New dispersion-compensated Raman-amplifier cascade with a single-pump parametric amplifier for dense wavelength-division multiplexing

In this work a dispersion-compensated Raman amplifier has been cascaded with a single-pump parametric amplifier to build a dense wavelengthdivision multiplexed (DWDM) system. This hybrid system demonstrates a flat gain in the L-band. Our hybrid has been evaluated for a 25 GHz 96-channel system at 40 Gbps in the band spreading from 189 to 191.375 THz. The results demonstrate the gain larger than 16.9 dB and the gain ripple less than 5.82 dB, with no gainflattening technique used. The novelty of our design lies in combining dispersion compensation with signal amplification in a long-length Raman-amplifier fibre followed by a short-length parametric amplifier implemented on a separate highly nonlinear fibre. For the data rate 10 Gbps, the achievable gain ripple is as low as 1.9 dB, without any gain-compensation technique. The optical signal-to-noise ratio larger than 18 dB and the flat gain confirm that our Raman fibre-optic parametric amplifier can be used as a tunable and broad-gain amplifier for the future long-haul DWDM systems. The results obtained for our system have been compared with those of the L-band optical amplifiers developed recently. The comparison testifies that our amplifier is the best of all existing analogues.