Automatic variable tilt device and optical signal gain equalizing method

Abstract

To provide an automatic variable tilt device capable of automatically adjusting inclination of an optical profile in a short time, and an optical signal gain equalizing method.SOLUTION: An automatic variable tilt device includes: a first Fi / Fo device configured to split a multi-core optical input signal into two single-core optical input signals; two variable tilt equalizers configured to respectively adjust a tilt level of the two single-core optical input signals; two optical couplers configured to respectively split two single-core optical output signals from the two variable tilt equalizers into two optical signals at a predetermined ratio; a feedback control unit configured to perform feedback control on the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals split by each of the two optical couplers; and a second Fi / Fo device configured to multiplex the other of the single-core optical output signals split by each of the two optical couplers and output a multiplexed multi-core optical output signal.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an automatic variable tilt device and an optical signal gain equalization method for a multicore fiber, and more particularly to an automatic variable tilt device and an optical signal gain equalization method used in an optical submarine system of a multicore system. [Background technology]

[0002] An equalization device, a communication system, and an equalization method for equalizing the slope levels of optical signals used in a submarine cable system (optical submarine system) are known (see, for example, Patent Document 1). The equalization device of Patent Document 1 includes an equalizer group including at least two equalizers in order to reduce the number of optical devices while maintaining the set number of slope levels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 167736 Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, optical submarine systems use single-core optical fiber (single-mode fiber (SMF) with only one core) and optical signals in the C-band signal band. Therefore, in order to increase the communication capacity of optical submarine systems, it is necessary to increase the number of optical fibers (number of cores) installed.

[0005] However, in optical submarine systems, where the number of optical fibers that can be installed in an optical submarine cable is limited due to factors such as the cross-sectional area of ​​the optical fiber, it is difficult to increase the number of optical fibers, and the manufacturing costs become enormous.

[0006] The present disclosure has been made to solve such problems, and its purpose is to provide an automatic variable tilt device and an optical signal gain equalization method that can automatically adjust the tilt level (inclination) of an optical profile, which is an optical input signal, in a short period of time in an optical submarine system using a multicore fiber. [Means for solving the problem]

[0007] The automatic variable tilt device of the present disclosure is a first fan-in / fan-out device for splitting a multi-core optical input signal from a multi-core fiber into two single-core optical input signals; two variable tilt equalizers for adjusting tilt levels of the two single-core optical input signals, respectively; two optical couplers that split the two single-core optical output signals from the two variable tilt equalizers into two optical signals at a predetermined ratio; a feedback control unit that feedback-controls the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; a second fan-in / fan-out device that combines the other of the single-core optical output signals branched by each of the two optical couplers and outputs a combined multi-core optical output signal; It is equipped with the following.

[0008] The optical signal gain equalization method of the present disclosure includes: A first fan-in / fan-out device separates a multi-core optical input signal from a multi-core fiber into two single-core optical input signals; The two single-core optical input signals are input to two variable tilt equalizers, respectively; Each of the two optical couplers splits the single-core optical output signal from the corresponding variable tilt equalizer into two optical signals at a predetermined ratio; feedback-controlling the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; A second fan-in / fan-out device multiplexes the other of the single-core optical output signals branched by each of the two optical couplers, and outputs a multiplexed multi-core optical output signal. [Effects of the Invention]

[0009] The present disclosure provides an automatic variable tilt device and an optical signal gain equalization method that can automatically adjust the tilt level (inclination) of an optical profile, which is an optical input signal, in an optical submarine system using a multicore fiber in a short period of time. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing an example of the configuration of an automatic variable tilt device according to the present disclosure. [Figure 2] FIG. 2 is a diagram illustrating an example of an optical input signal to an automatic variable tilt device according to the present disclosure. [Figure 3] 1 is a block diagram illustrating an example configuration of a variable tilt equalizer of an automatic variable tilt device according to the present disclosure. [Figure 4] FIG. 2 is a block diagram showing an example configuration of a feedback control unit of an automatic variable tilt device according to the present disclosure. [Figure 5] 10 is a conceptual diagram showing the state of an optical signal after gain equalization by an automatic variable tilt device according to the present disclosure. FIG. [Figure 6] 10 is a block diagram showing an example of connection of a variable tilt equalizer after gain equalization by an automatic variable tilt device according to the present disclosure. FIG. [Figure 7] 1 is a simplified diagram showing the state of an optical signal after gain equalization by an automatic variable tilt device according to the present disclosure and the connection of a tilt equalizer. FIG. [Figure 8] 10 is a flowchart illustrating an example of an optical signal gain equalization process executed by an automatic variable tilt device according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the invention according to the claims is not limited to the following embodiments. Furthermore, not all of the configurations described in the present embodiments are necessarily essential means for solving the problems. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary.

[0012] (Embodiment) An automatic variable tilt device for a multicore fiber according to the present embodiment will be described below with reference to Fig. 1 to Fig. 8. Before describing the configuration and operation of the automatic variable tilt device for a multicore fiber (hereinafter abbreviated as "automatic variable tilt device"), the background to the present disclosure will be described.

[0013] <Background to this disclosure> As explained in the background art, in optical submarine systems, there is a limit to the number of optical fibers that can be installed in an optical submarine cable, so increasing the number of optical fibers is difficult and the manufacturing costs become enormous. For this reason, in recent years, there has been a movement to use C-band multicore fibers, in which multiple cores are installed in a single optical fiber, for optical communications, and there is a desire to put this to practical use in optical submarine systems as well.

