JP2024046628A - Wavelength conversion device and optical transmission system - Google Patents

Abstract

[Problem] It is an object of the present invention to provide a wavelength conversion device and an optical transmission system that suppress deterioration of signal quality on the receiving side in broadband transmission. [Solution] The wavelength conversion device has an optical medium that converts a first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band into a second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band, a first monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band, a storage unit that holds control information for adjusting the conversion characteristics of the optical medium, and a control unit that performs control to adjust the conversion characteristics of the optical medium using the control information obtained from the storage unit according to the first observation result by the first monitor. [Selected Figure] Figure 5

Description

This case relates to a wavelength conversion device and an optical transmission system.

A wavelength division multiplexing (WDM) transmission method is known that multiplexes and transmits optical signals of multiple wavelengths to enable high-speed, large-capacity communications. In addition, to expand transmission capacity, multi-band broadband transmission is known that uses multiple wavelength bands such as the C band (conventional band) and the L band (long band). For example, the C band is a wavelength band of 1530 nm to 1565 nm, and the L band is a long-wavelength wavelength band of 1565 nm to 1625 nm.

In WDM transmission systems, for example, due to the influence of stimulated Raman scattering (SRS) in the optical transmission path, a large power deviation (tilt) occurs between the short wavelength side and the long wavelength side during transmission. As a result, the signal quality on the receiving side deteriorates. Therefore, tilt compensation is required to suppress the deterioration of the signal quality on the receiving side (see, for example, Patent Documents 1 and 2).

JP 2019-186735 A Japanese Patent Application Publication No. 2014-229913

By the way, although the appearance of the above-mentioned tilt (primary tilt) caused by SRS has been confirmed in broadband transmission using C band and L band, for example, since it is limited to two wavelength bands, C band and L band, It was difficult to confirm the appearance of secondary tilt.

However, in new broadband transmission that uses not only the C and L bands but also the S band (Short band) to further expand transmission capacity, the appearance of secondary tilt caused by SRS is less likely due to the wider wavelength band. It has started to be confirmed. The S band is, for example, a wavelength band of 1460 nm to 1530 nm. In this way, in wideband transmission using the C band, L band, and S band, it is desirable to perform tilt compensation for the secondary tilt caused by SRS to suppress deterioration in signal quality on the receiving side.

One aspect of the present invention is therefore to provide a wavelength conversion device and an optical transmission system that suppress deterioration in signal quality on the receiving side in broadband transmission.

In one embodiment, the wavelength conversion device converts first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band into second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band. a first monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band; a storage unit that retains control information for adjusting conversion characteristics of the optical medium; and a control unit that performs control to adjust the conversion characteristics of the optical medium based on the control information acquired from the storage unit in accordance with a first observation result obtained by one monitor.

In one embodiment, the optical transmission system includes a receiving-side wavelength conversion device and a transmitting-side wavelength conversion device, and the receiving-side wavelength conversion device includes a first optical medium that converts a first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band into a second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band, a first monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band, a first storage unit that holds first control information for adjusting the conversion characteristics of the first optical medium, and a receiving-side control unit that performs control to adjust the conversion characteristics of the first optical medium using the first control information acquired from the first storage unit according to the first observation result by the first monitor, and the transmitting-side wavelength conversion device includes a second optical medium that converts the second wavelength multiplexed light output from a first transmitter into the first wavelength multiplexed light, and an optical coupler that combines the second wavelength multiplexed light output from a second transmitter and the first wavelength multiplexed light output from the second optical medium and outputs the combined light to a transmission path connecting the receiving-side wavelength conversion device and the transmitting-side wavelength conversion device.

It is possible to suppress degradation of signal quality on the receiving side during wideband transmission.

FIG. 1 is an example of an optical transmission system. FIG. 2 is a diagram illustrating an example of secondary tilt. FIG. 3 is an example of a transmission-side wavelength conversion device according to the first embodiment. FIG. 4 shows an example of a wavelength conversion device on the receiving side according to the first embodiment. FIG. 5 is an example of a wavelength conversion section on the reception side according to the first embodiment. FIG. 6 is an example of a graph illustrating the zero dispersion wavelength. FIG. 7 is a diagram illustrating the relationship between the wavelength difference, the amount of phase mismatch, and the parametric gain. FIG. 8 is an example of tilt due to wavelength conversion. FIG. 9 shows an example of a control unit on the receiving side according to the first embodiment. FIG. 10 is a flowchart showing an example of compensation for variations in zero-dispersion wavelength. FIG. 11 is a flowchart showing an example of tilt compensation according to the first embodiment. FIG. 12 is an example of a reception-side wavelength conversion device according to the second embodiment. FIG. 13 shows an example of a wavelength conversion unit on the receiving side according to the second embodiment. FIG. 14 shows an example of a control unit on the receiving side according to the second embodiment. FIG. 15 is a flowchart showing an example of tilt compensation according to the second embodiment. FIG. 16 shows an example of a wavelength converter on the transmitting side and a wavelength converter on the receiving side according to the third embodiment. FIG. 17 shows an example of a wavelength conversion unit on the receiving side according to the third embodiment. FIG. 18 shows an example of a wavelength conversion unit on the transmitting side according to the third embodiment. FIG. 19 is an example of a control unit according to the third embodiment. FIG. 20 is a flowchart showing an example of tilt compensation according to the third embodiment. FIG. 21 is an example of a spectrum change. FIG. 22 shows an example of a wavelength conversion unit on the receiving side according to the fourth embodiment. FIG. 23 is an example of a wavelength conversion section on the transmitting side according to the fourth embodiment. FIG. 24 is a flowchart showing an example of tilt compensation according to the fourth embodiment. FIG. 25 shows an example of a wavelength conversion unit on the transmitting side according to the fifth embodiment. FIG. 26 is an example of a control unit according to the fifth embodiment. FIG. 27 is a flowchart showing an example of tilt compensation according to the fifth embodiment. FIG. 28 is an example of a reception-side wavelength conversion device according to the sixth embodiment. FIG. 29 is an example of a transmission-side wavelength conversion device according to the sixth embodiment. FIG. 30 shows an example of a control unit according to the sixth embodiment. FIG. 31 is another example of the control unit according to the sixth embodiment. FIG. 32 is a flowchart showing an example of tilt compensation according to the sixth embodiment. FIG. 33 is an example of a control unit according to the seventh embodiment. FIG. 34 is a flowchart showing an example of tilt compensation according to the seventh embodiment.

The following describes the implementation of this invention with reference to the drawings.

First Embodiment
As shown in FIG. 1, the optical transmission system ST includes a wavelength converter 100 on the transmitting side and a wavelength converter 200 on the receiving side. The wavelength converter 100 and the wavelength converter 200 are connected to each other via an optical transmission path 300. The optical transmission path 300 includes, for example, an optical fiber. The wavelength converter 100 is connected to a first WDM transmitter 10, a second WDM transmitter 20, and a third WDM transmitter 30. The first WDM transmitter 10 and the third WDM transmitter 30 are an example of a first transmitter. The second WDM transmitter 20 is an example of a second transmitter. The wavelength converter 200 is connected to a first WDM receiver 40, a second WDM receiver 50, and a third WDM receiver 60.

The first WDM transmitter 10 includes a plurality of first single wavelength transmitters (denoted as Tx#1 in FIG. 1) 11 and an optical multiplexer 12 (denoted as MUX in FIG. 1). The plurality of first single wavelength transmitters 11 respectively transmit single wavelength lights λ11, . . . , λ1n of different wavelengths belonging to the C band. The single wavelength lights λ11, . . . , λ1n are, for example, signal lights. The single wavelength lights λ11, . . . , λ1n may be control lights. The optical multiplexer 12 multiplexes the single wavelength lights λ11, . . . , λ1n, and outputs the wavelength multiplexed light λ1C. Thereby, the first WDM transmitter 10 transmits the wavelength multiplexed light λ1C belonging to the C band.

The second WDM transmitter 20 includes a plurality of second single wavelength transmitters (denoted as Tx#2 in FIG. 1) 21 and an optical multiplexer 22. The plurality of second single wavelength transmitters 21 respectively transmit single wavelength lights λ21, . . . , λ2n of different wavelengths belonging to the C band. The single wavelength lights λ21, . . . , λ2n are signal lights. The single wavelength lights λ21, . . . , λ2n may be control lights. The optical multiplexer 22 multiplexes the single wavelength lights λ21, . . . , λ2n and outputs the wavelength multiplexed light λ2C. Thereby, the second WDM transmitter 20 transmits the wavelength multiplexed light λ2C belonging to the C band.

The third WDM transmitter 30 includes a plurality of third single wavelength transmitters (denoted as Tx#3 in FIG. 1) 31 and an optical multiplexer 32. The plurality of third single wavelength transmitters 31 respectively transmit single wavelength lights λ31, . . . , λ3n of different wavelengths belonging to the C band. The single wavelength lights λ31, . . . , λ3n are signal lights. The single wavelength lights λ31, . . . , λ3n may be control lights. The optical multiplexer 32 multiplexes the single wavelength lights λ31, . . . , λ3n and outputs the wavelength multiplexed light λ3C. Thereby, the third WDM transmitter 30 transmits the wavelength multiplexed light λ3C belonging to the C band.

