Fig. 1. (a) Dimer chain with intra-dimer coupling strength c1 and inter-dimer coupling strength c2. Each dimer is composed of two waveguides, denoted as waveguides A and B. (b) Two dimer chains with distinct topological invariants are placed next to each other. The shadow waveguide A is with the waveguide number zero where the light inputs.

Fig. 2. Berry phase spectra for (a) c1/c2=5.51 and (b) c1/c2=0.182, with increasing η/c1.

Fig. 3. (a) Eigen spectrum of the two-dimer-chain model illustrated in Fig. 1(b). The red “A” dot represents the topologically protected defect mode, and other dots (including the blue “B” dot and green “C” dot) represent the extended states. (b) Modal amplitude distribution of the topological defect mode, labeled the “A” dot in (a). (c), (d) Modal amplitude distribution of extended states, labeled the “B” dot and “C” dot in (a), respectively.

Fig. 4. SEM images of the fabricated SOI waveguide arrays. (a) Two-dimer-chain structure. (b) Uniform array. The input waveguide merges into the center waveguide of the arrays.

Fig. 5. (a), (c) Numerically simulated intensity distributions for light propagation in samples SWG-1 and SWG-2, respectively. (b), (d) Experimentally measured and simulated transmission at the output of samples SWG-1 and SWG-2, respectively.

Fig. 6. (a) Propagation constants of points A, E, and F as functions of the coupling ratio c1/c2. c2 is a variable, and other parameters are constants. (b) Modal amplitude distribution of the topological defect mode when c1/c2=1.2.

Fig. 7. Light field evolution for the disordered two-dimer-chain model.