JP2003287661A - Optical cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To design an optical cable which consists of a housing tube and a coated optical fiber so that the cable diameter can be easily reduced even though the optical cable employs, as the coated optical fiber, a fiber ribbon which is effective for improving connection work efficiency. <P>SOLUTION: A fiber ribbon 1a is inserted into a housing tube 2 as a coated optical fiber 1. The ratio d/D of the diameter d of a circle circumscribing the coated optical fiber 1 to the inside diameter D of the housing tube 2 is set to 0.7≥d/D≥0.4. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical cable formed by inserting an optical fiber core wire into a storage tube.

[0002]

2. Description of the Related Art Conventionally, there has been an optical cable constructed by inserting a plurality of single-core optical fiber core wires into a housing tube. In the optical cable configured as described above, the optical fiber core wire and the storage tube to be inserted are inserted so that the transmission characteristics are not deteriorated due to an undesired lateral pressure acting on the optical fiber core wire when the cable is bent. There is a certain amount of space between and. The optical cable having such a configuration is called a loose tube type optical cable.

In the loose-tube type optical cable, the inner diameter of the storage tube should be set as small as possible after providing a gap between the storage tube and the optical fiber core to prevent lateral pressure. Is required.

Therefore, conventionally, the inner diameter of the storage tube is set so that the ratio (space factor) of the total cross-sectional area of the inserted optical fiber core wire to the inner cross-sectional area of the storage tube is within an appropriate range. As a result, the diameter of the cable has been reduced.

[0005]

In the loose tube type optical fiber, the number of optical fiber cores is increasing in order to increase the transmission density of the entire optical fiber. However, in the loose tube type optical fiber, all the optical fiber cores to be inserted are single cores. Therefore, when a large number of core wires are inserted, the efficiency of the core wire connecting work is inevitably low. Therefore, conventionally, in the loose tube type optical fiber, it has been considered to use an optical fiber core having a structure in which a plurality of optical fibers are arranged in parallel and integrated by a sheath (coating resin). It has been put to practical use. Hereinafter, such an optical fiber core wire is referred to as a tape core wire.

However, since the tape core wire is formed by integrating a plurality of optical fiber core wires arranged in parallel, there is a difference in the change in transmission characteristics due to the lateral pressure depending on the bending direction. However, the thinning design based on the cross-sectional area does not consider the direction of the core wire at all. Therefore, it has been impossible to design a diameter reduction based on the cross-sectional area of a loose tube type optical fiber using a tape core wire.

The present invention has been made by paying attention to such an actual situation, and it is possible to perform a thin design while using a tape core wire effective for improving the efficiency of the core wire connecting work. The purpose is to be able to.

[0008]

In order to achieve the above object, the present invention is configured as follows.

That is, according to the first aspect of the invention, in an optical cable in which an optical fiber core wire is inserted into a storage tube, a ratio d between a diameter d of a circle circumscribing the optical fiber core wire and an inner diameter D of the storage tube. / D is 0.7 ≧ d / D ≧ 0.
It is characterized by setting to 4.

When a circumscribed circle is set around the optical fiber core wire, the circumscribed circle diameter is constant regardless of the direction of the optical fiber core wire, even if the optical fiber core wire has directionality. . Therefore, with the configuration of the present invention, which is intended to reduce the diameter based on the circumscribing circle, it is possible to achieve the optimal diameter reduction regardless of the direction of the optical fiber core wire.

The term "directional optical fiber core wire" means an optical fiber core wire having a directivity in the arrangement of optical fibers by arranging a plurality of optical fibers in parallel and then integrating them. The tape core wire described above is an example thereof.

Based on this point of view, the present invention
How much margin can be set for the size of the storage tube with respect to the circumscribed circle set on the outer circumference of the optical fiber core is specified by the above value of 0.7 ≧ d / D ≧ 0.4. ing.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a first example of the optical cable according to the present invention, and FIG. 2 is a sectional view thereof, and FIG. 3 is a sectional view of the second example. Shows a cross-sectional view of the third example.

