Extended measurement ranges with coherent ranging necessitate an increase in the digitizer sampling rate. Subsampled coherent ranging can reduce the sampling rate, but it has been demonstrated in a short range below around 10 cm. Herein, programmable optical Vernier-sampled coherent ranging over several tens of meters with a reduced sampling rate using a newly developed stepped-frequency-swept laser (stepped-FSL) is proposed. The measurable range of three-dimensional subsampled coherent ranging can be extended by increasing the coherence length of the stepped-FSL. The proposed stepped-FSL sequentially emits a discrete frequency output by applying a programmable voltage signal to an electro-optic modulator. The free spectral range of the stepped-FSL output can be rapidly and akinetically adjusted by changing the number of steps in the programmable voltage signal. The proposed system realizes an extended measurable range (over 20 m) and a high repetition rate (200 kHz). A low sampling rate of 10 MS s −1 is sufficient for operation at a subsampled interference frequency of 1 MHz. This rate is an order of magnitude lower than that of the conventional coherent ranging using an FSL. Experimental results demonstrate that the programmable optical Vernier-sampled coherent ranging can be improved by leveraging novel optical subsampling with a stepped-FSL.

Coherent light detection and ranging (LiDAR), particularly the frequency-modulated continuous-wave LiDAR, is a powerful optical imaging technology for long-distance three-dimensional (3D) ranging and velocity measurement. Spatio-spectral LiDAR was proposed to perform coherent ranging and solid-state beam scanning simultaneously; however, a complete four-dimensional (4D) implementation, combined with 3D distance and velocity measurements over tens of meters, has not yet been reported owing to the limitations of commercial wavelength-swept lasers. Herein, we propose a novel flutter-wavelength-swept laser that offers a simultaneous yet independent wavelength modulation of 5–6 pm for axial distance and velocity measurement, and a wavelength sweep of 160 nm for horizontal beam scanning. An acousto-optical scanner was synchronized to support the remaining vertical beam scanning for a perfect solid-state coherent LiDAR. The proposed spatio-spectral LiDAR system achieves a high-resolution coherent ranging over 20 m and 4D real-time imaging with 200 × 45 pixels in a 10 Hz frame rate.

Angular resolution variation with adaptive beam scanning of frequency-modulated continuous wave (FMCW) LiDAR was implemented using an acousto-optic deflector. Various beam scanning patterns were applied over 3 degrees of field of view.