Frequency-modulated continuous-wave laser ranging beyond the limits of bandwidth and phase noise

Frequency-modulated continuous-wave (FMCW) laser ranging typically applies an interferometer and linear frequency-modulated (LFM) signals to measure the distance, in which precision and resolution are limited by the phase noise of laser and the bandwidth of LFM signals, respectively. This work proposes an FMCW laser ranging method that overcomes the limits of phase noise and bandwidth, in which the beat frequency of the LFM signals is estimated via time-domain maximum likelihood estimation. Using this method, super-resolved FMCW laser ranging can be achieved within the coherence length. It can also break the limits of phase noise, enabling laser ranging beyond the coherence length. An experiment is conducted. Using a 5 GHz bandwidth, a ranging resolution of 0.8 cm is achieved within the coherence length, which is enhanced by 5.1 times compared to traditional FMCW LiDARS. Moreover, beyond the coherence length, the ranging resolution and precision are enhanced by 10 times and 4.5 times, respectively. The enhanced performance is feasible even though the acquisition time is reduced to 20 μs. In addition, three-dimensional imaging of static and dynamic targets is implemented to show the enhanced performance. The proposed method enables long-range, fast FMCW laser ranging using a low-cost laser, which is also helpful to enhance the performance of interferometry.