High-performance metamaterial sensors based on strong coupling between surface plasmon polaritons and magnetic plasmon resonances

Recently, there has been increasing interest in sensing by magnetic plasmon resonances (MPRs) in metamaterials. However, due to their fast radiative damping, MPRs usually have a broad bandwidth and thus a weak enhancement of electromagnetic fields, which is disadvantageous to sensing applications. In this work, we will numerically study near-infrared metamaterial sensors consisting of one-dimensional (1D) periodic array of nanogrooves drilled in Ag substrate. It is found that an ultra-narrow hybridized mode, whose full width at half maximum (FWHW) is only about 10 nm, can be formed by coupling MPRs confined within the nanogrooves to surface plasmon polaritons (SPPs) propagating on the substrate surface. When the hybridized mode is excited, the incident light is nearly completely absorbed, and thus the electric and magnetic fields in the nanogrooves are greatly enhanced. Moreover, the resonance wavelength of the hybridized mode will have a noticeable shift, even if the refractive index of the environment medium has a slight change. Thanks to these properties, the investigated metamaterial sensors have a high sensitivity (S) of more than 1500 nm/RIU and a large figure of merit (FOM) reaching to 150, and so may have potential applications in label-free biosensing.