Fusion splicer and fusion splicing method

Abstract

A fusion splicer (1) according to one embodiment of the present invention fusion splices an optical fiber (F). The fusion splicer (1) comprises: a light source (19) that radiates light to an optical fiber (F); a camera (18) that captures an image of an end surface (E) of the optical fiber (F) by receiving light which is emitted from the light source (19), passes through the optical fiber (F), and travels out from the end surface (E); and a core detection unit (32) that detects a core (F31) of the optical fiber (F) from the image of the end surface (E) captured by the camera (18). The camera (18) captures an image of the end surface (E) of the optical fiber (F) in a state in which the focus position of the camera (18) is set to an inner section of the end surface (E).

Description

Fusion splicer and fusion splicing method

[0001] This application claims priority to Japanese Patent Application No. 2023-213052 filed on December 18, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Document 1 describes an optical fiber splicing device. The splicing device includes a first drive unit that moves each of two photonic crystal fibers (PCFs), a second drive unit that moves a mirror located between the two PCFs, a camera that captures an image reflected in the mirror, and an image processing device that processes the image from the camera. The end faces of the PCFs are observed by the mirror and the camera, and the positions of the two PCFs are adjusted based on the observed image.

[0003] Patent Document 2 describes a method for connecting multi-core fibers. In this connection method, the multi-core fiber is arranged so as to face an object to be connected, and then the end face of the multi-core fiber is checked to determine the position of the marker part of the multi-core fiber. The positions of the core parts of the multi-core fiber are aligned with each other.

[0004] Patent Document 3 describes a fusion splicer. The fusion splicer includes an optical fiber holder that holds an optical fiber, a rotation mechanism that rotates the optical fiber, a bending unit that bends the optical fiber, a light source that introduces light from the side of the optical fiber, and a power supply unit that supplies power to the light source. The bending unit and the light source are located either closer to the tip of the optical fiber than the optical fiber holder, or in the optical fiber holder or the rotation mechanism.

[0005] JP 2004-53625 A JP 2013-50695 A International Publication No. 2022 / 244843

[0006] A fusion splicer according to the present disclosure fusion-splices optical fibers. The fusion splicer includes a light source that irradiates the optical fiber with light, a camera that captures an image of the end face using the light that is emitted from the light source and passes through the optical fiber to receive the light from the end face, and a core detector that detects the core of the optical fiber from the image of the end face captured by the camera. The camera captures the image of the end face with its focus positioned on the inner portion of the end face of the optical fiber.

[0007] FIG. 1 is a perspective view showing a fusion splicer according to an embodiment. FIG. 2 is a perspective view showing the internal structure of the fusion splicer according to an embodiment. FIG. 3 is a perspective view showing a rotation mechanism, an optical fiber holder, and an electrode of the fusion splicer according to an embodiment. FIG. 4 is a diagram schematically showing an image observation mechanism of the fusion splicer according to an embodiment. FIG. 5 is a block diagram for explaining the function of the fusion splicer according to an embodiment. FIG. 6 is a diagram schematically showing an image in a state where the focus position of the camera of the fusion splicer according to an embodiment is aligned with the end face of an optical fiber. FIG. 7 is a diagram schematically showing an image in a state where the focus position of the camera of the fusion splicer according to an embodiment is aligned with the inner portion of the end face of an optical fiber. FIG. 8 is a flowchart showing an example of steps of a fusion splicing method according to an embodiment.

[0008] One method for checking the position of the core at the end face of an optical fiber is to observe the end face with a camera. In this case, the focus position of the camera is adjusted to the end face of the optical fiber. When the end face of the optical fiber is photographed with the focus position of the camera adjusted to the end face, the outline of the optical fiber core in the photographed image of the end face may become unclear. In particular, the outline of the core is likely to become unclear when the end face has foreign matter such as dust attached to it, or has chips or roughness.

