Experimental Characteristic Analysis And Sensing Measurement Of Chaotic BDG

The distributed optical fiber sensing technology based on Brillouin scattering effect has obvious advantages over other optical fiber sensing technologies in terms of measurement accuracy,measurement range and spatial resolution in temperature and strain measurement.Therefore,Brillouin optical fiber sensing technology has gradually become the research hotspot of distributed optical fiber sensing technology.Brillouin dynamic grating(BDG)is a refractive index grating based on stimulated Brillouin scattering(SBS),which can be turned on and off at any time without damaging the optical fiber and permanent engraving.It inherits the characteristics of Bragg grating and has its own unique advantages,such as all-optical generation,fast reconstruction,read-write separation,position adjustable and so on;Therefore,it is widely used in the fields of distributed optical fiber sensing,variable optical delay line,alloptical signal processing and high-precision spectral analysis.However,due to the limitations of the current BDG generation mode,there are some problems,such as multi grating excitation,grating length limited by phonon lifetime,unable to maintain stability for a long time and so on.To break through the problems encountered by BDG at present,this dissertation proposes a scheme to excite chaotic BDG by using chaotic laser with low coherence characteristics,to solve the above problems of traditional BDG through chaotic BDG.Finally,we will realize the distributed sensing measurement without cross sensitivity of temperature and strain by using chaotic BDG.The specific research contents are as follows:(1)The feasibility of chaotic BDG experimental scheme is verified experimentally for the first time.Chaotic BDGs with grating lengths of 2.07 cm,1.66 cm,1.39 cm and 1.24 cm are generated by four chaotic lights with different spectral bandwidths.They are detected and preliminarily studied by phase-locked amplification technology.On this basis,chaotic BDG with grating length of 2.07 cm is used to realize distributed temperature sensing with spatial resolution of 2.7 cm in 100 m polarization-maintaining fiber.(2)The variation characteristics of Brillouin gain spectrum,reflection spectrum and temperature coefficient of chaotic BDG under different grating lengths are analyzed experimentally.The research shows that the center frequency of Brillouin gain spectrum moves to high frequency with the decrease of grating length,which is due to the asymmetry of chaotic spectrum.The Brillouin gain spectrum width increases with the decrease of grating length.Its essence is that the increase of chaotic spectrum bandwidth leads to the increase of Brillouin gain spectrum width.The reflection spectral width of chaotic BDG increases inversely with the decrease of grating length,which is in line with the theory of fiber Bragg grating.The gain spectrum temperature coefficient of chaotic BDG changes little with the decrease of grating length.However,the reflection spectrum temperature coefficient increases significantly with the decrease of grating length.It follows that various intrinsic parameters of chaotic BDG can be flexibly adjusted by grating length.More importantly,by reducing the grating length,the reflection spectrum bandwidth of GHz order can be obtained,and the reflection spectrum temperature coefficient can be increased by 20%.