Methods for making optical fiber preforms and microstructured optical fibers

A method of making an optical fiber preform, the method comprising:

• depositing porous layers of silica glass based soot inside a substrate tube via a chemical vapor deposition process;
• and
• consolidating the porous layers of silica glass based soot in a gaseous atmosphere by traversing a heat source on the outside of the substrate tube under conditions which are effective to trap a portion of the gaseous atmosphere inside the layers to form at least one silica glass layer comprising gaseous voids in at least a portion of a cladding region of the optical fiber perform, wherein, to form at least a portion of the cladding region comprising gaseous voids, the silica glass based soot is consolidated by heating the deposited silica glass based soot such that the heating rate in degrees ° C./sec>1820[soot thickness in microns(−0.9)].