A process for manufacturing an optical fibre comprises the steps of producing a glass core rod; measuring the refraction index profile in a plurality of sections of the core rod, for obtaining a corresponding plurality of refractive index profiles; processing the plurality of refractive index profiles for determining a drawing tension variation law; depositing glass soot onto the core rod to obtain a glass preform; consolidating the glass preform; and drawing the optical fiber form the glass perform by applying a drawing tension to the optical fibre, wherein drawing tension is varied in accordance to the drawing tension variation law.