OPTICAL SIGNAL TRANSMISSION THROUGH OPTICAL FIBRES USING BOTH CO AND COUNTER PROPAGATING MODES

An optical signal amplification device and a method of installing such a device are disclosed. The device comprises: a plurality of ports, the plurality of ports comprising a first pair of ports for connecting to a first pair of optical fibres and a further pair of ports for connecting to a further pair of optical fibres; a plurality of multiplexing devices, each multiplexing device being associated with a corresponding port, each of the multiplexing devices being operable to transform between a wider band signal and a plurality of narrower band signals; optical paths for transporting the plurality of narrower band signals between the plurality of multiplexing devices, the optical paths being configured to provide paths between multiplexers associated with the first pair of ports and multiplexers associated with the further pair of ports; two of the optical paths comprising amplifiers for amplifying signals travelling in a first direction from the first pair of ports to the further pair of ports and two of the optical paths comprise amplifiers for amplifying signals travelling in a reverse direction from the further pair of ports to the first pair of ports. In a path converting configuration of the optical signal amplification device, the optical paths are configured such that paths are provided between each of the multiplexing devices associated with one pair of ports and two of the multiplexers associated with the other pair of ports, such that co-propagating signals transported by one pair of optical fibres, are converted to counter propagating signals for transport by the other pair of optical fibres.