Study on Stimulated Raman Scattering Threshold Over Two-Mode Fiber

We investigate the stimulated Raman scattering (SRS) threshold ${{\bm{P}}}$ th for two-mode propagation state in two-mode fiber (TMF). We evaluated a model that can approximately derive the ${{\bm{P}}}$ th for the two-mode propagation state by the product of the effective area ${{{\bm{A}}}_{{\bm{eff}}}}$ and intensity ratio of each mode. We experimentally confirm that ${{\bm{P}}}$ th is increased with increasing 2nd mode (i.e., 1st higher-order mode) intensity ratio, and the derived values from our model agree well with the experimental results. From our proposed model, we showed that ${{\bm{P}}}$ th degradation due to modal crosstalk at the splice point is sufficiently small under conventional splicing conditions in the transmission links. Additionally, we confirmed that there is no mode dependence in the absorption spectrum due to SRS, and even if 2nd and 1st mode (i.e., fundamental mode) are utilized as the feed light and signal light, respectively, the signal light needs to be set to a shorter wavelength than the feed light by at least 0.2 μm.