Method and device for measuring optical characteristics of multi-core optical fiber

Abstract

A method for measuring optical characteristics of a multi-core optical fiber includes: connecting a first optical fiber having the same diameter as the multi-core optical fiber and connected to a light source to a first end surface of the multi-core optical fiber, and connecting a second optical fiber having the same diameter as the multi-core optical fiber and connected to a measuring instrument to a second end surface of the multi-core optical fiber; and irradiating the measurement light emitted from the light source to the first end surface via the first optical fiber, and measuring the light emitted from the second end surface by the measuring instrument via the second optical fiber. The connection step includes: a step for aligning the rotation angle of the first end surface; a step for aligning the rotation angle of the first connection end surface; a step for abutting the aligned first end surface with the first connection end surface; and a step in which the second end surface and the second connection end surface are brought into contact with each other.

Description

Technical Field

[0001] The present disclosure relates to a method and a device for measuring optical characteristics of a multi-core optical fiber. Background Art

[0002] In recent years, in order to cope with the remarkable development of information and communication technology and the resulting surge in data traffic, there is a demand to expand the communication capacity in optical communication networks. However, in existing optical communication networks using single-mode optical fiber (SMF), due to nonlinear Shannon limit, fiber melting limit and other reasons, it is expected that its communication capacity will reach its limit. As a method to break this limit, a space division multiplexing (SDM) transmission method, namely multi-core fiber (MCF), is expected. Unlike the existing SMF, which has only one core in one optical fiber, MCF has multiple cores in one optical fiber. For this reason, when evaluating the optical characteristics of MCF, it is necessary to measure each of the multiple cores, which increases the measurement time, so it is necessary to establish an efficient measurement method.

[0003] Patent Document 1 describes a method for measuring the optical characteristics of each core of an MCF using a fan-in / fan-out (FIFO) device. The FIFO device makes it possible to easily measure the optical characteristics of each core of an MCF without using a centering machine.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-1673 Summary of the invention

[0007] One aspect of the present disclosure relates to a method for measuring the optical characteristics of an MCF, which includes the following steps: connecting a first optical fiber having the same diameter as the MCF and connected to a light source to a first end face of the MCF, and connecting a second optical fiber having the same diameter as the MCF and connected to a measuring device to a second end face of the MCF; and irradiating the first end face with measuring light emitted from the light source via the first optical fiber, and measuring the light emitted from the second end face by the measuring device via the second optical fiber. The connection step includes the following steps: holding the MCF using a first rotating optical fiber holder and aligning the rotation angle of the first end face; holding the first optical fiber using a second rotating optical fiber holder and aligning the rotation angle of a first connection end face of the first optical fiber connected to the first end face; placing the first rotating optical fiber holder opposite to the second rotating optical fiber holder to align the first end faces that have been centered respectively with the first connection end face; and aligning the second end face with the second connection end face of the second optical fiber connected to the second end face. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1It is a diagram showing the configuration of a device for measuring the optical characteristics of the MCF according to the first embodiment.

[0009] Figure 2 is a cross-sectional view of MCF.

[0010] Figure 3 This is a flowchart showing a method for measuring the optical characteristics of the MCF according to the first embodiment.

[0011] Figure 4 This is an explanatory diagram of the first centering step using an end surface observation device.

[0012] Figure 5 It is an explanatory diagram of a first centering step using the end surface observation device involved in the modification example.

[0013] Figure 6 It is an explanatory diagram of the first connection step using the connection part.

[0014] Figure 7 It is a diagram showing the configuration of a device for measuring the optical characteristics of MCF according to the second embodiment.

[0015] Figure 8 It is a plan view showing the end surface of the MCF and the connection end surface of the MMF.

[0016] Fig. 9 It is a diagram showing the configuration of an apparatus for measuring optical characteristics of MCF according to the third embodiment.

[0017] Fig.10 It is a plan view showing the end surface of the MCF and the connection end surface of the eccentric MMF.

[0018] Fig.11 It is a diagram showing the configuration of an apparatus for measuring optical characteristics of MCF according to the fourth embodiment.

[0019] Fig.12 It is a diagram showing the configuration of an apparatus for measuring optical characteristics of MCF according to the fifth embodiment. DETAILED DESCRIPTION

[0020] [Technical Problems to be Solved by the Present Disclosure]

[0021] In the method for measuring the optical characteristics of the above-mentioned MCF using the FIFO device, it is necessary to use a welding machine corresponding to the MCF to align and weld the MCF to be measured and the dummy MCF with the FIFO device. When using a welding machine corresponding to the MCF, the operation from alignment to welding takes time, which increases the measurement time.

[0022] An object of the present disclosure is to provide a method and a device for measuring optical characteristics of MCF that can be easily performed in a short time.

[0023] [Effects of the present disclosure]

[0024] According to the present disclosure, a method and a device for measuring the optical characteristics of MCF that can be easily performed in a short time can be provided.

[0025] [Description of the implementation aspects of the present disclosure]

[0026] First, the implementation aspects of the present disclosure are listed for explanation. (1) A method for measuring the optical characteristics of an MCF according to one aspect of the present disclosure includes the following steps: connecting a first optical fiber having the same diameter as the MCF and connected to a light source to a first end face of the MCF, and connecting a second optical fiber having the same diameter as the MCF and connected to a measuring device to a second end face of the MCF; and irradiating the first end face with a measuring light emitted from the light source via the first optical fiber, and measuring the light emitted from the second end face via the second optical fiber. The connection step includes the following steps: holding the MCF using a first rotating optical fiber holder and aligning the rotation angle of the first end face; holding the first optical fiber using a second rotating optical fiber holder and aligning the rotation angle of the first connection end face of the first optical fiber connected to the first end face; placing the first rotating optical fiber holder and the second rotating optical fiber holder opposite each other so that the first end faces that have been centered are aligned with the first connection end face; and aligning the second end face with the second connection end face of the second optical fiber connected to the second end face. In this measuring method, the optical characteristics of the MCF can be measured simply and in a short time.

