High-fidelity and high-power vortex beam generation via all-fiberized Raman amplification in passive ring-core fiber

Optical angular momentum (OAM)-structured light beams enhance the dimensionality of light, offering what we believe to be new possibilities in applications from optical communication to laser material processing. Despite various techniques for OAM beam generation, achieving high power without degradation has been challenging. Here, we employ ring-core fiber (RCF) as the Raman gain medium and experimentally validate an all-fiberized Raman fiber amplifier capable of producing OAM beams with a record output power of 34 W and topological charges of |l|=1. A Mach-Zehnder self-interferometer is designed to verify the modal patters and the numerical mode-decomposition is conducted to quantify the purity. After amplification, a reduction in the OAM mode purity was observed, with a decrease from an initial ∼96% to ∼88%. Compared with using conventional step-index few-mode fiber, the superior characteristics of RCF is validated by experimental and theoretical analysis, showing its potential to surpass traditional fiber designs in terms of amplification and mode fidelity. This work delivers not only a robust high-power laser source for practical applications but also shows its potential to surpass traditional fiber designs in terms of amplification and mode fidelity.