Research On Fast Dynamic Signal Measurement Based On OFDR

Since the advent of the first single-mode fiber of the 70 th generation in the last century,with the development of optical fiber communication technology,optical fiber sensing technology has developed rapidly in several decades.The point fiber sensing technology is now quite mature and widely used in sonar and oil exploration,moreover,distributed optical fiber sensing technology due to the urgent needs in the field of object structure safety monitoring and its broad prospects,has become the hot spot in recent years.At present,most of the research on distributed optical fiber sensing technology focuses on optical time-domain technology,and few studies on optical frequency-domain technology.Moreover,the research on optical frequency-domain technology mostly focuses on how to improve the spatial resolution of the system,there are relatively few studies on the application of optical frequency domain technology to demodulate dynamic signals,especially fast dynamic signals.There are so many aspects need to be improved.Therefore,this paper aims to build an optical frequency domain reflection system that can demodulate fast disturbing signals and carry out experiments to demodulate the corresponding fast dynamic signals.In detail,this paper studies the Rayleigh scattering and optical frequency domain reflectometry(OFDR),then according to the objective of demodulating fast dynamic signals in this paper,the importance of these three parameters is explained in turn.Finally analyze the related modulation method and the demodulation algorithm.Furthermore,because the demodulation fast dynamic signal has very high requirements for sweeping light,this paper compares a variety of modulation method to produce swept-frequency light and firstly chooses the easier way of internal modulation to generate a sine sweep signal.Because the vicinity of the zero point of a sinusoidal signal can be seen as approximately linear,the sine sweep signal can be used as OFDR source.Then this paper simulates and experimentally verify sine frequency swept OFDR.The experimental results show that the sine frequency sweep OFDR has a good demodulation effect on the static system,but it is not suitable for dynamic demodulation,and determining the linear frequency sweep OFDR is the next research object.Finally,this paper selects a linear frequency sweep OFDR for experiments.this paper simulates linear frequency OFDR,the OFDR is performed with the same frequency sweeping range of linear and non-linear sweep sources.The simulation results show that the results of the linear sweep source are clearly visible,and the results of the nonlinear sweep source are mixed.Then build a linear sweep OFDR system,use external modulation method to produce single sideband sweep light with suppressed carrier.The linearity of the sweep signal is 0.999998,and the sweep speed is greater than 100 GHz/ms and the speed is adjustable.The sweep cycle is 10 kHz and the period is variable.This sweep signal is very suitable for the fast dynamic signal demodulation OFDR system,use this linear swept light to do OFDR experiment.The system first demodulates the optical fiber system with only static reflection points.From the demodulation results,it can be seen that the two reflection points with distance of 0.5 m can be clearly separated,and the spatial resolution reaches 0.2 m.After that,the system demodulates the fiber with a dynamic signal of 2.5 kHz,from the demodulation results,it can be seen that this system clearly locates the position of the disturbance signal and demodulates the frequency of the disturbance signal.This paper presents a stable modulation method to produce fast,linearly sweep signal,uses the sweep light as a light source to build a dynamic demodulator fast dynamic signal OFDR system.This work enriches the technique of fast dynamic signal demodulation in OFDR,has important significances to promote OFDR technology development.