Optical transmission system and optical transmission method

Abstract

This optical transfer system, which is used in a transfer path for transferring optical signals, comprises: a transmitter that transmits the optical signals; one or more optical elements that compensate for degradation of the optical signals; and a receiver that receives the optical signals. The compensation amount of each optical element with respect to the degradation is an amount that is determined in advance on the basis of: the spectrum of the optical signals at a first measurement position that is a predetermined position between the transmitter and the transfer path; and the spectrum of the optical signals at a second measurement position that is a predetermined position between the transfer path and the receiver.

Description

[Technical Field]

[0001] The present invention relates to an optical transmission system and an optical transmission method. [Background technology]

[0002] In optical communications, the increase in communication traffic has led to a demand for increased capacity in transmission systems. To this end, in addition to increasing bit rates through high baud rates and high multilevel modulation, high-density wavelength division multiplexing is being investigated. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Mark Filer and Sorin Tibuleac, “Cascaded ROADM Tolerance of mQAM Optical Signals Employing Nyquist Shaping”, IEEE Photonics Conference, IPC, 2014, pp. 268-269. [Non-patent document 2] Jie Pan and Sorin Tibuleac, “Real-time Pre-compensation of ROADM Filtering using a Generalized Pre-emphasis Filter”, IEEE Photonics Conference, IPC, 2016, pp. 548-549 [Non-patent document 3] Zichuan Zhou, et.al., “Impact of Analog and Digital Pre-Emphasis on the Signal-to-Noise Ratio of Bandwidth-Limited Optical Transceivers”, IEEE Photonics Journal, vol.12, No.2, April 2020. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the large-capacity transmission technologies proposed so far, signal degradation can be significant due to the effect of pass-band narrowing (PBN) that occurs when passing through optical repeater nodes connected in multiple stages on the transmission line.

[0005] One technique for compensating for a degraded signal waveform is to impart the inverse of the transmission characteristics to the signal using a compensation circuit (digital signal processing circuit) in either the optical transmitter or the optical receiver. However, with this type of signal compensation, if the digital signal processing circuit in the optical transmitter emphasizes the high-frequency range of the signal, the rise of the signal waveform becomes steeper, which can result in a large overshoot of the signal waveform.

[0006] In such cases, optical signals are significantly affected by signal waveform degradation due to electrical noise and nonlinear response in the optical transmitter, and by optical noise in the optical repeater nodes, resulting in a large peak-to-average power ratio (PAPR) of the signal waveform.

[0007] In this way, when signal degradation caused by the PBN is electrically compensated for, new optical signal degradation may occur as a result of the compensation. Furthermore, this situation is not limited to optical communications in which optical signal degradation caused by the PBN is electrically compensated for, but is common to optical communications in which optical signal degradation occurring in the transmission line is electrically compensated for.

[0008] In view of the above circumstances, an object of the present invention is to provide a technique for suppressing degradation of an optical signal that occurs in a transmission line. [Means for solving the problem]

[0009] One aspect of the present invention is an optical transmission system that uses a transmission path to transmit an optical signal, comprising: a transmitter that transmits the optical signal; one or more optical elements that compensate for degradation of the optical signal; and a receiver that receives the optical signal, wherein the amount of compensation of each of the optical elements for the degradation is a predetermined amount based on the spectrum of the optical signal at a first measurement position that is a predetermined position between the transmitter and the transmission path, and the spectrum of the optical signal at a second measurement position that is a predetermined position between the transmission path and the receiver.

[0010] One aspect of the present invention is an optical transmission method using an optical transmission system performed by a transmission path that transmits an optical signal, the optical transmission system including a transmitter that transmits the optical signal, one or more optical elements that compensate for degradation of the optical signal, and a receiver that receives the optical signal, the optical transmission method comprising a transmitting step in which the transmitter transmits the optical signal, a compensating step in which the optical elements compensate for degradation of the optical signal, and a receiving step in which the receiver receives the optical signal, wherein the amount of compensation for the degradation by each of the optical elements is a predetermined amount based on the spectrum of the optical signal at a first measurement position that is a predetermined position between the transmitter and the transmission path, and the spectrum of the optical signal at a second measurement position that is a predetermined position between the transmission path and the receiver. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress the deterioration of an optical signal that occurs in a transmission line. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram illustrating an outline of an optical transmission system according to an embodiment. [Figure 2] FIG. 1 is a first explanatory diagram illustrating an overview of a compensation amount acquisition system that determines the compensation amount of a compensation unit in an embodiment. [Figure 3] FIG. 2 is a second explanatory diagram illustrating an overview of the compensation amount acquisition system that acquires the compensation amount of the compensation unit in the embodiment. [Figure 4] FIG. 3 is a third explanatory diagram illustrating an outline of the compensation amount acquisition system that acquires the compensation amount of the compensation unit in the embodiment. [Figure 5] FIG. 2 is a diagram showing an example of the hardware configuration of an acquisition device according to an embodiment. [Figure 6] FIG. 2 is a diagram showing an example of the configuration of a control unit included in the acquisition device according to the embodiment. [Figure 7] FIG. 4 is a diagram showing an example of setting pattern list information according to the embodiment. [Figure 8] 10 is a flowchart showing a second example of the flow of processing executed in the compensation amount acquisition processing in the embodiment. [Figure 9] 10 is a flowchart showing a second example of the flow of processing executed in the compensation amount acquisition processing in the embodiment. [Figure 10] FIG. 2 is a diagram showing an example of the configuration of a transmitter according to an embodiment. [Figure 11] FIG. 2 is a diagram showing an example of the configuration of a receiver according to an embodiment. [Figure 12] FIG. 2 is a diagram showing an example of the configuration of a transmission path according to an embodiment. [Figure 13] 1 is a flowchart illustrating an example of a flow of processing executed by the optical transmission system according to the embodiment. [Figure 14] 10A and 10B are diagrams showing examples of experimental results of transmission characteristics using the optical transmission system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Embodiment) FIG. 1 is an explanatory diagram illustrating an overview of an optical transmission system 100 according to an embodiment. The optical transmission system 100 performs optical communication. The optical transmission system 100 includes a transmitter 1, a receiver 2, and a transmission path 3. The transmitter 1 transmits an optical signal. The receiver 2 receives the optical signal. The transmission path 3 transmits the optical signal.

