JP3966709B2 - Optical fiber preform manufacturing method - Google Patents

Optical fiber preform manufacturing method Download PDF

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JP3966709B2
JP3966709B2 JP2001328380A JP2001328380A JP3966709B2 JP 3966709 B2 JP3966709 B2 JP 3966709B2 JP 2001328380 A JP2001328380 A JP 2001328380A JP 2001328380 A JP2001328380 A JP 2001328380A JP 3966709 B2 JP3966709 B2 JP 3966709B2
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core tube
base material
furnace core
helium
optical fiber
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JP2003137583A (en
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裕之 和田
恭宏 仲
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THE FURUKAW ELECTRIC CO., LTD.
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P40/00—Technologies relating to the processing of minerals
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Description

【０００１】
【発明の属する技術分野】
本発明は、光ファイバ母材の製造方法に係り、特に多孔質母材を脱水透明ガラス化する工程のシーケンスに関するものである。
【０００２】
【従来の技術】
品質の良好な光ファイバを得るために、高品質な光ファイバ母材を製造する方法として、ＶＡＤ法やＯＶＤ法が一般に採用されている。このようなＶＡＤ法やＯＶＤ法により形成された光ファイバ用多孔質母材を脱水透明ガラス化するため、脱水ガス及びＨｅガスを下部の流入口から炉芯管に供給しながら管内を所定の圧力に調整している。そして、支持棒の先端に取り付けられた多孔質母材を一定速度で引き下げ、炉芯管の外周部に設置されているヒータによって加熱された高温雰囲気中で脱水及び透明ガラス化している。
【０００３】
特開平８−２２５３３８号公報では、多孔質母材を炉芯管内に挿入し、炉芯管の下部のガス導入口よりＨｅガスと塩素系ガスとを供給し、上部のガス排出口より排気しつつ炉内を脱水ガスで充満し、１１００℃に保たれた加熱部に多孔質母材を下端より順次送り込み脱水し、次いで、加熱部の温度を１５００℃に上げ、再度多孔質母材を下端より順次送り込むことにより透明ガラス化することが提案されている。また、特開平３−２６５５３３号公報には、多孔質母材を脱水処理後炉芯管内を真空にし、その後Ｈｅガスを充填し、高温に保持し透明ガラス化する技術が示されている。
また、近年、光ファイバの需要が拡大するのに対応して、光ファイバの生産量の増大、それに伴う価格の低減が強く求められており、そのために光ファイバ母材の大型化が図られている。
【０００４】
【発明が解決しようとする課題】
ところで、大型母材の処理用に炉芯管の容量が大きくなると、多孔質母材を炉芯管へ挿入した後、炉芯管内がヘリウムで完全に置換されるまでに、かなりの時間を要している。大型母材用の炉芯管は一例として、全長５ｍ、直径３００ｍｍ以上のものでは、例えば、へリウム２０ＳＬＭで操業する場合、炉芯管内が完全にヘリウムで置換されるまでに８０分以上が必要であり、ヘリウムガス１０ＳＬＭで操業する場合には、１２０分以上も要している。さらに、ガラス化待機中及び終了時にも炉芯管内にへリウムを流していたので、ヘリウム使用量の増大を招いている。
