Core position deviation amount measuring method, indicator core position measuring method, core position deviation amount measuring program, indicator core position measuring program, core position deviation amount measuring device, and indicator core position measuring device

Abstract

The core position misalignment measurement method includes the steps of acquiring the positions of multiple cores of a multi-core optical fiber and calculating the position misalignment of each of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions of the multiple cores. In the calculating 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 n-th powers of the position misalignments of the multiple cores, or the position misalignment when the maximum position misalignment among the position misalignments of the multiple cores becomes the smallest, is defined as the measured position misalignment. n is a number equal to or greater than 3.

Description

[Technical Field]

[0001] The present disclosure relates to a core position deviation measurement method, an indicator core position measurement method, a core position deviation measurement program, an indicator core position measurement program, a core position deviation measurement device, and an indicator core position measurement device. This application claims priority to Japanese Application No. 2024-170951, filed September 30, 2024, and incorporates the entire disclosure of said Japanese application by reference. background

[0002] Patent Document 1 discloses a method for aligning an optical waveguide component having multiple optical waveguides with an optical fiber array component having multiple optical fibers arranged therein. In this alignment method, the pitch deviation of each optical fiber facing each optical waveguide is calculated based on the pitch of the optical waveguides. 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 calculated pitch deviations becomes zero.

[0003] Patent Document 2 discloses an alignment device and an 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 captured, and the position coordinates of the two or more cores on the end face of each of the two optical fibers are determined. The position coordinates of the two or more cores are then substituted into a theoretical formula that represents the total axial misalignment loss when two or more cores are spliced ​​together. From the theoretical formula, the positional relationship of the end faces of the two optical fibers is determined so that the total axial misalignment loss is minimized. The two optical fibers are positioned so that the determined positional relationship is satisfied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-304667 [Patent Document 2] International Publication No. 2015 / 025629 [Non-patent literature]

[0005] [Non-Patent Document 1] "GSTR-SDM / Optical fiber, cable, and components for space division multiplexing transmission," International Telecommunication Union, ITU-T Technical Report (09 / 2022) [Non-patent document 2] "Measurement methods and test procedures - Fiber geometry," International Electrotechnical Commission, IEC 60793-1-20 (2014) [Non-patent document 3] 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) [Non-patent document 4] 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) Summary of the Invention

[0006] A core misalignment measurement method according to an embodiment of the present disclosure includes the steps of acquiring positions of multiple cores of a multi-core optical fiber, and calculating a misalignment amount of each of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions of the multiple cores. In the calculating step, the angular positions of the multiple reference core positions or the acquired multiple core positions around the fiber center are moved, and the measured misalignment amount is the sum of n-th powers (n is a number equal to or greater than 3) of the misalignment amounts of the multiple cores, or the misalignment amount when the maximum misalignment amount among the misalignment amounts of the multiple cores is minimized. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an end face of a multi-core optical fiber. [Figure 2] FIG. 2 is a flowchart showing the measurement method according to the embodiment. [Figure 3] FIG. 3 is a diagram showing how the angular positions of the central points of multiple cores are moved around the center of the fiber. [Figure 4] FIG. 4 is a diagram showing how the angular positions of a plurality of reference core positions are moved around the center of the fiber. [Figure 5] FIG. 5 is a diagram schematically illustrating the configuration of a measurement device according to an embodiment. [Figure 6] FIG. 6 is a graph showing the relationship between the core positional deviation amount and the probability density. [Figure 7] FIG. 7 is a graph showing the complementary cumulative distribution of the core misalignment amount. [Figure 8] FIG. 8 is a graph showing the complementary cumulative distribution of coupling loss caused by core misalignment. [Figure 9] FIG. 9 is a graph showing the complementary cumulative distribution of coupling loss caused by core misalignment. [Figure 10] FIG. 10 is a graph showing the complementary cumulative distribution of the core misalignment amount. [Figure 11] FIG. 11 is a graph showing the complementary cumulative distribution of the core misalignment amount. [Figure 12] FIG. 12 is a graph showing the complementary cumulative distribution of the core misalignment amount. [Figure 13] FIG. 13 is a graph showing the complementary cumulative distribution of the core misalignment amount. DETAILED DESCRIPTION OF THE INVENTION

[0008] When expressing the performance, specifications, or characteristics of a multi-core optical fiber, the amount of positional deviation of each of the multiple cores from a reference core position on a cross section orthogonal to the central axis of the multi-core optical fiber is used. The reference core position is a design core position or a nominal core position in a certain coordinate system, and splicing multi-core optical fibers in which the positions of the cores coincide with the reference core position can minimize the splice loss. In reality, the actual core positions deviate from the reference core position due to factors such as manufacturing variations. The greater the amount of positional deviation of the actual core positions from the reference core positions, the greater the splice loss between multi-core optical fibers.

