Optical fiber connector

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 to D, and M for multimode. The other parameter is return loss, with grades from 1 to 5.
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 and multi-fiber connectors have replaced larger, older styles, 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 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.

Short name	Full name	Coupling type	Screw thread	Ferrule diameter	Standard	Applications and notes	Image
Avio	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	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
FC	Ferrule Connector or Fiber Channel	Screw	M8×0.75	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 or Opti-Jack	Latch		2.5 mm		Building wiring, wall outlets
	Lucent Connector, Little Connector, or Local 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 or APC 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	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 or Media 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 or standard connector	Latch, push-pull		2.5 mm	IEC 61754-4	Datacom and telecom ; 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 or Bayonet 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
V-PIN	V-System	Snap-fit, push-pull				Industrial and electric utility networking; multimode 200 μm, 400 μm, 1 mm, 2.2 mm fibers
MMC		Push-pull		6.33mm × 1.83mm		Data centers, AI compute clusters

Obsolete connectors

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, 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 as 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" 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 and FC/APC-R. An FC/APC-N connector key will not fit into a FC/APC-R adapter key slot.