本発明は、このような現状に鑑み、脱水ガラス化処理の時間を短縮すると共にヘリウムの使用量を低減することを目的した、光ファイバ母材の製造方法を提供しようとするものである。
【０００５】
【課題を解決するための手段】
すなわち、本発明は、
（１）光ファイバ多孔質母材をへリウム含有ガス雰囲気下で脱水ガラス化する光ファイバ母材の製造方法であって、脱水ガラス化処理待機中は、炉芯管内にへリウム含有ガスを供給せずに窒素ガスを供給し、多孔質母材を炉芯管内に挿入後ヘリウム含有ガスを供給し、炉芯管内がへリウム含有ガスに完全に置換される時間を待たずに脱水処理位置への多孔質母材の引き下げを開始し、多孔質母材を脱水処理、ガラス化処理し、ガラス化処理終了後には、炉芯管内温度を降温しながら炉芯管内のヘリウム含有ガスを窒素ガスに置換することを特徴とする光ファイバ母材の製造方法、
（２）前記脱水ガラス化処理の脱水処理は１１００℃以上で、ガラス化処理は１５００℃〜１６５０℃で行うことを特徴とする（１）に記載の光ファイバ母材の製造方法、及び
（３）前記光ファイバ多孔質母材は、直径１００ｍｍ以上、長さ１２００ｍｍ以上であることを特徴とする（１）又は（２）に記載の光ファイバ母材の製造方法、
を提供するものである。
【０００６】
【発明の実施の形態】
本発明の光ファイバ母材の製造方法の好ましい実施の態様について、図１〜３を参照しながら詳細に説明をする。
図１は、本発明方法の脱水ガラス化に使用するに好ましい装置の一例を概略的に示すものである。図２は、操業中の多孔質母材の位置関係を示すものであり、図３は、脱水開始から最高温度点を通過する母材のスート部分を説明するものである。
この脱水ガラス化装置は、炉芯管４、これを囲むカーボンヒータ７、カーボンヒータ７を覆う炉体６、炉芯管のヘリウム含有ガス流入口５、炉芯管の開閉用の蓋９、排気フード１０、窒素流入口１１、及び炉芯管のガス流出口８と排気フードの排気口１２等を有する。これに、多孔質母材３を保持するターゲットホルダ２が先端に設けられた回転自在、上下動可能な支持棒１があり、圧力調整弁１３、差圧伝送器１４、コントローラ１５が付設されている。
【０００７】
本発明の処理対象とする多孔質母材は、ＶＡＤ法、ＯＶＤ法等により得られた大型のもので、外径が１００ｍｍ以上、好ましくは１００ｍｍ〜１５０ｍｍ程度、長さが１２００ｍｍ以上、好ましくは１５００ｍｍ〜２０００ｍｍ程度のものである。
次に、光ファイバ多孔質母材の脱水ガラス化処理工程のシーケンスについて以下に説明する。尚、本明細書では説明を明瞭にするために、脱水処理工程及びガラス化処理工程を区分して記載するが、脱水処理工程では主に脱水が行われ、ガラス化処理工程では主にガラス化が行われることを意味し、前者でガラス化が、後者で脱水が行われないものではない。
支持棒１の先端に設置されたターゲットホルダ２に多孔質母材３を取り付け、炉芯管４の外部で待機させる。この待機時、炉芯管４内は１１００℃〜１１５０℃程度の所定温度に保ち、ヘリウム、塩素ガスは供給せず、パージ用に窒素（１０〜２０ＳＬＭに設定）を窒素流入口１１から供給し、流出口８から一部流出させる。窒素を供給しながら、炉芯管４の蓋９を開け、図２に示すように多孔質母材３を炉芯管４内に挿入し、ヒータ７の最高温度位置（点Ｍ）よりも１２０〜１６０ｍｍ程度上方の脱水ガラス化処理開始位置（点Ｓ）で母材３を止める。この間、炉芯管内の圧力（Ｐ１）と炉体内の圧力（Ｐ２）との差圧の制御は行わない。
【０００８】
蓋９を閉めた後、次の三工程を同時に開始する。
１．図１に示すように、炉芯管４内のガスの置換を開始する。すなわち、窒素ガスの供給を止め、ヘリウム（１０〜３０ＳＬＭに設定)、塩素ガス（０．１５〜０．４５ＳＬＭに設定）の流入口５からの供給を始める。置換完了まで約６０〜１２０分を要する。
