High-precision absolute distance measurement based on double-pass intensity modulation with an S-G-filter-assisted...

A high-precision absolute distance measurement (ADM) system based on double-pass intensity modulation with an S-G-filter-assisted wobbling algorithm is proposed and experimentally demonstrated. In this scheme, the optical field is intensity-modulated by a Mach-Zehnder modulator (MZM) during the initial pass. After reflection from a target, it returns to the MZM along the same optical path, thereby realizing double-pass intensity modulation. By rapidly sweeping the modulation frequency, a frequency-sweep curve associated with the absolute distance is generated. The resulting frequency-sweep curve is smoothed using Savitzky-Golay (S-G) filtering, after which the wobbling algorithm is employed to locate two adjacent extrema. The absolute distance is then determined from the frequencies corresponding to the two adjacent extrema, and the ADM algorithm is implemented on a field-programmable gate array (FPGA) platform. Experimental results show that the proposed system achieves a relative measurement precision on the order of 10^-8 over a distance range from 1 to 100 m, which is realized by combining a single-mode fiber (SMF) delay path with an approximately 10 cm free-space path, with standard deviations of 0.17 μm at approximately 2 m and 8.91 μm at approximately 100 m.