Exceptional-point-enhanced nanoparticle sensor utilizing a linewidth broadening mechanism

Exceptional points (EPs) in non-Hermitian systems, where eigenvalues and eigenvectors coalesce, offer unique advantages in state transitions, non-reciprocal devices, and sensing, owing to their distinctive and extraordinary properties. Most prior studies for sensing at EPs focused on mode splitting, with limited focus on leveraging the linewidth broadening mechanism. In this study, we construct an EP by embedding two nanoholes within a microdisk cavity. With nanoparticle adsorption at the edge of the microcavity at the EP, the linewidth of two split modes exceeds the frequency splitting, enabling the use of the linewidth broadening mechanism for nanoparticle detection. By calculating the linewidth of the transmission spectra with or without the adsorption of the nanoparticle, an enhanced linewidth broadening based on the EP is achieved compared to that based on the diabolic point (DP). We observe that the linewidth broadening based on the EP varies periodically with the azimuthal position of the nanoparticle along the edge of the cavity. Specifically, the maximum of the linewidth broadening based on the EP is several times larger than that based on the diabolic point. This paper not only deepens our understanding of non-Hermitian physics in microcavities but also lays the groundwork for future research and applications in high-sensitivity sensing.