MCF connection device and MCF connection method

Abstract

To provide a technique to branch and couple optical signals propagating through a MCF without using FIFO.SOLUTION: A MCF (multicore fiber) connection device comprises: a first MCF, a second MCF, and a third MCF that are MCFs each including a plurality of cores; a first optical collimator that generates a light ray group including rays of light obtained through conversion of rays of light output from the plurality of cores included in the first MCF in one-to-one correspondence into rays of collimated light; a first optical splitter that branches at least part of the light ray group in a first direction and a second direction different from the first direction at a predetermined branch ratio; a second optical collimator that couples, one-to-one, the plurality of rays of collimated light included in the light ray group output in the first direction respectively to the plurality of cores of the second MCF; and a third optical collimator that couples, one-to-one, the plurality of rays of collimated light included in the light ray group output in the second direction respectively to the plurality of cores of the third MCF.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an MCF connection device and an MCF connection method. [Background technology]

[0002] The spatial light multiplexing transmission method using multicore fiber (MCF) is being put into practical use. MCF has multiple cores in one optical fiber. Therefore, by using MCF instead of single core fiber (SCF), it is possible to increase the transmission capacity of optical transmission systems.

[0003] Optical devices such as optical amplifiers may be placed along a transmission path that uses MCF (MCF transmission path). However, most optical devices use SCF as an interface, and there are still few optical devices that can be directly connected to MCF. For this reason, FIFOs (fan-in / fan-out) are used to connect MCF and optical devices. A FIFO is an optical component with an MCF on one end and multiple SCFs on the other end. A FIFO can connect each of the multiple cores in an MCF to optical components that use SCF as an interface. Therefore, by using a FIFO, an optical device that has an SCF as an interface can be inserted into an MCF transmission path.

[0004] In relation to the present disclosure, Patent Document 1 describes an optical amplifier including a wavelength division multiplexing coupler for coupling a pumping light source to a multi-core EDF. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 171103 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, in a loopback circuit in an optical transmission system, it is necessary to split a downstream optical signal and couple the split downstream optical signal with the optical path of an upstream optical signal. For such splitting and coupling, an optical coupler using an SCF as an interface is used. As described above, a FIFO is generally used to connect an optical component using an SCF as an interface to an MCF. For this reason, when splitting and coupling light propagating through an MCF for each core, it is necessary to convert each core of the MCF to an SCF using a FIFO and connect an optical coupler to each SCF. However, since a loss of a FIFO in practical use increases as the number of cores increases, when an MCF with a large number of cores is used as an optical transmission path, there is a risk that the loss of the optical signal will increase due to the loss of the FIFO.

[0007] An object of the present disclosure is to provide a technique for dropping and combining light propagating through an MCF without using a FIFO. [Means for solving the problem]

[0008] The MCF connection device according to the present disclosure includes a first MCF, a second MCF, and a third MCF, each of which is a multicore fiber (MCF) having a plurality of cores; a first optical collimator that generates a group of light beams obtained by converting each of the light beams output from the multiple cores of the first MCF into a collimated beam on a one-to-one basis; a first optical splitter that splits at least a portion of the group of light beams into a first direction and a second direction different from the first direction at a predetermined splitting ratio; a second optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the first direction with a plurality of cores of the second MCF in a one-to-one relationship; a third optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the second direction with a plurality of cores of the third MCF in a one-to-one relationship; Equipped with.

[0009] The MCF connection method according to the present disclosure is a method for connecting a first MCF, a second MCF, and a third MCF, each of which is an MCF (multicore fiber) having a plurality of cores, comprising: generating a light beam group by converting each of the light beams output from the multiple cores of the first MCF into a collimated beam on a one-to-one basis; branching at least a portion of the light beam group into a first direction and a second direction different from the first direction at a predetermined branching ratio; a plurality of collimated light beams included in the light beam group output in the first direction are coupled one-to-one with a plurality of cores of the second MCF; Each of the plurality of collimated beams included in the group of beams output in the second direction is coupled to a plurality of cores of the third MCF in a one-to-one relationship. It is characterized by: Effect of the Invention

[0010] The present disclosure provides a technique for dropping and combining light propagating through an MCF without using a FIFO. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 illustrates an example of the configuration of an MCF connected device. [Diagram 2] FIG. 2 is a diagram illustrating a configuration example of an optical collimator. [Diagram 3] FIG. 2 illustrates an example of the configuration of an MCF connected device. [Figure 4] 1A and 1B are diagrams illustrating examples of optical paths of MCF connection devices. [Diagram 5] FIG. 2 is a diagram illustrating an example of an optical path of a monitor light. [Figure 6] FIG. 2 is a diagram illustrating an example of wavelength characteristics of an optical splitter. [Figure 7] FIG. 2 is a diagram illustrating an example of an optical path of a monitor light. [Figure 8] FIG. 13 is a diagram illustrating an example of an optical path of return light. [Figure 9] FIG. 1 illustrates an example of the configuration of an MCF transmission system. [Figure 10] FIG. 1 illustrates an example of the configuration of an MCF transmission system. [Figure 11] FIG. 1 illustrates an example of the configuration of an MCF transmission system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The embodiments of the present disclosure will be described below with reference to the drawings. The directions of the arrows shown in the drawings are examples of the directions of signals, etc., and the length and thickness of the arrows do not indicate the strength of the signals, etc. In addition, in the embodiments and drawings, the same reference symbols are used for elements that have already been mentioned, and duplicate explanations may be omitted.

