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. [1]
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.
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. [2] Typical connectors are rated for 500–1,000 mating cycles. [3] 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. [4]
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.
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 | Long 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 [5] | ||
DMI | Diamond Micro Interface [6] | Latch, separate | — | 2.5 mm | Printed circuit boards | ||
LSH orE-2000 [7] | Latch, push-pull, integral dust cap | — | 2.5 mm | IEC 61754-15 | Telecom, DWDM systems | ![]() | |
| Latch, push-pull | — | IEC 1754-8 [8] | Telecom and CATV networks | |||
ELIO | Bayonet | — | 2.5 mm | ABS1379 | PC or UPC | ||
ESCON | Enterprise Systems Connection | Latch, integral shroud [1] | — | 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 or Fiber Channel [9] | Screw | M8×0.75 [10] | 2.5 mm | IEC 61754-13 [8] | Datacom, telecom, measurement equipment, single-mode lasers [11] | ![]() |
Fibergate | Latch, integral dust-cap | — | 1.25 mm | Backplane connector | |||
FJ | Fiber-Jack [13] or Opti-Jack [9] | Latch [1] | — | 2.5 mm | Building wiring, wall outlets | ||
LC | Lucent Connector, [9] Little Connector, [14] or Local Connector [14] | Latch | — | 1.25 mm | IEC 61754-20 [8] | High-density connections, SFP and SFP+ transceivers, XFP transceivers. [11] 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 [9] | Snap, push-pull, gendered | — | 2.5×6.4 mm [15] | IEC-61754-7; [8] EIA/TIA-604-5 (FOCIS 5) | SM or MM multi-fiber ribbon. Same ferrule as MT, but more easily reconnectable. [15] Used for indoor cabling and device interconnections. MTP is a brand name for an improved connector, which intermates with MPO. [16] | ![]() |
MT | Mechanical Transfer | Latch, gendered [1] | — | 2.5×6.4 mm | Pre-terminated cable assemblies; outdoor applications [15] | ![]() | |
MT-RJ | Mechanical Transfer Registered Jack or Media Termination - recommended jack [9] | Latch, gendered [1] | — | 2.45×4.4 mm | IEC 61754-18 | Duplex multimode connections | ![]() |
MU | Miniature unit [9] | Latch, push-pull | — | 1.25 mm | IEC 61754-6 | Common in Japan [1] | |
SC | Subscriber connector, [9] square connector [9] or standard connector | Latch, push-pull | — | 2.5 mm | IEC 61754-4 [8] | Datacom and telecom (most widely deployed)[ citation needed ]; GPON; EPON; GBIC; MADI | |
|
| Latch, push-pull | — | 2.5 mm | IEC 61754-4 | Datacom and telecom; GPON; EPON; GBIC | ![]() |
| Sub Miniature A | Screw, optionally keyed | 1/4″-36 UNS 2B | 3.17 mm [18] | IEC 60874-2 | Industrial lasers, optical spectrometers, military; telecom multimode | ![]() |
| Sub Miniature A | Screw | 1/4″-36 UNS 2B | Stepped;[ citation needed ]0.118 to 0.089 in 3.0 to 2.3 mm, typ. | IEC 60874-2 | Industrial lasers, military; telecom multimode | |
SMC[ citation needed ] | Sub Miniature C | Snap | — | 2.5 mm | |||
| Straight Tip [upper-alpha 9] [9] or Bayonet Fiber Optic Connector | Bayonet | — | 2.5 mm | IEC 61754-2 [8] | 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 fibers |
Short name | Long form | Coupling type | Screw thread | Ferrule diameter | Standard | Typical applications |
---|---|---|---|---|---|---|
Biconic [1] | Screw | 2.5 mm | ||||
D4 (NEC) [1] | Screw | 2.0 mm | Japanese telecom in the 1970s and 1980s | |||
Deutsch 1000 | Screw | Telecom | ||||
DIN (LSA) | Screw | 2.0 mm | IEC 61754-3 [8] | 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[ citation needed ] |
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. [20] [21] 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 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" (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 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, [22] 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.
Features of good connector design:
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. Insertion loss and 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.
In optics, an index-matching material is a substance, usually a liquid, cement (adhesive), or gel, which has an index of refraction that closely approximates that of another object.
