JP2006199517A - Method of manufacturing optical fiber preform - Google Patents
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- JP2006199517A JP2006199517A JP2005010279A JP2005010279A JP2006199517A JP 2006199517 A JP2006199517 A JP 2006199517A JP 2005010279 A JP2005010279 A JP 2005010279A JP 2005010279 A JP2005010279 A JP 2005010279A JP 2006199517 A JP2006199517 A JP 2006199517A
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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]
- C03B37/01446—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering
- C03B37/01453—Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering for doping the preform with flourine
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- 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
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Abstract
Description
本発明は光ファイバ用母材の製造方法に関する。特にフッ素を加圧状態で高濃度ドープする光ファイバ用母材の製造方法に関する。 The present invention relates to a method for manufacturing an optical fiber preform. In particular, the present invention relates to a method for manufacturing an optical fiber preform that is highly doped with fluorine in a pressurized state.
光ファイバの製造方法としては、以下の方法がある。例えば、まずＶＡＤ（Vapour phase Axial Deposition）法やＯＶＤ（Outside Vapour Deposition）法で合成した光ファイバ用多孔質母材を、ガラス化装置で脱水及び透明ガラス化して透明な光ファイバ用ガラス母材を作製する。次に、その母材を例えば酸水素火炎やプラズマ火炎もしくは電気炉で加熱延伸し、コアまたはコアの一部、あるいはコアとクラッドの一部を備えたガラスロッドを作製する。 As a method for manufacturing an optical fiber, there are the following methods. For example, first, a porous optical fiber base material synthesized by VAD (Vapor phase Axial Deposition) method or OVD (Outside Vapor Deposition) method is dehydrated and transparent vitrified using a vitrification device to produce a transparent optical fiber glass base material. Make it. Next, the base material is heated and stretched with, for example, an oxyhydrogen flame, a plasma flame, or an electric furnace, and a glass rod provided with a core, a part of the core, or a part of the core and the clad is produced.
得られたガラスロッドに、さらにＯＶＤ法等によりシリカガラス粒子を堆積させてクラッドとなる多孔質母材を形成し、ガラス化装置で脱水および透明ガラス化を必要な回数だけ行って、光ファイバ用ガラス母材（以下、プリフォームと呼ぶ）を作製する。 Silica glass particles are further deposited on the obtained glass rod by the OVD method or the like to form a porous base material to be a clad, and dehydration and transparent vitrification are performed as many times as necessary with a vitrification apparatus. A glass base material (hereinafter referred to as a preform) is produced.
光ファイバ用多孔質母材を加熱処理する工程では、雰囲気中のフッ素の分圧を高くすると、プリフォームにドープされるフッ素の量が多くなることが知られている。また、常圧ではフッ素系ガス濃度が１００容量％雰囲気中で光ファイバ用多孔質母材を処理しても、純粋な石英ガラスに対する比屈折率差が−０．７％程度にしかフッ素をドープすることができない。ところが、フッ素含有雰囲気で１気圧以上に加圧した状態で加熱処理すると、前記の比屈折率差で−０．７％以上のフッ素をドープすることが可能であることも知られている。 In the step of heat-treating the optical fiber porous preform, it is known that when the partial pressure of fluorine in the atmosphere is increased, the amount of fluorine doped into the preform increases. Moreover, even if the porous base material for optical fiber is processed in an atmosphere with a fluorine gas concentration of 100% by volume at normal pressure, the relative refractive index difference with respect to pure quartz glass is only doped with about −0.7%. Can not do it. However, it is also known that when the heat treatment is performed in a fluorine-containing atmosphere at a pressure of 1 atm or higher, −0.7% or more of fluorine can be doped with the above-mentioned relative refractive index difference.
前記加圧による高濃度フッ素ドープ方法としては、特開昭６０−２５５６３８号公報、特開昭６１−２４７６３３号公報、特開昭６２−５９５３５号公報、特開昭６３−１７６３２５号公報に記載がある。
上記の特開昭６０−２５５６３８号公報、特開昭６１−２４７６３３号公報、特開昭６３−１７６３２５号公報によれば、フッ素ドープ時の圧力が高く、処理温度が高温であればあるほど屈折率は低下し、純粋な石英ガラスに対する比屈折率差は大きくなる。ところが、圧力が２０気圧を越えるか、処理温度が１４００℃を越えると、透明化後のガラス体に気泡が残りやすいとの記載がある。また、フッ素をドープする際の温度が高いほど、ドープ量が多くなることも示されている。 According to the above-mentioned JP-A-60-255638, JP-A-61-247633, and JP-A-63-176325, the higher the pressure during fluorine doping and the higher the processing temperature, the higher the refraction. The rate decreases and the relative refractive index difference with respect to pure quartz glass increases. However, there is a description that if the pressure exceeds 20 atmospheres or the processing temperature exceeds 1400 ° C., bubbles are likely to remain in the glass body after the transparency. It is also shown that the doping amount increases as the temperature when doping fluorine is higher.
しかし、フッ素をドープする際の温度が高い場合には、多孔質母材の収縮および焼結速度が速まり、多孔質母材の表面のみ焼結が進むことになる。その結果、多孔質母材内部に微小な気泡が多数残留し、透明なプリフォームが得られなくなる。また、温度が高い場合には、多孔質母材が自重により変形して、伸び、曲がり、及び非円化が生じることがある。この傾向は、フッ素分圧が高いほど顕著になり、特に、フッ素分圧が１気圧を越えると非常に顕著となる。 However, when the temperature at the time of doping fluorine is high, the shrinkage and sintering speed of the porous base material are increased, and only the surface of the porous base material is sintered. As a result, many fine bubbles remain inside the porous base material, and a transparent preform cannot be obtained. In addition, when the temperature is high, the porous base material may be deformed by its own weight, resulting in elongation, bending, and non-circularization. This tendency becomes more prominent as the fluorine partial pressure is higher. In particular, when the fluorine partial pressure exceeds 1 atm, this tendency becomes very significant.
また、得られたプリフォームが全体としては透明であっても、気泡が多く残留することになる。また、ガラス化後は気泡がなくても、その後の延伸工程や、延伸後にさらにその表面にシリカガラス粒子を堆積させて製造した多孔質母材を焼結透明化した後、あるいはジャケット工程の後等の、さらに加熱処理を加える工程で、余分に固溶していた屈折率の変化に寄与していないフッ素系ガスが発泡して気泡になったり、線引中に発泡してそれが完成した光ファイバ中にエアラインの形で残留してしまうことがあった。 Further, even if the obtained preform is transparent as a whole, many bubbles remain. Moreover, even if there are no air bubbles after vitrification, after the subsequent stretching step, after the stretching, the porous base material produced by further depositing silica glass particles on the surface is sintered and transparentized, or after the jacket step In the process of further heat treatment, etc., the fluorine-based gas that did not contribute to the change in refractive index that was excessively dissolved foamed and became bubbles, or foamed during drawing to complete it In some cases, it remained in the form of an air line in the optical fiber.
