Study on the Performance Degradation of Lithium Niobate Modulators Under Atmospheric Neutron Irradiation

This paper focuses on the X-cut Y-propagating lithium niobate Mach–Zehnder modulator and studies how its performance degrades under atmospheric neutron irradiation. Since SRIM cannot directly simulate neutron-induced nuclear reactions, 1 MeV H+ ions are adopted as surrogate particles to compute displacement damage. SRIM is used to simulate the interaction between equivalent particles and lithium niobate lattices, constructing a material damage model that links neutron fluence to defect density, electro-optic coefficient degradation, and increased transmission loss. These material degradation relations are imported into COMSOL Multiphysics to build a multiphysics-coupled model integrating radiation damage, optical-field transmission, and electric-field modulation. Material-level simulation outputs are mapped onto three-dimensional real devices via structural equivalence principles. The simulation results show that lattice defect density rises with increasing neutron fluence, which further induces half-wave voltage drift, elevated insertion loss, and continuous extinction-ratio reduction. This work reveals the neutron displacement-damage-driven performance degradation mechanism and establishes a complete simulation workflow: neutron fluence → lattice defects → material property deterioration → device performance degradation. The established framework supports radiation-hardened design and on-orbit lifetime assessment for lithium-niobate-based space photonic devices. Limitations of the surrogate-particle approximation and model boundaries are also discussed, as all quantitative trends are simulation-derived rather than fully validated by experimental measurement.