Metasurfaces for multi-band or wideband polarization control are usually achieved by cascading or nesting several elements in a period, which complicate the structure and introduce crosstalk. In this work, independent polarization control is achieved around two terahertz frequencies, 0.14 THz and 0.3 THz, through a simple binary one-dimensional grating. The correlation of the phase retardation with frequency is broken, since it is determined by the propagation of a single mode at the lower frequency and by the interference of two modes at the higher frequency. Four gratings capable of different types of dual-band polarization control, a half-half wave plate, a half-quarter wave plate, a quarter-half wave plate and a quarter-quarter wave plate, are designed and experimentally tested. All the samples are made of polymers and 3D-printed as freestanding lightweight structures. The experimental results of all the samples validate polarization conversion with state-of-the-art high efficiency. Simulation results indicate their favorable bandwidth of more than 30%. The half-half wave plate gratings are further applied to build a metalens for efficient dual-band beam focusing based on the geometric phase. They show great potential in developing multifunctional terahertz elements using simple configurations.

通常，通过在一个周期内级联或嵌套几个元素来实现用于多频带或宽带极化控制的超颖表面，这使结构复杂并引入了串扰。在这项工作中，通过一个简单的二进制一维光栅，在两个太赫兹频率（0.14 THz和0.3 THz）附近实现了独立的偏振控制。相位延迟与频率的相关性被破坏了，因为它是由较低频率下的单个模式的传播以及较高频率下的两个模式的干扰决定的。设计并通过实验测试了四种具有不同类型的双波段偏振控制能力的光栅，一个半波片，一个四分之一波片，一个四分之一波片和一个四分之一波片。所有样品均由聚合物制成，并以独立式轻质结构进行3D打印。所有样品的实验结果均以最先进的高效率验证了偏振转换。仿真结果表明，它们的有利带宽超过30％。半波片光栅进一步被应用来构建金属元件，以基于几何相位有效地进行双波段光束聚焦。它们显示出使用简单配置开发多功能太赫兹元件的巨大潜力。半波片光栅进一步被应用来构建金属元件，以基于几何相位有效地进行双波段光束聚焦。它们显示出使用简单配置开发多功能太赫兹元件的巨大潜力。半波片光栅进一步被应用来构建金属元件，以基于几何相位有效地进行双波段光束聚焦。它们显示出使用简单配置开发多功能太赫兹元件的巨大潜力。