Petros Ramantanis

Mode coupling at connectors in mode-division multiplexed transmission over few-mode fiber

In mode-division multiplexed (MDM) transmission systems, mode coupling is responsible for inter-modal crosstalk. We consider the transmission of modulated signals over a few-mode fiber (FMF) having low mode coupling and large differential mode group delay in the presence of a non-ideal fiber connection responsible for extra mode coupling. In this context, we first analytically derive the coupling matrix of the multimode connector and we numerically study the dependence of the matrix coefficients as a function of the butt-joint connection characteristics. The numerical results are then validated through an experiment with a five-mode setup. Finally, through numerical simulations, we assess the impact of the connector on the signal quality investigating different receiver digital signal processing (DSP) schemes.

Nonlinear interference noise statistics in unmanaged coherent networks with channels propagating over different lightpaths

We show that a non pre-dispersed channel suffers a phase-noise-like nonlinear interference from neighboring channels with high cumulated pre-dispersion. In such a configuration we quantify the impact of fiber type and the relative Q-factor penalty.

Faster return of investment in WDM networks when elastic transponders dynamically fit ageing of link margins

We illustrate the cost reduction during 10-year life of a core WDM network enabled by elastic transponders when accounting directly for end-of-life OSNR detection margins, compared to margins progressively growing with network ageing.

Experimental investigation of the validity domain of the Gaussian noise model over dispersion managed systems

We measure the span-to-span noise covariance as indicator of Gaussian noise model accuracy over dispersion-managed systems. We found that covariance shouldnt exceed 1/3 of variance, which occurs once residual dispersion per span exceeds 60ps/nm.

Pitfalls of error estimation from measured non-Gaussian nonlinear noise statistics over dispersion-unmanaged systems

In dispersion-unmanaged 100-Gbit/s single-channel transmission, the one-to-one relationship between error-rate and noise variance does not hold at high powers. More accurate error assessment than with Gaussian modeling can be obtained by involving high order statistics.

On the performance prediction of optical transmission systems in presence of filtering

We investigate the impact of optical filtering from routing nodes in optical networks, and how to predict it. From measurements in presence of tight optical filtering, we propose a new method relying on an extended back-to-back model for improved prediction of the quality of transmission.

Cost benchmarking when deploying elastic transponders accounting for margins ageing versus when deploying only 100 Gb/s interfaces

We compare the cost efficiency of optical networks based on elastic transponders when accounting for link margins due to network ageing and on fixed 100 Gb/s PDM-QPSK interfaces technologies. Germany50 and Italian photonic backbone networks are used for providing results during a 10-year period given different throughputs, traffic growth rates and the cost erosions of elastic optical transponders. We also investigate the distribution of the ageing margins and modulation schemes that might be changed during the life of the network, before its end-of-life (EoL).

Semi-blind joint phase tracking, parameter estimation and detection in the context of nonlinear channels with memory

We consider a transmission system, where the emitted symbols are subject to unknown nonlinear intersymbol interference. Several methods have been proposed in the literature to mitigate the degradation introduced by such channels. However, the problem of nonlinear channel identification in the presence of carrier phase noise has not been addressed previously.In this paper, we derive an iterative receiver structure to detect the transmitted symbols, jointly with phase and channel estimation. At each iteration, the channel parameters are refined based on the expectation-maximization (EM) approach. Also, a pseudo maximum-likelihood (pseudo-ML) carrier recovery, operating in a decision-directed mode, re-estimates the time-varying phase at each iteration. The proposed technique is semi-blind, since a short training sequence is needed to initialize the phase and channel coefficients properly.We show that the proposed scheme allows symbol detection performances close to the genie-aided detector with data-aided channel coefficient estimation. Moreover, a theoretical analysis of the residual phase error confirms that coherent detection in the presence of strong phase noise is achieved. Numerical simulations are presented for systems with severe nonlinear distortions, including satellite communications with nonlinear amplifiers and coherent optical fiber transmissions. HighlightsEM parameter estimation of nonlinear channels with equalization and carrier recovery.Only a small number of known pilot symbols are required.Application to satellite links with HPA and dispersion managed optical fibers.