Exceptional point based sensing via nanostructured photonic waveguide

Non-Hermitian systems with varying loss-gain profiles are receiving significant attention due to their exotic behavior at a certain point called the exceptional point (EP). EPs are singularities of non-Hermitian systems where the eigenfrequencies as well as the associated eigenstates coalesce. These EP singularities are ultrasensitive to small perturbations. A conventional system follows a linear relation with perturbation whereas these singularities follow a square root dependence for small perturbations.

Here, we theoretically propose an EP sensor based on a grating waveguide structure of Silicon Nitride (Si3N4). We use finite element method-based numerical simulation (COMSOL Multiphysics) to calculate the eigenspectrum for our structure. We optimize our structure to support an EP at the wavelength of 635 nm. We confirm the EP by observing a polynomial intensity profile along the grating, as opposed to exponential, even for a lossy medium. We show the application of our optimized design for the development of an ultrahigh sensitivity refractive index sensor exploiting the physics of EPs.