Loop experiments and simulations for the wavelength division multiplex network signal path

The multichannel wavelength division multiplex technique offers the possibility to use the optical fiber amplifier bandwidth for high capacity transmission whereas single channels are routed via optical crossconnects. Linear and non-linear fiber effects as well as crossconnect characteristics influence the transmission length of the signal path. These effects are illustrated by the transparency length diagram. The basic knowledge for planning future optical networks is achieved from transmission experiments in recirculating fiber loops accompanied by the development of simulation tools. The loop experiments deliver a deeper insight in physical properties of fiber trunks carrying bundles of optical channels. The influence of crossconnects or single components on the signal quality can also be investigated by a repeated loop transit. The experimental results are used to improve a simulation model on the basis of "Ptolemy". This simulation tool permits a prediction of signal quality degradation during transmission through a network path. Another important topic of WDM network research are experiments with installed fiber trunks. As a first attempt the experiments on a replica of the Berlin-Darmstadt intercity connection are presented.