For singlemode fiber, the loss is about 0. 5 dB per km for 1310 nm sources, 0. 1 dB per 600 (200m) feet for 1310 nm . To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant. The estimate, called a "loss budget" is calculated using typical component losses for. Attenuation is the progressive loss of the light signal's power, or intensity, as it travels through the fiber, measured in decibels per kilometer (dB/km). This power loss determines the maximum distance a signal can travel before it becomes too weak for the receiver to reliably detect the incoming. Optical fiber loss is a fundamental concept in fiber optic communications, representing the attenuation of light signals as they travel through fiber optic cables. Bending: The fiber is squeezed, and other reasons cause bending, which causes part of the light to be lost.