Fiber optic adapter, sometimes also called coupler, is a small device designed to terminate or link the fiber optic cables or fiber optic connectors between two fiber optic lines.

The FC-ST Hybrid Fiber Optic Adapter is a special style of fiber optic adapter that supports precision connection of different types of fiber optic connectors. It is specially designed to incorporate the Small Form Factor FC into ST configured environment. The compact design enables network operators to reduce cost via space-savings, and by eliminating hybrid cable assemblies.