JP2004067418A - Method of manufacturing optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber preform causing no foaming phenomenon in transparent vitrification. <P>SOLUTION: In the method of manufacturing the optical fiber preform which has a process for forming a porous deposit layer composed of glass fine particles containing a dopant to increase the refractive index on the outer circumferential surface of a glass rod containing a core glass rod or a sensor core and a process for forming an annular core by heating to transparently vitrifying the porous deposit layer, the relative refractive index difference in a place 0.1 mm away from the boundary between the glass rod 1 and the annular core 2 to the outside is controlled as larger than 0% to smaller than 0.009% as a value for pure silica. <P>COPYRIGHT: (C)2004,JPO

Description

【００３９】
表１から次のことが明らかである。
試料１〜４で明らかなように、ガラスロッド（１）との界面から０．１ｍｍ離隔した箇所の比屈折率差が０％より大きく０．００９％より小さい場合は、発泡が生じなくなっている。
【００４０】
また、試料５〜９に関しては、焼結後における純シリカ層の厚みが０．１ｍｍ以上となるように初期堆積層の厚みを設定すると、発泡が生じなくなるという結果になっている。
【００４１】
また、初期堆積層の密度を０．２３ｇ／ｃｍ^３とドーパントを含むガラス微粒子の堆積層の密度よりも低くすると発泡が生じている（試料１０）。しかし、初期堆積層の密度を０．３１ｇ／ｃｍ^３とドーパントを含むガラス微粒子の堆積層の密度よりも高くすると発泡が生じなくなった（試料１１）。
【００４２】
なお、初期堆積層の密度が１．０４ｇ／ｃｍ^３とドーパントを含むガラス微粒子の堆積層の密度よりも可成り高くした試料１２の場合、合成時にクラックが発生して後工程に進むことができなかった。
【００４３】
【発明の効果】
以上の説明で明らかなように、本発明方法によれば、屈折率を高めるドーパントを含む多孔質堆積層を形成し、それを透明ガラス化したときに、ガラスロッドとの界面における発泡現象の発生が抑制される光ファイバ母材を製造することができる。
【００４４】
これは、上記多孔質堆積層の形成に先立ち、ガラスロッドの外周面に純シリカの初期堆積層を形成することにより、透明ガラス化時におけるドーパントの熱拡散に対するバリアとしたことによってもたらされる効果である。
【図面の簡単な説明】
【図１】ガラスロッドの外周面に純シリカ微粒子の初期堆積層とＧｅＯ_２を含むガラス微粒子の多孔質堆積層を形成した状態を示す断面図である。
【図２】図１の多孔質体を透明ガラス化した状態を示す断面図である。
【図３】屈折率分布プロファイル図である。
【図４】別の屈折率分布プロファイル図である。
【図５】更に別の屈折率分布プロファイル図である。
【図６】他の屈折率分布プロファイル図である。
【図７】ＯＶＤ装置の概略平面図である。
【図８】ＯＶＤ装置の概略側面図である。
【符号の説明】
１　　ガラスロッド
１ａ　ガラスロッドの外周面
２　　多孔質
２_０　　多孔質純シリカ堆積層
２_１　　ドーパントを含む多孔質ガラス微粒子堆積層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an optical fiber preform, and more specifically, as a material for an optical fiber having an intricate refractive index distribution profile, which is produced by an OVD method, does not easily cause a foaming phenomenon even during the process of transparent vitrification. A method for producing a useful optical fiber preform.
[0002]
[Prior art]
2. Description of the Related Art In an optical communication system for transmitting a high-speed and large-capacity optical signal, a transmission path network is configured using optical fibers. In that case, in order to construct an optical communication system capable of large-capacity transmission, it is preferable to use, for example, a dispersion-shifted optical fiber having zero chromatic dispersion in a 1550 nm wavelength band and a small transmission loss. ing.
[0003]
As such a dispersion-shifted optical fiber, there are various types of optical fibers in which the refractive index distribution in the cross section has a profile as shown in FIGS. 3 to 6, for example. Each of these optical fibers has a cross-sectional structure in which a plurality of glass annular regions having different refractive indexes are formed around a center core having a certain refractive index distribution.
Such an optical fiber is generally manufactured as follows.
