We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer （q0-OTDR） for acoustic measurement. Phase, amplitude, frequenc...We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer （q0-OTDR） for acoustic measurement. Phase, amplitude, frequency response, and location information can be directly obtained at the same time by using the passive 3 ×3 coupler demodulation. We also set an experiment and successfully restore the acoustic information. Meanwhile, our system has preliminary realized acoustic-phase sensitivity around -150 dB （re rad/μPa） in the experiment.展开更多
The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewi...The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser （FL） with 4-kHz linewidth at 3 dB and a distributed feedback （DFB） laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals （backscattered Brillouin light and local oscillator （LO）） is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.展开更多
The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensi...The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card （DAQ）. A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator （LO） in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio （SNR） has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.展开更多
We demonstrate a distributed two-dimensional(2D)strain-sensing system in optical frequency domain reflectometry(OFDR)with an Archimedean spiral arrangement of the sensing fiber.The Archimedean spiral describes a simpl...We demonstrate a distributed two-dimensional(2D)strain-sensing system in optical frequency domain reflectometry(OFDR)with an Archimedean spiral arrangement of the sensing fiber.The Archimedean spiral describes a simple relationship between the radial radius and polar angle,such that each circle(the polar angle from0 to 2π)can sense the 2D strain in all directions.The strain between two adjacent circles can also be easily obtained because an Archimedean spiral facilitates sensing of every angle covering the full 2D range.Based on the mathematical relation of Archimedean spirals,we deduce the relationship between the one-dimensional position of the sensing fiber and 2D distribution in polar coordinates.The results of the experiment show that an Archimedean spiral arrangement system can achieve 2D strain sensing with different strain load angles.展开更多
A phase-sensitive optical time domain reflectometer （φ-OTDR） based on a 120°-phase-difference Michelson in- terferometer is proposed. The Michelson interferometer with arm difference of 4m is used to test the ...A phase-sensitive optical time domain reflectometer （φ-OTDR） based on a 120°-phase-difference Michelson in- terferometer is proposed. The Michelson interferometer with arm difference of 4m is used to test the phase difference between the Rayleigh scattering from two sections of the fiber. A new demodulation method called the inverse transmission matrix demodulation scheme is utilized to demodulate the distributed phase from the backward scattering along the long fiber, The experimental results show that the 120°-phase-difference inter- ferometer φ-OTDR can detect the phase along the 3km fiber, and the acoustic signal within the whole human hearing range of 20 Hz-20 kHz is reproduced accurately and quickly.展开更多
In this paper, we show some recent experimental applications of Brillouin optical time-domain analysis （BOTDA） based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting ...In this paper, we show some recent experimental applications of Brillouin optical time-domain analysis （BOTDA） based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors.展开更多
A nonlinearity-compensation-free optical frequency domain reflectometry(OFDR)scheme is proposed and experimentally demonstrated based on the electrically-controlled optical frequency sweep.In the proposed scheme,the l...A nonlinearity-compensation-free optical frequency domain reflectometry(OFDR)scheme is proposed and experimentally demonstrated based on the electrically-controlled optical frequency sweep.In the proposed scheme,the linear frequency sweep light is generated by propagating an ultra-narrow-linewidth continuous-wave(CW)light through an electro-optic frequency shifter which consists of a dual-parallel Mach-Zehnder modulator(DPMZM)and an electronic 90°hybrid,where the electro-optic frequency shifter is driven by a linear frequency modulated signal generated by a direct digital synthesizer(DDS).Experimental results show that the spatial resolution and signal-to-noise ratio(SNR)of the proposed OFDR scheme without the nonlinear phase compensation are comparable to those of OFDR employing a commercial tunable laser source(TLS),an auxiliary interferometer,and a software-based nonlinear phase compensation method.The proposed OFDR scheme is helpful to reduce the complexity of the optical structure and eliminate the difficulty of developing the nonlinear phase compensation algorithm.展开更多