[0013] (First embodiment) 1 is a diagram showing a configuration example of an MCF-connected device 100 according to the present disclosure. The MCF-connected device 100 includes MCFs 101-103, optical collimators 111-113, and an optical splitter 121. Each of the MCFs 101-103 is a multicore fiber including multiple cores. In this disclosure, a case will be described in which the MCFs 101-103 have the same number of cores.

[0014] Here, the optical splitter 121 can be called a first optical splitter. The MCF 101, MCF 102, and MCF 103 can be called a first MCF, a second MCF, and a third MCF, respectively. Also, the optical collimator 111, the optical collimator 112, and the optical collimator 113 can be called a first optical collimator, a second optical collimator, and a third optical collimator, respectively.

[0015] The optical collimator 111 converts the light emitted from each cross section of the multiple cores included in the MCF 101 into one collimated light. That is, the optical collimator 111 converts the light propagating through each core of the MCF 101 into a collimated light on a one-to-one basis. Therefore, the optical collimator 111 converts the light output from the n cores of the MCF 101 into n collimated lights. The optical collimators 112 and 113 also have the same function as the optical collimator 111. The multiple collimated lights propagating between the optical collimators 111-113 may be referred to as a light beam group below. The collimated lights included in the light beam group do not overlap each other. Also, individual collimated lights are not shown in FIG. 1, and the dashed line between the optical collimators 111-113 in FIG. 1 indicates an area where the light beam group may exist. In the present disclosure, the "collimated light" output from an optical collimator or input to an optical collimator includes not only the case where the beam diameter of light propagating through space does not change depending on the propagation distance, but also the light whose beam diameter changes to such an extent that optical coupling between optical collimators is possible.

[0016] The optical splitter 121 splits the light beam group output from the optical collimator 111 into a first direction and a second direction at a predetermined split ratio. The collimated light not split into the second direction propagates in the first direction. The first direction is, for example, the same direction as the light beam group of the optical collimator 111, and the second direction is a direction perpendicular thereto. That is, in FIG. 1, the first direction is the direction from the optical collimator 111 to the optical collimator 112, and the second direction is the direction from the optical collimator 111 to the optical collimator 113. However, the second direction may be different from the first direction. The optical splitter 121 may split only a part of the collimated light included in the light beam group at a predetermined split ratio.

[0017] The optical splitter 121 may be one having general specifications used in spatial optical systems. For example, as shown in FIG. 1, the optical splitter 121 may be composed of two prisms, and a thin film that splits light with a predetermined characteristic may be formed on the bonding surface of the two prisms. FIG. 1 shows an example in which the two prisms are triangular prisms with a right-angled isosceles triangle as the base, and a thin film is formed on the side including the hypotenuse. Note that the "optical splitter" in this disclosure has not only the function of splitting light, but also the function of combining light, like a general optical splitter. The characteristics of the optical splitter to split or combine light include, for example, reflectance, transmittance, combining rate, and wavelength characteristics. The optical splitter is manufactured to have these predetermined characteristics.

[0018] The optical collimator 112 couples a plurality of collimated lights included in the light beam group transmitted through the optical splitter 121 one-to-one with the cores of the MCF 102. That is, the optical collimator 112 couples each of a plurality of collimated lights included in the light beam group output from the optical splitter 121 in the first direction with a plurality of cores of the MCF 102 one-to-one.

[0019] Moreover, the optical collimator 113 couples collimated light included in the light beam group output from the optical collimator 111 and reflected by the optical splitter 121 with the cores of the MCF 103 in a one-to-one relationship. That is, the optical collimator 113 couples each of the multiple collimated light included in the light beam group output from the optical splitter 121 in the second direction with the multiple cores of the MCF 103 in a one-to-one relationship.

[0020] The propagation direction of light in the MCF connection device 100 is not limited to the above description. For example, the optical collimator 112 may convert the light input from the MCF 102 into a group of light rays and output it to the optical splitter 121. In this case, the optical splitter transmits a part or all of the group of light rays toward the optical collimator 111. Each of the collimated lights transmitted through the optical splitter 121 can be coupled one-to-one with a core of the MCF 101 via the optical collimator 111. Similarly, each of the collimated lights output from the optical collimator 113 and reflected at the optical splitter 121 is coupled one-to-one with a core of the MCF 101 via the optical collimator 111.

[0021] The MCF connection device 100 having such a configuration can split and couple light propagating between MCFs without using a FIFO because the MCF connection device 100 couples the MCFs 101-103 for each core via an optical system using optical collimators 111-113, and has an optical splitter 121 between the optical collimators 111-113.

[0022] (Example of optical collimator configuration) FIG. 2 is a diagram showing a configuration example of the optical collimator 111. The optical collimators 112 and 113 have the same configuration as the optical collimator 111. The optical collimator 111 includes a lens 115, and one side of the lens 115 is optically coupled to the light emitted from each core of the MCF 101. The lens 115 converts the light output from the MCF 101 into collimated light for each core, and outputs the light as a group of rays from the other side of the lens 115. The propagation directions of the collimated lights are parallel to each other. That is, when the MCF 101 includes n cores, the lens 115 converts the light emitted from the n cores into n collimated lights, where n is a natural number. FIG. 2 shows an example in which the MCF 101 has four cores (n=4). However, in the present disclosure, the number of cores of each MCF is not limited to four.