２．炉芯管圧（Ｐ１）と炉体圧（Ｐ２）との差圧（Ｐ）を求め、差圧伝送器１４からコントローラ１５の制御信号による圧力調整弁１３の調節によって制御を開始する。差圧制御が安定するまでの所要時間は、次の脱水処理温度へ到達するまでの時間とほぼ同じであり、約２０分を要する。
尚、差圧を制御するのは高温に保持される炉芯管が変形するのを防ぎ、脱水、ガラス化が安定して行われるためである。
３．カーボンヒータ７を更に高温に設定し、多孔質母材３の所定脱水処理温度の１１００℃〜１３５０℃まで炉芯管４内の昇温を開始する。目標の温度到達までに約２０分を要する。
【０００９】
所定の脱水処理温度まで昇温し、差圧が安定した後、多孔質母材３を回転させながら一定速度（速度標準３００ｍｍ／時〜４００ｍｍ／時）で引き下げながら母材全体を加熱し、脱水処理を行う。所定のストローク（点Ｓから引き下げ最下位置まで）引き下げ後、脱水処理された母材を炉の上部開始位置（点Ｓ）まで引上げ、そこで母材を止め保持しておく（図２参照）。
続いて、ヘリウムだけを供給し続け、塩素ガスは供給を止め、カーボンヒータ７の加熱温度を高くして昇温を開始し、ガラス化処理に必要な１５００℃〜１６５０℃まで加熱する。所定のガラス化処理温度に達したら、母材を回転させながら所定のストロークまで引き下げながらガラス化処理を行う。次いで、母材を炉の上部（点Ｓ）まで引き上げて止める。
【００１０】
次いで、ヘリウムの供給を止め、カーボンヒータ７の加熱を弱めて炉芯管４内の温度を降下させると同時に窒素ガスを供給し、ヘリウム及び塩素ガスは流出口８から排出してガスの置換を行う。排出した塩素ガスは排ガス処理に付す。塩素ガスがパージされるまで所定時間（約１０分〜２０分）待ち、その後蓋９を開け、脱水ガラス化された母材を炉芯管４の外へ引き上げ、取り出す。塩素ガスがパージされる間に炉芯管４内の温度は、１１００℃〜１２００℃の待機温度となっている。続いて、ターゲットホルダ２から取り外し、次の被処理用の多孔質母材と取り替える。
炉芯管４内の温度が待機温度になったら、再度上記の工程を繰り返す。
窒素ガスの存在下で母材の出し入れを行うので、外気が炉芯管４内に流入するのを防ぐことができ、炉芯管の劣化を防止することもできる。
【００１１】
上記したように本発明では、パージ用に供給した窒素ガスが完全に置換される時間を待たずに、差圧の制御が安定し、脱水処理温度に達した時点で、脱水処理に付す多孔質母材の引き下げを開始し、脱水処理工程を遂行する。
本発明では、「炉芯管内がヘリウム含有ガスに完全に置換される時間を待たずに」とは、「炉芯管内のガス置換工程で、差圧の制御が安定し且つ所定の脱水処理温度になるまで」をいう。
したがって、脱水処理工程の開始を従来のように炉芯管内のガスの完全に置換される約８０分〜１２０分後にするものに比べ、本発明の差圧の制御が安定し、脱水処理温度に達する約２０分後のものは、その時間の短縮は６０分以上である。そして、同時にその間へリウムを使用しないことになるので、ヘリウムの使用量が少なくて済むことになる。
また、この短縮時間の間に多孔質母材が炉芯管の最高温度点Ｍを通過する部分は、多孔質母材のうちのほぼ光ファイバとして不良部分であるので、高純度のへリウム雰囲気である必要は特にない（図２、３参照）。
そして、脱水ガラス化処理の待機中及び終了後に炉芯管内にへリウムガスを供給せずに廉価な窒素ガスを流すので、ヘリウムの使用量を削減でき、コスト低減につながる。
【００１２】
【実施例】
次いで、実施例を示して本発明をさらに詳細に説明するが、本発明はこれに限定されるものではない。
ＶＡＤ法によって作製した外径１２５ｍｍ、長さ２０００ｍｍの多孔質母材を図１に示す炉芯管内で次に示す工程で脱水ガラス化した。
(１)ターゲットホルダ２に取り付けた多孔質母材３を炉芯管４の外で待機させている時、炉芯管４内の温度は１２００℃に保ち、ヘリウム、塩素ガスは供給せず、パージ用に窒素（１５ＳＬＭ）を供給した。
(２)蓋９を開け、上記した多孔質母材３を炉芯管４内に挿入し、カーボンヒータ７の最高温度点Ｍよりも１５０ｍｍ程度上方の開始位置（点Ｓ）で母材を止めた。この時、炉芯管圧Ｐ１と炉体圧Ｐ２との差圧制御は行わなかった。
