Silica-based optical fiber comprising at least a core and a cladding surrounding the core, both core and cladding material produced by a vapor phase deposition process. The core and/or the cladding comprise at least two substituents, one chosen from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, and the 4f-type rare earths (the "modifiers"), and the other chosen from B, Al, Ga, In, P, As, and Sb (the "homogenizers"). The maximum concentration of the substituents in the fiber is such that 3<(n.sub.1 M+n.sub.2 H)/H<20, preferably<10, where n.sub.1 and n.sub.2 are the valences of the modifier and the homogenizer, respectively, and M and H are the concentration, in mole %, of modifier and homogenizer, respectively. Fiber according to the invention comprises at least 50, frequently more than 80% by weight, SiO.sub.2, and further has a maximum modifier concentration of at least 0.2 mole %, preferably at least 1 mole %. The presence of homogenizer frequently permits achievement of modifier concentrations that lead to phase separation or crystallization in prior art fibers. Disclosed is also a method for producing optical fiber, the method comprising forming a metal halide complex having a relatively high vapor pressure.