Optical waveguide device, optical connection structure, and optical connection method

Abstract

An optical waveguide device according to the present disclosure comprises: a cladding that includes a first surface and a second surface different from the first surface; at least one first core that extends from the first surface to the second surface within the cladding; and a second core that is formed in a region excluding the first core within the cladding, and extends from the first surface so as to return to the first surface through the inside of the cladding.

Description

Optical waveguide device, optical connection structure, and optical connection method

[0001] This application claims priority to Japanese Patent Application No. 2023-083999, filed May 22, 2023, and incorporates by reference all of the contents of that application.

[0002] For example, Patent Document 1 discloses an optical waveguide device including a cladding and a plurality of cores surrounded by the cladding. In this optical waveguide device, the pitch between the cores inside the cladding is changed along the direction of light propagation. Such an optical waveguide device is disposed, for example, between two fiber arrays with different core pitches, enabling low-loss optical connection between these fiber arrays.

[0003] International Publication No. 2018 / 135411

[0004] An optical waveguide device according to one embodiment of the present disclosure comprises a cladding including a first surface and a second surface different from the first surface, at least one first core extending inside the cladding from the first surface to the second surface, and a second core formed in a region of the cladding excluding the first core and extending from the first surface through the inside of the cladding so as to return to the first surface.

[0005] FIG. 1 is a perspective view showing an optical connection structure according to a first embodiment. FIG. 2 is a perspective view showing the optical waveguide device of FIG. 1. FIG. 3 is a side view showing the optical waveguide device of FIG. 2. FIG. 4a is a front view showing the optical waveguide device of FIG. 2. FIG. 4b is a front view showing a first optical fiber array facing the optical waveguide device of FIG. 4a. FIG. 5a is a rear view showing the optical waveguide device of FIG. 2. FIG. 5b is a front view showing a second optical fiber array facing the optical waveguide device of FIG. 5a. FIG. 6 is a flowchart showing steps of an optical connection method according to a first embodiment. FIG. 7a is a plan view showing active alignment of an optical waveguide device and a first optical fiber array. FIG. 7b is a plan view showing active alignment of an optical waveguide device and a second optical fiber array. FIG. 8 is a perspective view showing an optical connection structure according to a second embodiment. FIG. 9 is a perspective view showing the optical waveguide device of FIG. 8. FIG. 10 is a side view showing the optical waveguide device of FIG. 9. FIG. 11a is a front view showing the optical waveguide device of FIG. 9. Figure 11b is a front view of a first optical fiber array facing the optical waveguide device of Figure 11a, Figure 12a is a rear view of the optical waveguide device of Figure 9, and Figure 12b is a front view of a second optical fiber array facing the optical waveguide device of Figure 12a.

[0006] [Problem to be Solved by the Present Disclosure] To optically connect the three components, the optical waveguide device and the two fiber arrays, an alignment operation is performed to adjust the relative positions of the three components so that the optical axes of the cores of these three components are aligned. Examples of such alignment methods include active alignment, in which test light is actually introduced into the three components and the alignment of the three components is adjusted while monitoring the optical coupling loss between the three components, and passive alignment, in which the alignment of the three components is adjusted while observing markers or other indicators formed on the three components or their peripheral components. With passive alignment, highly accurate alignment of the three components can be difficult due to errors in the position of the markers or errors in the detection position of the cores during observation. On the other hand, active alignment, in which the alignment of the three components is adjusted while monitoring the test light, allows for more accurate alignment of the three components than passive alignment.

[0007] In active alignment, for example, test light is input from a first fiber array, and the intensity of the test light that passes through an optical waveguide device and is output from a second fiber array is measured by a photodetector such as a power meter. Three-component alignment is then performed to adjust the positions of the three components relative to one another so that the intensity of the test light is maximized. Active alignment, which presupposes monitoring the test light, requires adjusting the positions of the three components with a certain degree of precision so that the test light passes through the cores of the three components. However, as described above, it is not easy to find the position of the three components so that the test light passes through while moving the three components relative to one another. Therefore, the alignment process until the optical axes of the cores of the three components are aligned may take more time than necessary. Therefore, it is desirable to more easily align the three components.

[0008] The present disclosure provides an optical waveguide device, an optical connection structure, and an optical connection method that allow for easier alignment of three components.

[0009] Effect of the Present Disclosure According to the optical waveguide device, optical connection structure, and optical connection method of the present disclosure, the alignment of three members can be performed more easily.

[0010] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0011] (1) An optical waveguide device according to one embodiment of the present disclosure comprises a cladding including a first surface and a second surface different from the first surface, at least one first core extending inside the cladding from the first surface to the second surface, and a second core formed in a region of the cladding excluding the first core and extending from the first surface through the inside of the cladding so as to return to the first surface.

[0012] The optical waveguide device described above is used, for example, to optically connect two optical fiber arrays. In this case, a first surface of the optical waveguide device faces one optical fiber array (hereinafter referred to as the "first optical fiber array"). A second surface of the optical waveguide device faces the other optical fiber array (hereinafter referred to as the "second optical fiber array"). A first core of the optical waveguide device is optically connected to the first optical fiber array on the first surface and to the second optical fiber array on the second surface. Therefore, the first core can be used as a communication core for transmitting communication light necessary for communication between these optical fiber arrays. In addition to the first core, the optical waveguide device includes a second core extending from the first surface through the inside of the cladding and returning to the first surface. The second core can be used as an alignment core for actively aligning two components, the optical waveguide device and the first optical fiber array. Test light for actively aligning these two components is emitted from the first optical fiber array to the first surface, passes through the second core, and returns from the first surface to the first optical fiber array. Therefore, by measuring the test light returning to the first optical fiber array using a power meter or the like, it is possible to adjust the positioning of the two components, the optical waveguide device and the first optical fiber array, to achieve the maximum intensity of the test light.

[0013] After the two-way alignment between the first optical fiber array and the optical waveguide device is completed in this manner, the remaining second optical fiber is simply aligned with the aligned optical waveguide device. As a result, the three components, namely the first optical fiber array, the optical waveguide device, and the second optical fiber array, are aligned by active alignment. Thus, using the above-described optical waveguide device, the two-way alignment for adjusting the relative positions of the three components is performed twice, rather than all at once. In this case, the position of the three components through which the test light passes can be more easily found compared to when the three-way alignment is performed all at once, thereby reducing the difficulty of adjusting the positions of the three components when actively aligning the three components. Furthermore, using active alignment in this manner allows the three components to be more reliably aligned while capturing the optical axis positions of the three components, thereby reducing the time required for alignment of the three components compared to when only passive alignment is performed. Therefore, the above-described optical waveguide device makes it easier to align the three components.

[0014] (2) In the optical waveguide device described in (1) above, the first core may include a core end face exposed on the first surface. The second core may include a first core end face and a second core end face exposed at positions on the first surface different from the core end faces. In this case, it is possible to preferably realize a mode in which the test light emitted from the first optical fiber array to the first surface passes through the second core and returns to the first optical fiber array.

[0015] (3) In the optical waveguide device described in (2) above, the first core end face and the second core end face may be arranged side by side with the core end face in one direction along the first surface. In this case, the second core can be formed on the same plane as the first core, facilitating the work of forming the second core inside the cladding.

[0016] (4) In the optical waveguide device described in (3) above, the first core end face and the second core end face may be arranged side by side on one of the two sides of the core end face in one direction. In this case, it is easy to form a second core that extends inside the cladding without intersecting with the first core. By preventing the first core and the second core from intersecting in this way, it is possible to avoid interference and loss of optical signals passing through the first core and the second core.

[0017] (5) In the optical waveguide device described in (4) above, the second core may extend inside the cladding along a plane that intersects the first surface and passes through the first core end face and the second core end face. In this case, the second core is formed on the same plane, which makes it easier to form the second core inside the cladding.

[0018] (6) In the optical waveguide device described in (3) above, the first core end face and the second core end face may be arranged on opposite sides of the core end face in one direction. In this case, the distance between the first core end face and the second core end face can be increased compared to when the first core end face and the second core end face are arranged adjacent to each other, thereby maintaining a large distance between the first core end face and the second core end face. As a result, when actively aligning the first optical fiber array with the optical waveguide device using alignment test light, the risk of rotational misalignment between the position of the first core end face from which the test light is incident or emitted and the position of the second core end face from which the test light is emitted or incident can be reduced. This makes it possible to more reliably align the optical waveguide device and the first optical fiber array. Furthermore, if the distance between the first core end face and the second core end face can be maintained large, the radius of curvature of the curved portion that may be formed in the path of the second core from the first core end face to the second core end face can be maintained large compared to when the first core end face and the second core end face are arranged adjacent to each other. This makes it possible to reduce the propagation loss of the test light introduced into the second core during alignment.

[0019] (7) In the optical waveguide device described in (6) above, the second core may include a first portion that intersects the first surface and extends along a plane that passes through the first core end face and the second core end face, and a second portion that is formed in a region away from the plane and extends so as to intersect with the first core when viewed along the normal to the plane. In this case, the path of the second core can be changed three-dimensionally so as not to intersect with the first core inside the cladding. By preventing the first core and second core from intersecting in this way, interference and loss of optical signals passing through the first core and the second core can be avoided.

[0020] (8) The optical waveguide device described in any one of (3) to (7) above may include a plurality of first cores. The core end faces of the plurality of first cores may include a first adjacent end face adjacent to one of the first core end face and the second core end face in one direction, and a second adjacent end face adjacent to the first adjacent end face in one direction. The distance between one of the first core end face and the second core end face and the first adjacent end face may be the same as the distance between the first adjacent end face and the first adjacent end face. For example, when optically connecting a first optical fiber array to an optical waveguide device, the plurality of optical fibers included in the first optical fiber array are held in a holder in a state where they are aligned corresponding to the first cores and the second cores. The holder has a plurality of holding portions (e.g., V-grooves) formed therein for holding the plurality of optical fibers. Such holding portions are typically formed to be aligned at regular intervals, assuming that the plurality of optical fibers will be aligned at regular intervals. Even in the above configuration, the plurality of first cores and second cores can be aligned at regular intervals, so that an existing holder that holds a plurality of optical fibers aligned at regular intervals can be used accordingly. In this way, the above-described configuration allows existing holders to be used as they are without modification, and is therefore highly versatile.

[0021] (9) In the optical waveguide device described in any one of (1) to (8) above, the mode field diameter of the second core at the first surface may be the same as the mode field diameter of the first core at the first surface. For example, when optically connecting a first optical fiber array to an optical waveguide device, the multiple optical fibers included in the first optical fiber array are held in a holder while being aligned corresponding to the first and second cores. The holder has multiple holding portions (e.g., V-grooves) for holding the multiple optical fibers. Such holding portions are usually formed with the same size and shape, assuming that general-purpose optical fibers will be used. Even in the above configuration, the mode field diameter of the second core is set to be the same as the mode field diameter of the first core, assuming that general-purpose optical fibers will be optically connected to the first and second cores. Therefore, the above configuration allows existing holders capable of holding general-purpose optical fibers to be used as is, resulting in excellent versatility.

[0022] (10) The optical waveguide device described in (1) to (9) above may further include a third core formed in a region of the cladding excluding the first core and the second core, extending from the second surface through the interior of the cladding and returning to the second surface. In this case, the third core can be used as an alignment core for actively aligning the two components, the optical waveguide device and the second optical fiber array. Test light for actively aligning these two components is emitted from the second optical fiber array to the second surface, passes through the third core, and returns to the second optical fiber array from the second surface. Therefore, by measuring the test light returned to the second optical fiber array with a power meter or the like, it is possible to perform two-component alignment, adjusting the positions of the two components, the optical waveguide device and the second optical fiber array, so as to maximize the intensity of the test light. In this way, by separately performing two-component alignment between the first optical fiber array and the optical waveguide device and two-component alignment between the optical waveguide device and the second optical fiber array, it is possible to more easily align the three components, the first optical fiber array, the optical waveguide device, and the second optical fiber array.

[0023] (11) An optical connection structure according to an embodiment of the present disclosure includes the optical waveguide device according to any one of (1) to (10) above, and an optical fiber array arranged to face the first surface. The optical fiber array includes at least one first optical fiber optically connected to a first core on the first surface, and a pair of second optical fibers optically connected to both ends of a second core on the first surface. Because this optical connection structure includes any one of the optical waveguide devices described above, it becomes possible to more easily align the three components, as described above.

[0024] (12) An optical connection method according to an embodiment of the present disclosure includes the steps of: preparing an optical waveguide device, a first optical fiber array, and a second optical fiber array according to any one of (1) to (10) above; actively aligning the optical waveguide device and the first optical fiber array with the first optical fiber array positioned to face a first surface of the optical waveguide device so that the first optical fiber array is optically connected to the optical waveguide device; and actively aligning the optical waveguide device and the second optical fiber array with the second optical fiber array positioned to face a second surface of the optical waveguide device so that the second optical fiber array is optically connected to the optical waveguide device after the active alignment. In the step of actively aligning the optical waveguide device and the first optical fiber array, alignment test light is emitted from a first alignment optical fiber of the first optical fiber array toward the first surface, the test light passes through a second core from the first surface and is incident on the second alignment optical fiber of the first optical fiber array, and the arrangement of the optical waveguide device and the first optical fiber array is adjusted so that the intensity of the test light is maximized.

[0025] According to the above optical connection method, when active alignment of the three components, the first optical fiber array, the optical waveguide device, and the second optical fiber array, is performed, the three-component alignment is not performed all at once, but rather the two-component alignment is performed twice. In this case, the position of the three components through which the test light passes can be more easily found compared to when the three-component alignment is performed all at once, thereby reducing the difficulty of adjusting the positions of the three components when actively aligning the three components. Furthermore, by using this active alignment, the three components can be more reliably aligned while capturing the optical axis positions of the cores of the three components, thereby reducing the time required to align the three components compared to when only passive alignment is performed. Therefore, the above optical connection method makes it easier to align the three components.

[0026] (13) According to an embodiment of the present disclosure, an optical waveguide device is disposed between a first optical fiber array and a second optical fiber array and optically connects the first optical fiber array and the second optical fiber array. The optical waveguide device includes a cladding including a first surface facing the first optical fiber array and a second surface facing the second optical fiber array, at least one communication core extending through the cladding from the first surface to the second surface and capable of transmitting communication light necessary for communication between the first optical fiber array and the second optical fiber array, and an alignment core formed in a region of the cladding excluding the communication core, extending from the first surface through the cladding to return to the first surface, and capable of transmitting test light for active alignment of the first optical fiber array and the optical waveguide device. This configuration, as described above, enables easier alignment of the three components, i.e., the first optical fiber array, the optical waveguide device, and the second optical fiber array.

[0027] [Details of the embodiments of the present disclosure] Specific examples of optical waveguide devices, optical connection structures, and optical connection methods according to the present disclosure are described below with reference to the drawings. The present disclosure is not limited to the following examples, but is intended to include all modifications set forth in the claims and within the scope equivalent to the claims. In the description of the drawings, identical or corresponding elements are designated by the same reference numerals, and redundant description will be omitted as appropriate. For ease of understanding, some parts of the drawings may be simplified or exaggerated, and dimensional proportions and the like are not limited to those shown in the drawings.

[0028] [First embodiment] Fig. 1 is a perspective view showing an optical connection structure 1 according to a first embodiment. As shown in Fig. 1, the optical connection structure 1 includes, for example, a first optical fiber array 10, a second optical fiber array 30, and an optical waveguide device 50. For convenience, covers 17 and 37, which will be described later, are shown by dashed lines in Fig. 1.

[0029] The first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30 are arranged in this order along the first direction D1. Therefore, the optical waveguide device 50 is disposed between the first optical fiber array 10 and the second optical fiber array 30 and in the first direction D1. The optical waveguide device 50 is used to optically connect the first optical fiber array 10 and the second optical fiber array 30. The optical waveguide device 50 is configured to transmit communication light (i.e., optical signals) to be transmitted between the first optical fiber array 10 and the second optical fiber array 30.

[0030] The first optical fiber array 10 includes, for example, a first optical fiber group 11 and a first holder 15 that holds the first optical fiber group 11. For example, the tip portions of the first optical fiber group 11 extend from the MT ferrule toward the optical waveguide device 50 in a first direction D1 and face the optical waveguide device 50 in the first direction D1. The first holder 15 is disposed at a position facing the optical waveguide device 50 in the first direction D1 and holds the tip portions of the first optical fiber group 11. The first holder 15 includes, for example, a base 16 that supports the tip portions of the first optical fiber group 11 and a lid 17 that is disposed on the base 16 so as to cover the tip portions of the first optical fiber group 11.

[0031] The first optical fiber group 11 includes, for example, a plurality of general-purpose single-core fibers (hereinafter referred to as "SCFs") 12. Each SCF 12 includes, for example, a single core extending along its central axis and a cladding surrounding the single core. The SCFs 12 extend along a first direction D1 and are aligned in a row along a second direction D2 (an example of a "direction") that intersects with the first direction D1. The SCFs 12 are aligned, for example, at regular intervals along the second direction D2.

[0032] The second optical fiber array 30 is disposed on the opposite side of the first optical fiber array 10 in the first direction D1, with the optical waveguide device 50 sandwiched therebetween. The second optical fiber array 30 includes, for example, a second optical fiber group 31 and a second holder 35 that holds the second optical fiber group 31. For example, the tip end portions of the second optical fiber group 31 extend from the MT ferrule toward the optical waveguide device 50 in the first direction D1 and face the optical waveguide device 50 in the first direction D1. The second holder 35 is disposed at a position facing the optical waveguide device 50 in the first direction D1 and holds the tip end portions of the second optical fiber group 31. The second holder 35 includes, for example, a base 36 that supports the tip end portions of the second optical fiber group 31 and a lid 37 that is disposed on the base 36 so as to cover the tip end portions of the second optical fiber group 31.

[0033] The second optical fiber group 31 includes, for example, a general-purpose multicore fiber (hereinafter referred to as "MCF") 32 and a pair of general-purpose SCFs 41 and 42. The MCF 32 includes, for example, a plurality of cores arranged at positions other than its central axis and a cladding surrounding the plurality of cores. The MCF 32 extends along a first direction D1. The cores of the MCF 32 are aligned at regular intervals in a plane along the second direction D2 and the third direction D3. The third direction D3 may be a direction intersecting both the first direction D1 and the second direction D2. The SCFs 41 and 42 extend along the first direction D1 and are aligned in a row with the MCF 32 along the second direction D2.

[0034] Fig. 2 is a perspective view showing the optical waveguide device 50. Fig. 3 is a side view showing the optical waveguide device 50. As shown in Fig. 2 and Fig. 3, the optical waveguide device 50 includes a cladding 51 and a core group 52 formed inside the cladding 51. In each figure, the core group 52 is shown by a solid line for convenience.

[0035] The cladding 51 has a refractive index smaller than that of the core group 52 and surrounds the core group 52. The cladding 51 has, for example, a rectangular plate-like appearance. The cladding 51 includes, for example, a first end face 51a (an example of a "first surface") facing the first optical fiber array 10 (see FIG. 1) in the first direction D1, and a second end face 51b (an example of a "second surface") facing the second optical fiber array 30 (see FIG. 1) in the first direction D1. The first end face 51a and the second end face 51b each extend along a plane intersecting the first direction D1 and are arranged side by side along the first direction D1.

[0036] The cladding 51 further includes a first side surface 51c, a second side surface 51d, a third side surface 51e, and a fourth side surface 51f extending in the first direction D1 between the first end surface 51a and the second end surface 51b. The first side surface 51c and the second side surface 51d extend along a plane intersecting the second direction D2 and are arranged side by side along the second direction D2. The third side surface 51e and the fourth side surface 51f extend along a plane intersecting the third direction D3 and are arranged side by side along the third direction D3.

[0037] The core group 52 includes a plurality of communication cores 55 (an example of a “first core”) for transmitting communication light between the first optical fiber array 10 and the second optical fiber array 30. The plurality of communication cores 55 extend along a first direction D1 inside the cladding 51 from the first end face 51 a to the second end face 51 b and are arranged side by side along a second direction D2. Each communication core 55 extends along the first direction D1 and is bent in the second direction D2 and a third direction D3. As a result, the communication cores 55 are transformed, for example, from being lined up in a row along the second direction at the first end face 51 a to being lined up in both the second direction D2 and the third direction D3 at the second end face 51 b. In this way, each communication core 55 forms a three-dimensional optical waveguide that extends inside the cladding 51 so as to change three-dimensionally in the first direction D1, the second direction D2, and the third direction D3.

[0038] Each communication core 55 is formed inside the cladding 51 by, for example, laser processing using a pulsed laser. The pulsed laser may be, for example, a titanium sapphire femtosecond laser. When a focal point of an optical pulse output from this pulsed laser is formed inside the cladding 51, the refractive index of the cladding 51 changes at the focal point. As this focal point moves in a first direction D1, a second direction D2, and a third direction D3, a plurality of communication cores 55 that change three-dimensionally are formed inside the cladding 51.

[0039] FIG. 4a is a front view showing the optical waveguide device 50. FIG. 4b is a front view showing the first optical fiber array 10. FIG. 5a is a rear view showing the optical waveguide device 50. FIG. 5b is a front view showing the second optical fiber array 30. As shown in FIG. 4a, first core end faces 56 of the multiple communication cores 55 are exposed at the first end face 51a. The core end faces 56 are aligned in a row along the second direction D2 at the first end face 51a to correspond to the alignment of the SCFs 12 (see FIG. 4b) of the first optical fiber array 10. As an example, four core end faces 56 are aligned at regular intervals along the second direction D2.

[0040] 5a, the second end faces 57 of the multiple communication cores 55 are exposed at the second end face 51b. The end faces 57 of each communication core 55 are arranged two-dimensionally along the second direction D2 and the third direction D3 at the second end face 51b to correspond to the arrangement of each core 32a (see FIG. 5b) of the MCF 32 of the second optical fiber array 30. As an example, four end faces 57 are arranged at regular intervals along the second direction D2 and the third direction D3.

[0041] Referring again to Fig. 2 , in this embodiment, as shown in Fig. 2 , in addition to the plurality of communication cores 55 described above, the core group 52 further includes a first alignment core C1 (an example of a "second core") that transmits alignment test light for actively aligning the first optical fiber array 10 and the optical waveguide device 50, and a second alignment core C2 (an example of a "third core") that transmits alignment test light for actively aligning the optical waveguide device 50 and the second optical fiber array 30. Like each communication core 55, the first alignment core C1 and the second alignment core C2 are formed inside the cladding 51 by, for example, laser processing using a pulsed laser. The test light used for active alignment may be any optical signal suitable for monitoring, and may be an optical signal having a different input / output direction or wavelength from the communication light guided through the communication core 55.

[0042] The first aligning core C1 and the second aligning core C2 are formed in a region of the cladding 51 excluding the plurality of communication cores 55, i.e., a region not overlapping with the plurality of communication cores 55. The first aligning core C1 extends from the first end face 51 a through the inside of the cladding 51 to return to the first end face 51 a. The second aligning core C2 extends from the second end face 51 b through the inside of the cladding 51 to return to the second end face 51 b in a region of the cladding 51 excluding the plurality of communication cores 55 and the first aligning core C1, i.e., a region not overlapping with the plurality of communication cores 55 and the first aligning core C1.

[0043] The configuration of the first aligning core C1 will be described in detail. As shown in FIG. 2 , the first core end face C11 (an example of a "first core end face") and the second core end face C12 (an example of a "second core end face") of the first aligning core C1 are both exposed at the first end face 51a. The first aligning core C1 is bent so as to extend from the core end face C11 through the inside of the cladding 51 to the core end face C12. When viewed along the third direction D3, the first aligning core C1 has, for example, a U-shape with an open end at the first end face 51a. The first aligning core C1 includes, for example, a pair of straight line portions P11 and P12 extending in the first direction D1 from the core end faces C11 and C12, respectively, and a curved line portion P13 that curves inside the cladding 51, connecting the ends of the straight line portions P11 and P12.

[0044] The straight line portions P11, P12 and the curved line portion P13 are formed at the same height inside the cladding 51 when viewed with the third direction D3 as the height direction. In other words, the straight line portions P11, P12 and the curved line portion P13 extend along the same plane PL (see FIG. 3 ) along the first direction D1 and the second direction D2 inside the cladding 51. The plane PL may be, for example, an imaginary plane that is perpendicular to the first end face 51 a and passes through the optical axis of the first aligning core C1 at each of the core end faces C11, C12. The normal direction of the plane PL may be, for example, a direction along the third direction D3. In this way, the first aligning core C1 constitutes a two-dimensional waveguide that is bent in the plane PL along the first direction D1 and the second direction D2, but not in the third direction D3.

[0045] As shown in FIG. 4a , the core end faces C11 and C12 are aligned in a row with the core end faces 56 of the multiple communication cores 55 along the second direction D2. In this embodiment, the core end faces C11 and C12 are arranged in one of the regions on either side of the core end faces 56 of the multiple communication cores 55 in the second direction D2. The core end face C12 is, for example, arranged adjacent to the core end face 56A (an example of a “first adjacent end face”) that is located outermost among the multiple core end faces 56 in the second direction D2. The core end face C11 is, for example, arranged on the opposite side of the core end face C12 from the core end face 56A in the second direction D2, and is aligned adjacent to the core end face C12. The mode field diameter of the first aligning core C1 at each of the core end faces C11 and C12 may be, for example, the same as the mode field diameter of the communication core 55 at each core end face 56. The mode field diameter is a value defined based on the light intensity, and is an index indicating the core diameter.

[0046] As described above, the core end faces 56 are arranged at regular intervals along the second direction D2. Similarly, the core end faces C11 and C12 are arranged at the same intervals as the intervals between the core end faces 56. Therefore, if the interval between core end face 56A and core end face 56B (an example of a "second adjacent end face") adjacent to core end face 56A is defined as W1, the interval between core end face C12 and core end face 56A is defined as W2, and the interval between core end face C11 and core end face C12 is defined as W3, then the interval W2 and the interval W3 are each equal to the interval W1. Thus, the core end faces 56, core end face C11, and core end face C12 are arranged at regular intervals along the second direction D2.

[0047] The interval W1 between the core end face 56A and the core end face 56B may be, for example, the distance between the optical axis (i.e., the central axis) of the communication core 55 at the core end face 56A and the optical axis (i.e., the central axis) of the communication core 55 at the core end face 56B. The interval W2 between the core end face C12 and the core end face 56A may be, for example, the distance between the optical axis (i.e., the central axis) of the first aligning core C1 at the core end face C12 and the optical axis (i.e., the central axis) of the communication core 55 at the core end face 56A. The interval W3 between the core end face C11 and the core end face C12 may be, for example, the distance between the optical axis (i.e., the central axis) of the first aligning core C1 at the core end face C11 and the optical axis (i.e., the central axis) of the first aligning core C1 at the core end face C12.

[0048] As shown in FIG. 4b , the multiple SCFs 12 of the first optical fiber array 10 include a pair of aligning SCFs 21, 22 (an example of a "second optical fiber") for transmitting test light for alignment, in addition to a plurality of communication SCFs 13 (an example of a "first optical fiber") for transmitting communication light. The multiple communication SCFs 13 extend along the first direction D1 and are aligned in a row along the second direction D2. The aligning SCFs 21, 22 extend along the first direction D1 and are aligned in a row with the multiple communication SCFs 13 along the second direction D2. The aligning SCFs 21, 22 are disposed, for example, in one of the regions on both sides of the multiple communication SCFs 13 in the second direction D2. The multiple communication SCFs 13 and the aligning SCFs 21, 22 are aligned in a row at regular intervals along the second direction D2, for example.

[0049] The plurality of communication SCFs 13 and the aligning SCFs 21, 22 are respectively placed in a plurality of V-grooves 18 formed in the base 16 of the first holder 15. The plurality of V-grooves 18 extend along the first direction D1 and are aligned at regular intervals along the second direction D2 corresponding to the arrangement of the plurality of communication SCFs 13 and aligning SCFs 21, 22. Each communication SCF 13 is arranged so that its first end face 51a faces a core end face 56 (see FIG. 4a) of each communication core 55. The core 13a of each communication SCF 13 is optically connected to each communication core 55 at its first end face 51a. Each aligning SCF 21, 22 is arranged so that its first end face 51a faces a core end face C11, C12 (see FIG. 4a) of the first aligning core C1. The cores 21a and 22a of the aligning SCFs 21 and 22 are optically connected to the first aligning core C1 at the first end face 51a.

[0050] The aligning SCFs 21 and 22 and the first aligning core C1 are used for active alignment between the first optical fiber array 10 and the optical waveguide device 50. The aligning SCFs 21 and 22 and the first aligning core C1 constitute an optical waveguide for transmitting test light for active alignment. For example, when test light is emitted from the aligning SCF 21, the test light enters the first aligning core C1 from the core end face C11, exits from the core end face C12, and enters the aligning SCF 22. In this manner, the first aligning core C1 has a loop-back structure that returns the test light emitted from the first optical fiber array 10 back to the same first optical fiber array 10. Then, while monitoring the intensity of the test light returned to the first optical fiber array 10, the positions of the first optical fiber array 10 and the optical waveguide device 50 can be adjusted so that the intensity is maximized, thereby enabling active alignment between the first optical fiber array 10 and the optical waveguide device 50.

[0051] Next, the configuration of the second aligning core C2 will be described in detail. As shown in FIG. 2 , both ends of the second aligning core C2, i.e., the first core end face C21 and the second core end face C22, are exposed at the second end face 51b. The second aligning core C2 is bent so as to extend from the core end face C21 through the inside of the cladding 51 to the core end face C22. When viewed along the third direction D3, the second aligning core C2 has, for example, a U-shape with an open end at the second end face 51b. The second aligning core C2 includes, for example, a pair of straight line portions P21, P22 extending from the core end faces C21, C22, respectively, in the first direction D1, and a curved line portion P23 that curves inside the cladding 51, connecting the ends of the straight line portions P21, P22. The straight line portions P21, P22 and the curved line portion P23 extend along the same plane PL (see FIG. 3), similar to the first aligning core C1. Therefore, similar to the first aligning core C1, the second aligning core C2 constitutes a two-dimensional waveguide that is bent in the plane PL along the first direction D1 and the second direction D2, but not in the third direction D3.

[0052] 5a, the core end faces C21, C22 are arranged in one of the regions on either side of the end faces 57 of the multiple communication cores 55 in the second direction D2. For example, the core end face C22 is arranged in a position adjacent to the end faces 57 of the multiple communication cores 55 in the second direction D2, and the core end face C21 is arranged on the opposite side of the core end face C22 in the second direction D2 from the end faces 57 of the multiple communication cores 55. The mode field diameter of the second aligning core C2 at each of the core end faces C21, C22 may be the same as the mode field diameter of the communication core 55 at each end face 57, for example.

[0053] 5b, the second optical fiber array 30 includes a communication MCF 32 for transmitting communication light, as well as a pair of alignment SCFs 41, 42 (hereinafter referred to as "alignment SCFs 41, 42") for transmitting alignment test light. The MCF 32 and the alignment SCFs 41, 42 are, for example, aligned in a row at a regular interval along the second direction D2. The alignment SCFs 41, 42 are, for example, arranged in one of the regions on either side of the MCF 32 in the second direction D2.

[0054] The MCF 32 and the aligning SCFs 41, 42 are respectively placed in a plurality of V-grooves 38 formed in the base 36 of the second holder 35. The V-grooves 38 extend along the first direction D1 and are aligned at regular intervals along the second direction D2, corresponding to the arrangement of the MCF 32 and the aligning SCFs 41, 42. The MCF 32 is arranged so that its second end face 51b faces the end face 57 (see FIG. 5a) of each communication core 55. Each core 32a of the MCF 32 is optically coupled to each communication core 55 at the second end face 51b. Each aligning SCF 41, 42 is arranged so that its second end face 51b faces the core end faces C21, C22 (see FIG. 5a) of the second aligning core C2. Each core 41a, 42a of the aligning SCFs 41, 42 is optically coupled to the second aligning core C2 at the second end face 51b.

[0055] The aligning SCFs 41 and 42 and the second aligning core C2 are used to actively align the second optical fiber array 30 and the optical waveguide device 50. The aligning SCFs 41 and 42 and the second aligning core C2 constitute an optical waveguide for transmitting test light for active alignment. For example, when test light is emitted from the aligning SCF 21, the test light enters the second aligning core C2 from the core end face C21, exits from the core end face C22, and is then incident on the aligning SCF 22. In this manner, the second aligning core C2 has a loop-back structure that returns the test light emitted from the second optical fiber array 30 back to the same second optical fiber array 30. Then, while monitoring the intensity of the test light returned to the second optical fiber array 30, the positions of the second optical fiber array 30 and the optical waveguide device 50 can be adjusted so that the intensity is maximized, thereby enabling active alignment of the second optical fiber array 30 and the optical waveguide device 50.

[0056] Next, a description will be given of an optical connection method using the above-described optical waveguide device 50. Fig. 6 is a flowchart showing steps of the optical connection method according to this embodiment.

[0057] First, the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30 are prepared (step P11). Next, the first optical fiber array 10 and the optical waveguide device 50 are actively aligned (step P12). To actively align them, it is desirable to adjust the positions of the first optical fiber array 10 and the optical waveguide device 50 with a certain degree of accuracy. Therefore, before the active alignment, the first optical fiber array 10 and the optical waveguide device 50 may be passively aligned. In this case, for example, identifiable grooves or markers are formed on the mounting substrates of each component, and the first optical fiber array 10 and the optical waveguide device 50 are positioned using these as guides. Then, with the positions of the first optical fiber array 10 and the optical waveguide device 50 adjusted with a certain degree of accuracy in this manner, the active alignment of the first optical fiber array 10 and the optical waveguide device 50 may be performed.

[0058] 7a is a plan view showing active alignment of the optical waveguide device 50 and the first optical fiber array 10. When the first optical fiber array 10 and the optical waveguide device 50 are actively aligned, as shown in FIG. 7a, the first optical fiber array 10 is positioned so as to face the first end face 51a of the optical waveguide device 50, and test light L1 is emitted from the aligning SCF 21 of the first optical fiber array 10 toward the core end face C11 of the first aligning core C1. The test light L1 emitted from the aligning SCF 21 passes through the first aligning core C1 and is emitted from the core end face C12 toward the aligning SCF 22 of the first optical fiber array 10. The intensity of the test light L1 incident on the aligning SCF 22 is measured by a photodetector such as a power meter.

[0059] Thereafter, while monitoring the intensity of the test light L1, the first optical fiber array 10 is moved relative to the optical waveguide device 50 in a plane along the second direction D2 and the third direction D3 so as to maximize the intensity of the test light L1, i.e., so as to minimize the transmission loss between the first optical fiber array 10 and the optical waveguide device 50. By performing two-way centering in this manner to adjust the relative positions of the first optical fiber array 10 and the optical waveguide device 50, the optical axes of the aligning SCFs 21, 22 and the first aligning core C1 are aligned. This results in the alignment of the two components, the first optical fiber array 10 and the optical waveguide device 50.

[0060] Next, the second optical fiber array 30 and the optical waveguide device 50 are actively aligned (step P13). To achieve this active alignment, it is desirable to adjust the positions of the second optical fiber array 30 and the optical waveguide device 50 with a certain degree of precision. Therefore, before the active alignment, the second optical fiber array 30 and the optical waveguide device 50 may be passively aligned. In this case, for example, identifiable grooves or markers are formed on the mounting substrates of each component, and the second optical fiber array 30 and the optical waveguide device 50 are positioned using these as guides. Then, with the positions of the second optical fiber array 30 and the optical waveguide device 50 adjusted with a certain degree of precision in this manner, active alignment of the second optical fiber array 30 and the optical waveguide device 50 may be performed.

[0061] 7b is a plan view showing active alignment of the optical waveguide device 50 and the second optical fiber array 30. When the second optical fiber array 30 and the optical waveguide device 50 are actively aligned, as shown in FIG. 7b, the second optical fiber array 30 is positioned so as to face the second end face 51b of the optical waveguide device 50, and test light L2 is emitted from the aligning SCF 41 of the second optical fiber array 30 toward the core end face C21 of the second aligning core C2. The test light L2 emitted from the aligning SCF 41 passes through the second aligning core C2 and is emitted from the core end face C22 toward the aligning SCF 42 of the second optical fiber array 30. The intensity of the test light L2 incident on the aligning SCF 42 is measured by a photodetector such as a power meter.

[0062] Thereafter, while monitoring the intensity of the test light L2, the second optical fiber array 30 is moved relative to the optical waveguide device 50 in a plane along the second direction D2 and the third direction D3 so as to maximize the intensity of the test light L2, i.e., so as to minimize the transmission loss between the second optical fiber array 30 and the optical waveguide device 50. By performing two-way centering in this manner to adjust the relative positions of the second optical fiber array 30 and the optical waveguide device 50, the optical axes of the aligning SCFs 41, 22 and the second aligning core C2 are aligned. This results in the alignment of the two components, the second optical fiber array 30 and the optical waveguide device 50.

[0063] In this way, two-way centering is performed to adjust the positions of the first optical fiber array 10 and the optical waveguide device 50 while monitoring the intensity of the test light L1, and two-way centering is performed to adjust the positions of the first optical fiber array 10 and the optical waveguide device 50 while monitoring the intensity of the test light L2, thereby aligning the three components, i.e., the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30. By fixing these three components in this state, an optical connection structure 1 can be obtained in which the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30 are connected to one another. The order of the steps in the connection method using the optical waveguide device 50 is not limited to the method of sequentially performing steps P11 to P13 described above. For example, the order of the steps may be changed as appropriate, such as performing step P12 after step P13.

[0064] From the viewpoint of aligning these three components with higher accuracy, conventional active alignment may be performed on the three components after the above-described active alignment (i.e., after step P13). In this case, test light may be incident on the first optical fiber array 10, pass through the optical waveguide device 50, and be measured as the test light emitted from the second optical fiber array 30. Test light may be incident on the second optical fiber array 30, pass through the optical waveguide device 50, and be measured as the test light emitted from the first optical fiber array 10. Then, while monitoring the test light, three-way alignment may be performed to adjust the positions of the three components, the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30, relative to one another.

[0065] The effects obtained by the optical waveguide device 50, the optical connection structure 1, and the optical connection method according to this embodiment described above will now be described.

[0066] The optical waveguide device 50 according to this embodiment includes, in addition to a plurality of communication cores 55 for transmitting communication light, a first alignment core C1 for transmitting test light L1 for actively aligning the two components, the optical waveguide device 50 and the first optical fiber array 10. The test light L1 is emitted from the first end face 51a of the first optical fiber array 10, passes through the first alignment core C1, and returns to the first optical fiber array 10 from the first end face 51a. Therefore, by measuring the test light L1 returned to the first optical fiber array 10 with a power meter, it is possible to perform two-way alignment, adjusting the positions of the two components, the optical waveguide device 50 and the first optical fiber array 10, so as to maximize the intensity of the test light L1. Then, by similarly introducing test light L2 into the two components, the optical waveguide device 50 aligned with the first optical fiber array 10 and the remaining second optical fiber array 30, it is possible to perform two-way alignment for these two components as well. As a result, the three components, the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30, are actively aligned.

[0067] In this way, when the optical waveguide device 50 is used, the three-component alignment process for adjusting the positions of the three components is not performed all at once, but rather the two-component alignment process for adjusting the positions of the two components is performed twice. In this case, the position of the three components through which the test light passes can be more easily found compared to when the three-component alignment process is performed all at once, thereby reducing the difficulty of adjusting the positions of the three components when actively aligning the three components. Furthermore, by using active alignment in this way, the three components can be more reliably aligned while capturing the optical axis positions of the cores of the three components, thereby reducing the time required for aligning the three components compared to when only passive alignment is performed. Therefore, according to this embodiment, the alignment of the three components can be performed more easily.

[0068] As in the present embodiment, the core end faces C11, C12 of the first alignment core C1 may be exposed at a position different from the core end face 56 of the communication core 55. In this case, it is possible to preferably realize a mode in which the test light L1 emitted from the first optical fiber array 10 to the first end face 51a passes through the first alignment core C1 and returns to the first optical fiber array 10 again.

[0069] As in the present embodiment, the core end faces C11, C12 of the first aligning core C1 may be arranged side by side with the core end face 56 in the second direction D2. In this case, the first aligning core C1 can be formed on the same plane PL as the communication core 55, which makes it easier to form the first aligning core C1 inside the cladding 51.

[0070] As in the present embodiment, the core end faces C11, C12 of the first aligning core C1 may be located on one of both sides of the core end face 56 in the second direction D2. In this case, it is easy to form the first aligning core C1 so as to extend inside the cladding 51 without intersecting with the communication core 55. By preventing the communication core 55 and the first aligning core C1 from intersecting in this way, it is possible to avoid interference and loss of optical signals passing through the communication core 55 and the first aligning core C1.

[0071] As in the present embodiment, the first aligning core C1 may extend along the plane PL inside the cladding 51. In this case, the first aligning core C1 is formed on the same plane PL. Therefore, when forming the first aligning core C1 inside the cladding 51, it is not necessary to move the focal point of the pulsed laser inside the cladding 51 in the height direction (third direction D3), which makes it easier to form the first aligning core C1.

[0072] As in the present embodiment, the distance W2 between the core end face C12 of the first aligning core C1 and the core end face 56A of the communication core 55 may be the same as the distance W1 between the core end face 56A of the communication core 55 and the core end face 56B of the communication core 55. For example, when optically connecting the first optical fiber array 10 to the optical waveguide device 50, the multiple SCFs 12 are held in the first holder 15 in a state where they are aligned corresponding to the communication core 55 and the first aligning core C1. The first holder 15 is formed with multiple V-grooves 18 for holding the multiple SCFs 12. These V-grooves are typically formed to be aligned at regular intervals, assuming that multiple optical fibers will be aligned at regular intervals. Even in the above configuration, the multiple communication cores 55 and the first aligning core C1 can be aligned at regular intervals, so that an existing holder (first holder 15) that holds the multiple SCFs 12 aligned at regular intervals can be used. In this way, the above-described configuration allows existing holders to be used as they are without modification, and is therefore highly versatile.

[0073] As in the present embodiment, the mode field diameter of the first aligning core C1 at the first end face 51 a may be the same as the mode field diameter of the communication core 55 at the first end face 51 a. As described above, the multiple SCFs 12 are held by the multiple V-grooves 18 of the first holder 15. These V-grooves are typically formed to have the same size and shape, assuming that a general-purpose optical fiber will be used. In the above configuration, too, the mode field diameter of the first aligning core C1 is set to be the same as the mode field diameter of the communication core 55, assuming that a general-purpose SCF 12 will be optically connected to the communication core 55 and the first aligning core C1. Therefore, with the above configuration, an existing holder (first holder 15) capable of holding a general-purpose SCF 12 can be used as is, resulting in excellent versatility.

[0074] As in the present embodiment, the optical waveguide device 50 may include a second aligning core C2. In this case, the second aligning core C2 can be used as an aligning core for actively aligning the two components, the optical waveguide device 50 and the second optical fiber array 30. The test light L2 for actively aligning these two components is emitted from the second optical fiber array 30 to the second end face 51b, passes through the second aligning core C2, and returns to the second optical fiber array 30 from the second end face 51b. Therefore, by measuring the test light L2 returned to the second optical fiber array 30 with a power meter or the like, it is possible to perform two-component alignment, adjusting the positions of the two components, the optical waveguide device 50 and the second optical fiber array 30, so as to maximize the intensity of the test light L2. Therefore, in the above configuration, by separately performing two-way centering of the first optical fiber array 10 and the optical waveguide device 50, and two-way centering of the optical waveguide device 50 and the second optical fiber array 30, it becomes possible to more easily align the three components of the first optical fiber array 10, the optical waveguide device 50, and the second optical fiber array 30.

[0075] Second Embodiment Next, an optical connection structure 1A according to a second embodiment will be described. Fig. 8 is a perspective view showing the optical connection structure 1A. As shown in Fig. 8, the optical connection structure 1A includes a first optical fiber array 10A, an optical waveguide device 50A, and a second optical fiber array 30A. The main difference between the optical connection structure 1A according to the second embodiment and the optical connection structure 1 according to the first embodiment is the configuration of the core group formed in the optical waveguide device. The following description will focus on the differences between the optical connection structure 1A and the optical connection structure 1.

[0076] 9 is a perspective view showing the optical waveguide device 50A. FIG. 10 is a side view showing the optical waveguide device 50A. As shown in FIGS. 9 and 10 , the core group 52A of the optical waveguide device 50A includes a first aligning core C1A and a second aligning core C2A instead of the first aligning core C1 and the second aligning core C2 of the optical waveguide device 50. The first aligning core C1A is formed inside the cladding 51 so as to extend from the first end face 51 a across the multiple communication cores 55 and return to the first end face 51 a. The second aligning core C2A is formed inside the cladding 51 so as to extend from the second end face 51 b across the multiple communication cores 55 and return to the second end face 51 b.

