JP2005298287A - Method of manufacturing glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently obtain an optical fiber having a transmission loss reduced by suppressing the diffusion of impurities to a glass preform to become the optical fiber to the utmost. <P>SOLUTION: A porous glass preform 4a formed on a dummy rod 2 is heated to vitrified. The OH group contained in a layer of the depth of 0.5-3 mm from the surface of the dummy rod 2 is controlled to ≤150 ppm. A transition metal element contained in a layer of the depth of 0.5-3 mm from the surface of the dummy rod 2 is controlled to be ≤30 ppm. The surface of the dummy rode 2 is previously cleaned with a dry process heating source. The vitrification of the porous glass preform 4a is carried out so that the dummy rod 2 side comes lastly. In the vitrification of the porous glass preform 4a, an atmospheric gas is supplied from a side far from the dummy rod 2 and exhausted from a side near to the dummy rod 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a glass base material in which a combustion gas and a glass raw material gas are sprayed onto a dummy rod to deposit glass fine particles, and then heated to vitrify.

  In general, an optical fiber composed of a core and a clad is manufactured by heating a porous glass layer for optical fiber to make it transparent to form a glass base material, and then drawing. Examples of a method for producing the porous glass layer include a VAD method (Vapor phase Axial Deposition). In this VAD method, combustion gas and glass raw material gas are blown out from a burner, the glass raw material is hydrolyzed in an oxyhydrogen flame generated by combustion of the combustion gas, and glass particles are deposited on the dummy rod. .

Here, in the process of heating and sintering the porous glass base material and vitrifying it, there is a technology for suppressing contamination of impurities from the jig by using platinum as the jig for hanging the porous glass preform. It is known (see, for example, Patent Document 1).
In addition, a technique is known in which the use of a glass rod having the same composition or the same linear expansion coefficient as the glass fine particles to be deposited suppresses the dropout of the core portion and the occurrence of cracks during the sintering of the porous glass preform ( For example, see Patent Document 2).

JP-A-6-298540 JP 2000-7380 A

Incidentally, in order to manufacture an optical fiber with low transmission loss, it is important to increase the purity of the core through which light propagates. In particular, in recent years, it has been desired to suppress transmission loss at a wavelength of 1.38 μm, which is greatly affected by transmission loss due to OH groups.
Here, since the dummy rod used for manufacturing the glass base material is not a portion that becomes an optical fiber, for example, a low-cost material such as natural quartz is used to reduce the production cost.
However, when a low cost material is used for the dummy rod, impurities such as heavy metals and compounds containing OH groups that diffuse the absorption loss of quartz diffuse into the glass base material when the porous glass layer is vitrified. However, when an optical fiber is used, the core transmission loss in the vicinity of the dummy rod becomes high, so that it cannot be used as a product, resulting in a decrease in yield.

  An object of the present invention is to provide a glass base material manufacturing method capable of efficiently obtaining an optical fiber with reduced transmission loss by suppressing the diffusion of impurities into the glass base material to be an optical fiber. .

In order to achieve the above object, a method for producing a glass base material according to the present invention is a method for forming a glass base material by forming a porous glass layer on a dummy rod and heating the porous glass layer to perform a transparent treatment. A manufacturing method comprising:
The layer at a depth of 0.5 to 3 mm from the surface of the dummy rod is characterized in that the OH group is 150 ppm or less and the total amount of additives is 0.1 wt% or less.

  In addition, the manufacturing method according to the present invention includes a glass base material in which a porous glass layer is formed on a starting rod in which a dummy rod is connected to a tip of a glass rod, and the porous glass layer is heated to be transparentized. The layer at a depth of 0.5 to 3 mm from the surface of the dummy rod is characterized in that OH groups are 150 ppm or less.

In the manufacturing method according to the present invention, it is preferable that the transition metal element contained in a layer having a depth of 0.5 to 3 mm from the surface of the dummy rod is 30 ppm or less.
In the manufacturing method according to the present invention, it is preferable to reduce impurities by heating the surface of the dummy rod in advance using an anhydrous process heat source.
In the manufacturing method according to the present invention, the dummy rod is preferably made of synthetic quartz.

