Exceptional point sensing in nanostructured photonic waveguides

We present a theoretical proposal for an EP sensor utilizing a grating waveguide structure made up of silicon nitride(Si3N4). EPs are singularities where eigenfrequencies as well as eigenvectors coalesce. EP singularities demonstrate extraordinary sensitivity to small perturbations. Unlike conventional systems that respond linearly to perturbations, EP singularities exhibit square root dependence on small perturbations. Employing a finite element method-based numerical simulation using Comsol Multiphysics, we calculate the eigenspectrum of our structure. To confirm the presence of the EP, we examine the intensity profile along the grating, which exhibits a polynomial trend, contrary to the typical exponential behavior expected in lossy media. Moreover, we showcase the practical application of our optimized design by developing an ultrahigh sensitive refractive index sensor, capitalizing on the unique physics associated with EPs.