Measurement method of core-positional misalignment amount, measurement method of index core position, measurement program of core-positional misalignment amount, measurement program of index core position, measurement device of core-positional misalignment amount, and measurement device of index core position

Abstract

This core-positional misalignment amount measurement method comprises: a step for acquiring the positions of a plurality of cores of a multicore optical fiber; and a step for calculating a positional misalignment amount of each of the plurality of cores from each of a plurality of reference core positions that are design core positions or nominal core positions of the plurality of cores. In the calculation step, an angular position, around the fiber center, of the plurality of reference core positions or the acquired positions of the plurality of cores is moved to cause the n-th power sum of the positional misalignment amounts of the plurality of cores, or a positional misalignment amount when the maximum positional misalignment amount among the positional misalignment amounts of the plurality of cores is minimum to be set as a measured positional misalignment amount. n is an integer equal to or greater than 3.

Description

Method for measuring core displacement, method for measuring index core position, program for measuring core displacement, program for measuring index core position, device for measuring core displacement, and device for measuring index core position

[0001] This disclosure relates to a method for measuring core displacement, a method for measuring the position of an index core, a program for measuring core displacement, a program for measuring the position of an index core, a device for measuring core displacement, and a device for measuring the position of an index core. This application claims priority under Japanese application No. 2024-170951, filed on 30 September 2024, and incorporates all the provisions of the said Japanese application. Background

[0002] Patent Document 1 discloses a method for aligning an optical waveguide component having multiple optical waveguides and an optical fiber array component having multiple optical fibers arranged in a row. In this alignment method, the amount of pitch deviation of each optical fiber facing each optical waveguide is determined with respect to the pitch of the optical waveguide as a reference. Then, at least one of the optical waveguide component and the optical fiber array component is moved relative to each other so that the average value of the determined pitch deviation amounts becomes zero.

[0003] Patent Document 2 discloses an optical fiber alignment device and alignment method for optical fibers having two or more cores, such as multicore fibers. In this alignment method, images of the end faces of two optical fibers having two or more cores are taken, and the position coordinates of the two or more cores at the end face are determined for each of the two optical fibers. Then, the position coordinates of the two or more cores are substituted into a theoretical formula that represents the sum of the misalignment losses when the two or more cores are connected to each other. From the theoretical formula, the positional relationship of the end faces of the two optical fibers is determined so as to minimize the sum of the misalignment losses. The two optical fibers are then arranged to satisfy the determined positional relationship.

[0004] Japanese Patent Publication No. 08-304667, International Publication No. 2015 / 025629

[0005] "GSTR-SDM / Optical fiber, cable, and components for space division multiplexing transmission," International Telecommunication Union, ITU-T Technical Report (09 / 2022)"Measurement methods and test procedures - Fiber geometry," International Electrotechnical Commission, IEC 60793-1-20 (2014)Nobutomo Hanzawa et al., "Relationship between Cross-Sectional geometry and splice loss in a Multicore fiber," Technical Committee in Optical Fiber Technologies, Optical Fiber Technology, 75, 103152 (2023)T. Hayashi et al., "Ultra-High-Density Microduct Cable with Uncoupled 12-Core Fibers with Standard 250-μm Coating," Optical Fiber Communication Conference, Tu2C.2 (2023)

[0006] A method for measuring core misalignment according to one embodiment of the present disclosure comprises the steps of: acquiring the positions of multiple cores of a multicore optical fiber; and calculating the misalignment of each of the multiple cores from each of the multiple reference core positions, which are the design core positions or nominal core positions of the multiple cores. In the calculation step, the angular positions of the multiple reference core positions or the acquired multiple core positions around the fiber center are moved, and the sum of the nth powers of the misalignment amounts of the multiple cores (where n is a number of 3 or more), or the misalignment amount at which the maximum misalignment amount among the multiple cores is minimized, is defined as the measured misalignment amount.

[0007] Figure 1 shows the end face of a multicore optical fiber. Figure 2 is a flowchart of the measurement method according to the embodiment. Figure 3 shows the movement of the angular positions of the center points of multiple cores around the fiber center. Figure 4 shows the movement of the angular positions of multiple reference core positions around the fiber center. Figure 5 is a schematic diagram showing the configuration of the measurement device according to the embodiment. Figure 6 is a graph showing the relationship between the amount of core misalignment and the probability density. Figure 7 is a graph showing the complementary cumulative distribution of the amount of core misalignment. Figure 8 is a graph showing the complementary cumulative distribution of coupling loss caused by core misalignment. Figure 9 is a graph showing the complementary cumulative distribution of coupling loss caused by core misalignment. Figure 10 is a graph showing the complementary cumulative distribution of the amount of core misalignment. Figure 11 is a graph showing the complementary cumulative distribution of the amount of core misalignment. Figure 12 is a graph showing the complementary cumulative distribution of the amount of core misalignment. Figure 13 is a graph showing the complementary cumulative distribution of the amount of core misalignment.

[0008] When describing the performance, specifications, or characteristics of a multicore optical fiber, the positional deviation of each core from a reference core position on a cross-section perpendicular to the central axis of the multicore optical fiber is used. The reference core position is the design core position or nominal core position in a given coordinate system, and connections between multicore optical fibers where the position of each core coincides with the reference core position can minimize connection loss. In reality, due to factors such as manufacturing variations, the actual core position deviates from the reference core position. The greater the positional deviation of the actual core position from the reference core position, the greater the connection loss between multicore optical fibers.