さらに、多孔質母材の加熱処理室内をフッ素を含有する雰囲気にする際に、温度が高すぎると、完全にガスが置換される前に反応や収縮が進み、多孔質母材の径方向や長手方向で均一にフッ素がドープされないという問題がある。同様に、前記加熱処理室内をフッ素を含有する雰囲気にする際に、既に１気圧以上に加圧されていると、ガスの置換効率が落ち、多孔質母材の径方向や長手方向で均一にフッ素がドープされないという問題がある。また、加圧状態で完全にガスを置換しようとすると時間が長くかかり、非効率である。しかしこれらの問題の解消方法については、前記の公知文献には全く開示されていない。 Furthermore, when the temperature in the heat treatment chamber of the porous base material is set to a fluorine-containing atmosphere, if the temperature is too high, the reaction and shrinkage proceed before the gas is completely replaced, and the radial direction of the porous base material There is a problem that fluorine is not uniformly doped in the longitudinal direction. Similarly, when the inside of the heat treatment chamber is made an atmosphere containing fluorine, if the pressure has already been increased to 1 atm or more, the gas replacement efficiency is lowered, and the porous base material is uniformly distributed in the radial direction and the longitudinal direction. There is a problem that fluorine is not doped. Further, when the gas is completely replaced in a pressurized state, it takes a long time and is inefficient. However, methods for solving these problems are not disclosed at all in the above-mentioned known documents.
特開昭６２−５９５３５号公報においては、加熱処理の雰囲気中に含有されるドープ剤は５〜９５容量％であり、圧力は２〜８気圧とし、多孔質母材の密度は０．１〜１．５ｇ／ｃｍ３とし、温度は１５００〜１６００℃程度まで１００℃／時の昇温速度で昇温することが開示されている。しかし、多孔質母材の初期密度が０．５ｇ／ｃｍ３を越えると、母材中の空孔すなわち表面積が少なくなり、高濃度にフッ素をドープすることができない。仮にできたとしても、必要以上に雰囲気の圧力を高めなければならず、非効率である。 In Japanese Patent Laid-Open No. 62-59535, the dopant contained in the heat treatment atmosphere is 5 to 95% by volume, the pressure is 2 to 8 atm, and the density of the porous base material is 0.1 to It is disclosed that the temperature is 1.5 g / cm 3 and the temperature is raised to about 1500 to 1600 ° C. at a temperature raising rate of 100 ° C./hour. However, if the initial density of the porous base material exceeds 0.5 g / cm 3 , the vacancies, that is, the surface area in the base material decreases, and fluorine cannot be doped at a high concentration. Even if it can be made, the pressure of the atmosphere must be increased more than necessary, which is inefficient.
また特開昭６２−５９５３５号公報では、フッ素ドープ処理開始時の温度について全く開示していないが、多孔質母材を投入する都合上、室温に近いところから行っていると思われる。１００℃／時で、室温の２５℃から１５００℃まで加熱する場合には１４．８時間を要し、脱水工程や、母材を取り出すために室温まで下げる時間を含めると２０時間以上もかかることになる。 Japanese Patent Application Laid-Open No. 62-59535 does not disclose the temperature at the start of the fluorine doping process, but it is considered that the temperature is close to room temperature for the convenience of introducing the porous base material. When heating from 25 ° C. to 1500 ° C. at 100 ° C./hour, it takes 14.8 hours, and it takes more than 20 hours including the dehydration step and the time to lower the temperature to take out the base material. become.
この場合は、処理時間が長すぎで量産には不向きである。また、１４００℃以上の高温に１時間以上さらすことになり、伸び、曲がり、及び非円のような母材の変形が生じる可能性がある。この傾向は、フッ素を高濃度にドープするほど顕著となる。 In this case, the processing time is too long and it is not suitable for mass production. Moreover, it will be exposed to the high temperature of 1400 degreeC or more for 1 hour or more, and deformation | transformation of a preform | base_material like elongation, a bending, and a noncircle may arise. This tendency becomes more prominent as fluorine is doped at a higher concentration.
本発明は、上記の状況に鑑みてなされたものであり、下記記載の発明を提供することにある。
(1)高濃度のフッ素を含有する雰囲気中、又は高濃度のフッ素を含有する雰囲気でかつ１気圧以上の加圧下で発泡や気泡の残留を起こさず、高濃度にフッ素をドープする方法。
(2)光ファイバ用多孔質母材の径方向、及び長手方向にフッ素を均一にドープする方法。
The present invention has been made in view of the above situation, and is to provide the invention described below.
(1) A method of doping fluorine at a high concentration without causing foaming or residual bubbles in an atmosphere containing a high concentration of fluorine or an atmosphere containing a high concentration of fluorine under a pressure of 1 atm or more.
(2) A method of uniformly doping fluorine in a radial direction and a longitudinal direction of a porous preform for an optical fiber.
(3)伸び、曲がり、及び非円の無い、又は、ほとんど無い高濃度にフッ素がドープされたプリフォームを製造する方法。
(4)後工程で加熱処理を施しても発泡しない、又は、ほとんど発泡しない高濃度にフッ素がドープされたプリフォームを製造する方法。
(3) A method for producing a preform doped with fluorine at a high concentration with no or almost no elongation, bending and non-circle.
(4) A method for producing a preform doped with fluorine at a high concentration that does not foam or hardly foams even when heat treatment is performed in a subsequent step.
前記課題を解決するために、本発明の第１の態様は、光ファイバ用ガラス母材の前駆体である多孔質母材を製造し、次いでフッ素を含む雰囲気中で１気圧以上の圧力で加熱処理し、前記多孔質母材にフッ素をドープし、透明ガラス化して光ファイバ用ガラス母材を得る光ファイバ母材の製造方法において、
密度が０．５ｇ／ｃｍ3以下の前記多孔質母材を用意し、
フッ素ドープを開始する前に前記用意した多孔質母材の密度が２０％より大きくならないように、かつ、前記フッ素ドープを開始する前に前記多孔質母材の少なくとも光ファイバとなる部分に相当する部分の径方向の最高温度と最低温度の差が２０℃以下となるように加熱処理することを特徴とする光ファイバ母材の製造方法である。
In order to solve the above-mentioned problems, a first aspect of the present invention is to manufacture a porous base material that is a precursor of a glass base material for an optical fiber, and then heat at a pressure of 1 atm or more in an atmosphere containing fluorine. In the method of manufacturing an optical fiber preform, the porous preform is doped with fluorine, and is made into a transparent glass to obtain a glass preform for an optical fiber.
Preparing the porous base material having a density of 0.5 g / cm 3 or less,
Before starting the fluorine doping, the density of the prepared porous preform does not exceed 20%, and corresponds to at least a portion of the porous preform that becomes an optical fiber before the fluorine doping is started. A method of manufacturing an optical fiber preform, wherein a heat treatment is performed so that a difference between a maximum temperature and a minimum temperature in a radial direction of a portion is 20 ° C. or less.
