Evaluation Method and Evaluation Apparatus for Multi-Core Optical Fiber

Abstract

The present invention provides an evaluation method and an evaluation device for a multi-core optical fiber, which can simply determine whether the structural parameters of the multi-core optical fiber meet the desired connection loss value (specification). In the observed cross-sectional structure of the multi-core optical fiber to be evaluated, the center coordinates of each core with the center coordinate when the cladding is approximated by a circle as the origin are measured, the lengths of the line segments connecting the origin and the centers of each core, and the angles formed by two line segments connecting the origin and two adjacent cores are obtained. Based on whether these values satisfy a specified determination formula, it is determined whether the desired connection loss characteristics are met.

Description

Technical Field

[0001] The present invention relates to an evaluation method and an evaluation apparatus for evaluating the structure of a multi-core optical fiber. Background Art

[0002] In current single-mode optical fibers or multi-mode optical fibers, in order to ensure interconnectivity, optical characteristics and geometric structure parameters are standardized (for example, refer to Non-Patent Documents 1 and 2). These disclosed optical fibers are single-core optical fibers having a core at the center of a cladding. For such optical fibers, test methods for evaluating the offset between the center of the cladding and the center of the core have also been disclosed (for example, refer to Non-Patent Documents 3 and 4).

[0003] Existing Patent Documents

[0004] Non-Patent Document 1: ITU-T G.652, “Characteristics of a single-mode fibre and cable,” 2016.

[0005] Non-Patent Document 2: ITU-T G.651.1, “Characteristics of a 50 / 125μm multimode graded index optical fibre cable for the optical access network,” 2018.

[0006] Non-Patent Document 3: ITU-T G.650.1, “Definitions and test methods for linear, deterministic attributes of single-mode fibre and cable,” 2018.

[0007] Non-Patent Document 4: JIS-C 6822, “Test method for optical fiber structure parameters - dimensional characteristics,” 2009.

[0008] Non-Patent Document 5: T. Matsui et.al., “118.5 Tbit / s Transmission over 316 km-Long Multi-Core Fiber with Standard Cladding Diameter”, OECC2017, 2-s2892, 2017.

[0009] Non-Patent Document 6: ITU-T L.12, "Construction, installation and protection of cables and other elements of outside plant," 2008.

[0010] Regarding the optical characteristics of a multi-core fiber (MCF) having multiple cores in a cladding, they can be evaluated for each core by the method shown in Non-Patent Document 3. On the other hand, the methods shown in Non-Patent Documents 3 and 4 assume that there is one core relative to the cladding and the core is arranged at the center of the cladding, and regarding the structural parameters, it is not limited to the evaluation of the offset between the center of the cladding and the center of the core. Therefore, the methods shown in Non-Patent Documents 3 and 4 cannot be applied to the MCF disclosed in Non-Patent Document 5. Therefore, in order to achieve the interconnection of MCFs that do not have a core at the center of the cladding, a method for evaluating the structural parameters of MCFs is required.

[0011] An optical fiber has a tolerance in the cladding diameter. For example, consider a four-core fiber in which four cores are formed with an adjacent core spacing of 40 μm in a cladding with a diameter of 125 μm. Even if the core arrangement is ideal, due to the change in the cladding diameter, the core spacing measured for each cross-section changes in a similar shape from 40 μm. Therefore, when connecting MCFs, it is necessary to calculate the core spacing based on the center coordinates of each core calculated according to the design value of the optical fiber, make the center coordinates of the cores change in a similar shape in accordance with the cladding diameter, and determine whether the connection loss satisfies the expected value (specification). Summary of the Invention

[0012] Therefore, an object of the present invention is to provide an evaluation method and an evaluation device for simply determining whether the structural parameters of an MCF satisfy an expected connection loss value (specification).

[0013] To achieve the above object, the evaluation method of the present invention makes a judgment based on whether the core center coordinates in the cross-section of the MCF are within a specified region obtained according to the expected connection loss.

[0014] Specifically, the first evaluation method of the present invention is characterized in that in a cross-section, N (N is an integer of 3 or more) cores are arranged at intervals of Λ to form an N-sided polygon, and the evaluation method of the multi-core fiber is as follows:

[0015] Observing the cross-section of the multi-core fiber using a camera;

[0016] Approximating the cladding of the multi-core fiber when observing the cross-section with a circle;

[0017] Taking the center coordinates of the circle as the origin and measuring the center coordinates of each of the cores located within the cladding; and

[0018] the length R of each line segment connecting the origin and the center coordinates of the core i (where i is the number of the core, a natural number not exceeding N) satisfies

[0019] r s -r d ≤R i ≤r s +r d

[0020] and within the range of

[0021] the angle θ formed by the line segments of adjacent cores i-j (where j is the number of the core adjacent to the core numbered i, a natural number not exceeding N) satisfies

[0022] θ s -θ d ≤θ i-j ≤θ s +θ d

[0023] it is determined that the desired connection loss characteristics are obtained.

[0024] Herein

[0025] [Mathematical formula 1]

[0026]

[0027] [Mathematical formula 2]

[0028]

[0029] [Mathematical formula 3]

[0030]

[0031] [Mathematical formula 4]

[0032]

[0033] [Mathematical formula 5]

[0034]

[0035] W i is the mode field radius of the core numbered i at the desired wavelength.

[0036] In addition, the second evaluation method of the present invention is characterized in that N (N is an integer of 3 or more) cores are arranged in a polygon at intervals of Λ in a cross section, and the evaluation method of the multi-core optical fiber is

[0037] Observing the cross-section of the multi-core optical fiber using a camera;

[0038] The cladding of the multi-core optical fiber when observing the cross-section by approximating it with a circle;

[0039] Taking the center coordinates of the circle as the origin, measuring the center coordinates of each of the cores located within the cladding; and

[0040] The offset δΛ between the designed center coordinates, which are the center coordinates of the cores in terms of design calculated by Mathematical Formula 6, and the measured center coordinates x Satisfying

[0041] δΛ x ≤r d

[0042] When this is the case, it is determined that the desired connection loss characteristics are obtained.

[0043] [Mathematical Formula 6]

[0044]

[0045] Wherein,

[0046] r = R i -r s ,

[0047] θ = θ i-j -θ s ,

[0048] R i is the length of each line segment connecting the origin and the center coordinates of the core (i is the number of the core, a natural number not exceeding N),

[0049] θ i-j is the angle formed by the line segments of adjacent cores (j is the number of the core adjacent to the core with number i, a natural number not exceeding N).

[0050] In addition, the evaluation device of the present invention includes:

[0051] The camera for observing the cross-section of the multi-core optical fiber; and

[0052] A processor for performing the evaluation method of the multi-core optical fiber,

[0053] The evaluation device determines whether the multi-core optical fiber has the desired connection loss characteristics.

[0054] In the evaluation method of the MCF of the present invention, the outer diameter of the cladding is approximated by a circle, with the center coordinate of the cladding as the origin, and it is determined according to whether the coordinates of the center of each of the multiple cores located within the cladding from the designed core interval are within the desired range. Therefore, it is possible to simply determine based on the cross-section of the MCF whether the connection loss is suppressed to the desired value when connecting MCFs to each other.

[0055] Therefore, the present invention can provide an evaluation method and an evaluation device for simply determining whether the structural parameters of the MCF meet the desired connection loss value (specification).

[0056] In addition, the above-mentioned inventions can be combined as much as possible.

[0057] The present invention can provide an evaluation method and an evaluation device for simply determining whether the structural parameters of the MCF meet the desired connection loss value (specification). BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a diagram illustrating the cross-section of an optical fiber. (a) is a single-core optical fiber, and (b) is a multi-core optical fiber.

[0059] Figure 2 It is a diagram illustrating the cross-section of an optical fiber. (a) illustrates the core arrangement of a four-core optical fiber, and (b) illustrates the offset δΛx of the core position.

[0060] Figure 3 It is a diagram illustrating the distribution of the connection loss (connection loss characteristic) of a four-core optical fiber.

