JPH0624780A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To provide a method for producing optical fiber preform free from detects and minimized in the eccentricity of its core by a hybrid method. CONSTITUTION:The production method comprises the steps of providing a clad material formed from the powder of quarts glass on the outer periphery of a core material to produce a porous molding; impregnating the porous molding with a resin; curing the resin; slicing or grinding the outer periphery of the porous molding to correct the eccentricity of the clad material on the basis of the core material; and defatting and transparently vitrifying the eccentricity- corrected porous molding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a base material of an optical fiber used for optical communication.

[0002]

2. Description of the Related Art As a method of manufacturing an optical fiber preform,
In particular, the hybrid method is used in which the core material (including the one in which the clad material is partially covered on the outside of the core material) is produced by the vapor phase method, and the clad material formed on the outside of the core material is produced by the powder molding method. The existing method is recognized as industrially advantageous. However, this hybrid method has a problem of eccentricity of the clad material with respect to the core material.

Eccentricity of the clad material with respect to the core material (hereinafter,
The eccentricity of the core) has a great influence on the characteristics of the optical fiber. In particular, single-mode fibers, which are most frequently used among optical fibers, have a core diameter of about 10 μm, and thus eccentricity is a serious problem. This eccentricity causes a large connection loss in the connection between the optical fibers or the connection between the light source and the optical fiber. Therefore, in order to reduce the connection loss, it is necessary to reduce the eccentricity of the core as much as possible. It is preferable that the core has no eccentricity at all, but it is necessary to set it to 0.5 μm, preferably 0.3 μm or less for practical use.

Conventionally, as a method of correcting the eccentricity of the core, a method of fixing the porous compact obtained by the hybrid method to a lathe and cutting the outer periphery of the clad material (porous compact) with a diamond blade is adopted. Has been done.

[0005]

However, when the porous molded body is cut by such a method, crushed pieces, that is, silica powder, remains on the surface of the porous molded body or penetrates into the pores. The crushed pieces remaining on the surface or entering the pores in this manner cause bubbles to be generated when the porous molded body is made into transparent glass.

Further, the cutting scratches formed when the porous molded body is cut serve as a starting point of cracks and cause bubbles when the porous molded body is made into transparent glass. Further, since the porous molded body is brittle, there is a risk that the surface will be cracked by cutting. If this crack becomes large, the porous molded body itself will be destroyed.

[0007] Such bubbles and cracks appear as surface defects when an optical fiber is manufactured from an optical fiber preform formed by making a porous molded body into transparent glass. The surface defects impair the characteristics of the optical fiber and reduce the reliability.

In order to improve the mechanical strength of the porous molded body, it is possible to increase the amount of binder in the clad material formed on the outer side of the core material. Inclusion increases, and as a result, the transmission characteristics of the optical fiber deteriorate.

The present invention has been made in view of the above circumstances, and provides a method for producing an optical fiber preform using a hybrid method for producing an optical fiber having no defects and having a very small core eccentricity. The purpose is to provide.

[0010]

According to the present invention, a step of producing a porous molded body by providing a clad material formed by molding quartz glass powder on the outside of a core material, and impregnating the porous molded body with a resin. Step, curing the resin, cutting or grinding the outer periphery of the porous molded body to correct the eccentricity of the clad material with respect to the core material, and degreasing the porous molded body after correcting the eccentricity -Providing a method for producing an optical fiber preform characterized by comprising a step of forming a transparent glass.

As described above, the hybrid method is a clad formed on the outside of the core material after the core material is produced by the vapor phase method or the powder molding method, and if necessary, it is made into transparent glass. A material is produced by a powder molding method, and both are combined to obtain a porous molded body. The powder molding method is, for example, a pressing method (Japanese Patent Application No. 2-244817),
MSP method (Journal of Optical Communications, 10
Vol. 1, No. 1, pp. 2-5, 1989), etc., dry molding method, casting method (Japanese Patent Laid-Open No. 64-56331), extrusion method (Japanese Patent Application No. 2-244815), slurry coating method (Japanese patent application). Flat 2-2
44816) and the like using a wet molding method. It is meant to exclude the method of producing a porous molded body only by the vapor phase method. In addition to the transparent glass material, the core material includes a porous body.

