Choosing A Fiber Optic Connector
Fiber optic connectors provide a critical piece of infrastructure for telecommunications, Datacom processes, precision measurement equipment, and lasers, among other applications. Ferrules are an important component of fiber optic connectors, making precision alignment of fibers possible.
Fiber optic connectors use light to transmit information. Secure, precise connections between fibers are essential to high-quality, reliable transmissions. Ferrules make those connections possible, ensuring that the fibers align properly and that the connection isn’t thrown off by jolts, bumps, or other forms of interference. In fiber optic connections, two critical factors their users must worry about are insertion loss and reflection loss. Insertion loss refers to a loss of signal power resulting from the way fibers connect. Reflection loss, or return loss, refers to a loss of signal power resulting from a portion of the signal being reflected back to its source. When choosing fiber optic connectors, users must consider how much insertion and reflection loss is acceptable, and what connector will most effectively and cheaply keep them within this range.
Fiber Optic Connectors
In fiber optic connectors, the fiber end being connected is encased in a 2.5 mm ferule, typically made of ceramic, metal, or a composite material. The tips of the connectors are polished to create a rounded surface. This smooth surface allows fibers being connected to touch only at their cores, creating a better quality connection.
How the connector is polished is important to its quality. Manufacturers often have several grades of polish for connectors. The higher the grade of polish used, the less insertion loss and lower back-reflection the fiber optic connection will have.
PC Polish – This form of polish is used to reduce connector loss resulting from gaps between fiber ends. This is the original polish used. Insertion loss remains an issue for connectors polished in this manner.
UPC Polish – UPC polish requires advanced polishing techniques, and it also adjusts the curvature at ferrule ends to reduce return loss. UPC polish is now used widely for single mode connectors. It is not used for multimode fibers, however.
APC & SPC Polish - For applications that need to have little back-reflection, manufacturers will polish the end-face of the fiber at an angle. This polishing method will ensure that light reflecting from the interface won’t reverse course. The angle will cause reflected light to exit the fiber core. Angle-polished connectors should not be mated with non-angle-polished connectors, as this will cause a high level of insertion loss.
Fiber optic ferrules are typically made of ceramic, metal, or composite materials. Each material has its benefits and drawbacks. Ferules are typically the most costly component of a fiber optic adapter, often accounting for about 80 percent of its full cost.
Ceramic ferrule sleeves are typically easier for manufacturers to precisely mold and align to the fiber, making them best suited for single-mode cable connections. Because manufacturers are able to create a closer fit, these ferrules provide a much lower optical loss than ferrules made from other materials. Ceramic ferrule sleeves are used for the most vital network connections, like high-security networks or connections in wiring closets.
Ferrules made of metal, bronze for instance, are more durable than ceramic ferrules, but they often do not offer the same level of precision alignment as their ceramic cousins. Drilling an accurate hole through the metal ferrule sleeve can be difficult, and that can result in less accurate fiber alignment. The use of watch-jeweled centering improves alignment, but overall, metal ferrule sleeves are better suited for multimode fiber applications where absolute alignment isn’t crucial.
Composite ferrules act as a great compromise material. Less expensive than ceramic ferrules, these ferrules also provide a greater level of precision than metal ferrules.