JP2020014113A - Optical communication system and connection device of the optical communication system - Google Patents

Abstract

To provide a technique for equalizing between cores without deteriorating the quality of the entire system.SOLUTION: An optical communication system has a first communication device, a second communication device, an optical transmission line to be divided into M sections, and (M-1) connection devices for connecting two adjoining sections out of the M sections, respectively. The optical transmission line transmits optical signals, respectively, in N cores (N is an integer of 2 or more), a first optical communication device is connected with a first section out of the M sections, a second optical communication device is connected with an M-th section out of the M sections, a k-th connection device (k is an integer of 1 through (M-1)) in the (M-1) connection devices connects a k-th section and a (k+1)th section out of the M sections, and the k-th connection device includes connection means for connecting a core of the highest total gain from the first section to the k-th section, out of th N cores in the k-th section, and a core of the lowest gain out of th N cores in the (k+1)th section.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an equalization technique between cores for transmitting an optical signal in an optical communication system.

  As disclosed in Non-Patent Documents 1 to 3, in a wavelength division multiplexing optical communication system, a gain deviation of an optical signal of each wavelength is compensated using a gain equalizer after a plurality of stages of relay transmission.

Optical Submarine Cable Writing Committee, "Optical Submarine Cable", ISBN 978-4-4344-1494-3, pp102-105 H. Takahashi et al. , "First demonstration of MC-EDFA-repeated SDM transmission of 40x128-Gbit / s PDM-QPSK signals per core over 6,160-km 7-core MCF", Optics. 21, Issue 1, pp. 789-795, 2013 Roland Ryf et al,. "Long-Distance Transmission over Coupled-Core Multicore Fiber", 42nd European Conference and Exhibition on Optical Communications (ECOC2016), TH. 3. C. 3, PDP, 2016

  For example, in a wavelength division multiplexing optical communication system using a multi-core optical fiber, when a future modulation scheme is changed or a path is set using the optical communication system, the quality depends on the core and wavelength in which the path is accommodated. In order to suppress the difference in the optical signal, it is desired to make not only the optical signals of different wavelengths in the same core but also the optical signals of different wavelengths between different cores uniform. For example, it is assumed that the power of the optical signal of each wavelength of each core at a certain position in an optical communication system using a multi-core optical fiber having three cores is as shown in FIG. In FIG. 1A, a square indicates the power of the optical signal of each wavelength of the first core, a triangle indicates the power of the optical signal of each wavelength of the second core, and a circle indicates the power of the optical signal of each wavelength of the third core. It shows the power of the signal. In the configurations of Non-Patent Documents 1 to 3, the powers of the optical signals in the same core are made equal as shown in FIG. 1B, but equalization is performed independently between the cores, so that the optical The signal quality will be different.

  The simplest configuration for equalizing the quality between the cores is to attenuate the optical signals of the other cores in accordance with the core having the weakest optical signal power. That is, in the state of FIG. 1B, the power of each optical signal of the first core and the second core is attenuated so as to be the same as the power of the optical signal of the third core indicated by a circle. However, such a configuration degrades the quality of the entire optical communication system.

  The present invention provides a technique for performing equalization between cores without deteriorating the quality of the entire system.

  According to one aspect of the present invention, an optical communication system connects a first optical communication device, a second optical communication device, the first optical communication device and the second optical communication device, and has M (M is An optical transmission line divided into sections of (2 or more integers), and (M-1) connecting devices connecting each of two adjacent sections of the M sections. The transmission path transmits an optical signal through each of N (N is an integer of 2 or more) cores, and the first optical communication device is connected to a first section of the M sections, and the second optical communication apparatus The device is connected to an Mth section of the M sections, and a kth connection device (k is an integer from 1 to (M-1)) of the (M-1) connection devices is: The k-th section and the (k + 1) -th section of the M sections are connected, and the k-th connection device connects the first section of the N cores of the k-th section. And the highest core total gain of the k-th interval from among the N core of the (k + 1) th interval, characterized in that the gain is provided with a connecting means for connecting the lowest core, the.