[0009] When measuring the amount of misalignment, in an actual multi-core optical fiber, it is not possible to identify the coordinate system used to determine the core positions when the multi-core optical fiber is designed. Therefore, an index core position, which is a core position, is identified as an index of the characteristics of the multi-core optical fiber, which is uniquely determined for each core based on the measured actual core positions. Then, the distance between the reference core position and the index core position is used as the amount of core misalignment and as an index of the performance, specifications, or characteristics of the multi-core optical fiber. Therefore, the amount of core misalignment of the multi-core 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 multi-core optical fiber.

[0010] An object of the present disclosure is to provide a core misalignment measurement method, a core misalignment measurement program, and a core misalignment measurement device that can determine an appropriate core misalignment amount in a multi-core optical fiber. In addition, an object of the present disclosure is to provide an index core position measurement method, an index core position measurement program, and an index core position measurement device that can determine an index core position with an appropriate misalignment amount in a multi-core optical fiber.

[0011] According to the present disclosure, it is possible to provide a core misalignment measurement method, a core misalignment measurement program, and a core misalignment measurement device that can determine an appropriate core misalignment amount in a multi-core optical fiber. In addition, it is possible to provide an index core position measurement method, an index core position measurement program, and an index core position measurement device that can determine an index core position with an appropriate misalignment amount in a multi-core optical fiber.

[0012] The contents of the embodiments of the present disclosure will be described.

[0013] [1A] A core position misalignment measurement method according to an embodiment of the present disclosure includes the steps of acquiring positions of multiple cores of a multi-core optical fiber, and calculating a position misalignment amount of each of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions of the multiple cores. In the calculating step, the angular positions of the multiple reference core positions or the acquired multiple core positions around the fiber center are moved, and the measured position misalignment amount is the sum of n-th powers (n is a number equal to or greater than 3) of the position misalignments of the multiple cores, or the position misalignment amount when the maximum position misalignment amount among the position misalignments of the multiple cores becomes the smallest.

[0014] [1B] A core misalignment measurement program according to an embodiment of the present disclosure causes a computer to execute the steps of acquiring positions of multiple cores of a multi-core optical fiber and calculating a misalignment amount of each of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions of the multiple cores. In the calculating 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 n-th powers (n is a number equal to or greater than 3) of the misalignment amounts of the multiple cores, or the misalignment amount of each of the multiple cores when the maximum misalignment amount among the misalignment amounts of the multiple cores becomes the smallest, is defined as the measured misalignment amount.

[0015] [1C] A core misalignment measurement device according to an embodiment of the present disclosure includes a storage unit that stores positions of multiple cores of a multi-core optical fiber, and a calculation unit that calculates a misalignment amount of each of the multiple cores from a plurality of reference core positions, which are design core positions or nominal core positions of the multiple cores. The calculation unit moves the angular positions of the multiple reference core positions or the acquired multiple core positions around the fiber center, and determines the sum of n-th powers (n is a number equal to or greater than 3) of the misalignment amounts of the multiple cores, or the misalignment amount of each of the multiple cores when the maximum misalignment amount among the misalignment amounts of the multiple cores is minimum, as the measured misalignment amount.

[0016] In the measurement method, measurement program, and measurement device described above in [1A] to [1C], the angular positions of the multiple reference core positions or the multiple acquired core positions around the fiber center are moved, and the measured misalignment amount of each of the multiple cores is the amount of misalignment when the sum of the n-th power of the misalignment amounts of the multiple cores is minimized. n is a number equal to or greater than 3. In this case, compared to when n is 2 or less, for example, the proportion of the maximum misalignment amount among the multiple core misalignments that contributes to the sum of the n-th power is further increased, thereby further reducing the maximum misalignment amount. Alternatively, in the measurement method, measurement program, and measurement device described above in [1A] to [1C], the angular positions of the multiple reference core positions or the multiple acquired core positions around the fiber center are moved, and the measured misalignment amount of each of the multiple cores is the amount of misalignment when the maximum misalignment amount among the multiple core misalignments is minimized. In this case, the maximum misalignment amount is also further reduced.

[0017] When judging the quality of the performance, specifications, or characteristics of a multi-core optical fiber, the maximum core misalignment amount is mainly used as a reference, since a smaller core misalignment amount is preferable. Therefore, by reducing the maximum core misalignment amount, the multi-core optical fiber can be evaluated as a desirable multi-core optical fiber with a small core misalignment amount. According to the measurement methods, measurement programs, and measurement devices described above in [1A] to [1C], it is possible to obtain an appropriate core misalignment amount in a multi-core optical fiber without calculating an excessively large core misalignment amount.

