Abstract: A wavelength division multiplex (WDM) optical telecommunications network comprises a plurality of nodes interconnected by optical fiber waveguides. Communication traffic is communicated between nodes by optical radiation modulated with the communication traffic, the radiation being partitioned into aplurality (N) of wavelength channels each channel having a discrete non-overlapping waveband. Each node drops at least one of the wavelength channels to thereby define a connection to the node and adds at least one wavelength channel to the network to define a connection to another node of the network. The network is characterized is that at least one node has ascribed to it a fixed subset of the N wavelength channels and drops each of the wavelength channels of the fixed subset from the network.

Abstract: An optical modulator includes an optical input; an optical output; at least one optical path connecting the optical input and output; and an electrode structure for selectively changing the optical characteristic of a part of the at least one optical path in response to a control signal such as to modulate light passing along the optical path. The optical path further includes a structure which slows the passage of light along the part of the optical path to enhance the modulation effect of the modulator for a given length of optical path. Preferably the structure comprises a sequence of coupled resonator structures in which each resonator structure is defined by a pair of partially reflecting planes which define an optical resonator cavity within the optical parts.