[0014] In long-distance optical submarine systems, in order to ensure the transmission quality of multicore fibers, it is desirable to flatten the tilt level (inclination) of the optical signal profile (optical profile) during system operation from BOL (beginning of life) to EOL (end of life), that is, to adjust the tilt level of the optical profile to substantially 0 dB.

[0015] However, the tilt level of the optical profile increases as the optical submarine cable is repaired or deteriorates over time. Therefore, in order to keep the tilt level flat during operation of the optical submarine system, it is necessary to provide a variable tilt equalizer device that can arbitrarily adjust the tilt level of the optical profile.

[0016] In addition, the operation of multi-core systems, which require many signal lines, is progressing, but the increase in system signal lines means that system monitoring and tilt adjustment take time. As a result, there is a problem that the operating costs of optical submarine cables using multi-core fiber are increasing. Furthermore, there has been a demand for automating system monitoring and tilt adjustment.

[0017] To address this issue, the inventors of the present application came up with the idea of ​​separating a multi-core optical input signal input from a multi-core fiber into multiple single-core optical input signals for single-mode fibers, and feeding back a portion of the optical output signal in each single-mode fiber to switch between multiple tilt equalizers within the variable tilt equalizer. The automatic variable tilt device according to the present disclosure will be described below.

[0018] <Configuration of automatic variable tilt device> First, the configuration of an automatic variable tilt device according to this embodiment will be described. The automatic variable tilt device according to the present disclosure is inserted between multi-core fibers in a multi-core system. Fig. 1 is a block diagram showing an example configuration of an automatic variable tilt device 1 according to this disclosure. The configuration of the automatic variable tilt device 1 according to this embodiment will be described with reference to Fig. 1.

[0019] In this example, a case where a two-core multi-core fiber is used as the multi-core fiber will be described. However, the present disclosure is not limited to the case where a two-core multi-core fiber is used, and can also be applied to the case where a multi-core fiber with three or more cores is used. In that case, it is sufficient to provide the same number of processing systems as the number of cores, as described below, in accordance with the number of cores.

[0020] 1, the automatic variable tilt apparatus 1 includes an input-side fan-in / fan-out device (hereinafter referred to as Fi / Fo device) 11, two variable tilt equalizers 12 and 13, a feedback control unit 14, two optical couplers 15 and 16, and an output-side Fi / Fo device 17. A multi-core optical input signal is input from a multi-core fiber to the automatic variable tilt apparatus 1. The system including the variable tilt equalizer 12 is referred to as system A, and the system including the variable tilt equalizer 13 is referred to as system B.

[0021] In this example, the multi-core fiber is composed of two single-core optical input signals Ai and Bi. FIG. 2 is a diagram showing an example of an optical input signal to the automatic variable tilt device 1 according to the present disclosure. As shown in FIG. 2, each of the single-core optical input signals Ai and Bi has a spectrum consisting of five wavelengths λ1 to λ5. Each of the wavelengths λ1 to λ5 is the center wavelength of a predetermined wavelength range. Here, the single-core optical input signal Ai has a characteristic that the longer the wavelength, the higher the gain, and the single-core optical input signal Bi has a characteristic that the longer the wavelength, the lower the gain.

[0022] The Fi / Fo device 11 on the input side is configured to separate multi-core optical input signals Ai and Bi input from a multi-core fiber into single-core optical input signals Ai and Bi. The signal line between the Fi / Fo device 11 and the Fi / Fo device 17 is a single-mode fiber (SMF).

[0023] A single-core optical input signal Ai is input to a variable tilt equalizer 12, and a single-core optical input signal Bi is input to a variable tilt equalizer 13. The variable tilt equalizers 12 and 13 are configured to adjust the tilt (inclination) levels of the single-core optical input signals Ai and Bi, respectively. Fig. 3 is a block diagram showing an example configuration of the variable tilt equalizers 12 and 13 of the automatic variable tilt device 1 according to the present disclosure.

[0024] 3(a), variable tilt equalizer 12 includes input-side optical switch (optical matrix switch) 121, nine tilt equalizers 1201-1209 corresponding to nine types of gain, and output-side optical switch 122. Switching of tilt equalizers 1201-1209 by optical switches 121 and 122 is controlled by feedback control unit 14.

[0025] The nine tilt equalizers 1201-1209 of variable tilt equalizer 12 include tilt equalizer 1205 with a gain of 0 dB, and eight tilt equalizers 1201-1204 and 1206-1209 with gains set at predetermined intervals in both positive and negative directions. Here, the predetermined interval is 1 dB. That is, the eight tilt equalizers 1201 to 1204, 1206 to 1209 are tilt equalizer 1201 with a gain of -4 dB, tilt equalizer 1202 with a gain of -3 dB, tilt equalizer 1203 with a gain of -2 dB, tilt equalizer 1204 with a gain of -1 dB, tilt equalizer 1206 with a gain of +1 dB, tilt equalizer 1207 with a gain of +2 dB, tilt equalizer 1208 with a gain of +3 dB, and tilt equalizer 1209 with a gain of +4 dB.

