JP3977082B2 - Optical fiber preform manufacturing method - Google Patents

Optical fiber preform manufacturing method Download PDF

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JP3977082B2
JP3977082B2 JP2002001812A JP2002001812A JP3977082B2 JP 3977082 B2 JP3977082 B2 JP 3977082B2 JP 2002001812 A JP2002001812 A JP 2002001812A JP 2002001812 A JP2002001812 A JP 2002001812A JP 3977082 B2 JP3977082 B2 JP 3977082B2
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optical fiber
glass
base material
fiber preform
manufacturing
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JP2003206153A (en
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禎則 石田
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THE FURUKAW ELECTRIC CO., LTD.
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    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01Manufacture of glass fibres or filaments
    • C03B37/012Manufacture of preforms for drawing fibres or filaments
    • C03B37/014Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/01413Reactant delivery systems
    • C03B37/0142Reactant deposition burners
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01Manufacture of glass fibres or filaments
    • C03B37/012Manufacture of preforms for drawing fibres or filaments
    • C03B37/014Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/01413Reactant delivery systems
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2207/00Glass deposition burners
    • C03B2207/60Relationship between burner and deposit, e.g. position
    • C03B2207/66Relative motion
    • CCHEMISTRY; METALLURGY
    • C03GLASS; MINERAL OR SLAG WOOL
    • C03BMANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2207/00Glass deposition burners
    • C03B2207/70Control measures

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  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
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  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)

Description

【0001】
【発明の属する技術分野】
本発明は、光通信などに用いられる光ファイバの製造に有用な光ファイバ母材とその光ファイバ母材の製造方法およびその母材から光ファイバを製造する方法に関する。
【0002】
【従来の技術】
従来の光ファイバの製造方法として、光ファイバ化後にコアとなる部分を含むガラスロッドの外周に原料ガスの火炎加水分解によりガラス微粒子を堆積させて複合母材を形成し、その後堆積したガラス微粒子を脱水焼結(ガラス化)することにより光ファイバ母材を製造し、その光ファイバ母材の一端を加熱溶融して線引きし、一定外径の光ファイバとする方法が一般に知られている。
【0003】
ここで、光ファイバ母材を製造する方法について見ると、例えば、本出願人の提案した特開平10−7430号公報に開示された方法がある。この方法は、ガラスロッドを回転させながら複数のガラス微粒子発生装置(バーナ)をガラスロッドの長手方向に移動させることにより、ガラスロッドの外周にガラス微粒子を堆積させる技術に関するものである。
このような技術により製造される複合母材には、図4に示されるように一般に良質な光ファイバとなる外径一定部と、その両端に外径が端部に向かって徐々に小さくなるテーパ部とが形成されるが、このテーパ部は図に示されるように両端がほぼ同一傾斜である。
また、このようにして得られた複合母材を脱水焼結して光ファイバ母材とする工程においては、複合母材を加熱炉内に鉛直方向につり下げて、回転させながらゆっくり引き下げを行うことで処理するのが一般的である。
そして、脱水焼結して得られた光ファイバ母材は線引き炉に導入されてその下部を加熱溶融され、線引きされ光ファイバとなる。
【0004】
【発明が解決しようとする課題】
