JP3823341B2 - Optical fiber preform, optical fiber and manufacturing method thereof - Google Patents

Optical fiber preform, optical fiber and manufacturing method thereof Download PDF

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JP3823341B2
JP3823341B2 JP18594695A JP18594695A JP3823341B2 JP 3823341 B2 JP3823341 B2 JP 3823341B2 JP 18594695 A JP18594695 A JP 18594695A JP 18594695 A JP18594695 A JP 18594695A JP 3823341 B2 JP3823341 B2 JP 3823341B2
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stress applying
softening temperature
hole
applying member
tubular member
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JPH0930823A (en
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政浩 高城
毅 京極
洋一 石黒
幸一 内山
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Sumitomo Electric Industries Ltd
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
    • C03B37/01211—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
    • C03B37/01217—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube for making preforms of polarisation-maintaining optical fibres
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2203/00—Fibre product details, e.g. structure, shape
    • C03B2203/30—Polarisation maintaining [PM], i.e. birefringent products, e.g. with elliptical core, by use of stress rods, "PANDA" type fibres
    • C03B2203/31—Polarisation maintaining [PM], i.e. birefringent products, e.g. with elliptical core, by use of stress rods, "PANDA" type fibres by use of stress-imparting rods, e.g. by insertion

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)

Description

【０００１】
【産業上の利用分野】
本発明は、偏波保持光ファイバを製造するための光ファイバ母材及びその製造方法、並びに偏波保持光ファイバ及びその製造方法に関するものである。
【０００２】
【従来の技術】
偏波保持光ファイバの製造方法としては、従来から特公平３−７６１３に開示されるような方法が知られている。これは、通常の光ファイバ母材のコア中心に対して対称の位置に少なくとも一組の貫通孔を形成し、その貫通孔にクラッドとは熱膨張係数の異なる応力付与部材を挿入してから、▲１▼加熱処理によりクラッドと応力付与部材を一体化した後、線引を行って、あるいは▲２▼加熱による一体化と同時に線引を行って応力型の偏波保持光ファイバを製造する方法である。
【０００３】
【発明が解決しようとする課題】
しかしながら、通常、応力付与部材とクラッドでは、両者の物性値、特に軟化温度が大きく異なっており、そのため、加熱一体化の際に、両者の接合界面に気泡が残存することが多々あった。これは、軟化温度に差があると、どちらか一方のみが軟化してしまい、他方の表面が加熱により十分に平滑化される前に一体化してしまう結果、接合界面に気泡が発生しやすくなるからである。
【０００４】
このため、上記の方法▲１▼によりクラッドと応力付与部材を加熱一体化した場合には、クラッドと応力付与部材との界面に気泡が発生した光ファイバ母材が作製されてしまうことになる。光ファイバ母材の内部に気泡が発生しているとそれだけで割れの原因になるほか、母材を線引して得られる光ファイバの特性を劣化させることになり、好ましくない。
【０００５】
また、上記の方法▲２▼によりクラッドと応力付与部材を加熱一体化しながら線引を行った場合は、クラッドと応力付与部材との界面に気泡が発生しながら線引が行われるため、線引途中で光ファイバが断裂しやすい。また、断裂せず光ファイバが製造されたとしても、その光ファイバは内部に気泡を含んでいるため、十分な伝送特性や強度を有していない。
【０００６】
本発明は、上記の問題点を解決するためになされたもので、気泡の発生を防止しながら製造することのできる構造を有し、偏波保持光ファイバを良好に製造できる光ファイバ母材及びその製造方法、並びに気泡が発生しにくい光ファイバの製造方法及び気泡の発生を防止しながら製造することのできる構造の光ファイバを提供することを目的とする。
【０００７】
【課題を解決するための手段】
上記の問題点を解決するために、本発明に係る光ファイバ母材は、（ａ）柱状のコアと、（ｂ）このコアを包囲する管状のクラッドであって、その管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられ、その貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものと、（ｃ）上記の貫通孔に挿入され、第１の熱膨張係数と異なる第２の熱膨張係数及び第１の軟化温度と異なる第２の軟化温度をその表層部において有する柱状の応力付与部材と、（ｄ）上記の貫通孔に挿入され、応力付与部材を包囲する管状部材であって、第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものとを備えている。
【０００８】
上記の管状部材は、略一定の径方向軟化温度分布を有していても良い。ここで、略一定の径方向軟化温度分布とは、管状部材がその表面側から中心側まで第１及び第２の軟化温度の間の軟化温度をほぼ一定に維持していることをいう。このとき、この一定の軟化温度は、第１及び第２の軟化温度のいずれとも異なっており、特に、第１及び第２の軟化温度を平均した軟化温度であると好ましい。
【０００９】
また、上記の管状部材は、その表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有していても良い。
【００１０】
また、応力付与部材及び管状部材の屈折率は、クラッドの屈折率以下であると良い。
【００１１】
次に、本発明に係る光ファイバ母材の製造方法の第１の態様は、（ａ）▲１▼柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、▲２▼上記の貫通孔に挿入されるべき柱状の応力付与部材であって、第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、（ｂ）応力付与部材を包囲すべき管状部材であって上記の第１及び第２の間で設定された径方向軟化温度分布を有するものを、i)上記の貫通孔の表面上、 ii)応力付与部材の表面と貫通孔の表面との中間、あるいはiii)応力付与部材の表面上、のうち一以上の位置に設けるとともに、孔開き母材、応力付与部材及び管状部材を一体化する第２の工程とを備えている。
【００１２】
上記の第２工程は、貫通孔の表面上に管状部材を形成し、次いで、応力付与部材をこの管状部材の中空部に挿入し、この後、応力付与部材と管状部材を一体化する工程であっても良い。
【００１３】
また、上記の第２工程は、応力付与部材の表面上に管状部材を形成し、次いで、応力付与部材及び管状部材からなる柱状体を孔開き母材の貫通孔に挿入し、この後、柱状体と孔開き母材を一体化する工程であっても良い。
【００１４】
また、上記の第２工程は、管状部材を前記貫通孔に挿入するとともに、この管状部材の中空部に応力付与部材を挿入し、この後、孔開き母材、応力付与部材及び管状部材を一体化する工程であっても良い。
【００１５】
なお、孔開き母材、応力付与部材及び管状部材の一体化は、これらの部材がガラスである場合には、例えば加熱処理によりガラス同士を接合することで達成することができる。
【００１６】
本発明に係る光ファイバ母材の製造方法の第２の態様は、（ａ）▲１▼柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、▲２▼第１の熱膨張係数と異なる第２の熱膨張係数及び第１の軟化温度と異なる第２の軟化温度をその表層部において有する中央部を備えた柱状の応力付与部材であって第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材をその表層部（応力付与部材の表層部）に備えたものとを用意する第１の工程と、（ｂ）応力付与部材を孔開き母材の貫通孔に挿入する第２の工程と、（ｃ）応力付与部材と孔開き母材を一体化する第３の工程とを備えている。
【００１７】
なお、孔開き母材と応力付与部材の一体化は、これらの部材がガラスである場合には、例えば加熱処理によりガラス同士を接合することで達成することができる。
【００１８】
上記第１及び第２の態様に係る母材製造方法において、上記の管状部材は、略一定の径方向軟化温度分布を有していても良い。ここで、略一定の径方向軟化温度分布とは、管状部材がその表面側から中心側まで第１及び第２の軟化温度の間の軟化温度をほぼ一定に維持していることをいう。このとき、この一定の軟化温度は、第１及び第２の軟化温度のいずれとも異なっており、特に、第１及び第２の軟化温度を平均した軟化温度であると好ましい。
【００１９】
また、上記第１及び第２の態様において、上記の管状部材は、表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有していても良い。
【００２０】
次に、本発明に係る光ファイバの製造方法の第１の態様は、（ａ）▲１▼柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、▲２▼上記の貫通孔に挿入されるべき柱状の応力付与部材であって、第１の熱膨張係数と異なる第２の熱膨張係数及び第１の軟化温度と異なる第２の軟化温度をその表層部において有するものを用意する第１の工程と、（ｂ）応力付与部材を包囲すべき管状部材であって第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、i)上記の貫通孔の表面上、 ii)応力付与部材の表面と貫通孔の表面との中間、あるいはiii)応力付与部材の表面上、のうち一以上の位置に設ける第２の工程と、（ｃ）孔開き母材、応力付与部材及び管状部材からなる複合体を加熱して、孔開き母材、応力付与部材及び管状部材を一体化しながらこの複合体を線引する第３の工程とを備えている。
【００２１】
なお、孔開き母材、応力付与部材及び管状部材の一体化は、これらの部材がガラスである場合には、例えば加熱処理によりガラス同士を接合することで達成することができる。
【００２２】
上記の第２工程は、孔開き母材の貫通孔の表面上に管状部材を形成し、次いで、応力付与部材をこの管状部材の中空部に挿入する工程であっても良い。
【００２３】
また、第２工程は、応力付与部材の表面上に管状部材を形成し、次いで、応力付与部材及び管状部材からなる柱状体を孔開き母材の貫通孔に挿入する工程であっても良い。
【００２４】
また、第２工程は、管状部材を貫通孔に挿入するとともに、この管状部材の中空部に応力付与部材を挿入する工程であっても良い。
【００２５】
本発明に係る光ファイバの製造方法の第２の態様は、（ａ）▲１▼柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、▲２▼第１の熱膨張係数と異なる第２の熱膨張係数及び第１の軟化温度と異なる第２の軟化温度をその表層部において有する中央部を備えた柱状の応力付与部材であって、第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材をその表層部（応力付与部材の表層部）に備えたものとを用意する第１の工程と、（ｂ）応力付与部材を孔開き母材の貫通孔に挿入する第２の工程と、（ｃ）孔開き母材及び応力付与部材からなる複合体を加熱して、孔開き母材及び応力付与部材を一体化しながらこの複合体を線引する第３の工程とを備えている。
【００２６】
上記第１及び第２の態様に係る光ファイバ製造方法において、上記の管状部材は、略一定の径方向軟化温度分布を有していても良い。ここで、略一定の径方向軟化温度分布とは、管状部材がその表面側から中心側まで第１及び第２の軟化温度の間の軟化温度をほぼ一定に維持していることをいう。このとき、この一定の軟化温度は、第１及び第２の軟化温度のいずれとも異なっており、特に、第１及び第２の軟化温度を平均した軟化温度であると好ましい。
【００２７】
また、上記第１及び第２の態様において、上記の管状部材は、その表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有していても良い。
【００２８】
次に、本発明の光ファイバは、（ａ）柱状のコアと、（ｂ）このコアを包囲する管状のクラッドであって、その管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられ、その貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものと、（ｃ）上記の貫通孔に挿入され、第１の熱膨張係数と異なる第２の熱膨張係数及び第１の軟化温度と異なる第２の軟化温度をその表層部において有する柱状の応力付与部材と、（ｄ）上記の貫通孔に挿入され、応力付与部材を包囲する管状部材であって、前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものとを備えている。
【００２９】
上記の管状部材は、略一定の径方向軟化温度分布を有していても良い。ここで、略一定の径方向軟化温度分布とは、管状部材がその表面側から中心側まで第１及び第２の軟化温度の間の軟化温度をほぼ一定に維持していることをいう。このとき、この一定の軟化温度は、第１及び第２の軟化温度のいずれとも異なっており、特に、第１及び第２の軟化温度を平均した軟化温度であると好ましい。
【００３０】
また、上記の管状部材は、その表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有していても良い。
【００３１】
また、応力付与部材及び管状部材の屈折率は、クラッドの屈折率以下であると良い。
【００３２】
【作用】
（１）本発明の光ファイバ母材では、第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材がクラッドと応力付与部材との間に存在しているため、クラッドの表層部と管状部材との間、あるいは管状部材と応力付与部材の表層部との間の軟化温度変化は、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和される。従って、本発明の光ファイバ母材は、その製造時において加熱処理によりクラッドと応力付与部材を一体化する際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい構造を有している。
【００３３】
管状部材が第１及び第２の軟化温度の間で設定された略一定の径方向軟化温度分布を有している場合は、クラッドと管状部材との軟化温度差、あるいは管状部材と応力付与部材との軟化温度差が、クラッドと応力付与部材との軟化温度差よりも小さくなるため、気泡が発生しにくい構造となる。
【００３４】
また、管状部材がその表面側から中心側に向かってクラッドの下限となる軟化温度から応力付与部材の上限となる軟化温度まで連続的に変化する径方向軟化温度分布を有する場合は、クラッドの表層部から応力付与部材の表層部までほぼ連続的に変化するような軟化温度分布が形成されるため、より気泡が発生しにくい構造となる。特に、クラッドと応力付与部材との接合界面で軟化温度が等しくなっていれば、その接合界面において気泡が極めて発生しにくい構造となる。
【００３５】
また、上記の応力付与部材や管状部材の屈折率がクラッドの屈折率以下であると、本発明の光ファイバ母材を線引して得られる偏波保持光ファイバにおいて光を伝搬させた場合にも、コアから応力付与部材または管状部材への光パワーの移動は生じにくくなる。
【００３６】
（２）次に、本発明に係る光ファイバ母材の製造方法の第１の態様では、第２工程において、孔開き母材の貫通孔の表面上、応力付与部材の表面と貫通孔の表面との中間、あるいは応力付与部材の表面上のうち一以上の位置に管状部材を設けるとともに、孔開き母材、応力付与部材及び管状部材を一体化することで本発明の光ファイバ母材が製造される。
【００３７】
