On the Filter Narrowing Issues in Elastic Optical Networks

This paper describes the problematic filter narrowing effect in the context of next-generation elastic optical networks. First, three possible scenarios are introduced: the transition from an actual fixed-grid to a flexigrid network, the generic full flexi-grid network, and a proposal for a filterless optical network. Next, we investigate different transmission techniques and evaluate the penalty introduced by the filtering effect when considering Nyquist wavelength division multiplexing, single side-band direct-detection orthogonal frequency division multiplexing, and symbol-rate variable dual polarization quadrature amplitude modulation. Also, different approaches to compensate for the filter narrowing effect are discussed. Results show that the specific needs per each scenario can be fulfilled by the aforementioned technologies and techniques or a combination of them, when balancing performance, network reach, and cost

Hitless wavelength assignment in filterless optical access networks

Advantages offered by coherent detection systems in access networks are not limited to the increase of power budget due to the superior sensitivity. Channel selectivity is another intriguing feature offered by coherent systems that can be exploited to enable advanced system and network functionalities for access systems. Among them, we focus here on the implementation of filterless optical networks and network reconfiguration capabilities which might be required to satisfy dynamic load balancing requests and new terminal activations. We show that in the access domain these functionalities do not require DSP-aided coherent receivers, but can be easily realized by means of simpler, fully analogue real-time coherent terminals matching the access network low-cost paradigm. This paper discusses these concepts and how they can be experimentally implemented by using a novel wavelength allocation algorithm and real-time analogue coherent transceivers based on DFB lasers, whose wavelengths are tuned by a simple temperature control

Spectral processing techniques for efficient monitoring in optical networks

Having ubiquitous optical monitors in dense wavelength-division multiplexing (DWDM) or flex-grid networks allows the estimation in real time of crucial parameters. Such monitoring would be even more important in disaggregated optical networks, to inspect performance issues related to inter-vendor interoperability. Several important parameters can be retrieved using optical spectrum analyzers (OSAs). However, omnipresent OSAs represent an infeasible solution. Nevertheless, the advent of new, relatively cheap, compact and medium-resolution optical channel monitors (OCMs) enable a more intensive deployment of these devices. In this paper, we identify two main scenarios for the placement of such monitors: at the ingress and at the egress of the optical nodes. In the ingress scenario, we can directly estimate the parameters related to the signals, but not those related to the filters. On the contrary, in the egress scenario, the filter-related parameters can be easily detected, but not those related to amplified spontaneous emission. Therefore, we present two methods that, leveraging a curve fitting and a machine learning regression algorithm, allow detection of the missing parameters. We verify the proposed solutions with spectral data acquired in simulation and experimental setups. We obtained good estimation accuracy for both setups and for both studied placement scenarios. It is noteworthy that in the experimental assessment of the ingress scenario, we achieved a maximum absolute error (MAE) lower than 1 GHz in filter bandwidth estimation and a MAE lower than 0.5 GHz in filter frequency shift estimation. In addition, by comparing the relative errors of the considered parameters, we identified the ingress scenario as the more beneficial. In particular, we estimated the filter central frequency shift with 84% and the filter 6 dB bandwidth with 75% higher accuracy, with respect to datasheet/reference values. This translates into a total reduction of the estimated signal-to-noise ratio (SNR) penalty, introduced by a single optical filter, of 0.24 dB.Funding: Horizon 2020 Framework Programme (765275). This work is part of the Future Optical Networks for Innovation, Research and Experimentation (ONFIRE) project (https://h2020-onfire.eu), which is supported by the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie Action.Peer ReviewedPostprint (author's final draft

Dantzig–Wolfe decomposition for the design of filterless optical networks

International audienceFilterless optical networks use passive splitters and combiners with coherent optics, providing wavelength selection in the digital domain, while forming a passive fiber-tree topology between nodes. In this study, we investigate the optimal design of filterless optical networks while minimizing the number of required wavelengths. We propose a Dantzig-Wolfe decomposition model in which each subproblem aims to generate a potential filterless optical subnetwork, with a directed tree topology. The master problem then selects the best combination of subnetworks. Numerical experiments demonstrate significant performance improvement over previous work, reducing previous computational results by a factor of 2 to 10 depending on the size of the data instances

