JP2585286B2 - Manufacturing method of optical fiber and preform for optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a quartz glass optical fiber and a structure of a preform for the quartz glass optical fiber.

[Conventional technology]

In order to manufacture an optical fiber from a quartz glass optical fiber base material, as shown in FIG. 6, usually, a line drawing base material (hereinafter also referred to as a preform) 11 composed of an optical fiber base material 1 and a dummy rod 5 is used. At a constant speed, the preform 11 softened inside the heating furnace 7 is lowered into a furnace tube 7 of a heating furnace equipped with the heater 6, and the fiber 10 is drawn out and wound at a certain speed. At this time, an inert gas such as Ar gas is flowing in the furnace tube 7 in a direction indicated by an arrow in the figure. As the drawing speed at this time, that is, the drawing speed, a speed for keeping the outer diameter of the optical fiber 10 constant is selected. The first reason for doing this is that if the diameter of the fiber fluctuates in the longitudinal direction of the fiber, the core diameter of the fiber also changes accordingly, affecting transmission characteristics such as transmission frequency band and transmission loss. That is.

The fusion splicing between the fibers is performed by fixing the optical fiber from which the coating has been removed on the V-groove and fusing the fibers facing each other. However, the core diameter fluctuates and the core axis shifts. If there is, the connection loss increases, which also causes a problem in transmission characteristics. Especially the core diameter of single mode fiber etc. is 10μ
In the connection of a fiber that is as small as possible, if the outer diameters differ by 1 μm, the center of the core is shifted as much as 0.5 μm, which is a major problem in connection loss.

As a cause of the variation in the optical fiber diameter in the optical fiber drawing process, a change in the preform supply speed or the optical fiber withdrawal speed can be considered, but one of the major causes is shown as 9 in FIG. Fluctuation of the gas flow in the heating furnace at the tip of the neckdown (the portion where the preform gradually becomes smaller in diameter and the optical fiber is drawn out). For example, Japanese Patent Application Laid-Open No. 52-12952 describes that the diameter of an optical fiber can be freely controlled by controlling a gas flow in a neck-down portion.

Alternatively, in the drawing step, the portion fixed by the feeder at the upper end of the optical fiber base material can only be lowered to the upper surface of the drawing furnace, and the optical fiber base material is necessarily left behind. Therefore, in order to effectively convert the expensive optical fiber preform into a fiber, an inexpensive quartz glass dummy rod 5 is connected to the upper end of the optical fiber preform 1 as shown in FIGS. Conventionally, the rod 5 is fixed to a feeder by setting it as a preform 11. At this time, if there is a difference between the diameter of the optical fiber base material 1 and the diameter of the dummy rod 5, the gas flow is disturbed near the connection portion in the drawing furnace, and the outer diameter of the optical fiber is disturbed. . Conventionally, the problem has been solved by a method in which a dummy rod having a diameter substantially the same as that of the optical fiber base material is smoothly melt-connected and drawn.

As another conventionally known method, Japanese Patent Application Laid-Open No. 54-883
There is a method using a cylindrical tube, which is disclosed in Japanese Patent Publication No. 25.
In this method, as shown in FIG.
A cylindrical member 56 having a length of 10 cm or more is in contact with the handle 50 and is in contact with the handle 50. In this method, the gas supplied from the gas inlet 34 is heated through the narrow area of the muffle 26 and the cylindrical member 56, so that even if the fiber 10 is shortened, the gas is uniformly heated, so that the gas outside the optical fiber glass is removed. The diameter is stable.

[Problems to be solved by the invention]

By the way, in recent years, the development of mass production technology for optical fibers has progressed.
Large preforms with a very large diameter have been manufactured (Reference: Optical Fiber Communication Confere)
nce and 6th International Conference on Integrated
Optics and Optical Fiber Communication, Proceedings 198
Report on the seventh page of the afternoon of January 19, 2007, publication number MC2). In a base material for a large-diameter optical fiber, the loss due to the remaining material per base material is much larger than in the case of a small-diameter fiber, and it is considered essential to connect a dummy rod and draw a wire.

However, fusion connection of large diameter glass rods with a diameter exceeding 50 mm is extremely difficult, and even if connected,
Since the distortion due to the cooling of the connecting portion increases as the diameter increases, there is a problem of strength.

Furthermore, when joining the large diameter optical fiber base material and the dummy rod in a state where both are melted, it is difficult to finish the outer surface of the connecting portion smoothly, and in the above-described furnace, it is difficult to finish smoothly. There was a problem that led to air turbulence. FIG. 5 shows an unsmooth connection between the large-diameter base material and the large-diameter dummy rod surrounded by a broken line.

