JP2020016798A - Method for manufacturing optical fiber - Google Patents

Abstract

To provide a method for manufacturing an optical fiber that enables manufacture of a favorable optical fiber.SOLUTION: A method for manufacturing an optical fiber comprises: a drawing step P1 of drawing an optical fiber preform to form a bare optical fiber; a coating layer forming step P2 of providing the bare optical fiber with a coating layer made by subjecting a thermosetting resin to primarily curing, to form an optical fiber; a winding step P6 of winding the optical fiber around a heating bobbin while the coating layers of the adjacent optical fibers are spaced from each other; and a heating step P7 of heating the heating bobbin around which the optical fiber is wound, to subject the thermosetting resin to secondary curing.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing an optical fiber, and more specifically, to a method for manufacturing an optical fiber in which a coating layer is formed from a thermosetting resin.

  In recent years, high-power fiber lasers have been put to practical use. In such a high-output fiber laser, the coating layer of the optical fiber tends to be heated to a high temperature due to leakage light or the like, so that the coating layer may be formed from a material having excellent heat resistance. As such an optical fiber, there is known an optical fiber in which a bare optical fiber consisting of a core and a clad is covered with a coating layer made of a thermosetting resin. Patent Document 1 listed below discloses a method for manufacturing such an optical fiber.

  In the method for manufacturing an optical fiber described in Patent Document 1 below, an optical fiber is formed by covering an optical fiber bare wire with a coating layer made of a thermosetting resin, winding the optical fiber around a bobbin, and then winding the optical fiber. Is heated together with the bobbin. According to such a manufacturing method, since the optical fiber wound around the bobbin is heated together with the bobbin, compared to the case where the drawing speed is reduced during drawing and the thermosetting resin is sufficiently heated and cured, It is said that the manufacturing time can be reduced.

JP 2007-230838 A

  However, in the method for manufacturing an optical fiber disclosed in Patent Document 1, since the optical fiber is wound around the bobbin in a multilayer, the coating layers of the optical fiber are in contact with each other. When the bobbin is heated in such a state, the coating layers tend to adhere to each other due to the curing of the uncured component of the thermosetting resin. For this reason, when the optical fiber is removed from the bobbin, there arises a problem that the coating layer peels off from the bare optical fiber, and there is a concern that it is difficult to produce a good optical fiber.

  Then, an object of the present invention is to provide an optical fiber manufacturing method capable of manufacturing a good optical fiber.

  In order to achieve the above object, a method of manufacturing an optical fiber according to the present invention includes a drawing step of drawing an optical fiber preform to form a bare optical fiber, and a coating layer formed by primary curing of a thermosetting resin. Providing a coating layer on the bare optical fiber to form an optical fiber, and winding the optical fiber on a bobbin capable of heating the optical fiber by separating the coating layers on at least a part of the adjacent optical fiber from each other. And a heating step of heating the optical fiber wound on the bobbin and secondary curing the thermosetting resin.

  According to this method of manufacturing an optical fiber, the coating layers of adjacent optical fibers are wound around a bobbin while being separated from each other. Therefore, when the uncured component of the primary cured thermosetting resin is heated in the heating step, fixation of the coating layers due to curing of the uncured component is suppressed. By suppressing the adhesion between the coating layers as described above, the separation of the coating layer from the bare optical fiber when the optical fiber is removed from the bobbin is suppressed. Therefore, a good optical fiber can be manufactured.

  In addition, according to this method for manufacturing an optical fiber, the entire optical fiber having the wound coating layer is heated together with the bobbin. Therefore, when the uncured component of the thermosetting resin remains in the coating layer, the uncured component is heated. The curing component can be cured simultaneously throughout the optical fiber. Since the heating step of curing the uncured component is performed after drawing, before the optical fiber is wound around the bobbin, the drawing speed is not reduced to secure a heating time for curing the uncured component. Can be drawn. As described above, according to the method for manufacturing an optical fiber in the present embodiment, it is not necessary to reduce the drawing speed, and since the uncured components can be simultaneously cured, a decrease in the production speed of the optical fiber is suppressed. obtain.

  Preferably, the coating layers are separated from each other over the entire optical fiber wound around the bobbin.

  Thereby, fixation of the coating layers can be more effectively suppressed.

  Further, in the winding step, the optical fiber may be wound in a single layer around the outer peripheral surface of the bobbin.

  In this case, it may be easy to wind the optical fiber with the coating layers separated from each other.

