. Understanding Optical Fiber THREADED CONNECTOR The threaded type of connector is used by a submulti assembly (SMA) connector. The SMA connector was intro- duced by Amphenal Corporation and included a threaded cap and housing. This is a first-generation connector whose use has considerably decreased in favor of ST (straight tip)- and SC-(stick and click)-type con- nectors. One problem associated with the use of a threaded connector is the airgap caused by a poor connection. Because a poor connection results in the medium changing from fiber to air and back to fiber, this results in a change in the index of refraction. This change results in a Fresnel reflection loss, in which light is reflected back toward the transmitter. BAYONET CONNECTOR A second type of connector coupling results in the use of a keyed bayonet similar to a bayonet coaxial (BNC) connector, a male connector mounted at each end of a coaxial cable (used in Ethernet configurations). This type of connector requires a twist-turn fastening operation, which reduces the possibility of an air- gap formation commonly associated with a threaded connector, which lacks a control for rotational alignment. Two popular keyed bayonet-type connectors are the ST (straight tip) and ST-II connectors pioneered by AT&T during the mid-1980s. Both are used with single-mode and multimode fiber and are keyed and spring-loaded, respectively. Connections are established via a push-in and twist movement. PUSH-PULL CONNECTOR A third coupling method can be catego- rized as push-pull. One popular push-pull connector is the SC connec- tor, which includes a locking tab. This connector is used primarily with single-mode fiber optic cable and uses a ceramic ferrule. The ferrule is a long, thin sleeve in which a fiber is placed. The ferrule acts as an align- ment mechanism and represents a critical component of the push-pull coupling method. PLASTIC FIBER CONNECTORS It is common to encounter connec- tors such as SMA and ST, which were developed for glass fibers used with plastic fi