APC and UPC connectors are two popular connectors in the field of Fiber Cabling. In this blog post, we’ll discuss the major difference between Ultra Physical contact or UPC Connector and Angled Physical Contact or APC fiber connector.
The most visible difference off course is the Colour of the connector. UPC connectors are blue while APC connectors are green.
The main difference between APC and UPC connectors is the fiber end face. Angled Physical Contact is an angled polished end face (usually 8°), so that the reflected light is not traveling back in the fiber, but can escape sideways. Thereby an even lower back reflection can be achieved as with UPC., while UPC connectors are polished with no angle, therefore, have a lower back
reflection. UPC connectors are not exactly flat, however, as they have a slight curvature for better core alignment. The back reflection of the UPC connector is about -50 dB which is lower than that of a standard PC connector. Return loss is inevitable when installing a connector on the end of the fiber. APC connector has the best return loss performance of -60dB. The return loss of the UPC connector is -50 dB, which is higher than the PC but lower than APC.
Remember, return loss is different than insertion loss, which refers to the amount of optical power loss through a connection or splice. Achieving low insertion loss is typically easier with UPC connectors due to fewer air gaps than APC connectors.
There are some applications that are more sensitive to return loss and others that call for an APC connector specifically. APC connectors are being used by most cable companies and other fiber providers in outside plant applications. If your application is sensitive to return loss, the APC connector is recommended.
In fiber optic termination, you should not connect a UPC connector to an APC connector. This is because the light will not pass through properly between terminated UPC and APC connectors due to their nonmatching end face. There is a presence of air gaps that will lead to high attenuation loss leading to failing the test in the OTDR testing. OTDR testing measures the data loss or attenuation coefficient of fiber and is extremely useful to analyze discreet events in a link such as splice
points or connector pairs. This test is extremely useful in locating damaged or distressed cable or broken fibers.