Sub-Wavelength Grating Enhanced Ultra-Narrow Graphene Perfect Absorber

A sub-wavelength grating has been elaborately designed to enhance the absorption of the monolayer graphene at λ = 1.55 μm based on the coupled leaky mode theory (CLMT). The results indicate that the absorption can reach 99.8% at the resonant wavelength, and the absorption peak is ultra-narrow due to the excitation of TM31 mode in the grating structure. Taking advantages of the tunable chemical potential of graphene which is bias voltage controllable, the proposed structure can function as an adjustable absorber. The high figure of merit up to 1329 and sensitivity with the value of 66 are achieved. With the ultra-narrow absorption band and tunable peak positions, the graphene perfect absorber holds great potential application in sensing and biology.