JP2012171802A - Method for producing optical fiber preform - Google Patents

Method for producing optical fiber preform Download PDF

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JP2012171802A
JP2012171802A JP2011031989A JP2011031989A JP2012171802A JP 2012171802 A JP2012171802 A JP 2012171802A JP 2011031989 A JP2011031989 A JP 2011031989A JP 2011031989 A JP2011031989 A JP 2011031989A JP 2012171802 A JP2012171802 A JP 2012171802A
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base material
optical fiber
soot
preform
core
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Kazumasa Osono
和正 大薗
Hei Yo
兵 姚
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Hitachi Cable Ltd
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Hitachi Cable 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
    • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
    • C03B37/01211—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments by inserting one or more rods or tubes into a tube
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
    • C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2203/00—Fibre product details, e.g. structure, shape
    • C03B2203/10—Internal structure or shape details
    • C03B2203/22—Radial profile of refractive index, composition or softening point

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

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform collectively formable of a part used as an inside clad layer of an optical fiber and a part used as an outside clad layer, and reducing cost effectively.SOLUTION: In this method for producing an optical fiber preform 21 by drawing, an optical fiber having an inside clad layer and an outside clad layer having a higher refractive index than the inside clad layer on the outer periphery of a core, a soot preform 1 is formed, in which the bulk density of a soot preform outer peripheral part 3 which is used as the outside clad layer is furthermore heightened than the bulk density of a soot preform center part 2 which is used as the inside clad layer, and fluorine is added to the soot preform 1 at the sintering time of the soot preform 1, to thereby produce a glass preform 11 in which the fluorine addition amount of a glass preform center part 12 formed by sintering the soot preform center part 2 is adjusted to be more than that of a glass preform outer peripheral part 13 formed by sintering the soot preform outer peripheral part 3, and thereafter a hollow part 14 is formed in the axial direction of the glass preform center part 12, and a core preform 15 used as a core is inserted into the hollow part 14 and unified.

Description

本発明は、コスト低減に効果のある光ファイバ母材の製造方法に関するものである。   The present invention relates to a method for manufacturing an optical fiber preform that is effective in reducing costs.

通信用光ファイバの中でもシングルモード光ファイバ（ＳＭＦ：Ｓｉｎｇｌｅ−Ｍｏｄｅ ｏｐｔｉｃａｌ Ｆｉｂｅｒ）は、低損失・広帯域な伝送路として広く実用化されている。ＳＭＦ中を伝搬する信号光の伝送特性の劣化を招く非線形効果現象を抑制するためには、モードフィールド径（ＭＦＤ：Ｍｏｄｅ Ｆｉｅｌｄ Ｄｉａｍｅｔｅｒ）を拡大する必要がある。ところが、ＭＦＤを拡大すると、曲げ損失特性が劣化する。その対策として、クラッド層の屈折率分布を、図２に示すような２段構造にするディプレスト型屈折率分布が用いられている。このディプレスト型屈折率分布を形成するためには、光ファイバのクラッド層を屈折率の異なる内側クラッド層と外側クラッド層とで構成する必要がある。   Among communication optical fibers, a single-mode optical fiber (SMF) has been widely put into practical use as a low-loss, wide-band transmission line. In order to suppress the nonlinear effect phenomenon that causes deterioration of the transmission characteristics of the signal light propagating in the SMF, it is necessary to enlarge the mode field diameter (MFD: Mode Field Diameter). However, when the MFD is enlarged, the bending loss characteristics deteriorate. As a countermeasure, a depressed type refractive index distribution is used in which the refractive index distribution of the cladding layer is a two-stage structure as shown in FIG. In order to form this depressed type refractive index profile, the optical fiber cladding layer must be composed of an inner cladding layer and an outer cladding layer having different refractive indexes.

光ファイバは、光ファイバ母材を線引きして製造されるので、光ファイバのクラッド層を２層構造とするためには、クラッド層となる部分を屈折率の異なる２層構造とした光ファイバ母材を製造する必要がある。   Since an optical fiber is manufactured by drawing an optical fiber preform, in order to make the clad layer of the optical fiber have a two-layer structure, an optical fiber preform having a two-layer structure in which the clad layer has a different refractive index is used. It is necessary to manufacture the material.

