Maximum utilisation of an existing optical trunk network

Mercury communications operates a network that includes some 12000 km of trunk optical line systems. The ever increasing demand for additional capacity has presented a challenge to extract the maximum possible benefit from this network. The approach taken by Mercury has been to increase the number of line systems sharing a pair of fibres through the introduction of bidirectional (duplex) working and wavelength division multiplexing. These techniques have been made possible through the availability in commercial quantities of suitable passive optical devices. Using them, it is now possible to support up to four 565 Mbit/s systems on a single pair of fibres. The features of optical couplers and filters are described, together with the criteria to be considered when designing them into a network