An optical fiber includes an outer diameter less than 220 m, a glass fiber that includes a glass core and a glass cladding, a primary coating, and a secondary coating. The glass cladding surrounds and is in direct contact with the glass core. The primary coating surrounds and is in direct contact with the glass fiber. The primary coating can have a Young's modulus less than 0.5 MPa and a thickness less than 30.0 m. The secondary coating surrounds and is in direct contact with the primary coating. The secondary coating can have a thickness less than 27.5 m. A pullout force of the optical fiber can be less than a predetermined threshold when in an as-drawn state. The pullout force may increase by less than a factor of 2.0 upon aging the primary and secondary coatings on the glass fiber for at least 60 days.

The glasses of the present disclosure are highly transparent and have very good resistance to solarization. The resistance to solarization arises from the production method. The concentrations of reduced polyvalent ion species are reduced by targeted use of bubbling with an oxidizing gas. Methods for producing glasses and to the uses thereof, particularly as core glasses in optical waveguides, are also provided.

An optical material including: a silica host; and a Praseodymium dopant; wherein the Praseodymium atoms are configured to form nanoclusters in the silica host. In addition, the optical material may include an Ytterbium co-dopant. The nanoclusters include Ge, Te, Ta, Lu and/or F, Cl to minimize multi-phonon quenching. Moreover, the nanoclusters may be encapsulated in a low phonon energy shell to minimize energy transfer to the host matrix.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

An optical fiber preform includes a silica-glass core portion, and a cladding portion surrounding the core portion, the cladding portion being composed of a fluorine-containing silica glass having a lower refractive index than the core portion, the core portion including a first region that does not include the central axis thereof, the first region containing a first dopant selected from sodium, potassium, and compounds thereof, and a second region that includes the central axis, the second region containing a second dopant that reduces the viscosity of the silica glass, the second dopant having a diffusion coefficient of 110.sup.12 cm.sup.2/s or more and less than the first dopant at 2,000 C. to 2,300 C., in which the entire core portion has an average first dopant concentration of 10 atomic ppm or more and 2,000 atomic ppm or less and an average second dopant concentration of 10 atomic ppm or more.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

A glass substrate for a high-frequency device, which contains 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 alkaline earth metal oxides in the range of 0.1-13% in terms of mole percent on the basis of oxides, wherein 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 wideband multimode co-doped optical fiber has a silica core co-doped with GeO.sub.2 and Al.sub.2O.sub.3. The GeO.sub.2 concentration is maximum at the fiber centerline and monotonically decreases radially out to the core radius. The Al.sub.2O.sub.3 concentration is minimum at the centerline and monotonically increases radially out to maximum concentration at the core radius. The cladding has an inner cladding region of relative refractive index 2, an intermediate cladding region having a relative refractive index 3, and an outer cladding region having a relative refractive index 4, wherein 3<2, 4. The optical fiber has a bandwidth BW5 GHz.Math.km with a peak wavelength .sub.P within a wavelength range of 800 nm to 1200 nm and over a wavelength band of at least 100 nm.

Provided is a fluorine-containing synthetic silica glass powder which contains a sufficient amount of fluorine, and in which a reduction in the fluorine concentration caused by dissociation of fluorine from silica can be inhibited. Problems are solved by a fluorine-containing silica glass powder which contains particles having a particle size of more than 150 m but 300 m or less in an amount of 25% by weight or more as a whole. Also provided as a method of producing the glass powder is, for example, a method of producing a fluorine-containing silica glass powder, which method includes: prefiring a silicon oxide at a temperature of lower than 1,000 C. in the presence of SiF.sub.4 to prepare a fluorine-containing silica; and subsequently firing the fluorine-containing silica at a temperature of 1,000 C. or higher but lower than 1,400 C. to produce a silica glass powder.

An optical element is provided. The optical element may comprise a material, the material being a matrix and a set of particles included in the matrix, the material having a molar fraction of SiO.sub.2 higher than or equal to 65 percent, each particle having a dimension smaller than or equal to 80 nanometers.