Degradation mechanisms of thin-film lithium niobate electro-optic modulator under temperature cycling stress

Thin-film lithium niobate (TFLN) electro-optical modulators (EOMs) have garnered significant interest because of their potential applications in next-generation high-speed optical communication systems. However, despite their promise, TFLN EOMs are plagued by temperature sensitivity and various reliability issues in practical application scenarios. To address this, the study investigates the impact of temperature cycle stress on modulator performance and reliability, coupled with COMSOL simulations. The experimental results indicate a significant increase in the loss of insertion of approximately 3 dB, a slight increase in half-wave voltage Vπ and a modulation phase drift rate of 1.3%. Furthermore, the electro-optical response curve demonstrates a decrease in modulation bandwidth, a reduction in output optical power, and an increase in noise. The simulation results showed that thermal stress altered the effective refractive index of the waveguide, leading to mode divergence and increased loss. Through characterization techniques such as optical emission microscope (EMMI), focused ion beam (FIB), and scanning electron microscope (SEM), the performance degradation behavior and failure mechanisms of the device are revealed. Thermal stress fatigue and waveguide defect evolution are the main causes of device failure. This research holds significant reference value for enhancing the reliability of TFLN EOMs.