JPH09178991A - Optical fiber cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the transmission loss increase of optical fiber by setting the inverting angle of SZ groove of spacer with groove into specified value and housing a tapered optical fiber core into the groove in a specified state. SOLUTION: An optical fiber cable is provided with a spacer 11 with groove having an SZ helical groove 13, whose helical direction is cyclically inverted, around the outer periphery. At a central part between the inverted parts of groove 13, a tapered optical fiber core 17 is housed in the groove 13 while turning the tapered surface toward the bottom of the groove. At the inverted part of the groove 13, the core 17 is housed in the groove 13 while turning the tapered side edge toward the bottom of the groove. The inverting angle of the groove 13 is set larger than 180 deg.. The width and depth of the groove 13 are set into certain dimensions so that the laminated body of core 17 can be rotated inside the groove 13. Opening part width W2 , of the groove 13 at the inverted part is formed narrower than an opening part W1 of the groove 13 at the central part between the inverted parts. The depth of the groove 13 is fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable in which a tape-shaped optical fiber core is accommodated in a groove of a grooved spacer having an SZ spiral groove whose spiral direction is periodically reversed on the outer periphery. Things.

[0002]

2. Description of the Related Art An optical fiber cable in which an SZ spiral groove is formed on the outer periphery and an optical fiber core wire is housed in the groove is used for connection and terminal processing.
There is an advantage that it is easy to take out the optical fiber from the groove. This type of cable uses a tape-shaped optical fiber core as the optical fiber core.Conventionally, multiple tape-shaped optical fiber cores are stacked in the depth direction of the groove and stored in the groove. (Japanese Unexamined Patent Publication No. 2-83)
No. 507) and a device laminated in the width direction of the groove and housed in the groove (Japanese Patent Application Laid-Open No. 4-55803) are known.

[0003]

A tape-shaped optical fiber core is formed by arranging a plurality of optical fibers in parallel on the same plane and applying a common coating to form a tape. For this reason, each optical fiber bends uniformly in the direction of bending the tape surface, and almost no increase in transmission loss occurs,
When bending in the direction of bending the tape side edge (edgewise bending) in the tape surface, distortion occurs in the compression direction in the optical fiber on the inner side of the bend, and the optical fiber on the outer side of the bend in the tape. Causes strain in the tensile direction, causing a large increase in transmission loss.

In a conventional optical fiber cable, a plurality of tape-shaped optical fiber cores are housed in an SZ spiral groove of a grooved spacer in a state of being laminated in a certain direction with respect to the direction of the groove. Therefore, there is a portion where each tape-shaped optical fiber is necessarily bent in the direction of bending the side edge of the tape. For example, in a cable in which a plurality of tape-shaped optical fiber cores are stacked in the depth direction of the groove, each tape-shaped optical fiber core mainly has a tape side edge at a reversal part of the groove (a part where the spiral direction is reversed). Subject to bending in the direction of bending. In a cable in which a plurality of tape-shaped optical fibers are laminated in the width direction of the groove, the tape side edge is mainly located at an intermediate portion between the inverted portions of the groove (between one inverted portion and the next inverted portion). Is subjected to bending in the direction of bending.

As described above, the optical fiber cable of the type in which the grooved spacer having the SZ spiral groove is used and the tape-shaped optical fiber is accommodated in the groove is inevitably impossible with the tape-shaped optical fiber. Bending stress is applied,
In addition to the increase in transmission loss of the optical fiber, there is also a problem in terms of long-term reliability, and it has been said that practical use is difficult.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an optical fiber cable of a type in which a tape-shaped optical fiber core is accommodated in an SZ groove of a grooved spacer, and the transmission loss of the optical fiber is sufficiently reduced. To provide a cable structure that can be used.

