JP2003020238A - Method for producing optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber preform, by which the fluctuation of the opening diameter in the longitudinal (drawing) direction of an opening part can be suppressed, in the method for producing the optical fiber preform which comprises forming an opening part in first quartz glass, then inserting second quartz glass and melt-bonding/integrating. SOLUTION: The first quartz glass 1, 2 for the optical fiber preform is ground by ultrasonic processing using a grinding tool 10 in whose tip end diamond abrasive grains having at least first coarseness are buried so as to form an opening part having a predetermined opening diameter, then the opening diameter above is expanded by 0.1 to 1 mm by the ultrasonic processing using the grinding tool 10 in whose tip end diamond abrasive grains having second coarseness finer than the first coarseness are buried, and further, the opening part H3 is formed by subjecting the quartz glass to mechanical polishing using cerium oxide abrasive grains or colloidal silica. Thereafter, second quartz glass for the optical fiber preform is inserted in the formed opening part H3 , melt-bonded and integrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION A light for forming an opening in quartz glass for an optical fiber preform and inserting a core glass rod for the optical fiber preform or a stress applying material for the optical fiber preform, and heating and integrating them. The present invention relates to a method for manufacturing a fiber preform.

[0002]

2. Description of the Related Art The amount of information transmitted has increased dramatically due to the spread of the Internet in recent years, and in order to cope with this increasing amount of information, it is possible to increase the transmission capacity of an optical fiber (WDM). Wavelength division multiplexing) transmission is performed. In the above WDM transmission,
Optical fiber with complex refractive index profile, PA
A polarization maintaining fiber such as an NDA fiber is required.

As a general method for manufacturing the above optical fiber, for example, VAD (vapor-phase axial depositio) is used.
n) method or OVD (outside vapor deposition) method is used to deposit soot (glass particles) to synthesize a porous soot base material, which is then dehydrated, sintered and stretched into a glass rod, or MCVD (modified chemical vapor). de
position) method to directly form a glass rod, and a soot to be a clad is deposited on the outer peripheral portion of the obtained glass rod by an OVD method or the like, and is dehydrated and sintered to be an optical fiber preform (preform). An optical fiber is drawn from the tip.

In contrast to the above-mentioned general manufacturing method, in order to simplify the process and reduce the manufacturing cost, an opening is formed at the center of the silica glass rod for optical fiber preform to form a core for optical fiber preform. A method for manufacturing optical fiber preforms has been developed, in which a glass rod is inserted, or openings are formed on both sides of the core of the optical fiber preform to insert stress applying materials for the optical fiber preform, and heating and fusion are integrated. Has been done.

As a method of forming an opening in the above-mentioned quartz glass rod for optical fiber preform or in the optical fiber preform, an opening is made by grinding by ultrasonic machining using a core drill having diamond abrasive grains embedded at the tip. Then, a method is known in which the inner wall surface of the opening is ground by using abrasive grains such as diamond, SiC, or alumina, and the inner wall surface of the opening is mechanically polished by using cerium oxide abrasive grains.

[0006]

However, in the method for producing an optical fiber preform by the method of forming an opening in the above-mentioned quartz glass rod for optical fiber preform or the optical fiber preform, the above-mentioned core drill is used. In order to remove the crushed layer by sonication, it is necessary to widen the opening diameter of the formed opening by 0.5 to 1 mm by grinding,
When grinding for expanding the opening diameter is performed using abrasive grains such as diamond, SiC, or alumina and a brush, it is difficult to accurately control the opening diameter, and the opening diameter in the longitudinal (stretching) direction of the opening is There was a problem of large fluctuations.

When the opening diameter varies greatly in the longitudinal (stretching) direction of the opening as described above, a core glass rod for optical fiber preform is inserted into the obtained opening and heated to be integrated by welding. When drawn from the optical fiber preform formed as described above, inconveniences such as a large core eccentricity and a large number of bubbles are generated.

The present invention has been made in view of the above circumstances. Therefore, an object of the present invention is to form an opening in a first quartz glass such as a quartz glass rod for an optical fiber preform,
In a method of manufacturing an optical fiber preform by inserting a second quartz glass such as a core glass rod for an optical fiber preform, and heating and fusion-integrating the same, a change in opening diameter in the longitudinal (stretching) direction of the opening An object of the present invention is to provide a method for manufacturing an optical fiber preform capable of suppressing the above.

[0009]

In order to achieve the above object, a method of manufacturing an optical fiber preform according to the present invention comprises a step of forming an opening in a first quartz glass for an optical fiber preform, and the opening. A step of inserting the second quartz glass for an optical fiber preform into the above, and a step of heating to fuse and integrate the first quartz glass and the second quartz glass, and an opening is formed in the first quartz glass. The forming step includes at least a first grinding step of grinding to a predetermined opening diameter by ultrasonic processing using a grinding tool having a tip with diamond abrasive grains of a first roughness embedded therein, and the above first step. A second grinding step of expanding the above-mentioned predetermined opening diameter by ultrasonic processing using a grinding tool in which diamond abrasive grains having a second roughness finer than the roughness is embedded at the tip.

In the above-described method for producing an optical fiber preform of the present invention, preferably, the second quartz glass is a core glass rod for an optical fiber preform or a stress applying preform for an optical fiber preform.

In the above-described method for producing an optical fiber preform according to the present invention, the diamond abrasive grains having the first roughness are preferably
The diamond abrasive grains are 100 to 160, and the diamond abrasive grains having the second roughness are # 600 to 2000 diamond abrasive grains.

In the method for producing an optical fiber preform according to the present invention, preferably, the predetermined opening diameter is expanded by 0.1 to 1 mm in the second grinding step.

In the above-described method for producing an optical fiber preform of the present invention, preferably, the step of forming the opening in the first quartz glass is performed after the second grinding step, after the cerium oxide abrasive grains or colloidal silica. The method further includes a step of mechanically polishing the inner wall surface of the opening using. More preferably, in the mechanical polishing step, a nylon brush is applied to the inner wall surface of the opening and reciprocally driven in the extending direction of the opening while rotating.

The above-described method for producing an optical fiber preform according to the present invention comprises at least the first quartz glass for optical fiber preform,
Grinding to a predetermined opening diameter by ultrasonic machining using a grinder having a diamond abrasive grain with a first roughness of about # 100 to 160 embedded in its tip, and then finer than the first roughness. The predetermined opening diameter is expanded by about 0.1 to 1 mm by ultrasonic processing using a grinding tool having diamond abrasive grains with a second roughness of about # 600 to 2000 embedded in the tip, and further, cerium oxide grinding is performed. A nylon brush is applied to the inner wall surface of the opening using particles or colloidal silica, and the inner wall surface of the opening is mechanically polished by reciprocally driving the nylon brush in the extending direction of the opening to form the opening. Next, a second quartz glass for optical fiber preform such as a core glass rod for optical fiber preform or a stress applying preform for optical fiber preform is inserted into the opening and heated to heat the first quartz glass and the second quartz glass.
Quartz glass is fused and integrated.

According to the above-described method for producing an optical fiber preform of the present invention, the optical fiber preform is formed by forming an opening in the first quartz glass, inserting the second quartz glass, and heating and integrating them. In the manufacturing method of the material, when forming the opening in the first quartz glass, ultrasonic machining using a grinding tool having diamond abrasive grains of the first roughness embedded at the tip and finer than the first roughness are used. By performing ultrasonic processing using a grinding tool having diamond abrasive grains of the second roughness embedded at the tip, it is possible to suppress variation in the opening diameter in the longitudinal (stretching) direction of the opening.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

First Embodiment The optical fiber according to the present embodiment is a PANDA fiber which is a kind of polarization maintaining fiber, and its sectional view is shown in FIG.
Shown in. The PANDA fiber includes, for example, a core 1a made of a high refractive index material such as silica glass containing germanium, and a clad 2a made of a material such as silica glass having a refractive index lower than that of the core 1a and covering the outer periphery of the core 1a. The core 1a in the clad 2a
A stress applying portion 3a made of a material having a thermal expansion coefficient several times larger than that of the clad 2a such as silica glass containing B ₂ O ₃ is provided on both sides of the. Due to the difference in the coefficient of thermal expansion between the clad 2a and the stress imparting portion 3a, asymmetric stress is applied to the core 1a, which increases birefringence and keeps the polarization state of light stable. It is a polarization-maintaining fiber that is transmitted and has excellent characteristics such as transmission characteristics and crosstalk.

Next, a method of manufacturing the optical fiber preform (preform) according to this embodiment will be described. For example, VAD (vapor-phase axial deposition) method and OV
Soot (glass fine particles) is deposited by the D (outside vapor deposition) method to synthesize a porous soot base material, and the core glass rod 1 is obtained through dehydration, sintering and stretching, or MCVD (modified chemical vapor depo
sition) method to directly form the core glass rod 1,
Soot to be a clad is deposited on the outer peripheral portion of the obtained core glass rod 1 by the OVD method or the like, and after dehydration and sintering, as shown in the schematic cross-sectional view of FIG. The optical fiber preform P having the cladding 2 formed on the outer peripheral portion is formed.

In the subsequent steps, the optical fiber preform P is cut into a predetermined length to obtain a cylindrical preform shown in FIGS. 2B and 2C. Here, FIG. 2 (B)
2C is a top view, and FIG. 2C is XX ′ in FIG.
FIG.

In the next step, an opening having a predetermined opening diameter is formed at a predetermined position in the above-mentioned cylindrical base material. Here, the core drill 10 having the structure shown in the sectional view of FIG. 3 is used. In the core drill 10, for example, a sintered metal 12 mixed with diamond abrasive grains is attached to one end of a pipe 11 made of metal such as stainless steel, and the holding portion 1 is attached to the other end.
3 is a grinding tool having a structure to which 3 is attached.

Next, as shown in the cross-sectional view of FIG. 4, the core drill 10 is used at a predetermined position of the cylindrical base material while rotating the core drill 10 with the longitudinal direction of the core drill 10 as a rotation axis from the sintered metal 12 side. By pressing and ultrasonic vibration,
Openings H ₃ are formed on both sides of the core glass rod 1 in the clad 2. In this grinding, first, as a first grinding step, for example, a core drill having diamond abrasive grains of a first roughness of about # 100 to 160 embedded in its tip is ground to a predetermined opening diameter. Then the second
As a grinding step, a core drill finer than the first roughness, for example, a diamond abrasive having a second roughness of about # 600 to 2000 is embedded in the tip, is ground so as to widen the predetermined opening diameter. To do. Here, the amount of expanding the opening diameter is preferably about 0.1 to 1 mm.

By the above-mentioned grinding process, the base material having the structure shown in FIG. 5 is obtained. Here, FIG. 5A is a top view.
5B is a cross-sectional view taken along line XX ′ in FIG. That is, in the cylindrical base material in which the cladding 2 is formed on the outer peripheral portion of the core glass rod 1, the openings H ₃ are formed on both sides of the core glass rod 1 in the cladding 2. The opening H ₃ is opened by two grinding steps using diamond abrasive grains having different roughnesses, and the surface roughness of the inner wall surface of the opening and the variation in the opening diameter in the longitudinal direction are adjusted by the conventional opening method. The opening is more suppressed.

Next, as shown in the sectional view of FIG. 6, while supplying abrasive grains 30 such as cerium oxide abrasive grains or colloidal silica into the opening H ₃ , the nylon brush 2
Applying a 0 on the inner wall surface of the opening H _3, while rotating reciprocally so driven in the extending direction of the opening H _3, mechanically polishing the inner wall surface of the opening H _3.

Next, as shown in the sectional view of FIG. 7, the stress-applying material 3 formed separately is inserted into the opening H ₃ . The stress applying material 3 is formed as a rod of silica glass containing B ₂ O ₃ by, for example, the VAD method, the MCVD method, or another method.

Next, the cylindrical base material having the clad 2 formed on the outer peripheral portion of the core glass rod 1 and the stress applying material 3 are heated and fused and integrated, and the optical fiber preform having the structure shown in FIG. And Here, FIG. 8 (A) is a top view of the base material main body portion, and FIG. 8 (B) is provided with a line quoting weight 40 at the lower portion of the main body, and a pressing material 41 for pressing the stress applying material 3 at the upper portion of the main body.
FIG. 9 is a cross-sectional view of a configuration in which a weight 42 and a quartz pipe 43 are provided, and XX ′ in FIG. 8A is XX ′ in FIG. 8B.
Corresponds to X '. The PANDA fiber shown in FIG. 1 can be manufactured by drawing from the above optical fiber preform.

According to the above-described method of manufacturing the optical fiber preform of the present embodiment, the opening is formed in the cylindrical preform (first quartz glass) having the clad 2 formed on the outer periphery of the core glass rod 1. In the method of manufacturing the optical fiber preform by inserting the stress-applying material 3 (second quartz glass) into the first quartz glass and then heating and integrating them together, when the opening is formed in the first quartz glass, Ultrasonic processing using a grinding tool with a diamond abrasive grain of roughness embedded in the tip and ultrasonic processing with a grinding tool with a second roughness diamond abrasive finer than the first roughness in the tip By performing the above, it is possible to suppress the variation of the opening diameter in the longitudinal (stretching) direction of the opening. As a result, the number of bubbles generated in the optical fiber after drawing can be suppressed.

Second Embodiment FIG. 9 is a sectional view of an optical fiber according to this embodiment.
For example, it has a core 1a made of a high refractive index material such as silica glass containing germanium, and a clad 2a made of a material such as silica glass having a lower refractive index than the core 1a and covering the outer periphery of the core 1a.

Next, a method of manufacturing the optical fiber preform (preform) according to this embodiment will be described. First,
As shown in the sectional view of FIG. 10, for example, the VAD method or the OV method is used.
Soot (glass particles) is deposited by the D method to synthesize a porous soot base material, and after dehydration, sintering and stretching,
A core glass rod 2 serving as a clad is formed, and an opening is formed in the center of the core glass rod 2 as in the first embodiment. That is, first, as the first grinding step, for example, # 100 to 160
Using a core drill in which diamond abrasive grains having a first roughness of a certain degree are embedded at the tip, grinding is performed so as to have a predetermined opening diameter. Next, in the second grinding step, using a core drill having a finer than the first roughness, for example, diamond abrasive grains having a second roughness of about # 600 to 2000 embedded in the tip thereof, the above predetermined opening diameter is used. Grind to spread.

By the above grinding process, the base material having the structure shown in FIG. 11 is obtained. Here, FIG. 11A is a top view,
FIG. 11B is a cross-sectional view taken along line XX ′ in FIG. That is, the opening H ₁ is formed in the center of the glass rod 2 serving as the clad. The opening H ₁ is opened by two grinding steps using diamond abrasive grains having different roughnesses, and the surface roughness of the inner wall surface of the opening and the variation in the longitudinal direction of the opening system are adjusted by the conventional opening method. The opening is more suppressed.

Next, as shown in FIG. 12, in the opening H _1, for example, while supplying the abrasive grains 30, such as cerium oxide abrasive grains or colloidal silica, a nylon brush 20 on the inner wall surface of the opening H ₁ The inner wall surface of the opening H ₁ is mechanically polished by reciprocating in the extending direction of the opening H ₃ while rotating.

Next, as shown in FIG. 13, the separately formed core glass rod 1 is inserted into the opening H ₁ . The core glass rod 1 is formed by, for example, the VAD method, the OVD method, the MCVD method, or the like.

Next, the glass rod 2 serving as the clad and the core glass rod 1 are heated to be fused and integrated, and
The optical fiber preform having the structure shown in FIG. Here, FIG.
14A is a top view, and FIG. 14B is a cross-sectional view taken along line XX ′ in FIG. By drawing from the above optical fiber preform, the optical fiber shown in FIG. 9 can be manufactured.

According to the above-described method of manufacturing the optical fiber preform of the present embodiment, the core glass rod 1 (second quartz glass) is formed by forming an opening in the glass rod 2 (first quartz glass) which becomes the cladding. In a method of manufacturing an optical fiber preform by a method of inserting and heating to integrate by fusion, a grinding tool having diamond abrasive grains of a first roughness embedded at the tip when forming an opening in a first quartz glass. Of the opening portion (stretching) by performing ultrasonic processing using a tool and ultrasonic processing using a grinding tool in which diamond abrasive grains having a second roughness smaller than the first roughness are embedded in the tip. It is possible to suppress the variation of the opening diameter in the direction. This makes it possible to suppress the amount of core eccentricity and the number of times bubbles are generated in the optical fiber after drawing.

Example 1 An optical fiber preform (diameter 40 mm, length 3) having a clad formed on the outer periphery of a core.
Two cores having a diameter of 10.8 mm were opened on both sides of the core (00 mm) by an ultrasonic machine using a core drill having # 140 diamond abrasive grains embedded in the tip. Next, the core drill was replaced with a core drill having # 600 diamond abrasive grains embedded at its tip, and ultrasonic processing was performed to widen the opening diameter to 11.0 mm. The opening diameters of the two openings after the above-mentioned processing were the same, and the average surface roughness Ra of the inner wall surface of the opening measured by the contact type roughness meter was 0.1 μm. Next, while pouring cerium oxide abrasive grains into the opening, the nylon brush was rotated at 3000 rpm, reciprocated in the axial direction of the optical fiber preform, and polished for 30 minutes. The average surface roughness Ra of the inner wall surface of the opening after polishing is 0.
It was 03 μm. A stress imparting material made of silica glass doped with B ₂ O ₃ and having a diameter of 10.9 mm was inserted into the above-mentioned opening and heated in a drawing furnace to perform wire drawing while welding and integrating. No bubbles were observed when the wire was drawn for a distance of 20 km.

(Embodiment 2) An optical fiber preform having a structure in which a clad is formed on the outer peripheral portion of a core (diameter 40 mm, length 3)
Two cores having a diameter of 10.5 mm were opened on both sides of the core (00 mm) by an ultrasonic machine using a core drill having # 100 diamond abrasive grains embedded in the tip. # 1
For a drill with 00 diamond abrasive grains embedded, # 1
The processing speed can be made higher than that of a drill having 40 diamond abrasive grains embedded therein. Next, the core drill # 6
The diamond was replaced with a core drill in which the diamond abrasive grains of No. 00 were embedded in the tip, and ultrasonic processing was performed to widen the opening diameter to 10.8 mm. Further, the core drill was replaced with a core drill having # 2000 diamond abrasive grains embedded at the tip, and ultrasonic processing was performed to widen the opening diameter to 11.0 mm. After the above-mentioned processing, the opening diameters of the two openings are equal, and the average surface roughness Ra of the inner wall surface of the opening measured by a contact type roughness meter is 0.
It was 07 μm. Next, while pouring colloidal silica into the opening, the nylon brush was rotated at 5000 rpm, reciprocated at a speed of 100 mm / min in the axial direction of the optical fiber preform, and polished for 30 minutes. The average surface roughness Ra of the inner wall surface of the opening after polishing was 0.03 μm. Colloidal silica has advantages in that precipitation is less likely to occur as compared with cerium oxide, so that the polishing liquid can be easily managed, and the amount of abrasive grains remaining after cleaning is small. In the above opening,
Diameter of silica glass doped with B ₂ O ₃ 10.
A 9 mm stress-applying material was inserted and heated in a drawing furnace to perform wire drawing while integrally welding. No bubbles were observed when the wire was drawn for a distance of 20 km.

(Comparative Example 1) An optical fiber preform having a clad formed on the outer periphery of a core (diameter 40 mm, length 3)
Two openings having a diameter of 10.5 mm were opened on both sides of the (00 mm) core by an ultrasonic machine using a core drill having # 140 diamond abrasive grains embedded in the tip. Next, while pouring SiC abrasive grains into the opening,
Lapping was performed for 2 hours by rotating at 00 rpm and reciprocatingly moving in the axial direction of the optical fiber preform to habituate the scratches and irregularities formed in the above-mentioned grinding process and flatten the surface. When the opening diameter was measured after processing, the opening diameter of one of the two openings was 11.1 mm, while the opening diameter of the other opening was 11.0 mm. The average surface roughness Ra of the inner wall surface of the opening was 0.15 μm. Next, while pouring the cerium oxide abrasive grains into the opening,
It was rotated at 000 rpm, reciprocated in the axial direction of the optical fiber preform, and polished for 30 minutes. The average surface roughness Ra of the inner wall surface of the opening after polishing was 0.05 μm.
A stress imparting material made of silica glass doped with B ₂ O ₃ and having a diameter of 10.9 mm was inserted into the above-mentioned opening and heated in a drawing furnace to perform wire drawing while welding and integrating. 20 km
When the line for the distance of was drawn, bubbles were observed 5 times.

(Embodiment 3) Ultrasonic machining was performed at the center of the core of an optical fiber quartz preform (diameter 125 mm, length 300 mm) produced by the VAD method using a core drill having # 140 diamond abrasive grains embedded in the tip. Machine diameter 9.8
One mm opening was opened. Next, the core drill # 1
The diamond was replaced with a core drill having 200 diamond abrasive grains embedded in the tip, and ultrasonic processing was performed to widen the opening diameter to 10.1 mm. The variation in the opening diameter of the opening after the above-mentioned processing in the longitudinal direction was 10 μm, and the average surface roughness Ra of the inner wall surface of the opening measured by the contact type roughness meter was 0.07 μm. Next, while pouring colloidal silica into the opening, the nylon brush was rotated at 5000 rpm, reciprocated at a speed of 100 mm / min in the axial direction of the optical fiber preform, and polished for 30 minutes. The average surface roughness Ra of the inner wall surface of the opening after polishing was 0.03 μm. A core glass rod with a diameter of 10.0 mm produced by the MCVD method was inserted into the above-mentioned opening, and the lower end was welded by inserting it from above the electric furnace at 2000 ° C. and then from below while decompressing with a vacuum pump. The pieces were heated in order and integrated by welding. The obtained base material was drawn to a diameter of 60 mm and then drawn to 300 km.
Manufactured optical fiber. Bubbles were generated twice during the drawing, and the core eccentricity of the drawn optical fiber was 0.2 μm.

(Comparative Example 2) Ultrasonic machining was performed using a core drill in which # 140 diamond abrasive grains were embedded at the center of the core of an optical fiber quartz preform (diameter 125 mm, length 300 mm) produced by the VAD method. Machine diameter 9.5
One mm opening was opened. Next, a lap treatment was performed for 2 hours by rotating the brush at 2000 rpm while pouring SiC abrasive grains into the opening and reciprocating the brush in the axial direction of the optical fiber preform. The opening diameter of the opening after the above processing is 1
Although it was 0.1 mm, the variation in the longitudinal direction was 50 μm, and the average surface roughness Ra of the inner wall surface of the opening measured by the contact type roughness meter was 0.15 μm. Next, while pouring cerium oxide abrasive grains into the opening, the nylon brush was rotated at 5000 rpm, reciprocated in the axial direction of the optical fiber preform, and polished for 30 minutes. The average surface roughness Ra of the inner wall surface of the opening after polishing was 0.05 μm. In the opening, a diameter of 10.
After inserting a 0 mm core glass rod and inserting it from the upper side of an electric furnace at 2000 ° C. to weld the lower end, the pressure was reduced by a vacuum pump and the layers were heated in order from the bottom to be welded and integrated. The obtained base material was drawn to have a diameter of 60 mm and then drawn to manufacture an optical fiber of 300 km. Bubbles were generated 10 times during drawing, and the core eccentricity of the drawn optical fiber was 0.5 μm.

The present invention is not limited to the above embodiment. For example, a stress imparting material or quartz glass other than the core glass rod may be inserted into the opening formed in the first quartz glass such as the quartz glass rod for optical fiber preform. In addition, various modifications can be made without changing the gist of the present invention.

[0040]

According to the present invention, there is provided a method for manufacturing an optical fiber preform by a method of forming an opening in a first quartz glass, inserting a second quartz glass, and heating and integrating them together. When forming an opening in quartz glass, ultrasonic processing using a grinding tool having diamond abrasive grains of the first roughness embedded at the tip and diamond grinding of the second roughness finer than the first roughness It is possible to provide a method for manufacturing an optical fiber preform capable of suppressing the variation of the opening diameter in the longitudinal (stretching) direction of the opening by performing ultrasonic processing using a grinding tool having grains embedded in the tip. .

[Brief description of drawings]

FIG. 1 is an optical fiber (PA according to a first embodiment.
It is sectional drawing of (NDA fiber).

FIG. 2A is a schematic cross-sectional view of an optical fiber preform manufactured by the method for manufacturing an optical fiber according to the first embodiment, and FIG. 2B is an optical fiber base of FIG. FIG. 2 is a top view of a base material cut out from a material in a predetermined length.
FIG. 2C is a sectional view taken along line XX ′ in FIG.

FIG. 3 is a cross-sectional view of a core drill used in the first embodiment.

FIG. 4 is a cross-sectional view showing a step of forming openings on both sides of a core glass rod in a clad in the method of manufacturing an optical fiber according to the first embodiment.

5 (A) is a top view of a base material in which an opening is formed in the optical fiber manufacturing method according to the first embodiment, and FIG. 5 (B) is a plan view of FIG. 5 (A). It is sectional drawing in XX '.

FIG. 6 is a cross-sectional view showing a step of mechanically polishing the inner wall surface of the opening in the method for manufacturing an optical fiber according to the first embodiment.

FIG. 7 is a cross-sectional view showing a step of inserting a stress applying material into an opening in the method for manufacturing an optical fiber according to the first embodiment.

FIG. 8 (A) is a top view of a main body portion of an optical fiber preform manufactured by the optical fiber manufacturing method according to the first embodiment, and FIG. 8 (B) is a cross-sectional view. Figure 8
XX ′ in (A) corresponds to XX ′ in FIG.

FIG. 9 is a sectional view of an optical fiber according to a second embodiment.

FIG. 10 is a cross-sectional view showing a step of forming an opening at the center of a glass rod serving as a clad in the optical fiber manufacturing method according to the second embodiment.

FIG. 11 (A) is a top view of a base material in which an opening is formed in the optical fiber manufacturing method according to the second embodiment, and FIG. 11 (B) is a plan view of FIG. 11 (A). It is sectional drawing in XX '.

FIG. 12 is a cross-sectional view showing a step of mechanically polishing the inner wall surface of the opening in the method for manufacturing an optical fiber according to the second embodiment.

FIG. 13 is a cross-sectional view showing a step of inserting a core glass rod into an opening in the method for manufacturing an optical fiber according to the second embodiment.

FIG. 14 (A) is a top view of an optical fiber preform manufactured by the method for manufacturing an optical fiber according to the second embodiment, and FIG. 14 (B) is an X in FIG. 14 (A). -X '
FIG.

[Explanation of symbols]

1a ... core 2a ... clad 3a ... stress imparting material 1 ... core glass rod 2 ... cladding 3 ... stress imparting material 10 ... core drill 11 ... pipe 12 ... sintered metal 13 ... supporting portion 20 ... nylon brush 30 ... abrasive grain H ₁ , H ₃ ... Opening P ... Optical fiber preform

Continued front page    (72) Inventor Akinari Uchikoshi             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F-term (reference) 2H050 AA03 AA04 AA05 AB04Y                       AB05X AB73 AC44                 3C058 AA06 AA07 CA02 CB01 DA02                 4G021 BA23

Claims (6)

[Claims] 1. A step of forming an opening in a first quartz glass for an optical fiber preform, a step of inserting a second quartz glass for an optical fiber preform in the opening, and the heating to heat the first quartz glass. And a step of welding and integrating the second quartz glass, wherein the step of forming an opening in the first quartz glass includes a grinding tool in which at least diamond abrasive grains of the first roughness are embedded in the tip. A first grinding step of grinding to a predetermined opening diameter by the ultrasonic processing used, and a grinding tool in which diamond abrasive grains having a second roughness finer than the above-mentioned first roughness were embedded at the tip were used. A second grinding step of expanding the predetermined opening diameter by ultrasonic processing. 2. The method for producing an optical fiber preform according to claim 1, wherein the second quartz glass is a core glass rod for an optical fiber preform or a stress-applying preform for an optical fiber preform. 3. The diamond grain of the first roughness is # 1.
0 to 160 diamond abrasive grains, wherein the second roughness diamond abrasive grains are # 600 to 200.
The method for producing an optical fiber preform according to claim 1, wherein the number of diamond abrasive grains is 0. 4. The method for producing an optical fiber preform according to claim 1, wherein the predetermined opening diameter is increased by 0.1 to 1 mm in the second grinding step. 5. The step of forming an opening in the first quartz glass further comprises a step of mechanically polishing the inner wall surface of the opening with cerium oxide abrasive grains or colloidal silica after the second grinding step. The method for manufacturing an optical fiber preform according to claim 1. 6. The method for producing an optical fiber preform according to claim 5, wherein in the step of mechanically polishing, a nylon brush is applied to the inner wall surface of the opening and is reciprocally driven in the extending direction of the opening while being rotated.