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

By linking two connectors precisely, fiber optic adapters allow the light sources to be transmitted at most and lower the loss as much as possible. At the same time, fiber optic adapters have the merits of low insertion loss, good interchangeability and reproducibility.