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-modulated continuous-wave laser LiDAR is a robust optical technology for long-range three-dimensional distance and velocity measurement. However, inherent sweep chirp nonlinearity severely constrains distance resolution and precision. Conventional compensation methods fail to address residual nonlinearity, particularly in rapid, long-range measurement, posing a critical bottleneck to practical applications. Herein, we present a high-order nonlinear solving model and fundamentally compensate for residual nonlinearity, which can improve precision by one to two orders of magnitude over traditional methods. It yields 19.58 μm precision over 25 m for a non-cooperative target without resolution loss, even under experimental conditions where the absolute distance is overwhelmed by noise using traditional methods. This method exhibits robustness across various laser types and achieves precision near the quantum noise limit. This study lays the groundwork for more precise frequency-sweeping coherent detection technologies.

The frequency-scanning interferometer (FSI) is an advantageous distance measurement method. We propose an FSI-based non-cooperative target distance measurement system that is combined with a heterodyne interferometer. The heterodyne interferometer is parallel to the FSI and can measure the vibration of the target synchronously, and the measuring result is used to correct the Doppler effect in the FSI signal. To extract the vibration accurately, a circle fitting in the Lissajous curve is used to correct the influence of the multipath interference, which may damage the vibration measurement result, especially when the target is non-cooperative. Then, with a post-processing algorithm, the distance could be obtained. Finally, the distance to a non-cooperative target located at 15 m is experimentally measured using this method, and a standard deviation of 3.39 $\mu \text{m}$ is obtained.

This study aims to enhance the measurement accuracy of a dual-sweep frequency modulated continuous wave (FMCW) system used for Doppler compensation for non-cooperative targets in vibration environments. A distance spectrum reconstruction algorithm was developed to improve the ranging accuracy of the dual-sweep FMCW system, and its feasibility was validated through simulation and experimental data. Experiments yielded a standard deviation of 12.12 µm for a measured distance of about 10 m. The proposed method effectively mitigates the colored noise introduced by multiplication without increasing hardware complexity, thereby enhancing measurement accuracy. Thus, the proposed method can provide excellent outcomes in long-distance measurements of non-cooperative targets using FMCW ranging systems.

Frequency-modulated continuous wave (FMCW) laser interferometry is an ideal large-scale absolute distance measurement method. It has advantages of high precision and noncooperative target measurement capability, with no blind spot for ranging. To meet the requirements of high-precision, high-speed 3D topography measurement technologies, a faster measurement speed of FMCW LiDAR at each measurement point is required. To solve the shortcomings of the existing technology, a real-time high-precision hardware solution method (including but not limited to FPGA and GPU) for lidar beat frequency signals is provided here based on hardware multiplier arrays to reduce lidar beat frequency signal processing time and to save energy and resource consumption during processing. A high-speed FPGA architecture was also designed for the frequency-modulated continuous wave lidar range extraction algorithm. The whole algorithm was designed and implemented in real time based on the principle of full-pipelines and parallelism. The results show that the processing speed of the FPGA system is faster than that of current top-performing software implementations.