Reconfigurable and transparent wavelength division multiplexed optical transport networks

• Main Author: Almström, Erland
• Format: Doctoral Thesis
• Language: English
• Published: KTH, Elektroniksystemkonstruktion 1999
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2847; http://nbn-resolving.de/urn:isbn:99-3016054-X

This thesis is about reconfigurable and transparentwavelength division multiplexed (WDM) networks.Reconfigurability is used to achieve higher surveillance andthroughput in the network. This is done by wavelength selectiveand independent network elements. These network elements canaccomplish bypass and protection switching ofthe traffic.Transparency in the optical layer enables the transport networkto accept new bit rates, codes and formats of the clients. Theenabling technologies to achieve a reconfigurable andtransparent network are integrated tuneable devices andswitches. In this thesis some of these devices have beenexperimentally evaluated according to theirs cascadability andcrosstalk performance. A unidirectional self-healing wavelength divisionmultiplexed ring was designed, assembled and evaluated. Byutilising WDM, logical networks could be constructed withoptical add drop multiplexers (OADM) to support communicativeand distributive services. The main transmission limitation ofthe ring was homogenous broadening of the opticalamplifiers. The second network element investigated, was the opticalcrossconnect (OXC). The OXC was comprised of optical InP andLiNbO3 switches and tuneable filters, which were experimentallyevaluated. Two OXCs and an OADM were installed in the Stockholmgigabit network (SGN) with fault and configurationmanagement. The cascadability of OXCs with reshaping repeaters andoptical or electrical switches was investigated. The jitter ofthe OXC with electrical switches limited its performance, whilethe OXC with optical switch was limited by its crosstalk.Crosstalk especially intra-band crosstalk, which beats with thesignal, is a severe limitation of optical networks. Experimentsand simulations were performed on the time dependence of theintra-band crosstalk. It was shown and experimentally confirmedthat the quasi-correlated intra-band crosstalk could be theworst case. In the next phase of the network five OADMs and one OXC,which interconnected a unidirectional and a bidirectionalprotected ring, were integrated into SGN with a web basedmanagement system. The OADMs were evaluated in a recirculating loop toinvestigate the cascadability of the nodes. The nodes could bedivided into optical channel or fibre protection and notch ordemultiplex filtering. An optimum of loss of the cascadedoptical amplifiers were found, which maximised the gainflatness and the signal to noise ratio. The OXC utilising fixedWDMs and polymer switches was designed and evaluated takinginto account the configuration, fault handling and performancemonitoring of the optical layer. Data services were evaluatedas clients to the optical layer, especially to provide opticalprotection without interfering with its client. <b>Keywords:</b>Optical Network, Wavelength DivisionMultiplexing, Reconfigurable Network, Optical Cross Connect,Optical Add Drop Multiplexer, Transparency, Crosstalk,Cascading, Protection, Optical Switch, Electrical Switch,Tuneable Filter, Self-Healing Ring, Logical Network, StockholmGigabit Network, Internetworking