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Increased global traffic puts tough requirements not just on fiber communications links but on the entire network. This manifests itself in multiple ways, including how to optimize wavelength routing around the network, how to maximize the benefits arising from fine-control DSP with increasingly accurate real-time monitoring, and how to best deploy multiband or multiple fiber connectivity. This article will summarize research into all these areas to present a full picture of how future optical networks will play their role in supporting the continuing traffic demands of broadband, 5G, and associated applications. [ABSTRACT FROM AUTHOR]

The migration of DataCenters into Metropolitan Area Networks creates new challenges which include the need for rapid service provisioning and recovery and new, cost-effective, connectivity schemes. Here we propose and demonstrate a truly dynamic transportation platform tailored for a metro network. The novelty of the proposed architecture is that the dynamic data-plane exploits available commercial PON technology while the dynamic control-plane is SDN-enabled using OpenFlow/Netconf. The dynamic operation of the platform in several interesting scenarios is demonstrated on an experimental test-bed. [ABSTRACT FROM AUTHOR]

In high speed optical transmission networks, OSNR is the key optical performance parameter. We propose a novel technique for non-intrusive in-band OSNR derivation based on real-time pre-FEC bit error rate (BER) measurement from optical transponders, which exploits pre-measured and calibrated pre-FEC BER versus OSNR curves and multiple modulation formats to ensure accurate OSNR derivation over a wide range. We report a successful field trial of this novel in-band OSNR technique, in which we have demonstrated and verified the accurate OSNR derivation over both a 359 km field trial link and a live 727 km flexible grid optical link using 64 GBaud flexible rate optical transponders with modulation formats 100G DP-QPSK, 200G DP-16QAM, and 200G DP–QPSK. Compared with standard signal “on” and “off” measurement, an OSNR accuracy within ±1 dB was achieved for all three modulation formats. We also investigated the impact of fiber nonlinearity at different signal powers on the accuracy of this technique. It is shown that this novel technique provides reliable and accurate OSNR derivation for the optical signals operating in normal power regime making it suitable for practical network applications. [ABSTRACT FROM PUBLISHER]

We report the first successful real-time optical superchannel field trials of 5.6 Tb/s over 359 km and 2 Tb/s over a live 727 km flexible grid link using production grade 64 GBaud flexible rate optical transponders. Up to 5.6 Tb/s optical superchannels were successfully demonstrated over a 359 km fully managed flexible grid optical link, where the superchannel comprises a maximum of 28 × 64 GBaud 200 G DP – QPSK subchannels. A 100 GE client signal was transported over all the subchannels, demonstrating stable, long term end-to-end error free performance. A record net spectral efficiency of 3.92 bit/s/Hz was achieved for the 64 GBaud 200 G DP – QPSK, with channel spacing as narrow as 51 GHz. We also successfully demonstrated fast superchannel capacity turn-up, via software configuration of the flexible rate transponders, from 2.6 to 5.2 Tb/s including 100 GE client mappings, which is equivalent to a capacity up-lift of approximately 2 Tb/min. In a further trial over a 727 km live flexible grid optical link between London and Dublin, we successfully demonstrated real-time 2 Tb/s superchannel transport using long reach 64 GBaud 200 G DP – QPSK operating together with 100 G DP – QPSK and 200 G DP – 16 QAM channels enabled by the flexible rate transponders. Stable, long term error free performance was measured of the terabit optical channels alongside live customer traffic. [ABSTRACT FROM PUBLISHER]

The switchless elastic rate node (SERANO) is an elastic optical network block architecture facilitating reduction in network cost and blocking due to spectral fragmentation while extending the capacity-reach product in translucent optical networks. We present an analytical mathematical method for minimizing the number of transceivers that are solely used to construct this block, albeit a finite blocking probability. Moreover, based on a realistic traffic matrix and making use of a networking planning tool, we deduce a SERANO's block dimension for BT's national backbone network. Finally, we estimate the conditions under which the cost of a SERANO block is lower to the corresponding electronic switch for providing important networking functions like 3R regeneration, defragmentation, and network reoptimization. [ABSTRACT FROM PUBLISHER]

