JP3917022B2 - Method for producing porous preform for optical fiber - Google Patents

Method for producing porous preform for optical fiber Download PDF

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JP3917022B2
JP3917022B2 JP2002189082A JP2002189082A JP3917022B2 JP 3917022 B2 JP3917022 B2 JP 3917022B2 JP 2002189082 A JP2002189082 A JP 2002189082A JP 2002189082 A JP2002189082 A JP 2002189082A JP 3917022 B2 JP3917022 B2 JP 3917022B2
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burner
deposition
distance
optical fiber
tube
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JP2004026610A (en
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浩史 町田
忠克 島田
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Shin Etsu Chemical Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/01413—Reactant delivery systems
    • C03B37/0142—Reactant deposition burners
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2207/00—Glass deposition burners
    • C03B2207/50—Multiple burner arrangements
    • C03B2207/52—Linear array of like burners
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2207/00—Glass deposition burners
    • C03B2207/60—Relationship between burner and deposit, e.g. position
    • C03B2207/66—Relative motion
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2207/00—Glass deposition burners
    • C03B2207/70—Control measures

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Geochemistry & Mineralogy (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、外付け法(OVD法)によりコア用ガラス棒にガラス微粒子を堆積させて形成する光ファイバ用多孔質母材、特には、堆積表面に発生する凹凸の小さい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】
光ファイバ用プリフォームの製造方法としては、コアを有するガラス棒の周囲に、酸水素火炎中にガラス原料を供給して生じたガラス微粒子を付着・堆積させ、得られた多孔質母材を高温下にて、脱水・透明ガラス化処理を行う方法が知られている。これには、一般に外付け法(OVD法)と呼ばれ、水平にセットされたガラス棒に対して直角にガラス微粒子発生用バーナを配置し、このバーナをガラス棒に沿って平行に往復移動させ、ガラス微粒子をガラス棒に付着・堆積させ、所望の多孔質母材を製造する方法が主に用いられている。
【０００３】
近年、プリフォームのサイズの大型化に伴い、多孔質母材に対しても大型化および生産性を上げる要求が高まってきており、実際に幾つかの方法が提案されている。この生産性向上の一例として、光ファイバ用母材を製造するものではないが、複数のバーナに供給されるガス量を調整したり、バーナの先端面とガラス微粒子の堆積面との距離を調整して、あるいは耐熱性基体の回転数を調整して、ガラス微粒子の堆積密度を半径方向に沿って変化させ多孔質母材のひび割れを防止する方法(特開昭64-9821号公報参照)等が提案されている。
【０００４】
しかし、特開昭64-9821号公報に開示されている方法は、堆積速度が速く、大型の多孔質母材を製造できるという利点があるものの、バーナを芯材の長手方向に沿って一定の振幅で往復移動させるため、バーナの往復移動の開始位置（停止折返し点）と移動領域が常に同一位置で繰り返される結果、堆積ムラが生じ、堆積体の表面に凹凸を生じる。また、この方法は、芯材のアルミニウムが金属不純物としてシリカ層にドープされるという欠点があり、光ファイバ用母材の製造には利用できない。
【０００５】
複数のバーナを用いて大型の光ファイバプリフォームを高速で生産する方法として、同一設計の複数のバーナーを等間隔に配置し、バーナーの往復移動の開始位置を順次移動分散させる方法(特許第2612949号公報参照)が提案されている。この方法は、堆積速度を飛躍的に増やすことができる。
