JP2003131093A - Sz slot for optical cable, method for manufacturing slot and optical fiber cable having ribbon coated optical fiber accommodated in slot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide SZ slots for an optical cable, a method for manufacturing the slots and the optical fiber cable having ribbon coated optical fiber accommodated in the slots which does not direct only a turning part of the ribbon coated optical fiber accommodated in a specific groove outside a take-up drum, and reduce the breaking probability of the ribbon coated optical fiber. SOLUTION: In the SZ slots 23 for the optical cable having SZ spiral grooves I-V which are carved on an outer circumference and whose directions alternately turn around at a predetermined turning angle, circumferential angular positions in a slot cross section of a plurality of the turning centers of each spiral groove do not always exist at the same angular position in the longitudinal direction of the slot.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SZ slot for an optical cable in which a plurality of SZ spiral grooves whose spiral directions are alternately inverted at a predetermined reversal angle are engraved on the outer peripheral surface thereof, a method for manufacturing the slot, and a plurality of the slots. The present invention relates to an optical fiber cable in which a tape-shaped optical fiber core wire is housed in an SZ spiral groove of a strip.

[0002]

2. Description of the Related Art FIG. 7 is a sectional view of an optical fiber cable having a conventional SZ slot, FIG. 8 is a schematic view of an SZ slot structure in which the direction of the spiral is reversed, and FIG. 9 is a sectional view showing an SZ slot manufacturing apparatus. FIG. 10 is an explanatory view showing a state in which the optical fiber cable is wound around the winding drum.

In FIG. 7, an optical fiber cable 1 is provided on the outer peripheral surface of a slot 3 made of a thermoplastic resin having a tension member 2 made of a single steel wire or a steel stranded wire at its center.
Five SZ spiral grooves 4 (grooves I to V) in which the spiral direction is alternately inverted at a predetermined reversal angle θ are engraved, and the tape-shaped optical fiber core wire 5 is attached to the five SZ spiral grooves 4. The sheath 7 is housed, and the outermost circumference is covered with a sheath 7 via a press-winding layer 6.

As shown in FIG. 8, the SZ spiral groove 4 is formed by engraving an S-shaped spiral groove with a predetermined reversal angle θ from the reversal center portion 0 to the next reversal center portion 0 ', and then Z. The spiral groove is inverted from the inversion center 0 ', and it is S again with the inversion angle θ.
The reversal angle is generally 230 degrees to 330 degrees in consideration of the ease of taking out the tape-shaped optical fiber core wire 5 and the fact that the distortion due to the bending of the cable does not become large because the tape-shaped optical fiber core wire 5 is periodically repeated. A predetermined reversal angle is selected from the range of degrees, and the reversal pitch P (distance from the reversal center portion 0 to 0 ′ in FIG. 8) is set to about 125 mm to 300 mm to form the spiral groove.

In FIG. 8, when the reversal angle is, for example, 280 degrees, the reversal center portion 0 reversing from S to Z is a circumferential angular position in the slot cross section, which is always an angular position of 40 degrees measured clockwise from the point K. And the inversion center 0 ′ that inverts from Z to S will always always be at an angular position of 320 degrees.

The SZ slot 3 having the SZ spiral groove 4 is manufactured by the manufacturing apparatus shown in FIG. This manufacturing apparatus includes a die body 9, a rotary die 10, and a heater 11.
And a cooling device 12 for cooling the SZ slot extruded by the extruder with air in the extruding direction of the SZ slot in the subsequent stage of the crosshead die 8.

In the method of manufacturing the SZ slot 3, first, a metal wire to be the tension member 2 is introduced into the mandrel 14 and fed into the crosshead die 8 of the extruder. Next, the rotary die 10 provided in the crosshead die 8 is rotated in the normal rotation direction and the reverse rotation direction alternately within the range of the reversal angle to extrude the resin onto the metal wire, and thereafter, is cooled by the cooling device 12 to produce several strips. It is possible to obtain the slot 3 in which the spiral groove 4 in the SZ direction is formed.