An optical attenuator, or fiber optic attenuator, is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable.
An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. It is the optical equivalent of an electronic time domain reflectometer which measures the impedance of the cable or transmission line under test. An OTDR injects a series of optical pulses into the fiber under test and extracts, from the same end of the fiber, light that is scattered or reflected back from points along the fiber. The scattered or reflected light that is gathered back is used to characterize the optical fiber. The strength of the return pulses is measured and integrated as a function of time, and plotted as a function of length of the fiber.
In fiber-optic communication, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber. The standards G.652 and G.657 define the most widely used forms of single-mode optical fiber.
A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modulate sound, and a transmission medium for sounds may be air, but solids and liquids may also act as the transmission medium. Vacuum or air constitutes a good transmission medium for electromagnetic waves such as light and radio waves. While a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by absorption or reflection or refraction at the interfaces between media. Technical devices can therefore be employed to transmit or guide waves. Thus, an optical fiber or a copper cable is used as transmission media.
A ferrule is any of a number of types of objects, generally used for fastening, joining, sealing, or reinforcement. They are often narrow circular rings made from metal, or less commonly, plastic. Ferrules are also often referred to as eyelets or grommets within the manufacturing industry.
A fiberscope is a flexible optical fiber bundle with an eyepiece on one end and a lens on the other that is used to examine and inspect small, difficult-to-reach places such as the insides of machines, locks, and the human body.
In physics, backscatter is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light.
A mechanical splice is a junction of two or more optical fibers that are aligned and held in place by a self-contained assembly. The fibers are not permanently joined, just precisely held together so that light can pass from one to another. This impermanence is an important advantage over fusion splicing, as splice loss, the amount of power that the splice fails to transmit, can be better measured and prevented.
Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 800 Gbit/s. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion. The standard G.651.1 defines the most widely used forms of multi-mode optical fiber.
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths than electrical cables. Fibers are used instead of metal wires because signals travel along them with less loss and are immune to electromagnetic interference. Fibers are also used for illumination and imaging, and are often wrapped in bundles so they may be used to carry light into, or images out of confined spaces, as in the case of a fiberscope. Specially designed fibers are also used for a variety of other applications, such as fiber optic sensors and fiber lasers.
Modal dispersion is a distortion mechanism occurring in multimode fibers and other waveguides, in which the signal is spread in time because the propagation velocity of the optical signal is not the same for all modes. Other names for this phenomenon include multimode distortion, multimode dispersion, modal distortion, intermodal distortion, intermodal dispersion, and intermodal delay distortion.
A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable is used. Different types of cable are used for optical communication in different applications, for example long-distance telecommunication or providing a high-speed data connection between different parts of a building.
Fiber Optic cable termination is the addition of connectors to each optical fiber in a cable. The fibers need to have connectors fitted before they can attach to other equipment. Two common solutions for fiber cable termination are pigtails and fanout kits or breakout kits.
Electrical or fiber-optic connectors used by U.S. Department of Defense were originally developed in the 1930s for severe aeronautical and tactical service applications, and the Type "AN" (Army-Navy) series set the standard for modern military circular connectors. These connectors, and their evolutionary derivatives, are often called Military Standard, "MIL-STD", or (informally) "MIL-SPEC" or sometimes "MS" connectors. They are now used in aerospace, industrial, marine, and even automotive commercial applications.
A fiber-optic sensor is a sensor that uses optical fiber either as the sensing element, or as a means of relaying signals from a remote sensor to the electronics that process the signals. Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or because no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using light wavelength shift for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflectometer and wavelength shift can be calculated using an instrument implementing optical frequency domain reflectometry.
The FC connector is a fiber-optic connector with a threaded body, which was designed for use in high-vibration environments. It is commonly used with both single-mode optical fiber and polarization-maintaining optical fiber. FC connectors are used in datacom, telecommunications, measurement equipment, and single-mode lasers. They are becoming less common, displaced by SC and LC connectors. The FC connector has been standardized in TIA fiber optic connector intermateability standard EIA/TIA-604-4.
A fiber-optic patch cord is a fiber-optic cable capped at each end with connectors that allow it to be rapidly and conveniently connected to telecommunication equipment. This is known as interconnect-style cabling.
A fiber-optic adapter connects two optical fiber connectors in the fiber optic lines.