  According to the present invention, equalization between cores can be performed without deteriorating the quality of the entire system.

FIG. 4 is a diagram illustrating a conventional method for equalizing optical signals of each wavelength. FIG. 1 is a configuration diagram of an optical communication system according to an embodiment. FIG. 1 is a configuration diagram of an equalizer according to an embodiment. FIG. 7 is an explanatory diagram of a process for determining a correspondence between cores according to the embodiment; FIG. 3 is a system configuration diagram in a direction opposite to the optical communication system in FIG. 2. FIG. 1 is a configuration diagram of an equalizer according to an embodiment. FIG. 2 is a cross-sectional view of a multi-core optical fiber. FIG. 7 is an explanatory diagram of a process for determining a correspondence between cores according to the embodiment;

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiment is an exemplification, and the present invention is not limited to the content of the embodiment. In the following drawings, components not necessary for the description of the embodiment are omitted from the drawings.

<First embodiment>
FIG. 2 is a configuration diagram of a wavelength division multiplexing optical communication system using a multi-core optical fiber according to the present embodiment. The optical transmitter 1 communicates with the optical receiver 2 via the optical transmission line 4. The optical transmission line 4 includes a multi-core optical fiber and an optical amplifier that amplifies a wavelength-division multiplexed optical signal transmitted by each core of the multi-core optical fiber. The optical transmission path 4 is divided into a plurality of blocks (sections). For example, in FIG. 2, the optical transmission line 4 is divided into a total of four blocks, block # 1 to block # 4. Then, two adjacent blocks are connected via an equalizer (connection device) 3. In the example of FIG. 3, since the optical transmission line 4 is divided into four blocks, three equalizers are used. Hereinafter, it is assumed that the optical transmission path 4 is more generally divided into M blocks (M is an integer of 2 or more). In this case, M-1 equalizers 3 are used in the optical communication system. In the following description, it is assumed that the multi-core optical fiber of the optical transmission line 4 has a total of N (N is an integer of 2 or more) cores from a first core to an Nth core. For simplicity of description, the n-th core (n is an integer from 1 to N) of the multi-core optical fiber of the optical transmission line 4 of the block #m (m is an integer from 1 to M) will be described below. It is simply referred to as the n-th core of block #m.

  FIG. 3 is a configuration diagram of the equalizer 3 that connects the block #k (k is an integer from 1 to (M−1)) and the block # k + 1. The equalizer 32-n is connected to the n-th core of the block #k via the fan-out unit 31. The equalizer 32-n suppresses a difference in power of the optical signal of each wavelength transmitted by the n-th core of the block #k. The output port of the equalization unit 32-n is connected to the input port #n of the connection unit 33. On the other hand, the output port #n of the connection unit 33 is connected to the n-th core of the block # k + 1 via the Fan-in unit 34. There is a one-to-one correspondence between the input port and the output port of the connection unit 33, and the wavelength multiplexed optical signal input to the input port #n of the connection unit 33 is output from the corresponding output port.

  As the connection unit 33, a structure for transmitting a wavelength-division multiplexed optical signal or an arbitrary configuration for physically connecting the input port and the corresponding output port by a communication line can be used. The connection unit 33 may be one that can dynamically switch the correspondence between the input port and the output port, or one that cannot dynamically switch. For example, an optical switch can be used as the connection unit 33. In this case, the correspondence between the input port and the output port can be dynamically (ex-post) switched. In addition, the connection unit 33 can be configured to physically connect the input port and the corresponding output port by an optical fiber (waveguide) with a connector. In this case, the correspondence between the input port and the output port cannot be dynamically switched, but can be manually changed afterward by changing the connection of the optical fiber, that is, manually. Further, as the connection unit 33, an optical member having a structure (waveguide) formed such that the wavelength multiplexed optical signal input to each input port is transmitted to the corresponding output port can be used. In this case, the correspondence between the input port and the output port cannot be dynamically switched, and it is necessary to replace the connection unit 33 itself in order to change the correspondence.

