Non-Hermitian geometric phase metasurfaces for linearly polarized light

Geometric phase phenomena play a foundational role in modern wave physics. In optics, they provide the basis for geometric phase metasurfaces (GPMs), a powerful platform for versatile wavefront shaping. However, conventional GPMs remain fundamentally restricted to circularly polarized light because their operation relies on the symmetry of orthogonal linear eigenstates, preventing their direct use in the linearly polarized platforms widely employed in mainstream optics. Here, we address this longstanding challenge by harnessing the non-Hermitian physics of exceptional points (EPs). We introduce and experimentally realize quasi-EP GPMs, in which engineered singularities drive the coalescence of eigen-polarizations and allow a geometric phase to be directly imparted to linearly polarized light. Proof-of-principle metagratings and holograms demonstrate high-fidelity wavefront shaping under arbitrary linearly polarized illumination over a broad spectral range. Our results reveal an intrinsic connection between geometric phase and EPs, extend GPMs beyond their conventional circular-polarization regime, and provide a practical framework for scalable polarization manipulation, advanced imaging, holography, integrated photonics, and quantum optics.