[0018] [2A] A method for measuring an index core position according to an embodiment of the present disclosure includes steps of acquiring positions of multiple cores of a multi-core optical fiber and calculating index core positions of the multiple cores. In the calculating step, 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 n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions, or the maximum positional deviation among the positional deviations of the multiple cores is minimized are defined as the measured index core positions. Alternatively, in the calculating step, the angular positions of the multiple reference core positions, which are design core positions or nominal core positions, are moved around the fiber center to obtain the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from the multiple reference core positions, or the maximum positional deviation among the positional deviations of the multiple cores is minimized, and the multiple core positions when the multiple core positions are moved in a counterclockwise direction by an angle equal to the movement angle of the multiple reference core positions from their original positions are defined as the measured index core positions.

[0019] [2B] A measurement program for index core positions according to an embodiment of the present disclosure causes a computer to execute the steps of acquiring positions of multiple cores of a multi-core optical fiber and calculating index core positions of the multiple cores. In the calculating step, the angular positions of the acquired multiple core positions around the fiber center are moved to obtain the multiple core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions, or the maximum positional deviation amount among the multiple core positional deviations, is smallest, as the measured multiple index core positions. Alternatively, in the calculating step, the angular positions of the multiple reference core positions, which are design core positions or nominal core positions, around the fiber center are moved to obtain the multiple reference core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from the multiple reference core positions, or the maximum positional deviation amount among the multiple core positional deviations, is smallest, and the multiple core positions when the multiple core positions are moved in the opposite direction by the same angle as the movement angle of the multiple reference core positions from their original positions are obtained, as the measured multiple index core positions.

[0020] [2C] An index core position measurement device according to an embodiment of the present disclosure includes a storage unit that stores positions of multiple cores of a multi-core optical fiber, and a calculation unit that calculates index core positions of the multiple cores. The calculation unit moves the angular positions of the acquired multiple core positions around the fiber center, and determines the multiple core positions at which the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions, or the maximum positional deviation amount among the multiple core positional deviations, is smallest as the measured multiple index core positions. Alternatively, the calculation unit moves the angular positions of the multiple reference core positions, which are design core positions or nominal core positions, around the fiber center to determine the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from the multiple reference core positions, or the maximum positional deviation amount among the multiple core positional deviations, is smallest, and determines the multiple core positions when the multiple core positions are moved in a counterclockwise direction by an angle equal to the movement angle of the multiple reference core positions from their original positions as the measured multiple index core positions.

[0021] In the measurement methods, measurement programs, and measurement devices described above in [2A] to [2C], the angular positions of the acquired core positions around the fiber center are moved, and the multiple core positions at which the sum of the n-th power of the misalignment amounts of the multiple cores is minimized are defined as the measured multiple index core positions. n is a number equal to or greater than 3. Alternatively, the angular positions of the multiple reference core positions around the fiber center are moved to determine the multiple reference core positions at which the sum of the n-th power of the misalignment amounts of the multiple cores is minimized, and the multiple core positions are moved in the counterclockwise direction by the same angle as the movement angle of the multiple reference core positions from their original positions. n is a number equal to or greater than 3. In these cases, the contribution of the maximum misalignment amount among the multiple core misalignment amounts to the sum of the n-th power is further increased compared to when n is 2 or less, and the maximum misalignment amount is further reduced. Alternatively, in the measurement methods, measurement programs, and measurement devices described above in [2A] to [2C], 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 deviation among the multiple core positional deviations is minimized are taken as the measured multiple index core positions. Alternatively, the angular positions of multiple reference core positions around the fiber center are moved to obtain multiple reference core positions at which the maximum positional deviation among the multiple core positional deviations is minimized, and the multiple core positions are moved in the opposite direction by the same angle as the movement angle of the multiple reference core positions from their original positions, and the measured multiple index core positions are taken as the measured multiple index core positions. In this case as well, the maximum positional deviation is further reduced.

[0022] As described above, when determining the quality of the performance, specifications, or characteristics of a multi-core optical fiber, the core misalignment amount is mainly evaluated with reference to the maximum core misalignment amount. Therefore, by measuring the maximum core misalignment amount at an appropriate value rather than an excessively large value, the misalignment amount of the core positions of the multi-core optical fiber can be more appropriately evaluated. That is, according to the measurement methods, measurement programs, and measurement devices described above in [2A] to [2C], it is possible to obtain an index core position where the misalignment amount is appropriate in the multi-core optical fiber.

