JP2013033865A - Optical fiber and manufacturing method of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-core optical fiber capable of inexpensively and comparatively easily injecting excitation light.SOLUTION: An optical fiber 100 comprises: a plurality of cores 10; a first clad 20 which surrounds the peripheries of the plurality of cores 10; and a second clad 30 which surrounds the periphery of the first clad 20. At least one of the plurality of cores 10 contains a rare earth element. The first clad 20 has a lower refractive index than any core 10 of the plurality of cores 10, and the second clad 30 has a higher refractive index than the first clad 20.

Description

  The present invention relates to an optical fiber having a plurality of cores and a method for manufacturing the optical fiber.

  In recent years, optical amplifiers using optical fibers in which rare earth elements such as Er (erbium), Pr (praseodymium), Nd (neodymium), and Yb (ytterbium) are added in the core of an optical fiber have been put into practical use. In particular, an optical fiber amplifier doped with Er is applied to various systems because it has a high gain and a high saturation output in the 1.55 μm band. Among them, application to high-speed, large-capacity, long-distance transmission and CATV systems by wavelength division multiplexing using several wavelengths of signal light in the 1.53 μm to 1.56 μm wavelength band has been studied and is now in practical use.

  An optical amplifier using an optical fiber in which a rare earth element is added in the core is a system in which both signal light and pumping light are incident on the core and propagated to amplify the signal light. A rare earth element using a WDM coupler or the like is used. Signal light and excitation light are incident on the doped optical fiber.

Japanese Patent Laid-Open No. 10-242548 Japanese Patent Laid-Open No. 9-159846

  A normal optical fiber is a single core optical fiber having a single core. However, if a single optical fiber is provided with a plurality of cores, signal light can be amplified simultaneously by the plurality of cores. For example, Patent Documents 1 and 2 disclose a multi-core optical fiber having such a plurality of rare earth element-added cores.

  However, in the techniques disclosed in Patent Documents 1 and 2, both the signal light and the excitation light need to be incident independently on each core, and the signal light and the light are incident on each core at the end face of the thin optical fiber. It is very difficult to cause both excitation lights to enter without being displaced, and an excitation light incidence device is required for each core, which increases costs. In Patent Document 1, the structure of the entire optical amplifier is shown in FIG. 5 of the document, but the incident portion of the signal light / pumping light is not clearly described, and the signal light / pumping light is not displaced in each core. There is no description of the problem of incident light.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a multi-core optical fiber capable of performing excitation light incidence at a low cost and relatively easily.

  The optical fiber of the present invention includes a plurality of cores, a first cladding surrounding the periphery of the plurality of cores, and a second cladding surrounding the periphery of the first cladding, and at least one of the plurality of cores Includes a rare earth element, and the first cladding has a lower refractive index than the cores of the plurality of cores, and the second cladding has a lower refractive index than the first cladding. It is. Two or more cores containing rare earth elements are preferable.

  The first clad is circular in the cross section of the optical fiber, and the first clad has an optical direction changing portion having a refractive index different from that of the first clad and extending along the optical fiber axis. It may be.

  The optical direction changing unit may be located closer to the second cladding than the core closest to the second cladding among the plurality of cores.

  The optical direction changing unit may have a refractive index lower than that of the first cladding.

  There may be a plurality of the light direction changing units, each of which is not line symmetric in a plane including the optical fiber central axis.

  In the cross section of the optical fiber, the shape of the outer periphery of the first cladding may be a combination of an arc and a chord or a polygon.

  In the first optical fiber manufacturing method of the present invention, at least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod, and a quartz capillary is provided in a hole portion of a quartz pipe, and a rare earth element is provided in a central axis portion. Inserting a plurality of contained quartz cylinders to form an optical fiber preform; heating and stretching the optical fiber preform to form an optical fiber precursor; and Covering the outer periphery with a resin having a lower refractive index than quartz. The quartz pipe is a cylindrical body made of quartz, and the quartz rod is a rod made of quartz. The quartz capillary is a hollow rod made of quartz and having a hole extending in the central axis portion.

  The second optical fiber manufacturing method of the present invention includes a step of opening a plurality of holes along the center axis of the rod in the quartz rod, and a fluorine-containing quartz rod, a boron-containing quartz rod, and a quartz capillary in the plurality of holes. Inserting at least one selected one and a plurality of quartz pillars containing a rare earth element in the central axis portion to form an optical fiber preform; heating and stretching the optical fiber preform; The structure includes a step of forming an optical fiber precursor and a step of coating the outer periphery of the optical fiber precursor with a resin having a refractive index lower than that of quartz.

  According to a third method for producing an optical fiber of the present invention, at least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary is provided in a hole portion of a quartz pipe, and a rare earth element is provided in a central axis portion. A step of forming an optical fiber preform by inserting a plurality of contained quartz pillars and surrounding an outer periphery of the quartz pipe with a low refractive index member having a refractive index lower than that of quartz; and And a step of heating and stretching.

  The fourth optical fiber manufacturing method of the present invention includes a step of opening a plurality of holes along a central axis of the rod in a quartz rod, and a fluorine-containing quartz rod, a boron-containing quartz rod, and a quartz capillary in the plurality of holes. At least one selected one and a plurality of quartz pillars containing rare earth elements in the central axis portion are inserted, and the outer periphery of the quartz rod is surrounded by a low refractive index member having a lower refractive index than quartz. It is the structure including the process of forming an optical fiber preform, and the process of heating and extending the said optical fiber preform.

