According to different grinding methods, it can be divided into the following three types: APC PC UPC:
PC (physical contact), physical contact. PC is a micro-sphere grinding and polishing, and the surface of the ferrule is ground into a micro-sphere;
APC (Angular physical contact), inclined plane physical contact, the end face of optical fiber is usually polished into 8 inclined plane;
UPC (super physical contact), super physical end face. The end face of UPC connector is not completely flat, but has a slight curvature to achieve more accurate docking.
Insertion loss: The typical insertion loss of PC, UPC and APC connectors should be less than 0.3dB (larger value), and the typical value is generally less than 0.2dB. UPC/PC connectors are usually easier to achieve low insertion loss;
Return loss: The end face of APC connector is polished on an inclined plane, so the return loss of APC connector is usually better than that of UPC connector. In general, the return loss of PC is -45dB. The return loss of UPC is generally -50dB (even higher), and the return loss of APC industry standard is -60dB.