JP4097982B2

JP4097982B2 - Method for producing porous preform for optical fiber

Info

Publication number: JP4097982B2
Application number: JP2002122279A
Authority: JP
Inventors: 学齋藤; 雅博堀越
Original assignee: Fujikura Ltd
Current assignee: Fujikura Ltd
Priority date: 2002-04-24
Filing date: 2002-04-24
Publication date: 2008-06-11
Anticipated expiration: 2022-04-24
Also published as: JP2003313043A

Description

【０００１】
【発明の属する技術分野】
本発明は、酸水素火炎中でガラス原料ガスを反応させてガラス微粒子を生成し、これを出発部材の外周部に堆積させる外付け法に適用される光ファイバ用多孔質母材の製造方法に関する。
【０００２】
【従来の技術】
光ファイバ母材の製造方法の１つとしては、バーナからガラス原料ガスを、添加ガス、可燃性ガス、支燃性ガスとともに噴出し、ガラス原料ガスを火炎中で加水分解反応させてガラス微粒子（スート）を生成し、コアとなるガラス材を備えた円柱形の出発部材の外周部にガラス微粒子を堆積させて、複数層からなる多孔質層を形成して光ファイバ用多孔質母材を得て、これを電気炉中で脱水、焼結しながら透明ガラス化し光ファイバ母材を得る外付け法（ＯＶＤ法、Outside Vapor Phase Deposition）がある。
【０００３】
【発明が解決しようとする課題】
近年、高速通信の需要の増加に伴って、光ファイバの需要も年々増加してきている。そのため、光ファイバの価格を下げることが望まれている。そこで、このような要望に応えるためには、光ファイバの製造を高速化して製造時間を短縮し、光ファイバを一度に大量に製造して、製造コストを低減する必要がある。これを実現するためには、光ファイバの紡糸に供される光ファイバ母材を大型化する必要がある。
【０００４】
外付け法において、光ファイバ用多孔質母材の製造時間を短縮するには、例えば、ガラス微粒子の生成に供されるガラス原料ガスの流量を増加して、ガラス微粒子の堆積速度を速める方法がある。
しかしながら、単にガラス原料ガスの流量を増加しても、大型の光ファイバ母材を短時間に作製できるとは限らない。なぜならば、大型の光ファイバ母材を短時間に作製するためには、ガラス原料ガスの流量を多くしてガラス微粒子の堆積速度を速めると同時に、ガラス微粒子の堆積効率も高める必要があるからである。
ここで、ガラス微粒子の堆積効率とは、使用したガラス原料ガスが全て化学反応によってガラス微粒子に変化したと仮定したときのガラス微粒子の総量に対する、出発部材の表面に堆積されたガラス微粒子の総量の割合で定義するものである。また、堆積速度とは、単位時間当りに出発部材の表面に堆積されたガラス微粒子の重量で表されるものである。
【０００５】
一般に、ガラス微粒子を堆積する出発部材、または、ガラス微粒子堆積中の光ファイバ用多孔質母材（以下、「ターゲット部材」と記す。）の外径が細い場合、ガラス原料ガスおよび添加ガスの混合ガスの流速を大きくすれば、ガラス微粒子の堆積効率の向上に有効である。これは、ターゲット部材の外径が細い場合、ガラス微粒子の慣性力を大きくし、ガラス微粒子が直接、ターゲット部材に当る確率を大きくすれば、堆積効率が向上するからである。
一方、ターゲット部材の外径が太い場合、ガラス原料ガスおよび添加ガスの混合ガスの流速を小さくすれば、ガラス微粒子の堆積効率の向上に有効である。これは、ターゲット部材の外径が太い場合、ガラス原料ガスが反応する時間を長くし、生成したガラス微粒子を火炎中で拡散させることで、サーモフォレシス効果によるガラス微粒子の堆積効果が期待できるからである。
【０００６】
ところが、ターゲット部材の外径が細いときは、ガラス原料ガスの流速を上げるために、ガラス原料ガスおよび添加ガスの混合ガスの流量を多くすると、この混合ガス中の添加ガスの比率が大きくなってしまう。このような状況下では、ターゲット部材に堆積されないガラス微粒子の量が多くなり、結果として、製造コストが増加する。
一方、ターゲット部材の外径が太いときは、ガラス原料ガスの流速を下げるために、ガラス原料ガスおよび添加ガスの混合ガスの流量を少なくすると、この混合ガス中の添加ガスの比率が小さくなってしまう。このような状況下では、ガラス微粒子の生成量が少なくなり、ガラス微粒子の堆積に要する時間が長くなり、結果として、製造コストが増加する。
【０００７】
光ファイバ用多孔質母材の製造において、ガラス原料ガスおよび添加ガスの混合ガスが同一の噴出口から噴出される場合、この混合ガスの流速を最適とするために、添加ガスの流量を決定すると、混合ガス中のガラス原料ガスと添加ガスの比率もそれに応じて決定される。
しかしながら、ガラス原料ガスの反応促進、堆積中のガラス微粒子の表面温度やかさ密度の大きさなどを考慮すると、添加ガスの流量を調整することによって、ガラス原料ガスの流量を最適量に設定することができるとは限らない。したがって、このような方法では、ガラス微粒子の堆積効率を向上させることができないこともある。
【０００８】
例えば、図１１に示すようなバーナを用いて、第１の噴出口１よりガラス原料ガスおよび添加ガス、第２の噴出口２より不活性ガス、第３の噴出口３より可燃性ガス、第４の噴出口４および第５の噴出口５、５、…より支燃性ガスを噴出して、光ファイバ用多孔質母材の製造を行なう光ファイバ用多孔質母材の製造方法において、ターゲット部材の外径が細い場合、第１の噴出口１から噴出される添加ガスの流量が多くなり、ガラス微粒子の生成反応に寄与しない添加ガスが多くなる。一方、ターゲット部材の外径が太くなると、第１の噴出口１から噴出される添加ガスの流量が少なくなるため、ガラス原料ガスが十分に反応しなくなるという問題があった。
【０００９】
ところで、ガラス原料ガスおよび添加ガスの混合ガスを、複数の噴出口から噴出する光ファイバ用多孔質母材の製造方法について、例えば、特開平１０−１０１３４３号公報に開示されている。また、添加ガスを、ガラス原料ガスが噴出される噴出口に隣接する噴出口から噴出する光ファイバ用多孔質母材の製造方法については、特開平１０−１６７７４８号公報に開示されている。
