Non-Hermitian singularities in a single nanowire resonator

Photonic structures with non-Hermitian characteristics show unique phenomena that are not accessible in Hermitian systems. However, most of these intriguing findings are demonstrated in conventionally active or passive systems, such as microcavities, metasurfaces, and waveguides. Till now, the non-Hermitian singularities in nanowire Fabry-Pérot (F-P) resonators were only demonstrated in parity-time symmetric cases, while still absent in the passive situation, which is practical but more important. Here, we show that strong mode coupling intrinsically exists in passive nanowires, by which the quality factors can be improved over an order of magnitude. Furthermore, by tuning the effective index contrast at the end-facets of the nanowire, which corresponds to the energy leakage rate, the transition from strong to weak coupling of eigenstates is realized. Consequently, an exceptional point (EP) is observed in nanowire resonators through this transition, exhibiting enhanced sensitivity compared to conventional nanowires. Our results underpin the general non-Hermitian singularities in a single nanowire F-P cavity, substantially broadening the application scenarios of dielectric resonators.