Journal of Optics (United Kingdom)

A lithography-free plasmonic–photonic hybrid nanostructure exhibiting an interesting phenomenon of cavity-mediated normal-mode splitting among doubly-degenerate Tamm plasmon polariton modes has been designed and optimized to manifest three strongly coupled modes. The exotic dispersion of these supermodes is used to design a self-referenced spectroscopic refractive index sensor at optical frequencies with a substantial sensitivity value of 1410 nm RIU⁻¹. The same structure is also shown to function as a singular-phase-based refractometric biosensing platform with multiple near-singular points, exhibiting a maximum sensitivity of around 27 000^∘ RIU⁻¹ with a sufficiently broad dynamic range of operation. Furthermore, the presence of three near-singular points provides the necessary flexibility in striking an appropriate balance between sensitivity and dynamic range of operation. The concomitant existence of the mentioned functionalities is an outcome of the strong coupling between the modes, which enables us to exhibit exquisite control over the dispersion of the supermodes. These distinctions enable our proposal to be of direct utility in highly demanding point-of-care biosensing applications.