Abstract: A wavelength division multiplex communication system comprises a head station (2) and a plurality of terminal stations (1) interconnected by an optical fibre cable (3). The head station (2) transmits continuous wave modulated wavelengths (.lambda..sub.1 -.lambda..sub.k), and a signalling wavelength (.lambda..sub.0) which is used to indicate, in each time slot, which wavelengths in the following time slot are available for transmission. Each terminal station (1) is arranged to receive the signalling wavelength, to determine therefrom whether the next time slot contains any data packets for that terminal station and, if so, to receive the packets. The terminal station (1) is arranged, if it has a data packet to transmit, to determine from the signalling wavelength whether the next time slot already contains data packets for the destination station and, if so, to avoid data collision by not transmitting its own data packet. The terminal station (1) then determines a free wavelength (.lambda..sub.

Abstract: In a high speed optical clock extraction arrangement, an incoming digital signal is divided between two paths (11, 25). The signal on one path (25) is fed direct to a receiver (203), while the signal on the other path (11) is fed to a non-linear optical amplifier (1) which has separate gain and absorbing regions. The non-linear optical amplifier (1) is triggered by the incoming signal to pulsate at a clock frequency contained in the signal, and the resultant strong output clock signal is coupled into the path (25) carrying the incoming signal to the receiver (203). The non-linear optical amplifier (1) can provide a very high frequency clock output as a result of selective modification of the carrier lifetime.

Abstract: A wavelength division multiplex communications system has a head station and a plurality of terminal stations interconnected by an optical fiber cable. The head station transmits CW modulated wavelengths (.lambda.-.sub.1 -.lambda..sub.k), and a signalling wavelength (.lambda..sub.0) which is used to indicate, in each time slot, which wavelengths in the following time slot are available for transmission. Each terminal station is arranged to receive the signalling wavelength (.lambda..sub.0), to determine therefrom whether the next time slot contains any data packets for that terminal station and, if so, to receive the packets. Each terminal station is arranged, if it has a data packet to transmit, to determine from the signalling wavelength (.lambda..sub.0) whether the next time slot already contains data packets for the destination station and, if so, to avoid data collision by not transmitting its own data packet. The terminal station then determines a free wavelength (.lambda..sub.

Abstract: A telecommunications system comprising first and second nodes interconnected by a network transmission line. The first node comprises an optical data generator for producing an optical data signal at a first wavelength, an optical header generator for producing an optical control signal at a second wavelength, and means for multiplexing the data and control signals onto the transmission line. The second node comprises a switch and a controller responsive to signals at the second wavelength for controlling the routing of optical signals through the switch. A delay unit and associated control means are provided to ensure that sufficient delay occurs between the transmission start times of the control and data signals that the control signal completely overlaps the data signal at the second node.

Abstract: A method of generating a clock signal from a digital optical data signal not having a significant clock component, wherein the digital optical data signal is input into an opto-electronic device and the non-linear variation in the opto-electronic device caused by the digital optical data signal in the device is detected, resulting in the generation of a further signal from the device. A component at a clock frequency for the digital optical data signal is extracted from said further signal.