Today's Optical Networks Research Articles

WDM Network Issues: QOT Impairments, Dynamic Bandwidth Allocation, Modeling and Monitoring Schemes based on ML

Machine Learning (ML) has recently drawn the interest of both academics and professionals in the optical networking area to solve several problems. This trend has been triggered largely by the vast amount of available data (i.e., signal strength metrics, network alerts, etc.) and the large range of optimization criteria available in today's optical networks (such as modulation format, light path routes, transport wavelength, etc.). WDM systems are popular in the telecommunications industry. It increases network bandwidth without laying more cable. WDM technology in optical communication transports multiple optical carrier signals on a single fibre using various wavelengths of laser light. Wavelength division multiplexing (WDM) is an efficient strategy for leveraging the wide bandwidth of optical fibres to meet the rapid rise in demand for bandwidth on the Internet. WDM plays an essential role in both core and access networks in the communication network and faces various issues like its network performance is affected due to QoT impairments, Dynamic Bandwidth Allocation problem, Modeling, and Monitoring issues. Physical impairments are an issue in WDM and can cause calls to be blocked if the transmission quality is calculated in terms of minimum bit-error-rate. Dynamic allocation of bandwidth in WDM provides a crucial challenge for the effective and equal usage of the passive optical network upstream bandwidth when supporting the QoS specifications of various traffic groups. Fast attack monitoring can prevent the failure of vast volumes of data on all-optical networks. So, monitoring and modeling in a WDM network is also a critical issue. To solve these issues in WDM networks, more intelligence resources in scalable optical networks are necessary. ML techniques are demonstrating superiority in solving these issues. In this paper, a small detail about the WDM network is presented. Then, some WDM issues like QOT impairments, Dynamic Bandwidth Allocation, and modeling and monitoring are discussed, and then, in the next section focus on some ML techniques for solving these issues are presented.

Applying cognitive dynamic learning strategies for margins reduction in operational optical networks

Today's optical transport networks are complex already and the support of the new arising services will further increase such complexity. Traditional deterministic network procedures will need to be revisited, especially their operations. Network Operators will require more dynamic approaches to get the best out of their infrastructure. In this context, cognition and machine learning techniques can provide innovative management solutions for traditional telecom operators. In this paper, we explore a dynamic cognitive approach to improve the adaption of Network Operators' operational processes to the new digital age. We propose a dynamic strategy considering the Case-Base Reasoning (CBR) technique for helping to reduce overall costs by optimizing operation margins. In this way, highly competitive exploitation methods to support new services can be deployed. The proposed dynamic algorithms can achieve higher transmitted power efficiency, up to 20% versus previously proposed static solutions, prolonging the transceivers' lifetime and thus addressing telco operator costs reduction.

Solid-Type Low-Latency Optical Fiber With Large Effective Area

Low-latency transmission is required by services emerging in today's optical communication networks, such as machine-to-machine communication. As transmission distances are now reaching several thousands of kilometers, the propagation latency in optical fiber cannot be ignored. In this study, we propose a solid-type low-latency optical fiber that has lower group delay than conventional silica core fibers. Numerical analyses and measurements show 0.3% lower group delay than a conventional silica core fiber, and its excellent optical properties include its large effective area, low nonlinearity and low loss comparable to that of conventional single mode fiber.

Scaling SDM Optical Networks Using Full-Spectrum Spatial Switching

In today's optical networks, the capacity supported by a single optical fiber is far higher than the demand between source–destination pairs. Thus, to take advantage of the installed capacity, lightpaths allocated between distinct source–destination pairs share the capacity provided by an optical fiber. This sharing is only possible if these lightpaths have different wavelengths. With the exponential evolution of traffic, the demand between source– destination pairs in a network can approach or exceed the capacity of a single fiber. In this scenario, spacedivision multiplexing (SDM) networks appear as a viable option, and new network-sharing technologies become relevant. In this paper, we study different switching approaches for SDM networks with uncoupled spatial superchannels—such as networks with multicore fibers or bundles of single-mode fibers—which result in different network-sharing strategies. We start by comparing three switching architectures considering the evolution of traffic over time: (1) full-spectrum spatial switching (full-spectrum SS); (2) wavelength switching (WS) of uncoupled spatial superchannels; and (3) independent switching (IS) of spatial and wavelength channels. IS provides high network flexibility at the cost of complex switching nodes. On the other hand, full-spectrum SS and WS simplify network nodes but reduce flexibility by switching superchannels. Simulation results indicate that WS offers poor utilization in the long term. Full-spectrum SS, in contrast, exhibits low utilization in the short term, but outperforms IS in the long term. We also propose alternative hybrid switching strategies that start with IS and change to full-spectrum SS after a certain number of spatial channels are activated. The simulations suggest that well-designed strategies for migration from IS to full-spectrum SS delay premature activation investments while saving on switching costs.

SBS-enhanced FWM for polarization division multiplexed signals in coherent communication systems.

