Optical amplification device and optical amplification method

Abstract

To provide an optical amplifier, an optical transmission system, and an optical amplification method that enable performance evaluation of an optical amplifier using a coupled multi-core optical fiber and construction of an optical transmission system using the same.SOLUTION: An optical amplifier 100 using a coupled multi-core optical fiber includes bandwidth control means 110 that controls the wavelength band of an optical carrier to generate bandwidth control light, and bandwidth control light amplification means 120 that has a plurality of optical amplification media through which the bandwidth control light propagates, and the bandwidth control light amplification means 120 amplifies the bandwidth control light in a coupled state in which the propagating light propagating through the plurality of optical amplification media crosstalks, and the bandwidth control means 110 controls the wavelength band so as to reduce the coherence of the bandwidth control light that has propagated through the plurality of optical amplification media.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] The rapid expansion of mobile traffic and video services has led to a demand for increased communication capacity in core networks. This demand for increased capacity is likely to continue in the future. Up until now, this expansion 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] When using a single-core optical fiber, there is a limit to the number of multiplexed optical signals that can be transmitted through a single core, i.e., a single optical fiber core, and in recent years, this limit has been reached. This limit is determined by the wavelength bandwidth available in optical fiber communications and the input optical power tolerance of the single-core optical fiber.

[0004] In this situation, spatial multiplexing technology, which is a multiplexing technology of a different dimension from previous multiplexing technologies, has been developed to further expand communication capacity. Spatial multiplexing technologies include multi-core technology, which increases the number of cores per optical fiber, and multi-mode 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.

[0005] However, if the number of cores or modes of an optical fiber is increased, it is not possible to use currently widely used optical transceivers and optical amplifiers as they are. This is because currently popular optical transceivers and optical amplifiers were developed for single-core optical fibers and are not compatible with multi-core optical fibers or multi-mode optical fibers. Therefore, technologies have been proposed to realize optical transceivers and optical amplifiers suitable for multi-core optical fibers and multi-mode optical fibers.

[0006] There are two types of multi-core optical fibers: coupled and uncoupled. Uncoupled multi-core optical fibers have the advantage that the distance (pitch) between cores is large, making it possible to ignore the influence of crosstalk between cores. However, they have the disadvantage that it is difficult to increase the number of cores because the cores cannot be arranged densely. On the other hand, coupled multi-core optical fibers, in contrast to uncoupled multi-core optical fibers, have a small distance (pitch) between cores (see, for example, Patent Document 1). Therefore, they have the disadvantage that the influence of crosstalk between cores is large, but they have the advantage that the number of cores can be easily increased because the cores can be arranged densely. Furthermore, coupled multi-core optical fibers have excellent optical transmission characteristics in that they are less affected by nonlinear optical effects than uncoupled multi-core optical fibers, making them capable of extending the transmission distance of optical signals. This characteristic is extremely advantageous in constructing long-distance optical transmission systems.

[0007] There are two optical amplification methods suitable for multi-core optical fibers: a core pumping method and a cladding pumping method. In the core pumping method, the intensity of an optical signal transmitted through each core is amplified individually using an individual pumping light source for each core. In the cladding pumping method, the intensity of an optical signal transmitted through each core is amplified collectively using a common pumping light source (see, for example, Patent Document 2). The cladding pumping method can be used when using either an uncoupled multi-core optical fiber or a coupled multi-core optical fiber.

[0008] In order to efficiently amplify the optical intensity of an optical signal transmitted through a multi-core optical fiber, a cladding pumping scheme is desirable, in which the intensity of the optical signals transmitted through each core is collectively amplified using a common pumping light source. In addition, in the cladding pumping scheme, the configuration of a conventional optical amplifier using a single-core pumping scheme can, in principle, be used as is for the cladding pumping optical amplifier. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6372598 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-21070 Summary of the Invention [Problem to be solved by the invention]

[0010] In the above-mentioned coupled multi-core optical fiber, the distance between cores (core spacing) is small, so crosstalk occurs, in which a part of the optical signal leaking from each core couples with the optical signal passing through other cores. The amount of this crosstalk optical signal largely depends on the effective refractive index difference between the cores. The effective refractive index difference between the cores is affected by parameters such as the bending and temperature of the coupled multi-core optical fiber, but these parameters depend on the installation environment. Furthermore, these parameters can change in a complex manner over time, so it is very difficult to predict their changes. Therefore, it is also very difficult to predict the time change of the crosstalk between cores of a coupled multi-core optical fiber, which depends on parameters such as the bending and temperature of the optical fiber. If the crosstalk cannot be ignored, the optical intensity of the optical signal passing through each core of the coupled multi-core optical fiber will fluctuate over time.

