Reduction of four-wave mixing in raman amplified optical transmission systems

An optical transmission system comprising

• an optical fiber path, said optical fiber exhibiting a nonlinear susceptibility so as to cause four-wave mixing between various optical waves passing therethrough;
• an optical signal source for providing an input optical signal, said optical signal source coupled to said optical fiber path;
• and
• at least two separate optical pump sources, coupled to said optical fiber transmission path, for introducing separate Raman gain amplification pumps at first and second wavelengths λC and λL onto said optical fiber path and providing Raman gain to the input optical signal passing therethrough, wherein the first and second wavelengths are chosen such that none of the four-wave mixing products of said first and second pump wavelengths coincide with the input signal wavelength, the pumps providing a composite gain spectrum whose width is at least 50% larger than the width of the gain spectrum associated with a monochromatic pump, where gain spectrum width is measured at the gain equal to one-half the peak gain in decibels.