  In the fifth optical fiber manufacturing method of the present invention, a double-layered quartz rod is used in which the outer layer side is made of quartz containing fluorine or boron or quartz having a plurality of holes extending along the central axis, and the inner layer side is made of quartz. A step of preparing, a step of opening a plurality of holes along the central axis of the rod on the inner layer side of the double-layered quartz rod, and a plurality of holes selected from a fluorine-containing quartz rod, a boron-containing quartz rod, and a quartz capillary A step of forming an optical fiber preform by inserting at least one of them and a plurality of quartz pillars containing a rare earth element in the central axis portion, and a step of heating and stretching the optical fiber preform. It is the structure containing.

  Since the plurality of cores are surrounded by the first cladding and the first cladding is surrounded by the second cladding having a lower refractive index, the signal light is incident on the plurality of cores and the excitation light is incident on the first cladding. By using the first cladding as a pumping guide, excitation light can be simultaneously introduced into a plurality of cores.

1 is a cross-sectional view of an optical fiber according to Embodiment 1. FIG. FIG. 2 is a cross-sectional view of a semi-finished product in the process of manufacturing the optical fiber according to the first embodiment. FIG. 3 is a cross section of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the first embodiment. FIG. 4 is a cross section of the optical fiber according to the second embodiment. FIG. 5 is a cross-sectional view of a semi-finished product in the middle of the optical fiber manufacturing process according to the second embodiment. FIG. 6 is a cross-sectional view of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the second embodiment. FIG. 7 is a cross-sectional view of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the second embodiment. FIG. 8 is a cross section of an optical fiber according to the first modification of the second embodiment. FIG. 9 is a cross section of an optical fiber according to Modification 2 of Embodiment 2. FIG. 10 is a cross-sectional view of an optical fiber according to Modification 3 of Embodiment 2. FIG. 11 is a cross section of an optical fiber according to the third embodiment. FIG. 12 is a cross-sectional view of a semi-finished product in the process of manufacturing an optical fiber according to the third embodiment. FIG. 13 is a cross section of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the third embodiment. FIG. 14 is a cross-sectional view of an optical fiber according to a modification of the third embodiment. FIG. 15 is a cross section of an optical fiber according to the fourth embodiment. FIG. 16 is a cross-sectional view of a semi-finished product in the process of manufacturing an optical fiber according to the fourth embodiment. FIG. 17 is a cross-sectional view of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the fourth embodiment. FIG. 18 is a cross-sectional view of a semi-finished product in the middle of another manufacturing process of the optical fiber according to the fourth embodiment. FIG. 19 is a cross-sectional view of an optical fiber according to modification a of the fourth embodiment. FIG. 20 is a cross-sectional view of an optical fiber according to Modification b of Embodiment 4. FIG. 21 is a cross-sectional view of an optical fiber according to a modification c of the fourth embodiment. FIG. 22 is a cross-sectional view of an optical fiber according to Modification d of Embodiment 4. FIG. 23 is a cross-sectional view of an optical fiber according to Modification e of Embodiment 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

(Embodiment 1)
A cross section of the optical fiber 100 according to Embodiment 1 is shown in FIG. The optical fiber 100 of this embodiment is a multi-core optical fiber in which seven cores 10, 10,... Extend in the optical fiber axial direction. In the cross section of the optical fiber, the cores 10, 10,... Are arranged so as to be positioned at the six apexes and the center of the regular hexagon, and the center of the regular hexagon substantially coincides with the central axis of the optical fiber.

  The plurality of cores 10 are surrounded by a single first cladding 20. The first clad 20 has a circular shape centered on the optical fiber central axis in the cross section of the optical fiber, and a plurality of cores 10, 10,... Are embedded in the first clad 20. Each of the cores 10, 10,... Is surrounded by the first cladding 20, but is exposed together with the first cladding 20 at both ends of the optical fiber. That is, the plurality of cores 10, 10,... Exist in the single first cladding 20 except for the optical fiber end portions.

  The first cladding 20 is surrounded by the second cladding 30. The outer periphery of the second cladding 30 is a circle centered on the optical fiber central axis, and the second cladding 30 is in a state in which the outer peripheral surface of the first cladding 20 is covered with a layer having a substantially uniform thickness. Of course, the end faces of the first cladding 20 are exposed together with the end faces of the second cladding 30 at both ends of the optical fiber.

  In the optical fiber 100 of the present embodiment, each of the cores 10, 10,... Is made of quartz glass added with rare earth elements such as Er, Pr, Nd, Yb and Ge (germanium). The first cladding 20 is made of pure quartz glass. The second cladding 30 is made of a silicone resin having a lower refractive index than that of the first cladding or an acrylic resin having a lower refractive index than that of the first cladding. Because of such a configuration, the refractive index of the core 10 is the highest, the next is the refractive index of the first cladding 20, and the lowest is the refractive index of the second cladding 30. Therefore, light propagating through the core 10 is confined in the core 10 by the first cladding 20, and light propagating through the first cladding 20 is confined in the first cladding 20 and the core 10 by the second cladding 30. That is, the optical fiber 100 of this embodiment has a structure called a double clad optical fiber.

  This optical fiber 100 can be used for optical amplification. Specifically, a coupler is connected to one end of the optical fiber 100 so that signal light is incident on each of the cores 10, 10,..., And excitation light is incident on the first cladding 20. That is, the first cladding 20 is used as a pump guide. In general, since different signal lights are transmitted through the cores 10, 10,..., When the optical fiber 100 of this embodiment is used, seven signals can be transmitted simultaneously with one optical fiber. . The excitation light traveling through the first cladding 20 is reflected at the boundary between the first cladding 20 and the second cladding 30 and changes its direction, and sometimes passes through the core 10. The excitation light passing through the core 10 amplifies the signal light by the action of the rare earth element.

  The optical fiber 100 of this embodiment can easily introduce pumping light simultaneously into the plurality of cores 10, 10,... With a simple structure. Therefore, efficient optical amplification can be performed at low cost.