[0077] 9 , the first aligning core C1A, when viewed along the third direction D3, has, for example, a U-shape with an open end at the first end face 51 a. The first aligning core C1A includes, for example, a pair of first straight line portions P31, P32 (an example of a “first portion”) extending in the first direction D1 from the core end faces C11, C12, respectively, a pair of second straight line portions P33, P34 (an example of a “second portion”) further extending from the tips of the pair of first straight line portions P31, P32, and a curved line portion P35 (an example of a “second portion”) that curves inside the cladding 51 and connects the tips of the pair of second straight line portions P33, P34.

[0078] As shown in FIG. 10 , the first straight line portions P31 and P32 extend along the same plane PL along the first direction D1 and the second direction D2 inside the cladding 51. Meanwhile, the second straight line portions P33 and P34 and the curved line portion P35 extend in a region away from the plane PL1. For example, the second straight line portions P33 and P34 extend in a direction bent from the tip of the first straight line portions P31 and P32 toward the fourth side surface 51f in the third direction D3. That is, when viewed along the second direction D2, the second straight line portions P33 and P34 extend in a direction inclined toward both the first direction D1 and the third direction D3. The plane PL1 may be, for example, a virtual plane perpendicular to the first end face 51a and passing through the optical axis of the first alignment core C1A at each of the core end faces C11 and C12.

[0079] The curved portion P35 extends along a plane PL2 that is shifted from the plane PL1 toward the fourth side surface 51f in the third direction D3. As shown in Fig. 9, the curved portion P35 extends so as to intersect with the plurality of communication cores 55 when viewed along the third direction D3. The first aligning core C1A, including the first straight portion P31, P32, the second straight portion P33, P34, and the curved portion P35, configures a three-dimensional waveguide that is bent in the first direction D1, the second direction D2, and the third direction D3.

[0080] FIG. 11a is a front view showing the optical waveguide device 50A. FIG. 11b is a front view showing the first optical fiber array 10A. As shown in FIG. 11a, the core end faces C11 and C12 are aligned in a row with the core end faces 56 of the multiple communication cores 55 along the second direction D2. In this embodiment, the core end faces C11 and C12 are respectively arranged in regions on both sides of the core end faces 56 of the multiple communication cores 55 in the second direction D2. The core end face C11 is arranged, for example, in a position adjacent to the core end face 56A (an example of a "first adjacent end face") that is located outermost among the multiple core end faces 56 in the second direction D2. The core end face C12 is arranged, for example, on the opposite side of the core end face C11 across the multiple core end faces 56 in the second direction D2. The mode field diameter of the first aligning core C1A at each of the core end faces C11 and C12 may be the same as the mode field diameter of the communication core 55 at each of the core end faces 56, for example.

[0081] If the distance between core end face 56A of the multiple core end faces 56 and core end face 56B (an example of a "second adjacent end face") adjacent to core end face 56A is W4, the distance between core end face C11 and core end face 56A is W5, and the distance between core end face C12 and the core end face 56 adjacent to core end face C12 is W6, then distance W5 and distance W6 are each equal to distance W4. In this way, each core end face 56, core end face C11, and core end face C12 are arranged at equal intervals along the second direction D2.

[0082] As shown in Fig. 11b, the aligning SCFs 21, 22 of the first optical fiber array 10A are arranged, for example, in regions on both sides of the plurality of communication SCFs 13 in the second direction D2. The plurality of communication SCFs 13 and the aligning SCFs 21, 22 are, for example, aligned in a row at regular intervals along the second direction D2. Each aligning SCF 21, 22 is arranged so that its first end face 51a faces each of the core end faces C11, C12 (see Fig. 11a) of the first aligning core C1A. Each of the cores 21a, 22a of the aligning SCFs 21, 22 is optically connected to the first aligning core C1A at the first end face 51a.

[0083] 9 , when viewed along the third direction D3, the second alignment core C2A has, for example, a U-shape with an open end at the second end face 51 b. The second alignment core C2A includes, for example, a pair of first straight line portions P41, P42 extending in the first direction D1 from the core end faces C21, C22, respectively, a pair of second straight line portions P43, P44 extending further from the tips of the pair of first straight line portions P41, P42, and a curved line portion P45 that curves inside the cladding 51 and connects the tips of the pair of second straight line portions P43, P44.

[0084] 10 , the first straight line portions P41, P42 extend along the same plane PL within the cladding 51. Meanwhile, the second straight line portions P43, P44 and the curved line portion P45 extend in a region away from the plane PL1. For example, the second straight line portions P43, P44 extend in a direction bent from the tip of the first straight line portions P41, P42 toward the fourth side surface 51f in the third direction D3. In other words, when viewed along the second direction D2, the second straight line portions P43, P44 extend in a direction inclined toward both the first direction D1 and the third direction D3.

[0085] The curved portion P45 extends along a plane PL2 that is shifted from the plane PL1 toward the fourth side surface 51f in the third direction D3. As shown in Fig. 9, the curved portion P45 extends so as to intersect with the plurality of communication cores 55 when viewed along the third direction D3. The second aligning core C2A, including the first straight portion P41, P42, the second straight portion P43, P44, and the curved portion P45, configures a three-dimensional waveguide that is bent in the first direction D1, the second direction D2, and the third direction D3.

[0086] 12a is a rear view of the optical waveguide device 50A. FIG. 12b is a front view of the second optical fiber array 30A. As shown in FIG. 12a, the core end faces C21 and C22 of the second aligning core C2A are disposed in regions on both sides of the end faces 57 of the multiple communication cores 55 in the second direction D2. For example, the core end face C22 is disposed adjacent to the end faces 57 of the multiple communication cores 55 in the second direction D2. The core end face C21 is disposed on the opposite side of the end faces 57 of the multiple communication cores 55 from the core end face C22 in the second direction D2. The mode field diameter of the second aligning core C2A at each of the core end faces C21 and C22 may be the same as the mode field diameter of the communication cores 55 at each end face 57, for example.

[0087] As shown in Fig. 12b, the aligning SCFs 41, 42 of the second optical fiber array 30A are, for example, aligned in a row at regular intervals along the second direction D2. The aligning SCFs 41, 42 are, for example, arranged in one of the regions on either side of the MCF 32 in the second direction D2. Each aligning SCF 41, 42 is arranged so that its second end face 51b faces the respective core end faces C21, C22 (see Fig. 12a) of the second aligning core C2A. Each core 41a, 42a of the aligning SCFs 41, 42 is optically connected to the second aligning core C2A at the second end face 51b.

[0088] According to the optical connection structure 1A described above, similarly to the optical connection structure 1, it is possible to perform two-way centering, in which the positions of the first optical fiber array 10A and the optical waveguide device 50A are adjusted while monitoring the intensity of the test light L1, and two-way centering, in which the positions of the first optical fiber array 10A and the optical waveguide device 50A are adjusted while monitoring the intensity of the test light L2, thereby making it possible to more easily align the three components of the first optical fiber array 10A, the optical waveguide device 50A, and the second optical fiber array 30A.

[0089] As in the present embodiment, the core end faces C11 and C12 of the first alignment core C1A may be disposed in regions on both sides of the core end face 56 in the second direction D2. In this case, the distance between the core end faces C11 and C12 can be increased compared to when the core end faces C11 and C12 are arranged adjacent to each other, thereby maintaining a large distance between the core end faces C11 and C12. As a result, when actively aligning the first optical fiber array 10A with the optical waveguide device 50A using the alignment test light L1, the risk of rotational misalignment between the position of the core end face C11 from which the test light L1 is incident or emitted and the position of the core end face C12 from which the test light L1 is emitted or incident can be reduced. This allows for more reliable alignment between the optical waveguide device 50A and the first optical fiber array 10A. Furthermore, if the distance between the core end faces C11 and C12 can be maintained large in this way, the radius of curvature of the curved portion P35 of the first alignment core C1A from the core end face C11 to the core end face C12 can be maintained large compared to when the core end faces C11 and C12 are arranged next to each other, which makes it possible to reduce the propagation loss of the test light L1 introduced into the first alignment core C1A during alignment.

[0090] As in the present embodiment, the curved portion P35 of the first aligning core C1A may be formed in an area away from the plane PL and extend so as to intersect with the multiple communication cores 55 when viewed along the third direction D3. In this case, the first aligning core C1A can be changed three-dimensionally so as not to intersect with the multiple communication cores 55 inside the cladding 51. By preventing the communication cores 55 from intersecting with the first aligning core C1A in this way, it is possible to avoid interference and loss of optical signals passing through the communication cores 55 and the first aligning core C1A.

[0091] Although the above describes each embodiment, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. For example, the number and arrangement of cores in the optical waveguide device can be modified within the scope of the claims. For example, the two surfaces of the cladding 51 that the first optical fiber array 10 and the second optical fiber array 30 face, respectively, are not limited to the first end surface 51 a and the second end surface 51 b, but may be any two surfaces that are different from each other, such as the first end surface 51 a and the first side surface 51 c.

[0092] The mode field diameter of the first aligning core C1 at the first end face 51a may be set larger than the mode field diameter of the communication core 55 at the first end face 51a. In this case, the difference in mode field diameters can be used to easily distinguish between the communication core 55 and the first aligning core C1. As a result, it is possible to prevent the alignment test light L1 from being erroneously introduced into the communication core 55, thereby more reliably aligning the optical waveguide device 50 and the first optical fiber array 10 using the first aligning core C1. Similarly, the mode field diameter of the second aligning core C2 at the second end face 51b may be set larger than the mode field diameter of the communication core 55 at the second end face 51b.

[0093] The distance between the communication core 55 and the first alignment core C1 at the first end face 51a may be larger than the distance between adjacent communication cores 55 at the first end face. In this case, the difference in distance can be used to easily distinguish the communication core 55 from the first alignment core C1. As a result, it is possible to prevent the alignment test light L1 from being erroneously introduced into the communication core 55, and therefore, alignment between the optical waveguide device 50 and the first optical fiber array 10 using the first alignment core C1 can be more reliably performed.

[0094] DESCRIPTION OF SYMBOLS 1, 1A...Optical connection structure 10, 10A...First optical fiber array 11...First optical fiber group 12...SCF 13...Communication SCF (an example of a "first optical fiber") 13a, 21a, 22a, 32a, 41a, 42a...Core 15...First holder 16, 36...Base 17, 37...Cover 18, 38...V-groove 21, 22...Aligning SCF (an example of a "second optical fiber") 30, 30A...Second optical fiber array 31...Second optical fiber group 32...MCF 35...Second holder 41, 42...Aligning SCF 50, 50A...Optical waveguide device 51...Cladding 51a...First end face (an example of a "first surface") 51b...Second end face (an example of a "second surface") 51c...First side surface 51d...Second side surface 51e...Third side surface 51f...Fourth side surface 52, 52A...Core group 55...Communication core (an example of a "first core") 56...Core end face 56A...Core end face (an example of a "first adjacent end face") 56B...Core end face (an example of a "second adjacent end face") 57...End face C1, C1A...First alignment core (an example of a "second core") C2, C2A...Second alignment core (an example of a "third core") C11...Core end face (an example of a "first core end face") C12...Core end face (an example of a "second core end face") D1...First direction D2...Second direction (an example of a "one direction") D3...Third direction P11, P12, P21, P22...Straight portion P31, P32, P41, P42...First straight portion (an example of a "first portion") P33, P34, P43, P44...Second straight line part (an example of a "second part") P13, P23...curved part P35, P45...curved part (an example of a "second part") L1, L2...test light PL, PL1, PL2...plane W1, W2, W3, W4, W5...interval

Claims

1. a cladding including a first surface and a second surface different from the first surface; at least one first core extending inside the cladding from the first surface to the second surface; a second core formed in a region of the cladding excluding the first core and extending from the first surface through the inside of the cladding so as to return to the first surface; An optical waveguide device comprising:

2. the first core includes a core end surface exposed to the first surface, the second core includes a first core end face and a second core end face that are exposed at positions different from the core end face on the first surface, 2. The optical waveguide device according to claim 1.

3. the first core end face and the second core end face are arranged side by side with the core end face in one direction along the first surface, 3. The optical waveguide device according to claim 2.

4. the first core end face and the second core end face are disposed on one of both sides sandwiching the core end face in the one direction, 4. The optical waveguide device according to claim 3.

5. the second core extends inside the cladding along a plane that intersects the first surface and passes through the first core end face and the second core end face.

5. The optical waveguide device according to claim 4.

6. the first core end face and the second core end face are disposed on both sides of the core end face in the one direction, 4. The optical waveguide device according to claim 3.

7. The second core is a first portion extending along a plane that intersects the first surface and passes through the first core end face and the second core end face; a second portion formed in a region away from the plane and extending so as to intersect with the first core when viewed along a normal direction of the plane, 7. The optical waveguide device according to claim 6.

8. a plurality of the first cores; The core end surfaces of the plurality of first cores are a first adjacent end face adjacent to one of the first core end face and the second core end face in the one direction; a second adjacent end surface adjacent to the first adjacent end surface in the one direction; Including, a distance between the one of the first core end face and the second core end face and the first adjacent end face is the same as a distance between the first adjacent end face and the second adjacent end face; 8. The optical waveguide device according to claim 3.

9. a mode field diameter of the second core at the first surface is the same as a mode field diameter of the first core at the first surface; 3. The optical waveguide device according to claim 1.

10. a third core formed in a region of the cladding excluding the first core and the second core, the third core extending from the second surface through the inside of the cladding and returning to the second surface, 3. The optical waveguide device according to claim 1.

11. The optical waveguide device according to claim 1 or 2; an optical fiber array arranged to face the first surface; Equipped with The optical fiber array includes: at least one first optical fiber optically connected to the first core at the first surface; a pair of second optical fibers optically connected to both ends of the second core on the first surface, An optical connection structure comprising:

12. a step of preparing the optical waveguide device according to claim 1 or 2, a first optical fiber array, and a second optical fiber array; performing active alignment between the optical waveguide device and the first optical fiber array so that the first optical fiber array is optically connected to the optical waveguide device, with the first optical fiber array being disposed so as to face the first surface of the optical waveguide device; performing active alignment between the optical waveguide device and the second optical fiber array so that the second optical fiber array is optically connected to the optical waveguide device after the active alignment, with the second optical fiber array being disposed so as to face the second surface of the optical waveguide device; Equipped with In the step of performing the active alignment between the optical waveguide device and the first optical fiber array, emitting alignment test light from a first alignment optical fiber of the first optical fiber array toward the first surface, measuring the test light that passes from the first surface through the second core and is incident on a second alignment optical fiber of the first optical fiber array, and adjusting the arrangement of the optical waveguide device and the first optical fiber array so that the intensity of the test light is maximized; Optical connection method.

13. An optical waveguide device disposed between a first optical fiber array and a second optical fiber array, optically connecting the first optical fiber array and the second optical fiber array, a cladding including a first surface facing the first optical fiber array and a second surface facing the second optical fiber array; at least one communication core extending from the first surface to the second surface inside the cladding and capable of transmitting communication light necessary for communication between the first optical fiber array and the second optical fiber array; an alignment core formed in a region of the cladding excluding the communication core, extending from the first surface through the inside of the cladding so as to return to the first surface, and capable of transmitting test light for active alignment of the first optical fiber array and the optical waveguide device; An optical waveguide device comprising: