JPH07133127A - Production of single-mode optical fiber - Google Patents

Abstract

PURPOSE:To obtain a high-quality single-mode optical fiber not contg. any bubble and with its axial center aligned with that of a core. CONSTITUTION:A preform 1 having a preform clad part 1B on the outer periphery of a preform core part 1A and consisting of a quartz column, a covering tube 30 consisting of a quartz tube having the hollow hole into which the preform 1 with the upper part held and hung with a covering tube chuck 17 is loosely inserted and having an inner diameter larger than the outer diameter of the preform 1 by >=1mm and a dummy rod 20-1 with the lower end face connected to the upper end face of the preform 1 so that both axial centers are aligned and consisting of a quartz column with the upper part held by a chuck 16 and suspended in the covering tube 30 are used. A means for aligning the axial center of the rod 20-1 with that of the covering tube 30 and a means for discharging the air between the preform 1 and covering tube 30 to the outside are formed, the preform is inserted and suspended in the hollow hole of the covering tube 30, the lower parts of the preform 1 and covering tube 30 are heated and softened, and the preform is drawn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a single mode optical fiber. Single mode optical fiber has an outer diameter (outer diameter of the clad) of 125 μm and a core diameter of 10 μm.
The diameter is m to 8 μm, and the core diameter is very small as compared with the multimode optical fiber.

Therefore, a solid cylindrical base material for a multimode optical fiber manufactured by an internal chemical vapor deposition method (quartz having a base material clad outer diameter of 13 mm and a base material core outer diameter of 1 mm) It is difficult to simply heat and soften the base material) and draw it.

[0003]

2. Description of the Related Art FIG. 4 is a diagram showing a conventional method for a single mode optical fiber, and FIG. 5 is a diagram showing another conventional method.

In FIG. 4, reference numeral 1 denotes a solid columnar cylinder manufactured by an internal chemical vapor deposition method having an outer diameter (outer diameter of the base material clad portion 1B) of 13 mm and an outer diameter of the base material core portion 1A of 1 mm. (Length 300mm-60
It is a base material made of quartz (0 mm).

Reference numeral 2 is a dummy rod made of a quartz column (having a length of about 1000 mm) having an outer diameter equal to the outer diameter of the base material 1, the lower end surface of which is welded and connected to the upper end surface of the base material 1 by an oxyhydrogen burner. Is.
3-1 is a covering tube made of a quartz tube having a hole diameter of 14 mm and an outer diameter of about 25 mm.

An apparatus for producing a single mode optical fiber is a heating furnace such as a high frequency induction furnace or a resistance furnace (having a heating temperature of about 2000) which has a vertical hollow hole having an inner diameter sufficiently larger than the outer diameter of the cover tube 3-1. 10) and a single-mode optical fiber 10 installed on the same axis below the heating furnace 10 and drawn.
0, a primary coating portion 11 composed of a coating material accommodating die 11A for applying a primary coating layer such as a silicone resin and a drying oven (temperature is about 800 ° C.) 11B, and a single mode optical fiber 10 after primary coating.
It consists of a capstan 12 that pulls in 0.

Further, a guide bar 13 installed vertically adjacent to the heating furnace 10, a sliding body 15 fitted to the guide bar 13 and performing a uniform downward motion, and a heating furnace from the outer peripheral portion of the sliding body 15
A chuck 16 extending in the shape of a horizontal arm and a cover tube chuck 17 are provided above 10.

The upper part of the cover tube 3-1 is held vertically by the cover tube chuck 17 so that the lower part of the cover tube 3-1 is inserted into the axis of the hollow portion of the heating furnace 10. Further, the dummy rod 2 is inserted into the cover pipe 3-1 with the base material 1 facing downward, and the chuck 16 holds the upper part of the dummy rod 2 so that the axial center of the base material 1 and the axial center of the cover pipe 3-1. The base material 1 is suspended vertically so that Therefore, the gap between the outer peripheral surface of the base material 1 and the inner wall of the cover tube 3-1 is almost zero.
It will be 5 mm.

