JPH09230182A - Spacer type optical fiber cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate the occurrence of excessive bending strains in the optical fibers housed in the grooves of a spacer even if a cable is bent by respectively specifying the relation between the outside diameter of the cable and the winding pitch of the grooves and the radius of curvature of the optical fibers determined by the pitch of the grooves and the diameter of a layer center diameter. SOLUTION: The cable outside diameter of the cable 1 is defined as D(mm), the winding pitch of the grooves 6 as P(mm), the layer core diameter which is the distance from the center O1 of the spacer 2 to the center O2 of the optical fibers 8 housed in the grooves 6 as A(mm) and the radius of curvature of the optical fibers 8 determined by the winding pitch P of the grooves 6 and the layer core diameter A as R(mm). At this time, the values defined above are so set that the conditions of R>=1400 and P<=40πD are both satisfied. The radius R of curvature of the optical fibers 8 in the state that the optical fibers are housed in the grooves 6 is given by R=A+(P/2π)<2> /A. As a result, the optical fibers 8 housed in the grooves of the spacer 2 are kept free from the excess bending strains even if the cable 1 is bent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spacer type optical fiber cable capable of easily branching an optical fiber on the way.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a spacer type optical fiber cable.

This spacer type optical fiber cable (hereinafter, simply referred to as a cable) 1 is provided with a spacer 2 made of polyethylene resin or the like, and a tension member 4 made of FRP, steel wire or the like is provided at the center of the spacer 2. Grooves 6 which are embedded and have a U-shaped cross section are formed at a plurality of locations (8 locations in this example) on the outer peripheral portion of the spacer 2, and the optical fibers 8 are housed in the respective grooves 6. These optical fibers 8 are formed by sequentially forming a buffer layer 12 such as an ultraviolet resin and an outer coat layer 14 made of nylon or foamed polyethylene on a fiber element wire 10. A press winding layer 16 made of polyethylene tape or the like is wound around the outer periphery of the spacer 2 in a state of closing each groove 6, and a protective sheath made of polyethylene resin, polyvinyl chloride resin, or the like is further provided thereon. 18 is provided. Each groove 6 for accommodating the above-mentioned optical fiber 8 extends along the axial direction of the spacer 2 and is spirally formed at a predetermined pitch P along the peripheral surface of the spacer 2. That is, now
When focusing on one groove 6, as shown in FIG. 2, the groove 6 is formed at a constant winding pitch P so as to form a right-handed (or left-handed) spiral shape along the peripheral surface of the spacer 2. Has been done.

If each groove 6 is formed in a spiral shape and the optical fiber 8 is housed therein, the groove 6 is formed linearly along the axial direction of the spacer 2 and the inside of the groove is formed. As compared with the case where the optical fiber 8 is housed in the optical fiber 8, since a large extra length is secured per unit length of the cable 1, even if the cable 1 is bent as a whole, the bending strain generated in the optical fiber 8 It has the advantage of being reduced.

Now, in the case of branching from the cable 1 which has been previously crossed in the form as shown in FIG. 3 and performing the subscriber wiring of the optical fiber to the one building 22 between the electric poles 20a and 20b, conventionally In this construction method, the corresponding core wire in the cable 1 and the drop cable 8 for pulling down at the closure 24b
It was connected to the optical fiber inside.

However, this construction method has a problem in that connection is required at a withdrawal point, line loss is increased due to connection loss, and expensive connecting equipment such as a fusion splicer is required.

In order to solve this problem, the following construction method can be considered.

First, at the portion of the closure 24a attached to one of the utility poles 20a, the protective sheath 1 of the cable 1 is
After removing 6 and the press winding layer 14 to expose the groove 6, the required optical fiber 8 housed in the exposed groove 6 is cut.

Next, in the portion of the closure 24b attached to the other electric pole 20b, the protective sheath 16 and the press winding layer 14 of the cable 1 are similarly removed to expose the groove 6, and then the groove 6 is housed in the exposed groove 6. Among the optical fibers 8 that have been cut, one of the optical fibers 8 that has already been cut is pulled out by the closure 24a.

The optical fiber thus drawn out is connected to a filament previously inserted in the drop cable 8 having a hollow structure and drawn in, or sent by a method such as pneumatic feeding, or protected by another method. While being guided to the building 22, it is connected to an indoor wiring (not shown) using a connector or the like.

