An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

A method of manufacturing multi-mode optical fiber is disclosed. The method of manufacturing includes: a step of forming a first glass base material while controlling a supply rate of an additive for adjusting a refractive index to achieve a desired refractive index distribution; a step of drawing the first glass base material; a step of measuring a residual stress distribution in a radial direction of the multi-mode optical fiber after being drawn; a step of readjusting the supply rate of the additive in accordance with deviation of a refractive index, acquired from the residual stress distribution measured, from the desired refractive index distribution; a step of forming a second glass base material while supplying the additive at the supply rate after being readjusted; and a step of drawing the second glass base material.

Described is a process for the production of synthetic fused silica in which the deposition surface is located for a period of at least 50% of the build-up time of the soot body at a burner distance in which the horizontally integrated luminous intensity of the flame of the burner used in the targetless state is still at least of the maximum horizontally integrated luminous intensity of the flame.

A soot deposition burner assembly, having at least one burner including a burner face on a first surface of a burner support. The burner produces a flame which extends generally perpendicularly to the first surface. A burner shield includes a first wall extending generally perpendicularly from the first surface surrounding the burner face. The burner shield has a base end with a first surface area facing toward the first surface and a shield face with a second surface area facing away from the first surface. To reduce the buildup of soot material, the second surface area is smaller than the first surface area, and the wall thickness is less at the shield face than the base end. Additionally, air can be directed along an exterior surface of the first wall from the base end toward the shield face to further reduce soot buildup.

The present invention provides an optical fiber with improved optical properties such as zero dispersion wavelength by suppressing the volatilization of dopant materials such as germanium dioxide and optimizing the refractive index distribution by adjusting the setting position of the core portion burner for deposition in a larger optical fiber preform. An optical fiber preform includes a core portion with a relatively high refractive index and a clad portion with a relatively low refractive index, wherein a position having a value of 45% of a refractive index difference between a center of the core portion and the clad portion is a boundary rcore (mm) between the core portion and the clad portion; and when a radius position r at which a refractive index difference with the clad portion being a maximum value is rside (mm), rside/rcore is 0.745 to 1.