このような光ファイバ母材を製造するには、図３に示すように、気相軸付法（ＶＡＤ法：Ｖａｐｏｒ ｐｈａｓｅ Ａｘｉａｌ Ｄｅｐｏｓｉｔｉｏｎ ｍｅｔｈｏｄ）によってシリカガラス微粒子（スート）を堆積させ、次にＨｅとＣｌ2ガスの雰囲気中で脱水焼結処理し、さらに、延伸してコア母材を製造する（工程（i））。 In order to manufacture such an optical fiber preform, silica glass fine particles (soot) are deposited by a vapor phase axial deposition method (VAD method) as shown in FIG. 3, and then He and A core base material is manufactured by performing dehydration sintering treatment in an atmosphere of Cl 2 gas and further stretching (step (i)).

また、別工程にて、ＶＡＤ法によってスートを堆積させ、次にＨｅとＳｉＦ4ガスの雰囲気中で焼結時にフッ素ドープし、得られたガラス母材にコア母材を挿入するための中空部をチュービング加工して、内側クラッド層となる内側フッ素クラッド（フッ素添加管）を製造する（工程（ii））。 In another process, soot is deposited by the VAD method, then fluorine-doped during sintering in an atmosphere of He and SiF 4 gas, and a hollow portion for inserting the core base material into the obtained glass base material The inner fluorine clad (fluorine-added pipe) to be the inner clad layer is manufactured (step (ii)).

以上のようにして製造したコア母材と内側フッ素クラッドとをロッドインチューブ法により一体化する（工程（iii））。さらに、外付けＶＡＤ法により内側フッ素クラッドの外周にスートを堆積させた後、ＨｅとＳｉＦ4ガスの雰囲気中で焼結時にフッ素ドープし、外側クラッド層となる外側フッ素クラッドを形成すると、クラッド層が２層構造の光ファイバ母材が得られる（工程（iv））。 The core base material and the inner fluorine clad manufactured as described above are integrated by a rod-in-tube method (step (iii)). Furthermore, after soot is deposited on the outer periphery of the inner fluorine cladding by the external VAD method, fluorine doping is performed during sintering in an atmosphere of He and SiF 4 gas to form an outer fluorine cladding as an outer cladding layer. Thus, an optical fiber preform having a two-layer structure is obtained (step (iv)).

このように、従来は光ファイバ母材の製造に際して、光ファイバの内側クラッド層となる部分と外側クラッド層となる部分の形成を２つの工程に分けて行っていた。   Thus, conventionally, when manufacturing the optical fiber preform, the formation of the inner cladding layer and the outer cladding layer of the optical fiber are divided into two steps.

特開平１−２４６１５７号公報JP-A-1-246157

しかしながら、光ファイバの内側クラッド層となる部分と外側クラッド層となる部分の形成を２つの工程に分けて行うことは、光ファイバ母材のコストアップの要因となる。   However, the formation of the portion to be the inner cladding layer and the portion to be the outer cladding layer of the optical fiber in two steps is a factor in increasing the cost of the optical fiber preform.

そこで本発明の目的は、上記課題を解決し、光ファイバの内側クラッド層となる部分と外側クラッド層となる部分の形成を一括して行うことができ、コスト低減に効果のある光ファイバ母材の製造方法を提供することにある。   SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and can form a portion to be an inner cladding layer and a portion to be an outer cladding layer of an optical fiber all at once, which is effective for cost reduction. It is in providing the manufacturing method of.

上記課題を解決するために創案された本発明は、コアの外周に、内側クラッド層と該内側クラッド層より屈折率の高い外側クラッド層とを形成した光ファイバを線引きにより製造するための光ファイバ母材の製造方法において、前記内側クラッド層となるスート母材中心部のかさ密度に対して前記外側クラッド層となるスート母材外周部のかさ密度を高くしたスート母材を形成し、前記スート母材の焼結時に、前記スート母材にフッ素を添加して、前記スート母材中心部を焼結してなるガラス母材中心部のフッ素添加量を、前記スート母材外周部を焼結してなるガラス母材外周部より多くしたガラス母材を作製し、しかる後、前記ガラス母材中心部の軸方向に中空部を形成し、その中空部に前記コアとなるコア母材を挿入すると共に一体化する光ファイバ母材の製造方法である。   In order to solve the above problems, the present invention provides an optical fiber for producing an optical fiber in which an inner cladding layer and an outer cladding layer having a higher refractive index than the inner cladding layer are formed on the outer periphery of a core by drawing. In the manufacturing method of the base material, a soot base material is formed in which the bulk density of the outer periphery of the soot base material to be the outer cladding layer is higher than the bulk density of the central portion of the soot base material to be the inner cladding layer. During sintering of the base material, fluorine is added to the soot base material, and the amount of fluorine added to the central portion of the glass base material obtained by sintering the central portion of the soot base material is sintered to the outer periphery of the soot base material. The glass base material is made larger than the outer periphery of the glass base material, and then a hollow part is formed in the axial direction of the central part of the glass base material, and the core base material to be the core is inserted into the hollow part. And integrate A method for manufacturing an optical fiber preform.

