Laser Ranging With Micrometer Precision and kHz Rate via Joint Frequency-Phase Measurement

Abstract

A joint frequency-phase measurement is proposed for high-precision and fast laser ranging, in which a frequency-modulated continuous-wave (FMCW) method is used for coarse long-distance ranging, while a phase-shift method is used for high-precision ranging. Since a low-duty-cycle linear-frequency-modulated (LFM) signal is used, the precision of the FMCW method can be reduced to be smaller than the unambiguous distance of the phase-shift method. Therefore, fast phase unwrapping can be achieved for the phase-shift method using a small bandwidth LFM signal. In the experiment, a lightwave is simultaneously modulated by a 1–7 GHz low-duty-cycle LFM signal and a 15 GHz single-tone signal, which are frequency-separated so that the FMCW ranging and the phase-shift ranging can be simultaneously achieved. The measurement precision and measurement rate are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$58~\mu \text{m}$ </tex-math></inline-formula> and 1.7 kHz, respectively. The measurement range can be 300 m. Therefore, the proposed method can be used to achieve laser ranging with kHz rate and decades of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> precision at hundreds of meters distance.