Stationary Inflection Point Based Hypersensitive Sensors with Enhanced Signal-to-Noise Ratio

Stationary inflection points (SIPs) are spectral singularities in the Bloch dispersion relations of periodic metamaterials. They emerge due to the formation of exceptional point degeneracies of the transfer matrix, indicating a coalescing of the Bloch modes of the system. At the SIP, both the group velocity and second derivative of the dispersion relation with respect to the wavenumber are equal to zero, allowing for slow light that is robust to losses and structural imperfections. One significant feature of SIP structures is the near-total conversion of an input signal into the slow mode, leading to the formation of the Frozen Mode Regime (FMR). We analyze the transport properties of nonlinear periodic structures exhibiting SIPs and their use in the realization of sublinear sensors, where the response of the reflectance is sublinear with respect to frequency detuning. We show that such sensors provide an enhanced signal-to-noise ratio, while also being hypersensitive to small perturbations. We demonstrate our proposal by using a complex photonic network that operates in the microwave regime.