しかしながら、これらの光ファイバ用多孔質母材の製造方法では、各噴出口から噴出するガスの種類と流量の関係が例示されているにすぎず、ターゲット部材の外径が大きくなるに伴なって、ガスの流量を変化させる方法や、ガラス原料ガスと添加ガスの流量比を略一定に保つなどの方法については記載されていない。
【００１０】
本発明は、前記事情に鑑みてなされたもので、バーナの噴出口から噴出されるガラス原料ガスと添加ガスの流量をガラス微粒子堆積中に制御し、ガラス原料ガスと添加ガスの流量比を最適な状態として、ガラス微粒子の堆積効率を向上する光ファイバ用多孔質母材の製造方法を提供することを課題とする。
【００１１】
本発明の光ファイバ用多孔質母材の製造方法は、中心軸を同じくして配列された複数のノズルを備えたバーナに、ガラス原料ガスと、これに添加する添加ガスを導入し、該ガラス原料ガスを酸水素火炎中で火炎加水分解反応させてガラス微粒子を生成し、該ガラス微粒子を出発部材の外周部に堆積して光ファイバ用多孔質母材を得る光ファイバ用多孔質母材の製造方法において、前記バーナは、中心に前記ガラス原料ガスおよび前記添加ガスの混合ガスを噴出するノズルを有し、該ノズルに隣接する前記添加ガスを噴出するノズルを有し、さらにこれらの外層に酸水素火炎を形成するためのガスを噴出するためのノズルを有し、前記ガラス微粒子の堆積中に、前記出発部材の外径変化に伴って、前記２つの噴出口から噴出される前記添加ガスの流量を、前記中心の噴出口から噴出される前記添加ガスの流量を単調に減少させるように１回以上変化させ、かつ前記中心の噴出口に隣接する噴出口から噴出される前記添加ガスの流量を単調に増加させるように１回以上変化させ、かつ、前記ガラス原料ガスの流量をＶ１リットル／分とし、前記隣接する２つの噴出口から噴出される添加ガスの総流量をＶ２リットル／分とし、前記ガラス微粒子の堆積の初期段階におけるＶ１／Ｖ２をＲｂとし、前記ガラス微粒子の堆積の終了段階におけるＶ１／Ｖ２をＲｆとすると、ＲｂとＲｆの関係を０．２５≦Ｒｂ／Ｒｆ≦４．０とすることを特徴とする。
なお、ここでガラス微粒子を堆積する初期段階とは、光ファイバ用多孔質母材の製造開始から、ガラス微粒子が総堆積量の５〜１５％程度堆積したときを示し、終了段階とは、ガラス微粒子が総堆積量の８５〜９５％程度堆積したときを示す。
本発明の光ファイバ用多孔質母材の製造方法は、中心軸を同じくして配列された複数のノズルを備えたバーナに、ガラス原料ガスと、これに添加する添加ガスを導入し、該ガラス原料ガスを酸水素火炎中で火炎加水分解反応させてガラス微粒子を生成し、該ガラス微粒子を出発部材の外周部に堆積して光ファイバ用多孔質母材を得る光ファイバ用多孔質母材の製造方法において、前記バーナは、中心に前記添加ガスを噴出するノズルを有し、該ノズルに隣接する前記ガラス原料ガスおよび前記添加ガスの混合ガスを噴出するノズルを有し、さらにこれらの外層に酸水素火炎を形成するためのガスを噴出するためのノズルを有し、前記ガラス微粒子の堆積中に、前記出発部材の外径変化に伴って、前記２つの噴出口から噴出される前記添加ガスの流量を、前記中心の噴出口から噴出される前記添加ガスの流量を単調に減少させるように１回以上変化させ、かつ前記中心の噴出口に隣接する噴出口から噴出される前記添加ガスの流量を単調に増加させるように１回以上変化させ、かつ、前記ガラス原料ガスの流量をＶ１リットル／分とし、前記隣接する２つの噴出口から噴出される添加ガスの総流量をＶ２リットル／分とし、前記ガラス微粒子の堆積の初期段階におけるＶ１／Ｖ２をＲｂとし、前記ガラス微粒子の堆積の終了段階におけるＶ１／Ｖ２をＲｆとすると、ＲｂとＲｆの関係を０．２５≦Ｒｂ／Ｒｆ≦４．０とすることを特徴とする。
本発明の光ファイバ用多孔質母材の製造方法は、中心軸を同じくして配列された複数のノズルを備えたバーナに、ガラス原料ガスと、これに添加する添加ガスを導入し、該ガラス原料ガスを酸水素火炎中で火炎加水分解反応させてガラス微粒子を生成し、該ガラス微粒子を出発部材の外周部に堆積して光ファイバ用多孔質母材を得る光ファイバ用多孔質母材の製造方法において、前記バーナは、中心に前記ガラス原料ガスおよび前記添加ガスの混合ガスを噴出するノズルを有し、該ノズルに隣接する前記ガラス原料ガスおよび前記添加ガスを噴出するノズルを有し、さらにこれらの外層に酸水素火炎を形成するためのガスを噴出するためのノズルを有し、前記ガラス微粒子の堆積中に、前記出発部材の外径変化に伴って、前記２つの噴出口から噴出される前記ガラス原料ガスと前記添加ガスの合計の流量を、前記中心の噴出口から噴出される前記ガラス原料ガスと前記添加ガスの合計の流量を単調に減少させるように１回以上変化させ、かつ前記中心の噴出口に隣接する噴出口から噴出される前記ガラス原料ガスと前記添加ガスの合計の流量を単調に増加させるように１回以上変化させ、かつ、前記ガラス原料ガスの流量をＶ１リットル／分とし、前記隣接する２つの噴出口から噴出される添加ガスの総流量をＶ２リットル／分とし、前記ガラス微粒子の堆積の初期段階におけるＶ１／Ｖ２をＲｂとし、前記ガラス微粒子の堆積の終了段階におけるＶ１／Ｖ２をＲｆとすると、ＲｂとＲｆの関係を０．２５≦Ｒｂ／Ｒｆ≦４．０とすることを特徴とする。
上記光ファイバ用多孔質母材の製造方法において、製造中における前記原料ガス供給量を一定とすることが好ましい。
上記光ファイバ用多孔質母材の製造方法において、前記添加ガスを、酸素または水素とすることが好ましい。
【００１２】
【発明の実施の形態】
以下、本発明を詳しく説明する。
本発明の光ファイバ用多孔質母材製造用バーナ装置は、ガラス微粒子を生成するバーナと、このバーナにガラス原料ガス、可燃性ガス、支燃性ガスおよび不活性ガスを供給するガス供給源と、これらのガスの流量または流速を制御するガス制御部とから概略構成されている
【００１３】
図１は、本発明の光ファイバ用多孔質母材製造用バーナ装置に備えられているバーナの一例を示す概略構成図である。
このバーナ１０の端面において、その中心に第１のノズル１１が設けられ、この第１のノズル１１の周囲に、第１のノズル１１と中心軸を同じくして第２のノズル１２が設けられ、さらに、この第２のノズル１２の周囲に、第１のノズル１１と中心軸を同じくして第３のノズル１３が設けられ、以下、同様に、第４のノズル１４および第５のノズル１５が設けられている。また、第３のノズル１３と第４のノズル１４の間で、第１のノズル１１の同心円上には、複数個の内径および外径の等しい第６のノズル１６、１６、…が設けられている。
