Optical equalizer, method and non-transitory computer readable medium

Abstract

An object of the present invention is to provide an optical equalizer, a method and a program capable of flattening the tilt characteristic of a wavelength division multiplexed optical signal with a simple configuration. The optical equalizer (11) includes: a detection unit (111) that detects the tilt characteristic based on the intensity of at least two optical signals among a plurality of optical signals multiplexed into the wavelength division multiplexed optical signal; an optical attenuation unit (112) that attenuates the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; and an optical amplification unit (113) that amplifies the attenuated wavelength division multiplexed optical signal using a gain characteristic according to the intensity of the attenuated wavelength division multiplexed optical signal, wherein the optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

Description

Technical Field

[0001] The present disclosure relates to an optical equalizer, a method, and a program, and in particular, to an optical equalizer, a method, and a program configured to be able to flatten a tilt characteristic of a wavelength-division-multiplexed optical signal with a simple configuration. Background Art

[0002] In a submarine optical cable system using a wavelength division multiplexed optical signal, in order to ensure transmission performance, it is preferred to flatten the tilt characteristic (tilt) of the wavelength division multiplexed optical signal. The tilt characteristic represents the difference between the intensities of a plurality of optical signals multiplexed into the wavelength division multiplexed optical signal. The state in which the tilt characteristic is flat is a state in which there is a slight difference between the intensities of the optical signals multiplexed into the wavelength division multiplexed optical signal.

[0003] Patent document 1 discloses a technology for flattening the tilt characteristics of a wavelength division multiplexed optical signal by controlling the output of an excitation light input to an optical amplifier according to the tilt characteristics after detecting the tilt characteristics of the wavelength division multiplexed optical signal amplified by an optical amplifier in a repeater device on an optical transmission line. However, in the technology described in patent document 1, it may not be possible to maintain the intensity of the output wavelength division multiplexed optical signal at a constant level. For example, when the intensity of the wavelength division multiplexed optical signal output from the optical amplifier decreases without changing the tilt characteristics of the wavelength division multiplexed optical signal, the output of the excitation light does not change. Therefore, since the gain in the amplifier does not change even when the intensity of the wavelength division multiplexed optical signal output from the optical amplifier decreases, it is impossible to maintain the intensity of the output wavelength division multiplexed optical signal at a constant level.

[0004] Patent document 2 discloses a technology for flattening the tilt characteristics of a wavelength division multiplexed optical signal by assigning an attenuation that varies depending on the wavelength to the wavelength division multiplexed optical signal using a gain equalizer in a repeater. In the technology described in patent document 2, the wavelength division multiplexed optical signal is separated depending on the wavelength, and a varying attenuation is assigned to each separated signal, thereby assigning an attenuation that varies depending on the wavelength to flatten the tilt characteristics. In the technology described in patent document 2, in order to assign the attenuation that varies depending on the wavelength, a plurality of variable attenuators are arranged in the repeater, and thus the configuration of the repeater becomes complicated. The wavelength division multiplexed optical signal may also be referred to as a WDM (wavelength division multiplexing) signal.

[0005] Citation List

[0006] Patent Literature

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-9864

[0008] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-348017 Summary of the invention

[0009] Technical issues

[0010] As described above, it is difficult to provide an optical equalizer configured to be able to flatten the tilt characteristic of a wavelength-division-multiplexed optical signal with a simple configuration while maintaining the optical signal intensity of the wavelength-division-multiplexed optical signal at a constant level.

[0011] An object of the present disclosure is to provide an optical equalizer, a method, and a program configured to solve any of the above-mentioned problems.

[0012] Solution to the problem

[0013] The optical equalizer according to the present disclosure includes:

[0014] a detection unit configured to detect a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into the wavelength division multiplexed optical signal;

[0015] an optical attenuation unit configured to attenuate the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; and

[0016] an optical amplification unit configured to amplify the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal,

[0017] Here, the optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0018] The optical equalizer according to the present disclosure includes:

[0019] an optical attenuation unit configured to attenuate the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0020] an optical amplification unit configured to amplify the attenuated wavelength-division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength-division multiplexed optical signal; and

[0021] a detection unit configured to detect a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into the attenuated wavelength division multiplexed optical signal,

[0022] Here, the optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0023] The method according to the present disclosure comprises:

[0024] detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal;

[0025] attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0026] amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; and

[0027] The optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0028] The program according to the present disclosure is configured to cause a computer to execute:

[0029] detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal;

[0030] attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0031] amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; and

[0032] The optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0033] Advantageous Effects of the Invention

[0034] According to the present disclosure, an optical equalizer, a method, and a program configured to be able to flatten the tilt characteristic of a wavelength-division-multiplexed optical signal with a simple configuration can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment;

[0036] Figure 2 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment;

[0037] Figure 3A is a view illustrating gain characteristics of an optical amplifying unit according to a first exemplary embodiment;

[0038] Figure 3B is a view illustrating gain characteristics of an optical amplifying unit according to a first exemplary embodiment;

[0039] Figure 3C is a view illustrating gain characteristics of an optical amplifying unit according to a first exemplary embodiment;

[0040] Figure 4Ais a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment;

[0041] Figure 4B is a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment;

[0042] Figure 4C is a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment;

[0043] Figure 5 is a flowchart illustrating the operation of the control unit according to the first example embodiment;

[0044] Figure 6 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment;

[0045] Figure 7 is a block diagram illustrating an optical equalizer according to a comparative example of the first exemplary embodiment; and

[0046] Figure 8 is a block diagram illustrating an optical equalizer according to a second exemplary embodiment. DETAILED DESCRIPTION

[0047] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. The same or corresponding elements are denoted by the same reference numerals in each figure, and redundant descriptions thereof are omitted if necessary to make the description clear.

