US Patent 7376355 Optical transmission apparatus and optical transmission system

An optical transmission apparatus includes a return line for connecting a first transmission line and a second transmission line opposed to the first transmission line in order to make it possible to commonly use a transmitter-receiver or a repeater, for example, between a trunk line and a branch line and prevent a situation that the power of branched signal lights increases excessively. The optical transmission apparatus is configured so that dummy lights inputted together with signal lights to be added to signal lights transmitted through the first transmission line are sent to the second transmission line through the return line and are outputted together with signal lights to be dropped from the second transmission line.