JP2002356341A - Method for producing optical fiber preform ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a preform ingot having excellent eccentricity ratio of core part and capable of obtaining an optical fiber excellent in connection loss and eccentricity of core part by spinning at a low cost. SOLUTION: This method for producing an optical fiber preform ingot 1 comprising piling up soot on the starting core member, glassifying by dehydrating and sintering, thereafter cylindrically grinding the surface while rotating, characterized in that the radius of the master ingot is measured with an outer shape measuring device for each 90 deg. or 180 deg. of rotation in advance to the grinding, the position of rotating axis of the cylindrical grinder 4 is obtained by calculation based on the measured values, and the outer circumference of the preform ingot 1 is finished by grinding based on the calculated value.

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 an optical fiber preform ingot having an excellent core eccentricity (hereinafter simply referred to as preform ingot).

[0002]

2. Description of the Related Art In a manufacturing process of a base material ingot, for example, after a cladding portion is deposited on the surface of a starting core member by an OVD (external attachment) method, the base material ingot is subjected to processes such as dehydration and sintering. Become. In the OVD method, in the step of depositing soot on the surface of the starting core member, generally known methods for improving the production speed include:
A method of increasing the diameter of a burner for supplying a raw material gas and depositing glass fine particles generated by hydrolysis in an oxyhydrogen flame and a method of increasing the number of the burners are known.

As a technique for increasing productivity in the OVD method, there is known a method in which the length of a core is increased to increase the ratio of a straight body portion which is a product of a base material ingot.

[0004]

When a method of increasing the production rate by increasing the diameter of a burner for supplying a raw material gas is adopted, soot is extremely deposited at the initial stage of depositing soot on the surface of a starting core member. There is a problem of bad. Further, when a plurality of burners having a large diameter are used, there is a problem that flame interference occurs and the deposition efficiency is not improved as expected.

[0005] When the method of increasing the number of burners is adopted, the surface of the soot deposited becomes uneven due to the presence of a plurality of burners. In particular, when a high-speed deposition is performed by increasing the amount of source gas, There is a problem that the phenomenon appears remarkably. As a result, the resulting optical fiber does not have good optical properties, especially the desired cut-off wavelength or dispersion wavelength in a single mode optical fiber.

On the other hand, the method of increasing the length of the core has a problem in that since the length of the core is increased, the bending is increased and the shape is often non-uniform.

A method for aligning the rotation axis of the core with the rotation axis of the base material ingot as a method of bringing the unevenness and the core portion of the base material ingot to the center of the base material ingot is disclosed in Japanese Patent Application Laid-Open No. 2000-47039. Are known. However, since there is no method for simply measuring the actual rotation axis of the base material ingot, it is not possible to perform a regular check every day, and errors have occurred due to factors such as temperature changes.

As a means for solving the above-mentioned problem, a method is provided in which a device for measuring the position of the core of the base material ingot is provided in a cylindrical grinding device, and the position of the core is measured every time the base material ingot is rotated by 90 ° or 180 °. However, the cost is high and the operation rate of the apparatus is not increased.

The present invention has been made in view of the above problems, and has an excellent core eccentricity which can be spun to obtain an optical fiber having excellent connection loss and core eccentricity. The main object of the present invention is to provide a method for manufacturing a base material ingot which can be manufactured at low cost.

[0010]

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and a method of manufacturing a base material ingot of the present invention comprises depositing soot on a starting core member, dehydrating and sintering the glass, Next, in a method for manufacturing a base material ingot in which the surface is cylindrically ground while rotating, the radius of the master ingot is set to 90 ° or 1 by a contour measuring machine before grinding.
It is characterized in that it is measured every 80 ° rotation, the rotational axis position of the cylindrical grinding device is calculated and obtained based on the measured value, and based on this, the outer periphery of the base material ingot is ground and finished.

The master ingot has a roundness of 50 μm.
m and a length of 1 m or more are used, and the measurement of the radius of the master ingot or the base material ingot is preferably performed twice or more. The position of the core with respect to the rotation axis of the cylindrical grinding device can be estimated from the calculated rotation axis position of the cylindrical grinding device and the position of the base metal ingot whose core center is known with respect to the outer shape of the ingot. Based on the position of the core with respect to the rotation axis of the cylindrical grinding device obtained by this estimation, the outer periphery of the base material ingot may be ground and finished so that the center of the base material ingot coincides with the center of the core.

[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 is a schematic cross-sectional view showing how a radius of a base material ingot attached to a chuck of a cylindrical grinding device is measured using an external shape measuring machine. The radius of the base material ingot 1 from the measurement standard O of the contour measuring machine is determined by moving the tracing styluses 3 and 3 'attached to the left and right tracing stylus moving parts 2 and 2' to the base material ingot 1 by driving a servomotor or the like. The ingots are moved until they come into contact with each other, and radii ra and rb of the ingot with respect to the contour measuring machine are measured from the positions where the tracing styluses 3 and 3 'are stopped.

As shown in FIG. 1, in order to obtain the X coordinate of the rotation axis of the cylindrical grinding machine with respect to the contour measuring machine, the origin and the 18
The radius measurement is performed twice at the 0 ° rotation position, the measurement value at the origin (ra0 °, rb0 °) and the measurement value at the 180 ° rotation position are calculated.
Assuming (ra180 °, rb180 °), the X coordinate of the rotation axis of the cylindrical grinding device with respect to the contour measuring machine can be calculated by ((ra0 ° −rb0 °) + (ra180 ° −rb180 °)) / 2. .

The X coordinate position of the rotation axis of the cylindrical grinding device with respect to the contour measuring machine is obtained by the above calculation using a master ingot having a high roundness whose core position with respect to the contour is known. By estimating the position and attaching the base material ingot to a cylinder having the center of the core as the center, a base material ingot with less eccentricity can be manufactured. Further, by rotating the base material ingot and measuring the radius at every 90 ° or 180 °, it was found that this method was effective even when the mounting of the master ingot was poor and the rotational runout was large. The base material ingot of the present invention is then drawn by a known method to obtain an optical fiber preform, and then spun into an optical fiber.

Although a known grinding device can be used, for example, it is desirable to use a cylindrical grinding device, which enables simultaneous grinding with a plurality of cylindrical grinding wheels. At that time, in order to shorten the grinding time, the cylindrical grinding may be performed by multi-blade grinding using a plurality of cylindrical grindstones having different roughnesses. For example, as shown in FIG. 2, the base material ingot 1 to be ground is attached to the cylindrical grinding device 4 by the chucks 5, 5 ', and the desired core / clad ratio is determined using diamond wheels 6, 7, 8 having different roughness. Grind until it becomes. At this time, the position of the grindstone is adjusted according to the position of the core and the cutting depth.

Conventionally, the rotational axis position of a cylindrical grinding device has been measured at the time of starting the device or at the time of periodic inspection.
Due to factors such as room temperature changes, the position of the actual rotation axis of the cylindrical grinding device and the estimated value are different from each other, and the eccentricity may not be improved even if grinding is performed. According to this, the position of the rotation axis of the cylindrical grinding device can be easily and accurately calculated, and not only the obtained base material ingot has a high roundness without irregularities, but also the core part is formed of the base material ingot. It becomes possible to arrange it accurately in the center. As a result, the optical fiber obtained by spinning the fiber has good optical characteristics, and particularly, in terms of optical characteristics such as connection loss in fiber fusion splicing work when laying an optical fiber cable, which has been a problem in the past. The problem was solved.

[0018]

The present invention will be described below in detail with reference to examples and comparative examples. (Example 1) First, a master ingot having a length of 2 m, a diameter of 150 mmφ, and a maximum roundness of 30 μm, and a transparent deground and vitrified transparent base material ingot having an outer diameter of about 140 mmφ were prepared. Observation of the surface of the base material ingot with the naked eye revealed that irregularities with a maximum depth of 1.11 mm were spirally formed.

Next, the master ingot was attached to a chuck of a cylindrical grinding device, and a radius of 180 mm at a position 250 mm from the end of the master ingot was measured by an external shape measuring machine.
Measured twice per ° rotation. The measured value obtained is
0 ° = 70.11mm, rb0 ° = 69.92mm, 180 °
In the rotation position, ra180 ° = 69.67mm, rb180 ° = 7
0.39 mm. When the X coordinate of the rotation axis of the cylindrical grinding device with respect to the external shape measuring machine is calculated and obtained from these measured values, it becomes -0.265 mm as described below. ((70.
11−69.92) + (69.67−70.39)) / 2 = −
0.265 mm Further, the measurement was continued at 500 mm intervals in the longitudinal direction of the master ingot, and each measurement was -0.257.
mm, -0.248 mm and -0.238 mm.

Next, the master ingot is removed, the base material ingot to be ground is attached to the chuck of the cylindrical grinding device, and the shape of the base material ingot is measured by an external shape measuring machine. Was estimated and calculated over the longitudinal direction of the base material ingot. Based on the obtained results, the finishing dimensions of the base material ingot are designed so that the center of the base material ingot and the center of the core match over the longitudinal direction of the base material ingot, and the outer periphery of the base material ingot is ground along this. Finished.

The grinding was performed four times with a maximum cutting depth of 0.3 mm using a # 120 diamond wheel. Next, finish grinding was performed once using a # 300 diamond wheel at a cutting depth of 0.05 mm. The roughness of the ground surface was 0.01 mm.

The preform ingot obtained as described above was drawn in an electric furnace to a diameter of 45 mmφ to obtain a preform for optical fiber, which was spun with a wire drawing machine to obtain an outer diameter of 125 μm.
An optical fiber of mφ was obtained. Connection loss of this optical fiber,
When the core eccentricity was measured by a measuring method described later, good results were obtained as shown in Table 1.

Comparative Example 1 First, as a base material ingot to be ground, a transparent base material ingot dehydrated and vitrified and having an outer diameter of about 140 mmφ was prepared. The maximum depth of the irregularities on the surface of the base material ingot was 1.04 mm. Using this base material ingot, in the same manner as in Example 1, the X coordinate of the rotation axis of the cylindrical grinding device with respect to the outer shape measuring device was measured at four points at 500 mm intervals, and was -0.05 mm and -0.16 respectively.
mm, -0.19 mm and -0.33 mm were obtained. Furthermore, the outer shape was measured with an outer shape measuring machine, and the position of the core with respect to the rotation axis of the cylindrical grinding device was estimated and calculated.

Next, based on the obtained results, the finishing dimensions of the base material ingot are designed so that the center of the base material ingot and the center of the core coincide with each other in the longitudinal direction of the base material ingot, and the base material is aligned with this. The outer periphery of the material ingot was cylindrically ground. For this, four rough grindings were performed with a maximum cutting depth of 0.3 mm using a # 120 diamond wheel. Next, finish grinding was performed once using a # 300 diamond wheel at a cutting depth of 0.05 mm. The depth of the asperities on the polished finished surface was 0.01 mm.

The base material ingot thus obtained was stretched in an electric furnace in the same manner as in Example 1 to obtain a base material ingot having a diameter of 45 mm.
An optical fiber preform having a diameter of φ was spun with a drawing machine to obtain an optical fiber having an outer diameter of 125 μm. The connection loss and the core eccentricity of this optical fiber were measured in the same manner as in Example 1. As shown in Table 1, the connection loss and the core eccentricity were large.

The method for measuring the connection loss and the eccentricity of the core of the optical fiber is as follows. a. Connection loss: OTDR (Optical Time Domain Refractom)
etory) method. b. Core eccentricity: Optical fiber structure measurement device (Photon Kine
The measurement was performed using "Models 2400" manufactured by tics.

[0027]

[Table 1]

The present invention is not limited to the above embodiment, but is merely an example. The present invention has substantially the same structure as the technical idea described in the claims of the present invention, and has the same operation and effect. Whatever is played is included in the technical scope of the present invention.

[0029]

The method for producing a base material ingot of the present invention comprises:
As compared with the conventional manufacturing method, a base material ingot having an excellent core eccentricity can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing how a radius of a base material ingot is measured using a profile measuring instrument.

FIG. 2 is a schematic front view showing a state of grinding using a cylindrical grinding device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base material ingot, 2, 2 '... Contact point moving part, 3, 3' ... Contact point, 4 ... Cylindrical grinding device, 5, 5 ... Chuck, 6, 7, 8 ... Diamond wheel, ra, rb ... Ingot radius.

Continuation of the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma F-term in the Shin-Etsu Kagaku Kogyo Co., Ltd. Precision Functional Materials Laboratory 3C034 AA01 BB91 CA01 CB01 DD01 3C043 AA01 CC02 4G021 BA00

Claims (5)

[Claims] 1. A method for manufacturing an optical fiber preform ingot in which a soot is deposited on a starting core member, dehydrated and sintered into a glass, and then the surface is cylindrically ground while being rotated. Is measured at every 90 ° or 180 ° rotation, the rotational axis position of the cylindrical grinding device is calculated and obtained based on the measured value, and the outer periphery of the base material ingot is ground and finished based on this. A method for producing an optical fiber preform ingot. 2. The master ingot has a roundness of 50.
The method for manufacturing an optical fiber preform ingot according to claim 1, wherein the length is 1 m or less and 1 m or more. 3. The method of manufacturing an optical fiber preform ingot according to claim 1, wherein the measurement of the radius of the optical fiber preform ingot is performed twice or more. 4. The position of the core with respect to the rotation axis of the cylindrical grinding device from the calculated rotation axis position of the cylindrical grinding device and the position of the optical fiber preform ingot whose core center is known with respect to the outer shape of the ingot. The method for producing an optical fiber preform ingot according to claim 1, wherein 5. An outer periphery of the optical fiber preform ingot is ground so that the center of the optical fiber preform ingot coincides with the center of the core based on the position of the core with respect to the rotation axis of the cylindrical grinding device obtained by the estimation. The method for producing an optical fiber preform ingot according to claim 4, which is finished.