Optical fibre, optical fibre preform and method for producing the preform having a deformed first clad

摘要

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 fist 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.