Fan-in fan-out device

Abstract

A FIFO device (10) is provided with: an MCF (20); a first lens (30) having a first optical axis parallel to a central axis of the MCF; a second lens group (40) having a same number of second lenses (41 to 44) as the number of cores of the MCF, the second lenses having a second optical axis parallel to the first optical axis; and a single-core fiber group (50) having a same number of single-core fibers (51 to 54) as the number of the second lenses. End faces (51a to 54a) of the single-core fibers are each bevel polished in a manner that inclines a prescribed polishing angle with respect to a prescribed inclination direction orthogonal to a central axis thereof, and the bevel polishing direction of the peripheral single-core fibers (51 to 54) is set so that the position of the corresponding second lens is closer to the first optical axis or closer to the first lens than when the peripheral single-core fibers are not bevel polished.

Description

Technical Field

[0001] This invention relates to a fan-in / fan-out device. More particularly, it relates to a spatially coupled fan-in / fan-out device comprising a multi-core optical fiber and multiple single-core optical fibers optically coupled together. Background Technology

[0002] With the increasing demand for Internet-based communication traffic year by year, there is a growing expectation for further high-speed and high-capacity optical communication. To meet this demand, technologies such as Wavelength Division Multiplexing (WDM) and digital coherent communication have been used to increase transmission capacity.

[0003] In recent years, space division multiplexing (SDM) technology, which utilizes multi-core optical fibers, has attracted attention as a new multiplexing technology. SDM technology can further achieve high speed and high capacity. With the progress of SDM technology research and development, the demand for fan-in / fan-out (hereinafter also referred to as "FIFO") devices is increasing. A FIFO device is an optical device that incorporates multi-core optical fibers and multiple single-core optical fibers, optically coupling the two together.

[0004] Examples of FIFO devices include spatially coupled, fiber bundle, and fused-to-the-loop types. Spatially coupled FIFO devices are characterized by using lenses (including glass blocks) to optically couple multi-core and single-core fibers. Compared to fiber bundle and fused-to-the-loop FIFO devices, spatially coupled FIFO devices have the advantage of reduced insertion loss, although the components are larger.

[0005] Patent Document 1 discloses a spatially coupled FIFO device arranged along a certain axis. This FIFO device optically couples the cores of a multi-core optical fiber with the same number of single-core optical fibers as the cores. The FIFO device includes a first optical system and a second optical system. The first optical system consists of GRIN (Gradient Index) lenses and a glass block, while the second optical system consists of a lens array. The lens array has the same number of lenses as the single-core optical fibers. The first optical system is arranged on the multi-core fiber side along the axis, and the second optical system is arranged on the single-core fiber side along the same axis. The first optical system is configured to collimate (parallelize) and deflect the light rays emitted from each core of the multi-core optical fiber. The second optical system is configured to use lenses corresponding to each core to deflect and converge the light rays emitted from each core of the first optical system onto the end face of the single-core optical fiber corresponding to each lens.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 6554891 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Furthermore, when each single-core fiber is formed with its end face orthogonal to the axis, light emitted from the second optical system via the first optical system is reflected at the end face of each single-core fiber. This reflected light may then pass through a FIFO device and enter the cores of the multi-core fiber. This reflected light is commonly referred to as "reflected return light." The reflected return light may then enter the communication device on the transmitting side via the multi-core fiber or undergo multiple reflections, thus degrading the optical properties of the signal light.

[0011] Therefore, the following method has been implemented: by grinding the end face of a single-core fiber in a manner that tilts it relative to a plane orthogonal to the axis, the incident light reflected onto each core of a multi-core fiber is suppressed (i.e., the reflected return light is reduced). Hereinafter, the method of grinding in a manner that tilts the end face of the fiber relative to a plane orthogonal to the axis will be referred to as "oblique grinding." In the FIFO device of Patent Document 1, the end faces of multiple single-core fibers are obliquely ground together in a bundled state, thereby reducing the reflected return light.

[0012] However, according to the technology in Patent Document 1, there is a problem that the size of the coupling part of the FIFO device (the part in the FIFO device that optically couples the multi-core fiber to the single-core fiber) is further increased. That is, generally, when the end face of the fiber is obliquely ground, in order to converge the light to that end face, it is necessary to use a lens to deflect the light (in other words, change the angle of the light emitted from the lens (the angle with the axis)). The angle of the light emitted from the lens depends on the incident position of the incident light incident on the lens (distance from the optical axis of the lens). Here, in Patent Document 1, since each end face of the single-core fiber is obliquely ground together, the end faces are parallel to each other. Therefore, in order to converge the light to each end face, it is necessary to make the angle of the light emitted from each lens consistent, that is, it is necessary to make the incident position of the incident light incident on each lens consistent. This means that each lens is moved in the same direction (i.e., the lens array is moved in a direction intersecting the axis). According to this structure, the size of the coupling part of the FIFO device increases due to the movement of the second optical system (lens array) in a direction away from the axis.

[0013] This invention was made to address the aforementioned problems. Specifically, one object of this invention is to provide a technique that enables miniaturization of the coupling section of a fan-in / fan-out (FIFO) device while reducing reflected light.

[0014] Solution for solving the problem

[0015] The fan-in / fan-out devices (10, 110, 210) of the present invention include:

[0016] Multi-core optical fiber (20, 120, 220) is columnar and has multiple first cores (C1 to C4, C1 to C7) extending along the axial direction and a common cladding (CL) surrounding the multiple first cores.

[0017] A first lens (30) has a first optical axis parallel to the central axis of the multi-core optical fiber (20, 120, 220). The first lens is disposed corresponding to the multi-core optical fiber. The first lens causes the light rays emitted from each of the first cores (C1 to C4, C1 to C7) and whose main rays (B1 to B4, B1 to B7) are parallel to each other to be emitted in such a way that each of the main rays is tilted in a predetermined direction.

[0018] The second lens group (40, 140, 240) has a plurality of second lenses (41 to 44, 141 to 144, 241 to 247) having a second optical axis parallel to the first optical axis. The second lens group causes light rays emitted from each of the first cores from the first lens (30) to converge through the corresponding second lenses (41 to 44, 141 to 144, 241 to 247); and

[0019] A single-core fiber group (50, 150, 250) has the same number of single-core fibers (51 to 54, 151 to 154, 251 to 257) as the second lenses (41 to 44, 141 to 144, 241 to 247). The single-core fibers are columnar, each having a second core (C) extending along a central axis and a cladding (CLs) surrounding the second core (C). The end faces (51a to 54a, 151a to 154a, 251a to 257a) of each single-core fiber (51 to 54, 151 to 154, 251 to 257) are arranged such that light rays emitted from the first core (C1 to C4, C1 to C7) from the corresponding second lenses (41 to 44, 141 to 144, 241 to 247) converge onto the second core (C).

[0020] In the fan-in and fan-out devices (10, 110, 210),

[0021] The end faces (51a to 54a, 151a to 154a, 251a to 257a) of each of said single-core fibers (51 to 54, 151 to 154, 251 to 257) are obliquely ground in such a manner that they are inclined at a first grinding angle in a first inclined direction relative to a plane orthogonal to the central axis of the single-core fiber,

[0022] the oblique grinding direction of a peripheral single-core fiber (51 to 54, 151 to 154, 251 to 253 and 255 to 257), whose central axis is located at a position away from the first optical axis, among said single-core fibers is set such that the position of the corresponding second lens (41 to 44, 141 to 144, 241 to 243 and 245 to 247) is closer to the first optical axis or closer to the first lens (30) compared to the non-grinding position where the second lens is located when said peripheral single-core fiber is not obliquely ground,

[0023] said end face (51a to 54a, 151a to 154a, 251a to 257a) of any one of said peripheral single-core fibers (51 to 54, 151 to 154, 251 to 257) is not parallel to at least one said end face (51a to 54a, 151a to 154a, 251a to 257a) of said peripheral single-core fibers (51 to 54, 151 to 154, 251 to 257) other than said one peripheral single-core fiber.

[0024] Herein, "peripheral single-core fiber" refers to a single-core fiber onto which light emitted from a core extending along an axis other than the central axis of a multi-core fiber is incident.

[0025] In addition, "oblique grinding direction of an optical fiber" refers to a direction when viewed along the central axis of the end face of the optical fiber from a distal end farther from the corresponding lens toward a proximal end closer to the corresponding lens along the "oblique grinding reference axis", and the "oblique grinding reference axis" is a line segment that passes through the center of the end face of the optical fiber, is orthogonal to the end face and intersects, at the end face, a plane parallel to a predetermined inclined direction. Furthermore, when the optical fiber is a single-core fiber, "corresponding lens" is the second lens of the second lens group, and "predetermined inclined direction" is the first inclined direction. In addition, when the optical fiber is a multi-core fiber, "corresponding lens" is the first lens, and "predetermined inclined direction" is the second inclined direction.

[0026] Furthermore, in the present specification, "converging (Japanese: 集光)" means that a lens concentrates light (strictly speaking, the chief ray of light) from a plurality of light sources (e.g., the first cores of a multi-core fiber) onto one point, and "focusing (Japanese: 収束) (focusing (Japanese: 集束))" means that a lens reduces the diameter of light from one light source (e.g., each first core of a multi-core fiber) and concentrates the light onto one point.

[0027] In addition, another fan-in / fan-out device of the present invention includes:

[0028] The aforementioned single-core fiber groups (50, 150, 250) include a plurality of the aforementioned single-core fibers (51 to 54, 151 to 154, 251 to 257); the aforementioned second lens groups (40, 140, 240) include a number of second lenses (41 to 44, 141 to 144, 241 to 247) equal to the number of the single-core fibers; the aforementioned first lens (30); and the aforementioned multi-core fiber groups (20, 120, 220) include at least one first core (C1 to C4, C1 to C7) equal to the number of the single-core fibers.

[0029] Specifically, light propagates in a direction opposite to the direction of light propagation of the aforementioned fan-in / fan-out devices (10, 110, 210).

[0030] The effects of the invention

[0031] According to the present invention, the coupling part of the FIFO device can be miniaturized while reducing reflected light. Attached Figure Description

[0032] Figure 1 This is a side view showing an example of a FIFO device according to the first embodiment of the present invention.

[0033] Figure 2 It is a diagram showing the end face of the single-mode fiber in the FIFO device, and it is also a diagram used to illustrate the angle of rotation for oblique grinding.

[0034] Figure 3A This is a side view showing the direction of movement of the second lens of the FIFO device.

[0035] Figure 3B It is shown Figure 3A The front view of the direction of movement of the second lens.

[0036] Figure 4 Is as Figure 1 A three-dimensional view of a comparative example of a FIFO device.

[0037] Figure 5 This is a side view of the comparator.

[0038] Figure 6 This is a diagram showing the end face of the multi-core optical fiber of the comparator.

[0039] Figure 7A This is the front view of the second lens of the comparator.

[0040] Figure 7BThis diagram illustrates the process of the main ray of light emitted from one core of a multi-core optical fiber from a comparator passing through the corresponding second lens.

[0041] Figure 8 This is a diagram showing the end face of the single-mode fiber in the comparator.

[0042] Figure 9A It is stipulated Figure 1 A graph showing the relationship between the oblique grinding rotation angle and the radial movement of the FIFO device.

[0043] Figure 9B It is stipulated Figure 1 A graph showing the relationship between the oblique grinding rotation angle and the amount of movement in the z-axis direction for the FIFO device.

[0044] Figure 10 This is a front view of the second lens.

[0045] Figure 11A yes Figure 10 The diagram shows a partial magnified view of the range R1, and is a diagram showing the corresponding relationship between the radial movement direction of the second lens, the incident position of the principal ray incident on the second lens, and the rotation angle of the oblique grinding.

[0046] Figure 11B yes Figure 10 The diagram shows a partial magnified view of the range R1, and is a diagram showing the corresponding relationship between the movement direction of the second lens in the z-axis direction, the incident position of the principal ray incident on the second lens, and the rotation angle of the oblique grinding.

[0047] Figure 12 It is a diagram showing how the principal ray of the emitted light is refracted due to the movement of the second lens.

[0048] Figure 13 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles, such as the angle of rotation for oblique grinding when the radial condition is met.

[0049] Figure 14 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles for oblique grinding rotation when the z-axis direction condition is met.

[0050] Figure 15 This is a diagram showing the end face of a multi-core optical fiber in another example of a FIFO device according to the first embodiment of the present invention.

[0051] Figure 16 It shows that it has Figure 15 A top view of a multi-core fiber optic FIFO device.

[0052] Figure 17 Is as Figure 16A top view of a comparative example of a FIFO device.

[0053] Figure 18A It is stipulated Figure 16 A graph showing the relationship between the oblique grinding rotation angle and the radial movement of the FIFO device.

[0054] Figure 18B It is stipulated Figure 16 A graph showing the relationship between the oblique grinding rotation angle and the amount of movement in the z-axis direction for the FIFO device.

[0055] Figure 19 This is a front view of the second lens.

[0056] Figure 20 yes Figure 19 The diagram shows a partial magnified view of the range R2, and is a diagram showing the corresponding relationship between the movement direction of the second lens in the radial and z-axis directions, the incident position of the principal ray incident on the second lens, and the rotation angle of the oblique grinding.

[0057] Figure 21 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles, such as the angle of rotation for oblique grinding when the radial condition is met.

[0058] Figure 22 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles for oblique grinding rotation when the z-axis direction condition is met.

[0059] Figure 23 This is a diagram showing the end face of a multi-core optical fiber in another example of the FIFO device according to the first embodiment of the present invention.

[0060] Figure 24 It shows that it has Figure 23 A side view of a multi-core fiber optic FIFO device.

[0061] Figure 25 Is as Figure 24 A top view of a comparative example of a FIFO device.

[0062] Figure 26A It is stipulated Figure 24 A graph showing the relationship between the oblique grinding rotation angle and the radial movement of the FIFO device.

[0063] Figure 26B It is stipulated Figure 24 A graph showing the relationship between the oblique grinding rotation angle and the amount of movement in the z-axis direction for the FIFO device.

[0064] Figure 27 This is a front view of the second lens.

[0065] Figure 28A yes Figure 27 The diagram is a magnified view of the area R3, and it shows the relationship between the radial movement direction of the second lens, the incident position of the principal ray incident on the second lens, and the rotation angle of the oblique grinding.

[0066] Figure 28B yes Figure 27 The diagram is a magnified view of the area R3, and it shows the relationship between the movement direction of the second lens in the z-axis direction, the incident position of the principal ray incident on the second lens, and the rotation angle of the oblique grinding.

[0067] Figure 29 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles, such as the angle of rotation for oblique grinding when the radial condition is met.

[0068] Figure 30 It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles for oblique grinding rotation when the z-axis direction condition is met.

[0069] Figure 31A This is a side view showing the multi-core optical fiber and the first lens of the FIFO device according to a variation of the present invention.

[0070] Figure 31B It shows that Figure 31A A side view of the FIFO device with its multi-core fiber moving in the -y-axis direction.

