Test method and test system

Abstract

The present invention implements a fusion splicing method in which it is easy to know whether a fiber connection body having low coupling efficiency between cores has been obtained. A fusion splicing method (S1) comprises a post-fusion measurement step (S16) for specifying the position of a marker of one multi-core fiber (OF1) out of two multi-core fibers (OF1, OF2), end faces of which are fused to each other, from a direction in which a predetermined first shape appears in a graph representing the direction dependency of transmitted light intensity of the one multi-core fiber (OF1), and specifying the position of a marker of the other multi-core fiber (OF2) from a direction in which a predetermined second shape appears in a graph representing the direction dependency of transmitted light intensity of the other multi-core fiber (OF2).

Description

Inspection method and inspection system

[0001] The present invention relates to an inspection method and an inspection system for inspecting the state of a fusion splice between two optical fibers.

[0002] Fusion splicing is an example of a method for connecting optical fibers. Fusion splicing typically involves butting the end faces of two optical fibers together and heating and melting the butted end faces. When the end faces of the two optical fibers are solidified by natural cooling, the two optical fibers are fused together. Patent Document 1, for example, is an example of a document disclosing an optical fiber fusion splicing device and a fusion splicing method.

[0003] International Publication No. 2019 / 163150

[0004] In recent years, optical fibers having an anisotropic refractive index profile in their cross sections have been widely used. Examples include multicore fibers having multiple cores and PANDA (Polarization-Maintaining and Absorption-Reducing) fibers having polarization-maintaining functionality. Fusion splicing of such optical fibers requires rotational alignment prior to fusion splicing. Rotational alignment of two multicore fibers each having a marker for identifying the core number requires that the core positions of the two multicore fibers coincide with each other, and that the positional relationship of the markers satisfy a predetermined condition. Rotational alignment of two PANDA fibers each having a stress-applying portion for achieving polarization-maintaining functionality requires that the core positions of the two PANDA fibers coincide with each other, and that the positional relationship of the stress-applying portion satisfy a predetermined condition.

[0005] One aspect of the present invention has been made in view of the above-mentioned problems, and its object is to provide an inspection method or inspection system that can inspect, after fusion splicing, whether or not the fusion splicing has been performed properly.

[0006] An inspection method according to one aspect of the present invention includes two multi-core fibers having markers formed in claddings, end faces of which are fused together, and includes a post-fusion measurement step of identifying the position of the marker of one of the multi-core fibers from a direction in which a predetermined first shape appears in a graph representing the directional dependence of transmitted light intensity of the one multi-core fiber, and identifying the position of the marker of the other of the two multi-core fibers from a direction in which a predetermined second shape appears in a graph representing the directional dependence of transmitted light intensity of the other multi-core fiber.

[0007] An inspection system according to one aspect of the present invention includes a single light source or a plurality of light sources, a single photodetector or a plurality of photodetectors, and a single controller or a plurality of controllers, and the single controller or at least one of the plurality of control units performs a post-fusion measurement step, using the single light source or at least one of the plurality of light sources and the single photodetector or at least one of the plurality of photodetectors, of two multicore fibers having a marker formed in a cladding, the two multicore fibers having end faces fused together, to identify the position of the marker of one of the multicore fibers from a direction in which a predetermined first shape appears in a graph representing the directional dependence of transmitted light intensity of the one multicore fiber, and to identify the position of the marker of the other of the two multicore fibers from a direction in which a predetermined second shape appears in the graph representing the directional dependence of transmitted light intensity of the other multicore fiber.

[0008] According to an aspect of the present invention, it is possible to inspect after fusion splicing whether the fusion splicing has been performed properly.

[0009] 1 is a flow diagram showing the flow of a fusion splicing method according to one embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a fusion splicing device for carrying out the fusion splicing method shown in FIG. 1 is a diagram showing a multi-core fiber as an example of an optical fiber to which the fusion splicing method shown in FIG. 1 is applied. (a) is a side view of the multi-core fiber, (b) is a front view of one end face of the multi-core fiber as seen from a line of sight E1 direction, and (c) is a front view of the other end face of the multi-core fiber as seen from a line of sight E2 direction. FIG. 3 is a diagram showing a splice point of two normally spliced ​​optical fibers. (a) is a side view of the two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from a line of sight E2 direction, and (c) is a front view of the other end face of the two optical fibers as seen from a line of sight E1 direction. FIG. 4 is a diagram showing a fusion splice point of two non-normally spliced ​​optical fibers. 1A is a side view of the two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1. It shows a fusion splice site of two optical fibers that are non-conventional spliced. 1A is a side view of the two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1. It shows a fusion splice site of two optical fibers that are non-conventional spliced. 1A is a side view of the two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1. It shows a fusion splice site of two optical fibers that are reverse spliced ​​(reverse spliced ​​with respect to axis L1). 1A is a side view of the two optical fibers, FIG. 1B is a front view of one end face of the two optical fibers as seen from the line of sight E2, and FIG. 1C is a front view of the other end face of the two optical fibers as seen from the line of sight E1. The figure shows the fusion splice points of two optical fibers that are reverse-spliced ​​(reverse-spliced ​​relative to the axis L2).1A is a side view of two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1.

[0034] FIG. 1B is a diagram showing a fusion splice location of two optical fibers that are reverse spliced ​​(reversed splice relative to axis L3). 1A is a side view of two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1.

[0035] FIG. 1C is a diagram showing a fusion splice location of two optical fibers that are reverse spliced ​​(reversed splice relative to axis L4). 1A is a side view of two optical fibers, (b) is a front view of one end face of the two optical fibers as seen from the line of sight E2, and (c) is a front view of the other end face of the two optical fibers as seen from the line of sight E1. 1A is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers (multicore fibers including low-refractive index markers) normally connected as shown in FIG. 4 ; 1B is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers reversely connected as shown in FIG. 8 ; 1C is a diagram showing a method for estimating the coupling efficiency or connection loss of two optical fibers; 1A is a side view of the two optical fibers; 1B is a front view of one end face of the two optical fibers as seen from the line of sight E2; and 1C is a front view of the other end face of the two optical fibers as seen from the line of sight E1. 1A is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers (multicore fibers including high-refractive index markers) normally connected as shown in FIG. 4 ; 1B is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers reversely connected as shown in FIG. 8 . 1(a) is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers (multicore fibers including a low refractive index marker surrounded by a high refractive index region) normally connected as shown in Figure 4. 1(b) is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers reversely connected as shown in Figure 8. 1(a) is a graph showing the directional dependence of the transmitted light intensity of each of two optical fibers normally connected as shown in Figure 4.9B is a graph showing the directional dependence of the transmitted light intensity of each of the two optical fibers connected in reverse as shown in FIG. 8. FIG.

[0010] (Flow of Fusion Splicing Method) The flow of a fusion splicing method S1, including an inspection method S10, according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2. The fusion splicing method S1 is a method for fusion-splicing two optical fibers OF1 and OF2, each having an anisotropic cross-sectional refractive index distribution, using a fusion splicing device 1. The inspection method S10 is a method for inspecting whether rotational alignment has been properly performed. FIG. 1 is a flow diagram showing the flow of the fusion splicing method S1, and FIG. 2 is a perspective view showing the state of the optical fibers OF1 and OF2 at each step included in the fusion splicing method S1. Note that in this embodiment, the optical fibers OF1 and OF2 are assumed to be multicore fibers having a cladding, multiple cores formed within the cladding, and a single marker formed within the cladding. Specific examples of the optical fibers OF1 and OF2 will be described later with reference to different drawings. The fusion splicing method S1 can also be considered a method for manufacturing a fiber splicing assembly obtained by fusing the optical fibers OF1 and OF2.

[0011] 1, fusion splicing method S1 includes a preparation step S11, a pre-fusion measurement step S12, an aligning step S13, a butting step S14, a fusion step S15, a post-fusion measurement step S16, a determination step S17, and an estimation step S18. Inspection method S10 is composed of these steps except for the butting step S14 and the fusion splicing step S15. Note that in fusion splicing method S1 and inspection method S10, preparation step S11, pre-fusion measurement step S12, and aligning step S13 are not essential and can be omitted.

[0012] The fusion splicing method S1, including the inspection method S10 according to this embodiment, is performed, for example, using a fusion splicing apparatus 1, including an inspection system 10 according to this embodiment. As shown in FIG. 2 , the fusion splicing apparatus 1 includes a light source 11, a photodetector 12, a heating unit 13, an alignment mechanism (not shown), and a control unit 15. The inspection system 10 is configured with these components except for the heating unit 13. Note that while FIG. 2 illustrates only one combination of the light source 11 and the photodetector 12, the fusion splicing apparatus 1 may include two or more combinations of the light source 11 and the photodetector 12. Note that in the following description, the axial direction of the optical fibers OF1 and OF2 is defined as the z-axis direction, and two directions perpendicular to the z-axis direction are defined as the x-axis direction and the y-axis direction. The x-axis direction and the y-axis direction are mutually perpendicular directions.

[0013] The light source 11 is configured to irradiate light onto the optical fibers OF1 and OF2. In this embodiment, an LED is used as the light source 11. Instead of an LED, an LD may be used as the light source 11. The photodetector 12 is configured to detect light transmitted through the optical fibers OF1 and OF2. In this embodiment, a photodiode or a photoconductor is used as the photodetector 12. Instead of a photodiode or a photoconductor, a camera may be used as the photodetector 12. The photodetector 12 is disposed on the optical path of light emitted from the light source 11 and transmitted through the optical fibers OF1 and OF2. FIG. 2 illustrates an example in which the light source 11 and the photodetector 12 face each other via the optical fibers OF1 and OF2, but the arrangement is not limited thereto. For example, if an optical element such as a mirror that bends the optical path is disposed between the light source 11 and the optical fibers OF1, OF2 and / or between the photodetector 12 and the optical fibers OF1, OF2, the light source 11 and the photodetector 12 may not be disposed opposite each other via the optical fibers OF1, OF2. The heating unit 13 is configured to heat the end faces of the optical fibers OF1 and OF2 to be fused. In this embodiment, an electrode pair consisting of two electrodes is used as the heating unit 13. Instead of the electrode pair, an electrode group consisting of three or more electrodes, or a CO ２A laser device such as a laser may be used as the heating unit 13. The alignment mechanism is configured to hold the optical fibers OF1, OF2 and to translate and rotate each of the optical fibers OF1, OF2 independently. In this embodiment, an alignment mechanism including a holding member, a translation mechanism, and a rotation mechanism is used as the alignment mechanism. The holding member is detachable from the alignment mechanism and may therefore be considered a component of the fusion splicing device 1, the inspection system 10, or a fusion splicing system or inspection system described below, independent of the alignment mechanism. The holding member is a member for holding the optical fibers OF1, OF2 and has the function of chucking or fixing the ends of the optical fibers OF1, OF2. In this embodiment, the holding member may be configured, for example, by a plate-shaped member having a V-groove formed therein for accommodating the optical fibers OF1, OF2, and a pressing member that presses the optical fibers OF1, OF2 accommodated in the V-groove to fix the optical fibers OF1, OF2 to the plate-shaped member. The translation mechanism is a mechanism for independently moving the optical fibers OF1 and OF2 held by the holding members in the x-axis, y-axis, and z-axis directions while the fixation by the pressing members is disabled. The rotation mechanism is a mechanism for independently rotating the optical fibers OF1 and OF2 held by the holding members in the x-axis, y-axis, and z-axis directions while the fixation by the pressing members is disabled. When the alignment by the translation mechanism and the rotation mechanism is completed, the fixation by the pressing members is enabled, and the optical fibers OF1 and OF2 are fixed to the holding members. Note that this holding member is a component required when the aligned optical fibers OF1 and OF2 are transferred to another device while maintaining their state, and can be omitted. Furthermore, in addition to or instead of this holding member, another holding member may be used that is used in a state where fixation is enabled during the alignment operation and in a state where fixation is disabled after the alignment operation. In this case, the translation mechanism translates the optical fibers OF1, OF2 together with the other holding members in the z-axis direction, the y-axis direction, and the z-axis direction, while the rotation mechanism rotates the optical fibers OF1, OF2 together with the other holding members about the z-axis.The control unit 15 is configured to control the light source 11, the photodetector 12, the heating unit 13, and the alignment mechanism to carry out each step included in the fusion splicing method S1. In this embodiment, a microcontroller is used as the control unit 15. Instead of a microcontroller, an integrated circuit such as an IC (Integrated Circuit), an LSI (Large-scale Integrated Circuit), or an ASIC (Application Specific Integrated Circuit), or an NC (Numerical Control) device may be used as the control unit 15. The NC device may use a machine learning machine.

[0014] The light source 11 may be provided as a single light source or multiple light sources, the photodetector 12 may be provided as a single photodetector or multiple photodetectors, the heating unit 13 may be provided as a single heating unit or multiple heating units, the aligning mechanism may be provided as a single aligning mechanism or multiple aligning mechanisms, and the control unit 15 may be provided as a single control unit or multiple control units. In this case, the single control unit or at least one of the multiple control units performs the pre-fusion measurement step S12 or the post-fusion measurement step S16 using a single light source or at least one of multiple light sources and a single photodetector or at least one of multiple photodetectors. Furthermore, the single control unit or at least one of the multiple control units performs the aligning step S13 or the butting step S14 using a single aligning mechanism or at least one of multiple aligning mechanisms. Furthermore, the single control unit or at least one of the multiple control units performs the fusion step S15 using a single heating unit or at least one of multiple heating units. Furthermore, the above-mentioned single control unit or at least one of the multiple control units executes the determination step S17 or the estimation step S18.

