We report a thorough analysis on the Brillouin frequency shift as a function of geometrical param... more We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO 2-doped core, P 2 O 5 , and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.
Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute... more Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute d measurement by multiplexing configuration. OTDR sensor system with displacement sensors has been developed to monitor slope stability in soil layers. The displac ement was determined from the difference between the reflecte d signal of the sensing optical connector and the signal of the reference optical connector. Laboratory tests indic ate that displacements can be measured with the resolution o f several mm and the maximum measurable displacement is about 10 cm, which is enough to apply for the monit oring of soil movements.
We present a compact fiber optic Brillouin optical time domain analysis (BOTDA) sensor system, wh... more We present a compact fiber optic Brillouin optical time domain analysis (BOTDA) sensor system, which has the capability of detecting and locating intrusion attempts over several tens of kilometers long paths. The system employs a laser diode and two electro-optic modulators. Simulation of an intrusion effect was achieved by use of a strain-inducing setup. Distance resolution of 3 m was obtained for a 4.81 km long optical fiber within 1.5 s. Actual intrusion detection experiment was also performed using a step-on stage setup and clearly discernable detection signals were obtained in less than 1.5 s. # 2002 Published by Elsevier Science B.V.
The fiber optic extrinsic Fabry-Perot sensor was embedded in composite beam to sense the strain a... more The fiber optic extrinsic Fabry-Perot sensor was embedded in composite beam to sense the strain and failure of composite structures. A tensile test was performed to confirm the strain sensitivity of the fiber optic sensor embedded in composite specimens. The strain sensitivity of the extrinsic Fabry-Perot sensor showed very good agreement with the theoretical value. The bending deformation and matrix cracking were investigated through four-point bending tests of cross-ply composite beams with embedded fiber optic extrinsic Fabry-Perot sensor. The failure due to matrix cracks in the composite beam was confirmed by an edge replica method. The strain and failure signals were separated by digital filtering from the signal of fiber optic sensor. The failure instants were obviously noticeable from the failure signal obtained from the fiber optic signal by high pass filtering. The dominant failure strain of the composite beam was determined by strain signal obtained by low pass filtering.
We have demonstrated a feasibility study of the fiber optic sensor to monitor the distributed tem... more We have demonstrated a feasibility study of the fiber optic sensor to monitor the distributed temperature on a building construction. A fiber optic BOTDA sensor system, which has a capability of measuring the temperature distribution, attempted over several kilometers of long fiber paths. This simple fiber optic sensor system employs a laser diode and two electro-optic modulators. The optical fiber of the length of 1400 m was installed on the surfaces of the building. The change of the distributed temperature on the building construction was well measured by this fiber optic sensor. The temperature changed normally up to 4 °C through one day. Also, The temperature distribution of spring season was compared with that of early winter season.
Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute... more Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distributed measurement by multiplexing configuration. OTDR sensor system with displacement sensors has been developed to monitor slope stability in soil layers. The displacement was determined from the difference between the reflected signal of the sensing optical connector and the signal of the reference optical connector. Laboratory tests indicate that displacements can be measured with the resolution of several mm and the maximum measurable displacement is about 10 cm, which is enough to apply for the monitoring of soil movements.
Continuous monitoring of soil movements is important to maintain civil structures. Fiber optic se... more Continuous monitoring of soil movements is important to maintain civil structures. Fiber optic sensors can give the sensing solution for continuous displacement monitoring because they can be multiplexed with various sensors on one line of optical fiber, have the durability to harsh environments, and also are not affected by electro-magnetic effects. In this study, we work on the development of a multiplexed optical loss based fiber optic sensor for measuring displacements using the signal difference between the two reflected signals from a pair of optical connectors with various bending losses between them through an optical time domain reflectometer. We fabricate a multiplexed optical loss based fiber-optic sensor detecting linear displacements of 5 measuring positions of an object by setting these new 5 fiber-optic sensor probes on a single mode fiber simultaneously. We find that these sensors have a good capability to measure the displacements.
A novel method for auto-correction of fiber optic distributed temperature sensor using anti-Stoke... more A novel method for auto-correction of fiber optic distributed temperature sensor using anti-Stokes Raman back-scattering and its reflected signal is presented. This method processes two parts of measured signal. One part is the normal back scattered anti-Stokes signal and the other part is the reflected signal which eliminate not only the effect of local losses due to the micro-bending or damages on fiber but also the differential attenuation. Because the beams of the same wavelength are used to cancel out the local variance in transmission medium there is no differential attenuation inherently. The auto correction concept was verified by the bending experiment on different bending points.
This paper presents compact CW sub-THz imaging system using terahertz transmitter (Tx) that gener... more This paper presents compact CW sub-THz imaging system using terahertz transmitter (Tx) that generating 0.34 THz electromagnetic wave based on electronic device. Using this THz imaging system, we measured transmitting terahertz wave magnitude and phase information of several samples for non destructive test.
