Ultrahigh-Q Fano resonance using topological corner modes in second-order pseudospin-Hall photonic systems

Physica Status Solidi (b)

2022

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Topological phases appearing in photonic systems have recently attracted much attention in the community of photonics due to the fundamental and practical significances. Despite extensive investigations, the preceding results show that the photonic systems exhibit single topological phases with few exceptions. This work presents the simultaneous appearance of different topological phases in a single photonic crystal structure, which are characterized by bulk polarization and valley‐Chern number. Square‐lattice photonic crystals with unit cells consisting of four dielectric rods, one of which has the size different from the other three ones, exhibit the topological phase characterized by bulk polarization in the first bandgap, depending on the distance between the dielectric rods. Due to the broken inversion symmetry, in the meantime, the photonic systems show the valley‐Hall topological phase in the fourth bandgap. The proposed structures have the advantage of flexible design for generating the dual‐band topological edge and corner states compared with other photonic systems exhibiting single topological phases. From the fundamental and practical significances, the presented results will trigger the extensive investigations for exploring the photonic systems with multiple topological phases and find important practical applications.

Section: Introductionmentioning

confidence: 99%

Simultaneous Appearance of Different Topological Phases in a Single Photonic System: Coexisting Phases Characterized by Bulk Polarization and Valley‐Chern Number Enabling Dual‐Band Second‐Order Topological States

Physica Status Solidi (b)

2022

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“…Recently, higher order topological systems [ 25–32 ] have been proposed and extensively investigated, leading to potential applications for low‐threshold topological nanolasing, [ 33 ] topological Fano resonance, [ 34 ] topological photonic crystal fibers, [ 35 ] and disorder‐immune coherent subwavelength source. [ 36 ] The aforementioned concept has been generalized to the non‐Hermitian systems [ 37–40 ] and second‐order corner states induced by gain and loss [ 41,42 ] have been investigated only using analytical tight‐binding model, restricting the quantitative characterization and practical applicability.…”

Section: Introductionmentioning

confidence: 99%

Parity‐Time Phase Transition of Topological Corner States in Square Lattice Photonic Crystal Structures

Advanced Photonics Research

2022

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Marriage of the concepts of parity‐time (PT) symmetry and topology recently gave rise to PT‐symmetric topological photonics, triggering great interest in the community of photonics. This work reveals PT‐symmetric phase transition in second‐order topological photonic systems: the photonic systems consisting of square lattice topological photonic crystals with balanced gain and loss support the corner states, two of which are in thresholdless PT broken phase and the other two exhibit PT phase transition with a threshold determined by the coupling strength between the corner modes. The main advantage of the proposed photonic system is the significantly high gain contrast between the corner states and unnecessary background modes originating from bulk and edge ones, enabling diverse photonic applications such as nanolasing with significantly high power compared with the preceding topological nanolasers made of only gain sublattices. The results presented in this work pave the way toward potential applications such as biological sensing and spectroscopy at the nanoscale.

Tunable Second‐Order Topological States in Rhombic Photonic Crystals

Physica Rapid Research Ltrs

2023

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Topological photonic devices with dynamically tunable functions are highly on demand in practice, but the majority of previously proposed photonic systems have been limited to fixed performances, once fabricated. Although several approaches have been proposed for obtaining the tunability in topological photonic systems, they are limited to first‐order topological states and require rather complicated structures. Herein, second‐order topological properties of rhombic photonic crystals (PCs) are revealed, for the first time, enabling to realize tunable photonic devices. For this purpose, the conventional square lattice PCs composed of four rigid dielectric rods are reshaped to rhomboid ones with preserved inversion symmetry, which exhibit well‐quantized bulk polarizations. Since the eigenfrequencies of topological edge and corner states depend on the angle between the neighboring sides of unit cells, the second‐order topological systems exhibit dynamic tunability, being useful for diverse applications such as optical switching and flexible beam control. Unlike the previous results for reconfigurable routing limited to special angles, this lattice‐reshaping mechanism has the ability to realize dynamically tunable routing, extending the realm of applications of topological photonics. For its simplicity and feasibility, this mechanical lattice‐reshaping approach paves the way toward higher‐order topological photonic devices with dynamically controlled functions.