【００１４】
また、第１のノズル１１が第１の噴出口２１をなし、第１のノズル１１と第２のノズル１２の間の部分が第２の噴出口２２をなし、第２のノズル１２と第３のノズル１３の間の部分が第３の噴出口２３をなし、第３のノズル１３と第４のノズル１４の間の部分が第４の噴出口２４をなし、第４のノズル１４と第５のノズル１５の間の部分が第５の噴出口２５をなし、第６のノズル１６、１６、…が第６の噴出口２６、２６、…をなしている。
【００１５】
このバーナ１０は、外径４０〜６０ｍｍ程度の円筒形で、一般的には石英ガラスで形成されている。また、第１のノズル１１の内径は２．５〜６ｍｍ程度、第２のノズル１２の内径は４〜１０ｍｍ程度、第３のノズル１３の内径は６〜１５ｍｍ程度、第３のノズル１３の内径は６〜１５ｍｍ程度、第４のノズル１４の内径は２５〜４５ｍｍ程度、第５のノズル１５の内径は３５〜５５ｍｍ程度、第６のノズル１６の内径は１〜２ｍｍ程度となっている。また、第１のノズル１１の中心から、第６のノズル１６の中心までの距離は１０〜３０ｍｍ程度となっている。
バーナ１０を構成する各ノズルの内径を上記のような範囲とすることにより、後述の光ファイバ用多孔質母材の製造方法が可能となる。
【００１６】
さらに、ガス供給源は、ガラス原料ガス、酸素、水素、不活性ガスなどが充填されたガスボンベ（図示略）などからなり、バーナ１０の後端部に、ガス供給管路（図示略）を介して接続されている。
そして、ガス制御部は、電磁バルブ、流量制御装置などからなり、上述のガス供給管路の中途に設けられており、流量制御装置により、ガスの流量または流速を制御する。
【００１７】
以下、本発明の光ファイバ用多孔質母材の製造方法を説明する。
本発明の多孔質ガラス母材の製造方法では、まず、その軸周りに回転する出発部材の外周部に、例えば、バーナ１０の第１の噴出口２１からガラス原料ガスのＳｉＣｌ₄、ＧｅＣｌ₄など、および、添加ガスの酸素ガスまたは水素ガスを供給し、第２の噴出口２２から支燃性ガスの酸素ガスを供給し、第３の噴出口２３から不活性ガスのアルゴンガスを供給し、第４の噴出口２４からは可燃性ガスの水素ガスを供給し、第５の噴出口２５および第６の噴出口２６からは支燃性ガスの酸素ガスを供給し、バーナ１０の酸水素火炎中における加水分解反応により、ガラス微粒子を合成し、このガラス微粒子を出発部材の外周部に堆積し、光ファイバ用多孔質母材を得る。
【００１８】
本発明の光ファイバ用多孔質母材の製造方法にあっては、第１の噴出口２１および第２の噴出口２２から供給されるガスを、組成の等しいガラス原料ガスおよび添加ガスの混合ガスとするか、または、第１の噴出口２１または第２の噴出口２２から供給されるガスのうち、一方をガラス原料ガスおよび添加ガスの混合ガスとし、他方を添加ガスとする。
そして、ガラス微粒子の堆積中に、ガラス微粒子の堆積時間の経過に伴なって増加する光ファイバ用多孔質母材の外径変化に応じて、第１の噴出口２１または第２の噴出口２２のうち、少なくとも１つの噴出口から噴出されるガラス原料ガスおよび添加ガスの混合ガスの流速を１回以上変化させて、ガラス微粒子の堆積の初期段階で速く、終了段階で遅くなるようにする。さらに、第１の噴出口２１から噴出されるガラス原料ガスの流量をＶ１リットル／分とし、第１の噴出口２１および第２の噴出口２２から噴出される添加ガスの酸素ガスの総流量をＶ２リットル／分とし、これらの比Ｖ１／Ｖ２を、ガラス微粒子の堆積の初期段階でＲｂとし、ガラス微粒子の堆積の終了段階でＲｆとすると、ＲｂとＲｆの関係を０．２５≦Ｒｂ／Ｒｆ≦４．０とする。ＲｂとＲｆのより好ましい関係は０．５≦Ｒｂ／Ｒｆ≦２．０であり、さらに好ましくは０．８≦Ｒｂ／Ｒｆ≦１．２である。
【００１９】
このように、本発明の光ファイバ用多孔質母材の製造方法にあっては、バーナの隣接する２つの噴出口のうち、少なくとも１つの噴出口から噴出されるガラス原料ガスおよび添加ガスの混合ガスの流速を、ガラス微粒子の堆積の初期段階で速く、終了段階で遅くなるようにし、かつ、ガラス微粒子の堆積の初期段階と終了段階において、ＲｂとＲｆとの比率を大きく変化させないようにすれば、常に反応に過不足のない酸素ガスが、ガラス原料ガス周辺に存在するようになる。すなわち、ガラス原料ガスと酸素ガスの流量比が、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、常に最適な状態となる。したがって、ガラス原料ガスが十分に反応するようになるから、ガラス微粒子の堆積効率が向上する。
【００２０】
さらに、添加ガスを、酸素ガスから水素ガスへ変えた場合も同様である。この場合、好ましいＲｂ、Ｒｆの値は、添加ガスが酸素ガスの場合とは必然的に異なるが、ＲｂとＲｆとの比率を、ガラス微粒子の堆積の初期段階と終了段階で大きく変化させないことが望ましいことは全く同様である。
【００２１】
なお、ガラス原料ガスに添加する添加ガスは、ガラス微粒子の生成反応に寄与するという観点から、上述のように酸素ガスまたは水素ガスのいずれかであることが好ましい。
また、光ファイバ用多孔質母材製造用バーナ装置に備えられたバーナの構造は図１に示すような、その中心に、中心軸を同じくして設けられた３重のノズルを有する構造でも、図１１に示すような、その中心に、中心軸を同じくして設けられた２重ノズルを有する構造であっても、上述の条件を満たしていれば、どちらであってもよい。
【００２２】
以下、図１および図１１を用いて具体的な実施例を示し、本発明の効果を明らかにする。
なお、以下に示す実施例において、バーナの構造、ガスの流量、出発部材の大きさなどは、ここで示したものに限定されるものではない。また、この実施例をもって本発明が限定されるものでもない。
【００２３】
（実施例１）
直径３０ｍｍ、長さ１１００ｍｍの円柱形の出発部材を、その軸周りに毎分３０回転させ、バーナ端面の概略形状が図１に示したようなバーナを複数個用いて、このバーナを出発部材の長手方向と平行に往復移動させながら、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。ガラス原料ガスの添加ガスには水素ガスを用い、第１の噴出口２１のみにガラス原料ガスを供給した。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表１および図２のように変化させた。
【００２４】
【表１】

