Experiments have been performed to evaluate the increase in loss due to an outer layer around the cladding in a multimode step-index fiber composed of core and cladding. Liquid has been used to simulate the outer layer. Measured excess loss for each mode group is in agreement with our previously developed electromagnetic theory. Total excess loss for all guided modes existing in the fiber has also been measured by varying the mode power distribution, the refractive index of the outer layer, the cladding thickness, and the wavelength. Results are found to be in good agreement with the theory, and it is concluded that the theory is correct.
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