Even if the method shown in FIG. 7 is used, the preform 1
There is a difference between the diameters of the handle 50, the cylindrical member 56, and the diameter of the cylindrical member 56, and this portion has a complicated shape, causing gas turbulence, and the stability of the outer diameter of the optical fiber glass is not sufficient.
In particular, in the case of a large preform having a large diameter, the upper end of the preform is tapered, and the turbulence of the airflow in this portion is large.

Under these circumstances, even though a large-diameter large-sized optical fiber base material can be obtained, it is still used at present to process it into a preform for wire drawing after reducing its stretched diameter. The urgent development of a method that can reduce the waste of parts and the like and can draw a high-quality optical fiber has been awaited.

An object of the present invention is to provide a novel optical fiber manufacturing method which solves the above-mentioned problems and a novel fiber optical fiber preform for melt spinning.

[Means for solving the problem]

In the present invention, a quartz glass pipe having a uniform outer diameter equal to the outer diameter of the quartz glass optical fiber preform at one end of the outer periphery of the quartz glass optical fiber preform having a diameter exceeding 50 mm is attached to the outer peripheral surfaces of the quartz glass pipes. The present invention relates to a method for producing an optical fiber, comprising melt-spinning an optical fiber preform formed in contact with and in contact with the optical fiber.

In addition, the present invention provides a quartz glass optical fiber preform having a uniform outer diameter equal to the outer diameter of the quartz glass optical fiber preform at one end of an outer peripheral surface of the quartz glass optical fiber preform having a diameter exceeding 50 mm. And a preform for an optical fiber for melt spinning, which is in contact with the preform.

In the present invention, the preform for optical fiber is
The quartz glass pipe has an outer diameter equal to the outer diameter of the base material for the quartz glass optical fiber, and the two have an outer peripheral surface in contact with each other, and both are fused or simply contacted. Is a particularly preferred embodiment.

According to the present invention, a glass tube is connected as a dummy pipe instead of the conventional dummy rod or glass rod connected to the feeder side of the optical fiber base material, thereby solving the problems of the conventional method. .

 This will be described below with reference to the drawings.

FIG. 1 (a) shows an embodiment of the present invention, in which a dummy pipe 2 which is a quartz glass pipe having the same outer diameter as the base material 1 is melt-connected to a base material 1 for a large diameter optical fiber. The following shows a preform. The dummy pipe 2 is fixed to a feeder in the same manner as a conventional dummy rod, and a drawing step is performed.

FIG. 1 (b) shows another embodiment of the present invention, in which a small diameter dummy rod 3 is fusion-bonded to a large diameter optical fiber base material 1, and the outer periphery of the dummy rod 3 has the same diameter as the outer diameter of the base material. A preform formed by fusing and connecting a quartz glass dummy pipe 2 is shown. In this case, the dummy rod 3 is used for supporting the preform at the time of drawing, and the dummy pipe 2 is used for alleviating the influence on the gas flow.

FIG. 1 (c) shows a further embodiment of the present invention, in which a dummy rod 3 made of a small-diameter quartz glass is melt-connected to a base material 1 for a large-diameter optical fiber, and a pipe support mounted on the upper part of the dummy rod 3. 4, a dummy pipe 2 made of quartz glass having the same diameter as the outer diameter of the preform is attached so as to cover the small-diameter dummy rod 3, and the lower end surface of the dummy pipe 2 is brought into close contact with the optical fiber base material 1. It is.

The method of drawing a preform according to the present invention may use the conventional apparatus shown in FIG. 5, and various fixing methods can be used as described above.

[Action]

The preform of the present invention is a preform having a uniform diameter from a base material portion to a dummy portion, in which a quartz glass pipe is connected to a large diameter optical fiber base material having a diameter exceeding 50 mm, and the optical fiber base material is processed into a preform. The process is performed only by fusion connection between a thin glass pipe and a large-diameter base material, or additionally, a small-diameter dummy rod and a large-diameter base material. In comparison, the distortion remaining inside the glass is much smaller, processing is very easy, and sufficient fusion is possible, so that the strength of the connection portion can be sufficiently maintained.

In addition, since the processing is easy, the fluctuation of the preform diameter at the connecting portion between the preform and the pipe is small, and the gas flow in the drawing furnace is not disturbed. Therefore, the optical fiber is manufactured from the preform of the present invention. According to this method, a high-quality optical fiber having a stable outer diameter and a small variation in core diameter can be obtained.