この方法では、管状部材を設けることでクラッドの表層部と管状部材との間の軟化温度変化、あるいは管状部材と応力付与部材の表層部との間の軟化温度変化が、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和される。このため、孔開き母材、応力付与部材及び管状部材を一体化して母材を完成させる際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい。
【００３８】
次に、本発明に係る光ファイバ母材の製造方法の第２の態様では、表層部に第１及び第２の軟化温度の間の径方向軟化温度分布を有する管状部材を備えた応力付与部材を孔開き母材の貫通孔に挿入した後、応力付与部材と孔開き母材を一体化することで、本発明の光ファイバ母材が製造される。
【００３９】
この方法では、応力付与部材の表層部に上記の管状部材が存在しているため、クラッドの表層部と応力付与部材の中央部の表層部（管状部材がないとした場合の応力付与部材の表層部）との間の軟化温度変化が、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和される。このため、孔開き母材と応力付与部材を一体化して母材を完成させる際にも、クラッドと応力付与部材の接合界面に気泡が発生しにくい。
【００４０】
上記第１及び第２の態様に係る母材製造方法において、第１及び第２の軟化温度の間で設定された略一定の径方向軟化温度分布を有している場合は、クラッドと管状部材との軟化温度差、あるいは管状部材と応力付与部材との軟化温度差がクラッドと応力付与部材との軟化温度差よりも小さくなることにより、気泡が発生しにくくなる。
【００４１】
また、管状部材がその表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有している場合は、クラッドから応力付与部材までほぼ連続的に変化するような軟化温度分布が形成されることにより、気泡が発生しにくくなる。
【００４２】
（３）次に、本発明に係る光ファイバ製造方法の第１の態様では、第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材をクラッドと応力付与部材との間に介在させた後、孔開き母材、応力付与部材及び管状部材を一体化しながら線引を行うことで光ファイバが製造される。得られた光ファイバは、応力付与部材がコアに付与する応力の作用によって偏波保持光ファイバとなる。
【００４３】
この方法では、管状部材を介在させることでクラッドの表層部と管状部材との間の軟化温度変化、あるいは管状部材と応力付与部材の表層部との間の軟化温度変化が、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和される。このため、孔開き母材、応力付与部材及び管状部材を一体化しながら線引を行う際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい。
【００４４】
次に、本発明に係る光ファイバの製造方法の第２の態様では、表層部に第１及び第２の軟化温度の間の径方向軟化温度分布を有する管状部材を備えた応力付与部材を孔開き母材の貫通孔に挿入した後、応力付与部材と孔開き母材を一体化しながら線引を行うことで、光ファイバが製造される。得られた光ファイバは、応力付与部材がコアに付与する応力の作用によって偏波保持光ファイバとなる。
【００４５】
この方法では、応力付与部材の表層部に上記の管状部材が存在しているため、クラッドの表層部と応力付与部材の中央部の表層部（管状部材がないとした場合の応力付与部材の表層部）との間の軟化温度変化が、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和される。このため、孔開き母材と応力付与部材を一体化しながら線引を行う際にも、クラッドと応力付与部材の接合界面に気泡が発生しにくい。
【００４６】
上記第１及び第２の態様に係る光ファイバ製造方法において、管状部材が第１及び第２の軟化温度の間で設定された略一定の径方向軟化温度分布を有している場合は、クラッドと管状部材との軟化温度差、あるいは管状部材と応力付与部材との軟化温度差がクラッドと応力付与部材との軟化温度差よりも小さくなることにより、気泡が発生しにくくなる。
【００４７】
また、管状部材がその表面側から中心側に向かって第１の軟化温度から第２の軟化温度まで連続的に変化する径方向軟化温度分布を有している場合は、母材の内部でクラッドから応力付与部材までほぼ連続的に変化するような軟化温度分布が形成されることにより、気泡が発生しにくくなる。
【００４８】
（４）次に、本発明の光ファイバは、第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材がクラッドと応力付与部材との間に存在しているため、クラッドの表層部と管状部材との間の軟化温度変化、あるいは管状部材と応力付与部材の表層部との間の軟化温度変化は、管状部材がない場合のクラッドの表層部と応力付与部材の表層部との間の軟化温度変化よりも緩和されている。従って、本発明の光ファイバは、その製造時において加熱処理によりクラッドと応力付与部材を一体化する際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい構造を有している。
【００４９】
管状部材が第１及び第２の軟化温度の間で設定された略一定の径方向軟化温度分布を有している場合は、クラッドと管状部材との軟化温度差、あるいは管状部材と応力付与部材との軟化温度差がクラッドと応力付与部材との軟化温度差よりも小さくなることにより、気泡が発生しにくい構造となる。
【００５０】
また、管状部材がその表面側から中心側に向かってクラッドの下限となる軟化温度から応力付与部材の上限となる軟化温度まで連続的に変化する径方向軟化温度分布を有する場合は、母材の内部でクラッドから応力付与部材までほぼ連続的に変化するような軟化温度分布が形成されることで、気泡が発生しにくい構造となる。特に、クラッドと応力付与部材との接合界面で軟化温度が等しくなっていれば、クラッドと応力付与部材との接合界面に気泡が極めて発生しにくい構造となる。
【００５１】
上記の応力付与部材や管状部材の屈折率がクラッドの屈折率以下であると、光ファイバ内で光を伝搬させた場合にも、コアから応力付与部材または管状部材への光パワーの移動は生じにくい。
【００５２】
【実施例】
以下、添付図面を参照しながら本発明の実施例を詳細に説明する。なお、図面の説明において同一の要素には同一の符号を付し、重複する説明を省略する。また、図面の寸法比率は説明のものと必ずしも一致していない。
【００５３】
実施例１
図１は、本実施例の光ファイバ母材１００の構造を示す斜視図である。この光ファイバ母材１００は、偏波保持光ファイバの作製用のもので、コア１０、クラッド２０、管状部材３０及び３１、並びに応力付与部材４０及び４１から構成されている。
【００５４】
コア１０は円柱状のガラスロッドであり、クラッド２０はこのコア１０の側面を包囲する円管状のガラスチューブである。コア１０とクラッド２０の中心軸は一致している。
【００５５】
コア１０及びクラッド２０は、ともに石英（ＳｉＯ2 ）系ガラスから構成されている。クラッド２０はほぼ純粋な石英ガラスから構成されているが、コア１０を構成する石英ガラスには屈折率上昇材である酸化ゲルマニウム（ＧｅＯ2 ）が添加されており、これによりコアの屈折率はクラッドよりも高くなっている。
【００５６】
管状部材３０及び３１は石英系ガラス製の円管であり、自らの軸方向とクラッド２０の軸方向とを一致させながらクラッド２０内に埋設されている。この管状部材３０及び３１は、コア１０の中心軸に対して互いに対称な位置に配置されている。
【００５７】
応力付与部材４０及び４１は、石英系ガラスからなる円柱であり管状部材３０及び３１の中空部にそれぞれ挿入されている。この応力付与部材４０及び４１は、クラッド２０よりも大きな熱膨張係数を有している。周知の通り、光ファイバ母材１００を線引した後に光ファイバが冷却する過程において応力付与部材４０及び４１は強く収縮するので、これによりコアに大きな応力が付与される。この結果、線引により得られる光ファイバは偏波保持光ファイバとなる。
【００５８】
図２〜図６は、光ファイバ母材１００の製造方法を示す工程図である。以下、これらの図を参照しながら、光ファイバ母材１００の製造方法を説明する。
【００５９】
まず、コア１０及びこのコアを密着して覆うクラッド２０から構成されるガラス円柱１１０を用意する（図２）。このガラス円柱１１０の外径は２５ｍｍであり、コア１０の外径は１．３５ｍｍである。ガラス円柱１１０は、通常の光ファイバ母材と同様の方法、すなわち公知のＶＡＤ（気相軸付け）法、ＯＶＤ（外付け）法、ＭＣＶＤ（内付け）法、ロッドインチューブ法などを用いて製造することができる。本実施例では、ＭＣＶＤ法を用いてこれを製造する。
【００６０】
次いで、図示しない超音波開孔機を用いてガラス円柱１１０のクラッド２０にガラス円柱１１０の軸方向に沿って延びる直径８ｍｍの貫通孔５０及び５１を形成する（図３）。貫通孔５０及び５１はコア１０と平行であり、コア１０の中心軸に対して対称な位置に形成される。貫通孔５０及び５１の中心軸とコア１０の中心軸との距離は、１１．６ｍｍである。以下では、貫通孔５０及び５１が設けられたガラス円柱１１０を、孔開き母材１１１と呼ぶことにする。
【００６１】
次に、貫通孔５０及び５１の表面上に厚さ０．５ｍｍのガラス層、すなわち上記の管状部材３０及び３１を形成する（図４）。この管状部材３０及び３１は、ＢＣｌ3 （三塩化ホウ素）を毎分１５０ｍｌ、ＳｉＣｌ4 （四塩化珪素）を毎分４００ｍｌ、Ｏ2 （酸素）を毎分１ｌの流量で貫通孔５０及び５１の内部に導入しながら、孔開き母材１１１の外面に酸水素炎バーナの火炎をあてて貫通孔５０及び５１の内部を加熱することで形成することができる。酸水素炎バーナの火炎は、バーナ内に燃料ガスとしてＨ2 （水素）を毎分７０ｌ、Ｏ2 （酸素）を毎分３０ｌずつ導入して形成したものである。管状部材３０及び３１を形成した後には、管状部材３０及び３１の内部に貫通孔５２及び５３が残る。なお、図４では、管状部材３０及び３１が形成された後の孔開き母材を符号１１２で示してある。
【００６２】
次に、予め用意しておいた応力付与部材４０及び４１を貫通孔５２及び５３に挿入し、固定する（図５及び図６）。この応力付与部材４０及び４１は、公知のＶＡＤ法により作製することができる。具体的には、まず、バーナ内に燃料ガスとしてＨ2 を毎分５０ｌ、Ｏ2 を毎分１２ｌずつ導入して酸水素炎を形成し、この酸水素炎中にＳｉＣｌ4 を毎分４００ｍｌ、ＢＣｌ3 を毎分３００ｍｌずつ導入してガラス微粒子（ＳｉＯ2 ＋Ｂ2 Ｏ3 ）を生成する。次いで、棒状の出発材を回転させながらバーナからのガラス微粒子を吹きつけると、出発材の表面上にガラス微粒子がほぼ均一の厚さに堆積する。出発材を引き上げながらガラス微粒子を吹きつけることで、軸方向にガラス微粒子を成長させることができる。これにより、出発材の表面全体にガラス微粒子が均一に堆積するので柱状のガラス微粒子体が得られる。次に、このガラス微粒子体を焼結炉に入れ、焼結炉内のヘリウム雰囲気中にＢＦ3 を導入しながら約１２００℃の温度で６０分間加熱し、次いで、約１４００℃の温度で６０分間加熱した後、徐冷する。これにより、ガラス微粒子が透明ガラス化して、柱状のガラス体（ＳｉＯ2 −Ｂ2 Ｏ3 ）が得られる。このガラス体を外径が約６．８ｍｍになるように加熱延伸すると、本実施例の応力付与部材４０及び４１が得られる。二つの応力付与部材の組成は、ほぼ同一である。なお、応力付与部材４０及び４１は、貫通孔５２及び５３よりも短くしておく。
【００６３】
応力付与部材４０及び４１に添加されたＢ2 Ｏ3 はＳｉＯ2 ガラスの熱膨張係数を高める作用を有しているため、応力付与部材４０及び４１はクラッド２０よりも大きな熱膨張係数を有している。
【００６４】
上記のようにして得られた応力付与部材４０及び４１は、孔開き母材１１２の貫通孔５２及び５３に挿入され孔の内部に固定される。以下では、図５及び図６を参照しながらこの固定方法について説明する。なお、この固定方法は、特開平４−９７９２０号公報にも開示されている。
【００６５】
この固定方法を実行するために、まず、外径約６．８ｍｍの石英ガラス棒６０ａ、６０ｂ、６１ａ及び６１ｂ、並びに石英ガラス管７０を用意する。ガラス管７０は、図５に示されるように、内径の小さなガラスリング７０ｂの両端にこれよりも内径の大きいガラス管７０ａ、７０ｃが取り付けられたものである。
【００６６】
応力付与部材４０及び４１を固定するためには、まず、ガラス管７０を孔開き母材１１２の一端面に溶着する。次いで、孔開き母材１１２の他端側から貫通孔５２にガラス棒６０ａ、応力付与部材４０、ガラス棒６０ｂをこの順で挿入する。貫通孔５３についても同様に、ガラス棒６１ａ、応力付与部材４１、ガラス棒６１ｂの順に挿入する。ガラス棒６０ａ及び６１ａの先端は、それぞれ孔開き母材１１２の端面から突出し、その端面がガラスリング７０ｂの底面に押し付けられる。これにより、ガラス棒６０ａ及び６１ａは固定される。ガラス棒６０ｂ及び６１ｂとクラッド２０とは孔開き母材１１２の端部を加熱延伸加工することで一体化される。これによって、孔開き母材１１２の一端部が封止される（図６）。
【００６７】
ガラス管７０には真空コネクタ（図示せず）を接続できるようになっているので、これを利用して貫通孔５２及び５３の内部を減圧する。この後、ガラス管７０の先端を加熱処理によりコラプス（中実化）して封止する。これにより、応力付与部材４０及び４１が孔開き母材１１２に固定される。なお、応力付与部材４０及び４１の固定方法が上記方法に限られないことは言うまでもない。
【００６８】
次に、上記のようにして応力付与部材４０及び４１が固定された孔開き母材１１２に対して、加熱温度１９００度、加熱時間１２０分の加熱処理を施し、その後、徐冷する。これにより、クラッド２０、管状部材３０及び３１、並びに応力付与部材４０及び４１を構成するガラスが溶融して一体化する。こうして、光ファイバ母材が完成する。
【００６９】
上記のようにして得られた光ファイバ母材のうち実際に光ファイバの作製に利用できるのは応力付与部材４０及び４１を含む部分であり、したがって上記の方法は実質的に図１の光ファイバ用母材１００を製造するものである。
【００７０】
図７は、光ファイバ母材１００について径方向の屈折率分布と軟化温度分布を示す図である。この図では、光ファイバ母材１００の右半分の分布しか示されていないが、左半分の分布も右半分のものと同様である。この図に示されるように、管状部材３０及び３１は、クラッド２０の軟化温度と応力付与部材４０及び４１の軟化温度とを平均した軟化温度を有している。このような軟化温度を持たせるには、上述した管状部材３０及び３１の形成工程においてＳｉＯ2 の軟化温度低下材であるＢ2 Ｏ3 の添加量を調節すると良い。
【００７１】
応力付与部材を含む光ファイバ母材を製造するには、加熱処理を施して応力付与部材とクラッドを一体化する必要がある。二つの物体を一体化する際は、一般に、両者の接合部分の物性が互いに近いことが望ましい。特に、加熱処理により一体化する場合は両者の軟化温度が近いことが望ましい。接合部分両者の軟化温度に差がある場合には、どちらか一方のみが先に軟化し、他方の表面が加熱による効果で十分に平滑化される前に一体化してしまうため、接合界面に気泡が発生しやすくなる。
【００７２】
本実施例の光ファイバ母材１００は、クラッド２０と応力付与部材４０、４１との間に両者の平均の軟化温度を有する管状部材３０、３１が存在しているので、クラッド２０と管状部材３０、３１との軟化温度差、並びに管状部材３０、３１と応力付与部材４０、４１との軟化温度差は、クラッド２０と応力付与部材４０、４１との軟化温度差よりも小さくなっている。このため、製造時に加熱処理によってクラッド２０と応力付与部材４０及び４１とを一体化する際にも、表面平滑化効果が十分に作用する。この結果、クラッド２０と管状部材３０、３１との接合界面や管状部材３０、３１と応力付与部材４０、４１との接合界面における気泡発生が防止あるいは低減されることになる。従って、光ファイバ母材１００を線引して光ファイバを製造する際にも、光ファイバの断裂は生じにくく、また、得られる光ファイバは良好な伝送特性や偏波特性を有している。
【００７３】
また、光ファイバ内では光は屈折率の高い部分を伝搬することから、一般的にコア近傍にクラッドより屈折率の高い部分が存在するとコアからその部分への光パワーの移動が起こり、結果的に伝送損失が増加する。この点に鑑み、本実施例では、管状部材３０及び３１、並びに応力付与部材４０及び４１の屈折率をクラッドよりも低く設定している（図７）。光ファイバは母材と同様の屈折率分布を有することから、このように屈折率を設定することで、光ファイバ母材を線引して得られる光ファイバ内での光パワーの移動を防ぐことができ、光ファイバの伝送損失の増加を抑えることができる。
【００７４】
本実施例では、上述のようにして製造された光ファイバ母材１００を通常の線引装置を用いて線引し、偏波保持光ファイバを製造する。具体的には、まず、光ファイバ母材１００を加熱炉にて約２０００度に加熱し、線速毎分１００ｍにて外径が１２５μｍになるように線引する。線引された光ファイバには、２度にわたってＵＶ樹脂のコーティングが施される。被覆後の光ファイバの外径は約２５０μｍになる。このようにして、長さ１０ｋｍの偏波保持光ファイバを製造する。
【００７５】
上記のようにして製造した偏波保持光ファイバについて偏波特性の一つであるクロストーク特性を波長１．３μｍにて測定したところ、−２４ｄＢと非常に良好な結果を得た。
【００７６】
本実施例との比較のため、本発明者らは、管状部材３０及び３１を形成せずに応力付与部材を挿入した光ファイバ母材を線引して１０ｋｍの偏波保持光ファイバを製造した。光ファイバ母材の製造方法は、管状部材３０及び３１を形成しない点を除いて本実施例と同様である。この偏波保持光ファイバについてクロストーク特性を測定したところ、−８ｄＢと本実施例よりも劣っていた。この偏波保持光ファイバを詳細に調べた結果、光ファイバ全長で３箇所にわたりガラス内に気泡が発見された。この気泡は、応力付与部材とクラッドとの界面に発生していた。
【００７７】
なお、本実施例では、クラッド２０、管状部材３０及び３１、並びに応力付与部材４０及び４１を加熱一体化して光ファイバ母材１００を完成させてから線引を行って光ファイバを製造したが、加熱一体化と線引を同時に行うことにより光ファイバを製造することも可能である。
【００７８】
例えば、上記の方法によって応力付与部材４０及び４１を孔開き母材１１２に固定した後、応力付与部材４０及び４１並びに孔開き母材１１２の複合体を加熱炉にて約２０００度に加熱し、応力付与部材４０及び４１とクラッド２０と管状部材３０及び３１とを一体化しながら、線速毎分１００ｍで外径が１２５μｍになるように線引しても光ファイバを製造することができる。この場合は、母材の状態を経ずに光ファイバが製造されることになる。
【００７９】
この場合も、管状部材３０及び３１の存在により加熱一体化の際に表面平滑化効果が十分に作用するため、クラッド２０と管状部材３０、３１との接合界面や管状部材３０、３１と応力付与部材４０、４１との接合界面における気泡発生が防止あるいは低減される。従って、上記の方法によっても、光ファイバの断裂を防止しながら、良好な特性の偏波保持光ファイバを製造することができる。
【００８０】
実施例２
本実施例では、実施例１と異なる方法で光ファイバ母材１００（図１）を製造する。図８は、本実施例の母材製造方法を示す図である。本実施例では、まず、ＶＡＤ法によってガラス円柱１１０（図２と同様のもの）を製造し、超音波開孔機によりクラッド２０に軸方向に沿って延びる貫通孔５０及び５１を形成して、孔開き母材１１１を作製する。貫通孔５０及び５１の直径は、８ｍｍである。以上の工程は実施例１とほぼ同様であるが、本実施例ではコアの組成はＳｉＯ2 であり、クラッドの組成はＳｉＯ2 −Ｆである。ＦはＳｉＯ2 の屈折率低下材であり、これがクラッドに添加されていることによりコアの屈折率はクラッドよりも高くなっている。
【００８１】
次に、本実施例では、ＶＡＤ法を用いて実施例１と同一の応力付与部材４０及び４１（外径１８ｍｍ）を作製した後、この応力付与部材４０及び４１の表面上に管状部材３０及び３１を堆積形成する。この堆積形成は、公知のＯＶＤ（外付け）法を用いて行うことができる。具体的には、酸水素炎バーナ内にＳｉＣｌ4 （四塩化珪素）を毎分３００ｍｌ、Ｈ2 （水素）を毎分５０ｌ、Ｏ2 （酸素）を毎分１２ｌずつ導入し、応力付与部材４０及び４１を自らの軸を回転軸として回転させながらバーナの火炎をあて、バーナを軸方向に沿って応力付与部材４０及び４１に対し相対的に移動させていく。これにより、ＳｉＯ2 のガラス微粒子が応力付与部材４０及び４１の側面上にほぼ均一な厚さで堆積する。
【００８２】
次いで、ガラス微粒子が堆積した応力付与部材４０及び４１を加熱炉に入れ、加熱炉内のヘリウム雰囲気中にＢＦ3 及びＳｉＦ4 を導入しながら約１２００℃の温度で３０分間加熱し、続いて、約１４００℃の温度で３０分間加熱した後、徐冷する。この作業により、ＳｉＯ2 のガラス微粒子にＢ及びＦが添加されるとともに、ガラス微粒子が透明ガラス化し、応力付与部材４０、４１と一体化する。
【００８３】
本実施例では、上記の方法により、応力付与部材４０及び４１の表面に厚さ約２．５ｍｍのガラス層（ＳｉＯ2 −Ｂ2 Ｏ3 −Ｆ）を形成する。このガラス層が、本実施例の管状部材３０、３１である。なお、応力付与部材４０、４１の表面に管状部材３０、３１を形成する方法としては、管状部材３０、３１の材料を用いて予め作製したガラスパイプの内面に、応力付与部材となるべきガラス層をＭＣＶＤ法により形成し、その後ガラスパイプをコラプス（中実化）する方法を採ることもできる。
【００８４】
この後、管状部材３０、３１と応力付与部材４０、４１からなる二つの柱状体を、それぞれ外径が約７．７ｍｍになるように加熱延伸する。こうして得られた柱状体８０、８１を、図８のように孔開き母材１１１の貫通孔５０、５１にそれぞれ挿入した後、実施例１と同様にして固定する。この後、加熱処理を行って柱状体８０及び８１とクラッド２０とを一体化すると、光ファイバ母材１００（図１）が完成する。
【００８５】
本実施例により製造された光ファイバ母材も、図７に示される屈折率分布および軟化温度分布を有している。なお、軟化温度の調節は、上述した管状部材３０及び３１の形成工程においてＳｉＯ2 の軟化温度変化材であるＢ2 Ｏ3 及びＦの添加量を調節することで行うことができる。ここで、Ｂ2 Ｏ3 はＳｉＯ2 の軟化温度を低下させる作用を有しており、ＦはＳｉＯ2 の軟化温度を低下させる作用を有している。
【００８６】
本発明者らが上記のようにして製造した光ファイバ母材を実施例１と同様に線引して長さ１０ｋｍの偏波保持光ファイバを製造し、この光ファイバについて偏波特性の一つであるクロストーク特性を波長１．３μｍにて測定したところ、−２６ｄＢと非常に良好な結果を得た。
【００８７】
なお、上記の方法に代えて、柱状体８０及び８１とクラッド２０の加熱一体化を線引と同時に行うことにより、母材の状態を経ずに光ファイバを製造することが可能なことは、実施例１と同様である。
【００８８】
実施例３
本実施例も、実施例１及び２と異なる方法で光ファイバ母材１００（図１）を製造するものである。図９は、本実施例の母材製造方法を示す図である。本実施例でも、まず、実施例２と同様にして孔開き母材１１１（図３と同様のもの）を作製する。本実施例の場合、貫通孔５０及び５１の直径は９ｍｍである。次いで、実施例１と同様の方法により、外径約７．８ｍｍの応力付与部材４０及び４１を作製する。
【００８９】
次に、本実施例では、管状部材３０及び３１を孔開き母材１１１や応力付与部材４０、４１と独立して形成する。このためには、まず、ＶＡＤ法を用いて柱状のガラス体を作製する。具体的には、酸水素炎バーナにＨ2 （水素）を毎分５０ｌ、Ｏ2 （酸素）を毎分１２ｌずつ導入して形成した酸水素炎中に、ＳｉＣｌ4 （四塩化珪素）を毎分３００ｍｌの流量で導入し、火炎中で生成されるＳｉＯ2 のガラス微粒子を出発材上に堆積、成長させて棒状のガラス微粒子体を形成する。このガラス微粒子体を焼結炉に入れ、焼結炉内のヘリウム雰囲気中にＳｉＦ4 を導入しながら約１２００℃の温度で３０分間加熱し、次いで、約１４００℃の温度で６０分間加熱した後、徐冷する。これにより、ＳｉＯ2 のガラス微粒子はＦが添加された後、透明ガラス化する。こうして、ＳｉＯ2 −Ｆのガラス柱状体が得られる。このガラス柱状体を、外径が２２ｍｍになるように加熱延伸した後、超音波開孔機を用いて中央に内径２０ｍｍの貫通孔を形成し、再び加熱延伸して、外径８．８ｍｍ、内径８ｍｍのガラス管を形成する。これが、本実施例の管状部材３０及び３１である。
【００９０】
次に、孔開き母材１１１の一端側から貫通孔５０に管状部材３０、応力付与部材４０をこの順で挿入する。貫通孔５１についても同様に、管状部材３１、応力付与部材４１をこの順で挿入する。応力付与部材４０、４１は、それぞれ管状部材３０、３１の中空部に挿入される。管状部材３０及び３１、並びに応力付与部材４０及び４１は実施例１と同様の方法により固定される。この後、加熱処理を施して、クラッド２０と、管状部材３０及び３１と、応力付与部材４０及び４１とを一体化すれば、光ファイバ母材１００（図１）が完成する。
【００９１】
本実施例により製造された光ファイバ母材も、図７に示される屈折率分布および軟化温度分布を有している。なお、軟化温度の調節は、上述した管状部材３０及び３１の形成工程においてＳｉＯ2 の軟化温度変化材であるＦの添加量を調節することで行うことができる。
【００９２】
本発明者らが上記のようにして製造した光ファイバ母材を線引して長さ９．７ｋｍの偏波保持光ファイバを製造し、この光ファイバについて偏波特性の一つであるクロストーク特性を波長１．３μｍにて測定したところ、−２６ｄＢと非常に良好な結果を得た。
【００９３】
なお、本実施例の製造工程において、管状部材３０及び３１の内面や外面に対して研磨等の機械的平滑化または火炎放射等による加熱平滑化を行い、或いはこれらの面を洗浄して付着している不純物を除去しておくと、線引時の加熱一体化による気泡の発生を一層効果的に防止することができる。
【００９４】
また、上記の方法に代えて、クラッド２０と管状部材３０及び３１と応力付与部材４０及び４１との加熱一体化を線引と同時に行うことにより、母材の状態を経ずに光ファイバを製造することが可能なことは、上記実施例と同様である。
【００９５】
参考例
本参考例では、図１の光ファイバ母材１００とは異なる光ファイバ母材を製造する。最初に、本参考例の光ファイバ母材の製造方法を詳細に説明する。図１０は、本参考例の母材製造方法を示す図である。
【００９６】
本参考例では、まず、公知のＭＣＶＤ法を用いてガラス円柱１１０（図２と同様のもの）を作製し、超音波開孔機を用いてクラッド２０に軸方向に沿って延びる貫通孔５０及び５１を形成して、孔開き母材１１１を作製する。貫通孔５０及び５１の直径は８ｍｍである。
【００９７】
次に、ＶＡＤ法を用いて応力付与部材４２及び４３を作製する。具体的には、酸水素炎バーナにＨ2 を毎分５０ｌ、Ｏ2 を毎分１２ｌずつ導入して形成した酸水素炎中に、ＳｉＣｌ4 を毎分３００ｍｌ、ＢＣｌ3 （三塩化ほう素）を毎分３００ｍｌずつ導入し、火炎中で生成されるガラス微粒子（ＳｉＯ2 −Ｂ2 Ｏ3 ）を出発材上に堆積、成長させて柱状のガラス微粒子体を形成する。このガラス微粒子体にはＳｉＯ2 の熱膨張係数を高めるＢ2 Ｏ3 が添加されており、この結果、ガラス微粒子体は孔開き母材１１１のクラッド２０よりも高い熱膨張係数を有するようになる。また、Ｂ2 Ｏ3 はＳｉＯ2 の軟化温度低下材なので、このガラス微粒子体はクラッド２０よりも低い軟化温度を有している。
【００９８】
次いで、このガラス微粒子体を焼結炉に入れ、焼結炉内のヘリウム雰囲気中でＢＦ3 を導入しながら約１１００℃の温度で６０分間加熱し、続いて、焼結炉内をヘリウムのみの雰囲気としてから、約１４００℃の温度で６０分間加熱した後、徐冷する。これにより、ガラス微粒子体の表面からＢが添加され、ガラス微粒子体の内部でＢの酸化物（Ｂ2 Ｏ3 ）が形成される。
【００９９】
焼結炉内をヘリウムのみの雰囲気とすると、焼結炉内でガラス微粒子体に添加されるＢ２Ｏ３は、ガラス微粒子体の外表面から雰囲気中へと拡散する。拡散される量はガラス微粒子体の表面側ほど多い。拡散と同時に透明ガラス化が進行するので、ガラス体の中央部にはほぼ均一な濃度でＢ２Ｏ３が添加されるが、表面から中心に向かって外径の約１／４の厚さを有する表層部では添加濃度が徐々に減少し、表面近傍では殆どＢ２Ｏ３が添加されないことになる。このようにして得られたガラス体を外径約７．７ｍｍに加熱延伸すると、本参考例の応力付与部材４２及び４３（ＳｉＯ２−Ｂ２Ｏ３）が得られる。
【０１００】
この応力付与部材４２及び４３は、その表層部において軟化温度が部材の表面側から中心側に向かってクラッド２０の軟化温度から中央部４２ａ及び４３ａの軟化温度まで連続的に変化する。すなわち、応力付与部材４２及び４３は、軟化温度が表面側から中心側に向かってクラッド２０の軟化温度から中央部４２ａ及び４３ａの軟化温度まで連続的に変化するような軟化温度分布を有する管状の部材をその表層部４２ｂ及び４３ｂにおいて備えている。
【０１０１】
こうして得られた応力付与部材４２及び４３を、図１０のように孔開き母材１１１の貫通孔５０、５１にそれぞれ挿入、固定した後、加熱処理を施してクラッド２０と応力付与部材４２及び４３を一体化すると、本参考例の光ファイバ母材が完成する。図示はしないが、応力付与部材４２及び４３の固定は、実施例１と同様の方法により行っている。
【０１０２】
本参考例により製造された光ファイバ母材は、図１１に示されるような屈折率分布および軟化温度分布を有している。本参考例の光ファイバ母材は、孔開き母材１１１の貫通孔５０及び５１に挿入される応力付与部材の軟化温度分布に特徴がある。すなわち、図１１に示されるように、応力付与部材４２及び４３の表層部４２ｂ及び４３ｂは、部材の表面側から中心側に向かってクラッド２０の軟化温度から中央部４２ａ及び４３ａの軟化温度まで連続的に変化するような軟化温度分布を有している。
【０１０３】
本参考例の光ファイバ母材では、応力付与部材がこのような表層部４２ｂ及び４３ｂを有しているために、クラッド２０と応力付与部材４２、４３との軟化温度差が緩和されている。特に、クラッド２０と応力付与部材４２、４３との接合界面では軟化温度がほぼ等しいので、加熱処理によりクラッド２０と応力付与部材４２、４３とを一体化する際にも表面平滑化効果が十分に作用し、クラッド２０と応力付与部材４２、４３との接合界面における気泡発生が防止あるいは大幅に低減される。
【０１０４】
また、本参考例の光ファイバ母材でも、応力付与部材４２及び４３の屈折率はクラッドよりも低く設定されている（図１１）。これにより、コアから応力付与部材４２及び４３への光パワーの移動が防止されるので、本参考例の光ファイバ母材を線引して得られる光ファイバの伝送損失の増加を抑えることができる。
【０１０５】
本参考例の光ファイバ母材を加熱炉にて約２０００℃に加熱し、応力付与部材４２及び４３と孔開き母材１１１とを一体化しながら線速毎分１００ｍにて線引して外径１２５μｍの光ファイバを製造し、さらにＵＶ樹脂で被覆して外径約２５０μｍ、長９．５ｋｍの偏波保持光ファイバを製造した。この光ファイバについて偏波特性の一つであるクロストーク特性を、波長１．３μｍにて測定したところ、−２５ｄＢと非常に良好な結果を得た。
【０１０６】
なお、上記の方法に代えて、応力付与部材４２及び４３とクラッド２０の加熱一体化を線引と同時に行うことにより、母材の状態を経ずに光ファイバを製造することが可能なことは、上記実施例と同様である。
【０１０７】
実施例５
本実施例では、図１１に示される屈折率分布および軟化温度分布を有する光ファイバ母材を実施例１に類似した方法で製造する。具体的には、実施例１と同様の方法により孔開き母材１１１を作製した後、貫通孔５０及び５１の表面上に厚さ０．５ｍｍの管状部材３０及び３１を形成する。ここで、管状部材３０及び３１の形成方法は、実施例１と若干異なっている。すなわち、本実施例の管状部材３０及び３１は、ＳｉＣｌ４を毎分４００ｍｌ、Ｏ２を毎分１ｌの流量で貫通孔５０及び５１の内部に導入すると共に、ＢＣｌ３の流量を制御しながら、孔開き母材１１１の外面に酸水素炎バーナの火炎をあてて貫通孔５０及び５１の内部を加熱することで形成する。ＢＣｌ３は、加熱の当初は全く導入せず、その後、徐々に流量を増加させて、最終的に毎分１５０ｍｌの流量で導入する。これにより、参考例の表層部４２ｂ、４３ｂと同様の屈折率分布と軟化温度分布を有する管状部材３０、３１が形成される。この後、実施例１と同様の製造工程を実行することで、図１１の屈折率分布および軟化温度分布を有する光ファイバ母材が製造される。
【０１０８】
実施例６
本実施例では、図１１に示される屈折率分布および軟化温度分布を有する光ファイバ母材を実施例３に類似の方法で製造する。具体的には、実施例３と同様にして孔開き母材１１１及び応力付与部材４０及び４１を作製すると共に、管状部材３０及び３１を、孔開き母材１１１や応力付与部材４０、４１と独立して形成する。ここで、管状部材３０及び３１の形成方法は、実施例３と異なっている。
【０１０９】
すなわち、本実施例では、実施例３と同様にして棒状のガラス微粒子体を形成した後、これを焼結炉に入れ、焼結炉内のヘリウム雰囲気中にＳｉＦ4 を導入しながら約１２００℃の温度で６０分間加熱し、続いて、焼結炉内をヘリウムのみの雰囲気としてから、約１４００℃の温度で６０分間加熱した後、徐冷する。焼結炉内をヘリウムのみの雰囲気とすると、焼結炉内でガラス微粒子体に添加されるＦは、ガラス微粒子体の外表面から雰囲気中へと拡散する。拡散される量はガラス微粒子体の表面側ほど多い。拡散と同時に透明ガラス化が進行するので、ガラス体の中心側から表面側に向かってＦ濃度が連続的に変化したＳｉＯ2 のガラス柱状体が得られることになる。
【０１１０】
このガラス柱状体を、外径が２２ｍｍになるように加熱延伸した後、超音波開孔機を用いて中央に内径２０ｍｍの貫通孔を形成し、再び加熱延伸して、外径８．８ｍｍ、内径８ｍｍのガラス管を形成する。これにより、参考例の表層部４２ｂ、４３ｂと同様の屈折率分布と軟化温度分布を有する管状部材３０及び３１が形成される。この後、実施例３と同様の製造工程を実行することで、図１１の屈折率分布および軟化温度分布を有する光ファイバ母材が製造される。
【０１１１】
以上、本発明の実施例を詳細に説明したが、本発明は上記実施例に限定されるものではなく、様々な変形が可能である。例えば、コア及びクラッドからなるガラス円柱、ガラスパイプ或いは応力付与部材の製造については、ＶＡＤ法、ＯＶＤ法、ＭＣＶＤ法等、一般に知られている製造方法のいかなるものを用いても良い。貫通孔の表面或いは応力付与部材の表面にガラス層を形成する場合も、同様である。応力付与部材を挿入するための貫通孔の形成方法も、公知技術から種々の方法を選択することができる。同様に、貫通孔及び応力付与部材の断面形状も、偏波保持光ファイバに関する公知技術から任意に選択することができる。
【０１１２】
また、貫通孔の表面或いは応力付与部材の表面にガラス層を形成した後、ガラス層の表面に対して研磨等の機械的平滑化または火炎放射等による加熱平滑化を行い、或いはこれらの面を洗浄して付着している不純物を除去しておくと、加熱一体化の際の気泡発生をより効果的に防止することができる。
【０１１３】
また、石英ガラスの軟化温度の調節に用いる軟化温度変化材としては、以下のようなものがある。
【０１１４】
第１グループ（軟化温度、屈折率とも低下させるもの）
…Ｂ、Ｆ
第２グループ（軟化温度を低下させ、屈折率を上昇させるもの）
…Ｇｅ、Ｐ
第３グループ（軟化温度、屈折率とも上昇させるもの）
…Ａｌ、Ｔｉ、Ｚｒ
これらの軟化温度変化材は、▲１▼第１グループから一つ以上を選択して添加する、▲２▼第１グループから一つ以上を選択し、かつ、第２グループから一つ以上を選択して添加する、▲３▼第１グループから一つ以上を選択し、かつ、第３グループから一つ以上を選択して添加する、▲４▼第１グループから一つ以上、第２グループから一つ以上、第３グループから一つ以上をそれぞれ選択して添加する、のいずれかの方法により使用すると良い。
【０１１５】
【発明の効果】
以上、詳細に説明した通り、本発明の光ファイバ母材は、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい構造を有しているので、割れが生じにくく、また、この母材を線引することで良好な伝送特性及び偏波特性を示す偏波保持光ファイバを製造することができる。
【０１１６】
本発明の光ファイバ母材のうち応力付与部材或いは管状部材の屈折率がクラッドの屈折率以下であるものによれば、母材を線引して得られる光ファイバにおいてコアから応力付与部材或いは管状部材への光パワーの移動は生じにくいので、伝送損失の少ない偏波保持光ファイバを得ることができる。
【０１１７】
次に、本発明に係る光ファイバ母材の製造方法の第１の態様によれば、応力付与部材及び管状部材を一体化して母材を完成させる際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくいので、偏波保持光ファイバ用の母材を好適に製造することができる。
【０１１８】
また、本発明に係る光ファイバ母材の製造方法の第２の態様によれば、孔開き母材と応力付与部材を一体化して母材を完成させる際にも、クラッドと応力付与部材の接合界面に気泡が発生しにくいので、偏波保持光ファイバ用の母材を好適に製造することができる。
【０１１９】
次に、本発明に係る光ファイバ製造方法の第１の態様によれば、孔開き母材、応力付与部材及び管状部材を一体化しながら線引を行う際にも、クラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくいので、線引中の光ファイバの断裂を防止するとともに、良好な伝送特性及び偏波特性を示す偏波保持光ファイバを得ることができる。
【０１２０】
また、本発明に係る光ファイバの製造方法の第２の態様では、孔開き母材と応力付与部材を一体化しながら線引を行う際にも、クラッドと応力付与部材の接合界面に気泡が発生しにくいので、線引中の光ファイバの断裂を防止するとともに、良好な伝送特性及び偏波特性を示す偏波保持光ファイバを得ることができる。
【０１２１】
次に、本発明の光ファイバは、製造時にクラッドと管状部材との接合界面や管状部材と応力付与部材との接合界面に気泡が発生しにくい構造を有しているので、線引中に断裂することなく製造でき、良好な伝送特性及び偏波特性を有している。
【０１２２】
本発明の光ファイバのうち応力付与部材や管状部材の屈折率がクラッドの屈折率以下であるものは、コアから応力付与部材或いは管状部材への光パワーの移動が生じにくいため、伝送損失が少ないという利点を有している。
【図面の簡単な説明】
【図１】実施例１〜３で製造される光ファイバ母材の構成を示す斜視図である。
【図２】実施例１の母材製造方法を説明するための第１の工程図である。
【図３】実施例１の母材製造方法を説明するための第２の工程図である。
【図４】実施例１の母材製造方法を説明するための第３の工程図である。
【図５】実施例１の母材製造方法を説明するための第４の工程図である。
【図６】実施例１の母材製造方法を説明するための第５の工程図である。
【図７】実施例１〜３で製造される光ファイバ母材について径方向に沿った屈折率分布及び軟化温度分布を示す図である。
【図８】実施例２の母材製造方法を説明するための図である。
【図９】実施例３の母材製造方法を説明するための図である。
【図１０】 参考例の母材製造方法を説明するための図である。
【図１１】 参考例で製造される光ファイバ母材について径方向に沿った屈折率分布及び軟化温度分布を示す図である。
【符号の説明】
１０…コア、２０…クラッド、３０及び３１…管状部材、４０及び４１…応力付与部材、５０〜５３…貫通孔、１００…光ファイバ母材。[0001]
[Industrial application fields]
The present invention relates to an optical fiber preform for manufacturing a polarization maintaining optical fiber and a manufacturing method thereof, and a polarization maintaining optical fiber and a manufacturing method thereof.
[0002]
[Prior art]
As a method for manufacturing a polarization maintaining optical fiber, a method disclosed in Japanese Patent Publication No. 3-7613 has been known. This is because at least one set of through-holes is formed at a symmetric position with respect to the core center of a normal optical fiber preform, and a stress applying member having a thermal expansion coefficient different from that of the cladding is inserted into the through-holes. (1) A method for producing a stress-type polarization-maintaining optical fiber by drawing a clad and a stress-applying member after integration by heat treatment, or (2) drawing at the same time as integration by heating. It is.
[0003]
[Problems to be solved by the invention]
However, usually, the physical properties of the stress applying member and the clad are greatly different from each other, particularly the softening temperature, and therefore, in many cases, bubbles remain at the joint interface between the two during the heat integration. This is because if there is a difference in softening temperature, only one of them will soften, and the other surface will be integrated before it is sufficiently smoothed by heating, so that bubbles are likely to be generated at the joint interface. Because.
[0004]
For this reason, when the clad and the stress applying member are heated and integrated by the above method (1), an optical fiber preform in which bubbles are generated at the interface between the clad and the stress applying member is produced. If bubbles are generated inside the optical fiber preform, it alone causes cracking, and deteriorates the characteristics of the optical fiber obtained by drawing the preform.
[0005]
In addition, when drawing is performed while heating and integrating the cladding and the stress applying member by the above method (2), drawing is performed while bubbles are generated at the interface between the cladding and the stress applying member. The optical fiber is easily broken along the way. Even if the optical fiber is manufactured without tearing, the optical fiber contains bubbles inside, and thus does not have sufficient transmission characteristics and strength.
[0006]
The present invention has been made to solve the above problems, and has an optical fiber preform that has a structure that can be manufactured while preventing the generation of bubbles and that can satisfactorily manufacture a polarization-maintaining optical fiber, and It is an object of the present invention to provide a manufacturing method thereof, an optical fiber manufacturing method in which bubbles are not easily generated, and an optical fiber having a structure that can be manufactured while preventing the generation of bubbles.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an optical fiber preform according to the present invention includes (a) a columnar core and (b) a tubular clad surrounding the core, and the tube wall is axially provided on the tube wall. A through hole is provided at a predetermined interval from the central axis, and has a first thermal expansion coefficient and a first softening temperature in a surface layer portion of the through hole, and (c) is inserted into the through hole. A columnar stress applying member having a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion; and (d) the through hole A tubular member that is inserted and surrounds the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures.
[0008]
The tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, the constant softening temperature is different from both the first and second softening temperatures, and is particularly preferably a softening temperature obtained by averaging the first and second softening temperatures.
[0009]
The tubular member may have a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side.
[0010]
Moreover, the refractive index of a stress provision member and a tubular member is good in it being below the refractive index of a clad.
[0011]
Next, a first aspect of the method for manufacturing an optical fiber preform according to the present invention is as follows: (a) (1) a columnar core and a tubular clad surrounding the core, the tube wall extending along the axial direction. A perforated base material provided with a through hole provided at a predetermined interval from the central axis and having a first thermal expansion coefficient and a first softening temperature at a surface layer portion of the through hole; and (2) A columnar stress applying member to be inserted into the through-hole, having a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion And (b) a tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second, i ) On the surface of the above-mentioned through hole, ii) intermediate between the surface of the stress applying member and the surface of the through hole Or iii) on the surface of the stress-applying member, provided with one or more positions among the perforated matrix, and a second step of integrating the stress applying member and the tubular member.
[0012]
The second step is a step of forming a tubular member on the surface of the through hole, then inserting the stress applying member into the hollow portion of the tubular member, and thereafter integrating the stress applying member and the tubular member. There may be.
[0013]
In the second step, a tubular member is formed on the surface of the stress applying member, and then a columnar body made of the stress applying member and the tubular member is inserted into the through hole of the perforated base material. It may be a step of integrating the body and the perforated base material.
[0014]
In the second step, the tubular member is inserted into the through hole, and the stress applying member is inserted into the hollow portion of the tubular member. Thereafter, the perforated base material, the stress applying member, and the tubular member are integrated. It may be a step of converting.
[0015]
In addition, the integration of the perforated base material, the stress applying member, and the tubular member can be achieved by joining the glasses together by, for example, heat treatment when these members are made of glass.
[0016]
A second aspect of the method for manufacturing an optical fiber preform according to the present invention is as follows: (a) (1) a columnar core and a tubular clad surrounding the core, and a through hole along the axial direction of the tube wall A perforated base material provided with a first thermal expansion coefficient and a first softening temperature in the surface layer portion of the through-hole provided at a predetermined interval from the central axis, and (2) the first thermal expansion A columnar stress applying member having a central portion having a second thermal expansion coefficient different from the coefficient and a second softening temperature different from the first softening temperature in the surface layer portion, wherein the first and second softening temperatures are A first step of preparing a tubular member having a radial direction softening temperature distribution set between the surface layer portion (surface layer portion of the stress applying member) and (b) a perforated mother of the stress applying member A second step of inserting into the through-hole of the material, (c) stress applying member and perforated mother And a third step of integrating.
[0017]
The integration of the perforated base material and the stress applying member can be achieved by bonding the glasses together by, for example, heat treatment when these members are made of glass.
[0018]
In the base material manufacturing method according to the first and second aspects, the tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, the constant softening temperature is different from both the first and second softening temperatures, and is particularly preferably a softening temperature obtained by averaging the first and second softening temperatures.
[0019]
In the first and second aspects, the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. You may do it.
[0020]
Next, a first aspect of the optical fiber manufacturing method according to the present invention is: (a) (1) a columnar core and a tubular clad surrounding the core, and penetrating along the axial direction in the tube wall. A perforated base material provided with a hole having a first thermal expansion coefficient and a first softening temperature in a surface layer portion of the through hole provided at a predetermined interval from the central axis; and (2) the above through hole Prepared is a columnar stress applying member to be inserted into the surface, having a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion And (b) a tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures, i) On the surface of the through-hole, ii) intermediate between the surface of the stress applying member and the surface of the through-hole Iii) a second step provided at one or more positions on the surface of the stress applying member, and (c) heating the composite comprising the perforated base material, the stress imparting member and the tubular member, And a third step of drawing the composite while integrating the material, the stress applying member, and the tubular member.
[0021]
In addition, the integration of the perforated base material, the stress applying member, and the tubular member can be achieved by joining the glasses together by, for example, heat treatment when these members are made of glass.
[0022]
The second step may be a step of forming a tubular member on the surface of the through hole of the perforated base material and then inserting the stress applying member into the hollow portion of the tubular member.
[0023]
The second step may be a step of forming a tubular member on the surface of the stress applying member and then inserting a columnar body made of the stress applying member and the tubular member into the through hole of the perforated base material.
[0024]
The second step may be a step of inserting the tubular member into the through hole and inserting the stress applying member into the hollow portion of the tubular member.
[0025]
A second aspect of the optical fiber manufacturing method according to the present invention is as follows: (a) (1) a columnar core and a tubular clad surrounding the core, and the through-hole along the axial direction is centered on the tube wall. A perforated base material provided with a first thermal expansion coefficient and a first softening temperature in a surface layer portion of the through-hole provided at a predetermined interval from the shaft, and (2) a first thermal expansion coefficient A columnar stress applying member having a central portion having a different second thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion, between the first and second softening temperatures A first step of preparing a tubular member having a radial softening temperature distribution set in the step (a surface layer portion of the stress applying member) and (b) a base material in which the stress applying member is perforated A second step of inserting into the through-hole of the metal, and (c) perforated base material and stress applying portion And heating the composite comprising, while integrating the base material and the stress applying member aperture and a third step of drawing the complex.
[0026]
In the optical fiber manufacturing method according to the first and second aspects, the tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, the constant softening temperature is different from both the first and second softening temperatures, and is particularly preferably a softening temperature obtained by averaging the first and second softening temperatures.
[0027]
In the first and second aspects, the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side. You may have.
[0028]
Next, an optical fiber according to the present invention includes: (a) a columnar core; and (b) a tubular clad surrounding the core, and a through-hole along the axial direction is formed in the tube wall with a central axis and a predetermined axis. And a first thermal expansion coefficient and a first softening temperature at the surface layer of the through hole, and (c) inserted into the through hole and different from the first thermal expansion coefficient. A columnar stress applying member having a second thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion; and (d) a tube which is inserted into the through hole and surrounds the stress applying member. A member having a radial softening temperature distribution set between the first softening temperature and the second softening temperature.
[0029]
The tubular member may have a substantially constant radial softening temperature distribution. Here, the substantially constant radial softening temperature distribution means that the tubular member maintains the softening temperature between the first and second softening temperatures substantially constant from the surface side to the center side. At this time, the constant softening temperature is different from both the first and second softening temperatures, and is particularly preferably a softening temperature obtained by averaging the first and second softening temperatures.
[0030]
The tubular member may have a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side.
[0031]
Moreover, the refractive index of a stress provision member and a tubular member is good in it being below the refractive index of a clad.
[0032]
[Action]
(1) In the optical fiber preform of the present invention, a tubular member having a radial softening temperature distribution set between the first and second softening temperatures exists between the clad and the stress applying member. The softening temperature change between the surface layer portion of the clad and the tubular member, or between the tubular member and the surface layer portion of the stress applying member, is caused between the surface layer portion of the clad and the surface layer portion of the stress applying member when there is no tubular member. It is more relaxed than the softening temperature change. Therefore, the optical fiber preform of the present invention can also be used when the clad and the stress applying member are integrated by heat treatment at the time of manufacture. Has a structure in which bubbles are not easily generated.
[0033]
When the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, the softening temperature difference between the cladding and the tubular member, or the tubular member and the stress applying member Is smaller than the softening temperature difference between the clad and the stress-applying member, so that bubbles are hardly generated.
[0034]
When the tubular member has a radial softening temperature distribution that continuously changes from the softening temperature that is the lower limit of the clad toward the center side from the surface side to the softening temperature that is the upper limit of the stress applying member, the surface layer of the clad Since a softening temperature distribution is formed so as to change almost continuously from the surface portion to the surface layer portion of the stress applying member, a structure in which bubbles are less likely to occur is obtained. In particular, if the softening temperatures are equal at the joint interface between the clad and the stress applying member, a structure in which bubbles are hardly generated at the joint interface is obtained.
[0035]
In addition, when the refractive index of the stress applying member or the tubular member is equal to or lower than the refractive index of the cladding, when light is propagated in the polarization maintaining optical fiber obtained by drawing the optical fiber preform of the present invention, However, the movement of optical power from the core to the stress applying member or the tubular member is less likely to occur.
[0036]
(2) Next, in the first aspect of the optical fiber preform manufacturing method according to the present invention, in the second step, on the surface of the through hole of the perforated base material, the surface of the stress applying member and the surface of the through hole The optical fiber preform of the present invention is manufactured by providing a tubular member at one or more positions on the surface of the stress applying member, or by integrating the perforated preform, the stress applying member, and the tubular member. Is done.
[0037]
In this method, when the tubular member is provided, the softening temperature change between the surface layer portion of the cladding and the tubular member, or the softening temperature change between the tubular member and the surface layer portion of the stress applying member, It is more relaxed than the softening temperature change between the surface layer portion of the clad and the surface layer portion of the stress applying member. For this reason, even when the base material is completed by integrating the perforated base material, the stress applying member and the tubular member, bubbles are generated at the joining interface between the clad and the tubular member and the joining interface between the tubular member and the stress applying member. Hard to do.
[0038]
Next, in the second aspect of the method for manufacturing an optical fiber preform according to the present invention, a stress applying member provided with a tubular member having a radial direction softening temperature distribution between the first and second softening temperatures in the surface layer portion. Is inserted into the through hole of the perforated base material, and then the optical fiber base material of the present invention is manufactured by integrating the stress applying member and the perforated base material.
[0039]
In this method, since the tubular member described above exists in the surface layer portion of the stress applying member, the surface layer portion of the clad and the central portion of the stress applying member (the surface layer of the stress applying member when there is no tubular member) Softening temperature change between the surface layer portion of the clad and the surface layer portion of the stress applying member when there is no tubular member. For this reason, even when the perforated base material and the stress applying member are integrated to complete the base material, bubbles are hardly generated at the joint interface between the clad and the stress applying member.
[0040]
In the base material manufacturing method according to the first and second aspects, the cladding and the tubular member have a substantially constant radial softening temperature distribution set between the first and second softening temperatures. Since the difference in softening temperature between the pipe member and the stress applying member becomes smaller than the softening temperature difference between the clad and the stress applying member, bubbles are hardly generated.
[0041]
Also, when the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side, from the cladding to the stress applying member By forming a softening temperature distribution that changes substantially continuously, bubbles are less likely to be generated.
[0042]
(3) Next, in the first aspect of the optical fiber manufacturing method according to the present invention, a tubular member having a radial softening temperature distribution set between the first and second softening temperatures is used as a clad and a stress applying member. Then, the optical fiber is manufactured by performing drawing while integrating the perforated base material, the stress applying member and the tubular member. The obtained optical fiber becomes a polarization maintaining optical fiber by the action of stress applied to the core by the stress applying member.
[0043]
In this method, when the tubular member is interposed, the softening temperature change between the surface layer portion of the clad and the tubular member or the softening temperature change between the tubular member and the surface layer portion of the stress applying member is not present in the tubular member. This is more relaxed than the softening temperature change between the surface layer portion of the clad and the surface layer portion of the stress applying member. For this reason, even when drawing is performed while integrating the perforated base material, the stress applying member, and the tubular member, bubbles are generated at the joining interface between the cladding and the tubular member and the joining interface between the tubular member and the stress applying member. Hateful.
[0044]
Next, in the second aspect of the method for manufacturing an optical fiber according to the present invention, a stress applying member provided with a tubular member having a radial softening temperature distribution between the first and second softening temperatures in the surface layer portion is perforated. After being inserted into the through hole of the open base material, the optical fiber is manufactured by drawing while integrating the stress applying member and the open base material. The obtained optical fiber becomes a polarization maintaining optical fiber by the action of stress applied to the core by the stress applying member.
[0045]
In this method, since the tubular member described above exists in the surface layer portion of the stress applying member, the surface layer portion of the clad and the central portion of the stress applying member (the surface layer of the stress applying member when there is no tubular member) Softening temperature change between the surface layer portion of the clad and the surface layer portion of the stress applying member when there is no tubular member. For this reason, even when drawing is performed while integrating the perforated base material and the stress applying member, bubbles are hardly generated at the bonding interface between the cladding and the stress applying member.
[0046]
In the optical fiber manufacturing method according to the first and second aspects, when the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, the clad Since the softening temperature difference between the tubular member and the tubular member and the softening temperature difference between the tubular member and the stress applying member are smaller than the softening temperature difference between the cladding and the stress applying member, bubbles are less likely to be generated.
[0047]
When the tubular member has a radial softening temperature distribution that continuously changes from the first softening temperature to the second softening temperature from the surface side toward the center side, the cladding is formed inside the base material. By forming a softening temperature distribution that changes substantially continuously from the stress applying member to the stress applying member, bubbles are hardly generated.
[0048]
(4) Next, in the optical fiber of the present invention, a tubular member having a radial softening temperature distribution set between the first and second softening temperatures exists between the clad and the stress applying member. Therefore, the change in the softening temperature between the surface layer portion of the clad and the tubular member, or the change in the softening temperature between the surface portion of the tubular member and the stress applying member causes the surface layer portion of the clad and the stress applying member when there is no tubular member. It is more relaxed than the change in softening temperature between the surface layer portion of each of them. Therefore, the optical fiber of the present invention has a bubble at the bonding interface between the clad and the tubular member or at the bonding interface between the tubular member and the stress applying member even when the clad and the stress applying member are integrated by heat treatment at the time of manufacture. It has a structure that is difficult to generate.
[0049]
When the tubular member has a substantially constant radial softening temperature distribution set between the first and second softening temperatures, the softening temperature difference between the cladding and the tubular member, or the tubular member and the stress applying member Is smaller than the softening temperature difference between the clad and the stress-applying member, so that bubbles are hardly generated.
[0050]
Further, when the tubular member has a radial softening temperature distribution that continuously changes from the softening temperature that is the lower limit of the clad toward the center side from the surface side to the softening temperature that is the upper limit of the stress applying member, By forming a softening temperature distribution that changes almost continuously from the clad to the stress applying member inside, a structure in which bubbles are hardly generated is obtained. In particular, if the softening temperatures are equal at the bonding interface between the cladding and the stress applying member, a structure in which bubbles are hardly generated at the bonding interface between the cladding and the stress applying member is obtained.
[0051]
When the refractive index of the stress applying member or the tubular member is equal to or lower than the refractive index of the cladding, even when light is propagated in the optical fiber, the optical power is transferred from the core to the stress applying member or the tubular member. Hateful.
[0052]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.
[0053]
Example 1
FIG. 1 is a perspective view showing the structure of the optical fiber preform 100 of this embodiment. This optical fiber preform 100 is for producing a polarization-maintaining optical fiber, and is composed of a core 10, a clad 20, tubular members 30 and 31, and stress applying members 40 and 41.
[0054]
The core 10 is a cylindrical glass rod, and the clad 20 is a cylindrical glass tube surrounding the side surface of the core 10. The central axes of the core 10 and the clad 20 coincide.
[0055]
Both the core 10 and the clad 20 are made of quartz (SiO 22) It is composed of glass. The clad 20 is made of substantially pure quartz glass, but the quartz glass constituting the core 10 is made of germanium oxide (GeO) which is a refractive index increasing material.2) So that the refractive index of the core is higher than that of the cladding.
[0056]
The tubular members 30 and 31 are circular tubes made of quartz glass, and are embedded in the clad 20 with their own axial direction coincident with the axial direction of the clad 20. The tubular members 30 and 31 are disposed at positions symmetrical to each other with respect to the central axis of the core 10.
[0057]
The stress applying members 40 and 41 are cylindrical columns made of quartz glass, and are inserted into the hollow portions of the tubular members 30 and 31, respectively. The stress applying members 40 and 41 have a thermal expansion coefficient larger than that of the clad 20. As is well known, since the stress applying members 40 and 41 are strongly contracted in the process of cooling the optical fiber after drawing the optical fiber preform 100, a large stress is applied to the core. As a result, the optical fiber obtained by drawing becomes a polarization maintaining optical fiber.
[0058]
2 to 6 are process diagrams showing a method for manufacturing the optical fiber preform 100. FIG. Hereinafter, a method for manufacturing the optical fiber preform 100 will be described with reference to these drawings.
[0059]
First, a glass cylinder 110 composed of a core 10 and a clad 20 that closely covers and covers the core is prepared (FIG. 2). The glass cylinder 110 has an outer diameter of 25 mm, and the core 10 has an outer diameter of 1.35 mm. The glass cylinder 110 is formed by using a method similar to that of a normal optical fiber preform, that is, a known VAD (vapor phase axis attachment) method, OVD (external attachment) method, MCVD (internal attachment) method, rod-in-tube method, or the like. Can be manufactured. In this embodiment, this is manufactured using the MCVD method.
[0060]
Next, through holes 50 and 51 having a diameter of 8 mm extending in the axial direction of the glass cylinder 110 are formed in the clad 20 of the glass cylinder 110 using an ultrasonic aperture machine (not shown) (FIG. 3). The through holes 50 and 51 are parallel to the core 10 and are formed at symmetrical positions with respect to the central axis of the core 10. The distance between the central axis of the through holes 50 and 51 and the central axis of the core 10 is 11.6 mm. Hereinafter, the glass cylinder 110 provided with the through holes 50 and 51 is referred to as a perforated base material 111.
[0061]
Next, a glass layer having a thickness of 0.5 mm, that is, the tubular members 30 and 31 are formed on the surfaces of the through holes 50 and 51 (FIG. 4). The tubular members 30 and 31 are made of BClThree150 ml / min (boron trichloride), SiClFour400 ml / min (silicon tetrachloride), O2While introducing (oxygen) into the through holes 50 and 51 at a flow rate of 1 liter per minute, the inside of the through holes 50 and 51 is heated by applying a flame of an oxyhydrogen flame burner to the outer surface of the perforated base material 111. Can be formed. The flame of the oxyhydrogen flame burner is H as fuel gas in the burner.2(Hydrogen) at 70 l / min, O2(Oxygen) is formed by introducing 30 l per minute. After the tubular members 30 and 31 are formed, the through holes 52 and 53 remain in the tubular members 30 and 31. In FIG. 4, the perforated base material after the tubular members 30 and 31 are formed is denoted by reference numeral 112.
[0062]
Next, the stress applying members 40 and 41 prepared in advance are inserted into the through holes 52 and 53 and fixed (FIGS. 5 and 6). The stress applying members 40 and 41 can be manufactured by a known VAD method. Specifically, first, as a fuel gas in the burner, H250 liters per minute, O2Is introduced at a rate of 12 liters per minute to form an oxyhydrogen flame, and SiCl in this oxyhydrogen flameFour400 ml per minute, BClThreeIs introduced at a rate of 300 ml per minute, and glass fine particles (SiO2+ B2OThree) Is generated. Next, when the glass fine particles are sprayed from the burner while rotating the rod-shaped starting material, the glass fine particles are deposited on the surface of the starting material in a substantially uniform thickness. By spraying the glass particles while pulling up the starting material, the glass particles can be grown in the axial direction. Thereby, since the glass fine particles are uniformly deposited on the entire surface of the starting material, a columnar glass fine particle body is obtained. Next, this glass fine particle body is put in a sintering furnace, and BF is put in a helium atmosphere in the sintering furnace.ThreeThen, the mixture is heated at a temperature of about 1200 ° C. for 60 minutes, then heated at a temperature of about 1400 ° C. for 60 minutes, and then gradually cooled. As a result, the glass particles become transparent vitrified, and columnar glass bodies (SiO2-B2OThree) Is obtained. When this glass body is heated and stretched so that the outer diameter is about 6.8 mm, the stress applying members 40 and 41 of this embodiment are obtained. The compositions of the two stress applying members are almost the same. The stress applying members 40 and 41 are made shorter than the through holes 52 and 53.
[0063]
B added to stress applying members 40 and 412OThreeIs SiO2Since it has the effect | action which raises the thermal expansion coefficient of glass, the stress provision members 40 and 41 have a larger thermal expansion coefficient than the clad 20.
[0064]
The stress applying members 40 and 41 obtained as described above are inserted into the through holes 52 and 53 of the perforated base material 112 and fixed inside the holes. Below, this fixing method is demonstrated, referring FIG.5 and FIG.6. This fixing method is also disclosed in Japanese Patent Laid-Open No. 4-97920.
[0065]
In order to execute this fixing method, first, quartz glass rods 60a, 60b, 61a and 61b having an outer diameter of about 6.8 mm and a quartz glass tube 70 are prepared. As shown in FIG. 5, the glass tube 70 is formed by attaching glass tubes 70a and 70c having a larger inner diameter to both ends of a glass ring 70b having a smaller inner diameter.
[0066]
In order to fix the stress applying members 40 and 41, first, the glass tube 70 is welded to one end face of the perforated base material 112. Next, the glass rod 60a, the stress applying member 40, and the glass rod 60b are inserted into the through hole 52 from the other end side of the perforated base material 112 in this order. Similarly, the through hole 53 is inserted in the order of the glass rod 61a, the stress applying member 41, and the glass rod 61b. The tips of the glass rods 60a and 61a protrude from the end surface of the perforated base material 112, and the end surfaces are pressed against the bottom surface of the glass ring 70b. Thereby, the glass rods 60a and 61a are fixed. Glass rods 60b and 61b and clad 20 are integrated by subjecting the end of perforated base material 112 to heat drawing. As a result, one end of the perforated base material 112 is sealed (FIG. 6).
[0067]
Since a vacuum connector (not shown) can be connected to the glass tube 70, the inside of the through holes 52 and 53 is decompressed using this. Thereafter, the tip of the glass tube 70 is collapsed (solidified) by heat treatment and sealed. As a result, the stress applying members 40 and 41 are fixed to the perforated base material 112. Needless to say, the method of fixing the stress applying members 40 and 41 is not limited to the above method.
[0068]
Next, the perforated base material 112 to which the stress applying members 40 and 41 are fixed as described above is subjected to a heat treatment at a heating temperature of 1900 degrees and a heating time of 120 minutes, and then gradually cooled. Thereby, the glass which comprises the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41 is melted and integrated. Thus, the optical fiber preform is completed.
[0069]
Of the optical fiber preform obtained as described above, what can actually be used for the production of the optical fiber is a portion including the stress applying members 40 and 41. Therefore, the above method is substantially the same as the optical fiber of FIG. The base material 100 for manufacture is manufactured.
[0070]
FIG. 7 is a diagram showing a refractive index distribution and a softening temperature distribution in the radial direction for the optical fiber preform 100. In this figure, only the distribution of the right half of the optical fiber preform 100 is shown, but the distribution of the left half is the same as that of the right half. As shown in this figure, the tubular members 30 and 31 have a softening temperature obtained by averaging the softening temperature of the clad 20 and the softening temperatures of the stress applying members 40 and 41. In order to have such a softening temperature, in the formation process of the tubular members 30 and 31 described above, SiO2B which is a softening temperature lowering material2OThreeIt is good to adjust the amount of addition.
[0071]
In order to manufacture an optical fiber preform including a stress applying member, it is necessary to perform heat treatment to integrate the stress applying member and the clad. In general, when two objects are integrated, it is desirable that the physical properties of the joint portion between the two objects are close to each other. In particular, when integrating by heat treatment, it is desirable that the softening temperatures of both are close. If there is a difference in the softening temperature between the two joints, only one of them will soften first, and the other surface will be integrated before it is sufficiently smoothed by the effect of heating. Is likely to occur.
[0072]
In the optical fiber preform 100 of the present embodiment, since the tubular members 30 and 31 having an average softening temperature between the clad 20 and the stress applying members 40 and 41 exist, the clad 20 and the tubular member 30 are present. , 31 and the softening temperature difference between the tubular members 30, 31 and the stress applying members 40, 41 are smaller than the softening temperature difference between the clad 20 and the stress applying members 40, 41. For this reason, even when the clad 20 and the stress applying members 40 and 41 are integrated by heat treatment at the time of manufacture, the surface smoothing effect sufficiently acts. As a result, the generation of bubbles at the bonding interface between the clad 20 and the tubular members 30 and 31 and at the bonding interface between the tubular members 30 and 31 and the stress applying members 40 and 41 is prevented or reduced. Therefore, even when an optical fiber is manufactured by drawing the optical fiber preform 100, the optical fiber is hardly broken and the obtained optical fiber has good transmission characteristics and polarization characteristics. .
[0073]
In addition, since light propagates in a portion having a high refractive index in the optical fiber, generally, when a portion having a refractive index higher than that of the clad is present in the vicinity of the core, the optical power moves from the core to that portion, and as a result Transmission loss increases. In view of this point, in this embodiment, the refractive indexes of the tubular members 30 and 31 and the stress applying members 40 and 41 are set lower than that of the cladding (FIG. 7). Since the optical fiber has the same refractive index distribution as the base material, setting the refractive index in this way prevents the movement of optical power in the optical fiber obtained by drawing the optical fiber base material. And increase in transmission loss of the optical fiber can be suppressed.
[0074]
In the present embodiment, the optical fiber preform 100 manufactured as described above is drawn using a normal drawing device to manufacture a polarization maintaining optical fiber. Specifically, first, the optical fiber preform 100 is heated to about 2000 degrees in a heating furnace, and drawn so that the outer diameter becomes 125 μm at a linear speed of 100 m / min. The drawn optical fiber is coated with UV resin twice. The outer diameter of the coated optical fiber is about 250 μm. In this way, a polarization maintaining optical fiber having a length of 10 km is manufactured.
[0075]
When the crosstalk characteristic, which is one of the polarization characteristics, was measured at a wavelength of 1.3 μm for the polarization maintaining optical fiber manufactured as described above, a very good result of −24 dB was obtained.
[0076]
For comparison with the present embodiment, the present inventors manufactured a 10 km polarization-maintaining optical fiber by drawing an optical fiber preform into which a stress applying member was inserted without forming the tubular members 30 and 31. . The manufacturing method of the optical fiber preform is the same as that of the present embodiment except that the tubular members 30 and 31 are not formed. When the crosstalk characteristic of this polarization maintaining optical fiber was measured, it was -8 dB, which was inferior to the present example. As a result of examining this polarization maintaining optical fiber in detail, bubbles were found in the glass at three locations along the entire length of the optical fiber. This bubble was generated at the interface between the stress applying member and the clad.
[0077]
In the present example, the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41 were heated and integrated to complete the optical fiber preform 100, and then the optical fiber was manufactured by drawing. It is also possible to manufacture an optical fiber by performing heating integration and drawing simultaneously.
[0078]
For example, after fixing the stress applying members 40 and 41 to the perforated base material 112 by the above method, the composite of the stress applying members 40 and 41 and the perforated base material 112 is heated to about 2000 degrees in a heating furnace, An optical fiber can be manufactured by drawing the stress applying members 40 and 41, the clad 20, and the tubular members 30 and 31 so that the outer diameter is 125 μm at a drawing speed of 100 m / min. In this case, the optical fiber is manufactured without going through the state of the base material.
[0079]
Also in this case, the presence of the tubular members 30 and 31 provides a sufficient surface smoothing effect during the heat integration, so that the joining interface between the clad 20 and the tubular members 30 and 31 and the stress applied to the tubular members 30 and 31 are applied. The generation of bubbles at the joint interface with the members 40 and 41 is prevented or reduced. Therefore, also by the above method, it is possible to manufacture a polarization maintaining optical fiber having good characteristics while preventing the optical fiber from being broken.
[0080]
Example 2
In this embodiment, the optical fiber preform 100 (FIG. 1) is manufactured by a method different from that in the first embodiment. FIG. 8 is a diagram showing a base material manufacturing method according to the present embodiment. In this example, first, a glass cylinder 110 (similar to FIG. 2) is manufactured by the VAD method, and through holes 50 and 51 extending in the axial direction are formed in the clad 20 by an ultrasonic aperture machine, A perforated base material 111 is produced. The diameter of the through holes 50 and 51 is 8 mm. The above steps are almost the same as those in Example 1, but in this example, the composition of the core is SiO.2And the composition of the cladding is SiO2-F. F is SiO2Since this is added to the clad, the refractive index of the core is higher than that of the clad.
[0081]
Next, in this example, the same stress applying members 40 and 41 (outer diameter 18 mm) as in Example 1 were prepared using the VAD method, and then the tubular member 30 and the stress applying members 40 and 41 were formed on the surfaces of the stress applying members 40 and 41. 31 is deposited. This deposition can be performed using a known OVD (external) method. Specifically, SiCl in the oxyhydrogen flame burnerFour(Silicon tetrachloride) 300 ml / min, H2(Hydrogen) at 50 l / min, O2(Oxygen) is introduced at a rate of 12 liters per minute, the burner flame is applied while rotating the stress applying members 40 and 41 around their own axes, and the burner is relative to the stress applying members 40 and 41 along the axial direction. Move it. As a result, SiO2Are deposited on the side surfaces of the stress applying members 40 and 41 with a substantially uniform thickness.
[0082]
Next, the stress applying members 40 and 41 on which the glass fine particles are deposited are put in a heating furnace, and BF is put in a helium atmosphere in the heating furnace.ThreeAnd SiFFourThen, the mixture is heated at a temperature of about 1200 ° C. for 30 minutes, followed by heating at a temperature of about 1400 ° C. for 30 minutes, followed by slow cooling. By this work, SiO2B and F are added to the glass fine particles, and the glass fine particles become transparent vitrified and integrated with the stress applying members 40 and 41.
[0083]
In this embodiment, a glass layer (SiO 2 having a thickness of about 2.5 mm is formed on the surfaces of the stress applying members 40 and 41 by the above method.2-B2OThree-F). This glass layer is the tubular members 30 and 31 of the present embodiment. In addition, as a method of forming the tubular members 30 and 31 on the surfaces of the stress applying members 40 and 41, a glass layer to be a stress applying member is formed on the inner surface of a glass pipe prepared in advance using the material of the tubular members 30 and 31. Can be formed by MCVD, and then the glass pipe can be collapsed (solidified).
[0084]
Thereafter, the two columnar bodies composed of the tubular members 30 and 31 and the stress applying members 40 and 41 are stretched by heating so that the outer diameter is about 7.7 mm. The columnar bodies 80 and 81 thus obtained are inserted into the through holes 50 and 51 of the perforated base material 111 as shown in FIG. 8 and then fixed in the same manner as in the first embodiment. Thereafter, heat treatment is performed to integrate the columnar bodies 80 and 81 and the clad 20 to complete the optical fiber preform 100 (FIG. 1).
[0085]
The optical fiber preform manufactured according to this example also has a refractive index distribution and a softening temperature distribution shown in FIG. The softening temperature is adjusted by adjusting SiO in the tubular members 30 and 31 described above.2B, a softening temperature change material2OThreeAnd it can carry out by adjusting the addition amount of F. Where B2OThreeIs SiO2Has the effect of lowering the softening temperature of F, F is SiO2Has the effect of lowering the softening temperature.
[0086]
The optical fiber preform manufactured by the inventors as described above is drawn in the same manner as in Example 1 to manufacture a polarization maintaining optical fiber having a length of 10 km. As a result, when the crosstalk characteristic was measured at a wavelength of 1.3 μm, a very good result of −26 dB was obtained.
[0087]
In place of the above method, it is possible to manufacture an optical fiber without passing through the state of the base material by performing heating integration of the columnar bodies 80 and 81 and the clad 20 simultaneously with drawing. The same as in the first embodiment.
[0088]
Example 3
In this embodiment, the optical fiber preform 100 (FIG. 1) is manufactured by a method different from the first and second embodiments. FIG. 9 is a diagram illustrating a base material manufacturing method according to the present embodiment. Also in this example, first, a perforated base material 111 (similar to FIG. 3) is produced in the same manner as in Example 2. In the present embodiment, the diameters of the through holes 50 and 51 are 9 mm. Next, stress applying members 40 and 41 having an outer diameter of about 7.8 mm are manufactured by the same method as in Example 1.
[0089]
Next, in this embodiment, the tubular members 30 and 31 are formed independently of the perforated base material 111 and the stress applying members 40 and 41. For this purpose, a columnar glass body is first produced using the VAD method. Specifically, H is added to the oxyhydrogen flame burner.2(Hydrogen) at 50 l / min, O2In an oxyhydrogen flame formed by introducing 12 l per minute (oxygen), SiClFour(Silicon tetrachloride) is introduced at a flow rate of 300 ml per minute, and SiO produced in the flame2The glass fine particles are deposited and grown on the starting material to form rod-like glass fine particles. This glass fine particle is put in a sintering furnace, and SiF is put in a helium atmosphere in the sintering furnace.FourThen, the mixture is heated at a temperature of about 1200 ° C. for 30 minutes, and then heated at a temperature of about 1400 ° C. for 60 minutes, followed by slow cooling. As a result, SiO2The glass fine particles are transparently vitrified after F is added. Thus, SiO2A glass columnar body of -F is obtained. This glass columnar body was heated and stretched so that the outer diameter was 22 mm, then a through-hole having an inner diameter of 20 mm was formed at the center using an ultrasonic aperturer, and again heated and stretched to obtain an outer diameter of 8.8 mm. A glass tube having an inner diameter of 8 mm is formed. This is the tubular members 30 and 31 of the present embodiment.
[0090]
Next, the tubular member 30 and the stress applying member 40 are inserted into the through hole 50 from one end side of the perforated base material 111 in this order. Similarly, for the through hole 51, the tubular member 31 and the stress applying member 41 are inserted in this order. The stress applying members 40 and 41 are inserted into the hollow portions of the tubular members 30 and 31, respectively. The tubular members 30 and 31 and the stress applying members 40 and 41 are fixed by the same method as in the first embodiment. Thereafter, heat treatment is performed to integrate the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41, thereby completing the optical fiber preform 100 (FIG. 1).
[0091]
The optical fiber preform manufactured according to this example also has a refractive index distribution and a softening temperature distribution shown in FIG. The softening temperature is adjusted by adjusting SiO in the tubular members 30 and 31 described above.2This can be done by adjusting the amount of F which is a softening temperature change material.
[0092]
The optical fiber preform manufactured by the inventors as described above is drawn to manufacture a polarization-maintaining optical fiber having a length of 9.7 km. When the talk characteristics were measured at a wavelength of 1.3 μm, a very good result of −26 dB was obtained.
[0093]
In the manufacturing process of this embodiment, the inner and outer surfaces of the tubular members 30 and 31 are subjected to mechanical smoothing such as polishing or heat smoothing by flame radiation or the like, or these surfaces are washed and adhered. If the impurities are removed, the generation of bubbles due to heat integration during drawing can be more effectively prevented.
[0094]
Further, instead of the above method, the heating, integration of the clad 20, the tubular members 30 and 31, and the stress applying members 40 and 41 is performed at the same time as the drawing, so that an optical fiber is manufactured without passing through the state of the base material. What can be done is the same as in the above embodiment.
[0095]
  Reference example
  BookreferenceIn the example, an optical fiber preform different from the optical fiber preform 100 of FIG. 1 is manufactured. First, bookreferenceA method for manufacturing an example optical fiber preform will be described in detail. Figure 10 shows the bookreferenceIt is a figure which shows the base material manufacturing method of an example.
[0096]
  BookreferenceIn the example, first, a glass cylinder 110 (similar to FIG. 2) is manufactured using a known MCVD method, and through holes 50 and 51 extending along the axial direction are formed in the clad 20 using an ultrasonic aperture machine. Then, a perforated base material 111 is produced. The diameter of the through holes 50 and 51 is 8 mm.
[0097]
Next, the stress applying members 42 and 43 are produced using the VAD method. Specifically, H is added to the oxyhydrogen flame burner.250 liters per minute, O2In an oxyhydrogen flame formed by introducing 12 l per minute.Four300 ml per minute, BClThree(Boron trichloride) is introduced at a rate of 300 ml per minute, and glass fine particles (SiO2) generated in the flame2-B2OThree) Are deposited and grown on the starting material to form columnar glass particles. This fine glass particle has SiO2Increases the thermal expansion coefficient of B2OThreeAs a result, the glass fine particles have a higher thermal expansion coefficient than the clad 20 of the perforated base material 111. B2OThreeIs SiO2Therefore, the glass fine particles have a softening temperature lower than that of the clad 20.
[0098]
Next, the glass fine particles are put in a sintering furnace, and BF is added in a helium atmosphere in the sintering furnace.ThreeThen, heating is performed at a temperature of about 1100 ° C. for 60 minutes while the inside of the sintering furnace is made an atmosphere of only helium, followed by heating at a temperature of about 1400 ° C. for 60 minutes and then slow cooling. Thereby, B is added from the surface of the glass fine particles, and the oxide of B (B2OThree) Is formed.
[0099]
  If the sintering furnace has an atmosphere of only helium, B added to the glass fine particles in the sintering furnace2O3Diffuses from the outer surface of the glass particulate material into the atmosphere. The amount of diffusion is larger on the surface side of the glass fine particles. Since transparent vitrification proceeds at the same time as the diffusion, the glass body has a substantially uniform concentration of B at the center.2O3Is added, but in the surface layer portion having a thickness of about 1/4 of the outer diameter from the surface toward the center, the addition concentration gradually decreases, and almost no B is present near the surface.2O3Will not be added. When the glass body thus obtained is heated and stretched to an outer diameter of about 7.7 mm,referenceExample stress applying members 42 and 43 (SiO 22-B2O3) Is obtained.
[0100]
In the stress applying members 42 and 43, the softening temperature in the surface layer portion continuously changes from the softening temperature of the clad 20 to the softening temperatures of the central portions 42a and 43a from the surface side to the center side of the member. That is, the stress applying members 42 and 43 have a tubular shape having a softening temperature distribution in which the softening temperature continuously changes from the softening temperature of the clad 20 to the softening temperatures of the central portions 42a and 43a from the surface side toward the center side. Members are provided in the surface layer portions 42b and 43b.
[0101]
  The stress applying members 42 and 43 obtained in this way are inserted and fixed in the through holes 50 and 51 of the perforated base material 111 as shown in FIG. 10, and then subjected to heat treatment to provide the clad 20 and the stress applying members 42 and 43. Integrate the bookreferenceThe example optical fiber preform is completed. Although not shown, the stress applying members 42 and 43 are fixed by the same method as in the first embodiment.
[0102]
  BookreferenceThe optical fiber preform manufactured according to the example has a refractive index distribution and a softening temperature distribution as shown in FIG. BookreferenceThe example optical fiber preform is characterized by the softening temperature distribution of the stress applying member inserted into the through holes 50 and 51 of the perforated preform 111. That is, as shown in FIG. 11, the surface layer portions 42b and 43b of the stress applying members 42 and 43 are continuous from the softening temperature of the clad 20 to the softening temperatures of the central portions 42a and 43a from the surface side to the center side of the members. It has a softening temperature distribution that changes with time.
[0103]
  BookreferenceIn the optical fiber preform of the example, since the stress applying member has such surface layer portions 42b and 43b, the softening temperature difference between the clad 20 and the stress applying members 42 and 43 is alleviated. In particular, since the softening temperature is substantially equal at the bonding interface between the clad 20 and the stress applying members 42 and 43, the surface smoothing effect is sufficient even when the clad 20 and the stress applying members 42 and 43 are integrated by heat treatment. This acts to prevent or greatly reduce the generation of bubbles at the bonding interface between the clad 20 and the stress applying members 42 and 43.
[0104]
  Also bookreferenceEven in the example optical fiber preform, the refractive indexes of the stress applying members 42 and 43 are set lower than those of the clad (FIG. 11). This prevents the optical power from moving from the core to the stress applying members 42 and 43.referenceAn increase in transmission loss of the optical fiber obtained by drawing the optical fiber preform of the example can be suppressed.
[0105]
  BookreferenceThe optical fiber preform of the example is heated to about 2000 ° C. in a heating furnace, and the stress applying members 42 and 43 and the perforated preform 111 are integrated with a drawing speed of 100 m / min. An optical fiber was manufactured and further coated with a UV resin to manufacture a polarization maintaining optical fiber having an outer diameter of about 250 μm and a length of 9.5 km. When the crosstalk characteristic which is one of the polarization characteristics of this optical fiber was measured at a wavelength of 1.3 μm, a very good result of −25 dB was obtained.
[0106]
In place of the above method, it is possible to manufacture an optical fiber without passing through the state of the base material by performing heating integration of the stress applying members 42 and 43 and the clad 20 simultaneously with the drawing. The same as in the above embodiment.
[0107]
  Example 5
  In this embodiment, an optical fiber preform having a refractive index distribution and a softening temperature distribution shown in FIG. 11 is manufactured by a method similar to that of the first embodiment. Specifically, after the perforated base material 111 is produced by the same method as in Example 1, tubular members 30 and 31 having a thickness of 0.5 mm are formed on the surfaces of the through holes 50 and 51. Here, the method of forming the tubular members 30 and 31 is slightly different from that of the first embodiment. That is, the tubular members 30 and 31 of this example are made of SiCl.4400 ml per minute, O2Is introduced into the through holes 50 and 51 at a flow rate of 1 l / min, and BCl is introduced.3The inside of the through holes 50 and 51 is heated by applying a flame of an oxyhydrogen flame burner to the outer surface of the perforated base material 111 while controlling the flow rate of the through holes 50 and 51. BCl3Is not introduced at all at the beginning of heating, then gradually increased in flow rate and finally introduced at a flow rate of 150 ml per minute. ThisReference exampleTubular members 30 and 31 having the same refractive index distribution and softening temperature distribution as the surface layer portions 42b and 43b are formed. Then, the optical fiber preform which has the refractive index distribution and softening temperature distribution of FIG. 11 is manufactured by performing the manufacturing process similar to Example 1. FIG.
[0108]
Example 6
In this example, an optical fiber preform having a refractive index distribution and a softening temperature distribution shown in FIG. 11 is manufactured by a method similar to Example 3. Specifically, the perforated base material 111 and the stress applying members 40 and 41 are produced in the same manner as in Example 3, and the tubular members 30 and 31 are made independent of the perforated base material 111 and the stress applying members 40 and 41. To form. Here, the method of forming the tubular members 30 and 31 is different from that of the third embodiment.
[0109]
That is, in this example, after forming rod-shaped glass fine particles in the same manner as in Example 3, this was put in a sintering furnace, and SiF was placed in a helium atmosphere in the sintering furnace.FourThen, heating is performed at a temperature of about 1200 ° C. for 60 minutes while the inside of the sintering furnace is made an atmosphere of only helium, followed by heating at a temperature of about 1400 ° C. for 60 minutes and then slow cooling. If the sintering furnace has an atmosphere of only helium, F added to the glass fine particles in the sintering furnace diffuses from the outer surface of the glass fine particles into the atmosphere. The amount of diffusion is larger on the surface side of the glass fine particles. Since transparent vitrification proceeds simultaneously with diffusion, SiO concentration in which the F concentration continuously changed from the center side to the surface side of the glass body2Thus, a glass columnar body is obtained.
[0110]
  This glass columnar body was heated and stretched so that the outer diameter was 22 mm, then a through-hole having an inner diameter of 20 mm was formed at the center using an ultrasonic aperturer, and again heated and stretched to obtain an outer diameter of 8.8 mm. A glass tube having an inner diameter of 8 mm is formed. ThisReference exampleTubular members 30 and 31 having the same refractive index distribution and softening temperature distribution as the surface layer portions 42b and 43b are formed. Thereafter, by performing the same manufacturing process as in Example 3, the optical fiber preform having the refractive index distribution and the softening temperature distribution of FIG. 11 is manufactured.
[0111]
As mentioned above, although the Example of this invention was described in detail, this invention is not limited to the said Example, A various deformation | transformation is possible. For example, for the production of a glass cylinder, glass pipe or stress applying member comprising a core and a clad, any generally known production method such as VAD method, OVD method, MCVD method, etc. may be used. The same applies when the glass layer is formed on the surface of the through hole or the surface of the stress applying member. Various methods can be selected from known techniques as a method of forming the through hole for inserting the stress applying member. Similarly, the cross-sectional shapes of the through hole and the stress applying member can be arbitrarily selected from known techniques related to the polarization maintaining optical fiber.
[0112]
Further, after forming a glass layer on the surface of the through hole or the surface of the stress applying member, the surface of the glass layer is subjected to mechanical smoothing such as polishing or heat smoothing by flame radiation or the like, or these surfaces are If the impurities adhered by washing are removed, the generation of bubbles during heating integration can be more effectively prevented.
[0113]
Further, examples of the softening temperature changing material used for adjusting the softening temperature of quartz glass include the following.
[0114]
1st group (both softening temperature and refractive index are reduced)
... B, F
Second group (those that lower the softening temperature and increase the refractive index)
... Ge, P
Third group (both softening temperature and refractive index increase)
... Al, Ti, Zr
One or more of these softening temperature change materials are selected and added from (1) the first group, (2) one or more are selected from the first group, and one or more are selected from the second group (3) Select one or more from the first group and add one or more from the third group (4) One or more from the first group, from the second group One or more and one or more from the third group may be selected and added.
[0115]
【The invention's effect】
As described above in detail, the optical fiber preform of the present invention has a structure in which bubbles are unlikely to occur at the bonding interface between the clad and the tubular member and the bonding interface between the tubular member and the stress applying member. A polarization-maintaining optical fiber exhibiting good transmission characteristics and polarization characteristics can be manufactured by drawing this base material hardly.
[0116]
According to the optical fiber preform of the present invention, when the refractive index of the stress applying member or the tubular member is equal to or lower than the refractive index of the clad, in the optical fiber obtained by drawing the preform, the stress applying member or the tubular member is drawn from the core. Since the optical power does not easily move to the member, a polarization maintaining optical fiber with a small transmission loss can be obtained.
[0117]
Next, according to the first aspect of the method for manufacturing an optical fiber preform according to the present invention, when the stress applying member and the tubular member are integrated to complete the preform, the bonding interface between the cladding and the tubular member is also provided. In addition, since bubbles are hardly generated at the bonding interface between the tubular member and the stress applying member, a base material for the polarization maintaining optical fiber can be preferably manufactured.
[0118]
Further, according to the second aspect of the method for manufacturing an optical fiber preform according to the present invention, when the perforated preform and the stress applying member are integrated to complete the preform, the cladding and the stress applying member are joined. Since bubbles are hardly generated at the interface, the base material for the polarization maintaining optical fiber can be suitably manufactured.
[0119]
Next, according to the first aspect of the optical fiber manufacturing method of the present invention, when drawing is performed while integrating the perforated base material, the stress applying member, and the tubular member, the cladding and the tubular member are joined. Since bubbles are unlikely to be generated at the interface or the joining interface between the tubular member and the stress applying member, a polarization maintaining optical fiber that exhibits good transmission characteristics and polarization characteristics while preventing breakage of the optical fiber during drawing Obtainable.
[0120]
In the second aspect of the optical fiber manufacturing method according to the present invention, bubbles are generated at the bonding interface between the cladding and the stress applying member even when drawing is performed while integrating the perforated base material and the stress applying member. Therefore, it is possible to obtain a polarization-maintaining optical fiber that exhibits good transmission characteristics and polarization characteristics while preventing breakage of the optical fiber during drawing.
[0121]
Next, since the optical fiber of the present invention has a structure in which bubbles are not easily generated at the joint interface between the clad and the tubular member and the joint interface between the tubular member and the stress applying member at the time of manufacture, the optical fiber is broken during drawing. And can have good transmission characteristics and polarization characteristics.
[0122]
Of the optical fibers of the present invention, those in which the refractive index of the stress applying member or the tubular member is equal to or lower than the refractive index of the clad are less likely to cause the optical power to move from the core to the stress applying member or the tubular member, and therefore transmission loss is small Has the advantage.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a configuration of an optical fiber preform manufactured in Examples 1 to 3. FIG.
FIG. 2 is a first process diagram for explaining a base material manufacturing method according to the first embodiment;
FIG. 3 is a second process diagram for explaining the base material manufacturing method according to the first embodiment;
FIG. 4 is a third process diagram for explaining the base material manufacturing method according to the first embodiment;
5 is a fourth process diagram for explaining the base material manufacturing method of Example 1. FIG.
6 is a fifth process diagram for explaining the manufacturing method of the base material of Example 1. FIG.
7 is a diagram showing a refractive index distribution and a softening temperature distribution along the radial direction for the optical fiber preforms manufactured in Examples 1 to 3. FIG.
8 is a diagram for explaining a base material manufacturing method of Example 2. FIG.
9 is a diagram for explaining a base material manufacturing method of Example 3. FIG.
FIG. 10Reference exampleIt is a figure for demonstrating the base material manufacturing method of this.
FIG. 11Reference exampleIt is a figure which shows the refractive index distribution and softening temperature distribution along a radial direction about the optical fiber preform manufactured in (1).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Core, 20 ... Cladding, 30 and 31 ... Tubular member, 40 and 41 ... Stress applying member, 50-53 ... Through-hole, 100 ... Optical fiber preform | base_material.

Claims (14)

柱状のコアと、
このコアを包囲する管状のクラッドであって、その管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられ、その貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものと、
前記貫通孔に挿入され、前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有する柱状の応力付与部材と、
前記貫通孔に挿入され、前記応力付与部材を包囲する管状部材であって、前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものと、
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に沿ってほぼ一定に維持している、光ファイバ母材。Columnar core,
A tubular clad surrounding the core, and a through hole along the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion coefficient and a surface layer portion of the through hole Having a first softening temperature;
A columnar stress applying member inserted into the through-hole and having a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member inserted into the through hole and surrounding the stress applying member, and having a radial softening temperature distribution set between the first and second softening temperatures;
With
The tubular member is an optical fiber preform in which a softening temperature different from any of the first and second softening temperatures is maintained substantially constant along a radial direction . 前記応力付与部材及び前記管状部材の屈折率が、前記クラッドの屈折率以下であることを特徴とする請求項１記載の光ファイバ母材。  2. The optical fiber preform according to claim 1, wherein a refractive index of the stress applying member and the tubular member is equal to or lower than a refractive index of the clad. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設けるとともに、前記孔開き母材、応力付与部材及び管状部材を一体化する第２の工程と、
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に沿ってほぼ一定に維持している、光ファイバ母材の製造方法。A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole, or on the surface of the stress applying member, and integrating the perforated base material, the stress applying member and the tubular member; ,
With
The method for manufacturing an optical fiber preform , wherein the tubular member maintains a softening temperature different from any of the first and second softening temperatures substantially constant along a radial direction . 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設けるとともに、前記孔開き母材、応力付与部材及び管状部材を一体化する第２の工程と、
を備え、
前記第２の工程は、前記貫通孔の表面上に前記管状部材を形成し、次いで、前記応力付与部材をこの管状部材の中空部に挿入し、この後、前記応力付与部材と前記管状部材を一体化する工程である、光ファイバ母材の製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole, or on the surface of the stress applying member, and integrating the perforated base material, the stress applying member and the tubular member; ,
With
In the second step, the tubular member is formed on the surface of the through hole, and then the stress applying member is inserted into a hollow portion of the tubular member, and then the stress applying member and the tubular member are inserted. A method of manufacturing an optical fiber preform , which is a process of integrating. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設 定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設けるとともに、前記孔開き母材、応力付与部材及び管状部材を一体化する第２の工程と、
を備え、
前記第２の工程は、前記応力付与部材の表面上に前記管状部材を堆積形成し、次いで、前記応力付与部材及び前記管状部材からなる柱状体を前記孔開き母材の貫通孔に挿入し、この後、前記柱状体と前記孔開き母材を一体化する工程である、光ファイバ母材の製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
Those having a radial softening temperature distribution is set between a tubular member to be surrounding the stress applying members of the first and second softening temperature, said through-holes on the surface, the stress applying member And a second step of integrating the perforated base material, the stress applying member, and the tubular member, at an intermediate position between the surface of the through hole and the surface of the through hole or at one or more positions on the surface of the stress applying member. When,
With
In the second step, the tubular member is deposited on the surface of the stress applying member, and then a columnar body made of the stress applying member and the tubular member is inserted into the through hole of the perforated base material, Then, the manufacturing method of the optical fiber preform which is a process of integrating the columnar body and the perforated preform. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設けるとともに、前記孔開き母材、応力付与部材及び管状部材を一体化する第２の工程と、
を備え、
前記第２の工程は、前記管状部材を前記貫通孔に挿入するとともに、前記管状部材の中空部に前記応力付与部材を挿入し、この後、前記孔開き母材、応力付与部材及び管状部材を一体化する工程である、光ファイバ母材の製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole, or on the surface of the stress applying member, and integrating the perforated base material, the stress applying member and the tubular member; ,
With
In the second step, the tubular member is inserted into the through-hole, and the stress applying member is inserted into a hollow portion of the tubular member. Thereafter, the perforated base material, the stress applying member, and the tubular member are inserted. A method of manufacturing an optical fiber preform , which is a process of integrating. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有する中央部を備えた柱状の応力付与部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材をその表層部に備えたものとを用意する第１の工程と、
前記応力付与部材を前記孔開き母材の貫通孔に挿入する第２の工程と、
前記応力付与部材と前記孔開き母材を一体化する第３の工程と、
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に沿ってほぼ一定に維持している、光ファイバ母材の製造方法。A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature, a second thermal expansion coefficient different from the first thermal expansion coefficient, and a second softening temperature different from the first softening temperature. A columnar stress applying member having a central portion in the portion, the tubular member having a radial direction softening temperature distribution set between the first and second softening temperatures provided in the surface layer portion thereof. A first step to be prepared;
A second step of inserting the stress applying member into the through hole of the perforated base material;
A third step of integrating the stress applying member and the perforated base material;
With
The method for manufacturing an optical fiber preform , wherein the tubular member maintains a softening temperature different from any of the first and second softening temperatures substantially constant along a radial direction . 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設ける第２の工程と、
前記孔開き母材、応力付与部材及び管状部材からなる複合体を加熱して、前記孔開き母材、応力付与部材及び管状部材を一体化しながら前記複合体を線引する第３の工程と
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に 沿ってほぼ一定に維持している、光ファイバの製造方法。A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole or on the surface of the stress applying member;
A third step of heating the composite comprising the perforated base material, the stress applying member and the tubular member, and drawing the composite while integrating the perforated base material, the stress applying member and the tubular member;
With
The method for manufacturing an optical fiber , wherein the tubular member maintains a softening temperature different from any of the first and second softening temperatures substantially constant along a radial direction . 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設ける第２の工程と、
前記孔開き母材、応力付与部材及び管状部材からなる複合体を加熱して、前記孔開き母材、応力付与部材及び管状部材を一体化しながら前記複合体を線引する第３の工程と
を備え、
前記第２の工程は、前記孔開き母材の貫通孔の表面上に前記管状部材を形成し、次いで、前記応力付与部材をこの管状部材の中空部に挿入する工程である、光ファイバの製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole or on the surface of the stress applying member;
A third step of heating the composite comprising the perforated base material, the stress applying member and the tubular member, and drawing the composite while integrating the perforated base material, the stress applying member and the tubular member;
With
The second step is a process for producing an optical fiber , which is a step of forming the tubular member on the surface of the through hole of the perforated base material and then inserting the stress applying member into a hollow portion of the tubular member. Method. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設ける第２の工程と、
前記孔開き母材、応力付与部材及び管状部材からなる複合体を加熱して、前記孔開き母材、応力付与部材及び管状部材を一体化しながら前記複合体を線引する第３の工程と
を備え、
前記第２の工程は、前記応力付与部材の表面上に前記管状部材を堆積形成し、次いで、前記応力付与部材及び前記管状部材からなる柱状体を前記孔開き母材の貫通孔に挿入する工程である、光ファイバの製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole or on the surface of the stress applying member;
A third step of heating the composite comprising the perforated base material, the stress applying member and the tubular member, and drawing the composite while integrating the perforated base material, the stress applying member and the tubular member;
With
The second step is a step of depositing and forming the tubular member on the surface of the stress applying member, and then inserting a columnar body made of the stress applying member and the tubular member into a through hole of the perforated base material. An optical fiber manufacturing method. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記貫通孔に挿入されるべき柱状の応力付与部材であって前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有するものとを用意する第１の工程と、
前記応力付与部材を包囲すべき管状部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものを、前記貫通孔の表面上、前記応力付与部材の表面と前記貫通孔の表面との中間、あるいは前記応力付与部材の表面上のうち一以上の位置に設ける第２の工程と、
前記孔開き母材、応力付与部材及び管状部材からなる複合体を加熱して、前記孔開き母材、応力付与部材及び管状部材を一体化しながら前記複合体を線引する第３の工程と
を備え、
前記第２の工程は、前記管状部材を前記貫通孔に挿入するとともに、この管状部材の中空部に前記応力付与部材を挿入する工程である、光ファイバの製造方法。 A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature; a columnar stress applying member to be inserted into the through hole; a second thermal expansion coefficient different from the first thermal expansion coefficient; A first step of preparing a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member that should surround the stress applying member and has a radial softening temperature distribution set between the first and second softening temperatures is formed on the surface of the through hole. A second step of providing at one or more positions between the surface and the surface of the through hole or on the surface of the stress applying member;
A third step of heating the composite comprising the perforated base material, the stress applying member and the tubular member, and drawing the composite while integrating the perforated base material, the stress applying member and the tubular member;
With
The second step is a method of manufacturing an optical fiber , which is a step of inserting the tubular member into the through hole and inserting the stress applying member into a hollow portion of the tubular member. 柱状のコア及びこのコアを包囲する管状のクラッドであってその管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられその貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものを備える孔開き母材と、前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有する中央部を備えた柱状の応力付与部材であって前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有する管状部材をその表層部に備えたものとを用意する第１の工程と、
前記応力付与部材を前記孔開き母材の貫通孔に挿入する第２の工程と、
前記孔開き母材及び応力付与部材からなる複合体を加熱して、前記孔開き母材及び応力付与部材を一体化しながら前記複合体を線引する第３の工程と、
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に沿ってほぼ一定に維持している、光ファイバの製造方法。A columnar core and a tubular clad surrounding the core, and a through hole extending in the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion is formed in a surface layer portion of the through hole A perforated base material having a coefficient and a first softening temperature, a second thermal expansion coefficient different from the first thermal expansion coefficient, and a second softening temperature different from the first softening temperature. A columnar stress applying member having a central portion in the portion, the tubular member having a radial direction softening temperature distribution set between the first and second softening temperatures provided in the surface layer portion thereof. A first step to be prepared;
A second step of inserting the stress applying member into the through hole of the perforated base material;
A third step of drawing the composite while heating the composite comprising the perforated base material and the stress applying member and integrating the perforated base material and the stress applying member;
With
The method for manufacturing an optical fiber , wherein the tubular member maintains a softening temperature different from any of the first and second softening temperatures substantially constant along a radial direction . 柱状のコアと、
このコアを包囲する管状のクラッドであって、その管壁に軸方向に沿った貫通孔が中心軸と所定の間隔をあけて設けられ、その貫通孔の表層部において第１の熱膨張係数及び第１の軟化温度を有するものと、
前記貫通孔に挿入され、前記第１の熱膨張係数と異なる第２の熱膨張係数及び前記第１の軟化温度と異なる第２の軟化温度をその表層部において有する柱状の応力付与部材と、
前記貫通孔に挿入され、前記応力付与部材を包囲する管状部材であって、前記第１及び第２の軟化温度の間で設定された径方向軟化温度分布を有するものと、
を備え、
前記管状部材は、前記第１及び第２の軟化温度のいずれとも異なる軟化温度を径方向に沿ってほぼ一定に維持している、光ファイバ。Columnar core,
A tubular clad surrounding the core, and a through hole along the axial direction is provided in the tube wall at a predetermined interval from the central axis, and a first thermal expansion coefficient and a surface layer portion of the through hole Having a first softening temperature;
A columnar stress applying member inserted into the through-hole and having a second thermal expansion coefficient different from the first thermal expansion coefficient and a second softening temperature different from the first softening temperature in the surface layer portion;
A tubular member inserted into the through hole and surrounding the stress applying member, and having a radial softening temperature distribution set between the first and second softening temperatures;
With
The tubular member is an optical fiber in which a softening temperature different from any of the first and second softening temperatures is maintained substantially constant along a radial direction . 前記応力付与部材及び前記管状部材の屈折率が、前記クラッドの屈折率以下であることを特徴とする請求項１３記載の光ファイバ。The optical fiber according to claim 13 , wherein the refractive index of the stress applying member and the tubular member is equal to or lower than the refractive index of the cladding.
JP18594695A 1995-07-21 1995-07-21 Optical fiber preform, optical fiber and manufacturing method thereof Expired - Lifetime JP3823341B2 (en)

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CN104536085B (en) * 2015-01-07 2017-06-20 烽火通信科技股份有限公司 A kind of thin footpath polarization maintaining optical fibre
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