Abstract: In a fiber optic communications system in which channel insertion and removal is carried out by a plurality of modular cascaded multiplexer and demultiplexer components, the respective common outputs and inputs of the multiplexer and demultiplexer components are connected to bi-directional or uni-directional combiners arranged to combine or separate groups of channels for transmission over a single fiber transmission cable. The combiners each include one or more optical circulators.

Abstract: A multiple channel fiber optic multiplexer, demultiplexer, multiplexer/demultiplexer, and/or add/drop component includes a plurality of Mach-Zehnder interferometer units, each unit including a pair of 50/50 fiber optic couplers connected by a pair of Bragg gratings and three functional ports including two multi-channel input output ports, one single channel input/output port, the Bragg gratings being tuned to a wavelength of the single channel input/output port, and input/output ports of adjacent interferometer units being connected to each other by fusion splices in a cascade configuration, the component including a first common input/output connector on a first of said cascaded interferometer units and a second common input/output connector on a last of said cascaded interferometer units, with the second common input/output connector being arranged to permit the addition of add-on multi-channel components.