Impact of physical layer impairments on multi-band metro networks

The traffic increase in optical metro networks will saturate the network capacity in a near future, mainly due to new cloud and 5G services, as well as to an increasing number of network users. The use of other fiber bands, than the usual C-band, is seen as a possible near term solution, for this probable capacity crunch. In this work, a metro network horseshoe topology with nodes capable of switching both C and L-band signals is studied. In particular, we have considered for switching Cband signals, reconfigurable optical add/drop multiplexer and Filterless Drop and Waste (FD&W) node architectures, whereas for switching L-band signals, we have considered only FD&W solutions, both amplified and unamplified. An analytical formalism was developed to assess the impact of the physical layer impairments due to fiber transmission and switching node in a horseshoe network performance. Moreover, the cost and power consumption of the C-band and L-band nodes are analyzed. We concluded that in a network end of life scenario, the L-band nodes cost is 3.5 times higher than the C-band nodes, being 99% of this cost attributed to the transponders. In L-band transmission, a lightpath can cross several spans with 10 or 60 km in the amplified solution. In the unamplified solution, where frequency reuse is allowed, a lightpath consists only on a single 10 km span due to the maximum optical link budget. Considering a -20 dB crosstalk level, a 1.5 dB degradation on the optical power budget is observed.O aumento de tráfego nas redes metropolitanas irá saturar a capacidade das redes num futuro próximo, principalmente devido aos novos serviços em nuvem e 5G, bem como ao aumento do número de utilizadores. O uso de novas bandas na fibra ótica, além da banda C, é visto como uma possível solução para responder a esse aumento de capacidade. Neste trabalho, é apresentada a topologia de rede ”horseshoe”, que contém nós com capacidade para comutar sinais nas bandas C e L. Na banda C, consideram-se as arquiteturas com multiplexadores de inserção/extração reconfiguráveis e arquiteturas sem filtragem, e na banda L, consideram-se apenas soluções sem filtragem, com e sem amplificação. São estudadas, analiticamente, as limitações físicas da transmissão na fibra e comutação dos sinais nos nós da rede ”horseshoe”. Além disso, é realizado um estudo do custo, consumo e capacidade dos nós nas bandas C e L. Num cenário de fim de vida da rede, o custo dos nós na banda L é 3.5 vezes superior aos da banda C. O custo dos transponders constitui 99% do custo final. Na banda L, o sinal pode atravessar várias secções de 10 ou 60 km na solução amplificada. Na solução não amplificada, onde existe reuso de frequência, só há uma secção de 10 km devido ao orçamento máximo de potência na ligação. Para um nível de diafonia de -20 dB, o orçamento de potência diminui 1.5 dB

Minimizing equipment and energy cost in mixed 10G and 100G/200G filterless horseshoe networks with hierarchical OTN boards

Emerging 5G services are changing the way operators manage and optimize their optical metro networks, and the transmission technology and network design process must be tailored to the specific conditions in this segment of the network. Ensuring cost-efficient and energy-efficient network design requires novel approaches that optimize across all network layers. Therefore, to moderate the growth of operators’ expenses, in this paper, we investigate low-cost and energy-efficient cross-layer deployment of hierarchical optical transport network (OTN) boards minimizing equipment and energy consumption cost in mixed 10G and 100G/200G filterless metro networks. We propose an integer linear programming (ILP) model and a genetic algorithm (GA) approach that decide: (i) the node structure by deploying various stacked OTN boards (performing traffic-grooming at the electrical layer) and (ii) lightpath establishment considering coherent and non-coherent transmission technologies. Simulative results on real filterless horseshoe networks with real traffic matrices show that our proposed approaches achieve up to 50% cost savings compared to real-world benchmark deployments

A Transponder Aggregator with Efficient Use of Filtering Function for Transponder Noise Suppression

Colorless, directionless, and contentionless reconfigurable optical add/drop multiplexing (CDC-ROADM) provides highly flexible physical layer network configuration. Such CDC-ROADM must operate in multiple wavelength bands which are being increasingly implemented in optical transmission systems. The operation in C+L bands requires switch devices used in CDC-ROADM to also be capable of multiband operation. Recent studies on wavelength division multiplexing (WDM) systems have pointed out the impact of amplified spontaneous emission (ASE) noise generated by signals of different wavelengths, which causes OSNR degradation. Therefore, it is desirable to filter out the ASE noise from different transponders when multiplexing multiple wavelengths at the transmitter side, especially in a system with non-wavelength selective combiners such as directional couplers and multicast switches. The use of transponder aggregators with filtering functions, such as the M x N wavelength selective switch (WSS), is preferable for this filtering. However, the downside of these devices is that it is difficult to provide economical multiband support. Therefore, we propose an economical transponder aggregator configuration by allowing a certain amount of ASE superposition and reducing the number of filtering functions. In this paper, we fabricated a prototype of the proposed transponder aggregator by combining silica-based planar lightwave circuit technology and C+L band WSS, both commercially available, and verified its feasibility through transmission experiments. The novel transponder aggregator is a practical solution for a multiband CDC-ROADM system with improved OSNR performance.Comment: 10 pages, 11 figures. Submitted to IEEE Journal of Lightwave Technology for possible publicatio