[0011] When such a coupled multi-core fiber is applied to a cladding-pumped optical amplifier, the optical amplification process changes over time. As a result, the performance indices of the optical amplifier, such as the optical gain and noise figure, change over time, and these changes are difficult to predict. This poses a major problem in evaluating the performance of the optical amplifier itself and in the operation of optical transmission systems that use optical amplifiers. This is because the performance indices of currently used optical amplifiers, such as the optical gain and noise figure, are assumed to be constant over time and are not expected to change over time.

[0012] Since optical amplifiers amplify both optical signal components and inter-core crosstalk components, the effects of inter-core crosstalk are also amplified. Therefore, if the optical amplification factor and noise figure change over time and are difficult to predict, the design of the optical level and optical S / N ratio of optical transmission systems becomes extremely complicated. In particular, in cases where there is little margin for design of the optical level and optical S / N ratio, such as in long-distance optical transmission systems, the design and operation of optical transmission systems becomes virtually impossible.

[0013] As described above, an optical amplifier using a coupled multi-core optical fiber has a problem in that its figure of merit changes over time, making it difficult to evaluate its performance and to construct an optical transmission system using it.

[0014] An object of the present invention is to provide an optical amplifier, an optical transmission system, and an optical amplification method that solve the above-mentioned problems. [Means for solving the problem]

[0015] The optical amplification device of the present invention comprises a bandwidth control means for controlling the wavelength band of an optical carrier wave to generate bandwidth control light, and a bandwidth control light amplification means provided with a plurality of optical amplification media through which the bandwidth control light propagates, wherein the bandwidth control light amplification means amplifies the bandwidth control light in a coupled state in which the propagating light propagating through the plurality of optical amplification media crosstalks, and the bandwidth control means controls the wavelength band so as to reduce the coherence of the bandwidth control light that has propagated through the plurality of optical amplification media.

[0016] The optical transmission system of the present invention includes an optical amplification means that controls the wavelength band of an optical carrier wave to generate bandwidth control light and amplifies the bandwidth control light, an optical detection means that detects the intensity of the bandwidth control light amplified by the optical amplification means and generates optical intensity information, and a control means that controls the optical amplification means to adjust the wavelength band based on the optical intensity information.

[0017] The optical amplification method of the present invention controls the wavelength band of an optical carrier wave to generate bandwidth control light, introduces the bandwidth control light into multiple optical amplification media, amplifies the bandwidth control light in a coupled state in which the propagating light propagating through the multiple optical amplification media crosstalks, and controls the wavelength band so as to reduce the coherence of the bandwidth control light that has propagated through the multiple optical amplification media. [Effects of the Invention]

[0018] According to the optical amplifier, optical transmission system, and optical amplification method of the present invention, it becomes possible to evaluate the performance of an optical amplifier using a coupled multi-core optical fiber and to construct an optical transmission system using the same. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a block diagram showing a configuration of an optical amplifying device according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a block diagram showing another configuration of the optical amplifying device according to the first embodiment of the present invention. [Figure 3] FIG. 10 is a block diagram showing the configuration of an optical amplifying device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating an example of the spectrum of output light from a signal light source included in an optical amplifying device according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing an example of measured values ​​of optical intensity detected by an optical monitor included in the optical amplifier according to the second embodiment of the present invention. [Figure 6] FIG. 10 is a block diagram showing a configuration of an optical transmission system according to a third embodiment of the present invention. [Figure 7] FIG. 10 is a block diagram showing another configuration of the optical transmission system according to the third embodiment of the present invention. [Figure 8] FIG. 10 is a block diagram showing a configuration of an optical transmission system according to a fourth embodiment of the present invention. [Figure 9] FIG. 10 is a diagram illustrating a multiplexing method in an optical transmission system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] [First embodiment] 1 is a block diagram showing the configuration of an optical amplifier 100 according to a first embodiment of the present invention. The optical amplifier 100 includes a bandwidth control unit 110 and a bandwidth controlled optical amplifier unit 120.

[0022] The bandwidth control means 110 controls the wavelength band of the optical carrier wave to generate bandwidth control light. The bandwidth control light amplification means 120 includes a plurality of optical amplification media through which the bandwidth control light propagates. Here, the bandwidth control light amplification means 120 amplifies the bandwidth control light in a coupled state in which the propagating light propagating through the plurality of optical amplification media crosstalks. The bandwidth control means 110 then controls the wavelength band so as to reduce the coherence of the bandwidth control light that has propagated through the plurality of optical amplification media.

