Abstract: 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 1×10?12 cm2/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.

Abstract: Provided is an optical fiber containing an alkali metal element or the like having a smaller diffusion coefficient than K and having a low Rayleigh scattering loss. An optical fiber is composed of silica glass and includes a core and a cladding arranged to surround the core which has a lower refractive index than the core. The core includes a first core including a central axis and a second core arranged to surround the first core. The average concentration of an alkali metal element or alkaline-earth metal element in the first core is 10 mol ppm or less. The average concentration of chlorine in the first core is 2000 mol ppm or more. The average concentration of an alkali metal element or alkaline-earth metal element in the second core is 10 mol ppm or more. The average concentration of chlorine in the second core is 10 to 600 mol ppm.

Abstract: A low attenuation optical fiber having a core doped with Ge is offered. The optical fiber consists of a glass part and a covering part formed around the glass part. The glass part is made of silica glass and includes: a Ge-doped center core region; an optical cladding layer formed around the center core region; and an optical cladding layer formed around the cladding layer. The relationship of ?1>?3??2 holds, where ?1, ?2, and ?3 are the relative refractive index differences of the center core region, the cladding layer, and the cladding layer 30, respectively with respect to pure silica glass. The average outer diameter of the glass part is in the range of 125±0.5 ?m in the longitudinal direction, and 3? is in the range of 0.1 ?m to 0.5 ?m, where ? is the standard deviation of the outer diameter in the longitudinal direction.

Abstract: An optical fiber containing alkali metal elements or the like in which Rayleigh scattering loss can be reduced is provided. An optical fiber includes a core composed of silica glass and a cladding which surrounds the core, has a refractive index lower than a refractive index of the core, and is composed of silica glass containing fluorine. The core contains a first group of dopants and a second group of dopants having a diffusion coefficient lower than a diffusion coefficient of the first group of dopants. The difference between the maximum value and the minimum value of residual stress in the optical fiber is 150 MPa or less.

Abstract: A low attenuation optical fiber having a core doped with Ge is offered. The optical fiber consists of a glass part and a covering part formed around the glass part. The glass part is made of silica glass and includes: a Ge-doped center core region; an optical cladding layer formed around the center core region; and an optical cladding layer formed around the cladding layer. The relationship of ?1>?3??2 holds, where ?1, ?2, and ?3 are the relative refractive index differences of the center core region, the cladding layer, and the cladding layer 30, respectively with respect to pure silica glass. The average outer diameter of the glass part is in the range of 125±0.5 ?m in the longitudinal direction, and 3? is in the range of 0.1 ?m to 0.5 ?m, where ? is the standard deviation of the outer diameter in the longitudinal direction.

Abstract: An optical fiber containing alkali metal elements or the like in which Rayleigh scattering loss can be reduced is provided. An optical fiber includes a core composed of silica glass and a cladding which surrounds the core, has a refractive index lower than a refractive index of the core, and is composed of silica glass containing fluorine. The core contains a first group of dopants and a second group of dopants having a diffusion coefficient lower than a diffusion coefficient of the first group of dopants. The difference between the maximum value and the minimum value of residual stress in the optical fiber is 150 MPa or less.

Abstract: A method of making a glass is provided in which the time needed for doping a refractive index control substance such as fluorine into a soot glass deposit body can be reduced. The method comprises the steps of: (1) putting a soot glass deposit body in a container; (2) doping a refractive index control substance into the soot glass deposit body by supplying an doping gas into the container, the doping gas containing the substance; and (3) consolidating the soot glass deposit body by heating, wherein the final set-value concentration of the substance is determined beforehand depending on the target refractive index of the glass, and in step (2), the container is supplied with the doping gas including the substance having a concentration set to be higher than the final set-value concentration, and subsequently, the doping gas including the substance having the final set-value concentration is supplied into the container.

Abstract: A method of making a glass is provided in which the time needed for doping a refractive index control substance such as fluorine into a soot glass deposit body can be reduced. The method comprises the steps of: (1) putting a soot glass deposit body in a container; (2) doping a refractive index control substance into the soot glass deposit body by supplying an doping gas into the container, the doping gas containing the substance; and (3) consolidating the soot glass deposit body by heating, wherein the final set-value concentration of the substance is determined beforehand depending on the target refractive index of the glass, and in step (2), the container is supplied with the doping gas including the substance having a concentration set to be higher than the final set-value concentration, and subsequently, the doping gas including the substance having the final set-value concentration is supplied into the container.

Abstract: There is prepared an optical fiber preform 2 whose core region is doped with Ge in such a quantity of dopant that the relative refractive-index difference [Ge] expressed in % with respect to pure SiO2 satisfies the condition [Ge]?0.3%, where upon after being heat drawn with a drawing furnace 11 into an optical fiber 3, the optical fiber 3 is annealed in a heating furnace 21 downstream of the drawing furnace 11 under a condition that the cooling speed is 2000° C./second or less, and the period of annealing time is equal to or longer than the relaxation time. Further, the annealed optical fiber 3 is introduced into a cooling means 31 at an entry temperature of 700° C. or more, and the optical fiber 3 is forcibly cooled by the cooling means 31. As a consequence, there are achieved an optical fiber and a method of fabricating the same capable of fabricating the optical fiber having a reduced Rayleigh scattering loss as well as excellent hydrogen-resisting property with favorably high productivity.