What is PC,UPC,APC?

PC/UPC/APC means the fiber optic connector cross-section technology, that is to say the grinding way.
“PC” is the most widely used in the equipment of telecom operators and the joint cross-section is flat.
“UPC” is another style and its attenuation is smaller than the PC and it has a spherical cross-section.
For the “APC”, its attenuation is the smallest that means that the process is more accurate. Cause it have an oblique cross-section of octave.