(３)蓋９を閉めた後、次の(４)、(５)、(６)の工程を同時に開始した。
(４)炉芯管内の窒素ガスの置換を開始した。すなわち、ヘリウム（設定２０ＳＬＭ）及び塩素ガス（設定０．３０ＳＬＭ）の供給を行った。全ガス置換完了まで８０分を要した。
(５)炉芯管差圧制御を開始した。差圧の制御が安定するまで約２０分を要した。
(６)カーボンヒータ７の加熱温度を上げ、脱水温度までの昇温を開始し、目標温度（約１３００℃）の到達まで約２０分要した。
【００１３】
(７)昇温完了及び差圧変動幅が１００Ｐａ以内に安定した後、多孔質母材３の引き下げ（速度標準３５０ｍｍ／時）を開始し、炉内温度を１３００℃でほぼ一定圧に保ち、所定ストローク（ほぼ、母材の長さ）回転させながら引き下げた。
(８)所定ストローク引き下げ後、母材３を炉の上部の点Ｓまで引き上げ、母材３を止めた。
(９)塩素ガスの供給は止め、ガス量は同一に保って、カーボンヒータ７の加熱で昇温を開始し（昇温速度３０℃／分）、ガラス化温度（約１６５０℃）に加熱した。
(10)Ｍ点の温度がガラス化処理温度になれば、母材を所定ストローク引き下げ（速度標準１８０ｍｍ／時）ながら母材３のガラス化処理を行った。その後、処理の終わった母材を炉の上部Ｓ点まで引き上げて止めた。
(11)ヘリウムの供給を止め、加熱を弱め炉芯管４内の温度を下げると共に窒素の供給を開始し、ガスの置換を行った。
(12)塩素ガスがパージされるまで約１５分間待ち、（その間に炉芯管内温度は１２００℃程度まで下がる）その後蓋を開け、母材を炉の外へ引き上げた。
(13)処理済みの母材をターゲットホルダ２から取り外し、次の被処理用の多孔質母材と取り替えた。
【００１４】
上記したように、(４)のガスが完全に置換される時間を待たずに、脱水工程の多孔質母材引き下げを開始した。すなわち、(５)、(６)が安定した所（約２０分）で、(７)の母材の引き下げを始めたので、これにより、短縮時間は

Figure 0003966709
となり、脱水ガラス化の工程時間がこの分短縮された。と同時にへリウムガス使用量の低減につながった。
また、この６０分は引き下げ距離に換算すると６０／６０×３５０ｍｍ／時＝３５０ｍｍに相当し、この間に最高温度点Ｍを通過する多孔質母材の部分は３５０ｍｍ−１５０ｍｍ＝２００ｍｍである。この大型多孔質母材の先端から２００ｍｍ程度は、光ファイバとして良品部分ではないので、高純度のへリウム、塩素ガス雰囲気である必要はない（図２、図３参照）。
さらに、(１)及び(11)、(12)のように脱水ガラス化待機中、終了時に炉芯管内にへリウムガス２０ＳＬＭを流さずに窒素ガスを流すので、ヘリウム使用量を削減できた。
【００１５】
【発明の効果】
以上説明したように本発明では、パージ用に流した窒素ガスが完全に置換されるまで待たずに、差圧の制御が安定し、脱水処理温度に達した時点で、脱水処理の多孔質母材の引き下げを開始し、脱水処理工程を行うものであるので、処理時間を大幅に短縮できる。そして、同時にその間のへリウムの使用量が削減できる。
そして、脱水ガラス化処理の待機中及び終了時に炉芯管内にへリウムを供給せずに廉価な窒素ガスを供給するので、同様にヘリウムの使用量を削減でき、工程全体でコスト低減につながる。
【図面の簡単な説明】
【図１】本発明方法に使用するのに好ましい脱水ガラス化装置の概略図である。
【図２】操業中の多孔質母材の位置関係を示す説明図である。
【図３】最高温度点を通過する母材のスート部分の説明図である。
【符号の説明】
１ 支持棒
２ ターゲットホルダ
３ 多孔質母材
４ 炉芯管
５ ヘリウム含有ガス流入口
６ 炉体
７ ヒータ
８ ガス流出口
９ 蓋
１１ 窒素流入口
Ｓ 開始位置
Ｍ 最高温度点[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a sequence of steps for forming a porous preform into dehydrated transparent glass.
