In the following years, future Metropolitan Area Networks (MANs) will be required to support a large range of resource-hungry applications, but on the same time they will have to be efficient in terms of cost and energy consumption. This thesis takes into account a modular solution based on Sliceable Bandwidth/Bitrate Variable Transceivers (S-BVTs) developed in PASSION project. The S-BVTs are composed of transmitters constituted of directly modulated Vertical-Cavity Surface-Emitting Lasers (VCSELs) and coherent receivers. The optimization of the transmission bandwidth is achieved by choosing adaptive modulation formats, such as Discrete Multitone (DMT). A particular focus is put on the hierarchical structure of MANs, especially taking into account the presence of two Hierarchical Levels (HLs): HL4 and HL3. The focus of the work is to analyze the potentialities of S-BVTs in MANs organized in hierarchical levels in terms of transmitted capacity. In order to achieve these results, a MATLAB simulator has been created to emulate the behaviour of the main MAN network components: the VCSEL and its direct modulation with DMT format, the network nodes, the Standard Single-Mode Fiber (SSMF), and the coherent receiver. The evaluation of the interplay between laser chirp parameters and tight optical filtering due to a 25-GHz channel spacing Wavelength Selective Switch (WSS) highlights that a source with lower chirp is preferred, but a small amount of chirp is however useful for higher noise levels. Moreover, due to a higher spectral efficiency, Single Sideband (SSB) DMT modulation outperforms Dual Sideband (DSB) DMT modulation. The dependence of the interchannel crosstalk on the modulating signal bandwidth is proved and a trade off between the impairments due to the crosstalk and the traffic carried by each channel has to be found. The Volterra equalization algorithm is demonstrated to be useful to mitigate both interchannel crosstalk and fiber non-linear impairments for hundred-km propagation of three 25-GHz spaced channels modulated with SSB DMT signal. The effect of HL4 and HL3 nodes on the transmission performance is evaluated in terms of required Optical Signal-to Noise Ratio (OSNR) to achieve given target capacities. Real network topologies are considered, and a target capacity of 50 Gb/s per channel per polarization can be reached by optimizing the launch power and the optical amplification in a 170-km scenario. Furthermore, the presence in the network nodes of Semiconductor Optical Amplifiers (SOAs) working as Wavelength Blockers (WBLs) is evaluated in terms of capacity reduction due signal distortion caused by Self-Gain Modulation (SGM) of the amplifier. This nonlinear impairment introduces a high-pass filtering, emphasised for higher saturation conditions. The analysis is performed with two different optical sources, a Distributed FeedBack (DFB) laser and a VCSEL, which are externally and directly modulated respectively. They are modulated both with a DSB and a SSB DMT signal. SSB is more resilient to the distortion due to the SOA filtering for high currents and to the Amplified Spontaneous Emission (ASE) noise introduced by the amplifier in direct modulation systems. At last, the performance of a system composed of a DSB DMT-modulated optical signal crossing a complete HL4 node, i.e., constituted of a channel Demultiplexing (DEMUX) filter, an SOA, and a Multiplexing (MUX) filter, followed by an optical SSB filtering and the addition of two SSB DMT-modulated adjacent channels in a 25-GHz grid is experimentally measured. The three channels propagate for 100 km. In this system a capacity higher than the target 50 Gb/s per channel per polarization is demonstrated.
Nei prossimi anni, le future reti metropolitane (MAN) dovranno supportare un numero sempre crescente di applicazioni che richiedono molte risorse, ma nel contempo dovranno essere efficienti in termini di costo e consumo energetico. Questa tesi prende in considerazione una soluzione modulare basata su Sliceable Bandwidth/Bitrate Variable Transceiver (S-BVT) sviluppata dal progetto PASSION. Gli S-BVT sono costituiti da trasmettitori formati da Vertical-Cavity Surface-Emitting Laser (VCSEL) modulati direttamente e da ricevitori coerenti. L’ottimizzazione della banda di trasmissione è ottenuta sfruttando formati di modulazione adattativi, come il Discrete Multitone (DMT). Particolare attenzione è stata posta alla struttura gerarchica delle reti metro, prendendo in considerazione due livelli gerarchici (HL): HL4 e HL3. L’obiettivo del lavoro è valutare le potenzialità dell’uso di S-BVT nell’ambito di una rete MAN organizzata a livello gerarchico in termini di capacità trasportata. Per ottenere questi risultati, è stato sviluppato un simulatore MATLAB che emula il comportamento dei principali dispositivi costituenti la rete metro: il VCSEL e la sua modulazione diretta con formato DMT, i nodi di rete, la fibra ottica standard a singolo modo e il ricevitore coerente. La valutazione dell’interazione tra parametri di chirp della sorgente e filtraggio ottico stretto proveniente da Wavelength Selective Switch (WSS) per spaziatura tra canali a 25 GHz evidenzia come parametri di chirp più bassi siano preferibili, ma che, specialmente per livelli di rumore alti, un piccolo quantitativo di chirp sia utile. Inoltre, grazie ad una migliore efficienza spettrale, il segnale DMT Single Sideband (SSB) mostra una migliore performance rispetto al segnale DMT Dual Sideband (DSB). Si dimostra la dipendenza del crosstalk tra canali dalla banda del segnale modulante, sottolineando la necessità di un compromesso tra deterioramento della performance dovuto al crosstalk e traffico trasportato da ciascun canale. L’efficacia dell’algoritmo di equalizzazione di Volterra è verificata in uno scenario a tre canali spaziati di 25 