Marco Bertolini

Cross-Phase Modulation Induced by OOK Channels on Higher-Rate DQPSK and Coherent QPSK Channels

In this paper we show that, in hybrid wavelength division multiplexed systems, the performance of high datatrate QPSK channels impaired by cross-phase modulation (XPM) induced by the lower rate OOK channels can be simply estimated by an extension of a well-known linear model for XPM, and novel analytical expressions of the sensitivity penalty are provided. From such a model we prove that the reported QPSK penalty decrease with QPSK baud rate increase should be attributed to the action of the phase estimation process rather than to the walkoff effect. The model also simply shows how coherent QPSK is more affected by XPM than incoherent DQPSK, and allows to infer that even more impact is expected when the baudrate is further reduced through polarization multiplexing.

Investigation on WDM Nonlinear Impairments Arising From the Insertion of 100-Gb/s Coherent PDM-QPSK Over Legacy Optical Networks

In the perspective of smooth capacity upgrades of legacy systems, we experimentally investigate the performance of one 100-Gb/s coherent polarization-division-multiplexed quaternary-phase-shift-keying (PDM-QPSK) channel inserted in a 10-Gb/s ultra-long-haul (ULH) wavelength-division-multiplexing system relying on nonzero dispersion-shifted fibers. The impact of copropagating 10-Gb/s nonreturn-to-zero (NRZ) channels operating ULH distances onto the operational power range of the inserted 100-Gb/s coherent PDM-QPSK channel is analyzed. Moreover, the performance penalties brought by copropagating 10-Gb/s NRZ channels onto 100-Gb/s PDM-QPSK data are also analyzed depending on the number of channels in the multiplex and on the introduction of guardbands between both type of channels.

Stratified Sampling Monte Carlo Algorithm for Efficient BER Estimation in Long-Haul Optical Transmission Systems

We propose an efficient stratified sampling (SS) algorithm for estimating the bit error rate (BER) of a digital communication system. Our algorithm efficiently exploits the observations of an approximate, but usually fast, model of the system under investigation to drive a clever Monte Carlo (MC) estimation based on SS. The proposed method is faster than standard MC even at BER in the range 10-3 to 10-5 . Moreover, it is possible to evaluate the estimated standard deviation of the measured BER, such as in an MC simulation, so that it is possible to associate a confidence to the results. We test the algorithm both in a simple optical system distorted by group velocity dispersion (GVD) and in more complex differential quadrature phase shift keying (DQPSK) systems. In the last case, we measured computational savings up to 70% compared with standard MC.

Monte Carlo Estimation of PDM-QPSK/OOK and DQPSK/OOK Hybrid Systems Tolerance Against Nonlinear Effects

We compare through Monte Carlo simulations the performance of polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK)/on-off keying (OOK) and differential QPSK (DQPSK)/OOK hybrid systems, taking into account nonlinear phase noise. DQPSK turns out to be better with optimal dispersion-management, while PDM-QPSK proves to be a good candidate for bit rates higher than 40 Gb/s.

PDM-QPSK: on the system benefits arising from temporally interleaving polarization tributaries at 100Gb/s.

We experimentally study, over a dispersion-managed link relying on low chromatic dispersion fibre, the origins of the system benefits provided by temporally interleaving the polarization tributaries of 100Gb/s coherent RZ-PDM-QPSK by half a symbol period. Hence, we demonstrate that the amount of benefits provided by this technique is dependent on the configuration of the WDM transmission system.

Numerical Monte Carlo comparison between coherent PDM-QPSK/OOK and incoherent DQPSK/OOK Hybrid systems

We asses through Monte Carlo simulations PDM-QPSK/OOK and DQPSK/OOK Hybrid systems performance. DQPSK works better with optimal dispersion-management. PDM-QPSK is more robust to system impairments.

Narrow filtered DPSK: An attractive solution for Hybrid systems

We propose an efficient Hybrid system based on 40G DQPSK and 10G narrow filter DPSK in place of OOK. This technique reduces XPM on DQPSK channels at low inline dispersion.

XPM reduction in hybrid 10G/40G transmission using 10-Gb/s narrow-filtered DPSK modulation

We propose a possible improvement for optical hybrid transmission systems, based on 40G differential quadrature shift Keying (DQPSK) and 10G differential phase shift keying (DPSK) received by means of a Gaussian narrow filter. We report a reduced cross phase modulation (XPM), at the cost of a slightly more complex setup. This technique is especially effective for systems with low inline dispersion and offers similar performances on different types of fiber.

A stratified sampling Monte Carlo algorithm for efficient BER measurement and its application to DQPSK terrestrial systems

We propose an efficient stratified sampling algorithm for BER estimation and apply it to FEC-coded DQPSK systems. We measured computational savings up to 70% compared with standard Monte Carlo.