  Further, in the winding step, the optical fiber is formed into a multi-layer winding around the outer peripheral surface of the bobbin, and an intervening member that can be separated from the coating layer after the heating step is disposed between the layers of the multi-layered optical fiber. May be done.

  With such an intervening member, the optical fiber can be wound into a multilayer while suppressing the contact between the coating layers of the optical fiber in the radial direction of the bobbin. Therefore, it is possible to increase the amount of the optical fiber wound around one bobbin while suppressing the contact between the coating layers of the optical fiber. Therefore, the number of bobbins to be prepared can be reduced as compared with the case where the optical fiber is wound in one layer. Further, in this case, it is possible to perform multilayer winding without cutting the optical fiber. Alternatively, after the optical fiber is cut, the intervening member may be interposed between the cut optical fibers to form a multilayer winding.

  The intervening member may be a flexible sheet.

  Since such a flexible interposed member tends to have elasticity, the load applied to the optical fiber is dispersed, and a better optical fiber can be manufactured.

  Further, the method for producing an optical fiber further includes a cutting step of cutting the optical fiber to a predetermined length before the winding step, wherein the optical fiber cut in the cutting step in the winding step May be wound around the bobbin.

  In this case, since the winding step can be performed after the optical fiber is cut to a predetermined length, the optical fiber can be easily wound around the bobbin.

  Further, it is preferable that the bobbin is formed of a material having a linear expansion coefficient equal to or less than the bare optical fiber.

  In this case, in the heating step, the bobbin is prevented from expanding more than the bare optical fiber, and the stress caused by the expansion of the bobbin can be suppressed from being applied to the optical fiber.

  The core of the optical fiber may be doped with ytterbium (Yb).

  In an optical fiber in which the core is doped with ytterbium, if the drawing speed is low, the dopant added to the core may be crystallized to cause an increase in transmission loss. However, according to the method for manufacturing an optical fiber, since the drawing can be performed without reducing the drawing speed as described above, even when ytterbium is added to the core, the crystallization of the dopant is suppressed. Thus, an optical fiber with small transmission loss can be manufactured.

  As described above, according to the method for manufacturing an optical fiber of the present invention, a good optical fiber can be manufactured.

FIG. 3 is a cross-sectional view perpendicular to the central axis of the optical fiber manufactured by the manufacturing method of the present invention. 4 is a flowchart illustrating steps of a manufacturing method according to the first embodiment of the present invention. It is a figure which shows the mode of a drawing process schematically. It is a figure showing roughly a mode of a bobbin after a winding process. It is a flow chart which shows a process of a manufacturing method concerning a 2nd embodiment of the present invention. FIG. 3 is a diagram schematically illustrating a state in which an optical fiber is wound around a bobbin by one layer. It is a figure which shows the state where the optical fiber was covered with the interposition member schematically. FIG. 3 is a diagram schematically illustrating a state in which the optical fiber is wound around a bobbin in two layers. It is a figure explaining an example of the present invention. 4 is a graph illustrating an example of the present invention.

  Hereinafter, embodiments for carrying out a method for manufacturing an optical fiber according to the present invention will be exemplified with reference to the accompanying drawings. The embodiments illustrated below are for the purpose of facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be modified and improved from the following embodiments without departing from the gist thereof. In this specification, the dimensions of each member may be exaggerated for ease of understanding.

  FIG. 1 is a sectional view perpendicular to the central axis of an optical fiber manufactured by the method for manufacturing an optical fiber according to the present invention. As shown in FIG. 1, the optical fiber 1 includes a core 11, a clad 12 surrounding the outer peripheral surface of the core 11 without any gap, and a coating layer 15 covering the outer peripheral surface of the clad 12. The coating layer 15 has an inner coating layer 13 covering the outer peripheral surface of the clad 12 and an outer coating layer 14 covering the outer peripheral surface of the inner coating layer 13.

  In the example of the present embodiment, the core 11 and the clad 12 are each made of silica glass, and the refractive index of the core 11 is higher than the refractive index of the clad 12. For example, when the core 11 is made of silica glass to which a dopant such as germanium or ytterbium for increasing the refractive index is added, the clad 12 is made of pure silica glass or silica glass to which a dopant such as fluorine is added. When the core 11 is made of pure silica glass, for example, the clad is made of silica glass to which a dopant such as fluorine for lowering the refractive index is added. In the example of the present embodiment, the inner coating layer 13 of the coating layer 15 is made of a predetermined thermosetting resin, and the outer coating layer 14 of the coating layer 15 is made of a thermosetting resin different from the inner coating layer 13. Is done.