本発明の第２の態様は、前記加熱処理をする際の雰囲気をフッ素を含む雰囲気に置換するさいに、前記雰囲気の最高温度を１２００℃以下、又は加熱処理される多孔質母材の脱水処理温度以下で置換することを特徴とする光ファイバ母材の製造方法である。 In the second aspect of the present invention, when the atmosphere during the heat treatment is replaced with an atmosphere containing fluorine, the maximum temperature of the atmosphere is 1200 ° C. or lower, or the porous base material to be heat-treated is dehydrated. An optical fiber preform manufacturing method is characterized in that substitution is performed at a temperature or lower.
本発明の第３の態様は、前記加熱処理をする際の雰囲気をフッ素を含む雰囲気に置換するさいに、前記フッ素を含む雰囲気のフッ素分圧が高いほど、前記加熱処理を低温で行うことを特徴とする光ファイバ母材の製造方法である。 According to a third aspect of the present invention, when the atmosphere during the heat treatment is replaced with an atmosphere containing fluorine, the heat treatment is performed at a lower temperature as the fluorine partial pressure of the atmosphere containing fluorine is higher. It is the manufacturing method of the optical fiber preform characterized by the above.
本発明の第４の態様は、前記加熱処理をする際の雰囲気を１気圧以上の加圧雰囲気とする前に、フッ素を含む雰囲気への置換を行うことを特徴とする光ファイバ母材の製造方法である。 According to a fourth aspect of the present invention, there is provided an optical fiber preform characterized by substituting a fluorine-containing atmosphere before changing the atmosphere for the heat treatment to a pressurized atmosphere of 1 atm or higher. Is the method.
本発明の第５の態様は、前記加熱処理をする際、前記加熱処理を行う温度より低く、かつ、前記多孔質母材が焼結を起こさない温度まで一端降温し、該降温した温度から前記加熱処理する温度まで、５℃／分以下の昇温速度で昇温することを特徴とする光ファイバ母材の製造方法である。 In the fifth aspect of the present invention, when the heat treatment is performed, the temperature is lowered to a temperature lower than the temperature at which the heat treatment is performed and the porous base material does not sinter, and the temperature is lowered from the lowered temperature. A method for producing an optical fiber preform, wherein the temperature is raised to a temperature for heat treatment at a rate of temperature rise of 5 ° C./min or less.
本発明の第６の態様は、多孔質母材をフッ素を含む雰囲気中で１気圧以上の圧力で加熱処理してフッ素をドープし、透明ガラス化した光ファイバ母材を得る際に、
フッ素ドープ後に、前記フッ素ド−プ時の温度からの昇温速度を１０℃／分以下として所望の温度まで昇温し、透明ガラス化することを特徴とする光ファイバ母材の製造方法である。
In a sixth aspect of the present invention, when a porous preform is heat-treated in a fluorine-containing atmosphere at a pressure of 1 atm or more to dope fluorine and obtain an optical fiber preform that is made into a transparent glass,
A method for producing an optical fiber preform characterized in that after fluorine doping, the temperature is raised to a desired temperature at a rate of temperature rise of 10 ° C./min or less from the temperature at the time of fluorine doping, and is made into a transparent glass. .
本発明の第７の態様は、前記透明ガラス化の温度が１３５０℃以下であることを特徴とする光ファイバ母材の製造方法である。 A seventh aspect of the present invention is a method for producing an optical fiber preform, wherein the temperature of the transparent vitrification is 1350 ° C. or lower.
本発明の第８の態様は、前記フッ素を含む雰囲気が、ＳＦ６、ＣＦ４、ＣｌＦ３、ＳｉＦ４、Ｓｉ２Ｆ６等のフッ素系ガスの少なくとも１種のガスを含む雰囲気、又は前記ＳＦ６、ＣＦ４、ＣｌＦ３、ＳｉＦ４、Ｓｉ２Ｆ６等のフッ素系ガスの少なくとも１種のガスと、Ａｒ、Ｈｅ等の不活性ガスの少なくとも１種とを含む雰囲気であることを特徴とする光ファイバ母材の製造方法である。 In an eighth aspect of the present invention, the atmosphere containing fluorine contains an atmosphere containing at least one kind of fluorine-based gas such as SF 6 , CF 4 , ClF 3 , SiF 4 , Si 2 F 6 , or the SF 6 , an atmosphere containing at least one kind of fluorine-based gas such as CF 4 , ClF 3 , SiF 4 , Si 2 F 6 , and at least one kind of inert gas such as Ar and He. An optical fiber preform manufacturing method.
本発明の第９の態様は、前記多孔質母材がシリカガラス粒子より構成され、密度が０．１〜０．５ｇ／ｃｍ３の範囲であることを特徴とする光ファイバ母材の製造方法である。 According to a ninth aspect of the present invention, in the method for producing an optical fiber preform, the porous preform is composed of silica glass particles, and the density is in the range of 0.1 to 0.5 g / cm 3. It is.
本発明の効果を以下に示した。
(1)本発明によれば、フッ素ドープを開始する直前の前記多孔質母材の密度が０．５ｇ／ｃｍ3以下であり、前記密度に比べて２０％より大きくならないように、かつ、フッ素ドープの直前に多孔質母材の少なくとも径方向の温度がほぼ均一となるように、多孔質母材を加熱する工程を有する。
The effects of the present invention are shown below.
(1) According to the present invention, the density of the porous base material immediately before the start of fluorine doping is 0.5 g / cm 3 or less, so that it does not exceed 20% compared to the density, and fluorine There is a step of heating the porous base material so that at least the temperature in the radial direction of the porous base material becomes substantially uniform immediately before the dope.
そのため、多孔質母材中の気孔を大幅に減少させることがなく、少なくとも、径方向に気孔分布がほぼ均一な状態をつくることができる。そのため、必要以上にフッ素分圧を上げることなく、発泡や気泡の残留を起こさずに、高濃度にフッ素をドープすることが可能である。 Therefore, the pore distribution in the porous base material is not significantly reduced, and at least the pore distribution can be made almost uniform in the radial direction. Therefore, it is possible to dope fluorine at a high concentration without raising the fluorine partial pressure more than necessary and without causing foaming or residual bubbles.
(2)本発明によれば、フッ素ドープを行う際の雰囲気への置換を、前記加熱処理の前に行うことで、少なくとも径方向に均一にフッ素をドープする事ができる。 (2) According to the present invention, fluorine can be uniformly doped at least in the radial direction by performing substitution to the atmosphere when performing fluorine doping before the heat treatment.
(3)本発明によれば、フッ素ドープ時の昇温速度を５℃／分以下とすることで、径方向の温度差がほとんどなく、均一にフッ素をドープする事ができる。さらに、径方向の温度差がないため、多孔質母材が径方向に均一に収縮し、内部に気泡が残留しない。 (3) According to the present invention, it is possible to dope fluorine evenly with almost no temperature difference in the radial direction by setting the temperature rising rate during fluorine doping to 5 ° C./min or less. Furthermore, since there is no temperature difference in the radial direction, the porous base material uniformly shrinks in the radial direction, and no bubbles remain inside.
