RESUMEN
Topological photonic crystals (PCs) provide an effective method for controlling how light propagates and concentrates through their topological states. However, it remains unclear whether topological states can be obtained by combining two different two-dimensional (2D) PCs with topological non-trivial states. In this Letter, two types of 2D Penrose-square (P-S) PCs are proposed. These PCs can generate topological edge states (TESs) and topological corner states (TCSs) within the low-frequency part of the bandgap. Moreover, by combining these two non-trivial PCs, a total of two groups of TESs and four groups of TCSs can be generated in both the high-frequency and low-frequency parts of the common bandgap. To the best of our knowledge, the two proposed P-S PCs offer a new platform for investigating topological photonics and related devices, providing novel approaches and perspectives for generating topological states in 2D PCs.
RESUMEN
Topological rainbows (TRs) possess the potential to separate and localize topological photonic states across different frequencies. However, previous works on TRs have been confined to a single-frequency band. Furthermore, the achievement of multiband TRs within a single structure is still a significant challenge. In this paper, a composed structure waveguide is designed based on Penrose-triangle photonic crystals. By adjusting the size of scatterers and introducing non-Hermitian terms, we successfully realize dual-band TRs. This achievement will not only enhance the uniformity of the electric field intensity distribution but also provide the potential to introduce a new avenue for the development of robust photonic devices dedicated to processing vast amounts of data information.
RESUMEN
The topological edge state (TES) and topological corner state (TCS) in photonic crystals (PCs) provide effective ways to manipulate the propagation of light. To improve the performance and integration of topological photonic devices, the realization of multiband topological states by PCs combined with quasi-periodic structure needs to be urgently explored. In this Letter, a Penrose-triangle (P-T) PC, which arranges the basic structural unit of a 12-fold Penrose-type photonic quasi-crystal (PQC) in a triangular lattice, is proposed. The TES and TCS at low- and high-frequency bands can be generated in the same structure, accompanied by the realization of three groups of TCSs. This will provide a new structure for the generation of TESs and TCSs in PCs, and will provide a new way to improve the performance and integration of topological photonic devices.
RESUMEN
In this Letter, the higher-order topological state (HOTS) and its mechanism in two-dimensional Stampfli-Triangle (2D S-T) photonic crystals (PhCs) is explored. The topological corner states (TCSs) in 2D S-T PhCs are based on two physical mechanisms: one is caused by the photonic quantum spin Hall effect (PQSHE), and the other is caused by the topological interface state. While the former leads to the spin-direction locked effect which can change the distribution of the TCSs, the latter is conducive to the emergence of multiband TCSs in the same structure due to the characteristics of plentiful photonic bandgap (PBG) and broadband in 2D S-T PhCs. These findings allow new, to the best of our knowledge, insight into the HOTS, and are significant to the future design of photonic microcavities, high-quality factor lasers, and other related integrated multiband photonic devices.
RESUMEN
The quantum spin Hall effect protected by C6 symmetry [realized in the domain wall (DW) formed by a trivial-photonic crystal (TPC) and a nontrivial-PC (NPC)] and the quantum valley Hall effect protected by C3 symmetry [realized in the DW formed by two valley PCs (VPCs)] have been widely researched due to their excellent topological properties. The topological edge states (TESs) and topological corner states (TCSs) at DWs between different symmetric structures remain to be explored, which is essential for connecting waveguides with different symmetries to construct optical communication devices. In this Letter, there is (are) one TES (two TESs) for the DW1 and DW3 (DW2 and DW4) between the TPC (NPC) and two VPCs. Through simulation calculations of the Wilson-loop of the TPC and NPC and the Berry curvature distribution of VPCs, the corresponding relationship between the topological invariant and the number of TESs is obtained. Based on the TPC, NPC, and two VPCs, the waveguides are constructed to verify the realization of TESs. The parity of the gapped TESs is analyzed, and its relationship with the TCSs is obtained. Moreover, box-shaped structures are constructed to verify the appearance of TCSs. These results have a guiding significance for the research of the interaction between topological states protected by different symmetries.
RESUMEN
Novel phenomena found in non-Hermitian systems and robust edge states have attracted much attention. When non-Hermitian parameters (gain and loss) are above a critical value, the non-Hermitian photonic crystal (PC) bandgaps close, leading to a mixture of the topological edge state (TES) and topological corner state (TCS) with the bulk state. Meanwhile, new bandgaps also open, in which new TES and TCS can appear. Thus, with appropriate non-Hermitian parameters, TES can emerge in both the original bandgaps and the newly opened bandgaps. The results described here will further enrich understanding of the topological properties of non-Hermitian systems.
RESUMEN
Fragile topology (FT) opens a new direction in topological photonics, but a new type of photonic crystal (PC) with FT remains to be proposed. In this Letter, the double-site honeycomb lattice (DSHL) PC is proposed by rotating the double dielectric rods (DDR) six times, forming unit cell, and then arraying the unit cells in a triangular lattice. Quantum spin Hall effect occurs by manipulating the DDR in the tangential and radial directions of the unit cell. First, the band structures of DSHL PCs with different structural parameters are calculated, and the laws of topological phase transition are analyzed statistically. Then, to prove the FT properties of two groups of topological nontrivial DSHL PCs, the Wannier-center positions of the bulk bands are calculated by the Wilson-Loop method. Finally, the topological edge states and two groups of topological corner states, which are in the same bulk-state bandgap, are realized successfully. The DSHL PC provides good platforms for both the research of topological photonics and the device design and application, which has a broad prospect.
RESUMEN
The topological corner state (TCS) and topological edge state (TES) have created new approaches to manipulate the propagation of light. The construction of a topological coupled cavity-waveguide (TCCW) based on the TCS and TES is worth looking forward to, due to its research prospects in realizing high-performance micro-nano integrated photonic devices. In this Letter, the TCCW is proposed in two-dimensional (2D) photonic crystal (PC), which possesses strong optical localization, high quality factor, and excellent robustness compared with the conventional coupled cavity-waveguide (CCCW). This work will pave the way toward designing high-performance logic gates, lasers, filters, and other micro-nano integrated photonics devices and expanding their applications.
RESUMEN
In this paper, a side-coupled liquid sensor and its array based on magneto-optical photonic crystal are proposed. The sensitivity and quality factor of a single magneto-optical photonic crystal sensor are 0.492 mm/RIU and 181,760, respectively. After arraying, the sensitivity of the single microcavity sensor can reach from 0.1 to 0.35 mm/RIU, and the corresponding quality factor can reach from 5×104 to 7×104. Moreover, the structure has good robustness. This work will provide reference for the design of high-performance photonic crystal microcavity sensor arrays.
