Modified VAD method for optical-fibre fabrication

New techniques for protecting the burner flame and controlling gas pressure in a reaction vessel have been developed for the vapour-phase axial-deposition (VAD) method of soot preform. The growth of soot preform became more stable. It is found that there is a close correlation between the bottom shape of the soot preform and the refractive-index profile of a fibre preform. Optical fibres thus produced indicate improved reproducibility in the bandwidth above 800 MHz km at a wavelength of 0.85 ¿m.