(4)本発明によれば、透明ガラス化の温度を１３５０℃以下とすることで、フッ素が高濃度にドープされた母材の軟化を防ぐことができ、伸び、曲がり、および非円の少ないプリフォームが得られる。 (4) According to the present invention, by setting the temperature of transparent vitrification to 1350 ° C. or lower, softening of the base material doped with fluorine at a high concentration can be prevented, and there is little elongation, bending, and non-circle. A preform is obtained.
(5)本発明によれば、透明ガラス化の温度を１３５０℃以下とすることで、余分なフッ素系ガスがガラス中へ固溶することを防ぐことができるため、後工程で加熱処理を施しても発泡することがないプリフォームを作製できる。 (5) According to the present invention, by setting the temperature of transparent vitrification to 1350 ° C. or less, it is possible to prevent excessive fluorine-based gas from being dissolved in the glass, so that heat treatment is performed in a subsequent step. However, a preform that does not foam can be produced.
本発明は、ＶＡＤ法やＯＶＤ法で合成した多孔質母材を、ガラス化炉にて脱水、透明ガラス化等の加熱処理を行い、透明なプリフォームを形成する光ファイバの製造方法に関する。 The present invention relates to a method for manufacturing an optical fiber in which a porous preform synthesized by a VAD method or an OVD method is subjected to heat treatment such as dehydration and transparent vitrification in a vitrification furnace to form a transparent preform.
本発明は、加熱処理の過程で、少なくともある一定時間、フッ素を含有する雰囲気中で１気圧より高い圧力下で加熱処理する工程を備えている。また、フッ素ドープを開始する前の密度が０．５ｇ／ｃｍ3の多孔質母材を用いて、フッ素ドープを開始する前の密度に比べて２０％より大きくならないように、かつ、前記フッ素ドープを開始する前に前記多孔質母材の少なくとも光ファイバとなる部分に相当する部分の径方向の温度分布がほぼ均一になるように加熱する工程を備えるものである。 The present invention includes a step of performing a heat treatment in a fluorine-containing atmosphere at a pressure higher than 1 atm for at least a certain time during the heat treatment. Further, by using a porous base material having a density before start of fluorine doping of 0.5 g / cm 3 , the density is not more than 20% as compared with the density before start of fluorine doping, and the fluorine doping Before starting the process, heating is performed so that the temperature distribution in the radial direction of at least the portion corresponding to the optical fiber of the porous preform becomes substantially uniform.
この目的は、フッ素をドープするまでに多孔質母材の気孔を大幅に減少させず、さらに、均一にフッ素をドープするために少なくとも径方向にほぼ均一な密度状態をつくりだすことにある。 The purpose is not to significantly reduce the pores of the porous base material before doping with fluorine, and to create a substantially uniform density state at least in the radial direction in order to dope fluorine uniformly.
なお、フッ素ドープを開始する前の多孔質母材の密度が０．５ｇ／ｃｍ３を越えると、母材中の空孔すなわち表面積が少なくなり、高濃度にフッ素をドープすることができない。仮にできたとしても、必要以上に雰囲気の圧力を高めなければならず、非効率である。そのため、多孔質母材の密度は０．５ｇ／ｃｍ３以下とする。また、フッ素ドープを開始する直前の前記多孔質母材の密度が、製造された直後の密度に比べて２０％より大きくなると、所望の濃度のフッ素をド−プできなくなる場合がある。 If the density of the porous base material before the start of fluorine doping exceeds 0.5 g / cm 3 , vacancies in the base material, that is, the surface area decreases, and fluorine cannot be doped at a high concentration. Even if it can be made, the pressure of the atmosphere must be increased more than necessary, which is inefficient. Therefore, the density of the porous base material is 0.5 g / cm 3 or less. In addition, if the density of the porous base material immediately before the start of fluorine doping is higher than 20% compared to the density immediately after the manufacture, there may be a case where a desired concentration of fluorine cannot be doped.
ここで、上記のほぼ均一な温度とは、好適には径方向の最高温度と最低温度の差が２０℃以下、さらに好適には１０℃以下とする。これにより、多孔質母材の密度を変化させないので、フッ素がドープされる量も増加する。また温度が均一になるため、フッ素と多孔質母材が部分的に反応することがなく、発泡や気泡の残留を防ぐことができる。 Here, the substantially uniform temperature is preferably such that the difference between the maximum temperature and the minimum temperature in the radial direction is 20 ° C. or less, more preferably 10 ° C. or less. Thereby, since the density of a porous preform | base_material is not changed, the quantity by which fluorine is doped also increases. Further, since the temperature becomes uniform, the fluorine and the porous base material do not partially react, and foaming and remaining bubbles can be prevented.
例えば、図１には、本発明の実施形態の一例を図示した。図１は、いわゆるヒートゾーンが短い炉を示したものである。炉は雰囲気ガスが漏れないように、耐圧性を有した密閉構造となっている。すなわち、炉体２の内側には、加熱処理室１５を構成する炉心管１と、炉心管１の外側中央部に設けられた均熱管４と均熱管の外周に設けられたヒータ３と、ヒータ３の外側の断熱材５とで構成されている。
For example, FIG. 1 illustrates an example of an embodiment of the present invention. FIG. 1 shows a furnace with a short so-called heat zone. The furnace has a sealed structure with pressure resistance so that atmospheric gas does not leak. That is, inside the
加熱処理室７の底部開口部、及び炉体６の底部には、ガス供給口６、７が設けられている。また、加熱処理室１５の上部、および炉体２には、ガス排出口８．９が設けられている。多孔質母材１０は、加熱処理室１５内で回転させながら、また、加熱処理室１５内を上下に移動させて加熱処理が行われる。
図２には、本発明の別の実施形態例を示した。図１の炉に比べて相異するところは、均熱管２４、及びヒーター部が充分に長いことである。いわゆる、ヒートゾーンが長い炉を示したものである。
FIG. 2 shows another embodiment of the present invention. The difference from the furnace of FIG. 1 is that the soaking
例えば、図１に示した、ヒートゾーンが多孔質母材よりも短く、多孔質母材を引き下げる、あるいは引き上げることで、ヒートゾーンを通過させて加熱処理する加熱炉を用いる場合は、昇温する速さは多孔質母材を引き下げる、あるいは引き上げる速度と炉内の温度分布の関係に基づく数値となる。 For example, the heating zone shown in FIG. 1 is shorter than the porous base material, and the temperature is raised when using a heating furnace that passes through the heat zone and lowers or raises the porous base material. The speed is a numerical value based on the relationship between the speed of pulling down or lifting the porous base material and the temperature distribution in the furnace.
図２に示した炉の場合、多孔質母材全体の温度を均一にすることが容易で、処理時間も短くて済むという点で、本発明の実施にはより好適である。 In the case of the furnace shown in FIG. 2, it is easy to make the temperature of the entire porous base material uniform, and the processing time can be shortened.
