Singlemode optical fiber

Optical fiber connector

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 that light can pass. A variety of optical fiber connectors are available. 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, or per type of fiber (one for multimode, one for singlemode).


Fiber connector types
Short name Long form Coupling type Ferrule diameter Standard Typical applications
Avio (Avim) Screw Aerospace and avionics
ADT-UNI Screw 2.5 mm Measurement equipment
Biconic Screw 2.5 mm Obsolete
D4 Screw Telecom in the 1970s and 1980s, obsolete
Deutsch 1000 Screw Telecom, obsolete
DIN (LSA) Screw IEC 61754-3 Telecom in Germany in 1990s; measurement equipment; obsolete
DMI Screw 2.5 mm Printed circuit boards
E-2000 (aka LSH) Snap, with light and dust-cap 2.5 mm IEC 61754-15 Telecom, DWDM systems; becoming less common
ESCON Enterprise Systems Connection Snap (duplex) 2.5 mm IBM mainframe computers and peripherals
F-3000 Snap, with light and dust-cap Not as popular as LC
FC Ferrule Connector Screw 2.5 mm IEC 61754-13 Datacom, telecom, measurement equipment, single mode lasers (becoming less common)
FSMA Screw 3.175 mm IEC 60874-2 Datacom, telecom, test & measurment
LC Lucent Connector or
Local Connector
Snap 1.25 mm IEC 61754-20 High-density connections, SFP transceivers
LX-5 Snap, with light- and dust-cap IEC 61754-23 High-density connections, rarely used
MIC Media Interface Connector Snap 2.5 mm Fiber distributed data interface (FDDI)
MPO Multi-Fibre Push On Snap
MT Mechanical Transfer Snap (12-plex) Pre-terminated cable assemblies
MTP/MPO Snap multi fiber
MT-RJ Mechanical Transfer Registered Jack Snap (duplex) IEC 61754-18 Duplex multimode connections
MU Snap 1.25 mm IEC 61754-6 Common in Japan
NEC D4 Screw Common in Japan telecom in 1980s
Opti-Jack Snap (duplex)
OPTIMATE Screw Plastic fiber, obsolete
SC Subscriber Connector or
Standard Connector or
Siemon Connector
Snap 2.5 mm IEC 61754-4 Datacom and telcom. Extremely common.
SMA Sub Miniature A Screw typ. 3.14 mm Industrial lasers, military applications
SMC Sub Miniature C Snap 2.5 mm
ST / BFOC Straight Tip / Bayonet Fiber Optic Connector Bayonet 2.5 mm IEC 61754-2 Multimode networks
TOSLINK Toshiba Link Snap Digital audio
VF-45 Snap Datacom


  • 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.
  • Many connectors are available with the fiber endface 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.
  • 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 endface.
  • SMA 905 features a "step" in the ferrule, while SMA 906 uses a straight ferrule. SMA 905 is also available as a keyed connector, used e.g. for special spectrometer applications.
  • E-2000 and F-3000 are registered trademarks of Diamond SA, Switzerland. ST is a registered trademark of AT&T/Lucent Technologies.


  • LC connectors are sometimes called "Little Connectors".
  • MT-RJ connectors look like a miniature 8P8C connector — commonly (but erroneously) referred to as RJ-45.
  • ST connectors have a mnemonic of "Stab and Twist", referring to how it is inserted (the cable is pushed into the receiver, and the outer barrel is twisted to lock it into place). Also they are known as "Square Top" due to the flat end face.
  • SC connectors have a mnemonic of "Square Connector", and some people believe that to be the correct name. This refers to the fact the connectors themselves are square. Another term often used for SC connectors is "Stick and Click".
  • FCA are referred to as "Fiber Connector Angled".


  • FC connectors' floating ferrule provides good mechanical isolation. FC connectors need to be mated more carefully than the push-pull types due to the need to align the key, and due to the risk of scratching the fiber endface while inserting the ferrule into the jack. FC connectors have been replaced in many applications by SC and LC connectors.
  • There are two incompatible standards for key widths on FC/APC and polarization-maintaining FC/PC connectors: 2 mm ("Reduced" or "type R") and 2.14 mm ("NTT" or "type N"). Connectors and receptacles with different key widths either cannot be mated, or will not preserve the angle alignment between the fibers, which is especially important for polarization-maintaining fiber. Some manufacturers mark reduced keys with a single scribe mark on the key, and mark NTT connectors with a double scribe mark.
  • SC connectors offer excellent packing density, and their push-pull design reduces the chance of fiber endface contact damage during connection.
  • LC connectors are replacing SC connectors in corporate networking environments due to their smaller size; they are often found on small form-factor pluggable transceivers.
  • ST connectors have a key which prevents rotation of the ceramic ferrule, and a bayonet lock similar to a BNC shell.
  • In general the insertion loss should not exceed 0.75 dB and the return loss should be higher than 20 dB. Typical insertion repeatability, the difference in insertion loss between one plugging and another, is 0.2 dB.
  • On all connectors, cleaning the ceramic ferrule before each connection helps prevent scratches and extends the connector life substantially.
  • Only connector with the same ferrule diameter can be mated with special adapters. E.g. a 1.25 mm ferrule diameter LC connector can not be connected to a 2.5 mm ferrule diameter SC connector.
  • Connectors on polarization-maintaining fiber are sometimes marked with a blue strain relief boot or connector body, although this is far from a universal standard. Sometimes a blue buffer tube is used on the fiber instead.

See also


External links

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