[0048] [First exemplary embodiment]

[0049] First, an overview of an optical equalizer according to a first exemplary embodiment will be described.

[0050] Figure 1 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment.

[0051] Figure 1 Each of the abscissas of the graphs Gh1 and Gh2 illustrated in indicates a wavelength, and each of the ordinates thereof indicates an optical signal intensity.

[0052] Figure 2 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment.

[0053] like Figure 1 As shown in , the optical equalizer 11 includes a detection unit 111 , an optical attenuation unit 112 , an optical amplification unit 113 , and a control unit 114 .

[0054] A wavelength-division multiplexed optical signal obtained by wavelength-division multiplexing a plurality of optical signals relayed by the repeater device 12 connected in a multi-stage manner is input to the optical equalizer 11. In the wavelength-division multiplexed optical signal before the repeater device 12 relays the signal, the intensity of the optical signal having a plurality of wavelengths is substantially constant, and the inclination of the intensity is close to zero, as shown in the graph Gh1. In other words, its inclination characteristic is flat. The inclination characteristic may also be referred to as "inclination". For example, the repeater device 12 includes an optical amplification unit configured to be able to amplify the wavelength-division multiplexed optical signal.

[0055] In contrast, in the wavelength-division multiplexed optical signal relayed by the repeater device 12, the intensity of the optical signal having a plurality of wavelengths is not constant but inclined as shown in the graph Gh2. In other words, its inclined characteristic is not flat.

[0056] The detection unit 111 detects a tilt characteristic indicating a tilt of the intensity of the optical signal based on the intensity of at least two optical signals among the plurality of optical signals multiplexed into the input wavelength division multiplexed optical signal. The detection unit 111 detects the tilt characteristic based on, for example, the optical signal intensity of the optical signal having the smallest wavelength λ1 among the plurality of optical signals and the optical signal intensity of the optical signal having the largest wavelength λ2 among the plurality of optical signals. The intensity of the optical signal is referred to as "optical signal intensity".

[0057] Specifically, first, the detection unit 111 determines the difference between the optical signal intensity at the minimum wavelength λ1 and the optical signal intensity at the maximum wavelength λ2 as the optical signal intensity difference. Then, the detection unit 111 determines the difference between the minimum wavelength λ1 and the maximum wavelength λ2 as the wavelength difference. Then, the detection unit 111 determines the tilt characteristic (tilt) of the wavelength division multiplexing optical signal by dividing the optical signal intensity difference by the wavelength difference.

[0058] The optical attenuation unit 112 attenuates the optical signal intensity of the wavelength-division-multiplexed optical signal by an optical attenuation amount. The optical attenuation unit may also be referred to as a "VOA (variable optical attenuator) module".

[0059] The optical amplification unit 113 amplifies the wavelength division multiplexed optical signal attenuated by the optical attenuation unit 112. The optical amplification unit 113 is an optical amplification unit in which a gain characteristic is changed based on the intensity of the attenuated optical signal. In other words, the optical amplification unit 113 amplifies the attenuated wavelength division multiplexed optical signal based on a gain characteristic that depends on the intensity of the attenuated wavelength division multiplexed optical signal. The gain characteristic of the optical amplification unit 113 is a characteristic that represents the gain of each of the optical signals having a plurality of wavelengths. The gain may also be referred to as an amount of amplification.

[0060] The optical amplification unit 113 is excited by excitation light from an excitation light source (not shown). The wavelength-division-multiplexed optical signal output from the optical amplification unit 113 is kept at a constant level by adjusting the intensity of the excitation light based on the intensity of the wavelength-division-multiplexed optical signal output from the optical amplification unit 113.

[0061] The control unit 114 controls the optical attenuation amount set in the optical attenuation unit 112 based on the tilt characteristic of the wavelength division multiplexed optical signal detected by the detection unit 111 and the gain characteristic of the optical amplification unit 113. In other words, the control unit 114 sets the optical attenuation amount determined based on the tilt characteristic and the gain characteristic in the optical attenuation unit 112.

[0062] The optical equalizer 11 may further include an optical coupler 116 configured to branch a portion of the input wavelength division multiplexed optical signal. Figure 2 The detection unit 111 detects the tilt characteristic from a portion of the wavelength division multiplexed optical signal branched by the optical coupler 116. The branched portion of the wavelength division multiplexed optical signal may also be referred to as a "signal for automatic control".

