Method for inspecting optical fiber, optical fiber inspection device, and method for manufacturing optical fiber winding reel

Abstract

An inspection method for an optical fiber (1) consisting of a bare optical fiber (1N) and a light-transmitting cladding layer (12) covering the outer peripheral surface of the bare optical fiber (1N) includes: an irradiation step (S1) in which directional illumination light (L) is irradiated onto the outer peripheral surface (30s) of a winding body (30) formed by winding the optical fiber (1) in a multi-layer winding manner on a spool (20); an image data generation step (S2) in which the illumination light (L) reflected by the winding body (30) is received and image data is generated, the image data including at least a portion of an image (IM) of the illumination light (L); and an inspection step (S3) in which, based on the image data, it is determined whether there is a stripe pattern (SP) in the image (IM) in which the state of the illumination light (L) repeats along the winding direction of the optical fiber (1).

Description

Technical Field

[0001] This invention relates to a method for inspecting optical fibers, an apparatus for inspecting optical fibers, and a method for manufacturing an optical fiber winding spool. Background Technology

[0002] Conventionally, optical fibers are known to have a cladding layer covering the outer periphery of the bare fiber. Furthermore, optical fibers are typically inspected before leaving the factory. Inspection methods for optical fibers include, for example, using an OTDR (Optical Time Domain Reflectometer) to check for optical characteristics and defects such as damage to the cladding layer. For instance, Patent Document 1 describes an inspection method for detecting cladding layer defects.

[0003] Regarding the inspection method in Patent Document 1 below, light is irradiated onto a wound body formed by winding optical fibers in multiple layers onto a spool, and image data of the light reflected by the wound body is obtained. Image processing is then performed on the image data to detect defects such as bubbles in the cladding layer.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6585056 Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] The inspection method described in Patent Document 1 detects defects such as bubbles in the cladding layer, i.e., defects in the cladding layer that are locally generated along the length of the optical fiber. However, there are also cases where defects in the cladding layer are continuously generated along the length of the optical fiber. For example, a defect such as the outer peripheral surface of the cladding layer being a wavy surface that bends along the length of the optical fiber needs to be detected.

[0009] Therefore, the object of the present invention is to provide a method for inspecting optical fibers, an apparatus for inspecting optical fibers, and a method for manufacturing optical fiber winding spools, which can detect defects that are continuously generated along the length direction of the optical fiber.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the present invention provides an inspection method for an optical fiber consisting of a bare optical fiber and a transparent cladding layer covering the outer peripheral surface of the bare optical fiber. The method comprises: an illumination step of irradiating the outer peripheral surface of a wound body formed by winding the optical fiber in a multi-layered manner with directional illumination light; an image data generation step of receiving the illumination light reflected from the wound body and generating image data, the image data including at least a portion of an image of the illumination light; and an inspection step of determining, based on the image data, whether there is a stripe pattern in the image in which the state of the illumination light repeats along the winding direction of the optical fiber.

[0012] Furthermore, in order to achieve the above-mentioned objective, the optical fiber inspection apparatus of the present invention is characterized by comprising: an illumination unit that irradiates directional illumination light onto the outer peripheral surface of a wound body formed by winding an optical fiber in a multi-layer winding manner, the optical fiber being composed of bare optical fiber wire and a light-transmitting cladding layer covering the outer peripheral surface of the bare optical fiber wire; an image data generation unit that receives the illumination light reflected by the wound body and generates image data, the image data including at least a portion of an image of the illumination light; and an inspection unit that determines, based on the image data, whether there is a stripe pattern in the image in which the state of the illumination light repeats along the winding direction of the optical fiber.

[0013] In this inspection method and apparatus, directional illumination light is irradiated onto the outer peripheral surface of the wound body, and image data is generated, which includes at least a portion of the image of the illumination light reflected by the wound body. The inventors have discovered that when the interface of the cladding layer is a surface that is wavy along the length of the optical fiber, a stripe pattern in the image of the illumination light generated as described above can be produced where the state of the illumination light, such as color or intensity, repeats along the winding direction of the optical fiber. Although the reason for this is not yet determined, it can be considered as follows: The outer peripheral surface of the wound body is the outer peripheral surface of the cladding layer of the outermost portion of the outermost layer of the optical fiber, and is the interface on the outside of the cladding layer. For the illumination light reflected by the interface of this portion of the cladding layer of the optical fiber, the light reflected at the concave portion and the light reflected at the convex portion adjacent to the concave portion have different propagation path lengths. When the illumination light contains a specific light whose path length difference is an integer multiple of the wavelength, the specific light reflected at the concave portion and the specific light reflected at the convex portion interfere with each other in a manner that mutually enhances their intensity. The difference in path length corresponds to the variation in the height of the concave and convex sections, which is typically not constant along the length of the fiber. Furthermore, the winding direction of the fiber on the winding body is the same as the length direction of the wound portion. Therefore, considering that the aforementioned interference occurs discontinuously along the winding direction of the fiber, a stripe pattern, such as color or intensity, is formed in the image of the reflected illumination light, showing a repeating pattern along the winding direction of the fiber.

[0014] Furthermore, in this inspection method and apparatus, since the cladding layer is translucent, the illumination light also enters the inner portion of the optical fiber that is closer to the outermost layer of the winding. Therefore, it is considered that the interface of the cladding layer in this inner portion will also reflect the illumination light in the same way as the outermost portion, forming a striped pattern in the image of the reflected illumination light. Considering that the illumination light reflected in the inner portion coincides with the illumination light reflected in the outermost portion, a striped pattern is formed in the overall image of these illumination lights, where the illumination light state, such as color or intensity, repeats and varies along the winding direction of the optical fiber. Furthermore, since the illumination light is reflected in both the outermost and inner portions of the optical fiber, the amount of illumination light reflected by the winding is greater than when the optical fiber is wound in a single layer. Therefore, it is considered that in this inspection method and apparatus, the striped pattern can be identifiable in the image data containing the overall image of the illumination light. In this inspection method and apparatus, the presence or absence of the striped pattern is determined based on the image data. Therefore, according to this inspection method and inspection device, it is possible to detect defects that are continuously generated along the length of the optical fiber, i.e., the interface of the cladding layer is a wavy and curved surface.

