Programmable Optical Vernier‐Sampled Coherent Ranging

Abstract

AbstractExtended 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.