The <i>infinity-loop microresonator</i>: A new integrated photonic structure working on an exceptional surface

Exceptional points, where eigenvalues and eigenvectors coalesce, impact the behavior of different photonics components that show, e.g., enhanced sensing, coherent perfect absorption, unidirectional lasing, chirality. However, only a few passive geometries have been developed work on these points. Here, we introduce novel non-Hermitian structure based microresonator shaped as infinity symbol twice coupled to bus waveguide: infinity-loop microresonator. Unlike other structures working an exceptional surface, can achieve either high- or low-contrast reflection with negligible identical for counterpropagating light. It allows easy walking through Riemann sheet by simply controlling phase light propagating in waveguide, which makes it tunable component build more complex topological structures. Furthermore, sensors show features both point device diabolic simultaneously.