JPS6317779B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quartz glass tube used in the production of optical fibers used in optical communications, and more particularly to improvements in quartz glass tubes used as cladding materials and holder materials for optical fibers.

As is well known, this type of optical fiber has a core at the center that transmits light, and a cladding with a refractive index lower than that of the core that reflects light and prevents light from leaking to the outside. It's structured. If necessary, the optical fiber is provided with a holder (support material) further around the cladding to protect the cladding.

To manufacture the above-mentioned optical fiber, first, a quartz glass core material of a desired diameter is inserted into a quartz glass tube as a cladding material having an inner diameter approximately equal to the diameter of the core material, and the quartz glass core material is brought into close contact with the quartz glass core material as needed. After inserting the glass tube into the quartz glass tube that serves as the holder material and bringing them into close contact, one end is sealed, and the air in the gap between the core material and the cladding material (or between the cladding material and the holder material) is removed from the other end using a vacuum pump. A base rod with a diameter of 1 to 2 cm is made of a core material and a cladding material (core material, cladding material, and holder material as necessary) by heating them sequentially from one end with an oxyhydrogen burner and bringing them into close contact. After that, this original rod is drawn into a 100-200 μm fiber using a drawing machine to create an optical fiber.

Incidentally, conventionally, ordinary quartz glass tubes have been used as cladding materials and holder materials used in the manufacture of optical fiber base rods. However, if the base rod is manufactured from these materials, the adhesion to the core material (or cladding material) will be insufficient, and in severe cases, the base rod will have microbubbles between these materials. As a result, when this original rod is drawn, not only the optical properties of the obtained optical fiber deteriorate, but also there is a risk of the fiber being cut during drawing.

For this reason, recently, clad materials made of quartz glass tubes with ring-shaped or spiral-shaped irregularities on the inner peripheral surface have been used to control the adhesion to the core material. However, even with such a clad material, even during the production of the base rod, it may not adhere sufficiently to the core material, or microbubbles may remain between them. especially,
If the quartz glass tube is not a perfect circle but somewhat oval, poor adhesion to the core material and residual microbubbles will become apparent.

On the other hand, as a result of extensive research in order to eliminate the above-mentioned drawbacks, the present inventor used a quartz glass tube with linear grooves of a predetermined depth formed in the length direction of the surface as the cladding material or holder material. In some cases, after inserting the core material into the cladding material (or inserting them into the holder material), if one end is sealed and heated while suction is applied from the other end, the surface of the cladding material and holder material (especially the inner part) may be damaged. We have developed a quartz glass tube for optical fibers that has improved adhesion between the core material and cladding material (or between the cladding material and holder material) by improving the circumferential surface), and can produce a base rod with no microbubbles remaining between them. I found it. Therefore, by drawing a base rod manufactured using the quartz glass tube of the present invention, an optical fiber with excellent light transmission characteristics can be obtained without causing breakage during drawing.

That is, in the quartz glass tube for optical fiber of the present invention, the inner surface of the quartz glass tube into which the quartz glass core material is inserted is etched with hydrofluoric acid to a depth of 0.1 μm or more.
A linear groove of 5 μm for gas suction is formed in the longitudinal direction of the inner surface of a quartz glass tube.

The linear grooves in the present invention may be formed continuously or discontinuously in the longitudinal direction of the surface. The surface on which these linear grooves are formed is only the inner surface, or the inner and outer surfaces, when the quartz glass tube is used as the clad material, and only the inner surface when it is used as the holder material.

The reason why the depth of the linear grooves formed on the surface in the present invention is limited to the above range is that the depth is 0.1 μm.
If the diameter is less than 5μm, the adhesion to the core material during the production of the base rod cannot be improved or the effect of preventing the residual microbubbles will not be sufficiently achieved, while if it exceeds 5μm, the degassing effect during suction will increase, but the adhesion will be reduced. This is because it gets worse.

In order to manufacture the quartz glass tube for optical fiber of the present invention, for example, a quartz glass ingot is drawn into a base tube using a carbon mold in which a mandrel having minute irregularities on the surface is inserted. The inner surface of this original tube was coated with 5-50 μm of 5-30% hydrofluoric acid.
A method of removing etching and washing with water can be adopted. The quartz glass tube obtained by this method has a depth of 0.1~
A plurality of 5 μm linear grooves are formed in the longitudinal direction, and it is activated by etching and has the property of easily adhering to other quartz glass bodies at high temperatures.

Next, examples of the present invention will be described.

Example 1 A synthetic quartz glass ingot was drawn into a tube using a carbon mold in which a mandrel with fine irregularities on the surface was inserted to produce a tubular body with an outer diameter of 20 mm, an inner diameter of 11 mm, and a length of 1 m. When the side surface was etched to a depth of 20 μm with 20% hydrofluoric acid, many linear grooves with a depth of 2 μm were found on the inner surface as shown in Figure 1.
... A quartz glass tube 2 in which 1 was formed in the longitudinal direction was obtained.

Next, using the quartz glass tube 2 as a cladding material, a core material 3 made of a quartz glass rod with an outer diameter of 10 mm is inserted into the cladding material 2 as shown in FIG. 2, one end is sealed, and the other end is sealed. A gas suction pipe 4 is attached, and the air between the core material 3 and the cladding material (quartz glass tube) is degassed from the suction pipe 4 while rotating in the direction of the arrow, and heated from one end with oxyhydrogen burners 5. Then, the two materials 2 and 3 were brought into close contact with each other to produce a base rod 6 for optical fiber. In this original rod 6, the core material and the cladding material were in good contact with each other, and no microbubbles were observed to remain between them.

Comparative example: Outer diameter 20mm, inner diameter 11mm (inner diameter tolerance 0.2mm),
A core material consisting of a quartz glass rod with an outer diameter of 10 mm was inserted into a quartz glass tube (clad material) with a length of 1 mm and a gentle ridge of 3 μm in the circumferential direction on the inner surface. Next, these were degassed in the same manner as in the previous example, and the core material and cladding material were brought into close contact with each other while rotating to produce a base rod for an optical fiber. In this original bar, not only were there some areas where the core material and cladding material were not in close contact with each other, but it was also observed that microbubbles remained between them.

The original rods of Example 1 and Comparative Example were then drawn using a wire drawing machine to produce an optical fiber 9 having an outer diameter of 120 μm and consisting of a core 7 and a cladding 8 as shown in FIG. As a result, in the case of Example 1, there were no accidents due to cutting during drawing of the original rod, and the optical fiber obtained had extremely good characteristics with an optical loss of 2 dB/Km. On the other hand, in the case of the comparative example, there was one breakage accident during drawing, and the optical loss of the obtained optical fiber was the same wavelength as that of the example.
The characteristics were low at 4dB/Km.

Example 2 A synthetic quartz glass ingot was drawn into a tube using a carbon mold in which a mandrel with fine irregularities on the surface was inserted to create a tubular body with an inner diameter of 21 mm and a length of 1 m. When the tube was etched to a depth of 30 μm with hydrofluoric acid, a quartz glass tube was obtained in which a large number of linear grooves with a depth of 3 μm were formed in the longitudinal direction on the inner surface.

Next, the above-mentioned quartz glass tube is used as the holder material, and the inner diameter obtained in the above example is applied to this holder material.
After inserting a cladding material of 11 mm and an outer diameter of 20mm, and then inserting a core material made of a quartz glass rod with an inner diameter of 10mm into this cladding material, these are degassed and heated while rotating to form the core material, cladding material, and holder. A triple-layered base rod for optical fiber was created by closely adhering the materials. Thereafter, this original rod was drawn using a drawing machine to produce an optical fiber 9' having an outer diameter of 180 μm and consisting of a core 7, a cladding 8, and a holder 10, as shown in FIG. As a result, there were no accidents caused by the original rod being cut during drawing, and the optical fiber obtained had extremely good characteristics, with an optical loss of 2 dB/Km.

As described in detail above, according to the present invention, by using a quartz glass tube with linear grooves of a predetermined depth formed in the longitudinal direction of the surface as the cladding material or holder material, the quartz glass tube can be easily attached to the core material. It is possible to produce a base rod with a double or triple structure that has a clad material that is in close contact with the clad material or a holder material that is in good contact with the clad material, and there are no residual microbubbles between them, and then this base rod can be drawn. By doing so, it is possible to provide a quartz glass tube for an optical fiber that can produce an optical fiber with excellent light transmission characteristics without causing breakage during drawing.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the quartz glass tube obtained in Example 1 of the present invention, and Fig. 2 shows the state in which the quartz glass tube in Fig. 1 is used as a cladding material and is brought into close contact with the core material to produce a base rod. FIG. 3 is a sectional view showing a double structure optical fiber, and FIG. 4 is a sectional view showing a triple structure optical fiber. 1... Linear groove, 2... Quartz glass tube (clad material), 3... Core material, 6... Original rod, 7...
Core, 8...Clad, 10...Holder, 9,
9'...Optical fiber.

Claims (1)

[Claims] 1. Etch the inner surface of the quartz glass tube into which the quartz glass core material is inserted with hydrofluoric acid to a depth of 0.1 μm or more.
A quartz glass tube for optical fiber, characterized in that a linear groove of 5 μm for gas suction is formed in the longitudinal direction of the inner surface of the quartz glass tube.