JP2004002140A - Method and apparatus for manufacturing optical fiber preform or optical fiber intermediate preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for manufacturing an optical fiber preform or an optical fiber intermediate preformed wherein the transmission loss due to the light absorption of OH group is reduced. <P>SOLUTION: In the method of manufacturing the optical fiber preform or the optical fiber intermediate preform by the collapse method for solidifying a glass pipe or integrating the glass pipe with a glass rod inserted into the glass pipe by heating, the collapse method is performed by providing glass pipe connection parts each formed by a separated pipe line system and having a gas supply port and a gas exhaust port in one end part or both end parts and introducing a dehydrating and transition metal removing gas or a gaseous mixture containing the gas into the glass pipe from the gas supply port while exhausting the gas in the glass pipe from the gas exhausting port. <P>COPYRIGHT: (C)2004,JPO

Description

となる。
パイプ内に流入するガスの全量はＳ_１＋Ｓ_２であるから、プロセスガスの流量Ｓ_２が巻き込まれる大気の流量Ｓ_１のｋ倍とすれば、定常状態になったときの割合ｒ_０は
【数２】

となる。
【００２１】
パイプ内の圧力Ｐ及び空間の体積をＶ、温度をＴとすると、ガラスパイプ内の水素分子または水素元素を含む化合物（水素元素含有化合物と総称）の量Ｎは、
【数３】

で表されるから水素元素含有化合物の濃度Ｃは、
【数４】

によって推測することができる。
従って、Ｐ、ｒ_１、ｒ_２が小さいほど、また、ｒ_２は必ず１より小さいのでｋが大きいほど上記濃度Ｃは小さくなる。
【００２２】
そして、この濃度Ｃが低ければ低いほど、下記式
【化１】

で表される反応によって生成するＳｉＯＨ又はＧｅＯＨの量が減るため、波長１．４μｍ帯で見られるＯＨ基による過剰な伝送損失の上昇を抑制することが可能となる。
ガラスパイプ内の圧力Ｐは、大気の巻き込み量、プロセスガスの流量が大きいほど大きくなってしまうので、真空ポンプを用いるのが望ましく、排気系統には、ガラスパイプ内の到達真空度が絶対圧力で１ｋＰａ以下、好ましくは０．１ｋＰａ以下、更に好ましくは０．０１ｋＰａ以下である排気手段を接続する。真空ポンプを用いて排気することで、ガラスパイプ内の圧力を低減することができ、その結果、ガラスと反応してＯＨ基となるＨ_２やＨ_２Ｏ等のガスが存在する絶対量自体を減少させ、伝送損失を低減させることができる。勿論、ポンプの能力が高く、より低い圧力まで排気できればできるほど望ましい〔上記発明（４）〕。
【００２３】
通常、コラップス時に真空排気してしまうと、コラップス後に楕円化してしまうという問題点があるが、ロッドを挿入して、パイプをその周囲に一体化させるような場合であれば、ロッドが心棒となって楕円化を抑制することが可能である。
例えば、水素含有化合物ガスとしてＨ_２Ｏを考えれば、２４℃におけるＨ_２Ｏの飽和蒸気圧は、約３ｋＰａであるから、その濃度は最大で３．２％＝３２０００ｐｐｍとなる。この量を変えるためには、巻き込みが最も懸念される、ガラスパイプと配管部との継手部をカバーで覆い、そのカバー内を不活性ガス、酸素、または酸素及び不活性ガスの混合ガスでパージするのが望ましい。
【００２４】
前記したようにプロセスガス中の水素分子又は水素含有化合物の濃度が小さければ小さいほど望ましいが、１００ｐｐｍ以下、より好ましくは１０ｐｐｍ以下であれば好適である〔上記発明（４）〕。こうすることで、大気よりも水素分子又は水素含有化合物の濃度を十分に低くすることが可能であるため、プロセスガスがガラスパイプ内に供給される流量は、大気の巻き込み量の１０倍以上、より好ましくは１００倍以上であることが望ましい。すなわち、前記数４におけるｋが１０以上、より好ましくは１００以上である。
プロセスガスがＨｅ、Ｎ_２、Ａｒなどの不活性ガス、Ｏ_２、またはＯ_２及び不活性ガスの混合ガスであると、コラップスの界面での気泡や微結晶形成等の、欠陥の形成を抑制する。特に、ロッド表面またはパイプ内表面がＧｅＯ_２添加ＳｉＯ_２であるような場合、
【化２】

の反応によってＧｅＯが生成し、ガラス欠陥や気泡が形成されてしまうが、酸素または酸素含有ガスを用いればこの平衡反応は左辺にかたよるので、欠陥や気泡の形成を抑制することが可能である。
【００２５】
上述の場合とは逆に、ガラスパイプ１内を陽圧とすることで大気からガラスパイプ１内にガスが巻き込まれるのを大幅に抑制することができる。加えて特にプロセスガスがＣｌ_２等脱水性ガスの場合、そのガスの濃度が高くなるので界面におけるＯＨ基の発生防止効果は一層増大する。ガラスパイプ内の圧は余り高くても、上記のようにコラプスに必要な時間が長くなったり、逆にパイプが膨張したりするので、外気圧との差を＋１ｋＰａ以下、好ましくは＋０．０１ｋＰａ〜＋０．１０ｋＰａとするのが良い〔前記発明（６）〕。これによりパイプの膨張を抑え、コラップスを良好に実施可能となる。
【００２６】
ガラスパイプ又はガラスパイプ及びガラスロッドを縦型に配置する場合、（ｉ）プロセスガスが空気の比重よりも大きいときは、前記発明（８）のようにコラップスをガラスパイプの下方から上方に向かって行い、また、（ｉｉ）プロセスガスが空気より小さい比重を有するときは、前記発明（９）のように、ガラスパイプの上方から下方に向かってコラップスを実施する。すなわち、Ｃｌ_２やＳＯＣｌ_２，Ｏ_２などを含み重いプロセスガスのときには、ガスが下方にたまるようにしてコラップスを実施する。パイプを回転する必要はない。「鉛直方向」だけでなく、斜めであっても良い（図４参照）。
一方、Ｈｅ，Ｎ_２などを含む軽いプロセスガスの時には、ガスが上方にたまるようにしてコラップスを実施する。パイプを回転する必要はない。この場合も（ｉ）と同様、「鉛直方向」だけでなく、斜めであっても良い（図５参照）。
いずれにしても重いガスの場合は、下方に帯留するので巻き込んだ空気を置換する効果が高く、軽いガスの場合も、上方に帯留する結果、同様の効果は大きい。
【００２７】
上記した各発明の効果は、巻き込まれた大気とプロセスガスが完全に混じり合う装置でないと実現できない。該装置としては、上記発明（１０）〜（１１）に示されるものが好ましい。これ以外の装置では例えばガラスパイプ部と配管部の継手や回転部があれば、回転部で巻き込まれた大気の濃度が徐々に上昇しＯＨ基の光吸収による過剰な伝送損失（過剰損失ともいう）が大きくなってしまう。
【００２８】
ところで、ＯＨ基はガラスパイプ内の雰囲気中だけでなく、ガラス表面に吸着したＨ_２やＨ_２Ｏなどの水素分子又は水素元素含有化合物とガラスとの反応によっても発生してしまう。従って、ガラス表面に吸着している水素分子又は水素元素含有化合物の量は、単分子層を形成するに足る量（表面状態や吸着物種類で異なるが１０^−３ｍｏｌ／ｃｍ^３程度）以下に少なければ、少ないほど良好である。ガラスパイプ表面の吸着ガスを低減する手法としては、気相エッチングによって、ガラス表面を削り取り、その後は不活性ガスなど水素分子又は水素元素含有化合物の濃度が低い、清浄なガスでパージするなどすればよい。ガラスロッドをパイプ内に挿入後に、Ｃｌ_２、ＳＯＣｌ_２などの脱水性ガスをガラスパイプ内に流しながら、熱源で１１５０℃程度以上に加熱しても良い結果が得られる。
【００２９】
更に好ましいのは、ガラスロッドをガラスパイプ内に挿入後、４ｋＰａ以下、好ましくは０．４ｋＰａ以下（低い程好ましい）への真空引きを実施し、その後プロセスガスによって５０ｋＰａ以上、好ましくは１０１ｋＰａ（約１気圧）以上にパージする、ということを１回または複数回繰り返すことである。真空状態にすることによって、ガラスパイプ、ガラスロッド表面に吸着したＨ_２、Ｈ_２Ｏなどを脱離させることが可能であり、それを一旦プロセスガスでパージすることで、再付着を抑制することが可能となる。
【００３０】
本発明により回転可能なガラスパイプ（以下、補助パイプを取り付けたものを含む総称）又は回転可能なガラスパイプ及びガラスロッドから光ファイバ母材を製造する装置においては、例えばガラス旋盤を設け（図３）、該ガラスパイプの一端（または両端）にガス供給口８の先端部８′とガス排気口９の先端部９′をそれぞれ取付け、該ガス供給口８からプロセスガスを該ガラスパイプ１内に供給するとともに、該ガス排出口９の先端部９′から該ガラスパイプ１内のガスを排出しつつ該ガラスパイプ１をコラップスすることが可能となるので光ファイバの品質に悪影響を与えることはない。この場合、ガス供給と排気それぞれの配管は別ラインで行い、途中で１本の配管にまとまることはない。継手部５で大気を巻き込んでも直ちに排気することができる。また上記のガス供給用の配管と排気用配管は二重構造に配置するのが好ましい。〔前記発明（１０）〕。
【００３１】
図１、図２又は図３において、ガス排気口９は外側に配置された配管（外筒１４）及びロータリージョイントを介してガス排気系統と接続されている。ロータリージョイントは回転体と非回転体とを結ぶもので継手６及びキャップ１８からなる。　一方、ガス供給口８は内側に配置された配管（内筒１３）によって直接ガス供給系統（図６の１１）に接続される。このとき内筒１３は回転せず、従ってガラスパイプ接続部５において配管の接続点を有さない。すなわち、ロータリージョイント部で大気を巻き込んだとしてもガス供給する配管内（内筒１３）には、大気は混入することがなく、直ちに排気することができる。従って、ガラスパイプ内部に水分等の不純物が混入せず高品質の光ファイバを製造することができる。
【００３２】
上記したガス供給口８の先端部８′及びガス排気口９の先端部９′は、それぞれガラスパイプ１内の位置を同じとしてもよい（図１）が、ガス供給口先端部８′を大気巻き込みの可能性のある位置よりもコラップスの界面に近い位置とし、ガス排気口先端部９′はガス供給口先端部８′よりもコラップス界面に遠い位置にするのが好ましい〔前記発明（７）、図２参照〕。
図２は、本発明の別の実施形態を示す軸線に沿った部分断面図で、ガス供給口先端部８′がキャップ１６よりも更にパイプ長手方向の内側にあり、ガス排気口先端部９′は図１と同じ位置に設けてある。この構成により、コラプス界面では高純度なプロセスガスが充満され、巻き込んだ大気を含まないガスを供給することが可能となる。すなわち、仮に回転継手部（継手６，キャップ１９等）等から大気がガラスパイプ１内に入ってもガラスパイプ１内のコラプス界面側にはプロセスガスが充満しているので排気口先端部９′から排気口９（通路１５）を経て排気される。これによりＯＨ基光吸収による伝送損失を低減できる。
なお、ガス供給口８及びガス排気口９は、図１，図２及び図３のような同心円構造とせず、図４（ａ）に示されるようにそれぞれ別のガス供給管とガス排気管を設ける形としてもよい。この場合は、回転できないので縦型で回転を必要としない場合に用いられる。しかし、ガス供給口８とガス排気口９を、図４（ｂ）に示されるように、断面円形となるように合体する形〔図４（ｃ），（ｄ）参照〕とすれば回転可能となる。
【００３３】
ここで、ガラスパイプ接続部５は、各々別個の配管系統で構成されたガス供給口８とガス排気口９、継手６及びキャップ１８等からなる回転継手部、継手７及びキャップ２０等からなる継手部とで構成し、それぞれガラスパイプ１の片一方の端部若しくは必要に応じ両方の端部に設けることができる。
ガス供給口８、ガス排気口９は例えばポリフッ化エチレンの他、アルミナ、シリコンカーバイト、ＳＵＳ等で形成するのが一般的である。
図３ではガラスパイプ１を把持しているが、図７に示すようにガラスパイプ１の端部に接続したガラスパイプ接続部５を把持するようにしても良い。また、ガラスパイプ１の端部に接続した作業用ガラスパイプの端部にさらにガラスパイプ接続部を接続し、これを把持するようにしても良い。
図７ではガラスパイプ１のみを示しているが、ガラスパイプ１中にガラスロッドを配置することもできる。また、熱源３が移動可能としているが、把持部を移動可能としてガラスパイプやガラスロッドが移動可能であっても良い。
【００３４】
図１の装置で、ガラスパイプ接続部５全体をケーシングで覆いその内部にＮ_２，Ａｒ等の不活性ガス、Ｃｌ_２等の脱不純物性のガス、若しくはそれらの混合ガスを充填しておくと得られる光ファイバの品質低下を防止することができる〔前記発明（１１）〕。
更に、前記ロータリージョイントを覆うカバーを設け、そのカバーに上記ケーシング内に充填するのと同様のガスを供給する手段を設けることができる（図８）。こうすることによりたとえ外気を巻き込んでも、不活性ガス又は脱不純物性、脱遷移金属性のガスである為、得られる光ファイバの品質を劣化させることはない。
【００３５】
【実施例】
以下本発明を実施例により更に詳細に説明するがそれより限定されるものではない。
【００３６】
〔実施例１〕
▲１▼　公知のＶＡＤ法により、中心コア部となるＧｅＯ_２添加ＳｉＯ_２ガラス体（ＧｅＯ_２の添加量の最大値は中心近傍で１４ｍｏｌ％）を製造し、加工して外径φ１０ｍｍ×長さ６００ｍｍ程度のガラスロッドとした。
▲２▼　公知のＶＡＤ法により、ディプレスト部となるＦ添加ＳｉＯ_２ガラス体（Ｆ添加濃度は１．２ｗｔ％程度）を製造し、加工して外径φ３５ｍｍ×内径φ１２ｍｍ×長さ５００ｍｍ程度のガラスパイプとした。
▲３▼　▲２▼で合成したパイプ内に▲１▼で合成したガラスロッドを挿入、ロッドインコラップス法により、一体化し、外径φ３３ｍｍ×長さ４００ｍｍ程度のガラス体を得た。ここでのＧｅＯ_２添加ＳｉＯ_２ガラス体やＦ添加パイプは例えばＯＶＤ法といった方法を用いても良好に作製可能である。
〔この時、実施例１として、図３の本発明に係る光ファイバ母材製造装置を用い、比較例（従来方法）１として、図９に示される製造装置を用いた。本発明では、熱源としてＨ_２／Ｏ_２火炎バーナーを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。〕
【００３７】
▲４▼　▲３▼で合成したガラス体を外径φ１０．６ｍｍに延伸した後、機械的な研削やＨＦ溶液によるエッチングなどで外周を研削して外径φ６．６ｍｍ、長さ６００ｍｍのガラスロッドとした。
▲５▼　公知のＶＡＤ法により、クラッド部となるＣｌ添加ＳｉＯ_２ガラス体（Ｃｌ添加濃度は０．３ｍｏｌ％程度）を製造し、加工して外径φ３５ｍｍ×内径φ８ｍｍ×長さ５００ｍｍ程度のガラスパイプとした。勿論、ＯＶＤ法によっても作製可能である。
▲６▼　▲５▼で合成したガラスパイプ内に▲４▼で合成したガラスロッドを挿入、ロッドインコラップス法により、一体化し、外径φ３３ｍｍ×長さ４００ｍｍ程度のガラス体を得た。コラップス中、ガラスパイプ内にはプロセスガスとしてＣｌ_２を５００ｓｃｃｍ、Ｏ_２を２５０ｓｃｃｍ流し、ガラスパイプ内圧を外気圧に対して−０．０５ｋＰａとした。
〔この時、実施例１として、図３の本発明による光ファイバ母材製造装置を用い、比較例１として図９に示される製造装置を用いた。本発明では、熱源としてＨ_２／Ｏ_２火炎バーナーを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。〕
【００３８】
▲７▼　公知のＶＡＤ法により、▲６▼のガラス体の外周に０．３ｍｏｌ％のＣｌ添加ＳｉＯ_２ガラスを合成し、中心コア部の直径（２ａ）とクラッド部の外径の直径（Ｄ）との倍率Ｄ／２ａを３１．３倍に拡大し、光ファイバ母材を得た。勿論、ＯＶＤ法、ロッドインコラップス法等でも可能である。
▲８▼　この光ファイバを公知の方法で線引きし、ガラス部の径が１２５μｍの光ファイバとした。
【００３９】
▲９▼　この光ファイバの波長１５５０ｎｍにおける伝送特性は、伝送損失＝０．２７ｄＢ／ｋｍ、分散＝−４７ｐｓ／ｋｍ／ｎｍ、分散スロープ＝−０．１４ｐｓ／ｋｍ／ｎｍ^２、Ａｅｆｆ＝２０μｍ^２、ＭＦＤ＝５μｍ、カットオフ波長＝８００ｎｍ、ＰＭＤ＝０．１ｐｓ／√ｋｍの光ファイバを得た。
この時、波長１３８０ｎｍのＯＨ基の光吸収による、図１０に示される過剰損失Δα１．３８の分布を調べた。
▲９▼’従来方法による、Δα１．３８の分布は、図１１のとおりで、非常に分布が大きい。また、Δα１．３８自体が小さいところの分布が非常に少ない。
一方、本発明の方法を用いれば、Δα１．３８を安定して低くすることが可能である（図１２参照）。
結局、本実施例で得られた光ファイバは図１３に示される屈折率差分布を有し、分散補償ファイバとして有用なものであった。
【００４０】
分散補償ファイバは導波する光が分散シフトファイバ以上に広く広がっているため、コラップス界面におけるＯＨ基による光の吸収の影響が大きいものであるが、本発明によりコラップス界面におけるＯＨ基発生の量を減じることで、ＯＨ基による光の吸収による伝送損失が低くでき、信号伝送帯域が広くなるという優れた効果が達せられた。また、ラマン増幅の際に必要な励起光の強度が小さくて済むこと、その結果、信号光の増幅効率が高められることが明らかとなった。
【００４１】
〔実施例２〕
１）　公知のＶＡＤ法により、中心コア部となるＧｅＯ_２添加ＳｉＯ_２ガラス体（ＧｅＯ_２の添加量の最大値は中心近傍で１４ｍｏｌ％）を製造し、加工して外径φ１０ｍｍ×長さ６００ｍｍ程度のガラスロッドとした。
２）　公知のＶＡＤ法により、ディプレスト部となるＦ添加ＳｉＯ_２ガラス体（Ｆ添加濃度は３．８ｍｏｌ％程度）を製造し、加工して外径φ３５ｍｍ×内径φ１２ｍｍ×長さ５００ｍｍ程度のガラスパイプとした。
３）　２）で合成したパイプ内に１）で合成したガラスロッドを挿入、ロッドインコラップス法により、一体化し、外径φ３３ｍｍ×長さ４００ｍｍ程度のガラス体を得た。ここでのＧｅＯ_２添加ＳｉＯ_２ガラス体やＦ添加パイプは例えばＯＶＤ法といった方法を用いても良好に作製可能である。コラップス中、ガラスパイプ内にはプロセスガスとしてＣｌ_２を５００ｓｃｃｍ、Ｏ_２を２５０ｓｃｃｍ流し、ガラスパイプ内圧を外気圧に対して＋０．０５ｋＰａとした。
〔この時、実施例２として、図３の本発明に係る光ファイバ母材製造装置を用い、比較例（従来方法）２として、図９に示される製造装置を用いた。本発明では、熱源としてＨ_２／Ｏ_２火炎バーナーを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。〕
【００４２】
４）　３）で合成したガラス体を外径φ１０．６ｍｍに延伸した後、機械的な研削やＨＦ溶液によるエッチングなどで外周を研削して外径φ６．６ｍｍ、長さ６００ｍｍのガラスロッドとした。
５）　公知のＶＡＤ法により、クラッド部となるＣｌ添加ＳｉＯ_２ガラス体（Ｃｌ添加濃度は０．３ｍｏｌ％程度）を製造し、加工して外径φ３５ｍｍ×内径φ８ｍｍ×長さ５００ｍｍ程度のガラスパイプとした。勿論、ＯＶＤ法によっても作製可能である。
６）　５）で合成したガラスパイプ内に４）で合成したガラスロッドを挿入、ロッドインコラップス法により、一体化し、外径φ３３ｍｍ×長さ４００ｍｍ程度のガラス体を得た。コラップス中、ガラスパイプ内にはプロセスガスとしてＣｌ_２を２００ｓｃｃｍ、Ｈｅを１００ｓｃｃｍ流し、ガラスパイプ内圧を外気圧に対して−０．５ｋＰａとした。
〔この時、実施例２として、図３の本発明による光ファイバ母材製造装置を用い、比較例２として図９に示される製造装置を用いた。本発明では、熱源としてＨ_２／Ｏ_２火炎バーナーを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。〕
【００４３】
７）　公知のＶＡＤ法により、６）のガラス体の外周に０．３ｍｏｌ％のＣｌ添加ＳｉＯ_２ガラスを合成し、中心コア部の直径（２ａ）とクラッド部の外径の直径（Ｄ）との倍率Ｄ／２ａを３１．３倍に拡大し、光ファイバ母材を得た。勿論、ＯＶＤ法、ロッドインコラップス法等でも可能である。
８）　この光ファイバを公知の方法で線引きし、ガラス部の径が１２５μｍの光ファイバとした。
【００４４】
９）　この光ファイバの波長１５５０ｎｍにおける伝送特性は、伝送損失＝０．２７ｄＢ／ｋｍ、分散＝−４７ｐｓ／ｋｍ／ｎｍ、分散スロープ＝−０．１４ｐｓ／ｋｍ／ｎｍ^２、Ａｅｆｆ＝２０μｍ^２、ＭＦＤ＝５μｍ、カットオフ波長＝８００ｎｍ、ＰＭＤ＝０．１ｐｓ／√ｋｍの光ファイバを得た。
この時、波長１３８０ｎｍのＯＨ基の光吸収による、図１０に示される過剰損失Δα１．３８の分布を調べた。
９）’従来方法による、Δα１．３８の分布は、図１１のとおりで、非常に分布が大きい。また、Δα１．３８自体が小さいところの分布が非常に少ない。
一方、本発明の方法を用いれば、Δα１．３８を安定して低くすることが可能である（図１２参照）。
結局、本実施例で得られた光ファイバは図１３に示される屈折率差分布を有し、分散補償ファイバとして有用なものであった。
【００４５】
分散補償ファイバは導波する光が分散シフトファイバ以上に広く広がっているため、コラップス界面におけるＯＨ吸収の影響が大きいものであるが、本発明によりコラップス界面におけるＯＨ基発生の量を減じることで、ＯＨ基による光の吸収による伝送損失が低くでき、信号伝送帯域が広くなるという優れた効果が達せられた。また、ラマン増幅の際に必要な励起光の強度が小さくて済むこと、その結果、信号光の増幅効率が高められることが明らかとなった。
【００４６】
〔実施例３〕
［１］　公知のＶＡＤ法により、中心コア部となるＧｅＯ_２添加ＳｉＯ_２ガラス体（ＧｅＯ_２の添加量の最大値は中心近傍で２５ｍｏｌ％）を製造し、加工してφ７．５ｍｍ×６００ｍｍ程度のガラスロッドとした。
［２］公知のＶＡＤ法またはＯＶＤ法により、ディプレスト部となるＦ添加ＳｉＯ_２ガラス体（Ｆ添加濃度は１．２質量％程度）を製造し、加工して外径φ４０ｍｍ×内径φ８．５ｍｍ×５００ｍｍ程度のガラスパイプとした。このパイプは、コラップスする前に、ＳＦ_６などのエッチングガスを流し、熱源によって１５００℃程度に加熱、気相エッチング処理を実施した。
［３］上記［２］で合成したガラスパイプ内に上記［１］で合成したガラスロッドを挿入した。真空ポンプによってパイプ内を０．１ｋＰａ以下の真空状態にした後、水素分子もしくは水素元素含有化合物の濃度が１ｐｐｍ以下である窒素ガスをパイプ内に導入、真空ポンプを停止して１０５ｋＰａまで加圧した。これを３回繰り返し、ロッド表面、パイプ内面の吸着ガス（主にＨ_２Ｏ）を脱離させた。その後、Ｃｌ_２を５００ｓｃｃｍだけパイプ内に導入、１１５０℃まで加熱して金属不純物を除去した。
【００４７】
［４］上記［３］のガラスパイプ、ガラスロッド、図２記載の継手及び図３記載の装置でロッドインコラップス法により、一体化し、φ３９ｍｍ×４００ｍｍ程度のガラス体を得た。このとき、大気の巻き込み量を調査した結果、０．１ｓｃｃｍ程度であり、水素分子もしくは水素元素含有化合物の濃度が１ｐｐｍ以下のプロセスガスであるＯ_２を４００ｓｃｃｍだけパイプ内に導入した。ガスを供給しないとき、０．０３ｋＰａまでパイプ内の圧力を低減することができる真空ポンプで真空排気した。プロセス中のパイプ内の圧力は０．１ｋＰａであった。
本実施例では、熱源としてＨ_２／Ｏ_２火炎バーナを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。横型ではなく、縦型のコラップスとしても良い。
【００４８】
［５］上記［４］で合成したガラス体をφ１１．７ｍｍに延伸した後、機械的な研削やＨＦ溶液によるエッチングなどで外周を研削して外径７．５ｍｍφ、長さ６００ｍｍのガラスロッドとした。
［６］公知のＶＡＤ法またはＯＶＤ法により、クラッド部となるＣｌ添加ＳｉＯ_２ガラス体（Ｃｌ添加濃度は０．３ｍｏｌ％程度）を製造し、加工して外径φ４３ｍｍ×内径φ９ｍｍ×５００ｍｍ程度のガラスパイプとした。このパイプは、コラップスする前に、ＳＦ_６などのエッチングガスを流し、熱源によって１５００℃程度に加熱、気相エッチング処理を実施した。
［７］上記［６］で合成したパイプ内に上記［５］で合成したガラスロッドを挿入した。真空ポンプによってパイプ内を０．１ｋＰａ以下の真空状態にした後、水素分子もしくは水素元素含有化合物の濃度が１ｐｐｍ以下の窒素ガスをパイプ内に導入、真空ポンプを停止して１０５ｋＰａまで加圧した。これを１回だけ実施し、ロッド表面、パイプ内面の吸着ガス（主にＨ_２Ｏ）を脱離させた。その後、Ｃｌ_２を標準状態（０℃、１気圧）で５００ｓｃｃｍだけパイプ内に導入、１１５０℃まで加熱して金属不純物を除去した。
【００４９】
［８］上記［７］のパイプ、ガラスロッド、図２記載の継手及び図３記載の装置によるロッドインコラップス法により一体化し、φ４２ｍｍ×４００ｍｍ程度のガラス体を得た。このとき、大気の巻き込み量を調査した結果、０．０５ｓｃｃｍ程度であり、水素分子もしくは水素元素含有化合物の濃度が１ｐｐｍ以下であるプロセスガスであるＯ_２を１００ｓｃｃｍだけパイプ内に導入した。ガスを供給しないとき、０．０３ｋＰａまでパイプ内の圧力を低減することができる真空ポンプで真空排気した。プロセス中のパイプ内の圧力は０．０８ｋＰａであった。本発明では、熱源としてＨ_２／Ｏ_２火炎バーナを用いたが、プラズマ火炎や誘導炉など、他の熱源を用いることもできる。横型ではなく、図５に示されるような縦型のコラップスとしても良い。
［９］公知のＶＡＤ、ＯＶＤ、ロッドインコラップス法により、上記［６］のガラス体の外周に０．３ｍｏｌ％のＣｌ添加ＳｉＯ_２ガラスを合成し、中心コア部の径（２ａ）とクラッド部の外径（Ｄ）との倍率Ｄ／２ａを５２．１倍に拡大し、光ファイバ母材を得た。
【００５０】
［１０］この光ファイバを公知の方法で線引きし、ガラス部の径が１２５μｍの光ファイバとした。
［１１］この光ファイバの波長１５５０ｎｍにおける伝送特性が、伝送損失＝０．５０ｄＢ／ｋｍ、分散＝−１０５ｐｓ／ｋｍ／ｎｍ、分散スロープ＝−０．３７ｐｓ／ｋｍ／ｎｍ^２、Ａｅｆｆ＝１２μｍ^２、カットオフ波長＝７３０ｎｍ、ＰＭＤ＝０．１ｐｓ／√ｋｍ程度の１．３μｍ帯にゼロ分散波長を有する光ファイバの１．５５μｍ帯における分散及び分散スロープを補償する、良好な分散補償ファイバを得た。
このファイバの伝送損失−波長特性は図１４のとおりであり、ＯＨ基による１．４μｍ帯の過剰な伝送損失を抑制していることがわかる。
結局、本実施例で得られた光ファイバは図１５に示される屈折率差分布を有し、分散補償ファイバとして有用なものであった。
【００５１】
分散補償ファイバは導波する光が分散シフトファイバ以上に広く広がっているため、コラップス界面におけるＯＨ吸収の影響が大きいものであるが、本発明によりコラップス界面におけるＯＨ基発生の量を減じることで、ＯＨ基による光の吸収による伝送損失が低くでき、信号伝送帯域が広くなるという優れた効果が達せられた。また、ラマン増幅の際に必要な励起光の強度が小さくて済むこと、その結果、信号光の増幅効率が高められることが明らかとなった。
【００５２】
以上、図３の装置を用いた実施例１〜３では、Ｃｌ_２，Ｏ_２等のプロセスガスの供給口先端部がガラスパイプ１内にあり、ガス供給部１０の配管部（内筒１３）には継ぎ目がないので大気は混入しない。回転シール部（図６の継手７と外筒１４の接続部）で大気が混入してもガス排気部１１（減圧部）にあたるのでガラスパイプ側には供給されない。
従って、ＯＨ基による過剰損失を抑制できる。
一方、図９の装置を用いた比較例１，２では、ガラスパイプ接続部５の特に回転シール部（継手７の接続部）は完全に気密にすることが難しく大気が混入し易い。また、配管部９の途中でガス排気部１１（減圧部）があるため、プロセスガスが石英パイプに迄到達することができない。
従って、ＯＨ基による過剰損失が生じ易い。
【００５３】
【発明の効果】
本発明により前記の構成を採ることで、コラップス界面におけるＯＨ基混入量を減少させＯＨ基による光の吸収に基づく伝送損失を低くし、信号伝送帯域を広く保つことのできる光ファイバを提供することができる。
更に本発明は、複雑な屈折率分布パターンを有する光ファイバや中心コアのΔが２％以上もあるような高Δコアファイバ（分散補償ファイバや高非線形性ファイバ）等コラップス法に適する光ファイバの製造に有用である。
【図面の簡単な説明】
【図１】本発明に係る光ファイバ母材の製造装置の具体例を示すもので軸線に沿った部分断面図。
【図２】本発明に係る光ファイバ母材の製造装置の他の具体例を示すもので軸線に沿った部分断面図。
【図３】ガラス旋盤を用いたコラップス法により本発明に係る光ファイバ母材を製造する装置の概念図。
【図４】（ａ）、（ｂ）、（ｃ）、（ｄ）は本発明において用いられるガス供給口、ガス排気口の模式図で、（ａ）、（ｂ）は部分側面図、（ｃ）、（ｄ）は合体した場合の断面図。
【図５】本発明の方法を縦型装置を用いてコラップスを実施する場合、脱水性ガスの比重が大きいときの状態を示す模式図。
【図６】本発明の方法を縦型装置を用いてコラップスを実施する場合、脱水性ガスの比重が小さいときの状態を示す模式図。
【図７】本発明の装置において、ガラスパイプ接続部を把持するようにした状態を示す模式図。
【図８】本発明の装置においてロータリージョイントを覆うカバーを設け、カバー内に不活性ガスを供給するようにした装置を示す模式図。
【図９】従来法でガラス旋盤を用いたコラップス法により光ファイバ母材を製造する装置の一例を示す概念図。
【図１０】波長１３８０ｎｍにおけるＯＨ基による光の吸収損失による過剰損失Δα１．３８（ｄＢ／ｋｍ）を示すグラフ図。
【図１１】従来法（比較例）により得られたガラス光ファイバのＯＨ基による光の吸収による過剰損失を示すグラフ図。
【図１２】本発明の方法（実施例）により得られたガラスファイバのＯＨ基による光の吸収による過剰損失を示すグラフ。
【図１３】本発明の方法により得られた光ファイバ（分散補償ファイバ）の屈折率プロファイル。
【図１４】本発明の方法（実施例）により得られたガラスファイバの伝送損失−波長特性の関係を示すグラフ。
【図１５】
本発明の方法により得られた分散補償ファイバの屈折率プロファイル。
【符号の説明】
１　ガラスパイプ、　　２　ガラスロッド、　　　　　３　熱源、
４　把持部、　　　　　５　ガラスパイプ接続部、　　６及び７　継手、
８　ガス供給口、　　　８′ガス供給口先端部、
９　ガス排気口、　　　９′ガス排気口先端部、
１０　ガス供給部、　　１１　ガス排気部。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for manufacturing an optical fiber preform or an optical fiber intermediate preform, and more particularly to a method and an apparatus for manufacturing an optical fiber preform capable of reducing transmission loss due to light absorption of an OH group.
[0002]
[Prior art]
The so-called collapse method, which is well known in a method for manufacturing an optical fiber preform or the like, is a method of obtaining an optical fiber preform or a preform intermediate by heating and solidifying a glass pipe. Generally, the inside of the glass pipe is under a reduced pressure lower than the atmospheric pressure. In this case, a glass rod may be inserted into the glass pipe to be integrated.
[0003]
[Problems to be solved by the invention]
The collapse method is, for example, one or a mixture of gases capable of removing impurities such as water and metals in a glass pipe such as chlorine, for example, oxygen and chlorine, an inert gas and a gas such as chlorine or a gas such as these. It is desirable to carry out the collapse while introducing a mixed gas containing gas into the glass pipe. However, since the operation is generally performed under reduced pressure, there is a problem that impurities such as moisture are mixed into the glass pipe due to entrainment in the atmosphere, and transmission loss increases. This is "2SiO ₂ + H → SiOH + 1 / 2O ₂ "Or" GeO ₂ + H → GeOH + 1 / 2O ₂ OH group is generated by such a reaction, and as a result, transmission loss occurs due to absorption of light by the OH group in the wavelength band of 1.4 μm.
In particular, in a horizontal type collaps, a so-called rotary joint (rotary joint) is used as a joint for connecting a glass pipe and a pipe during the collapse because the pipe rotates but the pipe must not rotate. Therefore, since it is difficult to maintain the airtightness of the rotary joint, air is entrapped from this portion, which is a serious problem in the production of optical fibers.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and reduce the amount of OH groups generated at the collapse interface to reduce transmission loss due to light absorption of OH groups (also referred to as absorption loss due to OH groups), thereby reducing signal transmission An optical fiber preform or an intermediate optical fiber for manufacturing an optical fiber capable of maintaining a wide band even on the short wavelength side and increasing the efficiency of Raman amplification when used as a medium for Raman amplification. An object of the present invention is to provide a method for manufacturing a base material and an apparatus therefor.
In the present specification, the optical fiber preform refers to a glass member that is drawn into an optical fiber, and the optical fiber intermediate preform refers to a glass member that is drawn into an optical fiber after further adding a glass layer to the outside thereof. .
[0005]
[Means for Solving the Problems]
The above object can be achieved by the inventions summarized as follows.
(1) In a method of manufacturing an optical fiber preform or an optical fiber intermediate preform by a collapse method in which a glass pipe is solidified by heating or a glass pipe and a glass rod inserted into the glass pipe are integrated, A glass pipe connecting portion having a gas supply port and a gas exhaust port formed by a piping system is provided at one or both ends in the glass pipe, and a process gas is introduced into the glass pipe from the gas supply port. A method for producing an optical fiber preform or an optical fiber intermediate preform, wherein the collapse method is performed while exhausting gas in the glass pipe from the gas exhaust port.
(2) The method for producing an optical fiber preform or an optical fiber intermediate preform according to the above (1), wherein the collapse method is performed while rotating the glass pipe or the glass pipe and the glass rod.
(3) The process gas according to (1), wherein the process gas is a gas composed of one or more selected from the group consisting of an inert gas, a gas containing a halogen element, and an oxygen gas. 3. The method for producing an optical fiber preform or an optical fiber intermediate preform according to 2.
(4) The optical fiber preform or the optical fiber intermediate according to any one of the above (1) to (3), wherein the concentration of the hydrogen component or the compound containing a hydrogen element in the process gas is 100 ppm or less. Manufacturing method of base material.
(5) The method for producing an optical fiber preform or an optical fiber intermediate preform according to any of (1) to (4), wherein the degree of vacuum in the glass pipe is set to 10 kPa or less in absolute pressure. .
(6) The optical fiber preform or the optical fiber intermediate according to any one of the above (1) to (4), wherein the pressure in the glass pipe is higher than the outside air pressure, and the pressure difference is +1 kPa or less. Manufacturing method of base material.
[0006]
(7) The gas supply port and the gas exhaust port, each of which is constituted by a separate piping system, are positioned such that a tip end of the gas supply port is closer to the interface of the collapsed position than a position where the gas may be trapped in the atmosphere. The optical fiber preform or the optical fiber intermediate preform according to any one of the above (1) to (6), wherein the tip of the exhaust port is located farther from the interface of the collapse than the tip of the gas supply port. Manufacturing method.
[0007]
(8) The glass pipe, or the glass pipe and the glass rod, are arranged vertically, and when the process gas is larger than the specific gravity of air, collapsing is performed upward from below the glass pipe. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of the above (1) to (7).
(9) The glass pipe or the glass pipe and the glass rod are arranged vertically, and when the process gas is smaller than the specific gravity of air, collapse is performed from above the glass pipe to below. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of the above (1) to (7).
[0008]
(10) In an apparatus for manufacturing an optical fiber preform that solidifies a rotatable glass pipe or integrates a rotatable glass pipe and a glass rod inserted in the glass pipe, the glass pipe or the glass pipe And a heating source for heating the glass rod, a glass pipe connection portion attached to one or both ends of the glass pipe, each including a separate gas supply port tip and a gas exhaust port tip, and via the glass pipe connection. Means for introducing gas into the glass pipe (gas supply system), and means for exhausting gas from the glass pipe through the glass pipe connection (gas exhaust system). Is a rotary joy connecting the rotatable glass pipe to a non-rotating gas supply system and a gas exhaust system. A pipe connected to one of a gas supply system and a gas exhaust system is disposed inside the glass pipe connection portion, and a pipe connected to the other via a rotary joint is disposed around the pipe. An apparatus for producing an optical fiber preform.
(11) The optical fiber preform according to the above (10), further comprising, outside the glass pipe connection portion, a cover for covering the glass pipe connection portion, and means for supplying gas to the inside of the cover. Manufacturing equipment.
[0009]
First, the conventional method will be described.
For example, when a preform for optical fiber is manufactured by integrating a quartz glass rod and a glass pipe by a collapse method using a horizontal glass lathe, a conventional apparatus is used as shown in FIG. . That is, the glass rod 2 is inserted into the glass pipe 1, and is heated and heated by the heat source 3 moving in the direction of the arrow while being rotated to be collapsed and integrated. At this time, both ends of the glass pipe 1 are gripped by the gripper 4 and rotate synchronously. The holding part 4 has a rotary chuck, and the glass pipe 1 is connected to a pipe part 9 via a joint 6.
Here, a process gas such as chlorine (Cl ₂ The gas supply unit 10 and the gas exhaust unit 11 supply and exhaust gas such as de-impurity, de-transition metal gas, etc., respectively. The glass pipe connection section 5 is connected to a gas supply system 10 (flow meter, pressure gauge, flow control, switching valve, filter, etc.) and a gas exhaust section 11 (a pipe section 9 having a gas supply port 8 (common to a gas exhaust port)). Flow meter, pressure gauge, switching valve, abatement device, etc.).
[0010]
The conventional method using the apparatus shown in FIG. 9 has a drawback that the air is entrained in the collaps and impurities such as OH groups are mixed therein, due to the following reasons:
[0011]
(A) In the connection between the glass pipe 1 and the joint 6, it is difficult to secure perfect airtightness because the diameter of the glass pipe 1 is slightly different for each pipe, and therefore, it is easy to involve the atmosphere in the collapse. Here, if the atmosphere is entrained, moisture is mixed in the glass pipe 1 and poses a problem.
(A) Although the rotating part of the joint 6 is sealed, it has a problem that the possibility of entraining the atmosphere is extremely high in order to realize the contradictory purpose of "securing airtightness while rotating".
(C) Atmosphere is also drawn in from the joint between the joint 7 and the pipe section 9.
(D) In the system of the pipe section 9, a process gas (eg, Cl ₂ Gas) is exhausted from the gas exhaust unit 11 before reaching the glass pipe 1, and the concentration of the process gas is reduced.
[0012]
If air is involved in any of the above (A) to (C), the air concentration in the glass pipe 1 increases for the above reason. This means that hydrogen molecules (H ₂ ) And H ₂ This means that the concentration of a compound containing a hydrogen element (H) such as O in the glass pipe is increased, which causes a problem that an OH group is generated at the interface of the collapse. When the process gas is Cl ₂ In the case of ₂ The concentration decreases and Cl ₂ The dewatering effect cannot be obtained, and water remains at the interface of the collapses, which again causes the problem of generation of OH groups.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention has been developed to solve the above-mentioned drawbacks of the conventional method.
An embodiment of the present invention will be specifically described with reference to FIGS. 1 and 2 are partial longitudinal sectional views along the axis of an apparatus for manufacturing an optical fiber preform used in the present invention, and schematically show a glass pipe connecting portion 5 holding a glass pipe 1. FIG.
[0014]
The configuration of the glass pipe connecting portion (joint portion) 5 is an important feature of the present invention, and a de-impurity gas such as Cl ₂ The present invention is characterized in that the inner cylinder 13 and the outer cylinder 14 are double cylinders in order to supply and exhaust gas or the like as process gas [the invention (1)]. That is, from the tip 8 ′ of the gas supply port 8 provided at the end of the inner cylinder 13 to the end of the glass pipe (if an auxiliary pipe (dummy pipe) is attached, this may be the end of the dummy pipe). Process gas supplied, for example Cl ₂ The gas enters the glass pipe 1 and passes through the inside of the pipe. ₂ The inside of the pipe is dehydrated as a high-concentration gas, and is exhausted from the gas exhaust port 9 through a passage 15 formed between the outer cylinder 14 and the inner cylinder 13 and having an opening 9 ′ in the joint 6.
[0015]
Here, as shown in FIG. 3, the glass pipe 1 may be rotatably gripped by a glass lathe and collapsed while being rotated [the invention (2)]. The glass pipe 1, the joint 6, and the outer cylinder 14 of FIGS. 1, 2, and 3 are rotated, while the inner cylinder 13 and the joint 7, which form the flow path of the process gas to be introduced, do not rotate.
[0016]
As used herein, the term "process gas" refers to at least one gas selected from the group consisting of an inert gas, a gas containing a halogen element, and oxygen gas, or a gas containing at least one gas selected from the group. , Specifically N ₂ , He, Ar, Cl ₂ , SOCl ₂ , O ₂ And other gases. N as an inert gas ₂ , He, Ar, a gas containing a halogen element is Cl ₂ Is preferable [the invention (3)].
[0017]
In this case, the flow rate of the process gas supplied to the glass pipe 1 is generally about 50 to 1000 ml / min (hereinafter abbreviated as "sccm") in a standard state (0 ° C., 1 atm), but is not limited thereto. At the same time, O ₂ And He, N ₂ Cl flowed ₂ May be used. Most of them enter the glass pipe 1 and some are exhausted at the same time.
[0018]
The process gas according to the present invention preferably does not substantially contain a gas such as a compound containing a hydrogen molecule or a hydrogen element, and the concentration of the compound containing a hydrogen molecule or a hydrogen element is more preferably 100 ppm or less in total [the invention ( 4)], particularly preferably 10 ppm or less. By flowing these process gases, it is possible to prevent the outside air containing a large amount of impurities such as water and organic substances from flowing into the glass pipe. The process gas does not necessarily need to include a dehydrating or de-impurifying gas. Of course, it may be included.
[0019]
The pressure in the glass pipe 1 is desirably 10 kPa or less in absolute pressure in terms of the degree of vacuum (the invention (5)), more preferably 1 kPa or less. However, according to the present invention, even if the air is entrained in the glass pipe, the entrained air can be sufficiently mixed and replaced with the process gas. In the joint structure, the process gas does not easily flow into the glass pipe when the air is entrained from the connection between the pipe and the glass pipe, that is, from the rotary joint. ₂ And H ₂ Although the impurity concentration of a hydrogen-containing compound such as O becomes high, this can be prevented in the present invention.
[0020]
Assuming that the entrapped atmosphere is completely mixed with the process gas, introduced into the glass pipe, and evacuated, the ratio r of the hydrogen molecule or the compound containing the hydrogen element in the atmosphere is r ₁ , The flow rate S of the entrained atmosphere ₁ Ratio of a compound containing a hydrogen molecule or a hydrogen element in the process gas ₂ , Process gas flow rate S ₁ Then, the flow rate S of the compound containing hydrogen molecules or hydrogen element flowing into the pipe ₀ Is
(Equation 1)

It becomes.
The total amount of gas flowing into the pipe is S ₁ + S ₂ Therefore, the flow rate S of the process gas ₂ Flow rate S of the atmosphere ₁ Is k times, the ratio r at the time of steady state becomes ₀ Is
(Equation 2)

It becomes.
[0021]
Assuming that the pressure P in the pipe, the volume of the space is V, and the temperature is T, the amount N of a compound containing hydrogen molecules or a hydrogen element (collectively referred to as a hydrogen element-containing compound) in the glass pipe is
[Equation 3]

The concentration C of the hydrogen-containing compound is represented by
(Equation 4)

Can be inferred by:
Therefore, P, r ₁ , R ₂ Is smaller, r ₂ Is always less than 1, so that the larger the k is, the smaller the density C becomes.
[0022]
Then, the lower the concentration C, the more the following equation
Embedded image

Since the amount of SiOH or MeOH generated by the reaction represented by the formula (1) is reduced, it is possible to suppress an excessive increase in transmission loss due to OH groups observed in the wavelength band of 1.4 μm.
Since the pressure P in the glass pipe increases as the amount of air entrained and the flow rate of the process gas increases, it is desirable to use a vacuum pump. In the exhaust system, the ultimate degree of vacuum in the glass pipe is expressed as an absolute pressure. An exhaust means having a pressure of 1 kPa or less, preferably 0.1 kPa or less, more preferably 0.01 kPa or less is connected. By evacuating using a vacuum pump, the pressure in the glass pipe can be reduced, and as a result, H which reacts with the glass to form an OH group can be obtained. ₂ And H ₂ It is possible to reduce the absolute amount of the gas such as O itself and reduce the transmission loss. Of course, it is more desirable that the pump has a higher capacity and can exhaust the gas to a lower pressure [the above invention (4)].
[0023]
Usually, if the vacuum is evacuated during the collapse, there is a problem that it becomes elliptical after the collapse, but if the rod is inserted and the pipe is integrated around it, the rod becomes a mandrel. Thus, it is possible to suppress ovalization.
For example, as a hydrogen-containing compound gas, H ₂ Considering O, H at 24 ° C. ₂ Since the saturated vapor pressure of O is about 3 kPa, its concentration is 3.2% = 32000 ppm at the maximum. In order to change this amount, cover the joint between the glass pipe and the pipe, where entrainment is most concerned, and purge the inside of the cover with an inert gas, oxygen, or a mixed gas of oxygen and an inert gas. It is desirable to do.
[0024]
As described above, the smaller the concentration of hydrogen molecules or hydrogen-containing compounds in the process gas, the better. However, the concentration is preferably 100 ppm or less, more preferably 10 ppm or less (the above invention (4)). By doing so, the concentration of the hydrogen molecule or the hydrogen-containing compound can be sufficiently lower than that of the atmosphere, so that the flow rate at which the process gas is supplied into the glass pipe is at least 10 times the entrainment amount of the atmosphere, More preferably, it is desirably 100 times or more. That is, k in Equation 4 is 10 or more, more preferably 100 or more.
Process gas is He, N ₂ , Ar or other inert gas, O ₂ Or O ₂ When the gas mixture is a mixture of an inert gas and an inert gas, the formation of defects such as bubbles and microcrystals at the interface of the collapse is suppressed. In particular, when the rod surface or pipe inner surface is GeO ₂ Added SiO ₂ If
Embedded image