The wavelength conversion device 100 receives wavelength multiplexed light λ1C transmitted from the first WDM transmitter 10, wavelength multiplexed light λ2C transmitted from the second WDM transmitter 20, and wavelength multiplexed light λ3C transmitted from the third WDM transmitter 30. When wavelength multiplexed light λ1C is input, the wavelength conversion device 100 converts the wavelength multiplexed light λ1C into wavelength multiplexed light λ1S belonging to the S band. When wavelength multiplexed light λ3C is input, the wavelength conversion device 100 converts the wavelength multiplexed light λ3C into wavelength multiplexed light λ3L belonging to the L band. After conversion, the wavelength conversion device 100 multiplexes the wavelength multiplexed light λ1S, wavelength multiplexed light λ2C, and wavelength multiplexed light λ3L, and outputs the multiplexed light λ1S to the optical transmission path 300 as multiband light λmb. As a result, the multiband light λmb passes through the optical transmission path 300. Note that the multiband light λmb is an example of broadband wavelength multiplexed light.

When the multiband light λmb passes through the optical transmission line 300, tilt occurs due to SRS. Specifically, a primary tilt and a secondary tilt occur due to SRS. For example, as shown in FIG. 2, when multiband light λmb is transmitted with a transmission power of -2 dBm, as the transmission distance increases, the reception power of wavelengths belonging to the L band decreases. The received power of wavelengths belonging to the C band and the received power of wavelengths belonging to the S band also decrease as in the case of the L band. In this way, the amount of reduction changes with the transmission distance.

Here, when the broken line curve connecting the shortest wavelength and the longest wavelength belonging to the L band is approximated to a straight line (not shown) connecting the shortest wavelength and the longest wavelength, the amount of change in power at the center of the curve and the straight line is small. In this way, even if a power deviation occurs between the short wavelength side and the long wavelength side belonging to the L band, if the curve can be linearly approximated by a linear approximation, this power deviation is treated as a primary tilt and the wavelength conversion described later is performed. The optical amplifier included in the device 200 compensates for the first-order tilt. Note that since the C band is the same as the L band, detailed explanation will be omitted.

On the other hand, when the transmission distance is extended to 80 km, for example, if the solid curve connecting the shortest and longest wavelengths belonging to the S band is approximated by a dashed line connecting the shortest and longest wavelengths, the amount of change in power in the center between the solid curve and the dashed line becomes larger than in the case of the L band or C band. For example, the amount of change in power in the center between the solid curve and the dashed line is about 2 dBm. This causes the OSNR (Optical Signal to Noise Ratio) on the receiving side to decrease by about 2 dB.

In this way, when the transmission distance is extended and a power deviation occurs on the short and long wavelength sides belonging to the S band, it becomes difficult to linearly approximate the curve to a straight line. In this case, this power deviation is treated as a secondary tilt, and the secondary tilt is compensated for by the wavelength conversion unit provided in the wavelength conversion device 200 described later.

Returning to FIG. 1, the multiband light λmb that has passed through the optical transmission path 300 is input to the wavelength conversion device 200. When the multiband light λmb is input, the wavelength conversion device 200 splits the multiband light λmb into wavelength multiplexed light λ1S, wavelength multiplexed light λ2C, and wavelength multiplexed light λ3L. After splitting, the wavelength conversion device 200 converts the wavelength multiplexed light λ1S to wavelength multiplexed light λ1C and outputs the wavelength multiplexed light λ1C to the first WDM receiver 40. The wavelength conversion device 200 outputs the wavelength multiplexed light λ2C to the second WDM receiver 50 without converting the wavelength multiplexed light λ2C. The wavelength conversion device 200 converts the wavelength multiplexed light λ3L to wavelength multiplexed light λ3C and outputs the wavelength multiplexed light λ3C to the third WDM receiver 60.

The first WDM receiver 40 includes a plurality of first receivers (denoted as Rx#1 in FIG. 1) 41 and an optical demultiplexer 42 (described as DEMUX in FIG. 1). The optical demultiplexer 42 demultiplexes the wavelength multiplexed light λ1C into single wavelength lights λ11,..., λ1n, and sends each single wavelength light λ11,..., λ1n to each of the first receivers 41 with corresponding wavelengths. Output. Thereby, each of the first receivers 41 receives the single wavelength lights λ11, . . . , λ1n belonging to the C band.

The second WDM receiver 50 includes a plurality of second receivers (denoted as Rx#2 in FIG. 1) 51 and an optical demultiplexer 52. The optical demultiplexer 52 demultiplexes the wavelength multiplexed light λ2C into single wavelength lights λ21,..., λ2n, and sends each single wavelength light λ21,..., λ2n to each of the second receivers 51 with corresponding wavelengths. Output. Thereby, each of the second receivers 51 receives the single wavelength lights λ21, . . . , λ2n.

The third WDM receiver 60 includes a plurality of third receivers (shown as Rx#3 in FIG. 1) 61 and an optical splitter 62. The optical splitter 62 splits the wavelength-multiplexed light λ3C into single-wavelength light λ31, ..., λ3n, and outputs each single-wavelength light λ31, ..., λ3n to the third receiver 61 with the corresponding wavelength. As a result, each of the third receivers 61 receives the single-wavelength light λ31, ..., λ3n.

Next, the wavelength conversion device 100 will be described in detail with reference to FIG. 3.

As shown in FIG. 3, the wavelength conversion device 100 includes optical amplifiers 101, 102, 103, 104, and 105, an optical coupler 106, and wavelength conversion sections 110 and 160. The optical amplifier 101 is provided before the wavelength conversion section 110, and the optical amplifier 104 is provided after the wavelength conversion section 110. The optical amplifier 103 is provided before the wavelength conversion section 160, and the optical amplifier 105 is provided after the wavelength conversion section 160.

The optical amplifier 101 is connected to the first WDM transmitter 10. The optical amplifier 102 is connected to the second WDM transmitter 20. The optical amplifier 103 is connected to the third WDM transmitter 30. The optical amplifiers 102, 104, and 105 are connected to the optical coupler 106. The optical coupler 106 is connected to the optical transmission path 300.

Optical amplifier 101 amplifies wavelength-multiplexed light λ1C belonging to the C band and outputs it to wavelength conversion unit 110. Wavelength conversion unit 110 converts wavelength-multiplexed light λ1C to wavelength-multiplexed light λ1S belonging to the S band and outputs it to optical amplifier 104. Optical amplifier 104 amplifies wavelength-multiplexed light λ1S belonging to the S band and outputs it to optical coupler 106. Optical amplifier 102 amplifies wavelength-multiplexed light λ2C belonging to the C band and outputs it to optical coupler 106.

The optical amplifier 103 amplifies the wavelength multiplexed light λ3C belonging to the C band and outputs it to the wavelength conversion section 160. The wavelength converter 160 converts the wavelength multiplexed light λ3C into the wavelength multiplexed light λ3L belonging to the L band, and outputs it to the optical amplifier 105. Optical amplifier 105 amplifies wavelength multiplexed light λ3L belonging to the L band and outputs it to optical coupler 106. The optical coupler 106 multiplexes the wavelength multiplexed light λ1S, the wavelength multiplexed light λ2C, and the wavelength multiplexed light λ3L, and outputs the multiplexed light to the optical transmission line 300 as a multiband light λmb.

Next, details of the wavelength conversion device 200 will be described with reference to FIG. 4.

As shown in FIG. 4, the wavelength conversion device 200 according to the first embodiment includes a WDM filter 201, optical amplifiers 202, 203, 204, 205, and 206, and wavelength conversion sections 210 and 260. Further, the wavelength conversion device 200 includes OCMs (Optical channel monitors) 207, 208 and control units 209, 209-1. The OCMs 207 and 208 are examples of first monitors on the receiving side. The OCM 207 may be included in the control unit 209. OCM 208 may be included in control unit 209-1.

The optical amplifier 202 is provided before the wavelength conversion section 210, and the optical amplifier 204 is provided after the wavelength conversion section 210. The optical amplifier 203 is provided before the wavelength conversion section 260, and the optical amplifier 206 is provided after the wavelength conversion section 260.

Optical amplifier 204 is connected to first WDM receiver 40 . Optical amplifier 205 is connected to second WDM receiver 50 . Optical amplifier 206 is connected to third WDM receiver 60 . Optical amplifiers 202, 203, and 205 are connected to WDM filter 201. WDM filter 201 is connected to optical transmission line 300.

The multiband light λmb that has passed through the optical transmission path 300 is input to the WDM filter 201. The WDM filter 201 splits the multiband light λmb into wavelength multiplexed light λ1S, wavelength multiplexed light λ2C, and wavelength multiplexed light λ3L. The optical amplifier 202 amplifies the wavelength multiplexed light λ1S belonging to the S band and outputs it to the wavelength conversion unit 210. The wavelength conversion unit 210 converts the wavelength multiplexed light λ1S belonging to the S band to wavelength multiplexed light λ1C belonging to the C band and outputs it to the optical amplifier 204. The optical amplifier 204 amplifies the wavelength multiplexed light λ1C belonging to the C band so as to compensate for the primary tilt and outputs it to the first WDM receiver 40.