[0023] As described above, in the optical amplifier 100 of this embodiment, the bandwidth control light amplifying means 120 is configured to amplify the bandwidth control light in a coupled state in which the propagating lights crosstalk. Specifically, the bandwidth control light amplifying means 120 includes a coupled multi-core optical fiber in which a plurality of cores are arranged closely to each other, and this coupled multi-core optical fiber can be configured to include an optical amplifying medium in at least a part of each of the plurality of cores.

[0024] Here, crosstalk can cause interference between optical signals (propagating light). However, in the optical amplifier 100 of this embodiment, the bandwidth control means 110 controls the wavelength band so as to reduce the coherence of the bandwidth control light propagating through multiple optical amplification media. Therefore, even if crosstalk occurs between optical signals passing through different cores of a coupled multi-core optical fiber, interference between the optical signals does not occur. As a result, it is possible to suppress the time variation in the intensity of the optical signal output from each core of the coupled multi-core optical fiber. As a result, the optical amplifier 100 of this embodiment makes it possible to evaluate the performance of an optical amplifier using a coupled multi-core optical fiber and to construct an optical transmission system using the same.

[0025] Interference between optical signals is greatest for optical signals of a single wavelength, and decreases as the wavelength component, i.e., the wavelength band, increases. The reason for this is that the larger the wavelength band, i.e., the more various wavelength components are mixed, the more difficult it is to satisfy the phase condition for interference between the wavelength components. This condition is determined by the coherence length Lc. If the central wavelength of the optical signal is λ and the wavelength band is Δλ, the coherence length Lc is expressed by the following equation (1): TIFF0007775947000001.tif10150

[0026] When the length L of the coupled multi-core optical fiber is sufficiently longer than the coherence length Lc determined by equation (1), no interference occurs between optical signals passing between different cores. Therefore, the bandwidth control means 110 can be configured to control the wavelength band so that the coherence length of the bandwidth control light is shorter than the length of the coupled multi-core optical fiber.

[0027] When the length L of the coupled multi-core optical fiber is constant, the larger the wavelength band Δλ, i.e., the more wavelength components there are, the more the interference between optical signals passing between different cores is suppressed. Here, the wavelength band Δλ can be expanded by modulating the optical carrier. Therefore, as shown in Figure 2, the bandwidth control means 110 may be configured to include optical modulation means 111 that modulates the optical carrier. In this case, the optical modulation means may modulate the optical carrier at a period shorter than the coherence time determined from the coherence length. That is, the optical modulation means may be configured to modulate the optical carrier at a frequency greater than the reciprocal of the time required for the bandwidth control light to propagate through the coupled multi-core optical fiber. With this configuration, the interference between optical signals passing through different cores can be suppressed.

[0028] Next, the optical amplification method according to this embodiment will be described.

[0029] In the optical amplification method according to this embodiment, first, the wavelength band of an optical carrier wave is controlled to generate bandwidth control light, and this bandwidth control light is introduced into multiple optical amplification media. The bandwidth control light is then amplified in a coupled state where the propagating lights propagating through the multiple optical amplification media cause crosstalk. The wavelength band is then controlled so as to reduce the coherence of the bandwidth control light that has propagated through the multiple optical amplification media.

[0030] The introduction of the bandwidth control light into the plurality of optical amplification media may be configured to include introduction of the bandwidth control light into a coupled multi-core optical fiber, where the coupled multi-core optical fiber has a plurality of cores arranged closely together, and at least a part of each of the plurality of cores includes an optical amplification medium.

[0031] In the optical amplification method according to the present embodiment, controlling the wavelength band can be performed so that the coherence length of the band control light is shorter than the length of the coupled multi-core optical fiber.

[0032] In the optical amplification method according to the present embodiment, controlling the wavelength band may be modulating the optical carrier at a frequency greater than the reciprocal of the time required for the bandwidth control light to propagate through the coupled multi-core optical fiber.

[0033] As described above, the optical amplifier 100 and the optical amplification method of this embodiment make it possible to evaluate the performance of an optical amplifier using a coupled multi-core optical fiber and to construct an optical transmission system using the same.

[0034] Second Embodiment Next, a second embodiment of the present invention will be described. Fig. 3 shows the configuration of an optical amplifier 200 according to this embodiment.

[0035] The optical amplifying device 200 includes a signal light source 210, a coupled multi-core optical fiber 220, a coupled multi-core fiber optical amplifier 230, and a light detecting section (light detecting means) 240.

