FMCW LiDAR with an FM nonlinear kernel function for dynamic-distance measurement

Abstract

Frequency-modulated continuous-wave (FMCW) LiDAR is an absolute-distance measurement technology with the advantages of high-precision, non-cooperative target measurement capabilities and the ability to measure distance and speed simultaneously. However, the existing range extraction method for FMCW LiDAR is associated with problems, such as requiring a high sample rate and dispersion mismatch. Here, we propose and demonstrate a dynamic range extraction method based on an FM nonlinear kernel function, which improves measurement accuracy without the use of a long auxiliary interferometer (as is required for the traditional method), reduces the influence of dispersion mismatch and the Doppler effect caused by target movement and can simultaneously measure the target motion information dynamically, with a lower measurement error than that of the existing range extraction method under the same conditions.

Frequency-swept feedback interferometry for noncooperative-target ranging with a stand-off distance of several hundred meters

“…To avoid device damage, the frequency of the triangular wave is less than 100 Hz. Overall, the swept frequency of the system is less than 60 Hz, comparable with other reported research with mechanical modulation, such as motor-based externalcavity-tunable diode lasers [49,50]. Consequently, the usage of mechanical modulation in our system makes the ranging rate slower than electrical modulation for laser diodes (LDs).…”

“…Second, we use another laser source and set up DC-LFI for OPL drift compensation, and it is still effective even if the echo power from the noncooperative target is weak, or the target suffers intensive disturbance. The dual-laser configuration is also employed in the reported FSI-based ranging systems [37,49]. Overall, compared with other methods, the methods adopted here for calibrating the nonlinearity and OPL drift are advantageous, in terms of cost and effectiveness, for noncooperative-target ranging, although they possess moderate sophistication.…”

Microcavity Raman Laser-Based FMCW LiDAR with Enhanced Echo Sensitivity

“…This challenge is attributed to the measuring rates being dictated by the sweeping period, which is constrained by the thermal cycling response of the microcavity. As a result, the swept frequency of the system remains below 100 Hz, a range that aligns with other reported research utilizing the mechanical modulation methods. , Another limitation is the temperature tuning technique employed in the WGM resonators. In this approach, the achievable tuning range is constrained to tens of GHz, and the tuning process is slow.…”

“…(See the Supporting Information for discussions about laser frequency tuning linearity.) These nonlinear tuning characteristics will deteriorate the signal spectrum and degrade the spatial resolution of the FMCW ranging. ,, As mentioned above, we utilize the k -sampling technique to mitigate the impact of nonlinearity in optical frequency sweep. The interference signal obtained from the main interferometer is transformed into the frequency domain, with constant frequency intervals.…”

“…The interference signal obtained from the main interferometer is transformed into the frequency domain, with constant frequency intervals. It is performed using the interference signal obtained from the auxiliary interferometer. , After k-clock resampling, the ranging signal is analyzed in the frequency domain using fast Fourier transform (FFT), leading to a revision of the measured distance, as eq shows: L = m n N L aux where L aux represents the optical length in the auxiliary path, which employs a 210.43 m delay fiber calibrated with an HCN gas cell, N is the FFT data length after resampling, and m is the peak position . (See the Supporting Information for more details about the resampling and distance calibration methods.)…”