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Fiber Connectors Demystified

Fiber optic connectors are unique. Fiber cables transmit pulses of light instead of electrical signals, so the terminations must be much more precise. Instead of merely allowing pins to make metal-to-metal contact, fiber optic connectors must align microscopic glass fibers perfectly in order to allow for communication. While there are many different types of fiber connectors, they share similar design characteristics. Simplex vs. duplex: Simplex means one connector per end while duplex means two connectors per end. There are three major components of a fiber connector: the ferrule, the connector body, and the coupling mechanism.


This is a thin structure (often cylindrical) that actually holds the glass fiber. It has a hollowed-out center that forms a tight grip on the fiber. Ferrules are usually made from ceramic, metal, or high-quality plastic, and typically will hold one strand of fiber.

Connector body

This is a plastic or metal structure that holds the ferrule and attaches to the jacket and strength members of the fiber cable itself.

Coupling mechanism

This is a part of the connector body that holds the connector in place when it gets attached to another device (a switch, NIC, bulkhead coupler, etc.). It may be a latch clip, a bayonet-style nut, or similar device.


One popular Small Form Factor (SFF) connector is the LC type. This interface was developed by Lucent Technologies (hence, Lucent Connector). It uses a retaining tab mechanism, similar to a phone or RJ45 connector, and the connector body resembles the squarish shape of SC connector. LC connectors are normally held together in a duplex configuration with a plastic clip. The ferrule of an LC connector is 1.25mm.

LC Connector


SC connectors also use a round 2.5mm ferrule to hold a single fiber. They use a push-on/pull-off mating mechanism which is generally easier to use than the twist-style ST connector when in tight spaces. The connector body of an SC connector is squarish, and two SC connectors are usually held together with a plastic clip (this is referred to as a duplex connection). The SC connector was developed in Japan by NTT (the Japanese telecommunications company), and is believed to be an abbreviation for Subscriber Connector, or possibly Standard Connector.

SC Connector


The ST connector was one of the first connector types widely implemented in fiber optic networking applications. Originally developed by AT&T, it stands for Straight Tip connector. ST connections use a 2.5mm ferrule with a round plastic or metal body. The connector stays in place with a "twist-on/twist-off" bayonet-style mechanism. Although extremely popular for many years, the ST connector is slowly being supplanted by smaller, denser connections in many installations.

ST Connector


This is another popular SFF connector. Based on a specification by NTT, it was developed by AMP/Tyco and Corning, and stands for Mechanical Transfer-Registered Jack. The MTRJ connector closely resembles an RJ-style modular plug, even getting part of its name from the resemblance. MTRJ connectors are always duplex in that they hold two fibers. The body and ferrule are normally made from plastic or plastic composite, and lock into place with a tab (just like a modular RJ-style plug).

MTRJ Connector


MTP is a special type of fiber optic connector. Made by US Conec, it is an improvement of the original MPO (Multi-fiber Push-On) connector designed by NTT. The MTP connector is designed to terminate several fibers — up to 12 strands — in a single ferrule. MTP connections are held in place by a push-on/pull-off latch, and can also be distinguished by a pair of metal guide pins that protrude from the front of the connector. Because of the high number of fiber strands available in a small connection, MTP assemblies are used for backbone, cross-connect, and break-out applications.

MTP® Connector


FDDI stands for Fiber Distributed Data Interface, and it actually refers to a local area network standard such as Ethernet or Token Ring. The termination on the fiber optic cable itself is called an FDDI connector, or is also known as an MIC (Media Interface Connector) connector. It contains two ferrules in a large, bulky plastic housing that uses a squeeze-tab retention mechanism.

FDDI Connector

This white paper is for informational purposes only and is subject to change without notice. C2G makes no guarantees, either expressed or implied, concerning the accuracy, completeness or reliability of the information found in this document.