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

摘要： Quarter-wavelength cavity, as a classical structure for preventing wave re?ection, 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 re?ecting plane, which equals to an odd number of quarter-wavelengths, fundamental and higher order cavity modes are excited, whose ?elds couple to graphene with different spectral bandwidths, leading to bandwidth-controllable absorption in graphene. Absorption ef?ciencies 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 re?ecting plane increases from a quarter wavelength to seven quarter wavelengths. Our ?ndings 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.