[0015] In addition, in the above-described inspection method, the angle between the direction of the illumination light illuminating the winding body in the illumination step and the direction of the illumination light reflected by the winding body in the image data generation step may be 30° or less.

[0016] In addition, in the above-described inspection method, when the angle between the direction of irradiating the illumination light onto the winding body in the irradiation step and the direction of receiving the illumination light reflected by the winding body in the image data generation step is set to φ (°), the band of the illumination light is included in a specific band with a width of 200 nm or more in the specified band WB (nm) represented by the following formulas (1) and (2).

[0017] WB≥2·0.1×10 3 ·sin((180°-Φ) / 2) / 1…(1)

[0018] WB≤2·1.0×10 3 ·sin((180°-Φ) / 2) / 3…(2)

[0019] The inventors of this case discovered that by employing such a structure, when the interface of the coating layer is a wavy surface with an unevenness of 0.1 μm to 1.0 μm in height, a stripe pattern can be generated in the image of the illumination light in the image data. Therefore, according to this inspection method, it is possible to detect cases where the interface of the coating layer is such a wavy surface.

[0020] In this case, the specific band may have a width of more than 300 nm in the specified band WB.

[0021] The inventors of this case discovered that by employing such a structure, when the interface of the coating layer is a wavy surface with an unevenness of 0.1 μm to 1.0 μm in height, it is possible to further generate a stripe pattern in the image of the illumination light in the image data. Therefore, according to this inspection method, it is possible to more appropriately inspect whether the interface of the coating layer is such a wavy surface.

[0022] In the above inspection method, the covering layer may be a multi-layer structure.

[0023] By employing this structure, illumination light irradiating the wound body can be reflected at the interfaces between the multiple layers constituting the cladding layer. Therefore, when the interface between these layers is a wavy surface along the length of the optical fiber, the stripe pattern caused by this unevenness can be included in the image of the illumination light reflected by the wound body. Thus, according to this inspection method, it is possible to detect cases where the interfaces between the multiple layers constituting the cladding layer are wavy surfaces.

[0024] Furthermore, the method for manufacturing the optical fiber winding spool of the present invention is characterized by comprising: a winding process in which an optical fiber consisting of a bare optical fiber and a light-transmitting cladding layer covering the outer periphery of the bare optical fiber is wound onto a spool in a multi-layer winding manner; and an inspection process in which the optical fiber wound onto the spool is inspected using the aforementioned optical fiber inspection method.

[0025] (III) Beneficial Effects

[0026] As described above, according to the present invention, a method for inspecting optical fibers, an apparatus for inspecting optical fibers, and a method for manufacturing optical fiber winding spools can be provided, which can inspect defects that are continuously generated along the length direction of the optical fiber. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing a wound body formed by winding an optical fiber onto a spool for inspection using the optical fiber inspection method according to an embodiment of the present invention.

[0028] Figure 2 It means Figure 1 The diagram shows the cross-section of the optical fiber perpendicular to its length direction.

[0029] Figure 3 This is a diagram that schematically illustrates the inspection apparatus of this embodiment.

[0030] Figure 4 From and Figure 3 Diagrams showing the optical fiber winding reel and illumination section viewed from different angles.

[0031] Figure 5 This is a flowchart illustrating the steps of the optical fiber inspection method according to this embodiment.

[0032] Figure 6 This is a schematic diagram illustrating an example of an image containing a portion of the image of illumination light reflected by the coil.

[0033] Figure 7 It is a cross-sectional view schematically showing the reflection state of illumination light on the wound body.

[0034] Figure 8 This is a flowchart illustrating the process of manufacturing the optical fiber winding reel according to this embodiment.

[0035] Figure 9 This is a diagram showing the manufacturing process of an optical fiber winding spool.

[0036] Figure 10 It is a graph showing the relationship between the wavelength of the illumination light and the height of the unevenness of the coating layer interface. Detailed Implementation

[0037] The following detailed description, with reference to the accompanying drawings, outlines embodiments of the optical fiber inspection method, optical fiber inspection apparatus, and optical fiber winding reel manufacturing method for implementing the present invention. The illustrative embodiments described below are intended to facilitate understanding of the invention and are not intended to limit its scope. The invention can be modified and improved upon without departing from its spirit. Furthermore, the dimensions of various components have been altered for ease of understanding in the accompanying drawings.

[0038] Figure 1 This diagram schematically illustrates a wound body formed by winding an optical fiber, which is inspected using the optical fiber inspection method of this embodiment, onto a spool. It also schematically illustrates an optical fiber winding spool consisting of a spool and the optical fiber wound on that spool. Figure 1 As shown, the spool 20 of this embodiment has: a cylindrical shaft 21, a first flange 22, a second flange 23, and a rib 24. The second flange 23 is disposed at one end of the shaft 21, the rib 24 is disposed at the other end of the shaft 21, and the first flange 22 is disposed between the second flange 23 and the rib 24.

[0039] Between the first flange 22 and the second flange 23 on the shaft 21, one side of the optical fiber 1 in the longitudinal direction is wound in a multi-layer winding manner. Additionally, the other side of the optical fiber 1 in the longitudinal direction is led out through a cut (not shown) provided in the first flange 22 and wound in a multi-layer winding manner between the first flange 22 and the rib 24 on the shaft 21, and wound in that location. By winding the optical fiber 1 in a multi-layer winding manner onto the spool 20 in this way, a wound body 30 is formed, and the spool 20 and the optical fiber 1 constitute an optical fiber winding spool 70. Furthermore, in a cross-section along the central axis 21a of the shaft 21, the optical fiber 1 is arranged in directions parallel to the central axis 21a and in directions perpendicular to the central axis 21a.

[0040] Furthermore, there are no particular limitations on the winding body 30 as long as the optical fiber 1 is wound on the spool 20 in a multi-layer winding manner. For example, the winding body 30 can also be a structure in which the optical fiber 1 is wound in a multi-layer winding manner only between the first flange 22 and the second flange 23 on the shaft 21. In this case, the rib 24 may not be formed on the shaft 21, and the first flange 22 may be located at the end opposite to the second flange 23 on the shaft 21.