The optical amplifier 205 amplifies the wavelength multiplexed light λ2C belonging to the C band so as to compensate for the first-order tilt, and outputs the amplified wavelength multiplexed light λ2C to the second WDM receiver 50. The optical amplifier 203 amplifies the wavelength multiplexed light λ3L belonging to the L band and outputs it to the wavelength conversion section 260. The wavelength converter 260 converts the wavelength multiplexed light λ3L into the wavelength multiplexed light λ3C belonging to the C band, and outputs it to the optical amplifier 206. The optical amplifier 206 amplifies the wavelength multiplexed light λ3C belonging to the C band so as to compensate for the first-order tilt, and outputs the amplified wavelength multiplexed light λ3C to the third WDM receiver 60.

The OCM 207 observes the power of the wavelength multiplexed light λ1C belonging to the C band outputted from the wavelength conversion unit 210. More specifically, the OCM 207 observes the wavelength power, which is the optical power of the plurality of single wavelength lights λ11, . . . , λ1n included in the wavelength multiplexed light λ1C. The OCM 207 outputs the observation results to the control unit 209 using an electrical control signal. The OCM 208 observes the power of the wavelength multiplexed light λ3C belonging to the C band output from the wavelength converter 260. More specifically, the OCM 208 observes the wavelength power that is the optical power of the plurality of single wavelength lights λ31, . . . , λ3n included in the wavelength multiplexed light λ3C. The OCM 208 outputs the observation results to the control unit 209-1 using an electrical control signal. Note that the observation results output by the OCMs 207 and 208 are an example of the first observation results.

Based on the observation results output from the OCM 207, the control unit 209 adjusts the conversion characteristics of the wavelength conversion unit 210 so as to compensate for the secondary tilt that occurs in the optical transmission path 300 that transmits the multiband light λmb. As will be described in detail later, the wavelength conversion unit 210 includes a wavelength conversion medium such as a nonlinear optical medium, and the control unit 209 adjusts the conversion characteristics of the wavelength conversion unit 210 by controlling the temperature of the wavelength conversion medium.

Based on the observation results output from the OCM 208, the control unit 209-1 adjusts the conversion characteristics of the wavelength conversion unit 260 so as to compensate for the secondary tilt that occurs in the optical transmission path 300 that transmits the multiband light λmb. As will be described in detail later, the wavelength conversion unit 260 includes a wavelength conversion medium such as a nonlinear optical medium, and the control unit 209-1 adjusts the conversion characteristics of the wavelength conversion unit 260 by controlling the temperature of the wavelength conversion medium.

Next, the WDM filter 201 and the wavelength conversion unit 210 will be described in detail with reference to FIG. 5. Note that the wavelength conversion unit 260 basically has the same configuration as the wavelength conversion unit 210, so a detailed description will be omitted.

As shown in FIG. 5, the WDM filter 201 includes an optical filter 21A and an optical filter 21B. The optical filter 21A separates the wavelength-multiplexed light λ1S from the multiband light λmb and outputs the multiband residual light λr to the optical filter 21B. The wavelength-multiplexed light λ1S is input to the optical amplifier 202.

Since the wavelength-multiplexed light λ1S is separated from the multiband light λmb, the multiband afterglow λr contains wavelength-multiplexed light λ2C and wavelength-multiplexed light λ3L. The optical filter 21B separates the multiband afterglow λr into wavelength-multiplexed light λ2C and wavelength-multiplexed light λ3L and outputs them. The wavelength-multiplexed light λ2C is input to the optical amplifier 205 (see Figure 4). The wavelength-multiplexed light λ3L is input to the optical amplifier 203 (see Figure 4).

The wavelength conversion unit 210 includes an excitation light source 211, an optical coupler 212, a wavelength conversion medium 213, an optical filter 214, an optical branch tap (referred to as TAP (Terminal Access Point) in FIG. 5) 215, a temperature sensor 216, and a heater 217. The wavelength conversion unit 210 may include a TEC (Thermo Electric Cooler) together with the heater 217. The wavelength conversion medium 213 is an example of an optical medium and a first optical medium. Specifically, the wavelength conversion medium 213 is a nonlinear optical medium. The nonlinear optical medium may be an optical fiber or a nonlinear optical crystal element such as a PPLN (Periodically Poled Lithium Niobate) waveguide element.

The pumping light source 211 outputs pumping light λp in a wavelength band longer than the S band (for example, the 1520 nm band). The pumping light λp contains two different wavelengths. The optical coupler 212 is connected to the optical amplifier 202. Therefore, the pumping light λp and the wavelength-multiplexed light λ1S are input to the optical coupler 212. The optical coupler 212 adds the pumping light λp to the wavelength-multiplexed light λ1S and outputs it to the wavelength conversion medium 213.

The wavelength conversion medium 213 converts the wavelength multiplexed light λ1S into wavelength multiplexed light λ1C based on the wavelength dispersion characteristics of the wavelength conversion medium 213 and the refractive index fluctuation in the wavelength conversion medium 213 caused by the pump light λp, and outputs it together with the wavelength multiplexed light λ1S. In this way, the wavelength conversion medium 213 converts the wavelength multiplexed light λ1S including multiple wavelengths belonging to the S band, which is an example of the first wavelength band, into wavelength multiplexed light λ1C including multiple wavelengths belonging to the C band, which is an example of the second wavelength band. Meanwhile, the pump light λp passes through the wavelength conversion medium 213. Therefore, the wavelength conversion medium 213 outputs the wavelength multiplexed light λ1S, the wavelength multiplexed light λ1C, and the pump light λp. The L band is an example of the third wavelength band.

The optical filter 214 removes the wavelength multiplexed light λ1S and the pump light λp from the wavelength multiplexed light λ1S, the wavelength multiplexed light λ1C, and the pump light λp output from the wavelength conversion medium 213, and outputs the wavelength multiplexed light λ1C. Although not shown, the optical filter 214 includes a wavelength filter and a polarization filter. First, the wavelength filter removes the wavelength multiplexed light λ1S, and then the polarization filter removes the pumping light λp. As a result, the wavelength-multiplexed light λ1C remains without being removed, and the wavelength-multiplexed light λ1C is output from the optical filter 214.

The optical branching tap 215 branches the wavelength multiplexed light λ1C and outputs the wavelength multiplexed light λ1C to the optical amplifier 204 and the OCM 207. Thereby, the optical amplifier 204 can amplify the wavelength multiplexed light λ1C. Further, the OCM 207 can observe the wavelength power of a plurality of single wavelength lights λ11, . . . , λ1n included in the wavelength multiplexed light λ1C.

Temperature sensor 216 detects the temperature of wavelength conversion medium 213 and outputs the detected temperature to control unit 209 as an electrical signal. The control unit 209 controls the temperature of the heater 217 based on the observation results output from the OCM 207 and the temperature of the wavelength conversion medium 213 detected by the temperature sensor 216 so as to compensate for the secondary tilt. When the wavelength conversion section 210 includes a TEC, the control section 209 may control the temperature of the TEC. In this way, the control unit 209 controls the temperature of the wavelength conversion medium 213 via the heater 217 and the TEC, and adjusts the conversion characteristics of the wavelength conversion medium 213.

For example, when the heater 217 heats the wavelength conversion medium 213 based on the control of the control unit 209, the conversion characteristics of the wavelength conversion medium 213 change. The change in the conversion characteristics of the wavelength conversion medium 213 generates a secondary tilt in the opposite direction to the secondary tilt, compensating for the secondary tilt. Therefore, by offsetting the secondary tilt generated in the optical transmission path 300 with this opposite secondary tilt, it is possible to suppress the decrease in OSNR caused by the secondary tilt.

A mechanism in which the conversion characteristics of the wavelength conversion medium 213 change depending on temperature will be described with reference to FIGS. 6 to 8.

As shown in FIG. 6, the wavelength conversion medium 213 has dispersion characteristics that depend on the wavelength λ, as shown by a dispersion curve Dw. This dispersion curve Dw has a zero dispersion wavelength at which the second-order dispersion β ₂ becomes zero at predetermined wavelengths λa and λb. However, since there are variations in the zero-dispersion wavelength, the control unit 209 shifts the dispersion curve Dw in the horizontal axis direction by controlling the temperature of the wavelength conversion medium 213 to compensate for the variations in the zero-dispersion wavelength. Note that the control unit 209 may compensate for variations in the zero-dispersion wavelength by moving and adjusting the wavelength of the excitation light λp input to the wavelength conversion medium 213.

算出式（１）における係数ω_ｐ，ω_０は以下のとおりである。
ω_ｐ：励起光の周波数
ω_０：ゼロ分散周波数
ここで、β_２ｍは係数（励起光の周波数）ω_ｐでの２ｍ次の分散を意味している。 In addition, in FIG. 6, the explanation was given using the second-order dispersion β ₂ as an example, but the even-order higher-order dispersion β _2m (m=1, 2, 3, ...) is calculated using the following calculation formula (1) and the coefficients ω _p , It can be expressed as ω ₀ .
<Calculation formula (1)>

The coefficients ω _p and ω ₀ in calculation formula (1) are as follows.
ω _p : Frequency of pumping light ω ₀ : Zero dispersion frequency Here, β _2m means the 2m-th order dispersion at the coefficient (frequency of pumping light) ω _p .

