JP2001335338A - Method of manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of bubbles in the vicinity of rod/dummy rod interface and to prevent the breaking of fibers when drawn, in a method of manufacturing an optical fiber, in which deposits of fine-grained glass are formed around the periphery of a glass rod connected to a dummy rod, then heated untill being transparent, and drawn. SOLUTION: In a method of manufacturing an optical fiber including the process to connect a dummy rod to one or both ends of a starting glass rod, the viscosity of the dummy rod is set to be lower than that of the pure quartz and higher than that of the lowest viscosity portion of the starting glass rod when heated at high temperatures. Since the user of the dummy rod having the viscosity close to that of the starting glass rod enables to lessen the difference in the vertical shrinkage, both the generation of bubbles in the glass rod/ dummy rod interface and the breaking of fibers when drawn can be prevented.

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 an optical fiber.

[0002]

2. Description of the Related Art A core glass rod or a glass rod composed of a core and a part of a clad provided on the outer periphery of the core is defined as a starting glass rod.
Glass particles are deposited by AD method and
A glass particle deposit composite is synthesized, and the composite is sintered in a heating furnace to form a glass body. If necessary, the glass body is subjected to a stretching step to form an optical fiber preform (hereinafter referred to as a preform). In the method of manufacturing an optical fiber by spinning the preform in a drawing furnace after forming a dummy rod, a dummy rod is connected to a starting glass rod so that the upper part of the dummy rod can be operated in each step. The effective length of the expensive starting glass rod is effectively used by combining the holding portion and the tapered portion of the glass fine particle deposit so as to be the outer periphery of the dummy portion.

As shown in FIG. 1, cylindrical or cylindrical dummy rods 2 and 3 are welded and connected to both ends of the starting glass rod 1 in advance, respectively, and a base material for an optical fiber to be subjected to subsequent steps. Is disclosed in Japanese Unexamined Patent Publication No.
Has been proposed. In FIG. 1, reference numeral 4 denotes a glass particle deposit, 5 denotes a glass rod / glass particle deposit composite,
6 is a sintering furnace, 7 is a preform, 8 is a drawing furnace, and 9 is an optical fiber. By this method, the gripping of a large base material (preform) is stable, and it is possible to grip both ends even when stretching with a glass lathe, and without damaging the glass rod, mixing impurities, cracking, cracking, etc. Large preforms and optical fibers can be manufactured.

[0004]

When the starting glass rod includes a soft glass portion to which fluorine is added, the following problem occurs when a quartz dummy rod is connected in the conventional manner. When sintering the glass fine particle deposit, the longitudinal shrinkage rate near the connection part changes rapidly, and the outer diameter fluctuation increases. Fluctuations in the outer diameter of the preform lead to fluctuations in the wire diameter during spinning, resulting in an increase in loss of the optical fiber and a connection loss during connection. When the preform is heated and made transparent, bubbles are generated at the connection between the dummy rod and the glass rod. The presence of bubbles causes disconnection during drawing, and reduces the transmission characteristics of the optical fiber. When the molten rod is heated and melted in a drawing furnace from the side of the dummy rod connected to the lower end and then spun, when the molten portion moves from the dummy rod portion to the glass rod, the drawing speed changes drastically and disconnection is likely to occur. An object of the present invention is to solve the above-mentioned problems, and the present invention can form a large-sized preform without generating bubbles during sintering and fluctuation in outer diameter, and has excellent transmission characteristics without disconnection during spinning. It is an object of the present invention to provide a method for manufacturing an optical fiber.

[0005]

According to the present invention, there is provided a method for manufacturing an optical fiber comprising the steps of: (1) connecting a dummy rod to one or both ends of a starting glass rod; The method of manufacturing an optical fiber, wherein the viscosity is smaller than the viscosity of the starting glass rod and larger than the viscosity of the portion having the lowest viscosity of the starting glass rod, (2) a step of connecting a dummy rod to one or both ends of the starting glass rod, And a method of manufacturing an optical fiber having a process of spinning a glass rod with a rod connected to a dummy as a preform in a drawing furnace, wherein the viscosity of the dummy rod during heating at a high temperature is smaller than the viscosity of pure quartz, and A method of manufacturing an optical fiber characterized in that the viscosity is larger than the viscosity of the portion having the smallest viscosity; and (3) VAD is applied to the outer periphery of the glass rod connected to the dummy rod. A step of synthesizing a glass fine particle deposit by depositing glass fine particles by a method of sintering the glass fine particle deposit to form an optical fiber preform, and a step of spinning the optical fiber preform in a drawing furnace. In the method for producing a fiber, the viscosity of the dummy rod at the time of high-temperature heating is smaller than the viscosity of pure quartz, and is larger than the viscosity of the portion of the starting glass rod where the viscosity is the smallest (1) or (2). )).

