Experimental observation of bulk Fermi arc in single dielectric resonator
The bulk Fermi arc is a fundamental non-Hermitian topological feature that connects two exceptional points (EPs), featuring the transition between Hermitian and non-Hermitian worlds. The bulk Fermi arc emerges when losses are introduced into a Hermitian system, causing a Dirac point to split into two EPs, where both the eigenvalues and eigenfunctions coalesce. Although theoretically predicted in various systems, experimental confirmation has been limited to a two-dimensional photonic crystal slab. Here, we present the first experimental observation of a bulk Fermi arc in a single dielectric resonator. Specifically, we consider a ring resonator made of high-refractive index ceramic. The inner radius and height are varied, enabling the observation of a two-sheeted Riemann surface with two EPs connected by a bulk Fermi arc, confirmed through numerical calculations and experimentally measured extinction spectra at GHz frequencies. These results establish dielectric resonators as a powerful platform for investigating non-Hermitian topological physics and open new avenues for designing topologically robust photonic devices and EP-based sensors.