JPH01275444A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber completely free of bubbles by preheating a rod-shaped transparent glass preform at a temp. lower than the softening point and close to the softening point on the upstream side of the drawing point of the preform to degasify the preform, and then drawing the preform to efficiently degasify the preform in a short time. CONSTITUTION:The transparent glass preform 4 inserted into a drawing furnace 10 is preheated by a preheater 11 to a temp. lower than the melting point of the preform 4 and as high as possible, e.g., about 800-1,500 deg.C. As a result, the gas remaining in the preform 4 is diffused and discharged to the outside, and the preform 4 is degasified. The degasified preform 4 is moved to a drawing and heating zone, heated 2 to a drawing temp., and continuously drawn. Consequently, a high-quality optical fiber 5 completely free of bubbles is obtained. The drawing heater 2, a heat insulator 3, and an inert gas inlet hole 6 are shown in the figure.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical fiber manufacturing method for manufacturing an optical fiber that does not contain bubbles.

<Prior art> Optical fibers are produced by feeding a transparent glass base material from the top of a drawing furnace, heating and melting the tip, and pulling out this molten part from the bottom of the drawing furnace to reduce the diameter to a desired diameter. The line is drawn by! ! ! It is built.

FIG. 4 shows such a conventional optical fiber drawing apparatus. As shown in the figure, a drawing heater 2 and a heat insulating material 3 are provided in the drawing furnace 1, and an upper opening 1 of the drawing furnace 1 is provided.
A transparent glass preform 4 is pushed in through the opening 1b, and the drawn optical fiber 5 is drawn from the lower opening 1b. Note that an inert gas inlet 6 is provided on the lower end side wall of the drawing furnace 1, and the inside of the furnace is filled with inert gas.

The transparent glass base material 4 supplied here is generally VAD
A porous optical fiber base material on which fine silica glass powder is deposited is made transparent by a dehydration sintering process using, for example, a zone furnace or a soaking furnace. ing. In this dehydration and sintering process, transparent vitrification is generally performed by heating in an atmosphere of He gas or He gas mixed gas, which has a particularly high diffusion rate within the glass. This prevents closed pores from remaining within the transparent glass base material.

However, in the past, in the transparent glass base material made transparent by dehydration and sintering, residual He gas may be dissolved or microscopic pores may remain in which He may be trapped.
It was found that a large amount of gas remained. When drawing a wire using the conventional drawing device shown in FIG. 4 using such a conventional transparent glass base material, residual dissolved gas may vaporize and foam, or the resulting optical fiber There are problems such as small air bubbles remaining and increasing transmission loss.

For this reason, in the past, various methods have been studied to prevent gas from remaining in the transparent glass base material by varying the sintering temperature, temperature raising method, and sintering time conditions in the dehydration and sintering process. has been done.

<Problems to be Solved by the Invention> However, a trace amount of degassing treatment in the dehydration and sintering process, which has been variously studied in the past, requires, for example, a sintering time of 3 to 4
Since it needs to be twice as long, there is a problem that a large amount of energy is required to maintain the temperature, which increases ordinary expenses such as an increase in heater power, and also delays the work process and takes a considerable amount of time. In addition, in order to shorten this work time, for example, if the dehydration sintering process is carried out at a higher temperature, it becomes difficult to maintain that temperature with high precision, and if the temperature exceeds the softening point, it becomes transparent. There is a problem that the glass base material may be deformed, which in turn may cause fluctuations in the drawing speed during drawing.

In view of the above-mentioned circumstances, an object of the present invention is to provide an optical fiber manufacturing method for manufacturing an optical fiber that is efficiently degassed in a short time and does not contain any bubbles.

Means for Solving the Problems> The structure of the optical fiber manufacturing method of the present invention for achieving the above object is to produce an optical fiber by drawing an optical fiber by stretching a rod-shaped transparent glass base material while heating and softening it. In the manufacturing method, the transparent glass base material is preheated at a temperature below the softening point and near the softening point to degas it on the upstream side of the drawing point, and this is then continuously drawn. .

Effect> In the above structure, during the process of preheating the transparent glass base material near its softening point, the gas remaining inside is diffused and released to the outside. The degassed transparent glass preform is then continuously drawn to obtain a bubble-free optical fiber.

<Embodiments> Hereinafter, preferred embodiments of an optical fiber drawing apparatus for implementing the optical fiber manufacturing method of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows an optical fiber drawing apparatus according to this embodiment. Note that the same members as in FIG. 4 according to the prior art are given the same reference numerals, and repeated explanations will be omitted.

As shown in the figure, in the drawing furnace lO of the drawing apparatus of this embodiment, a drawing heater 2 for drawing the drawing is provided in the same manner as in the conventional drawing apparatus, and a drawing heating area is formed, and the upstream side thereof A preheating heater 11 for preheating for degassing is provided to constitute a preheating area. Preferably, the preheater 11 has the same diameter as the wire drawing heater 2 and a length equal to or longer than the wire drawing heater 2.

This is to achieve more complete degassing by heating the transparent glass base material 4 in the preheater 11 for as long as possible.

Here, the temperature of the preheating region by the preheating heater 11 varies depending on various factors such as the composition of the supplied transparent glass base material 4 and the drawing speed, but is as high as possible below the softening point of the base material 4. For example, about 800℃~
A range of about 1500°C is suitable. This is about 800℃
If heated below, the residual gas remaining in the center of the base material will not be sufficiently degassed, and if heated above approximately 1,500°C, the base material itself will deform and the linear speed will fluctuate. It is.

