JPH0699166B2 - High strength, high weather resistance optical fiber manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber having excellent mechanical strength and long-term reliability.

The optical fiber made of glass is likely to have fine defects on the surface during the manufacturing process or the handling process thereafter, and easily breaks when an external force or the like is applied thereto. In addition, moisture penetrates into these defects, and the optical fiber strength deteriorates over time. Among them, the latter problem is particularly important, and in order to improve this drawback, a method of coating the fiber surface with a metal such as Al, Sn, or coating an inorganic compound such as Si ₃ N ₄ is used. There is. However, at present, these coatings are not preferable in terms of the characteristics of the optical fiber, such as increase in transmission loss and deterioration of initial strength.

The present invention makes it possible to manufacture an optical fiber having excellent initial strength, no increase in transmission loss, and long-term reliability by selecting an appropriate metal coating material.

The present invention coats the optical fiber surface with a so-called low melting point alloy having a melting point of 250 ° C. or less composed of at least two components of Bi, Pb, Sn, and Cd, and the melting point is extremely easy to perform melt coating, There is no increase in transmission loss and no deterioration in initial strength. The low melting point alloy used is In, Ga, Sb, at least two components of Bi, Pb, Sn and Cd.
Zn, Mn, Ag, etc. are added as necessary, and specific examples thereof include Bi: Sn: Zn = 56: 40: 4, Bi: Pb: Sn = 12.8:
49: 38.2, Sn: Cd = 67.75: 32.25, Bi: Pb: Sn: Cd: In = 56.2:
An example of the composition is 2.0: 40.7: 0.7: 0.4. Bi is 48
% Or less, solidification shrinkage causes compressive stress on the fiber surface, and the initial strength is also improved. The preferable coating thickness of the low melting point alloy is 1 to 20 μm. It is also possible to coat nylon or the like on this through a cushioning layer of silicone resin or the like.

For reference, as another embodiment, a fiber coated with the resin composition and coated with the low melting point alloy may be mentioned. Usually, a silicone resin, an epoxy resin or the like is used as the primary coating of the optical fiber, and nylon, polyethylene or the like is used as the secondary coating. These resins are thermally decomposed or melted at about 300 ° C,
It was not possible to apply a conventional metal coating on this. However, by doing so, it is possible to provide a coating of the low melting point alloy on the resin composition, while making use of the characteristics of the ordinary optical fiber, and yet to manufacture an optical fiber having long-term reliability. Is possible.

In the production of the optical fiber of the present invention, first, the optical fiber base material is drawn by a resistance furnace or the like to form a glass fiber. Next, the low melting point alloy is coated on the surface of the glass fiber which is not in contact with other solid matter with a die, a crucible or the like.

Example 1 A base material for optical fibers was heated to 2200 ° C. in a carbon resistance furnace,
A 125 μm glass fiber was formed. Then Bi: Pb: Sn
An alloy having a composition ratio of 11.4%: 45.6%: 43% was melted at 170 ° C. and coated with a die to form a fiber of 145 μm. After that, a buffer layer of silicon resin was formed to have a thickness of 400 μm, and nylon coating was performed to obtain a core A of 900 μm. The structure of this optical fiber core wire is shown in FIG. In the figure, 1 is a glass fiber, 2 is a low melting point alloy coating layer, 3 is a silicon buffer layer, and 4 is a nylon coating layer.

The transmission loss of this core wire A is that without alloy coating B
Although an increase of 0.1 dB / Km was observed over (glass + silicone + nylon), it was not less than the increase due to conventional metal coating, and the initial strength was shown in the Weibull distribution of the long tensile test in Fig. 3. As shown in the graph of FIG. 4, the deterioration with time was significantly suppressed as compared with the case without the alloy coating.

Reference example Heat the base material for optical fiber to 2200 ℃ in a carbon resistance furnace.
The glass fiber of 125 μm was used and coated with silicone resin to 400 μm. This wire is Bi: Pb: Sn: Cd = 5%: 32%:
It was soaked in an alloy having a composition ratio of 45%: 18% to form a 410 μm alloy-coated wire, which was nylon-coated to form a 900 μm core wire C. The structure of the optical fiber core wire C is shown in FIG. The numbers in the figure are the same as those in FIG. 1, 1 is a glass fiber, 2 is a low melting point alloy coating layer, 3 is a silicon buffer layer,
4 is a nylon coating layer.

Although the transmission loss was not increased by this alloy coating and the initial strength was not different from that without alloy coating B, the deterioration over time was remarkably improved as shown in the graph regarding the static fatigue characteristics in FIG.

[Brief description of drawings]

1 is a sectional view showing the structure of the optical fiber core wire shown in Example 1, FIG. 2 is a sectional view showing the structure of the optical fiber core wire shown in Reference Example, and FIG. Line A and conventional glass + silicon +
Wipe distribution of long tensile test of nylon core wire B, FIG. 4 shows core wire A of Example 1 and conventional glass + silicon +
FIG. 5 is a graph showing the static fatigue characteristics of the nylon core wire B and FIG. 5 shows the static fatigue characteristics of the core wire C of the reference example and the conventional glass + silicon + nylon core wire B.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Yamanishi Toru Yamanishi 1 Taya-cho, Totsuka-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (56) References JP-B-55-40841 (JP, B2)

Claims (1)

[Claims] 1. A glass preform for optical communication is drawn to form a fiber, which is then composed of at least two components of Bi, Pb, Sn, and Cd, and the composition range thereof is Bi 0 to 60%, Pb 0. ~ 88%, Sn 0-98
%, Cd 0-40%, and melting point of 250 ° C. or less alloy is applied on the fiber.