Abstract: A single-mode optical fiber preform is produced by a process where a porous glass body of a core rod for a single-mode optical fiber is dehydrated and made into a glass to prepare a core rod for the optical fiber, clad layers are deposited on the circumference of the core rod for the optical fiber so as to give an outer diameter of a desired value, and then these are dehydrated and made into glass. At this time, the diameter of a part corresponding to the core rod for the optical fiber in the optical fiber obtained by drawing the preform for optical fiber is controlled to 1.9 times or more the mode field diameter, which is a diameter that allows light having a wavelength of 1.55 .mu.m to pass therethrough. As a result, a preform for a single-mode optical fiber with which an optical fiber little influenced by defects can be obtained can be produced.

Abstract: The invention relates to a method of drying and sintering porous optical fiber preforms, especially those consisting of a solid glass core cane surrounded by a layer of cladding soot. After it is dried in a dehydrating atmosphere, the porous preform is heated to a presinter temperature just below that at which it would begin to rapidly densify. The various temperature holds and ramp rates are such that the preform is consolidated in a relatively short time without becoming cloudy or exhibiting other defects that would adversely affect the optical fiber drawn from the consolidated draw blank.

Abstract: During the gradual build-up of porous quartz glass by the combustion of a hydrolysis gas mixture and preferably for a certain period of time thereafter, a drying gas mixture is conducted under positive pressure through the porous tubular deposit from the inside to the outside as it is being built-up. This is accomplished by depositing the quartz on a tubular substrate in which a drying gas is introduced at positive pressure.

Abstract: Sol-gel processing of a silica glass body is facilitated by rapid drying. The body, having been heated to a temperature of about 200.degree. C. in a hermetically sealed vessel, is vented while reducing temperature. Termination of drying coincides with reduction to atmospheric pressure.

Abstract: Heating a wet colloidal gel body in an autoclave above its 1-atmosphere boiling point, under rigorously defined conditions, avoids shrinkage during subsequent drying. As a consequence, drying rates may be increased, and handling care becomes less critical.

Abstract: A method for making a glass preform substantially free of OH impurities is disclosed. The method comprises the steps of introducing a moving stream of a vapor mixture including at least one compound glass-forming precursor together with an oxidizing medium into a tube, while generating a hydrogen-free isothermal plasma on an outer surface of the tube to react the mixture and produce a glassy deposit on an inner surface of the tube. The method uses a plasma torch or a radio frequency furnace.