Anna Tzanakaki

Optical add/drop multiplexers and optical cross-connects for wavelength routed networks

WDM optical communication systems are evolving from simple point-to-point links to complex network architectures. In wavelength routed networks switching is performed through optical add/drop multiplexer (OADM) and optical cross-connect (OXC) nodes. These nodes provide provisioning capabilities as well as protection and restoration at the optical layer. Routing and management of the traffic demands are applied through the generalised multiprotocol label switching (GMPLS) a control plane offering intelligence at the optical layer. A central subject of debate has been the comparison of optical and electrical switching technologies, however transparent solutions offer attractive features associated with reduced unnecessary optoelectronic conversions supporting transparent networks with reduced capital and operational cost. A number of different OADM and OXC architectures based on various technologies have been proposed to date. A detailed discussion on the different architecture and technology choices supporting a variety of features are given and specific design and implementation examples are analysed. The impact of impairments introduced by transparent elements present in the network, such as OADM and/or optical switches, is discussed and optimised solutions introducing low penalties proposed. In addition, the use of novel modulation formats improving the concatenation performance of such elements is covered.

Field trial of WDM-OTDM transmultiplexing employing photonic switch fabric-based buffer-less bit-interleaved data grooming and all-optical regeneration

We report, for the first time, a field trial of a novel 42.7Gbps/128.1Gbps WDM/OTDM grooming node, and confirm node interoperability and the data integrity of asynchronous retiming.

Optical interconnection of core and metro networks

A network concept is introduced that exploits transparent optical grooming of traffic between an access network and a metro core ring network. This network is enabled by an optical router that allows bufferless aggregation of metro network traffic into higher-capacity data streams for core network transmission. A key functionality of the router is WDM to time-division multiplexing (TDM) transmultiplexing.

An all-optical grooming switch to interconnect access and metro ring networks

A novel switch concept is introduced that offers transparent optical grooming of 10 and 40 Gb/s traffic in an access network onto a metro core ring network operated at 130 Gb/s traffic. Key functionalities of the router are the traffic aggregation with time-slot interchanging (TSI) functionality, the TDM to WDM demultiplexing of the high-speed channel into lower bit-rate tributaries as well as multi-wavelength all-optical 2R regeneration of several highest-speed signals.

Guest Editorial: Computer networks journal special issue on: Challenges and opportunities in advanced optical networking

Optical communication systems and networks will continue to play a significant role in the development and deployment of emerging network infrastructures. These networks are expected to support the diverse requirements of a broad range of existing and future applications. To accommodate this wide spectrum of applications, network infrastructures are evolving rapidly in terms of technology and architecture towards a more flexible and intelligent optical layer based on Dense Wavelength Division Multiplexing (DWDM) that utilizes new optical switching architectures and technologies as well as advanced control and management protocols. Optical component technology is rapidly maturing, offering cost-effective solutions to a point where optical networks are currently being deployed in core backbone networks, and are gaining increased interest for deployment in metro and access environments. The widespread deployment of optical communication systems and networks introduces many challenges and opportunities, which this special issue aims to address.

Cascadability Performance of Continuous Spectrum WB/WSS at 10/40/160 Gb/s

Optical switching technologies such as reconfigurable add/drop multiplexers and cross-connects (OADMs/OXCs) have the ability to perform wavelength routing, provisioning, protection/restoration and traffic management thus enabling to cope with the dynamic nature of the data traffic that is met especially in the metro environment. Wavelength selective switches (WSS) and wavelength blockers (WB) are crucial elements in this kind of nodes offering flexible connectivity between the add/drop and through ports as well as the ability to selectively block the transit traffic. For the so called continuous spectrum WBAVSS (CS-WBAVSS), the overall filtering pass-band of the WSS device can be adjusted in a quasi-continuous way by grouping two or more adjacent pixels offering enhanced switching flexibility at arbitrary channel spacing or multi line rates. However loss and group delay ripples appear at each slot boundary causing degradations to the transmitted signal. In this work a system perspective analytical modelling has been developed and through detailed simulation studies we identify the relative impact of each imperfection on the overall cascadability of the WBAVSS. Different switching scenarios at various line rates (10 Gb/s, 40 Gb/s, 160 Gb/s) have been investigated and the corresponding specifications for the WSS device have been identified

Nonlinear penalty suppression through the use of optical add drop multiplexers

A study of WDM systems that utilize a number of optical add drop multiplexers (OADMs) to enable transparent add and drop of wavelengths at specific network locations as required by the traffic demands were presented in this paper. Through extensive simulation results it will be shown that the presence of OADMs and in particular the optical filtering associated with them improves the overall system performance. This is due to that in the case of systems suffering by nonlinear effects, periodic optical filtering assists in suppressing the spectral broadening imposed by nonlinear interactions between the WDM channels and therefore suppresses the associated penalty. This is in contrast to the effect of optical filtering in linear systems, where it introduces spectral narrowing and hence transmission penalties. The effect of nonlinear suppression directly impacts the power level that can be tolerated by the system before nonlinear penalties start degrading the overall performance. In such systems higher launch power can be used supporting improved optical signal to noise ratio and suppressed nonlinear penalties providing a significant improvement in the overall system performance. A large number of simulations have been run in order to identify the optimum operating point in terms of launch power in this type of systems. The analysis focuses on 10 Gbit/s systems supporting 100 GHz and 50 GHz channel spacing. A number of scenarios supporting varying transmission distances, different number of OADMs and various optical filter bandwidths are studied and compared. Significant attention is paid on the interplay of the variety of impairments and the identification of suitable trade-offs to ensure optimized system performance.