo Martínez-Manuel and Natanael Cuando-Espitia

Sensors 2023, 23(1), 484; https://doi.org/10.3390/s23010484 - 02 Jan 2023

Cited by 1 | Viewed by 1583

Abstract

In this paper, a ratiometric approach to sensing temperature variations is shown using specialty fiber optic devices. We analyzed the transmission response of cascaded segments of multicore fibers (MCFs), and dissimilar lengths were found to generate an adequate scheme for ratiometric operation. The [...] Read more.

In this paper, a ratiometric approach to sensing temperature variations is shown using specialty fiber optic devices. We analyzed the transmission response of cascaded segments of multicore fibers (MCFs), and dissimilar lengths were found to generate an adequate scheme for ratiometric operation. The perturbation of optical parameters in the MCFs translates to a rich spectral behavior in which some peaks increase their intensity while others decrease their intensity. Thus, by selecting opposite-behavior peaks, highly sensitive ratiometric measurements that provide robustness against spurious fluctuations can be performed. We implemented this approach using seven-core fiber (SCF) segments of 5.8 cm and 9.9 cm. To test the system’s response under controlled perturbations, we heated one of the segments from ambient temperature up to 150 °C. We observed defined peaks with opposite behavior as a function of temperature. Two pairs of peaks within the interrogation window were selected to perform ratiometric calculations. Ratiometric measurements exhibited sensitivities 6–14 times higher than single-wavelength measurements. A similar trend with enhanced sensitivity in both peak pairs was obtained. In contrast to conventional interferometric schemes, the proposed approach does not require expensive facilities or micrometric-resolution equipment. Moreover, our approach has the potential to be realized using commercial splicers, detectors, and filters. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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8 pages, 5359 KiB

Open AccessCommunication

High-Spatial-Resolution OFDR Distributed Temperature Sensor Based on Step-by-Step and Image Wavelet Denoising Methods

by Cailing Fu, Pengfei Li, Ronglong Sui, Zhenwei Peng, Huajian Zhong, Xiaoyu Yin and Yiping Wang

Sensors 2022, 22(24), 9972; https://doi.org/10.3390/s22249972 - 17 Dec 2022

Cited by 4 | Viewed by 1684

Abstract

A high-spatial-resolution OFDR distributed temperature sensor based on Au-SMF was experimentally demonstrated by using step-by-step and image wavelet denoising methods (IWDM). The measured temperature between 50 and 600 °C could be successfully demodulated by using SM-IWDM at a spatial resolution of 3.2 mm. [...] Read more.

A high-spatial-resolution OFDR distributed temperature sensor based on Au-SMF was experimentally demonstrated by using step-by-step and image wavelet denoising methods (IWDM). The measured temperature between 50 and 600 °C could be successfully demodulated by using SM-IWDM at a spatial resolution of 3.2 mm. The temperature sensitivity coefficient of the Au-SMF was 3.18 GHz/°C. The accuracy of the demodulated temperature was approximately 0.24 °C. Such a method has great potential to expand the temperature measurement range, which is very useful for high-temperature applications. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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16 pages, 943 KiB

Open AccessArticle

Singlemode-Multimode-Singlemode Fiber-Optic Interferometer Signal Demodulation Using MUSIC Algorithm and Machine Learning

by Nikolai Ushakov, Aleksandr Markvart and Leonid Liokumovich

Photonics 2022, 9(11), 879; https://doi.org/10.3390/photonics9110879 - 20 Nov 2022

Cited by 5 | Viewed by 1517

Abstract

The paper is aimed at improving the efficiency of signal processing for intermode fiber-optic interferometers. To do so, we propose to use the MUSIC algorithm. It is shown that the use of traditional methods for estimating the number of signal components leads to [...] Read more.