そこで、バーナ先端と堆積表面との距離を最も付着率が良くなる位置に設定し、上記の方法で、実際に直径300 mmφの大型多孔質母材の製造を行った結果、以下の問題が生じることが判明した。
【０００６】
すなわち、堆積当初より直径がほぼ200 mmφに達するまでは、堆積表面にピッチの非常に細かい凹凸が観察されたが、まだ問題のないレベルであった。しかし、直径が200 mmφを超え、さらに大型の多孔質母材を製造しようとすると、その非常に細かいピッチの凹凸が無視できないレベルまで大きくなり始め、堆積終了時には、山の部分が鋭角で凹部の深さが10 mmもあるような凹凸が多孔質母材の表面に生じた。表面にこの様な凹凸のある多孔質母材の脱水・透明ガラス化処理を行うと、処理後も表面に凹凸が残留し、最終的に光ファイバとしたとき、コアとクラッド比率の不安定の要因となる。
【０００７】
【発明が解決しようとする課題】
本発明は、外付け法(OVD法)により大型の光ファイバ用多孔質母材を高速で生産することができ、堆積表面に発生するピッチが細かくて凹部の深い凹凸を解消した、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している。
【０００８】
【課題を解決するための手段】
上記課題を解決するため鋭意検討した結果、堆積中のバーナ先端と堆積表面との距離(Ｌ)を、付着率が最大となる距離(Ｌmax)よりも大きな値を維持しながら堆積することにより、堆積面の凹凸が解消できることを見出し、上記課題を解決したものである。
すなわち、本発明の光ファイバ用多孔質母材の製造方法は、外付け法(OVD法)によりコア用ガラス棒の周面に、これに沿って配置した複数のバーナを往復移動させてガラス微粒子を堆積させる方法であって、堆積面におけるガラス微粒子の付着率が最大となる堆積表面とバーナ先端との距離(Ｌmax)を避けて、ガラス微粒子の堆積を行うことを特徴としている。
【０００９】
このとき、該距離(L)を、付着率が最大となる距離(Ｌmax)よりも大きくして、好ましくは、150 mmを超え250 mm以下に維持して、バーナの往復移動の開始位置（停止折返し位置）を３箇所以上として順次移動させながら堆積させる。
バーナは、同心円状３重管バーナとし、該バーナの中心管に原料ガスと酸素を供給し、その外側の第２管に酸素を、最外層の第３管に水素を供給する。
上記製造方法によれば、堆積表面の凹凸がピッチ20 mm以下、深さがほぼ８mm以下の光ファイバ用多孔質母材が得られる。
【００１０】
【発明の実施の形態】
上記多孔質母材の表面の凹凸は、特許第2612949号公報が記述している凹凸、すなわち、バーナを長手方向に一定の振幅で往復移動することにより、バーナの停止と折返し移動が常に同一位置で繰り返されるために生じる堆積ムラによる凹凸とは、明らかに異なるものである。該公報が問題にしている凹凸のピッチは、バーナの往復移動量とほぼ一致しており、ピッチ幅の広い鈍角またはＲを有する凹凸が主である。
【００１１】
本発明によれば、堆積表面の凹凸がピッチ20 mm以下で、その深さもほぼ５mm以下の多孔質母材が得られる。そのためには、バーナ先端と堆積表面との距離(Ｌ)を、付着率が最大となる距離(Ｌmax)よりも大きい150 mmを超え250 mm以下に維持して堆積するものであり、この範囲外では十分な堆積効率が得られない。
ガラス微粒子の堆積は、バーナをこのような位置に配置し、バーナの往復移動の開始位置を３箇所以上として順次移動させながら行われる。
【００１２】
本発明の光ファイバ用多孔質母材の製造方法においては、同心円状３重管バーナを使用するのが好ましい。この理由は、通常用いられている同心円状５重管バーナよりも製作が安易であり、供給する水素ガス量が５重管と比べて少量で済み、装置への熱負荷が低減できることによる。
この同心円状３重管バーナは、その中心管に原料ガスと酸素、第２管に酸素、第３管に水素が供給される。
以下、本発明について実施例を用いて説明するが、本発明はこれに限定されるものではなく様々な態様が可能である。
【００１３】
(事前準備)
事前準備として、バーナ先端と堆積表面との距離（Ｌ）と、付着率との関係を調査した。これには、図１に示す装置を使用し、石英製円筒管１の表面に、バーナ先端と堆積表面との距離（Ｌ）を様々に変えてガラス微粒子の堆積を行い、付着率と距離(Ｌ)との関係を調査した。
先ず、直胴部の長さ1500 mm、外径250 mmφの石英製円筒管１を、この両端部に接続したダミー棒８，８を介してチャック２，２に取り付け、回転用モータ３で回転させ、堆積を行った。
【００１４】
堆積用バーナ４には同心円状３重管バーナを使用し、石英製円筒管１に沿って150 mm間隔で６本をバーナ台５上に配置し、バーナ台５を移動させることでバーナ４の移動を行った。
該バーナ４ヘのガス供給条件は、中心管に原料ガスSiCl4を2.6 Nl/min/バーナ、酸素を5 Nl/min/バーナとし、第２管には酸素を10 Nl/min/バーナ、さらに第３管には水素を50 Nl/min/バーナとした。
【００１５】
上記条件で、石英製円筒管１を30 rpmで回転させ、バーナ４の往復移動長を300 mmとし、またバーナ４の往復移動の開始位置を順次移動させながら1050 mmの範囲にわたり２時間堆積を行った。なお、堆積はバーナ先端と堆積表面との距離(Ｌ)を変えて複数回行い、該距離(Ｌ)と付着率との関係を求めた。図２にその結果を示した。なお、付着率は、堆積重量と供給原料ガス量から算出した。
この結果、バーナ先端と堆積表面の距離を150 mmとしたときに、最も付着率が高くなる距離(Ｌmax)となることが判明した。
【００１６】
