JP3571834B2 - Fiber optic cable - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber cable formed by twisting a rod-shaped unit accommodating a tape-shaped optical fiber core around an outer periphery of a central rod-shaped member.
[0002]
[Prior art]
Conventionally, as this type of optical fiber cable, a concave member accommodating a tape-shaped optical fiber core wire is provided on the outer periphery of the center rod-shaped member so that the tape surface of the tape-shaped optical fiber core wire always faces the outer peripheral surface of the center rod-shaped member. In addition, an SZ twisted cable has been proposed (JP-A-4-182611).
This type of optical fiber cable can be easily removed by taking out the concave member including the tape-shaped optical fiber core from the middle of the cable when it is necessary to branch the desired tape-shaped optical fiber core after the cable is laid. There is an advantage that a branching operation can be performed.
[0003]
[Problems to be solved by the invention]
By the way, 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, the optical fibers bend uniformly in the direction of bending the tape surface, and almost no increase in transmission loss occurs. However, bending in the direction of bending the tape side edge in the tape surface (edgewise bending). Is applied, a strain in the compression direction is generated in the optical fiber on the inner side of the bend, and a strain in the tensile direction is generated on the optical fiber on the outer side of the bend, resulting in a large increase in transmission loss. .
[0004]
In the above-described conventional optical fiber cable, the concave member accommodating the tape-shaped optical fiber core is disposed on the outer periphery of the center rod-shaped member so that the tape surface of the tape-shaped optical fiber core always faces the outer peripheral surface of the center rod-shaped member. , SZ twisted, each tape-shaped optical fiber core is mainly bent in a direction in which the tape side edge is bent at a reversal part of the twisting direction of the rod-shaped member. As a result, an unreasonable bending stress is applied to the tape-shaped optical fiber core, which not only increases the transmission loss of the optical fiber, but also has a problem in long-term reliability.
[0005]
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 rod-shaped unit containing a tape-shaped optical fiber core is SZ twisted around the outer periphery of a central rod-shaped member. It is an object of the present invention to provide a cable structure that solves the problem of excessive bending strain, the accompanying increase in optical fiber transmission loss, and the problem of long-term reliability.
[0006]
[Means for Solving the Problems]
The optical fiber cable of the present invention that achieves this object is:
A state in which one or more tape-shaped optical fibers are oriented in the grooves of the grooved round bar-shaped member having one groove or two grooves symmetrical with respect to the center axis in the longitudinal direction, with the tape surface facing the groove bottom surface. A bar-shaped unit that is stacked and stored in the outer periphery and is provided with a holding roll on the outer periphery, and a center rod-shaped member having a tension member,
The depth of the groove of the round bar-shaped member with a groove in the center of the bar-shaped member between the reversal portions in the twisting direction (the center between one reversal portion in the twisting direction and the next reversal portion) When it is assumed that the round bar-shaped member with a groove is SZ-twisted while the depth direction of the groove is directed in the radial direction of the center rod-shaped member at the reversal part of the twisting direction so that the direction is substantially in the radial direction of the center rod-shaped member SZ twisted so that the groove side wall located inside the bend at the reversal part of the twist direction is located between the groove side wall on the opposite side and the outer peripheral surface of the center rod-shaped member,
A holding roll is applied to the outer periphery of the SZ twisted rod-shaped unit, and a sheath is applied to the outer periphery thereof.
It is characterized by the following.
[0007]
With such a configuration, the tape-shaped optical fiber core is mainly subjected to bending in a direction in which the tape surface is curved at both the reversal portion in the twist direction of the rod-shaped unit and the center portion between the reversal portions. Unreasonable bending stress is not applied to the fiber core, and the increase in the transmission loss of the optical fiber can be suppressed, and the long-term reliability is improved.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
[Embodiment 1]
1 to 3 show a first embodiment of the present invention. In this optical fiber cable, as shown in FIG. 1, basically, a rod-shaped unit 15 including a tape-shaped optical fiber core 13 is SZ-twisted on the outer periphery of a center rod-shaped member 11, and a presser winding 17 is formed on the outer periphery. And a sheath 19 on the outer periphery thereof.