[0071] Figure 32A This is the FIFO device involved in the second embodiment of the present invention. Figure 10 A magnified view of the area R1.

[0072] Figure 32B It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles for oblique grinding rotation when the z-axis direction condition is met.

[0073] Figure 33A This is the FIFO device involved in the second embodiment of the present invention. Figure 27 A magnified view of the area R3.

[0074] Figure 33B It is a front view of a single-mode optical fiber and a diagram used to illustrate the range of angles for oblique grinding rotation when the z-axis direction condition is met.

[0075] Figure 34A This is a diagram showing the oblique grinding direction of the multi-core optical fiber of the FIFO device according to the third embodiment of the present invention.

[0076] Figure 34BThis is a diagram showing another oblique grinding direction for multi-core optical fibers.

[0077] Figure 35 It is a chart that specifies the relationship between the positional offset of a multi-core optical fiber and the deviation of the light angle.

[0078] Figure 36 This is a front view of the second lens of the FIFO device according to the fourth embodiment of the present invention.

[0079] Figure 37 Is as Figure 36 The front view of the second lens in the comparative example of the second lens.

[0080] Figure 38 It is shown Figure 36 The front view of the other layouts of the second lens. Detailed Implementation

[0081] (First Implementation)

[0082] Figures 1 to 3B This is a diagram showing a FIFO device 10, which is an example of a FIFO device according to the first embodiment of the present invention. Figures 4 to 8 This diagram shows a FIFO device 310, which is a comparative example of FIFO device 10. The structure of FIFO device 310 will be described first, followed by a description of the structure of FIFO device 10. Hereinafter, "FIFO device" will be simply referred to as "device".

[0083] Figure 4 This is a 3D view of device 310. Figure 5 This is a side view of device 310. (As shown) Figure 4 and Figure 5 As shown, device 310 includes a multi-core fiber 20, a first lens 30, a second lens group 40, and a single-mode fiber group 350. These components are arranged in the order described above along axis A1. An orthogonal coordinate system is established for device 310 (and device 10 described later). The z-axis extends parallel to axis A1 with the direction from the multi-core fiber 20 toward the first lens 30 as the positive direction. The y-axis is orthogonal to the z-axis and extends with the top of the paper as the positive direction. The x-axis is orthogonal to both the z-axis and the y-axis. Hereinafter, the multi-core fiber and the single-mode fiber will also be referred to as "MCF" and "SMF," respectively. Furthermore, in this specification, for ease of reading, illustrations are provided with variations in the dimensions of specific components (e.g., MCF 20 and SMF group 350) and the angle of light rays.

[0084] MCF 20 is cylindrical, and at least its central axis at its end in the +z direction coincides with axis A1. The end face 20a of MCF 20 (refer to...) Figure 5It is parallel to the plane (xy plane) orthogonal to axis A1. Figure 6 This is a diagram showing the end face 20a viewed along the central axis of MCF 20. (See diagram below.) Figure 6 As shown, MCF 20 comprises four cores C1 to C4 and a common cladding CL surrounding these cores C1 to C4. Cores C1 to C4 are located at the vertices of a square centered on the center of end face 20a and extend along the axial direction. The distance between adjacent cores (core spacing) is 50 μm. Cores C1 to C4 and the cladding CL are all formed of glass with quartz as the main component. The refractive index of cores C1 to C4 is greater than that of the cladding CL. MCF 20 is a single-mode fiber. Furthermore, the material of cores C1 to C4 and the cladding CL is not limited to glass with quartz as the main component and can be formed of other materials. In addition, in this specification, the cylinder also includes cases where the axis is bent.

[0085] like Figure 4 and Figure 5 As shown, the +z-axis end of the MCF 20 is held through a cylindrical ferrule 22. The end face 22a of the ferrule 22 and the end face 20a of the MCF 20 are on the same plane. This is because the end face 20a of the MCF 20 is ground together with the end face 22a of the ferrule 22 while penetrating through it. Figure 5 In the diagram, the MCF 20 inside the collar 22 is shown in dashed lines, but the illustrations of cores C1 to C4 are omitted.

[0086] Light rays propagating from the cores C1 to C4 of the MCF 20 are emitted from the end face 20a toward the first lens 30. That is, the MCF 20 functions as an emission element. Figure 4 The diagrams only show the cores C1 through C4 (see reference). Figure 6 The principal rays B1 to B4 of the emitted light, in Figure 5 The diagram only shows the principal rays B2 and B3 emitted from cores C2 and C3. The principal rays emitted from each core C1 to C4 are parallel to each other, but each emitted ray is a diverging ray as it travels.

[0087] The first lens 30 is a collimating lens with a focal length of 1.3 mm; more specifically, it is an aspherical lens with a rotationally symmetric curved surface. The first lens 30 collimates (parallelizes) the diverging light rays emitted from each core C1 to C4. The optical axis of the first lens 30 is located on the central axis of the MCF 20 (i.e., on axis A1). The first lens 30 deflects the parallel principal rays B1 to B4 emitted from each core C1 to C4 (more specifically, the principal rays B1 to B4 are each emitted at an angle in a predetermined direction). In other words, the first lens 30 focuses the light rays from each core C1 to C4 to a focal point f1. That is, the first lens 30 is a lens corresponding to the multi-core optical fiber. Furthermore, the curved surface of the first lens 30 only needs to deflect the light rays from each core C1 to C4, and can also be non-rotationally symmetric. Additionally, the first lens 30 can be a spherical lens, a GRIN lens, or a single-sided flat lens.

[0088] The second lens group 40 has the same number of second lenses 41 to 44 as the MCF 20 (4 in this example) (refer to...). Figure 4 The second lenses 41 to 44 are all collimating lenses with a focal length of 2.5 mm; more specifically, they are aspherical lenses with rotationally symmetric curved surfaces. Hereinafter, the second lenses 41 to 44 will be simply referred to as "lenses 41 to 44". The optical axes of each lens 41 to 44 are parallel to the optical axis of the first lens 30. Furthermore, the principal points of lenses 41 to 44 lie on the same plane, which is orthogonal to axis A1. Figure 5 The diagram only shows lenses 42 and 43, which are among lenses 41 to 44, and are the incident points for principal rays B2 and B3.

[0089] Figure 7A This is a diagram showing the view of lenses 41 to 44 when viewed along axis A1 (i.e., along the optical axis of the first lens 30). Figure 7A As shown, the principal points Cs1 to Cs4 of lenses 41 to 44 are located at the vertices of a square centered on axis A1. More specifically, lenses 41 to 44 are configured such that the principal rays B1 to B4 of the light rays from the cores C1 to C4 of MCF 20 emitted from the first lens 30 pass through the focal point f2 of the corresponding lens 41 to 44 (described later).

[0090] Reference Figure 7B To explain in detail. Figure 7B This diagram illustrates the passage of the principal ray B3 of the emitted light from core C3 through the corresponding lens 43. (As shown) Figure 4 , Figure 5 as well as Figure 7BAs shown, the light ray from core C3 of MCF 20 emitted from the first lens 30 passes through focal point f1. The principal ray B3, having passed through focal point f1, passes directly through focal point f2 of lens 43 (see reference). Figure 7B The principal ray B3 incident at position Ps3 of lens 43 is incident at a specified angle of incidence (1.6° in this example) and is directed at the optical axis As3 of lens 43 (see reference). Figure 7B Parallel light rays are emitted from lens 43.

[0091] Here, as Figure 7A As shown, when lens 43 is observed along axis A1, the incident position Ps3 of the principal ray B3 lies on the "half-line connecting axis A1 and the principal point Cs3 of lens 43". More specifically, the incident position Ps3 is located at a position equidistant from the principal point Cs3 in the +x-axis and +y-axis directions, respectively. This is because, as... Figure 6 As shown, the core C3 of the MCF 20 corresponding to lens 43 is positioned at equal distances (25 μm in this example) from the center of the MCF 20 in the -x-axis direction and the -y-axis direction, respectively.

[0092] Similarly, as Figure 4 As shown, the principal rays B1, B2, and B4, which pass through focal point f1, travel straight through focal point f2 (not shown) of lenses 41, 42, and 44, respectively, and are incident at positions Ps1, Ps2, and Ps4 of lenses 41, 42, and 44 at a predetermined angle of incidence (1.6° in this example). The principal rays B1, B2, and B4 incident at positions Ps1, Ps2, and Ps4 exit from lenses 41, 42, and 44 as rays parallel to the optical axes of lenses 41, 42, and 44, respectively. Figure 7A As shown, when lenses 41, 42, and 44 are observed along axis A1, the incident positions Ps1, Ps2, and Ps4 of the principal rays B1, B2, and B4 are located at the remaining three vertices of a square centered on axis A1 and having one vertex at incident position Ps3. This depends on the core configuration of MCF 20 (see reference). Figure 6 That is, the incident positions Ps1 to Ps4 are symmetrical with respect to the axis A1.

[0093] like Figure 4 and Figure 5 As shown, the second lens group 40 causes the light rays emitted from the first lens 30 from each core C1 to C4 to converge through the corresponding lenses 41 to 44 (in... Figure 4 and Figure 5(Only the principal ray is shown in the diagram). Furthermore, the curved surfaces of each lens 41 to 44 only need to deflect the light rays from their respective cores C1 to C4, and can be non-rotationally symmetric. Additionally, each lens 41 to 44 can be a spherical lens, a GRIN lens, or a single-sided flat lens.

[0094] SMF group 350 has the same number of SMFs 351 to 354 as lenses 41 to 44 (4 in this example) (see reference). Figure 4 SMF 351 to 354 are all optical fibers that propagate light in one propagation mode. SMF 351 to 354 have the same structure as each other; therefore, the structure of SMF 353 will be described below. SMF 353 is cylindrical, and at least the central axis of its end in the -z-axis direction is aligned with the optical axis As3 of the corresponding lens 43 (see reference). Figure 7B Parallel. Furthermore, SMF 353 is located separately from the optical axis of the first lens 30. The end face 353a of SMF 353 is parallel to the xy plane. Figure 8 This is a diagram showing the end face 353a viewed along the central axis of SMF 353. (See diagram below.) Figure 8 As shown, SMF 353 comprises a core C extending along its central axis and cladding layers CLs surrounding the core C. Both the core C and the cladding layers CLs are formed of glass with quartz as the primary component. The refractive index of the core C is greater than that of the cladding layers CLs. Furthermore, the material of the core C and the cladding layers CLs is not limited to glass with quartz as the primary component, and can also be formed of other materials.

[0095] like Figure 4 and Figure 5 As shown, the -z-axis end of the SMF 353 is held through a cylindrical collar 363. The end face 353a of the SMF 353 is ground together with the end face 363a of the collar 363, both passing through the collar. Thus, the end face 353a of the SMF 353 and the end face 363a of the collar 363 are located on the same plane (xy plane). Figure 5 In the image, SMF 353 inside the collar 363 is shown by a dashed line.

[0096] The end face 353a of the SMF 353 is positioned such that light rays emitted from the lens 43 from the core C3 converge onto the core C (more precisely, onto the center of the core C). That is, the SMF 353 is configured to direct the principal ray B3 toward the center of the core C. Thus, the light emitted from the core C3 enters the core C of the SMF 353 with low loss.

[0097] Similarly, SMFs 351, 352, and 354 are located at positions separated from the optical axis of the first lens 30, and these end faces 351a, 352a, and 354a (refer to...) Figure 4 The lenses 41, 42, and 44 are configured such that the light rays emitted from cores C1, C2, and C4 converge onto core C (more precisely, at the center of core C). That is, SMFs 351, 352, and 354 are configured such that the principal rays B1, B2, and B4 are incident towards the center of core C. Thus, the emitted light from cores C1, C2, and C4 is incident on core C of SMFs 351, 352, and 354 with low loss.

[0098] In this way, the first lens 30 and the second lens group 40 optically couple the MCF 20 to the SMF group 350. In other words, the first lens 30 and the second lens group 40 function as the coupling part of the device. The above is a description of the structure of the device 310 as a comparative example.

[0099] Next, refer to Figures 1 to 3B The structure of device 10 will be described. Figure 1 This is a side view of device 10. (As shown) Figure 1 As shown, device 10 includes MCF 20, first lens 30, second lens group 40, and SMF group 50. These components are arranged along axis A1 in the order described above. That is, device 10 uses the same components as those used in device 310, except for SMF group 50. Furthermore, the positional relationship between MCF 20 and first lens 30 is the same as their positional relationship in device 310. In contrast, the positional relationship between MCF 20 and first lens 30 and second lens group 40 is different from their positional relationship in device 310. Hereinafter, the differences from device 310 will be mainly explained. In addition, the cores C1 to C4 of MCF 20 correspond to an example of "first core". In addition, the optical axis of first lens 30 and the optical axes of lenses 41 to 44 correspond to an example of "first optical axis" and "second optical axis", respectively.

[0100] SMF group 50 has the same number of SMFs 51 to 54 as lenses 41 to 44 (4 in this example). The difference between SMFs 51 to 54 and SMFs 351 to 354 is that their end faces 51a to 54a (in...) Figure 1Only end faces 52a and 53a are shown in the illustration, which have undergone oblique grinding. Here, oblique grinding means that each end face 51a to 54a is obliquely ground at a predetermined grinding angle (8° in this example) relative to a plane orthogonal to its central axis (the xy plane in this embodiment) in a predetermined oblique direction (described later). By obliquely grinding SMFs 51 to 54, reflected light at end faces 51a to 54a is reduced. The -z-axis ends of SMFs 51 to 54 are held through cylindrical collars 61 to 64. End faces 51a to 54a of SMFs 51 to 54 are obliquely ground together with end faces 61a to 64a of collars 61 to 64. Furthermore, SMF group 50 and SMFs 51 to 54 correspond to an example of a "single-core fiber group" and a "peripheral single-core fiber," respectively. Additionally, core C of SMFs 51 to 54 corresponds to an example of a "second core." Furthermore, the aforementioned tilting direction and the aforementioned grinding angle are respectively equivalent to an example of the "first tilting direction" and the "first grinding angle".

[0101] Here, the line segment that intersects the end faces 51a to 54a of SMFs 51 to 54, is orthogonal to the end faces 51a to 54a, and is parallel to the aforementioned tilting direction, is defined as the "oblique grinding reference axis". In this case, each oblique grinding direction of SMFs 51 to 54 is defined as the direction along the oblique grinding reference axis when viewed from the central axis of each end face 51a to 54, "from the distal end E1 farther from the corresponding lens 41 to 44 toward the proximal end E2 closer to the corresponding lens 41 to 44". In this embodiment, SMFs 51 to 54 are cylindrical. Therefore, each end face 51a to 54a after oblique grinding is elliptical when viewed from a direction perpendicular to it. Therefore, the oblique grinding reference axis is the long axis of each end face 51a to 54a. The direction when observing along the central axis of each end face 51a to 54a from the end farther from the corresponding lens 41 to 44 (far end E1) towards the other end closer to the corresponding lens 41 to 44 (proximal end E2) is the "oblique grinding direction of each SMF 51 to 54". Hereinafter, the observation of a component along its central axis will also be referred to as "frontal observation of the component". Figure 2 This is a diagram obtained by observing the end faces 53a and 52a of SMF 53 and 52 from the front. (See diagram below.) Figure 1 and Figure 2As shown, the oblique grinding direction D3 of end face 53a is from the distal end E1 of the oblique grinding reference axis toward the proximal end E2 (+y-axis direction), and the oblique grinding direction D2 of end face 52a is from the distal end E1 of the oblique grinding reference axis toward the proximal end E2 (-y-axis direction). Furthermore, the oblique grinding direction can also refer to the grinding direction in which the z-axis component of end faces 51a to 54a decreases.

