JPH0894893A - Slot unit of optical fiber cable - Google Patents

Abstract

PURPOSE: To prevent the infiltration of the water entering the inside of slot units made higher in density in an optical fiber cable by forming spiral grooves for housing optical fibers to multiple stages into a joint box by running water. CONSTITUTION: The narrow spiral grooves 23 are formed at the bottoms of the broad spiral grooves 22 of a slot rod 20 to form the optical fiber housing grooves as the multistage spiral grooves. Cover plate 26 consisting of thin plastic sheets are laid on the bottoms of the broad spiral grooves 22 of this slot rod 20 to cover the narrow spiral grooves 23 and broad optical fiber ribbons are laminated thereon. These cover plates 26 are formed as water absorbent tapes by sticking water absorbent materials on plastic tapes, by which the slot unit of the optical fiber cable is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slot rod of an optical fiber cable, and more particularly to the shape and structure of a spiral groove for accommodating the optical fiber tape, and an optical fiber which can be accommodated in one slot rod. It is possible to dramatically increase the number of tapes, which makes it possible to increase the density of optical fiber cables.
It is possible to effectively prevent water from entering the joint box through the optical fiber tapes that are stored at a high density.

[0002]

2. Description of the Related Art A synthetic resin core of an optical fiber cable having a tension member buried in the center and manufactured by extrusion molding and having an optical fiber tape accommodating groove on the outer periphery, so-called slot rod, has various sectional shapes. However, it has a large number of radial grooves for storing optical fiber tapes with high density (see Fig. 4).
Is conventionally used (hereinafter referred to as "conventional slot rod"). In recent years, there has been a demand for higher density of optical fiber cables. In order to meet this demand, the spiral groove 2 of the slot rod 10 should be deepened to increase the number of optical fiber tapes that can be accommodated in one groove. There is no choice but to try. However, if the depth of the spiral groove 2 is increased, the wall thickness A (see FIG. 4) at the root of the rib 3 between the grooves is reduced, and the strength of the rib is insufficient. Therefore, there is a limit in increasing the depth of the spiral groove 2, and there is a limit in increasing the density in the cross-sectional shape of the conventional slot rod. For this,
Conventionally, the diameter of the optical fiber was made as small as possible, the coating layer of the optical fiber was made as thin as possible, and the protective layer of the optical fiber was made as thin as possible, thereby increasing the density of the optical fiber cable. However, it will be extremely difficult to dramatically increase the density in the future with only such measures. In order to dramatically improve the density of optical fiber cables in the future, it is important to devise the shape and structure of the slot rod so that the number of tapes that can be accommodated in the slot rod can be increased as much as possible. Become. Furthermore, when the tape storage density is improved, water that has entered the inside of the slot unit from the damaged portion of the sheath (outer sheath) flows into the joint box by water running (due to the capillary phenomenon), corrodes its constituent members, and Since it lowers durability etc.,
It is an important issue to take effective measures to prevent this effectively.

[0003]

SUMMARY OF THE INVENTION With respect to the conventional slot rod, the present invention devises the cross-sectional shape of the above-mentioned spiral groove to make it possible to further increase the density, and to prevent water that has entered the slot unit. Water run (due to capillarity)
The problem is to take effective measures to prevent the flow into the joint box.

[0004]

Means for Solving the Problems The measures taken to solve the above problems are constituted by the following elements (a) to (c). (A) A narrow spiral groove is formed at the bottom of the wide spiral groove to form the optical fiber storage groove as a multi-step spiral groove,
(B) A cover plate made of a thin plastic sheet is laid on the bottom of the wide spiral groove of the slot rod to cover the narrow spiral groove, and a wide optical fiber tape is laminated thereon.
(C) The lid plate is a water-absorbing tape in which a water-absorbing material is attached to a plastic tape.

[0005]

[Operation] The depth of the wide spiral groove should be such that the wall thickness of the rib at the bottom of the wide spiral groove ensures the necessary strength, and the depth of the narrow spiral groove formed at the bottom is also The thickness of the ribs at the bottom of the narrow spiral groove is set so that the required strength can be secured, and the narrow optical fiber tape is stored in the narrow spiral groove, and the wide optical fiber tape is formed into the wide spiral shape. Store in the groove. The number of optical fiber tapes that can be stored in the wide spiral groove is the same as the conventional one, but the storage density of optical fibers increases as much as the narrow optical fiber tape can be stored in the narrow spiral groove. . Therefore, the density of the optical fiber cable can be increased. When the wide optical fiber tape is an 8-fiber tape and the narrow optical fiber tape is a 4-fiber tape, the spiral groove is a two-step spiral groove. When the wide optical fiber tape is an 8-core tape, a 6-core tape or a 4-core tape, the spiral groove is a spiral groove having three stages. When a narrow spiral groove is formed on the bottom of the spiral groove, the side end of the wide optical fiber tape housed in the wide spiral groove falls into the narrow spiral groove and becomes wider. The fiber optic tape may be twisted resulting in reduced transmission efficiency. In order to prevent this reliably, a thin plastic sheet cover plate is laid on the bottom of the wide spiral groove to cover the narrow spiral groove, and a wide optical fiber tape is laminated on top of it. Configure a cable slot unit. Since the lid plate is a plastic sheet, its strength never deteriorates even if water enters and is exposed to the damaged portion of the sheath (outer sheath). There is no risk that the side edge of the stored wide optical fiber tape will fall into the narrow spiral groove. By the way, with respect to the slot unit in which the spiral groove is vertically arranged in the upper and lower grooves and the optical fiber tape is housed at a high density, even if a little water enters from the damaged portion of the sheath, it is transmitted through the optical fiber tape by the capillary phenomenon and diffused to a wide area. It This water running phenomenon is hardly a problem for an optical fiber tape accommodated in a wide spiral groove, but it is remarkable especially in an optical fiber tape accommodated in a narrow spiral groove, and for this reason, the narrow spiral The spread of water that has entered the groove may reach the joint box over a long distance and water may enter the joint box. This is fatal for a slot unit that requires special waterproofing, but by using a plastic sheet with a water absorbing material for the lid plate, a wide spiral groove can be created from the damaged portion of the sheath (outer sheath). The water that has entered is absorbed by the water absorbing material of the cover plate before entering the narrow spiral groove, and thus it is surely prevented from entering the narrow spiral groove.

[0006]

Example Next, an example will be described with reference to FIGS. 1, 2, and 3. Slot rod 2 with a diameter of 14 mm
Five spiral two-stage grooves 21 are provided at 0 at equal intervals. This spiral two-stage groove 21 has a width B of 2.7 mm and a depth D of 2.5.
wide groove 22 with a width b of 1.5 mm and a depth d of 2.
It is a two-step groove consisting of a narrow groove 23 of 4 mm and a wide groove 2
The thickness t ₁ of the rib 24 at the bottom of _{No. 2} is 2.9 mm, and the thickness t ₂ of the rib 24 at the bottom of the narrow groove is 1.2 mm. The wall thickness t ₁ is the wall thickness A of the rib 3 at the bottom of the spiral groove in the conventional slot rod for 8-core tape.
The strength of the rib is sufficiently secured. The thickness t ₂ of the rib 24 at the bottom of the narrow groove 23 is sufficient to secure the strength of the rib 24. 250 in narrow groove 23
4-core tape 25 of μmφ element wire (width 1.1 mm, thickness 0.
4mm), 5 sheets are laminated, thickness 0.1mm, width 2.6mm
Of the polyethylene terephthalate sheet 26a is covered with a polyacrylate water absorbing material 26b having a thickness of 0.1 mm to cover the narrow groove 23 with a cover plate (water absorbing tape) 26, on which 8 cores of 250 μmφ wire Tape 2
Five sheets of 7 (width 2.1 mm, thickness 0.4 mm) are stacked, housed in the wide groove 22, and covered with the sheath 28. As a result, a total of 300 cords are accommodated in one slot rod to form a slot unit of 300 cords. Since the number of cords that can be stored in the conventional slot rod shown in FIG. 4 is 200, a larger number of cords can be stored by 100. As the water-absorbing material coated on the plastic sheet of the lid plate, various materials such as carboxymethylcellulose-based and starch-based materials can be used, and various commercially available water-absorbing tapes can be used as long as they have high water absorption. The water-absorbing material may be coated on the lower surface of the tape, on both the upper and lower surfaces, or on the upper surface only, but it is preferable that the lower surface is coated. It is more desirable because it can be further increased. The slot unit of the above example was subjected to a transmission test with light having a wavelength of 1.55 μm. As a result, the transmission loss of all the cores was 0.02 dB / km or less, which was the same as the conventional one. A cable was wound around a pulley having a radius of 400 mm, a tensile force of 100 kg was applied to squeeze the slot unit, and then a transmission test was performed with light having a wavelength of 1.55 μm. As a result, the transmission loss is 0.02 for all cores.
It was below dB / km, which was the same as the conventional one. Further, the sheath was cut into an annular shape with a width w (25 mm), one end was sealed and the other end was opened, and the five slot units of the embodiment having a total length of 170 cm and the lid plate were made of polyethylene terephthalate, which was not a water-absorbing tape. For the same 5 slot units as above, 1m in the sheath cutout part
A water leakage test was conducted by applying the above water head pressure for 24 hours (see FIG. 5). As a result, in the former case, no water leakage was confirmed from the narrow groove at the open end of the five cases, and in the latter case, water leakage was confirmed in three of the five cases.

