Optical transmission system and optical transmission method

Abstract

In optical transmission systems configured to control the optical intensities of optical signals propagating through each core of a multi-core transmission path individually in each optical repeater, since the number of components in the overall optical transmission system increases and the cost increases, the optical transmission system of the present invention includes a multi-core transmission path which is provided with a plurality of cores, and in which optical signals propagate through the plurality of cores, a first optical repeating means for amplifying the optical signals by individually exciting first multi-core optical amplification mediums, and a second optical repeating means for amplifying the optical signals by collectively exciting second multi-core optical amplification mediums, wherein the first optical repeating means is positioned spaced apart from the second optical repeating means by a distance determined on the basis of either a first transmissible distance due to the first optical repeating means and a second transmissible distance due to the second optical repeating means.

Description

[Technical field]

[0001] The present invention relates to an optical transmission system and an optical transmission method, and more particularly to an optical transmission system and an optical transmission method using a multi-core optical fiber. [Background technology]

[0002] The rapid expansion of mobile traffic and video services has created a demand for increased communication capacity in core networks. This demand for increased capacity is likely to continue in the future. Up until now, the expansion of communication capacity has been achieved by using time-division multiplexing and wavelength-division multiplexing technologies. These time-division multiplexing and wavelength-division multiplexing technologies have been applied to optical communication systems using single-core optical fibers.

[0003] In order to further expand communication capacity, spatial multiplexing technology, which is a multiplexing technology of a different dimension from previous multiplexing technologies, has been developed. Spatial multiplexing technologies include multicore technology, which increases the number of cores per optical fiber, and multimode technology, which increases the number of propagation modes. Conventional optical fiber communications use one core and one mode each. Therefore, it is possible to dramatically expand communication capacity by increasing the number of cores and modes.

[0004] There are two optical amplification methods suitable for multi-core optical fibers used in multi-core technology: core pumping and cladding pumping. In the core pumping method, the intensity of the optical signal transmitted through each core is individually amplified using an individual pumping light source for each core. On the other hand, in the cladding pumping method, the intensity of the optical signal transmitted through each core is collectively amplified using a common pumping light source. Furthermore, a hybrid pumping method that combines the core pumping and cladding pumping methods has been proposed.

[0005] An example of such an optical amplifier repeater using a hybrid pumping method is described in Patent Document 1. The related optical amplifier repeater described in Patent Document 1 includes a multimode optical demultiplexer, an individual pumping (core pumping) multi-core optical amplifier, a collective pumping multi-core optical amplifier, a waveform shaper, and a multimode optical multiplexer.

[0006] Here, the collective pumping multi-core optical amplifier is a cladding-pumped multi-core optical amplifier with N=7 channels. The separate pumping multi-core optical amplifier uses multiple optical amplifiers to adjust the amplification amount of each light transmitted through multiple optical transmission paths. And, a related optical amplifier repeater system is configured using multiple related optical amplifier repeaters and multiple optical fibers.

[0007] According to the related optical amplifier repeater, it is possible to obtain the advantages of both power saving and controllability by combining a collective pumping multi-core optical amplifier and an individually pumped multi-core optical amplifier. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2020-9999 A Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, the related optical amplifier repeater system is configured to include an optical amplifier repeater using a hybrid pumping method, which includes a collective pumping multi-core optical amplifier and an individual pumping multi-core optical amplifier, at each repeater point. The collective pumping multi-core optical amplifier and the individual pumping multi-core optical amplifier included in the hybrid pumping method optical amplifier repeater do not have any common components (hardware). Therefore, the hybrid pumping method optical amplifier repeater has more components than a single-core optical repeater, and the optical repeater becomes larger.

[0010] That is, in an optical transmission system that has an optical amplifier repeater using a hybrid pumping method at each repeater point, like the related optical amplifier repeater system, each optical amplifier repeater needs a core pumping laser for the number of cores. In addition, a fan-in / fan-out device for introducing individual pumping lights into each core must be provided for each optical amplifier repeater. This increases the number of components (amount of hardware) in the entire optical transmission system, and increases costs.

[0011] In this way, in an optical transmission system configured to individually control the optical intensity of an optical signal propagating through each core of a multi-core optical transmission line for each optical repeater, there is a problem in that the number of components of the entire optical transmission system increases, resulting in increased costs.

[0012] An object of the present invention is to provide an optical transmission system and an optical transmission method that solve the above-mentioned problems. [Means for solving the problem]

[0013] The optical transmission system of the present invention comprises a multi-core optical transmission line having a plurality of cores through which an optical signal propagates, a first optical repeater means for individually exciting a first multi-core optical amplification medium to amplify the optical signal, and a second optical repeater means for collectively exciting a second multi-core optical amplification medium to amplify the optical signal, wherein the first optical repeater means is located away from the second optical repeater means by a distance determined based on either a first transmission distance achieved by the first optical repeater means or a second transmission distance achieved by the second optical repeater means.