[0102] Below, when observing the end faces 51a to 54a of SMF 51 to 54 from the front, the angle formed by any oblique grinding direction relative to the "reference direction D0 passing through the center of each end face 51a to 54a and towards the +y axis" in a counterclockwise direction is defined as the "oblique grinding rotation angle Ψ with a positive value". Figure 2 In the example, the oblique grinding direction D3 of SMF 53 is consistent with the reference direction D0. Therefore, the oblique grinding rotation angle Ψ of SMF 53 is 0°. On the other hand, the oblique grinding direction D2 of SMF 52 is opposite to the reference direction D0. Therefore, the oblique grinding rotation angle Ψ of SMF 52 is 180°. Furthermore, although in Figure 1 The illustration is omitted, but in this example, the angled grinding rotation angles Ψ of SMF 54 and 51 are 0° and 180°, respectively. Hereinafter, the angled grinding rotation angle Ψ will also be referred to as "rotation angle Ψ".

[0103] When SMFs 51 to 54 are obliquely ground, in order to ensure that light is incident on these end faces 51a to 54a with low loss, it is necessary to control the emitted light so that the principal rays B1 to B4 of the emitted light from lenses 41 to 44 are located on a plane that passes through the major axis of end faces 51a to 54a and is orthogonal to these end faces 51a to 54a, i.e., the plane orthogonal to the major axis, and the ray angle θ1 of the principal rays B1 to B4 (the angle formed with the optical axis of lenses 41 to 44) is a predetermined angle. When the grinding angle of end faces 51a to 54a is 8°, the ray angle θ1 when the wavelength of the light is 1.55 μm is preferably 3.8°. Furthermore, more specifically, the angle formed by the principal rays B1 to B4 incident on end faces 51a to 54a and the line segment connecting the incident position on end faces 51a to 54a to the proximal end E2 is preferably 78.2°.

[0104] Furthermore, according to a known ray matrix, the ray angle θ1 of the light emitted from any lens depends on the incident position p and the incident angle θ of the incident light incident on that lens. The incident position p is defined as the relative position with respect to the principal point of the lens, and the incident angle θ is defined as the angle between the incident light and the optical axis of the lens. In this example, the light paths (principal rays B1 to B4) of the incident light incident on lenses 41 to 44 are constant. Therefore, the incident angle θ of the incident light is fixed. Consequently, in order to ensure that the principal rays B1 to B4 of the emitted light from lenses 41 to 44 are located on the plane orthogonal to their major axes and that their ray angle θ1 is the desired angle, it is necessary to control the incident position p of the incident light incident on lenses 41 to 44.

[0105] Figure 3A and Figure 3B yes Figure 1 A magnified view of lens 43. Figure 3A and Figure 3B In the diagram, lens 43 of device 10 is shown in solid lines, and lens 43 of device 310 is shown in dashed lines. For example... Figure 3A and Figure 3B As shown, the lens 43 of device 10 is moved relative to the lens 43 of device 310 in the -y-axis direction (hereinafter, the layout of device 310 will also be referred to as "before the movement"). Consequently, the incident position Ps3 of the principal ray B3 incident on the lens 43 is moved relatively in the +y-axis direction compared to before the movement, therefore the principal ray B3 emitted from the lens 43 is tilted in the -y-axis direction compared to before the movement (see reference). Figure 3A In this example, moving lens 43 (i.e., moving the incident position Ps3) causes the angle θ1 of the principal ray B3 to become 3.8°. Therefore, according to this structure, as... Figure 1 As shown, the light emitted from lens 43 (in) Figure 1 The principal ray B3 is appropriately incident on the end face 53a of the SMF 53, as shown in the diagram. In addition, the SMF 53 also moves in the -y-axis direction as the angle θ1 of the incident light rays incident on itself changes, so that the principal ray B3 is incident on the center of the core C.

[0106] On the other hand, if Figure 1 and Figure 5 As the comparison clarifies, lens 42 of device 10 moves relative to lens 42 of device 310 in the +y-axis direction. Consequently, the incident position Ps2 of the principal ray B2 incident on lens 42 (refer to...) Figure 7A Compared to before the movement, it moves relatively towards the -y axis, therefore the principal ray B2 emitted from lens 42 is tilted towards the +y axis compared to before the movement (see reference). Figure 1When lens 42 is moved the same distance as lens 43, due to the symmetry between principal rays B2 and B3, the angle θ1 of principal ray B2 becomes 3.8°. Therefore, according to this structure, as... Figure 1 As shown, the light emitted from lens 42 (in) Figure 1 The principal ray B2 is appropriately incident on the end face 52a of the SMF 52, as shown in the diagram. In addition, the SMF 52 also moves in the +y-axis direction as the angle θ1 of the incident light rays incident on itself changes, so that the principal ray B2 is incident on the center of the core C.

[0107] In addition, although Figure 1 The diagram is omitted, but lenses 44 and 41 also move in the same way. That is, as described above, the oblique grinding rotation angle Ψ of SMF 54 is 0°, so lens 44 (and SMF 54) also moves relative to lens 44 (and SMF 54) of device 310 in the -y-axis direction. Additionally, the oblique grinding rotation angle Ψ of SMF 51 is 180°, so lens 41 (and SMF 51) also moves relative to lens 41 (and SMF 51) of device 310 in the +y-axis direction. The moving distance of lenses 44 and 41 is equal to the moving distance of lenses 43 and 42. According to this structure, the light emitted from lenses 44 and 41 is also appropriately incident on the end faces 54a and 51a of SMF 54 and 51.

[0108] according to Figure 1 Device 10, and Figure 5 Compared to the device 310, this reduces reflected light. Furthermore, lenses 41 to 44 and SMFs 51 to 54 can be moved along the y-axis towards the axis A1. Therefore, a device 10 with a coupling section that is significantly smaller than conventional devices can be realized.

[0109] As explained above, there is a correlation between the oblique grinding direction of SMFs 51 to 54 and the moving direction of lenses 41 to 44. Therefore, the inventors of this application have studied the range of oblique grinding rotation angle Ψ that enables radial miniaturization of the coupling portion of device 10 by calculating the radial movement Δr of lenses 41 to 44 when the oblique grinding rotation angle Ψ of SMFs 51 to 54 varies within the range of 0°≤Ψ≤360°.

[0110] Furthermore, regarding the incident positions Ps1 to Ps4 of lenses 41 to 44, these incident positions can be controlled not only when lenses 41 to 44 are moved in the xy plane, but also when lenses 41 to 44 are moved at least in the z-axis direction. Therefore, the inventors of this application have also calculated the amount of movement Δz of lenses 41 to 44 in the z-axis direction when the oblique grinding rotation angle Ψ of SMFs 51 to 54 is varied in the range of 0°≤Ψ≤360°, and studied the angle range of the oblique grinding rotation angle Ψ that enables miniaturization of device 10 in the z-axis direction (i.e., the direction of axis A1).

[0111] Furthermore, the aforementioned "radial" refers to the direction along which "axis A1" intersects with the principal points Cs1 to Cs4 of each lens 41 to 44 (see reference). Figure 7A The direction of the half-line connecting "axis A1" and "the center of the end faces 51a to 54a of each SMF 51 to 54" is also referred to. Furthermore, "lenses 41 to 44 move radially" means "the direction of movement of lenses 41 to 44 has at least a radial component," not that "the direction of movement has only a radial component." Although lenses 41 to 44 and SMFs 51 to 54 are housed in components not shown, these housing components do not interfere with each other due to the movement of lenses 41 to 44, etc.

[0112] Figure 9A It is a graph that specifies the relationship between the oblique grinding rotation angle Ψ of device 10 and the radial movement Δr. Figure 9B This is a graph that defines the relationship between the oblique grinding rotation angle Ψ of device 10 and the amount of movement Δz in the z-axis direction. Δr has a positive value when lenses 41 to 44 move radially outward (enlarging the coupling part of device 10) and a negative value when lenses 41 to 44 move radially inward (miniaturizing the coupling part of device 10). Furthermore, "radially outward" refers to the side that moves radially away from axis A1, and "radially inward" refers to the side that moves radially closer to axis A1. On the other hand, Δz has a positive value when lenses 41 to 44 move in the +z-axis direction (enlarging the coupling part of device 10) and a negative value when lenses 41 to 44 move in the -z-axis direction (miniaturizing the coupling part of device 10).

[0113] Below, in the discussion Figure 9A and Figure 9B Before explaining the charts, let's take lens 43 as an example to illustrate the relationship between the oblique grinding rotation angle Ψ and the moving direction of lenses 41 to 44. Figure 10 This is a diagram obtained by observing lens 43 from the front. Figure 11A and Figure 11B yes Figure 10 A magnified view of the area R1. Figures 10 to 11B The circle 43a shown is a circle with a radius of 0.16 mm centered at the incident position Ps3. Furthermore, the incident position Ps3 in these figures is the position where the principal ray B3 is incident on the lens 43 of the device 310 used as a comparative example (i.e., the position where the principal ray B3, passing through the focal point f2 of the lens 43, is incident). Figure 7B As described above, the optical path of the incident light incident on lens 43 remains unchanged. Therefore, when lens 43 is moved, the incident position Ps3 moves relatively. Based on the above calculations, the following insights are derived.

[0114] • By moving lens 43 so that the incident position Ps3 is located at any point on circle 43a, the angle θ1 of the principal ray B3 of the emitted light can be controlled to 3.8°.

[0115] • When lens 43 is moved in the xy plane, the principal ray B3 of the emitted light is refracted in the same direction as the direction of movement of lens 43 (3.8°).

[0116] Explain these insights in detail. For example... Figure 11A and Figure 11B As shown, on circle 43a, eight points P1 to P8 are arranged at equal intervals in a counterclockwise direction. Point P1 is located in the +y-axis direction relative to the incident position Ps3. Points P1 to P8 are fixed points on lens 43. Figure 12 This diagram illustrates how the principal ray B3 of the emitted light is refracted when lens 43 is moved a predetermined distance in a predetermined direction (described later). Furthermore, Figure 12 The principal ray B3 is the principal ray of the light emitted from lens 43 of device 310, and therefore travels in the +z direction (in other words, it travels in the same direction as the optical axis As3 of lens 43). Figure 7B (Moving in parallel).

[0117] First, refer to Figure 10 and Figure 11A The case where lens 43 is moved in the xy plane will be explained. For example, when lens 43 is moved radially inward by 0.16 mm, the incident position Ps3 moves to point P2. At this time, as... Figure 12 As shown, the principal ray B3_P2 of the emitted light is refracted by 3.8° towards point P6 on the virtual plane S1 (a plane that passes through line segment P2P6 and extends in the z-axis direction) relative to the principal ray B3 before the movement. Here, point P6 is the radially inward side, that is, the direction of movement of lens 43. As a result, the ray angle θ1 of the principal ray B3_P2 becomes 3.8°.

[0118] Additionally, for example, when lens 43 is moved radially outward by 0.16 mm, the incident position Ps3 moves to point P6. At this time, as... Figure 12As shown, the principal ray B3_P6 of the emitted light is refracted by 3.8° towards point P2 on the virtual plane S1 relative to the principal ray B3 before the movement. Here, point P2 is the radially outward side, that is, the direction of movement of lens 43. As a result, the ray angle θ1 of the principal ray B3_P6 becomes 3.8°.

[0119] Similarly, when lens 43 is moved in the xy plane such that the incident position Ps3 is located at points P1, P3, P4, P5, P7, and P8, the principal ray B3 of the emitted light after the movement is refracted by 3.8° relative to the principal ray B3 before the movement in the direction of movement of lens 43. As a result, the angle θ1 of the principal ray B3 after the movement becomes 3.8°.

[0120] As explained above, when lens 43 is moved in the xy plane, the actual distance moved is fixed regardless of the direction of movement (0.16 mm in this example). However, since this calculation focuses on the radial distance of lens 43, the amount of movement Δr is defined as the "radial component of the actual distance moved by lens 43." That is, the "radial component" of the actual distance moved is ignored. For example, when lens 43 is moved such that the incident position Ps3 is located at point P1 or P3, the amount of movement Δr is equal to the length of line segment Ps3Q1 (0.11 mm in this example). Furthermore, point Q1 is the foot of the perpendicular line drawn from point P1 or P3 to line segment P2P6. In addition, when lens 43 is moved such that the incident position Ps3 is located at point P4 or P8, since the distance moved does not have a radial component, the amount of movement Δr is 0.

[0121] Next, refer to Figure 10 and Figure 11B The case where lens 43 is moved at least in the z-axis direction will be explained. When lens 43 is moved in the -z-axis direction, the incident position Ps3 moves radially inward; when lens 43 is moved in the +z-axis direction, the incident position Ps3 moves radially outward. In this calculation, the incident position Ps3 is further moved to any point on circle 43a by moving lens 43 in the x-axis direction.

[0122] For example, when lens 43 is moved 6.2 mm in the -z axis direction, the incident position Ps3 moves to point P6. The refraction direction of the principal ray B3_P6 of the emitted light at this time is as described above (refer to...). Figure 12 When lens 43 is moved 0.23 mm further in the +x axis direction from this state, the incident position Ps3 moves to point P4.

[0123] Additionally, for example, when lens 43 is moved 8.7 mm in the -z-axis direction, the incident position Ps3 moves to point Q2. Point Q2 is the intersection of the line P2P6 and the tangent to circle 43a at point P5. When lens 43 is further moved 0.16 mm in the +x-axis direction from this state, the incident position Ps3 moves to point P5.

[0124] That is, in this calculation, when lens 43 is moved such that the incident position Ps3 is located at point P2 or P6, lens 43 is moved only in the z-axis direction. On the other hand, when lens 43 is moved such that the incident position Ps3 is located at "any point on circle 43a other than points P2 and P6", lens 43 is moved in both the z-axis and x-axis directions. The principal ray B3 of the emitted light after the movement is refracted in the same direction as in the case where lens 43 is moved in the xy plane, relative to the principal ray B3 before the movement. As a result, the angle θ1 of the principal ray B3 after the movement becomes 3.8°. Furthermore, lens 43 can also be moved in the y-axis direction instead of in the x-axis direction.

[0125] As clarified in the above explanation, when lens 43 is moved at least in the z-axis direction, it may sometimes be moved in the x-axis direction depending on the direction of movement. However, since this calculation focuses on the distance the second lens moves in the z-axis direction, the amount of movement Δz is defined as "the distance the lens 43 moves in the z-axis direction". Therefore, when lens 43 is moved such that the incident position Ps3 is located at point P3 or point P7, the amount of movement Δz is 0.

