Suppression of WDM four-wave mixing crosstalk in fibre optic parametric amplifier using Raman-assisted pumping

Abstract

Abstract:We perform an extensive numerical analysis of Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPA) in the context of WDM QPSK signal amplification. A detailed comparison of the conventional FOPA and RA-FOPA is reported and the important advantages offered by the Raman pumping are clarified. We assess the impact of pump power ratios, channel count, and highly nonlinear fibre (HNLF) length on crosstalk levels at different amplifier gains. We show that for a fixed 200 m HNLF length, maximum crosstalk can be reduced by up to 7 dB when amplifying 10x58Gb/s QPSK signals at 20 dB net-gain using a Raman pump of 37 dBm and parametric pump of 28.5 dBm in comparison to a standard single-pump FOPA using 33.4 dBm pump power. It is shown that a significant reduction in four-wave mixing crosstalk is also obtained by reducing the highly nonlinear fibre interaction length. The trend is shown to be generally valid for different net-gain conditions and channel grid size. Crosstalk levels are additionally shown to strongly depend on the Raman/parametric pump power ratio, with a reduction in crosstalk seen for increased Raman pump power contribution.

Characterisation of Cascaded Raman-Assisted Fibre Optical Parametric Amplifiers using WDM QPSK Signals

“…To understand and illustrate this phenomenon, three 20dB netgain scenarios were compared for the same 0. A key conclusion of the above is that under a fixed gain condition the RA-FOPA can be operated with lower parametric pump power than the equivalent C-FOPA which results in reduced FWM crosstalk [4]. To understand the behavior, the signal to crosstalk power ratio (S-to-X) was simulated at different wavelengths across the band.…”

“…The Raman-Assisted Fibre Optical Parametric Amplifier (RA-FOPA) has been shown to be a promising candidate for achieving this [2][3][4]. The RA-FOPA combines numerous useful properties of discrete Raman (low crosstalk, non-resonant gain) with those of conventional FOPAs (high gain coefficient, non-resonant gain) to offer a tuneable gain-region and potentially high discrete gain together with a potential for reduced four-wave mixing (FWM) WDM crosstalk over the standard FOPA [3,4].…”

“…In our previous work [4] we reported that the RA-FOPA crosstalk can be minimised by combining a short HNLF length with maximum available Raman pump power and a parametric pump power subsequently-adjusted to achieve the required operating net gain level. In this paper, we extend our previous work by examining the evolution of crosstalk growth in a cascaded series of both RA-FOPAs and conventional FOPAs carrying WDM QPSK signals.…”

20 dB net-gain polarization-insensitive fiber optical parametric amplifier with >2 THz bandwidth

“…Alternatively in the pumped case, the signal input power to the HPL-FOPA is much lower, even though the output power is the same due to the gain experienced by the signals. The signal power thus undergoes a considerably different evolution versus propagation length [24,25]. As such, it might be expected that crosstalk growth be reduced over the unpumped case for the same output power because the signals are at lower power for a higher proportion of propagation distance, thus producing less nonlinearity.…”

Simple geometric interpretation of signal evolution in phase-sensitive fibre optic parametric amplifier

“…Recently, fiber OPA has attracted a great deal of renewed interest as a promising technology for low-noise parametric amplification in high-capacity optical communications [3][4][5][6][7][8][9][10][11][12]. This recent revival of rather classical field is strongly supported by advances in the technology of highlynonlinear fibers (HNLF) with a good figure of merit (high nonlinear coefficient with a reasonably low losses).…”