算出式（２）におけるΔωはω_ｐ－ω_ｓによって表される。係数ω_ｓは信号光の周波数である。 Next, the phase mismatch amount Δβ taking into consideration the above-mentioned even-order high-order dispersion β _2m can be expressed by the following calculation formula (2) and coefficient _ωs .
<Calculation formula (2)>

In the formula (2), Δω is expressed by ω _p −ω _s , where the coefficient ω _s is the frequency of the signal light.

Therefore, based on the calculation formula (1) and the calculation formula (2), the phase mismatch amount Δβ up to the sixth order (m=3) dispersion can be expressed by the following calculation formula (3).
<Calculation formula (3)>

Here, in the above calculation formula (3), the influence of the sixth-order dispersion β ₆ on the amount of phase mismatch Δβ is slight and may be ignored. Therefore, as long as the fourth-order dispersion _β4 is not zero, the phase mismatch amount Δβ can be approximated to a fourth-order equation, and as shown in FIGS. 7(a) and (b), the phase mismatch amount Δβ is 4 It can be represented by the following graph. Note that the upper part of FIG. 7(a) shows the case where both the variance β ₂ and the variance β ₄ are positive (+), and the lower part of FIG. 7(a) shows the case where the variance β ₂ is positive and the variance β The case where ₄ is negative (-) is shown. On the other hand, the upper part of FIG. 7(b) shows the case where the variance β ₂ is negative and the variance β ₄ is positive, and the lower part of FIG. 7(b) shows that both the variance β ₂ and the variance β ₄ are negative. The case of is shown.

なお、Ｐｓｏｕｔは波長変換媒質２１３から出力される信号光の出力パワーを表している。Ｐｓｉｎは波長変換媒質２１３に入力される信号光の入力パワーを表している。 When the phase mismatch amount Δβ is expressed by a fourth-order equation, a second-order tilt occurs as shown in Figures 7(c) and 7(d). The parametric gain G can be calculated, for example, by the following calculation formula (4).
<Calculation formula (4)>

Here, Psout represents the output power of the signal light output from the wavelength conversion medium 213. Psin represents the input power of the signal light input to the wavelength conversion medium 213.

Here, as shown in Figures 7(c) and (d), the direction of the secondary tilt is determined by the positive or negative of the dispersion _β2 . For example, if the dispersion _β2 is positive, an upwardly convex secondary tilt occurs, and if the dispersion _β2 is negative, a downwardly convex secondary tilt occurs. Since the dispersion _β2 is shifted by the temperature of the wavelength conversion medium 213, the control unit 209 can control the secondary tilt by controlling the temperature of the wavelength conversion medium 213. As a result, if a secondary tilt occurs in the wavelength conversion medium 213, for example, as shown in Figure 8, the shape of the secondary tilt occurring in the optical transmission line 300 can be changed.

For convenience, parametric amplification has been used here, but similar secondary tilt changes can also be confirmed with wavelength conversion. Figure 21 shows the change in the spectrum (wavelength range 1575-1608 nm) of a quasi-WDM signal converted to the L band when temperature control is performed in 1°C increments using a highly nonlinear fiber. With a temperature change of 5°C, almost no intensity change due to temperature change is observed in the wavelength range of 1575-1585 nm, but it can be confirmed that a change of up to 2 dB occurs in the wavelength range of 1585-1608 nm. Although the amount of tilt control is smaller than with parametric amplification, this shows the possibility of compensating for secondary tilt of around 2 dB.

Next, details of the control unit 209 will be explained with reference to FIG. Note that since the control unit 209-1 basically has the same configuration as the control unit 209, detailed explanation will be omitted.

The control unit 209 includes, as a hardware circuit, a first calculation unit 29A, a first control unit 29B, a second calculation unit 29C, a second control unit 29D, and a memory 29E. The first control section 29B and the second control section 29D are examples of a control section (specifically, a receiving side control section). The memory 29E is an example of a storage section (specifically, a first storage section). The first calculation section 29A, the first control section 29B, the second calculation section 29C, the second control section 29D, and the memory 29E are realized by, for example, a single LSI (Large-Scale Integration). The first calculation unit 29A and the first control unit 29B cooperate to compensate for variations in zero-dispersion wavelength. The second calculation unit 29C and the second control unit 29D cooperate to compensate for the secondary tilt occurring in the optical transmission line 300. The details of the operation of the first calculation section 29A and the first control section 29B that compensate for the variation in zero dispersion wavelength, and the operation of the second calculation section 29C and the second control section 29D that compensate for the secondary tilt will be described later.

Note that the first calculation unit 29A, the first control unit 29B, the second calculation unit 29C, and the second control unit 29D may be realized, for example, by a single CPU (Central Processing Unit), or each may be implemented by a separate CPU. It may be realized by The first calculation unit 29A, the first control unit 29B, the second calculation unit 29C, and the second control unit 29D may be realized by a single or multiple ASICs (Application Specific Integrated Circuits), or may be implemented by a single or multiple ASIC (Application Specific Integrated Circuit). It may be realized by a plurality of FPGAs (Field Programmable Gate Arrays). The memory 29E includes, for example, RAM (Random Access Memory) and ROM (Read Only Memory). The wavelength conversion device 200 operates when, for example, a CPU or the like reads a program stored in the memory 29E and executes the process. The program may be based on the flowchart described later.

Next, the first compensation operation of the wavelength conversion device 200 according to the first embodiment will be described with reference to FIG. 10. The first compensation operation is an operation in which the OCM 207, the first calculation unit 29A, and the first control unit 29B compensate for the variation in the zero dispersion wavelength.

For example, when power is supplied to the wavelength conversion device 200 and operation of the wavelength conversion device 200 begins, the OCM 207 observes the power of the wavelength-multiplexed light λ1C (step S1). More specifically, the OCM 207 observes the wavelength power of the multiple single-wavelength lights λ11, ..., λ1n contained in the wavelength-multiplexed light λ1C. After observing the wavelength power, the OCM 207 outputs the observation result to the first calculation unit 29A by an electrical control signal. The observation result includes each wavelength and the wavelength power of each wavelength.

When the observation results are input, the first calculation unit 29A estimates the average power of the wavelength multiplexed light λ1C based on the observation results (step S2). Specifically, the first calculation unit 29A estimates the average power by dividing the wavelength power of each wavelength by the number of wavelengths. After estimating the average power, the first calculation unit 29A estimates the tilt of the wavelength multiplexed light λ1C based on the observation results (step S3). Specifically, the first calculation unit 29A estimates the tilt of the wavelength multiplexed light λ1C by calculating the difference between the wavelength power on the long wavelength side and the wavelength power on the short wavelength side. Note that the first calculation unit 29A may estimate the average power and tilt based on the observation results and a known calculation formula. Also, the processing order of steps S2 and S3 may be reversed.

When the first calculation unit 29A estimates the tilt, the first control unit 29B controls the temperature of the heater 217 (step S4). For example, the first control unit 29B sets the temperature of the heater 217 to a temperature corresponding to the average power based on a calculation formula (or function) that defines the relationship between the average power and the temperature. The first control unit 29B may set the temperature of the heater 217 to a temperature corresponding to the average power by referring to a table that defines the relationship between the average power and the temperature. Such a table that defines the relationship between the average power and the temperature may be stored in the memory 29E. When the first control unit 29B controls the temperature of the heater 217 and the temperature of the wavelength conversion medium 213 rises, the conversion characteristics of the wavelength conversion medium 213 are adjusted, and the average power estimated by the first calculation unit 29A changes.

When the temperature of the heater 217 is controlled, the first calculation unit 29A determines whether the average power has improved (step S5). For example, the first calculation unit 29A compares the average power before and after the temperature increase to determine whether the average power has improved. If the average power has not improved (step S5: NO), the first control unit 29B executes the process of step S4. This causes the first control unit 29B to control the temperature of the heater 217 again. In this way, the first control unit 29B controls the temperature of the heater 217 until the average power improves.

When the average power improves (step S5: YES), the first calculation unit 29A determines whether or not the tilt decreases (step S6). For example, the first calculation unit 29A compares the tilt before and after the temperature rises, and determines whether the tilt decreases. If the tilt has not decreased (step S6: NO), the first control unit 29B executes the process of step S4. That is, the first control unit 29B controls the temperature of the heater 217 until the tilt decreases. Thereby, the first control unit 29B controls the temperature of the heater 217 again. In this way, the first control unit 29B controls the temperature of the heater 217 until the average power increases and the tilt decreases.

When the tilt has not decreased, the first control unit 29B controls the temperature of the heater 217 based on a calculation formula (or function) that defines the relationship between the tilt and the temperature. The first control unit 29B may control the temperature of the heater 217 by referring to a table that defines the relationship between the tilt and the temperature. Such a table that defines the relationship between the tilt and the temperature may be stored in the memory 29E.

