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中国物理学会期刊

低对称性能谷光子晶体中的拓扑光传输

CSTR: 32037.14.aps.73.20240040

Topological light transport in low-symmetry valley photonic crystals

CSTR: 32037.14.aps.73.20240040
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  • 能谷光子晶体是研究拓扑光子学的重要平台之一, 基于能谷光子晶体的新型光波导支持抗散射传输的能谷依赖边界态, 提高了波导中的急弯传输效率, 为光信息高效传输提供了新思路. 另一方面, 对称性在拓扑学和光子晶体研究中具有重要的物理意义和研究价值. 例如, 能谷光子晶体在破缺空间反演对称性的情况下表现出类量子能谷霍尔效应. 目前, 大多数能谷光子晶体具有C3对称性, 而具有更低对称性的能谷光子晶体是否能够支持拓扑光传输仍然需要研究. 本文通过调整能谷光子晶体的原胞形貌, 构建了低对称性能谷光子晶体, 并研究了其边界态的传输特性. 研究结果表明, 相对于C3对称性能谷光子晶体, 低对称性能谷光子晶体的光子禁带变窄, 但其边界态仍然能够实现单向激发以及抗散射传输. 这一发现丰富了拓扑光子结构的多样性, 为在低对称性结构中寻找拓扑保护光传输行为提供了指导.

     

    Valley photonic crystals represent a cornerstone in the field of topological photonics, which promotes the development of cutting-edge photonic waveguides. These waveguides support robust transmission by using valley-dependent edge states. This innovation marks a great leap forward in enhancing transmission efficiency, (especially in sharp bends), thus opening up a new way for efficient optical information transmission. However, although the role of symmetry in topology and photonic crystals cannot be exaggerated, it is worth noting that valley photonic crystals provide a unique platform for exploring the interplay between symmetry and topological phenomena. An intriguing analogy between valley photonic crystals and the quantum valley Hall effect is an example, which will be shown when the symmetry of spatial inversion is broken. At present, the characteristic of most valley photonic crystals is C3-rotational symmetry, which leads to an interesting study, that is, whether crystals with lower symmetry can also support topological light transmission. In order to solve this problem head-on, our work focuses on constructing and characterizing valley photonic crystals with low symmetry by carefully adjusting the unit cell morphology. Through theoretical analysis and numerical simulation, we unveil the remarkable ability of these low-symmetry valley photonic crystals to facilitate topological light transport. Initially, we analyze the bulk bands of these low-symmetry crystals, observing a narrowed photonic band gap and a shift in the irreducible Brillouin zone compared with C3-rotation symmetric crystals. To examine edge state transmission, we calculate dispersion relations and electric field distributions, revealing two edge states with opposite phase chirality at the same frequency. Using this point, we achieve unidirectional excitation of edge states. Additionally, we manipulate the refractive index of the surrounding medium and explore various scenarios of external light beam coupling. Moreover, we investigate the robust transmission of edge states, demonstrating smooth passage of light through sharp corners in Z-shaped bend waveguides without backscattering. In conclusion, our findings underscore the pivotal role played by edge states in facilitating unidirectional excitation and robust transmission in low-symmetry valley photonic crystals. By enriching the diversity of topological photonic structures and providing valuable insights into the behavior of topological light transport in structures with lower symmetry, our work contributes to the ongoing quest for novel photonic platforms with enhanced functions and performance.

     

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