Highly Efficient Thermal Tuning Interferometer in Lithium Niobate Thin Film Using Air Bridge

We propose and demonstrate a type of highly efficient thermally tuned interferometer in lithium niobate on insulator (LNOI) thin film using an air bridge structure. By removing the oxide below the lithium niobate (LN) waveguide, the heat transferred to the substrate is greatly reduced. Thus, more heat is confined inside the LN waveguide and a higher tuning efficiency is realized. Additionally, by directly placing the thermal electrode above the LN waveguide, a more uniform and stronger thermal distribution is realized compared with a horizontal structure. Both the design and process details of the proposed device are demonstrated. The improvement of the proposed new structure is about 4.9-fold compared with a typical structure without the air bridge modification according to our measured results. The proposed structure can be extended to other application scenarios easily and will likely boost the development of integrated lithium niobate photonics.