本発明では、ガラス化炉の加熱処理室の雰囲気をフッ素を含む雰囲気に置換する際には、フッ素ドープを開始する直前の前記多孔質母材の密度が、製造された直後の密度に比べて２０％より大きくならない温度、好適には１２００℃以下、さらに好適には１２００℃以下で、かつ脱水処理温度以下の温度で行うことが望ましい。 In the present invention, when the atmosphere of the heat treatment chamber of the vitrification furnace is replaced with an atmosphere containing fluorine, the density of the porous base material immediately before the start of fluorine doping is compared with the density immediately after the manufacture. It is desirable that the temperature is not higher than 20%, preferably 1200 ° C. or lower, more preferably 1200 ° C. or lower, and a temperature not higher than the dehydration temperature.
この目的は、まず、多孔質母材とフッ素との反応がほとんど進まず、多孔質母材の密度変化がほとんど起きない温度で雰囲気の置換を行うことである。また、その雰囲気で多孔質母材の少なくとも径方向に、好適には全体をほぼ均一に加熱することである。さらに、多孔質母材密度が低く（０．１〜０．５ｇ／ｃｍ３の範囲）多孔質母材の気孔が開気孔の状態で、フッ素を含む雰囲気ガスが多孔質母材の径方向と長手方向に渡り前記気孔の内部を均一に置換することである。 The purpose is to first replace the atmosphere at a temperature at which the reaction between the porous base material and fluorine hardly proceeds and the density change of the porous base material hardly occurs. Further, it is preferable to heat the whole of the porous base material almost uniformly in the atmosphere in at least the radial direction. Furthermore, the porous base material density is low (in the range of 0.1 to 0.5 g / cm 3 ), and the porous base material has open pores, and the fluorine-containing atmospheric gas is in the radial direction of the porous base material. It is to uniformly replace the inside of the pores in the longitudinal direction.
また、前記加熱処理は、好適には、フッ素を含む雰囲気中のフッ素分圧が高いほど低温で行うこととする。例えば、１００容量％のフッ素系ガスを用いて１気圧で前記加熱処理を行う場合、温度は１２００℃とする。２気圧の場合は、１１５０℃とする。３気圧の場合は、１１００℃とする。４気圧の場合は、１０００℃とする。 The heat treatment is preferably performed at a lower temperature as the fluorine partial pressure in the atmosphere containing fluorine is higher. For example, when the heat treatment is performed at 1 atmosphere using 100% by volume of a fluorine-based gas, the temperature is 1200 ° C. In the case of 2 atm, the temperature is set to 1150 ° C. In the case of 3 atmospheres, it is set to 1100 ° C. In the case of 4 atmospheres, the temperature is set to 1000 ° C.
また、特に好適には、例えば、加圧する前に雰囲気をヘリウムなどの不活性ガスで満たし、次に所望の雰囲気になるまでフッ素を含有するガスを吹き流すことにより置換を行う。加圧状態でこのような雰囲気の置換を行なっても良いが、置換したガスを炉心管内より排出しにくく、置換時間が長くかかることから、現実的ではない。 Particularly preferably, for example, the replacement is performed by filling the atmosphere with an inert gas such as helium before pressurization and then blowing a gas containing fluorine until a desired atmosphere is obtained. Although replacement of such an atmosphere may be performed in a pressurized state, it is difficult to exhaust the replaced gas from the inside of the furnace core tube, and it takes a long time for replacement, which is not realistic.
本方法により、雰囲気の置換中に多孔質母材の収縮が進んで密度が高まり、多孔質母材内部までフッ素を含有するガスに置換することができずにフッ素ドープ量が減少したり、プリフォ−ムの径方向や長手方向のフッ素含有濃度の差が生じることを防止できる。また、フッ素系ガスの分圧が高くても透明ガラス化後の気泡の残留が起きず、さらに、効率良く高濃度のフッ素をドープすることが可能となる。 By this method, the shrinkage of the porous base material progresses during the replacement of the atmosphere and the density increases, so that the inside of the porous base material cannot be replaced with the fluorine-containing gas, and the fluorine doping amount is reduced. -It is possible to prevent the difference in fluorine-containing concentration in the radial direction and longitudinal direction of the film. Moreover, even if the partial pressure of the fluorine-based gas is high, bubbles do not remain after transparent vitrification, and it becomes possible to dope high-concentration fluorine efficiently.
また、本発明では、好適には、フッ素をドープする際の加熱処理時に昇温速度を５℃／分以下とする。これは、フッ素ドープや透明ガラス化する際に、多孔質母材の径方向に温度差をつけないためである。光ファイバ用多孔質母材は熱伝導性が悪く、昇温速度が速いと径方向に温度差が生じる。すると、温度の高い表面部分のみ焼結が進み、内部に気泡が残留してしまうことがある。 In the present invention, preferably, the heating rate is set to 5 ° C./min or less during the heat treatment when doping fluorine. This is because a temperature difference is not made in the radial direction of the porous base material during fluorine doping or transparent vitrification. The optical fiber porous preform has poor thermal conductivity, and if the rate of temperature rise is high, a temperature difference occurs in the radial direction. Then, only the surface portion having a high temperature is sintered, and bubbles may remain inside.
また、加熱処理をする際には、加熱処理を行う温度より低く、かつ、多孔質母材が焼結を起こさない温度まで一端温度を下げ、下げた温度から加熱処理する温度まで５℃／分以下の昇温速度で昇温することも望ましい。 In addition, when performing the heat treatment, the temperature is lowered to a temperature lower than the temperature at which the heat treatment is performed and the porous base material does not cause sintering, and the temperature from the lowered temperature to the temperature at which the heat treatment is performed is 5 ° C./min. It is also desirable to raise the temperature at the following rate of temperature rise.
さらに好適には、ドープする際のフッ素分圧が高いほど、また多孔質母材の径が大きいほど、昇温する速さを遅くすることが望ましい。ここで昇温する速さというのは、均熱温度部分の長さが多孔質母材よりも長い場合は単純に昇温する速さである。 More preferably, the higher the partial pressure of fluorine during doping and the larger the diameter of the porous base material, the slower the rate of temperature rise. Here, the rate of temperature increase is simply the rate of temperature increase when the soaking temperature portion is longer than the porous base material.
また、焼結が進み、多孔質母材の密度が１．５〜１．８ｇ／ｃｍ３を越える（ガラス化時の理論密度の７０％を越える）密度となると、多孔質母材の熱伝導率が向上するので、昇温速度を１０℃／分程度まで上げても径方向にほぼ均一に加熱できるようになる。これにより、透明ガラス化するまでにかかる時間を短縮することができる。また、密度が石英ガラスの理論密度（２．２ｇ／ｃｍ３）となった後も、一部に気泡が残る場合があり、透明化を完全に行うためにはさらにしばらく高温に保持するか、昇温する必要がある。 Further, when the sintering progresses and the density of the porous base material exceeds 1.5 to 1.8 g / cm 3 (exceeds 70% of the theoretical density at the time of vitrification), the heat conduction of the porous base material. Since the rate is improved, even if the temperature rising rate is increased to about 10 ° C./min, it can be heated almost uniformly in the radial direction. Thereby, the time taken for transparent vitrification can be shortened. In addition, even after the density reaches the theoretical density (2.2 g / cm 3 ) of quartz glass, bubbles may remain in part, and for complete transparency, hold the temperature at a higher temperature for a while, It is necessary to raise the temperature.
しかし、あまり温度を上げすぎると、屈折率には寄与しない余分なフッ素系ガスがガラス中に固溶してしまい、後工程で加熱処理をする際にそれが発泡するので、例えばフッ素ド−プされたガラス部分の純粋な石英ガラスに対する比屈折率差が−０．７％かそれより小さい場合では、１３５０℃程度が上限である。好適には、１３５０℃以下、さらに好適には１３００℃以下とすると、後工程で加熱した際に発泡することがないか、あるいはほとんど発泡が起きなくなる。また、母材が変形して伸びたり、曲がったり、あるいは非円が生じたりすることがない。また、フッ素のドープ量が多いほど、透明化する際の温度を低くする方がより好適である。 However, if the temperature is raised too much, excess fluorine-based gas that does not contribute to the refractive index will be dissolved in the glass and foamed during the heat treatment in the subsequent process. In the case where the relative refractive index difference of the produced glass portion with respect to pure quartz glass is −0.7% or less, the upper limit is about 1350 ° C. When the temperature is preferably 1350 ° C. or lower, more preferably 1300 ° C. or lower, foaming does not occur or hardly occurs when heated in a subsequent process. Further, the base material is not deformed and stretched, bent, or non-circular. Further, it is more preferable to lower the temperature at the time of transparency as the fluorine doping amount is larger.
本発明では、フッ素を含む雰囲気として、ＳＦ６、ＣＦ４、ＣｌＦ３、ＳｉＦ４、Ｓｉ２Ｆ６等のフッ素系ガスの少なくとも１種のガスを含む雰囲気とすることが望ましい。また、ＳＦ６、ＣＦ４、ＣｌＦ３、ＳｉＦ４、Ｓｉ２Ｆ６等のフッ素系ガスの少なくとも１種のガスと、Ａｒ、Ｈｅ等の不活性ガスの少なくとも１種とを含む雰囲気であっても良い。 In the present invention, the atmosphere containing fluorine is preferably an atmosphere containing at least one kind of fluorine-based gas such as SF 6 , CF 4 , ClF 3 , SiF 4 , Si 2 F 6 . And an atmosphere containing at least one kind of fluorine-based gas such as SF 6 , CF 4 , ClF 3 , SiF 4 , Si 2 F 6 , and at least one kind of inert gas such as Ar and He. Also good.
本発明では、多孔質母材がシリカガラス粒子より構成される。また、多孔質母材の密度は０．１〜０．５ｇ／ｃｍ３の範囲であることが望ましい。なお、多孔質母材の密度が０．５ｇ／ｃｍ３を越えると、母材中の空孔すなわち表面積が少なくなり、高濃度にフッ素をドープすることができない。また、０．１ｇ／ｃｍ３を下回ると多孔質母材の形状を保持するのが困難となるからである。 In the present invention, the porous base material is composed of silica glass particles. The density of the porous base material is desirably in the range of 0.1 to 0.5 g / cm 3 . If the density of the porous base material exceeds 0.5 g / cm 3 , vacancies in the base material, that is, the surface area decreases, and fluorine cannot be doped at a high concentration. Moreover, it is because it will become difficult to maintain the shape of a porous preform | base_material if it is less than 0.1 g / cm < 3 >.
図１に示したガラス化装置を用い、密度が０．４ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１１５０℃以下に保った状態で、ＳＦ６を３ＳＬＭ流して１．１気圧まで加圧した。その後、１２５０℃まで５℃／分の昇温速度で昇温してフッ素をドープした後、同一雰囲気のまま同一の昇温速度で１３００℃まで昇温して透明ガラス化した。 Using the vitrification apparatus shown in FIG. 1, a porous base material having a density of 0.4 g / cm 3 was inserted into the heat treatment chamber. In a state where the temperature in the heat treatment chamber was kept at 1150 ° C. or lower, SF 6 was flowed in 3 SLM and pressurized to 1.1 atm. Then, after heating up to 1250 degreeC with the temperature increase rate of 5 degree-C / min and doping with fluorine, it heated up to 1300 degreeC with the same temperature increase rate with the same atmosphere, and was transparent glass.
この時得られたプリフォームに泡はなく、屈折率は純粋な石英ガラスとの比屈折率差で−０．７８％であり、径方向および長手方向で±３％以内の均一さでフッ素がドープされていた。このプリフォームを酸水素火炎で加熱し延伸したが、発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 The preform obtained at this time has no bubbles, and the refractive index is -0.78% in terms of the relative refractive index difference from pure quartz glass, and the fluorine is uniform within ± 3% in the radial and longitudinal directions. It was doped. This preform was heated and stretched with an oxyhydrogen flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
（比較例１）
図１に示したガラス化装置を用い、密度が０．６ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１１５０℃以下に保った状態で、フッ素を含むガスとしてＳＦ６を３ＳＬＭ流して１．１気圧まで加圧した。その後、１２５０℃まで５℃／分の昇温速度で昇温してフッ素をドープした後、同一雰囲気で同一の昇温速度で１３００℃まで昇温して透明化を試みた。しかし、取り出したプリフォームは全体が白濁しており、これを酸水素火炎で加熱し延伸すると発泡が起こった。
(Comparative Example 1)
Using the vitrification apparatus shown in FIG. 1, a porous base material having a density of 0.6 g / cm 3 was inserted into the heat treatment chamber. With the temperature in the heat treatment chamber kept at 1150 ° C. or lower, SF 6 was flowed as 3 SLM as a fluorine-containing gas and pressurized to 1.1 atm. Then, after heating up to 1250 degreeC with the temperature increase rate of 5 degree-C / min and doping with fluorine, it heated up to 1300 degreeC with the same temperature increase rate in the same atmosphere, and attempted transparency. However, the taken out preform was entirely cloudy, and foaming occurred when the preform was heated and stretched with an oxyhydrogen flame.
図１に示したガラス化装置を用い、密度が０．３ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。脱水を塩素ガスとＨｅガスの混合雰囲気中で１２００℃の温度で行なった。続いて、加熱処理室内をＨｅガスで置換後に、１１００℃以下の温度で、炉心管内を常圧とし、ＳｉＦ４を５ＳＬＭ、Ｈｅガスを０．２５ＳＬＭ流しながら４０分間保持した後、１．４気圧まで加圧した。 Using the vitrification apparatus shown in FIG. 1, a porous base material having a density of 0.3 g / cm 3 was inserted into the heat treatment chamber. Dehydration was performed at a temperature of 1200 ° C. in a mixed atmosphere of chlorine gas and He gas. Subsequently, after replacing the heat treatment chamber with He gas, at a temperature of 1100 ° C. or lower, the inside of the furnace core tube is kept at normal pressure, SiF 4 is held at 5 SLM, He gas is held at 0.25 SLM for 40 minutes, and then 1.4 atm. Until pressurized.