[0009] An object of the present disclosure is to provide a fusion splicer and a fusion splicing method that can clearly show the outline of a core in an image of an end face.

[0010] According to the present disclosure, the outline of the core can be made clear in an image of the end face.

[0011] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. (1) A fusion splicer according to one embodiment fusion-splices optical fibers. The fusion splicer includes a light source that irradiates light onto an optical fiber, a camera that receives light that passes through the optical fiber and is emitted from an end face of the optical fiber and captures an image of the end face, and a core detection unit that detects the core of the optical fiber from the image of the end face captured by the camera. The camera captures the image of the end face with the focus position of the camera set to the inner portion of the end face of the optical fiber.

[0012] In the above-described fusion splicer and fusion splicing method, a light source inputs light into an optical fiber, and the light emitted from the light source passes through the optical fiber and exits from the end face of the optical fiber. A camera receives the light emitted from the end face of the optical fiber to capture an image of the end face, and the core of the optical fiber is detected from the image of the end face. The camera captures the image of the end face with its focus position set to the inner portion of the end face of the optical fiber. By focusing on the inner portion of the end face of the optical fiber, the outline of the core can be clearly defined in the captured image. By clearly defining the outline of the core, the position of the core can be detected with high accuracy, which contributes to reducing optical loss that occurs during fusion splicing.

[0013] (2) In the above (1), the fusion splicer may include a drive unit that moves at least one of the optical fiber and the camera. The camera may capture an image of the end face with the focus position of the camera set to the end face of the optical fiber. When the outline of the core in the image of the end face is blurred, the drive unit may move at least one of the optical fiber and the camera to a position where the focus position of the camera is the inner part of the end face. The camera may capture an image of the end face with the focus position set to the inner part of the end face. In this case, the camera captures the end face with the focus position set to the end face of the optical fiber, and when the outline of the core in the image of the end face is blurred, at least one of the optical fiber and the camera is moved to a position where the focus position of the camera is the inner part of the end face. By moving the optical fiber or the camera when the outline of the core in the image of the end face is blurred, the outline of the core can be clearly captured with the focus position set to the inner part of the end face.

[0014] (3) In the above (1) or (2), the fusion splicer may include a drive unit that moves at least one of the optical fiber and the camera. The drive unit may move at least one of the optical fiber and the camera a predetermined distance so as to reduce the distance from the optical fiber to the camera, thereby positioning the focus of the camera at an inner portion of the end face. In this case, by moving at least one of the optical fiber and the camera a predetermined distance, the outline of the core can be clearly captured by the camera with the focus position set at the inner portion of the end face.

[0015] (4) In the above (1) or (2), the fusion splicer may include a drive unit that moves at least one of the optical fiber and the camera. The core detection unit may determine whether the outline of the core of the optical fiber is clear in the image of the end face. The drive unit may move at least one of the optical fiber and the camera to a position where the core detection unit determines that the outline of the core is clear as the distance from the optical fiber to the camera decreases, thereby setting the focus position of the camera to the inner part of the end face. In this case, by moving at least one of the optical fiber and the camera to a position where the core detection unit determines that the outline of the core is clear, the outline of the core can be clearly captured with the focus position set to the inner part of the end face.

[0016] (5) A fusion splicing method according to one embodiment includes the steps of: irradiating an optical fiber with light from a light source; capturing an image of the end face of the optical fiber by a camera receiving the light that passes through the optical fiber and is emitted from the end face; and detecting the core of the optical fiber from the image of the end face captured by the camera. In the step of capturing an image of the end face, the image of the end face is captured with the camera focused on an inner portion of the end face of the optical fiber.

[0017] [Details of the embodiment of the present disclosure] Specific examples of a fusion splicer and a fusion splicing method according to an embodiment of the present disclosure will be described. In the description of the drawings, the same or corresponding elements are designated by the same reference numerals, and duplicate explanations will be omitted as appropriate. The drawings may be partially simplified or exaggerated for ease of understanding, and the dimensional ratios and the like are not limited to those shown in the drawings.

[0018] FIG. 1 is a perspective view showing a fusion splicer 1 according to an embodiment. The fusion splicer 1 has a windshield cover 2 on its top. FIG. 2 is a perspective view of the fusion splicer 1 with the windshield cover 2 open. As shown in FIGS. 1 and 2 , the fusion splicer 1 includes a box-shaped housing 3. The top of the housing 3 is provided with a fusion splicing unit 4 that fusion splices optical fibers together, and a heater 5 that heats and shrinks a fiber reinforcement sleeve that covers the spliced ​​optical fibers at the fusion splicing unit 4. The windshield cover 2 is provided to prevent wind from entering the fusion splicing unit 4. The fusion splicer 1 includes a monitor 7 that displays the state of the fusion splicing of the optical fibers, photographed by a camera 18 (see FIG. 4 ) located inside the housing 3. The fusion splicer 1 also includes a power switch 8 that turns the power of the fusion splicer 1 on and off, and a splicing start switch 9 that fusion splices the optical fibers.

[0019] Fig. 3 is a perspective view schematically illustrating the fusion splicing unit 4. As shown in Figs. 2 and 3, the fusion splicing unit 4 fusion-splices a first optical fiber F1 and a second optical fiber F2 to each other. The fusion splicing unit 4 includes a first optical fiber holder 10A that holds the first optical fiber F1, a second optical fiber holder 10B that holds the second optical fiber F2, a first rotation mechanism 20A that rotates the first optical fiber holder 10A, and a second rotation mechanism 20B that rotates the second optical fiber holder 10B. Hereinafter, when it is not necessary to distinguish between the first optical fiber F1 and the second optical fiber F2, the first optical fiber F1 and the second optical fiber F2 may be collectively referred to as the optical fiber F.

[0020] The first optical fiber F1 and the second optical fiber F2 are, for example, optical fibers that require rotational alignment in the fusion splicer 1. The first optical fiber F1 and the second optical fiber F2 are optical fibers that require matching of their positions in the θ direction, which is the direction around the Z axis. For example, the first optical fiber F1 and the second optical fiber F2 are multi-core optical fibers (MCFs) or polarization-maintaining fibers (PMFs).

[0021] The fusion splicer 1 has a pair of discharge electrodes 15. The pair of discharge electrodes 15 are disposed at positions where the first end face E1 of the first optical fiber F1 and the second end face E2 of the second optical fiber F2 face each other. The pair of discharge electrodes 15 fuse the first end face E1 of the first optical fiber F1 and the second end face E2 of the second optical fiber F2 to each other by electric discharge. Hereinafter, when it is not necessary to distinguish between the first end face E1 and the second end face E2, the first end face E1 and the second end face E2 may be collectively referred to as the end face E. The pair of discharge electrodes 15 are disposed at positions where they face each other along a direction (e.g., the X-axis direction) intersecting the first optical fiber F1 and the second optical fiber F2.

[0022] The first optical fiber holder 10A and the second optical fiber holder 10B are aligned along the Z-axis direction, which is the direction in which the axis of the first optical fiber F1 extends. The first rotation mechanism 20A and the second rotation mechanism 20B are aligned along the Z-axis direction. The first optical fiber holder 10A and the second optical fiber holder 10B each have a V-groove 11 in which the first optical fiber F1 or the second optical fiber F2 is placed. The first optical fiber F1 is positioned in the V-groove 11 of the first optical fiber holder 10A, and the second optical fiber F2 is positioned in the V-groove 11 of the second optical fiber holder 10B. The first optical fiber holder 10A and the second optical fiber holder 10B each have a base 12 in which the V-groove 11 is formed, and a lid 13 that is placed on the base 12. The base 12 and the lid 13 are arranged, for example, aligned along the Y-axis direction, which intersects both the X-axis direction and the Z-axis direction.

[0023] The fusion splicer 1 is equipped with an image observation mechanism that observes the first optical fiber F1 and the second optical fiber F2 arranged in the V-groove 11. Fig. 4 is a diagram showing the configuration of an example of the image observation mechanism 16. The image observation mechanism 16 includes, for example, a mirror 17 that is installed so as to be movable in the Y-axis direction, a camera 18 that captures an image of the end face E of the optical fiber F, and a light source 19 that irradiates light L onto the optical fiber F from the side of the optical fiber F.

[0024] The mirror 17 has, for example, a triangular prism shape. The cross-sectional shape of the mirror 17 in the YZ plane is an isosceles triangle, and the mirror 17 extends in the X-axis direction. The mirror 17 has two reflective surfaces 17b that are inclined, for example, at 45 degrees with respect to both the Y-axis direction and the Z-axis direction. The mirror 17 is movable along the Y-axis direction from a middle position in the Z-axis direction when the central axis of the first optical fiber F1 coincides with the central axis of the second optical fiber F2.

[0025] The image observation mechanism 16 has a light source 19 that inputs light L into the first optical fiber F1 and a light source 19 that inputs light L into the second optical fiber F2. The light L input from each light source 19 to the first optical fiber F1 and the second optical fiber F2 is output from the first end face E1 and the second end face E2, which face each other. The light L output from the first end face E1 and the second end face E2 is reflected by the reflecting surface 17b of the mirror 17 toward the camera 18. The camera 18 receives the light L that passes through the optical fiber F and is output from the end face E of the optical fiber F. The camera 18 observes each of the first end face E1 and the second end face E2 by receiving the light L reflected by the mirror 17 and traveling along the Y-axis direction.

[0026] The camera 18 may include a first camera 18b for observing the end face of the first optical fiber F1 and a second camera 18c for observing the end face of the second optical fiber F2. The above describes the light source 19 that causes light L to be incident on the optical fiber F from the side of the optical fiber F. However, instead of the light source 19, light may be incident on the optical fiber F from the opposite sides of the first end face E1 and the second end face E2 that face each other, and any method may be used to cause light L to be incident on the optical fiber F as long as the camera 18 can obtain a sufficient amount of light L to observe the end face E.

[0027] 5 is a diagram schematically illustrating the positional relationship between the mirror 17, the optical fiber F (the first optical fiber F1 or the second optical fiber F2), and the camera 18. As shown in FIG. 5, the fusion splicer 1 has a control unit 30 that controls the operation of each unit of the fusion splicer 1. The mirror 17 and the end face E of the optical fiber F, and the mirror 17 and the camera 18 are arranged to face each other. As described above, the camera 18 observes the end face E by receiving light L that is emitted from the optical fiber F and reflected by the mirror 17. In the above example, the mirror 17 has two reflecting surfaces 17b. However, a mirror having a single reflecting surface may be provided instead of the mirror 17.

[0028] The camera 18 is, for example, a charge-coupled device (CCD) camera or a complementary metal oxide semiconductor (CMOS) camera. The camera 18 captures an image of the optical fiber F (e.g., the first optical fiber F1 and the second optical fiber F2), and the image of the optical fiber F captured by the camera 18 is transmitted to the control unit 30 of the fusion splicer 1 as image data.

[0029] The control unit 30 has, for example, a CPU (Central Processing Unit) configured by one or more integrated circuits (ICs). Functional elements of the control unit 30 (a display unit 31, a core detection unit 32, and a drive unit 33, which will be described later) are executed by the CPU. The control unit 30 acquires, for example, an image of the optical fiber F from the camera 18 and stores the image of the optical fiber F. The control unit 30 has, for example, the display unit 31, the core detection unit 32, and the drive unit 33. The display unit 31 displays an image of the end face E of the optical fiber F, which is imaged by the camera 18, on the monitor 7.

[0030] 6 , the optical fiber F has, for example, a core F31, a cladding F32 surrounding the core F31, and a marker F33. The display unit 31 displays an image of the end face E so that the rotation state of the optical fiber F can be seen using the marker F33. The core detection unit 32 detects the core F31 of the optical fiber F from the image of the end face E captured by the camera 18. In this embodiment, the core detection unit 32 determines whether or not the core F31 is present based on the image data of the end face E, and identifies the center position of the core F31. For example, the core detection unit 32 calculates the outline and center position of the core F31 from brightness information of the image of the end face E. The core detection unit 32 may also determine whether the outline of the core F31 in the image of the end face E is clear.

[0031] 6 is a diagram schematically illustrating a state in which the outline of the core F31 is blurred in an image of the end face E. As shown in Fig. 6, when the end face E is photographed with the focus position of the camera 18 adjusted to the end face E, the outlines of the core F31 and the marker F33 may become unclear in the image of the end face E. In contrast, in this embodiment, the camera 18 photographs the image of the end face E with the focus position of the camera 18 set to the inner portion of the end face E of the optical fiber F.

[0032] 5 , the driving unit 33 moves at least one of the optical fiber F and the camera 18. For example, the driving unit 33 moves the optical fiber F in a direction D1 so that the optical fiber F approaches the mirror 17. At this time, the driving unit 33 may move the first optical fiber holder 10A (or the second optical fiber holder 10B) that holds the optical fiber F in the direction D1. The driving unit 33 may move the camera 18 in a direction D2 so that the camera 18 approaches the mirror 17.

[0033] By moving the optical fiber F in the direction D1 and the camera 18 in the direction D2, the optical path length of the light L from the end face E to the camera 18 is shortened, and the focus position of the camera 18 is set to the inner portion of the end face E. In other words, the optical path length of the light L from the end face E to the camera 18 is made shorter than the distance (focal length) from the focus position of the camera 18 to the camera 18. As a result, even if the outlines of the core F31 and the marker F33 are blurred as in FIG. 6, the outlines of the core F31 and the marker F33 can be made clear as in FIG. 7.

[0034] As described above, the driving unit 33 moves at least one of the optical fiber F and the camera 18 so as to shorten the optical path length of the light L from the optical fiber F to the camera 18. The driving unit 33 may pre-store the focus position of the camera 18 at which the contours of the core F31 and the marker F33 become clear, and may move the optical fiber F or the camera 18 to the pre-stored focus position. The driving unit 33 may move the optical fiber F or the camera 18 by a predetermined distance.

[0035] The amount of movement of the optical fiber F in the direction D1 or the amount of movement of the camera 18 in the direction D2 may be, for example, greater than 0 μm and less than or equal to 100 μm. For example, the amount of movement of the optical fiber F in the direction D1 or the amount of movement of the camera 18 in the direction D2 is greater than or equal to 5 μm and less than or equal to 50 μm.

[0036] The driving unit 33 does not need to store in advance the focus position of the camera 18 at which the contours of the core F31 and the marker F33 become clear. In this case, the detection of the core F31 by the core detection unit 32 and the movement of the optical fiber F or the camera 18 by the driving unit 33 may be repeated until the driving unit 33 moves the optical fiber F or the camera 18 to a position where the core detection unit 32 determines that the contour of the core F31 is clear.

[0037] Next, an example of the fusion splicing method according to this embodiment will be described with reference to the flowchart in Fig. 8. First, a light source 19 irradiates an optical fiber F with light L (light irradiation process, step S1). The light L incident on the optical fiber F passes through the optical fiber F and exits from an end face E. The light L exiting from the end face E is reflected by a mirror 17 toward a camera 18 and reaches the camera 18.

[0038] The camera 18 receives the light L emitted from the end face E and captures an image of the end face E (step of capturing an image of the end face, step S2). The core detector 32 detects the core F31 of the optical fiber F from the image of the end face E captured by the camera 18 (step of detecting the core, step S3). For example, the core detector 32 detects the marker F33 of the optical fiber F along with the core F31. This makes it possible to grasp the positional deviation of the optical fiber F in the rotational direction (the θ direction).

[0039] If the core detection unit 32 successfully detects the core F31 in step S4, for example, the first optical fiber F1 and the second optical fiber F2 are rotationally aligned, and then the first optical fiber F1 and the second optical fiber F2 are fusion-spliced ​​by discharge heating. This completes the series of steps in the fusion splicing method according to this embodiment. On the other hand, if it is determined in step S4 that it is difficult to detect the core F31 (if detection of the core F31 fails), the driver 33 moves at least one of the optical fiber F and the camera 18 (moving step, step S5). At this time, at least one of the optical fiber F and the camera 18 is moved to a position where the focus position of the camera 18 is the inner portion of the end face E.

[0040] The camera 18 captures an image of the end face E with its focus positioned on the inner portion of the end face E (step of capturing an image of the end face, step S6). Then, the core detector 32 detects the core F31 (step of detecting the core, step S7). After rotational alignment of the first optical fiber F1 and the second optical fiber F2 is performed, for example, the first optical fiber F1 and the second optical fiber F2 are fusion-spliced ​​by discharge heating. This completes the series of steps in the fusion splicing method according to this embodiment.

[0041] The following describes the effects achieved by the fusion splicer 1 and fusion splicing method according to this embodiment. In the fusion splicer 1 and fusion splicing method according to this embodiment, the light source 19 inputs light L into the optical fiber F, and the light L, which is emitted from the light source 19 and passes through the optical fiber F, exits from the end face E of the optical fiber F. The camera 18 receives the light L emitted from the end face E of the optical fiber F to capture an image of the end face E, and the core F31 of the optical fiber F is detected from the image of the end face E. The camera 18 captures the image of the end face E with its focus position set to the inner portion of the end face E of the optical fiber F. By focusing on the inner portion of the end face E of the optical fiber F, the outline of the core F31 can be clearly defined in the captured image. The ability to clearly define the outline of the core F31 allows the position of the core F31 to be detected with high accuracy, thereby contributing to a reduction in optical loss that occurs during fusion splicing. In this embodiment, the positions of the marker F33 as well as the core F31 can be detected with high accuracy, so the position of the optical fiber F in the rotational direction can be determined with high accuracy.

[0042] As described above, the fusion splicer 1 may include a drive unit 33 that moves at least one of the optical fiber F and the camera 18. The camera 18 may capture an image of the end face E with the focus position of the camera 18 set to the end face E of the optical fiber F. When the outline of the core F31 in the image of the end face E is blurred, the drive unit 33 may move at least one of the optical fiber F and the camera 18 to a position where the focus position of the camera 18 is the inner portion of the end face E. Thereafter, the camera 18 may capture an image of the end face E with the focus position set to the inner portion of the end face E. In this case, the camera 18 captures the end face E with the focus position set to the end face E of the optical fiber F, and when the outline of the core in the image of the end face E is blurred, at least one of the optical fiber F and the camera 18 is moved to a position where the focus position of the camera 18 is the inner portion of the end face E. When the core contour in the image of the end face E is blurred, the drive unit 33 moves the optical fiber F or the camera 18, so that the contour of the core F31 can be clearly photographed with the focus position set to the inner part of the end face E.

[0043] As described above, the driving unit 33 may move at least one of the optical fiber F and the camera 18 by a predetermined distance so as to reduce the distance from the optical fiber F to the camera 18, thereby setting the focus position of the camera 18 to the inner portion of the end face E. In this case, by the driving unit 33 moving at least one of the optical fiber F and the camera 18 by a predetermined distance, the outline of the core F31 can be clearly photographed by the camera 18 with the focus position set to the inner portion of the end face E.

[0044] As described above, the core detection unit 32 may determine whether the outline of the core F31 of the optical fiber F is clear in the image of the end face E. The drive unit 33 may move at least one of the optical fiber F and the camera 18 to a position where the distance from the optical fiber F to the camera 18 becomes smaller and the core detection unit 32 determines that the outline of the core F31 is clear, thereby setting the focus position of the camera 18 to the inner portion of the end face E. In this case, by moving at least one of the optical fiber F and the camera 18 to a position where the core detection unit 32 determines that the outline of the core F31 is clear, the outline of the core F31 can be clearly captured with the focus position set to the inner portion of the end face E.

[0045] The above describes embodiments of the fusion splicer and fusion splicing method according to the present disclosure. However, the present invention is not limited to the above-described embodiments. Those skilled in the art will readily recognize that various modifications and variations of the present invention are possible within the scope of the gist of the claims. In other words, the shape, size, number, materials, and arrangement of each part of the fusion splicer, as well as the content and order of the steps of the fusion splicing method, can be modified as appropriate within the scope of the gist described above.

[0046] REFERENCE SIGNS LIST 1...Fusion splicer 2...Windshield cover 3...Housing 4...Fusion splicer 5...Heater 7...Monitor 8...Power switch 9...Connection start switch 10A...First optical fiber holder 10B...Second optical fiber holder 11...V-groove 12...Base 13...Cover 15...Discharge electrode 16...Image observation mechanism 17...Mirror 17b...Reflecting surface 18...Camera 18b...First camera 18c...Second camera 19...Light source 20A...First rotation mechanism 20B...Second rotation mechanism 30...Control unit 31...Display unit 32...Core detection unit 33...Drive unit E...End face E1...First end face E2...Second end face F...Optical fiber F1...First optical fiber F2...Second optical fiber F31...Core F32...Cladding F33...Marker L...Light

Claims

1. A fusion splicer for fusion splicing optical fibers, comprising: a light source that irradiates light onto the optical fiber; a camera that receives light that passes through the optical fiber and is emitted from an end face of the optical fiber and captures an image of the end face; and a core detection unit that detects the core of the optical fiber from the image of the end face captured by the camera, wherein the camera captures the image of the end face with the focus position of the camera set to an inner portion of the end face of the optical fiber.

2. A fusion splicer as described in claim 1, further comprising a drive unit which moves at least one of the optical fiber and the camera, wherein the camera takes an image of the end face with the focus position of the camera set to the end face of the optical fiber, wherein the drive unit moves at least one of the optical fiber and the camera to a position where the focus position of the camera is the inner portion of the end face when the outline of the core in the image of the end face is blurred, and wherein the camera takes an image of the end face with the focus position set to the inner portion of the end face.

3. A fusion splicer as claimed in claim 1 or claim 2, further comprising a drive unit which moves at least one of the optical fiber and the camera, the drive unit moving at least one of the optical fiber and the camera a predetermined distance so as to reduce the distance from the optical fiber to the camera, thereby setting the focus position of the camera to an inner portion of the end face.

4. A fusion splicer as described in claim 1 or claim 2, further comprising a drive unit which moves at least one of the optical fiber and the camera, wherein the core detection unit determines whether the outline of the core of the optical fiber in the image of the end face is clear or not, and the drive unit moves at least one of the optical fiber and the camera to a position where the distance from the optical fiber to the camera becomes small and the core detection unit determines that the outline of the core is clear, thereby setting the focus position of the camera to an inner portion of the end face.

5. A fusion splicing method for fusion splicing optical fibers, comprising: a step of using a light source to irradiate light onto the optical fiber; a step of using a camera to capture an image of the end face by receiving the light that passes through the optical fiber and is emitted from the end face of the optical fiber; and a step of detecting a core of the optical fiber from the image of the end face captured by the camera, wherein in the step of capturing an image of the end face, the image of the end face is captured with the focus position of the camera set to an inner portion of the end face of the optical fiber.

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