Stimulated Brillouin scattering (SBS) is applied to improve the performance of polarization insensitive four-wave mixing (FWM) realized with two orthogonal pumps. By manipulating the phase matching condition with SBS-induced phase change, we achieve conversion efficiency improvement up to 6dB with negligible polarization dependence. Our approach is implemented in a coherent communication system where polarization division multiplexing (PDM) quadrature phase shift keying (QPSK) signal is applied. The quality of the converted idler is evaluated in both back-to-back (BtB) and transmission systems. Our experimental results show that the converted signal enjoys an improved conversion efficiency with negligible polarization-induced distortion. The SBS-enhanced Q factor leads to an extension of the transmission distance by 240km. The results indicate that SBS-enhanced FWM can accommodate the advanced modulation formats and multiplexing schemes in today's optical networks.

Compact sorting of optical vortices by means of diffractive transformation optics.

The orbital angular momentum (OAM) of light has recently attracted a growing interest as a new degree of freedom in order to increase the information capacity of today's optical networks, both for free-space and optical fiber transmission. Here we present our work of design, fabrication, and optical characterization of diffractive optical elements for compact OAM mode division demultiplexing based on optical transformations. Samples have been fabricated with 3D high-resolution electron beam lithography on a polymethylmethacrylate resist layer spun over a glass substrate. Their high compactness and efficiency make these optical devices promising for integration into next-generation platforms for OAM modes processing in telecom applications.

A Hybrid Barium Titanate–Silicon Photonics Platform for Ultraefficient Electro-Optic Tuning

Ultrafast and highly efficient optical modulators that are based on the Pockels effect are key components of today's optical communication networks. For the next generation of photonic links, silicon photonic technology is used to establish a new wave of densely integrated optic components. However, this new technology cannot exploit the advantages of using the Pockels effect for optical switching for two reasons: First, silicon does not exhibit any Pockels effect, and second, attempts to combine nonlinear materials with silicon photonics have been cumbersome. Here, we demonstrate a path to integrate barium titanate thin films with strong Pockels coefficients into silicon photonic structures. We highlight various design options, discuss the actual fabrication process, and present experimental results of functional passive and active structures. Examples include couplers and interferometers, as well as active, electrically driven nonvolatilely tunable ring resonators with a tunability of 4 μW/nm. Our results represent a major advancement in the field of ultralow-power silicon photonic switches based on nonlinear oxides, and demonstrate the potential of novel applications based on the hybrid barium titanate–silicon photonic platform.

100G Super-Channel Transmission Over 1500 km of NZ-DSF With 10G Neighbors

We demonstrate the successful transmission of a direct-detection 100G super-channel over 1500 km of non-zero dispersion-shifted fiber in a dispersion managed link configuration. The 100G duobinary super-channel was stressed by being tuned to the 1530 nm wavelength band and co-propagated with 76 × 10G, on-off keying modulated channels, on a 50-GHz channel grid, which represents one of the worst-case cross phase modulation scenarios in today's optical networks.

New Strategies for Connection Protection in Mixed-Line-Rate Optical WDM Networks

Today's optical wavelength division multiplexing backbone networks need to support traffic demands with very diverse capacity requirements. Recent studies have shown how to design an optical transport network that supports mixed line rates (MLR), where the wavelength channels of the optical paths (i.e., lightpaths) can have a variety of capacities (10/40/100 Gbps). Some preliminary work on the design of MLR optical networks has already appeared, but survivability, which is a key concern in optical network design, is a nascent topic in MLR networks. This study investigates the problem of protection in MLR optical networks: in particular, we study how to design a cost-effective transparent MLR network that provides dedicated protection at the lightpath level. We propose three mechanisms: MLR-at-p-lightpath protection (MLR-p), MLR-at-lightpath protection (MLR-l), and MLR-with-backup-flow-grooming protection (MLR-g). The design problem is solved by two different approaches: (1) a two-step approach that formulates part of the problem as an integer linear program and (2) a heuristic approach. Our results show that, by appropriate assignment of rates to lightpaths, MLR networks can provide protection for diverse traffic demands with much lower transponder cost compared to single-line-rate networks.

Optical fiber transport systems and networks: fundamentals and prospects

Abstract This article presents first the history of the optical fiber transport networks, from the introduction of the first high capacity systems in the 1990s to the 10 Gbit/s per channel WDM (Wavelength Division Multiplexing) systems deployed today, and the tremendous evolution of performance within this period. The effects of propagation in optical fibers and their consequences for optical system engineering, the architecture of today's optical transport networks, the choices made in France are recalled. We then have a look at the future of optical transport networks from an operator's point of view: the expected evolutions in terms of transmission system capacity and network architecture are presented. We conclude that capacity, transparency, and agility are the main drivers of the evolution of optical fiber transport systems and networks and that a lot of changes have yet to be expected in these domains during the next decade. To cite this article: M. Joindot, S. Gosselin, C. R. Physique 9 (2008).

