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. The basic connector unit is a connector assembly. A connector assembly consists of an adapter and two connector plugs. 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 applications
Avio (Avim)Aviation Intermediate MaintenanceScrewAerospace and avionics
ADT-UNIScrew2.5 mmMeasurement equipment
DMIClipn/a2.5 mmPrinted circuit boards
E-2000 (AKA LSH)Snap, with light and dust-capn/a2.5 mmIEC 61754-15Telecom, DWDM systems;
ECpush-pull typen/aIEC 1754-8Telecom & CATV networks
ESCONEnterprise Systems ConnectionSnap (duplex)n/a2.5 mmIBM mainframe computers and peripherals
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 [3]Screw2.5 mmIEC 61754-13Datacom, telecom, measurement equipment, single-mode lasers; becoming less common
FibergateSnap, with dust-capn/a1.25 mmBackplane connector
FSMAScrew3.175 mmIEC 60874-2Datacom, telecom, test and measurement
LCLucent Connector,[3] Little Connector, or
Local Connector[citation needed]
Snapn/a1.25 mmIEC 61754-20High-density connections, SFP transceivers, XFP transceivers
ELIOBayonetn/a2.5 mmABS1379PC or UPC
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)
MPO / MTPMultiple-Fiber Push-On/Pull-off [3]Snap (multiplex push-pull coupling)n/a2.5×6.4 mm [4]IEC-61754-7; EIA/TIA-604-5 (FOCIS 5)SM or MM multi-fiber ribbon. Same ferrule as MT, but more easily reconnectable.[4] Used for indoor cabling and device interconnections. MTP is a brand name for an improved connector, which intermates with MPO.[5]
MTMechanical TransferSnap (multiplex)n/a2.5×6.4 mmPre-terminated cable assemblies; outdoor applications[4]
MT-RJMechanical Transfer Registered Jack or Media Termination - recommended jack [3]Snap (duplex)n/a2.45×4.4 mmIEC 61754-18Duplex multimode connections
MUMiniature unit [3]Snapn/a1.25 mmIEC 61754-6Common in Japan
Opti-JackSnap (duplex)n/a
SCSubscriber Connector [3] or
square connector [3] or
Standard Connector
Snap (push-pull coupling)n/a2.5 mmIEC 61754-4Datacom and telcom; GBIC; extremely common
SMA 905Sub Miniature AScrew1/4"-36 UNS 2ATyp. 3.14 mmIndustrial lasers, optical spectrometers, military; telecom multimode
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[3]/Bayonet Fiber Optic ConnectorBayonetn/a2.5 mmIEC 61754-2Multimode, rarely single-mode; APC not possible (note 3)
TOSLINKToshiba LinkSnapn/amost common is JIS F05Digital audio
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
D4 (NEC)Screw2.0 mmJapanese telecom in the 1970s and 1980s; obsolete
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 curved surface, so that when fibers are mated only the fiber cores touch, not the surrounding ferrules. 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.



FC connector 
E2000 connector 
ESCON connector 
LC connector (duplex) 
LuxCis connector 
MIC (FDDI) connector 
MPO connector 
MT-RJ connector 
SC connector 
SC connector (duplex) 
SMA 905 connectors 
ST connector 
TOSLINK connector 


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 [10] contains the industry’s most recent 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, and an optical time-domain reflectometer may be used to identify significant point losses or return losses. A power meter and light source or loss test set may also be used to check end-to-end loss.

See also[edit]


  1. ^ a b "Connector identifier". The Fiber Optic Association. 2010. Retrieved March 31, 2013. 
  2. ^ Alwayn, Vivek (2004). "Fiber-Optic Technologies". Retrieved Aug 15, 2011. 
  3. ^ a b c d e f g h i Keiser, Gerd (August 2003). Optical Communications Essentials. McGraw-Hill Networking Professional. p. 132–. ISBN 0-07-141204-2. 
  4. ^ a b c Shimoji, Naoko; Yamakawa, Jun; Shiino, Masato (1999). "Development of Mini-MPO Connector". Furukawa Review (18): 92. 
  5. ^ "Frequently asked questions". US Conec. Retrieved 12 Feb 2009. 
  6. ^ Trulove, James (December 19, 2005). "Designing LAN Wiring Systems". LAN wiring (3rd ed.). McGraw-Hill Professional. p. 23. ISBN 0-07-145975-8. "The 8-pin modular jack is sometimes referred to as an "RJ-45," because the connector/jack components are the same. However, RJ-45 actually applies to a special purpose jack configuration that is not used in LAN or standard telephone wiring." 
  7. ^ Trulove, James (December 19, 2005). "Work Area Outlets". LAN wiring (3rd ed.). McGraw-Hill Professional. p. 132. ISBN 0-07-145975-8. "Modular jacks are often referred to as "RJ-45" jacks. This is not really the correct moniker, although it is in very common use." 
  8. ^ Sezerman, Omur; Best, Garland (December 1997). "Accurate alignment preserves polarization". Laser Focus World. Retrieved March 12, 2009. 
  9. ^ "Polarization maintaining fiber patchcords and connectors" (pdf). OZ Optics. Retrieved Feb 6, 2009. 
  10. ^ GR-3120, Issue 2, April 2010, Generic Requirements for Hardened Fiber Optic Connectors (HFOCs) and Hardened Fiber Optic Adapters (HOFAs),

External links[edit]