JP3070604B2 - Manufacturing method of optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber having reduced polarization dispersion characteristics.

[0002]

2. Description of the Related Art In a conventional manufacturing method in which one end of an optical fiber preform is heated and softened, and an optical fiber is drawn downward from the one end, a cross-sectional shape of a core portion of the optical fiber and a cladding portion around the core portion are formed. It is difficult to make it completely circular and concentric, and it is customary to have a slightly elliptical or distorted circular shape. Therefore, the refractive index distribution in the cross section of the optical fiber is not completely uniform, and this causes a difference in the group velocity between the two polarized waves in the cross section of the optical fiber, thereby increasing the polarization dispersion. was there.

[0003] This polarization dispersion is particularly problematic when an optical fiber cable is put to practical use as a submarine cable or a trunk cable requiring large-capacity and long-distance transmission.
As a method of solving such a problem of polarization dispersion, after drawing and coating an optical fiber, the optical fiber is periodically guided by a guide roller whose direction of a rotation axis oscillates. A method of producing an optical fiber by twisting has been proposed in Japanese Patent Application Laid-Open No. 9-243833.

FIG. 4 is a view showing a manufacturing process of an optical fiber strand, wherein 1 is an optical fiber preform, 2 is a drawing furnace, 3 is an optical fiber, 4 is an outer diameter measuring device, and 5 and 8 are coating dies. , 6 and 9 are ultraviolet curing resins, 7 and 10 are ultraviolet irradiation devices, 11 is an optical fiber strand, 12 is a guide roller for suppressing line deflection, 13 is a swing guide roller, 14 is a fixed guide roller, and 15 is a take-up roller. It is a reel.

Optical fiber preform 1 placed in drawing furnace 2
Is softened at one end, from which the optical fiber 3 is drawn downward in the vertical direction. The outer diameter of the optical fiber 3 is measured by an outer diameter measuring device 4, and a controller (not shown) controls the drawing speed, the feed speed of the optical fiber preform, and the like so that the wire diameter is within a predetermined range. I do.

An ultraviolet curable resin 6 is applied around the optical fiber 3 by a coating die 5 and is irradiated with ultraviolet rays by an ultraviolet irradiation device 7 to be cured to form a coating. Further, an ultraviolet-curing resin 9 is applied around the coating by a coating die 8, and is irradiated with ultraviolet rays by an ultraviolet irradiation device 10 to be cured to form a second-layer coating, thereby forming an optical fiber 11.

Thereafter, the optical fiber 11 is wound on a take-up reel 15 through a guide roller 12, a swing guide roller 13, a fixed guide roller 14, and the like. 5A and 5B are views for explaining the positional relationship between the optical fiber and each guide roller. FIG. 5A is a front view, and FIG.
(B) is a top view. 6A and 6B are views for explaining the positional relationship between the optical fiber and the line deflection suppressing guide roller. FIG. 6A is a top view, FIG. 6B is a side view, and FIG.
(C) is a front view. FIG. 7 is a top view illustrating the swinging state of the swinging guide roller.

When the swing guide roller 13 is at the swing reference position, the optical fiber 11 descending vertically from above as shown in FIG.
2 and descends downward along the roller surface 13a of the oscillating guide roller 13, the direction is bent by 90 °, the horizontal direction is reached, and the direction is further shifted by 90 degrees by the fixed guide roller 14.
° bends upwards.

The guide roller 12 has a pair of cylindrical rollers arranged in parallel with an interval d of about 2 mm as shown in FIG. 6, and the rotating shaft 12a of the cylindrical roller has a rotating shaft 12a. Each is oriented horizontally,
When viewed from above, as shown in FIG. 5B, the direction of the rotation axis 12a of the cylindrical line-sway suppression guide roller 12 is perpendicular to the rotation axis 13b of the swing guide roller 13. Then, the optical fiber 11 moves downward through a space between the pair of line runout suppressing guide rollers.

