JPH0686305B2 - Manufacturing method of rare earth element-doped core optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical fiber having a core doped with a rare earth element, and particularly enables high-concentration doping.

[Prior Art] Conventionally, when manufacturing a rare earth element-doped core optical fiber, a general MCVD method has been used as a means for doping a rare earth element.

FIG. 2 shows a configuration diagram for explaining a method of doping a rare earth element by the MCVD method. That is, by pouring silicon tetrachloride together with a carrier gas (O ₂ ) into an evaporation chamber 2 in which a rare earth element chloride 1 is enclosed and heating with a heating burner 3 from the outside, oxide glass fine particles and rare earth element ions are added. To generate quartz glass 4
The rare earth element-doped core portion 6 is formed by depositing it on the inner wall of the tube, melting it into vitrified glass, sweeping the external moving heating burner 5 and repeating this glass deposition step.

[Problems to be Solved by the Invention] However, according to such a method, there is a problem that it is difficult to perform high concentration doping because the vapor pressure of the rare earth element chloride is low. In particular, it is very difficult to dope erbium (Er) in high concentration among rare earth elements, and it is impossible to dope more than 100 ppm.

In addition, this method has a drawback that the solid of the unsublimated rare earth element chloride flows from the evaporation chamber 2 into the quartz glass tube 4 and becomes a bubble so that it is not doped.

One of the methods proposed to solve these problems is to prepare a rare earth chloride, a solution in which alcohol or water is dissolved as a solvent, and in this solution, glass fine particles are deposited by the VAD method. The soot body is dipped to impregnate the rare earth element solution, dried, and then dehydrated and sintered to form the rare earth element-doped core portion.

However, when alcohol is used as the solvent, cracks are generated in the soot body during the impregnation of the alcohol solution and the subsequent drying step, and the alcohol is dehydrated after being sufficiently dried. There were also safety problems such as the danger of explosion without sintering.

Moreover, when water was used as the solvent, it was not possible to prepare a high-concentration solution of a rare earth element chloride such as Er. For this reason, there are drawbacks that high-concentration dope cannot be achieved and cracks are easily generated in the soot body during impregnation with the aqueous solution.

An object of the present invention is to provide a method for manufacturing a rare-earth element-doped core optical fiber that solves the above-mentioned problems, suppresses the occurrence of cracks, etc., and enables high-concentration doping.

[Means for Solving the Problem] In the present invention, a soot body obtained by depositing glass fine particles synthesized by flame hydrolysis or thermal oxidation is heat-treated to have a bulk density of 0.4 to 1.4 g / cc. The soot body is immersed in a solution in which a rare earth element chloride is dissolved in a hydrochloric acid aqueous solution to impregnate the soot body with the rare earth element solution, and then the soot body is dried and sintered to form a rare earth element-doped core portion. The solution was to create it.

[Action] As a solvent for dissolving the rare earth element chloride in this way,
By using an aqueous solution of hydrochloric acid, it is possible to prepare a high-concentration rare earth element solution. Therefore, by impregnating the soot body with the rare earth element solution, there is an advantage that high-concentration doping can be performed.

Also, before impregnating the soot body with the rare earth element solution,
If the soot body is heat-treated to increase the bulk density of the soot body, there are advantages that the soot body does not crack such as cracks and that the high concentration rare earth element doping can be performed smoothly.

Hereinafter, the present invention will be described in detail.

First, a soot body is created by the normal VAD method. That is, by supplying a raw material gas such as silicon tetrachloride into the oxyhydrogen flame,
A soot body is obtained by generating glass particles by a hydrolysis reaction in a flame, adhering the glass particles to the tip of the starting material, and depositing the starting material in the axial direction while rotating the starting material. Here, the soot body refers to a porous base material in which glass particles are deposited on a starting material. Also,
As the raw material gas, a dopant gas for adjusting the refractive index such as GeCl ₄ may be supplied together with silicon tetrachloride. The size of the soot body obtained is not particularly limited, but a diameter of about 80 mm and a length of about 200 mm are preferable.

