High-Performance Tunable Plasmonic Absorber Based on the Metal-Insulator-Metal Grating Nanostructure

A new high-performance plasmonic absorber based on the metal-insulator-metal grating nanostructure is proposed and numerically studied. The effect of geometric parameters of grating stripe and insulator layer on light absorption is investigated. Four main absorption bands with efficiencies nearly 100 % are obtained by modulating duty cycle of the metal grating, which show redshift with the increased stripe width. The physical mechanism responsible for the absorption is discussed based on distributions of the magnetic field and the Poynting vector and is found to be different for the four bands. It is also found that perfect absorption of the nanostructure can be achieved when the insulator layer thickness ranges from 20 to 70 nm; meanwhile, the resonant wavelength corresponding to perfect absorption can be tuned and it shifts towards red side with the increase of the grating thickness when the air slit is narrow. The proposed highly efficient light absorber exhibits a very simple geometrical structure and is easy to be fabricated, which has potential applications in photonic device, such as photodetectors, sensors, and so on.