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

Photonic band gap widths and slow-light optical guided modes are theoretically investigated for Bravais-Moire (BM) photonic crystals (PCs) made of cylindrical dielectric cores which are formed from the combination of two square Bravais lattices. The Moire 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 BM unit cell (UC). Guided modes are considered within the framework of coupled-resonator optical waveguides (CROWs), 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 UC, 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 PCs with simple square lattices were found for the investigated CROWs.