JP4413715B2 - Optical fiber, preform for optical fiber, quartz glass tube used for manufacturing the same, and manufacturing method thereof - Google Patents

Description

The present invention relates to an optical fiber, a preform for an optical fiber, a quartz glass tube used for manufacturing them, and a manufacturing method thereof.

In particular, optical fiber bending is an important characteristic of optical fibers when connecting multi-fiber optical fiber cables, and fiber curl is used as an index of the bending. This is the bend in a state where no force is applied to the optical fiber, expressed by the radius of curvature (m). The larger the value, the better the characteristic.
As a method for improving the fiber curl, Japanese Patent No. 3160422 states that a fiber curl of 10 m can be obtained by improving the optical fiber drawing machine.

In addition, a core rod including only the core part or a part of the clad is created by the VAD method (Vapor phase axial deposition method) or the MCVD method (Modified chemical vapor deposition method), which is the main manufacturing method of silica glass optical fiber, With respect to the rod-in-tube method in which the core rod is inserted into a quartz glass tube and integrated by heating and melting, in WO03 / 080522A1, an optical fiber having a fiber curl of 6 m or more can be obtained by using a high-precision machine-ground quartz glass tube. It is said that an OVD method (Outer vapor phase deposition method) is suitable as a method for producing a quartz glass tube.
Japanese Patent No. 3160422

However, an optical fiber can be produced using a quartz glass tube made by mechanically grinding a quartz glass base material (mother ingot) manufactured by the OVD method directly or by melting and stretching this quartz glass tube. When manufactured, there is a problem that even if the dimensional accuracy of the quartz glass tube is improved and an improved drawing machine is used, the fiber curl may be reduced.
When the cause was investigated, soot deposition by the OVD method formed a concentric layered structure centered on the target, and this layered structure remains as a striae after vitrification of the soot body, but as shown in FIG. It has been found that the fiber curl deteriorates when the difference between the center 1 of the layered striae and the center 2 of the quartz glass tube after grinding is large. In FIG. 1, the thin line indicates the layered striae of the mother ingot, and the thick line indicates the inner and outer periphery of the quartz glass tube after grinding.

  The present invention is based on this finding, and a method for manufacturing a quartz glass tube for optical fiber and a method for manufacturing the same, which can minimize the deviation between the center of striae of the layer structure and the center of the quartz glass tube after grinding. An optical fiber preform having a good fiber curl value and a method for producing the optical fiber obtained by using the silica glass tube for optical fiber obtained by the above method Another object is to provide an optical fiber preform and an optical fiber obtained by the manufacturing method.

Said subject is achieved by the structure in any one of following (1)-( 7 ).
(1)
The soot body made by the soot method is sintered and made into transparent glass. The mother ingot made by mechanical grinding is directly applied to the quartz glass tube made, or after the quartz glass tube is melt-drawn, and only from the core part made core rod or a part of the cladding to insert the core rod containing the 0000, with the core rod and the quartz glass tube fiber curl using rod-in-tube method which melts integrated optical fiber or fiber curl is at least 20m or more 20m, In an optical fiber preform manufacturing method, the amount of deviation between the center of the concentric layered striae observed in the cross section of the quartz glass tube and the center of the outer diameter of the quartz glass tube is equal to the average outer diameter of the quartz glass tube. A method of manufacturing an optical fiber or a preform for optical fiber, wherein a quartz glass tube of 1% or less is used.
(2)
The method for producing an optical fiber according to the above (1), wherein the core rod and the quartz glass tube are melted and integrated and simultaneously drawn to the outer diameter of the target optical fiber to directly obtain the optical fiber.
(3)
The method for producing a preform for an optical fiber according to the above (1), wherein the preform is prepared by performing melt-integration of the core rod and the quartz glass tube only or simultaneously, and drawing.
(4)
The method for producing an optical fiber according to the above (1), wherein a preform is produced by performing melt-integration of the core rod and the quartz glass tube only or simultaneously, and then producing an optical fiber from the preform by a drawing machine.
( 5 )
While rotating a heat-resistant cylindrical or columnar target, a soot body is created by depositing soot of quartz glass on the outer periphery of the target, and a sintered quartz vitrification is applied to the cylindrical quartz glass mother ingot created. In the method for manufacturing a silica glass tube for optical fiber, which is mechanically ground to obtain a silica glass tube, the outer periphery is first ground while maintaining the inner diameter of the shape-stable part inside the defective shape part at both ends of the mother ingot, and then The inner circumference of the quartz glass tube is ground while holding the ground outer circumference, and the amount of deviation between the center of the concentric layered striae observed in the cross section of the quartz glass tube and the center of the outer diameter of the quartz glass tube after grinding is A method for producing a quartz glass tube for optical fiber and / or preform for optical fiber, characterized in that a quartz glass tube having an average outer diameter of 1% or less of the quartz glass tube after grinding is obtained .
(6)
The method for producing a quartz glass tube for an optical fiber and / or optical fiber preform as described in ( 5) above, wherein OH group removal treatment of the soot body is performed.
(7)
The method for producing a quartz glass tube for optical fiber and / or preform for optical fiber according to the above ( 5) or (6) , wherein the melt-drawing is performed after grinding.

