JP4019252B2 - Manufacturing method of glass pipe for optical fiber - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a glass pipe for optical fiber.
[0002]
[Prior art]
As a method for manufacturing an optical fiber glass pipe, a method of press-fitting a drilling jig into the center of a quartz glass rod while heating and softening the quartz glass rod with a heat source is known (see JP-A-7-109135). . According to the above method, the impurities present in the drilling jig adhere to and diffuse on the glass pipe. Therefore, for the purpose of removing impurities, the inner peripheral surface of the glass pipe is usually used with HF (hydrofluoric acid) solution or the like. Etching is performed.
[0003]
However, in the conventional etching method, a large amount of impurities may remain on the inner peripheral surface of the glass pipe due to an insufficient etching amount. Especially, when the impurities are transition metals, transmission loss is reduced. There was a problem that a high optical fiber might be obtained. On the other hand, in order to avoid the problem, the method of increasing the etching amount has a problem that the etching is actually performed more than necessary.
[0004]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a glass pipe for an optical fiber that can reliably obtain an optical fiber having excellent optical transmission characteristics. It is in.
[0005]
[Means for Solving the Problems]
The manufacturing method of the glass pipe for optical fibers which concerns on Claim 1 heats the elongate glass raw material with the heat source which moves relatively along the longitudinal direction of a glass raw material, The perforated area | region where the said glass raw material was softened A glass pipe is manufactured by press-fitting along a central axis from the end face of the glass material a drilling jig that is provided and maintained at a constant relative position to the heat source, and the content of transition metal contained in the drilling jig When a heating temperature in the perforated region, estimate the depth distribution of the impurity concentration of the heating time in the perforated region, to determine the necessary and sufficient amount of etching, then, the inner circumferential surface of the glass pipe, in the etching amount It is characterized by chemical etching. Now, the present inventor has a correlation between the above-mentioned “content of transition metal, heating temperature, heating time” and “etching amount necessary to reliably obtain an optical fiber having excellent optical transmission characteristics”. I found out. Therefore, according to the method for manufacturing an optical fiber glass pipe according to claim 1, based on the transition metal content contained in the drilling jig, the heating temperature in the drilling region, and the heating time in the drilling region, By etching, the depth from the inner peripheral surface of the glass pipe where the impurity concentration is below a certain level can be determined, and a necessary and sufficient amount of etching can be performed based on this depth. Therefore, it can be set as the manufacturing method of the glass pipe for optical fibers which can obtain the optical fiber excellent in the optical transmission characteristic reliably, without performing etching more than necessary.
[0006]
In addition, the present inventor, when the content of the transition metal is 1% by weight or less, the heating temperature in the perforated region is 1700 ° C. to 1800 ° C., the heating time in the perforated region is 10 minutes or less, and the etching amount is 35 μm or more, It has been found that an optical fiber excellent in optical transmission characteristics can be obtained with certainty.
Therefore, in the method for manufacturing the optical fiber glass pipe according to claim 2, the transition metal content is 1 wt% or less, the heating temperature in the perforated region is 1700 ° C. to 1800 ° C., and the heating time in the perforated region is 10 minutes or less. The etching amount is 35 μm or more.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram for explaining a method of manufacturing an optical fiber glass pipe according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the penetration depth from the inner peripheral surface of the glass pipe and the impurity concentration according to the embodiment of the present invention. It is.
[0008]
As shown to (A) and (B) of FIG. 1, the manufacturing method of the glass pipe for optical fibers which concerns on embodiment of this invention is a heat source which relatively moves the elongate glass raw material 10 along the longitudinal direction. 11 is used to provide a perforated region in which the glass material is softened. At the same time, a punching jig 12 whose relative position with respect to the heat source 11 is kept constant is press-fitted along the central axis X from the end face 10A of the glass material 10 to form a glass pipe 13.
[0009]
As the glass material 10, a columnar one or a cylindrical one whose inner diameter is set smaller than the maximum outer diameter of the drilling jig 12 can be suitably used. Moreover, since the heat source 11 and the perforation jig | tool 12 and the glass raw material 10 should just move relatively, the heat source 11 and the perforation jig | tool 12 may be moved, and the glass raw material 10 may be moved. Furthermore, both may be moved. However, in any case, the relative positional relationship between the heat source 11 and the drilling jig 12 is usually constant.
[0010]
Next, as shown in the schematic cross-sectional view of the glass pipe 13 in FIG. 1C, the inner peripheral surface 13A of the glass pipe (hereinafter also referred to as the pipe inner peripheral surface) is etched at an etching depth h (etching amount). Glass pipe for optical fiber is manufactured by chemical etching.
[0011]
In a communication optical fiber, a wavelength band of 1.3 to 1.7 μm is generally used. However, when transition metals such as Fe, Cr, Ni, Co, Cu, V, and Mn are contained in the optical fiber, these wavelengths are used. Loss increases over a wide range of wavelength bands.
In order to prevent such an increase in loss due to the transition metal, it is necessary to suppress the concentration of the transition metal contained as an impurity to a level lower than 1.0 wtppb. Accordingly, the material used for manufacturing the optical fiber is also required to have an impurity concentration suppressed to a level lower than 1.0 wtppb.
[0012]
Then, as described above, when the punching jig 12 is press-fitted into the heated glass material 10 to produce an optical fiber glass pipe, the impurities contained in the punching jig 12 are caused by heat during processing to cause the pipe inner periphery. There is concern that a layer that diffuses from the surface 13A and contains an impurity is formed (see FIG. 1C).
