Laser Feedback FMCW Ranging System Based on Multiple-Equal-Phase-Subdivision Resampling

Abstract

In this article, we propose a laser feedback frequency-modulated continuous-wave (FMCW) ranging system based on multiple-equal-phase-subdivision (MEPS) resampling. An auxiliary interferometer is employed to generate clock signal for resampling to suppress the spectral broadening caused by the nonlinearity of frequency modulation. Different from the conventional FMCW system, interference occurs between the light returning from the target and the intra-cavity light, which enables the reference arm of the measuring interferometer to be removed. The length of the auxiliary fiber required by the Nyquist sampling theorem is compressed through MEPS resampling, which reduces the size of the auxiliary path and expands the detection range. The MEPS-resampling-based distance ranging by an auxiliary delay fiber (shorter than the target distance) is demonstrated through simulation and tests. And a series of experiments are conducted to evaluate the effectiveness of the proposed system. Experimental results show that the system has a resolution of 1.98 mm and linearity of 4.99×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> . The repeatability, characterized by the standard deviation, is tested to be less than 35.2 μm. The combination of the laser feedback interferometry (which has the advantages of compactness and auto-alignment), MEPS resampling, and the FMCW optical ranging enables the proposed system to maintain high resolution and precision with a simpler structure.