  Next, the manufacturing method of the optical fiber 100 of this embodiment is demonstrated.

-Manufacturing method A1-
In the manufacturing method A1, as shown in FIG. 2 (a), first, a core pipe 70 which is a quartz pipe 60 and a quartz cylinder containing a rare earth element such as Er, Pr, Nd, Yb in the central shaft portion 75 is provided. , 70,... The central axis portion 75 of the core base material 70 also contains Ge.

  Then, the core preforms 70, 70,... Are inserted into the hole portion at the center of the quartz pipe 60, and the optical fiber preform 200 is produced.

  Next, when the optical fiber preform 200 is heated, softened and stretched in the central axis direction, the gap between the quartz pipe 60 and the core preforms 70, 70,..., And the core preform 70 and the core preform 70. And the optical fiber precursor 201 shown in FIG. 2B is formed.

  Next, the optical fiber precursor 201 is coated with a silicone resin or an acrylic resin by applying a silicone resin or an acrylic resin to the outer periphery of the optical fiber precursor 201. Thus, the optical fiber 100 shown in FIG. 1 is completed.

-Manufacturing method B1-
A manufacturing method B1, which is another manufacturing method, will be described with reference to FIG. First, a quartz rod is prepared, and a plurality of holes are formed along the central axis of the rod. The holes are opened so as to be arranged at the apexes of the regular hexagon and the center thereof in the cross section of the quartz rod.

  Next, the seven core preforms 70, 70,... Are inserted into the holes of the perforated quartz rod 62 having the holes formed therein, thereby producing the optical fiber preform 202. The outer diameter of the core base materials 70, 70,... Is set slightly smaller than the diameter of the hole.

  When the optical fiber preform 202 is heated, softened, and stretched in the central axis direction, the gap between the perforated quartz rod 62 and the core preforms 70, 70,... Disappears, and the optical fiber precursor 201 is completed.

  Next, the optical fiber precursor 201 is coated with a silicone resin or an acrylic resin by applying a silicone resin or an acrylic resin to the outer periphery of the optical fiber precursor 201. Thus, the optical fiber 100 shown in FIG. 1 is completed.

(Embodiment 2)
FIG. 4 shows a cross section of the optical fiber 101 according to the second embodiment. The difference between the optical fiber 101 of the present embodiment and the optical fiber 100 of the first embodiment resides in the second clad 31 and the others are the same, so the differences from the first embodiment will be mainly described.

  The optical fiber 101 of this embodiment is made of quartz glass in which a second cladding 31 surrounding the first cladding 20 made of pure quartz glass is fluorine-doped. Since the second cladding 31 is made of fluorine-containing quartz glass, the refractive index is lower than that of pure quartz glass. Accordingly, the excitation light passing through the first cladding 20 is confined in the first cladding 20 by the second cladding 31 as in the first embodiment. Therefore, the optical fiber 101 of the present embodiment can easily introduce the excitation light simultaneously into the plurality of cores 10, 10,... With a simple structure. Therefore, efficient optical amplification can be performed at low cost.

-Manufacturing method C1-
A manufacturing method C1 for manufacturing the optical fiber 101 of the present embodiment will be described with reference to FIG.

  First, core pipes 61 and core base materials 70, 70,..., Which are quartz cylinders containing rare earth elements such as Er, Pr, Nd, and Yb in the central shaft portion 75 are prepared. The central axis portion 75 of the core base material 70 also contains Ge.

  Then, core base materials 70, 70,... Are inserted and packed into the hole in the center of the quartz pipe 61. Further, the optical fiber preform 210 is formed by inserting the quartz pipe 61 into a hole at the center of the fluorine-containing quartz pipe (low refractive index member) 76.

  Next, when the optical fiber preform 210 is heated, softened and stretched in the central axis direction, the gap between the quartz pipe 61 and the core preforms 70, 70,..., The core preform 70 and the core preform 70. The gap between the quartz pipe 61 and the fluorine-containing quartz pipe 76 is eliminated, and the optical fiber 101 shown in FIG. 4 is formed.

-Manufacturing method D1-
A manufacturing method D1 which is another manufacturing method will be described with reference to FIG. First, a quartz rod is prepared, and a plurality of holes are formed along the central axis of the rod. The holes are opened so as to be arranged at the apexes of the regular hexagon and the center thereof in the cross section of the quartz rod.

  Next, a plurality of core base materials 70, 70,... Are inserted into the holes of the perforated quartz rod 63 having holes. The outer diameter of the core base materials 70, 70,... Is set slightly smaller than the diameter of the hole. Further, the optical fiber preform 211 is formed by inserting the perforated quartz rod 63 into the hole at the center of the fluorine-containing quartz pipe (low refractive index member) 76.

  Next, when the optical fiber preform 211 is heated, softened and stretched in the central axis direction, the gap between the perforated quartz rod 63 and the core preforms 70, 70,. The gap between the quartz pipe 76 is eliminated and the optical fiber 101 shown in FIG. 4 is formed.

-Manufacturing method E1-
Another manufacturing method E1 will be described with reference to FIG. First, a two-layer quartz rod is prepared. In this double-layered quartz rod, the inner layer 64 is made of quartz and the outer layer 77 is made of fluorine-containing quartz. A plurality of holes are made in the inner layer 64 of the two-layer structure quartz rod along the center axis of the rod. The holes are opened so as to be arranged at the apexes of the regular hexagon and the center thereof in the cross section of the quartz rod.

  Next, a plurality of core preforms 70, 70,... Are inserted into the holes of the perforated double-layered structure quartz rod 78, and the optical fiber preform 212 is formed. The outer diameter of the core base materials 70, 70,... Is set slightly smaller than the diameter of the hole.