[0014] The optical transmission method of the present invention comprises arranging a first multi-core optical amplifying medium and a second multi-core optical amplifying medium at different positions of a multi-core optical transmission line, propagating an optical signal within multiple cores of the multi-core optical transmission line, individually pumping the first multi-core optical amplifying medium to amplify the optical signal, and collectively pumping the second multi-core optical amplifying medium to amplify the optical signal, wherein the first multi-core optical amplifying medium is located away from the second multi-core optical amplifying medium by a distance determined based on either a first transmittable distance of the optical signal when the first multi-core optical amplifying medium is individually pumped or a second transmittable distance of the optical signal when the second multi-core optical amplifying medium is collectively pumped. Effect of the Invention

[0015] According to the optical transmission system and optical transmission method of the present invention, even if the optical intensity of optical signals propagating through each core of a multi-core optical transmission line is controlled individually, it is possible to suppress an increase in the number of components of the entire optical transmission system. [Brief description of the drawings]

[0016] [Figure 1] 1 is a block diagram showing a configuration of an optical transmission system according to a first embodiment of the present invention. [Figure 2A] 1 is a block diagram showing a configuration of an optical repeater group included in an optical transmission system according to a first embodiment of the present invention. [Figure 2B] FIG. 4 is a block diagram showing another configuration of the optical repeater group included in the optical transmission system according to the first embodiment of the present invention. [Diagram 3] 1 is a block diagram showing a configuration of a first optical repeater included in an optical transmission system according to a first embodiment of the present invention. [Figure 4] 5 is a flowchart illustrating an operation of a first optical repeater included in the optical transmission system according to the first embodiment of the present invention. [Diagram 5] FIG. 2 is a block diagram showing a configuration of a second optical repeater included in the optical transmission system according to the first embodiment of the present invention. [Figure 6]FIG. 2 is a diagram showing the amount of hardware of the entire optical transmission system according to the first embodiment of the present invention for each number of cores in a multi-core optical transmission line. [Figure 7A] FIG. 1 is a block diagram showing a configuration of an optical transmission system according to a related method. [Figure 7B] FIG. 1 is a block diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention, showing the configuration of the optical transmission system in the case where the first possible transmission distance is equal to the second possible transmission distance. [Figure 7C] FIG. 1 is a block diagram for explaining the effect of the optical transmission system according to the first embodiment of the present invention, showing the configuration of the optical transmission system in the case where the second possible transmission distance is half the first possible transmission distance. [Figure 8] FIG. 11 is a block diagram showing a configuration of an optical transmission system according to a second embodiment of the present invention. [Figure 9] 10 is a flowchart illustrating an operation of a control device included in an optical transmission system according to a second embodiment of the present invention. [Figure 10] 10 is a flowchart illustrating another operation of the control device included in the optical transmission system according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0018] [First embodiment] 1 is a block diagram showing a configuration of an optical transmission system 100 according to a first embodiment of the present invention. The optical transmission system 100 includes a multi-core optical transmission line 101, a first optical repeater (first optical repeating means) 110, and a second optical repeater (second optical repeating means) 120.

[0019] The multi-core optical transmission line 101 has multiple cores, and an optical signal propagates through these multiple cores. The first optical repeater 110 individually excites the first multi-core optical amplifying medium to amplify the optical signal. The second optical repeater 120 collectively excites the second multi-core optical amplifying medium to amplify the optical signal. Here, the first optical repeater 110 is located away from the second optical repeater 120 by a distance determined based on either a first transmission distance L1 by the first optical repeater 110 or a second transmission distance L2 by the second optical repeater 120.

[0020] With such a configuration, in the optical transmission system 100 of this embodiment, the first optical repeater 110 can individually control the optical intensity of an optical signal propagating through each core of the multi-core optical transmission line 101. Furthermore, since the second optical repeater 120 is configured to collectively pump the second multi-core optical amplifying medium to amplify an optical signal, the number of pumping light sources is smaller than that of the first optical repeater 110. That is, according to the optical transmission system 100 of this embodiment, even when the optical intensity of an optical signal propagating through each core of the multi-core optical transmission line 101 is individually controlled, an increase in the number of components (amount of hardware) of the entire optical transmission system 100 can be suppressed.

[0021] In an optical transmission system using a multi-core optical transmission line, a loss difference occurs between cores in the multi-core optical fiber due to manufacturing variations and mounting accuracy of a multi-core optical fiber, which is a typical example of a multi-core optical transmission line. Even if such a loss difference is small, in a long-distance optical transmission system having many optical repeaters, it becomes a loss difference that cannot be ignored in the optical transmission system as a whole, and a difference in optical intensity occurs between the cores. The difference in optical intensity between the cores cannot be equalized by a collective pumping (cladding pumping) type optical repeater. However, since the optical transmission system according to the present embodiment is configured to include the first optical repeater 110 of the individual pumping (core pumping) type, the power of the pumped light can be controlled for each core according to the intensity of the optical signal input to the first optical repeater 110. This makes it possible to equalize the optical intensity between the cores.

[0022] In the above-mentioned related optical amplifier repeater system, a hybrid pumping type optical amplifier repeater is provided at each repeater point. In contrast, in the optical transmission system 100 of the present embodiment, the first optical repeater 110 of the individual pumping type and the second optical repeater 120 of the collective pumping type are located at a distance determined based on the transmission distance that the optical repeater can transmit, that is, the span length. That is, the optical transmission system 100 of the present embodiment is configured to perform hybrid pumping on a group basis of multiple optical repeaters, rather than performing hybrid pumping on an optical repeater basis as in the related optical amplifier repeater system. That is, the multi-core optical transmission line is provided with two types of optical repeaters, the first optical repeater and the second optical repeater, and the hybrid pumping method is realized by individual pumping (core pumping) by the first optical repeater and collective pumping (clad pumping) by the second optical repeater.

[0023] Specifically, the first optical repeater 110 and the second optical repeater 120 can be configured to configure an optical repeating means group consisting of at least one first optical repeater 110 and at least one second optical repeater 120. The first optical repeater 110 included in each of the optical repeating means groups can be configured to amplify the optical signal so that the difference in optical intensity of the optical signal between the multiple cores included in the multi-core optical transmission line is reduced. With this configuration, the number of components (amount of hardware) can be reduced while maintaining optical transmission performance by individually controlling the intensity of the optical signal propagating through each core by the first optical repeater 110 of the separately pumped type.