We report the first successful field trial of up to 3 Tb/s real-time DP-16 QAM optical superchannel transport over 359-km EDFA-amplified fully managed flexible grid optical infrastructure using production grade hardware and management software from a live network operation center. The spectrum of the flexible grid ROADM was configured according to the requirement of the optical superchannel from a minimum of 37.5 up to 400 GHz with a resolution of 12.5 GHz. Spectral windows larger than 400 GHz were achieved by configuring multiple adjacent spectral slots enabling higher superchannel capacities. The optical superchannels of up to 3 Tb/s propagated alongside standard 50-GHz grid wavelength channels at 100 Gb/s. Stable error-free performance was measured for all sub-channel spacings down to 33.5 GHz, where a record net spectral efficiency of 5.97 b/s/Hz was achieved, an improvement of 49.25% over standard 50 GHz grid. We also show results on optical margin requirements when operating across a range of sub-channel spacings corresponding to different spectral efficiencies. Furthermore, a key technology building block for the 3-Tb/s optical superchannel, 200 G DP-16 QAM was trialed in a live WDM network to evaluate and demonstrate its applicability for deployment. [ABSTRACT FROM PUBLISHER]

We demonstrate how maximum entropy (MaxEnt) allocation strategies can optimally determine links within a flexgrid elastic optical network, thus requiring multiple fiber pairs to support 100% capacity growth with 34.3% improvement in the uniformity of spectrum allocations. We show how adding additional fiber to those links, which feature the highest number of demands in a link, allows optimum allocation of network capacity resources to all source-destination (S-D) demand pairs and maximizes the available spectral capacity to each demand. We also analyze the case of adding additional fiber to a link in order to reduce the number of contiguous demands present in the associated fiber, as an additional means to maximize the allowable channel capacity for each S-D demand. [ABSTRACT FROM PUBLISHER]

We report the first successful field trial of a realtime alien superchannel over a 410-km DCM-less optical fiber link using only EDFA amplification. We have demonstrated a record 1.4-Tb/s alien superchannel transported alongside native 40G and 100G wavelengths over a third party optical infrastructure using software reconfigurable DP-16QAM/QPSK production hardware, achieving spectral efficiency of up to 5.7 bit/s/Hz. Stable long term error-free performance was measured in a real network environment for subchannel spacing as narrowas 36 GHz, giving a spectral efficiency improvement of~40% compared with standard 50 GHz grid. We have also demonstrated, for the first time, software reconfigurable modulation and capacity of an optical superchannel with subminute switching time. The subchannels can be flexibly and independently reconfigured to enable variable capacity in future flexible optical networks. In addition, robust PMD tolerance of the DP-16 QAM superchannel is measured, which allows network operators to make use of their old, high PMD fibers without the requirement of fiber measurement and selection. [ABSTRACT FROM AUTHOR]

This article reports the work on next generation transponders for optical networks carried out within the last few years. A general architecture supporting super-channels (i.e., optical connections composed of several adjacent subcarriers) and sliceability (i.e., subcarriers grouped in a number of independent super-channels with different destinations) is presented. Several transponder implementations supporting different transmission techniques are considered, highlighting advantages, economics, and complexity. Discussions include electronics, optical components, integration, and programmability. Application use cases are reported. [ABSTRACT FROM PUBLISHER]

We present two complementary routing and spectrum assignment (RSA) algorithms that use a quantitative fragmentation metric using the concept of Shannon entropy in flexgrid networks. Applying the minimum-entropy (MinEnt) approach to the BT network, support for almost 10% more demands in a static growth scenario is shown. We also present results for a maximum-entropy (MaxEnt) RSA approach, implemented using a genetic algorithm, and operated on the same real BT network topology. The MaxEnt approach avoids fragmentation problems, and it is anticipated that this can increase network utilization. [ABSTRACT FROM PUBLISHER]

Flexgrid technology has recently been presented as the most promising option for upgrading the currently operating fixed grid optical networks and extending their capacity to be able to deal with the massive traffic volumes forecast for the next decade. Although the current traffic is successfully supported on fixed grid networks, flexgrid technology brings features that are not offered by the fixed grid networks, such as transporting optical connections with a capacity beyond 100 Gb/s and elasticity against time-varying traffic. In light of this, a gradual fixed grid to flexgrid migration is generally accepted in order to add these useful features to the network. In this article, we study the migration process where flexgrid is deployed in the network progressively, and review the main drivers and open issues induced by its deployment. [ABSTRACT FROM AUTHOR]