Next, the principle of twisting the optical fiber by the swing guide roller will be described. As shown in FIG. 7, the rotating shaft 13b of the swing guide roller 13 is always in the horizontal plane even during swing, and is rotated around a vertical axis 13c passing through the center of the swing guide roller 13 by ± θ (°) from the reference position. Oscillation by reciprocating motion at a constant cycle is performed in the angle range of ()). Therefore, the roller surface 1 where the optical fiber strand comes into contact first
The swing amplitude D (mm) of 3a is expressed by roller diameter (mm) × π
× θ / 360.

The traveling direction of the optical fiber 11 is changed by 90 ° by the swing guide roller 13, and
As shown in FIG. 7, the optical fiber strand attempts to move along the roller surface 13a in the direction perpendicular to the traveling direction of the optical fiber strand by the swing of the roller surface 13a. At this time, the optical fiber 11 rolls around the optical fiber axis.

The rolling state of the optical fiber at that time will be described in more detail. In FIG. 7, the swing guide roller 13 indicated by a solid line indicates a state when the swing guide roller 13 is at the reference position, and the swing guide roller 13 'indicated by the one-dot chain line is rotated by the swing swing angle θ (°) by swing. Thus, a state in which one side is displaced by the swing amplitude is shown. When the roller surface 13a is at the reference position, the position of the optical fiber 11 that first comes into contact with the roller surface 13a is the point Pa.

When the roller face 13'a is displaced by the swing amplitude due to the swing, if the optical fiber strand does not move on the roller face, the optical fiber strand 11 which first comes into contact with the roller face 13'a is Although the position is the point Qa, the optical fiber 1
Since tension is applied to 1, the optical fiber strand moves on the roller surface 13'a in an attempt to travel the shortest distance.

Thus, the position of the optical fiber 11 that first comes into contact with the roller surface 13'a is the roller surface 13'a
It moves to the position of the point Qb on the upper side. At this time, since the frictional force acts on the optical fiber strand 11 and the roller surface 13'a, the optical fiber strand 11 does not slide on the roller surface 13'a but moves. While rotating on the roller surface 13'a. That is, a rotational movement occurs.

When the optical fiber 11 rotates around its axis at the position where the optical fiber 11 first comes into contact with the swing guide roller, the rotational force is transmitted straight up along the optical fiber 11 and the optical fiber 11 rotates. It propagates to the lower softening point of the optical fiber preform that draws the fiber. Since the optical fiber drawn at the lower softening point of the optical fiber preform is still in a softened state and is soft, the rotational force transmitted by the optical fiber directly acts on the glass composition in the optical fiber to be drawn. Torsion. Then, a coating is applied on the twisted optical fiber to form an optical fiber.

The optical fiber generates a rotational force by swinging and mainly serves to transmit the rotational force to the drawn portion of the optical fiber. Therefore, the optical fiber becomes twisted together with the coating. Almost no. The above is the principle of the twist generation of the optical fiber by the swing guide roller.

Since the roller surface swings in the forward and reverse directions with respect to the reference position, the moving direction of the rotational movement of the optical fiber changes at a constant period. Therefore, since the direction of rotation also changes at a constant cycle, the twist generated in the optical fiber is reversed at a constant cycle in the length direction.

[0018]

In order to reduce the polarization dispersion of an optical fiber by twisting the optical fiber, it is necessary to make the degree of twist more than a certain value. At least one twist / m or more in the longitudinal direction of the optical fiber is required. When the drawing speed of the optical fiber is as small as 200 m / min or less, the number of swings per hour of the swing guide roller does not need to be too large, and is 20 to 150 reciprocations / hour.
It is possible to apply a desired twist to the optical fiber in about a minute.

However, when the drawing speed is increased, it is necessary to increase the number of swings per time in order to impart the same degree of twist per optical fiber length. However, when the number of times of swing per hour is increased, the outer diameter of the optical fiber and the outer diameter of the optical fiber strand fluctuate in the longitudinal direction, and a good product with a small fluctuation in the wire diameter cannot be obtained.

