Multi-core bidirectional optical transmission system and method

Abstract

This multi-core bidirectional optical transmission system comprises: cores of a first group that are provided in first and second multi-core fibers in order to transmit signal light in a first direction; cores of a second group that are provided in the first and second multi-core fibers in order to transmit signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the signal light in the first direction passing through the cores of the first group; and another device that is provided spaced apart from the first optical isolator. The first optical isolator and the other device have an elongated shape and partially overlap when viewed from the transmission direction of signal light. The multi-core bidirectional optical transmission system is configured so as to transmit signal light in the first direction at least at one end of the first optical isolator not overlapping the other device, and to transmit signal light in the second direction at least at one end of the other device not overlapping the first optical isolator.

Description

Multi-core bidirectional optical transmission system and method

[0001] The present disclosure relates to a multi-core bidirectional optical transmission system and method.

[0002] Multi-core bidirectional optical transmission systems, such as multi-core optical fibers for submarine cables, are attracting attention.

[0003] For example, in a fiber-type optical amplifier such as an erbium-doped fiber amplifier (EDFA), it is essential to introduce an optical isolator to prevent degradation of optical amplification performance due to multiple reflections and the like.

[0004] International Publication No. 2021 / 224977

[0005] In bidirectional optical transmission using multicore fibers, crosstalk noise can be suppressed and the signal transmission distance can be extended by pairing two cores and reversing the signal propagation direction in each core. Optical amplifiers used in multicore bidirectional optical transmission require optical isolators that can reverse the signal propagation direction in two cores within a single multicore fiber.

[0006] Until now, it has been necessary to use a FIFO (Fan In / Fan Out) or similar to separate the signal light from the multi-core input into each core, then use an optical isolator for single-core fiber to output it to the multi-core fiber again using a FIFO. This method requires an additional FIFO, which was not necessary for single-core fiber EDFA. As a result, the insertion loss and crosstalk of the FIFO are added, which are factors that reduce the optical amplification performance and power efficiency, making it difficult to achieve the same performance with a multi-core optical amplifier as with a single-core optical amplifier.

[0007] The present disclosure has been made to solve such problems, and aims to provide an optical transmission system and an optical transmission method suitable for multi-core bidirectional optical transmission.

[0008] a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction of the signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape as viewed from the signal light transmission direction and partially overlap each other as viewed from the signal light transmission direction, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the second direction at at least one end of the other device that is not overlapped with the first optical isolator.

[0009] a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction of the signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape as viewed from the signal light transmission direction and partially overlap each other as viewed from the signal light transmission direction, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the second direction at at least one end of the other device that is not overlapped with the first optical isolator.

[0010] A multi-core bidirectional optical transmission method according to the present disclosure uses a multi-core bidirectional optical transmission system including: a first group of cores provided in first and second multi-core fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multi-core fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the cores of the first group; and another device provided at a distance from the first optical isolator, wherein the signal light from the cores of the first group that has passed through the first optical isolator passes through an ambient space outside the other device, and the signal light from the cores of the second group that has passed through the other device passes through an ambient space outside the first optical isolator.

[0011] According to the present disclosure, it is possible to provide an optical transmission system and an optical transmission method suitable for multi-core bidirectional optical transmission.

[0012] FIG. 1 is a diagram illustrating a first optical isolator and other devices used in a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 2 is a diagram illustrating another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 3 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 4 is a diagram illustrating first and second optical isolators used in a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 5 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 6 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 7 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 8 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 9 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 10 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 11 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. FIG. 12 is a diagram illustrating an example in which an optical isolator is included in a transparent glass housing.

[0013] Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments. In addition, the following description and drawings have been simplified as appropriate for clarity of explanation.

[0014] FIG. 1 is a diagram illustrating a first optical isolator and other devices used in a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 1 is a diagram illustrating the first optical isolator and other devices as viewed from the transmission direction of signal light. FIG. 2 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 2 is a diagram as viewed from the top arrow shown in FIG. 1. FIG. 3 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. FIG. 3 is a diagram as viewed from the side arrow shown in FIG. 2. Note that FIG. 2 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line X-X. FIG. 3 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line Y-Y.

