Impact of transmitting light's modulation characteristics on LFMCW Lidar systems

The performance of linear frequency-modulated continuous-wave (LFMCW) coherent Lidar system is inevitably influenced by the modulation characteristics of the transmitting light and some issues may arise when the system does not work under the ideally specified conditions. The relationship between the asymmetric and nonlinear modulation of transmitting light with the quality of the resulting beat frequency signal (BFS) for the non-zero velocity cases is mathematically modeled and the effective means for eliminating or alleviating these harmful influences are given. The results that are obtained from both numerical simulations and practical system experiments demonstrate that the errors of range and velocity measurement are proportional to the asymmetric coefficients and its square, respectively, and 30% relative error of range measurement occurs even through the values of normalized 2nd- and 3rd-order polynomial nonlinear-coefficients is as low as 0.1%. The rating of merit experiments of a Lidar system in range and velocity measurement is conducted, and the obtained results are in good agreement with their analytical and numerical simulation counterparts.