Exceptional point degeneracies (EPDs) in the resonant spectrum of non-Hermitian systems have been recently employed for sensing due to the sublinear response of the resonance splitting when a perturbant interacts with the sensor. The sublinear response provides high sensitivity to small perturbations and a large dynamic range. However, the resonant-based EPD sensing abides to the resolution limit imposed by the resonant quality factors and by the signal-to-noise ratio reduction due to gain-elements. Moreover, it is susceptible to local mechanical disturbances and imperfections. Here, we propose a passive non-resonant (NR) EPD-sensor that is resilient to losses, local cavity variations, and noise. The NR-EPD describes the coalescence of Bloch eigenmodes associated with the spectrum of transfer matrices of periodic structures. This coalescence enables scattering cross-section cusps with a sublinear response to small detunings away from an NR-EPD. We show that these cusps can be utilized for enhanced noise-resilient sensing.

A stationary inflection point (SIP) of the Bloch dispersion relation of a periodic system is a prominent example of an exceptional point degeneracy (EPD) where three Bloch eigenmodes coalesce. The scattering problem for a bounded photonic structure supporting a SIP features the frozen mode regime (FMR), where the incident wave is converted into the “frozen mode” with vanishing group velocity and diverging amplitude. We analyze the effect of losses and disorder on the FMR and develop a scaling formalism for the absorbance in the FMR that takes into consideration losses, disorder, and system size. The signatures of the EPD appear as an abrupt growth of absorbance for system sizes greater than a characteristic length that follows a parallel resistance law involving the absorption length and the Anderson localization length.

We investigate the emission characteristics of a tri-atomic photonic meta-molecule with asymmetric intra-modal couplings which is uniformly excited by an incident waveform tuned to coherent virtual absorption conditions. By analyzing the dynamics of the discharged radiation, we identify a parameter domain where its directional re-emission properties are optimal.