JPH03284710A - Hermetically coated optical fiber - Google Patents

Abstract

PURPOSE:To prevent the peeling of a hermetic coating film by providing an inorg. compd. doped layer having the Young's modulus higher than that of an optical fiber and lower than a hermetic coating film on the surface of the optical fiber, thereby forming the hermetically coated optical fiber. CONSTITUTION:The hermetically coated optical fiber 1 is formed by providing the inorg. compd. doped layer 2A having the Young's modulus higher than that of the optical fiber 2 consisting of quartz glass on the outer periphery of the optical fiber 2 and providing the hermetic coating film 3 having the Young's modulus higher than the doped layer 2A on the outer periphery of the layer 2A. The elongation at the time of stress loading of the optical fiber 2 is relieved by the doped layer 2A and the peeling of the hermetic coating film 3 is prevented if the inorg. compd. doped layer 2A having the Young's modulus higher than that of the optical fiber 2 and lower than the hermetic coating film 3 is provided on the surface of the optical fiber 2 in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hermetic coated optical fiber, which is known as an optical fiber with high long-term reliability.

[Prior Art] When an optical fiber made of quartz glass or the like is left for a long period of time, moisture acts on minute scratches on the surface of the optical fiber, gradually increasing the number of scratches. Further, when the optical fiber is installed, it is subjected to a certain degree of stress, and in an atmosphere where moisture is present, its strength deteriorates over time for the reasons described above. Furthermore, under adverse environments such as high temperature and high humidity, the effects of moisture further increase, significantly accelerating the deterioration of the strength of the optical fiber. Furthermore, when H2 molecules exist near the core of the optical fiber due to diffusion, an absorption peak appears around 1.24 μm, which adversely affects transmission characteristics.

In order to prevent such moisture or hydrogen from entering the optical fiber, a hermetic coated optical fiber is used, which has a hermetic coating film with a water-sealing structure made of a high-density inorganic material film such as amorphous carbon on the surface of the optical fiber. Proposed. The hermetic coating film is a coating method or a plasma CVD method.

Film formation is performed by a thermal CVD method or the like.

FIG. 2 shows the structure of a conventional hermetic coated optical fiber 1. As shown in FIG. The hermetic coated optical fiber 1
The optical fiber 2 has a structure in which a hermetic coating film 3 made of amorphous carbon or the like with a thickness of about 100 to 500 layers is provided around the outer periphery of an optical fiber 2 made of quartz glass and having a diameter of about 1.25 μm.

FIG. 3 shows an apparatus for manufacturing a hermetic-coated optical fiber using the thermal CVD method, which is known as a method suitable for uniformly providing the hermetic coating film 3 in the longitudinal direction among the above-mentioned methods. This is an example.

In this apparatus, an optical fiber preform 4 is heated in a drawing furnace 5, and the lower molten portion is drawn to obtain an optical fiber 2. The outer diameter of the optical fiber 2 is measured with an outer diameter measuring device 6 and introduced into a reaction tube 7. A raw material gas such as C2H2, He,
N2. A mixed gas with a diluting gas such as Ar is introduced. These gases are heated in a reaction tube heating furnace 9 provided outside the reaction tube 7. As a result, a thermal CVD reaction occurs within the reaction tube 7, and a hermetic coating film 3 made of an inorganic substance such as amorphous carbon is formed on the surface of the optical fiber 2.

The obtained hermetic coated optical fiber l is coated with a coating die 1.
0 to provide a resin coating layer on the surface of the hermetic coating film 3, and then wind it up with a winder 11.

[Problems to be Solved by the Invention] However, in the conventional hermetic coated optical fiber 1, since the hermetic coating film 3 is directly coated on the surface of the optical fiber 2, the contact between the optical fiber 2 and the hermetic coating film 3 is Due to the difference in elastic modulus, when stress is applied, the hermetic coating 3 cannot keep up with the elongation of the optical fiber 2, and as a result, the hermetic coating 3 peels off from the surface of the optical fiber 2, which becomes the starting point for cracks. There was a problem in that the initial tensile rupture strength of the hermetic coated optical fiber 1 decreased.

In addition, in the conventional hermetic coated optical fiber 1, the adhesion between the hermetic coating film 3 and the resin coating layer is good, and the internal optical fiber 2 may be damaged and its strength may be reduced when the skin is peeled off during connection, etc. There was also the problem that there were too many.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hermetic coated optical fiber having a structure that can prevent a decrease in initial tensile rupture strength during manufacture and improve trauma resistance during peeling.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above object, the hermetic coated optical fiber according to the present invention has an optical fiber having a height higher than that of the optical fiber on the outer periphery of the optical fiber made of quartz glass. It is characterized in that an inorganic compound doped layer having a Young's modulus is provided, and a hermetic coating film having a Young's modulus higher than that of the inorganic compound doped layer is provided around the outer periphery of the inorganic compound doped layer.

