Ultra-wideband slow light transmission with high normalized delay bandwidth product in W3 photonic crystal waveguide

By separating two photonic crystals with a distance of 23a, where a is the lattice constant, shifting the positions of some discriminatory air holes in the upper and lower edges, and inserting a defect central row, a specific waveguide is set up, W3 photonic crystal waveguide (W3 PCW). An equivalent transmission line model is given, giving the theoretical basis of for the proposed waveguide to have a wider transmission bandwidth and thus higher normalized delay bandwidth product (NDBP). Slow-light properties and performance are studied by using plane-wave expansion and finite-difference time-domain methods. We obtained ultra-wideband of 65.70 nm with low group-velocity dispersion and at the same time a high NDBP of 0.496 through optimization which is a worthy indicator for slow light device performance. Wider bandwidth can allow shorter duration of pulse waves, causing higher field intensity and stronger nonlinear effect.