Simple design method for gain-flattened three-pump Raman amplifiers

We propose a simple and efficient approach to the design of 3-wavelength backward-pumped Raman amplifiers with increased gain flatness over a wide spectral band. Three different methods dealing with the optimization of one or two different simple parameters are studied. Various examples are provided for illustration, and the dependence of both amplifier gain and gain flatness with pump power is shown. Gain flatness in the spectral range of 1,520-1,595 nm of about 1 dB for a 7.5 dB gain and of 1.8 dB for a 13.5 dB gain is demonstrated using only three pumps with wavelengths within the 1,420-1,480 nm interval.