Rare earth-doped core optical fiber and manufacturing method thereof

Abstract

A rare earth-doped core optical fiber of the present invention includes a core comprising a silica glass containing at least aluminum and ytterbium, and a clad provided around the core and comprising a silica glass having a lower refraction index than that of the core, wherein the core has an aluminum concentration of 2% by mass or more, and ytterbium is doped into the core at such a concentration that the absorption band which appears around a wavelength of 976 nm in the absorption band by ytterbium contained in the core shows a peak absorption coefficient of 800 dB/m or less.

1 . The manufacturing method of a rare earth-doped core optical fiber, comprising:
 a deposition step which includes introducing raw material gases composed of various kinds of a halide gas and an oxygen gas from a first cross-section of the glass tube having silica as a main component into a hollow portion of the glass tube, heating the glass tube by a heating means, subjecting the halide gas to oxidization to form a soot-like exit, depositing the soot-like exit on the inner surface of the glass tube, and sintering deposited soot-like exit to deposit the porous glass layer;   a doping step which includes doping an additive into the porous glass layer of the inner surface of the glass tube after the deposition step;   a transparentization step which includes heating the glass pipe to subject the porous glass layer to transparent glass after the doping step;   a core solidification step which includes collapsing a hollow portion of the glass tube for core solidification to form a preform after the transparentization step; and   a fiber-drawing step which includes fiber-drawing the optical fiber preform comprising the preform to obtain a rare earth-doped core optical fiber after the core solidification step,   wherein the halide gas contains at least SiCl4 and AlCl3, the additive contains at least a rare earth element, and in either or both of the deposition step and the transparentization step, a fluoride gas is introduced from a first cross-section of the glass tube to a hollow portion of the glass tube.   
     
     
         2 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 1 , wherein the rare earth element used as an additive contains at least ytterbium. 
     
     
         3 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 2 , wherein the core of the obtained rare earth-doped core optical fiber has an aluminum concentration of 2% by mass or more, and ytterbium is doped into the core at such a concentration that the absorption band of ytterbium doped into the core, which appears around a wavelength of 976 nm, shows a peak absorption coefficient of the absorption band of 800 dB/m or less. 
     
     
         4 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 1 , which further comprises a step for forming a polymer layer having a lower refraction index than that of the clad on the outer periphery of the glass clad of the optical fiber in the fiber-drawing step. 
     
     
         5 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 4 , wherein the clad is composed of an inner clad positioned on the exterior of the core, and an outer clad positioned outside the inner clad, and the refractive index n1 of the core, the refractive index n2 of the inner clad, the refractive index n3 of the outer clad, and the refractive index n4 of the polymer layer satisfy the relationship of n1>n2>n3>n4. 
     
     
         6 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 2 , which further comprises a step for forming a polymer layer having a lower refraction index than that of the clad on the outer periphery of the glass clad of the optical fiber in the fiber-drawing step. 
     
     
         7 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 3 , which further comprises a step for forming a polymer layer having a lower refraction index than that of the clad on the outer periphery of the glass clad of the optical fiber in the fiber-drawing step. 
     
     
         8 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 6 , wherein the clad is composed of an inner clad positioned on the exterior of the core, and an outer clad positioned outside the inner clad, and the refractive index n1 of the core, the refractive index n2 of the inner clad, the refractive index n3 of the outer clad, and the refractive index n4 of the polymer layer satisfy the relationship of n1>n2>n3>n4. 
     
     
         9 . The manufacturing method of a rare earth-doped core optical fiber according to  claim 7 , wherein the clad is composed of an inner clad positioned on the exterior of the core, and an outer clad positioned outside the inner clad, and the refractive index n1 of the core, the refractive index n2 of the inner clad, the refractive index n3 of the outer clad, and the refractive index n4 of the polymer layer satisfy the relationship of n1>n2>n3>n4.