Diffusion of OH in optical fiber preform by oxy-hydrogen burner

OH diffusion in pure silica rods was investigated by heat-treatment using an oxy-hydrogen burner with different oxygen and hydrogen gas flows. The radial distribution of OH concentration across the cross-section of the heat-treated silica rods was measured by a microscope-equipped FTIR spectrometer. OH diffusion characteristic was found to be dependent on the relative amount of oxygen and hydrogen gas flow in the burner. Surplus hydrogen gas in the burner, remaining after combustion reaction to form water, was found to be a source of OH contamination in optical fiber preforms.