Nonlinear correction of FMCW LIDAR based on the superlets transform algorithm

In frequency-modulated continuous wave (FMCW) light detection and ranging (LIDAR), the nonlinearity of the laser frequency modulation causes an increase in the full width at half maximum (FWHM) of the beat signal. This increase seriously affects the ranging precision. In this Letter, a nonlinear correction method based on superlets transform (SLT) is proposed to build a FMCW LIDAR measurement system with an auxiliary interferometer. The time-frequency relation is extracted from the SLT result of the auxiliary path beat signal, and an interpolation sequence is generated to resample the measurement path beat signal, so as to improve the linearity. Experiment results show that the nonlinearity after resampling reaches 2.60 × 10^-10, and when the length of the extended fiber for simulating laser transmission is 13 times to the length of the auxiliary fiber, the spectrum still has obvious peaks. The average standard deviation (SD) and average resolution of the ranging within 2.5 m are 2.3 mm and 4.8 cm, respectively. The average SD of the velocity measurement within 6 cm/s is 7.7 mm/s.