Conception et analyse des réseaux sans filtre pour applications sous-marines

Les commutateurs sélectifs en longueurs d’onde (WSS) ne peuvent pas encore être déployés dans les unités de branchement (BU) immergées des liaisons sous-marines, ce qui limite la flexibilité des réseaux optiques sous-marins. À cet égard, l'architecture de réseau optique sans filtre, qui est basée sur des nœuds équipés de transpondeurs cohérents et de diviseurs optiques passifs et qui a déjà été proposée pour des applications terrestres, peut être considérée comme une solution prometteuse pour les applications sous-marines. Dans ce mémoire, des solutions architecturales sans filtre sont proposées et évaluées pour trois topologies physiques de réseau optique sous-marin. Les solutions sont comparées à des solutions conventionnelles à WSS en termes de coûts, de consommation de longueur d’onde et de spectre. Il est aussi démontré que l'architecture sans filtre peut apporter d'importantes économies pour les équipements de terminal et la consommation de spectre, par rapport à un réseau conventionnel, en offrant la possibilité de réassigner dynamiquement les transpondeurs et le spectre entre les différentes connexions optiques d’un réseau sous-marin longue distance

Algorithms and Subsystems for Next Generation Optical Networks

This thesis investigates algorithms and subsystems for digital coherent optical networks to alleviate system requirements and enable spectrally efficient systems. Spectral shaping of individual channel is investigated to mitigate backreflections in bi-directional Passive Optical Network (PON) enabling more than 1000 users operating at 10 Gbit/s. It is then shown that temporal delay skews, caused by misalignment in the coherent receiver, induce a large penalty for Nyquist filtered signals. An adaptive 4×4 equaliser is developed to compensate the imperfections dynamically. This is subsequently demonstrated experimentally with Polarisation Division Multiplexed (PDM) Quadrature Phase Shift Keying (QPSK) and 16-level Quadrature Amplitude Modulation (QAM). Furthermore, a modified blind equaliser is designed to adaptively compensate for unknown amount of Chromatic Dispersion (CD). The equaliser is demonstrated experimentally using 10.7 GBd PDM-QPSK transmission over 5,200 km. To simplify the computational complexity of the equalisers a multiplier free update scheme is explored in simulations. Optical frequency combs are investigated as phase and frequency synchronised sub- carrier sources for Dense Wavelength Division Multiplexing (DWDM) systems. The effect of phase synchronisation between sub-channels of a superchannel is examined in simulations without showing performance deviation when no additional optical or digital processing is applied. Afterwards, the transmission performance of two generation techniques implementing 400 Gbit/s superchannels, utilising PDM-16QAM, is evaluated. Although, the average performance of the two combs is identical subchannel fluctuations are observed due to uneven spectral profile. Carrier Phase Estimation (CPE) is explored for both single channel and superchannels systems. An equaliser interleaved with CPE, is explored for PDM-64QAM with minor improvement. Alternatively, Digital Coherence Enhancement (DCE) allowed the detection of 6 GBd PDM-64QAM with a 1.4 MHz linewidth laser, an order of magnitude improvement in linewidth tolerance. Finally, a joint CPE across a comb superchannel is demonstrated with a factor of 5 tolerance improvement

Digital signal processing for sensing in software defined optical networks

Optical networks are moving from static point-to-point to dynamic configurations, where transmitter parameters are adaptively changing to meet traffic demands. Dynamic network reconfigurability is achievable through software-defined transceivers, capable of changing the data-rate, overhead, modulation format and reach. Additionally, flexibility in the spectral allocation of channels ensures that the available resources are efficiently distributed, as the increase in fibre capacity has reached a halt. The complexity of such highly reconfigurable systems and cost of their maintenance increase exponentially. Implemented as part of digital signal processing of coherent receivers, sensing is an enabling technology for future software defined optical networks, as it makes possible to both control and optimise transmission parameters, as well as to manage faulty links and mitigate channel impairments in a cost-effective manner. Symbol-rate is one of the parameters most likely to adaptively change according to existing fibre impairments, such as optical signal-to-noise ratio or chromatic dispersion. A single-channel symbol-rate estimation technique is demonstrated initially, yielding a sufficient accuracy to distinguish between different typical error-correction overheads, in the presence of dispersion and white Gaussian noise. Further increasing the capacity over fibre to 1 Tb/s and beyond means moving towards superchannel configurations that employ Nyquist pulse shaping to increase spectral efficiency. Novel sensing techniques applicable to such information dense configurations, that can jointly monitor the channel bandwidth, frequency offset, optical signal-to-noise ratio and chromatic dispersion are proposed and demonstrated herein. Based on time-domain and frequency-domain functions derived from the theory of cyclostationarity, the performance of this joint estimator is investigated with respect to a wide range of parameters. The required acquisition time of the receiver is approximately 6.55 μs, three orders of magnitude faster compared to the round-trip time in core networks. The pulse shaping at the transmitter limits the performance of this estimator, unless the excess bandwidth is 30% of the symbol-rate, or more