Insertion loss measures how much optical power is lost as light passes through a component or link. Ever connected a fiber optic cable only to find your signal dropping like a bad cell call in a basement? You're not alone—poor fiber performance metrics like insertion loss and return loss plague even seasoned network pros, costing time, money, and sanity. They represent distinct aspects of signal transmission and differ for both media types. Here we explain the key differences between these two parameters, why. In the test report for a fiber cable, you may often see some data related to fiber insertion loss (IL) and return loss (RL), but do you know what insertion loss and return loss actually mean? How do the values of IL and RL impact the quality of the fiber cable? Are higher values better, or lower. Insertion Loss (IL) is the amount of optical power lost as the signal travels from one point to another in a fiber optic link, usually across connectors or splices. What Is Insertion Loss and Return Loss for Fiber Connectors? What Is Insertion Loss? In telecommunications, insertion loss refers to the loss of signal. Insertion loss (IL) and return loss (RL) are key performance indicators of fiber optic patch cords. This article explains their concepts, standards, testing methods, and FiberMania's quality assurance workflow to ensure optimal network performance.