[0014] The transmission line 3 transmits the optical signal transmitted by the transmitter 1. The transmission line 3 includes an optical fiber 31 and one or more compensation units 32. The optical fiber 31 is an optical fiber through which the optical signal incident on the transmission line 3 is transmitted.

[0015] The compensating units 32 compensate for degradation of the optical signal without converting the optical signal into an electrical signal. The amount of compensation for degradation of the optical signal by each compensating unit 32 is a predetermined amount. The compensation amount is the amount by which the compensating unit 32 compensates for degradation of the optical signal. Specifically, the compensating units 32 are optical elements. Because the compensating units 32 are optical elements, they compensate for degradation without converting the optical signal into an electrical signal.

[0016] <About setting the compensation amount> The compensation amount of the compensator 32 is a predetermined compensation amount that is determined in advance to suppress degradation of the optical signal in accordance with a predetermined compensation amount rule. Therefore, a method for determining the compensation amount of the compensator 32 will be described below using the operation of a system that determines the compensation amount of the compensator 32 as an example.

[0017] 2 is a first explanatory diagram illustrating an overview of a compensation amount acquisition system 200 that determines the compensation amount of the compensator 32 in an embodiment. The compensation amount acquisition system 200 includes a transmitter 1, a receiver 2, a transmission path 3, a transmitting-side spectrum analyzer 41, a receiving-side spectrum analyzer 42, and an acquisition device 5.

[0018] The transmitting-side spectrum analyzer 41 measures the spectrum of the optical signal output from the transmitter 1 before it enters the transmission path 3 (hereinafter referred to as the “transmitting-side spectrum”). The measurement result by the transmitting-side spectrum analyzer 41 is output to the acquisition device 5.

[0019] The receiver spectrum analyzer 42 measures the spectrum of the optical signal (hereinafter referred to as the "receiver spectrum") emitted from the transmission path 3 before reaching the receiver 2. The measurement result by the receiver spectrum analyzer 42 is output to the acquisition device 5.

[0020] The acquisition device 5 acquires the compensation amount of the compensation unit 32 based on the transmission side spectrum and the reception side spectrum.

[0021] Incidentally, when measurement is performed by the transmitting-side spectrum analyzer 41, the optical signal is received by the transmitting-side spectrum analyzer 41 and does not reach the receiving-side spectrum analyzer 42. Therefore, when the compensation unit 32 acquires the compensation amount, there are periods when the compensation amount acquisition system 200 is in the first state and periods when it is in the second state.

[0022] The period in the first state (hereinafter referred to as the "first period") is a period during which measurement is performed by the transmitting-side spectrum analyzer 41. The period in the second state (hereinafter referred to as the "second period") is a period during which measurement is performed by the receiving-side spectrum analyzer 42. Therefore, the first state is a state of the compensation amount acquisition system 200 in which the optical signal is received by the transmitting-side spectrum analyzer 41.

[0023] The first state is, for example, a state of the compensation amount acquisition system 200 in which the transmitting-side spectrum analyzer 41 is located between the transmitter 1 and the transmission path 3. The second state is, for example, a state of the compensation amount acquisition system 200 in which the transmitting-side spectrum analyzer 41 is not located between the transmitter 1 and the transmission path 3, and the receiving-side spectrum analyzer 42 is located between the transmission path 3 and the receiver 2.

[0024] Fig. 3 is a second explanatory diagram illustrating an overview of the compensation amount acquisition system 200 that acquires the compensation amount of the compensator 32 in the embodiment. More specifically, Fig. 3 is a diagram illustrating an example of a first state of the compensation amount acquisition system 200 in the embodiment.

[0025] In the example of Fig. 3, the transmitting-side spectrum analyzer 41 is located between the transmitter 1 and the transmission path 3. In the example of Fig. 3, the optical signal is received by the transmitting-side spectrum analyzer 41. In the example of Fig. 3, the transmitting-side spectrum analyzer 41 acquires the transmitting-side spectrum. On the other hand, in the example of Fig. 3, the receiving-side spectrum analyzer 42 is not located between the transmission path 3 and the receiver 2. Therefore, in the example of Fig. 3, the receiving-side spectrum analyzer 42 does not acquire the receiving-side spectrum.

[0026] In the first state, the receiving-side spectrum analyzer 42 may also be located between the transmission path 3 and the receiver 2. Even in this case, the optical signal does not reach the receiving-side spectrum analyzer 42, and therefore the receiving-side spectrum analyzer 42 does not acquire the receiving-side spectrum.

