JPS60239703A - Optical fiber with hydrogen gas absorption preventing means - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

TECHNICAL FIELD The present invention relates to optical fibers, in particular those incorporated in one cable and provided with protection against absorption of hydrogen in the gas phase during the Z phase.

Prior art and its problems In cables consisting of one or more optical fibers, (
When these optical fibers are subjected to the action of hydrogen, regardless of how it is generated (by either internal or external members of the cable), a deterioration in the transmission characteristics of the optical fibers is often observed.

In practice, it is, as a rule, first of all noticeable deterioration effects, which are particularly visible, that even the mechanical properties of the optical fiber change.

In fact, optical fibers under such conditions are particularly
Wavelengths longer than microns, ie, the wavelength interval used to transmit the signal, exhibit increased attenuation.

In general, optical fibers are coated with a glass structure formed by a coating to prevent the optical fiber from coming into direct contact with the outside world.
) or [equilibrium refractive index] (gra-ded 1nde
x) type 6 parts, otherwise consisting of further structures and a primary coating applied to the optical fiber immediately after formation.

On top of this secondary coating is applied another protective coating, for example consisting of a layer of silicone rubber and a further rigid layer, or a tube made of nylon, for example.

Generally, fiber optic cables consist of one or more optical fibers housed within a sheath along with one or more tensile strength members. The sheath, which may be metallic or non-metallic, is surrounded by other physical elements such as armor, sheathing, etc.

Tests conducted by the applicant have shown that hydrogen, once diffused inside the optical fiber, can absorb energy with an absorption spectrum that includes the wavelength used for the optical signal. This made it possible to confirm that the main cause of attenuation is composed of

Under the terms of the patent, this phenomenon is reversible, and if hydrogen diffuses outside the optical fiber (e.g.
Due to the decrease in external hydrogen concentration that caused this phenomenon)
This damping phenomenon can be significantly reduced if

In other cases, the source of the second attenuation is diffused within the main component of the optical fiber (e.g., 5in2) and/or its dopants (e.g., GeO2, P, 05, etc.) and within the optical fiber itself. It has now been possible to demonstrate that this is due to a chemical reaction that occurs between hydrogen and hydroxyl groups (OH), which are also responsible for absorption at other wavelengths used in transmission.
A group containing This latter reaction is not a reversible reaction, so a corresponding deterioration of the properties of the optical fiber can be expected under all conditions of use.

Parameters that control such phenomena, apart from the chemical composition of the optical fiber, include the partial pressure of hydrogen, temperature, and time to which the optical fiber is exposed.

Optical fibers can come into contact with hydrogen generated inside the cable during the manufacturing process of the cable or during use of the cable itself; It can be produced by metallic or non-metallic elements present in the cable.

Hydrogen can also be produced by the oxidation of the organic materials that make up the cable, or even by the reaction of moisture present in the cable (either in liquid or gas phase) with the metal components that make up the cable itself.

Organic materials used to coat optical fibers can generate hydrogen through chemical reactions of various nature. One hydrogen source is
It has been found that, assuming that the protective coating itself is constituted in particular by silicone rubber, the duration of the crosslinking process is lengthened to provide a free state of hydrogen in exact correspondence with the optical fiber surface. Hydrogen diffusion occurs not only into the optical fiber but also outside it.
In this case, since it is in a diffused state in the surrounding environment, no noticeable phenomenon occurs on the insulated optical fiber.

Nevertheless, when the optical fiber is placed in a closed cable without sufficient free space, the concentration of hydrogen is helped by the fact that the coating in which hydrogen is generated is very close to the optical fiber. can reach relatively large values resulting in its sufficient diffusion even to the optical fiber itself.

The rate of hydrogen diffusion through various materials increases as one goes from metals to polymers to liquids to gases. Therefore, depending on the type of cable and the environment in which the cable is used, the rate of release of hydrogen generated by the components that make up the cable varies, and hydrogen that is generated on the outside of the cable and passes through the environment in which the cable is used is absorbed by the cable. The speed at which it is performed also varies. On these different velocities, the value of the partial pressure of hydrogen in the cable depends, and therefore as a function of time, the greater the pressure and the greater the duration, the greater the risk to the culm fiber.

Under predictable temperature conditions and given the service life of a fiber optic cable, the diffusion rate of hydrogen through metal is so slow that a metal sheath of normal thickness is actually impermeable to hydrogen. It can be considered that it is impossible to conduct.

In particular, cables with metal sheaths, especially if they have small spaces in their four parts, are freed from elements inside the sheath and can exhibit increased attenuation in short periods of time as well as at high levels due to hydrogen filtration. Become something.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber provided with protection against the absorption of gas phase hydrogen which may be present in cables containing the optical fiber.

This protective measure is achieved, according to the invention, by providing around the outermost glass layer of the optical fiber one or more coatings containing metals that can combine with hydrogen and thereby form a barrier. .

An optical fiber according to the invention having at least one protective coating comprises at least one of said protective coatings.
As a protective measure against the absorption of hydrogen in the gas phase, the optical fiber *=contains one or more metals from Groups Ⅰ, V, V, and Ⅰ of the periodic table. Among these metals, those which have proven particularly suitable are as follows. That is, in the form of pure metals, Group I includes lanthanides, Group V includes titanium, zirconium, and hafnium, and Group V includes vanadium,
Niobium and tantalum, palladium in group II,
and their alloys and/or intermetallic compounds.

In the presence of hydrogen, the elements listed above tend to form solid bodies that can be assimilated into hydrogen compounds that exhibit good stability;
This can cause the partial pressure of hydrogen in the cable to be reduced to a value that balances the hydrogen solubility in the component itself.

The above elements may have absorbed hydrogen and (
or) It is advisable to provide it with a heat treatment under vacuum at a temperature of several hundred degrees Celsius before being used in the production of cables for the purpose of removing any associated oxygen.

EXAMPLE The present invention will now be described with reference to the preferred but non-limiting embodiment shown in the drawings. The optical fiber of FIG. or any other type of glass 6 consisting of a section 1 and a primary coating 2 adjacent to the glass wall and protecting it from the external environment.

According to a first embodiment of the invention, said protective measure is obtained by a metallized layer made of one or more of the above-mentioned materials. This layer may constitute a primary coating 2, which is shown in the figure in intimate contact with the glass structure of the optical fiber. An optical fiber is thus obtained, in which the secondary coating is of a metallic type and at the same time performs a mechanical function as well as a protective function against the absorption of hydrogen by the environment surrounding the optical fiber during use. It is.

According to one variation (not shown), this metallized layer is applied immediately above a conventional primary coating made of crosslinked resin.

This construction is used whenever it is impossible or inconvenient to modify the optical fiber manufacturing plant to remove the protective coating immediately after the optical fiber has been drawn to the required dimensions.

A further variation (also not shown) concerns the application of a metallized layer around one of the successive coatings.

In a second embodiment, shown schematically in FIG. 2, the primary coating 2 of acrylic resin or other suitable material comprises one or more of said metals, or alloys thereof, or intermetallic materials in a dispersed state. Contains compounds. This makes it possible to provide protective properties against hydrogen in conventional manufacturing processes.

A third embodiment (FIG. 3) is the addition of a metallic powder to the coating 3 immediately surrounding the secondary coating. This coating is generally formed from silicone rubber, which, as mentioned above, can be a particularly hazardous source of hydrogen. The presence of metal in this coating effectively neutralizes the generated hydrogen before it diffuses into the optical fiber.

The optical fiber shown schematically in FIG. 4 constitutes a fourth embodiment of the invention, which comprises a secondary coating 4 composed of, for example, nylon or other thermoplastic polymers, with dispersed metallic Contains powder materials. In this embodiment, the particles constituting the powder material have a particle size that is preferably smaller than 10 microns, and the amount of powder material per unit length of optical fiber is 0.1 to 10 phr (unit: 1/100th of the amount of resin). ) is determined to reach a concentration within the range of

It should be borne in mind that this protective function according to the invention can be achieved in various ways by coatings containing one metal. Furthermore, whereas the outer protective coach ink (e.g. on silicone rubber) is intended specifically to protect against hydrogen originating from the cable elements, the presence of a protective layer in close proximity to the optical fibers provides the most inner protection. It protects the optical fiber against hydrogen generated in the coating.

From what has been stated above, along with other factors depending on the construction of the cable and its foreseeable conditions of use, the various embodiments described above can be combined in the same optical fiber.

Finally, a further embodiment of the invention is shown in FIG. 5, in which the optical fiber 1 with a secondary coating 2 has an inner diameter larger than the outer diameter of this optical fiber and is soft. It is housed inside a small diameter tube 9 made of plastic material provided with the usual coatings constituting an optical fiber of type (1oo, se type ).

In addition, optical fibers of this type with a non-adhesive coating both have a coating as described above and have a small diameter tube 9 containing a dispersed powder of the metal or its alloy or an intermetallic compound. Gel containing material 8
The above protection measures can be provided by providing a

Alternatively, whether or not in combination with this embodiment, the material constituting the small-diameter chives may include a dispersed powder of the above-mentioned metals, alloys thereof, or intermetallic compounds.

Although the present invention has been illustrated with particular reference to certain embodiments, it is not intended to be limited to such embodiments, as various changes and modifications that fall within the scope of the present invention are obvious to those skilled in the art. do not have.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a cross section of an optical fiber with a primary metal coating, FIG. 2 is a schematic diagram showing a cross section of an optical fiber with a primary coating, and FIG. 3 is a schematic diagram showing a cross section of an optical fiber with a primary and secondary coating. a schematic diagram showing a cross section of the fiber;
FIG. 4 is a schematic diagram showing a cross-section of an optical fiber with primary and secondary coatings with a buffer layer interposed therebetween, and FIG. It is a schematic diagram showing a cross section. 1...6 parts of glass, 2...-next coating, 3.
... Coating, 4... Secondary coating, 8...
・Gel, 9...Small diameter tube (5 people)

Claims (1)

Scope of Claims: (1) An optical fiber provided with at least one protective coating, wherein in the at least one protective coating, as a protective measure to prevent absorption of hydrogen in the gas phase in the optical fiber, according to the periodic table. Optical fiber 0 characterized in that it contains one or more metals from Group (1), Group V, Group V, and Group (2). 2. The optical fiber according to claim 1, wherein the optical fiber is made of tantalum, palladium, or an alloy or intermetallic compound thereof. (3) The optical fiber according to claim 1 or 2, wherein the protective coating is a metallized layer covering the optical fiber. (4) The optical fiber according to claim 3, wherein the metallized layer is a primary coating that is in close contact with the outermost glass layer of the optical fiber. (5) The metallizing layer is one of the optical fibers.
4. Optical fiber according to claim 3, characterized in that it is surrounded by one or more protective coatings. 6. An optical fiber according to claim 1 or 2, wherein the metal is included in the form of a powder material in one or more protective coatings of the optical fiber. (7) The particle size of the particles constituting the powder material is smaller than 10μ, and the amount of the powder material is 0.
7. Optical fiber according to claim 6, characterized in that it reaches a concentration in the range of 1 to 10 phr. (8) The optical fiber according to claim 6 or 7, wherein the powder material is included in the primary coating of the optical fiber in close contact with the outermost glass layer of the optical fiber. Fainoku. (9) The optical fiber according to claim 6 or 7, characterized in that the powder material is included in one coating that is in close contact with the next coating of the optical fiber ino. 10. The optical fiber of claim 9, wherein said coating is silicone rubber. (II) The optical fiber according to claim 6 or 7, wherein the coating is a secondary coating. (12) In a soft-form optical fiber housed in a small-diameter cheep having an inner diameter larger than the outer diameter of the optical fiber provided with a protective coating, the metal is dispersed in a gel-like state held inside the small-diameter tube. The optical fiber according to claim 1 or 2, wherein the optical fiber is in the form of powdered material. (13) a soft-form optical fiber housed within a small diameter tube having an inner diameter greater than the outer diameter of the optical fiber provided with an adhesive protective coating, wherein said metal is dispersed within said small diameter tube; The optical fiber according to claim 1 or 2, which is in the form of powder material.