Y-Shaped Topological Photonic Crystal Waveguide Design on Lithium Niobate for Integrated Beam Splitter and Combiner

Integrated optoelectronic systems are widely used in optical communications and other fields. As an important unit in the system, optical waveguide is the basis of optical information processing and transmission. In the past decade, the emerging field of topological photons has shown great potential in applications. The topological edge state and backscattering suppression of photonic crystal can realize the lossless transmission of light. Therefore, in the construction of optical waveguide, photonic topological insulator provides a novel idea for the study of compact volume waveguide devices. In this paper, a simple two-dimensional photonic crystal is designed. By changing the distance between the dielectric column and the center of the unit cell, the band inversion of the double degenerate p state and d state is realized in the center of the Brillouin zone, and it is proved that the essence of the band inversion is the topological phase transition. The numerical simulation results reveal that unidirectional transmission can be realized on the interface between topological trivial and nontrivial photonic crystals. The photonic crystals in this paper are only composed of lithium niobate (LN) materials and the lattice structure is simple. When topological phase transition is realized, it is not necessary to change the filling rate and size of the dielectric column, but only to move the distance of the dielectric column. Therefore, this structure is more effective in the application of topological boundary states.