[0027] (2) In the measurement method of (1) above, the rotation angle alignment of the first end face and the first connection end face may be performed based on end face observation using a camera. In this case, the rotation rough alignment can be easily performed.

[0028] (3) In the measurement method of (2) above, the end face observation of the first end face may be performed by causing light emitted from a first light source for end face observation to be incident on the side of the MCF, and the end face observation of the first connection end face may be performed by causing light emitted from a second light source for end face observation to be incident on the side of the first optical fiber. In this case, end face observation can be performed with a simple configuration compared to the case of using a coaxial incident light source.

[0029] (4) In the measurement method of (3) above, the MCF may include glass fibers and a light-transmitting coating resin coating the outer peripheral surface of the glass fibers. In this case, light can be reliably incident from the side.

[0030] (5) In the measurement method of (2) above, the end face observation of the first end face may be performed by causing light emitted from a first coaxial incident light source for end face observation disposed between the first end face and the camera to be incident on the first end face, and the end face observation of the first connection end face may be performed by causing light emitted from a second coaxial incident light source for end face observation disposed between the first connection end face and the camera to be incident on the first connection end face. In this case, the degree of freedom of the arrangement location of the light source is increased.

[0031] (6) In the measurement method of (5) above, the MCF may include glass fibers and a light-shielding coating resin coating the outer peripheral surface of the glass fibers. In this case, the coaxial incident light method is particularly effective.

[0032] (7) In the measurement method of any one of (2) to (6) above, the camera may be a camera that supports image processing for calculating the MCF and the rotation angle of the first optical fiber. In this case, precise centering is not required.

[0033] (8) In the measurement method of any one of (1) to (6) above, the connection step may further include a step of finely aligning the first end face with the first connection end face by the first rotating optical fiber holder or the second rotating optical fiber holder after the step of bringing the first end face into contact with the first connection end face. In this case, the connection loss can be reduced.

[0034] (9) In the measurement method of any one of (1) to (8) above, the butting step may be performed using a V-groove or a capillary filled with a refractive index matching agent. In this case, the splicing loss can be reduced.

[0035] (10) In the measurement method of any one of (1) to (9) above, the connection process may further include the following steps: holding the MCF using a third rotating optical fiber holder and adjusting the rotation angle of the second end face; and holding the second optical fiber using a fourth rotating optical fiber holder and adjusting the rotation angle of the second connection end face, and the second end face and the second connection end face are connected by placing the third rotating optical fiber holder and the fourth rotating optical fiber holder opposite each other in a state where the second end face and the second connection end face are respectively aligned. In this case, the optical characteristics of the MCF can be easily measured in a shorter time.

[0036] (11) In the measurement method of any one of (1) to (9) above, the second optical fiber may be a single-core optical fiber having a core having a diameter greater than the diameter of the circumscribed circle of a plurality of cores having a core diameter of MCF. In this case, the second end face and the second connection end face can be joined without rotational alignment.

[0037] (12) In the measurement method of any one of (1) to (9) above, the first optical fiber may be a single-core optical fiber, and the distance between the central axis of the first optical fiber and the central axis of the core may be equal to the distance between the central axis of the MCF and the central axis of each core. In this case, the core of the first optical fiber can be connected to each core of the MCF by rotating the first end face and the first connecting end face.

[0038] (13) An apparatus for measuring the optical characteristics of an MCF according to one aspect of the present disclosure comprises: a light source for injecting measuring light into a first end face of the MCF via a first optical fiber having the same diameter as the MCF; a measuring device for measuring light emitted from a second end face of the MCF via a second optical fiber having the same diameter as the MCF; a first rotating optical fiber holder for holding the MCF and performing rotational centering on the first end face of the MCF; a second rotating optical fiber holder for holding the first optical fiber and performing rotational centering on a first connection end face of the first optical fiber connected to the MCF; a first connecting portion for butting the first end face after rotational centering by the first rotating optical fiber holder with the first connection end face after rotational centering by the second rotating optical fiber holder; and a second connecting portion for butting the second end face of the MCF with the second optical fiber. In this measuring apparatus, the optical characteristics of the MCF can be measured simply and in a short time.

[0039] (14) Another aspect of the present disclosure relates to a method for measuring the optical characteristics of an MCF, including the following steps: connecting a single-core optical fiber having the same diameter as the MCF and connected to a light source to a first end face of the MCF, and connecting an optical fiber having the same diameter as the MCF and connected to a measuring device to a second end face of the MCF; and irradiating the first end face with measuring light emitted from the light source via the single-core optical fiber, and allowing the light emitted from the second end face to be measured by the measuring device via the optical fiber. In the connection step, the single-core optical fiber is connected to the MCF in such a way that the core of the single-core optical fiber covers the entire core of the MCF to be measured at the first end face. In this measuring method, the optical characteristics of the MCF can be simply measured in a short time.