前記スート母材の前記中心部のかさ密度が０．３ｇ／ｃｍ3以下であり、前記スート母材の前記外周部のかさ密度が０．５ｇ／ｃｍ3以上０．６ｇ／ｃｍ3以下であるとよい。 The bulk density of the central portion of the soot base material is 0.3 g / cm 3 or less, and the bulk density of the outer peripheral portion of the soot base material is 0.5 g / cm 3 or more and 0.6 g / cm 3 or less. Good.

前記中空部は、前記ガラス母材を加熱し、プラグにより前記ガラス母材の中心部を押し広げて形成されるとよい。   The hollow portion may be formed by heating the glass base material and expanding a center portion of the glass base material with a plug.

前記コア母材は、純粋シリカからなってもよい。   The core base material may be made of pure silica.

前記コア母材は、Ｇｅを添加したコア部の外周にコア外周クラッド部を有していてもよい。   The core base material may have a core outer periphery cladding part on the outer periphery of the core part to which Ge is added.

本発明によれば、光ファイバの内側クラッド層となる部分と外側クラッド層となる部分の形成を一括して行うことができ、コスト低減に効果のある光ファイバ母材の製造方法を提供できる。   ADVANTAGE OF THE INVENTION According to this invention, the part used as the inner side cladding layer and the part used as an outer side cladding layer of an optical fiber can be formed collectively, and the manufacturing method of the optical fiber preform which is effective in cost reduction can be provided.

（ａ）〜（ｄ）は、本実施の形態に係る光ファイバ母材の製造方法を説明する図である。(A)-(d) is a figure explaining the manufacturing method of the optical fiber preform which concerns on this Embodiment. ディプレスト型光ファイバの屈折率分布の一例を示す図である。It is a figure which shows an example of the refractive index distribution of a depressed type optical fiber. 従来のディプレスト型光ファイバの製造に用いる光ファイバ母材の製造方法を説明する図である。It is a figure explaining the manufacturing method of the optical fiber preform used for manufacture of the conventional depressed type optical fiber. スートのかさ密度と比屈折率差との関係を示す図である。It is a figure which shows the relationship between the bulk density of soot, and a relative refractive index difference.

以下、本発明の好適な一実施の形態を添付図面に基づいて詳述する。   A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

本実施の形態に係る光ファイバ母材は、コアの外周に、内側クラッド層と、内側クラッド層より屈折率の高い外側クラッド層とを形成した光ファイバを線引きにより製造するためのものである。この光ファイバ母材を製造するための製造方法を図１（ａ）〜（ｄ）により説明する。   The optical fiber preform according to the present embodiment is for manufacturing an optical fiber in which an inner cladding layer and an outer cladding layer having a higher refractive index than the inner cladding layer are formed on the outer periphery of a core by drawing. A manufacturing method for manufacturing this optical fiber preform will be described with reference to FIGS.

まず、図１（ａ）に示すように、内側クラッド層となるスート母材中心部２と外側クラッド層となるスート母材外周部３とからなるスート母材１を気相軸付法（ＶＡＤ法）により形成する。   First, as shown in FIG. 1 (a), a soot base material 1 comprising a soot base material central portion 2 serving as an inner clad layer and a soot base material outer peripheral portion 3 serving as an outer clad layer is formed by a vapor phase axis method (VAD). Method).

