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Abstract

An improved multimode optical fiber having substantially higher bandwidth and lower loss is made by controlling process parameters such as the volume of the silica which is deposited in each pass of a torch assembly (41) along a substrate tube (31) to form a preform tube which is collapsed to provide a preform (80) from which the optical fiber is drawn. As a result, the amplitude variation of the refractive index across each layer is controlled to be within desired limits. Should the volume of the silica deposited in each pass be controlled to control the amplitude variation, the thicknesses of the outermost deposited glassy layers in the preform tube are greater and those of the innermost layers are less than those of layers in a preform tube made by prior art MCVD processes. Because the difference in the index of refraction across each glassy layer is reduced, the bandwidth is enhanced and the loss of the drawn optical fiber is reduced over those properties of optical fiber drawn from preforms made by prior art MCVD processes. Inasmuch as the inventive process also allows a higher deposition rate than before, it may be used to produce single-mode optical fiber at lower costs than before achieved.

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