Mechanical strength improvement of sol-gel derived dry gels for optical fiber preforms

Crack-free dry gels 85 mm in diameter for optical fiber preforms have been successfully fabricated by increasing their mechanical strength. Additions of fluorinated silicon ethoxide and SiO2 powder of low specific surface area into sol solution were effective in increasing the fracture strength of dry gels. The empirical relation of the apparent density and the strength of dry gels was found to be applicable in the range 0.45−0.65 g/cm2 d.