Fiber optic connector

Abstract

This invention provides a connector for optical fibers suitable for bidirectional communication using spatial division multiplexing. [Solution] The optical fiber connector 100 optically couples the corresponding cores of a first optical fiber 110 and a second optical fiber 120, each having multiple cores. The optical fiber connector includes a first separation / coupling system 10 that spatially separates multiple light beams emitted into space from multiple cores of the first optical fiber and introduces multiple light beams emitted from multiple cores of the second optical fiber into the corresponding cores of the first optical fiber; a second separation / coupling system 20 that spatially separates multiple light beams emitted into space from multiple cores of the second optical fiber and introduces multiple light beams emitted from multiple cores of the first optical fiber into the corresponding cores of the second optical fiber; and a propagation control system 30 that is positioned between the first separation / coupling system and the second separation / coupling system and includes an optical non-reciprocal element 31 that blocks or attenuates light moving in the opposite direction.

Description

Technical Field

[0001] The present invention relates to an optical fiber connector for connecting optical fibers having a plurality of cores.

Background Art

[0002] In response to the increasing traffic volume in optical fiber networks, space division multiplexing (SDM) has been proposed to meet the demand. As one of the methods, transmission using a multi-core fiber (MCF) is known. An MCF is an optical fiber in which a plurality of optical propagation cores are formed in one optical fiber. Also, in space division multiplexing, it is known to use a fiber bundle in which a plurality of single mode fibers (SMFs) each having one core are bundled as a substitute for an MCF.

[0003] However, MCFs and fiber bundles have a structural characteristic that the distance between adjacent cores is short. Therefore, MCFs and the like tend to have a large crosstalk between cores in principle and have a problem of not being suitable for long-distance transmission. Therefore, in order to solve this problem, bidirectional communication has been proposed in which adjacent cores are used for reverse transmission instead of同向 transmission (Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Figure 3 shows a conventional isolator module 1 having a spatial optical system for connecting MCFs. This isolator module 1 includes a first aspherical lens 1a that collimates diffuse light emitted from each core of the first MCF2, a second aspherical lens 1b that images parallel light that has passed through the first aspherical lens 1a onto the end face of the corresponding core of the second MCF3, and an isolator (non-reciprocal optical element) 1c provided in the space between these first and second aspherical lenses 1a and 1b through which parallel light passes. The isolator 1c transmits only light traveling in the forward direction and blocks light traveling in the reverse direction. Therefore, by inserting this isolator 1c between the MCF collimator opposing system, which consists of MCF2,3 and lenses 1a,1b paired together, it is possible to prevent noise generation and interference due to reflected light, and to improve the stability and security of optical transmission.

[0006] However, in the conventional isolator module 1 shown in Figure 3, all the light emitted from the multiple cores of MCF2 and MCF3 passes through a single isolator 1c. Therefore, this conventional isolator module 1 has the problem that it cannot be used for bidirectional communication where adjacent cores are used for transmission in the reverse direction. In other words, in this conventional isolator module 1, since the isolator 1c only functions in the same direction for all cores, it is fundamentally impossible to connect two MCF2 and MCF3 to achieve bidirectional communication.

[0007] Therefore, the main objective of the present invention is to provide a connector for optical fibers suitable for bidirectional communication using spatial division multiplexing. [Means for solving the problem]

[0008] The inventors of the present invention diligently studied means to solve the problems of the prior art described above, and as a result, they found that by emitting the light propagating through each core of an MCF or the like into space and separating it, and by providing multiple non-reciprocal optical elements in the spatial optical system through which each light beam passes individually, the core of an MCF or the like can be used for transmission in the reverse direction. Based on this finding, the inventors conceived that a connector for optical fibers suitable for bidirectional communication could be realized, and thus completed the present invention. Specifically, the present invention has the following configuration.

[0009] The present invention relates to an optical fiber connector 100. The optical fiber connector 100 according to the present invention is configured to optically couple corresponding cores of a first optical fiber 110 having multiple cores and a second optical fiber 120 having multiple cores. An example of the first optical fiber 110 and the second optical fiber 120 is a multicore fiber (MCF) in which multiple optical propagation cores are formed within a single optical fiber. However, each optical fiber 110, 120 is not limited to an MCF, and may be a bundle fiber formed by bundling multiple single-mode fibers (SMFs) having one core, or a bundle fiber formed by bundling multiple MCFs. Furthermore, the combination of the first optical fiber 110 and the second optical fiber 120 is not limited to a combination of two MCFs or a combination of two bundle fibers, and it is also possible to combine one MCF and the other bundle fiber.