When the tilt decreases (step S6: YES), the first control unit 29B associates the average power and tilt that were confirmed in the processing of steps S5 and S6, and the temperature setting value for the heater 217 when the average power and tilt were confirmed, and records them in the memory 29E as control information (specifically, the first control information) (step S7). For the association, for example, a calculation formula (or function) or a table may be used. The first control unit 29B may instruct the temperature sensor 216 to record the temperature when the average power and tilt were confirmed in the memory 29E, and the temperature sensor 216 may record this temperature in the memory 29E as the temperature setting value. When the average power, tilt, and temperature setting value are recorded, the first compensation operation for the variation in the zero dispersion wavelength by the OCM 207, the first calculation unit 29A, and the first control unit 29B is completed. In this way, the control unit 209 performs control to adjust the conversion characteristics of the wavelength conversion medium 213 so as to compensate for the variation in the zero dispersion wavelength.

Next, with reference to FIG. 11, the second compensation operation of the wavelength conversion device 200 according to the first embodiment will be described. The second compensation operation is an operation in which the OCM 207, the second calculation unit 29C, and the second control unit 29D compensate for the secondary tilt.

First, the second calculation unit 29C reads out control information from the memory 29E in which the average power, tilt, and temperature setting value are correlated with each other (step S11). Here, in order to achieve fine precision, the control information used is that recorded in the memory 29E in step S7. Note that predetermined control information within the controllable range may be recorded in the memory 29E and used.

After reading the control information, the second control unit 29D controls the temperature of the heater 217 (step S12). For example, the second control unit 29D sets the temperature of the heater 217 to a temperature corresponding to the average power based on a calculation formula (or function) that defines the relationship between average power and temperature. The second control unit 29D may set the temperature of the heater 217 to a temperature corresponding to the average power by referring to a table that defines the relationship between average power and temperature. When the second control section 29D controls the temperature of the heater 217 and the temperature of the wavelength conversion medium 213 increases, the conversion characteristics of the wavelength conversion medium 213 are adjusted, and the average power estimated by the second calculation section 29C changes. Note that the first control section 29B may control the temperature of the TEC. In this case, the temperature of the wavelength conversion medium 213 decreases.

After controlling the temperature, the OCM 207 observes the power of the wavelength multiplexed light λ1C (step S13). More specifically, the OCM 207 observes the wavelength power of a plurality of single wavelength lights λ11, . . . , λ1n included in the wavelength multiplexed light λ1C. After observing the wavelength power, the OCM 207 outputs the observation result to the second calculation unit 29C using an electrical control signal.

When the observation results are input, the second calculation unit 29C estimates the average power of the wavelength multiplexed light λ1C based on the observation results (step S14). Specifically, the second calculation unit 29C estimates the average power by dividing the wavelength power of each wavelength by the number of wavelengths. After estimating the average power, the second calculation unit 29C estimates the tilt of the wavelength multiplexed light λ1C based on the observation results (step S15). Specifically, the second calculation unit 29C estimates the tilt of the wavelength multiplexed light λ1C by calculating the difference between the wavelength power on the long wavelength side and the wavelength power on the short wavelength side. Note that the second calculation unit 29C may estimate the average power and tilt based on the observation results and a known calculation formula. Further, the processing order of steps S14 and S15 may be reversed.

When the second calculation unit 29C estimates the tilt, the second control unit 29D determines whether the tilt estimated by the second calculation unit 29C is less than the read tilt, which is the tilt read in the processing of step S11 (step S16). If the estimated tilt is equal to or greater than the read tilt (step S16: NO), the processing of steps S12 to S15 is repeated. In other words, the processing of steps S12 to S15 is repeated until the estimated tilt becomes less than the read tilt. This maintains compensation for the variation in the zero dispersion wavelength.

If the estimated tilt is less than the read tilt (step S16: YES), the second control unit 29D determines whether the average power estimated by the second calculation unit 29C is less than the read power, which is the average power read in the processing of step S11 (step S17). If the estimated average power is equal to or greater than the read power (step S17: NO), the second calculation unit 29C instructs the second control unit 29D to control the temperature based on the read temperature, which is the temperature setting value read in the processing of step S11 (step S18).

Thereby, the second control unit 29D controls the temperature of the heater 217 based on the read temperature (step S19). In this way, if there is a possibility that compensation for variations in zero-dispersion wavelength may be impaired due to excessive average power, tilt compensation is reset in the middle of processing. This maintains compensation for zero-dispersion wavelength variations.

On the other hand, if the estimated average power is less than the read power (step S17: YES), the processing of steps S18 and S19 is skipped. This allows compensation for the variation in the zero dispersion wavelength and tilt compensation to be performed simultaneously. If the estimated average power is less than the read power, or when the processing of step S19 is completed, the second compensation operation for the secondary tilt by the OCM 207, the second calculation unit 29C, and the second control unit 29D is completed.

In this manner, in the wavelength conversion device 200 according to the first embodiment, the OCM 207 observes the power of the wavelength multiplexed light λ1C, and the control unit 209 controls the wavelength conversion medium 213 based on the control information acquired from the memory 29E according to the observation result. control to adjust the conversion characteristics of For example, the control unit 209 controls the temperature of the heater 217 to adjust the temperature of the wavelength conversion medium 213 and the wavelength of the excitation light λp. As a result, the second-order tilt is compensated for while the variation in zero-dispersion wavelength is compensated for.

When the control unit 209 adjusts the conversion characteristics of the wavelength conversion medium 213, the conversion efficiency of the wavelength conversion medium 213 may decrease based on the adjustment of the conversion characteristics. Specifically, the conversion efficiency of the wavelength band from the S band to the C band may decrease, and high-precision conversion may be suppressed. For this reason, the control unit 209 determines whether the decrease in conversion efficiency based on the adjustment of the conversion characteristics of the wavelength conversion medium 213 is equal to or greater than a predetermined amount. If the decrease in conversion efficiency is equal to or greater than a predetermined amount, the control unit 209 resets the compensation for the secondary tilt and adjusts the conversion characteristics of the wavelength conversion medium 213 so as to compensate for the variation in the zero-dispersion wavelength in preference to the compensation for the secondary tilt.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to Figures 12 to 15. In Figures 12 to 14, the same components as those shown in Figures 4, 5, and 9 are generally designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 12, the wavelength conversion device 200 according to the second embodiment further includes OCMs 221 and 271 in comparison with the wavelength conversion device 200 according to the first embodiment. The OCMs 221 and 271 are examples of a receiving side second monitor. The OCM 221 may be included in the control unit 209. The OCM 271 may be included in the control unit 209-1.

As shown in FIG. 13, the wavelength conversion unit 210 according to the second embodiment includes a TAP 218 in front of the optical coupler 212, and the TAP 218 is connected to the OCM 221. Therefore, when the wavelength multiplexed light λ1S belonging to the S band is input to the wavelength converter 210, the wavelength multiplexed light λ1S is branched by the TAP 218 and input to the OCM 221. That is, the OCM 221 observes the power of the wavelength multiplexed light λ1S before being input to the wavelength conversion medium 213. More specifically, the OCM 221 observes the wavelength power of a plurality of wavelength lights included in the wavelength multiplexed light λ1S. The OCM 221 outputs the observation results to the control unit 209 using an electrical control signal.

Note that the wavelength converter 260 according to the second embodiment basically has the same configuration as the wavelength converter 210 according to the first embodiment. Therefore, when the wavelength multiplexed light λ3L belonging to the L band is input to the wavelength converter 260, the wavelength multiplexed light λ3L is branched by a TAP (not shown) included in the wavelength converter 260 and input to the OCM 271 (see FIG. 12). be done. That is, the OCM 271 observes the power of the wavelength multiplexed light λ3L before being input to the wavelength conversion medium included in the wavelength conversion unit 260. More specifically, the OCM 271 observes the wavelength power of a plurality of wavelength lights included in the wavelength multiplexed light λ3L. The OCM 271 outputs the observation results to the control unit 209-1 using an electrical control signal. Note that the observation results output by the OCMs 221 and 271 are examples of second observation results.

As shown in FIG. 14, the control section 209 according to the second embodiment includes a first calculation section 29A, a first control section 29B, and a memory 29E. The control unit 209 according to the second embodiment differs from the control unit 209 according to the first embodiment in that it does not include a second calculation unit 29C and a second control unit 29D. The observation results output by the OCM 221 are input to the first calculation unit 29A. Therefore, the observation results output by the OCM 207 and the observation results output by the OCM 221 are input to the first calculation unit 29A. Note that the control unit 209-1 according to the second embodiment basically has the same configuration as the control unit 209 according to the second embodiment, so a detailed explanation will be omitted.

Next, with reference to FIG. 15, a second compensation operation of the wavelength conversion device 200 according to the second embodiment will be described. The second compensation operation according to the second embodiment is an operation in which the OCMs 207 and 221, the first calculation unit 29A, and the first control unit 29B compensate for the secondary tilt. Note that the first compensation operation for compensating for variations in zero-dispersion wavelength is the same as in the first embodiment, and therefore detailed description thereof will be omitted in the second embodiment.

First, the OCM 221 observes the power of the wavelength-multiplexed light λ1S before converting the wavelength band (step S21). More specifically, the OCM 221 observes the wavelength power of the multiple wavelengths of light contained in the wavelength-multiplexed light λ1S. After observing the wavelength power, the OCM 207 outputs the observation result to the first calculation unit 29A by an electrical control signal.

Next, the OCM 207 observes the power of the wavelength multiplexed light λ1C after wavelength band conversion (step S22). More specifically, the OCM 207 observes the wavelength power of a plurality of single wavelength lights λ11, . . . , λ1n included in the wavelength multiplexed light λ1C. After observing the wavelength power, the OCM 207 outputs the observation result to the first calculation unit 29A using an electrical control signal.

When the observation results from each of the OCMs 207 and 221 are input to the first calculation unit 29A, the first calculation unit 29A estimates the first average power and the second average power (step S23). Specifically, the first calculation unit 29A estimates the first average power of the wavelength multiplexed light λ1C based on the observation results input from the OCM 207. Furthermore, the first calculation unit 29A estimates the second average power of the wavelength multiplexed light λ1S based on the observation results input from the OCM 221.

After estimating the first average power and the second average power, the first calculation unit 29A estimates the first tilt and the second tilt (step S24). Specifically, the first calculation unit 29A estimates the first tilt of the wavelength multiplexed light λ1C based on the observation results input from the OCM 207. In addition, the first calculation unit 29A estimates the second tilt of the wavelength multiplexed light λ1S based on the observation results input from the OCM 221.

After estimating the first tilt and the second tilt, the first control unit 29B controls the temperature of the heater 217 (step S25). As described in the first embodiment, the first control unit 29B controls the temperature of the heater 217 based on the calculation formula or with reference to the table. After controlling the temperature of the heater 217, the first calculation unit 29A determines whether the first tilt is less than or equal to the second tilt (step S26). If the first tilt is not less than or equal to the second tilt (step S26: NO), the first control unit 29B executes the process of step S25. Thereby, the first control unit 29B controls the temperature of the heater 217 again. In this way, the first control unit 29B controls the temperature of the heater 217 until the first tilt becomes equal to or less than the second tilt.

When the first tilt becomes equal to or less than the second tilt (step S26: YES), the first calculation unit 29A determines whether the first average power is less than the second average power (step S27). Note that in FIG. 15, the first average power is simply referred to as the first power, and the second average power is simply referred to as the second power. If the first average power is not less than the second average power (step S27: NO), the first calculation unit 29A reads the temperature setting value from the memory 29E and instructs the first control unit 29B to control the temperature based on the read temperature, which is the read temperature setting value (step S28).

Thereby, the first control unit 29B controls the temperature of the heater 217 based on the read temperature (step S29). In this way, if there is a possibility that compensation for variations in zero-dispersion wavelength may be impaired due to the first average power becoming greater than or equal to the second average power, tilt compensation is reset in the middle of the process. This maintains compensation for zero-dispersion wavelength variations.

On the other hand, if the first average power is less than the second average power (step S27: YES), the processes of steps S28 and S29 are skipped. Thereby, compensation for variations in zero-dispersion wavelength and tilt compensation are compatible. If the first average power is less than the second average power, or if the process in step S29 ends, the second compensation operation for the secondary tilt by the OCMs 207 and 221, the first calculation unit 29A, and the first control unit 29B ends. do.

In this way, in the wavelength conversion device 200 according to the second embodiment, the OCMs 207 and 221 respectively observe the power of the wavelength-multiplexed light λ1C and the power of the wavelength-multiplexed light λ1S, and the control unit 209 controls the power based on these observation results. The conversion characteristics of the wavelength conversion medium 213 are adjusted. As a result, the second-order tilt is compensated for while the variation in zero-dispersion wavelength is compensated for.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS. 16 to 20. In addition, in FIGS. 16 to 19, the same components as those shown in FIGS. 3 to 5, and FIG. 9 are basically designated by the same reference numerals, and the explanation thereof will be omitted.

As shown in FIG. 16, the wavelength conversion device 100 according to the third embodiment has OCMs 107 and 108, control units 109 and 109-1, and OSC (Optical It further includes supervisory channel (optical supervisory channel) communication units (indicated simply as OSC in FIG. 16) 131 and 181. The OCMs 107 and 108 are examples of first monitors on the transmitting side. In contrast to the wavelength conversion device 200 according to the first embodiment, the wavelength conversion device 200 according to the third embodiment further includes OSC communication units 231 and 281. The OSC communication units 131 and 181 are examples of OSC reception units. The OSC communication units 231 and 281 are examples of OSC transmission units.

As shown in FIG. 17, the OSC communication unit 231 optically transmits OSC light λx according to the control signal output from the control unit 209. Although omitted in FIG. 17, the OSC communication unit 281 optically transmits the OSC light λy according to the control signal output from the control unit 209-1. Note that the OSC light λx may pass through the optical transmission line 300 or may pass through another optical transmission line different from the optical transmission line 300.

As shown in FIG. 18, the wavelength conversion unit 110 includes an excitation light source 111, an optical coupler 112, a wavelength conversion medium 113, an optical filter 114, an optical branch tap (referred to as TAP in FIG. 18) 115, a temperature sensor 116, and a heater 117. The wavelength conversion unit 210 may include a TEC together with the heater 117. The wavelength conversion medium 113 is an example of a second optical medium.

The excitation light source 111 outputs excitation light λq in a wavelength band shorter than the C band. Excitation light λq includes two different wavelengths. Optical coupler 112 is connected to optical amplifier 101. Therefore, the pump light λq and the wavelength multiplexed light λ1C are input to the optical coupler 112. The optical coupler 112 adds excitation light λq to the wavelength multiplexed light λ1C and outputs it to the wavelength conversion medium 113.

Like the wavelength conversion medium 213, the wavelength conversion medium 113 converts the wavelength multiplexed light λ1C to wavelength multiplexed light λ1S and outputs it together with the wavelength multiplexed light λ1C. On the other hand, the pump light λq passes through the wavelength conversion medium 113. Therefore, the wavelength conversion medium 113 outputs the wavelength multiplexed light λ1C, the wavelength multiplexed light λ1S, and the pump light λq.

The optical filter 114 removes the wavelength multiplexed light λ1C, the wavelength multiplexed light λ1S, and the pump light λq from the wavelength multiplexed light λ1C, the wavelength multiplexed light λ1S, and the pump light λq output from the wavelength conversion medium 113, and outputs the wavelength multiplexed light λ1S. The optical branching tap 115 branches the wavelength multiplexed light λ1S and outputs the wavelength multiplexed light λ1S to the optical amplifier 104 and the OCM 107. Thereby, the optical amplifier 104 can amplify the wavelength multiplexed light λ1S. Further, the OCM 107 can observe the wavelength power of a plurality of wavelength lights included in the wavelength multiplexed light λ1S.

Temperature sensor 116 detects the temperature of wavelength conversion medium 113 and outputs the detected temperature to control unit 109 as an electrical signal. The OSC communication unit 131 optically receives the OSC light λx transmitted from the OSC communication unit 231 and transmits a control signal corresponding to the OSC light λx to the control unit 109.

The control unit 109 compensates for the secondary tilt based on the observation results output from the OCM 107, the temperature of the wavelength conversion medium 213 detected by the temperature sensor 116, and the control signal transmitted from the OSC communication unit 131. Controls the temperature of the heater 117. Thereby, the conversion characteristics of the wavelength conversion medium 113 are adjusted.

Note that, as shown in FIG. 16, the OSC communication unit 281 optically transmits the OSC light λy according to the control signal output from the control unit 209-1. The OSC communication unit 181 optically receives the OSC light λy transmitted from the OSC communication unit 281, and transmits a control signal corresponding to the OSC light λy to the control unit 109-1. The OSC light λy may pass through the optical transmission line 300 or may pass through another optical transmission line different from the optical transmission line 300. The control unit 109-1 controls the temperature of a heater (not shown) included in the wavelength conversion unit 160 based on the control signal, and adjusts the conversion characteristics of a wavelength conversion medium (not shown) included in the wavelength conversion unit 160.

As shown in FIG. 19(a), the control unit 109 according to the third embodiment includes a third calculation unit 19A, a third control unit 19B, and a memory 19E. The third control unit 19B is an example of a transmission side control unit. The memory 19E is an example of a second storage unit. As in the first embodiment, the third control unit 19B associates the average power and tilt with the temperature setting value for the heater 117 and records them in the memory 19E as control information (specifically, second control information). The observation results transmitted by the OSC 131 are input to the third calculation unit 19A. Note that the control unit 109-1 according to the third embodiment basically has the same configuration as the control unit 109 according to the third embodiment, so a detailed description will be omitted.

As shown in FIG. 19(b), the control section 209 according to the third embodiment includes a first calculation section 29A, a first control section 29B, and a memory 29E. A control signal transmitted by the first control unit 29B is input to the OSC 231. Note that the control unit 209-1 according to the third embodiment basically has the same configuration as the control unit 209 according to the third embodiment, so a detailed explanation will be omitted.

Next, with reference to FIG. 20, a second compensation operation of the wavelength conversion device 200 according to the third embodiment will be described. The second compensation operation according to the third embodiment is an operation in which the OCM 107, 207, the first calculation unit 29A, the first control unit 29B, the third calculation unit 19A, the third control unit 19B, etc. compensate for the secondary tilt. It is. Note that the first compensation operation for compensating for variations in zero-dispersion wavelength is the same as in the first embodiment, and therefore detailed explanation will be omitted in the third embodiment.