その後、１２００℃まで５℃／分の昇温速度で昇温してフッ素をドープした後、同一雰囲気で１３００℃まで５℃／分の昇温速度で昇温した後、その温度で保持し透明化した。この時得られたプリフォームに泡はなく、屈折率は石英との比屈折率差で−０．７８％であり、径方向および長手方向に均一にフッ素がドープされていた。このとき得られたプリフォームを酸水素火炎で加熱し延伸したが発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 Then, after heating up to 1200 ° C. at a rate of 5 ° C./min and doping with fluorine, the temperature was raised to 1300 ° C. at a rate of 5 ° C./min in the same atmosphere, and then kept at that temperature and transparent Turned into. The preform obtained at this time had no bubbles, the refractive index was -0.78% in terms of the relative refractive index difference from quartz, and fluorine was uniformly doped in the radial direction and the longitudinal direction. The preform obtained at this time was heated and stretched with an oxyhydrogen flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
図２に示したガラス化装置を用い、密度が０．３ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１０７０℃に保持した状態で、Ｓｉ２Ｆ６を２ＳＬＭ流して１．５気圧まで加圧した。その後、１２５０℃まで４℃／分の昇温速度で昇温し、１２５０℃で６０分間保持し、フッ素をドープした後、同一雰囲気で１２９０℃まで８℃／分の昇温速度で昇温し、その温度を保持し、透明化した。 Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.3 g / cm 3 was inserted into the heat treatment chamber. In a state where the temperature in the heat treatment chamber was maintained at 1070 ° C., 2 SLM of Si 2 F 6 was flowed and pressurized to 1.5 atm. Then, the temperature was raised to 1250 ° C. at a rate of 4 ° C./min, held at 1250 ° C. for 60 minutes, doped with fluorine, and then heated to 1290 ° C. at a rate of 8 ° C./min in the same atmosphere. The temperature was kept clear.
この時得られたプリフォームに泡はなく、屈折率は石英との比屈折率差で−０．８５％であり、径方向および長手方向に均一にフッ素がドープされていた。このとき得られたプリフォームを火炎で延伸したが発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 The preform obtained at this time had no bubbles, the refractive index was -0.85% in terms of the relative refractive index difference from quartz, and fluorine was uniformly doped in the radial and longitudinal directions. The preform obtained at this time was stretched with a flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
（比較例２）
図２に示したガラス化装置を用い、密度が０．３ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１０７０℃に保持した状態で、Ｓｉ２Ｆ６を２ＳＬＭ流して、１．５気圧まで加圧した。その後、１１５０℃まで８℃／分の昇温速度で昇温し、１１５０℃で６０分間保持しフッ素をドープした後、同一雰囲気で１２９０℃まで８℃／分の昇温速度で昇温し、その温度を保持し透明化を試みた。この時得られたプリフォームは、径方向でフッ素のドープ量が不均一であった。
(Comparative Example 2)
Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.3 g / cm 3 was inserted into the heat treatment chamber. While maintaining the temperature in the heat treatment chamber at 1070 ° C., 2 SLM of Si 2 F 6 was flowed and pressurized to 1.5 atm. Thereafter, the temperature was raised to 1150 ° C. at a rate of 8 ° C./min, held at 1150 ° C. for 60 minutes and doped with fluorine, and then heated to 1290 ° C. at a rate of 8 ° C./min in the same atmosphere, At that temperature, an attempt was made to make it transparent. The preform obtained at this time had a non-uniform fluorine doping amount in the radial direction.
図２に示したガラス化装置を用いて、密度が０．３ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１０７０℃に保持した状態で、Ｓｉ２Ｆ６を２ＳＬＭ流して１．５気圧まで加圧した。その後、１２９０℃まで３℃／分の昇温速度で昇温してフッ素ドープと透明化を同時に行なった。 Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.3 g / cm 3 was inserted into the heat treatment chamber. In a state where the temperature in the heat treatment chamber was maintained at 1070 ° C., 2 SLM of Si 2 F 6 was flowed and pressurized to 1.5 atm. Thereafter, the temperature was increased to 1290 ° C. at a rate of 3 ° C./min, and fluorine dope and transparency were simultaneously performed.
この時得られたプリフォームに泡はなく、屈折率は石英との比屈折率差で−０．８５％であり、径方向および長手方向に均一にフッ素がドープされていた。このとき得られたプリフォームを酸水素火炎で加熱し延伸したが、発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 The preform obtained at this time had no bubbles, the refractive index was -0.85% in terms of the relative refractive index difference from quartz, and fluorine was uniformly doped in the radial and longitudinal directions. The preform obtained at this time was heated and stretched with an oxyhydrogen flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
図２に示したガラス化装置を用い、密度が０．２ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１０００℃に保持した状態で、Ｓｉ２Ｆ６を２ＳＬＭとＳｉＦ４を２ＳＬＭ、それぞれ混合して合計４ＳＬＭの混合ガスを流し、２．５気圧まで加圧し、１１００℃まで１．５℃／分の昇温速度で昇温し、１１００℃で保持してフッ素をドープした後、同一雰囲気で１２７０℃まで３℃／分の昇温速度で昇温し、その温度を保持し、透明化した。 Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.2 g / cm 3 was inserted into the heat treatment chamber. In a state where the temperature in the heat treatment chamber is maintained at 1000 ° C., 2 SLM of Si 2 F 6 and 2 SLM of SiF 4 are mixed, and a total of 4 SLM mixed gas is flowed, pressurized to 2.5 atm, and 1 up to 1100 ° C. The temperature was raised at a rate of 5 ° C / min, held at 1100 ° C and doped with fluorine, and then heated to 1270 ° C at a rate of 3 ° C / min in the same atmosphere to maintain the temperature. , Became transparent.
この時得られたプリフォームに泡はなく、屈折率は石英との比屈折率差で−０．９８％であり、径方向および長手方向に均一にフッ素がドープされていた。このとき得られたプリフォームを酸水素火炎で加熱し延伸したが発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 The preform obtained at this time had no bubbles, the refractive index was -0.98% in terms of the relative refractive index difference from quartz, and fluorine was uniformly doped in the radial direction and the longitudinal direction. The preform obtained at this time was heated and stretched with an oxyhydrogen flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
（比較例３）
図２に示したガラス化装置を用いて、密度が０．３ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を１０００℃に保持した状態で、Ｓｉ２Ｆ６を２ＳＬＭとＳｉＦ４を２ＳＬＭそれぞれ混合して合計４ＳＬＭの混合ガスを流して、２．５気圧まで加圧した。その後、１１００℃まで１．５℃／分の昇温速度で昇温し、１１００℃を保持してフッ素をドープした後、同一雰囲気で１５００℃まで３℃／分で昇温し、その温度で保持して透明化を行なった。この時得られたプリフォームは、長手方向に伸びてしまっており、径変動、非円、曲がりがあり、後工程で使用することができなかった。
(Comparative Example 3)
Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.3 g / cm 3 was inserted into the heat treatment chamber. While maintaining the temperature at 1000 ° C. heat treatment chamber, the Si 2 F 6 to 2SLM and SiF 4 by flowing a mixed gas of total 4SLM mixed 2SLM respectively and pressurized to 2.5 atm. Thereafter, the temperature was raised to 1100 ° C. at a rate of 1.5 ° C./min, and after maintaining 1100 ° C. and doping with fluorine, the temperature was raised to 1500 ° C. at 3 ° C./min in the same atmosphere. It was kept transparent. The preform obtained at this time was elongated in the longitudinal direction, had a diameter variation, non-circularity, and bending, and could not be used in a subsequent process.
