JP2970890B2 - 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 square groove type optical fiber cable capable of mounting optical fiber cores at high density.

[0002]

2. Description of the Related Art FIG. Reference numeral 10 denotes an optical fiber unit, which is a unit in which a tape core 20 is accommodated in a square groove 12 described below. Corner groove 12
Is made of a long body of a channel-like plastic (for example, polyethylene) having a U-shaped cross section, and has a square groove 14. In addition, it has flexibility to enable twisting and assembling. The tape core 20 is formed by arranging, for example, about 8 to 16 optical fibers 22 in a horizontal line and applying a common coating 24 thereon. This tape core 20 is, for example, 10
Approximately one sheet is stored in the groove 14 in an overlapping manner. Therefore, one optical fiber unit 10 has about 80 to 160 cores. A large number of the above optical fiber units 10 are twisted together in a layer around the tension member 30. At this time, the opening side 16 of the corner groove 12 is on the outside and the bottom 1
8 is inside. Reference numeral 32 denotes a presser winding, and reference numeral 34 denotes a sheath.

[0003]

When a cable is bent, bending strain (tensile strain and compression strain) is generated in the optical fibers outside and inside the bend. This strain must be small from the viewpoint of the life of the optical fiber, and is generally set to 0.2% or less.

[0004]

When a cable is bent with a minimum allowable bending radius, a pulling force F at a half pitch of the square groove is made smaller than a maximum tensile load acting on the square groove.

[Drawing Force] FIG. 1A schematically shows a square groove type optical fiber cable. This cable is connected to the twist pitch p of the groove 12 by 1 /.
It is cut into two lengths, and a tensile load F is applied to one groove 12. While F is small, the glue 12 does not move. F
Is gradually increased, the groove 12 moves at a certain value, and is pulled out. F when this movement started
Is the pulling force. The value of F changes depending on the presser winding tension of the presser winding 32, the material of the presser winding 32, the material of the square groove 12, and the like.

[Reason for Half Pitch] FIG. 2 schematically shows a state in which one square groove 12 is spirally wound around the center tension member 30. When this is subjected to bending, a tensile stress is generated outside the neutral surface 40, for example, near P, and a compressive stress is generated near Q. When the angle grease 12 can move freely in the axial direction, the angle grease 12
Moves in the direction of the arrow to relax the stress. The movement of the corner groove 12 is performed within a range of 1/2 pitch. Therefore, it is sufficient to consider a square groove having a half pitch.

[About the maximum tensile load] FIG.
As in the case of FIG. 2 described above, a model in which a single square groove 12 is spirally wound around the center tension member 30 is shown. Assuming that when this is bent, the angular groom 12 is deformed integrally (without moving in the longitudinal direction) with the central tension member 30, as described above, the maximum near the point P farthest from the neutral surface 40 is reached. Tensile stress occurs, Q
Near the maximum compressive stress occurs. The magnitudes of the tensile stress and the compressive stress are equal. Assuming that the Young's modulus of the angular groove 12 is E, the cross-sectional area is A, the layer core radius is r, and the bending radius of the center tension member 30 is R, the magnitude of the total tensile stress generated at P is EA (r / R). Become. Since the total stress is equal to the load, the term tensile load has been used in the claims.

[Regarding the Movement of the Corner Glue 12] Since the pulling force F is a force capable of moving the corner gutter 12 in the cable, if F <EA (r / R),
When the cable is bent, the square grease 12 can move due to the total stress (= load) generated in the square gutter 12. Therefore, stress is relieved.

[Stress of Optical Fiber] If the angled groove 12 is deformed integrally with the center tension member 30 when the cable is bent as described above, a stress is generated by receiving the above tensile load. However, a similar stress may occur in the optical fiber tape in the corner groove 12. If the stress is not removed, residual strain is generated in the optical fiber as described above, and there is a possibility that the optical fiber will be broken by long-term use.

In order to prevent the residual distortion from occurring, two types of distortions are required: 1) the optical fiber tape moves within the angular groove 12; and 2) the angular groove 12 containing the optical fiber tape moves. There is a mitigation mechanism. The present invention provides the mechanism of 2).

[0011]

EXAMPLES corner Gurugu 12 is a dimension shown in FIG. 3, the cross-sectional area A 9.5 mm ^2, the Young's modulus E is 25 kgf / mm ^2. Ten pieces of the tape core wires 20 having a thickness of 0.2 mm and a width of 3.0 mm are laminated in the square groove 12, and the square groove 12 is formed with an acrylic adhesive.
After that, the cable was twisted with a center tension member 30 having a diameter of 10 mm at a pitch of 700 mm, and presser windings 32 and 34 were applied to obtain a cable. Further, the winding tension of the presser winding 32 was changed so that the pulling force F was different. Using this cable, the relationship between the pulling force F and the bending strain when bent at R = 200 mm was investigated, and shown in Table 1.

[0012]

[Table 1]

As can be seen from Table 1, when the pulling force per half pitch is smaller than AE (r / R), the bending strain of the optical fiber is at a level that hardly causes a problem.

[0014]

The pull-out force of a half pitch of the square groove is
When the cable was bent with the minimum allowable bending radius, it was smaller than the maximum tensile load acting on the square groove,
When the cable is temporarily bent with a bend radius smaller than the allowable radius, the total stress (= load) generated in the angular grease 12 allows the angular grease 12 to move.
Therefore, stress is relieved, there is no residual strain, and there is no possibility that the optical fiber will be broken by long-term use.

[Brief description of the drawings]

FIG. 1 (a) is an explanatory view of a pulling force in the present invention,
(B) is an explanatory view of a load acting on the square gutter 12 due to bending of the cable.

FIG. 2 is an explanatory view of a reason for taking a half-pitch pull-out force in the present invention.

FIG. 3 is a dimensional view of a corner grease 12 according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical fiber unit 12 Square groove 14 Groove 16 Opening side 18 Bottom 20 Tape core wire 22 Optical fiber 24 Coating 30 Center tension member 32 Presser winding 34 Sheath 40 Neutral surface

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kiyoshi Sakuma 1440, Rokkazaki, Sakura City, Chiba Prefecture Inside the Sakura Plant Fujikura Electric Wire Co., Ltd. (72) Inventor Suehiro Miyamoto 1440, Misaki, Sakura City, Chiba Prefecture Fujikura Electric Wire & Cable Company Sakura Plant (72) Inventor Hideo Suzuki 1440 Mutsuzaki, Sakura-shi, Chiba Prefecture Fujikura Electric Cable Co., Ltd.Sakura Plant (72) Inventor Shigeru Tomita 1-6-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-54-15542 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6/44

Claims (1)

(57) [Claims] 1. A plurality of optical fiber units having a structure in which an optical fiber ribbon is accommodated in a groove of a channel-shaped square groove, around a central tension member, with the opening side of the square groove being outside. An optical fiber cable, wherein when the cable is bent with a minimum allowable bending radius, a pulling force at a half pitch of the angular groove is smaller than a maximum tensile load acting on the angular groove. cable.