JP2018198287A - Amplifying fiber - Google Patents

Abstract

To provide an amplifying fiber that is able to reduce power of excitation light.SOLUTION: A double clad multi-core erbium doped fiber 11 comprises: a plurality of cores 1 filled most densely in a cross-sectional view orthogonal to an axis J; a first clad 2 encompassing all the plurality of cores 1; and a second clad 4 lower in index of refraction than the first clad 2 and encompassing the first clad 2. At least one outermost shell core 1F of a plurality of outermost shell cores 1R, arranged on the outermost shell, among the plurality of cores 1 is longer than the other outermost shell cores 1S in terms of a distance from a base point B in the cross-sectional view. The center C2 of the first clad 2 is disposed at the position in which respective distances by which the outermost shell cores 1X and outermost shell cores 1Y are separate from each other longest in the cross-sectional view are equal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an amplification fiber used inside a fiber amplifier.

  In order to dramatically increase the transmission capacity of an optical transmission system, development of a multi-core optical transmission system using a multi-core fiber in which a plurality of cores are provided in one fiber as a transmission path is underway. By transmitting a wavelength division multiplexing (WDM) signal that transmits different information to each core of the multi-core fiber, a single core fiber in which one core is provided in one fiber as a transmission line is used as a transmission line. Compared with the case where it does, transmission capacity can be increased dramatically.

  In a long-distance multi-core optical transmission system, a multi-core fiber amplifier is indispensable to amplify signal light whose intensity is reduced during transmission, as in the conventional optical transmission system using a single-core fiber as a transmission line. .

  As an example of the configuration of the multi-core fiber amplifier, there is a multi-core optical amplification (that is, a clad-pumped multi-core fiber amplifier) using a double-clad rare earth-doped fiber and one high-power multi-mode pump light source. The double clad rare earth-doped fiber has a plurality of cores doped with rare earth ions and a double clad structure (that is, an inner first clad and an outer second clad). In the double-clad rare earth-doped fiber, the refractive index of the first cladding material (glass) is smaller than the refractive index of the core material (glass) and larger than the refractive index of the second cladding material (glass).

  As an amplification fiber used in a clad pumped multi-core fiber amplifier, for example, a double-clad 7-core erbium-doped fiber (see Non-Patent Document 1) and a double-clad 12-core erbium / ytterbium-doped fiber (see Non-Patent Document 2) are known. It has been.

  FIG. 7 is a cross-sectional view of the double-clad 7-core erbium-doped fiber 101. As shown in FIG. 7, in the double clad 7-core erbium-doped fiber 101, the first clad 2 is disposed so as to include the seven erbium-doped cores 1 that are closely packed. The second cladding 4 is disposed on the outer periphery of the first cladding 2. In addition, the six cores 1B of the outermost shell are arranged on the same circle with the core 1A at the center as the center. In such an arrangement, since the intensity distribution of the signal light spreads from the core region, when the fiber is bent, the signal light leaks to the outside of the first cladding 2, resulting in optical loss. In order to avoid such light loss, a certain thickness (that is, cladding thickness) is ensured between the outside of the six cores 1 of the outermost shell and the outside of the first cladding 2.

  When the core arrangement is the same as that of the double-clad 7-core erbium-doped fiber 101 of FIG. 7 and the total number of cores is further increased, the double-clad 19-core erbium-doped fiber 102 having the cross section shown in FIG. As shown in FIG. 8, in the double-clad 19-core erbium-doped fiber 102, twelve outermost shells on the same circle having a radius larger than the same circle in which the six cores 1B are arranged with respect to the central core 1A. The first cladding 2 is disposed so as to include the 19 erbium-added cores 1A, 1B, and 1C that are closely packed. As described above, when the close-packed core arrangement and the core arrangement having good consistency with the circular first clad 2 that is easy to manufacture are adopted, 7 cores and 19 cores, and 37 cores with the total number of cores increased. 61 core double clad erbium-doped fiber.

Y. Mimura, et al., “Batch multicore amplification with cladding-pumped multicore EDF,” Proc. ECOC2012, paper Tu.4.F.1. H. Ono et al. “12-core double-clad Er / Yb-doped fiber amplifier using free-space coupling pump / signal combiner module,” Proc. ECOC2013, paper We4.A.4.

  The advantage of the clad pumped multi-core fiber amplifier is that pump light is input to the first clad and propagates through the first clad, so that all cores in the first clad can be pumped together to amplify the signal light. is there. On the other hand, as a problem of the clad pump multi-core fiber amplifier, the pump light propagates almost uniformly spread through the first clad having a large cross section, so that the pump light necessary for amplifying the signal light with sufficient gain and low noise can be obtained. In order to secure the power density, the power of the excitation light must be increased.

