Multicore fiber connection method and multicore fiber connection device

Abstract

A multicore fiber connection method comprises: a determination step (S3) for determining the rotational position for multicore fibers (2), where the distance dispersion between a line (L) connecting respective tips of a pair of high-voltage discharge electrodes (61a), (61b) located across a butting position of the multicore fibers (2) and the central axes (CC) of the respective cores (21) becomes a prescribed value equal to or lower than the value intermediate between the minimum value and the maximum value in a dispersion distribution when the multicore fibers (2) are rotated around the central axis (C) of a cladding (22); an installation step (S4) for installing the respective multicore fibers (2) at the determined rotational position; and a fusion step (S5) for performing discharge from the pair of high-voltage discharge electrodes (61a), (61b) and for fusing the respective multicore fibers (2) to each other.

Description

Multi-core fiber splicing method and multi-core fiber splicing device

[0001] The present invention relates to a multi-core fiber splicing method and a multi-core fiber splicing device.

[0002] A multicore fiber splicing device is a device used to splice a pair of multicore fibers, and its main components include an alignment device for accurately aligning the parts to be spliced, and a heater unit for generating heat to fuse the ends of the multicore fibers together. As the heater unit, for example, a pair of opposing high-voltage discharge electrodes is used.

[0003] When connecting multi-core fibers, rotational alignment is performed to make the cores of each multi-core fiber face each other. Patent Document 1 listed below discloses a method for adjusting the relative positions of multi-core fibers when the core positions do not have rotational symmetry.

[0004] Patent Document 2 listed below discloses a technology for fusing rotationally aligned multi-core fibers by discharge between a pair of opposing high-voltage discharge electrodes. The ends of the aligned multi-core fibers are butted together, and a high voltage is applied to the high-voltage discharge electrodes between them to generate an arc discharge, which melts the glass portion of the optical fiber with the generated heat. Fusion by discharge forms a physically strong joint, and a stable connection is maintained for a long period of time.

[0005] JP 2018-4685 A International Publication No. 2019 / 163150

[0006] In the case of fusion splicing by discharge, the temperature distribution during arc discharge tends to change in a direction perpendicular to the line connecting the tips of a pair of opposing high-voltage discharge electrodes. Therefore, when fusion splicing multicore fibers, if there is a large variation in the distance from the line connecting the tips of the pair of high-voltage discharge electrodes to the central axis of each core, there will be a variation in the melting of the glass in each core during discharge, which will increase the variation in the connection state between the cores, and as a result, there may be a large variation in the connection loss between the cores.

[0007] Therefore, an object of the present invention is to provide a multi-core fiber splicing method and a multi-core fiber splicing device that can suppress variations in splice loss between cores.

[0008] Aspect 1 of the present invention is a method for connecting a pair of multi-core fibers, comprising: a determining step of determining a rotational position of the multi-core fiber at which a dispersion of a distance between a line connecting tips of a pair of high-voltage discharge electrodes sandwiching a butt joint position of the multi-core fibers and the central axis of each core becomes a predetermined value equal to or less than a median value between a minimum value and a maximum value of a distribution of the dispersion when the multi-core fiber is rotated around the central axis of a cladding; an installing step of installing each of the multi-core fibers at the determined rotational position; and a fusing step of performing discharge by the pair of high-voltage discharge electrodes to fuse each of the multi-core fibers together.

[0009] According to aspect 1, the rotational position of each multi-core fiber is determined and installed so that the dispersion distribution at a plurality of rotational positions has a predetermined value equal to or less than the intermediate value between the minimum and maximum values, thereby reducing the variation in the distance from the line connecting the pair of high-voltage discharge electrodes to the central axis of each core. Therefore, according to aspect 1, the variation in temperature during discharge can be reduced. Therefore, the variation in the connection state of each core can be reduced. As a result, the variation in connection loss between cores can be reduced.

[0010] A second aspect of the present invention is the multi-core fiber splicing method according to the first aspect, characterized in that it further comprises, before the determining step, a calculating step of calculating the dispersion of the distances at a plurality of rotational positions of the multi-core fiber when the multi-core fiber is rotated around the central axis of the cladding.

[0011] According to Aspect 2, since it is possible to calculate the dispersion distribution when the multi-core fibers sandwiching the butt position of the multi-core fibers are rotated around the central axis of the cladding before the determining step, it is possible to determine the rotation position of the multi-core fiber. Therefore, according to Aspect 2, it is possible to reduce the variation in temperature during discharge. Therefore, it is possible to reduce the variation in the connection state of each core. As a result, it is possible to reduce the variation in connection loss between cores.

[0012] Aspect 3 of the present invention is the multi-core fiber splicing method according to Aspect 2, characterized in that it further comprises, before the calculation step, a measurement step of measuring, in a cross section perpendicular to the longitudinal direction of the multi-core fiber, the angle formed by a line connecting the central axis of the cladding and the central axis of the core and a line connecting the tips of the pair of high-voltage discharge electrodes, and the distance from the central axis of the cladding to the central axis of the core.

[0013] According to the third aspect, it is easy to calculate the variance of the distance between the central axis of the core and the pair of high-voltage discharge electrodes.

[0014] A fourth aspect of the present invention is the multi-core fiber splicing method according to any one of the first to third aspects, characterized in that in the determining step, the rotational position of the multi-core fiber at which the dispersion becomes the minimum value is determined.

[0015] According to aspect 4, the variation in the distance from the line connecting the pair of high-voltage discharge electrodes to the central axis of each core can be minimized, and therefore, according to aspect 4, the variation in temperature during discharge can be minimized, and the variation in splice loss between cores can be minimized.

[0016] A fifth aspect of the present invention is a multi-core fiber splicing device that splices a pair of multi-core fibers, the multi-core fiber splicing device comprising: an alignment device that can adjust a rotational position of each of the multi-core fibers; a fusion splicer that generates an electric discharge using a pair of high-voltage discharge electrodes to fuse each of the multi-core fibers together; and a control device, wherein the control device comprises: a determination unit that determines a rotational position of the multi-core fiber at which a dispersion of a distance between a line connecting tips of the pair of high-voltage discharge electrodes that sandwich a butt-joint position of the multi-core fibers and the central axis of each core becomes a predetermined value that is equal to or less than a median value between a minimum value and a maximum value of a distribution of the dispersion when the multi-core fiber is rotated around the central axis of a cladding; an installation control unit that controls the alignment device to install each of the multi-core fibers at the determined rotational position; and a fusion splicing control unit that controls the fusion splicer that generates an electric discharge using the pair of high-voltage discharge electrodes to fuse each of the multi-core fibers together.

[0017] According to Aspect 5, the rotational position of each multi-core fiber is determined so that the dispersion distribution at a plurality of rotational positions has a predetermined value equal to or less than the intermediate value between the minimum and maximum values, and each multi-core fiber is installed at the determined rotational position. Therefore, it is possible to reduce the variation in the distance from the line connecting the pair of high-voltage discharge electrodes to the central axis of each core. Therefore, according to Aspect 5, it is possible to reduce the variation in temperature during discharge, and it is possible to reduce the variation in splice loss between cores.

[0018] As described above, according to the present invention, a multi-core fiber splicing method and a multi-core fiber splicing device are provided that can suppress variations in splice loss between cores.

[0019]

[0023] Fig. 1 is a diagram schematically showing the appearance of a cross section perpendicular to the longitudinal direction of a multicore fiber. Fig. 2 is a diagram schematically showing a multicore fiber splicing device according to an embodiment of the present invention. Fig. 3 is a flowchart showing a method for splicing multicore fibers using the multicore fiber splicing device according to an embodiment of the present invention. Fig. 4 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber having three cores and each core located at the vertex of an equilateral triangle with the central axis of the cladding as the center of symmetry. Fig. 5 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber having four cores and each core located at the vertex of a square with the central axis of the cladding as the center of symmetry. Fig. 6 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber having six cores and each core located at the vertex of a regular hexagon with the central axis of the cladding as the center of symmetry. Fig. 7 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber having eight cores and each core located at the vertex of a regular octagon with the central axis of the cladding as the center of symmetry. Fig. 8 is a schematic diagram of an end face of a multicore fiber when the cores are arranged linearly. Fig. 9 is a schematic diagram of an end face of a multi-core fiber corresponding to Fig. 8, which is arranged so as to reduce the variance of the distance between a straight line connecting the tips of high-voltage discharge electrodes and the central axis of each core. Fig. 10 is a flowchart showing a method for connecting a multi-core fiber using a multi-core fiber splicing device according to a modified example. Fig. 11 is an explanatory diagram of a method for calculating the variance of the distance between a straight line connecting the tips of high-voltage discharge electrodes and the central axis of each core, according to a modified example.

[0020] Hereinafter, embodiments for carrying out a multicore fiber splicing method and a multicore fiber splicing device according to the present invention will be illustrated with reference to the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be modified and improved from the following embodiments within the scope of the claims without departing from the spirit thereof. Furthermore, in this specification, the dimensions of each component may be exaggerated to facilitate understanding.

[0021] First, a multi-core fiber to be connected according to this embodiment will be described.

[0022] 1 is a diagram schematically showing a cross section perpendicular to the longitudinal direction of a multicore fiber. The multicore fibers to be connected to each other have the same configuration. The multicore fiber 2 includes a plurality of cores 21, a cladding 22 surrounding the outer peripheral surface of each core 21, an inner protective layer 23 covering the outer peripheral surface of the cladding 22, and an outer protective layer 24 covering the outer peripheral surface of the inner protective layer 23.

[0023] 1 shows a straight line L connecting the tips of high-voltage discharge electrodes (described later). Also shown are a central axis C of the cladding 22 and a central axis CC of the core 21. Note that the central axis CC is shown for only one core 21, and the central axes CC of the cores 21 are omitted for the other cores 21. Furthermore, in the drawings of this specification, hatching indicating the end faces of the cladding 22 has been omitted to simplify the drawings.

[0024] Next, the configuration of the multi-core fiber splicing device according to this embodiment will be described.

[0025] 2 is a diagram schematically illustrating a multicore fiber splicing device 1. The multicore fiber splicing device 1 is a multicore fiber splicing device that splices a pair of multicore fibers 2 a, 2 b, and mainly includes an alignment device 40 that adjusts the positions of the multicore fibers 2 a, 2 b, a fusion splicer 60 that fuses the multicore fibers 2 a, 2 b together, a control device 30, and a memory 35.

[0026] In this specification, when the multicore fiber 2 a and the multicore fiber 2 b are described without distinction, they are referred to as the multicore fiber 2. Furthermore, when the end faces 50 a and 50 b of the multicore fibers 2 a and 2 b that are fused to each other are described without distinction, they are referred to as the end faces 50.

[0027] The alignment device 40 includes XYZ position adjustment devices 41 a and 41 b that adjust the position of the multicore fiber 2 in the X, Y, and Z directions, and rotary alignment devices 42 a and 42 b that rotate the multicore fiber 2 around the central axis of the cladding 22 .

[0028] The alignment device 40 includes an end face measuring device 70. The end face measuring device 70 measures the end faces 50 a, 50 b of the multicore fibers 2 a, 2 b, and acquires information such as the position of the central axis CC of each core 21 of the multicore fiber 2 in order to calculate dispersion, which will be described later.

[0029] Regarding the end face measuring device 70, if the distance between the end faces 50a, 50b is short and it is difficult to install an image acquiring device such as a camera, a reflecting mirror may be inserted between the end faces 50a, 50b, and a reflected image of the end faces 50a, 50b reflected in the reflecting mirror may be acquired by the image acquiring device, and position information and the like of each core 21 may be acquired from the acquired image. Also, an image of the side surface of the multicore fiber 2 may be directly acquired by the image acquiring device, and position information and the like of each core 21 may be acquired from the acquired image.

[0030] The control device 30 controls the alignment device 40 based on the position information to adjust the rotational positions of the opposing multi-core fibers 2 a and 2 b to a state in which the cores 21 face each other.

[0031] The fusion splicer 60 has a pair of high-voltage discharge electrodes 61 a, 61 b, and generates an arc discharge by applying a high voltage between the pair of high-voltage discharge electrodes 61 a, 61 b ​​to fuse the end faces 50 a, 50 b of the butted multi-core fibers 2 a, 2 b. Note that in this embodiment, the fusion splicer 60 is configured so that the multi-core fibers 2 a, 2 b to be spliced ​​are each horizontally arranged.

[0032] The control device 30 is formed of, for example, an integrated circuit such as a microcontroller, an integrated circuit (IC), a large-scale integrated circuit (LSI), or an application specific integrated circuit (ASIC), or an NC (numerical control) device. Furthermore, when the control device 30 uses an NC device, the control device 30 may or may not use a machine learning device.

[0033] The control device 30 executes a program to realize the functions described below. The control device 30 includes a calculation unit 31, a determination unit 32, an installation control unit 33, and a fusion control unit 34. The calculation unit 31, the determination unit 32, the installation control unit 33, and the fusion control unit 34 are connected to one another by a bus line (not shown).

[0034] The calculation unit 31 calculates the variance of the distance between a straight line L connecting the tips of a pair of high-voltage discharge electrodes 61 a, 61 b ​​sandwiching the butt joint position of each multi-core fiber 2 and the central axis CC of each core 21, at a plurality of rotation positions of the multi-core fiber 2 when the multi-core fiber 2 is rotated around the central axis C of the cladding 22. Note that the distance between two straight lines is generally the length of a line segment connecting both straight lines in a direction perpendicular to both straight lines. This line segment passes through the straight line L and is located on a plane perpendicular to the longitudinal direction of the multi-core fiber 2. However, it may also be a line segment connecting the central axis CC of each core to the straight line L, perpendicular to the line L, on a plane shifted a predetermined distance from the plane in the longitudinal direction of the multi-core fiber 2.

[0035] Returning to FIG. 1, the above-mentioned distance dispersion will now be described.

[0036] Distance dispersion is a value that represents the variation in distance. For example, when the multi-core fiber 2 has N cores, the distance between the central axis CC of the i-th core 21 and the tip of the high-voltage discharge electrode is defined as D ｉ And D ｉ The average value of D ＡＶ Then, {Σ ｉ (D ｉ -D AV ) ２} / N. For example, in the case where the relationship between the multicore fiber 2 and the straight line L is as shown in FIG. 1, the central axis CC of one of the five cores 21 is on the straight line L, so the distance dispersion is defined as {(0-D AV ) ２ + (D １ -D AV ) ２ + (D ２ -D AV ) ２ + (D ３ -D AV )２ + (D ４ -D AV ) ２} / 5.

[0037] The calculation unit 31 calculates the dispersion at each of a plurality of rotation positions while the multi-core fiber 2 rotates 360° around the central axis C of the cladding 22 as the rotation axis.

[0038] The determination unit 32 determines a rotational position of the multicore fiber 2 that results in a predetermined value that is equal to or less than the intermediate value between the minimum and maximum values ​​of the multiple dispersions calculated by the calculation unit 31. For example, the determined rotational position is a position that results in the minimum value of the multiple dispersions.

[0039] The installation control unit 33 controls the alignment device 40 to install the multi-core fiber 2 at the determined rotational position.

[0040] The fusion control unit 34 controls the fusion splicer 60 to generate a discharge between a pair of high-voltage discharge electrodes 61 a and 61 b ​​of the fusion splicer 60, thereby fusing the multi-core fibers 2 that have been butted together and rotationally aligned.

[0041] The memory 35 is electrically connected to the control device 30 and stores programs, various data, and the like. The memory 35 is, for example, a non-transitory recording medium, and is preferably a semiconductor recording medium such as a random access memory (RAM) or a read-only memory (ROM), but may include any type of recording medium, such as an optical recording medium or a magnetic recording medium. Note that the term "non-transitory" recording medium includes all computer-readable recording media except for transient, propagating signals, and does not exclude volatile recording media.

[0042] Next, a method for connecting the multi-core fibers 2 using the multi-core fiber connection device 1 will be described.

[0043] 3 is a flowchart showing a method for connecting a pair of multi-core fibers 2. The method for connecting a pair of multi-core fibers 2 includes, as main steps, an aligning step S1, a calculating step S2, a determining step S3, an installing step S4, and a fusion step S5.

[0044] <Aligning step S1> This step is a step of setting the multicore fiber 2 in the fusion splicer 60 so that the end faces 50a, 50b of the multicore fibers 2a, 2b to be connected to each other face each other with a predetermined gap between them. In this step, the position of each of the multicore fibers 2a, 2b in the X, Y, and Z axes directions is adjusted, and the multicore fibers 2a, 2b are set so that the central axes C of the claddings 22 of the respective multicore fibers 2a, 2b coincide with each other. At this time, it is preferable that the angle formed between the end face 50a of one multicore fiber 2a and the end face 50b of the other multicore fiber 2b is 0.5 degrees or less.

[0045] In this embodiment, the aligning step S1 is provided before the calculation step S2, but this is not limitative, and for example, it may be provided after the calculation step S2 or after the determination step S3.

[0046] <Calculation Step S2> This step is a step of calculating the variance of the distance between the line L and the central axis CC of each core 21 at a plurality of rotation positions of the multi-core fiber 2 when the multi-core fiber 2 is rotated around the central axis C of the cladding 22. First, the distance between the line L and the central axis CC of each core 21 is obtained from the position information of the central axis C of the cladding 22, the central axis CC of each core 21, and the position information of the line L, which are acquired by the end face measuring device 70. Next, the variance of the distance between the line L and the central axis CC of each core 21 is calculated at a plurality of rotation positions of the multi-core fiber 2 when the multi-core fiber 2 is rotated 360° around the central axis C of the cladding 22. Here, it is preferable to calculate the variance of the distance at each rotation angle when the multi-core fiber 2 is rotated around the central axis C of the cladding 22. That is, it is preferable to calculate the distribution of the variance of the distance with respect to the rotation position when the multi-core fiber 2 is rotated around the central axis C of the cladding 22. For example, the initial position of the multi-core fiber 2 is set to an angle of 0°, and the dispersion of the distances is calculated for each rotational position of 60° up to 360°. This angle is not limited to every 60°, but may be every 30° or every 10°.

[0047] <Determining Step S3> In this step, a rotational position of the multicore fiber 2 is determined at which a predetermined value equal to or less than the intermediate value between the minimum and maximum values ​​of the dispersion distribution calculated in the calculation step is obtained. In this step, it is preferable to determine the rotational position of the multicore fiber 2 at which the dispersion is at its minimum value. Note that in this step, it is preferable to select a state in which the cores 21 of the multicore fibers 2 a, 2 b face each other as the rotational position at which the dispersion is at its minimum value. Furthermore, in the case where the multicore fiber 2 includes a marker, it is preferable to select a state in which the cores 21 identified by a common method using the marker face each other.

[0048] <Installation Step S4> In this step, the installation control unit 33 of the control device 30 controls the alignment device 40 to install each of the multicore fibers 2 a, 2 b at the rotational positions determined in the determination step S3. At this time, each of the multicore fibers 2 a, 2 b is installed while maintaining a state in which each core 21 of one multicore fiber 2 a and each corresponding core 21 of the other multicore fiber 2 b face each other.

[0049] <Fusion step S5> In this step, the fusion control unit 34 of the control device 30 controls the fusion splicer 60 to cause discharge to occur between the pair of high-voltage discharge electrodes 61 a, 61 b, and fuse the multi-core fibers 2 a, 2 b. At this time, it is preferable that the straight line L of the fusion splicer 60 is positioned between the end faces 50 a, 50 b of the multi-core fibers 2 to be fused.

[0050] In this way, the multi-core fibers 2a and 2b are connected to each other.

[0051] As described above, the method for connecting the multi-core fibers 2 of this embodiment includes a calculation step S2 of calculating the variance of the distance between the line L and the central axis CC of each core 21 at a plurality of rotation positions of the multi-core fiber 2 when the multi-core fiber 2 is rotated around the central axis C of the cladding 22; a determination step S3 of determining the rotation position of the multi-core fiber 2 at which the rotation position becomes a predetermined value equal to or less than the intermediate value between the minimum value and the maximum value of the plurality of calculated variances; an installation step S4 of installing each multi-core fiber 2 at the determined rotation position; and a fusion step S5 of generating an electric discharge using the pair of high-voltage discharge electrodes 61 a, 61 b ​​to fuse the respective multi-core fibers together.