[0041] Figure 2 It means Figure 1 The diagram shows a cross-section of fiber 1 perpendicular to its length direction. Figure 2 As shown, the optical fiber 1 is composed of a bare optical fiber 1N and a cladding layer 12 covering the outer peripheral surface of the bare optical fiber 1N. In this embodiment, the bare optical fiber 1N is composed of a fiber core 10 and a cladding layer 11 surrounding the outer peripheral surface of the fiber core 10. The fiber core 10 in a cross-section perpendicular to the length direction of the optical fiber 1 has a circular shape, and the fiber core 10 is disposed at the center of the cladding layer 11. In addition, the shape of the cladding layer 11 in this cross-section may also be non-circular, such as elliptical or polygonal, and the bare optical fiber 1N may have multiple fiber cores 10.

[0042] The refractive index of the fiber core 10 is higher than that of the cladding 11. In this embodiment, the fiber core 10 is made of silica glass with dopants such as germanium (Ge) added to increase the refractive index, and the cladding 11 is made of silica glass without any additives. Alternatively, the fiber core 10 may be made of silica glass with dopants added to increase the refractive index, and the cladding 11 may be made of silica glass with dopants such as fluorine (F) added to decrease the refractive index. Furthermore, the fiber core 10 may be made of silica glass without any additives, and the cladding 11 may be made of silica glass with dopants added to decrease the refractive index.

[0043] The coating layer 12 is composed at least of a light-transmitting resin, as described later, that transmits illumination light. Examples of resins constituting the coating layer 12 include thermosetting resins and UV-curable resins. In this embodiment, the coating layer 12 is free of coloring pigments and has a two-layer structure, consisting of an inner layer 12a covering the outer peripheral surface of the coating layer 11 and an outer layer 12b covering the outer peripheral surface of the inner layer 12a. Furthermore, the number of layers in the coating layer 12 is not particularly limited; the coating layer 12 can be a multilayer structure composed of three or more resin layers, or a single-layer structure composed of a single resin layer covering the outer peripheral surface of the coating layer 11.

[0044] The inspection device for optical fiber 1 in this embodiment will now be described.

[0045] Figure 3 This is a schematic diagram of the inspection apparatus of this embodiment, and is a view taken from a direction parallel to the central axis 21a of the shaft 21 of the reel 20. Figure 3 As shown, the main structure of the inspection device 40 includes: an illumination unit 50, an image data generation unit 55, an inspection unit 60, a display unit 65, and a control unit CO. The fiber optic winding spool 70 is placed on the mounting surface 35 such that the outer edges of the first flange 22 and the second flange 23 abut against the mounting surface 35. The inspection device 40 detects defects in the cladding layer 12 of the fiber optic cable 1 constituting the winding body 30.

[0046] The control unit CO can be, for example, a microcontroller, an integrated circuit (IC), a large-scale integrated circuit (LSI), an application-specific integrated circuit (ASIC), or an NC (numerical control) device. Furthermore, when the control unit CO employs an NC device, it may or may not use a machine learning machine. As explained below, some structures of the inspection device 40 are controlled by the control unit CO.

[0047] The illumination unit 50 is configured to irradiate directional illumination light L onto the outer peripheral surface 30s of the winding body 30. Figure 4 From and Figure 3 The diagram shows the optical fiber winding reel 70 and the illumination unit 50 viewed from different directions, specifically from a direction perpendicular to the central axis 21a of axis 21 and parallel to the horizontal direction. (See diagram for example.) Figure 3 , Figure 4As shown, in this embodiment, the illumination unit 50 is a row illumination unit comprising a plurality of light sources 51 arranged in a direction parallel to the central axis 21a. The illumination unit 50 is positioned above the winding body 30 such that, when the winding body 30 is viewed from above, the intersection point of the optical axis 51a of each light source 51 with the outer peripheral surface 30s of the winding body 30 is located on or near the central axis 21a. Furthermore, it is preferable that the angle between the tangent of the outer peripheral surface 30s at the aforementioned intersection point and the optical axis 51a is 30° or less. Additionally, in Figure 4 The description of the optical axis 51a is omitted. The illumination unit 50 emits illumination light L from each light source 51 according to a control signal from the control unit CO, and illuminates the outer peripheral surface 30s of the winding body 30 with the illumination light L. In this embodiment, the area on the outer peripheral surface 30s illuminated by the illumination light L is a linear region extending in a direction approximately parallel to the central axis 21a and approximately perpendicular to the winding direction of the optical fiber 1, and traversing the upper side of the outer peripheral surface 30s. Thus, a portion of the illumination light L illuminating the winding body 30 is reflected by the winding body 30.

[0048] Furthermore, directional light can be, for example, light emitted from a light source with a directional angle of ±40° or less, within that directional angle, which is sometimes referred to as the half-value angle or the reduced angle. Additionally, the optical axis 51a of the light source 51 is a straight line parallel to the emission direction of the strongest light emitted from the light source 51 and passing through the portion of that light emission point. In this embodiment, the light source 51 is an LED that emits white directional illumination light L, but the color of the illumination light L is not particularly limited.

[0049] Furthermore, the illumination unit 50 only needs to irradiate the outer peripheral surface 30s of the winding body 30 with directional illumination light L, and there are no particular restrictions on the structure of the illumination unit 50, the wavelength range of the illumination light L, or the type of the light source 51. For example, the illumination unit 50 may also include a collimating lens corresponding to the light source 51, and use the collimating lens to calibrate the light emitted from the light source 51. In addition, the illumination unit 50 may also include a light shield, which has a slit and covers the light source 51. In this case, the slit is shaped such that a portion of the light emitted from the light source 51 passes through and the passed light has the aforementioned directional angle.

[0050] The image data generation unit 55 has an imaging element (not shown) with a plurality of light-receiving elements arranged thereon, and is configured to generate image data of light incident from the incident surface 55s that receives light and projected onto the light-receiving surface of the imaging element. This image data consists of multiple pixel data representing the intensity or color of light received by each light-receiving element, and is information representing the distribution of the intensity or color of light incident on the light-receiving surface of the imaging element. For example, a camera equipped with a CCD image sensor or a CMOS image sensor can be cited as an example of such an image data generation unit 55. The image data generation unit 55 is configured such that illumination light L reflected by the winding body 30 is incident on the light-receiving surface of the imaging element and an image of illumination light L is projected onto that surface. In this embodiment, the image data generation unit 55 is configured to generate two-dimensional image data and is positioned above the winding body 30. For a straight line 55a passing through the center of the incident surface 55s and perpendicular to the incident surface 55s, the straight line 55a passes through the area on the outer peripheral surface 30s of the winding body 30 that is illuminated by the illumination light L. The intersection of this area and the straight line 55a is located between the first flange 22 and the second flange 23. Therefore, at least a portion of the image of the illumination light L reflected between the first flange 22 and the second flange 23 of the winding body 30 is projected onto the aforementioned illuminated surface. In addition, when viewed along the central axis 21a, the angle between the straight line 55a and the optical axis 51a of the light source 51 is 30° or less. Therefore, it can be understood that the angle between the direction in which the illumination unit 50 illuminates the winding body 30 with the direction in which the image data generation unit 55 receives the illumination light L reflected by the winding body 30 is 30° or less.