[0040] [Details of the embodiments of the present disclosure]

[0041] Hereinafter, with reference to the accompanying drawings, a specific example of a method for measuring the optical properties of the MCF disclosed in the present invention and a measuring device will be described. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims. In the description of the drawings, the same elements are marked with the same reference numerals, and repeated descriptions are omitted.

[0042] (First Embodiment)

[0043] Figure 1 FIG. 2 is a diagram showing the structure of a device for measuring the optical characteristics of MCF according to the first embodiment. Figure 1 As shown, the measuring device 1 involved in the first embodiment is a device for measuring the optical characteristics of MCF2 as a measuring object. The measuring device 1 includes: a light source 10, which makes the measuring light incident on the end face 2a (first end face) of MCF2; and a measuring device 20, which measures the light emitted from the end face 2b (second end face) of MCF2. The end face 2a is one end face of MCF2 in the length direction. The end face 2b is the other end face of MCF2 in the length direction.

[0044] Figure 2 is the cross-sectional view of MCF. Figure 2 As shown, MCF2 has a glass fiber 21 and a translucent coating resin 22 that covers the outer peripheral surface of the glass fiber 21. The glass fiber 21 includes a plurality of cores 23, a cladding 24, and a marker 25. The plurality of cores 23 are arranged at equal intervals on concentric circles centered on the central axis of MCF2 in a cross section orthogonal to the central axis of MCF2. The cladding 24 is a common cladding surrounding the plurality of cores 23 and the marker 25. The marker 25 has a refractive index different from that of the cladding 24. The marker 25 is arranged at a position that destroys the symmetry of the arrangement of the plurality of cores 23.

[0045] The MCF 2 is, for example, a square four-core MCF, and includes four cores 23. The coating resin 22 is, for example, a transparent resin or a colored resin. The coating resin 22 is not provided at both ends of the glass fiber 21 in the longitudinal direction.

[0046] like Figure 1 As shown, the measuring device 1 includes FIFO devices 11, 12, rotating optical fiber holders 13, 14, 15, 16 and connecting parts 17, 18. The FIFO device 11 has MCF3 and multiple SMF4 connected to each core of MCF3. MCF3 (first optical fiber) is an optical fiber with the same diameter as MCF2, and has a connection end face 3a connected to the end face 2a. MCF3 is a dummy MCF. Among the multiple SMF4, the SMF4 corresponding to the core 23 as the measurement object is connected to the light source 10 one by one. The FIFO device 12 has MCF5 and multiple SMF6 connected to each core of MCF5. MCF5 (second optical fiber) is an optical fiber with the same diameter as MCF2, and has a connection end face 5a connected to the end face 2b. MCF5 is a dummy MCF. Among the multiple SMF6, the SMF6 corresponding to the core 23 as the measurement object is connected to the measuring device 20 one by one.

[0047] The rotating fiber holders 13, 14, 15, and 16 have the function of rotatably holding the optical fiber and maintaining the rotation state of the optical fiber at an arbitrary rotation angle. The rotating fiber holders 13 and 14 hold the MCF 2. The rotating fiber holder 13 (first rotating fiber holder) holds, for example, a portion of the MCF 2 close to the end face 2a and performs rotation centering on the end face 2a. The rotating fiber holder 14 holds, for example, a portion of the MCF 2 close to the end face 2b and performs rotation centering on the end face 2b.

[0048] The rotating fiber holder 15 (second rotating fiber holder) holds the MCF3 of the FIFO device 11. The rotating fiber holder 15 holds, for example, a portion of the MCF3 close to the connection end face 3a, and performs rotational centering on the connection end face 3a (first connection end face). The rotating fiber holder 16 holds the MCF5 of the FIFO device 12. The rotating fiber holder 16 holds, for example, a portion of the MCF5 close to the connection end face 5a (second connection end face), and performs rotational centering on the connection end face 5a.

[0049] Each connection part 17, 18 is, for example, a V-groove (V-groove substrate) filled with a refractive index matching agent. The connection part 17 makes the end face 2a of MCF2 after rotation and centering by the rotating optical fiber holder 13 butt with the connection end face 3a of MCF3 after rotation and centering by the rotating optical fiber holder 15. The connection part 18 makes the end face 2b of MCF2 after rotation and centering by the rotating optical fiber holder 14 butt with the connection end face 5a of MCF5 after rotation and centering by the rotating optical fiber holder 16 (V connection). The refractive index matching agent is, for example, matching oil. The refractive index matching agent reduces the connection loss.

[0050] Each connecting portion 17, 18 may also be a capillary filled with a refractive index matching agent. The maximum manufacturing error of the inner diameter of the capillary is set to within the diameter of the bare fiber (i.e., the diameter of the glass fiber 21) + 1 μm. As the material of the capillary, silica glass (SiO2) and zirconium oxide (ZrO2) can be used.

[0051] In the measurement of the optical characteristics of MCF2 using the measuring device 1, the measuring light emitted from the light source 10 is incident on the end face 2a of MCF2 via SMF4 and MCF3 of the FIFO device 11. The light that passes through MCF2 and is emitted from the end face 2b of MCF2 is incident on the measuring device 20 via MCF5 and SMF6 of the FIFO device 12, and is measured by the measuring device 20.

[0052] In the measuring device 1, when replacing the MCF2 to be measured, for example, the MCF2 is removed together with the rotating fiber holders 13 and 14. The removed MCF2 can also be moved to another measuring device 1 together with the rotating fiber holders 13 and 14 to measure other optical characteristics. The MCF2 newly installed in the measuring device 1 can also be moved to the measuring device 1 together with the rotating fiber holders 13 and 14 to measure the optical characteristics. Since the FIFO devices 11 and 12 are not moved, the centering of the connection end faces 3a and 5a does not need to be performed for the second time and thereafter.