[0015] As shown in FIG. 1 , the first optical isolator 5 is a rectangle extending along the Y-axis. However, this is not limited thereto and may be any other shape, such as an ellipse, as long as it is elongated when viewed in the signal light transmission direction. In this specification, the term "elongated shape" refers to the functional area of ​​the first optical isolator, and includes, for example, the case where the optical isolator 5 is contained in a transparent glass housing 15 (with a square cross section) as shown in FIG. 12 . In other words, the term "elongated shape" does not necessarily refer to a physical shape but also includes a functional shape. The other device 60 is a rectangle extending along the X-axis, but is not limited thereto. The first optical isolator 5 and the other device 60 are generally the same shape, but may also be different. When viewed in the signal light transmission direction, only the central portions of the rectangles of the first optical isolator 5 and the other device 60 overlap. In other words, the ends of the first optical isolator 5 and the other device 60 do not overlap. The first optical isolator 5 is configured to allow signal light (e.g., C1L, C3L) in a first direction (forward direction) to pass through both sides of the first optical isolator 5, excluding the central portion where the first optical isolator 5 overlaps with the other device 60. Similarly, the other device 60 is configured to allow signal light (e.g., C2L, C4L) in a second direction (reverse direction) opposite to the first direction to pass through both sides of the first optical isolator 5, excluding the central portion where the first optical isolator 5 overlaps with the other device 60. Specifically, in FIG. 1 , the first optical isolator 5 and the other device 60 are overlapped so as to be approximately perpendicular to each other when viewed from the transmission direction of the signal light, but this is not limited to this. The first optical isolator 5 and the other device 60 may intersect at any angle.

[0016] As shown in the cross-sectional view of Figure 2, the first and second multicore fibers 11 and 12 are provided with a first group of cores (e.g., C1, C3) for transmitting signal light in a first (forward) direction, and a second group of cores (e.g., C2, C4) for transmitting signal light in a second (reverse) direction opposite to the first (forward) direction.

[0017] 2, a first optical isolator 5 and another device 60 are provided spaced apart from each other between the first and second multicore fibers 11 and 12. The first optical isolator 5 is a first optical isolator for a first direction that blocks signal light traveling in a direction opposite to the first (forward) direction signal light passing through the first group of cores (e.g., C1, C3).

[0018] The other device 60 may be any device having various functions, such as, but not limited to, an optical isolator, a gain flattening filter (GFF), a pump combiner, or a dichroic mirror.

[0019] As described in FIG. 1, the first optical isolator 5 and the other device 60 each have an elongated shape and are partially overlapped when viewed from the transmission direction of the signal light, with at least one end of the first optical isolator 5 and at least one end of the other device 60 not overlapping.

[0020] At least one end of the first optical isolator 5 that is not overlapped with the other device 60 is configured to transmit signal light (e.g., at least one of C1L and C3L) in the first (forward) direction. Also, at least one end of the other device 60 that is not overlapped with the first optical isolator 5 is configured to transmit signal light (e.g., at least one of C2L and C4L) in the second (reverse) direction. That is, although a four-core bidirectional optical transmission system is shown in FIGS. 1 to 3 , in some embodiments, it may be a two-core bidirectional optical transmission system.

[0021] In another embodiment, as shown in Fig. 1, the first optical isolator 5 and the other device 60 each have an elongated shape and overlap at the center of the elongated shape when viewed from the direction of transmission of the signal light. In other words, as shown in Fig. 1, both ends of the first optical isolator 5 and both ends of the other device 60 do not overlap.

[0022] The first optical isolator 5 is configured to transmit two optical signals (e.g., C1L and C3L) in the first (forward) direction at both ends thereof that are not overlapped with the other device 60. The first optical isolator 5 is also configured to transmit two optical signals (e.g., C2L and C4L) in the second (reverse) direction at both ends thereof that are not overlapped with the other device 60.

