Tunable ultra-high quality factor graphene absorber based on semicylindrical silica array and distributed Bragg reflector structure

Abstract

We propose a tunable narrowband absorber by utilizing a graphene monolayer placed between a dielectric semicylindrical array and a multilayer silica/silicon distributed Bragg reflector (DBR) structure. The multi-band perfect absorption can be achieved due to the excitation of multiple resonant modes in the absorber, including the guided mode resonance of the dielectric silica array and BR-based guided mode resonance in the DBR structure. The ultra-high quality factor (Q) is mainly attributed to the low external leakage loss of the resonator and the low intrinsic loss of the graphene monolayer. Moreover, the Q-factor of absorption peaks can be tuned by electrically controlling the Fermi energy of graphene. The sensitivity of a spectral wavelength shift for the refractive index change of the resonator is up to 730 nm/RIU, and the figure of merit is 1043. The proposed graphene-based metamaterial offers potential applications for photodetectors, optical modulators, and sensors in the near infrared frequency regime.