Stimulated Raman generation in two-mode long-length fibers pumped by a mode-locked laser

Single-pass Raman generation pumped by a mode-locked Nd:YAG laser has been investigated for two-mode fibers each 35 km long. From input power dependence of stimulated Raman scattering, it was found that the peak wavelength of the first Stokes jumps dramatically from 1.114 to 1.12 microm at 1.65-W input power and that total output power of the first Stokes also increases rapidly at this power for a fiber with a 1.27-microm cutoff wavelength, when the fiber is pumped at the LP(11) mode exciting condition. These experimental results can be explained by the group delay for LP(01) and LP(11) modes. The maximum interaction length and the threshold power were determined from the group delay, which showed fairly good agreement with the experimental results.