JPH05196847A - Optical cable - Google Patents

Abstract

PURPOSE:To provide the optical cable which can prevent the running water at the terminal part of the optical cable even if a water infiltration accident arises in the optical cable. CONSTITUTION:The optical cable 1 is constituted by housing an optical fiber 2 into a stainless steel tube 3 coated with a polyethylene sheath. The optical cable 1 does not house a running water preventive material therein. A sealing material 6 of a cold curing type is injected by an injector into the terminal part and an SC type connector 5 is mounted after curing. Since the terminal is subjected to the running water preventive treatment by the sealing material 6, the infiltration of the water into the part of the SC type connector 5 does not arise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical cable in which an optical fiber is housed in a hollow tubular member, and more particularly to an optical cable having a connecting portion on at least one terminal.

[0002]

2. Description of the Related Art It is known that the adhesion of water to the glass surface of an optical fiber reduces the strength of the optical fiber. As a structure of a conventional optical cable, in order to prevent a portion whose strength is reduced due to adhesion of water from being distributed over a long distance, a structure using an anti-running material is adopted.

For example, the optical cable described in Japanese Utility Model Laid-Open No. 62-49114 discloses an optical fiber core wire or a tape-shaped optical fiber in a pipe in which polyethylene is coated on the outer peripheral surface of a wrap tape formed into a cylindrical shape. In the optical fiber cores or the tape-shaped optical fiber cores containing the fiber cores, continuous long fibers having a high water absorption property or short fibers having a high water absorption property processed into a sheet are used as a water-running prevention material. As a structure, a structure with vertical or horizontal winding is adopted. In such a cable structure, when a certain section of the optical cable is damaged, the water-prevention material swells to fill the voids in the cable and has the effect of stopping the water so that the water does not spread over a wide area. The abnormal parts due to the accident are limited. Therefore, the structure has only to repair this abnormal section at an appropriate time after flooding.

However, in recent years, an optical fiber having high reliability in water, such as a hermetically coated optical fiber, has been developed, and the influence of flooding is becoming less important in terms of strength reduction.

Also, with the expansion of optical communication networks, optical cables have spread from trunk lines to branch lines and wiring, and the price has become cheaper. For an inexpensive optical cable with a short length of about 100 m for repairing, the entire length of the optical cable has been changed in case of an accident.

Therefore, when the conventional optical cable containing the water running preventive material is used as a wiring cable for pulling down, the effectiveness of preventing the expansion of the abnormal point until the replacement is small, and in particular, the hermetically coated optical fiber is used. In this case, since the strength of the optical fiber itself does not easily decrease in water, it can be said that the use of the water-running prevention material is practically meaningless.

On the other hand, when bending or lateral pressure is applied to the optical fiber, a force may be applied to the optical fiber due to the presence of the water-running prevention material, which may cause an increase in loss. Further, due to freezing of the flooded optical cable or the like, the loss increases over the entire length, which may cause a large increase in loss.

Such a problem is particularly remarkable in a structure in which a water-absorbent fiber is arranged along an optical fiber and accommodated in a pipe or a narrow groove. Further, in terms of manufacturing, it is necessary to control and store both the optical fiber and the water flow preventive material, and the structure is inferior in productivity.

On the other hand, in the above-mentioned short cable of about 100 m, about one optical cable is installed for each customer, so that the required number of optical cables may be small, and conversely, the size and weight of the optical fiber can be reduced. Is required. Therefore, in the prior art, the storage groove and the storage pipe containing the optical fiber and the water-prevention material are required to be downsized, the interaction between the optical fiber and the water-prevention material becomes stronger, and the loss increase described above is caused. The problem was becoming more prominent.

However, in such a short cable, if the running preventive material is removed, when the optical fiber is flooded, another optical cable that is often at a low position,
There is also a problem that water may run to the end of the optical cable connected to the device and the strength of the connection part may be impaired, the connection loss may be increased, and the device may be contaminated.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides an optical cable capable of preventing running water to the end portion of the optical cable even if a water flood accident occurs in the optical cable. The purpose is to do.

