Micro-pulse upconversion Doppler lidar for wind and visibility detection   in the atmospheric boundary layer
  For the first time, a versatile, eyesafe, compact and direct detection Doppler lidar is developed using upconversion single-photon detection method. An all-fiber and polarization maintaining architecture is realized to guarantee the high optical coupling efficiency and the system stability. Using integrated-optic components, the conservation of etendue of the optical receiver is achieved by manufacturing a fiber-coupled periodically poled Lithium niobate waveguide and an all-fiber Fabry-Perot interferometer (FPI). The so-called double-edge direct detection is implemented using a single-channel FPI and a single upconversion detector, incorporating time-division multiplexing method. The relative error of the system is lower than 0.1% over 9 weeks. To show the robust of the system, atmospheric wind and visibility over 48 hours are detected in the boundary layer. In the intercomparison experiments, lidar shows good agreement with the ultrasonic wind sensor (Vaisala windcap WMT52), with standard deviation of 1.04 m/s in speed and 12.3{\deg} in direction. 
Haiyun Xia, Mingjia Shangguan, Chong Wang, Guoliang Shentu, Jiawei   Qiu, Qiang Zhang, Xiankang Dou, Jianwei Pan
astro-ph.IM physics.ins-det physics.optics