Slow light optimization in symmetric photonic crystal waveguide with elliptical holes

In this paper, we propose a slow light structure formed by circular and elliptic air hole where the innermost two rows on each side of the waveguide is shifted vertically. By adjusting radii of shifted holes, we obtained a large value of Normalized Delay Bandwidth Product (NDBP) about 0.42, group index of 50 and ratio normalized bandwidth/normalized central frequency of 0.0084.