When the number of times of swing per time is increased, even if the guide roller is provided for suppressing the line deflection, the line deflection of the optical fiber near the guide roller becomes large, and bubbles in the coating of the optical fiber line are formed there. Even if an attempt is made to install a bubble sensor or the like for detection, there has been a problem that the operation accuracy of the bubble sensor is degraded due to line deflection. In addition, since the line deflection suppressing guide roller is composed of a pair of cylindrical rollers, if the distance between the columnar rollers is large, the line deflection is large, the operation accuracy of the bubble sensor is deteriorated, and the twisting of the optical fiber becomes unstable. When the diameter is small, there is a problem that the optical fiber is squeezed by the cylindrical roller and a gap is formed between the coating and the optical fiber.

Therefore, even if the drawing speed increases, the optical fiber and the outer diameter of the optical fiber in the longitudinal direction vary while giving the optimum twist to the optical fiber and reducing the polarization dispersion characteristics. To provide a method for manufacturing an optical fiber that can reduce the size of the optical fiber. The present invention also provides a method for manufacturing an optical fiber that can further reduce the deflection of the optical fiber and improve the accuracy of a bubble sensor or the like.

[0022]

SUMMARY OF THE INVENTION According to the present invention, an optical fiber preform is heated and softened to draw an optical fiber downward, draw a wire, apply a coating on the optical fiber, and oscillate periodically. In a method of manufacturing an optical fiber while giving an optical fiber a twist around an axis by an oscillating guide roller, a line having a V-shaped narrow groove between the step of applying the coating and the oscillating guide roller The swing guide roller is installed with its rotation axis horizontal, and the swing guide roller is installed at a position where the traveling direction of the optical fiber is bent by the linear shake guide roller. Then, the coated optical fiber is passed through the line deflection suppressing guide roller and the swinging guide roller to impart a twist to the optical fiber.

Thus, the line deflection of the optical fiber before and after the line deflection suppressing guide roller is minimized, and the line deflection of a bubble sensor or the like installed between the ultraviolet irradiation device and the line deflection suppressing guide roller is reduced. Accuracy of sensitive devices can be increased.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view for explaining the swing of a swing guide roller used in a method of manufacturing an optical fiber, and FIGS. It is a top view of a roller. 1A and 1B, the swing guide roller 13 drawn by a solid line shows a case where it is at a swing reference position, and the swing guide roller 1 drawn by an alternate long and short dash line.
3 ′ or 13 ″ indicates a state where the vibration has been displaced to the maximum amplitude, and shows only a state where the vibration has occurred to one side with respect to the reference position. Vibrates in the same way on the side.

In the case of FIG. 1A, the rotating shafts 13b and 13'b of the swinging guide roller are always positioned in the horizontal plane during the swinging, and the rotating shaft 13b swings around the vertical axis 13c. Rotate by θ (°) to reach the position of the rotation axis 13′b. At this time, the roller surface 13a of the swing guide roller 13
Is D (mm) = roller diameter (mm) × π × θ / 360
Only swings to reach the roller surface 13'a. The swing amplitude D is set to be within ± 10 mm and ± 0.5 mm or more. It is more preferable that the swing amplitude D be within ± 7 mm and ± 0.5 mm or more.

Roller surface 13a of swing guide roller 13
However, the optical fiber 11 reciprocates while rolling on the roller surface 13a by swinging at a swing amplitude ± D (mm). The rotational force of the optical fiber 11 is transmitted to the softened and drawn portion of the optical fiber, and the drawn optical fiber itself twists in the longitudinal direction. Since the rolling direction of the optical fiber 11 on the roller surface 13a is reversed by the reciprocating movement of the swing, the twisting direction of the optical fiber is also reversed in the longitudinal direction according to the swing cycle.

Next, a description will be given of how the finding that the amplitude D is preferably in the above range has been obtained. As the drawing speed increases, it is necessary to increase the number of swings of the swing guide roller per time in order to give the optical fiber a twist of a fixed value or more per length. However, it was found that the wire diameter of the optical fiber and the coated wire diameter of the optical fiber wire fluctuated in the longitudinal direction simply by increasing the number of swings. The experiment was repeated to find a condition in which the wire diameter of the optical fiber and the coated wire diameter of the optical fiber did not fluctuate in the longitudinal direction, and the following results were obtained.

