Dark Lines and Polarization Singularities in Bright Metasurface‐Enhanced Fluorescence

Abstract 2D scattering lattices can turn incoherent emitter ensembles into bright, spatially coherent sources, a well‐established concept in thermal emission control and solid‐state lighting communities. Here, a surprising phenomenon is reported: networks of sharp dark lines and polarization singularities in momentum space, observed alongside the usual bright light extraction features of plasmon antenna lattices optimized for extracting light from fluorophores in a 2D waveguide. Using Fourier microscopy with Stokes polarimetry, supported by reciprocity‐based T‐matrix calculations, these unexpected features are traced to destructive far‐field interference between transverse electric (TE) and transverse magnetic (TM) waveguide modes, diffractively coupled through the meta‐atoms. Remarkably, these modes generate strong elliptical far‐field polarization signatures, with cancellations leading to polarization singularities such as L‐lines, V‐points, and C‐points, analogous to those observed in the incoherent sunlight field in the sky.