Composite graphene-metal microstructures for enhanced multiband absorption covering the entire terahertz range

Abstract

We numerically demonstrate a novel route to effectively enhancing multi-band terahertz absorption enabled by a variety of tunable polarization-insensitive multiband terahertz absorbers based on composite graphene and metal microstructures. In these devices, the multiband plasmon resonance absorption in graphene, resulted from the Fabry–Pérot cavity between the continuous graphene and the underneath metal reflector, can be effectively enhanced by the designed metal microstructures. As a demonstration, we simulate several multiband absorbers based on composite graphene and several patterned metal microstructures (spiral, ring, disk, square). It is interesting to find that the number of absorption bands can be arbitrarily manipulated by the dielectric spacer hight. By setting the same spacer height of 60 μm, all absorbers exhibit identical absorption properties with six near-unity absorption bands in the whole terahertz region ranging from 0.1 to 10.0 THz under normal incidence regardless of the shapes of microstructures. These absorption bands also show clear independence of polarization under normal incidence and the absorbance peaks can be flexibly adjusted by changing the graphene chemical potential. Our work opens up a new avenue for the development of various multiband graphene absorbers, which may have enormous potential applications in terahertz photoelectric detectors, sensors, modulators, and switches.