First, the OCM 207 observes the power of the wavelength multiplexed light λ1C after wavelength band conversion (step S31). More specifically, the OCM 207 observes the wavelength power of a plurality of single wavelength lights λ11, . . . , λ1n included in the wavelength multiplexed light λ1C. After observing the wavelength power, the OCM 207 outputs the observation result to the first calculation unit 29A using an electrical control signal.

Next, OCM 107 observes the power of wavelength multiplexed light λ1S before the wavelength band is converted by wavelength conversion medium 113 (step S32). More specifically, OCM 107 observes the wavelength power of the multiple wavelengths of light contained in wavelength multiplexed light λ1S after the wavelength band is converted by wavelength conversion medium 113 and before the wavelength band is converted by wavelength conversion medium 213. After observing the wavelength power, OCM 107 outputs the observation result to third calculation unit 19A by an electrical control signal.

Next, the first calculation unit 29A estimates the first average power, and the third calculation unit 19A estimates the second average power (step S33). Specifically, when the observation result is input from the OCM 207 to the first calculation unit 29A, the first calculation unit 29A estimates the first average power based on the observation result input from the OCM 207. When the observation results are input from the OCM 107 to the third calculation unit 19A, the third calculation unit 19A estimates the second average power based on the observation results input from the OCM 107.

Next, the first calculation unit 29A estimates the first tilt, and the third calculation unit 19A estimates the second tilt (step S34). Specifically, the first calculation unit 29A estimates the first tilt of the wavelength multiplexed light λ1C based on the observation results input from the OCM 207. Furthermore, the third calculation unit 19A estimates the second tilt of the wavelength multiplexed light λ1S based on the observation results input from the OCM 107.

When the first calculation unit 29A estimates the first average power and the first tilt, the first control unit 29B transmits a control signal including the first average power, the first tilt, and the temperature setting value stored in the memory 29E to the OSC communication unit 231. As a result, the OSC communication unit 231 transmits OSC light λx according to the control signal. The OSC communication unit 131 receives the OSC light λx transmitted from the OSC communication unit 231, and transmits a control signal according to the OSC light λx to the third calculation unit 19A.

When the first tilt and the second tilt are estimated, the third control unit 19B controls the temperature of the heater 117 (step S35). As in the first embodiment, the third control unit 19B controls the temperature of the heater 117 based on a calculation formula or by referring to a table. After controlling the temperature of the heater 117, the third calculation unit 19A determines whether the first tilt is equal to or less than the second tilt (step S36). If the first tilt is not equal to or less than the second tilt (step S36: NO), the third control unit 19B executes the process of step S35. This causes the third control unit 19B to control the temperature of the heater 117 again. In this way, the third control unit 19B controls the temperature of the heater 117 until the first tilt becomes equal to or less than the second tilt.

When the first tilt becomes equal to or less than the second tilt (step S36: YES), the third calculation unit 19A determines whether the first average power is less than the second average power (step S37). Note that in FIG. 20, the first average power is simply referred to as the first power, and the second average power is simply referred to as the second power. If the first average power is not less than the second average power (step S37: NO), the third calculation unit 19A reads the temperature setting value from the control signal, and instructs the third control unit 19B to control the temperature based on the read temperature, which is the read temperature setting value (step S38).

The third control unit 19B then controls the temperature of the heater 117 based on the read temperature (step S39). In this way, if the first average power becomes equal to or greater than the second average power, and there is a possibility that compensation for the variation in the zero-dispersion wavelength may be lost, the tilt compensation is reset midway through the process. This maintains compensation for the variation in the zero-dispersion wavelength.

On the other hand, if the first average power is less than the second average power (step S37: YES), the processing of steps S38 and S39 is skipped. This allows compensation for the variation in the zero dispersion wavelength and tilt compensation to be performed simultaneously. If the first average power is less than the second average power, or when the processing of step S39 is completed, the second compensation operation for the secondary tilt by the OCMs 107 and 207, the first calculation unit 29A, the first control unit 29B, the third calculation unit 19A, and the third control unit 19B, etc., is completed.

In this way, in the wavelength conversion device 100 according to the third embodiment, the OCM 107 observes the power of the wavelength multiplexed light λ1S, and the OCM 207 observes the power of the wavelength multiplexed light λ1C. The control unit 109 adjusts the conversion characteristics of the wavelength conversion medium 113 based on these observation results. This compensates for the variation in the zero dispersion wavelength while also compensating for the secondary tilt.

Fourth Embodiment
Next, the fourth embodiment of the present invention will be described with reference to Figures 22 to 24. In Figure 22, the same components as those shown in Figures 13 and 17 are generally given the same reference numerals, and their description will be omitted. In Figure 23, the same components as those shown in Figure 18 are generally given the same reference numerals, and their description will be omitted. In Figures 22 and 23, the configurations related to the C band and the L band are omitted. The configurations related to the L band are basically the same as the configurations related to the S band, as described with reference to Figure 16, for example.

As shown in FIG. 22, the OSC communication unit 231 optically transmits OSC light λx in response to a control signal output from the control unit 209. Although omitted in FIG. 22, similar to the third embodiment, the OSC communication unit 281 optically transmits OSC light λy in response to a control signal output from the control unit 209-1 (see FIG. 16). Note that the OSC light λx may pass through the optical transmission path 300, or may pass through another optical transmission path different from the optical transmission path 300.

As shown in FIG. 22, the wavelength conversion device 200 according to the fourth embodiment includes a WSS (Wavelength Selective Switch) 232. The WSS 232 is disposed between the optical amplifier 204 and the first WDM receiver 40. The WSS 232 selects a route for the wavelength multiplexed light λ1C output from the optical amplifier 204 and outputs it. For example, the WSS 232 outputs the wavelength multiplexed light λ1C including some wavelengths to the first WDM receiver 40. The WSS 232 also outputs the wavelength multiplexed light λ1C including the remaining wavelengths to another wavelength conversion device (not shown) disposed downstream of the wavelength conversion device 200.

On the other hand, as shown in FIG. 23, the OSC communication unit 131 optically receives the OSC light λx transmitted from the OSC communication unit 231, and transmits a control signal corresponding to the OSC light λx to the control unit 109. Although omitted in FIG. 23, similar to the third embodiment, the OSC communication unit 181 optically receives the OSC light λy corresponding to the control signal output from the control unit 209-1 (see FIG. 16). Note that the OSC light λx may pass through the optical transmission path 300, or may pass through another optical transmission path different from the optical transmission path 300.

As shown in FIG. 23, the wavelength conversion device 100 according to the fourth embodiment includes a WSS 132 instead of the optical amplifier 101. The WSS 132 is disposed between the first WDM transmitter 10 and the optical coupler 112 included in the wavelength conversion unit 110. The WSS 132 selects a route for the wavelength multiplexed light λ1C output from the first WDM transmitter 10 and outputs it. For example, the WSS 132 outputs the wavelength multiplexed light λ1C including some wavelengths to the optical coupler 112. The WSS 132 also outputs the wavelength multiplexed light λ1C including the remaining wavelengths to another wavelength conversion device (not shown) different from the wavelength conversion devices 100 and 200.

Furthermore, the optical amplifier 104 according to the fourth embodiment includes a preamplifier 14A, a tilt compensation unit 14B, and a postamplifier 14C. The tilt compensation unit 14B can be realized by a hardware circuit such as a VOA (Variable Optical Attenuator). The preamplifier 14A amplifies the wavelength-multiplexed light λ1S output from the TAP 115 of the wavelength conversion unit 110. The tilt compensation unit 14B attenuates the wavelength-multiplexed light λ1S output from the preamplifier 14A based on the control of the control unit 209. The postamplifier 14C amplifies the wavelength-multiplexed light λ1S output from the tilt compensation unit 14B and outputs it to the optical coupler 106.

Next, tilt compensation of the optical transmission system ST having the wavelength conversion devices 100 and 200 according to the fourth embodiment will be described with reference to FIG. 24. The optical transmission system ST according to the fourth embodiment compensates for the primary tilt, secondary tilt, and residual tilt after the tertiary tilt by cooperation between the wavelength conversion devices 100 and 200.

First, OCMs 207 and 221 each observe power (step S41). More specifically, OCM 207 observes the wavelength power of the multiple single wavelength light beams λ11, ..., λ1n contained in wavelength multiplexed light λ1C. OCM 221 also observes wavelength power, which is the optical power of the multiple single wavelength light beams λ11, ..., λ1n contained in wavelength multiplexed light λ1S. That is, OCM 207 observes the wavelength power of wavelength multiplexed light λ1C after conversion by wavelength conversion unit 210, and OCM 221 observes the wavelength power of wavelength multiplexed light λ1S before conversion by wavelength conversion unit 210. After observing the wavelength power, OCMs 207 and 221 each output the observation result (i.e., wavelength power) to control unit 209 by an electrical control signal.

Next, the control unit 209 outputs the power information (step S42). More specifically, the control unit 209 transmits power information including the results of each observation by the OCMs 207 and 221 to the OSC communication unit 231 based on the control signal. The power information includes, for example, a wavelength power spectrum (i.e., wavelength characteristics). When the control unit 209 transmits the power information to the OSC communication unit 231, the OSC communication unit 231 transmits OSC light λx according to the power information. The OSC communication unit 131 receives the OSC light λx transmitted from the OSC communication unit 231 and transmits power information according to the OSC light λx to the control unit 109.

