The acronyms SC, LC, FC and ST refer to the most common types of optical connectors in FTTH applications and data networks. As for the PC/UPC/APC terminology, it refers to the type of polishing applied to the optical terminal (ferrule) which makes possible laser light pulses to cross through two optical fibers.
Then, for example, a typical FTTH pigtail with an SC/APC connector is referring to an SC connector with an APC polishing.
Most Common Optical Connectors
FC Connector
“FC” stands for: Ferrule Connector.
A brief history: It was the first optical connector using a ceramic ferrule, developed by Nippon Telephone and Telegraph. Its use is becoming less common in favor of SC and LC connectors.
Features: The screwed fitting of the connector is vibration-proof; therefore it is used in applications under motion. It is also used in precision instruments (such as OTDR) and it is very popular in CATV.
Optical features: For single mode fibers. Its insertion losses reach the 0.3 dB.
ST Connector
“ST” stands for: Straight Tip.
A brief history: Developed in the USA by AT&T and used in professional environments such as corporate networks as well as the military field.
Features: Its shape reminds of the Japanese FC connector, except for its BNC-type fitting system (twist lock also called bayonet style fitting).
Optical features: For multimode fibers. Losses about 0.25 dB.
LC Connector
“LC” stands for: Lucent Connector or Little Connector.
A brief history: Developed by Lucent Technologies and released in 1997.
Features: Push-and-pull fitting (it reminds an RJ45). Safer and more compact than the SC-type, this makes the connector density higher in racks, panels and FTTH.
Optical features: For single mode and multimode fibers. Losses of 0.10 dB.
SC Connector
“SC” stands for: Subscriber Connector or Square Connector.
A brief history: Developed by Nippon Telegraph and Telephone, it has become the most popular because of its decreasing production costs.
Features: Quick push-and-pull fitting. It is compact, allowing a big density of connectors per instrument. It is used in FTTH, telephony, CATV, etc.
Optical features: For single mode and multimode fibers. Losses of 0.25 dB
Polishing types
PC: Physical Contact. The ferrule is beveled and finished in a plain surface. This avoids empty spaces between the ferrules of the connectors being coupled, and achieves insertion losses among -30 dB and -40 dB. Its use is increasingly falling out.
UPC: Ultra Physical contact. They are similar to the PC connectors, allowing decreasing return losses to a margin between -40 and -55 dB thanks to the sharper curve of the bevel. The current trend is using it in deadlines to allow operators to perform networks tests for example by using an OTDR.
APC: Angled Physical Contact. The ferrule ends in a plain, 8 degree angled surface making it the connector that achieves a best optical link because it cuts down the return losses up the -60 dB thus allowing increasing the number of users in single mode fibers. For this reason, combined to its constantly decreasing manufacturing costs, APC has become the most used polishing type.
