Study On Direct Detection Doppler Wind Lidar Receive Optical System

The Doppler Wind Lidar emit laser beams into atmosphere, then receive the echo scattering signal. Due to the Doppler effect, the echo signal will produce a certain a frequency shift from the-emitting laser. The frequency shift related to atmosphere wind velocity in radial direction, The Doppler Wind Lidar use F-P discriminate the Doppler frequency shift to inverse the wind velocity in radial direction. The design of the optical system of the DWL is critical in the overall systems, especially so the design and analysis of receiving system is the most important task.In this paper, in order to design and study the optical systems, the main contents include the following aspects:First, designing the reception optical system. Based on the lidar equation and expected indicators of lidar, we define the key parameters such as the receive aperture and the receive field of view. Considered the overall structure and Processing technology, we use Zemax software to design a reasonable Cassegrain system.Second, leading and design the fiber-coupled systems into the DWL. Considered the overall structure, we couple the radar echo signal though the fiber into the frequency discriminator system. However, the telescope focal length is too long, the spot of the echo signal on the focal plane is to large which will limit the coupling efficiency. Therefore, we need to design the fiber coupling system to compress the fiber coupling spot and improve the coupling efficiency. This paper proposes three feasible coupling system design programs, and complete the three designs with the Zemax software.Third, analysising the optical coupling efficiency. Analysis factors which influent the fiber coupling efficiency focusing on the fiber position deviation and study the way they affect the coupling efficiency. This theoretical introduction Zernike polynomials to explan the theoretical model and Zemax is also auxiliary to verify the theory.Finally, experimental measurements for the coupling efficiency. According to the previous design of the coupling lens, we complete the processing and put them in optical path to measure the coupling efficiency. Then we design experiment to verify the theory fiber end face how affect the coupling efficiency.