Optical Lattice-Type Add–Drop Multiplexing Filters and Their Use in WDM Networks

This paper examines the use of optical lattice filters as wavelength add/drop devices in WDM ring or bus networks. Various filter design methodologies are investigated, including methods to produce passband-flattened low sidelobe filters. The effects of cascading such devices are examined from the viewpoint of net transmission bandwidth and coherent or “in-band” crosstalk and are compared with the use of pairs of 1:nwavelength multiplexer/demultiplexers to perform the add/drop function. We find that the use of optical lattice-type add/drop filters results in a much broader net transmission bandwidth than even the use of pairs of passband-flattened 1:nwavelength multiplexer/demultiplexers. The use of passband-flattened optical lattice filters with correspondingly broad stopbands helps to significantly broaden the coherent crosstalk-limited bandwidth. The characteristics of a four-channel add/drop filter fabricated using silica waveguide technology and the performance of a three-node 3×2.5 Gbps WDM ring network built using a number of these devices are reported.