Then a predetermined speed (tens of meters / min)
Slide the sliding body 15 down, and in the heating furnace 10, the base material 1 and cover pipe 3-
The lower part of 1 is heated and softened to form a spindle shape. From the lower tip of the spindle shape, pull out a thread-shaped single-mode optical fiber 100 with a core diameter of 10 μm to 8 μm and an outer diameter of 125 μm. We are producing a single mode optical fiber.

In another manufacturing method, as shown in FIG. 5, a dummy rod 2 having the same diameter is welded to the upper end surface by an oxyhydrogen burner. The outer diameter is 13 mm. The outer diameter of the base metal core is 1 mm. A base material 1 made of quartz in the shape of an actual cylinder and a cover tube 3-2 having an inner diameter (17 mm) larger than the cover tube shown in FIG. 4 and an outer diameter of about 26 mm are used.

Then, the dummy rod 2 is inserted with the base material 1 facing downward into the cover pipe 3-2 which is vertically suspended by the cover pipe chuck 17, and the chuck 16 holds the upper part of the dummy rod 2 and The base material 1 is suspended vertically so that the axis of the material 1 and the axis of the cover pipe 3-2 are aligned.

Therefore, the outer peripheral surface of the base material 1 and the covering pipe 3-1
The inner wall gap is about 2 mm, which is larger than the method shown in Fig. 4. After that, the sliding body 15 is lowered at a predetermined speed, and the base material 1 and the lower portion of the covering tube 3-2 are heated and softened in the heating furnace 10 to have a spindle shape, and the core diameter is 10 μm from the lower tip of the spindle shape.
It is manufactured by drawing a filamentous single mode optical fiber 100 with a diameter of m to 8 μm and an outer diameter of 125 μm.

[0013]

A single mode optical fiber drawn by using a base material and a cover tube as described above has a core in which the base material core portion is thinned as shown in FIG.
101, a clad 102A surrounding the core 101 whose base material clad portion is thinned, and a clad 10 where the cover tube is thinned.
The clad 102B formed on the outer side of 2A is integrally formed.

By the way, in the former method, that is, the manufacturing method shown in FIG. 4, since the gap between the base material and the cover tube is small, they coincide with each other when the axes of the base material and the cover tube are heated and softened. Therefore, the core of the obtained single mode optical fiber does not decenter.

However, since the air escape path between the base material and the cover tube is narrow when heated and softened, the bubble M is confined between the clad 102A and the clad 102B as shown in FIG. 6 (A). I was afraid of being hit.

On the other hand, in the latter method, that is, in the manufacturing method shown in FIG. 5, since the gap between the base material and the covering tube is large, the air escapes well and air bubbles are not trapped. However, since the gap between the base material and the cover tube is large and only the upper part of the dummy bar is held, the tip of the base material deviates from the axis of the cover tube and the tip of the base material during heat softening. Is unevenly attached to the cover tube.

As a result, as shown in FIG. 6B,
The obtained single mode optical fiber has a problem that the core 101 is eccentric. The present invention was created in view of the above point, and a manufacturing method capable of obtaining a high-quality single-mode optical fiber in which bubbles do not exist and the axis of the fiber and the axis of the core coincide with each other are provided. It is intended to be provided.

[0018]

In order to achieve the above object, the present invention provides a base material clad portion 1B on the outer periphery of a base material core portion 1A.
And a quartz tube having an inner diameter of a hollow hole that is at least 1 mm larger than the outer diameter of the parent material 1. The parent material 1 is held in a state of being held by a tube chuck 17 and suspended. A cover tube 30 loosely inserted in the axis of the hollow hole, and a lower end surface connected to the upper end surface of the base material 1 so that the axes coincide with each other, and the upper part is held by the chuck 16 and suspended in the cover tube 30. In the manufacturing method using the dummy rod 20-1 formed of a pillar, a means for aligning the axis of the dummy rod 20-1 with the axis of the cover tube 30 and an air between the base material 1 and the cover tube 30. The base material 1 is inserted into the hollow hole of the cover tube 30, and the central axis of the base material 1 and the center axis of the cover tube 30 are aligned with each other by the means for aligning the central axis and suspended. , The lower part of the base material 1 and the covering tube 30 is inserted and penetrated into the axial center of the heating furnace 10 to heat and soften, and the air is discharged to the outside through a means for letting the air escape. One, a structure in which to draw.

