New design strategy for broadband perfect absorber by coupling effects between metamaterial and epsilon-near-zero mode

We propose a novel and simple method to achieve perfect light absorption over a broadband by coupling a gap plasmon mode to an epsilon-near-zero (ENZ) mode, which is a new path for tailoring light-matter interactions. Near-perfect light absorption (over 99%) in the wavelength range of 1400 nm-1655 nm can be achieved utilizing a gold-disk periodically patterned metal-dielectric-metal (MDM) device by integrating an ultrathin ITO (indium tin oxide) film. The ENZ mode can be excited effectively by coupling the gap plasmon resonance to conducting ITO (indium tin oxide) nanolayer (ENZ wavelength of the ITO nanofilm close to 1403 nm) under normal incidence. Compared with the device without ITO nanolayer, the device integrating ITO ultrathin film shows wideband perfect light absorption. Besides, the thickness of SiO2 spacer layer is critical for the coupling strength of metamaterial resonator and ENZ mode. To achieve broadband absorption, the coupling strength of the ENZ mode and gap plasmon mode should be between the strong coupling and weak coupling regimes. The method is also effective for the design of multiband optoelectronic devices with simple structure and low cost.