This optical cable has a single optical fiber core wire 1. The optical fiber core wire 1 is inserted into a storage tube 2 made of PBT (polybutylene terephthalate). The storage tube 2 is filled with a compound 3 containing urea grease. The storage tube 2 is covered with a sheath 4 made of PE (polyethylene).
Two tension members 5 and 2 are provided at diagonal positions of the sheath 4.
The tear string 6 of the book is buried.

Further, in the first example, as the optical fiber core wire 1, one piece of a two-core type tape core wire 1a in which two single core wires are collectively covered with a sheath resin is used. In the second example, the optical fiber core wire 1a is used. As the core wire 1, two pieces of the two-core type tape core wire 1a are stacked and used, and in the third example, the optical fiber core wire 1 is used.
For this, one 4-core type tape core wire 1b is used.

FIG. 5 shows the transmission characteristics of the SMF (single mode fiber) type and MMF (multimode fiber) type optical cables in which the optical fiber core wire 1 of each of the above examples is inserted into the storage tube 2 having various inner diameters. The results of testing the are shown. It should be noted that the quality of the transmission characteristic is determined by the following threshold value.

SMF type: At a measurement wavelength of 1.55 μm, a value of less than 0.25 dB / km is considered good, and a value of more than 0.25 dB / km is considered bad.

MMF type: At a measurement wavelength of 1.30 μm, a value of less than 0.45 dB / km is regarded as good and a value of more than 0.45 dB / km is regarded as defective.

Looking at the test results, the optical fiber core wire 1
Ratio d of the diameter d of the circle circumscribing to the inner diameter D of the storage tube
When / D is 0.7 ≧ d / D, it is determined that good transmission characteristics can be secured. However, as the ratio d / D becomes smaller, the margin formed around the optical fiber core wire 1 becomes larger and the influence on bending is reduced. However, if the ratio d / D is made smaller, the inner diameter D of the storage tube 2 becomes smaller.
Becomes larger and the diameter of the cable becomes larger.

Here, it is considered to be practically appropriate to keep the ratio d / D within the range of d / D ≧ 0.4.

That is, the ratio d / of the circumscribed circle diameter d of the optical fiber core wire 1 made of the tape core wire and the inner diameter D of the storage tube.
By setting D such that 0.7 ≧ d / D ≧ 0.4, it is possible to reduce the diameter of the optical cable without deteriorating the transmission characteristics.

[0023]

As is apparent from the above description, according to the present invention, a taper core, which is effective for improving the efficiency of the core wire connecting work, is used as an optical fiber core, but a thin design is possible. An easy optical cable can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical cable in which one piece of a two-fiber ribbon is used as an optical fiber.

FIG. 2 is a vertical sectional view thereof.

FIG. 3 is a cross-sectional view of an optical cable in which two optical fiber ribbons are used as two optical fiber ribbons.

FIG. 4 is a cross-sectional view of an optical cable in which a single four-core tape core wire is used for the optical fiber core wire.

FIG. 5 is a chart showing test results.

[Explanation of symbols]

1 Optical fiber core 1a 2 core tape core wire 1b 4 core tape core wire 2 storage tubes d Diameter of circumscribed circle of optical fiber D Storage tube inner diameter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiya Hoshino             4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Electric Cable             Industrial Co., Ltd. Itami Works F-term (reference) 2H001 BB05 BB15 BB16 DD06 DD17                       DD24 KK17 KK22 PP01

Claims (2)

[Claims] 1. An optical cable in which an optical fiber core wire is inserted into a storage tube, wherein a ratio d / D of a diameter d of a circle circumscribing the optical fiber core wire and an inner diameter D of the storage tube, An optical cable characterized by setting 0.7 ≧ d / D ≧ 0.4. 2. The optical fiber according to claim 1, wherein the optical fiber core wire is an integration of a plurality of optical fibers arranged in parallel.