Optical singularity protractor for rotating metrology with neuromorphic sensing.

The development of singular optics and vortex beams has facilitated numerous novel optical applications, with optical sensing being one prominent direction. By leveraging the rotational energy flow properties of vortex beams, rotational Doppler effect-based sensing for rotating objects has achieved significant progress. However, due to fundamental constraints of orbital angular momentum (OAM) and interferometry-based experimental methods, rotational Doppler sensing typically requires stringent axial alignment (single-point or multi-point) in practical scenarios, which limits their applicability. To address these limitations, this study focuses on developing rotating metrology utilizing singularities inherently associated with vortex phases, akin to the recently developed singularity ruler employing intrinsic/extrinsic modification of OAM density. In this work, we propose a sensing technique termed the "Optical Singularity Protractor (OSinP)", which utilizes the angular velocity of singularities to reflect the rotational speed of optical fields. To extend the stable singularity ruler to dynamic rotation sensing, we developed a real-time neuromorphic singularity perception system capable of acquiring microsecond-level-resolution time-series data regarding singularity positions and movement directions, thereby enabling the sensing of optical field rotation velocity. Furthermore, we challenged the OSinP system with practical constraints, notably off-axis rotation and non-steady-state velocity, to verify its robust operational capabilities. This singularity sensing technique distinguishes itself from traditional rotation sensing by introducing neuromorphic computing into topological structured light and holds promise for neuromorphic applications in fields with stringent energy-efficiency requirements, such as astronomical metrology and embodied intelligence.