[0015] In the preparation step S11, a user sets the optical fibers OF1 and OF2 in the fusion splicing apparatus 1. The optical fibers OF1 and OF2 are each held by an alignment mechanism of the fusion splicing apparatus 1 so that their central axes are parallel to the z-axis. The state of the optical fibers OF1 and OF2 after the preparation step S11 is shown in FIG. 2A. Note that cleaning discharge may be performed in the preparation step S11. Cleaning discharge is a process for cleaning the surfaces of the optical fibers OF1 and OF2 by blowing off or melting away foreign matter such as glass debris adhering to the surfaces of the optical fibers OF1 and OF2. When cleaning discharge is performed, it is preferable to clean the surfaces of the optical fibers OF1 and OF2 at the locations to be measured in the pre-fusion measurement step S12, which will be described later. A confirmation process may be further performed using the light source 11 and the photodetector 12 to confirm whether the surfaces of the optical fibers OF1 and OF2 have been cleaned. Furthermore, the cleaning discharge and the checking operation may be repeated until it is confirmed that the surfaces of the optical fibers OF1 and OF2 are cleaned.

[0016] Thus, the subject of the operation in the preparation step S11 may be a worker or a device. Furthermore, this device may be a mechanism incorporated in the fusion splicing device 1 (a part of the fusion splicing device 1) or a mechanism separate from the fusion splicing device 1 (for example, a robot).

[0017] After the preparation step S11 is completed, the pre-fusion measurement step S12 is performed. In the pre-fusion measurement step S12, the fusion splicing apparatus 1 measures the center or outer periphery positions and the core or marker positions of the optical fibers OF1 and OF2 before fusion. Note that measurement of the center or outer periphery positions of the optical fibers OF1 and OF2 may be omitted if not necessary. In the pre-fusion measurement step S12, the control unit of the fusion splicing apparatus 1 uses the alignment mechanism of the fusion splicing apparatus 1 to move the optical fiber OF1 in the negative direction of the z-axis. This positions the end of the optical fiber OF1 between the light source 11 and the photodetector 12. The control unit of the fusion splicing apparatus 1 also uses the alignment mechanism of the fusion splicing apparatus 1 to move the optical fiber OF2 in the positive direction of the z-axis. This positions the end of the optical fiber OF2 between the light source 11 and the photodetector 12. As a result, the distance d between the end faces of the optical fibers OF1 and OF2 becomes sufficiently small. The distance d may be small enough to allow the detection process described below to be performed, for example, 0<d≦200 μm. The distance d may be greater than 200 μm as long as the detection process described below can be performed. In this embodiment, the distance d is set to 50 μm. The ends of the optical fibers OF1 and OF2 may be previously fitted with the holding members described above, for example, fiber holders. If the optical fibers OF1 and OF2 include markers, the fiber holders are attached to the optical fibers OF1 and OF2 so that the positions of the reference planes of the fiber holders and the positions of the markers on the optical fibers satisfy a specific relationship.

[0018] The control unit of the fusion splicing device 1 then uses the light source 11 and the photodetector 12 to measure the directional dependence of (1) the intensity I1 of light emitted from the light source 11, incident on the end of the optical fiber OF1 through the side of the optical fiber OF1, passing through the end of the optical fiber OF1, and emerging from the end of the optical fiber OF1 through the side of the optical fiber OF1 (hereinafter referred to as the transmitted light intensity I1), and (2) the intensity I2 of light emitted from the light source 11, incident on the end of the optical fiber OF2 through the side of the optical fiber OF2, passing through the end of the optical fiber OF2, and emerging from the end of the optical fiber OF2 through the side of the optical fiber OF2 (hereinafter referred to as the transmitted light intensity I2). When a photodiode or photoconductor is used as the photodetector 12, the control unit of the fusion splicing apparatus 1 repeats the detection process of detecting the transmitted light intensities I1 and I2 while rotating the optical fibers OF1 and OF2 around the z-axis or while rotating the light source 11 and the photodetector 12 around the z-axis. This allows the control unit of the fusion splicing apparatus 1 to obtain data representing the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2. Here, the data obtained by each detection process is, for example, a luminance value representing the intensity of light detected by the photodiode or photoconductor. In this case, the data representing the directional dependence of the transmitted light intensities I1 and I2 obtained by repeating the detection process is a one-dimensional array of luminance values ​​representing the intensity of light detected by the photodiode or photoconductor. On the other hand, when a camera is used as the photodetector 12, the control unit of the fusion splicing apparatus 1 repeats an imaging process of imaging the ends of the optical fibers OF1, OF2 and a calculation process (e.g., an integration process, an averaging process, or a weighted averaging process) of deriving the transmitted light intensities I1, I2 of the optical fibers OF1, OF2 from the images obtained by the imaging process while rotating the optical fibers OF1, OF2 about the z-axis or while rotating the light source 11 and the photodetector 12 about the z-axis. In this way, the control unit of the fusion splicing apparatus 1 obtains data representing the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2.Here, the data obtained by each imaging process is, for example, a two-dimensional array (i.e., an image) of brightness values ​​representing the intensity of light detected by each cell constituting the camera's image sensor, and the data obtained by each arithmetic process is, for example, an integrated value, average value, or weighted average value (hereinafter referred to as "integrated value, etc.") of the intensity detected by each cell constituting the camera's image sensor. In this case, the data representing the directional dependency of the transmitted light intensities I1 and I2 obtained by repeating the imaging process and arithmetic process becomes a one-dimensional array of integrated values ​​of the intensities detected by each cell constituting the camera's image sensor. Then, the control unit of the fusion splicing apparatus 1 identifies the center position or outer periphery position of the optical fiber OF1 and the core position or marker position based on (data representing) the directional dependency of the transmitted light intensity I1 of the optical fiber OF1. Furthermore, the control unit of the fusion splicing apparatus 1 identifies the center position or outer periphery position and the core position or marker position of the optical fiber OF2 based on (data representing) the directional dependency of the transmitted light intensity I2 of the optical fiber OF2. The state of the optical fibers OF1 and OF2 during the pre-fusion measurement step S12 is shown in FIG.

[0019] In the pre-fusion measurement step S12, the directions in which the optical measurements (the detection process or the imaging process described above) are performed may be distributed over a range of 360° or may be distributed over a range less than 360°. In other words, the domain of the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 (corresponding to the range of the horizontal axis when shown in a graph) may be 360° or may be less than 360°. When the range of directions in which the optical measurements are performed is less than 360°, it is preferable that, in the pre-fusion measurement step S12, the marker positions be identified by optical measurements from directions within this range, in the preparation step S11, (1) the optical fibers OF1 and OF2 are set in the alignment mechanism of the fusion splicer 1, and then coarse rotational alignment of the optical fibers OF1 and OF2 is performed, or (2) the optical fibers OF1 and OF2 are set in the alignment mechanism of the fusion splicer 1. In the former case, the coarse rotation alignment is performed by the alignment mechanism of the fusion splicer 1. In the latter case, the coarse rotation alignment is performed by an operator or a device other than the fusion splicer 1. In either case, the time required to identify the marker positions of the optical fibers OF1 and OF2 in the pre-fusion measurement step S12 can be shortened.

[0020] After the pre-fusion measurement step S12 is completed, the alignment step S13 is performed. The alignment step S13 is a step in which the fusion splicer 1 aligns the optical fibers OF1 and OF2. In the alignment step S13, the control unit of the fusion splicer 1 uses the alignment mechanism of the fusion splicer 1 to move each of the optical fibers OF1 and OF2 in the x-axis and / or y-axis directions so that the central positions or outer circumferential positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12 coincide. The control unit of the fusion splicer 1 also uses the alignment mechanism of the fusion splicer 1 to rotate each of the optical fibers OF1 and OF2 about the z-axis as a rotation axis so that the core positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12 coincide or so that the marker positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12 satisfy a predetermined relationship. The order of the movement in the x-axis direction and / or the y-axis direction and the rotation about the z-axis direction may be arbitrary. The movement in the x-axis direction and / or the y-axis direction may be followed by the rotation about the z-axis direction, or the rotation about the z-axis direction may be followed by the movement in the x-axis direction and / or the y-axis direction. The state of the optical fibers OF1 and OF2 during the alignment step S13 is shown in Figure 2(c).

[0021] In this embodiment, the pre-fusion measurement step S12 is performed once, followed by the alignment step S13, but the present invention is not limited to this. For example, the pre-fusion measurement step S12 and the alignment step S13 may be alternately and repeatedly performed to perform the alignment step in stages.

[0022] After the aligning step S13 is completed, the butting step S14 is performed. In the butting step S14, the fusion splicer 1 butts the end faces of the optical fibers OF1 and OF2 together. In the butting step S14, the control unit of the fusion splicer 1 uses the aligning mechanism of the fusion splicer 1 to move the optical fiber OF1 in the negative direction of the z-axis by d / 2 (approximately 5 μm in this embodiment). The control unit of the fusion splicer 1 also uses the aligning mechanism of the fusion splicer 1 to move the optical fiber OF2 in the positive direction of the z-axis by d / 2 (approximately 5 μm in this embodiment). The state of the optical fibers OF1 and OF2 after the butting step S14 is shown in FIG. 2(d). Note that pre-discharge may be performed in the butting step S14. The pre-discharge is a step for softening the tips of the optical fibers OF1 and OF2. By butting the tips of the optical fibers OF1 and OF2 together after performing pre-discharge, it is possible to reliably bring the tips of the optical fibers OF1 and OF2 into close contact. In this case, it is preferable to set the amount of movement of the optical fibers OF1 and OF2 to d / 2+ε, where ε is an additional amount of movement required to overlap the tips of the optical fibers OF1 and OF2, and is, for example, 10 μm. This makes it possible to more reliably bring the tips of the optical fibers OF1 and OF2 into close contact.

[0023] After the butting step S14 is completed, the fusion splicing step S15 is performed. In the fusion splicing step S15, the fusion splicing device 1 fuses the optical fiber OF1 and the optical fiber OF2 together. In the fusion splicing step S15, the control unit of the fusion splicing device 1 uses the heating unit 13 (for example, generates an arc discharge using an electrode pair) to heat and melt the ends of the optical fiber OF1 and the optical fiber OF2. When the heated and melted ends of the optical fiber OF1 and the optical fiber OF2 solidify due to natural cooling, the optical fiber OF1 and the optical fiber OF2 are fused together. The state of the optical fibers OF1 and OF2 after the fusion splicing step S15 is shown in FIG. 2( e).

[0024] Hereinafter, the portion of the optical fibers OF1 and OF2 where the refractive index distribution changes due to heating in the fusion step S15 will be referred to as the "heat-affected portion." In FIG. 2E, the heat-affected portion is indicated by hatching. The heat-affected portion extends from the center of the heated portion 13 (the electrode pair in this embodiment) in the positive z-axis direction and the negative z-axis direction by approximately 0.3 mm to 2 mm.

[0025] After the fusion step S15 is completed, a post-fusion measurement step S16 is performed. In the post-fusion measurement step S16, the fusion splicing apparatus 1 measures the core positions or marker positions of the optical fibers OF1 and OF2 after fusion. In the post-fusion measurement step S16, the control unit of the fusion splicing apparatus 1 measures the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the transmitted light intensity I2 of the optical fiber OF2. When a photodiode or photoconductor is used as the light detector 12, the control unit of the fusion splicing apparatus 1 repeats the detection process of detecting the transmitted light intensities I1 and I2 while rotating the optical fibers OF1 and OF2 about the z-axis or while rotating the light source 11 and the light detector 12 about the z-axis. In this way, the control unit of the fusion splicing apparatus 1 obtains data representing the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2. In this case, the data representing the directional dependence of the transmitted light intensities I1 and I2 will be, for example, a one-dimensional array of brightness values ​​representing the intensities of light detected by a photodiode or photoconductor, as in the pre-fusion measurement step S12. On the other hand, when a camera is used as the photodetector 12, the control unit of the fusion splicing apparatus 1 repeats the imaging process of imaging the ends of the optical fibers OF1 and OF2 and the calculation process of deriving the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 from the images obtained by the imaging process, while rotating the optical fibers OF1 and OF2 about the z-axis or while rotating the light source 11 and the photodetector 12 about the z-axis. In this way, the control unit of the fusion splicing apparatus 1 obtains data representing the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2. In this case, the data representing the directional dependence of the transmitted light intensities I1 and I2 obtained by repeating the imaging process and the calculation process will be, for example, a one-dimensional array of integrated values ​​of the intensities detected by each cell constituting the image sensor of the camera, similar to the pre-fusion measurement step S12. Then, the control unit of the fusion splicing apparatus 1 identifies the core position or marker position of the optical fiber OF1 based on (the data representing) the directional dependence of the transmitted light intensity I1 of the optical fiber OF1.Furthermore, the control unit of the fusion splicer 1 identifies the core position or marker position of the optical fiber OF2 based on (data representing) the directional dependency of the transmitted light intensity I2 of the optical fiber OF2.

[0026] In the post-fusion measurement step S16, the transmitted light intensities I1 and I2 of the heat-affected areas of the optical fibers OF1 and OF2 may be measured, or the transmitted light intensities I1 and I2 of the non-heat-affected areas of the optical fibers OF1 and OF2 may be measured. The state of the optical fibers OF1 and OF2 during the former post-fusion measurement step S16 is shown in Figure 2(f), and the state of the optical fibers OF1 and OF2 during the latter post-fusion measurement step S16 is shown in Figure 2(g) and (h). In the post-fusion measurement step S16, both the transmitted light intensities I1 and I2 of the heat-affected areas of the optical fibers OF1 and OF2 and the transmitted light intensities I1 and I2 of the non-heat-affected areas of the optical fibers OF1 and OF2 may be measured. In the post-fusion measurement step S16, the transmitted light intensities I1 and I2 may be measured at the ends of the optical fibers OF1 and OF2, or at a location other than the ends of the optical fibers OF1 and OF2. However, if the core is spirally formed, the core position may vary significantly depending on the measurement location, or if the marker is spirally formed, the marker position may vary significantly depending on the measurement location. Therefore, it is preferable to measure the transmitted light intensities I1 and I2 at the ends of the optical fibers OF1 and OF2. Furthermore, after the fusion step S15 is completed, a visual inspection may be performed before the post-fusion measurement step S16 is started. The visual inspection is a step for determining whether the fusion was successful based on the presence or absence of air bubbles, foreign matter, the amount of cladding misalignment, etc.

