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Final Report Summary - CEEOALAN (Cost and Energy Efficient Optical Access and Local Area Networks)

The Internet traffic continues to grow exponentially fuelled by bandwidth-hungry applications such as high definition TV, video-on-demand, virtual private networks, and cloud computing. This pushes hard for bit rate upgrade and technology evolution on the network infrastructures at every scale. For medium- and short-haul optical networks, cost- and power-effectiveness are the highest priority for the bit rate upgrade.

The CEEOALAN project (No: 623515) aims to identify and demonstrate cost and energy efficient modulation formats for very high speed short- and medium-haul optical links including intra- and inter-data centre connects as well as next generation passive optical networks (NG-PONs). Preferred candidates are formats with intensity modulation and direct detection (IMDD). In addition, formats with high spectral efficiency and/or multiplexing capability are considered such as pulse amplitude modulation (PAM), partial response (Duobinray as an example), carrierless amplitude and phase modulation (CAP) and discrete multi-tone (DMT), as high transmission rates can be achieved by using existing components with relatively low bandwidths.

The major objectives of this project therefore include a theoretical analysis and fair comparison of the different advanced modulation formats on aspects of optical power budget, cost, and power dissipation to identify optimum formats for the application scenarios of interest; the digital implementation of one or two variants using state-of-the-art convertors and measurements in the relevant application scenarios, and analogue implementation of the most promising format (if applicable) and measurements for relevant scenarios. All demonstrations are based on existing equipment offered by ADVA Optical Networking SE, Germany to guarantee the feasibility and flexibility of the project. A number of high speed optical link demonstrations are expected to be the world first.

The administrative objectives include generation peer-reviewed papers in world-leading journals and top international conferences; Development of new transferable knowledge/skills/competencies on experimentation, project management, proposal generation, decision making, patent filing, commercialization of research and related skills by means of flexible training programmes and hands-on training provided by ADVA Optical Networking SE, Germany.

The researcher and the scientist in charge managed to make the project progress well in liaison with plan. At the end of the project, all critical objectives have been achieved and the project outputs generated strong impact in both academia and industry.

For NG-PON applications, detailed analysis and comparison have been conducted of optical power budget, cost, and power dissipation of 28- and 40-Gb/s/l NG-PONs using PAM-4, Electrical three-level Duobinary and optical Duobinary. The results indicate that the optimum scheme depends on the fiber length. The world first experimental demonstration of a real time 40-Gb/s PAM-4 over 20-km SMF link was performed for high speed optical access applications by using 10-G transmitter only. The experimental results were published at ECOC2015 as a post-deadline paper and a following invited journal paper. The real time demonstration paves strong path to practical implementation of high speed NG-PONs using low bandwidth components. Offline DSP based 40-Gb/s PAM-4 PON has also been demonstrated experimentally with successful transmission over 30-km SMF, as far as we know, representing today's best reach performance using only 10-G optics and simple post-DSP (submitted to OFC2017). In addition, 40-Gb/s NG-PON system transmitting multi-band CAP signal over an 80-km SMF using 10-G class transceivers only has also been demonstrated and will be presented at OFC2017 as an invited talk.

For intra-data centre connects scenarios, a comprehensive review work was done of 400 Gigabit Ethernet links using Duobinary, PAM-4, CAP and DMT and comparisons were made between these schemes on aspects of optical power budget, DSP complexity, and power dissipation. Results show that optimum scheme depends on fiber length (up to 10 km SMF), optical modulator (directly vs externally modulated lasers) and lane count used (4 or 8 wavelengths). A novel hybrid multi-band CAP/QAM was proposed and investigated. Experimental demonstrations mainly include a single lane 56-Gb/s multi-band CAP signal transmission over 10-km SMF, a 56-Gb/s (84-Gb/s) PAM-4 signal transmission over 15-km (1.6-km) SMF using long-wavelength VCSEL (top-scored at ECOC2016), and a real time single lane 112-Gb/s DMT link.

For inter-data centre connects covering geographic areas up to 80 km, focus was on experimental demonstration of schemes including PAM-4, multi-band CAP and DMT. The world first demonstration of a real time 400-Gb/s PAM-4 signal transmission over 80-km SMF was performed (top-scored at OFC2016), which was reported by major press such as Reuters, Businesswire, Yahoo and so on. The real time demonstration consolidates following commercialization of the technology for data centre interconnects. In addition, a first experimental demonstration of a 56 Gb/s multi-band CAP signal transmission over an 80-km SMF link was performed with zero overhead pre-FEC signal recovery and enhanced timing jitter tolerance. Experimental comparisons were also made between PAM-4, multi-band CAP and DMT regarding OSNR performance. Results show that PAM-4 has the best OSNR sensitivity and least complex DSP but requires use of dispersion compensation fibre (DCF) to support transmission over 80-km SMF. Both multi-band CAP and DMT need no DCF and both show similar (DMT is slightly better) OSNR performance by utilizing optical vestigial sideband (VSB) and multi-band CAP needs moderate DSP complexity.

In addition to the technical excellence, the project also achieves high level administrative goals. Over 30 publications including 8 invited ones were submitted to and/or published at leading journals (IEEE Comm. Magazine, JLT, OE, OL, etc.,) and top conferences (OFC, ECOC, ACP, WOCC etc.,) in this field. The researcher attended a number of training course/program including a “ADVA FSP 3000R7 Technical Training Course” (4 days) and a German language course (over 10 classes, each takes 90 mins) by ADVA, two short courses by OFC'15 and OFC'16, daily lab hands-on kill improvement by ADVA, and attendance as well of the most important conferences in the field (OFC, ECOC, ACP), and other relevant conferences including WOCC, ITG-Fachtagung Photonische Netze, PIERS and so on. In order to disseminate research output, the research delivered about 8 outreach talks/academic visits to European universities including Bangor University, Aston University, Loughborough University, Southampton University, Bristol University as well as Chinese universities including Southwest Jiaotong University and Shanghai University. The researcher also presented invited talks at prestigious conferences including OFC2017, WOCC2016, PIERS2015/2016, ACP2015, and EMN Meenting on Photonics 2016 and organized/chaired session at WOCC2016, PIERS2015 and DNCOCO2015 (a special session). The esearcher also served as a frequent reviewer for leading journals such as JLT, Opt. Express, PTL, Photonics J. and so on. These activities enable the researcher to significantly improve capacity and reputation as well as establish a wide network with both academy and industry, which underpins the future career success.

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