JPS60210540A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled base material contg. no impurities and causing no increase in transmission loss and no reduction in tensile strength by spouting a gaseous starting material for glass from an oxyhydrogen flame burner while feeding clean air into a protective vessel. CONSTITUTION:Air is passed through an air feeding inlet 10 and a filter box 9 contg. a built-in filter 8 having high performance by suction with a suction blower connected to an exhaust pipe 1 to remove dust of >=0.5mum particle size by 99.97%, and the resulting clean air is fed into a protective vessel 2. Gaseous starting materials for glass and a dopant are spouted from an oxyhydrogen flame burner 3 fixed in the bottom of the vessel 2, and glass particles produced by hydrolysis in a flame are deposited on the lower end of a support rod 4 suspended from the ceiling of the vessel 2 and connected to a lifting and rotating device 5 to form a porous base material 6 for an optical fiber.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention cleans the air supplied into the protective container in the VAD method to reduce the increase in transmission loss and decrease in tensile strength of the manufactured fiber. The present invention relates to a method of manufacturing a base material for optical fiber that prevents the above-mentioned problems.

<Prior art> As typical manufacturing methods for optical fiber base materials, the filling method, external deposition method, and VAD method (vapor phase attachment method) have been known, and this VAD method is usually shown in Fig. 1. Proceed as shown in
It is.

That is, on the bottom of the protective container (referred to as Matsufuru) 2, there is an oxyhydrogen flame burner 3 that spouts out gaseous glass raw materials and dopant raw materials as well as oxygen, hydrogen, etc. in a predetermined spatial distribution.
is provided so that glass raw materials etc. ejected from the nucleic acid-hydrogen flame burner 3 can be flame-hydrolyzed to produce granular glass. A support rod 4 on which the granular glass is deposited is suspended from the ceiling of the protective container 3, and the granular glass is deposited on the lower end of the support rod 4 to form a porous base material 6. The support rod 4 is connected to an elevating and rotating device 5, so that it can be moved up and down while rotating. Further, an exhaust pipe 1 is connected to a side wall of the protective container 2 at the lower left side in the drawing, and a suction blower (not shown) is connected to the exhaust pipe 1. An air supply pipe 7 is connected to the upper right side wall of the protective container 20 in the figure, and this air supply pipe 7 is open to the atmosphere. Therefore, when suction is performed by the suction floor, air is supplied into the protective container 3g2 through the air supply pipe 7, and at the same time, reaction surpluses such as granular glass and hydrogen chloride that have not adhered are exhausted from the exhaust pipe 1. The reason why the exhaust pipe 1 and the air supply pipe 7 are connected to the protection container 1 diagonally with respect to the container 2 is to ensure a stable flow of waste inside the protection container 2.
Mochit: To make it happen.

In such a VAD method, electricity is supplied into the protective container 2 from an air supply pipe 7 in addition to the oxyhydrogen flame burner 3 to exhaust unattached particulate glass and reaction surplus materials. , 0 (impurities in the supplied air or porous gas I'1. If impurities enter the 6 or adhere to the 15 surface, the transmission loss of the optical fiber increases and the tensile strength decreases. There was a fear.At the current technological level,
Impurities are mixed in in processes other than the VAD method, and VAD
Since the contamination of impurities in the VAD method is also accidental, it can be said that even if the contamination of impurities is completely prevented in the VAD method, there will not be a noticeable reduction in transmission loss. V
It is considered that the inclusion of impurities in the AD method would have a great effect on the increase in transmission loss.

<Object of the Invention> In view of the above-mentioned circumstances, the present invention aims to solve the problems of the VAD method that will surely arise in the future with technological progress by purifying the air supplied to the protective container. purpose.