[0012]

DISCLOSURE OF THE INVENTION The present invention provides an optical cable in which an optical fiber is housed in a hollow tubular member,
The present invention is characterized in that at least one end has a connecting portion, and water running prevention treatment is performed only in the tubular member near the end. A solid resin or a water-absorbing material can be used as a water-running prevention measure.

[0013]

According to the present invention, water running into the optical cable due to an accident such as breakage of the optical cable caused by water running prevention measures only near the end,
Even when water vapor is condensed, water does not flow into the connection part of the terminal and damage the connection part and the device. Further, since the water running prevention treatment is applied only partially, there is no loss change due to the interaction between the optical fiber and the water running prevention material. The manufacturability is good and the weight can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of the essential parts of a first embodiment of an optical cable according to the present invention. In the figure, 1 is an optical cable, 2 is an optical fiber, 3 is a stainless tube, 4 is a polyethylene sheath, 5 is an SC type connector, and 6 is a sealing material. The optical cable 1 is constructed by housing an optical fiber 2 in a stainless steel tube 3 provided with a polyethylene sheath 4. In addition, the optical cable 1 does not contain a running water prevention material. This optical cable 1 is manufactured by manufacturing an optical cable in which an optical fiber 2 is housed in a stainless steel tube 3, cutting the optical cable into a predetermined length, and injecting a room temperature curing type sealing material from a terminal portion with a syringe or the like. After being cured, the SC type connector 5 is attached. As the sealing material 6, a silicone resin or the like can be used.

In this optical cable, since water running prevention treatment is applied by the sealing material 6, even if water is flooded in the middle of the optical cable, the water entering the stainless tube 3 is stopped by the sealing material 6. Even if the SC type connector 5 is placed at a position lower than the optical cable 1, the SC type connector 5 will not be flooded.

FIG. 2 is a sectional view of the essential parts of a second embodiment of the optical cable of the present invention. In the figure, the same parts as those in FIG. 7 is a water absorbent fiber string. In this embodiment, the water-absorbent fiber string 7 is used to carry out water running prevention treatment. The water-absorbent fiber string 7 expands when it absorbs water, and water running can be prevented.

FIG. 3 is a sectional view of the essential parts of a third embodiment of the optical cable of the present invention. In the figure, the same parts as those in FIG. Reference numeral 8 is a flexible tube, 9 is a vinyl chloride resin coating, and 10 is an adhesive. In this embodiment, the diameter of the optical fiber storage pipe near the end of the optical cable 1 is increased.

With regard to an optical cable having a connector at its terminal, good transmission characteristics can be obtained by reducing pressure on the optical cable by the running water preventive material. The third embodiment is based on such a demand. As a method of constructing an optical cable, the stainless tube 3 at the end of the optical cable 1 is set to several tens of cm to several meters.
It was removed over a period of time, and a large-diameter pipe was put over this part. In this embodiment, a stainless flexible tube 8 with a vinyl chloride resin coating 9 is used as a large diameter pipe. This was joined to the rest of the stainless steel tube 3 of the optical cable 1 with an adhesive 10, and a silicone sealing material 6 was inserted as a water running prevention material. By using the flexible pipe as the large-diameter pipe portion, it is possible to obtain an effect that the work of attaching and detaching the terminal can be easily performed.

As a concrete example of this embodiment, an inner diameter of 0.9
mm stainless steel tube 3 having an outer diameter of 1.2 mm and a polyethylene sheath 4 applied thereto, the end of the optical cable 1 accommodating a single 250 μm optical fiber 2 is covered with vinyl chloride resin by removing the stainless steel tube over 1 m. Cover with a flexible tube 8 made of stainless steel having an inner diameter of 3 mm and an outer diameter of 5 mm, which has been subjected to 9;
Fill the section of m with silicone resin sealing material 6,
The SC type connector 5 is attached.

An optical cable corresponding to the first and second embodiments was manufactured as a prototype. The prototype optical cables are all 250 μm in outer diameter, 50 mm in core diameter, and 125 μm in clad diameter.
Of a multimode optical fiber obtained by coating the above glass fiber with an ultraviolet curable resin has an inner diameter of 2 mm and an outer diameter of 2.4.
It is housed in a stainless steel tube of SUS316 of mm and covered with polyethylene to have an outer diameter of 3.4 mm.