[0063] The optical equalizer 11 may further include a storage unit 115. An attenuation table 115a in which the tilt characteristic of the wavelength division multiplexed optical signal, the gain characteristic of the optical amplifying unit 113, and the optical attenuation amount of the optical attenuating unit 112 are associated with each other is stored in advance in the storage unit 115.

[0064] The tilt characteristic is detected by the detection unit 111. Referring to the attenuation table 115a, the control unit 114 determines the intensity of the optical signal input to the optical amplification unit 113, which allows the gain characteristic of the optical amplification unit 113 to become a characteristic opposite to the detected tilt characteristic. The control unit 114 determines the optical attenuation amount to achieve the determined optical signal intensity, and sets the optical attenuation amount in the optical attenuation unit 112. In other words, the control unit 114 selects the optical attenuation amount from the attenuation table 115a based on the tilt characteristic and the gain characteristic, and sets the selected optical attenuation amount in the optical attenuation unit 112. The optical attenuation unit 112 attenuates the optical signal intensity of the wavelength division multiplexed optical signal by the selected optical attenuation amount.

[0065] In setting the optical attenuation amount, the difference between the determined optical signal intensity and a preset reference intensity may be determined as the optical attenuation amount.

[0066] In the setting of the optical attenuation amount, the difference between the determined optical signal intensity and the intensity of the optical signal input to the optical attenuation unit 112 may be determined as the optical attenuation amount. In this case, the intensity of the optical signal input to the optical attenuation unit 112 is determined by, for example, allowing the detection unit 111 to detect the intensity of the wavelength division multiplexed optical signal input to the detection unit 111.

[0067] The optical equalizer 11 according to the first exemplary embodiment controls the optical attenuation amount of the optical attenuation unit 112 provided in the preceding stage of the optical amplifying unit 113 based on the tilt characteristic of the wavelength-division-multiplexed optical signal and the gain characteristic of the optical amplifying unit 113. Therefore, in the optical equalizer 11, the number of components can be reduced, and in addition, compared with an apparatus including a plurality of variable attenuators for assigning attenuation that varies depending on each of optical signals having a plurality of wavelengths, a wavelength-division-multiplexed optical signal having a flattened tilt characteristic can be output.

[0068] Therefore, it is possible to provide an optical equalizer configured to be able to flatten the tilt characteristic of a wavelength division multiplexed optical signal with a simple configuration.

[0069] One optical equalizer 11 can flatten the intensity of an optical signal having a plurality of wavelengths in a wavelength-division multiplexed optical signal. Therefore, the number of optical equalizers 11 in a multi-core system can be reduced, and the price of the system can be reduced.

[0070] In addition, the optical equalizer 11 can automatically flatten the intensity of the optical signal having multiple wavelengths in the wavelength division multiplexed optical signal. Therefore, the tilt characteristics when the system is constructed or after installation can be automatically adjusted, thus simplifying and reducing the operation steps, and thus reducing costs.

[0071] Details of the optical equalizer according to the first exemplary embodiment will now be described.

[0072] <Gain Characteristics of Optical Amplification Unit>

[0073] Figure 3A is a diagram illustrating gain characteristics of the optical amplifying unit according to the first exemplary embodiment.

[0074] Figure 3A The gain characteristics are shown in the figure when the optical signal intensity of the input wavelength division multiplexed optical signal is moderate.

[0075] Figure 3B is a diagram illustrating gain characteristics of the optical amplifying unit according to the first exemplary embodiment.

[0076] Figure 3B The gain characteristics are shown in the figure when the optical signal intensity of the input wavelength division multiplexed optical signal is low.

[0077] Figure 3C is a diagram illustrating gain characteristics of the optical amplifying unit according to the first exemplary embodiment.

[0078] Figure 3C The gain characteristics are shown in the figure when the optical signal intensity of the input wavelength division multiplexed optical signal is high.

[0079] The abscissa and ordinate of each of the graphs Gh11 , Gh12 , Gh21 , Gh22 , Gh311 , and Gh32 indicate the wavelength and the optical signal intensity, respectively.

[0080] like Figure 3A As shown in FIG. 1 , in the case where a wavelength division multiplexed optical signal whose optical signal intensity is in a stable state (moderate) (see graph Gh11) is input to the optical amplifying unit 113, the optical signal intensity of the wavelength division multiplexed optical signal output from the optical amplifying unit 113 is illustrated in graph Gh12. The tilt (i.e., tilt characteristic) of the optical signal intensity of the output wavelength division multiplexed optical signal has a negative value. As described above, the optical amplifying unit 113 has a gain characteristic in that, in the case where the wavelength division multiplexed optical signal is attenuated by the optical attenuation unit 112 and the input optical signal intensity is less than a predetermined optical signal intensity, the gain at the minimum wavelength λ1 is greater than the gain at the maximum wavelength λ2.

[0081] Furthermore, when the value obtained by subtracting the intensity of the optical signal having the maximum wavelength λ2 from the intensity of the optical signal having the minimum wavelength λ1 among the optical signals having a plurality of wavelengths is a negative value, the tilt level is considered to be negative. In the graph Gh12, the tilt level is negative.

