Fig. 1: The SSH model, topological waveguide schematic, and calculated coupling coefficients between two waveguides.

a Diagram of the dimer chain making up the SSH model with a domain wall. b Device schematic and scanning electron micrograph of the USRN topological waveguide. c Coupling coefficient and coupling length for two coupled waveguides as a function of gap distance for a size of 0.6 µm × 0.3 µm waveguide fabricated with a USRN core and SiO₂ cladding. d Measured output powers versus waveguide index positions at diverse wavelengths from 1.53 to 1.62 µm. The output power is observed to be well localized at the boundary waveguide indexed to be |0〉. e Topological mode profile numerically calculated using the finite-element method. It is observed that the mode is well-localized to the topological domain wall and as expected from the chiral symmetry, the amplitude at waveguides |±1〉 is suppressed.