[0026] 3(b), variable tilt equalizer 13 includes input-side optical switch 131, nine tilt equalizers 1301-1309 corresponding to nine types of gain, and output-side optical switch 132. Switching of tilt equalizers 1301-1309 by optical switches 131 and 132 is controlled by feedback control unit 14.

[0027] The nine tilt equalizers 1301 to 1309 of the variable tilt equalizer 13 include a tilt equalizer 1305 with a gain of 0 dB, and eight tilt equalizers 1301 to 1304 and 1306 to 1309 with gains set at predetermined intervals in both positive and negative directions. Similarly to the variable tilt equalizer 12, the eight tilt equalizers 1301 to 1304, 1306 to 1309 are tilt equalizer 1301 with a gain of -4 dB, tilt equalizer 1302 with a gain of -3 dB, tilt equalizer 1303 with a gain of -2 dB, tilt equalizer 1304 with a gain of -1 dB, tilt equalizer 1306 with a gain of +1 dB, tilt equalizer 1307 with a gain of +2 dB, tilt equalizer 1308 with a gain of +3 dB, and tilt equalizer 1309 with a gain of +4 dB.

[0028] The number of tilt equalizers included in each of variable tilt equalizers 12, 13 is not limited to nine. The number of tilt equalizers included in each of variable tilt equalizers 12, 13 can be generalized to 2N+1 (N is a positive integer), but to prevent the entire automatic variable tilt device 1 from becoming large, N may be any number between 2 and 4, for example. That is, the number of tilt equalizers included in each of variable tilt equalizers 12, 13 may be any number between 5, 7, and 9. Furthermore, the predetermined interval between tilt equalizers may be adjusted as appropriate depending on the number of tilt equalizers.

[0029] 3, in the initial state, variable tilt equalizer 12 selects tilt equalizer 1205 with a gain of 0 dB, and variable tilt equalizer 13 selects tilt equalizer 1305 with a gain of 0 dB. As a result, as shown in FIG. 1, each of variable tilt equalizers 12 and 13 outputs the input single-core optical input signals Ai and Bi without modification.

[0030] The two optical couplers 15, 16 are configured to split the two single-core optical output signals Ai, Bi from the two variable tilt equalizers 12, 13 into two optical signals at a predetermined ratio. Here, the predetermined ratio may be, for example, 1:9, taking into account the strength of the optical output signal at the subsequent stage, but is not limited to this. Each of the optical couplers 15, 16 outputs a split optical signal that is one of the split single-core optical output signals Ai, Bi, which is a small ratio, to the feedback control unit 14. That is, each of the optical couplers 15, 16 outputs optical feedback signals Af, Bf to the feedback control unit 14.

[0031] On the other hand, each of the optical couplers 15 and 16 outputs a branched optical signal, which is the other of the branched single-core optical output signals Ai and Bi, that accounts for a large proportion of the total, to the Fi / Fo device 17. That is, each of the optical couplers 15 and 16 outputs the single-core optical output signals Ao and Bo to the Fi / Fo device 17.

[0032] The output-side Fi / Fo device 17 is configured to combine the single-core optical output signals Ao and Bo branched by the two optical couplers 15 and 16, and output the combined multi-core optical output signals Ao and Bo.

[0033] Feedback control unit 14 is configured to feedback control corresponding variable tilt equalizers 12, 13 based on the tilt levels of optical feedback signals Af, Bf branched by each of two optical couplers 15, 16. The configuration of feedback control unit 14 will be described below with reference to Fig. 4. Fig. 4 is a block diagram showing an example configuration of feedback control unit 14 of automatic variable tilt device 1 according to the present disclosure.

[0034] As shown in FIG. 4, the feedback control unit 14 includes a bandpass filter (BPF) 141, a photodiode (PD) 142, an analysis unit 143, and a control unit 144 of an A system, a bandpass filter (BPF) 145, a photodiode (PD) 146, an analysis unit 147, and a control unit 148 of a B system, and a memory 149.

[0035] The bandpass filters 141 and 145 are configured to extract an optical signal of a specific wavelength (here, an optical signal of wavelength λ1) from the optical feedback signals Af and Bf, respectively, and output the optical signal to the photodiodes 142 and 146. Specifically, the bandpass filters 141 and 145 are configured to extract an optical signal of wavelength λ1, the shortest wavelength among the optical signals of multiple wavelengths λ1 to λ5, as the optical signal of the specific wavelength, and output the optical signal to the photodiodes 142 and 146. The photodiodes 142 and 146 are configured to receive the optical signal of the specific wavelength λ1 and convert the optical signal into two electrical signals, respectively.

[0036] The analyzers 143 and 147 are configured to analyze the tilt levels of the single-core optical input signals Ai and Bi, respectively, based on two electrical signals corresponding to the optical signal of the specific wavelength λ1. The memory 149 is configured to store a target tilt level. Here, the target tilt level means a tilt level at which the gain of the optical fiber in the optical submarine system is approximately constant (0 dB) at each of the wavelengths λ1 to λ5. This target tilt level is set in advance depending on the type of optical fiber used, the transmission distance, etc., and is stored in the memory 149.