【００２５】
（実施例２）
バーナ端面の概略形状が図１に示したようなバーナを用い、ガラス原料ガスの添加ガスには酸素ガスを用いた以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表２および図３のように変化させた。
【００２６】
【表２】

【００２７】
（実施例３）
バーナ端面の概略形状が図１１に示したようなバーナを用い、ガラス原料ガスの添加ガスには水素ガスを用い、第１の噴出口１のみにガラス原料ガスを供給した以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表３および図４のように変化させた。
【００２８】
【表３】

【００２９】
（実施例４）
バーナ端面の概略形状が図１に示したようなバーナを用い、第２の噴出口２２のみにガラス原料ガスを供給した以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表４および図５のように変化させた。
【００３０】
【表４】

【００３１】
（実施例５）
バーナ端面の概略形状が図１に示したようなバーナを用い、ガラス原料ガスの添加ガスには酸素ガスを用い、第１の噴出口２１およにび第２の噴出口２２にガラス原料ガスを供給した以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表５および図６のように変化させた。
【００３２】
【表５】

【００３３】
（比較例１）
バーナ端面の概略形状が図１に示したようなバーナを用い、ガラス原料ガスの添加ガスには酸素ガスを用いた以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表６および図７のように変化させた。
【００３４】
【表６】

【００３５】
（比較例２）
バーナ端面の概略形状が図１１に示したようなバーナを用い、ガラス原料ガスの添加ガスには酸素ガスを用い、第１の噴出口１のみにガラス原料ガスを供給した以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表７および図８のように変化させた。
【００３６】
【表７】

【００３７】
（比較例３）
バーナ端面の概略形状が図１に示したようなバーナを用い、ガラス原料ガスの添加ガスに酸素ガスを用いた以外は、実施例１と同様にして、出発部材の外周部にＳｉＯ₂ガラス微粒子を堆積させた。バーナに供給するガスを、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、表８および図９のように変化させた。
【００３８】
【表８】

