Investigation of the gain spectrum near the pumps of two-pump fiber-optic parametric amplifiers

We investigated the gain of two-pump fiber-optic parametric amplifiers (OPAs) when the signal is close to one pump. We considered all eight types of OPAs introduced in [J. Opt. Soc. Am. B 20, 2425 (2003)], and we extended the analysis of that paper from a four- to a six-wave model. We started from six coupled-wave equations and derived exact expressions for the parametric gain coefficients in all cases. The results were verified by simulations based on the split-step Fourier method. We found a variety of possible behaviors: the gain near the pumps may be higher or lower than the gain at the center wavelength, depending on the type of OPA and the operating conditions. In addition, the gain spectrum generally exhibits narrow peaks or dips on either side of the pumps. However, for one type of OPA the gain predicted by the six-wave model is the same as that predicted by the four-wave model, and the gain spectrum is very smooth near the pump. (c) 2007 Optical Society of America.