Abstract: A communications network has a communications station, such as a telephone exchange, and at least one interface, such as a cabinet. A plurality of optical carriers are provided between the exchange and a cabinet, thereby allowing modulation of the signals, for example xDSL modulation, to be carried out at the exchange, rather than at the cabinet. This arrangement reduces the need to power the cabinet.

Abstract: An optical component fabricated from a semi-conductor wafer in which the epilayers are in the InCaAsP system comprises a pair of ridge waveguides. The ridge waveguides are proximate and parallel to each other in a first region, and diverge from each other in a second region. Each waveguide has a continuous electric contact over its upper surface to provide a first light amplification zone through or beneath at least a portion of both first and second light guiding paths and a second light amplification zone through or beneath at least a portion of both the first and a third light guiding path. The component can be used as a low loss 1.times.2 switch, or as a low loss 2.times.1 combiner.

Abstract: A method and control system for controlling a signal from each outstation in a multiple access passive optical network including a central node and a plurality of outstations involves monitoring, at the exchange, the value of a parameter of a signal from reach outstation. The value of the parameter is monitored relative to a predetermined discrimination value to detect the signal relative to predetermined first and second reference values defining a range of acceptable values for the parameter. If the value of the parameter for a detected signal falls outside the range, a control signal is transmitted from the node to instruct the relevant outstation to alter the value of the parameter as required to bring the value into the acceptable range for subsequent signals originating from that outstation. The method and system are particularly adapted for controlling the temporal position and the amplitude of outstation signals in a TDM passive optical network.

Abstract: Light is amplified in a semiconductor laser structure through which a current is passed and (a) the wavelength of the light is greater than the wavelength of maximum gain of the laser structure, or (b) injection locking is avoided, or (c) the current is controlled so as at least partly to compensate for the decrease in the monitored light output at a wavelength or over a wavelength range distinct from that of the emitted amplified signal.In this way relatively high input powers can be amplified.