[0036] The signal light source 210 includes a bandwidth control means for controlling the wavelength band of the optical carrier wave to generate bandwidth controlled light.

[0037] The coupled multi-core optical fiber 220 and the coupled multi-core fiber amplifier 230 comprise coupled multi-core optical fibers in which multiple cores are arranged closely to each other. Here, the inter-core distance of both the coupled multi-core optical fiber 220 and the coupled multi-core fiber amplifier 230 can be, for example, 25 micrometers (μm) or less. The coupled multi-core optical fiber 220 and the coupled multi-core fiber amplifier 230 constitute a bandwidth-controlled optical amplification means.

[0038] The coupled multi-core fiber optical amplifier 230 includes a plurality of optical amplification media through which the bandwidth control light propagates, and amplifies the bandwidth control light in a coupled state in which the propagating light propagating through these optical amplification media crosstalks. The coupled multi-core fiber optical amplifier 230 typically has cores as optical amplification media doped with erbium ions, which are rare earth ions, and a double clad structure. The coupled multi-core fiber optical amplifier 230 configured as described above can use a clad pumping method as an optical amplification method.

[0039] The optical detection unit (optical detection means) 240 detects the intensity of the bandwidth control light that has propagated through at least one of the multiple cores of the coupled multi-core fiber optical amplifier 230, and generates optical intensity information. Here, the optical detection unit 240 includes fan-out connection means 241 and fan-in connection means 242 that connect each core of the multi-core fiber to a single-mode fiber 243, and an optical monitor 244. Fig. 3 shows an example of a configuration in which the coupled multi-core fiber optical amplifier 230 has four cores, the fan-out connection means 241 is connected to four single-mode fibers 243, and four optical monitors 244 monitor the intensity of the bandwidth control light that has propagated through each core.

[0040] The bandwidth control means provided in the signal light source 210 controls the wavelength band based on the light intensity information from the light detection unit 240 so as to reduce the coherence of the bandwidth control light propagated through the multiple optical amplification media (cores) of the coupled multi-core fiber optical amplifier 230.

[0041] Specifically, for example, the optical detection unit 240 determines whether the intensity fluctuation value of the output light from each core of the coupled multi-core fiber optical amplifier 230 exceeds a predetermined constant value. If the intensity fluctuation value of the output light exceeds the predetermined constant value, the optical detection unit 240 generates optical intensity information to that effect. In this case, the bandwidth control means included in the signal light source 210 adjusts the wavelength band of the optical carrier wave input to each core so that the intensity fluctuation value of the output light from each core falls within a predetermined range.

[0042] With this configuration, it is possible to suppress the time fluctuation of the optical signal intensity output from each core of the coupled multi-core optical fiber. As a result, the optical amplifier 200 of this embodiment makes it possible to evaluate the performance of an optical amplifier using a coupled multi-core optical fiber and to construct an optical transmission system using the same.

[0043] The signal light source 210 can be configured with an optical modulation means for modulating the optical carrier wave. The optical modulation means modulates the optical carrier wave, thereby expanding the wavelength band of the optical carrier wave. Figure 4 shows an example of the spectrum of the output light from the signal light source 210. It can be seen that the wavelength band of the modulated wave is expanded compared to the spectrum of a continuous wave (CW) wave without modulation. The figure shows an example of the spectrum when modulated at a baud rate of 66 giga-baud. The wider the wavelength band, the more wavelength components are included, so interference between optical signals passing between different cores is suppressed. Figure 5 shows an example of the measured optical intensity detected by the optical monitor 244 in this case. It can be seen that modulation (66 Gbaud) significantly reduces the fluctuations in optical intensity compared to the case without modulation (CW).

[0044] Next, the optical amplification method according to this embodiment will be described.

[0045] In the optical amplification method according to this embodiment, first, the wavelength band of an optical carrier wave is controlled to generate bandwidth control light, and this bandwidth control light is introduced into multiple optical amplification media. The bandwidth control light is then amplified in a coupled state where the propagating lights propagating through the multiple optical amplification media cause crosstalk. The wavelength band is then controlled so as to reduce the coherence of the bandwidth control light that has propagated through the multiple optical amplification media.

[0046] When the above-mentioned bandwidth control light is introduced into the plurality of optical amplification media, the bandwidth control light is introduced into a coupled multi-core optical fiber, where the coupled multi-core optical fiber has a plurality of cores arranged closely to each other and includes an optical amplification medium in at least a part of each of the plurality of cores.