[0009] When measuring the amount of misalignment, it is not possible to identify the coordinate system used to determine the core position during the design of an actual multicore optical fiber. Therefore, based on the measured actual core position, an index core position is identified as a unique characteristic of the multicore optical fiber, determined for each core. The distance between the reference core position and the index core position is then used as the amount of core misalignment, and as an indicator of the performance, specifications, or characteristics of the multicore optical fiber. Consequently, the amount of core misalignment of a multicore optical fiber varies depending on the result of identifying the index core position. Depending on the result of identifying the index core position, the amount of core misalignment may be overestimated, leading to a decrease in the manufacturing yield of the multicore optical fiber.

[0010] This disclosure aims to provide a method for measuring core misalignment, a program for measuring core misalignment, and a device for measuring core misalignment that can determine an appropriate misalignment amount in a multicore optical fiber. In addition, this disclosure aims to provide a method for measuring an index core position, a program for measuring an index core position, and a device for measuring an index core position that can determine an index core position for which the misalignment amount is appropriate in a multicore optical fiber.

[0011] This disclosure provides a method for measuring core misalignment, a program for measuring core misalignment, and a device for measuring core misalignment that can determine an appropriate core misalignment in a multicore optical fiber. In addition, this disclosure provides a method for measuring an index core position, a program for measuring an index core position, and a device for measuring an index core position that can determine an index core position for which the misalignment is appropriate in a multicore optical fiber.

[0012] The contents of this disclosed embodiment will be explained.

[0013] [1A] A method for measuring core misalignment according to one embodiment of the present disclosure comprises the steps of: acquiring the positions of a plurality of cores of a multicore optical fiber; and calculating the misalignment of each of the plurality of cores from each of a plurality of reference core positions, which are the design core positions or nominal core positions of the plurality of cores. In the calculation step, the angular positions of the plurality of reference core positions or the acquired plurality of core positions around the fiber center are moved, and the sum of the nth powers of the misalignment amounts of the plurality of cores (where n is a number of 3 or more), or the misalignment amount at which the maximum misalignment amount among the plurality of cores is minimized, is defined as the measured misalignment amount.

[0014] [1B] A core misalignment measurement program according to one embodiment of the present disclosure causes a computer to perform the following steps: acquire the positions of multiple cores of a multicore optical fiber; and calculate the misalignment of each of the multiple cores from each of a plurality of reference core positions, which are the design core positions or nominal core positions of the multiple cores. In the calculation step, the angular positions of the plurality of reference core positions or the acquired plurality of core positions around the fiber center are moved, and the sum of the nth powers of the misalignment amounts of the multiple cores (where n is a number of 3 or more), or the misalignment amount of each of the multiple cores when the maximum misalignment amount among the multiple cores is minimized, is defined as the measured misalignment amount.

[0015] [1C] A core misalignment measuring device according to one embodiment of the present disclosure comprises a storage unit for storing the positions of a plurality of cores of a multicore optical fiber, and a calculation unit for calculating the misalignment amount of each of the plurality of cores from each of a plurality of reference core positions, which are the design core positions or nominal core positions of the plurality of cores. The calculation unit moves the angular positions of the plurality of reference core positions or the acquired plurality of core positions around the fiber center and takes as the n-th power sum of the misalignment amounts of the plurality of cores (where n is a number of 3 or more), or the misalignment amount of each of the plurality of cores when the maximum misalignment amount among the plurality of cores is minimized, as the measured misalignment amount.

[0016] In the measurement methods, measurement programs, and measurement devices described in [1A] to [1C] above, the angular positions of multiple reference core positions or multiple acquired core positions around the fiber center are moved, and the measured positional displacement of each of the multiple cores is defined as the amount at which the sum of the nth powers of the positional displacement amounts of the multiple cores is minimized. n is a number of 3 or greater. In this case, for example, compared to the case where n is 2 or less, the proportion of the largest positional displacement amount contributing to the nth power sum of the positional displacement amounts of the multiple cores becomes larger, so the maximum positional displacement amount is further reduced. Alternatively, in the measurement methods, measurement programs, and measurement devices described in [1A] to [1C] above, the angular positions of multiple reference core positions or multiple acquired core positions around the fiber center are moved, and the measured positional displacement of each of the multiple cores is defined as the amount at which the maximum positional displacement amount of the multiple cores is minimized. In this case as well, the maximum positional displacement amount is further reduced.

[0017] When judging the quality of the performance, specifications, or characteristics of a multicore optical fiber, a smaller core misalignment is desirable, and therefore, the maximum misalignment is primarily used for evaluation. Consequently, by reducing the maximum core misalignment, a desirable multicore optical fiber with a small core misalignment can be evaluated. According to the measurement methods, measurement programs, and measurement devices described in [1A] to [1C] above, an appropriate core misalignment can be determined for a multicore optical fiber without overestimating it.

[0018] [2A] A method for measuring an index core position according to one embodiment of the present disclosure comprises the steps of: acquiring the positions of a plurality of cores of a multicore optical fiber; and calculating the index core positions of the plurality of cores. In the calculation step, the angular positions of the acquired plurality of core positions are moved around the fiber center, and the sum of the n-th powers of the displacement amounts of the plurality of cores from a plurality of reference core positions, which are the design core positions or nominal core positions (n ​​is a number of 3 or more), or the plurality of core positions at which the maximum displacement amount among the plurality of cores is minimized, is defined as the measured plurality of index core positions. Alternatively, in the calculation step, the angular positions of the plurality of reference core positions, which are the design core positions or nominal core positions, are moved around the fiber center, and the sum of the n-th powers of the displacement amounts of the plurality of cores from a plurality of reference core positions (n ​​is a number of 3 or more), or the plurality of reference core positions at which the maximum displacement amount among the plurality of cores is minimized is determined, and the plurality of core positions at which the plurality of core positions are moved in the opposite direction by the same angle as the movement angle from the original position of the plurality of reference core positions are defined as the measured plurality of index core positions.