In the manufacturing method according to the present invention, it is preferable that the transparent glass layer is subjected to the transparent treatment so that the dummy rod side comes last.
In the manufacturing method according to the present invention, it is preferable that the atmospheric gas is supplied from the far side of the dummy rod and exhausted from the side close to the dummy rod in the transparent treatment of the porous glass layer.

  According to the method for producing a glass base material of the present invention, the porous glass formed in the dummy rod is obtained by setting the OH group contained in the portion having a depth of 0.5 to 3 mm from the surface of the dummy rod to 150 ppm or less. When a glass base material is manufactured by heating a layer and performing a transparent treatment, diffusion of OH groups from the dummy rod to the glass base material can be suppressed as much as possible. That is, it is possible to manufacture a glass base material capable of efficiently obtaining an optical fiber with reduced transmission loss when drawn into an optical fiber.

Embodiments of a manufacturing method according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an embodiment of a manufacturing method according to the present invention. In this embodiment, a VAD method will be described as an example of a method for forming a porous glass layer.
In order to manufacture a porous glass layer by the VAD method, as shown in the figure, the dummy rod 2 is connected to the lower end of the seed rod 3 in the container 1 via the connecting member 3a and arranged vertically. Then, the dummy rod 2 is lifted while rotating the shaft, glass fine particles are deposited on the lower end portion of the dummy rod 2 to form the porous glass layer 4, and the porous glass base material 4a having the porous glass layer 4 is formed. Form.

When the porous glass layer 4 is formed on the dummy rod 2, the core burner 5 and the cladding burner 6 are fixedly disposed to the dummy rod 2 from below to obliquely upward, and the core burner 5 and the cladding burner 6 are arranged. Then, glass fine particles are sprayed and deposited on the dummy rod 2 to simultaneously synthesize a portion to be the core of the optical fiber and a portion to be a part of the clad (first clad).
The core burner 5 is supplied with hydrogen (H ₂ ) and oxygen (O ₂ ) as combustion gases together with silicon tetrachloride (SiCl ₄ ) and germanium tetrachloride (GeCl ₄ ) as glass raw material gases. The cladding burner 6 is supplied with hydrogen (H ₂ ) and oxygen (O ₂ ) as combustion gases together with silicon tetrachloride (SiCl ₄ ) as a glass raw material gas.
The core burner 5 and the cladding burner 6 blow out the combustion gas and the glass raw material gas from the tip of each burner, and hydrolyze the glass raw material in the oxyhydrogen flame generated by the combustion of the combustion gas. Then, glass fine particles are adhered and deposited on the dummy rod 2.

The dummy rod 2 is a quartz rod having a OH group content (weight concentration) of 150 ppm or less in a layer at a depth of 0.5 to 3 mm from the surface (hereinafter, this portion is referred to as a “surface layer portion”). Is used. As such a dummy rod 2, natural quartz or synthetic quartz may be used, and a commercially available product may be used.
By making the OH group contained in the surface layer portion of the dummy rod 2 150 ppm or less, the porous glass base material 4a is heated and transparentized to produce a glass base material (described later). Can suppress the diffusion of OH groups from glass to glass base as much as possible

  In addition, about the part of the depth below 0.5 mm from the surface, content of OH group is not specifically limited. This is because a portion having a depth of less than 0.5 mm from the surface is a portion where OH groups easily enter from the outside air, but can be easily removed by means such as surface polishing described later. Further, the OH group content in the portion having a depth of 3 mm or more from the surface is not particularly limited, and may be the same as or different from the OH group content in the surface layer portion of the dummy rod 2.

The OH group content in the surface layer portion of the dummy rod 2 is preferably 0 to 30 ppm, more preferably 0 to 10 ppm. The OH group content of the dummy rod 2 can be obtained, for example, by measuring the infrared absorption spectrum of the dummy rod 2.
Thus, by using the dummy rod 2 with a low OH group content, it is possible to prevent OH groups from being mixed into the glass base material from the dummy rod 2 when performing a transparentization process to be described later.

