Experimental Demonstration of Geometrically-Shaped Constellations Tailored to the Nonlinear Fibre Channel

A geometrically-shaped 256-QAM constellation, tailored to the nonlinear optical fibre channel, is experimentally demonstrated. The proposed constellation outperforms both uniform and AWGN-tailored 256-QAM, as it is designed to optimise the trade-off between shaping gain, nonlinearity and transceiver impairments

Achievable rate degradation of ultra-wideband coherent fiber communication systems due to stimulated Raman scattering

As the bandwidths of optical communication systems are increased to maximize channel capacity, the impact of stimulated Raman scattering (SRS) on the achievable information rates (AIR) in ultra-wideband coherent WDM systems becomes significant, and is investigated in this work, for the first time. By modifying the GN-model to account for SRS, it is possible to derive a closed-form expression that predicts the optical signal-to-noise ratio of all channels at the receiver for bandwidths of up to 15 THz, which is in excellent agreement with numerical calculations. It is shown that, with fixed modulation and coding rate, SRS leads to a drop of approximately 40% in achievable information rates for bandwidths higher than 15 THz. However, if adaptive modulation and coding rates are applied across the entire spectrum, this AIR reduction can be limited to only 10%

MB2.1 - Coherent Technologies for Passive Optical Networks (Invited)

To date, optical access networks have been exclusively based on intensity modulation with direct detection. However, recent advances in coherent transceivers offer the potential to overcome the many limitations of these systems. This work reviews such candidate technologies for low complexity coherent optical access networks

Challenges in Modelling Optical Fibres for Spatial Division Multiplexing

We review recent studies of the nonlinear interference in spatial division multiplexing systems. Different solution methods of the multimode Schrödinger equation are compared, highlighting the accuracy of a stochastic solution method including distributed mode coupling

Modeling and mitigation of fiber nonlinearity in wideband optical signal transmission [Invited]

The adoption of open optical networks (OONs) requires the development of open and effective network planning tools, enabling the use of multi-vendor or white-box transport solutions. Such tools for studying and planning optical networks must be able to take into account the physical layer impairments, including fiber nonlinearity. The use of wideband wavelength division multiplexing in OONs, with channel frequencies extending across the short, conventional, and long bands and beyond, offers a pathway to increasing data rates through the installed fiber infrastructure. However, achievable information rates are limited by the resulting signal distortion due to fiber nonlinearity as signal bandwidths are increased, in particular, inter-channel stimulated Raman scattering (ISRS). In this paper, we describe the nonlinear effects observed in wideband transmission systems, and review recently developed analytical tools, based on the Gaussian noise (GN) model of nonlinear interference with the inclusion of ISRS. Using the ISRS GN model, we assess the impact of fiber nonlinearity on the achievable information rates in transmission systems with bandwidths of up to 12 THz. We demonstrate the use of the model in the optimization of launch power spectral profiles for a variety of dynamic gain equalizer arrangements in a 1000 km standard single-mode fiber link, using particle swarm optimization and the steepest descent algorithm. Such nonlinear models and optimization methods could be applied in OON planning tools, for example, in optical link emulators to estimate quality-of-transmission and data throughput, and in impairment-aware software-defined network control and management

A Closed-form Expression for the Gaussian Noise Model in the Presence of Raman Amplification

A closed-form model for the nonlinear interference (NLI) in Raman amplified links is presented, the formula accounts for both forward (FW) and backward (BW) pumping schemes and inter-channel stimulated Raman scattering (ISRS) effect. The formula also accounts for an arbitrary number of pumps, discrete or distributed Raman amplification setup, wavelength-dependent fibre parameters, and launch power profiles. The formula is suitable for ultra-wideband (UWB) optical transmission systems and is applied in a system with 13 THz optical bandwidth corresponding to transmission over the S-, C-, and L- band. The accuracy of the closed-form formula is validated through comparison with numerical integration of the Gaussian noise (GN) model and split-step Fourier method (SSFM) simulations in a point-to-point transmission link.Comment: arXiv admin note: text overlap with arXiv:2210.0906

A Modulation-Format Dependent Closed-form Expression for the Gaussian Noise Model in the Presence of Raman Amplification

A closed-form expression that estimates the nonlinear interference of arbitrary modulation formats in Raman amplified links is presented. Accounting for any pumping schemes and inter-channel stimulated Raman scattering effect, the formula is applied to an optical bandwidth of 20~THz and validated using numerical simulations.Comment: Presented at European Conference on Optical Communications (ECOC) 202

Comparison of Linear and Nonlinear Equalization for Ultra-High Capacity Spectral Superchannels

In ultra-high-speed (>400Gb/s per wavelength), high-spectral efficiency coherent optical communication systems using multi-carrier spectral superchannels, the maximum reach is severely limited due to linear and, foremost, nonlinear impairments. Hence, the implementation of advanced digital signal processing (DSP) techniques in optical transceivers is crucial for alleviating the impact of such impairments. However, the DSP performance improvement comes at the expense of increased cost and power consumption. Given that the computational complexity of the applied linear and nonlinear equalizers is the factor that determines the trade-off between the performance improvement and cost, in this study we provide an extended analysis on the computational complexity of various linear and nonlinear equalization approaches. First, we draw a complexity comparison between a conventional OFDM coherent receiver versus a filter-bank based OFDM receiver and it is shown that the latter provides significant complexity savings. Second, we present a comparison between the digital back-propagation split-step Fourier (DBP-SSF) method and the inverse Volterra series transfer function nonlinear equalizer (IVSTF-NLE) in terms of performance and computational complexity for a 32 Gbaud polarization multiplexed (PM)-16 quadrature amplitude modulation (QAM) OFDM superchannel

A Closed-Form Approximation of the Gaussian Noise Model in the Presence of Inter-Channel Stimulated Raman Scattering

An accurate, closed-form expression evaluating the nonlinear interference (NLI) power in coherent optical transmission systems in the presence of inter-channel stimulated Raman scattering (ISRS) is derived. The analytical result enables a rapid estimate of the signal-to-noise ratio and avoids the need for integral evaluations and split-step simulations. The formula also provides a new insight into the underlying parameter dependence of ISRS on the NLI. Additionally, it accounts for the dispersion slope and arbitrary launch power distributions including variably loaded fiber spans. The latter enables real-time modeling of optical mesh networks. The results is applicable for lumped amplified, dispersion unmanaged, and ultra-wideband transmission systems. The accuracy of the closed-form expression is compared to numerical integration of the ISRS Gaussian noise model and split-step simulations in a point-to-point transmission, as well as in a mesh optical network scenario

Challenges in Extending Optical Fibre Transmission Bandwidth beyond C+L Band and How to Get There

Recently, we demonstrated a record single-mode fibre net throughput of 178.08 Tbit/s. In this paper, we model this experiment, investigating the main limitations and challenges behind this total throughput, together with the details of some approaches to overcome them, and an outlook for the future ultra-wideband network design and optimisation