[0082] like Figure 3B As shown in FIG. 1 , when a wavelength-division multiplexed optical signal having an optical signal intensity less than that in a stable state (see graph Gh21) is input into the optical amplifying unit 113, the optical signal intensity of the wavelength-division multiplexed optical signal output from the optical amplifying unit 113 is as shown in graph Gh22. Compared with that in graph Gh12, the inclination (i.e., inclination characteristic) of the optical signal intensity of the output wavelength-division multiplexed optical signal is a high negative value. Its inclination level is higher in the negative direction.

[0083] like Figure 3CAs shown in , when a wavelength-division multiplexed optical signal having an optical signal intensity greater than the optical signal intensity in a steady state (see graph Gh31) is input into the optical amplifying unit 113, the optical signal intensity of the wavelength-division multiplexed optical signal output from the optical amplifying unit 113 is as shown in graph Gh32. The tilt (i.e., tilt characteristic) of the optical signal intensity of the output wavelength-division multiplexed optical signal is a positive value. In addition, its tilt level is positive. As described above, the optical amplifying unit 113 has a gain characteristic in that, in the case where the wavelength-division multiplexed optical signal is attenuated by the optical attenuation unit 112 and the input optical signal intensity is greater than a predetermined optical signal intensity, the gain at the minimum wavelength λ1 is less than the gain at the maximum wavelength λ2.

[0084] By changing the optical signal intensity of the wavelength-division multiplexed optical signal input to the optical amplifying unit 113, the tilt characteristic (tilt) of the optical signal intensity of the wavelength-division multiplexed optical signal output from the optical amplifying unit 113 can be changed, such as FIG. 3A to FIG. 3C In other words, its tilt level can be changed.

[0085] <Throughput Characteristics of the Optical Attenuation Unit and the Optical Amplification Unit>

[0086] Figure 4A is a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment.

[0087] Figure 4A The through characteristic of the optical equalizer 11 according to the first exemplary embodiment is illustrated in the case where the tilt characteristic of the optical signal intensity of the input wavelength-division-multiplexed optical signal is flat.

[0088] Figure 4B is a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment.

[0089] Figure 4B The through characteristic of the optical equalizer 11 according to the first exemplary embodiment is illustrated in the case where the tilt characteristic of the optical signal intensity of the input wavelength-division-multiplexed optical signal is positive.

[0090] Figure 4C is a view illustrating the through characteristics of the optical attenuation unit and the optical amplification unit according to the first exemplary embodiment.

[0091] Figure 4C The through characteristic of the optical equalizer 11 according to the first exemplary embodiment is illustrated in the case where the tilt characteristic of the optical signal intensity of the input wavelength-division-multiplexed optical signal is negative.

[0092] Figure 5 is a flowchart illustrating the operation of the control unit according to the first example embodiment.

[0093] like Figure 4A As shown in , when the tilt characteristic of the optical signal intensity of the wavelength division multiplexed optical signal input to the optical attenuation unit 112 is flat, the control unit 114 controls the optical attenuation amount set in the optical attenuation unit 112 so that the tilt characteristic (tilt) of the wavelength division multiplexed optical signal output from the optical amplification unit 113 is flat.

[0094] Specifically, Figure 5 As shown in FIG. 1 , the control unit 114 confirms the intensity of the optical signal having the minimum wavelength λ1 and the intensity of the optical signal having the maximum wavelength λ2 among the plurality of optical signals multiplexed into the wavelength division multiplexed optical signal (step S101). When the intensity of the optical signal having the minimum wavelength λ1 among the plurality of optical signals multiplexed into the wavelength division multiplexed optical signal is equal to the intensity of the optical signal having the maximum wavelength λ2 among the plurality of optical signals, the control unit 114 allows the optical attenuation amount to become a predetermined optical attenuation amount (step S102).

[0095] The control unit 114 changes the inclination of the optical signal intensity of the wavelength-division-multiplexed optical signal output from the optical amplification unit 113 based on the optical attenuation amount (predetermined attenuation amount) set in this case.

[0096] When the tilt characteristic of the optical signal intensity of the wavelength division multiplexed optical signal input to the optical attenuation unit 112 is as follows Figure 4B As shown in FIG. , the tilt characteristic (tilt) of the wavelength division multiplexed optical signal output from the optical amplification unit 113 is as follows: Figure 3B Therefore, the control unit 114 allows the optical attenuation amount set in the optical attenuation unit 112 to be greater than the reference optical attenuation amount.

[0097] Specifically, when the intensity of the optical signal having the smallest wavelength λ1 among the plurality of optical signals multiplexed into the wavelength division multiplexed optical signal is smaller than the intensity of the optical signal having the largest wavelength λ2 among the plurality of optical signals, the control unit 114 allows the optical attenuation to be greater than the predetermined optical attenuation (step S103), such as Figure 5 as shown in .

[0098] Therefore, the slope characteristic of the optical signal intensity of the wavelength-division multiplexed optical signal output from the optical amplification unit 113 can be allowed to become flat.