Terahertz time-domain spectroscopy(THz-TDS)system,as a new means of spectral analysis and detection,plays an increasingly pivotal role in basic scientific research.However,owing to the long scanning time of the tradit...Terahertz time-domain spectroscopy(THz-TDS)system,as a new means of spectral analysis and detection,plays an increasingly pivotal role in basic scientific research.However,owing to the long scanning time of the traditional THz-TDS system and the complex control of the asynchronous optical scanning(ASOPS)system,which requires frequent calibration,we combine traditional THz-TDS and ASOPS systems to form a composite system and propose an all-fiber trigger signal generation method based on the time overlapping interference signal generated by the collinear motion of two laser pulses.Finally,the time-domain and frequency-domain spectra are obtained by using two independent systems in the integrated systems.It is found that the full width at half maximum(FWHM)of the time-domain spectra and the spectral width of the frequency-domain spectra are almost the same,but the sampling speed of the ASOPS system is significantly faster than that of the traditional THz-TDS system,which conduces to the study of the transient characteristics of substances.展开更多
AIM:To compare the RTVue spectral optical coherence tomography(SD-OCT),Sirius Scheimpflug-Placido topographer,Lenstar optical low coherence reflectometry(OLCR)and ultrasound pachymetry(USP)devices in terms of their ag...AIM:To compare the RTVue spectral optical coherence tomography(SD-OCT),Sirius Scheimpflug-Placido topographer,Lenstar optical low coherence reflectometry(OLCR)and ultrasound pachymetry(USP)devices in terms of their agreement and repeatability of measuring central corneal thickness(CCT).METHODS:In this prospective study,50 eyes of 50patients were included.Three repeated measures were obtained using SD-OCT,Scheimpflug-Placido topographer and USP and five measurements were determined with the OLCR.Bland-Altman plots were used to assess agreement among the instruments,and 95%limits of agreement(LoA)for each comparison were calculated.Intra-examiner repeatability was assessed using intraclass correlation coefficients(ICCs).RESULTS:The mean CCT by SD-OCT,ScheimpflugPlacido topographer,OLCR,and USP were 525.90±34.08μm,525.92±34.10μm,530.30±35.62μm,and543.50±37.11μm respectively.All 4 modalities of CCT measurements correlated closely with each other,with Pearson correlation coefficients ranging from 0.977 to0.995.The mean differences(and upper/lower LoA)for CCT measurements were-0.05±6.77μm(13.3/-13.3)between SD-OCT and Scheimpflug-Placido topographer,4.38±3.79μm(11.8/-3.1)between OLCR and SD-OCT,4.38±6.03μm(16.2/-7.5)between OLCR and ScheimpflugPlacido topographer,13.20±6.46μm(25.9/0.5)between USP and OLCR,17.59±6.76μm(30.8/4.3)between USP and SD-OCT,and 17.58±8.13μm(33.5/1.6)between USP and Scheimpflug-Placido topographer.Intra-examiner repeatability was excellent for all devices with ICCs】0.98.CONCLUSION:For most practical purposes,CCT measurements with the RTVue,Sirius and Lenstar can be used interchangeably.Although highly correlated,CCTmeasurement differences between USP and these 3optical instruments can be significant depending on the clinical situation.展开更多
We propose a method for reconstructing the distributed forward state of polarization(SOP)in single-mode fibers(SMFs)to solve the problem of an unpredictable blind box of SOP evolution in many applications such as fibe...We propose a method for reconstructing the distributed forward state of polarization(SOP)in single-mode fibers(SMFs)to solve the problem of an unpredictable blind box of SOP evolution in many applications such as fiber-optic parametric amplification systems.Using polarization-sensitive optical frequency domain reflectometry(POFDR)and a quaternion-based model to describe polarization changes,our approach achieves high spatial resolution and precision.By an improved iterative fitting algorithm,the mean square error(MSE)of forward SOP reconstruction for approximately 100 consecutive measurement points was reduced to below 0.1%.This method enables visualization of SOP dynamics along the fiber,offering critical insights for polarization-dependent systems.展开更多
