Triple narrow-band plasmonic perfect absorber for refractive index sensing applications of optical frequency

A simple and effective polarization-insensitive triple narrow-band plasmonic perfect absorber is proposed and investigated numerically. This device can serve as an ultra-sensitive refractive index sensor from the near-infrared to the visible region. The triple narrow-band perfect absorber consists of a structured metal film constructed with an assembly of vertical-square-split-ring (VSSR) resonators. The triple narrow-band perfect absorption is due to the hybrid modes between the surface plasmon polaritons and guided modes with different order. Furthermore, the absorption peak shows a highly sensitive response to the change of refractive index in the surrounding medium. A careful design for the perfect absorption based refractive index sensor can yield a sensitivity of 1194, 816, and 473 nm/refractive index unit (RIU), respectively. Due to the high sensing performance, the triple narrow-band perfect absorber provides great potential for applications in enhanced sensing and spectroscopy.