Abstract

We consider the capacity optimization of submarine links when including a realistic model of the constant-pump erbium doped fiber amplifiers (EDFA) with gain-shaping filters (GSF). While Perin et al.[1] numerically attacked this optimization for Constant-Signal (CS) amplified links, we extend the analysis also to constant power-spectral-density (CPSD) links, which mimic the way modern submarine links are gain-designed at cable assembly. Given the practical tolerances in GSF fabrication, the CS and CPSD approaches will be shown to essentially model the same link at large-enough pumps, but the CPSD approach yields a much simpler analysis. As in [1], we concentrate on a single spatial mode of a spatial division multiplexed (SDM) link at low EDFA pump power $P_{p}$ , and thus consider only the impairments of amplified spontaneous emission noise. Here we adopt a novel semi-analytical approach which consists of fixing the inversion $x_{1}$ of the first EDFA (the state-variable of the link) and analytically finding capacity $C(x_{1})$ by searching over the $x_{1}$ -feasible input wavelength division multiplexed (WDM) PSD distributions. Then the optimum inversion $x_{1}$ that maximizes $C(x_{1})$ is numerically obtained. This approach enables us to get both approximate (for CS links) and exact (for CPSD links) capacity-maximizing WDM input distributions, which vary inversely with the EDFA gain profile. For CS links the optimal WDM allocation is called the gain-shaped water-filling. Other practical allocations are analyzed, such as the signal to noise ratio equalizing allocation (CSNR), and the constant input power (CIP) allocation which uses a flat WDM distribution. We find that, for typical submarine span attenuations around 10 dB and when the link works at the optimal inversion $x_{1}$ , CIP and CSNR achieve essentially the same capacity as the optimal allocation. At sufficiently large pump $P_{p}$ ( $\gtrsim 30$ mW) the optimal inversion $x_{1}$ is such that the EDFA gain at 1538 nm equals the span attenuation, for EDFA emission and absorption as in [1]. When span attenuations increase to 20 dB, then we start seeing an advantage of the optimal allocation.

Multicore Fibers for High-Capacity Submarine Transmission Systems

Md. Nooruzzaman and Toshio Morioka
J. Opt. Commun. Netw. 10(2) A175-A184 (2018)

Cost-effective network capacity upgrade by heterogeneous wavelength division multiplexing density with bandwidth-variable virtual direct links

Kazuki Hayashi, Yojiro Mori, and Hiroshi Hasegawa
J. Opt. Commun. Netw. 15(9) D23-D32 (2023)

Optical frequency transfer over submarine fiber links

Cecilia Clivati, Anna Tampellini, Alberto Mura, Filippo Levi, Giuseppe Marra, Pauline Galea, André Xuereb, and Davide Calonico
Optica 5(8) 893-901 (2018)

Theoretical investigations of weakly- and strongly-coupled multi-core fibers for the applications of optical submarine communications under power and fiber count limits

Lin Sun, Junwei Zhang, Gai Zhou, Bin Chen, Gordon Ning Liu, Yi Cai, Zhaohui Li, Chao Lu, and Gangxiang Shen
Opt. Express 31(3) 4615-4629 (2023)

Link optimization for DWDM transmission with an optical phase conjugation

Paweł Rosa, Giuseppe Rizzelli, and Juan Diego Ania-Castañón
Opt. Express 24(15) 16450-16455 (2016)