[0011]

[Problems to be Solved by the Invention] When this method is adopted,
When the groove 6 formed in the spacer 2 has a spiral shape, even if the cable 1 is bent in its entirety, there is an advantage that the bending strain generated in the optical fiber 8 is reduced. When the optical fiber 8 housed in the groove 6 is pulled out in order to branch 8, the groove 6 having a spiral shape has a larger frictional resistance than that in the case of a straight shape, and an excessive pulling force. Is required.

However, in the prior art, in the cable 1 having the structure shown in FIGS. 1 and 2, when the optical fiber 8 is drawn out, the drawing length L (in the example of FIG. 3, the utility pole 20a,
The relationship between the distance between 20b) and the winding pitch P of the groove 6 and the pulling force has not been sufficiently studied.

Therefore, the drawing length L of the optical fiber 8
Is relatively short, the frictional resistance in the groove 6 is also small,
The optical fiber 8 can be pulled out from the cable 1 relatively easily, but when the pull-out length L of the optical fiber 8 becomes long, the friction resistance in the groove 6 becomes large,
There has been a problem that the tensile force applied to the optical fiber 8 exceeds the allowable range.

The present invention has been made in order to solve the above-mentioned problems, so that even if the cable is bent, an extra bending strain does not occur in the optical fiber housed in the groove of the spacer. At the same time, it is an object of the present invention to easily pull out the optical fiber with a pulling force equal to or less than an allowable range when pulling out the optical fiber for branch connection.

[0015]

In order to achieve the above object, the present invention provides a plurality of grooves on the outer peripheral portion of a spacer, each groove extending along the axial direction of the spacer. A spacer type optical fiber cable, which is formed in a spiral shape at a predetermined pitch along the peripheral surface of the spacer and has an optical fiber housed in each of these grooves, employs the following configuration.

That is, in this cable, the outer diameter of the cable is D (mm), the winding pitch of the groove is P (mm), and the layer core diameter is the distance from the center of the spacer to the center of the optical fiber housed in the groove. Is A (mm) and the radius of curvature of the optical fiber determined by the groove pitch P and the layer core diameter A is R (mm),
Are set so that R ≧ 1400 and P ≦ 40πD are both satisfied.

[0017]

The basic structure of the spacer type optical fiber cable in this embodiment is the same as that shown in FIG. 1, but the outer diameter of the cable 1 and the shape of the groove 6 of the spacer 2 are different. It is characterized in that it is preset to satisfy the following conditions.

That is, in this cable 1, the outer diameter of the cable is D (mm), the winding pitch of the groove 6 is P (mm), and the spacer 2 is
Of the optical fiber 8 determined by the winding pitch P of the groove 6 and the layer diameter A, where A is the distance from the center O ₁ of the groove 6 to the center O ₂ of the optical fiber 8 housed in the groove 6. Radius of curvature of R
(mm), the following conditions, R ≧ 1400 P ≦ 40πD, are both satisfied. However, groove 6
The radius of curvature R (see FIG. 2) of the optical fiber 8 stored inside is given by the following equation.

R = A + (P / 2π) ² / A Next, the reason why the condition of, is required will be described.

Regarding the condition (a), considering the optical fiber 8 having an outer diameter of about 0.7 mm,
When pulling out the optical fiber 8 from the cable 1, the tensile force applied to the optical fiber 8 must be 100 g · f or less in order to prevent distortion of 0.1% or more in the optical fiber 8. is there. Moreover, since the average length between the electric poles 20a and 20b as shown in FIG. 3 is about 35 m, the drawable length L of the optical fiber 8 is 3
It is necessary to secure at least 5 m.

Therefore, the outer diameter of the optical fiber 8 housed in the groove 6 is 0.7 mm, the outer diameter D of the cable 1 is 14 mm,
The layer core diameter A is set to 4.5 mm, the tensile force of the optical fiber 8 is set to 100 g · f, and in this case, the winding pitch P of the groove 6 is P = 250, 300, 400, 500, respectively.
Radius of curvature R of optical fiber 8 when changed to 600 mm
(mm) and pullable length (m) were examined. Table 1 shows the results.