Software Defined Applications in Cellular and Optical Networks

abstract: Small wireless cells have the potential to overcome bottlenecks in wireless access through the sharing of spectrum resources. A novel access backhaul network architecture based on a Smart Gateway (Sm-GW) between the small cell base stations, e.g., LTE eNBs, and the conventional backhaul gateways, e.g., LTE Servicing/Packet Gateways (S/P-GWs) has been introduced to address the bottleneck. The Sm-GW flexibly schedules uplink transmissions for the eNBs. Based on software defined networking (SDN) a management mechanism that allows multiple operator to flexibly inter-operate via multiple Sm-GWs with a multitude of small cells has been proposed. This dissertation also comprehensively survey the studies that examine the SDN paradigm in optical networks. Along with the PHY functional split improvements, the performance of Distributed Converged Cable Access Platform (DCCAP) in the cable architectures especially for the Remote-PHY and Remote-MACPHY nodes has been evaluated. In the PHY functional split, in addition to the re-use of infrastructure with a common FFT module for multiple technologies, a novel cross functional split interaction to cache the repetitive QAM symbols across time at the remote node to reduce the transmission rate requirement of the fronthaul link has been proposed.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Data transport over optical fibre for ska using advanced modulation flexible spectrum technology

Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA.We optimise the flexible spectrum for real-time dynamic channel wavelength assignment, to ensure optimum network performance. We needed to identify and develop novel hardware and dynamic algorithms for these networks to function optimally to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. The antennas of the Square Kilometre Array (SKA) network connect to the correlator and data processor in a simple point-to-point fixed configuration. The connection of the astronomer users to the data processor, however, requires a more complex network architecture. This is because the network has users scattered around South Africa, Africa and the whole world. This calls for upgrade of the classical fixed wavelength spectrum grids, to flexible spectrum grid that has improved capacity, reliable, simple and cost-effectiveness through sharing of network infrastructure. The exponential growth of data traffic in current optical communication networks requires higher capacity for the bandwidth demands at a reduced cost per bit. All-optical signal processing is a promising technique to improve network resource utilisation and resolve wavelength contention associated with the flexible spectrum. Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Each DWDM channel is capable of 10 Gbps transmission rate, which is sliceable into finer flexible grid 12.5 GHz granularity to offer the network elastic spectrum and channel spacing capable of signal routing and wavelength switching for the scalability of aggregate bandwidth. The variable-sized portions of the flexible spectrum assignment to end users at different speeds depend on bandwidth demand, allowing efficient utilisation of the spectrum resources. The entire bandwidth of dynamic optical connections must be contiguously allocated. However, there is an introduction of spectrum fragmentation due to spectrum contiguity related to the optical channels having different width. Thus large traffic demands are likely to experience blocking regardless of available bandwidth. To minimise the congestion and cost-effectively obtain high performance, the optical network must be reconfigurable, achievable by adding wavelength as an extra degree of freedom for effectiveness. This can introduce colourless, directionless and contentionless reconfigurability to route individual wavelengths from fibre to fibre across multiple nodes to avoid wavelength blocking/collisions, increasing the flexibility and capacity of a network. For these networks to function optimally, novel hardware and dynamic algorithms identification and development is a critical task. Such tasks include wavelength assignment, signal routing, network restoration and network protection. In this work, we for the first time to our knowledge proposed a spectrum defragmentation technique through reallocation of the central frequency of the optical transmitter, to increase the probability of finding a sufficient continuous spectrum. This is to improve network resource utilisation, capacity and resolve wavelength contention associated with a flexible spectrum in optical communication networks. The following chapter provides details on a flexible spectrum in optical fibre networks utilising DWDM, optimising transmitter-receivers, advanced modulation formats, coherent detection, reconfigurable optical add and drop multiplexer (ROADM) technology to implement hardware and middleware platforms which address growing bandwidth demands for scalability, flexibility and cost-efficiency. A major attribute is tunable lasers, an essential component for future flexible spectrum with application to wavelength switching, routing, wavelength conversion and ROADM for the multi-node optical network through spectrum flexibility and cost-effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub-carriers and assigning several frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a spectral efficient technique for bandwidth variability, wavelength allocation, routing, defragmentation and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing using low cost, high bandwidth, power-efficient and wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) transmitter directly modulated with 10 Gbps data. This to ensure that majority of the spectrum utilisation at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint reduction and it improves bandwidth utilisation. The technique is flexible in terms of modulation formats and accommodates various formats with spectrally continuous channels, fulfilling the future bandwidth demands with transmissions beyond 100 Gbps per channel while maintaining spectral efficiency