The resin to be impregnated into the porous molded article is
It is preferable that the viscosity is low and the cured product can be completely decomposed by heating, and that it does not contain inorganic impurities other than Si. Such resins include silicone-based,
A thermosetting resin such as a vinyl or acrylic resin, or an ultraviolet curable resin such as an acrylic or epoxy resin can be used.

As a method of impregnating the porous molded body with a resin, a method of immersing the porous molded body in a liquid resin,
A method of spraying a liquid resin onto the porous molded body, a method of applying the resin, or the like can be adopted. How much the resin is impregnated into the porous molded body affects the type of resin, the molecular weight, the surface tension, and the viscosity, and the pore diameter and the porosity of the porous molded body. Therefore, it is desirable to perform an impregnation test using a porous molded body and a resin to be used in advance, confirm the correlation between the impregnation time and the impregnation thickness, and perform the actual impregnation treatment based on the result.

As a means for curing the resin, heat, ultraviolet rays, electron beams or the like can be used.

In the method of the present invention, cutting means cutting the outer periphery of the porous molded body with a cutting tool, and grinding means polishing the outer periphery of the porous molded body with a grindstone, both of which are porous molding. The purpose is to remove a part of the outer circumference of the body. Since this cutting / grinding is performed to correct the eccentric porous molded body, the amount of cutting / grinding is determined according to the eccentric state of the porous molded body. When actually cutting and grinding,
For example, the clad material is removed so that the distance from the center of the core material to the outer circumference of the clad material is equal in the cross section of the porous molded body. In order to reduce the eccentricity at a more severe level, the X-ray transmission device is connected to a cutting / grinding device, the eccentricity of the porous compact is detected by the X-ray transmission device, and the detection information is cut / ground. It transmits to the control means of the device and performs cutting and grinding based on the information.

When cutting and grinding, a lubricant such as cutting oil may be used as long as it does not adversely affect the porous compact. This can reduce friction during cutting and grinding. As a result, a porous molded body having a smooth surface can be obtained.

The resin remaining on the surface of the porous molded body after cutting and grinding can be removed at the same time in the so-called degreasing step of removing the molding aid.

The degreasing step and the transparent vitrification step of the porous molded body are carried out under the conditions generally used.

[0019]

According to the method of the present invention, the eccentricity of the core material is corrected by cutting or grinding the outer periphery of the porous molded body by impregnating the porous molded body with a resin and curing the resin.

By impregnating the porous molded body with a resin, the pores of the porous molded body are closed. Therefore, cutting
It is possible to prevent crushed pieces during grinding from entering the pores of the porous molded body. Further, by impregnating the porous molded body with a resin and curing the resin, the adhesion between particles in the porous molded body becomes strong. For this reason, the mechanical strength of the porous molded body is increased, and it is possible to prevent cracks from occurring when cutting and grinding are performed.

As a result, it is possible to prevent the occurrence of defects in the optical fiber preform formed by making the porous molded body into transparent glass. Therefore, it is possible to manufacture an optical fiber preform that is free from defects and has an extremely small eccentricity of the core.

[0022]

Embodiments of the present invention will be specifically described below with reference to the drawings.

Example 1 To 100 parts by weight of silica powder having an average particle diameter of 8 μm, 3 parts by weight of methyl cellulose as a binder, 22 parts by weight of pure water, and SN Wet 366 (trade name, manufactured by San Nopco) as a surfactant were used. 3 parts by weight were mixed and kneaded uniformly to prepare a plastic material.

