Research On Phase Modulation Technology Of Doppler Lidar

Doppler lidar is a wind measurement lidar.It measures the wind speed by measuring the Doppler shift generated by atmospheric molecules and aerosol motion.Solving the accuracy problem in wind speed measurement is a frequently mentioned issue in the development of Doppler lidar.Based on this,this paper proposes a locking method of laser working point and a detection method using phase modulation technology to measure the Doppler frequency shift.In terms of the locking method of the laser working point,this paper first describes the working principle of the working point locking method through theoretical research,then describes the PID control program written on the Lab VIEW platform in detail,then use the relevant tuning method to set the parameters of the PI controller used in this paper.The PI controller performs parameter tuning and brings the tuning parameters into the control system,and this control system can achieve a locking accuracy of 0.75 MHz.In terms of phase modulation technique,this paper first elaborates on the phase modulation technique.This method utilizes the spatial phase modulator and the FP etalon to perform the frequency shift measurement.The signal light modulated by the phase modulator can be seen as the original frequency band and two phase opposite sidebands.The transmission rate of the F-P etalon corresponding to the original frequency band is different,so the two sidebands are affected by the FP etalon after passing through the FP etalon.Therefore,the Doppler shift at this time can be obtained by extracting the modulation components in the signal light.Then from the simulation point of view,this paper studies the phase demodulation technique frequency discriminating method,conducts relevant research on some parameters in the frequency discrimination method,and obtains parameters that can improve the frequency discrimination efficiency of the phase modulation technique.Based on the simulation model,the influence of Mie scattering and Rayleigh scattering on the phase modulation technology is investigated.It is found that the greater the proportion of Mie scattering light intensity in the backscattered light intensity is,the better the frequency discrimination effect is.In the end,this dissertation studies the phase modulation technique frequency discrimination method from the experimental point of view.The experimental contents include nontarget experiments and target measurement experiments.The effects of some parameters on frequency discrimination efficiency are compared and analyzed in non-target experiments.Based on the optical systems used in the experiments,relevant parameters suitable for the use of phase modulation techniques are summarized and it was confirmed that the measurement error near the ideal operating point can be guaranteed in the 2 MHz range.