arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2004.14538physics.optics
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光子晶体平板动量空间中的偏振奇点

Singular points of polarizations in the momentum space of photonic crystal slabs

Weimin Ye, Yang Gao, Jianlong Liu

摘要:

连续束缚态(BIC)、圆偏振态(C点)和简并态都是动量空间中的三种偏振奇点。对于具有线偏振远场的光子晶体平板(PhCS),BIC被发现是偏振涡旋的中心,在以往的研究中受到了更多的关注。在这里,我们从理论上证明了PhCS的远场可以表现出显着不同的偏振,由于在连续的C点的强大存在。只有一对具有相同旋向和相反拓扑荷的C点可以一起湮灭。在不破坏PhCS对称性的前提下,通过对PhCS结构参数的不断微调,一对拓扑电荷相同、旋向相反的C点能够合并成BIC,然后BIC再次分裂成C点。有趣的是,当两对分别来自上带和下带的具有相同拓扑荷的C点同时合并在Dirac-退化点时,观察到具有一半拓扑荷的Dirac-退化BIC。证明了拓扑电荷守恒定律在不同类型极化奇点的演化和相互转换中起着重要作用。我们的研究结果可能会揭示奇异偏振点的起源,可能会打开一个大门,他们在矢量光束的产生和操作的应用。

英文摘要:

Bound states in the continuum (BICs), circularly polarized states (C points) and degenerate states are all of three types of singular points of polarization in the momentum space. For photonic crystal slabs (PhCSs) with linearly polarized far fields, BICs were found to be the centers of polarization vortices and attracted more attention in the previous studies. Here, we theoretically demonstrate that the far fields of PhCSs can exhibit remarkably diverse polarizations due to the robust existences of C points in the continuum. Only a pair of C points with identical handedness and opposite topological charge can be annihilated together. Continuously fine tuning of the structure parameters of PhCSs without breaking their symmetry, a pair of C points with identical topological charge and opposite handedness are able to merge into a BIC, then the BIC splits into C points again. Interestingly, a Dirac-degenerate BIC with one half of topological charge is observed when two pairs of C points with identical topological charge from the upper and lower band, respectively, simultaneously merge at the Dirac-degenerate point. The law of topological charge conservation is verified to play an important role in the evolutions and interconversions between different types of polarization singularities. Our findings might shed light on the origin of singular points of polarization, could open a gateway towards the applications of them in the generation and manipulation of vector beams.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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