  In the present embodiment, the correspondence between the input port and the output port of the connection unit 33 includes the gain (loss) of each core from block # 1 to block #k and the gain (loss) of each core of block # k + 1. Is determined based on Note that the optical transmission line 4 includes an optical amplifier, so that the power of the optical signal output from each block can be increased from the power input to the block, and hence the term “core gain” will be used below. . In this case, the loss is represented by a negative gain. In the present embodiment, there are (k-1) equalizers 3 in blocks # 1 to #k, and in the connection unit 33 of each equalizer 3, the n-th core of a block is Is connected to any one of the first core to the Nth core of the block. That is, the optical signal output from the n-th core of the block #k is not necessarily propagated through the n-th core of the blocks # 1 to # (k-1). Hereinafter, a case where a first-power optical signal is input to the core of block # 1 connected to the n-th core of block #k, and a second-power optical signal is output from the n-th core of block #k , The ratio of the second power to the first power is denoted as “total gain” of the n-th core of the block #k. The ratio of the second power to the first power when an optical signal of the first power is input to the nth core of the block #k and an optical signal of the second power is output from the nth core of the block #k Is denoted as “gain” of the n-th core of the block #k.

  In the present embodiment, as shown in FIG. 4, the total gain of each core of the block #k is obtained, and each core of the block #k is arranged in descending order of the total gain, that is, in order from the highest total gain to the lowest total gain. , A number corresponding to the rank is assigned to each core of the block #k. Similarly, the gain of each core of the block # k + 1 is obtained, the cores of the block # k + 1 are arranged in ascending order of the gains, that is, in order from the one with the lowest gain to the one with the highest gain, and the core of the block # k + 1 is ranked according to the rank Assign a number. Then, as shown in FIG. 4, it is assumed that the core of block #k to which the same rank is assigned corresponds to the core of block # k + 1. That is, in the case of the order shown in FIG. 4, the first core of the block #k corresponds to the fourth core of the block # k + 1, and therefore, the connection unit 33 connects the input port # 1 and the output port # 4. It is configured like this. Similarly, the fifth core of the block #k corresponds to the second core of the block # k + 1, and thus the connection unit 33 is configured to connect the input port # 5 and the output port # 2.

  Thus, the core with the highest total gain of block #k is connected to the core with the lowest gain of block # k + 1, and the core with the highest total gain of block #k is connected with the second highest gain of block # k + 1. Connect to lower core. More generally, the p-th (p is an integer from 1 to N) high total gain core of block #k is connected to the p-th low gain core of block # k + 1. By connecting in this manner at the connection unit 33 of the equalizer 3, the gain of each core is averaged in the entire section from the optical transmitter 1 to the optical receiver 2, so that the optical signal of each core is Quality averaging, ie, equalization between cores, can be performed. In this embodiment, in order to average the quality of the optical signal of each core, it is not necessary to attenuate the optical signals of the other cores in accordance with the core of the lowest quality (lower gain). The quality of the optical signal of each core can be averaged without deteriorating the quality.

  Subsequently, a method of measuring the gain of each core of each block will be described. First, the measurement of the gain of the core #n of a certain block will be described. The gain of the n-th core is obtained by inputting the measurement optical signal from the input terminal of the n-th core and measuring the measurement optical signal output from the output terminal of the n-th core. For example, an optical signal including a signal having the same wavelength as the wavelength multiplexed optical signal to be used can be used as the measurement optical signal. In this case, the optical power of each wavelength included in the measurement optical signal output from the output terminal of the n-th core is measured, and the gain of each wavelength is obtained. The wavelength gain is the ratio of the power of the output signal of the wavelength to the power of the signal of the input wavelength. The gain of each wavelength can be easily determined by making the power of each wavelength signal included in the measurement optical signal the same. For example, the average value of the gain for each wavelength can be used as the gain of the n-th core. Note that the minimum value or the maximum value, instead of the average value, can be used as the gain of the n-th core. Furthermore, the gain of the n-th core can be the ratio of the power of the entire measurement optical signal output from the n-th core to the power of the entire measurement optical signal input to the n-th core without discriminating the wavelength. Further, instead of using a measurement optical signal including a signal having the same wavelength as the wavelength multiplexed signal to be used, an optical signal including a signal having a predetermined wavelength and a predetermined bandwidth may be used as the measurement optical signal.

