Realizing Tunable Evolution of Bound States in the Continuum and Circularly Polarized Points by Symmetry Breaking,ACS Photonics

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Realizing Tunable Evolution of Bound States in the Continuum and Circularly Polarized Points by Symmetry Breaking
ACS Photonics ( IF 6.5 ) Pub Date : 2022-11-20 , DOI: 10.1021/acsphotonics.2c01522
Xinhao Wang ₁ , Jiajun Wang ₁ , Xingqi Zhao ₁ , Lei Shi _{1,

2,

3} , Jian Zi _{1,

2,

3}

Affiliation

Bound states in the continuum (BICs) and circularly polarized points (C points), being well-known momentum-space polarization singularities in photonic crystal (PhC) slabs, have attracted much attention due to their novel properties. The further investigations on the generation and evolution of BICs and C points in momentum space have provided more perspectives to modulate these polarization singularities by tuning parameters. Recently, it was theoretically proposed that starting from a high-order BIC, various tunable evolutions of BICs and C points could be realized by symmetry breaking, offering an effective method to create and modulate polarization singularities in momentum space. To date, there is still no experimental realization of tunable evolution of polarization singularities from a high-order BIC. Here, we experimentally realized tunable evolution of BICs and C points in momentum space by symmetry breaking on purpose. The studied high-order BIC of −2 charge exists in a PhC slab of C₆ symmetry. The off-Γ BICs of −1 charge were observed by breaking the C₆ symmetry to the C₂ symmetry. The at-Γ BIC of +1 charge and off-Γ C points of −12−12 $- \frac{1}{2}$ charge were observed by breaking the C₆ symmetry to the C₃ symmetry. The symmetry breaking factors and unit-cell configurations were further applied to continuously modulate the movement of polarization singularities in momentum space. Our results can promote the understanding of polarization singularities’ evolution and provide effective approaches of symmetry breaking to on-purpose design BICs and C points in momentum space.

中文翻译：

通过对称破缺实现连续体和圆偏振点束缚态的可调演化

连续体束缚态（BIC）和圆偏振点（C点）是光子晶体（PhC）板中众所周知的动量空间偏振奇点，由于其新颖的性质而备受关注。对动量空间中BIC 和C点的生成和演化的进一步研究为通过调整参数来调制这些偏振奇点提供了更多的视角。最近，从理论上提出，从高阶 BIC 开始，BIC 和C的各种可调演化点可以通过对称破缺来实现，为在动量空间中创建和调制偏振奇点提供了一种有效的方法。迄今为止，还没有实验实现高阶 BIC 偏振奇点的可调谐演化。在这里，我们通过故意对称破缺实验实现了动量空间中BIC 和C点的可调演化。所研究的 -2 电荷高阶 BIC 存在于C ₆对称性的 PhC 板中。通过将C ₆对称性破坏为C ₂对称性来观察-1电荷的off-Γ BIC 。+1 电荷的 at-Γ BIC 和 off- gamma C点- 12-12 $- \frac{1}{2}$ 通过将C ₆对称性破坏为C ₃对称性来观察电荷。对称性破缺因子和晶胞结构进一步应用于连续调制动量空间中偏振奇点的运动。我们的结果可以促进对极化奇点演化的理解，并为动量空间中特意设计 BIC 和C点提供对称破缺的有效方法。

更新日期：2022-11-20

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