Manipulating bandwidth of light absorption at critical coupling: An example of graphene integrated with dielectric photonic structure

For an optical absorber, its efficiency and bandwidth determine ultimately its light-collection performance. A general way to realize the high-efficiency absorption and manipulate the absorption bandwidth is certainly important and highly desired. In this paper, based on the coupled-mode theory, a general strategy for tailoring the bandwidth of an absorber (to broaden or narrow it) is presented. A graphene-based absorber integrated with a lossless resonator is designed, and it is shown that by increasing the layer number of graphene and adjusting structure parameters, the broadband absorber at critical coupling could be realized. Meanwhile, by adjusting the location of graphene in the structure, an ultra-narrow-band absorber could also be realized. Present work of controlling both efficiency and bandwidth of an absorber would be particularly favorable for applications in light harvesting, light emitting devices, and optical modulators.