Windows Knowledge Base

[NOC Tutor] Fiber Channel - Fiber Optic Connector Types

If you have been working with twisted-pair copper, you are in for a bit of a surprise when you
start trying to figure out which fiber-optic connectors you need to use. There’s a regular
rogues’ gallery of them, likely the result of competing proprietary systems in the early days of
fiber deployment.

Fiber-Optic Connector Types
Fiber-optic connectors use bayonet, screw-on, or “snap ‘n lock” methods to attach to the jacks;
a newer connector called the MT-RJ is remarkably similar to the eight-position modular connectors
(a.k.a. RJ-45) that copper folks have been using for years.
To transmit data, two fibers are required: one to send and the other to receive. Fiber-optic
connectors fall into one of two categories based on how the fiber is terminated:
?  Simplex connectors terminate only a single fiber in the connector assembly.
?  Duplex connectors terminate two fibers in the connector assembly.

The disadvantage of simplex connectors is that you have to keep careful track of polarity. In
other words, you must always make sure that the plug on the “send” fiber is always connected
to the “send” jack and that the “receive” plug is always connected to the “receive” jack. The real
issue is when normal working folk need to move furniture around and disconnect from the jack
in their work area and then get their connectors mixed up. Experience has shown us that they
are not always color coded or labeled properly. Getting these reversed means, at the least, that
link of the network won’t work.
Duplex plugs and jacks take care of this issue. Once terminated, color coding and keying
ensures that the plug will be inserted only one way in the jack and will always achieve correct
polarity.
Table below  lists some common fiber-optic connectors, along with their corresponding figure
numbers. These connectors can be used for either single-mode or multimode fibers, but make
sure you order the correct model connector depending on the type of cable you are using.

Picuture-1 SC Fiber optic

picture-2 SC duplex connectors

SC duplex connectors allow the user to connect two SC fiber cables yet only have to run one solid cable. This cable comes with a clip which helps manage the connectors on installation.

picture-3 ST connectors

ST connectors features a closed key design enabling fiber cables to far exceed the performance specifications of tensile strength

picture-4 ST duplex Connector

ST duplex connectors feature closed keyway designs allowing for a much more secure connection

picture-5 FDDI connectors

FDDI connectors have a built-in channel guide which is designed to prevent the mis-connection of segments and devices

picture-6 FC Connectors

FC connectors are terminated with threaded coupling for durable pull proof connections used in telecommunication networks, CAT networks, active device termination and instrumentation

Of the four layers of a tight-buffered fiber (the core, cladding, coating, and buffer), only the
core where the light is actually transmitted differs in diameter. In their infinite wisdom and
foresight, the lesser gods who originally created fiber cables made the cladding, coating, and
buffer diameters identical, allowing universal use of stripping tools and connectors.
Of the connectors in Table 1 above, the ST used to be the most widely deployed, but now the
duplex SC is specified in the Standard as the connector to be used. Other connector styles are
allowed, but not specified. Other specifications, including those for ATM, FDDI, and broadband
ISDN, now also specify the duplex SC.
This wide acceptance in system specifications and standards (acceptance in one begets acceptance
in others), along with ease of use and positive assurance that polarity will be maintained,
are all contributors to the duplex SC being the current connector of choice.

SFF (small-form-factor)

SFF connectors were not included in previous versions of the TIA Standard because the standards
committees felt that none of the SFF connector designs were mature enough. Different
manufacturers were proposing different designs, all of which were new to the market. None of
the designs had achieved widespread acceptance, so there was no clear de facto standard. ANSI
frowns on, if not prohibits outright, adoption of single-manufacturer proprietary designs as
standards because such action awards competitive advantage.

However, SFF fiber-optic connectors continue to be promoted and supported by equipment
vendors. Three of the connectors are the LC, the VF-45, and the MT-RJ. The MT-RJ currently
may have a slight popularity edge, but the market has not produced an overwhelming (or
underwhelming) choice. The LC connector is also widely used and is regarded by many optical-fiber professionals as the superior connector. SFF was taken up as a subject of consideration in TIA working group TR-48.8.1. With the publication of ANSI/TIA/EIA-568-B.3, “alternate” connector designs are allowed, provided they meet particular performance requirements. Small-form-factor connectors are now allowed as alternative connectors for use in fiber-optic installations, though no particular
design is called out.

Installing Fiber-Optic Connectors

With twisted-pair and coax cables, connectors are joined to the cable and conductors using
some form of crimping or punch down, forcing the components into place. With fiber-optic
cables, a variety of methods can join the fiber with its connector. Each manufacturer of connectors,
regardless of type, specifies the method to be used, the materials that are acceptable,
and sometimes, the specialized tools required to complete the connection.
When the fiber connector is inserted into the receptacle, the fiber-optic core in the plug is
placed in end-to-end contact with the fiber in the jack. Two issues are of vital importance:
- The fiber-optic cores must be properly aligned. The end-to-end contact must be perfectly
flush with no change in the longitudinal axis. In other words, they can’t meet at an angle.
-The surfaces must be free of defects such as scratches, pits, protrusions, and cracks.