[0023] [3] In each of the above measurement methods, programs, and devices, n may be 4 or greater. In this case, the contribution of the maximum misalignment amount among the misalignment amounts of the multiple cores to the sum of n-th powers becomes even greater, so the maximum misalignment amount is further reduced. Therefore, a more appropriate misalignment amount, or an index core position with a more appropriate misalignment amount, 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 positional deviation amount among the multiple core positional deviation amounts that contributes to the sum of n-th powers is appropriately increased, and the other positional deviation amounts excluding the largest positional deviation amount also appropriately contribute to the sum of n-th powers. Therefore, the largest positional deviation amount is appropriately reduced, and the other positional deviation amounts can be prevented from becoming excessively large. This makes it possible to determine a more appropriate positional deviation amount or an index core position with a more appropriate positional deviation amount.

[0025] [Details of the embodiments of the present disclosure] Specific examples of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. In the following description, the same elements in the description of the drawings will be given the same reference numerals, and duplicate explanations will be omitted.

[0026] FIG. 1 is a diagram showing an end face 11 of a multi-core optical fiber 10. The multi-core optical fiber 10 has a plurality of cores 12 arranged in a dispersed manner on the end face 11, and a cladding 13 surrounding the plurality of cores 12. In the illustrated example, the number of the plurality of cores 12 is four. The refractive index of the plurality of cores 12 is larger than the refractive index of the cladding 13. The shape of the end face 11 is circular, and the shape of each core 12 on 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. FIG. 1 shows a Cartesian coordinate system with the fiber center 11a as the origin. In the following description, the core position of each core 12 means the position of the center point 12a in the Cartesian coordinate system (XY orthogonal coordinate system).

[0027] FIG. 1 shows multiple reference core positions 12b. Each reference core position 12b is an ideal core position for each core 12 and is used as a reference core position without any deviation when evaluating the misalignment amount of each core 12. The multiple reference core positions 12b have a designed or nominal relative positional relationship among the multiple cores 12. 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 whose center is the fiber center 11a. The center point 12a of each core 12 is shifted by a misalignment amount D from the corresponding reference core position 12b due to factors such as manufacturing variations. The smaller the misalignment amount D, the smaller the splice loss with other multi-core optical fibers or optical components. In many cases, the performance, specifications, or characteristics of a multi-core optical fiber 10 are evaluated based on the maximum misalignment amount D among the multiple cores 12. Therefore, it is desirable to determine a plurality of reference core positions 12b so that the maximum positional deviation D is as small as possible.

[0028] 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 deviation amount D of each core 12 of the multi-core optical fiber 10 and the positions of multiple index cores, and includes an acquiring step ST1 and a calculating step ST2. In the acquiring step ST1, the positions of the center points 12a of the multiple cores 12 of the multi-core optical fiber 10 and the position of the fiber center 11a of the multi-core 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 related to 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 related to the positions of the center points 12a and the fiber center 11a that have already been digitized may be acquired.

[0029] In calculation step ST2, each of the multiple reference core positions 12b is associated with each of the multiple cores 12, and a positional deviation D from the corresponding reference core position of each of the multiple cores 12 and multiple index core positions are calculated. In calculation step ST2, as shown in FIG. 3, the origin of coordinates is set to the fiber center 11a, and the sum of n-th powers of the positional deviation D of the multiple cores 12 is calculated multiple times while moving (i.e., rotating) the angular positions of the center points 12a of the multiple cores 12 around the fiber center 11a (i.e., the coordinate origin). Here, n is a number equal to or greater than 3 or 4. n may be an integer or a real number. If the positional deviation D of the four cores 12 are D1, D2, D3, and D4, respectively, the sum of n-th powers S is expressed as follows: S=D1 n +D2 n +D3 n +D4 n In calculation step ST2, the positional deviation amounts D1, D2, D3, and D4 at the angular position when the sum of n powers S is minimum are set as the positional deviation amount D finally measured in this measurement method. The position of the center point 12a of the multiple cores 12 at the angular position when the sum of n powers S is minimum are set as the multiple index core positions finally measured in this measurement method.

[0030] Alternatively, in calculation step ST2, as shown in Fig. 3, the origin of coordinates is set to the fiber center 11a, and the maximum positional deviation D among the positional deviations 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. In this case, if the angular positions are different, the cores 12 having the maximum positional deviation D may be different from each other. In calculation step ST2, the positional deviation D of each core 12 at the angular position where the maximum positional deviation D is smallest is determined to be the positional deviation D finally measured in this measurement method. The position of the center point 12a of the multiple cores 12 at the angular position where the maximum positional deviation D is smallest is determined to be 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 a positional deviation D from the corresponding reference core position of each of the multiple cores 12 and multiple indicator core positions are calculated. In calculation step ST2, as shown in FIG. 4, the fiber center 11a is set as the coordinate origin, and the sum of n-th powers S of the positional deviations 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 deviations D1, D2, D3, and D4 at the angular position at which the sum of n-th powers S is minimum are defined as the positional deviation D finally measured in this measurement method. The multiple reference core positions 12b at the angular position at which the sum of n-th power S is minimum are determined, and the positions of the center points 12a of the multiple cores 12 when the multiple reference core positions 12b are moved in the counterclockwise direction by the same angle as the movement angle from the original positions of the multiple reference core positions 12b are defined as the multiple indicator core positions finally measured in this measurement method.

