Christopher A. White

Design tools for transparent optical networks

Optical technology promises to revolutionize data networking by providing enormous bandwidth for data transport at minimal cost. A key to cost reduction is to increase transparency, that is, to keep a data stream encoded as an optical signal for as long as possible. Wavelength switching increases transparency by allowing different data streams, each encoded in a different wavelength of light, to be independently routed through an optical network. We discuss Bell Labs-developed software tools that help design wavelength-switched optical networks. The software tools simultaneously minimize the cost of the designed network, reduce the time and cost to perform the design, and ensure compliance with engineering constraints. The tools span three levels of abstraction, from routing and reconfigurable add/drop multiplexer (ROADM) choice, to span engineering, to power dynamics simulation. Each level represents a different tradeoff between design scope and level of detail. For each class of tool, we briefly describe design philosophy, algorithms, performance, and resulting value for Lucents customers.

GERI - Bell Labs Smart Grid Research Focus: Economic Modeling, Networking, and Security & Privacy

In this paper, we outline the Grid 2.0 Research, a collaborative Smart Grid research program between Gachon Energy Research Institute (GERI) of Kyungwon University and Bell Labs of Alcatel-Lucent. Salient features of the Grid 2.0 Research are the active role of distributed fixed and mobile energy storage, distributed renewable energy sources, and active load-side participation. Our focus is not on the energy storage itself but rather on the supporting infrastructure including communication network, security, and economics of the Smart Grid. Grid 2.0 Research views the Smart Grid as an ecosystem. In this regard, we pay close attention to the components and systems which require significant fundamental advancement or systems which do not exist today, thus requiring innovative solutions or greater sophistication. In order to realize a functioning ecosystem, critical components and tools of the envisioned Smart Grid are identified. This research work has been motivated by the Smart Grid roadmap of KEPCO and the Jeju Island Smart Grid Test-bed of Korea which will be discussed following the introduction section. Areas of research focus will be explained in a concise manner in the subsequent sections.

Transient gain dynamics of cascaded erbium doped fiber amplifiers with re-configured channel loading

Wavelength-division-multiplexed channel power transients are examined in cascaded EDFAs with variable pre-transient channel loading through the chain. We identify different orders of transient events and characterize their uncontrolled time response and steady-state power excursions.

Simulation of power evolution and control dynamics in optical transport systems

The design and analysis of control strategies for high-capacity, reconfigurable optical transmission systems require an understanding of optical system dynamics involving the time-dependent interaction of many components. This paper describes system simulation software that couples continuous physical-layer models of optical transmission components with discrete models for events such as channel add/drops. The simulator computes detailed time traces of signal and noise power propagation along a line system consisting of multiple controlled transmission elements and monitoring devices in response to a particular discrete event. Examples are given illustrating the rich variety of experimentation modes the software supports, including the evaluation of control algorithms, systematic exploration of design parameters, and investigation of cost reduction plans. Details of the development effort are presented, illustrating the contributions of the optical physicists, applied mathematicians, system engineers, and computer scientists who were involved in this collaborative project.

Monitoring and Diagnostics of Power Anomalies in Transparent Optical Networks

Challenges in monitoring optically-transparent networks are highlighted for dynamically-controlled Raman amplification systems. We use models of amplifier physics together with statistical estimation to automatically discriminate between measurement errors, anomalous losses, and pump failures.

Amplifier Issues for Physical Layer Network Control

Publisher Summary One of the major consequences of the introduction of transparent network elements such as reconfigurable optical add/drop multiplexers (ROADMs) is that the optically transparent portion of the network evolves from the point-to-point links of the original dense wavelength division multiplexing (DWDM) systems to more complex topologies such as optically transparent mesh networks. In such networks, mechanisms that couple power fluctuations between different channels can cause fluctuations to propagate through the network beyond the originating channels and to links in the network beyond those traversed by the originating channels, giving rise to feedback that can destabilize the network. As a result, the challenge of managing interactions among channels is more complex than in point-to-point systems. The local controls (based on mid-amplifier variable optical attenuator, pump control, and adjustment of channel powers at the transmitter) used in point-to-point systems are no longer adequate. Network-wide control algorithms that employ the capabilities of the ROADMs to control individual channel powers and optimize these globally across the network must supplement them. This chapter examines the mechanisms of dynamic and static power coupling between channels in both constant gain and constant output power erbium-doped fiber amplifiers (EDFAs), and the resultant issues of power stability in complex transparent networks. It focuses on network-wide control algorithms to compensate interchannel coupling effects and to maintain network stability. Simulations are used to demonstrate the ability of such global optimization to control the instabilities that would otherwise occur with even the best local control.

Channel Power Coupling in Constant Gain Controlled Amplifiers

Channel power coupling due to gain ripple and tilt in constant gain controlled erbium doped fiber amplifiers is measured in a transmission line and shown to grow in cascade.

Model-Based Anomaly Detection for a Transparent Optical Transmission System

In this chapter, we present an approach for anomaly detection at the physical layer of networks where detailed knowledge about the devices and their operations is available. The approach combines physics-based process models with observational data models to characterize the uncertainties and derive the alarm decision rules. We formulate and apply three different methods based on this approach for a well-defined problem in optical network monitoring that features many typical challenges for this methodology. Specifically, we address the problem of monitoring optically transparent transmission systems that use dynamically controlled Raman amplification systems. We use models of amplifier physics together with statistical estimation to derive alarm decision rules and use these rules to automatically discriminate between measurement errors, anomalous losses, and pump failures. Our approach has led to an efficient tool for systematically detecting anomalies in the system behavior of a deployed network, where pro-active measures to address such anomalies are key to preventing unnecessary disturbances to the system’s continuous operation.

Power stability and control in optically transparent mesh networks

We explore the impact of topology, traffic, and amplifier physics on node-to-node channel-power coupling effects in an optically transparent mesh network and describe a simple control strategy for scheduling the adjustment of control elements.

Wavelength-dependent channel power transient response in broadband Raman-amplified transmission

The time evolution of uncontrolled amplifier gain transients due to dropped or cut dense-wavelength-division multiplexed channels in a broadband all-Raman amplified recirculating loop experiment is measured for different surviving channel wavelength configurations with propagation up to 7200 km. Different time signatures develop depending on whether the surviving channels are located at the long- or short-wavelength end of the spectrum. Channel power tilt and gain error within a surviving channel group can vary with distance and are shown to correlate with growth of amplified spontaneous emission noise at the dropped channel wavelengths.