  For example, in an optical communication system such as an optical submarine cable system, manufacturing and laying are performed in parallel rather than laying after manufacturing all the optical transmission lines to be used. Hereinafter, a case in which blocks # 1 to #M are manufactured in order will be described. First, when the manufacture of the blocks # 1 and # 2 is completed, the gain of each core of the blocks # 1 and # 2 is measured. Thereby, as described with reference to FIG. 4, the correspondence between the cores of the blocks # 1 and # 2 is determined, and thus the connection of the connection unit 33 of the equalizer 3 that connects the blocks # 1 and # 2. Is determined. Therefore, even if the connection unit 33 performs a fixed connection, the equalizer 3 that connects the block # 1 and the block # 2 can be manufactured at this stage. Next, when the manufacture of the block # 3 is completed, the gain of each core of the block # 3 is measured. The total gain of each core of the block # 2 is obtained by calculation based on the gain of each core of the block # 1 and the gain of each core of the block # 2 in consideration of the determined correspondence. That is, when the first core of the block # 1 corresponds to the fourth core of the block # 2, the total gain of the fourth core of the block # 2 is equal to the gain of the first core of the block # 1 and the gain of the block # 1. 2 as the sum of the gains of the fourth core. Thereafter, when the production of the next block is completed, the same processing is repeated.

  By calculating the total gain of each core of the block #k as described above, even if a block before the block #k is already laid, the connection unit 33 of the equalizer 3 that connects the block #k and the block # k + 1 is connected. The correspondence between the input port and the output port can be determined.

  FIG. 2 shows only a one-way system in the optical communication system. However, in actuality, as shown in FIG. 5, there is a system for performing communication in the opposite direction to that shown in FIG. That is, the optical receiving device 11 is installed at the same location as the optical transmitting device 1, and the optical transmitting device 21 is installed at the same location as the optical receiving device 2. Each block has an optical transmission path 41 in a direction opposite to the optical transmission path 4. In an optical submarine cable system or the like, the multi-core optical fibers of the optical transmission line 4 and the optical transmission line 41 of the same block are housed in the same cable, and the optical amplifier is housed in the same housing. That is, when manufacturing blocks in ascending order from block # 1, there are a system (FIG. 2) in which blocks are manufactured in order from the transmitting side and a system (FIG. 5) in which blocks are manufactured in order from the receiving side. However, the concept of the system manufactured from the receiving side is the same as that of the system manufactured from the transmitting side.

  That is, when the manufacture of the blocks # 1 and # 2 is completed, the gain of each core of the blocks # 1 and # 2 is measured. Thus, the correspondence between the cores of the blocks # 1 and # 2 is determined, and thus the connection of the connection unit 33 of the equalizer 3 that connects the blocks # 1 and # 2 is determined. Next, when the manufacture of the block # 3 is completed, the gain of each core of the block # 3 is measured. The total gain of each core of the block # 2 is obtained by calculation based on the gain of each core of the block # 1 and the gain of each core of the block # 2 in consideration of the determined correspondence. That is, when the first core of the block # 1 corresponds to the fourth core of the block # 2, the total gain of the fourth core of the block # 2 is equal to the gain of the first core of the block # 1 and the gain of the block # 1. 2 as the sum of the gains of the fourth core. Thereafter, when the production of the next block is completed, the same processing is repeated. At this time, the output of the block # 1 in the system shown in FIG. 5 manufactured from the receiving side is the side where the optical receiving device 11 is located, and conversely, the input is the side where the block # 2 is located. That is, the order of the numbers of the blocks from the transmission side to the reception side in the system of FIG. 5 is reverse to that of the system of FIG. 2 manufactured from the transmission side. Further, in the system of FIG. 2 manufactured from the transmitting side, as shown in FIG. 4, the total gain descending order of the block #k is connected to the gain increasing order of the block # k + 1, but it is manufactured from the receiving side. The system of FIG. 5 will connect the output of block # k + 1 to the input of block #k. At this time, the ascending order of the gain of the block # k + 1 is connected to the descending order of the total gain of the block #k.

