Frequency-Modulated Continuous-Wave Coherent Lidar With Downlink Communications Capability

A frequency-modulated continuous-wave (FMCW) coherent lidar with downlink communication capability is proposed based on phase-diversity coherent detection, by which laser ranging, laser velocimetry and free-space optical downlink communications can be simultaneously achieved. In the local transceiver, a linear-frequency modulated (LFM) optical signal is generated and used as the lidar signal. The LFM optical signal is received by the remote transceiver and coded with data via amplitude modulation. Then, the light is transmitted back to the local transceiver, in which a phase-diversity coherent optical receiver is used to simultaneously extract the range, velocity, and communication data. The in-phase and quadrature outputs from the phase-diversity coherent optical receiver are simultaneously recorded to reform a complex signal. The data is extracted from the intensity of the complex signal, while the range and velocity are obtained from the argument of it. A demonstration experiment is carried out. Different digital baseband signals are encoded on the reflected signal via an intensity modulator, while the 80-MHz Doppler frequency shift is simulated by an acousto-optic modulator. The impact of the digital signal on lidar detection is removed. Meanwhile, the communication quality is little affected by the varied frequency of the de-chirped signal. Therefore, the lidar detection and the free-space optical communications are simultaneously implemented.