Abstract
Polarization conversion devices are key components in spectroscopy and wireless communications systems. Conventional terahertz waveplates made of natural birefringent materials typically suffer from low efficiency, narrow bandwidth, and substantial thickness. To overcome the limitations associated with conventional waveplates, a terahertz quarter-wave metasurface with enhanced efficiency and wide bandwidth is proposed. The transmissive quarter-wave metasurface is rigorously designed based on an extended semi-analytical approach employing network analysis and genetic algorithm. Simulation results suggest that the design can achieve linear-to-circular polarization conversion with a 3-dB axial ratio relative bandwidth of 53.3%, spanning 205 GHz–354 GHz. The measurement results confirm that the proposed design enables a 3-dB axial ratio from 205 GHz to at least 340 GHz with a total efficiency beyond 70.2%, where the upper frequency bound is limited by the available experimental facility. This quarter-wave metasurface can cover an entire terahertz electronics band and can be scaled to cover other nearby bands under the same convention, which are technologically significant for future portable systems.
Highlights
The terahertz spectral range defined between 0.1 THz and 10 THz1 presents a unique potential for diverse applications, including wireless communications,[2,3] medical imaging,[4,5] and substance identification.[6]
Conventional terahertz waveplates made of natural birefringent materials typically suffer from low efficiency, narrow bandwidth, and substantial thickness
Simulation results suggest that the design can achieve linear-to-circular polarization conversion with a 3-dB axial ratio relative bandwidth of 53.3%, spanning 205 GHz–354 GHz
Summary
The terahertz spectral range defined between 0.1 THz and 10 THz1 presents a unique potential for diverse applications, including wireless communications,[2,3] medical imaging,[4,5] and substance identification.[6] In order to harness the terahertz waves for those applications, various terahertz devices have been developed, such as modulators,[7] filters,[8] and antennas.[3,9] Waveplates that alter the polarization state of incident beams provide additional degrees of freedom to manipulate the terahertz waves Birefringent materials such as crystalline dielectrics[10,11] and wood[12] provide distinct refractive indices to electric field components along two orthogonal directions, leading to different phase accumulations. The multi-layer quartz-based waveplate was presented to improve the relative bandwidth to 32% but exhibited a bulky configuration and an efficiency of merely 50%.11
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