（実施例１）
そこで、図３に示す装置を使用し、バーナ先端と堆積表面との距離(Ｌ)が200 mmを維持するようにして、最も付着率の高い距離(Ｌmax) 150 mmを避け、外径40 mmφのコア用ガラス棒６に対する堆積を行った。このとき、バーナ先端と堆積表面との距離(Ｌ)が200 mmを維持するように、堆積が進み外径が大きく成長するのに合わせて、バーナ４の先端の位置も後退させた。
堆積用バーナ４には同心円状３重管バーナを使用し、150 mm間隔にて６本をバーナ台５上に配置し、バーナ台５を移動させることでバーナ４の移動を行った。またそのときのバーナ４の移動長は300 mmとした。
【００１７】
バーナ４ヘのガス供給条件は、堆積初期においては、中心管に原料ガスSiCl4を0.5 Nl/min/バーナ、酸素を5 Nl/min/バーナとし、第２管には酸素を6 Nl/min/バーナ、さらに第３管には水素を30 Nl/min/バーナとし、堆積終了時には、中心管に原料ガスSiCl4を2.6 Nl/min/バーナ、酸素を5 Nl/min/バーナとし、第２管には酸素を12 Nl/min/バーナとし、第３管には水素を80 Nl/min/バーナとなるように供給し、堆積スート外径の増加に伴い調整した。
【００１８】
上記条件にて、バーナ４の往復移動の開始位置を順次移動させながら、多孔質母材７の外径が300 mmφとなるまで堆積を行った。
この様にして得られた多孔質母材７の表面には、目視で確認できるような凹凸は全く無く、平坦な多孔質母材であった。
【００１９】
(比較例１)
実施例１と同じ図３に示す装置を使用し、バーナ先端と堆積表面との距離を最も付着率の高い距離(Ｌmax) 150 mmに設定して、外径40 mmφのコア用ガラス俸６に対する堆積を行った。堆積中、この距離が150 mmを維持するように、堆積が進み外径が大きくなるのに合わせてバーナ４の先端位置も後退させた。
ここで、堆積用バーナ４としては実施例１と同様に同心円状３重管バーナを使用し、150 mm間隔で６本配置し、バーナ台５を移動させることでバーナ４の移動を行った。またそのときのバーナ４の移動長は300 mmとした。
【００２０】
バーナ４ヘのガス供給条件は、堆積初期においては、中心管に原料ガスSiCl4を0.5 Nl/min/バーナ、酸素を5 Nl/min/バーナとし、第２管には酸素を6 Nl/min/バーナ、さらに第３管には水素を30 Nl/min/バーナとし、堆積終了時には、中心管に原料ガスSiCl4を2.6 Nl/min/バーナ、酸素を5 Nl/min/バーナとし、第２管には酸素を12 Nl/min/バーナとし、第３管には水素を80 Nl/min/バーナとなるように供給し、堆積スート外径の増加に伴い調整した。
【００２１】
上記条件にて、バーナの往復移動の開始位置を順次移動させながら、多孔質母材７の外径が300 mmφとなるまで堆積を行った。
この様にして得られた多孔質母材７の表面には、8〜12 mmピッチで深さ最大10 mmにもなる凹凸が生じていた。
【００２２】
【発明の効果】
本発明によれば、堆積表面に発生するピッチが細かくて凹部の深い凹凸は解消され、外付け法による大型の光ファイバ用多孔質母材の高速生産を可能とし、これを脱水・透明ガラス化して得られる光ファイバ用プリフォームの特性を安定させることができる。
【図面の簡単な説明】
【図１】 外付け法による多孔質母材の製造装置の１例を示す概略図である。
【図２】 バーナ先端から堆積表面までの距離と付着率との関係を示すグラフである
【図３】 外付け法による多孔質母材の製造装置の１例を示す概略図である。
【符号の説明】
１.……石英製円筒管、
２. ……チャック、
３. ……回転用モータ、
４. ……バーナ、
５. ……バーナ台、
６. ……コア用ガラス棒、
７. ……多孔質母材、
８. ……ダミー棒。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous optical fiber preform formed by depositing glass particles on a core glass rod by an external method (OVD method), and in particular, an optical fiber porous preform with small irregularities generated on the deposition surface. The present invention relates to a method for manufacturing a material.
[0002]
[Prior art]
As a method of manufacturing a preform for an optical fiber, glass fine particles generated by supplying a glass raw material into an oxyhydrogen flame are attached and deposited around a glass rod having a core, and the resulting porous base material is heated to a high temperature. A method of performing dehydration and transparent vitrification processing is known below. This is generally called the external method (OVD method), in which a glass particle generating burner is placed at a right angle to a horizontally set glass rod, and this burner is reciprocated in parallel along the glass rod. A method of manufacturing a desired porous base material by attaching and depositing glass fine particles on a glass rod is mainly used.