[0008]

The conventional optical fiber cable 1 having an SZ slot described above is housed by being wound around a drum 15 as shown in FIG. 10, but a groove I formed in the SZ slot 3 is provided. ~ Of the five grooves consisting of groove V, for example, the reversal center (0 or 0 ') of groove I is drum 15
When the winding starts in the state of facing the outside of the slot, the reversal center of the reversing center is always the same angular position in the slot length direction in the slot cross section as described above. Will face the outside of the drum 15. This is because only the tape-shaped optical fiber core wire 5-I housed in the groove I is always subjected to tensile strain due to a large bending stress at the inversion center, and the tape is housed in the other grooves (II to V). Optical fiber core wire (5-II to 5-
Compared with V), the tape contained in this groove I had a higher probability of breakage.

The present invention has been made in view of such a situation, and an object thereof is that only the inversion center portion of the tape-shaped optical fiber core wire housed in a specific groove is outside the winding drum. SZ slot for an optical cable in which the probability of breakage of the tape-shaped optical fiber core is reduced so that the tape-shaped optical fiber core is not oriented toward the end, a method of manufacturing the slot, and an optical fiber having the tape-shaped optical fiber core housed in the slot To provide the cable.

[0010]

In order to solve the above-mentioned problems, in the SZ slot for an optical cable of the present invention, a plurality of spiral grooves whose spiral directions are alternately reversed at a predetermined reversal angle are engraved on the outer peripheral surface. The SZ slot for an optical cable is characterized in that the circumferential angular positions in the slot cross section of the plurality of inversion center portions of each spiral groove do not always exist at the same angular position in the longitudinal direction of the slot. According to this feature, even when the tape-shaped optical fiber core is stored in the SZ spiral groove of the SZ slot and wound around the winding drum, the tensile strain applied to the optical fiber core can be suppressed low.

In the SZ slot for an optical cable of the present invention, the reversal angle is gradually increased and then decreased from the predetermined reversal angle,
Alternatively, it is preferable that the size of the predetermined inversion angle is partially changed over the predetermined length range of the SZ slot by periodically repeating the decrease, the increase, and the return to the predetermined inversion angle. . By doing so, the circumferential angular position in the SZ slot at the inversion center is gradually changed, so that the tensile strain of the tape-shaped optical fiber core housed in the specific groove can be gradually reduced.

In the SZ slot for an optical cable of the present invention, the predetermined reversal angle is changed by periodically changing the reversal angle from the predetermined reversal angle by a certain angle and then returning to the initial predetermined reversal angle. Is preferably partially modified over a predetermined length range of the SZ slot. By doing this, the SZ of the center of inversion
Since the circumferential angular position in the slot is partially changed, a large tensile strain is not applied only to the tape-shaped optical fiber core wire housed in the specific groove.

In the SZ slot for an optical cable of the present invention, it is preferable that the deviation of the circumferential position at the center of reversal due to the change of the predetermined reversal angle is at least 360 ° / the number of grooves and 360 ° or less. By doing so, at least the predetermined groove and the tape-shaped optical fiber core wire accommodated in the groove adjacent thereto can share the tensile strain due to bending.

In the SZ slot for an optical cable of the present invention, it is preferable that the predetermined reversal angle is in the range of approximately 230 degrees to 330 degrees. By doing so, the strain caused in the specific tape-shaped optical fiber core wire against bending is small.

In the method of manufacturing an SZ slot for an optical cable according to the present invention, a plurality of SZ spiral grooves in which the direction of the spiral is alternately reversed at a predetermined reversal angle by extruding a molten resin through a rotating die that alternately rotates forward and backward are provided. A method for manufacturing an SZ slot for an optical cable engraved on an outer peripheral surface, wherein the angle for forward and reverse rotation of the rotary die is changed,
It is characterized in that the magnitude of the predetermined inversion angle is changed. According to this feature, only by changing the forward / reverse rotation angle of the rotary die, the circumferential angular positions in the slot cross section of the plural reversing center portions of each spiral groove are always the same angular position in the longitudinal direction of the slot. It is possible to form grooves that are not present.

In the method of manufacturing an SZ slot for an optical cable according to the present invention, a forward / reverse inversion period signal waveform of a rotary die having the SZ spiral groove having the predetermined inversion angle and a signal having a longer wavelength and a smaller amplitude than the signal waveform. It is preferable that the rotary die is normally and reversely rotated by combining with a waveform. By doing so, the rotation dice inversion control is performed by combining the forward / reverse inversion periodic signal waveform and the signal waveform having a longer wavelength and a smaller amplitude than the signal waveform. It is possible to obtain an SZ spiral groove whose position changes gradually in the longitudinal direction of the slot.

In the method for manufacturing an SZ slot for an optical cable according to the present invention, a plurality of waveforms in which the start point and the end point are out of phase are prepared, and by switching these waveforms, the cycle of the forward and reverse inversion of the rotary die is set. It is preferable to vary. By doing so, it is possible to obtain the SZ spiral groove having a desired changed reversal angle by performing reversal control of the rotary die by combining various waveforms.

In the method for manufacturing an SZ slot for an optical cable according to the present invention, the cycle of reciprocal reversal of the rotary die is varied by repeatedly using waveforms in which the start point and the end point are out of phase. By doing so, it is possible to perform the inversion control for changing the forward / reverse inversion angle of the rotary die using only one waveform signal wave.

An optical fiber cable having an SZ slot according to the present invention is provided with a tension member at the center, and an SZ slot in which a plurality of SZ spiral grooves whose spiral directions are alternately reversed at a predetermined reversal angle are engraved on the outer peripheral surface. And the multiple SZ
An optical fiber cable comprising a tape-shaped optical fiber core wire housed in a spiral groove and a sheath covering the outermost periphery, wherein a plurality of tape-shaped optical fiber core wires housed in the respective spiral grooves are inverted. The magnitude of the predetermined reversal angle is partially changed over a predetermined length range of the slot so that the circumferential angular position in the slot cross section of the central portion does not always exist at the same angular position in the longitudinal direction of the slot. It is characterized by being. According to this feature, the tape-shaped optical fiber core wire housed in the SZ spiral groove whose angular angular position in the SZ slot cross section of the inversion center portion is displaced can be wound around the winding drum. The tensile strain applied to the core wire can be kept low and it can be stored on the winding drum for a long time.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. 1 is a sectional view of an optical fiber cable having an SZ slot of the present invention, FIG. 2 is an explanatory view showing a state in which the optical fiber cable is wound around a winding drum, and FIG. 3 is an optical fiber core wire for winding the optical cable. 4A is a diagram showing a change in strain, FIG. 7A is a strain change diagram of a conventional optical cable, and FIG. 7B is a strain change diagram of the present invention.

In FIG. 1, an optical fiber cable 20 of the present invention has a predetermined shape on the outer peripheral surface of an SZ slot 23 made of a thermoplastic resin having a tension member 22 made of a single steel wire or a steel stranded wire at the center. A groove V is engraved from five spiral grooves I in which the reversal angle θ is 250 degrees and the direction of the spiral is alternately reversed, and four tape-shaped optical fiber core wires are formed from the five spiral grooves I to V. 24 (24-I to 24-V) are housed in a stacked state of 5 sheets each, and the outermost circumference is covered with a sheath 26 via a press winding layer 25.

The inversion angle has a predetermined value of 250 degrees, but when the length of the optical fiber cable is 40 m, the inversion angle is gradually increased to 80 degrees to reach 330 degrees, and then the inversion angle is 40 m when the length is 40 m. Is gradually reduced to 80 degrees to return to a predetermined reversal angle of 250 degrees.
A spiral groove is engraved in the SZ slot 23.

Therefore, as shown in FIG. 2, even when the winding drum 27 having a drum body shape of 600 mmφ is first wound so that the reversal center of the groove I faces outward, the reversal center gradually shifts, A spiral groove is engraved so that the reversal angle becomes 330 degrees after being wound 40 m after being wound by 40 degrees, and the reversal angle becomes a predetermined reversal angle of 250 degrees when being wound again by 40 m.
m) repeated.

Since the circumferential angular position in the SZ slot of the reversal center portion is shifted by 80 degrees at 40 m, the reversal center portion of the adjacent groove V is directed to the outside of the winding drum 27,
After that, at 40 m, the reversal center of the groove I again faces the outside of the take-up drum 27, so that a large bending stress is exerted on the tape core wire 2 contained in the groove I and the groove V.
Since it is shared by 4-I and 24-V, it is possible to avoid that the tensile strain acts strongly only on the tape core wire 24-I housed in the groove I.

