The relationship between divergent angle and structure of the optical fiber with tapered endsfor light transmission is discussed.It is shown that the diverging characteristics for the outputlight are only related to the structure of the output end,and a small divergent angle can be obtainedwith ends of longer length and smaller conical angle.The input end acts as a mode filter whichmakes the divergent angle for the optical fiber independent of the divergent angle for the inputbeam.This featurc is explained by the theory of geometric optics.