[0019] [2B] A program for measuring an index core position according to one embodiment of the present disclosure causes a computer to perform the steps of acquiring the positions of multiple cores of a multicore optical fiber and calculating the index core positions of the multiple cores. In the calculation step, the angular positions of the acquired multiple core positions are moved around the fiber center to determine the sum of the n-th powers of the displacement amounts of the multiple cores from the multiple reference core positions, which are the design core positions or nominal core positions (n ​​is a number of 3 or more), or the multiple core positions at which the maximum displacement amount among the multiple core displacement amounts is minimized, and these are defined as the measured multiple index core positions. Alternatively, in the calculation step, the angular positions of the multiple reference core positions, which are the design core positions or nominal core positions, are moved around the fiber center to determine the sum of the n-th powers of the displacement amounts of the multiple cores from the multiple reference core positions (n ​​is a number of 3 or more), or the multiple reference core positions at which the maximum displacement amount among the multiple core displacement amounts is minimized, and the multiple core positions at which the multiple core positions are moved in the opposite direction by the same angle as the movement angle from the original position of the multiple reference core positions are defined as the measured multiple index core positions.

[0020] [2C] An indicator core position measuring device according to one embodiment of the present disclosure comprises a storage unit for storing the positions of a plurality of cores of a multicore optical fiber, and a calculation unit for calculating the indicator core positions of the plurality of cores. The calculation unit moves the angular positions of the acquired plurality of core positions around the fiber center and sets the measured plurality of indicator core positions as the n-th power sum of the displacement amounts of the plurality of cores from a plurality of reference core positions which are the design core positions or nominal core positions (n ​​is a number of 3 or more), or the plurality of core positions where the maximum displacement amount among the plurality of core displacement amounts is minimized. Alternatively, the calculation unit moves the angular positions of the plurality of reference core positions which are the design core positions or nominal core positions around the fiber center to determine the n-th power sum of the displacement amounts of the plurality of cores from a plurality of reference core positions which are the design core positions or nominal core positions (n ​​is a number of 3 or more), or the plurality of reference core positions where the maximum displacement amount among the plurality of core displacement amounts is minimized, and sets the measured plurality of indicator core positions as the plurality of core positions when the plurality of core positions are moved in the opposite direction by the same angle as the angle of movement from the original position of the plurality of reference core positions.

[0021] In the measurement methods, measurement programs, and measurement devices described in [2A] to [2C] above, the angular positions of the acquired multiple core positions around the fiber center are moved, and the multiple core positions at which the sum of the n-th powers of the positional displacement amounts of the multiple cores is minimized are defined as the measured multiple index core positions. n is a number of 3 or greater. Alternatively, the angular positions of the multiple reference core positions around the fiber center are moved, and the multiple reference core positions at which the sum of the n-th powers of the positional displacement amounts of the multiple cores is minimized are determined. The multiple core positions at which the multiple core positions are moved in the opposite direction by the same angle as the movement angle from the original position of the multiple reference core positions are defined as the measured multiple index core positions. n is a number of 3 or greater. In these cases, for example, compared to the case where n is 2 or less, the proportion of the maximum positional displacement amount contributing to the n-th power sum of the positional displacement amounts of the multiple cores becomes even larger, so the maximum positional displacement amount is further reduced. Alternatively, in the measurement methods, measurement programs, and measurement devices described in [2A] to [2C] above, the angular positions of the acquired multiple core positions around the fiber center are moved, and the multiple core positions at which the maximum positional displacement among the multiple cores is minimized are defined as the measured multiple index core positions. Alternatively, the angular positions of the multiple reference core positions around the fiber center are moved, and the multiple reference core positions at which the maximum positional displacement among the multiple cores is minimized are determined. The multiple core positions at which the multiple core positions are moved in the opposite direction by the same angle as the movement angle from the original position of the multiple reference core positions are defined as the measured multiple index core positions. In this case as well, the maximum positional displacement is further reduced.

[0022] As mentioned above, when judging the quality of the performance, specifications, or characteristics of a multicore optical fiber, the amount of core misalignment is mainly evaluated by referring to the maximum misalignment. Therefore, by measuring the maximum core misalignment at an appropriate value rather than measuring it excessively large, the amount of core misalignment in a multicore optical fiber can be evaluated more appropriately. In other words, according to the measurement methods, measurement programs, and measurement devices described in [2A] to [2C] above, it is possible to determine an appropriate index core position for the amount of misalignment in a multicore optical fiber.

[0023] [3] In each of the above measurement methods, measurement programs, and measurement devices, n may be 4 or greater. In this case, the proportion of the maximum positional displacement among the multiple core positional displacements that contributes to the sum of the nth powers becomes even larger, so the maximum positional displacement is further reduced. Therefore, a more appropriate positional displacement, or an index core position where the positional displacement is more appropriate, can be determined.

[0024] [4] In each of the above measurement methods, measurement programs, and measurement devices, n may be 4. In this case, the proportion of the largest displacement amount among the displacement amounts of multiple cores that contributes to the n-th power sum becomes appropriately large, and the other displacement amounts excluding the largest also contribute appropriately to the n-th power sum. Therefore, the largest displacement amount is appropriately reduced, and it is possible to prevent the other displacement amounts from becoming excessively large. This makes it possible to find a more appropriate displacement amount, or an index core position where the displacement amount is more appropriate.

