JPH0648756A - Production of preformed material for optical fiber - Google Patents

Abstract

PURPOSE:To provide a production method based on hybrid process for porous preformed material, small in the deviation of a core rod from the center of a mold and enabling the eccentricity of the core for optical fibers as the final product to be made very small. CONSTITUTION:A core glass rod 11 is placed in the space of a mold 12 and this space is filled with a molding material 14 containing silica glass powder followed by pressure molding of the powder 14 to produce the objective porous preformed material for optical fibers. In this process, the location of the glass rod 11 is detected by detectors 18, 21 during filling the molding material 14, and based on the result, the location of the rod is regulated.

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 porous preform for optical fibers used in optical communication.

[0002]

BACKGROUND OF THE INVENTION As an industrially advantageous method for manufacturing a base material for an optical fiber,
There is a hybrid method in which a clad portion of a glass rod for core (hereinafter also referred to as a core rod) is manufactured by a powder molding method. However, the problem with this method is the eccentricity of the core. The eccentricity of the core is an extremely important factor in the characteristics of the optical fiber. When connecting the light source and the optical fiber or the optical fibers to each other with a connector, the eccentricity of the core must be minimized in terms of light receiving efficiency or connection efficiency. .

On the other hand, in the case of the single-mode fiber, which is the most widely used optical fiber, the core diameter is generally about 10 μm and the relative refractive index difference is as small as 0.3 to 0.4%. The eccentricity of the core becomes a big problem. Generally, the smaller the amount of eccentricity of the core, the better, but it is said that 0.5 μm, preferably 0.3 μm or less is preferable for practical use.

Conventionally, as a method of correcting the eccentricity of the core, a method of fixing the porous base material obtained by the hybrid method to a lathe and cutting the outer periphery of the clad material with a diamond blade has been adopted.

However, when the porous molded body is cut by such a method, (1) a lathe for cutting, etc., especially a machine must be prepared, and (2) the number of steps is increased and the molded body is increased. You have to consider the cutting yield of
(3) There is a problem that cutting skills are required, which complicates the manufacturing process and leads to an increase in manufacturing cost.

On the other hand, the eccentricity of the core mostly occurs in the step of filling the silica raw material. An example thereof will be described with reference to FIG. FIG. 3 is a diagram illustrating a conventional silica raw material filling method when forming a porous molded body by a pressing method. The rubber mold support cylinder 3 is installed vertically on the vibrator 6, and the rubber mold 2 is inserted into the support cylinder 3. The rubber mold 2 has a high degree of verticality, and a lower lid 7 is provided below the rubber mold 2. Then, the core rod 1 is inserted into the lower lid 7 of the rubber mold 2, the distance from the outer periphery of the rubber mold 2 is measured, the center position of the core rod 1 with respect to the rubber mold 2 is determined, and the rod support 5
Fix with. Then, while the silica raw material 4 is being filled around the core rod 1 from the hopper 8 provided above the support cylinder 3, the vibrator 6 is operated and the rubber mold 2 is vibrated. By vibrating, the packing density of the silica powder is increased and the packing density is made uniform.

However, during vibration, the rubber rod, the core rod, and the rod support member (made of metal) have different natural vibrations, which causes a problem that the core rod is slightly displaced from the set position.

The present invention has been made in view of the above circumstances, and is premised on the hybrid method, and the deviation of the core rod from the center of the molding die is small, and the eccentricity of the core of the optical fiber as the final product is extremely small. It is an object of the present invention to provide a method for manufacturing a porous preform for optical fibers, which can be made small.

[0009]

In order to solve the above-mentioned problems, the present invention has a glass rod for a core arranged in a molding space of a molding die, and a quartz glass in the molding space of the molding die. A method for producing a porous base material for an optical fiber, which comprises filling a molding material containing a powder and then molding the powder by pressurization to obtain a porous base material for an optical fiber, wherein the core material is used for filling the molding material. Provided is a method for producing a porous preform for optical fibers, which comprises detecting the position of a glass rod-shaped body by a detection device and adjusting the position of the glass rod-shaped body for core according to the detection result.

A video camera, for example, may be used as the detecting device, and the information is displayed on the monitor while monitoring the center position of the glass rod for core from above the glass rod for core. The position of the glass rod for core is adjusted according to the detection result of this detection device. In this case, it is preferable that the position information thus obtained is fed back to the holding mechanism of the glass rod for core to control the position so that the glass rod for core is always at the center of the molding die.

This makes it possible to correct the eccentricity of the core rod with respect to the clad material when the raw material powder is molded, and subsequently degreasing and transparent vitrifying the optical fiber with less eccentricity of the core rod. A base material for use can be obtained.

The present invention is premised on the hybrid method, but this method is one in which a glass rod for core is produced by a vapor phase method or a powder molding method, and if necessary, this is made into a transparent glass, and then the core material is used. This is a method in which a clad material formed on the outside of the glass rod-shaped body is manufactured by a powder molding method and the two are combined to obtain a porous molded body. In addition, the powder molding method,
For example, the pressurizing method (Japanese Patent Application No. 2-244817) and the MSP method (Journal of Optical Communi).
"Cations", Volume 10, Issue 1, Pages 2-5, 19
1989), etc., dry molding method, casting molding method (JP-A-64-
56331), extrusion method (Japanese Patent Application No. 2-24481).
No.) etc. is used.

The glass rod for core includes not only a transparent glass material but also a porous material. In addition, as a means for detecting the position of the glass rod for core, a TV camera, a fiberscope, a CCD camera, or the like can be used. As a method of adjusting the position of the glass rod-shaped body for core, the center position of the molding die is obtained on the monitor, and the deviation amount of the position of the glass rod-shaped body for core is determined by the X-axis and the Y-axis of the holding mechanism of the glass rod-shaped body for core. The manual adjustment can be made using the attached micrometer. Further, it is also possible to feed back to the stepping motors respectively provided on the X axis and the Y axis of the holding mechanism and drive them to automatically control the position of the glass rod for core.

After the powder is filled by the above method, the molded porous molded article can be degreased and made into a transparent vitrification under the conditions which are usually used.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing an example of an implementation state of the present invention. A rubber mold support cylinder 13 is placed on the vibrator 16, and the rubber mold 12 is inserted into the support cylinder 13.
The rubber mold 12 has a high degree of verticality, and the lower lid 1 is below the rubber mold 12.
7 is provided. Then, the core rod 11 is inserted into the lower lid 17 and is located at the center of the rubber mold 12. Above the support cylinder 13, a hopper 22 in which the silica raw material 14 is stored is provided.

The upper end of the core rod 11 has a gripping arm 15
The gripping arm 15 is connected to the XY stage 19, and the XY stage 19 can move the upper end of the core rod 11.

A TV camera 1 is provided above the core rod 11.
8 is installed, and this TV camera 18 is a monitor 2
Connected to 1. As shown in FIG. 2, the monitor 21 is capable of monitoring the position deviation of the core rod 11 from the center of the rubber mold 12, and further has a position detection function added to the core 21. Rod 11
It is possible to electrically take out the amount of positional deviation. The monitor 21 is connected to the control system 20 of the XY stage 19, and the positional deviation information signal from the monitor is input to the control system 20. Then, based on this signal, a control signal is output from the control system 20 to the XY stage 19,
The position of the upper end of the core rod 11 is controlled.

In such an apparatus, the silica raw material 14 from the hopper 22 is fed to the core rod 11 in the rubber mold 12.
The vibrator 16 is operated while filling the periphery of the rubber mold 12 to increase the packing density of the silica powder, and the rubber mold 12 is vibrated in order to make the packing density uniform. At this time, the core rod 11
May shift from the center of the molding die, but in this embodiment, the position of the core rod 11 is monitored by the TV camera 18, the position is detected by the monitor 21 having a position detecting function, and the position information signal is output. Based on this, the control system 20 drives the XY stage 19 to drive the core rod 1
1 is controlled so that its position is always located in the center of the rubber mold 12 for molding, so that the core rod can be accurately held in the center of the rubber mold 12 from the start to the end of powder filling regardless of vibration. it can.

After the powder is filled in this way, the rubber mold 12 is taken out from the support cylinder 13 and loaded into, for example, a hydrostatic pressure device, the powder therein is pressure-molded, and porous molding is performed. The body. As described above, since the core rod is prevented from being displaced during the raw material filling step, the eccentricity of the rod is extremely small even in this porous molded body, and the eccentricity of the core of the optical fiber obtained from this porous material is also extremely small. It will be small.