  Next, when the optical fiber preform 212 is heated, softened, and stretched in the direction of the central axis, there is no gap between the perforated double-layered quartz rod 78 and the core preforms 70, 70,... An optical fiber 101 is formed.

<Modifications 1 and 2 of Embodiment 2>
8 and 9 show cross sections of optical fibers 102 and 103 according to Modifications 1 and 2 of the present embodiment. In these modified examples, the shapes of the first claddings 21 and 22 are different from those of the above-described embodiment, and thereby the inner peripheral side shape of the second cladding 31 is also different. Therefore, the description of the same part is omitted.

  The first clad 21 of the optical fiber 102 according to the first modification has a combination of a circular arc and a chord on the outer periphery, with a part of the outer periphery circle notched in the cross section of the optical fiber. The inner peripheral shape of the second cladding 31 is also a combination of an arc and a string, but the outer peripheral shape is a circle.

  In the above embodiment, since the outer periphery of the first cladding 20 is circular, a part of the excitation light traveling inside the first cladding 20 is repeatedly reflected at the boundary between the first cladding 20 and the second cladding 31. In other words, only the first cladding 20 outside the range where the cores 10, 10,. Since the skew light does not pass through the cores 10, 10,..., It does not contribute to light amplification. Therefore, a part of the excitation light is wasted. However, in the first modification, since the outer peripheral portion of the first cladding 21 has the above-described shape, the reflection at the chord portion causes the skew light to travel toward the core, so that all of the excitation light is amplified. Can contribute. In addition, the intensity of the excitation light in the plane of the first cladding 21 becomes uniform, and it is possible to prevent the gains from varying in each of the cores 10, 10,.

  The outer circumference of the first cladding 22 of the optical fiber 103 according to Modification 2 has a regular hexagonal shape in the cross section of the optical fiber. With this shape, the traveling direction of the skew light can be changed as in the second modification. Therefore, the same effect as that of the first modification can be obtained.

<Modification 3 of Embodiment 2>
FIG. 10 shows a cross-sectional view of an optical fiber 104 according to Modification 3 of the present embodiment. In this modified example, the second clad 32 is different from that of the above-described embodiment, and other than that is the same as that of the above-described embodiment.

  The second clad 32 according to the optical fiber 104 of the modification 3 is made of quartz glass and has a large number of holes 35, 35, 35 so as to surround the first clad 20 at the boundary with the first clad 20. ... are arranged. The holes 35, 35,... Extend along the optical fiber central axis.

  In the optical fiber 104 according to this modification, since the refractive index of the holes 35, 35,... Is smaller than that of quartz glass, the light introduced into the first cladding 20 is confined in the first cladding 20, and the above-mentioned The same effect as the first embodiment is obtained.

(Embodiment 3)
As shown in FIG. 11, the optical fiber 110 according to the third embodiment is obtained by adding an optical direction changing unit 40 to the optical fiber 100 according to the first embodiment.

  The optical fiber 110 of this embodiment is a multi-core optical fiber in which seven cores 10, 10,... Extend in the optical fiber axial direction. In the cross section of the optical fiber, the cores 10, 10,... Are arranged so as to be positioned at the six apexes and the center of the regular hexagon, and the center of the regular hexagon substantially coincides with the central axis of the optical fiber.

  The plurality of cores 10 are surrounded by a single first cladding 20. The first clad 20 has a circular shape centered on the optical fiber central axis in the cross section of the optical fiber, and a plurality of cores 10, 10,... Each of the cores 10, 10,... And the optical direction changing unit 40 is surrounded by the first cladding 20 at the outer periphery, but is exposed together with the first cladding 20 at both ends of the optical fiber. That is, the plurality of cores 10, 10,... And the light direction changing unit 40 exist in the single first clad 20 except for the optical fiber end.

  The first cladding 20 is surrounded by the second cladding 30. The outer periphery of the second cladding 30 is a circle centered on the optical fiber central axis, and the second cladding 30 is in a state where the outer periphery of the first cladding 30 is covered with a layer having a substantially uniform thickness. Of course, the end faces of the first cladding 20 are exposed together with the end faces of the second cladding 30 at both ends of the optical fiber.

  In the optical fiber 110 of the present embodiment, each of the cores 10, 10,... Is formed of quartz glass to which rare earth elements such as Er, Pr, Nd, Yb and Ge (germanium) are added. The first cladding 20 is made of pure quartz glass. The second cladding 30 is made of a silicone resin having a lower refractive index than that of the first cladding or an acrylic resin having a lower refractive index than that of the first cladding. Because of such a configuration, the refractive index of the core 10 is the highest, the next is the refractive index of the first cladding 20, and the lowest is the refractive index of the second cladding 30. Therefore, light propagating through the core 10 is confined in the core 10 by the first cladding 20, and light propagating through the first cladding 20 is confined in the first cladding 20 and the core 10 by the second cladding 30. That is, the optical fiber 110 of this embodiment has a structure called a double clad optical fiber.

  The optical direction changing part 40 existing in the first cladding 20 is closer to the second cladding 30 than the core 10 (core located at the apex of the regular hexagon) closest to the second cladding 30 among the cores 10, 10,. And extends along the optical fiber axis. That is, the distance between the optical direction changing unit 40 and the second cladding 30 is smaller than the shortest distance between the plurality of cores 10, 10,. The light direction changing unit 40 is made of fluorine-containing quartz glass and has a refractive index smaller than that of the first cladding 20.