[0025] [Details of Embodiments of the Disclosure] Specific examples of the Disclosure are described below with reference to the drawings. The Disclosure is not limited to these examples, but is indicated by the claims, and all changes within the meaning and scope of the claims are intended to be included. In the following description, the same elements are denoted by the same reference numerals in the description of the drawings, and redundant descriptions are omitted.

[0026] Figure 1 shows the end face 11 of a multicore optical fiber 10. The multicore optical fiber 10 has a plurality of cores 12 distributed at the end face 11 and a cladding 13 surrounding the plurality of cores 12. In the illustrated example, the number of plurality of cores 12 is four. The refractive index of the plurality of cores 12 is greater than the refractive index of the cladding 13. The shape of the end face 11 is circular, and the shape of each core 12 at the end face 11 is also circular. The end face 11 has a fiber center 11a, which is the center of the circle. The fiber center 11a is the center of the cladding 13. Each of the plurality of cores 12 has a center point 12a, which is the center of the circle. Figure 1 shows a Cartesian coordinate system with the fiber center 11a as the origin. In the following explanation, the core position of each core 12 means the position of the center point 12a in the Cartesian coordinate system (XY Cartesian coordinate system).

[0027] Figure 1 shows multiple reference core positions 12b. Each reference core position 12b is the ideal core position for each core 12 and is used as a reference core position without deviation when evaluating the amount of deviation of each core position 12. The multiple reference core positions 12b have a relative positional relationship of multiple cores 12 in design or nominal terms. In the illustrated example, four reference core positions 12b are shown that are equidistant from the fiber center 11a and equally spaced from each other. In other words, the four reference core positions 12b are the four vertices of a square Q centered on the fiber center 11a. The center point 12a of each core 12 is shifted by a deviation amount D from the corresponding reference core position 12b due to factors such as manufacturing variations. The smaller the deviation amount D, the smaller the connection loss with other multicore optical fibers or optical components. In many cases, the performance, specifications, or characteristics of the multicore optical fiber 10 are evaluated based on the largest deviation amount D among the deviation amounts D of the multiple cores 12. Therefore, it is desirable to determine multiple reference core positions 12b such that the maximum positional displacement D is as small as possible.

[0028] Figure 2 is a flowchart showing a measurement method according to an embodiment of the present disclosure. This measurement method is a method for determining the positional displacement D of each core 12 of a multicore optical fiber 10 and the positions of a plurality of indicator cores, and includes an acquisition step ST1 and a calculation step ST2. In the acquisition step ST1, the positions of the center points 12a of the plurality of cores 12 of the multicore optical fiber 10 and the position of the fiber center 11a of the multicore optical fiber 10 are acquired. The positions of the center points 12a and the fiber center 11a may be acquired by photographing the end face 11 with a camera and analyzing the image. Alternatively, data regarding the positions of the center points 12a and the fiber center 11a acquired by analyzing the image of the end face 11 may be prepared. Alternatively, data regarding the positions of the center points 12a and the fiber center 11a that have already been digitized may be acquired.

[0029] In the calculation step ST2, each of the plurality of reference core positions 12b is associated with each of the plurality of cores 12, and the displacement amount D from the corresponding reference core position of each of the plurality of cores 12 and the plurality of index core positions are calculated. In the calculation step ST2, as shown in FIG. 3, with the fiber center 11a as the coordinate origin, while moving (i.e., rotating) the angular positions of the center points 12a of the plurality of cores 12 around the fiber center 11a (i.e., the coordinate origin), the sum of the nth powers of the displacement amounts D of the plurality of cores 12 is obtained a plurality of times. However, n is a number of 3 or more or 4 or more. n may be an integer or a real number. When the displacement amounts D of the four cores 12 are D １ , D ２ , D ３ , D ４ respectively, the sum of the nth powers S is expressed as follows. S = D １ ｎ + D ２ ｎ + D ３ ｎ + D ４ ｎ In the calculation step ST2, the displacement amounts D １ , D ２ , D ３ , D ４ at the angular position when the sum of the nth powers S is minimized are taken as the finally measured displacement amount D in this measurement method. The positions of the center points 12a of the plurality of cores 12 at the angular position when the sum of the nth powers S is minimized are taken as the finally measured plurality of index core positions in this measurement method.

[0030] Alternatively, in calculation step ST2, as shown in Figure 3, the coordinate origin is set to the fiber center 11a, and the maximum positional displacement D of the multiple cores 12 is determined multiple times while moving the angular position of the center point 12a of the multiple cores 12 around the fiber center 11a. At this time, if the angular positions are different, the cores 12 having the maximum positional displacement D may be different from each other. In calculation step ST2, the positional displacement D of each core 12 at the angular position when the maximum positional displacement D is minimized is set as the positional displacement D finally measured in this measurement method. The positions of the center points 12a of the multiple cores 12 at the angular position when the maximum positional displacement D is minimized are set as the multiple index core positions finally measured in this measurement method.