ところで、近年は、光ファイバ需要の拡大によって製造の効率化およびコストダウンを目的として、光ファイバ母材を大型化する傾向があり、この光ファイバ母材の大型化に伴い、脱水焼結工程および線引き工程において種々の問題点が明らかになってきた。
まず、脱水焼結(ガラス化)工程における問題点として、複合母材のつり下げ部分に非常に大きな荷重が加わっており、つり下げ部分に焼結時の高温度が加わると軟化して母材が変形することが挙げられる。
例えば、図5に従って説明すると、良好な光ファイバ母材を十分に取ろうとして、テーパ部も含めガラス微粒子堆積部分を全てガラス化すると、ガラスロッド1が延びて図5(a)に示すように母材が落下することになる。したがって、これを回避するために、複合母材を脱水焼結して光ファイバ母材を得る際には、つり下げ部分に焼結時の高温度が加わらないように、つり下げ部分側のテーパ部の一部にガラス微粒子が完全に焼結されない部分(非焼結部)を適度に残しておく必要がある。それは、非焼結部が断熱材としての役割を果たし、つり下げ部分の軟化変形を抑制する効果をもつからである。
【0005】
次に、脱水焼結工程および線引き工程における問題点として、良質の光ファイバを効率よく取ろうとして、図6に示すように複合母材の外径一定部を多くしテーパ部の傾斜を急にしてテーパ部の長さを短くした場合でも、その効果が表れないことが挙げられる。例えば、テーパ部の傾斜および長さが複合母材の両端でほぼ同じである傾斜(図6)では、未焼結部を適度に残し、図5(a)に示すような母材の変形を防止しようとすると、図5(b)に示すように外径一定部の外径に対して未焼結部の外径が大幅に大きくなり、この母材をこのまま線引きすると、線引き炉心管の入口あるいは管内壁面にぶつかり、最後まで効率よく線引きすることができないものとなる。したがって、未焼結部を形成する側のテーパ部の傾斜を急にして長さを短くし、外径一定部を多くすることには限界がある。
また、線引き工程における問題点として、良品を効率よく取ろうとしてテーパ部の傾斜を急にして長さを短くするために、脱水焼結工程と線引き工程との間に別の工程を必要とすることが挙げられる。
例えば、脱水焼結後の光ファイバ母材の線引き開始側の端部を、線引きに最適な傾斜に加工することが一般的に行われており、具体的には、光ファイバ母材を延伸したり、切り割ったりして線引きに最適な形状を作っている。しかし、この方法では、設備や多くの労力や時間を要し、また、光ファイバ母材にこの加工を施すと、良品部のロスも多くなり、甚だ効率が良くないものである。
【0006】
ここで、光ファイバ母材のテーパ部の傾斜を規定したものが、例えば特開平9−100132号公報、特開2000−264662公報に開示されている。
しかし、特開平9−100132号公報に開示されたテーパ部は、ガラスロッドと同一の径まで小さくなっていない。また、例示されたテーパ部は、かりにガラスロッドと同一の径まで小さくなっていたとしても、テーパ部は線引き開始部が線引き終了部より長くなってしまう。また、この公報に示されるテーパ部はあくまでも均質な光ファイバの一部として利用することを想定しており、ガラス特性の長手変動を低減させることが目的であり、本発明の解決すべき課題とは関連がない。
また、特開2000−264662公報に開示されたテーパ部は、ファイバ母材を加熱加工により所定の傾斜とされるが、加熱加工を行う前のテーパ部の傾斜については言及されておらず不明である。さらに、加熱加工を行うことを実質的に必須の要件としており、工程が追加されることによる生産性の低下をもたらすことは前述のとおりである。
そこで、本発明では、複合母材が変形することなく焼結でき且つファイバ化の有効部を多く得ることが可能な光ファイバ母材の製造方法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】
本発明者は上記課題に鑑み鋭意研究した結果、光ファイバ母材の両端部に形成されるテーパ部の傾斜を異なるものにするのが良いことが判明し、本発明に至った。
すなわち、本発明は、
)光ファイバ化後にコアとなる部分を含むガラスロッドを形成する第1工程、該ガラスロッドをその軸を中心に回転させながらガラス微粒子発生装置を前記ガラスロッドの長手方向に相対的に往復移動させることにより前記ガラスロッドの外周にガラス微粒子を堆積させて複合母材を形成する第2工程、前記複合母材を加熱炉内にほぼ鉛直に支持しながら回転させて脱水焼結して光ファイバ母材を得る第3工程を有する光ファイバ母材の製造方法であって、前記第2工程が、前記ガラス微粒子発生装置を前記ガラスロッドに対して垂直方向(噴付方向で言えば90°)に配置し、複合母材の両端部に形成されるテーパ部の傾斜が異なるように前記ガラスロッドの外周にガラス微粒子を堆積させることを特徴とする光ファイバ母材の製造方法、
前記第2工程が複合母材の両端部に形成されるテーパ部の傾斜が線引きに適した形状となるように前記ガラスロッドの外周にガラス微粒子を堆積させることを特徴とする請求項1に記載の光ファイバ母材の製造方法、
(3)前記第2工程のガラス微粒子発生装置の前記ガラスロッドの長手方向への相対移動速度を、前記往復移動の一方の折り返し点付近で徐々に上昇させることを特徴とする(1)又は(2)に記載の光ファイバ母材の製造方法、
(4)前記第2工程のガラス微粒子発生装置に供給されるガラス微粒子原料の供給量を、前記往復移動の一方の折り返し点付近で徐々に減少させることを特徴とする(1)又は(2)に記載の光ファイバ母材の製造方法、
(5)前記第2工程のガラス微粒子発生装置は複数使用し、複数のガラス微粒子発生装置の往復移動の振幅をそれぞれで異ならせ、かつ前記往復移動の周期をそれぞれほぼ等しくすることを特徴とする(1)又は(2)に記載の光ファイバ母材の製造方法、および、
(6)前記第3工程は、前記複合母材両端部に形成される前記テーパ部のうち、傾斜が急な側のテーパ部を下向きにして複合母材を脱水焼結することを特徴とする(1)又は(2)記載の光ファイバ母材の製造方法
を提供するものである。
【0008】
【発明の実施の形態】
次に、本発明の好ましい実施の態様について、添付の図面に基づいて詳細に説明する。なお、各図の説明において同一の要素には同一の符号を付して重複する説明を省略する。
まず、第1工程は、光ファイバ化後にコアとなる部分を含むガラス微粒子集合体を例えば周知のVAD法などにより形成し、その集合体を脱水焼結し、必要に応じて目的の外径となるように延伸し、所望のガラスロッドを得る。その外径は30mm〜50mm、長さ500〜2000mmが好ましい。
