JP6666882B2 - Method of manufacturing single-core optical fiber preform and method of manufacturing single-core optical fiber - Google Patents

Description

  The present invention relates to a method for manufacturing a single-core optical fiber preform and a method for manufacturing a single-core optical fiber.

  In a fiber laser device used as a laser processing machine, a single-core optical fiber in which a rare earth element is added to a core is used. In addition, in such a single-core optical fiber, a double clad structure is generally applied in order to make more pump light enter the core. A single core optical fiber having a double clad structure generally has a core doped with a rare earth element, an inner clad surrounding the core, and an outer clad surrounding the inner clad, and the outer clad has a lower refractive index than the inner clad. Excitation light incident on the inner cladding is reflected on the core side at the interface between the inner cladding and the outer cladding, enters the core, and excites the rare earth element added to the core. However, in such a single-core optical fiber having a double clad structure, when the cross-sectional shape perpendicular to the longitudinal direction of the inner clad is circular, the excitation light continues to be reflected at a certain angle at the interface between the inner clad and the outer clad. In some cases, the excitation light propagates through the inner cladding without entering the core. Such light that propagates through the clad without passing through the core is called skew light. When the skew light is generated, the amount of the excitation light incident on the core is reduced, so that the rare earth element added to the core is hardly excited.

  As a technique for suppressing the generation of skew light, for example, Patent Document 1 below discloses a single-core optical fiber having a polygonal cross section perpendicular to the longitudinal direction of an inner cladding. It is considered that the non-circular cross-sectional shape of the inner cladding makes it easier for the excitation light propagating through the inner cladding to repeatedly reflect while changing the reflection angle on the outer peripheral surface of the inner cladding and to enter the core.

International Publication No. 2009-028614

  When manufacturing a single-core optical fiber having a non-circular cross-sectional shape of the cladding as described above, a single-core optical fiber preform for manufacturing the single-core optical fiber has a non-circular cross-sectional shape perpendicular to the longitudinal direction. It needs to be round. However, when a glass rod having a circular cross section perpendicular to the longitudinal direction is cut so that the cross section becomes non-circular and used as a base material for a single-core optical fiber, the length at which the glass rod can be cut by a machine is: They tend to be restricted. By the way, there is a demand for manufacturing a long single-core optical fiber from one single-core optical fiber preform due to a request for reduction of manufacturing cost and the like. However, since the length at which the glass rod can be cut by a machine tends to be limited as described above, a preform for a single-core optical fiber having a large length and a non-circular cross section perpendicular to the longitudinal direction is produced. It is difficult. For this reason, it is also difficult to produce a long single-core optical fiber having a non-circular cross-sectional shape perpendicular to the longitudinal direction.

  Therefore, the present invention provides a method for manufacturing a single-core optical fiber preform capable of manufacturing a single-core optical fiber preform having a non-circular cross-sectional shape perpendicular to the longitudinal direction and a large length, and a single-core optical fiber. It is intended to provide a manufacturing method.

  A method for manufacturing a preform for a single-core optical fiber according to the present invention for solving the above-mentioned problems includes a plurality of glass rods including a core rod having a core portion serving as a core, and a plurality of clad rods serving as a part of a clad. Bundling step, an external step of depositing soot to be another part of the clad on the outer peripheral surface of the bundled glass rods, and heating the plurality of glass rods on which the soot has been deposited. A sintering step in which the soot and each of the glass rods are integrated into a glass body. In the bundling step, each of the clad rods is in contact with an outer peripheral surface of the core rod and surrounds the core rod. It is characterized by being arranged at a position overlapping with each vertex of the polygon.

  By depositing the soot on the outer peripheral surface of the bundled glass rods, the soot is easily deposited along the outer peripheral surface of the bundle of glass rods. Therefore, by depositing soot in a state where a plurality of clad rods are arranged around the core rod as described above, in a cross section perpendicular to the longitudinal direction of the core rod, the outer peripheral shape of the portion where the soot is deposited surrounds the core rod. The polygon may have a rounded corner. That is, in a cross section perpendicular to the longitudinal direction of the core rod, the soot may be deposited in a non-circular area surrounding the core rod. By sintering the soot thus deposited and integrating it with a plurality of glass rods, it is possible to manufacture a single-core optical fiber preform having a non-circular cross section perpendicular to the longitudinal direction. Further, since the length of the single-core optical fiber preform can be adjusted by adjusting the length of the glass rod, the length of the single-core optical fiber preform can be increased. Therefore, it is possible to manufacture a single-core optical fiber preform having a large length and a non-circular cross section perpendicular to the longitudinal direction.

  Further, each of the clad rods may have the same diameter as each other, and in the bundling step, each of the clad rods may be arranged at a position overlapping each vertex of a regular polygon centered on the center of the core rod. preferable.

  By depositing soot in a state where a plurality of clad rods are arranged, soot can be deposited in a region centered on the core rod in a cross section perpendicular to the longitudinal direction of the core rod. Further, by sintering the soot thus deposited and integrating it with a plurality of glass rods, it is possible to manufacture a single core optical fiber preform whose central axis coincides with the central axis of the core rod. By using such a single-core optical fiber preform, a single-core optical fiber having a core disposed at the center of the clad can be manufactured.

  Further, it is preferable that the core rod has a clad glass layer which becomes a part of the clad on an outer peripheral surface of the core portion.