[0052] Moreover, the multi-core fiber connection device of the present embodiment includes an alignment device 40 capable of adjusting the rotational position of each multi-core fiber 2, a fusion splicer 60 that generates an electric discharge using a pair of high-voltage discharge electrodes 61 a, 61 b ​​to fuse each of the multi-core fibers together, and a control device 30. The control device 30 includes: a calculation unit 31 that calculates the variance of the distance between a line L that sandwiches the butt-joint position of each multi-core fiber 2 and the central axis CC of each core 21, at a plurality of rotational positions of the multi-core fiber 2 when the multi-core fiber 2 is rotated around the central axis C of the cladding 22; a determination unit 32 that determines the rotational position of the multi-core fiber 2 that becomes a predetermined value that is equal to or less than the intermediate value between the minimum and maximum values ​​of the plurality of calculated variances; an installation control unit 33 that controls the alignment device 40 to install each of the multi-core fibers 2 at the determined rotational position; and a fusion control unit 34 that controls the fusion splicer 60 to generate an electric discharge using the pair of high-voltage discharge electrodes 61 a, 61 b ​​to fuse each of the multi-core fibers 2 together.

[0053] According to such a method for connecting the multi-core fibers 2 and the multi-core fiber connecting device 1, it is possible to reduce the variation in the distance from the straight line L connecting the pair of high-voltage discharge electrodes 61 a, 61 b ​​to the central axis CC of each core 21. Therefore, it is possible to reduce the variation in temperature during discharge and the variation in the connection state of each core 21. Therefore, it is possible to reduce the variation in connection loss between the cores 21.

[0054] Although the present invention has been described above using the embodiments as examples, the present invention is not limited to these.

[0055] In the above embodiment, the rotation position determined in the determination step S3 is a predetermined value that is equal to or less than the midpoint between the minimum and maximum values ​​of the distribution of the variance. However, the variance is not limited to the minimum value as long as it is a predetermined value that is equal to or less than the midpoint between the minimum and maximum values ​​of the distribution of the variance.

[0056] Furthermore, in the above embodiment, the connection method for a pair of multi-core fibers 2 includes the calculation step S2, but is not limited to this. For example, the calculation step S2 may be performed in advance, and the calculation result may be stored in the memory 35. In this case, the determination step S3 is performed based on the calculation result stored in the memory 35.

[0057] Furthermore, for example, the relationship between the rotational position of the multicore fiber 2 and the dispersion may be stored in advance in the memory 35. In this case, a rotational position of the multicore fiber 2 at which the dispersion becomes a predetermined value equal to or less than the intermediate value between the minimum and maximum values ​​of the dispersion distribution may be determined from the dispersion with respect to the rotational position of the multicore fiber 2 stored in the memory 35. The rotational position may be obtained by the end face measuring device 70 and adjusted by the control device 30.

[0058] As another example, in the aligning step S1, the multicore fibers 2 a, 2 b may be set to a rotational position where the dispersion becomes a predetermined value equal to or less than the intermediate value between the minimum value and the maximum value. In this case, the aligning step S1 also serves as the setting step S4, and this rotational position may be determined in advance in the determining step S3.

[0059] Next, some examples of calculation of dispersion in the multi-core fiber 2 will be illustrated.

[0060] 4 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber 2 having three cores 21, with each core 21 located at the vertex of an equilateral triangle with the central axis C of the cladding 22 as the center of symmetry. Note that this example shows the relationship between dispersion and rotation position when the central axis C of the cladding 22 of the multicore fiber 2 is on a straight line L. The horizontal axis represents the rotation angle around the central axis C of the cladding 22 of the multicore fiber 2 as the center of rotation, and the vertical axis represents the dispersion of the distance between the central axis CC of each core 21 and the straight line L.

[0061] The lower part of Fig. 4 is a schematic diagram showing the relationship between the central axis CC of each core 21 of the multi-core fiber 2 and the line L at installation positions corresponding to angles A and B in Fig. 4 . At angle A, dispersion is minimized. Therefore, by generating discharge using a pair of high-voltage discharge electrodes 61a, 61b at this position and fusing the multi-core fibers 2a, 2b together, the variation in the distance from the line L to the central axis CC of each core 21 can be reduced. Therefore, the temperature variation during discharge can be reduced, and the variation in the connection state of each core 21 can be reduced. As a result, the variation in the splice loss between the cores 21 can be reduced. Furthermore, at angle B in Fig. 4 , dispersion is maximized. Therefore, when the multi-core fibers 2a, 2b are fused together at this position, the variation in the distance from the line L to the central axis CC of each core 21 increases, which can increase the variation in the splice loss between the cores 21.

