Launch dependent loss in short lengths of graded-index multimode fibers.

In this paper we describe the effect of different launching conditions on the loss measured with a calorimeter in short (~1-m) lengths of multimode optical fiber. A qualitative description of the relation between the energy distribution in the fiber and various excitation variables is given, and many examples are presented that illustrate the effect that launch conditions have on the fiber loss. The use of launch-dependent loss phenomena to diagnose loss mechanisms in optical fibers is discussed. In particular, loss plots are shown for two germania-doped silica-core fibers that indicate a strong absorption loss mechanism located deep within the fiber core.