JPH07104453B2 - Optical fiber cable connection box - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a connection box for accommodating a connection part of an optical fiber cable, and is intended to prevent an increase in optical fiber transmission loss due to the influence of hydrogen.

<Prior Art> There are various specifications of connection boxes for optical fiber cables depending on the intended use of the cables. FIG. 4 shows a connection box for an optical fiber composite overhead ground wire as a conventional example.

The connection box 1 shown in FIG. 4 is usually installed on a steel tower, and the optical fiber cables 4a and 4b are drawn into the connection box 1 through the cap portion 3 thereof, and the optical fiber is connected in the connection box 1 as shown in the figure. They are fusion-spliced together, and finally the lid of the connection box 1 is closed with a screw 2. The base portion 3 is screwed to the connection box 1 at its flange portion 3a. 5 in FIG.
Is an optical fiber connection, and 10 is a cable sheath made of an aluminum pipe.

In addition to the example shown in FIG. 4, there are optical fiber cable connection boxes installed on the seabed, underground, manholes, etc., but the basic structure is the same as that shown in FIG.

Generally, the performance required for the connection box of the optical fiber cable is that it can be easily assembled and disassembled, that the connection work is easy, and that it is airtight.

<Problems to be solved by the invention> However, although airtightness is required, if there is a pinhole or a minute defect in the end face in the portion tightened by the mouthpiece 3 or the screw 2, complete airtightness is achieved. Is very difficult to keep.

In addition, even if a certain degree of airtightness was maintained with rubber packing in the initial stage of use, in long-term use,
The packing may deteriorate and the airtightness may be gradually lost.

As described above, if the airtightness is not maintained, the external moisture may enter the connection box 1. Since the moisture reacts with the constituent metals of the connection box 1 to generate hydrogen gas, if hydrogen penetrates into the optical fiber glass, it causes an increase in transmission loss of the optical fiber for a long period of time, which is not preferable for optical communication. Occur. (For example, Noguchi et al. "Increase in optical fiber loss due to hydrogen and long-term loss stability of optical fiber cable", IEICE Transactions (B), J68 (B), No. 7, P795, 1986). In view of the above problem, it is an object to provide an optical fiber cable connection box that prevents an increase in optical fiber transmission loss due to the influence of hydrogen.

<Means for Solving Problems> Even if hydrogen gas is generated in the connection box, if the hydrogen gas is absorbed by the hydrogen absorbent, it is considered that there should be no increase in optical fiber transmission loss due to hydrogen. The experiment shown in FIG. 3 was performed.

In this experiment, as shown in FIG. 3, a spacer type optical fiber cable unit 8 for an optical fiber composite overhead ground wire was housed in a constant temperature bath 9, and one end of the optical fiber cable connection box was filled with a hydrogen absorbent 6. 1, and the optical fibers were fusion-spliced at the connection portion 5. Then, the other end is connected to a light source (not shown) so that the optical fiber transmission loss can be measured by the cutback method, and the optical fiber cable unit 8 is subjected to a heat cycle of -40 ° C to 150 ° C to continuously emit light. Fiber transmission loss was measured. The measurement was performed under the three conditions shown in Table 1, and the hydrogen partial pressure in the optical fiber cable was estimated from the increase in optical fiber transmission loss after 200 heat cycles.

As is clear from the experimental results shown in Table 1, by filling the connection box 1 with the hydrogen absorbent 6, the hydrogen gas in the connection box 1 is absorbed and the diffusion of hydrogen gas into the optical fiber cable is prevented. It was found that the hydrogen partial pressure in the optical fiber cable can be reduced as well as the above.

The present invention has been made based on the above findings,
The connection box of the optical fiber cable according to the present invention is characterized by including a hydrogen absorbent. There are various methods of providing the hydrogen absorbent, such as filling the inside of the connection box with the hydrogen absorbent or detachably communicating a container containing the hydrogen absorbent with the connection box.

<Operation> When hydrogen gas is generated by the reaction between the moisture that has entered the connection box and the constituent metal of the connection box, the hydrogen absorbent absorbs the hydrogen gas. This prevents hydrogen gas from entering the fiber optic cable splice and then diffusing into the fiber optic cable.

Also, since the connection box is always kept in a low hydrogen atmosphere due to the function of the hydrogen absorbent, if the hydrogen partial pressure inside the optical fiber cable is high, the hydrogen gas will always diffuse into the low hydrogen atmosphere. Reduce the hydrogen partial pressure in the fiber cable. This is particularly effective for an optical fiber cable having a structure with a high porosity.

Furthermore, an optical fiber cable used in a fictitious environment is easily affected by external temperature changes, and hydrogen gas in the optical fiber cable repeats expansion, contraction, and other breathing in response to temperature changes along with other gases. However, in such a case, the hydrogen absorbent provided in the connection box of the terminal absorbs hydrogen gas in the gas flowing out to the connection box and acts as a kind of filter for hydrogen gas.

<Example> An example of the present invention will be described with reference to FIG.

In the connection box 1 of the optical fiber cable shown in FIG. 1, the hydrogen absorbent 6 is directly filled in the connection box 1.

