A Little Fiber Optic History Background
~3000BC – Earliest known making of glass in the Bronze Ages.
~27BC – Romans draw glass into fibre.
1840s – Jacques Babinet guides light in water and bent glass rods.
1888 – Bent glass rods used to illuminate body cavities for medical purposes.
1920s – Microscope illumination achieved using bent glass rods.
1931 – Mass production of glass fibres conceived.
1951 – First discussions of using transparent cladding on glass or plastic fibres.
1959 – American Optical draws fibres so fine they can only transmit a single mode of light.
1960 – First lasers demonstrated.
1965 – Charles Kao and George Hockham showed that if optical fiber’s attenuation can be reduced to less than 20dB/km, then it can be used as a transportation media for communication
1966 – Charles Kao indicates that fibre losses could be reduced to below 20dB per kilometre for office to office communications.
1967 – Corning starts making high-loss fibres. Research into sing titanium doping and silica cladding commences.
1970 – Robert Maurer, Donald Keck, Peter Schultz, and Frank Zimar from Corning made a silica glass fiber with an attenuation of 17dB/km.
1970 – Corning develop single-mode fibre with losses of 17dB per kilometre by using titanium doping. Also first room-temperature, continuous-wave semiconductor lasers made.
1971 – Bell Labs, University of Southampton and CSIRO in Australia experiment with liquid-core fibres.
1973 – Diode laser lifetime reaches 1000 hours.
1975 – First non-experimental fibre optic link installed by Dorset police.
1976 – First fibres manufactured with low loss of 0.47 dB per kilometre. Lifetime of lasers reaches 100,000 hours (10 years).
1977 – General Telephone and Electronics sent the first live telephone traffic through optical fiber, at 6 Mbit/s, in Long Beach, California.
1977 – Bell Labs extrapolates 100-year lifetime for diode lasers.
1978 – First Fibre Optic Con trade show held in Boston.
1980 – Fibre system carries video signal for Lake Placid Winter Olympics. 9.5km submarine cable lay in Loch Fyne.
1981 – Canada trials fibre optics to homes in Manitoba.
1982 – MCI prepares to lay single-mode fibre from Washington to New York.
1984 – First fibre optic submarine cable laid to Isle of Wight by BT.
1986 – David Payne and Emmanuel Desurvire invented EDFA (Erbium-Doped Fiber Amplifier) which eliminated the need for O-E-O repeaters, significantly reduced the cost for long distance fiber optic systems.
1986 – English Channel fibre optic service commences.
1988 – TAT-8 becomes operational as first transatlantic fibre optic cable.
1996 – One trillion bits per second transmitted over single mode fibre.
1997 – FLAG (fibre optic link around the globe) went into service spanning over 28,000kms and offering 10Gbps services.
1998 – Large effective are fibres are introduced.
2000 – Sumitomo Z-PLUS Fiber, was introduced with lower attenuation of 0.168 dB/km
2002 – Z+ Ultra low loss Pure Silica Core Fibre with much lower attenuation was demonstrated in 2002
2006 – Ribbon fibre cable is introduced to increase fibre core counts in smaller diameter cables.
2009 – Bend insensitive (G.657) fibre introduced.
Fiber Optic Connector Standards
- TIA/EIA-4750000-B
Generic Specification for Fiber Optic Connectors
- TIAEIA-604
Fiber Optic Connector Intermateability Standards (FOCIS)
- TIA/EIA-568-B.3 /C.0 /C.3
Commercial Building Fiber Optic Standards
- GR-326
Generic Requirements for Single Mode Optical Fiber Connectors
- GR-1435
Generic Requirements for Multi-fiber Optical Connectors
Key IEEE Standards and Media for 10 Gigabit Ethernet
IEEE Ethernet protocol standard 802.3 for Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications
IEEE standard 802.3ae for 10 Gigabit Ethernet over Optical Fiber (single mode and multimode)
IEEE standard 802.3aq for 10 Gigabit Ethernet over Installed Multimode Optical Fiber up to 220 meters
Key Physical Layer Interfaces (PHY) and Media
- 10GBase-SR (“short range”)
This standard supports short distances over deployed multimode fiber cabling. It has a range of between 26m to 550m depending on the bandwidth of the glass cores. Uses wavelength at 850nm and typically VCSEL lasers.
