JPH08201668A - S-z twisted spacer type optical fiber cable - Google Patents

Abstract

PURPOSE: To obviate the occurrence of a large strain in inverting parts where grooves invert from an S direction to a Z direction and from the Z direction to the S direction even if a 4-fiber coated fiber ribbon or 8-fiber coated fiber ribbon is used by setting the twist pitch longer than the twist pitch on other parts. CONSTITUTION: This optical fiber cable is constituted by providing the outer periphery of a spacer formed around a tension member 1 with the grooves inverting alternately in the S direction and the Z direction along the longitudinal direction and housing the optical fibers in S-Z twists in these grooves. The twist pitch near the inverting parts where the grooves invert from the S direction to the Z direction and from the Z direction to the S direction is set longer than the twist pitch in the other parts. The strain generated in the coated fiber ribbons housed in the grooves of the inverting parts is made small by setting the twist pitch near the inverting parts longer than the twist pitch on the other parts according to such constitution. Namely, the strain that the optical fibers receive is made uniform over the entire part and, therefore, the breakage of the optical fibers is prevented and the life of the optical fibers is prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical fiber cable,
In particular, the present invention relates to an SZ twist spacer type optical fiber cable in which the grooves of the spacers are twisted alternately in the S and Z directions.

[0002]

2. Description of the Related Art FIG. 4 shows an SZ twist spacer used in a conventional SZ twist spacer type optical fiber cable.

This SZ twist spacer is provided with a spacer 2 made of a thermoplastic resin around a tension member 1, and a groove 3 which alternates in the S direction and the Z direction along the longitudinal direction on the outer periphery thereof. Are formed. That is, the groove 3 is
From the S-twisted groove 3S rotated 360 degrees in the S direction (S twist), that is, right twist, at the reversing portion 61, rotated 360 degrees in the Z direction (Z
Twist), that is, it is formed so as to be inverted to the left-twisted Z-twisted groove 3Z. The twist pitch of the groove is uniform over the entire area between the adjacent reversing portions. That is, the grooves 3 are uniformly formed with a twist pitch of the distance L between the adjacent inversion parts.

An optical fiber is placed in the groove of such an SZ twist spacer, and the optical fiber is held in the groove by a press winding.
What is covered with a sheath is an SZ twist spacer type optical fiber cable.

The characteristic of the SZ twist spacer type optical fiber cable is that after laying or erection, the sheath and the press winding are stripped in the middle of the cable, and the optical fiber at the inverted portion of the S twist and Z twist in the groove of the spacer is taken out. Only the necessary optical fiber can be connected to the branch cable. Like this, S
The excellent post-branching property of the Z twist spacer type optical fiber cable is expected as a joining optical cable to be realized in the future.

At present, a single fiber or a double fiber ribbon is used as the optical fiber provided in the groove of the spacer.
Considering the trend of increasing the number of optical fibers in the future, it is desired to use a 4-fiber ribbon or 8-fiber ribbon in an SZ twist spacer type optical fiber cable having an excellent post-branching property.

[0007]

However, when four or eight optical fiber cores coated with four or eight optical fibers all together are arranged in the groove of the SZ twist spacer,
As shown in FIG. 5, at the reversing portion 6 where S twist is changed to Z twist and Z twist is changed to S twist, the tape core wire 4 is largely bent in the width direction, and the optical fiber in the tape core wire 4 is greatly distorted. Therefore, it has been impossible to use a 4-fiber ribbon or 8-fiber ribbon in the conventional SZ twist spacer type optical fiber cable having a groove with a twist pitch.

For example, the outer periphery has a depth of 0.9 mm and a width of 1.4.
Outer diameter with square groove with groove pitch of 250 mm and groove pitch of 250 mm 11.
A 5 mm spacer has a diameter D = 0.1 as shown in FIG.
25 mm optical fiber 10 is coated to have an outer diameter Y = 0.
Four optical fiber core wires 11 having a size of 25 mm are arranged side by side and collectively covered, and have a width H = 1.1 mm and a thickness J = 0.4 mm.
The strain generated in the optical fiber when the core tape core wire 4 is arranged is obtained as follows.

First, the radius of curvature of the bent optical fiber 10 is obtained. The radius of curvature ρ when the optical fiber 10 is twisted at the twist pitch P is given by the following equation (1).