[0006] Particularly preferred embodiments of the present invention include the following. (4) The method for producing an optical fiber according to the above (1) to (3), wherein the difference between the viscosity of the dummy rod and the viscosity of the starting glass rod during heating at a high temperature is within ± 50%. (5) The above (1) to (4), wherein the viscosity of the dummy rod is adjusted by adding at least one selected from the group consisting of fluorine, chlorine, boron and phosphorus to quartz glass.
The method for producing an optical fiber according to any one of the above. (6) The method for producing an optical fiber according to any one of (1) to (5), wherein the starting glass rod is a core rod. (7) The above (1) to (5), wherein the starting glass rod has a core and at least a part of a clad.
The method for producing an optical fiber according to any one of the above.

The inventors of the present invention connect a quartz glass dummy rod to a starting glass rod including a soft glass portion to which fluorine or the like is added, and thereby, the softness of the starting glass rod and the softness of the dummy rod when heated at a high temperature. That is, since the viscosities of the two greatly differ from each other, it was considered that the above problems 1 to 5 occurred, and the present invention was reached. Regarding the above, when a base material in which glass fine particles are volumed around the outer periphery of the starting glass rod and the dummy rod is sintered, when the glass fine particles around the starting glass rod shrink, they also shrink in the vertical direction (center axis direction). Therefore, the starting glass rod and the glass fine particle deposit shrink together in the vertical direction. If the starting glass rod and the dummy rod have different viscosities as shown in FIG. 2, the one having a lower viscosity (the starting glass rod in FIG. 2) is more likely to shrink in the vertical direction,
That is, the shrinkage increases, and the outer diameter increases accordingly.
For this reason, the contraction rate in the vertical direction greatly fluctuates near the connection portion between the two. At this time, a void is generated at the interface between the starting glass rod / dummy rod at the connection portion and becomes a bubble. As described above, it is considered that the glass diameter of the starting glass rod side having a large shrinkage ratio becomes larger than that of the dummy rod side by the amount of the vertical shrinkage, and the outer diameter fluctuates in the vertical direction. About, when moving from drawing on the dummy rod side to drawing on the starting glass rod side, the glass suddenly softens, so the drawing tension decreases rapidly or the drawing speed increases rapidly, It is considered that the control could not catch up and the fiber was cut.

Accordingly, the present invention provides a method for producing a dummy rod in which the "viscosity during heating at a high temperature in a sintering step or a spinning step (hereinafter, simply referred to as" viscosity ")" is close to the viscosity of the starting glass rod. When the rod is made of a core and a cladding layer having a different viscosity from the core provided on the outer periphery of the core, the material of the dummy rod is selected so as to be intermediate between the respective viscosities of the core and the outer periphery of the core. This solves the problems of and.

In general, as the optical fiber material, quartz glass (also referred to as SiO ₂ , pure quartz) and doped quartz glass obtained by adding a dopant such as a refractive index adjusting agent to quartz glass are used. Doped quartz glass has a lower viscosity than pure quartz. In the present invention, the viscosity of the dummy rod is
When the viscosity of the starting glass rod is smaller than the viscosity of quartz glass and is close to the viscosity of the starting glass rod, or when the starting glass rod is made of two materials having a difference in viscosity, the viscosity is intermediate between the two. Specifically, various kinds of dopants added to the quartz glass for optical fibers may be added, and particularly preferably, a group consisting of fluorine (F), chlorine (Cl), boron (B), and phosphorus (P) in quartz. One or more kinds selected from the following are added in an appropriate amount to adjust the viscosity.

In the present invention, the starting glass rod (core
As a specific example of the combination of the clad) configuration and the dummy rod,
The magnitude relationship of the respective viscosities may be as follows, but is not limited to the exemplified ones.

[0011]

[Table 1]

The difference in viscosity between the dummy rod and the starting glass rod (core, clad) is preferably in the range of ± 50%, regardless of whether the starting glass rod is made of a single material or two materials. If the difference in viscosity becomes too large, it is considered that the above-mentioned problem may become a problem. The method of adding a dopant to quartz may be any of the means known in the art, such as a method of reacting a gas containing a dopant with a glass raw material in a VAD method, or a method of depositing a glass fine particle in a gas atmosphere containing a dopant. Sintering.

The dummy rod having a viscosity close to that of the starting glass rod may be attached to both ends of the starting glass rod, or may be attached to only one end and a quartz glass dummy rod may be attached to the other end in the same manner as in the prior art. Is also good. In the latter case, holding the quartz glass dummy rod side and spinning from the viscosity-adjusted dummy rod side will not cause bubbles, disconnection, or change in outer diameter, and stable gripping by the upper quartz glass is possible. Becomes

[0014]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. (Example 1) A starting glass rod having an outer diameter of 23 mm and a length of 500 mm having a core (made of pure quartz and having an outer diameter of 4.6 mm) and a part of a clad was prepared. The cladding is made of quartz to which 1.25% by mass of fluorine is added. A dummy rod made of quartz having an outer diameter of 23 mm was connected to the upper part of the starting glass rod, and a dummy rod made of quartz to which 1% by mass of fluorine was added was connected to the lower part. Next, a deposit of uniform glass fine particles (pure SiO ₂ ) having an outer diameter of 150 mm was synthesized around the starting glass rod (and the dummy rod). The obtained composite of the starting glass rod (and the dummy rod) and the glass fine particle deposit was heated to 1500 ° C. in a sintering furnace to form a transparent glass, and an optical fiber preform was obtained. Observation was made of the connection between the fluorine rod-added dummy rod and the starting glass rod of the preform. As a result, no bubbles were found inside, and no change was observed in the outer diameter of the preform. As a result of spinning this preform in a drawing furnace, an optical fiber could be manufactured without breaking for 1000 km. The viscosity of the starting glass rod and the dummy rod made of fluorine-added quartz at the time of vitrification by heating were 2.1 × 10 ⁷ Pa · s and 3 × 10 ⁷ P, respectively.
a · s (+ 43%) and the viscosity during spinning are each 1.4 × 10
^{It was 5} Pa · s and 2 × 10 ⁵ Pa · s (+ 43%).

Comparative Example 1 In the same manner as in Example 1, a starting glass rod having an outer diameter of 23 mm and a length of 500 mm having a core (made of pure quartz and having an outer diameter of 4.6 mm) and a part of a clad was prepared. The cladding is made of quartz containing 1.25% by mass of fluorine. A quartz dummy rod was connected to the upper part of the starting glass rod, and a quartz dummy rod was also connected to the lower part. Next, an outer diameter of 1 around this starting glass rod
A 50 mm uniform glass fine particle (pure SiO ₂ ) deposit was synthesized. The obtained composite of the starting glass rod and the glass fine particle deposit was heated to 1500 ° C. in a sintering furnace to form a transparent glass, thereby obtaining a preform for an optical fiber. Observation of the connecting portion of the core rod of the lower dummy rod revealed that bubbles were present around the connection interface, and the outer diameter of the preform body was also large on the core rod side. When the preform was spun with a drawing rod, the drawing speed was rapidly increased and the wire was disconnected when just drawing the vicinity of the connection interface. In addition, the viscosity of the starting glass rod and the dummy rod made of pure quartz at the time of heat transparent vitrification are 2.1 × 10 ⁷ Pa ·
s, 1 × 10 ⁸ Pa · s (+ 476%), and the viscosities during spinning are 1.4 × 10 ⁵ Pa · s and 4 × 10 ⁵ Pa · s, respectively.
(+ 285%).

[0016]

By using a dummy rod having a viscosity close to the viscosity of the starting glass rod, the difference in the contraction rate in the longitudinal direction can be reduced, so that the generation of bubbles near the interface between the starting glass rod and the dummy rod can be prevented. Further, it is possible to prevent the occurrence of disconnection at the time of drawing.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory view schematically showing the relationship between glass viscosity and shrinkage during sintering.

[Explanation of symbols]

1 Departure glass rod, 2 Dummy rod,
3 Dummy rod, 4 glass particle deposit, 5 glass rod / glass particle deposit composite 6 sintering furnace, 7 preform,
8 draw furnace, 9 optical fiber.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kiichiro Kawasaki 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Hideyuki Ijiri 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Ki Kogyo Co., Ltd. Yokohama Works F-term (reference) 4G021 CA00 EA01 EA03 EB01

Claims (7)

[Claims] 1. A method for manufacturing an optical fiber comprising a step of connecting a dummy rod to one or both ends of a starting glass rod, wherein the viscosity of the dummy rod during heating at a high temperature is smaller than that of pure quartz, and A method for manufacturing an optical fiber, wherein the viscosity of the optical fiber is higher than the viscosity of a portion having the lowest viscosity. 2. A method for producing an optical fiber, comprising: a step of connecting a dummy rod to one or both ends of a starting glass rod; and a step of spinning a glass rod to which the dummy is connected as a preform in a drawing furnace with a drawing furnace. A method of manufacturing an optical fiber, wherein the viscosity of the dummy rod is sometimes lower than the viscosity of pure quartz and higher than the viscosity of the lowest viscosity portion of the starting glass rod. 3. V is formed around the outer periphery of a glass rod to which a dummy rod is connected.
A step of depositing glass particles by the AD method to synthesize a glass particle deposit, a step of sintering the glass particle deposit to form a preform for an optical fiber, and a step of spinning the preform for optical fiber in a drawing furnace. A method of manufacturing an optical fiber, wherein the viscosity of the dummy rod at the time of high-temperature heating is smaller than the viscosity of pure quartz, and larger than the viscosity of the portion of the starting glass rod having the lowest viscosity. . 4. The method according to claim 1, wherein the difference between the viscosity of the dummy rod and the viscosity of the starting glass rod during heating at a high temperature is within ± 50%. 5. The viscosity of the dummy rod is adjusted by adding at least one selected from the group consisting of fluorine, chlorine, boron and phosphorus to quartz glass. 13. The method for producing an optical fiber according to 6. The method for manufacturing an optical fiber according to claim 1, wherein said starting glass rod is a core rod. 7. The method of claim 1, wherein the starting glass rod has a core and at least a portion of a cladding.
A method for manufacturing an optical fiber according to claim 5.