Optical connection structure and optical connection method

Abstract

An optical connection structure (1) is provided with: cladding (11); a plurality of cores (12) provided to the cladding (11); a multicore fiber (10) having a connection surface (15) on the side surface (14); and an optical transmission path (20) that optically connects to at least one core (12A) of the plurality of cores (12) via the connection surface (15). The connection surface (15) is formed by thinning the cladding (11) to said at least one core (12A) or the vicinity thereof.

Description

Optical connection structure and optical connection method

[0001] The present disclosure relates to an optical connection structure and an optical connection method.

[0002] Multicore fibers have been studied to overcome the capacity limit of existing single-mode optical fibers (SMF) (see Non-Patent Document 1). Multicore fibers have multiple cores, and in order to connect the multicore fiber to SMF transmission equipment, optical devices, light-emitting elements, and light-receiving elements, a fan-in fan-out (FIFO) is required to input and output light to each core (see Non-Patent Document 1).

[0003] T. Matsui, et al., “Weakly coupled multicore fiber technology, deployment, and systems,” Proceedings of the IEEE, vol. 110, no. 11, pp. 1772-1785, Nov. 2022.

[0004] When each core of a multicore fiber is used for a different communication service, it is necessary to input and output light only from a specific core. Conventional FIFOs, on the other hand, separate and multiplex all cores collectively. Therefore, when inputting and outputting light only from a specific core in a communication network using a multicore fiber, all cores of the multicore fiber are separated into their respective SMFs using a FIFO, and the SMFs other than the SMF that inputs and outputs light from the specific core are multiplexed again using another FIFO and connected to another multicore fiber. In other words, in this case, two FIFOs must be used. Therefore, there is a problem that the loss of light propagating through cores other than the core to be input or output increases due to the loss of the FIFO itself and the connection between the FIFO and the multicore fiber.

[0005] Therefore, an object of the present disclosure is to provide an optical connection structure and an optical connection method that allow light to be input and output to only a specific core without increasing the loss of light propagating through other cores in a multicore fiber.

[0006] An optical connection structure according to a first aspect of the present disclosure includes a cladding, a plurality of cores provided in the cladding, and a multicore fiber having a connection surface on a side surface formed by thinning the cladding up to at least one of the plurality of cores or its vicinity, and an optical transmission line optically connecting to the cores via the connection surface.

[0007] An optical connection method according to a second aspect of the present disclosure forms a connection surface on the side of a multicore fiber by thinning the cladding up to at least one of a plurality of cores or its vicinity, and optically connects an optical transmission line to the core via the connection surface.

[0008] According to the present disclosure, it is possible to provide an optical connection structure and an optical connection method that can input and output light to only a specific core without increasing the loss of light propagating through other cores in a multicore fiber.

[0009] FIG. 1A is a configuration diagram of an optical connection structure according to a first embodiment. FIG. 1B is a cross-sectional view of an example of a multi-core fiber. FIG. 2A is a perspective view showing an example of a polishing device. FIG. 2B is a cross-sectional view of a holding section shown in FIG. 2A. FIG. 3 is a view for explaining an example of a cladding polishing process. FIG. 4 is a configuration diagram of an optical connection structure according to a modified example of the first embodiment. FIG. 5A is a side view of a multi-core fiber according to a second embodiment. FIG. 5B is a configuration diagram of an optical connection structure according to the second embodiment. FIG. 6 is a configuration diagram of an optical connection structure according to a modified example of the second embodiment.

[0010] Hereinafter, optical connection structures and optical connection methods according to some embodiments of the present disclosure will be described. Note that common parts in the various drawings are designated by the same reference numerals, and redundant explanations will be omitted.

[0011] First Embodiment Fig. 1A is a configuration diagram of an optical connection structure 1 according to a first embodiment of the present disclosure. Fig. 1A also shows cross-sectional views of a multi-core fiber 10 at positions A and B. As shown in Fig. 1A, the optical connection structure 1 includes a multi-core fiber 10 and an optical transmission line 20. The optical transmission line 20 is optically connected to the cores 12 of the multi-core fiber 10 via a connection surface 15 formed on a side surface 14 of the multi-core fiber 10. Note that the optical connection referred to here means a connection between two optical materials that does not involve significant reflection due to the presence of space or the like, and refers to, for example, a connection between two optical materials via a refractive index matching material.

