Imperfect joints can cause problems like excessive insertion loss. The tolernances depend a lot on the fiber type. In any case, it is essential that the fiber endfaces are carefully prepared before joining them. In many cases, fiber ends with perpendicularly cut surfaces are. 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. When light is transmitted in an optical fiber, a loss will occur, and this loss is mainly composed of the transmission loss of the optical fiber itself and the splice loss at the optical fiber joint. Can be reduced to a very low level using index matching fluid in the gap between jointed fibers. Deviation in Geometrical & Optical Parameters Core mismatch NA mismatch Index Profile.