[0023] As shown in FIG. 3 , the signal light (e.g., C1L, C3L) from the first group of cores (e.g., C1, C3) that has passed through the lens 8 and the first optical isolator 5 is configured to pass through the ambient space outside the other device 60 without passing through the other device 60.

[0024] As shown in FIG. 2 , the signal light (e.g., C2L, C4L) from the second group of cores (e.g., C2, C4) that has passed through the lens 9 and other devices 60 is configured to pass through the ambient space outside the first optical isolator 5 without passing through the first optical isolator 5.

[0025] As described above, by partially overlapping an optical isolator with another device, the signal transmission direction is reversed between the end of the optical isolator that does not overlap with the other device and the end of the other device that does not overlap with the optical isolator. This makes it possible to provide various devices suitable for multi-core bidirectional optical transmission.

[0026] 1, the optical isolator and other devices are arranged perpendicular to each other at 90 degrees, but this is not limiting. In other embodiments, a six-core bidirectional optical transmission system may be used in which an optical isolator and two other devices are arranged with their centers overlapping and offset by 60 degrees from each other. Similarly, a bidirectional optical transmission system having 2n (n is a natural number) cores may be used in which an optical isolator and three or more other devices are arranged with their centers overlapping.

[0027] Next, with reference to FIGS. 4 to 6, an embodiment in which the other device 60 is replaced by the optical isolator 6, thereby using two optical isolators 5 and 6, will be described.

[0028] Fig. 4 is a diagram illustrating first and second optical isolators used in a multi-core bidirectional optical transmission system according to the present disclosure. Fig. 4 is a diagram illustrating the first and second optical isolators as viewed from the transmission direction of signal light. Fig. 5 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. Fig. 5 is a diagram as viewed from the top arrow shown in Fig. 4. Fig. 6 is a diagram illustrating a multi-core bidirectional optical transmission system according to the present disclosure. Fig. 6 is a diagram as viewed from the side arrow shown in Fig. 4. Fig. 5 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line X-X. Fig. 6 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line Y-Y.

[0029] As shown in FIG. 4 , the first optical isolator 5 has a rectangular shape extending along the Y-axis, but is not limited to this and may have any other shape, such as an ellipse, as long as it is elongated. The second optical isolator 6 has a rectangular shape extending along the X-axis, but is not limited to this. The first optical isolator 5 and the second optical isolator 6 may have substantially the same shape or may have different shapes. When viewed from the signal light transmission direction, only the central portions of the rectangles of the first optical isolator 5 and the second optical isolator 6 overlap. In other words, both end portions of the first optical isolator 5 and the second optical isolator 6 do not overlap. The first optical isolator 5 is configured to allow the signal light beams C1L and C3L in a first direction to pass through both sides excluding the central portion overlapping with the second optical isolator 6. Similarly, the second optical isolator 6 is configured to allow the signal light beams C2L and C4L in a second direction opposite to the first direction to pass through both sides excluding the central portion overlapping with the first optical isolator 5. Specifically, in FIG. 4, the first optical isolator 5 and the second optical isolator 6 are stacked so as to be substantially perpendicular to each other when viewed from the transmission direction of the signal light, but this is not limiting.

[0030] As shown in Fig. 5, the multi-core bidirectional optical transmission system 1 includes a first multi-core fiber (MCF) 11 and a second multi-core fiber 12. As shown in the cross-sectional view of Fig. 5, the first and second multi-core fibers 11 and 12 have circular cross sections and four cores C1, C2, C3, and C4 arranged at 90-degree intervals within a cladding 120. The opposing cores C1 and C3 (also referred to as a first group of cores) are provided for transmitting signal light in a first direction (forward direction). Although not shown, two optical transmitters that transmit signal light in the first direction (forward direction) to the cores C1 and C3 and two optical receivers that receive the signal light transmitted through the cores C1 and C3 are also provided.

