JP3300224B2 - Method for producing quartz-based doped glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silica-doped glass which is doped with a light-absorbing transition metal such as cobalt (Co) and used for an optical attenuator or the like.

[0002]

2. Description of the Related Art A transition metal-doped fiber in which a transition metal such as cobalt is doped in a core portion of an optical fiber has an effect of absorbing transmitted light. Therefore, application to an optical attenuator using such an optical attenuation function is expected. In order to manufacture such an optical fiber, it is necessary to dope a transition metal such as cobalt at a high concentration in the core of the optical fiber. However, since a transition metal chloride such as CoCl _{2 as} a dope raw material does not vaporize at around room temperature, when producing a core porous preform by a flame hydrolysis method generally used for optical fiber production, a dope is used. It is difficult to add raw materials at the same time.

[0003] For this, conventionally, the porous preform produced by the VAD method or the like shrinkage ratio of 60% to 75%, once preliminary sintering to about bulk density 0.5~0.3g / cm ^3. Then, the porous base material is immersed in an alcohol solution in which a transition metal, for example, a chloride of Co or the like is dissolved. Thereafter, the porous base material taken out of the solution is dried, and the alcohol content of the solution is evaporated to deposit a transition metal chloride in the porous base material. After that, if this is sintered and made transparent, a quartz-based doped glass doped with a transition metal is manufactured.

[0004]

The above-described conventional method for producing a quartz-based doped glass has the following problems to be solved. FIG. 2 shows a side view of the porous preform in the drying step. As shown in this figure, this porous base material 1 was placed in an alcohol solution in which a transition metal chloride was dissolved.
When the alcohol is evaporated after immersion of 0, the alcohol moves from the inside of the porous base material 10 to the outside and evaporates as shown by the arrow. That is, the porous base material 10
The alcohol solution containing the transition metal element that has penetrated into the inside of the base material moves toward the surface of the porous base material 10 in order and evaporates near the surface. As a result, chlorides and the like of transition metal elements are likely to remain near the surface of the porous base material 10 in a concentrated manner.
For example, when a Co rod is used as the transition metal and the glass rod prepared by the above method is used to measure the Co concentration distribution in the radial direction by using the well-known EPMA method, the following result is obtained.

FIG. 3 shows a graph of Co doping distribution.
The horizontal axis shows the radial position of the glass rod, and the vertical axis shows Co
The content is expressed in%. As shown in this figure, Co is actually concentrated at the peripheral portion of the core, and the central portion has a relatively low concentration distribution. In this case, Co
Although the optical fiber is designed on the assumption that the density is distributed, the error becomes large. In addition, when Co is distributed at a high concentration near the surface of the core, crystallization occurs near the outer surface, and sometimes cracks occur to make the product defective. That is, the above-described manufacturing method has a problem that it is difficult to increase the dopant concentration to the upper limit obtained when the dopant element is dissolved in the transparent glass.

In the case of a single mode fiber in which the refractive index distribution of the waveguide is large at the center and becomes smaller toward the outer periphery, the interaction between the dopant and light is greatest at the center of the base material. Therefore, it is desirable that the dopant concentration in the core be uniform or a convex shape in which the center is deeper and becomes thinner toward the outer periphery. Therefore, in the concave refractive index distribution opposite to the above, the concentration of Co that acts substantially becomes lower than the amount of Co doped. Further, when the dopant is Co, there is a problem that the wavelength dependence of the resulting optical attenuator is relatively large. The present invention has been made in view of the above points, and an object of the present invention is to provide a method for producing a silica-based doped glass for providing a uniform dopant concentration distribution in a radial direction of an optical fiber as much as possible. is there.

[0007]

According to the method of the present invention, a base material made of porous quartz is immersed in a dopant solution to impregnate the base material with a dopant, and the base material after the dopant impregnation is dried. And a step of sintering the dried base material, wherein the base material is dried at a temperature of 1000 ° C. or higher after the step of drying the base material.
Temporary sintering in the temperature range below ℃, the base material density 0.4g / cm
^After increasing to ^{3 to} 1.2 g / cm ³ , the outer peripheral portion of the base material is removed, the base material surface is polished, and then the base material is sintered. It is.