[0007]

[Effect] The invention which has solved the above-mentioned problems is not yet known. Therefore, it is an effect peculiar to the present invention that the new problem can be solved and the conventional problem can be solved, whereby the density of the optical fiber cable can be dramatically improved. In addition, the density of the optical fiber cable was improved by devising the shape of the groove without changing the thickness of the slot rod.The groove processing method is the same as the conventional slot rod groove processing method. There is no particular difference, and there is no particular disadvantage in terms of processing efficiency and processing cost. Further, since the application of the present invention does not cause any problems in other aspects such as the attachment of the optical fiber cable, the optical fiber cable can be laid in the same manner as the conventional one. We could completely solve the problem of water leakage caused by running water as a result of accommodating optical fiber tape in a narrow groove to achieve high density, and extremely simple means of using lid plate as water absorbing tape Is. Therefore, the density of the optical fiber cable can be dramatically improved without increasing the manufacturing cost of the slot rod and without causing additional problems with the application of the present invention, and the water in the joint box can be prevented from entering. The greatest effect of the present invention is that it is possible to surely prevent functional deterioration due to and improve its durability.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is an enlarged view of the groove of FIG.

FIG. 3 is an enlarged view of a cover plate (water absorbing tape).

FIG. 4 is a cross-sectional view of a conventional technique.

FIG. 5 is a schematic diagram of a water leakage test.

[Explanation of symbols]

2 ... Spiral groove 3, 24 ... Rib 10, 20 ... Slot rod 21 ... Spiral two-stage groove 22 ... Wide groove 23 ... Narrow groove 25 ... 4 cores Tape 26 ... Lid plate 26a ... Polyethylene terephthalate sheet 26b ... Water absorbing material 27 ... 8-core tape 28 ... Sheath A ... Wall thickness of root of rib 3 B ... Wide groove 22 Width of the wide groove 22 b ... width of the narrow groove 23 d ... depth of the narrow groove 23 t ₁ ... rib thickness t _{2 at} the bottom of the wide groove 22 ... Thickness of ribs at the bottom of the narrow groove 23

Claims (1)

[Claims] 1. A slot unit for an optical fiber cable in which a tension member is embedded in the center and a large number of spiral optical fiber tape accommodating grooves are provided on the outer periphery of a synthetic resin slot rod of the optical fiber cable manufactured by extrusion molding. The spiral optical fiber tape accommodating groove is a multi-step spiral groove in which a narrow spiral groove is formed at the bottom of the wide spiral groove, and a thin plastic sheet lid is provided on the bottom of the wide spiral groove of the slot rod. A plate is laid to cover the narrow spiral groove, and a wide optical fiber tape is laminated on the narrow spiral groove, and the lid plate is a water absorbing tape in which a water absorbing material is attached to a plastic tape. Slot unit.