[0002]
[Prior art]
In order to obtain a high-quality optical fiber, a VAD method or an OVD method is generally employed as a method for manufacturing a high-quality optical fiber preform. In order to convert the porous optical fiber preform formed by the VAD method or the OVD method into a dehydrated transparent glass, a predetermined pressure is applied to the inside of the tube while supplying dehydrated gas and He gas from the lower inlet to the furnace core tube. It is adjusted to. And the porous preform | base_material attached to the front-end | tip of a support rod is pulled down at a fixed speed, and it spin-dry | dehydrates and transparentizes in the high temperature atmosphere heated by the heater installed in the outer peripheral part of the furnace core pipe.
[0003]
In JP-A-8-225338, a porous base material is inserted into a furnace core tube, He gas and chlorine-based gas are supplied from a gas inlet at the bottom of the furnace core tube, and exhausted from an upper gas outlet. While the furnace was filled with dehydrated gas, the porous base material was sequentially fed from the lower end to the heated part maintained at 1100 ° C. and dehydrated. Then, the temperature of the heated part was raised to 1500 ° C., and the porous base material was again moved to the lower end. It has been proposed that the glass is made into a transparent glass by feeding more sequentially. Japanese Patent Application Laid-Open No. 3-265533 discloses a technique in which a porous base material is dehydrated, the inside of the furnace core tube is evacuated, then filled with He gas, kept at a high temperature, and made into a transparent glass.
In recent years, in response to the growing demand for optical fibers, there has been a strong demand for an increase in optical fiber production and a corresponding reduction in price, which has led to an increase in the size of the optical fiber preform. Yes.
[0004]
[Problems to be solved by the invention]
By the way, when the capacity of the furnace core tube is increased for processing a large base material, it takes a considerable time until the inside of the furnace core tube is completely replaced with helium after the porous base material is inserted into the furnace core tube. is doing. For example, if the furnace core tube for large base metal has a total length of 5 m and a diameter of 300 mm or more, when operating with helium 20 SLM, it takes 80 minutes or more to completely replace the furnace core tube with helium. In the case of operating with 10 SLM of helium gas, it takes 120 minutes or more. Furthermore, since helium was allowed to flow into the furnace core tube during and after vitrification, the amount of helium used was increased.
In view of such a current situation, the present invention intends to provide an optical fiber preform manufacturing method that aims to shorten the time for dehydration vitrification and to reduce the amount of helium used.
[0005]
[Means for Solving the Problems]
That is, the present invention
(1) A method of manufacturing an optical fiber preform in which an optical fiber porous preform is dehydrated and vitrified in a helium-containing gas atmosphere, and the helium-containing gas is supplied into the furnace core tube during the dehydration vitrification process. Without supplying the nitrogen gas, and after inserting the porous base material into the furnace core tube, the helium containing gas is supplied, and the reactor core tube is completely replaced with the helium containing gas to the dehydration position. The porous base material is started to be lowered, and the porous base material is dehydrated and vitrified.After the vitrification process is completed, the helium-containing gas in the furnace core tube is changed to nitrogen gas while the temperature in the furnace core tube is lowered. A method of manufacturing an optical fiber preform, wherein
(2) The method for producing an optical fiber preform according to (1), wherein the dehydration treatment of the dehydration vitrification treatment is performed at 1100 ° C. or more, and the vitrification treatment is performed at 1500 ° C. to 1650 ° C. The method for producing an optical fiber preform according to (1) or (2), wherein the optical fiber porous preform has a diameter of 100 mm or more and a length of 1200 mm or more,
Is to provide.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the method for producing an optical fiber preform of the present invention will be described in detail with reference to FIGS.
FIG. 1 schematically shows an example of an apparatus preferable for use in dehydration vitrification of the method of the present invention. FIG. 2 shows the positional relationship of the porous base material during operation, and FIG. 3 explains the soot portion of the base material that passes through the maximum temperature point from the start of dehydration.
The dehydration vitrification apparatus includes a furnace core tube 4, a carbon heater 7 surrounding the furnace tube, a furnace body 6 covering the carbon heater 7, a helium-containing gas inlet 5 of the furnace core tube, a lid 9 for opening and closing the furnace core tube, and an exhaust. It has a hood 10, a nitrogen inlet 11, a gas outlet 8 of the furnace core tube, an exhaust outlet 12 of the exhaust hood, and the like. In this, there is a support rod 1 which can be rotated and moved up and down with a target holder 2 for holding the porous base material 3 at its tip, and a pressure regulating valve 13, a differential pressure transmitter 14 and a controller 15 are attached. Yes.