Ρ = a + (P / 2π) ² / a (1) ρ radius of curvature (mm) a layer core radius (distance from center to center of tape core wire) (mm) P twist pitch (mm) In the case of the spacer of 1), the core radius is 11.5 / 2- (0.9-0.4 + 0.4 / 2) = 5.
05 a = 5.05 mm, and the groove pitch P = 250 mm.
It will be 8 mm.

In the reversing part 6, since the tape core wire 4 is bent in the width direction, the center of the 4-core tape core wire 4 in the width direction is bent with the neutral axis 5 at R = 318 mm as shown in FIG. Is equivalent to that. That is, the outermost optical fiber of the four-core tape is w = 0.4375 from the neutral axis 5.
Since they are separated by mm, the strain to be received is 0.4375 / 318 × 100 = 0.138% and 0.138%.

Since the four-core tape is bent in the thickness direction except at the inversion portion, the surface of the optical fiber is most distorted in this case. If the center of the thickness of the four-core tape is the neutral axis, the surface of the optical fiber of the four-core tape is X = 0.0625 mm away from the neutral axis, and therefore 0.0625 / 318 × 100 = 0.02. % 0.02% distortion occurs.

From the above, it can be seen that a particularly large strain occurs in the reversal portion due to bending in the tape width direction.

In order to alleviate this distortion, a method of lengthening the groove pitch can be mentioned. However, if the groove pitch is lengthened, when the cable is laid and then branched, the tape core wire take-out property becomes poor. That is, the effective length inside the connection closure currently used for taking out the tape core wire is 500 mm to 600 mm, and at least one S-twisted or Z-twisted inversion portion is included in the length. In order to ensure that the average twist pitch of the grooves between the reversals is half the effective length of the closure, 250 mm to 300 mm.
Must be: Therefore, the average twist pitch cannot be easily lengthened.

There is also a method of reducing the outer diameter of the spacer, but this method cannot be adopted because of structural limitations.

Therefore, an object of the present invention is to solve the above-mentioned problems, and even if a four-core tape core wire or an eight-core tape core wire is used without increasing the average twisting pitch between the inversion parts, a large amount is generated in the inversion part. An object is to provide an SZ twist spacer type optical fiber cable that does not cause distortion.

[0017]

In order to achieve the above object, the invention of claim 1 is a groove which is alternately inverted in the S direction and the Z direction along the longitudinal direction on the outer periphery of a spacer provided around a tension member. In the optical fiber cable in which the optical fiber is arranged in the groove and accommodated in the SZ twist, the twist pitch in the vicinity of the inversion part where the groove is inverted from the S direction to the Z direction and from the Z direction to the S direction is The SZ twist spacer type optical fiber cable is characterized in that it is made longer than other portions.

According to a second aspect of the present invention, the section in which the twist pitch of the groove of the spacer is lengthened is within a range of 90 ° or less from the reversal portion in the circumferential direction of the spacer. It is a spacer type optical fiber cable.

According to the invention of claim 3, the average twist pitch between adjacent reversal parts is 300 mm or less.
It is a Z twist spacer type optical fiber cable.

[0020]

According to the above construction, the twist pitch in the vicinity of the reversal portion is made longer than that in the other portions, whereby the strain generated in the tape core wire accommodated in the groove of the reversal portion can be reduced.

[0021]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows the SZ twist spacer of the present invention.
A spacer 2 composed of a thermoplastic resin such as polyethylene having an outer diameter of 11.5 mm is provided around the tension member 1, and the outer periphery of the spacer 2 is directed in the S direction while extending in the longitudinal direction.
A groove 3 was provided which was rotated once and was inverted and then alternately inverted in the Z direction by 360 °. The groove pitch of the groove 3 is the same as that of the inversion parts 61, 6
2 to 350 m in the circumferential direction of spacer 2 ± 90 °
m, the other section is 150 mm, and the shape of the groove 3 is a square groove having a depth of 0.9 mm and a width of 1.4 mm.

The solid line shows the groove 3 visible on the front side of the drawing, and the dotted line shows the groove 3 on the back side of the drawing.

FIG. 2 is a schematic view showing the groove pitch of the spacer shown in FIG.

The reversal portions 61 and 62 appear every time the groove 3 rotates 360 °, and the reversal portion 61 from S twist to Z twist or the reversal portion 62 from Z twist to S twist is 9 in the circumferential direction of the spacer.
The twist pitch in the section N from the point a to the point b and the point c to the point d below 0 ° is 350 mm, and the groove pitch in the section K from the point b to the point c is 150 mm.

