Investigation of a high precision ranging system based on free-running dual comb ranging

Abstract

Fast, real-time, high-precision distance measurement is of great significance for satellite formation flying, large-scale equipment manufacturing, and gravitational wave detection. These applications require ranging precision in the micrometer level for large-scale ranging. The dual comb ranging (DCR) technique reaches high precision range measurement by using a pair of optical frequency combs with a slight pulse repetition rate difference, which ensures asynchronous optical sampling. The stability of the pulse repetition rate, carrier envelope offset frequency, and mutual coherence of the two combs are the key issues to keep the high range precision. However, the complex locking units makes the DCR ranging system complicated, which limits its application significantly. To address this problem, we propose a free-running DCR high-precision ranging system. Software self-correction algorithm replaces the complicated hardware control system. The software signal processing algorithm utilizes mutual ambiguity processing, cross-correlation and repetition rate correction. The signal processing effect is also compared with the direct envelope peaks extraction algorithm. The feasibility of the system is verified both from simulation and experiment. The range precision can achieve 3.63 um in a single measurement when the target distance is about 1 m, the laser repetition frequency is about 100 MHz, and the frequency difference of the two combs is about 774 Hz. The precision can further drop below 700 nm with 90 times averaging. This work shows prospect that the free-running DCR system can be used in the field application.