[0024] For example, when the first transmission distance L1 is equal to the second transmission distance L2, the optical repeater group can be an optical repeater group 131 consisting of one first optical repeater 110 and one second optical repeater 120, as shown in Fig. 2A. That is, the first optical repeater 110 and the second optical repeater 120 can be arranged alternately. For example, a core-pumped optical repeater can be installed in the even spans, and a cladding-pumped optical repeater can be installed in the odd spans, so that a hybrid pumping method can be used for even and odd spans.

[0025] Also, when the first transmission distance L1 is longer than the second transmission distance L2, it is possible to use an optical repeater group 132 including at least one first optical repeater 110 and multiple second optical repeaters 120, as shown in FIG. 2B.

[0026] FIG. 3 shows a configuration example of the first optical repeater 110. The first optical repeater 110 includes a first multi-core optical fiber 111, a plurality of core pumping lasers 112, and a fan-in fan-out means 113. The first multi-core optical fiber 111 includes a first multi-core optical amplification medium in each core. As the first multi-core optical fiber 111, a multi-core erbium doped fiber (MC-EDF) can typically be used. Each of the plurality of core pumping lasers 112 generates individual pumping light for individually pumping the first multi-core optical amplification medium. Then, the fan-in fan-out (FIFO) means 113 introduces the individual pumping light into each core of the first multi-core optical fiber. Note that the number of core pumping lasers 112 needs to be the same as the number of cores of the first multi-core optical fiber 111, but FIG. 3 shows a configuration in which the number of cores is four and four core pumping lasers 112 are provided as an example.

[0027] The fan-in fan-out (FIFO) means 113 causes loss in the optical signal. Therefore, in an optical transmission system that includes an optical amplifier repeater including an optical amplifier using an individual pumping (core pumping) method at each relay point, such loss increases, causing a shortening of the transmission distance. In particular, since a submarine optical transmission system requires several hundred optical repeaters in total, the influence of optical loss due to fan-in fan-out (FIFO) is large. However, in the optical transmission system 100 according to the present embodiment, hybrid excitation is performed in groups of a plurality of optical repeaters. Therefore, the number of optical repeaters of the individual pumping (core pumping) type is reduced, and the number of fan-in fan-out (FIFO) units can be reduced, so that optical loss due to fan-in fan-out (FIFO) can be reduced. In addition, since the number of optical repeaters of the individual pumping (core pumping) type is reduced, the number of components that need to be controlled is also reduced, resulting in an effect of simplifying control.

[0028] Next, a description will be given of the operation of the first optical repeater 110. FIG.

[0029] The first optical repeater 110 first monitors the power of an optical signal propagating through multiple cores of the multi-core optical transmission line 101 and input to the first optical repeater 110 for each core (step S11). Then, it is determined whether the power difference between the cores of the input optical signal is within a predetermined allowable error range (step S12). If the difference in input optical power between the cores is not within the predetermined allowable error range (step S12 / NO), the first optical repeater 110 determines that an input error has occurred, generates an alarm signal (step S13), and ends the operation.

[0030] If the difference in input optical power between the cores is within a predetermined tolerance (step S12 / YES), the first optical repeater 110 monitors the power of the output optical signal for each core (step S14). Then, it is determined whether the difference in power of the output optical signal between the cores is within a predetermined tolerance (step S15). If the difference in output optical power between the cores is within a predetermined tolerance (step S15 / YES), the first optical repeater 110 continues to monitor the power of the input optical signal for each core (step S11).

[0031] If the difference in output optical power between the cores is not within a predetermined tolerance (step S15 / NO), the first optical repeater 110 increases or decreases the drive current of the core pumping laser 112 by a predetermined step for each core (step S16). Then, it is determined whether the drive current value of the core pumping laser 112 is within the specification range of each core pumping laser (step S17). If the drive current value of the core pumping laser 112 is within the specification range of each core pumping laser (step S17 / YES), the first optical repeater 110 continuously monitors the power of the output optical signal for each core (step S14).

[0032] If the drive current value of the core pump laser 112 is not within the specification range of each core pump laser (step S17 / NO), the first optical repeater 110 determines that there is an output error, generates an alarm signal (step S18), and terminates operation.

[0033] Through the above operation, the first optical repeater 110 can amplify the optical signal so that the difference in optical intensity of the optical signal between the multiple cores included in the multi-core optical transmission line 101 is reduced.

[0034] 5 shows a configuration example of the second optical repeater 120. The second optical repeater 120 includes a second multi-core optical fiber 121 and a cladding pumping laser 122. The second multi-core optical fiber 121 includes a second multi-core optical amplification medium in each core. As the second multi-core optical fiber 121, a multi-core erbium doped fiber (MC-EDF) can typically be used. The cladding pumping laser 122 generates collective pumping light that collectively pumps the second multi-core optical amplification medium.

[0035] As described above, the optical transmission system 100 of this embodiment is characterized by including two types of optical repeaters: the first optical repeater 110 of an individual pumping (core pumping) type and the second optical repeater 120 of a collective pumping (clad pumping) type. Here, there are no particular limitations on the configurations of the first optical repeater 110 and the second optical repeater 120. Therefore, an existing optical repeater of an individual pumping (core pumping) type can be used as the first optical repeater 110, and an existing optical repeater of a collective pumping (clad pumping) type can be used as the second optical repeater 120.

[0036] Next, the effects of the optical transmission system 100 of this embodiment will be described in more detail.

[0037] Figure 6 shows the amount of hardware required for the entire optical transmission system for each number of cores in the multi-core optical transmission line. The vertical axis shows the amount of hardware (number of components) expressed in arbitrary units, and the horizontal axis shows the number of cores in the multi-core optical transmission line.