Furthermore, while the preform to which the conventional quartz glass dummy rod is connected is very heavy, the preform to which the dummy pipe of the present invention is connected is light and easy to handle in operation. Further, since the amount of quartz glass in the dummy portion can be reduced, there is also an effect that the material cost of this portion can be greatly reduced.

The preform of the present invention in which the quartz glass pipe shown in FIGS. 1 (a) and 1 (b) is connected to an optical fiber preform,
The connection portion has good airtightness, and there is no problem if the gas in the drawing furnace flows from the connection portion into the glass pipe and disturbs the gas flow in the furnace.

A small-diameter quartz glass rod is connected to the large-diameter optical fiber base material shown in FIG. 1C, and the rod is used as a support for the optical fiber base material. The preform of the present invention in which a quartz glass pipe having a diameter is fixed at another place and closely adhered to the optical fiber base material is not connected by thermal processing between the pipe and the optical fiber base material, The outer diameter of the connecting part of the preform does not change, and the stability is very excellent. Further, since the heat processing is not performed, the shape change is small, and the quartz glass pipe can be reused without any problem. As a method for fixing the quartz glass-based pipe in the type shown in FIG. 1 (c), in addition to the method for fixing with the pipe support 4 as shown in the figure, the pipe is supported from a drawing furnace or a feeder and responds to the descent of the preform. A method of lowering the quartz glass pipe by using the above method is also possible.

Then, as is clear from the embodiment described below, the first
When drawing is performed using the preform of the present invention as shown in FIGS. (B) and (c), distortion remaining at the connection with the small-diameter dummy rod supporting the weight of the optical fiber base material is small,
Since accidents such as dropping of the optical fiber base material due to the destruction of the connecting portion do not occur, stable and efficient production of the fiber is possible.

Although the operation and effects of the present invention have been described by taking the case of a large diameter optical fiber base material as an example, the same effect can be obtained by applying the present invention to a thinner size optical fiber base material. Of course.

〔Example〕

Example 1 Three types of preforms according to the present invention shown in FIGS. 1 (a) to 1 (c) were produced to give the names A, B and C of the present invention, and the preforms shown in FIG. 5 used in the conventional method were produced. As a conventional product D, these processed products A to D were compared in terms of strength.

As a base material for optical fiber, a pure quartz glass rod having a diameter of 75 m was used, and as a dummy pipe shown in FIGS. 1A to 1C, a quartz pipe having an outer diameter of 75 mm and a thickness of 4 mm was used. The diameter rod is 25 mm for the small diameter rods shown in FIGS.
A quartz glass rod of mm was used. The conventional method shown in FIG. 5 used a quartz glass rod having a diameter of 75 mm.

In order to compare the strength of the joints due to strain during processing, the four types of preforms A to D were supported. In order to compare the strength of the joints, they were supported in a furnace heated to 1400 ° C and in air at room temperature. The number of ingresses and egresses that caused destruction was measured by the heat cycle in and out. The results were as follows:

A: Breaked 16 times B: The welded portion of the pipe broke in 22 times, but the connection between the small glass rod inside and the base material for optical fiber did not break, and the base material of optical fiber did not fall. Was.

C: Even at 30 times or more, the connection did not break, and the strength of the processed product was extremely large.

D: Four times, the joint was broken and the optical fiber base material was dropped.

From the above results, it can be seen that the products A, B and C of the present invention have a much higher strength than the conventional product D.

Example 2 The preform B of the present invention produced in Example 1 was replaced with an outer diameter of 12 mm.
A 5 μm optical fiber was drawn to evaluate the variation width of the glass outer diameter. FIG. 2 (a) shows the state of the connection between the small diameter dummy rod and the quartz glass pipe and the optical fiber preform. The numerical value indicates the outer diameter (mm), and the dummy rod, connection part,
The optical fiber base materials all have the same diameter.

Drawing was performed by using the drawing furnace shown in Fig. 6 and furnace core tube temperature 2150 ° C, A
r The process was performed at a gas flow rate of 10 l / min. The preform and the upper part of the furnace body are hermetically sealed by a sealing material 8 made of a heat-resistant elastomer so that the gas in the drawing furnace does not escape upward.
The supplied Ar gas passes from the upper part of the drawing furnace through the side of the preform and the gap between the furnace core tube, and is discharged from the lower part of the drawing furnace.
The outer diameter of the glass optical fiber 10 was measured by an outer diameter monitor installed at a position 50 cm below the drawing furnace.

FIG. 3 shows the fluctuation range of the glass outer diameter with respect to the distance between the connection point of the dummy rod or the dummy pipe and the tip of the neck down by a solid circle.

On the other hand, the conventional product D manufactured in Example 1 was also drawn in the same manner as described above, and the variation width of the outer diameter of the glass fiber was examined. As shown in FIG. 2 (b), the shape of the conventional product D in the vicinity of the dummy rod connection portion was slightly constricted near the connection surface, and the upper and lower portions were slightly thicker.

As is clear from FIG. 3, in the case of the conventional product D, as the connection portion approaches the tip of the neckdown, that is, as the remaining length of the preform becomes shorter, the fluctuation range of the glass outer diameter becomes larger and the fiber quality deteriorates. ing. On the other hand, in the case of the product B of the present invention, the fluctuation width of the glass outer diameter due to the pipe connecting portion approaching the neckdown tip is much smaller,
A fiber with much better characteristics than the conventional product D was obtained.

〔The invention's effect〕

As described above, the preform of the present invention uses a lightweight dummy glass pipe, so that even a large diameter optical fiber base material can be easily processed and used as a preform. This is a preform in which the outer diameter of the connecting portion between the fiber base material and the dummy pipe is small. Also, by using the dummy glass pipe, it is light in weight, easy to handle in operation, and the preform manufacturing cost is reduced. In addition, it is an excellent preform that has a much higher strength as a preform than the one using a conventional dummy rod.

Further, the preform of the present invention shown in FIG. 1 (c) has an advantage that the dummy rod can be used repeatedly.

The method for producing an optical fiber by drawing a preform according to the present invention uses a preform that is lightweight, has high strength, and has no variation in outer diameter as described above. This produces an effect that the optical fiber can be manufactured stably.

[Brief description of the drawings]

1 (a), 1 (b) and 1 (c) are schematic sectional views showing various embodiments of the preform of the present invention. FIG. 2 (a) is a view showing the outer diameter of each part of the preform of the present invention, and FIG. 2 (b) is a view showing the outer diameter of each part of the conventional product. FIG. 3 is a table showing a relationship between a distance (cm) between a connection portion between a tip end of a neck down and a dummy pipe or a dummy rod and a variation width (μm) of an optical fiber glass outer diameter in a preform drawing process. The solid circles indicate the case of the present invention, and the broken lines indicate the case of the conventional method. 4 and 5 are schematic cross-sectional views showing a conventional small diameter and large diameter preform, respectively, and FIG. 6 is a schematic cross sectional view for explaining a drawing step of drawing an optical fiber glass by drawing a preform. . FIG. 7 is a schematic sectional view showing a conventional method.

Claims (8)

(57) [Claims] 1. A quartz glass pipe having a uniform outer diameter equal to the outer diameter of the quartz glass optical fiber preform at one end of an outer peripheral surface of the quartz glass optical fiber preform having a diameter exceeding 50 mm. A method for producing an optical fiber, comprising: melt-spinning an optical fiber preform that is brought into contact with a surface thereof. 2. The method for manufacturing an optical fiber according to claim 1, wherein the optical fiber preform is formed by fusing a quartz-based glass pipe with a quartz-based glass optical fiber base material. 3. An optical fiber preform is a quartz glass pipe in which a quartz glass rod connected to a quartz glass optical fiber base material penetrates a hollow portion of the quartz glass pipe, and the rod supports the preform. 3. The method for producing an optical fiber according to claim 1, wherein the fiber is melt-spun. 4. The optical fiber according to claim 3, wherein the rod supports the quartz glass pipe which is in contact with the base material for the quartz glass optical fiber but is not fused and spun. Production method. 5. A quartz glass pipe having a uniform outer diameter equal to the outer diameter of the quartz glass optical fiber base material at one end of the outer peripheral surface of the quartz glass optical fiber base material having a diameter exceeding 50 mm. An optical fiber preform for melt-spinning, which is in contact with the surface. 6. The optical fiber preform for melt-spinning according to claim 5, wherein the quartz glass pipe is fusion-spliced to a quartz glass optical fiber base material. 7. A melt spinning apparatus according to claim 5, wherein a quartz glass rod connected to a base material for a quartz glass optical fiber penetrates a hollow portion of the quartz glass pipe. Preform for optical fiber. 8. The quartz glass pipe is in contact with and not fused to the quartz glass optical fiber base material, but is connected to the quartz glass rod at an end different from the base material side. 8. A preform for an optical fiber for melt spinning according to item 7.