  Next, a method for manufacturing such an optical fiber 1 will be described.

(1st Embodiment)
FIG. 2 is a flowchart showing steps of a method for manufacturing an optical fiber according to the first embodiment of the present invention. As shown in FIG. 2, this manufacturing method includes a drawing step P1, a coating layer forming step P2, an intermediate winding step P3, a first inspection step P4, a cutting step P5, and a winding step P6. The method includes a heating step P7, a rewinding step P8, and a second inspection step P9. Hereinafter, these steps will be described.

<Drawing process P1>
This step is a step of forming a bare optical fiber by drawing an optical fiber preform. FIG. 3 is a diagram schematically showing the state of the drawing step P1. First, as a preparation stage for performing this step, the optical fiber preform 1P is placed in the spinning furnace 110. The optical fiber preform 1P is formed of silica glass having a refractive index distribution substantially the same as the core 11 and the clad 12 of the optical fiber 1 described above.

  Next, the heating unit 111 of the spinning furnace 110 is heated to heat the optical fiber preform 1P. At this time, the lower end of the optical fiber preform 1P is heated to, for example, 2000 ° C. and becomes a molten state. Then, the glass is melted from the optical fiber preform 1P, and the glass is drawn at a predetermined drawing speed. When the drawn glass in the molten state exits from the spinning furnace 110, it is immediately solidified to form the bare optical fiber 1N including the core 11 and the clad 12. Thereafter, the bare optical fiber 1N passes through the cooling device 120 and is cooled to an appropriate temperature. When entering the cooling device 120, the temperature of the bare optical fiber 1N is, for example, about 1000 ° C., but when exiting the cooling device 120, it becomes, for example, 40 ° C. to 50 ° C.

<Coating layer forming step P2>
This step is a step of forming the optical fiber by providing the coating layer on the bare optical fiber by first curing the thermosetting resin. As shown in FIG. 3, the bare optical fiber 1N exiting from the cooling device 120 passes through a first coating device 131 containing a first thermosetting resin made of a predetermined material, and the first thermosetting resin For the primary coating. In the example of the present embodiment, the first thermosetting resin is formed from a material that is crosslinked by heating under predetermined conditions. The primary coated bare optical fiber 1N passes through a first heating furnace 132 and is heated in the first heating furnace 132 at, for example, 250 to 600 ° C. for 2.0 to 5.0 seconds. By this heating, the material forming the first thermosetting resin is crosslinked, and the first thermosetting resin is primarily cured. As a result, the inner coating layer 13 made of the first thermosetting resin is formed on the outer peripheral surface of the bare optical fiber 1N.

  The bare optical fiber 1N covered with the inner coating layer 13 passes through a second coating device 133 containing a second thermosetting resin made of a material different from the first thermosetting resin, and this second thermosetting Secondary coating with a conductive resin. In the example of the present embodiment, the second thermosetting resin is formed of a material that is crosslinked by heating under predetermined conditions, like the first thermosetting resin. The second coated bare optical fiber 1N passes through the second heating furnace 134 and is heated in the second heating furnace 134 at, for example, 250 to 600 ° C. for 2.0 to 5.0 seconds. Due to this heating, the material forming the second thermosetting resin is crosslinked, and the second thermosetting resin is primarily cured. As a result, the outer coating layer 14 made of the second thermosetting resin is formed on the outer peripheral surface of the inner coating layer 13.

  Through the above steps, the optical fiber 1 in which the bare optical fiber 1N is covered with the coating layer 15 including the inner coating layer 13 and the outer coating layer 14 is formed. At this stage, the thermosetting resin is in a primary cured state, and the coating layer 15 tends to remain uncured components of the thermosetting resin.

  Note that, although different from the above description, after the primary coating with the first thermosetting resin to be the inner coating layer 13, the second coating with the second thermosetting resin to be the outer coating layer 14, and the primary coating and The first coated thermosetting resin and the second thermosetting resin may be first-cured at a time by heating the bare second-coated optical fiber through a heating furnace.

  In addition, the optical fiber may be covered with a single coating layer, and in this case, the step of secondary coating by the second coating device 133 and the second heating furnace 134 is not required.

<Intermediate winding step P3>
This step is a step of winding the optical fiber formed in the coating layer forming step P2 around an intermediate winding bobbin. As shown in FIG. 3, the optical fiber 1 formed in the coating layer forming step P2 is turned by a turn pulley 141 and wound around an intermediate winding bobbin 142 at a predetermined winding speed.