[0027] When performing the post-fusion measurement step S16 shown in (g) and (h) of Figure 2, the control unit of the fusion splicing apparatus 1 (process 1) moves the optical fibers OF1 and OF2 in the negative direction of the z-axis using the alignment mechanism, (process 2) detects the transmitted light intensity I1 of the optical fiber OF1 using the light source 11 and the photodetector 12 as shown in (g) of Figure 2, (process 3) moves the optical fibers OF1 and OF2 in the positive direction of the z-axis using the alignment mechanism, and (process 4) detects the transmitted light intensity I1 of the optical fiber OF1 using the light source 11 and the photodetector 12 as shown in (h) of Figure 2. Here, the movement amount of the optical fibers OF1 and OF2 in process 1 is preferably 0.3 mm or more, and more preferably 0.5 mm or more. Furthermore, the movement amount of the optical fibers OF1 and OF2 in process 3 is preferably twice the movement amount of the optical fibers OF1 and OF2 in process 1. When a camera capable of simultaneously capturing the heat-affected areas of optical fibers OF1 and OF2 and the non-heat-affected areas on both sides of the heat-affected areas within its angle of view is used as the photodetector 12, processes 1 and 3 may be omitted, and processes 2 and 3 may be performed simultaneously (the transmitted light intensity I1 of optical fiber OF1 and the transmitted light intensity I2 of optical fiber OF2 may be measured simultaneously).

[0028] After the post-fusion measurement step S16 is completed, the determination step S17 is performed. The determination step S17 is a step in which the fusion splicing apparatus 1 determines whether the optical fibers OF1 and OF2 have been properly fused. In the determination step S17, the control unit of the fusion splicing apparatus 1 determines whether the core positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16 match, or whether the marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16 satisfy a predetermined relationship. If the core positions of the optical fibers OF1 and OF2 match and the marker positions of the optical fibers OF1 and OF2 satisfy the predetermined relationship, the determination result indicates successful fusion. On the other hand, if the core positions of the optical fibers OF1 and OF2 do not match or the marker positions of the optical fibers OF1 and OF2 do not satisfy the predetermined relationship, the determination result indicates unsuccessful fusion. This determination result may or may not be notified to the user. When notifying the user of the determination result, the method of notifying the user of the determination result is not particularly limited. For example, when the core positions of the optical fibers OF1 and OF2 do not match, or when the marker positions of the optical fibers OF1 and OF2 do not satisfy a predetermined relationship, the method of notifying the user of the determination result may include turning on a lamp, sounding a buzzer, outputting a visual message from a display, or outputting a voice message from a speaker.

[0029] Whether the core positions of the optical fibers OF1 and OF2 are aligned can also be determined by whether the degree of overlap between a peak corresponding to a core among peaks in a graph representing the directional dependence of the transmitted light intensity I1 and a peak corresponding to a core among peaks in a graph representing the directional dependence of the transmitted light intensity I2 is equal to or greater than a predetermined threshold. Also, whether the marker positions of the optical fibers OF1 and OF2 are aligned can also be determined by whether the degree of overlap between a peak corresponding to a marker among peaks in a graph representing the directional dependence of the transmitted light intensity I1 and a peak corresponding to a marker among peaks in a graph representing the directional dependence of the transmitted light intensity I2 is equal to or greater than a predetermined threshold.

[0030] Whether the core positions of the optical fibers OF1 and OF2 coincide can also be determined by whether the difference between the direction (angle) at which a peak corresponding to a core exists among peaks in a graph representing the directional dependence of the transmitted light intensity I1 and the direction (angle) at which a peak corresponding to a core exists among peaks in a graph representing the directional dependence of the transmitted light intensity I2 is within a predetermined range. Whether the marker positions of the optical fibers OF1 and OF2 satisfy a predetermined relationship can also be determined by whether the difference between the direction (angle) at which a peak corresponding to a marker exists among peaks in a graph representing the directional dependence of the transmitted light intensity I1 and the direction (angle) at which a peak corresponding to a marker exists among peaks in a graph representing the directional dependence of the transmitted light intensity I2 is within a predetermined range.

[0031] After the determination step S17 is completed, the estimation step S18 is performed. The estimation step S18 is a step of estimating the coupling efficiency or the splice loss of the optical fibers OF1 and OF2. In the estimation step S18, the control unit of the fusion splicer 1 estimates the magnitude of the coupling efficiency or the splice loss of the optical fibers OF1 and OF2 from the core positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16. The control unit of the fusion splicer 1 may or may not notify the user of the estimation result obtained in the estimation step S18. When notifying the user of the estimation result, the method of notifying the user of the estimation result is not particularly limited. For example, when the estimated coupling efficiency falls below a predetermined threshold value or when the estimated splice loss exceeds a predetermined threshold value, the method of notifying the user of the estimation result may include lighting a lamp or sounding a buzzer, outputting the estimated coupling efficiency or splice loss as an image on a display, or outputting the estimated coupling efficiency or splice loss as sound from a speaker. By notifying the user of the estimation result, the user can be informed of the coupling efficiency or the magnitude of the connection loss of the optical fibers OF1 and OF2.

[0032] The core number is an identification number assigned to each core of the multicore fiber, and is set, for example, according to the distance from the marker. As an example, when multiple cores are arranged on a circumference, the core numbers of each core can be set as follows. First, the core number of the core closest to the marker is set to "1." Next, the core number of the core second closest to the marker is set to "2." When the circumference is traced so as to pass through the core closest to the marker and the core second closest to the marker in this order, the core number of the third core passed is set to "3," the core number of the fourth core passed to "4," ..., and the core number of the nth core passed to "n." Furthermore, instead of setting the core numbers with reference to a marker, the core numbers may be set with reference to marks (e.g., symbols, letters, etc.) formed on the surface of the cladding. Furthermore, when the cladding is covered with a coating, the core numbers may be set with reference to marks formed on the surface of the coating. Furthermore, when a connector is attached to the end of the multicore fiber, a configuration may be adopted in which the cores are set with reference to keys (e.g., protrusions) formed on the connector. Furthermore, for example, when a flat portion is provided on the side surface of the cladding so that the cross-sectional shape of the cladding has anisotropy (e.g., D-shape), the core number may be set by referring to this flat portion. Furthermore, when a notch is provided on the side surface of the cladding, the core number may be set by referring to this notch. Furthermore, when a multicore fiber is connected to a transceiver, the core number of each core may be set by referring to the port number of the transceiver connected to that core.

[0033] In the estimation step S18, in addition to or instead of estimating the coupling efficiency or connection loss of the optical fibers OF1 and OF2 (hereinafter also referred to as "first estimation"), at least one of the following estimations may be performed. That is, from the core positions and marker positions of the optical fiber OF1 identified in the post-fusion measurement step S16, a correspondence relationship between the core numbers of each core of the optical fiber OF1 and the core numbers of the cores of the optical fiber OF2 optically coupled to the cores may be estimated. This estimation may be also referred to as "second estimation" hereinafter. Furthermore, from the marker positions of the optical fiber OF1 identified in the post-fusion measurement step S16, it may be estimated which of multiple regions obtained by dividing the cladding of the optical fiber OF1 includes the marker of the optical fiber OF1 (hereinafter also referred to as third estimation). Furthermore, it may be possible to estimate, from the marker positions of the optical fiber OF2 identified in the post-fusion measurement step S16, which of the multiple regions obtained by dividing the cladding of the optical fiber OF2 includes the marker of the optical fiber OF2. These estimations are hereinafter also referred to as "third estimations." Furthermore, it may be possible to estimate, from the marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16, the amount of overlap and / or the amount of misalignment between the markers of the optical fiber OF1 and the markers of the optical fiber OF2. This estimation is hereinafter also referred to as "fourth estimations." Here, examples of the amount of overlap of the markers include the area of ​​the region where the markers of the optical fiber OF1 and the markers of the optical fiber OF2 overlap, or the ratio of the area of ​​the region to the area of ​​the markers of the optical fiber OF1 or the optical fiber OF2. Examples of the amount of misalignment of the markers include the difference (distance) between the marker positions in the radial and / or circumferential directions of the cladding. Furthermore, the angle (difference) between the direction (angle) of the marker of optical fiber OF1 as viewed from the center of the cladding and the direction (angle) of the marker of optical fiber OF2 as viewed from the center of the cladding may be regarded as the amount of misalignment of the markers. Furthermore, from the core positions of optical fibers OF1 and OF2 identified in the post-fusion measurement step S16, one or both of the overlap amount and misalignment amount between each core of optical fiber OF1 and the core of optical fiber OF2 optically coupled thereto may be estimated. Hereinafter, this estimation will also be referred to as the "fifth estimation."Here, the amount of core overlap may be, for example, the area of ​​the region where the core of the optical fiber OF1 and the core of the optical fiber OF2 overlap, or the ratio of the area of ​​that region to the area of ​​the core of the optical fiber OF1 or OF2. Furthermore, the amount of core misalignment may be, for example, the difference (distance) between the core positions in the radial and / or circumferential directions of the cladding. Furthermore, the angle (difference) between the direction (angle) of the core of the optical fiber OF1 as viewed from the center of the cladding and the direction (angle) of the core of the optical fiber OF2 connected to the core as viewed from the center of the cladding may be regarded as the amount of core misalignment. Furthermore, the polarity of the optical fibers OF1 and OF2 (whether the end face to be fusion-spliced ​​is end face σ1 or end face σ2, described below) may be estimated from the core positions and markers of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16. This estimation is hereinafter also referred to as the "sixth estimation." The control unit of the fusion splicing apparatus 1 may or may not notify the user of these estimation results. When notifying the user of these estimation results, the method of notifying the user of these estimation results is not particularly limited. For example, the estimation results may be output as an image from a display or as sound from a speaker. By notifying the user of these estimation results, the user can be informed of the estimation results.

[0034] As described above, the inspection method S10 of this embodiment includes a fusion step S15 for fusing optical fibers OF1 and OF2 having anisotropic refractive index distributions in their cross sections, and a post-fusion measurement step S16 for, after performing the fusion step S15, identifying the core position or marker position of the optical fiber OF1 based on the spatial distribution or directional dependence of the transmitted light intensity I1 of the optical fiber OF1, and identifying the core position or marker position of the optical fiber OF2 based on the spatial distribution or directional dependence of the transmitted light intensity I2 of the optical fiber OF2. Therefore, the inspection method S10 of this embodiment can determine whether the fusion splice was successful based on the measurement results of the post-fusion measurement step S16. Furthermore, at least a portion of the foreign matter adhering to the surfaces of the optical fibers OF1 and OF2 before performing the fusion step S15 can be eliminated by performing the fusion step S15. As a result, the data obtained in the post-fusion measurement step S16 can have less noise due to foreign matter adhering to the surfaces of the optical fibers OF1 and OF2 than the data obtained in the pre-fusion measurement step S12. Furthermore, in the post-fusion measurement step S16, in which the optical fibers OF1 and OF2 have already been fused, twisting of the optical fibers OF1 and OF2 is less likely to occur than in the pre-fusion measurement step S12, in which the optical fibers OF1 and OF2 have not yet been fused. As a result, the data obtained in the post-fusion measurement step S16 may contain less noise caused by twisting of the optical fibers OF1 and OF2 than the data obtained in the pre-fusion measurement step S12. Therefore, even if the core positions or marker positions cannot be correctly identified in the pre-fusion measurement step S12 due to a foreign object, there is a high possibility that the core positions and marker positions can be correctly identified in the post-fusion measurement step S16.

[0035] Determining the success or failure of the fusion splice after fusion splicing has the following significance. Consider a manufacturing method for a fiber splice assembly including three optical fibers. This manufacturing method includes a first splicing step of fusion splicing a first optical fiber to a second optical fiber, and a second splicing step of fusion splicing either the first optical fiber or the second optical fiber to a third optical fiber. By using the fusion splicing method S1 according to this embodiment for the first splicing step, the success or failure of the fusion splice between the first optical fiber and the second optical fiber can be determined before the second splicing step is performed. Therefore, if the fusion splice between the first optical fiber and the second optical fiber fails, the fusion splice between the first optical fiber and the second optical fiber can be redone before the second splicing step is performed. This avoids unnecessary execution of the second splicing step, thereby realizing a more efficient manufacturing method. The same applies to a manufacturing method for a fiber splice assembly including four or more optical fibers.

[0036] Furthermore, the inspection method S10 of this embodiment further includes a determination step S17 for determining whether the fusion splice has been successful based on the core positions or marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16. Therefore, the fusion splicing method S1 of this embodiment allows the success or failure of the fusion splice to be determined automatically. This makes it easier for the user to know whether the fusion splice has been successful, compared to when the user determines the success or failure of the fusion splice. In particular, when the user determines the success or failure of the fusion splice, there is a high likelihood of an erroneous determination when the determination criteria are complex or have changed. However, when the success or failure of the fusion splice is determined automatically, such an erroneous determination is less likely to occur.

[0037] In the inspection method S10 of this embodiment, the optical fibers OF1 and OF2 are optical fibers including markers, and in the determination step S17, if the marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16 satisfy a predetermined relationship, it is determined that the fusion has been successful, or if the marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16 do not satisfy the predetermined relationship, it is determined that the fusion has been unsuccessful. Therefore, according to the inspection method S10 of this embodiment, it is possible to appropriately automatically determine whether the fusion splice has been successful.