[0032] Alternatively, in calculation step ST2, the maximum positional deviation D among the positional deviations D of the multiple cores 12 is determined multiple times while moving the angular positions of the multiple reference core positions 12b around the fiber center 11a, as shown in FIG. 4 . In this case, if the angular positions are different, the cores 12 having the maximum positional deviation D may be different from one another. In calculation step ST2, the positional deviation D of each core 12 at the angular position where the maximum positional deviation D is smallest is defined as the positional deviation D finally measured in this measurement method. Multiple reference core positions 12b at the angular position where the maximum positional deviation D is smallest are determined, and the positions of each center point 12a of the multiple cores 12 when the center point 12a of the multiple cores 12 is moved in the counterclockwise direction by the same angle as the movement angle of the multiple reference core positions 12b from the original positions are defined as the multiple index core positions finally measured in this measurement method.

[0033] In the above explanation, the sum of n powers S or the maximum positional deviation amount D is calculated multiple times, but if possible using a mathematical algorithm, the positional deviation amount D of each core 12 that minimizes the sum of n powers S or the maximum positional deviation amount D may be calculated directly in one calculation and used as the finally measured positional deviation amount. Similarly, the position of the center point 12a of the multiple cores 12 that minimizes the sum of n powers S or the maximum positional deviation amount D may be calculated directly in one calculation and used as the finally measured positions of the multiple indicator cores.

[0034] 5 is a diagram schematically illustrating a 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 multiple cores 12 of the multi-core optical fiber 10. The core positions of the multiple cores 12 may be acquired by photographing the end face 11 with a camera provided in the measuring device 20 and analyzing the image. Alternatively, the storage unit 21 may store in advance data related to the core positions acquired by analyzing the image of the end face 11. The calculation unit 22 calculates the positional deviation amount D of each of the multiple cores 12 and the multiple indicator core positions by performing the calculation step ST2 described above.

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

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

[0037] In the reference example, the sum or sum of squares of the misalignment amounts D of the multiple cores 12 is calculated multiple times while moving the angular positions of the center points 12a of the multiple cores 12 around the fiber center 11a. Then, the misalignment amount D of each of the multiple cores 12 when the sum or sum of squares is minimized is defined as the measured misalignment amount D. In this case, the misalignment amount D may be overestimated, which may reduce the manufacturing yield of the multi-core optical fiber 10, resulting in a decrease in production volume and an increase in manufacturing costs. Specifically, when minimizing the sum of the misalignment amounts D, both the cores 12 with small misalignment amounts D and the cores 12 with large misalignment amounts D contribute equally to the sum of the misalignment amounts D. Therefore, when minimizing the sum of the misalignment amounts D, it is often the case that the misalignment amounts D of the cores 12 with small misalignment amounts D are further reduced and the misalignment amounts D of the cores 12 with large misalignment amounts D are further increased. A similar phenomenon may occur when minimizing the sum of squares of the misalignment amounts D.

[0038] To address this problem, the measurement method, measurement device 20, and measurement program of this embodiment move the angular positions of the center points 12a of the multiple cores 12 around the fiber center 11a, and the positional misalignment D of each core 12 when the sum of n-th powers S of the positional misalignment D of the multiple cores 12 is minimized is defined as the measured positional misalignment D. n is a number greater than or equal to 3. The positions of the center points 12a of the multiple cores 12 when the sum of n-th power S is minimized are defined as the measured index core positions. Alternatively, the angular positions of the multiple reference core positions 12b around the fiber center 11a are moved to determine the multiple reference core positions 12b when the sum of n-th power S is minimized, and the positions of the center points 12a of the multiple cores 12 when the center points 12a 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 measured index core positions. In these cases, compared to the reference example in which n is 2 or less, the contribution of the largest positional misalignment D among the positional misalignment amounts D of the multiple cores 12 to the sum of n-th power S is greater. Therefore, the frequency of occurrence of further increasing the positional deviation amount D of the core 12 having a large positional deviation amount D decreases, and the maximum positional deviation amount D is further reduced.