Here, the average twist pitch between the adjacent inversion parts 61 and 62 is obtained. The distance between the inverting portion 61 and the point b and between the point c and the inverting portion 62 is 1
Since it is rotated by 80 degrees, it is 175 mm, and the distance between the points bc is 150 mm because the twist pitch is 150 mm, and since it is rotated by 180 degrees, it is 75 mm.
The distance M between 1 and 62 is 175 + 75 = 250 mm, so the average twist pitch is 250 mm, which is the same as the conventional groove pitch.

As described above, the groove pitch in the section N is longer than the average, and the groove pitch in the section K is shorter than the average.

Next, the operation of the embodiment will be described.

In the groove of the spacer, the diameter D =
The outer diameter Y is obtained by applying a coating to the 0.125 mm optical fiber 10.
= 4 mm, the four optical fiber core wires 11 arranged side by side are collectively covered, and the width H = 1.1 mm and the thickness J = 0.4 m.
The strain generated in the optical fiber when the 4-core tape core wire 4 of m is arranged is obtained.

When the groove pitch is 350 mm and 150 mm, the radii of curvature are 619 mm and 118 according to the above-mentioned formula (1).
mm.

At the reversing portion, since the 4-core tape is bent in the width direction, it is equivalent to bending the center of the 4-core tape in the width direction at a neutral axis of R = 619 mm, which is the outermost side of the 4-core tape. The optical fiber located at the position has a strain of 0.4375 / 619 × 100 = 0.0706%.

Further, since the 4-core tape is bent in the thickness direction except at the inversion portion, it is equivalent to bending at R = 118 mm with the center of the 4-core tape in the thickness direction as the neutral axis. The surface of the optical fiber of the core tape is most distorted, and its value is 0.0625 / 118 × 100 = 0.0529%.

From the above, by increasing the groove pitch in the vicinity of the inversion portion, the strain applied to the four-core tape is about 0.07.
% And the strain when the groove pitch is made uniform (0.1
38%).

Further, since the twist pitch is made small except for the inversion portion, the strain (0.0
2%), the strain received was larger, but the strain was about 0.05%, which was slightly smaller than the strain at the inversion part. That is, it is possible to make the strain received throughout the optical fiber uniform and suppress the absolute value.

Although the spacer of FIG. 1 has only one groove,
When the spacer of the present invention is actually used as an SZ twist spacer type optical fiber cable, a plurality of grooves are provided, an optical fiber such as a multi-core tape core wire is arranged in each groove, press-wrapping is performed, and a polyethylene sheath is covered. Then, a moisture-proof jelly is pressed into the gap between the cable cores.

For example, as a spacer having a plurality of grooves, six grooves are provided at every 60 degrees from the center of the spacer.
A core tape core wire can also be arranged in each groove.

[0037]

In summary, according to the present invention, even when a multi-core tape such as a 4-core or 8-core tape is used, the strain generated in the vicinity of the inversion portion is suppressed to be small, and the strain received by the optical fiber is uniform throughout. Therefore, it is possible to prevent breakage of the optical fiber and extend the life of the optical fiber.

[Brief description of drawings]

FIG. 1 is a diagram showing an SZ twist spacer of the present invention.

FIG. 2 is a schematic diagram showing the groove pitch of the grooves in FIG.

[Fig. 3] R = with the center in the width direction of the 4-fiber tape as the neutral axis
It is a figure which shows the state bent by 318 mm.

FIG. 4 is a diagram showing a conventional SZ twist spacer.

5 is a diagram showing a state in which a multi-core tape core wire is arranged on the spacer of FIG.

FIG. 6 is a structural diagram of a 4-fiber ribbon.

[Explanation of symbols]

 1 Tension member 2 Spacer 3 Grooves 61, 62 Inversion section

Claims (3)

[Claims] 1. A spacer provided around a tension member is provided with a groove which is alternately inverted in the S direction and the Z direction along the longitudinal direction on the outer circumference of the spacer, and the optical fiber is arranged in the SZ twist and accommodated in the groove. In the optical fiber cable, the SZ twist spacer type optical fiber is characterized in that a twist pitch in the vicinity of a reversal portion where the groove is reversed from the S direction to the Z direction and from the Z direction to the S direction is longer than other portions. cable. 2. The SZ twist spacer type optical fiber cable according to claim 1, wherein a section in which the twist pitch of the groove of the spacer is lengthened is within a range of 90 ° or less from the inversion portion in the circumferential direction of the spacer. . 3. The average twist pitch between adjacent reversals is 3
The SZ twist spacer type optical fiber cable according to claim 1, which has a length of 00 mm or less.