基于曲折线型介质超材料的宽带太赫兹四分之一波片

Broadband terahertz quarter wave plate based on meander-line dielectric metamaterials

采用基于高阻硅的曲折线型(meander-line)介质超材料,设计了一种宽带的太赫兹四分之一波片,可以在较宽的频率范围内将入射的线偏振太赫兹波转换为圆偏振太赫兹波出射。三维全波模拟显示,通过恰当地设计超材料微结构的几何尺寸,可以调节微结构的双折射特性,进而改变沿微结构两个正交方向偏振的太赫兹波的透射振幅和相位,使之振幅相近(约0.55),相位相差90°。实验上,通过离子束刻蚀硅的方法按照设计加工了一个样品,并利用太赫兹时域频谱系统进行了表征。实验结果和模拟结果吻合得很好,实现了带宽在1.07~1.41 THz范围内有效的四分之一波片,对应的归一化椭圆率高达0.99,证实了该设计的有效性。此外,还通过改变微结构的几何参数,进一步在模拟上设计了两个在其他太赫兹波段工作的四分之一波片,证明了该微结构的可调谐特性。

In this work, a broadband terahertz quarter wave plate was designed using high-resistance silicon based on meander-line dielectric metamaterials, which could convert the terahertz linear-polarization incidence to circular-polarization output. The 3D full-wave simulation shows that the birefringence property of the structure can be freely adjusted by properly designing the geometric parameters, which allows to engineer the transmission amplitudes of two orthogonal terahertz linear polarizations to be close to each other（about 0.55）, while the phase difference to be 90°. Based on the design, a terahertz quarter wave plate was fabricated using ion-beam etching method, and then experimentally characterized using terahertz time-domain spectroscopy system. The experimental results agree well with the simulations, which indicates that a broadband terahertz quarter wave plate that functions at 1.07-1.41 THz with a high normalized ellipticity over 0.99 was realized, demonstrating the validity of our designing scheme very well. Besides, by changing the geometrical parameters of the structure, two different broadband terahertz quarter wave plates that function at other frequency ranges were further designed, which confirms the tunability of the proposed structure.