[0037] Control units 144, 148 are configured to select one tilt equalizer from among the plurality of tilt equalizers 1201-1209, 1301-1309 of the corresponding variable tilt equalizers 12, 13, respectively, based on the analysis results of each analysis unit 143, 147 and the target tilt level stored in memory 149. Control units 144, 148 are then configured to control optical switches 121, 122, 131, 132 of variable tilt equalizers 12, 13, based on the selected one tilt equalizer, to switch the tilt equalizers.

[0038] <Operation of terminal device> Next, an example of the operation of the automatic tilt device 1 according to this embodiment will be described with reference to the above-mentioned FIGS. 1 to 4 and 5 to 7. In this embodiment, the automatic tilt device 1 executes an optical signal gain equalization method (optical signal gain equalization processing). Here, the operation of each system will be explained, divided into system A and system B. FIG. 5 is a conceptual diagram showing the state of an optical signal after gain equalization by the automatic tilt device 1 according to the present disclosure. FIG. 6 is a block diagram showing an example of the connection of variable tilt equalizers after gain equalization by the automatic tilt device 1 according to the present disclosure. FIG. 7 is a simplified diagram showing the state of an optical signal after gain equalization by the automatic tilt device 1 according to the present disclosure and the connection of tilt equalizers.

[0039] First, multi-core optical input signals Ai and Bi are input from the multi-core fiber of the multi-core system to the Fi / Fo device 11, which separates them into single-core optical input signals Ai and Bi and branches them into two single-mode fibers (SMF). First, the operation of system A will be explained.

[0040] In the A system, the single-core optical input signal Ai is input to the optical switch 121 of the variable tilt equalizer 12. Here, in the initial stage, the tilt equalizer 1205 with a gain of 0 dB of the variable tilt equalizer 12 is selected and is electrically connected to the optical switch 122 (see FIG. 3(a)). Next, the single-core optical input signal Ai is output from the variable tilt equalizer 12 as the single-core optical output signal Ai via the tilt equalizer 1205 and the optical switch 122 (see FIG. 1).

[0041] Next, the single-core optical output signal Ai is input to the optical coupler 15. In the optical coupler 15, the single-core optical output signal Ai is branched into two optical signals at a predetermined ratio. A part of the branched single-core optical output signal Ai is input to the feedback control unit 14 as an optical feedback signal Af.

[0042] Here, in order to obtain tilt information of the single-core optical input signal Ai from the branched optical feedback signal Af, it is necessary to extract an optical signal of a specific wavelength. For this purpose, the feedback control unit 14 inputs the optical feedback signal Af to a bandpass filter 141. The bandpass filter 141 extracts and outputs the optical signal of the specific wavelength λ1. Next, the extracted optical signal of the specific wavelength λ1 is input to a photodiode 142. The photodiode 142 converts the extracted optical signal of the specific wavelength λ1 into an electrical signal, and the electrical signal is output.

[0043] This electrical signal is input to the analysis unit 143. The analysis unit 143 analyzes the tilt level of the single-core optical input signal Ai based on the electrical signal and outputs the analysis result (analysis information). The analysis result of the analysis unit 143 is input to the control unit 144. Upon receiving the tilt level of the single-core optical input signal Ai, which is the analysis result of the analysis unit 143, the control unit 144 acquires target tilt information stored in the memory 149.

[0044] The control unit 144 compares the tilt level of the single-core optical input signal Ai with the target tilt information, and calculates the required tilt level adjustment amount according to the comparison result. In this example, the tilt level (slope) of the single-core optical input signal Ai is larger than the tilt level (slope) of the single-core optical input signal Bi, and the control unit 144 selects the tilt equalizer 1201 with a gain of −4 dB from the multiple tilt equalizers 1201 to 1209 of the variable tilt equalizer 12 (see FIG. 6(a)). Next, the optical switches 121 and 122 of the variable tilt equalizer 12 switch from the tilt equalizer 1205 with a gain of 0 dB to the tilt equalizer 1201 with a gain of −4 dB under the control of the control unit 144, and the execution of the optical signal gain equalization method is terminated.

[0045] After completing such operation of the A system, when the tilt equalizer 1201 corresponding to the tilt level of the single-core optical input signal Ai is selected, the spectrum of the optical signal becomes as shown in the A system of Fig. 5. That is, the spectral tilt of the single-core optical input signal Ai is adjusted by the variable tilt equalizer 12, and the single-core optical output signal Ae after the tilt adjustment is output from the variable tilt equalizer 12. Here, as shown in Fig. 5, the single-core optical output signal Ae has a spectrum in which the gains of the wavelengths λ1 to λ5 are substantially the same.

[0046] Since the optical feedback signal Aef branched by the optical coupler 15 also has a flat tilt level where the gains of the wavelengths λ1 to λ5 are substantially the same, the feedback control unit 14 does not adjust the tilt level, and the tilt equalizer 1201 with a gain of −4 dB remains selected in the variable tilt equalizer 12. Meanwhile, the remainder of the single-core optical output signal Ae branched by the optical coupler 15 after tilt adjustment is input to the Fi / Fo device 17 as a single-core optical output signal Aeo, which is a part of the multi-core optical output signal of the automatic variable tilt device 1.

[0047] Next, the operation of the B system will be described. In the B system, the single-core optical input signal Bi is input to the optical switch 131 of the variable tilt equalizer 13. Here, as in the A system, in the initial stage, the tilt equalizer 1305 of the variable tilt equalizer 13, which has a gain of 0 dB, is selected and is electrically connected to the optical switch 132 (see FIG. 3(b)). Next, the single-core optical input signal Bi is output from the variable tilt equalizer 13 as the single-core optical output signal Bi via the tilt equalizer 1305 and the optical switch 132 (see FIG. 1).