[0047] Furthermore, the intensity of the band control light propagating through at least one of the multiple cores is detected to generate light intensity information, and when controlling the wavelength band described above, the wavelength band is controlled based on this light intensity information.

[0048] As described above, the optical amplifier 200 and the optical amplification method of this embodiment can suppress the time variation in the intensity of the optical signal output from each core of the coupled multi-core optical fiber, thereby enabling performance evaluation of an optical amplifier using a coupled multi-core optical fiber and construction of an optical transmission system using the same.

[0049] Third Embodiment Next, a third embodiment of the present invention will be described. Fig. 6 shows the configuration of an optical transmission system 300 according to this embodiment. Note that the same components as those in the optical amplifier 200 according to the second embodiment are denoted by the same reference numerals, and detailed descriptions thereof may be omitted.

[0050] The optical transmission system 300 according to this embodiment includes a signal light source 210, a coupled multi-core optical fiber 220, a coupled multi-core fiber optical amplifier 230, and an optical detection unit 240. The configuration up to this point is the same as that of the optical amplifying device 200 according to the second embodiment. The optical transmission system 300 according to this embodiment further includes an optical intensity fluctuation detector 310 and a control unit (control means) 320. Here, the signal light source 210, the coupled multi-core optical fiber 220, and the coupled multi-core fiber optical amplifier 230 constitute optical amplification means, and the optical detection unit 240 and the optical intensity fluctuation detector 310 constitute optical detection means.

[0051] The signal light source 210 includes a bandwidth control means for controlling the wavelength band of the optical carrier wave to generate bandwidth controlled light.

[0052] The coupled multi-core optical fiber 220 and the coupled multi-core fiber amplifier 230 comprise a coupled multi-core optical fiber in which multiple cores are arranged closely to each other. The coupled multi-core fiber amplifier 230 comprises multiple optical amplification media through which bandwidth control light propagates, and amplifies the bandwidth control light in a coupled state in which the propagating light propagating through these multiple optical amplification media crosstalks. The coupled multi-core optical fiber 220 and the coupled multi-core fiber amplifier 230 constitute bandwidth control light amplification means.

[0053] The optical detector 240 detects the intensity of the bandwidth control light that has propagated through at least one of the multiple cores of the coupled multi-core fiber optical amplifier 230, and generates optical intensity information.

[0054] The control unit (control means) 320 controls the band control means to adjust the wavelength band based on the optical intensity information. At this time, the band control means controls the wavelength band so as to reduce the coherence of the band control light propagated through the multiple optical amplification media (cores) of the coupled multi-core fiber optical amplifier 230.

[0055] Next, the operation of the optical transmission system 300 according to this embodiment will be described.

[0056] The optical intensity fluctuation detector 310 generates warning information as optical intensity information when the change over time in the intensity of the bandwidth control light amplified by the coupled multi-core fiber optical amplifier 230 exceeds a predetermined threshold. In this case, the control unit 320 controls the bandwidth control means provided in the signal light source 210 based on the warning information so as to increase the wavelength bandwidth.

[0057] More specifically, the optical intensity fluctuation value for each core (four cores in the case shown in FIG. 6 ) output from the optical detection unit 240 is input to the optical intensity fluctuation detector 310. For example, a peak-to-peak value can be used as the optical intensity fluctuation value. The optical intensity fluctuation detector 310 issues an alarm (warning information) to the control unit 320 when a statistical value, such as the maximum or average value of the optical intensity fluctuation value for each core, exceeds a predetermined threshold value. While this alarm is being issued, the control unit 320 sends a control signal to the bandwidth control means of the signal light source 210 to instruct it to gradually widen the wavelength band of the signal light. By gradually widening the wavelength band of the optical signal input to each core of the coupled multi-core fiber optical amplifier 230, the optical intensity fluctuation value of the output from the coupled multi-core fiber optical amplifier 230 can be reduced. The optical intensity fluctuation detector 310 stops issuing the alarm when it determines that the optical intensity fluctuation value has fallen below the threshold value.

[0058] 7, the optical transmission system 301 may be configured to include a plurality of coupled multi-core fiber optical amplifiers 231, 232, a plurality of optical detection units 241, 242, and a plurality of optical intensity fluctuation detectors 311, 312. In the optical transmission system 301 configured in this way, a plurality of alarm information (alarm 1, alarm 2) is issued. In this case, the control unit 320 may be configured to continue sending control signals until all alarms are cleared.

[0059] As described above, according to the optical transmission systems 300 and 301 of the present embodiment, it is possible to suppress the time variation in the intensity of the optical signal output from each core of the coupled multi-core optical fiber, and as a result, it becomes possible to construct an optical transmission system using a coupled multi-core optical fiber.

