Return Loss - APC connector has the best return loss performance of -60dB. The return loss of the UPC connector is -50dB, which is higher than the PC but lower than APC. What is a PC Connector? PC connector stands for physical contact fiber connector, which allows the end faces of two fibers to be in direct contact. In PC fiber connector design, there is a slightly cylindrical cone head with the aiming to eliminate the air gap, so that the typical return loss in single mode applications is about -40dB, higher than the return loss of the original flat polish style (-14 dB or roughly 4%). What is APC Fiber Connector? APC stands for Angled. PC, UPC, and APC describe ferrule endface polish types used in fiber optic connectors. These polishing styles directly affect optical return loss (ORL), insertion loss, compatibility with different optical systems, and overall network stability. PC connectors provide basic physical contact; UPC. Why does it matter whether I use PC, UPC or APC? One of the major differences is the amount of light that gets returned or reflected as the light travels between two mated connections, called reflection.