JP2957171B1 - Optical fiber preform, optical fiber preform, and methods for producing them - Google Patents

Abstract

A porous optical fiber preform with reduced large pores in a glass fine powder deposit and an optical fiber preform with few air bubbles obtained therefrom are provided. SOLUTION: In an optical fiber porous preform in which glass fine powder is deposited around a center member, pores having a size of 10 μm or more in the deposit are 1% by volume or less with respect to all pores. In the method of manufacturing a porous optical fiber preform by depositing glass fine powder around the central member while rotating the central member, the peripheral speed of the deposited central member is 17 m / min or more during the deposition of the glass fine powder. A method for producing a porous optical fiber preform in which the number of rotations is controlled to be as follows.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous optical fiber preform, an optical fiber preform, and a method for producing the same.
In particular, the present invention relates to a porous optical fiber preform capable of reducing the number of bubbles in a sintered body obtained by melt-vitrifying a glass fine powder deposit, an optical fiber preform obtained therefrom, and a method for producing the same. .

[0002]

2. Description of the Related Art Conventionally, an optical fiber porous preform is manufactured by depositing a glass fine powder around a member of the optical fiber porous preform while rotating a member of the optical fiber porous preform, for example, by an external method. . In order to deposit the glass fine powder around the above-mentioned member, for example, the member is placed in a device called a chamber which surrounds both ends in the axial direction of the member, and a fuel gas is supplied from a flame burner located at the front of the chamber. Or raw material gas to generate fine glass powder around the member in the flame,
A mechanism is provided for depositing this gas and exhausting unreacted gas, reaction product gas, undeposited glass fine powder, and the like from an exhaust port (rear portion of the chamber) of the chamber opposite to the flame burner.

The porous optical fiber preform obtained by depositing the glass fine powder around the member as described above has excellent various quality characteristics. As described above, in recent years, the manufacturing technology of the optical fiber porous preform has made remarkable progress in quality.

[0004]

However, in the past, a sintered body (optical fiber preform) obtained by melt-vitrifying the above-mentioned porous optical fiber preform sometimes contained a bright spot. Bright spots remain even after the optical fiber conversion, which is a cause of loss in light transmission. The cause of such a bright spot is considered to be either foreign matter entering from the outside or bubbles contained therein. Therefore, the present invention further improves the conventional optical fiber porous preform, and can significantly reduce the number of bubbles in the optical fiber preform after melt vitrification. It is an object of the present invention to provide an optical fiber preform having almost no bright spots.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventors investigated the structure of glass deposits, and in particular, ascertained the pore distribution. The present inventors have found a causal relationship with bubbles in the condensed matter, and have completed the present invention.

That is, according to the invention of claim 1 of the present invention, in a porous optical fiber preform in which glass fine powder is deposited around a member, pores of 10 μm or more in the deposit correspond to all pores. It is an optical fiber porous preform having 1% by volume or less. As described above, in the glass fine powder deposit of the porous optical fiber preform, the pores of 10 μm or more account for 1% by volume with respect to all the pores.
Due to the following, the number of bubbles in the sintered body obtained by melt vitrification of the glass fine powder deposit can be significantly reduced.

Further, the invention according to claim 2 is an optical fiber preform obtained by fusing the above optical fiber porous preform. As described above, the porous optical fiber preform of the present invention has very few large pores of 10 μm or more as compared with the conventional one. Therefore, by using the optical fiber porous preform of the present invention, an optical fiber preform having a very small number of bubbles can be manufactured. As a result, the optical fiber manufactured from this optical fiber preform has very few bright spots and has excellent optical characteristics with little loss in light transmission.

According to a third aspect of the present invention, there is provided a method of manufacturing a porous optical fiber preform by depositing a glass fine powder around a member while rotating the member.
A method for producing a porous optical fiber preform, characterized in that pores of at least μm are controlled to 1% by volume or less of all pores. By controlling the pore distribution during the deposition of the fine glass powder, it is possible to obtain a porous optical fiber preform capable of reducing the number of bubbles in the sintered body after melt vitrification.