As illustrated in FIG. 1, the means for aligning the axis of the dummy rod with the axis of the cover tube is such that the difference between the inner diameter of the cover tube 30 and the outer diameter of the dummy bar 20-1 is 0.2. The outer diameter of the dummy rod 20-1 is formed to be less than or equal to mm, and the means for letting the air between the base material and the covering pipe escape to the outside is the base material 1
And an air vent hole 31 provided in the shell of the cover tube 30 corresponding to the connection between the dummy rod 20-1 and the dummy rod 20-1.

Further, as illustrated in FIG. 2, the means for aligning the axis of the dummy rod with the axis of the cover tube is larger than (radius dimension of cover tube-radius dimension of dummy bar-0.2 mm). A gap adjusting bar 40 made of quartz having an outer diameter dimension is loosely inserted and arranged at an equal pitch between the outer peripheral surface of the dummy rod 20-2 and the inner wall of the cover tube 30, and covers the base material. The means for releasing the air between the pipe and the outside is the adjacent gap adjustment bar.
It shall be the gap between 40.

Alternatively, as illustrated in FIG. 3, the means for aligning the axis of the dummy rod with the axis of the cover tube is larger than (radius dimension of cover tube-radius dimension of dummy bar-0.1 mm). The protrusions 50 made of a plurality of protrusions of quartz are arranged at equal pitches on the two circles in the upper and lower portions of the outer peripheral surface of the dummy rod 20-3, respectively. The means for letting the air between them escape to the outside is the gap between the adjacent protrusions 50.

[0022]

In the present invention, when the base material and the lower end portion of the cover tube are heated and softened while the base material is inserted into the hollow hole of the cover tube,
Experimental results have confirmed that if there is a large gap of 0.5 mm or more between the outer peripheral surface of the base material and the inner wall of the cover tube, the air can rise almost completely toward the dummy rod.

On the other hand, since the means for letting the air between the base material and the covering pipe escape to the outside is provided, the air raised in the direction of the dummy rod is discharged to the outside. Therefore, no bubbles remain in the single mode optical fiber.

Further, since the means for aligning the axis of the dummy rod with the axis of the cover tube is provided, the axis of the base material connected to the lower portion of the dummy rod is substantially aligned with the axis of the cover tube. Therefore, the core of the single mode optical fiber in which the base material and the covering tube are heated and softened and drawn is not decentered.

[0025]

The present invention will be described in detail with reference to the drawings. The same reference numerals denote the same objects throughout the drawings.

FIG. 1 is a sectional view of an embodiment of the method of the present invention, FIG. 2 is a view of another embodiment of the method of the present invention, (A) is a sectional view, and (B) is a plan view. 3 (A) is a sectional view and FIG. 3 (B) is a plan view showing still another embodiment of the method of the present invention.

In FIG. 1, reference numeral 1 denotes a solid cylindrical column manufactured by an internal chemical vapor deposition method having an outer diameter (outer diameter of the base material clad portion 1B) of 13 mm and an outer diameter of the base material core portion 1A of 1 mm. (Length 300mm-60
It is a base material made of quartz (0 mm).

Reference numeral 30 is a covering tube made of a quartz tube having a hole diameter of 15 mm and an outer diameter of 26 mm. Numeral 20-1 is a dummy rod made of a quartz column having an outer diameter of 14.8 mm (the length is about 1000 mm), the lower end surface of which is welded and connected to the upper end surface of the base material 1 by an oxyhydrogen burner.

The base material 1 is inserted into the hollow hole of the cover tube 30, and the base material 1 and the dummy rod 20-1 are connected to each other with the lower end surface of the base material 1 and the lower end surface of the cover tube 30 aligned. A plurality of (eg, four) air vent holes 31 are provided in the shell portion of the covering pipe 30 corresponding to the connection portion of
Is provided.