  A double-clad erbium-doped fiber having a total number of cores between 7, 9, 37,... With the same core arrangement as the conventional double-clad erbium-doped fiber described above, for example, as shown in FIG. A double-clad 12-core erbium-doped fiber 103 that uses only the 12 cores 1C of the outermost shell filled, or a part of the cores 1B and 1C that are close-packed with the central core 1A as shown in FIG. There is a double-clad 16-core erbium-doped fiber 104 that eliminates. Non-Patent Document 2 discloses a double-clad 12-core fiber in which an erbium-doped core is an erbium / ytterbium-doped core. However, the double-clad 12-core erbium-doped fiber 103 and the double-clad 16-core erbium-doped fiber 104 have a problem in that the power of the pumping light required increases because the region where the core is not arranged becomes wide.

  This invention is made | formed in view of such a situation, and makes it a subject to provide the fiber for amplification which can reduce the power of excitation light.

  The amplification fiber according to the present invention includes a plurality of cores that are close-packed in a cross-sectional view orthogonal to the axis, a first cladding that includes all of the plurality of cores, a refractive index lower than that of the first cladding, and A second clad including a first clad, wherein at least one outermost core of the plurality of outermost cores arranged in the outermost shell among the plurality of cores is a base point in the cross-sectional view. Is longer than other outermost cores, and the center of the first clad has the same distance from the outermost cores that are farthest apart from each other in the sectional view among the plurality of outermost cores. It is arrange | positioned in the position which becomes.

In the amplification fiber of the present invention, in the above-described configuration, the total number of the plurality of cores is N, and the first cladding is virtually closest packed in the cross-sectional view, and the center of the first cladding And M ₁ is the total number of first virtual cores that are virtually arranged on one or more of the same circles in the center, and the total number greater than the total number of the first virtual cores in the cross-sectional view, virtually the closest packing, and when the total number of the second virtual cores virtually plurality placed on two or more same circle center and said center of said first clad was M ₂ in, M ₁ < N <holds the relationship of M _2, and satisfies the shown N next (1).

  According to the present invention, the required pumping light power of the amplification fiber can be reduced.

It is sectional drawing of the double clad 8 core erbium doped fiber which concerns on this invention. It is sectional drawing of the double clad 10 core erbium doped fiber which concerns on this invention. It is sectional drawing of the double clad 12 core erbium doped fiber which concerns on this invention. It is sectional drawing of the double clad 14 core erbium doped fiber which concerns on this invention. It is sectional drawing of the double clad 16 core erbium doped fiber which concerns on this invention. It is sectional drawing of the double clad 18 core erbium doped fiber which concerns on this invention. It is sectional drawing of the conventional double clad 7 core erbium addition fiber. It is sectional drawing of the conventional double clad 19 core erbium doped fiber. It is sectional drawing of the conventional double clad 12 core erbium doped fiber. It is sectional drawing of the conventional double clad 16 core erbium addition fiber.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. Each embodiment can be combined as much as possible.

  Note that in this specification and the drawings, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted. Also, the drawings used in the following description are schematic, and the lengths, widths, thickness dimensions, ratios, and the like are not necessarily the same as the actual ones.

  1 to 6 are cross-sectional views of double clad multi-core erbium-doped fibers (amplification fibers) 11, 12, 13, 14, 15, 16 to which the present invention is applied. The double clad multi-core erbium-doped fibers 11, 12, 13, 14, 15, 16 include a plurality of cores 1, a first clad 2 that includes all of the plurality of cores 1, a refractive index lower than that of the first clad 2, and A second clad 4 including the first clad 2.

  The plurality of cores 1 are close-packed in a cross-sectional view orthogonal to the axis J (that is, the central axis of each of the double-clad multi-core erbium-doped fibers 11, 12, 13, 14, 15, 16). A plurality of outermost cores 1R arranged in the outermost shell among 1 are not on the same circle. In addition, at least one outermost core 1F among the plurality of outermost cores 1R has a longer interval from a certain base point B than the other outermost core 1S. In other words, in each of the double clad multi-core erbium-doped fibers 11, 12, 13, 14, 15, and 16, there is no point at which the distances from all the outermost cores 1R are equal.

  The center C2 of the first cladding is disposed at a position where the distances between the outermost core 1X and the outermost core 1Y that are farthest apart from each other are equal among the outermost cores 1R. When the pitch of the core 1 is 38.5 μm and the minimum distance (cladding thickness) between the outer side of the outermost core 1R and the outer side of the first cladding 2 is 30 μm, the distance between the outermost cores 1X and 1Y is 1 double-clad multi-core erbium-doped fiber 11 is 56.9 μm, double-clad multi-core erbium-doped fiber 12 in FIG. 2 is 57.8 μm, double-clad multi-core erbium-doped fiber 13 in FIG. 3 is 63.2 μm, double-clad multi-core in FIG. It is 79.4 μm for the erbium-doped fiber 14, 77.2 μm for the double-clad multicore erbium-doped fiber 15 in FIG. 5, and 86.6 μm for the double-clad multicore erbium-doped fiber 16 in FIG. 6.

