In this paper, we propose a transmissive quarter wave plate (QWP) which can provide linear-to-circular polarization conversion in terahertz (THz). The structure is composed of one dielectric layer with staggered split ring resonators (SSRRs) on both sides. The simulation results show that the proposed structure can offer a nearly pure left circularly polarized wave with 3 dB axial ratio bandwidth of 0.337 THz; meanwhile, the bandwidth of polarization conversion efficiency beyond 80% reaches 0.170 THz. Additionally, the distributions of surface currents and electric field are discussed to explain the physical mechanism of the proposed structure. The linear-to-circular polarization conversion can be attributed to the inductance effect and capacitance effect between SSRRs. Finally, we validate the performance of the proposed THz-QWP. Such a device could potentially be used in THz communications, THz imaging, and THz sensing.
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