[0007]

In order to achieve this object, the present invention provides a grooved spacer having an SZ spiral groove in which the spiral direction is periodically reversed on the outer periphery, and a grooved spacer having the groove formed in the grooved spacer. In an optical fiber cable provided with a stored tape-shaped optical fiber core wire, the reversal angle of the groove of the grooved spacer (rotational angle in the circumferential direction of the grooved spacer from one reversal part of the groove to the next reversal part) θ Is greater than 180 °, and the tape-shaped optical fiber has the tape surface directed to the groove bottom at the central portion between the inversion portions of the groove (the central portion between one inversion portion of the groove and the next inversion portion). In the reversing part of the groove, assuming that the tape surface is stored in the groove with the groove bottom facing, with the side edge of the tape located inside the bend of the groove of the reversing part facing the groove bottom, The groove opening of the grooved spacer is housed in the groove The width of the portion is narrower in the inverted portion than in the central portion between the inverted portions.

The direction of the SZ spiral type groove (the direction of the opening) of the grooved spacer constantly changes in the longitudinal direction of the grooved spacer. In the cable of the present invention, the direction of the tape-shaped optical fiber core with respect to the direction of the groove changes in the groove. In other words, the tape-shaped optical fiber core wire has the tape surface facing the groove bottom at the center between the inverted portions of the groove, but at the inverted portion of the groove, when the tape is stored in the groove with the tape surface facing the groove bottom. The orientation in the groove changes such that the side edge of the tape that is on the inside of the bend faces the groove bottom (the tape stands in the groove).

When the orientation in the groove is changed in this way, the tape-shaped optical fiber core is bent mainly in the direction in which the tape surface is curved at the central portion between the reversing portions of the groove and also at the reversing portion of the groove. Therefore, the bending in the direction of bending the side edge of the tape is hardly applied. Also, the twist applied to the tape-shaped optical fiber core is reduced. For this reason, the increase in the transmission loss of the optical fiber in the optical fiber ribbon is extremely small.

When the tape-shaped optical fiber core is housed in the SZ spiral groove of the grooved spacer as described above,
The side edges of the tape-shaped optical fiber core are most likely to be subjected to lateral pressure at the groove reversal portion, but if the groove opening width is made narrow at the groove reversal portion, the sheath groove at the groove reversal portion is The influence of deformation due to the drop in pressure or external pressure is reduced, and the lateral pressure applied to the tape-shaped optical fiber core wire can be reduced.

The opening width of the groove of the grooved spacer is preferably set so that the inverted portion is the narrowest as compared with the portion other than the inverted portion. More preferably, the opening width of the groove of the grooved spacer is, when comparing the opening widths at any two positions from the central portion between the reversing portions to the reversing portion,
It is preferable that the inversion portion side is always narrower than the central portion side between the inversion portions.

In order to reduce the lateral pressure applied to the tape-shaped optical fiber core at the groove reversal portion, the groove opening width is narrowed at the groove reversal portion, and the groove depth is reduced at the groove reversal portion. Deepening is effective. In this case, it is preferable that the depth of the groove is such that the inverted portion is deepest than the portion other than the inverted portion. More preferably, the depth of the groove is always closer to the inversion portion side than to the inversion portion central portion side when comparing the depths at arbitrary two points between the inversion portion central portion and the inversion portion. It should be deep.

The reversal angle of the groove is set to be larger than 180 ° because the tape-shaped optical fiber core wire is oriented from the state where the tape surface faces the groove bottom at the central portion between the reversal parts of the groove and the reversal part of the groove. A rotation angle of at least 90 ° is required to change the direction of the tape until the side edge of the tape faces the groove bottom, which requires a reversal angle of the groove to be greater than 180 °. Is.

On the other hand, when the reversal angle of the groove is 360 ° or more, the ease of taking out the tape-shaped optical fiber core wire from the groove is impaired. Considering the ease of taking out the tape-shaped optical fiber from the groove, it is preferable that the reversal angle of the groove is 360 ° or less. Therefore, the reversal angle of the groove is usually selected within a range of more than 180 ° and 360 ° or less. A preferable range of the inversion angle of the groove is 210 ° to 330 °, and a more preferable range is 270 ° to 300 °.