具体的には、スート母材中心部２形成用のバーナー４及びスート母材外周部３形成用のバーナー５に、酸素、水素、原料ガス（例えばＳｉＣｌ4）を供給し、酸素と水素の混合気体の火炎中で、原料ガスを燃焼（加水分解）させて不純物の少ないシリカガラス微粒子（スート）を生成し、それを回転するロッド（種棒）６の下端に堆積させながらロッド６を引き上げていき、多孔質体のスート母材１を形成する。 Specifically, oxygen, hydrogen, and source gas (for example, SiCl 4 ) are supplied to the burner 4 for forming the soot base material central portion 2 and the burner 5 for forming the soot base material outer peripheral portion 3 to mix oxygen and hydrogen. In a gas flame, the raw material gas is burned (hydrolyzed) to produce silica glass fine particles (soot) with few impurities, and the rod 6 is pulled up while being deposited on the lower end of the rotating rod (seed rod) 6. Then, the soot base material 1 of the porous body is formed.

このとき、バーナー４からの火炎の温度をバーナー５からの火炎の温度より低くして、中心部にスートを低密度に堆積させ、外周部にはスートを高密度に堆積させる。これにより、内側クラッド層となるスート母材中心部２のかさ密度に対して外側クラッド層となるスート母材外周部３のかさ密度が高くなるようにする。スート母材中心部２のかさ密度が０．３ｇ／ｃｍ3以下であり、スート母材外周部３のかさ密度が０．５ｇ／ｃｍ3以上０．６ｇ／ｃｍ3以下であることが好ましい。内側クラッド層と外側クラッド層の比屈折率差及びコアと内側クラッド層の比屈折率差を十分に設けることができるからである。 At this time, the temperature of the flame from the burner 4 is set lower than the temperature of the flame from the burner 5, soot is deposited at a low density at the center, and soot is deposited at a high density at the outer periphery. Accordingly, the bulk density of the soot base material outer peripheral portion 3 serving as the outer cladding layer is made higher than the bulk density of the soot base center portion 2 serving as the inner cladding layer. It is preferable that the bulk density of the soot base material central portion 2 is 0.3 g / cm 3 or less, and the bulk density of the soot base material outer peripheral portion 3 is 0.5 g / cm 3 or more and 0.6 g / cm 3 or less. This is because the relative refractive index difference between the inner cladding layer and the outer cladding layer and the relative refractive index difference between the core and the inner cladding layer can be sufficiently provided.

次に、スート母材１の焼結時に、スート母材１にフッ素をドープ（添加）する。このとき、スート母材中心部２のかさ密度をスート母材外周部３のかさ密度より低くしているので、スート母材外周部３よりスート母材中心部２のフッ素添加量を多くできる。こうして、スート母材１から、図１（ｂ）に示すような、スート母材中心部２を焼結してなるガラス母材中心部１２（すなわち、内側クラッド層）のフッ素添加量を、スート母材外周部３を焼結してなるガラス母材外周部１３（すなわち、外側クラッド層）より多くしたガラス母材１１を作製する。ガラス母材１１は、ガラス母材中心部１２のフッ素添加量がガラス母材外周部１３より多いため、ガラス母材中心部１２の屈折率がガラス母材外周部１３の屈折率より低くなる。   Next, when the soot base material 1 is sintered, the soot base material 1 is doped (added) with fluorine. At this time, since the bulk density of the soot base material central portion 2 is set lower than the bulk density of the soot base material outer peripheral portion 3, the amount of fluorine added to the soot base material central portion 2 can be increased more than the soot base material outer peripheral portion 3. In this way, the amount of fluorine added to the soot base material 1 from the glass base material center portion 12 (that is, the inner cladding layer) obtained by sintering the soot base material center portion 2 as shown in FIG. The glass base material 11 having a larger number than the glass base material outer peripheral portion 13 (that is, the outer cladding layer) formed by sintering the base material outer peripheral portion 3 is produced. In the glass base material 11, the amount of fluorine added to the glass base material central portion 12 is larger than that of the glass base material outer peripheral portion 13, so that the refractive index of the glass base material central portion 12 is lower than the refractive index of the glass base material peripheral portion 13.