  Since the core rod has the clad glass layer as described above, it is possible to suppress the core portion of the core rod from being damaged in the bundling process.

  In the bundling step, it is preferable that the outer peripheral surfaces of the clad rods adjacent to each other are in contact with each other.

  In the case where the same number of clad rods are used, when a plurality of clad rods are arranged so as to be in contact with each other as described above, each clad rod is compared with a case where a plurality of clad rods are arranged to be separated from each other. Can be increased in diameter. Therefore, a single core optical fiber having a thick cladding can be manufactured. That is, a single-core optical fiber having a large distance from the center of the core to the outer peripheral surface of the clad can be manufactured. In such a single-core optical fiber, bending loss and loss due to micro venting can be suppressed.

  Further, in the bundling step, it is preferable that outer peripheral surfaces of the clad rods adjacent to each other are separated.

  In the case where the same number of clad rods are used, when a plurality of clad rods are arranged so as to be separated from each other as described above, a core rod having a larger diameter than when a plurality of clad rods are arranged so as to be in contact with each other. Can be used. Therefore, a single-core optical fiber having a larger core diameter when compared with the same fiber diameter can be manufactured.

  In the bundling step, a filling glass rod having a lower refractive index than the core portion and a smaller diameter than the clad rod surrounds the plurality of clad rods by tangent lines that are in contact with the outer peripheral surfaces of the adjacent clad rods. It is preferable to be arranged inside a polygon formed as described above.

  By arranging the filling glass rod in this manner, the cross-sectional shape perpendicular to the longitudinal direction of the single-core optical fiber preform can approach a polygon.

  In the bundling step, it is preferable that the filling glass rod is disposed so as to be in contact with an outer peripheral surface of at least one clad rod.

  By arranging the filling glass rod and the cladding rod in this manner, the deformation of the filling glass rod and the cladding rod in the sintering process can be suppressed.

  In the bundling step, it is preferable that the filling glass rod is disposed so as to be in contact with an outer peripheral surface of the core rod.

  By disposing the filling glass rod and the core rod in this manner, the deformation of the filling glass rod and the core rod in the sintering process can be suppressed.

  In the bundling step, it is preferable that a plurality of the filling glass rods are arranged between the cladding rods adjacent to each other, and the outer peripheral surfaces of the filling glass rods adjacent to each other are in contact with each other.

  By arranging the filling glass rod in this way, deformation of the filling glass rod in the sintering step can be suppressed.

  In the bundling step, it is preferable that the filling glass rod is arranged so as to be in contact with the outer peripheral surface of each of the clad rods adjacent to each other.

  By arranging the filling glass rod and the cladding rod in this way, the deformation of the filling glass rod and the cladding rod in the sintering process is smaller than in the case where the filling glass rod is in contact with only one of the adjacent cladding rods. Can be further suppressed.

  Preferably, an active element is added to the core.

  By adding an active element to the core, a single-core optical fiber manufactured using a single-core optical fiber preform can be used as an amplification optical fiber.

  Further, after the sintering step, the refractive index of another part of the clad made of the soot may be lower than the refractive index of the clad rod.

  By making the refractive index of the part of the clad made of soot lower than the refractive index of the clad rod, the part made of the clad rod in the base material for a single-core optical fiber is made to be a part that becomes a part of the inner clad and made of soot. The portion may be a portion that becomes the outer cladding having a lower refractive index than the inner cladding. By using such a single-core optical fiber preform, a single-core optical fiber having a double clad structure can be manufactured.

  In addition, a method for manufacturing a single-core optical fiber according to the present invention for solving the above-mentioned problem includes a line for drawing a single-core optical fiber preform manufactured by the method for manufacturing a single-core optical fiber preform according to the present invention. It is characterized by comprising a drawing step.

  As described above, according to the method for manufacturing a preform for a single-core optical fiber of the present invention, a preform for a single-core optical fiber having a non-circular cross section perpendicular to the longitudinal direction and a large length can be manufactured. Therefore, by using the single-core optical fiber preform, a long single-core optical fiber having a non-circular cross-sectional shape of the clad can be manufactured.

  As described above, according to the present invention, a method for producing a single-core optical fiber preform capable of producing a single-core optical fiber preform having a non-circular cross-sectional shape perpendicular to the longitudinal direction and a large length, and A method for manufacturing a single core optical fiber is provided.

It is a figure showing the section perpendicular to the longitudinal direction of the single core optical fiber concerning the embodiment of the present invention. 2 is a flowchart illustrating a method for manufacturing the single-core optical fiber of FIG. 1. It is a perspective view showing a bundle of a plurality of glass rods. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods. It is a perspective view showing signs that a dummy glass rod was fixed to an end face of a bundle of a plurality of glass rods. It is a figure showing a situation of an external attachment process. It is a figure showing a situation after an external attachment process. It is a figure showing the section perpendicular to the longitudinal direction of the preform for single core optical fibers concerning the embodiment of the present invention. It is a figure showing a situation of a drawing process. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process concerning a modification of the present invention. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process concerning another modification of the present invention. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process concerning a further modification of the present invention. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process concerning a further modification of the present invention. It is a figure showing a section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process concerning a further modification of the present invention.