The width / thickness of the tape-shaped optical fiber core increases as the number of cores of the optical fiber increases, and the adverse effect of bending in the direction of bending the side edge of the tape increases. It is particularly effective when using a tape-shaped optical fiber core having four or more cores having a relatively large size.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIGS. 1 to 4 show an embodiment of the present invention. As shown in FIG. 1, this optical fiber cable has an SZ spiral groove 1 in which the spiral direction is periodically reversed on the outer circumference.
3 and has a tension member 15 such as steel stranded wire at the center
It is provided with a grooved spacer 11 having. A plurality of tape-shaped optical fiber core wires 17 are stored in the groove 13 of the grooved spacer 11 in a laminated state, and a press winding 19 and a sheath 21 are provided on the outer periphery of the grooved spacer 11.

Although FIG. 1 shows the case where the number of the grooves 13 is four, the number of the grooves 13 may be any number. Further, although FIG. 1 shows the case where the tape-shaped optical fiber core wire 17 is housed in only one groove 13 for the sake of easy understanding of the explanation, even if the tape-shaped optical fiber core wire 17 is housed in all the grooves 13, Alternatively, it may be housed in some of the grooves 13. FIG. 2A shows a cross section of the grooved spacer 11, and FIG. 2B shows a grooved spacer 11.
The side surface of is schematically shown. Reference numeral 13 'denotes one SZ spiral groove 13 accommodating the tape-shaped optical fiber core wire 17 in FIG.
It is a locus of. 3 (a) to 3 (k) are shown in FIG.
It is sectional drawing in the aa line-kk line of (B).

In FIG. 3, one of the three tape-shaped optical fiber core wires 17 housed in the groove 13 and one of the two outer-side tape-shaped optical fiber core wires 17 are used to identify the orientation. Are marked with ○ and ×.

As shown in FIG. 2B, the groove 13 is formed on the outer periphery of the grooved spacer 11 so that the spiral direction is periodically inverted. Reference numeral 23 denotes a spirally inverted portion of the groove 13, 25 denotes a central portion between the inverted portions of the groove 13 (a central portion between one inverted portion 23 and the next inverted portion 23 of the groove 13), P
Is the inversion pitch of the groove 13 (the central axis line distance of the grooved spacer 11 from one inversion part 23 to the next inversion part 23). Further, in FIG. 2A, θ is the reversal angle of the groove 13 (the rotation angle in the circumferential direction of the grooved spacer from one reversing portion 23 of the groove 13 to the next reversing portion 23). In this example, θ = 300 °. In FIG. 3, only one inversion pitch from (a) to (k) is shown, but in the subsequent one inversion pitch, the states from (k) to (a) are reversed, and this is repeated thereafter. It will be.

At the central portion 25 between the reversal portions of the groove 13, as shown in FIG.
As shown in (f), the tape-shaped optical fiber core wire 17 is housed in the groove 13 with the tape surface facing the groove bottom, and at the reversing portion 23 of the groove 13, as shown in FIGS. As shown in the figure, the tape-shaped optical fiber core wire 17 has the side edge of the tape facing the groove bottom (the tape stands in the groove).
It is stored in. However, in FIG. 3A and FIG.
The direction of the tape-shaped optical fiber core wire 17 is opposite to the direction of 3. That is, in FIG. 3A, the side edge of the tape-shaped optical fiber core wire 17 opposite to the mark .circle-circle. Faces the groove bottom, but in FIG. The side edge on the X mark side faces the groove bottom. This state is located "inside the bend of the groove of the reversing part" when it is assumed that the tape-shaped optical fiber core wire 17 is housed in the groove with the tape surface facing the groove bottom in any of the reversing parts 23. This means that the side edge of the tape on one side faces the groove bottom.

The "inside the bend of the groove of the reversal portion" is the portion 23a in FIG. Figure 4 shows one SZ spiral groove 1
7 shows a side surface of a grooved spacer 11 having 7. 2
Reference numeral 3 denotes a reversal portion of the groove 17, reference numeral 23a denotes an inner side of the bend of the reversal portion 23, reference numeral 23b denotes an outer side of the reflex portion 23,
Is the central part between the reversal parts. FIG. 1A described above is a cross-sectional view of the central portion (f of FIG. 3) between the inverted portions of the groove 13, and FIG. 1B is a sectional view of one inverted portion (a of FIG. 3) of the groove 13. 1C is a cross-sectional view of the other inversion portion (k in FIG. 3) of the groove 13.

