JP5471776B2 - Multi-core optical fiber - Google Patents

Description

  The present invention relates to a multi-core optical fiber.

  In a multi-core optical fiber, a plurality of cores extending in the fiber axial direction are covered with a common cladding. Since each of the plurality of cores functions as an optically independent optical waveguide, the multi-core optical fiber can transmit a large amount of information.

  The multi-core optical fiber described in Non-Patent Document 1 has different refractive indexes between two adjacent cores out of a plurality of cores, whereby the propagation constant is different between two adjacent cores, It is said that crosstalk can be suppressed. In addition, the multi-core optical fiber suppresses crosstalk due to a difference in propagation constant between two adjacent cores even when the core diameter is different between two adjacent cores among a plurality of cores. Can do.

  If the crosstalk between two adjacent cores can be suppressed in this way, the distance between the two adjacent cores can be reduced, and the number of cores included in one multicore optical fiber can be increased. This makes it possible to transmit a larger amount of information. That is, it is possible to reduce both crosstalk and increase the core density.

  In addition, when a plurality of cores are made of pure silica glass and a clad is made of fluorine-added silica glass, the multi-core optical fiber can reduce transmission loss of each core, thereby enabling long-distance transmission, or The incident signal light power can be reduced.

Masanori Koshiba, et al, "Heterogeneous multi-core fibers: proposal and design principle," IEICE Electronics Express, Vol.6, No.2, pp.98-103 (2009).

  In a multi-core optical fiber having a plurality of cores made of pure silica glass and a cladding made of fluorine-added silica glass, when one end of the base material is heated and melted and drawn, the core is made of pure silica glass with high viscosity. Since strain concentrates, stress may remain in a specific core among the plurality of cores. Due to this residual stress, the refractive index of a specific core is different from the design value, which may cause a problem that crosstalk between the specific core and the adjacent core increases. There is also a problem that the transmission loss of a specific core increases due to residual stress.

  In order to suppress the occurrence of such a problem, it is conceivable to reduce the drawing tension. That is, the residual stress of the core can be reduced by performing low tension drawing. However, in order to perform low tension drawing, it is necessary to raise the temperature of the drawing furnace. On the other hand, it is necessary to raise the temperature of the drawing furnace in order to increase the drawing speed. When drawing multi-core optical fiber, there is a problem of equipment furnace temperature restriction before drawing normal optical fiber, and it is necessary to manage drawing conditions that are not necessary for normal optical fiber drawing. Become. Moreover, it is difficult for the low tension drawing to increase the line speed for reducing the production cost.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a multi-core optical fiber that can be easily manufactured so that the refractive index of each core is as designed.

The multi-core optical fiber of the present invention has a plurality of cores, a common clad having a refractive index lower than that of the plurality of cores and surrounding the plurality of cores, and a high-viscosity region provided in contact with the clad. Multiple cores and high-viscosity regions extend in the fiber axis direction.At the time of drawing, the maximum viscosity of the multiple cores is greater than the viscosity of the cladding, and the viscosity of the high-viscosity regions is greater than the maximum viscosity of the multiple cores. the size rather, a plurality of high-viscosity region in a cross section perpendicular to the fiber axis, characterized in that it is provided at a position having two or more rotational symmetry with respect to the cross-sectional center.

  In the multi-core optical fiber of the present invention, the plurality of cores are quartz glass to which chlorine is added, the high viscosity region is quartz glass having a chlorine addition amount smaller than the chlorine addition amount of the plurality of cores, and the clad is A quartz glass to which fluorine is added is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, the multi-core optical fiber which can be manufactured easily so that the refractive index of each core may become as designed can be provided.

It is sectional drawing of the multi-core optical fiber 2 of a comparative example. It is sectional drawing of 1 A of multi-core optical fibers of 1st Embodiment. It is sectional drawing of the multi-core optical fiber 1B of 2nd Embodiment. It is sectional drawing of 1 C of multi-core optical fibers of 3rd Embodiment. It is sectional drawing of multi-core optical fiber 1D of 4th Embodiment. It is sectional drawing of the multi-core optical fiber 1E of 5th Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a cross-sectional view of a multi-core optical fiber 2 of a comparative example. This figure shows a cross section perpendicular to the fiber axis. The multi-core optical fiber 2 of the comparative example includes seven cores 10 to 16 extending in the fiber axis direction and a common clad 20 surrounding the cores 10 to 16. The cores 10 to 16 and the clad 20 are made of glass.

  The refractive index of the cores 10 to 16 is higher than that of the clad 20. Each of the cores 10 to 16 has a circular cross-sectional shape. In the cross section perpendicular to the fiber axis, the core 10 is disposed in the center, and the six cores 11 to 16 are sequentially disposed on the circumference of a circle centering on the core 10 at an equal pitch. The core interval is 20 μm to 50 μm.

  Each of the cores 10 to 16 and the clad 20 is mainly composed of quartz glass, and impurities for adjusting the refractive index are added as necessary. For example, the cores 10 to 16 are pure quartz glass, and the clad 20 is quartz glass doped with fluorine. “Pure quartz glass” includes the case where chlorine is added.

The core 10 has a core diameter _{d 0.} Core 11, core 13 and core 15 have a common core diameter _{d 1.} The core 12, the core 14 and core 16 have a common core diameter _{d 2.} The core diameter d ₀ , the core diameter d ₁ and the core diameter d ₂ are different. That is, the core diameter is different between any two adjacent cores among the seven cores 10 to 16.

Alternatively, the core 10 has a refractive index _{n 0.} Core 11, core 13 and core 15 have a common refractive index _{n 1.} The core 12, the core 14 and core 16 have a common refractive index _{n 2.} The refractive index n ₀ , the refractive index n ₁ and the refractive index n ₂ are different. That is, the refractive index is different between any two adjacent cores among the seven cores 10 to 16.

  According to the design, the multi-core optical fiber 2 has different propagation constants between two adjacent cores because the core diameter or refractive index is different between two adjacent cores among the seven cores 10 to 16. However, crosstalk can be suppressed.

  However, the multi-core optical fiber 2 that is actually manufactured has a plurality of cores because strain concentrates on a pure silica glass core having high viscosity when one end of a base material is heated and melted and drawn. Stress may remain in certain of these cores. Due to this residual stress, the refractive index of a specific core is different from the design value, which may cause a problem that crosstalk between the specific core and the adjacent core increases. There also arises a problem that the transmission loss of a specific core increases due to the residual stress. In addition, when a low tension drawing is performed in order to suppress the occurrence of such a problem, another problem occurs. The multi-core optical fibers 1A to 1E of the present embodiment described below can solve the problems of the multi-core optical fiber 2 of the comparative example.

  FIG. 2 is a cross-sectional view of the multi-core optical fiber 1A of the first embodiment. This figure also shows a cross section perpendicular to the fiber axis. Compared with the multi-core optical fiber 2 of the comparative example shown in FIG. 1, the multi-core optical fiber 1 </ b> A of the first embodiment shown in FIG. 2 is different in that it further has a highly viscous region 31. . The highly viscous region 31 extends in the fiber axis direction. The cross-sectional shape of the highly viscous region 31 is arbitrary. The highly viscous region 31 is provided in contact with the clad 20. The highly viscous region 31 is preferably provided away from any of the cores 10 to 16.

  At the time of drawing, the maximum viscosity of the seven cores 10 to 16 is larger than the viscosity of the clad 20, and the viscosity of the high-viscosity region 31 is larger than the maximum viscosity of the seven cores 10 to 16. For example, the seven cores 10 to 16 are quartz glass to which chlorine is added. The high-viscosity region 31 is quartz glass having a chlorine addition amount smaller than that of the seven cores 10 to 16. The clad 20 is quartz glass to which fluorine is added.

  In the multi-core optical fiber 1A of the first embodiment, when one end of a base material is heated and melted and drawn and drawn, strain concentrates on the highly viscous region 31 having the highest viscosity. Stress remains. Since there is no (or small) residual stress in the cores 10 to 16, there is no change (or small) in the refractive index of the cores 10 to 16 due to the residual stress. Therefore, the multi-core optical fiber 1A of the first embodiment does not need to be manufactured by low tension drawing, and can be easily manufactured such that the refractive index of each core is as designed.

  FIG. 3 is a cross-sectional view of the multi-core optical fiber 1B of the second embodiment. This figure also shows a cross section perpendicular to the fiber axis. Compared with the multi-core optical fiber 1A of the first embodiment shown in FIG. 2, the multi-core optical fiber 1B of the second embodiment shown in FIG. 3 has a high-viscosity region 32 and a high-viscosity region in addition to the high-viscosity region 31. The difference is that the region 33 is also included.

  The high viscosity region 32 and the high viscosity region 33 are the same as the high viscosity region 31. The viscosity of the three high-viscosity regions 31 to 33 is larger than the maximum viscosity of the seven cores 10 to 16 at the temperature at the time of drawing. Therefore, the multi-core optical fiber 1B of the second embodiment does not need to be manufactured by low tension drawing, and can be easily manufactured such that the refractive index of each core is as designed.