  Hereinafter, preferred embodiments of a method for manufacturing a preform for a single-core optical fiber and a method for manufacturing a single-core optical fiber according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a cross section perpendicular to the longitudinal direction of a single-core optical fiber according to an embodiment of the present invention. As shown in FIG. 1, the single-core optical fiber 1 of the present embodiment mainly includes a core 10, a clad 20 surrounding the outer peripheral surface of the core 10 without any gap, and a protective layer 30 covering the outer peripheral surface of the clad 20. Provide as a configuration. In the single-core optical fiber 1 of the present embodiment, the core 10 is disposed at the center of the clad 20. The clad 20 includes an inner clad 21 surrounding the outer peripheral surface of the core 10 without any gap, and an outer clad 22 covering the outer peripheral surface of the inner clad 21, and the single-core optical fiber 1 has a so-called double clad structure. . The refractive index of the inner cladding 21 is lower than the refractive index of the core 10, and the refractive index of the outer cladding 22 is lower than the refractive index of the inner cladding 21.

  In a cross section perpendicular to the longitudinal direction of the single-core optical fiber 1, the outer shape of the inner cladding 21 is non-circular. Specifically, in the cross section perpendicular to the longitudinal direction of the single core optical fiber 1, the outer shape of the inner cladding 21 is such that each vertex of the hexagon is rounded and chamfered, and each side is rounded inward. It has a curved shape. As a material for forming the inner cladding 21, for example, pure quartz to which no dopant is added can be given. It should be noted that an element such as fluorine (F) that lowers the refractive index may be added to the material forming the inner cladding 21.

  The outer cladding 22 of the present embodiment is made of a resin, and examples of the resin include an ultraviolet curable resin.

  The single-core optical fiber 1 of the present embodiment is an amplification optical fiber. Therefore, as a material constituting the core 10, for example, quartz to which an active element such as ytterbium (Yb) is added is given. Examples of such an active element include rare earth elements. Examples of the rare earth element include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), and erbium (Er) in addition to Yb. No. Further, as the active element, bismuth (Bi) or the like can be given in addition to the rare earth element. In addition, an element such as germanium (Ge) that increases the refractive index may be added to a material forming the core 10.

  As a material for forming the protective layer 30, for example, an ultraviolet curable resin different from the resin for forming the outer cladding 22 may be used.

  Next, a method for manufacturing the single-core optical fiber 1 will be described.

  FIG. 2 is a flowchart showing a method of manufacturing the single core optical fiber of FIG. As shown in FIG. 2, the manufacturing method of the single core optical fiber 1 includes a bundling step P1, an external step P2, a sintering step P3, and a drawing step P4 as main steps.

<Bundling process P1>
This step is a step of bundling a plurality of glass rods. FIG. 3 is a perspective view showing a bundle of a plurality of glass rods. FIG. 4 is a diagram showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods. In the present embodiment, the plurality of glass rods are a core rod 2, a plurality of clad rods 3, and a plurality of filling glass rods 4.

  The core rod 2 is a cylindrical glass rod having a core portion 10R serving as the core 10 of the single-core optical fiber 1 of FIG. 1 and a cladding glass layer 20R serving as a part of an inner cladding 21 covering the outer peripheral surface of the core portion 10R. It is. The core portion 10 </ b> R of the core rod 2 is formed of the same material as the core 10 because it becomes the core 10. Further, the clad glass layer 20 </ b> R becomes a part of the inner clad 21 and is made of the same material as the inner clad 21.

  Each of the plurality of clad rods 3 is a columnar glass rod that becomes a part of the inner clad 21. In the present embodiment, six clad rods 3 are prepared. The clad rods 3 are cylindrical glass rods having the same diameter, and are made of the same material. Further, since each clad rod 3 becomes a part of the inner clad 21, it is made of the same material as the inner clad 21. Therefore, the refractive index of each clad rod 3 is lower than the refractive index of the core 10R.

  The plurality of filling glass rods 4 are columnar glass rods each of which becomes a part of the inner cladding 21. In the present embodiment, six filling glass rods 4 are prepared. The filling glass rods 4 are cylindrical glass rods having the same diameter as each other and smaller in diameter than the cladding rod 3. Further, each filling glass rod 4 is made of the same material and becomes a part of the inner cladding 21 so that it is made of the same material as the inner cladding 21. Therefore, the refractive index of each filling glass rod 4 is lower than the refractive index of the core 10R. In the present embodiment, the cladding glass layer 20R, the cladding rod 3, and the filling glass rod 4 are made of the same silica glass.

  The plurality of glass rods are prepared, and then arranged at a position where these glass rods are bundled. As shown in FIG. 3 and FIG. 4, each clad rod 3 is disposed at a position in contact with the outer peripheral surface of the core rod 2 and overlapping with each vertex of a regular hexagon surrounding the core rod 2 around the center of the core rod 2. . The outer peripheral surfaces of the clad rods 3 adjacent to each other are separated, and a glass rod 4 for filling is arranged between the clad rods 3 adjacent to each other. The glass rods 4 for filling arranged in this way are arranged so as to fit inside a regular hexagon formed by tangents to the outer peripheral surfaces of the clad rods 3 adjacent to each other. The regular hexagon is indicated by a broken line in FIG. Further, each filling glass rod 4 is arranged so as to be in contact with the outer peripheral surface of the core rod 2 and to be in contact with each outer peripheral surface of the clad rods 3 adjacent to each other.

  Then, the plurality of glass rods arranged at the positions to be bundled as described above are bound by the binding band 51. The binding band 51 may be made of resin or metal, but is preferably made of resin from the viewpoint of preventing the outer peripheral surface of the glass rod from being damaged, and in terms of high heat resistance. It is preferably made of metal. Thus, a plurality of glass rods are bound as shown in FIG.