- 10GBase-LX4
Uses WDM (wavelength division multiplexing) to support ranges of between 240m and 300m over deployed multimode cabling. Also supports 10km over single mode fiber. Uses wavelength of 1310nm.
- 10Gbase-LR (“long range”)
This standard supports distances of up to 10km over single mode fiber using 1310nm wavelength.
- 10GBase-ER (“extended range”)
This standard supports distances up to 40km over single mode fiber using 1550nm. Recently several manufacturers have introduced 80km range ER pluggable interfaces.
- 10GBase-LRM
This standard will support distances up to 220m 10Gbit/s on FDDI-grade multimode cable. Various combinations of offset and center launch cables on both ends of the link. Very complex.
- 10GBase-SW, 10GBase-LW and 10GBase-EW
These varieties use the WAN PHY, designed to interoperate with OC-192/STM-64 SDH/SONET equipment using a light-weight SDH/SONET frame. They correspond at the physical layer to 10GBase-SR, 10GBase-LR and 10GBase-ER respectively, and hence use the same types of fiber and support the same distances. (There is no WAN PHY standard corresponding to 10GBase-LX4).
A Little Bit Background Info about Fiber Optic Connectors
Fiber optic connectors have traditionally been the biggest concern in using fiber optic systems.
Connectors were once unwieldy and difficult to use.
Connector manufacturers have standardized and simplified connectors greatly.
This increasing use-friendliness has contributed to the increase in the use of fiber optic systems.
The sole purpose of a connector is to mate fiber optic cable with minimal loss of light.
Connectors are designed for many different applications including telecommunications, local area networks, and harsh environments.
The Fiber Optic Connector Body
Also called the connector housing, the connector body holds the ferrule
Usually constructed of metal or plastic and includes one or more assembled pieces which hold the fiber in place.
Details vary among connectors, but bonding and/or crimping is commonly used to attach strength members and cable jackets to the connector body.
The ferrule extends past the connector body to slip into a coupling device.
The Fiber Cable
The cable is attached to the connector body.
Typically, a strain-relief boot is added over the junction between the cable and the connector body, providing extra strength to the junction.
The Ferrule
- The fiber is mounted in a long, thin cylinder, the ferrule, which acts as a fiber alignment mechanism.
- The ferrule is bored through the center at a diameter that is slightly larger than the diameter of the fiber
cladding.
- The end of the fiber is located at the end of the ferrule.
- Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic.
- The most distinct differentiations between connector types are the diameter of the ferrule, 2.5mm or
1.25mm, and the type of polish.
The Fiber Connector Coupling Device – Mating Sleeves and Adapters
- Most fiber optic connectors do not use the male-female configuration common to electronic connectors.
- Instead, a coupling device such as an alignment sleeve is used to mate the connectors.
- Similar devices may be installed in fiber optic transmitters and receivers to allow these devices to be
mated via a connector.
- These devices are also known as feed-through bulkhead adapters.
Fiber Optic Connector Performance Definitions
- Insertion Loss (IL)
Insertion loss is the amount of optical power lost as a result of a connection. Expressed in decibels, it is the ratio of measured optical power before and after the connector. It always is tested because it is the most important connector parameter.
- Return Loss (RL)
Return loss is a term applied to the light reflection in the connector’s interface that return to the source. The greater the absolute value, the better. Such as –60dB return loss is better than –35dB return loss.
- Back Reflection
Back reflection represents the total accumulated light reflected back to the source along a link. This return of the light is due to different physical phenomena such as multiple connector back-reflections, bad splicing, etc. High back reflection can cause bad or harmful consequences such as light source wavelength fluctuations, output power fluctuations, or even damage the light source permenantly.
Fiber Connector Coupling Loss
- Connector loss is caused by a number of factors.
- Loss is minimized when the two fiber cores are identical and perfectly aligned, the connectors are
properly finished and no dirt is present.
- Only the light that is coupled into the receiving fiber’s core will propagate, so all the rest of the light
becomes the connector loss.
Types of Connection Polishing
- The polish on a fiber connector determines the amount of back reflection.
- Back reflection is a measure of the light reflected off the polished end of a fiber connector measured in
negative dB.
