Apparatus and methods for signal routing within fibre optic networks are described. Switching means (11, 18, 21, 22) are provided within or outside the ports of an add/drop multiplexer having passive optical components such as circulators (13, 14) to change the routing of signals at predetermined carrier wavelengths, for example between ports of a branching unit. This can be used to divert all signals away from a given port of a branching unit, or to add capacity to a particular path. The switching principles employed can be extended to other forms of wavelength routing element and add/drop multiplexers.
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