[0003]
In recent years, with an increase in the size of a preform, demands for increasing the size and productivity of a porous base material have increased, and several methods have been proposed in practice. As an example of this productivity improvement, we do not manufacture optical fiber preforms, but adjust the amount of gas supplied to multiple burners or adjust the distance between the burner tip and the glass particle deposition surface. Or by adjusting the number of revolutions of the heat-resistant substrate to change the deposition density of the glass fine particles along the radial direction to prevent cracking of the porous base material (see JP-A-64-9821), etc. Has been proposed.
[0004]
However, although the method disclosed in Japanese Patent Application Laid-Open No. 64-9821 has the advantage that the deposition rate is high and a large porous base material can be produced, the burner is fixed along the longitudinal direction of the core material. Since the reciprocating movement is performed with the amplitude, the start position (stop turning point) and the moving region of the reciprocating movement of the burner are always repeated at the same position, resulting in uneven deposition and unevenness on the surface of the deposit. In addition, this method has a drawback in that the core aluminum is doped as a metal impurity in the silica layer, and cannot be used for manufacturing an optical fiber preform.
[0005]
As a method for producing a large-sized optical fiber preform at high speed using a plurality of burners, a method in which a plurality of burners of the same design are arranged at equal intervals and the start positions of the reciprocating movement of the burners are sequentially moved and dispersed (Patent No. 2612949). No. gazette) has been proposed. This method can dramatically increase the deposition rate.
Therefore, the distance between the burner tip and the deposition surface is set to the position where the adhesion rate is the best, and the following problems occur as a result of actually manufacturing a large porous base material with a diameter of 300 mmφ by the above method. It has been found.
