Fig. 4: Degree of topological protection. | Light: Science & Applications

Fig. 4: Degree of topological protection.

From: Direct quantification of topological protection in symmetry-protected photonic edge states at telecom wavelengths

Fig. 4

a Schematic of the mode contributions in a Ω-shaped defect VPC waveguide. Red arrows indicate the forward-propagating modes, with F1 and F2 denoting the modes before and after the defect, respectively. Blue arrows indicate backward-propagating modes before (B1) and after (B2) the defect. Yellow dashed circles show the locations of in- and out-coupling facets. White dashed circles indicate the four 120° corners. b Plot of the transmission coefficient ηT, with the inset demonstrating transmission over a small region ([189.5 THz–190.5 THz]). c Backward/forward energy ratio before (ηR1) and after (ηR2) the Ω-shaped defect in the VPC domain wall. The inset shows how the back-propagation energies before and after the defect are almost indistinguishable over the considered frequency range. d and e show the corresponding plots of b and c for the W1 waveguide, respectively

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