Fiber optic couplers are optical appliances that divide one or more input fibers amongst two or more output fibers. These couplers can also combine two or more input fibers into one output fiber. Fiber optic couplers are able to be constructed with single or multimode fiber optic cables.

Single mode fiber optic couplers are made with fibers that only tolerate the transmission of one mode. Multimode fiber optic couplers are made with fibers that permit the usage of LED light sources and hold coupling as being not as vital as single mode fibers do. These devices are also able to be either active or passive.