<First inspection step P4>
This step is a step of inspecting the optical fiber 1 wound around the intermediate winding bobbin 142. For example, it is measured whether the strength, transmission loss, and the like of the optical fiber 1 satisfy a predetermined standard. . In the first inspection process P4, the optical fiber 1 that satisfies the predetermined standard proceeds to a subsequent process. In this step, items other than the strength and the transmission loss may be inspected.

<Cutting step P5>
This step is a step of cutting the optical fiber 1 wound around the intermediate winding bobbin 142 into a predetermined length while unwinding the optical fiber 1 from the intermediate winding bobbin 142. The optical fiber 1 is cut into a length suitable for winding on a heating bobbin in a winding step P6 to be performed thereafter, and at least one optical fiber 1 having such a length is obtained.

<Winding process P6>
This step is a step of winding the optical fiber 1 around a heating bobbin. In the present embodiment, the optical fiber cut in the cutting step P5 is wound around a heating bobbin. FIG. 4 is a diagram schematically showing the winding step P6. In FIG. 4, a winding pitch λ described later is enlarged for easy understanding.

  As shown in FIG. 4, the heating bobbin 150 is a bobbin that can be heated in a heating step P7 described later, and includes a tubular bobbin main body 151 and flanges 152 provided at both ends of the bobbin main body 151. Have. Note that the heating bobbin 150 may be used for purposes other than the heating step P7. At the center in the radial direction of the heating bobbin 150, a through space 150A that penetrates the heating bobbin 150 in the axial direction is formed. A rotary shaft of a winding machine (not shown) for winding an optical fiber around a bobbin is inserted into the through space 150A. In the present embodiment, the heating bobbin 150 is formed of a material having a linear expansion coefficient equal to or less than the linear expansion coefficient of the bare optical fiber 1N, for example, glass, ceramic, stainless steel, or the like. First, in the present embodiment, as a preparation stage for performing this step, the heating bobbins 150 are prepared by the number of optical fibers 1 cut and prepared in the cutting step P5.

  Next, each of the optical fibers 1 is wound around each of the prepared heating bobbins 150. Specifically, the heating bobbin 150 is set in the winding machine by inserting the rotation shaft of the winding machine into the through space 150A. Thereafter, the optical fiber 1 is wound around the bobbin main body 151 of the heating bobbin 150 in a single layer by rotating the rotating shaft to rotate the heating bobbin 150. As shown in FIG. 4, in this step, the winding pitch λ of the optical fiber 1 wound around the bobbin main body 151 is made larger than the outer diameter of the optical fiber 1. That is, the optical fiber 1 is wound around the bobbin body 151 in one layer so that the coating layers 15 are separated from each other over the entire optical fiber 1 wound around the heating bobbin 150.

  It is preferable that the winding pitch λ is, for example, larger than the outer diameter of the optical fiber and smaller than twice the outer diameter of the optical fiber. By setting the winding pitch λ to such a length, the distance between optical fibers adjacent in the axial direction of the bobbin main body 151 becomes smaller than the outer diameter of the optical fiber. Can be lengthened.

  It is preferable that both ends of the wound optical fiber 1 be fixed by using a tape 170 or the like in order to prevent the optical fiber 1 from being displaced after winding and coming into contact with each other. . Further, in consideration of the heating step P7 to be performed thereafter, it is preferable that the tape 170 is a glass tape or the like having heat resistance to the temperature of the heating step.

<Heating process P7>
This step is a step of heating the heating bobbin around which the optical fiber 1 is wound, and secondary curing the first thermosetting resin and the second thermosetting resin forming the coating layer 15. As described above, the first thermosetting resin and the second thermosetting resin are primarily cured in the coating layer forming step P2, but are not sufficiently cured only by heating in the coating layer forming step P2. Cured components tend to remain. If the optical fiber is used in such a state, the surface of the optical fiber may exhibit adhesiveness due to the uncured component, so that the handleability is reduced, and it is difficult for the optical fibers to separate from each other when they come into contact with each other. Problems can occur. This step is a step of curing the uncured component by reheating the primary cured thermosetting resin. In this step, the heating bobbin 150 around which the optical fiber 1 is wound is reheated in a heating furnace (not shown), the thermosetting resin is secondarily cured, and the resin of the uncured component of the coating layer 15 is reduced. .

  Note that the heating in this step may be heating at a lower temperature and for a longer time than when, for example, the thermosetting resin is primarily cured. Specifically, for example, heating at 80 to 200 ° C. for 0.5 to 48 hours may be performed.