[0038] Furthermore, in the inspection method S10 of this embodiment, a configuration is adopted in which, in the pre-fusion measurement step S12, the marker position of the optical fiber OF1 is identified from the spatial distribution or directional dependency of the transmitted light intensity I1 of the optical fiber OF1, and the marker position of the optical fiber OF2 is identified from the directional dependency of the transmitted light intensity I2 of the optical fiber OF2. Therefore, according to the inspection method S10 of this embodiment, the pre-fusion measurement step S12 can be performed in the same manner as the post-fusion measurement step S16, using the light source 11 and photodetector 12 used in the post-fusion measurement step S16.

[0039] Furthermore, in the inspection method S10 of this embodiment, based on one or both of the core positions and marker positions of the optical fibers OF1 and OF2 identified in the post-fusion measurement step S16, (1) the coupling efficiency or connection loss of the optical fibers OF1 and OF2, (2) the correspondence between the core number of each core of the optical fiber OF1 and the core number of the core of the optical fiber OF2 optically coupled to that core, and (3) which of the multiple regions obtained by dividing the clad of the optical fiber OF into multiple regions contains the marker of the optical fiber OF1. The inspection method S10 of this embodiment further includes an estimation step of estimating at least one of (1) whether the marker of the optical fiber OF1 is included in the cladding of the optical fiber OF1, (2) which of the multiple regions obtained by dividing the cladding of the optical fiber OF2 contains the marker of the optical fiber OF2, (3) the amount of overlap or misalignment between the marker of the optical fiber OF1 and the marker of the optical fiber OF2, (4) the amount of overlap or misalignment between each core of the optical fiber OF1 and the core of the optical fiber OF2 optically coupled thereto, and (5) the amount of overlap or misalignment between each core of the optical fiber OF1 and the core of the optical fiber OF2 optically coupled thereto, and (6) the polarities of the optical fibers OF1 and OF2. Therefore, the inspection method S10 of this embodiment can automatically derive various estimated values. Therefore, compared to when the various estimated values ​​are derived by the user, the user can easily know the various estimated values.

[0040] In this embodiment, in the pre-fusion measurement step S12 and the post-fusion measurement step S16, the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2 are measured using the same light source 11 and the same photodetector 12, but the present invention is not limited to this. For example, in the pre-fusion measurement step S12 and the post-fusion measurement step S16, a configuration may be adopted in which the directional dependence of the transmitted light intensity I2 of the optical fiber OF2 is measured using a light source and a photodetector different from those used to measure the directional dependence of the transmitted light intensity I1 of the optical fiber OF1.

[0041] Furthermore, in this embodiment, the pre-fusion measurement step S12 and the post-fusion measurement step S16 (when the heat-affected area is the measurement target) employ a configuration in which the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 and the directional dependence of the transmitted light intensity I2 of the optical fiber OF2 are measured simultaneously, but the present invention is not limited to this. For example, in the pre-fusion measurement step S12 or the post-fusion measurement step S16 (when the heat-affected area is the measurement target), a configuration in which the directional dependence of the transmitted light intensity I1 of the optical fiber OF1 is measured first and then the directional dependence of the transmitted light intensity I1 of the optical fiber OF2 is measured, or conversely, a configuration in which the directional dependence of the transmitted light intensity I2 of the optical fiber OF1 is measured first and then the directional dependence of the transmitted light intensity I2 of the optical fiber OF1 is measured.

[0042] Furthermore, in this embodiment, in the pre-fusion measurement step S12 and the post-fusion measurement step S16, a configuration (also referred to as "side-view scanning") is employed in which the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 is measured by repeating a detection process (using a photodiode or photoconductor as the optical detector 12) or an imaging process (using a camera as the optical detector 12) while rotating the optical fibers OF1 and OF2 about the z-axis as the rotation axis, or while rotating the light source 11 and the photodetector 12 about the z-axis as the rotation axis. However, the present invention is not limited to this. For example, a configuration (also referred to as "side-view imaging") may be employed in which the spatial distribution of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 is measured by using a camera as the photodetector 12 to image the side of the optical fibers OF1 and OF2 from a specific direction. In this case, the control unit of the fusion splicing apparatus 1 identifies the core positions or marker positions of the optical fibers OF1, OF2 based on image data (a two-dimensional array of brightness values) that represents the spatial distribution of the transmitted light intensities I1, I2 of the optical fibers OF1, OF2, instead of identifying the core positions or marker positions of the optical fibers OF1, OF2 based on data that represents the directional dependence of the transmitted light intensities I1, I2 of the optical fibers OF1, OF2. Note that in the pre-fusion measurement step S12, as described above, in addition to identifying the core positions or marker positions, the center position or outer periphery position may also be identified, but if not necessary, the identification of the center position and outer periphery position may be omitted.

[0043] In the pre-fusion measurement step S12, instead of side-view scanning or side-view imaging, the core positions or marker positions of the optical fibers OF1, OF2 may be identified by end-view imaging. Here, end-view imaging refers to a method of identifying the core positions or marker positions of the optical fibers OF1, OF2 based on an image obtained by using a camera as the photodetector 12 to image the end faces of the optical fibers from a specific direction. When the center positions or outer periphery positions and the core positions or marker positions of the optical fibers OF1, OF2 are identified by end-view imaging, the control unit of the fusion splicing apparatus 1 performs the following steps in the pre-fusion measurement step S12: (1) move the photodetector 12 between the optical fibers OF1, OF2, (2) orient the photodetector 12 toward the end face of the optical fiber OF1 to image the end face of the optical fiber OF1, (3) redirect the photodetector 12 toward the end face of the optical fiber OF2 to image the end face of the optical fiber OF2, and (4) retract the photodetector 12 from between the optical fibers OF1, OF2. Alternatively, (1) a mirror is inserted between the optical fibers OF1 and OF2 so that the reflective surface of the mirror faces the end face of the optical fiber OF1 at 45 degrees with the optical axis of the optical fiber OF1, (2) the end face of the optical fiber OF1 reflected in the mirror is imaged using the photodetector 12, (3) the orientation of the mirror is changed so that the reflective surface of the mirror faces the end face of the optical fiber OF2 at 45 degrees with the optical axis of the optical fiber OF2, (4) the end face of the optical fiber OF2 reflected in the mirror is imaged using the photodetector 12, and (5) the mirror is retracted from between the optical fibers OF1 and OF2. Note that in the pre-fusion measurement step S12, as described above, the center position or outer periphery position may be identified in addition to identifying the core position or marker position, but identifying the center position and outer periphery position may be omitted if not necessary.

[0044] Side-view scanning or side-view imaging has the advantage of being able to shorten the time required for the pre-fusion measurement step S12 and the post-fusion measurement step S16. On the other hand, end-view imaging has the advantage of being able to accurately identify the center position or outer periphery position, or core position or marker position, of the optical fibers OF1, OF2 in the pre-fusion measurement step S12.

[0045] Note that, in this embodiment, the success or failure of the fusion splice is determined by performing the determination step S17, but this is not limiting. For example, instead of performing the determination step S17, another determination process may be performed in which the success or failure of the fusion splice is determined based on the estimation result in the estimation step S18. Furthermore, if the estimation result in the estimation step S18 is notified to a user, the user may determine the success or failure of the fusion splice based on this estimation result. Alternatively, if the estimation result in the estimation step S18 is notified to another device, the other device may determine the success or failure of the fusion splice based on this estimation result. For example, in the case where the first estimation described above is performed in the estimation step S18, if the splice loss of the optical fibers OF1 and OF2 is equal to or less than a predetermined first threshold, or if the coupling efficiency of the optical fibers OF1 and OF2 is equal to or greater than a predetermined second threshold, it can be determined that the fusion splice is successful. On the other hand, if the splice loss of the optical fibers OF1 and OF2 exceeds the first threshold, or if the coupling efficiency of the optical fibers OF1 and OF2 is less than the predetermined second threshold, it can be determined that the fusion splice is unsuccessful. In this case, the fusion splicer 1 can determine the success or failure of the fusion splice from the value of the coupling efficiency or splice loss. Furthermore, the fusion splicer 1 can determine the success or failure of the fusion splice without actually measuring the value of the coupling efficiency or splice loss. Furthermore, in the case where the second estimation described above is performed in the estimation step S18, if the correspondence relationship between the core numbers of the optical fibers OF1 and OF2 matches a predetermined correspondence relationship, it can be determined that the fusion splice was successful. If the correspondence relationship between the core numbers of the optical fibers OF1 and OF2 does not match the predetermined correspondence relationship, it can be determined that the fusion splice was unsuccessful. In this case, the fusion splicer 1 can determine the success or failure of the fusion splice from the correspondence relationship between the core numbers. Furthermore, the fusion splicer 1 can determine the success or failure of the fusion splice without actually measuring the coupling efficiency or splice loss. Furthermore, in the case where the third estimation described above is performed in the estimation step S18, it can be determined that the fusion splice was successful if the areas including the markers in the optical fibers OF1 and OF2 match. If the areas including the markers in the optical fibers OF1 and OF2 do not match, it can be determined that the fusion splice was unsuccessful.In this case, the fusion splicing apparatus 1 can determine the success or failure of the fusion splice from the region containing the markers. Furthermore, the fusion splicing apparatus 1 can determine the success or failure of the fusion splice without actually measuring the coupling efficiency or splice loss. Furthermore, in the case where the fourth estimation described above is performed in the estimation step S18, if the overlap amount of the markers on the optical fibers OF1 and OF2 is equal to or greater than a predetermined threshold, the fusion splice can be determined to be successful. If the overlap amount of the markers on the optical fibers OF1 and OF2 is equal to or less than a predetermined threshold, the fusion splice can be determined to be unsuccessful. Alternatively, if the misalignment amount of the markers on the optical fibers OF1 and OF2 is equal to or less than a predetermined threshold, the fusion splice can be determined to be successful. If the misalignment amount of the markers exceeds the predetermined threshold, the fusion splice can be determined to be unsuccessful. In this case, the fusion splicing apparatus 1 can determine the success or failure of the fusion splice from the overlap amount or misalignment amount of the markers. Furthermore, the fusion splicing apparatus 1 can determine the success or failure of the fusion splice without actually measuring the coupling efficiency or splice loss. Furthermore, in the case where the fifth estimation described above is performed in the estimation step S18, if the overlap amount of the cores in the optical fibers OF1 and OF2 is equal to or greater than a predetermined threshold, it can be determined that the fusion splice was successful, and if the overlap amount of the cores is less than the predetermined threshold, it can be determined that the fusion splice was unsuccessful. Alternatively, if the misalignment amount of the cores in the optical fibers OF1 and OF2 is equal to or less than a predetermined threshold, it can be determined that the fusion splice was successful, and if the misalignment amount of the cores exceeds the predetermined threshold, it can be determined that the fusion splice was unsuccessful. In this case, the fusion splicer 1 can determine the success or failure of the fusion splice from the overlap amount or misalignment amount of the cores. Furthermore, the fusion splicer 1 can determine the success or failure of the fusion splice without actually measuring the coupling efficiency or splice loss. Furthermore, in the case where the sixth estimation described above is performed in the estimation step S18, if the polarities of the optical fibers OF1 and OF2 are the predetermined polarity, it can be determined that the fusion splice was successful, and if the polarities of the optical fibers OF1 and OF2 are not the predetermined polarity, it can be determined that the fusion splice was unsuccessful. In this case, the fusion splicer 1 can determine the success or failure of the fusion splice from the polarity of the optical fibers OF1 and OF2. Furthermore, the fusion splicer 1 can determine the success or failure of the fusion splice without actually measuring the coupling efficiency or splice loss.If the estimation result is notified to the user in estimation step S18, determination step S17 can be omitted. Conversely, if determination step S17 is performed, estimation step S18 can be omitted. In either case, the user can know whether the fusion splice was successful or not.

[0046] In this embodiment, the optical fibers OF1 and OF2 are assumed to be multicore fibers with markers formed thereon, and the core and marker are used as the structure to be measured in the post-fusion measurement step S16 (the “specific structure” in the claims). However, this is not limiting. For example, the optical fibers OF1 and OF2 may be assumed to be multicore fibers with flat portions provided on the side surfaces of the cladding so that the cross section of the cladding is D-shaped, and the core and flat portions may be used as the structure to be measured in the post-fusion measurement step S16 (the “specific structure” in the claims). The optical fibers OF1 and OF2 may be assumed to be multicore fibers with notches formed in the cladding, and the core and the notches may be used as the structure to be measured in the post-fusion measurement step S16 (the “specific structure” in the claims). In these cases, the markers may be omitted. Furthermore, optical fibers other than multicore fibers, such as PANDA fibers with stress-applying portions formed thereon and photonic crystal fibers with microstructures formed thereon, may also be used as the inspection targets of the present invention. In a PANDA fiber, the stress-applying portion can be a specific structure that replaces the marker. Also, in a photonic crystal fiber, a microstructure can be a specific structure that replaces the marker. Even in this case, the above-mentioned effects can be achieved. Note that an optical fiber having an anisotropic refractive index distribution in its cross section can also be referred to as an optical fiber having a refractive index distribution in its cross section that does not have rotational symmetry.

[0047] (Specific Example of Optical Fiber) A specific example of the optical fibers OF1 and OF2 will be described with reference to Fig. 3. The optical fibers OF1 and OF2 according to this specific example are multi-core fibers MF. In Fig. 3, (a) is a side view of the multi-core fiber MF, (b) is a front view of one end face σ1 of the multi-core fiber MF as seen from the line of sight E1 direction, and (c) is a front view of the other end face σ2 of the multi-core fiber MF as seen from the line of sight E2 direction.

[0048] The multicore fiber MF includes n cores a1 to an (n is a natural number of 2 or more) and a cladding b. The cladding b is a cylindrical member. The cladding b is made of, for example, silica glass. Each core ai (i is a natural number of 1 to n) is a cylindrical region provided inside the cladding b, has a higher refractive index than the cladding b, and extends in the same direction as the cladding b. Each core ai is made of, for example, silica glass doped with an up-dopant such as germanium. The cladding b may have any cross-sectional shape as long as it is cylindrical. The cross-sectional shape of the cladding b may be, for example, a polygonal shape such as a square or a hexagon, or may be a barrel shape.

[0049] At the end faces σ1 and σ2, the cores a1 to an are arranged line-symmetrically with respect to an axis L1 that is orthogonal to the central axis L0 of the multicore fiber MF. Furthermore, at the end faces σ1 and σ2, the cores a1 to an are arranged so as to avoid the axis L1. In other words, at the end faces σ1 and σ2, the cores a1 to an are arranged at positions other than the axis L1.

[0050] The multicore fiber MF further includes a marker c. The marker c is a columnar region provided inside the cladding b, which has a refractive index different from that of the cladding b and extends in the same direction as the cladding b. The cross-sectional shape of the marker c is arbitrary, such as a circle, a triangle, or a rectangle. The marker c is made of, for example, silica glass doped with a down dopant such as fluorine or boron. In this case, the refractive index of the marker c is lower than that of the cladding b. The marker c may alternatively be made of silica glass doped with an up dopant such as germanium, aluminum, phosphorus, or chlorine. In this case, the refractive index of the marker c is higher than that of the cladding b. The marker c can be formed by, for example, a drilling method or a stack-and-draw method. The outer diameter of the marker c is usually smaller than that of the core ai.

[0051] On the end faces σ1 and σ2, the centers of the markers c are arranged so as to avoid the axis L1. In other words, on the end faces σ1 and σ2, the centers (geometric centers) of the markers c are arranged at positions other than the axis L1. Note that the markers c only need to be arranged so that their centers avoid the axis L1, and it is acceptable for a portion of the markers c to overlap the axis L1.

[0052] The cores a1 to a4 of the multi-core fiber MF illustrated in Fig. 3 can be regarded as being arranged line-symmetrically with respect to the axis L2, as being arranged line-symmetrically with respect to the axis L3, or as being arranged line-symmetrically with respect to the axis L4. Here, the axis L2 is an axis that is orthogonal to both the central axis L0 and the axis L1. The axes L3 and L4 are axes that are orthogonal to the central axis L0 and form an angle of 45 degrees with the axis L1. However, the core arrangement in the multi-core fiber MF is not limited to an arrangement having four-axis symmetry as illustrated in Fig. 3. As long as the core arrangement is line-symmetric with respect to at least one of these four axes, normal connection and inverted connection, which will be described later, can be realized.

[0053] Furthermore, the multicore fiber MF may include dummy cores (not shown in FIG. 3 and the like) that are not used for communication in addition to the cores a1 to an used for communication. In this case, the cores whose positions are identified in the pre-fusion measurement step S12 and the post-fusion measurement step S16 may be (1) only the cores a1 to an used for communication, (2) only the dummy cores that are not used for communication, or (3) both the cores a1 to an used for communication and the dummy cores that are not used for communication.

[0054] (Specific Examples of Connection Points of Optical Fibers) Specific examples of connection points of the optical fibers OF1, OF2 will be described with reference to Fig. 4 to Fig. 6. Here, a connection configuration of the optical fibers OF1, OF2 when the optical fibers OF1, OF2 are multi-core fibers MF will be described.

[0055] The connection modes of the optical fibers OF1 and OF2 include normal connection, non-normal connection, and reverse connection.

[0056] 4A and 4B are diagrams showing splices for a normal splice, with (a) being a side view of optical fibers OF1 and OF2, (b) being a front view of the end face σ2 of optical fiber OF1 as seen from the line of sight E2, and (c) being a front view of the end face σ1 of optical fiber OF2 as seen from the line of sight E1. The splice for a normal splice is a splice that connects the end face σ2 of optical fiber OF1 to the end face σ1 of optical fiber OF2, or a splice that connects the end face σ1 of optical fiber OF1 to the end face σ2 of optical fiber OF2 (the former is shown in FIG. 4). The splice for a normal splice satisfies the following conditions:

[0057] Condition 1: Each of the cores a1 to an of the end face σ1 of the optical fiber OF2 overlaps with one of the cores a1 to an of the end face σ2 of the optical fiber OF1. Specifically, (1) the core a1 of the end face σ1 of the optical fiber OF2 overlaps with the core a1 of the end face σ2 of the optical fiber OF1, (2) the core a2 of the end face σ1 of the optical fiber OF2 overlaps with the core a2 of the end face σ2 of the optical fiber OF1, (3) the core a3 of the end face σ1 of the optical fiber OF2 overlaps with the core a3 of the end face σ2 of the optical fiber OF1, and (4) the core a4 of the end face σ1 of the optical fiber OF2 overlaps with the core a4 of the end face σ2 of the optical fiber OF1.

[0058] Condition 2a: The marker c on the end face σ1 of the optical fiber OF2 overlaps with the marker c on the end face σ2 of the optical fiber OF1.

[0059] In short, the normal connection is a connection form in which the cores a1 to an are optically coupled and the marker c is in communication.

[0060] In addition, when the optical fibers OF1 and OF2 are the multi-core fibers MF illustrated in Figure 3, the connection modes for connecting the end face σ2 of the optical fiber OF1 and the end face σ1 of the optical fiber OF2 can be, in addition to the normal connection, the connection modes shown in Figure 5, the connection mode shown in Figure 6, and the connection mode shown in Figure 7.

[0061] 5 shows a connection state in which a core a1 of an optical fiber OF1 is connected to a core a2 of an optical fiber OF2, in which (a) is a side view of the optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1.

[0062] 6 shows a connection state in which a core a1 of an optical fiber OF1 is connected to a core a3 of an optical fiber OF2, in which (a) is a side view of the optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1.

[0063] 7 shows a connection state in which a core a1 of an optical fiber OF1 is connected to a core a4 of an optical fiber OF2, in which (a) is a side view of the optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1.

[0064] 5 to 7 satisfy condition 1 but do not satisfy condition 2a. For this reason, the connection modes shown in Figures 5 to 7 are called non-normal connections rather than normal connections.

[0065] 8A and 8B are diagrams showing the connection points of a reverse connection, with (a) being a side view of optical fibers OF1 and OF2, (b) being a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) being a front view of the end face σ2 of the optical fiber OF2 as seen from the line of sight E1. The connection points of a reverse connection are the connection points where the end face σ2 of the optical fiber OF1 is connected to the end face σ2 of the optical fiber OF2, or the connection points where the end face σ1 of the optical fiber OF1 is connected to the end face σ1 of the optical fiber OF2 (FIG. 5 shows the former). The connection points of a reverse connection satisfy the following conditions:

[0066] Condition 1: Each of the cores a1 to an of the end face σ1 of the optical fiber OF2 overlaps with one of the cores a1 to an of the end face σ2 of the optical fiber OF1. Specifically, (1) the core a1 of the end face σ2 of the optical fiber OF2 overlaps with the core a4 of the end face σ2 of the optical fiber OF1, (2) the core a2 of the end face σ2 of the optical fiber OF2 overlaps with the core a3 of the end face σ2 of the optical fiber OF1, (3) the core a3 of the end face σ2 of the optical fiber OF2 overlaps with the core a2 of the end face σ2 of the optical fiber OF1, and (4) the core a4 of the end face σ2 of the optical fiber OF2 overlaps with the core a1 of the end face σ2 of the optical fiber OF1.

[0067] Condition 2b: The marker c on the end face σ2 of the optical fiber OF2 overlaps with the position x on the end face σ2 of the optical fiber OF1 that is symmetrical with the marker c on the optical fiber OF1 with respect to the axis L1.

[0068] In short, the inverted connection is a connection form in which the cores a1 to an are optically coupled and the marker c is not connected.

[0069] In addition, when the optical fibers OF1 and OF2 are the multi-core fibers MF illustrated in FIG. 3, possible connection modes for connecting the end face σ2 of the optical fiber OF1 and the end face σ2 of the optical fiber OF2 include the inverted connection shown in FIG. 8, as well as the connection modes shown in FIG. 9, FIG. 10, and FIG. 11.

[0070] 9 shows a connection mode in which a core a1 of an optical fiber OF1 is connected to a core a3 of an optical fiber OF2. In FIG. 9, (a) is a side view of optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1. The connection mode shown in FIG. 9 satisfies condition 1 and also satisfies condition 2b when axis L1 is replaced with axis L3. Therefore, the connection mode shown in FIG. 9 is referred to as a reverse connection with respect to axis L3.

[0071] Figure 10 shows a connection mode in which a core a1 of an optical fiber OF1 is connected to a core a2 of an optical fiber OF2. In Figure 10, (a) is a side view of optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1. The connection mode shown in Figure 10 satisfies condition 1 and also satisfies condition 2b when axis L1 is replaced with axis L2. Therefore, the connection mode shown in Figure 10 is called a reverse connection with respect to axis L2.

[0072] Figure 11 shows a connection mode in which the core a1 of the optical fiber OF1 is connected to the core a1 of the optical fiber OF2. In Figure 11, (a) is a side view of the optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ1 of the optical fiber OF2 as seen from the line of sight E1. The connection mode shown in Figure 11 satisfies condition 1 and also satisfies condition 2b when axis L1 is replaced with axis L4. Therefore, the connection mode shown in Figure 11 is called a reverse connection with respect to axis L4.

[0073] (Predetermined Relationship) As described above, in the aligning step S13, the control unit of the fusion splicer 1 aligns the optical fibers OF1, OF2 so that the marker positions of the optical fibers OF1, OF2 satisfy a "predetermined relationship." Furthermore, in the determining step S17, the control unit of the fusion splicer 1 determines whether the marker positions of the optical fibers OF1, OF2 satisfy the "predetermined relationship." Here, the "predetermined relationship" refers to the positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that can arise when each of the cores a1 to an of the optical fiber OF1 is optically coupled to any of the cores a1 to an of the optical fiber OF2, when the optical fibers OF1, OF2 are multicore fibers MF.

[0074] When the optical fibers OF1 and OF2 are the multi-core fibers MF illustrated in FIG. 3, the following eight positional relationships are considered as the "predetermined relationship."

[0075] Relationship 1: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode (normal connection) shown in FIG.

[0076] Relationship 2: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode (non-normal connection) shown in FIG.

[0077] Relationship 3: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode (non-normal connection) shown in FIG.

[0078] Relationship 4: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode (non-normal connection) shown in FIG.

[0079] Relationship 5: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode shown in FIG. 8 (reverse connection with respect to the axis L1).

[0080] Relationship 6: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode shown in FIG. 9 (reverse connection with respect to the axis L3).

[0081] Relationship 7: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode shown in FIG. 10 (reverse connection with respect to the axis L2).

[0082] Relationship 8: The positional relationship between the marker c of the optical fiber OF1 and the marker c of the optical fiber OF2 that occurs in the connection mode shown in FIG. 11 (reverse connection with respect to the axis L4).

[0083] For example, when the fusion splice of the optical fibers OF1 and OF2 is a normal splice (relationship 1), the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 is, for example, as shown in Figure 12(a). When the fusion splice of the optical fibers OF1 and OF2 is a reverse splice with respect to the axis L1 (relationship 5), the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 is, for example, as shown in Figure 12(b). The directional dependence of the transmitted light intensities I1 and I2 shown in Figure 12 was obtained by side-view scanning using a camera as the photodetector 12.

[0084] In the directional dependence of the transmitted light intensities I1 and I2, the direction in which a peak appears corresponds to the direction in which the light source 11, the core ai, and the photodetector 12 are aligned, in which the core ai is closer to the light source 11. In addition, in the directional dependence of the transmitted light intensities I1 and I2, the direction in which a dip appears corresponds to the direction in which the light source 11, the marker c, and the photodetector 12 are aligned, in which the marker c is closer to the light source 11. Therefore, the control unit of the fusion splicing apparatus 1 can identify the core positions of the optical fibers OF1 and OF2 from the direction in which a peak appears in the directional dependence of the transmitted light intensities I1 and I2, and can identify the marker positions of the optical fibers OF1 and OF2 from the direction in which a dip exists in the directional dependence of the transmitted light intensities I1 and I2.

[0085] The control unit of the fusion splicing apparatus 1 selects one relationship from the relationships 1 to 8 described above. For example, from the relationships 1 to 8 described above, the control unit selects the relationship that is closest (most similar) to the relationship between the marker positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12. Note that "the relationship that is closest to the relationship between the marker positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12" can be defined, for example, as follows. That is, consider rotational alignment of the optical fibers OF1 and OF2 so that the core position of the optical fiber OF1 and the core position of the optical fiber OF2 are aligned with as small an amount of rotation as possible. In this case, the condition that "the core positions and marker positions of the optical fibers OF1 and OF2 after rotational alignment coincide with the core positions and marker positions of the optical fibers OF1 and OF2 that satisfy any one of the relationships 1 to 8" is satisfied. Alternatively, any one of relations 1 to 8 satisfies the condition that "the core positions and marker positions of the optical fibers OF1 and OF2 after rotational alignment coincide with the core positions and marker positions of the optical fibers OF1 and OF2 that satisfy that relationship." Of relations 1 to 8, the relationship that satisfies this condition is referred to as "the relationship that is closest to the relationship between the marker positions of the optical fibers OF1 and OF2 identified in the pre-fusion measurement step S12." Then, in the aligning step S13, the control unit of the fusion splicer 1 aligns the optical fibers OF1 and OF2 so that the marker positions of the optical fibers OF1 and OF2 satisfy the selected relationship. Furthermore, in the determination step S17, the control unit of the fusion splicer 1 determines whether the marker positions of the optical fibers OF1 and OF2 satisfy the selected relationship. Therefore, according to the inspection method S10 of this embodiment, it is possible to identify which of relations 1 to 8 the connection mode of the optical fibers OF1 and OF2 satisfies, and to fusion-splice the optical fibers OF1 and OF2 in the identified connection mode.

[0086] The range of directions for measuring the transmitted light intensities I1 and I2 in the post-fusion measurement step S16 may be limited depending on the selected relationship. For example, when the marker positions of the optical fibers OF1 and OF2 satisfy Relationship 1 ( FIG. 4 ), Relationship 2 ( FIG. 5 ), Relationship 5 ( FIG. 8 ), or Relationship 8 ( FIG. 11 ), the directions in which the markers c of the optical fibers OF1 and OF2 exist are within a range of 90° or less as viewed from the centers of the optical fibers OF1 and OF2. Therefore, in this case, the range of directions for measuring the transmitted light intensities I1 and I2 in the post-fusion measurement step S16 can be limited to, for example, 90°. This reduces the time required for side-view scanning in the post-fusion measurement step S16. In this case, to further reduce the time required for side-view scanning in the post-fusion measurement step S16, it is preferable to align the optical fibers OF1 and OF2 in the alignment step S13 so that the markers c of the optical fibers OF1 and OF2 face the light source 11.

[0087] Furthermore, when the arrangement of cores in the cross sections of the optical fibers OF1 and OF2 has n-fold symmetry, the range of directions around the axes of the optical fibers OF1 and OF2 in which the transmitted light intensities I1 and I2 are measured in the post-fusion measurement step S16 can be limited to a range of k × 360° / n or less, where k is a natural number less than n. Alternatively, the range can be limited to a range of (3 / 2) × k × 360° / n or less, where k is a natural number less than (2 / 3) × n. As an example, the range in which the transmitted light intensities I1 and I2 are measured in the post-fusion measurement step S16 can be limited to a range of 360° / n or less, or a range of (3 / 2) × 360° / n or less (when k = 1). Alternatively, the range in which the transmitted light intensities I1 and I2 are measured in the post-fusion measurement step S16 can be limited to a range of 2×360° / n or less, or a range of (3 / 2)×2×360° / n or less (when k = 2). The lower limit of the range is arbitrary, and may be, for example, (k-1)×360° / n+15°.

[0088] This makes it possible to determine the alignment of k cores (when the upper limit of the range is k × 360° / n) or k + 1 cores (when the upper limit of the range is 1.5 × k × 360° / n). Furthermore, the time required for the side-view scan in the post-fusion measurement step S16 can be shortened compared to when the optical fibers OF1 and OF2 are rotated 360° and side-view scans are performed from all directions. The smaller k is, the shorter the time required for the side-view scan. This is because the range over which the side-view scan is performed is narrower. On the other hand, the larger k is, the higher the accuracy of determining core alignment. This is because the number of cores whose positions can be measured increases.

[0089] In this case, the range of directions around the axes of the optical fibers OF1 and OF2 for measuring the transmitted light intensities I1 and I2 in the post-fusion measurement step S16 is preferably a range of k×360° / n or less, including the marker c, where k is a natural number less than n. Alternatively, the range is preferably a range of (3 / 2)×k×360° / n or less, including the marker c, where k is a natural number less than (2 / 3)×n. This makes it possible to determine the alignment of the marker c in addition to the alignment of the cores in the post-fusion measurement step S16. Furthermore, the time required for the side-view scan in the post-fusion measurement step S16 can be shortened compared to when the optical fibers OF1 and OF2 are rotated 360° and side-view scans are performed from all directions. Instead of setting the upper limit of the range to (3 / 2) × k × 360° / n, the upper limit of the range may be set to k × 360° / n + (the half-width of the peak corresponding to the core in the graph showing the directional dependence of the transmitted light intensities I1 and I2). Even in this case, it is possible to determine the alignment of k+1 cores. Furthermore, compared to rotating the optical fibers OF1 and OF2 360° and performing side-view scans from all directions, the time required for side-view scanning in the post-fusion measurement step S16 can be shortened.

[0090] The control unit of the fusion splicing apparatus 1 may be configured to select two or more relationships from the above-described relationships 1 to 8, and determine in the determination step S17 whether the marker positions of the optical fibers OF1 and OF2 satisfy any of the two or more selected relationships. Among relationships 5 to 8 corresponding to reverse splicing, the relationships in which the markers of the optical fibers OF1 and OF2 are particularly close to each other are relationship 5 ( FIG. 8 ), in which the markers are sandwiched between two cores, and relationship 8 ( FIG. 11 ), in which the markers are sandwiched between one core. Which relationship is satisfied to minimize the range of directions in which the transmitted light intensities I1 and I2 are measured depends on the position of marker c. Therefore, when selecting one relationship corresponding to normal splicing and one relationship corresponding to reverse splicing, it is preferable to select relationship 1 ( FIG. 4 ) and relationship 5 ( FIG. 8 ), or relationship 1 ( FIG. 4 ) and relationship 8 ( FIG. 11 ). Regardless of which method is selected, the markers are close to each other, so the range in the direction in which the transmitted light intensities I1 and I2 are measured can be made sufficiently small, making it easier to measure the marker positions. When relationship 5 is selected, marker c of optical fiber OF1 and marker c of OF2 are sandwiched between two cores and are close to each other. Therefore, even if the side-view scan range is limited to between these two cores, the positions of both marker c of optical fiber OF1 and marker c of OF2 can be measured. On the other hand, when relationship 8 is selected, marker c of optical fiber OF1 and marker c of OF2 are sandwiched between two cores and are close to each other. Therefore, if the side-view scan range is limited to between that core and its adjacent core, the position of only one of marker c of optical fiber OF1 and marker c of OF2 can be measured. Therefore, when the latter method is selected, the side-view scan range needs to be widened to measure the positions of both marker c of optical fiber OF1 and marker c of OF2. As a result, the time required for side-view scanning is longer than when the former method is selected. Therefore, selecting relations 1 and 5 is preferable to selecting relations 1 and 8.

[0091] (Estimation of Splice Loss) As described above, in the determination step S17, the magnitude of the coupling efficiency or the splice loss may be estimated from the core positions of the optical fibers OF1 and OF2. A method of estimating the coupling efficiency or the splice loss that can be used in this case will be further described with reference to Fig. 13. In Fig. 13, (a) is a side view of the optical fibers OF1 and OF2, (b) is a front view of the end face σ2 of the optical fiber OF1 as seen from the line of sight E2, and (c) is a front view of the end face σ2 of the optical fiber OF2 as seen from the line of sight E1.

[0092] First, the difference Δθi between the peak directions of the transmitted light intensities I1 and I2 measured in the post-fusion measurement step S16 corresponding to the core ai is identified. This difference Δθi represents the difference between the direction in which the core ai of the optical fiber OF exists and the direction in which the core ai of the optical fiber OF2 exists, as viewed from the center of the optical fibers OF1 and OF2, as shown in Figure 13. Hereinafter, this difference Δθi will be referred to as the rotational deviation Δθi of the core ai.

[0093] Next, the positional deviation Δdi of the core ai is calculated from the rotational deviation Δθi of the core ai according to the following equation (1): where r is a predetermined constant representing the distance from the center of the optical fiber OF1, OF2 to the cores a1 to an. Next, the coupling efficiency η of the core a is calculated from the positional deviation Δd of the core a according to the following equation (2): where w1 is a predetermined constant representing the mode field radius of the core a of the optical fiber OF1, and w2 is a predetermined constant representing the mode field radius of the core a of the optical fiber OF2.

[0094] Finally, the average coupling efficiency η is calculated by averaging the coupling efficiencies ηi of each core ai. Alternatively, (1) the average rotational deviation Δθ is calculated by averaging the rotational deviation Δθi of each core ai, (2) the average positional deviation Δd is calculated from the average rotational deviation Δθ, and (3) the average coupling efficiency η is calculated from the average positional deviation Δd. Alternatively, (1) when one of two graphs (see FIG. 12 ) showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 is shifted in the rotational angle direction, the shift amount at which the correlation coefficient between these two graphs becomes maximum is defined as the average rotational deviation Δθ, (2) the average positional deviation Δd is calculated from the average rotational deviation Δθ, and (3) the average coupling efficiency η is calculated from the average positional deviation Δd.

[0095] In addition, when estimating the connection loss, it is sufficient to calculate the known connection loss from the average coupling efficiency η.

[0096] (Fusion splicing system and inspection system) The fusion splicing system is a system composed of a single device or multiple devices that perform each step (excluding steps performed by an operator) that make up the fusion splicing method S1. Each device may be configured to perform a single step, or multiple steps. When the fusion splicing system is composed of a single device, the fusion splicing system is configured in the same manner as the fusion splicing device 1 described above. When the fusion splicing system is composed of multiple devices, the fusion splicing system may be configured, for example, as follows.

[0097] For example, the fusion splicing system may include a first apparatus that performs the pre-fusion measurement step S12, the aligning step S13, the butting step S14, and the fusion step S15, and a second apparatus that performs the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first apparatus may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), heating unit, and controller. In this case, the controller of the first apparatus may perform the pre-fusion measurement step S12, the aligning step S13, the butting step S14, and the fusion step S15 using the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), and heating unit. Furthermore, the second apparatus may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the control unit of the second device can execute the post-fusion measurement step S16, the determination step S17, and the estimation step S18 using the light source, photodetector, and alignment mechanism (rotation mechanism, etc.) described above.

[0098] In this case, the fusion-spliced ​​optical fibers OF1, OF2 are transferred from the first apparatus to the second apparatus while being fixed to a holding member (e.g., a fiber holder detachable between the first apparatus and the second apparatus). The holding member may be left in the first apparatus, and only the fusion-spliced ​​optical fibers OF1, OF2 may be transferred from the first apparatus to the second apparatus. Furthermore, the measurement results of the pre-fusion measurement step S12 may be transmitted via communication from the first apparatus to the control unit of the second apparatus. Note that, if a device such as a robot performs the preparation step S11, the device performing the preparation step S11 may also be included in the fusion splicing system. A mechanism performing the preparation step S11 (e.g., the above-mentioned aligning mechanism) may be built into the first apparatus. Furthermore, the transfer of the optical fibers OF1, OF2 from the first apparatus to the second apparatus may be performed by an operator or by a device such as a robot. If the transfer is performed by a device, the device may be added to the components of the fusion splicing system.

[0099] Alternatively, the fusion splicing system may be a system including a first device that performs the pre-fusion measurement step S12 and a second device that performs the aligning step S13, the butting step S14, the fusion step S15, the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first device may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the controller of the first device may perform the pre-fusion measurement step S12 using the above-described light source, photodetector, and aligning mechanism (rotation mechanism, translation mechanism, etc.). Furthermore, the second device may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), heating unit, and controller. In this case, the control unit of the second device performs the alignment process S13, the butting process S14, the fusion process S15, the post-fusion measurement process S16, the judgment process S17, and the estimation process S18 using the light source, photodetector, alignment mechanism (rotation mechanism, translation mechanism, etc.), and heating unit described above.

[0100] In this case, the optical fibers OF1 and OF2 are transferred from the first device to the second device while being fixed to holding members (e.g., fiber holders detachable from the first device and the second device). The measurement results of the pre-fusion measurement step S12 are transmitted from the first device to the second device via communication. The optical fibers OF1 and OF2 may be transferred from the first device to the second device by an operator or by a device such as a robot. When this transfer is performed by a device, this device may be added to the components of the fusion splicing system.

[0101] Alternatively, the fusion splicing system may be a system including a first apparatus that performs the pre-fusion measurement step S12 and the aligning step S13, and a second apparatus that performs the butting step S14, the fusion splicing step S15, the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first apparatus may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the controller of the first apparatus may perform the pre-fusion measurement step S12 and the aligning step S13 using the above-described light source, photodetector, and aligning mechanism (rotation mechanism, translation mechanism, etc.). Furthermore, the second apparatus may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), heating unit, and controller. In this case, the control unit of the second device performs the butting step S14, the fusion step S15, the post-fusion measurement step S16, the judgment step S17, and the estimation step S18 using the light source, photodetector, alignment mechanism (rotation mechanism, translation mechanism, etc.), and heating unit described above.

[0102] In this case, the optical fibers OF1 and OF2 are transferred from the first device to the second device while being fixed to holding members (e.g., fiber holders detachable from the first device and the second device). The measurement results of the pre-fusion measurement step S12 may be transmitted from the first device to the second device via communication. The optical fibers OF1 and OF2 may be transferred from the first device to the second device by an operator or by a device such as a robot. When this transfer is performed by a device, this device may be added to the components of the fusion splicing system.

[0103] Alternatively, the fusion splicing system may be a system including a first apparatus that performs the pre-fusion measurement step S12 and the aligning step S13, a second apparatus that performs the butting step S14 and the fusion splicing step S15, and a third apparatus that performs the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first apparatus may be configured, for example, with the above-described light source, photodetector, aligning mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the controller of the first apparatus may perform the pre-fusion measurement step S12 and the aligning step S13 using the above-described light source, photodetector, and aligning mechanism (rotation mechanism, translation mechanism, etc.). Furthermore, the second apparatus may be configured, for example, with the above-described aligning mechanism (translation mechanism, etc.), heating unit, and controller. In this case, the controller of the second apparatus may perform the butting step S14 and the fusion splicing step S15 using the above-described aligning mechanism (translation mechanism, etc.) and heating unit. The third device may be configured with, for example, the above-described light source, photodetector, alignment mechanism (rotation mechanism, etc.), and control unit. In this case, the control unit of the third device may execute the post-fusion measurement step S16, the determination step S17, and the estimation step S18 using the above-described light source, photodetector, and alignment mechanism (rotation mechanism, etc.).

[0104] In this case, the aligned optical fibers OF1 and OF2 are transferred from the first apparatus to the second apparatus while being fixed to a holding member (e.g., a fiber holder detachable from the first apparatus, the second apparatus, and the third apparatus). The positional relationship between the optical fibers OF1 and OF2 is maintained by matching the manner in which the holding member is set in the second apparatus with the manner in which the holding member is set in the first apparatus. The fusion-spliced ​​optical fibers OF1 and OF2 are then transferred from the second apparatus to the third apparatus while being fixed to the holding member. The holding member may be left in the second apparatus, and only the fusion-spliced ​​optical fibers OF1 and OF2 may be transferred from the second apparatus to the third apparatus. Furthermore, the measurement results of the pre-fusion measurement step S12 are transmitted by communication from at least the first apparatus to the second apparatus, and, if necessary, from the first apparatus or the second apparatus to the third apparatus. Note that if the preparation step S11 is performed by a device such as a robot, the device that performs the preparation step S11 may also be included in the fusion splicing system. A mechanism that performs the preparation step S11 (for example, the above-mentioned aligning mechanism) may be built into the first device. Furthermore, the transfer of the optical fibers OF1 and OF2 from the first device to the second device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be added to the components of the fusion splicing system. Similarly, the transfer of the optical fibers OF1 and OF2 from the second device to the third device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be added to the components of the fusion splicing system.

[0105] The inspection system is a system including a single or multiple devices that perform each step (excluding steps performed by an operator) that constitutes the inspection method S10. Each device may be configured to perform a single step, or may be configured to perform multiple steps. When the inspection system is configured with a single device, the inspection system is configured similarly to the above-described inspection system 10 (the configuration of the above-described fusion splicing device 1 excluding the heating unit 13). When the inspection system is configured with multiple devices, the inspection system is configured, for example, as follows.

[0106] For example, the inspection system may include a first device that performs the pre-fusion measurement step S12 and the alignment step S13, and a second device that performs the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first device may be configured, for example, with the above-described light source, photodetector, alignment mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the controller of the first device may perform the pre-fusion measurement step S12 and the alignment step S13 using the above-described light source, photodetector, alignment mechanism (rotation mechanism, translation mechanism, etc.). Furthermore, the second device may be configured, for example, with the above-described light source, photodetector, alignment mechanism (rotation mechanism, etc.), and controller. In this case, the controller of the second device may perform the post-fusion measurement step S16, the determination step S17, and the estimation step S18 using the above-described light source, photodetector, and alignment mechanism (rotation mechanism, etc.).

[0107] In this case, the aligned optical fibers OF1 and OF2 are transferred from the first device to a fusion splicing device (an apparatus separate from the first and second devices, which performs the butting step S14 and the fusion splicing step S15) while being fixed to a holding member (e.g., a fiber holder attachable to and detachable from the first device, the fusion splicing device described below, and the second device). The positional relationship between the optical fibers OF1 and OF2 is maintained by matching the manner in which the holding member is set in the fusion splicing device to the manner in which the holding member is set in the first device. Furthermore, the fusion-spliced ​​optical fibers OF1 and OF2 are transferred from the fusion splicing device to the second device while being fixed to the above-described holding member. The holding member may be left in the fusion splicing device, and only the fusion-spliced ​​optical fibers OF1 and OF2 may be transferred from the fusion splicing device to the second device. Furthermore, the measurement results of the pre-fusion measurement step S12 are transmitted via communication from at least the first device to the fusion splicing device, and, as necessary, from the first device or the fusion splicing device to the second device via communication. Note that, if the preparation step S11 is performed by a device such as a robot, the device performing the preparation step S11 may also be included in the inspection system. A mechanism performing the preparation step S11 (e.g., the above-mentioned aligning mechanism) may be built into the first device. Furthermore, the transfer of the optical fibers OF1 and OF2 from the first device to the fusion splicing device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be included as a component of the inspection system. Similarly, the transfer of the optical fibers OF1 and OF2 from the fusion splicing device to the second device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be included as a component of the inspection system.

[0108] Alternatively, the inspection system may be a system including a first apparatus that performs the pre-fusion measurement step S12, a second apparatus that performs the alignment step S13, and a third apparatus that performs the post-fusion measurement step S16, the determination step S17, and the estimation step S18. In this case, the first apparatus may be configured, for example, with the above-described light source, photodetector, alignment mechanism (rotation mechanism, translation mechanism, etc.), and controller. In this case, the controller of the first apparatus may perform the pre-fusion measurement step S12 using the above-described light source, photodetector, and alignment mechanism (rotation mechanism, translation mechanism, etc.). Furthermore, the second apparatus may be configured, for example, with the above-described alignment mechanism (translation mechanism, etc.) and controller. In this case, the controller of the second apparatus may perform the alignment step S13 using the above-described alignment mechanism (translation mechanism, etc.). Furthermore, the third apparatus may be configured, for example, with the above-described light source, photodetector, alignment mechanism (rotation mechanism, etc.), and controller. In this case, the control unit of the third device can execute the post-fusion measurement step S16, the determination step S17, and the estimation step S18 using the light source, photodetector, and alignment mechanism (rotation mechanism, etc.) described above.

[0109] In this case, the aligned optical fibers OF1 and OF2 are transferred from the first apparatus to the second apparatus while being secured to holding members (e.g., fiber holders detachable from the first apparatus, the fusion splicing apparatus described below, the second apparatus, and the third apparatus). The positional relationship between the optical fibers OF1 and OF2 is maintained by matching the manner in which the holding member is set in the second apparatus with the manner in which the holding member is set in the first apparatus. The aligned optical fibers OF1 and OF2 are transferred from the second apparatus to a fusion splicing apparatus (an apparatus separate from the first apparatus, the second apparatus, and the third apparatus, which performs the butting step S14 and the fusion splicing step S15) while being secured to the holding members. The positional relationship between the optical fibers OF1 and OF2 is maintained by matching the manner in which the holding member is set in the fusion splicing apparatus with the manner in which the holding member is set in the second apparatus. The fusion-spliced ​​optical fibers OF1 and OF2 are then transferred from the fusion splicing device to the third device while being fixed by the holding member. The holding member may be left in the fusion splicing device, and only the fusion-spliced ​​optical fibers OF1 and OF2 may be transferred from the fusion splicing device to the third device. Furthermore, the measurement results of the pre-fusion measurement step S12 are transmitted via communication from at least the first device to the second device, and from the second device to the fusion splicing device, and, as necessary, from the first device, the second device, or the fusion splicing device to the third device. Note that, if the preparation step S11 is performed by a device such as a robot, the device performing the preparation step S11 may also be included in the fusion splicing system. A mechanism performing the preparation step S11 (e.g., the above-mentioned aligning mechanism) may be built into the first device. Furthermore, the transfer of the optical fibers OF1, OF2 from the first device to the second device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be added to the components of the fusion splicing system. Similarly, the transfer of the optical fibers OF1, OF2 from the second device to the fusion splicing device may be performed by an operator or by a device such as a robot. If this transfer is performed by a device, this device may be added to the components of the fusion splicing system. Similarly, the transfer of the optical fibers OF1, OF2 from the fusion splicing device to the third device may be performed by an operator or by a device such as a robot.If this transfer is performed by a device, this device may be added to the components of the fusion splicing system.

[0110] (Modification) When the markers of the optical fibers OF1 and OF2 are low-refractive index markers (markers with a refractive index lower than that of the cladding), a dip shape appears in a direction corresponding to the marker position in a graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2, as shown in Figure 12. Here, the dip shape refers to a graph shape in which the transmitted light intensity changes from decreasing to increasing as the direction is changed. For this reason, in this embodiment, a configuration is adopted in which the marker positions of the optical fibers OF1 and OF2 are identified from the direction in which the dip shape appears in the graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2.

[0111] However, the present invention is not limited to this. That is, when a predetermined specific shape (first shape) appears in a direction corresponding to a marker position in a graph representing the directional dependence of the transmitted light intensity of the optical fiber OF1, a configuration can be adopted in which the marker position of the optical fiber OF1 is identified from the direction in which the shape (first shape) appears in the graph. Similarly, when a predetermined specific shape (second shape) appears in a direction corresponding to a marker position in a graph representing the directional dependence of the transmitted light intensity of the optical fiber OF2, a configuration can be adopted in which the marker position of the optical fiber OF2 is identified from the direction in which the shape (second shape) appears in the graph. Here, the specific shape (first shape) appearing in the direction corresponding to the marker position in the graph representing the directional dependence of the transmitted light intensity of the optical fiber OF1 and the specific shape (second shape) appearing in the direction corresponding to the marker position in the graph representing the directional dependence of the transmitted light intensity of the optical fiber OF2 may be the same shape or different shapes.

[0112] For example, if the markers of the optical fibers OF1 and OF2 are high-refractive index markers (markers with a refractive index higher than that of the cladding), as shown in FIG. 14 , a peak shape appears in a direction corresponding to the marker position in a graph showing the directional dependence of the transmitted light intensity of the optical fibers OF1 and OF2. Here, the peak shape refers to a graph shape in which the transmitted light intensity changes from increasing to decreasing as the direction is changed. In this case, a configuration can be adopted in which the marker positions of the optical fibers OF1 and OF2 are identified from the direction in which the peak shape appears in the graph showing the directional dependence of the transmitted light intensity of the optical fibers OF1 and OF2. Note that, as can be seen from FIG. 14 , peak shapes corresponding to the core positions appear periodically in the graph showing the directional dependence of the transmitted light intensity of the optical fibers OF1 and OF2. Therefore, in the graph showing the directional dependence of the transmitted light intensity of the optical fibers OF1 and OF2, it is possible to identify the core positions from the direction in which the periodic peak shapes appear, and to identify the marker positions from the direction in which other peak shapes appear.

[0113] 14(a) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a normal splice (relationship 1). Also, FIG. 14(b) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a reverse splice with respect to the axis L1 (relationship 5).

[0114] Furthermore, when the markers of the optical fibers OF1 and OF2 are low-refractive-index markers (markers with a refractive index lower than that of the cladding) surrounded by a high-refractive-index region (region with a refractive index higher than that of the cladding), a sawtooth shape appears in a direction corresponding to the marker position in a graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2, as shown in Figure 15. Here, the sawtooth shape refers to a graph shape in which the transmitted light intensity changes from (1) increase to decrease, (2) decrease to increase, (3) increase to decrease, or (4) decrease to increase as the direction is changed. In this case, a configuration may be adopted in which the marker positions of the optical fibers OF1 and OF2 are identified from the direction in which the sawtooth shape appears in the graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2.

[0115] 15(a) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a normal splice (relationship 1). Also, FIG. 15(b) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a reverse splice with respect to the axis L1 (relationship 5).

[0116] Furthermore, depending on the refractive index distribution of the markers of the optical fibers OF1 and OF2, a top hat shape may appear in a direction corresponding to the marker position in a graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2, as shown in Figure 16. Here, the top hat shape refers to a graph shape in which the transmitted light intensity changes from (1) increasing to a constant state and (2) from a constant state to a decreasing state as the direction is changed. In this case, a configuration may be adopted in which the marker positions of the optical fibers OF1 and OF2 are identified from the direction in which the top hat appears in the graph showing the directional dependency of the transmitted light intensity of the optical fibers OF1 and OF2.

[0117] 16(a) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a normal splice (relationship 1). Also, FIG. 16(b) is a graph showing the directional dependence of the transmitted light intensities I1 and I2 of the optical fibers OF1 and OF2 obtained in the post-fusion measurement step S16 when the fusion splice of the optical fibers OF1 and OF2 is a reverse splice with respect to the axis L1 (relationship 5).

[0118] Furthermore, in a graph showing the directional dependence of the transmitted light intensity of two optical fibers, the shapes corresponding to the marker positions may be different from each other. For example, if the marker of one of the optical fibers OF1 and OF2 is a low-refractive-index marker and the marker of the other optical fiber is a high-refractive-index marker, a dip shape and a peak shape will appear.

[0119] (Additional Notes) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the above-described embodiments are also included in the technical scope of the present invention.

[0120] For example, the inspection method according to the present invention is sufficient to include at least the post-fusion measurement step described above, and may or may not include other steps. The inspection system according to the present invention is sufficient to include the components necessary to perform at least the post-fusion measurement step described above, and may or may not include the components necessary to perform the other steps. The fusion splicing method according to the present invention is sufficient to include at least the post-fusion measurement step and the fusion step described above, and may or may not include the other steps. The fusion splicing system according to the present invention is sufficient to include the components necessary to perform at least the post-fusion measurement step and the fusion step described above, and may or may not include the components necessary to perform the other steps. Similarly to the fusion splicing method according to the present invention, the method for manufacturing a fiber splice assembly according to the present invention is sufficient to include at least the post-fusion measurement step and the fusion step described above, and may or may not include the other steps.

[0121] (Summary) The inspection method according to aspect 1 is two multi-core fibers having markers formed in their claddings, the end faces of which are fused together, and includes a post-fusion measurement step of identifying the position of the marker of one of the multi-core fibers from a direction in which a predetermined first shape appears in a graph representing the directional dependence of transmitted light intensity of the one multi-core fiber, and identifying the position of the marker of the other of the two multi-core fibers from a direction in which a predetermined second shape appears in a graph representing the directional dependence of transmitted light intensity of the other multi-core fiber.

[0122] The inspection method according to aspect 2 is the inspection method according to aspect 1, further including a determination step of determining whether the fusion was successful or not from the positions of the cores of the two multi-core fibers or the markers identified in the post-fusion measurement step.

[0123] In the inspection method according to aspect 3, in the determination step, if the positional relationship between the markers in the two multi-core fibers identified in the post-fusion measurement step is a predetermined positional relationship, it is determined that the fusion was successful, or if the positional relationship between the markers in the two multi-core fibers identified in the post-fusion measurement step is not the predetermined positional relationship, it is determined that the fusion was unsuccessful.

[0124] The inspection method according to aspect 4 is the inspection method according to aspect 3, further comprising a pre-fusion measurement step of specifying a positional relationship between the markers in the two multi-core fibers before carrying out the step of fusing the two multi-core fibers, and the predetermined positional relationship is a positional relationship that is closest to the positional relationship between the markers in the two multi-core fibers specified in the pre-fusion measurement step, among positional relationships of the markers in the two multi-core fibers that can occur when each core of one of the multi-core fibers is optically coupled to any core of the other multi-core fiber.

[0125] An inspection method according to a fifth aspect is the inspection method according to the fourth aspect, wherein in a cross section of the two multi-core fibers, an arrangement of cores has n-fold symmetry, and a range of directions for measuring the transmitted light intensity in the post-fusion measurement step is limited to any range of k×360° / n or less, where k is any natural number less than n, or is limited to any range of (3 / 2)×k×360° / n or less, where k is any natural number greater than or equal to 1 and less than (2 / 3)×n.

[0126] An inspection method according to Aspect 6 is an inspection method according to any one of Aspects 1 to 5, wherein in a cross section of the two multi-core fibers, an arrangement of cores has n-fold symmetry, and a range of directions for measuring the transmitted light intensity in the post-fusion measurement step is limited to any range of k×360° / n or less, where k is any natural number less than n, or is limited to any range of (3 / 2)×k×360° / n or less, where k is any natural number greater than or equal to 1 and less than (2 / 3)×n.

[0127] An inspection method according to aspect 7 is the inspection method according to aspect 6, wherein the range of directions for measuring the transmitted light intensity in the post-fusion measurement step is limited to any range of k×360° / n or less, including the marker, where k is any natural number less than n, or is limited to any range of (3 / 2)×k×360° / n or less, including the marker, where k is any natural number greater than or equal to 1 and less than (2 / 3)×n.

[0128] An inspection method according to an eighth aspect is the inspection method according to any one of the first to seventh aspects, further comprising: determining, based on one or both of the positions of the cores of the two multi-core fibers and the positions of the markers specified in the post-fusion measurement step, (1) the coupling efficiency or the connection loss of the two multi-core fibers; (2) a correspondence relationship between the core numbers of the cores of one of the multi-core fibers and the core numbers of the cores of the other multi-core fiber optically coupled to the cores; and (3) which of a plurality of regions obtained by dividing the clad of one of the multi-core fibers into a plurality of regions includes the marker of the one of the multi-core fibers. and which of a plurality of regions obtained by dividing the clad of the other multi-core fiber contains the marker of the other multi-core fiber; (4) one or both of an overlap amount and a shift amount between the marker of one multi-core fiber and the marker of the other multi-core fiber; (5) one or both of an overlap amount and a shift amount between a core of the one multi-core fiber and a core of the other multi-core fiber optically coupled to the core of the one multi-core fiber; and (6) an estimation step of estimating at least any of the polarities of the two multi-core fibers.

[0129] The inspection method according to aspect 9 is the inspection method according to any one of aspects 1 to 8, further including an alignment step of rotationally aligning the two multi-core fibers before performing the step of fusing the two multi-core fibers so that the marker faces a light source used in the post-fusion measurement step.

[0130] An inspection method according to aspect 10 is the inspection method according to any one of aspects 1 to 9, wherein the marker is a low refractive index marker having a refractive index lower than that of the cladding, and the first shape and the second shape are dip shapes.

[0131] An inspection method according to aspect 11 is the inspection method according to any one of aspects 1 to 9, wherein the marker is a high refractive index marker having a refractive index higher than that of the cladding, and the first shape and the second shape are peak shapes.

[0132] An inspection method according to aspect 12 is the inspection method according to any one of aspects 1 to 9, wherein the marker is a low refractive index marker having a refractive index lower than that of the cladding and surrounded by a high refractive index region having a refractive index higher than that of the cladding, and the first shape and the second shape are saw-tooth shapes.

[0133] An inspection method according to aspect 13 is the inspection method according to any one of aspects 1 to 9, wherein the marker of one multi-core fiber is a low-refractive index marker having a refractive index lower than that of the cladding, and the marker of the other multi-core fiber is a high-refractive index marker having a refractive index higher than that of the cladding, and the first shape is a dip shape, and the second shape is a peak shape.

[0134] An inspection method according to Aspect 14 is an inspection method for two multi-core fibers having a marker formed in a clad, end faces of which are fused together, the method comprising: a post-fusion measurement step of specifying a position of a core or a marker of one of the two multi-core fibers from a spatial distribution or directional dependency of transmitted light intensity of the one multi-core fiber, and specifying a position of a core or a marker of the other of the two multi-core fibers from a spatial distribution or directional dependency of transmitted light intensity of the other multi-core fiber; and based on one or both of the positions of the cores and the positions of the marker of the two multi-core fibers specified in the post-fusion measurement step, determining (1) the coupling efficiency or connection loss of the two multi-core fibers, (2) a correspondence relationship between the core numbers of the cores of one of the multi-core fibers and the core numbers of the cores of the other multi-core fiber optically coupled to the cores, (3) which of a plurality of regions obtained by dividing the clad of one of the multi-core fibers into a plurality of regions contains the marker of one of the multi-core fibers, and The method includes an estimation step of estimating which of a plurality of regions obtained by dividing the cladding of a fiber into a plurality of regions includes the marker of the other multi-core fiber, (4) one or both of the amount of overlap and the amount of misalignment between the marker of one multi-core fiber and the marker of the other multi-core fiber, (5) one or both of the amount of overlap and the amount of misalignment between the core of one multi-core fiber and the core of the other multi-core fiber optically coupled to the core of the one multi-core fiber, and (6) at least any of the polarities of the two multi-core fibers.

[0135] An inspection system according to Aspect 15 includes a single light source or a plurality of light sources, a single photodetector or a plurality of photodetectors, and a single controller or a plurality of controllers, and the single controller or at least one of the plurality of controllers performs a post-fusion measurement step, using the single light source or at least one of the plurality of light sources and the single photodetector or at least one of the plurality of photodetectors, of two multicore fibers having a marker formed in a clad, the two multicore fibers having end faces fused together, specifying a position of the marker of one of the multicore fibers from a direction in which a predetermined first shape appears in a graph representing the directional dependence of the transmitted light intensity of the one multicore fiber, and specifying a position of the marker of the other of the two multicore fibers from a direction in which a predetermined second shape appears in the graph representing the directional dependence of the transmitted light intensity of the other multicore fiber.

[0136] S1 Fusion splicing method S10 Inspection method S11 Preparation process S12 Pre-fusion measurement process S13 Alignment process S14 Butting process S15 Fusion process S16 Post-fusion measurement process S17 Judgment process

Claims

1. the method includes a post-fusion measurement step of specifying the position of the marker of one of the two multi-core fibers having markers formed in the cladding, the end faces of which are fused together, from a direction in which a predetermined first shape appears in a graph representing the directional dependence of transmitted light intensity of one of the multi-core fibers, and specifying the position of the marker of the other of the two multi-core fibers from a direction in which a predetermined second shape appears in a graph representing the directional dependence of transmitted light intensity of the other of the two multi-core fibers, An inspection method characterized by:

2. The method further includes a determination step of determining whether the fusion has been successful or not from the positions of the cores of the two multi-core fibers or the markers identified in the post-fusion measurement step.

2. The inspection method according to claim 1.

3. In the determination step, if the positional relationship between the markers in the two multi-core fibers identified in the post-fusion measurement step is a predetermined positional relationship, it is determined that the fusion has been successful, or if the positional relationship between the markers in the two multi-core fibers identified in the post-fusion measurement step is not the predetermined positional relationship, it is determined that the fusion has been unsuccessful.

3. The inspection method according to claim 2.

4. The method further includes a pre-fusion measurement step of specifying a positional relationship between the markers on the two multi-core fibers before performing the step of fusing the two multi-core fibers, the predetermined positional relationship is a positional relationship that is closest to the positional relationship of the markers in the two multi-core fibers identified in the pre-fusion measurement step, among positional relationships of the markers in the two multi-core fibers that can occur when each core of one multi-core fiber is optically coupled to any core of the other multi-core fiber.

4. The inspection method according to claim 3.

5. in the pre-fusion measurement step, a position of the marker in the one multicore fiber is identified based on a spatial distribution or directional dependency of a transmitted light intensity of the one multicore fiber, and a position of the marker in the other multicore fiber is identified based on a spatial distribution or directional dependency of a transmitted light intensity of the other multicore fiber.

5. The inspection method according to claim 4.

6. In cross sections of the two multi-core fibers, the cores are arranged with n-fold symmetry, the range of directions in which the transmitted light intensity is measured in the post-fusion measurement step is limited to any range of k×360° / n or less, where k is any natural number less than n, or is limited to any range of (3 / 2)×k×360° / n or less, where k is any natural number greater than or equal to 1 and less than (2 / 3)×n; The inspection method according to any one of claims 1 to 5.

7. The range of directions in which the transmitted light intensity is measured in the post-fusion measurement step is limited to any range of k×360° / n or less, including the marker, where k is any natural number less than n, or is limited to any range of (3 / 2)×k×360° / n or less, including the marker, where k is any natural number greater than or equal to 1 and less than (2 / 3)×n.

7. The inspection method according to claim 6.

8. Based on one or both of the positions of the cores of the two multi-core fibers and the positions of the markers specified in the post-fusion measurement step, (1) the coupling efficiency or connection loss of the two multi-core fibers, (2) the correspondence relationship between the core numbers of the cores of one of the multi-core fibers and the core numbers of the cores of the other multi-core fiber optically coupled to the cores, (3) which of a plurality of regions obtained by dividing the clad of one of the multi-core fibers into a plurality of regions includes the marker of one of the multi-core fibers, and the method further includes an estimation step of estimating at least any of: (1) which of a plurality of regions obtained by dividing the clad of the optical fiber into a plurality of regions contains the marker of the other multicore fiber; (2) one or both of an overlap amount and a shift amount between the marker of the one multicore fiber and the marker of the other multicore fiber; (3) one or both of an overlap amount and a shift amount between a core of the one multicore fiber and a core of the other multicore fiber optically coupled to the core of the one multicore fiber; and (4) the polarities of the two multicore fibers. The inspection method according to any one of claims 1 to 5.

9. the method further includes an aligning step of rotating and aligning the two multi-core fibers before performing the step of fusing the two multi-core fibers so that the marker faces a side of a light source used in the post-fusion measurement step. The inspection method according to any one of claims 1 to 5.

10. the marker is a low refractive index marker having a refractive index lower than that of the cladding, the first shape and the second shape are dip shapes; The inspection method according to any one of claims 1 to 5.

11. the marker is a high refractive index marker having a refractive index higher than that of the cladding, the first shape and the second shape are peak shapes; The inspection method according to any one of claims 1 to 5.

12. the marker is a low refractive index marker having a refractive index lower than that of the cladding and surrounded by a high refractive index region having a refractive index higher than that of the cladding, the first shape and the second shape are sawtooth shapes; The inspection method according to any one of claims 1 to 5.

13. the marker of the one multi-core fiber is a low-refractive index marker having a refractive index lower than that of the cladding, the marker of the other multi-core fiber is a high-refractive index marker having a refractive index higher than that of the cladding, the first shape is a dip shape, and the second shape is a peak shape. The inspection method according to any one of claims 1 to 5.

14. a post-fusion measurement step of specifying the position of a core or a marker of one of two multi-core fibers having markers formed in a clad, end faces of which are fused together, from the spatial distribution or directional dependency of transmitted light intensity of the one multi-core fiber, and specifying the position of a core or a marker of the other of the two multi-core fibers from the spatial distribution or directional dependency of transmitted light intensity of the other multi-core fiber; Based on one or both of the positions of the cores and the positions of the markers of the two multi-core fibers specified in the post-fusion measurement step, (1) the coupling efficiency or the connection loss of the two multi-core fibers, (2) the correspondence relationship between the core numbers of the cores of one of the multi-core fibers and the core numbers of the cores of the other multi-core fiber optically coupled to the cores, (3) which of a plurality of regions obtained by dividing the clad of one of the multi-core fibers into a plurality of regions includes the marker of one of the multi-core fibers, and an estimation step of estimating which of a plurality of regions obtained by dividing the clad of a fiber into a plurality of regions includes the marker of the other multi-core fiber; (4) one or both of an overlap amount and a shift amount between the marker of the one multi-core fiber and the marker of the other multi-core fiber; (5) one or both of an overlap amount and a shift amount between the core of the one multi-core fiber and the core of the other multi-core fiber optically coupled to the core of the one multi-core fiber; and (6) at least any of the polarities of the two multi-core fibers. An inspection method characterized by:

15. A single light source or a plurality of light sources, a single photodetector or a plurality of photodetectors, and a single control unit or a plurality of control units, the single control unit or at least one of the plurality of control units executes a post-fusion measurement step, using the single light source or at least one of the plurality of light sources and the single photodetector or at least one of the plurality of photodetectors, of specifying a position of the marker of one of the two multi-core fibers having a marker formed in a clad, the one of the two multi-core fibers having end faces fused together, from a direction in which a predetermined first shape appears in a graph representing the directional dependence of transmitted light intensity of the one multi-core fiber, and specifying a position of the marker of the other of the two multi-core fibers from a direction in which a predetermined second shape appears in a graph representing the directional dependence of transmitted light intensity of the other multi-core fiber. An inspection system characterized by: