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Micro-pulse polarization lidar at 1.5 μm using a single superconducting nanowire single-photon detector

Abstract:

An all-fiber, eye-safe and micro-pulse polarization lidar is demonstrated with a polarization-maintaining structure, incorporating a single superconducting nanowire singlephoton detector (SNSPD) at 1.5 μm. The time-division multiplexing technique is used to achieve a calibration-free optical layout. A single piece of detector is used to detect the backscatter signals at two orthogonal states in an alternative sequence. Thus, regular calibration of the two detectors in traditional polarization lidars is avoided. The signal-tonoise ratio of the lidar is guaranteed by using an SNSPD, providing high detection efficiency and low dark count noise. The linear depolarization ratio (LDR) of the urban aerosol is observed horizontally over 48 h in Hefei [N31°50'37", E117°15'54"], when a heavy air pollution is spreading from the north to the central east of China. Phenomena of LDR bursts are detected at a location where a building is under construction. The lidar results show good agreement with the data detected from a sun photometer, a 532 nm visibility lidar, and the weather forecast information.

Fig. 1. (a) Optical layout of the polarization lidar. EOM, electrooptic modulator; PG, pulse generator; EDFA, erbium-doped fiber amplifier; PBS, polarization beam splitter; PMF, polarizationmaintaining fiber; FA, fiber adaptor; OS, optical switch; FBG, fiber Bragg grating; SNSPD, superconducting nanowire single-photon detector; MCS, multi-channel scaler; P, parallel polarization; S, perpendicular polarization; (b) calibration layout. VOA, variable optical attenuator; L1, first lens as a collimator; L2, second lens as a coupler; HWP, half-wave plate; LP, linear polarizer; BS, polarization-maintaining beam splitter; PM, power meter.

Fig. 2. (a) Raw signal of the polarization lidar over 48 h and (b) 48 h continuous measurement results of the LDR.

Fig. 3. LDR at the location of (a) 3.44, (b) 3.56, and (c) 3.68 km away from the lidar; the red arrows indicate the moments of the bursts of the LDR. (d) Measurement error of the LDR at 3.56 km. The inset is a photo of the building under construction.

Fig. 4. (a)–(c) Volume spectrum detected by a sun photometer in the experiment; (d)–(f ) visibility data and photographs of the scene in the experiment; (g)–(i) haze distribution forecast released by the China Meteorological Administration in the experiment. VS, volume spectrum; V, visibility.