Zhao Zhenyu, Zheng Xiaobo, Peng Wei, Zhang Jianbing, Zhao Hongwei, Luo Zhijian, Shi Wangzhou
Opt Express. 2017 Oct 2;25(20):24410-24424. doi: 10.1364/OE.25.024410.
We experimentally investigate the terahertz (THz) electromagnetically-induced transparency (EIT)-like phenomenon in a metamolecule (MM) of three-body system. This system involves a couple of geometrically identical split-ring resonators (SRRs) in orthogonal layout conductively coupled by a cut-wire resonator. Such a three-body system exhibits two frequency response properties upon to the polarization of incident THz beam: One is the dark-bright-bright layout to the horizontally polarized THz beam, where there is no EIT-like effect; the other is bright-dark-dark layout to the vertically polarized THz beam, where an EIT-like effect is observable. The transparency window can be tuned from 0.71 THz to 0.74 THz by the displacement of cut-wire inside the trimer MM. A maximum of 7.5 ps group delay of THz wave is found at the transparent window of 0.74 THz. When the cut-wire moved to the mid-point of lateral-side of SRR, the EIT-like phenomenon disappears, this leads to a localized THz slow-light effect. The distribution of surface currents and electric energy reveals that the excited inductive-capacitive (LC) oscillation of bright-SRR dominates the high frequency side-mode, which is isolated to the displacement of cut-wire resonator. However, the low frequency side-mode originates from the constructive hybridization of LC resonance in dark-SRR coupled with a localized S-shaped dipole oscillator, which is tunable by the displacement of cut-wire. As a consequence, the group delay as well as the spectral configuration of transparency window can be manipulated by tuning one side-mode while fixing the other. Such an experimental finding reveal the EIT-like effect in a conductively coupled three-body system and manifests a novel approach to achieve tunable THz slow-light device.
我们通过实验研究了三体系统的超分子(MM)中的太赫兹(THz)电磁诱导透明(EIT)类现象。该系统包括一对几何形状相同的开口环谐振器(SRR),它们以正交布局通过切割线谐振器进行导电耦合。这样的三体系统对于入射太赫兹光束的偏振呈现出两种频率响应特性:一种是对于水平偏振太赫兹光束的暗 - 亮 - 亮布局,其中不存在类似EIT的效应;另一种是对于垂直偏振太赫兹光束的亮 - 暗 - 暗布局,其中可以观察到类似EIT的效应。通过三聚体MM内部切割线的位移,透明窗口可以从0.71太赫兹调谐到0.74太赫兹。在0.74太赫兹的透明窗口处发现太赫兹波的最大群延迟为7.5皮秒。当切割线移动到SRR侧面的中点时,类似EIT的现象消失,这导致了局部太赫兹慢光效应。表面电流和电能的分布表明,亮SRR激发的电感 - 电容(LC)振荡主导高频边模,该边模与切割线谐振器的位移无关。然而,低频边模源于暗SRR中LC共振与局部S形偶极振荡器的相长杂化,其可通过切割线的位移进行调谐。因此,在固定另一侧模的同时调谐一侧模,可以操纵群延迟以及透明窗口的光谱配置。这一实验发现揭示了导电耦合三体系统中的类似EIT效应,并展示了一种实现可调谐太赫兹慢光器件的新方法。