As shown in FIGS. 1 (a) and 1 (b), the core / cladding ratio is 1/3, the refractive index difference between the core and the cladding is 0.3%, the outer diameter is 10.8 mm, and the length is long. 300 mm
The core rod 10 was prepared by the VAD method, and was dehydrated and made into a transparent vitreous material. The above-mentioned plastic material was vacuum extruded and formed into a clad portion 11 to produce a porous molded body 1 having an outer diameter of 50 mm and a length of 350 mm. Then, the porous molded body 1 was dried at 110 ° C. for 5 hours. When the pore diameter and the porosity of this porous molded article were measured, the pore diameter was 0.8 μm and the porosity was 35%. The eccentric amount (A shown in FIG. 1) of this porous molded body was 0.7 mm. This is because when an optical fiber is manufactured using this porous molded body, the eccentricity is about 1.6 μm.
It means that it becomes m.

Then, the porous molded body was treated with a viscosity of 100 cp.
It was immersed in a liquid acrylic resin of s 2 for 20 seconds, and then heat-treated at 80 ° C. for 2 hours to cure the acrylic resin. At this time, the resin was impregnated to a depth of about 2 mm from the surface of the porous molded body.

The lathe 20 shown in FIG.
Attached to. The lathe 20 includes a mounting table 21 and a mounting table 21.
Lathe body 22 movably attached to the lathe, and side wall 22 a (side wall 2 movably attached to the lathe body 22.
It suffices if only one of 2a is movable). A hole 22b is formed in the side wall 22a of the lathe body 22 so that the core rod 10 of the porous molded body 1 can be inserted therein. Also, the side wall 2
A core chuck 23 is attached to the outside of 2a. A clad chuck 24 is attached to the inside of the side wall 22a. The core chuck 23 and the clad chuck 24 are connected to a driving unit (not shown), and the core rod 10 and the clad portion 11 are connected.
It is possible to rotate integrally while gripping.

Next, while the porous molded body is rotated by driving the driving means, the axis of the porous molded body 1 is turned on the lathe 2 around the outer periphery of the clad portion 11 by the diamond blade 25.
Cutting was performed until it coincided with the axis of rotation of 0.

Next, N ₂ was added to the porous molded body 1 after cutting,
A crushed piece was removed by blowing a clean gas such as air, and this was subjected to a degreasing treatment at 600 ° C. for 5 hours. Then, a transparent vitrification treatment was performed at 1600 ° C. in a He atmosphere by an ordinary method to prepare an optical fiber preform having an outer diameter of 45 mm and a length of 250 mm. The obtained base material for an optical fiber was drawn to prepare an optical fiber having an outer diameter of 125 μm, and the eccentricity thereof was examined, and it was 0.12 μm.

Ten optical fiber preforms were produced by the above-mentioned method, and these were drawn to produce optical fibers, which were evaluated. All optical fibers were found to have defects or bubbles caused by breakage during cutting. Was not observed.
The eccentricity of the optical fibers was 0.3 μm or less. Further, it was confirmed that the fluctuation of the outer diameter of the optical fiber was 1 μm or less, the mechanical strength was 5 kgf when measured with a gauge length of 10 m and a strain rate of 5%, which was sufficiently practical.

Example 2 Polyvinyl alcohol (manufactured by Shin-Etsu Chemical Co., Ltd., P
A-05) 3 parts by weight and 67 parts by weight of pure water were mixed to prepare a slurry, and this slurry was granulated by a spray drying method to obtain a granulated powder having an average particle size of 100 μm.

On the other hand, the core / cladding ratio is 1/3,
The refractive index difference between the core and the cladding is 0.3%, and the outer diameter is 12
A core rod having a length of 300 mm and a length of 300 mm was prepared by the VAD method, and dehydrated / transparent vitrified to form the rod. This core rod is placed in the center of the cavity of a tubular mold with an outer diameter of 70 mm, the above granulated powder is filled in the cavity while applying vibration to the mold, and the mold is set to 1000 kgf / cm.
A hydrostatic pressure of ² was applied to produce a porous molded body having an outer diameter of 60 mm and a length of 300 mm. When the pore diameter and the porosity of this porous molded article were measured, the pore diameter was 0.08 μm.
m, and the porosity was 35%. The eccentricity of this porous molded body was 0.5 mm. This is because when an optical fiber is manufactured using this porous molded body, the amount of eccentricity is about 1.
It means that it becomes 3 μm.

