Armando Vannucci

The RP method: a new tool for the iterative solution of the nonlinear Schrodinger equation

An original approach to the solution of the nonlinear Schrodinger equation (NLSE) is pursued in this paper, following the regular perturbation (RP) method. Such an iterative method provides a closed-form approximation of the received field and is thus appealing for devising nonlinear equalization/compensation techniques for optical transmission systems operating in the nonlinear regime. It is shown that, when the nonlinearity is due to the Kerr effect alone, the order n RP solution coincides with the order 2n + 1 Volterra series solution proposed by Brandt-Pearce and co-workers. The RP method thus provides a computationally efficient way of evaluating the Volterra kernels, with a complexity comparable to that of the split-step Fourier method (SSFM). Numerical results on 10 Gb/s single-channel terrestrial transmission systems employing common dispersion maps show that the simplest third-order Volterra series solution is applicable only in the weakly nonlinear propagation regime, for peak transmitted power well below 5 dBm. However, the insight in the nonlinear propagation phenomenon provided by the RP method suggests an enhanced regular perturbation (ERP) method, which allows the first order ERP solution to be fairly accurate for terrestrial dispersion mapped systems up to launched peak powers of 10 dBm.

Fast and Efficient Dynamic WDM Semiconductor Optical Amplifier Model

A novel state-variable model for semiconductor optical amplifiers (SOAs) that is amenable to block diagram implementation of wavelength division multiplexed (WDM) signals and fast execution times is presented. The novel model is called the reservoir model, in analogy with similar block-oriented models for Raman and erbium-doped fiber amplifiers (EDFAs). A procedure is proposed to extract the needed reservoir model parameters from the parameters of a detailed and accurate space-resolved SOA model due to Connelly, which was extended to cope with the time-resolved gain transient analysis. Several variations of the reservoir model are considered with increasing complexity, which allow the accurate inclusion of scattering losses and gain saturation induced by amplified spontaneous emission. It is shown that at comparable accuracy, the reservoir model can be 20 times faster than the Connelly model in single-channel operation; much more significant time savings are expected for WDM operation. The model neglects intraband SOA phenomena and is thus limited to modulation rates per channel not exceeding 10 Gb/s. The SOA reservoir model provides a unique tool with reasonably short computation times for a reliable analysis of gain transients in WDM optical networks with complex topologies

The performance of polarization switched-QPSK (PS-QPSK) in dispersion managed WDM transmissions

We investigate for the first time the performance of PS-QPSK in WDM nonlinear propagation. We show that the theoretical performance improvement of PS-QPSK compared to PDM-QPSK is even larger in nonlinear propagation.

Statistics of the Jones matrix of fibers affected by polarization mode dispersion

We carry out a statistical characterization of Jones matrix eigenvalues and eigenmodes to gain deeper insight into recently proposed fiber models based on Jones matrix spectral decomposition. A set of linear dynamic equations for the Pauli coordinates of the Jones matrix is established. Using stochastic calculus, we determine the joint distribution of the retardation angle of the eigenmodes and, indirectly, their autocorrelation function. The correlation bandwidth of the eigenmodes is found to be radical2/3 that of the polarization mode dispersion vector. The results agree well with simulations performed with the standard retarded plate model.

Intra- Versus Inter-Channel PMD in Linearly Compensated Coherent PDM-PSK Nonlinear Transmissions

We investigate the interaction between Kerr nonlinearity and polarization mode dispersion (PMD) in homogeneous multi-channel polarization division multiplexing coherent phase shift keying transmissions. Assuming linear distortions can be fully equalized by the coherent receiver, we concentrate the investigation on the residual nonlinear penalty. We introduce a novel simulation procedure to discriminate intra-channel PMD, i.e., PMD within the channel, from inter-channel PMD, i.e., PMD among different channels, showing their relative impact on system performance in the nonlinear regime. A simple yet effective description of intra-channel PMD is proposed, which helps identify the PMD realizations giving the best/worst performance in the nonlinear regime. We show that on average PMD improves the performance of dispersion-managed links by reducing both nonlinear interactions among signals and nonlinear phase noise, while it has no effect in non-dispersion managed links.

Experimental statistical assessment of XPM impact on optical PMD compensator efficiency

In this paper, we report experiments on the statistical assessment of the reduction of PMD mitigator efficiency in presence of XPM effects. The XPM-induced depolarization limits compensation in polarization dispersive ultra-long haul system at 10 Gb/s.

Optical Fiber Sensors for Label-Free DNA Detection

Optical fiber-based biosensors are an emerging field of research with an extremely broad area of possible applications and a disruptive potential to turn the paradigm known as lab-on-fiber into reality. In the past few years, a variety of system choices has been explored, ranging from the type of sensing fiber, to the optical transducing element, to possible sensing amplification strategies. We revise some of the possible approaches to the design of a biosensor, highlighting their advantages and disadvantages, based on previous literature and on the experience of our research groups. The discussion is focused onto DNA sensing systems, especially in a label-free format, where the hybridization and recognition of the sought DNA sequence is translated directly into a modification of the optical fiber properties.

Performance characterization and guidelines for the design of a counter-propagating nonlinear lossless polarizer

We characterize the performance of a nonlinear lossless polarizer, an all-optical fiber-based device that allows for the control of the state of polarization of an optical signal. The device relies on the lossless polarization attraction generated by the nonlinear interaction between the controlled signal and a controlling pump. Choosing a counter-propagating pump, we quantify its performance by introducing the degree of attraction (DOA), which highlights the trade-off between the average attraction of the signal polarization and the unavoidable degradation of its degree of polarization (DOP). We investigate, by numerical simulations, the dependence of the DOA on the injected power and on the fiber length, thus providing the design guidelines to reach the desired performance. We find that an effective attraction can occur even for strongly unbalanced signal and pump power levels, and that fibers longer than a few kilometers yield only a marginal improvement of the DOA.

A simple formula for the degree of polarization degraded by XPM and its experimental validation

We derive a closed-form expression for the DOP of polarized signals affected by XPM, in a modulated pump-probe scheme. Results are checked against simulations and experiments on a dispersion managed 3 /spl times/100 km link.

Is there life beyond the principal states of polarization

In this paper we show that it is possible to describe exactly the field intensity distorted by polarization mode dispersion (PMD) at the output of a single-mode fiber, without resorting to the principal states of polarization (PSPs). Such description is based on the eigenmodes of what we call the extracted matrices,for which we establish relationships with the PSPs, e.g., by showing their alignment with the PSPs when these are not depolarized over the signal bandwidth. We also show that the eigenmodes of the extracted matrices are less depolarized than the PSPs, and are thus the most convenient frame of reference to express the output field and intensity for high bit rate transmitted signals. We thoroughly investigate the properties of a recently introduced fiber model, which we refer to as the rotation model, based on the rotation of the extracted eigenmodes, which extends the intuition of Bruyere’s PSPs rotation model (1996) to the most stable frame of reference, and hence is expected to give the most accurate description of the PMD fiber for large bandwidth signals. We finally provide a novel eye closure penalty (ECP) formula based on the extracted eigenmodes, and show its relation with the currently available ECP formulas. The accuracy of the novel ECP formula is tested against simulation results of transmission through a fiber synthesized by the rotation model.