[0004]
First, a porous base material, which is an aggregate of glass fine particles, is manufactured by, for example, a VAD (Vapour-phase Axial Deposition) method. Next, this porous base material is heated in a vitrification furnace, dehydrated and vitrified to obtain a transparent intermediate base material. Next, the intermediate base material is stretched using a combustion flame, a plasma flame, or an electric furnace to form a glass rod having a desired diameter.
[0005]
The glass rod itself is a united rod of the precursor of the center core in relation to the optical fiber to be manufactured, and is usually called a core target. For the glass rod (core target) thus manufactured, for example, an OVD (Outside Vapor Deposition) method is applied to manufacture a target optical fiber preform.
[0006]
That is, first, glass fine particles are deposited on the outer peripheral surface of the glass rod to form a porous deposited layer having a desired thickness.
Here, FIGS. 7 and 8 show an example of an apparatus used when performing the above-described OVD method. FIG. 7 is a schematic diagram when viewed from the top, and FIG. 8 is a schematic diagram when viewed from the side.
[0007]
The apparatus 10 includes a support member 12 and a burner 13 in a chamber 11, and a glass chuck (core target) 15 described above is held on a rotary chuck 14 provided on the support member 12. Then, an oxyhydrogen flame containing a raw material to be glass fine particles is blown from the burner 13 to the outer peripheral surface of the glass rod 15 to deposit the glass fine particles on the outer peripheral surface of the glass rod.
[0008]
At this time, the glass rod 15 is axially rotated by the rotary chuck 14, and traverses in the longitudinal direction by the action of the drive unit 16 to which the support member 12 is attached.
Therefore, the deposited layer 17 of fine glass particles formed on the outer peripheral surface of the glass rod 15 is porous as a whole and has a uniform thickness.
[0009]
Next, the obtained porous body is once subjected to a heat treatment, so that the above-mentioned porous deposition layer 17 is made into a transparent glass, and as a whole a new glass rod is formed.
Next, the glass rod is set in the OVD apparatus 10 again, and another kind of glass fine particles is deposited on the outer peripheral surface to form a porous deposited layer.
[0010]
Again, heat treatment is performed to make the above porous deposition layer transparent vitrified.
According to the refractive index distribution profile to be formed, the operation of forming the porous deposition layer of glass fine particles by the above-described OVD method and vitrifying the porous deposition layer by heat treatment is repeated to obtain the desired optical fiber base. The material is manufactured.
[0011]
Therefore, the manufactured optical fiber preform has a cross-sectional structure in which a plurality of annular regions having different refractive indexes are formed on the outer periphery of the center core by the OVD method.
[0012]
The refractive index of each annular region depends on the type and concentration of the dopant contained in the glass particles deposited by the OVD method. For example, when forming a ring region having a high refractive index, it is necessary to deposit glass fine particles containing a dopant for raising the refractive index.
The target optical fiber is manufactured by drawing the optical fiber preform manufactured as described above to a predetermined wire diameter.
[0013]
Therefore, in order to manufacture an optical fiber preform capable of drawing an optical fiber having a desired refractive index distribution profile, that is, an optical fiber having desired fiber characteristics, it is necessary to accurately measure the refractive index distribution of the optical fiber preform. is necessary. For that purpose, it is necessary to control the production conditions of the optical fiber preform and the production conditions of the porous preform which is the starting preform.
[0014]
For example, as shown in FIG. 5, an optical fiber having a depressed layer having a lower refractive index than the center core and a segment layer having a higher refractive index than the depressed layer on the outer periphery of the center core having a high refractive index. When manufacturing an optical fiber preform for use, the following is important.
[0015]
In manufacturing the optical fiber preform, first, a center core is manufactured by a VAD method. Next, a deposited layer of glass fine particles (SiO ₂ ) containing fluorine (F), which is a dopant for lowering the refractive index, is formed on the outer peripheral surface of the center core by an OVD method. A deposited layer of glass particles (SiO ₂ ) containing, for example, GeO ₂ , which is a dopant for increasing the refractive index, is formed on the outer peripheral surface of the depressed layer by the OVD method. After forming a deposition layer of glass fine particles (SiO ₂ ) containing no dopant on the outer peripheral surface of the segment layer by the OVD method, it is formed into a transparent glass to form a clad.
