JPS5934139B2 - Optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 1) Field of Application of the Invention The present invention relates to a method for manufacturing an optical fiber, the purpose of which is to manufacture an optical fiber strand with high mechanical strength.

(2) Prior art Normally, a low-loss silica-based optical fiber is produced by flowing a source gas 2 into a hollow quartz glass pipe 1 having a coaxial circular cross section, and then forming a gas on the inner wall surface of the quartz glass pipe 1, as shown in Figure 1a. Single layer or multilayer glass film 3 using phase chemical reaction method
After depositing, as shown in FIG. 1b, the preform 5 is rotated using a glass lathe, heated and melted by an oxyhydrogen burner 4 that repeatedly moves in the axial direction, and the hollow part is welded. Let's call it a rod.

Thereafter, as shown in FIG. By rotating at a high speed, the optical fiber 8 is drawn. It is thought that the cause of optical fiber breakage is the presence of minute scratches called "Griffith's scratches" on the surface of the optical fiber, and breakage occurs around these scratches.

Therefore, the fewer scratches the optical fiber has on its surface, the greater its mechanical strength. Generally, the surface of a quartz glass pipe has many scratches of different sizes and distributions due to the manufacturing process and subsequent handling of the quartz glass pipe.

Also, in the optical fiber manufacturing process described above, there is a possibility that the preform surface will be damaged. An optical fiber drawn from a preform with scratches on its surface has scratches on its surface and has low mechanical strength. Conventional methods for removing or reducing scratches on glass surfaces include optical polishing, chemical etching, and flame polishing. However, these methods have little effect and are not suitable for removing or reducing scratches on the surface of the optical fiber parab ohm for the reasons described below. That is, optical polishing ultimately leaves polishing marks as "Griffith's scratches", and its effect on improving the mechanical strength of the optical fiber is indisputable. Chemical etching is usually
This method attempts to remove scratches by dissolving the entire surface using hydrofluoric acid as an etching solution, but as shown in Figure 2, stress concentration can be reduced by rounding the shape of the scratches 9 on the surface as shown by the dotted line. However, in the case of an optical fiber preform in which various scratches of different sizes are unevenly distributed, the effect is small. Flame polishing uses a flame that has the melting temperature of glass to create surface tension on the molten surface and the pressure of the flame blowing onto the surface. However, like chemical etching, it is difficult to uniformly remove scratches of different sizes and distributions and create a smooth surface, and optical fiber Improvement in the mechanical strength of strands is still insufficient. (3) Purpose of the Invention The present invention aims to improve optical fiber γ, which has a large effect on strength deterioration, in order to manufacture optical fiber strands with high mechanical strength. The purpose is to remove scratches on the surface of Ibapreform.

(4) General description of the invention The scratches existing on the surface of the optical fiber preform vary in size and distribution, and it is difficult to uniformly remove the scratches.

The object of the present invention is to uniformly remove such surface scratches and to produce an optical fiber strand with high mechanical strength. That is, the optical fiber preform surface I
By performing this polishing, the surface is made to have uniform scratch size and distribution. After that, it's all about fire polishing! Its function is to remove these scratches and create a smooth surface. (5) Examples Hereinafter, the present invention will be explained in detail with reference to examples.

