Optical add/drop multiplexers and optical cross-connects for wavelength routed networks

WDM optical communication systems are evolving from simple point-to-point links to complex network architectures. In wavelength routed networks switching is performed through optical add/drop multiplexer (OADM) and optical cross-connect (OXC) nodes. These nodes provide provisioning capabilities as well as protection and restoration at the optical layer. Routing and management of the traffic demands are applied through the generalised multiprotocol label switching (GMPLS) a control plane offering intelligence at the optical layer. A central subject of debate has been the comparison of optical and electrical switching technologies, however transparent solutions offer attractive features associated with reduced unnecessary optoelectronic conversions supporting transparent networks with reduced capital and operational cost. A number of different OADM and OXC architectures based on various technologies have been proposed to date. A detailed discussion on the different architecture and technology choices supporting a variety of features are given and specific design and implementation examples are analysed. The impact of impairments introduced by transparent elements present in the network, such as OADM and/or optical switches, is discussed and optimised solutions introducing low penalties proposed. In addition, the use of novel modulation formats improving the concatenation performance of such elements is covered.