  Next, dummy glass rods are fixed to both ends of the plurality of glass rods that have been bound. FIG. 5 is a diagram showing a state in which a plurality of glass rods are fixed as described above. First, one dummy glass rod 52 is fixed to one end of each glass rod in a state where the plurality of glass rods are bound by the binding band 51. Next, another dummy glass rod 52 is fixed to the other end of each glass rod. From the viewpoint of suppressing the adhesion of impurities to the glass rod, this fixing is preferably performed by welding. By fixing the dummy glass rods 52 at both ends of each glass rod in this way, the state in which the glass rods are bundled can be maintained. Next, the binding band 51 binding the respective glass rods is removed. Thus, a plurality of glass rods are bundled as shown in FIG.

  In this step, after the respective glass rods are bundled using the binding band 51, the dummy glass rods 52 are welded to the respective glass rods. However, such a procedure is not necessarily required. For example, dummy glass rods 52 are fixed at appropriate positions to both ends of one glass rod. Next, another glass rod is arranged so as to be adjacent to the glass rod already fixed to the dummy glass rod 52, and both ends of the other glass rod arranged are fixed to the respective dummy glass rods 52. I do. By repeating this, all the glass rods are fixed to the dummy glass rods 52 at appropriate positions. Even if each glass rod is fixed to the dummy glass rod 52 in this way, a plurality of glass rods are bundled as shown in FIG.

<External process P2>
FIG. 6 is a diagram showing a state of the externally attached process P2. The external process P2 is performed by, for example, an OVD (Outside vapor deposition method) method, and soot that becomes a part of the inner cladding 21 is deposited on the outer peripheral surfaces of the plurality of glass rods bundled in the bundle process P1.

  First, each dummy glass rod 52 is fixed to a chuck of a lathe (not shown), and the bundled plural glass rods are rotated about the axis of the dummy glass rod 52. Then, as shown in FIG. 6, while rotating a plurality of glass rods, soot to be the inner cladding 21 is deposited. FIG. 7 is a diagram illustrating a state after the externally attached process P2.

In the soot 5 deposited in this step, the vaporized SiCl ₄ is introduced into the flame of the oxyhydrogen burner 53 by a carrier gas whose flow rate is controlled to convert the SiCl ₄ into SiO ₂ (silica glass). At the same time, while the oxyhydrogen burner 53 is reciprocated a plurality of times in the longitudinal direction of the glass rod, the soot 5 of SiO ₂ is deposited so as to cover the outer peripheral surface of each glass rod. By the deposition of the soot 5, a porous glass body which becomes a part of the inner cladding 21 is formed. In this embodiment, the soot 5 is composed of the same silica glass as the cladding glass layer 20R, the cladding rod 3, and the filling glass rod 4. Therefore, when the inner cladding 21 is made of silica glass to which no dopant is added as described above, the soot 5 is deposited without adding any dopant. When the inner cladding 21 is made of silica glass to which a dopant is added, a dopant is added to the soot 5. In this case, a gas containing a dopant whose amount is controlled together with the vaporized SiCl ₄ is introduced into the flame of the oxyhydrogen burner. When the inner cladding 21 is made of silica glass to which fluorine is added as described above, and when fluorine is also added to the soot 5, the vaporized SiF ₄ is vaporized together with the vaporized SiCl ₄ into the flame of the oxyhydrogen burner. Introduce.

  Thus, the soot 5 is deposited on the outer peripheral surfaces of the plurality of glass rods bundled as shown in FIG. In this embodiment, in the cross section perpendicular to the longitudinal direction of the plurality of glass rods, the soot 5 has a vertex of a regular hexagon centered on the center of the core rod 2 rounded and chamfered, and each side is rounded inward. And is deposited in a curved area.

<Sintering process P3>
As shown in FIG. 7, after the soot 5 is deposited, a dehydration process is performed, if necessary, prior to the sintering step P3. The dehydration process is performed by aging for a predetermined time in a furnace provided with a heater and filled with a gas such as Ar or He.

  Next, a sintering step P3 is performed. The sintering step P3 is a step of heating the plurality of glass rods on which the soot 5 is deposited on the outer peripheral surface to make the soot 5 and each of the glass rods into an integrated glass body. In the sintering step P3, sintering is performed at a higher temperature in the furnace than in the case of performing the above-mentioned dehydration treatment, until the porous glass body of soot 5 deposited becomes a transparent glass body. The furnace used at this time may be a furnace used for the dehydration treatment, or may be a different furnace from the furnace used for the dehydration treatment. Thus, the single-core optical fiber preform 1P shown in FIG. 8 is obtained. When the core rod 2, the clad rod 3, the filling glass rod 4, and the soot 5 become the single-core optical fiber base material 1P, the core portion 10R of the core rod 2 hardly changes, and the single-core optical fiber base material is not changed. It becomes a 1P base material core portion 10P. Further, each of the clad glass layer 20R, the plurality of clad rods 3, the plurality of filling glass rods 4 and the soot 5 of the core rod 2 becomes a part of the preform clad portion 20P of the preform 1P for a single-core optical fiber.

