Breaking the Efficiency–Stability Limit in Soliton Fiber Lasers via an Intelligent In-Cavity Tunable Directional Coupler

The operational efficiency of soliton fiber lasers is fundamentally constrained by the fixed output coupling ratio, creating a rigid trade-off between robust self-starting capabilities and maximum energy extraction. In this work, we break this efficiency–stability limit by demonstrating a reconfigurable laser system enabled by an intelligent in-cavity tunable directional coupler. Unlike static designs, our system employs an evolutionary algorithm to actively manipulate the coupling ratio, creating a dynamic trajectory through the fragmented solution space. We experimentally demonstrate that the laser can initiate in a low-loss stability basin and adiabatically evolve to a high-efficiency regime, achieving stable fundamental soliton operation at output coupling ratios approaching 50%. Furthermore, the system exhibits emergent physics-aware adaptability, arising without predefined physical constraints, by autonomously limiting the coupling ratio at high pump powers to prevent soliton quantization instabilities. This work establishes the active tunable coupler as a critical enabler for next-generation adaptive ultrafast sources, offering a hardware-driven solution to decouple gain saturation from nonlinear accumulation.