A theoretical and experimental investigation of catastrophic amplification of broadband noise in optical fibers near the zero-dispersion frequency (v(0)) pumped by two lasers with frequencies that are symmetrically tuned relative to v(0) is presented. The effect is due to a four-wave mixing (FWM) process, phase matched up to third-order dispersion, between the spectral components of noise and the lasers. We observed a FWM gain of 16 dB (10-dB net gain) over a 22-nm bandwidth (limited by fourth-order dispersion) for 18-dBm power lasers at +/-1 THz (8 nm) from v(0) in a 25-km-long dispersion-shifted fiber. A simple analytical model is proposed that will permit us to investigate this effect numerically in amplified links with concatenated amplifiers and consider random fluctuations of v(0) along the fiber. (C) 2001 Optical Society of America.181014281435