We have known that PC, UPC, APC is standard of the fiber optic connectors, PC, UPC, APC are short for: Physical Contact (PC), Ultra Physical Contact (UPC), and Angled Physical Contact (APC), they are actually the polish style of fiber optic ferrules. Below is a picture of the fiber optic ferrules. Unlike copper cables with copper thread in the connectors as connection media, fiber optic connectors are with these ceramic ferrules for connection, and different fiber optic connectors the ferrule size and length and polish styles are different, as can be seen on the picture. Such ferrules is inside the fiber optic connectors and with fiber glass from the fiber optic cable to plug into the ferrule for linking.  The different polish of the fiber optic connector ferrules result in different performance of them, mainly on the back reflection (return loss),.Generally, PC type is required at least 40dB return loss or higher, UPC is 50dB or higher, APC
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