[0099] When the tilt characteristic of the optical signal intensity of the wavelength division multiplexed optical signal input to the optical attenuation unit 112 is as follows Figure 4C When the value shown in FIG. 1 is negative, the tilt characteristic (tilt) of the wavelength division multiplexed optical signal output from the optical amplification unit 113 is as follows: Figure 3CTherefore, the control unit 114 allows the optical attenuation amount set in the optical attenuation unit 112 to be smaller than the reference optical attenuation amount.

[0100] Specifically, when the intensity of the optical signal having the smallest wavelength λ1 among the plurality of optical signals multiplexed into the wavelength division multiplexed optical signal is greater than the intensity of the optical signal having the largest wavelength λ2 among the plurality of optical signals, the control unit 114 allows the optical attenuation amount to be less than the predetermined optical attenuation amount (step S104), such as Figure 5 as shown in .

[0101] Therefore, the slope characteristic of the optical signal intensity of the wavelength-division multiplexed optical signal output from the optical amplification unit 113 can be allowed to become flat.

[0102] The operation of the optical equalizer according to the first exemplary embodiment will now be described.

[0103] Figure 6 is a block diagram illustrating an optical equalizer according to a first exemplary embodiment.

[0104] like Figure 6 As shown in FIG. 1 , the wavelength-division-multiplexed optical signal input to the optical equalizer 11 is separated into a main signal and a signal for automatic control by an optical coupler 116. The signal for automatic control may also be referred to as "a part of the wavelength-division-multiplexed optical signal".

[0105] The signal for automatic control passes through the optical filter 117, thereby extracting only the optical signal with the smallest wavelength λ1 and the optical signal with the largest wavelength λ2 among the multiple optical signals multiplexed into the wavelength division multiplexed optical signal to pass. The optical filter may also be called a "bandpass filter".

[0106] The optical signal obtained by extracting only the optical signal with the minimum wavelength λ1 and the optical signal with the maximum wavelength λ2 is branched into the optical signal with the minimum wavelength λ1 and the optical signal with the maximum wavelength λ2 by the wavelength branching device 111a. Examples of the wavelength branching device 111a include an AWG (arrayed waveguide grating) filter and an OADM (optical add / drop multiplexer) filter.

[0107] The optical signal with the minimum wavelength λ1 is converted into an electrical signal by the photodiode PD1 and sent to the analysis unit 111b. The optical signal with the maximum wavelength λ2 is converted into an electrical signal by the photodiode PD2 and sent to the analysis unit 111b. The detection unit 111 includes a wavelength branching device 111a, an analysis unit 111b, a photodiode PD1, and a photodiode PD2.

[0108] The analysis unit 111b compares the optical signal intensity of the optical signal having the minimum wavelength λ1 and the optical signal intensity of the optical signal having the maximum wavelength λ2 to calculate the tilt level of the optical input signal. In other words, the analysis unit 111b calculates the tilt characteristic based on the wavelength division multiplexed optical signal that has passed through the optical filter 117. The analysis unit 111b transmits information about the calculated tilt level of the optical input signal to the control unit 114.

[0109] The control unit 114 compares the information about the target tilt level and the information about the calculated tilt level of the optical input signal which are pre-stored in the storage unit 115. The control unit 114 determines the optical attenuation amount of the optical attenuation unit 112 based on the result of the comparison. In other words, the control unit 114 determines the optical attenuation amount so that the tilt characteristic of the wavelength division multiplexed optical signal of the main signal which has been amplified by the optical amplification unit 113 is within the range of the target tilt level (within a predetermined tilt range).

[0110] The control unit 114 controls the optical attenuation amount by transmitting an optical attenuation amount control signal including the determined optical attenuation amount to the optical attenuation unit 112 .

[0111] Therefore, the optical signal intensity of the main signal input to the optical amplifying unit 113 changes. The main signal whose optical signal intensity changes is input to the optical amplifying unit 113, whereby the tilt level (tilt characteristic) of the wavelength division multiplexed optical signal output from the optical amplifying unit 113 changes, converges to the target tilt level, and becomes flat.

[0112] Furthermore, the optical equalizer 11 allows the optical attenuation unit 112 to flatten the tilt, thereby eliminating the need to finely control the output of the excitation light source compared to the case where the tilt is flattened by the excitation light source of the optical amplification unit 113, and thus supports suppression of damage to the excitation light source.

[0113] [Comparative example]

[0114] Figure 7 is a block diagram illustrating an optical equalizer according to a comparative example of the first exemplary embodiment.

[0115] like Figure 7 As shown in FIG. 1 , the optical equalizer 51 according to the comparative example includes an optical switch 511, an optical switch 512, and a tilt equalizer 513. The tilt equalizer 513 includes, for example, a plurality of -4dB (decibel) to +4dB (decibel) tilt equalizers 5131 to 5139. The optical equalizer 51 may also be referred to as a "variable tilt equalizer device".

[0116] The optical equalizer 51 adjusts the tilt level by switching the tilt equalizer 513 using the optical switch 511 and the optical switch 512. Since an increase in the adjustable range of the tilt level leads to an increase in the number of the tilt equalizers 513, it is difficult to reduce the size of the optical equalizer 51.