[0031] The opposing cores C2 and C4 (also referred to as a second group of cores) are provided to transmit signal light in a second direction (reverse direction) opposite to the first direction. Although not shown, two optical transmitters (not shown) are provided to transmit signal light in the second direction (reverse direction) to cores C2 and C4, and two optical receivers (not shown) are provided to receive the signal light propagated through cores C2 and C4. In this way, by pairing two cores and reversing the signal transmission direction of each core, crosstalk noise can be suppressed and the signal transmission distance can be extended.

[0032] As shown in the side cross-sectional view of Figure 5, a first lens 8, a first optical isolator 5, a second optical isolator 6, and a second lens 9 are provided along a first direction (forward direction) between a first multi-core fiber (MCF) 11 and a second multi-core fiber 12.

[0033] As shown in Figure 5, the first optical isolator 5 is a first-direction optical isolator that blocks signal light traveling in the opposite direction to the first-direction signal light C1L, C3L passing through the cores C1, C3 (cores of the first group).

[0034] The second optical isolator 6 is a second-direction optical isolator that blocks signal light traveling in the opposite direction to the second-direction signal light C2L, C4L passing through the cores C2, C4 of the second group. That is, the first optical isolator 5 and the second optical isolator 6 are used for signal light traveling in opposite directions to each other.

[0035] As shown in Figures 4 and 6, the signal lights C1L and C3L from the cores C1 and C3 of the first group that have passed through the first lens 8 and the first optical isolator 5 are configured to pass through the surrounding space outside the second optical isolator 6 without passing through the second optical isolator 6.

[0036] As shown in Figures 4 and 5, the signal lights C2L and C4L from the cores C2 and C4 of the second group that have passed through the second lens 9 and the second optical isolator 6 are configured to pass through the surrounding space outside the first optical isolator 5 without passing through the first optical isolator 5.

[0037] As described above, two optical isolators are overlapped at their centers, and their ends are shifted to reverse the signal transmission direction at each end. This allows us to provide a device that combines two optical isolators suitable for multi-core bidirectional optical transmission. By using this bidirectional optical isolator, we can realize a multi-core EDFA (eddy-doped fiber amplifier) ​​that supports bidirectional transmission without a FIFO.

[0038] Next, a multi-core bidirectional optical transmission system using a GFF (Gain Flattening Filter) or a pump combiner as another device 60 will be described.

[0039] 7 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure, which includes an erbium-doped fiber amplifier (EDFA).

[0040] In the multi-core bidirectional optical transmission system 1 according to this embodiment, a first multi-core fiber 11 and a second multi-core fiber 12 are arranged on both sides of the system. Between the first and second multi-core fibers 11 and 12, a GFF 62, an optical isolator 5, an optical isolator 6, a pump combiner 71, a multi-core EDF 50, a pump combiner 72, an optical isolator 5, an optical isolator 6, and a GFF 61 are arranged along a first direction (forward direction). Among these, the optical isolator 5, the pump combiner 71, the multi-core EDF 50, the optical isolator 5, and the GFF 61 are intended for a first group of cores (e.g., C1 and C3) and are rectangular devices extending in the Y-axis direction shown in FIG. 1. On the other hand, the GFF 62, the optical isolator 6, the multi-core EDF 50, the pump combiner 72, and the optical isolator 6 are intended for a second group of cores (e.g., C2 and C4) and are rectangular devices extending in the X-axis direction shown in FIG. 1.

[0041] Among the above-mentioned components, a rectangular device extending in the Y-axis direction and a rectangular device extending in the X-axis direction can be combined for use in multi-core bidirectional optical transmission. For example, an example of combining a GFF 62 and an optical isolator 5 will be described below with reference to Figures 8 and 9.

[0042] Fig. 8 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. Fig. 9 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. Fig. 8 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line X-X. Fig. 9 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line Y-Y.

[0043] As shown in Figures 8 and 9, a first lens 8, a first optical isolator 5, a GFF 62, and a second lens 9 are arranged along a first direction (forward direction) between a first multi-core fiber (MCF) 11 and a second multi-core fiber 12.