- The Physical Contact (PC) polish is a flat finish of the connecting area.
- The Angled Physical Contact (APC) is at an 8° angle.
- An APC greatly reduces back reflections caused by the physical interface.
Fiber Optic Connector Termination Types
- Anaerobic Adhesive
Anaerobic adhesive connectors use a quick setting adhesive. They work well if your technique is repeatable, but often they do not have the wide temperature range of epoxies, so they are only used indoors. Thus, generally used for factory terminations only.
- Epoxy/Polish
These connectors are the simple “epoxy/polish” type where the fiber is glued into the connector with epoxy and the end polished with special polishing film. These provide a very reliable connection with low losses. They can be factory or field installed.
- Crimp/Polish
Rather than glue the fiber in the connector, these connectors use a crimp on the fiber to hold it in. Early types offered “iffy” performance, but today they are pretty good, if you practice a lot. Expect to trade higher losses for the faster termination speed. And they are more costly than epoxy polish types.
- Pre-Polished
Many manufacturers offer connectors that have a short stub fiber already epoxied into the ferrule and polished perfectly, so you just cleave a fiber and insert it like a splice. While it sounds like a great idea, it has several downsides. First it is very costly, 2 to 3 times as much as an epoxy polish type. Second, you have to make a good cleave to make them low loss.
Fiber Optic Common Connector Types
The common types of fiber optic connectors are LC, SC, MTP/MPO, ST, and FC. LC connector, as a main fiber optic connector, tends to be the most preferred one.
Fiber Optic Connector Types
BICONIC Connector (FOCIS 1)
- The Biconic connector was developed by AT&T and became the de facto standard for long haul
telecommunications.
- The Biconic connector features a cone-shaped tip, which holds a single fiber.
- It is non-metallic, using polymer and epoxy in its construction.
- Telcos have long since adopted other connectors, mainly the SC due to the drawbacks of the Biconic
such as its large size and the fact that it is mated by screwing into its coupling.
- Screw coupling makes its performance sensitive to rotational changes.
ST Connector (FOCIS 2)
- ST stands for Straight Tip – a quick release style connector developed by AT&T. ST’s were the
predominant connector in the late 80s and early 90s.
- ST connectors are among the most commonly used fiber optic connectors in networking applications.
They are cylindrical with twist lock coupling, 2.5mm keyed ferrule.
- The ST connector has a bayonet mount and a long cylindrical ferrule to hold the fiber. Because they are
spring-loaded, you have to make sure they are seated properly. If you experience high loss, try
reconnecting.
SC Connector (FOCIS 3)
- The SC (Subscriber Connector) was developed by NTT specifically as a telecom connector.
- It features push-pull coupling which eliminates rotation which can damage fiber end-faces. This design
also allows higher packaging density.
- An important element of the design is an isolated ferrule, which protects the ferrule and fiber from
cable stresses.
- The SC is available in the usual simple configuration and with duplex adapters as well.
- For maximum density, quad and “six-pack” configurations are available.
FC Connector (FOCIS 4)
- FC stands for Ferrule Connector or Fixed Connection.
- The FC connector was developed by NTT as a single mode telecom connector.
- It uses a combination of thread (screw-on) and keyed design to provide high repeatability and good
fiber end-face protection.
MTP/MPO Connector (FOCIS 5)
- The MPO connector family is defined by two different standards. International the MPO is defined by
IEC-61754-7. In the USA, the MPO is defined by TIA-604-5 (FOCIS 5).
- The MTP multi-fiber connector is US Conec’s trademarked name for their MPO connector.
- The MTP connector is fully compliant with both FOCIS 5 and IEC-61754-7; therefore it is an
MPO connector.
- The MTP connector design is distinctly different than the MPO.
- The MTP connector is a high performance MPO!
- The MTP/MPO is a connector manufactured specifically for a multi-fiber ribbon fiber.
- MPO = Multi-fiber Push On
The Comparison between MTP and MPO Connector.
LC Connector (FOCIS 10)
LC is a small form factor (SFF) fiber optic connector.
The LC connector uses a 1.25mm ferrule, half the size of the ST. Otherwise, it is a standard ceramic ferrule connector.
