Optical response of the single modes. a The reflectance spectra of the structure of silver groove only (red line) and graphene only (blue line) in normal incidence, respectively. b The reflectance spectra of the structure of graphene-Si groove for different period P of unit cell. c The numerical modeling and analytical results of the resonant frequency f, respectively. d The electric field Ex distributions of F-P mode (left) and graphene quasi-guided resonance mode (right).