JPH05241053A - Large-diameter hermetically coated fiber - Google Patents

Abstract

PURPOSE:To improve mechanical strength and water resistant characteristics by providing a carbon coating layer having a specific film thickness and specific center line average roughness on the surface of a clad. CONSTITUTION:This optical fiber is constituted by forming the clad 2 of quartz glass doped with, for example, fluorine F, boron B, boron trifluoride BF3, etc., on the outer side of a core 1 consisting of, for example, pure quartz glass. The carbon coating layer 3 is formed on the surface of the clad 2 and further a UV curing resin layer 4 is formed thereon. The film thickness of the carbon coating layer 3 is specified to >=300Angstrom and the center line average roughness of the carbon coating layer 3 to <=1nm. The deterioration in tensile strength is substantially eliminated as the center line average roughness of the carbon coating layer 3 is as small as 1nm in such a manner. Since the film thickness is >=300Angstrom and is sufficient for preventing the infiltration of moisture, the water resistant characteristic is good.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter hermetically coated fiber having an outer cladding diameter of more than 125 μm, for example.

[0002]

2. Description of the Related Art Generally, in a large-diameter optical fiber,
Because of its many applications under high temperature and high humidity environmental conditions, conventional fibers have a sheath made of polymer material on the clad surface so that they can be used in such environments. There is one

[0003]

However, in such a sheath made of a polymer material, by increasing the film thickness, the effect of preventing moisture from entering the clad can be obtained, so that the sheath can be used under the above environmental conditions. However, the preventive effect is not always perfect from a practical point of view. Therefore, carbon coating was provided on the clad surface in order to further improve the moisture-preventing effect, that is, the water resistance. However, simply increasing the thickness of the carbon coating improves the water resistance, but the mechanical strength However, it was difficult to put into practical use a large-diameter one because it requires mechanical strength in particular.

The present invention aims to solve the above technical problems.

[0005]

As a result of earnest research, the present inventor has been able to sufficiently prevent the invasion of water and, at the same time, realizes practical use of mechanical strength which is a problem when a carbon coating is used for a large-diameter fiber. The present invention, which has been made possible, has been completed.

The present invention relates to a large-diameter hermetically coated fiber with a film thickness of 300 Å or more on the cladding surface.
In addition, a carbon coating having a center line average roughness of 1 nm or less is provided.

[0007]

According to the above construction, since the center line average roughness of the carbon coating on the surface is as small as 1 nm or less, the tensile strength is hardly deteriorated, and the film thickness is 300 Å or more, which is sufficient to prevent the infiltration of water. Therefore, the water resistance property is good.

[0008]

EXAMPLES Examples of the present invention will be described in detail below.

In this embodiment, the cladding outer diameter is, for example, 12
An optical fiber having a large diameter exceeding 5 μm is coated with carbon, and is manufactured, for example, as follows.

That is, in a spinning furnace, a preform (base material) is heated and softened, and drawn from one end thereof to form an optical fiber elemental wire. In a CVD reaction furnace, a hydrocarbon-based raw material gas is supplied and this is used. A carbon coating is formed on the surface of the optical fiber strand by heating, and
An ultraviolet curable resin is applied to the surface of carbon and irradiated with ultraviolet rays to form a resin coat.

Since the characteristics of the optical fiber coated with carbon as described above greatly depend on the quality of the deposited carbon film, the inventor of the present invention has found that the tensile strength and the water resistance which are important characteristics in the large diameter optical fiber. The following study was conducted on the relationship with carbon coating, and the present invention was completed in which carbon is coated with a film thickness of 300 Å or more and a center line average roughness of 1 nm or less.

That is, by using the above-mentioned manufacturing method, only the reaction temperature at the time of carbon deposition was set as a parameter, and
Prototype No. shown in. 7 carbon-coated optical fibers 2 to 8 were manufactured as prototypes, and the carbon-coated optical fibers were not manufactured. In addition to the conventional example shown by 1, the evaluation was carried out for four items of carbon film thickness, center line average roughness Ra, initial strength and strength after immersion. Of these eight prototypes, the prototype No. 4, 5, 6
Are examples of the present invention, and others are comparative examples.

