An optical fiber connector is a device used to link optical fibers, facilitating the efficient transmission of light signals. An optical fiber connector enables quicker connection and disconnection than splicing.

They come in various types like SC, LC, ST, and MTP, each designed for specific applications. In all, about 100 different types of fiber optic connectors have been introduced to the market.

These connectors include components such as ferrules and alignment sleeves for precise fiber alignment. Quality connectors lose very little light due to reflection or misalignment of the fibers.

Optical fiber connectors are categorized into single-mode and multimode types based on their distinct characteristics. Industry standards ensure compatibility among different connector types and manufacturers. These connectors find applications in telecommunications, data centers, and industrial settings.

Application Optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are often assembled onto optical fiber in a supplier's manufacturing facility. However, the assembly and polishing operations involved can be performed in the field, for example, to terminate long runs at a patch panel.

Optical fiber connectors are used in telephone exchanges, for customer premises wiring, and in outside plant applications to connect equipment and fiber-optic cables, or to cross-connect cables.

Most optical fiber connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated. The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers.

Performance of optical fiber connectors can be quantified by insertion loss and return loss. Measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A (best) to D (worst), and M for multimode. The other parameter is return loss, with grades from 1 (best) to 5 (worst).

A variety of optical fiber connectors are available, but SC and LC connectors are the most common types of connectors on the market. Typical connectors are rated for 500–1,000 mating cycles. The main differences among types of connectors are dimensions and methods of mechanical coupling. Generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use.

In many data center applications, small (e.g., LC) and multi-fiber (e.g., MTP/MPO) connectors have replaced larger, older styles (e.g., SC), allowing more fiber ports per unit of rack space.

Outside plant applications may require connectors be located underground, or on outdoor walls or utility poles. In such settings, protective enclosures are often used, and fall into two broad categories: hermetic (sealed) and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, can become hot if exposed to sunlight or other sources of heat. Free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, and environmental factors.

Types Many types of optical connector have been developed at different times, and for different purposes. Many of them are summarized in the tables below.

+ Fiber connector types Short name Full name Coupling type Screw thread Ferrule diameter Standard Applications and notes Image Avio (Avim) Aviation Intermediate Maintenance Screw Aerospace and avionics ADT-UNI Screw 2.5 mm Measurement equipment CS Corning/Senko Latch, push-pull 1.25 mm Listed in SFF-8024 DMI Diamond Micro Interface Latch, separate 2.5 mm Printed circuit boards LSH or Latch, push-pull, integral dust cap 2.5 mm IEC 61754-15 Telecom, DWDM systems Latch, push-pull IEC 1754-8 Telecom and CATV networks ELIO Bayonet 2.5 mm ABS1379 PC or UPC ESCON Enterprise Systems Connection Latch, integral shroud 2.5 mm IBM mainframe computers and peripherals F07 2.5 mm Japanese Industrial Standard (JIS) LAN, audio systems; for 200 μm fibers, simple field termination possible, mates with ST connectors F-3000 Latch, integral light- and dust-cap 1.25 mm IEC 61754-20 Fiber To The Home (LC compatible) FC Ferrule Connector orFiber Channel Screw M8×0.75TIA Standard FOCIS-4, TIA-604-4-B 2.5 mm IEC 61754-13 Datacom, telecom, measurement equipment, single-mode lasers Fibergate Latch, integral dust-cap 1.25 mm Backplane connector FJ Fiber-Jack orOpti-Jack Latch 2.5 mm Building wiring, wall outlets Lucent Connector,Little Connector, orLocal Connector Latch 1.25 mm IEC 61754-20 High-density connections, SFP and SFP+ transceivers, XFP transceivers. Duplex LC is comparable in size to RJ-45. Luxcis 1.25 mm ARINC 801 PC (straight physical contact) or APC (angled physical contact) configurations LX-5 Latch, integral light- and dust-cap IEC 61754-23 High-density connections; rarely used M12-FO Screw M16 2.5 mm EN 61754-27, ISO/IEC 61754-27 Machine, process and plant engineering. IP-67 dust and water resistant Snap 2.5 mm Multiple-fiber Push-On/Pull-off Snap, push-pull, gendered 2.5×6.4 mm IEC-61754-7; EIA/TIA-604-5 (FOCIS 5) SM or MM multi-fiber ribbon. Same ferrule as MT, but more easily reconnectable. Used for indoor cabling and device interconnections. MTP is a brand name for an improved connector, which intermates with MPO. MT Mechanical Transfer Latch, gendered 2.5×6.4 mm Pre-terminated cable assemblies; outdoor applications Mechanical Transfer Registered Jack orMedia Termination - recommended jack Latch, gendered 2.45×4.4 mm IEC 61754-18 Duplex multimode connections MU Miniature unit Latch, push-pull 1.25 mm IEC 61754-6 Common in Japan Subscriber connector,square connector orstandard connector Latch, push-pull 2.5 mm IEC 61754-4 Datacom and telecom (most widely deployed); GPON; EPON; GBIC; MADI; BiDi Latch, push-pull 2.5 mm IEC 61754-4 Datacom and telecom; GPON; EPON; GBIC Sub Miniature A Screw, optionally keyed ″-36 UNS 2B 3.17 mm IEC 60874-2 Industrial lasers, optical spectrometers, military; telecom multimode Sub Miniature A Screw ″-36 UNS 2B Stepped; , IEC 60874-2 Industrial lasers, military; telecom multimode SMC Sub Miniature C Snap 2.5 mm Straight Tip orBayonet Fiber Optic Connector Bayonet 2.5 mm IEC 61754-2 Datacom F05 Snap-in, clip JIS C 5974 Digital audio, used in select TOSLINK devices Volition Fiber Latch None, V-grooves as guidance Datacom 1053 HDTV Broadcast connector interface Push-pull coupling 1.25 mm ceramic Audio & data (broadcasting) V-PIN V-System Snap-fit, push-pull Industrial and electric utility networking; multimode 200 μm, 400 μm, 1 mm, 2.2 mm fibersMMCMiniature multifiber connector Push-pull6.33mm × 1.83mmData centers