Moreover, the total amount of the additive contained in the surface layer portion of the dummy rod 2 is 0.1% by weight or less. Of course, it is not limited to a surface layer part, The total amount of the additive contained in the whole dummy rod 2 may be 0.1 weight% or less.
In the present invention, regardless of whether or not the “additive” is intentionally added, when the dummy rod 2 is synthetic quartz, for example, during the synthesis of the dummy rod 2 such as fluorine, chlorine, or nitrogen In the case where the dummy rod 2 is natural quartz, for example, impurities or the like naturally contained in quartz. These substances are substances that are considered to have little influence on transmission loss, and the additive does not include causative substances that increase transmission loss such as “transition metal elements”.

Moreover, it is preferable that the transition metal element contained in the surface layer part of the dummy rod 2 is 30 ppm or less, and it is more preferable that it is 0-5 ppm. By setting the transition metal element contained in the surface layer portion of the dummy rod 2 to 30 ppm or less, the diffusion of the transition metal element from the dummy rod 2 can be suppressed as much as possible, and thereby an optical fiber with further reduced transmission loss can be efficiently used. A glass base material that can be obtained well can be manufactured.
Further, the dummy rod 2 preferably has a light metal element contained in the surface layer portion of 50 ppm or less, and more preferably 20 ppm or less.
In addition, about content of the light metal element and transition metal element which are contained in the dummy rod 2, it can measure by conducting elemental analysis of the dummy rod 2, for example.

The dummy rod 2 is preferably cleaned by polishing its surface in advance. This surface polishing method is shown in FIG. As shown in FIG. 2, both ends of the dummy material 2a serving as the dummy rod 2 (FIG. 1) are held by the pair of chucks 11a, and the chuck 11a is supported by the pair of support portions 11 so that the dummy material 2a. Is rotated about the axis, and a flame is radiated from the burner 12 installed below the axis toward the dummy material 2a. And the dummy material 2a is flame-polished by the flame from the burner 12, moving the burner 12 along a longitudinal direction.
By performing the flame polishing of the dummy material 2a in this manner, impurities on the surface of the dummy material 2a (including a portion of about 0.5 mm from the surface) can be reduced and cleaning can be performed. The dummy material 2a thus flame-polished can be cut into an appropriate length and used as the dummy rod 2.

  As the burner 12 which is a heat source used for this flame polishing, it is preferable to use an anhydrous process heat source such as a laser or a plasma flame burner. When such a heat source is used, air is not mixed into the flame, and therefore, generation of OH groups by flame polishing is unlikely to occur on the surface of the dummy material 2a. Therefore, impurities such as transition metal elements can be removed, OH groups can be prevented from being generated in the dummy material 2a during flame polishing, and the dummy material 2a can be maintained with high purity.

As described above, when the glass fine particles are deposited on the dummy rod 2 to form the porous glass base material 4a, the porous glass base material 4a is heated and subjected to a transparent treatment to form a glass base material. FIG. 3 shows a method of forming the glass base material 4b from the porous glass base material 4a.
As shown in FIG. 3, first, the dummy rod 2 is connected to the connecting rod 23, and the porous glass base material 4 a is suspended in the heating furnace 22 using the resistance heater 21. For example, an atmospheric gas containing a dehydrating gas containing chlorine is supplied into the heating furnace 22.
In this atmospheric gas, the porous glass base material 4a is heated at about 1200 ° C. while slowly moving downward to dehydrate the porous glass base material 4a and remove OH groups. Thereafter, the porous glass base material 4a is heated at about 1550 ° C., and the porous glass base material 4a is subjected to a transparent treatment so that a glass base material 4b having a portion that becomes the core of the optical fiber and a portion that becomes the first cladding; To do.

  Here, when the transparent treatment is performed by heating as described above, it is desirable that the dummy rod 2 side be heated last. That is, it is desirable that heating by the resistance heater 21 is performed from the lower end side of the porous glass base material 4b toward the upper end side (that is, from the side opposite to the dummy rod 2 to the dummy rod 2 side). When the transparent treatment is performed in this direction, the glass fine particles in the vicinity of the dummy rod 2 are heated at the end of the transparent treatment of the porous glass base material 4b. The diffusion of impurities can be suppressed. Further, even when impurities slightly contained in the dummy rod 2 are mixed into the porous glass base material 4a (particularly the core portion), it is possible to prevent the impurities from diffusing toward the lower end side of the glass base material 4b.

  The atmospheric gas is preferably supplied from below the heating furnace 22 (that is, the side far from the dummy rod 2) and exhausted from above the heating furnace 22 (that is, the side close to the dummy rod 2). By supplying the atmospheric gas in such a direction, when the porous glass base material 4a is heated, OH groups can be prevented from diffusing into the glass base material 4b.

  The transparent glass base material 4b is further stretched to form an elongated glass rod (not shown). The stretched glass rod is cut into several glass rods, and a porous glass layer is further deposited on the outer periphery of each glass rod to provide a clad having a thickness necessary for satisfying the characteristics as an optical fiber (second clad). The part which becomes becomes. This process is called jacketing.

  FIG. 4A shows an example of a jacketing process. As shown in FIG. 4A, a dummy rod 2b is connected to the tip of the glass rod 4c manufactured from the glass base material 4b (FIG. 3), and another dummy rod 2c is connected to the other end of the glass rod 4c. A starting rod 42 is prepared, and this starting rod 42 is connected to the connecting rod 25 and arranged vertically. The burner 24 is installed below the reaction vessel 26 and obliquely upward, and the porous glass layer 41 is gradually deposited from the upper end side of the starting rod 42 by the burner 24. In this way, the porous glass base material 4d having a portion to be the second cladding is formed.

  As a method of synthesizing the portion to be the second cladding, the multilayer attaching method shown in FIG. 5 may be used. In the method shown in FIG. 5, the burner 24 is arranged substantially perpendicular to the longitudinal direction of the starting rod 42. The burner 24 is relatively reciprocated in the longitudinal direction of the starting rod 42, the porous glass layer 41 is adhered to the outer periphery of the starting rod 42 in multiple layers, and the porous glass base material 4d having a portion that becomes the second cladding is formed. Form.

  The dummy rods 2b and 2c used in the method shown in FIG. 4 and FIG. 5 have a depth of 0.5 to 3 mm from the surface of the dummy rods 2b and 2c, similarly to the dummy rod 2a (FIG. 1) described above. The layer of this portion (surface layer portion) has an OH group of 150 ppm or less. By setting the OH group contained in the surface layer portion of the dummy rods 2b and 2c to 150 ppm or less, the compound having the OH group from the dummy rods 2b and 2c is converted into the glass base material when the porous glass base material 4d described later is sintered. Can be prevented from diffusing.

After performing the jacketing as described above, as shown in FIG. 6 again, the porous glass base material 4d having a portion to become the second cladding in the heating furnace 22 is heated and transparentized to obtain a light A glass base material 4e having a core portion and a clad portion when a fiber is formed.
In the case of this clearing treatment, it is preferable to heat the porous glass base material 4d from the lower end side toward the upper end side by the resistance heater 21. Further, it is desirable that the atmospheric gas is supplied from below the heating furnace 22 and exhausted from above the heating furnace 22.
Furthermore, an optical fiber having a core and a clad can be manufactured by stretching and stretching the glass base material 4e thus transparentized and drawing it in a drawing furnace.

  As described above, according to the method for manufacturing a glass base material according to the present embodiment, the OH group contained in the surface layer portion of the dummy rods 2, 2b, 2c is 150 ppm or less, so the dummy rods 2, 2b, When the glass base material 4b is manufactured by forming a porous glass base material using 2c, diffusion of OH groups from the dummy rods 2, 2b, 2c to the glass base material can be suppressed as much as possible. That is, when a glass base material is drawn into an optical fiber, a glass base material capable of efficiently obtaining an optical fiber with reduced transmission loss can be manufactured.

