JPS5951500B2 - 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 of manufacturing an optical fiber used as a transmission line for optical communications.

(2) Prior Art FIG. 1 is an example of a process for manufacturing an optical fiber using a conventional gas phase chemical reaction method.

Figure a shows a hollow glass tube 3 (usually made of quartz tube, Vycor tube, etc.) attached to the chucks 8 and 8' of the glass lathe 1, and rotated as shown by arrow 5 (or in the opposite direction). A source gas for glass film formation is introduced from
In the case of heating source 4, an oxyhydrogen burner is used. ) in the direction of arrow 7 (or 7') to deposit a glass film 6, which will become the cladding material and core material of the optical fiber, on the inner wall surface of the hollow glass tube 3. Figure b shows a hollow glass tube on which a glass film has been deposited, which is heated by a heat source 4 and welded so that the cross section of the hollow glass tube becomes dense.
It is the process of making a circular bar optical fiber into a paralibe ohm made of a layered (or multi-layered) glass structure. In the figure c, the preform 9 is attached to the chuck 15 of the preform support stand 14 of the drawing device, and by moving the support stand 14 in the direction of the arrow 13, the preform 9 is inserted into the heating furnace 10 at a constant speed and heated. , the thin optical fiber 11 is stretched while being melted, and then transferred to the drum 1 by the motor 16.
This is a wire drawing process in which the wire is wound into two. However, as a result of experimental studies conducted by the present inventor regarding the process shown in FIG. 1, it has become clear that the manufacturing yield of optical fibers is reduced for the following reasons. (1) Hollow glass tube 3
Usually, crystals made by melting natural or artificial crystals are used.

Commercially available products have many scratches on the surface. The scratches included in this surface are heated by the θ process shown in Figure 1 a and b above.
Although it is melted to some extent and disappears, some parts remain and as a result, a preform with scratches on the surface is produced.
(2) The preform with the scratches remaining is shown in Figure 1c above.
When optical fiber is drawn in the drawing process, scratches on the surface of the preform are melted, stretched, and reduced in size; In some cases, scratches may be left on the optical fiber surface.

This is the starting point and causes deterioration of the mechanical properties of the optical fiber. (3) Since there are variations in the outer diameter and inner diameter of the hollow glass tube, it is difficult to obtain an optical fiber with a uniform outer diameter and core diameter.

The present invention relates to a method for solving the above problems.

(3) Purpose of the Invention The object of the present invention is to provide a method for producing an optical fiber with fewer scratches on its surface.

As a result, the objective is to obtain an optical fiber with excellent mechanical properties. (4) General description of the invention The present invention is a method for obtaining an optical fiber by precoating a glass film on the surface of an optical fiber hub rib ohm and then drawing the glass film.

The pre-coating method is as follows: (1) Apply a solution of a silicon compound dissolved in alcohol and a solution of a silicon compound and a diffusing agent for controlling the refractive index (for example, phosphorus, boron, antimony, etc.) dissolved in alcohol to the preform surface, and then dry. method, (2) method of dissolving oxide powder in an organic solvent, applying it to the preform surface, and then baking and drying it; (
3) A method of applying a potassium silicate aqueous solution (K2O-NSiO2) to the preform surface and then baking it to dry, (4)
A method is used in which water glass (Na2SiO3.NH2O) is applied and then baked to dry, and (5) a method in which a glass film is deposited on the preform surface by a flame hydrolysis method. (5
) Examples Hereinafter, the present invention will be explained in detail with reference to Examples.

This will be explained in comparison with the conventional method. First, FIG. 2a is a schematic view of the surface of a preform produced by a conventional method, taken with one end inserted into the electric furnace shown in FIG. 1C.

It can be seen that the radiant light from the electric furnace is scattered from the scratches on the preform surface. Draw such a preform using the method shown in Figure 1C, and attach the optical fiber to drum 1.
During the winding process, a photodiode detector detected the fused radiation light scattered by the scratches on the surface of the optical fiber. However, the photodiode detector is placed close to the surface of the optical fiber (non-contact). Figure 3a shows the recorded scattered light output, and the part that changes in a pulsed manner is due to imperfections in the optical fiber (scratches, bubbles, dirt, etc., but most of them are due to scratches on the surface). ). The tensile strength at break of this optical fiber is approximately 800 g, which is significantly deteriorated compared to the original properties of quartz glass. As described above, the conventional method has the disadvantage that scratches tend to remain on the surface of the optical fiber. Next, Fig. 2b shows a preform produced by the conventional method, which is rotated, and a liquid containing a silicon compound dissolved in alcohol (trade name: Si-Fil) is applied to the surface of the preform.
This is a photograph taken after coating the sample with a coating material (M, manufactured by Tokyo Ohka Kogyo Co., Ltd.) and then heating it at 1000° C. for 30 minutes in an oxygen atmosphere, and inserting the sample into an electric furnace in the same manner as in FIG. 2a.

