Return loss, also known as reflection loss or back reflection, is the measurement of the amount of light reflected back towards the source when it encounters a fiber optic connector. It is caused by variations in refractive index, mismatches in fiber core diameter, and surface. 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. 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. In this post, we'll demystify these. Beginning with software release 1. 8, OptiFiber is able to measure optical return loss. When high-speed signals enter or exit a part of an optical fiber, such as an optical fiber connector, discontinuity and impedance mismatch may cause reflection, which is the return loss of an optical fiber. It is expressed in decibels (dB) and represents the forward power loss due to attenuation and connection inefficiencies.