System for determining the marker position of multicore optical fibers

Abstract

The marker position of the MCF is determined based on a side view of the MCF that has only one marker. [Solution] The determination system includes means for capturing a first image and a second image showing the brightness distribution of the side surface of the MCF when viewed in a first direction and a second direction; means for determining the first center position of the MCF based on the brightness distribution in the second direction and determining the second center position of the MCF based on the brightness distribution in the first direction; means for determining a first brightness difference, which is the difference in brightness between two positions that are equally far from the first center position, and a second brightness difference, which is the difference in brightness between two positions that are equally far from the second center position; and means for determining the marker position in the second direction based on the first brightness difference and determining the marker position in the first direction based on the second brightness difference.

Description

Technical Field

[0001] The present disclosure relates to a technique for determining the position of a marker of a multi-core optical fiber (MCF) including a plurality of cores.

Background Art

[0002] To increase the transmission capacity, an MCF having a plurality of cores provided in a cladding is used. The plurality of cores are arranged, for example, at equal intervals on the circumference of a circle having a predetermined radius from the center of the MCF. To identify the rotational phase of the MCF, a marker having a refractive index different from that of the cladding and the core is provided in the MCF. The rotational phase of the MCF is specified by the position of the marker of the MCF (marker position). By determining the rotational phase of the MCF, each core of the MCF can be identified.

[0003] For example, when two MCFs are fused, it is necessary to identify the marker positions of the two MCFs to match the rotational phases of the two MCFs. At that time, the workability is improved if the marker position can be identified from the side view of each MCF instead of the cross-sectional view of each MCF. Patent Document 1 discloses a configuration for determining the rotational phase of an MCF based on the side view of the MCF by providing a plurality of markers in the MCF.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The marker provided in the MCF is usually one, and the configuration described in Patent Document 1 cannot be applied to an MCF having only one marker.

[0006] This disclosure provides a technique for determining the marker position of an MCF based on a side view of the MCF having only one marker. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a determination system for determining the marker position of a multicore optical fiber includes: a first imaging means for capturing a first image showing the brightness distribution of the side surface of the multicore optical fiber when viewed in a first direction orthogonal to the longitudinal direction of the multicore optical fiber; a second imaging means for capturing a second image showing the brightness distribution of the side surface of the multicore optical fiber when viewed in a second direction orthogonal to both the longitudinal direction and the first direction; and a center determination means for determining the first center position of the multicore optical fiber in the first image based on the brightness distribution in the second direction shown in the first image, and for determining the second center position of the multicore optical fiber in the second image based on the brightness distribution in the first direction shown in the second image. The device includes: a step; a difference determination means that determines the relationship between the first distance from the first center position and the first luminance difference in the second direction by determining the first luminance difference, which is the difference in luminance between two positions that are the same distance from the first center position in the luminance distribution in the second direction shown in the first image; and a position determination means that determines the marker position in the second direction based on the relationship between the first distance and the first luminance difference, and determines the marker position in the first direction based on the relationship between the second distance and the second luminance difference. [Effects of the Invention]

[0008] According to this disclosure, the marker position of an MCF can be determined based on a side view of the MCF having only one marker. [Brief explanation of the drawing]

[0009] [Figure 1] Diagram of the judgment system configuration. [Figure 2] Configuration diagram of the processing unit. [Figure 3] A diagram showing an example of the brightness distribution of a single line. [Figure 4] A diagram illustrating the direction of light propagation when emitted towards an optical fiber. [Figure 5] A diagram showing an example of the distribution of brightness differences. [Figure 6] A diagram showing an example of refractive index distribution. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features from the multiple features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0011] Figure 1 shows an example configuration of a determination system that determines the marker position of the MCF and, therefore, the rotational phase of the MCF, based on a side view. In the following description, the longitudinal direction of the optical fiber 5 is defined as the Z direction, and the two mutually orthogonal directions within the cross-section perpendicular to the Z direction are defined as the X direction and the Y direction (the X-axis and Y-axis directions in Figure 1). Also, X=0 and Y=0, that is, the position of the Z-axis, is defined as the center of the cross-section of the optical fiber 5. The optical fiber 5 has multiple cores (shaded areas in Figure 1) and markers (black circles in Figure 1) within its cladding.

