High-power fiber oscillators are critical tools for modern industry: they cut and weld tough materials, make precision components for high-end devices, and even support delicate biomedical procedures. But as these lasers get more powerful, a major issue arises: stimulated Raman scattering (SRS). SRS converts the laser’s useful “signal light” into useless “Raman light,” lowering power efficiency and even risking damage to the laser system. Traditional methods to suppress SRS often involve complex setups that reduce compactness and reliability. In this study, the team from the National University of Defense Technology introduced a composite fiber Bragg grating (FBG) written directly into the fiber using femtosecond lasers. This innovative design combines a chirped and tilted FBG (CTFBG) with a low-reflectivity FBG on the same fiber, eliminating the need for extra splices and boosting system stability. This component acts like a sophisticated filter, selectively blocking the unwanted Raman light while allowing the main laser beam to pass through unimpeded. Moreover, the femtosecond laser writing technique avoids the heating problems associated with conventional methods, allowing for higher power handling. The fiber oscillator laser system achieved a 97.5% reduction in unwanted Raman light, and reached 9 kW of output power—the highest ever achieved for fiber oscillators using this type of filtering technology.
“This work opens new possibilities for high-power laser applications,” the researchers note. “By effectively controlling SRS, we can push laser technology to new limits while maintaining the precision required for advanced manufacturing and scientific applications.” The work entitled “Composite fiber Bragg grating written by femtosecond laser for Raman suppression in high-power fiber oscillators” was published in Frontiers of Optoelectronics (published on Oct. 21, 2025).
DOI：10.1007/s12200-025-00165-3