[0010] The optical fiber connector 100 comprises a first separation / coupling system 10, a second separation / coupling system 20, and a propagation control system 30. The first separation / coupling system 10 is configured to spatially separate multiple optical beams emitted into space from multiple cores of the first optical fiber 110. The first separation / coupling system 10 is also configured to introduce multiple optical beams emitted from multiple cores of the second optical fiber 120 into the corresponding cores of the first optical fiber 110. Similarly, the second separation / coupling system 20 is configured to spatially separate multiple optical beams emitted into space from multiple cores of the second optical fiber 120. The second separation / coupling system 20 is also configured to introduce multiple optical beams emitted from multiple cores of the first optical fiber 110 into the corresponding cores of the second optical fiber 120. The propagation control system 30 is positioned between the first separation / coupling system 10 and the second separation / coupling system 20. The propagation control system 30 includes, for each optical beam, an optical non-reciprocal element 31 that transmits light traveling in one direction and blocks or attenuates light traveling in the opposite direction. At least two optical non-reciprocal elements 31 are arranged in the propagation control system 30 such that the light transmission directions are opposite.

[0011] As described above, the present invention provides an optical fiber connector 100 for connecting first and second optical fibers 110 and 120, wherein the optical fiber connector 100 spatially separates the optical beams emitted from multiple cores of each optical fiber 110 and 120, and arranges multiple non-reciprocal optical elements 31 in opposite directions on the optical path of each optical beam. As a result, the optical fiber connector 100 according to the present invention enables bidirectional communication, for example, by introducing an optical beam emitted from the first core of the first optical fiber 110 into the first core of the second optical fiber 120 through the first non-reciprocal optical element 31(a), and introducing an optical beam emitted from the second core of the second optical fiber 120 into the second core of the first optical fiber 110 through the second non-reciprocal optical element 31(b). Therefore, the optical fiber connector 100 according to the present invention can realize bidirectional communication using spatial division multiplexing.

[0012] In the optical fiber connector 100 according to the present invention, the first separation / coupling system 10 preferably includes a first aspherical lens 11, a first convex meniscus lens 13a, a first biconcave lens 13b, and a first inverted convex meniscus lens 13c. The first convex meniscus lens 13a, the first biconcave lens 13b, and the first inverted convex meniscus lens 13c are collectively referred to as the first triplet lens 13. The first aspherical lens 11 converts diffuse light emitted from the first optical fiber 110 into parallel light. The first convex meniscus lens 13a is positioned convexly to the first aspherical lens 11. The light beam focused by the first convex meniscus lens 13a is incident on the first biconcave lens 13b. The first inverted convex meniscus lens 13c is positioned such that the light beam diverged by the first biconcave lens 13b is incident on it, the image point is on the front side of the second separation / coupling system 20, and it is convex in the opposite direction to the first convex meniscus lens 13a. Similarly, the second separation / coupling system 20 preferably includes a second aspherical lens 21, a second convex meniscus lens 23a, a second biconcave lens 23b, and a second inverted convex meniscus lens 23c. The second convex meniscus lens 23a, the second biconcave lens 23b, and the second inverted convex meniscus lens 23c are collectively referred to as the second triplet lens 23. The second aspherical lens 21 converts the diffused light emitted from the second optical fiber 120 into parallel light. The second convex meniscus lens 23a is positioned convex to the second aspherical lens 21. The second biconcave lens 23b receives the light beam focused by the second convex meniscus lens 23a. The second inverse convex meniscus lens 23c receives the light beam diverged by the second biconcave lens 23b, has its image point in front of the first separation / coupling system 10, and is positioned to be convex in the opposite direction to the second convex meniscus lens 23a. In this way, by providing triplet lenses 13 and 23, composed of multiple lenses arranged optically symmetrically, in the first separation / coupling system 10 and the second separation / coupling system 20, spherical aberration can be corrected by adjusting the curvature of each lens and controlling the direction of propagation of the light beam. Furthermore, chromatic aberration can be corrected by adjusting the refractive index of each lens and focusing light of different wavelengths (colors) to a single point.

[0013] In the optical fiber connector 100 according to the present invention, it is preferable that the propagation control system 30 has a portion in which optical non-reciprocal elements 31 are arranged such that the light transmission directions of the light beams emitted from circumferentially adjacent cores of the first optical fiber 110 and the second optical fiber 120 are opposite. Note that the number of cores in each optical fiber 110, 120 does not need to be more than two, for example, it may be four, six, or eight cores. In other words, in the cross-section of the first and second optical fibers 110, 120, each core is arranged in multiples in the circumferential direction. In this case, the distance between circumferentially adjacent cores is the shortest. Therefore, by making the light beams emitted from circumferentially adjacent cores opposite in direction, it is possible to suppress the occurrence of crosstalk between cores within each optical fiber 110, 120. In addition, it is preferable that the light beams emitted from adjacent cores in the circumferential direction in each optical fiber 110, 120 are all in opposite directions. However, there may be parts where the light beams emitted from partially adjacent cores are in the same direction, for example, when the number of cores is odd.