[0061] Figure 4 It is the result of calculating the average loss and the occurrence probability of the maximum loss being 0.2 dB or less with respect to the offset of the core in a four-core optical fiber.

[0062] Figure 5 It is a flowchart illustrating the evaluation method of the multi-core optical fiber of the present invention.

[0063] Figure 6 It is a diagram illustrating the cross-section of an optical fiber. (a) illustrates the circumferential core position offset, and (b) illustrates the radial core position offset.

[0064] Figure 7 It is a diagram illustrating the distribution of the connection loss (connection loss characteristic) of a four-core optical fiber.

[0065] Figure 8 It is a flowchart illustrating the evaluation method of the multi-core optical fiber of the present invention.

[0066] Figure 9 It is a diagram illustrating the offset δΛx of the core position on the cross-section of the optical fiber.

[0067] Figure 10This is a diagram illustrating an evaluation apparatus for a multi-core optical fiber of the present invention.

[0068] Figure 11 This is a diagram illustrating a fiber holding section of an evaluation apparatus for a multi-core optical fiber of the present invention. (a) is a top view, and (b) is a side view. Detailed Embodiments

[0069] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In addition, in this specification and the drawings, components having the same reference numerals represent the same components.

[0070] Before describing each embodiment, the structure of the MCF will be described. In an MCF having N cores with a core pitch Λ, the angle θs [degrees] formed by two cores adjacent to the center of the cladding is determined by Equation (1).

[0071] [Mathematical Formula 1]

[0072]

[0073] In addition, the distance rs from the center of the cladding to the center of the outer core is determined by Equation (2).

[0074] [Mathematical Formula 2]

[0075]

[0076] Figure 1 (a) of is a cross-sectional view of a currently used single-core optical fiber (SCF). As Figure 1 shown in (a) of, the SCF has a structure in which only one core 12 exists within the cladding 11 and the core 12 is disposed at the center C of the cladding 11. On the other hand, as Figure 1 shown in (b) of, the MCF has a plurality of cores 12 disposed within the cladding 11. Sometimes a core 12 is also disposed at the center C of the cladding 11, but in the present embodiment, an MCF in which no core 12 is disposed at the center C will be described. In addition, it is assumed that the optical characteristics of the cores in the MCF conform to G.652.D described in Non-Patent Document 1.

[0077] Figure 2 (a) of is a diagram illustrating a 4CF (4-Core Fiber: four-core optical fiber) in which four cores (12-1 to 12-4) are disposed at intervals of Λ within the cladding 11. In order to connect 4CFs to each other with low connection loss, it is necessary for the four cores (12-1 to 12-4) to be located at substantially the same positions between the respective 4CFs. However, as Figure 2 shown in (b) of, due to manufacturing deviations or the like, the positions of the respective cores (12-1 to 12-4) have a positional offset δΛ from the designed positions (13-1 to 13-4)x (x is any one of 1 to 4).

[0078] Here, in the 4CF designed with a core pitch Λ of 40 μm, the connection loss caused by the core position offset is calculated. In the calculation of the connection loss, the coupling efficiency η with respect to the axial offset d (μm) is calculated by Equation (3), and then the loss is calculated. In addition, in each core, as the position offset δΛ x (μm), the maximum position offset δmax from the designed core position is set, and values within δmax are randomly assigned.

[0079] [Mathematical formula 3]

[0080]

[0081] Here, W1 and W2 are the mode field radii of the respective connected 4CFs. That is, when the connected 4CFs are regarded as optical fiber 1 and optical fiber 2, the mode field radius of each core (12-1 to 12-4) of optical fiber 1 is W1, and the mode field radius of each core (12-1 to 12-4) of optical fiber 2 is W2.

[0082] Figure 3 is a graph showing the distribution of the calculated connection loss (connection loss characteristics). The parameters used in the calculation are as follows. When the cladding diameters of both optical fibers are 125 μm (without tolerance), and when the cladding diameter of one optical fiber is 125 μm and the other is 125 μm ± 1.0 μm (when the cladding diameters are different), δmax is set to 1.0 μm, 10,000 random position offsets are given, and the calculation is performed. The connection loss characteristics are represented by the occurrence probability (%) of the connection loss (maximum loss) of the magnitude shown on the horizontal axis (dB).