The paper is aimed at improving the efficiency of signal processing for intermode fiber-optic interferometers. To do so, we propose to use the MUSIC algorithm. It is shown that the use of traditional methods for estimating the number of signal components leads to poor operation of the MUSIC algorithm when applied to intermode interference signals. The possibility of using machine learning to estimate the number of signal components was investigated. The advantage of the proposed signal processing for demodulating the signals of an intermode interferometer over the Fourier transform has been experimentally demonstrated on the examples of simultaneous strain and curvature measurement, as well as pulse-wave sensing. The results can be also applied for processing signals of other optical-fiber sensors and multi-component signals of a different nature, for example, optical coherence tomography and radar signals. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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8 pages, 2636 KiB

Open AccessCommunication

Optically Tunable Diffraction Efficiency in Reflection Grating Written in Photomobile Polymers

by Riccardo Castagna, Andrea Di Donato, Oriano Francescangeli and Daniele Eugenio Lucchetta

Photonics 2022, 9(10), 751; https://doi.org/10.3390/photonics9100751 - 11 Oct 2022

Viewed by 1373

Abstract

In this work, we report the fabrication and optical characterization of a one-dimensional reflection holographic volume phase grating recorded in a recently developed holographic photomobile composite polymer mixture. The reflection grating recorded on the photomobile material was a periodic one-dimensional arrangement of hard [...] Read more.

In this work, we report the fabrication and optical characterization of a one-dimensional reflection holographic volume phase grating recorded in a recently developed holographic photomobile composite polymer mixture. The reflection grating recorded on the photomobile material was a periodic one-dimensional arrangement of hard polymeric walls and viscous regions. The reflection notch was located in the near-infrared region of the electromagnetic spectrum. The transmission efficiency of the grating was modulated by an external CW laser light source operating at

λ

= 532 nm. The transmission efficiency increased with the increase in the power of the external laser source, and in the range of the used power values, the phenomenon was completely reversible. At the highest power levels, a 48% increase in the diffraction efficiency was achieved. The increase in the diffraction efficiency was related to the growth of the refractive-index contrast of the grating. In particular, under illumination, the viscous material escaped from the irradiated area. This feature explains the experimentally observed changes in the values of the grating’s refractive index. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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11 pages, 3912 KiB

Open AccessCommunication

Coaxial Mach–Zehnder Digital Strain Sensor Made from a Tapered Depressed Cladding Fiber

by Sergio Celaschi, Nicolas Grégoire, Younès Messaddeq, Claudecir R. Biazoli and Gilliard N. Malheiros-Silveira

Sensors 2022, 22(19), 7145; https://doi.org/10.3390/s22197145 - 21 Sep 2022

Cited by 2 | Viewed by 1230

Abstract

An in-line digital optical sensor was proposed. It was built from a tapered depressed-cladding single-mode fiber and modeled as a coaxial Mach–Zehnder interferometer. The principle of operation of the optical digital sensor is based on the computation of the number of optical power [...] Read more.

An in-line digital optical sensor was proposed. It was built from a tapered depressed-cladding single-mode fiber and modeled as a coaxial Mach–Zehnder interferometer. The principle of operation of the optical digital sensor is based on the computation of the number of optical power transfer turning points (PTTP) from the transmission data of the component. Biconic tapers with high values of PTTP, high spectral resolution, high extinction ratio, and low insertion loss were modeled, fabricated, and characterized. As a proof of concept, an in-line digital strain sensor was fabricated and characterized. It presents a free spectral range of 1.3 nm, and produced 96 PTTP, at λ₀ = 1.55 μm, under stretch of ΔL = 707 µm, therefore producing a digital resolution of 7.4 µm/PTTP. The sensor also produced a quasi-symmetric response to stretch and compression. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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31 pages, 11905 KiB

Open AccessReview

Research Progress in Distributed Acoustic Sensing Techniques

by Ying Shang, Maocheng Sun, Chen Wang, Jian Yang, Yuankai Du, Jichao Yi, Wenan Zhao, Yingying Wang, Yanjie Zhao and Jiasheng Ni

Sensors 2022, 22(16), 6060; https://doi.org/10.3390/s22166060 - 13 Aug 2022

Cited by 24 | Viewed by 5198

Abstract

Distributed acoustic sensing techniques based on Rayleigh scattering have been widely used in many applications due to their unique advantages, such as long-distance detection, high spatial resolution, and wide sensing bandwidth. In this paper, we provide a review of the recent advancements in [...] Read more.

Distributed acoustic sensing techniques based on Rayleigh scattering have been widely used in many applications due to their unique advantages, such as long-distance detection, high spatial resolution, and wide sensing bandwidth. In this paper, we provide a review of the recent advancements in distributed acoustic sensing techniques. The research progress and operation principles are systematically reviewed. The pivotal technologies and solutions applied to distributed acoustic sensing are introduced in terms of polarization fading, coherent fading, spatial resolution, frequency response, signal-to-noise ratio, and sensing distance. The applications of the distributed acoustic sensing are covered, including perimeter security, earthquake monitoring, energy exploration, underwater positioning, and railway monitoring. The potential developments of the distributed acoustic sensing techniques are also discussed. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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16 pages, 3546 KiB

Open AccessArticle

Sensing System Based on FBG for Corrosion Monitoring in Metallic Structures

by Israel Sousa, Luis Pereira, Esequiel Mesquita, Vitória L. Souza, Walney S. Araújo, Antônio Cabral, Nélia Alberto, Humberto Varum and Paulo Antunes

Sensors 2022, 22(16), 5947; https://doi.org/10.3390/s22165947 - 09 Aug 2022

Cited by 5 | Viewed by 1879

Abstract

As corrosion has slow development, its detection at an early age could be an alternative for reducing costs of structural rehabilitation. Therefore, the employment of structural health monitoring (SHM) systems, sensing configurations collecting data over time allowing for observing changes in the properties [...] Read more.

As corrosion has slow development, its detection at an early age could be an alternative for reducing costs of structural rehabilitation. Therefore, the employment of structural health monitoring (SHM) systems, sensing configurations collecting data over time allowing for observing changes in the properties of the materials and damage emergence, for monitoring corrosion can be a good strategy to measure the damage and to decide the better moment for intervention. Nonetheless, the current corrosion sensor technology and the high costs of the sensing system implementation are limiting this application in the field. In this work, an optical fiber Bragg grating (FBG)-based sensing system is proposed for monitoring the thickness loss of a 1020 carbon steel metal plate subjected to controlled corrosion. The natural frequency of the plate was collected as a function of the corrosion time over 3744 h. To validate the experimental results, ultrasound measures and electrochemical tests were also carried out under similar conditions. The experimental results show adequate reliability, indicating the suitable functionality of the proposed system for monitoring the thickness loss caused by corrosion in metallic structures, in comparison with traditional methods, as ultrasonic and electrochemical measures. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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10 pages, 2848 KiB

Open AccessArticle

Temperature Fluctuations Compensation with Multi-Frequency Synchronous Manipulation for a NV Magnetometer in Fiber-Optic Scheme

by Ning Zhang, Qiang Guo, Wen Ye, Rui Feng and Heng Yuan

Sensors 2022, 22(14), 5218; https://doi.org/10.3390/s22145218 - 12 Jul 2022

Cited by 1 | Viewed by 1409

Abstract

Nitrogen-vacancy (NV) centers in diamonds play a large role in advanced quantum sensing with solid-state spins for potential miniaturized and portable application scenarios. With the temperature sensitivity of NV centers, the temperature fluctuations caused by the unknown environment and the system itself will [...] Read more.

