Optical fiber connector
Encyclopedia
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. Better connectors lose very little light due to reflection or misalignment of the fibers.
Optical fiber connectors are used in telephone company central offices, at installations on customer premises, and in outside plant
applications. Connectors are used to connect equipment and cables, or to cross-connect cables within a system.
Most optical fiber connectors are spring-loaded. The end faces of the fibers in the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic contact. This avoids a trapped layer of air between two fibers, which would increase connector insertion loss and reflection loss.
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. 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. Different connectors are required for for multimode
, and for single-mode
fibers.
In datacom and telecom applications nowadays small connectors (e.g., LC) and multi-fiber connectors (e.g., MTP) are replacing the traditional connectors (e.g., SC), mainly to provide a higher number of fibers per unit of rack space.
Features of a good connector design:
Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles. The closures that enclose them may be hermetic, or may be free-breathing. Hermetic closures will subject the connectors within to temperature swings but not to humidity variations unless they are breached. Free-breathing closures will subject them to temperature and humidity swings, and possibly to condensation and biological action from airborne bacteria, insects, etc. Connectors in the underground plant may be subjected to groundwater immersion if the closures containing them are breached or improperly assembled.
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.
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 contains the industry’s most recent requirements for HFOCs and HFOAs.
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 that 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.
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
, and enables quicker connection and disconnection than splicing
Mechanical splice
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 connectors mechanically couple and align the cores of fibers so that light can pass. Better connectors lose very little light due to reflection or misalignment of the fibers.
Application
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
Outside plant
In telecommunication, the term outside plant has the following meanings:*In civilian telecommunications, outside plant refers to all of the physical cabling and supporting infrastructure , and any associated hardware located between a demarcation point in a switching facility and a demarcation...
applications. Connectors are used to connect equipment and cables, or to cross-connect cables within a system.
Most optical fiber connectors are spring-loaded. The end faces of the fibers in the two connectors are pressed together, resulting in a direct glass to glass or plastic to plastic contact. This avoids a trapped layer of air between two fibers, which would increase connector insertion loss and reflection loss.
Every fiber connection has two values :
- Attenuation or insertion lossInsertion lossIn telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels ....
- Reflection or return lossReturn lossIn telecommunications, return loss or reflection loss is the loss of signal power resulting from the reflection caused at a discontinuity in a transmission line or optical fiber. This discontinuity can be a mismatch with the terminating load or with a device inserted in the line...
.
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. 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. Different connectors are required for for multimode
Multi-mode optical fiber
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...
, and for single-mode
Single-mode optical fiber
In fiber-optic communication, a single-mode optical fiber is an optical fiber designed to carry only a single ray of light . Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions...
fibers.
In datacom and telecom applications nowadays small connectors (e.g., LC) and multi-fiber connectors (e.g., MTP) are replacing the traditional connectors (e.g., SC), mainly to provide a higher number of fibers per unit of rack space.
Features of a good connector design:
- Low Insertion Loss
- Low Return Loss
- Ease of installation
- Low cost
- Reliability
- Low environmental sensitivity
- Ease of use
Outside plant applications may involve locating connectors underground in subsurface enclosures that may be subject to flooding, on outdoor walls, or on utility poles. The closures that enclose them may be hermetic, or may be free-breathing. Hermetic closures will subject the connectors within to temperature swings but not to humidity variations unless they are breached. Free-breathing closures will subject them to temperature and humidity swings, and possibly to condensation and biological action from airborne bacteria, insects, etc. Connectors in the underground plant may be subjected to groundwater immersion if the closures containing them are breached or improperly assembled.
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.
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 | 2.0 mm | 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 | Clip | 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; | |
| EC | push-pull type | IEC 1754-8 | Telecom & CATV networks | ||
| ESCON ESCON ESCON is a data connection created by IBM, and is commonly used to connect their mainframe computers to peripheral devices such as disk storage and tape drives. ESCON is an optical fiber, half-duplex, serial interface. It originally operated at a rate of 10 Mbyte/s, which was later increased to... |
Enterprise Systems Connection | Snap (duplex) | 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 | Snap, with light and dust-cap | 1.25 mm | IEC 61754-20 | Fiber To The Home (LC Compatible) | |
| FC FC connector 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... |
Ferrule Ferrule A ferrule is a name for types of metal objects, generally used for fastening, joining, or reinforcement... Connector or Fiber Channel |
Screw | 2.5 mm | IEC 61754-13 | Datacom, telecom, measurement equipment, single-mode lasers; becoming less common |
| Fibergate | Snap, with dust-cap | 1.25 mm | Backplane connector | ||
| FSMA | Screw | 3.175 mm | IEC 60874-2 | Datacom, telecom, test and measurement | |
| LC | Lucent Connector , Little Connector, or Local Connector |
Snap | 1.25 mm | IEC 61754-20 | High-density connections, SFP transceivers, XFP transceiver XFP transceiver The XFP is a standard for transceivers for high-speed computer network and telecommunication links that use optical fiber. It was defined by an industry group in 2002, along with its interface to other electrical components which is called XFI.-Description:XFP modules are hot-swappable and... s |
| ELIO | Bayonet | 2.5 mm | ABS1379 | PC or UPC | |