[0014] In the optical fiber connector 100 according to the present invention, it is preferable that the first separation / coupling system 10 and the second separation / coupling system 20 are arranged so that the imaging points of the optical beams coincide. In this case, it is preferable that the propagation control system 30 is arranged such that the non-reciprocal optical elements 31 with the same direction of light transmission are on the same side with respect to the imaging point, and the non-reciprocal optical elements 31 with the opposite direction of light transmission are on the opposite side of the imaging point. By arranging non-reciprocal optical elements 31 with the same direction of light transmission close together in this way, the physical structure of the optical fiber connector 100 can be miniaturized. Furthermore, the non-reciprocal optical elements 31 may be, for example, optical isolators that control the direction of light propagation to one direction by utilizing the phenomenon (Faraday effect) in which the polarization of light rotates when affected by an external magnetic field. In this case, if non-reciprocal optical elements 31 with opposite directions of light transmission are arranged close together, their performance may deteriorate due to interference of magnetic fields. Therefore, by placing the optical non-reciprocal element 31, whose light transmission direction is opposite, at positions relatively far apart from the imaging point, the influence of such a magnetic field can be avoided. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a connector for optical fibers that is suitable for bidirectional communication using spatial division multiplexing. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 schematically shows a first embodiment of the optical fiber connector. [Figure 2] Figure 2 schematically shows a second embodiment of the optical fiber connector. [Figure 3] Figure 3 shows an example of a conventional optical fiber connector. [Modes for carrying out the invention]

[0017] The following describes embodiments for carrying out the present invention with reference to the drawings. The present invention is not limited to the embodiments described below, but also includes modifications made to the embodiments described below within the scope that would be obvious to those skilled in the art.

[0018] FIG. 1 shows an optical fiber connector 100 according to a first embodiment of the present invention. As shown in FIG. 1, the optical fiber connector 100 is used for bidirectional communication, and couples light propagating through a first optical fiber 110 having a plurality of cores to a second optical fiber 120 also having a plurality of cores, and at the same time, couples light propagating through the second optical fiber 120 to the first optical fiber 110. Therefore, the optical fiber connector 100 basically has an optically symmetric structure on the first optical fiber 110 side and the second optical fiber 120 side.

[0019] In this embodiment, multi-core fibers (MCFs) are adopted as the first and second optical fibers 110 and 120, respectively. In this embodiment, the first and second optical fibers 110 and 120 will be described by taking MCFs having four cores each as an example. However, the number of cores of the first and second optical fibers 110 and 120 is not limited to four, and may be, for example, two cores, five cores, six cores, or seven cores.

[0020] As shown in FIG. 1, in this embodiment, one end of the optical fiber connector 100 is connected to the end of the first optical fiber 110, and the other end is connected to the end of the second optical fiber 120. Since the inside of the optical fiber connector 100 is hollow, light propagating through the cores of the first and second optical fibers 110 and 120 is emitted into the optical fiber connector 100 from the emission ends of the first and second optical fibers 110 and 120. In this specification, the light propagating through the space in this way is referred to as an "optical beam". The optical beams from the cores of the first and second optical fibers 110 and 120 are emitted into the optical fiber connector 100 while diffusing so that the beam diameter expands.

[0021] The optical fiber connector 100 has a structure in which a propagation control system 30 is provided between a first separation / coupling system 10 and a second separation / coupling system 20. The optical beam emitted into the optical fiber connector 100 from a part of the core of the first optical fiber 110 is spatially separated by the first separation / coupling system 10, and the distance between the optical paths of each optical beam increases. Subsequently, the optical beam from the first optical fiber 110 reaches the second separation / coupling system 20 via the propagation control system 30, and is imaged onto the corresponding core of the second optical fiber 120 by this second separation / coupling system 20. The same applies in the reverse direction. That is, the optical beam emitted into the optical fiber connector 100 from a part of the core of the second optical fiber 120 is spatially separated by the second separation / coupling system 20, and the distance between the optical paths of each optical beam increases. Subsequently, the light beam from the second optical fiber 120 passes through the propagation control system 30 to the first separation and coupling system 10, where it is imaged onto the corresponding core of the first optical fiber 110. In this way, each optical fiber 110, 120 has a portion of its multiple cores that function as the core for the emission of the light beam, and the remainder that functions as the core for the injection of the light beam.

[0022] In this embodiment, the first separation / combination system 10 is configured to include a first aspherical lens 11 and a first imaging lens 12. Similarly, the second separation / combination system 20 is configured to include a second aspherical lens 21 and a second imaging lens 22.