【００３９】
実施例１〜５および比較例１〜３におけるガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス微粒子の堆積効率の関係を図１０に示す。
図１０の結果から、第１の噴出口１１または第２の噴出口１２、あるいは、第１の噴出口１または第２の噴出口２のうち少なくとも１つの噴出口から噴出されるガラス原料ガスおよび添加ガスの混合ガスの流速を、ガラス微粒子の堆積の初期段階で速く、終了段階で遅くなるようにし、かつ、ガラス微粒子の堆積の初期段階と終了段階において、ＲｂとＲｆとの比率を大きく変化させないようにすれば、ガラス微粒子の堆積効率を向上することができることが確認された。
【００４０】
【発明の効果】
以上説明したように、本発明の光ファイバ用多孔質母材の製造方法によれば、バーナの隣接する２つの噴出口のうち、少なくとも１つの噴出口から噴出されるガラス原料ガスおよび添加ガスの混合ガスの流速を、ガラス微粒子の堆積の初期段階で速く、終了段階で遅くなるようにし、かつ、ガラス微粒子の堆積の初期段階と終了段階において、ガラス原料ガスの総流量と添加ガスの総流量との比率を大きく変化させないようにするから、常に反応に過不足のない酸素ガスが、ガラス原料ガス周辺に存在するようになり、ガラス原料ガスと酸素ガスの流量比が、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、常に最適な状態となる。したがって、ガラス原料ガスが十分に反応するようになるから、ガラス微粒子の堆積効率が向上する。
また、本発明の光ファイバ用多孔質母材製造用バーナ装置によれば、ガラス原料ガスと酸素ガスの流量比を、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径変化に応じて、常に最適な状態とすることができるから、ガラス原料ガスが十分に反応し、ガラス微粒子の堆積効率を向上させることができる。
【図面の簡単な説明】
【図１】本発明の光ファイバ用多孔質母材製造用バーナ装置に備えられたバーナの一例を示す概略構成図である。
【図２】実施例１において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図３】実施例２において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図４】実施例３において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図５】実施例４において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図６】実施例５において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図７】比較例１において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図８】比較例２において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図９】比較例３において、ガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス原料ガスの総流量Ｖ１と添加ガスの総流量Ｖ２の比率との関係を示すグラフである。
【図１０】実施例１〜５および比較例１〜３におけるガラス微粒子堆積中の光ファイバ用多孔質母材の外径と、ガラス微粒子の堆積効率の関係を示すグラフである。
【図１１】光ファイバ用多孔質母材の製造に用いられるバーナの一例を示す概略構成図である。
【符号の説明】
１０・・・バーナ、１１・・・第１のノズル、１２・・・第２のノズル、１３・・・第３のノズル、１４・・・第４のノズル、１５・・・第５のノズル、１６・・・第６のノズル、２１・・・第１の噴出口、２２・・・第２の噴出口、２３・・・第３の噴出口、２４・・・第４の噴出口、２５・・・第５の噴出口、２６・・・第６の噴出口[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for producing a porous preform for an optical fiber applied to an external method in which a glass raw material gas is reacted in an oxyhydrogen flame to produce glass fine particles and deposited on the outer periphery of a starting member.To the lawRelated.
[0002]
[Prior art]
As one method for producing an optical fiber preform, glass raw material gas is ejected from a burner together with additive gas, combustible gas, and flammable gas, and the glass raw material gas is hydrolyzed in a flame to produce glass fine particles ( Soot) is formed, and glass particulates are deposited on the outer periphery of a cylindrical starting member having a glass material as a core to form a porous layer composed of a plurality of layers, thereby obtaining a porous preform for an optical fiber. There is an external method (OVD method, Outside Vapor Phase Deposition) in which an optical fiber preform is obtained by making it transparent glass while dehydrating and sintering it in an electric furnace.
[0003]
[Problems to be solved by the invention]
In recent years, with the increase in demand for high-speed communication, demand for optical fibers has been increasing year by year. Therefore, it is desired to reduce the price of optical fibers. Therefore, in order to meet such a demand, it is necessary to reduce the manufacturing cost by increasing the manufacturing speed of the optical fiber to shorten the manufacturing time and manufacturing the optical fiber in large quantities at a time. In order to realize this, it is necessary to increase the size of the optical fiber preform used for spinning the optical fiber.
[0004]
In order to shorten the manufacturing time of the optical fiber porous preform in the external method, for example, there is a method of increasing the deposition rate of the glass fine particles by increasing the flow rate of the glass raw material gas used for the production of the glass fine particles. is there.
However, simply increasing the flow rate of the glass source gas does not always produce a large optical fiber preform in a short time. This is because, in order to produce a large optical fiber preform in a short time, it is necessary to increase the deposition rate of glass particles by increasing the flow rate of glass raw material gas and at the same time increase the deposition efficiency of glass particles. is there.
Here, the deposition efficiency of glass particulates is the total amount of glass particulates deposited on the surface of the starting member with respect to the total amount of glass particulates when it is assumed that all the glass source gas used has been changed to glass particulates by chemical reaction. It is defined as a percentage. The deposition rate is expressed by the weight of the glass fine particles deposited on the surface of the starting member per unit time.
[0005]
In general, when the outer diameter of the starting member for depositing glass fine particles or the porous optical fiber preform (hereinafter referred to as “target member”) during the glass fine particle deposition is thin, the glass raw material gas and the additive gas are mixed. Increasing the gas flow rate is effective in improving the deposition efficiency of glass particles. This is because when the outer diameter of the target member is small, the deposition efficiency is improved by increasing the inertial force of the glass fine particles and increasing the probability that the glass fine particles directly hit the target member.
On the other hand, when the outer diameter of the target member is large, reducing the flow rate of the mixed gas of the glass raw material gas and the additive gas is effective for improving the deposition efficiency of the glass fine particles. This is because, when the outer diameter of the target member is large, the deposition time of the glass fine particles can be expected due to the thermophoresis effect by extending the reaction time of the glass raw material gas and diffusing the generated glass fine particles in the flame. is there.
[0006]
However, when the outer diameter of the target member is thin, increasing the flow rate of the mixed gas of the glass raw material gas and the additive gas in order to increase the flow rate of the glass raw material gas increases the ratio of the additive gas in the mixed gas. End up. Under such circumstances, the amount of glass particles not deposited on the target member increases, resulting in an increase in manufacturing cost.
On the other hand, when the outer diameter of the target member is large, if the flow rate of the mixed gas of the glass raw material gas and the additive gas is decreased in order to reduce the flow rate of the glass raw material gas, the ratio of the additive gas in the mixed gas becomes small. End up. Under such circumstances, the amount of generated glass particles is reduced, the time required for deposition of the glass particles is increased, and as a result, the manufacturing cost is increased.
[0007]
In the production of a porous preform for an optical fiber, when the mixed gas of the glass raw material gas and the additive gas is ejected from the same outlet, the flow rate of the additive gas is determined in order to optimize the flow rate of the mixed gas. The ratio of the glass raw material gas to the additive gas in the mixed gas is also determined accordingly.
However, considering the acceleration of the reaction of the glass source gas, the surface temperature of the glass fine particles during deposition, the bulk density, etc., it is possible to set the flow rate of the glass source gas to an optimum amount by adjusting the flow rate of the additive gas. It is not always possible. Therefore, such a method may not be able to improve the deposition efficiency of glass particles.
[0008]
For example, using a burner as shown in FIG. 11, the glass raw material gas and additive gas from the first outlet 1, the inert gas from the second outlet 2, the combustible gas from the third outlet 3, In the method for producing a porous optical fiber preform, the target material is produced by ejecting a combustion-supporting gas from the 4 ejection openings 4 and the fifth ejection openings 5, 5. When the outer diameter of the member is thin, the flow rate of the additive gas ejected from the first ejection port 1 increases, and the additive gas that does not contribute to the glass fine particle formation reaction increases. On the other hand, when the outer diameter of the target member is increased, the flow rate of the additive gas ejected from the first ejection port 1 is reduced, so that there is a problem that the glass raw material gas does not sufficiently react.
