Compensation of nonlinear fibre impairments in coherent systems employing spectrally efficient modulation formats

We investigate electronic mitigation of linear and non-linear fibre impairments and compare various digital signal processing techniques, including electronic dispersion compensation (EDC), single-channel back-propagation (SC-BP) and back-propagation with multiple channel processing (MC-BP) in a nine-channel 112 Gb/s PM-mQAM (m=4,16) WDM system, for reaches up to 6,320 km. We show that, for a sufficiently high local dispersion, SC-BP is sufficient to provide a significant performance enhancement when compared to EDC, and is adequate to achieve BER below FEC threshold. For these conditions we report that a sampling rate of two samples per symbol is sufficient for practical SC-BP, without significant penalties.

Scaling the Advantages of Intra-channel Nonlinearity Compensation in Future Flexible Optical Networks

We report that, contrary to common perception, intra-channel nonlinearity compensation offers significant improvements of up to 4dB, in nonlinear tolerance (Q-factor), in a flexible traffic scenario, and further improvements with increasing local link dispersion, for an optical transport network employing flexible 28Gbaud PM-mQAM transponders.

All-optical OFDM and distributed Raman amplification : challenges to enable high capacities and extend reach

We review recent advances in all-optical OFDM technologies and discuss the performance of a field trial of a 2 Tbit/s Coherent WDM over 124 km with distributed Raman amplification. The results indicate that careful optimisation of the Raman pumps is essential. We also consider how all-optical OFDM systems perform favourably against energy consumption when compared with alternative coherent detection schemes. We argue that, in an energy constrained high-capacity transmission system, direct detected all-optical OFDM with `ideal' Raman amplification is an attractive candidate for metro area datacentre interconnects with ~100 km fibre spans, with an overall energy requirement at least three times lower than coherent detection techniques.

Innovation in leadership development

In the light of the financial crisis and the radically changed conditions in the market place, international leadership development is facing new demands. The Danish-based International Leadership Institute Mannaz has researched the new conditions in collaboration with the Institute of Executive Development in the United States. The research, conducted in 2008 and 2009, combines, in an innovative way, quantitative and qualitative inputs, from both current and future perspectives, from some 111 senior Corporate Executives, Heads of Human Resources and of Learning and Organisational Development in large international corporations headquartered in Europe and the United States; together with the thoughts of some 50 experienced practitioners involved in executive coaching as well as in designing, developing and facilitating leadership development programmes. Also we include a section summarising the key findings from recently published research from other leadership development surveys. Conclusions reveal that the crisis has propelled a long-awaited decline of the traditional classroom-based educational approach to leadership development. Instead, effective leadership development is suggested to build on experiential learning approaches rooted in real life, real time and allowing for more immediate impact and providing for considerably higher relevance and motivation. Coaching, leaders teaching leaders, stretch assignments, action learning, peer networking, customer insights and selective use of technology are seen as important contributors to the leadership development process going forward.

Impact of power allocation strategies in long-haul few-mode fiber transmission systems

We report for the first time on the limitations in the operational power range of few-mode fiber based transmission systems, employing 28Gbaud quadrature phase shift keying transponders, over 1,600km. It is demonstrated that if an additional mode is used on a preexisting few-mode transmission link, and allowed to optimize its performance, it will have a significant impact on the pre-existing mode. In particular, we show that for low mode coupling strengths (weak coupling regime), the newly added variable power mode does not considerably impact the fixed power existing mode, with performance penalties less than 2dB (in Q-factor). On the other hand, as mode coupling strength is increased (strong coupling regime), the individual launch power optimization significantly degrades the system performance, with penalties up to ∼6dB. Our results further suggest that mutual power optimization, of both fixed power and variable power modes, reduces power allocation related penalties to less than 3dB, for any given coupling strength, for both high and low differential mode delays. © 2013 Optical Society of America.

„Fern im dänischen Norden ein Bruder”:Thomas Mann und Herman Bang. Eine literarische Spurensuche

This study for the first time demonstrates and analyses the full extent of Danish impressionist writer Herman Bang’s influence on one of Germany’s major authors, Thomas Mann. Mann was an avid reader of Bang’s works and he regarded the Scandinavian writer as a kindred spirit, a “brother up north”, who “taught [him] much”. It has previously been accepted that Bang was an inspiration for Mann in his formative years. However, as this study conclusively shows, references to Bang’s works occur throughout Mann’s writings, from the early novellas to the late novels. The book argues that Mann was not only impressed by Bang’s highly individual style of impressionist writing but that his fascination for Bang’s works was to a large extent based on this author’s recurrent depiction of decadence, his handling of artistic motifs and his treatment of erotic themes. Bang’s topical focus on the problematically isolated lives of artists and aristocrats as well as his insights on the destructive nature of love and sexuality – particularly of homoerotic desire – were surprisingly similar to Mann’s own views on these topics and yet provoked him to produce heavily referenced counter versions of Bang’s works. This phenomenon is explored in the context of Mann’s struggle with his own homosexuality and the attraction that death and decadence exerted over him. Most of Mann’s writings are in that way indebted to Bang. In addition, Mann’s frequent use of homoerotic subtexts and his depiction of female characters were noticeably influenced by Bang’s literary techniques. All these different, yet closely interlinked, aspects of Mann’s creative appropriation of Bang’s works are analysed and discussed in this study. To conclude, Mann’s references to Bang’s works are schematised and an attempt is made to characterise Mann’s intertextual practice in general in the context of his famous use of irony.

Digital fiber nonlinearity compensation:toward 1-Tb/s transport

The world is connected by a core network of long-haul optical communication systems that link countries and continents, enabling long-distance phone calls, data-center communications, and the Internet. The demands on information rates have been constantly driven up by applications such as online gaming, high-definition video, and cloud computing. All over the world, end-user connection speeds are being increased by replacing conventional digital subscriber line (DSL) and asymmetric DSL (ADSL) with fiber to the home. Clearly, the capacity of the core network must also increase proportionally. © 1991-2012 IEEE.

Intra-channel nonlinearity compensation for PM-16QAM traffic co-propagating with 28Gbaud m-ary QAM neighbours

We quantify the benefits of intra-channel nonlinear compensation in meshed optical networks, in view of network configuration, fibre design aspect, and dispersion management. We report that for a WDM optical transport network employing flexible 28Gbaud PM-mQAM transponders with no in-line dispersion compensation, intrachannel nonlinear compensation, for PM-16QAM through traffic, offers significant improvements of up to 4dB in nonlinear tolerance (Q-factor) irrespective of the co-propagating modulation format, and that this benefit is further enhanced (1.5dB) by increasing local link dispersion. For dispersion managed links, we further report that advantages of intra-channel nonlinear compensation increase with in-line dispersion compensation ratio, with 1.5dB improvements after 95% in-line dispersion compensation, compared to uncompensated transmission. © 2012 Optical Society of America.

Nonlinearity compensation via spectral inversion and digital back-propagation:a practical approach

We report performance enhancements enabled by pre-dispersed spectral inversion equivalent to that of ideal back-propagation, with further x2 increase in reach from multi-channel compensation, with spectral inversion employed upto 400km (from mid-link) with <1dB penalties. © 2012 OSA.

Multi-wavelength regeneration of differentially phase-encoded signals using phase sensitive amplification

We summarize the results of our recent demonstration of the first multi-channel regenerator for phase encoded signals. By developing a novel inline phase sensitive amplification scheme simultaneous suppression of deterministic phase distortion on two independent 42.66 Gbit/s DPSK modulated signal wavelengths was achieved. © 2012 SEE.

The Experience of the Arnamagnæan Institute, Copenhagen

The Arnamagnæan Institute, principally in the form of the present writer, has been involved in a number of projects to do with the digitisation, electronic description and text-encoding of medieval manuscripts. Several of these projects were dealt with in a previous article 'The view from the North: Some Scandinavian digitisation projects', NCD review, 4 (2004), pp. 22-30. This paper looks in some depth at two others, MASTER and CHLT. The Arnamagnæan Institute is a teaching and research institute within the Faculty of Humanities at the University of Copenhagen. It is named after the Icelandic scholar and antiquarian Árni Magnússon (1663-1730), secretary of the Royal Danish Archives and Professor of Danish Antiquities at the University of Copenhagen, who in the course of his lifetime built up what is arguably the single most important collection of early Scandinavian manuscripts in the world, some 2,500 manuscript items, the earliest dating from the 12th century. The majority of these are from Iceland, but the collection also contains important Norwegian, Danish and Swedish manuscripts, along with approximately 100 manuscripts of continental provenance. In addition to the manuscripts proper, there are collections of original charters and apographa: 776 Norwegian (including Faroese, Shetlandic and Orcadian) charters and 2895 copies, 1571 Danish charters and 1372 copies, and 1345 Icelandic charters and 5942 copies. When he died in 1730, Árni Magnússon bequeathed his collection to the University of Copenhagen. The original collection has subsequently been augmented through individual purchases and gifts and the acquisition of a number of smaller collections, bringing the total to nearly 3000 manuscript items, which, with the charters and apographa, comprise over half a million pages.

Impact of longitudinal power budget in coherent transmission systems employing digital back-propagation

We report the impact of longitudinal signal power profile on the transmission performance of coherently-detected 112 Gb/s m-ary polarization multiplexed quadrature amplitude modulation system after compensation of deterministic nonlinear fibre impairments. Performance improvements up to 0.6 dB (Q(eff)) are reported for a non-uniform transmission link power profile. Further investigation reveals that the evolution of the transmission performance with power profile management is fully consistent with the parametric amplification of the amplified spontaneous emission by the signal through four-wave mixing. In particular, for a non-dispersion managed system, a single-step increment of 4 dB in the amplifier gain, with respect to a uniform gain profile, at similar to 2/3(rd) of the total reach considerably improves the transmission performance for all the formats studied. In contrary a negative-step profile, emulating a failure (gain decrease or loss increase), significantly degrades the bit-error rate.

Polarization multiplexed 16QAM transmission employing modified digital back-propagation

We experimentally demonstrate performance enhancements enabled by weighted digital back propagation method for 28 Gbaud PM-16QAM transmission systems, over a 250 km ultra-large area fibre, using only one back-propagation step for the entire link, enabling up to 3 dB improvement in power tolerance with respect to linear compensation only. We observe that this is roughly the same improvement that can be obtained with the conventional, computationally heavy, non-weighted digital back propagation compensation with one step per span. As a further benchmark, we analyze performance improvement as a function of number of steps, and show that the performance improvement saturates at approximately 20 steps per span, at which a 5 dB improvement in power tolerance is obtained with respect to linear compensation only. Furthermore, we show that coarse-step self-phase modulation compensation is inefficient in wavelength division multiplexed transmission.

All-optical OFDM and distributed Raman amplification:challenges to enable high capacities and extend reach

We review recent advances in all-optical OFDM technologies and discuss the performance of a field trial of a 2 Tbit/s Coherent WDM over 124 km with distributed Raman amplification. The results indicate that careful optimisation of the Raman pumps is essential. We also consider how all-optical OFDM systems perform favourably against energy consumption when compared with alternative coherent detection schemes. We argue that, in an energy constrained high-capacity transmission system, direct detected all-optical OFDM with `ideal' Raman amplification is an attractive candidate for metro area datacentre interconnects with ~100 km fibre spans, with an overall energy requirement at least three times lower than coherent detection techniques.

Scaling the Advantages of Intra-channel Nonlinearity Compensation in Future Flexible Optical Networks

We report that, contrary to common perception, intra-channel nonlinearity compensation offers significant improvements of up to 4dB, in nonlinear tolerance (Q-factor), in a flexible traffic scenario, and further improvements with increasing local link dispersion, for an optical transport network employing flexible 28Gbaud PM-mQAM transponders.