[0023] As described above, the lens 115 converts the light output from each core into collimated light. The configuration of the lens 115 is not limited. For example, the lens 115 is a lens that optically enlarges the cross section of the MCF 101. Alternatively, an array lens may be used as the lens 115. The array lens has a configuration in which a plurality of micro lenses are arranged on a plane. Each of the micro lenses corresponds one-to-one with a core of the MCF 101, and is arranged so that one micro lens can convert the light output from one core of the MCF 101 into collimated light. The multiple cores of the MCFs 101-103 are optically connected one-to-one via the optical collimators 111-113 having such a configuration.

[0024] Second embodiment 3 is a diagram showing a configuration example of an MCF connection device 200 according to the present disclosure. The MCF connection device 200 includes MCFs 101-104, optical collimators 111-114, and optical splitters 121-124. Each of the MCFs 101-104 is a multicore fiber including multiple cores. The MCFs 101 and 103 are included in an MCF cable 105, and the MCFs 102 and 104 are included in an MCF cable 106. In addition, in the present disclosure, the number of cores n of the MCFs 101-104 is described as being the same. The MCFs 101-104 can be referred to as first to fourth MCFs, respectively. Furthermore, the optical collimators 111-114 can be referred to as first to fourth optical collimators, respectively.

[0025] The optical collimators 111-114 convert the light emitted from the cross sections of the MCFs 101-104 into collimated light for each core. That is, the optical collimators 111-113 convert the light output from the multiple cores of the MCFs 101-103 into collimated light, respectively, in the same manner as the MCF connection device 100. The optical collimator 114 converts the light output from the multiple cores of the MCF 104 into collimated light on a one-to-one basis.

[0026] Compared to the MCF connection device 100, the MCF connection device 200 further includes optical splitters 123 and 124, an optical collimator 114, and an MCF 104. Optical splitters 121 and 122 are disposed between the optical collimator 111 and the optical collimator 112. Optical splitters 123 and 124 are disposed between the optical collimator 113 and the optical collimator 114. The optical splitters 121-124 may be independent optical components, or may have a structure in which a plurality of these optical splitters are integrated.

[0027] Here, the optical splitter 122 can be called a second optical splitter. The optical splitters 123 and 124 can be collectively called a third optical splitter, and the optical splitters 123 and 124 can be called a fourth optical splitter and a fifth optical splitter, respectively. That is, the third optical splitter includes the fourth and fifth optical splitters.

[0028] In the MCF connection device 200, each core of the MCF 101 is optically coupled to each core of the MCF 102 on a one-to-one basis. Each core of the MCF 101 is optically coupled to each core of the MCF 103 on a one-to-one basis. Furthermore, each core of the MCF 103 is optically coupled to each core of the MCF 104 on a one-to-one basis. Furthermore, each core of the MCF 102 is optically coupled to each core of the MCF 103 on a one-to-one basis. The propagation direction of light in these connections is not limited.

[0029] The optical collimators 111 and 112 are arranged such that the MCF 101 and the MCF 102 are connected for each core by an optical path that passes through the optical splitters 121 and 122. The optical collimators 113 and 114 are arranged such that the MCF 103 and the MCF 104 are connected for each core by an optical path that passes through the optical splitters 123 and 124. Furthermore, the optical collimators 111 and 113 are arranged such that the MCF 101 and the MCF 103 are connected for each core by an optical path that is reflected at the optical splitters 121 and 123. In addition, the optical collimators 112 and 114 are arranged such that the MCF 102 and the MCF 103 are connected for each core by an optical path that is reflected at the optical splitters 122 and 124 and passes through the optical splitter 123.

[0030] Fig. 4 is a diagram for explaining the optical path of a group of light rays propagating inside the MCF connection device 200. The arrows in Fig. 4 simply show the optical path of the group of light rays, and do not show the position of a specific collimated light. In Fig. 4, the group of light rays output from the optical collimator 111 passes through the optical splitters 121 and 122 with a predetermined transmittance and is coupled to the optical collimator 112 (optical path 1). On the other hand, the group of light rays output from the optical collimator 111 and reflected by the optical splitters 121 and 123 with a predetermined reflectance is coupled to the optical collimator 113 (optical path 2).

[0031] Furthermore, the light beam group output from the optical collimator 114 passes through the optical splitters 124 and 123 at a predetermined transmittance and is coupled to the optical collimator 113 (optical path 3). The light beam group output from the optical collimator 112 is reflected by the optical splitters 122 and 124 at a predetermined reflectance, and further passes through the optical splitter 123 at a predetermined transmittance and is coupled to the optical collimator 113 (optical path 4).

[0032] The MCF connection device 200 having such a configuration can split and couple optical signals propagating through the MCFs 101-104 without using a FIFO. This is because the MCF connection device 200 couples the MCFs 101-104 for each core via an optical system using the optical collimators 111-114, and has optical splitters 121-124 between the optical collimators 111-114.

[0033] 5 to 7, a loopback circuit using the MCF connecting device 200 will be described. Fig. 5 is a diagram showing an example of a configuration in which the optical splitters 121 and 123 are extracted from the MCF connecting device 200. As will be described below, the optical splitters 121 and 122 can be used to loop back light in a wavelength band including the monitor light from the MCF 101 to the MCF 103.