[0023] First, the case of making the light beam emitted from the first optical fiber 110 enter the second optical fiber 120 will be described. The light beam emitted from the first optical fiber 110 into the optical fiber connector 100 enters the first aspherical lens 11. The first aspherical lens 11 functions as a collimating lens having a front focal position at the emission end of the first optical fiber 110. Therefore, if the light beam is incident on the optical axis of the first aspherical lens 11, the light beam will be collimated (made parallel) and travel straight along the optical axis of the first aspherical lens 11. However, as shown in the example of FIG. 1, when the light beam is incident at a position deviated from the optical axis of the first aspherical lens 11, the light beam is collimated and travels straight with an angular difference with respect to the optical axis of the first aspherical lens 11. For this reason, the light beam emitted from the core of the first optical fiber 110 intersects at the rear focal position of the first aspherical lens 11 after passing through the first aspherical lens 11, and then is gradually spatially separated. As a result, the separation width of each light beam expands. Thus, the first aspherical lens 11 has a function of collimating a plurality of light beams and a function of expanding the separation width.

[0024] A first imaging lens 12 is provided behind the first aspherical lens 11. When the parallelized light beams that have passed through the first aspherical lens 11 enter the first imaging lens 12, the first imaging lens 12 functions as a focusing lens. The front focal position of the first imaging lens 12 is aligned with the rear focal position of the first aspherical lens 11 (i.e., the intersection point of each light beam). As a result, the multiple light beams that have passed through the first imaging lens 12 are sufficiently separated before entering the first imaging lens 12, where they are focused and diffused while being aligned substantially parallel to each other. That is, as shown in Figure 1, each light beam that has passed through the first imaging lens 12 is focused so that its beam diameter gradually decreases, converges at the rear focal position of the first imaging lens 12, then diffuses again so that its beam diameter expands as it travels through space, and enters the second imaging lens 22. At this time, the optical axes of each light beam are substantially parallel in the space between the first imaging lens 12 and the second imaging lens 22.

[0025] Furthermore, it is preferable that the first imaging lens 12 is a condensing lens with a longer focal length than the first aspherical lens 11. That is, the spacing between each light beam between the first imaging lens 12 and the second imaging lens 22 can be changed by the ratio of the focal lengths of the first aspherical lens 11 (collimating lens) and the first imaging lens 12 (condensing lens). For example, if a condensing lens with a focal length 10 times that of the first aspherical lens 11 is used as the first imaging lens 12, the spacing between each light beam between the first imaging lens 12 and the second imaging lens 22 can be increased to 10 times the spacing between each core in the first optical fiber 110. From the viewpoint of ensuring sufficient spacing between each light beam, it is preferable that the first imaging lens 12 has a focal length 2 times or more, 5 times or more, or 10 times or more that of the first aspherical lens 11.

[0026] As shown in Figure 1, the combination of the second imaging lens 22 and the second aspherical lens 21 is positioned symmetrically to the combination of the first aspherical lens 11 and the first imaging lens 12, with respect to the line connecting the focal points (convergence points) of each light beam as the axis of symmetry. Thus, these lenses 11, 12, 22, and 21 constitute a relay optical system that couples the first optical fiber 110 and the second optical fiber 120.

[0027] Specifically, a second imaging lens 22 is provided behind the first imaging lens 12. When the light beam focused by the first imaging lens 12 enters the second imaging lens 22, the second imaging lens 22 functions as a collimating lens. The front focal position of the second imaging lens 22 is aligned with the rear focal position of the first imaging lens 12 (i.e., the convergence point of each light beam). As shown in the example in Figure 1, when a light beam that has passed through the first imaging lens 12 enters the second imaging lens 22 at a position offset from the optical axis, it is collimated and travels in a straight line with an angular difference relative to the optical axis of the second imaging lens 22. As a result, the multiple light beams that have passed through the second imaging lens 22 intersect at the rear focal position of the second imaging lens 22, gradually reducing their separation width, and are then spatially separated again. This reduces the separation width of each light beam. Thus, the second imaging lens 22 has the function of collimating multiple light beams and reducing the separation width.

[0028] A second aspherical lens 21 is provided behind the second imaging lens 22. When the parallelized light beam that has passed through the second imaging lens 22 enters the second aspherical lens 21, the second aspherical lens 21 functions as a focusing lens. The front focal position of the second aspherical lens 21 is aligned with the rear focal position of the second imaging lens 22 (i.e., the intersection point of each light beam). Furthermore, the rear focal position of the second aspherical lens 21 is aligned with the entrance end of the second optical fiber 120. As a result, as shown in Figure 1, the light beam that has passed through the second aspherical lens 21 is aligned substantially parallel to the second aspherical lens 21 and focused towards the core of the second optical fiber 120. At this time, the optical axis of the light beam is substantially parallel in the space between the second aspherical lens 21 and the second optical fiber 120.