[0062] Fig. 5 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber 2 in which the number of cores 21 is four and the cores 21 are located at the vertices of a square with the central axis C of the cladding 22 as the center of symmetry, similar to Fig. 4. Note that this example shows the relationship between dispersion and rotation position when the central axis C of the cladding 22 of the multicore fiber 2 is on a straight line L.

[0063] The lower part of Fig. 5 is a schematic diagram showing the relationship between the central axis CC of each core 21 of the multicore fiber 2 and the straight line L at installation positions corresponding to angles A and B in Fig. 5. In the case of angle A, dispersion is minimum, so by fusing the respective multicore fibers 2a, 2b together, it is possible to reduce the variation in the distance from the straight line L to the central axis CC of each core 21, and it is possible to reduce the variation in the splice loss between the cores 21. In the case of angle B, dispersion is maximum, so if the respective multicore fibers 2a, 2b are fusing together at this position, the variation in the distance from the straight line L to the central axis CC of each core 21 increases, and this may increase the variation in the splice loss between the cores 21.

[0064] 6 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber 2 in which the number of cores 21 is six and the cores 21 are located at the vertices of a regular hexagon with the central axis C of the cladding 22 as the center of symmetry, similar to Fig. 4. Note that this example shows the relationship between dispersion and rotation position in the case where the central axis C of the cladding 22 of the multicore fiber 2 is on a straight line L.

[0065] The lower part of Fig. 6 is a schematic diagram showing the relationship between the central axis CC of each core 21 of the multicore fiber 2 and the straight line L at installation positions corresponding to angles A and B in Fig. 6. In the case of angle A, dispersion is minimum, so by fusing the multicore fibers 2a, 2b together at this position, it is possible to reduce the variation in the distance from the straight line L to the central axis CC of each core 21, and it is possible to reduce the variation in the splice loss between the cores 21. In the case of angle B, dispersion is maximum, so if the multicore fibers 2a, 2b are fusing together at this position, the variation in the distance from the straight line L to the central axis CC of each core 21 increases, and this may increase the variation in the splice loss between the cores 21.

[0066] 7 is an example showing the relationship between each rotation angle and dispersion in a multicore fiber 2 in which the number of cores 21 is eight and the cores 21 are located at the vertices of a regular octagon with the central axis C of the cladding 22 as the center of symmetry, similar to Fig. 4. Note that this example shows the relationship between dispersion and rotation position when the central axis C of the cladding 22 of the multicore fiber 2 is on a straight line L.

[0067] The lower part of Fig. 7 is a schematic diagram showing the relationship between the central axis CC of each core 21 of the multicore fiber 2 and the straight line L at installation positions corresponding to angles A and B in Fig. 7. In the case of angle A, dispersion is minimum, so by fusing the respective multicore fibers 2a, 2b together at this position, it is possible to reduce the variation in the distance from the straight line L to the central axis CC of each core 21, and it is possible to reduce the variation in the splice loss between the cores 21. In the case of angle B, dispersion is maximum, so if the respective multicore fibers 2a, 2b are fusing together at this position, the variation in the distance from the straight line L to the central axis CC of each core 21 becomes large, and it is possible to increase the variation in the splice loss between the cores 21.

[0068] Fig. 8 is a schematic diagram of an end face 50 in a case where the cores 21 are linearly arranged in the multicore fiber 2. In the state of Fig. 8, the line connecting the central axes CC of the cores 21 and the line L are perpendicular to each other.

[0069] Fig. 9 is a schematic diagram of the end face 50 of the multi-core fiber 2 shown in Fig. 8 in a state where the dispersion of the distance between the straight line L and the central axis CC of each core 21 is minimum. In the state of Fig. 9, the dispersion is smaller than in the state of Fig. 8, and therefore, by fusing the multi-core fibers 2a, 2b together at the rotational positions shown in Fig. 9, the dispersion of the distance from the straight line L to the central axis CC of each core 21 can be reduced, and the dispersion of the splice loss between the cores can be reduced.