ここで、図４に、スートの材料としてＳｉＯ2、ガスとしてＨｅとＳＦ6（流量比：ＳＦ6／（Ｈｅ＋ＳＦ6）＝０．０４）を用いたときの、スートのかさ密度とフッ素添加・焼結後の比屈折率差との関係を示す。図４に示したフッ素濃度では、かさ密度が０．３ｇ／ｃｍ3以下の場合にはフッ素添加による屈折率低下量はほぼ一定となることが判る。また、かさ密度が１．０ｇ／ｃｍ3以上の場合には、フッ素添加による屈折率低下はほとんどなく、純粋シリカと略等しいことが判る。つまり、図４に示した条件では、かさ密度を０．３〜１．０ｇ／ｃｍ3に制御することにより、それぞれのかさ密度に対応した屈折率低下量を得ることができる。このように、ガラス母材１１へのフッ素添加量はスート母材１のかさ密度に依存するため、本発明ではかさ密度をスート母材１の径方向に制御することで、フッ素添加濃度をその径方向に２段階に違えるようにした。なお、ＨｅとＳＦ6の流量比（フッ素ガス濃度）を制御することによっても、フッ素添加量（屈折率低下量）を制御することができるので、かさ密度と流量比（フッ素ガス濃度）を適宜設定することにより、色々な光ファイバを実現可能である。例えば、図２に示す光ファイバは、スート母材中心部２のかさ密度を０．３ｇ／ｃｍ3以下とし、スート母材外周部３のかさ密度を０．５ｇ／ｃｍ3以上０．６ｇ／ｃｍ3以下とし、ＳＦ6／（Ｈｅ＋ＳＦ6）＝０．１とすることにより実現可能である。 Here, in FIG. 4, the soot bulk density and fluorine addition when SiO 2 is used as the soot material and He and SF 6 are used as the gas (flow rate ratio: SF 6 / (He + SF 6 ) = 0.04). The relationship with the relative refractive index difference after sintering is shown. With the fluorine concentration shown in FIG. 4, it can be seen that when the bulk density is 0.3 g / cm 3 or less, the amount of decrease in the refractive index due to the addition of fluorine is substantially constant. In addition, when the bulk density is 1.0 g / cm 3 or more, it can be seen that there is almost no decrease in the refractive index due to the addition of fluorine, which is substantially equal to pure silica. That is, under the conditions shown in FIG. 4, by controlling the bulk density to 0.3 to 1.0 g / cm 3 , it is possible to obtain a refractive index reduction amount corresponding to each bulk density. Thus, since the amount of fluorine added to the glass base material 11 depends on the bulk density of the soot base material 1, in the present invention, the fluorine density is controlled by controlling the bulk density in the radial direction of the soot base material 1. Different in two stages in the radial direction. In addition, since the fluorine addition amount (refractive index reduction amount) can also be controlled by controlling the flow ratio (fluorine gas concentration) of He and SF 6 , the bulk density and the flow ratio (fluorine gas concentration) are appropriately set. By setting, various optical fibers can be realized. For example, in the optical fiber shown in FIG. 2, the bulk density of the soot base material central portion 2 is 0.3 g / cm 3 or less, and the bulk density of the soot base material outer peripheral portion 3 is 0.5 g / cm 3 or more and 0.6 g / cm 2. This can be realized by setting it to cm 3 or less and SF 6 / (He + SF 6 ) = 0.1.

図１に戻り、ガラス母材１１を形成した後、図１（ｃ）に示すように、ガラス母材中心部１２の軸方向に中空部１４を形成し、フッ素添加濃度をその径方向に２段階に違えた円筒形状の管（クラッド管）を得る。   Returning to FIG. 1, after forming the glass base material 11, as shown in FIG. 1C, a hollow portion 14 is formed in the axial direction of the glass base material central portion 12, and the fluorine addition concentration is 2 in the radial direction. A cylindrical tube (clad tube) with different stages is obtained.

本実施の形態では、中空部１４を形成する方法としてガラス母材１１を加熱し、プラグによりガラス母材中心部１２を押し広げて形成する方法（熱間プラグ法）を用いる。ここで、熱間プラグ法とは、シームレス鋼管を作製する際のマンネスマン法をガラス管の作製に適用したものである。   In the present embodiment, as a method for forming the hollow portion 14, a method (hot plug method) in which the glass base material 11 is heated and the glass base material central portion 12 is expanded by a plug is used. Here, the hot plug method is an application of the Mannesmann method for producing a seamless steel pipe to the production of a glass tube.

中空部１４を形成する方法はこれに限定されるものではなく、例えば、中空部１４は、くり抜き法によりガラス母材中心部１２の一部をくり抜いて形成しても良い。ただし、くり抜き法では、ガラス母材中心部１２の一部を捨てることになるため、これを想定してより大きな径でスート母材中心部２を形成する必要がある。   The method for forming the hollow portion 14 is not limited to this. For example, the hollow portion 14 may be formed by hollowing out a part of the glass base material central portion 12 by a hollowing method. However, in the hollowing out method, a part of the glass base material central portion 12 is discarded, so that it is necessary to form the soot base material central portion 2 with a larger diameter assuming this.

