Broadband photonic topological insulator based on triangular-holes array with higher energy filling efficiency

Abstract

<jats:title>Abstract</jats:title><jats:p>Photonic topological insulators (PTIs) bring markedly new opportunities to photonic devices with low dissipation and directional transmission of signal over a wide wavelength range due to the broadband topological protection. However, the maximum gap/mid-gap ratio of PTIs is below 10% and hardly further improved duo to the lack of new bandwidth enhancement mechanism. In this paper, a PTI with the gap/mid-gap ratio of 16.25% is proposed. The designed PTI has a honeycomb lattice structure with triangular air holes, and such a wide bandwidth is obtained by optimizing the refractive-index profile of the primitive cell for increasing the energy proportion in the geometric perturbation region. The PTI shows a large topological nontrivial gap (the gap/mid-gap ratio 33.4%) with the bandwidth approaching its theoretical limit. The edge states propagate smoothly around sharp bends within 1430–1683 nm. Due to topological protection, the bandwidth only decreases 1.38% to 1450–1683 nm under 1%-random-bias disorders. The proposed PTI has a potential application in future high-capacity and nonlinear topological photonic devices.</jats:p>

Topological edge and corner states of valley photonic crystals with zipper-like boundary conditions

“…In this paper, we study two-dimensional (2D) dielectric column topological photonic crystals (PhCs), considering only their TM [35,36] modes. The Hamiltonian of the valley photonic crystals can be determined based on the specific system and structure.…”

“…Regarding valley photonic crystals, one can traditionally transform a photonic structure with C 6v symmetry into one with C 3 symmetry by breaking spatial inversion symmetry. [35] In addition to the above method, as we know, spatial inversion symmetry can also be broken by moving the dielectric pillars in a photonic structure with C 3 symmetry. By changing the distance between the dielectric pillars and the center of the unit cell, the Wannier centers in the photonic crystal are affected, thereby adjusting the degree of inter-cell/intra-cell coupling in the structure to achieve a topological phase transition, open a band gap, and also realize valley photonic crystals.…”

High Transmission in 120-degree Sharp Bends of Inversion-symmetric and Inversion-asymmetric Photonic Crystal Waveguides

“…IA-PhCWGs based on a triangular lattice have been already proposed and high transmissions through 120-degree bends have been observed 19,22,29,30,32,38 . Here, we employ slightly different IA-PhCWGs based on triangular air-hole lattices and focus on the first bandgap in TE-polarization (Fig.…”