Optical fiber connector

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LC and ST optical fiber connectors

An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so light can pass. Better connectors lose very little light due to reflection or misalignment of the fibers. In all, about 100 fiber optic connectors have been introduced to the market.[1]


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 generally 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 make cross-connect jumpers to size.

Optical fiber connectors are used in telephone company central offices, at installations on customer premises, and in outside plant applications to connect equipment and 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.

Every fiber connection has two values:

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.[citation needed] Typical connectors are rated for 500–1,000 mating cycles.[2] 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. Different connectors are required for multimode, and for single-mode fibers.

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

Features of good connector design:

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. Careful assembly is required to ensure good protection against the elements.

Depending on user requirements, housings for outside plant applications may be tested by the manufacturer under various environmental simulations, which could include physical shock and vibration, water spray, water immersion, dust, etc. to ensure the integrity of optical fiber connections and housing seals.


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 nameLong formCoupling typeScrew threadFerrule diameterStandardTypical applicationsImage
Avio (Avim)Aviation Intermediate MaintenanceScrewAerospace and avionics
ADT-UNIScrew2.5 mmMeasurement equipment
DMIDiamond Micro Interface [3]Clipn/a2.5 mmPrinted circuit boards
E-2000 (AKA LSH)Snap, with light and dust-capn/a2.5 mmIEC 61754-15Telecom, DWDM systems;E2000-Connector.jpg
ECpush-pull typen/aIEC 1754-8Telecom & CATV networks
ELIOBayonetn/a2.5 mmABS1379PC or UPC
ESCONEnterprise Systems ConnectionSnap (duplex)[1]n/a2.5 mmIBM mainframe computers and peripheralsESCON connector.jpg
F072.5 mmJapanese Industrial Standard (JIS)LAN, audio systems; for 200 μm fibers, simple field termination possible, mates with ST connectors
F-3000Snap, with light and dust-capn/a1.25 mmIEC 61754-20Fiber To The Home (LC Compatible)
FCFerrule Connector or Fiber Channel [4]Screw2.5 mmIEC 61754-13Datacom, telecom, measurement equipment, single-mode lasers; becoming less common[5]FCPC 002.jpg
FibergateSnap, with dust-capn/a1.25 mmBackplane connector
FJFiber-Jack [6] or
Opti-Jack [4]
Snap (duplex)[1]n/a2.5 mmBuilding wiring, wall outlets
FSMAScrew3.175 mmIEC 60874-2Datacom, telecom, test and measurement
LCLucent Connector,[4] Little Connector,[7] or
Local Connector [7]
Snapn/a1.25 mmIEC 61754-20High-density connections, SFP and SFP+ transceivers, XFP transceivers[5]LC-optical-fiber-connector-hdr-0a.jpg
Lucxis1.25 mmARINC 801PC or APC configurations (note 3)
LX-5Snap, with light- and dust-capn/aIEC 61754-23High-density connections; rarely used
MICMedia Interface ConnectorSnapn/a2.5 mmFiber distributed data interface (FDDI)FDDI-optical-fiber-connector-hdr-0a.jpg
MPO / MTPMultiple-Fiber Push-On/Pull-off [4]Snap (multiplex push-pull coupling)n/a2.5×6.4 mm [8]IEC-61754-7; EIA/TIA-604-5 (FOCIS 5)SM or MM multi-fiber ribbon. Same ferrule as MT, but more easily reconnectable.[8] Used for indoor cabling and device interconnections. MTP is a brand name for an improved connector, which intermates with MPO.[9]MPO Stecker HR.jpg
MTMechanical TransferSnap (multiplex)[1]n/a2.5×6.4 mmPre-terminated cable assemblies; outdoor applications[8]Lwl mtrj.jpg
MT-RJMechanical Transfer Registered Jack or Media Termination - recommended jack [4]Snap (duplex)[1]n/a2.45×4.4 mmIEC 61754-18Duplex multimode connectionsLwl mtrj.jpg
MUMiniature unit [4]Snapn/a1.25 mmIEC 61754-6Common in Japan[1]
SCSubscriber Connector [4] or
square connector [4] or
Standard Connector
Snap (push-pull coupling)n/a2.5 mmIEC 61754-4Datacom and telecom; GPON; EPON; GBICSC-optical-fiber-connector-hdr-0a.jpg
SC-DCSC - Dual Contact[6] or
SC-QC(Quattro Contact)[6]
Snap (push-pull coupling; duplex)n/a2.5 mmIEC 61754-4Datacom and telecom; GPON; EPON; GBICSC-optical-fiber-connector-hdr-0a.jpg
SMA 905Sub Miniature AScrew1/4"-36 UNS 2ATyp. 3.14 mmIndustrial lasers, optical spectrometers, military; telecom multimodeFSMA.jpg
SMA 906Sub Miniature AScrewStepped; typ. 0.118 in (3.0 mm), then 0.089 in (2.3 mm)[citation needed]Industrial lasers, military; telecom multimode
SMCSub Miniature CSnapn/a2.5 mm
ST / BFOCStraight Tip[4]/Bayonet Fiber Optic ConnectorBayonetn/a2.5 mmIEC 61754-2Multimode, rarely single-modeST-optical-fiber-connector-hdr-0a.jpg
TOSLINKToshiba LinkSnapn/amost common is JIS F05Digital audioToslink kabel.jpg
VF-45Volition FiberSnapn/aDatacom
1053 HDTVBroadcast connector interfacePush-pull couplingn/aIndustry-standard 1.25 mm diameter ceramic ferruleAudio & Data (broadcasting)
V-PINV-SystemSnap (Duplex) Push-pull couplingn/aIndustrial and electric utility networking; multimode 200 μm, 400 μm, 1 mm, 2.2 mm fibers

Obsolete connectors[edit]