最後に、図１（ｄ）に示すように、中空部１４にコアとなるコア母材１５を挿入すると共にロッドインチューブ法により一体化することで、ディプレスト構造の光ファイバ母材２１を得る。コア母材１５としては、純粋シリカからなるものを用いる。コア母材１５は、ガラス母材１１の製造ラインとは別のラインで予め形成しておくことが望ましい。コア母材１５の形成方法は特に限定されるものではなく、コア母材１５は、例えば、図３（i）に示したように、ＶＡＤ法によってスートを堆積させ、脱水焼結処理を行った後、延伸して形成される。   Finally, as shown in FIG. 1 (d), a core preform 15 serving as a core is inserted into the hollow portion 14 and integrated by a rod-in-tube method, thereby obtaining an optical fiber preform 21 having a depressed structure. . As the core base material 15, a material made of pure silica is used. The core base material 15 is desirably formed in advance on a line different from the production line of the glass base material 11. The method for forming the core base material 15 is not particularly limited. For example, as shown in FIG. 3 (i), the core base material 15 was subjected to a dehydration sintering process by depositing soot by the VAD method. Thereafter, it is formed by stretching.

本発明に係る光ファイバ母材２１の製造方法では、かさ密度の異なるスート母材中心部２とスート母材外周部３とを一括で形成した後、スート母材中心部２及びスート母材外周部３へのフッ素ドープを一括で行うことで、内側クラッド層となるガラス母材中心部１２と外側クラッド層となるガラス母材外周部１３の形成工程を１つにし、コスト低減を可能にしている。また、クラッド層中のフッ素濃度の均一性も保つことができる。   In the method of manufacturing the optical fiber preform 21 according to the present invention, the soot preform central portion 2 and the soot preform outer peripheral portion 3 having different bulk densities are collectively formed, and then the soot preform central portion 2 and the soot preform outer periphery. By carrying out fluorine doping to the part 3 at once, the process of forming the glass base material central part 12 that becomes the inner cladding layer and the glass base material outer peripheral part 13 that becomes the outer cladding layer is made one, thereby enabling cost reduction. Yes. Also, the uniformity of the fluorine concentration in the cladding layer can be maintained.

また、ガラス母材１１に中空部１４を形成する方法として熱間プラグ法を用いるため、くり抜きによるロスが無く、さらに、この方法で拡径して形成した円筒形状の管を用いてロッドインチューブ法を実施することにより光ファイバ母材２１の大型化が可能である。   Further, since a hot plug method is used as a method of forming the hollow portion 14 in the glass base material 11, there is no loss due to hollowing, and a rod-in tube is formed using a cylindrical tube formed by expanding the diameter by this method. By implementing this method, the size of the optical fiber preform 21 can be increased.

さらにまた、本発明では、コアとなるコア母材１５を内側クラッド層及び外側クラッド層となるガラス母材１１とは別工程で製造するので、コア母材１５の製造の際にかさ密度を従来よりも低くでき、コア母材１５を製造する際の脱水処理を容易に行え、更なるコスト低減が可能である。また、脱水処理が容易なためコア母材１５を従来よりも大型化できる。   Furthermore, in the present invention, the core base material 15 serving as the core is manufactured in a separate process from the glass base material 11 serving as the inner clad layer and the outer clad layer. Lower, the dehydration process when the core base material 15 is manufactured can be easily performed, and further cost reduction is possible. Further, since the dehydration process is easy, the core base material 15 can be made larger than before.

さらに、コア母材１５とガラス母材１１とを別々に作製した後一体化するので、スート堆積時の酸水素火炎に基づくＯＨ基の光ファイバ母材２１への混入を防ぐことができる。つまり、本発明では、スート堆積時にコア母材１５を酸水素火炎で炙らずに光ファイバ母材２１を製造するため、酸水素火炎に起因するＯＨ基がコア母材１５内に拡散して光ファイバの伝送特性を劣化させることを防止できる。   Furthermore, since the core preform 15 and the glass preform 11 are separately manufactured and then integrated, it is possible to prevent the OH group from being mixed into the optical fiber preform 21 based on the oxyhydrogen flame during the soot deposition. That is, in the present invention, the optical fiber preform 21 is manufactured without soaking the core preform 15 with the oxyhydrogen flame at the time of soot deposition, so that the OH groups resulting from the oxyhydrogen flame diffuse into the core preform 15. It is possible to prevent the transmission characteristics of the optical fiber from deteriorating.