[0007]
The porous base material to be treated in the present invention is a large material obtained by the VAD method, OVD method or the like, and has an outer diameter of 100 mm or more, preferably about 100 mm to 150 mm, and a length of 1200 mm or more, preferably 1500 mm. ˜2000 mm.
Next, the sequence of the dehydration vitrification process of the optical fiber porous preform will be described below. In this specification, for the sake of clarity, the dehydration process and the vitrification process are described separately. However, dehydration is mainly performed in the dehydration process, and vitrification is mainly performed in the vitrification process. Means that the former is vitrified and the latter is not dehydrated.
The porous base material 3 is attached to the target holder 2 installed at the tip of the support rod 1 and is kept waiting outside the furnace core tube 4. During this standby, the furnace core tube 4 is kept at a predetermined temperature of about 1100 ° C. to 1150 ° C., helium and chlorine gas are not supplied, and nitrogen (set to 10 to 20 SLM) is supplied from the nitrogen inlet 11 for purging. , Partly flows out from the outlet 8. While supplying nitrogen, the lid 9 of the furnace core tube 4 is opened, and the porous base material 3 is inserted into the furnace core tube 4 as shown in FIG. 2, and 120 ° higher than the maximum temperature position (point M) of the heater 7. The base material 3 is stopped at a dehydration vitrification processing start position (point S) about 160 mm above. During this time, the pressure difference between the pressure in the furnace core tube (P 1 ) and the pressure in the furnace body (P 2 ) is not controlled.
[0008]
After closing the lid 9, the following three steps are started simultaneously.
1. As shown in FIG. 1, replacement of the gas in the furnace core tube 4 is started. That is, supply of nitrogen gas is stopped, and supply of helium (set to 10 to 30 SLM) and chlorine gas (set to 0.15 to 0.45 SLM) from the inlet 5 is started. It takes about 60 to 120 minutes to complete the replacement.
2. A differential pressure (P) between the furnace core tube pressure (P 1 ) and the furnace body pressure (P 2 ) is obtained, and control is started by adjusting the pressure regulating valve 13 from the differential pressure transmitter 14 using a control signal from the controller 15. The time required until the differential pressure control is stabilized is substantially the same as the time required to reach the next dehydration temperature, and takes about 20 minutes.
The reason for controlling the differential pressure is to prevent the furnace core tube held at a high temperature from being deformed and to stably perform dehydration and vitrification.
3. The carbon heater 7 is set to a higher temperature, and the temperature inside the furnace core tube 4 is started up to a predetermined dehydration processing temperature of the porous base material 3 of 1100 ° C. to 1350 ° C. It takes about 20 minutes to reach the target temperature.
[0009]
After the temperature is raised to a predetermined dehydration temperature and the differential pressure is stabilized, the whole base material is heated while being pulled down at a constant speed (standard speed 300 mm / hour to 400 mm / hour) while rotating the porous base material 3 to dehydrate it. Process. After lowering a predetermined stroke (from point S to the lowest lowered position), the dehydrated base material is pulled up to the upper start position (point S) of the furnace, where the base material is stopped and held (see FIG. 2).
Subsequently, the supply of only helium is continued, the supply of chlorine gas is stopped, the heating temperature of the carbon heater 7 is increased, and the temperature rise is started to heat to 1500 ° C. to 1650 ° C. necessary for vitrification treatment. When the predetermined vitrification temperature is reached, the vitrification is performed while rotating the base material to a predetermined stroke. The base material is then pulled up to the top of the furnace (point S) and stopped.
[0010]
Next, the supply of helium is stopped, the heating of the carbon heater 7 is weakened to lower the temperature in the furnace core tube 4, and simultaneously nitrogen gas is supplied. Helium and chlorine gas are discharged from the outlet 8 to replace the gas. Do. The discharged chlorine gas is subjected to exhaust gas treatment. It waits for a predetermined time (about 10 to 20 minutes) until the chlorine gas is purged, and then the lid 9 is opened, and the dehydrated glass base material is pulled out of the furnace core tube 4 and taken out. While the chlorine gas is purged, the temperature inside the furnace core tube 4 is a standby temperature of 1100 ° C to 1200 ° C. Subsequently, it is removed from the target holder 2 and replaced with the next porous base material for processing.