[0012] The multicore fiber 10 has a cladding 11 and a plurality of cores 12 provided in the cladding 11. The plurality of cores 12 are arranged at positions with a periodicity such as a line, a ring, a square lattice, or a triangular lattice, depending on the number of cores. For example, when the multicore fiber 10 has four cores 12, these may be arranged in a 2×2 pattern as shown in Fig. 1A or may be lined up in a line as shown in Fig. 1B.

[0013] The multicore fiber 10 has a connection surface 15 on its side surface 14. The connection surface 15 is formed by thinning the cladding 11 up to at least one core 12A of the multiple cores 12 or its vicinity. Thinning the cladding 11 refers to processing that reduces the thickness of the cladding 11 at the portion radially outward of the cores 12. Such processing includes, for example, removing the cladding 11 by polishing or chemical etching the side surface 14, or melt drawing that deforms the cladding 11.

[0014] By thinning the clad 11, the core 12A is exposed from the connection surface 15, or is located near the connection surface 15 via the clad 11 having a thickness of several μm (e.g., 1 to 2 μm) or less. In the former case, the core 12A may be divided by the connection surface 15, or may remain on the connection surface 15. In the latter case, the remaining thickness of the clad 11 is set to a value that allows evanescent coupling between the core 12 and the optical transmission line 20 to be obtained.

[0015] The optical transmission line 20 is, for example, an optical fiber, a lens, or an optical waveguide. In any case, the optical transmission line 20 is optically connected to the core 12A. For convenience of explanation, the following description will be given taking an optical fiber 30 as an example of the optical transmission line 20.

[0016] The optical fiber 30 serving as the optical transmission line 20 has a cladding 31 and one core 32 provided in the cladding 31. The end face 30a of the optical fiber 30 facing the connection surface 15 may be perpendicular to the central axis of the optical fiber 30 or may be inclined with respect to the central axis. The core 32 is optically connected to the core 12A exposed at the connection surface 15 or closest to the connection surface 15. In other words, the optical fiber 30 inputs and outputs light to and from the core 12A of the multicore fiber 10.

[0017] Fig. 1A shows a configuration in which the optical fiber 30 is optically connected to the core 12A on the left side in Fig. 1A. However, the optical fiber 30 may also be optically connected to the core 12A on the right side in Fig. 1A.

[0018] In this embodiment, one optical transmission path 20 is optically connected to one of the multiple cores 12 in the multicore fiber 10. That is, no FIFO is interposed between the multicore fiber 10 and the optical transmission path 20. Furthermore, regarding the loss of light in a core other than the core closest to the polishing surface 16, an increase in the loss of light propagating through that core can be suppressed by separating that core sufficiently (for example, several μm or more) from the polishing surface 16. Therefore, it is possible to input and output light only to a specific core without increasing the loss of light propagating through other cores in the multicore fiber.

[0019] The number of cores 12A exposed at the connection surface 15 or closest to the connection surface 15 may be one or more. In the latter case, the optical transmission lines 20 corresponding to the number of cores 12A are optically connected to the corresponding cores 12A.

[0020] Next, an optical connection method according to this embodiment will be described. In this embodiment, first, a connection surface 15 is formed on a side surface 14 of a multicore fiber 10 by thinning the cladding 11 up to or near at least one core 12A of the multiple cores 12. Next, an optical transmission line 20 is optically connected to the core 12A via the connection surface 15.

[0021] Polishing will be taken as an example of thinning the clad 11. As described below, polishing of the side surface 14 forms a polished surface 16 serving as the connection surface 15. FIG. 2A is a perspective view of a polishing device 40 used for polishing. As shown in FIG. 2A, the polishing device 40 includes a polishing table 41 and a holding portion 42. The polishing table 41 and the holding portion 42 are made of, for example, glass. The polishing table 41 has a flat upper surface 41a, and a polishing sheet 43 is placed on this upper surface 41a.

