Photonic exceptional points in engineered materials and their emerging applications

Abstract

Enabled by the coalescence of eigenvalues and eigenstates, exceptional points (EPs) in non-Hermitian photonic systems have revolutionized the control of light–matter interactions and sparked growing interest across diverse material and structural platforms. This Review synthesizes advances in engineered materials that harness EPs across three key domains: band EPs in dielectric photonic crystals, wherein radiation-induced loss transforms Hermitian degeneracies into exceptional rings and bulk Fermi arcs; scattering EPs in hybrid dielectric or lossy metasurfaces, enabling unidirectional reflectionless propagation; and Jones EPs in plasmonic and anisotropic materials, which exploit chiral degeneracies for asymmetric scattering and holographic multiplexing. We highlight emerging phenomena in dynamic EP control using tunable materials such as graphene, phase-change media and micro-electromechanical systems, which enable real-time modulation, topological phase transitions and the direct observation of non-Hermitian braiding. The topological properties of EPs, manifested in phase accumulation and half-integer polarization charges, support key applications in wavefront shaping and singular optics. New frontiers involve the integration of EPs with other concepts, including bound states in the continuum, Dirac points, nonreciprocity and magnetic tunability. Bridging non-Hermitian physics with material-engineered platforms paves the way for adaptive photonic devices, topological meta-architectures and machine learning-driven designs, charting a path towards next-generation nanophotonics. Exceptional points enable unique light–matter interactions in non-Hermitian systems. This Review surveys band, scattering and Jones exceptional points in engineered materials, highlighting emerging applications and phenomena including topological properties, dynamic control, braiding, wavefront shaping and special states.