Results show no measurable difference in insertion loss or return loss between connector types. Both LC and SC UPC connectors achieved insertion loss ≤0. 15dB and return loss ≥50dB—well within single-mode fiber standards for long-haul transmission. The SC connector was the dominant fiber optic connector of the 1990s and 2000s, and it remains widely deployed in telecom outside plant, CATV. These connectors are polished to reduce the loss of signal, but there will be some signal that is reflected back and can cause interference. Meanwhile, an APC connector is cut at an angle, resembling a mirror, that pushes the reflected light away from the fiber's core, which drastically reduces the. This small, inexpensive component is critical for aligning and mating two SC/APC connectors while preserving low insertion loss and ultra‑high return loss performance. In this beginner-friendly guide, we'll explain what it is, why the “APC” matters, the different types you can buy, how to select. Optical fiber coupling is the process of efficiently transferring light energy from one optical component into a receiving optical fiber, or between two separate fibers. This transfer involves channeling the light, which carries data, from a source such as a laser or LED directly into the hair-thin. Two key performance indicators used to assess the quality of fiber connections are Insertion Loss (IL) and Return Loss (RL).