Overcoming Capacity and Energy Limits in Optical Communications

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The world's Internet infrastructure is of ever increasing importance to both the national and global economy, enabling ever more efficient international trade and a host of new business opportunities. As a result data traffic on the world's networks has steadily been growing at around 40% per year over the past decade and no respite in this trend is anticipated for the foreseeable future. However, it is becoming impractical to satisfy this increased demand through the obvious and traditional measures such as improving spectral efficiency and utilization, installing more optical fibres, and increasing the number or size of the data centres, since today's telecommunications infrastructure is already estimated to be responsible for about 2% of world carbon emission (more than the aviation industry!). Consequently further capacity scaling using the existing technology is likely to have a significant impact on the environment. Another key issue is that the heat dissipation in data centres has reached its limit per unit volume, which effectively means that if current technological platforms are used to upgrade capacity then this will require new strategies for thermal management, likely further increasing the power consumption, cost and complexity. Clearly such a situation is unsustainable in the longer term. Current networks are mostly limited - both in terms of capacity and energy efficiency - by the architectures/technologies used. These in turn have traditionally been driven by the philosophy of designing the network so as to minimize the usage of expensive and relatively unreliable optical components and exploiting the maturity of electronics - with its potential for cost reduction when mass produced - to do the majority of the signal routing, processing and transmission impairment mitigation. However, this approach - given the previously discussed energy scaling constraints - will not be sustainable moving forward, dictating a change in this approach. Specifically it will be necessary to increase the amount of optics in the network to reduce the burden placed upon the electronics. I strongly believe that the transition to more optically empowered systems is simply unavoidable. The aim of this proposal is to investigate the possibility of employing the array of new optical components and subsystems that I am currently researching (which includes Optical Comb generators, injection locked lasers and devices that amplify signals differently depending on their phase) into optical networks, in a manner that allows for scaling to larger data transmission capacities with a simultaneous reduction in power consumption and/or better thermal management characteristics. Today, there are several main concepts relevant to future optical communications, all of them relying on having higher quality optical signals (e.g., signal-to-noise ratio), or tight control of the coherence properties of optical signals carrying independent data streams (called 'superchannel' technologies). My current research deals with development of high purity (low noise) Optical Combs that allow for tight control of coherence - promising to give both the key parameters necessary. Within the Fellowship, I plan to implement this technology into the generation and reception part of optical links. Higher signal-to-noise ratio transmitters and lower-noise and higher speed demultiplexing of data at the detection side should allow for extended reach without the need for additional in-line amplification and allow the use of modulation formats carrying more information inside the same spectral bandwidth. Among other advantages, the energy-per-transmitted-bit can be reduced in both these cases. However, I will not limit my research to optical communications and will investigate other fields where the results might also be helpful - e.g., ultraprecise transfer of time and frequency. I will work in close collaboration with academic as well as non-academic partners.