The dummy rod 2 (FIG. 1) may be used by removing OH groups and transition metal elements on the surface of a glass rod made of natural quartz, for example, but a part of a glass base material that is not used as an optical fiber. May be reused as the dummy rod 2 at the time of manufacturing a new glass base material.
As a part of the glass base material that can be reused as the dummy rod 2, for example, an upper end portion 16 of the porous glass base material 4d surrounded by a dotted line in FIG. Available. As shown in the enlarged view of FIG. 4B, the upper end portion 16 of the porous glass base material 4d is connected to the upper end portion of the porous glass layer 41 deposited on the outer periphery of the dummy rod 2 and the dummy rod 2b. It is a part which is comprised from the upper end part of the glass rod 4c which is, and is not normally used as an optical fiber product. After the porous glass base material 4d is stretched, the elongated upper end portion 16a as shown in FIG. 4C can be cut out from the glass base material and further sized so that it can be used as the dummy rod 2.

  Synthetic quartz synthesized as a glass base material has a high purity, and the content (weight concentration) of OH groups and transition metal elements contained is extremely low. By using the end of the material, it is possible to suppress the diffusion of impurities into the newly manufactured glass base material, and it is possible to reuse the end portion of the glass base material that has been disposed as an unnecessary part. . This is advantageous not only in terms of quality improvement but also economically.

  Moreover, in the said embodiment, although the part (FIG. 1) which synthesize | combines simultaneously the part which becomes a core of a fiber, and a part of the part which becomes a clad was demonstrated (FIG. 1), manufacture of this invention was demonstrated. The method is not limited to this. That is, the production method of the present invention is a form in which after forming a porous glass base material having only a core portion, the substrate is stretched by heating / transparency treatment, and the cladding portion is jacketed at a time. May be.

Glass base materials were manufactured under the conditions of Examples 1 and 2 and Comparative Examples below, and optical losses were drawn from the respective glass base materials to measure transmission loss.
(Example 1)
A quartz rod (made by GE) with a light metal element content of 15 ppm, a transition metal element of 2.8 ppm, and an OH group content of 10 ppm is used as a dummy rod. did. The total amount of additive contained in the dummy rod used in Example 1 was 0.1% by weight or less.
On this dummy rod, glass fine particles of the core and the clad were simultaneously deposited by the VAD method to form a porous glass base material. Thereafter, dehydration was performed at about 1200 ° C. in the heating furnace, OH groups were removed, and heating was performed at about 1550 ° C. to perform a transparent treatment. The glass base material obtained in this way was stretched and jacketed, and a portion to be a clad was synthesized on the outer periphery thereof, and a transparent treatment was again performed in a heating furnace.

(Example 2)
As the dummy rod, an unnecessary portion (portion surrounded by a dotted line shown in FIG. 4A) of the upper end portion of the glass base material formed into a rod shape was reused. This dummy rod has a synthetic quartz formed on the surface of a commercially available quartz rod, and the content of impurities on the surface portion was 0 ppm for light metal elements, 0.1 ppm or less for transition metal elements, and 1 ppm or less for OH groups. . This dummy rod was previously cleaned by flame polishing with a laser. The total amount of additive contained in the dummy rod used in Example 2 was 0.1% by weight or less.
On this dummy rod, a glass particle deposit in the core and clad is formed at the same time by the VAD method, then dehydrated at about 1200 ° C in a heating furnace, OH group removed, and transparentized at about 1550 ° C. Processed. The glass base material obtained in this way was stretched, and a portion to be a clad was synthesized on the outer periphery thereof, and a transparent treatment was again performed in a heating furnace.

(Comparative Example 1)
A commercially available quartz rod having an impurity content of 40 ppm and a transition metal element of 40 ppm and OH group of 200 ppm was used as a dummy rod, and this dummy rod was previously cleaned by flame polishing with an oxyhydrogen flame. On this dummy rod, a glass particle deposit in the core and clad is formed at the same time by the VAD method, then dehydrated at about 1200 ° C in a heating furnace, OH group removed, and transparentized at about 1550 ° C. To process. The glass base material obtained in this manner was stretched, and a portion to be a clad was synthesized on the outer periphery thereof, and a transparent treatment was again performed in a heating furnace.

