The Generalized Droop Formula

TL;DR

This paper introduces a theoretical model supporting the generalized droop formula (GDF) for calculating SNR in low-SNR, nonlinear optical links, outperforming traditional Gaussian noise models, especially in complex amplifier configurations.

Contribution

The paper provides a comprehensive theoretical foundation for the GDF, extending its applicability to various amplifier types and nonlinear regimes, surpassing existing models like the GN model.

Findings

GDF accurately models SNR in highly nonlinear systems

GDF extends to partially filled bandwidths and different amplifier types

GDF outperforms traditional GN models in complex scenarios

Abstract

We present a theoretical model that fully supports the recently disclosed generalized droop formula (GDF) for calculating the signal-to-noise ratio (SNR) of constant-output power (COP) amplified dispersion-uncompensated coherent links operated at very low SNR. We compare the GDF to the better known Gaussian noise (GN) model. A key finding is that the end-to-end model underlying the GDF is a concatenation of per-span first-order regular perturbation (RP1) models with end-span power renormalization. This fact allows the GDF to well reproduce the SNR of highly nonlinear systems, well beyond the RP1 limit underlying the GN model. The GDF is successfully extended to the case where the bandwidth/modes of the COP amplifiers are not entirely filled by the transmitted multiplex. Finally, the GDF is extended to constant-gain (CG) amplifier chains and is shown to improve on known GN models of highly nonlinear propagation with CG amplifiers.