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
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
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
In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or exp...In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.展开更多
This paper deals with the nonlinear effect of the drift motion of multi-chain mooring buoys. The buoy's motion in time domain is determined for the case that the wave and mooring force are nonlinear. The Kotorayam...This paper deals with the nonlinear effect of the drift motion of multi-chain mooring buoys. The buoy's motion in time domain is determined for the case that the wave and mooring force are nonlinear. The Kotorayama's method of hydrodynamic effect in a single mooring chain is expanded to multi-mooring chains. The time history of drift motion of the mooring buoy in regular waves and wave groups is calculated. The relation between the drift motion and the wave height or difference frequency is discussed. It can be shown that the effect of the hydrodynamic force acting on the mooring chain has remarkable influence on the total drift motion of the mooring buoy. In a wave group, its amplitude is mainly controled by the wave height and has little relation with difference frequency.展开更多
Aiming at the problem of large fading noise in Rayleigh Brillouin optical time domain analysis system, a wavelength scanning technique is proposed to enhance the performance of the temperature sensing system. The prin...Aiming at the problem of large fading noise in Rayleigh Brillouin optical time domain analysis system, a wavelength scanning technique is proposed to enhance the performance of the temperature sensing system. The principle of the proposed technique to reduce the fading noise is introduced based on the analysis of Rayleigh Brillouin optical time domain analysis system. The experimental results show that the signal-to-noise ratio(SNR) at the end of optical fiber with length of 50 m after 17 times wavelength scanning is 5.21 d B higher than that with single wavelength, the Brillouin frequency shift(BFS) on the heated fiber with length of 70 m inserted at the center of sensing fiber can be accurately measured as 0.19 MHz, which is equivalent to a measurement accuracy of 0.19 °C. It indicates that the proposed technique can realize high-accuracy temperature measurement and has huge potential in the field of long-distance and high-accuracy sensing.展开更多
The application of Golay pulse coding technique in spontaneous Brillouin-based distributed temperature sensor based on self-heterodyne detection of Rayleigh and Brillouin scattering is theoretically and experimentally...The application of Golay pulse coding technique in spontaneous Brillouin-based distributed temperature sensor based on self-heterodyne detection of Rayleigh and Brillouin scattering is theoretically and experimentally analyzed. The enhancement of system signal to noise ratio(SNR) and reduction of temperature measurement error provided by coding are characterized. By using 16-bit Golay coding, SNR can be improved by about 2.77 d B, and temperature measurement error of the 100 m heated fiber is reduced from 1.4 °C to 0.5 °C with a spatial resolution of 13 m. The results are believed to be beneficial for the performance improvement of self-heterodyne detection Brillouin optical time domain reflectometer.展开更多
An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the...An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells,i.e.used memory,while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer.The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions.To demonstrate the efficiency of the parallelized FDTD model,a mirrored cavity is analyzed.The analysis shows that the proposed model reduces computation time and memory cost,and the parallel computation result matches the theoretical model.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
We present a full three-dimensional, featured-data algorithm for time-domain fluorescence diffuse optical tomography that inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of a...We present a full three-dimensional, featured-data algorithm for time-domain fluorescence diffuse optical tomography that inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of appropriate transform-factors to effectively separate the fluorescent yield and lifetime parameters. By use of a time-correlation single-photon counting system and the normalized Born formulation, we experimentally validate that the proposed scheme can achieve simultaneous reconstruction of the fluorescent yield and lifetime distributions with a reasonable accuracy.展开更多
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.
文摘In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.
文摘This paper deals with the nonlinear effect of the drift motion of multi-chain mooring buoys. The buoy's motion in time domain is determined for the case that the wave and mooring force are nonlinear. The Kotorayama's method of hydrodynamic effect in a single mooring chain is expanded to multi-mooring chains. The time history of drift motion of the mooring buoy in regular waves and wave groups is calculated. The relation between the drift motion and the wave height or difference frequency is discussed. It can be shown that the effect of the hydrodynamic force acting on the mooring chain has remarkable influence on the total drift motion of the mooring buoy. In a wave group, its amplitude is mainly controled by the wave height and has little relation with difference frequency.
基金supported by the National Natural Science Foundation of China(No.61377088)the Natural Science Foundation of Hebei Province of China(Nos.E2015502053 and F2015502059)the Fundamental Research Funds for the Central Universities(No.2016XS104)
文摘Aiming at the problem of large fading noise in Rayleigh Brillouin optical time domain analysis system, a wavelength scanning technique is proposed to enhance the performance of the temperature sensing system. The principle of the proposed technique to reduce the fading noise is introduced based on the analysis of Rayleigh Brillouin optical time domain analysis system. The experimental results show that the signal-to-noise ratio(SNR) at the end of optical fiber with length of 50 m after 17 times wavelength scanning is 5.21 d B higher than that with single wavelength, the Brillouin frequency shift(BFS) on the heated fiber with length of 70 m inserted at the center of sensing fiber can be accurately measured as 0.19 MHz, which is equivalent to a measurement accuracy of 0.19 °C. It indicates that the proposed technique can realize high-accuracy temperature measurement and has huge potential in the field of long-distance and high-accuracy sensing.
基金supported by the National Natural Science Foundation of China(No.61377088)the Natural Science Foundation of Hebei Province of China(Nos.E2015502053 and F2014502098)
文摘The application of Golay pulse coding technique in spontaneous Brillouin-based distributed temperature sensor based on self-heterodyne detection of Rayleigh and Brillouin scattering is theoretically and experimentally analyzed. The enhancement of system signal to noise ratio(SNR) and reduction of temperature measurement error provided by coding are characterized. By using 16-bit Golay coding, SNR can be improved by about 2.77 d B, and temperature measurement error of the 100 m heated fiber is reduced from 1.4 °C to 0.5 °C with a spatial resolution of 13 m. The results are believed to be beneficial for the performance improvement of self-heterodyne detection Brillouin optical time domain reflectometer.
基金Supported by the Scientific Research Foundation of Nanjing University of Posts and Telecommunications(NY212008,NY213116)the National Science Foundation of Jiangsu Province(BK20131383)
文摘An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells,i.e.used memory,while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer.The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions.To demonstrate the efficiency of the parallelized FDTD model,a mirrored cavity is analyzed.The analysis shows that the proposed model reduces computation time and memory cost,and the parallel computation result matches the theoretical model.
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.
基金supported by the National Natural Science Foundation of China(No.60578008,60678049)the National Basic Research Program of China(No.2006CB705700)Tianjin Municipal Government of China(No.07JCYBJC06600)
文摘We present a full three-dimensional, featured-data algorithm for time-domain fluorescence diffuse optical tomography that inverts the Laplace-transformed time-domain coupled diffusion equations and employs a pair of appropriate transform-factors to effectively separate the fluorescent yield and lifetime parameters. By use of a time-correlation single-photon counting system and the normalized Born formulation, we experimentally validate that the proposed scheme can achieve simultaneous reconstruction of the fluorescent yield and lifetime distributions with a reasonable accuracy.
