Control device and program for optical communication system

Abstract

To transmit a plurality of wavelength-multiplexed signal lights in a wavelength band including a wavelength at which wavelength dispersion becomes zero.SOLUTION: The control apparatus includes an acquisition unit configured to acquire a signal-to-noise ratio of each of the plurality of signal lights from the optical reception apparatus, and a calculation unit configured to calculate the signal-to-noise ratio of the signal light based on a level of the signal light and a zero dispersion wavelength of an optical transmission path. And control means for determining a target value of a level of each of the plurality of signal lights output to the optical transmission line by the optical transmission device, and controlling the optical transmission device such that the level of each of the plurality of signal lights output to the optical transmission line by the optical transmission device becomes the target value, wherein the control means sets a wavelength of a signal light at which a signal-to-noise ratio in the optical reception device is lowest in a state where the optical transmission device is controlled such that the level of each of the plurality of signal lights output to the optical transmission line by the optical transmission device is the same, as a zero dispersion wavelength in a closed form.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a technique for suppressing the influence of optical noise caused by four-wave mixing in an optical transmission line. [Background technology]

[0002] Regarding power saving in optical communication systems, Non-Patent Document 1 discloses that by using the O-band, which is the wavelength band of 1260 nm to 1360 nm, part of the signal processing can be omitted, thereby achieving more power saving than the conventionally used wavelength band of 1530 nm to 1565 nm (C-band). On the other hand, Non-Patent Document 2 discloses that in the wavelength range around 1310 nm, the influence of optical noise (non-linear optical noise) caused by the non-linear optical effect of optical fiber becomes extremely large, and therefore the O-band is not suitable for wavelength division multiplexing transmission. Note that wavelengths around 1310 nm have a chromatic dispersion value of zero or close to zero.

[0003] Non-Patent Document 3 discloses a closed form for simulation that takes into account optical noise caused by nonlinear optical effects in optical fibers. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Seiler,PM,et.al.,Toward coherent O-band data center interconnects.Front.Optoelectron.14,414-425,2021 [Non-patent document 2] A.Ferrari,et.al.,"Assessment on the Achievable Throughput of Multi-Band ITU-T G.652.D Fiber Transmission Systems", in Journal of Lightwave Technology,vol.38,no.16,pp.4279-4291,15,August 15, 2020 [Non-patent document 3] P. Poggiolini, et.al., "The GN-Model of Fiber Non-Linear Propagation and its Applications", in Journal of Lightwave Technology, vol. 32, no. 4, pp. 694-721, February 15, 2014 Summary of the Invention [Problem to be solved by the invention]

[0005] Non-Patent Document 3 takes into account self-phase modulation and cross-phase modulation as non-linear effects, but does not consider the effect of four-wave mixing, resulting in large errors in wavelength bands such as O-band where the effect of four-wave mixing cannot be ignored.

[0006] The present disclosure provides a technique for transmitting a plurality of wavelength-multiplexed signal lights in a wavelength band including wavelengths at which chromatic dispersion is zero. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a control device for an optical communication system including an optical transmitting device that outputs a plurality of wavelength-multiplexed signal lights to an optical transmission line and an optical receiving device that receives the plurality of signal lights from the optical transmission line comprises: an acquisition means that acquires a signal-to-noise ratio of each of the plurality of signal lights from the optical receiving device; and a control means that determines a target value for the level of each of the plurality of signal lights that the optical transmitting device outputs to the optical transmission line by using a closed form to calculate the signal-to-noise ratio of the signal lights based on the level of the signal lights and the zero-dispersion wavelength of the optical transmission line, and controls the optical transmitting device so that the level of each of the plurality of signal lights that the optical transmitting device outputs to the optical transmission line becomes the target value, and the control means determines the zero-dispersion wavelength in the closed form as the wavelength of the signal light that has the lowest signal-to-noise ratio at the optical receiving device when the optical transmitting device is controlled so that the levels of the plurality of signal lights that the optical transmitting device outputs to the optical transmission line are the same. [Effects of the Invention]

[0008] According to the present disclosure, a plurality of wavelength-multiplexed signal lights can be transmitted in a wavelength band including wavelengths at which chromatic dispersion is zero. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an optical communication system. [Figure 2] 4 is a flowchart of a process executed by a control device. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of a control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Furthermore, the same reference numerals are used for the same or similar components, and redundant explanations will be omitted.

[0011] 1 is a schematic diagram of an optical communication system according to this embodiment. An optical transmitter 10 has adjustment units 1-1 to 1-N to which N (N is an integer equal to or greater than 2) optical signals #1 to #N are input. The adjustment units 1-n (n is an integer from 1 to N) adjust the level (power) of the optical signals #n under control of a control device 50, and output the level-adjusted optical signals #n to a multiplexer 2. The multiplexer 2 outputs optical wavelength-multiplexed signals obtained by wavelength-multiplexing N optical signals to an amplifier 3. The amplifier 3 optically amplifies the optical wavelength-multiplexed signals and outputs the optically amplified optical wavelength-multiplexed signals to a tap 4. The tap 4 outputs most of the input optical wavelength-multiplexed signals to an optical transmission line 20, and outputs the remaining part to an optical spectrum analyzer 40.

