Theory of the Synchronously Pumped Fiber Raman Laser

Analyses of the synchronously pumped fiber Raman laser are presented under the parabolic approximation for gain shaping in both frequency and time domains, A master equation for the Stokes pulse consists of the group velocity dispersion of the fiber, the gain dispersion of the stimulated Raman scattering, a gain-shaping term due to the pump curvature, small depletion, and a walk-off effect. The pump power dependences of the Stokes power and the pulse width and the threshold condition are revealed. The frequency tunability of the present laser is also discussed. It is shown that the oscillation wavelength (carrier frequency of the Stokes pulse) will change linearly with Stokes power because of walk off during depletion.