[0006]
In other words, from the beginning of the deposition until the diameter reached approximately 200 mmφ, very fine irregularities of the pitch were observed on the deposition surface, but the level was still satisfactory. However, when trying to manufacture a larger porous base material with a diameter exceeding 200 mmφ, the unevenness of the very fine pitch begins to increase to a level that cannot be ignored. Unevenness with a depth of 10 mm was generated on the surface of the porous base material. If a porous preform with such irregularities on the surface is subjected to dehydration and transparent vitrification treatment, irregularities remain on the surface even after the treatment, and when the optical fiber is finally formed, the core and cladding ratio is unstable. It becomes a factor.
[0007]
[Problems to be solved by the invention]
The present invention is capable of producing a large-scale porous optical fiber preform at a high speed by the external method (OVD method), and has a fine pitch generated on the deposition surface and eliminates deep irregularities in the recesses. An object is to provide a method for producing a porous base material.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the distance (L) between the burner tip during deposition and the deposition surface is deposited while maintaining a value larger than the distance (L max ) at which the adhesion rate is maximum. The present inventors have found that the unevenness of the deposited surface can be eliminated and solved the above problems.
That is, the method for producing a porous preform for an optical fiber of the present invention is such that a glass particulate is obtained by reciprocating a plurality of burners arranged along the peripheral surface of a core glass rod by an external method (OVD method). The glass particles are deposited while avoiding the distance (L max ) between the deposition surface and the tip of the burner where the adhesion rate of the glass particles on the deposition surface is maximum.
[0009]
At this time, the distance (L) is set to be larger than the distance (L max ) at which the adhesion rate is maximum, and preferably is maintained to be more than 150 mm and not more than 250 mm to start the reciprocating movement of the burner ( Deposition is performed while sequentially moving the stop folding position) to three or more locations.
The burner is a concentric triple tube burner, which supplies the source gas and oxygen to the central tube of the burner, supplies oxygen to the second tube outside it, and supplies hydrogen to the third tube in the outermost layer.
According to the manufacturing method described above, a porous preform for optical fibers having unevenness on the deposition surface with a pitch of 20 mm or less and a depth of approximately 8 mm or less can be obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The unevenness of the surface of the porous base material is the unevenness described in Japanese Patent No. 2612949, that is, when the burner is reciprocated with a constant amplitude in the longitudinal direction, the burner is always stopped and folded back at the same position. The unevenness caused by the uneven deposition caused by the repetition of the above is clearly different. The pitch of the unevenness which is a problem in this publication is almost the same as the reciprocating amount of the burner, and is mainly an unevenness having an obtuse angle or R having a wide pitch width.
[0011]
According to the present invention, it is possible to obtain a porous base material having unevenness on the deposition surface with a pitch of 20 mm or less and a depth of approximately 5 mm or less. For this purpose, deposition is carried out while maintaining the distance (L) between the burner tip and the deposition surface to be greater than 150 mm and less than or equal to 250 mm, which is greater than the distance (L max ) at which the adhesion rate is maximum. Outside, sufficient deposition efficiency cannot be obtained.
Glass fine particles are deposited while the burner is placed at such a position and the burner is moved sequentially at three or more starting positions.
[0012]
In the method for producing a porous preform for optical fiber of the present invention, it is preferable to use a concentric triple tube burner. This is because it is easier to manufacture than the commonly used concentric quintuple burner, the amount of hydrogen gas supplied is smaller than that of the quintuple tube, and the heat load on the apparatus can be reduced.
This concentric triple tube burner is supplied with a raw material gas and oxygen in the central tube, oxygen in the second tube, and hydrogen in the third tube.
Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to this, A various aspect is possible.
[0013]
(Advance preparation)
As a preliminary preparation, the relationship between the distance (L) between the burner tip and the deposition surface and the adhesion rate was investigated. For this purpose, the apparatus shown in FIG. 1 is used, glass particles are deposited on the surface of the quartz cylindrical tube 1 with various distances (L) between the burner tip and the deposition surface, and the adhesion rate and distance ( The relationship with L) was investigated.
First, a quartz cylindrical tube 1 having a straight body length of 1500 mm and an outer diameter of 250 mmφ is attached to chucks 2 and 2 via dummy rods 8 and 8 connected to both ends, and is rotated by a rotation motor 3. And was deposited.
