Straight tip (ST) fiber optic connectors are a type of connector used in fiber optic networking, which uses light rather than electrical signals to transmit data. They are carefully designed to align and protect two segments of optical fiber, and were among the first connectors widely used in optical networking. ST fiber-optic connectors use a bayonet-style twist and lock mechanism and can be used with both single and multimode fiber. The connectors are used in data centers, short to medium range network links, and military and security applications.
Using light as a transmission medium allows fiber optic cables to carry much more data than their electrical copper-based counterparts, but it also presents some unique problems. Fiber optic connectors must be designed with precision as a top priority, because even a small amount of dust or slight misalignment between fiber segments can greatly reduce performance and reliability. ST fiber-optic connectors, also known as a bayonet fiber optic connector (BFOC), were one of the first widely used connectors designed for fiber-optic use, becoming popular in the 1980s and 90s.
There are two different styles of ST fiber-optic connectors: the original ST connector, which uses a keyed design, and the newer ST-II, which is spring loaded. Both designs use a bayonet-style coupling mechanism that is mated to another connector through a push and twist action. In the center of the connector is the ferrule, a hard cylindrical tube that contains the actual fiber. The ferrule of an ST style connector is 0.1 inch (2.5 mm) in diameter and is most often made of a ceramic material that protects the fiber and holds it in place for optimal transmission. ST style connectors are relatively quick and easy to install and are generally designed to last between 500 and 1,000 connect-disconnect cycles.
ST fiber-optic connectors can be used with either multi-mode optical fiber, typically used in short-distance application, or single-mode optical fiber, which is used in links spanning several miles or more. Like all types of fiber-optic connectors, they suffer from a small amount of insertion loss, a loss of light at the connection point, and return loss, a type of signal loss that occurs when a portion of the optical signal is reflected back at the source. A typical amount of insertion loss for ST fiber-optic connectors is between 0.25 and 0.5 decibels (dB), while return loss is generally 20 to 50 dB depending on the quality of the connector.
Typical uses of ST fiber-optic connectors include telecommunications data centers and networks that cover a building or campus sized area. They may also carry digital audio and video signals, and have been used in the cable television (CATV) industry for long-distance or high-bandwidth links. The U.S. Navy has approved this type of connector in some of its networks, and it can sometimes be found in advanced security systems.