Anti-slide piles are one of the most important reinforcement structures against landslides,and evalu-ating the working conditions is of great significance for landslide mitigation.The widely adopted analytical methods...Anti-slide piles are one of the most important reinforcement structures against landslides,and evalu-ating the working conditions is of great significance for landslide mitigation.The widely adopted analytical methods of pile internal forces include cantilever beam method and elastic foundation beam method.However,due to many assumptions involved in calculation,the analytical models cannot be fully applicable to complex site situations,e.g.landslides with multi-sliding surfaces and pile-soil interface separation as discussed herein.In view of this,the combination of distributed fiber optic sensing(DFOS)and strain-internal force conversion methods was proposed to evaluate the working conditions of an anti-sliding pile in a typical retrogressive landslide in the Three Gorges reservoir area,China.Brillouin optical time domain reflectometry(BOTDR)was utilized to monitor the strain distri-bution along the pile.Next,by analyzing the relative deformation between the pile and its adjacent inclinometer,the pile-soil interface separation was profiled.Finally,the internal forces of the anti-slide pile were derived based on the strain-internal force conversion method.According to the ratio of calculated internal forces to the design values,the working conditions of the anti-slide pile could be evaluated.The results demonstrated that the proposed method could reveal the deformation pattern of the anti-slide pile system,and can quantitatively evaluate its working conditions.展开更多
基金This work was supported by the Shandong Natural Science Foundation （No. ZR2013FL028）, Science and Technology Development Project of Shandong Province （2014GGX 103019）, and Innovation and Achievement Transformation Projects of Shandong Province （2014ZZCX04206）.
文摘We demonstrate a distributed optical fiber sensing system based on the Michelson interferometer of the phase sensitive optical time domain reflectometer （q0-OTDR） for acoustic measurement. Phase, amplitude, frequency response, and location information can be directly obtained at the same time by using the passive 3 ×3 coupler demodulation. We also set an experiment and successfully restore the acoustic information. Meanwhile, our system has preliminary realized acoustic-phase sensitivity around -150 dB （re rad/μPa） in the experiment.
基金the National High Technology Research and Development Program of China(Grant No.2012AA041203)the Science and Technology Commission of Shanghai Municipality,China(Grant No.13XD1425400)the Pudong New Area Science and Technology Development Fund,China(Grant No.PKJ2012-D04)
文摘The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry （BOTDR） are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser （FL） with 4-kHz linewidth at 3 dB and a distributed feedback （DFB） laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals （backscattered Brillouin light and local oscillator （LO）） is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.
基金supported by the National High Technology Research and Development Program of China(Grant No.2012AA041203)the National Natural Science Foundation of China(Grant Nos.61377062 and 31201377)+1 种基金the Program of Shanghai Excellent Technical Leaders,China(Grant No.13XD1425400)the Doctorial Fund of Zhengzhou University of Light Industry,China(Grant No.2013BSJJ012)
文摘The digital coherent detection technique has been investigated without any frequency-scanning device in the Brillouin optical time domain reflectometry （BOTDR）, where the simplex pulse codes are applied in the sensing system. The time domain signal of every code sequence is collected by the data acquisition card （DAQ）. A shift-averaging technique is applied in the frequency domain for the reason that the local oscillator （LO） in the coherent detection is fix-frequency deviated from the primary source. With the 31-bit simplex code, the signal-to-noise ratio （SNR） has 3.5-dB enhancement with the same single pulse traces, accordant with the theoretical analysis. The frequency fluctuation for simplex codes is 14.01 MHz less than that for a single pulse as to 4-m spatial resolution. The results are believed to be beneficial for the BOTDR performance improvement.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.61505138,61635008,61475114,61735011)in part by the Tianjin Science and Technology Support Plan Program Funding(Grant No.16JCQNJC01800)+2 种基金in part by the China Postdoctoral Science Foundation(Grant Nos.2015M580199,2016T90205)in part by the National Instrumentation Program(Grant No.2013YQ030915)in part by the National Key Research and Development Program(Grant No.2016YFC0100500)
文摘We demonstrate a distributed two-dimensional(2D)strain-sensing system in optical frequency domain reflectometry(OFDR)with an Archimedean spiral arrangement of the sensing fiber.The Archimedean spiral describes a simple relationship between the radial radius and polar angle,such that each circle(the polar angle from0 to 2π)can sense the 2D strain in all directions.The strain between two adjacent circles can also be easily obtained because an Archimedean spiral facilitates sensing of every angle covering the full 2D range.Based on the mathematical relation of Archimedean spirals,we deduce the relationship between the one-dimensional position of the sensing fiber and 2D distribution in polar coordinates.The results of the experiment show that an Archimedean spiral arrangement system can achieve 2D strain sensing with different strain load angles.