Next, the soot body is heat-treated to increase the bulk density of the soot body. The method of heat treatment is not particularly limited, but for example, a method of putting the soot body 8 in a soaking furnace 7 as shown in FIG. 1 and heating it in an inert gas atmosphere such as helium gas while rotating it. There is. The heating conditions are
The soot body 8 having a bulk density of about 0.4 to 1.4 g / cc can be obtained by carrying out under conditions of a normal temperature of about 1280 to 1320 ° C. and a time of about 2 to 6 hours, although it may be appropriately determined according to the desired bulk density and the like. It is preferable to select the conditions.

Next, a rare earth element solution is prepared. For rare earth elements,
Erbium chloride (ErCl ₃ .0.5H ₂ O), neodymium chloride, and the like are preferably used, and they are appropriately selected and used according to the purpose and application of the obtained optical fiber. A hydrochloric acid aqueous solution obtained by adding hydrochloric acid to water is preferably used as the solvent. The hydrochloric acid concentration of this solvent may be a concentration that can completely dissolve the above-mentioned rare earth element chlorides, and for example, a concentration of about 1 to 5 cc of 35 wt% hydrochloric acid added to 300 cc of water is preferable. In addition, the concentration of the rare earth element chloride in this solution is preferably as high as it can be completely dissolved, from the viewpoint that high-concentration doping can be performed, and is preferably about 2 to 10% by weight.

The soot body is immersed in this rare earth element solution to impregnate the soot body with the rare earth element solution. Impregnation temperature
Perform at 10-25 hours at 20-25 ° C for 10-100cc as a solution
Impregnate to a degree. The rare earth element impregnated here is considered to be in the form of chloride or ion.

Next, the soot body after the impregnation is dried. The drying method is not particularly limited, for example, the soot body is housed in a drying cylinder, and from one end of this cylinder, dry nitrogen gas is sprayed onto the soot body in the cylinder at a supply rate of about 2 l / min, A method of drying at room temperature for about 60 hours is adopted.

After drying, dehydration is performed in a zone sintering furnace, and then sintering is performed. First, in the dehydration step, dehydration is performed for about 2 to 3 hours under the condition of a temperature of about 1000 ° C. in a helium gas atmosphere containing about 0.2% of chlorine gas (Cl ₂ ) in this zone sintering furnace.

Further, in the sintering step, after dehydration, the supply of chlorine gas into the zone sintering furnace is stopped and the process is continued in an atmosphere of helium gas only. The temperature in the furnace is preferably about 1500 to 1550 ° C., and the soot body is subjected to transparent vitrification to form a rare earth element-doped core portion. Here, it is considered that the rare earth element in the rare earth element-doped core portion after the sintering is in the form of an oxide or an ion.

Next, glass is externally attached to the periphery of the rare earth element-doped core portion by a normal external attachment method or the like to form a clad portion. That is, when the core portion is used as a starting material and is rotated, the fine particles are generated when the raw material gas such as silicon tetrachloride supplied in the oxyhydrogen gas is hydrolyzed to generate fine particles. And then sequentially deposited in the radial direction to form a clad portion.

Next, insert this into an electric furnace, dehydrate it in an atmosphere of chlorine gas, etc., and then sinter it at a temperature of about 1400 to 1500 ° C and in an atmosphere of helium and SiF ₄ to make the clad part transparent. To obtain a core-clad type preform.

Thereafter, the preform thus obtained is subjected to fusion drawing to manufacture a rare earth element-doped core optical fiber having an outer diameter of about 125 μm. The method of melt drawing may be a well-known and conventional method, for example, the preform is fed into a heating furnace heated to a high temperature of about 2000 ° C. so that the wire diameter becomes constant under an inert gas atmosphere. While controlling, 100-600m /
Delineate at a speed of about a minute.

According to such a manufacturing method, since the hydrochloric acid aqueous solution obtained by adding hydrochloric acid to water is used as the solvent for dissolving the chloride of the rare earth element, the high concentration solution of the rare earth element chloride can be prepared. Therefore, when the soot body is dipped in this solution, the rare earth element solution can be highly impregnated, and as a result, an optical fiber having a highly doped core can be obtained.

Further, before impregnating the soot body with the rare earth element solution, the soot body is subjected to heat treatment to increase the bulk density of the soot body, so that cracks such as cracks do not occur in the soot body, and also smoothly. High-concentration rare earth element doping can be performed.

Hereinafter, the present invention will be described in detail with reference to examples.

Example First, a soot body having an outer diameter of 80 mm and a length of 200 mm was prepared by the usual VAD method. The bulk density of this soot body was 0.2 g / cc.