[0126] Furthermore, the movement distance in the x-axis direction (e.g., 0.23 mm) is extremely short compared to the movement distance in the z-axis direction (e.g., 6.2 mm). Therefore, even when the lens 43 moves along the -x-axis direction (i.e., moves away from axis A1), the resulting change in the size of the coupling portion of the device 10 is minimal. Consequently, in this calculation, the movement distance of the lens 43 in the x-axis direction is ignored (in other words, miniaturization of the coupling portion of the device 10 in the z-axis direction is prioritized).

[0127] Based on the above insights, it can be seen that by setting the oblique grinding direction of the SMF 53 according to the refraction direction of the principal ray B3 of the emitted light from the moved lens 43, the emitted light can be appropriately incident on the end face 53a of the SMF 53. Specifically, in such cases... Figure 11A and Figure 11B As shown, the lens 43 is moved in such a way that the incident position Ps3 is located at point P2 (refer to...). Figure 12The oblique grinding rotation angle Ψ of SMF 53 can be set to 45°. Additionally, when the lens 43 is moved such that the incident position Ps3 is located at point P6 (see reference...). Figure 12 The oblique grinding rotation angle Ψ of SMF 53 can be set to 225°. Similarly, when the lens 43 is moved such that the incident position Ps3 is located at points P1, P3, P4, P5, P7, and P8, the oblique grinding rotation angle Ψ of SMF 53 can be set to 0° (=360°), 90°, 135°, 180°, 270°, and 315°, respectively.

[0128] The same idea can be applied to lenses 41, 42, and 44, as well as SMFs 51, 52, and 54. The above explains the relationship between the oblique grinding rotation angle Ψ and the direction of movement of lenses 41 to 44.

[0129] Next, refer to Figure 9A This will illustrate the calculation results of the movement Δr. Based on... Figure 9A For lens 41, Δr is negative when the oblique grinding rotation angle Ψ of SMF 51 is 135° < Ψ < 315°, and Δr is minimum when Ψ = 225°. For lens 42, Δr is negative when the oblique grinding rotation angle Ψ of SMF 52 is 45° < Ψ < 225°, and Δr is minimum when Ψ = 135°. For lens 43, Δr is negative when the oblique grinding rotation angle Ψ of SMF 53 is 315° < Ψ < 135° (i.e., 315° < Ψ ≤ 360°, 0° ≤ Ψ < 135°), and Δr is minimum when Ψ = 45°. For lens 44, when the oblique grinding rotation angle Ψ of SMF 54 is 225°<Ψ<45° (i.e., 225°<Ψ≤360°, 0°≤Ψ<45°), Δr is negative, and when Ψ=315°, Δr is minimum.

[0130] Figure 13 This diagram shows the angle range of the oblique grinding rotation angle Ψ, Rr1 to Rr4, when the radial condition of negative Δr is met, under the condition of frontal viewing of the end faces 51a to 54 of each SMF 51 to 54, and the oblique grinding directions Dr1 to Dr4 when Δr is at its minimum (maximum on the radially inner side). Figure 13 The diagram of core C is omitted in the image. Figure 13As shown, the angle ranges Rr1 to Rr4 correspond to the angle ranges of the outer peripheries Cir1 to Cir4. Here, the outer peripheries Cir1 to Cir4 are the radially outer portions of the outer peripheries relative to line segments L1 to L4. Line segments L1 to L4 are line segments that pass through the centers of end faces 51a to 54a and are orthogonal to the radial direction. The radial condition is met when the oblique grinding rotation angles Ψ of SMFs 51 to 54 are respectively contained within the angle ranges Rr1 to Rr4. In other words, the radial condition is met when the oblique grinding direction is set such that the proximal end E2 of the long axis of end faces 51a to 54a is located on the outer peripheries Cir1 to Cir4.

[0131] Furthermore, it is valid that the oblique grinding directions Dr1 to Dr4 are radially outward and point-symmetric with respect to axis A1. In other words, the orientation of the oblique grinding directions Dr1 to Dr4 is set such that the proximal ends E2 of the long axes of end faces 51a to 54a are located at the midpoints of the outer periphery Cir1 to Cir4, respectively.

[0132] In other words, line segments L1 to L4 are respectively "line segments that pass through the center of end faces 51a to 54a and are orthogonal to the line segment connecting axis A1 and that center". Additionally, the outer perimeters Cir1 to Cir4 are respectively "the portion of the outer perimeter of end faces 51a to 54a that is opposite to the side containing axis A1 relative to line segments L1 to L4". Line segments L1 to L4 and outer perimeters Cir1 to Cir4 are examples of "first orthogonal lines" and "first outer perimeter", respectively.

[0133] Next, refer to Figure 9B This will illustrate the calculation results of the movement Δz. Based on... Figure 9B For lenses 41 and 42, when the oblique grinding rotation angle Ψ of SMF 51 and 52 is 270° < Ψ < 90° (i.e., 270° < Ψ ≤ 360°, 0° ≤ Ψ < 90°), Δz is negative, and Δz is minimum when Ψ = 0° (360°). For lenses 43 and 44, when the oblique grinding rotation angle Ψ of SMF 53 and 54 is 90° < Ψ < 270°, Δz is negative, and Δz is minimum when Ψ = 180°.

[0134] Figure 14 This diagram shows the angle range of the oblique grinding rotation angle Ψ, Rz1 to Rz4, when the z-axis condition of negative Δz is met, under the condition of frontal viewing of the end faces 51a to 54 of each SMF 51 to 54, and the oblique grinding directions Dz1 to Dz4 when Δz is minimum (maximum in the -z-axis direction). Figure 14 The diagram of core C is omitted in the image. Figure 14As shown, the angle ranges Rz1 to Rz4 are the angle ranges corresponding to the outer perimeters Ciz1 to Ciz4. Here, the outer perimeters Ciz1 to Ciz4 are the portions of the outer perimeter relative to the side of axis A1 relative to line segments Lz1 to Lz4. Furthermore, when a straight line orthogonal to axis A1 and extending along the x-axis is defined as the "reference line Lb", line segments Lz1 to Lz4 are line segments passing through the centers of end faces 51a to 54a and parallel to the reference line Lb. When the oblique grinding rotation angles Ψ of SMFs 51 to 54 are respectively contained within the angle ranges Rz1 to Rz4, the z-axis direction condition is met. In other words, when the oblique grinding direction is set such that the proximal end E2 of the major axis of end faces 51a to 54a is located on the outer perimeters Ciz1 to Ciz4, the z-axis direction condition is met.

[0135] Furthermore, the oblique grinding directions Dz1 and Dz2 are respectively oriented towards the +y axis direction (i.e., towards the direction that extends perpendicularly to the reference line Lb), and the oblique grinding directions Dz3 and Dz4 are respectively oriented towards the -y axis direction (i.e., towards the direction that extends perpendicularly to the reference line Lb). That is, it is valid that the oblique grinding directions Dz1 to Dz4 are point-symmetric with respect to the axis A1. In other words, the oblique grinding directions Dz1 to Dz4 are set such that the proximal ends E2 of the major axes of end faces 51a to 54a are located at the midpoints of the outer peripheries Ciz1 to Ciz4, respectively.

[0136] Furthermore, line segments Lz1 to Lz4 and outer perimeters Ciz1 to Ciz4 correspond to examples of "parallel lines" and "second outer perimeter," respectively. Additionally, the reference line Lb does not pass through the center of each SMF 51 to 54. Therefore, "the case where each SMF 51 to 54 is arranged as illustrated in device 10" corresponds to an example of "the first case." Furthermore, the reference line Lb is not limited to a straight line extending along the x-axis. The reference line Lb can be any straight line extending in any direction orthogonal to axis A1. In this case, when moving lenses 41 to 44 at least in the z-axis direction, it is sufficient to move lenses 41 to 44 parallel to the reference line Lb after moving them in the z-axis direction.

[0137] The inventors of this application, through MCF 20 (refer to...), Figure 1 and Figure 6 The same calculations were performed on other MCF 120 and 220 models with different core counts and / or core configurations, and the range of angles of the oblique grinding rotation angle Ψ that enables miniaturization of the coupling portion of the device in the radial or z-axis direction was studied in more detail.

[0138] Figure 15 This is a diagram showing the end face 120a of the MCF 120 used for research. MCF 120 is an MCF that differs from MCF 20 only in its core configuration. Figure 15As shown, MCF 120 has four cores C1 to C4 and a common cladding CL surrounding these cores C1 to C4. The cores C1 to C4 are arranged linearly along the x-axis in a manner of quadratic rotational symmetry with the center of end face 120a as the center. The core spacing is 50 μm. The cores C1 to C4 of MCF 120 are an example of a "first core".

[0139] Figure 16 This is a top view of device 110, which uses MCF 120. Figure 17 This is a top view of device 410, which serves as a comparative example of device 110. Below, we will first describe the structure of device 410, focusing on its comparison with device 310 (see reference 310). Figure 4 and Figure 5 The differences between the two devices will be discussed, and then the structure of device 110 will be explained.

[0140] like Figure 17 As shown, device 410 includes MCF 120, first lens 30, second lens group 140, and SMF group 450. Second lens group 140 has lenses 141 to 144. Lenses 141 to 144 are collimating lenses identical to lenses 41 to 44, but their positions differ. Specifically, the principal points Cs1 to Cs4 (not shown) of lenses 141 to 144 are located on a straight line orthogonal to axis A1 and extending along the x-axis. Furthermore, lenses 141 to 144 are configured such that the principal rays B1 to B4 of the light rays emitted from the first lens 30 from each core C1 to C4 of MCF 120 pass through the focal points (not shown) of the corresponding lenses 141 to 144. Thus, the principal rays B1 to B4 incident on lenses 141 to 144 are emitted as rays parallel to the optical axes of lenses 141 to 144. The incident positions of the incident light incident on lenses 141 to 144, Ps11 to Ps14 (illustration omitted), are also located on the aforementioned straight line (the straight line where the principal points Cs1 to Cs4 are located).

[0141] SMF group 450 includes SMFs 451 to 454. SMFs 451 to 454 are identical to SMFs 351 to 354. The end faces 451a to 454a of SMFs 451 to 454 are respectively positioned such that light rays from cores C1 to C4 emitted from the corresponding lenses 141 to 144 converge at the center of core C. That is, SMFs 451 to 454 are respectively configured such that principal rays B1 to B4 are incident on the center of core C. The centers of end faces 451a to 454a are located on a straight line orthogonal to axis A1 and extending along the x-axis. That is, principal rays B1 to B4 are all located on the xz plane passing through axis A1. The ends of SMFs 451 to 454 in the -z-axis direction are held by cylindrical collars 461 to 464.

[0142] The first lens 30 and the second lens group 140 optically couple the MCF 120 and the SMF group 450, functioning as the coupling part of the device. The above is a description of the structure of the device 410 as a comparative example.

[0143] Next, the structure of device 110 will be described. For example... Figure 16 As shown, device 110 uses the same components as those used in device 410, except for SMF group 150.

[0144] SMF group 150 includes SMFs 151 to 154. SMFs 151 to 154 differ from SMFs 451 to 454 in that their end faces 151a to 154a are beveled. SMFs 151 to 154 are identical to SMFs 51 to 54, with a bevel angle of 8°. The z-axis ends of SMFs 151 to 154 are held in place by cylindrical ferrules 161 to 164. SMFs 151 to 154 are equivalent to an example of a "peripheral single-core fiber".

[0145] exist Figure 16 In the examples, the rotation angle Ψ of SMF 153 and 151 is 90°, and the rotation angle Ψ of SMF 152 and 154 is 270°. Figure 16 and Figure 17 As shown, lenses 143 and 141 of device 110 are moved relative to lenses 143 and 141 of device 410 in the -x-axis direction (i.e., the direction close to axis A1). Consequently, the principal rays B3 and B1 emitted from lenses 143 and 141, respectively, are tilted in the -x-axis direction in the xz-plane compared to before the movement. Furthermore, lenses 142 and 144 of device 110 are moved relative to lenses 142 and 144 of device 410 in the +x-axis direction (i.e., the direction close to axis A1). Consequently, the principal rays B2 and B4 emitted from lenses 142 and 144, respectively, are tilted in the +x-axis direction in the xz-plane compared to before the movement. That is, principal rays B1 to B4 are all located in the xz-plane passing through axis A1. In this example, moving lenses 141 to 144 (i.e., moving the incident positions Ps11 to Ps14) causes the principal rays B1 to B4 of the emitted light from lenses 141 to 144 to have an angle θ1 of 3.8°. Therefore, according to this structure, as... Figure 16 As shown, the emitted light from lenses 141 to 144 (in) Figure 16 The diagram shows only the principal rays (B1 to B4) properly incident on the end faces 151a to 154a of SMF 151 to 154.

[0146] Figure 18A It is a graph that specifies the relationship between the rotation angle Ψ and the movement Δr of device 110. Figure 18BThis is a graph that specifies the relationship between the rotation angle Ψ and the movement Δz of device 110. Below, in the section on... Figure 18A and Figure 18B Before explaining the diagram, let's take lens 143 as an example to illustrate the direction of movement of lenses 141 to 144. Figure 19 This is a diagram obtained by observing lens 143 from the front. Figure 20 yes Figure 19 A magnified view of the area R2. Figure 19 and Figure 20 The circle 143a shown is a circle with a radius of 0.16 mm centered at the incident position Ps13. Furthermore, the incident position Ps13 in these figures is the position where the principal ray B3 is incident on the lens 43 of the device 410 used as a comparative example. As described above, the incident position Ps13 and the principal point Cs3 are located at the intersection of axis A1 (in...). Figure 19 (Illustration omitted) and along a straight line extending in the x-axis direction. Therefore, in this example, the x-axis direction is equivalent to the radial direction.

[0147] like Figure 20 As shown, on circle 143a, eight points P11 to P18 are arranged relative to points P1 to P8 (refer to...). Figure 11A and Figure 11B The corresponding position. First, let's explain the case where lens 143 is moved in the xy plane. For example, when lens 143 is moved radially inward by 0.16 mm, the incident position Ps13 moves to point P13. At this time, the principal ray B3 of the emitted light after the movement is refracted by 3.8° towards point P17 (i.e., radially inward) relative to the principal ray B3 before the movement (in the xz plane). The amount of movement Δr at this time is equal to the length of line segment Ps13P13 (0.16 mm).

[0148] Additionally, for example, when lens 143 is moved such that the incident position Ps13 is located at point P12 or point P14, the principal ray B3 of the emitted light after the movement is refracted by 3.8° towards point P16 or point P18 relative to the principal ray B3 before the movement. The amount of movement Δr at this time is equal to the length (0.12 mm) of line segment Ps13Q11. Furthermore, point Q11 is the foot of the perpendicular line drawn from point P12 or P14 onto line segment P13P17.