Demonstration of latency-aware 5G network slicing on optical metro networks

The H2020 METRO-HAUL European project has architected a latency-aware, cost-effective, agile, and programmable optical metro network. This includes the design of semi-disaggregated metro nodes with compute and storage capabilities, which interface effectively with both 5G access and multi-Tbit/s elastic optical networks in the core. In this paper, we report the automated deployment of 5G services, in particular, a public safety video surveillance use case employing low-latency object detection and tracking using on-camera and on-the-edge analytics. The demonstration features flexible deployment of network slice instances, implemented in terms of ETSI NFV Network Services. We summarize the key findings in a detailed analysis of end-to-end quality of service, service setup time, and soft-failure detection time. The results show that the round-trip-time over an 80 km link is under 800 µs and the service deployment time under 180 seconds.Horizon 2020 Framework Programme (761727); Bundesministerium für Bildung und Forschung (16KIS0979K).Peer ReviewedArticle signat per 25 autors/es: B. Shariati, Fraunhofer HHI, Berlin, Germany / L. Velasco, Universitat Politècnica de Catalunya, Barcelona, Spain / J.-J. Pedreno-Manresa, ADVA, Munich, Germany / A. Dochhan, ADVA, Munich, Germany / R. Casellas, Centre Tecnològic Telecomunicacions Catalunya, Castelldefels, Spain / A. Muqaddas, University of Bristol, Bristol, UK / O. Gonzalez de Dios, Telefónica, Madrid, Spain / L. Luque Canto, Telefónica, Madrid, Spain / B. Lent, Qognify GmbH, Bruchsal, Germany / J. E. Lopez de Vergara, Naudit HPCN, Madrid, Spain / S. Lopez-Buedo, Naudit HPCN, Madrid, Spain / F. Moreno, Universidad Politécnica de Cartagena, Cartagena, Spain / P. Pavon, Universidad Politécnica de Cartagena, Cartagena, Spain / M. Ruiz, Universitat Politècnica de Catalunya, Barcelona, Spain / S. K. Patri, ADVA, Munich, Germany / A. Giorgetti, CNIT, Pisa, Italy / F. Cugini, CNIT, Pisa, Italy / A. Sgambelluri, CNIT, Pisa, Italy / R. Nejabati, University of Bristol, Bristol, UK / D. Simeonidou, University of Bristol, Bristol, UK / R.-P. Braun, Deutsche Telekom, Germany / A. Autenrieth, ADVA, Munich, Germany / J.-P. Elbers, ADVA, Munich, Germany / J. K. Fischer, Fraunhofer HHI, Berlin, Germany / R. Freund, Fraunhofer HHI, Berlin, GermanyPostprint (author's final draft

Real-time digital signal processing for new wavelength-to-the-user optical access networks