[0034] FIG. 6 shows an example of wavelength characteristics of the optical splitter 121. The transmittance of the wavelength band W1 (first wavelength band) of the optical splitter 121 is 100%, and the transmittance of the wavelength band W2 (second wavelength band) is 90%. The range of the wavelength band W1 is from λ1 to less than λ2, and the range of the wavelength band W2 is from λ2 to less than λ3. In this disclosure, a transmittance of 100% indicates that the transmission loss in the optical splitter 121 is small enough to be negligible. The optical splitter 123 is a half mirror with a transmittance of 90% (i.e., a reflectance of 10%). In this disclosure, the term "half mirror" is also used in cases where the transmittance is other than 50%.

[0035] The light propagating through the MCF 101 may include signal light and supervisory light. The signal light is an optical signal including user data, and is transmitted from n optical transmitters connected to the other end of the MCF 101 to each of the n cores. n is the number of cores in each of the MCFs 101-104. The signal light is transmitted independently using the n cores of the MCF 101. Wavelength band W1 is used to transmit the signal light. Wavelength band W2 is used to transmit the signal light or supervisory light. Wavelength band W1 and wavelength band W2 do not overlap. The wavelength characteristics in FIG. 6 show that the optical splitter 121 splits collimated light of a specified wavelength at a splitting ratio different from other wavelengths. This specified wavelength is a wavelength band including supervisory light.

[0036] The signal light is a WDM (wavelength division multiplexing) signal in which multiple carriers are wavelength-multiplexed. The monitor light is an optical signal used for monitoring the optical transmission line and does not include user data. The monitor light is looped back from the MCF 101 to the MCF 103 by the MCF connection device 200. The monitor light is transmitted by only one carrier having a wavelength of λ21. The allocation of the signal light and the monitor light to the wavelength bands W1 and W2 differs for each core. Note that, in general, the MCF transmission line is monitored for each MCF. For this reason, only one core out of the multiple cores included in the MCF 101 is used for transmitting the monitor light. That is, in the MCFs 101-104, the wavelength band of the monitor light is assigned to only one core. In a core in which the wavelength band W2 is used for transmitting the monitor light, the wavelength band W2 is not used for transmitting the signal light. In a core in which the wavelength band W2 is not used for transmitting the monitor light, the wavelength band W2 may be used for transmitting the signal light.

[0037] In FIG. 5, the optical signal propagated through the MCF 101 is converted into a group of light rays in the optical collimator 111. The monitor light is transmitted by one core of the MCF 101. That is, the monitor light is included in one collimated light in the group of light rays. In FIG. 5, three collimated lights are illustrated as an example, and only one of the three collimated lights, the central one, contains the monitor light. In the collimated light containing the monitor light, the signal light is transmitted using only the wavelength band W1. In the other two collimated lights, the signal light is transmitted using the wavelength bands W1 and W2. The optical splitter 121 reflects the light in the wavelength band W2, which is the wavelength band containing the monitor light, with a reflectance of 10%, and outputs it in the direction of the optical splitter 123. The optical splitter 121 transmits the light in the wavelength band W1, which is the wavelength band not containing the monitor light, with a transmittance of 100%, and outputs it in the direction of the optical splitter 122. The optical splitter 123 reflects the light in the wavelength band W2 reflected by the optical splitter 121 with a reflectance of 10% and outputs the light to the optical collimator 113. At this time, the optical splitter 123 combines a group of rays propagating from the MCF 104 to the MCF 103 with a group of rays reflected by the optical splitter 121, and outputs the combined group of rays to the optical collimator 113.

[0038] The MCF connection device 200 having such a configuration can connect the MCF 104 and the MCF 102 for each core, and can loop back the monitor light propagated through the MCF 101 to the MCF 103. Here, the reflectance of the optical splitter 121 and the optical splitter 123 for the monitor light is both 10% (loss 10 dB), so the loss of the looped back monitor light is about 20 dB in total. This is equivalent to the loss of the monitor light in a general loopback circuit. Therefore, by connecting a general optical receiver to the other end of the MCF 103, the monitor light can be detected by the optical receiver. Note that, among the light propagating through the MCF 102, the light transmitted as collimated light to be combined with the monitor light in the optical splitter 123 is set in advance not to use the wavelength band W2.

[0039] 5, even if any of the collimated lights output from the optical collimator 111 contains signal light in the wavelength band W2, the signal light in the wavelength band W2 is reflected by the optical splitter 121 with a reflectance of 10%. Then, the light reflected by the optical splitter 121 is combined with the collimated light propagating through the MCF 104 by the optical splitter 123. Here, there may be cases where the light reflected by the optical splitter 121 and the signal light of the collimated light propagating from the MCF 104 to the MCF 103 both use the wavelength band W2 and are directed toward the same core of the MCF 103. In such a case, there is a risk of interference of signal light in the collimated light directed toward that core.

[0040] In order to avoid such interference, it is preferable to propagate only collimated light including the monitor light from the optical splitter 121 to the optical splitter 123. For example, the MCF connection device 200 may have a configuration in which only collimated light including the monitor light to be looped back (hereinafter referred to as monitor collimated light) is transmitted from the optical splitter 121 to the optical splitter 123. With such a configuration, it is possible to prevent the signal light of the wavelength band W2 propagated through the MCF 101 from being coupled with the light of the wavelength band W2 propagated through the MCF 104 in the optical splitter 123. As described above, with regard to the light input from the MCF 104 to be coupled with the monitor light in the optical splitter 123, it is set in advance so that the signal light does not use the wavelength band W2.

