Ge-padded Enhanced Plasmonic Hyperbolic Metamaterial for Ultrahigh Refractive Index Sensing

Owing to supporting the highly sensitive plasmonic modes, hyperbolic metamaterials (HMMs) have gathered considerable attention in the field of refractive index biochemical sensing. The high modal group velocity of the plasmonic modes supported by HMMs has been proved to directly determine their high sensitivity. To date, the method to increase the modal group velocity is still focused on improving the filling ratio of the host material in HMMs. In this work, a simple system consisting of Ge-padded nanohyperbolic gratings is proposed to enhance the group velocity of plasmonic modes. The introduction of Ge filling in the proposed structure significantly enhances the transverse permittivity of the HMM, thereby increasing the modal group velocity and, in turn, improving the sensitivity of the plasma modes. Under the condition of easy large-scale manufacturing and integration with a structural height of only 35 nm, it achieves a maximum sensitivity of approximately 126,667 nm/RIU in the visible to near-infrared region. This offers a more cost-effective and efficient solution for enhancing the optical sensitivity of integrated biosensor chips.