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Investigation on threshold of stimulated Raman scattering in optical fibers

The evolutions of residual pump power and forward Raman Stokes scattering light power with increasing pump power level are investigated by numerical simulation. The Stokes power variation shows obviously threshold characteristic which is similar to that of laser diode, and the pump power corresponding to the maximum of the second derivative of the Raman Stokes signal vs. pump power curve was defined as the pump threshold. A threshold equation was obtained by fitting the results obtained for different fiber characteristic parameters β. Simple experiments were carried out with a pulse pump laser and a 24 km long single mode fiber, and the experimental results agree well with the result obtained threshold equation numerically.