Are few-mode fibres a practical solution to the capacity crunch?

In this paper, we compare the nonlinear Shannon capacity of few-mode fibre systems operating with spatial-temporal digital signal processing to the nonlinear Shannon capacity of single-mode fibre systems operating with spectral-temporal digital signal processing. Combining these results with estimates of digital signal processing complexity for each option offers valuable insights to system designers

An RZ DPSK receiver design with significantly improved dispersion tolerance

We show an improved DPSK receiver design which can increase useful dispersion tolerance by up to a factor of two. The increased dispersion tolerance is achieved through optimization of the optical filter at the receiver and the delay of the Mach-Zehnder interferometer. In this paper we fully explain the concept, quantify the gain and provide an explanation for the operation of the receiver

Towards wide-bandwidth ultra-flat FOPAs

Fibre optical parametric amplifiers (FOPAs) offer the potential for high gain and >100 nm bandwidth at arbitrary wavelengths for increased transmission capacity. We will cover the main principles of the FOPA and discuss our approach to obtaining broad flat gain and performance improvement via simultaneous Raman amplification

Design of an interferometric fiber optic parametric amplifier for the rejection of unwanted four-wave mixing products

We introduce a novel (to our knolwedge) interferometric fiber optic parametric amplifier (FOPA), allowing for the suppression of unwanted four-wave mixing products. We perform simulations of two configurations where one rejects idlers and, the other rejects nonlinear crosstalk from the signal output port. The numerical simulations presented here demonstrate the practical feasibility of suppressing idlers by >28 dB across at least 10 THz enabling the reuse of the idler frequencies for signal amplification and thus doubling the employable FOPA gain bandwidth. We demonstrate it can be achieved even when the interferometer employs real-world couplers by introducing a small attenuation in one of the interferometer arms

Digital Back Propagation Performance in Spatial Multiplexing Systems

We review digital methods to mitigate the Kerr nonlinearity in multi-mode and/or multi-core fibres operating in different operational regimes as determined by differential mode delay and linear mode coupling. The results demonstrate that transmission performance can be more than doubled for feasible fibres characteristics

DISCUS: the distributed core for ubiquitous broadband access

A new end to end architecture based on Long-Reach Passive Optical Network (LR-PON) with wireless integration, a distributed core built of optical transparency islands and an OpenFlow-based control plane, which is being developed in the EU project DISCUS, is described in this paper. The main technological advances and the network modelling and optimization approach are reported

Fibre Optical Parametric Amplifiers for Communications

We present our recent achievements with polarisation-insensitive fibre optical parametric amplifiers (PI-FOPAs) for optical communications. We have demonstrated a robust fully automated (black-box) PI-FOPA operation in the C and L bands simultaneously with gain of ~20 dB and output power over 23 dBm when amplifying polarisation-multiplexed WDM QAM signals and a bursty traffic. Additionally, we have demonstrated a PI-FOPA to amplify WDM signals in the S band and across a continuous bandwidth of 40 nm. Finally, we have demonstrated a power budget improvement of a transient-sensitive link by up to 8 dB when employing a PI-FOPA with noise figure of ~6 dB as a drop-in replacement of an EDFA

Simultaneous demultiplexing, data regeneration, and clock recovery with a single semiconductor optical amplifier-based nonlinear-optical loop mirror

We demonstrate simultaneous demultiplexing, data regeneration and clock recovery at 10Gbits/s, using a single semiconductor optical amplifier–based nonlinear-optical loop mirror in a phase-locked loop configuration

Blind nonlinearity equalization by machine learning based clustering for single- and multi-channel coherent optical OFDM

Fiber-induced intra- and inter-channel nonlinearities are experimentally tackled using blind nonlinear equalization (NLE) by unsupervised machine learning based clustering (MLC) in ∼46-Gb/s single-channel and ∼20-Gb/s (middle-channel) multi-channel coherent multi-carrier signals (OFDM-based). To that end we introduce, for the first time, Hierarchical and Fuzzy-Logic C-means (FLC) based clustering in optical communications. It is shown that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs Hierarchical can compensate more effectively nonlinearities only for low-level modulation formats. FLC also outperforms K-means, Fast-Newton support vector machines, supervised artificial neural networks and a NLE with deterministic Volterra analysis, when employing BPSK and QPSK. In particular, for the middle channel of a QPSK WDM coherent optical OFDM system at optimum -5 dBm of LOP and 3200 km of transmission, FLC outperforms Volterra-NLE by 2.5 dB in Q-factor. However, for a 16-quadrature amplitude modulated single-channel system at 2000 km, the performance benefit of FLC over IVSTF reduces to ∼0.4 dB at a LOP of 2 dBm (optimum). Even when using novel sophisticated clustering designs in 16 clusters, no more than additional ∼0.3 dB Q-factor enhancement is observed. Finally, in contrast to the deterministic Volterra-NLE, MLC algorithms can partially tackle the stochastic parametric noise amplification

On the Performance of Digital Back Propagation in Spatial Multiplexing Systems

Nonlinear performance in spatial multiplexing systems is strongly determined by the interplay between differential mode delay, linear mode coupling, and Kerr nonlinearity. In this article we review and extend the analysis of different solution methods for the linear coupling operator in the coupled nonlinear Schrödinger equation for spatial multiplexed propagation. Numerical solution methods are compared for different operational regimes as determined by differential mode delay and linear mode coupling. Finally, we review and extend the study of digital methods to mitigate the Kerr nonlinearity for arbitrary levels of random linear mode coupling. For the first time, it is shown that in spatial multiplexing systems transmission performance can be improved by reducing the number of back propagated channels for non-negligible levels of differential mode delay