  The three high-viscosity regions 31 to 33 are provided at positions having three-fold rotational symmetry with respect to the center of the cross section in a cross section perpendicular to the fiber axis. As described above, the multi-core optical fiber 1B of the second embodiment is formed in the high-viscosity regions 31 to 33 by providing the plurality of high-viscosity regions at positions having two or more rotational symmetry with respect to the center of the cross section. Even when the residual stress is concentrated, the occurrence of fiber curl can be prevented.

  The fiber curl is a bending curve of the glass portion of the optical fiber. When the fiber curl is large, for example, centering becomes difficult in the operation of fusion splicing. In the multi-core optical fiber 1B of the second embodiment, since the occurrence of fiber curl is suppressed, centering is easy in the fusion splicing operation.

  FIG. 4 is a cross-sectional view of the multi-core optical fiber 1C of the third embodiment. This figure also shows a cross section perpendicular to the fiber axis. Compared with the multicore optical fiber 2 of the comparative example shown in FIG. 1, the multicore optical fiber 1 </ b> C of the third embodiment shown in FIG. 4 is different in that it further has a high viscosity region 30. . The highly viscous region 30 extends in the fiber axis direction. The cross-sectional shape of the high viscosity region 30 is a ring shape. The highly viscous region 30 is continuously provided on the outer periphery of the clad 20.

  At the temperature at the time of drawing, the maximum viscosity of the seven cores 10 to 16 is higher than the viscosity of the clad 20, and the viscosity of the high viscosity region 30 is higher than the maximum viscosity of the seven cores 10 to 16. For example, the seven cores 10 to 16 are quartz glass to which chlorine is added. The high-viscosity region 30 is quartz glass having a chlorine addition amount smaller than that of the seven cores 10 to 16. The clad 20 is quartz glass to which fluorine is added.

  In the multi-core optical fiber 1C of the third embodiment, when one end of a base material is heated and melted and drawn and drawn, strain concentrates in the highly viscous region 30 having the highest viscosity. Stress remains. Since there is no (or small) residual stress in the cores 10 to 16, there is no change (or small) in the refractive index of the cores 10 to 16 due to the residual stress. Therefore, the multi-core optical fiber 1C of the third embodiment does not need to be manufactured by low tension drawing, and can be easily manufactured such that the refractive index of each core is as designed.

  In addition, a highly viscous region 30 is provided so as to have rotational symmetry with respect to the center of the cross section. Therefore, the multi-core optical fiber 1C of the third embodiment can prevent the occurrence of fiber curl even when the residual stress is concentrated in the highly viscous region 30, and the centering can be performed in the fusion splicing operation. Easy.

  FIG. 5 is a cross-sectional view of the multi-core optical fiber 1D of the fourth embodiment. This figure also shows a cross section perpendicular to the fiber axis. Compared with the multi-core optical fiber 2 of the comparative example shown in FIG. 1, the multi-core optical fiber 1D of the fourth embodiment shown in FIG. 5 is different in that it further has high-viscosity regions 31-34. ing.

  The viscosity of the four high-viscosity regions 31 to 34 is higher than the maximum viscosity of the seven cores 10 to 16 at the temperature at the time of drawing. Therefore, the multi-core optical fiber 1D of the fourth embodiment does not need to be manufactured by low tension drawing, and can be easily manufactured such that the refractive index of each core is as designed.

  The four high-viscosity regions 31 to 34 are provided so as to have four-fold rotational symmetry with respect to the center of the cross section in a cross section perpendicular to the fiber axis. Therefore, the multi-core optical fiber 1D of the fourth embodiment can prevent the occurrence of fiber curl even when residual stress is concentrated in the high-viscosity regions 31 to 34. Easy to put out.

  In addition, in the cross section perpendicular to the fiber axis, the seven cores 10 to 16 are arranged so as to have three-fold rotational symmetry, whereas four high-viscosity regions are located at positions where the symmetry is broken. 31-34 are arranged. Further, the arrangement of the cores 10 to 16 and the high viscosity regions 31 to 34 does not have line symmetry with respect to an arbitrary line on the cross section. Therefore, in the multi-core optical fiber 1D of the fourth embodiment, the four high-viscosity regions 31 to 34 can function as core identification markers for identifying each of the seven cores 10 to 16.

  FIG. 6 is a cross-sectional view of a multi-core optical fiber 1E according to the fifth embodiment. This figure also shows a cross section perpendicular to the fiber axis. The multi-core optical fiber 1E according to the fifth embodiment shown in FIG. 6 includes eight cores 11 to 18, three high-viscosity regions 31 to 33, these eight cores 11 to 18 and three high cores. And a common clad 20 surrounding the viscous regions 31 to 33.