[0027] Fig. 4 is a third explanatory diagram illustrating an overview of the compensation amount acquisition system 200 that acquires the compensation amount of the compensator 32 in the embodiment. More specifically, Fig. 4 is a diagram illustrating an example of a second state of the compensation amount acquisition system 200 in the embodiment.

[0028] In the example of FIG. 4, the transmitting-side spectrum analyzer 41 is not located between the transmitter 1 and the transmission path 3. Therefore, in the example of FIG. 4, the optical signal is not received by the transmitting-side spectrum analyzer 41. Therefore, in the example of FIG. 4, the transmitting-side spectrum analyzer 41 does not acquire the transmitting-side spectrum. On the other hand, in the example of FIG. 4, the receiving-side spectrum analyzer 42 is located between the transmission path 3 and the receiver 2. Therefore, in the example of FIG. 4, the receiving-side spectrum analyzer 42 acquires the receiving-side spectrum.

[0029] FIG. 5 is a diagram illustrating an example of the hardware configuration of the acquisition device 5 according to the embodiment.

[0030] The acquisition device 5 includes a control unit 51 having a processor 91 such as a CPU (Central Processing Unit) and a memory 92 connected by a bus, and executes a program. The acquisition device 5 functions as a device including the control unit 51, an input unit 52, a communication unit 53, a storage unit 54, and an output unit 55 by executing the program.

[0031] More specifically, the processor 91 reads out a program stored in the storage unit 54 and stores the read out program in the memory 92. When the processor 91 executes the program stored in the memory 92, the acquisition device 5 functions as a device including the control unit 51, the input unit 52, the communication unit 53, the storage unit 54, and the output unit 55.

[0032] The control unit 51 controls the operation of various functional units included in the acquisition device 5. The control unit 51 controls, for example, each compensator 32. The control unit 51 controls, for example, each compensator 32, and calculates the amount of compensation for each compensator 32 based on the transmitting-side spectrum and receiving-side spectrum obtained as a result of the control. Hereinafter, the process of controlling each compensator 32 and calculating the amount of compensation by each compensator 32 based on the transmitting-side spectrum and receiving-side spectrum obtained as a result of the control will be referred to as compensation amount acquisition process.

[0033] Note that controlling the compensator 32 means, for example, moving the optical elements that make up the compensator 32. For example, if the compensator 32 is a combination of a semiconductor optical amplifier and a rotary density filter, moving the optical elements that make up the compensator 32 is controlling the rotation of the filter. The rotation of the filter is performed by, for example, a motor.

[0034] Therefore, in this case, the compensation unit 32 also includes a motor. More specifically, controlling the compensation unit 32 in this case means controlling the rotation of the motor that rotates the filter. In the case of such a compensation unit 32, for example, the intensity of an optical signal amplified by a semiconductor optical amplifier is attenuated by a rotating density filter. Therefore, the degree of amplification of the optical signal by the compensation unit 32 is adjusted by the rotation of the rotating density filter.

[0035] The control of the compensation unit 32 does not necessarily have to be control to move the optical elements that make up the compensation unit 32, but may be, for example, a process of applying heat to the optical elements that make up the compensation unit 32 to change the optical constants of the optical elements, such as the dielectric constant. In such a case, the compensation unit 32 includes a device that applies heat to the optical elements. The device that applies heat to the optical elements is, for example, a heater.

[0036] The optical element constituting the compensation section 32 may be, for example, a WSS (Wavelength Selective Switch) of a MEMS (Micro Electro Mechanical Systems) or a WSS based on LCoS (Liquid Crystal on Silicon).

[0037] The input unit 52 includes input devices such as a mouse, a keyboard, and a touch panel. The input unit 52 may be configured as an interface that connects these input devices to the acquisition device 5. The input unit 52 accepts input of various information to the acquisition device 5. For example, a command from a user to start the compensation amount acquisition process is input to the input unit 52.

[0038] The communication unit 53 includes a communication interface for connecting the acquisition device 5 to an external device. The communication unit 53 communicates with the external device via wired or wireless communication. The external device is, for example, each compensation unit 32. The external device is, for example, the transmission-side spectrum analyzer 41.

[0039] The communication unit 53 acquires the transmission-side spectrum by communicating with the transmission-side spectrum analyzer 41. The external device is, for example, the reception-side spectrum analyzer 42. The communication unit 53 acquires the reception-side spectrum by communicating with the reception-side spectrum analyzer 42.

[0040] The external device is, for example, a transmitter 1. The external device is, for example, a receiver 2.

[0041] The storage unit 54 is configured using a computer-readable storage medium device such as a magnetic hard disk drive or a semiconductor storage device. The storage unit 54 stores various information related to the acquisition device 5. The storage unit 54 stores information input via, for example, the input unit 52 or the communication unit 53. The storage unit 54 stores, for example, the history of control of the compensation unit 32. The storage unit 54 stores, for example, the history of the transmission-side spectrum and the reception-side spectrum according to the control of the compensation unit 32. The storage unit 54 stores, for example, the calculated compensation amount of each compensation unit 32.

[0042] The output unit 55 outputs various types of information. The output unit 55 includes a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display. The output unit 55 may be configured as an interface that connects these display devices to the acquisition device 5. The output unit 55 outputs information input to the input unit 52 or the communication unit 53, for example.

[0043] 6 is a diagram illustrating an example of the configuration of the control unit 51 included in the acquisition device 5 according to the embodiment. The control unit 51 includes a compensation amount acquisition unit 511, an input control unit 512, a communication control unit 513, a storage control unit 514, and an output control unit 515.