[0014]
As the deposition burner 4, a concentric triple tube burner is used, and six burners are arranged on the burner base 5 at intervals of 150 mm along the quartz cylindrical tube 1, and the burner base 5 is moved to move the burner 4. Moved.
The gas supply conditions to the burner 4 are as follows: raw material gas SiCl 4 is 2.6 Nl / min / burner, oxygen is 5 Nl / min / burner, oxygen is 10 Nl / min / burner in the second pipe, The third pipe was hydrogen at 50 Nl / min / burner.
[0015]
Under the above conditions, the quartz cylindrical tube 1 is rotated at 30 rpm, the reciprocating length of the burner 4 is set to 300 mm, and the start position of the reciprocating movement of the burner 4 is sequentially moved to deposit for 2 hours over a range of 1050 mm. went. The deposition was performed a plurality of times while changing the distance (L) between the burner tip and the deposition surface, and the relationship between the distance (L) and the adhesion rate was determined. The results are shown in FIG. The adhesion rate was calculated from the deposition weight and the amount of feed gas.
As a result, it was found that when the distance between the burner tip and the deposition surface was 150 mm, the distance (L max ) with the highest adhesion rate was obtained.
[0016]
Example 1
Therefore, by using the apparatus shown in FIG. 3, the distance (L) between the burner tip and the deposition surface is maintained at 200 mm, the distance with the highest adhesion rate (L max ) of 150 mm is avoided, and the outer diameter 40 Deposition was performed on a glass rod 6 for core of mmφ. At this time, the position of the tip of the burner 4 was also retracted as the deposition progressed and the outer diameter increased greatly so that the distance (L) between the tip of the burner and the deposition surface was maintained at 200 mm.
As the deposition burner 4, a concentric triple tube burner was used. Six burners were arranged on the burner base 5 at intervals of 150 mm, and the burner 4 was moved by moving the burner base 5. The moving length of the burner 4 at that time was 300 mm.
[0017]
The gas supply conditions to the burner 4 are as follows. At the initial stage of deposition, the raw material gas SiCl 4 is 0.5 Nl / min / burner, the oxygen is 5 Nl / min / burner, and the second pipe is oxygen 6 Nl / min. / Burner, hydrogen is 30 Nl / min / burner in the 3rd pipe, and at the end of deposition, the source gas SiCl 4 is 2.6 Nl / min / burner and oxygen is 5 Nl / min / burner at the center pipe. Oxygen was supplied to the tube at 12 Nl / min / burner and hydrogen was supplied to the third tube at 80 Nl / min / burner, which was adjusted as the outer diameter of the deposition soot increased.
[0018]
Under the above conditions, deposition was performed until the outer diameter of the porous base material 7 reached 300 mmφ while sequentially moving the start position of the reciprocating movement of the burner 4.
The surface of the porous base material 7 thus obtained had no irregularities that could be visually confirmed, and was a flat porous base material.
[0019]
(Comparative Example 1)
Using the same apparatus as shown in FIG. 3 as in Example 1, the distance between the burner tip and the deposition surface was set to the distance with the highest adhesion rate (L max ) 150 mm, and the core glass rod 6 having an outer diameter of 40 mmφ 6 Was deposited against. During the deposition, the tip position of the burner 4 was also retracted as the deposition progressed and the outer diameter increased so that this distance was maintained at 150 mm.
Here, a concentric triple tube burner was used as the deposition burner 4 in the same manner as in Example 1, and six burners were arranged at intervals of 150 mm, and the burner base 5 was moved to move the burner 4. The moving length of the burner 4 at that time was 300 mm.
[0020]
The gas supply conditions to the burner 4 are as follows. At the initial stage of deposition, the raw material gas SiCl 4 is 0.5 Nl / min / burner, the oxygen is 5 Nl / min / burner, and the second pipe is oxygen 6 Nl / min. / Burner, hydrogen is 30 Nl / min / burner in the 3rd pipe, and at the end of deposition, the source gas SiCl 4 is 2.6 Nl / min / burner and oxygen is 5 Nl / min / burner at the center pipe. Oxygen was supplied to the tube at 12 Nl / min / burner and hydrogen was supplied to the third tube at 80 Nl / min / burner, which was adjusted as the outer diameter of the deposition soot increased.