The surface roughness of the optical fiber hub rib ohm used in this example was measured using a Talystep surface roughness measuring device, and the results are shown in FIG. It can be seen that there are scratches with sharp shapes. For this preform, the maximum scratch depth is 33μ
It was m. Traditional flame polishing (
The surface roughness of the product coated with fire polish is shown by 10 in Figure 4. This is done by placing the preform on a glass lathe and rotating it at 10 revolutions per minute.
! Flame polishing was performed five times back and forth using an oxyhydrogen burner moving at a speed of /mm, and the temperature of the oxyhydrogen flame was 19
The temperature is 50°C. As can be seen from the figure, the shape of the scratches has become more or less rounded, but the depth and size of the scratches have not changed much.
What is shown at 11f in FIG. 4 is the surface roughness of the preform according to the present invention. First of all, the particle size≠3000
The entire surface of the preform is polished using a green carborundum abrasive (average particle size: 5 μm) to make the surface uniform in size and distribution of scratches. Thereafter, this preform was rotated on a glass lathe at a speed of 10 revolutions per minute.
Oxygen hydrogen moving in the axial direction at a speed of 6 m/m
Flame polishing was performed five times back and forth, and the temperature of the oxyhydrogen flame was 1950°C. As is clear from the figure,
According to the present invention, scratches on the surface are clearly removed, resulting in a uniform and smooth surface. These preforms were drawn into optical fibers with a wire diameter of 130 μm. Figure 5f shows the frequency distribution of tensile breaking strength of the optical fiber drawn from an untreated preform with the surface roughness shown in Figure 3. Frequency Distribution of Tensile Breaking Strength of Optical Fiber FIG. 7 shows the frequency distribution of tensile breaking strength of an optical fiber drawn from a preform according to the present invention.

Tensile breaking strength is 100m7 in length! L, using 50 samples, 5mm/
It was measured at a tensile speed of Mm. The strength of the optical fibers produced by the preforms treated with this process was 0.62 kg on average, and the strength of the optical fibers produced by the preforms subjected to conventional flame polishing was 0.64 k9 on average. The optical fiber manufactured from the preform according to the present invention has an average strength of 1.33 ky, which clearly shows an improvement in mechanical strength. According to this example, the present invention was able to improve the strength by more than twice. The present invention is not limited to this first embodiment.

For example, when performing flame polishing (fire gamma polishing), the heating source is not limited to an oxyhydrogen flame, but may be any combustion gas such as city gas or propane gas.
Further, the conditions for flame polishing are different from the size and distribution of scratches on the preform, and the moving speed of the burner, the number of reciprocations, and the number of revolutions are determined as appropriate. for example,
By reducing the speed at which the burner moves and increasing the number of reciprocations, it becomes possible to erase even large scratches. Further, the polishing performed before the flame polishing may be performed by any method that makes the preform surface uniform in size and distribution of scratches. for example,
In polishing using abrasive grains as shown in this embodiment, the type of abrasive used is not limited. Other methods include a sandblasting method (a method in which thick abrasive grains are sprayed with high-pressure gas) and a method using a grinder. Further, the optical fiber hub rib ohm may be a glass rod or a glass pipe made of a one-in-one system or a multi-component system. for example,
A glass rod or pipe made by a gas phase chemical reaction method can be used. In the above embodiment, a method was described in which flame polishing was performed after polishing the surface of the optical fiber hub rib ohm, but in the case of a gas phase chemical reaction method as shown in FIG. The process shown in FIGS. 1A and 1B flame polishes the surface and provides the same effect as the method of the present invention.

Therefore, the present invention also includes such a method. (6) Summary As explained above, according to the present invention, it is possible to uniformly remove scratches on the surface of the optical fiber preform, which greatly affect the strength deterioration of the optical fiber, and the damage is more than doubled. It is possible to improve the strength, which has a great effect on improving the quality of the optical fiber.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the manufacturing method of optical fiber 'N, Figure 2 is a diagram showing how scratches caused by conventional chemical etching and flame polishing1 are rounded up, and Figure 3 is a diagram showing the optical fiber of this process. FIG. 4 is a diagram showing the surface roughness of the preform surface obtained by conventional flame polishing (fire γ polishing) and the preform according to the present invention. FIG. ′〈
Figure 6 is a frequency distribution diagram of the tensile strength at break of an optical fiber subjected to conventional flame polishing, and Figure 7 is a frequency distribution diagram of the tensile strength at FIG. 2 is a frequency distribution diagram of tensile breaking strength of γ fibers.

Claims (1)

[Claims] 1 After polishing the surface of the optical fiber material to make it a uniform surface, the surface of the optical fiber material is flame-polished using a flame that has the melting temperature of the material of the outermost shell of the optical fiber preform. 1. A method for manufacturing an optical fiber, which comprises applying polishing to make the surface smooth, and then drawing the optical fiber.