JP2001172038A - Preform ingot for optical fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a preform ingot having excellent optical characteristics and to provide a method for producing the preform ingot by which the surface of the preform ingot obtained by sintering and vitrifying a soot material having unevennesses formed on the surface by high-speed deposition is smoothly ground and worked so as not to decenter a core part and the surface unevennesses are removed. SOLUTION: This method is characterized as smoothly working the outer peripheral surface near both ends of the preform ingot 21, mounting the resultant ingot 21 on a grinding machine and preventing the positional shift during the working when depositing glass microparticles produced by a flame hydrolytic reaction on a starting core member 1, forming a clad part, sintering and vitrifying the soot material, then grinding the unevennesses caused on the surface of the resultant preform ingot 21 and removing the unevennesses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a base material ingot for optical fiber (hereinafter, referred to as a fiber ingot) obtained by depositing glass fine particles produced by a flame hydrolysis reaction on a starting core member at a high speed.
The present invention relates to a base material ingot in which surface irregularities are removed by grinding.

[0002]

2. Description of the Related Art A base material ingot is produced by, for example, depositing glass fine particles (soot) generated by a flame hydrolysis reaction on the surface of a starting core member by an OVD method (external method) to produce a porous base material. Furthermore, it is manufactured through processes such as dehydration and sintering. In the OVD method, in order to increase the production rate, the starting core member is formed by a method of increasing the diameter of a burner for depositing glass particles by hydrolyzing a raw material gas in an oxyhydrogen flame, or by increasing the number of burners. Methods for increasing the rate of soot deposition on top are generally known.

A method of increasing the supply gas amount by increasing the diameter of the burner for supplying the raw material gas is as follows. The soot deposition rate on the surface of the starting core member is extremely low in the initial stage of soot deposition, and the method using a plurality of burners is as follows. There is flame interference between the burners, and the deposition efficiency does not rise as expected. Further, as is generally known, a method of increasing the number of burners is to move the burners in parallel and left and right along the starting core member to deposit soot. The defective part which is a disadvantage of this method is generated. In addition, since a plurality of burners are used, the surface of the soot body has irregularities. This phenomenon may be conspicuous on the surface due to the size and number of burners for soot deposition by an external method, or the method of moving the burners from side to side. In particular, when the high-speed deposition is performed by increasing the amount of the raw material gas, it appears more remarkably.

As described above, the surface of a base material ingot obtained by depositing soot around the starting core member by an external method may have irregularities. Such a base material ingot may have a desired diameter. When the diameter of the preform is reduced to form a preform, and the preform is spun into an optical fiber, the optical characteristics of the optical fiber may be affected by irregularities on the surface of the base material ingot. Therefore, when forming the clad portion, it must be performed under conditions that do not cause unevenness on the surface. However, under such conditions, there is a limit to the soot deposition rate, which hinders speeding up.

[0005]

When a base material ingot is manufactured using the OVD method as described above, these problems must be solved in order to dramatically increase the soot deposition rate. Therefore, a method of using multiple burners for soot deposition, increasing the amount of source gas, performing high-speed soot deposition, and grinding and removing irregularities on the surface of the base material ingot obtained by sintering vitrification to smooth it. Can be considered. But,
In order to attach to the grinder, the conical portions at both ends of the base material ingot must be gripped by the grinder. As a result, the core may be eccentric.

An object of the present invention is to grind the surface of a base material ingot obtained by sintering and vitrifying a soot body having an uneven surface due to high-speed deposition so that the core portion is not eccentric. To provide a base material ingot having excellent optical characteristics by removing surface irregularities and a method for producing the same.

[0007]

According to a method of manufacturing a base material ingot of the present invention, a soot (glass fine particles) generated by a flame hydrolysis reaction is deposited on a starting core member to form a clad portion, and a sintered glass is formed. Then, when grinding and removing irregularities generated on the surface of the obtained base material ingot,
The present invention is characterized in that the outer peripheral surfaces near both ends of the base material ingot are processed smoothly and attached to a grinding machine to prevent displacement during processing.