[0083] In the case without tolerance, it is the loss characteristic corresponding to the difference in the position offset δΛ of each core x difference. In the case of different cladding diameters, it is the loss characteristic that includes not only the difference in the position offset δΛ of each core x difference but also the random offset of the cladding diameter.

[0084] Here, Non-Patent Document 6 shows that in the fusion splicing of SMF according to the standard of Non-Patent Document 1, the occurrence probability of the average loss being 0.1 dB or less and the maximum loss being 0.2 dB or less is 97% such a standard. As Figure 3 such, whether in the case of different cladding diameters or without tolerance, the average loss and the maximum loss do not meet the above standards.

[0085] Figure 4It is a graph showing the calculation results of the average loss and the occurrence probability of the maximum loss below 0.2 dB with respect to δmax. The horizontal axis is δmax (μm), the first vertical axis is the average loss (dB), and the second vertical axis is the occurrence probability (%) of the maximum loss below 0.2 dB. The solid line is the result without tolerance, and the dashed line is the result with different cladding diameters. From Figure 4 It can be confirmed that without tolerance, δmax is below 0.7 μm, satisfying either the average loss or the maximum loss standard. With different cladding diameters (difference amount 1.0 μm), δmax is below 0.65 μm, satisfying either the average loss or the maximum loss standard.

[0086] From the above, it can be seen that in order to connect MCFs to each other with the loss standard shown in Non-Patent Document 6, it is effective to evaluate the deviation from the center coordinates of each core.

[0087] (Embodiment 1)

[0088] Figure 5 It is a flowchart showing the evaluation method of the MCF of this embodiment. This evaluation method is an evaluation method of a multi-core optical fiber in which N (N is an integer of 3 or more) cores are arranged at intervals Λ in a cross section to form an N-sided polygon. The characteristics of the multi-core optical fiber evaluation method are

[0089] observing the cross section of the multi-core optical fiber using a camera (Steps S01 to S03);

[0090] approximating the cladding of the multi-core optical fiber when observing the cross section with a circle (Step S04);

[0091] measuring the center coordinates of each of the cores located within the cladding with the center coordinates of the circle as the origin (Step S05); and

[0092] for the length R of each line segment connecting the origin and the center coordinates of the core i (i is the number of the core, a natural number not exceeding N) within

[0093] r s -r d ≤R i ≤r s +r d

[0094] within the range, and

[0095] for the angle θ formed by the line segments of adjacent cores i-j (j is the number of the core adjacent to the core numbered i, a natural number not exceeding N) within

[0096] θ s -θ d≤θ i-j ≤θ s +θ d

[0097] When it is within the range of, it is determined that the desired connection loss characteristic is obtained (Steps S06 to S11).

[0098] The method of this embodiment is a method for determining the core pitch that can achieve the reference connection loss characteristic regardless of the change in the cladding diameter.

[0099] This method first performs a process of measuring the structural parameters of the MCF. The MCF is cut using an optical fiber cutter or the like, and the cross-section is polished to form a horizontal plane (a plane perpendicular to the long side direction) (Step S01). Then, an image of the entire horizontal plane (image of the cladding) is obtained using a camera (Step S02), and further an image of the cores inside the cladding is obtained (Step S03). Then, the outer periphery of the cladding is approximated by a circle based on the image of the cladding, and its center coordinates and cladding diameter are calculated (Step S04). In addition, each core is also approximated by a circle, and its respective center coordinates are calculated (Step S05). In addition, the center of the cladding and the center positions of the respective cores can be obtained, for example, by the measurement methods shown in Non-Patent Documents 3 and 4.

[0100] The measurement process ends at Step S05.