Referring to FIG. 3, comparing the change in strain of the optical fiber core wire with the winding of the optical cable between the conventional optical fiber and the optical fiber of the present invention, as shown in FIG. 3 (a), Of the SZ spiral groove formed with a reversal angle of 250 degrees as a predetermined reversal angle, when the reversal center of the groove I starts to face toward the outside of the winding drum, the reversal center of the groove I is wound until the end of winding. Since it faces the outer side of the drum, the optical fiber contained in the groove I always has a fiber strain of 0. 0 regardless of the winding distance of the optical fiber.
It is in a high state of 6%, the fiber strain of the optical tape core wire stored in the groove V is about 0.2%, and the fiber compression strain of the optical tape core wire stored in the groove IV is 0.5. %
The probability of breakage is higher than that of

On the other hand, as shown in FIG. 3 (b), in the optical cable of the present invention, after winding 40 m, the winding center is first wound so that the reversal center portion of the groove I faces the outside of the winding drum 27. What started is that the reversing center of the groove V is directed to the outside of the winding drum 27, and the fiber core wire 24-I housed in the groove I has a fiber strain of 0.
The fiber strain 24-V stored in the groove V instead has a fiber strain of less than 0.1%.
It has increased from 2% to about 0.6%.

As described above, in the conventional optical fiber cable, when winding is started so that the reversal center part of a certain groove faces the outside of the winding drum 27, unless the reversal angle is changed,
The reversal center of the groove always faces the outside of the take-up drum, and the reversal center of the fiber core wire housed in the specific groove receives tensile strain due to a large bending stress. According to the invention, the size of the predetermined reversal angle is S so that a part of the plurality of reversal center portions of each spiral groove is displaced from the circumferential angular position in the slot.
The breaking probability of the optical fiber tape is lowered by partially changing the Z slot over a predetermined length range.

The deviation of the circumferential position at the center of the reversal due to the change of the reversal angle is 360 degrees / the number of spiral threads or more (72 or more for 5 threads) and 360 degrees or less, at least the reversal of the adjacent groove The central part faces the outside of the winding drum.

From the viewpoint of ease of taking out the tape-shaped optical fiber core wire 24 (post-branching property) and strain strength against bending of the cable, the reversal angle is generally 230 degrees to 330 degrees.
A predetermined reversal angle is selected from the range of degrees.

As described above, the tape-shaped optical fiber core wire is housed in the SZ spiral groove whose circumferential angular position in the cross section of the SZ slot at the center of inversion is displaced to form an optical fiber cable, and this cable is wound on the winding drum. If it is wound, the tensile strain applied to a specific optical fiber core wire can be suppressed to a low level and it can be stored in the winding drum for a long time.

Next, a method of controlling reversal of the rotary die for forming the SZ spiral groove will be described with reference to FIGS. 4 to 6. The method of manufacturing the SZ slot is basically the same as the method of manufacturing the conventional slot shown in FIG. 9, but the reversal angle is set so that the circumferential angular position in the slot at the reversal center of each spiral groove is displaced. The difference is that the timing of forward and reverse rotation of the rotary die is changed for the purpose of changing it.

FIG. 4 (a) shows two signal waveforms given to the rotary die, and FIG. 4 (b) shows an inversion control waveform of the rotary die based on the combination of the two signal waveforms.
In (a), “A” is a forward / reverse inversion periodic signal waveform that has been conventionally used for inversion control at a predetermined inversion angle (275 degrees), and “B” is from this forward / inverse inversion periodic signal waveform. The signal waveform has a long wavelength and a small amplitude.

When the inversion control of the rotary die is performed using the signal waveform obtained by synthesizing these two signal waveforms, the inversion control wave "C" as shown in FIG. 4B is obtained. Due to this inversion control wave “C”, the circumferential angular position in the slot at the inversion center gradually changes in the length direction of the slot S
A Z spiral groove can be obtained.

In FIG. 5A, the reversal angle is 275 degrees, and the rotation start point of the die is 0 for each 300 mm of the slot length.
The inverted signal waveform "D" of the rotating die whose phase is shifted from the end point to 30 degrees is shown in FIG. 5 (b).
There is shown a phase-shifted rotary die reversal signal waveform [E] in which the reversal angle is 275 degrees, the rotation start point of the die is 0 degrees, and the end point is -30 degrees for a slot length of 300 mm.

When the rotary die is controlled to be inverted while switching the inverted signal waveforms "D" and "E", an inverted control wave "F" as shown in FIG. 5C is obtained. By this inversion control wave "F", it is possible to obtain a spiral groove in which the circumferential angular position in the slot cross section of the inversion center portion changes periodically in the length direction of the slot. In addition to the inverted signal waveforms “D” and “E”, the SZ spiral groove having a desired changed inversion angle can be obtained by combining other arbitrarily set waveforms out of phase with each other.

