Real-time measurement of dynamic micro-displacement and direction using light's orbital angular momentum

In this Letter, we propose an orbital angular momentum (OAM) sensor to simultaneously measure the dynamic micro-displacement and the direction of a moving object in real time. The micro-displacement of the moving object can be detected by the calculation of the petals' rotation angle caused by the coaxial interference between the measured OAM beam and its reference OAM beam, and the direction (forward or backward) of the moving object can be achieved by the clockwise or anticlockwise of the petals' rotation. We also develop an algorithm to monitor the petals' rotation angle and the rotation direction. The experimental results demonstrate that the proposed sensor can achieve high precision (±16.5995 nm) and a longer measuring range (0–1100 cm). Additionally, the OAM sensor is sensitive to the topological charge in the OAM mode, the initial distance, and the velocity of the moving object. The sensor can perform the non-contact measurement, so it will be a promising method in micro-vibration sensing, surface unevenness sensing, and microbial movement sensing.