It is expressed in decibels as the ratio of power received at the load before insertion to the power received at the load after insertion. The total optical power loss caused by the insertion of a component such as a splice or connector in an optical fiber system: insertion loss from absorption. Insertion loss from misalignment either from mismatched core diameters or from lateral misalignment. Insertion loss from an air gap: this occurs from no physical contact. Insertion loss from contamination; contamination is the most common cause of insertion loss, such as dirt, scratches, or chips.