分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: In the known field of topological photonics, what remains less so is the breakdown effect of topological phases deteriorated by perturbation. In this paper, we investigate the variance on topological invariants for a periodic Kekul\'e medium perturbed in unit cells, which is a gyromagnetic photonic crystal holding topological phases induced by \emph{synchronized rotation} of unit cells. Two parameters for geometric and material perturbation are respectively benchmarked to pinpoint the topological degradation. Our calculation demonstrates that such a periodic perturbation easily destructs the original topological phase, and thus calls for further checkups on robustness under such unit-cell-perturbation in possible realization.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Synchronized rotation of unit cells in a periodic structure provides a novel design perspective for manipulation of band topology. We then design a two-dimensional version of higher-order topological insulators (HOTI), by such rotation in a triangular photonic lattice with $\mathcal{C}_3$ symmetry. This HOTI supports the hallmark zero-dimensional corner states and simultaneously the one-dimensional edge states. We also find that our photonic corner states carry chiral orbital angular momenta locked by valleys, whose wavefunctions are featured by the phase vortex (singularity) positioned at the maximal Wyckoff points. Moreover, when excited by a fired source with various frequencies, the valley topological states of both one-dimensional edges and zero-dimensional corners emerge simultaneously. Extendable to higher or synthetic dimensions, our work provides access to a chiral vortex platform for HOTI realisations in the THz photonic system.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Generating and manipulating Dirac points in artificial atomic crystals has received attention especially in photonic systems due to their ease of implementation. In this paper, we propose a two-dimensional photonic crystal made of a Kekul\'e lattice of pure dielectrics, where the internal rotation of cylindrical pillars induces optical Dirac-degeneracy breaking. Our calculated dispersion reveals that the synchronized rotation reverses bands and switches parity as well so as to induce a topological phase transition. Our simulation demonstrates that such topologically protected edge states can achieve robust transmission in defect waveguides under deformation, and therefore provides a pragmatically tunable scheme to achieve reconfigurable topological phases.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Maxwell fisheye lens was proposed to pinpoint super-resolution with the addition of wave drain and the interaction of multiple drains is theoretically predicted to improve subwavelength resolution further. In this paper we discuss the role played by port drains in optical absolute instruments, and verify by full-wave simulation that coupling nature for wave source and drain applies correctly in the picture of scanning imaging for absolute instrument. This work prospects for scanning near fields shaped from far-field wave propagation.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound states in the continuum (BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.