[0117] Therefore, it is difficult to provide an optical equalizer configured to be able to flatten the tilt characteristic of a wavelength-division-multiplexed optical signal with a simple configuration.

[0118] [Second exemplary embodiment]

[0119] Figure 8 is a block diagram illustrating an optical equalizer according to a second exemplary embodiment.

[0120] like Figure 8 As shown in , the optical equalizer 21 according to the second exemplary embodiment is different from the optical equalizer 11 according to the first exemplary embodiment in that a signal for automatic control is separated from a wavelength-division-multiplexed optical signal output from an optical amplifying unit 113. Therefore, an optical coupler 116 for output from the optical amplifying unit 113 is installed to separate the main signal and the signal for automatic control.

[0121] The optical equalizer 21 according to the second exemplary embodiment includes an optical attenuation unit 112 , an optical amplification unit 113 , a detection unit 111 , and a control unit 114 .

[0122] The optical attenuation unit 112 attenuates the intensity of the wavelength-division-multiplexed optical signal input to the optical equalizer 21 by an optical attenuation amount.

[0123] In the optical amplifying unit 113, the gain characteristic is changed based on the intensity of the wavelength division multiplexed optical signal attenuated by the optical attenuating unit 112. The optical amplifying unit 113 amplifies the attenuated wavelength division multiplexed optical signal based on the gain characteristic based on the intensity of the wavelength division multiplexed optical signal attenuated by the optical attenuating unit 112.

[0124] The detection unit 111 detects the tilt characteristic (tilt) of the optical signal intensity based on the intensities of at least two optical signals among the plurality of optical signals multiplexed into the wavelength-division-multiplexed optical signal that has been amplified by the optical amplification unit 113 .

[0125] The control unit 114 controls the optical attenuation amount set in the optical attenuation unit 112 in accordance with the tilt characteristic detected by the detection unit 111 and the gain characteristic of the optical amplification unit 113 .

[0126] The details of the optical equalizer 21 will be described.

[0127] The wavelength-division-multiplexed optical signal that has been attenuated by the optical attenuation unit 112 and has been amplified by the optical amplification unit 113 is separated into a main signal and a signal for automatic control by the optical coupler 116 .

[0128] The separated signal for automatic control passes through the optical filter 117, thereby extracting only the optical signal having the smallest wavelength λ1 among the plurality of optical signals included in the wavelength division multiplexed optical signal and the optical signal having the largest wavelength λ2 among the plurality of optical signals.

[0129] The optical signal from which only the optical signal having the minimum wavelength λ1 and the optical signal having the maximum wavelength λ2 are extracted is branched into the optical signal having the minimum wavelength λ1 and the optical signal having the maximum wavelength λ2 by the wavelength branching device 111 a .

[0130] The optical signal with the minimum wavelength λ1 is converted into an electrical signal by the photodiode PD1 and sent to the analysis unit 111b. The optical signal with the maximum wavelength λ2 is converted into an electrical signal by the photodiode PD2 and sent to the analysis unit 111b.

[0131] The analyzing unit 111b compares the optical signal intensity of the optical signal having the minimum wavelength λ1 with the optical signal intensity of the optical signal having the maximum wavelength λ2 to calculate the tilt level of the optical input signal. The analyzing unit 111b sends information about the calculated tilt level of the optical input signal to the controlling unit 114.

[0132] The control unit 114 compares the information about the target tilt level and the information about the calculated tilt level of the optical input signal pre-stored in the storage unit 115. The control unit 114 determines the optical attenuation amount of the optical attenuation unit 112 based on the result of the comparison. The control unit 114 controls the optical attenuation amount by transmitting an optical attenuation amount control signal including the determined optical attenuation amount to the optical attenuation unit 112.

[0133] Therefore, the optical signal intensity of the wavelength-division multiplexed optical signal input to the optical amplifying unit 113 changes. The wavelength-division multiplexed optical signal whose optical signal intensity changes is input to the optical amplifying unit 113, whereby the tilt level (tilt characteristic) of the wavelength-division multiplexed optical signal output from the optical amplifying unit 113 changes, converges to a target tilt level, and becomes flat.

[0134] In the above exemplary embodiments, the present invention has been described as a hardware configuration. However, the present invention is not limited thereto. In the present invention, the processing of each component can also be achieved by allowing the CPU (Central Processing Unit) to execute a computer program.

[0135] In the above-described example embodiments, various types of non-transitory computer-readable media are used to store the program, and the program can be supplied to the computer. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (specifically, floppy disks, magnetic tapes, and hard disk drives), magneto-optical recording media (specifically, magneto-optical disks), CD-ROMs (read-only memories), CD-Rs, CD-R / Ws, semiconductor memories (specifically, mask ROMs, PROMs (programmable ROMs), and EPROMs (erasable PROMs)), flash ROMs, and RAMs (random access memories). The program can also be supplied to the computer via various types of temporary computer-readable media. Examples of temporary computer-readable media include electrical signals, optical signals, and electromagnetic waves. Temporary computer-readable media enable the program to be supplied to the computer via a wired communication channel or a radio channel such as an electric wire or optical fiber.

[0136] The present invention is not limited to the above-described exemplary embodiments, but may be appropriately modified without departing from the gist of the present invention.

[0137] Some or all of the above exemplary embodiments may also be described in the following supplementary descriptions, but are not limited thereto.

[0138] (Supplementary Note 1)

[0139] An optical equalizer, comprising:

[0140] a detection unit for detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into the wavelength division multiplexed optical signal;

[0141] an optical attenuation unit, the optical attenuation unit being used to attenuate the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; and

[0142] an optical amplification unit for amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal,

[0143] Here, the optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0144] (Supplementary Note 2)

[0145] The optical equalizer according to Supplementary note 1, wherein the detection unit detects the tilt characteristic based on an intensity of an optical signal having a minimum wavelength among the plurality of optical signals and an intensity of an optical signal having a maximum wavelength among the plurality of optical signals.

[0146] (Supplementary Note 3)

[0147] The optical equalizer according to Supplementary Note 2, wherein the optical amplification unit includes a gain characteristic, wherein,

[0148] When the intensity of the attenuated wavelength division multiplexed optical signal is lower than a predetermined optical signal intensity, the gain at the minimum wavelength is greater than the gain at the maximum wavelength, and

[0149] When the intensity of the attenuated wavelength-division multiplexed optical signal is greater than a predetermined optical signal intensity, the gain at the minimum wavelength is smaller than the gain at the maximum wavelength.

[0150] (Supplementary Note 4)

[0151] The optical equalizer according to Supplementary Note 3, wherein

[0152] When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is smaller than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be greater than a predetermined optical attenuation amount,

[0153] When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is equal to the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be equal to a predetermined optical attenuation amount, and

[0154] When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is greater than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be smaller than a predetermined optical attenuation amount.

[0155] (Supplementary Note 5)

[0156] The optical equalizer according to any one of Supplementary Notes 1 to 4, further comprising a control unit configured to control an optical attenuation amount based on a tilt characteristic and a gain characteristic,

[0157] The control unit controls the optical attenuation amount so that the tilt characteristic of the amplified wavelength division multiplexed optical signal is within a predetermined tilt range.

[0158] (Supplementary Note 6)

[0159] The optical equalizer according to Supplementary Note 5, further comprising a storage unit configured to store an attenuation table in which the tilt characteristic, the gain characteristic, and the optical attenuation amount are associated with each other, wherein

[0160] The control unit selects an optical attenuation amount from the attenuation table based on the tilt characteristic and the gain characteristic, and sets the selected optical attenuation amount in the optical attenuation unit, and

[0161] The optical attenuation unit attenuates the intensity of the wavelength division multiplexed optical signal by a selected optical attenuation amount.

[0162] (Supplementary Note 7)

[0163] The optical equalizer according to any one of Supplementary Notes 1 to 6, further comprising an optical coupler configured to branch a portion of the wavelength division multiplexed optical signal,

[0164] The detection unit detects the tilt characteristic from a portion of the wavelength division multiplexed optical signal.

[0165] (Supplementary Note 8)

[0166] The optical equalizer according to any one of Supplementary Notes 1 to 7, further comprising an optical filter through which an optical signal having a smallest wavelength among the plurality of optical signals and an optical signal having a largest wavelength among the plurality of optical signals pass,

[0167] Here, the detection unit detects the tilt characteristic from the wavelength-division-multiplexed optical signal that has passed through the optical filter.

[0168] (Supplementary Note 9)

[0169] An optical equalizer, comprising:

[0170] an optical attenuation unit configured to attenuate the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0171] an optical amplification unit configured to amplify the attenuated wavelength-division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength-division multiplexed optical signal; and

[0172] a detection unit configured to detect a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into the attenuated wavelength division multiplexed optical signal,

[0173] Here, the optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0174] (Supplementary Note 10)

[0175] A method comprising:

[0176] detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal;

[0177] attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0178] amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; and

[0179] The optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0180] (Supplementary Note 11)

[0181] A program configured to cause a computer to:

[0182] detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal;

[0183] attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount;

[0184] amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; and

[0185] The optical attenuation amount is controlled based on the tilt characteristic and the gain characteristic.

[0186] The present invention has been described above with reference to exemplary embodiments. However, the present invention is not limited to the above description. Various modifications that can be understood by those skilled in the art can be made within the scope of the present invention in the composition and details of the present invention.

[0187] This application claims priority based on Japanese Patent Application No. 2019-056829 filed on March 25, 2019, and the entire disclosure of the Japanese Patent Application is incorporated herein.

[0188] Reference numerals list

[0189] 11, 21, 51 Optical equalizer

[0190] 111 Detection Unit

[0191] 111a wavelength branching equipment

[0192] 111b Analysis Unit

[0193] 112 Optical attenuation unit

[0194] 113 Optical magnification unit

[0195] 114 Control Unit

[0196] 115 Storage Unit

[0197] 115a Attenuation table

[0198] 116 Optical Coupler

[0199] 117 Optical Filter

[0200] 12 Repeater Device

[0201] 511, 512 Optical Switch

[0202] 513 Tilt EQ

[0203] PD1, PD2 photodiode

[0204] Gh1, Gh2, Gh11, Gh12, Gh21, Gh22, Gh31, Gh32 curve graph

Claims

1. An optical equalizer, comprising: a detection device for detecting a tilt characteristic based on the intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal; An optical attenuation device, the optical attenuation device is used to attenuate the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; as well as an optical amplifying device for amplifying the attenuated wavelength-division-multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength-division-multiplexed optical signal, wherein the optical attenuation is controlled based on the tilt characteristic and the gain characteristic, wherein the detection device detects the tilt characteristic based on the intensity of the optical signal with the smallest wavelength among the plurality of optical signals and the intensity of the optical signal with the largest wavelength among the plurality of optical signals, Wherein, the optical amplification device comprises the gain characteristic, wherein, When the intensity of the attenuated wavelength division multiplexed optical signal is lower than a predetermined optical signal intensity, the gain at the minimum wavelength is greater than the gain at the maximum wavelength, and When the intensity of the attenuated wavelength-division multiplexed optical signal is greater than the predetermined optical signal intensity, the gain at the minimum wavelength is less than the gain at the maximum wavelength, wherein when the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is smaller than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be greater than a predetermined optical attenuation amount, When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is equal to the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be equal to the predetermined optical attenuation amount, and When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is greater than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be smaller than the predetermined optical attenuation amount.

2. The optical equalizer according to claim 1, further comprising a control device for controlling the optical attenuation amount based on the tilt characteristic and the gain characteristic, in, The control device controls the optical attenuation amount so that the tilt characteristic of the amplified wavelength-division-multiplexed optical signal is within a predetermined tilt range.

3. The optical equalizer according to claim 2, further comprising a storage device for storing an attenuation table in which the tilt characteristic, the gain characteristic, and the optical attenuation amount are associated with each other, wherein: The control means selects the optical attenuation amount from the attenuation table based on the tilt characteristic and the gain characteristic, and sets the selected optical attenuation amount in the optical attenuation means, and The optical attenuation device attenuates the intensity of the wavelength division multiplexed optical signal by the selected optical attenuation amount.

4. The optical equalizer according to any one of claims 1 to 3, further comprising an optical coupler configured to branch a portion of the wavelength division multiplexed optical signal, in, The detection means detects the tilt characteristic from the portion of the wavelength division multiplexed optical signal.

5. The optical equalizer according to any one of claims 1 to 3, further comprising an optical filter through which an optical signal having a minimum wavelength among the plurality of optical signals and an optical signal having a maximum wavelength among the plurality of optical signals pass, in, The detection means detects the tilt characteristic from the wavelength-division-multiplexed optical signal having passed through the optical filter.

6. A method comprising: detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal; Attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; as well as controlling the optical attenuation amount based on the tilt characteristic and the gain characteristic, detecting the tilt characteristic based on the intensity of an optical signal having a smallest wavelength among the plurality of optical signals and the intensity of an optical signal having a largest wavelength among the plurality of optical signals, When the intensity of the attenuated wavelength division multiplexed optical signal is lower than a predetermined optical signal intensity, the gain at the minimum wavelength is made greater than the gain at the maximum wavelength, and When the intensity of the attenuated wavelength-division multiplexed optical signal is greater than the predetermined optical signal intensity, the gain at the minimum wavelength is made smaller than the gain at the maximum wavelength, wherein when the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is less than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation is controlled to be greater than a predetermined optical attenuation, When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is equal to the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be equal to the predetermined optical attenuation amount, and When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is greater than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be smaller than the predetermined optical attenuation amount.

7. A non-transitory computer-readable medium storing a program, the program being configured to cause a computer to execute: detecting a tilt characteristic based on intensities of at least two optical signals among a plurality of optical signals multiplexed into a wavelength division multiplexed optical signal; Attenuating the intensity of the wavelength division multiplexed optical signal by an optical attenuation amount; amplifying the attenuated wavelength division multiplexed optical signal based on a gain characteristic associated with the intensity of the attenuated wavelength division multiplexed optical signal; as well as controlling the optical attenuation amount based on the tilt characteristic and the gain characteristic, detecting the tilt characteristic based on the intensity of an optical signal having a smallest wavelength among the plurality of optical signals and the intensity of an optical signal having a largest wavelength among the plurality of optical signals, When the intensity of the attenuated wavelength division multiplexed optical signal is lower than a predetermined optical signal intensity, the gain at the minimum wavelength is made greater than the gain at the maximum wavelength, and When the intensity of the attenuated wavelength-division multiplexed optical signal is greater than the predetermined optical signal intensity, the gain at the minimum wavelength is made smaller than the gain at the maximum wavelength, wherein when the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is less than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation is controlled to be greater than a predetermined optical attenuation, When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is equal to the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be equal to the predetermined optical attenuation amount, and When the intensity of the optical signal having the smallest wavelength among the plurality of optical signals is greater than the intensity of the optical signal having the largest wavelength among the plurality of optical signals, the optical attenuation amount is controlled to be smaller than the predetermined optical attenuation amount.

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