[0021]
Under the above conditions, deposition was performed until the outer diameter of the porous base material 7 reached 300 mmφ while sequentially moving the start position of the reciprocating movement of the burner.
On the surface of the porous base material 7 obtained in this way, irregularities having a maximum depth of 10 mm were formed at a pitch of 8 to 12 mm.
[0022]
【The invention's effect】
According to the present invention, the pitch generated on the deposition surface is fine and the deep irregularities of the concave portions are eliminated, enabling the high-speed production of a large-sized porous optical fiber preform by an external method, which is dehydrated and made into transparent glass. The properties of the optical fiber preform obtained in this way can be stabilized.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an apparatus for producing a porous base material by an external method.
FIG. 2 is a graph showing the relationship between the distance from the burner tip to the deposition surface and the adhesion rate. FIG. 3 is a schematic diagram showing an example of an apparatus for producing a porous base material by an external method.
[Explanation of symbols]
1 .... Cylinder cylindrical tube,
2. …… Chuck,
3. ...... Rotary motor,
4. ... Burna,
5. …… Burna stand,
6. ... glass rod for core,
7. ... porous matrix,
8. Dummy stick.

Claims (5)

外付け法(OVD法)によりコア用ガラス棒の周面に、これに沿って配置した複数のバーナを往復移動させてガラス微粒子を堆積させる方法であって、堆積面におけるガラス微粒子の付着率が最大となる堆積表面とバーナ先端との距離(Ｌmax)を避けて、ガラス微粒子の堆積を行うことを特徴とする光ファイバ用多孔質母材の製造方法。  A method of depositing glass particulates by reciprocating a plurality of burners arranged along the peripheral surface of a core glass rod by an external method (OVD method). A method for producing a porous optical fiber preform, wherein glass particles are deposited while avoiding a maximum distance (Lmax) between a deposition surface and a burner tip. バーナ先端と堆積表面との距離(Ｌ)を、付着率が最大となる距離(Ｌmax)よりも大きくし、該距離(Ｌ)を維持して、バーナの往復移動の開始位置を３箇所以上として順次移動させながら堆積する請求項１に記載の光ファイバ用多孔質母材の製造方法。The distance (L) between the burner tip and the deposition surface is made larger than the distance (L max ) at which the adhesion rate is maximum, and the distance (L) is maintained, and the start position of the reciprocating movement of the burner is three or more. The method for producing a porous preform for optical fibers according to claim 1, wherein the depositing is performed while sequentially moving as follows. バーナ先端と堆積表面との距離(Ｌ)を、150 mmを超え250 mm以下に維持して堆積する請求項１又は２に記載の光ファイバ用多孔質母材の製造方法。  The method for producing a porous preform for an optical fiber according to claim 1 or 2, wherein the deposition is performed while maintaining the distance (L) between the burner tip and the deposition surface to be more than 150 mm and not more than 250 mm. バーナが同心円状３重管バーナである請求項１乃至３のいずれかに記載の光ファイバ用多孔質母材の製造方法。  The method for producing a porous preform for an optical fiber according to any one of claims 1 to 3, wherein the burner is a concentric triple tube burner. 同心円状３重管バーナの中心管に原料ガスと酸素を供給し、その外側の第２管に酸素を、最外層の第３管に水素を供給する請求項４に記載の光ファイバ用多孔質母材の製造方法。  5. The optical fiber porous material according to claim 4, wherein source gas and oxygen are supplied to a central tube of a concentric triple tube burner, oxygen is supplied to a second tube outside thereof, and hydrogen is supplied to a third tube of the outermost layer. A manufacturing method of a base material.
JP2002189082A 2002-06-28 2002-06-28 Method for producing porous preform for optical fiber Expired - Fee Related JP3917022B2 (en)

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