Velocity Measurement via Single-Pulse Polarization Interferometry

We present a novel method for measuring the radial velocity of high-speed targets equipped with retro-reflectors, using polarization changes in a single light pulse. A polarized pulse is split into two orthogonally polarized, time-delayed components via a birefringent medium and directed at the target. Upon reflection, the pulse passes through a second, perpendicular birefringent element. For a stationary target, this cancels the delay; for a moving target, a residual phase shift remains, causing a rotation in the output polarization. This rotation is proportional to the target’s velocity and can be detected with one or two detectors. The technique works with both pulsed and continuous-wave sources, particularly low-coherence lasers. We validate the method in the lab using an all-fiber setup, a single-photon source and detectors at 1560 nm, and a simulated target moving over 100 km/h. The system’s principles, key parameters, and initial experimental results are discussed.