We propose and demonstrate a type of highly efficient tunable Mach-Zehnder interferometer (MZI) in Z-cut lithium niobate thin film (TFLN) based on the thermo-optical effect. By placing the electrode directly above the TFLN waveguide, a more uniform and higher heat distribution was obtained, compared with the conventional horizontal structure. Both the principle and design strategies of the proposed scheme are described. The process flow of the device fabrication is demonstrated in Z-cut TFLN. The measured static results accord well with the simulations. About 0.121 nm/V tuning efficiency is observed, which is nearly double the tuning efficiency based on the electro-optic effect, and may prove useful when high switching speed is not the primary consideration. The presented thermo-optic tuning scheme can be extended to other scenarios easily and may satisfy many different application requirements in integrated lithium niobate photonics (LNPs).

中文翻译：

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在 Z-Cut 铌酸锂薄膜中集成热调谐 Mach-Zehnder 干涉仪

我们提出并展示了一种基于热光效应的 Z 切割铌酸锂薄膜 (TFLN) 中的高效可调谐 Mach-Zehnder 干涉仪 (MZI)。与传统的水平结构相比，通过将电极直接放置在 TFLN 波导上方，可以获得更均匀和更高的热量分布。描述了所提出方案的原理和设计策略。Z-cut TFLN 演示了器件制造的工艺流程。实测静态结果与模拟吻合较好。观察到大约 0.121 nm/V 的调谐效率，几乎是基于电光效应的调谐效率的两倍，当高开关速度不是主要考虑因素时，这可能是有用的。