| LuxCis | 1.25 mm | ARINC 801 | PC or APC configurations (note 3) | ||
| 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 Fiber distributed data interface Fiber Distributed Data Interface provides a 100 Mbit/s optical standard for data transmission in a local area network that can extend in range up to . Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis; instead, its... (FDDI) |
|
| MPO / MTP | Multiple-Fibre Push-On/Pull-off | Snap (multiplex push-pull coupling) | 2.5×6.4 mm | IEC-61754-7; EIA/TIA-604-5 (FOCIS 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 | Snap (multiplex) | 2.5×6.4 mm | Pre-terminated cable assemblies; outdoor applications | |
| MT-RJ | Mechanical Transfer Registered Jack or Media Termination - recommended jack | Snap (duplex) | 2.45×4.4 mm | IEC 61754-18 | Duplex multimode connections |
| MU | Miniature unit | Snap | 1.25 mm | IEC 61754-6 | Common in Japan |
| NEC D4 | Screw | 2.0 mm | Common in Japan telecom in 1980s | ||
| Opti-Jack | Snap (duplex) | ||||
| OPTIMATE | Screw | Plastic fiber, obsolete | |||
| SC | Subscriber Connector or square connector or Standard Connector |
Snap (push-pull coupling) | 2.5 mm | IEC 61754-4 | Datacom and telcom; GBIC GBIC A gigabit interface converter is a standard for transceivers, commonly used with Gigabit Ethernet and fibre channel in the 1990s... ; extremely common |
| SMA 905 | Sub Miniature A | Screw | Typ. 3.14 mm | Industrial lasers, military; telecom multimode | |
| SMA 906 | Sub Miniature A | Screw | Stepped; typ. 0.118 in (3 mm), then 0.089 in (2.3 mm) | Industrial lasers, military; telecom multimode | |
| SMC | Sub Miniature C | Snap | 2.5 mm | ||
| ST / BFOC | Straight Tip/Bayonet Fiber Optic Connector | Bayonet | 2.5 mm | IEC 61754-2 | Multimode, rarely single-mode; APC not possible (note 3) |
| TOSLINK TOSLINK TOSLINK is a standardized optical fiber connection system. Also known generically as an "optical audio cable," its most common use is in consumer audio equipment , where it carries a digital audio stream from components such as MiniDisc, CD and DVD players, DAT recorders, computers, and modern... |
Toshiba Link | Snap | Digital audio | ||
| VF-45 | Snap | Datacom | |||
| 1053 HDTV Fischer Connectors Fischer Connectors is a manufacturer of rugged circular push-pull electrical and fibre optic connectors. Founded in 1954, its headquarters and production centre are based in Switzerland, with subsidiaries located worldwide.... |
Broadcast connector interface | Push-pull coupling | Industry-standard 1.25 mm diameter ceramic ferrule | Audio & Data (broadcasting) | |
| V-PIN | V-System | Snap (Duplex) Push-pull coupling | Industrial and electric utility networking; multimode 200 μm, 400 μm, 1 mm, 2.2 mm fibers |
Mnemonics
- 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 refer to having a "straight tip", as the sides of the ceramic (which has a lower temperature coefficient of expansion than metal) tip are parallel—as opposed to the predecessor bi-conic connector which aligned as two nesting ice cream cones would. Other mnemonics include "Set and Twist", "Stab and Twist", and "Single 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, rather than the more official "Subscriber Connector". This refers to the fact the connectors themselves are square. Other terms often used for SC connectors are "Set and Click" or "Stab and Click".
Analysis
- 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 end face 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 end face contact damage during connection; frequently found on the previous generation of corporate networking gear, using GBICs.
- LC connectors have replaced 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 BNCBNC connectorThe BNC connector ' is a common type of RF connector used for coaxial cable. It is used with radio, television, and other radio-frequency electronic equipment, test instruments, video signals, and was once a popular computer network connector. BNC connectors are made to match the characteristic...
shell. The single index tab must be properly aligned with a slot on the mating receptacle before insertion; then the bayonet interlock can be engaged, by pushing and twisting, locking at the end of travel which maintains spring-loaded engagement force on the core optical junction.
- In general the insertion lossInsertion lossIn telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels ....
should not exceed 0.75 dBDecibelThe decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
and the return lossReturn lossIn telecommunications, return loss or reflection loss is the loss of signal power resulting from the reflection caused at a discontinuity in a transmission line or optical fiber. This discontinuity can be a mismatch with the terminating load or with a device inserted in the line...
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.
- 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.
- MT-RJ (Mechanical Transfer Registered Jack) uses a form factor and latch similar to the 8P8C (RJ45) connectors. Two separate fibers are included in one unified connector. It is easier to terminate and install than ST or SC connectors. The smaller size allows twice the port density on a face plate than ST or SC connectors do. The MT-RJ connector was designed by AMP, but was later standardized as FOCIS 12 (Fiber Optic Connector Intermateability Standards) in EIA/TIA-604-12. There are two variations: pinned and no-pin. The pinned variety, which has two small stainless steel guide pins on the face of the connector, is used in patch panels to mate with the no-pin connectors on MT-RJ patch cords.
- Hardened Fiber Optic Connectors (HFOCs) and Hardened Fiber Optic Adapters (HFOAs) are passive telecommunications components used in an Outside Plant (OSP) environment. They provide drop connections to customers from fiber distribution networks. These components may be provided in pedestal closures, aerial and buried closures and terminals, or equipment located at customer premises such as a Fiber Distribution Hub (FDH) or an Optical Network Terminal or Termination (ONT) unit.
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 contains the industry’s most recent requirements for HFOCs and HFOAs.
Testing
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 that 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
Optical microscope
The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. Optical microscopes are the oldest design of microscope and were possibly designed in their present compound form in the...
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
- Optical fiber cableOptical fiber cableAn optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed....
Color coding of connector boot and fiber cable jackets - Optical attenuatorOptical attenuatorAn optical 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....
Fiber optic attenuator - Gap lossGap lossGap loss is a type of signal strength loss that occurs in fiber optic transmission when the signal is transferred from one section of fiber or cable to another....
Attenuation sources and causes