[0022]

[Table 1]

As can be seen from the results in Table 1, the pulling force of the optical fiber 8 can be 35 m or more when the pulling force is 100 g · f when the radius of curvature R is 1400 mm or more. That is, it is necessary to satisfy the condition: R ≧ 1400 (mm).

Regarding Condition (b) In general, from the viewpoint of long-term reliability of the protective sheath 16 of the cable 1, as shown in FIG. 4, the allowable bending radius r of the cable 1 is 10 times the outer diameter D of the cable 1. Double, that is r = 10
Often referred to as D.

Assuming that the cable 1 is wound around the drum 24 having the same diameter as the allowable bending radius r for one round, the groove is longer than the length (2πr) of the wound cable 1 for one round. Half the winding pitch P of 6
When (= P / 2) is longer (P / 2> 2πr), in the worst case, one round of the cable 1 is always outside the optical fiber 8 than the center line of the cable 1 (shown by a chain line in the figure). (Or always inside) the optical fiber 8
Tensile strain (or compressive strain) is constantly applied to, which adversely affects the fracture life.

Therefore, in order to reduce the influence of the strain applied to the optical fiber 8, it is necessary to set P / 2 ≦ 2πr = 2π (10D). That is, the condition of: P ≦ 40πD
Needs to be satisfied.

After all, in order to pull out the optical fiber 8 with a pulling force below the allowable range without causing an excessive bending strain in the optical fiber 8 housed in the groove 6,
Both conditions must be met.

When the outer diameter D of the cable 1 is 14 mm as described above, the winding pitch P (mm) of the groove 6 for satisfying the condition is P ≦ 40π × 14 = 1758.4. In the above cable 1, the winding pitch P required to satisfy both conditions of, is 500 mm ≦ P ≦ 17
It should be 00 mm.

In the above embodiment, the grooves 6 are formed at eight locations on the outer peripheral portion of the spacer 2, but the number of the grooves 6 is not limited to this example. The values of the outer diameter D of the cable 1 and the outer diameter of the optical fiber 8 (hence the layer core diameter A) are not limited to those in this example.

[0030]

According to the present invention, the following effects can be obtained.

(1) Even if the cable is bent, no extra bending strain occurs in the optical fiber housed in the groove of the spacer. Moreover, when pulling out the optical fiber for branch connection, it is possible to easily pull out the optical fiber with a pulling force equal to or less than the allowable range, and it is possible to prevent damage to the optical fiber.

(2) Since the optical fiber thus drawn out from the cable can be drawn into the building as it is and connected to the indoor wiring, the number of connection points can be reduced and the branch connection work can be facilitated. Become.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a spacer type optical fiber cable.

FIG. 2 is a diagram schematically showing the shape of a groove formed on the outer periphery of a spacer.

FIG. 3 is an explanatory diagram of a laid state of a spacer type optical fiber cable.

FIG. 4 is an explanatory diagram showing a state in which an optical fiber cable is wound around a drum.

[Explanation of symbols]

1 ... Spacer type optical fiber cable, 2 ... Spacer, 4
... tension member, 6 ... groove, 8 ... optical fiber, D ... outer diameter of optical fiber cable, P ... groove winding pitch, A ... layer core diameter, R ... radius of curvature of optical fiber in groove.

Front page continued (72) Inventor Haruo Oizumi 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Koji Tsuji 4-3 Ikejiri, Itami City, Hyogo Mitsubishi Cable Industries Itami Co., Ltd. Inside the factory

Claims (1)

[Claims] 1. A plurality of grooves are provided on an outer peripheral portion of the spacer, and each of the grooves extends in the axial direction of the spacer and is formed in a spiral shape at a predetermined pitch along the peripheral surface of the spacer. In a spacer type optical fiber cable in which an optical fiber is housed in each of these grooves, the cable outer diameter is D (mm), the groove winding pitch is P (mm), and the light stored in the groove from the center of the spacer The core diameter, which is the distance to the center of the fiber, is A (mm), the groove pitch P and the core diameter A.
When the radius of curvature of the optical fiber determined by is R (mm),
The spacer type optical fiber cable is set such that the following conditions, R ≧ 1400 and P ≦ 40πD are both satisfied.