[0039] Alternatively, in the measurement method, measurement device 20, and measurement program of this embodiment, the angular positions of the center points 12a of the multiple cores 12 about the fiber center 11a are moved, and the positional deviation D of each core 12 when the maximum positional deviation D among the positional deviations D of the multiple cores 12 is minimized is defined as the measured positional deviation D. The positions of the center points 12a of the multiple cores 12 when the maximum positional deviation D is minimized are defined as the measured multiple index core positions. Alternatively, the angular positions of the multiple reference core positions 12b about the fiber center 11a are moved to determine the multiple reference core positions 12b when the maximum positional deviation D among the positional deviations D of the multiple cores 12 is minimized, and the positions of each center point 12a of the multiple cores 12 when the center points 12a 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 measured multiple index core positions. In this case, the positional deviation D of cores 12 with a large positional deviation D is not further increased, and the maximum positional deviation D is further reduced.

[0040] When determining whether the performance, specifications, or characteristics of the multi-core optical fiber 10 are good or bad, the maximum misalignment amount D of the cores 12 is preferably small, and therefore the evaluation is mainly performed with reference to the maximum misalignment amount D. Therefore, by reducing the maximum misalignment amount D of the cores 12, the multi-core optical fiber can be evaluated as a desirable multi-core optical fiber with a small core misalignment amount. According to the measurement method, measurement device 20, and measurement program of the present embodiment, in the multi-core optical fiber 10, an appropriate misalignment amount D and an index core position where the misalignment amount D is appropriate can be obtained without calculating an excessively large core misalignment amount.

[0041] As mentioned above, n may be 4 or more. In this case, the contribution of the maximum positional deviation amount D among the positional deviation amounts D of the multiple cores 12 to the sum of n powers S becomes even greater, and the maximum positional deviation amount D is further reduced. Therefore, a more appropriate positional deviation amount D or an index core position where the positional deviation amount D is more appropriate can be obtained.

[0042] In this embodiment, n may be 4. In this case, the proportion that the maximum positional deviation amount D among the positional deviation amounts D of the multiple cores 12 contributes to the sum of n powers S becomes appropriately large, and the other positional deviation amounts D other than the maximum positional deviation amount D also appropriately contribute to the sum of n powers S. Therefore, the maximum positional deviation amount D is appropriately reduced, and it is possible to prevent the other positional deviation amounts D from becoming excessively large. This makes it possible to determine a more appropriate positional deviation amount D and an indicator core position where the positional deviation amount D is more appropriate.

[0043] The above effects were verified by calculation. The verification results are explained below. In the following explanation, Comparative Examples 1 to 3 and Examples 1 to 4 are defined as follows. Comparative Example 1: The amount of positional deviation D of each core 12 from the core position at the time of design is taken as the measured amount of positional deviation D. Comparative Example 2: The positional deviation amount D of each core 12 when the sum of the positional deviation amounts D of the plurality of cores 12 is minimum is defined as the measured positional deviation amount D. Comparative Example 3: The positional deviation amount D of each core 12 when the sum of the squares of the positional deviation amounts D of the plurality of cores 12 is minimum is defined as the measured positional deviation amount D. Example 1: The positional deviation amount D of each core 12 when the sum of the cubes of the positional deviation amounts D of the plurality of cores 12 is minimum is defined as the measured positional deviation amount D. Example 2: The positional deviation amount D of each core 12 when the sum of the fourth powers of the positional deviation amounts D of the plurality of cores 12 is minimum is defined as the measured positional deviation amount D. Example 3: The positional deviation amount D of each core 12 when the sum of the eighth powers of the positional deviation amounts D of the plurality of cores 12 is minimum is defined as the measured positional deviation amount D. Example 4: The positional deviation amount D of each core 12 when the maximum positional deviation amount D among the positional deviation amounts D of the plurality of cores 12 becomes the minimum is defined as the measured positional deviation amount D.

[0044] FIG. 6 is a graph showing the relationship between the misalignment amount D and the probability density for Comparative Examples 1 to 3 and Examples 1 to 4 in a case where the four design core positions (reference core positions 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 vary according to a normal distribution with a standard deviation of 0.25 μm. The upper graph in FIG. 6 linearly represents the probability density on the vertical axis. The lower graph in FIG. 6 logarithmically represents the probability density on the vertical axis. FIG. 7 is a graph showing the complementary cumulative distribution of the misalignment amount 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, a distribution indicating the probability that the misalignment amount D will be equal to or greater than a certain value. The upper graph in Fig. 7 shows the complementary cumulative distribution on the vertical axis as a linear plot, while the lower graph in Fig. 7 shows the complementary cumulative distribution on the vertical axis as a logarithmic plot.

[0045] 6 and 7 , in Comparative Example 1 to Comparative Example 3, the tails of the probability distribution are distributed over larger misalignment amounts and are longer than those in Examples 1 to 4. That is, in Comparative Example 1 to Comparative Example 3, the maximum misalignment amount D is overestimated compared to Examples 1 to 4. In other words, Examples 1 to 4 prevent the maximum misalignment amount D from being overestimated, and a decrease in the manufacturing yield of the multi-core optical fiber 10 can be avoided. With reference to FIGS. 6 and 7 , in Example 2, the tails of the probability distribution are shorter than those in Example 1, so the maximum misalignment amount D can be estimated even smaller. In Examples 3 and 4, the tails of the probability distribution are shorter than those in Example 2, so the maximum misalignment amount D can be estimated even smaller. Here, being able to estimate the maximum misalignment amount D smaller is not simply a matter of manipulating apparent values. This means that there is an appropriate rotation angle around the fiber center of the multi-core optical fiber at which the maximum misalignment amount D is actually small, and the misalignment amount D can be measured at an appropriate rotation angle in the examples.

[0046] Here, we consider the impact of underestimating the misalignment amount D on the splice loss. Assume 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 coupling loss caused by misalignment amount D for Comparative Examples 1 to 3 and Examples 2 and 4. The coupling loss is the loss of butt coupling, or so-called splice loss. Figure 8 shows the case where the cores in the butt coupling are located at the reference core position. Figure 9 shows the case where the cores in the butt coupling also vary according to a similar distribution. The upper graphs in Figures 8 and 9 linearly represent the complementary cumulative distribution on the vertical axis. The lower graphs in Figures 8 and 9 logarithmically represent the complementary cumulative distribution on the vertical axis. Referring to Figures 8 and 9, the tails of the complementary cumulative distribution of coupling loss can be shortened in the Examples compared to the Comparative Examples. As can be seen from Fig. 8, when it is assumed that the multi-core optical fibers are rotated at an appropriate rotation angle so that the misalignment D can be estimated to be small and are spliced ​​to an ideal multi-core optical fiber with no core misalignment, the worst value of the coupling loss can be reduced, and the Examples are more suitable and advantageous for predicting reduced splice loss than the Comparative Examples. As can be seen from Fig. 9, when multi-core optical fibers rotated at an appropriate rotation angle so that the misalignment D can be estimated to be small are spliced ​​to each other, the worst value of the coupling loss can be reduced, and the Examples are more suitable and advantageous for predicting reduced splice loss than the Comparative Examples.

[0047] The MFD is set to 8.6 μm in the examples of Figures 6 to 9. Even if the MFD is different, it is expected that similar results will be obtained, since only the scale of the horizontal axis of the graph will change.

[0048] 6 to 9, the four designed core positions (reference core positions 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. Fig. 10 is a graph showing the complementary cumulative distribution of the misalignment 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). FIG. 11 is a graph showing the complementary cumulative distribution of the misalignment 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 FIGS. 10 and 11 linearly represent the complementary cumulative distribution on the vertical axis. The lower graphs in FIGS. 10 and 11 logarithmically represent the complementary cumulative distribution on the vertical axis. Referring to FIGS. 10 and 11, similar to FIG. 7, the tails of the complementary cumulative distribution are shorter in the example than in the comparative example.

[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. FIG. 12 is a graph showing the complementary cumulative distribution of the misalignment amount D when eight cores 12 are provided and the designed core center interval (the interval between reference core positions 12b) is 30 μm. The upper graph in FIG. 12 linearly displays the complementary cumulative distribution on the vertical axis. The lower graph in FIG. 12 logarithmically displays the complementary cumulative distribution on the vertical axis. Referring to FIG. 12, similar to FIG. 7, the tail of the complementary cumulative distribution is shorter in the example than in the comparative example.

[0050] The arrangement of the multiple cores 12 is not limited to those having two-fold or more rotational symmetry as in the above-mentioned examples. Fig. 13 is a graph showing the complementary cumulative distribution of the misalignment amount D when the designed core center spacing is 35 µm in a 12-core multi-core optical fiber not having two-fold or more rotational symmetry as described in Non-Patent Document 4. The upper graph in Fig. 13 linearly displays the complementary cumulative distribution on the vertical axis. The lower graph in Fig. 13 logarithmically displays the complementary cumulative distribution on the vertical axis. Referring to Fig. 13, similar to Fig. 7, the tail of the complementary cumulative distribution is shorter in the example than in the comparative example.

[0051] The cases of FIGS. 10 to 13 are also examples in which the actual core positions vary according to a normal distribution with a standard deviation of 0.25 μm.

[0052] The core position deviation measuring method, measuring device, and measuring program, as well as the index core position measuring method, measuring device, and measuring program according to the present disclosure are not limited to the above-described embodiments, and various other modifications are possible. For example, the number of cores in the multi-core optical fiber, the core arrangement, and the distribution of variations in the actual core positions are not limited to those described in the above embodiments. [Explanation of symbols]

[0053] 10...Multi-core optical fiber 11...End face 11a...Fiber center 12...Core 12a...center point 12b...Reference core position 13...Clad 20...Measuring device 21...Storage section 22...Calculation section D: Positional deviation amount ST1...Acquisition step ST2: Calculation step

Claims

1. obtaining the positions of a plurality of cores of a multi-core optical fiber; calculating a positional deviation amount of each of the plurality of cores from a plurality of reference core positions, which are design core positions or nominal core positions of the plurality of cores; Equipped with a core misalignment measurement method, wherein in the calculating step, the angular positions of the plurality of reference core positions or the acquired positions of the plurality of cores are moved around the center of the fiber, and the measured misalignment amount is determined to be the sum of n-th powers (n is a number equal to or greater than 3) of the misalignment amounts of the plurality of cores, 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 minimum.

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

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

4. obtaining the positions of a plurality of cores of a multi-core optical fiber; calculating a plurality of indicator core positions for the plurality of cores; Equipped with In the calculating step, the angular positions of the acquired core positions around the fiber center are moved, and the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions, which are design core positions or nominal core positions, or the positions of the multiple cores when the maximum positional deviation amount among the positional deviations of the multiple cores is minimum, is set as the measured index core positions, or a method for measuring an index core position, wherein in the calculating step, the angular positions of the plurality of reference core positions around the center of a fiber are moved to find the plurality of reference core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the plurality of cores from the plurality of reference core positions or the maximum positional deviation amount among the positional deviations of the plurality of cores is minimized, and the positions of the plurality of cores when the positions of the plurality of cores are moved in the opposite direction by the same angle as the movement angle from the original positions of the plurality of reference core positions are taken as the measured plurality of index core positions.

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

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

7. obtaining the positions of a plurality of cores of a multi-core optical fiber; calculating a positional deviation amount of each of the plurality of cores from a plurality of reference core positions, which are design core positions or nominal core positions of the plurality of cores; on the computer, a core misalignment amount measurement program, wherein in the calculating step, the angular positions of the plurality of reference core positions or the acquired positions of the plurality of cores are moved around the center of the fiber, and the measured misalignment amount is the sum of n-th powers (n is a number equal to or greater than 3) of the misalignment amounts of the plurality of cores, 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 minimum.

8. obtaining the positions of a plurality of cores of a multi-core optical fiber; calculating a plurality of indicator core positions for the plurality of cores; on the computer, In the calculating step, the angular positions of the acquired core positions around the fiber center are moved, and the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions that are design core positions or nominal core positions, or the positions of the multiple cores when the maximum positional deviation amount among the positional deviations of the multiple cores is minimum, is set as the measured index core positions, or an index core position measurement program that, in the calculating step, moves the angular positions of the plurality of reference core positions around the center of the fiber to determine the plurality of reference core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the plurality of cores from the plurality of reference core positions or the maximum positional deviation amount among the positional deviations of the plurality of cores is minimum, and determines the positions of the plurality of cores when the positions of the plurality of cores are moved in the opposite direction by the same angle as the movement angle from the original positions of the plurality of reference core positions as the measured plurality of index core positions.

9. a storage unit that stores the positions of a plurality of cores of the multi-core optical fiber; a calculation unit that calculates a positional deviation amount of each of the plurality of cores from a plurality of reference core positions that are design core positions or nominal core positions of the plurality of cores; Equipped with the calculation unit moves the angular positions of the plurality of reference core positions or the acquired positions of the plurality of cores around the center of the fiber, and determines the sum of n-th powers (n is a number equal to or greater than 3) of the positional misalignment amounts of the plurality of cores, or the positional misalignment amount of each of the plurality of cores when the maximum positional misalignment amount among the positional misalignment amounts of the plurality of cores is minimum, as the measured positional misalignment amount.

10. a storage unit that stores the positions of a plurality of cores of the multi-core optical fiber; a calculation unit that calculates a plurality of indicator core positions of the plurality of cores; Equipped with the calculation unit moves the angular positions of the acquired core positions around the fiber center, and determines the multiple core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the multiple cores from multiple reference core positions that are design core positions or nominal core positions, or the maximum positional deviation amount among the positional deviations of the multiple cores, is minimum, as the multiple measured index core positions, or The calculation unit moves the angular positions of the plurality of reference core positions around the center of the fiber to obtain the plurality of reference core positions when the sum of n-th powers (n is a number equal to or greater than 3) of the positional deviations of the plurality of cores from the plurality of reference core positions or the maximum positional deviation amount among the positional deviations of the plurality of cores is smallest, and the positions of the plurality of cores when the positions of the plurality of cores are moved in the opposite direction by the same angle as the movement angle from the original positions of the plurality of reference core positions are set as the measured plurality of index core positions.

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