Simulation and Analysis of Single-Mode Beam Splitter in Lithium Niobate Thin Film

Lithium niobate on insulator (LNOI) thin film maintains the attractive material properties of lithium niobate, while also offering a stronger optical confinement and a high optical element integration density. The structure of integrated chips needs to be redesigned because the LNOI chip is quite different from the single crystal LN one. Beam splitter has been widely used in integrated optical devices, such as MZM modulator, AM modulator and light switch. In this paper, two kinds of beam splitters, including directional coupler (DC) and Multi-Mode interference (MMI) structure were designed by using finite difference time domain. The gap and coupling length of directional coupler were analyzed. An MMI beam splitter structure was designed and simulated. The key parameters of beam splitter such as free spectral range, splitting ratio and propagation loss were compared. The analysis of the two beam splitter structures can supply guidance for the design of the LNOI devices.