[0101] This method then performs a process of determining whether the measured structural parameters of the MCF are within the reference. First, it is determined whether the cladding diameter is within the reference (Step S06). If the cladding diameter is outside the reference ("No" in Step S06), it is determined as defective (Step S11). If the cladding diameter is within the reference ("Yes" in Step S06), with the cladding center coordinates as the origin (0, 0), the center coordinates on the end face image of each measured core are transformed into coordinates with the cladding center as the origin (Step S07). This step is based on the following reason. Since there is a case where the end face image of the MCF obtained in Step S02 has the center of the entire image or any one of the four corners of the screen as the origin, the coordinate positions of each core are shifted in order to perform this determination process so that the cladding center becomes the origin.

[0102] Next, it is determined whether the length R i (μm) of the line segment between the cladding center and the center of each core obtained from the image relative to the length r s (μm) of the line segment between the cladding center and the center of each core in the design is within the specified range r d (μm) (Step S08, regarding r s and r d refer to Figure 6 of (b)). If the length R iOutside the range (No in step S08), it is determined as defective (step S11).

[0103] If the length R i Within the range (Yes in step S08), the next determination is made (step S09). Let the line segment connecting core i and the origin be the first line segment, and the line segment connecting core j adjacent to the core i and the origin be the second line segment. Let the angle formed by the first line segment and the second line segment obtained from the image be θ i-j [degrees]. Determine the angle θ i-j Relative to the angle θ s [degrees] formed by the first line segment and the second line segment in the design d Is it within the specified range θ s And θ d Refer to Figure 6 Of (a)). If the angle θ i-j Is within the range (Yes in step S09), it is determined as a good structure and the process ends (step S10). On the other hand, if the angle θ i-j Is outside the range (No in step S09), it is determined as defective (step S11).

[0104] The determination process ends with step S10 or step S11.

[0105] The tolerance r d And the angular tolerance θ d Are determined by equations (4) and (5).

[0106] [Mathematical formula 4]

[0107]

[0108] [Mathematical formula 5]

[0109]

[0110] W i Is the mode field radius of the core numbered i at the desired wavelength. η is the same as the coupling efficiency described in equation (3), and the desired connection loss value (linear value) is substituted.

[0111] Figure 7 Is a graph showing the distribution (connection loss characteristics) of the connection loss when the MCFs selected as good by the above evaluation method are connected to each other.

[0112] This connection loss characteristic is the result calculated under the following conditions: The MCF is a four-core optical fiber with Λ = 40 μm, and the mode field radii of each core are set to W1 = W2 = 8.6 μm, r s= 28.3 μm, θ s = 90 degrees, r d = 0.6 μm, θ d = 2.0 degrees, δmax = 0.8 μm. A 10,000 - time random position offset is given to the core. The meanings of the horizontal axis and the vertical axis are the same as those in Figure 3 the same.

[0113] From Figure 7 the results, it can be seen that if the determination process of Figure 5 is used to select MCFs, the loss criteria shown in Non - Patent Document 6 are satisfied. That is, by using the determination method of the present invention, MCFs that satisfy good connection characteristics can be selected.

[0114] In addition, an example of determining the end - face structure in a manner that satisfies the connection loss conditions described in Non - Patent Documents 3 and 4 is shown here. However, for other connection loss conditions, it is also possible to perform the determination in the same steps by obtaining the necessary core eccentricity as Figure 4 described.

[0115] (Embodiment 2)

[0116] Figure 8 is a flowchart for explaining the evaluation method of the MCF in this embodiment. This evaluation method is the same as the steps described in Figure 5 up to step S07. Therefore, only the parts different from Embodiment 1 will be described in this embodiment.

[0117] The feature of this evaluation method is that after step S07, when the offset δΛ x between the design center coordinates, which are the center coordinates of the core calculated by Mathematical Formula 6 as a design value, and the measured center coordinates

[0118] δΛ x ≤ r d

[0119] is satisfied, it is determined that the desired connection loss characteristics are obtained (steps S18 - S21, S10, S11).

[0120] The method of this embodiment is as follows: According to whether the measured core center position is within the allowable position offset with respect to the design core center position, it is determined whether the MCF satisfies the desired connection loss characteristics.

[0121] Figure 9 is a diagram for explaining the offset δΛ x between the design core center position and the measured core center position of the MCF. The offset δΛ x can be expressed by the following formula.

