FC Connectors

The FC connector is a threaded fiber optic connector used in telecommunications, laboratory optics, laser systems, and instrumentation where secure, vibration-resistant, and precisely aligned fiber connections are required.

Connector Structure

An FC connector consists of several main components that ensure accurate fiber alignment and reliable mating:

  • Ferrule – A precision cylindrical component, typically made of zirconia ceramic, that holds and aligns the fiber. The standard ferrule outer diameter is 2.5 mm.
  • Connector body – The external housing that provides mechanical support and alignment features.
  • Threaded coupling nut – A screw-on interface used to secure the connector to an adapter or mating connector.
  • Alignment key – A slot or key that maintains rotational orientation between the connector and the adapter.
  • Spring mechanism – Applies controlled pressure to maintain physical contact between mating ferrules.

Polish Types

FC connectors are commonly available with several end-face polish types:

  • FC/PC (Physical Contact) – Standard physical contact polish used in early fiber systems.
  • FC/UPC (Ultra Physical Contact) – Improved polish that reduces back reflection compared with standard PC.
  • FC/APC (Angled Physical Contact) – Typically uses an 8° angled end face to minimize back reflection.

Does FC only hold single-mode fiber?

No. FC connector can terminate both single-mode and multimode fibers.

However, FC connectors are most commonly used with single-mode fibers because the threaded coupling provides stable alignment and low back-reflection, which is important for precision optics.

Is the ferrule OD fixed?

Yes, for standard FC connectors.

Typical specification:

  • Ferrule outer diameter: 2.5 mm
  • Material: ceramic (zirconia) or metal

This 2.5 mm ferrule standard is shared by several connectors:

  • FC
  • ST
  • SC

What changes between them is the coupling mechanism, not the ferrule size.

Note that the bore diameter inside the ferrule changes depending on the fiber.

What defines an FC connector?

An FC connector is defined mainly by its mechanical interface, not just the ferrule.

Key defining features:

  • Threaded coupling mechanism
  • 2.5 mm ferrule
  • keyed alignment slot

So the identity of an FC connector comes from both the connector body and the ferrule format.