Types of Fiber Optics Connectors

Few types of Fiber Optics Connectors currently being used in the market....

ST ST (an AT&T Trademark) is probably still the most popular connector for multimode networks (ca. 2005), like most buildings and campuses. It has a bayonet mount and a long cylindrical 2.5 mm ceramic (usually) or polymer ferrule to hold the fiber. Most ferrules are ceramic, but some are metal or plastic. And because they are spring-loaded, you have to make sure they are seated properly. If you have high loss, reconnect them to see if it makes a difference. The ST/SC/FC/FDDI/ESON connectors have the same ferrule size - 2.5 mm or about 0.1 inch - so they can be mixed and matched to each other using hybrid mating adapters. This makes it convenient to test, since you can have a set of multimode reference test cables with ST or SC connectors and adapt to all these connectors.
SC SC is a snap-in connector also with a 2.5 mm ferrule that is widely used for it's excellent performance. It was the connector standardized in TIA-568-A, but was not widely used at first because it was twice as expensive as a ST. Now it's only a bit more expensive and much more common It's a snap-in connector that latches with a simple push-pull motion. It is also available in a duplex configuration.
FC FC was one of the most popular singlemode connectors for many years. It also uses a 2.5 mm ferrule, but some of the early ones use ceramic inside stainless steel ferrules. It screws on firmly, but you must make sure you have the key aligned in the slot properly before tightening. It's been mostly replaced by SCs and LCs.
LC LC is a small form factor connector that uses a 1.25 mm ferrule, half the size of the SC. Otherwise, it's a standard ceramic ferrule connector, easily terminated with any adhesive. Good performance, highly favored for singlemode. The LC, MU and LX-5 use the same ferrule but cross-mating adapters are not easy to find.
FDDI - ESCON Besides the SC Duplex, you may occasionally see the FDDI and ESCON* duplex connectors which mate to their specific networks. They are generally used to connect to the equipment from a wall outlet, but the rest of the network will have ST or SC connectors. Since they both use 2.5 mm ferrules, they can be mated to SC or ST connectors with adapters. FDDI - above - has a fixed shroud over the ferrules ESCON - below - the shroud over the ferrules is spring-loaded and retracts *ESCON is an IBM trademark
MT-RJ MT-RJ is a duplex connector with both fibers in a single polymer ferrule. It uses pins for alignment and has male and female versions. Multimode only, field terminated only by prepolished/splice method. MT-RJ, Volition and Opti-Jack (below) are difficult connectors to test, as most test sets do not allow direct adaptation to the connector. If you have to use hybrid (ST or SC to MT-RJ) reference cables, you cannot do a Method B (one jumper reference) insertion loss test. Usually the solution is to do a three cable (Method C) reference.
Opti-Jack The Panduit Opti-Jack is a neat, rugged duplex connector cleverly designed aournd two ST-type ferrules in a package the size of a RJ-45. It has male and female (plug and jack) versions.
Volition 3M's Volition is a slick, inexpensive duplex connector that uses no ferrule at all. It aligns fibers in a V-groove like a splice. Plug and jack versions, but field terminate jacks only.
LX-5 LX-5 is like a LC but with a shutter over the end of the fiber.
MU MU looks a miniature SC with a 1.25 mm ferrule. It's more popular in Japan.
MT MT is a 12 fiber connector for ribbon cable. It's main use is for preterminated cable assemblies and cabling systems. Here is a 12 fiber MT broken out into 12 STs.
Obsolete Connectors Deutsch 1000 Deutsch 1000 was probably the first commercially successful fiber optic connector. It was really a "pin vise" holding a stripped fiber. The nose piece is spring loaded and was pushed back when the connector was inserted into a mating adapter. The fiber stuck out into a drop of index matching fluid on a plastic lens. This solution was state of the art in the late 70s, yielding about 3 dB loss. Many users remember it as the connector on the front panel of the original Tektronix OTDR.
Obsolete Connectors SMA Amphenol developed the SMA from the "Subminiature A" hence SMA, microwave connector. The model 905 had a machined ferrule exactly 1/8 inch in diameter that mated in a machined adapter. When the adapters were not precise enough for better fibers, a necked-down ferrule that mated with a Delrin adapter for better insertion loss performance. These connectors are still in use on some military and industrial systems.
Obsolete Connectors BICONIC This is the Biconic, the yellow body indicating a SM version - MMs were usually black. Developed by a team led by Jack Cook at Bell Labs in Murray Hill, NJ, the Biconic was molded from a glass-filled plastic that was almost as hard as ceramic. It started with the fiber being molded into the ferrule. This lasted until the company could get a 125 micron/5mil pin insert into the plastic mold, at which point the fiber was glued into the ferule with epoxy. When singlemode versions first appeared, the ferrules were ground to center the fiber core in the ferrule to reduce loss. Since it was not keyed and could rotate in the mating adapters, it had an airgap between the ferrules when mated, meaning loss was never less than 0.3 dB due to fresnel reflection. Usually MM Biconics had losses of 0.5-1 dB and SM 0.7 dB or higher. Jacj Cook retired from Bell Labs and started Dorran Photonics which became 3M fiber optics.
Obsolete Connectors NEC D4 The NEC D4 was probably the first connector to use ceramic or hybrid ceramic/stainless steel ferrules. It uses a smaller ferrule than SCs or FCs. It was widely used in telco networks in the 80s to early 90s and some may still be in use.
Obsolete Connectors OPTIMATE The AMP optimate was popular in the early 80s. It used a conical plastic ferrule and screw-on nut. It was available for every fiber size including plastic fiber. Some may still be in use in utility and industrial systems.