[0038] The black circles (●) in the figure indicate the amount of hardware in an optical transmission system using a related method that has an optical amplifier repeater including an optical amplifier using an individual pumping (core pumping) method at each relay point. The white circles (◯) and triangles (▲) in the figure indicate the amount of hardware in the optical transmission system of this embodiment. The white circles (◯) indicate the amount of hardware when the first possible transmission distance L1 and the second possible transmission distance L2 are each equal to the span length L0 in the optical transmission system using the related method. The triangles (▲) indicate the amount of hardware when the first possible transmission distance L1 is equal to the span length L0 in the optical transmission system using the related method, and the second possible transmission distance L2 is half the first possible transmission distance L1.

[0039] 6, it can be seen that the amount of hardware required for the optical transmission system according to this embodiment (white circles (◯) and triangles (▲)) is significantly reduced compared to the optical transmission system according to the related method (black circles (●)). A more detailed explanation will be given below using a specific configuration as an example.

[0040] 7A, a specific example will be described in which five associated optical repeaters 10 are used in an optical transmission system according to the related method, and the number of cores in the multi-core optical transmission line is 10. In this case, since all five associated optical repeaters 10 in the optical transmission system according to the related method are provided with core pumping lasers equal to the number of cores (10), the entire optical transmission system according to the related method requires 50 lasers.

[0041] Next, with reference to Figs. 7B and 7C, a configuration will be described in which one of five optical repeaters is the first optical repeater 110 of the core pumping type, and the other optical repeaters are the second optical repeater 120 of the cladding pumping type in the optical transmission system according to this embodiment. Fig. 7B shows a configuration in which the first transmission distance L1 of the first optical repeater 110 and the second transmission distance L2 of the second optical repeater 120 are equal to the span length L0 in the optical transmission system according to the related method. In this case, the first optical repeater 110 of the core pumping type has 10 core pumping lasers, which is the number of cores (10), and the four second optical repeaters 120 of the cladding pumping type each have one cladding pumping laser, for a total of four. Therefore, the number of lasers required in the entire optical transmission system is 14. In this way, the optical transmission system according to this embodiment can reduce the total number of lasers to be implemented from 50 to 14, compared to the optical transmission system according to the related method.

[0042] FIG. 7C shows the optical transmission system configuration according to this embodiment in the case where the first transmission distance L1 is equal to the span length L0 in the optical transmission system according to the related method, and the second transmission distance L2 is half the first transmission distance L1. In this case, eight second optical repeaters 120 are required, which is twice as many as in the case where the transmission distances L1 and L2 are equal (see FIG. 7B). That is, the first optical repeater 110, which is a core pumping type, has ten core pumping lasers, which is the number of cores (10), and the eight second optical repeaters 120, which are clad pumping types, each have one clad pumping laser, for a total of eight clad pumping lasers. Therefore, the total number of lasers required for the entire optical transmission system is 18. Even in this case, the optical transmission system according to this embodiment can reduce the total number of lasers to be implemented from 50 to 18, compared to the optical transmission system according to the related method. In this way, the total number of lasers to be implemented is reduced from 14 to 18 due to the reduction in the transmission distance by the optical repeaters. However, compared to the case of an optical transmission system using a related method (total number of 50), the impact of the shortened transmission distance due to the optical repeaters on the hardware amount (number of components) of the entire optical transmission system is small.

[0043] Next, the optical transmission method according to this embodiment will be described.

[0044] In the optical transmission method according to the present embodiment, first, a first multi-core optical amplifying medium and a second multi-core optical amplifying medium are arranged at different positions of a multi-core optical transmission line, and an optical signal is propagated in a plurality of cores of the multi-core optical transmission line. Then, the first multi-core optical amplifying medium is pumped individually to amplify the optical signal, and the second multi-core optical amplifying medium is pumped collectively to amplify the optical signal. At this time, the first multi-core optical amplifying medium is located away from the second multi-core optical amplifying medium by a distance determined based on either the first transmittable distance or the second transmittable distance. Here, the first transmittable distance is a transmittable distance of an optical signal when the first multi-core optical amplifying medium is pumped individually. Also, the second transmittable distance is a transmittable distance of an optical signal when the second multi-core optical amplifying medium is pumped collectively.

[0045] As described above, in the optical transmission method of the present embodiment, the first multi-core optical amplifying medium is pumped individually to amplify the optical signal, and the second multi-core optical amplifying medium is pumped collectively at a different position of the multi-core optical transmission line to amplify the optical signal. Therefore, compared with the case where the multi-core optical amplifying medium is pumped individually at each relay point of the multi-core optical transmission line, the number of pumping light sources for individually pumping the multi-core optical amplifying medium can be reduced. That is, according to the optical transmission method of the present embodiment, even if the optical intensity of the optical signal propagating through each core of the multi-core optical transmission line is individually controlled, it is possible to suppress an increase in the number of components (amount of hardware) of the entire optical transmission system.

[0046] In the optical transmission method of the present embodiment, the first multi-core optical amplifying medium and the second multi-core optical amplifying medium may be arranged to configure an optical amplifying medium group consisting of at least one first multi-core optical amplifying medium and at least one second multi-core optical amplifying medium. Also, the individual pumping of the first multi-core optical amplifying medium may include amplifying the optical signal so that a difference in optical intensity of the optical signal between the multiple cores is reduced.

[0047] As described above, according to the optical transmission system 100 and the optical transmission method of this embodiment, even when the optical intensity of an optical signal propagating through each core of a multi-core optical transmission line is controlled individually, it is possible to suppress an increase in the number of components of the entire optical transmission system.

[0048] Second Embodiment Next, a second embodiment of the present invention will be described. Fig. 8 shows the configuration of an optical transmission system 200 according to this embodiment.

