Nonlinear Dual-Core Fibers Kerr Effects, Cross-Phase Modulation, and Optical Switching Applications

Abstract

Nonlinear dual-core optical fibers represent an emerging class of waveguides that combine spatial mode coupling with intensity-dependent nonlinear effects, offering functionalities beyond conventional single-core fibers. Unlike linear dual-core fibers primarily investigated for space-division multiplexing, nonlinear dual-core fibers exploit Kerr-induced refractive index variations to enable power-dependent energy transfer, cross-phase modulation, and all-optical control. In this work, we investigate the nonlinear dynamics of dual-core fibers by analyzing Kerr effects and inter-core nonlinear interactions under continuous-wave and pulsed excitation regimes. Numerical modeling based on coupled nonlinear Schrödinger equations demonstrates that, for input powers exceeding a critical threshold (typically in the range of  depending on core separation and nonlinear coefficient), the linear periodic power exchange between the two cores is progressively suppressed, leading to nonlinear self-trapping and asymmetric energy localization. Cross-phase modulation between adjacent cores induces additional phase shifts proportional to the optical intensity, reaching several radians for peak powers above  over propagation lengths of a few meters. These effects enable controllable power-dependent switching, where the output port can be deterministically selected by adjusting the input power or pulse energy. Simulation results show switching contrasts exceeding 20 dB and response times limited only by the optical pulse duration, indicating suitability for ultrafast operation beyond 100 GHz. Furthermore, the nonlinear coupling mechanism provides intrinsic bistability, which can be exploited for optical logic and signal regeneration. The applicability of nonlinear dual-core fibers to fiber laser systems is also discussed, where Kerr-induced mode imbalance can act as a passive, power-dependent mode selector or dynamic saturable absorber. Compared to multi-core or photonic crystal fibers, dual-core nonlinear fibers offer a simpler geometry, reduced fabrication complexity, and enhanced controllability of nonlinear interactions. Despite these advantages, their potential remains largely underexplored in current literature. The results highlight nonlinear dual-core fibers as a promising platform for all-optical switching, ultrafast signal processing, and advanced fiber laser architectures, paving the way for compact, low-latency, and electronics-free photonic devices.