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Centers of Excellence (CEs)
The concept of EURO-FOS CEs
Research within EURO-FOS was organized in a number of research topics (RTs) that were falling within 4 centres of excellence (CEs), i.e. within 4 areas of optical communications. Notably, the relevant research was implemented by joint experimental activities that were usually spanning across multiple RTs and areas, as they were representing complex experimental endeavours, enabled by the diverse expertise of the network participants and the availability of a large variety of advanced equipment. The four scientific areas of interest within EURO-FOS were the following:
CE1: Digital Optical Transmission Systems

The advent of WDM, the realization of broadband fiber amplifiers combined with the development of high-speed electronics has unlocked the potential of fiber-optic technology for transporting data at ultra-high capacities in the same fiber. Core and metro-core networks have been in the spotlight due to the ever increasing requirements for more capacity. This CE is dedicated to the investigation, design and experimental evaluation of new photonic subsystems that enable higher capacities, longer reach, better transmission performance and higher bandwidth efficiency that are key issues for enabling multi-Terabit capacity transmission systems.

The relevant activities were led by Heinrich-Hertz Institut (HHI) and were dedicated to the investigation, design and experimental evaluation of new photonic subsystems that enable higher capacities, longer reach, better transmission performance and higher bandwidth efficiency for high (multi-Terabit) capacity transmission systems. The development of such systems is considered today as the only viable way to meet the increasing capacity demands across Internet that are generated today by the end-users and are associated with a number of popular broadband services and applications such as high-definition tv, social media etc. Topics of interest within CE1 included multi-carrier transmission systems for core and metro networks with particular emphasis on orthogonal frequency division multiplexing (OFDM) techniques, coherent transmission systems using spectrally efficient (higher-order) modulation formats, combination of optical time-division multiplexing (OTDM) technology with multi-level modulation formats, and in the last year of the network transmission systems using multi-mode and multi-core optical fibres.

The concepts developed and the results obtained during the 4 years of the network have been really many and significant. Examples include the demonstration by HHI of transmission of eight 28 Gbaud 16-QAM channels over 480 km using a real-time transmitter, the development of a Nyquist-WDM Tb/s super-channel transmission system by POLITO, with symbol rate up to 30 Gbaud, subcarrier spacing down to Nyquist limit and maximum distance up to trans-oceanic distances, the demonstration by KIT and industrial associates of EURO-FOS of an all-optical OFDM system accommodating 26 Tb/s line-rate OFDM streams, the development and experimental testing by ACREO, HHI, Chalmers, TNI, IT, POLITO and Inst. TELECOM of algorithms and techniques for the mitigation of nonlinear effects during propagation of optical signals, the demonstration by TU/e and DTU of optical packet switching and detection of high-speed OTDM data packets up to a speed of 640 Gb/s, a record transmission over 110 km of an 0.87 Terabit/s OTDM signal with D8PSK modulation format and polarization diversity by Chalmers, Inst. TELECOM, DTU and ICCS/NTUA, and the design and implementation of signal processing techniques for gridless/elastic networking environments by UEssex and SSSUP.

CE2: Optical Sources & Amplification Systems

The CE on optical sources and amplification systems focuses on the realization of cost-effective, small footprint and low power consumption optical source subsystems. The functional integration of photonic components can lead to new concepts on CW or pulsed sources with superior performance and characteristics compared to traditional approaches followed in today’s networks. Moreover, an integral part of this center is research of amplification solutions using semiconductor or fiber. The EDFA has revolutionized photonics during the 1990s and has fuelled cost-effective WDM networks. Today, research on amplification is more active than ever with new issues to be solved and agreed upon, including high-functionality amplification systems, ultra-wideband amplifier implementations and higher power and high conversion efficiencies.

This subset of activities was coordinated by Scuola Superiore Sant' Anna (SSSUP) and was related to the investigation of novel amplification systems for access and burst-traffic networks, new types of semiconductor optical amplifiers based on quantum dots (QD-SOAs), techniques and applications of parametric amplification and development of novel schemes for tunable laser sources for telecom and sensing applications.

Also for this set of activities the concepts that were developed and the results that were obtained have been significant. Main activities included the investigations by UPC, IT and AIT on remotely pumped amplification schemes that are suitable for amplification in extended reach passive optical network (PON) architectures, the investigations of quantum dot semiconductor optical amplifiers (QD-SOAs) by KIT and HHI, the development by UPVLC of mode-locked lasers based on novel nanomaterials (carbon-nanotubes), the development by UPVLC, SSSUP and DTU of high-quality mode-locked lasers as multi-wavelength comb sources in integrated WDM-PON and millimeter-wave radio architectures, the development by Inst. TELECOM in collaboration with Orange Labs of low-chirp, multi-wavelength sources based on electro-optic modulation, with excellent perspectives for use in WDM-PONs, and the joint investigations by Chalmers, DTU, TNI and HHI on the topic and the optimization parameters of optical parametric amplification that can further extend the reach of transmission systems with significant positive impact on their cost and energy efficiency.