  The outer shape of a cross section perpendicular to the longitudinal direction of the single-core optical fiber preform 1P obtained in this manner is non-circular. Specifically, the outer shape of the cross section perpendicular to the longitudinal direction of the single-core optical fiber preform 1P has a shape resulting from the outer shape of the cross section perpendicular to the longitudinal direction of the bundle of the plurality of glass rods. In the present embodiment, each of the plurality of clad rods 3 is arranged at a position overlapping each vertex of the regular hexagon, and each of the plurality of filling glass rods 4 is arranged inside a regular hexagon surrounding the plurality of clad rods 3. You. Therefore, the outer shape of the single-core optical fiber preform 1P is such that the vertices of a regular hexagon centered on the center of the preform core portion 10P are rounded and chamfered, and each side is rounded inward and curved. Shaped.

When the clad glass layer 20R, the clad rod 3, and the filling glass rod 4 are made of silica glass to which fluorine is added as described above, this step may be performed in an atmosphere containing a fluorine-based gas. Specifically, a fluorine-based gas such as SiF ₄ , CF ₄ , C ₂ F ₆ or the like is introduced into a furnace for performing this step. By adopting such a process, when the porous glass body made of the soot 5 causes viscous flow, fluorine tends to be added to the glass body derived from the soot 5.

<Drawing process P4>
FIG. 9 is a diagram illustrating a state of the drawing step P4. First, as a preparation stage for performing the drawing process P4, the single-core optical fiber preform 1P manufactured by the above process is placed in the spinning furnace 110.

  Next, the heating unit 111 of the spinning furnace 110 is heated to heat the single core optical fiber preform 1P. At this time, the lower end of the single-core optical fiber preform 1P is heated to, for example, 2000 ° C. to be in a molten state. Then, the glass is melted from the single-core optical fiber preform 1P, and the glass is drawn. When the drawn glass in the molten state exits from the spinning furnace 110, it is immediately solidified, and the base material core portion 10P becomes the core 10 and the base material clad portion 20P becomes the clad 20, whereby the core 10 A single core optical fiber composed of the clad 20 is obtained. FIG. 8 illustrates the preform 1P for a single-core optical fiber having no gap formed therein. However, when a gap is formed in the preform 1P for a single-core optical fiber, the pressure is reduced or the melting is performed in this step. It is preferable that the void is crushed by utilizing the surface tension of glass.

  After the single-core optical fiber is manufactured as described above, the single-core optical fiber is passed through the cooling device 120 and cooled to an appropriate temperature. When entering the cooling device 120, the temperature of the single-core optical fiber is, for example, about 1800 ° C., but when exiting the cooling device 120, the temperature of the single-core optical fiber is, for example, 40 ° C. to 50 ° C. Becomes

  The single-core optical fiber coming out of the cooling device 120 passes through a coating device 131 containing an ultraviolet-curable resin to be the outer cladding 22, and is coated with the ultraviolet-curable resin. Further, by passing through the ultraviolet irradiation device 132 and being irradiated with ultraviolet light, the ultraviolet curable resin is cured and the outer cladding 22 is formed. Next, the multi-core fiber covered with the outer cladding 22 passes through a coating device 133 containing an ultraviolet-curable resin to be the protective layer 30, and is coated with this ultraviolet-curable resin. Further, by passing through the ultraviolet irradiation device 134 and being irradiated with ultraviolet light, the ultraviolet curable resin is cured and the protective layer 30 is formed, and the single core optical fiber 1 shown in FIG. 1 is obtained.

  Then, the direction of the single core optical fiber 1 is changed by the turn pulley 141 and wound by the reel 142.

  Thus, the single core optical fiber 1 shown in FIG. 1 is manufactured.

  As described above, the method for manufacturing the single-core optical fiber preform 1P of the present embodiment includes the core rod 2 having the core portion 10R serving as the core 10 and a part of the inner clad 21 which is a part of the clad 20. Bundling step P1 for bundling a plurality of glass rods including a plurality of clad rods 3 to be formed, and an external part for depositing a soot 5 to be another part of the inner clad 21 on the outer peripheral surface of the bundled glass rods. Step P2 and a sintering step P3 of heating the plurality of glass rods on which the soot 5 is deposited to form the soot 5 and each of the glass rods into an integrated glass body. Further, in the bundling step P1, the plurality of clad rods 3 are arranged at positions in contact with the outer peripheral surface of the core rod 2 and overlapping respective vertexes of a regular hexagon surrounding the core rod 2.

  By depositing the soot 5 on the outer peripheral surfaces of the bundled glass rods, the soot 5 is easily deposited along the outer peripheral surface of the bundle of the glass rods. Therefore, by depositing the soot 5 in a state in which the plurality of clad rods 3 are arranged around the core rod 2 as described above, in the cross section perpendicular to the longitudinal direction of the core rod 2, The shape can be a rounded corner of a regular hexagon surrounding the core rod 2. That is, in a cross section perpendicular to the longitudinal direction of the core rod 2, the soot 5 can be deposited in a non-circular region surrounding the core rod 2. Further, by sintering the soot 5 thus deposited and integrating it with a plurality of glass rods, it is possible to manufacture the single-core optical fiber preform 1P having a non-circular cross section perpendicular to the longitudinal direction. . Further, since the length of the single-core optical fiber preform 1P can be adjusted by adjusting the length of the glass rod, the length of the single-core optical fiber preform 1P can be increased. Therefore, a single-core optical fiber preform 1P having a non-circular cross section perpendicular to the longitudinal direction and a large length can be manufactured.