基金Supported by the National Natural Science Foundation of China under Grant Nos U0934001 and 11076028the Science and Technology Commission of Shanghai Municipality under Grant Nos 11DZ1140202 and 13XD1425400the Pudong New Area Science and Technology Development Fund of China under Grant No PKJ2012-D04
文摘A phase-sensitive optical time domain reflectometer （φ-OTDR） based on a 120°-phase-difference Michelson in- terferometer is proposed. The Michelson interferometer with arm difference of 4m is used to test the phase difference between the Rayleigh scattering from two sections of the fiber. A new demodulation method called the inverse transmission matrix demodulation scheme is utilized to demodulate the distributed phase from the backward scattering along the long fiber, The experimental results show that the 120°-phase-difference inter- ferometer φ-OTDR can detect the phase along the 3km fiber, and the acoustic signal within the whole human hearing range of 20 Hz-20 kHz is reproduced accurately and quickly.
文摘In this paper, we show some recent experimental applications of Brillouin optical time-domain analysis （BOTDA） based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors.
基金the National Natural Science Foundation of China under Grants No.61927821 and No.61575037.
文摘A nonlinearity-compensation-free optical frequency domain reflectometry(OFDR)scheme is proposed and experimentally demonstrated based on the electrically-controlled optical frequency sweep.In the proposed scheme,the linear frequency sweep light is generated by propagating an ultra-narrow-linewidth continuous-wave(CW)light through an electro-optic frequency shifter which consists of a dual-parallel Mach-Zehnder modulator(DPMZM)and an electronic 90°hybrid,where the electro-optic frequency shifter is driven by a linear frequency modulated signal generated by a direct digital synthesizer(DDS).Experimental results show that the spatial resolution and signal-to-noise ratio(SNR)of the proposed OFDR scheme without the nonlinear phase compensation are comparable to those of OFDR employing a commercial tunable laser source(TLS),an auxiliary interferometer,and a software-based nonlinear phase compensation method.The proposed OFDR scheme is helpful to reduce the complexity of the optical structure and eliminate the difficulty of developing the nonlinear phase compensation algorithm.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFB3200100)the National Natural Science Foundation of China(Grant No.61575131)。
文摘Terahertz time-domain spectroscopy(THz-TDS)system,as a new means of spectral analysis and detection,plays an increasingly pivotal role in basic scientific research.However,owing to the long scanning time of the traditional THz-TDS system and the complex control of the asynchronous optical scanning(ASOPS)system,which requires frequent calibration,we combine traditional THz-TDS and ASOPS systems to form a composite system and propose an all-fiber trigger signal generation method based on the time overlapping interference signal generated by the collinear motion of two laser pulses.Finally,the time-domain and frequency-domain spectra are obtained by using two independent systems in the integrated systems.It is found that the full width at half maximum(FWHM)of the time-domain spectra and the spectral width of the frequency-domain spectra are almost the same,but the sampling speed of the ASOPS system is significantly faster than that of the traditional THz-TDS system,which conduces to the study of the transient characteristics of substances.
