On Semiconductor Optical Amplifiers and Optical Coherent Detection

In questa tesi sono affrontate due tematiche inerenti il campo delle telecomunicazioni ottiche: gli amplificatori ottici a semiconduttore e un nuovo tipo di ricevitore ottico coerente. Nel corso della tesi vengono sviluppati nuovi modelli matematici per gli amplificatori a semiconduttore tradizionali e per quelli di tipo gain-clamped. Questi modelli vengono verificati tramite un confronto sperimentale. Infine, tramite una dettagliata verifica sperimentale, vengono confrontate le prestazioni di diverse tipologie di amplificatori a semiconduttore. Il nuovo tipo di ricevitore ottico coerente analizzato nella tesi ricorre all'utilizzo dell'elaborazione numerica del segnale per recuperare le differenze di fase e frequenza tra il segnale ricevuto e l'oscillatore locale che non è agganciato tramite PLL. Una notevole quantità di esperimenti mostra tutti i vantaggi derivanti da questa nuova tecnologia, che permette di recuperare facilmente le distorsioni del segnale dovute agli effetti di dispersione cromatica e dispersione modale di polarizzazione presenti in fibra. Queste potenzialità rilassano enormemente i vincoli di progettazione dei sistemi ottici permettendo di superare i limiti attuali e di aggiornare gli attuali sistemi a 10GBit/s con nuovi sistemi con elevata densità spettrale funzionanti a 40GBit/s e oltre

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

Physical activity practiced at a young age is associated with a less severe subsequent clinical presentation in facioscapulohumeral muscular dystrophy

Background: In facioscapulohumeral muscular dystrophy (FSHD), it is not known whether physical activity (PA) practiced at young age is associated with the clinical presentation of disease. To assess this issue, we performed a retrospective cohort study concerning the previous practice of sports and, among them, those with medium-high cardiovascular commitment in clinically categorized carriers of a D4Z4 reduced allele (DRA). Methods: People aged between 18 and 60 were recruited as being DRA carriers. Subcategory (classical phenotype, A; incomplete phenotype, B; asymptomatic carriers, C; complex phenotype, D) and FSHD score, which measures muscle functional impairment, were assessed for all participants. Information on PAs was retrieved by using an online survey dealing with the practice of sports at a young age. Results: 368 participants were included in the study, average age 36.6 years (SD = 9.4), 47.6% male. The FSHD subcategory A was observed in 157 (42.7%) participants with average (± SD) FSHD score of 5.8 ± 3.0; the incomplete phenotype (category B) in 46 (12.5%) participants (average score 2.2 ± 1.7) and the D phenotype in 61 (16.6%, average score 6.5 ± 3.8). Asymptomatic carriers were 104 (subcategory C, 28.3%, score 0.0 ± 0.2). Time from symptoms onset was higher for patients with A (15.8 ± 11.1 years) and D phenotype (13.3 ± 11.9) than for patients with B phenotype (7.3 ± 9.0). The practice of sports was associated with lower FSHD score (-17%) in participants with A phenotype (MR = 0.83, 95% CI = 0.73-0.95, p = 0.007) and by 33% in participants with D phenotype (MR = 0.67, 95% CI = 0.51-0.89, p = 0.006). Conversely, no improvement was observed in participants with incomplete phenotype with mild severity (B). Conclusions: PAs at a young age are associated with a lower clinical score in the adult A and D FSHD subcategories. These results corroborate the need to consider PAs at the young age as a fundamental indicator for the correct clinical stratification of the disease and its possible evolution

Nonlinear Cross-Polarization Mitigation Algorithm

The present document relates to optical transmission systems. In particular, the present document relates to methods and systems for the mitigation of Cross- Polarization Modulation (XPOLM) in optical transmission systems. A coherent optical receiver (200) adapted to receive an optical signal transmitted over an optical transmission channel exhibiting XPOLM is described. The received optical signal comprises a first polarization component and a second polarization component. The first and second polarization components comprise sequences of Mary phase shift keying, referred to as MPSK, symbols, respectively, M being an integer, with M > 2. The coherent optical receiver (200) comprises a conversion and processing unit (201, 202) adapted to generate a set of digital signals based on the received optical signal; a polarization de-multiplexing unit (203) adapted to demultiplex the set of digital signals into a first two dimensional, referred to as complex, component in a first polarization axis and a second complex component in a second polarization axis; and an XPOLM compensation unit (204) adapted to transform the first and second complex components into the Stokes space, thereby yielding a set of Stokes parameters; determine a rotation of the first and second polarization axes based on the set of Stokes parameters; and determine XPOLM compensated first and second complex components by transforming the first and second complex components in accordance to the determined rotation of the first and second polarization axes

Multicarrier offset-QAM for long-haul coherent optical communications

The availability of high-speed digital-to-Analog converters for coherent optical communication systems makes it possible to digitally divide the available electrical bandwidth into subchannels on each optical carrier which enables a parallel implementation of the digital signal processing. In this paper, we use electrical multicarrier offset-QAM modulations to achieve crosstalk-free modulation for subcarriers spaced at the symbol rate. We show that in coherent optical communication systems, several impairments are bound to break the subcarrier orthogonality and cause failures of payload symbol recovering. We propose a dedicated digital signal processing architecture which implements channel estimation and a new algorithm to track the phase in multicarrier offset-QAM modulation. We experimentally compare the latter with conventional multicarrier and single carrier QAM modulation so as to assess the benefits of crosstalk mitigation via offset-QAM modulation. We carry out experiments to test the transmission performance of multicarrier offset-QAM modulation in a dispersion-unmanaged long-haul transmission link.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Decision-feedback equalization of bandwidth-constrained N-WDM coherent optical communication systems

Nyquist Wavelength division multiplexing (N-WDM), is a promising scheme in order to enhance the spectral efficiency of future coherent optical communication systems. In N-WDM systems, the channel bandwidth and spacing are selected to maximize the spectral efficiency while maintaining acceptable levels of inter-carrier and inter symbol interference. To further increase the spectral efficiency, bandwidth constrained N-WDM, where baudrate is higher than channel bandwidth can be considered. We propose to combine the bandwidth-constrained N-WDM scheme with a decision feedback equalizer (DFE) designed according to the minimum mean square error (MMSE) criterion. We show that the enhanced resilience to the inter symbol interference offered by DFE provides an effective gain on spectral efficiency. We compare system benefits of DFE and maximum a posteriori sequence detection (MAP) for coherent optical receivers, and show that DFE is as efficient as MAP in mitigating inter symbol interference at a considerably lower complexity.info:eu-repo/semantics/publishe

Multicarrier offset-QAM modulations for coherent optical communication systems

We study the performance of multicarrier offset modulation and root-raised-cosine shaped multicarrier modulation with aggregate 32.5 GBd symbol rate and show that offset modulation is preferable for non-zero rolloff factors.info:eu-repo/semantics/publishe

New gain parameterization for fast semiconductor optical amplifier model

Numerical simulations of semiconductor optical amplifiers (SOA) often are time consuming. Making simplifying assumptions, we obtain a fast model based on the reservoir , representing the total number of useful carriers. In this paper, we explain how this model is developed and how the gain is parameterized. We demonstrate that the scattering losses, dropped in the derivation of the reservoir model, can be re-introduced by applying a simple transformation to the gain coefficient. In this way, the accuracy of the model is greatly increased, but its level of complexity remains low

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 blockoriented 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