  In the present embodiment, each clad rod 3 has the same diameter as each other, and in the bundling step P1, each clad rod 3 is arranged at a position overlapping each vertex of a regular hexagon centered on the center of the core rod 2. Is done. By depositing the soot 5 with the plurality of clad rods 3 arranged in this manner, the soot 5 can be deposited in a region centered on the core rod 2 in a cross section perpendicular to the longitudinal direction of the core rod 2. Further, by sintering the soot 5 thus deposited and integrating it with a plurality of glass rods, for a single core optical fiber whose central axis coincides with the base material core 10P composed of the core 10R of the core rod 2. The base material 1P can be manufactured. By using such a single-core optical fiber preform 1P, the single-core optical fiber 1 in which the core 10 is disposed at the center of the clad 20 can be manufactured.

  Further, in the present embodiment, in the bundling step P1, the cladding rods 3 are arranged so that the outer peripheral surfaces of the adjacent cladding rods 3 are separated from each other. In the case where the same number of clad rods 3 are used, when the plurality of clad rods 3 are arranged so as to be separated from each other, the diameter is larger than when the plurality of clad rods 3 are arranged so as to be in contact with each other. A core rod 2 can be used. Therefore, when compared with the same fiber diameter, the single core optical fiber 1 in which the diameter of the core 10 is large can be manufactured.

  In the present embodiment, the filling glass rod 4 is disposed so as to be in contact with the outer peripheral surface of the clad rod 3 in the bundling step P1. By disposing the filling glass rod 4 so as to be in contact with the outer peripheral surface of at least one clad rod 3 in this manner, the deformation of the filling glass rod 4 and the clad rod 3 in the sintering step P3 can be suppressed.

  In the present embodiment, the filling glass rod 4 is disposed so as to be in contact with the outer peripheral surface of the core rod 2 in the bundling step P1. By arranging the filling glass rod 4 and the core rod 2 in this manner, the deformation of the filling glass rod 4 and the core rod 2 in the sintering step P3 can be suppressed.

  In the present embodiment, in the bundling step P1, the filling glass rods 4 are arranged so as to be in contact with the respective outer peripheral surfaces of the clad rods 3 adjacent to each other. By arranging the filling glass rod 4 and the cladding rod 3 in this manner, the filling glass rod 4 in the sintering step P3 is compared with a case where the filling glass rod 4 is in contact with only one of the adjacent cladding rods 3. 4 and the deformation of the clad rod 3 can be further suppressed.

  In the present embodiment, the core rod 2 has a clad glass layer 20R that becomes a part of the clad 20 on the outer peripheral surface of the core 10R. Since the core rod 2 has the clad glass layer 20R as described above, it is possible to prevent the core portion 10R of the core rod 2 from being damaged in the bundling step P1. However, the cladding glass layer 20R is not an essential component.

  In the present embodiment, in the bundling step P1, the filling glass rods 4 having a lower refractive index than the core part 10R and a smaller diameter than the clad rod 3 are formed by a plurality of tangent lines which are in contact with the outer peripheral surfaces of the adjacent clad rods 3. Is disposed inside a regular hexagon formed so as to surround the clad rod 3. By arranging the filling glass rod 4 in this manner, the cross-sectional shape perpendicular to the longitudinal direction of the single-core optical fiber preform 1P can be made closer to a regular hexagon.

  The method for manufacturing the single-core optical fiber 1 of the present embodiment includes a drawing step P4 for drawing the single-core optical fiber preform 1P manufactured by the method for manufacturing the single-core optical fiber preform 1P of the above embodiment. Is provided. As described above, according to the method for manufacturing the single-core optical fiber preform 1P of the present embodiment, the single-core optical fiber preform 1P having a large non-circular cross-sectional shape perpendicular to the longitudinal direction and a large length is manufactured. obtain. Therefore, by using the single-core optical fiber preform 1P, the long single-core optical fiber 1 having the non-circular cross-sectional shape of the inner cladding 21 can be manufactured as described above.

  As described above, the present invention has been described with reference to the above embodiments, but the present invention is not limited to these embodiments.

  For example, in the above embodiment, in the bundling step P1, each clad rod 3 has been described as an example in which each clad rod 3 is arranged at a position overlapping each vertex of a regular hexagon centered on the center of the core rod 2; It is not limited to this. The plurality of clad rods 3 may be arranged at positions overlapping respective vertices of the polygon surrounding the core rod 2, and the number of clad rods 3 is not particularly limited as long as it is three or more. That is, in the bundling step P1, each clad rod 3 may be disposed at a position having the same number of corners as the number of clad rods 3 and overlapping each vertex of the polygon surrounding the core rod 2. However, the polygon is preferably a polygon centered on the center of the core rod 2, and the polygon is preferably a regular polygon. When the number of clad rods 3 is increased, the polygon becomes closer to a circle. Therefore, in the cross section perpendicular to the longitudinal direction of the core rod 2, the area where the soot 5 is deposited approaches a circle, and the cross-sectional shape of the inner cladding 21 also approaches a circle. From the viewpoint of making the shape of the inner cladding 21 an effective shape for suppressing the generation of skew light, the number of cladding rods 3 is preferably eight or less. That is, the polygon is preferably a polygon having eight or less corners.

