OPTICAL CROSS-CONNECT SYSTEM IN BROAD-BAND NETWORKS - SYSTEM CONCEPT AND DEMONSTRATORS DESCRIPTION

A future-proof transport network, robust to future evolution in networ k topologies or transmission formats and bit rates, would be achieved by introducing an all-optical transparent layer in the transport netwo rk hierarchy. The transparency would permit usage of physically common fiber lines and nodes for different transmission hierarchies and/or f ormats. A transparent network could be achieved by combining photonic switching with electronic switching technology in the network nodes. A network node would be designed as an optical cross-connect (OXC) in a n optical layer, interfacing the transmission links and as a digital c ross-connect (DXC) in a electrical layer. A combination of wavelength routing and space division switching in the optical layer would increa se the capacity, as well as the flexibility in a network. The latter i s especially important, since it allows routing with higher granularit y within the optical layer. Two optical cross-connect demonstrators ha ve been set up. The first one demonstrates protection switching and re storation of traffic in a future transport network, while the other on e demonstrates routing of subscriber signals to different service swit ches in a local exchange. Space switches, tunable lasers and filters a re key technologies used to obtain enhanced flexibility in a transpare nt wavelength-routed network. Optical amplifiers are needed in order t o maintain the signal level through an optical node. With new technolo gy, e.g., InP, larger monolithic matrices can be made, because both th e elementary switches are smaller and because loss can be compensated for by integrating optical amplifiers. Optical building practises is a n area that deserves more attention, in order to put it all together.