Then, the porous molded body was treated with a viscosity of 100 cp.
It was immersed for 60 seconds in a liquid vinyl-based resin, which was s, and then subjected to heat treatment at 80 ° C. for 2 hours to cure the vinyl-based resin. At this time, the resin was impregnated to a depth of about 1.5 mm from the surface of the porous molded body.

Next, this porous compact was attached to the lathe 20 shown in FIG. 2, and the outer periphery of the clad portion was cut until the axis of the porous compact coincided with the axis of rotation of the lathe.

Then, a clean gas such as N ₂ or air was blown to the cut porous molded article to remove the crushed pieces, and this was subjected to degreasing treatment at 500 ° C. for 5 hours. Then, a transparent vitrification treatment was performed at 1600 ° C. in a He atmosphere by an ordinary method to produce an optical fiber preform having an outer diameter of 50 mm and a length of 270 mm. The obtained base material for an optical fiber was drawn to prepare an optical fiber having an outer diameter of 125 μm, and the eccentricity thereof was examined. As a result, it was 0.1 μm.

Ten optical fiber preforms were produced by the above-mentioned method, and these were drawn to produce optical fibers, which were evaluated. As a result, all the optical fibers had defects and bubbles caused by breakage during cutting. Was not observed.
The eccentricity of the optical fibers was 0.3 μm or less. Furthermore, it was confirmed that the fluctuation of the outer diameter of the optical fiber was ± 1 μm or less, and the mechanical strength was 5 kgf when measured at a gauge length of 10 m and a strain rate of 5%, which was sufficiently practical. .

Comparative Example Ten porous molded bodies were produced in the same manner as in Example 1.
This porous molded body was dried at 110 ° C. for 5 hours. next,
This porous molded body was attached to the lathe 20 shown in FIG. 2, and the outer periphery of the clad portion was cut until the axis of the porous molded body coincided with the rotation axis of the lathe.

As a result, cracks occurred in the three porous compacts during cutting. The remaining porous molded body was subjected to degreasing and transparent vitrification in the same manner as in Example 1 to prepare a preform for optical fibers. At this time, bubbles were confirmed on the surface of the obtained optical fiber preform. Further, when an optical fiber was manufactured by drawing this optical fiber preform, the variation of the outer diameter of the optical fiber was as large as about ± 3 μm, and the gauge length was 10 mm.
The mechanical strength when measured at m and a strain rate of 5% was 4 kgf, which was a problem in practical use.

[0038]

INDUSTRIAL APPLICABILITY The present invention is capable of producing an optical fiber preform capable of obtaining an optical fiber having no defects and having a very small core eccentricity. Thereby, an optical fiber with a small transmission loss can be obtained.

[Brief description of drawings]

1A is a front view showing a porous molded body obtained by a hybrid method, and FIG. 1B is a side view of FIG.

FIG. 2 is a schematic illustration of an apparatus used in an embodiment of the method according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Porous molded object, 10 ... Core rod, 11 ... Clad part, 20 ... Lathe, 21 ... Mounting stand, 22 ... Lathe body, 2
2a ... Side wall, 22b ... Hole, 23 ... Core chuck, 2
4 ... Clad chuck, 25 ... Diamond blade.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kazuaki Yoshida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A step of producing a porous molded body by providing a clad material formed by molding quartz glass powder on the outside of a core material, a step of impregnating the porous molded body with a resin, and a step of curing the resin. A step of cutting or grinding the outer periphery of the porous molded body to correct the eccentricity of the clad material with respect to the core material, and a step of degreasing and transparent vitrifying the porous molded body after correcting the eccentricity A method for manufacturing a preform for an optical fiber, comprising: