Methods of Measurement Propagation Losses in Thin Film Lithium Niobate Waveguides

We studied the methods for measuring propagation losses in thin-film lithium niobate (TFLN) waveguides. Thin-film lithium niobate is a promising platform for integrated photonics, enabling the fabrication of compact waveguide structures and topologies. The fabrication process of TFLN waveguides includes several stages: design, fabrication, and testing. This paper focuses on the testing stage, which allows for an objective evaluation of the fabrication process and the correctness of the design. The methodology for measuring propagation losses in waveguides is an important research topic in integrated photonics. Several measurement approaches are considered, including interferometric methods based on Fabry–Pérot resonances within the waveguide and the cut-back method. A comparison of these methods in terms of universality, repeatability, and accuracy shows that the cut-back method is the most promising among those considered.