【0009】
次いで、第2工程は図2(a)に示すようにそのガラスロッド1をその長手軸を中心に回転させながらその外周にガラス微粒子発生装置(バーナ)Aをガラスロッド1の長手方向に相対的に往復移動させてガラスロッド1の外周にガラス微粒子2を堆積させて複合母材3を得る工程である。
ここで、第2工程では、複合母材両端部に形成されるテーパ部の傾斜が異なるように前記ガラスロッドの外周にガラス微粒子を堆積させることが望ましい。
本発明の複合母材3の形状の一例を図1(a)に正面図として示す。図1(a)の複合母材は、その両端のテーパ部の傾斜が異なるものであり、本発明の光ファイバ母材の製造方法は、図1(b)に例示される傾斜のファイバ母材を製造するために適するものである。本発明の母材のテーパ部は、その面の母線が直線だけでなく、図1(a)や図4に示すように曲線であってもよい。
ここで、テーパ部の傾斜S(%)は、テーパ部の長さをL、外径一定部の外径をD、ガラスロッドの平均外径をdとしたとき、
S=L×100/{(D−d)/2}で表される。
図1(a)におけるテーパ部の傾斜Sは、傾斜が緩やかな側(上部)のテーパ部で約150〜350%の範囲が好ましく、さらに好ましくは約200〜300%であり、傾斜が急な側(下部)のテーパ部は約50〜150%の範囲が好ましく、さらに好ましくは約70〜120%である。
図1(b)は、図1(a)の複合母材を脱水焼結した場合の本発明の光ファイバ母材の形状の一例を示す正面図である。図1(b)におけるテーパ部の傾斜Sは、傾斜が緩やかな側のテーパ部で約200〜600%の範囲が好ましく、さらに好ましくは約350〜550%であり、傾斜が急な側のテーパ部で約100〜300%の範囲が好ましく、さらに好ましいのは約130〜250%である。
また、未焼結部の外径は焼結後の外径一定部の外径の約95〜120%の範囲が好ましい。
【0010】
本発明のテーパ部の傾斜が異なる光ファイバ母材の製造方法の例を図2にしたがって説明する。
まず、ガラス微粒子発生装置の移動速度を変更することによる方法である。例えば光ファイバ化後にコアとなる部分を含むガラスロッドをその長手軸を中心に回転させながらその外周にガラス微粒子を堆積させて複合母材を製造するものであるが、ガラス微粒子発生装置を長手軸方向(上下方向)に往復移動させる場合の複合母材製造中のガラスロッド1とガラス微粒子発生装置(バーナ)Aとの位置関係を図2(a)に示す。図2(a)の位置関係に配置されたガラス微粒子発生装置(バーナ)Aの移動速度の様子を図2(b)にグラフで示す。図2(b)において、縦軸のバーナの位置は図2(a)のバーナ位置に相当するものであり、点線は折り返し点を示し、横軸はその位置でのバーナの速度を表す。
原料ガス及び燃料ガス等の供給条件を同じにしてガラス微粒子発生装置を定速度で移動させた後、往復移動の一方(図では上方)の折り返し点付近(点P)で徐々に移動速度を上昇し、折り返し後はP点までは徐々に速度を下降し、以後定速で移動させる。移動速度はガス供給量やガラスロッドの長さ等に応じて適宜定まるが、定速度は約20〜50mm/秒の範囲内に設定するのが好ましく、速度上昇後の最大速度は約100〜300mm/秒程度が好ましい。したがって、移動速度が上昇する位置においては、母材の単位面当たりのガラス微粒子の付着量が減少するため、図1(a)に示すような両端部に形成されるテーパ部の傾斜が異なる複合母材を容易に得ることができる。テーパ部の終了端は図示のようにバーナの折り返し点(点線位置)より外側となる。
ここでは、ガラス微粒子発生装置の移動について述べたが、ガラス微粒子発生装置を定位置に固定し、ガラスロッドを移動させて同様の操作を行っても良いのは勿論である。
次に、ガラス微粒子発生装置への原料ガス供給量を変更することによる方法を示す。図2(c)はガラス微粒子発生装置の位置と原料ガス供給量の関係を示すグラフの一例である。図2(c)において、縦軸のバーナの位置は図2(a)のバーナ位置に相当するものであり、横軸はその位置でのバーナからの原料ガス供給量を表す。
相対移動速度を一定にして原料ガス供給量を図2(c)に示すように往復移動の一方の折り返し点付近(点P)で徐々に減少させるようにしても、折り返し点付近で徐々に母材の単位面当たりのガラス微粒子の付着量が減少するため、同様に図1(a)に示すような複合母材が得られる。
さらに、図2(b)と図2(c)とを組み合わせた、移動速度と原料供給量をともに制御する方法をガラス微粒子発生装置に対して行っても同様にテーパ部の傾斜が異なる複合母材が得られることはいうまでもない。
【0011】
さらに、本発明の両端部に形成されるテーパ部の傾斜が異なる光ファイバ母材の製造方法の他の一例を図3に示す。
図3(a)は、複数のガラス微粒子発生装置(バーナ)を上下方向に往復移動させてガラスロッドの外周にガラス微粒子を堆積させるものであり、複数のガラス微粒子発生装置(この場合は3本)は、お互いに接触しないように配置されており独立して往復移動を行うものである。
この方法はガラス微粒子発生装置の往復移動について、その振幅をそれぞのガラス微粒子発生装置(バーナ)で異ならせながら周期をほぼ等しくするものである。図3(b)及び(c)は、それぞれのガラス微粒子発生装置(バーナ)の振幅即ち移動範囲を図3(a)に対応させて表示するものである。形成されるテーパ部の傾斜が異なるようにするならばその振幅はどのような範囲でも適宜設定できるが、例えば、図3(a)に示すように上部折り返し位置では、それぞれのバーナ折り返し位置は、150mmずつずらすのが好ましく、下部折り返し位置では、50mmずつずらすのが好ましい。図3(c)の場合は、3本のバーナの移動範囲の差を小さくしたパターンである。いずれの場合でも、バーナは一往復の時間が同じになるようにその速度は異なる設定となっている。
このように複数のガラス微粒子発生装置のそれぞれの振幅を変えることにより、図1(a)に示すような両端部のテーパ部の傾斜が異なる複合母材を容易に得ることができる。そして、それぞれのバーナ折り返し位置を適宜ずらすことで、テーパ傾斜を容易に調節することもできる。なお、この場合には、ガラス微粒子発生装置への原料ガス供給量は、適宜調整してよく、図2(c)に相当するような折り返し点付近で供給量を減少させるといった供給量調整を行ってもよい。
【0012】
このようにして効率よく図1(a)に示すような複合母材を得ることがでる。そして、第3工程として、この複合母材の傾斜が急な側のテーパ部を下にして加熱炉内にほぼ垂直に支持しながら回転させ、ヘリウムガス、塩素ガス等を送りながら約1100℃以上で脱水を行い、さらに1400℃〜1600℃の高温で焼結を行い、図1(b)に示すような上部に未焼結部5を少し残した光ファイバ母材4を製造する。複合母材の上方の支持部側はテーパが長いので支持部付近のガラスロッドが高温に曝されず軟化変形の恐れがなく、焼結処理操作が容易である。
続いて、第4工程として、得られた光ファイバ母材に望むなら適宜の処理を加えてもよいが、さらに形状が変化するような特別な処理や加工を施すことなく、そのまま線引き炉へ導入し線引きを行うことができる。そして、伝送損失の少ない良好で均質な光ファイバを得ることができる。
この結果従来の光ファイバの製造方法と比較して、光ファイバ母材製造後線引きまでに光ファイバ母材を加熱加工する工程を必要としないため工程が数時間短縮し、得られる光ファイバの良品率が約10〜20%増加した。
なお、本発明の実施の形態は上述のものに限られず、特許請求の範囲に記載された発明の範囲内で種々の変更が可能である。
【0013】
【実施例】
周知のVAD法によりコアとなる部分を含む外径36mm、長さ1800mmの石英ガラスロッドを作製した。図2(a)に示すように、このガラスロッドを垂直に配置し、時間と共に回転数を200〜25rpmに変化させて回転させながらバーナを上下方向に移動させてガラス微粒子を堆積させ複合母材を製造した。バーナには各ガス供給装置から水素200リットル/分、酸素90リットル/分、四塩化ケイ素100g/分、シール用にアルゴンガス1.5リットル/分を供給し、火炎分解反応によってガラス微粒子を生成させた。
図2(b)に示すように上部折り返し点より約200mm下方に速度変更点Pを設定した。バーナは下部折り返し点からP点まで50mm/秒の一定速度で移動し、P点から上部折り返し点までその速度を徐々に上げ、折り返し直前には最高速度150mm/秒とした。このバーナ移動を繰り返し、ガラス微粒子を堆積した。
【0014】
得られた複合母材は、外径一定部の外径が約250mmであり、上部のテーパ部の長さが約300mm、下部約100mmの図1(a)に示すような形状であり、その傾斜は上部で280%、下部で93%であった。この複合母材を傾斜が急な側のテーパ部を下にして、加熱炉内に垂直に支持し回転させながら脱水焼結処理を約15時間行った。
得られた光ファイバ母材は、外径一定部の外径が150mmであり、上部の未ガラス化部分を含むテーパ部の最大外径は約160mmであった。そして、上部のテーパ部の長さが約300mm、下部テーパ部の長さ100mmは変わりなかった。したがって、その傾斜は上部で約530%、下部で約180%である。このように両端部に形成されるテーパ部の傾斜が異なった光ファイバ母材が得られた。
この光ファイバ母材は、このまま線引き炉に投入し良好に線引きを行うことができた。
【0015】
【発明の効果】
以上のとおり、本発明によれば、焼結後の光ファイバ母材は特別の処理を必要とすることなく光ファイバの製造が可能であるので、光ファイバの製造工程を簡略化するとともに、その製造コストを低減させることができる。また、複合母材の焼結時にファイバ化に有効な部分を多く取っても母材の軟化による変形が抑制でき、焼結操作が容易である。
【図面の簡単な説明】
【図1】(a)は本発明の光ファイバ母材の製造過程で得られる複合母材の正面図であり、(b)は(a)の複合母材を脱水焼結した場合の光ファイバ母材の正面図である。
【図2】本発明の光ファイバ母材の製造方法の第2工程の例を示す説明図であり、(a)はガラスロッドとガラス微粒子発生装置(バーナ)との位置関係の状態を示す正面図であり、(b)はバーナの位置と移動速度の関係を示すグラフであり、(c)はバーナ位置と原料ガス供給量の関係を示すグラフである。
【図3】本発明の光ファイバ母材の製造方法の第2工程の他の例を示す説明図であり、(a)はガラスロッドとガラス微粒子発生装置(バーナ)との位置関係の状態を示す正面図であり、(b)、(c)はそれぞれバーナの移動範囲を示すものである。
【図4】従来の複合母材の製造方法と得られた複合母材の形状とを説明する概略図である。
【図5】(a)は焼結時に母材つり下げ部が変形した状態の説明図であり、(b)は従来の光ファイバ母材の形状の例を示す説明図である。
【図6】従来のテーパ部の傾斜を急にした複合母材の概略図である。
【符号の説明】
1 ガラスロッド
2 ガラス微粒子
3 複合母材
4 光ファイバ母材
5 未焼結部
A、B、C ガラス微粒子発生装置(バーナ)
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber preform useful for manufacturing an optical fiber used for optical communication, a method for manufacturing the optical fiber preform, and a method for manufacturing an optical fiber from the preform.
[0002]
[Prior art]
As a conventional optical fiber manufacturing method, glass fine particles are deposited by flame hydrolysis of a raw material gas on the outer periphery of a glass rod including a core portion after optical fiber formation to form a composite base material. A method is generally known in which an optical fiber preform is manufactured by dehydration sintering (vitrification), and one end of the optical fiber preform is heated and melted to draw an optical fiber having a constant outer diameter.
