Unified analysis of coherence property of a Stokes wave generated via a stimulated Raman process in optical fiber

We investigate the evolution of coherence property of a noise-seeded Stokes wave in short (<1ps) and long pulse (>1ps) regimes numerically through a set of coupled nonlinear equations. The simulations include quantum noise by incorporating noise seed in the pump field. The spectral phase fluctuations of the Stokes wave for both regimes are characterized, and the degrees of first-order mutual spectral coherence are calculated for different conditions. Statistical analysis demonstrates the effect of spectral coherence of the Stokes wave in optical fiber on pump power, fiber length, and pump pulse width for short and long pulse regimes. It is observed that the noise-seeded stimulated Raman process causes degradation of spectral coherence with the increase in pump power, fiber length, and pulse width of the pump wave. The degradation of the spectral coherence is manifested by the transition of the Stokes wave from a quasi-coherent to incoherent spectrum.