▎ 摘　　要

High-efficiency tunable asymmetric transmission (AT) based on simple-constructed metasurface is highly desired for next generation optical polarization devices. Here, we numerically investigate high-efficiency and frequency-tunable circular AT effect in mid-infrared region by combining simple-shape silicon array with a graphene sheet. The asymmetric parameter of the dielectric nanostrip structure reaches 0.92 at 12.68 THz and the width of tunable spectra (AT > 0.7) is 1100 nm, which represent a major advance compared with previously reported AT. The AT behavior originates from extrinsic chirality induced by oblique illumination, and the high AT efficiency results from the constructive and deconstructive interferences of selectively excited electric and magnetic resonances. In addition, the working waveband of AT is shifted by dynamically modulating graphene's Fermi energy, which offers a new degree of freedom to achieve multifunctions without refabricating structures. The proposed array system possessing the merits of high efficiency, simple inclusions and frequency-tunability has significant potentials for practical applications in polarization devices such as polarization sensor, polarizer, etc. (C) 2017 Optical Society of America