JP2989444B2 - Fiber optic cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a groove type multi-core optical fiber cable mainly using an optical fiber tape.

[0002]

2. Description of the Related Art A groove type cable shown in FIG. 3 has been proposed as a multi-core optical fiber cable for achieving high density and multi-core. Reference numeral 10 denotes an optical fiber unit in which an optical fiber ribbon 16 is accommodated in a groove 14 of a groove 12. This optical fiber unit 1
0 are twisted and gathered around the central tensile strength member 18 to form an optical fiber cable.

However, when the number of optical fiber ribbons 16 entering one groove 12 is large, the groove type optical cable having the above-mentioned structure is not suitable for the lower layer when the cable is bent such as when the drum is wound. There is a problem that a large compressive stress is applied to the optical fiber ribbon 16 to deteriorate the optical transmission characteristics. Further, for this reason, it is not possible to manufacture only the unit 10 first and wind it around the drum, and then to perform large twist assembly later, which also has a problem that the manufacturing and equipment become complicated.

[0004]

In order to solve this problem, we have previously proposed the following two-groove groove type. In FIGS. 4A and 4B, reference numeral 20 denotes a two-groove groove. In this embodiment, two elongated grooves 24 and 26 are provided on the elongated cylindrical main body 22 and twisted around a center line 28. (B) shows a B section of (a). Grooves 24, 26 of this two-groove groove 20
The optical fiber unit 16 is put into the optical fiber unit 30 (c), and the optical fiber unit 30 is twisted around the central strength member 32 to form an optical fiber cable 34 (d).

[0005] In this way, 1) ease of branching for each unit, 2) diversification of branching units (80-core units and 160-core units are possible), 3) cable characteristics by reducing the number of tapes in one groove Improvement (Since the number of cores in one groove is halved, the stress applied to the lowermost tape core is reduced and deterioration of cable characteristics is prevented) 4) Tape identification by reducing the number of tapes in one groove 5) Improvement in manufacturing (Since the grooves 24 and 26 are helical, even if the optical fiber unit 30 is manufactured first and wound around a drum, the lower core wire does not receive a large compressive stress. Therefore, the unit assembly and the large twist assembly can be performed separately, which simplifies manufacturing and equipment).

The two-groove groove 20 is also shown in FIG.
When the grooves 24 and 26 are small, there is not much problem. However, as shown in (b), when the grooves 24 and 26 become large to accommodate a large number of optical fiber ribbons 16 having a large number of cores. Then, bending directionality occurs in the optical fiber unit 30. That is, as shown in FIG.
6 is easy to bend, but hard to bend around the axis 38 in the depth direction of the groove as shown in FIG. Therefore, when the optical fiber unit 30 is drum-wound, it is not uniformly wound, and when it is formed into a large twist, it is not evenly twisted. Deteriorates. The present invention has been made in view of such a point, and an optical fiber ribbon 1 having a large number of cores is provided.
It is an object of the present invention to provide an optical fiber cable in which the transmission characteristics are hardly deteriorated even when a large number of 6 are stored.

[0007]

As illustrated in FIGS. 1 (a) SUMMARY OF THE INVENTION, the body 22 of the spiral 2 grooves grooves, notches reduce the value of geometrical moment of inertia with respect to the neutral axis 40 in the depth direction of the groove 42 is provided (claim 1). FIG.
As shown in (b), the notch 42 is provided.
In example, may be entering the tension member 46 to further center axis (請
Claim 2).

The value of the second moment of area with respect to the neutral axis 40 in the depth direction of the groove is the product of [small sectional area of the main body 22] and [square of the distance from the neutral axis 40 to the minute part]. In a groove made of a homogeneous material, it is determined by the shape of the cross section. Therefore, in order to reduce the value of the second moment of area, it is more effective to provide the notch 42 away from the neutral shaft 40. In the case of FIG. 1, as an example, a round concave notch 42 is formed between the grooves 24 and 26 at the place where the thickness of the main body 22 is the largest. The notch 42 is formed, so that the value of the second moment of area with respect to the neutral axis 40 in the depth direction of the groove in the body 22 is: The value of the second moment of area with respect to the neutral axis 44 in the width direction of the groove, Equal to or approach.