  FIG. 10 is a diagram showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process P1 according to a modification of the present invention. In this modification, three clad rods 3 are arranged around the core rod 2. Each clad rod 3 is arranged at a position in contact with the outer peripheral surface of the core rod 2 and overlapping each vertex of an equilateral triangle surrounding the core rod 2. Two glass rods 4 for filling are arranged between the clad rods 3 adjacent to each other. Each filling glass rod 4 is arranged inside an equilateral triangle formed so as to surround the plurality of clad rods 3 by tangent lines which are in contact with the outer peripheral surfaces of the adjacent clad rods 3. The equilateral triangle is indicated by a broken line in FIG. Further, the filling glass rods 4 adjacent to each other are arranged so that their outer peripheral surfaces are in contact with each other. By arranging a plurality of filling glass rods 4 between the clad rods 3 adjacent to each other in this way, even if the gap between the clad rods 3 adjacent to each other is large, the gap is filled with the glass rods 4 for filling. be able to. Therefore, the cross-sectional shape perpendicular to the longitudinal direction of the single-core optical fiber preform 1P can approach a polygon. Further, a plurality of filling glass rods 4 are arranged between the clad rods 3 adjacent to each other in the bundling step P1 as described above, and the outer peripheral surfaces of the filling glass rods 4 adjacent to each other are in contact with each other, so that the sintering step P3 is performed. The deformation of the filling glass rod 4 can be suppressed.

  FIG. 11 is a view showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process P1 according to another modification of the present invention. In this modification, four clad rods 3 are arranged around the core rod 2. Each clad rod 3 is arranged at a position in contact with the outer peripheral surface of the core rod 2 and overlapping each vertex of a square surrounding the core rod 2. One glass rod 4 for filling is arranged between the clad rods 3 adjacent to each other. Each filling glass rod 4 is arranged inside a square formed so as to surround the plurality of clad rods 3 by tangents that are in contact with the outer peripheral surfaces of the adjacent clad rods 3. The square is indicated by a broken line in FIG.

  FIG. 12 is a diagram showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process P1 according to still another modified example of the present invention. In this modification, four clad rods 3 are arranged around the core rod 2. Each clad rod 3 is arranged at a position in contact with the outer peripheral surface of the core rod 2 and overlapping each vertex of a square surrounding the core rod 2. The outer peripheral surfaces of the clad rods 3 adjacent to each other are in contact with each other. In the case where the same number of clad rods 3 are used, when the plurality of clad rods 3 are arranged so as to be in contact with each other, each of the clad rods 3 is arranged as compared with the case where the plurality of clad rods 3 are arranged to be separated from each other. The diameter of the clad rod 3 can be increased. Therefore, the single core optical fiber 1 having the thick clad 20 can be manufactured. That is, the single core optical fiber 1 having a large distance from the center of the core 10 to the outer peripheral surface of the clad 20 can be manufactured. In such a single-core optical fiber 1, bending loss and loss due to micro-venting can be suppressed.

  FIG. 13 is a view showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling process P1 according to still another modified example of the present invention. In this modification, five clad rods 3 are arranged around the core rod 2. Each clad rod 3 is arranged at a position in contact with the outer peripheral surface of the core rod 2 and overlapping each vertex of a regular pentagon surrounding the core rod 2. One glass rod 4 for filling is arranged between the clad rods 3 adjacent to each other. Each filling glass rod 4 is arranged inside a regular pentagon formed so as to surround a plurality of clad rods 3 by tangents in contact with the outer peripheral surfaces of the clad rods 3 adjacent to each other. The regular pentagon is indicated by a broken line in FIG.

  FIG. 14 is a view showing a cross section perpendicular to the longitudinal direction of a bundle of a plurality of glass rods after a bundling step P1 according to still another modification of the present invention. In this modification, six clad rods 3 are arranged around the core rod 2. Each clad rod 3 is arranged at a position in contact with the outer peripheral surface of the core rod 2 and overlapping each vertex of a regular hexagon surrounding the core rod 2. The outer peripheral surfaces of the clad rods 3 adjacent to each other are in contact with each other.

  In the above-described embodiment, an example has been described in which the filling glass rods 4 are in contact with the respective outer peripheral surfaces of the adjacent clad rods 3 in the bundling step P1. However, the filling glass rod 4 may be separated from the outer peripheral surface of the clad rod 3. However, in the bundling step P1, the filling glass rod 4 is preferably arranged so as to be in contact with the outer peripheral surface of at least one clad rod 3.

  Further, in the above embodiment, the example in which the clad rods 3 have the same diameter has been described, but the diameters of the clad rods 3 may be different from each other. Further, in the above embodiment, the example in which the filling glass rods 4 have the same diameter is described, but the diameters of the filling glass rods 4 may be different from each other.

  Further, in the above embodiment, the example in which the outer cladding 22 is made of resin is described, but the outer cladding 22 may be made of silica glass. In this case, for example, the outer cladding 22 can be formed by the soot 5 by making the refractive index of a part of the cladding 20 made of the soot 5 lower than the refractive index of the cladding rod 3. By making the refractive index of a part of the clad 20 made of the soot 5 lower than the refractive index of the clad rod 3, the part made of the clad rod 3 becomes a part that becomes a part of the inner clad 21, and the part made of the soot 5 becomes A single-core optical fiber preform 1P that is to be a portion to be the outer cladding 22 having a lower refractive index than the inner cladding 21 can be manufactured. When the outer cladding 22 is formed by the soot 5 as described above, it is preferable that the externally attaching step P2 be performed a plurality of times. That is, it is preferable that the soot 5 to be the inner clad 21 is deposited in the first or several external steps P2, and the soot 5 to be the outer clad 22 is deposited in the remaining external steps P2. By using the single-core optical fiber preform 1P thus manufactured, the single-core optical fiber 1 having a double clad structure suitable for an amplification optical fiber can be manufactured.

