In-situ integrated nonlocal Huygens metasurfaces enable robust vortex beams from multimode fibers

Abstract

A fundamental hurdle for multimode fiber (MMF) integrated photonics is achieving robust and deterministic wavefront shaping against fiber perturbation, which induces random modal interference and scrambles the real-space output into speckle patterns. Existing wavefront shaping methods typically rely on pixelated phase or polarization pre-compensation, rendering them highly sensitive to fiber deformation. Here, we show that in-situ integration of a silicon nonlocal metasurface onto an MMF end facet enables direct conversion of arbitrary speckle patterns into optical vortex beams without pre-compensation. The metasurface supports overlapped Mie resonances and nonlocal bound states in the continuum (BICs), yielding high-transmission bands by satisfying the generalized nonlocal Huygens condition. Through momentum-space coupling between MMF modes and Huygens-BICs with topological polarization-vortex nature, the output maintains doughnut-shaped profiles under static and dynamic perturbations, demonstrating exceptional robustness against fiber deformation. This approach provides a compact, alignment-tolerant platform for robust structured light generation in MMFs for endoscopy, optical trapping and communications.