  This optical fiber 110 can be used for optical amplification. Specifically, a coupler is connected to one end of the optical fiber 110 so that signal light is incident on each of the cores 10, 10,..., And excitation light is incident on the first cladding 20. That is, the first cladding 20 is used as a pump guide. In general, since different signal lights are transmitted through the cores 10, 10,..., When the optical fiber 110 of this embodiment is used, seven signals can be transmitted simultaneously with one optical fiber. . The excitation light traveling through the first cladding 20 sometimes passes through the core 10. Light that does not pass through the core 10 even if it is reflected many times at the boundary between the first clad 20 and the second clad 30 passes through the optical direction changing unit 40 and is refracted by the first clad 20 and the optical direction changing unit 40. Due to the difference in rate, the traveling direction is changed and eventually the core 10 is passed. The excitation light passing through the core 10 amplifies the signal light by the action of the rare earth element.

  The optical fiber 110 of this embodiment can easily introduce pumping light simultaneously into the plurality of cores 10, 10,... With a simple structure. Therefore, efficient optical amplification can be performed at low cost. In addition, since the optical direction changing unit 40 exists on the outer layer side of the first clad 20 so that the skew light travels in the core direction, all of the excitation light can be used for optical amplification, and efficient optical amplification. Can do. In addition, the intensity of the excitation light in the plane of the first cladding 20 becomes uniform, and it is possible to suppress the gain from varying in each of the cores 10, 10,. Further, in the first and second modifications of the first embodiment, when the optical fibers 102 and 103 and the other optical fibers are fusion-bonded, the first claddings 21 and 22 tend to be circular in the cross section of the optical fiber due to surface tension. Although the core position shifts and connection loss occurs, the optical fiber 110 of this embodiment has no connection loss due to the core position shift because the first cladding 20 is circular in the cross section of the fiber.

  Next, the manufacturing method of the optical fiber 110 of this embodiment is demonstrated.

-Manufacturing method A2-
In the manufacturing method A2, as shown in FIG. 12A, first, a core pipe 70 which is a quartz pipe 60 and a quartz cylinder containing a rare earth element such as Er, Pr, Nd, Yb in the central shaft portion 75 is provided. , 70,... And a fluorine-containing quartz rod 80 are prepared. The central axis portion 75 of the core base material 70 also contains Ge.

  Then, core preforms 70, 70,... Are inserted into a regular hexagonal arrangement in the hole portion in the center of the quartz pipe 60, and a fluorine-containing quartz rod 80 is packed into the outer space of the regular hexagon to fill the optical fiber preform. 204 is produced.

  Next, when the optical fiber preform 204 is heated, softened and stretched in the central axis direction, the gap between the quartz pipe 60 and the core preforms 70, 70,..., The quartz pipe 60 and the fluorine-containing quartz rod 80. The gap between the core preform 70, 70 and the fluorine-containing quartz rod 80 and the gap between the core preform 70 and the core preform 70 are eliminated, and the optical fiber precursor shown in FIG. 203 is formed.

  Next, the optical fiber precursor 203 is coated with a silicone resin or an acrylic resin by applying a silicone resin or an acrylic resin to the outer periphery of the optical fiber precursor 203. Thus, the optical fiber 110 shown in FIG. 11 is completed.

-Manufacturing method B2-
A manufacturing method B2 which is another manufacturing method will be described with reference to FIG. First, a quartz rod is prepared, and a plurality of holes are formed along the central axis of the rod. The holes are drilled so as to be arranged on each vertex of the regular hexagon and its center and outside the regular hexagonal arrangement in the cross section of the quartz rod.

  Next, a plurality of core preforms 70, 70,... And a fluorine-containing quartz rod 80 are inserted into the outer holes of the regular hexagonal arrangement in the hole of the perforated quartz rod 65 with holes, and the optical fiber preform 206. Is made. The outer diameters of the core base materials 70, 70,... And the fluorine-containing quartz rod 80 are set to be slightly smaller than the diameters of the holes.

  When the optical fiber preform 206 is heated, softened and stretched in the central axis direction, the gap between the perforated quartz rod 62 and the core preforms 70, 70,..., And the perforated quartz rod 62 and the fluorine-containing quartz rod. The gap between the optical fiber precursor 203 and the optical fiber precursor 203 is completed.

  Next, the optical fiber precursor 203 is coated with a silicone resin or an acrylic resin by applying a silicone resin or an acrylic resin to the outer periphery of the optical fiber precursor 203. Thus, the optical fiber 110 shown in FIG. 11 is completed.

<Modification of Embodiment 3>
FIG. 14 shows a cross-sectional view of an optical fiber 120 according to a modification of the present embodiment. In this modified example, the number and arrangement of the cores 11, 11,... Are different from those of the above-described embodiment, and other than that are the same as those of the above-described embodiment.

  The cores 11, 11,... According to the optical fiber 120 of the present modification have eight positions excluding one apex among nine positions, three on each side of the square and one at the center, in the cross section of the optical fiber. The center of the square is substantially coincident with the optical fiber central axis. The material of the cores 11, 11,... Is obtained by adding rare earth elements such as Er, Pr, Nd, and Yb and Ge to quartz glass as in the above embodiment. The light direction changing unit 40 is arranged in the vicinity of the apex of the square where the core 11 does not exist and at a position closer to the second cladding 30 than the apex.

  The optical fiber 120 of this modification has the same effect as that of the third embodiment.

(Embodiment 4)
FIG. 15 shows a cross section of the optical fiber 111 according to the fourth embodiment. The difference between the optical fiber 111 of the present embodiment and the optical fiber 110 of the third embodiment is that the second cladding 31 and the two light direction changing portions 40 and 41 are the same, and the others are the same. The difference from Embodiment 3 will be mainly described.