<Configuration of the Invention> The configuration of the present invention that achieves the above-mentioned object is to eject gaseous frit gas from an oxyhydrogen flame burner, perform flame hydrolysis, and deposit the resulting granular glass in a rod shape to form a porous optical fiber. When manufacturing I in a protective container, the method is characterized in that, in addition to the oxyhydrogen flame burner, clean air is supplied into the protective container as described in (1) if.

<Effects of the Invention> Therefore, in the present invention, although clean air is supplied into the protective container, impurities may be mixed into the material for optical fibers, and impurities may be formed on the surface of the material. Therefore, the transmission loss of this optical fiber does not increase, and the tensile strength does not decrease.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 1n1. Note that the same parts as those in the prior art described in 1'IiJ are given the same numbers and redundant explanations will be omitted.

FIG. 2 shows an apparatus for carrying out an embodiment of the present invention. As shown in the figure, a filter hook 9 containing a high-performance filter 8 is installed in the air supply pipe 7. Therefore,
When air is taken in through the intake flow (not shown) connected to the exhaust pipe 1, the air sucked in from the air supply port 10 of the filter box 9 is supplied into the protective container 2 via the filter 8, and at the same time, the air is supplied to the protective container 2 through the oxyhydrogen flame burner 3. Reaction surplus gas such as HCl ejected from the reactor and granular glass (S, O2) that could not be deposited on the 4 materials 6 are exhausted through the exhaust pipe 1. As the high-performance filter 8, it is preferable to use one that is generally commercially available under the name HEPA. This HE
A high-performance filter called PA has the ability to remove 9997% of dust with a particle size of 05 μm or more, and is widely used in the air conditioning industry for clean rooms due to its easy availability, stable quality, and high performance. This is because they are also commercially available.

When 100 optical fibers were actually manufactured using the apparatus having the above configuration and the transmission loss thereof was investigated, the results shown in FIG. 4 were obtained. Further, as a comparative example, 100 optical fibers were manufactured using the conventional apparatus shown in FIG. 1, and the transmission loss thereof was investigated, and the results shown in FIG. 3 were obtained. In either case, the effects of transition metal contamination are likely to appear1.
Measurement was performed at a wavelength of 3 μm. At the current technological level, V
Since the influence of technical defects in processes other than the AD method is strongly reflected in transmission loss, it is not possible to confirm whether the optical fiber according to the method of the present invention has significantly lower transmission loss or i1t than the conventional one. However, Figures 3 and 4
As is clear from the results shown in the figure, it is recognized that there was a slight but overall loss of Buddhahood. In particular, as shown in FIG. 3, two fibers were manufactured in the prior art exhibiting particularly high transmission losses (09 to 0.95 dB/km 1 due to accidental causes), whereas the present invention Regardless of the method, the optical fiber has a transmission loss of 0.65 as shown in Figure 4.
There was nothing above dB/km, and this result shows that the present invention reliably prevents non-NJL atoms from being mixed in due to accidental causes.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the conventional VAD method implementation apparatus;
FIG. 2 is a schematic configuration diagram of a specific device for carrying out an embodiment of the present invention, FIGS. 3 and 4 are histograms showing the number of fibers with respect to transmission loss, and FIG. FIG. 4 relates to the present invention. In the drawing, 1 is an exhaust pipe, 2 is a protective container, 3 is an oxyhydrogen flame burner, 4 is a support rod, 5 is an elevating and rotating device, 5 is a porous 4 material, 7 is an air supply pipe, 8 is a high-performance filter, 9 is a filter box, and 10 is an air supply port. Patent application Representative of Sumitomo Electric Industries, Ltd. Patent attorney Mitsuishi Shibu (1 person) Figure 2

Claims (1)

[Claims] When a gaseous glass raw material is ejected from an oxyhydrogen flame burner and subjected to flame hydrolysis, and the resulting granular glass is deposited in a rod shape to produce porous optical fiber material in a protective container, the oxyhydrogen flame burner A method for manufacturing a material for a diagonal optical fiber, which is characterized by supplying clean air into the protective container separately.