The LC has good performance and is highly favored for single mode and LO multimode and has been gaining the preference of equipment manufacturers because of its compact size and performance.
MTRJ Connector (FOCIS 12)
MTRJ stands for Mechanical Transfer Registered Jack. MTRJ connector is a small form factor (SFF) duplex connector with both fibers in a single polymer ferrule.
MTRJ Connector uses pins for alignment and has male and female versions.
MTJR connector is multimode only.
The MTRJ connector resembles the RJ-45 connector used in Ethernet networks. The MTRJ was designed by AMP, but was later standardized as FOCIS 12 (Fiber Optic Connector Intermateability Standards) in EIA/TIA-604-12.
MU Connector (FOCIS 17)
MU is a small form factor SC.
MU has the same push/pull style, but can fit 2 channels in the same footprint of a single SC.
MU was developed by NTT.
The MU connector looks like a miniature SC with a 1.25mm ferrule.
Currently it is a popular connector type in Japan.
Other Fiber Optic Connector Types
SMA, D4, Mini-BNC, FDDI, ESCON, SCDC (Corning), Opti-Jack(Panduit), VF-45 (3M Volition), E2000/LX.5 …
Proprietary – No license available.
Old / Never adopted by equipment manufacturers.
No wide spread acceptance in the market.
Fiber Optic Connector Applications
Private Networks (Enterprise)
- Small to medium networks
ST, SC are predominant
- Large Networks
ST, SC with LC growing rapidly
- Data Centers
LC and MTP dominate
Public Networks (Service Providers)
- Telcos
SC with LC growing due to density
- CATV
FC, SC
Future Fiber Optic Connector Trends
- Higher performance
10 gig, 40 gig, 100 gig
- Grater density (data centers)
- OSP capable (FTTH networks)
- FTTx Advancements
— Fiber to the Home
— Fiber in the Home
— Fiber to the Wall Plate
— Fiber to the Desk
Demand for ease of use, greater durability and repeatable performance over time will drive connector technology for decades to come!
Fiber Optic Connector Grade
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.
Fiber optic connector grades
Good fiber optic connectors have low attenuation and high return loss. But what exactly is “good“? IEC 61753-1 specifies performance grades for fiber optic connectors.
IEC 61753-1 and the European issue EN IEC 61753-1 specify performance grades for attenuation and return loss. For attenuation grades letters from A to D are used and for return loss grades numbers ranging from 1 to 4. Not all grades are finalized yet, some are still for further studies.
Attenuation
Connectors for singlemode fibers
Attenuation at 1310 nm, 1550 nm and 1625 nm
Grade A
for further studies
Grade B
max. 0.12 dB average value max. 0.25 dB limit for min. 97% of all connectio
Grade C
> max. 0.25 dB average value
max. 0.5 dB limit for min. 97% of all connections
Grade D
max. 0.5 dB average value max. 1.0 dB limit for min. 97% of all connections
Return loss Connectors for singlemode fibers Return loss at 1310 nm, 1550 nm and 1625 nm
Grade 1 min. 60 dB plugged-in and min. 55 dB unplugged
Grade 2 min. 45 dB
Grade 3 min. 35 dB
Grade 4 min. 26 dB
Attenuation Connectors for multimode fibers Attenuation at 850 nm
Grade Am for further studies
Grade Bm max. 0.3 dB average value max. 0.6 dB limit for min. 97% of all connection
Grade Cm max. 0.5 dB average value max. 1.0 dB limit for min. 97% of all connections
Grade Dm for further studies
Return loss Connectors for multimode fibers
Grade 1m for further studies
Grade 2m min. 20 dB
Caption: Performance grades of randomly mated fiber optic connectors as specified by IEC 61753-1:2018. Testing singlemode connectors at 1625 nm are optional for enterprise applications but mandatory for carrier applications. Performance grades of field-installable singlemode connectors are still under discussion.
Quality classes according to DIN EN IEC 61753-1:2019-10 for randomly assembled fibre optic connectors. Tests of single-mode connectors at 1625 nm are optional for enterprise applications, but required for carrier applications; however, the standard does not define these applications. Attenuation classes for field-mountable single-mode connectors are under consultation according to DIN EN IEC 61753-1:2019-10.