Using the roller having various roller diameters shown in Table 1 as a rocking guide roller, rocking in the form shown in FIG. 1A was performed, and the number of rocking per minute was 200 reciprocations. The corners were as shown in Table 1. The drawing speed is 400 m
/ Min, and the drawing tension was 90 to 100 g. as a result,
Table 1 shows the diameter of the optical fiber and the diameter of the optical fiber. The swing amplitude is a value calculated by the following equation. Swing amplitude (mm) = Roller diameter (mm) x π x (Swing swing angle (°) / 360)

[0029]

[Table 1]

According to the results shown in Table 1, it can be seen that the smaller the swing amplitude, the smaller the fluctuation of the optical fiber wire diameter and the optical fiber wire diameter. Swing amplitude ±
When the length is set to 10 mm or less, a practically usable optical fiber can be obtained for the time being. However, in order to obtain a high quality optical fiber, the swing amplitude is desirably set to ± 7 mm or less. Further, when the swing amplitude is set to ± 5 mm or less, the fluctuation of the wire diameter can be further reduced, which is more preferable. Further, if the swing amplitude is too small, it becomes difficult to give a predetermined twist to the optical fiber. Therefore, the swing amplitude is set to ± 0.5 mm or more.

In FIG. 1A, the oscillating guide roller 13 oscillates in a form in which its rotating shaft 13b reciprocates around a vertical shaft 13c, and the oscillating swing angle is ± θ (°). Although an example in which a swing amplitude of ± D (mm) is generated in the direction parallel to the surface of the roller surface by way of example, a swing type shown in FIG. 1B can be used.

FIG. 1B shows a swing guide roller 13 which reciprocates in the direction of the rotation shaft 13b instead of rotating the rotation shaft 13b of the swing guide roller 13 around the vertical axis 13c. "Indicates the swing guide roller 13
2 shows a state displaced by D ′ to one side from the reference position. The swing amplitude in this case is ± D ′.

FIG. 2 is a view for explaining the relationship between the swing guide roller and the front and rear rollers, and is a front view around the swing guide roller. When the optical fiber strand is in contact with the line deflection suppression guide roller, the distance between the line deflection suppression guide roller 12 and the swing guide roller 13 where the optical fiber strand 11 does not contact the rollers on both sides is La, Guide roller 13
The distance between the optical fiber 11 and the fixed guide roller 14 where the optical fiber 11 does not contact the rollers on both sides is Lb, the smaller of La and Lb is L, and the swing amplitude of the swing guide roller is ± D.
(Mm), the relationship of D / L> 0.005 is satisfied.

A description will be given of how the knowledge about the relationship between the distance between the swing guide roller and the front and rear rollers and the swing amplitude of the swing guide roller is obtained. We were studying whether sufficient twist could be given to the optical fiber even when the swing amplitude was reduced, and found that the swing amplitude of the swing guide roller, the linear runout suppression guide roller, and the swing guide roller It was found that the ratio of the distance between the optical fiber and the roller on both sides between the roller and the roller between the roller and the roller was greatly related to the twisting of the optical fiber. Tables 2 and 3 show the results. The number of swings per minute is 200 reciprocations, the drawing speed is 400 m / min, and the drawing tension is 90 to 100 g.
And

[0035]

[Table 2]

[0036]

[Table 3]

According to Tables 2 and 3, the ratio of the swing amplitude D to the distance La between which the optical fiber strand does not contact the rollers on both sides between the line deflection suppressing guide roller and the swing guide roller, that is, the swing When the amplitude D / distance La increases, the number of twists of the optical fiber increases, and the number of twists of the optical fiber is 1 / m.
To achieve the above, the swing amplitude D / the distance La is set to about 0.005.
It turns out that it is sufficient to do the above. That is, if the swing amplitude is the same, a desired value can be obtained by reducing the distance between the shafts between the line deflection suppressing guide roller and the swing guide roller so that the optical fiber does not contact the rollers on both sides. The number of twists of the optical fiber described above can be obtained.