[0012] Multiple cores are arranged at equal intervals on a circumference of a predetermined radius from the center of the optical fiber 5 in a cross-section. The optical fiber 5 may also have multiple cores arranged at equal intervals on a circumference of a first radius from its center, and multiple cores arranged at equal intervals on a circumference of a second radius from its center. More generally, the optical fiber 5 may have multiple cores arranged at equal intervals on two or more circumferences of different radii. The refractive index of the marker is different from that of the cladding and cores.

[0013] As shown in Figure 1, in the X direction, a light source 11 and an imaging unit 12 are positioned on both sides of the optical fiber 5. The light source 11 emits parallel light toward the optical fiber 5. The light that has passed through the optical fiber 5 is incident on the imaging unit 12. The imaging unit 12 captures an image showing the side of the optical fiber 5 as viewed in the -X direction of Figure 1, and outputs the image data of this image to the processing unit 4. In the following description, the image captured by the imaging unit 12 will be referred to as the "X side image". The X side image is an image showing the brightness distribution in the YZ plane of the transmitted light emitted by the light source 11 in the X direction and passed through the optical fiber 5.

[0014] Furthermore, as shown in Figure 1, a light source 21 and an imaging unit 22 are positioned on both sides of the optical fiber in the Y direction. The light source 21 emits parallel light toward the optical fiber 5. The light that has passed through the optical fiber 5 is incident on the imaging unit 22. The imaging unit 22 captures an image showing the side of the optical fiber 5 as viewed in the -Y direction in Figure 1, and outputs the image data of this image to the processing unit 4. In the following description, the image captured by the imaging unit 22 will be referred to as the "Y side image". The Y side image is an image showing the brightness distribution in the XZ plane of the transmitted light emitted by the light source 21 in the Y direction and passed through the optical fiber 5.

[0015] Figure 2 is a functional block diagram of the processing unit 4. The processing unit 4 may be configured to cause one or more processors in a device having one or more processors to execute an appropriate program.

[0016] The center determination unit 41 determines the center position (position on the Z-axis) of the optical fiber 5 in each of the X-side image and the Y-side image. FIG. 3 shows the luminance distribution of one line in the Y direction in the X-side image. Note that the vertical axis in FIG. 3 indicates luminance, and the horizontal axis indicates the position on the Y-axis. As shown in FIG. 3, the luminance in the regions 61 and 62 on the Y-axis is lower than that in other regions. Hereinafter, the reason for the lower luminance in the regions 61 and 62 will be described using FIG. 4. In FIG. 4, the size (diameter) of the optical fiber 5 is assumed to be 2B.

[0017] As shown in FIG. 4, among the light emitted from the light source 11, the light traveling in the X direction at the position of Y = 0 mainly travels straight through the optical fiber 5 and enters the imaging unit 12. The light traveling in the X direction within the range where the absolute value of the Y value is within A is refracted when entering and exiting the optical fiber 5 due to the difference in refractive index between air and the optical fiber 5, and travels in a direction different from the X direction and enters the imaging unit 12. On the other hand, the light that reaches the surface of the optical fiber 5 within the range where the absolute value of the Y value is greater than A is totally reflected on the surface of the optical fiber 5 and does not enter the imaging unit 12. Note that within the range where the absolute value of the Y value is greater than B, the light travels along the X direction and enters the imaging unit 12. The regions 61 in FIG. 4 and the regions 62 in FIG. 4 are caused by the light from the light source 11 being totally reflected by the optical fiber 5 and thus not entering the imaging unit 12.