[0031] Alternatively, in calculation step ST2, each of the multiple reference core positions 12b is associated with each of the multiple cores 12, and the positional displacement D from the corresponding reference core position for each of the multiple cores 12, and the positions of the multiple index cores are calculated. In calculation step ST2, as shown in Figure 4, the coordinate origin is set to the fiber center 11a, and the sum S of the nth powers of the positional displacement D of the multiple cores 12 is calculated multiple times while moving the angular positions of the multiple reference core positions 12b around the fiber center 11a (i.e., the coordinate origin). In calculation step ST2, the positional displacement D at the angular position where the sum S is minimized is calculated. １ , D ２ , D ３ , D ４ This is defined as the final measured positional displacement D in this measurement method. Multiple reference core positions 12b are determined at the angular position where the sum of the nth powers S is minimized. The positions of each center point 12a when the center points 12a of the multiple cores 12 are moved in the opposite direction by the same angle as the movement angle of the multiple reference core positions 12b from their original positions are defined as the multiple index core positions finally measured in this measurement method.

[0032] Alternatively, in the calculation step ST2, as shown in FIG. 4, while moving the angular positions of the plurality of reference core positions 12b around the fiber center 11a, the maximum displacement amount D among the displacement amounts D of the plurality of cores 12 is obtained multiple times. At this time, when the angular positions are different, the cores 12 having the maximum displacement amount D may be different from each other. In the calculation step ST2, the displacement amount D of each core 12 at the angular position when the maximum displacement amount D is minimized is set as the finally measured displacement amount D in this measurement method. The plurality of reference core positions 12b at the angular position when the maximum displacement amount D is minimized are obtained, and the positions of the center points 12a of the plurality of cores 12 are moved counterclockwise by the same angle as the moving angle from the original positions of the plurality of reference core positions 12b, and the positions of the center points 12a at this time are set as the finally measured plurality of index core positions in this measurement method.

[0033] In the above description, the sum of nth powers S or the maximum displacement amount D is obtained multiple times. However, when it is possible by a mathematical algorithm, the displacement amount D of each core 12 when the sum of nth powers S or the maximum displacement amount D is minimized may be directly calculated by one calculation and set as the finally measured displacement amount. Similarly, the positions of the center points 12a of the plurality of cores 12 when the sum of nth powers S or the maximum displacement amount D is minimized may be directly calculated by one calculation and set as the finally measured plurality of index core positions.

[0034] FIG. 5 is a diagram schematically showing the configuration of a measuring device 20 according to an embodiment of the present disclosure. The measuring device 20 includes a storage unit 21 and a calculation unit 22. The storage unit 21 stores the core positions (positions of the center points 12a) of the plurality of cores 12 of the multi-core optical fiber 10. The core positions of the plurality of cores 12 may be obtained by photographing the end face 11 with a camera included in the measuring device 20 and analyzing the image. Alternatively, the storage unit 21 may store in advance data related to the core positions obtained by analyzing the image of the end face 11. The calculation unit 22 calculates the displacement amount D of each of the plurality of cores 12 and the plurality of index core positions by performing the above-described calculation step ST2.

[0035] The measuring device 20 may be configured as a computer including, for example, a processor (CPU), main memory such as ROM and RAM, and auxiliary storage such as a hard disk. The storage unit 21 is performed by the main memory or auxiliary storage. The computer's processor can perform the calculation unit 22 described above by a measurement program. The measurement program causes the computer's processor to execute the acquisition step ST1 and calculation step ST2 described above. The measurement program is stored in an internal or external storage device or storage medium of the computer, such as an auxiliary storage device.

[0036] The effects obtained by the measurement method, measurement device 20, and measurement program of this embodiment, as described above, will be explained along with the problems that the reference example has.

[0037] In the example, the sum of the displacement amounts D of multiple cores 12, or the sum of the squares of the displacement amounts D of multiple cores 12, is calculated multiple times while moving the angular position of the center point 12a of multiple cores 12 around the fiber center 11a. Then, the displacement amount D of each of the multiple cores 12 when the sum or sum of the squares is minimized is taken as the measured displacement amount D. In this case, the displacement amount D may be overestimated, which may lead to a decrease in the manufacturing yield of the multicore optical fiber 10, resulting in a decrease in production volume and an increase in manufacturing costs. Specifically, when minimizing the sum of displacement amounts D, the contribution of both cores 12 with small displacement amounts D and cores 12 with large displacement amounts D to the sum of displacement amounts D is the same. Therefore, when minimizing the sum of displacement amounts D, it is often possible to further reduce the displacement amount D of cores 12 with small displacement amounts D and further increase the displacement amount D of cores 12 with large displacement amounts D. A similar situation may occur when minimizing the sum of the squares of the displacement amounts D.

[0038] In view of such problems, in the measurement method, measurement apparatus 20, and measurement program of the present embodiment, the angular positions of the center points 12a of the plurality of cores 12 around the fiber center 11a are moved, and the displacement amount D of each core 12 when the sum S of the nth powers of the displacement amounts D of the plurality of cores 12 is minimized is set as the measured displacement amount D. n is a number of 3 or more. The positions of the center points 12a of the plurality of cores 12 when the sum S of the nth powers is minimized are set as the measured plurality of reference core positions. Alternatively, the angular positions of the plurality of reference core positions 12b around the fiber center 11a are moved to obtain the plurality of reference core positions 12b when the sum S of the nth powers is minimized, and the positions of the center points 12a of the plurality of cores 12 when the center points 12a of the plurality of cores 12 are moved counterclockwise by the same angle as the movement angle from the original positions of the plurality of reference core positions 12b are set as the measured plurality of reference core positions. In these cases, compared with a reference example in which n is 2 or less, the ratio of the maximum displacement amount D among the displacement amounts D of the plurality of cores 12 contributing to the sum S of the nth powers increases. Therefore, the frequency of increasing the displacement amount D of the core 12 with a large displacement amount D is reduced, and the maximum displacement amount D is further reduced.