When the optical fiber is in contact with the guide roller, the distance between the guide roller and the swing guide roller is defined as La, the distance between the rollers on both sides where the optical fiber is not in contact with the swing roller. When the distance between the guide roller and the fixed guide roller where the optical fiber is not in contact with the rollers on both sides is Lb, and the swing amplitude of the swing guide roller is D, the slip of the optical fiber on the roller surface is assumed. Is not considered, the torque acting on the optical fiber by the rolling motion of the optical fiber generated on the roller surface of the swing guide roller is proportional to D / La + D / Lb.

Here, assuming that the smaller of La and Lb is L, since 2 × D / L> D / La + D / Lb> D / L, the rotation of the optical fiber around the axis is roughly. , D /
It is almost proportional to L. Therefore, it can be considered that the rotation of the optical fiber around the axis is substantially determined by the distance between the swing guide roller and the roller closer to the swing guide roller among the line deflection suppressing guide roller and the fixed guide roller. Table 2,
Taking these into consideration with the results in Table 3, D / L is set to 0.
005 or more, the twist of the optical fiber can be set to a desired value.
It is considered that the number can be increased to times / m or more.

FIG. 3A is a view for explaining the guide roller and the swing guide roller used in the present invention, and is a front view of the vicinity of the swing guide roller. Also,
FIGS. 3B, 3C and 3D are a side view of the guide roller for suppressing line deflection, a top view of the swing guide roller, and a top view of the fixed guide roller, respectively. The swing guide roller 13 is the same as that shown in FIGS. 1 and 2, and the fixed guide roller 14 is the same as that shown in FIG. 2. However, the line deflection suppression guide roller 12 'is different from the line deflection suppression guide roller 12 shown in FIG.

The guide roller 12 ′ for suppressing line deflection is
The following swing guide roller 13 is provided so that the traveling direction of the optical fiber 11 is bent by the angle α by the line deflection suppressing guide roller 12 ′.
Has been arranged. The angle α is preferably in the range of 5 degrees to 45 degrees, but is more preferably in the range of 10 degrees to 30 degrees. Further, the V-shaped groove of the guide roller 12 ′ may have a V-shape with a sharp bottom or a flat V-shape with a narrow bottom. However, in this case, the width of the bottom is desirably set to such a size that the optical fiber does not slide in the width direction of the bottom, that is, substantially equal to or less than the outer diameter of the optical fiber.

As a result, the optical fiber 11 always passes through the groove bottom of the guide roller 12 'for suppressing line deflection, and the line deflection near the guide roller 12' for suppressing line deflection is reduced. Therefore, the guide roller 12 ′
Even if an air bubble sensor or the like for detecting air bubbles in the coating of the non-contact type optical fiber is installed near the non-oscillating guide roller side, the operation accuracy of the air bubble sensor is degraded due to line deflection. Such a trouble does not occur, and highly accurate bubble detection can be performed. Further, the rotation force about the axis given to the optical fiber 11 by the swing of the swing guide roller 13 needs to be transmitted to the drawing portion of the optical fiber above the line deflection suppressing guide roller 12 ′.
Although the optical fiber 11 is in contact with the groove bottom of the line deflection suppressing guide roller 12 ′, it is traveling at a high speed, so that there is no problem in transmitting the rotational force upward.

[0043]

According to the method of manufacturing an optical fiber according to the present invention, the guide roller has a V-shaped narrow groove, and the guide direction of the optical fiber is controlled by the guide roller. Since the next swing guide roller is disposed at a position where the guide roller is bent, it is possible to make the line runout near the line runout suppressing guide roller extremely small. Therefore, even if a device such as a non-contact type bubble sensor is arranged near the line deflection suppressing guide roller, its accuracy can be sufficiently secured.

When the guide roller for suppressing line deflection according to the prior art shown in FIG. 6 is used, the optical fiber strand passes between the two cylindrical rollers while vibrating. The phenomenon that the gap between the coating of the optical fiber and the optical fiber was peeled off by the roller and a gap was formed was frequently observed. However, the guide roller having the V-shaped narrow groove according to the present invention has been described. Since the optical fiber is not squeezed on the roller surface by the use of, the separation between the coating and the optical fiber is reduced.

