Rao Binyu, Zhao Xiaofan, Li Hongye, Tian Xin, Wang Meng, Wang Zefeng
Opt Express. 2021 Mar 29;29(7):11277-11292. doi: 10.1364/OE.420771.
Recently, chirped and tilted fiber Bragg gratings (CTFBGs) have received great attention because they can realize suppression of stimulated Raman scattering (SRS) in high-power fiber lasers. In this study, the possible coupling between the core modes and cladding modes in CTFBGs inscribed in large-mode-area double-cladding fibers is investigated for the first time. Theoretical results show that the coupling between the LP mode and cladding modes would destroy the transmission spectra envelope only considering the coupling of LP for single-mode CTFBGs, which will degenerate the SRS suppression performance. This was confirmed experimentally by measuring the spectral response under different mode excitations. A reliable method is demonstrated to ease the LP-excitation-induced spectral deterioration by choosing an appropriate chirp rate for the inscription of CTFBGs, which is useful for improving the Raman suppression effect of large-mode-area double-cladding CTFBGs in high-power fiber lasers.
近年来，啁啾倾斜光纤布拉格光栅（CTFBGs）受到了广泛关注，因为它们能够在高功率光纤激光器中实现受激拉曼散射（SRS）的抑制。在本研究中，首次对大模面积双包层光纤中写入的CTFBGs的纤芯模式与包层模式之间的可能耦合进行了研究。理论结果表明，对于单模CTFBGs，仅考虑LP模式的耦合时，LP模式与包层模式之间的耦合会破坏传输光谱包络，这将使SRS抑制性能退化。通过测量不同模式激发下的光谱响应，这一点在实验中得到了证实。结果表明，通过为CTFBGs的写入选择合适的啁啾率，可以缓解LP激发引起的光谱劣化，这对于提高高功率光纤激光器中大模面积双包层CTFBGs的拉曼抑制效果是有用的。