  As shown in Fig. 2 (a), the mother ingot after vitrification is shaped more than the inner surface that is vitrified so as to be hugged by the target due to variations in the soot accumulation amount and density. Is not stable. In addition, both the inner and outer surfaces are disordered due to uneven soot deposition at both ends. According to the present invention, grinding is started on the basis of the inner diameter where the shape is stable while avoiding the defective shape portions at both ends, and the deviation between the center after sintered glass formation and the center after grinding is minimized. A silica glass tube suitable for an optical fiber with excellent dimensional accuracy after grinding and suppressing fiber curling can be obtained.

According to the present invention, in a quartz glass tube made by the OVD method having an outer diameter of 100 to 250 mm, an inner diameter of 40 to 80 mm, and a length of about 1.5 to 3.5 m, the deviation can be suppressed to 1% or less. . Further, when an optical fiber is produced using a quartz glass tube having a displacement of 1% or less of the outer diameter of the quartz glass tube, a fiber curl of 20 m or more is obtained.
In addition, even if it uses it, after adding a hot-melt extending | stretching process to the quartz glass tube after grinding, the effect of this invention does not change.
In addition, even in the case of a mother ingot made by the VAD method, the striae of the layer structure remain in the cross section, so there is a gap when drilling this mother ingot with a core drill etc. to make a quartz glass tube. When it occurs, good fiber curl cannot be obtained.

Hereinafter, with reference to FIG. 2 and subsequent drawings, a method for manufacturing a quartz glass tube for an optical fiber according to an embodiment of the present invention will be described.
First, as shown in FIG. 2B, the shape defect portions at both ends are cut off. Next, as shown in FIG. 2C, the outer surface is ground with a rotating grindstone 12 or the like while rotating with the inner diameters of both ends held by the enlarged chuck 10. Instead of cutting off the defective shape portions at both ends, the shaft 10a to which the enlarged-diameter retaining chuck for maintaining the inner diameter is attached as shown in FIG. 3 may be lengthened to hold the inner diameter while avoiding the defective shape portion. Next, as shown in FIG. 2D, the outer periphery of the well-shaped portion is held by the chuck 14 or the like, and the inner surface is ground by the rotating grindstone 16 or the like attached to the tip of the shaft. For each grinding, a general peripheral grinding machine or honing machine may be used. However, the present invention does not specify a grinding apparatus and a holding jig, and any grinding machine capable of obtaining sufficient grinding accuracy can be used. A simple grinding means may be used.

  If the mother ingot is bent, lay the mother ingot on a plate made of graphite or other V groove as shown in Fig. 4 and heat the whole to lower the viscosity. What is necessary is just to perform a mechanical grinding process, after correcting bending | flexion using along. Further, if the bend is a simple shape at one place as shown in FIG. 5, it may be cut at the inflection point of the bend and subjected to grinding. Moreover, what is necessary is just to weld and connect if you want to use it in one state.

As described above, a quartz glass tube in which the amount of deviation between the center of the concentric layered striae observed in the cross section and the center of the outer diameter is 1% or less of the average outer diameter of the quartz glass tube is obtained.
The striae of this layer structure can be observed as shown in FIG. 6 by observing the end face of the quartz glass tube with a simple strain observation device such as simply using a polarizing filter.
In FIG. 6, the thick line represents the outer periphery of the quartz glass tube, and the thin line represents the striae of the layer structure. 1 is the center of the layer striae, 2 is the center of the outer periphery of the quartz glass tube, and 3 is the amount of deviation between the center of the layer striae and the center of the quartz glass tube. In this patent, this deviation amount is divided by the outer diameter of the quartz glass tube of 4 and defined as a ratio to the outer diameter as a percentage display.

Even if the quartz glass tube after grinding is heated, melted and stretched by a conventional method to reduce the tube diameter, there is no problem because the displacement is not affected.
An optical fiber and / or an optical fiber preform can be produced by a normal rod-in-tube method using a quartz glass tube having an amount of deviation of 1% or less obtained as described above. A fiber curl of 20 m or more can be achieved.

  A soot body having an outer diameter of 300 mm was prepared by the multi-burner OVD method, and after dehydration, it was vitrified by the zone melt method to prepare a mother ingot. While the inside diameter of this mother ingot is 8cm and the other side is 10cm, the inner diameter was not hugged to the target when it was vitrified, so that part was cut and removed, and the inner diameter was held with an enlarged collet chuck and rotated. The outer periphery was ground with a rotating diamond grindstone using an NC lathe. Next, both ends of the ground outer periphery are held by a normal chuck, and the inner periphery is ground by inserting a shaft with a diamond grindstone attached to the tip, and a straight quartz having an outer diameter of 180 mm, an inner diameter of 45 mm, and a length of 3 m. Finished into a glass tube. A total of three round samples were taken from both ends and near the center of this quartz glass tube, and when the amount of misalignment between the center of striae of the layer structure and the center of the quartz glass tube was determined using an interferometer, The maximum was 0.7 mm. This is about 0.4% of the outer diameter after mechanical grinding.

  After welding the quartz glass tube that became two by sampling, the rod with 42mm outer diameter core and clad made by VAD method is inserted, and the outer diameter is 125μm at the same time as the collapse in the electric furnace Stretched to produce a single mode optical fiber. When the fiber curl of the obtained optical fiber was measured, it was a good value of 83 m at the minimum.

  A soot body having an outer diameter of 200 mm was prepared by an OVD method using a single burner, and a mother ingot was prepared by vitrification by a zone melt method after dehydration. This mother ingot is 4cm on one end and 6cm on the opposite side. When the vitrification is vitrified, it was not hugging the target and the shape was not stable, so the expanded collet chuck was inserted from both ends to 8cm from both ends. The outer periphery was ground with a rotating diamond grindstone using an NC lathe while being held and rotated. Next, both ends of the ground outer periphery are held by a normal outer peripheral chuck and ground by inserting a shaft with a diamond grindstone attached to the inner periphery at the tip, and straight with an outer diameter of 135 mm, an inner diameter of 45 mm, and a length of 1 m. Finished in a quartz glass tube. A total of three round samples were taken from both ends and near the center of this quartz glass tube, and when the amount of misalignment between the center of striae of the layer structure and the center of the quartz glass tube was determined using an interferometer, The maximum was 0.8 mm. This is about 0.6% of the outer diameter after mechanical grinding.

  Insert a rod with 42 mm outer diameter core and clad made by the MCVD method into two quartz glass tubes that have been sampled, and draw simultaneously with collapse in an electric furnace to obtain a preform with an outer diameter of 80 mm. It was. A single mode optical fiber having an outer diameter of 125 μm was prepared from the preform using a wire drawing machine, and the fiber curl was measured.

Comparative Example 1

  A shaft in which a portion of 8 cm from the both ends of the mother ingot produced in exactly the same manner as in Example 1 is stable as much as possible is selected and held by an outer chuck, and a shaft with a diamond grindstone attached to the inner periphery at the tip is provided. Grinded by inserting. Next, both ends of the ground inner periphery are held using an expanded diameter type collet chuck, and while rotating, the outer periphery is ground using a rotating diamond grindstone by an NC lathe, and the outer diameter is 178 mm, the inner diameter is 45 mm, and the length is 3. Finished into a 1 m straight quartz glass tube. A total of three round samples were taken from both ends and near the center of this quartz glass tube, and the amount of deviation between the center of striae of the layer structure and the center of the quartz glass tube was obtained using an interferometer. The minimum was 4.3 mm. This is about 2.4% of the outer diameter after mechanical grinding.

After welding the two quartz glass tubes into one, insert a rod with a 41 mm outer diameter core and clad made by the VAD method and stretch to an outer diameter of 125 μm simultaneously with collapse in an electric furnace. When a single mode optical fiber was prepared and the fiber curl was measured, the minimum value was 5.8 m, which was not good.
As described above, the effect of the present invention is clear.

It is explanatory drawing for demonstrating the center of the layered striae of a mother ingot, and the center after grinding. FIG. 2A to FIG. 2E are explanatory views for explaining an example of a method for producing a quartz glass tube for optical fiber according to an embodiment of the present invention. It is explanatory drawing for demonstrating the other example of the manufacturing method of the quartz glass tube for optical fibers by the embodiment of this invention. It is explanatory drawing for demonstrating the correction method of the bending before the grinding process of the quartz glass tube for optical fibers by the embodiment of this invention. It is explanatory drawing for demonstrating the method of grinding avoiding the bending before the grinding process of the silica glass tube for optical fibers by the embodiment of this invention. It is a figure for demonstrating the striae etc. of a quartz glass tube end surface.

Explanation of symbols

1 Center of layered striae of mother ingot 2 Center after grinding 3 Aberration between center of stratum striae and center of quartz glass tube 4 Outer diameter of quartz glass tube 10 Expanded chuck 12 Rotating wheel 14 Chuck 16 Rotation Whetstone

Claims (6)

The soot body made by the soot method is sintered and made into transparent glass. The mother ingot made by mechanical grinding is directly applied to the quartz glass tube made, or after the quartz glass tube is melt-drawn, and only from the core part An optical fiber or fiber curl is 20 m or more using a rod-in-tube method in which a core rod or a core rod including a part of a clad is inserted and the core rod and the quartz glass tube are fused and integrated. In the optical fiber preform manufacturing method, the amount of deviation between the center of the concentric layered striae observed in the cross section of the quartz glass tube and the center of the outer diameter of the quartz glass tube is 1 of the average outer diameter of the quartz glass tube. A method for producing an optical fiber or a preform for an optical fiber, characterized by using a quartz glass tube having a percentage of no more than 50%.   2. The method of manufacturing an optical fiber according to claim 1, wherein the core rod and the quartz glass tube are melted and integrated and simultaneously drawn to the outer diameter of the target optical fiber to obtain a direct optical fiber.   2. The method for producing a preform for an optical fiber according to claim 1, wherein the preform is formed by performing melting and integration of the core rod and the quartz glass tube only or simultaneously.   The method for producing an optical fiber according to claim 1, wherein a preform is produced by performing melt-integration of the core rod and the quartz glass tube only or simultaneously, and then producing an optical fiber from the preform by a drawing machine. While rotating a heat-resistant cylindrical or columnar target, a soot body is created by depositing soot of quartz glass on the outer periphery of the target, and a sintered quartz vitrification is applied to the cylindrical quartz glass mother ingot created. In the method for manufacturing a silica glass tube for optical fiber, which is mechanically ground to obtain a silica glass tube, the outer periphery is first ground while maintaining the inner diameter of the shape-stable part inside the defective shape part at both ends of the mother ingot, and then The inner circumference of the quartz glass tube is ground while holding the ground outer circumference, and the amount of deviation between the center of the concentric layered striae observed in the cross section of the quartz glass tube and the center of the outer diameter of the quartz glass tube after grinding is A method for producing a quartz glass tube for optical fiber and / or preform for optical fiber, characterized in that a quartz glass tube having an average outer diameter of 1% or less of the quartz glass tube after grinding is obtained . The method for producing a quartz glass tube for optical fiber and / or preform for optical fiber according to claim 5 , wherein the melt-drawing is performed after grinding.

Images