When smoothing the outer peripheral surfaces near both ends of the base material ingot, the position of the core is detected, and the core is attached to a grinding machine so that the core is located at the center of the rotation axis. To grind the outer peripheral surface of the base material ingot. Also,
When the outer peripheral surfaces near both ends are processed smoothly, it is preferable to process the outer peripheral surface into a conical shape that spreads toward the center of the length of the base material ingot. Further, it is preferable to grind and provide a reference azimuth plane (orientation flat) for detecting a tilt angle in a circumferential direction on a conical portion processed into a conical shape. The base material ingot of the present invention is manufactured in this manner.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION If there is unevenness on the surface of a base material ingot obtained by dehydrating and sintering a soot body manufactured by the OVD method, the core is stretched to a predetermined diameter in order to obtain an optical fiber preform. The diameter fluctuates and adversely affects the optical properties of the optical fiber obtained by spinning the diameter. In order to prevent this, when the surface of the base material ingot has irregularities, it is necessary to smoothly grind the surface into a cylindrical shape (hereinafter, referred to as cylindrical grinding). What is important at this time is the roundness of the base material ingot that has been vitrified and the amount of eccentricity of the core. In particular, the roundness of the optical fiber and the amount of eccentricity of the core have a large adverse effect on optical characteristics (connection loss) when connecting the optical fiber when laying the optical fiber cable.

Therefore, in cylindrical grinding of the base material ingot, the position of the core portion of the base material ingot is optically measured to determine the rotation center position at the time of grinding. After processing a conical shape with the rotation axis center that matches the true circle of the part, and grinding the reference azimuth plane (orientation flat) on the conical part so that the circumferential direction of the core part can be confirmed , Set at the center of rotation of the grinding machine. By performing cylindrical grinding in this state, it is possible to prevent the occurrence of non-circularity, eccentricity failure of the core portion, and the like. As a result, a base material ingot having optically stable characteristics can be synthesized at a high speed, and a preform obtained by stretching the preform to a predetermined diameter is spun to obtain an optical fiber having good optical characteristics. . The present invention will be described in more detail with reference to Examples, Comparative Examples and Figures, but the present invention is not limited thereto.

[0011]

(Embodiment 1) FIG. 1 shows an example of an apparatus for producing a soot body (porous glass base material) for an optical fiber. As the starting core member 1, a quartz glass rod for a core whose outer diameter was 25 mmφ and whose refractive index was adjusted for a single mode optical fiber having a length of 1200 mm was used. The starting core member 1 is welded to a dummy rod 2 made of quartz glass, and this is attached to a core member rotating motor 4 provided in a closed-type reaction furnace 3 at 40 rpm.
And rotated.

The oxyhydrogen flame burner 5 is provided with a plurality of large-diameter and large-sized burners, which are conventionally used, and is supplied with an oxygen gas of 80 cm ³ / mi from a raw material supply device (not shown).
n, hydrogen gas 160 cm ³ / min, oxygen gas 10 cm ³ / min as carrier gas
40 g / min of iCl ₄ was supplied. The burner 5 was reciprocated by the traverse motor 6 at a speed of 150 mm / min within a range of 1600 mm, and glass fine particles generated by flame hydrolysis of SiCl ₄ were deposited on the starting core member 1. As the deposition proceeded, the amount of the raw material gas was further increased, and a soot body having an outer diameter of 230 mmφ was obtained after 24 hours. Immediately before the end of the deposition, an oxygen gas 240 cm ³ / min and a hydrogen gas 48
0 cm ³ / min, oxygen gas 25 as carrier gas
Source gas SiCl ₄ 125c accompanied by 0 cm ³ / min
m ³ / min.

The surface of the soot body 7 deposited at a high speed of the average deposition rate of 30 g / min was found to have spiral irregularities. Further, the soot body 7 was placed in a sintering furnace and dewatered and sintered to obtain a transparent base material ingot. However, even after the sintering and vitrification, spiral irregularities remained on the surface. The maximum depth of the irregularities is 1.35 mm. In this state, when the optical fiber is formed into a preform and further spun into an optical fiber, one of the optical characteristics of the optical fiber is large due to eccentricity during fusion splicing of the optical fiber. Connection loss occurs.

Next, as a first grinding step, both ends of the sintered and vitrified base material ingot are subjected to conical processing having a rotation axis center that matches the perfect circle of the core portion.
The reference azimuth plane (orientation flat) was ground on the formed conical part so that the inclination angle of the core part in the circumferential direction, that is, the circumferential azimuth, could be confirmed. After forming a smooth conical portion on both ends in this way, the conical portion is mounted on a cylindrical grinder.

More specifically, as shown in FIG. 2, a base material ingot 21 was attached to a chuck 23 of a taper grinder 22 and fixed by a chuck support 24. Next, while rotating the base material ingot 21, the core position is measured by an optical measuring device (optical measuring device using polarizing glass) not shown, and the center position of the core is moved by the chuck 23, and the chuck is moved. The base material ingot 21 was set by adjusting to the center of rotation of the support portion 24. The tapered portion 8 at the end of the base material ingot was ground using a diamond wheel 25 having a roughness of # 600 using a diamond wheel 25 with a roughness of # 600 and a conical shape at an angle of 10 degrees with respect to the center axis of the core. This was performed for both ends of the base material ingot 21. Further, as shown in FIG. 3, an orientation flat 26 serving as an origin in the circumferential direction (a reference azimuth plane for detecting a tilt angle in the circumferential direction) is provided on one tapered portion 8 by grinding.

Further, in the second grinding step, the peripheral surface of the straight body portion of the base material ingot 21 is ground smoothly to remove irregularities on the surface. First, the base material ingot 21 having both ends conically ground was attached to the chuck 28 of the cylindrical grinder 27 shown in FIG. One of the chucks 28 is processed so that the base material ingot 21 is fixed by the orientation flat 26.
Next, the base material ingot 21 is rotated, and the eccentricity of the core portion is measured in the longitudinal direction of the base material ingot 21 by an optical measuring device (not shown), and the rotation angle and the eccentricity with respect to the orientation flat 26 are measured. The quantity and the position in the longitudinal direction are stored in the control device. 2 and 4
In the figure, the support mechanism of the diamond wheel supported by the grinding machine is not shown.

Based on these data, the cylindrical grinder 2
Diamond wheels 31, 32, and 33 were attached to 7 and rotated as described below, and were ground once at a feed speed of the base material ingot 21 of 50 mm / min while cooling the ground portion with water. By this grinding, the surface of the base material ingot 21 was finished smoothly, and the core portion was clearly measured. In addition,
The roughness of each of the diamond wheels 31, 32, and 33 is # 60, # 140, and # 600, respectively.
Grinding depth of each wheel, 0.75m for wheel 31
m, the wheel 32 was set at a position 0.3 mm deeper than the cut surface of the wheel 31, and the wheel 33 was set at a position 0.05 mm deeper than the cut surface of the wheel 32 (see FIGS. 5 and 6).

Next, while rotating the base material ingot 21, the diameter ratio of the core and the clad and the eccentricity of the core were measured by an optical measuring instrument. Based on this measurement result, fine adjustment of the center of rotation of the core is performed with the chuck, and
In order to adjust the diameter ratio of the clad, finish grinding is performed once using only the # 600 wheel 33 at a grinding depth of 0.05 mm and a feed rate of the base material ingot of 50 mm / min. Grinding of the trunk surface was completed.
It took about 120 minutes to grind the straight body part,
The surface of the base material ingot is extremely smooth, and is not inferior to the one manufactured by the conventional manufacturing method having a low deposition rate, and the manufacturing time is reduced to about 1/2 that of the conventional one even when the cylindrical grinding for removing the surface irregularities is included. Could be shortened.

The ground preform ingot was drawn to 45 mmφ in an electric furnace to form an optical fiber preform, which was spun with a wire drawing machine to obtain an optical fiber having an outer diameter of 125 μm. When the optical characteristics of this optical fiber were measured, as shown in Table 1, both the eccentricity of the core and the connection loss were extremely small, and good results were obtained.

Comparative Example 1 A soot body synthesized in the same manner as in Example 1 was placed in a sintering furnace, and dehydrated and sintered to obtain a transparent base material ingot. Spiral irregularities remained on the surface of the base material ingot. The depth of the unevenness was 1.20 mm at the maximum. A base material ingot is set on a cylindrical grinder by a conventional method, and three times while using a diamond wheel having a roughness of # 60 with a grinding depth of 0.5 mm and a feed speed of the base material ingot of 70 mm / min while cooling the ground portion with water. After grinding, using a # 600 diamond wheel, the depth is 0.1 mm and the feed rate of the base material ingot is 50 m.
The finish grinding was performed once at m / min, and once at a grinding depth of 0.05 mm and a feed rate of the base material ingot of 50 mm / min, and the grinding of the body portion of the base material ingot was completed.

The produced base material ingot was drawn to a diameter of 45 mmφ in an electric furnace to obtain an optical fiber preform.
This preform is spun with a wire drawing machine and has an outer diameter of 125 μm.
Was obtained. When the optical characteristics of this optical fiber were measured, the results showed that the eccentricity of the core varied. The reason for this is that the shape of the taper at both ends of the base material ingot is not uniform, so when mounting it on a cylindrical grinder, the fitting at the chuck is poor and the mounting position shifts due to vibration etc. during grinding. found. Table 1 shows the measurement results of the optical characteristics of the optical fibers obtained in Examples and Comparative Examples.

[0022]

[Table 1]

[0023]

As described above, according to the present invention, even in a base material ingot manufactured by performing high-speed synthesis under such a condition that irregularities are generated on the surface of the soot body, the tapered portions at both ends are ground into conical shapes. By applying orientation flat processing to this conical portion, positional deviation during grinding of the outer peripheral surface of the base body ingot straight body portion is prevented, and furthermore, the origin flat in the circumferential direction is determined by the orientation flat, and By adjusting the shaving depth, the delicate bending of the core that occurs during vitrification is corrected, the eccentricity of the core is improved, and the same optical characteristics as those manufactured by the conventional method are obtained. I got it. The optical fiber obtained by stretching this base material ingot to a desired diameter to form a preform and spinning the fiber had extremely small eccentricity and connection loss of the core, and had good optical characteristics.

[Brief description of the drawings]

FIG. 1 is a front view schematically showing an apparatus for manufacturing an optical fiber soot body.

FIG. 2 is a schematic front view showing a state in which the end of a base material ingot is processed into a conical shape by a taper portion grinding machine.

FIG. 3 is a schematic plan view showing an orientation flat provided on a tapered portion.

FIG. 4 is a schematic front view showing how a cylindrical grinder is used to smoothly grind a peripheral surface of a straight body of a base material ingot.

FIG. 5 is a schematic side view showing a state in which a peripheral surface of a straight body portion of a base material ingot is ground smoothly.

FIG. 6 is a schematic plan view showing a state in which a peripheral surface of a straight body portion of a base material ingot is ground smoothly.

[Explanation of symbols]

 1. Starting core member 2. Dummy stick 3. Closed reactor 4. Motor for core member rotation 5. 5. Oxy-hydrogen flame burner 6. Traverse motor Soot body 8. Tapered section 9. Burner guide mechanism 10. Exhaust hood 21. Base material ingot 22. Taper grinding machine 23, 28. Chuck 24, 29. Chuck support 25, 31, 32, 33. Diamond wheel 26. Orientation flat 27. Cylindrical grinding machine

Claims (5)

[Claims] 1. A method in which glass fine particles generated by a flame hydrolysis reaction are deposited on a starting core member to form a clad portion, and after sintering and vitrification, the irregularities formed on the surface of the obtained base material ingot are ground. A method of manufacturing a preform ingot for an optical fiber, wherein the outer peripheral surfaces near both ends of the preform ingot are smoothed and attached to a grinder to prevent displacement during processing. . 2. The method according to claim 1, wherein when the outer peripheral surface near both ends of the base material ingot is machined smoothly, a position of a core is detected, and the core is attached to a grinding machine such that the core is located at the center of the rotation axis. The method for manufacturing a preform ingot for optical fibers according to claim 1, wherein the outer peripheral surface of the preform ingot is ground along the center. 3. The optical fiber mother according to claim 1, wherein, when the outer peripheral surfaces near both ends of the base material ingot are processed smoothly, the base material ingot is processed into a conical shape extending toward the center of the length of the base material ingot. Method of manufacturing material ingot. 4. A conical part machined in a conical shape, wherein a reference azimuth plane (orientation flat) for detecting a tilt angle in a circumferential direction is provided by grinding. A method for producing a preform ingot for optical fibers according to the above. 5. A preform ingot for an optical fiber, produced by the production method according to claim 1. Description: