二维太赫兹拓扑光子晶体的远场探测

Far-field detection of two-dimensional terahertz topological photonic crystals

随着量子霍尔效应(QHE)在凝聚态物理中的深入研究,一类具有非平庸特性的新型材料——拓扑绝缘体引起了人们极大的兴趣.与此同时,随着人工超材料的发展,一种可以产生新型单向传输模式且无背散射的拓扑光子晶体(Topological Photonic Crystals)引起非常大的关注.在本文中,根据时空反演对称性和量子自旋霍尔效应(QSHE)理论,我们构建了一个工作频率在太赫兹波段的拓扑光子晶体,当扩展或压缩六角蜂窝状晶格时,空间反演对称性会被打破,从而打破能带简并实现光子能隙结构,将具有相反拓扑特性的光子晶体摆放在一起,在它们的交界面可实现具有单向传输且不受缺陷影响的拓扑边界态.本文在太赫兹波段实验表征了该拓扑光子晶体的反射谱特性,发现扩展和压缩六角蜂窝状晶格获得的拓扑光子晶体的反射谷频率分别对应他们各自第一能带p±在Г点处的频率,由此可得知光子能隙的宽度,为拓扑光子晶体的验证提供了新的手段.

Originating from the investigation of condensed matter states,we have discovered a new material with phase transition no-trivial properties——topological insulators.With the progress in artificial metamaterials,the photonic crystals which can give rise to topological edge states that propagate around sharp corners immune to scattering have captured much attention.In this paper,according to the spatial and time reversal symmetry and quantum spin Hall effect theory,we presented a topological photonic crystal made of metallic cylinders at terahertz frequencies.By slightly expanding and shrinking the unit cell,the spatial reversal symmetry was broken and therefore,the band degeneracy was broken,realizing the topological band gap.Unidirectional topological edge states were proven to exist on a domain wall connecting two photonic crystals with opposite topological properties without back-scattering.Then we investigated the reflection spectra of the designed topological photonic crystals in the terahertz regime,which provided a new means to verify topological photonic crystals.