[0018] The center determination unit 41 determines, for example, the ends of the regions 61 and 62 where the light from the light source 11 does not reach the imaging unit 12 based on the luminance distribution. As an example, the center determination unit 41 determines the position where the luminance value first becomes less than or equal to the threshold value along the Y direction as the first end on the side opposite to the region 62 of the region 61. Also, the center determination unit 41 determines the position where the luminance value first becomes less than or equal to the threshold value along the -Y direction as the second end on the side opposite to the region 61 of the region 62. Then, the center determination unit 41 can determine the center of the first end and the second end as the center position of the optical fiber 5 in the X-side image. Note that the threshold value for determining the first end and the second end can be set based on the overall luminance distribution in the Y direction.

[0019] Further, the center determination unit 41 determines that the position where the luminance value first becomes equal to or greater than the threshold value after first becoming equal to or less than the threshold value along the Y direction is the first end on the region 62 side of the region 61. Similarly, the center determination unit 41 determines that the position where the luminance value first becomes equal to or greater than the threshold value after first becoming equal to or less than the threshold value along the -Y direction is the second end on the region 61 side of the region 62. Then, the center determination unit 41 can determine the center position of the optical fiber 5 in the X side image as the center between the first end and the second end. The threshold value for determining the first end and the second end can be set based on the overall luminance distribution in the Y direction. The center determination unit 41 similarly determines the center position of the optical fiber 5 for the Y side image.

[0020] In the following description, the center position in the Y direction determined by the center determination unit 41 is set as the position where Y = 0. Therefore, a position downstream in the Y direction from the center position in the Y direction has a positive Y value, and hereinafter, it is referred to as a positive-side position in the Y direction. Also, a position upstream in the Y direction from the center position in the Y direction has a negative Y value, and hereinafter, it is referred to as a negative-side position in the Y direction. The same applies to the X direction.

[0021] Returning to FIG. 2, the difference determination unit 42 obtains the difference in luminance (hereinafter referred to as luminance difference) between two positions (a positive-side position and a negative-side position) at the same distance in the Y direction from the center position determined by the center determination unit 41 for the X side image. The luminance difference is a signed value, not an absolute value, and can be obtained, for example, by subtracting the luminance of the negative-side position from the luminance of the positive-side position in the Y direction. Alternatively, the luminance difference can be obtained by subtracting the luminance of the positive-side position from the luminance of the negative-side position in the Y direction. The difference determination unit 42 similarly obtains the luminance difference between two positions at the same distance in the X direction from the center position determined by the center determination unit 41 for the Y side image.

[0022] Figure 5 shows the luminance difference determined by the difference determination unit 42 for each distance from the center position determined by the center determination unit 41. The dotted lines in Figure 5 show the relationship between the distance in the Y direction obtained from the X side image and the luminance difference, while the solid lines in Figure 5 show the relationship between the distance in the X direction obtained from the Y side image and the luminance difference.

[0023] The position determination unit 43 determines the position where the absolute value of the brightness difference is largest in the X direction, and determines the determined position as the marker position in the X direction. Note that if the brightness difference is calculated by subtracting the brightness of the negative position from the brightness of the positive position in the X direction, then if the brightness difference at the position with the largest absolute value is positive, the marker position in the X direction is on the positive side, and if the brightness difference at the position with the largest absolute value is negative, the marker position in the X direction is on the negative side. If the brightness difference is calculated by subtracting the brightness of the positive position from the brightness of the negative position in the X direction, then if the brightness difference at the position with the largest absolute value is positive, the marker position in the X direction is on the negative side, and if the brightness difference at the position with the largest absolute value is negative, the marker position in the X direction is on the positive side.

[0024] The position determination unit 43 determines the marker position in the Y direction in the same way as in the X direction. For example, the position determination unit 43 determines position XM in Figure 5 as the marker position in the X direction and YM as the marker position in the Y direction. If the brightness difference is calculated by subtracting the negative brightness from the positive brightness in both the X and Y directions, then position XM is the negative position and position YM is the positive position.