The invention according to claim 4 is an optical fiber porous mother in which the number of pores of 10 m or more in the deposit is controlled to 1% by volume or less of all the pores by controlling the number of rotations of the member. It is a method of manufacturing a material. As described above, the control of the pore distribution can be specifically performed by controlling the rotation speed of the member.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a porous optical fiber preform by depositing a glass fine powder around the member while rotating the member, wherein the glass fine powder is deposited during the deposition. This is a method for producing a porous optical fiber preform in which the rotational speed is controlled so that the peripheral speed of the member is 17 m / min or more. As described above, in particular, if the rotation speed of the rotating member is controlled so that the peripheral speed of the member is 17 m / min or more, pores of 10 μm or more in the sediment can be reliably reduced.

Further, the invention according to claim 6 is a method for producing an optical fiber preform, characterized in that the optical fiber porous preform produced by the above-mentioned production method of the present invention is produced by melt vitrification. . As described above, the porous optical fiber preform of the present invention has very few pores of 10 μm or more as compared with the conventional one. Therefore, by vitrifying using the porous optical fiber preform of the present invention, an optical fiber preform having a very small number of bubbles can be produced. As a result, the bright spots in the optical fiber preform are reduced, and the optical fiber manufactured from this optical fiber preform also has very few bright spots and excellent optical characteristics with little loss in light transmission. It becomes what has.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. FIG. 1 shows a state in which a soot 6 has been deposited on the target 1. In the porous optical fiber preform of the present invention, as shown in FIG. 1, a glass fine powder 6 is deposited around a member (hereinafter sometimes referred to as a “target”) 1.
The target 1 serves as an optical fiber core.
Specifically, it is a quartz glass rod or the like.

In the optical fiber porous preform of the present invention, the glass fine powder 6 is deposited on the periphery of the target 1 (hereinafter, this deposit may be referred to as “soot”). The present invention is characterized in that the pore distribution of the soot 6 is controlled. As described above, by controlling the pore distribution of the soot, the number of bubbles in the sintered body obtained by melt-vitrifying the soot can be reduced, and as a result, an optical fiber having no bright spot can be manufactured. That is, the pore distribution of the soot 6 is controlled so that pores having a diameter of 10 μm or more account for 1% by volume or less of all the pores. Preferably, pores having a diameter of 10 μm or more account for 0.5% by volume or less of all the pores. In particular, since the normal pore diameter is about 0.4 μm, it is more preferable that there is no large pore of 10 μm or more. This is because pores smaller than 10 μm can be eliminated during sintering.

The optical fiber preform of the present invention is obtained by melting the above optical fiber porous preform of the present invention by vitrification. By using the optical fiber porous preform of the present invention, it is possible to obtain an optical fiber preform having almost no air bubbles and therefore no bright spots. Furthermore, the optical fiber obtained therefrom also has very few bright spots and has excellent optical properties with little loss in light transmission.

In the method for producing a porous optical fiber preform according to the present invention, soot is deposited around the target while rotating the target. By rotating the target 1, the soot 6 can be uniformly deposited. In FIG. 1, a target 1 is rotatably housed in a chamber 2 and both ends thereof are held by a chuck 3 or the like. Then, while rotating the target 1 and reciprocating the flame burner 4 at a constant speed, the flame 5 from the burner 4
Is sprayed around the target 1. As a result, the glass fine powder (soot) 6 is uniformly deposited around the target 1.

A source gas for soot (for example, a silicon compound such as SiCl ₄ ) and a fuel gas (for example, H ₂ , O ₂ ) are supplied from the flame burner 4. Then, the raw material gas is hydrolyzed in an oxyhydrogen flame to produce glass fine powder, and the generated glass fine powder is
It is sprayed around and accumulates. Note that the arrangement of the target 1 can be applied by a mechanism that stands up and down or a mechanism that places it sideways.

The chamber 2 usually has a chuck cover 2 that covers one end of the target 1 as is apparent from the schematic diagram of the overall configuration of the optical fiber porous preform manufacturing apparatus shown in FIG.
a and a chuck cover 2b for covering the other end of the target 1. The flame burner 4 is provided with an opening 2c of the chamber 2.
Are reciprocated along the axial direction of the member. On the other hand, on the rear side (right side in the figure) of the chamber 2, for example, a plurality (one or more) of exhaust ports 2d for exhausting unreacted gas, reaction product gas, undeposited glass fine powder and the like are provided. . The exhaust port 2d is connected to the exhaust pipe 7, and the inside of the chamber 2 is given a predetermined suction force (exhaust suction pressure) by an exhaust means 8, for example, a suction pump incorporated in the exhaust pipe 7 or the like. It sucks and exhausts.

