  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.