  The glass base materials obtained in Example 1, Example 2, and Comparative Example 1 were each drawn to form an optical fiber, and the transmission loss of the optical fiber was measured with a loss wavelength characteristic measuring device (manufactured by PK). . The measurement wavelength of the transmission loss was 1.30 μm, which is easily affected by the transmission loss due to the inclusion of the transition metal element, and 1.38 μm, which is easily affected by the transmission loss due to the inclusion of the OH group. The results are shown in the graphs of FIGS. 7 to 9, the vertical axis represents the measured transmission loss amount, and the horizontal axis represents the fiber length based on the end on the dummy rod side.

(Result of Example 1)
As shown in FIGS. 7A and 7B, in Example 1, at any wavelength, a low transmission loss (about 0.35 dB / at a wavelength of 1.30 μm) from a location about 300 km away from the dummy rod. km or less, and about 0.30 dB / km or less at a wavelength of 1.38 μm. The same applies to Example 2 and Comparative Example 1.).
(Results of Example 2)
As shown in FIGS. 8A and 8B, in Example 2, an optical fiber having a low transmission loss was obtained from a position about 70 km away from the dummy rod at any wavelength.
(Result of comparative example)
As shown in FIGS. 9A and 9B, in the comparative example, an optical fiber having a low transmission loss was not obtained at any wavelength unless the distance from the dummy rod was about 450 km.

  Thus, in the comparative example, transmission loss is high in a considerable portion of the drawn optical fiber, and cannot be used as a product, and the yield decreases. It was found that the transmission loss was reduced as much as possible and the yield reduction could be suppressed.

It is a schematic block diagram explaining the manufacturing method of the glass base material of this invention. It is the schematic side view and sectional drawing explaining the flame grinding | polishing to a dummy rod. It is a schematic block diagram explaining the method to heat and clarify a porous glass layer and to manufacture a glass base material. It is a schematic block diagram explaining the method of jacketing by VAD method. It is a schematic block diagram explaining the method of performing jacket attachment by the multilayer attachment method. It is a schematic block diagram explaining the method to heat and clarify a porous glass layer and to manufacture a glass base material. It is a graph explaining the result of Example 1 of the manufacturing method of a glass base material. It is a graph which shows the result of Example 2 of the manufacturing method of a glass base material. It is a graph which shows the result of the comparative example 1 of the manufacturing method of a glass base material.

Explanation of symbols

2, 2b, 2c Dummy rod 4, 41 Porous glass layer 4b Glass base material 4c Glass rod 42 Starting rod 12 Burner (anhydrous process heating source)

Claims (7)

A method for producing a glass base material, wherein a porous glass layer is formed on a dummy rod, and the porous glass layer is heated and subjected to a transparent treatment,
The glass base material, wherein the layer at a depth of 0.5 to 3 mm from the surface of the dummy rod has an OH group of 150 ppm or less and a total amount of additives of 0.1 wt% or less. Manufacturing method. Forming a porous glass layer on a starting rod in which a dummy rod is connected to the tip of the glass rod, and heating the porous glass layer to carry out a transparent treatment;
The method for producing a glass base material, wherein the layer at a depth of 0.5 to 3 mm from the surface of the dummy rod has an OH group of 150 ppm or less. The method for producing a glass base material according to claim 1 or 2, wherein a transition metal element contained in a layer having a depth of 0.5 to 3 mm from the surface of the dummy rod is 30 ppm or less. The method for producing a glass base material according to any one of claims 1 to 3, wherein impurities are reduced by heating the surface of the dummy rod in advance using an anhydrous process heat source. The method for producing a glass base material according to claim 1, wherein the dummy rod is made of synthetic quartz. The method for producing a glass base material according to any one of claims 1 to 3, wherein the transparent glass layer is transparentized so that the dummy rod side is heated last. 7. The method according to claim 1, wherein an atmosphere gas is supplied from a side far from the dummy rod and exhausted from a side near the dummy rod in the transparent treatment of the porous glass layer. The manufacturing method of the glass base material as described in 2.

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