Optical add/drop multiplexers for WDM communication systems

Wavelength-division multiplexing (WDM) is currently introduced worldwide into existing optical communication systems for capacity enhancement. OADM (optical add/drop multiplex) nodes are key elements of such systems, assuring network survivability by fast reconfiguration and enabling add/drop of WDM channels. OADM nodes comprising a variety of different OADM devices are developed within the ACTS project METON (Metropolitan Optical Network) for operation and comparative analysis in the Stockholm Gigabit Network. The paper will compare various OADM devices, highlight recent achievements, and discuss the potential and the limitations of the different approaches. The presentation comprises arrayed waveguides, Bragg gratings in fibers and in SiO₂/Si waveguides, advanced InP-based interferometric structures and grating-assisted couplers. The advanced approaches will be discussed in detail and their characteristics will be compared to that of standard, commercially available OADMs such as Fabry-Perot interferometers or bulk optics. Cascading of SiO₂/Si arrayed waveguide WDMs with a -3-dB passband of 1 nm has been tested in a recirculating loop at 10 Gbit/s. More than 40 WDMs could be passed before a significant penalty was introduced