[0053] Figure 3 FIG. 1 is a flow chart showing a method for measuring the optical characteristics of the MCF according to the first embodiment. Figure 3 As shown, the measuring method involved in the first embodiment includes a connecting step S10 and a measuring step S20. The connecting step S10 is a step of connecting the connecting end face 3a of the MCF3 of the FIFO device 11 to the end face 2a of the MCF2, and connecting the connecting end face 5a of the MCF5 of the FIFO device 12 to the end face 2b of the MCF2. The measuring step S20 is a step of irradiating the measuring light from the light source 10 to the end face 2a via the SMF4 and MCF3 of the FIFO device 11, and making the light emitted from the end face 2b be measured by the measuring device 20 via the MCF5 and SMF6 of the FIFO device 12.

[0054] The connecting step S10 includes a first centering step S11 , a second centering step S12 , a third centering step S13 , a fourth centering step S14 , a first connecting step S15 , a second connecting step S16 , a first precise centering step S17 , and a second precise centering step S18 .

[0055] The first alignment step S11 is a step of holding MCF2 using the rotating fiber holder 13 and aligning the rotation angle of the end face 2a. The second alignment step S12 is a step of holding MCF3 using the rotating fiber holder 15 and aligning the rotation angle of the connection end face 3a of MCF3. The third alignment step S13 is a step of holding MCF2 using the rotating fiber holder 14 and aligning the rotation angle of the end face 2b. The fourth alignment step S14 is a step of holding MCF5 using the rotating fiber holder 16 and aligning the rotation angle of the connection end face 5a of MCF5.

[0056] In each centering step S12, S13, S14, the rotation angle of the end face 2a, the connection end face 3a, the end face 2b, and the connection end face 5a is aligned based on the end face observation using a camera. In each centering step S12, S13, S14, for example, a process of performing rough centering of the rotation angle (rotational rough centering) is performed. In the rotational rough centering, although the rotational centering of MCF2 and MCF3, 5 is not complete, if only the optical characteristics of each fiber core 23 of MCF2 are measured, sufficient centering accuracy can be obtained. In the case where the accuracy of the rotational rough centering is not sufficient, precise rotational centering can be performed by rotationally adjusting the rotating optical fiber holders 13, 14, 15, 16 in subsequent steps.

[0057] Figure 4 This is an explanatory diagram of the first centering step using an end surface observation device. Figure 4 The end face observation device 30 shown is used to observe the end faces 2a, 2b and the connection end faces 3a, 5a in the centering steps S11, S12, S13, and S14. Figure 4 As an example, the case of the first centering step S11 is shown. The end face observation device 30 includes a light source 31 and a camera 32. The following describes each centering step S11, S12, S13, and S14. It should be noted that one end face observation device 30 may be used to perform each centering step S11, S12, S13, and S14, or different end face observation devices 30 may be used to perform each centering step S11, S12, S13, and S14.

[0058] In the case of the first centering step S11, the end face observation device 30 is further provided with a rotating optical fiber holder 13. MCF2 is arranged on the rotating optical fiber holder 13. The light source 31 (the first light source for end face observation) is arranged on the side of MCF2 to irradiate light to the side of MCF2. The light source 31 injects light from the side through the coating resin 22 of MCF2. The camera 32 is arranged at a position opposite to the end face 2a. The camera 32 receives light that passes through MCF2 and is emitted from the end face 2a. That is, the end face observation of the end face 2a is performed by making the light incident from the side of MCF2 using the light source 31 for end face observation. In other words, the end face observation of the end face 2a is performed by making the light emitted from the light source 31 for end face observation incident on the side of MCF2.

[0059] In the case of the second centering step S12, the end face observation device 30 is further provided with a rotating optical fiber holder 15. MCF3 is arranged on the rotating optical fiber holder 15. The light source 31 (the second light source for end face observation) is arranged on the side of MCF3 to irradiate light to the side of MCF3. The light source 31 injects light from the side through the coating resin of MCF3. The camera 32 is arranged at a position opposite to the connection end face 3a. The camera 32 receives the light passing through MCF3 and emitted from the connection end face 3a. That is, the end face observation of the connection end face 3a is performed by making the light incident from the side of MCF3 using the light source 31 for end face observation. In other words, the end face observation of the connection end face 3a is performed by making the light emitted from the light source 31 for end face observation incident on the side of MCF3.

[0060] In the case of the third centering step S13, the end face observation device 30 is further provided with a rotating optical fiber holder 14. MCF2 is arranged on the rotating optical fiber holder 14. The light source 31 is arranged on the side of MCF2 to irradiate light to the side of MCF2. The light source 31 injects light from the side through the coating resin 22 of MCF2. The camera 32 is arranged at a position opposite to the end face 2b. The camera 32 receives light that passes through MCF2 and is emitted from the end face 2b. That is, the end face observation of the end face 2b is performed by making the light incident from the side of MCF2 using the light source 31 for end face observation. In other words, the end face observation of the end face 2b is performed by making the light emitted from the light source 31 for end face observation incident on the side of MCF2.

