Directional couplers are high-frequency components with which a partial energy is diverted from a high-frequency or optical transmission.
Directional couplers are similar to splitters; they are inserted into the transmission medium and unidirectionally couple out part of the electrical energy in coaxial cables, part of the electromagnetic waves in waveguides, and part of the optical signal in optical fib ers.
In optical directional couplers, signal components are transmitted from a continuous optical waveguide into one or more directly coupled optical waveguides. The transmission is unidirectional in all coupled optical fibers. The most important parameters for optical directional couplers are the transmission loss, which is the signal loss between the output and the input signal, the insertion loss, the output loss and the return loss.
Directional couplers are used in many areas of RF measurement technology, such as for the separation of transmit and receive signals, for power measurement and automatic level control, as phase shifters and as modulators and demodulators, and in push-pull mixers.