  The eight cores 11 to 18 extend in the fiber axis direction. The refractive indexes of the cores 11 to 18 are higher than the refractive index of the clad 20. The cross-sectional shape of each of the cores 11 to 18 is a circle. In the cross section perpendicular to the fiber axis, the cores 11 to 18 are arranged in 2 rows and 4 columns. The cores 11 to 14 are arranged in order from the left in the first row, and the cores 15 to 18 are arranged in order from the right in the second row. The core interval is 20 μm to 50 μm.

The core 11, the core 13, the core 15 and the core 17 have a common core diameter _{d 1.} The core 12, the core 14, the core 16 and core 18 have a common core diameter _{d 2.} Core diameter _{d 1} and a core diameter _{d 2} are different. That is, the core diameter is different between any two adjacent cores among the eight cores 11 to 18.

Alternatively, the core 11, the core 13, the core 15 and the core 17 have a common refractive index _{n 1.} The core 12, the core 14, the core 16 and core 18 have a common refractive index _{n 2.} The refractive index n ₁ and the refractive index n ₂ are different. That is, the refractive index is different between any two adjacent cores among the eight cores 11 to 18.

  In the multi-core optical fiber 1E, the core diameter or the refractive index is different between two adjacent cores among the eight cores 11 to 18, so that the propagation constants are different between the two adjacent cores. Talk can be suppressed.

  Three high-viscosity regions 31 to 33 also extend in the fiber axial direction. The cross-sectional shape of the high viscosity regions 31 to 33 is arbitrary. The highly viscous regions 31 to 33 are provided in contact with the clad 20. The highly viscous regions 31 to 33 are preferably provided apart from any of the cores 11 to 18.

  At the temperature at the time of drawing, the maximum viscosity of the eight cores 11 to 18 is higher than the viscosity of the clad 20, and the viscosity of the three high-viscosity regions 31 to 33 is higher than the maximum viscosity of the eight cores 11 to 18. For example, the eight cores 11 to 18 are quartz glass to which chlorine is added. The three high-viscosity regions 31 to 33 are quartz glass having a chlorine addition amount smaller than the chlorine addition amount of the eight cores 11 to 18. The clad 20 is quartz glass to which fluorine is added.

  In the multi-core optical fiber 1E of the fifth embodiment, when one end of a base material is manufactured by being heated and melted and drawn, strain concentrates on the highly viscous regions 31 to 33 having the highest viscosity. Stress remains in 31-33. Since there is no (or small) residual stress in the cores 11 to 18, there is no change (or small) in the refractive index of the cores 11 to 18 due to the residual stress. Therefore, the multi-core optical fiber 1E of the fifth embodiment does not need to be manufactured by low tension drawing, and can be easily manufactured such that the refractive index of each core is as designed.

  The three high-viscosity regions 31 to 33 are provided so as to have three-fold rotational symmetry with respect to the center of the cross section in a cross section perpendicular to the fiber axis. Therefore, the multi-core optical fiber 1E of the fifth embodiment can prevent the occurrence of fiber curl even when residual stress is concentrated in the high-viscosity regions 31 to 33. Easy to put out.

  Further, in the cross section perpendicular to the fiber axis, the eight cores 11 to 18 are arranged so as to have two-fold rotational symmetry, whereas three high-viscosity regions are located at positions where the symmetry is broken. 31-33 are arranged. Therefore, in the multi-core optical fiber 1E of the fifth embodiment, the three high-viscosity regions 31 to 33 can also function as core identification markers for identifying each of the eight cores 11 to 18.

1A to 1E ... multi-core optical fiber, 10 to 18 ... core, 20 ... cladding, 30 to 34 ... high viscosity region.

Claims (2)

A plurality of cores, a common cladding having a refractive index lower than that of the plurality of cores and surrounding the plurality of cores, and a highly viscous region provided in contact with the cladding,
The plurality of cores and the highly viscous region extend in a fiber axial direction;
At the temperature at the time of drawing, the maximum viscosity of the plurality of cores is larger than the viscosity of the clad, and the viscosity of the high viscosity region is larger than the maximum viscosity of the plurality of cores,
A multi-core optical fiber, wherein a plurality of the high-viscosity regions are provided at a position having rotational symmetry twice or more with respect to the center of the cross section in a cross section perpendicular to the fiber axis. The plurality of cores are quartz glass to which chlorine is added,
The high-viscosity region is quartz glass having a chlorine addition amount smaller than the chlorine addition amount of the plurality of cores,
The clad is quartz glass doped with fluorine,
The multi-core optical fiber according to claim 1.

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