文摘AIM:To compare the RTVue spectral optical coherence tomography(SD-OCT),Sirius Scheimpflug-Placido topographer,Lenstar optical low coherence reflectometry(OLCR)and ultrasound pachymetry(USP)devices in terms of their agreement and repeatability of measuring central corneal thickness(CCT).METHODS:In this prospective study,50 eyes of 50patients were included.Three repeated measures were obtained using SD-OCT,Scheimpflug-Placido topographer and USP and five measurements were determined with the OLCR.Bland-Altman plots were used to assess agreement among the instruments,and 95%limits of agreement(LoA)for each comparison were calculated.Intra-examiner repeatability was assessed using intraclass correlation coefficients(ICCs).RESULTS:The mean CCT by SD-OCT,ScheimpflugPlacido topographer,OLCR,and USP were 525.90±34.08μm,525.92±34.10μm,530.30±35.62μm,and543.50±37.11μm respectively.All 4 modalities of CCT measurements correlated closely with each other,with Pearson correlation coefficients ranging from 0.977 to0.995.The mean differences(and upper/lower LoA)for CCT measurements were-0.05±6.77μm(13.3/-13.3)between SD-OCT and Scheimpflug-Placido topographer,4.38±3.79μm(11.8/-3.1)between OLCR and SD-OCT,4.38±6.03μm(16.2/-7.5)between OLCR and ScheimpflugPlacido topographer,13.20±6.46μm(25.9/0.5)between USP and OLCR,17.59±6.76μm(30.8/4.3)between USP and SD-OCT,and 17.58±8.13μm(33.5/1.6)between USP and Scheimpflug-Placido topographer.Intra-examiner repeatability was excellent for all devices with ICCs】0.98.CONCLUSION:For most practical purposes,CCT measurements with the RTVue,Sirius and Lenstar can be used interchangeably.Although highly correlated,CCTmeasurement differences between USP and these 3optical instruments can be significant depending on the clinical situation.
基金supported by the National Key R&D Program of China(No.2023YFB2804900)the National Natural Science Foundation of China(Nos.62275151 and 62405178)。
文摘We propose a method for reconstructing the distributed forward state of polarization(SOP)in single-mode fibers(SMFs)to solve the problem of an unpredictable blind box of SOP evolution in many applications such as fiber-optic parametric amplification systems.Using polarization-sensitive optical frequency domain reflectometry(POFDR)and a quaternion-based model to describe polarization changes,our approach achieves high spatial resolution and precision.By an improved iterative fitting algorithm,the mean square error(MSE)of forward SOP reconstruction for approximately 100 consecutive measurement points was reduced to below 0.1%.This method enables visualization of SOP dynamics along the fiber,offering critical insights for polarization-dependent systems.
基金The authors gratefully acknowledge the financial support pro-vided by the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.41907232)the National Science Fund for Distinguished Young Scholars of China(Grant No.42225702)the State Key Program of National Natural Science Foundation of China(Grant No.41230636).
文摘Anti-slide piles are one of the most important reinforcement structures against landslides,and evalu-ating the working conditions is of great significance for landslide mitigation.The widely adopted analytical methods of pile internal forces include cantilever beam method and elastic foundation beam method.However,due to many assumptions involved in calculation,the analytical models cannot be fully applicable to complex site situations,e.g.landslides with multi-sliding surfaces and pile-soil interface separation as discussed herein.In view of this,the combination of distributed fiber optic sensing(DFOS)and strain-internal force conversion methods was proposed to evaluate the working conditions of an anti-sliding pile in a typical retrogressive landslide in the Three Gorges reservoir area,China.Brillouin optical time domain reflectometry(BOTDR)was utilized to monitor the strain distri-bution along the pile.Next,by analyzing the relative deformation between the pile and its adjacent inclinometer,the pile-soil interface separation was profiled.Finally,the internal forces of the anti-slide pile were derived based on the strain-internal force conversion method.According to the ratio of calculated internal forces to the design values,the working conditions of the anti-slide pile could be evaluated.The results demonstrated that the proposed method could reveal the deformation pattern of the anti-slide pile system,and can quantitatively evaluate its working conditions.