To prevent possible threats to public safety and economic loss from chemical leakage accidents, n... more To prevent possible threats to public safety and economic loss from chemical leakage accidents, novel chemical sensing techniques for regular monitoring and leakage detection have been developed for various fields. We propose a fiber optic liquid chemical sensor (FOCS) system using specialty optical fibers and an optical time domain reflectometer (OTDR), and is based on the leaky wave mode sensing principle. OTDR enables simple multiplexing where individual sensor nodes along the fiber length could be interrogated by a common OTDR. The sensor node in the optical fiber is prepared by removing the desired length of a protective layer using mechanical stripping and chemical etching techniques. A novel laser stripping technique with superior capability to fabricate quasi-distributed dense sensor nodes is devised as well. The FOCS system is further analyzed to characterize the sensor response behavior in relation to the sensor node length and possible environmental and chemical temperature effect. Under the condition satisfying the leaky wave mode principle and within the minimum acceptable refractive index (RI) range by the system, this FOCS system could monitor numerous liquid chemicals with variable refractive indices and has been tested with positive results. In addition, the system shows the possibility for multi-point detection and is further expanded into a hybrid technique capable of estimating the refractive index range of the detected chemical.
The oil leakage of off-shore pipelines will cause ocean contamination and economic losses. These ... more The oil leakage of off-shore pipelines will cause ocean contamination and economic losses. These accidents may happen by the failures of offshore pipelines due to corrosion, impulse and free-spanning. So, it is very urgent on pipeline health monitoring. Fiber optic distributed sensors should be used to know when and where failures may occur. In this study, a feasibility of BOTDA (Brillouin Optical Time Domain Analysis) system is studied on off-shore pipeline distributed strain monitoring influenced by free spanning. Strain distribution of an off-shore pipeline is calculated by numerical analysis and strain measurement experiments are carried on a beam bending test using BOTDA system. BOTDA could be an excellent tool to monitor the long-distance pipeline.
Recently, optical fiber sensors have been increasingly applied to monitor various engineering and... more Recently, optical fiber sensors have been increasingly applied to monitor various engineering and civil structural components. These fiber optic smart structures allow engineers to add nervous systems to their designs, giving structures capabilities that ...
Stimulated Brillouin scattering in optical fibers can be used to measure strain or temperature in... more Stimulated Brillouin scattering in optical fibers can be used to measure strain or temperature in a distributed manner. Brillouin optical time domain analysis (BOTDA) is the most common sensor system based on the Brillouin scattering. To improve the spatial resolution of these measurements, shorter pulses must be used, resulting in reduced signal powers causing a decrease of the dynamic range. In this paper, a doublepulse technique was proposed to enhance the spatial resolution of BOTDA. Experimental results showed that the ability to resolve two adjacent events could be enhanced, about twice, by using a double-pulsed pump light without decreases in the dynamic range.
Page 1. Intensity-modulated multiplexing of fiber Bragg grating sensors This article has been dow... more Page 1. Intensity-modulated multiplexing of fiber Bragg grating sensors This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 Smart Mater. Struct. 14 177 (http://iopscience.iop.org/0964-1726/14/1/017) ...
This paper presents a pulse base effect on the Brillouin gain spectrum that can be obtained by Br... more This paper presents a pulse base effect on the Brillouin gain spectrum that can be obtained by Brillouin optical time-domain analysis (BOTDA), which uses a pump-probe system. For theoretical analysis of the pulse base effect, we propose a theoretical model in which the interaction between the pulse base and probe light is taken into consideration. Strain underestimation caused by the pulse base is demonstrated by experiments and theoretical simulations.
The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber senso... more The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor has good sensitivity and resolution compared with other types of optical fiber sensors. However, they have the disadvantage that the distinction of strain direction of EFPI is difficult because of measurement method by only fringe counting. This paper presents the newly developed transmission-type EFPI (TEFPI) optical fiber sensor, which has been improved by additional functions, and whose measuring system differs from that of the reflection-type EFPI optical fiber sensors using a single-mode fiber (SMF) and multimode (MMF) fibers as light guides and reflectors, respectively. The output signal of the TEFPI optical fiber sensor was analyzed with the uniform plane wave-based model, the SMF power distribution-based model and the splice loss-based model; the analyzed signals were then verified experimentally. Based on the results of analysis, the TEFPI optical fiber sensor was fabricated using two single-mode fibers connected to the light source and optical receiver; this was then used in strain measurement. The strain measured by the TEFPI optical fiber sensor was compared with that measured by the electric strain gauge
We report a thorough analysis on the Brillouin frequency shift as a function of geometrical param... more We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO 2-doped core, P 2 O 5 , and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.
Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute... more Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute d measurement by multiplexing configuration. OTDR sensor system with displacement sensors has been developed to monitor slope stability in soil layers. The displac ement was determined from the difference between the reflecte d signal of the sensing optical connector and the signal of the reference optical connector. Laboratory tests indic ate that displacements can be measured with the resolution o f several mm and the maximum measurable displacement is about 10 cm, which is enough to apply for the monit oring of soil movements.
We present a compact fiber optic Brillouin optical time domain analysis (BOTDA) sensor system, wh... more We present a compact fiber optic Brillouin optical time domain analysis (BOTDA) sensor system, which has the capability of detecting and locating intrusion attempts over several tens of kilometers long paths. The system employs a laser diode and two electro-optic modulators. Simulation of an intrusion effect was achieved by use of a strain-inducing setup. Distance resolution of 3 m was obtained for a 4.81 km long optical fiber within 1.5 s. Actual intrusion detection experiment was also performed using a step-on stage setup and clearly discernable detection signals were obtained in less than 1.5 s. # 2002 Published by Elsevier Science B.V.
The fiber optic extrinsic Fabry-Perot sensor was embedded in composite beam to sense the strain a... more The fiber optic extrinsic Fabry-Perot sensor was embedded in composite beam to sense the strain and failure of composite structures. A tensile test was performed to confirm the strain sensitivity of the fiber optic sensor embedded in composite specimens. The strain sensitivity of the extrinsic Fabry-Perot sensor showed very good agreement with the theoretical value. The bending deformation and matrix cracking were investigated through four-point bending tests of cross-ply composite beams with embedded fiber optic extrinsic Fabry-Perot sensor. The failure due to matrix cracks in the composite beam was confirmed by an edge replica method. The strain and failure signals were separated by digital filtering from the signal of fiber optic sensor. The failure instants were obviously noticeable from the failure signal obtained from the fiber optic signal by high pass filtering. The dominant failure strain of the composite beam was determined by strain signal obtained by low pass filtering.
We have demonstrated a feasibility study of the fiber optic sensor to monitor the distributed tem... more We have demonstrated a feasibility study of the fiber optic sensor to monitor the distributed temperature on a building construction. A fiber optic BOTDA sensor system, which has a capability of measuring the temperature distribution, attempted over several kilometers of long fiber paths. This simple fiber optic sensor system employs a laser diode and two electro-optic modulators. The optical fiber of the length of 1400 m was installed on the surfaces of the building. The change of the distributed temperature on the building construction was well measured by this fiber optic sensor. The temperature changed normally up to 4 °C through one day. Also, The temperature distribution of spring season was compared with that of early winter season.
Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distribute... more Fiber optic optical time domain reflectometry (OTDR) sensors are suitable to apply the distributed measurement by multiplexing configuration. OTDR sensor system with displacement sensors has been developed to monitor slope stability in soil layers. The displacement was determined from the difference between the reflected signal of the sensing optical connector and the signal of the reference optical connector. Laboratory tests indicate that displacements can be measured with the resolution of several mm and the maximum measurable displacement is about 10 cm, which is enough to apply for the monitoring of soil movements.
Continuous monitoring of soil movements is important to maintain civil structures. Fiber optic se... more Continuous monitoring of soil movements is important to maintain civil structures. Fiber optic sensors can give the sensing solution for continuous displacement monitoring because they can be multiplexed with various sensors on one line of optical fiber, have the durability to harsh environments, and also are not affected by electro-magnetic effects. In this study, we work on the development of a multiplexed optical loss based fiber optic sensor for measuring displacements using the signal difference between the two reflected signals from a pair of optical connectors with various bending losses between them through an optical time domain reflectometer. We fabricate a multiplexed optical loss based fiber-optic sensor detecting linear displacements of 5 measuring positions of an object by setting these new 5 fiber-optic sensor probes on a single mode fiber simultaneously. We find that these sensors have a good capability to measure the displacements.
A novel method for auto-correction of fiber optic distributed temperature sensor using anti-Stoke... more A novel method for auto-correction of fiber optic distributed temperature sensor using anti-Stokes Raman back-scattering and its reflected signal is presented. This method processes two parts of measured signal. One part is the normal back scattered anti-Stokes signal and the other part is the reflected signal which eliminate not only the effect of local losses due to the micro-bending or damages on fiber but also the differential attenuation. Because the beams of the same wavelength are used to cancel out the local variance in transmission medium there is no differential attenuation inherently. The auto correction concept was verified by the bending experiment on different bending points.