[0049] The optical transmission system 200 includes a multi-core optical transmission line 201, a first optical repeater (first optical repeating means) 210, and a second optical repeater (second optical repeating means) 220.

[0050] The multi-core optical transmission line 201 has multiple cores, and an optical signal propagates through these multiple cores. The first optical repeater 210 individually excites the first multi-core optical amplifying medium to amplify the optical signal. The second optical repeater 220 collectively excites the second multi-core optical amplifying medium to amplify the optical signal. Here, the first optical repeater 210 is located away from the second optical repeater 220 by a distance determined based on either a first transmission distance L1 by the first optical repeater 210 or a second transmission distance L2 by the second optical repeater 220.

[0051] The first optical repeater 210 and the second optical repeater 220 configure an optical repeater means group 230 consisting of at least one first optical repeater 210 and at least one second optical repeater 220. In this case, the first optical repeater 210 included in each of the optical repeater means groups 230 amplifies the optical signal so as to reduce the difference in optical intensity of the optical signal between the multiple cores included in the multi-core optical transmission line.

[0052] The configuration up to this point is the same as that of the optical transmission system 100 according to the first embodiment. In the optical transmission system 200 according to this embodiment, the optical repeater group 230 includes a front-stage optical repeater group 231 and a rear-stage optical repeater group 232. Here, the front-stage optical repeater group 231 is located on the front side of the rear-stage optical repeater group 232.

[0053] The front stage first optical repeater (front stage first optical repeating means) 211 is configured to amplify the optical signal so as to reduce the difference in optical intensity of the optical signal between the multiple cores in the rear stage first optical repeater (rear stage first optical repeating means) 212. Here, the front stage first optical repeater 211 is the first optical repeater belonging to the front stage optical repeating means group 231. The rear stage first optical repeater 212 is the first optical repeater belonging to the rear stage optical repeating means group 232.

[0054] By adopting such a configuration, according to the optical transmission system 200 of this embodiment, even when the optical intensity of the optical signal propagating through each core of the multi-core optical transmission line 201 is individually controlled, an increase in the number of components of the entire optical transmission system 200 can be suppressed.

[0055] Next, the operation of the optical transmission system 200 according to the present embodiment will be described. Here, the operation of the control device will be described in the case where the optical transmission system 200 has a control device that controls the front-stage first optical repeater 211 and the rear-stage first optical repeater 212.

[0056] The control device is configured to increase the optical intensity output by the first optical repeater 211 when it determines that the difference in optical intensity between the multiple cores of the optical signal output by the first optical repeater 212 at the rear stage is greater than a predetermined value. The operation of the control device in this case will be described in further detail with reference to the flowchart shown in FIG.

[0057] The control device first monitors the power of the optical signal output by the rear stage first optical repeater 212 for each core (step S21). Then, it determines whether the difference in power between the cores of the optical signal output by the rear stage first optical repeater 212 is within a predetermined allowable error range (step S22). If the difference in output optical power between the cores is within the predetermined allowable error range (step S22 / YES), the control device continues to monitor the power of the optical signal output by the rear stage first optical repeater 212 for each core (step S21).

[0058] If the power difference between the cores of the optical signal output by the rear stage first optical repeater 212 is not within a predetermined allowable error range (step S22 / NO), the control device increases the power of the optical signal output by the front stage first optical repeater 211 (step S23). This reduces the burden on the rear stage first optical repeater 212 when equalizing the difference in output optical power between the cores.

[0059] The control device monitors the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 at this time (step S24). Then, the control device determines whether the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is within the specification range of the rear stage first optical repeater 212 (step S25).

[0060] If the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is within the specification range of the rear stage first optical repeater 212 (step S25 / YES), the control device continuously monitors the power of the optical signal output by the rear stage first optical repeater 212 for each core (step S21). On the other hand, if the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is not within the specification range of the rear stage first optical repeater 212 (step S25 / NO), the control device determines that an error has occurred, generates an alarm signal (step S26), and ends the operation.

[0061] As described above, in the optical transmission system 200 of the present embodiment, the control device controls the rear stage first optical repeater 212 and the front stage first optical repeater 211 located on the front stage side of the rear stage first optical repeater 212 in cooperation with each other. Therefore, even if the difference in output optical power between the cores is large and it is difficult to equalize it by the rear stage first optical repeater 212 alone, it is possible to equalize the difference in output optical power between the cores.

[0062] A case will now be described in which the control device determines that the difference in optical intensity between the multiple cores of the optical signal input to the rear-stage first optical repeater 212 is greater than a predetermined value and that the difference in optical intensity between the multiple cores of the optical signal output by the front-stage first optical repeater 211 is smaller than a predetermined value. In this case, the control device may be configured to increase the optical intensity output by the front-stage first optical repeater 211. The operation of the control device in this case will now be described in further detail with reference to the flowchart shown in FIG.

[0063] The control device first monitors the power of the optical signal input to the rear stage first optical repeater 212 for each core (step S31). Then, it is determined whether the difference in power between the cores of the optical signal input to the rear stage first optical repeater 212 is within a predetermined allowable error range (step S32). If the difference in input optical power between the cores is within the predetermined allowable error range (step S32 / YES), the control device continues to monitor the power of the optical signal input to the rear stage first optical repeater 212 for each core (step S31).

[0064] If the power difference between the cores of the optical signals input to the rear stage first optical repeater 212 is not within the predetermined tolerance (step S32 / NO), an abnormality occurs in an optical repeater or a multi-core optical transmission line located upstream of the rear stage first optical repeater 212. The control device then monitors the power of the optical signal output by the front stage first optical repeater 211 for each core (step S33). Then, it determines whether the power difference between the cores of the optical signals output by the front stage first optical repeater 211 is within the predetermined tolerance (step S34). If the difference in the output optical power between the cores is not within the predetermined tolerance (step S34 / NO), the control device determines that the front stage first optical repeater 211 is not operating normally, generates an error warning (alarm) signal (step S35), and ends the operation.