[0060] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described. Fig. 8 shows the configuration of an optical transmission system 400 according to this embodiment.

[0061] The optical transmission system 400 according to this embodiment includes an optical amplifier (optical amplifying means) 410, an optical detector (optical detecting means) 420, and a control unit (control means) 430.

[0062] The optical amplifier 410 controls the wavelength band of the optical carrier to generate bandwidth control light and amplifies the bandwidth control light. The optical detector 420 detects the intensity of the bandwidth control light amplified by the optical amplifier 410 and generates optical intensity information. The controller 430 then controls the optical amplifier 410 to adjust the wavelength band based on the optical intensity information.

[0063] Here, the optical amplifying section 410 can be configured to include a band control section (band control means) 411 and a band control optical amplifying section (band control optical amplifying means) 412.

[0064] The band control unit 411 controls the wavelength band of the optical carrier wave to generate band control light. The band control light amplifier 412 includes multiple optical amplification media through which the band control light propagates. In this case, the band control light amplifier 412 amplifies the band control light in a coupled state in which the propagating lights propagating through the multiple optical amplification media cause crosstalk. The band control unit 411 then controls the wavelength band so as to reduce the coherence of the band control light that has propagated through the multiple optical amplification media.

[0065] The bandwidth control optical amplifier 412 may be configured to include a coupled multi-core optical fiber in which multiple cores are arranged closely to each other. Here, the coupled multi-core optical fiber includes an optical amplification medium in at least a part of each of the multiple cores.

[0066] In the optical transmission system 400 according to this embodiment, the bandwidth control section 411 is configured to include an optical modulator (optical modulation means) 413 that modulates an optical carrier wave.

[0067] Next, the operation of the optical transmission system 400 according to this embodiment will be described.

[0068] The optical detection unit 420 generates warning information as optical intensity information when the change over time in the intensity of the bandwidth control light amplified by the optical amplification unit 410 exceeds a predetermined threshold. Then, based on this warning information, the control unit 430 controls the optical amplification unit 410 to increase the modulation speed of the optical carrier wave and reduce the number of cores through which the bandwidth control light propagates among the multiple cores.

[0069] The operation of the optical transmission system 400 according to this embodiment will be described in further detail below.

[0070] As described above, in the optical transmission system 400 of this embodiment, the number of cores used to propagate the bandwidth control light and the modulation rate (transmission rate), i.e., the multiplexing method, are changed based on the results of monitoring optical intensity fluctuations by the optical detection unit 420. Fig. 9 shows an example of the multiplexing method.

[0071] The control unit 430 first controls the optical amplifying unit 410 to send out a transmission signal under the conditions of multiplexing method 1 shown in Fig. 9. That is, N cores out of the multiple cores of the coupled multi-core optical fiber are used to send out a transmission signal at a transmission rate B, respectively. In this case, the transmission capacity per multi-core optical fiber is N × B.

[0072] When the control unit 430 receives an alarm (warning information) from the light detection unit 420, the control unit 430 instructs the optical amplification unit 410 to switch the multiplexing method from multiplexing method 1 to multiplexing method 2. When the optical amplification unit 410 changes the multiplexing method to multiplexing method 2, the transmission speed doubles (2×B) and the number of cores in the multi-core optical fiber used is halved (1 / 2×N). In this case, in both the multiplexing method 1 and the multiplexing method 2, the transmission capacity per multi-core optical fiber is the same (N×B), and changing the multiplexing method does not change the transmission capacity per multi-core optical fiber.

[0073] By changing to multiplexing method 2 and increasing the transmission speed, the wavelength band of the transmission signal can also be expanded, making it possible to suppress interference between the transmission signals propagating through each core. In other words, by changing the temporal multiplexing degree (transmission speed) and spatial multiplexing degree (number of cores) based on the results of monitoring optical intensity fluctuations, it is possible to suppress optical intensity fluctuations at the receiving end of the transmission system. As a result, optical signals that could not be received using multiplexing method 1 can be received using multiplexing method 2.

[0074] As described above, according to the optical transmission system 400 of this embodiment, it is possible to suppress the time variation in the intensity of the optical signal output from each core of the coupled multi-core optical fiber, and as a result, it is possible to construct an optical transmission system using a coupled multi-core optical fiber.

