Fig. 1: Comparison of the pseudospin-polarized slow light waveguide and other two types of slow light waveguides.
From: Pseudospin-polarized slow light waveguides with large delay-bandwidth product
a Schematic of a photonic-wire waveguide. b Dispersion and group index of photonic-wire waveguide. In this type of waveguides, slow light can be obtained in a finite frequency regime (shaded in blue), relative bandwidth is usually <10% and group index is usually <10. c Schematic of a photonic crystal (PC) line defect waveguide. d Dispersion and group index of PC line defect waveguide. In PC line defect waveguides, slow light can be achieved near the Brillouin zone boundary (middle in the figure) due to the crossing coupling between forward and backward guided modes. Its relative bandwidth is usually <10% and group index is usually <100. e Schematic of a pseudospin-polarized folded edge waveguide. f Dispersion and group index of folded edge waveguide. In this type of waveguides, pseudospin-polarized edge mode (blue lines) exists from zero frequency to a finite frequency, naturally indicating a relative bandwidth of 200%. Group index can be increased by lengthening the optical path via a folded edge configuration. Thus, an extremely large DBP can be obtained. This densely folding would not introduce backscattering and subsequent GVD, due to pseudospin-momentum locking.