[0041] FIG. 7 shows an example in which the portion related to the optical splitter 121 shown in FIG. 5 is modified. In this modification, a shielding portion 141 is provided between the optical splitter 121 and the optical splitter 123. The shielding portion 141 has an aperture (opening). The aperture propagates only the monitoring collimated light from the optical splitter 121 to the optical splitter 123 and blocks other light. The shielding portion 141 is, for example, an opaque plate disposed between the optical splitter 121 and the optical splitter 123 and having a small hole only at the position where the monitoring collimated light is incident. That is, the shielding portion 141 outputs only the monitoring collimated light from the group of light rays reflected by the optical splitter 121. Alternatively, the shielding portion 141 may be a thin film formed on an end face of a prism integrated with the optical splitter 121 or 123. The thin film is transparent to the wavelength λ21 of the monitor light only at the position where the collimated monitor light propagates, and other portions are opaque to the wavelength bands W1 and W2. With this configuration, the optical splitter 121 can output only collimated light including the monitor light to the optical splitter 123, thereby preventing signal lights of wavelength band W2 from being coupled together in the optical splitter 123. Therefore, the configuration of Fig. 7 can prevent interference caused by the signal light from the MCF 101 being looped back to a core in the MCF 103 other than the core used for looping back the monitor light.

[0042] The optical splitter 121 and the optical splitter 123 may be connected by an optical waveguide capable of propagating the collimated monitor light. This makes it possible to suppress the influence of stray light existing between the optical splitter 121 and the optical splitter 122 on the monitor light.

[0043] Fig. 8 is a diagram showing an example of a configuration in which the optical splitters 122, 123, and 124 are extracted from the MCF connection device 200. In Fig. 8, an optical path (optical path 4 in Fig. 4) between the optical collimator 112 and the optical collimator 113 via the optical splitters 122, 123, and 124 will be described. For simplicity, Fig. 8 shows only the test light input from the MCF 101 and the return light generated corresponding to the test light.

[0044] 8, the optical splitter 122 is an optical filter having the wavelength characteristics shown in FIG. 6, and the optical splitters 123 and 124 are half mirrors with a transmittance of 90%. That is, the transmittance of the optical splitter 122 in the wavelength band W1 is 100%, and the transmittance of the wavelength band W2 is about 90%. As described below, the optical splitter 122 is used to guide light (return light) propagating through the MCF 102 in the opposite direction to the signal light from the MCF 102 to the MCF 103.

[0045] In an optical fiber transmission line, return light may propagate in the opposite direction to the propagating light. The return light is generated due to a nonlinear phenomenon occurring in the optical fiber. A technique is known for monitoring the state of the optical fiber transmission line by transmitting test light (optical pulse) to the optical fiber transmission line and analyzing the generated return light. For such monitoring, it is preferable to input test light from an optical transmitter of an OTDR (optical time domain reflectometer) connected to the MCF 101 and analyze the return light using an optical receiver connected to the MCF 102. Since the MCFs 101 and 102 are housed in the same MCF cable 105, the optical transmitter and receiver of the OTDR can be installed in the same station.

[0046] 8, return light propagating through the MCF 102 in the opposite direction to the test light is guided to the MCF 103 via an optical collimator 113. The return light is then detected by an optical receiver of an OTDR connected to the other end of the MCF 103. By analyzing the detected return light, information regarding the state of the MCF 102 and the optical fiber transmission line beyond it can be obtained.

[0047] In general, the wavelength λ22 of the return light caused by the nonlinear phenomenon is different from the wavelength of the test light. In addition, in Fig. 8, the wavelength of the test light is set so that the wavelengths of the test light and the return light are both within the wavelength band W2. If the wavelength λ22 of the return light is within the wavelength band W2, the wavelength of the test light may be λ21, the same as that of the monitoring light.

[0048] The test light is input to one core selected by the OTDR among the multiple cores included in the MCF 101. When observing the return light, the transmission of the signal light using the core through which the test light and the return light propagate may be stopped. The return light propagating through the MCF 102 is converted into collimated light for each core by the optical collimator 112. The optical splitter 122 reflects light in a wavelength band W2, which is a wavelength band including the return light, and outputs it toward the optical splitter 124. The optical splitter 124 combines the optical signal propagating from the MCF 104 to the MCF 103 and the return light reflected by the optical splitter 122 for each collimated light, and outputs the combined collimated light to the optical splitter 123. The core for observing the return light is the same core as the core for transmitting the test light, and is one of the multiple cores of the MCF 102.

[0049] 8 combines the return light input from the optical splitter 124 and the test light reflected at the optical splitter 121 for each collimated light, and outputs the combined collimated light to the optical collimator 113. The optical collimators 111-114 are optically connected so that the above-mentioned effect is obtained by combining the cores of the MCFs 101-104.

[0050] 3, the MCF connecting device 200 can connect the cores of the MCFs 101-104 one-to-one. The MCF connecting device 200 can guide the return light propagated through the MCF 102 to the MCF 103. By connecting an OTDR optical receiver to the other end of the MCF 103, the optical receiver can receive the return light and monitor the state of the MCF 102.

[0051] (Third embodiment) An MCF transmission system using an MCF-connected device 200 will be described. FIG. 9 is a diagram showing a configuration example of an MCF transmission system 1 according to the present disclosure. The MCF transmission system 1 includes an MCF transmission line 11-14, an MCF-connected device 200, an optical repeater 30, and optical transceivers 21 and 22. The MCF transmission line 11-14 is connected to the MCF-connected device 200 via MCFs 101-104, respectively. In this figure, the MCF transmission line 11-14 and the MCF-connected device 200 include a 7-core MCF. The MCFs 101-104 are described as an interface that connects the MCF transmission line 11-14 and the MCF-connected device 200. The MCF transmission line 11-14 and the MCFs 101-104 may be connected to each other by fusion splicing or optical connectors.

[0052] The optical transceiver 21 includes seven optical transmitters Tx1-Tx7, seven optical receivers Rx1-Rx7, and FIFOs 211 and 212. The seven optical transmitters included in the optical transceiver 21 are connected to different cores of the MCF transmission line 11 using the FIFO 211. The seven optical receivers included in the optical transceiver 21 are connected to different cores of the MCF transmission line 13 using the FIFO 212. The optical transmitters and optical receivers of the optical transceiver 22 are similarly connected to the MCF transmission lines 12 and 14 using FIFOs 221 and 222.

[0053] The signal lights transmitted from the optical transmitters Tx1-Tx7 (first optical transmitters) of the optical transceiver 21 are received by the optical receivers Rx1-Rx7 (second optical receivers) of the optical transceiver 22. Also, the signal lights transmitted from the optical transmitters Tx1-Tx7 (second optical transmitters) of the optical transceiver 22 are received by the optical receivers Rx1-Rx7 (first optical receivers) of the optical transceiver 21.

[0054] The optical transceiver 21 transmits downstream signal light to seven cores of the MCF transmission line 11. The downstream signal light is transmitted from the MCF transmission line 11 to the MCF transmission line 12 and received by the optical transceiver 22. The optical transceiver 22 transmits upstream signal light to seven cores of the MCF transmission line 14. The upstream signal light is transmitted from the MCF transmission line 14 to the MCF transmission line 13 and received by the optical transceiver 21. The optical repeater 30 includes two MCF optical amplifiers using MCF as an amplification medium, one of which amplifies downstream light and the other of which amplifies upstream light. The MCF optical amplifiers are directly connected to the MCF transmission line 11, the MCF transmission line 13 and the MCF connecting device 200 without going through a FIFO. The MCF connecting device 200 has the configuration described in the second embodiment.

[0055] 9, downstream signal light transmitted by Tx1 of the optical transceiver 21 is amplified by the optical repeater 30, passes through the MCF connecting device 200 via optical path 1 in FIG. 4, propagates through the MCF transmission line 12, and is received by Rx1 of the optical transceiver 22. Upstream signal light transmitted by Tx1 of the optical transceiver 22 passes through the MCF connecting device 200 via optical path 3 in FIG. 4, propagates through the optical repeater 30 and the MCF transmission line 13, and is received by Rx1 of the optical transceiver 21.

[0056] On the other hand, when Tx1 of the optical transceiver 21 transmits downstream monitoring light, a part of the downstream monitoring light is amplified by the optical repeater 30 and then looped back to the MCF transmission line 13 via the optical path 2 in Fig. 4. Alternatively, when an OTDR is connected to the core to which Tx1 was connected in the optical transceiver 21 to output test light, return light generated due to the downstream test light propagating through the MCF transmission line 12 propagates from the MCF transmission line 12 to the MCF transmission line 13 via the optical path 4 in Fig. 4. The return light propagated through the MCF transmission line 13 is received by the optical transceiver 21 from the core connected to Rx1.

[0057] In this way, in addition to the upstream signal light, the looped-back supervisory light and the return light generated in the MCF transmission line 12 are input to the optical transceiver 21 from the MCF transmission line 13. With this configuration, the optical transceiver 21 can receive the downstream supervisory light or the return light from the MCF transmission line 12 in addition to the upstream signal light.

[0058] In the MCF transmission system 1, when a FIFO is used in the loopback circuit, it is necessary to increase the output of the optical repeater 30 to compensate for the loss of the FIFO, which increases the power consumption of the optical repeater 30. From this viewpoint, it is preferable that the optical circuit that guides the monitor light and return light to the optical receiver does not use a FIFO in order to reduce the insertion loss of the optical circuit.

[0059] In the MCF transmission system 1, an MCF connection device 200 is used as an optical circuit that enables the optical receiver to receive the monitoring light and the return light. The MCF connection device 200 can branch the light propagating through each core of the MCF transmission lines 11-14 and couple it with the core of another MCF without using a FIFO. Therefore, by using the MCF connection device 200, the MCF transmission system 1 can couple the monitoring light and the return light with the signal light without using a FIFO.

