Blue singlemode connectors feature a UPC (ultra physical contact) fiber endface, while green singlemode connectors feature an APC (angled physical contact) fiber enface. And yes, it's important to understand the difference – especially when it comes to testing. Previously, in accordance with the classification criteria of different structures of fiber connector types, we have introduced. Understanding fiber connector types—SC/APC, SC/PC, LC/UPC, LC/APC, ST/PC, FC/PC, and FC/APC—is essential for selecting the right interface for your application. Each type varies by shape, polish (APC, PC, or UPC), and return loss performance, which affect PC, UPC, and APC Polish Styles: What's the. To put it simply, PC, UPC, and APC refer to the polish styles of the ferrules inside the fiber optic connectors, just as the following figure shows. The ferrule is the housing for the exposed end of a fiber, designed to be connected to another fiber, or into a transmitter or receiver. APC. Executive Summary: With data center traffic doubling every three years and enterprise networks pushing toward 400G and 800G speeds, choosing the wrong fiber optic patch cable does more than create a bad connection—it creates a cascading performance bottleneck that haunts your operations team for. The singlemode fiber connectors you likely encounter the most feature a blue connector body, but if you're working with any passive optical networks (PONs), carrier networks or large cloud/colo or hyperscale data centers, you may encounter singlemode fiber connectors with a green connector body –.