Once the optical fiber is terminated with a particular connector, the connector endface preparation will determine what the connector return loss, also known as back reflection, will be. The back reflection is the ratio between the light propagating through the connector in the forward direction and the light reflected back into the light source by the connector surface.
Minimizing back reflection is of great importance in high-speed and analog fiber optic links, utilizing narrow linewidth sources such as DFB lasers, which are prone to mode hopping and fluctuations in their output. There are several different polish options on the fiber connectors. Extreme accuracy is required, and therefore the polishing is done by a machine.
Flat Polished (Flat)
A flat polished connector has zero dome-shaped geometry.
Physical Contact (PC)
A "physical contact" connector is polished in a dome-shaped geometry to maximize the signal transmitted at the connection.
Ultra Physical Contact (UPC)
UPC, or "ultra physical contact," describes connectors that undergo extended polishing to render the fiber endface more suitable for optical contact with another fiber than an ordinary PC connector.
Angled Physical Contact (APC)
An "angled physical contact" connector is polished on an 8° angle. When compared with a normal "physical contact" (PC) connector, an APC connector exhibits better reflectance properties, because the angled polish reduces the amount of light reflected at the connector interface. Connector types available with an angled polish include SC, ST, FC, LC, MU, MT, and MTP.