It is also possible to repeatedly and continuously use the inverted signal waveform "D" of FIG. 5 (a). FIG. 6 shows the reversal control wave “G” of the rotary die showing the result when the reversal signal waveform “D” is repeatedly used. Since the reversal position of the rotary die is gradually displaced in the positive direction, the SZ spiral groove is formed. The angular position of the circumference in the slot cross section of the reversal center part of is gradually changed on the circumference. As described above, even if only one inverted signal waveform is used, the inverted center portion of the SZ slot can be changed in the longitudinal direction of the slot by using a waveform in which the phases of the start point and the end point are shifted.

Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments. For example, as a method of changing the magnitude of a predetermined reversal angle, , Length with optical cable (80m)
Although the reversal angle is gradually increased and then decreased is illustrated, of course, conversely, the reverse angle may be gradually decreased and then increased. Alternatively, the spiral groove may be engraved at a predetermined reversal angle for several pitches (at least 5 pitches or more), and then the reversal angle may be changed by 360 ° ÷ the number of spiral threads. When the pitch interval that allows the inversion center of the adjacent groove to face the outside of the winding drum is 2 m or less in the length of the optical cable, it becomes difficult to assemble the optical fibers, and when it is 100 m or more, The length is preferably about 2 m to 100 m because it takes time to manufacture the slot.

[0038]

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

(A) According to the invention of claim 1, SZ
Even when the tape-shaped optical fiber core is housed in the SZ spiral groove of the slot and wound around the winding drum, the tensile strain applied to a specific optical fiber core can be suppressed low.

(B) According to the second aspect of the invention, since the circumferential angular position in the SZ slot at the reversal center is gradually changed, the tape-shaped optical fiber core wire housed in the specific groove is pulled. The strain can be gradually reduced.

(C) According to the third aspect of the invention, since the circumferential angular position in the SZ slot at the reversal center is partially changed, the tape-shaped optical fiber core wire housed in a specific groove. Only a large tensile strain is not applied.

(D) According to the invention described in claim 4, at least the predetermined groove and the tape-shaped optical fiber core wire accommodated in the groove adjacent thereto can share the tensile strain due to bending. .

(E) According to the invention described in claim 5, the strain generated in the tape-shaped optical fiber core wire against bending is small and the post-branching property is good.

(F) According to the sixth aspect of the invention, the circumferential angular position in the slot cross section of the plurality of reversing center portions of each spiral groove can be changed by simply changing the forward and reverse angles of the rotary die. It is possible to form a groove that does not always exist at the same angular position in the longitudinal direction of the.

(G) According to the invention described in claim 7, by performing the inversion control of the rotary die by combining the forward / reverse inversion periodic signal waveform and the signal waveform having a longer wavelength and a smaller amplitude than the signal waveform, The circumferential angular position in the slot at the center of inversion gradually changes in the longitudinal direction of the slot S
A Z spiral groove can be obtained.

(H) According to the invention described in claim 8, the SZ spiral groove having a desired changed reversal angle can be obtained by performing reversal control of the rotary die by combining various waveforms.

(I) According to the ninth aspect of the invention, it is possible to perform the inversion control for changing the forward / reverse inversion angle of the rotary die by using only one waveform signal wave.

(J) According to the tenth aspect of the invention, the tape-shaped optical fiber core wire housed in the SZ spiral groove whose circumferential angular position in the SZ slot cross section of the inversion center portion is displaced is wound up. If it is wound around a drum, the tensile strain applied to a specific optical fiber core wire can be kept low and it can be stored for a long time on a winding drum.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical fiber cable having an SZ slot of the present invention.

FIG. 2 is an explanatory view showing a state in which the optical fiber cable of the present invention is wound around a winding drum.

FIG. 3 is a diagram showing a change in strain of an optical fiber core wire with respect to winding of an optical cable, (a) is a strain change diagram of a conventional optical cable, and (b) is a strain change diagram of the present invention.

FIG. 4A is a graph showing two signal waveforms given to the rotary die, and FIG. 4B is a graph showing an inversion control wave of the rotary die based on a combination of the two signal waveforms.

FIG. 5A shows a reversal control waveform of a phase-shifted rotary die in which the rotation start point of the die is 0 degrees and the end point is 30 degrees, and FIG. Shows a reversal control waveform of a rotating die with a phase shift of −30 degrees at the end point, and (c) shows a reversal control waveform of the rotating die when different waveforms are used by switching. is there.

