Fabrication of fluorine-doped silica glasses by the sol-gel method

Fluorine-doped silica glasses are produced by the sol-gel method for optical fiber preforms. In order to dope fluorine into silica glass, fluorinated silicon alkoxide, Si(OC₂H₅)₃F, is titrated into SiO₂ sol solutions. The fluorine content in silica glass depends on: the fluorine concentration in the gel, the specific surface area of SiO₂ particles and the heating rate in the sintering process. Fluorine-doped silica glass with a maximum relative refractive index difference of ?0.93% is obtained. Using this technique, optical fibers with a triangular refractive index profile are fabricated with a minimum optical loss of 1.6 dB/km at 1.69 μm wavelength.