FIG. 1 shows the cross-sectional structure of the large-diameter hermetically-coated fiber produced as a trial. In this optical fiber, for example, the outer diameter of the core 1 of pure silica glass is 200 μm, the outer diameter of the cladding 2 of silica glass doped with fluorine F, boron B, boron trifluoride BF _3, etc. is 250 μm, and carbon coating is performed. The layer 3 is formed, and the ultraviolet curable resin layer 4 is further formed so that the outer diameter is 330 μm.

In the evaluation of the above four items, the carbon film thickness is
Create an ultrathin section of the hermetically coated fiber and TE
The measurement was performed using M (transmission electron microscope), and the centerline average roughness Ra was measured using STM (scanning tunneling microscope). The initial strength was a tensile test with a span of 1 m and a strain rate of 5% / min.
The same tensile test as described above was performed after immersion in 0 ° C. pure water for 300 hours.

[0015]

[Table 1]

As shown in Table 1, it is understood that as the film thickness of the carbon coating increases, the center line average roughness tends to increase.

FIG. 2 shows the relationship between carbon film thickness and tensile strength.
3 shows the relationship between the center line average roughness and the tensile strength, respectively. In these figures, the initial strength is indicated by ●, the strength after immersion is indicated by ■, and for comparison, the initial strength of the conventional example without carbon coating is indicated by ○,
The strength after immersion is also shown by □.

First, regarding the initial strength, the carbon coated optical fiber is slightly deteriorated in strength as compared with the conventional example not coated with carbon, and the film thickness is increased.
Since the tendency becomes stronger as the center line average roughness of the carbon coating becomes rougher, the deterioration of the initial strength is considered to be due to the center line average roughness. That is, it is considered that the stress is likely to be concentrated on the rough portion of the surface and is easily broken. Therefore, the centerline average roughness of the carbon coating is, as in the present invention,
By setting the thickness to 1 nm or less, as shown in FIG.
It can be seen that it is possible to maintain almost the same initial strength as the conventional example.

On the other hand, with respect to the strength after immersion, in the conventional example not coated with carbon, remarkable strength deterioration is observed, whereas in the hermetically coated fiber coated with carbon, the strength deterioration is small. However, even in the hermetically coated fiber coated with carbon, if the carbon film thickness is less than 300 Å, the strength after immersion is considerably deteriorated. It is considered that this is because if the carbon film becomes too thin, it is not possible to sufficiently prevent the intrusion of water. Therefore, the film thickness of carbon is
By setting it to 300 Å or more, as shown in FIG. 2, the deterioration of the strength after immersion can be reduced.

As described above, by coating carbon with a film thickness of 300 Å or more and a center line average roughness of 1 nm or less, as shown in FIGS. 2 and 3, moisture is sufficiently blocked. Thus, it is possible to obtain an optical fiber having a large diameter, which has extremely good water resistance and also has good tensile strength.

[0021]

As described above, in the large-diameter hermetically coated fiber of the present invention, the cladding surface is coated with carbon, and moreover, 300 Å, which is sufficient to prevent the intrusion of water.
Since it has the above-mentioned film thickness and the center line average roughness is as small as 1 nm or less, there is almost no deterioration in mechanical strength and the water resistance is extremely good.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a large-diameter optical fiber coated with carbon.

FIG. 2 is a characteristic diagram showing the relationship between carbon film thickness and strength.

FIG. 3 is a characteristic diagram showing a relationship between surface roughness and strength.

[Explanation of symbols]

 1 core 2 clad 3 carbon coating layer Ra center line average roughness

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Takeda 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Hiroyuki Tanaka 4-3 Ikejiri, Itami City, Hyogo Mitsubishi Cable Industries Itami Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. A large-diameter hermetically coated fiber characterized in that a carbon coating having a film thickness of 300 Å or more and a center line average roughness of 1 nm or less is provided on the cladding surface.