Excess loss caused by a lossy outer layer in multimode optical fibers.

Theoretical and experimental investigations are made on an excess loss arising due to a lossy outer layer attached around a cladding in multimode step-index fibers. Equations for evaluating the excess loss are derived using the electromagnetic theory for LP modes. Experiments are made on fibers with a pure fused silica jacket around a cladding, focusing on the wavelength dependence of the excess loss. It is found that the loss increases as the wavelength becomes long and that the measured values are in good agreement with the calculated ones.