Next, put this soot body in the soaking furnace shown in FIG.
In a helium gas atmosphere, heat treatment was performed at 1300 ° C for 4.5 hours, and the bulk density of the soot body was increased to 0.56 g / cc.
The soot body after heating has a diameter of 44.5 mm and a length of 110 m.
It was m.

Next, a rare earth element solution was prepared. As a rare earth element
Using Er chloride (ErCl ₃ · 0.5H ₂ O), H ₂ O 300cc 35wt
% HCl to an aqueous hydrochloric acid solution containing 3.6 cc of ErCl ₃
0.5H ₂ O was completely dissolved to obtain a pink transparent solution.

When the soot body was immersed in this solution and left to stand for 4 hours for impregnation, the impregnation amount was 100 cc.

The soot body after the impregnation was inserted into a drying cylinder, and the soot body was dried while blowing dry nitrogen gas from one end of the cylinder. The supply rate of nitrogen gas was 2 l / min, and drying was performed at room temperature for 60 hours.

Then, the soot body was placed in a zone sintering furnace in a helium gas atmosphere containing 0.2% chlorine gas, and dehydration was performed at 1000 ° C.

After that, the supply of chlorine gas was stopped and the soot body was sintered into transparent glass by heating at 1550 ° C. in a helium gas atmosphere to form a rare earth element-doped core portion.

Next, glass particles were deposited on the rare earth element-doped core portion by an ordinary external attachment method, and dehydration and sintering were sequentially performed in an atmosphere of He and SiO ₄ to form a clad portion.

After the core-clad type preform was formed in this manner, melt drawing was performed at a temperature of 200 ° C. to manufacture a rare earth-doped core optical fiber.

When the loss wavelength characteristics of the optical fiber thus obtained were measured, a large absorption peak characteristic of Er doping appeared and it was revealed that Er was doped.

Further, in the same manner, when Er-doped glass was prepared and the Er concentration was quantitatively analyzed, the Er doping amount was 9000 ppm,
It was found that it was highly doped.

[Effects of the Invention] As described above, according to the method for producing a rare earth element-doped core optical fiber of the present invention, a soot body obtained by depositing glass fine particles synthesized by flame hydrolysis or thermal oxidation is used as a rare earth element chloride. The rare earth element is soaked in a solution dissolved in an aqueous solution of hydrochloric acid to impregnate the soot body with the rare earth element solution, and then the soot body is dried and sintered to form the rare earth element-doped core portion. A high concentration solution of chloride can be prepared, and when the soot body is immersed in this solution, the rare earth element solution can be impregnated at a high concentration. Therefore, there is an advantage that an optical fiber having a core in which a rare earth element is highly doped can be obtained.

In addition, before the soot body is impregnated with the rare earth element solution, the soot body is heat-treated to increase the bulk density of the soot body, so that the soot body does not crack such as cracks and is smooth. High-concentration rare earth element doping can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a heat treatment method for a soot body implemented in the present invention, and FIG. 2 is a schematic configuration diagram showing an example of a conventional doping method by the MCVD method. 8 ... suit body.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigetoshi Yamada, 1440 Rokuzaki, Sakura City, Chiba Prefecture, Fujikura Cable Co., Ltd.Sakura Factory (72) Inventor, Tetsuro Nozawa, 1440, Rosaki, Sakura City, Chiba Fujikura Cable Company, Sakura Factory ( 72) Inventor Suehiro Miyamoto, 1440 Rokuzaki, Sakura City, Chiba Prefecture, Sakura Factory, Fujikura Cable Co., Ltd. (72) Ryozo Yamauchi, 1440, Rokuzaki, Sakura City, Chiba Prefecture, Sakura Factory, Fujikura Cable (56) References JP 63 -176315 (JP, A)

Claims (1)

[Claims] 1. A soot body obtained by depositing glass fine particles synthesized by flame hydrolysis or thermal oxidation to heat the soot body to a bulk density of 0.4 to 1.4 g / cc, and then adding a rare earth element chloride to an aqueous hydrochloric acid solution. By immersing it in a solution dissolved in
A method for producing a rare earth element-doped core optical fiber, which comprises impregnating a soot body with the rare earth element solution, and then drying and sintering the soot body to form a rare earth element-doped core optical fiber.