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.

Methods and apparatuses for forming optical preforms from silica glass soot are disclosed. According to one embodiment, a method for forming an optical preform may include loading silica glass soot in a mold cavity of a mold body. The mold body may be rotated at a rotational speed sufficient to force the silica glass soot towards an inner wall of the mold body. Thereafter the silica glass soot is compressed in an inward radial direction as the mold body is rotated to form a soot compact layer.

The present disclosure provides a separator system for performing separation and dehydroxylation of fumed silica particles. The separator system includes a first inlet, a second inlet, a main body, a first outlet and a second outlet. The first inlet collects a primary feed of fumed silica particles from a gaseous stream into a double entry cyclone. The second inlet collects a secondary feed of chlorine gas into the double entry cyclone. The main body of the double entry cyclone is utilized in treating the primary feed and the secondary feed along with heat inside the double entry cyclone. Furthermore, the first outlet is utilized for releasing the dehydrated fumed silica particles and the second outlet is utilized for releasing the water molecules and other gases.