Abstract: Optical signals used for telecommunications in time division multiplexed format are processed to remove channels for local demodulation and to replace the removed channels with locally modulated data. The received signals are subjected to a wavelength modulation so that signals in selected channels are given distinctive wavelengths. After wavelength modulation, the time division multiplexed signals are separated using wavelength sensitive splitters and the various channels are sent to their correct destinations. In one embodiment, one channel is selected and given a distinctive wavelength and all the non-selected channels retain their original wavelength. The channels with the original wavelength are provided to an output terminal for onward transmission whereas the selected channel is provided for local demodulation.

Abstract: Optical signals used for telecommunications in time division multiplexed format are processed to remove channels for local demodulation and to replace the removed channels with locally modulated data. The received signals are subjected to a wavelength modulation so that signals in selected channels are given distinctive wavelengths. After wavelength modulation, the time division multiplexed signals are separated using wavelength sensitive splitters and the various channels are sent to their correct destinations. In one embodiment, one channel is selected and given a distinctive wavelength and all the non-selected channels retain their original wavelength. The channels with the original wavelength are provided to an output terminal for onward transmission whereas the selected channel is provided for local demodulation.

Abstract: A node for an optical time division multiplexed communication system, and a method of operating such a node, are disclosed. In embodiments of the invention, the node comprises a multiplexer for receiving a plurality of optical signals, and a source of optical radiation, which may be a continuous wave source, or a source of optical pulses. The node is arranged so that the outgoing optical time division multiplexed signal consists only of optical pulses from the source of optical radiation.

Abstract: An all-optical processing system coverts or interfaces optical signals from a wavelength division multiplexed (WDM) form to an optical time divisional multiplexed (OTDM) form. The initial WDM signal typically comprises a non-return to zero (NRZ) signalling format. The system includes a plurality of NRZ data modulated, cw optical WDM channels which are cross-phase modulated, and thus are spectrally broadened, in an optical non-linear element, by a strong clock pulse signal. The resultant signal comprises an RZ representation of the original NRZ signal. The RZ signal is temporally shifted by a dispersive element which temporally shifts each wavelength channel by a predetermined amount, to produce a wavelength-interleaved OTDM signal. The signal is then wavelength converted by cross-phase modulation with a cw control beam in a second non-linear optical element to provide a single wavelength OTDM signal.

Abstract: A fault signalling system for an optical fiber-based communications link having erbium doped fiber amplifier repeaters comprises a broadband optical source for generating a fault signal in the event of a fault occurring. Each repeater includes such a broadband source, which will output a characteristic fault signal onto the link for transmission to a receiving station, in the event of a fault being detected at that repeater. Advantageously, a control circuit which enables the source to emit its fault signal when appropriate is also used as part of an automatic gain control for the output of the amplifier repeater in normal operation.