[0044] The compensation amount acquisition unit 511 executes compensation amount acquisition processing. The input control unit 512 controls the operation of the input unit 52. The communication control unit 513 controls the operation of the communication unit 53. The memory control unit 514 controls the operation of the memory unit 54. The output control unit 515 controls the operation of the output unit 55.

[0045] Here, two examples of the details of the compensation amount acquisition process will be described. <First Example of Compensation Amount Acquisition Processing> In a first example of the compensation amount acquisition process, setting pattern list information is used. The setting pattern list information is information indicating a plurality of setting patterns and the order in which control is executed to realize the state indicated by each setting pattern in the compensation amount acquisition process. The setting patterns are information indicating the compensation amounts of each compensation unit 32.

[0046] For the sake of simplicity in the following explanation, the execution of control to realize the state indicated by the setting pattern is referred to as the execution of the setting pattern. In the compensation amount acquisition process, each compensation unit 32 is controlled so that the compensation amount of each compensation unit 32 is the compensation amount indicated by the setting pattern. The process of controlling each compensation unit 32 so that the compensation amount of each compensation unit 32 is the compensation amount indicated by the setting pattern is the process of executing the setting pattern.

[0047] FIG. 7 is a diagram showing an example of the setting pattern list information in the embodiment. N " respectively indicate different compensators 32 that are included in the transmission path 3. Data D101 is an example of a setting pattern. Setting pattern D101 is the setting pattern that is executed first in the compensation amount acquisition process.

[0048] 7, the setting patterns indicate the compensation amounts of the compensators 32. Setting pattern D101 indicates that the compensator b1 is controlled to increase the optical signal by 10 dB, and the compensator b2 is controlled to increase the optical signal by 0 dB.

[0049] 8 is a flowchart showing a first example of the flow of processing executed in the compensation amount acquisition process in the embodiment. The compensation amount acquisition unit 511 executes the setting pattern with the lowest order among the setting patterns that have not been executed for each compensator 32 via the communication unit 53 (step S101). Next, the compensation amount acquisition unit 511 controls the operation of the transmission-side spectrum analyzer 41 via the communication unit 53 to move the transmission-side spectrum analyzer 41 to a predetermined position (hereinafter referred to as the "first measurement position") between the transmitter 1 and the transmission path 3 (step S102).

[0050] <An example of a mechanism for moving the transmitting spectrum analyzer 41> An example of a movable transmitting-side spectrum analyzer 41 will be described. For example, the transmitting-side spectrum analyzer 41 includes a piezoelectric driving stage and a spectrum analyzer, and the spectrum analyzer is positioned on the piezoelectric driving stage. In this case, by moving the piezoelectric driving stage, the transmitting-side spectrum analyzer 41 can be moved between a first measurement position and a position that is not between the transmitter 1 and the transmission path 3. Therefore, moving the transmitting-side spectrum analyzer 41 means, for example, moving the piezoelectric driving stage to move the transmitting-side spectrum analyzer 41.

[0051] After step S102, the compensation amount acquisition unit 511 controls the operation of the transmitter 1 via the communication unit 53 to cause the transmitter 1 to transmit an optical signal (step S103). The transmission-side spectrum analyzer 41 receives the transmitted optical signal and acquires the spectrum of the received optical signal as the transmission-side spectrum (step S104). Next, the transmission-side spectrum analyzer 41 outputs the acquired transmission-side spectrum to the acquisition device 5 (step S105). That is, the acquisition device 5 acquires the transmission-side spectrum.

[0052] Next, the compensation amount acquisition unit 511 controls the transmitting-side spectrum analyzer 41 and the receiving-side spectrum analyzer 42 via the communication unit 53 to move them. Specifically, the compensation amount acquisition unit 511 moves the transmitting-side spectrum analyzer 41 from the first measurement position to a position not between the transmitter 1 and the transmission path 3, and moves the receiving-side spectrum analyzer 42 to the second measurement position (step S106). The second measurement position is a predetermined position between the transmission path 3 and the receiver 2.

[0053] <An example of a mechanism for moving the receiving spectrum analyzer 42> An example of a movable receiving-side spectrum analyzer 42 will be described. For example, the receiving-side spectrum analyzer 42 includes a piezoelectric driving stage and a spectrum analyzer, and the spectrum analyzer is positioned on the piezoelectric driving stage. In such a case, by moving the piezoelectric driving stage, the receiving-side spectrum analyzer 42 can be moved between the second measurement position and a position that is not between the transmission path 3 and the receiver 2. Therefore, moving the receiving-side spectrum analyzer 42 means, for example, moving the piezoelectric driving stage to move the receiving-side spectrum analyzer 42.

[0054] Next, the compensation amount acquisition unit 511 controls the operation of the transmitter 1 via the communication unit 53 to cause the transmitter 1 to transmit an optical signal (step S107). The receiving-side spectrum analyzer 42 receives the transmitted optical signal and acquires the spectrum of the received optical signal as the receiving-side spectrum (step S108). Next, the receiving-side spectrum analyzer 42 outputs the acquired receiving-side spectrum to the acquisition device 5 (step S109). That is, the acquisition device 5 acquires the receiving-side spectrum.