[0061] In the case of the fourth centering step S14, the end face observation device 30 is further provided with a rotating optical fiber holder 16. MCF5 is arranged on the rotating optical fiber holder 16. The light source 31 is arranged on the side of MCF5 to irradiate light to the side of MCF5. The light source 31 injects light from the side through the coating resin of MCF5. The camera 32 is arranged at a position opposite to the connection end face 5a. The camera 32 receives light that passes through MCF5 and is emitted from the connection end face 5a. That is, the end face observation of the connection end face 5a is performed by using the light source 31 for end face observation to make light incident from the side of MCF5.

[0062] The camera 32 may be, for example, a camera that supports image processing and calculates the rotation angles of the end face 2a, the end face 2b, the connection end face 3a, and the connection end face 5a. In this case, since precise rotation alignment is not required in the subsequent process, the measurement time can be further shortened. The end face observation device 30 may also be provided with an adsorption table or V-groove capable of vacuum adsorption to fix the observation end face when observing with the camera 32.

[0063] Figure 5 It is an explanatory diagram of a first centering step using the end surface observation device involved in the modification example. Figure 5The end face observation device 30A involved in the illustrated modification example further includes an optical component 33 composed of a beam splitter or a half mirror. The optical component 33 is arranged on the camera observation axis connecting the center of the observation end face (i.e., each of the end faces 2a, 2b, and the connecting end faces 3a, 5a) and the center of the camera 32. The light source 31 is arranged between the observation end face and the camera 32, and irradiates light to the optical component 33 from a direction perpendicular to the camera observation axis. The optical component 33 reflects the light irradiated from the light source 31 so that the light is incident on the observation end face in parallel with the camera observation axis. The camera 32 receives the light reflected by the observation end face and transmitted through the optical component 33.

[0064] That is, in each centering step S11, S12, S13, S14, the end face observation of the end face 2a, the end face 2b, and the connecting end faces 3a, 5a is performed by causing light to be incident on each observation end face in a coaxial incident manner using a light source 31 (a first coaxial incident light source and a second coaxial incident light source) disposed between the observation end face and the camera 32 as a coaxial incident light source for end face observation. In other words, the end face observation of the end face 2a, the end face 2b, and the connecting end faces 3a, 5a is performed by causing light emitted from the light source 31 as a coaxial incident light source for end face observation to be incident on each observation end face. In the coaxial incident method, since the light is incident from the observation end face, the coating resin 22 of MCF2 can also be light-shielding. Similarly, the coating resin of MCF3, 5 can also be light-shielding.

[0065] After the centering steps S11, S12, S13, and S14 are performed in this manner, the rotational states of the rotating optical fiber holders 13, 14, 15, and 16 are fixed, and while each MCF 2, 3, and 5 is held by the rotating optical fiber holders 13, 14, 15, and 16, each MCF 2, 3, and 5 is moved together with the rotating optical fiber holders 13, 14, 15, and 16 to a location where each connection step S15, S16 is performed.

[0066] Figure 6 : is an illustration of the first connection process using the connection part. Figure 6 As shown, the first connection step S15 includes the following steps: using the connection part 17, the rotating optical fiber holder 13 and the rotating optical fiber holder 15 are opposed to each other, and the end faces 2a and the connection end faces 3a that have been aligned are butted. At this time, the connection part 17 and the rotating optical fiber holders 13 and 15 constitute an optical fiber abutment device. The first connection step S15 also includes the step of connecting the SMF4 corresponding to the core 23 as the measurement object among the multiple SMF4 of the FIFO device 11 to the light source 10.

[0067] Although not shown in the figure, the second connection process S16 includes a process of docking the end face 2b with the connection end face 5a using the connection part 18. In the present embodiment, the docking of the end face 2b with the connection end face 5a is performed by placing the rotating optical fiber holder 14 and the rotating optical fiber holder 16 opposite to each other in the state where the centering is completed. That is, the second connection process S16 is a process of placing the rotating optical fiber holder 14 and the rotating optical fiber holder 16 opposite to each other and docking the end face 2b with the connection end face 5a after the centering is completed. At this time, the connection part 18 and the rotating optical fiber holders 14 and 16 constitute an optical fiber abutment device. The second connection process S16 also includes a process of connecting the SMF6 corresponding to the core 23 to be measured among the multiple SMF6 of the FIFO device 12 to the measuring instrument 20.

[0068] The first precision centering step S17 is a step of performing precision centering of the end face 2a and the connection end face 3a by rotating the optical fiber holder 13 or rotating the optical fiber holder 15 after the first connection step S15. The first precision centering step S17 is performed when the precision of the rotational rough centering of the end face 2a and the connection end face 3a is low and the coupling of light is insufficient. The coupling state of light can be confirmed by irradiating the measurement light from the light source 10 and measuring the light by the measuring device 20.

[0069] The second precision centering step S18 is a step of performing precision centering of the end face 2b and the connection end face 5a by rotating the optical fiber holder 14 or rotating the optical fiber holder 16 after the second connection step S16. The second precision centering step S18 is performed when the precision of the rotational rough centering of the end face 2b and the connection end face 5a is low and the coupling of light is insufficient. The coupling state of light can be confirmed by irradiating the measurement light from the light source 10 and measuring the light by the measuring device 20.

[0070] Since rough rotation centering (rotation rough centering) has been performed in each centering step S11, S12, S13, and S14, each precision centering step S17 and S18 is substantially unnecessary, or is very simple and can be completed in a short time. As a result, MCF2 can be easily connected to MCF3 and 5. Therefore, the optical characteristics of each core 23 of MCF2 can be easily measured using FIFO devices 11 and 12.