[Effect] When an inorganic compound-doped layer is provided on the surface of an optical fiber, the Young's modulus is higher than that of an optical fiber and lower than that of a hermetic coating, the elongation of the optical fiber under stress is moderated by the inorganic compound-doped layer, and the hermetic coating is Peeling of the coating film can be prevented. Therefore, the initial tensile rupture strength of the hermetic coated optical fiber is improved compared to the conventional hermetic coated optical fiber.

Furthermore, since the hard inorganic compound doped layer is present on the surface of the optical fiber, the damage resistance of the optical fiber is improved.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. The hermetic coated optical fiber 1 of this embodiment has two layers doped with an inorganic compound such as TiO2 on the surface of the optical fiber 2 with a thickness of about 1 to 2 μm, and has an overall outer diameter of 125 μm.
It is formed in μm. A hermetic coating film 3 made of amorphous carbon is provided on the outer periphery of the inorganic compound doped layer 2A with a thickness of about 10 (1 to 5 flOA). In this example, the Young's modulus of the optical fiber 2 is 10.3 to 13.7x 1010P.
The Young's modulus of the inorganic compound doped layer (Ti02 doped layer) 2A is approximately 1.0 to 1.5x 1010P a larger than the Young's modulus of the optical fiber 2, and the Young's modulus of the hermetic coating film 3 is 19. ,6~40.0x1
It is set at about 0.010 Pa.

In the hermetic coated optical fiber l having such a structure, the inorganic compound doped layer 2A acts as a buffer layer to prevent cracks from occurring in the amorphous carbon film that is the hermetic coating film 3, and the initial tensile rupture strength is higher than that of conventional products. improves.

Tables 1 and 2 show a product of the present invention in which an amorphous carbon film (hermetic coating film) 3 is provided on the surface of a silica glass optical fiber 2 having a TlO2 doped layer (inorganic compound doped layer) 2A on the surface, and an optical fiber 2. This figure shows the experimental conditions and evaluation results for a conventional product in which an amorphous carbon film (hermetic coating film) 3 was directly provided on the surface of the product.

Table 2 (evaluation results) °Hydrogen test was carried out in 100% H2, 24°C in a hydrogen furnace at 100°C.
I did it by letting it sit for a while.

The zero hydrogen loss increase peak was indicated by the amount of increase in the loss peak at 1.24 μm.

As an evaluation method, five long hermetic coated optical fibers 1 with a length of 101 ann were prototyped, and the tensile rupture strength of each sample was evaluated by a long tensile test, and at the same time, a dynamic fatigue test and a hydrogen test were conducted. .

The initial tensile strength at break of the conventional product was about 4.0 to 4.5 kg, but the initial tensile strength at break of the product of the present invention was 5.6 k.
A remarkable improvement was seen. In addition, it was found that the products of the present invention maintain the same properties as conventional products in terms of fatigue properties and hydrogen resistance.

In addition, as an evaluation of trauma resistance, after removing the resin coating layer, A
A tensile test was conducted by colliding the J2 powder onto a portion without a resin coating layer to avoid scratches on the surface of the optical fiber 2. Table 2
As shown in Figure 2, the product of the present invention showed improved trauma resistance compared to the conventional product.

In the above embodiment, Ti is used as the inorganic compound doped layer 2A.
Although an amorphous carbon film was provided as the O2 doped layer and the hermetic coating film 3, the transparency of the fiber surface was not lost even when doped, and the Young's modulus of the doped layer 2A was between that of the optical fiber 2 and the hermetic coating film 3. If you take the value of
The combination of the inorganic compound doped layer 2A and the hermetic coating film 3 may be any combination of inorganic materials.

E. Effects of the Invention As explained above, the hermetic coated optical fiber according to the present invention has an inorganic compound doped layer on the surface of the optical fiber, which has a Young's modulus higher than that of the optical fiber and lower than that of the hermetic coating film. The inorganic compound doped layer moderates the elongation during stress loading, making it possible to prevent the hermetic coating from peeling off. Therefore, the initial tensile strength at break of the hermetic coated optical fiber can be improved compared to the conventional hermetic coated optical fiber.

Further, according to the present invention, since the hard inorganic compound doped layer is present on the surface of the optical fiber, the damage resistance of the optical fiber can be improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an embodiment of a hermetic-coated optical fiber according to the present invention, Fig. 2 is a cross-sectional view of a conventional hermetic-coated optical fiber, and Fig. 3 is a cross-sectional view of a conventional hermetic-coated optical fiber manufacturing apparatus. FIG. DESCRIPTION OF SYMBOLS 1... Hermetic coated optical fiber, 2... Optical fiber, 2A... Inorganic compound doped layer, 3.../'%
- Meticulous coating. Diagram

Claims (1)

[Claims] An inorganic compound doped layer having a Young's modulus higher than that of the optical fiber is provided on the outer periphery of an optical fiber made of quartz glass, and a hermetic coating film having a Young's modulus higher than the inorganic compound doped layer is provided on the outer periphery of the inorganic compound doped layer. A hermetic coated optical fiber characterized in that it is provided with.