Fiber Optic Adapters (also called couplers) are designed to connect two fiber optic cables together. They come in versions to connect single fibers together (Simplex), two fibers together (Duplex), or sometimes four fibers together (Quad).
Adapters are designed for multimode or singlemode cables. The singlemode adapters offer more precise alignment of the tips of the connectors (ferrules). It is ok to use singlemode adapters to connect multimode cables, but you should not use multimode adapters to connect singlemode cables. This can cause misalignment of the small singlemode fibers and loss of signal strength (attenuation).
Fiber adapters can be categorized with the below.
Fiber Connection Type: SC fiber adapter,lc fiber optic adapter, ST fiber adapter,FC optical adapter, MU fiber optic adapters, E2000 fiber adapters and MPO fiber adapters