When the temperature in the furnace core tube 4 reaches the standby temperature, the above steps are repeated again.
Since the base material is taken in and out in the presence of nitrogen gas, it is possible to prevent outside air from flowing into the furnace core tube 4 and to prevent deterioration of the furnace core tube.
[0011]
As described above, in the present invention, without waiting for the time for the nitrogen gas supplied for purging to be completely replaced, the control of the differential pressure is stabilized, and when the dehydration temperature is reached, the porous material that is subjected to the dehydration process Start to lower the base material and perform the dehydration process.
In the present invention, “without waiting for the time during which the furnace core tube is completely replaced with the helium-containing gas” means “in the gas replacement step in the furnace core tube, the differential pressure control is stable and the predetermined dehydration temperature is set. "Until."
Therefore, the control of the differential pressure of the present invention is more stable and the dehydration temperature is higher than in the case where the start of the dehydration process is about 80 to 120 minutes after the gas in the furnace core tube is completely replaced as in the conventional case. About 20 minutes after reaching, the time reduction is 60 minutes or more. At the same time, helium is not used, so the amount of helium used is small.
Further, the portion where the porous preform passes through the maximum temperature point M of the furnace core tube during this shortening time is a defective portion of the porous preform as an almost optical fiber. There is no particular requirement (see FIGS. 2 and 3).
In addition, since inexpensive nitrogen gas is allowed to flow into the furnace tube without supplying helium gas during and after waiting for dehydration vitrification, the amount of helium used can be reduced, leading to cost reduction.
[0012]
【Example】
Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
A porous base material having an outer diameter of 125 mm and a length of 2000 mm produced by the VAD method was dehydrated and vitrified in the furnace core tube shown in FIG.
(1) When the porous base material 3 attached to the target holder 2 is waiting outside the furnace core tube 4, the temperature inside the furnace core tube 4 is kept at 1200 ° C., and helium and chlorine gas are not supplied. Nitrogen (15 SLM) was supplied for purging.
(2) Open the lid 9, insert the porous base material 3 into the furnace core tube 4, and stop the base material at the start position (point S) about 150 mm above the maximum temperature point M of the carbon heater 7. It was. At this time, the differential pressure control between Roshinkan圧P 1 and furnace pressure P 2 was not performed.
(3) After the lid 9 was closed, the following steps (4), (5) and (6) were started simultaneously.
(4) Replacement of nitrogen gas in the furnace core tube was started. That is, helium (setting 20 SLM) and chlorine gas (setting 0.30 SLM) were supplied. It took 80 minutes to complete the gas replacement.
(5) Furnace core pipe differential pressure control was started. It took about 20 minutes for the differential pressure control to stabilize.
(6) The heating temperature of the carbon heater 7 was raised, the temperature was raised to the dehydration temperature, and it took about 20 minutes to reach the target temperature (about 1300 ° C.).
[0013]
(7) After completion of the temperature rise and the differential pressure fluctuation range is stabilized within 100 Pa, the lowering of the porous base material 3 (speed standard 350 mm / hour) is started, and the furnace temperature is kept at a substantially constant pressure at 1300 ° C. It was pulled down while rotating a predetermined stroke (approximately the length of the base material).
(8) After lowering the predetermined stroke, the base material 3 was pulled up to a point S at the top of the furnace, and the base material 3 was stopped.
(9) The supply of chlorine gas is stopped, the gas amount is kept the same, and the temperature rise is started by heating the carbon heater 7 (temperature rise rate 30 ° C./min) and heated to the vitrification temperature (about 1650 ° C.). .
(10) When the temperature at point M reached the vitrification temperature, the base material 3 was vitrified while lowering the base material by a predetermined stroke (speed standard 180 mm / hour). Thereafter, the treated base material was pulled up to the upper S point of the furnace and stopped.
(11) The supply of helium was stopped, the heating was weakened, the temperature in the furnace core tube 4 was lowered, and the supply of nitrogen was started to replace the gas.
(12) Wait for about 15 minutes until chlorine gas is purged (while the temperature in the furnace core tube drops to about 1200 ° C.), then open the lid and lift the base material out of the furnace.
(13) The treated base material was removed from the target holder 2 and replaced with the next porous base material for processing.
