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Abstract
We have proposed a multi-layered chiral nanostructure consisting of two sub-wavelength gratings and a T resonator sandwiched on two sides of dielectric substrates. Numerical simulation results indicate the scheme can realize large and broadband asymmetric transmission (AT) of linearly polarized waves, with huge asymmetric parameter similar to optical diode and broadband almost 90° polarization rotation in the near-infrared spectral region. Due to the delicate combination of broadband polarization conversion and Fabry–Perot-like resonance effect, the AT magnitude can reach a maximum value of 0.96 and exceed 0.9 ranging from 83 to 233 THz, exhibiting a magnitude improvement compared with previously reported chiral metamaterials. Especially, the mechanism of high AT magnitude in a multi-layered chiral structure is analyzed in detail based on the Fabry–Perot-like resonance effect. By scaling down the structure parameters properly, the structure can also achieve broadband AT in visible region. These metamaterials have a great potential to be used as linear polarization rotators or diode-like devices in the near-infrared and visible regions.