This FOTP is intended to characterize the encircled flux of two types of light sources: transmission light sources, which are usually coherent and substantially under-excite the mode volume of a multimode fiber, and measurement light sources, which are incoherent and must excite most of the mode volume of a multimode fiber.

This FOTP sets forth a standard procedure for the collection of two-dimensional fiber optic nearfield grayscale data and subsequent reduction to one-dimensional data expressed as a set of three sampled parametric functions of radius from the fiber's optical center. This revision of this FOTP continues to fulfill its original purpose, characterization of transmission light sources, which enables the accurate mathematical prediction of minimum guaranteed link length in 1 gigabit per second or greater fiber optic data communication systems. New to this revision is support for improved measurement precision of insertion loss in multimode fiber optic links through the characterization of measurement light sources.

Estimation of the fiber core diameter is not an objective of this FOTP.