In an imprint mold-forming synthetic quartz glass substrate (1) of rectangular shape having dimensions L1 and L2 with L1≥L2, a circular region is delineated on the substrate back surface by a circle of radius R with L2−2R≥10 mm. When approximation analysis is performed from the 1st to 8th term in the Zernike polynomials on the circular region, a coefficient of the 4th term is equal to or greater than −(2R/100,000×1) μm.

A resin composition for coating an optical fiber is a resin composition comprising: a base resin containing an oligomer comprising urethane (meth)acrylate, a monomer, and a photopolymerization initiator; and hydrophobic zirconium oxide, wherein the content of the zirconium oxide is 0.5% by mass or more and 65% by mass or less based on the total amount of the resin composition.

A Photonic Crystal Fiber (PCF) a method of its production and a supercontinuum light source comprising such PCF. The PCF has a longitudinal axis and includes a core extending along the length of said longitudinal axis and a cladding region surrounding the core. At least the cladding region includes a plurality of microstructures in the form of inclusions extending along the longitudinal axis of the PCF in at least a microstructured length section. In at least a degradation resistant length section of the microstructured length section the PCF includes hydrogen and/or deuterium. In at least the degradation resistant length section the PCF further includes a main coating surrounding the cladding region, which main coating is hermetic for the hydrogen and/or deuterium at a temperature below T.sub.h, wherein T.sub.h is at least about 50° C., preferably 50° C.<T.sub.h<250° C.

Provided are a silica glass yarn and a silica glass cloth which have a signal transmission speed that is made stable through stabilization of a characteristic impedance in addition to a low dielectric constant and a low loss. The silica glass yarn has a yarn habit density of 0.10 piece/cm or less of yarn habits each having a bending point with a radius of curvature of 5 mm or less and a bending angle of 120° or less. It is preferred that the silica glass yarn have a tensile strength of 2.0 GPa or more, and silica glass filaments forming the silica glass yarn each have a breaking start strength of 80.0% or more of the tensile strength of the silica glass yarn.

Systems and methods for forming a permanent plug in a subterranean formation include providing a solution of colloidal silica and pumping the colloidal silica into a bore of a subterranean well so that the colloidal silica penetrates pores of the subterranean formation. The colloidal silica within the pores of the subterranean formation is dehydrated to form a glass-like material within the pores of the subterranean formation.

Provided is a silica glass member for hermetic sealing of an ultraviolet SMD LED element to be suitably used for hermetic sealing of, and as a transmission window material for, a surface mount-type package (SMD) having an ultraviolet LED mounted thereon and configured to emit ultraviolet light in a wavelength range of from 200 nm to 350 nm. The silica glass member for hermetic sealing includes a silica glass substrate, which is homogeneously and integrally formed without an internal boundary, wherein the silica glass substrate has: a first surface on an inside opposed to an SMD LED element; and a second surface on an outside corresponding to the first surface, wherein an outer peripheral portion of the first surface has formed therein a substrate joining plain surface for joining to the container outer periphery joining plain surface, and wherein the second surface on the outside corresponding to the first surface has formed therein a lens-like convex portion configured to process emitted light from the ultraviolet SMD LED element.

The invention relates to an optical fiber preform (20) comprising a primary preform (21) and one or more purified silica-based overclad layers (22) surrounding said primary preform (21), the purified silica-based overclad layers (22) comprising lithium and aluminium, and having a ratio between lithium concentration [Li] and aluminium concentration [Al] satisfying the following inequality:
1×10.sup.−3≤[Li]/[Al]≤20×10.sup.−3.

A quartz glass plate has a quartz glass plate body and a quartz glass member adhered to the quartz glass plate body through an adhesive layer, where the adhesive layer contains silica, and a sum of concentrations of Li, Na, and K ions, being alkali metal ions and Ca ions, being alkaline earth metal ions contained in the adhesive layer is 10 ppm by mass or less. Consequently, a step with a uniform thickness can be formed, and a quartz glass plate is not easily damaged by irradiation with a light containing an ultraviolet ray.

A resin composition for coating an optical fiber comprises a base resin containing an oligomer, a monomer, and a photopolymerization initiator, and hydrophobic inorganic oxide particles, wherein the oligomer comprises urethane (meth)acrylate and epoxy (meth)acrylate, and the mass ratio of the content of urethane (meth)acrylate to the content of epoxy (meth)acrylate is 0.25 or more.

An optical fiber according to an embodiment includes a core and a cladding. The average value n1_ave of the refractive index of the core, the minimum value nc_min of the refractive index of the cladding, and the refractive index n0 of pure silica glass satisfy relationships of n1_ave>nc_min and nc_min<n0. The cladding contains fluorine. The fluorine concentration in the cladding is adjusted to be minimum in the outermost portion of the cladding including the outer peripheral surface of the cladding.