Nowadays, optical access networks provide high capacity to end users with growing availability of multimedia contents that can be streamed to fixed or mobile devices. In this regard, one of the most flexible and low-cost approaches is Passive Optical Network (PON) that is used in Fiber-to-the-Home (FTTH). Due to the growing of the bandwidth demands, Wavelength Division Multiplexing (WDM), and later on ultra-dense WDM (udWDM) PON, with a narrow channel spacing, to increase the number of users through a single fiber, has been deployed. The udWDM-PON with coherent technology is an attractive solution for the next generation optical access networks with advanced digital signal processing (DSP). Thanks to the higher sensitivity and improved channel selectivity in coherent detection with efficient DSP, optical networks support larger number of users in longer distances. Since the cost is the main concern in the optical access networks, this thesis presents DSP architectures in coherent receiver (Rx), based on low-cost direct phase modulated commercial DFB lasers. The proposals are completely in agreement with consept of wavelength-to-the-user, where each client in optical network is dedicated to an individual wavelength. Next, in a 6.25 GHz spaced udWDM grid with the optimized DSP techniques and phase-shift-keying (PSK) modulation format, the high sensitivity is achieved in real-time field-programmable-gate-array (FPGA) implementations. Moreover, this thesis reduces hardware complexity of optical carrier recovery (CR) with two various strategies. First, based on differential mth-power frequency estimator (FE) by using look-up-tables (LUTs) and second, LUT-free CR architecture, with optimizing the power consumption and hardware resources, as well as improving the channel selectivity in terms of speed and robustness. Furthermore, by designing very simple but efficient clock recovery, a symbol-rate DSP architecture, which process data using only one sample per symbol (1-sps), for polarization diversity (POD) structure, becomes possible. It makes the DSP independent from state-of-polarization (SOP), even in the case of low-cost optical front-end and low-speed analog-to-digital converters (ADCs), keeps the performance high as well as sensitivity in real-time implementations on FPGA.Avui en dia, les xarxes d'accés òptic proporcionen una alta capacitat als usuaris finals amb una creixent disponibilitat de continguts multimèdia que es poden transmetre a dispositius fixos o mòbils. En aquest sentit, un dels enfocaments més flexibles i de baix cost és la Xarxa Òptica Passiva (PON) que s'utilitza a Fibra-fins-la-Llar (FTTH). A causa del creixent requeriment de l'ample de banda, s'ha desplegat la multiplexació de divisió d'ona (WDM) i, posteriorment, el PON amb WDM d'alta densitat (udWDM), amb un espaiat estret de canals, per augmentar el nombre d'usuaris a través d'una sola fibra. L'udWDM-PON amb tecnologia coherent és una solució atractiva per a les xarxes d'accés òptic d'última generació amb processament avançat de senyal digital (DSP). Gràcies a la major sensibilitat i a la selectivitat millorada del canal en la detecció coherent amb DSP eficient, les xarxes òptiques suporten un nombre més gran d'usuaris a distàncies més llargues. Atès que el cost és la principal preocupació en les xarxes d'accés òptic, aquesta tesi presenta arquitectures DSP en receptor coherent (Rx), basades en làsers DFB comercials modulats en fase directa de baix cost. Les propostes estan d'acord amb la asignació de la longitud d'ona a l'usuari, on a cada client de la xarxa òptica se li dedica a una longitud d'ona individual. A continuació, en una graella udWDM espaciada de 6,25 GHz amb les tècniques de DSP optimitzades i el format de modulació de fase (PSK), s'aconsegueix l'alta sensibilitat en implementacions field-programable-gate-array (FPGA) en temps real. A més, aquesta tesi redueix la complexitat del maquinari de recuperació òptica de portadors (CR) amb dues estratègies diverses. Primer, basat en un estimador de freqüència de potència diferencial (FE) mitjançant l'ús de taules de cerca (LUTs) i, en segon lloc, l'arquitectura CR sense LUT, amb l'optimització del consum d'energia i els recursos de maquinari, a més de millorar la selectivitat del canal en termes de velocitat i robustesa. A més, al dissenyar una recuperació de rellotge molt simple, però eficaç, es fa possible una arquitectura DSP a la velocitat dels símbols, que processa dades utilitzant només una mostra per símbol (1-sps) per a l'estructura de la diversitat de polarització òptica (POD). Fa que el DSP sigui independent de l'estat de polarització (SOP), fins i tot en el cas dels analog-to-digital converters (ADC) de front-end òptics de baix cost, i manté el rendiment alt i la sensibilitat en les implementacions en temps real de FPGA

Study and application of spectral monitoring techniques for optical network optimization

