Yuhan Li

Ultrafast, high-precision roll-angle metrology is crucial for dynamic motion control yet remains challenging because roll is not directly accessible to conventional geometric optical methods. Here, we present a roll-angle measurement method based on a polarization-modulated optical frequency comb (PMOFC). By modulating the offset frequency, a sequence of femtosecond pulses with periodically varying polarization was generated. After passing through a birefringent target and a fixed-angle analyzer, the roll angle is retrieved from the corresponding intensity sequence. Experimental results demonstrate an absolute non-ambiguous range of 0°–90°, and a single-shot measurement time of ∼71 ns. At the worst-case angular position, the Allan deviation decreases below 20 ^{′ ′} after 3.93 μs of averaging. These results establish a practical route to high-rate absolute roll-angle measurement.

High-precision six-degree-of-freedom (6-DOF, pitch, yaw, roll, axial displacement, and two lateral displacements) measurement is essential in advanced manufacturing and precision assembly, particularly in aerospace, semiconductors, and precision engineering. However, achieving high-precision absolute 6-DOF measurement directly on the target remains challenging. This study proposes a novel method for absolute 6-DOF measurement directly on non-cooperative targets, employing low-coherence light and temporal phase-shifting. This method extracts position and orientation information from the coherence envelope shape and the geometric texture of the target background without relying on cooperative targets. The proposed method achieves favorable results in verifying the resolution, linearity, and repeatability indicators of 6-DOF. Additionally, a simulation of the 6-DOF tracking of a satellite antenna central support plate during the manufacturing process demonstrates good agreement between the measured and reference values. This study presents a novel approach for high-precision absolute and direct 6-DOF measurements on non-cooperative targets, offering significant guidance for the processing and assembly of aerospace components in advanced manufacturing.