[0009]
Incidentally, a method for producing a porous preform for an optical fiber in which a mixed gas of a glass raw material gas and an additive gas is ejected from a plurality of ejection ports is disclosed, for example, in JP-A-10-101343. Japanese Patent Application Laid-Open No. 10-167748 discloses a method for producing a porous preform for an optical fiber in which an additive gas is ejected from an ejection port adjacent to an ejection port from which a glass raw material gas is ejected.
However, in these methods for manufacturing a porous preform for an optical fiber, the relationship between the type of gas ejected from each ejection port and the flow rate is merely illustrated, and as the outer diameter of the target member increases. There is no description of a method for changing the gas flow rate or a method for maintaining the flow rate ratio of the glass raw material gas and the additive gas substantially constant.
[0010]
  The present invention has been made in view of the above circumstances, and controls the flow rate of the glass raw material gas and the additive gas ejected from the burner outlet during the glass fine particle deposition to optimize the flow rate ratio of the glass raw material gas and the additive gas. To manufacture a porous preform for optical fiber that improves the deposition efficiency of glass particlesThe lawThe issue is to provide.
[0011]
  Method for producing porous preform for optical fiber of the present inventionIntroduces a glass raw material gas and an additive gas to be added to a burner having a plurality of nozzles arranged in the same central axis, and causes the glass raw material gas to undergo a flame hydrolysis reaction in an oxyhydrogen flame. In the method for producing a porous optical fiber preform, the glass fine particles are produced, and the glass fine particles are deposited on the outer periphery of the starting member to obtain the optical fiber porous preform.The burner has a nozzle that ejects the mixed gas of the glass raw material gas and the additive gas at the center, a nozzle that ejects the additive gas adjacent to the nozzle, and further forms an oxyhydrogen flame in these outer layers Has a nozzle to spout gas forDuring the deposition of the glass particles, the outer diameter of the starting member changes.AccompanyingAnd saidTwoSpoutThe flow rate of the additive gas ejected from the center is changed at least once so as to monotonously decrease the flow rate of the additive gas ejected from the central jet port, and from the jet port adjacent to the central jet port To increase monotonously the flow rate of the additive gasChange it more than once,And the glass source gasThe flow rate is V1 liter / min, the total flow rate of the additive gas ejected from the two adjacent outlets is V2 liter / min, V1 / V2 in the initial stage of the deposition of the glass particulates is Rb, and the glass particulates Assuming that V1 / V2 at the final stage of deposition of Rf is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0It is characterized by.
  Here, the initial stage of depositing the glass microparticles indicates the time when the glass microparticles are deposited about 5 to 15% of the total deposition amount from the start of the production of the optical fiber porous preform, and the end stage is the glass The time when the fine particles are deposited is about 85 to 95% of the total deposition amount.
  The method for producing a porous preform for an optical fiber according to the present invention introduces a glass raw material gas and an additive gas added thereto into a burner having a plurality of nozzles arranged with the same central axis, and the glass A porous base material for an optical fiber is obtained by subjecting a raw material gas to a flame hydrolysis reaction in an oxyhydrogen flame to produce glass fine particles, and depositing the glass fine particles on the outer periphery of a starting member to obtain a porous base material for an optical fiber. In the manufacturing method, the burner has a nozzle for ejecting the additive gas in the center, a nozzle for ejecting the mixed gas of the glass raw material gas and the additive gas adjacent to the nozzle, and further in these outer layers. A nozzle for ejecting a gas for forming an oxyhydrogen flame, and the additive gas ejected from the two ejection ports in accordance with a change in the outer diameter of the starting member during the deposition of the glass fine particles; The flow rate is changed at least once so that the flow rate of the additive gas jetted from the central jet port is monotonously decreased, and the flow rate of the additive gas jetted from the jet port adjacent to the central jet port The flow rate of the glass raw material gas is V1 liter / min, and the total flow rate of the additive gas ejected from the two adjacent outlets is V2 liter / min. When V1 / V2 in the initial stage of the deposition of the glass particulates is Rb and V1 / V2 in the end stage of the deposition of the glass particulates is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4. It is characterized by zero.
  The method for producing a porous preform for an optical fiber according to the present invention introduces a glass raw material gas and an additive gas added thereto into a burner having a plurality of nozzles arranged with the same central axis, and the glass A porous base material for an optical fiber is obtained by subjecting a raw material gas to a flame hydrolysis reaction in an oxyhydrogen flame to produce glass fine particles, and depositing the glass fine particles on the outer periphery of a starting member to obtain a porous base material for an optical fiber. In the manufacturing method, the burner has a nozzle for ejecting a mixed gas of the glass raw material gas and the additive gas at the center, and has a nozzle for ejecting the glass raw material gas and the additive gas adjacent to the nozzle, Further, a nozzle for ejecting a gas for forming an oxyhydrogen flame in these outer layers is provided, and during the deposition of the glass fine particles, the two outlets are changed in accordance with a change in the outer diameter of the starting member. The total flow rate of the glass raw material gas and the additive gas ejected is changed at least once so that the total flow rate of the glass raw material gas and the additive gas ejected from the central outlet is monotonously reduced. And the flow rate of the glass raw material gas is changed at least once so as to monotonously increase the total flow rate of the glass raw material gas and the additive gas ejected from the jet outlet adjacent to the central jet port. V1 liter / min, and the total flow rate of the additive gas ejected from the two adjacent outlets is V2 liter / min. When V1 / V2 in the initial stage of deposition of the fine particles is Rb and V1 / V2 in the final stage of the deposition of the glass fine particles is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. It is characterized by doing.
  In the method for producing a porous preform for an optical fiber, it is preferable that the supply amount of the raw material gas is constant during the production.
  In the method for producing a porous preform for an optical fiber, the additive gas is preferably oxygen or hydrogen.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
A burner device for producing a porous preform for an optical fiber according to the present invention includes a burner that generates glass fine particles, a gas supply source that supplies glass raw material gas, combustible gas, combustion-supporting gas, and inert gas to the burner. And a gas control unit for controlling the flow rate or flow rate of these gases.
[0013]
FIG. 1 is a schematic configuration diagram showing an example of a burner provided in a burner device for producing a porous preform for an optical fiber according to the present invention.
A first nozzle 11 is provided at the center of the end face of the burner 10, and a second nozzle 12 is provided around the first nozzle 11 with the same central axis as the first nozzle 11. Further, a third nozzle 13 is provided around the second nozzle 12 so as to have the same central axis as that of the first nozzle 11. Hereinafter, similarly, the fourth nozzle 14 and the fifth nozzle 15 are provided. Is provided. Further, between the third nozzle 13 and the fourth nozzle 14, a plurality of

