JP2001058840A - Method for smoothing surface of optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for smoothing the surface of an optical fiber preform, by which the breakage of the optical fiber preform can be prevented when drawn, by covering and fusing the surface uneven portion of the optical fiber preform produced from quartz glass with a glass material having the same quality as the surface glass of the preform, thus burying the uneven portion. SOLUTION: Glass particles produced by the supply of a glass raw material gas to an oxyhydrogen flame burner are sequentially accumulated on a starting rod by a VAD method, and then passed through a heating oven to obtain the sintered optical fiber preform 1. A concave portion 2 such as a flaw or a recess or a convex portion such as a projection exits on the surface of the preform 1. A plate-like glass material 3 is melted and simultaneously fused to the concave portion 2 with the oxyhydrogen flame 4 of a burner 5. Thus, the concave portion 2 is wholly covered and buried with the glass material 3 to smooth the surface of the preform 1. On the other hand, when the glass material 3 is fused over a wide range around a convex portion, the convex portion is buried in a slope covered with the glass material 3 to smooth the surface of the preform 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simply and surely smoothing out irregularities on the surface of an optical fiber preform which is a raw material of an optical fiber.

[0002]

2. Description of the Related Art An optical fiber preform is formed by depositing glass fine particles supplied from an oxyhydrogen flame burner by a vapor phase axial method (VAD method) or the like, and then sintering the glass fine particles into a transparent glass. This is stretched to a predetermined diameter and drawn to obtain an optical fiber.

If the surface of the optical fiber preform has an uneven portion such as a scratch, a dent, or a projection, the preform will be broken when the preform is drawn. When the preform has a deep flaw or the like exceeding 500 μm in unevenness, as shown in FIG. 3, the disconnection rate at the time of drawing sharply increases,
Production efficiency decreases.

Conventionally, the surface of the preform has been subjected to cylindrical grinding or flame polishing. In this method, although fine scratches and projections can be removed, scratches with a large difference in unevenness cannot be removed, so that there is a problem that disconnection frequently occurs at the time of wire drawing, production efficiency is poor, and wire drawing cannot be performed at high speed. Was.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for smoothing the surface of an optical fiber preform so as not to cause disconnection during drawing. With the goal.

[0006]

A method for smoothing the surface of an optical fiber preform according to the present invention, which has been made to achieve the above object, will be described with reference to FIG. The glass material 3 having the same quality as the glass on the surface of the preform 1 is fused by covering the uneven portion 2 on the surface of the optical fiber preform 1, and the surface of the preform 1 is smoothed by burying the uneven portion 2. It is to do.

[0007] As shown in FIG. 1, the concave portion 2, which is a scratch or a dent, becomes smooth with respect to the surface of the preform 1 near the concave portion 2 by being covered with the glass material 3. As shown in FIG. 2, the projections 6 serving as projections are covered with a foot 7 formed over a wide area by fusing a glass material around the projections 6, so that the surface of the preform 1 becomes smooth.

The fusion of the glass material can be achieved by heating the glass material to a temperature of about 2000 ° C. or higher, which is the melting temperature of the glass.

After fusing the glass material, the surface may be polished. The surface polishing may be cylindrical grinding or flame polishing. Fine irregularities newly formed on the preform surface due to fusion of the glass material are removed by surface polishing, so that the surface of the preform 1 is further smoothed.

The glass material 3 is preferably a lump, plate, or powder glass. This can be suitably performed by bringing the block-shaped or plate-shaped glass into contact with the irregularities and heating and melting it with a burner to cover and fuse the irregularities. It can also be carried out by putting powdery glass over the uneven portion and passing it through a heating furnace to melt it.

The glass material 3 may be glass fine particles supplied from an oxyhydrogen flame burner. The glass fine particles are sintered and fused at the same time. Sintering is performed by passing through a heating furnace.

In the optical fiber preform of the present invention, the irregularities on the surface of the optical fiber preform made of quartz glass are:
It is buried and smoothed by fusing a glass material of the same quality as the glass on the surface.

[0013] In the optical fiber preform, it is preferable that the maximum unevenness difference of the uneven portion on the surface of the optical fiber preform made of quartz glass is 500 µm or less. 500 μm
If it exceeds, the disconnection rate will increase sharply during drawing.

