Spectral losses in unclad optical fibers have been measured in the region between 0.5 and 1.12 μm with the filtered light of a xenon-arc lamp. Total losses were obtained nondestructively by measuring the light refracted from the fiber when it was immersed in a higher-index liquid. The radial irradiance distribution of the refracted light was used as a measure of the mode spectrum. Because scattering losses could be shown to approach the Rayleigh-scattering limit, and total losses were between 6 and 8 dB/km, i.e., 75 to 84% per kilometer, for some of the highest-purity synthetic vitreous silicas, we tentatively conclude that the spectral losses of unclad fibers represent a good approximation to the spectral losses of the bulk material.
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