System Design And Experiment Of Doppler Lidar Based On Fiber Mach-zehnder Interferometer

The atmospheric wind field is an important meteorological parameter.Doppler lidar is an effective detection tool for atmospheric wind field.The wind speed value is obtained by retrieving the Doppler shift of the atmospheric backscatter signal.Fiber Mach-Zehnder interferometer(FMZI)is used as the frequency discriminator of Doppler lidar system,which has advantages of light weight,small volume and high stability.On the basis of previous theoretical analysis and simulation experiment verification,the lidar system based on FMZI is established for atmospheric wind field detection.The Nd:YAG solid-state laser at the doubled wavelength 532 nm is used as the light source.The backscattered signals are received by Newtonian telescope and their frequency is discriminated by the spectral discriminator of FMZI.Then they are shown on oscilloscope after coverting into electric signals by PMT.To solve the problem of low coupling efficiency between multimode fiber for lidar return collection and single-mode fiber for FMZI,a method for fusing a single-mode optical fiber to a multi-mode fiber end-taper is proposed.Simulation analysis and experimental results show that the method can improve the coupling efficiency to a certain extent.For different wind speed detection sensitivity and dynamic range requirements,FMZI with different optical path difference was designed and manufactured,and the actual atmospheric wind field measurements were carried out.In order to overcome the problem of laser frequency drift,this system uses the method of Zero wind speed calibration to improve the accuracy of wind speed detection.In this method,atmospheric wind speed inversion results are subtracted to wind speed obtained by inversion of real-time reference signal(Zero wind speed deviation)to obtain the actual wind speed measured value.The system uses two different optical path differences of FMZIs as discriminators to conduct preliminary experimental exploration studies.The experimental results show that the system can achieve the detection of vertical wind speed of sight(zenith angle is approximately zero)and wind speed of sight under certain zenith angle(max.3.2°)within a height range of 200 m-600 m.The comparison of atmospheric wind profile detection results with real-time coherent Doppler vertical wind velocity data has good consistency and verified the effectiveness of system detection.