Typical Fiber Optic Connector Types
Connector Style	Description
Biconic	Used in singlemode and multimode assemblies. An early connector design that is rarely used today.
D4	Used in singlemode and multimode assemblies. A keyed, threaded connector that is rarely used today.
FC	Used in singlemode and multimode assemblies. Used in both computer networks and telecommunications applications.
FDDI	Used in multimode assemblies for computer networks; Always a duplex (2-fiber) assembly; Bodies are made of plastic with plastic or ceramic ferrules.
LC	Used in singlemode and multimode connector, adapters and associated components. The LC is a small form factor (SFF) connector that is ideal for high-density applications.
MIL-Spec	Generally used in multimode assemblies;. Made of aluminum or stainless steel; Available for multiple fiber cables.
MPO/MPT	The MPO is a multi-fiber connector suitable for high-density backplane and printed circuit board (PCB) applications for data and telecom systems. MPO/MPT connectors offer up to 12-times the density of standard fiber optic connectors that results in significant space and cost savings.
MTRJ	Used in singlemode and multimode connector, adapters and associated components. The MTRJ is a small form factor (SFF) connector that uses a standard RJ-45 telephone plug interface providing a reliable and robust latching mechanism. The duplex ferrule concept is ideal for high-density applications. MTRJ adapters occupy the same space as a simplex SC adapter and meet the ANSI/TIA/EIA requirements.
MU	MU connectors are small form factor (SFF) connectors that provide superior singlemode or multimode optical performance. MU connectors are approximately half the size of a standard SC connector and feature a push-pull SC latching mechanism. In addition, MU connectors are feature low insertion losses, long-term reliability; and, repeatable performance characteristics.
SC	Used in singlemode and multimode assemblies. Used in both computer networks and telecommunications. Bodies are plastic with ceramic ferrules. Their small size allows them to be densely packed in patch panels and enclosure.
SMA	Used in multimode assemblies. Rarely used today.
SMC	The SMC connector is currently under consideration by the ANSI/TIA/EIA 604 Standards Committee as an industry standard connector. It is designed for use with 12-fiber optic ribbon cable and is based on the MT ferrule incorporating many features of the ESCON connector design. Three SMC connector configuration styles support jacketed and/or unjacketed cable for both internal and external applications.
ST	Used in singlemode and multimode assemblies. Used in both computer networks and telecommunications. Bodies and ferrules come in different materials, including plastic and metal.

Typical Fiber Optic Connector Ferrule Materials
Connector Style	Description
Ceramic	Material used in both singlemode and multimode connectors. Most durable and produces the best performance.
Polymer	Composite plastic used in some multimode connectors and biconic singlemode connectors. Less expensive than ceramic.
Stainless Steel	Used only in multimode connectors

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