| As an effective method to obtain distributed information of strain and temperature along the large structures,distributed optical fiber sensor based on Brillouin scattering is of great important to accelerate the construction of optical fiber neural system for structural health monitoring and promote the social and economic development.The traditional Brillouin-scattering based sensor is only suitable for the measurement of static parameters.In order to meet the actual needs of modern society for real-time monitoring of dynamic parameters,a variety of improved new technologies have been proposed.Among them,the slope-assisted technology attracts tremendous attention as it exhibits significant advantages of simple structure,strong adaptability,and the ability to effectively improve the sampling rate of the system.However,the dynamic strain information is extracted from the Brillouin gain changes experienced by the probe light in the linear region of the Brillouin gain spectrum(BGS),so the narrow linewidth(? 30 MHz)of the BGS limits the measurable dynamic strain range of the system to a few hundred ??.In addition,the gain of the probe light is not only related to the applied strain,but also highly dependent on the power of the pump light,leading to aworsening measurement accuracy.In the light of these two scientific problems,a slope-assisted chaotic Brillouin dynamic strain monitoring scheme is proposed in this paper,for the hope of achieving large-scale and high-precision dynamic strain measurement.The specific research work is carried out as follows:(1)A single-slope-assisted chaotic BOCDA(SSA-CBOCDA)scheme is proposed to extend the dynamic strain measurement range,and the dynamic strain measurement with vibration range of 0-1200 ?? is realized,which is twice as large as the traditional slope assisted scheme.Firstly,the broadening effect of chaotic laser on BGS is described,and the deterioration of BGS envelope caused by time delay signature(TDS)of chaotic laser is analyzed theoretically.Secondly,the linear negative correlation between the main-sub-peak ratio(MSPR)of BGS and TDS is established by the experiment,which verifies that TDS is the main reason for the existence of the sub-peak in chaotic BGS.Then,the influence of MAPR value on the measurable dynamic range of the system is investigated experimentally,where the range is not greater than 400 ?? at MSPR < 0 d B,and 600 ?? at MSPR > 0 d B.Finally,by eliminating the TDS,the BGS without sub peak is obtained,and the dynamic strain with amplitude of 1200 ?? is identified under a centimeter level spatial resolution by using the SSA-CBOCDA scheme.(2)A dual-slope-assisted chaotic BOCDA(DSA-CBOCDA)scheme is proposed to improve the strain measurement accuracy and resolution,where the static strain measurement accuracy of 3.9 ??,the dynamic strain measurement accuracy of 6.2 ??,the static strain resolution of 10 ?? and the dynamic strain resolution of 15 ?? are achieved.Firstly,the suppression effect of DSA scheme on the power fluctuation of chaotic pump is analyzed theoretically.Then,the improvement of strain accuracy and resolution are proved by experiments.Compared with the previous SSA-CBOCDA scheme,DSA-CBOCDA can improve the static strain measurement accuracy from 25.0 ?? to 3.9 ??,and the dynamic strain measurement accuracy from 28.5 ?? to 6.2 ??.The static strain resolution of the system can reach 10 ?? and the dynamic strain resolution can reach 15 ??.The dynamic strain measurement with amplitude of 800 ?? is realized,and the spatial resolution is 3.75 cm,the absolute error is 0.9 ??,and the measurement accuracy is 6.5 ??.Finally,the stability of DSA-CBOCDA is verified,and the measurement accuracy of the system is basically the same in different dynamic strain ranges,with an average value of 6.3 ??. |
PDF Full Text Request