Slow light in ellipse-hole photonic crystal line-defect waveguide with high normalized delay bandwidth product

Abstract

In this paper, a novel flatband slow light device with low group velocity dispersion (GVD) is presented in an ellipse-hole photonic crystal (PC) line-defect waveguide. Utilizing dispersion engineering in the proposed structure, normalized delay-bandwidth product (NDBP) under a constant group index criterion is significantly improved. A step-by-step optimization process is done on the adjacent rows to the waveguide, which are filled by silica. For optimum case a high NDBP of 0.461 with a group index of 41.86 and a bandwidth of 17.06 nm is obtained by three-dimensional plane-wave expansion method. To the best of our knowledge, this NDBP is one of the highest values in PC waveguides reported to date, in which the group index value is relatively high. The numerical results show that GVD is negligible over a broad wavelength range. Also, optical pulse propagation through the waveguide is performed based on the finite-difference time-domain method. The results indicate that the shape of output pulse experiences a broadening of 2.1% compared with the incoming pulse after traveling a distance of 30a.