GeO is generated by the reaction described above, and glass defects and bubbles are formed. However, if oxygen or an oxygen-containing gas is used, the equilibrium reaction depends on the left side, so that formation of defects and bubbles can be suppressed.
[0025]
Contrary to the case described above, by making the inside of the glass pipe 1 a positive pressure, it is possible to greatly suppress the gas from being drawn into the glass pipe 1 from the atmosphere. In addition, especially when the process gas is Cl ₂ In the case of an iso-dewatering gas, the effect of preventing the generation of OH groups at the interface is further increased because the concentration of the gas is increased. Even if the pressure in the glass pipe is too high, the time required for the collapse becomes longer as described above or the pipe expands, so that the difference from the outside air pressure is +1 kPa or less, preferably +0.01 kPa or more. +0.10 kPa is preferable [the invention (6)]. Thereby, the expansion of the pipe is suppressed, and the collapse can be performed well.
[0026]
When the glass pipe or the glass pipe and the glass rod are arranged vertically, (i) when the process gas is larger than the specific gravity of air, the collaps is moved upward from below the glass pipe as in the invention (8). (Ii) When the process gas has a specific gravity smaller than that of air, the collapse is performed from above to below the glass pipe as in the invention (9). That is, Cl ₂ And SOCl ₂ , O ₂ In the case of a heavy process gas including, for example, the collapse is performed such that the gas accumulates downward. There is no need to rotate the pipe. Not only the “vertical direction” but also an oblique direction (see FIG. 4).
On the other hand, He, N ₂ In the case of a light process gas including, for example, the collapse is performed such that the gas accumulates upward. There is no need to rotate the pipe. Also in this case, similarly to (i), not only the “vertical direction” but also an oblique direction may be used (see FIG. 5).
In any case, in the case of a heavy gas, the gas is trapped below, so that the effect of replacing the entrained air is high. In the case of a light gas, the same effect is large as a result of the trapping of the gas upward.
[0027]
The effects of the inventions described above cannot be realized unless the apparatus is a device in which the entrapped atmosphere and the process gas are completely mixed. As the apparatus, those described in the above inventions (10) to (11) are preferable. In other devices, for example, if there is a joint or a rotating part between the glass pipe part and the piping part, the concentration of the air entrained in the rotating part gradually increases and excessive transmission loss due to light absorption of OH groups (also referred to as excess loss) ) Becomes large.
[0028]
By the way, the OH groups are absorbed not only in the atmosphere in the glass pipe but also in the glass surface. ₂ And H ₂ It is also generated by a reaction between a glass and a hydrogen molecule such as O or a hydrogen element-containing compound. Therefore, the amount of the hydrogen molecule or the hydrogen element-containing compound adsorbed on the glass surface is sufficient to form a monomolecular layer. ^-3 mol / cm ³ The extent is less than or equal to or less, the smaller the better. As a method of reducing the adsorption gas on the surface of the glass pipe, the surface of the glass is scraped off by gas phase etching, and then the concentration of hydrogen molecules or hydrogen element-containing compounds such as inert gas is low, purging with a clean gas, etc. Good. After inserting the glass rod into the pipe, ₂ , SOCl ₂ Good results can be obtained by heating to about 1150 ° C. or more with a heat source while flowing a dehydrating gas such as this into the glass pipe.
[0029]
More preferably, after inserting the glass rod into the glass pipe, vacuum evacuation is performed to 4 kPa or less, preferably 0.4 kPa or less (preferably lower), and then 50 kPa or more, preferably 101 kPa (about 1 kPa) by the process gas. Purging to a pressure of at least (atmospheric pressure) or more is repeated one or more times. By applying a vacuum, H adsorbed on the surface of the glass pipe or glass rod ₂ , H ₂ O and the like can be desorbed, and once it is purged with a process gas, re-adhesion can be suppressed.
[0030]
In an apparatus for manufacturing an optical fiber preform from a rotatable glass pipe (hereinafter, collectively including an auxiliary pipe attached) or a rotatable glass pipe and a glass rod according to the present invention, for example, a glass lathe is provided (FIG. 3). ), A tip 8 'of a gas supply port 8 and a tip 9' of a gas exhaust port 9 are respectively attached to one end (or both ends) of the glass pipe, and process gas is supplied from the gas supply port 8 into the glass pipe 1. The glass pipe 1 can be collapsed while supplying gas and discharging the gas in the glass pipe 1 from the tip 9 ′ of the gas discharge port 9, so that the quality of the optical fiber is not adversely affected. . In this case, the pipes for the gas supply and the exhaust are performed on separate lines, and there is no possibility that the pipes are put together in the middle. Even if air is entrained in the joint portion 5, the air can be exhausted immediately. Preferably, the gas supply pipe and the exhaust pipe are arranged in a double structure. [The above invention (10)].
[0031]
1, 2 or 3, the gas exhaust port 9 is connected to a gas exhaust system via a pipe (outer cylinder 14) and a rotary joint arranged outside. The rotary joint connects the rotating body and the non-rotating body and includes a joint 6 and a cap 18. On the other hand, the gas supply port 8 is directly connected to a gas supply system (11 in FIG. 6) by a pipe (inner cylinder 13) arranged inside. At this time, the inner cylinder 13 does not rotate, and therefore does not have a pipe connection point at the glass pipe connection portion 5. That is, even if the atmosphere is entrained in the rotary joint, the air can be immediately exhausted without mixing into the air in the gas supply pipe (inner cylinder 13). Therefore, a high-quality optical fiber can be manufactured without impurities such as moisture entering the glass pipe.
[0032]
The tip 8 'of the gas supply port 8 and the tip 9' of the gas exhaust port 9 may be located at the same position in the glass pipe 1 (FIG. 1). It is preferable that the position is closer to the interface of the collapse than the position where there is a possibility of entrainment, and the distal end 9 ′ of the gas exhaust port is farther from the interface of the collapse than the distal end 8 ′ of the gas supply [the invention (7)]. , FIG. 2].
FIG. 2 is a partial cross-sectional view taken along an axis showing another embodiment of the present invention. The gas supply port tip 8 ′ is further inside the pipe 16 than the cap 16 and the gas exhaust port tip 9 ′. Are provided at the same positions as in FIG. With this configuration, the collapse interface is filled with a high-purity process gas, and it is possible to supply a gas that does not include the entrained atmosphere. That is, even if the atmosphere enters the glass pipe 1 from the rotary joint (joint 6, cap 19, etc.), the process gas is filled on the collapse interface side in the glass pipe 1, so the exhaust port tip 9 '. From the exhaust port 9 (passage 15). Thereby, transmission loss due to OH-based light absorption can be reduced.
The gas supply port 8 and the gas exhaust port 9 do not have a concentric structure as shown in FIGS. 1, 2 and 3, and separate gas supply pipes and gas exhaust pipes as shown in FIG. It may be provided. In this case, since it cannot be rotated, it is used when it is a vertical type and does not require rotation. However, as shown in FIG. 4B, the gas supply port 8 and the gas exhaust port 9 can be rotated if they are combined so as to have a circular cross section [see FIGS. 4C and 4D]. It becomes.
[0033]
Here, the glass pipe connection part 5 is a rotary joint part composed of a gas supply port 8 and a gas exhaust port 9, a joint 6, a cap 18 and the like, each composed of a separate piping system, and a joint composed of a joint 7 and a cap 20 and the like. The glass pipe 1 may be provided at one end or both ends as needed.
The gas supply port 8 and the gas exhaust port 9 are generally made of, for example, alumina, silicon carbide, SUS, or the like, in addition to polyfluorinated ethylene.
Although the glass pipe 1 is gripped in FIG. 3, the glass pipe connection part 5 connected to the end of the glass pipe 1 may be gripped as shown in FIG. Further, a glass pipe connecting portion may be further connected to the end of the working glass pipe connected to the end of the glass pipe 1 and may be gripped.
FIG. 7 shows only the glass pipe 1, but a glass rod can be arranged in the glass pipe 1. Further, although the heat source 3 is movable, the glass pipe or the glass rod may be movable by moving the gripping part.
[0034]
In the apparatus of FIG. 1, the entire glass pipe connection portion 5 is covered with a casing, and N ₂ , Ar or other inert gas, Cl ₂ Filling with a de-impurity gas such as above or a mixed gas thereof can prevent deterioration of the quality of the obtained optical fiber [the invention (11)].
Further, a cover for covering the rotary joint may be provided, and the cover may be provided with a means for supplying the same gas as that for filling the casing (FIG. 8). By doing so, even if external air is involved, the quality of the obtained optical fiber is not deteriorated because the gas is an inert gas or a gas of a de-impurity or de-transition metal.
[0035]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0036]
[Example 1]
{Circle around (1)} GeO that becomes the central core by the known VAD method ₂ Added SiO ₂ Glass body (GeO ₂ (The maximum value of the addition amount is 14 mol% in the vicinity of the center) was manufactured and processed into a glass rod having an outer diameter of about 10 mm and a length of about 600 mm.
{Circle around (2)} F-added SiO serving as a depressed portion by a known VAD method ₂ A glass body (F addition concentration was about 1.2 wt%) was manufactured and processed to obtain a glass pipe having an outer diameter of about 35 mm, an inner diameter of about 12 mm, and a length of about 500 mm.
(3) The glass rod synthesized in (1) was inserted into the pipe synthesized in (2) and integrated by a rod in collapse method to obtain a glass body having an outer diameter of about 33 mm and a length of about 400 mm. GeO here ₂ Added SiO ₂ The glass body and the F-added pipe can be satisfactorily produced by using, for example, an OVD method.
[At this time, the apparatus for manufacturing an optical fiber preform according to the present invention shown in FIG. 3 was used as Example 1, and the apparatus shown in FIG. 9 was used as Comparative Example (conventional method) 1. In the present invention, H is used as the heat source. ₂ / O ₂ Although a flame burner was used, other heat sources such as a plasma flame or induction furnace could be used. ]
[0037]
(4) After stretching the glass body synthesized in (3) to an outer diameter of 10.6 mm, a glass rod having an outer diameter of 6.6 mm and a length of 600 mm is obtained by grinding the outer periphery by mechanical grinding or etching with an HF solution. And
{Circle around (5)} Cl-added SiO to be a clad portion by a known VAD method ₂ A glass body (with a Cl addition concentration of about 0.3 mol%) was manufactured and processed to obtain a glass pipe having an outer diameter of about 35 mm, an inner diameter of about 8 mm, and a length of about 500 mm. Of course, it can also be manufactured by the OVD method.
(6) The glass rod synthesized in (4) was inserted into the glass pipe synthesized in (5), and integrated by a rod in collapse method to obtain a glass body having an outer diameter of 33 mm and a length of about 400 mm. During the collapse, Cl is contained as a process gas in the glass pipe. ₂ 500 sccm, O ₂ Was flowed at 250 sccm, and the internal pressure of the glass pipe was set to −0.05 kPa with respect to the external pressure.
[At this time, the optical fiber preform manufacturing apparatus according to the present invention of FIG. 3 was used as Example 1, and the manufacturing apparatus shown in FIG. 9 was used as Comparative Example 1. In the present invention, H is used as the heat source. ₂ / O ₂ Although a flame burner was used, other heat sources such as a plasma flame or induction furnace could be used. ]
[0038]
{Circle around (7)} By the known VAD method, 0.3 mol% of Cl-added SiO ₂ Glass was synthesized, and the ratio D / 2a of the diameter (2a) of the central core portion and the outer diameter (D) of the cladding portion was enlarged to 31.3 times to obtain an optical fiber preform. Of course, an OVD method, a rod-in collapse method, or the like is also possible.
{Circle around (8)} This optical fiber was drawn by a known method to obtain an optical fiber having a glass part diameter of 125 μm.
[0039]
{Circle around (9)} The transmission characteristics of this optical fiber at a wavelength of 1550 nm are as follows: transmission loss = 0.27 dB / km, dispersion = −47 ps / km / nm, dispersion slope = −0.14 ps / km / nm. ² , Aeff = 20 μm ² , MFD = 5 μm, cut-off wavelength = 800 nm, and PMD = 0.1 ps / √km.
At this time, the distribution of the excess loss Δα1.38 shown in FIG. 10 due to the light absorption of the OH group having a wavelength of 1380 nm was examined.
{9} ′ The distribution of Δα1.38 according to the conventional method is very large as shown in FIG. The distribution where Δα1.38 itself is small is very small.
On the other hand, by using the method of the present invention, it is possible to stably reduce Δα1.38 (see FIG. 12).
As a result, the optical fiber obtained in this example had the refractive index difference distribution shown in FIG. 13 and was useful as a dispersion compensating fiber.
[0040]
The dispersion compensating fiber has a large influence on light absorption by the OH group at the collapsed interface because the guided light spreads more widely than the dispersion-shifted fiber, but the present invention reduces the amount of OH group generation at the collapsed interface. By reducing the amount, transmission loss due to absorption of light by the OH group can be reduced, and an excellent effect that the signal transmission band is widened has been achieved. Further, it has been clarified that the intensity of pump light required for Raman amplification can be reduced, and as a result, the amplification efficiency of signal light can be increased.
[0041]
[Example 2]
1) GeO to be the central core by known VAD method ₂ Added SiO ₂ Glass body (GeO ₂ (The maximum value of the addition amount is 14 mol% in the vicinity of the center) was manufactured and processed into a glass rod having an outer diameter of about 10 mm and a length of about 600 mm.
2) F-added SiO that becomes a depressed part by a known VAD method ₂ A glass body (with an F concentration of about 3.8 mol%) was manufactured and processed to obtain a glass pipe having an outer diameter of about 35 mm, an inner diameter of about 12 mm, and a length of about 500 mm.
3) The glass rod synthesized in 1) was inserted into the pipe synthesized in 2) and integrated by a rod-in collapse method to obtain a glass body having an outer diameter of about 33 mm and a length of about 400 mm. GeO here ₂ Added SiO ₂ The glass body and the F-added pipe can be satisfactorily produced by using, for example, an OVD method. During the collapse, Cl is contained as a process gas in the glass pipe. ₂ 500 sccm, O ₂ Was flowed at 250 sccm, and the internal pressure of the glass pipe was set to +0.05 kPa with respect to the external pressure.
[At this time, as Example 2, the optical fiber preform manufacturing apparatus according to the present invention in FIG. 3 was used, and as Comparative Example (conventional method) 2, the manufacturing apparatus shown in FIG. 9 was used. In the present invention, H is used as the heat source. ₂ / O ₂ Although a flame burner was used, other heat sources such as a plasma flame or induction furnace could be used. ]
[0042]
4) After stretching the glass body synthesized in 3) to an outer diameter of 10.6 mm, the outer periphery is ground by mechanical grinding or etching with an HF solution to obtain a glass rod having an outer diameter of 6.6 mm and a length of 600 mm. .
5) Cl-added SiO to be a clad portion by a known VAD method ₂ A glass body (with a Cl addition concentration of about 0.3 mol%) was manufactured and processed to obtain a glass pipe having an outer diameter of about 35 mm, an inner diameter of about 8 mm, and a length of about 500 mm. Of course, it can also be manufactured by the OVD method.
6) The glass rod synthesized in 4) was inserted into the glass pipe synthesized in 5), and integrated by a rod-in collapse method to obtain a glass body having an outer diameter of about 33 mm and a length of about 400 mm. During the collapse, Cl is contained as a process gas in the glass pipe. ₂ Was flowed at 200 sccm, and He was flowed at 100 sccm, and the internal pressure of the glass pipe was set to -0.5 kPa with respect to the external pressure.
[At this time, the apparatus for manufacturing an optical fiber preform according to the present invention shown in FIG. 3 was used as Example 2, and the apparatus shown in FIG. 9 was used as Comparative Example 2. In the present invention, H is used as the heat source. ₂ / O ₂ Although a flame burner was used, other heat sources such as a plasma flame or induction furnace could be used. ]
[0043]
7) By the known VAD method, 0.3 mol% of Cl-added SiO ₂ Glass was synthesized, and the ratio D / 2a of the diameter (2a) of the central core portion and the outer diameter (D) of the cladding portion was enlarged to 31.3 times to obtain an optical fiber preform. Of course, an OVD method, a rod-in collapse method, or the like is also possible.
8) This optical fiber was drawn by a known method to obtain an optical fiber having a glass part diameter of 125 μm.
[0044]
9) The transmission characteristics of this optical fiber at a wavelength of 1550 nm are as follows: transmission loss = 0.27 dB / km, dispersion = −47 ps / km / nm, dispersion slope = −0.14 ps / km / nm. ² , Aeff = 20 μm ² , MFD = 5 μm, cut-off wavelength = 800 nm, and PMD = 0.1 ps / √km.
At this time, the distribution of the excess loss Δα1.38 shown in FIG. 10 due to the light absorption of the OH group having a wavelength of 1380 nm was examined.
9) ′ The distribution of Δα1.38 according to the conventional method is very large as shown in FIG. The distribution where Δα1.38 itself is small is very small.
On the other hand, by using the method of the present invention, it is possible to stably reduce Δα1.38 (see FIG. 12).
As a result, the optical fiber obtained in this example had the refractive index difference distribution shown in FIG. 13 and was useful as a dispersion compensating fiber.
[0045]
In the dispersion compensating fiber, since the guided light is spread more widely than the dispersion-shifted fiber, the influence of OH absorption at the collapse interface is large.However, by reducing the amount of OH group generation at the collapse interface according to the present invention, The transmission loss due to the absorption of light by the OH group can be reduced, and an excellent effect of widening the signal transmission band has been achieved. Further, it has been clarified that the intensity of pump light required for Raman amplification can be reduced, and as a result, the amplification efficiency of signal light can be increased.
[0046]
[Example 3]
[1] GeO to be the central core by known VAD method ₂ Added SiO ₂ Glass body (GeO ₂ (The maximum value of the added amount is 25 mol% in the vicinity of the center), and processed to obtain a glass rod having a diameter of about 7.5 mm × 600 mm.
[2] F-added SiO serving as a depressed portion by a known VAD method or OVD method ₂ A glass body (F concentration was about 1.2% by mass) was manufactured and processed to obtain a glass pipe having an outer diameter of about 40 mm, an inner diameter of about 8.5 mm, and about 500 mm. This pipe is SF before collapsing ₆ An etching gas such as that described above was flown, heated to about 1500 ° C. by a heat source, and a gas phase etching process was performed.
[3] The glass rod synthesized in [1] was inserted into the glass pipe synthesized in [2]. After the inside of the pipe was evacuated to 0.1 kPa or less by a vacuum pump, nitrogen gas having a concentration of hydrogen molecules or a compound containing a hydrogen element of 1 ppm or less was introduced into the pipe, and the vacuum pump was stopped and pressurized to 105 kPa. . This is repeated three times, and the adsorbed gas (mainly H ₂ O) was eliminated. Then, Cl ₂ Was introduced into the pipe by 500 sccm, and heated to 1150 ° C. to remove metal impurities.
[0047]
[4] The glass pipe and glass rod of the above [3], the joint shown in FIG. 2 and the apparatus shown in FIG. 3 were integrated by a rod-in-collapse method to obtain a glass body of about φ39 mm × 400 mm. At this time, as a result of examining the amount of entrainment in the atmosphere, it was about 0.1 sccm, and the concentration of hydrogen molecules or hydrogen element-containing compounds was a process gas of 1 ppm or less. ₂ Was introduced into the pipe by 400 sccm. When the gas was not supplied, the gas was evacuated with a vacuum pump capable of reducing the pressure in the pipe to 0.03 kPa. The pressure in the pipe during the process was 0.1 kPa.
In this embodiment, the heat source is H ₂ / O ₂ Although a flame burner was used, other heat sources, such as a plasma flame or induction furnace, could be used. It is good also as a vertical collaps instead of a horizontal collapsible.
[0048]
[5] After stretching the glass body synthesized in the above [4] to φ11.7 mm, the outer periphery is ground by mechanical grinding or etching with an HF solution to form a glass rod having an outer diameter of 7.5 mmφ and a length of 600 mm. did.
[6] Cl-added SiO to be a clad portion by known VAD or OVD method ₂ A glass body (with a Cl addition concentration of about 0.3 mol%) was manufactured and processed to obtain a glass pipe having an outer diameter of about 43 mm, an inner diameter of about 9 mm, and about 500 mm. This pipe is SF before collapsing ₆ An etching gas such as that described above was flown, heated to about 1500 ° C. by a heat source, and a gas phase etching process was performed.
[7] The glass rod synthesized in [5] was inserted into the pipe synthesized in [6]. After the inside of the pipe was evacuated to 0.1 kPa or less by a vacuum pump, a nitrogen gas having a concentration of hydrogen molecules or a hydrogen element-containing compound of 1 ppm or less was introduced into the pipe, and the vacuum pump was stopped to increase the pressure to 105 kPa. This was carried out only once, and the adsorbed gas (mainly H ₂ O) was eliminated. Then, Cl ₂ Was introduced into the pipe under a standard condition (0 ° C., 1 atm) by 500 sccm, and heated to 1150 ° C. to remove metal impurities.
[0049]
[8] The pipe and glass rod of the above [7], the joint shown in FIG. 2 and the rod-in-collapse method using the apparatus shown in FIG. 3 were integrated to obtain a glass body of about φ42 mm × 400 mm. At this time, as a result of examining the amount of entrainment in the atmosphere, it was found to be about 0.05 sccm, and the concentration of hydrogen molecules or hydrogen element-containing compounds was 1 ppm or less. ₂ Was introduced into the pipe by 100 sccm. When the gas was not supplied, the gas was evacuated with a vacuum pump capable of reducing the pressure in the pipe to 0.03 kPa. The pressure in the pipe during the process was 0.08 kPa. In the present invention, H is used as the heat source. ₂ / O ₂ Although a flame burner was used, other heat sources, such as a plasma flame or induction furnace, could be used. Instead of a horizontal type, a vertical type collaps as shown in FIG. 5 may be used.
[9] By the known VAD, OVD, rod-in-collapse method, 0.3 mol% of Cl-added SiO ₂ Glass was synthesized, and the ratio D / 2a of the diameter (2a) of the central core portion and the outer diameter (D) of the clad portion was enlarged to 52.1 times to obtain an optical fiber preform.
[0050]
[10] This optical fiber was drawn by a known method to obtain an optical fiber having a glass part diameter of 125 μm.
[11] The transmission characteristics of this optical fiber at a wavelength of 1550 nm are as follows: transmission loss = 0.50 dB / km, dispersion = −105 ps / km / nm, dispersion slope = −0.37 ps / km / nm. ² , Aeff = 12 μm ² A good dispersion compensating fiber for compensating the dispersion and dispersion slope in the 1.55 μm band of an optical fiber having a zero-dispersion wavelength in the 1.3 μm band with a cutoff wavelength of 730 nm and a PMD of about 0.1 ps / √km. Was.
The transmission loss-wavelength characteristics of this fiber are as shown in FIG. 14, and it can be seen that excessive transmission loss in the 1.4 μm band due to OH groups is suppressed.
As a result, the optical fiber obtained in this example had the refractive index difference distribution shown in FIG. 15, and was useful as a dispersion compensating fiber.
[0051]
In the dispersion compensating fiber, since the guided light is spread more widely than the dispersion-shifted fiber, the influence of OH absorption at the collapse interface is large.However, by reducing the amount of OH group generation at the collapse interface according to the present invention, The transmission loss due to the absorption of light by the OH group can be reduced, and an excellent effect of widening the signal transmission band has been achieved. Further, it has been clarified that the intensity of pump light required for Raman amplification can be reduced, and as a result, the amplification efficiency of signal light can be increased.
[0052]
As described above, in Examples 1 to 3 using the apparatus of FIG. ₂ , O ₂ Since the front end of the supply port for the process gas is located in the glass pipe 1 and the pipe section (inner cylinder 13) of the gas supply section 10 has no joint, the atmosphere does not enter. Even if air is mixed in the rotary seal portion (the connection portion between the joint 7 and the outer cylinder 14 in FIG. 6), it is not supplied to the glass pipe side because it hits the gas exhaust portion 11 (decompression portion).
Therefore, excess loss due to OH groups can be suppressed.
On the other hand, in Comparative Examples 1 and 2 using the apparatus of FIG. 9, it is difficult to make the glass pipe connection portion 5 particularly the rotary seal portion (the connection portion of the joint 7) completely airtight, and the air easily mixes. Further, since the gas exhaust section 11 (decompression section) is provided in the middle of the pipe section 9, the process gas cannot reach the quartz pipe.
Therefore, excessive loss due to OH groups is likely to occur.
[0053]
【The invention's effect】
According to the present invention, there is provided an optical fiber capable of reducing the amount of OH group contamination at the collapse interface, reducing the transmission loss based on light absorption by the OH group, and maintaining a wide signal transmission band by adopting the above configuration. Can be.
Further, the present invention provides an optical fiber suitable for the collapse method such as an optical fiber having a complicated refractive index distribution pattern or a high Δ core fiber (dispersion compensating fiber or highly nonlinear fiber) having Δ of the central core of 2% or more. Useful for manufacturing.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view along an axis showing a specific example of an optical fiber preform manufacturing apparatus according to the present invention.
FIG. 2 is a partial cross-sectional view taken along an axis showing another specific example of the apparatus for manufacturing an optical fiber preform according to the present invention.
FIG. 3 is a conceptual diagram of an apparatus for manufacturing an optical fiber preform according to the present invention by a collapse method using a glass lathe.
4 (a), (b), (c), and (d) are schematic diagrams of a gas supply port and a gas exhaust port used in the present invention, (a) and (b) are partial side views, (c) and (d) are cross-sectional views when they are combined.
FIG. 5 is a schematic view showing a state in which the specific gravity of the dehydrating gas is large when performing the collapse of the method of the present invention using a vertical apparatus.
FIG. 6 is a schematic view showing a state in which the specific gravity of the dehydrating gas is small when performing the collapse of the method of the present invention using a vertical apparatus.
FIG. 7 is a schematic diagram showing a state in which a glass pipe connection portion is gripped in the apparatus of the present invention.
FIG. 8 is a schematic view showing an apparatus of the present invention in which a cover for covering a rotary joint is provided and an inert gas is supplied into the cover.
FIG. 9 is a conceptual view showing an example of an apparatus for manufacturing an optical fiber preform by a collapse method using a glass lathe in a conventional method.
FIG. 10 is a graph showing excess loss Δα1.38 (dB / km) due to light absorption loss due to OH groups at a wavelength of 1380 nm.
FIG. 11 is a graph showing excess loss due to light absorption by OH groups in a glass optical fiber obtained by a conventional method (Comparative Example).
FIG. 12 is a graph showing excess loss due to light absorption by OH groups in a glass fiber obtained by the method (Example) of the present invention.
FIG. 13 is a refractive index profile of an optical fiber (dispersion compensating fiber) obtained by the method of the present invention.
FIG. 14 is a graph showing the relationship between transmission loss and wavelength characteristics of a glass fiber obtained by the method (Example) of the present invention.
FIG.
3 is a refractive index profile of a dispersion compensating fiber obtained by the method of the present invention.
[Explanation of symbols]
1 glass pipe, 2 glass rod, 3 heat source,
4 gripper, 5 glass pipe connection, 6 and 7 joint,
8 gas supply port, 8 'gas supply port tip,
9 gas exhaust port, 9 'gas exhaust port tip,
10 gas supply unit, 11 gas exhaust unit.