  In the configuration of FIG. 3, the connection unit 33 is provided on the downstream side of the equalization units 32-1 to 32-N, but the connection unit 33 is connected to the upstream of the equalization units 32-1 and 32-N. It is also possible to adopt a configuration provided on the side. When the optical amplifying device included in each block is provided with an equalizing function for suppressing a difference in the power of the optical signal of each wavelength in the core, the equalizing unit 32 in the equalizing device 3 It is also possible to omit -1-32-N. Further, the present invention can be applied to an optical communication system that transmits a single-wavelength optical signal instead of transmitting a wavelength-multiplexed optical signal in each core. The present invention can be applied to an optical communication system using a plurality of single-core optical fibers, instead of an optical communication system using a multi-core optical fiber, based on the same concept.

<Second embodiment>
Subsequently, the second embodiment will be described focusing on differences from the first embodiment. In the first embodiment, the input port and output port correspondence in the connection unit 33 can be set to an arbitrary relationship. That is, there is no restriction on the 1: 1 correspondence between the input port and the output port. In the present embodiment, the configuration of the connection unit 33 is simplified by limiting the 1: 1 correspondence between the input port and the output port. FIG. 6 is a configuration diagram of the equalizer 3 according to the present embodiment. Note that the same reference numerals are given to the same components as those of the equalizer 3 of the first embodiment shown in FIG. The wavelength multiplexed optical signals output from the equalizers 32-1 to 32-N are input to the corresponding cores of the multi-core optical fiber 35 via the fan-in unit 34. That is, the multi-core optical fiber 35 has a total of N cores from the first core to the N-th core, and the wavelength multiplexed optical signal output from the equalizer 32-n is output to the multi-core optical fiber via the Fan-in unit 34. The signal is input to the n-th core of the optical fiber 35. The multi-core optical fiber 36 also has a total of N cores from the first core to the N-th core, and the n-th core of the multi-core optical fiber 36 is connected to the n-th core of the block # k + 1. In the connection section 33, the multi-core optical fiber 35 and the multi-core optical fiber 36 are connected by, for example, fusion processing.

  In the following, a description will be given assuming that N = 6. FIG. 7 shows multi-core optical fibers 35 and 36 having a total of six cores from a first core to a sixth core. For example, a state in which cores having the same number are connected to each other corresponds to a state in which the relative phase difference between the two multi-core optical fibers 35 and 36 is zero. In the present embodiment, one or both of the two multi-core optical fibers 35 and 36 are rotated in the circumferential direction, thereby giving a relative phase difference and fusing to connect the cores having different numbers, and block #k Of the block # k + 1 and the core of the block # k + 1.

  When N = 6, there are six patterns as shown in FIG. 8 as possible correspondences between the core of block #k and the core of block # k + 1. In the present embodiment, the core with the highest total gain of the block #k is connected to the core with the lowest gain of the block # k + 1. For example, if the core with the highest total gain in block #k is the third core and the core with the lowest gain in block # k + 1 is the first core, pattern # 3 is selected. Note that a configuration may be employed in which the core with the lowest total gain of the block #k and the core with the highest gain of the block # k + 1 are connected. In the connection section 33, the two multi-core optical fibers 35 and 36 are subjected to fusion processing according to the determined pattern.