[0003]
Here, regarding a method for manufacturing an optical fiber preform, for example, there is a method disclosed in Japanese Patent Laid-Open No. 10-7430 proposed by the present applicant. This method relates to a technique for depositing glass particles on the outer periphery of a glass rod by moving a plurality of glass particle generators (burners) in the longitudinal direction of the glass rod while rotating the glass rod.
As shown in FIG. 4, the composite base material manufactured by such a technique generally has a constant outer diameter portion that becomes a high-quality optical fiber, and a taper at which both outer diameters gradually decrease toward the end portion. The tapered portion has substantially the same inclination at both ends as shown in the figure.
Further, in the process of dehydrating and sintering the composite base material obtained in this way to form an optical fiber base material, the composite base material is suspended vertically in the heating furnace and slowly pulled down while rotating. It is common to process.
Then, the optical fiber preform obtained by dehydration and sintering is introduced into a drawing furnace, the lower part thereof is heated and melted, and drawn to form an optical fiber.
[0004]
[Problems to be solved by the invention]
By the way, in recent years, there is a tendency to increase the size of the optical fiber preform for the purpose of increasing the efficiency of manufacturing and reducing the cost due to the expansion of the demand for optical fibers. Various problems have become apparent in the drawing process.
First, as a problem in the dehydration sintering (vitrification) process, a very large load is applied to the suspended portion of the composite base material, which softens when a high temperature is applied to the suspended portion during sintering. May be deformed.
For example, referring to FIG. 5, when all the glass particle deposition portions including the taper portion are vitrified in an attempt to sufficiently obtain a good optical fiber preform, the glass rod 1 extends, as shown in FIG. The base material will fall. Therefore, in order to avoid this, when the composite preform is dehydrated and sintered to obtain an optical fiber preform, the suspended portion side taper is not applied to the suspended portion so that a high temperature during sintering is not applied. It is necessary to leave a part (non-sintered part) where the glass fine particles are not completely sintered in a part of the part. This is because the non-sintered portion serves as a heat insulating material and has an effect of suppressing softening deformation of the suspended portion.
[0005]
Next, as a problem in the dehydration sintering process and the drawing process, an attempt is made to efficiently obtain a high-quality optical fiber, and as shown in FIG. Even when the length of the tapered portion is shortened, the effect is not exhibited. For example, in the inclination (FIG. 6) in which the inclination and length of the taper portion are substantially the same at both ends of the composite base material, the unsintered portion is left appropriately, and the base material is deformed as shown in FIG. If it tries to prevent, as shown in FIG.5 (b), the outer diameter of a non-sintered part will become large largely with respect to the outer diameter of a constant outer diameter part, and if this preform | base_material is drawn as it is, the entrance of a drawing core tube will be carried out. Or it hits the inner wall surface of the tube and cannot be drawn efficiently until the end. Therefore, there is a limit to increasing the number of constant outer diameter portions by steeply inclining the tapered portion on the side where the unsintered portion is formed to shorten the length.
Also, as a problem in the drawing process, another process is required between the dehydration sintering process and the drawing process in order to shorten the length by steeply inclining the tapered portion in order to efficiently take good products. Can be mentioned.
For example, it is common practice to process the end of the drawing start side of the optical fiber preform after dehydration and sintering into an optimum slope for drawing. Specifically, the optical fiber preform is stretched. Or cut and cut to create the best shape for drawing. However, this method requires equipment, a lot of labor and time, and when this processing is performed on the optical fiber preform, the loss of non-defective parts increases and the efficiency is extremely poor.
[0006]
Here, what prescribes | regulates the inclination of the taper part of an optical fiber preform | base_material is disclosed by Unexamined-Japanese-Patent No. 9-100132, Unexamined-Japanese-Patent No. 2000-264661, for example.
However, the tapered portion disclosed in JP-A-9-100132 is not reduced to the same diameter as the glass rod. Moreover, even if the taper part illustrated is reduced to the same diameter as the glass rod, the taper part has a drawing start part longer than the drawing end part. In addition, the tapered portion shown in this publication is supposed to be used as a part of a homogeneous optical fiber, and the purpose is to reduce the longitudinal fluctuation of the glass characteristics, and the problem to be solved by the present invention is Is not relevant.
Further, the tapered portion disclosed in Japanese Patent Laid-Open No. 2000-264661 has a predetermined inclination by heating the fiber preform, but the inclination of the tapered portion before the heating is not mentioned and is unknown. is there. Furthermore, it is a substantially essential requirement to perform heat processing, and as described above, the productivity is reduced by adding a process.
Therefore, in the present invention aims to provide a manufacturing how sintering can and fiber of the effective portion can be obtained much optical fiber preform without composite preform is deformed.
[0007]
[Means for Solving the Problems]
As a result of diligent research in view of the above problems, the present inventor has found that it is preferable to make the slopes of the tapered portions formed at both ends of the optical fiber preform different, and the present invention has been achieved.
