Dynamic Frequency-Modulated Continuous-Wave LiDAR Coupled Through a Rotary Interface

In order to acquire the tracking information across a rotary joint, a dynamic frequency-modulated continuous-wave (FMCW) laser ranging system is designed to couple through a rotary interface. A setup for FMCW light detection and ranging (LiDAR) is proposed to couple through a fiber optic rotary joint (FORJ), whose optical path is able to eliminate the influence of rotary coupling on the generation of beat frequency. This FMCW LiDAR uses real-time correction for nonlinear laser chirps by synchronizing the FMCW measurement signals with laser injection current at data acquisition (DAQ). Then, phase variations induced by rotary coupling are excluded from the FMCW measurements. The acquisition rate is kept much higher than the rotation speed of FORJ, in order to reduce the influence of rotary coupling on the real-time nonlinearity correction. The linearization of laser frequency modulation through a FORJ is conducted by resampling of over 3000 intervals interpolated in every up-sweep or down-sweep of 25 μs, with measurement signals stretched or compressed in time domain. With the FORJ rotating at the speed of 10°/s in both clockwise and anticlockwise directions, the clear and robust beat signals are achieved. The statistical distributions of measured 50-cm distance under rotary conditions are found out to be similar to that under stationary condition.