Photonic band gaps and waveguide slow-light propagation in Bravais–Moiré two-dimensional photonic crystals

Abstract

Photonic band gap widths and slow-light optical guided modes are theoretically investigated for Bravais-Moiré photonic crystals made of cylindrical dielectric cores which are formed from the combination of two square Bravais lattices. Moiré pattern forms due to a commensurable rotation of one of these lattices with respect to the other. The analysis of gap maps is made versus the radii of dielectric cores -both rotated and unrotated- contained in the Bravais-Moiré unit cell. Guided modes are considered within the framework of coupled-resonator optical waveguides, built from the generation of a point defect chain along the direction of electromagnetic wave propagation. For the analyzed structures, rather wide photonic band gaps were found. It was noticed that changing the core radii can significantly affect the dielectric contrast in the unit cell, leading to wider gaps. In addition, due to the kind of crystal cell structure considered, guided modes with group velocities smaller than those typically observed in photonic crystals with simple square lattices were found for the investigated coupled-resonator optical waveguides.

Tunable Photonic Band Gaps in Two-Dimensional Bravais–Moiré Photonic Crystal Composed of High-Tc Superconductors

“…Previous works on these systems have reported wide PBGs, isotropy in the band structure, and radiation localization properties in the structure [26,[30][31][32][33][34]. Additionally, guided modes have been considered [26,[35][36][37] in both conventional PC waveguides [35,37] and CROWs [26]. These works have shown how BM networks favor the appearance of wide PBGs and the low group velocity of guided modes.…”

“…Another way to construct them involves building a chain of point defects or strongly coupled cavities, known as coupled resonator optical waveguides (CROWs) [25]. In previous works involving CROWs with multiple cores in the unit cell (UC), low group velocities have been found in the guided modes [23,26]. Additionally, isotropy in the PBGs has been reported in those systems.…”

“…Bravais-Moiré (BM) lattices are a particular case of systems with multiple cores in their unit cell (UC). This type of system can be seen as the superposition of two or more Bravais lattices, which are rotated with respect to each other by a commensurate angle, providing an additional parameter for tuning the optical properties of the considered systems [26]. Previous works on these systems have reported wide PBGs, isotropy in the band structure, and radiation localization properties in the structure [26,[30][31][32][33][34].…”

“…This type of system can be seen as the superposition of two or more Bravais lattices, which are rotated with respect to each other by a commensurate angle, providing an additional parameter for tuning the optical properties of the considered systems [26]. Previous works on these systems have reported wide PBGs, isotropy in the band structure, and radiation localization properties in the structure [26,[30][31][32][33][34]. Additionally, guided modes have been considered [26,[35][36][37] in both conventional PC waveguides [35,37] and CROWs [26].…”

“…Structures are assumed to be composed of copper oxide high-temperature superconductors (HTSCs). The BM PCs are made of cylindrical cores formed from the combination of two square Bravais lattices, such as the one considered in [26]. A waveguide is built into the system by means of defect lines within the structure.…”