  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 the tunable SPR via manipulating its
Fermi energy and enhances light-matter interaction at the selective wavelength.
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 light-absorbing materials nearby to more than one order.
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.