In the case of a cylindrical roller, the degree of transmission of the rotation of the optical fiber by the swing guide roller to the upper side changes depending on the degree of contact between the optical fiber and the roller. In some cases, the transmission of the rotation of the optical fiber was always uniform because the guide roller was made V-shaped so that the optical fiber always contacted the roller. And uniform twisting of the optical fiber is obtained.

Further, the optical fiber is passed through the swing guide roller while the swing is performed so that the swing amplitude of the roller surface of the swing guide roller is ± 10 mm or less and ± 0.5 mm or more. The method of imparting twist to an optical fiber is based on the method of controlling the polarization dispersion characteristics of the optical fiber, the diameter of the optical fiber, and the wire of the optical fiber even when the production line speed of the optical fiber is increased. Fluctuation of each diameter can be suppressed to below the allowable value.

Further, the distance between the swinging guide roller and the guide roller or the fixed guide roller can be reduced.
The method of setting the ratio of the swing amplitude to the smaller one of the above distances to 0.005 or more is to impart a sufficient twist to the optical fiber even if the swing amplitude is small, and to improve the polarization dispersion characteristics of the optical fiber. It is possible to manufacture a suppressed optical fiber.

[Brief description of the drawings]

FIG. 1 is a view for explaining the swing of a swing guide roller used in a method of manufacturing an optical fiber, and FIG.
(B) is a top view of each swing guide roller.

FIG. 2 is a diagram for explaining the relationship between a swing guide roller and rollers before and after the swing guide roller, and is a front view around the swing guide roller.

FIG. 3A is a diagram for explaining a line deflection suppressing guide roller, a swing guide roller, and the like used in the present invention, and is a front view around the swing guide roller. (B)
(C) and (D) are a side view of a line deflection suppressing guide roller, a top view of a swing guide roller, and a top view of a fixed guide roller, respectively.

FIG. 4 is a view showing a manufacturing process of an optical fiber.

5A and 5B are diagrams illustrating a positional relationship between an optical fiber and each guide roller, wherein FIG. 5A is a front view and FIG. 5B is a top view.

FIGS. 6A and 6B are diagrams illustrating a positional relationship between an optical fiber and a line deflection suppressing guide roller, wherein FIG. 6A is a top view and FIG.
Is a side view, and (C) is a front view.

FIG. 7 is a top view illustrating a swing state of a swing guide roller.

[Explanation of symbols]

 1: Optical fiber preform 2: Drawing furnace 3: Optical fiber 4: Outer diameter measuring device 5, 8: Coating die 6, 9: UV curable resin 7, 10: UV irradiation device 11: Optical fiber wire 12, 12 ': Line runout suppressing guide rollers 13, 13', 13 ": Swing guide rollers 13a, 13'a: Roller surfaces 13b, 13'b: Rotating shaft 13c: Vertical shaft 14: Fixed guide roller 15: Take-up reel θ : Swing deflection angle (°)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-97463 (JP, A) JP-A-8-295528 (JP, A) JP-A-9-2834 (JP, A) JP-A-9-98 243833 (JP, A) Patent 2981088 (JP, B2) Table 11-508221 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00-6/54 C03B 37 / 12

Claims (1)

(57) [Claims] An optical fiber preform is heated and softened to draw out the optical fiber, draw the optical fiber downward, coat the optical fiber, and apply a coating to the optical fiber by a swinging guide roller that swings periodically. In the method of manufacturing an optical fiber while giving a twist around an axis, a linear runout suppressing guide roller having a V-shaped narrow groove between the step of applying the coating and the swing guide roller is provided on a rotating shaft thereof. Is installed horizontally, the swinging guide roller is installed at a position where the traveling direction of the optical fiber strand is bent by the line deflection suppressing guide roller, and the coated optical fiber strand is moved to the line deflection suppressing guide roller and A method for manufacturing an optical fiber, wherein the optical fiber is twisted by passing through the swing guide roller.