Ellipticity-Controlled Exceptional Points and Cross-Polarized Phase Singularities in Multi-Layer Silicon Guided Mode Resonant Metasurfaces

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, a novel metasurface platform with high-Q resonators is developed that enables tunable control of polarization exceptional points across arbitrary ellipticity for transmitted light. This design employs 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. By leveraging high-quality factor resonances, strong orthogonal mode coupling over distances up to a quarter wavelength is achieved. 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.