GHz propaganti per qualche centinaio di chilometri e modulati con DMT SSB. L’effetto del filtraggio dovuto alla presenza di nodi di rete a livello HL4 e HL3 è valutato in termini di rapporto segnale-rumore ottico (OSNR) richiesto per ottenere date capacità target. Sono analizzate due topologie di rete reali e la capacità target di 50 Gb/s per canale per polarizzazione può essere raggiunta ottimizzando la potenza di lancio e l’amplificazione ottica in una rete lunga 170 km. Dunque si considera la presenza nei nodi di rete di amplificatori ottici a semiconduttore (SOA) utilizzati come Wavelength Blocker (WBL) in termini di riduzione della capacità dovuta alla distorsione del segnale ottico causata da Self-Gain Modulation (SGM). Questo effetto non lineare introduce un filtraggio passa-alto, accentuato per condizioni di saturazione alte. L’analisi è condotta con due sorgenti ottiche diverse, un laser Distributed FeedBack (DFB) ed un VCSEL, modulati rispettivamente esternamente e direttamente. I due laser sono modulati con un segnale DMT sia DSB sia SSB. La modulazione SSB si dimostra più resistente sia alle distorsioni introdotte dal SOA ad alte correnti e potenze sia al rumore dovuto all’amplificazione dell’emissione spontanea (ASE) introdotto dall’amplificatore in sistemi a modulazione diretta. Infine si valuta la capacità trasmessa in un sistema costituito da un canale DMT DSB che attraversa un nodo di rete HL4 completo, cioè costituito da un demultiplatore, il SOA ed un multiplatore, seguito da un filtraggio ottico SSB e l’aggiunta di canali adiacenti a 25 GHz, anch’essi modulati con un segnale DMT SSB. I tre canali sono fatti propagare per 100 km. In questo sistema si dimostra una capacità superiore ai 50 Gb/s per canale per polarizzazione.
Metro network capacity increase via innovative photonic technologies and communication systems
RAPISARDA, MARIANGELA
2020/2021
Abstract
In the following years, future Metropolitan Area Networks (MANs) will be required to support a large range of resource-hungry applications, but on the same time they will have to be efficient in terms of cost and energy consumption. This thesis takes into account a modular solution based on Sliceable Bandwidth/Bitrate Variable Transceivers (S-BVTs) developed in PASSION project. The S-BVTs are composed of transmitters constituted of directly modulated Vertical-Cavity Surface-Emitting Lasers (VCSELs) and coherent receivers. The optimization of the transmission bandwidth is achieved by choosing adaptive modulation formats, such as Discrete Multitone (DMT). A particular focus is put on the hierarchical structure of MANs, especially taking into account the presence of two Hierarchical Levels (HLs): HL4 and HL3. The focus of the work is to analyze the potentialities of S-BVTs in MANs organized in hierarchical levels in terms of transmitted capacity. In order to achieve these results, a MATLAB simulator has been created to emulate the behaviour of the main MAN network components: the VCSEL and its direct modulation with DMT format, the network nodes, the Standard Single-Mode Fiber (SSMF), and the coherent receiver. The evaluation of the interplay between laser chirp parameters and tight optical filtering due to a 25-GHz channel spacing Wavelength Selective Switch (WSS) highlights that a source with lower chirp is preferred, but a small amount of chirp is however useful for higher noise levels. Moreover, due to a higher spectral efficiency, Single Sideband (SSB) DMT modulation outperforms Dual Sideband (DSB) DMT modulation. The dependence of the interchannel crosstalk on the modulating signal bandwidth is proved and a trade off between the impairments due to the crosstalk and the traffic carried by each channel has to be found. The Volterra equalization algorithm is demonstrated to be useful to mitigate both interchannel crosstalk and fiber non-linear impairments for hundred-km propagation of three 25-GHz spaced channels modulated with SSB DMT signal. The effect of HL4 and HL3 nodes on the transmission performance is evaluated in terms of required Optical Signal-to Noise Ratio (OSNR) to achieve given target capacities. Real network topologies are considered, and a target capacity of 50 Gb/s per channel per polarization can be reached by optimizing the launch power and the optical amplification in a 170-km scenario. Furthermore, the presence in the network nodes of Semiconductor Optical Amplifiers (SOAs) working as Wavelength Blockers (WBLs) is evaluated in terms of capacity reduction due signal distortion caused by Self-Gain Modulation (SGM) of the amplifier. This nonlinear impairment introduces a high-pass filtering, emphasised for higher saturation conditions. The analysis is performed with two different optical sources, a Distributed FeedBack (DFB) laser and a VCSEL, which are externally and directly modulated respectively. They are modulated both with a DSB and a SSB DMT signal. SSB is more resilient to the distortion due to the SOA filtering for high currents and to the Amplified Spontaneous Emission (ASE) noise introduced by the amplifier in direct modulation systems. At last, the performance of a system composed of a DSB DMT-modulated optical signal crossing a complete HL4 node, i.e., constituted of a channel Demultiplexing (DEMUX) filter, an SOA, and a Multiplexing (MUX) filter, followed by an optical SSB filtering and the addition of two SSB DMT-modulated adjacent channels in a 25-GHz grid is experimentally measured. The three channels propagate for 100 km. In this system a capacity higher than the target 50 Gb/s per channel per polarization is demonstrated.| File | Dimensione | Formato | |
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Rapisarda_PhD_thesis.pdf
Open Access dal 27/02/2022
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https://hdl.handle.net/10589/170484