[0039] Alternatively, in the measurement method, measurement apparatus 20, and measurement program of the present embodiment, the angular positions of the center points 12a of the plurality of cores 12 around the fiber center 11a are moved, and the displacement amount D of each core 12 when the maximum displacement amount D among the displacement amounts D of the plurality of cores 12 is minimized is set as the measured displacement amount D. The positions of the center points 12a of the plurality of cores 12 when the maximum displacement amount D is minimized are set as the measured plurality of reference core positions. Alternatively, the angular positions of the plurality of reference core positions 12b around the fiber center 11a are moved to obtain the plurality of reference core positions 12b when the maximum displacement amount D among the displacement amounts D of the plurality of cores 12 is minimized, and the positions of the center points 12a of the plurality of cores 12 when the center points 12a of the plurality of cores 12 are moved counterclockwise by the same angle as the movement angle from the original positions of the plurality of reference core positions 12b are set as the measured plurality of reference core positions. In this case, the displacement amount D of the core 12 with a large displacement amount D is not increased any further, and the maximum displacement amount D is further reduced.

[0040] When determining the quality of the performance, specifications, or characteristics of a multicore optical fiber 10, a smaller core displacement amount D is desirable, and therefore, the evaluation is mainly based on the maximum displacement amount D. Accordingly, by reducing the maximum displacement amount D of the core 12, it is possible to evaluate the multicore optical fiber as having a small core displacement amount and being desirable. According to the measurement method, measurement device 20, and measurement program of this embodiment, it is possible to determine an appropriate displacement amount D and an appropriate index core position for the displacement amount D in the multicore optical fiber 10 without calculating an excessively large core displacement amount.

[0041] As mentioned above, n may be 4 or greater. In this case, the proportion that the largest displacement amount D among the multiple cores 12 contributes to the n-th power sum S becomes even larger, so the largest displacement amount D is further reduced. Therefore, a more appropriate displacement amount D, or an index core position for which the displacement amount D is more appropriate, can be determined.

[0042] In this embodiment, n may be 4. In this case, the proportion of the largest displacement amount D among the multiple core displacement amounts D that contributes to the n-th power sum S becomes appropriately large, and the other displacement amounts D excluding the largest displacement amount D also contribute appropriately to the n-th power sum S. Therefore, the largest displacement amount D is appropriately reduced, and it is possible to prevent the other displacement amounts D from becoming excessively large. This makes it possible to determine a more appropriate displacement amount D and an index core position where the displacement amount D is more appropriate.

[0043] The above effects were verified by calculation. The verification results are described below. In the following description, Comparative Examples 1 to 3 and Examples 1 to 4 are defined as follows. Comparative Example 1: The amount of displacement D of each core 12 from the core position at the time of design is defined as the measured displacement D. Comparative Example 2: The amount of displacement D of each core 12 when the sum of the displacement amounts D of multiple cores 12 is minimized is defined as the measured displacement D. Comparative Example 3: The amount of displacement D of each core 12 when the sum of the squares of the displacement amounts D of multiple cores 12 is minimized is defined as the measured displacement D. Example 1: The amount of displacement D of each core 12 when the sum of the cubes of the displacement amounts D of multiple cores 12 is minimized is defined as the measured displacement D. Example 2: The amount of displacement D of each core 12 when the sum of the fourth powers of the displacement amounts D of multiple cores 12 is minimized is defined as the measured displacement D. Example 3: The measured displacement D of each core 12 is defined as the displacement D of each core 12 when the sum of the eighth powers of the displacement D of the multiple cores 12 is minimized. Example 4: The measured displacement D of each core 12 is defined as the displacement D of each core 12 when the largest displacement D among the multiple cores 12 is minimized.

[0044] Figure 6 is a graph showing the relationship between the amount of displacement D and the probability density for Comparative Examples 1 to 3 and Examples 1 to 4, where the four design core positions (reference core position 12b) are (20 μm, 20 μm), (-20 μm, 20 μm), (-20 μm, -20 μm), and (20 μm, -20 μm) in a Cartesian coordinate system with the fiber center 11a as the origin, and the actual core positions are scattered according to a normal distribution with a standard deviation of 0.25 μm. The upper graph in Figure 6 shows the probability density on the vertical axis linearly. The lower graph in Figure 6 shows the probability density on the vertical axis logarithmically. Figure 7 is a graph showing the complementary cumulative distribution of the amount of displacement D for Comparative Examples 1 to 3 and Examples 1 to 4 in the same case. The complementary cumulative distribution is the number obtained by subtracting the cumulative distribution from 1, in other words, it is a distribution that shows the probability that the amount of displacement D is greater than or equal to a certain value. The upper graph in Figure 7 shows the complementary cumulative distribution on the vertical axis in a linear fashion. The lower graph in Figure 7 shows the complementary cumulative distribution on the vertical axis in a logarithmic fashion.

[0045] Referring to Figures 6 and 7, in Comparative Examples 1 to 3, the tails of the probability distribution are distributed over larger displacement amounts, and the tails of the probability distribution are longer, compared to Examples 1 to 4. In other words, Comparative Examples 1 to 3 overestimate the maximum displacement amount D compared to Examples 1 to 4. To put it another way, Examples 1 to 4 prevent overestimation of the maximum displacement amount D and avoid a decrease in the manufacturing yield of the multicore optical fiber 10. Referring to Figures 6 and 7, Example 2 has shorter tails of the probability distribution than Example 1, so the maximum displacement amount D can be estimated even smaller. Examples 3 and 4 have shorter tails of the probability distribution than Example 2, so the maximum displacement amount D can be estimated even smaller. Here, being able to underestimate the maximum displacement amount D is not merely a manipulation of apparent numbers. This means that there is an appropriate rotation angle around the fiber center of the multicore optical fiber that actually reduces the maximum displacement amount D, and in the examples, the displacement amount D can be measured at an appropriate rotation angle.

[0046] Here, we consider the effect of underestimating the misalignment amount D on the connection loss. We assume that the mode field diameter (MFD) is 8.6 μm and that MFD mismatch can be ignored. Figures 8 and 9 are graphs showing the complementary cumulative distribution of the coupling loss caused by the misalignment amount D for Comparative Examples 1 to 3, and Examples 2 and 4. The coupling loss is the loss of abutment coupling, also known as connection loss. Figure 8 shows the case where the core of the abutment partner is at the reference core position. Figure 9 shows the case where the core of the abutment partner also varies according to a similar distribution. The upper graphs in Figures 8 and 9 show the complementary cumulative distribution on the vertical axis linearly. The lower graphs in Figures 8 and 9 show the complementary cumulative distribution on the vertical axis logarithmically. Referring to Figures 8 and 9, the tails of the complementary cumulative distribution of the coupling loss can be made shorter in the examples than in the comparative examples. From Figure 8, it can be seen that when a multicore optical fiber is rotated to an appropriate rotation angle so as to minimize the misalignment amount D, and connected to an ideal multicore optical fiber with no core misalignment, the worst-case value of the coupling loss can be reduced. Thus, the embodiment is more suitable and advantageous than the comparative example for predicting the reduced connection loss. From Figure 9, it can be seen that when multicore optical fibers rotated to an appropriate rotation angle so as to minimize the misalignment amount D are connected, the worst-case value of the coupling loss can be reduced. Thus, the embodiment is more suitable and advantageous than the comparative example for predicting the reduced connection loss.

[0047] In the examples shown in Figures 6 to 9 above, the MFD is set to 8.6 μm. Even if the MFD is different, it is presumed that similar results can be obtained because only the scale of the horizontal axis of the graph changes.

[0048] In the examples shown in Figures 6 to 9 above, the four design core positions (reference core position 12b) are (20 μm, 20 μm), (-20 μm, 20 μm), (-20 μm, -20 μm), and (20 μm, -20 μm) in a Cartesian coordinate system with the fiber center 11a as the origin, but the core positions are not limited to these. Figure 10 is a graph showing the complementary cumulative distribution of the displacement amount D when the four core positions are (12.5 μm, 12.5 μm), (-12.5 μm, 12.5 μm), (-12.5 μm, -12.5 μm), and (12.5 μm, -12.5 μm). Figure 11 is a graph showing the complementary cumulative distribution of the displacement amount D when the four core positions are (10 μm, 10 μm), (-10 μm, 10 μm), (-10 μm, -10 μm), and (10 μm, -10 μm). The upper graphs in Figures 10 and 11 show the complementary cumulative distribution on the vertical axis linearly. The lower graphs in Figures 10 and 11 show the complementary cumulative distribution on the vertical axis logarithmically. Referring to Figures 10 and 11, similar to Figure 7, the tails of the complementary cumulative distribution are shorter in the examples compared to the comparative examples.

[0049] The number of cores 12 is not limited to four. For example, eight cores 12 may be provided, and eight reference core positions 12b may be arranged at equal intervals on a circle centered on the fiber center 11a. Figure 12 is a graph showing the complementary cumulative distribution of the displacement amount D when eight cores 12 are provided and the design core center spacing (spacing of reference core positions 12b) is 30 μm. The upper graph of Figure 12 shows the complementary cumulative distribution on the vertical axis linearly. The lower graph of Figure 12 shows the complementary cumulative distribution on the vertical axis logarithmically. Referring to Figure 12, similar to Figure 7, the tail of the complementary cumulative distribution is shorter in this embodiment compared to the comparative example.

[0050] The arrangement of the multiple cores 12 is not limited to those having two or more rotational symmetries, as in the examples described above. Figure 13 is a graph showing the complementary cumulative distribution of the displacement amount D in a 12-core multicore optical fiber without two or more rotational symmetries, as described in Non-Patent Literature 4, when the design core center spacing is 35 μm. The upper graph of Figure 13 shows the complementary cumulative distribution on the vertical axis linearly. The lower graph of Figure 13 shows the complementary cumulative distribution on the vertical axis logarithmically. Referring to Figure 13, similar to Figure 7, the tail of the complementary cumulative distribution is shorter in the embodiment compared to the comparative example.

[0051] Figures 10 to 13 also represent examples where the actual core positions are scattered according to a normal distribution with a standard deviation of 0.25 μm.

[0052] The method, apparatus, and program for measuring core misalignment, as well as the method, apparatus, and program for measuring the index core position, as described herein, are not limited to the embodiments described above and can be modified in various ways. For example, the number of cores in a multicore optical fiber, the core arrangement, and the distribution of variations in the actual core position are not limited to those described in the embodiments above.

