Kerr-Effect-Based Online Characterization of Splitting Ratio in Integrated Phase Modulators for Fiber-Optic Gyroscopes

Multifunctional integrated optical modulators (MIOCs) are essential in fiber-optic gyroscopes (FOGs) and emerging on-chip photonic systems. Among their performance metrics, the splitting ratio requires high-precision characterization due to fabrication tolerances. The Kerr effect—traditionally treated as a bias error—has been largely overlooked in broadband FOGs. However, because the Kerr-induced phase error directly depends on the MIOC splitting ratio, it can serve as a diagnostic signal. This work extends the traditional Kerr-effect theory into a fully quantitative model applicable to both laser and broadband light sources. Based on this framework, we propose a novel method that converts the Kerr effect from a bias source into a metrological tool for in-situ, online measurement of the MIOC splitting ratio, without disassembling the gyro module. The proposed technique enables real-time performance monitoring of MIOC-based optical drivers and provides a new route for characterizing individual splitters in integrated photonic circuits. This approach establishes a unified theoretical and experimental basis for using nonlinear effects in precision photonic metrology.