The tape-shaped optical fiber core wire 17 housed in the groove 13 as described above is bent mainly in the direction in which the tape surface is curved in both the reversing portion 23 and the center portion 25 between the reversing portions. Therefore, in this state, the bending of the tape-shaped optical fiber core wire 17 in the direction of bending the side edge of the tape is the smallest.

Further, with such a storage method, the twist applied to the tape-shaped optical fiber core wire 17 is reduced. At first glance at FIGS. 3A to 3K, it seems that the laminated body of the tape-shaped optical fiber core wires 17 is rotated and twisted in the groove 13, but in reality, from FIG. In the section of () and the section of (h) to (k), only the direction of the groove 13 changes, and the direction of the tape-shaped optical fiber core wire 17 hardly changes.

This means that the tape-shaped optical fiber core wire 17 is hardly twisted in the above section. The twisting of the tape-shaped optical fiber 17 is mainly applied only in the section from FIG. 3D to FIG.
Only about 120 ° out of 0 °). In the conventional cable, the tape-shaped optical fiber core is twisted at any position from one inversion part to the next inversion part, but in comparison with this, the cable of the present invention has a tape-shaped optical fiber core. The twist applied to the wire is significantly reduced.

Next, the reversal angle θ of the groove of the grooved spacer will be described. The direction of the groove 13 changes from the state of the tape-shaped optical fiber core wire 17 in which the side edges are directed to the groove bottom to the state of FIG. 3 (a) in which the tape surface is directed to the groove bottom (d). It is necessary to rotate by an angle larger than 90 °. Similarly, from the state of (h) to the state of (k), the groove 13
Must be rotated by an angle greater than 90 °.
In other words, in order to obtain a state in which the tape-shaped optical fiber core wire 17 directs the tape side edge toward the groove bottom at the reversal portion of the groove 13 and directs the tape surface toward the groove bottom at the center portion between the reversal portions of the groove 13. It is necessary to rotate the grooves on both sides of the reversing portion in the circumferential direction of the grooved spacer at least at an angle larger than 90 °.

Therefore, the reversal angle θ of the groove 13 of the grooved spacer 11 needs to be larger than 180 °. Groove 13
As described above, it is desirable that the upper limit of the reversal angle θ of is 360 ° or less. Therefore, the reversal angle θ of the groove is usually 18
It is set to an appropriate value within the range of 0 ° <θ ≦ 360 °.

Next, the width and depth of the groove 13 of the grooved spacer 11 will be described. The width and the depth of the groove 13 are set so that the laminated body of the tape-shaped optical fiber core wires 17 can rotate in the groove 13. Further, the opening width of the groove 13 is formed such that the opening width W ₂ of the groove 13 in the reversing portion is narrower than the opening width W ₁ of the groove 13 in the center portion between the reversing portions.
The depth of the groove 13 is constant. More specifically, the groove 13
As shown in FIG. 3, the opening width is gradually narrowed from the central portion (f) between the reversing portions to the reversing portions (a) and (k). That is, when comparing the opening widths at any two positions from the central portion between the reversing portions to the reversing portion, the opening width on the reversing portion side is the opening portion on the central portion side between the reversing portions. It is formed so that it is always narrower than the width.

When the tape-shaped optical fiber core wire 17 is in a state where the side edge of the tape is directed to the groove bottom at the reversal portion, the tape-shaped optical fiber core wire 17 is particularly susceptible to lateral pressure,
As described above, if the opening width of the groove 13 is narrowed at the reversal portion of the groove 13, it is difficult for the sheath 21 to fall into the groove 13, and side pressure is applied to the tape-shaped optical fiber core wire 17. Less likely. Further, if the opening width of the groove 13 is narrowed at the reversal portion, the clearance between the tape-shaped optical fiber core wire 17 and the inner wall of the groove 13 at the reversal portion becomes small, and the tape-shaped optical fiber core wire 17 becomes difficult to move. ,
The movement of the tape-shaped optical fiber core wire 17 during the overhead installation is reduced, and the long-term reliability can be improved.

[Second Embodiment] FIGS. 5 and 6 show another embodiment of the present invention. FIG. 5 is a sectional view corresponding to FIG. 1 of the first embodiment, and FIG. 6 is a sectional view corresponding to FIG.

