Towards an Optimal Photonic Network: Optimising Performance, Cost and Flexibility

This thesis investigates optical fibre transmission system technologies, and their impact on network architectures with the objective of lowering unit cost ($/Gb/s/km) of data transmission in long-haul, and ultra long-haul dense wavelength division multiplexing (DWDM) photonic networks. The importance of this work is driven by the exponential growth in Internet traffic of around 40% p.a., and economic pressures constraining network operators’ ability to invest in their networks. Optical transport networks must therefore be designed to meet future bandwidth demands of end users, with optimum performance, cost and flexibility. Dynamic gain equalisers (DGEs) are a key sub-system of ultra long-haul networks, enabling increased un-regenerated transmission reach and elimination of expensive optical-electrical-optical (OEO) regeneration. A theoretical framework was developed integrating models of wideband power variation, together with narrowband nonlinear propagation simulations using the split-step Fourier method. The optimum spacing of the also costly DGEs was determined for a 3,000km network field deployment. Optimum power pre-emphasis profiles were predicted and compared with simple linear calculations, showing <0.7dB performance penalty using the much faster, simplified method. Optical dispersion management schemes were studied, with optical dispersion compensating fibre placed after every other span resulting in 6% cost reduction and little performance degradation compared to compensation after every span. A techno-economic comparison of optical and electronic dispersion compensation (EDC) strategies showed 25% cost reduction using EDC. Tolerance to fibre nonlinearities is reduced compared to optical compensation; splitting the EDC function equally between transmitter and receiver optimises performance. Economic benefits of a single flexible, multi-reach DWDM system were investigated showing almost 20% cost savings compared to separate long-haul and ultra long-haul systems. Finally, the techno-economic benefits of optical bypass in meshed networks were analysed for increasing levels of optical transparency: from OEO regenerated to multi-degree reconfigurable optical add-drop multiplexers (MD-ROADMs), enabling up to 46% cost saving

Energy-efficient design of optical transport networks

Energy efficiency is becoming a key factor in the design and operation of telecommunications networks as a way to reduce operational expenditures and the carbon footprint associated to telecom operators. This Ph.D. thesis evaluates and proposes novel energy-efficient approaches in three design areas of optical transport networks: (1) Network architectures and operation modes; (2) Resilience schemes; and (3) Optical amplifier placements. The solutions proposed in these areas are shown to significantly reduce the power consumption in realistic deployment scenarios and could be applied by telecom operators in the near and medium-term future to enhance the energy efficiency of optical transport networks