JPH04158311A - Hermetically covered optical fiber cable and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a hermically covered optical fiber not increasing the initial transmission loss by forming a hydroxyl group infiltration preventing film on the outside of a core before forming a hermetic cover film. CONSTITUTION:A hydroxyl group infiltration preventing film (e.g., natural quartz jacket layer) 2 is provided at the lower section of a hermetic cover film 3 and on the outside of a core 1a (surface of a clad 1b) on an optical fiber 1 constituted of the core 1a and clad 1b in the pre-stage to form the hermetic cover film 3. Hydrogen atoms are reacted with alkaline metal and the like by the hydroxyl group infiltration preventing film 2, and hydrogen atoms are captured there and do not infiltrate into the core 1a. The hermetic cover film (carbon film) is then formed. The initial transmission loss is not increased, the mechanical strength is not reduced, and the hermetically covered optical fiber 1 stably usable for a long period can be manufactured.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an optical fiber cable, and in particular, it has high reliability over a long period of time even when a hermetic coating is provided. The present invention relates to a hermetically coated optical fiber cable that does not increase initial transmission loss and a method for manufacturing the same.

[Conventional technology]

When a silica glass optical fiber is left for a long period of time, moisture acts on minute scratches on the surface of the optical fiber, increasing the number of scratches. Further, since tension is applied to the optical fiber when it is installed, it is under a certain degree of stress, and its strength decreases over time in an atmosphere where moisture is present. especially,
In adverse environments such as high temperature and high humidity, the above-mentioned effects of moisture become significant, the damage increases significantly, and the strength of the optical fiber deteriorates significantly. Furthermore, when hydrogen enters the core portion of the optical fiber, an absorption peak occurs around a wavelength of 1.24 μm, increasing transmission loss.

In order to prevent such characteristic deterioration, a hermetic coating layer is applied to the surface of the optical fiber, that is, the surface of the cladding.
It has been proposed to deposit a dense carbon or carbon compound coating (hereinafter referred to as carbon coating) to prevent hydrogen or water ingress (e.g., U.S. Pat.
Publication No. 83621, European Patent Application Publication No. 03
08143).

FIG. 3 shows a cross-sectional view of a conventional optical fiber cable coated with a carbon coating layer. The optical fiber 1 consists of a core 1a and a cladding 1b formed on the surface of the core 1a,
A carbon coating 3 is formed on the outer surface of the cladding 1b. The outer diameter of the optical fiber 1 is about 125 μm, and the thickness of the carbon coating 3 is about 100-500 μm.

Figure 4 shows the heat C applied to uniformly form the carbon coating 3 in the longitudinal direction on the outer surface of the optical fiber 1 shown in Figure 3.
A schematic configuration of a manufacturing apparatus using the VD method is shown. In the figure, an optical fiber preform 4 is heated in a drawing furnace 5 to soften and draw it to form an optical fiber 1 consisting of a core 1a and a crut 1b and having an outer diameter of about 125 μm. When the optical fiber 1 thus formed passes through an outer diameter measuring device 7, its outer diameter is measured and the optical fiber 1 is guided into a second reaction tube 8.

A raw material gas, for example, is supplied to the reaction tube 8 from the gas inlet 8A.
C2H, and diluent gases such as He, NZ
, Ar, etc. are introduced. Further, the used gas is discharged from the discharge port 8B. The amount of gas introduced that defines the thickness of the hermetic carbon coating film is determined by a microcomputer 9 that controls the flow rate of the introduced gas. A heating section 10 is attached to the outer periphery of the reaction tube 8, and the gas introduced into the reaction tube 8 is made of an inorganic substance such as carbon through a thermal CVD reaction caused by the heat of the optical fiber 1 and the heat of the heating section 10. A carbon hermetic layer 3 is formed on the outer surface of the optical fiber 1 . [ [Problems to be Solved by the Invention] Since the hermetic carbon film 3 made of carbon or a carbon compound is formed by thermally decomposing hydrocarbon gas or the like as a main raw material, there are usually hydrogen molecules inside the reaction tube 8. exist. Therefore, during the thermal CVD reaction process, hydrogen molecules often enter the optical fiber 1 and become trapped within the optical fiber 1 before the carbon film 3 is synthesized to a sufficient thickness.

In particular, when the optical fiber 1 is made of high-purity synthetic quartz containing almost no alkali metals, hydrogen molecules easily diffuse to the central core 1a of the optical fiber 1 and react with the core dopant germanium. Generates a large amount of hydroxyl (OH) groups.

This OH group increases the initial transmission loss of the optical fiber as described above.

Therefore, an object of the present invention is to form a hermetically coated optical fiber that does not increase the initial transmission loss of the optical fiber even when a hermetic coat is formed.

[Means to solve the problem] In order to solve the above problems, the present invention has the following features.

A hydroxyl group intrusion prevention film is provided on the outside of the optical fiber, at least the core.

As the hydroxyl group invasion prevention film, a hydrogen molecule trapping film formed of natural quartz containing an alkali metal or an alkali ion is suitable.

The present invention also provides a method of forming this hermetic coated optical fiber.

[Effect]

Hydrogen atoms react with alkali metals and the like and are captured by the hydroxyl group intrusion prevention film, preventing hydrogen atoms from entering the core. As a result, the initial transmission loss of the optical fiber does not increase.

[Embodiment] An embodiment of the hermetic coated optical fiber cable of the present invention and its manufacturing method will be described below. Fig. 1 shows a sectional view of a hermetically coated optical fiber cable of the first embodiment of the present invention. A natural quartz jacket layer 2 as a hydroxyl group-preventing film is applied to the outer surface of an optical fiber 1 consisting of a core 1a and a cladding lb, and a hermetic carbon film 3 is further applied to the outer surface. The l of the optical fiber 1 is approximately 90 μm, the thickness of the natural quartz jacket layer 2 is within 35 μm, the thickness of the carbon film 3 is approximately 500 μm, and the outer diameter of the entire hermetic coated optical fiber is approximately 125 μm.

To form the natural quartz jacket layer 2, a natural quartz glass pipe is jacketed around the outer periphery of the optical fiber base material 4, and the natural quartz glass pipe is drawn together with the optical fiber base material 4 in the apparatus shown in FIG. Underline it with 5. An optical fiber halo a to which a natural quartz jacket layer 2 is attached is formed, and when this optical fiber halo a passes through an outer diameter measuring device 7, its outer diameter is measured, and carbon is deposited on the natural quartz jacket layer 2 in a reaction tube 8. A membrane 3 is formed.

Natural quartz glass contains alkali metals, which trap hydrogen atoms. Therefore, the natural quartz jacket layer 2 formed on the outside of the optical fiber 1 traps hydrogen atoms and prevents them from entering the core 1a.

Note that the natural quartz jacket layer 2 only needs to be formed outside the core 1a, and may be formed between the inner cladding lb and the outer cladding 1b as shown in FIG.

Such a natural quartz jacket layer 2A constitutes a part of the cladding lb. The outer diameter of the hermetically coated optical fiber in this case is the same as that of the hermetically coated optical fiber illustrated in FIG.

The manufacturing conditions for a hermetic coated optical fiber according to an embodiment of the present invention and a conventional hermetically coated optical fiber are shown below. The manufacturing conditions for the hermetic coated optical fiber of the embodiment of the present invention and the conventional hermetic coated optical fiber are as follows: In the embodiment of the present invention, the natural quartz jacket layer 2 or 2
The same except that A is formed.

Manufacturing conditions (1) Line length: 10. Okm (2) Drawing speed: 30. Om/min(3)
Raw material gas: CzHz (4) Raw material gas flow rate: 3. Om/m1n (5) Reaction temperature = 800 to 900°C (6) Differential pressure inside and outside the furnace 0.3 mmAq Table 1 shows the hermetic coated optical fiber according to the embodiment of the present invention, the hermetic coated optical fiber according to the conventional example, and The measured values of initial transmission loss at each wavelength are shown for a standard silica optical fiber without hermetic coating (comparative example).

Table 1 The standard quartz optical fiber as a comparative example has a small initial transmission loss because hydrogen atoms do not penetrate into the core during the formation of the carbon coating described above. The hermetic coated optical fiber according to the example of the present invention has almost the same initial transmission loss as this comparative example, and even at the stage of carbon 113 formation, the natural quartz jacket layer 2 or 2A prevents hydrogen atoms from entering the core lla, resulting in initial transmission. There is no increase in losses. On the other hand, all conventional hermetically coated optical fibers have a large initial transmission loss due to the influence of hydrogen atoms in the formation of the carbon film 3, and the transmission loss peak is particularly large at a wavelength of 1.39 μm, which is the OH group absorption band.

2 In carrying out the present invention, the natural quartz jacket layer 2
Alternatively, the method for forming the carbon film 3 after forming 2A may be other than the thermal CVD method described as a conventional example.

It can be formed by various methods such as plasma CVD method and PVD method.

Further, forming a resin film after forming the carbon coating 3 to produce a hermetic coated optical fiber cable is the same as in the conventional method.

〔Effect of the invention〕

As described above, according to one aspect of the present invention, the lower part of the hermetic coating film is
By forming a hydroxyl group penetration prevention layer outside the core, hydrogen atoms are prevented from entering the core during the step of forming a hermetic coating film, and initial transmission loss does not increase. Further, by forming a hermetic coating, it is possible to produce a hermetic-coated optical fiber that can be stably used for a long period of time without decreasing its mechanical strength.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a hermetically coated optical fiber according to a first embodiment of the present invention. FIG. 2 is a sectional view of a hermetically coated optical fiber according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a conventional hermetic coated optical fiber. FIG. 4 is a configuration diagram of an embodiment of the present invention and a conventional hermetic coated optical fiber manufacturing apparatus. (Explanation of symbols) ■...Optical fiber. 2...Natural quartz Jaquent layer. 3...Carbon film. 1a...Core. 1b...Clad. Patent applicant Furukawa Electric Co., Ltd. Agent Patent attorney Takahisa Sato Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. A hermetic coated optical fiber cable comprising a hydroxyl group intrusion prevention film provided outside the core of an optical fiber, and a hermetic coating film provided outside the prevention film. 2. The hermetic coated optical fiber cable according to claim 1, wherein the hydroxyl group prevention film is a natural quartz film. 3. The hermetic coated optical fiber cable according to claim 2, wherein the natural quartz hydroxyl group-preventing film contains an alkali metal or an alkali ion. 4. A method for producing an optical fiber having a hermetic coating, the method comprising forming a hydroxyl group invasion prevention film on the outside of the core of the optical fiber before forming the hermetic coating film.