Physical Layer Aware Optical Networks

This thesis describes novel contributions in the field of physical layer aware optical networks. IP traffic increase and revenue compression in the Telecom industry is putting a lot of pressure on the optical community to develop novel solutions that must both increase total capacity while being cost effective. This requirement is pushing operators towards network disaggregation, where optical network infrastructure is built by mix and match different physical layer technologies from different vendors. In such a novel context, every equipment and transmission technique at the physical layer impacts the overall network behavior. Hence, methods giving quantitative evaluations of individual merit of physical layer equipment at network level are a firm request during network design phases as well as during network lifetime. Therefore, physical layer awareness in network design and operation is fundamental to fairly assess the potentialities, and exploit the capabilities of different technologies. From this perspective, propagation impairments modeling is essential. In this work propagation impairments in transparent optical networks are summarized, with a special focus on nonlinear effects. The Gaussian Noise model is reviewed, then extended for wideband scenarios. To do so, the impact of polarization mode dispersion on nonlinear interference (NLI) generation is assessed for the first time through simulation, showing its negligible impact on NLI generation. Thanks to this result, the Gaussian Noise model is generalized to assess the impact of space and frequency amplitude variations along the fiber, mainly due to stimulated Raman scattering, on NLI generation. The proposed Generalized GN (GGN) model is experimentally validated on a setup with commercial linecards, compared with other modeling options, and an example of application is shown. Then, network-level power optimization strategies are discussed, and the Locally Optimization Global Optimization (LOGO) approach reviewed. After that, a novel framework of analysis for optical networks that leverages detailed propagation impairment modeling called the Statistical Network Assessment Process (SNAP) is presented. SNAP is motivated by the need of having a general framework to assess the impact of different physical layer technologies on network performance, without relying on rigid optimization approaches, that are not well-suited for technology comparison. Several examples of applications of SNAP are given, including comparisons of transceivers, amplifiers and node technologies. SNAP is also used to highlight topological bottlenecks in progressively loaded network scenarios and to derive possible solutions for them. The final work presented in this thesis is related to the implementation of a vendor agnostic quality of transmission estimator for multi-vendor optical networks developed in the context of the Physical Simulation Environment group of the Telecom Infra Project. The implementation of a module based on the GN model is briefly described, then results of a multi-vendor experimental validation performed in collaboration with Microsoft are shown

Polarization-Related Statistics of Raman Crosstalk in Single-Mode Optical Fibers

We present a novel comprehensive theory for the pump-to-probe interactions caused by the stimulated Raman scattering (SRS) in glass optical fibers. The developed theory applies to both theRaman gainwith the undepleted pump assumption, and to themaximum loss induced by the Raman crosstalk (RXT loss). The latter is an effect that is the limiting propagation impairment in passive optical networks (PON). The main novelty of the paper is a rigorous mathematical analysis, describing the interaction of SRS with the polarization evolution due to polarization mode dispersion (PMD). The Raman gain (or the RXT loss) is modeled as a random process for which a comprehensive theory is developed, giving for the first time to our best knowledge, an exact closed-form expression for the mean and variance of the gain (or depletion), and a computationally efficient algorithm to numerically derive the gain probability density function. The developed theory is validated by the comparison with Monte Carlo analyses, based on the waveplate model for the optical fiber. The validation showed excellent agreement, confirming the validity of the developed theory. As an example of application, we used our theoretical results to analyze next-generation PON (NG-PON2) architectures, confirming that, in this scenario, RXT loss may be a limiting propagation effect

Observing the effect of polarization mode dispersion on nonlinear interference generation in wide-band optical links

With the extension of the spectral exploitation of optical fibers beyond the C-band, accurate modeling and simulation of nonlinear interference (NLI) generation is of the utmost performance. Models and numerical simulation tools rely on the widely used Manakov equation (ME): however, this approach when also considering the effect of polarization mode dispersion (PMD) is formally valid only over a narrow optical bandwidth. In order to analyze the range of validity of the ME and its applicability to future wide-band systems, we present numerical simulations, showing the interplay between NLI generation and PMD over long dispersion-uncompensated optical links, using coherent polarization division multiplexing (PDM) quadrature amplitude modulation (QAM) formats. Using a Monte-Carlo analysis of different PMD realizations based on the coupled nonlinear Schrödinger equations, we show that PMD has a negligible effect on NLI generation, independently from the total system bandwidth. Based on this, we give strong numerical evidence that the ME can be safely used to estimate NLI generation well beyond its bandwidth of validity that is limited to the PMD coherence bandwidth

Internal Communications, Engagement and Trust in a Mission-Based Organization: Examining how the strength of the mission of an organization plays a role in engagement, trust in leadership and communication

This paper describes a SDN-based solution that, by leveraging and coordinating many functionalities that reside at both WDM and Ethernet layers, orchestrates network resources with the aim to maximize host-to-host data transfer rate

A statistical analysis of transparent optical networks comparing merit of fiber types and elastic transceivers

We perform a benchmarking of three different fiber types and two different implementation of flexible rate transceivers in a fixed-grid reconfigurable transparent optical network scenario. Results are obtained through a Monte Carlo based method called the Statistical Network Assessment Process (SNAP). Using the SNAP framework, we derive the statistics of the average bitrate per lightpath on a Pan European network scenario. We consider the average of such metric as a unique merit parameter to compare the use SMF, PSCF or NZDSF. We also consider two different implementations of elastic transceivers, namely one based on pure PM-M-QAM and the other using Time Division Hybrid Modulation Formats (TDHMF). TDHMF always outperforms PM-M-QAM, of 23% in SMF and PSCF and of 27% in the poorer transmission quality NZDSF. Results show that using flexible PM-M-QAM, PSCF are able to support a capacity increase in terms of average bitrate per LP of 48% with respect to NZDSF, while the improvement granted by SMF is 34%