[0008]

The quartz porous base material is immersed in a dopant solution and dried, and then temporarily sintered in a predetermined temperature range to increase the base material density to a predetermined range. To an appropriate level. Thereafter, the surface is polished to remove the high concentration portion of the dopant near the surface. If the bulk density is insufficient, the soot is broken during this polishing. If the bulk density is too high, the surface of the soot is crystallized at that stage and cracks are likely to occur. Therefore, a core having a uniform concentration distribution can be obtained by heat treatment and polishing under a certain condition.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is an explanatory view showing an embodiment of a method for producing a quartz-based doped glass of the present invention. In the present invention, a fiber doped with a dopant such as cobalt with a substantially uniform concentration distribution in the radial direction when viewed from the cross section of the core is manufactured by, for example, the procedure shown in FIG. Therefore, first, as shown in FIG. 1A, a quartz porous base material 3 is manufactured by a well-known VAD method. Burner 2
325 cc per minute of SiCl ₄ as a raw material
eCl ₄ is supplied at a rate of 40 cc / min, and 9 liters of O ₂ and 6.5 liters of H ₂ are supplied as combustion gases per minute.
Further, 1.5 liters of Ar is supplied per minute as a reaction control gas to cause a flame hydrolysis reaction. The fine particles thus obtained are continuously deposited on a quartz target rod 1 which is pulled up while rotating in the direction of the arrow as shown in the figure. The size of the base material 3 thus obtained was, for example, 72 mm in diameter and 290 mm in length. The base material 3 completed through this process is illustrated as a base material 5 made of porous quartz in FIG.

Next, a dipping step is performed as shown in FIG. 1B, but before that, a simple sintering is performed to fix the fine particles of the porous quartz base material 5. The apparatus is set to a temperature of 1320 ° C. as shown in FIG.
The quartz porous base material 5 completed in the step (a) is sent from the top to the bottom of the electric furnace at a speed of 200 mm per minute. When this is heated by the heater 8, a porous quartz base material 5 having a shrinkage of 70% and a bulk density of 0.4 g / cm ³ is obtained.

Next, an immersion step is performed by using the apparatus shown in FIG.
Is carried out. The container 7 contains the dopant ion solution 6.
Is in. The dopant ion solution 6 is specifically Co
Cl _Two ・ 6H_Two A methanol solution in which O is dissolved at 4.5 wt%
Consists of A quartz porous base material 5 is immersed therein for 20 hours.
Dipping impregnates the dopant. afterwards,
The quartz porous base material 5 is pulled up and air-dried. So
After drying, the temperature is set by an electric furnace shown in FIG.
Heat to a temperature of 1150 ° C.

In this manner, the quartz porous base material 5 is
When sent from the top to the bottom of the electric furnace at a speed of
%, And a base material 5 having a bulk density of about 0.8 g / cm ³ is obtained. Thereafter, the outer peripheral portion of the porous quartz base material 5 is cut off to a thickness of about 3 mm using a Co ₂ laser. Further, the outer surface of the base material 5 is also smoothly polished by a Co ₂ laser or the like.
Finally, when sintering is performed in an atmosphere of He (helium) using an electric furnace shown in (c) of the figure and vitrification is performed, a base material having a substantially constant Co concentration distribution in the radial direction is obtained.

FIG. 4 shows the distribution of Co concentration in such a base material. The horizontal axis in the figure shows the radial position of the core, and the vertical axis shows the Co content in%. As shown in this figure, the portion where Co was distributed at a high concentration near the outer surface of the core was scraped off at the stage of the base material, and an optical fiber having a substantially uniform concentration from the center to the outer periphery was manufactured. .

Here, after the above-mentioned drying step, the temperature range for temporarily sintering the quartz porous base material 5 is 1000 ° C. or more and 1 ° C.
It is desirable that the temperature range is about 350 ° C. Also,
In this case it increased by the provisional sintering the bulk density of the base material 5 made of quartz porous to about 0.4 g / cm ³ or more 1.2 g / cm ^3. This is done for the following reason. Usually, fine particles of the porous silica base material 5 are partially in contact with each other, and maintain a state in which the fine particles are fused together. If the fine particles are mechanically polished, the base material itself is broken by an external force applied at that time. There is a risk that it will. Therefore, it is necessary to reinforce the base material before such a polishing treatment. Therefore, in the present invention, the bulk density of the porous quartz base material 5 is set to 0.4 g / g before the polishing treatment.
cm ³ or more.

On the other hand, if the bulk density of the porous quartz base material is increased to 1.2 g / cm ³ or more, the surface of the base material may be crystallized due to the high concentration of Co and cracks may occur. . For this reason, the polishing is performed after the bulk density is within a certain range.

The present invention is not limited to the above embodiment. In order to polish the surface of the base material 5, ion etching other than CO ₂ laser and various other mechanical polishing methods can be adopted.
Further, as the dopant, a transition metal other than Co can be employed, and further, a rare earth element dopant other than the transition metal, Al,
The use of an alkali metal, an alkaline earth metal or the like as a dopant is similarly effective. In addition, as a method of manufacturing a quartz porous glass preform, in addition to the VAD method, an external method,
A sol-gel method can also be used. Further, the above-described processing can be performed not only on the core of the optical fiber but also on the clad.

[0017]

According to the method for producing a quartz-based doped glass of the present invention described above, a known doping step, drying step,
When manufacturing a quartz porous base material through a sintering process,
Since the outer peripheral portion of the base material is removed by mechanical polishing or the like, a base material having a uniform dopant concentration distribution in the radial direction can be obtained. In addition, before polishing a quartz porous base material, the base material is pre-sintered in a certain temperature range to increase the base material density, so that the base material may be broken by mechanical external force such as polishing. Absent.

[Brief description of the drawings]

FIG. 1 is a front view of each step showing a method for producing a quartz-based doped glass of the present invention.

FIG. 2 is a side view of a porous base material for explaining a conventional method.

FIG. 3 is a graph showing a Co doping concentration distribution of a conventional core.

FIG. 4 is a graph showing a Co doping concentration distribution of a core according to the present invention.

[Explanation of symbols]

 3, 5 quartz porous base material 6 dopant ion solution 8 heater

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI G02B 6/00 356 G02B 6/00 356A (72) Inventor Ryo Nagase Nippon Telegraph and Telephone 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Within Telephone Co., Ltd. (72) Asahi Kumagai 2-1-1, Sakae Oda, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside of Showa Electric Wire & Cable Co., Ltd. No. 1 Inside Showa Electric Wire & Cable Co., Ltd. (72) Inventor Chishu Fukada 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside 1 Showa Electric Wire & Cable Co., Ltd. 2-1-1, Sakae Showa Electric Wire & Cable Co., Ltd. (72) Koji Matsuura 2-1, 1-1 Odaei, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Electric Wire & Cable Co., Ltd. In-house (56) References JP-A-59-146946 (JP, A) JP-A-6-61552 (JP, A) JP-A-7-333407 (JP, A) JP-A-2-137742 (JP, A) JP-A-57-42549 (JP, A) JP-A-9-142864 (JP, A) JP-A-6-80434 (JP, A) JP-A-63-8706 (JP, A) (58) (Int.Cl. ⁷ , DB name) C03B 20/00 C03B 8/04 C03B 37/014 C03C 13/04

Claims (1)

(57) [Claims] A step of immersing a porous quartz base material in a dopant solution to impregnate the base material with a dopant;
In a method for producing a quartz-based doped glass comprising a step of drying the base material after impregnation with the dopant and a step of sintering the base material after drying, after the step of drying the base material, Temporary sintering in the temperature range of not less than 1 ° C. and not more than 1350 ° C. After increasing the density of the base material to 0.4 g / cm ³ or more and 1.2 g / cm ³ or less, the outer peripheral portion of the base material is removed. A method for producing quartz-based doped glass, comprising sintering a base material after polishing the surface.