[0065] If the power difference between the cores of the optical signal output by the front-stage first optical repeater 211 is within a predetermined tolerance (step S34 / YES), it is found that the front-stage first optical repeater 211 is normally performing the operation of equalizing the power difference between the cores. Therefore, in this case, an abnormality occurs in the second optical repeater 220 of the collective pumping (cladding pumping) type located between the front-stage first optical repeater 211 and the rear-stage first optical repeater 212 or in the multi-core optical transmission line. Therefore, the control device increases the power of the optical signal output by the front-stage first optical repeater 211 (step S36). This reduces the burden on the rear-stage first optical repeater 212 when equalizing the output optical power difference between the cores.

[0066] The control device monitors the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 at this time (step S37). Then, the control device determines whether the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is within the specification range of the rear stage first optical repeater 212 (step S38).

[0067] If the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is within the specification range of the rear stage first optical repeater 212 (step S38 / YES), the control device continuously monitors the power of the optical signal input to the rear stage first optical repeater 212 for each core (step S31). On the other hand, if the amount of change in the power of the optical signal input to the rear stage first optical repeater 212 is not within the specification range of the rear stage first optical repeater 212 (step S38 / NO), the control device determines that an error has occurred, generates an alarm signal (step S39), and ends the operation.

[0068] In the optical transmission system 200 of the present embodiment described above, the control device is also configured to control the rear stage first optical repeater 212 and the front stage first optical repeater 211 located on the front stage side of the rear stage first optical repeater 212 in cooperation with each other. Therefore, even if the difference in output optical power between the cores is large and it is difficult to equalize it by the rear stage first optical repeater 212 alone, it is possible to equalize the difference in output optical power between the cores.

[0069] Next, the optical transmission method according to this embodiment will be described.

[0070] In the optical transmission method according to the present embodiment, first, a first multi-core optical amplifying medium and a second multi-core optical amplifying medium are arranged at different positions of a multi-core optical transmission line, and an optical signal is propagated in a plurality of cores of the multi-core optical transmission line. Then, the first multi-core optical amplifying medium is pumped individually to amplify the optical signal, and the second multi-core optical amplifying medium is pumped collectively to amplify the optical signal. At this time, the first multi-core optical amplifying medium is located away from the second multi-core optical amplifying medium by a distance determined based on either the first transmittable distance or the second transmittable distance. Here, the first transmittable distance is a transmittable distance of an optical signal when the first multi-core optical amplifying medium is pumped individually. Also, the second transmittable distance is a transmittable distance of an optical signal when the second multi-core optical amplifying medium is pumped collectively.

[0071] Furthermore, the first multi-core optical amplifying medium and the second multi-core optical amplifying medium are arranged to configure an optical amplifying medium group consisting of at least one first multi-core optical amplifying medium and at least one second multi-core optical amplifying medium, and the individually pumping of the first multi-core optical amplifying medium includes amplifying the optical signal so that a difference in optical intensity of the optical signal between the multiple cores is reduced.

[0072] The configuration up to this point is the same as that of the optical transmission method according to the first embodiment. In the optical transmission method according to this embodiment, the optical amplification medium group includes a front-stage optical amplification medium group and a rear-stage optical amplification medium group, and the front-stage optical amplification medium group is disposed on the front side of the rear-stage optical amplification medium group. When the front-stage first optical amplification medium is individually pumped, the optical signal is amplified so that the difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical amplification medium is reduced. Here, the front-stage first optical amplification medium is a first multi-core optical amplification medium belonging to the front-stage optical amplification medium group. Also, the rear-stage first optical amplification medium is a first multi-core optical amplification medium belonging to the rear-stage optical amplification medium group.

[0073] When the front-stage first optical amplifying medium is individually pumped, if the difference in optical intensity between the multiple cores of the optical signal amplified and output by the rear-stage first optical amplifying medium is greater than a predetermined value, the optical signal can be amplified. Also, if the difference in optical intensity between the multiple cores of the optical signal input to the rear-stage first optical amplifying medium is greater than a predetermined value and the difference in optical intensity between the multiple cores of the optical signal amplified and output by the front-stage first optical amplifying medium is smaller than a predetermined value, the optical signal may be amplified.

[0074] As described above, according to the optical transmission system 200 and the optical transmission method of the present embodiment, even if the optical intensity of the optical signal propagating through each core of the multi-core optical transmission line is individually controlled, it is possible to suppress an increase in the number of components of the entire optical transmission system. Furthermore, even if the difference in output optical power between the cores is large and it is difficult to equalize it using an optical repeater alone, it is possible to equalize the difference in output optical power between the cores.

[0075] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes.

[0076] (Supplementary Note 1) An optical transmission system comprising: a multi-core optical transmission line having a plurality of cores through which an optical signal propagates; a first optical repeater means for individually exciting a first multi-core optical amplification medium to amplify the optical signal; and a second optical repeater means for collectively exciting a second multi-core optical amplification medium to amplify the optical signal, wherein the first optical repeater means is located away from the second optical repeater means by a distance determined based on either a first transmission distance achieved by the first optical repeater means or a second transmission distance achieved by the second optical repeater means.

[0077] (Supplementary Note 2) The optical transmission system according to Supplementary Note 1, wherein the first optical repeater means and the second optical repeater means constitute an optical repeater means group consisting of at least one of the first optical repeater means and at least one of the second optical repeater means, and the first optical repeater means included in each of the optical repeater means groups amplifies the optical signal so that a difference in optical intensity of the optical signal between the multiple cores is reduced.