The above-mentioned base material 1, dummy rod 20-1, cover tube
A method of manufacturing a single mode optical fiber using 30 will be described. First, the cover tube chuck 17 covers the cover tube 30 so that the lower part of the cover tube 30 is inserted into the axial center of the hollow portion of the heating furnace 10.
Hold the top of 30 and hang it vertically.

Then, the dummy rod 20-1 is inserted into the cover tube 30 with the base material 1 facing downward, and the upper portion of the dummy rod 20-1 is held by the chuck 16 to cover the dummy rod 20-1 with the axial center thereof. Adjust the position of the chuck 16 so that the axial center of the tube 30 is aligned, and cover the base material 1
Suspend vertically in the hollow hole.

At this time, the upper portion of the dummy rod 20-1 is a chuck.
However, since the gap between the outer peripheral surface of the dummy rod 20-1 and the inner wall of the cover tube 30 is as small as 0.1 mm, the parallelism between the dummy rod 20-1 and the cover tube 30 is reduced. Even if the base material 1
The axis of the cover tube 30 and the axis of the cover tube 30 substantially coincide with each other, and the gap between the outer peripheral surface of the base material 1 and the inner wall of the cover tube 30 is maintained at about 1 mm.

Then, the sliding body 15 is lowered along the guide bar 13 at a predetermined speed (several tens of meters / minute), and the base material 1 and the lower portion of the covering pipe 3-1 are heated and softened in the heating furnace 10. Spindle-shaped, the core diameter is 10μm-8 from the lower tip of the spindle-shaped
A thread-shaped single-mode optical fiber 100 having an outer diameter of 125 μm and a diameter of 125 μm is drawn out by a capstan 12, and a primary coating portion 11 is provided with a primary coating film of silicon resin or the like on the outer peripheral surface of the single-mode optical fiber 100.

In the above manufacturing method, the gap between the outer peripheral surface of the base material 1 and the inner wall of the cover tube 30 is set to 1 mm, and the inner diameter of the cover tube 30 and the outer diameter of the dummy rod 20-1 are set. Difference of 0.2
The outer diameter of the dummy rod 20-1 is formed so as to be less than or equal to mm. Further, the cover tube 30 is provided with an air vent hole 31.

Therefore, when the base material 1 and the lower tip portion of the cover tube 30 are softened by heating, the air between the outer peripheral surface of the base material 1 and the inner wall of the cover tube 30 is discharged to the outside through the air vent hole 31. To be done.

However, bubbles are not confined in the single mode optical fiber 100 obtained by drawing.
Further, it goes without saying that the core of the obtained single mode optical fiber 100 is hardly decentered.

The length of the dummy rod 20-1 is increased to about 1000 mm so that the tip end of the dummy rod 20-1 is separated from the manufactured base material 1.
By connecting to another new base material 1, it can be used repeatedly.

In FIG. 2, reference numeral 1 is an outer diameter (base material clad portion).
1B outer diameter) is 13 mm, and the base material core 1A has an outer diameter of 1 mm and is a solid cylindrical base material (300 mm to 600 mm in length), 30 is a quartz tube with a hole diameter of 15 mm and an outer diameter of 26 mm. A covering tube, 20-2
Is a dummy rod made of a quartz column having an outer diameter of 13 mm (the length is about 1000 mm), the lower end surface of which is welded and connected to the upper end surface of the base material 1 by an oxyhydrogen burner.

Reference numeral 40 is a gap adjusting bar made of quartz and having an outer diameter of 0.8 mm and a length substantially equal to the length of the dummy rod 20-2. Two gap adjusting bars 40 are arranged side by side, and the required parts are welded together by an oxyhydrogen burner to be integrated, and then a head member 41 made of a quartz plate is welded to each head so as to have an inverted L shape. .

Gap adjusting bar that integrates the above two
Three pairs of 40 are provided, each of which is loosely inserted between the outer peripheral surface of the suspended dummy rod 20-2 and the inner wall of the cover tube 30, and the head member 41 is locked to the upper end surface of the cover tube 30 to form a dummy rod. The single-mode optical fiber 100 is drawn by arranging it at an equal pitch on the outer circumference of 20-2 and heating and softening the base material 1 and the covering tube 30 in this state.

