Ultra-broadband near-infrared absorption enhancement of monolayer graphene by multiple-resonator approach

We theoretically study how to achieve an ultra-broadband near-infrared absorption enhancement of monolayer graphene through the multiple-resonator approach. The monolayer graphene (about 0.34 nm in thickness) is on nanostructured metal surfaces with multiple one-dimensional nanogrooves. The investigated nanostructure has an advantage of easy fabrication, because the monolayer graphene needs not to be sandwiched between different material layers. The metallic nanogrooves are able to support magnetic plasmon resonances whose resonance wavelengths are largely tuned, by changing the nanogroove depth from 70 to 210 nm or the nanogroove width from 20 to 40 nm. In a very wide near-infrared wavelength range from 850 nm to 1500 nm, the light absorption efficiency of graphene is enhanced to be more than 60 %, by carefully designing multiple magnetic plasmon resonances to be partly overlapped in optical spectra. Our work is of interest for some photoelectric devices, for example infrared photodetectors.