Patent ID: 7641969
Filing Date: 2010-01-05
Classification: C03B,Y10T

Abstract:
1. An overclad optical fiber preform, comprising: a first glass overclad tube having a tube axis, and a number of core rod segments arranged axially end to end inside the first overclad tube; the first overclad tube has a first wall thickness and a first concentration of a given impurity in the first overclad tube, and the impurity includes one or more dopants or chemicals that contribute to signal attenuation in a fiber to be drawn from the preform; and a second glass overclad tube disposed coaxially about the first overclad tube, wherein the second overclad tube has a second wall thickness and a second concentration of the given impurity in the second overclad tube, and each of the first and the second overclad tubes are circular cylindrical in form; the second concentration of the given impurity in the second overclad tube is greater than the first concentration of the impurity in the first overclad tube; the first wall thickness of the first overclad tube is minimally about 4 mm, and the second wall thickness of the second overclad tube is at least about 28 mm and is substantially greater than the first wall thickness of the first overclad tube by an amount sufficient to obtain a certain cladding to core mass ratio for the fiber to be drawn from the preform; and wherein the signal attenuation in the fiber is substantially unaffected by the greater concentration of the given impurity in the second overclad tube.