[0122] [Mathematical Formula 6]

[0123]

[0124] where r = R i -r s and θ = θ i-j -θ s respectively represent the offsets of the measurement results in the radial direction and circumferential direction relative to the design position.

[0125] In the determination process of this method, first, the length R i (μm) of the line segment connecting the cladding center and the center of each core obtained from the image is subtracted by the length r s (μm) of the line segment connecting the design cladding center and the center of each core, and the offset r in the radial direction is calculated for each core (step S18). Next, the angle θ i-j [degrees] formed by the first line segment and the second line segment obtained from the image is subtracted by the angle θ s [degrees] formed by the first line segment and the second line segment in the design, and the offset θ [degrees] in the circumferential direction is calculated for each core (step S19). Furthermore, the offset δΛ x is calculated for each core by Equation (6) (step S20).

[0126] Next, it is determined whether the offset δΛ x is within r d (refer to Equation (4)) obtained based on the allowable loss (step S21). If the offset δΛ x is within r d (“Yes” in step S21), it is determined as a good structure and the process ends (step S10). On the other hand, if the offset δΛ x is greater than r d (“No” in step S21), it is determined as defective (step S11).

[0127] The determination process ends with step S10 or step S11.

[0128] The evaluation method of this embodiment can perform determination by considering two offsets in the radial direction and circumferential direction simultaneously, so it is preferable.

[0129] (Embodiment 3)

[0130] Figure 10 This is a diagram illustrating the evaluation device 301 of this embodiment. The evaluation device 301 includes:

[0131] a camera 31 for observing the cross-section of the multi-core optical fiber 50; and

[0132] a processor 32 for performing the evaluation method described in Embodiment 1 or Embodiment 2

[0133] The evaluation device 301 determines whether the multi-core optical fiber 50 has the desired connection loss characteristics.

[0134] Use Figure 10 The evaluation device 301 will be further described. The evaluation device 301 also includes a light source 30, an optical fiber holding unit 32, and an objective lens 33. The camera 31 includes an image imager 31a, an optical image imager 31b, and a switching unit 34 that moves these imagers relative to the optical axis Lax. The light source 30 is a white light source such as a halogen lamp, and can also be condensed by a lens or the like as long as it can irradiate the entire cladding of the MCF 50. The optical fiber holding unit 32 horizontally arranges the MCF 50 and suppresses it so that the MCF 50 does not move. For example, as Figure 11 shown, the optical fiber holding unit 32 has a V-groove 32a, in which the MCF 50 is horizontally arranged, and has a jig (not shown) that suppresses the MCF 50 from above so that the MCF 50 does not move.

[0135] The objective lens 33 can also be structured as follows: It is a magnification that can photograph the entire cladding of the MCF 50, or even if it is a magnification that can only photograph a part, the image imager 31a or the optical image imager 31b can be made to act simultaneously through the switching unit 34, so as to photograph the entire cladding of the MCF 50.

[0136] The image imager 31a and the optical image imager 31b can photograph a range that fully satisfies the field of view of the objective lens 33. The image imager 31a can photograph the entire end face of the MCF 50. The optical image imager 31b can photograph the intensity distribution of the near-infrared light emitted from the core of the MCF 50.

[0137] The image imager 31a and the optical image imager 31b can be moved by the switch 34, and can be respectively arranged linearly with the light source 31, the MCF 50, and the objective lens 33 so that the optical axes are aligned. The switch 34 is, for example, a rail or a rotator. That is, by switching the image imager 31a and the optical image imager 31b through the switch 34, two end face images (an image of the entire end face of the MCF 50 and an image of the intensity distribution of the near-infrared light emitted from the core) can be photographed. The camera 31 is connected to the processor 32, and the two end face images obtained by the camera 31 are sent to the processor 32.

[0138] The processor 32 synthesizes the two end face images, measures the cladding diameter of the optical fiber and the center coordinates of each core, and evaluates based on Figure 5 or Figure 8 the determination process described. Therefore, the evaluation device 301 can easily determine whether the inspected MCF 50 has the desired connection loss characteristics.

[0139] In addition, the operations of the processor 32 can also be implemented by a computer and a program. The program can be recorded on a recording medium or provided via a network.

