Fig. 1. Schematic diagram of the structure of the trimer lattice model

Fig. 2. Dispersion relations under the scenarios of v1=v2=1 and v1≠v2 in k space

Fig. 3. Optical evolution of waveguide arrays under symmetric protection and the sum of the optical intensities within the two waveguides

Fig. 4. Optical evolution of waveguide arrays at v1=1,v2=2,w=2 and the sum of the optical intensities within the two waveguides

Fig. 5. Optical evolution of waveguide arrays at v1=1,v2=2,w=4 and the sum of the optical intensities within the two waveguides

Fig. 6. The intensity distribution of the real space band and eigenstates when the system is in the symmetric state （v1=v2） and the broken state （v1≠v2）

Fig. 7. Phase diagram of the distribution of topological edge states

Fig. 8. Optical evolution of incident light from different sites and the distribution of the eigenwave function ψ1 and ψ3

Fig. 9. Optical evolution in the waveguide array with introduced defects when v1=v2

Fig. 10. Optical evolution in the waveguide array with introduced defects when v1≠v2