FSI-based non-cooperative target absolute distance measurement method using PLL correction for the influence of a nonlinear clock.

We propose a frequency swept interferometry (FSI)-based absolute distance measurement method that can be used to measure a noncooperative target located at a distance of 10s of m. In this method, an external cavity laser serves as the frequency tuning laser, and a single frequency laser and two acoustic optical modulators (AOMs) are used to measure the optical path difference (OPD) variation during the frequency tuning, which can correct the Doppler effect. A phase-locked loop (PLL) is introduced to synchronize the nonlinearities between the OPD variation measurement signal and the absolute distance measurement signal, improving the signal-to-noise ratio (SNR) of the OPD variation measurement signal. The distance to a noncooperative target located at 15 m is experimentally measured using this method, and a precision of 3.43 μm is obtained.