[0078] (Supplementary Note 3) The optical transmission system according to Supplementary Note 2, wherein the optical repeater means group includes a front-stage optical repeater means group and a rear-stage optical repeater means group, the front-stage optical repeater means group is located on the front side of the rear-stage optical repeater means group, and the front-stage first optical repeater means which is the first optical repeater means belonging to the front-stage optical repeater means group amplifies the optical signal so that a difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical repeater means which is the first optical repeater means belonging to the rear-stage optical repeater means group is reduced.

[0079] (Appendix 4) An optical transmission system as described in Appendix 3, further comprising a control device for controlling the front-stage first optical repeater means and the rear-stage first optical repeater means, wherein the control device increases the optical intensity output by the front-stage first optical repeater means when it determines that a difference in optical intensity between the multiple cores of the optical signal output by the rear-stage first optical repeater means is greater than a predetermined value.

[0080] (Supplementary Note 5) An optical transmission system as described in Supplementary Note 3, further comprising a control device for controlling the front-stage first optical repeater means and the rear-stage first optical repeater means, wherein the control device increases the optical intensity output by the front-stage first optical repeater means when it determines that the difference in optical intensity between the multiple cores of the optical signal input to the rear-stage first optical repeater means is greater than a predetermined value and that the difference in optical intensity between the multiple cores of the optical signal output by the front-stage first optical repeater means is smaller than a predetermined value.

[0081] (Supplementary Note 6) The optical transmission system according to any one of Supplementary Notes 1 to 5, wherein the first transmission distance is equal to the second transmission distance, and the first optical relay means and the second optical relay means are alternately positioned.

[0082] (Supplementary Note 7) The optical transmission system according to any one of Supplementary Notes 2 to 5, wherein the first possible transmission distance is greater than the second possible transmission distance, and the group of optical repeaters includes at least one of the first optical repeater and a plurality of the second optical repeater.

[0083] (Supplementary Note 8) The optical transmission system according to any one of Supplementary Notes 1 to 7, wherein the first optical repeater means comprises a first multi-core optical fiber including the first multi-core optical amplification medium in each core, a plurality of core pumping lasers each generating individual pumping light for individually pumping the first multi-core optical amplification medium, and fan-in / fan-out means for respectively introducing the individual pumping light into each core of the first multi-core optical fiber, and the second optical repeater means comprises a second multi-core optical fiber including the second multi-core optical amplification medium in each core, and a cladding pumping laser generating collectively pumping light for collectively pumping the second multi-core optical amplification medium.

[0084] (Supplementary Note 9) An optical transmission method comprising: arranging a first multi-core optical amplifying medium and a second multi-core optical amplifying medium at different positions of a multi-core optical transmission line; propagating an optical signal within multiple cores of the multi-core optical transmission line; individually pumping the first multi-core optical amplifying medium to amplify the optical signal; and collectively pumping the second multi-core optical amplifying medium to amplify the optical signal; the first multi-core optical amplifying medium is located away from the second multi-core optical amplifying medium by a distance determined based on either a first transmittable distance of the optical signal when the first multi-core optical amplifying medium is individually pumped or a second transmittable distance of the optical signal when the second multi-core optical amplifying medium is collectively pumped.

[0085] (Supplementary Note 10) The optical transmission method according to Supplementary Note 9, wherein the first multi-core optical amplifying medium and the second multi-core optical amplifying medium are arranged to configure an optical amplifying medium group consisting of at least one of the first multi-core optical amplifying medium and at least one of the second multi-core optical amplifying medium, and individually pumping the first multi-core optical amplifying medium includes amplifying the optical signal so that a difference in optical intensity of the optical signal among the multiple cores is reduced.

[0086] (Supplementary Note 11) The optical transmission method according to Supplementary Note 10, wherein the group of optical amplification media includes a front-stage optical amplification medium group and a rear-stage optical amplification medium group, the front-stage optical amplification medium group being disposed on the front side of the rear-stage optical amplification medium group, and individually pumping the front-stage first optical amplification medium which is the first multi-core optical amplification medium belonging to the front-stage optical amplification medium group includes amplifying the optical signal so that a difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical amplification medium which is the first multi-core optical amplification medium belonging to the rear-stage optical amplification medium group is reduced.

[0087] (Appendix 12) The optical transmission method according to appendix 11, wherein individually pumping the front-stage first optical amplifying medium includes amplifying the optical signal when a difference in optical intensity between the multiple cores of the optical signal amplified and output by the rear-stage first optical amplifying medium is greater than a predetermined value.

[0088] (Supplementary Note 13) The optical transmission method according to Supplementary Note 11, wherein individually pumping the front-stage first optical amplifying medium includes amplifying the optical signal when a difference in optical intensity between the multiple cores of the optical signal input to the rear-stage first optical amplifying medium is greater than a predetermined value and a difference in optical intensity between the multiple cores of the optical signal amplified and output by the front-stage first optical amplifying medium is smaller than a predetermined value.

[0089] (Supplementary Note 14) The optical transmission method according to any one of Supplementary Notes 9 to 13, wherein arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium includes arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium alternately when the first capable transmission distance is equal to the second capable transmission distance.

[0090] (Supplementary Note 15) The optical transmission method according to any one of Supplementary Notes 10 to 13, wherein arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium includes arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium so as to configure the optical amplifying medium group consisting of at least one first multi-core optical amplifying medium and a plurality of second multi-core optical amplifying mediums when the first capable transmission distance is longer than the second capable transmission distance.

