Fiber Optic Connectors-The Complete Guide

by Network Cabling Guy on August 9, 2011

The network cabling industry’s fiber optic manufacturers over the last few decades have been on a constant mission to develop the better fiber connector. This means lower cost, lower dB losses, easier to terminate out in the field. There have been over 100 connectors developed over the years but a select few have stood the test of time and beat out their competition. Below we will talk about the most common.

     A fiber optic connector terminates at the end of a fiber optic cable and is used when you need a means to connect and disconnect the fiber cable quickly. A fiber splice would be used in a more permanent application. The connectors provide a mechanical connection for the two fiber cables and align both cores precisely so the light can pass through with little loss. There are many different types of connectors but many share similar characteristics. Many connectors are spring loaded. This will push the fiber ends very close to each other so as to eliminate airspace between them, which would result in higher dB losses.

There are generally five main components to a fiber connector: the ferrule, the body, the coupling structure, the boot and the dust cap.

Ferrule-the ferrule is the small round cylinder that actually makes contact with the glass and holds it in place. These are commonly made of ceramic today but also are made of metal and plastic.

Body-This sub assembly holds the ferrule in place. It then fits into the connector housing.

Connector Housing-This holds all sub assembly parts in place and has the coupling that will connect to the customer’s equipment. The securing mechanism is usually bayonet, snap-in or a screw on type.

Boot-This will cover the transition from the connector to the fiber optic cable. Provides stress relief.

Dust Cap-Just as it implies will protect the connector from accumulating dust.

There are many types of connectors on the market. The major differences are the dimensions and the method of connection to equipment. Most companies will settle on one type of connector and keep that as a standard across the board. It makes sense because all equipment has to be ordered with that specific connector type and to have 2 or 3 different connector types can get messy. For typical network cabling projects today LC is fast becoming the shining star of fiber connectors. LC is a small form factor connector which means it requires a much smaller footprint in your IT closet. Thus you can fit many more LC connectors into you fiber panels then say ST or SC connectors.

ST Connector

The ST connector (or Straight Tip) was the first popular connector type to be used as a standard for many organizations in their fiber network applications. It was first developed by AT&T. Often called the “round connector” it has a spring loaded twist bayonet mount with a 2.5mm round ferrule and a round body. The ST connector is fast being replaced with the smaller, denser SFF connectors.

SC Connector

The SC connector is a push-in/pull-out type connector that also has a 2.5 mm ferrule. It is very popular for its excellent performance record. The SC connector was standardized in TIA-568-A, and has been very popular for the last 15 years or so. It took a while to surpass the ST because of price and the fact that users were comfortable with the ST. Now it’s much more competitive with pricing and it is a very easy install, only requiring a push in and pull out connection. This is very helpful in tight spaces. Simplex and duplex SC connectors are available. The SC was developed by the Japanese and some say stands for Standard Connector.

 

FDDI/ ESCON Connectors

You may see FDDI and ESCON(IBM) duplex fiber connectors in older installations. These connectors will mate to their own networks and usually will be seen at the wall outlet locations. These connectors use a squeeze tab coupling mechanism. The closet side of the fiber will usually have a standard ST or SC connector. The FDDI/ESCON connectors can be mated to SC or ST connectors since they both have a 2.5mm ferrule. An adaptor would be required in this case. The FDDI stands for Fiber Distributed Data Interface.

 

LC Connector

The LC connector was developed by Lucent Technologies, hence the LC. It is a Single Form Factor Connector that has a 1.25mm ferrule. The attaching mechanism is similar to an RJ-45 connector with the retaining clip. It is a smaller square connector, similar to the SC. LC connectors are often held together with a duplex plastic retainer. They are also very common in single mode fiber applications.

MT-RJ Connector

MTRJ stands for Mechanical-Transfer Registered Jack and was developed by Amp/Tyco and Corning. MTRJ is very similar to an RJ type modular plug. The connector is always found in duplex form. The body assembly of the connector is usually made from plastic and clips and locks  into place. There are small pins present that guide the fiber for correct alignment. MTRJ’s  also are available in male or female orientation. They are only used for multi-mode applications. They can also be difficult to test because many testers on the market do not accept a direct connection. You usually need to rig up a patch cord adaptor kit to make testing possible.

 

FC Connector

The FC connector you may find in older single mode installations. It was a popular choice that has been replaced by mostly ST or SC type connectors. It also has a 2.5mm ferrule. They have a screw on retaining mechanism but you need to be sure the key and slot on the connector are aligned correctly. FC connectors can also be mated to ST & SC’s through the use of an adaptor.

 

 

Panduit Opti-Jack Connector

The Panduit Opti-Jack is a clean, tough duplex connector cleverly designed around two ST-type ferrules in a package the size of a RJ-45. It has male and female (plug and jack) versions.

 

 

Volition Connector

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 Connector

LX-5 is like a LC but with a shutter over the end of the fiber.

 

 

 

 

MU Connector

MU looks a miniature SC with a 1.25 mm ferrule. It’s more popular in Japan.

 

 

 

MT Connector

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.
This connector is sometimes called a MTP or MPO which are commercial names.

 

 

Hopefully this guide may help you get an idea of what options are out there for your fiber optic connector needs.

 


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