本発明は、上記実施の形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で種々の変更を加え得ることは勿論である。   The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

上記実施の形態では、コア母材として純粋シリカを用いた場合を説明したが、コア母材は、Ｇｅを添加して屈折率を上昇させたシリカコア部の外周にコア外周クラッド部を有するものでもよい。コア外周クラッド部は、線引きして光ファイバとした際に、コアより屈折率が低く、内側クラッド層より屈折率が高いコア外周クラッド層となる部分であり、純粋シリカ（あるいは純粋シリカに屈折率上昇もしくは下降用のドーパントを添加したもの）で形成される。このようなコア外周クラッド部を有するコア母材をガラス母材１１の中空部１４に挿入し一体化することで、クラッド層となる部分が内側から順に、コア外周クラッド部、ガラス母材中心部１２、ガラス母材外周部１３で構成されたトレンチ構造の光ファイバ母材を製造することができる。   In the above embodiment, the case where pure silica is used as the core base material has been described. However, the core base material may have a core outer peripheral cladding portion on the outer periphery of the silica core portion whose refractive index is increased by adding Ge. Good. The core outer cladding portion is a portion that becomes a core outer cladding layer having a refractive index lower than that of the core and higher than that of the inner cladding layer when drawn into an optical fiber. Pure silica (or pure silica has a refractive index) And a dopant for ascending or descending). By inserting and integrating the core base material having such a core outer peripheral cladding part into the hollow part 14 of the glass base material 11, the core layer cladding part and the glass base material central part are formed in order from the inner side. 12. An optical fiber preform having a trench structure composed of the glass preform outer peripheral portion 13 can be manufactured.

トレンチ型屈折率分布をもつ光ファイバとしては、内側クラッド層にフッ素が添加され、外側クラッド層が純粋シリカで形成されたものが知られている。この光ファイバを製造するためには、ガラス母材１１において、内側クラッド層となるガラス母材中心部１２にフッ素を添加し、外側クラッド層となるガラス母材外周部１３を純粋シリカで形成する必要がある。   As an optical fiber having a trench type refractive index profile, one in which fluorine is added to the inner cladding layer and the outer cladding layer is made of pure silica is known. In order to manufacture this optical fiber, in the glass preform 11, fluorine is added to the glass preform central portion 12 serving as the inner cladding layer, and the glass preform outer peripheral portion 13 serving as the outer cladding layer is formed of pure silica. There is a need.

本発明では、ガラス母材１１へのフッ素添加量をスート母材１のかさ密度で制御しているので、例えば、スート母材中心部２をフッ素がドープされるかさ密度で形成し、スート母材外周部３をフッ素がドープされないかさ密度（例えば、１ｇ／ｃｍ3以上）で形成することで、ガラス母材中心部１２にはフッ素を添加する一方、ガラス母材外周部１３へのフッ素の添加を防ぎ、ガラス母材外周部１３を純粋シリカで形成できる。 In the present invention, since the amount of fluorine added to the glass base material 11 is controlled by the bulk density of the soot base material 1, for example, the soot base material central portion 2 is formed at a bulk density doped with fluorine, and the soot base material is formed. By forming the material outer peripheral portion 3 with a bulk density not doped with fluorine (for example, 1 g / cm 3 or more), fluorine is added to the glass base material central portion 12 while fluorine on the glass base material outer peripheral portion 13 is added. Addition is prevented and the glass base material outer peripheral part 13 can be formed with a pure silica.

