The present invention relates to a glass substrate for a high-frequency device, which includes SiO.sub.2 as a main component, the glass substrate having a total content of alkali metal oxides in the range of 0.001-5% in terms of mole percent on the basis of oxides, the alkali metal oxides having a molar ratio represented by Na.sub.2O/(Na.sub.2O+K.sub.2O) in the range of 0.01-0.99, and the glass substrate having a total content of Al.sub.2O.sub.3 and B.sub.2O.sub.3 in the range of 1-40% in terms of mole percent on the basis of oxides and having a molar ratio represented by Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3) in the range of 0-0.45, in which at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less in terms of arithmetic average roughness Ra, and the glass substrate has a dielectric dissipation factor at 35 GHz of 0.007 or less.

The present invention relates to a glass substrate for a high-frequency device, which includes SiO.sub.2 as a main component, the glass substrate having a total content of alkali metal oxides in the range of 0.001-5% in terms of mole percent on the basis of oxides, the alkali metal oxides having a molar ratio represented by Na.sub.2O/(Na.sub.2O+K.sub.2O) in the range of 0.01-0.99, and the glass substrate having a total content of Al.sub.2O.sub.3 and B.sub.2O.sub.3 in the range of 1-40% in terms of mole percent on the basis of oxides and having a molar ratio represented by Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3) in the range of 0-0.45, in which at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less in terms of arithmetic average roughness Ra, and the glass substrate has a dielectric dissipation factor at 35 GHz of 0.007 or less.

A method of forming an optical fiber preform includes the steps: igniting a burner having a fume tube assembly to produce a first spray size of silicon dioxide particles; depositing the silicon dioxide particles on a core cane to produce a soot blank; and adjusting an effective diameter of an aperture of the fume tube assembly to produce a second spray size of the silicon dioxide particles. The second spray size is larger than the first spray size.

Preparation of halogen-doped silica is described. The preparation includes doping silica with high halogen concentration and sintering halogen-doped silica to a closed-pore state. The sintering includes a high pressure sintering treatment and a low pressure sintering treatment. The high pressure sintering treatment is conducted in the presence of a high partial pressure of a gas-phase halogen doping precursor and densifies a silica soot body to a partially consolidated state. The low pressure sintering treatment is conducted in the presence of a low partial pressure of gas-phase halogen doping precursor and transforms a partially consolidated silica body to a closed-pore state. The product halogen-doped silica glass exhibits little foaming when heated to form fibers in a draw process or core canes in a redraw process.

A synthetic quartz glass substrate having a controlled hydrogen molecule concentration is prepared by (a) hot shaping a synthetic quartz glass ingot into a glass block, (b) slicing the glass block into a glass plate, (c) annealing the glass plate at 500-1,250 C. for 15-60 hours, (d) hydrogen doping treatment of the glass plate in a hydrogen gas atmosphere at 300-450 C. for 20-40 hours, and (e) dehydrogenation treatment of the glass plate at 200-400 C. for 5-10 hours.

A mold includes a lower mold core and an upper mold core. The lower mold core has a first outside surface and a first molding surface including a first molding portion and a first supporting portion surrounding the molding portion. The upper mold core has a second molding surface opposite to the first molding surface and encloses a molding cavity with the first molding surface. The lower mold core includes a first gas inlet on the first outside surface, a first gas outlet on the first supporting portion, and a first gas channel in the lower mold core, the first gas channel connecting the first gas inlet and the first gas outlet. Gas flow out from the first gas outlet to separate the glass product from the lower mold core before the glass product is completely cooled down, which can avoid many adverse effects during the glass product process.

A mold includes a lower mold core and an upper mold core. The lower mold core has a first outside surface and a first molding surface including a first molding portion and a first supporting portion surrounding the molding portion. The upper mold core has a second molding surface opposite to the first molding surface and encloses a molding cavity with the first molding surface. The lower mold core includes a first gas inlet on the first outside surface, a first gas outlet on the first supporting portion, and a first gas channel in the lower mold core, the first gas channel connecting the first gas inlet and the first gas outlet. Gas flow out from the first gas outlet to separate the glass product from the lower mold core before the glass product is completely cooled down, which can avoid many adverse effects during the glass product process.

An additive manufacturing process includes forming an object material stack using sheet materials without use of binder material between the sheet materials and forming features of the cross-sectional layers of a 3D object in the corresponding sheet materials. Another process involves forming features of the cross-sectional layers of a 3D object in soot layers of a laminated soot sheet. A manufactured article includes three or more glass layers laminated together without any binder material between the glass layers. At least one of the glass layers is composed of silica or doped silica, and at least one feature is formed in at least one of the glass layers.

Bromine doping of silica glass is demonstrated. Bromine doping can be achieved with SiBr.sub.4 as a precursor. Bromine doping can occur during heating, consolidation or sintering of a porous silica glass body. Doping concentrations of bromine increase with increasing pressure of the doping precursor and can be modeled with a power law equation in which doping concentration is proportional to the square root of the pressure of the doping precursor. Bromine is an updopant in silica and the relative refractive index of silica increases approximately linearly with doping concentration. Bromine can be used as a dopant for optical fibers and can be incorporated in the core and/or cladding regions. Core doping concentrations of bromine are sufficient to permit use of undoped silica as an inner cladding material in fibers having a trench in the refractive index profile. Co-doping of silica glass with bromine and chlorine is also demonstrated.

A method of forming an optical fiber preform includes the steps: igniting a burner having a fume tube assembly to produce a first spray size of silicon dioxide particles; depositing the silicon dioxide particles on a core cane to produce a soot blank; and adjusting an effective diameter of an aperture of the fume tube assembly to produce a second spray size of the silicon dioxide particles. The second spray size is larger than the first spray size.