One of the possible ways to address the constantly increasing amount of heterogeneous and variable internet traffic is the evolution of the current optical networks towards a more flexible, open, and disaggregated paradigm. In such scenarios, the role played by Optical Performance Monitoring (OPM) is fundamental. In fact, OPM allows to balance performance and specification mismatches resulting from the disaggregation adoption and provides the control plane with the necessary feedback to grant the optical networks an adequate automation level. Therefore, new flexible and cost-effective OPM solutions are needed, as well as novel techniques to extract the desired information from the monitored data and process and apply them. In this dissertation, we focus on three aspects related to OPM. We first study a monitoring data plane scheme to acquire the high resolution signal optical spectra in a nonintrusive way. In particular, we propose a coherent detection based Optical Spectrum Analyzer (OSA) enhanced with specific Digital Signal Processing (DSP) to detect spectral slices of the considered optical signals. Then, we identify two main placement strategies for such monitoring solutions, enhancing them using two spectral processing techniques to estimate signal- and optical filter-related parameters. Specifically, we propose a way to estimate the Amplified Spontaneous Emission (ASE) noise or its related Optical Signal-to-Noise (OSNR) using optical spectra acquired at the egress ports of the network nodes and the filter central frequency and 3/6 dB bandwidth, using spectra captured at the ingress ports of the network nodes. To do so, we leverage Machine Learning (ML) algorithms and the function fitting principle, according to the considered scenario. We validate both the monitoring strategies and their related processing techniques through simulations and experiments. The obtained results confirm the validity of the two proposed estimation approaches. In particular, we are able to estimate in-band the OSNR/ASE noise within an egress monitor placement scenario, with a Maximum Absolute Error (MAE) lower than 0.4 dB. Moreover, we are able to estimate the filter central frequency and 3/6 dB bandwidth, within an ingress optical monitor placement scenario, with a MAE lower than 0.5 GHz and 0.98 GHz, respectively. Based on such evaluations, we also compare the two placement scenarios and provide guidelines on their implementation. According to the analysis of specific figures of merit, such as the estimation of the Signal-to-Noise Ratio (SNR) penalty introduced by an optical filter, we identify the ingress monitoring strategy as the most promising. In fact, when compared to scenarios where no monitoring strategy is adopted, the ingress one reduced the SNR penalty estimation by 92%. Finally, we identify a potential application for the monitored information. Specifically, we propose a solution for the optimization of the subchannel spectral spacing in a superchannel. Leveraging convex optimization methods, we implement a closed control loop process for the dynamical reconfiguration of the subchannel central frequencies to optimize specific Quality of Transmission (QoT)-related metrics. Such a solution is based on the information monitored at the superchannel receiver side. In particular, to make all the subchannels feasible, we consider the maximization of the total superchannel capacity and the maximization of the minimum superchannel subchannel SNR value. We validate the proposed approach using simulations, assuming scenarios with different subchannel numbers, signal characteristics, and starting frequency values. The obtained results confirm the effectiveness of our solution. Specifically, compared with the equally spaced subchannel scenario, we are able to improve the total and the minimum subchannel SNR values of a four subchannel superchannel, of 1.45 dB and 1.19 dB, respectively.Una de las posibles formas de hacer frente a la creciente cantidad de tráfico heterogéneo y variable de Internet es la evolución de las actuales redes ópticas hacia un paradigma más flexible, abierto y desagregado. En estos escenarios, el papel que desempeña el modulo óptico de monitorización de prestaciones (OPM) es fundamental. De hecho, el OPM permite equilibrar los desajustes de rendimiento y especificación, los cuales surgen con la adopción de la desagregación; del mismo modo el OPM también proporciona al plano de control la realimentación necesaria para otorgar un nivel de automatización adecuado a las redes ópticas. En esta tesis, nos centramos en tres aspectos relacionados con el OPM. En primer lugar, estudiamos un esquema de monitorización para adquirir, de forma no intrusiva, los espectros ópticos de señales de alta resolución. En concreto, proponemos un analizador de espectro óptico (OSA) basado en detección coherente y mejorado con un específico procesado digital de señal (DSP) para detectar cortes espectrales de las señales ópticas consideradas. A continuación, presentamos dos técnicas de colocación para dichas soluciones de monitorización, mejorándolas mediante dos técnicas de procesamiento espectral para estimar los parámetros relacionados con la señal y el filtro óptico. Específicamente, proponemos un método para estimar el ruido de emisión espontánea amplificada (ASE), o la relación de señal-ruido óptica (OSNR), utilizando espectros ópticos adquiridos en los puertos de salida de los nodos de la red. Del mismo modo, estimamos la frecuencia central del filtro y el ancho de banda de 3/6 dB, utilizando espectros capturados en los puertos de entrada de los nodos de la red. Para ello, aprovechamos los algoritmos de Machine Learning (ML) y el principio de function fitting, según el escenario considerado. Validamos tanto las estrategias de monitorización como las técnicas de procesamiento mediante simulaciones y experimentos. Se puede estimar en banda el ruido ASE/OSNR en un escenario de colocación de monitores de salida, con un Maximum Absolute Error (MAE) inferior a 0.4 dB. Además, se puede estimar la frecuencia central del filtro y el ancho de banda de 3/6 dB, dentro de un escenario de colocación de monitores ópticos de entrada, con un MAE inferior a 0.5 GHz y 0.98 GHz, respectivamente. A partir de estas evaluaciones, también comparamos los dos escenarios de colocación y proporcionamos directrices sobre su aplicación. Según el análisis de específicas figuras de mérito, como la estimación de la penalización de la relación señal-ruido (SNR) introducida por un filtro óptico, demostramos que la estrategia de monitorización de entrada es la más prometedora. De hecho, utilizar un sistema de monitorización de entrada redujo la estimación de la penalización del SNR en un 92%. Por último, identificamos una posible aplicación para la información monitorizada. En concreto, proponemos una solución para la optimización del espaciado espectral de los subcanales en un supercanal. Aprovechando los métodos de optimización convexa, implementamos un proceso cíclico de control cerrado para la reconfiguración dinámica de las frecuencias centrales de los subcanales con el fin de optimizar métricas específicas relacionadas con la calidad de la transmisión (QoT). Esta solución se basa en la información monitorizada en el lado del receptor del supercanal. Validamos el enfoque propuesto mediante simulaciones, asumiendo escenarios con un diferente número de subcanales, distintas características de la señal, y diversos valores de la frecuencia inicial. Los resultados obtenidos confirman la eficacia de nuestra solución. Más específicatamente, en comparación con el escenario de subcanales igualmente espaciados, se pueden mejorar los valores totales y minimos de SNR de los subcanales de un supercanal de cuatro subcanales, de 1.45 dB y 1.19 dB, respectivamentePostprint (published version