[0009]

[Operation] The bending stiffness is the product of the secondary moment of the section and the Young's modulus. Therefore, if a notch for reducing the value of the secondary moment of section is provided, the bending rigidity decreases. If the bending rigidity in the depth direction of the groove of the groove and the bending direction in the width direction of the groove become substantially equal, the directionality of the bending is lost.

[0010] As shown in FIG. 1 (b), the notch 42 of the
In addition to the above, the strength member 46 is further attached to the central axis of the main body 22.
When a tensile strength member having a large Young's modulus is arranged at the center of the unit, even if the bending rigidity in the depth direction of the groove and in the width direction of the groove is slightly increased without the tensile strength member 46, , The difference is very small or negligible
To the extent.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A in FIG. 2A is a product of the present invention. Body 22
Has an outer diameter a of 7.0 mm, a width b of the notch 42 of 2.7 mm, and a depth c of
0.75mm. The tensile member 46 is made of 2480d aramid fiber (Kevlar, trade name). Each of the grooves 24 and 26 accommodates five 16-core tape cords each having a thickness of 0.25 mm and a width of 3.00 mm to form an optical fiber unit. B and C are comparative examples, in which B has no notch 42 and C is a tensile strength member 46.
Are provided near both ends in the depth direction of the two grooves. Other conditions are the same. (B) shows the relationship between the diameter of the drum of the optical fiber unit and the transmission loss, and (c) shows the change in the loss between processes when the cable is made (both bottom tapes). Average value of fiber at both ends). In particular, C has a tensile member at both ends, so that the bending directionality is large, and the loss tends to be large when the drum is wound or assembled. On the other hand, it can be seen that the loss of the product of the present invention does not change.

[0012]

(1) The groove main body 22 is provided with a notch 42 for reducing the value of the second moment of area with respect to the neutral shaft 40 in the depth direction of the groove, or the notch 42 is provided.
In addition , since the tensile strength member 46 is further inserted in the center axis,
The directionality of bending in the groove depth direction and the groove width direction can be eliminated, and good transmission characteristics can be obtained. (2) The two-groove groove type described earlier, 1) Ease of branching for each unit, 2) Diversification of branch units, 3) Improvement of cable characteristics by reducing the number of tapes in one groove, 4) One groove The advantages such as improved tape discrimination by reducing the number of tapes inside, 5) improved manufacturing, etc. are maintained as they are.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a drum winding characteristic and a change in loss between processes together with a conventional product according to an embodiment of the present invention.

FIG. 3 is an explanatory view of a conventional groove type optical fiber cable.

FIG. 4 is an explanatory view of a two-groove groove type optical fiber cable of a comparative example.

FIG. 5 is an explanatory view of a problem of the comparative example technology.

[Explanation of symbols]

 10, 30 Optical fiber unit 12 Groove 14, 24, 26 groove 16 Optical fiber tape core wire 18, 32 Center tensile strength member 20 2-groove groove 22 Groove main body 28 Center line 34 Optical fiber cable 36, 38 Axis 40, 44 Neutral axis 42 Notch 46 Strength member

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Suehiro Miyamoto 1440, Rokkazaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd. Sakura Plant (72) Inventor Shigeru Tomita 1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Stock Corporation In-house (56) References JP-A-6-337335 (JP, A) JP-A-7-27957 (JP, A) JP-A-1-103812 (JP, U) JP-A-60-169607 (JP, U) (58) Fields surveyed (Int.Cl. ⁶ , DB name) G02B 6/44

Claims (2)

(57) [Claims] 1. An optical fiber cable having a structure in which a groove type optical fiber unit in which an optical fiber ribbon is accommodated in a groove of a groove is twisted and assembled, wherein the main body of the groove has a cylindrical shape. The groove body having two back-to-back grooves and being twisted around a central axis, wherein the groove main body is provided with a cross-sectional secondary moment relative to a neutral axis in the depth direction of the groove. Fiber optic cable with notches to reduce the value. 2. A tension member 4 to the central axis of the groove body
The optical fiber cable according to claim 1, wherein the optical fiber cable contains 6.