Plasmonic metamaterial using metal-insulator-metal nanogratings for high-sensitive refraction index sensor

We propose two designs of plasmonic metamaterial mid-infrared (MIR) sensors, which are composed of metallic nanograting on SiO2 layer with a bottom mirror to form metal-insulator-metal (MIM) configurations. These MIM configurations are denoted as MIM-S and MIM-D to represent MIM composed of single metal nanograting and double metal nanogratings, respectively. The electromagnetic responses of MIM-S and MIM-D are investigated and compared with and without embedded a SiO2 layer between top nanograting and bottom mirror layer. By changing the height of insulator layer, the absorption spectra of MIM-S can be tuned with a linearly wavelength tuning range of 2.4 mu m. Furthermore, MIM-D exhibits not only tunable resonance by changing the gap between top and bottom nanogratings, but also switch characteristics by changing the horizontal shift of top nanograting. For the environment sensor application, MIM-S and MIM-D exhibit the sensitive/insensitive to refraction index and tunable FSR characteristics by changing ambient refraction index. Such results provide the MIM devices can be used as multifunctional sensors. This study proposes an implementation strategy of actively tunable filter, switch, and high-sensitive refraction index sensor in the MIR wavelength range.