Optical frequency shifted FMCW Lidar system for unambiguous measurement of distance and velocity

A new frequency-modulated continuous-wave (FMCW) Lidar system is proposed to measure distance and velocity unambiguously by using a frequency-shifted probe light. The optical frequency shift is induced by an acousto-optic modulator (AOM). The generated beat signal is up converted to high frequency, sparing sufficient RF bandwidth to avoid signal aliasing caused by high Doppler frequency shifts. The aliasing-free beat signal thus can be used to extract distance and velocity information unambiguously. Here, we experimentally demonstrated real-time measurement on a disk spinning up to 26.43 m/s at 1.267 m away. The precision of the measured distance and velocity are 16 mm and 0.037 m/s respectively. Furthermore, the proposed scheme is capable of discriminating the direction of rotation based on a single Fast Fourier Transform analysis. In addition, we apply a free space circulator to the system to weaken the mirror-scattered signals and thus to achieve continuous measurement of beats signal over wide frequency range. Finally, a three-dimensional image of the spinning disk is reconstructed.