Nitrogen-vacancy (NV) centers in diamonds play a large role in advanced quantum sensing with solid-state spins for potential miniaturized and portable application scenarios. With the temperature sensitivity of NV centers, the temperature fluctuations caused by the unknown environment and the system itself will mix with the magnetic field measurement. In this research, the temperature-sensitive characteristics of different diamonds, alongside the temperature noise generated by a measurement system, were tested and analyzed with a homemade NV magnetometer in a fiber-optic scheme. In this work, a multi-frequency synchronous manipulation method for resonating with the NV centers in all axial directions was proposed to compensate for the temperature fluctuations in a fibered NV magnetic field sensing scheme. The symmetrical features of the resonance lines of the NV centers, the common-mode fluctuations including temperature fluctuations, underwent effective compensation and elimination. The fluorescence change was reduced to 1.0% by multi-frequency synchronous manipulation from 5.5% of the single-frequency manipulation within a ±2 °C temperature range. Additionally, the multi-frequency synchronous manipulation improved the fluorescence contrast and the magnetic field measurement SNR through an omnidirectional manipulation scheme. It was very important to compensate for the temperature fluctuations, caused by both internal and external factors, to make use of the NV magnetometer in fiber-optic schemes’ practicality. This work will promote the rapid development and widespread applications of quantum sensing based on various systems and principles. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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12 pages, 3293 KiB

Open AccessArticle

Cavity Length Sequence Matching Algorithm Based on Combined Valley Peak Positioning for Fiber-Optic Fabry-Perot Sensors

by Liang Nie, Xiaonan Li, Hongwei Chen, Junying Zhang, Haibin Chen, Xueqing Zhao, Sheng Wang and Guanghai Liu

Photonics 2022, 9(7), 451; https://doi.org/10.3390/photonics9070451 - 28 Jun 2022

Cited by 2 | Viewed by 1535

Abstract

To solve the problem of low demodulation accuracy of conventional peak-to-peak algorithm for fiber-optic Fabry-Perot (FP) sensors due to failure of determining the interference order, a novel cavity length sequence matching demodulation algorithm based on a combined valley peak positioning is proposed. Firstly, [...] Read more.

To solve the problem of low demodulation accuracy of conventional peak-to-peak algorithm for fiber-optic Fabry-Perot (FP) sensors due to failure of determining the interference order, a novel cavity length sequence matching demodulation algorithm based on a combined valley peak positioning is proposed. Firstly, a pair of a peak and its neighboring valley in the reflection spectrum is selected and positioned, and two groups of interference orders are supposed to generate two groups of cavity length sequences. Finally, these cavity lengths are compared to find the real interference order of the peak and valley for the extraction of the accurate cavity length. In order to verify the feasibility and performance of the proposed algorithm, simulations and experiments were carried out for fiber-optic FP sensors with cavity lengths in the range of 15–115 μm. A demodulation accuracy better than 8.8 nm was found. The proposed algorithm can achieve highly accurate cavity length demodulation of fiber-optic FP sensors. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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11 pages, 3414 KiB

Open AccessArticle

SNR Enhancement of Direct Absorption Spectroscopy Utilizing an Improved Particle Swarm Algorithm

by Lin Zhang, Yanfang Li, Yubin Wei, Zhaowei Wang, Tingting Zhang, Weihua Gong and Qinduan Zhang

Photonics 2022, 9(6), 412; https://doi.org/10.3390/photonics9060412 - 10 Jun 2022

Cited by 6 | Viewed by 1551

Abstract

A noise elimination method based on an improved particle swarm algorithm is applied to direct absorption spectroscopy. The algorithm combines the theory of spectral line shape to calculate a fitness function according to the original spectra. Comparing the particles and the fitness function [...] Read more.

A noise elimination method based on an improved particle swarm algorithm is applied to direct absorption spectroscopy. The algorithm combines the theory of spectral line shape to calculate a fitness function according to the original spectra. Comparing the particles and the fitness function to calculate the updating direction, and position of particles, the iterative update finally finds the optimal solution. The algorithm is applied to direct absorption spectroscopy to measure methane; compared with the signal without algorithm processing, the signal-to-noise ratio (SNR) is improved by 4.17 times, and the minimum detection limit in the experiment is 15.3 ppb. R² = 0.9999 is calculated in the calibration experiment, and the error is less than 0.1 ppm in the repeatability experiment of constant methane at 2 ppm concentration. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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20 pages, 7296 KiB

Open AccessArticle

Simulation and Experiment Analysis of Temperature Field of Magnetic Suspension Support Based on FBG

by Huachun Wu, Cong Huang, Ruifang Cui and Jian Zhou

Sensors 2022, 22(12), 4350; https://doi.org/10.3390/s22124350 - 08 Jun 2022

Cited by 3 | Viewed by 1826

Abstract

Temperature rise is an important factor limiting the development of magnetic suspension support technology. Traditional temperature sensors such as thermocouples are complicated and vulnerable to electromagnetic interference due to their point contact temperature measurement methods. In this paper, the equivalent model of magnetic [...] Read more.

Temperature rise is an important factor limiting the development of magnetic suspension support technology. Traditional temperature sensors such as thermocouples are complicated and vulnerable to electromagnetic interference due to their point contact temperature measurement methods. In this paper, the equivalent model of magnetic suspension support is established, and the temperature field is simulated and analyzed by magnetic thermal coupling calculation in ANSYS software. Then, a quasi-distributed temperature measurement system is designed, and the FBG temperature sensor is introduced to measure the temperature of the magnetic suspension support system by “one-line and multi-point”. By comparing the analysis experiments and simulations, the equivalent accuracy of the simulation model and the FBG temperature sensor can accurately measure the temperature of the magnetic suspension support. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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14 pages, 5112 KiB

Open AccessArticle

Fiber Bragg Grating-Based Smart Garment for Monitoring Human Body Temperature

by Xiujuan Wang, Yaming Jiang, Siyi Xu, Hao Liu and Xiaozhi Li

Sensors 2022, 22(11), 4252; https://doi.org/10.3390/s22114252 - 02 Jun 2022

Cited by 7 | Viewed by 2624

Abstract

Body temperature provides an insight into the physiological state of a person, and body temperature changes reflect much information about human health. In this study, a garment for monitoring human body temperature based on fiber Bragg grating (FBG) sensors is reported. The FBG [...] Read more.

Body temperature provides an insight into the physiological state of a person, and body temperature changes reflect much information about human health. In this study, a garment for monitoring human body temperature based on fiber Bragg grating (FBG) sensors is reported. The FBG sensor was encapsulated with a PMMA tube and calibrated in the thermostatic water bath. The results showed that FBG sensors had good vibration resistance, and the wavelength changed about 0–1 pm at a 0.5–80 Hz vibration frequency. The bending path of the optical fiber after integration with clothing is discussed. When the bending radius is equal to or greater than 20 mm, a lower bending loss can be achieved even under the bending and stretching of the human body. The FBG sensor, the optical fiber, and the garment were integrated together using hot melt glue by the electric iron and the hot press machine. Through experiments of monitoring human body temperature, the sensor can reach the human armpit temperature in about 10–15 min with the upper arm close to the torso. Because it is immune to electromagnetic interferences, the smart garment can be used in some special environments such as ultrasonography, magnetic resonance (MR), and aerospace. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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8 pages, 1502 KiB

Open AccessCommunication

Microwave Photonic Fiber Ring Resonator

by Chen Zhu and Yiyang Zhuang

Sensors 2022, 22(10), 3771; https://doi.org/10.3390/s22103771 - 16 May 2022

Cited by 5 | Viewed by 1982

Abstract

In this article, a new concept of microwave photonic (MWP) fiber ring resonator is introduced. In particular, the complex transmission spectra of the resonator in the microwave domain, including magnitude and phase spectra, are measured and characterized. Multiple resonance peaks are obtained in [...] Read more.

In this article, a new concept of microwave photonic (MWP) fiber ring resonator is introduced. In particular, the complex transmission spectra of the resonator in the microwave domain, including magnitude and phase spectra, are measured and characterized. Multiple resonance peaks are obtained in the magnitude spectrum; rapid variations in phase near resonance (i.e., enhanced group delay) are observed in the phase spectrum. We also experimentally demonstrate that the MWP fiber ring resonator can be potentially employed as a novel optical fiber sensor for macro-bending and fiber length change sensing (strain sensing). The experimental results are in good agreement with theoretical predictions. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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18 pages, 5110 KiB

Open AccessArticle

Measurement and Region Identification in Deep Displacement of Slopes Based on Rod-Fiber Coupling Structure

by Pengzhen Liu, Zhen Liu and Cuiying Zhou

Sensors 2022, 22(10), 3623; https://doi.org/10.3390/s22103623 - 10 May 2022

Cited by 1 | Viewed by 1208

Abstract

For measuring and region-identifying the deep displacement of slopes, a rod-fiber coupling structure based on optical time-domain reflection technology was designed. Accuracy of measurement and region identification in the deep displacement of slopes were studied by calibration experiment and model experiment. A rod-fiber [...] Read more.

For measuring and region-identifying the deep displacement of slopes, a rod-fiber coupling structure based on optical time-domain reflection technology was designed. Accuracy of measurement and region identification in the deep displacement of slopes were studied by calibration experiment and model experiment. A rod-fiber coupling structure was able to calculate the variation and accurately identify the region of deep displacement of a slope compared with the measured downslide displacement of the slope model. The maximum measurement error of the deep displacement of the slope was 10.1%, the identification error of the displacement region was less than 4.4%, and the accuracy of the displacement-region identification of the rod-fiber coupling structure was 3.1 cm. Thus, the rod-fiber coupling structure based on optical time-domain reflection technology can be used for measuring and for region identification in the deep displacement of the slopes, and can provide a new method for the identification of the sliding surfaces of slopes. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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17 pages, 3279 KiB

Open AccessArticle

Feasibility and Error Analysis of Using Fiber Optic Temperature Measurement Device to Evaluate the Electromagnetic Safety of Hot Bridge Wire EEDs

by Xuxu Lyu, Guanghui Wei, Xinfu Lu, Haojiang Wan and Xue Du

Sensors 2022, 22(9), 3505; https://doi.org/10.3390/s22093505 - 05 May 2022

Cited by 6 | Viewed by 1489

Abstract

Most studies assessing the safety of hot bridge wire EEDs employ temperature sensors that directly use the measurements of the temperature measurement device without analyzing the accuracy of the temperature measurement. This study establishes the response function of the exposed bridge and exposed [...] Read more.

Most studies assessing the safety of hot bridge wire EEDs employ temperature sensors that directly use the measurements of the temperature measurement device without analyzing the accuracy of the temperature measurement. This study establishes the response function of the exposed bridge and exposed bridge temperature rise system of hot bridge wire EEDs through the Rosenthal’s temperature rise equation and Laplace transformation as well as experimental tests, and through the response function, the response law and numerical characteristics of the two are compared and analyzed under four typical excitations. Under steady current injection and continuous-wave radiation, both exposed bridge and exposed bridge temperature measurement systems can reach thermal equilibrium, and the equilibrium temperature of both are the same. However, under pulse excitation, the temperature rise measurement value is significantly different from the actual value due to the large difference in response time of the exposed bridge (1 ms) and the exposed bridge temperature measurement device (0.82 s). Studies have shown that under steady current injection and continuous-wave radiation, temperature rise measurements can be directly applied to the safety assessment of hot bridge wire EEDs, while under pulsed conditions, temperature rise measurements cannot be directly applied. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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17 pages, 4852 KiB

Open AccessArticle

Temperature Compensation of Fiber Bragg Grating Sensors in Smart Strand

by Se-Jin Jeon, Sung Yong Park and Sung Tae Kim

Sensors 2022, 22(9), 3282; https://doi.org/10.3390/s22093282 - 25 Apr 2022

Cited by 6 | Viewed by 1909

Abstract

Compared to other types of sensors, fiber optic sensors have improved accuracy and durability. Recently, the Smart Strand was developed to maximize the advantages of fiber optic sensors for measuring the cable forces in prestressed concrete structures or cable-supported bridges. The Smart Strand [...] Read more.

Compared to other types of sensors, fiber optic sensors have improved accuracy and durability. Recently, the Smart Strand was developed to maximize the advantages of fiber optic sensors for measuring the cable forces in prestressed concrete structures or cable-supported bridges. The Smart Strand has fiber Bragg gratings (FBGs) embedded in a core wire of the seven-wire strand. Similar to other sensors, the strain measured at an FBG is affected by temperature; therefore, the temperature effect that is not related to the mechanical strain should be compensated for or corrected in the long-term measurement subjected to temperature variation. However, a temperature compensation procedure for the FBG has yet to be established, and relevant studies have used different formulas for the compensation. Moreover, when the FBG sensors are packaged with a certain material—such as fiber reinforced polymer—for protection, it is important to consider the interaction between the FBG, packaging material, and host material during thermal behavior. Therefore, this study proposed a reasonable procedure for temperature compensation for the FBG sensors embedded in packaging material and host material. In particular, the thermal sensitivity of the Smart Strand was intensively investigated. The proposed theoretical formulas were validated through comparison with data obtained from various specimens in a temperature-controlled chamber. Finally, the procedure was applied to correct the data measured using the Smart Strands in a 20-m-long full-scale specimen for about a year, thus resulting in a realistic trend of the long-term prestressing force. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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10 pages, 37598 KiB

Open AccessArticle

Phase Unwrapping and Frequency Points Subdivision of the Frequency Sweeping Interferometry Based Absolute Ranging System

by Luming Song, Guang Shi, Hong Liu, Hongyi Lin, Fumin Zhang and Dong Sun

Sensors 2022, 22(8), 2904; https://doi.org/10.3390/s22082904 - 10 Apr 2022

Cited by 1 | Viewed by 1589

Abstract

Frequency sweeping interferometry (FSI) based absolute distance ranging has high precision and no ranging blind area. It can be used to realize large-scale and non-cooperative target measurement. However, the nonlinear frequency modulation of the laser seriously affects the ranging accuracy. In this manuscript, [...] Read more.

Frequency sweeping interferometry (FSI) based absolute distance ranging has high precision and no ranging blind area. It can be used to realize large-scale and non-cooperative target measurement. However, the nonlinear frequency modulation of the laser seriously affects the ranging accuracy. In this manuscript, a measurement method assisted by Hilbert Transform (HT) and Chirp-z Transform (CZT) is proposed, which can realize the phase unwrapping of the beat signal, the length reduction in the delay fiber of auxiliary optical path, and the improvement of the frequency resolution. The narrow-band frequency suitable for HT is further studied. In the experiment, the ranging resolution is 70 μm and the standard deviation is 12.6 μm within a distance of 4005 mm. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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8 pages, 2051 KiB

Open AccessBrief Report

Ultra-High SNR Demodulation Method for Optical Fiber Sensors Applied in Power Transformer Partial Discharge Detection

by Jixian Qiao, Weichao Zhang, Yanqi Wang, Qibing Shao, Jianlong Cai and Hong Zhao

Sensors 2022, 22(8), 2828; https://doi.org/10.3390/s22082828 - 07 Apr 2022

Cited by 5 | Viewed by 1746

Abstract

The demodulation method of optical fiber sensors utilized in power transformer partial discharge (PD) detection is insufficient for engineering applications. We design a distributed feedback fiber laser (DFB-FL) PD detection system with an asymmetric 3 × 3 coupler and propose an ultra-high signal-to-noise [...] Read more.

The demodulation method of optical fiber sensors utilized in power transformer partial discharge (PD) detection is insufficient for engineering applications. We design a distributed feedback fiber laser (DFB-FL) PD detection system with an asymmetric 3 × 3 coupler and propose an ultra-high signal-to-noise ratio (SNR) demodulation scheme by eliminating the main factors that affect the traditional method using an asymmetric 3 × 3 coupler. The power transformer PD detection results reveal that the proposed scheme is free from 3 × 3 coupler asymmetry issues, with an average SNR of 38.30 dB, which is much higher than the widely used demodulation method and the piezoelectric transducer sensor. The average SNR of the system is increased by 24.2 dB with the proposed method. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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21 pages, 2925 KiB

Open AccessReview

Advanced Fiber Sensors Based on the Vernier Effect

by Yunhao Chen, Li Zhao, Shuai Hao and Jianing Tang

Sensors 2022, 22(7), 2694; https://doi.org/10.3390/s22072694 - 31 Mar 2022

Cited by 37 | Viewed by 3395

Abstract

For decades, optical fiber interferometers have been extensively studied and applied for their inherent advantages. With the rapid development of science and technology, fiber sensors with higher detection sensitivity are needed on many occasions. As an effective way to improve measurement sensitivity, Vernier [...] Read more.

For decades, optical fiber interferometers have been extensively studied and applied for their inherent advantages. With the rapid development of science and technology, fiber sensors with higher detection sensitivity are needed on many occasions. As an effective way to improve measurement sensitivity, Vernier effect fiber sensors have drawn great attention during the last decade. Similar to the Vernier caliper, the optical Vernier effect uses one interferometer as a fixed part of the Vernier scale and the other as a sliding part of the Vernier scale. This paper first illustrates the principle of the optical Vernier effect, then different configurations used to produce the Vernier effect are classified and discussed. Finally, the outlook for Vernier effect fiber sensors is presented. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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22 pages, 5450 KiB

Open AccessArticle

A Machine Learning Study on Internal Force Characteristics of the Anti-Slide Pile Based on the DOFS-BOTDA Monitoring Technology

by Chaoqun Wei, Qinglu Deng, Yueming Yin, Mengyao Yan, Meng Lu and Kangqing Deng

Sensors 2022, 22(6), 2085; https://doi.org/10.3390/s22062085 - 08 Mar 2022

Cited by 3 | Viewed by 1760

Abstract

Long-term monitoring of constructed anti-slide piles can help in understanding the processes by which anti-slide piles are subjected to the thrust of landslides. This paper examined the landslide control project of Badong No. 3 High School. The internal force of an anti-slide pile [...] Read more.

Long-term monitoring of constructed anti-slide piles can help in understanding the processes by which anti-slide piles are subjected to the thrust of landslides. This paper examined the landslide control project of Badong No. 3 High School. The internal force of an anti-slide pile subjected to long-term action of landslide thrust was studied by Distributed Optical Fiber Sensing (DOFS) technology. The BP neural network was used for model training on the monitored strain values and the calculated bending moment values. The results show the following: (1) The monitoring results of the sensor fibers reflect the actual situation more accurately than steel rebar meters do and can locate the position of the sliding zone more accurately. (2) The bending moments distributed along the anti-slide pile have staged characteristics under the long-term action of landslide thrust. Three stages can be summarized according to the development trend of the bending moment values. These three stages can be divided into two change periods of landslide thrust. (3) The model produced by the BP neural network training can predict the bending moment values. In this paper, the sensing fibers monitoring over a long time interval provides a basis for long-term performance analysis of anti-slide piles and stability evaluation of landslides. Using the BP neural network for training relevant data can provide directions for future engineering monitoring. More novel methods can be devised and utilized that will be both accurate and convenient. Full article

(This article belongs to the Topic Advance and Applications of Fiber Optic Measurement)

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