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

[0076] (Supplementary Note 1) An optical amplification device comprising: a band control means for controlling the wavelength band of an optical carrier wave to generate band control light; and a band control light amplification means having a plurality of optical amplification media through which the band control light propagates, wherein the band control light amplification means amplifies the band control light in a coupled state in which propagating light propagating through the plurality of optical amplification media crosstalks, and the band control means controls the wavelength band so as to reduce the coherence of the band control light propagated through the plurality of optical amplification media.

[0077] (Supplementary Note 2) The optical amplifier device according to Supplementary Note 1, wherein the bandwidth-controlled optical amplifier comprises a coupled multi-core optical fiber in which a plurality of cores are arranged closely to each other, and the coupled multi-core optical fiber includes the optical amplification medium in at least a part of each of the plurality of cores.

[0078] (Supplementary Note 3) The optical amplifier according to Supplementary Note 2, wherein the bandwidth control means controls the wavelength band so that the coherence length of the bandwidth control light is shorter than the length of the coupled multi-core optical fiber.

[0079] (Supplementary Note 4) The optical amplifying device according to Supplementary Note 2, wherein the bandwidth control means comprises optical modulation means for modulating the optical carrier, and the optical modulation means modulates the optical carrier at a frequency greater than the reciprocal of a time required for the bandwidth control light to propagate through the coupled multi-core optical fiber.

[0080] (Appendix 5) An optical amplifier according to appendix 2, further comprising a light detection means for detecting the intensity of the bandwidth control light propagated through at least one of the plurality of cores and generating optical intensity information, wherein the bandwidth control means controls the wavelength band based on the optical intensity information.

[0081] (Supplementary Note 6) An optical transmission system comprising: an optical amplifier that controls a wavelength band of an optical carrier wave to generate bandwidth control light and amplifies the bandwidth control light; an optical detection unit that detects the intensity of the bandwidth control light amplified by the optical amplifier and generates optical intensity information; and a control unit that controls the optical amplifier to adjust the wavelength band based on the optical intensity information.

[0082] (Supplementary Note 7) An optical transmission system according to Supplementary Note 6, wherein the optical amplifying means comprises: a band control means for controlling a wavelength band of the optical carrier wave to generate band control light; and a band control light amplifying means provided with a plurality of optical amplifying media through which the band control light propagates, the band control light amplifying means amplifying the band control light in a coupled state in which the propagating light propagating through the plurality of optical amplifying media crosstalks, and the band control means controls the wavelength band so as to reduce the coherence of the band control light propagated through the plurality of optical amplifying media.

[0083] (Supplementary Note 8) The optical transmission system according to Supplementary Note 7, wherein the bandwidth-controlled optical amplifier comprises a coupled multi-core optical fiber in which a plurality of cores are arranged closely to each other, and the coupled multi-core optical fiber includes the optical amplification medium in at least a part of each of the plurality of cores.

[0084] (Appendix 9) An optical transmission system according to appendix 8, wherein the optical detection means detects the intensity of the bandwidth control light propagating through at least one of the plurality of cores to generate the optical intensity information, and the bandwidth control means controls the wavelength band based on the optical intensity information.

[0085] (Appendix 10) An optical transmission system according to any one of Appendices 6 to 9, wherein the optical detection means generates alarm information as the light intensity information when a change over time in the intensity of the bandwidth control light amplified by the optical amplification means exceeds a predetermined threshold, and the control means controls the optical amplification means to increase the wavelength band based on the alarm information.

[0086] (Supplementary Note 11) An optical transmission system according to any one of Supplementary Notes 7 to 9, wherein the bandwidth control light amplifying means comprises a plurality of bandwidth control light amplifying means, the light detecting means comprises a plurality of light detecting means, each of the plurality of light detecting means detects the intensity of the bandwidth control light amplified by one of the plurality of bandwidth control light amplifying means, and when a change in the intensity over time exceeds a predetermined threshold, generates alarm information as the light intensity information, and the control means controls the bandwidth control means to increase the wavelength band based on the alarm information.

[0087] (Supplementary Note 12) An optical transmission system according to Supplementary Note 8 or 9, wherein the bandwidth control means comprises optical modulation means for modulating the optical carrier wave, and the optical detection means generates alarm information as the optical intensity information when a change over time in the intensity of the bandwidth control light amplified by the optical amplification means exceeds a predetermined threshold, and the control means controls the optical amplification means based on the alarm information to increase the speed at which the optical carrier wave is modulated and to reduce the number of cores through which the bandwidth control light propagates among the plurality of cores.

