Research On Key Technologies Of Continuous Wave Laser Coherent Doppler Wind Lidar

The laser wind measurement lidar has gradually integrated into human life,and has been widely used in the fields of weather forecast,aerospace safety and smart wind power.Compared with the traditional microwave wind lidar,the laser wind lidar uses shorter wavelength light source,so it is easier to produce Mie scattering on the small aerosol particles,which can effectively detect the wind field information in clear sky.Among all kinds of existing lidar,all fiber continuous wave(CW)lidar with 1550 nm laser has some special advantages,such as high maximum permissible exposure of human eye,simple structure,low cost of key devices,good reliability,and natural optical stability of all fiber structure.However,this kind of lidar also has some disadvantages.One of the main problems is that multiple stray light sources will be introduced into each optical end face of the system,such as the crosstalk of the circulator and polarization controller,and the reflection of APC end face.These spurious light sources will introduce phase induced intensity noise(PIIN)into the beat signal,and excessive PIIN will reduce the signal-to-noise ratio(SNR)of the system,resulting in the loss of data in practical applications.In this paper,we propose to use optical frequency domain reflectometer(OFDR)to locate the PIIN source and evaluate its intensity.According to the OFDR information,it is proved that the PIIN in the CW laser coherent Doppler lidar system designed in this paper is mainly caused by the crosstalk of the polarization beam splitter.Aiming at the PIIN in the system,optical fiber delay line,polarization control and antireflection(AR)coating are set to reduce the PIIN.The optimized CW laser coherent Doppler lidar can obtain the wind Doppler signal with a range of80 m on sunny days,and the SNR reached 19.4d B.The first chapter is the introduction.In this chapter,the common scenes of lidar and its important value in application are introduced,and the development of lidar is summarized and reviewed.The second chapter describes the basic principle of coherent Doppler lidar.The basic principle of measurement in this paper,including the Doppler effect of light and the homodyne detection,is discussed.The noise in the all-fiber continuous wave lidar system is explained in detail.At the same time,the calculation method of the lidar wind speed inversion designed in this paper is introduced,which provides a theoretical basis for the system to accurately measure the wind speed.The third chapter is the basic principle of OFDR technology.Starting from the theoretical model of OFDR technology,the basic functions of OFDR technology and the main factors affecting system performance are described.By adding an auxiliary interferometer,the nonlinear error of the system has been improved.The evaluation method of all fiber optic lidar system using OFDR technology is also introduced.In the fourth chapter,the design,numerical simulation and experiment of CW laser coherent Doppler lidar are discussed.The four schemes in the system design process are introduced respectively,and the advantages and disadvantages of the schemes are described in detail.The scheme 4 was selected as the final design scheme of the lidar,and a series of performance speed measurement and field experiments were conducted on the lidar samples of scheme 4.The feasibility of the lidar system based on scheme 4 is verified.