Investigation On Tunable Polarization-independent Coherent Perfect Absorption Based On Metal-graphene Nanostructure

Coherent perfect absorption have the ability to realize the perfect absorption of two incident beams,and also have the capability to all-optically modulate the absorption of the device with the phase difference between the two incident beams.Recently,with the development of graphene,the coherent perfect absorber(CPA)based on graphene or metal-graphene nanostructure has been proposed.A polarization-independent tunable coherent perfect absorber based on metal-grapheen nanostructure hase been proposed in this paper.The main contents includes:The incoherent absorption limit and scattering matrix have been used to demonstrate the principle of coherent absorption.And the finite-difference time-domain(FDTD)method is employed to analyze the tunability of the CPA.Based on these theories,a polarization-independent tunable coherent perfect absorber based on metal-grapheen nanostructure has been proposed.The CPA is composed of the hollowed-out cross array in the golden film placed on the graphene covered glass substrate.The coherent perfect absorption has been realized at 9969 nm with the proposed CPA.By adjusting the phase difference between the incident beams,the coherent absorption at 9969 nm is all-optically modulated from 99.97% to nearly 0 with the modulation depth over 80 dB.The proposed CPA is polarization-independent.Meanwhile it has been found to be angular insensitive of incident beams within the range from-12° to 12°.The absorption resonance of the CPA has been tuned by geometric parameter of the CPA.For the introducing of graphene,the absorption resonance of the CPA is also tuned by the gate controlled Fermi energy with the coherentabsorption remaining nearly 100%.