[0029] In this way, the first separation / coupling system 10 and the second separation / coupling system 20 form a spatial optical system that optically couples the first optical fiber 110 and the second optical fiber 120. Here, we have described the case in which the light beam emitted from the first optical fiber 110 is incident on the second optical fiber 120 (first communication direction), but it is also possible to reverse this and have the light beam emitted from the second optical fiber 120 incident on the first optical fiber 110 (second communication direction). A detailed explanation of the second communication direction will be omitted as it is a repetition of the case of the first communication direction, but in the case of the second communication direction, the functions of the first aspherical lens 11 and the second aspherical lens 21 are swapped, and the functions of the first imaging lens 12 and the second imaging lens 22 are swapped. Therefore, for the second communication direction, one can simply swap the terms "first imaging lens 12" and "second imaging lens 22" in the explanation given for the first communication direction, and then swap the terms "first imaging lens 12" and "second imaging lens 22" in the same way.

[0030] Here, as shown in Figure 1, a propagation control system 30 is provided between the first separation / coupling system 10 and the second separation / coupling system 20. This propagation control system 30 includes a plurality of non-reciprocal optical elements 31(a), (b). A non-reciprocal optical element 31 is an optical element that transmits light traveling in one direction and blocks or attenuates light traveling in the opposite direction. An example of a non-reciprocal optical element 31 is an optical isolator. An optical isolator is an optical element that allows light to travel only in one direction and blocks or attenuates light traveling in the opposite direction. An optical isolator mainly consists of a pair of birefringent crystals with a wedge angle, a Faraday rotator, and a 45-degree quartz photon placed between them. The Faraday rotator has the function of rotating the plane of polarization of light by an external magnetic field using the Faraday effect, and the pair of birefringent crystals have the function of separating the incident light by its polarization state and aligning or shifting the exit angle by adjusting the direction of the respective crystal axis and wedge angle. Light traveling in the forward direction is separated into ordinary and extraordinary light by a birefringent crystal. Then, the polarization state is rotated by 90 degrees by the action of a Faraday rotator and a quartz photon, so that the ordinary light becomes extraordinary light and the extraordinary light becomes ordinary light. In the subsequent birefringent crystal, the emission angles of the two polarization states are aligned, making it easier to couple to the optical fiber. When traveling in the reverse direction, the action of the Faraday rotator and the 45-degree quartz photon maintains the same polarization state, so the ordinary light remains ordinary light and the extraordinary light remains extraordinary light. The emission angles of the two polarization states shift, so they do not couple to the optical fiber and are blocked or attenuated. As shown in Figure 1, the non-reciprocal optical elements 31 are located between the first separation / coupling system 10 and the second separation / coupling system 20, with one placed on each of the optical paths of multiple optical beams. The number of non-reciprocal optical elements 31 is basically the same as the number of light beams propagating through the space of the optical fiber connector 100, that is, the number of cores in the first and second optical fibers 110 and 120. In Figure 1, only two non-reciprocal optical elements 31(a) and (b) are shown, but in reality, since the first and second optical fibers 110 and 120 have 4 cores, there are actually four non-reciprocal optical elements 31.

[0031] As shown in Figure 1, the two non-reciprocal optical elements 31(a) and (b) are arranged so that the light transmission directions are opposite to each other. That is, the first non-reciprocal optical element 31(a) transmits the light beam emitted from the first optical fiber 110, but blocks or attenuates the light beam emitted from the second optical fiber 120. Therefore, the first light beam emitted from the first core of the first optical fiber 110 passes through the first non-reciprocal optical element 31(a) and enters the second core of the second optical fiber 120. On the other hand, the second non-reciprocal optical element 31(b) transmits the light beam emitted from the second optical fiber 120, but blocks or attenuates the light beam emitted from the first optical fiber 110. Therefore, the second light beam emitted from the second core of the second optical fiber 120 passes through the second non-reciprocal optical element 31(b) and enters the first core of the first optical fiber 110. By arranging two or more non-reciprocal optical elements 31 with opposite light transmission directions in this way, bidirectional communication becomes possible between the first optical fiber 110 and the second optical fiber 120.

[0032] Furthermore, in the embodiment shown in Figure 1, the non-reciprocal optical element 31 is positioned to overlap the imaging points of the first imaging lens 12 and the second imaging lens 22. Since the imaging point is the point where light converges most intensely, placing the non-reciprocal optical element 31 here effectively blocks or attenuates light attempting to travel in the opposite direction. However, it is not always necessary to place the non-reciprocal optical element 31 on the imaging point; it can also be placed at a position offset in front of or behind this imaging point.

[0033] Next, with reference to Figure 2, a second embodiment of the optical fiber connector 100 according to the present invention will be described. The second embodiment will be described focusing on the differences from the first embodiment described above, and components identical to those in the first embodiment will be denoted by the same reference numerals, and their descriptions will be omitted.

[0034] Figure 2 shows two different sides of a single optical fiber connector 100. In the example shown in Figure 2, four-core MCFs are used as the first optical fiber 110 and the second optical fiber 120, and these optical fibers 110 and 120 are connected bidirectionally by the optical fiber connector 100. In a cross-sectional view, the four cores of the four-core MCF are arranged circumferentially. In the first optical fiber 110, in the cross-section shown in Figure 2, the cores are numbered 1, 2, 3, and 4 in a clockwise direction. In the second optical fiber 120, in the cross-section shown in Figure 2, the cores are numbered 1, 2, 3, and 4 in a counterclockwise direction. The first optical fiber 110 and the second optical fiber 120 are connected at the cores with the same number. In addition, in each optical fiber 110 and 120, the 1st and 3rd cores are located diagonally opposite each other, and the 2nd and 4th cores are located diagonally opposite each other. Figure 2(a) shows the optical paths of core 1 and core 3, which are located on a certain diagonal, while Figure 2(b) shows the optical paths of core 2 and core 4, which are located on a different diagonal.

[0035] In the second embodiment (Figure 2), the first imaging lens 12 and the second imaging lens 22 in the first embodiment (Figure 1) are replaced with a first triplet lens 13 and a second triplet lens 23, respectively. As shown in Figure 2, the first triplet lens 13 is included in the first separation / coupling system 10, located after the first aspherical lens 11 in the outgoing optical path, and before the first aspherical lens 11 in the incident optical path. Similarly, the second triplet lens 23 is included in the second separation / coupling system 20, located after the second aspherical lens 21 in the outgoing optical path, and before the second aspherical lens 21 in the incident optical path. The first and second triplet lenses 13 and 23 share the same functions as the first and second imaging lenses 12 and 22 described above in terms of focusing a parallelized light beam and parallelizing diffused light. On the other hand, each triplet lens 13, 23 is composed of three lenses, and has an advantage over the aforementioned imaging lenses 12, 22 in that it can simultaneously correct spherical aberration and chromatic aberration through a combination of convex and concave lenses.

[0036] The first triplet lens 13 is composed of a first convex meniscus lens 13a, a first biconcave lens 13b, and a first inverted convex meniscus lens 13c, in the order through which the light beam emitted from the first optical fiber 110 passes. Similarly, the second triplet lens 23 is composed of a second convex meniscus lens 23a, a second biconcave lens 23b, and a second inverted convex meniscus lens 23c, in the order through which the light beam emitted from the second optical fiber 120 passes. The first triplet lens 13 and the second optical fiber 120 have an optically symmetrical configuration.

[0037] Each convex meniscus lens 13a, 23a has one convex surface and the other concave surface with a smaller curvature than the convex surface, and is positioned convex relative to each aspherical lens 11, 21. Therefore, in the outgoing optical path, the convex meniscus lenses 13a, 23a have the function of focusing parallel light that has passed through the aspherical lenses 11, 21. Conversely, when diffuse light is incident from the concave side, the convex meniscus lenses 13a, 23a convert this diffuse light into parallel light. The front focal position of the convex meniscus lenses 13a, 23a is aligned with the rear focal position of the first aspherical lens 11 (i.e., the intersection point of each light beam).

[0038] Each of the biconcave lenses 13b and 23b has concave surfaces on both sides and is positioned between the convex meniscus lenses 13a and 23a and the inverted convex meniscus lenses 13c and 23c. The biconcave lenses 13b and 23b have the function of diffusing the light beam focused by the convex meniscus lenses 13a and 23a or the inverted convex meniscus lenses 13c and 23c.

[0039] Each inverted convex meniscus lens 13c, 23c has one convex surface and the other concave surface with a smaller curvature than the convex surface, and is positioned to be convex in the opposite direction to the aforementioned convex meniscus lenses 13a, 23a. In other words, the concave surfaces of the inverted convex meniscus lenses 13c, 23c face the biconcave lenses 13b, 23b. Therefore, in the optical path on the exit side, the convex meniscus lenses 13a, 23a have the function of focusing diffused light that has passed through the biconcave lenses 13b, 23b. Conversely, when diffused light is incident from the convex side, the convex meniscus lenses 13a, 23a focus this diffused light and introduce it into the biconcave lenses 13b, 23b. Each light beam that passes through the first inverted convex meniscus lens 13c is focused so that its beam diameter gradually decreases, converges at the rear focal point (image point) of the first inverted convex meniscus lens 13c, then spreads out again so that its beam diameter expands, and travels through space before entering the second inverted convex meniscus lens 23c. The same applies to light beams traveling in the opposite direction. The focal points of the first inverted convex meniscus lens 13c and the second inverted convex meniscus lens 23c are aligned to coincide with each other.

[0040] As with the triplet lenses 13 and 23, spherical aberration can be corrected by combining convex and concave lenses in a multi-lens system. This principle is based on the fact that the aberration direction generated by the convex lens and the aberration generated by the concave lens are in opposite directions and therefore cancel each other out. While it is possible to correct only spherical aberration using aspherical lenses, in that case correction is possible without increasing the number of lenses as with the triplet lenses 13 and 23, a single aspherical lens cannot correct chromatic aberration, making it insufficient in this embodiment. In bidirectional communication using multicore fibers, it is expected that light in a wide wavelength range from 1530 nm to 1620 nm, known as wavelengths for long-distance optical transmission, will be used. In this case, if chromatic aberration occurs, there is a risk that the coupling efficiency of light to the optical fiber will deteriorate when it deviates from the tuned wavelength of the optical system. Therefore, in order to correct this phenomenon, in this embodiment, triplet lenses 13 and 23 are employed, and chromatic aberration is corrected by selecting materials for the convex and concave lenses that have appropriate dispersion. This makes it possible to construct an optical system that maintains constant coupling efficiency over a wide range of wavelengths in bidirectional communication using multicore fibers.

[0041] In the second embodiment, as shown in Figure 2(a), the light beams emitted from the first and third cores of the first optical fiber 110 are incident on the first and third cores of the second optical fiber 120, respectively. These first and third cores are diagonally opposite each other in the optical fibers 110 and 120 (i.e., cores that are not adjacent in the circumferential direction). In this case, the propagation control system 30 places a first non-reciprocal optical element 31(a) and a third non-reciprocal optical element 31(c), respectively, on the optical paths of the first and third cores, with the light transmission direction being the same. Furthermore, these first and third non-reciprocal optical elements 31(a) and 31(c) are both located on the same side (i.e., the side closer to the first optical fiber 110) with respect to the imaging points of the triplet lenses 13 and 23. In other words, the first and third non-reciprocal optical elements 31(a) and 31(c) are positioned between the first separation / coupling system 10 and the imaging point. Therefore, these first and third non-reciprocal optical elements 31(a) and 31(c) are positioned relatively close together and parallel to each other within the optical fiber connector 100. However, since both the first and third non-reciprocal optical elements 31(a) and 31(c) are isolators with the same direction of light transmission, the influence of magnetic field interference between these first and third non-reciprocal optical elements 31(a) and 31(c) is minimal.

[0042] Similarly, in the second embodiment, as shown in Figure 2(b), the light beams emitted from the second and fourth cores of the second optical fiber 120 are incident on the second and fourth cores of the first optical fiber 110, respectively. These second and fourth cores are diagonally opposite cores (i.e., not adjacent in the circumferential direction) in each optical fiber 110 and 120. In this case, the propagation control system 30 places a second non-reciprocal optical element 31(b) and a fourth non-reciprocal optical element 31(d), respectively, on the optical paths of the second and fourth cores, with the light transmission direction being the same. Furthermore, these second and fourth non-reciprocal optical elements 31(b) and 31(d) are both located on the same side (i.e., the side closer to the second optical fiber 120) with respect to the imaging points of the triplet lenses 13 and 23. In other words, the second and fourth non-reciprocal optical elements 31(b) and 31(d) are positioned between the second separation / coupling system 20 and the imaging point. Therefore, these second and fourth non-reciprocal optical elements 31(b) and 31(d) are positioned relatively close together and parallel to each other within the optical fiber connector 100. However, since both the second and fourth non-reciprocal optical elements 31(b) and 31(d) are isolators with the same direction of light transmission, the influence of magnetic field interference between these second and fourth non-reciprocal optical elements 31(b) and 31(d) is minimal.

[0043] Furthermore, as can be seen by comparing Figure 2(a) and Figure 2(b), for example, the first non-reciprocal optical element 31(a) is located on opposite sides of the image point from the second non-reciprocal optical element 31(b) and the fourth non-reciprocal optical element 31(d). As mentioned above, the first non-reciprocal optical element 31(a) is located on the optical path of the first core of each optical fiber 110, 120, the second non-reciprocal optical element 31(b) is located on the optical path of the second core of each optical fiber 110, 120, and the fourth non-reciprocal optical element 31(d) is located on the optical path of the fourth core of each optical fiber 110, 120. In each optical fiber 110, 120, the first core is adjacent to the second and fourth cores in the circumferential direction, so the optical path of the first core is relatively close to the optical paths of the second and fourth cores. Furthermore, the first non-reciprocal optical element 31(a) located on the optical path of core 1 has a light transmission direction opposite to that of the second non-reciprocal optical element 31(b) located on the optical path of core 2 and the fourth non-reciprocal optical element 31(d) located on the optical path of core 4. In this way, if non-reciprocal optical elements 31 with opposite light transmission directions are located in spatially close positions, there is a risk that the magnetic fields will interfere with each other and degrade performance. Therefore, by placing the first non-reciprocal optical element 31(a) on opposite sides of the image point from the second non-reciprocal optical element 31(b) and the fourth non-reciprocal optical element 31(d), and increasing the spatial distance between them, the influence of the magnetic field can be minimized. The same applies to the other non-reciprocal optical elements 31(b), 31(c), and 31(d).

