JPS6146915A - Optical fiber - Google Patents

Abstract

PURPOSE:To prevent the corrosion owing to the adsorption of the moisture in the atmospheric air and the generation of microcracks owing to the corrosion and to obtain an optical fiber having excellent durability by covering the surface of the optical fiber with a film of BN within a specific thickness range. CONSTITUTION:The BN film is formed on the optical fiber consisting of glass base or acryl base by such a method consisting in heating the fiber, subjecting a gaseous mixture composed of B2H6 and NH3 to high-frequency cracking and covering the fiber with the BN film in the case of the glass and by an ion beam deposition method, etc. in the case of the plastic base. The BN film may be formed to a 500Angstrom -30mu thickness range and may be formed by either the crystalline or non-crystalline film. The covering effect is not enough at <=500Angstrom and the fiber is liable to crack at >=30mu. The covering which has the high mechanical strength is thus obtd. The generation of the microcracks as a result of the absorption of the moisture in the atmospheric air and the stress corrosion cracking of the fiber and the easy tendency to breakage on progression of the cracks in a long period are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to an optical fiber whose mechanical strength does not deteriorate even after long-term use.

(III) Background Art So-called optical fibers that transmit visible light or infrared light are capable of large-capacity transmission as a means of communication, have little noise contamination, and can keep the attenuation rate to a minimum, so they are being put into practical use. There is. The fiber is made of glass, plastic, or alkali halide to provide a refractive index distribution to reduce the MR rate.

The major disadvantage of these fibers is that they become increasingly susceptible to breakage when used in normal atmosphere. This is because the condensation of moisture in the atmosphere causes a phenomenon similar to stress corrosion cracking and the development of microcracks.

The present inventors have studied fiber surface treatments for suppressing the aging of optical fibers as described above, and have arrived at the present invention.

(c) Disclosure of the invention The present invention prevents moisture absorption on the fiber surface,
In addition, to prevent cracks from progressing due to corrosion, use a boron nitride system (
The present invention relates to an optical fiber coated with BN). B
N is extremely stable against any corrosive substances and is a suitable substance for preventing the growth of the above-mentioned cracks.

Depending on the deposition conditions, BN can deposit not only a crystalline structure but also an amorphous structure. Provides corrosion resistance equivalent to IBN.

These films do not exhibit sufficient effects at 5 GOA or less, but this is thought to be because they cannot sufficiently cover minute irregularities on the fibers. Moreover, if it is 30μ or more, cracks will propagate more easily and the strength and resistance to bending will decrease.

BN coating on optical fibers can be done by CVD method or plasma CV method.
This can be performed by a known method such as the D method or the ion beam evaporation method.

The details of the present invention will be described below with reference to Examples.

Example 1 90% 5iOz and the remaining amount is 0 consisting of GeO2 and P2O6
, a 25 amφ fiber is heated to 800°C, and the (B2H6 + NH3) mixed gas is decomposed using the high frequency decomposition method.
．． A 3μ thick layer of crystalline BN was coated, and a further 0.3 μl layer of silicone resin was applied.

These were exposed to the atmosphere at a temperature of 60° C. and a humidity of 90%, and an accelerated test was conducted by applying a load of 12 kg to each of 100 pieces. The time required for 50% of the fibers to break was 411 minutes, and it was 14 minutes for the material of the present invention and 0.8 minutes for the comparative material.

Example 2 0, 1 consisting of 95% 5i02 and remaining amount Be203, F
A fiber of 5a+mφ was coated with BN having an amorphous structure in a thickness of 300 Å to 50 mm by a known plasma CVD method using a CBCQ3+NH3) mixed gas.

100 each, tensile span 5, tensile speed 5%l■
Table 1 shows the results of measuring the tensile strength at break.

Example 3 0.2+u+φ acrylic plastic fibers were coated with a crystalline BN film to the thickness shown in Table 2 using the ion beam deposition method, and 50 of each fiber was subjected to Go
Table 2 compares the results of a test to see if 200 pieces broke under a load of 2 kg in 95% air and a test to see if 200 pieces broke when bent into an arc shape with a diameter of 5001111. Shown below.

As shown in the examples, it can be seen that the coated fibers of the present invention have extremely high breaking strength.

The same effects of the present invention could be obtained for 5i02 fibers having compositions other than those shown in the examples.

Claims (2)

[Claims] (1) An optical fiber coated with a boron nitride (BN) film. (2) The optical fiber according to claim 1, wherein the BN film has a thickness of 500 Å to 30 μm.