As a work procedure, first, the optical fiber cables 4a and 4b are drawn through the base portion 3, and the optical fibers are fusion-spliced at the connection portion 5. After that, the hydrogen absorbent 6 is filled, and finally the screw 2 is tightened to close the lid, and the connection box 1 is sealed.
Appropriate packing is used for the tightening portion of the screw 2, the base portion 3, and the like, if necessary. 3a is a flange for screwing the base portion 3, and 10 is a cable sheath of the optical fiber cable.

In the embodiment shown in FIG. 1, the optical fiber cables 4a and 4b are optical fiber cable units for an optical fiber composite overhead ground wire, and the units are four 0.7 mmφ fluorine resin (for example, Teflon) coated core wires. Was housed in a grooved aluminum spacer, and the outer circumference was covered with an aluminum pipe, and the outer diameter was about 5 mmφ. The connection box 1 was installed on the steel tower.

Next, another embodiment of the present invention will be described with reference to FIG.

In the optical fiber cable connection box 1 shown in FIG. 2, the container 7 containing the hydrogen absorbent 6 is detachably connected to the connection box 1 by a screw method, a spring method, or the like. Thus, by using the detachable container 7, the hydrogen absorbent 6 can be provided in the connection box 1 without opening the lid of the connection box 1, the cable connection work is easy, and the cable connection The container can be easily attached and removed from the outside without affecting the workability, and the workability is very good.

As a work procedure, first, the optical fiber cables 4a and 4b are drawn through the base portion 3, the optical fibers are fusion-spliced at the connection portion 5, and the lid of the connection box 1 is closed with the screw 2. After that, the container 7 containing the hydrogen absorbent 6 is attached to the mounting opening 1a of the connection box 1.
Install on. Appropriate packing is used to attach the container 7 if necessary. 11 is a flange of the container 7.

In the embodiment shown in FIG. 2, the container 7 has a stainless steel outer diameter.
It was 50 mmφ and 100 mm long. Container 7 and connection box 1
The mounting structure for and was a screw type. Further, the optical fiber cables 4a and 4b have an outer diameter of about 5 mmφ as in the embodiment shown in FIG.
It was an optical fiber cable unit for the optical fiber composite overhead ground wire.

In any of the embodiments shown in FIG. 1 and FIG. 2, even if the connection box 1 is not completely airtight, the hydrogen absorbent 6 absorbs the hydrogen gas generated when the invading moisture reacts with the metal, and the hydrogen is absorbed. The gas could be prevented from entering the fiber optic cable. Further, the hydrogen gas flowing out into the connection box 1 through the insides of the optical fiber cables 4a and 4b was also absorbed by the hydrogen absorbent 6 and the hydrogen partial pressure could be lowered.

Incidentally, comparing the hydrogen absorption capacities of the two embodiments, the embodiment shown in FIG. 1 has a slightly better hydrogen absorption capacity because the hydrogen absorbent 6 is filled in the connection box 1. ,
It can be said to be advantageous when used in the deep sea or underground manholes that are constantly humid.

<Effect of the Invention> According to the present invention, even if the moisture that has entered the connection box reacts with the constituent metals of the connection box to generate hydrogen gas, the hydrogen absorbent absorbs this hydrogen gas. This makes it possible to prevent the hydrogen gas from entering the connection portion of the optical fiber cable and diffusing into the optical fiber cable. Therefore, an increase in optical fiber transmission loss can be prevented and the transmission life is extended.

In addition, since the connection box is always kept in a low hydrogen atmosphere by the action of the hydrogen absorbent, even if hydrogen gas is generated inside the optical fiber cable, it diffuses into the low hydrogen atmosphere, so that the inside of the optical fiber cable is indirectly This will reduce the hydrogen partial pressure and prevent an increase in optical fiber transmission loss. This is particularly effective for an optical fiber cable having a structure with a high porosity.

Furthermore, an optical fiber cable used in a fictitious environment is easily affected by external temperature changes, and hydrogen gas in the optical fiber cable repeats expansion, contraction, and other breathing in response to temperature changes along with other gases. However, in such a case, the hydrogen absorbent provided in the connection box of the terminal absorbs the hydrogen gas in the gas flowing out to the connection box, and acts as a kind of filter for the hydrogen gas. Prevents an increase in transmission loss.

From the above, the connection box does not have to be a completely airtight one, so that the structure of the connection box can be simplified and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an optical fiber cable connection box according to the present invention, FIG. 2 is a sectional view of another embodiment, FIG. 3 is an explanatory view of an experimental method, and FIG. 4 is a conventional example. FIG. In the drawings, 1 is a connection box, 1a is a mounting port, 2 is a screw, 3 is a base part, 4a, 4b and 8 are optical fiber cables, 5 is a connection part, 6
Is a hydrogen absorbent, 7 is a container, and 9 is a constant temperature bath.

Claims (3)

[Claims] 1. A connection box for an optical fiber cable, characterized in that a connection box for accommodating a connection section between optical fibers is provided with a hydrogen absorbent. 2. A connection box for an optical fiber cable according to claim 1, wherein the connection box is filled with a hydrogen absorbent. 3. A connection box for an optical fiber cable according to claim 1, wherein a container containing a hydrogen absorbent is detachably connected to the connection box.