[0140] (Other Embodiments)

[0141] In the above embodiments, 4CF has been described. However, the number of cores of the MCF that can be evaluated is not limited to 4. As long as the number of cores of the MCF is 3 or more, it can be evaluated. In addition, in the above embodiments, an MCF without a core at the center of the optical fiber has been described. However, an MCF having a core at the center of the optical fiber can also be evaluated. In addition, an MCF in which the cores are arranged in a circular ring rather than a polygon can also be evaluated.

[0142] An MCF in which the cores are arranged in a hexagonal close-packed structure can also be evaluated using the outermost cores.

[0143] Description of Reference Numerals

[0144] 11: Cladding

[0145] 12, 12-1, 12-2, 12-3, 12-4: Cores

[0146] 13, 13-1, 13-2, 13-3, 13-4: Designed Core Positions

[0147] 30: Light Source

[0148] 31: Camera

[0149] 31a: Image Photographer

[0150] 31b: Optical Image Photographer

[0151] 32: Optical Fiber Holding Portion

[0152] 32a: V-Groove

[0153] 33: Objective Lens

[0154] 34: Switching Portion

[0155] 35: Processor

[0156] 50: Multi-Core Optical Fiber

[0157] 301: Evaluation Device

Claims

1. A method for evaluating a multi-core optical fiber, wherein N cores are arranged in an N-sided polygon with a pitch Λ in a cross-section, and N is an integer of 3 or more. The method for evaluating the multi-core optical fiber is characterized in that the cross-section of the multi-core optical fiber is observed using a camera; the cladding of the multi-core optical fiber when the cross-section is observed by circular approximation; with the center coordinates of the circle as the origin, the center coordinates of each of the cores located within the cladding are measured; and The length R of each line segment connecting the origin to the center coordinates of the core i At r s -r d ≤R i ≤r s +r d within the range of, and The angle θ formed by the line segments of the adjacent cores i-j at θ s -θ d ≤ θ i-j ≤ θ s + θ d within the range of, it is determined that the desired connection loss characteristics are obtained. wherein, i is the number of the core, which is a natural number not exceeding N, j is the number of the core adjacent to the core numbered i, which is a natural number not exceeding N, [Mathematical formula 1] [Mathematical formula 2] [Mathematical formula 3] [Mathematical formula 4] [Mathematical formula 5] d is the axis offset, η is the coupling efficiency of the core with respect to the axis offset, W i is the mode field radius of the core of number i at the desired wavelength.

2. A method for evaluating a multi-core optical fiber, wherein N cores are arranged in an N-sided polygon with a pitch Λ in a cross-section, and N is an integer of 3 or more. The method for evaluating the multi-core optical fiber is characterized in that the cross-section of the multi-core optical fiber is observed using a camera; the cladding of the multi-core optical fiber when the cross-section is observed by circular approximation; with the center coordinates of the circle as the origin, the center coordinates of each of the cores located within the cladding are measured; and The offset δΛ between the design center coordinates, which are the center coordinates of the core in terms of design calculated by mathematical formula 6, and the measured center coordinates x satisfies δΛ x ≤r d when, it is determined that the desired connection loss characteristics are obtained. [Mathematical formula 6] wherein, r＝R i -r s ， θ = θ i-j -θ s , R i is the length of each line segment connecting the origin and the center coordinates of the core, i is the number of the core, which is a natural number not exceeding N, θ i-j is the angle formed by the line segments of the adjacent cores, j is the number of the core adjacent to the core numbered i, which is a natural number not exceeding N, [Mathematical formula 1] [Mathematical formula 2] [Mathematical formula 3] [Mathematical formula 4] d is the axis offset, η is the coupling efficiency of the offset of the core relative to the axis, W i is the mode field radius of the core of number i at the desired wavelength.

3. An evaluation device, characterized in that comprising: a camera for observing the cross-section of the multi-core optical fiber; and a processor for performing the method for evaluating the multi-core optical fiber according to claim 1 or claim 2, and the evaluation device determines whether the multi-core optical fiber has the desired connection loss characteristics.

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