Hosting exceptional points in a tapered dual-core optical fiber

Exceptional points (EPs) are known to arise as non-Hermitian degeneracies in coupled systems, and offer unique opportunities for highly sensitive sensing applications, unconventional mode dynamics, and new device functionalities. Realizing EPs in optical fiber platforms is, in particular, an attractive option in view of the maturity of fiber fabrication technology, long interaction lengths, and compatibility with existing optical systems. In this paper, we present a tapered dual-core optical fiber having asymmetric loss as a feasible platform to realize a second-order EP. The tapering enables smooth modulation of inter-core coupling, while selective loss in one of these cores provides the additionally required nonHermitian perturbation. Our eigenvalue analysis and numerical simulations confirm the hosting of an EP, where the eigenvalue trajectories coalesce and exhibit the characteristic topological behavior. Encirclement of the EP further demonstrates eigenstate flipping, with the fundamental mode (Ψ_FM) transforming into the higher-order mode (Ψ_HOM) and vice versa. These results highlight tapered dual-core fibers as a practical and experimentally realizable platform for EP-based photonic devices, with potential applications in unconventional mode conversion, switching, and ultrasensitive detection.