This paper presents compact CW sub-THz imaging system using terahertz transmitter (Tx) that gener... more This paper presents compact CW sub-THz imaging system using terahertz transmitter (Tx) that generating 0.34 THz electromagnetic wave based on electronic device. Using this THz imaging system, we measured transmitting terahertz wave magnitude and phase information of several samples for non destructive test.
To prevent possible threats to public safety and economic loss from chemical leakage accidents, n... more To prevent possible threats to public safety and economic loss from chemical leakage accidents, novel chemical sensing techniques for regular monitoring and leakage detection have been developed for various fields. We propose a fiber optic liquid chemical sensor (FOCS) system using specialty optical fibers and an optical time domain reflectometer (OTDR), and is based on the leaky wave mode sensing principle. OTDR enables simple multiplexing where individual sensor nodes along the fiber length could be interrogated by a common OTDR. The sensor node in the optical fiber is prepared by removing the desired length of a protective layer using mechanical stripping and chemical etching techniques. A novel laser stripping technique with superior capability to fabricate quasi-distributed dense sensor nodes is devised as well. The FOCS system is further analyzed to characterize the sensor response behavior in relation to the sensor node length and possible environmental and chemical temperature effect. Under the condition satisfying the leaky wave mode principle and within the minimum acceptable refractive index (RI) range by the system, this FOCS system could monitor numerous liquid chemicals with variable refractive indices and has been tested with positive results. In addition, the system shows the possibility for multi-point detection and is further expanded into a hybrid technique capable of estimating the refractive index range of the detected chemical.
The oil leakage of off-shore pipelines will cause ocean contamination and economic losses. These ... more The oil leakage of off-shore pipelines will cause ocean contamination and economic losses. These accidents may happen by the failures of offshore pipelines due to corrosion, impulse and free-spanning. So, it is very urgent on pipeline health monitoring. Fiber optic distributed sensors should be used to know when and where failures may occur. In this study, a feasibility of BOTDA (Brillouin Optical Time Domain Analysis) system is studied on off-shore pipeline distributed strain monitoring influenced by free spanning. Strain distribution of an off-shore pipeline is calculated by numerical analysis and strain measurement experiments are carried on a beam bending test using BOTDA system. BOTDA could be an excellent tool to monitor the long-distance pipeline.
Recently, optical fiber sensors have been increasingly applied to monitor various engineering and... more Recently, optical fiber sensors have been increasingly applied to monitor various engineering and civil structural components. These fiber optic smart structures allow engineers to add nervous systems to their designs, giving structures capabilities that ...
Stimulated Brillouin scattering in optical fibers can be used to measure strain or temperature in... more Stimulated Brillouin scattering in optical fibers can be used to measure strain or temperature in a distributed manner. Brillouin optical time domain analysis (BOTDA) is the most common sensor system based on the Brillouin scattering. To improve the spatial resolution of these measurements, shorter pulses must be used, resulting in reduced signal powers causing a decrease of the dynamic range. In this paper, a doublepulse technique was proposed to enhance the spatial resolution of BOTDA. Experimental results showed that the ability to resolve two adjacent events could be enhanced, about twice, by using a double-pulsed pump light without decreases in the dynamic range.
Page 1. Intensity-modulated multiplexing of fiber Bragg grating sensors This article has been dow... more Page 1. Intensity-modulated multiplexing of fiber Bragg grating sensors This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 Smart Mater. Struct. 14 177 (http://iopscience.iop.org/0964-1726/14/1/017) ...
This paper presents a pulse base effect on the Brillouin gain spectrum that can be obtained by Br... more This paper presents a pulse base effect on the Brillouin gain spectrum that can be obtained by Brillouin optical time-domain analysis (BOTDA), which uses a pump-probe system. For theoretical analysis of the pulse base effect, we propose a theoretical model in which the interaction between the pulse base and probe light is taken into consideration. Strain underestimation caused by the pulse base is demonstrated by experiments and theoretical simulations.
The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber senso... more The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor has good sensitivity and resolution compared with other types of optical fiber sensors. However, they have the disadvantage that the distinction of strain direction of EFPI is difficult because of measurement method by only fringe counting. This paper presents the newly developed transmission-type EFPI (TEFPI) optical fiber sensor, which has been improved by additional functions, and whose measuring system differs from that of the reflection-type EFPI optical fiber sensors using a single-mode fiber (SMF) and multimode (MMF) fibers as light guides and reflectors, respectively. The output signal of the TEFPI optical fiber sensor was analyzed with the uniform plane wave-based model, the SMF power distribution-based model and the splice loss-based model; the analyzed signals were then verified experimentally. Based on the results of analysis, the TEFPI optical fiber sensor was fabricated using two single-mode fibers connected to the light source and optical receiver; this was then used in strain measurement. The strain measured by the TEFPI optical fiber sensor was compared with that measured by the electric strain gauge
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