[0060] (Fourth embodiment) FIG. 10 is a diagram showing a configuration example of an MCF transmission system 2 according to the present disclosure. The MCF transmission system 2 is obtained by adding an MCF connection device 201 to the MCF transmission system 1 shown in FIG. 9. The MCF connection device 201 provides the optical transceiver 22 with the function of the MCF connection device 200 related to the optical transceiver 21. That is, the MCF connection device 201 configures a loopback circuit of the monitoring light transmitted by the optical transceiver 22, and guides the return light propagating through the MCF transmission line 13 toward the optical transceiver 22 to the optical transceiver 22 via the MCF transmission line 12. The configuration of the MCF connection device 201 in the MCF transmission system 2 is the same as that of the MCF connection device 200. The arrangement of the MCF connection device 201 in FIG. 10 is such that the MCF connection device 200 in FIG. 9 is applied to light in the reverse direction. For this reason, detailed description will be omitted.

[0061] With this configuration, the optical transceiver 22 connected to the MCF transmission line 12 can receive, in addition to the downstream signal light, the monitor light looped back from the MCF transmission line 14 and the return light propagating through the MCF transmission line 13 in the opposite direction to the upstream signal light. With this configuration, the MCF transmission system 2 can monitor the monitor light and return light in both the downstream and upstream directions.

[0062] Fifth embodiment 11 is a diagram showing a configuration example of an MCF transmission system 3 according to the present disclosure. In the MCF transmission system 3, optical repeaters 31-33 are arranged between the optical transceiver 21 and the optical transceiver 22 in a cascade connection. Each of the optical repeaters 31-33 includes two MCF optical amplifiers 34. One of the two MCF optical amplifiers 34 amplifies downstream light, and the other amplifies upstream light. The optical repeaters 31-33 include the MCF connection devices 200 and 201 described in the MCF transmission system 2 before and after the MCF optical amplifier 34. With this configuration, the MCF transmission system 3 can transmit the monitoring light and the return light propagating through the sections before and after each of the optical repeaters 31-33 to the optical transceiver 21 or 22. As a result, the MCF transmission system 3 can monitor the MCF transmission lines in the sections before and after each of the optical repeaters 31-33.

[0063] In addition, the embodiment of the present disclosure can be described as follows, but is not limited to the following.

[0064] (Appendix 1) A first MCF, a second MCF, and a third MCF, each of which is a multicore fiber (MCF) having a plurality of cores; a first optical collimator that generates a group of light beams obtained by converting each of the light beams output from the multiple cores of the first MCF into a collimated beam on a one-to-one basis; a first optical splitter that splits at least a portion of the group of light beams into a first direction and a second direction different from the first direction at a predetermined splitting ratio; a second optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the first direction with a plurality of cores of the second MCF in a one-to-one relationship; a third optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the second direction with a plurality of cores of the third MCF in a one-to-one relationship; 1. An MCF connection device comprising:

[0065] (Appendix 2) 2. The MCF connection device of claim 1, wherein the collimated light beams included in the light beam groups do not overlap each other.

[0066] (Appendix 3) 3. The MCF connection device according to claim 1, wherein the first optical splitter splits collimated light of a predetermined wavelength from the collimated light included in the group of rays at a splitting ratio different from other wavelengths.

[0067] (Appendix 4) 4. The MCF connection device according to claim 3, wherein the predetermined wavelength is a wavelength band including a monitoring light.

[0068] (Appendix 5) 3. The MCF connection device according to claim 1, wherein the first optical splitter splits only collimated light including a monitor light from among collimated light included in the group of rays.

[0069] (Appendix 6) 6. The MCF connection device of claim 5, wherein the first optical splitter has an opening that transmits only collimated light including the monitor light.

[0070] (Appendix 7) The fourth MCF, a fourth optical collimator that generates a group of light beams obtained by converting each of the light beams output from the plurality of cores of the fourth MCF into a collimated beam on a one-to-one basis; a second optical splitter that combines the light beam group split in the second direction with the light beam group generated in the fourth optical collimator; the third optical collimator couples each of the plurality of collimated lights combined by the second optical splitter to a plurality of cores of the third MCF in a one-to-one relationship; 6. An MCF connection device according to any one of claims 1 to 5.

[0071] (Appendix 8) a third optical splitter; the second optical collimator generates a group of light rays by converting each of the light beams output from the multiple cores of the second MCF into a collimated beam on a one-to-one basis; the third optical splitter combines the group of light rays generated in the second optical collimator with the group of light rays generated in the fourth optical collimator; MCF connection devices as described in Appendix 7.

[0072] (Appendix 9) The third optical splitter comprises: a fourth optical splitter disposed between the first optical collimator and the second optical collimator, the fourth optical splitter redirecting the light beams generated by the second optical collimator; a fifth optical splitter that combines the group of light rays redirected in the fourth optical splitter with the group of light rays generated in the fourth optical collimator; 9. The MCF connection device of claim 8, comprising:

[0073] (Appendix 10) an optical transmitter that transmits a signal light to the first MCF; an optical receiver that receives a signal light from the third MCF; An MCF transmission system comprising an MCF connection device according to any one of claims 1 to 8.

[0074] (Appendix 11) a first optical transmitter that transmits a signal light to the first MCF; a first optical receiver for receiving a signal light from the third MCF; a second optical transmitter that transmits a signal light to the fourth MCF; a second optical receiver that receives a signal light from the second MCF; An MCF transmission system comprising an MCF connection device according to any one of claims 1 to 8.

