The type of fiber connection Polish Type determines the quality of the light-wave transmission, and as technology progresses, connections improve.
Flat Connector Polish Type
The original fiber connector is a flat-surface connection, or a flat connector. When mated, an air gap naturally forms between the two surfaces from small imperfections in the flat surfaces. The back reflection in flat connectors is about -14 dB or roughly 4%.
PC Connector Polish Type
The most common connection is the Physical Contact (PC) connector. With the PC connector, the two fibres meet as they do with the flat connector, but the end faces are polished to be slightly curved or spherical. This eliminates the air gap and forces the fibres into contact. The back reflection is about -40 dB.
UPC Connector Polish Type
An improvement to the PC connector is the Ultra Physical Contact (UPC) connector. The end faces are given an extended polishing for a better surface finish. The back reflection is reduced even more to about -55 dB. These connectors are often used in digital, CATV, and telephony systems.
APC Connector Polish Type
The latest technology is the Angled Physical Contact (APC) connector. The end faces are still curved, but they’re angled at an industry-standard eight degrees. This maintains a tight connection, and it reduces back reflection to about -70 dB. These connectors are preferred for CATV and analogue systems.