Trident Spot-Size Convertor for Thin-Film Lithium Niobate

Thin-film lithium niobate on insulator (LNOI) is a promising material for integrated photonics due to its excellent optical properties. In this paper, we propose a trident-shaped LNOI spot-size converter (SSC) that enables efficient coupling between optical fiber and waveguide. The coupler achieves a coupling efficiency of 93% at 1550 nm wavelength. The coupler also has a large mode spot size of 4 $\mu \mathrm{m}$ and a high tolerance to optical misalignment.