覆盖八度的太赫兹四分之一波片基于反射金属-介电-金属超构表面中的过耦合法布里-珀罗共振
Octave-Spanning Terahertz Quarter-Wave Plates Based on Over-Coupled Fabry-Pérot Resonances in Reflective Metal-Dielectric-Metal Metasurfaces
AI总结：
本文提出基于过耦合反射金属-介电-金属超构表面的太赫兹四分之一波片，通过设计相位色散实现宽频带偏振控制，实验验证了其高反射率和高效偏振转换性能。
摘要：
紧凑型宽频带太赫兹偏振控制器件面临双折射材料和共振结构固有相位色散的挑战。本文展示了一种基于过耦合反射金属-介电-金属超构表面的高性能宽频带太赫兹四分之一波片。该器件作为单端口各向异性法布里-珀罗腔体，通过工程化过耦合共振的相位色散，产生近似恒定的正交场分量相对相位延迟。通过优化超构表面几何结构，实现了高效的线偏振到圆偏振转换，同时保持高反射率。四种互补的超构表面设计在45度入射角下共同覆盖0.25-3 THz频率范围，该范围适用于典型的太赫兹时域光谱系统。每个器件具有约八度宽的带宽，轴比低于3 dB，偏振转换效率超过80%。系统优化抑制了高阶衍射和表面波模式的耦合，进一步扩展了可用带宽，同时保持所需的相位关系。这些超构表面兼容晶圆级制造，实验结果与模拟结果高度一致。这些发现确立了过耦合反射超构表面作为宽频带太赫兹偏振控制的稳健且多功能平台。
英文摘要：
Compact devices for broadband polarization control in the terahertz (THz) regime are challenging due to the intrinsic phase dispersion of birefringent materials and resonant structures. Here, we demonstrate high-performance broadband THz quarter-wave plates based on over-coupled metal-dielectric-metal reflective metasurfaces. The devices operate as single-port anisotropic Fabry-Pérot cavities in which the phase dispersion of over-coupled resonances is engineered to produce an approximately constant relative phase delay between orthogonal field components. By tailoring the metasurface geometry, efficient linear-to-circular polarization conversion is achieved while maintaining high reflectance. Four complementary metasurface designs, operated at an incidence angle of $45^\circ$, collectively cover the 0.25--3 THz frequency range accessible to a typical THz time-domain spectroscopy system. Each device exhibits an approximately octave-wide bandwidth with an axial ratio below 3\,dB and polarization conversion efficiencies exceeding 80\% across most of the operating band. Systematic optimization suppresses coupling to higher-order diffraction and surface wave modes, further extending the usable bandwidth while preserving the required phase relationship. The metasurfaces are compatible with wafer-scale fabrication, and experimental results show excellent agreement with simulations. These findings establish over-coupled reflective metasurfaces as a robust and versatile platform for broadband THz polarization control.
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