[0051] Furthermore, the image data generation unit 55 only needs to be able to generate image data that includes at least a portion of the image of the illumination light L reflected by the winding body 30. There are no particular limitations on the structure, configuration, or orientation of the image data generation unit 55. For example, the image data generation unit 55 may also be configured to generate image data that includes the entire image of the illumination light L reflected by the winding body 30. Alternatively, the angle between the direction in which the illumination unit 50 irradiates the illumination light L onto the winding body 30 and the direction in which the image data generation unit 55 receives the illumination light L reflected by the winding body 30 may be greater than 30°.

[0052] In this embodiment, the inspection unit 60 determines whether there are defects in the cladding layer 12 of the optical fiber 1 based on image data input from the image data generation unit 55, and outputs an electrical signal corresponding to the determination to the control unit CO. The inspection unit 60 in this embodiment uses a learning model pre-built through machine learning to perform this determination, which will be explained later. For example, a structure similar to that of the control unit CO can be used as an example of the structure of such an inspection unit 60.

[0053] The display unit 65 displays the inspection results, which are based on the determination of whether or not there are defects made by the inspection unit 60. For example, a liquid crystal display (LCD) can be used as the display unit 65.

[0054] The inspection method for optical fiber 1 in this embodiment will now be described.

[0055] Figure 5 This is a flowchart illustrating the steps of the inspection method for optical fiber 1 according to this embodiment. For example... Figure 5 As shown, the inspection method for optical fiber 1 in this embodiment includes: an illumination step S1, an image data generation step S2, and an inspection step S3.

[0056] <Irradiation Step S1>

[0057] This step involves irradiating the outer peripheral surface 30s of the wound body 30 with directional illumination light L. In this embodiment, the illumination unit 50 emits illumination light L from the light source 51 according to a control signal from the control unit CO, and irradiates the outer peripheral surface 30s of the wound body 30 with the illumination light L. A portion of the illumination light L is reflected by the wound body 30.

[0058] <Image data generation step S2>

[0059] This step involves receiving illumination light L reflected by the winding body 30 and generating image data, wherein the image data includes at least a portion of the image of the illumination light L. In this embodiment, as described above, the image data generation unit 55 is configured such that at least a portion of the image of the illumination light L reflected by the winding body 30 is projected onto the light-receiving surface of the imaging element. The image data generation unit 55 generates image data according to a signal from the control unit CO and outputs the image data, which includes at least a portion of the image of the illumination light L reflected by the winding body 30, to the inspection unit 60.

[0060] The inventors of this case discovered that when the interface of the cladding layer 12 of the optical fiber 1 is a surface that is wavy and curved along the length direction of the optical fiber 1, a stripe pattern in which the state of the illumination light repeats along the winding direction of the optical fiber 1 can be generated in the image of the illumination light in the image data generated as described above.

[0061] Figure 6 This is a schematic diagram illustrating an example of an image containing a portion of the image of illumination light L reflected by the coil 30. Figure 6 An image showing the striped pattern produced in this image is displayed. This image is based on image data generated by the image data generation unit 55. Figure 6 In this configuration, the winding direction of fiber 1 is approximately parallel to the vertical direction. Figure 6In the image IM of the illumination light L shown, region AR1 is the region with the highest light intensity, and region AR2 is the region with a lower light intensity than region AR1. Regions AR1 and AR2 are approximately white. Region AR1 is held in place by region AR2 along the winding direction of optical fiber 1. Multiple stripe patterns SP are formed within region AR2. These stripe patterns SP are stripe patterns that repeat along the winding direction of optical fiber 1, representing a state of illumination light L such as color or intensity.

[0062] Although the reason for the appearance of the striped pattern SP has not yet been determined, the following considerations can be made. Figure 7 This is a schematic cross-sectional view showing the reflection state of the illumination light L on the wound body 30, and it is a magnified cross-sectional view showing the area near the outer peripheral surface 30s of the wound body 30, and it is a cross-sectional view along the winding direction of the optical fiber 1. The outer peripheral surface 30s of the wound body 30 is the outer peripheral surface 12s of the cladding layer 12 of the outermost part of the outermost layer of the optical fiber 1 in the wound body 30, and this outer peripheral surface 12s is the interface on the outside of the cladding layer 12. Figure 7 As shown, the path lengths of the light Lc reflected from the outermost peripheral surface 12s of the illumination light L, the light Ls reflected from the concave portion 12sc, and the light Ls reflected from the convex portion 12ss adjacent to the concave portion 12sc, are different. When the angle of the sum of the incident angle and the reflection angle of these lights Lc and Ls is set to φ (°), and the height of the concave and convex portions is set to d (μm), the difference in the path lengths of these lights Lc and Ls is approximately 2d·sin((180°-φ) / 2). Furthermore, since the image data generation unit 55 receives the illumination light L reflected from the winding body 30, it can be understood that the aforementioned angle φ is the angle between the direction in which the illumination unit 50 irradiates the illumination light L onto the winding body 30 and the direction in which the image data generation unit 55 receives the illumination light L reflected from the winding body 30. If the wavelengths of light Lc and Ls are set to λ (nm), then when the difference in the path lengths described above is related by the following equation (3), these light beams Lc and Ls interfere with each other in a way that enhances their intensity. Furthermore, n is a natural number.

[0063] nλ=2d·sin((180°-φ) / 2)…(3)

[0064] In other words, when the difference in path length is an integer multiple of the wavelengths of light Lc and Ls, that is, when the illumination light L contains light Lc and Ls of such wavelengths, these light Lc and Ls interfere with each other in a way that enhances each other's intensity.