FIG. 6 is a graph showing an inversion control wave of a rotary die when one inversion control waveform having a phase shift is repeatedly used.

FIG. 7 is a cross-sectional view of a conventional optical fiber cable having an SZ slot.

FIG. 8 is a structural schematic view of a conventional SZ slot in which the direction of the spiral is reversed.

FIG. 9 is a cross-sectional view showing an SZ slot manufacturing apparatus.

FIG. 10 is an explanatory diagram showing a state in which a conventional optical fiber cable is wound around a winding drum.

[Explanation of symbols]

20 optical fiber cable 22 Tension members 23 SZ slots 24 (24-I to 24-V) Tape-shaped optical fiber core wire 25 Pressing layer 26 sheath 27 winding drum I to V spiral groove

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Michio Suematsu             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office F term (reference) 2H001 BB10 BB16 DD04 MM01 PP01

Claims (10)

[Claims] 1. An SZ slot for an optical cable in which a plurality of SZ spiral grooves whose spiral directions are alternately inverted at a predetermined reversal angle are engraved on a plurality of outer peripheral surfaces, and a plurality of reversal center portions of each spiral groove are provided. The SZ slot for an optical cable is characterized in that the circumferential angular position in the slot cross section of the slot does not always exist at the same angular position in the longitudinal direction of the slot. 2. The magnitude of the predetermined reversal angle is obtained by periodically repeating the step of gradually increasing and then decreasing the reversal angle from the predetermined reversal angle or decreasing and then increasing the reversal angle to return to the predetermined reversal angle. 2. The SZ slot for an optical cable according to claim 1, wherein the SZ slot is partially modified over a predetermined length range of the SZ slot. 3. The magnitude of the predetermined reversal angle is set to a predetermined value of the SZ slot by periodically repeating the process of changing the reversal angle from the predetermined reversal angle by a certain angle and then returning to the initial predetermined reversal angle. The SZ slot for an optical cable according to claim 1, which is partially modified over a length range. 4. The optical cable according to any one of claims 1 to 3, wherein the deviation of the circumferential position at the reversal center portion due to the change of the predetermined reversal angle is at least 360 degrees / number of grooves and 360 degrees or less. SZ slot. 5. The predetermined reversal angle is about 230 degrees to 33 degrees.
The SZ slot for an optical cable according to any one of claims 1 to 4, wherein the SZ slot has a range of 0 degree. 6. An SZ for an optical cable in which a plurality of SZ spiral grooves, whose spiral directions are alternately inverted at a predetermined reversal angle, are formed on the outer peripheral surface of a plurality of threads by extruding a molten resin through a rotating die that alternately rotates forward and backward. A method of manufacturing a slot,
A method for manufacturing an SZ slot for an optical cable, characterized in that the magnitude of the predetermined reversal angle is changed by changing the angle at which the rotary die rotates in the forward and reverse directions. 7. The rotating die is formed by combining a forward / reverse inversion periodic signal waveform of a rotating die having an SZ spiral groove having the predetermined inversion angle and a signal waveform having a longer wavelength and a smaller amplitude than the signal waveform. 7. The SZ for optical cable according to claim 6, wherein the SZ is forward and reverse.
Slot manufacturing method. 8. The SZ for optical cable according to claim 6, wherein a plurality of waveforms in which the start point and the end point are out of phase with each other are prepared, and the forward and reverse inversion angles of the rotary die are changed by switching and using these waveforms. Slot manufacturing method. 9. The method of manufacturing an SZ slot for an optical cable according to claim 6, wherein the angle of forward and reverse inversion of the rotary die is varied by repeatedly using waveforms in which the phases of the start point and the end point are out of phase. 10. An SZ slot provided with a tension member at the center thereof, in which a plurality of SZ spiral grooves in which the spiral direction is alternately inverted at a predetermined reversal angle are engraved, and an SZ slot of the plurality of threads.
An optical fiber cable comprising a tape-shaped optical fiber core wire housed in a Z spiral groove and a sheath covering the outermost periphery, wherein the plurality of tape-shaped optical fiber core wires housed in the respective SZ spiral grooves. The optical fiber cable, wherein the circumferential angular position in the slot cross section of the reversal center is not always at the same angular position in the longitudinal direction of the slot.