<Rewinding process P8>
This step is a step of unwinding the optical fiber 1 in which the thermosetting resin has been secondarily cured from the heating bobbin 150, and rewinding the optical fiber 1 onto a shipping bobbin (not shown), for example. Thus, the optical fiber 1 from which the resin of the uncured component has been reduced from the coating layer 15 is wound around a shipping bobbin or the like.

<Second inspection process P9>
This step is a step of inspecting the optical fiber 1 on which the thermosetting resin has been secondarily cured, for example, measuring whether the strength, transmission loss, etc. of the optical fiber 1 satisfy the criteria as a finished product. Is done. In this step, items other than the strength and the transmission loss may be inspected.

  Note that the first inspection step P4 may be omitted and only the second inspection step P9 may be performed. Alternatively, only the first inspection step P4 may be performed, and the second inspection step P9 may be omitted. Alternatively, both the first inspection step P4 and the second inspection step P9 may be omitted.

  As described above, the drawing step P1, the coating layer forming step P2, the intermediate winding step P3, the first inspection step P4, the cutting step P5, the winding step P6, the heating step P7, the rewinding step P8, and the second inspection Through step P9, an optical fiber whose covering layer is made of a thermosetting resin shown in FIG. 1 is manufactured.

  As described above, according to the method for manufacturing an optical fiber in the present embodiment, when the optical fiber 1 is wound around the bobbin main body 151, the coating layers 15 adjacent to each other in the axial direction of the heating bobbin 150 are separated from each other. Therefore, in the heating step P7, it is suppressed that the uncured component of the thermosetting resin is cured in a state where the coating layer 15 is in contact with the coating layer 15 and the coating layers 15 are fixed to each other. For this reason, when the optical fiber 1 is unwound from the heating bobbin 150 in the rewinding step P8, the coating layer 15 is prevented from peeling off from the bare optical fiber 1N. Therefore, according to the present manufacturing method, a good optical fiber can be manufactured.

  Further, according to the method for manufacturing an optical fiber in the present embodiment, since the heating bobbin 150 is formed from a material having a linear expansion coefficient of 1 N or less of the bare optical fiber, the heating bobbin 150 is Expansion that is greater than that of the bare wire 1N can be suppressed, and application of stress caused by expansion of the heating bobbin 150 to the optical fiber 1 can be suppressed. Therefore, better optical fibers can be manufactured.

  Further, according to the method for manufacturing an optical fiber in the present embodiment, since the entire optical fiber 1 having the wound coating layer 15 is heated together with the heating bobbin 150, the uncured thermosetting resin is applied to the coating layer 15. When the components remain, the uncured components can be simultaneously cured over the entire optical fiber 1. Since the heating step P7 for curing the uncured component is performed after drawing, the drawing speed is reduced before the optical fiber is wound around the bobbin in order to secure a heating time for curing the uncured component. You can draw without drawing. As described above, according to the method for manufacturing an optical fiber in the present embodiment, it is not necessary to reduce the drawing speed, and since the uncured components can be simultaneously cured, a decrease in the production speed of the optical fiber is suppressed. You.

  By the way, when ytterbium is added to the core 11 of the optical fiber, if the drawing speed is low, the dopant added to the core 11 tends to crystallize and increase the transmission loss. However, according to this method of manufacturing an optical fiber, it is not necessary to reduce the drawing speed as described above, so that an optical fiber with a small transmission loss can be manufactured even when ytterbium is added to the core. obtain.

(2nd Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. It should be noted that components that are the same as or equivalent to those in the first embodiment are given the same reference numerals and may not be described repeatedly unless otherwise specified.

  FIG. 5 is a flowchart illustrating steps of a method for manufacturing an optical fiber according to the second embodiment. As shown in FIG. 5, the optical fiber manufacturing method according to the second embodiment differs from the first embodiment in that the cutting step P5 is not performed and the winding step P6 is different as follows. Is different from the optical fiber manufacturing method described in

  In the winding step P6 in the present embodiment, first, as shown in FIG. 6, similarly to the winding step P6 in the first embodiment, the coating layers 15 adjacent in the axial direction of the heating bobbin 150 are not in contact with each other. Next, the optical fiber 1 is wound in a single layer around the outer peripheral surface of the bobbin main body 151 of the heating bobbin 150. However, in the present embodiment, since the cutting step P5 is not performed as described above, the optical fiber 1 wound around the heating bobbin 150 is a long light having a length longer than a single-layer winding. Fiber.

