NONLINEAR DISPERSION EFFECTS IN A BROAD-BAND RAMAN AMPLIFIER

We report the dependence of Raman gain on the correlation between the pump and the Stokes waves in a broadband Raman amplifier. Experimental ly, the Raman correlation function is obtained by measurement of the S tokes output energy as a function of pump delay. When the Stokes wave precedes the pump, the Stokes output is larger than in the opposite ca se. The correlation function becomes more asymmetric as the pump energ y increases. We propose that this asymmetry is caused by the nonlinear Raman dispersion. Using a multimode model, we perform numerical simul ations to confirm this idea. The results of the simulations agree well with the experimental data. (C) 1995 Optical Society of America