[0044] Furthermore, if, for example, all four non-reciprocal optical elements 31(a) to (d) are placed on the imaging point, the arrangements of each non-reciprocal optical element 31(a) to (d) will overlap, requiring a greater spacing between the light beams emitted from each core, which could lead to an increased length of the optical path within the optical fiber connector 100. On the other hand, as shown in the embodiment in Figure 2, by arranging the non-reciprocal optical elements 31(a) to (d) at positions offset to both sides of the imaging point, all non-reciprocal optical elements 31(a) to (d) do not overlap on the imaging point, thus eliminating the need to significantly widen the spacing between the light beams emitted from each core. Therefore, this arrangement allows for a smaller internal structure within the optical fiber connector 100.

[0045] In this specification, embodiments of the present invention have been described with reference to the drawings in order to express the content of the present invention. However, the present invention is not limited to the above embodiments, and includes modifications and improvements that are obvious to those skilled in the art based on the matters described in this specification. [Explanation of Symbols]

[0046] 10…First separation / binding system 11…First aspherical lens 12…First imaging lens 13…First triplet lens 13a...First convex meniscus lens 13b...First biconcave lens 13c... First inverted convex meniscus lens 20…Second separation and bonding system 21…Second aspherical lens 22…Second imaging lens 23…Second triplet lens 23a...Second convex meniscus lens 23b...Second biconcave lens 23c... Second inverted convex meniscus lens 30…Propagation control system 31…Non-reciprocal optical elements 100… Fiber optic connector 110...First optical fiber 120...Second optical fiber

Claims

1. An optical fiber connector that optically couples corresponding cores of a first optical fiber having multiple cores and a second optical fiber having multiple cores, A first separation and coupling system spatially separates multiple light beams emitted into space from multiple cores of the first optical fiber, and introduces multiple light beams emitted from multiple cores of the second optical fiber into the corresponding cores of the first optical fiber. A second separation and coupling system spatially separates multiple light beams emitted into space from multiple cores of the second optical fiber, and introduces multiple light beams emitted from multiple cores of the first optical fiber into corresponding cores of the second optical fiber. The system includes a propagation control system positioned between the first separation / coupling system and the second separation / coupling system, which includes an optical non-reciprocal element that transmits light traveling in one direction and blocks or attenuates light traveling in the opposite direction for each optical beam. The propagation control system includes at least two optical non-reciprocal elements whose light transmission directions are opposite. Fiber optic connector.

2. The first separation and coupling system described above is: A first aspherical lens that converts diffuse light emitted from the first optical fiber into parallel light, A first convex meniscus lens positioned convexly with respect to the first aspherical lens, A first biconcave lens into which the light beam focused by the first convex meniscus lens is incident, The light beam diverged by the first biconcave lens is incident on a first inverted convex meniscus lens which is oriented opposite to the first convex meniscus lens and has an image point on the front side of the second separation / combination system. The second separation and coupling system described above is: A second aspherical lens that converts diffuse light emitted from the second aspherical lens into parallel light, A second convex meniscus lens is positioned convexly with respect to the second optical fiber, A second biconcave lens into which the light beam focused by the second convex meniscus lens is incident, The light beam diverged by the second biconcave lens is incident on a second inverted convex meniscus lens, which is oriented in the opposite direction to the second convex meniscus lens and has an image point on the front side of the first separation / combination system. The optical fiber connector according to claim 1.

3. The propagation control system has a portion where the non-reciprocal optical elements are arranged such that the light transmission directions of the light beams emitted from cores adjacent to each other in the circumferential direction of the first optical fiber and the second optical fiber are opposite. The optical fiber connector according to claim 1.

4. The first separation / coupling system and the second separation / coupling system are arranged such that the imaging points of the light beams coincide. In the propagation control system, the non-reciprocal optical elements are arranged such that those with the same direction of light transmission are on the same side of the imaging point, and those with opposite directions of light transmission are on the opposite side of the imaging point. The optical fiber connector according to claim 3.

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