All‐Fiber Dual‐Band Laser at 1.0 and 1.5 µm via Structured Core Engineering in Phosphate Glass Fiber

Abstract Dual‐band lasers are essential for applications of broadband light sources, mid‐infrared generation, advanced microscopy, and pump‐probe sensing. Yet, achieving compact all‐fiber configurations remains challenging due to the difficulties in dual‐band gain fiber fabrication, high gain requirement, and the competitive energy transfer process of rare earth (RE) ions. Herein, a strategy of co‐engineering fiber structure and gain material is proposed to address these challenges. A dual semicircular structured core fiber (DSSCF) is designed, featuring spatially separated Er 3+ /Yb 3+ and Yb 3+ doped regions in multicomponent phosphate glass. This design enables independent emission at 1.0 and 1.5 µm, supported by an exceptional Yb 3+ → Er 3+ energy transfer efficiency of 99.7% that minimizes the influence of Yb 3+ emission in the co‐doped region. Experimental results demonstrate dual‐band lasing at 1.0 and 1.5 µm using a short gain fiber of 4.6 cm. Notably, the dual‐band laser system achieves outstanding performance with slope efficiencies of 24.0% and 5.6% at 1.0 and 1.5 µm, respectively, coupled with low dual thresholds below 180 mW. This work highlights the potential of DSSCFs for compact and efficient dual‐band all‐fiber lasers and advances the integration and miniaturization of laser systems.