図２に示したガラス化装置を用いて、密度が０．２ｇ／ｃｍ３の多孔質母材を加熱処理室内に挿入した。加熱処理室内の温度を９５０℃に保持した状態で、Ｓｉ３Ｆ３を３ＳＬＭ流して４気圧まで加圧した。その後、１０７０℃まで１．２℃／分の昇温速度で昇温し、１０７０℃を保持してフッ素をドープした後、同一雰囲気で同一の昇温速度で１２４０℃まで昇温し、その温度を保持し、透明化した。 Using the vitrification apparatus shown in FIG. 2, a porous base material having a density of 0.2 g / cm 3 was inserted into the heat treatment chamber. In a state where the temperature in the heat treatment chamber was maintained at 950 ° C., 3 SLM of Si 3 F 3 was flowed and pressurized to 4 atm. Thereafter, the temperature was raised to 1070 ° C. at a rate of 1.2 ° C./min, held at 1070 ° C. and doped with fluorine, and then heated to 1240 ° C. at the same temperature rise rate in the same atmosphere. Was kept transparent.
この時得られたプリフォームに泡はなく、屈折率は石英との比屈折率差で−１．１％であり、径方向および長手方向に均一にフッ素がドープされていた。このとき得られたプリフォームを酸水素火炎で加熱し延伸したが、発泡は起こらなかった。また、線引も行なったが、発泡は問題とならなかった。 The preform obtained at this time had no bubbles, the refractive index was -1.1% in terms of the relative refractive index difference from quartz, and fluorine was uniformly doped in the radial direction and the longitudinal direction. The preform obtained at this time was heated and stretched with an oxyhydrogen flame, but foaming did not occur. Drawing was also performed, but foaming was not a problem.
なお、本明細書において、多孔質母材の密度は、特に断らない限り多孔質母材の全体重量から、既にガラスとなっている部分の重量を差し引いたシリカガラス粒子の重量を多孔質母材の体積で割った平均密度とする。また、純粋な石英ガラスに対する比屈折率差は、純粋な石英ガラスの屈折率をｎ１、対象とするガラスの屈折率をｎ２とした場合、比屈折率差Δ＝（ｎ１−ｎ２）／ｎ１×１００（％）で表される値とする。 In this specification, unless otherwise specified, the density of the porous base material is obtained by subtracting the weight of the silica glass particles obtained by subtracting the weight of the already glass portion from the total weight of the porous base material. The average density divided by the volume of. Further, the relative refractive index difference with respect to pure quartz glass is as follows: relative refractive index difference Δ = (n1−n2) / n1 × where n1 is the refractive index of pure quartz glass and n2 is the refractive index of the target glass. The value is represented by 100 (%).
多孔質母材中の気孔を大幅に減少させることがなく、少なくとも、径方向に気孔分布がほぼ均一な状態をつくることができる。そのため、必要以上にフッ素分圧を上げることなく、発泡や気泡の残留を起こさずに、高濃度にフッ素をドープすることが可能である。また、フッ素が高濃度にドープされた母材の軟化を防ぐことができ、伸び、曲がり、および非円の少ないプリフォームが得られるとともに、余分なフッ素系ガスがガラス中へ固溶することを防ぐことができるため、後工程で加熱処理を施しても発泡することがないプリフォームを作製できる。 The pores in the porous base material are not significantly reduced, and at least the pore distribution can be made almost uniform in the radial direction. Therefore, it is possible to dope fluorine at a high concentration without raising the fluorine partial pressure more than necessary and without causing foaming or residual bubbles. In addition, softening of the base material doped with high concentration of fluorine can be prevented, and a preform with less elongation, bending and non-circle can be obtained, and excess fluorine-based gas can be dissolved in the glass. Therefore, it is possible to produce a preform that does not foam even when heat treatment is performed in a later step.
１ 炉心管
２ 炉体
３ ヒータ
４ 均熱管
５ 断熱材
６ ガス供給口
７ ガス供給口
８ ガス排気管
９ ガス排気
１０ 多孔質母材
１１ 支持棒
１５ 加熱処理室
２３ ヒータ
２４ 均熱管
２５ 加熱処理室
DESCRIPTION OF
Claims (9)
密度が０．５ｇ／ｃｍ3以下の前記多孔質母材を用意し、
フッ素ドープを開始する前に前記用意した多孔質母材の密度が２０％より大きくならないように、かつ、前記フッ素ドープを開始する前に前記多孔質母材の少なくとも光ファイバとなる部分に相当する部分の径方向の最高温度と最低温度の差が２０℃以下となるように加熱処理することを特徴とする光ファイバ母材の製造方法。 A porous base material, which is a precursor of a glass base material for optical fibers, is manufactured, and then heat-treated in a fluorine-containing atmosphere at a pressure of 1 atmosphere or more, and the porous base material is doped with fluorine to form a transparent glass. In the manufacturing method of the optical fiber preform to obtain the glass preform for the optical fiber,
Preparing the porous base material having a density of 0.5 g / cm 3 or less,
Before starting the fluorine doping, the density of the prepared porous preform does not exceed 20%, and corresponds to at least a portion of the porous preform that becomes an optical fiber before the fluorine doping is started. A method of manufacturing an optical fiber preform, wherein a heat treatment is performed so that a difference between a maximum temperature and a minimum temperature in a radial direction of a portion is 20 ° C. or less.
フッ素ドープ後に、前記フッ素ド−プ時の温度からの昇温速度を１０℃／分以下として所望の温度まで昇温し、透明ガラス化することを特徴とする光ファイバ母材の製造方法。 When a porous preform is heat-treated in a fluorine-containing atmosphere at a pressure of 1 atm or more to dope fluorine, to obtain a transparent glass-made optical fiber preform.
A method for producing an optical fiber preform, wherein after the doping with fluorine, the temperature is raised to a desired temperature by setting the rate of temperature rise from the temperature at the time of fluorine doping to 10 ° C./min or less to form a transparent glass.
The optical fiber preform according to any one of claims 1 to 8, wherein the porous preform is composed of silica glass particles and has a density in the range of 0.1 to 0.5 g / cm 3. A method of manufacturing the material.
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| JP2012086999A (en) * | 2010-10-18 | 2012-05-10 | Sumitomo Electric Ind Ltd | Optical fiber and method for producing glass preform for optical fiber |
| JP2012246157A (en) * | 2011-05-26 | 2012-12-13 | Ohara Inc | Method for producing synthetic silica glass and the synthetic silica glass |
| EP2977359A1 (en) * | 2014-07-21 | 2016-01-27 | Heraeus Quarzglas GmbH & Co. KG | Method for producing fluorine doped quartz glass |
| CN112266162A (en) * | 2020-11-03 | 2021-01-26 | 江苏亨通光导新材料有限公司 | Fluorine-doped quartz tube suitable for large-size optical fiber preform and preparation method thereof |
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