Enhanced absorption of graphene with variable bandwidth in quarter-wavelength cavities

Quarter-wavelength cavity, as a classical structure for preventing wave reflection, presents an effective way to enhance the interaction between light and material of ultrathin thickness. In this paper, we propose a method to control the bandwidth of graphene’s enhanced absorption in quarter-wavelength cavity. By varying the spacing distance between graphene and a metallic reflecting plane, which equals to an odd number of quarter-wavelengths, fundamental and higher order cavity modes are excited, whose fields couple to graphene with different spectral bandwidths, leading to bandwidth-controllable absorption in graphene. Absorption efficiencies of 9% and 40% are measured for graphene monolayer at 15° and 85° incident angles, respectively. Its absorption bandwidth varies between 52% and 10% of the central wavelength when the spacing distance between graphene and metallic reflecting plane increases from a quarter wavelength to seven quarter wavelengths. Our findings pave a way in engineering graphene for strong absorption with a controllable bandwidth, which has potential applications in tailoring spectral response of graphene-based optoelectronic devices.