Absolute and angular transmission measurements were made on a single sheathed fiber 0.15 mm in diameter and 2.1 m long, and an optical angular transfer function was defined and calculated. The effective transmission of the source brightness was calculated as a function of the f numbers of the entrance and output optics of the fiber, and these results were used to choose a suitable optical system for illumination of a spectrometer.
F. Robben and R. Fraser, "Fiber Optics for Spectroscopic Illumination," Appl. Opt. 10, 1141-1147 (1971)