[0088] (Appendix 13) An optical amplification method that controls a wavelength band of an optical carrier wave to generate bandwidth control light, introduces the bandwidth control light into a plurality of optical amplification media, amplifies the bandwidth control light in a coupled state in which the propagating light propagating through the plurality of optical amplification media crosstalks, and controls the wavelength band so as to reduce the coherence of the bandwidth control light that has propagated through the plurality of optical amplification media.

[0089] (Supplementary Note 14) The optical amplification method according to Supplementary Note 13, wherein introducing the bandwidth control light into the plurality of optical amplification media includes introducing the bandwidth control light into a coupled multi-core optical fiber, the coupled multi-core optical fiber having a plurality of cores arranged closely together, and at least a part of each of the plurality of cores including the optical amplification medium.

[0090] (Supplementary Note 15) The optical amplification method according to Supplementary Note 14, wherein controlling the wavelength band includes controlling the wavelength band so that a coherence length of the band control light is shorter than a length of the coupled multi-core optical fiber.

[0091] (Supplementary Note 16) The optical amplification method according to Supplementary Note 14, wherein controlling the wavelength band includes modulating the optical carrier, and modulating the optical carrier includes modulating the optical carrier at a frequency greater than an inverse number of a time required for the bandwidth control light to propagate through the coupled multi-core optical fiber.

[0092] (Supplementary Note 17) An optical amplification method according to Supplementary Note 14, further comprising detecting the intensity of the band control light propagated through at least one of the plurality of cores and generating light intensity information, wherein controlling the wavelength band includes controlling the wavelength band based on the light intensity information.

[0093] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. [Explanation of symbols]

[0094] 100, 200 Optical amplifier 110 Bandwidth Control Means 111 Optical modulation means 120 Bandwidth control optical amplifier means 210 Signal light source 220 Coupled multi-core optical fiber 230, 231, 232 Coupled multicore fiber optical amplifier 240, 241, 242, 420 Light detection unit 241 Fan-out Connection Method 242 Fan-in connection method 243 Single-mode fiber 244 Optical Monitor 300, 301, 400 Optical Transmission Systems 310, 311, 312 Light intensity fluctuation detector 320, 430 Control section 410 Optical amplifier 411 Bandwidth control section 412 Bandwidth control optical amplifier 413 Optical Modulator

Claims

1. an optical amplifier including a coupled multi-core optical fiber in which a plurality of cores are arranged closely to each other and an optical amplification medium included in at least a part of each of the plurality of cores; a bandwidth control means for controlling a wavelength band of an optical carrier wave input to the coupled multi-core optical fiber to generate bandwidth control light; Equipped with The band control means controls the wavelength band of the optical carrier so that the intensity fluctuation value of the optically amplified band control light falls within a predetermined range. Optical amplifier.

2. The band control means adjusts the wavelength band of the optical carrier wave input to the optical amplifier means so that the intensity fluctuation value of the output light from the optical amplifier means falls within a predetermined range.

2. The optical amplifier according to claim 1.

3. The band control means controls the optical carrier wave to expand the wavelength band by modulating the optical carrier wave.

2. The optical amplifier according to claim 1.

4. the bandwidth control means includes optical modulation means for modulating the optical carrier wave, The optical modulation means modulates the optical carrier at a frequency greater than the reciprocal of the time required for the bandwidth control light to propagate through the coupled multi-core optical fiber.

2. The optical amplifier according to claim 1.

5. further comprising a light detection means for detecting the intensity of the bandwidth control light that has propagated through at least one of the plurality of cores; The light sensing means generates light intensity information.

5. An optical amplifier according to claim 1.

6. further comprising a light fluctuation detection means for receiving an output from the light detection means; The light fluctuation detection means generates alarm information when the change over time in the intensity of the bandwidth control light exceeds a predetermined threshold.

6. An optical amplifier according to claim 5.

7. The bandwidth control means receives a signal for changing the multiplexing method of the bandwidth control light based on the optical intensity information.

6. An optical amplifier according to claim 5.

8. The change in the multiplexing method is a change in the number of cores used for propagating the bandwidth control light or a change in the transmission speed.

8. The optical amplifier according to claim 7.

9. The plurality of cores are arranged close to each other such that the inter-core distance is 25 μm or less.

9. An optical amplifier according to claim 1.

10. An optical amplifier including a coupled multi-core optical fiber in which a plurality of cores are arranged closely to each other, and an optical amplification medium included in at least a part of each of the plurality of cores, generating bandwidth-controlled light by controlling a wavelength band of an optical carrier wave input to the coupled multi-core optical fiber; The wavelength band of the optical carrier is controlled so that the intensity fluctuation value of the optically amplified band control light falls within a predetermined range. Optical amplification method.

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