In the method for producing a porous optical fiber preform of the present invention, the large pores of 10 μm or more in the soot are made up to 1% by volume, preferably 0.5% by volume, based on all the pores.
It is characterized by the following control. The control of the pore diameter is specifically performed by controlling the rotation speed of the member.

In the production of the above-mentioned optical fiber porous preform, glass fine powders of various diameters are produced and deposited on the target depending on production conditions such as the number of rotations of the target. Therefore, here, it is considered that a soot microstructure that may cause a bright spot (bubble) after sintering occurs. On the other hand, conventionally, the rotation speed of the target is constant regardless of the outer diameter of the soot, and the peripheral speed increases as the diameter increases. Therefore, the present inventor examined the radial structure of the soot in the porous base material, particularly the pore distribution, and found the fine structure that caused the bright spot (bubbles) from the abnormality, and thereby obtained the bright spot (bubbles). In order to find a way to reduce the amount, the following investigation was made.

FIG. 3 shows that the rotation speed of the target 1 is 30 rpm.
5 shows the change in the ratio of the pore volume of 10 μm or more to the total pore volume in the radial direction of the soot 6 when the soot is deposited while keeping it constant at m. As is clear from FIG. 3, as the outer diameter of the soot increases, the proportion of pores of 10 μm or more decreases. That is, it can be seen that as the peripheral speed increases, the ratio of pores of 10 μm or more in the deposited soot decreases.

Therefore, if the peripheral speed is controlled by controlling the number of revolutions of the target, the proportion of pores of 10 μm or more in the soot can be controlled. As a result, the number of bubbles in the soot after sintering can be reduced. As described above, it is preferable to control the number of rotations of the target so that the number of pores of 10 μm or more in the soot is 1% by volume or less of all the pores. Specifically, as can be seen from FIG. 3, the target 1 is set so that the peripheral speed of the target 1 becomes 17 m / min or more.
By controlling the number of revolutions of the soot, 10 μm
The above pore ratio can be 1% by volume or less with respect to all the pores (outside diameter: about 180 mm, 1% at 30 rpm).

In particular, conventionally, since the target was rotated at a constant speed regardless of the diameter of the soot, a large number of pores having a diameter of 10 μm or more existed in the soot portion at the initial stage of deposition at a low peripheral speed. Such pores hardly disappear even by sintering. However, according to the manufacturing method of the present invention, if the rotation speed of the target is controlled so that the peripheral speed of the soot outer diameter becomes, for example, 17 m / min or more from the start of soot deposition, even in the soot portion at the initial stage of deposition. The pores having a diameter of 10 μm or more can be significantly reduced. As a result, an optical fiber preform and an optical fiber having almost no bright spots can be manufactured.

As described above, it is not clear why the ratio of the pores of 10 μm or more decreases as the peripheral speed increases, but the peripheral speed of the soot is related and the peripheral speed is low when the glass particles adhere. It is thought that the number of particles piled up in the radial direction increases, and the length of this daisy chain becomes longer, so that pores having a large pore diameter are generated. Although this was not affixed, it was confirmed by observation of SEM photographs that glass fine particles were connected linearly. Alternatively, the pore distribution may be further controlled by controlling the flow rate of the above-described gas such as the source gas and the fuel gas.

In the method for producing an optical fiber preform of the present invention, the above optical fiber porous preform of the present invention is produced by melt vitrification. Specifically, the optical fiber porous preform having a small number of pores of 10 μm or more is placed in, for example, an electric furnace or the like, and a dehydration step is performed using chlorine gas or the like as necessary.
For example, by heating to 1300 to 1700 ° C., the optical fiber preform of the present invention is obtained.

Thereafter, the optical fiber preform of the present invention produced as described above can be converted into an optical fiber by a usual method, for example, by melt drawing. The optical fiber manufactured in this manner has excellent optical characteristics with very few bright spots and little loss in light transmission.