[0010]
The central rod-shaped member 11 has a tension member 21 made of a steel stranded wire or the like at the center, and has a structure in which plastic is extrusion-coated in a circular cross section around the tension member 21.
The rod-shaped unit 15 has a grooved round rod-shaped member 25 having one groove 23 in the longitudinal direction. In the groove 23, a plurality of tape-shaped optical fiber cores 13 are oriented with the tape surface facing the groove bottom. This is a structure in which the sheets are stacked and stored in a state where they are held, and a holding roll 27 is provided on the outer periphery.
[0011]
The grooved round bar-shaped member 25 is made of an extruded plastic body, and in this example, a tensile strength line 29 is embedded at a position symmetrical with respect to a plane passing through the center of the groove width. When the tensile strength line 29 is embedded in this way, the grooved round bar-shaped member 25 is difficult to bend in a plane including the tensile strength line 29, but is easily bent in a plane perpendicular to the same plane. As a result, the bendable direction of the grooved round bar-shaped member 25 and the bendable direction of the tape-shaped optical fiber core 13 coincide with each other. The direction and the direction of the groove 23 of the grooved round bar member 25 can be kept substantially the same.
[0012]
The SZ twist of the rod-shaped unit 15 has a form as shown in FIGS. FIG. 2 is a side view showing the central rod-shaped member 11 and one of a large number of rod-shaped units 15 SZ-twisted on the outer periphery thereof. 3 (a) to 3 (k) are cross-sectional views taken along the line aa to kk in FIG. 2, respectively. As shown in FIG. 2, the rod unit 15 is twisted (SZ twisted) around the center rod member 11 so that the twist direction is periodically reversed. Reference numeral 31 denotes a reversal portion of the rod-shaped unit 15 in the twisting direction, 33 denotes a center portion between the reversal portions in the twisting direction of the rod-shaped unit 15 (a central portion between one reversal portion 31 in the twisting direction and the next reversal portion 31), P is the reversal pitch in the twisting direction (the center axis distance from one reversal part 31 to the next reversal part 31).
[0013]
In FIG. 3, only one inversion pitch from (a) to (k) is shown, but in the next one inversion pitch, the state is reversed from (k) to (a), and this is repeated thereafter. Will be. In order to indicate the direction of the tape-shaped optical fiber core 13, a circle mark is provided on one side of the tape-shaped optical fiber core 13, and a reversal angle of the SZ twist is marked with a cross mark on the opposite side (from one reversal part 31 to The rotation angle in the circumferential direction up to the reversing portion 31) is preferably larger than 180 ° and smaller than 360 °, and is set to 300 ° in this example (see FIG. 2).
[0014]
As is clear from FIG. 3, the rod unit 15 is arranged such that the depth direction of the groove 23 of the grooved round bar member 25 faces the radial direction of the center rod member 11 at the center portion (f) between the inversion portions in the twisting direction. In the inversion portions (a) and (k) of the twisting direction, when it is assumed that the round bar-shaped member 25 with a groove is SZ-twisted while the depth direction of the groove 23 is directed to the radial direction of the center rod-shaped member 11, the twisting direction is changed. The groove side wall 35 located on the inside of the bend at the reversing portion (in FIG. 2, S is inside and T is outside) is located between the groove side wall 37 on the opposite side and the outer peripheral surface of the central rod-shaped member 11. SZ twist.
[0015]
When the rod-shaped unit 15 is SZ-twisted as described above, the tape-shaped optical fiber core 13 is accommodated in the groove 23 with the tape surface facing the groove bottom. (K) As shown in (k), the tape surface of the tape-shaped optical fiber core 13 is oriented substantially in the radial direction of the central rod-shaped member 11. However, in FIGS. 3A and 3K, the directions of the optical fibers 13 are opposite. That is, in FIG. 3A, the side edge of the tape-shaped optical fiber core 13 on the side of the mark O is located on the side of the center rod-shaped member 11, but in FIG. The side edge is located on the side of the center rod-shaped member 11. In this state, the tape-shaped optical fiber core 13 is subjected to bending in the direction of bending the tape surface at the reversal part in the twisting direction.
[0016]
Therefore, the tape-shaped optical fiber core 13 is bent in the direction in which the tape surface is curved mainly at the inverted portion 31 and the center portion 33 between the inverted portions, and this state is the same as that of the tape-shaped optical fiber core 13. This is a state where bending in the direction of bending the tape side edge is the least.
[0017]
When the SZ twist is performed as described above, the twist applied to the tape-shaped optical fiber core 13 is reduced. As is clear from FIGS. 3A to 3K, even when the circumferential position of the rod unit 15 with respect to the center rod member 11 changes, the tape surface of the tape-shaped optical fiber core 13 faces in substantially the same direction. I have. This means that the torsion applied to the tape-shaped optical fiber core 13 is small.
[0018]
FIG. 1A shows a cross section (corresponding to f in FIG. 3) of the rod-shaped unit 15 at the center between the reversing portions in the twisting direction, and FIG. 1B shows a cross section at one reversing portion (corresponding to a in FIG. 3). (C) shows a cross section (corresponding to k in FIG. 3) at the other inversion portion.
[0019]
The optical fiber cable of this embodiment was prototyped, and the transmission loss after applying the sheath 19 was measured. The number of laminated tape-shaped optical fiber cores 13 in the rod-shaped unit 15 is 5, and the measurement wavelength is 1.55 μm. As a result, the average transmission loss was 0.21 dB / km, the minimum was 0.20 dB / km, and the maximum was 0.22 dB / km. Since the target value of the transmission loss is 0.25 dB / km or less on average, it was confirmed that this cable had sufficient performance.
[0020]
[Embodiment 2]
FIG. 4 shows a second embodiment of the present invention. In this optical fiber cable, a groove 39 is formed on the outer peripheral surface of the central rod-shaped member 11, a single-core optical fiber core wire 41 is accommodated in the groove 39, and a holding roll 43 is provided on the outer periphery. Other configurations are the same as those of the first embodiment. FIG. 4 shows a cross section of the rod-shaped unit 15 at the center between the reversing portions in the twisting direction. With such a configuration, the number of optical fibers to be stored can be increased as compared with the first embodiment.
[0021]
[Embodiment 3]
FIG. 5 shows a third embodiment of the present invention. In this optical fiber cable, a groove 45 is formed on the outer peripheral surface of the central rod-shaped member 11, a plurality of tape-shaped optical fiber core wires 47 are stored in a stacked state in the groove 45, and a holding roll 43 is provided on the outer periphery thereof. It was done. Other configurations are the same as those of the first embodiment. FIG. 5 shows a cross section of the rod-shaped unit 15 at the center between the reversing portions in the twisting direction. With such a configuration, the number of optical fibers that can be stored can be further increased as compared with the second embodiment.
[0022]
[Embodiment 4]
FIG. 6 shows a fourth embodiment of the present invention. This optical fiber cable differs from the first embodiment in the structure of the rod-shaped unit 15. That is, the rod-shaped unit 15 uses a grooved round rod-shaped member 25 having two grooves 23 symmetrical with respect to the central axis in the longitudinal direction, and a plurality of tape-shaped optical fiber cores 13 are provided in the groove 23. Are stacked and stored with the tape surface facing the groove bottom surface, and a presser winding 27 is applied to the outer periphery thereof. A tensile strength line 29 is embedded in the grooved round bar member 25 at a position symmetrical with respect to a plane passing through the center of the groove width.
[0023]
The configuration other than the rod-shaped unit 15 is the same as that of the first embodiment. 6 (A) to 6 (C) correspond to FIGS. 1 (A) to 1 (C). With such a configuration, the cable outer diameter is slightly larger than in the first embodiment, but there is an advantage that the number of optical fibers to be stored can be significantly increased.
Also in the case of this embodiment, if the center rod-shaped member as in the second or third embodiment is used, the number of optical fibers that can be stored can be further increased.
[0024]
[Embodiment 5]
7 to 9 show a fifth embodiment of the present invention. This optical fiber cable uses, as the central rod-shaped member 11, an SZ spiral groove 49 whose spiral direction is periodically inverted on the outer periphery. The rod-shaped unit 15 is SZ twisted along the SZ spiral groove 49. Other configurations are the same as those of the first embodiment. 7 (A) to 7 (C) correspond to FIGS. 1 (A) to 1 (C), FIG. 8 corresponds to FIG. 2, and FIGS. 9 (a) to 9 (k) are FIGS. 3 (a) to 3 (k). ). However, FIG. 8 is a developed view showing one SZ spiral groove 49 on the outer peripheral surface of the central rod-shaped member 11 and the rod-shaped unit 15 twisted therein.
With such a configuration, the SZ twisting state of the rod-shaped unit 15 can be reliably maintained, so that the SZ twisting can be easily performed.
[0025]
In the case of an optical fiber cable having such a configuration, it is desirable that the SZ spiral groove 49 has a size in which the direction of the rod-like unit 15 can be freely changed. In this way, when the cable is bent or twisted, the rod-shaped unit 15 can be turned together with the tape-shaped optical fiber core 13 in a direction in which the distortion is reduced, so that the tape-shaped optical fiber core is generated. The internal stress is easily dispersed, and an increase in transmission loss can be suppressed.
[0026]
The cross-sectional shape of the SZ spiral groove 49 of the central rod-shaped member 11 is a trapezoidal groove in the embodiment of FIGS. 7 to 9, but may be a groove whose bottom is curved as shown in FIG. It may be a simple rectangular groove.
In this embodiment, a round bar-shaped member having one groove is used as the round bar-shaped member 25 having a groove of the bar-shaped unit 15. However, a round bar-shaped member having two grooves as in the fourth embodiment can be used. .
[0027]
[Embodiment 6]
FIG. 12 shows a sixth embodiment of the present invention. In this optical fiber cable, a groove 39 is formed on the outer peripheral surface of the center rod-shaped member 11, a single-core optical fiber core wire 41 is accommodated in the groove 39, a holding roll 43 is provided on the outer periphery, and SZ is further provided on the outer periphery. A grooved spacer 51 for forming a spiral groove 49 is provided. The rod-shaped unit 15 is SZ twisted along the SZ spiral groove 49 of the grooved spacer 51. Other configurations are the same as in the fifth embodiment.
[0028]
[Embodiment 7]
FIG. 13 shows a seventh embodiment of the present invention. In this optical fiber cable, a groove 45 is formed on the outer peripheral surface of the center rod-shaped member 11, a plurality of tape-shaped optical fiber cores 47 are stored in the groove 45 in a stacked state, and a holding roll 41 is formed on the outer periphery. And a grooved spacer 51 for forming an SZ spiral groove 49 on the outer periphery thereof. The rod-shaped unit 15 is SZ twisted along the SZ spiral groove 49 of the grooved spacer 51. Other configurations are the same as in the fifth embodiment.
[0029]
【The invention's effect】
As described above, according to the present invention, a rod-shaped unit accommodating a tape-shaped optical fiber core is added to a tape-shaped optical fiber core in an optical fiber cable of a type in which SZ is twisted around the outer periphery of a central rod-shaped member. Since the twist and the bending in the direction of bending the tape side edge in the tape surface can be reduced, the transmission loss of the tape-shaped optical fiber core can be suppressed sufficiently. Therefore, the present invention greatly contributes to the practical use of this type of optical fiber cable.
[Brief description of the drawings]
1A and 1B show a first embodiment of an optical fiber cable according to the present invention, in which FIG. 1A is a cross-sectional view at a center portion between the inversion portions in the twisting direction, and FIGS. 1B and 1C are cross-sectional views in an inversion portion in the twisting direction. .
FIG. 2 is a side view showing the SZ twisted state of the rod unit in the cable of FIG. 1;
FIGS. 3A to 3K are cross-sectional views taken along lines aa to kk in FIG. 2, respectively.
FIG. 4 is a cross-sectional view showing a second embodiment of the optical fiber cable of the present invention, which is taken at a central portion between the inversion portions in the twisting direction.
FIG. 5 is a sectional view showing a third embodiment of the optical fiber cable according to the present invention, which is taken at a central portion between the inversion portions in the twisting direction.
FIG. 6 shows a fourth embodiment of the optical fiber cable of the present invention, wherein (A) is a cross-sectional view at the center between the inversion parts in the twisting direction, and (B) and (C) are cross-sectional views at the inversion part in the twisting direction. .
FIGS. 7A and 7B show a fifth embodiment of the optical fiber cable of the present invention, in which FIG. 7A is a cross-sectional view at the center between the inversion portions in the twisting direction, and FIGS. .
FIG. 8 is a developed view of an outer peripheral surface of a center rod-shaped member in the cable of FIG. 7;
FIGS. 9A to 9K are cross-sectional views taken along lines aa to kk in FIG. 8, respectively.
FIG. 10 is a sectional view showing another example of the shape of the SZ spiral groove of the center rod-shaped member in the cable of FIG. 7;
FIG. 11 is a sectional view showing still another example.
FIG. 12 is a cross-sectional view showing a sixth embodiment of the optical fiber cable according to the present invention, which is taken at a central portion between the inversion portions in the twisting direction.
FIG. 13 is a sectional view showing a seventh embodiment of the optical fiber cable according to the present invention, which is taken at a central portion between the inversion portions in the twisting direction.
[Explanation of symbols]
11: central rod-shaped member 13: tape-shaped optical fiber core wire 15: rod-shaped unit 17: holding roll 19: sheath 21: tension member 23: groove 25: grooved round bar-shaped member 27: holding roll 29: tensile strength wire 31: twisting direction Reversal part 33: center part between reversal parts in twist direction 49: SZ spiral groove

Claims (4)

A state in which one or more tape-shaped optical fibers are oriented in the groove of a round bar-shaped member having a groove having one groove or two grooves symmetrical with respect to the central axis in the longitudinal direction, with the tape surface facing the groove bottom surface. A bar-shaped unit that is stacked and housed in the outer periphery and is provided with a presser winding on the outer periphery, and a center rod-shaped member having a tension member,
The rod-shaped unit is provided on the outer periphery of the central rod-shaped member, and at the center between the reversing portions in the twisting direction (the center between the one reversing portion in the twisting direction and the next reversing portion), the depth of the groove of the grooved round bar-shaped member. When it is assumed that SZ twist is performed at the reversal part of the twisting direction such that the direction is substantially in the radial direction of the central rod-shaped member, with the grooved round rod-shaped member oriented with the depth direction of the groove in the radial direction of the central rod-shaped member. SZ twisted so that the groove side wall located inside the bend at the reversal part of the twist direction is located between the opposite groove side wall and the outer peripheral surface of the center rod-shaped member,
A press winding is applied to the outer periphery of the SZ twisted rod-shaped unit, and a sheath is applied to the outer periphery thereof.
An optical fiber cable, characterized in that: 2. The optical fiber cable according to claim 1, wherein the grooved round bar-shaped member has a tensile strength line at a position symmetric with respect to a plane passing through the center of the groove width. The center rod-shaped member has an SZ spiral groove on the outer periphery of which the spiral direction is periodically inverted, and the rod-shaped unit is twisted SZ along the SZ spiral groove. Fiber optic cable. The optical fiber cable according to claim 3, wherein the rod-shaped unit is in a state where it can rotate freely in the SZ spiral groove.

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