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کلمات اختصاری 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 (فرول) which makes possible laser light pulses to cross through two optical fibers.
مثلا, a typical FTTH pigtail with an SC/APC connector is referring to an SC connector with an APC polishing.

Most commonly used optical connectors

FC CONNECTOR

Detail of an FC optical connector (Ferrule 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.
امکانات: 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 دسی بل.

ST CONNECTOR

Detail of an ST (Straight Tip) optical 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.
امکانات: 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 of about 0.25 دسی بل.

LC CONNECTOR

Detail of an LC optical connector (Lucent Connector or Little Connector)
“LC” stands for… Lucent Connector or Little Connector.
A brief history: Developed by Lucent Technologies and released in 1997.
امکانات: Push-and-pull fitting (it reminds an RJ45). Safer and more compact that the SC-type, allowing even more density of connectors in racks, panels and FTTH.
Optical features: For monomode and multimode fibres. Losses of 0,10 دسی بل.

SC CONNECTOR

Detail of an SC optical connector (Subscriptor Connector or Square Connector)
“SC” stands for… Suscriptor 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.
امکانات: Quick push-and-pull fitting. It is compact, allowing a big density of connectors per instrument. It is used in FTTH, telephony, مقداری, و غیره.
Optical features: For single mode and multimode fibers. Losses of 0.25 دسی بل.

Polishing types

• کامپیوتر: 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 دسی بل. 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 و -55 dB thanks to the sharper curve of the bevel. The current trend is using it in dead lines 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. به این دلیل, combined to its constantly decreasing manufacturing costs, APC has become the most used polishing type.

Optical Fiber Connectors Color Chart