Non-Hermitian systems based on 3D chirality enabled asymmetrical polarization switching and omni-polarizer action at an EP

Abstract Asymmetric mode/state switching and omni-polarizer action have demonstrated application potential and can be realized in non-Hermitian systems, which required a slow encircling process in the non-Hermitian parameter space in general. Is it possible to achieve the above functions only at an exceptional point (EP) without the encircling process? Here, we propose constructing a non-Hermitian system using three-dimensional (3D) chiral materials to realize the above functions at an EP instead of through the encircling process. Our results show that the 3D chiral non-Hermitian system exhibits properties that are quite different from those of traditional non-Hermitian optical systems. In our system, the eigenstates are different when propagating forward and backward, thus enabling asymmetric state switching. At the EP, the degenerate eigenstates of forward and backward propagations of the system become mutually orthogonal, which enables the system to act as an omni-polarizer. Crucially, to validate our claims, we propose a straightforward and widely applicable method to adjust a 3D chiral non-Hermitian system from a state far from an EP to near an EP. Based on this, we construct a free-space optical 3D chiral non-Hermitian system experimentally to directly observe the evolution of light polarization states near the EP. The experimental results prove that the proposed optical systems can achieve asymmetric state switching and omni polarizers at the EP, which is consistent with our theoretical expectations. Our work holds promise for various 3D chiral non-Hermitian optical applications, such as highly sensitive chirality measurements and polarization manipulation.