Abstract
A tunable linear-to-circular polarization converter (LTCPC) for the terahertz (THz) regime which consists of two conductive layers and a graphene transmissive metasurface layer separated by two dielectric layers is reported in this work. The equivalent surface resistance modeling method is adopted to investigate the peculiar electronic properties of graphene. The simulation results show that when the Fermi energy (Ef) is 1.1 eV, the linearly-polarized wave can be transformed into the circularly-polarized wave in the working band ranging from 0.9498 to 1.3827 THz (the relative bandwidth is 37.1%) with axial ratio (AR) less than 3 dB. Moreover, the bandwidth can be regulated to the desired one by varying the Fermi level of graphene metasurface via a bias voltage rather than manually modifying the structure. We have analyzed the mechanism of the polarization conversion, especially, the magnitudes and the phase difference of cross- and co-polarization transmission coefficients, AR curves, and surface current diagrams at y-polarized incidence. Our findings open up promising possibilities towards the realization of graphene controllable devices for polarization modulation, which has advantages of adjustability over traditional devices.
Highlights
Manipulating the polarization states is of central interest in various fields, and the ability of which enables us to control electromagnetic (EM) waves for a wide range of applications due to the fact that many phenomena are inherently polarization-sensitive like sensors [1] and imaging [2]
To evaluate the polarization conversion performance of our linear-to-circular polarization converter (LTCPC) more intuitively and numerically, we suppose that the y-polarized incident EM wave is along the z-direction perpendicularly
For such a LTCPC, the cross-coupling between electric and magnetic fields exists and works at the resonance frequencies, the right-hand circularly polarized waves and left-hand circularly polarized waves encounter different transmission coefficients which mainly depend on φ=+π/2+2kπ or φ=-π/2+2kπ, endowing the LTCPC a broad application prospect in the manufacture of the anisotropic components
Summary
Manipulating the polarization states is of central interest in various fields, and the ability of which enables us to control electromagnetic (EM) waves for a wide range of applications due to the fact that many phenomena are inherently polarization-sensitive like sensors [1] and imaging [2]. Wide bandwidth enables the flexible manipulation of the EM waves in a wide range avoiding generating frequency offset, that is to say, polarization converters can have larger system capacity and stronger anti-interference ability, which save space cost and help to solve electromagnetic compatibility problems. A high-efficiency transmissive metasurface was put forward by Li et al [14] obtained the function of LTCPC in 9.8-18.3 GHz with a relative bandwidth (RB) of 60.5% with the formula of 2×(fH-fL)/(fH+fL). From another angle, Wang et al [15] proposed a frequency selective surface realizing LTCPC at several resonant frequencies, which can be interpreted as a narrow bandwidth compared with the previous one
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