  Further, in the above embodiment, the example in which the single-core optical fiber 1 is an amplification optical fiber has been described, but the single-core optical fiber 1 may be an optical fiber in which the core 10 is not doped with an active element. Good. For example, when the active element is not added to the core 10, the single-core optical fiber 1 can be used as a delivery fiber connected to an amplification optical fiber such as the single-core optical fiber 1 of the above embodiment.

  As described above, according to the present invention, a method for manufacturing a single-core optical fiber preform capable of producing a single-core optical fiber preform having a non-circular cross-sectional shape perpendicular to the longitudinal direction and a large length, and And a method of manufacturing a single-core optical fiber, which is expected to be used in the field of fiber laser devices and the like.

DESCRIPTION OF SYMBOLS 1 ... Single core optical fiber 1P ... Single core optical fiber base material 2 ... Core rod 3 ... Cladding rod 4 ... Filling glass rod 5 ... Soot 10 ... Core 10R. ..Core part 20 ... Clad 20R ... Clad glass layer 21 ... Inner clad 22 ... Outer clad P1 ... Bundling step P2 ... External step P3 ... Sintering step P4 ..Drawing process

Claims (13)

A core rod having a core part serving as a core, and a bundle step of bundling a plurality of glass rods including a plurality of clad rods that become a part of the clad,
An external step of depositing soot that becomes another part of the clad on the outer peripheral surface of the bundled glass rods,
A sintering step of heating the plurality of glass rods on which the soot is deposited to form the soot and each of the glass rods into an integrated glass body,
With
In the bundling step, each of the clad rods is disposed at a position in contact with an outer peripheral surface of the core rod and overlapping each vertex of a polygon surrounding the core rod ,
The method of manufacturing a preform for a single-core optical fiber , wherein in the bundling step, outer peripheral surfaces of the clad rods adjacent to each other are separated from each other .   In the bundling step, the filling glass rod having a lower refractive index than the core portion and a smaller diameter than the clad rod surrounds the plurality of clad rods by tangent lines that are in contact with the outer peripheral surfaces of the adjacent clad rods. Placed inside the formed polygon
The method for manufacturing a preform for a single-core optical fiber according to claim 1, wherein:   A core rod having a core part serving as a core, and a bundle step of bundling a plurality of glass rods including a plurality of clad rods that become a part of the clad,
  An external step of depositing soot that becomes another part of the clad on the outer peripheral surface of the bundled glass rods,
  A sintering step of heating the plurality of glass rods on which the soot is deposited to form the soot and each of the glass rods into an integrated glass body,
With
  In the bundling step, each of the clad rods is disposed at a position in contact with an outer peripheral surface of the core rod and overlapping each vertex of a polygon surrounding the core rod,
  In the bundling step, the filling glass rod having a lower refractive index than the core portion and a smaller diameter than the clad rod surrounds the plurality of clad rods by tangent lines that are in contact with the outer peripheral surfaces of the adjacent clad rods. Placed inside the formed polygon
A method for producing a preform for a single-core optical fiber, comprising: The method for manufacturing a preform for a single-core optical fiber according to claim 3 , wherein in the bundling step, outer peripheral surfaces of the clad rods adjacent to each other are in contact with each other. 5. The single-core optical fiber preform according to claim 3 , wherein in the bundling step, the glass rod for filling is arranged so as to be in contact with an outer peripheral surface of at least one clad rod. 6. Production method. 6. The preform for a single-core optical fiber according to claim 3 , wherein in the bundling step, the filling glass rod is arranged so as to be in contact with an outer peripheral surface of the core rod. 7 . Production method. In the bundle step, the plurality of the filling glass rod between the cladding rod is arranged, one of claims 3, wherein 6 to the outer peripheral surface of the filling glass rod is in contact adjacent to each other adjacent to each other The method for producing a preform for a single-core optical fiber according to claim 1. In the bundle step, the filled glass rod, single-core according to any one of claims 3 6, characterized in that it is arranged in contact with each of the outer peripheral surface of the clad rod adjacent to each other A method for manufacturing a preform for an optical fiber.   Each of the clad rods has the same diameter as each other,
  In the bundling step, each of the clad rods is disposed at a position overlapping each vertex of a regular polygon centered on the center of the core rod.
The method for producing a preform for a single-core optical fiber according to any one of claims 1 to 8, wherein:   The core rod has a clad glass layer that becomes a part of the clad on an outer peripheral surface of the core portion.
The method for producing a single-core optical fiber preform according to any one of claims 1 to 9, wherein: The method for producing a preform for a single-core optical fiber according to any one of claims 1 to 10, wherein an active element is added to the core portion. The single core according to any one of claims 1 to 11, wherein, after the sintering step, the refractive index of another part of the clad made of the soot is made lower than the refractive index of the clad rod. A method for manufacturing a preform for an optical fiber. A single-core optical fiber comprising a drawing step of drawing a single-core optical fiber preform manufactured by the method for manufacturing a single-core optical fiber preform according to any one of claims 1 to 12. Fiber manufacturing method.

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