Abstract: An optical fiber has a core region, a cladding region and at least one spacer layer disposed between the core region and the cladding region. The core region is positively doped and has a positive refractive index with respect to the glass matrix of the optical fiber. The cladding region is negatively doped and has a refractive index of at most zero with respect to the glass matrix. The numerical aperture of the optical fiber is composed of variable proportions of the positively doped core region and the negatively doped cladding region and results from the refractive indices of both regions.

Abstract: The invention relates to an optical waveguide and a semifinished product for producing an optical waveguide having optimized diffraction properties, comprising a trench structure that has a radius-dependent graded refractive index curve and/or a concentric depressed refractive index profile within a core zone (2) and/or within a cladding zone (4). In one embodiment of the optical waveguide and semifinished product, the structure is formed from a succession of differently doped regions containing dopants that are introduced into a base matrix and lower and/or increase the refractive index.

Abstract: A method and apparatus for making optical fiber preforms using modified chemical vapor deposition (MCVD) A starting tubular member is installed on a chemical vapor deposition apparatus and, using MCVD, a predetermined amount of selectively doped silica is deposited and consolidated on the inner surface to form an intermediate uncollapsed preform tube. At least a portion of the intermediate uncollapsed preform tube is removed from the chemical vapor deposition apparatus, installed in a collapsing apparatus and collapsed. The collapsing uses an oxy-hydrogen burner or a plasma torch. Optionally, additional deposition is performed during the collapsing operation. A stretching may be performed concurrent with the collapsing.