[0048] Next, the single-core optical output signal Bi is input to the optical coupler 16. The optical coupler 16 branches the single-core optical output signal Bi into two optical signals at a predetermined ratio. A part of the branched single-core optical output signal Bi is input to the feedback control unit 14 as an optical feedback signal Bf.

[0049] Here, in order to obtain tilt information of the single-core optical input signal Bi from the branched optical feedback signal Bf, it is necessary to extract an optical signal of a specific wavelength. For this purpose, the feedback control unit 14 inputs the optical feedback signal Bf to a bandpass filter 145. The bandpass filter 145 extracts and outputs the optical signal of the specific wavelength λ1. Next, the extracted optical signal of the specific wavelength λ1 is input to a photodiode 146. The photodiode 146 converts the extracted optical signal of the specific wavelength λ1 into an electrical signal, and the electrical signal is output.

[0050] This electrical signal is input to the analysis unit 147. The analysis unit 147 analyzes the tilt level of the single-core optical input signal Bi based on the electrical signal and outputs the analysis result (analysis information). The analysis result of the analysis unit 147 is input to the control unit 148. Upon receiving the tilt level of the single-core optical input signal Bi, which is the analysis result of the analysis unit 147, the control unit 148 acquires target tilt information stored in the memory 149.

[0051] The control unit 148 compares the tilt level of the single-core optical input signal Bi with the target tilt information, and calculates the required tilt level adjustment amount according to the comparison result. In this example, the tilt level (gradient) of the single-core optical input signal Bi is smaller than the tilt level (gradient) of the single-core optical input signal Ai, and the control unit 148 selects the tilt equalizer 1307 with a gain of +2 dB from the multiple tilt equalizers 1301 to 1309 of the variable tilt equalizer 13 (see FIG. 6(b)). Next, the optical switches 131 and 132 of the variable tilt equalizer 13 switch from the tilt equalizer 1305 with a gain of 0 dB to the tilt equalizer 1307 with a gain of +2 dB under the control of the control unit 148, and the execution of the optical signal gain equalization method is terminated.

[0052] After completing such operation of the B system, when the tilt equalizer 1307 corresponding to the tilt level of the single-core optical input signal Bi is selected, the spectrum of the optical signal becomes as shown in the B system in Fig. 5. That is, the spectral tilt of the single-core optical input signal Bi is adjusted by the variable tilt equalizer 13, and the single-core optical output signal Be after the tilt adjustment is output from the variable tilt equalizer 13. Here, as shown in Fig. 5, the single-core optical output signal Be has a spectrum in which the gains of the wavelengths λ1 to λ5 are substantially the same.

[0053] Since the optical feedback signal Bef branched by the optical coupler 16 also has a flat tilt level where the gains of the wavelengths λ1 to λ5 are substantially the same, the feedback control unit 14 does not adjust the tilt level, and the tilt equalizer 1307 with a gain of +2 dB remains selected in the variable tilt equalizer 13. Meanwhile, the remainder of the single-core optical output signal Be branched by the optical coupler 16 after tilt adjustment is input to the Fi / Fo device 17 as a single-core optical output signal Beo, which is a part of the multi-core optical output signal of the automatic variable tilt device 1.

[0054] Finally, the Fi / Fo device 17 multiplexes the single-core optical output signal Aeo input from the optical coupler 15 and the single-core optical output signal Beo input from the optical coupler 16, and the multiplexed multi-core optical output signals Aeo and Beo are output from the Fi / Fo device 17 (see Figure 5).

[0055] Regarding the series of operations of the optical signal gain equalization method described above, the state of the optical signal after gain equalization by the automatic variable tilt device 1 and the connection of the tilt equalizer will be briefly described with reference to Fig. 7. First, multi-core optical input signals Ai and Bi are input from the multi-core fiber of the multi-core system to the Fi / Fo device 11, and are separated into a single-core optical input signal Ai and a single-core optical input signal Bi.

[0056] Next, the single-core optical input signal Ai is input to a tilt equalizer 1201 with a gain of −4 dB, which outputs a tilt-adjusted single-core optical output signal Ae with a flat tilt level, while the single-core optical input signal Bi is input to a tilt equalizer 1307 with a gain of +2 dB, which outputs a tilt-adjusted single-core optical output signal Be with a flat tilt level.

[0057] Finally, although not shown, single-core optical output signals Aeo and Beo, which are the difference between the optical feedback signals Aef and Bef, are input to the Fi / Fo device 17, and after being multiplexed by the Fi / Fo device 17, multi-core optical output signals Aeo and Beo are output from the Fi / Fo device 17.

[0058] Next, the operation of the automatic variable tilt device 1 will be described again using the flowchart shown in Fig. 8. Fig. 8 is a flowchart showing an example of an optical signal gain equalization process executed by the automatic variable tilt device 1 according to the present disclosure.

[0059] The automatic variable tilt device 1 according to this embodiment performs optical signal gain equalization processing, for example, at a predetermined timing or constantly. When the optical signal gain equalization processing starts, first, the Fi / Fo device 11 separates multi-core optical input signals Ai, Bi from a multi-core fiber of a multi-core system into two single-core optical input signals Ai, Bi (step S1).

[0060] Next, optical couplers 15 and 16 split each of the single-core optical output signals Ai and Bi output from variable tilt equalizers 12 and 13 into two optical signals (i.e., single-core optical output signals Ao and Bo and optical feedback signals Af and Bf) (step S2).

[0061] Next, the optical feedback signals Af and Bf are input to the feedback control unit 14 (step S3), and in the feedback control unit 14, the analyzers 143 and 147 analyze the tilt levels of the optical signals of the specific wavelength λ1 extracted by the bandpass filters 141 and 145, respectively (step S4).

[0062] Next, control units 144, 148 compare the tilt level analyzed by analysis units 143, 147 with the target tilt level stored in memory 149 (step S5), and calculate the required tilt level adjustment amount based on the comparison result. Then, control units 144, 148 select one tilt equalizer from each of variable tilt equalizers 12, 13 based on the comparison result (tilt level adjustment amount) (step S6).

[0063] Next, under the control of control units 144 and 148, the connection is switched to one tilt equalizer selected from among variable tilt equalizers 12 and 13 (step S7), and this optical signal gain equalization process is completed.

[0064] As described above, the automatic variable tilt apparatus 1 according to this embodiment includes a first fan-in / fan-out device 11 that separates multi-core optical input signals Ai, Bi from a multi-core fiber into two single-core optical input signals Ai, Bi, two variable tilt equalizers 12, 13 that adjust the tilt levels of the two single-core optical input signals Ai, Bi, respectively, and two single-core optical output signals Ai, Bi or Ae, Be from the two variable tilt equalizers 12, 13 at a predetermined ratio to two optical signals Ao, Af and Bo, Bf or Aeo, Aef and Beo, B. a feedback control unit 14 that feedback-controls the corresponding variable tilt equalizers 12, 13 based on the tilt levels of one of the single-core optical output signals Af, Bf branched by each of the two optical couplers 15, 16, and a second fan-in / fan-out device 17 that combines the other of the single-core optical output signals Ao, Bo or Aeo, Beo branched by each of the two optical couplers 15, 16, and outputs a combined multi-core optical output signal Ao, Bo or Aeo, Beo. By configuring the automatic variable tilt apparatus 1 in this way, the gain of the variable tilt equalizers 12, 13 can be changed in accordance with the control of the feedback control unit 14, and the tilt levels of the single-core optical input signals Ai, Bi can be automatically adjusted to be flat. As described above, the automatic variable tilt device 1 according to this embodiment can automatically adjust the tilt level (inclination) of the optical profile (spectrum) which is an optical input signal in an optical submarine system using a multi-core fiber in a short time. Furthermore, by automatically adjusting the optical profile (spectrum), it is possible to simplify the monitoring of the optical submarine system.

[0065] Furthermore, in the automatic variable tilt device 1 according to this embodiment, the feedback control unit 14 is configured to include two bandpass filters 141, 145 that extract and output optical signals of specific wavelengths λ1 from one of the single-core optical output signals Af, Bf corresponding to each of the two single-core optical output signals Ai, Bi, respectively; two photodiodes 142, 146 that receive the two optical signals of specific wavelengths λ1 and convert them into two electrical signals, respectively; two analyzers 143, 147 that analyze the tilt levels of the two single-core optical input signals Ai, Bi based on the two electrical signals; a memory 149 that stores the target tilt level; and two control units 144, 148 that select one tilt equalizer from each of the variable tilt equalizers 12, 13 based on the analysis results of the analyzers 143, 147 and the target tilt level, and control switching of the tilt equalizers in the variable tilt equalizers 12, 13. Each of the two variable tilt equalizers 12 and 13 is configured to include a plurality of tilt equalizers 1201 to 1209, 1301 to 1309 corresponding to a plurality of gains, and optical switches 121, 122, 131, 132 corresponding to the number of tilt equalizers 1201 to 1209, 1301 to 1309. By configuring the automatic variable tilt device 1 according to this embodiment in this way, in addition to the above-mentioned effects, it is possible to automatically adjust the tilt levels of the single-core optical input signals Ai and Bi to be flat by switching between a small number of tilt equalizers.

[0066] Moreover, the optical signal gain equalization method according to the present embodiment is configured to: separate, by a first fan-in / fan-out device 11, multi-core optical input signals Ai, Bi from a multi-core fiber into two single-core optical input signals Ai, Bi; input the two single-core optical input signals Ai, Bi to two variable tilt equalizers 12, 13, respectively; branch, by two optical couplers 15, 16, the single-core optical output signals Ai, Bi from the corresponding variable tilt equalizers 12, 13 into two optical signals at a predetermined ratio; feedback-control the corresponding variable tilt equalizers 12, 13 based on the tilt levels Af, Bf of one of the single-core optical output signals branched by each of the two optical couplers 15, 16; and combine, by a second fan-in / fan-out device 17, the other of the single-core optical output signals Aeo, Beo branched by each of the two optical couplers 15, 16, respectively, and output the combined multi-core optical output signals Aeo, Beo. By configuring the optical signal gain equalization method in this way, it is possible to achieve the same effects as the automatic variable tilt device 1 according to this embodiment.