[0016]
In this case, in the above-described series of steps, by adjusting the doping amount of F or GeO ₂ , the refractive index of each annular region, in particular, the depressed layer or the segment layer is accurately controlled, and the profile of the design purpose is adjusted. It is formed.
[0017]
[Problems to be solved by the invention]
However, in the above-described optical fiber preform manufacturing process, spherical bubbles may be generated near the interface between the depressed layer and the segment layer or near the interface between the segment layer and the clad when the deposited layer is made vitrified.
[0018]
This foaming phenomenon is a phenomenon based on the vaporization of GeO ₂ , which is both a dopant and a volatile chemical species. That is, GeO ₂ dissolved in the glass fine particles has the following equilibrium relationship.
[0019]
GeO ₂ {Ge (g)} + GeO (g) ↑ + (GeO) _2.3 (g) ↑
+ Ge ₂ O (g) {+ O ₂ (g)}
When the temperature rises to 1250 ° C. or higher, the equilibrium shifts to the right, and the vaporization of GeO ₂ dissolved in the glass microparticles proceeds, leaving traces of the bubbles as spherical bubbles. This foaming phenomenon is more likely to occur as the GeO ₂ concentration at the interface between the layers increases.
[0020]
Since such a foaming phenomenon causes the manufactured optical fiber preform to be defective, the optical fiber preform needs to be manufactured so as not to cause the foaming phenomenon.
An object of the present invention is to provide an optical fiber preform manufacturing method for manufacturing an optical fiber preform while preventing the occurrence of the above-described foaming phenomenon.
[0021]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a step of forming a porous deposition layer made of glass fine particles containing a dopant that increases the refractive index on the outer peripheral surface of a glass rod including a core glass rod or a center core, Performing a heat treatment to form a toroidal core by vitrifying the porous deposition layer to form a toroidal core.
The relative refractive index difference at a point 0.1 mm outward from the interface between the glass rod and the annular core is set to a value larger than 0% and smaller than 0.009% with respect to pure silica. (Hereinafter, referred to as manufacturing method A).
[0022]
In this case, it is preferable that the method is a method for manufacturing an optical fiber preform including a step of forming an initial deposited layer consisting of pure silica fine particles only on the outer peripheral surface of the glass rod before forming the porous deposited layer.
[0023]
Further, in the present invention, a step of forming a first porous deposition layer composed of pure silica fine particles only on the outer peripheral surface of a core glass rod or a glass rod including a center core; Forming a second porous deposited layer composed of glass fine particles containing a dopant for increasing the refractive index on the outer peripheral surface of the porous deposited layer, and performing a heat treatment to form the first porous deposited layer and the second porous deposited layer; And a step of vitrifying the porous deposited layer, the method comprising the steps of:
With respect to said first porous deposited layer, the method for manufacturing an optical fiber preform thickness after vitrification is characterized in that so as to be above 0.10 mm (hereinafter, referred to as the production method B ₁₎ which is provided You.
[0024]
Further, in the present invention, a step of forming a first porous deposition layer composed of pure silica fine particles only on an outer peripheral surface of a core glass rod or a glass rod including a center core; Forming a second porous deposited layer composed of glass fine particles containing a dopant for increasing the refractive index on the outer peripheral surface of the porous deposited layer, and performing a heat treatment to form the first porous deposited layer and the second porous deposited layer; And a step of vitrifying the porous deposited layer, the method comprising the steps of:
The density of the first porous deposition layer is set higher than the density of the second porous deposition layer. Specifically, the density of the first porous deposition layer is 0.3 to 1.0 g. / method for manufacturing an optical fiber preform, characterized in that cm is ³ (hereinafter, referred to as the production method B ₂₎ is provided.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
In any of the methods of the present invention, the optical fiber preform is manufactured by applying the OVD method.
[0026]
In the manufacturing method A, first, as shown in FIG. 1, glass fine particles containing a dopant for increasing the refractive index are deposited on the outer peripheral surface 1a of the glass rod 1 by the OVD method to form the porous deposited layer 2. You. Note that GeO ₂ is preferable as the above-mentioned dopant.
