40.2: Programmable topological waveguide via nematic liquid crystals

Abstract

With the rapid development of display technology, liquid crystals have gained significant attention. The unique optical properties of liquid crystals, such as birefringent optical performance and adaptive stimulus-responsiveness, provide a soft material platform for optical communication, biosensing, spatial light modulation, and topological photons. In this paper, based on the tunable refractive index of nematic liquid crystal and the robust transmission characteristics of topological photonic crystals, a valley photonic crystal based on liquid crystal (LCs-VPC) is proposed. The LCs-VPC has graphene-like lattice structure, and the liquid crystal molecules with different refractive indexes are confined in cylinders and hopingly arranged at six vertices of the lattice to break the space inversion symmetry. The topological non-trivial state is generated by adjusting the LCs’ refractive index via bias voltages. Topological waveguides with valley-protected edge modes are designed by stacking different states of lattice cells in the plane. The programmability of the waveguide is achieved by applying an external voltage to encode the state of the LCs in each cylinder. Based on the programmable topological waveguide, a programmable beam splitter has been designed. Our proposed LCs-VPC devices are beneficial for the development of integrated topological photonic circuits.