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
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
Distributed optical fiber sensors have been widely used to monitor temperature, strain, vibration, and so on. Specifically, the sensors based on Brillouin scattering have been studied extensively to measure the strain...Distributed optical fiber sensors have been widely used to monitor temperature, strain, vibration, and so on. Specifically, the sensors based on Brillouin scattering have been studied extensively to measure the strain or temperature along an oDtical fiber.展开更多
This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spe...This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spectrum in a specially-designed fiber is firstly introduced. The complete discrimination of strain and temperature based on the Brillouin dynamic grating in a polarization maintaining fiber is extensively presented. The basic principle and two experimental schemes of distributed discrimination based on fiber optic nerve systems are demonstrated. The performance of the high discriminative accuracy （0.1 ~C-0.3 ~C and 5 kte-12~te） and high spatial resolution （-10 cm） with the effective measurement points of about 50 for a standard system configuration or about 1000 for a modified one will be highly expected in real industry applications.展开更多
煤炭一直是中国的主体能源,煤矿地质监测是煤矿安全生产的重要保障.分布式光纤传感技术具有感测点连续、高精度、抗电磁干扰、耐腐蚀等优点,在煤矿地质监测中有重要的应用.该文介绍了布里渊光时域反射(Brillouin optical time domain re...煤炭一直是中国的主体能源,煤矿地质监测是煤矿安全生产的重要保障.分布式光纤传感技术具有感测点连续、高精度、抗电磁干扰、耐腐蚀等优点,在煤矿地质监测中有重要的应用.该文介绍了布里渊光时域反射(Brillouin optical time domain reflectometry,BOTDR)技术在煤矿地质监测中的应用.重点介绍了采用分布式光纤传感技术进行采空区地层变形监测的方法和结果.结果表明,分布式光纤监测技术能够满足煤矿地质监测需求,具有良好的应用前景.展开更多
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.
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(Nos.61377089 and 61527819)the International Science&Technology Cooperation Program of China(No.2014DFA50870)the Natural Science Foundation of Shanxi(Nos.2015011049 and201601D021069)
文摘Distributed optical fiber sensors have been widely used to monitor temperature, strain, vibration, and so on. Specifically, the sensors based on Brillouin scattering have been studied extensively to measure the strain or temperature along an oDtical fiber.
文摘This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spectrum in a specially-designed fiber is firstly introduced. The complete discrimination of strain and temperature based on the Brillouin dynamic grating in a polarization maintaining fiber is extensively presented. The basic principle and two experimental schemes of distributed discrimination based on fiber optic nerve systems are demonstrated. The performance of the high discriminative accuracy （0.1 ~C-0.3 ~C and 5 kte-12~te） and high spatial resolution （-10 cm） with the effective measurement points of about 50 for a standard system configuration or about 1000 for a modified one will be highly expected in real industry applications.
文摘煤炭一直是中国的主体能源,煤矿地质监测是煤矿安全生产的重要保障.分布式光纤传感技术具有感测点连续、高精度、抗电磁干扰、耐腐蚀等优点,在煤矿地质监测中有重要的应用.该文介绍了布里渊光时域反射(Brillouin optical time domain reflectometry,BOTDR)技术在煤矿地质监测中的应用.重点介绍了采用分布式光纤传感技术进行采空区地层变形监测的方法和结果.结果表明,分布式光纤监测技术能够满足煤矿地质监测需求,具有良好的应用前景.
