Petabit Energy Aware Capacity Enhancement (PEACE)

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As recently discussed by the Wall Street Journal, the remarkable success of the internet may be attributed to the tremendous capacity of unseen underground and undersea optical fibre cables and the technologies associated with them. Indeed, the initial surge in web usage in the mid 1990s coincides with the commissioning of the first optically amplified transatlantic cable network, TAT12/13 allowing ready access to information otherwise inaccessible. Tremendous progress has been made since then, with the introduction of wavelength division multiplexing, where multiple colours of light are used to establish independent connections through the same fibre and coherent detection, the optical analogue of an advanced radio receiver able to detect both amplitude and frequency (or phase) modulation simultaneously enabling the information carrying capacity to be doubled and the required signal power to be reduced. To manage the costs, communication networks typically aggregate connections between many users onto a single communications link within the core of the network, avoiding the tremendous costs associated with dedicated links for all users across vast distances. Typically the trade of between cost and reliability has resulted in traffic from several thousand customers being aggregated onto a single fibre resulting in bit rates in the region of 100 Gbit/s per wavelength channel to support broadband connections of around 10 Mbit/s. However, this has resulted in intensities in optical fibres that are a million times greater than sunlight at the surface of the Earth's atmosphere and so the signal is significantly distorted by nonlinearly (a similar effect to overdriving load speakers). This distortion limits the maximum amount of information which may be transmitted across and optical fibre link, and unless combated, the nonlinear response will result in a capacity crunch, limiting access to the internet to today's levels.This project aims to allow the continued increase of the bandwidth of these fibre networks underpinning modern communications, including 17.6 million UK mobile internet connections and 70% penetration of home broadband connections. To increase capacity we will maximise spectral use, by adapting techniques found in mobile phones for use in fibre networks, resolving the significant issues associated with processing data with 1,000,000 times greater bandwidth using a balance of digital and analogue electronic and optical processing. This will reduce cost, size and power consumption associated with producing Tb/s capacities per wavelength. Critically, the project will develop techniques to understand and mitigate the nonlinear signal distortions. Nonlinear distortions occur within a channel, between channels and between each channels and noise originating in the optical amplifiers. By transforming the signal mid way along the link, we will exploit the nonlinear response of the second half of the fibre link to cancel the nonlinear distortion of the first to minimise the impact of nonlinear distortion associated with the channels themselves, and optimise the configuration of the system to minimise the nonlinear interaction with the noise, resulting in orders of magnitude increases in the maximum capacity of the optical fibre system.