Topological edge states in photonic decorated trimer lattices

In recent years, topological insulators have been exten-sively studied in one-dimensional periodic systems, such as Su-Schrieffer-Heeger and trimer lattices. The remark-able feature of these one-dimensional models is that they support topological edge states, which are protected by lattice symmetry. To further study the role of lattice sym-metry in one-dimensional topological insulators, here we design a modified version of the conventional trimer lat-tices, i.e., decorated trimer lattices. Using the femtosecond laser writing technique, we experimentally establish a series of one-dimensional photonic decorated trimer lattices with and without inversion symmetry, thereby directly observ-ing three kinds of topological edge state. Interestingly, we demonstrate that the additional vertical intracell coupling strength in our model can change the energy band spec-trum, thereby generating unconventional topological edge states with a longer localization length in another boundary. This work offers novel insight into topological insulators in one-dimensional photonic lattices. (c) 2023 Optica Publishing Group