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. This reduction of signal, also called attenuation, is directly related to the length of a cable—the. Optical Splitter Loss Calculator the quick 10·log₁₀ (N) estimate, plus your datasheet excess. Lower IL means more light reaches the receiver. Mathematically: Where: If you launch –2 dBm into a fiber and receive –2.