Effective excitation of bulk plasmon-polaritons in hyperbolic metamaterials for high-sensitivity refractive index sensing

The study of hyperbolic metamaterial (HMM) refractive index sensors is an active field of plasmonics and nanophotonics, and the effective excitation of the bulk plasmon-polariton (BPP) modes in anisotropic HMM for highly sensitive sensing is a key issue. In this study, we analytically and numerically investigated a strategy to achieve highly sensitive nanorod HMM (NHMM) and multilayer HMM (MHMM) sensors using prism-coupling and grating-coupling technology, respectively. For a prism-coupled NHMM model, the analytical model showed increased sensitivities for lower-order modes, increasing the filling factor (f) and height (h) of the nanorod. Under the critical condition of attenuated total reflection (ATR), a sensitivity of 55 750 nm RIU-1 was achieved by the rigorous coupled-wave analysis method. Furthermore, to overcome the difficulty of exciting the BPP mode in the MHMM under the critical condition of ATR, we used Teflon AF, a low-refractive-index material, to design a MHMM with a low modal index of the fundamental mode and a sensitivity of up to 155 000 nm RIU-1. Moreover, a sensitivity of 27 500 nm RIU-1 was achieved for the first time by directly exciting the BPP mode in a MHMM without using any coupling approach, which provides a new path for the realization of a portable high-sensitivity MHMM sensor. Our study provides the basis for the development of ultrasensitive HMM sensors related to biochemical sensing, environmental monitoring and clinical diagnostics.