Chlorine incorporation into SiO2 beyond the chemical equilibrium

The long-haul subsea applications have driven recent development to focus on incorporation of chlorine replacing germania as index adapting component in ultralow loss fibers. We present a method to dope silica glass with a chlorine level above the one expected from thermodynamical equilibrium consideration. Gaseous SiCl4 was used as dopant for the treatment of porous green body prepared by the powder sinter technique (REPUSIL). To be able to optimize the chlorination process steps, the exhaust species of the individual steps had been analyzed using an online process monitoring of exhaust gases via IR spectroscopy. Finally, we could realize a chlorine level of 1.2 wt% Cl with an initial pressure of SiCl4 of 0.1 bar while the calculation of thermodynamic chemical equilibrium predicted only a maximum level of less than 1.0 wt% Cl in SiO2 under those optimized conditions.