[0044] 9, the first optical isolator 5 is a first-direction optical isolator that blocks signal light traveling in the opposite direction to the first-direction signal light C1L, C3L passing through the cores C1, C3 (first group of cores). The first optical isolator 5 is intended for the first group of cores (e.g., C1, C3) and is a rectangular device extending in the Y-axis direction shown in FIG.

[0045] The GFF 62 is a filter for reducing the wavelength dependence of the gain of the EDFA for the second-direction signal lights C2L and C4L passing through the cores C2 and C4 of the second group. The GFF 62 is intended for the cores of the second group (e.g., C2 and C4) and is a rectangular device extending in the X-axis direction shown in FIG. 1.

[0046] As shown in Figure 9, the signal lights C1L and C3L from the cores C1 and C3 of the first group that have passed through the first lens 8 and the first optical isolator 5 are configured to pass through the surrounding space outside the GFF 62 without passing through the GFF 62.

[0047] As shown in Figure 8, the signal lights C2L and C4L from the cores C2 and C4 of the second group that have passed through the second lens 9 and the GFF 62 are configured to pass through the surrounding space outside the first optical isolator 5 without passing through the first optical isolator 5.

[0048] In this way, a multi-core bidirectional optical transmission system and method using a GFF and an optical isolator can also be provided.

[0049] Next, an example in which a pump combiner 72 and an optical isolator 5 are combined will be described below with reference to FIGS.

[0050] Fig. 10 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. Fig. 11 is a diagram illustrating yet another multi-core bidirectional optical transmission system according to the present disclosure. Fig. 10 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line X-X. Fig. 11 also shows a cross-sectional view of the multi-core fiber (MCF) taken along line Y-Y.

[0051] As shown in Figures 10 and 11, a first lens 8, a first optical isolator 5, a pump combiner 72, and a second lens 9 are arranged along a first direction (forward direction) between a first multi-core fiber (MCF) 11 and a second multi-core fiber 12.

[0052] 11, the first optical isolator 5 is a first-direction optical isolator that blocks signal light traveling in the opposite direction to the first-direction signal light C1L, C3L passing through the cores C1, C3 (first group of cores). The first optical isolator 5 is intended for the first group of cores (e.g., C1, C3) and is a rectangular device extending in the Y-axis direction shown in FIG.

[0053] The pump combiner 72 has a pump light source 721 and a dichroic mirror 722, and combines each pump light with the second-direction signal lights C2L and C4L passing through the second group of cores C2 and C4. The pump combiner 72 is intended for the second group of cores (e.g., C2 and C4) and is a rectangular device extending in the X-axis direction shown in FIG.

[0054] As shown in Figure 11, the signal light C1L, C3L from the cores C1, C3 of the first group that has passed through the first lens 8 and the first optical isolator 5 is configured to pass through the ambient space outside the pump combiner 72 without passing through the pump combiner 72.

[0055] As shown in Figure 11, the signal lights C2L and C4L from the cores C2 and C4 of the second group that have passed through the second lens 9 and the pump combiner 72 are configured to pass through the ambient space outside the first optical isolator 5 without passing through the first optical isolator 5.