As is clear from the comparison with FIG. 2a, the number of imperfections on the preform surface has been drastically reduced. This suggests that the liquid penetrated into the scratches on the preform surface by capillary action, and when heated, the scratches were covered with a glass film, and the entire surface of the preform was covered with the glass film. This preform was then drawn, and the melting radiation scattered from the surface of the optical fiber was detected in the same manner as in FIG. 3a. Figure 3b shows its characteristics. Second
As is clear from the comparison with Figure a, almost no pulsed scattered light is detected. That is, it is shown that the method of the present invention produces an optical fiber with fewer imperfections. The tensile strength at break of this optical fiber was measured and found to be approximately 1 kg. Moreover, the frequency distribution of tensile strength at break had a minimum value of about 600 g, and the yield was improved. In the above example, after applying the liquid to the preform surface, it was heated at 1000°C for 30 minutes in an oxygen atmosphere, but if the preform surface was then heated by blowing the flame of an oxyhydrogen burner, an optical fiber with higher tensile breaking strength could be obtained. I was able to get This is presumed to be because the flame of the oxyhydrogen burner heated and melted the glass film on the preform surface, and the preform was covered with a dense glass film with small particle diameters. In order to reduce scratches on the surface of the preform, it is more effective to dissolve a silicon compound and a diffusing agent for controlling the refractive index in alcohol because the melting point of the glass film is lower. An example of such a liquid is P-Si-Film. B-Si-Film. S
bSi-Film (all product names, manufactured by Tokyo Ohka Kogyo)
etc. is good. 1. As mentioned above, applying a low-viscosity liquid and baking and drying was effective as a method of filling scratches on the preform surface with a glass film. K.

O-NSiO. ) can be used. A commercially available product is Orka Seal (trade name, manufactured by Tokyo Ohka Kogyo). This is a colorless, transparent and odorless alkaline aqueous solution with a molar ratio (SiO./K.O
) It is a 28% solution of potassium silicate from 3 to 4. When this is applied to the preform surface and then heated and dried, SiO is formed on the preform surface. -K. An O2 glass film is formed. Furthermore, the amount of K in the glass film varies depending on the heating time and temperature. This has the effect that O can be diffused and permeated into the preform, and the refractive index distribution within the cross section of the preform can be partially controlled. Water glass (N
a. SiO.・NH. O) is suitable. This is a soluble alkali silicate or its aqueous solution, Na2O:
SiO.

Those having a molar ratio of 2 to 4 can be used. This is also K above. O-
NSiO. It has the same effect as . Ru. That is, by applying it to the preform surface and then heating and drying it,
SiO on the preform surface. -Na. An O glass film is formed. Then, Na2O diffuses and permeates into the preform. SiO2-K. O glass, SiO. -Na2
Melting point of O glass film. is usually lower (around 1000° C.) than the melting point of the preform produced by the method shown in FIG.
For this reason, it has the advantage that the glass film easily burrows into scratches on the preform surface. After applying the liquid to the preform surface, it is baked and dried. As a pre-coating method other than the above method, it is preferable to deposit a glass film on the preform surface by a flame hydrolysis method.

With this method, it is difficult to embed the glass film deep into the scratches as with the liquid coating method, but it is possible to completely cover the scratches on the surface and improve the mechanical properties of the optical fiber. is possible. Moreover, it has the advantage that the outer diameter of the preform can be set to a desired value by controlling the glass film thickness, and the yield of producing optical fibers with uniform outer diameters and core diameters can be increased. As for the method of depositing a glass film by flame hydrolysis, the method previously proposed by the present inventor (Japanese Patent Application No. 128289/1982) can be applied. Note that the method of the present invention is not limited to the preform produced by the method shown in FIG. That is,
It is also applicable to drawing ordinary glass rods and tubes. (6) Summary As explained above <According to the present invention, scratches on the preform surface are covered with a filler or a glass film by applying a liquid and baking and drying the scratches without using chemical or mechanical polishing. As a result, an optical fiber with excellent mechanical strength is obtained.

[Brief explanation of the drawing]

Figure 1 shows an example of an optical fiber manufacturing method using a conventional gas phase chemical reaction method, and Figure 2a shows the surface of a preform manufactured by the conventional method with one end inserted into an electric furnace. Fig. 2b is an overview of the surface of a preform produced by the method of the present invention, and Fig. 3a is a diagram of molten radiation scattered from an optical fiber obtained by drawing a conventional preform into an optical fiber. FIG. 3(b) is a characteristic diagram of light characteristics measured by the same measuring method as in FIG. 3(a) when the preform of the present invention is drawn.

Claims (1)

[Claims] 1. Applying a liquid that forms a glass composition by heating to the surface of a preform that will become an optical fiber material,
A method for producing an optical fiber, which comprises heating, drying, reheating, melting, and drawing into an optical fiber. 2. An optical fiber characterized in that a gas that forms a glass composition by heating is blown onto the surface of a preform that becomes an optical fiber material, and after heating, the preform is reheated and melted to be drawn into an optical fiber. Production method. 3. Before drawing the preform on the surface of which the glass composition is formed, the glass composition is heat-treated by blowing flame from an oxyhydrogen burner onto the surface of the preform on which the glass composition is formed. A method for manufacturing an optical fiber according to claim 1 or 2.