The first difference of this embodiment from the first embodiment is the orientation of the tape-shaped optical fiber core wire 17. The orientation of the tape-shaped optical fiber core wire 17 with respect to the orientation of the groove 13 shown in FIGS. 3A to 3K is in an almost ideal state. In practice, the tape-shaped optical fiber core wire 17 is free in the groove 13, so that the tape-shaped optical fiber core wire 17 changes its direction to the most stable state in the groove 13 due to its elasticity, rigidity, bending force at the inversion portion, or the like. A specific example thereof is shown in FIGS.

In the central portion 25 between the inversion portions of the groove 13, FIG.
As shown in (f), the tape-shaped optical fiber core wire 17 is housed in the groove 13 with the tape surface facing the groove bottom. This point is the same as the case of FIG. 3, but in the case of FIG.
When the direction of the groove 13 is rotated by 90 ° from (f), that is, in (c) and (i), the tape-shaped optical fiber core wire 17 is placed in the groove 1.
In the reversal portion 23 of the groove 13, the tape-shaped optical fiber core wire 17 is directed to the inner side of the bend of the groove of the reversal portion 23 from the upright state as shown in FIGS. It has fallen down. In the present invention, "the tape-shaped optical fiber core is housed in the groove with the side edge of the tape facing the groove bottom at the inverted portion of the groove" is shown in FIG. 6 (a).
The state like (k) is also included. In this state, the laminated body of the tape-shaped optical fiber core wires 17 may be displaced at the inverted portion of the groove 13 as shown in FIGS. 5B and 5C.

Next, this embodiment is different from the first embodiment.
The second point is the depth of the groove 13. Ie this implementation
In the form, the depth D of the groove 13 in the inverted portion is_TwoThe inversion part
Depth D of the groove 13 in the central portion₁Deeper.
The opening width of the groove 13 is W₁> W _TwoIs the first embodiment
Is the same as. More specifically, the depth of the groove 13 is shown in FIG.
As shown in FIG.
It gets deeper as you go to (k). Ie groove
13 is an interval from the central part between the reversing parts to the reversing part.
When comparing the depths at the two desired points,
The depth is always deeper than the depth of the central part between the reversing parts
It is formed as follows. In this way, at the inverted part of the groove 13,
If the depth of the groove 13 is increased, the tape will not be formed at the inverted portion of the groove 13.
More surely that lateral pressure is applied to the optical fiber core 17
Can be prevented.

The configuration and effects other than the above are the same as those of the first embodiment.
The same parts are designated by the same reference numerals and the description thereof will be omitted.

[0034]

Example An optical fiber cable as in the second embodiment was manufactured as a prototype. The outer diameter of the grooved spacer 11 is 8.5 mm, and the groove 1
The cross-sectional dimension of 3 has an opening width of 2.7 mm at the inverted portion,
The bottom width is 1.6 mm, the depth is 2.5 mm, the opening width is 4.0 mm, the bottom width is 1.6 mm, and the depth is 2.1 mm in the central portion between the reversing portions. The reversal angle θ of the groove 13 is about 290
The reverse pitch P is about 250 mm. The grooved spacer 11 is a polyethylene round bar having a steel wire tension member at the center, and the SZ spiral groove 13 is formed by cutting. The groove 13 has a thickness of 0.32 mm and a width of 1.1 m.
Five 4-core tape-shaped optical fiber core wires of m were stacked and stored. For comparison, the same cable as the above was prototyped except that the cross-sectional dimensions of the grooved spacer were constant with an opening width of 4.0 mm, a bottom width of 1.6 mm, and a depth of 2.1 mm. Table 1 shows the results of measuring the transmission loss of the tape-shaped optical fiber core wire for these cables. Measurement wavelength is 1.55
μm.

[0035]

[Table 1]

It can be seen that the cable of the example of the present invention has less transmission loss than the cable of the comparative example having a uniform groove cross section. Further, according to the result of disassembling and examining the cable, in the comparative example, the sheath dropped into the groove over the entire length, but in the example, the sheath did not drop much into the groove at the inverted portion of the groove.

[0037]

As described above, according to the present invention, a light having a tape-shaped optical fiber core wire accommodated in the groove of a grooved spacer having an SZ spiral groove whose spiral direction is periodically inverted. In the fiber cable, it is possible to reduce the twist applied to the tape-shaped optical fiber core wire and the bending mainly in the direction of bending the tape side edge, and further, the lateral pressure is applied to the tape-shaped optical fiber core side edge part at the inversion portion of the groove. Since it is hard to take, the transmission loss of the tape-shaped optical fiber core wire can be suppressed sufficiently small. Therefore, the present invention greatly contributes to the practical use of this type of cable.

[Brief description of the drawings]

1A and 1B show an embodiment of an optical fiber cable according to the present invention, where FIG. 1A is a cross-sectional view of a central portion between groove inversion portions, and FIG. 1B is a cross-sectional view of one inversion portion of a groove. Sectional drawing in the other inversion part of a groove | channel.

2A and 2B are schematic cross-sectional views of the groove of the cable of FIG. 1 accommodating the tape-shaped optical fiber core wire, FIG.

3 (a) to (k) respectively show the relationship between the direction of the groove and the direction of the tape-shaped optical fiber core wire, and FIG.
Sectional drawing in a line-kk line.

FIG. 4 is a side view showing a groove state of the grooved spacer used in the present invention.

5A and 5B show another embodiment of the optical fiber cable according to the present invention, where FIG. 5A is a cross-sectional view at the center between the inversion portions of the groove, and FIG. 5B is a cross-sectional view at one inversion portion of the groove. FIG. 6 is a cross-sectional view of the other inversion portion of the groove.

6 (a) to (k) respectively show the relationship between the direction of the groove and the direction of the tape-shaped optical fiber core wire in the cable of FIG. 5, along lines aa to kk in FIG. Sectional view.

[Explanation of symbols]

 11: Spacer with groove 13: SZ spiral groove 17: Tape-shaped optical fiber core wire 19: Press winding 21: Sheath 23: Inverted portion of groove 23a: Inside groove bend in inverted portion of groove 25: Inverted groove Central part

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Eiji Imada 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Masami Hara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Fumiki Hosui 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Shigekazu Hayami 3-19, Nishishinjuku, Shinjuku-ku, Tokyo No. 2 inside Nippon Telegraph and Telephone Corporation (72) Inventor Masaru Okada 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. An SZ in which the spiral direction is periodically reversed on the outer circumference.
In an optical fiber cable including a grooved spacer having a spiral groove and a tape-shaped optical fiber core wire housed in the groove of the grooved spacer, the reversal angle of the groove of the grooved spacer (1 of the groove) Rotation angle in the circumferential direction of the grooved spacer from one reversing part to the next reversing part)
θ is greater than 180 °, and the tape-shaped optical fiber has the tape surface directed to the groove bottom in the central portion between the reversal portions of the groove (the central portion between one reversal portion of the groove and the next reversal portion). In this state, assuming that the tape surface is stored in the groove with the bottom of the tape facing the groove bottom, with the side edge of the tape located inside the bend of the groove of the reversing part facing the groove bottom. The optical fiber cable is housed in the groove, and the width of the groove opening of the grooved spacer is narrower in the reversing portion than in the central portion between the reversing portions. 2. The optical fiber cable according to claim 1, wherein the width of the opening of the groove of the grooved spacer is narrower in the inverted portion than in the portion other than the inverted portion. 3. The optical fiber cable according to claim 1, wherein the opening widths of the grooves are compared at any two points between the central portion between the reversing portions of the grooved spacer and the reversing portion. At times, the inversion part side is always narrower than the center part side between the inversion parts. 4. The optical fiber cable according to any one of claims 1 to 3, wherein the depth of the groove of the grooved spacer is deeper in the inverted portion than in the central portion between the inverted portions. 5. The optical fiber cable according to any one of claims 1 to 3, wherein the grooved spacer has a groove depth deeper in the inverted portion than in portions other than the inverted portion. 6. The optical fiber cable according to claim 1 or 3, wherein the depth of the grooved spacer at any two positions from the central portion between the reversing portions to the reversing portion. When compared, the inversion part side is always deeper than the central part side between the inversion parts.