Raman suppression in high-power fiber laser oscillator by long period fiber grating

Abstract Stimulated Raman scattering (SRS) is a major limiting factor for better performance of high-power fiber lasers. Several spectral filtering methods have been used for Raman suppression, among which long period fiber grating (LPFG) is relatively simple and effective due to its all-fiber structure and broadband rejection properties. Here, a broadband, low insertion loss and low thermal effect LPFG is easily fabricated using CO2 laser by galvanometer scanning, then is used for SRS suppression within a high-power fiber oscillator for the first time. Results show that a maximum SRS suppression ratio of ~16 dB was achieved and the extractable Raman-free output power was increased by about 13% with the insertion of LPFG. This work has demonstrated a potentially applicable method for Raman suppression in high-power fiber oscillators.