Ellipticity-Controlled Exceptional Points from Nanoscale Metasurfaces

Abstract: Precise control over light polarization is critical for advancing technologies in telecommunications, quantum computing, and image sensing. However, existing methods for manipulating polarization around exceptional points (EPs) in non-Hermitian systems, have exclusively focused on circular polarization and work with reflected light. To address this limitation, we develop a novel metasurface platform with high-Q resonators that enables tunable control of polarization exceptional points across arbitrary ellipticity for transmitted light. Our design uses orthogonally polarized guided mode resonators in a two-layer silicon metasurface, where careful tuning of the dipolar guided mode resonances (DGMRs) and layer spacing allows us to control the ellipticity of EPs. Leveraging high-quality factor resonances, we achieve strong orthogonal mode coupling over distances up to a quarter wavelength. This platform exhibits omnipolarizer behavior and the corresponding phase singularity can imprint phase shifts from 0 to 2π with small perturbations in the geometry. This approach opens new possibilities for polarization control and programmable wavefront shaping, offering significant potential for next-generation optical devices.