Reduction of optical fiber cane/preform deformation in consolidation

A method of manufacturing optical fiber cane comprising the steps of:

• (i) providing a core rod comprising relatively low viscosity glass having an alkali dopant;
• (ii) depositing relatively high viscosity Si based soot around said core rod to form a soot preform, wherein a softening point of the core rod is at least 300° C. lower than a softening point of the relatively high viscosity Si based soot at 107.6 Poise;
• (iii) consolidating said relatively high viscosity Si based soot of said soot preform on said core rod by exposure to a hot zone having a temperature T of 1200° 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 a viscosity of the core rod drops below 2×107 Poise in the hot zone, said heating rate being at least 12° C./min.

A method of manufacturing optical fiber cane comprising the steps of:

• (i) providing a core rod comprising relatively low viscosity glass having an alkali dopant;
• (ii) depositing Si based soot around said core rod to form a soot preform, said Si based soot having a relatively high viscosity, such that the softening point of the core rod is at least 200° C. lower than the softening point of the Si based soot at 107.6 poise;
• (iii) consolidating said Si based soot of said soot preform on said core rod by exposure to a hot zone at a temperature T of 1200° 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 a viscosity of the core rod in the hot zone decreases to less than 2×107 Poise.