Abstract: A coupler disposed between two optical signal transmission lines for extracting from the first transmission line a fraction of the energy transmitted thereby and for injecting an input optical signal into the other transmission line. The first transmission line is coupled to the input of a first mixer rod, the output end of which is connected to the input end of a second mixer rod by a first optical waveguide bundle. A second optical waveguide bundle, which is also connected to the output of the first mixer rod extracts a portion of the energy at the output end of the first mixer rod and couples it to output means. An input optical signal is coupled by a third optical waveguide bundle to the input end of the second mixer rod, the output end of which is coupled to the second transmission line.