  In the present embodiment, only the correspondence between one core of the block #k and one core of the block # k + 1 can be determined, whereby the correspondence of the other cores is also determined. That is, as in the first embodiment, it is not possible to appropriately determine the correspondence between all the cores. However, when the number of blocks is large, averaging is performed as a whole, so that the quality of the optical signal of each core can be averaged.

  In the present embodiment, the two multi-core optical fibers 35 and 36 are fusion-bonded in the connection unit 33. However, the configuration may be such that the two multi-core optical fibers 35 and 36 are connected by a connector. Further, the two multi-core optical fibers 35 and 36 are fixed at a predetermined distance so that the cross sections of the corresponding cores face each other, and an optical member such as a lens is used to cope with the wavelength multiplexed optical signal. A configuration in which space propagation is performed between cores may be employed. Further, a configuration in which the connection portion 33 is provided on the upstream side of the fan-out portion 31 may be adopted. Further, in a configuration in which a wavelength multiplexed optical signal is spatially propagated between corresponding cores, it is necessary to separate the first to Nth cores when the equalizers 32-1 to 32-N have the same equalization characteristics. If not, the Fan-out unit 31 and the Fan-in unit 34 can be omitted. Specifically, the multi-core optical fiber 35 is connected to the corresponding core of the multi-core optical fiber of the block #k, and the multi-core optical fiber 36 is connected to the corresponding core of the multi-core optical fiber of the block # k + 1. Then, with the corresponding cores of the multi-core optical fiber 35 and the multi-core optical fiber 36 facing each other, a spatial filter for equalizing wavelengths is arranged between the multi-core optical fiber 35 and the multi-core optical fiber 36. It can also be configured. Further, when the optical amplifying device included in each block is provided with an equalizing function for suppressing a difference in the power of the optical signal of each wavelength in the core, the equalizing device 3 includes a fan-out unit. 31, the equalizers 32-1 to 32-N and the fan-in unit 34 may be omitted. Further, the present invention can be applied to an optical communication system that transmits a single-wavelength optical signal instead of transmitting a wavelength-multiplexed optical signal in each core.

  In the first and second embodiments, the directions of optical signals transmitted by the N cores of the multi-core optical fiber are all the same, but the present invention is not limited to such a configuration. For example, a part of the N cores is a first group, the remaining cores are a second group, and the directions of optical signals transmitted by the cores of the first group and the cores of the second group are opposite to each other. It can also be configured.

  1: optical transmitter, 2: optical receiver, 3: equalizer, 33: connection unit

Claims (10)

