On the SNR Statistics in Coupled-Core Multi-Core Fiber Transmissions with Mode-Dependent Loss

Abstract

We investigate the impact of mode-dependent loss (MDL) on the statistics of the signal-to-noise ratio (SNR) in coupled-core multi-core fiber (CC-MCF) systems. Through numerical and theoretical simulations, we present an in-depth analysis of the impact of MDL on received amplified spontaneous emission (ASE) noise and nonlinear interference (NLI), as well as their joint contribution to the SNR. We show that MDL induces different statistics on the two noises and discuss the differences with single-mode polarization-dependent loss. Moreover, we investigate the impact of spatial mode dispersion (SMD) on the MDL-induced impairment, offering insights on their joint effects on ASE and NLI.

Figures (11)

• Figure 1: Probability density function of the system MDL expressed in dB. Results obtained from $10^{4}$ random realizations of the MDL transfer matrix, built by concatenation of $K=256$ sections. Top: single core. Bottom: four strongly coupled cores. Squares: distribution of a randomly-picked singular value of $\mathbf{M}$. Dots: marginal distribution of the $2N$ order statistics. Solid lines: expressions from Ho2011.
• Figure 2: Schematic MDL accumulation in a two-span optical system with lumped MDL and zero-forcing linear equalization. $A$: signal. $w_{i}$ and $n_{i}$: ASE noise and perturbative NLI, respectively, arising in the $i$th span.
• Figure 3: Sketch of the transmission under test. Five dual-polarizarion WDM channels transmitted in each core of 100-km four-core CC-MCFs. The MDL is applied at span end, with the last amplifier recovering the mode-averaged loss. After ten identical spans, ideal equalization of the linear effects and coherent detection are performed, and the SNR of the channel under test is estimated for each MDL realization.
• Figure 4: PDF of $\Delta\mathrm{\text{SNR}}$, i.e., SNR deviation from its mean, for the three cases under test in the absence of SMD. Top (a): core 1 of a four-core CC-MCF, peak-to-peak MDL of each amplifier equal to $1$ dB. Bottom (b): SMF, peak-to-peak PDL of each amplifier equal to $0.5$ dB. Markers: PDF estimated from SSFM results. Solid lines: PDL-GN model Serena20PDL results. Channel power set to maximize the SNR, in the absence of MDL, in both setups.
• Figure 5: Markers: deviation from the mean of the per-polarization SNR of the core under test in different random realizations, in the linear (a) and nonlinear (b) case. Dashed line: average between polarizations. Estimations obtained with the semi-analytical PDL-GN model.