Wide bandwidth slow light waveguide in a manipulated 2D photonic crystal

The bandwidth limitation of slow light may distort optical pulses, potentially affecting their practical application. Therefore, researching structures capable of overcoming this limitation could represent a valuable step forward. This theoretical work explores a 2D photonic crystal waveguide with high bandwidth. The optimized structure, comprised of Ge cylinders in an air background, is designed to be arranged in square lattices containing a line defect. The line defect consists of a series of half-cylinders, with their centers aligned with neighboring cylinders at half the lattice constant. This defect generates a waveguide mode that propagates along the line. Additionally, the group index and bandwidth of the mode were studied and optimized for different radii of the photonic crystal. With this relatively simple structure and the selection of appropriate geometric sizes, high bandwidth and a group-index-bandwidth-product of up to one could be achieved.