WDM network with control wavelength

A wavelength multiplexed optical communication system comprising:

• a plurality of terminal stations and at least one head station interconnected by a pair of rings comprising a pair of optical communications buses carrying data in opposite directions, the head station providing optical signals on a plurality of optical carriers, and the terminal stations each modulating the optical carriers to carry data signals, the terminal stations each comprising means for interconnecting said buses, the system thereby being operable as a single continuous bus in the event of a system or component failure, wherein there are provided a plurality of said buses connected to one another and the number of said head stations is less than the number of said buses, and there is provided a splitter arranged to split light from each said head station to a plurality of said buses.

A wavelength multiplexed optical communication system comprising:

• a plurality of terminal stations and at least one head station interconnected by a pair of rings comprising a pair of optical communications buses carrying data in opposite directions, the head station providing optical signals on a plurality of optical carriers, and the terminal stations each modulating the optical carriers to carry data signals, the terminal stations each comprising means for interconnecting said buses, the system thereby being operable as a single continuous bus in the event of a system or component failure, wherein there are provided a plurality of said buses connected to one another, and the interconnection between said buses is provided by electrical communications paths between terminal stations of said buses.

A wavelength multiplexed optical communication system comprising:

• a plurality of terminal stations and a head station interconnected by a pair of optical communication rings, each of said pair of rings carrying data in opposite directions, said head station providing optical signals on a plurality of optical carriers, and the terminal stations each modulating the optical carriers to carry data signals, the terminal stations further interconnecting said rings whereby the system is operable as a single continuous ring in the event of a system or component failure.