Investigation of dynamical pump control for backward-pumped fiber Raman amplifiers

Abstract

For a broadband backward-pumped distributed fiber Raman amplifier (B-DFRA) operated in long-haul transmission system with massive signal channels, not only the average level but also the tilt of the output power spectrum will vary due to the variation of signal-to-signal Raman scattering. So, when the signal channel number or channel power varies, dynamical control of both the average level and tilt of the on–off gain is necessary. In this paper, an approximate two-dimensional linear expression for the individual pump power at each pump wavelengths versus the average on–off gain level and tilt was derived based on the theoretical analysis and numerical simulation. The method to pre-determine the control constants based on measured data was also introduced. By using this linear relation, output power spectrum clamping over C+L band (1529.1–1602.7 nm) was demonstrated experimentally for a single 100 km B-DFRA and a 6×100 km cascaded hybrid Raman/erbium-doped fiber amplifiers with up to five pump-wavelengths on standard single mode fiber. The average clamping error was less than 0.32 dB for single span and 0.5 dB for 6 spans.