[0149] Next, the case where the lens 143 is moved at least in the z-axis direction will be explained. When the lens 143 is moved in the -z-axis direction, the incident position Ps13 moves radially inward (in the -x-axis direction), and when the lens 143 is moved in the +z-axis direction, the incident position Ps3 moves radially outward (in the +x-axis direction).

[0150] For example, when lens 143 is moved 2.8 mm in the -z-axis direction, the incident position Ps13 moves to point P17. At this time, the principal ray B3 of the emitted light after the movement is refracted 3.8° towards point P13 (i.e., radially outward) relative to the principal ray B3 before the movement (in the xz plane). The movement amount Δz is 2.8 mm. Alternatively, for example, when lens 143 is moved 2.0 mm in the -z-axis direction, the incident position Ps13 moves to point Q12. Point Q12 is the intersection of line segments P18P16 and P13P17. When lens 143 is further moved 2.0 mm in the +y-axis direction from this state, the incident position Ps13 moves to point P18. At this time, the principal ray B3 of the emitted light after the movement is refracted 3.8° towards point P16 relative to the principal ray B3 before the movement. The movement amount Δz is 2.0 mm. That is, in this calculation, when the lens 143 is moved such that the incident position Ps13 is located at point 13 or point 17, the lens 143 is moved only in the z-axis direction. On the other hand, when the lens 143 is moved such that the incident position Ps13 is located at "any point on circle 143a other than points P13 and P17", the lens 143 is moved in both the z-axis and y-axis directions.

[0151] The same idea can be applied to lenses 141, 142, and 144. The above is an explanation of the direction of movement for lenses 141 to 144.

[0152] according to Figure 18A For lenses 141 and 143, Δr is negative when the rotation angle Ψ of SMF 151 and 153 is 0° < Ψ < 180°, and Δr is minimum when Ψ = 90°. For lenses 142 and 144, Δr is negative when the rotation angle Ψ of SMF 152 and 154 is 180° < Ψ < 360°, and Δr is minimum when Ψ = 270°.

[0153] Figure 21 This diagram shows the range of rotation angle Ψ (Rr11 to Rr14) when the radial condition is met, and the oblique grinding directions Dr11 to Dr14 when Δr is minimized, under the condition of frontal viewing of the end faces 151a to 154 of each SMF 151 to 154. Figure 21 The diagram of core C is omitted in the image. Figure 21As shown, the angle ranges Rr11 to Rr14 correspond to the angle ranges of the outer periphery Cir11 to Cir14. Here, the outer periphery Cir11 to Cir14 are the outer peripheries of the radially outer portions relative to the line segments Lr11 to Lr14. The line segments Lr11 to Lr14 are line segments that pass through the centers of end faces 151a to 154a and are orthogonal to the radial direction. The radial condition is met when the rotation angles Ψ of SMFs 151 to 154 are respectively contained within the angle ranges Rr11 to Rr14. In other words, the radial condition is met when the oblique grinding direction is set such that the proximal end E2 of the long axis of end faces 151a to 154a is located on the outer periphery Cir11 to Cir14.

[0154] Furthermore, it is valid that the oblique grinding directions Dr11 to Dr14 are radially outward and point-symmetric with respect to axis A1. In other words, the orientation of the oblique grinding directions Dr11 to Dr14 is set such that the proximal ends E2 of the long axes of end faces 151a to 154a are located at the midpoints of the outer periphery Cir11 to Cir14, respectively.

[0155] In other words, line segments Lr11 to Lr14 are respectively "line segments that pass through the center of end faces 151a to 154a and are orthogonal to the line segment connecting axis A1 and that center". Additionally, the outer perimeters Cir11 to Cir14 are respectively "the portion of the outer perimeter of end faces 151a to 154a that is opposite to the side containing axis A1 relative to line segments Lr11 to Lr14". Line segments Lr11 to Lr14 and outer perimeters Cir11 to Cir14 are examples of "first orthogonal lines" and "first outer perimeter", respectively.

[0156] On the other hand, according to Figure 18B For lenses 141 and 143, when the rotation angle Ψ of SMF 151 and 153 is 180° < Ψ < 360°, Δz is negative, and when Ψ = 270°, Δz is minimum. Furthermore, within the aforementioned angle range, the Δz of lens 141 is smaller than that of lens 143 (the amount of movement in the -z axis direction is larger). This is because the incident angle of the incident light incident on lens 141 is smaller than that of the incident light incident on lens 143 (refer to...). Figure 16Therefore, in order to make the incident position Ps11 (the incident position of the incident light incident onto lens 141) move by the same distance as the incident position Ps13 (the incident position of the incident light incident onto lens 143), lens 141 needs to move more in the -z-axis direction than lens 143. Conversely, for lenses 142 and 144, Δz is negative when the rotation angle Ψ of SMFs 152 and 154 is 0° < Ψ < 180°, and is minimal when Ψ = 90°. Furthermore, within the aforementioned angle range, the Δz of lens 142 is smaller than that of lens 144. This is based on the same reasoning as above.

[0157] Figure 22 This diagram shows the rotation angle Ψ within the range of Rz11 to Rz14 when the z-axis condition is met, and the oblique grinding directions Dz11 to Dz14 when Δz is at its minimum (maximum in the -z-axis direction) when the end faces 151a to 154 of each SMF 151 to 154 are viewed from the front. Figure 22 The diagram of core C is omitted in the image. Figure 22 As shown, the angle ranges Rz11 to Rz14 are the angle ranges corresponding to the outer perimeters Ciz11 to Ciz14. Here, the outer perimeters Ciz11 to Ciz14 are the outer perimeters of the radially inward portion (the side where axis A1 is located) relative to line segments Lz11 to Lz14. When the rotation angles Ψ of SMF 151 to 154 are respectively contained within the angle ranges Rz11 to Rz14, the z-axis direction condition is met. In other words, when the oblique grinding direction is set such that the proximal end E2 of the long axis of end faces 151a to 154a is located on the outer perimeters Ciz11 to Ciz14, the z-axis direction condition is met. Furthermore, line segments Lz11 to Lz14 can also refer to line segments that pass through the center of end faces 151a to 154a and are orthogonal to the reference line Lb.

[0158] Furthermore, the oblique grinding directions Dz11 and Dz13 are oriented towards the -x-axis (i.e., along the reference line Lb towards the axis A1), and the oblique grinding directions Dz12 and Dz14 are oriented towards the +x-axis (i.e., along the reference line Lb towards the axis A1). That is, it is valid that the oblique grinding directions Dz11 to Dz14 are point-symmetric with respect to the axis A1. In other words, the orientation of the oblique grinding directions Dz11 to Dz14 is set such that the proximal ends E2 of the major axes of end faces 151a to 154a are located at the midpoints of the outer peripheries Ciz11 to Ciz14, respectively.

[0159] Furthermore, line segments Lz11 to Lz14 and outer perimeter Ciz11 to Ciz14 correspond to examples of the "second orthogonal line" and the "third outer perimeter," respectively. Additionally, the reference line Lb passes through the center of each SMF 151 to 154. Therefore, the case where "each SMF 151 to 154 is configured as illustrated in device 110" corresponds to an example of the "second case."

[0160] Figure 23 This is a diagram showing the end face 220a of the MCF 220 used for research. The MCF 220 differs from the MCF 20 only in the number of cores and core configuration. (As shown...) Figure 23 As shown, MCF 220 has seven cores C1 to C7 and a common cladding CL surrounding these cores C1 to C7. Core C4 extends along the central axis of MCF 220 (hereinafter also referred to as "central core C4"). Cores C1 to C3 and C5 to C7 are located at the vertices of a regular hexagon centered on central core C4 and extend along the axial direction (hereinafter also referred to as "peripheral cores C1 to C3 and C5 to C7" respectively). The core spacing is 38 μm. Cores C1 to C7 of MCF 220 correspond to an example of a "first core".

[0161] Figure 24 This is a side view of device 210 using MCF 220. Figure 25 This is a side view of device 510, which serves as a comparative example of device 210. Below, we will first describe the structure of device 510, focusing on its comparison with device 310 (see reference 310). Figure 4 and Figure 5 The differences between the two devices will be discussed, and then the structure of device 210 will be explained.

[0162] like Figure 25 As shown, device 510 includes MCF 220, first lens 30, second lens group 240, and SMF group 550. Figure 25 The diagram only shows the principal rays B1, B4, and B7 emitted from the cores C1, C4, and C7 of the MCF 220. The second lens group 240 has lenses 241 to 247 (in... Figure 25 Only lenses 241, 244, and 247 are shown in the diagram. Lenses 241 to 247 are the same collimating lenses as lenses 41 to 44, but their positions are different.

[0163] Specifically, the principal points Cs1 to Cs7 (not shown) of lenses 241 to 247 lie on the same plane, which is orthogonal to axis A1. Principal point Cs4 lies on axis A1. Principal points Cs1 to Cs3 and Cs5 to Cs7 are located at the vertices of a regular hexagon centered on axis A1 (principal point Cs4). More specifically, lenses 241 to 247 are configured such that the principal rays B1 to B7 of the rays emitted from the first lens 30 from the cores C1 to C7 of MCF 220 pass through the focal points of the corresponding lenses 241 to 247 (not shown). Thus, the principal rays B1 to B7 incident on lenses 241 to 247 emerge as rays parallel to the optical axes of lenses 241 to 247. Furthermore, the incident positions Ps21 to 23 and Ps25 to 27 of the principal rays B1 to B7 incident on lenses 241 to 247 (illustration omitted) are respectively located at the vertices of a regular hexagon centered on incident position Ps24. This depends on the core configuration of MCF 220 (see reference). Figure 23 That is, the incident positions Ps21 to 23 and Ps25 to 27 are symmetrical with respect to axis A1 (incident position Ps24).

[0164] SMF group 550 has SMF 551 to 557 (in Figure 25 (Only SMFs 551, 554, and 557 are illustrated in the diagram). SMFs 551 to 557 are the same as SMFs 351 to 354. The end faces 551a to 557a of SMFs 551 to 557 are respectively positioned such that the light rays from cores C1 to C7 emitted from the corresponding lenses 241 to 247 converge at the center of core C. That is, SMFs 551 to 557 are respectively configured such that the principal rays B1 to B7 are incident on the center of core C. The ends of SMFs 551 to 557 in the -z axis direction are held by passing through cylindrical collars 561 to 567 (in... Figure 25 (Only rings 561, 564, and 567 are shown in the diagram).

[0165] The first lens 30 and the second lens group 240 optically couple the MCF 220 and the SMF group 550, functioning as the coupling part of the device. The above is a description of the structure of the device 510 as a comparative example.

[0166] Next, the structure of device 210 will be described. For example... Figure 24 As shown, device 210 uses the same components as those used in device 510, except for SMF group 250.

[0167] SMF group 250 has SMF 251 to 257 (in Figure 24(Only SMFs 251, 254, and 257 are illustrated in the diagram). The difference between SMFs 251 to 257 and SMFs 551 to 557 is that their end faces 251a to 257a are beveled. SMFs 251 to 257 are all the same SMFs as SMFs 51 to 54. The z-axis ends of SMFs 251 to 257 are held in place by passing through cylindrical collars 261 to 267 (in... Figure 24 (Only rings 261, 264, and 267 are shown in the diagram). SMF 254 is an SMF through which light emitted from the center core C4 of MCF 220 enters via the first lens 30 and the second lens group 240. Therefore, SMF 254 is sometimes referred to as the "center SMF" below, and the other SMFs 251 to 253 and 255 to 257 are referred to as the "peripheral SMFs".

[0168] exist Figure 24 In the examples, the rotation angle Ψ of SMF 257 is 0°, and the rotation angle Ψ of SMF 251 is 180° (SMF254 will be described later). Additionally, although in Figure 24 The illustrations are omitted, but the rotation angle Ψ for SMF 255 and 256 is 0°, and the rotation angle Ψ for SMF252 and 253 is 180°. For example... Figure 24 and Figure 25 As shown, lens 247 (and lenses 245 and 246) of device 210 moves relative to lens 247 (and lenses 245 and 246) of device 510 in the -y-axis direction (i.e., the direction close to axis A1). Consequently, the principal rays B5 to B7 emitted from lenses 245 to 247 are tilted in the -y-axis direction in the yz-plane compared to before the movement. Furthermore, lens 241 (and lenses 242 and 243) of device 210 moves relative to lens 241 (and lenses 242 and 243) of device 510 in the +y-axis direction (i.e., the direction close to axis A1). Consequently, the principal rays B1 to B3 emitted from lenses 241 to 243 are tilted in the +y-axis direction in the yz-plane compared to before the movement. On the other hand, the rotation angle Ψ of SMF 254 is 0°. Lens 244 of device 210 moves relative to lens 244 of device 510 in the -y-axis direction. As a result, the principal ray B4 emitted from lens 244 is tilted towards the -y axis in the yz plane compared to before the movement.

[0169] In this example, moving lenses 241 to 247 (i.e., moving incident positions Ps21 to Ps27) causes the principal rays B1 to B7 of the emitted light from lenses 241 to 247 to have an angle θ1 of 3.8°. Therefore, according to this structure, as... Figure 24 As shown, the emitted light from lenses 241 to 247 (in) Figure 24(Only the principal ray is shown in the diagram) is appropriately incident on the end faces 251a to 257a of SMF 251 to 257.

[0170] Figure 26A It is a graph that specifies the relationship between the rotation angle Ψ and the movement Δr of device 210. Figure 26B This is a graph that specifies the relationship between the rotation angle Ψ and the movement Δz of device 210. Below, in the section on... Figure 26A and Figure 26B Before explaining the diagrams, let's take lens 245 as an example to illustrate the rotation angle Ψ and the direction of movement of lenses 241 to 247. Figure 27 This is a diagram obtained by observing lens 245 from the front. Figure 28A and Figure 28B yes Figure 27 A magnified view of the area R3. Figures 27 to 28B The circle 245a shown is a circle with a radius of 0.16 mm centered at the incident position Ps25. Furthermore, the incident position Ps25 in these figures is the position where the principal ray B5 is incident on the lens 245 of the device 510 used as a comparative example. The incident position Ps25 lies on the half-line connecting the axis A1 (not shown) and the principal point Cs5.

[0171] like Figure 28A and Figure 28B As shown, on circle 245a, 12 points P21 to P32 are arranged at equal intervals in a counterclockwise direction. Point P21 is located in the +y-axis direction relative to the incident position Ps25. Points P21 to P32 are fixed points on lens 245. First, refer to... Figure 27 and Figure 28A The case where lens 245 is moved in the xy plane will be explained. For example, when lens 245 is moved radially inward by 0.16 mm, the incident position Ps25 moves to point P23. At this time, the principal ray B5 of the emitted light after the movement is refracted by 3.8° towards point P29 (i.e., radially inward) relative to the principal ray B5 before the movement. The amount of movement Δr at this time is equal to the length (0.16 mm) of line segment Ps25P23.