[0053] 10...Multicore optical fiber 11...End face 11a...Fiber center 12...Core 12a...Center point 12b...Reference core position 13...Cladding 20...Measurement device 21...Storage unit 22...Calculation unit D...Positional displacement amount ST1...Acquisition step ST2...Calculation step

Claims

1. A method for measuring core misalignment, comprising the steps of: obtaining the positions of multiple cores of a multicore optical fiber; and calculating the amount of misalignment of each of the multiple cores from each of a plurality of reference core positions, each of which is the design core position or nominal core position of the multiple cores, wherein in the calculation step, the angular position of the plurality of reference core positions or the obtained positions of the plurality of cores around the fiber center is moved, and the sum of the nth powers of the misalignment amounts of the plurality of cores (where n is a number of 3 or more), or the amount of misalignment of each of the plurality of cores when the maximum misalignment amount among the misalignment amounts of the plurality of cores is minimized, is defined as the measured amount of misalignment.

2. The method for measuring the amount of core displacement according to claim 1, wherein n is 4 or more.

3. The method for measuring the amount of core displacement according to claim 1, wherein n is 4.

4. A method for measuring an index core position, comprising the steps of: acquiring the positions of multiple cores of a multicore optical fiber; and calculating the positions of multiple index cores of the multiple cores, wherein in the calculation step, the angular position of the acquired positions of the multiple cores is moved around the fiber center to determine the n-th power sum of the positional displacement amounts of the multiple cores from a plurality of reference core positions, which are the design core positions or nominal core positions (where n is a number of 3 or more), or the position of the multiple cores at which the maximum positional displacement amount among the multiple cores is minimized, and the position of the multiple cores at which this sum is minimized is defined as the measured index core position; or, in the calculation step, the angular position of the multiple reference core positions is moved around the fiber center to determine the plurality of reference core positions at which the n-th power sum of the positional displacement amounts of the multiple cores from the plurality of reference core positions (where n is a number of 3 or more), or the maximum positional displacement amount among the multiple cores is minimized, and the position of the multiple cores at which the positions of the multiple cores are moved in the opposite direction by the same angle as the angle of movement from the original position of the plurality of reference core positions is defined as the measured index core position.

5. The method for measuring the position of an index core according to claim 4, wherein n is 4 or more.

6. The method for measuring the position of an index core according to claim 4, wherein n is 4.

7. A core misalignment measurement program that causes a computer to perform the following steps: acquire the positions of multiple cores of a multicore optical fiber; calculate the misalignment amount of each of the multiple cores from each of a plurality of reference core positions, each of which is the design core position or nominal core position of the multiple cores; and in the calculation step, moves the angular position of the plurality of reference core positions or the acquired positions of the plurality of cores around the fiber center, and takes as the measured misalignment amount the sum of the nth powers of the misalignment amounts of the plurality of cores (where n is a number of 3 or more), or the misalignment amount of each of the plurality of cores when the maximum misalignment amount among the misalignment amounts of the plurality of cores is minimized.

8. A program for measuring index core positions, comprising the steps of: obtaining the positions of multiple cores of a multicore optical fiber; and calculating the positions of multiple index cores of the multiple cores, wherein in the calculation step, the program moves the angular position of the obtained positions of the multiple cores around the fiber center to determine the sum of the n-th powers of the positional displacement amounts of the multiple cores from the multiple reference core positions which are the design core positions or nominal core positions (n ​​is a number of 3 or more), or the position of the multiple cores where the maximum positional displacement amount among the multiple cores is minimized, and sets this position as the measured index core position; or, in the calculation step, the program moves the angular position of the multiple reference core positions around the fiber center to determine the sum of the n-th powers of the positional displacement amounts of the multiple cores from the multiple reference core positions (n ​​is a number of 3 or more), or the position of the multiple reference cores where the maximum positional displacement amount among the multiple cores is minimized, and sets the position of the multiple cores where the multiple cores are moved in the opposite direction by the same angle as the angle of movement from the original position of the multiple reference core positions, and sets this position as the measured index core position.

9. A core misalignment measuring device comprising: a storage unit for storing the positions of multiple cores of a multicore optical fiber; and a calculation unit for calculating the amount of misalignment of each of the multiple cores from each of a plurality of reference core positions which are the design core positions or nominal core positions of the multiple cores, wherein the calculation unit moves the angular position of the plurality of reference core positions or the acquired positions of the plurality of cores around the fiber center, and the measured amount of misalignment of each of the plurality of cores is the sum of the nth powers of the amount of misalignment of the plurality of cores (where n is a number of 3 or more), or the amount of misalignment of each of the plurality of cores when the maximum amount of misalignment of the plurality of cores is minimized.

10. An index core position measuring device comprising: a storage unit for storing the positions of multiple cores of a multicore optical fiber; and a calculation unit for calculating multiple index core positions of the multiple cores, wherein the calculation unit moves the angular position of the acquired multiple core positions around the fiber center to determine the n-th power sum of the positional displacement amounts of the multiple cores from a plurality of reference core positions which are design core positions or nominal core positions (n ​​is a number of 3 or more), or the position of the multiple cores when the maximum positional displacement amount among the multiple cores is minimized, and sets the position of the multiple cores when this sum is minimized, and sets the position of the multiple cores when this sum is minimized, or the calculation unit moves the angular position of the plurality of reference core positions around the fiber center to determine the n-th power sum of the positional displacement amounts of the multiple cores from the plurality of reference core positions (n ​​is a number of 3 or more), or the position of the plurality of reference core positions when the maximum positional displacement amount among the multiple cores is minimized, and sets the position of the multiple cores when the position of the multiple cores is moved in the opposite direction by the same angle as the angle of movement from the original position of the plurality of reference core positions, the measured index core position measuring device.

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