Multifunction Lidar System Based on Polarization-Division Multiplexing

A multifunction lidar system is proposed based on polarization-division multiplexing, by which the distance, velocity, and depolarization ratio of a target can be simultaneously measured. The key component of the lidar system is a polarization-division multiplexing dual-drive Mach-Zehnder modulator (PDM-DMZM). A linear frequency-modulated (LFM) waveform is applied to one sub-DMZM of the PDM-DMZM to modulate the light along one polarization direction, while a single-frequency RF signal is applied to the other sub-DMZM to modulate the light along the orthogonal polarization direction. As a result, a dual-polarization light beam containing both the LFM and single-frequency optical signals is generated. In the receiver, a polarization beam splitter is used to separate the two orthogonally-polarized optical signals of the reflected light, so that the distance and velocity can be separately measured in two channels. Meanwhile, the depolarization ratio of the reflected light can be measured according to the intensity ratio between the LFM and single-frequency RF signals. An experiment was carried out to test this lidar system, in which an 8-18 GHz saw-tooth LFM signal and a 10 GHz single-frequency signal were, respectively, used to modulate the orthogonally-polarized lights. The distance and velocity were simultaneously measured with resolutions of 1.8 cm and 1.1 mm/s, respectively. In addition, the depolarization ratio of the reflected light was measured simultaneously.