[0172] Additionally, for example, when lens 245 is moved such that the incident position Ps25 is located at point P22 or point P24, the principal ray B5 of the emitted light after the movement is refracted by 3.8° towards point P28 or point P30 relative to the principal ray B5 before the movement. The amount of movement Δr at this time is equal to the length (0.14 mm) of line segment Ps25Q21. Furthermore, point Q21 is the foot of the perpendicular line drawn from point P22 or P24 onto line segment P23P29.

[0173] Next, refer to Figure 27 and Figure 28BThe case where the lens 245 is moved at least in the z-axis direction will be explained. When the lens 245 is moved in the -z-axis direction, the incident position Ps25 moves radially inward, and when the lens 245 is moved in the +z-axis direction, the incident position Ps25 moves radially outward.

[0174] For example, when lens 245 is moved 6.0 mm in the -z-axis direction, the incident position Ps25 moves to point P29. At this time, the principal ray B5 of the emitted light after the movement is refracted 3.8° towards point P23 (i.e., radially outward) relative to the principal ray B5 before the movement. The amount of movement Δz at this time is 6.0 mm. When lens 245 is further moved 0.28 mm in the +x-axis direction from this state, the incident position Ps25 moves to point P25. At this time, the principal ray B5 of the emitted light after the movement is refracted 3.8° towards point P31 relative to the principal ray B5 before the movement. The amount of movement Δz at this time is also 6.0 mm (since the movement distance in the x-axis direction is ignored).

[0175] Additionally, for example, when lens 245 is moved 12 mm in the -z-axis direction, the incident position Ps25 moves to point Q22. Point Q22 is the intersection of the line P23P29 and the tangent to circle 245a at point P27. When lens 245 is further moved 0.28 mm in the +x-axis direction from this state, the incident position Ps3 moves to point P27. At this time, the principal ray B5 of the emitted light after the movement is refracted 3.8° towards point P21 relative to the principal ray B5 before the movement. The amount of movement Δz at this time is 12 mm. That is, in this calculation, when lens 245 is moved such that the incident position Ps25 is located at point 23 or point 29, lens 245 is moved only in the z-axis direction. On the other hand, when lens 245 is moved such that the incident position Ps25 is located at "any point on circle 245a other than points P23 and P29", lens 245 is moved in both the z-axis and x-axis directions.

[0176] The oblique grinding direction of SMF 255 can be set according to the refraction direction of the principal ray B5 of the emitted light from the moved lens 245. Specifically, when the lens 245 is moved such that the incident position Ps25 is located at point Pj (j: an integer from 21 to 32) (see reference). Figure 28A and Figure 28B The rotation angle Ψ of the SMF 255 can be set to 30×(j-21)°.

[0177] The same idea can be applied to lenses 241 to 243, as well as lenses 246 and 247. In contrast, the idea is slightly different for lens 244. That is, the same idea can be applied essentially when lens 244 is moved in the xy-plane. However, as... Figure 25As shown, the incident position Ps24 (not shown) of the principal ray B4 incident on the lens 244 before movement coincides with the principal point Cs4 in the front view of the lens 244, therefore, the radial direction cannot be specified. Therefore, for convenience in this calculation, the distance the lens 244 moves (i.e., the radius of the circle) when it is moved such that the incident position Ps24 is located at any point on a circle with a radius of 0.16 mm centered at the incident position Ps24 is calculated as Δr. That is, for the lens 244, Δr is fixed regardless of the rotation angle Ψ. On the other hand, when the lens 244 is moved in the z-axis direction, as... Figure 24 As shown, the principal ray B4 of the incident light incident on lens 244 is parallel to the axis A1. Therefore, even if lens 244 is moved in the z-axis direction, the incident position Ps24 of the light incident on lens 244 does not change (does not move). That is, Δz cannot be uniquely determined. Therefore, Δz of lens 244 is not calculated in this calculation. The above is an explanation of the relationship between the oblique grinding rotation angle Ψ and the moving direction of lenses 241 to 247.

[0178] according to Figure 26A For lens 241, Δr is negative when the rotation angle Ψ of SMF 251 is 90° < Ψ < 270°, and is minimal when Ψ = 180°. For lens 242, Δr is negative when the rotation angle Ψ of SMF 252 is 30° < Ψ < 210°, and is minimal when Ψ = 120°. For lens 243, Δr is negative when the rotation angle Ψ of SMF 253 is 150° < Ψ < 330°, and is minimal when Ψ = 240°. For lens 244, Δr has a fixed positive value regardless of the rotation angle Ψ. For lens 245, Δr is negative when the rotation angle Ψ of SMF 255 is 330° < Ψ < 150° (i.e., 330° < Ψ ≤ 360°, 0° ≤ Ψ < 150°), and is minimum when Ψ = 60°. For lens 246, Δr is negative when the rotation angle Ψ of SMF 256 is 210° < Ψ < 30° (i.e., 210° < Ψ ≤ 360°, 0° ≤ Ψ < 30°), and is minimum when Ψ = 300°. For lens 247, Δr is negative when the rotation angle Ψ of SMF 257 is 270° < Ψ < 90°, and is minimum when Ψ = 360°.

[0179] Figure 29This diagram shows the ranges of rotation angles Ψ (Rr21 to 23 and Rr25 to 27) when the radial condition is met, under frontal viewing of the end faces 251a to 253a and 255a to 257a of each SMF 251 to 253 and SMF 255 to 257 (peripheral SMFs). It also shows the oblique grinding directions Dr21 to 23 and Dr25 to 27 when Δr is at its minimum. Figure 29 The diagram of the core C of the peripheral SMF is omitted. Furthermore, for lens 244, since the radial condition does not hold, therefore... Figure 29 The illustration of SMF 254 (center SMF) is omitted. (See diagram below.) Figure 29 As shown, the angle ranges Rr21 to 23 and Rr25 to 27 are the angle ranges corresponding to the outer peripheries Cir21 to 23 and Cir25 to 27, respectively. Here, the outer periphery refers to the portion of the outer periphery that is radially outer relative to the line segments L21 to 23 and L25 to 27. These line segments are those that pass through the centers of end faces 251a to 253a and 255a to 257a and are orthogonal to the radial direction. The radial condition is met when the rotation angle Ψ of the peripheral SMF is included in the angle ranges Rr21 to 23 and Rr25 to 27, respectively. In other words, the radial condition is met when the oblique grinding direction is set such that the proximal ends E2 of the long axes of end faces 251a to 253a and 255a to 257a are located on the outer peripheries Cir21 to 23 and Cir25 to 27, respectively.

[0180] Furthermore, the oblique grinding directions Dr21 to Dr23 and Dr25 to Dr27 are respectively radially outward, and are point-symmetric with respect to the axis A1. In other words, the oblique grinding direction is set such that the proximal ends E2 of the long axes of end faces 251a to 253a and 255a to 257a are located at the midpoints of the outer peripheries Cir21 to 23 and Cir25 to 27, respectively.

[0181] In other words, line segments L21 to 23 and L25 to 27 are respectively "line segments that pass through the centers of end faces 251a to 253a and 255a to 257a and are orthogonal to the line segments connecting axis A1 and the centers". Additionally, the outer perimeter Cir21 to 23 and Cir25 to 27 are respectively "the portion of the outer perimeter of end faces 251a to 253a and 255a to 257a on the side opposite to the side containing axis A1, relative to line segments L21 to 23 and L25 to 27". The aforementioned line segments and outer perimeter of the peripheral SMF are examples of "first orthogonal lines" and "first outer perimeter", respectively.

[0182] On the other hand, according to Figure 26BFor lenses 241 to 243, when the rotation angle Ψ of SMF 251 to 253 is 270° < Ψ < 90°, Δz is negative, and when Ψ = 0° (360°), Δz is minimum. Furthermore, within the aforementioned angle range, the Δz of lenses 242 and 243 is smaller than that of lens 241 (the amount of movement in the -z axis direction is larger). This is because, since the incident angle of the incident light incident on lenses 242 and 243 is smaller than that of the incident light incident on lens 241, in order to move the incident positions Ps22 and Ps23 (the incident positions of the incident light incident on lenses 242 and 243) by the same distance as the incident position Ps21 (the incident position of the incident light incident on lens 241), lenses 242 and 243 need to move more in the -z axis direction than lens 241. In contrast, for lenses 245 to 247, Δz is negative when the rotation angle Ψ of SMF 255 to 257 is 90° < Ψ < 270°, and is minimal when Ψ = 180°. Furthermore, within the aforementioned angle range, the Δz of lenses 245 and 246 is smaller than that of lens 247. This is based on the same reasoning as above.

[0183] Figure 30 This diagram shows the rotation angle Ψ within the ranges Rz21 to 23 and Rz25 to 27 when the z-axis condition is met, under the condition of frontal viewing of the end faces 251a to 253a and 255a to 257a of the peripheral SMF, and the oblique grinding directions Dz21 to 23 and Dz25 to 27 when Δz is minimum (maximum in the -z-axis direction). Figure 30 The diagram of the core C of the peripheral SMF is omitted. Furthermore, since Δz is not calculated for lens 244, therefore... Figure 30 The illustration of SMF 254 (center SMF) is omitted. (See diagram below.) Figure 30 As shown, the angle ranges Rz21 to 23 and Rz25 to 27 are the angle ranges corresponding to the outer peripheries Ciz21 to 23 and Ciz25 to 27, respectively. Here, the outer periphery refers to the portion of the outer periphery on the side of the axis A1 relative to the line segments Lz21 to 23 and Lz25 to 27. Furthermore, these line segments are those that pass through the centers of end faces 251a to 253a and 255a to 257a and are parallel to the reference line Lb. The z-axis direction condition is met when the rotation angle Ψ of the peripheral SMF is included in the angle ranges Rz21 to 23 and Rz25 to 27, respectively. In other words, the z-axis direction condition is met when the oblique grinding direction is set such that the proximal ends E2 of the long axes of end faces 251a to 253a and 255a to 257a are located on the outer peripheries Ciz21 to 23 and Ciz25 to 27, respectively.

[0184] Furthermore, the oblique grinding directions Dz21 to Dz23 are oriented towards the +y axis (i.e., towards the direction perpendicular to the baseline Lb), and the oblique grinding directions Dz25 to Dz27 are oriented towards the -y axis (i.e., towards the direction perpendicular to the baseline Lb). That is, the oblique grinding directions Dz21 to 23 and Dz25 to 27 are point-symmetric with respect to the axis A1. In other words, the orientation of the oblique grinding directions Dz21 to 23 and Dz25 to 27 is set such that the proximal ends E2 of the major axes of end faces 251a to 253a and 255a to 257a are located at the midpoints of the outer peripheries Ciz21 to 23 and Ciz25 to 27, respectively.

[0185] Furthermore, the aforementioned line segments and outer perimeter of the peripheral SMFs correspond to examples of "parallel lines" and "second outer perimeter," respectively. Additionally, the reference line Lb does not pass through the center of each peripheral SMF. Therefore, the case where "each peripheral SMF is configured as illustrated in device 210" corresponds to an example of "the first case."

[0186] Based on the above calculations, in a FIFO device having an MCF with an arbitrary number and configuration of cores and an SMF with the same number of second lenses, when viewing each peripheral SMF from the front, the oblique grinding direction is set such that "the oblique grinding rotation angle Ψ is contained within an angle range corresponding to the outer periphery of the portion radially outward relative to the first orthogonal line, wherein the first orthogonal line is a line segment passing through the center of the end face of each peripheral SMF and orthogonal to the radial direction (along the direction of the semi-straight line connecting the axis A1 to the principal points of each second lens)," thereby enabling the coupling portion of the FIFO device to be miniaturized radially. Furthermore, by setting this direction so that the oblique grinding direction is radially outward, the coupling portion can be minimized radially.

[0187] On the other hand, when the second lens is moved at least in the z-axis direction using the method described in this embodiment, if the reference line Lb does not pass through the center of each peripheral SMF when viewed from the front (refer to...) Figure 14 and Figure 30 By setting the oblique grinding direction such that "the oblique grinding rotation angle Ψ is contained within the angular range corresponding to the outer periphery of the portion on the side of the axis A1 relative to the parallel line, wherein the parallel line is a line segment passing through the center of the end face of each peripheral SMF and parallel to the reference line Lb", the coupling part of the FIFO device can be miniaturized in the z-axis direction. Furthermore, by setting the oblique grinding direction to extend perpendicularly towards the reference line Lb, the coupling part can be minimized in the z-axis direction.

[0188] Alternatively, when the second lens is moved at least in the z-axis direction using the method described in this embodiment, when the reference line Lb passes through the center of each peripheral SMF during frontal observation of each peripheral SMF (refer to...). Figure 22 By setting the oblique grinding direction such that "the oblique grinding rotation angle Ψ is contained within an angle range corresponding to the outer periphery of the portion on the side of the axis A1 relative to the second orthogonal line, wherein the second orthogonal line is a line segment passing through the center of the end face of each peripheral SMF and orthogonal to the reference line Lb", the coupling part of the FIFO device can be miniaturized in the z-axis direction. Furthermore, by setting the oblique grinding direction so that it is along the reference line Lb toward the axis A1, the coupling part can be minimized in the z-axis direction.

[0189] As explained above, according to the FIFO device of the first embodiment, the oblique grinding direction of each peripheral SMF is set so that when each second lens is moved in a direction "close to axis A1" or "close to first lens 30", the emitted light from each second lens is appropriately incident on the corresponding peripheral SMF, thereby reducing the reflected light and miniaturizing the FIFO device.

[0190] (Modified Example)

[0191] Next, refer to Figure 31A and Figure 31B The FIFO device involved in the modified example will be described. Figure 31A and Figure 31B This diagram only shows the MCF 20p and the first lens 30 in the FIFO device. Figure 31A As shown, the MCF 20p is obliquely ground such that its end face 20ap is tilted relative to a plane orthogonal to its central axis (xy plane) at a predetermined angle (described later) (8° in this example). More specifically, the end face 20ap of the MCF 20p and the end face 22ap of the ferrule 22p are obliquely ground together. By obliquely grinding the MCF 20p, the reflected light caused by reflected light at the end face 20ap of the MCF 20p is reduced. Furthermore, the number of cores and the core arrangement of the MCF 20p are the same as those of the MCF 20. The aforementioned tilt direction and the aforementioned grinding angle correspond to examples of a "second tilt direction" and a "second grinding angle," respectively.

[0192] In this embodiment, the MCF 20p is cylindrical. Therefore, the end face 20ap of the obliquely ground MCF 20p appears elliptical when viewed from a direction perpendicular to the end face 20ap. Thus, the oblique grinding reference axis is the major axis of the end face 20ap, and the direction observed along the central axis of the end face 20ap from the end farther from the corresponding first lens 30 (far end E3) towards the end closer to the corresponding first lens 30 (proximal end E4) is the "oblique grinding direction of the MCF 20p". Hereinafter, when viewing the end face 20ap from the front, the angle formed by any oblique grinding direction counterclockwise relative to the "reference direction Dm0 passing through the center of the end face 20ap and towards the +y axis" is defined as the "oblique grinding rotation angle Ψm with a positive value". In this example, Ψm of the MCF 20p is 0°.

[0193] When the MCF 20p is obliquely ground, the principal rays of the light emitted from its end face 20ap from each core C1 to C4 (not shown in the figure) (in this modified example, only principal rays B1 and B3 are shown) are inclined at a predetermined angle relative to the axis in a predetermined direction. Here, as Figure 31A As shown, if MCF 20p is configured so that its central axis is aligned with axis A1, the angle θ1 of the principal rays B1 to B4 emitted from the first lens 30 will deviate, and the emitted light from the first lens 30 may not be properly incident on the second lens group (not shown). That is, the FIFO device may not function properly.

[0194] Therefore, in this variation, as Figure 31B As shown, MCF 20p is moved a predetermined distance in the -y-axis direction. Specifically, MCF 20p is moved such that a virtual line VL extending from the center of the end face 20ap of MCF 20p, parallel to the principal rays B1 and B3, passes through the focal point f1 of the first lens 30. Consequently, the ray angles θ1 of the principal rays B1 to B4 from each core C1 to C4 emanating from the first lens 30 are equal. According to this structure, the coupling portion of the FIFO device can be miniaturized while further reducing reflected light. Furthermore, this structure can also be applied to MCFs other than MCF 20p (e.g., MCFs whose end faces have been beveled).

[0195] (Second Implementation)

[0196] Next, refer to Figures 32A to 33BThe FIFO device according to the second embodiment will be described. In the second embodiment, the "method of moving the second lens at least in the z-axis direction" is different from that in the first embodiment. In this embodiment, the lens 43 of the FIFO device 10 and the lens 245 of the FIFO device 210 will be used as examples for explanation.

[0197] Figure 32A yes Figure 10 (A diagram showing lens 43 of device 10) is a partially enlarged view of the area R1. In the first embodiment, the incident position Ps3 is moved by moving lens 43 in the z-axis direction and the x-axis direction, but in this embodiment, the incident position Ps3 is moved by moving lens 43 in the z-axis direction and in an "orthogonal direction orthogonal to the radial direction". Hereinafter, the direction in which lens 43 moves itself from the incident position Ps3 toward point P8 will be defined as a positive orthogonal direction, and the direction in which lens 43 moves itself from the incident position Ps3 toward point P4 will be defined as a negative orthogonal direction.

[0198] For example, when lens 43 is moved 4.3 mm in the -z-axis direction, the incident position Ps3 moves to point Q3. Point Q3 is the foot of the perpendicular line drawn from point P5 or P7 to line segment P2P6. Then, when lens 43 is moved 0.12 mm in the negative orthogonal direction, the incident position Ps3 moves to point P5. In this case, the movement distance in the orthogonal direction is extremely short compared to the movement distance in the z-axis direction; therefore, the movement distance of lens 43 in the orthogonal direction is ignored in this calculation (in other words, miniaturization of the coupling part of device 10 in the z-axis direction is prioritized). That is, Δz = 4.3 mm. The same idea can be applied to lenses 41, 42, and 44.

[0199] Figure 32B This diagram shows the rotation angle Ψ within the range Rz31 to Rz34 when the z-axis condition is met, under the condition of frontal viewing of the end faces 51a to 54 of each SMF 51 to 54, and the oblique grinding directions Dz31 to Dz34 when Δz is at its minimum (maximum in the -z-axis direction). Figure 32B The diagram of core C is omitted in the text (for...). Figure 33B Similarly). Figure 32B As shown, the angle range Rz31 to Rz34 corresponds to the angle range of the outer perimeter Ciz31 to Ciz34. Here, the outer perimeter Ciz31 to Ciz34 are relative to line segments L1 to L4 (refer to...). Figure 13Regarding the outer periphery of the portion closest to the radial inner side (the side where axis A1 is located), the z-axis direction condition holds when the rotation angles Ψ of SMFs 51 to 54 are respectively contained within the angle ranges Rz31 to Rz34. In other words, the z-axis direction condition holds when the oblique grinding direction is set such that the proximal end E2 of the long axis of end faces 51a to 54a is located on the outer periphery Ciz31 to Ciz34. Furthermore, the outer periphery Ciz31 to Ciz34 is an example of a "fourth outer periphery".

[0200] Furthermore, it is valid that the oblique grinding directions Dz31 to Dz34 are respectively radially inward, and are point-symmetrical with respect to the axis A1. In other words, the orientation of the oblique grinding directions Dz31 to Dz34 is set such that the proximal ends E2 of the long axes of end faces 51a to 54a are respectively located at the midpoints of the outer periphery Ciz31 to Ciz34.

[0201] Figure 33A yes Figure 27 (A partial enlarged view of the area R3 of the lens 245 of device 210 is shown.) In this example, the positive orthogonal direction is the direction in which the lens 245 moves from the incident position Ps25 toward point P32, and the negative orthogonal direction is the direction in which the lens 245 moves from the incident position Ps25 toward point P26.

[0202] For example, when lens 245 is moved 3.0 mm in the -z-axis direction, the incident position Ps25 moves to point Q23. Point Q23 is the foot of the perpendicular line drawn from point P27 or P31 to line segment P23P29. Then, when lens 43 is moved 0.14 mm in the positive orthogonal direction, the incident position Ps25 moves to point P27. In this case, Δz = 3.0 mm. The same idea can be applied to lenses 241 to 243, as well as 246 and 247.

[0203] Figure 33B This diagram shows the rotation angle Ψ within the ranges Rz41 to 43 and Rz45 to 47 when the z-axis direction condition is met, and the oblique grinding directions Dz41 to 43 and Dz45 to 47 when Δz is minimized, under the condition of frontal viewing of the end faces 251a to 253a and 255a to 257a of the peripheral SMF. Figure 33B As shown, the angle ranges Rz41 to 43 and Rz45 to 47 are the angle ranges corresponding to the outer perimeters Ciz41 to 43 and Ciz45 to 47, respectively. Here, the outer perimeters are relative to line segments L21 to 23 and L25 to 27 (see reference). Figure 29Regarding the outer periphery of the radially inner side (the side where axis A1 is located), the z-axis condition is met when the rotation angle Ψ of the peripheral SMF is contained within the angle ranges Rz41 to 43 and Rz45 to 47, respectively. In other words, the z-axis condition is met when the oblique grinding direction is set such that the proximal end E2 of the long axis of end faces 251a to 253a and 255a to 257a is located on the outer periphery Ciz41 to 43 and Ciz45 to 47, respectively. Furthermore, the aforementioned outer periphery is an example of a "fourth outer periphery".

[0204] Furthermore, the oblique grinding directions Dz41 to 43 and Dz45 to 47 are respectively radially inward, and are point-symmetric with respect to the axis A1. In other words, the oblique grinding direction is set such that the proximal ends E2 of the long axes of end faces 251a to 253a and 255a to 257a are located at the midpoints of the outer peripheries Ciz41 to 43 and Ciz45 to 47, respectively.

[0205] As explained above, when the second lens is moved at least in the z-axis direction using the method described in this embodiment, when observing each peripheral SMF from the front, the oblique grinding direction is set such that "the oblique grinding rotation angle Ψ is contained within an angle range corresponding to the outer periphery of the portion radially inward relative to the first orthogonal line, wherein the first orthogonal line is a line segment that passes through the center of the end face of each peripheral SMF and is radially orthogonal." This allows the coupling portion of the FIFO device to be miniaturized in the z-axis direction. Furthermore, by setting the oblique grinding direction to be radially inward, the coupling portion can be minimized in the z-axis direction.

[0206] (Third Implementation)

[0207] Next, refer to Figures 34A to 35 The FIFO device according to the third embodiment will be described. In the third embodiment, similar to the modified example, the FIFO device includes MCF 20p instead of MCF 20 (see [reference]). Figure 31A and Figure 31BIn this case, as described above, by moving the MCF 20p a predetermined distance in the -y-axis direction, the ray angles θ1 of the principal rays B1 to B4 of the emitted light from the first lens 30 are made consistent. In such a FIFO device, there is a possibility that the MCF 20p may shift position relative to the first lens 30. This is caused by reasons such as thermal expansion of the components of the device due to rising ambient temperature, and / or changes in the positional relationship of the components over time due to continuous vibration of the device caused by external factors. If the MCF 20p shifts position relative to the first lens 30, the ray angles θ1 of the principal rays B1 to B4 of the light emitted from the first lens 30 will deviate as described above, thereby affecting the optical characteristics.

[0208] Therefore, the inventors of this application investigated the relationship between the position offset Δd of MCF 20p and the deviation Δθ1 of the light angle θ1 by examining two oblique grinding directions (oblique grinding rotation angle Ψm) for MCF 20p, and studied the oblique grinding direction that can suppress the increase of deviation Δθ1 caused by the change of position offset Δd. Figure 34A and Figure 34B This is a diagram showing the end face 20ap of the MCF 20p used in the study. Figure 34A In the example, MCF 20p was obliquely ground in the oblique grinding direction Dm1 with Ψm = 0°. Figure 34B In the example, MCF 20p was obliquely ground in an oblique grinding direction Dm2 with Ψm = 45°.

[0209] Figure 35 This is a graph that defines the relationship between the positional offset Δd of the MCF 20p and the deviation Δθ1 of the ray angle θ1. Δd is defined relative to the state in which the MCF 20p is configured to align its central axis with axis A1 (see reference). Figure 31A Δd is the positional offset along the oblique grinding direction. When the MCF 20p shifts positionally in the direction opposite to the oblique grinding direction, Δd has a positive value. Δθ1 is defined as the difference (θ1max - θ1min) between the minimum and maximum ray angles θ1 of the principal rays B1 to B4. In this example, Δθ1 is the difference between the ray angles θ1 of principal ray B1 and principal ray B3.

[0210] like Figure 35As shown, when the oblique grinding direction is direction Dm1, compared to when the oblique grinding direction is direction Dm2, the increase in deviation Δθ1 caused by the change in position offset Δd can be suppressed. For example, when Δd = 0.07 mm, when the oblique grinding direction is direction Dm1, Δθ1 can be reduced by about 45% compared to when the oblique grinding direction is direction Dm2. This is believed to be based on the relationship between the oblique grinding direction and the core configuration of MCF 20p. The following is a detailed explanation. First, when viewing the end face 20a from the front, a straight line extending along the oblique grinding direction through the center of the end face 20a is defined as the "reference axis". A direction along an orthogonal axis orthogonal to the central axis of MCF 20p and the reference axis, pointing towards the left side of the paper relative to the reference axis, is defined as the "first orthogonal direction". A direction along this orthogonal axis, pointing towards the right side of the paper relative to the reference axis, is defined as the "second orthogonal direction".

[0211] According to this regulation, Figure 34A In the example case, the cores furthest from the reference axis in the first orthogonal direction (i.e., the -x-axis direction) are cores C2 and C3, and the cores furthest from the reference axis in the second orthogonal direction (i.e., the +x-axis direction) are cores C1 and C4. The sum of the distance from the reference axis to core C2 or C3 and the distance from the reference axis to core C1 or C4 (separation distance) is 50 μm. On the other hand, in Figure 34B In the example, the core farthest from the reference axis in the first orthogonal direction is core C3, and the core farthest from the reference axis in the second orthogonal direction is core C1. The sum of the distances from the reference axis to core C3 and from the reference axis to core C1 (separation distance) is 71 μm. That is, the separation distance when the oblique grinding direction is direction Dm1 is shorter than the separation distance when the oblique grinding direction is direction Dm2.

[0212] The inventors of this application conducted the above-described research on MCFs with various core configurations. As a result, the following insight was gained: by setting the oblique grinding direction of the MCF 20p in a manner that minimizes the separation distance, it is possible to suppress to the greatest extent possible the increase in deviation Δθ1 caused by changes in position offset Δd. Therefore, in the FIFO device of this embodiment, by setting the oblique grinding direction to the direction that minimizes the separation distance, it is possible to achieve a FIFO device that is highly robust to thermal expansion and / or vibration while further reducing reflected light.

[0213] (Fourth Implementation)

[0214] Next, refer to Figures 36 to 38 The FIFO device according to the fourth embodiment will be described. In the fourth embodiment, the layout of the second lens is different from that in the first embodiment. In this embodiment, lenses 41 to 44 of the FIFO device 10 (lenses corresponding to MCF 20) will be used as examples for explanation.

[0215] Figure 36 This shows the arrangement of lenses 41 to 44 in this embodiment, and the state in which the second lens group 40 is minimized in the radial direction. Figure 37 This illustrates the arrangement of lenses 41 to 44 according to the first embodiment, and the state in which the second lens group is minimized radially. For example... Figure 36 and Figure 37 As shown, lenses 41 to 44 are respectively housed in housing members 71 to 74. Housing members 71 to 74 are cylindrical members of the same size, and each holds lens 41 to 44 inside.

[0216] like Figure 37 As shown, in the first embodiment, the principal points Cs1 to Cs4 of lenses 41 to 44 are located on the same plane. Furthermore, the four lenses 41 to 44 are arranged such that their housing members 71 to 74 abut against each other in the x-axis and y-axis directions. When lenses 41 to 44 are viewed along axis A1, the principal points Cs1 to Cs4 are located at the vertices of a square centered on axis A1. The two diagonals r3 and r4 of this square are orthogonal to axis A1 at the same position on axis A1.

[0217] In contrast, in this embodiment, such as Figure 36 As shown, the principal points Cs1 and Cs3 of lenses 41 and 43 (lenses positioned between axes A1) are located on the same plane orthogonal to axis A1, while the principal points Cs2 and Cs4 of lenses 42 and 44 (lenses positioned between axes A1) are located on another plane orthogonal to axis A1. The housing members 71 and 73 of lenses 41 and 43 abut against each other, and the housing members 72 and 74 of lenses 42 and 44 abut against each other. Additionally, the housing members 71 and 73 of a pair of lenses 41 and 43 abut against each other and the housing members 72 and 74 of a pair of lenses 42 and 44 also abut against each other in the z-axis direction (illustration omitted). When viewing lenses 41 to 44 along axis A1, the principal points Cs1 to Cs4 are located at the vertices of a square centered on axis A1. The two diagonals r1 and r2 of this square are orthogonal to axis A1 at different positions along axis A1. The lengths of diagonals r1 and r2 are... Figure 37 The lengths of the diagonals r3 and r4 are short.

[0218] Figure 36 The second lens group 40 and Figure 37The second lens group 40 is more miniaturized radially. This is because by arranging a pair of lenses 41 and 43 offset from a pair of lenses 42 and 44 in the axial direction, the housing members of the two lenses (lenses 41 and 43 or lenses 42 and 44) ​​located on the diagonal of the square abut against each other. Furthermore, in this case, the coupling part of the FIFO device can also be miniaturized in the z-axis direction. That is, since the incident angle of light rays incident on each lens 41 to 44 is fixed, the one with a shorter distance between the lenses (r1, r2 < r3, r4) can shorten the distance that light rays toward lenses 41 to 44 travel from the light emission position to the incident position in the z-axis direction.

[0219] According to this structure, the coupling part of the FIFO device can be further miniaturized. In addition, the oblique grinding direction of the SMF corresponding to each lens 41 to 44 can satisfy either the radial condition or the z-axis condition, but by using the SMF that satisfies the z-axis condition, the coupling part can be significantly miniaturized in both the radial and z-axis directions.

[0220] In addition, such as Figure 38 As shown, the structure can also be as follows: the principal points Cs1, Cs2, and Cs4 of three of the four lenses 41 to 44 are located on the same plane, while the principal point Cs3 of the remaining lens 43 is not located on this plane. In this case, it is preferable that the principal point Cs3 of lens 43 is closer to axis A1 than the principal point Cs3 of lens 43 in the case where "all the principal points Cs1 to Cs4 of lenses 41 to 44 are located on the same plane" (illustration omitted). According to this structure, the coupling part of the FIFO device can be miniaturized to a degree comparable to the distance by which lens 43 is close to axis A1. In addition, the focal lengths of the lenses do not necessarily have to be the same.

[0221] The above example illustrates the structure using a lens corresponding to MCF 20, but this structure can also be applied to lenses corresponding to other MCFs.

[0222] The FIFO devices involved in the embodiments and modifications have been described above. However, the present invention is not limited to the above embodiments and modifications. Various changes can be made as long as they do not depart from the purpose of the present invention.

[0223] For example, a single-core fiber group with multiple single-core fibers corresponding to multiple modes can be used instead of a single-mode fiber group. However, the FIFO device involved in this invention is based on the premise of propagating light in a single mode, so even when using multimode single-core fiber, the light propagated by the fiber is any one of the multiple modes.

[0224] Furthermore, the core configuration of the MCF can also be asymmetrical. Even if the core configuration is asymmetrical, the first lens 30 and the second lens groups 40, 140 or 240 can function properly as FIFO devices by positioning the second lens groups 40, 140 or 240 at positions corresponding to the light rays emitted from the first lens 30 from each core.

[0225] Furthermore, SMF and MCF are not limited to cylindrical shapes; they can also be cylindrical with arbitrary shapes (e.g., elliptical or polygonal) in cross-sections orthogonal to the axis.

[0226] Furthermore, it is also possible that not all cores of the MCF are used for light propagation. For example, only cores C1 to C3 of MCF 20 are used for light propagation, while core C4 is not used for light propagation. In this case, the second lens group 40 and the SMF group 50 can be configured to have three second lenses 41 to 43 and three SMFs 51 to 53 corresponding to cores C1 to C3. That is, the second lens group and the SMF group only need to have the same number of second lenses and SMFs as the number of cores in the MCF used for light propagation; they do not need to always have the same number of second lenses and SMFs as the number of cores in the MCF.

[0227] Furthermore, the central axis of each SMF in the SMF group may not be parallel to the optical axis of the corresponding lens in the second lens group. Let's take the FIFO device 10 as an example. As described above, when the grinding angle of the end faces 51a to 54a of SMFs 51 to 54 is 8° and the wavelength of the light is 1.55 μm, the main rays B1 to B4 are preferably incident at an angle of 78.2° relative to the end faces 51a to 54a (hereinafter also referred to as "incident angle θ2"). In the above embodiment, the central axis of each SMF is parallel to the optical axis of the corresponding lens, therefore the light angle θ1 that achieves θ2 = 78.2° is 3.8°, and the circle 43a that achieves θ1 = 3.8° (see reference) Figure 10 , Figure 11A as well as Figure 11B The radius of the SMF is 0.16 mm. However, as long as the structure can ensure an incident angle θ2 = 78.2°, the central axis of each SMF does not have to be parallel to the optical axis of the corresponding lens.

[0228] For example, it is assumed that if the diameter of circle 43a is increased and lens 43 is moved by 0.30 mm, the ray angle θ1 is greater than 3.8°. In this case, to ensure the incident angle θ2 = 78.2°, SMF 53 needs to be tilted in a specified direction (described later). As a result, the central axis of SMF 53 becomes non-parallel to the optical axis of lens 43. Thus, if the constraint of "making the central axis of each SMF parallel to the optical axis of the corresponding lens" is removed, the amount of movement of each lens in the radial or z-axis direction can be freely controlled, thereby increasing the degree of freedom in miniaturizing the coupling part of the FIFO device. Furthermore, the aforementioned "specified direction" means that the central axis of each SMF exists in a direction that "includes the oblique grinding reference axis of each SMF and the plane of the corresponding principal ray." That is, it is not possible to tilt each SMF in any direction simply by ensuring θ2 = 78.2°.

[0229] Furthermore, the FIFO devices 10, 110, and 210 in the above embodiments and variations propagate light from the MCFs 20, 120, and 220 via the first lens 30 and the second lens groups 40, 140, and 240 toward the SMF groups 50, 150, and 250. However, this structure is not limited to this; light can also propagate from the SMF groups 50, 150, and 250 via the second lens groups 40, 140, and 240 and the first lens 30 toward the MCFs 20, 120, and 220. In this case, the number of first cores of the MCFs can be greater than or equal to the number of SMFs in the SMF group. Additionally, the number of second lenses in the second lens group can be the same as the number of SMFs.

[0230] Explanation of reference numerals in the attached figures

[0231] 10: FIFO device; 20: multi-core optical fiber; 20a: end face; 30: first lens; 40: second lens group; 41, 42, 43, 44: second lenses; 50: single-mode optical fiber group; 51, 52, 53, 54: single-mode optical fiber.

Claims

1. A fan-in / fan-out device (10, 110, 210), comprising: Multi-core optical fiber (20, 120, 220) is columnar and has multiple first cores (C1 to C4, C1 to C7) extending along the axial direction and a common cladding (CL) surrounding the multiple first cores. A first lens (30) has a first optical axis parallel to the central axis of the multi-core optical fiber (20, 120, 220). The first lens is disposed corresponding to the multi-core optical fiber. The first lens causes the parallel principal rays (B1 to B4, B1 to B7) emitted from each of the first cores (C1 to C4, C1 to C7) to be emitted in a manner that is inclined in a predetermined direction. The second lens group (40, 140, 240) has a plurality of second lenses (41 to 44, 141 to 144, 241 to 247) having a second optical axis parallel to the first optical axis. The second lens group causes light rays emitted from each of the first cores from the first lens (30) to converge through the corresponding second lenses (41 to 44, 141 to 144, 241 to 247); and A single-core fiber group (50, 150, 250) has the same number of single-core fibers (51 to 54, 151 to 154, 251 to 257) as the second lenses (41 to 44, 141 to 144, 241 to 247). Each single-core fiber is cylindrical and has a second core (C) extending along a central axis and a cladding (CLs) surrounding the second core (C). The end faces (51a to 54a, 151a to 154a, 251a to 257a) of each single-core fiber (51 to 54, 151 to 154, 251 to 257) are arranged such that light rays emitted from the first cores (C1 to C4, C1 to C7) from the corresponding second lenses (41 to 44, 141 to 144, 241 to 247) converge onto the second core (C). In the aforementioned fan-in and fan-out devices (10, 110, 210), The end faces (51a to 54a, 151a to 154a, 251a to 257a) of each of the single-core optical fibers (51 to 54, 151a to 154a, 251a to 257a) were obliquely polished at a first polishing angle relative to a first tilting direction orthogonal to their central axis. The oblique grinding direction of the peripheral single-core fibers (51 to 54, 151 to 154, 251 to 253, and 255 to 257) whose central axis is located away from the first optical axis is set such that the position of the corresponding second lens (41 to 44, 141 to 144, 241 to 243, and 245 to 247) is closer to the first optical axis or closer to the first lens (30) compared to the non-grinding position of the second lens when the peripheral single-core fibers are not obliquely ground. The end face (51a to 54a, 151a to 154a, 251a to 253a and 255a to 257a) of any of the peripheral single-core optical fibers (51 to 54, 151 to 154, 251 to 253a and 255a to 257a) is not parallel to at least one end face (51a to 54a, 151a to 154a, 251a to 253a and 255a to 257a) of the peripheral single-core optical fibers (51 to 54, 151 to 154, 251 to 253a and 255a to 257a) other than the aforementioned peripheral single-core optical fiber.

2. The fan-in / fan-out device according to claim 1, wherein, The central axis of each of the single-core optical fibers (51 to 54, 151 to 154, 251 to 257) is parallel to the second optical axis of the corresponding second lens (41 to 44, 141 to 144, 241 to 247).

3. The fan-in / fan-out device according to claim 1 or 2, wherein, When viewing the end face of each of the peripheral single-core optical fibers (51 to 54, 151 to 154, 251 to 253, and 255 to 257) along the central axis, the line segment passing through the center of the end face of each peripheral single-core optical fiber and orthogonal to the line segment connecting the first optical axis and the center of the end face is defined as the first orthogonal line of each peripheral single-core optical fiber (L1 to L4, Lr11 to Lr14, L21 to 23, and L25 to 27); and The portion of the outer periphery of the end face that is opposite to the side containing the first optical axis relative to the first orthogonal line is defined as the first outer periphery (Cir1 to Cir4, Cir11 to Cir14, Cir21 to 23, and Cir25 to 27). When the aforementioned specification is made, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located on the first outer periphery.

4. The fan-in / fan-out device according to claim 3, wherein, The oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located at the midpoint of the first outer periphery (Cir1 to Cir4, Cir11 to Cir14, Cir21 to 23 and Cir25 to 27).

5. The fan-in / fan-out device according to claim 1 or 2, wherein, When viewing the end face of each of the peripheral single-core optical fibers (51 to 54, 251 to 253, and 255 to 257) along their central axes, in the first case where the reference line (Lb) extending in any direction orthogonal to the first optical axis does not pass through the center of each of the peripheral single-core optical fibers... The line segments passing through the center of the end face of each of the peripheral single-core optical fibers and parallel to the reference line (Lb) are defined as the parallel lines of each of the peripheral single-core optical fibers (Lz1 to Lz4, Lz21 to 23, and Lz25 to 27); and The portion of the outer periphery of the end face that is closest to the first optical axis relative to the parallel line is defined as the second outer periphery (Ciz1 to Ciz4, Ciz21 to 23, and Ciz25 to 27). When this specification is applied, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference shaft is located on the second outer periphery. When viewing the end face of each of the peripheral single-core optical fibers (151 to 154) along the central axis, in the second case where the reference line (Lb) passes through the center of each of the peripheral single-core optical fibers, The line segment passing through the center of the end face of each of the peripheral single-core optical fibers and orthogonal to the reference line (Lb) is defined as the second orthogonal line (segment Lz11 to Lz14) of each of the peripheral single-core optical fibers; and The portion of the outer periphery of the end face that is closest to the first optical axis relative to the second orthogonal line (segments Lz11 to Lz14) is defined as the third outer periphery (Ciz11 to Ciz14). When this specification is made, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference shaft is located on the third outer periphery.

6. The fan-in / fan-out device according to claim 5, wherein, In the first case, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located at the midpoint of the second outer periphery (Ciz1 to Ciz4, Ciz21 to 23, and Ciz25 to 27). In the second case, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located at the midpoint of the third outer periphery (Ciz11 to Ciz14).

7. The fan-in / fan-out device according to claim 1 or 2, wherein, When viewing the end face of each of the peripheral single-core optical fibers (51 to 54, 151 to 154, 251 to 253, and 255 to 257) along the central axis, the line segment passing through the center of the end face of each peripheral single-core optical fiber and orthogonal to the line segment connecting the first optical axis and the center of the end face is defined as the first orthogonal line of each peripheral single-core optical fiber (L1 to L4, Lr11 to Lr14, L21 to 23, and L25 to 27); and The portion of the outer periphery of the end face that is closest to the first optical axis relative to the first orthogonal line is defined as the fourth outer periphery (Ciz31 to Ciz34, Ciz41 to 43, and Ciz45 to 47). When the aforementioned specification is made, the oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located on the fourth outer periphery.

8. The fan-in / fan-out device according to claim 7, wherein, The oblique grinding direction is set such that the proximal end (E2) of the oblique grinding reference axis is located at the midpoint of the fourth outer periphery (Ciz31 to Ciz34, Ciz41 to 43 and Ciz45 to 47).

9. The fan-in / fan-out device according to claim 1 or 2, wherein, The end face (20ap) of the multi-core optical fiber (20p) was obliquely ground at a second grinding angle relative to the second tilt direction orthogonal to its central axis. When viewing the end face of the multi-core optical fiber along its central axis, a straight line passing through the center of the end face and extending along the oblique grinding direction is defined as the reference axis; and A first orthogonal direction is defined as a direction starting from the reference axis and extending along an orthogonal axis orthogonal to the side relative to the reference axis; a second orthogonal direction is defined as a direction starting from the reference axis and extending along the orthogonal axis and extending to the other side relative to the reference axis. When the aforementioned specification is made, the oblique polishing direction of the multi-core optical fiber is set to minimize the separation distance, which is the sum of the distance from the first core farthest from the reference axis in the first orthogonal direction and the distance from the first core farthest from the reference axis in the second orthogonal direction when viewing its end face along the central axis of the multi-core optical fiber.

10. The fan-in / fan-out device according to claim 1 or 2, wherein, The principal points (Cs2, Cs4) of all the second lenses (42, 44) except for at least one second lens (41, 43) are located on the same plane. The principal points (Cs1, Cs3) of the at least one second lens (41, 43) are closer to the first optical axis than the principal points (Cs1, Cs4) of the at least one second lens (41, 43) assuming that all the principal points (Cs1 to Cs4) of the second lenses (41 to 44) are located on the same plane.

11. The fan-in / fan-out device according to claim 10, wherein, The fan-in / fan-out device includes 2n second lenses (41 to 44), where n ≥ 2. When observing the second lens along the first optical axis The principal points (Cs1 to Cs4) of the second lens are located at the vertices of a regular polygon centered on the first optical axis. The n line segments (r1, r2) connecting the principal points of a pair of second lenses (41, 43; 42, 44) located on the diagonal of the regular polygon are orthogonal to the first optical axis at different positions on the first optical axis. The length of the line segment (r1, r2) is shorter than the length of the line segment (r3, r4) assuming that the n line segments are orthogonal to the first optical axis at the same position on the first optical axis.

12. The fan-in / fan-out device according to claim 1, in, The light propagates in a direction opposite to the direction in which the light propagates in the order of the multi-core optical fiber, the first lens, the second lens group, and the single-core optical fiber group.

13. The fan-in / fan-out device according to claim 1 or 2, wherein, The oblique polishing direction of the peripheral single-core optical fibers (51 to 54, 151 to 154, 251 to 253 and 255 to 257) is set to satisfy at least one of the following miniaturization configurations: A radially miniaturized configuration in which the corresponding second lenses (41 to 44, 141 to 144, 241 to 243 and 245 to 247) are all located closer to the first optical axis than the unpolished position; as well as The corresponding second lenses (41 to 44, 141 to 144, 241 to 243 and 245 to 247) are all located in a miniaturized configuration along the optical axis, closer to the position of the first lens (30) than the unpolished position.

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