[0071] In the measurement method according to the first embodiment, the core 23 to be measured can be easily changed by the FIFO devices 11 and 12 to measure the optical characteristics of all the cores 23. Specifically, the core 23 can be changed by simply replacing the SMF 4 connected to the light source 10 and the SMF 6 connected to the measuring device 20 with the SMF 4 and 6 corresponding to the next core 23 to be measured.

[0072] (Second Embodiment)

[0073] Figure 7 FIG. 2 is a diagram showing the structure of a device for measuring the optical characteristics of MCF according to the second embodiment. Figure 7 The measuring device 1A involved in the second embodiment shown is described around the differences from the measuring device 1. The measuring device 1A is equipped with a multimode optical fiber (MMF) 7 connected to the measuring device 20 instead of the FIFO device 12. The measuring device 1A does not include the FIFO device 12 and the rotating optical fiber holders 14 and 16. MMF7 (second optical fiber) is an optical fiber with the same diameter as MCF2, and has a connecting end face 7a (second connecting end face) connected to the end face 2b of MCF2. MMF7 is a dummy optical fiber. The connecting portion 18 makes the end face 2b of MCF2 butt with the connecting end face 7a of MMF7.

[0074] Figure 8 FIG. 1 is a top view showing the end face of the MCF and the connection end face of the MMF. Figure 8 In the figure, the circumscribed circle 26 of the plurality of cores 23 arranged at the outermost side in the end face 2b of the MCF2 is virtually shown. The MMF7 is a single-core optical fiber, and has a core 7c of a large diameter capable of receiving light from all the cores 23 of the MCF2. The core 7c has a core diameter greater than the diameter of the circumscribed circle 26. In other words, the diameter (core diameter) of the core 7c is greater than the diameter of the circumscribed circle 26. Therefore, the end face 2b and the connection end face 7a can be connected without rotation and centering.

[0075] The measuring method involved in the second embodiment is different from the measuring method involved in the first embodiment in that it does not include the third centering step S13, the fourth centering step S14 and the second precision centering step S18. In addition, in the second connection step S16, the end face 2b that has not been center-aligned is butted against the connection end face 7a, and the end face of the MMF 7 opposite to the connection end face 7a is connected to the measuring device 20.

[0076] The measuring method involved in the second embodiment can be used, for example, for measuring that the optical fiber on the receiving side (the measuring device 20 side) is multimode, like the truncation method. In the truncation method, it is necessary to reconnect the cut end face with the connection end face of the virtual optical fiber after cutting MCF2. Although it is also possible to reconnect by the measuring method involved in the first embodiment, since the third centering step S13 needs to be performed again, the measuring time increases accordingly. In the measuring method involved in the second embodiment, when reconnecting the end face 2b as the cut end face, there is no need to perform rotational centering of the end face 2b, and the measurement can be performed only by the abutment operation, so the measuring time is shortened.

[0077] In the measurement method according to the second embodiment, when changing the core 23 to be measured, the SMF 4 connected to the light source 10 may be replaced with the SMF 4 corresponding to the next core 23 to be measured.

[0078] (Third Embodiment)

[0079] Fig. 9 FIG. 2 is a diagram showing the structure of a device for measuring the optical characteristics of MCF according to the third embodiment. Fig. 9 The measuring device 1B involved in the third embodiment shown is described around the differences from the measuring device 1. The measuring device 1B includes: an eccentric MMF 8, which is connected to the light source 10 instead of the FIFO device 11; and an eccentric MMF 9, which is connected to the measuring device 20 instead of the FIFO device 12. The eccentric MMF 8 (first optical fiber) is an optical fiber with the same diameter as the MCF 2, and has a connection end face 8a (first connection end face) connected to the end face 2a of the MCF 2. The eccentric MMF 8 is a dummy optical fiber. The eccentric MMF 9 (second optical fiber) is an optical fiber with the same diameter as the MCF 2, and has a connection end face 9a (second connection end face) connected to the end face 2b of the MCF 2. The eccentric MMF 9 is a dummy optical fiber.

[0080] Fig.10 FIG. 1 is a top view showing the end face of the MCF and the connection end face of the eccentric MMF. Fig.10 As shown, the eccentric MMF8 is a single-core optical fiber having a core 8c disposed at a position eccentric from the center axis of the eccentric MMF8. The distance between the center axis of the eccentric MMF8 and the center axis of the core 8c is equal to the distance between the center axis of the MCF2 and the center axis of each core 23. In the core 8c, light from each core 23 of the MCF2 can be received. If the core pitch when the MCF2 is a square four-core MCF is set to Λ, the distance between the center axis of the eccentric MMF8 and the center axis of the core 8c is set to d1, and the distance between the center axis of the MCF2 and the center axis of each core 23 is set to d2, then d1=d2=Λ / √2 holds. That is, in the eccentric MMF8, the core center is eccentric from the center of the optical fiber by Λ / √2. Although not shown in the figure, the eccentric MMF9 has the same structure as the eccentric MMF8.

[0081] The measurement method involved in the third embodiment is used, for example, for cut-off wavelength measurement. In the cut-off wavelength measurement of a conventional SMF, the dummy optical fiber connected to both ends of the measured optical fiber is an MMF for multimode excitation. In the case of an MCF, if an MM-MCF capable of multimode waveguide is prepared as a dummy optical fiber, the cut-off wavelength can be measured independently for each core. On the other hand, the MM-MCF has an increased crosstalk between cores due to the expansion of the core diameter in its structure, which has an adverse effect on the measurement results, so sometimes the cut-off wavelength measurement is not suitable for using a FIFO device.

[0082] Since the measuring method according to the third embodiment does not use a FIFO device, the crosstalk between cores is suppressed. In the measuring method according to the third embodiment, when changing the core 23 to be measured, it is necessary to rotate and align the eccentric MMFs 8 and 9 and reconnect them to the end faces 2a and 2b. That is, by performing all the steps of the connection step S10 and the measuring step S20 the same number of times as the number of cores 23 of MCF2, the optical characteristics of each core 23 of MCF2 can be measured.

[0083] (Fourth Embodiment)

[0084] Fig.11 FIG. 4 is a diagram showing the structure of a device for measuring the optical characteristics of MCF according to the fourth embodiment. Fig.11 The measuring device 1C involved in the fourth embodiment shown is described around the differences from the measuring device 1B. The measuring device 1C is equipped with MMF7 (second optical fiber) which is also used in the measuring method involved in the second embodiment instead of the eccentric MMF9. The measuring device 1C does not have the rotating optical fiber holders 14 and 16. As in the measuring method involved in the second embodiment, the MMF7 that can receive the light of all the cores 23 is used as a dummy optical fiber on the receiving side (the measuring device 20 side), so there is no need to perform rotation alignment on the receiving side, and the measurement can be performed only by the abutment operation, so the measurement time is shortened.

[0085] (Fifth Embodiment)

[0086] Fig.12 FIG. 2 is a diagram showing the structure of a device for measuring the optical characteristics of MCF according to the fifth embodiment. Fig.12 The measuring device 1D according to the fifth embodiment shown will be described with focus on the differences from the measuring device 1. The measuring device 1D includes a FIFO device 41 used instead of the FIFO devices 11 and 12, and a FIFO device 42 used instead of the FIFO device 12. The FIFO device 41 includes an MM-MCF 43 (first optical fiber) including a connection end face 43a (first connection end face) connected to the end face 2a, and a plurality of MMFs 44 connected to the light source 10. The FIFO device 42 includes an MM-MCF 45 (second optical fiber) including a connection end face 45a (second connection end face) connected to the end face 2b, and a plurality of MMFs 46 connected to the measuring device 20. The measuring device 1D is used, for example, for cutoff wavelength measurement.

[0087] Although the embodiment has been described above, the present disclosure is not necessarily limited to the above embodiment and modified examples, and various changes can be made within the scope not departing from the gist thereof. The above embodiment and modified examples can also be combined as appropriate.

[0088] The third embodiment described above is described by taking the distance between the center axis of the eccentric MMF8 as a single-core optical fiber and the center axis of the core 8c as equal to the distance between the center axis of the MCF2 and the center axis of each core 23 as an example, but it is not limited to this. In the first connection step S15, the eccentric MMF8 can also be connected to the MCF2 in a manner that the center axis of the core 8c is consistent with the center axis of the core 23 as the measurement object, but the eccentric MMF8 may not be connected so that the center axis of the core 8c is consistent with the center axis of the core 23 as the measurement object. If the eccentric MMF8 is connected to the MCF2 in a manner that the core 23 as the measurement object is included in the core 8c, the optical characteristics can be measured. That is, in the first connection step S15, the eccentric MMF8 can be connected to the MCF2 as long as the core 8c covers the entire core 23 as the measurement object at the end face 2a. At this time, on the measuring device 20, the FIFO device 12 can be connected as in the first embodiment, and the MMF7 can also be connected as in the second embodiment. Regardless of which combination of measurement methods is used, the optical properties of MCF can be measured easily and in a short time.

[0089] Description of Reference Numerals

[0090] 1.1A, 1B, 1C, 1D measuring devices

[0091] 2MCF

[0092] 2a end face (first end face)

[0093] 2b end face (second end face)

[0094] 3MCF (First Fiber)

[0095] 3a Connecting end face (first connecting end face)

[0096] 4SMF

[0097] 5MCF

[0098] 5a Connecting end face (second connecting end face)

[0099] 6SMF

[0100] 7MMF (second optical fiber)

[0101] 7a Connecting end face (second connecting end face)

[0102] 7c core

[0103] 8 eccentric MMF (first optical fiber)

[0104] 8a Connecting end face (first connecting end face)

[0105] 8c core

[0106] 9 eccentric MMF (second optical fiber)

[0107] 9a Connecting end face (second connecting end face)

[0108] 10 Light Source

[0109] 11. 12FIFO devices

[0110] 13 Rotating optical fiber holder (first rotating optical fiber holder)

[0111] 14 Rotating optical fiber holder (third rotating optical fiber holder)

[0112] 15 Rotating optical fiber holder (second rotating optical fiber holder)

[0113] 16 Rotating optical fiber holder (fourth rotating optical fiber holder)

[0114] 17, 18 Connection

[0115] 20 Measuring device

[0116] 21. Fiberglass

[0117] 22 Coating resin

[0118] 23 Core

[0119] 24 Cladding

[0120] 25 Marks

[0121] 26 Circumcircle

[0122] 30, 30A end face observation device

[0123] 31 light sources (first light source for end face observation, second light source for end face observation, first coaxial incident light source, and second coaxial incident light source)

[0124] 32 Camera

[0125] 33 Optical components

[0126] 41, 42FIFO devices

[0127] 43MM-MCF

[0128] 43a connection end face

[0129] 44MMF

[0130] 45MM-MCF

[0131] 45a connection end face

[0132] 46MMF.

Claims

1. A method for measuring the optical properties of a multi-core optical fiber, comprising the following steps: Connecting a first optical fiber having the same diameter as the multi-core optical fiber and connected to a light source to a first end face of the multi-core optical fiber, and connecting a second optical fiber having the same diameter as the multi-core optical fiber and connected to a measuring device to a second end face of the multi-core optical fiber; and irradiating the first end face with measurement light emitted from the light source via the first optical fiber, and measuring the light emitted from the second end face via the second optical fiber by the measuring device, The connecting process includes the following steps: Using a first rotating optical fiber holder to hold the multi-core optical fiber, and adjusting the rotation angle of the first end face; Using a second rotating optical fiber holder to hold the first optical fiber, and aligning the rotation angle of a first connecting end face of the first optical fiber connected to the first end face; Placing the first rotating optical fiber holder and the second rotating optical fiber holder opposite to each other, so that the first end faces respectively aligned are butted against the first connecting end faces; and The second end face is butted against a second connection end face of the second optical fiber connected to the second end face.

2. The method for measuring the optical characteristics of a multi-core optical fiber according to claim 1, wherein: The rotation angles of the first end surface and the first connection end surface are adjusted based on end surface observation using a camera.

3. The method for measuring the optical characteristics of a multi-core optical fiber according to claim 2, wherein: The end face observation of the first end face is performed by causing light emitted from a first light source for end face observation to be incident on a side surface of the multi-core optical fiber. The end face observation of the first connection end face is performed by causing light emitted from a second light source for end face observation to be incident on a side surface of the first optical fiber.

4. The method for measuring the optical characteristics of a multi-core optical fiber according to claim 3, wherein: The multi-core optical fiber includes a glass fiber and a light-transmitting coating resin coating the outer peripheral surface of the glass fiber.

5. The method for measuring the optical characteristics of a multi-core optical fiber according to claim 2, wherein: The end surface observation of the first end surface is performed by causing light emitted from a first coaxial incident light source for end surface observation arranged between the first end surface and the camera to be incident on the first end surface. The end surface observation of the first connection end surface is performed by causing light emitted from a second coaxial incident light source for end surface observation arranged between the first connection end surface and the camera to be incident on the first connection end surface.

6. The method for measuring the optical characteristics of a multi-core optical fiber according to claim 5, wherein: The multi-core optical fiber includes a glass fiber and a light-shielding coating resin coating the outer peripheral surface of the glass fiber.

7. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 2 to 6, wherein: The camera is a camera supporting image processing and calculating the rotation angles of the multi-core optical fiber and the first optical fiber.

8. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 1 to 6, wherein: The connecting step further includes, after the step of bringing the first end face into contact with the first connecting end face, a step of performing precision centering of the first end face and the first connecting end face by the first rotating optical fiber holder or the second rotating optical fiber holder.

9. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 1 to 8, wherein: The docking process is performed using a V-groove or a capillary tube whose interior is filled with a refractive index matching agent.

10. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 1 to 9, wherein: The connecting process also includes the following steps: Using a third rotating optical fiber holder to hold the multi-core optical fiber, and adjusting the rotation angle of the second end face; and The second optical fiber is held by a fourth rotating optical fiber holder, and the rotation angle of the second connecting end face is adjusted. The second end face and the second connection end face are butted against each other by placing the third rotatable optical fiber holder and the fourth rotatable optical fiber holder opposite to each other in a state where the second end face and the second connection end face are aligned.

11. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 1 to 9, wherein: The second optical fiber is a single-core optical fiber having a core having a core diameter that is equal to or larger than a diameter of a circumscribed circle of a plurality of cores of the multi-core optical fiber.

12. The method for measuring the optical characteristics of a multi-core optical fiber according to any one of claims 1 to 9, wherein: The first optical fiber is a single-core optical fiber, The distance between the central axis of the first optical fiber and the central axis of the fiber core is equal to the distance between the central axis of the multi-core optical fiber and the central axis of each fiber core.

13. A device for measuring the optical characteristics of a multi-core optical fiber, comprising: A light source, which injects a measuring light into a first end face of the multi-core optical fiber via a first optical fiber having the same diameter as the multi-core optical fiber; a measuring device for measuring light emitted from a second end face of the multi-core optical fiber via a second optical fiber having the same diameter as the multi-core optical fiber; A first rotating optical fiber holder holds the multi-core optical fiber and performs rotational centering on a first end face of the multi-core optical fiber; a second rotating optical fiber holder, which holds the first optical fiber and performs rotational centering on a first connection end face of the first optical fiber connected to the multi-core optical fiber; a first connecting portion, for connecting the first end surface after the first rotating optical fiber holder is rotated and aligned with the first connecting end surface after the second rotating optical fiber holder is rotated and aligned; as well as The second connecting portion connects the second end face of the multi-core optical fiber to the second optical fiber.

14. A method for measuring the optical properties of a multi-core optical fiber, comprising the following steps: Connecting a single-core optical fiber having the same diameter as the multi-core optical fiber and connected to a light source to a first end face of the multi-core optical fiber, and connecting an optical fiber having the same diameter as the multi-core optical fiber and connected to a measuring device to a second end face of the multi-core optical fiber; and irradiating the first end face with measurement light emitted from the light source via the single-core optical fiber, and allowing the light emitted from the second end face to be measured by the measuring device via the optical fiber, In the connecting step, the single-core optical fiber is connected to the multi-core optical fiber in such a manner that the core of the single-core optical fiber covers the entire core of the multi-core optical fiber to be measured at the first end face.

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