Abstract: There is provided a method for manufacturing an optical fiber base material. The method includes: connecting a dummy rod 3 to an end of a target formed of a quartz glass rod to form a rod with dummy, the target becoming the optical fiber base material by depositing thereon glass particles; forming a taper portion 10 of which a diameter of the dummy rod side is narrower than a diameter of the target side in a connecting portion between the dummy road being chucked and the target 5 when processing the rod with dummy to transparently vitrify it; and depositing glass particles on an outer circumference of the glass rod with dummy after the processing the dummy rod so as to cover the outer circumference of a large diameter side of the taper portion 10 and forming soot.

Abstract: There is disclosed a method for producing a base material for optical fiber having a deformed first clad consisting of at least a core, a first clad and a second clad, comprising a step of deforming a shape of a section of the first clad so that it may have at least one linear part when the first clad is formed around the core, a step of depositing porous glass fine particles as the second clad made of the same material as that of the first clad on a glass rod having the deformed first clad to form a porous glass base material, and a step of forming the second clad having a round section by vitrifying it. There can be provided a method for producing a base material for optical fiber wherein a lot of breakages or cracks on the surface of the base material can be prevented in a step of depositing porous glass fine particles for the second clad on the first clad, and base material for optical fiber having no defects, and an optical fiber having an efficient effect of being excited with excitation light.

Abstract: A method for manufacturing a fluorine-doped quartz glass article by sintering a porous glass preform moving in a heat zone in an atmosphere of a fluorine gas is disclosed, wherein a fluorine gas process is performed by setting a moving speed of the porous glass preform in the heat zone heated at 1000° C. or more in order that L/V is 40 minutes or more, where L is the length (mm) of a heater, and V is the moving speed (mm/min). The temperature of the heat zone may be vitrification temperature. The fluorine gas process may be performed in the heat zone which is at 1000° C. or more not to perform a vitrification process, and then the vitrification process maybe performed by increasing the temperature of the heat zone.

Abstract: A method for manufacturing a synthesized silica glass optical member, the method comprising: providing a porous silica glass body; heating the porous' silica glass body in an atmosphere containing hydrogen or oxygen, and sintering the porous silica glass body in an atmosphere containing fluorine compound. Furthermore, a synthesized silica glass optical member manufactured by the method.

Abstract: A method for manufacturing a synthesized silica glass optical member, the method comprising: providing a porous silica glass body; heating the porous silica glass body in an atmosphere containing hydrogen or oxygen, and sintering the porous silica glass body in an atmosphere containing fluorine compound. Furthermore, a synthesized silica glass optical member manufactured by the method.

Abstract: There is disclosed a method for producing a base material for optical fiber having a deformed first clad consisting of at least a core, a first clad and a second clad, comprising a step of deforming a shape of a section of the first clad so that it may have at least one linear part when the first clad is formed around the core, a step of depositing porous glass fine particles as the second clad made of the same material as that of the first clad on a glass rod having the deformed first clad to form a porous glass base material, and a step of forming the second clad having a round section by vitrifying it. There can be provided a method for producing a base material for optical fiber wherein a lot of breakages or cracks on the surface of the base material can be prevented in a step of depositing porous glass fine particles for the second clad on the first clad, and base material for optical fiber having no defects, and an optical fiber having an efficient effect of being excited with excitation light.

Abstract: A grating optical fiber comprises a core, a first clad layer formed around the core, and a second clad layer formed around the first clad. Germanium is doped in the core, while germanium and fluorine are doped in the first clad layer. Gratings are formed on both the core and the first clad layer. The difference between the indexes of refraction between the first and second clad layers is smaller than the difference between the indexes of refraction between the core and the first clad layer.

Abstract: A method for manufacturing a glass base material, which is a base material of an optical fiber, comprising: forming a core of the glass base material; forming the core includes: accumulating glass particles on a starting rod to form a porous glass soot; sintering the porous glass soot in an atmosphere of mixed gas that contains fluorine-compound gas to form a GI type refractive index profile, the refractive index of which gradually decreases with a distance from a center of the core; and forming a clad of the glass base material around the core.

Abstract: A method for manufacturing a synthesized silica glass optical member, the method comprising: providing a porous silica glass body; heating the porous silica glass body in an atmosphere containing hydrogen or oxygen, and sintering the porous silica glass body in an atmosphere containing fluorine compound. Furthermore, a synthesized silica glass optical member manufactured by the method.

Abstract: A grating optical fiber comprises a core, a first clad layer formed around the core, and a second clad layer formed around the first clad. Germanium is doped in the core, while germanium and fluorine are doped in the first clad layer. Gratings are formed on both the core and the first clad layer. The difference between the indexes of refraction between the first and second clad layers is smaller than the difference between the indexes of refraction between the core and the first clad layer.