A first optical communication device;
A second optical communication device;
An optical transmission line that connects the first optical communication device and the second optical communication device and is divided into M (M is an integer of 2 or more) sections;
(M-1) connecting devices for connecting two adjacent sections of the M sections,
An optical communication system having
The optical transmission path transmits an optical signal through each of N (N is an integer of 2 or more) cores,
The first optical communication device is connected to a first section of the M sections,
The second optical communication device is connected to an Mth section of the M sections,
The k-th connection device (k is an integer from 1 to (M-1)) among the (M-1) connection devices is a k-th section and a (k + 1) -th section of the M sections. And connect
The k-th connection device may include, among the N cores in the k-th section, a core having the highest total gain in the first section to the k-th section, and a core in the N cores in the (k + 1) -th section. An optical communication system comprising: a connection unit that connects the core with the lowest gain. A first optical communication device;
A second optical communication device;
An optical transmission line that connects the first optical communication device and the second optical communication device and is divided into M (M is an integer of 2 or more) sections;
(M-1) connecting devices for connecting two adjacent sections of the M sections,
An optical communication system having
The optical transmission path transmits an optical signal through each of N (N is an integer of 2 or more) cores,
The first optical communication device is connected to a first section of the M sections,
The second optical communication device is connected to an Mth section of the M sections,
The k-th connection device (k is an integer from 1 to (M-1)) among the (M-1) connection devices is a k-th section and a (k + 1) -th section of the M sections. And connect
The k-th connection device includes a core having the lowest total gain in the first section to the k-th section among the N cores in the k-th section, and a N-core in the (k + 1) section. An optical communication system comprising: a connection unit that connects the core with the highest gain.   The connection means of the k-th connection device may be configured such that, of the N cores in the k-th section, the total gain from the first section to the k-th section is the p-th (p is an integer from 1 to N) high. The optical communication system according to claim 1, wherein the core is connected to a core having a p-th lowest gain among the N cores in the (k + 1) th section.   The total gain of the n-th core (n is an integer from 1 to N) of the n-th core of the k-th section from the first section to the k-th section is the gain of the n-th core in the k-th section. And the gain of each of the N cores transmitting the same optical signal transmitted by the n-th core in the k-th section among the N cores in each of the first to (k-1) -th sections. The optical communication system according to any one of claims 1 to 3, wherein: The optical signal transmitted by each of the N cores of the optical transmission line is a wavelength multiplexed optical signal;
The gain of the n-th core in the m-th section (m is an integer from 1 to M) is such that a measurement optical signal including a plurality of wavelengths same as the wavelength multiplexed optical signal is transmitted by the n-th core in the m-th section. The optical communication system according to any one of claims 1 to 4, wherein the gain is the maximum value, the minimum value, or the average value of the gain of each wavelength signal.   The optical communication system according to claim 1, wherein the connection unit includes an optical switch. The connection means,
N input ports connected to each of the N cores in the k-th section;
N output ports connected to each of the N cores in the (k + 1) th section;
N waveguides connecting one of the N input ports and one of the N output ports;
The optical communication system according to any one of claims 1 to 5, further comprising: The connection means,
A first multi-core optical fiber having N cores respectively connected to one of the N cores in the k-th section;
A second multi-core optical fiber having N cores respectively connected to one of the N cores in the (k + 1) th section;
Has,
In the connecting means, the first multi-core optical fiber and the second multi-core optical fiber are subjected to fusion processing, the first multi-core optical fiber and the second multi-core optical fiber are connected by a connector, or 3. The optical communication system according to claim 1, wherein a cross section of the multi-core optical fiber and a cross section of the second multi-core optical fiber are arranged to face each other via an optical member. A first optical communication device;
A second optical communication device;
An optical transmission line that connects the first optical communication device and the second optical communication device and is divided into M (M is an integer of 2 or more) sections;
(M-1) connecting devices for connecting two adjacent sections of the M sections,
Has,
The optical transmission path transmits an optical signal through each of N (N is an integer of 2 or more) cores,
The first optical communication device is connected to a first section of the M sections,
In the optical communication system connected to the M-th section of the M sections, the second optical communication device is a k-th section (k is 1 to (M−1) of the M sections). Integer) and the (k + 1) th section,
The connection device,
Among the N cores in the k-th section, a core having the highest total gain in the first to k-th sections and a core having the lowest gain in the N cores in the (k + 1) -th section. And a connection means for connecting the connection device and the connection device. A first optical communication device;
A second optical communication device;
An optical transmission line that connects the first optical communication device and the second optical communication device and is divided into M (M is an integer of 2 or more) sections;
(M-1) connecting devices for connecting two adjacent sections of the M sections,
Has,
The optical transmission path transmits an optical signal through each of N (N is an integer of 2 or more) cores,
The first optical communication device is connected to a first section of the M sections,
In the optical communication system connected to the M-th section of the M sections, the second optical communication device is a k-th section (k is 1 to (M−1) of the M sections). Integer) and the (k + 1) th section,
The connection device,
Among the N cores in the k-th section, a core having the lowest total gain in the first section to the k-th section and a core having the highest gain in the N cores in the (k + 1) -th section. And a connection means for connecting the connection device and the connection device.

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