Notes

Obsolete connectors + Obsolete fiber connector types Short name Long name Coupling type Screw thread Ferrule diameter Standard Applications and notes Image Biconic Screw 2.5 mm TIA-604-1 Telecom in the 1980s D4 (NEC) Screw 2.0 mm Telecom between the 1970s and early 1990s Deutsch 1000 Screw Telecom DIN (LSA) Screw 2.0 mm IEC 61754-3 Telecom in Germany in 1990s, measurement equipment OPTIMATE Screw Plastic fiber OptoClip II Snap (push-pull coupling) None - bare fiber used Proprietary Huber & Suhner Datacom and telecom, last made in 2005

Contact Modern connectors typically use a physical contact polish on the fiber and ferrule end. This is a slightly convex surface with the apex of the curve accurately centered on the fiber, so that when the connectors are mated the fiber cores come into direct contact with one another. Some manufacturers have several grades of polish quality, for example a regular FC connector may be designated FC/PC (for physical contact), while FC/SPC and FC/UPC may denote super and ultra polish qualities, respectively. Higher grades of polish give less insertion loss and lower back reflection.

Many connectors are available with the fiber end face polished at an angle to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the reflected light does not stay in the fiber core but instead leaks out into the cladding. Angle-polished connectors should only be mated to other angle-polished connectors. The APC angle is normally 8 degrees; however, SC/APC also exists at 9 degrees in some countries. Mating to a non-angle polished connector causes very high insertion loss. Generally, angle-polished connectors have higher insertion loss than good-quality straight physical contact ones. "Ultra" quality connectors may achieve comparable back reflection to an angled connector when connected, but an angled connection maintains low back reflection even when the output end of the fiber is disconnected.

Angle-polished connections are distinguished visibly by the use of a green strain relief boot, or a green connector body. The parts are typically identified by adding "/APC" (angled physical contact) to the name. For example, an angled FC connector may be designated FC/APC, or merely FCA. Non-angled versions may be denoted FC/PC or with specialized designations such as FC/UPC or FCU to denote an "ultra" quality polish on the fiber end face. Two different versions of FC/APC exist: FC/APC-N (NTT) and FC/APC-R (Reduced). An FC/APC-N connector key will not fit into a FC/APC-R adapter key slot.

Field-mountable connectors Field-mountable optical fiber connectors are used to join optical fiber jumper cables that contain one single-mode fiber. Field-mountable optical fiber connectors are used for field restoration work and to eliminate the need to stock jumper cords of various sizes.

These assemblies can be separated into two major categories: single-jointed connector assemblies and multiple-jointed connector assemblies. According to Telcordia GR-1081, a single-jointed connector assembly is a connector assembly where there is only one spot where two different fibers are joined together. This is the situation generally found when connector assemblies are made from factory-assembled optical fiber connector plugs. A multiple-jointed connector assembly is a connector assembly where there is more than one closely spaced connection joining different fibers together. An example of a multiple-jointed connector assembly is a connector assembly that uses the stub-fiber type of connector plug.

Attributes Features of good connector design: Low insertion loss - should not exceed 0.75 dB Typical insertion repeatability, the difference in insertion loss between one plugging and another, is 0.2 dB. High return loss (low amounts of reflection at the interface) - should be higher than 20 dB Ease of installation Low cost Reliability Low environmental sensitivity Ease of use

Analysis On all connectors, cleaning the ceramic ferrule before each connection helps prevent scratches and extends the connector life substantially. Connectors on polarization-maintaining fiber are sometimes marked with a blue strain relief boot or connector body. Sometimes a blue buffer tube is used on the fiber instead.