[0012] In this embodiment, the optical spectrum analyzer 40 is provided outside the optical transmitting device 10, but the optical spectrum analyzer 40 may also be a component of the optical transmitting device 10. The optical spectrum analyzer 40 outputs signals indicating the levels of the respective signal lights #1 to #N to the control device 50.

[0013] In this embodiment, the wavelength range of the wavelength multiplexed signal light includes the wavelength at which the chromatic dispersion value is zero in the optical fiber used in the optical transmission line 20, i.e., the zero-dispersion wavelength. The wavelength range of the wavelength multiplexed signal light includes, for example, 1260 nm to 1360 nm. In other words, the wavelength band of the wavelength multiplexed signal light includes the O band. The optical transmission line 20 may include one or more amplifiers that amplify the wavelength multiplexed signal light. Note that the optical transmission line 20 may not include an amplifier.

[0014] The amplifier 5 of the optical receiving device 30 optically amplifies the wavelength-multiplexed signal light received from the optical transmission line 20 and outputs the amplified signal light to the demultiplexer 6. The demultiplexer 6 demultiplexes the wavelength-multiplexed signal light and outputs signal lights #1 to #N. The optical receiving device 30 demodulates the signal lights #1 to #N output by the demultiplexer 6. In this process, the optical receiving device 30 determines the signal-to-noise ratio (SNR) of each of the signal lights #1 to #N. As an example, the optical receiving device 30 generates an electrical signal corresponding to the signal light by coherently detecting the signal light, and determines the SNR of each signal light by determining the noise component based on the coordinates in a complex plane of the amplitude and phase of the generated electrical signal and the coordinates of each signal point determined by the modulation method.

[0015] The control device 50 executes the process shown in Fig. 2. In S10, the control device 50 controls the adjustment units 1-1 to 1-N so that the levels of the signal lights #1 to #N received from the optical spectrum analyzer 40 are the same. In S11, the control device 50 acquires the SNR of each of the signal lights #1 to #N from the optical receiving device 30 and determines the signal light with the smallest SNR.

[0016] The wavelength at which chromatic dispersion becomes zero in the optical fibers that make up the optical transmission line 20, that is, the zero-dispersion wavelength, is not constant due to manufacturing variations. For example, the zero-dispersion wavelength of a single-mode optical fiber is specified to be within the range of 1300 nm to 1324 nm. Furthermore, the optical transmission line 20 is constructed by connecting multiple optical fibers by fusion splicing, and the zero-dispersion wavelengths of the multiple optical fibers may also differ from one another.

[0017] Here, the nonlinear effect of an optical fiber occurs most strongly at the zero-dispersion wavelength, and therefore, when the levels of signal light #1 to signal light #N output to the optical transmission line 20 are the same, the SNR of the signal light closest to the zero-dispersion wavelength is the lowest. Therefore, in this embodiment, when wavelength-multiplexed signal light with the same levels of signal light #1 to signal light #N is output to the optical transmission line 20, the control device 50 determines that the wavelength of the signal light at which the SNR at the optical receiving device 30 is the lowest is the zero-dispersion wavelength λ0 in the optical transmission line 20 (S12).

[0018] Next, the control device 50 uses the zero-dispersion wavelength λ0 determined in S12 to calculate the level (power) of optical noise due to four-wave mixing (multi-channel interference) using the following equation. Note that the values ​​of parameters other than the zero-dispersion wavelength λ0 in each of the following equations are stored in advance in a storage unit (not shown) of the control device 50. Furthermore, among the following parameters, the parameters related to the optical fiber are values ​​based on the optical fiber used in the optical transmission line 20.

[0019]

number

[0020] Based on the above formula, the control device 50 can calculate the signal-to-noise ratio (SNR) of each signal light using the following formula.

[0021]

number

[0022] In S13, the control device 50 determines the target value of the transmission level (transmission power) of each of the signal lights #1 to #N based on the above closed form. The target value of the transmission level of each of the signal lights #1 to #N is, for example, a transmission level that maximizes the average SNR of each of the signal lights #1 to #N. Alternatively, the target value of the transmission level of each of the signal lights #1 to #N is, for example, a transmission level that makes the average SNR of each of the signal lights #1 to #N equal to or greater than a predetermined value.

[0023] In S14, the control device 50 controls the adjustment units 1-1 to 1-N of the optical transmitter 10 so that the transmission levels of the signal lights #1 to #N each reach a target value.

[0024] The control device 50 executes the process of FIG. 2 based on an instruction from the user when the number N of signal lights changes or when the frequency allocation of the signal lights changes.

[0025] As described above, in this embodiment, a target value for the transmission level of each signal light to be output to the optical transmission line 20 is determined based on a closed-form method that takes into account optical noise due to four-wave mixing. The closed-form method uses the value of the zero-dispersion wavelength as one of the inputs to calculate the SNR of the signal light. Here, the value of the zero-dispersion wavelength differs depending on the optical transmission line 20. For this reason, in this embodiment, the SNR of each signal light after transmission through the optical transmission line 20 is measured in a state where the levels of multiple signal lights output to the optical transmission line 20 are adjusted to be the same, and the value of the zero-dispersion wavelength is thereby actually measured. With this configuration, multiple wavelength-multiplexed signal lights can be transmitted in a wavelength band that includes wavelengths where the chromatic dispersion is zero.

[0026] <Device configuration> FIG. 3 is a diagram illustrating an example configuration of the control device 50. The control device 50 includes, for example, one or more processors and one or more memory devices. The one or more memory devices may include volatile memory devices and non-volatile memory devices. The functional blocks illustrated in FIG. 3 may be realized by one or more processors executing computer programs stored in the one or more memory devices. The control device 50 may be realized by a single device. Alternatively, the control device 50 may be realized by multiple devices capable of communicating with each other. Note that FIG. 3 illustrates only parts necessary for understanding the embodiment, and the control device 50 may include other functional blocks not illustrated.

[0027] The acquiring unit 500 acquires the SNR of each of the plurality of signal lights #1 to #N from the optical receiving device 30. The receiving unit 501 receives information indicating the level of each of the plurality of signal lights #1 to #N output by the optical transmitting device 10 to the optical transmission line 20 from the spectrum analyzer 40. The spectrum analyzer 40 can be implemented in the optical transmitting device 10 as a component of the optical transmitting device 10.

[0028] The control unit 501 determines the target value of the level of each of the plurality of signal lights #1 to #N that the optical transmitting device 10 outputs to the optical transmission line 20, using the above closed-form method. The closed-form method calculates the SNR of the signal light based on the level and zero-dispersion wavelength of the signal light. Note that the optical noise in the SNR calculated using the above closed-form method includes optical noise generated by four-wave mixing of the plurality of signal lights #1 to #N in the optical transmission line 20. The control unit 501 controls the optical transmitting device 10 so that the level of each of the plurality of signal lights #1 to #N that the optical transmitting device 10 outputs to the optical transmission line 20 reaches the target value.

[0029] Here, the control unit 501 determines the wavelength of the signal light at which the SNR at the optical receiving device 30 is lowest as the zero-dispersion wavelength in a closed form when the optical transmitting device 10 controls the optical transmitting device 10 so that the levels of the multiple signal lights #1 to #N output from the optical transmitting device 10 to the optical transmission path 20 are the same.

[0030] For example, the control unit 50 determines target values ​​for the levels of the multiple signal lights #1 to #N so that the average SNR of each of the multiple signal lights #1 to #N is maximized, or so that the average SNR of each of the multiple signal lights #1 to #N is equal to or greater than a predetermined value.

[0031] The present disclosure also provides a computer program that, when executed by one or more processors in a device having one or more processors, causes the device to function as a control device 50, and a computer-readable storage medium having the computer program stored thereon.

[0032] The above configuration makes it possible to transmit multiple wavelength-multiplexed optical signals in a wavelength band that includes wavelengths where chromatic dispersion is zero. This makes it possible to contribute to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "Develop resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0033] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0034] 500: Acquisition unit, 502: Control unit

Claims

1. A control device for an optical communication system including an optical transmitting device that outputs a plurality of wavelength-multiplexed signal lights to an optical transmission line, and an optical receiving device that receives the plurality of signal lights from the optical transmission line, an acquisition unit for acquiring a signal-to-noise ratio of each of the plurality of signal lights from the optical receiving device; a control means for determining a target value of the level of each of the plurality of signal lights output by the optical transmitter to the optical transmission line by using a closed-form formula for calculating a signal-to-noise ratio of the signal light based on the level of the signal light and the zero-dispersion wavelength of the optical transmission line, and for controlling the optical transmitter so that the level of each of the plurality of signal lights output by the optical transmitter to the optical transmission line becomes the target value; Equipped with The control means controls the optical transmitting device so that the levels of the plurality of signal lights output from the optical transmitting device to the optical transmission path are the same, and sets the wavelength of the signal light at which the signal-to-noise ratio at the optical receiving device is the lowest as the zero-dispersion wavelength in the closed form.

2. 2. The control device according to claim 1, wherein the optical noise in the signal-to-noise ratio of the signal light obtained in the closed-form format includes optical noise generated by four-wave mixing of the plurality of signal lights in the optical transmission line.

3. 2. The control device according to claim 1, wherein the control means determines a target value for the level of each of the plurality of signal lights based on the closed form so that an average signal-to-noise ratio of each of the plurality of signal lights is maximized or so that an average signal-to-noise ratio of each of the plurality of signal lights is equal to or greater than a predetermined value.

4. 2. The control device according to claim 1, further comprising receiving means for receiving, from said optical transmitting device, information indicating the levels of said plurality of signal lights outputted from said optical transmitting device to said optical transmission line.

5. the optical communication system includes a spectrum analyzer that monitors the plurality of signal lights output from the optical transmitting device to the optical transmission line, 2. The control device according to claim 1, further comprising: a receiving means for receiving information indicating the level of each of the plurality of signal lights from the spectrum analyzer.

6. A program that, when executed by one or more processors of an apparatus having one or more processors, causes the apparatus to function as the control device according to any one of claims 1 to 5.

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