Patent ID: 8011208

Claim:
A method of manufacturing optical fiber cane comprising the steps of: (i) providing a core rod comprising relatively low viscosity glass having a softening point, T s1 , at 10 7.6 poise of less than or equal to 1470° C., said low viscosity glass including at least 0.5 mole % alkali dopant; (ii) depositing relatively high viscosity SiO 2 based soot around said core rod to form a soot preform, said relatively high viscosity SiO 2 based soot having a softening point, T s2 at 10 7.6 poise of greater than or equal to 1600° C., wherein the softening point T s1 of the low viscosity glass is at least 200° C. lower than the softening point T s2 of the relatively high viscosity SiO 2 based soot; and (iii) consolidating said relatively high viscosity SiO 2 based soot on said core rod by exposure to a hot zone at a temperature T of 1000° C.≦T≦1600° C., by heating an outer portion of said soot preform at a relatively fast heating rate sufficient to densify said soot before the core rod softens sufficiently to start puddling, said heating rate being at least 12° C./min.