In a method of manufacturing porous glass base for optical fiber, a liquid organic siloxane raw material stored in a raw material tank of internal pressure P1 is controlled by a mass flow controller at a predetermined flow rate and pumped through pipe of internal pressure P2 to a vaporizer, the liquid raw material is vaporized in the vaporizer and supplied as a gas raw material to a burner, and the silica fine particles formed by burning the gas raw material in the burner are deposited to form a porous glass base material, where P1?P2 is satisfied.

In a method of manufacturing porous glass base for optical fiber, a liquid organic siloxane raw material stored in a raw material tank of internal pressure P1 is controlled by a mass flow controller at a predetermined flow rate and pumped through pipe of internal pressure P2 to a vaporizer, the liquid raw material is vaporized in the vaporizer and supplied as a gas raw material to a burner, and the silica fine particles formed by burning the gas raw material in the burner are deposited to form a porous glass base material, where P1?P2 is satisfied.

A method for manufacturing quartz glass, wherein (a) an appropriate liquid starting material is evaporated by spraying it into a vertically arranged evaporation chamber, (b) the vaporous starting material is oxidized to form SiO.sub.2, and the SiO.sub.2is collected. The method is characterized in that the starting material to be evaporated is sprayed in on the bottom of the evaporation chamber and the vaporous starting material is removed at the top end of the evaporation chamber, wherein the evaporation chamber is designed such that components depositing in the chamber accumulate on the bottom of the evaporator and are sprayed once again, as well as an evaporator for applying the method.

Monolithic optical structures include a plurality of layer with each layer having an isolated optical pathway confined within a portion of the layer. The monolithic optical structure can be used as an optical fiber preform. Alternatively or additionally, the monolithic optical structure can include integrated optical circuits within one or more layers of the structure. Monolithic optical structures can be formed by performing multiple passes of a substrate through a flowing particle stream. The deposited particles form an optical material following consolidation. Flexible optical fibers include a plurality of independent light channels extending along the length of the optical fiber. The fibers can be pulled from an appropriate preform.

A titania and silica glass body that includes a first glass section having a crossover temperature of about 10 C. to about 60 C. and a second glass section comprising an average striae height of about 10 microns or less, wherein the average striae height of the second glass section is less than an average striae height of the first glass section, and wherein the first glass section and the second glass section form a single, monolithic glass body.

Hollow ingots of transparent synthetic vitreous silica glass of external diameter greater than 400 mm and internal diameter greater than 300 mm are disclosed. The ingots are substantially free from bubbles or inclusions greater than 100 m in diameter, have no more than 100 ppB of any individual metallic impurity, and have chlorine concentration less than 5 ppM. Also disclosed are methods for producing such ingots, in which a porous soot body of density greater than 0.4 g/cm.sup.3 is deposited on an oxidation resistant mandrel. The soot body is dehydrated on a mandrel comprising graphite, carbon fiber reinforced carbon, silicon carbide, silicon impregnated silicon carbide, silicon carbide-coated graphite or vitreous silica, either under vacuum or in the presence of a reducing gas, and then sintered to transparent pore-free glass under vacuum or in an atmosphere of helium.

A glass particle deposit producing method capable of preventing the variation in the outside diameter of a glass particle deposit and enhancing the yield of a glass raw material is provided. A glass particle deposit is produced by mounting a starting rod 11 and a glass particle generating burner 22 inside a reaction vessel 2, introducing a glass raw material into the burner 22, subjecting the glass raw material to a flame decomposition reaction inside a flame formed by the burner 22 to generate glass particles, and depositing the generated glass particles on the starting rod 11. At this time, the dispersion angle of the glass raw material jetted from the burner 22 with respect to the center axis of the burner 22 is set to the range of 5 to 70 degrees.

A production method for a glass particulate deposit which includes a deposition step in which, at least two liquid source material ejecting ports 31a for a glass source material 23 jetting out from a burner 22 are provided per one burner 22, the area of at least one liquid source material port 31a is 2.2510.sup.4 or less of the area of the flame forming part of the burner 22, the glass source material 23 is, in the form of a liquid thereof, supplied to each liquid material source port 31a, jetting gas ports 31b are arranged in such a manner that the inner periphery of the jetting gas port is positioned outside by 1.0 mm or less from the outer periphery of each liquid source material port 31a, and a gas is jetted out from each gas jetting port 31b.

A method of producing an optical fiber preform includes: an alkali-metal-doped silica glass body forming step of forming an alkali-metal-doped silica glass body doped with an alkali metal; a silica glass body forming step of forming a silica glass body to be at least a portion of a core portion around the alkali-metal-doped silica glass body such that the silica glass body contacts the alkali-metal-doped silica glass body; and a diffusing step of diffusing the alkali metal from the alkali-metal-doped silica glass body to the silica glass body by a heat treatment.

A method of manufacturing synthetic quartz glass through an outside vapor deposition (OVD) process with improved deposition efficiency. When a hollow cylindrical synthetic quartz glass product is manufactured through an OVD method or the like, it is environmentally friendly in view of using a smaller amount of chlorine and is economical in view of requiring no separate treatment equipment, as compared to a conventional technique using silicon chloride (SiCl.sub.4). Also, the method, in which octamethylcyclotetrasiloxane is supplied to a deposition burner while being sprayed in the form of a droplet along with a high-pressure carrier gas and vaporized by the deposition burner, can effectively address the high-temperature heating and slow decomposition involved when octamethylcyclotetrasiloxane ([(CH.sub.3).sub.2SiO].sub.4) is used as a source for depositing silicon dioxide particles.