Tunable light trapping and absorption enhancement with graphene ring arrays.

Surface plasmon resonance (SPR) has been intensively studied and widely employed for light trapping and absorption enhancement. In the mid-infrared and terahertz (THz) regime, graphene supports tunable SPR via manipulating its Fermi energy and enhances light-matter interaction at the selected wavelength. Most previous studies have concentrated on the absorption enhancement in graphene itself while little attention has been paid to trapping light and enhancing the light absorption in other light-absorbing materials with graphene SPR. In this work, periodic arrays of graphene rings are proposed to introduce tunable light trapping with good angle polarization tolerance and enhance the absorption in the surrounding light-absorbing materials by more than one order of magnitude. Moreover, the design principle here could be set as a template to achieve multi-band plasmonic absorption enhancement by introducing more graphene concentric rings into each unit cell. This work not only opens up new ways of employing graphene SPR, but also leads to practical applications in high-performance simultaneous multi-color photodetection with high efficiency and tunable spectral selectivity.