In all fiber optic systems, it is necessary to join two fibers together with low signal attenuation while maintaining low reflection levels depending upon the type of system used. Fiber optical connectors are used to the mechanical and optical means for cross connecting fibers and linking to fiber optic transmission equipment.
Fiber optical connectors have evolved with the communications industry. Today’s users have a multitude of connectivity needs and the fiber industry has responded with innovative solutions. The most common connector in use today is the SC connector, the ST connector, and the FC connector. In addition, the small form factor - LC connector is used in high-density optical transmission products, and also for applications including fiber-to-the-home and dense wavelength division multiplexing where space is at a premium. Another connector gaining in popularity for use in high fiber count terminations is the MPO/MTP connector which can handle fiber counts as high as 96 using ribbonized fibers.
To understand fiber optical connectors, one must understand both the mechanics and the optics involved. The ideal optical connector holds the fibers in perfect alignment, in three axes. This alignment must be maintained over hundreds or even thousands of connect-disconnect cycles to provide stable, repeatable attenuation characteristics.
The most important element of the connector plug is the ferrule, which provides the precise alignment and centering of the optical fiber. Ferrules can be made of ceramic, metal, glass, or plastic. Zirconia ceramic ferrules or ceramic ferrules with metal inserts are most widely used, providing the best tolerances and durability. The most common ferrule sizes are the 2.5 mm used in the SC, ST, and FC plugs, and the 1.25 mm ferrule that used in the LC plug. For connectors designed for military and aerospace connectors, the “termini” performs the same functions as the ferrule.
The body of the plug holds the ferrule, the coupling mechanism, and the boot. The body contains either a threaded, push-pull or bayonet coupling mechanism that mates the plug with the mating adapter and also provides a keying function that allows the connector to mate in only one position. Strain relief of the cable is usually by a crimp sleeve or by adhesives which firmly secures the aramid yard in the cable to the plug body. At the rear of the plug body is the “boot” which functions as a bend radius limiter for the cable entering the plug body.