[0027]
Then, heat treatment is performed to turn the porous deposition layer 2 into a transparent vitrified layer, thereby forming an annular core 2 ′ having a high refractive index as shown in FIG. Since the porous deposited layer 2 shrinks during the process of vitrification, the thickness (t ₁ ′) of the annular core 2 ′ becomes smaller than the thickness (t ₁ ).
[0028]
In the case of the annular core 2 ′ formed by the manufacturing method A, the relative refractive index difference (Δ) at a position 0.1 mm away from the outer peripheral surface 1 a of the glass rod 1 is larger than 0% and 0.009%. It is characterized in that it has a smaller value.
[0029]
To form such a relative refractive index difference in an annular core 2 ', the outer peripheral surface 1a of the glass rod 1, once certain thickness a porous initial deposition layer 2 ₀ made of pure silica fine particles (t ₀ formed in), to form a porous deposited layer 2 ₁ described above on the outer peripheral surface of the initial deposit layer 2 _0, heat treating the entire thereafter.
[0030]
In this way, the initial deposition layer 2 ₀ pure silica, when the transparent vitrification of the porous deposited layer 2 acts as a barrier to GeO ₂ coming to example thermal diffusion, GeO ₂ concentration at the interface of the first glass rod Is prevented from increasing, and the occurrence of a foaming phenomenon is suppressed.
[0031]
Any production method B _1, as shown in FIG. 1, in OVD method, the outer peripheral surface 1a of the glass rod 1, to form a first porous deposited layer 2 ₀ made of only pure silica fine particles, subsequently, the outer periphery thereof to form a porous deposited layer 2 ₁ glass particles containing a dopant to increase the refractive index to the surface, and subjected to heat treatment to the whole, to convert an annular core 2 'of high refractive index.
Also in this case, the pure silica layer described above functions as a barrier against the diffusion of GeO _{2 in} the annular core into the glass rod 1.
[0032]
The first porous deposited layer 2 ₀ thickness is thus varied by the level of the GeO ₂ concentration of the second porous deposited layer 2 in _1, the thickness after the transparent vitrification than 0.10mm It is necessary to make the thickness such that
If the thickness is smaller than this, the function of the pure silica layer as a barrier is reduced, and a foaming phenomenon occurs at the interface with the glass rod at the time of transparent vitrification.
[0033]
In the production method B _2, in the manufacturing method B _1, higher than the density of the first porous sedimentary layer 2 ₀ second density of the porous deposited layer 2 _1. Again as in the case of production method B _1, barrier function against the diffusion of GeO ₂ in the second porous sedimentary layer is exhibited during vitrification, occurrence of foaming phenomenon at the interface between the glass rod is suppressed You.
[0034]
Specifically, the density of the first porous deposited layer _{2 0} is required to be set to 0.3 to 1.0 g / cm ^3. If it is lower than 0.3 g / cm ³ , the function as a barrier is deteriorated. On the other hand, if it is higher than 1.0 g / cm ³ , cracks are formed at the time of forming the porous deposition layer and the process cannot proceed to the subsequent process. is there.
[0035]
【Example】
Example A glass rod (1) (length 200 mm, diameter 16 mm) containing a center core was prepared. This glass rod is set in the OVD apparatus shown in FIGS. 7 and 8, and a pure silica fine particle layer and a porous deposition layer made of glass fine particles containing a dopant such as GeO ₂ are formed by the OVD method, and then the glass is transparently vitrified. A new glass rod (2) was produced.
[0036]
The supply condition of the raw material gas to the _{burner, SiCl 4: 1.4L / min,} GeCl 4: 0.1~0.3L / min, H 2: 20~30L / min, O 2: 10~50L / min, Ar: 12 L / min.
[0037]
The burner traverse speed was 500 mm / min, and the synthesis time of the glass particles was about 80 minutes.
With respect to the obtained glass rod (2), the relative refractive index difference at a position 0.1 mm outside the interface with the glass rod (1) was measured, and the presence or absence of foaming was examined.
The above results are collectively shown in Table 1.
[0038]
[Table 1]

[0039]
The following is clear from Table 1.
As is clear from Samples 1 to 4, when the relative refractive index difference at a position separated by 0.1 mm from the interface with the glass rod (1) is larger than 0% and smaller than 0.009%, foaming does not occur. .