That is, the present invention
( 1 ) First step of forming a glass rod including a core portion after optical fiber formation, reciprocating the glass particle generator relatively in the longitudinal direction of the glass rod while rotating the glass rod around its axis A second step of depositing glass fine particles on the outer periphery of the glass rod by moving to form a composite base material; rotating the composite base material while supporting the composite base material substantially vertically in a heating furnace; A method of manufacturing an optical fiber preform having a third step of obtaining a fiber preform, wherein the second step is a step in which the glass fine particle generator is placed in a direction perpendicular to the glass rod (90 ° in the spraying direction). The glass fiber is deposited on the outer periphery of the glass rod so that the slopes of the tapered portions formed at both ends of the composite base material are different from each other. Law,
( 2 ) The glass particles are deposited on the outer periphery of the glass rod so that the slope of the tapered portions formed at both ends of the composite base material is suitable for drawing in the second step. A method of manufacturing the optical fiber preform according to 1,
(3) The relative movement speed in the longitudinal direction of the glass rod of the glass fine particle generating device in the second step is gradually increased near one turning point of the reciprocating movement (1) or ( 2) A method for producing an optical fiber preform according to
(4) The supply amount of the glass fine particle raw material supplied to the glass fine particle generator in the second step is gradually decreased in the vicinity of one turning point of the reciprocating movement (1) or (2) A method of manufacturing an optical fiber preform according to
(5) A plurality of glass fine particle generators in the second step are used, the amplitudes of the reciprocating movements of the plurality of glass fine particle generating apparatuses are different, and the reciprocating movement periods are substantially equal to each other. (1) The manufacturing method of the optical fiber preform as described in (2), and
(6) The third step is characterized in that the composite base material is dehydrated and sintered with the tapered portion on the steep side of the taper portion formed at both ends of the composite base material facing downward. (1) or the manufacturing method of the optical fiber preform according to (2) ,
Is to provide.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted.
First, in the first step, a glass fine particle aggregate including a core portion after optical fiber formation is formed by, for example, a well-known VAD method, and the aggregate is dehydrated and sintered. The desired glass rod is obtained by stretching. The outer diameter is preferably 30 mm to 50 mm and a length of 500 to 2000 mm.
[0009]
Next, in the second step, as shown in FIG. 2 (a), while rotating the glass rod 1 around its longitudinal axis, the glass fine particle generator (burner) A is relatively placed on the outer circumference in the longitudinal direction of the glass rod 1. And the fine particles 2 are deposited on the outer periphery of the glass rod 1 to obtain the composite base material 3.
Here, in the second step, it is desirable to deposit glass fine particles on the outer periphery of the glass rod so that the slopes of the tapered portions formed at both ends of the composite base material are different.
An example of the shape of the composite base material 3 of the present invention is shown as a front view in FIG. The composite base material of FIG. 1 (a) is different in the inclination of the taper portions at both ends, and the method of manufacturing the optical fiber base material of the present invention is an inclined fiber base material exemplified in FIG. 1 (b). It is suitable for manufacturing. The tapered portion of the base material of the present invention may have a curved surface as shown in FIG. 1A and FIG.
Here, the slope S (%) of the taper portion is defined as L for the length of the taper portion, D for the outer diameter of the constant outer diameter portion, and d for the average outer diameter of the glass rod.
S = L × 100 / {(D−d) / 2}.
The slope S of the tapered portion in FIG. 1 (a) is preferably in the range of about 150 to 350%, more preferably about 200 to 300% in the tapered portion on the side where the slope is gentle (upper), more preferably about 200 to 300%. The side (lower) taper portion is preferably in the range of about 50 to 150%, more preferably about 70 to 120%.
FIG. 1B is a front view showing an example of the shape of the optical fiber preform of the present invention when the composite preform of FIG. 1A is dehydrated and sintered. The slope S of the taper portion in FIG. 1B is preferably in the range of about 200 to 600%, more preferably about 350 to 550%, and more preferably about 350 to 550%. The range is preferably about 100 to 300%, more preferably about 130 to 250%.
The outer diameter of the unsintered portion is preferably in the range of about 95 to 120% of the outer diameter of the constant outer diameter portion after sintering.
[0010]
An example of a method for manufacturing an optical fiber preform having a different inclination of the tapered portion of the present invention will be described with reference to FIG.
First, it is a method by changing the moving speed of the glass particle generator. For example, a glass rod including a core portion after optical fiber is rotated around its longitudinal axis, and glass fine particles are deposited on its outer periphery to produce a composite base material. FIG. 2A shows the positional relationship between the glass rod 1 and the glass fine particle generator (burner) A during the production of the composite base material when reciprocating in the direction (vertical direction). FIG. 2B is a graph showing the movement speed of the glass fine particle generator (burner) A arranged in the positional relationship of FIG. In FIG. 2B, the position of the burner on the vertical axis corresponds to the position of the burner in FIG. 2A, the dotted line indicates the turning point, and the horizontal axis indicates the speed of the burner at that position.
After moving the glass particle generator at a constant speed under the same supply conditions for the raw material gas and fuel gas, the moving speed is gradually increased near the turning point (point P) in one of the reciprocating movements (upward in the figure). After the turn, the speed is gradually lowered to the point P and then moved at a constant speed. The moving speed is appropriately determined according to the gas supply amount, the length of the glass rod, etc., but the constant speed is preferably set in the range of about 20 to 50 mm / second, and the maximum speed after the speed increase is about 100 to 300 mm. / Second is preferable. Therefore, at the position where the moving speed is increased, the amount of glass fine particles attached per unit surface of the base material is reduced, so that the slopes of the tapered portions formed at both ends as shown in FIG. A base material can be obtained easily. The end of the taper portion is outside the burner folding point (dotted line position) as shown.
Although the movement of the glass particle generator has been described here, it is needless to say that the same operation may be performed by fixing the glass particle generator in a fixed position and moving the glass rod.
