Nonlinear Compensation Using Digital Back-Propagation in Few-Mode Fibre Spans with Intermediate Coupling

We investigate for the first time the performance of virtual back-propagation using multimode Manakov equations, derived for the weak- and strong-coupling regimes, after forward-propagation using a fully stochastic model over all linear coupling regimes

Nonlinear Performance of Few-Mode Fiber Links with Intermediate Coupling

This paper reviews and extends the study of nonlinear performance of few-mode fiber links operating in all different linear coupling regimes for different mode delay maps. Nonlinear performance was estimated using the four-wave-mixing theory and the split-step Fourier method including semi-analytical solutions for linear mode coupling of arbitrary strength. The optimum link configurations minimizing the nonlinear penalty at practical levels of training sequence length are presented, including: the required coupling strength to give nonlinear distortion below that of the single-mode propagation without mode coupling, and the impact of mode delay maps. Finally, different approximate solution methods of the multimode nonlinear Schr-dinger equation are compared, highlighting the accuracy of a stochastic solution method including distributed linear mode coupling

On the Feasibility of Mode-Division Multiplexed Transmission over Few-Mode Fibres

This paper reviews our most recent results on mode-division multiplexing systems based on few-mode fibres with low differential mode delay, spanning from the fibre design optimization to receiver memory dimensioning. First, an optimized refractive-index profile for low differential mode delay and low macro-bend losses is presented. Afterwards, we present a semi-analytical model of the linear mode coupling induced by fibre imperfections and stress. Finally, the interplay between the linear mode coupling and the differential mode delay is studied numerically and analytically, allowing to quantify the receiver memory required for a given fibre span

Nonamplified 100Gbps Doubly Differential QPSK Optical Signal Transmission Over 80 km SSMF Without Carrier Recovery

We numerically demonstrate a nonamplified 100-Gb/s doubly differential QPSK signal transmission over 80-km SSMF without carrier recovery or chromatic dispersion compensation. The receiver sensitivity after 80-km SSMF transmission was below -28.8 dBm for frequency offsets up to 2 GH

200-Gb/s Polarization Multiplexed Doubly Differential QPSK Signal Transmission over 80-km SSMF Using Tandem SSB without Optical Amplification

We propose 200-Gb/s polarization multiplexed tandem SSB DDQPSK with intradyne detection for 80-km SSMF transmission. Without optical amplification, dispersion compensation or carrier recovery, the simulated receiver sensitivity for 80-km transmission was below -25.5 dBm (at 7% HDFEC threshold)

Amplifier-free 200-Gb/s tandem SSB doubly differential QPSK signal transmission over 80-km SSMF with simplified receiver-side DSP

We numerically demonstrate 80-km standard single-mode fiber transmission without optical amplification, dispersion compensation or carrier recovery using 200-Gb/s tandem single sideband modulated doubly differential QPSK. Simulation results show that doubly differential encoding enables practically constant system performance for frequency offsets within ± 2.3 GHz and allows a linewidth tolerance of 2.5 × 10−3 at 1-dB receiver sensitivity penalty. Employing 2.9-MHz linewidth lasers, the receiver sensitivity penalty at 7% HD-FEC threshold for 80-km transmission is less than 0.2 dB. By adding a 12-symbol decision feedback in the 2nd differential operation of doubly differential decoding, the receiver sensitivity is improved by 3.7 dB

Advantages of strong mode coupling for suppression of nonlinear distortion in few-mode fibers

Nonlinear distortion in few-mode fibers for intermediate coupling is studied for the first time. Coupling strengths beyond -20 dB/100m give suppression of nonlinear distortion below the isolated mode without mode coupling

Semi-analytical modelling of linear mode coupling in few-mode fibers

This paper reviews and extends a method for the semi-analytical solution of the coupled linear differential equations that describe the linear mode coupling arising in few-mode fibers due to waveguide imperfections. The semi-analytical solutions obtained proved to be accurate when compared to numerical solution methods. These solutions were integrated into a multi-section model with split-steps for mode dispersion and mode coupling. Simulations using this model matched the analytical predictions for the statistics of group-delays in few-mode fiber links, considering different coupling regimes with and without mode delay management

Training-Aided Channel Estimation and Equalization in SDM Systems with MISO Pre-convergence under Strong Coupling

A simple DSP scheme receiver is proposed to circumvent laser frequency-offset effects in DA-CE based SDM systems using a MISO CMA pre-convergence stage. Numerical results demonstrate a successful operation for 12-mode fiber transmission under MDL, using QPSK and 16QAM mapping

Nonlinearity compensation using optical phase conjugation deployed in discretely amplified transmission systems

We introduce a closed form equation, validated by simulations and experimental results, that predicts the residual nonlinear noise ratio in mid-link OPC assisted discretely amplified systems. The model anticipates the reduction in performance enhancement achieved by mid-link OPC as the bandwidth of the modulated signals increases. The numerical analysis shows that uncompensated signal-signal interactions limit the performance improvement achieved by the introduction of additional OPCs. The numerical analysis predicts that the deployment of shorter amplifier spacing will lead to a greater performance enhancement. The numerical results are validated by experimentally testing of 2x, 4x, and 8x28Gbaud PM-QPSK systems with mid-link OPC compensation in a discretely amplified system with 100km amplifier spacing. The experimentally obtained reach enhancement (43%, 32%, and 24% for 2x28Gbaud, 4x28Gbaud, and 8x28Gbaud, respectively) confirms that the compensation efficiency of mid-link OPC is highly dependent on the number of channels (bandwidth) propagating along the system