CE3: High-Speed Optical Network Subsystems

Optical core/metro networks have evolved from point-to-point high-capacity links to dynamically re-configurable networks driven by the traffic generated from new bandwidth-hungry applications. This is also confirmed by the successful deployment of mesh-capable Reconfigurable Add-Drop Multiplexers (ROADMs). Next generation optical networks will be capable of dynamically allocating bandwidth, setting-up and tearring-down lightpaths and providing more advanced real-time resources allocation, evolving from static network topologies to “living networks” that change and adopt according to bandwidth requirements. This CE focuses on high-speed, high-performance photonic subsystems found in transmission and switching photonic systems. Specifically, this CE coordinates efforts on the development of photonic subsystems that are vital parts of routers and cross-connects in dynamic WDM network architectures. In addition, a major thrust in the CE is the identification of the role of all-optical technology in future networks.

Joint research activities within this area were coordinated by DTU and were devoted to the investigation of the role of all-optical techniques for developing next-generation routers and cross-connects in optical network architectures. Efforts focused in particular on the development of all-optical processing units for advanced modulation formats, the investigation of a variety of all-optical switching technologies, the development of novel clock-recovery and regeneration schemes, as well as the integration of sub-modules for the implementation of fundamental functionalities in optical routing systems.

The work within CE3 has been impressive. Significant outcome of this work relates to the development by KIT and HHI of a self-coherent receiver for polarization multiplexed DQPSK signals, the demonstration by DTU and Inst. TELECOM of the first 650 Gb/s OTDM detector performing clock recovery, channel identification and multiplexing, the demonstration by ICCS/NTUA, SSSUP and TU/e of a complex contention resolution scheme for nodes in optical packet switching (OPS) networks, the demonstration by ICCS/NTUA, HHI and industrial affiliates of a complex phase-insensitive regenerator for OOK, BPSK and QPSK signals, the demonstration by Inst. TELECOM, ICCS/NTUA and external academic partners of an optical code division multiple access (OCDMA)-based packet forwarding/switching optical node, and a large-scale experimental demonstration of an all-optical router relying on SOA-based switching elements.

CE4: Next-generation Optical Access Subsystems

Today we are witnessing an unprecedented growth of access networks worldwide with copper and optical technologies as the main technology solutions for providing ample bandwidth to the end-user in the Mb/s region. Photonic technology is already gaining ground over competing copper technology solutions and this is verified by the explosive deployment of passive optical networks (PONs) and point-to-point active Ethernet networks, in USA, Japan, Korea, and more recently in Europe. Broadband penetration rates are continuously increasing and new data connections now translate to fast internet, combined voice and data and even triple play applications with several Mb/s, offered by incumbents, alternative internet service providers (ISPs) or multi-service providers (MSOs) in the US. As such, optical access networks have attracted significant attention for creating components, subsystems and ultimately networks, capable of providing high symmetric bandwidth, on-demand and at low cost. The center of attention is now on the development of next generation of photonic components and their functional integration into subsystems for realizing the building blocks of such networks.

The research activities of CE4 were led by Universitat Polytècnica de Catalunya (UPC) and was devoted to the study of novel components and subsystems for passive optical networks (PONs) and wired-wireless hybrid networks that will implement fibre-to-the-x (FTTx) architectures and will allow for bringing the full potential of optical communications till the final users (i.e. the citizens) of the networks. Research focused on advanced radio-over-fiber (RoF) techniques, monitoring and mitigation of transmission impairments in extended reach PON architectures, novel designs of user terminals and optical line terminal (OLT) subsystems including burst-mode receivers, optical transmitters, optical signal generation devices, as well as remote node architectures and modules for metro-access convergence.

The work has been impressive also in this case. Research highlights include the first demonstration by TU/e and UPVLC of bidirectional transmission of ultra wide band (UWB) signals over a single 100 μm core plastic fiber, the transmission of multi-standard OFDM-based signals in coexistence with legacy baseband data signals by UPVLC, UEssex and IT, the demonstration by UPC of a variety of RSOA-based ONU designs, the demonstration by ICCS/NTUA and UPC of optically-assisted downstream cancellation techniques using Fabry-Perot filters at the ONU, and the design, development and application of novel burst-mode receivers in PON scenarios by IMEC, UPC, TNI and ICCS/NTUA.

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