[0014]
As described above, the porous base material lowering in the dehydration process was started without waiting for the time for the gas of (4) to be completely replaced. In other words, when (5) and (6) were stable (about 20 minutes), the base material of (7) was started to be lowered.
Figure 0003966709
Accordingly, the process time for dehydration vitrification was shortened by this amount. At the same time, helium gas consumption was reduced.
The 60 minutes corresponds to 60/60 × 350 mm / hour = 350 mm in terms of the pull-down distance, and the portion of the porous base material that passes through the maximum temperature point M during this period is 350 mm−150 mm = 200 mm. About 200 mm from the tip of the large porous preform is not a non-defective part as an optical fiber, so it is not necessary to have a high purity helium or chlorine gas atmosphere (see FIGS. 2 and 3).
Furthermore, as shown in (1), (11), and (12), during dehydration vitrification standby, nitrogen gas was allowed to flow into the furnace core tube without flowing the helium gas 20SLM at the end, so that the amount of helium used could be reduced.
[0015]
【The invention's effect】
As described above, the present invention does not wait until the purged nitrogen gas is completely replaced, and when the control of the differential pressure is stabilized and the dehydration temperature is reached, the porous mother for the dehydration process is reached. Since the material starts to be pulled down and the dehydration process is performed, the processing time can be greatly shortened. At the same time, the amount of helium used can be reduced.
Further, since inexpensive nitrogen gas is supplied without supplying helium into the furnace tube during and after the dehydration vitrification process, the amount of helium used can be similarly reduced, leading to cost reduction in the entire process.
[Brief description of the drawings]
FIG. 1 is a schematic view of a preferred dehydrating vitrification apparatus for use in the method of the present invention.
FIG. 2 is an explanatory diagram showing a positional relationship of a porous base material during operation.
FIG. 3 is an explanatory diagram of a soot portion of a base material that passes through a maximum temperature point.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support rod 2 Target holder 3 Porous base material 4 Core tube 5 Helium containing gas inlet 6 Furnace body 7 Heater 8 Gas outlet 9 Lid 11 Nitrogen inlet S Start position M Maximum temperature point

Claims (3)

光ファイバ多孔質母材をへリウム含有ガス雰囲気下で脱水ガラス化する光ファイバ母材の製造方法であって、脱水ガラス化処理待機中は、炉芯管内にへリウム含有ガスを供給せずに窒素ガスを供給し、多孔質母材を炉芯管内に挿入後ヘリウム含有ガスを供給し、炉芯管内がへリウム含有ガスに完全に置換される時間を待たずに脱水処理位置への多孔質母材の引き下げを開始し、多孔質母材を脱水処理、ガラス化処理し、ガラス化処理終了後には、炉芯管内温度を降温しながら炉芯管内のヘリウム含有ガスを窒素ガスに置換することを特徴とする光ファイバ母材の製造方法。A method of manufacturing an optical fiber preform in which an optical fiber porous preform is dehydrated and vitrified in a helium-containing gas atmosphere, and the helium-containing gas is not supplied into the furnace core tube during the dehydration vitrification process. Supply nitrogen gas, insert a porous base material into the furnace core tube, then supply helium-containing gas, and wait for the time to completely replace the inside of the furnace core tube with helium-containing gas. Starting to lower the base material, dehydrating and vitrifying the porous base material, and after completion of the vitrification process, replacing the helium-containing gas in the furnace core tube with nitrogen gas while lowering the temperature in the furnace core tube An optical fiber preform manufacturing method characterized by the above. 前記脱水ガラス化処理の脱水処理は１１００℃以上で、ガラス化処理は１５００℃〜１６５０℃で行うことを特徴とする請求項１に記載の光ファイバ母材の製造方法。2. The method for producing an optical fiber preform according to claim 1, wherein the dehydration treatment in the dehydration vitrification treatment is performed at 1100 ° C. or more, and the vitrification treatment is performed at 1500 ° C. to 1650 ° C. 前記光ファイバ多孔質母材は、直径１００ｍｍ以上、長さ１２００ｍｍ以上であることを特徴とする請求項１又は請求項２に記載の光ファイバ母材の製造方法。The method for producing an optical fiber preform according to claim 1 or 2, wherein the optical fiber porous preform has a diameter of 100 mm or more and a length of 1200 mm or more.
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