After the definition of three connector types, you will find that PC, UPC, and APC connectors vary in many aspects. The following lists their differences in appearance, performance, and application categories.
The major difference in terms of appearance is the fiber end face. PC connectors and UPC connectors are both polished with no angle, though end face of UPC has a slight curvature. Instead, an APC connector is featured with 8° angle end face.
Another obvious difference is the color. It is visible to distinguish which type of polish style the connector features by the color of the connector body. Take an FS LC APC single mode fiber optic patch cable as an example, the connectors on both fiber ends are all green. While for an LC UPC single mode fiber optic patch cable, the connectors are generally blue. It is also a simple way to tell these connectors apart.
It used to be hard to achieve low insertion loss using APC connectors owing to the air gap in the apex offsets, yet nowadays the improvement of connector design and manufacturing push APC connectors to perform better. The insertion difference between APC and UPC has been diminished.
As for the performance of return loss, you may have noticed APC connectors have the lowest back reflection of all the fiber connectors mentioned owing to the angled end face. For this reason, the values of the return loss are different. According to the industry standards, the return loss of PC, UPC, and APC connectors is respectively about -40dB, -50dB, and -60dB or higher. The higher the return loss is, the lower the reflection and the better the connector performance will be. It proves that APC connectors are higher-performing among the connectors listed.
Since some applications are more sensitive to return loss, APC connectors are preferred in these fields, for instance, in higher wavelength range like those used for RF video signals, especially FTTX applications and for applications such as passive optical networks and other WDM systems using high wavelength via single mode fiber.
For those applications where return loss is not paid much attention to, UPC or PC comes into play. PC connectors are generally seen in telecom operators’ equipment, while UPC connectors are popular in digital TV, telephony and data systems.