Experimental example 1 corresponds to the first embodiment. From the terminal on one side of the prototype optical cable 50m,
At a position of 60 mm, 2 ml of a room temperature curing type silicone sealing material was injected by a syringe to seal the vicinity of the terminal. As the silicone sealing material, one-pack type RTV rubber KE441T manufactured by Shin-Etsu Chemical Co., Ltd. was used.

Experimental example 2 corresponds to the second embodiment. From the terminal on one side of the prototype optical cable 50m,
Fifty pieces of 7-denier water absorbing fiber strings were inserted over 1 m. As the water-absorbent fiber string, Sumika Gel F-75 manufactured by Sumitomo Chemical Co., Ltd. was used.

On the other hand, an optical cable of Comparative Example 1 was prototyped.
Fifty water absorbent fiber cords described above are stored over the entire length of the optical cables used in the first and second embodiments.

Comparative Example 2 is 50 m of the optical cable used in the first and second examples. That is, it corresponds to the optical cable of Comparative Example 1 in which the water absorbent fiber string is not housed.

A test for comparing the transmission characteristics was conducted using the above-mentioned four kinds of samples. As an evaluation method, assuming a practically possible bending of the cable, a diameter of 100 m
A cylinder of m was wound 30 times, and the transmission loss in the 1.30 μm band before and after the winding was evaluated. The results are shown below with an increase in loss. Experimental example 1
In addition, in Experimental Example 2, the portion into which the running water preventive material was inserted was set to fall within the bending range. Experimental Example 1: 0 [dB] Experimental Example 2: 0.01 [dB] Comparative Example 1: 0.35 [dB] Comparative Example 2: 0 [dB]

Next, using the above-mentioned four kinds of samples, water running test was conducted. FIG. 4 is an explanatory diagram of the evaluation method. Each sample was cut into a length of 3 m, and experimental example 1
In addition, in Experimental Example 2, the treated terminal side was set downward. Reference numeral 11 in the figure is a sample, which is inserted into an opening provided on the lower surface of the water tank 12 in a state where the cross section is open at the upper side and is connected by a sealant. The results of leaving for 1 hour in this state are as follows. Experimental Example 1: No Running Water Experimental Example 2: No Running Water Comparative Example 1: No Running Water Comparative Example 2: With Running Water Based on these results, by using the optical cable of the present invention, when the optical cable is damaged due to an accident or the like, It was confirmed that problems such as dirty terminals did not occur.

The optical cable of the present invention can ensure higher reliability by being applied to an optical cable using an optical fiber provided with a hermetic coat that is less likely to be deteriorated in strength due to water immersion in the optical cable.

[0028]

As is apparent from the above description, by using the optical cable having the structure of the present invention, it is possible to easily manufacture an optical cable, such as a drop-down wiring cable, which is used in a short length and has a connecting portion at its end. .. Further, since the structure can be simplified, there is an effect that the cross-sectional area, weight, price, etc. can be reduced and high reliability around the connection point can be secured.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a first embodiment of an optical cable of the present invention.

FIG. 2 is a sectional view of an essential part of a second embodiment of the optical cable of the present invention.

FIG. 3 is a sectional view of an essential part of a third embodiment of the optical cable of the present invention.

FIG. 4 is an explanatory diagram of an evaluation method used in an experiment.

[Explanation of symbols]

 1 Optical Cable 2 Optical Fiber 3 Stainless Steel Tube 4 Polyethylene Sheath 5 SC Type Connector 6 Sealing Material 7 Water Absorbing Fiber String

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinobu Kitayama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Shigeru Tanaka 1-taya, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Denki Kogyo Co., Ltd. Yokohama Works (72) Inventor Shigeru Tomita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. An optical cable in which an optical fiber is housed in a hollow tubular member, wherein at least one end has a connecting portion, and water running prevention treatment is performed only in the tubular member near the end. The optical cable that is characterized.