sixth nozzles

16, 16,... Having the same inner diameter and outer diameter are provided on the concentric circle of the first nozzle 11. Yes.
[0014]
In addition, the first nozzle 11 forms the first jet port 21, the portion between the first nozzle 11 and the second nozzle 12 forms the second jet port 22, and the second nozzle 12 and the third nozzle The portion between the nozzles 13 forms a third jet port 23, the portion between the third nozzle 13 and the fourth nozzle 14 forms a fourth jet port 24, and the fourth nozzle 14 and the fifth nozzle The portion between the nozzles 15 forms a fifth jet port 25, and the

sixth nozzles

16, 16,... Form the

sixth jet ports

26, 26,.
[0015]
The burner 10 has a cylindrical shape with an outer diameter of about 40 to 60 mm, and is generally formed of quartz glass. The inner diameter of the first nozzle 11 is about 2.5 to 6 mm, the inner diameter of the second nozzle 12 is about 4 to 10 mm, the inner diameter of the third nozzle 13 is about 6 to 15 mm, and the inner diameter of the third nozzle 13. Is about 6 to 15 mm, the inner diameter of the fourth nozzle 14 is about 25 to 45 mm, the inner diameter of the fifth nozzle 15 is about 35 to 55 mm, and the inner diameter of the sixth nozzle 16 is about 1 to 2 mm. The distance from the center of the first nozzle 11 to the center of the sixth nozzle 16 is about 10 to 30 mm.
By setting the inner diameter of each nozzle constituting the burner 10 in the above-described range, a method for manufacturing a porous preform for an optical fiber described later becomes possible.
[0016]
Further, the gas supply source includes a gas cylinder (not shown) filled with glass raw material gas, oxygen, hydrogen, inert gas, and the like, and is connected to the rear end of the burner 10 via a gas supply line (not shown). Connected.
The gas control unit includes an electromagnetic valve, a flow rate control device, and the like, and is provided in the middle of the above-described gas supply pipe. The flow rate control device controls the gas flow rate or flow rate.
[0017]
Hereinafter, the manufacturing method of the porous preform for optical fiber of the present invention will be described.
In the method for producing a porous glass base material of the present invention, first, the glass source gas SiCl, for example, from the first jet port 21 of the burner 10 is formed on the outer periphery of the starting member rotating around its axis._Four, GeCl_FourAnd oxygen gas or hydrogen gas as an additive gas is supplied, oxygen gas as a combustion-supporting gas is supplied from the second jet port 22, and argon gas as an inert gas is supplied from the third jet port 23. The hydrogen gas of the combustible gas is supplied from the fourth jet port 24, the oxygen gas of the combustion-supporting gas is supplied from the fifth jet port 25 and the sixth jet port 26, and the oxyhydrogen of the burner 10 is supplied. Glass particles are synthesized by a hydrolysis reaction in a flame, and the glass particles are deposited on the outer periphery of the starting member to obtain a porous preform for an optical fiber.
[0018]
In the method for producing a porous preform for an optical fiber of the present invention, the gas supplied from the first jet port 21 and the second jet port 22 is a mixed gas of glass raw material gas and additive gas having the same composition. Alternatively, one of the gases supplied from the first jet port 21 or the second jet port 22 is a mixed gas of a glass raw material gas and an additive gas, and the other is an additive gas.
Then, during the deposition of the glass particulates, the first ejection port 21 or the second ejection port 22 according to the change in the outer diameter of the optical fiber porous preform that increases with the passage of the glass particulate deposition time. Among them, the flow rate of the mixed gas of the glass raw material gas and the additive gas ejected from at least one ejection port is changed one or more times so as to be faster at the initial stage of deposition of the glass fine particles and slower at the end stage. Further, the flow rate of the glass raw material gas ejected from the first ejection port 21 is V1 liter / min, and the total flow rate of the oxygen gas of the additive gas ejected from the first ejection port 21 and the second ejection port 22 is V2 liter / min, and the ratio V1 / V2 is Rb at the initial stage of the deposition of the glass particulates and Rf at the end of the deposition of the glass particulates, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. A more preferable relationship between Rb and Rf is 0.5 ≦ Rb / Rf ≦ 2.0, and more preferably 0.8 ≦ Rb / Rf ≦ 1.2.
[0019]
As described above, in the method for producing a porous preform for an optical fiber according to the present invention, a mixture of a glass raw material gas and an additive gas ejected from at least one of the two adjacent ejection ports of the burner. The flow rate of the gas should be fast at the initial stage of deposition of the glass particulates and slow at the end stage, and the ratio of Rb and Rf should not be changed greatly at the initial stage and the termination stage of the deposition of the glass particulates. For example, oxygen gas that is not excessive or deficient in the reaction always exists around the glass raw material gas. That is, the flow rate ratio between the glass raw material gas and the oxygen gas is always optimal in accordance with the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles. Therefore, since the glass raw material gas is sufficiently reacted, the deposition efficiency of the glass fine particles is improved.
[0020]
The same applies when the additive gas is changed from oxygen gas to hydrogen gas. In this case, preferable values of Rb and Rf are inevitably different from those in the case where the additive gas is oxygen gas, but the ratio of Rb and Rf may not be changed greatly at the initial stage and the end stage of the deposition of the glass fine particles. What is desirable is exactly the same.
[0021]
In addition, it is preferable that the additive gas added to glass raw material gas is either oxygen gas or hydrogen gas as mentioned above from a viewpoint that it contributes to the production | generation reaction of glass microparticles.
In addition, the structure of the burner provided in the optical fiber porous preform manufacturing burner apparatus as shown in FIG. 1 is a structure having a triple nozzle provided at the center with the same central axis. As shown in FIG. 11, even a structure having a double nozzle provided at the center with the same central axis may be used as long as the above conditions are satisfied.
[0022]
Specific examples will be described below with reference to FIGS. 1 and 11 to clarify the effects of the present invention.
In the following examples, the structure of the burner, the gas flow rate, the size of the starting member, and the like are not limited to those shown here. Further, the present invention is not limited to the embodiments.
[0023]
Example 1
A cylindrical starting member having a diameter of 30 mm and a length of 1100 mm is rotated about 30 times per minute around its axis, and a plurality of burners whose outline shape of the burner end surface is as shown in FIG. While reciprocating in parallel with the longitudinal direction, SiO₂Glass particulates were deposited. Hydrogen gas was used as an additive gas for the glass raw material gas, and the glass raw material gas was supplied only to the first outlet 21. The gas supplied to the burner was changed as shown in Table 1 and FIG. 2 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0024]
[Table 1]

[0025]
(Example 2)
The burner end face has a rough shape as shown in FIG. 1, and an oxygen gas is used as the additive gas of the glass raw material gas in the same manner as in Example 1 except that SiO is formed on the outer periphery of the starting member.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 2 and FIG. 3 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0026]
[Table 2]

[0027]
(Example 3)
Example 1 except that a burner having a schematic shape of the burner end surface as shown in FIG. 11 was used, hydrogen gas was used as the additive gas of the glass raw material gas, and the glass raw material gas was supplied only to the first jet nozzle 1. In the same manner as described above, the outer peripheral portion of the starting member is made of SiO.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 3 and FIG. 4 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0028]
[Table 3]

[0029]
Example 4
A burner having a schematic shape of the end face of the burner as shown in FIG. 1 is used, and the glass raw material gas is supplied only to the second jet port 22 in the same manner as in the first embodiment.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 4 and FIG. 5 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0030]
[Table 4]

[0031]
(Example 5)
A burner whose end face has a schematic shape as shown in FIG. 1 is used, an oxygen gas is used as the additive gas of the glass raw material gas, and the glass raw material gas is supplied to the first jet port 21 and the second jet port 22. In the same manner as in Example 1, except that the outer peripheral portion of the starting member is made of SiO.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 5 and FIG. 6 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0032]
[Table 5]

[0033]
(Comparative Example 1)
The burner end face has a rough shape as shown in FIG. 1, and an oxygen gas is used as the additive gas of the glass raw material gas in the same manner as in Example 1 except that SiO is formed on the outer periphery of the starting member.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 6 and FIG. 7 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0034]
[Table 6]

[0035]
(Comparative Example 2)
Example 1 except that the burner end face has a schematic shape as shown in FIG. 11, oxygen gas is used as the additive gas for the glass raw material gas, and the glass raw material gas is supplied only to the first outlet 1. In the same manner as described above, the outer peripheral portion of the starting member is made of SiO.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 7 and FIG. 8 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0036]
[Table 7]

[0037]
(Comparative Example 3)
A burner whose end face has a schematic shape as shown in FIG. 1 is used, and an oxygen gas is used as an additive gas for the glass raw material gas in the same manner as in the first embodiment.₂Glass particulates were deposited. The gas supplied to the burner was changed as shown in Table 8 and FIG. 9 according to the change in the outer diameter of the optical fiber porous preform during the deposition of the glass fine particles.
[0038]
[Table 8]