[0056] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0057] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0058] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. a first group of cores provided in first and second multicore fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multicore fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape as viewed from the signal light transmission direction and partially overlap each other as viewed from the signal light transmission direction, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the multicore bidirectional optical transmission system is configured to transmit signal light in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and to transmit signal light in the second direction to at least one end of the other device that is not overlapped with the first optical isolator. (Supplementary Note 2) The multi-core bidirectional optical transmission system according to Supplementary Note 1, wherein the first optical isolator and the other device each have an elongated shape when viewed from the transmission direction of the signal light, and overlap at the center of the elongated shape when viewed from the first direction which is the transmission direction of the signal light, and both ends of the first optical isolator and both ends of the other device do not overlap, and are configured to transmit two signal lights in the first direction at both ends of the first optical isolator that are not overlapped with the other device, and to transmit two signal lights in the second direction at both ends of the other device that are not overlapped with the first optical isolator.(Supplementary Note 3) The multi-core bidirectional optical transmission system according to Supplementary Note 1, wherein the signal light from the first group of cores that has passed through the first optical isolator passes through an ambient space outside the other device, and the signal light from the second group of cores that has passed through the other device passes through an ambient space outside the first optical isolator. (Supplementary Note 4) The multi-core bidirectional optical transmission system according to Supplementary Note 1, wherein the other device is a second optical isolator for a second direction that blocks signal light traveling in a direction opposite to the second direction signal light passing through the second group of cores. (Supplementary Note 5) The multi-core bidirectional optical transmission system according to Supplementary Note 1, wherein the first group of cores includes one or two or more cores, and the second group of cores includes one or two or more cores. (Supplementary Note 6) The multi-core bidirectional optical transmission system according to Supplementary Note 4, wherein the first and second optical isolators each have an elongated shape, and when viewed from the first direction which is a transmission direction of the signal light, only central portions of the elongated shapes of the first and second optical isolators overlap, and both end portions of the elongated shapes of the first and second optical isolators do not overlap, and the multi-core bidirectional optical transmission system is configured to transmit the signal light in the first direction to both end portions of the elongated shape of the first optical isolator, and to transmit the signal light in the second direction to both end portions of the elongated shape of the second optical isolator. (Supplementary Note 7) The multi-core bidirectional optical transmission system according to Supplementary Note 1, wherein the other device is a GFF (Gain Flattening Filter) or a pump combiner. (Supplementary Note 8) The multi-core bidirectional optical transmission system according to Supplementary Note 1, configured such that: a first lens is provided between the first multi-core fiber and the first optical isolator; a second lens is provided between the second multi-core fiber and the other device; signal light from the first group of cores that has passed through the first lens and the first optical isolator passes through an ambient space outside the other device; and signal light from the second group of cores that has passed through the second lens and the other device passes through an ambient space outside the first optical isolator.(Supplementary Note 9) The multi-core bidirectional optical transmission system according to Supplementary Note 1, comprising: one or more optical transmitting devices that transmit signal light in the first direction to cores of the first group; one or more optical receiving devices that receive the signal light that has propagated through cores of the first group; one or more optical transmitting devices that transmit signal light in the second direction to cores of the second group; and one or more optical receiving devices that receive the signal light that has propagated through cores of the second group. a first group of cores provided in first and second multicore fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multicore fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape as seen from the transmission direction of the signal light and partially overlap each other as seen from the transmission direction of the signal light, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the second direction to at least one end of the other device that is not overlapped with the first optical isolator.(Supplementary Note 11) A multi-core bidirectional optical transmission method using a multi-core bidirectional optical transmission system comprising: a first group of cores provided in first and second multi-core fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multi-core fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the cores of the first group; and another device provided at a distance from the first optical isolator, wherein the signal light from the cores of the first group that has passed through the first optical isolator passes through an ambient space outside the other device, and the signal light from the cores of the second group that has passed through the other device passes through an ambient space outside the first optical isolator.

[0059] Some or all of the elements (e.g., configurations and functions) described in Supplementary Notes 2 to 9 that are dependent on Supplementary Note 1 may also be dependent on Supplementary Note 10 in the same dependency relationship as Supplementary Notes 2 to 9. Some or all of the elements described in any Supplementary Note may be applied to various hardware, software, recording means for recording software, systems, and methods.

[0060] REFERENCE SIGNS LIST 1 Multi-core bidirectional optical transmission system 5 First optical isolator 6 Second optical isolator 8 First lens 9 Second lens 11 First multi-core fiber 12 Second multi-core fiber 15 Transparent glass housing 60 Other device 62 GFF 71 Pump combiner 72 Pump combiner 120 Cladding 721 Pumping light source 722 Dichroic mirror

Claims

1. A multi-core bidirectional optical transmission system comprising: a first group of cores provided in first and second multi-core fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multi-core fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape when viewed from the direction of transmission of the signal light and partially overlap when viewed from the direction of transmission of the signal light, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the system is configured to transmit signal light in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and to transmit signal light in the second direction at at least one end of the other device that is not overlapped with the first optical isolator.

