Coherent optical systems implemented for business traffic routing and access: the RACE COBRA project

The RACE COBRA consortium has performed four field trials to verify the suitability of dense WDM combined with heterodyne detection (for which the term CMC, "coherent multicarrier" is used) for different network applications. The main advantage in using heterodyne detection is the simple access to individual optical channels by only switching local lasers to the desired channel. Heterodyne detection acts as a perfect optical filter. Thus, a plurality of dense spaced optical carriers can be placed, e.g., within one WDM window. The additional freedom in the channel multiplex provides some advantages which are shown in the demonstrators: a routing flexibility in the RENO (reconfigurable node) cross-connect demonstrator supporting STM-16 at Philips Research in Eindhoven. A routing flexibility in the demonstrator at BBC in Kingswood Warren, UK, supporting uncompressed HDTV communication in a studio environment. By shifting switching functions to the terminals, the network is kept completely passive. This is also obtained in the local area videoconference trial at CET in Aveiro, Portugal, using high quality standard TV and in the BCPN trial at KPN Research in Leidschendam, NL, where ATM-streams are supported for multimedia services. The paper outlines the demonstrator concepts as well as some subsystems and key components developed by the consortium.