[0070] In the above calculation example, the central axis C of the cladding 22 of the multi-core fiber 2 is on the straight line L, but the present invention is not limited to this.

[0071] Next, a modified example of the method for connecting the multi-core fiber 2 will be described.

[0072] 10 is a flowchart showing a splicing method for multicore fibers 2 according to a modified example. This modified example differs from the above embodiment mainly in that, before the calculating step S2, a measuring step S6 is provided in which the angle formed by the line L connecting the central axis C of the cladding 22 and the central axis CC of the core 21 and the distance from the central axis C of the cladding 22 to the central axis CC of the core 21 are measured. The aligning step S1, the calculating step S2, the determining step S3, the installing step S4, and the fusion step S5 are the same as those in the above embodiment, and therefore descriptions thereof will be omitted.

[0073] 11 is an explanatory diagram of a method for calculating the dispersion of the distance between the line L and the central axis CC of each core 21 according to this modified example. The example shown in this explanatory diagram shows a case where the line L and the central axis C of the cladding 22 intersect perpendicularly. In this case, the distances from the central axis C of the cladding 22 to the central axis CC of each core 21 are all R, so the distance D between the central axis CC of each core 21 and the line L can be calculated as R·sin θ, where θ is the angle between the line L and a line connecting the central axis C of the cladding 22 and the central axis CC of each core 21. Therefore, the dispersion of the distance between the central axis CC of each core 21 and the line L, which face each other across the butt-joint position of each multicore fiber 2, can be easily calculated by measuring the angle θ between the line L and a line connecting the central axis C of the cladding 22 of each multicore fiber 2 and the central axis CC of each core 21, and the line L.

[0074] According to the present invention, a multi-core fiber splicing method and a multi-core fiber splicing device that can suppress variations in the connection state between cores are provided, and can be used in various fields related to optical fibers.

Claims

1. A method for connecting a pair of multi-core fibers, comprising: a determining step of determining a rotational position of the multi-core fiber at which a dispersion of the distance between a line connecting tips of a pair of high-voltage discharge electrodes sandwiching a butt joint position of the multi-core fibers and the central axis of each core becomes a predetermined value equal to or less than an intermediate value between a minimum value and a maximum value of the distribution of the dispersion when the multi-core fiber is rotated around the central axis of a cladding; an installing step of installing each of the multi-core fibers at the determined rotational position; and a fusing step of generating an electric discharge using the pair of high-voltage discharge electrodes to fuse the multi-core fibers together.

2. The multi-core fiber splicing method according to claim 1, further comprising, before said determining step, a calculating step of calculating the dispersion of each of said distances at a plurality of rotational positions of said multi-core fiber when said multi-core fiber is rotated around the central axis of the cladding.

3. The multi-core fiber splicing method according to claim 2, further comprising, before the calculation step, a measurement step of measuring, in a cross section perpendicular to the longitudinal direction of the multi-core fiber, the angle formed by a line connecting the central axis of the cladding and the central axis of the core and a line connecting the tips of the pair of high-voltage discharge electrodes, and the distance from the central axis of the cladding to the central axis of the core.

4. A multi-core fiber splicing method according to any one of claims 1 to 3, characterized in that in the determining step, the rotational position of the multi-core fiber at which the dispersion becomes a minimum value is determined.

5. A multi-core fiber splicing device for splicing a pair of multi-core fibers, comprising: an alignment device capable of adjusting a rotational position of each of the multi-core fibers; a fusion splicer capable of causing discharge by a pair of high-voltage discharge electrodes to fuse each of the multi-core fibers together; and a control device, wherein the control device comprises: a determination unit that determines a rotational position of the multi-core fiber at which a dispersion of the distance between a line connecting tips of the pair of high-voltage discharge electrodes that sandwich the butt joint position of the multi-core fibers and the central axis of each core becomes a predetermined value that is equal to or less than the median value between the minimum and maximum values ​​of the distribution of the dispersion when the multi-core fiber is rotated around the central axis of a cladding; an installation control unit that controls the alignment device to install each of the multi-core fibers at the determined rotational position; and a fusion splicing control unit that controls the fusion splicer to cause discharge by the pair of high-voltage discharge electrodes to fuse each of the multi-core fibers together.

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