Insertion Loss is defined as the reduction in optical power between the input and output of a fiber optic link. It is expressed in decibels (dB) and calculated using the formula: IL = –10 log (Pout / Pin) Where: Lower insertion loss values indicate better optical performance. For procurement teams and field engineers buying patch cords, MTP/MPO trunks. Insertion loss is measured by comparing signal power (or sound level) before and after it passes through a component or system, then expressing the difference in decibels (dB). For fiber connectors, for example, it is often of the order of 0. High-quality fusion splices may reach values like 0.