[0025] The center determination unit 41 determines the difference in brightness between two positions at the same distance from the center, and by calculating this difference, the brightness values ​​of the cladding and core cancel each other out, resulting in a lower brightness value. Therefore, the peak of the brightness difference represents the position of the marker, which has a different refractive index than the core and cladding. In this way, according to this embodiment, the marker position of the MCF can be determined based on a side view of the MCF, and thereby the rotational phase of the MCF can be determined.

[0026] In this embodiment, the absolute value of the marker position is determined by the position where the absolute value of the brightness difference is greatest. However, it is also possible to determine the full width at half maximum of the range including the position where the absolute value of the brightness difference is greatest, and set the center of this range as the absolute value of the marker position. In other words, the position determination unit 43 determines the marker positions in the X and Y directions based on the position where the absolute value of the brightness difference is greatest in each direction.

[0027] The X-side image is a two-dimensional image showing the luminance distribution of multiple lines in the Y direction. The center determination unit 41 can use the luminance distribution of any one of the multiple lines to determine the center position in the Y direction. Alternatively, the center determination unit 41 can calculate the statistical value of multiple luminance values ​​at the same position in the Y direction for each line, for example, the average value, and use this as the luminance distribution in the Y direction to determine the center position in the Y direction. The luminance difference used by the position determination unit 43 to determine the marker position can also be determined based on the luminance distribution of any one line in the Y direction, or based on the luminance distribution calculated by the center determination unit 41 using statistical values. The same applies to the Y-side image.

[0028] Furthermore, as explained using Figure 4, some light undergoes total internal reflection on the surface of the optical fiber 5. Therefore, a region is created inside the optical fiber 5 through which light emitted from the light source 11 and light emitted from the light source 21 do not pass. If the marker is located in this region, the marker's position cannot be determined. Therefore, the position determination unit 43 can determine that the marker is in a region inside the optical fiber 5 through which light does not pass, provided that a predetermined condition is met in at least one of the X and Y directions. The predetermined condition may be met, for example, when no maximum values ​​occur. Alternatively, the predetermined condition may be met when one maximum value occurs, but the absolute value of this maximum value is less than a predetermined value relative to the statistical value of the brightness difference, for example, the average value. Furthermore, the predetermined condition may be met when multiple maximum values ​​occur, and the difference between the absolute value of the largest maximum value and the absolute value of the second largest maximum value is less than a threshold. If the position determination unit 43 determines that there is a marker in a region within the optical fiber 5 where light does not pass, the optical fiber is rotated by a predetermined angle around the Z axis and the measurement is performed again.

[0029] <Second Embodiment> In the first embodiment, the imaging units 12 and 22 captured two brightness images in mutually orthogonal directions to determine the marker position. In this embodiment, a refractive index measuring device is used instead of the imaging units 12 and 22. For example, as shown in Figure 6, the refractive index measuring device, which is positioned in place of the imaging unit 12, can measure the refractive index distribution in the Y direction, and the refractive index measuring device, which is positioned in place of the imaging unit 22, can measure the refractive index distribution in the X direction. The refractive index distributions in the X direction and Y direction measured by the measuring devices are input to the processing device 4.

[0030] Since the refractive index of the marker is different from that of the core and cladding, the processing device 4 can determine the marker position in the X direction based on the refractive index distribution in the X direction, and the marker position in the Y direction based on the refractive index distribution in the Y direction. In Figure 6, reference numeral 71 corresponds to the marker position in the Y direction, and reference numeral 72 corresponds to the marker position in the X direction.

[0031] With the above configuration, the marker position of the MCF can be determined based on a side view of the MCF that has only one marker. Therefore, it becomes possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0032] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention. [Explanation of symbols]

[0033] 12, 22: Imaging unit, 41: Center determination unit, 42: Difference determination unit, 43: Position determination unit