Claims (11)

In a method for producing an optical fiber preform or an optical fiber intermediate preform by a collapse method in which a glass pipe is solidified by heating, or a glass pipe and a glass rod inserted in the glass pipe are integrated, a separate piping system is used. A glass pipe connecting portion having a gas supply port and a gas exhaust port configured at one end or both ends in the glass pipe, and introducing a process gas from the gas supply port into the glass pipe, A method of manufacturing an optical fiber preform or an optical fiber intermediate preform, wherein a collapse method is performed while gas in a glass pipe is exhausted from the gas exhaust port. The method for producing an optical fiber preform or an optical fiber intermediate preform according to claim 1, wherein the collapse method is performed while rotating the glass pipe or the glass pipe and the glass rod. 3. The process gas according to claim 1, wherein the process gas is at least one selected from the group consisting of an inert gas, a gas containing a halogen element, and an oxygen gas or a gas containing the at least one type. A method for producing an optical fiber preform or an optical fiber intermediate preform. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of claims 1 to 3, wherein a concentration of a hydrogen molecule or a compound containing a hydrogen element in the process gas is 100 ppm or less. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of claims 1 to 4, wherein the degree of vacuum in the glass pipe is set to 10 kPa or less in absolute pressure. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of claims 1 to 4, wherein the pressure in the glass pipe is higher than the outside air pressure, and the pressure difference is +1 kPa or less. The gas supply port and the gas exhaust port each formed by a separate piping system, the tip of the gas supply port is located closer to the interface of the collapse than the position where there is a possibility of entrainment in the atmosphere, the gas exhaust port The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of claims 1 to 6, wherein a front end portion is located at a position farther from the interface of the collapse than the front end portion of the gas supply port. The glass pipe, or the glass pipe and the glass rod are arranged vertically, and when the process gas is larger than the specific gravity of air, the collapse is performed from below to above the glass pipe. 8. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of 1 to 7. The glass pipe, or the glass pipe and the glass rod are arranged vertically, and when the process gas is smaller than the specific gravity of air, collapsing is performed from above to below the glass pipe. 8. The method for producing an optical fiber preform or an optical fiber intermediate preform according to any one of 1 to 7. Solidifying a rotatable glass pipe, or a rotatable glass pipe and an optical fiber preform manufacturing apparatus that integrates a glass rod inserted into the glass pipe, rotatably gripping the glass pipe. A glass pipe gripper, a heating source for heating the glass pipe or the glass pipe and the glass rod, and a gas supply port tip and a gas exhaust port tip attached to one or both ends of the glass pipe, respectively. A means for introducing gas into the glass pipe via the glass pipe connection (gas supply system), and a means for exhausting gas from the glass pipe via the glass pipe connection Gas exhaust system), and the glass pipe connection part is rotatable with the glass pipe, Including a rotary joint for connecting the gas supply system and the gas exhaust system without, a pipe connected to one of the gas supply system or the gas exhaust system is disposed inside the glass pipe connection portion, surrounding the pipe, the other An optical fiber preform manufacturing apparatus, wherein a pipe connected via a rotary joint is disposed on the optical fiber preform. 11. The apparatus for manufacturing an optical fiber preform according to claim 10, further comprising: a cover that covers the glass pipe connection portion outside the glass pipe connection portion, and a unit that supplies gas to the inside of the cover.

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