  The optical fiber 111 of the present embodiment is made of quartz glass in which the second cladding 31 surrounding the first cladding 20 made of pure quartz glass is fluorine-doped. Since the second cladding 31 is made of fluorine-containing quartz glass, the refractive index is lower than that of pure quartz. Therefore, the excitation light passing through the first cladding 20 is confined in the first cladding 20 by the second cladding 31 as in the third embodiment.

  In the present embodiment, there are two types of light direction changing units 40 and 41, that is, a light direction changing unit 40 made of fluorine-containing quartz glass and a light direction changing unit 41 that is a hole extending along the central axis of the optical fiber. ing. The two light direction changing portions 40, 41 are respectively present outside two adjacent sides of the regular hexagon formed by the cores 10, 10,. Thereby, the traveling direction of the skew light can be changed more efficiently, and at the same time, it becomes a mark indicating the order of the cores in the case of connection with another optical fiber. That is, the two types of light direction changing units 40 and 41 can be distinguished from each other by being viewed on the end face of the optical fiber, and can be used as markers because they are not line symmetric on the plane including the optical fiber central axis. . Therefore, the cores 10, 10,... Can be individually identified one by one by looking at either end of the optical fiber.

  As described above, the optical fiber 111 of the present embodiment can easily introduce the excitation light into the plurality of cores 10, 10,... Simultaneously with the same effect as the optical fiber 110 of the third embodiment, that is, with a simple structure. Efficient optical amplification can be performed at low cost, and all the pumping light can be used for optical amplification, so that efficient optical amplification can be performed. In addition, the intensity of the excitation light in the plane of the first cladding 20 becomes uniform, and it is possible to suppress the gain from varying in each of the cores 10, 10,. Further, in addition to the effects of the third embodiment, the light direction changing units 40, 41 can be used as markers that can individually identify the cores 10, 10,... When connecting to other optical fibers.

-Manufacturing method C2-
A manufacturing method C2 for manufacturing the optical fiber 111 of the present embodiment will be described with reference to FIG.

  First, a quartz pipe 61, a core base material 70, 70, which is a quartz cylinder containing a rare earth element such as Er, Pr, Nd, Yb in the central shaft portion 75, a fluorine-containing quartz rod 80, and a quartz capillary. 82 are prepared. The central axis portion 75 of the core base material 70 also contains Ge. Both ends of the quartz capillary 82 are sealed and closed.

  Then, first, seven core base materials 70, 70,... Are inserted and packed in the hole portion in the center of the quartz pipe 61, and the fluorine-containing quartz rod 80 and quartz are inserted between the core members 70, 70 and the quartz pipe 61. Capillary 82 is packed. The fluorine-containing quartz rod 80 and the quartz capillary 82 are arranged at a position sandwiching one core member 70 therebetween.

  Further, the optical fiber preform 220 is formed by inserting the quartz pipe 61 into a hole at the center of the fluorine-containing quartz pipe (low refractive index member) 76.

  Next, when the optical fiber preform 220 is heated, softened and stretched in the central axis direction, the gap between the quartz pipe 61 and the core preforms 70, 70,..., The core preform 70 and the core preform 70. The gap between the quartz pipe 61, the gap between the core preform 70 and the fluorine-containing quartz rod 80, the gap between the quartz pipe 61, the core preform 70 and the quartz capillary 80, and the quartz pipe 61 and the fluorine-containing quartz. There is no gap between the pipe 76 and the optical fiber 111 shown in FIG. 15 is formed.

-Manufacturing method D2-
A manufacturing method D2, which is another manufacturing method, will be described with reference to FIG. First, a quartz rod is prepared, and a plurality of holes are formed along the central axis of the rod. The holes are opened so that two holes are arranged on each vertex of the regular hexagon and its center and outside the regular hexagonal arrangement in the cross section of the quartz rod.

  Next, the fluorine-containing quartz rods 80 and the quartz capillaries 82 are inserted into the holes of the perforated quartz rod 63 ′ having the holes, and the plurality of core base materials 70, 70,. The outer diameters of the core base materials 70, 70,..., The fluorine-containing quartz rod 80, and the quartz capillary 82 are set to be slightly smaller than the diameters of the holes. Further, both ends of the quartz capillary 82 are sealed and closed.

  Further, this perforated quartz rod 63 ′ is put into the hole at the center of the fluorine-containing quartz pipe (low refractive index member) 76 to form the optical fiber preform 221.

  Next, when the optical fiber preform 221 is heated, softened, and stretched in the central axis direction, the gap between the perforated quartz rod 63 ′ and the core preforms 70, 70,. The gap between the capillaries 82, the gap between the perforated quartz rod 63 ′ and the fluorine-containing quartz rod 80, and the gap between the perforated quartz rod 63 ′ and the fluorine-containing quartz pipe 76 are eliminated, as shown in FIG. An optical fiber 111 is formed.

-Manufacturing method E2-
A manufacturing method E2 which is another manufacturing method will be described with reference to FIG. First, a two-layer quartz rod is prepared. In this double-layered quartz rod, the inner layer 64 is made of quartz and the outer layer 77 is made of fluorine-containing quartz. A plurality of holes are made in the inner layer 64 of the two-layer structure quartz rod along the center axis of the rod. The holes are drilled so as to be arranged in two at each vertex of the regular hexagon and its center and outside the regular hexagonal arrangement in the cross section of the quartz rod.

  Next, a plurality of core base materials 70, 70,... And a fluorine-containing quartz rod 80 and a quartz capillary 82 are provided in the outer holes of the regular hexagonal arrangement in the hole of the perforated double layer structure quartz rod 78 ′. The optical fiber preform 222 is formed by insertion. The outer diameters of the core base materials 70, 70,..., The fluorine-containing quartz rod 80, and the quartz capillary 82 are set to be slightly smaller than the diameters of the holes. Further, both ends of the quartz capillary 82 are sealed and closed.

  Next, when the optical fiber preform 222 is heated, softened, and stretched in the central axis direction, a gap between the perforated double-layered quartz rod 78 ′ and the core preform 70, 70,. The gap between the quartz rod 78 ′ and the quartz capillary 82 and the gap between the porous double-layered quartz rod 78 ′ and the fluorine-containing quartz rod 80 are eliminated, and the optical fiber 111 shown in FIG. 15 is formed.

<Modification of Embodiment 4>
-Modification a-
FIG. 19 shows a cross-sectional view of an optical fiber 121 according to Modification Example a of this embodiment. This modification is different from the above embodiment in the type, number, and arrangement of the light direction changing units 40a, 40b, and 40c, and is otherwise the same as the above embodiment. .

  There are three light direction changing portions 40a, 40b, and 40c related to the optical fiber 121 of this modification, and all are made of fluorine-containing quartz glass. One light direction changing part 40a exists outside one side of the regular hexagon formed by the cores 10 and 10, and the remaining two light direction changing parts 40b and 40c exist outside the next side. Yes. With such an arrangement, the optical direction changing portions 40a, 40b, and 40c can be used as markers for fusion-splicing with other optical fibers. , 10,... Can be specified individually.

  The optical fiber 121 of this modification has the same effect as that of the fourth embodiment.

-Modification b-
FIG. 20 shows a cross-sectional view of the optical fiber 122 according to the modification b of this embodiment. In this modification, the number and arrangement of the cores 12, 12,... And the number, type, and arrangement of the light direction changing units 40 are different from those in the above embodiment. The description of the same part is omitted.

  The four cores 12, 12,... According to the optical fiber 122 of the present modification are positioned at the apexes of the square in the cross section of the optical fiber, and the center of the square substantially coincides with the optical fiber central axis. The material of the cores 12, 12,... Is obtained by adding rare earth elements such as Er, Pr, Nd, and Yb and Ge to quartz glass as in the above embodiment.

  The light direction changing unit 40 is located on an extension line of one side of a square formed by the cores 12, 12,. With such an arrangement, the light direction changing unit 40 can be used as a marker for fusion splicing with another optical fiber, and the cores 12, 12,. Can be identified individually.

  The optical fiber 122 of this modification has the same effect as that of the fourth embodiment.

-Modification c-
FIG. 21 shows a cross-sectional view of the optical fiber 123 according to the modified example c of this embodiment. This modified example is different from the above embodiment in the number and arrangement of the cores 13, 13,... And the number, type, and arrangement of the light direction changing units 40, and is otherwise the same as the above embodiment. The description of the same part is omitted.

  The five cores 13, 13,... According to the optical fiber 123 of the present modification are located at the center of the square and each vertex in the cross section of the optical fiber, and the center of the square substantially coincides with the center axis of the optical fiber. Yes. The material of the cores 13, 13,... Is obtained by adding rare earth elements such as Er, Pr, Nd, Yb and Ge to quartz glass, as in the above embodiment.

  The light direction changing part 40 is located substantially on the extension line of one side of the square formed by the cores 13, 13,. With such an arrangement, the optical direction changing unit 40 can be used as a marker for fusion-splicing with another optical fiber, and the cores 13, 13,. Can be identified individually.

  The optical fiber 123 of this modification has the same effect as that of the fourth embodiment.

-Modification d-
FIG. 22 shows a cross-sectional view of an optical fiber 124 according to Modification d of this embodiment. This modification is different from the above embodiment in the number and arrangement of the cores 14, 14,... And the number, type, and arrangement of the light direction changing units 40, and is otherwise the same as the above embodiment. The description of the same part is omitted.

  The nine cores 14, 14,... According to the optical fiber 124 of the present modification are located at nine positions, three on each side of the square and one at the center in the cross section of the optical fiber. It substantially coincides with the fiber center axis. The material of the cores 14, 14,... Is obtained by adding rare earth elements such as Er, Pr, Nd, and Yb and Ge to quartz glass as in the above embodiment.

  The light direction changing unit 40 is arranged outside the one side of the square formed by the cores 14, 14,... And approximately equidistant from the two adjacent cores 14, 14. With such an arrangement, the optical direction changing unit 40 can be used as a mark for fusion splicing with another optical fiber, and the cores 14, 14,. Can be identified individually.

  The optical fiber 124 of this modification has the same effect as that of the fourth embodiment.

-Modification e-
FIG. 23 shows a cross-sectional view of an optical fiber 125 according to Modification Example e of this embodiment. This modification is different from the above embodiment in the number and arrangement of the cores 15, 15,... And the number, type, and arrangement of the light direction changing units 40, and is otherwise the same as the above embodiment. The description of the same part is omitted.

  The eight cores 15, 15,... According to the optical fiber 125 of the present modification are located at three positions on each side of the square in the cross section of the optical fiber, and the center of the square is the optical fiber central axis. Is almost the same. The material of the cores 15, 15,... Is obtained by adding rare earth elements such as Er, Pr, Nd, and Yb and Ge to quartz glass as in the above embodiment.

  The light direction changing unit 40 is disposed outside the one side of the square formed by the cores 15, 15,... And at a substantially equidistant position from the two adjacent cores 15 and 15. With such an arrangement, the optical direction changing unit 40 can be used as a marker for fusion splicing with another optical fiber, and the cores 15, 15,. Can be identified individually.

  The optical fiber 125 of this modification has the same effect as that of the fourth embodiment.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. The embodiments and examples may be combined. For example, a third cladding for support may be further provided outside the second cladding. In the above-described embodiment, rare earth elements may not be added to all the cores of the plurality of cores of each optical fiber, as long as at least one core in one optical fiber contains rare earth elements. Good.

