Optical waveguide soot preform with reduced inner layer stress and method of making

A cylindrical optical waveguide soot preform comprising a longitudinal center hole and a surrounding preform body comprising a core portion have a radially varying composition, the core portion being composed of a plurality of concentric core layers of vitreous soot including an inner layer defining the cylindrical surface of the longitudinal center hole and outer layers making up the remainder of the core portion, the soot layers proximate to the inner layer containing higher concentrations of refractive-index-increasing dopants than soot layers positioned exteriorly thereof, and being in a state of tensile stress at ambient temperatures, wherein, following soot deposition but prior to any treatment to remove residual water or consolidated the preform to clear glass, the inner layer defining the center hole of the preform has a thermal expansion coefficient lower than that of at least one of the layers proximate thereto, so as to exhibit a reduced level of tensile stress with respect to said proximate layer at ambient temperatures.