Acceptable dB loss for fiber depends on the component you're measuring: a single mated connector pair should lose no more than 0. 75 dB, a fusion splice should stay under 0. 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. Contractors often install, terminate, and certify cabling without knowing the client's specific requirements. Therefore. Optical fiber loss is a fundamental concept in fiber optic communications, representing the attenuation of light signals as they travel through fiber optic cables.