Claims

1. A determination system for determining the marker position of a multicore optical fiber, A first imaging means captures a first image showing the brightness distribution on the side surface of the multicore optical fiber when the multicore optical fiber is viewed in a first direction perpendicular to the longitudinal direction of the multicore optical fiber, A second imaging means for capturing a second image showing the brightness distribution on the side surface of the multicore optical fiber when viewed in a second direction perpendicular to both the longitudinal direction and the first direction, A center determination means that determines the first center position of the multicore optical fiber in the first image based on the brightness distribution in the second direction shown in the first image, and determines the second center position of the multicore optical fiber in the second image based on the brightness distribution in the first direction shown in the second image, A difference determination means for determining the relationship between the first distance from the first center position and the first luminance difference in the second direction by determining the first luminance difference, which is the difference in luminance between two positions that are equally far from the first center position in the luminance distribution in the second direction shown in the first image, and for determining the relationship between the second distance from the second center position and the second luminance difference in the first direction by determining the second luminance difference, which is the difference in luminance between two positions that are equally far from the second center position in the luminance distribution in the first direction shown in the second image, Position determination means for determining the marker position in the second direction based on the relationship between the first distance and the first brightness difference, and for determining the marker position in the first direction based on the relationship between the second distance and the second brightness difference, A judgment system equipped with this feature.

2. The determination system according to claim 1, wherein the position determination means determines the marker position in the second direction based on the first distance at which the absolute value of the first brightness difference is maximized, and determines the marker position in the first direction based on the second distance at which the absolute value of the second brightness difference is maximized.

3. The determination system according to claim 2, wherein the position determination means determines a first half-width including the first distance at which the first luminance difference is maximized, determines the marker position in the second direction based on the center of the first half-width, determines a second half-width including the second distance at which the second luminance difference is maximized, and determines the marker position in the first direction based on the center of the second half-width.

4. The determination system according to claim 2 or 3, wherein the position determination means further determines the marker position in the second direction based on whether the first luminance difference with the largest absolute value is a positive or negative value, and further determines the marker position in the first direction based on whether the second luminance difference with the largest absolute value is a positive or negative value.

5. A first light source is provided on the side of the multicore optical fiber opposite to the first imaging means and emits light toward the first imaging means, A second light source is provided on the side of the multicore optical fiber opposite to the second imaging means and emits light toward the second imaging means, Furthermore, The determination system according to any one of claims 1 to 3, wherein the center determination means determines a first position in a first range and a second position in a second range in the brightness distribution in the second direction shown in the first image in which light from the first light source does not reach the first imaging means, determines a third position in a third range and a fourth position in a fourth range in the brightness distribution in the first direction shown in the second image in which light from the second light source does not reach the second imaging means, determines the first center position based on the first and second positions, and determines the second center position based on the third and fourth positions.

6. The first position is the position in the second direction where the luminance first falls below the first threshold, The second position is the position in the second direction where the luminance first falls below the first threshold, along the side opposite to the second direction. The third position is the position in the first direction where the luminance first falls below the second threshold, The determination system according to claim 5, wherein the fourth position is the position in the first direction where the luminance first falls below the second threshold, along the side opposite to the first direction.

7. The first position is the position in the second direction where the luminance first falls below the first threshold and then first exceeds the first threshold, The second position is the position in the second direction where the luminance first falls below the first threshold and then first exceeds the first threshold, along the side opposite to the second direction. The third position is the position in the first direction where the luminance first falls below the second threshold and then first rises above the second threshold, The determination system according to claim 5, wherein the fourth position is a position in the first direction where the luminance first becomes below the second threshold and then first becomes above the second threshold, along the side opposite to the first direction.

8. A determination system for determining the marker position of a multicore optical fiber, A first measuring means for measuring the first refractive index distribution on the side surface of the multicore optical fiber when the multicore optical fiber is viewed in a first direction perpendicular to the longitudinal direction of the multicore optical fiber, A second measuring means for measuring the second refractive index distribution on the side surface of the multicore optical fiber when the multicore optical fiber is viewed in a second direction perpendicular to both the longitudinal direction and the first direction, Position determination means for determining the marker position in the second direction based on the first refractive index distribution, and for determining the marker position in the first direction based on the second refractive index distribution, A judgment system equipped with this feature.

Images