Gain-flattening of fibre Raman amplifiers using nonlinear pump spectral broadening and pump power modulation

Abstract

We propose a new technique for achieving gain-flattening of fibre Raman amplifiers based on nonlinear pump broadening and rapid pump power modulation. In our experiments, pump broadening of a continuous-wave Raman fibre laser tuned at 1455 nm is achieved by propagation in a non zero dispersion-shifted fibre (NZDSF). The amount of pump broadening is controlled by the pump power delivered into the NZDSF, and the flatness and center wavelength of the gain band is defined by the amount of pump broadening. With a rapid modulation of the pump power, flat gains of 9 dB with 0.2 dB ripples can be obtained in the case of three modulation levels (1.5/1.8/2.1 W) between 1580 and 1630 nm. Gains between 7 and 8.5 dB can be achieved in the spectral region between 1575 and 1640 nm