[0022] The holding part 42 has a flat surface 42a facing the upper surface 41a of the polishing table 41. A V-groove 44 curved with a radius R is formed on the flat surface 42a. The V-groove 44 is formed so that its depth from the flat surface 42a is shallowest near the center of the flat surface 42a. This minimum depth is set to a value such that a part of the cladding 11 is exposed from the V-groove 44 when the multi-core fiber 10 is placed on the V-groove 44.

[0023] When forming the polished surface 16 (connection surface 15) using the polishing device 40, the V-groove 44 of the holding part 42 is filled with adhesive (not shown), and the multi-core fiber 10 is fixed to the V-groove 44. As a result, a part of the side surface 14 of the multi-core fiber 10 is exposed from the V-groove 44 (plane 42 a).

[0024] Next, with a portion of the side surface 14 exposed from the V-groove 44, the flat surface 42a of the holding part 42 is made to face the polishing sheet 43 placed on the polishing table 41. Thereafter, the side surface 14 of the multi-core fiber 10 exposed from the V-groove 44 is pressed against the polishing sheet 43 and polished.

[0025] A light source 51 (see FIG. 3 ) is connected to one end of the core 12A, and a power meter 52 is connected to the other end of the core 12A. While the side surface 14 is being polished, the light source 51 inputs light of a constant intensity into the core 12A. Meanwhile, the power meter 52 measures the intensity of the light from the light source 51 having the core 12A as its diameter. In other words, the polishing of the side surface 14 is performed while monitoring the intensity of the light propagating through the core 12A. Note that when the multicore fiber 10 is used as an active optical fiber, for example, an optical line terminal (ONU) may be used as the light source 51, and the power meter 52 may measure leakage light from the core 12A that occurs when a bend is applied to the multicore fiber 10.

[0026] As polishing of the side surface 14 progresses, the cladding 11 is gradually removed, and the polished surface 16 approaches the core 12A. As the polished surface 16 approaches the core 12A, light leakage from the polished surface 16 increases, and the light intensity measured by the power meter 52 gradually decreases. Polishing is stopped when the light intensity decreases to a specified value, which indicates that the core 12A is exposed at the polished surface 16 or has reached a position within a few μm of the polished surface 16. This completes the formation of the polished surface 16 (connection surface 15).

[0027] Thereafter, the core 32 of the optical fiber 30 is brought into contact with the polished surface 16 via a refractive index matching material (not shown). Furthermore, while monitoring changes in the intensity of the light output from the optical fiber 30, the relative position of the core 32 with respect to the core 12A is adjusted using a moving mechanism (not shown) such as an XY stage. When the core 32 is positioned appropriately, the optical fiber 30 is fixed to the multi-core fiber 10 using a well-known curing material such as an ultraviolet-curing resin or adhesive. This completes the optical connection structure 1.

[0028] In addition, in forming the polished surface 16 (connection surface 15), the power meter 52 may monitor the intensity of light output from all of the cores 12. As an application example, a process of identifying the core 12A, of the three cores 12A, 12B, and 12C of the multicore fiber 10, as the core to be optically connected to the optical transmission line 20 will be described below.

[0029] 3, one end of the multi-core fiber 10 (i.e., one end of all of the cores 12A, 12B, and 12C) is connected to a light source 51. The other end of the multi-core fiber 10 (i.e., the other ends of all of the cores 12A, 12B, and 12C) is connected to a power meter 52. The side surface of the multi-core fiber 10 is polished by, for example, the above-described polishing device 40 (see FIG. 2A ).

[0030] While the cladding 11 is gradually removed by polishing the side surface 14, the power meter 52 measures the intensity of light propagating through each of the cores 12A, 12B, and 12C. As the removal of the cladding 11 progresses, the relative distance of the polishing surface 16 to each of the cores 12A, 12B, and 12C decreases. As shown in the graph in FIG. 3 , the light intensity of one of the cores 12A, 12B, and 12C begins to decrease. Meanwhile, the three relative distances decrease at a constant rate with the polishing time of the cladding 11, i.e., with the progress of the removal of the cladding 11, and the magnitude relationship does not change. Therefore, the core in which the light intensity decreases most rapidly can be identified as the core closest to the polishing surface 16.

