Optical transmission system, wavelength setting method, and program

Abstract

The present invention comprises: a first optical module (23); a second optical module (24) which is connected to the first optical module (23) by a DSF (26); and a control device (25) which controls the first optical module (23) and the second optical module (24). The control device (25) includes: a change unit (32) that changes the wavelength of an optical signal transmitted by the DSF (26); a first measurement unit (33) and a second measurement unit (34) that measure a BER or a wavelength dispersion value generated in the optical signal when the optical signal communicates between the first optical module (23) and the second optical module (24) and the wavelength of the optical signal is changed by the change unit (32); and a setting unit (35) that sets the wavelength of the optical signal such that the measured BER or wavelength dispersion value is a numerical value that causes nonlinear degradation of the optical signal to be equal to or less than a specific threshold value.

Description

Optical Transmission System, Wavelength Setting Method, and Program

[0001] The present disclosure relates to an optical transmission system, a wavelength setting method, and a program.

[0002] As disclosed in Non-Patent Document 1, in an optical transmission system that transmits an optical signal at a 100G rate (100 Gbit / sec) over a distance of about 80 km using an optical fiber at low cost, an optical module for optical-electric conversion is mounted on the client side (UNI side) of the transponder and the network side (NNI side) of the transmission device (e.g., router).

[0003] IEEE802.3. “154. PhysicalMedium Dependent (PMD)sublayer and medium,type 100GBASE-ZR”. 2022. p.6162-6182.

[0004] However, general-purpose optical modules (e.g., “100G-ZR-DCO”, etc.) are mainly products that only support optical signals in the C-band wavelength range (wavelength 1530 nm to 1565 nm) suitable for transmission by SMF (Single Mode Fiber) and the wavelength range around it. For optical transmission using DSF (Dispersion Shifted Fiber), it is not assumed. Hereinafter, the band of the above-mentioned wavelength 1530 nm to 1565 nm and the band including the wavelengths around it will be collectively referred to as the “C-band wavelength range”.

[0005] Therefore, when a general-purpose optical module is adopted in optical transmission using DSF, there is a problem that non-linear degradation occurs in the optical signal. Also, in optical transmission using DSF, if the wavelength is set to a wavelength near “zero (ps / nm / km)” of dispersion, the influence of non-linear degradation becomes remarkable. Therefore, it is desirable to set the wavelength to avoid zero dispersion. However, referring to an example of the dispersion mask of DSF, since there is a certain width in the wavelength where zero dispersion occurs, there is a problem that it is difficult to select a wavelength that avoids zero dispersion and minimizes non-linear degradation associated with DSF transmission.

[0006] This disclosure is made in view of the above circumstances, and its purpose is to provide an optical transmission system, a wavelength setting method, and a program that can set the wavelength of an optical signal used in optical transmission using an optical fiber to a wavelength that reduces nonlinear degradation.

[0007] An optical transmission system according to one aspect of the present disclosure comprises a first optical module, a second optical module connected to the first optical module by an optical fiber, and a control device for controlling the first optical module and the second optical module, wherein the control device includes a modification unit for changing the wavelength of an optical signal transmitted by the optical fiber, a measurement unit for measuring the code error rate or chromatic dispersion value that occurs in the optical signal when the optical signal is communicated between the first optical module and the second optical module and the wavelength of the optical signal is changed by the modification unit, and a setting unit for setting the wavelength of the optical signal such that the measured code error rate or chromatic dispersion value is a value that causes the nonlinear degradation of the optical signal to be below a predetermined threshold.

[0008] A wavelength setting method according to one aspect of the present disclosure is a method for setting the wavelength of an optical signal transmitted through an optical fiber between a first optical module and a second optical module, wherein a changing unit changes the wavelength of the optical signal when the optical signal is communicating through the optical fiber, a measuring unit measures the code error rate or chromatic dispersion value that occurs in the optical signal when the wavelength of the optical signal is changed, and a setting unit sets the wavelength of the optical signal such that the code error rate or chromatic dispersion value measured by the measuring unit becomes a value that causes the nonlinear degradation of the optical signal to be below a predetermined threshold.

[0009] One aspect of this disclosure is a program for causing a computer to function as the control device described above.

[0010] According to this disclosure, it becomes possible to set the wavelength of the optical signal used in optical transmission using optical fibers to a wavelength that reduces nonlinear degradation.

[0011] Figure 1 is an explanatory diagram showing an optical transmission network including an optical transmission system according to an embodiment. Figure 2 is an explanatory diagram showing the configuration of the optical transmission system according to an embodiment. Figure 3 is a block diagram showing the detailed configuration of the control device shown in Figure 2. Figure 4 is an example of a graph (dispersion mask) showing the relationship between the wavelength of an optical signal and the dispersion value of the DSF. Figure 5 is a flowchart showing the processing procedure of the optical transmission system according to an embodiment. Figure 6 is a block diagram showing the hardware configuration of this embodiment.

[0012] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is an explanatory diagram showing an optical transmission network NW including an optical transmission system according to an embodiment.

[0013] As shown in Figure 1, the optical transmission network NW according to this embodiment comprises transponders 1a and 1b, a client device 2, and DSFs (Dispersion Shifted Fibers) 3a and 3b. The client device 2 is installed on the client side (UNI side, right side in the figure) of the transponders 1a and 1b. The transponders 1a and 1b transmit and receive optical signals. Each transponder 1a and 1b is equipped with an optical module 4a and 4b, respectively. The client device 2 is equipped with two optical modules 5a and 5b.

[0014] In other words, the optical modules 4a and 4b mounted on transponders 1a and 1b are connected to optical modules 5a and 5b implemented in client device 2 via DSFs 3a and 3b, respectively. For example, "100G-ZR-DCO" can be used as optical modules 4a, 4b, 5a, and 5b.

[0015] Optical transmission between transponders 1a and 1b and client device 2 is performed using optical signals C1 and C2 in the C-band wavelength range, i.e., wavelengths of 1530 to 1565 [nm] and surrounding bands.

[0016] On the network side (NNI side, left side in the diagram) of each transponder 1a, 1b, ROADM (reconfigurable optical add / dropmultiplexer) 12, 13, optical fiber 14, and transponders 11a, 11b are installed.

[0017] ROADM 12 and 13 are equipped with a function that enables wavelength selection of optical signals without photoelectric conversion. ROADM 13 is connected to ROADM 12 via DSF 14. ROADM 12 is connected to transponders 11a and 11b. Optical transmission between transponders 1a and 11a, and between transponders 1b and 11b is performed using optical signals in the L-band, i.e., in the wavelength range of 1565 to 1625 [nm].

[0018] Figure 2 is an explanatory diagram showing the configuration of an optical transmission system 100 according to an embodiment. As shown in Figure 2, the optical transmission system 100 comprises a first device 21, a second device 22, and a control device 25. The first device 21 is equipped with a first optical module 23, and the second device 22 is equipped with a second optical module 24. A DSF 26 (optical fiber) is installed between the two optical modules 23 and 24, enabling optical transmission between the first device 21 and the second device 22. The control device 25 controls the first optical module 23 and the second optical module.

[0019] The first device 21 shown in Figure 2 is, for example, the transponders 1a and 1b shown in Figure 1, and the second device 22 is, for example, the client device 2 shown in Figure 1. When optical transmission is performed between the first device 21 and the second device 22, the control device 25 sets the wavelength of the optical signals transmitted and received between each optical module 23 and 24 so that the nonlinear degradation associated with DSF transmission of the optical signal is below a predetermined threshold that serves as a pre-set standard. For example, the wavelength at which the code error rate (hereinafter referred to as "BER") of the optical signal is minimized is measured, and this wavelength is set as the wavelength of the optical signal. Alternatively, the wavelength at which the chromatic dispersion value is maximized is measured, and this wavelength is set as the wavelength of the optical signal. The predetermined threshold is determined, for example, by user input.

[0020] BER (Bit Error Rate) refers to the ratio of erroneous data to the total data received by the receiver. BER can be calculated by dividing the number of erroneous bits by the total number of bits received. The closer the chromatic dispersion value approaches zero, the more pronounced the effects of nonlinear degradation become. Therefore, it is desirable to increase the absolute value of the chromatic dispersion value.

[0021] Figure 3 is a block diagram showing the detailed configuration of the control device 25. As shown in Figure 3, the control device 25 includes a control unit 31, a modification unit 32, a first measurement unit 33, a second measurement unit 34, and a setting unit 35.

[0022] The control unit 31 transmits control commands to instruct the first optical module 23 and the second optical module 24 to start and stop.

[0023] The modification unit 32 changes the wavelength of the optical signal transmitted by the DSF 26. The modification unit 32 intermittently or continuously changes the wavelength of the optical signal transmitted between each optical module 23, 24 within a predetermined range. The predetermined range can be, for example, the C-band wavelength range. Specifically, the modification unit 32 intermittently or continuously changes the wavelength within the C-band wavelength range.

[0024] The first measurement unit 33 measures the BER when the wavelength of the optical signal transmitted between each optical module 23, 24 is changed within the C-band wavelength range. As a result of the measurement by the first measurement unit 33, the BER can be obtained for each wavelength in the range of 1530 [nm] to 1565 [nm] and surrounding bands. The first measurement unit 33 is an example of a measurement unit that measures the code error rate (BER) that occurs in an optical signal when an optical signal is transmitted between the first optical module 23 and the second optical module 24 and the wavelength of the optical signal is changed by the modification unit 32.

[0025] The second measurement unit 34 measures the chromatic dispersion value when the wavelength of the optical signal transmitted between the optical modules 23 and 24 is changed within the C-band wavelength range. As a result of the measurement by the second measurement unit 34, the chromatic dispersion value can be obtained for each wavelength in the range of 1530 nm to 1565 nm. If the DSP (Digital Signal Processor) implemented in the first optical module 23 and the second optical module 24 has a function to monitor the chromatic dispersion value, the chromatic dispersion value may be obtained using this monitoring function. The second measurement unit 34 is an example of a measurement unit that measures the chromatic dispersion value generated in an optical signal when an optical signal is transmitted between the first optical module 23 and the second optical module 24 and the wavelength of the optical signal is changed by the modification unit 32.

[0026] The setting unit 35 sets the wavelength of the optical signal transmitted between the first optical module 23 and the second optical module 24 based on either the measurement result from the first measurement unit 33 or the measurement result from the second measurement unit 34. Specifically, as a first setting method, the wavelength at which the BER measured by the first measurement unit 33 is minimized is set as the wavelength of the optical signal. In addition to minimizing the BER, the wavelength may also be set to a value close to the minimum value of the BER. That is, the wavelength of the optical signal is set so that the BER (code error rate) measured by the first measurement unit 33 (measurement unit) is a value that keeps the nonlinear degradation of the optical signal below a predetermined threshold.

[0027] As a second setting method, the wavelength at which the wavelength dispersion value measured by the second measurement unit 34 is maximized is set as the wavelength of the optical signal. In addition to maximizing the wavelength dispersion value, the wavelength may also be set to a value close to the maximum value. That is, the wavelength of the optical signal is set such that the wavelength dispersion value measured by the second measurement unit 34 (measurement unit) is a value that keeps the nonlinear degradation of the optical signal below a predetermined threshold.

[0028] Figure 4 is a graph showing the relationship between the wavelength of the optical signal used in DSF transmission and the wavelength dispersion mask. As can be seen from the graph in Figure 4, the wavelength dispersion tends to increase as the wavelength increases. From the dispersion mask graph shown in Figure 4, it can be inferred that the absolute value of the wavelength dispersion is large around small wavelengths (1530 nm) or large wavelengths (1565 nm) in the C-band wavelength range. However, as shown in Figure 4, the dispersion value has a certain range of variation G1, and the wavelength dispersion value is not necessarily maximum near the minimum wavelength or maximum wavelength.

[0029] In the second setting method, the wavelength is varied in the C-band wavelength range to measure the chromatic dispersion value, and the setting unit 35 sets the wavelength at which the chromatic dispersion value is maximized as the wavelength of the optical signal. The setting unit 35 transmits the information of the set wavelength to the first device 21 and the second device 22.

[0030] Next, a procedure for setting the wavelength of the optical signal used for transmission to an appropriate value using the optical transmission system 100 configured as described above according to this embodiment will be explained with reference to the flowchart shown in Figure 5. First, in step S11 of Figure 5, the control unit 31 of the control device 25 instructs the first device 21 and the second device 22 to start up.

[0031] In step S12, the first device 21 and the second device 22 activate the optical modules 23, 23, respectively.

[0032] In step S13, the control unit 31 confirms that each optical module 23, 24 is emitting light and communicating. At this time, the wavelength of the optical signal transmitting the DSF between each optical module 23, 24 is set to, for example, 1530 [nm].

[0033] In step S14, the first measurement unit 33 measures the BER of the optical signal used for DSF transmission. The second measurement unit 34 measures the wavelength dispersion value of the optical signal used for DSF transmission.

[0034] In step S15, the modification unit 32 intermittently or continuously changes the wavelength of the optical signal. Specifically, the modification unit 32 intermittently or continuously changes the wavelength within the C-band wavelength range (1530 to 1565 nm and surrounding bands).

[0035] In step S16, the first measuring unit 33 and the second measuring unit 34 determine whether the measurement of BER and wavelength dispersion values ​​for the wavelengths within the above range has been completed. If it has been completed (S16; YES), the process proceeds to step S17; otherwise (S16; NO), the process returns to step S15.

[0036] In step S17, the setting unit 35 sets the wavelength of the optical signal used for DFS transmission between the two optical modules 23 and 24 to the wavelength at which the BER is minimized or the wavelength at which the chromatic dispersion value is maximized. After that, the process is terminated. That is, in the C-band wavelength range, the wavelength of the optical signal can be set such that the code error rate (BER) or chromatic dispersion value is below a predetermined threshold.

[0037] As described above, the optical transmission system 100 according to this embodiment includes a first optical module 23, a second optical module 24 connected to the first optical module 23 by an optical fiber (DSF 26), and a control device 25 for controlling the first optical module 23 and the second optical module 24. The control device 25 includes a changing unit 32 for changing the wavelength of the optical signal transmitted by the DSF 26, a measuring unit (first measuring unit 33, second measuring unit 34) for measuring the code error rate (BER) or chromatic dispersion value that occurs in the optical signal when the optical signal is transmitted between the first optical module 23 and the second optical module 24 and the wavelength of the optical signal is changed by the changing unit 32, and a setting unit 35 for setting the wavelength of the optical signal so that the code error rate or chromatic dispersion value measured by the measuring unit becomes a value that keeps the nonlinear degradation of the optical signal below a predetermined threshold.

[0038] In this embodiment, the wavelength of the optical signal is set such that the code error rate (BER) or chromatic dispersion value in the C-band wavelength range is a value that keeps the nonlinear degradation of the optical signal below a predetermined threshold. Therefore, even when optical transmission is performed using a DSF between the first optical module 23 mounted on the first device 21 and the second optical module 24 mounted on the second device 22, nonlinear degradation can be suppressed.

[0039] In this embodiment, the wavelength of the optical signal in the C-band wavelength range is set to the wavelength that minimizes the BER or maximizes the chromatic dispersion value. Therefore, even when optical transmission is performed using DSF between the first optical module 23 mounted on the first device 21 and the second optical module 24 mounted on the second device 22, nonlinear degradation can be suppressed. As a result, even when using optical modules that only support the C-band wavelength range, it is possible to reduce nonlinear degradation associated with DSF transmission.

[0040] Furthermore, it becomes possible to set the wavelength to the maximum value of the chromatic dispersion without installing measuring instruments for measuring the chromatic dispersion value in both the first and second optical modules 23 and 24.

[0041] In the above-described embodiment, the optical transmission between the transponder 1a, 1b shown in FIG. 1 and the client device 2 installed on the client side (UNI side) was described by way of example. However, it is also applicable to the DSF connected to the network side (NNI side) of the transponder 1a, 1b.

[0042] For example, as shown in FIG. 6, the control device 25 of the present embodiment described above can use a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906. The memory 902 and the storage 903 are storage devices. In this computer system, each function of the control device 25 is realized by the CPU 901 executing a predetermined program loaded onto the memory 902.

[0043] Note that the control device 25 may be implemented by one computer or by a plurality of computers. Further, the control device 25 may be a virtual machine implemented on a computer.

[0044] The program for the control device 25 can be stored in a computer-readable recording medium such as an HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or can be distributed via a network. The computer-readable recording medium is, for example, a non-transitory recording medium.

[0045] Note that the present disclosure is not limited to the above-described embodiment, and numerous modifications are possible within the scope of the gist thereof.

[0046] 1a, 1b, 11a, 11b Transponder 2 Client device 4a, 4b, 5a, 5b Optical module 14 Optical fiber 21 First device 22 Second device 23 First optical module 24 Second optical module 25 Control device 31 Control unit 32 Modification unit 33 First measurement unit 34 Second measurement unit 35 Setting unit 100 Optical transmission system

Claims

1. An optical transmission system comprising: a first optical module; a second optical module connected to the first optical module by an optical fiber; and a control device for controlling the first optical module and the second optical module, wherein the control device includes: a changing unit for changing the wavelength of an optical signal transmitted by the optical fiber; a measuring unit for measuring the code error rate or chromatic dispersion value that occurs in the optical signal when an optical signal is communicated between the first optical module and the second optical module and the wavelength of the optical signal is changed by the changing unit; and a setting unit for setting the wavelength of the optical signal such that the measured code error rate or chromatic dispersion value is a value that causes the nonlinear degradation of the optical signal to be below a predetermined threshold.

2. The optical transmission system according to claim 1, wherein the modification unit intermittently or continuously changes the wavelength of the optical signal within a predetermined range.

3. The optical transmission system according to claim 2, wherein the predetermined range is in the C-band wavelength range.

4. The optical transmission system according to claim 1, wherein the measuring unit measures the code error rate, and the setting unit sets the wavelength of the optical signal so that the code error rate is minimized.

5. The optical transmission system according to claim 1, wherein the measuring unit measures the wavelength dispersion value, and the setting unit sets the wavelength of the optical signal so that the wavelength dispersion value is maximized.

6. The optical transmission system according to claim 1, wherein the optical fiber includes a Dispersion Shifted Fiber (DSF).

7. A wavelength setting method for setting the wavelength of an optical signal transmitted through an optical fiber between a first optical module and a second optical module, comprising: a modification unit that changes the wavelength of the optical signal when the optical signal is communicating through the optical fiber; a measurement unit that measures the sign error rate or chromatic dispersion value that occurs in the optical signal when the wavelength of the optical signal is changed; and a setting unit that sets the wavelength of the optical signal such that the sign error rate or chromatic dispersion value measured by the measurement unit becomes a value that causes the nonlinear degradation of the optical signal to be below a predetermined threshold.

8. A program to cause a computer to function as a control device comprising: a modification unit for changing the wavelength of an optical signal transmitted between a first optical module and a second optical module connected by an optical fiber; a measurement unit for measuring the code error rate or chromatic dispersion value that occurs in the optical signal when the optical signal is transmitted between the first optical module and the second optical module and the wavelength of the optical signal is changed by the modification unit; and a setting unit for setting the wavelength of the optical signal such that the code error rate or chromatic dispersion value measured by the measurement unit becomes a value that causes the nonlinear degradation of the optical signal to be below a predetermined threshold.

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