Ultrafast roll-angle measurement via a polarization-modulated optical frequency comb

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.