The most critical part, the Cable and Fiber Preparation where the fiber is mounted, is the ferrule. The Ferrule is a long, thin cylinder with the fiber mounted in the center hole. The center hole is sized to match fiber’s cladding diameter which is usually 125um. When fiber connector ferrules are made from several types of materials including ceramic(Zirconia), stainless steel and plastic. The ferrule’s job is to center and align the fiber and protects it from mechanical damage. The end of fiber is at the end of the ferrule, where the fiber end is polished smooth either flat or with a curvature. The ferrule is mounted in the connector body and then the connector body is attached to the fiber optic cable structure. Finally, a strain-relief rubber boot protects the connector-cable junction. Fiber optic connectors usually do not have the male-female polarity. Most fiber connectors are male only. Instead, fiber connectors mate to each other in fiber adapters, which are often called mating sleeves or coupling receptacles.
Fiber optic adapters used to mate different connector types such as a FC connector to a SC connector are called hybrid adapters. Although this approach requires the use of separate adapters, it otherwise reduces fiber connector inventory requirements since now you need to stock one type of connector only. Another advantage is that fiber adapters can be designed to mate one type of connector to another, which is a big plus compared to electronic connectors. The fiber’s plastic coating is stripped first before the fiber is inserted in the ferrule. The center hole through the ferrule is large enough to fit the Fiber cladding (which is usually 125um after fiber coating stripped off) but tight enough to hold the fiber in a fixed position without any further moving. Standard bore diameters are 126 +1/-0 um for single mode connectors and 127 +2/-0 um for multimode connectors.
Because of fiber cladding diameter’s variation from manufacturing, some fiber connector manufacturers also supply a range of ferrule bore sizes such as 124um, 125um, 126um and 127um. Fiber optic epoxy or adhesive is injected into the ferrule hole before the fiber is pushed in to hold the fiber in place. The epoxy or adhesive is then cured with high temperature oven according to adhesive manufacturers’ instruction. Finally the fiber end is polished to a smooth face on polishing films. The ferrule is slipped inside another hollow cylinder before it is mounted in the connector body. The connector body includes one or more pieces that are assembled to hold the cable and fiber in place. Connector body is made of metal or plastic. The ferrule end protrudes beyond the connector body so it can slip into the mating sleeves (fiber adapters).
A stain-relief rubber boot is finally slipped over the cable end of the connector to protect the cable-connector junction point. In fiber optic cross connect boxes or fiber patch panels, an array of connector adaptors are mounted inside, ready for you to plug an input fiber cable in one side and an output cable in the other. Fiber connector adapters are also mounted in wall outlets, just like standard phone jacket. I think polishing the fiber is the last and very critical step in the connectorization process. Polishing finalizes the connector end face and cleans the surface, which has a direct impact on such optical performance parameters as insertion loss, return loss, and bit-error-rate for overall network performance. Reliable polishing processes rely on proper training and a well-equipped termination toolkit.