Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

All-optical wavelength conversion by semiconductor optical amplifiers

Semiconductor optical amplifiers are useful building blocks for all-optical gates as wavelength converters and OTDM demultiplexers. The paper reviews the progress from simple gates using cross-gain modulation and four-wave mixing to the integrated interferometric gates using cross-phase modulation. These gates are very efficient for high-speed signal processing and open up interesting new areas, such as all-optical regeneration and high-speed all-optical logic functions.

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Semiconductor optical amplifier-based all-optical gates for high-speed optical processing

Progress in optical networking has stimulated interest in optical performance monitoring (OPM), particularly regarding signal quality measures such as optical signal-to-noise ratio (SNR), Q-factor, and dispersion. These advanced monitoring methods have the potential to extend fault management and quality-of-service (QoS) monitoring into the optical domain. This paper reviews OPM applications and techniques, while examining the role of OPM as an enabling technology for advances in high-speed and optically switched networks.

Optical performance monitoring

In this paper routing, planning of working capacity, rerouting, and planning of spare capacity in wavelength division multiplexing (WDM) networks are investigated. Integer linear programming (ILP) and simulated annealing (SA) are used as solution techniques. A complex cost model is presented. The spare capacity assignment is optimized with respect to three restoration strategies. The benefit of wavelength conversion, the choice of the fiber line system, and the influence of cost parameter values are discussed, with respect to the different restoration strategies and solution techniques. Wavelength conversion is found to be of limited importance, whereas tunability at the end points of the connections has substantial benefits.

Dimensioning of survivable WDM networks

A fault recovery system that is fast and reliable is essential to today's networks, as it can be used to minimize the impact of the fault on the operation of the network and the services it provides. This paper proposes a methodology for performing automatic protection switching (APS) in optical networks with arbitrary mesh topologies in order to protect the network from fiber link failures. All fiber links interconnecting the optical switches are assumed to be bidirectional. In the scenario considered, the layout of the protection fibers and the setup of the protection switches is implemented in nonreal time, during the setup of the network. When a fiber link fails, the connections that use that link are automatically restored and their signals are routed to their original destination using the protection fibers and protection switches. The protection process proposed is fast, distributed, and autonomous. It restores the network in real time, without relying on a central manager or a centralized database. It is also independent of the topology and the connection state of the network at the time of the failure.

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Protection cycles in mesh WDM networks

For the enhancement of the existing electrical transport network a new one based on optical frequency division multiplexing (or wavelength division multiplexing) will be added to the existing one. This article focuses on the system/network supervision and operation and maintenance, which are of great importance for the success of the optical transport network. For a better understanding of these topics, it is necessary to derive a layered network model for the optical transport network and to make a workable definition of the term "network transparency." The proposed operation and maintenance concept deals with the identification of its related functions, the supervision of the optical regenerators, the maintenance signals required for failure localization, and the difficulty of defining a suitable mechanism for performance monitoring in transparent networks. Appropriate realization aspects are discussed too. Possible solutions for failure detectors are described. For transferring the individual maintenance signals between the associated network elements, a communication channel with a suitable structure is proposed.

Operation and maintenance for an all-optical transport network

The development of the information society will require the introduction of high-capacity transport networks with high performance and low cost. There are currently two ACTS (Advanced Communications Technologies and Services program launched by the European Commission) projects addressing specifically the problem of trans-European optical transport networks using WDM (wavelength division multiplexing). Important issues addressed are the high capacity transmission on existing fiber infrastructure and the introduction of flexibility in the network through the use of optical cross-connects. If these networks become a reality, they could drastically change the evolution of both telecommunication and computer networking because of their transparency and the abundance of inexpensive bandwidth.

Pan-European optical networking using wavelength division multiplexing

For the transport of the increasing traffic volume caused by existing and new narrowband services and evolving broadband services, the enhancement of the existing public telecommunication transport network is necessary. For this purpose an optical network layer with cross-connect and add/drop functionalities will be added to the existing transport network. A comparative analysis of space, time, and optical frequency division multiplexing has shown that for the time being optical frequency multiplexing is best suited for the realization of that new network layer. This multiplexing scheme offers the greatest advantages such as very high bandwidth utilization in the fiber and simple and efficient cross-connecting of high bitrate streams. In the near future, technology will be mature enough for the realization of a demonstrator network based on optical frequency division multiplexing. The functionalities of the optical network are evaluated and the results clearly show that optical frequency conversion and regeneration should be provided by the optical network. The article also deals with the realization aspects (cross-connecting, supervision, and operation and maintenance) of an optical node. >

M. N. Huber

Papers

Operation and maintenance for an all-optical transport network

Pan-European optical networking using wavelength division multiplexing

An optical infrastructure for future telecommunications networks

Pan-European optical networking using wavelength division multiplexing : Optical networks technology in Europe

Key issues of an optical FDM transport network