[0040]
Further, with respect to Samples 5 to 9, when the thickness of the initially deposited layer is set so that the thickness of the pure silica layer after sintering becomes 0.1 mm or more, foaming does not occur.
[0041]
In addition, when the density of the initial deposited layer is 0.23 g / cm ^3, which is lower than the density of the deposited layer of glass fine particles containing a dopant, foaming occurs (Sample 10). However, when the density of the initial deposited layer was 0.31 g / cm ^3, which was higher than the density of the deposited layer of glass fine particles containing the dopant, no foaming occurred (Sample 11).
[0042]
In the case of Sample 12, in which the density of the initial deposited layer is 1.04 g / cm ^{3, which is} considerably higher than the density of the deposited layer of glass fine particles containing a dopant, cracks occur during synthesis and the process can proceed to the subsequent steps. Did not.
[0043]
【The invention's effect】
As is apparent from the above description, according to the method of the present invention, when a porous deposition layer containing a dopant for increasing the refractive index is formed, and when it is formed into a transparent vitrified layer, a foaming phenomenon occurs at the interface with the glass rod. An optical fiber preform in which is suppressed can be manufactured.
[0044]
This is an effect brought about by forming an initial deposited layer of pure silica on the outer peripheral surface of the glass rod prior to the formation of the porous deposited layer, thereby serving as a barrier against thermal diffusion of the dopant during transparent vitrification. is there.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a state in which an initial deposited layer of pure silica fine particles and a porous deposited layer of glass fine particles containing GeO ₂ are formed on the outer peripheral surface of a glass rod.
FIG. 2 is a cross-sectional view showing a state in which the porous body of FIG.
FIG. 3 is a refractive index distribution profile diagram.
FIG. 4 is another refractive index distribution profile diagram.
FIG. 5 is another refractive index distribution profile diagram.
FIG. 6 is another refractive index distribution profile diagram.
FIG. 7 is a schematic plan view of the OVD device.
FIG. 8 is a schematic side view of the OVD apparatus.
[Explanation of symbols]
Porous glass-particle-deposited layer containing first glass rod 1a glass rod outer peripheral surface 2 porous 2 ₀ porous pure silica deposited layer 2 ₁ dopant

Claims (6)

A step of forming a porous deposited layer composed of glass fine particles containing a dopant for increasing the refractive index on the outer peripheral surface of the glass rod including the core glass rod or the center core, and performing heat treatment to make the porous deposited layer transparent vitrified. Forming an annular core, and a method for producing an optical fiber preform having a step of:
The relative refractive index difference at a point 0.1 mm outward from the interface between the glass rod and the annular core is set to a value larger than 0% and smaller than 0.009% with respect to pure silica. Of producing an optical fiber preform. 2. The method of manufacturing an optical fiber preform according to claim 1, further comprising the step of forming an initial deposited layer consisting of pure silica fine particles only on the outer peripheral surface of the glass rod before forming the porous deposited layer. _{3. The method according} to claim 1, wherein the dopant is GeO2. Forming a first porous deposition layer composed of pure silica fine particles only on the outer peripheral surface of the core glass rod or the glass rod including the center core; and, following the step, the outer peripheral surface of the first porous deposition layer Forming a second porous deposition layer made of glass fine particles containing a dopant that raises the refractive index, and performing a heat treatment to convert the first porous deposition layer and the second porous deposition layer to transparent glass. And a method of manufacturing an optical fiber preform including the step of
A method for producing an optical fiber preform, wherein the thickness of the first porous deposition layer is such that the thickness after vitrification is 0.10 mm or more. Forming a first porous deposition layer composed of pure silica fine particles only on the outer peripheral surface of the core glass rod or the glass rod including the center core; and, following the step, the outer peripheral surface of the first porous deposition layer Forming a second porous deposition layer made of glass fine particles containing a dopant that raises the refractive index, and performing a heat treatment to convert the first porous deposition layer and the second porous deposition layer to transparent glass. And a method of manufacturing an optical fiber preform including the step of
A method of manufacturing an optical fiber preform, wherein the density of the first porous deposition layer is higher than the density of the second porous deposition layer. Method for manufacturing an optical fiber preform according to claim 5 density of the first porous deposited layer is 0.3 to 1.0 g / cm ^3.

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