How To Tell The Difference Between Small Form-Factor Fiber Connectors

Several types of small form-factor fiber connectors have been developed in recent years to fill the demand for fiber optic devices that can fit into tight spaces and allow denser packing of connections. These connectors include LC, MU, MT-RJ and VF-45, to name a few.

Most of these small form-factor connectors use push-latch locking mechanism just like the standard old SC connector. This mechanism has the advantage of easily adapt to duplex connectors such as duplex LC, duplex MU, etc.

Some of the small form-factor connectors use 1.25mm fiber ferrule while others are based on smaller versions of MT type ferrules. Now let's examine them in more details below.

:: MTRJ connector

MTRJ connector is derived from the MT connector design with a miniature two-fiber ferrule and an overall size about the same as a standard telephone jack (an RJ45 connector). Two pins are used for fiber alignment while the two fibers are between these two pins.

MTRJ connector is used for intrabuilding communication systems such as interior telephone wiring, and can fit into the same slot in a wall plate as the socket for an RJ45 telephone jack. MTRJ connectors are designed as plugs and jacks, like RJ45 telephone connectors.

:: LC connector

LC connector is a combined design with features from both RJ45 telephone connectors and the 2.5mm ferrule SC connectors. Its outside shape resembles a RJ45 telephone jack, while internally it is actually a miniature version of SC, with a 1.25mm ferrule holding the fiber instead of the 2.5mm ferrule as in SC connectors.

There is a connector very similar to LC, which is called LX.5. LX.5 looks very much like a LC connector, but it has a integral end cap that covers the ferrule when it is out of the mating adapter. When plugging it into the adapter, the end cap opens automatically.

:: MU connector

The MU connector is also a miniatured version of SC connector with a 1.25mm ferrule. But unlike LC connector, it has a push-pull snap-in latching mechanism instead the push-latch locking mechanism as in LC connectors.

There are also some other types of small form-factor connectors designed around the 1.25mm ferrules. They are pretty similar but differ in details such as latching mechanism and assembly procedures. Such an example is the Fiber-Jack connector which is built around a 2.5mm ferrule though.

:: VF-45 connector

3M designed its own VF-45 connector. Its special design is to insert the connector into the socket at a 45° angle instead of the straight face-to-face design in all other type of connectors. The 45° angle presses the pair of fibers into V grooves inside the plastic adapter. The pressure and 45° angle holds the fibers in place in the grooves.

The advantage of VF-45 connectors is that it doesn't need expensive ferrules, thus reducing fiber connector costs in a communication system.

:: Duplex connectors

Duplex version of small form-factor connectors are also available. Duplex connector has a pair of fibers and an internal key so they can be mated in only one orientation. This is necessary since most communication systems use separate fibers to carry signals in each direction. Attach the connector the wrong way and you have one transmitter sending signals to the other transmitter.