Optical fiber for a fiber laser, fiber laser, and production method for optical fiber for a fiber laser

Abstract

An optical fiber for a fiber laser includes a core to which a rare-earth element is added, a first cladding formed around the core; and a second cladding formed around the first cladding, and excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light. An addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser.

What is claimed is: 
     
         1 . A production method for an optical fiber for a fiber laser including a core to which a rare-earth element is added, a first cladding formed around the core, and a second cladding formed around the first cladding, in which excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light, wherein an addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser, comprising:
 stacking a plurality of disks formed of silica glass in which the addition concentration of the rare-earth element is changed in a thickness direction on an inner side of a hollow silica glass tube;   fusing the tube and the plurality of disks together by heating to manufacture a preform; and   performing wire drawing while heating the preform.   
     
     
         2 . A production method for an optical fiber for a fiber laser including a core to which a rare-earth element is added, a first cladding formed around the core, and a second cladding formed around the first cladding, in which excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light, wherein an addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser, comprising:
 allowing a soot to grow while periodically changing the addition concentration of the rare-earth element in an axial direction by a vapor phase axial deposition method to manufacture a soot body;   subjecting the soot body to silica vitrification to manufacture a rod;   disposing the rod on an inner side of a hollow silica glass tube to manufacture a rod-in-tube;   allowing the rod-in-tube to collapse to manufacture a preform; and   performing wire drawing while heating the preform.   
     
     
         3 . The production method for the optical fiber for a fiber laser according to  claim 2 , wherein
 a manufacturing device for manufacturing the soot body includes a plurality of burners for depositing the soot by an oxyhydrogen flame hydrolysis method of a silicon tetrachloride and a surface shape monitoring device that monitors a surface shape of a soot deposition surface, and   a monitoring result obtained by the surface shape monitoring device is provided as a feedback and the soot is deposited while adjusting heating power of the burners so that the surface shape of the soot deposition surface is kept to be a flat surface vertical to a central axis of the soot body.   
     
     
         4 . A production method for an optical fiber for a fiber laser including a core to which a rare-earth element is added, a first cladding formed around the core, and a second cladding formed around the first cladding, in which excitation light is guided from at least one end of the first cladding to excite the rare-earth element to output a laser oscillation light, wherein an addition concentration of the rare-earth element to the core is different in a longitudinal direction of the optical fiber for a fiber laser, and a core diameter and a numerical aperture of the optical fiber for a fiber laser are constant in the longitudinal direction of the optical fiber for a fiber laser, comprising:
 supplying raw gas to an inner side of a hollow silica glass tube to deposit silica glass by a plasma activated chemical vapor deposition method while changing the concentration of the rare-earth element periodically according to movement in the longitudinal direction of the tube, of a deposition position of silica glass where a high-frequency induction thermal plasma is generated in the tube,   allowing the tube to collapse to manufacture a preform; and   performing wire drawing while heating the preform.