１ スート母材
２ スート母材中心部
３ スート母材外周部
１１ ガラス母材
１２ ガラス母材中心部
１３ ガラス母材外周部
１４ 中空部
１５ コア母材
２１ 光ファイバ母材 DESCRIPTION OF SYMBOLS 1 Soot base material 2 Soot base material center part 3 Soot base material outer peripheral part 11 Glass base material 12 Glass base material central part 13 Glass base material outer peripheral part 14 Hollow part 15 Core base material 21 Optical fiber base material

Claims (5)

コアの外周に、内側クラッド層と該内側クラッド層より屈折率の高い外側クラッド層とを形成した光ファイバを線引きにより製造するための光ファイバ母材の製造方法において、
前記内側クラッド層となるスート母材中心部のかさ密度に対して前記外側クラッド層となるスート母材外周部のかさ密度を高くしたスート母材を形成し、
前記スート母材の焼結時に、前記スート母材にフッ素を添加して、前記スート母材中心部を焼結してなるガラス母材中心部のフッ素添加量を、前記スート母材外周部を焼結してなるガラス母材外周部より多くしたガラス母材を作製し、
しかる後、前記ガラス母材中心部の軸方向に中空部を形成し、その中空部に前記コアとなるコア母材を挿入すると共に一体化することを特徴とする光ファイバ母材の製造方法。 In the manufacturing method of the optical fiber preform for manufacturing the optical fiber in which the inner cladding layer and the outer cladding layer having a higher refractive index than the inner cladding layer are formed on the outer periphery of the core by drawing,
Forming a soot base material in which the bulk density of the outer periphery of the soot base material to be the outer clad layer is higher than the bulk density of the soot base material central part to be the inner clad layer;
At the time of sintering the soot base material, fluorine is added to the soot base material, and the amount of fluorine added to the glass base material central portion formed by sintering the soot base material central portion is set to the soot base material outer peripheral portion. Make a glass base material that is larger than the outer periphery of the sintered glass base material,
Thereafter, a hollow part is formed in the axial direction of the central part of the glass base material, and the core base material to be the core is inserted into the hollow part and integrated with the hollow part. 前記スート母材中心部のかさ密度は０．３ｇ／ｃｍ3以下であり、前記スート母材外周部のかさ密度は０．５ｇ／ｃｍ3以上０．６ｇ／ｃｍ3以下である請求項１記載の光ファイバ母材の製造方法。 The bulk density of the soot base metal central part is 0.3 g / cm 3 or less, and the bulk density of the soot base metal outer peripheral part is 0.5 g / cm 3 or more and 0.6 g / cm 3 or less. Manufacturing method of optical fiber preform. 前記中空部は、前記ガラス母材を加熱し、プラグにより前記ガラス母材中心部を押し広げて形成される請求項１又は２記載の光ファイバ母材の製造方法。   The method of manufacturing an optical fiber preform according to claim 1 or 2, wherein the hollow portion is formed by heating the glass preform and expanding the center portion of the glass preform with a plug. 前記コア母材は、純粋シリカからなる請求項１〜３いずれかに記載の光ファイバ母材の製造方法。   The method for manufacturing an optical fiber preform according to any one of claims 1 to 3, wherein the core preform is made of pure silica. 前記コア母材は、Ｇｅを添加したコア部の外周にコア外周クラッド部を有する請求項１〜３いずれかに記載の光ファイバ母材の製造方法。   The said core preform | base_material is a manufacturing method of the optical fiber preform | base_material in any one of Claims 1-3 which have a core outer periphery clad part in the outer periphery of the core part which added Ge.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014071152A (en) * 2012-09-27 2014-04-21 Sumitomo Electric Ind Ltd Optical fiber, and manufacturing method thereof
JP2014527012A (en) * 2011-06-30 2014-10-09 コーニング インコーポレイテッド Method for manufacturing optical fiber preform having low refractive index trench
JP2014196219A (en) * 2013-03-29 2014-10-16 住友電気工業株式会社 Method of producing glass preform for optical fiber, glass preform for optical fiber and method of calculating optical characteristic of optical fiber
JP2017534551A (en) * 2014-09-16 2017-11-24 コーニング インコーポレイテッド Fabrication method of optical fiber preform having one-step fluorine trench and overcladding

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014527012A (en) * 2011-06-30 2014-10-09 コーニング インコーポレイテッド Method for manufacturing optical fiber preform having low refractive index trench
JP2014071152A (en) * 2012-09-27 2014-04-21 Sumitomo Electric Ind Ltd Optical fiber, and manufacturing method thereof
JP2014196219A (en) * 2013-03-29 2014-10-16 住友電気工業株式会社 Method of producing glass preform for optical fiber, glass preform for optical fiber and method of calculating optical characteristic of optical fiber
JP2017534551A (en) * 2014-09-16 2017-11-24 コーニング インコーポレイテッド Fabrication method of optical fiber preform having one-step fluorine trench and overcladding

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