Fiber Optic Connectors

To join two fibers, connectors are necessary as they provide a mechanical mechanism to achieve this link. These connections are made to active equipment that links with transmitters, receivers, among others. Currently, connectors (or almost all) use ceramic ferrules, and their regular measurements are 1.25 mm or 2.5 mm in diameter.

The functions of connectors, among others, are the following:

• Reduce optical loss during the connection of two fibers caused by inaccurate fiber connection and dirt on the ends.
• Provide mechanical protection for the union of two fibers.
• Reduce reflection through optimal contact between the fiber surfaces.

Since optical fiber was implemented, more than 100 types of connectors have been designed to offer better performance. Currently, the most common are three types, and their body essentially consists of the following: protective sleeve or boot, crimp tube or crimp sleeve, spacer, connector body or connector, ferrule, and protective cap or dust cover. Figure 1 shows these parts.

Figure 1. Components of a connector

The most commonly used connectors today are listed below.

The SC connector (Square Connector or Subscriber Connector) was manufactured in the 1980s by Nippon Telegraph and Telephone and was standardized by ISO/IEC in 1992. It is recognized as an industry favorite, and the ANSI/TIA-568-C.3 standard has defined it as the standard connector.

Connector characteristics:

• Used in single-mode and multi-mode applications.
• Uses a 2.5mm ferrule.
• Features a color code: beige for multi-mode and blue for UPC polish or green for APC polish in single-mode.
• Available in simplex and duplex.
• When inserted into an adapter, a "click" sound helps identify a good connection.

Figure 2. SC Connector

The FC or Ferrule Connector is a connector with a 2.5mm ceramic ferrule, very similar to the ST connector, but the difference lies in the design of the tab that secures the connection.

Characteristics:

• Metal body and zirconium ferrule to ensure greater durability.
• It is a widely used connector in technical equipment and laboratories.
• It screws into the adapter, which prevents easy disconnection.
• Used in single-mode and multi-mode applications.

The LC connector was created by Lucent Technologies, hence the name, and is widely used in single-mode applications as it can be easily connected.

Characteristics:

• Houses a 1.25mm ferrule.
• Can be UPC, APC, or PC.
• Used in single-mode and multi-mode applications.
• The reduced size of the connector allows space optimization by up to 50% compared to other types of connectors.
• Can be simplex or duplex. In duplex, it occupies the same space as a simplex SC connector.

Figure 4. LC Connector

The bayonet or ST type connector has been recognized by the TIA/EIA 568 and IEEE 10 BASE F standard. ST connectors are mostly used in applications with long distances.

Connector characteristics:

• Uses a 2.5 mm ferrule.
• As most standards are based on the SC connector, the use of the ST connector is declining in LAN networks; however, it will be used in CCTV systems and industrial applications.
• Its primary use is in LAN networks and CCTV security systems in multi-mode fiber.
• Used in both multi-mode and single-mode applications.
• It is installed by pushing and rotating the connector 90°.

Figure 5. ST Connector

Other types of connectors exist, one of them being the MTRJ (Mechanical Transfer-Registered Jack); which is a duplex connector, meaning it holds two fibers at the same time and is widely used in multi-mode fiber. The other is the MPO (Multi-fiber Push-on) connector, which is capable of holding 12 to 24 fibers and is commonly used for 40 and 100 Gbps Ethernet networks.