We report the first successful coherent 100G IP over WDM alien wavelength field trial over WDM infrastructures spanning a total distance of 769 km, demonstrating the feasibility and robust performance of a simplified 100G IP over WDM core network architecture. Key performance aspects have been investigated including co-propagation of a 100G IP over WDM alien wavelength and native wavelengths generated from WDM transponders, polarization mode dispersion tolerance, and operation without in-line dispersion compensation modules. We also demonstrated the feasibility of a 100G IP over WDM alien wavelength over multiple WDM systems and optical router or regenerator bypass. In addition, we show evaluation results on the key performance management and monitoring functions with a coherent 100G IP over WDM optical interface in the core router. [ABSTRACT FROM PUBLISHER]

Optical networks are undergoing significant changes, fueled by the exponential growth of traffic due to multimedia services and by the increased uncertainty in predicting the sources of this traffic due to the ever changing models of content providers over the Internet. The change has already begun: simple on-off modulation of signals, which was adequate for bit rates up to 10 Gb/s, has given way to much more sophisticated modulation schemes for 100 Gb/s and beyond. The next bottleneck is the 10-year-old division of the optical spectrum into a fixed ?wavelength grid,? which will no longer work for 400 Gb/s and above, heralding the need for a more flexible grid. Once both transceivers and switches become flexible, a whole new elastic optical networking paradigm is born. In this article we describe the drivers, building blocks, architecture, and enabling technologies for this new paradigm, as well as early standardization efforts. [ABSTRACT FROM PUBLISHER]

The explosion of current demand has brought the contemporary multidomain core network paradigm to its limit. In the quest for new approaches that exploit recent developments in optical technology, a novel network architecture that obviates most of the expensive and loss-prone centralized all-optical switches is described in this work. It is based on clustered architecture for nodes in optical networks and features a reconciliation between dynamic resource allocation and guaranteed end-to-end network performance in a multidomain network. This article enhances the distributed, collision-free slot aggregation inside domains of clustered core nodes with dynamic switching of slots/frames between the domains. Thus, it can support dynamic sub-wavelength allocations between network domains, using standard burst-switching techniques. This extends the high efficiency and multiplexing gain into the inter-domain network even under highly bursty traffic. It features both low-cost optical add/drop edge nodes exploiting WDM transmission and agile and modular centralized electro-optical switches that are presented in conjunction with the overall network architecture. Its performance exhibits very low burst loss probability traded for a higher but tolerable and bounded delay. [ABSTRACT FROM AUTHOR]

The manner and exact timing of the evolution of the widely used DWDM infrastructure to a transparent optical network will be judged on economic circumstances and network performance. In this context this article elaborates on a methodology developed within the Project 1ST NOBEL,¹ for integrating cost functions and other design constraints into the planning of a DWDM network while considering this evolution perspective to a transparent optical network. This systematic approach builds upon the experience of static network design and is sub- stantiated by specific examples in this article. [ABSTRACT FROM AUTHOR]

This paper discusses both UK-based and global Internet data bandwidth growth, beginning with historical data for the BT network. We examine the time variations in consumer behaviour and how this is statistically aggregated into larger traffic loads on national core fibre communications networks. The random nature of consumer Internet behaviour, where very few consumers require maximum bandwidth simultaneously, provides the opportunity for a significant statistical gain. The paper looks at predictions for how this growth might continue over the next 10-20 years, giving estimates for the amount of bandwidth that networks should support in the future. The paper then explains how national networks are designed to accommodate these traffic levels, and the various network roles, including access, metro and core, are described. The physical layer network is put into the context of how the packet and service layers are designed and the applications and location of content are also included in an overall network overview. The specific role of content servers in alleviating core network traffic loads is highlighted. The status of the relevant transmission technologies in the access, metro and core is given, showing that these technologies, with adequate research, should be sufficient to provide bandwidth for consumers in the next 10-20 years. [ABSTRACT FROM AUTHOR]