  In the second modification of the first embodiment, the outer peripheral shape of the first cladding may be a polygonal shape other than a regular hexagon.

  The rare earth element added to the core may be any rare earth element such as Er, Pr, Nd, and Yb, but the wavelengths of the signal light and the excitation light differ depending on the type of the rare earth element.

  The refractive indexes of the core, the first cladding, and the second cladding are the refractive indexes at the wavelength of the signal light to be used. In the present invention, they are the refractive indexes in the range of visible light to near infrared light.

  A boron-containing quartz glass may be used in place of the fluorine-containing quartz glass. However, when boron-containing quartz glass is used, stress is applied to the surrounding quartz glass to affect it, and therefore fluorine-containing quartz glass is preferred.

  Even if the material used for the light direction changing portion has a higher refractive index than that of the first cladding, the skew light is extinguished, so a member having a high refractive index may be used. However, if a material having a refractive index higher than that of the first cladding is used for the light direction changing portion, the light direction changing portion also functions as a core, and perturbation with other cores occurs.

  Instead of fluorine-containing quartz glass, holes may be used as the light direction changing portion.

  In the fourth embodiment and the modification thereof, the position and number of the optical direction changing unit in the cross section of the optical fiber are particularly the position / number as long as each core can be individually identified from both ends of the optical fiber. The number is not limited.

  As described above, the optical fiber according to the present invention is useful as an optical amplifier or the like.

10 Core 11 Core 12 Core 13 Core 14 Core 15 Core 20, 21, 22 First clad 30 Second clad 31, 32 Second clad 35 Air hole 40 Light direction changing parts 40a, 40b, 40c Light direction changing part 41 Light direction Change part 60 Quartz pipe 61 Quartz pipe 62, 63, 63 ', 65 Perforated quartz rod 64 Inner layer 70 Core base material 75 Center axis part 76 Fluorine containing quartz pipe (low refractive index member)
77 Outer layer 78, 78 ′ Perforated double-layer quartz rod 80 Fluorine-containing quartz rod 82 Quartz capillary 100 Optical fiber 101 Optical fibers 102, 103, 104 Optical fibers 110, 120 Optical fiber 111 Optical fibers 121, 122 Optical fibers 123, 124 Optical fiber 125 Optical fiber 200 Optical fiber preform 201, 203 Optical fiber precursor 202, 206 Optical fiber preform 210, 211, 212 Optical fiber preform 220, 221, 222 Optical fiber preform

Claims (11)

A plurality of cores, a first cladding surrounding the periphery of the plurality of cores, and a second cladding surrounding the periphery of the first cladding,
At least one of the plurality of cores contains a rare earth element,
The first cladding has a lower refractive index than any of the plurality of cores,
An optical fiber in which the second cladding has a lower refractive index than the first cladding. The first cladding is circular in cross section of the optical fiber;
2. The optical fiber according to claim 1, wherein an optical direction changing portion having a refractive index different from that of the first cladding and extending along the optical fiber axis is present in the first cladding.   3. The optical fiber according to claim 2, wherein the light direction changing unit is located closer to the second cladding than the core closest to the second cladding among the plurality of cores.   The optical fiber according to claim 3, wherein the optical direction changing unit has a refractive index lower than that of the first cladding.   The optical fiber according to claim 2, wherein there are a plurality of the light direction changing portions, and each of the light direction changing portions is not line symmetric in a plane including the optical fiber central axis. At least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary and a plurality of quartz cylinders containing a rare earth element in the central axis portion are inserted into the hole portion of the quartz pipe. Forming an optical fiber preform;
Heating and stretching the optical fiber preform to form an optical fiber precursor;
And coating the outer periphery of the optical fiber precursor with a resin having a refractive index lower than that of quartz. Opening a plurality of holes along the central axis of the rod in the quartz rod;
An optical fiber in which at least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary and a plurality of quartz columns containing a rare earth element in the central axis portion are inserted into the plurality of holes. Forming a base material;
Heating and stretching the optical fiber preform to form an optical fiber precursor;
And coating the outer periphery of the optical fiber precursor with a resin having a refractive index lower than that of quartz. At least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary and a plurality of quartz pillars containing a rare earth element in the central axis portion are inserted into the hole portion of the quartz pipe, Forming an optical fiber preform by surrounding an outer periphery of the quartz pipe with a low refractive index member having a lower refractive index than quartz;
Heating and drawing the optical fiber preform, and an optical fiber manufacturing method. Opening a plurality of holes along the central axis of the rod in the quartz rod;
At least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary and a plurality of quartz pillars containing a rare earth element in the central axis portion are inserted into the plurality of holes, and the quartz Forming an optical fiber preform by surrounding the outer periphery of the rod with a low refractive index member having a refractive index lower than that of quartz;
Heating and drawing the optical fiber preform, and an optical fiber manufacturing method. A step of preparing a double-layered quartz rod made of quartz containing fluorine or boron on the outer layer side or quartz having a plurality of holes extending along the central axis, and the inner layer side made of quartz;
A step of opening a plurality of holes along the central axis of the rod on the inner layer side of the two-layer structure quartz rod;
An optical fiber in which at least one selected from a fluorine-containing quartz rod, a boron-containing quartz rod and a quartz capillary and a plurality of quartz columns containing a rare earth element in the central axis portion are inserted into the plurality of holes. Forming a base material;
Heating and drawing the optical fiber preform, and an optical fiber manufacturing method.   2. The optical fiber according to claim 1, wherein in the cross section of the optical fiber, the shape of the outer periphery of the first cladding is a combination of an arc and a chord or a polygon.

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