The Impact of Zero-Dispersion Wavelength Fluctuations in a Parametric Amplifier Based on Dual Core Fibers

Fiber optics parametric amplifiers (FOPAs) based on coupled dual-core optical fibers are a promising solution for signal amplification in optical communications due to their flat gain profile[1], low noise-figure, and possibility of operating in phase-sensitive mode without using idler waves [2]. Coupled waveguides can offer as well solutions to phase-matching degradation occurring due to pump attenuation in integrated photonics [3]. Zero-dispersion wavelength (ZDW) fluctuations constitute an important limitation for the FOPA bandwidth. A theoretical analysis of the ZDW fluctuations impact on the gain of a standard single core fiber based FOPA has been presented by Karlsson[4] assuming an Ornstein–Uhlenbeck (OU) process for the fluctuations statistics. Here we present an analytical and numerical analysis of the impact of ZDW fluctuations in a dual-core fiber FOPA. Modelling the ZDW fluctuations as a multidimensional OU process with exponential correlation between the two cores, we have derived an analytical formula for the amplifier average gain and for the gain standard deviation, which we do not report here for the sake of brevity. We have compared analytical predictions with full Montecarlo simulations of the FOPA. Our theory agrees well both with numerical simulations and with experimental measurements (available so far in the single fiber core limit only[5]) as it can be appreciated from Fig. 1 a). In Fig 1 b) we show an example of the average gain spectrum obtained from theory and simulations for a dual core-fiber FOPA. Most importantly we demonstrate that the impact of ZDW fluctuations is less damaging in dual-core fiber FOPAs compared to single core ones: Fig. 1 c), obtained from simulations, shows that the average −3 dB gain bandwidth is about 10 nm larger, and the gain bandwidth fluctuations are in average about 20 nm smaller, for the dual-core fiber FOPA (coupling strength
$C=0.0133\ \mathrm{m}^{-1}$
in the figure legend) compared to the single core one
$(C=0\ \mathrm{m}^{-1})$
for all the values of dispersion fluctuations standard deviation
$\sigma$
considered.