[0055] Next, the compensation amount acquisition unit 511 calculates a bit error rate based on the obtained transmitting-side spectrum and receiving-side spectrum (step S110). The calculated bit error rate is recorded in the storage unit 54 together with information indicating the setting pattern. Next, the compensation amount acquisition unit 511 determines whether or not each setting pattern has been executed for all setting patterns indicated in the setting pattern list information (step S111).

[0056] If there is any setting pattern that has not been executed among the setting patterns indicated by the setting pattern list information (step S111: NO), the process returns to step S101.

[0057] On the other hand, if all the setting patterns indicated by the setting pattern list information have been executed (step S111: YES), the compensation amount acquisition unit 511 determines the compensation amount of each compensation unit 32 indicated by the setting pattern with the lowest bit error rate as the set compensation amount (step S112).

[0058] The set compensation amount is the actual compensation amount of each compensator 32. That is, the set compensation amount is the compensation amount of each compensator 32 when the optical signal transmitted from the transmitter 1 reaches the receiver 2 without being obstructed by the transmitting-side spectrum analyzer 41 or the receiving-side spectrum analyzer 42.

[0059] Therefore, the compensation amount rule in the first example of the compensation amount acquisition process is a rule that determines, based on the setting pattern list information, each compensation amount indicated by the setting pattern that minimizes the difference between the transmitting side spectrum and the receiving side spectrum as the actual compensation amount of each compensation unit 32.

[0060] As illustrated in the flowchart of Fig. 8, all of the setting patterns indicated by the setting pattern list information may be executed. Therefore, information indicating the order in which each setting pattern is executed is not necessarily required in the compensation amount acquisition process using the setting pattern list information. Therefore, the setting pattern list information only needs to indicate multiple setting patterns, and does not necessarily need to indicate information indicating the order in which each setting pattern is executed. Therefore, the setting pattern list information only needs to be information indicating multiple setting patterns.

[0061] This is a process that satisfies the condition that the sum of the compensation amounts of each setting pattern in the setting pattern list information approximately matches a value that indicates the inverse characteristic of the transmission characteristic of the transmission path 3. Note that the inverse characteristic of the transmission characteristic of the transmission path 3 is a characteristic that is expressed by the inverse function of the function that expresses the transmission characteristic of the transmission path 3.

[0062] <Compensation> Note that compensation in the optical transmission system 100 or the compensation amount acquisition system 200 refers to suppressing degradation of the spectral shape, and does not necessarily refer to compensation for the power of the optical signal. Therefore, compensation in the optical transmission system 100 or the compensation amount acquisition system 200 may be, for example, a process of passing the optical signal through a filter. Even if the power of the optical signal is attenuated by passing through the filter, the process of passing the optical signal through the filter is compensation as long as degradation of the spectral shape is suppressed. This is common to communications other than the optical transmission system 100 or the compensation amount acquisition system 200, such as the communications described in Non-Patent Document 1.

[0063] <Second Example of Compensation Amount Acquisition Processing> 9 is a flowchart showing a second example of the flow of processing executed in the compensation amount acquisition processing in the embodiment. In the explanation of FIG. 9, the same processes as those in FIG. 8 are denoted by the same reference numerals as in FIG. 8, and the explanation thereof will be omitted. The compensation amount acquisition unit 511 controls all the compensation units 32 so that the compensation amount is 0 dB (step S201). Since the compensation amount of all the compensation units 32 is 0 dB, the processing of step S201 is synonymous with the absence of any compensation unit 32 in the transmission path 3.

[0064] After step S201, the processes of steps S102 to S110 are executed. After step S110, the compensation amount acquisition unit 511 calculates the frequency characteristic C of the transmission path 3 defined by the following equation (1) based on the obtained transmission side spectrum and reception side spectrum. PBN (f) is obtained (step S202), where f represents frequency.

[0065]

number

[0066] S T (f) represents the transmitter spectrum. S R (f) represents the receiving-side spectrum. In this way, by the process of step S202, the transmission characteristics of the transmission path 3 in which the compensation amounts of all the compensators 32 are 0 dB are obtained based on the transmitting-side spectrum and the receiving-side spectrum.

[0067] Note that obtaining a characteristic means obtaining information indicating the characteristic. The information indicating the characteristic is, for example, the above-mentioned function C PBN This means obtaining the value of a function that expresses a characteristic such as (f).

[0068] Next, the compensation amount acquisition unit 511 calculates the obtained frequency characteristic C PBN Based on (f), the inverse characteristic of the transmission characteristic of the transmission path 3 is obtained (step S203). Specifically, by executing the process expressed by the following equation (2), the inverse characteristic of the transmission characteristic of the transmission path 3 is obtained as the compensation characteristic G(f).

[0069]

number

[0070] Next, the compensation amount acquisition unit 511 calculates the compensation amount of each compensation unit 32 at a predetermined distribution rate so that the sum of the compensation amounts is equal to the compensation characteristic G(f) (i.e., the inverse characteristic of the transmission characteristic of the transmission path 3) (step S204). Note that the ratio of the distribution rate in the frequency direction may be the same regardless of frequency. The compensation amount obtained in step S204 is an example of a set compensation amount.

[0071] As described above, in the second example of the compensation amount acquisition process, the compensation amount rule is a rule for calculating the compensation amount of each compensator 32 at a predetermined distribution rate so that the sum of the compensation amounts is equal to the inverse characteristic of the transmission characteristic of the transmission path 3. The calculated compensation amount is used as the actual compensation amount of each compensator 32.

[0072] In this way, the compensation amount rule is a predetermined rule that reduces the difference between the spectrum on the transmitting side and the spectrum on the receiving side, for example.

[0073] In this way, the compensation amount of each compensator 32 may be acquired in any manner as long as it is acquired based on the transmitting-side spectrum and the receiving-side spectrum. Therefore, the compensator 32 compensates for signal degradation due to the transmission path by an amount determined based on the transmitting-side spectrum and the receiving-side spectrum. For example, the compensator 32 compensates for signal degradation due to the transmission path by an amount determined in accordance with a predetermined rule that reduces the difference between the transmitting-side spectrum and the receiving-side spectrum.

[0074] <Example of the configuration of the transmitter 1> 10 is a diagram showing an example of the configuration of the transmitter 1 according to an embodiment. The transmitter 1 includes a signal processing unit 101, a DA converter 102, an amplifier 103, and an optical modulator 104.

[0075] The signal processing unit 101 performs electrical signal processing. That is, the signal processing unit 101 performs signal processing using electrical signals. The signal processing unit 101 includes a control unit 111 including a processor 93 such as a CPU and a memory 94, which are connected by a bus, and a storage unit 112, and executes a program.

[0076] More specifically, the processor 93 reads out a program stored in the storage unit 112 and stores the read program in the memory 94. The processor 93 executes the program stored in the memory 94, whereby the signal processing unit 101 functions as a device including the control unit 111 and the storage unit 112.

[0077] The control unit 111 controls the operation of various functional units included in the signal processing unit 101. The control unit 111 performs signal processing. The storage unit 112 is configured using a computer-readable storage medium device such as a magnetic hard disk device or a semiconductor storage device. The storage unit 112 stores various information related to the signal processing unit 101.

[0078] The DA converter 102 converts the digital signal into an analog signal, the amplifier 103 amplifies the signal, and the optical modulator 104 converts the electrical signal into an optical signal.

[0079] <Example of the configuration of receiver 2> 11 is a diagram showing an example of the configuration of the receiver 2 according to the embodiment. The receiver 2 includes a photodetector 201, an AD converter 202, and a signal processing unit 203.

[0080] The photodetector 201 converts the optical signal into an electrical signal, and the AD converter 202 converts the analog signal into a digital signal.

[0081] The signal processing unit 203 performs electrical signal processing. That is, the signal processing unit 203 performs signal processing using an electrical signal. The signal processing unit 203 includes a control unit 231 and a storage unit 232, which are connected by a bus and include a processor 95 such as a CPU and a memory 96, and executes a program.

[0082] More specifically, the processor 95 reads out the program stored in the storage unit 232 and stores the read program in the memory 96. The processor 95 executes the program stored in the memory 96, whereby the signal processing unit 203 functions as a device including the control unit 231 and the storage unit 232.

[0083] The control unit 231 controls the operation of various functional units included in the signal processing unit 203. The control unit 231 performs signal processing. The storage unit 232 is configured using a computer-readable storage medium device such as a magnetic hard disk device or a semiconductor storage device. The storage unit 232 stores various information related to the signal processing unit 203.

[0084] <Example of the configuration of the transmission path 3> An example of the configuration of the transmission path 3 will be described. Fig. 12 is a diagram showing an example of the configuration of the transmission path 3 in an embodiment. The transmission path 3 includes one or more relay nodes 30. The relay node 30 includes an optical fiber 31, an optical amplifier 321, and a tunable optical filter 322. The optical amplifier 321 amplifies an optical signal. The tunable optical filter 322 is an optical filter with variable transmittance, such as a rotary density filter.

[0085] The optical amplifier 321 and the tunable optical filter 322 are connected by, for example, an optical fiber 31. The relay nodes 30 are also connected by, for example, an optical fiber 31. The optical amplifier 321 and the tunable optical filter 322 are each an example of the compensation unit 32.

[0086] 13 is a flowchart showing an example of the flow of processing executed by the optical transmission system 100 according to the embodiment. The processing to be performed by each compensator 32 included in the optical transmission system 100 in FIG.

[0087] The transmitter 1 transmits an optical signal (step S301). Next, the compensator 32 compensates for degradation of the optical signal propagating through the transmission line 3 (step S302). The receiver 2 receives the optical signal (step S303).

[0088] 14 is a diagram illustrating an example of the results of an experiment on transmission characteristics using the optical transmission system 100 according to the embodiment. More specifically, the diagram illustrates an example of the results of an experiment on transmission characteristics when the transmission line 3 includes two compensation units 32.

[0089] The experiment used a 500Gbps / λ 66Gbaud PDM-32QAM optical signal generated by a real-time transponder. In the experiment, the 3dB bandwidth of the WSS (Wavelength Selective Switch) in transmission line 3 was set to 65GHz to simulate PBN (Pass-band Narrowing). The experiment was also conducted under conditions where the optical signal distortion caused by the WSS in transmission line 3 was divided and compensated by the two WSSs at the transmitting and receiving ends.

[0090] 14, the horizontal axis represents the optical signal-to-noise power ratio, and the vertical axis represents the Q factor margin from the FEC threshold. In the experiment, the optical signal was a 500 Gbps signal.

[0091] The results of "All-Rx DEQ" represent the results when the signals are converted into electrical signals and compensated by signal processing using the electrical signals without using the compensation unit 32. The results of "joint OEQ (Tx:Rx=50:50)" represent the results when the ratio of the compensation amounts of the two compensation units 32 is 50:50.

[0092] 14 shows that signal degradation was best suppressed when the ratio of the compensation amounts of the two compensators 32 was 50:50. The units of the compensation amounts are dB, for example. The compensation amount ratio of A:B means that the ratio between the compensation amount of one compensator 32 and the compensation amount of the other compensator 32 is A:B for each frequency component.

[0093] As shown by this experimental result, for example, when the optical transmission system 100 has two compensators 32 and the compensation amount of each compensator 32 is not zero, the compensation amounts of each compensator 32 may be equal.

[0094] In the optical transmission system 100 of the embodiment configured as described above, at least a portion of the compensation for signal degradation due to the transmission path is performed by the compensating unit 32, which is an optical element. Because the compensating unit 32 is an optical element, the compensating unit 32 can perform compensation without converting the optical signal to an electrical signal. Therefore, the optical transmission system 100 can suppress signal degradation caused by electrical compensation processing, such as signal waveform overshoot, compared to technologies that electrically compensate for optical signal degradation. Therefore, the optical transmission system 100 can suppress optical signal degradation.

[0095] Furthermore, the compensation amount of the compensator 32 is determined based on the transmitting-side spectrum and the receiving-side spectrum in the optical transmission system 100. The transmitting-side spectrum is the spectrum of the optical signal at the first measurement position, and the receiving-side spectrum is the spectrum of the optical signal at the second measurement position.

[0096] Furthermore, because the compensation amount of the compensator 32 is determined based on the transmitting-side spectrum and the receiving-side spectrum, compensation within the transmitter is not required. Compensation within the transmitter can only be performed electrically, but electrical compensation can cause signal waveform degradation due to signal waveform overshoot. In contrast, in the optical transmission system 100, because the compensation amount of the compensator 32 is determined based on the transmitting-side spectrum and the receiving-side spectrum, compensation within the transmitter is not required. Therefore, the optical transmission system 100 can suppress signal waveform degradation due to signal waveform overshoot. Therefore, the optical transmission system 100 can further suppress optical signal degradation. Furthermore, the optical transmission system 100 can prevent signal waveform degradation due to noise enhancement compared to when all compensation is performed within the receiver.

[0097] Therefore, the compensation amount determined based on the transmitting-side spectrum and the receiving-side spectrum is determined based on information including only information about signal degradation caused by the transmission path 3, and does not include information about signal degradation caused by the transmitter 1 or the receiver 2. In other words, the compensation amount of the compensator 32 is determined without based on information other than information about signal degradation caused by the transmission path 3, which information may become noise in the compensation for signal degradation caused by the transmission path 3.

[0098] Therefore, the optical transmission system 100 can more effectively compensate for signal degradation caused by the transmission line 3 than other systems that perform compensation not based on the results of the first and second measurement positions. As a result, the optical transmission system 100 can further suppress degradation of the optical signal.

[0099] The cause of signal degradation due to the transmission line 3 is, for example, PBN. The cause of signal degradation due to the transmission line 3 may be any phenomenon that occurs in the transmission line 3 and induces signal degradation. Therefore, the cause of signal degradation due to the transmission line 3 may be, for example, band limitation, polarization dependent loss, polarization mode dispersion, chromatic dispersion, or nonlinear optical effect.

[0100] (Variation) The optical transmission system 100 may also include an acquisition device 5, a transmitting-side spectrum analyzer 41, and a receiving-side spectrum analyzer 42. In such an optical transmission system 100, when a user communicates using the transmission path 3, the transmitting-side spectrum analyzer 41 is located at a position that is not between the transmitter 1 and the transmission path 3, and the receiving-side spectrum analyzer 42 is located at a position that is not between the transmission path 3 and the receiver 2.

[0101] On the other hand, in such an optical transmission system 100, during periods when the system is not in use by a user, for example, the acquisition device 5 executes a compensation amount acquisition process, and updates the compensation amount of each compensation unit 32 in accordance with changes in the transmission characteristics of the transmission path 3 due to use or deterioration over time.

[0102] The total amount of compensation by the compensators 32 included in the optical transmission system 100 only needs to compensate for at least a portion of the amount of degradation of the optical signal, and the remaining portion does not necessarily need to be compensated for by the compensator 32. Therefore, a portion of the amount of degradation of the optical signal may be compensated for by signal processing of the electrical signal after the optical signal is converted into an electrical signal.

[0103] Therefore, the condition may be that the sum of the compensation amounts indicated by the setting patterns indicated by the setting pattern list information is greater than 0 and smaller than the value of the inverse characteristic of the transmission characteristic of the transmission path 3, for example.

[0104] The compensation amount of the compensator 32 does not necessarily have to be a positive value and may be a negative value. Therefore, some of the multiple compensators 32 may have positive compensation amounts, and the remaining some may have negative compensation amounts. In such a case, the degree of freedom in the compensation amount is increased and not limited to only positive values, thereby increasing the degree of freedom in design and increasing the possibility of further suppressing signal degradation.

[0105] In the second example of the compensation amount acquisition process, the predetermined distribution rate may be a distribution rate according to the rule that the distribution rate corresponds to the distance the optical signal has traveled without being compensated (hereinafter referred to as the "uncompensated distance").

[0106] The predetermined distribution rate according to the uncompensated distance may be, for example, a distribution rate according to the rule that the longer the distance an optical signal is transmitted without compensation, the less compensation the compensation unit 32 at the transmission destination should provide.

[0107] Compensation using an optical filter is, for example, a process of shaping the waveform by cutting the spectrum. In this type of process, compensation means "adding loss." Therefore, if waveform shaping is performed using an optical filter in a section with large section loss, further loss due to waveform shaping is added. As a result, the optical signal to noise ratio (OSNR) deteriorates further, and signal quality decreases.

[0108] On the other hand, in areas where the section loss is small, even if compensation is performed using an optical filter, the amount of OSNR degradation can be reduced. As a result, degradation of signal quality due to OSNR degradation is suppressed. Note that a section with large section loss is, for example, a section where the distance over which an optical signal is transmitted without compensation is long. In other words, a section with large section loss is, for example, a section where the uncompensated distance is long. Therefore, by reducing the amount of compensation by the compensator 32 at the transmission destination as the uncompensated distance becomes longer, degradation of signal quality is suppressed.

[0109] The predetermined distribution ratio according to the uncompensated distance may be, for example, a distribution ratio according to the rule that the greater the sum of the noise amount of the amplifier and the insertion loss of the WSS, the greater the amount of compensation.

[0110] The compensation unit 32 does not necessarily have to be located within the transmission path 3 , but may be located between the transmitter 1 and the transmission path 3 , or between the receiver 2 and the transmission path 3 .

[0111] The acquisition device 5 does not necessarily have to be configured in a single housing. The acquisition device 5 may be implemented using a plurality of information processing devices communicably connected via a network. In this case, the respective functional units of the acquisition device 5 may be distributed and implemented in the plurality of information processing devices.

[0112] All or part of the functions of the acquisition device 5 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

[0113] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0114] 100...optical transmission system, 200...compensation amount acquisition system, 1...transmitter, 2...receiver, 3...transmission path, 31...optical fiber, 32...compensation unit, 41...transmitting side spectrum analyzer, 42...receiving side spectrum analyzer, 5...acquisition device, 51...control unit, 52...input unit, 53...communication unit, 54...storage unit, 55...output unit, 511...compensation amount acquisition unit, 512...input control unit, 513...communication control unit, 514...storage control unit, 515...output control unit, 101...signal processing unit, 102...DA converter, 103...amplifier, 104...optical modulator, 111...control unit, 112...storage unit, 201...photodetector, 202...AD converter, 203...signal processing unit, 231...control unit, 232...storage unit, 91...processor, 92...Memory, 93...Processor, 94...Memory, 95...Processor, 96...Memory

Claims

1. An optical transmission system using a transmission line for transmitting an optical signal, a transmitter for transmitting the optical signal; one or more optical elements that compensate for degradation of the optical signal; a receiver for receiving the optical signal; Equipped with a compensation amount of each of the optical elements for the deterioration is a predetermined amount determined based on a spectrum of the optical signal at a first measurement position, which is a predetermined position between the transmitter and the transmission line, and a spectrum of the optical signal at a second measurement position, which is a predetermined position between the transmission line and the receiver; the compensation amount is a predetermined amount determined according to a predetermined rule that reduces a difference between a transmitting-side spectrum, which is the spectrum of the optical signal at a first measurement position, and a receiving-side spectrum, which is the spectrum of the optical signal at a second measurement position; the rule is a rule for calculating the compensation amount of each of the optical elements at a predetermined distribution ratio so that the sum of the compensation amounts is equal to the inverse characteristic of the transmission characteristic of the transmission line. Optical transmission system.

2. the rule is a rule for determining, based on setting pattern list information indicating a plurality of setting patterns indicating compensation amounts for the optical elements, each compensation amount indicated by the setting pattern that minimizes the difference as the actual compensation amount for each of the optical elements.

2. The optical transmission system according to claim 1.

3. The predetermined distribution ratio is a distribution ratio according to an uncompensated distance, which is a distance over which the optical signal has been transmitted without being compensated.

2. The optical transmission system according to claim 1.

4. The predetermined distribution ratio is a distribution ratio that follows a rule that the longer the uncompensated distance, the smaller the compensation amount of the optical element at the transmission destination.

4. The optical transmission system according to claim 3.

5. When the number of the optical elements is two and the compensation amount of each of the optical elements is not zero, the compensation amounts of each of the optical elements are equal.

2. The optical transmission system according to claim 1.

6. An optical transmission method performed by an optical transmission system using a transmission path for transmitting an optical signal, the optical transmission system including: a transmitter for transmitting the optical signal; one or more optical elements for compensating for degradation of the optical signal; and a receiver for receiving the optical signal, the method comprising: a transmitting step in which the transmitter transmits the optical signal; a compensation step in which the optical element compensates for degradation of the optical signal; a receiving step in which the receiver receives the optical signal; and a compensation amount of each of the optical elements for the deterioration is a predetermined amount determined based on a spectrum of the optical signal at a first measurement position, which is a predetermined position between the transmitter and the transmission line, and a spectrum of the optical signal at a second measurement position, which is a predetermined position between the transmission line and the receiver; the compensation amount is a predetermined amount determined according to a predetermined rule that reduces a difference between a transmitting-side spectrum, which is the spectrum of the optical signal at a first measurement position, and a receiving-side spectrum, which is the spectrum of the optical signal at a second measurement position; the rule is a rule for calculating the compensation amount of each of the optical elements at a predetermined distribution ratio so that the sum of the compensation amounts is equal to the inverse characteristic of the transmission characteristic of the transmission line. Optical transmission method.

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