[0065] The difference in path length corresponds to the variation in the height d of the concave and convex parts, which is typically not constant along the length of the optical fiber. Furthermore, the winding direction of the optical fiber 1 on the winding body 30 is the same as the length direction of the wound portion of the optical fiber 1. Therefore, considering that the aforementioned interference occurs discontinuously along the winding direction of the optical fiber 1, a stripe pattern is formed in the image of the reflected illumination light L, where the state of the illumination light L, such as color or intensity, repeats along the winding direction of the optical fiber.

[0066] Furthermore, in this embodiment, since the cladding layer 12 is translucent, the illumination light L is also incident on the inner portion of the optical fiber 1, which is located inside the outermost portion of the outermost layer of the winding body 30. Therefore, it is considered that the interface of the cladding layer 12 in this inner portion, i.e., the outer peripheral surface 12s, will also be reflected by the illumination light L in the same way as the outermost portion, forming a striped pattern in the image of the reflected illumination light L. Considering that the illumination light L reflected in this inner portion coincides with the illumination light L reflected in the outermost portion, a striped pattern is formed in the overall image of these illumination light Ls, where the state of the illumination light L, such as color or intensity, repeats and varies along the winding direction of the optical fiber. Furthermore, since the illumination light L is reflected in both the outermost and inner portions of the optical fiber 1, the amount of illumination light L reflected by the winding body 30 is greater than when the optical fiber 1 is wound in a single layer. Therefore, it is considered that in this embodiment, the striped pattern can be displayed in a recognizable manner in the image data containing the overall image of the illumination light L.

[0067] Here, according to the above equation (3), it can be seen that the height d of the concave-convex surface that produces such interference is different depending on the wavelength of the light Lc and Ls. As mentioned above, the height d of the concave-convex surface is not constant in the length direction of the optical fiber. In this embodiment, the illumination light L irradiating the winding body 30 is white. Therefore, for example, a striped pattern of blue light and a striped pattern of red light can be reflected in the image data. Therefore, a striped pattern that repeats along the winding direction of the optical fiber 1 and changes in color can be reflected in the image data. Furthermore, for example, when the illumination light L is blue, a striped pattern in which the intensity of blue light changes in a repeating and increasing manner along the winding direction of the optical fiber 1 can be reflected in the image data.

[0068] <Inspection Step S3>

[0069] This step is based on the image data generated by the image data generation step S2 to determine whether there is a stripe pattern SP in the image IM of the illumination light L reflected by the winding body 30, in which the state of the illumination light L changes repeatedly along the winding direction of the optical fiber 1. In this embodiment, the inspection unit 60 uses a learning model pre-built by machine learning to determine whether the stripe pattern SP is present. The learning model in this embodiment is constructed from multiple image data generated in the same way as the image data generation step S2 described above, that is, from multiple learning image data that reflect the stripe pattern SP caused by the outer peripheral surface 12s of the cladding layer 12 being a wavy curved surface. Therefore, the machine learning used to construct this learning model is teacher-trained learning. When the inspection unit 60 determines that there is a stripe pattern SP in the image IM of the illumination light L in the image data generated by the image data generation step S2, it outputs a signal indicating that the cladding layer 12 is defective to the control unit CO. On the other hand, when the inspection unit 60 determines that there is no stripe pattern SP, it outputs a signal indicating that the cladding layer 12 is defect-free to the control unit CO.

[0070] Furthermore, there are no particular limitations on the image data used for learning. For example, the image data used for learning may include: image data generated by the winding body 30 of the optical fiber 1 whose outer peripheral surface of the cladding layer 12 is not a wavy, curved surface that causes defects; that is, multiple good image data in the image IM of the illumination light L that do not contain the stripe pattern SP. Additionally, by appropriately changing the image data used for learning, the criteria by which the inspection unit 60 determines the presence or absence of the stripe pattern SP can be adjusted. For example, the inspection unit 60 can determine that the stripe pattern SP is present when the change in the intensity of the light of the stripe pattern SP is greater than or equal to a predetermined amount.

[0071] The control unit CO outputs a control signal to the display unit 65 corresponding to the signal input from the inspection unit 60, causing the display unit 65 to display the inspection result. This is used to inspect for defects in the cladding layer 12 of the optical fiber 1, specifically whether the outer peripheral surface 12s, which serves as the interface of the cladding layer 12, is a surface that is wavy and curved along the length direction of the optical fiber 1.

[0072] The manufacturing method of the optical fiber winding spool of this embodiment will be described next.

[0073] Figure 8 This is a flowchart illustrating the process of manufacturing the optical fiber winding spool according to this embodiment. Figure 9 This is a diagram showing the manufacturing process of an optical fiber winding spool. For example... Figure 8 As shown, the manufacturing method of the optical fiber winding spool of this embodiment includes: optical fiber manufacturing process P1, winding process P2, and inspection process P3.

[0074] <Fiber Optic Manufacturing Process P1>

[0075] As a preparatory stage for this process, firstly, a roughly cylindrical fiber optic preform 1P is prepared. This fiber optic preform 1P consists of a rod-shaped core glass body that forms the core 10, and a cladding glass body that surrounds the outer peripheral surface of the rod-shaped core glass body and forms the cladding 11. Furthermore, as... Figure 9 As shown, the optical fiber preform 1P is placed in the spinning furnace 110, and the heating section 111 of the spinning furnace 110 is heated to heat the optical fiber preform 1P. At this time, the lower end of the optical fiber preform 1P becomes molten, and glass filaments are drawn from the lower end. The drawn glass filaments solidify immediately upon being drawn from the spinning furnace 110, the core glass body becomes the core 10, the cladding glass body becomes the cladding 11, and it becomes a bare optical fiber 1N composed of the core 10 and the cladding 11. The bare optical fiber 1N drawn from the optical fiber preform 1P is cooled to an appropriate temperature by the cooling device 120.

[0076] Next, resin, forming the inner layer 12a of the cladding layer 12, is coated onto the outer peripheral surface of the bare optical fiber 1N using the first coating section 131, and the resin is cured using the first curing section 132, thereby forming the inner layer 12a covering the outer peripheral surface of the cladding layer 11. Furthermore, resin, forming the outer layer 12b of the cladding layer 12, is coated onto the outer peripheral surface of the inner layer 12a using the second coating section 133, and the resin is cured using the second curing section 134, thereby forming the outer layer 12b covering the outer peripheral surface of the inner layer 12a. As a result, the bare optical fiber 1N becomes... Figure 2 The optical fiber 1 is shown. Furthermore, the first curing section 132 and the second curing section 134, for example, employ a structure that irradiates the resin with ultraviolet light when the resin being cured is a curable resin, and a structure that applies heat to the resin when the resin being cured is a thermosetting resin.

[0077] <Winding process P2>

[0078] This process involves winding the optical fiber onto a spool in multiple layers. For example... Figure 9 As shown, in this embodiment, the direction of the optical fiber 1 is changed by the steering pulley 140, and the winding section 150 rotates the spool 20 around the central axis 21a, thereby winding the optical fiber 1 onto the spool 20 and winding the optical fiber 1 on the spool 20 in a multi-layer winding manner. By winding the optical fiber 1 onto the spool 20 in this multi-layer winding manner, a winding body 30 is formed, and an optical fiber winding spool 70 composed of the spool 20 and the optical fiber 1 wound on the spool 20 is obtained.

[0079] <Inspection Procedure P3>

[0080] This process involves inspecting the optical fiber 1 wound on the reel 20 using the aforementioned optical fiber inspection method. For example... Figure 9As shown, in this embodiment, the illumination unit 50 and image data generation unit 55 of the aforementioned inspection device 40 are positioned above the spool 20, and the inspection device 40 is used to inspect the optical fiber 1 in the winding process P2. In this embodiment, the illumination unit 50 continuously illuminates the outer peripheral surface 30 of the winding body 30 with illumination light L for 30 seconds in the winding process P2, and the image data generation unit 55 generates image data at predetermined time intervals in the winding process P2. The image data includes at least a portion of the image IM of the illumination light L. In addition, the inspection unit 60 determines whether there is a stripe pattern SP in the image IM based on each image data generated by the image data generation unit 55, and displays the inspection result based on the determination on the display unit 65. In this way, an inspected optical fiber winding spool 70 is manufactured.

[0081] As described above, the inspection method for the optical fiber 1 in this embodiment includes: an illumination step S1, an image data generation step S2, and an inspection step S3. The optical fiber 1 is composed of a bare optical fiber 1N and a light-transmitting cladding layer 12 covering the outer peripheral surface of the bare optical fiber 1N. In the illumination step S1, a directional illumination light L is irradiated onto the outer peripheral surface 30s of a winding body 30 formed by winding the optical fiber 1 in multiple layers onto a spool 20. In the image data generation step S2, the illumination light L reflected by the winding body 30 is received and image data is generated, the image data including at least a portion of an image IM of the illumination light L. In the inspection step S3, based on the image data, it is determined whether there is a stripe pattern SP in the image IM where the state of the illumination light L repeatedly changes along the winding direction of the optical fiber 1.

[0082] Furthermore, the inspection apparatus 40 for the optical fiber 1 in this embodiment includes an illumination unit 50, an image data generation unit 55, and an inspection unit 60. The illumination unit 50 irradiates the outer peripheral surface 30s of the winding body 30 with directional illumination light L. The winding body 30 is formed by winding an optical fiber 1, consisting of a bare optical fiber 1N and a light-transmitting cladding layer 12 covering the outer peripheral surface of the bare optical fiber 1N, onto a spool 20 in a multi-layer winding manner. The image data generation unit 55 receives the illumination light L reflected by the winding body 30 and generates image data, which includes at least a portion of an image IM of the illumination light L. The inspection unit 60 determines, based on the image data, whether there is a stripe pattern SP in the image IM where the state of the illumination light L repeats along the winding direction of the optical fiber 1.

[0083] As described above, the inventors of this invention discovered that when the interface of the cladding layer 12 is a wavy surface along the length direction of the optical fiber 1, a stripe pattern SP in which the state of the illumination light L repeatedly changes along the winding direction of the optical fiber 1 can be generated in the image IM of the illumination light L in the image data generated as described above. Furthermore, in the inspection method and inspection apparatus 40 of this embodiment, it is determined whether the image data contains this stripe pattern SP. Therefore, according to the inspection method and inspection apparatus 40 of this embodiment, it is possible to detect defects that are continuously generated in the length direction of the optical fiber 1, i.e., the outer peripheral surface 12s of the interface of the cladding layer 12 is a wavy surface.

[0084] Here, Figure 10 This is a graph showing the relationship between the wavelength of the illumination light L and the height d of the unevenness of the interface of the cladding layer 12, and also a graph showing the relationships that satisfy the above equation (3). Furthermore, in Figure 10 The figure shows the relationship between the wavelength λ and the height d of the concavity / convexity, satisfying the above equation (3), when n is 1, 2, 3, and the angle φ is 10°, 20°, 30°. In the above equation (3), when n = 1, d = 0.1 (μm), and φ = 30 (°), λ is approximately 193 nm, and when n = 3, d = 1.0 (μm), and φ = 30 (°), λ is approximately 644 nm. Furthermore, in Figure 10 The text also records dashed lines representing λ = 193 nm and 644 nm. According to... Figure 10 For example, when the wavelength of the illumination light L includes 193nm to 644nm as a predetermined wavelength range and φ = 30 (°), and the interface of the cladding layer 12, i.e., the outer peripheral surface 12s, is a wavy surface with an unevenness and a height of 0.1μm or more and 1.0μm or less, a stripe pattern SP can be generated in the image IM of the illumination light L in the image data through at least one of the 1st, 2nd, and 3rd interferences. Furthermore, the 1st interference is the case where n = 1, and the 2nd and 3rd interferences are the cases where n = 2 and 3, respectively. Therefore, when checking whether the outer peripheral surface 12s of the cladding layer 12 is a surface with an unevenness and a height range, it is preferable that the wavelength of the illumination light L includes the aforementioned predetermined wavelength range. Furthermore, this predetermined wavelength range varies according to the angle φ. And, it is preferable that the wavelength of the illumination light L includes the predetermined wavelength range WB represented by the following formula (1) and the following formula (2). Furthermore, Equation (1) is the relationship when n = 1 and d = 0.1 μm (100 nm) in Equation (3), and Equation (2) is the relationship when n = 3 and d = 1.0 μm (1000 nm) in Equation (3). In addition, the unit of WB in Equations (1) and (2) is nm.

[0085] WB≥2·0.1×10 3 ·sin((180°-Φ) / 2) / 1…(1)

[0086] WB≤2·1.0×10 3·sin((180°-Φ) / 2) / 3…(2)

[0087] Furthermore, the height of the irregularities generated on the outer peripheral surface 12s is not constant along the length of the optical fiber 1. For example, when the height of the irregularities on the outer peripheral surface 12s includes any part in the range of 0.1 μm to 1.0 μm, there is a tendency for the height of the irregularities on the outer peripheral surface 12s to vary at least within the range of 0.1 μm to 1.0 μm. Therefore, if it is possible to detect irregularities within a portion of the range of 0.1 μm to 1.0 μm, it is possible to presume that irregularities of 0.1 μm to 1.0 μm have occurred. For example, it can be set such that the band of the illumination light L is a specific band with a width of 200 nm or more within the aforementioned specified band WB. In this case, it is possible to detect irregularities within approximately 50% of the range of 0.1 μm to 1.0 μm, and it is possible to roughly check whether irregularities of 0.1 μm to 1.0 μm have occurred. Furthermore, it is more preferable that the aforementioned specific band has a width of 300 nm or more. In this case, it is possible to detect approximately 80% of the unevenness in the range of 0.1μm to 1.0μm, and to more appropriately check whether unevenness in the range of 0.1μm to 1.0μm has occurred.

[0088] Furthermore, in this embodiment, the cladding layer 12 is a double-layer structure composed of an inner layer 12a and an outer layer 12b. Therefore, the illumination light L irradiated onto the winding body 30 can be reflected at the interface between the inner layer 12a and the outer layer 12b. Therefore, when the interface between these layers is a wavy surface along the length direction of the optical fiber 1, similarly to the outer peripheral surface 12s described above, the stripe pattern caused by this unevenness can be included in the image IM of the illumination light L reflected by the winding body 30. Therefore, according to the inspection method and inspection apparatus 40 of this embodiment, it is possible to detect cases where the interface between the inner layer 12a and the outer layer 12b constituting the cladding layer 12 is a wavy surface.

[0089] Furthermore, the manufacturing method of the optical fiber winding spool of this embodiment includes a winding process P2 and an inspection process P3. In the winding process P2, optical fiber 1 is wound on the spool 20 in a multi-layer winding manner. The optical fiber 1 is composed of a bare optical fiber 1N and a light-transmitting cladding layer 12 covering the outer peripheral surface of the bare optical fiber 1N. In the inspection process P3, the optical fiber 1 wound on the spool 20 is inspected using the aforementioned inspection method for optical fiber 1. In addition, the inspection process P3 is performed in the winding process P2. Therefore, according to the manufacturing method of the optical fiber winding spool 70 of this embodiment, defects in the cladding layer 12 of the optical fiber 1 can be detected in the winding process P2. Furthermore, the inspection process P3 preferably starts from a state where the optical fiber 1 has been wound with 5 or more layers, and more preferably from a state where it has been wound with 10 or more layers. This can suppress the situation where the outer peripheral surface of the shaft 21 of the spool 20 is seen through the light, and can make the stripe pattern SP generated in the image IM of the illumination light L clearly visible. In addition, the inspection process P3 can also be performed after the winding process P2.

[0090] The present invention has been described above using the above embodiments as examples, but the present invention is not limited thereto.

[0091] For example, in the above embodiment, an inspection apparatus 40 with one image data generation unit 55 was described as an example. However, the inspection apparatus 40 may also have multiple image data generation units 55. In this case, for example, these image data generation units 55 are configured such that the directions of the illumination light L reflected by the winding body 30 are different, and the inspection unit 60 determines whether there is a stripe pattern SP in the image data generated by each image data generation unit 55. By adopting such a structure, the detection accuracy of the inspection apparatus 40 can be improved. In addition, the inspection apparatus 40 may also have a rotating unit that rotates the winding body 30 about the central axis 21a of the axis 21 of the spool 20. By adopting such a structure, the image data generation unit 55 can generate multiple image data, which are obtained by changing the position of the illumination light L irradiating the winding body 30. Therefore, the inspection unit 60 can determine whether there is a stripe pattern SP in the image for each image data, thereby improving the detection accuracy of the inspection apparatus 40.

[0092] Furthermore, in the above embodiment, the image data generation unit 55 that generates two-dimensional image data was described as an example. However, the image data generation unit 55 can also generate one-dimensional image data. Examples of such an image data generation unit 55 include a line camera with light-receiving elements arranged in a row, and a light-receiving device that has light-receiving elements and moves in a direction not parallel to the propagation direction of the illumination light L reflected by the winding body 30 to scan the illumination light L. In addition, the stripe pattern SP described above is a stripe pattern in which the state of the illumination light L repeats along the winding direction of the optical fiber 1. Therefore, it is preferable that the light-receiving elements of the line camera are arranged in a direction substantially parallel to the winding direction of the optical fiber 1, and it is preferable that the light-receiving device scans in a direction substantially parallel to the winding direction of the optical fiber 1.

[0093] Furthermore, in the above embodiment, the inspection unit 60, which uses a learning model to determine the presence or absence of a striped pattern SP, was described as an example. However, there are no particular limitations on the method for determining the presence or absence of a striped pattern SP using the inspection unit 60. The inspection unit 60 can also determine the presence or absence of a striped pattern SP without using a learning model. For example, the inspection unit 60 can also determine the presence or absence of a striped pattern SP based on data obtained by performing a prescribed processing on the image data generated by the image data generation unit 55. For example, the inspection unit 60 can also determine that a striped pattern SP exists when the number of points in the image data that exceed a predetermined light intensity threshold is more than a predetermined number. In addition, the inspection unit 60 can also determine whether the ratio of the average light intensity of a predetermined number of points with higher light intensity to the average light intensity of a predetermined number of points with lower light intensity exceeds a predetermined threshold within a predetermined range of the image data, and perform this determination on the entire image data while avoiding the above range, and determine that a striped pattern SP exists when the ratio exceeds the threshold. In this way, the presence or absence of a striped pattern SP can be determined for the entire image data.

[0094] Furthermore, in the above embodiment, a coating layer 12 without coloring pigment was used as an example for explanation, but the coating layer 12 may also have coloring pigment. However, when the coating layer 12 is colorless, defects are easier to detect.

[0095] Furthermore, in the above embodiment, the winding process P2 is described as an example, in which the optical fiber 1 manufactured by the optical fiber manufacturing process P1 is wound on the spool 20 in a multi-layer winding manner. However, in the winding process P2, it is sufficient to simply wind the optical fiber 1 on the spool in a multi-layer winding manner. For example, the winding process P2 could also be a process of winding a portion of the optical fiber 1 wound on the spool onto another spool, or it could be a process of splitting a long optical fiber 1 into short optical fibers 1. Although the description based on the illustration is omitted, in such a winding process P2, the first spool is rotated around the central axis by the feed part, thereby feeding out the optical fiber 1 wound on the first spool. And, the second spool is rotated around the central axis by the take-up part, thereby taking in the optical fiber 1 fed from the first spool onto the second spool, and winding the optical fiber 1 on the second spool in a multi-layer winding manner. In this case, the winding process P2 is composed of, for example, an acceleration period during which the winding speed increases to a predetermined speed, a stabilization period during which the winding speed reaches the predetermined speed, and a deceleration period during which the winding speed decreases to zero. Furthermore, the inspection process P3 can be performed during the acceleration period, the stabilization period, the deceleration period, or after the winding process P2. Moreover, it is preferable to perform the inspection process P3 during the deceleration period. If the diameter of the winding body 30, which is composed of the optical fiber 1 wound on the second reel, is approximately 300 mm, it is preferable to perform the inspection process P3 at a rotational speed of 0.1 [round per sec (rps)] or less on the second reel. If the frame rate of the camera, which serves as the image data generation unit 55, is increased, shooting can be performed even during high-speed rotation. However, as the frame rate increases, flickering and insufficient light are prone to occur due to the structure of the illumination unit 50, resulting in a tendency for the stripe pattern SP to be difficult to clearly reflect in the captured image. Therefore, it is preferable to perform the inspection process P3 as described above. Furthermore, since increasing the frame rate tends to result in larger cameras, it is practically preferable to use a camera with a frame rate of 100fps or less. For example, when the diameter of the winding body 30 of the second reel is approximately 300mm and the rotation speed of the second reel is 0.1 rpm, the circumferential speed of the outer surface of the winding body 30 is approximately 94mm / s. Here, since each shot taken by a camera with a frame rate of 100fps takes 1 / 100s, the movement distance of the outer surface of the winding body 30 during one shot is approximately 0.94mm, which is less than 1mm. If the area reflected in the captured image is, for example, a square with a side length of 300mm, the aforementioned movement distance is approximately 0.3% of that side length, which is small enough to suppress the situation where the striped pattern SP is difficult to clearly reflect in the captured image.

[0096] As described above, according to the present invention, an inspection method for optical fibers, an inspection device for optical fibers, and a manufacturing method for optical fiber winding spools can be provided, which can detect defects continuously generated in the length direction of the optical fiber and can be applied to fields such as optical fiber communication.

Claims

1. A method for inspecting optical fibers, comprising an optical fiber bare wire and a transparent cladding layer covering the outer periphery of the optical fiber bare wire, characterized in that, have: The irradiation step involves irradiating the outer peripheral surface of a wound body formed by winding the optical fiber on a spool in a multi-layered manner with directional illumination light. The image data generation step involves receiving the illumination light reflected by the winding body and generating image data, which includes at least a portion of the image of the illumination light; as well as The inspection step involves determining, based on the image data, whether there is a stripe pattern in the image where the state of the illumination light repeats along the winding direction of the optical fiber, wherein the winding direction of the optical fiber on the winding body is the same as the length direction of the winding portion of the optical fiber, and the stripe pattern is generated when: the interface of the cladding layer has a wavy surface that bends along the length direction of the optical fiber, and the illumination light reflected from the interface of the cladding layer at the outermost part of the outermost layer of the optical fiber coincides with the illumination light reflected from the interface of the cladding layer at the innermost part of the cladding layer that is more inner than the outermost part.

2. The method for inspecting optical fibers according to claim 1, characterized in that, In the illumination step, the angle between the direction of the illumination light illuminating the winding body and the direction of the illumination light reflected by the winding body in the image data generation step is less than 30°.

3. The method for inspecting optical fibers according to claim 1 or 2, characterized in that, When the angle between the direction of the illumination light illuminating the winding body in the illumination step and the direction of the illumination light reflected by the winding body in the image data generation step is set as follows: When the illumination light band is included in a specific band with a width of 200 nm or more within the specified band WB represented by the following formulas (1) and (2), wherein, The unit for WB is °, and the unit for WB is nm. 。 4. The method for inspecting optical fibers according to claim 3, characterized in that, The specific band has a width of more than 300 nm in the specified band WB.

5. The method for inspecting optical fibers according to any one of claims 1 to 4, characterized in that, The coating layer has a multi-layer structure.

6. An inspection device for optical fibers, characterized in that, have: The illumination unit irradiates directional illumination light onto the outer peripheral surface of a wound body formed by winding optical fibers in a multi-layered manner onto a spool. The optical fibers consist of bare optical fibers and a light-transmitting cladding layer covering the outer peripheral surface of the bare optical fibers. An image data generation unit receives the illumination light reflected by the winding body and generates image data, the image data containing at least a portion of the image of the illumination light; as well as An inspection unit determines, based on the image data, whether there is a stripe pattern in the image where the state of the illumination light repeats along the winding direction of the optical fiber, wherein the winding direction of the optical fiber on the winding body is the same as the length direction of the winding portion of the optical fiber, and the stripe pattern is generated when: the interface of the cladding layer has a surface that is wavy along the length direction of the optical fiber, and the illumination light reflected from the interface of the cladding layer at the outermost part of the outermost layer of the winding body coincides with the illumination light reflected from the interface of the cladding layer at the innermost part of the innermost part of the outermost part.

7. A method for manufacturing an optical fiber winding spool, comprising: The winding process involves winding an optical fiber, consisting of a bare optical fiber and a transparent cladding layer covering the outer periphery of the bare optical fiber, onto a spool in a multi-layer winding manner; and The inspection process involves inspecting the optical fiber wound on the spool using the optical fiber inspection method according to any one of claims 1 to 5.

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