An optical fiber preform includes: a core formed of silica glass which does not contain Ge, wherein the core has at least one of characteristics in spectrometry of (1) an absorption peak is present at a wavelength of 240 nm to 255 nm, and (2) a wavelength at which an ultraviolet transmittance is 50% or lower is longer than 170 nm.

Layered glass structures and fabrication methods are described. The methods include depositing soot on a dense glass substrate to form a composite structure and sintering the composite structure to form a layered glass structure. The dense glass substrate may be derived from an optical fiber preform that has been modified to include a planar surface. The composite structure may include one or more soot layers. The layered glass structure may be formed by combining multiple composite structures to form a stack, followed by sintering and fusing the stack. The layered glass structure may further be heated to softening and drawn to control linear dimensions. The layered glass structure or drawn layered glass structure may be configured as a planar waveguide.

A method for producing rod lenses with an enveloping diameter of the rod lens face of up to 200 mm and an edge length of at least 800 mm. The method is characterized in that fabrication is performed from a cylindrical rod lens element made from synthetic quartz glass material configured as a fused silica ingot. This is performed using a flame hydrolysis method with a direct one stage deposition process of SIO.sub.x particles from a flame stream onto die that rotates and is moveable in a linear manner with respect to the flame stream.

An optical fiber includes a core, and a clad surrounding an outer circumference of the core, in which a first relative refractive index difference Δ1a is greater than 0, a second relative refractive index difference Δ1b is greater than 0, the first relative refractive index difference Δ1a is greater than the second relative refractive index difference Δ1b, the first relative refractive index difference Δ1a and the second relative refractive index difference Δ1b satisfy a relationship denoted by the following expression: 0.20≦(Δ1a−Δ1b)/Δ1a≦0.88, and a refractive index profile Δ of the core in an entire region of a section of 0≦r≦r1 as a function Δ(r) of a distance r from a center of the core in the radial direction is denoted by the following expression: Δ(r)=Δ1a−(Δ1a−Δ1b)r/r1.

An optical fiber includes a core, and a clad surrounding an outer circumference of the core, in which a first relative refractive index difference Δ1a is greater than 0, a second relative refractive index difference Δ1b is greater than 0, the first relative refractive index difference Δ1a is greater than the second relative refractive index difference Δ1b, the first relative refractive index difference Δ1a and the second relative refractive index difference Δ1b satisfy a relationship denoted by the following expression: 0.20≦(Δ1a−Δ1b)/Δ1a≦0.88, and a refractive index profile Δ of the core in an entire region of a section of 0≦r≦r1 as a function Δ(r) of a distance r from a center of the core in the radial direction is denoted by the following expression: Δ(r)=Δ1a−(Δ1a−Δ1b)r/r1.

A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index Δ.sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index Δ.sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650° C. of the second outer cladding minus the viscosity at 1650° C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and Δ.sub.1MAX>Δ.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index Δ.sub.3MAX, and Δ.sub.3MAX>Δ.sub.2MIN.

A method for manufacturing a glass fine particle deposit includes: emitting a siloxane gas, a carrier gas, and a combustion gas from a burner; setting volume concentration of a supply volume amount of the siloxane gas per unit time with respect to the sum of the supply volume amount of the siloxane gas per unit time and a supply volume amount of the carrier gas per unit time (C1) to 10.6 volume %<C1<20.0 volume %; and setting volume concentration of the supply volume amount of the siloxane gas per unit time with respect to the sum of the supply volume amount of the siloxane gas per unit time, the supply volume amount of the carrier gas per unit time, and a supply volume amount of the seal gas per unit time (C2) to 5.8 volume %<C2<10.0 volume %.

In a device for producing a large-sized porous base material by a VAD process, the cracking and variation of the outer diameter of the base material are suppressed by forming a smooth tapered part, without changing the length of a non-effective part. In producing the porous base material by a VAD process, the time for a gas to reach a flow amount of the gas in a steady state from starting of the deposition is extended more in a burner that deposits glass microparticles on a layer closer to the outside of the base material.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index Δ.sub.1MAX, and an inner cladding region having refractive index Δ.sub.2MIN surrounding the core, where Δ.sub.1MAX>Δ.sub.2MIN.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index Δ.sub.1MAX, and an inner cladding region having refractive index Δ.sub.2MIN surrounding the core, where Δ.sub.1MAX>Δ.sub.2MIN.