Data transport over optical fibre for ska using advanced modulation flexible spectrum technology

Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA.We optimise the flexible spectrum for real-time dynamic channel wavelength assignment, to ensure optimum network performance. We needed to identify and develop novel hardware and dynamic algorithms for these networks to function optimally to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. The antennas of the Square Kilometre Array (SKA) network connect to the correlator and data processor in a simple point-to-point fixed configuration. The connection of the astronomer users to the data processor, however, requires a more complex network architecture. This is because the network has users scattered around South Africa, Africa and the whole world. This calls for upgrade of the classical fixed wavelength spectrum grids, to flexible spectrum grid that has improved capacity, reliable, simple and cost-effectiveness through sharing of network infrastructure. The exponential growth of data traffic in current optical communication networks requires higher capacity for the bandwidth demands at a reduced cost per bit. All-optical signal processing is a promising technique to improve network resource utilisation and resolve wavelength contention associated with the flexible spectrum. Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Each DWDM channel is capable of 10 Gbps transmission rate, which is sliceable into finer flexible grid 12.5 GHz granularity to offer the network elastic spectrum and channel spacing capable of signal routing and wavelength switching for the scalability of aggregate bandwidth. The variable-sized portions of the flexible spectrum assignment to end users at different speeds depend on bandwidth demand, allowing efficient utilisation of the spectrum resources. The entire bandwidth of dynamic optical connections must be contiguously allocated. However, there is an introduction of spectrum fragmentation due to spectrum contiguity related to the optical channels having different width. Thus large traffic demands are likely to experience blocking regardless of available bandwidth. To minimise the congestion and cost-effectively obtain high performance, the optical network must be reconfigurable, achievable by adding wavelength as an extra degree of freedom for effectiveness. This can introduce colourless, directionless and contentionless reconfigurability to route individual wavelengths from fibre to fibre across multiple nodes to avoid wavelength blocking/collisions, increasing the flexibility and capacity of a network. For these networks to function optimally, novel hardware and dynamic algorithms identification and development is a critical task. Such tasks include wavelength assignment, signal routing, network restoration and network protection. In this work, we for the first time to our knowledge proposed a spectrum defragmentation technique through reallocation of the central frequency of the optical transmitter, to increase the probability of finding a sufficient continuous spectrum. This is to improve network resource utilisation, capacity and resolve wavelength contention associated with a flexible spectrum in optical communication networks. The following chapter provides details on a flexible spectrum in optical fibre networks utilising DWDM, optimising transmitter-receivers, advanced modulation formats, coherent detection, reconfigurable optical add and drop multiplexer (ROADM) technology to implement hardware and middleware platforms which address growing bandwidth demands for scalability, flexibility and cost-efficiency. A major attribute is tunable lasers, an essential component for future flexible spectrum with application to wavelength switching, routing, wavelength conversion and ROADM for the multi-node optical network through spectrum flexibility and cost-effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub-carriers and assigning several frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a spectral efficient technique for bandwidth variability, wavelength allocation, routing, defragmentation and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing using low cost, high bandwidth, power-efficient and wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) transmitter directly modulated with 10 Gbps data. This to ensure that majority of the spectrum utilisation at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint reduction and it improves bandwidth utilisation. The technique is flexible in terms of modulation formats and accommodates various formats with spectrally continuous channels, fulfilling the future bandwidth demands with transmissions beyond 100 Gbps per channel while maintaining spectral efficiency

Directly Phase Modulated Transmitters and Coherent Recivers for Future Passive Optical Networks (PON)

En los últimos años, el tráfico de dato transmitido en las redes ópticas de acceso ha crecido exponencialmente debido a nuevos servicios como pueden ser la computación en la nube, el video online, la realidad virtual y aumentada, el internet de las cosas (IoT) y la convergencia entre las redes ópticas y redes inalámbricas en el paradigma del 5G. Estos nuevos servicios endurecen los requerimientos de las redes ópticas de acceso, como pueden ser unas tasas de datos más altas, un mayor alcance y un mayor número de usuarios. Para abordar estos requerimientos, esta tesis ha investigado, desarrollado y analizado nuevas tecnologías para transmisores y receptores orientadas a los dos tipos de redes ópticas de acceso que la comunidad científica ha identificado como posibles candidatas. Estos dos tipos de redes ópticas son las redes uDWDM y las redes TWDM como las redes NG-PON2 y sus evoluciones.Las redes uDWDM están basadas en la transmisión de tasas de datos relativamente bajas, por debajo de 2.5 Gbps, que son dedicadas en su totalidad a los usuarios finales. Estas tasas de datos relativamente bajas son multiplexadas en longitud de onda usando intervalos frecuenciales estrechos, del orden de 12.5 GHz o 6.25 GHz. En esta tesis, los transmisores modulados directamente en fase se han propuesto como posibles candidatos para estas redes uDWDM. En concreto, se han propuesto un DFB modulado directamente en fase con una tasa de datos de 1 Gbps; un RSOA bombeado por un VCSEL y modulado directamente en fase con una tasa de datos de 1 Gbps; y un VCSEL modulado directamente en fase con una tasa de datos de 1.25 Gbps y 2.5 Gbps. Estas señales moduladas directamente en fase son recibidas con un receptor heterodino con un único fotodiodo (PD) para mantener el coste tan bajo como sea posible. La combinación de estos transmisores modulados directamente en fase con el receptor heterodino con un único PD ha sido probada como unos candidatos muy prometedores para las redes ópticas de acceso basadas en redes uDWDM. Estas combinaciones proveen sensibilidades que varían entre -39.5 dBm y -52 dBm, que se traducen en balances de potencia que van desde 38.5 dB a 51 dB y por lo tanto en ratios de división o número de usuarios de entre 128 y 1024 después de una transmisión de 50 km a través de fibra monomodo estándar (SSMF).Además, los links de 1 Gbps formados por la modulación directa de DFBs o de RSOAs bombeados por VCSELs y el receptor heterodino con un único PD son usados como enlace de subida en canales bidireccionales. Estos enlaces de subida son combinados con enlaces de bajada basados en Nyquist-DPSK generada con un MZM y recibidos con un receptor heterodino de un único PD. Como parte de análisis de los canales bidireccionales, se ha analizado el estudio de la viabilidad del uso de LOs de bajo coste, como DFBs o VCSELs, en los receptores heterodinos con un único PD. Estos canales bidireccionales son también unos candidatos prometedores para las futuras redes uDWDM, ya que en esta tesis se ha probado que pueden proveer enlaces full-duplex de 1 Gbps usando intervalos frecuenciales tan pequeños como 6.25 GHz o 5 GHz. Estos canales bidireccionales tienen balances de potencia que van desde 37 dB a 42 dB y tienen posibles ratios de división de 128 o 256 después de una transmisión de 50 km a través de SSMF.Esta tesis también ha investigado y desarrollado receptores quasicoherentes para redes NG-PON2 y sus evoluciones. Este tipo de redes están basadas en altas tasas de datos, como 10 Gbps para redes NG-PON2 y 25 Gbps para las futuras evoluciones de NG-PON2, en entornos multi longitud de onda donde los usuarios son multiplexados en tiempo y longitud de onda (TWDM). El receptor quasicoherente usa la amplificación coherente gracias a la recepción heterodina y por tanto la sensibilidad del receptor es mejorada en comparación con los esquemas de detección directa. El receptor quasicoherente es independiente a la polarización, lo cual es una característica importante para los receptores coherentes. Además, el receptor quasicoherente permite seleccionar el canal de trabajo sin la necesidad de filtros ópticos y es un receptor independiente de la longitud de onda debido a que el canal de trabajo se puede elegir ajustando la longitud de onda del LO. El receptor quasicoherente de 10 Gbps muestra una sensibilidad -35.2 dBm y por tanto permite un balance de potencias de 35.64 dB y un ratio de división de 128 después de una transmisión de 40 km a través de SSMF.La combinación del receptor quasicoherente con un ecualizador FFE/DFE permite combatir la dispersión cromática de la banda C y conseguir un link de 25 Gbps con un alcance de 20 km a través de SSMF. El receptor quasicoherente a 25 Gbps con ecualización FFE/DFE muestra una mejor sensibilidad de -30.5 dBm con el llamado ecualizador de altas prestaciones, lo que lleva a un balance de potencias de25 dB. Si se utilizada el llamado ecualizador de baja complejidad, la sensibilidad cae a -27 dBm y el balance de potencias cae a 23 dBm. En ambos casos, el receptor quasicoherente a 25 Gbps con ecualización FFE/DFE permite un ratio de división de 32 después de una transmisión de 20 km a través de SSMF.En conclusión, esta tesis ha presentado transmisores (DFB, RSOA y VCSEL) modulados directamente en fase combinados con un receptor heterodino con un único PD como potenciales candidatos para las redes uDWDM. Esta tesis también ha presentados los receptores quasicoherentes como unos candidatos muy prometedores para las redes NG-PON2 y sus futuras evoluciones.<br /