Blind modulation format identification for digital coherent receivers.

In this paper, a simple novel digital modulation format identification (MFI) scheme for coherent optical systems is proposed. The scheme is based on the evaluation of the peak-to-average-power ratio (PAPR) of the incoming data samples after analog-to-digital conversion (ADC), chromatic dispersion (CD) and polarization mode demultiplexing (PMD) compensation at the receiver (Rx). Since at a particular optical-signal-to-noise ratio (OSNR) value different modulation formats have distinct PAPR values, it is possible to identify them. The proposed scheme and the results are analyzed both experimentally and through numerical simulations. The results demonstrate successful identification among four modulation formats (MF) commonly used in digital coherent systems.

Physical exercise reduces synthesis of ADMA, SDMA, and L-Arg.

Increased levels of asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and low plasma level of L-arginine (L-ARG) are all conditions likely to decrease nitric oxide (NO) production. Aim of this study is to evaluate ADMA, SDMA, and L-ARG plasmatic levels before and after physical exercise in patients with coronary artery disease (CAD). We studied 30 patient with mean age 52 + 4.5 years. After inclusion in the study, before the execution of physical exercise, heparinized blood sample was drawn from an indwelling arterial line for determination of ADMA, L-ARG and SDMA (baseline values). Subsequently a blood sample was drawn after the physical exercise. The mean plasma concentrations of ADMA (0.68 + 0.06 vs 0.48 + 0.05 µmol/L) and SDMA (0.45 + 0.03 vs 0.30 + 0.03 µmol/L) were significantly lower after physical exercise in comparison to baseline value, while L-ARG mean levels were increased (44.20 + 10.5 vs 74.13 + 11.2 µmol/L). Physical exercise has a beneficial effect by reducing plasmatic ADMA and SDMA levels, and increasing L-ARG substrate for endothelial NO.

EGN model of non-linear fiber propagation.

The GN-model has been proposed as an approximate but sufficiently accurate tool for predicting uncompensated optical coherent transmission system performance, in realistic scenarios. For this specific use, the GN-model has enjoyed substantial validation, both simulative and experimental. Recently, however, it has been pointed out that its predictions, when used to obtain a detailed picture of non-linear interference (NLI) noise accumulation along a link, may be affected by a substantial NLI overestimation error, especially in the first spans of the link. In this paper we analyze in detail the GN-model errors. We discuss recently proposed formulas for correcting such errors and show that they neglect several contributions to NLI, so that they may substantially underestimate NLI in specific situations, especially over low-dispersion fibers. We derive a complete set of formulas accounting for all single, cross, and multi-channel effects, This set constitutes what we have called the enhanced GN-model (EGN-model). We extensively validate the EGN model by comparison with accurate simulations in several different system scenarios. The overall EGN model accuracy is found to be very good when assessing detailed span-by-span NLI accumulation and excellent when estimating realistic system maximum reach. The computational complexity vs. accuracy trade-offs of the various versions of the GN and EGN models are extensively discussed.

Extension and validation of the GN model for non-linear interference to uncompensated links using Raman amplification.

We show the extension of the Gaussian Noise model, which describes non-linear propagation in uncompensated links of multilevel modulation formats, to systems using Raman amplification. We successfully validate the analytical results by comparison with numerical simulations of Nyquist-WDM PM-16QAM channels transmission over multi-span uncompensated links made of a single fiber type and using hybrid EDFA/Raman amplification with counter-propagating pumps. We analyze two typical high- and low-dispersion fiber types. We show that Raman amplification always induces a limited non-linear interference enhancement compared to the dominant ASE noise reduction.

Experimental demonstration of a frequency-domain Volterra series nonlinear equalizer in polarization-multiplexed transmission.

Employing 100G polarization-multiplexed quaternary phase-shift keying (PM-QPSK) signals, we experimentally demonstrate a dual-polarization Volterra series nonlinear equalizer (VSNE) applied in frequency-domain, to mitigate intra-channel nonlinearities. The performance of the dual-polarization VSNE is assessed in both single-channel and in wavelength-division multiplexing (WDM) scenarios, providing direct comparisons with its single-polarization version and with the widely studied back-propagation split-step Fourier (SSF) approach. In single-channel transmission, the optimum power has been increased by about 1 dB, relatively to the single-polarization equalizers, and up to 3 dB over linear equalization, with a corresponding bit error rate (BER) reduction of up to 63% and 85%, respectively. Despite of the impact of inter-channel nonlinearities, we show that intra-channel nonlinear equalization is still able to provide approximately 1 dB improvement in the optimum power and a BER reduction of ~33%, considering a 66 GHz WDM grid. By means of simulation, we demonstrate that the performance of nonlinear equalization can be substantially enhanced if both optical and electrical filtering are optimized, enabling the VSNE technique to outperform its SSF counterpart at high input powers.

Novel figure of merit to compare fibers in coherent detection systems with uncompensated links.

We introduce an improved fiber figure of merit (FoM) in order to compare different fiber types used in uncompensated links for transmission of coherently-received modulation formats. The role of fiber dispersion in enhancing system performance is shown and verified by simulations and experiments, confirming the need for the inclusion of dispersion parameter in a FoM definition allowing to compare fiber types with relevant different dispersion parameters. Applicability of the proposed FoM has been demonstrated for channel spacing from the Nyquist limit up to 5/3 the symbol rate.