[0067] The feedback control unit 14 of the automatic variable tilt device 1 described above, particularly the processing performed by the analysis units 143 and 147 and the control units 144 and 148, can be partly or entirely implemented as a computer program that can be installed in the automatic variable tilt device 1. Such a program can be stored on various types of non-transitory computer-readable media and provided to a computer. Non-transitory computer-readable media include various types of tangible recording media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)). The program may also be provided to a computer by various types of temporary computer-readable media. Examples of temporary computer-readable media include electrical signals, optical signals, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire or an optical fiber, or via a wireless communication path.

[0068] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure.

[0069] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix 1) a first fan-in / fan-out device for splitting a multi-core optical input signal from a multi-core fiber into two single-core optical input signals; two variable tilt equalizers for adjusting tilt levels of the two single-core optical input signals, respectively; two optical couplers that split the two single-core optical output signals from the two variable tilt equalizers into two optical signals at a predetermined ratio; a feedback control unit that feedback-controls the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; a second fan-in / fan-out device that combines the other of the single-core optical output signals branched by each of the two optical couplers and outputs a combined multi-core optical output signal; An automatic variable tilt device comprising: (Appendix 2) each of the two variable tilt equalizers includes a plurality of tilt equalizers corresponding to a plurality of gains, and an optical switch corresponding to the number of the plurality of tilt equalizers; the feedback controller selects one tilt equalizer from the plurality of tilt equalizers for each of the two variable tilt equalizers based on a tilt level of one of the corresponding single-core optical output signals; the optical switch for each of the two variable tilt equalizers switches to the selected one of the tilt equalizers; 10. An automatic variable tilt device as described in appendix 1. (Appendix 3) The feedback control unit, corresponding to each of the two single-core optical output signals, two bandpass filters each extracting an optical signal of a specific wavelength from one of the single-core optical output signals and outputting the extracted optical signal; two photodiodes that receive the two optical signals of the specific wavelengths and convert them into two electrical signals, respectively; two analyzers for analyzing tilt levels of the two single-core optical input signals based on the two electrical signals; a memory for storing a target tilt level; two control units each selecting one of the tilt equalizers based on the analysis result of the analysis unit and the target tilt level, and controlling switching of the tilt equalizer in the variable tilt equalizer; Including, 1. An automatic variable tilt device as described in Appendix 2. (Appendix 4) each of the two single-core optical input signals is composed of optical signals of multiple wavelengths; the two bandpass filters extract, as the optical signal of the specific wavelength, the optical signal having the shortest wavelength from among the optical signals of the plurality of wavelengths; 1. An automatic variable tilt device as described in Appendix 3. (Appendix 5) Each of the two control units compares the analysis result of the corresponding analysis unit with the target tilt level to calculate a tilt level adjustment amount, and selects the one tilt equalizer based on the tilt level adjustment amount. 1. An automatic variable tilt device as described in Appendix 3. (Appendix 6) The plurality of tilt equalizers include a tilt equalizer with a gain of 0 dB and 2N (N is a positive integer) tilt equalizers with gains set at predetermined intervals in positive and negative directions. An automatic variable tilt device according to any one of appendixes 2 to 5. (Appendix 7) The N is any one of 2 to 4. 6. An automatic variable tilt device as described in Appendix 6. (Appendix 8) A first fan-in / fan-out device separates a multi-core optical input signal from a multi-core fiber into two single-core optical input signals; The two single-core optical input signals are input to two variable tilt equalizers, respectively; Each of the two optical couplers splits the single-core optical output signal from the corresponding variable tilt equalizer into two optical signals at a predetermined ratio; feedback-controlling the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; a second fan-in / fan-out device combines the other of the single-core optical output signals branched by each of the two optical couplers, and outputs a combined multi-core optical output signal; Optical signal gain equalization method. (Appendix 9) each of the two variable tilt equalizers includes a plurality of tilt equalizers corresponding to a plurality of gains, and an optical switch corresponding to the number of the plurality of tilt equalizers; In the feedback control, one tilt equalizer is selected from the plurality of tilt equalizers of each of the two variable tilt equalizers based on a tilt level of one of the corresponding single-core optical output signals, and the optical switch switches to the selected one tilt equalizer. 9. A method for optical signal gain equalization as recited in claim 8. (Appendix 10) In the feedback control, in response to each of the two single-core optical input signals, extracting an optical signal of a specific wavelength from one of the single-core optical output signals; converting the two optical signals of the specific wavelengths into two electrical signals; Analyzing a tilt level of each of the two single-core optical input signals based on the two electrical signals; selecting one of the tilt equalizers based on the target tilt level stored in a memory and the analysis result of the analysis, and switching to the selected one of the tilt equalizers; 10. A method for optical signal gain equalization as recited in claim 9. (Appendix 11) each of the two single-core optical input signals is composed of optical signals of multiple wavelengths; extracting, as the optical signal of the specific wavelength, the optical signal with the shortest wavelength from among the optical signals of the plurality of wavelengths; 11. An optical signal gain equalization method as recited in claim 10. (Appendix 12) In the step of switching to the selected one tilt equalizer, A result of the analysis is compared with the target tilt level to calculate a tilt level adjustment amount; selecting the one tilt equalizer based on the tilt level adjustment amount; 11. An optical signal gain equalization method as recited in claim 10. (Appendix 13) extracting optical signals of specific wavelengths from portions of each of two single-core optical input signals separated from the multi-core optical input signal by the fan-in / fan-out device; converting the two optical signals of the specific wavelengths into two electrical signals; analyzing tilt levels of the two single-core optical input signals based on the two electrical signals; a process of selecting one tilt equalizer from a plurality of tilt equalizers in each of the two variable tilt equalizers based on the target tilt level stored in the memory and the analysis result of the analysis, and switching to the selected one tilt equalizer; after the switching, combining the two optical output signals output from the two variable tilt equalizers and outputting a combined multi-core optical output signal; A program that causes a computer to execute the following. [Explanation of symbols]

[0070] 1 Automatic variable tilt device 11, 17 Fan-in / Fan-out (Fi / Fo) devices 12 variable tilt equalizer 121, 122, 131, 132 Optical switches 1201~1209 Tilt equalizer 13 Variable Tilt Equalizer 1301~1309 Tilt equalizer 14 Feedback control section 141, 145 Bandpass filter (BPF) 142, 146 Photodiode (PD) 143, 147 Analysis Department 144, 148 Control section 149 memory 15, 16 Optical coupler

Claims

1. a first fan-in / fan-out device for splitting a multi-core optical input signal from a multi-core fiber into two single-core optical input signals; two variable tilt equalizers for adjusting tilt levels of the two single-core optical input signals, respectively; two optical couplers that split the two single-core optical output signals from the two variable tilt equalizers into two optical signals at a predetermined ratio, respectively; a feedback control unit that feedback-controls the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; a second fan-in / fan-out device that combines the other of the single-core optical output signals branched by each of the two optical couplers and outputs a combined multi-core optical output signal; An automatic variable tilt device comprising:

2. each of the two variable tilt equalizers includes a plurality of tilt equalizers corresponding to a plurality of gains and an optical switch corresponding to the number of the plurality of tilt equalizers; the feedback controller selects one tilt equalizer from the plurality of tilt equalizers for each of the two variable tilt equalizers based on a tilt level of one of the corresponding single-core optical output signals; the optical switch for each of the two variable tilt equalizers switches to the selected one of the tilt equalizers; 2. The automatic variable tilt device according to claim 1.

3. The feedback control unit, corresponding to each of the two single-core optical output signals, two bandpass filters each extracting an optical signal of a specific wavelength from one of the single-core optical output signals and outputting the extracted optical signal; two photodiodes that receive the two optical signals of the specific wavelengths and convert them into two electrical signals; two analyzers that analyze tilt levels of the two single-core optical input signals based on the two electrical signals; a memory for storing a target tilt level; two control units that select one tilt equalizer based on the analysis result of the analysis unit and the target tilt level, and control switching of the tilt equalizer in the variable tilt equalizer; Including, 3. The automatic variable tilt device according to claim 2.

4. each of the two single-core optical input signals is composed of optical signals of multiple wavelengths; the two bandpass filters extract, as the optical signal of the specific wavelength, the optical signal having the shortest wavelength from among the optical signals of the plurality of wavelengths; 4. The automatic variable tilt device according to claim 3.

5. Each of the two control units compares the analysis result of the corresponding analysis unit with the target tilt level to calculate a tilt level adjustment amount, and selects the one tilt equalizer based on the tilt level adjustment amount.

4. The automatic variable tilt device according to claim 3.

6. the plurality of tilt equalizers include a tilt equalizer with a gain of 0 dB and 2N (N is a positive integer) tilt equalizers with gains set at predetermined intervals in positive and negative directions; 6. An automatic variable tilt device according to any one of claims 2 to 5.

7. N is any one of 2 to 4, 7. The automatic variable tilt device according to claim 6.

8. splitting a multi-core optical input signal from a multi-core fiber into two single-core optical input signals by a first fan-in / fan-out device; The two single-core optical input signals are input to two variable tilt equalizers, respectively; Each of the two optical couplers splits the single-core optical output signal from the corresponding variable tilt equalizer into two optical signals at a predetermined ratio; feedback-controlling the corresponding variable tilt equalizer based on a tilt level of one of the single-core optical output signals branched by each of the two optical couplers; a second fan-in / fan-out device is used to combine the other of the single-core optical output signals branched by each of the two optical couplers, and output a combined multi-core optical output signal; Optical signal gain equalization method.

9. each of the two variable tilt equalizers includes a plurality of tilt equalizers corresponding to a plurality of gains and an optical switch corresponding to the number of the plurality of tilt equalizers; the feedback control selects one tilt equalizer from the plurality of tilt equalizers of each of the two variable tilt equalizers based on a tilt level of one of the corresponding single-core optical output signals, and switches to the selected one tilt equalizer by the optical switch; 9. The method for gain equalizing an optical signal according to claim 8.

10. In the feedback control, in response to each of the two single-core optical input signals, extracting an optical signal of a specific wavelength from one of the single-core optical output signals; converting the two optical signals of the specific wavelengths into two electrical signals; Analyzing a tilt level of each of the two single-core optical input signals based on the two electrical signals; selecting one of the tilt equalizers based on the target tilt level stored in a memory and the analysis result of the analysis, and switching to the selected one of the tilt equalizers; 10. The method of claim 9, wherein the gain of the optical signal is equalized.

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