[0039]
FIG. 10 shows the relationship between the outer diameter of the optical fiber porous preform during the glass particle deposition in Examples 1 to 5 and Comparative Examples 1 to 3 and the deposition efficiency of the glass particles.
From the results of FIG. 10, the glass source gas ejected from the first ejection port 11 or the second ejection port 12, or at least one ejection port of the first ejection port 1 or the second ejection port 2, and The flow rate of the mixed gas of the additive gas is set to be high at the initial stage of deposition of the glass fine particles and slow at the end stage, and the ratio of Rb and Rf is greatly changed in the initial stage and the end stage of the glass fine particle deposition. It was confirmed that the deposition efficiency of the glass fine particles could be improved if not done.
[0040]
【The invention's effect】
As described above, according to the method for manufacturing a porous preform for an optical fiber of the present invention, the glass raw material gas and the additive gas that are ejected from at least one of the two ejection ports adjacent to the burner. The flow rate of the mixed gas is set to be high at the initial stage of deposition of the glass fine particles and slow at the end stage, and the total flow rate of the glass source gas and the total flow rate of the additive gas at the initial stage and the final stage of the deposition of the glass fine particles. Therefore, oxygen gas that is not excessive or deficient in the reaction always exists around the glass raw material gas, and the flow rate ratio of the glass raw material gas to the oxygen gas is the same as during the deposition of the glass fine particles. It is always in an optimum state according to the change in the outer diameter of the optical fiber porous preform. Therefore, since the glass raw material gas is sufficiently reacted, the deposition efficiency of the glass fine particles is improved.
Further, according to the burner device for producing a porous preform for optical fiber of the present invention, the flow rate ratio of the glass raw material gas and the oxygen gas is changed according to the change in the outer diameter of the porous preform for optical fiber during the deposition of the glass particles. Since it can always be in an optimum state, the glass raw material gas sufficiently reacts and the deposition efficiency of the glass fine particles can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a burner provided in a burner device for producing a porous preform for an optical fiber according to the present invention.
FIG. 2 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during the deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Example 1. .
FIG. 3 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Example 2. .
4 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during the deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Example 3. FIG. .
5 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Example 4. FIG. .
6 is a graph showing the relationship between the outer diameter of a porous optical fiber preform during deposition of glass particles and the ratio of the total flow rate V1 of glass source gas and the total flow rate V2 of additive gas in Example 5. FIG. .
7 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Comparative Example 1. FIG. .
FIG. 8 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during the deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Comparative Example 2. .
9 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during the deposition of glass particles and the ratio of the total flow rate V1 of the glass raw material gas and the total flow rate V2 of the additive gas in Comparative Example 3. FIG. .
FIG. 10 is a graph showing the relationship between the outer diameter of the optical fiber porous preform during the deposition of glass particles and the deposition efficiency of the glass particles in Examples 1 to 5 and Comparative Examples 1 to 3.
FIG. 11 is a schematic configuration diagram showing an example of a burner used for manufacturing a porous preform for an optical fiber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Burner, 11 ... 1st nozzle, 12 ... 2nd nozzle, 13 ... 3rd nozzle, 14 ... 4th nozzle, 15 ... 5th nozzle , 16 ... sixth nozzle, 21 ... first jet, 22 ... second jet, 23 ... third jet, 24 ... fourth jet, 25... Fifth outlet, 26... Sixth outlet

Claims

Glass raw material gas and additive gas added thereto are introduced into a burner having a plurality of nozzles arranged in the same central axis, and the glass raw material gas is subjected to a flame hydrolysis reaction in an oxyhydrogen flame to produce glass. In a method for producing a porous optical fiber preform, which generates fine particles and deposits the glass fine particles on the outer periphery of the starting member to obtain a porous preform for optical fibers.
The burner has a nozzle for ejecting a mixed gas of the glass raw material gas and the additive gas at the center, a nozzle for ejecting the additive gas adjacent to the nozzle, and an oxyhydrogen flame in these outer layers. A nozzle for ejecting a gas for forming ;
During the deposition of the fine glass particles, the flow rate of the additive gas ejected from the two ejection ports in accordance with the change in the outer diameter of the starting member ,
The flow rate of the additive gas ejected from the central jet port is changed at least once so as to monotonously decrease, and the flow rate of the additive gas jetted from the jet port adjacent to the central jet port is monotonously changed. Change it more than once to increase it ,
Further, the flow rate of the glass raw material gas is set to V1 liter / min, the total flow rate of the additive gas ejected from the two adjacent outlets is set to V2 liter / minute, and V1 / V2 in the initial stage of the deposition of the glass particulates. Where Rb is Rb, and V1 / V2 at the end of the deposition of the glass fine particles is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. A manufacturing method of a base material.

Glass raw material gas and additive gas added thereto are introduced into a burner having a plurality of nozzles arranged in the same central axis, and the glass raw material gas is subjected to a flame hydrolysis reaction in an oxyhydrogen flame to produce glass. In a method for producing a porous optical fiber preform, which generates fine particles and deposits the glass fine particles on the outer periphery of the starting member to obtain a porous preform for optical fibers.
The burner has a nozzle for ejecting the additive gas at the center, a nozzle for ejecting the mixed gas of the glass raw material gas and the additive gas adjacent to the nozzle, and further, an oxyhydrogen flame is formed in these outer layers. A nozzle for ejecting a gas for forming;
During the deposition of the glass fine particles, the flow rate of the additive gas ejected from the two ejection ports in accordance with the outer diameter change of the starting member,
The flow rate of the additive gas ejected from the central jet port is changed one or more times so as to monotonously decrease the flow rate of the additive gas jetted from the jet port adjacent to the central jet port. Change it more than once to increase it,
In addition, the flow rate of the glass raw material gas is V1 liter / min, the total flow rate of the additive gas ejected from the two adjacent jet ports is V2 liter / min, and V1 / V2 in the initial stage of the deposition of the glass particulates. Where Rb is Rb, and V1 / V2 at the end of the deposition of the glass fine particles is Rf, the relationship between Rb and Rf is 0.25 ≦ Rb / Rf ≦ 4.0. A manufacturing method of a base material.

Glass raw material gas and additive gas added thereto are introduced into a burner having a plurality of nozzles arranged in the same central axis, and the glass raw material gas is subjected to a flame hydrolysis reaction in an oxyhydrogen flame to produce glass. In a method for producing a porous optical fiber preform, which generates fine particles and deposits the glass fine particles on the outer periphery of the starting member to obtain a porous preform for optical fibers.
The burner has a nozzle for ejecting a mixed gas of the glass raw material gas and the additive gas at the center, and has a nozzle for ejecting the glass raw material gas and the additive gas adjacent to the nozzle, and these outer layers A nozzle for ejecting gas for forming an oxyhydrogen flame,
During the deposition of the glass fine particles, the total flow rate of the glass raw material gas and the additive gas ejected from the two ejection ports in accordance with the outer diameter change of the starting member,
The total flow rate of the glass raw material gas and the additive gas ejected from the central ejection port is changed one or more times so as to monotonously decrease, and is ejected from the ejection port adjacent to the central ejection port. Change the total flow rate of the glass source gas and the additive gas at least once to increase monotonously,
And the flow rate of the said glass raw material gas shall be V1 liter / min, and said two adjacent jet nozzles When the total flow rate of the additive gas ejected from the nozzle is V2 liters / minute, V1 / V2 at the initial stage of the glass particulate deposition is Rb, and V1 / V2 at the end stage of the glass particulate deposition is Rf, Rb And Rf satisfying 0.25 ≦ Rb / Rf ≦ 4.0, a method for producing a porous preform for optical fibers.

In the manufacturing method of the porous preform for optical fibers according to any one of claims 1 to 3,
A method for producing a porous preform for an optical fiber, characterized in that the supply amount of the raw material gas during production is constant.

In the manufacturing method of the porous preform for optical fibers according to any one of claims 1 to 3 ,
A method for producing a porous optical fiber preform, wherein the additive gas is oxygen gas or hydrogen gas.