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Research Progress and Applications of Distributed Optical Fiber Sensing

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (20 December 2024) | Viewed by 14786

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Special Issue Editors

Dr. Hailiang Zhang

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Guest Editor

Institute for Infocomm Research, Agency for Science, Technology and Research, Singapore 138632, Singapore
Interests: optical fiber sensors; multicore fiber sensors; distributed fiber sensors

Dr. Dora Juan Juan Hu

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Guest Editor

Institute for Infocomm Research, Agency for Science, Technology and Research, Singapore 138632, Singapore
Interests: photonics and optics; infrastructure and asset integrity; sensors
Special Issues, Collections and Topics in MDPI journals

Dr. Zhiyong Zhao

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Guest Editor

Wuhan National Lab for Optoelectronics (WNLO), School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
Interests: fiber optics; optical fiber sensor; nonlinear fiber optics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Distributed optical fiber sensors (DOFSs) have attracted increasing attention from academia and industry in the past several decades. The growing demands in fields such as gas and oil, structural health monitoring, and geophysical science have accelerated the research and development of DOFSs with high sensing performance. However, DOFSs still encounter challenges in both upstream research and downstream applications. For example, innovative ideas are needed to achieve performance enhancements including high measurement accuracy, high spatial resolution, long sensing length and large dynamic sensing range. The widespread implementation of the DOFSs in industry applications is often hindered by costly interrogation systems. We hope to collect innovative ideas and schemes of DOFSs to address the challenges and to provide new opportunities.

This Special Issue will focus on the latest developments of DOFS systems and their applications, including advanced signal processing, innovative DOFS techniques and solutions.

Relevant topics include, but are not limited to, the following:

Principles and schemes of innovative distributed optical fiber sensing techniques;
Novel distributed fiber sensing systems;
AI-assisted distributed optical fiber sensing and signal processing;
Applications of distributed optical fiber sensors in hash environments;
Field trial results of advanced DOFSs for practical applications.

Dr. Hailiang Zhang
Dr. Dora Juan Juan Hu
Dr. Zhiyong Zhao
Guest Editors

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Keywords

optical fiber sensors
distributed optical fiber sensing
sensing systems
sensing signal processing
machine learning and artificial intelligence
dynamic sensing

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Published Papers (9 papers)

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Research

17 pages, 4769 KiB

Open AccessArticle

Intelligent Pattern Recognition Using Distributed Fiber Optic Sensors for Smart Environment

by Brian Pamukti, Shofuro Afifah, Shien-Kuei Liaw, Jiun-Yu Sung and Daping Chu

Sensors 2025, 25(1), 47; https://doi.org/10.3390/s25010047 - 25 Dec 2024

Viewed by 759

Abstract

Distributed fiber optic sensors (DFOSs) have become increasingly popular for intrusion detection, particularly in outdoor and restricted zones. Enhancing DFOS performance through advanced signal processing and deep learning techniques is crucial. While effective, conventional neural networks often involve high complexity and significant computational demands. Additionally, the backscattering method requires the signal to travel twice the normal distance, which can be inefficient. We propose an innovative interferometric sensing approach utilizing a Mach–Zehnder interferometer (MZI) combined with a time forest neural network (TFNN) for intrusion detection based on signal patterns. This method leverages advanced sensor characterization techniques and deep learning to improve accuracy and efficiency. Compared to the conventional one-dimensional convolutional neural network (1D-CNN), our proposed approach achieves an 8.43% higher accuracy, demonstrating the significant potential for real-time signal processing applications in smart environments. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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10 pages, 2211 KiB

Open AccessCommunication

Track Deflection Monitoring for Railway Construction Based on Dynamic Brillouin Optical Time-Domain Reflectometry

by Tianfang Zhang, Liming Zhou, Weimin Liu and Linghao Cheng

Sensors 2024, 24(24), 8205; https://doi.org/10.3390/s24248205 - 23 Dec 2024

Viewed by 923

Abstract

Real-time online monitoring of track deformation during railway construction is crucial for ensuring the safe operation of trains. However, existing monitoring technologies struggle to effectively monitor both static and dynamic events, often resulting in high false alarm rates. This paper presents a monitoring technology for track deformation during railway construction based on dynamic Brillouin optical time-domain reflectometry (Dy-BOTDR), which effectively meets requirements in the monitoring of both static and dynamic events of track deformation. Dy-BOTDR can provide a two-dimensional spatial–temporal distribution map of track strain changes to characterize various events for better monitoring accuracy and lower false alarm rates. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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18 pages, 12673 KiB

Open AccessArticle

Analysis of Field Trial Results for Excavation-Activities Monitoring with φ-OTDR

by Hailiang Zhang, Hui Dong, Dora Juan Juan Hu, Nhu Khue Vuong, Lianlian Jiang, Gen Liang Lim and Jun Hong Ng

Sensors 2024, 24(18), 6081; https://doi.org/10.3390/s24186081 - 20 Sep 2024

Cited by 1 | Viewed by 1122

Abstract

Underground telecommunication cables are highly susceptible to damage from excavation activities. Preventing accidental damage to underground telecommunication cables is critical and necessary. In this study, we present field trial results of monitoring excavation activities near underground fiber cables using an intensity-based phase-sensitive optical time-domain reflectometer (φ-OTDR). The reasons for choosing intensity-based φ-OTDR for excavation monitoring are presented and analyzed. The vibration signals generated by four typical individual excavation events, i.e., cutting, hammering, digging, and tamping at five different field trial sites, as well as five different mixed events in the fifth field trial site were investigated. The findings indicate that various types of events can generate vibration signals with different features. Typically, fundamental peak frequencies of cutting, hammering and tamping events ranged from 30 to 40 Hz, 11 to 15 Hz, and 30 to 40 Hz, respectively. Digging events, on the other hand, presented a broadband frequency spectrum without a distinct peak frequency. Moreover, due to differences in environmental conditions, even identical excavation events conducted with the same machine may also generate vibration signals with different characteristics. The diverse field trial results presented offer valuable insights for both research and the practical implementation of excavation monitoring techniques for underground cables. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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9 pages, 2498 KiB

Open AccessCommunication

Distributed Vibration Sensing Based on a Forward Transmission Polarization-Generated Carrier

by Ming Chen, Xing Rao, Kuan Liu, Yuhang Wang, Shuqing Chen, Lin Xu, Rendong Xu, George Y. Chen and Yiping Wang

Sensors 2024, 24(16), 5257; https://doi.org/10.3390/s24165257 - 14 Aug 2024

Viewed by 1237

Abstract

For distributed fiber-optic sensors, slowly varying vibration signals down to 5 mHz are difficult to measure due to low signal-to-noise ratios. We propose and demonstrate a forward transmission-based distributed sensing system, combined with a polarization-generated carrier for detection bandwidth reduction, and cross-correlation for vibration positioning. By applying a higher-frequency carrier signal using a fast polarization controller, the initial phase of the known carrier frequency is monitored and analyzed to demodulate the vibration signal. Only the polarization carrier needs to be analyzed, not the arbitrary-frequency signal, which can lead to hardware issues (reduced detection bandwidth and less noise). The difference in arrival time between the two detection ends obtained through cross-correlation can determine the vibration position. Our experimental results demonstrate a sensitivity of 0.63 mrad/με and a limit of detection (LoD) of 355.6 pε/Hz^1/2 at 60 Hz. A lock-in amplifier can be used on the fixed carrier to achieve a minimal LoD. The sensing distance can reach 131.5 km and the positioning accuracy is 725 m (root-mean-square error) while the spatial resolution is 105 m. The tested vibration frequency range is between 0.005 Hz and 160 Hz. A low frequency of 5 mHz for forward transmission-based distributed sensing is highly attractive for seismic monitoring applications. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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16 pages, 8739 KiB

Open AccessArticle

Experimental Investigation of Low-Frequency Distributed Acoustic Sensor Responses to Two Parallel Propagating Fractures

by Teresa Reid, Gongsheng Li, Ding Zhu and A. Daniel Hill

Sensors 2024, 24(12), 3880; https://doi.org/10.3390/s24123880 - 15 Jun 2024

Cited by 1 | Viewed by 1297

Abstract

Low-frequency distributed acoustic sensing (LF-DAS) is a diagnostic tool for hydraulic fracture propagation with far-field monitoring using fiber optic sensors. LF-DAS senses strain rate variation caused by stress field change due to fracture propagation. Fiber optic sensors are installed in the monitoring wells in the vicinity of a fractured well. From the strain responses, fracture propagation can be evaluated. To understand subsurface conditions with multiple propagating fractures, a laboratory-scale hydraulic fracture experiment was performed simulating the LF-DAS response to fracture propagation with embedded distributed optical fiber strain sensors under these conditions. The experiment was performed using a transparent cube of epoxy with two parallel radial initial flaws centered in the cube. Fluid was injected into the sample to generate fractures along the initial flaws. The experiment used distributed high-definition fiber optic strain sensors with tight spatial resolutions. The sensors were embedded at two different locations on opposite sides of the initial flaws, serving as observation/monitoring locations. We also employed finite element modeling to numerically solve the linear elastic equations of equilibrium continuity and stress–strain relationships. The measured strains from the experiment were compared to simulation results from the finite element model. The experimentally derived strain and strain-rate waterfall plots from this study show the responses to both fractures propagating, while the fracture at the lower position took most of the fluid during the experiment. Interestingly, a fracture first began propagating from the upper flaw of the two flaws, but once the lower fracture was initiated, it grew much faster than the upper fracture. Both fibers were intercepted by the lower fracture, further verifying the strain signature as a fracture is approaching and intersecting an offset fiber. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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14 pages, 4645 KiB

Open AccessArticle

Decoupling of Temperature and Strain Effects on Optical Fiber-Based Measurements of Thermomechanical Loaded Printed Circuit Board Assemblies

by Tiago Maurício Leite, Cláudia Freitas, Roberto Magalhães, Alexandre Ferreira da Silva, José R. Alves, Júlio C. Viana and Isabel Delgado

Sensors 2023, 23(20), 8565; https://doi.org/10.3390/s23208565 - 18 Oct 2023

Cited by 2 | Viewed by 1548

Abstract

This study investigated the use of distributed optical fiber sensing to measure temperature and strain during thermomechanical processes in printed circuit board (PCB) manufacturing. An optical fiber (OF) was bonded to a PCB for simultaneous measurement of temperature and strain. Optical frequency-domain reflectometry was used to interrogate the fiber optic sensor. As the optical fiber is sensitive to both temperature and strain, a demodulation technique is required to separate both effects. Several demodulation techniques were compared to find the best one, highlighting their main limitations. The importance of good estimations of the temperature sensitivity coefficient of the OF and the coefficient of thermal expansion of the PCB was highlighted for accurate results. Furthermore, the temperature sensitivity of the bonded OF should not be neglected for accurate estimations of strains. The two-sensor combination model provided the best results, with a 2.3% error of temperature values and expected strain values. Based on this decoupling model, a methodology for measuring strain and temperature variations in PCB thermomechanical processes using a single and simple OF was developed and tested, and then applied to a trial in an industrial environment using a dynamic oven with similar characteristics to those of a reflow oven. This approach allows the measurement of the temperature profile on the PCB during oven travel and its strain state (warpage). Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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15 pages, 3699 KiB

Open AccessArticle

π-FBG Fiber Optic Acoustic Emission Sensor for the Crack Detection of Wind Turbine Blades

by Qi Yan, Xingchen Che, Shen Li, Gensheng Wang and Xiaoying Liu

Sensors 2023, 23(18), 7821; https://doi.org/10.3390/s23187821 - 12 Sep 2023

Cited by 4 | Viewed by 2151

Abstract

Wind power is growing rapidly as a green and clean energy source. As the core part of a wind turbine, the blades are subjected to enormous stress in harsh environments over a long period of time and are therefore extremely susceptible to damage, while at the same time, they are costly, so it is important to monitor their damage in a timely manner. This paper is based on the detection of blade damage using acoustic emission signals, which can detect early minor damage and internal damage to the blades. Instead of conventional piezoelectric sensors, we use fiber optic gratings as sensing units, which have the advantage of small size and corrosion resistance. Furthermore, the sensitivity of the system is doubled by replacing the conventional FBG (fiber Bragg grating) with a π-phase-shifted FBG. For the noise problem existing in the system, this paper combines the traditional WPD (wavelet packet decomposition) denoising method with EMD (empirical mode decomposition) to achieve a better noise reduction effect. Finally, small wind turbine blades are used in the experiment and their acoustic emission signals with different damage are collected for feature analysis, which sets the stage for the subsequent detection of different damage degrees and types. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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12 pages, 4582 KiB

Open AccessArticle

Spatially Modulated Fiber Speckle for High-Sensitivity Refractive Index Sensing

by Penglai Guo, Huanhuan Liu, Zhitai Zhou, Jie Hu, Yuntian Wang, Xiaoling Peng, Xun Yuan, Yiqing Shu, Yingfang Zhang, Hong Dang, Guizhen Xu, Aoyan Zhang, Chenlong Xue, Jiaqi Hu, Liyang Shao, Jinna Chen, Jianqing Li and Perry Ping Shum

Sensors 2023, 23(15), 6814; https://doi.org/10.3390/s23156814 - 31 Jul 2023

Cited by 4 | Viewed by 2183

Abstract

A fiber speckle sensor (FSS) based on a tapered multimode fiber (TMMF) has been developed to measure liquid analyte refractive index (RI) in this work. By the lateral and axial offset of input light into TMMF, several high-order modes are excited in TMMF, and the speckle pattern is spatially modulated, which affects an asymmetrical speckle pattern with a random intensity distribution at the output of TMMF. When the TMMF is immersed in the liquid analyte with RI variation, it influences the guided modes, as well as the mode interference, in TMMF. A digital image correlations method with zero-mean normalized cross-correlation coefficient is explored to digitize the speckle image differences, analyzing the RI variation. It is found that the lateral- and axial-offsets-induced speckle sensor can enhance the RI sensitivity from 6.41 to 19.52 RIU⁻¹ compared to the one without offset. The developed TMMF speckle sensor shows an RI resolution of 5.84 × 10⁻⁵ over a linear response range of 1.3164 to 1.3588 at 1550 nm. The experimental results indicate the FSS provides a simple, efficient, and economic approach to RI sensing, which exhibits an enormous potential in the image-based ocean-sensing application. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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16 pages, 6297 KiB

Open AccessArticle

Damage Analysis of Segmental Dry Joint Full-Scale Prestressed Cap Beam Based on Distributed Optical Fiber Sensing

by Duo Liu, Shengtao Li, Joan R. Casas, Xudong Chen and Yangyang Sun

Sensors 2023, 23(7), 3781; https://doi.org/10.3390/s23073781 - 6 Apr 2023

Cited by 2 | Viewed by 2122

Abstract

Distributed fiber optic sensors (DFOS) can detect structural cracks and structural deformation with high accuracy and wide measurement range. This study monitors the segmental prestressed bent cap, assembled with a large key dry joint, based on optical fiber technology, and it allows the comparison of its damaging process with that of a monolithic cast in place counterpart. The obtained results, comprising cross-section strain distributions, longitudinal strain profiles, neutral axis location, crack pattern, and the damage process, show that the DFOS technology can be successfully used to analyze the complex working stress state of the segmental beam with shear key joints, both in the elastic range and at the ultimate load, and to successfully identify the changing characteristics of the stress state of the segmental capping beam model when elastic beam theory no longer applies. The DFOS data confirm that the shear key joint, as the weak point of the segmental cap beam, results in the high stress concentration area, and the damage rate is higher than that of the cast-in-place beam. The accurate monitoring by the DFOS allows for the realization that the damage occurs at the premature formation of a concentrated compression zone on the upper part of the shear key. Full article

(This article belongs to the Special Issue Research Progress and Applications of Distributed Optical Fiber Sensing)

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