Since this optical fiber preform does not break at the time of drawing, the productivity in producing an optical fiber by drawing is high.

[0015]

Embodiments of the present invention will be described below in detail. FIG. 1 is a schematic diagram showing an embodiment of a method for smoothing the surface of an optical fiber preform to which the present invention is applied.

In this smoothing method, a glass material of the same quality as the glass on the surface is fused to the concave and convex portions on the surface of the optical fiber preform 1.

First, glass fine particles generated by supplying a glass raw material gas to an oxyhydrogen flame burner by the VAD method are sequentially deposited on a starting rod, and then sintered by passing through a heating furnace.
An optical fiber preform 1 is obtained. On the surface of this preform, there are a concave portion 2 which is a scratch or a dent, and a convex portion 6 which is a projection (see FIG. 2).

In order to smooth the dent 2, the plate-like glass material 3 is melted by the oxyhydrogen flame 4 of the burner 5 and fused to the dent 2. The dent 2 is covered with a glass material 3. When the entire dent 2 is covered with the glass material 3 and buried, the surface of the preform is smoothed. In addition,
The glass material 3 may fill the dent 2 by fusing a plate-like glass having the same thickness as the depth of the dent 2, and fusing a plurality of plate-like glasses having a thickness smaller than the depth of the dent 2. The dents 2 may be smoothed.

On the other hand, in order to smooth the projections 6, the glass material is melted by an oxyhydrogen flame, and the glass material is fused over a wide area around the projections 6. When the protrusion 6 is buried in the foot 7 covered with the glass material, the surface of the preform is smoothed.

The surface of the smoothed preform is subjected to cylindrical grinding and flame polishing to make it even smoother. After fusion, after shaping with a trowel, cylindrical grinding or flame polishing may be performed.

An example in which the irregularities on the surface of the preform are smoothed according to the above embodiment will be described. Outer diameter 61.6mm
When a quartz glass optical fiber preform having a length of φ and a length of 880 mm was experimentally produced, the surface had a local dent of 950 μm. A plate-like quartz glass having the same quality as the glass on the surface of the preform was melted by an oxyhydrogen flame burner, and then fused to the dent to smooth the surface of the preform. Further, the surface of the preform was subjected to flame grinding using a glass lathe after cylindrical grinding, and the preform surface was further smoothed. As a result, a preform without irregularities was obtained. When wire drawing was performed at a speed of 100 m / min using this preform, no breakage occurred.

[0022]

As described above in detail, according to the method for smoothing the surface of an optical fiber preform of the present invention, the optical fiber preform can be easily and reliably smoothed, so that the production efficiency is high. The resulting optical fiber has a high tensile strength and can be drawn at high speed without breaking during drawing.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a method for smoothing the surface of an optical fiber preform to which the present invention is applied, in the middle of execution.

FIG. 2 is a schematic view showing another embodiment of a method for smoothing the surface of an optical fiber preform to which the present invention is applied.

FIG. 3 is a diagram showing a correlation between a difference in irregularities on the surface of an optical fiber preform and a disconnection rate.

[Explanation of symbols]

1 is an optical fiber preform, 2 is a concave portion, 3 is a glass material, 4 is an oxyhydrogen flame, 5 is a burner, 6 is a convex portion, and 7 is a glass material.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma F-term in the Shin-Etsu Chemical Co., Ltd. Precision Materials Laboratory 4G015 DA01

Claims (6)

[Claims] An optical fiber preform is formed by fusing a glass material of the same quality as the glass on the surface of the preform by covering the unevenness on the surface of the optical fiber preform made of quartz glass and burying the unevenness. Method to smooth the surface of 2. The method of claim 1, wherein the surface is polished after the fusion. 3. The method for smoothing the surface of an optical fiber preform according to claim 1, wherein the glass material is a lump, plate, or powder glass. 4. The glass material according to claim 1, wherein the glass material is glass fine particles supplied from an oxyhydrogen flame burner, and the fusion is performed by sintering the glass fine particles. Method for smoothing the surface of an optical fiber preform. 5. An optical fiber preform characterized in that the irregularities on the surface of an optical fiber preform made of quartz glass are buried and smoothed by fusing a glass material of the same quality as the glass on the surface. 6. An optical fiber preform characterized in that the maximum unevenness difference of the unevenness on the surface of the optical fiber preform made of quartz glass is 500 μm or less.