[0075] (Appendix 12) A method for connecting a first MCF, a second MCF, and a third MCF, each of which is a multicore fiber (MCF) having a plurality of cores, comprising the steps of: generating a light beam group by converting each of the light beams output from the multiple cores of the first MCF into a collimated beam on a one-to-one basis; branching at least a portion of the light beam group into a first direction and a second direction different from the first direction at a predetermined branching ratio; a plurality of collimated light beams included in the light beam group output in the first direction are coupled one-to-one with a plurality of cores of the second MCF; Each of the plurality of collimated beams included in the group of beams output in the second direction is coupled to a plurality of cores of the third MCF in a one-to-one relationship. How to connect to MCF.

[0076] (Appendix 13) 13. The MCF connection method according to claim 12, wherein the collimated light beams included in the light beam group are arranged so as not to overlap each other.

[0077] (Appendix 14) 14. The MCF connection method according to claim 12 or 13, wherein among the collimated light included in the group of rays, collimated light of a predetermined wavelength is branched at a branching ratio different from that of other wavelengths.

[0078] (Appendix 15) 15. The MCF connection method according to claim 14, wherein the predetermined wavelength is a wavelength band including a monitoring light.

[0079] (Appendix 16) 16. The MCF connection method according to claim 14 or 15, wherein only collimated light including a monitor light is branched out from among the collimated light included in the light beam group.

[0080] (Appendix 17) 17. The MCF connection method according to claim 16, wherein an opening transmits only collimated light including the monitor light.

[0081] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above 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. For example, the present disclosure can be applied to not only optical submarine cable systems but also terrestrial optical transmission systems. In addition, the description of the MCF connection device in each embodiment also discloses the configuration of an MCF transmission system including the MCF connection device and an MCF connection method.

[0082] In addition, the configurations described in the respective embodiments are not necessarily mutually exclusive. The actions and effects of the present disclosure may be achieved by a configuration that combines all or part of the above-described embodiments. [Explanation of symbols]

[0083] 1-3 MCF transmission system 11-14 MCF transmission line 21, 22 Optical transceiver 211, 212, 221, 222 FIFO 30-33 Optical repeater 34 MCF Optical Amplifier 100, 200, 201 MCF connected devices 101-104 MCF 105, 106 MCF cable 111-114 Optical collimator 115 Lens 121-124 Optical splitter 141 Shielding part Rx1-Rx7 Optical receiver Tx1-Tx7 Optical Transmitter

Claims

1. A first MCF, a second MCF, and a third MCF, each of which is a multicore fiber (MCF) having a plurality of cores; a first optical collimator that generates a group of light beams obtained by converting each of the light beams output from the plurality of cores of the first MCF into a collimated beam on a one-to-one basis; a first optical splitter that splits at least a portion of the group of light beams into a first direction and a second direction different from the first direction at a predetermined splitting ratio; a second optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the first direction with a plurality of cores of the second MCF in a one-to-one relationship; a third optical collimator that couples each of a plurality of collimated light beams included in the group of light beams output in the second direction with a plurality of cores of the third MCF in a one-to-one relationship; 1. An MCF connection device comprising:

2. The MCF connection device of claim 1 , wherein the collimated light beams included in the light beam groups do not overlap each other.

3. 3. The MCF connection device according to claim 1, wherein the first optical splitter splits collimated light of a predetermined wavelength from among the collimated light contained in the light beam group at a splitting ratio different from that of other wavelengths.

4. 4. The MCF connection device according to claim 3, wherein the predetermined wavelength is a wavelength band including a monitor light.

5. 3. The MCF connection device according to claim 1, wherein the first optical splitter splits only collimated light including a monitor light from among the collimated light included in the light beam group.

6. The MCF connection device of claim 5 , wherein the first optical splitter has an opening that transmits only collimated light including the monitor light.

7. A fourth MCF; and a fourth optical collimator that generates a group of light beams obtained by converting each of the light beams output from the plurality of cores included in the fourth MCF into a collimated beam on a one-to-one basis; a second optical splitter that combines the group of rays split in the second direction with the group of rays generated in the fourth optical collimator; the third optical collimator couples each of the plurality of collimated lights combined by the second optical splitter to a plurality of cores of the third MCF in a one-to-one relationship; 3. An MCF connection device according to claim 1 or 2.

8. a third optical splitter; the second optical collimator generates a group of light rays by converting each of the light beams output from the multiple cores included in the second MCF into a collimated light beam on a one-to-one basis; the third optical splitter combines the group of light rays generated in the second optical collimator with the group of light rays generated in the fourth optical collimator; 8. The MCF connection device of claim 7.

9. The third optical splitter comprises: a fourth optical splitter disposed between the first optical collimator and the second optical collimator, the fourth optical splitter redirecting the light beams generated by the second optical collimator; a fifth optical splitter combining the group of light rays redirected in the fourth optical splitter with the group of light rays generated in the fourth optical collimator; 9. The MCF connection device of claim 8, comprising:

10. A method for connecting a first MCF, a second MCF, and a third MCF, each of which is a multicore fiber (MCF) having a plurality of cores, comprising the steps of: generating a light beam group by converting each of the light beams output from the plurality of cores of the first MCF into a collimated light beam on a one-to-one basis; At least a part of the group of light rays is branched into a first direction and a second direction different from the first direction at a predetermined branching ratio; a plurality of collimated light beams included in the group of light beams output in the first direction are coupled one-to-one with a plurality of cores of the second MCF; a plurality of collimated light beams included in the group of light beams output in the second direction are coupled one-to-one with a plurality of cores of the third MCF; How to connect MCF.

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