Fig. 5: Large DBP by lengthening the optical path of folded edge.
From: Pseudospin-polarized slow light waveguides with large delay-bandwidth product
a Group index as a function of the path length ratio (l + w) / w. The inset shows the groove structure of the folded edge and the geometry parameters. b Dispersion of the edge states of the waveguide with l = 19a, w = a and h = a. DBP of the folded edge waveguide is approximately 40. Zoom-in of the dispersion within 3.5–4.0 GHz is plotted, and a reference straight line is added to show the slight nonlinear of the dispersion. c Group index for different values of h. Fluctuations in group index are caused by the side coupling between adjacent edges and the resultant slight nonlinear of edge dispersion, see the zoom-in plot in b. Red curve shows the group index for h = 0.2a, showing a nearly constant group index of 20. Further lowering h would lead to more localized EM field and less side coupling between adjacent edges. d Field profile for the case of h = a. e Transverse decay lengths of the Hz fields for different h. f Field profile for the case of h = 0.2a.
