Dynamical evolution of multiple four-wave-mixing processes in an optical fiber

We present unique results of detailed experimental and theoretical investigations of the dynamical evolution of four-wave-mixing spectra in an optical fiber. The experimental measurements probe the evolution of sidebands generated through four-wave mixing as they copropagate with the pumps along the fiber. We find that standard theoretical models are inadequate to predict the experimental results and that it is necessary to modify the approach to modeling the dynamics in two ways. The first modification is to include a pump laser input with multiple longitudinal modes. This reflects the fact that the pump laser fields may actually have internal structure that is not resolved by the spectrometer used and is very small compared to the spacing of the central frequencies of the pump fields. Yet the evolution of the fields is dramatically altered for the sidebands generated by nonlinear processes in the fiber medium. The second is the inclusion of phase noise added along the propagation length; this causes damping of the sideband oscillations. These two modifications lead to excellent agreement of the measurements with numerical predictions of the sideband evolution.