  Table 1 shows the power of pumping light required in the multi-core optical amplifier using each of the double-clad multi-core erbium-doped fibers 11, 12, 13, 14, 15, and 16 shown in FIGS. For comparison, the power of pumping light required in a multi-core optical amplifier using a conventional double-clad multi-core erbium-doped fiber having the same total number of cores is shown. The conventional double-clad multi-core erbium-doped fiber shown in Table 2 is a part of the cores 1B and 1C arranged in the outer shell in the cross-sectional structure of FIG. 8 in which a maximum of 19 cores 1 can be arranged. By eliminating, the total number of cores is the same as the total number of cores 1 of each of the double-clad multi-core erbium doped fibers 11, 12, 13, 14, 15, 16 (ie, 8, 10, 12, 14, 16, 18). This is a double-clad multi-core erbium-doped fiber having a cross-sectional structure.

  As shown in Table 2, in the conventional double-clad multi-core erbium-doped fiber, the diameter of the first clad 2 is the same in any of the total number of cores 8 to 18, so that the required pumping light power is the total number of cores. It will be the same regardless of. From the comparison of Table 1 and Table 2, when the total number of cores is 8, 10, 12, the power of pumping light required for the double-clad multi-core erbium-doped fiber of this embodiment is the conventional double-clad multi-core erbium-doped It can be seen that the pump power is lower than that required for the fiber.

Specifically, N is the total number of cores 1 of the double clad multi-core erbium-doped fiber to which the present invention is applied. The total number N of the cores of each of the double clad multi-core erbium doped fibers 11, 12, 13, 14, 15, 16 is 8, 10, 12, 14, 16, 18 respectively. Here, in a cross-sectional view orthogonal to the axis J, the first cladding 2 is virtually closest packed, and a plurality of the centers C2 and C2 of the first cladding 2 are virtually arranged on one or more identical circles. Let M ₁ be the total number of first virtual cores. As an example, the first virtual core corresponds to, for example, the core 1 in FIG. 7 and M ₁ = 7. In the cross-sectional structure shown in FIG. 7, the core 1B is arranged on a single concentric circle with the core 1A as the center.

Furthermore, in many cases the total number than the total number M ₁ of the first virtual cores described above, in the cross section, is virtually closest packing in the first cladding 2, and two or more of the center C2 and the center C2 of the first cladding 2 Let M ₂ be the total number of second virtual cores virtually arranged on the same circle. As an example, for the cross-sectional structure shown in FIG. 7, the second virtual core corresponds to, for example, the core 1 in FIG. 8, and M ₁ = 19. In the cross-sectional structure shown in FIG. 8, the core 1 </ b> B and the core 1 </ b> C are arranged on concentric circles having different radii with the core 1 </ b> A as the center.

Assuming that the first virtual core and the second virtual core are assumed as described above, in the case where the total number of the cores 1 is N = 8, 10, 12, 14, 16, 18, M ₁ <N <M ₂ In the case where the total number of the cores 1 is N = 8, 10, 12, among them, the above equation (1) is established. That is, the pumping number required compared to the conventional double-clad multicore erbium-doped fiber is satisfied under the condition that the total number N of the cores 1 satisfies the relationship of M ₁ <N <M ₂ and satisfies the above-described equation (1). The light power is reduced.

  As described above, in the present embodiment, the area of the first cladding that inputs the pump light in the double-clad multi-core erbium-doped fiber having an arbitrary total number of cores by adopting the arrangement of the core and the first cladding described above. Can be minimized, and the power of the pumping light required can be reduced.

In the present embodiment, the pumping light power is reduced as compared with the conventional double-clad multi-core erbium-doped fiber under the condition that satisfies the relationship of M ₁ <N <M ₂ and satisfies the above-described formula (1). Can do.

  The aspect described above shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and has the configuration of the present invention to achieve the objects and effects. The deformation | transformation and improvement in the possible range are contained in the content of this invention. Further, the specific structure, shape, and the like in carrying out the present invention are not problematic as other structures, shapes, and the like as long as the objects and effects of the present invention can be achieved. The present invention is not limited to the above-described embodiments, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Core 1F, 1R, 1S, 1X, 1Y ... Outermost core 2 ... 1st clad 4 ... 2nd clad 11, 12, 13, 14, 15, 16 ... Double clad multi-core erbium doped fiber (amplification fiber)

Claims (2)

A plurality of cores that are closely packed in a cross-sectional view orthogonal to the axis;
A first clad including all of the plurality of cores;
A second cladding having a refractive index lower than that of the first cladding and including the first cladding;
With
At least one outermost core of the plurality of outermost cores arranged in the outermost shell among the plurality of cores has a longer interval from the base point in the cross-sectional view than other outermost cores,
The center of the first clad is disposed at a position where the distances between the plurality of outermost cores and the outermost cores farthest apart from each other in the sectional view are equal. Fiber. The total number of the plurality of cores is N,
In the cross-sectional view, the total number of first virtual cores that are virtually densely packed in the first clad and that are virtually arranged on the center of the first clad and at least one same circle at the center. M ₁
The total number of the first virtual cores is larger than the total number of the first virtual cores, and the first cladding is virtually closest packed in the cross-sectional view, and is virtually on the center of the first cladding and two or more identical circles of the center. when the total number of the second virtual cores plurality placed was M _2, the
The relationship of M ₁ <N <M ₂ holds,
2. The amplification fiber according to claim 1, wherein N satisfies the following expression (1).

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