2. The multi-core bidirectional optical transmission system according to claim 1, wherein the first optical isolator and the other device each have an elongated shape when viewed from the transmission direction of the signal light, and overlap at the center of the elongated shape when viewed from the first direction which is the transmission direction of the signal light, and both ends of the first optical isolator and both ends of the other device do not overlap, and the system is configured to transmit two signal lights in the first direction at both ends of the first optical isolator that are not overlapped with the other device, and to transmit two signal lights in the second direction at both ends of the other device that are not overlapped with the first optical isolator.

3. The multi-core bidirectional optical transmission system according to claim 1, wherein the signal light from the first group of cores that has passed through the first optical isolator passes through the ambient space outside the other device, and the signal light from the second group of cores that has passed through the other device passes through the ambient space outside the first optical isolator.

4. The multi-core bidirectional optical transmission system according to claim 1, wherein the other device is a second optical isolator for a second direction that blocks signal light traveling in a direction opposite to the second direction signal light passing through the second group of cores.

5. A multi-core bidirectional optical transmission system according to claim 1, wherein the first group of cores includes one or more cores, and the second group of cores includes one or more cores.

6. The multi-core bidirectional optical transmission system according to claim 4, wherein the first and second optical isolators each have an elongated shape when viewed from the transmission direction of the signal light, and when viewed from the first direction which is the transmission direction of the signal light, only the central portions of the elongated shapes of the first and second optical isolators overlap, and the opposite end portions of the elongated shapes of the second and second optical isolators are not overlapped, and the multi-core bidirectional optical transmission system is configured to transmit the signal light in the first direction to the opposite end portions of the elongated shape of the first optical isolator, and to transmit the signal light in the second direction to the opposite end portions of the elongated shape of the second optical isolator.

7. The multi-core bidirectional optical transmission system according to claim 1, wherein the other device is a GFF (Gain Flattening Filter) or a pump combiner.

8. The multi-core bidirectional optical transmission system according to claim 1, configured such that: a first lens is provided between the first multi-core fiber and the first optical isolator; a second lens is provided between the second multi-core fiber and the other device; signal light from the first group of cores that has passed through the first lens and the first optical isolator passes through an ambient space outside the other device; and signal light from the second group of cores that has passed through the second lens and the other device passes through an ambient space outside the first optical isolator.

9. The multi-core bidirectional optical transmission system according to claim 1, comprising: one or more optical transmitting devices that transmit signal light in the first direction to cores in the first group; one or more optical receiving devices that receive the signal light that has propagated through cores in the first group; one or more optical transmitting devices that transmit signal light in the second direction to cores in the second group; and one or more optical receiving devices that receive the signal light that has propagated through cores in the second group.

10. A multi-core bidirectional optical transmission method comprising: a first group of cores provided in first and second multi-core fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multi-core fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in a direction opposite to the first direction signal light passing through the first group of cores; and another device provided at a distance from the first optical isolator, wherein the first optical isolator and the other device each have an elongated shape when viewed from the signal light transmission direction and partially overlap when viewed from the signal light transmission direction, and at least one end of the first optical isolator and at least one end of the other device do not overlap, and the signal light is transmitted in the first direction at at least one end of the first optical isolator that is not overlapped with the other device, and the signal light is transmitted in the second direction at at least one end of the other device that is not overlapped with the first optical isolator.

11. A multi-core bidirectional optical transmission method using a multi-core bidirectional optical transmission system comprising: a first group of cores provided in first and second multi-core fibers for transmitting signal light in a first direction; a second group of cores provided in the first and second multi-core fibers for transmitting signal light in a second direction opposite to the first direction; a first optical isolator for the first direction that blocks signal light traveling in the opposite direction to the signal light in the first direction passing through the cores of the first group; and another device provided at a distance from the first optical isolator, wherein the signal light from the cores of the first group that has passed through the first optical isolator passes through an ambient space outside the other device, and the signal light from the cores of the second group that has passed through the other device passes through an ambient space outside the first optical isolator.

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