Ideally speaking, if the fiber patch cable has no connections, then the minimum loss will be realized—a continuous, straight-through glass fiber from Point A to Point B with no interruptions. However, the fiber optic networks are requiring connectors for modularity. The desired low IL and high RL performance are reduced consequently on account of the following three factors:
End-face Quality and Cleanliness
Evidently, fiber end-face defects like scratches, pits, cracks, and particle contamination will have a direct impact on the performance, contributing to poor insertion/return loss. Any irregularity that impedes light transmission from one fiber to the other will negatively affect IL and RL.
Misalignment Between the Two Cores
The main task of the connector is to hold the fibers precisely, ensuring the core of one fiber will align neatly and accurately with the core of the other fiber, so as to make every connector to mate with another connector with precise core alignment and core-to-core contact. Normally speaking, the smaller the ferrule hole diameter, the more precisely the fiber will be centered in the ferrule. If the ferrule hole is not perfectly centered, the fiber it holds will obviously never be perfectly centered. Therefore, the misalignment between two cores often happens when the fibers with the light-carrying cores are not aligned perfectly with each other, resulting in poor IL/RL.
Poor Core-to-core Contact
In order to achieve the desired low IL and high RL, optimized core-to-core contact must be achieved and maintained. Different polishing styles of fiber connectors have varied core-to-core contact performance regarding the connector’s insertion loss and return loss. Usually, the insertion loss of PC, UPC, and APC connectors is less than 0.3dB. However, UPC connectors have the lowest IL due to the smallest air gap while APC connectors have the highest RL due to the beveled fiber end-face. PC vs UPC vs APC Connector will help you to select the proper fiber connect type.