  Next, as shown in FIG. 7, the optical fiber 1 wound in one layer is covered with a predetermined intervening member 160. The intervening member 160 is a flexible sheet that can be separated from the coating layer 15 after the heating step P7. As the intervening member 160, for example, a polymethylpentene wrap, a layer containing polyethylene and a layer containing polypropylene are used. A multi-layered wrap, a sheet made of polytetrafluoroethylene, or the like can be used.

  Next, as shown in FIG. 8, the coating layers 15 adjacent to each other in the axial direction of the heating bobbin 150 come into contact with the surface of the interposition member 160 covering the optical fiber 1 wound in a single-layer winding as described above. The optical fiber 1 is wound into a single layer so as not to cause this. In this embodiment, the optical fiber 1 is wound around the bobbin main body 151 without being cut. That is, since the first-layer optical fiber 1 and the second-layer optical fiber 1 are wound via the intervening member 160, the light is emitted in a state where the coating layers 15 are separated in the radial direction of the heating bobbin 150. The fiber 1 is wound.

  By repeating the step of covering the wound optical fiber 1 with the intervening member 160 and the step of winding the optical fiber 1 on the intervening member 160 in a single-layer winding, without cutting the optical fiber 1, The optical fiber 1 can be formed into a multilayer winding while being spaced apart in the radial direction.

  As described above, according to the method for manufacturing an optical fiber in the present embodiment, the interposition member 160 is arranged in the winding step P6, so that the coating layers 15 of the optical fiber 1 are prevented from coming into contact with each other in the radial direction. The optical fiber 1 can be formed into a multilayer winding. For this reason, the length of the optical fiber 1 wound around the heating bobbin 150 can be lengthened, and the number of prepared heating bobbins 150 can be reduced as compared with the case where the optical fiber 1 is wound in one layer. Becomes possible.

  Further, according to the method for manufacturing an optical fiber in the present embodiment, as described above, the interposition member 160 can be separated from the coating layer 15 after the heating step P7, so that the coating layer 15 and the interposition member 160 can be separated after the heating step P7. It is possible to suppress that it is difficult to separate due to adhesion.

  Further, according to the method for manufacturing an optical fiber of the present embodiment, the winding step P6 may be performed immediately after the coating layer forming step P2 because the optical fiber is not cut as described above. In this case, the intermediate winding step P3 can be omitted.

  Further, according to the method for manufacturing an optical fiber in the present embodiment, as described above, the interposition member 160 is a flexible sheet. Since such a flexible material tends to have elasticity, the load applied to the optical fiber 1 can be dispersed by the intervening member 160. Therefore, a better optical fiber 1 can be manufactured.

  As described above, the first and second embodiments have been described as examples of the present invention, but the present invention is not limited to these.

  For example, in the above-described first and second embodiments, an example in which the heating bobbin 150 is formed from a material having a linear expansion coefficient equal to or less than the optical fiber bare wire 1N has been described. It may be formed from a material having a coefficient of linear expansion greater than 1N. However, from the viewpoint of reducing the stress on the optical fiber 1 as described above, the heating bobbin 150 is preferably formed of a material having a linear expansion coefficient equal to or less than the bare optical fiber 1N.

  In the above-described first embodiment, the example in which the cut optical fiber 1 is wound around the heating bobbin 150 after performing the cutting step P5 has been described. However, the optical fiber 1 may be wound one layer around the heating bobbin 150 without performing the cutting step P5. In this case, one end of the portion wound around the heating bobbin 150 is cut off to separate the portion wound around the heating bobbin 150 from the portion wound around the intermediate winding bobbin 142 in the optical fiber 1. You may.

  In the above-described first embodiment, an example in which the coating layers 15 are separated from each other over the entire optical fiber 1 wound around the heating bobbin 150 has been described. The coating layers 15 in at least a part of the matching optical fiber 1 may be wound so as to be separated from each other. Even in this case, it is possible to prevent the uncured components of the thermosetting resin from being cured after the heating step P7 and to fix the coating layers 15 to each other to some extent. However, in order to enhance the effect of suppressing the adhesion between the coating layers after the heating step P7, the optical fiber is wound so that the coating layers 15 are separated from each other over the entire optical fiber 1 wound around the heating bobbin 150. Preferably, it is turned.

  Further, in the above-described second embodiment, an example in which the optical fiber 1 is formed into a multilayer winding without cutting is described. However, similarly to the first embodiment, the optical fiber 1 is cut in the cutting step P5, and the cut light is cut. The optical fiber 1 may be wound in a multilayer by interposing an intervening member between the fibers 1. In this case, the optical fiber may be wound in one layer in a part of the multilayered winding, and the optical fiber 1 may be wound in other layers without being cut. Further, one layer of the optical fiber may be wound around a part of the plurality of heating bobbins 150, and a multilayer may be wound around the other heating bobbins 150.

