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Fiber Optic & Networking Connector Guide

What are fiber optic & networking connectors?

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 1 connector per end while duplex means 2 connectors per end. There are three major components of a fiber connector: the ferrule, the connector body, and the coupling mechanism.

- Ferrule: 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 strengthens 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.

ST

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.

SC

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 square shaped, 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.

MTP

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 breakout applications.

LC

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.

MTRJ

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).

RJ-45

An 8-position, 8-conductor modular connector that is most often used for data networks such as Ethernet. RJ-45 connectors are physically wider than the RJ-11/12 connectors used for telephone. In network applications, RJ-45 cable assemblies are used to connect from a patch panel to a network switch, and also to connect a computer's NIC to a data port.

10G-CX4

10G-CX4 was the first 10G copper standard published. The connector used is similar to that of the Infiniband connector. The 10G-CX4 specification is designed to work up to a distance of 15 meters. Each of the 4 lanes carries 3.125 G baud of signaling bandwidth. 10G-CX4 gives the advantage of low power, low cost, and low latency.

Infiniband™ (4x)

Infiniband is a high-bandwidth I/O communication technology that is typically deployed in data centers, server clusters, and HPC (High Performance Computing) applications. Infiniband cables use a connector based on the Micro GigaCN series developed by Fujitsu. The most common type of connector in use is the "4X", named because it supports four aggregated data links. The cable assembly will apear identical to the 10G-CX4 cables; however, the 10G-CX4 cables are tested for a different set of standards. Infiniband cables cannot be used in 10G-CX4 applications.

FDDI

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 a MIC (Media Interface Connector) connector. It contains two ferrules in a large, bulky plastic housing that uses a squeeze-tab retention mechanism.

Small Form Factor Connectors (SFF)

SFF connectors grew from the effort to make fiber connections smaller. In a rack or closet environment, space for several connections is limited, and thus manufacturers sought a way to increase port density. A standard was developed for smaller connectors called SFF (Small Form Factor). There are many different types of SFF connectors, but they are all smaller than normal ST or SC connections.