It is to be noted that the core rod 11 needs to be modified particularly at the filling start stage, and if the raw material powder is filled up to more than half of the core rod, the positional deviation does not occur much. In addition, as other uses of the TV camera as a monitoring device, important influences on the eccentricity of the core of the optical fiber such as the roundness and uneven thickness of the rubber mold and the position of the center hole of the rubber-shaped lower lid 11 are exerted. It can be used for inspection of the dimensional accuracy of the rubber mold 12 to be given. That is, since both the inspection and the position control of the core material can be performed by the same device, the eccentricity of the core can be prevented more effectively.

When vibrating while filling the silica raw material, the core rod may also vibrate and the screen of the monitor 21 may shake.
In that case, the image processing may be performed according to the vibration frequency to obtain the accurate position of the core rod, or the measurement of the position of the core rod-correction and filling-excitation may be repeated alternately. Good (measuring-no correction during filling-excitation).

Specific examples will be described below.

Example 1 To 100 parts of silica particles having an average particle diameter of 8 μm, 3 parts of polyvinyl alcohol (PA-05 manufactured by Shin-Etsu Chemical Co., Ltd.) as a binder and 67 parts of pure water were added to prepare a slurry, and this slurry was spray-dried. Granulation was performed by a method to obtain granulated powder having an average particle diameter of 100 μm.

On the other hand, the core / clad ratio is 1/3,
The difference in the refractive index of the clad is 0.3%, the outer diameter is 12 mm,
A core rod having a length of 300 mm was produced by the VAD method, dehydrated, and made into a transparent glass to form the rod.

This core rod is inserted into the center hole of the lower lid 17 of the rubber mold 12 of FIG. 1 and the silica raw material 14 is fed from the hopper 22 while controlling the position of the core rod as described above.
The mold was vibrated by the vibrator 16 while being supplied into the mold 12.

After filling to a predetermined position, the upper part of the rubber mold was covered with an upper lid (not shown), and the rubber mold 12 was taken out from the support cylinder 13. Set this rubber mold in the hydrostatic pressure device,
Outer diameter of 60 m when pressurized with hydrostatic pressure of 1000 kg / cm ^2.
A porous molded body having m and a length of 300 mm was produced.

The porous compact was subjected to a degreasing treatment at 500 ° C. for 5 hours in the atmosphere. Then, it is dehydrated in a He atmosphere containing 5% of chlorine by a conventional method, and further subjected to a transparent glass treatment at 1600 ° C. in a He atmosphere by an ordinary method to give an outer diameter of
A base material for an optical fiber having a length of 270 mm and a length of 270 mm was manufactured.
An optical fiber was produced by drawing the obtained optical fiber preform, and the amount of eccentricity of the core of the optical fiber was examined. As a result, the amount of eccentricity was 0.1 μm.

Ten optical fiber preforms were produced by such a method, and these were similarly used as optical fibers. The eccentricity of these cores was evaluated. All optical fibers were 0.3 μm or less. there were.

(Comparative Example 1) Using the apparatus shown in FIG. 3 (without a monitoring device for the core rod), 10 similar porous body moldings were produced according to the above-mentioned Example 1. After evaluating the eccentricity of the core after making the optical fiber,
The variation was in the range of 0.2 to 1.0 μm, which was a problem in practical use.

[0031]

According to the present invention, the deviation of the core rod from the center of the molding die is small, and the eccentricity of the core of the final optical fiber can be made extremely small. A manufacturing method is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an implementation state of the present invention.

FIG. 2 is a diagram showing a display of a monitor used in an embodiment of the present invention.

FIG. 3 is a view showing a conventional apparatus for filling a silica raw material by a hybrid method.

[Explanation of symbols]

11 ... Core rod, 12 ... Rubber type, 13 ... Support tube, 1
4 ... Silica raw material, 15 ... Grip arm, 16 ... Vibrator, 1
7 ... Lower lid, 18 ... TV camera, 19 ... XY stage, 2
0 ... Control system, 21 ... Monitor, 22 ... Hopper.

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

Claims (2)

[Claims] 1. A glass rod for core is arranged in a molding space of a molding die, a molding material containing quartz glass powder is filled in the molding space of the molding die, and then the powder is molded by pressurization. A method for manufacturing an optical fiber porous preform to obtain an optical fiber porous preform, the position of the glass rod for core is detected by a detection device at the time of filling the molding material,
A method for manufacturing a porous preform for optical fibers, which comprises adjusting the position of the glass rod for core according to the detection result. 2. The position information from the detection device is fed back to a holding mechanism for the core glass rod to control the position so that the core rod is always at the center of the molding die. Item 2. A method for producing a porous preform for optical fibers according to Item 1.