According to the manufacturing method shown in FIG. 2, since the gap adjusting bars 40 are inserted between the dummy rods 20-2 and the cover tube 30 at an equal pitch, the base material 1 and the cover tube 30 are separated from each other. The maximum eccentricity is 0.2 mm.

In the single mode optical fiber 100 obtained by drawing, the amount of eccentricity of the core decreases in proportion to the fine line ratio, so the amount of eccentricity between the base material 1 and the cover tube 30 is 0.2 mm at the maximum. If the line is drawn, the eccentricity of the core of the obtained single mode optical fiber becomes very small.

On the other hand, since there is an arc-shaped gap having a width of about 2 mm between the adjacent gap adjusting bars 40, the base material 1 and the cover pipe are covered.
When the lower tip portion of the lower pipe 30 is heated and softened, the air between the outer peripheral surface of the base material 1 and the inner wall of the cover pipe 30 rises through this arc-shaped gap and is discharged from the upper opening of the cover pipe 30. .

Therefore, no bubbles remain in the single mode optical fiber. In FIG. 3, 1 is the outer diameter (outer diameter of the base material clad portion 1B) is 13 mm, and the outer diameter of the base material core portion 1A is
A base material made of 1 mm solid cylindrical quartz (300 mm to 600 mm in length), 30 is a cover tube made of a quartz tube with a hole diameter of 15 mm and an outer diameter of 26 mm, and 20-3 is the base material 1 at the lower end surface. A quartz column with an outer diameter of 13 mm (length is approx.
It is a dummy rod made of 1000 mm).

Reference numeral 50 is a protrusion made of a quartz rod having a diameter of 0.9 mm and a length of about 20 mm. Providing 6 such protrusions 50,
The three rods are arranged along the circumference of the upper part of the dummy rod 20-3 at an equal pitch, and welded with an oxyhydrogen burner to be fixed to the dummy rod 20-3.

Further, the other three projections 50 are arranged along the circumference of the lower portion of the dummy rod 20-3 at an equal pitch and welded with an oxyhydrogen burner to be fixed to the dummy rod 20-3. And the tube
As the lower part of 30 is inserted into the axis of the hollow part of the heating furnace 10,
The upper portion of the cover tube 30 is held by the cover tube chuck 17 and suspended vertically.

Next, with the base material 1 facing downward, the dummy rod 20-3 is inserted into the cover tube 30, and the upper portion of the dummy rod 20-1 is held by the chuck 16 to cover the dummy rod 20-1 with the axial center thereof. The position of the chuck 16 is adjusted so that the axial center of the tube 30 is aligned, the base material 1 is covered, and the tube is suspended vertically in the hollow hole of the tube 30.

At this time, the upper part of the dummy rod 20-3 is a chuck.
It is only held by 16, but since the projections 50 are arranged at equal pitches on the outer peripheral surface of the dummy rod 20-3,
Even if the parallelism between 20-3 and the cover tube 30 decreases, the axis of the base material 1 and the axis of the cover tube 30 substantially coincide with each other, and the gap between the outer peripheral surface of the base material 1 and the inner wall of the cover tube 30 Is kept at about 1 mm.

Therefore, the amount of eccentricity of the core of the obtained single mode optical fiber is very small. On the other hand, since there is an arcuate gap having a width of about 2 mm between the adjacent protrusions 50, when the lower end portion of the base material 1 and the cover tube 30 is heated and softened, the outer peripheral surface of the base material 1 and the cover tube 30 are heated. The air from the inner wall of the cover rises through the arc-shaped gap and is discharged from the upper opening of the covering pipe 30.

Therefore, no bubbles remain in the single mode optical fiber.

[0051]

As described above, the present invention connects the dummy rod to the upper portion of the base material, loosely inserts the base material and the dummy rod into the hollow hole of the tube, and draws the single mode optical fiber. A single mode is provided by heating and softening the base material and the cover tube by providing means for aligning the axis of the dummy rod with the center axis of the cover tube and means for releasing the air between the base material and the cover tube to the outside. Since the optical fiber is drawn, there is an effect that bubbles are not present in the obtained single mode optical fiber and the axial center of the fiber and the axial center of the core coincide with each other to achieve high quality.

Further, there is an effect that the axial alignment between the base material and the covering pipe is easy and the setup work is shortened.

[Brief description of drawings]

1 is a cross-sectional view of an embodiment of the method of the present invention.

FIG. 2 is a sectional view of another embodiment of the method of the present invention,
(B) is a plan view.

FIG. 3 is a cross-sectional view and FIG. 3B is a plan view of still another embodiment of the method of the present invention.

FIG. 4 is a diagram showing a conventional method.

FIG. 5 is a diagram showing another conventional method.

FIG. 6A and FIG. 6B are cross-sectional views of a single mode optical fiber according to a conventional method.

[Explanation of symbols]

1 Base material 1A Base material core 1B Base material clad 100 Single-mode optical fiber 101 Core 102A, 102B
Clad 2,20-1,20-2,20-3 Dummy rod 3-1,3-2, 30
Cap tube 10 Heating furnace 11 Primary coating 12 Capstan 13 Guide bar 15 Sliding body 16 Chuck 17 Cap tube chuck 40 Gap adjustment bar 41 Head member 50 Projection

Claims (4)

[Claims] 1. A base material clad portion is provided on the outer periphery of the base material core portion (1A).
(1B) consisting of a quartz column base material (1) and a hollow hole consisting of a quartz tube having an inner diameter larger than the outer diameter of the base material (1) by at least 1 mm. A cover tube (30) for loosely inserting the base material (1) into the hollow hole while grasping and suspending
And the lower end surface is connected to the upper end surface of the base material (1) so that the axes of the base material (1) and the cover pipe (30) are aligned, and the upper part is chucked.
A method for producing a single-mode optical fiber, which comprises using a dummy rod (20-1) made of a quartz column, which is held by (16) and suspended in the covering pipe (30), the dummy rod (20- A means for aligning the axis of 1) with the axis of the cover tube (30) and a means for releasing air between the base material (1) and the cover tube (30) are provided. Insert the material (1) into the hollow hole of the cover tube (30), and align the axis of the base material (1) with the axis of the cover tube (30) by means of aligning the axis. Suspend, insert the lower part of the base material (1) and the cover tube (30) into the axial center of the heating furnace (10) to penetrate and heat, soften, and cover the air through a means for allowing the air to escape. While releasing it to the outside of the pipe (30),
A method for manufacturing a single-mode optical fiber, which comprises drawing. 2. The means for aligning the shaft center of the dummy rod with the shaft center of the cover tube according to claim 1, is the inner diameter of the cover tube (30) and the outer diameter of the dummy bar (20-1). The outer diameter of the dummy rod (20-1) is formed so that the difference between the two is 0.2 mm or less, and means for letting the air between the base material and the covering pipe escape to the outside. Is an air vent hole (31) provided in the shell portion of the cover pipe (30) corresponding to the connection portion between the base material (1) and the dummy rod (20-1). Manufacturing method of single mode optical fiber. 3. A means for making the axis of the dummy rod and the axis of the cover tube coincide with each other according to claim 1, wherein the outer diameter is larger than (radius dimension of cover tube-radius dimension of dummy rod-0.2 mm). A gap adjusting bar (40) made of a plurality of quartz is provided on the outer peripheral surface of the dummy rod (20-2) and the covering tube (30).
The gap adjusting bar (40) adjacent to the gap adjusting bar (40) is provided by loosely inserting and arranging the inner wall of the gap at an equal pitch, and means for releasing the air between the base material and the covering pipe to the outside. A method of manufacturing a single-mode optical fiber, characterized in that it is a gap between them. 4. The means for aligning the axial center of the dummy rod with the axial center of the cover tube according to claim 1 has a protrusion amount larger than (radius dimension of cover tube-radius dimension of dummy bar-0.1 mm). The projections (50) made of a plurality of quartz are arranged at equal pitches on two circles in the upper and lower portions of the outer peripheral surface of the dummy rod (20-3), respectively. A method for producing a single-mode optical fiber, characterized in that the means for releasing the air between the base material and the covering tube to the outside is a gap between the adjacent projections (50).