Next, a method by changing the amount of raw material gas supplied to the glass particle generator will be described. FIG.2 (c) is an example of the graph which shows the relationship between the position of a glass particulate generator, and raw material gas supply amount. In FIG. 2C, the position of the burner on the vertical axis corresponds to the position of the burner in FIG. 2A, and the horizontal axis represents the amount of source gas supplied from the burner at that position.
Even if the source gas supply amount is gradually decreased near one turn point (point P) of the reciprocating movement as shown in FIG. 2C with the relative movement speed kept constant, the mother gas is gradually raised near the turn point. Since the adhesion amount of the glass fine particles per unit surface of the material is reduced, a composite base material as shown in FIG.
Furthermore, even if the method for controlling both the moving speed and the raw material supply amount, which is a combination of FIG. 2B and FIG. It goes without saying that the material is obtained.
[0011]
Furthermore, FIG. 3 shows another example of a method for manufacturing an optical fiber preform in which the tapered portions formed at both ends of the present invention have different inclinations.
FIG. 3A shows a structure in which a plurality of glass particle generators (burners) are reciprocated in the vertical direction to deposit glass particles on the outer periphery of a glass rod. ) Are arranged so as not to contact each other, and reciprocate independently.
In this method, the reciprocating movement of the glass particle generator is made to have substantially the same period while varying the amplitude of each glass particle generator (burner). 3 (b) and 3 (c) display the amplitude, that is, the movement range of each glass particle generator (burner) in correspondence with FIG. 3 (a). If the inclination of the formed taper portion is made different, the amplitude can be appropriately set in any range. For example, as shown in FIG. It is preferable to shift by 150 mm, and it is preferable to shift by 50 mm at the lower folded position. In the case of FIG.3 (c), it is a pattern which made small the difference of the movement range of three burners. In either case, the burners are set to different speeds so that the time for one round trip is the same.
Thus, by changing the amplitude of each of the plurality of glass fine particle generators, a composite base material with different slopes of the taper portions at both ends as shown in FIG. 1A can be easily obtained. And taper inclination can also be easily adjusted by shifting each burner folding position suitably. In this case, the supply amount of the raw material gas to the glass fine particle generator may be adjusted as appropriate, and the supply amount is adjusted such that the supply amount is reduced in the vicinity of the turning point corresponding to FIG. May be.
[0012]
In this way, a composite base material as shown in FIG. 1 (a) can be obtained efficiently. Then, as the third step, the composite base material is rotated while supporting the taper portion on the side where the inclination is steeply inclined substantially vertically in the heating furnace, and about 1100 ° C. or higher while feeding helium gas, chlorine gas or the like. The optical fiber preform 4 is manufactured by performing dehydration and sintering at a high temperature of 1400 ° C. to 1600 ° C., leaving a few unsintered portions 5 on the top as shown in FIG. Since the support part side above the composite base material has a long taper, the glass rod in the vicinity of the support part is not exposed to high temperature and there is no fear of softening deformation, and the sintering process operation is easy.
Subsequently, as the fourth step, an appropriate treatment may be added to the obtained optical fiber preform, but it is directly introduced into the drawing furnace without any special treatment or processing that changes the shape. Line drawing can be performed. A good and uniform optical fiber with little transmission loss can be obtained.
As a result, compared with the conventional optical fiber manufacturing method, the process of heating the optical fiber preform is not required before drawing after the optical fiber preform is manufactured, so the process is shortened by several hours and the resulting optical fiber is good. The rate increased by about 10-20%.
The embodiment of the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention described in the claims.
[0013]
【Example】
A quartz glass rod having an outer diameter of 36 mm and a length of 1800 mm including a core portion was produced by a well-known VAD method. As shown in FIG. 2 (a), this glass rod is arranged vertically, and the rotating speed is changed to 200 to 25 rpm with time, and the burner is moved up and down while rotating to deposit glass particles. Manufactured. Each burner is supplied with 200 liters / minute of hydrogen, 90 liters / minute of oxygen, 100 g / minute of silicon tetrachloride, and 1.5 liters / minute of argon gas for sealing. I let you.
As shown in FIG. 2B, a speed change point P was set about 200 mm below the upper turn-around point. The burner moved from the lower folding point to the P point at a constant speed of 50 mm / second, gradually increasing its speed from the P point to the upper folding point, and immediately before the folding, the maximum speed was 150 mm / second. This burner movement was repeated to deposit glass particles.
[0014]
The obtained composite base material has a shape as shown in FIG. 1A in which the outer diameter of the constant outer diameter portion is about 250 mm, the length of the upper tapered portion is about 300 mm, and the lower portion is about 100 mm. The slope was 280% at the top and 93% at the bottom. The composite base material was dehydrated and sintered for about 15 hours while rotating and supported vertically in the heating furnace with the taper on the steep side down.
In the obtained optical fiber preform, the outer diameter of the constant outer diameter portion was 150 mm, and the maximum outer diameter of the tapered portion including the upper non-glass portion was about 160 mm. The length of the upper tapered portion was about 300 mm, and the length of the lower tapered portion was 100 mm. Therefore, the slope is about 530% at the top and about 180% at the bottom. Thus, optical fiber preforms having different slopes of the tapered portions formed at both ends were obtained.
This optical fiber preform was put in a drawing furnace as it was and was able to be drawn satisfactorily.
[0015]
【The invention's effect】
As described above, according to the present invention, since the optical fiber preform after sintering can be manufactured without requiring special treatment, the manufacturing process of the optical fiber can be simplified, Manufacturing cost can be reduced. Further, even if a large portion effective for fiber formation is taken during sintering of the composite base material, deformation due to softening of the base material can be suppressed, and the sintering operation is easy.
