CONNECTORS & SPLICES

Fiber optic connectors and splices are used to couple two fibers together. Splices, however, are used to connect two fibers in a permanent joint. Connectors are also used to connect fibers to transmitters or receivers, and, of course, connectors are designed to be demountable. While they share some common requirements, like low loss, high optical return loss and repeatability, connectors have the additional requirements of durability under repeated matings. Splices, meanwhile, are expected to last for many years through sometimes difficult environmental conditions, perhaps underground, underwater or suspended from aerial cables.

CONNECTORS & SPLICESSince fiber optics began, over 80 different

styles of connectors have been used commercially. Most have faded from use or never became popular, so only a few connector styles dominate today’s networks.

Multimode installations generally use the ST or SC connector, with a growing number of SFF (Small Form Factor) connectors.

Singlemode applications use mostly SC or LCs, but many installations are still using older designs.

CONNECTORS & SPLICESDIFFERENT FIBERS = DIFFERENT

CONNECTORS• Multimode– ST or SC– Small form factor– Terminate in field

• Singlemode– SC, LC, others– Splice on factory-made pigtails

CONNECTOR SPECS• Specifications– Loss (in dbs)– Repeatability– Environment (temp, humidity, stress, etc.)– Reliability– Back reflection – Ease of termination– Cost

CONNECTOR SPECS

What’s important in the performance of a fiber optic connector?

• Of course, the most important specification for a connector is loss - the less light loss the better.

• But we also want the connector to be repeatable - in two ways. If we terminate a lot of connectors, we need to be assured that most have about the same loss, so we can plan on that loss for calculating the likely loss of the cable. (We’ll look at power budgets later.) We also want it repeatable if we disconnect it and reconnect it many times, so we know the loss will not change when we reconnect it.

CONNECTOR SPECS

• Connectors must be designed to meet their specs over the environmental changes it will see. It’s no problem indoors, but outdoors, temperature and humidity can change, and think about connectors on an aircraft and the vibration they must endure!

• Reliability means maintaining low loss over its lifetime.

• Back reflection is very important for Laser sources, as light reflected back can disturb the performance of the laser, plus reflected light can create optical “background noise” which confuses receivers.

• Ease of termination and cost probably need no further explanation.

CONNECTORSHere are four generations of fiber

optic connectors, showing how their size in particular has shrunk.

On the bottom is the Deutsch 1000, one of the first commercial connectors. It held the fiber by vise-type action and connected fibers in a plastic lens with oil in it to assist the connection.

• Above it is a Biconic, AT&T’s first commercial connector and the first to work with SM fiber. The Biconic ferrule is a glass-filled thermoplastic. For

• The SC from NTT in Japan was one of the first to use ceramic ferrules and have very low loss, even with SM fiber. It’s still widely used today.

• The LC uses a very small ceramic ferrule to allow the connector to be so small, and it offers equal or perhaps even better performance than the SC.

LC

SC

Biconic

Deutsch

CONNECTOR IDENTIFIERST (an AT&T Trademark) is

probably still the most popular connector for multimode networks, like most buildings and campuses. It has a bayonet mount and a long cylindrical 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.

ST CONNECTOR

CONNECTOR IDENTIFIER

SC is a snap-in connector that is widely used in singlemode systems for it's excellent performance. It's a snap-in connector that latches with a simple push-pull motion. It is also available in a duplex configuration. SC CONNECTOR

CONNECTOR IDENTIFIERThe NTT FC/PC has been one of

the most popular singlemode connectors for many years. It screws on firmly, but make sure you have the key aligned in the slot properly before tightening. It's being replaced by SCs and LCs.

The NEC D4 was one of the first SM connectors and is rarely used - at least in the US - for new installations today.

FC CONNECTOR

D4 CONNECTOR

CONNECTOR IDENTIFIERThe SMA was developed by Amphenol from

a microwave connector (SMA means sub-miniature A type) with an 1/8 inch metal ferrule. It came in two varieties - the 905 with a straight ferrule and the 906 with a necked-down ferrule that used a Delrin alignment bushing. The SMA is obsolete but still commercially available to support old systems. It’s very rugged and still liked for harsh environments.

The AMP Optimate was one of the first commercial connectors. It used a conical plastic ferrule to align fibers. It’s also obsolete and practically impossible to find anymore.

SMA CONNECTORS

AMP OPTIMATE CONNECTOR

CONNECTOR IDENTIFIER

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. *ESCON is an IBM trademark

FDDI CONNECTOR

ESCON CONNECTOR

CONNECTOR IDENTIFIERLC is a new 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.  

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.

LC CONNECTOR

MT-RJ CONNECTOR

CONNECTOR IDENTIFIEROpti-Jack is a neat, rugged

duplex connector cleverly designed around two ST-type ferrules in a package the size of a copper RJ-45. It has male and female (plug and jack) versions. It uses adhesive or prepolished/splice termination.

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 are available, but you can field terminate jacks only.

OPTI-JACK

VOLITION CONNECTOR

CONNECTOR IDENTIFIER• MU looks a miniature SC with a

1.25 mm ferrule. It's more popular in Japan.

• E2000/LX-5 is like a LC but with a shutter over the end of the fiber. High power system users like DWDM and CATV like it for the safety factor of the shutter.

MU CONNECTOR

LX5 CONNECTOR

CONNECTOR IDENTIFIER• MT is a 12 fiber connector for

ribbon cable. It's main use is for preterminated cable assemblies which can be installed as complete systems to avoid field terminations.

MTP CONNECTOR

CONNECTOR IDENTIFIER

Since so many connectors use the 2.5 mm ceramic ferrule, you can cross-mate them with adapters like these. You can get adapters for ST to FDDI and ESCON also.

ST-FC >

SC-FC >

SC-ST >