[0026]

The present invention will be specifically described below with reference to examples. (Examples 1 to 3 and Comparative Examples 1 and 2) FIGS. 1 and 2
The optical fiber porous preform was manufactured using the manufacturing apparatus shown in FIG. That is, the target 1 having a diameter of 40 mm is mounted in the chamber 2, and the number of rotations of the target is 2 by the outer diameter of the soot 6.
30 rpm for 00 mm or more, and Table 1 for less than 200 mm
The soot 6 was deposited under the conditions shown in Table 1. At this time, the gas was introduced by injecting the raw material SiCl ₄ and the fuels H ₂ and O ₂ from the flame burner 4.
After hydrolysis in an oxyhydrogen flame, soot 6 was deposited using SiO ₂ as a glass fine powder, and the soot weight was reduced to 70 to 80 k.
g.

With respect to the soot 6 of each of the obtained optical fiber porous preforms, the ratio (volume%) of pores having a size of 10 μm or more to the total pore volume was measured in part by the pore distribution. The remaining portion was melt-vitrified at 1500 ° C. for 5 hours in a chlorine atmosphere to obtain a soot sintered body, and the number of bright spots (bubbles) was measured. The pore diameter was measured by cutting a soot into a 1 cm square block and using a mercury intrusion porosimeter.
The number of bright spots (bubbles) of the soot sintered body was counted visually by irradiating light in a dark room.

[0028]

[Table 1]

As is clear from Table 1, as the rotational speed of the target increases, the ratio of pores of 10 μm or more in the soot decreases, and accordingly, the number of bright spots in the soot sintered body also decreases significantly. You can see that.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention. For example, in the above description, the number of rotations of the target is changed only between the case where the diameter is 200 mm or less and the case where the diameter is more than 200 mm. It is optional as long as it is secured.

[0031]

According to the present invention, a porous optical fiber preform having a soot having almost no pores having a diameter of 10 μm or more can be manufactured. Therefore, the optical fiber preform obtained by sintering this hardly has a bright point (bubble). as a result,
An optical fiber manufactured from this optical fiber preform has very few bright spots and has excellent optical characteristics with little loss in light transmission.

[Brief description of the drawings]

FIG. 1 is a partially enlarged schematic view of an optical fiber porous preform manufacturing apparatus showing a state of soot deposition on a target.

FIG. 2 is a schematic diagram of the entire configuration of an optical fiber porous preform manufacturing apparatus.

FIG. 3 is a diagram showing the relationship between the outer diameter of soot and the volume ratio of pores having a diameter of 10 μm or more.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Target, 2 ... Chamber, 2a and 2b ... Chuck cover, 2c ... Opening, 2d ... Exhaust port, 3 ... Chuck, 4 ... Flame burner, 5 ... Flame, 6 ... Soot (glass fine powder), 7 ... Exhaust pipe, 8 ... Exhaust means.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideo Hirasawa 2-13-1 Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Research Laboratories (58) Field surveyed (Int. Cl. ⁶ , (DB name) C03B 37/00-37/16 C03B 8/04

Claims (6)

(57) [Claims] 1. An optical fiber porous preform in which glass fine powder is deposited around a member, wherein pores of 10 μm or more in the deposit are 1% by volume or less of all pores. Optical fiber porous preform. 2. An optical fiber preform obtained by melting and glassifying the porous optical fiber preform according to claim 1. 3. A method for producing a porous optical fiber preform by depositing a glass fine powder around the member while rotating the member, wherein pores of 10 μm or more in the deposit are 1% by volume with respect to all pores. A method for producing a porous optical fiber preform, which is controlled as follows. 4. A method of controlling the number of rotations of a member so that pores of 10 μm or more in the deposit are 1% by volume with respect to all pores.
The method for producing a porous optical fiber preform according to claim 3, wherein the control is performed as follows. 5. A method for producing a porous optical fiber preform by depositing glass fine powder around the member while rotating the member, wherein the peripheral speed of the member to be deposited is 17 m / min or more during the deposition of the glass fine powder. A method for producing a porous optical fiber preform, comprising controlling the number of revolutions so that 6. A method for producing an optical fiber preform, wherein the optical fiber porous preform produced by the method according to any one of claims 3 to 5 is produced by melt-vitrification. Method.