[Brief description of the drawings]
FIG. 1 (a) is a front view of a composite preform obtained in the process of manufacturing an optical fiber preform of the present invention, and FIG. 1 (b) is an optical fiber when the composite preform of (a) is dehydrated and sintered. It is a front view of a base material.
FIG. 2 is an explanatory view showing an example of a second step of the method for manufacturing an optical fiber preform of the present invention, in which (a) is a front view showing a positional relationship between a glass rod and a glass fine particle generator (burner). It is a figure, (b) is a graph which shows the relationship between the position of a burner, and moving speed, (c) is a graph which shows the relationship between a burner position and raw material gas supply amount.
FIG. 3 is an explanatory view showing another example of the second step of the manufacturing method of the optical fiber preform of the present invention, wherein (a) shows the state of the positional relationship between the glass rod and the glass fine particle generator (burner). It is a front view to show, (b), (c) shows the movement range of a burner, respectively.
FIG. 4 is a schematic diagram for explaining a conventional method for producing a composite base material and the shape of the obtained composite base material.
FIG. 5A is an explanatory view showing a state in which a preform hanging portion is deformed during sintering, and FIG. 5B is an explanatory view showing an example of the shape of a conventional optical fiber preform.
FIG. 6 is a schematic view of a composite base material with a steep inclination of a conventional taper portion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass rod 2 Glass particulate 3 Composite base material 4 Optical fiber preform 5 Unsintered part A, B, C Glass particulate generator (burner)

Claims (6)

光ファイバ化後にコアとなる部分を含むガラスロッドを形成する第1工程、該ガラスロッドをその軸を中心に回転させながらガラス微粒子発生装置を前記ガラスロッドの長手方向に相対的に往復移動させることにより前記ガラスロッドの外周にガラス微粒子を堆積させて複合母材を形成する第2工程、前記複合母材を加熱炉内にほぼ鉛直に支持しながら回転させて脱水焼結して光ファイバ母材を得る第3工程を有する光ファイバ母材の製造方法であって、前記第2工程が、前記ガラス微粒子発生装置を前記ガラスロッドに対して垂直方向に配置し、複合母材の両端部に形成されるテーパ部の傾斜が異なるように前記ガラスロッドの外周にガラス微粒子を堆積させることを特徴とする光ファイバ母材の製造方法。A first step of forming a glass rod including a core portion after the optical fiber is formed, and the glass particle generator is reciprocated relatively in the longitudinal direction of the glass rod while rotating the glass rod about its axis. A second step of depositing glass particles on the outer periphery of the glass rod to form a composite base material, and rotating and dehydrating and sintering the composite base material while supporting the composite base material substantially vertically in a heating furnace. A method of manufacturing an optical fiber preform having a third step of obtaining the optical fiber preform, wherein the second step is such that the glass fine particle generator is arranged in a direction perpendicular to the glass rod and formed at both ends of the composite preform. A method for producing an optical fiber preform, comprising depositing glass fine particles on the outer periphery of the glass rod so that the inclination of the tapered portion is different. 前記第2工程が複合母材の両端部に形成されるテーパ部の傾斜が線引きに適した形状となるように前記ガラスロッドの外周にガラス微粒子を堆積させることを特徴とする請求項1に記載の光ファイバ母材の製造方法。2. The glass particles are deposited on the outer periphery of the glass rod so that the second step forms an inclination of the tapered portion formed at both ends of the composite base material into a shape suitable for drawing. Manufacturing method of optical fiber preform. 前記第2工程のガラス微粒子発生装置の前記ガラスロッドの長手方向への相対移動速度を、前記往復移動の一方の折り返し点付近で徐々に上昇させることを特徴とする請求項1又は2に記載の光ファイバ母材の製造方法。The relative movement speed in the longitudinal direction of the glass rod of glass particles generator of the second step, according to claim 1 or 2, characterized in that is gradually increased in the vicinity of one of the turning points of the reciprocating movement Manufacturing method of optical fiber preform. 前記第2工程のガラス微粒子発生装置に供給されるガラス微粒子原料の供給量を、前記往復移動の一方の折り返し点付近で徐々に減少させることを特徴とする請求項1又は2に記載の光ファイバ母材の製造方法。The optical fiber according to claim 1 or 2, wherein the supply amount of glass particles feed to glass particles generator of the second step is gradually reduced in the vicinity of one of the turning points of the reciprocating movement A manufacturing method of a base material. 前記第2工程のガラス微粒子発生装置は複数使用し、複数のガラス微粒子発生装置の往復移動の振幅をそれぞれで異ならせ、かつ前記往復移動の周期をそれぞれほぼ等しくすることを特徴とする請求項1又は2に記載の光ファイバ母材の製造方法。Claim 1, wherein the second step the glass particles generator of multiple uses, at different amplitudes of the reciprocating movement of a plurality of glass particles generating device respectively, and approximately equal to the period of the reciprocating movement, respectively Or the manufacturing method of the optical fiber preform of 2. 前記第3工程は、前記複合母材両端部に形成される前記テーパ部のうち、傾斜が急な側のテーパ部を下向きにして複合母材を脱水焼結することを特徴とする請求項1又は2記載の光ファイバ母材の製造方法 Said third step, said one of the tapered portion formed on the composite base material opposite ends, claim, characterized in that the inclination is dehydrated sintered composite preform in the downward taper portion of the steep side 1 Or the manufacturing method of the optical fiber preform of 2 .
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