Research On High-Speed Measurement System Based On Fiber Optic Interference Frequency Reduction Technology

Photon Doppler velocity measurement system(PDV)is a kind of optical fiber laser interferometric velocity measurement system based on heterodyne technology.It is widely used to measure the speed of high-speed moving objects such as high-speed impact,detonation experiment and strong laser.But for the measurement of high speed and ultra-high speed field,the measurement range of laser interferometry technology will be limited directly because of the bandwidth limitation of digital to analog conversion technology.However,in the face of higher speed measurement requirements,photoelectric detectors and digital acquisition equipment with higher performance need to be used,which increases the cost and is restricted by technical bottlenecks.However,frequency reduction measurement plays an important role in some application scenarios,so this paper studies the high speed measurement system based on fiber interference frequency reduction technology.The details are as follows:1.To address the problem that the upper speed limit of fiber optic interferometric velocimetry system is limited by the "electronic bottleneck",this paper proposes two fiber optic interferometric downscaling velocimetry systems based on PDV structure,and the time stretching fiber down sampling system(TS-PDV)and cross gain fiber down sampling system(XGM-EOM)are analyzed from four aspects: technical principle,optical circuit design,optical simulation and key parameters,respectively.Among them,TS-PDV fiber optic speed measurement system is based on time stretching technology,according to the group velocity dispersion characteristics of pulsed light in dispersive medium,using two-stage dispersive fiber to form the stretching factor of the system,thus reducing the frequency of the interference signal;XGM-EOM fiber optic speed measurement system is a kind of frequency reduction speed measurement system based on SOA cross gain modulation technology and MZM electro-optical modulation technology.The XGM-EOM fiber optic velocimetry system is constructed according to the velocimetry demand under complex external field conditions.2.In order to solve the problem of uneven time-frequency energy distribution caused by noise and other factors in transient high-speed measurement,this paper uses STFT weighted post-processing algorithm to correct ridge extraction,so as to ensure smooth,continuous and true reliability of the speed curve demodulated from the interference signal.3.According to the characteristics of the system frequency reduction velocity measurement,design related experiments for verification.Under laboratory conditions,the peak velocity error is less than 0.5% in the comparison test with the third party equipment,which proves the accuracy of the measurement system.Under complex external field conditions,the detonation plate with the maximum velocity of 1050m/s is obtained by using a photodetector with 1GHz bandwidth,which proves the feasibility of the measurement system.