[0031] For ease of explanation, it is assumed that the core 12A is the core in which the decrease in light intensity occurs most rapidly among the cores 12A, 12B, and 12C. In this embodiment, when the intensity of light propagating through this core 12A decreases to a specified value, polishing of the side surface 14 is stopped. In other words, when one of the above-mentioned intensities decreases to a specified value while the cladding 11 is being thinned, the thinning of the cladding 11 is stopped.

[0032] For example, when the intensity measurement by the power meter 52 indicates that the optical loss in the core 12A is several dB or more and the optical loss in the other cores 12B and 12C is between 0 and 0.1 dB, polishing of the side surface 14 (clad 11) is terminated. This allows only the core 12A to be removed by polishing.

[0033] Fig. 4 is a configuration diagram of an optical connection structure according to a modified example of this embodiment. As shown in Fig. 4, the optical fiber 30 may be side-polished in the same manner as the multicore fiber 10. That is, the cladding 31 of the optical fiber 30 may be removed from the side surface 34 of the optical fiber 30 up to the core 32 of the optical fiber 30 or its vicinity. In this case, the optical fiber 30 has a polished surface 36 on the side surface 34. The polished surface 36 comes into contact with the connection surface 15 via a refractive index matching material.

[0034] In this modification as well, the relative position of the core 32 of the optical fiber 30 with respect to the core 12A of the multicore fiber 10 is adjusted so that the intensity of light output from one end of the optical fiber 30 is maximized. Then, the two are fixed together using the hardening material described above. Therefore, no FIFO is interposed between the multicore fiber 10 and the optical transmission line 20. Therefore, it is possible to input and output light to only a specific core without increasing the loss of light propagating through other cores in the multicore fiber.

[0035] Second Embodiment Fig. 5A is a side view of a multicore fiber 10 according to a second embodiment of the present disclosure. Fig. 5B is a configuration diagram of an optical connection structure 1 according to the second embodiment. The multiple cores 12 according to this embodiment are arranged on the same circle centered on the central axis of the multicore fiber 10. Furthermore, the multicore fiber 10 according to this embodiment has a connection surface 15 on the side surface 14, as in the first embodiment. However, the connection surface 15 is formed over the entire circumferential area of ​​the multicore fiber 10, at least in an area of ​​the side surface 14 that is connected to the optical transmission line 20. This connection surface 15 can also be formed by processing such as polishing, chemical etching, or melt drawing as described above.

[0036] The remaining thickness of the cladding 11 between the connection surface 15 and each core 12 is set to a value that allows evanescent coupling between each core 12 and the optical transmission line 20, and prevents light from being input to or output from a medium such as air that has a lower refractive index than the cladding 11 (for example, light cannot leak from the core 12 to the medium). This value depends on the refractive index of the cladding 11, but is typically several μm. In this way, in this embodiment, each core 12 remains in the cladding 11 and is not separated.

[0037] 5B , an optical transmission line 20 such as an optical fiber 30 having a polished surface 36 is connected to the connection surface 15 of the multicore fiber 10 via a refractive index matching material (not shown). This allows the optical transmission line 20 to arbitrarily select any of the multiple cores 12 and optically connect it to the selected core.

[0038] Since the connection surface 15 is formed over the entire circumferential area, the diameter of the multicore fiber 10 is partially reduced. However, since the remaining thickness of the cladding 11 is secured to the above-mentioned value, light does not leak from the cores 12 that are close to the area of ​​the connection surface 15 that is not in contact with the optical transmission line 20, and light loss is also suppressed. Furthermore, as in the first embodiment, light can be input / output between a specific core of the multiple cores 12 and the optical transmission line 20 without providing a FIFO.

[0039] 6 is a configuration diagram of an optical connection structure 1 according to a modified example of the second embodiment. As described above, in the second embodiment, the optical transmission line 20 can be optically connected to any one of the multiple cores 12 of the multicore fiber 10. Therefore, in this modified example, with the optical transmission line 20 connected to the connection surface 15 via a refractive index matching material, the multicore fiber 10 is supported so as to be rotatable about its central axis as the center of rotation. Therefore, by adjusting the rotation angle of the multicore fiber 10, the optical transmission line 20 can be optically connected to any one of the multiple cores 12.

[0040] 6 , the optical connection structure 1 according to this modification includes a connection switching device 60. The connection switching device 60 includes a holding portion 61 for the optical transmission line 20 and a holding portion 62 for the multi-core fiber 10. The holding portion 61 and the holding portion 62 are housed and fixed in, for example, a housing 63. Hereinafter, an optical fiber 30 will be described as an example of the optical transmission line 20.

[0041] The optical fiber 30 has its side polished in the same manner as in the modified example of the first embodiment (see FIG. 4 ), and has a polished surface 36. The holding portion 61 holds the optical fiber 30 with the polished surface 36 facing the connection surface 15. The holding portion 61 has, for example, a V-groove as shown in FIG. 2A , and the optical fiber 30 is placed in and held in the V-groove.

[0042] On the other hand, the holding unit 62 rotatably holds the multi-core fiber 10 on both sides of the connection surface 15 in the longitudinal direction (extension direction) of the multi-core fiber 10. As shown in Fig. 6 , the holding unit 62 has a gear 64 attached to the outer circumferential surface (for example, the side surface 14) of the multi-core fiber 10, and a driving unit 65 such as a servo motor or a stepping motor that rotates the gear 64. Alternatively, the holding unit 62 may be a disk (not shown) that comes into contact with the outer periphery of the multi-core fiber 10, instead of the gear 64. The driving unit 65 rotates this disk, which rotates the multi-core fiber 10.

[0043] In this modification, the multicore fiber 10 is rotated around its central axis as the center of rotation by the driving unit 65. Furthermore, the driving unit 65 stops the rotation of the multicore fiber 10 at a position where the optical transmission line 20 is optically connected to any of the multiple cores 12. This allows the optical transmission line 20 to be optically connected to any of the multiple cores 12 as desired.

[0044] As described above, also in the second embodiment, no FIFO is interposed between the multicore fiber 10 and the optical transmission path 20. Furthermore, the increase in loss of light propagating through a core other than the core closest to the polishing surface 16 can be suppressed by separating that core sufficiently (for example, several μm or more) from the polishing surface 16. Therefore, it is possible to input and output light only to a specific core without increasing the loss of light propagating through other cores in the multicore fiber.

[0045] REFERENCE SIGNS LIST 1 optical connection structure 10 multi-core fiber 11 cladding 12, 12A, 12B, 12C core 14 side surface 15 connection surface 16 polished surface 20 optical transmission path 30 optical fiber 31 cladding 32 core 34 side surface 36 polished surface 40 polishing device 51 light source 52 power meter 60 connection switching device

Claims

1. An optical connection structure comprising: a multicore fiber having a cladding, multiple cores provided in the cladding, and a connection surface on its side; and an optical transmission line that optically connects to at least one of the multiple cores via the connection surface, wherein the connection surface is formed by thinning the cladding up to or near the at least one core.

2. The optical connection structure according to claim 1, wherein the optical transmission path is an optical fiber having a core that is optically connected to the core of the multicore fiber, and the cladding of the optical fiber is removed from the side of the optical fiber up to the core of the optical fiber or the vicinity thereof.

3. The optical connection structure according to claim 1 or 2, wherein the connection surface is formed over the entire circumferential area of ​​the multi-core fiber.

4. The optical connection structure according to claim 3, wherein the multi-core fiber is supported so as to be rotatable about its central axis.

5. An optical connection method comprising forming a connection surface on the side of a multi-core fiber by thinning the cladding up to at least one of the multiple cores or its vicinity, and optically connecting an optical transmission line to the core via the connection surface.

6. The optical connection method according to claim 5, wherein the connection surface is formed over the entire circumferential area of ​​the multi-core fiber.

7. The optical connection method according to claim 6, wherein the multi-core fiber is rotated around its central axis as a center of rotation, and the rotation of the multi-core fiber is stopped at a position where the optical transmission line is optically connected to one of the plurality of cores.

8. The optical connection method according to claim 5, further comprising measuring the intensity of each of the light propagating through each of the plurality of cores, and stopping the thinning of the cladding when one of the intensities drops to a specified value while the thinning of the cladding is being performed.

Images