  Further, in the above-described second embodiment, an example in which the interposed member is formed from a flexible sheet has been described. However, the optical fiber can be separated in the radial direction of the heating bobbin 150, and the heating step can be performed. The interposed member may be formed from other materials as long as it can be separated from the coating layer later.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

(Comparative example)
First, in the drawing step P1, the optical fiber preform 1P was drawn at a drawing speed of 15 m / min to form a bare optical fiber 1N having an outer diameter of about 250 μm.

  After that, the optical fiber 1 was formed in the coating layer forming step P2. More specifically, first, after covering the bare optical fiber 1N with a first thermosetting resin (OF-180 manufactured by Shin-Etsu Chemical Co., Ltd.), the tube length is about 600 mm, and the heating temperature is about 450 ° C. The optical fiber bare wire 1N was passed through the first coating device 131. As a result, the first thermosetting resin was primarily cured, and the inner coating layer 13 was formed on the bare optical fiber 1N. The outer diameter of the inner coating layer 13 was about 400 μm. Next, after covering the inner coating layer 13 with a second thermosetting resin (OF-20 manufactured by Shin-Etsu Chemical Co., Ltd.), a second coating apparatus having a cylinder length of about 800 mm and a heating temperature of about 550 ° C. 133 was passed through the bare optical fiber 1N. Thereby, the second thermosetting resin was primarily cured, and the outer coating layer 14 was formed on the bare optical fiber 1N. That is, the optical fiber 1 in which the bare optical fiber 1N was covered with the coating layer 15 was formed. The outer diameter of the outer coating layer 14, that is, the outer diameter of the optical fiber 1 was about 450 μm.

  After the optical fiber 1 formed as described above was wound around the intermediate winding bobbin 142 in the intermediate winding step P3, three optical fibers 1 having a predetermined length were formed in the cutting step P5.

  Next, as shown in FIG. 9, each of these three optical fibers 1 was bent into a ring shape having a diameter of about 7 cm leaving both ends Ea and Eb. Thereafter, the one end Ea was spirally turned twice to form a spiral portion W, and the other end Eb was passed through the spiral portion W to form a ring-shaped sample 1S. For each of the three ring-shaped samples 1S thus formed, the other end Eb was fixed, and one end Ea was pulled at a speed of 5 mm / min. By doing so, the spiral diameter of the spiral portion W is narrowed, and the coating layer 15 at one end Ea and the coating layer 15 at the other end Eb rub against each other to generate a frictional force. The frictional force was measured for three ring-shaped samples 1S. The result is shown in FIG. As shown in the graph of “Comparative Example” in FIG. 10, the frictional force of these ring-shaped samples 1S was about 3.45 N on average.

  Thereafter, the spiral of the ring-shaped sample 1S was unwound to form a multilayer winding around the heating bobbin 150, and these three heating bobbins 150 were heated at 150 ° C. for 24 hours. As a result, it was confirmed that the coating layer 15 peeled off from the bare optical fiber 1N when the optical fiber 1 was unwound from the heating bobbin 150.

(Example 1)
Three optical fibers 1 similar to the comparative example were formed. Next, a winding step P6 was performed on each of these three optical fibers 1. That is, the optical fiber 1 was wound around the bobbin main body 151 of the heating bobbin 150 by one layer so that the coating layers 15 did not contact each other. The outer diameter of the bobbin main body 151 of the heating bobbin 150 was about 450 mm, and the axial length of the bobbin main body 151 was about 450 mm. The optical fiber 1 was wound around the bobbin body 151 so that the winding pitch λ was about 1.2 mm.

  Thereafter, the heating step P7 was performed on the three heating bobbins 150 around which the optical fiber 1 was wound. That is, the three heating bobbins 150 were placed in an additional heating furnace and heated at 150 ° C. for 3 hours.

  Next, the optical fiber 1 was unwound from each of the heating bobbins 150 after heating. At this time, the optical fiber 1 could be unwound from the heating bobbin 150 without any damage to the coating layer 15. Thereafter, as in the comparative example, three ring-shaped samples 1S shown in FIG. 9 were formed. The frictional force was measured for each of these three ring-shaped samples 1S in the same manner as in the comparative example. As shown in the graph of "Example 1" in FIG. .79N.

(Example 2)
Three optical fibers 1 similar to the comparative example were formed. Next, the winding step P6 was performed under the same conditions as in Example 1, and further, the heating step P7 was performed on the three heating bobbins 150 around which the optical fiber 1 was wound. The heating step P7 in this embodiment is different from that in the first embodiment and is performed at 150 ° C. for 24 hours. That is, the heating step P7 was performed for a longer time than in Example 1.

  Next, the optical fiber 1 was unwound from each of the heating bobbins 150 after heating. At this time, the optical fiber 1 could be unwound from the heating bobbin 150 without any damage to the coating layer 15. Thereafter, as in the comparative example, three ring-shaped samples 1S shown in FIG. 9 were formed. The frictional force of each of the three ring-shaped samples 1S was measured in the same manner as in the comparative example. As shown in the graph of “Example 2” in FIG. 10, the frictional force of the ring-shaped sample 1S was about 0 on average. .68N.

  Then, similarly to the comparative example, the spiral of the ring-shaped sample 1S was unwound to form a multilayer winding around the heating bobbin 150, and the three heating bobbins 150 were heated at 150 ° C. for 24 hours. As a result, it was confirmed that the coating layer 15 did not peel off from the bare optical fiber 1N when the optical fiber 1 was unwound from the heating bobbin 150.

  As described above, in the comparative example, the coating layer 15 was damaged when the optical fiber 1 was unwound from the heating bobbin 150 after heating at 150 ° C. × 24 hours in a multilayer winding. On the other hand, in Example 1 and Example 2, after the heating step P7, the coating layer 15 could be unwound from the heating bobbin 150 without any damage. For this reason, it was confirmed that a good optical fiber can be manufactured according to the optical fiber manufacturing method of the present invention.

  In the comparative example, the frictional force of the ring-shaped sample 1S was measured without performing the heating step P7, and in Example 1, the frictional force of the ring-shaped sample 1S was measured after the heating step P7 of 150 ° C. × 3 hours. In Example 2, the frictional force of the ring-shaped sample 1S was measured after the heating step P7 of 150 ° C. × 24 hours. As is clear from FIG. 10, the longer the heating step P7, the smaller the frictional force between the coating layers. That is, by performing the heating step P7 for a sufficiently long time within a range where the coating layer is not thermally damaged, the surface properties of the coating layer can be improved.

  According to the present invention, an optical fiber manufacturing method capable of manufacturing an excellent optical fiber is provided, and can be used in a fiber laser or the like.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber 1N ... Optical fiber bare wire 1P ... Optical fiber preform 11 ... Core 12 ... Cladding 13 ... Inner coating layer 14 ... Outer coating layer 15 ... Coating layer 110 spinning furnace 131 first coating device 132 first heating furnace 133 second coating device 134 second heating furnace 142 intermediate winding bobbin 150 ..Heating bobbin 151 ... Bobbin body 160 ... Intervening member

Claims (8)

A drawing step of drawing an optical fiber preform to form an optical fiber bare wire,
A coating layer forming step of forming an optical fiber by providing a coating layer formed by primary curing of a thermosetting resin on the bare optical fiber,
A winding step of winding the optical fiber around a heatable bobbin by separating the coating layers in at least a part of the adjacent optical fiber from each other,
A heating step of heating the optical fiber wound around the bobbin and secondary curing the thermosetting resin,
A method for manufacturing an optical fiber, comprising: The method for manufacturing an optical fiber according to claim 1, wherein the coating layers are separated from each other over the entirety of the optical fiber wound around the bobbin. 3. The method according to claim 1, wherein, in the winding step, the optical fiber is wound in a single layer around an outer peripheral surface of the bobbin. 4. In the winding step, the optical fiber is formed into a multi-layer winding around the outer peripheral surface of the bobbin, and an intervening member that can be separated from the coating layer after the heating step is disposed between the layers of the optical fiber that are formed into the multi-layer winding. The method for manufacturing an optical fiber according to claim 1, wherein: The method according to claim 4, wherein the intervening member is a flexible sheet. Further comprising a cutting step of cutting the optical fiber to a predetermined length before the winding step,
The method of manufacturing an optical fiber according to any one of claims 1 to 5, wherein, in the winding step, the optical fiber cut in the cutting step is wound around the bobbin. The method according to any one of claims 1 to 6, wherein the bobbin is formed of a material having a linear expansion coefficient equal to or less than the bare optical fiber. The method according to any one of claims 1 to 7, wherein ytterbium (Yb) is added to a core of the optical fiber.

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