Obsolete connector types
Short nameLong formCoupling typeScrew threadFerrule diameterStandardTypical applications
BiconicScrew2.5 mmObsolete[1]
D4 (NEC)Screw2.0 mmJapanese telecom in the 1970s and 1980s; obsolete[1]
Deutsch 1000ScrewTelecom, obsolete
DIN (LSA)ScrewIEC 61754-3Telecom in Germany in 1990s, measurement equipment; obsolete
OPTIMATEScrewPlastic fiber; obsolete
OptoClip IISnap (push-pull coupling)n/aNone - bare fiber usedProprietary Hüber & SuhnerDatacom and telecom; obsolete (last made in 2005)


  1. 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.[10][11] 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.
  2. 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. 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.
  3. 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.
  4. SMA 906 features a "step" in the ferrule, while SMA 905 uses a straight ferrule. SMA 905 is also available as a keyed connector, used e.g., for special spectrometer applications.


Field-mountable connectors[edit]

Field-mountable optical fiber connectors are used to join optical fiber jumper cables that contain one singlemode fiber. These assemblies can be separated into two major categories: single-jointed connector assemblies and multiple-jointed connector assemblies. According to Telcordia GR-1081,[12] 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.

Field-mountable optical fiber connectors are used for field restoration work and to eliminate the need to stock jumper cords of various sizes.


These connectors, which are field-mateable and hardened for use in the OSP, are needed to support Fiber to the Premises (FTTP) deployment and service offerings. HFOCs are designed to withstand climatic conditions existing throughout the U.S., including rain, flooding, snow, sleet, high winds, and ice and sand storms. Ambient temperatures ranging from –40°C (–40°F) to +70°C (158°F) can be encountered.
Telcordia GR-3120 [17] contains the industry’s most recent generic requirements for HFOCs and HFOAs.


Glass fiber optic connector performance is affected both by the connector and by the glass fiber. Concentricity tolerances affect the fiber, fiber core, and connector body. The core optical index of refraction is also subject to variations. Stress in the polished fiber can cause excess return loss. The fiber can slide along its length in the connector. The shape of the connector tip may be incorrectly profiled during polishing. The connector manufacturer has little control over these factors, so in-service performance may well be below the manufacturer's specification.

Testing fiber optic connector assemblies falls into two general categories: factory testing and field testing.

Factory testing is sometimes statistical, for example, a process check. A profiling system may be used to ensure the overall polished shape is correct, and a good quality optical microscope to check for blemishes. Optical Loss / Return Loss performance is checked using specific reference conditions, against a reference-standard single mode test lead, or using an "Encircled Flux Compliant" source for multi-mode testing. Testing and rejection ("yield") may represent a significant part of the overall manufacturing cost.

Field testing is usually simpler. A special hand-held optical microscope is used to check for dirt or blemishes. A power meter and light source or an optical loss test set (OLTS) is used to test end-to-end loss, and an optical time-domain reflectometer may be used to identify significant point losses or return losses.


  1. ^ Pedestal terminal closures are intended to house passive telecommunications components used in an Outside Plant (OSP) environment. According to Telcordia GR-13, these closures may house such components as copper terminal blocks, coaxial taps, or passive fiber optic distribution equipment used for the distribution of telephone service and broadband services.

See also[edit]


  1. ^ a b c d e f g h i "Connector identifier". The Fiber Optic Association. 2010. Retrieved Oct 18, 2014. 
  2. ^ Alwayn, Vivek (2004). "Fiber-Optic Technologies". Retrieved Aug 15, 2011. 
  3. ^ "DMI datasheet". DIAMOND SA. Retrieved 6 Oct 2014. 
  4. ^ a b c d e f g h i j Keiser, Gerd (August 2003). Optical Communications Essentials. McGraw-Hill Networking Professional. p. 132–. ISBN 0-07-141204-2. 
  5. ^ a b "Fiber Optic Connectors". Retrieved Oct 18, 2014. 
  6. ^ a b c "Small Form Factor Fiber Optic Connectors Tutorial". Fiberstore. June 3, 2014. Retrieved Oct 18, 2014. 
  7. ^ a b US patent 20140126875, Lou Guzzo, Inman, SC (US), "Connector Ferrule Holder", issued 2014-05-08 
  8. ^ a b c Shimoji, Naoko; Yamakawa, Jun; Shiino, Masato (1999). "Development of Mini-MPO Connector". Furukawa Review (18): 92. 
  9. ^ "Frequently asked questions". US Conec. Retrieved 12 Feb 2009. 
  10. ^ "The Importance of Geometry for Fiber Optic Connectors" (pdf). Corning Cable Systems. April 2006. 
  11. ^ Yin, Ling; Huang, H.; Chen, W.K.; Xiong, Z.; Liu, Y.C.; Teo, P.L. (May 2004). "Polishing of fiber optic connectors". International Journal of Machine Tools and Manufacture 44 (6): 659–668. doi:10.1016/j.ijmachtools.2003.10.029. 
  12. ^ GR-1081, Generic Requirements for Field-Mountable Optical Fiber Connectors, Telcordia.
  13. ^ Sezerman, Omur; Best, Garland (December 1997). "Accurate alignment preserves polarization". Laser Focus World. Retrieved March 12, 2009. 
  14. ^ "Polarization maintaining fiber patchcords and connectors" (pdf). OZ Optics. Retrieved Feb 6, 2009. 
  15. ^ "MTP/MPO Fiber Solution". 
  16. ^ GR-13-CORE, Generic Requirements for Pedestal Terminal Closures, Telcordia.
  17. ^ GR-3120, Generic Requirements for Hardened Fiber Optic Connectors (HFOCs) and Hardened Fiber Optic Adapters (HOFAs), Telcordia.

External links[edit]