Generally, gases such as He remaining in a transparent glass base material tend to diffuse through the glass and come out when the temperature is high.

This diffusion rate is generally expressed as D=Doexp (Q/RT) (Do, Q, and R are constants, and T is absolute temperature), and the higher the temperature, the faster the diffusion rate becomes. On the other hand, it is known that the solubility of gas in glass decreases as the temperature increases.

Therefore, as described above, by preheating the glass near the softening point using the preheating heater 11, the residual gas in the glass is diffused and released to the outside, thereby performing degassing.

Next, an example of measuring the residual gas concentration during the degassing process of this example according to the method of the present invention using a dehydrated and sintered transparent glass base material is shown in Figure 2 (al). The degassing state of the technology is shown in Figure 2 (bl).

In addition, Fig. 3(a) shows the temperature distribution in the preheating area and the drawing heating area in the drawing furnace of this embodiment, and Fig. 3(bl shows the drawing heating area in the drawing furnace of the conventional example). As shown in these drawings, at the initial stage of the transparent glass base material, a gas with a concentration of Co was dissolved from the center of the base material to the surface of the base material, as shown in a. However, as the method of the present invention passes through the preheating region, the concentration distribution changes from dl to d2, and at the end of preheating, the gas concentration increases from the center of the base material to the surface, causing bubbles to form in the optical fiber. The concentration was lower than the critical concentration at the softening point, which determines whether or not it exists.On the other hand, in the conventional example, because the heating time was short, the concentration distribution was b, and only a part of the surface of the base material was degassed, resulting in foaming. It was confirmed that toxic gas remained.

Furthermore, according to the present embodiment shown in FIG. 3(a), when the transparent glass base material 4 begins to be heated by the preheating heater 11, the temperature of the base material first rises to point A near the softening point. , by the time it rises to point A, the distribution of dissolved gas concentration d becomes as shown in Figure 2 (al).Then, the preheating is continued by being held in the preheating region (point A to point B) near the softening point. In the process of moving to this point B, d2 shown in Figure 2 (al)
Degassing is carried out so that the state is as follows.

Thereafter, the base material is moved to a drawing heating area, heated to a drawing temperature, and drawn. In one conventional example, the third
As shown in Figure (b), since preheating for a certain period of time was not performed near the softening temperature as in this example, the temperature rose rapidly to the drawing temperature, so the concentration distribution of the dissolved gas changed as shown in Figure 2 (
The state is b of bl, and degassing is insufficient.

Next, test examples showing the effects of the present invention will be explained.

In this embodiment, the wire drawing apparatus of this embodiment described above is used, and the drawing speed, the length of the preheating heater 11, and its temperature are adjusted to the first
Tests were conducted with changes as shown in the table. In Test Example 1 and Test Example 2, the same transparent glass base material was used.

In test example 1, an optical fiber with an outer diameter of 125 μmφ was used at a linear velocity of 30
In Test Example 2, an optical fiber with an outer diameter of 125 μmφ was manufactured at a linear speed of 200 m/min, and each
The number of bubbles present in the optical fiber per km was evaluated. Further, as a comparative example, using a conventional wire drawing apparatus in which the preheater 11 was not installed, prototypes were manufactured under each of the conditions shown in Table 1, and evaluated in the same manner.

These results are shown in Table 1.

Table 1 * Number of bubbles per 1100k of fiber Base material As is clear from the results in Table 1, according to the method of the present invention, before the transparent glass base material reaches the drawing heating region, the preliminary By passing through the heating area at a certain temperature (softening design fj!I) for a certain period of time, He gas, etc. remaining inside the base material is diffused and released to the outside, and the residual gas is completely removed. It was done. Since the transparent glass base material that has been gassed is then transferred to the drawing heating area,
It is possible to provide an optical fiber which has no fear of deformation of the base material, contains almost no bubbles, and has a constant wire diameter.

<Effects of the Invention> As explained above in detail together with Examples and Test Examples, according to the optical fiber manufacturing method of the present invention, the optical fiber can be drawn successively while being preheated and degassed. Since the preheating is performed efficiently, it is possible to provide a high-quality optical fiber that does not contain any bubbles.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a drawing furnace according to a preferred embodiment of the method of the present invention, FIG. Dissolved gas concentration distribution diagram in the base metal according to the conventional example, Figure 3 (a) ξ is a temperature distribution diagram in the drawing furnace according to this embodiment, Figure 3 (bl is the temperature distribution diagram in the drawing furnace according to the conventional example) 4 shows a schematic diagram of a conventional drawing furnace. In the drawings, 1.10 is a drawing furnace, 2 is a drawing heater, 3 is a heat insulating material, 4 is a transparent glass base material, and 5 is a drawing furnace. Optical fiber, 11 is a preheating heater. Patent applicant: Sumitomo Electric Industries, Ltd. Agent

Claims (1)

[Scope of Claims] 1) In an optical fiber manufacturing method in which an optical fiber is produced by drawing a rod-shaped transparent glass preform while softening it by heating, the transparent glass preform is heated to a softening point on the upstream side of the drawing point. 1. A method for producing an optical fiber, which comprises preheating at a temperature near the softening point to degas the fiber, and then drawing the fiber continuously. 2) The method for manufacturing an optical fiber according to claim 1, wherein the preheating and drawing are performed in the same drawing furnace.