[0091] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above embodiment. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. [Explanation of symbols]

[0092] 100, 200 Optical transmission system 101, 201 Multi-core optical transmission line 110, 210 First optical repeater 111 First Multi-Core Optical Fiber 112 Core-pumped laser 113 Fan-in and fan-out methods 120, 220 Second optical repeater 121 Second Multi-Core Optical Fiber 122 Cladding-pumped laser 131, 132, 230 Optical relay means group 211 First optical repeater 212 Rear stage first optical repeater 231 Front-stage optical repeater means group 232 Rear optical repeater means group 10 Related optical repeaters

Claims

1. a multi-core optical transmission line including a plurality of cores through which an optical signal propagates; a first optical repeater for individually pumping a first multi-core optical amplifying medium to amplify the optical signal; a second optical repeater for collectively pumping the second multi-core optical amplifying medium to amplify the optical signal; a first transmission distance by the first optical repeater is equal to a second transmission distance by the second optical repeater, The first optical relay means and the second optical relay means are alternately positioned. Optical transmission system.

2. the first optical relay means and the second optical relay means constitute an optical relay means group consisting of at least one first optical relay means and at least one second optical relay means, The first optical repeater included in each of the optical repeater groups amplifies the optical signal so that a difference in optical intensity of the optical signal between the multiple cores is reduced.

2. An optical transmission system according to claim 1.

3. the optical repeater group includes a front-stage optical repeater group and a rear-stage optical repeater group, the front-stage optical repeater group is located on the front side of the rear-stage optical repeater group, The front-stage first optical repeater means which is the first optical repeater means belonging to the front-stage optical repeater means group amplifies the optical signal so that a difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical repeater means which is the first optical repeater means belonging to the rear-stage optical repeater means group is reduced.

3. An optical transmission system according to claim 2.

4. a multi-core optical transmission line including a plurality of cores through which an optical signal propagates; a first optical repeater for individually pumping a first multi-core optical amplifying medium to amplify the optical signal; a second optical repeater for collectively pumping the second multi-core optical amplifying medium to amplify the optical signal; the first optical relay means is located away from the second optical relay means by a distance determined based on either a first transmission distance by the first optical relay means or a second transmission distance by the second optical relay means; the first optical relay means and the second optical relay means constitute an optical relay means group consisting of at least one first optical relay means and at least one second optical relay means, the first optical relay means included in each of the optical relay means groups amplifies the optical signal so that a difference in optical intensity of the optical signal among the multiple cores is reduced; the optical repeater group includes a front-stage optical repeater group and a rear-stage optical repeater group, the front-stage optical repeater group is located on the front side of the rear-stage optical repeater group, The front-stage first optical repeater means which is the first optical repeater means belonging to the front-stage optical repeater means group amplifies the optical signal so that a difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical repeater means which is the first optical repeater means belonging to the rear-stage optical repeater means group is reduced. Optical transmission system.

5. the first transmission distance is greater than the second transmission distance, The optical relay group includes at least one of the first optical relay means and a plurality of the second optical relay means.

5. An optical transmission system according to claim 4.

6. the first optical relay means comprises a first multi-core optical fiber including the first multi-core optical amplification medium in each core, a plurality of core pumping lasers each generating an individual pumping light for individually pumping the first multi-core optical amplification medium, and a fan-in / fan-out means for introducing the individual pumping light into each core of the first multi-core optical fiber, The second optical relay means includes a second multi-core optical fiber including the second multi-core optical amplification medium in each core, and a cladding pumping laser that generates collective pumping light that collectively pumps the second multi-core optical amplification medium.

6. An optical transmission system according to claim 1.

7. disposing a first multi-core optical amplifying medium and a second multi-core optical amplifying medium at different positions of a multi-core optical transmission line; Propagating an optical signal within a plurality of cores of the multi-core optical transmission line; amplifying the optical signal by individually pumping the first multi-core optical amplifying medium; collectively pumping the second multi-core optical amplifying medium to amplify the optical signal; Arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium includes arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium alternately when a first transmission distance of the optical signal when the first multi-core optical amplifying medium is individually pumped is equal to a second transmission distance of the optical signal when the second multi-core optical amplifying medium is collectively pumped. Optical transmission method.

8. disposing a first multi-core optical amplifying medium and a second multi-core optical amplifying medium at different positions of a multi-core optical transmission line; Propagating an optical signal within a plurality of cores of the multi-core optical transmission line; amplifying the optical signal by individually pumping the first multi-core optical amplifying medium; collectively pumping the second multi-core optical amplifying medium to amplify the optical signal; the first multi-core optical amplifying medium is located away from the second multi-core optical amplifying medium by a distance determined based on either a first transmission distance of the optical signal when the first multi-core optical amplifying medium is individually pumped or a second transmission distance of the optical signal when the second multi-core optical amplifying medium is collectively pumped; arranging the first multi-core optical amplifying medium and the second multi-core optical amplifying medium so as to configure an optical amplifying medium group consisting of at least one of the first multi-core optical amplifying medium and at least one of the second multi-core optical amplifying medium; Individually pumping the first multi-core optical amplifying medium includes amplifying the optical signal such that a difference in optical intensity of the optical signal among the multiple cores is reduced; the optical amplifying medium group includes a front-stage optical amplifying medium group and a rear-stage optical amplifying medium group, the front-stage optical amplifying medium group is disposed on the front side of the rear-stage optical amplifying medium group, Individually pumping the front-stage first optical amplifying medium which is the first multi-core optical amplifying medium belonging to the front-stage optical amplifying medium group includes amplifying the optical signal so that a difference in optical intensity of the optical signal between the multiple cores in the rear-stage first optical amplifying medium which is the first multi-core optical amplifying medium belonging to the rear-stage optical amplifying medium group is reduced. Optical transmission method.

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