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Optical Correlation-domain Distributed Fiber Sensors

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (31 March 2019) | Viewed by 57343

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Prof. Dr. Kwang Yong Song

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Department of Physics, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Korea
Interests: distributed fiber sensors; few-mode fiber devices and applications; slow light in optical fibers; optical signal processing

Special Issue Information

Dear Colleagues,

Distributed fiber sensors are one of the fields in which a great deal of research has been going on, with growing interest and demands for safety in advanced societies. Unlike conventional point sensors that measure physical quantities at specific locations, distributed fiber sensors measure the spatial distribution of physical parameters, such as strain and temperature, which enables the integrity monitoring of large structures including tunnels, bridges, pipelines, transmission and power lines. It can be also applied to various fields, such as intrusion monitoring based on pressure or vibration measurement, and radiation dose monitoring based on optical loss measurements. Since the beginning of Rayleigh scattering-based sensors in the 1970s and Raman and Brillouin scattering-based sensors in the 1980s, distributed fiber sensors of various types and performances have been developed.

The distributed fiber sensor can be classified according to the method used for localizing the sensing position: optical time domain sensor based on the time-of-flight measurement of an optical pulse, optical frequency domain sensor based on the frequency scanning of a light source, and optical correlation domain sensor based on the synthesis of optical coherence function (SOCF) by controlling frequency or phase. Among them the optical correlation domain sensor based on the SOCF provides an unique advantage of random access of sensing position, as well as high sampling rate and high spatial resolution, which can be applied to measure local reflection of Rayleigh scattering, Brillouin scattering, Brillouin dynamic grating and fiber Bragg grating. For example in the case of Brillouin optical correlation domain analysis (BOCDA) the spatial resolution in mm, the high sampling rate in several kHz, and the number of resolving points over one million were reported, and research for improving performance, such as the introduction of the phase correlation and differential measurements, have been steadily carried out.

This Special Issue of Applied Sciences is intended to present the state-of-the art technologies in distributed fiber sensors based on optical correlation, including the improvement of performance or practicality, new applications, and new results of field tests. It would be also important to investigate methodologies to directly or indirectly combine the correlation-domain approach with time/frequency-domain to clarify new trends in this field.

Prof. Dr. Kwang Yong Song
Guest Editor

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Keywords

distributed fiber sensor
correlation
brillouin scattering
rayleigh scattering
fiber Bragg grating
structural health monitoring
scattering measurement
strain sensor
temperature sensor
vibration sensor

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Published Papers (13 papers)

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Research

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12 pages, 2486 KiB

Open AccessArticle

Simultaneous OTDR Dynamic Range and Spatial Resolution Enhancement by Digital LFM Pulse and Short-Time FrFT

by Pu Zhang, Qiguang Feng, Wei Li, Qiang Zheng and You Wang

Appl. Sci. 2019, 9(4), 668; https://doi.org/10.3390/app9040668 - 15 Feb 2019

Cited by 12 | Viewed by 4070

Abstract

This paper proposes a novel optical time domain reflectometry (OTDR) method based on the digital linear frequency modulation (LFM) pulse, which can achieve a tradeoff between maximum measurable distance and spatial resolution. Direct modulation and detection are adopted at the transmitting and receiving ends, respectively, which is simple in construction and does not require additional optics. The short-time fractional Fourier transform (STFrFT) is introduced for the signal processing and noise filtering. The theoretical analysis of the working principle confirmed that the spatial resolution is determined by the sweep frequency range of the digital LFM signal rather than the pulse width. The influence of the STFrFT window on the peak sidelobe ratio of the reflection peak is also studied. By combining STFrFT and sidelobe suppression, the dynamic range and spatial resolution can be appreciably enhanced simultaneously. In the demo experiments testing the proposed method on a conventional OTDR development board for comparison, a 7-dB improvement in the dynamic range and an approximately 10-times improvement in the spatial resolution are simultaneously achieved. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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18 pages, 6880 KiB

Open AccessArticle

Fiber Optic Sensing for Geomechanical Monitoring: (1)-Distributed Strain Measurements of Two Sandstones under Hydrostatic Confining and Pore Pressure Conditions

by Ziqiu Xue, Ji-Quan Shi, Yoshiaki Yamauchi and Sevket Durucan

Appl. Sci. 2018, 8(11), 2103; https://doi.org/10.3390/app8112103 - 1 Nov 2018

Cited by 14 | Viewed by 4690

Abstract

In this study distributed optic fiber has been used to measure both the Rayleigh and Brillouin frequency shift of two different sandstone core samples under controlled hydrostatic confining and pore pressure in the laboratory. The Berea sandstone core is relatively homogeneous, whereas the Tako sandstone core is visibly heterogeneous with a coarse-grain and a fine-grain region. Rayleigh frequency has been found to have a superior performance over Brillouin frequency in terms of better consistency (less scattering) in the tests carried out. The strain gauge readings reveal considerable anisotropy in the stiffness of the Berea core between perpendicular (vertical) and parallel to the bedding (hoop) directions. The strains converted from Rayleigh frequency shift measurements agree reasonably well with readings by one of the four hoop strain gauge channels under increasing confining/pore pressure. For the Tako sandstone core, the contrast in the grain-size, and thus rock elastic properties, is clearly reflected in the hoop strain measurement by both strain gauges and distributed optic fiber. The outcomes of the test have demonstrated successfully the use of a single optic fiber for measuring rock strain response at different regions of a heterogeneous core sample along a continuous trajectory. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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10 pages, 5181 KiB

Open AccessArticle

Strain Measurement Distributed on a Ground Anchor Bearing Plate by Fiber Optic OFDR Sensor

by Yong-Seok Kwon, Dae-Cheol Seo, Bo-Hun Choi, Min Yong Jeon and Il-Bum Kwon

Appl. Sci. 2018, 8(11), 2051; https://doi.org/10.3390/app8112051 - 25 Oct 2018

Cited by 17 | Viewed by 5011

Abstract

The safety of soil slopes reinforced by ground anchors can be evaluated by monitoring the tensile force of the anchors. The tensile force of ground anchors can be determined by measuring the strain of the bearing plate that transfers the tensile force of the anchor to the ground. Therefore, in order to investigate the relation between the strain of the bearing plate and the tensile force of a ground anchor, the strain distributed on the bearing plate was measured by a fiber optic OFDR (optical frequency domain reflectometry) sensor, which was fabricated by a tunable laser source, auxiliary interferometer, and main interferometer. This OFDR sensor was operated through a sweep range of 500 GHz with a spatial resolution of 0.2 mm, and a strain accuracy of approximately 4 με, considering the system noise when operating in 5-cm segments. The sensing fiber was circularly bonded onto the bearing plate using epoxy, and the distributed strain was measured on the bearing plate while increasing the load up to 10 tons. From the experimental results, the difference between the strain near the anchor head and the strain at the far site is significant in the region where compression strain is dominant. However, such a tendency did not appear in areas where bending strain dominates. Therefore, in order to monitor an anchor tensile force, it is necessary to carefully study the calibration factor between the anchor tensile force and the strain of the bearing plate. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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9 pages, 1158 KiB

Open AccessFeature PaperArticle

Detection of Thermal Strain in Steel Rails with BOTDA

by Lijuan Gu, Liang Zhang, Xiaoyi Bao, Merrina Zhang, Chengxian Zhang and Yongkang Dong

Appl. Sci. 2018, 8(11), 2013; https://doi.org/10.3390/app8112013 - 23 Oct 2018

Cited by 6 | Viewed by 2769

Abstract

Rail transportation is one of the most important and efficient forms of transportation. Large thermal strain can develop in the rail steel due to extreme climatic conditions resulting in safety related issues. We carried out a thermal-strain monitoring test on the rail specimen [...] Read more.

^{\circ}

C to +50

^{\circ}

C using a Brillouin optical time-domain analyzer (BOTDA) for the first time, to the best of our knowledge. Two jacketed fibers and small-diameter carbon/polyimide-coating single-mode fiber were used for the purpose of investigating the jacket effect of thermal-strain detection on the rail. Although a nonlinear response to the temperature of the loose jacketed fiber was found, it was applicable for thermal strain monitoring when glued on the surface of the rail sample. The measured thermal strain in the rail specimen was validated by the results obtained by the strain gauge. The thermally induced strain from the large rail specimen was found to have suppressed the nonlinear impact of the fiber jacket. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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8 pages, 2753 KiB

Open AccessArticle

Sub-Meter Spatial Resolution Phase-Sensitive Optical Time-Domain Reflectometry System Using Double Interferometers

by Shengwen Feng, Tuanwei Xu, Jianfen Huang, Yang Yang, Lilong Ma and Fang Li

Appl. Sci. 2018, 8(10), 1899; https://doi.org/10.3390/app8101899 - 12 Oct 2018

Cited by 17 | Viewed by 3400

Abstract

An improved phase-sensitive optical time-domain reflectometry (φ-OTDR) system with sub-meter spatial resolution is demonstrated. Two Michelson interferometers (MIs) with different path length differences are used in the proposed system. One is 10 m, the other is 9.2 m. Two Rayleigh backscattering phase traces with different spatial resolution are obtained by a phase generated carrier (PGC) algorithm at adjacent times. After using differencing and adaptive 2-D bilateral filtering algorithms, a 0.8-m spatial resolution over 2 km is achieved. Experimental results indicate that the system shows an extraordinary linearity as high as 99.94% with amplitude-modulation and acquires a detection frequency from 5 to 500 Hz. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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11 pages, 6163 KiB

Open AccessArticle

Distributed Strain Monitoring of Railway Composite Bogies Using a Brillouin Optical Correlation Domain Analysis System

by Hyuk-Jin Yoon, Jung-Seok Kim, Kwang-Yong Song, Hyun-Woo Cho and Ju-Yeong Jung

Appl. Sci. 2018, 8(10), 1755; https://doi.org/10.3390/app8101755 - 28 Sep 2018

Cited by 4 | Viewed by 3543

Abstract

The structural deformation of a bogie frame manufactured using a composite material was monitored in real time using a distributed optical fiber sensor. The bogie frame contained an internally embedded standard single-mode optical fiber. Performance tests were conducted by applying a vertical load to the middle of the side beams on each side of the composite bogie frame. The strain distribution was monitored using an optical fiber sensor. A distributed optical fiber sensor system based on the Brillouin optical correlation domain analysis (BOCDA) technique with a 3 cm spatial resolution was used. The distributed strain measured using the optical fiber correlated well with the finite element (FE) analysis data, confirming that the composite bogie frame was fabricated as designed. For a vertical load of 182 kN, the maximum strain, which occurred in the middle of the side frame, increased by 1.3 times, as compared with a vertical load of 140 kN. The experiment was able to verify the balance and the structural stability of the left- and right-hand-side beams. Furthermore, it could confirm that there was a concentrated load where the side beam and the crossbeam meet, owing to a mismatch during the assembly of the composite bogie frame. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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13 pages, 4045 KiB

Open AccessArticle

Experiment and Numerical Study on Deformation Measurement of Cast-in-Place Concrete Large-Diameter Pipe Pile Using Optical Frequency Domain Reflectometer Technology

by Lei Gao, Yunhao Gong, Hanlong Liu, Baoquan Ji, Yining Xuan and Yuan Ma

Appl. Sci. 2018, 8(9), 1450; https://doi.org/10.3390/app8091450 - 24 Aug 2018

Cited by 22 | Viewed by 3393

Abstract

The Cast-in-place concrete large-diameter pipe (PCC) pile has been used as the foundation reinforcement and embankment in China due to its low cost and high bearing capacity. The deformation of PCC pile under different vertical loads is very important for the application of engineering. In order to study the deformation characteristics of PCC pile, a small-scale model test was carried out. The new distributed measuring technology, named Optical Frequency Domain Reflectometer (OFDR), was applied to measure the strain on the PCC pile. A single mode fiber (SMF) was used, and the methods of layout, packaging and protection of optical fiber are introduced in detail. The obtained data was dealt with by wavelet transform, and the strain curves were analyzed based on the experiments. The finite element (FE) analysis model was established by COMSOL Multiphysics, and the numerical results compared with the experiment results. It showed that the optical fiber sensor can measure the strain of PCC pile, and that the deformation of PCC pile can be successfully obtained by OFDR technology. The strain of the pile decreases with depth and increases with loading. The measured result agrees well with numerical simulation result. The potential application of OFDR technology to PCC pile in situ and PCC energy pile is discussed. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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Review

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48 pages, 20797 KiB

Open AccessFeature PaperReview

Brillouin Optical Correlation-Domain Technologies Based on Synthesis of Optical Coherence Function as Fiber Optic Nerve Systems for Structural Health Monitoring

by Kazuo Hotate

Appl. Sci. 2019, 9(1), 187; https://doi.org/10.3390/app9010187 - 7 Jan 2019

Cited by 49 | Viewed by 7362

Abstract

Brillouin optical correlation-domain technologies are reviewed as “fiber optic nerve systems” for the health monitoring of large structures such as buildings, bridges, and aircraft bodies. The Brillouin scattering property is used as a sensing mechanism for strain and/or temperature. Continuous lightwaves are used in the technologies, and their optical coherence properties are synthesized to realize position-selective measurement. This coherence manipulation technology is called the “synthesis of optical coherence function (SOCF)”. By utilizing SOCF technologies, stimulated Brillouin scattering is generated position-selectively along the fiber, which is named “Brillouin optical correlation domain analysis (BOCDA)”. Spontaneous Brillouin scattering, which takes place at any portion along the fiber, can also be measured position-selectively by the SOCF technology. This is called “Brillouin optical correlation domain reflectometry (BOCDR)”. When we use pulsed lightwaves that have the position information, sensing performances, such as the spatial resolution, are inherently restricted due to the Brillouin scattering nature. However, in the correlation-domain technologies, such difficulties can be reduced. Superior performances have been demonstrated as distribution-sensing mechanisms, such as a 1.6-mm high spatial resolution, a fast measurement speed of 5000 points/s, and a 7000-με strain dynamic range, individually. The total performance of the technologies is also discussed in this paper. A significant feature of the technologies is their random accessibility to discrete multiple points that are selected arbitrarily along the fiber, which is not realized by the time domain pulsed-lightwave technologies. Discriminative and distributed strain/temperature measurements have also been realized using both the BOCDA technology and Brillouin dynamic grating (BDG) phenomenon, which are associated with the stimulated Brillouin scattering process. In this paper, the principles, functions, and applications of the SOCF, BOCDA, BOCDR, and BDG-BOCDA systems are reviewed, and their historical aspects are also discussed. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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19 pages, 6328 KiB

Open AccessReview

High Resolution Brillouin Sensing of Micro-Scale Structures

by Atiyeh Zarifi, Birgit Stiller, Moritz Merklein and Benjamin J. Eggleton

Appl. Sci. 2018, 8(12), 2572; https://doi.org/10.3390/app8122572 - 11 Dec 2018

Cited by 7 | Viewed by 5262

Abstract

Brillouin distributed measurement techniques have been extensively developed for structural health monitoring using fibre optic nerve systems. The recent advancement in the spatial resolution capabilities of correlation-based Brillouin distributed technique have reached the sub-mm regime, making this approach a suitable candidate for monitoring and characterizing integrated photonic devices. The small dimension associated with the short length of these devices—on the order of the cm- and mm-scale—requires high sensitivity detection techniques and sub-mm spatial resolution. In this paper, we provide an overview of the different Brillouin sensing techniques in various micro-scale structures such as photonic crystal fibres, microfibres, and on-chip waveguides. We show how Brillouin sensing is capable of detecting fine transverse geometrical features with the sensitivity of a few nm and also extremely small longitudinal features on the order of a few hundreds of

μ m

. We focus on the technique of Brillouin optical correlation domain analysis (BOCDA), which enables such high spatial resolution for mapping the opto-acoustic responses of micro-scale waveguides. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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24 pages, 2350 KiB

Open AccessReview

A Brief Review of Specialty Optical Fibers for Brillouin-Scattering-Based Distributed Sensors

by Peter Dragic and John Ballato

Appl. Sci. 2018, 8(10), 1996; https://doi.org/10.3390/app8101996 - 20 Oct 2018

Cited by 26 | Viewed by 5668

Abstract

Specialty optical fibers employed in Brillouin-based distributed sensors are briefly reviewed. The optical and acoustic waveguide properties of silicate glass optical fiber first are examined with the goal of constructing a designer Brillouin gain spectrum. Next, materials and their effects on the relevant Brillouin scattering properties are discussed. Finally, optical fiber configurations are reviewed, with attention paid to fibers for discriminative or other enhanced sensing configurations. The goal of this brief review is to reinforce the importance of fiber design to distributed sensor systems, generally, and to inspire new thinking in the use of fibers for this sensing application. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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19 pages, 4594 KiB

Open AccessReview

Recent Advances in Brillouin Optical Correlation-Domain Reflectometry

by Yosuke Mizuno, Heeyoung Lee and Kentaro Nakamura

Appl. Sci. 2018, 8(10), 1845; https://doi.org/10.3390/app8101845 - 8 Oct 2018

Cited by 15 | Viewed by 3586

Abstract

Distributed fiber-optic sensing based on Brillouin scattering has been extensively studied and many configurations have been developed so far. In this paper, we review the recent advances in Brillouin optical correlation-domain reflectometry (BOCDR), which is known as a unique technique with intrinsic single-end accessibility, high spatial resolution, and cost efficiency. We briefly discuss the advantages and disadvantages of BOCDR over other Brillouin-based distributed sensing techniques, and present the fundamental principle and properties of BOCDR with some special schemes for enhancing the performance. We also describe the recent development of a high-speed configuration of BOCDR (slope-assisted BOCDR), which offers a beyond-nominal-resolution detectability. The paper is summarized with some future prospects. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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17 pages, 7112 KiB

Open AccessReview

Recent Progress in Fast Distributed Brillouin Optical Fiber Sensing

by Hongying Zhang, Dengwang Zhou, Benzhang Wang, Chao Pang, Pengbai Xu, Taofei Jiang, Dexin Ba, Hui Li and Yongkang Dong

Appl. Sci. 2018, 8(10), 1820; https://doi.org/10.3390/app8101820 - 4 Oct 2018

Cited by 50 | Viewed by 4205

Abstract

Brillouin-based optical fiber sensing has been regarded as a good distributed measurement tool for the modern large geometrical structure and the industrial facilities because it can demodulate the distributed environment information (e.g., temperature and strain) along the sensing fiber. Brillouin optical time domain analysis (BOTDA), which is an excellent and attractive scheme, has been widely developed thanks to its high performance in a signal-to-noise ratio, a spatial resolution, and sensing distance. However, the sampling rate of the classical BOTDA is severely limited by several factors (especially the serially frequency-sweeping process) so that it cannot be suitable for the quickly distributed measurement. In this work, we summarize some promising breakthroughs about the fast BOTDA, which can be named as an optical frequency comb technique, an optical frequency-agile technique, a slope-assisted technique, and an optical chirp chain technique. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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20 pages, 6779 KiB

Open AccessReview

Phase-Coded and Noise-Based Brillouin Optical Correlation-Domain Analysis

by Avi Zadok, Eyal Preter and Yosef London

Appl. Sci. 2018, 8(9), 1482; https://doi.org/10.3390/app8091482 - 28 Aug 2018

Cited by 17 | Viewed by 3531

Abstract

Correlation-domain analysis has enabled distributed measurements of Brillouin gain spectra along optical fibers with high spatial resolution, up to millimeter-scale. The method relies on the joint modulation of counter-propagating Brillouin pump and signal waves so that their complex envelopes are correlated in select positions only. Brillouin optical correlation-domain analysis was first proposed nearly 20 years ago based on frequency modulation of the two waves. This paper reviews two more recent variants of the concept. In the first, the Brillouin pump and signal waves are co-modulated by high-rate binary phase sequences. The scheme eliminates restricting trade-offs between the spatial resolution and the range of unambiguous measurements, and may also suppress noise due to residual Brillouin interactions outside the correlation peak. Sensor setups based on phase coding addressed 440,000 high-resolution points and showed potential for reaching over 2 million such points. The second approach relies on the amplified spontaneous emission of optical amplifiers, rather than the modulation of an optical carrier, as the source of Brillouin pump and signal waves. Noise-based correlation-domain analysis reaches sub-millimeter spatial resolution. The application of both techniques to tapered micro-fibers and planar waveguides is addressed as well. Full article

(This article belongs to the Special Issue Optical Correlation-domain Distributed Fiber Sensors)

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