In the present invention, the etching depth h refers to the content of the transition metal contained in the drilling jig 12, the heating temperature in the drilling region (processing temperature), and the heating time in the drilling region (time maintained at the processing temperature). ) And determined.
More specifically, the present inventor has found that the impurity concentration C (x) at the depth x from the pipe inner peripheral surface 13A is accurately given by (Equation 1).
[0013]
C (x) = C0 × exp (−x ² / 4Dt) (Formula 1)
Where C0: impurity concentration on the inner surface of the glass pipe x: depth from the inner surface of the glass pipe D: diffusion coefficient of impurities at the processing temperature of the quartz glass t: time for which the processing temperature is maintained
According to (Equation 1), it is possible to estimate the depth from the pipe inner peripheral surface 13A where the impurity concentration is 1 wtppb, whereby a necessary and sufficient amount of etching depth h can be determined.
Therefore, by etching the pipe inner peripheral surface 13A at the etching depth h, it is possible to manufacture an optical fiber pipe that can reliably obtain an optical fiber having excellent optical transmission characteristics without performing etching more than necessary. I found.
[0015]
Further, in view of the above (Equation 1), the present inventor has a transition metal content of 1% by weight or less in the drilling jig 12, the heating temperature in the drilling region is 1700 ° C. to 1800 ° C., and in the drilling region. It has been found that a glass pipe for optical fiber with a sufficiently small content of impurities can be reliably produced without performing etching more than necessary under the conditions of a heating time of 10 minutes or less and an etching amount of 35 μm to 50 μm (hereinafter, See Examples).
[0016]
As chemical etching, wet etching or dry etching may be performed.
As a wet etching method, there is a method using a solution containing hydrofluoric acid (HF). In this case, the etching depth can be finely adjusted by adjusting the concentration of the HF solution, and excessive etching can be prevented.
As a dry etching etching method, there is a method of flowing sulfur hexafluoride (SF ₆ ) or various types of chlorofluorocarbon gas to the inner peripheral surface while heating the pipe. In this case, there is an effect of smoothing the inner peripheral surface of the pipe, and an effect that the inner peripheral surface is not roughened even if it is etched excessively can be expected.
[0017]
【Example】
A pure quartz glass rod (manufactured by a method such as the VAD method) as the glass material 10 is set in a perforating apparatus, and the glass pipe 13 is created based on the above method.
The heating temperature (processing temperature) in the perforated region is set to 1700 ° C. to 1800 ° C. in order to make the pure quartz glass rod have a processable viscosity. In this temperature range, the diffusion coefficient at 1800 ° C. is the highest (that is, it is easy to diffuse). The value is, for example, 3.1 × 10 ⁻¹⁰ cm ² / s in Fe ³⁺ , and other transition metal elements are equivalent in order, and therefore in the above (formula 1) When 1.0 × 10 ⁻⁹ cm ² / s is used as the impurity diffusion coefficient D, it is sufficiently safe to estimate the thickness of the impurity layer existing at a predetermined depth from the pipe inner peripheral surface 13A.
[0018]
In addition, the time during which 1700 ° C. to 1800 ° C. is maintained (heating time in the perforated region) is 10 minutes.
[0019]
As the drilling jig 12, a carbon jig having a purity of 99 wt% is used. In this case, since the volume of the drilling jig 12 is sufficiently smaller than the quartz glass rod to be processed, it is sufficiently safe to estimate 1 wt% as the impurity concentration C0 of the inner peripheral surface 13A of the pipe.
[0020]
FIG. 2 shows the correlation between the penetration depth from the pipe inner surface 13a and the impurity concentration obtained by the above (Equation 1) using the impurity diffusion coefficient D and the impurity concentration C0 estimated as described above.
According to FIG. 2, in order to make the content of the transition metal impurity smaller than 1 wtppb, the etching may be performed at an etching depth h of 35 μm or more from the pipe inner surface 13a. In order not to perform etching more than necessary, the etching depth h is preferably 50 μm or less.
As described above, according to the present invention, the depth x from the pipe inner peripheral surface 13A at which the impurity concentration becomes a predetermined value can be determined by (Equation 1), and a necessary and sufficient amount based on the depth x By performing the etching at an etching depth h (etching amount), an optical fiber glass pipe with a sufficiently small impurity content can be reliably manufactured.
[0021]
【The invention's effect】
As described above, according to the present invention, the diffusion amount of transition metal impurities under the drilling conditions is predicted, and the etching amount is set to a necessary and sufficient amount, so that the light can be emitted without performing etching more than necessary. The manufacturing method of the glass pipe for optical fibers which can obtain the optical fiber excellent in the transmission characteristic reliably can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a method for producing a glass pipe for optical fibers according to the present invention.
FIG. 2 is a graph showing the relationship between the penetration depth from the inner peripheral surface of the glass pipe and the impurity concentration according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Glass material 11 Heat source 12 Drilling jig 13 Glass pipe 13A Inner peripheral surface of glass pipe

Claims (2)

By heating a long glass material with a heat source that relatively moves along the longitudinal direction of the glass material, a perforated region in which the glass material is softened is provided, and a relative position with respect to the heat source is kept constant. A glass pipe is manufactured by press-fitting a drilling jig along the central axis from the end face of the glass material,
Estimating the depth distribution of the impurity concentration from the transition metal content contained in the drilling jig, the heating temperature in the drilling region, and the heating time in the drilling region, and determining the necessary and sufficient etching amount,
Then, the manufacturing method of the glass pipe for optical fibers which chemically etches the internal peripheral surface of the said glass pipe with the said etching amount.   The content of the transition metal is 1% by weight or less, the heating temperature in the perforated region is 1700 ° C. to 1800 ° C., the heating time in the perforated region is 10 minutes or less, and the etching amount is 35 μm or more. The manufacturing method of the glass pipe for optical fibers of description.

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