A novel connection setup management approach for optical wdm networks

Wavelength Division Multiplexing (WDM) has significantly increased the transmission capacity of today's optical networks. An increase in the available bandwidth is promoting at the same time the introduction of new services, each having different Quality of Service (QoS) requirements. In this regard, QoS parameters applicable to connection setup, namely connection blocking probability and connection setup time, are expected to greatly influence the procedure of lightpath setup. In view of this, we propose to consider the connection setup time requirement as a (timely increasing) priority indicator during optical connection provisioning. In other words, we envisage in this letter the assignment of the highest setup priority to those optical connection requests having the shortest setup time requirements. To achieve this purpose, we adapt the well known Earliest Deadline First (EDF) scheduling discipline to the particular case of optical connection setup management. In order to gauge the impact of our proposal on the QoS perceived by optical clients, we introduce in this letter a computational method. This latter is used for the assessment of the percentage of optical connections that are successfully established under the proposed setup management approach.

Optical/packet transport convergence

Today's optical networks are designed to carry fixed-rate telephony and private line traffic in a reliable and resilient manner. Over the last decade, service providers have experienced tremendous growth in data services with the aggregate demand for data traffic now exceeding circuit-oriented traffic. As a result, service providers are challenged to bring their cost structure down so they can generate sustainable margins on competitive services. Lowering the cost structure of data services involves a reduction in capital expenditures, but even more importantly, it necessitates a reduction in operational expenses as well. Global optical/packet transport systems, such as Lucent Technologies' Universal Packet Mux (UPM), are among the network elements addressing this need. They integrate classical synchronous optical network/synchronous digital hierarchy (SONET/SDH) capabilities with multiprotocol label switching (MPLS) transport features on one platform. These new devices can support either connection-oriented or connectionless transport services. This paper describes the applications and value of a new type of universal packet transport system (UPT) for optical/packet networks.

Multifunctional integrated photonic switches

Traditional optical-electronic-optical (o-e-o) conversion in today's optical networks requires cascading separately packaged electronic and optoelectronic chips and propagating high-speed electrical signals through and between these discrete modules. This increases the packaging and component costs, size, power consumption, and heat dissipation. As a remedy, we introduce a novel, chip-scale photonic switching architecture that operates by confining high-speed electrical signals in a compact optoelectronic chip and provides multiple network functions on such a single chip. This new technology features low optical and electrical power consumption, small installation space, high-speed operation, two-dimensional scalability, and remote electrical configurability. We present both theoretical and experimental discussion of our monolithically integrated photonic switches that incorporate quantum-well waveguide modulators directly driven by on-chip surface-illuminated photodetectors. These switches can be conveniently arrayed two-dimensionally on a single chip to realize a number of network functions. Of those, we have experimentally demonstrated arbitrary wavelength conversion across 45 nm and dual-wavelength broadcasting over 20 nm, both spanning the telecommunication center band (1530-1565 nm) at switching speeds up to 2.5 Gb/s. Our theoretical calculations predict the capability of achieving optical switching at rates in excess of 10 Gb/s using milliwatt-level optical and electrical switching powers.

High-capacity multiservice optical label switching for the next-generation Internet

This article presents an optical label switching technology geared toward the next-generation Internet, and highlights its promising potential to accommodate packet, burst, and circuit traffic in a unified optical layer. In particular, we provide detailed discussions on an architecture design for a high capacity optical label switching router by considering enabling optical technologies. In pursuit of an effective contention resolution scheme, we investigate an end-to-end solution by incorporating a traffic shaping function at the network edge with wavelength, time, and space dimensions contention resolution in the core network. Experimental results indicate that this scheme is capable of achieving very low packet loss rates. Furthermore, due to its natural compatibility with GMPLS architecture, optical label switching has great potential for a seamless upgrade of today's optical networks toward the next generation Internet.

Managing the management communications network in optical transport systems

Management of today's optical transport networks typically includes some or all of fault, configuration, accounting, performance, and security (FCAPS) management. Carrying this management information across the network requires the presence of a management communications network (MCN), also referred to as the data communications network (DCN). The MCN itself needs FCAPS management. The availability of management for the MCN is very sparse in today's management systems, and this paper is a first step towards addressing the problem. We describe algorithms for planning, designing, and analyzing the MCN. Central to these algorithms is a graph representation of the entire network. Our treatment views the management of the MCN as an extension of the management of the transport network. We envision this work as the basis for a suite of applications that can improve the management of the communications infrastructure in optical transport networks.

A Multi-Hop Packet-Switched AWGM-Star-Network Realized with TX/RX Arrays

Some of today's optical networks are based on the well known WDM-star topology. In most cases, these are single-hop networks equipped with fast-tuneable wavelength transceivers. For these well studied packet-switched networks, several protocols have been designed. In order to avoid the costs of the fast tuneable devices, a network based on an array waveguided multiplexer (AWGM) and arrays of non-tuneable or slow tuneable transmitters and receivers is suggested. In order to enable communication among all stations, a multi-hop environment is introduced which is determined by the AWGM routing matrix. In the case of slow-tuneable devices, the topology can be reconfigured in dependence on changing traffic patterns. In order to get a first insight into the performance of these topologies, we focus on the case of fixed transceiver units and an uniformly distributed traffic matrix.