Next, the control unit 109 estimates the primary tilt and secondary tilt (step S43). More specifically, the control unit 109 adjusts the first and second tilts of the wavelength multiplexed light λ1S and the wavelength multiplexed light λ1C based on the power information transmitted from the OSC communication unit 131 and the observation results input from the OCM 107. Estimate. For example, based on one or two of the two types of observation results included in the power information and the observation results input from the OCM 107, the control unit 109 determines the wavelength multiplexed light λ1S and It is possible to estimate each primary tilt and secondary tilt of the wavelength multiplexed light λ1C. The control unit 109 determines the respective primary tilts of the wavelength-multiplexed light λ1S and the wavelength-multiplexed light λ1C after passing through the optical transmission line 300, based on the two types of observation results and all three observation results input from the OCM 107. A secondary tilt may also be estimated.

Next, the control unit 109 determines whether the primary tilt is within a predetermined range (step S44). More specifically, the control unit 109 determines whether the primary tilt of the wavelength-multiplexed light λ1C output from the wavelength conversion unit 210 to the OCM 207 is within the range of the primary tilt of the wavelength-multiplexed light λ1S output from the optical amplifier 202 to the wavelength conversion unit 210.

If the primary tilt is not within the predetermined range (step S44: NO), the control unit 109 controls the slope of the optical amplifier 104 (step S45). For example, the control unit 109 performs control to adjust the slope of the tilt compensation unit 14B of the optical amplifier 104 so that the deviation in power of each wavelength of the wavelength-multiplexed light λ1S is reduced. In this way, the control unit 109 compensates for the primary tilt in the wavelength-multiplexed light λ1S. The control unit 109 repeats the processing of steps S44 and S45 until the primary tilt falls within the above-mentioned predetermined range.

If the primary tilt is within the predetermined range (step S44: YES), the control unit 109 controls the temperature of the wavelength conversion unit 110 (step S46). More specifically, the control unit 109 controls the temperature of the heater 117 based on the temperature of the wavelength conversion medium 113 detected by the temperature sensor 116. As described in the first embodiment, the control unit 109 can control the temperature of the heater 117 based on a calculation formula or by referring to a table. In this way, the control unit 109 compensates for the secondary tilt in the wavelength multiplexed light λ1S by controlling the conversion characteristics of the wavelength conversion medium 113 to be adjusted by temperature.

Next, the control unit 109 determines whether the secondary tilt has decreased (step S47). For example, the control unit 109 determines whether the secondary tilt of the wavelength multiplexed light λ1C output from the wavelength conversion unit 210 is minimum. If the secondary tilt has not decreased (step S47: NO), the control unit 109 repeats the processing of steps S46 and S47 until the secondary tilt decreases.

When the secondary tilt is reduced (step S47: YES), the control unit 109 controls the average power of the WSS 132 (step S48) and ends the process. More specifically, the control unit 109 calculates the amount of compensation for the residual tilt based on the two types of observation results described above and one or two or all of the observation results input from the OCM 107, and performs control to adjust the average power of the WSS 132 based on the calculated compensation amount. In this way, the control unit 109 compensates for the residual tilt in the wavelength multiplexed light λ1S by performing control to adjust the average power of the WSS 132. As described above, according to the optical transmission system ST of the fourth embodiment, not only the secondary tilt but also the primary tilt and the residual tilt can be compensated for.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described with reference to FIGS. 25 to 27. In addition, in FIG. 25, the same components as those shown in FIGS. 16 and 23 are designated by the same or corresponding numerals in principle, and their explanations will be omitted. In FIG. 25, the configuration related to the L band is omitted. The configuration regarding the L band is basically the same as the configuration regarding the S band, as described with reference to FIG. 16, for example.

As shown in FIG. 25, the wavelength conversion device 100 according to the fifth embodiment includes a WSS 133. The optical amplifier 102 according to the fifth embodiment includes a tilt compensator 12B. WSS 133 is placed between second WDM transmitter 20 and optical amplifier 102. The WSS 133 selects and outputs the path of the wavelength multiplexed light λ2C output from the second WDM transmitter 20. For example, the WSS 133 outputs wavelength multiplexed light λ2C including some wavelengths to the optical amplifier 102. Further, the WSS 133 outputs the wavelength multiplexed light λ2C including the remaining wavelengths to another wavelength converter (not shown) different from the wavelength converters 100 and 200.

The wavelength conversion device 100 according to the fifth embodiment includes VOAs 142 and 143, TAPs 152 and 153, and PDs (Photo Diodes: photodetectors) 162 and 163. The VOA 142 is an example of a first variable optical attenuator. The VOA 143 is an example of a second variable optical attenuator. The PD 162 is an example of a first monitor on the transmitting side. The PD 163 is an example of a second monitor on the transmitting side. The VOA 142 and the TAP 152 are optically connected. The TAP 152 and the PD 162 are optically connected. The VOA 143 and the TAP 153 are optically connected. The TAP 153 and the PD 163 are optically connected.

On the other hand, in the wavelength conversion device 100 according to the fifth embodiment, unlike the wavelength conversion device according to the fourth embodiment (see FIG. 23), the OSC communication section 131 is excluded. Therefore, in the optical transmission system ST according to the fifth embodiment, the wavelength conversion apparatus 100 alone compensates for the primary tilt and the secondary tilt, without the wavelength conversion apparatuses 100 and 200 cooperating with each other.

Note that in the wavelength conversion device 100 according to the fifth embodiment, the OCM 107 and the TAP 115 are also excluded. That is, the wavelength converter 11A according to the fifth embodiment is different from the wavelength converter 110 according to the fourth embodiment.

Here, both VOA 142 and TAP 152 are arranged between the optical amplifier 104 and the optical coupler 106. VOA 142 is arranged downstream of the optical amplifier 104 and is optically connected to the optical amplifier 104. TAP 152 is arranged downstream of the VOA 142 and is optically connected to the optical coupler 106. On the other hand, both VOA 143 and TAP 153 are arranged between the optical amplifier 102 and the optical coupler 106. VOA 143 is arranged downstream of the optical amplifier 102 and is optically connected to the optical amplifier 102. TAP 153 is arranged downstream of the VOA 143 and is optically connected to the optical coupler 106.

The VOA 142 attenuates the wavelength multiplexed light λ1S output from the optical amplifier 104 and outputs it to the TAP 152. The TAP 152 branches the wavelength multiplexed light λ1S and outputs a part of the wavelength multiplexed light λ1S to the PD 162. The PD 162 detects the wavelength multiplexed light λ1S before passing through the optical transmission line 300, and observes the power of each wavelength of the wavelength multiplexed light λ1S. On the other hand, the VOA 143 attenuates the wavelength multiplexed light λ1C output from the optical amplifier 102 and outputs it to the TAP 153. The TAP 153 branches the wavelength multiplexed light λ1C and outputs a part of the wavelength multiplexed light λ1C to the PD 163. The PD 163 detects the wavelength multiplexed light λ1C before passing through the optical transmission line 300, and observes the power of each wavelength of the wavelength multiplexed light λ1C.

Next, details of the control unit 109 according to the fifth embodiment will be described with reference to FIG. 26. Note that the control unit (not shown) for the C band and the L band basically has the same configuration as the control unit 109, so a detailed description thereof will be omitted.

As shown in FIG. 26, the control section 109 according to the fifth embodiment includes a power calculation section 19F, a fourth calculation section 19G, a fifth calculation section 19H, a tilt control section 19I, and a power control section 19J. The power calculation unit 19F acquires the power of the wavelength belonging to the S band from the PD 162, and estimates the average power, primary tilt, and secondary tilt of the wavelength multiplexed light λ1S based on the acquired power. Similarly, the power calculation unit 19F acquires the power of the wavelength belonging to the C band from the PD 163, and estimates the average power, primary tilt, and secondary tilt of the wavelength multiplexed light λ1C based on the acquired power.

The fourth calculation unit 19G calculates a primary tilt compensation amount corresponding to the average power of the wavelengths belonging to the S band based on the average power of the wavelengths belonging to the S band estimated by the power calculation unit 19F. Similarly, the fourth calculation unit 19G calculates a primary tilt compensation amount corresponding to the average power of the wavelengths belonging to the C band based on the average power of the wavelengths belonging to the C band estimated by the power calculation unit 19F.

The fifth calculation unit 19H calculates a power compensation amount corresponding to the average power of the wavelengths belonging to the S band based on the average power of the wavelengths belonging to the S band estimated by the power calculation unit 19F. Similarly, the fifth calculation unit 19H calculates a power compensation amount corresponding to the average power of the wavelengths belonging to the C band based on the average power of the wavelengths belonging to the C band acquired by the power calculation unit 19F.

The tilt control unit 19I controls the optical amplifiers 102 and 104 based on the primary tilt compensation amount calculated by the fourth calculation unit 19G. Specifically, the tilt control section 19I controls the tilt compensation section 14B of the optical amplifier 104 based on the primary tilt compensation amount according to the power of the wavelength belonging to the S band. The tilt control section 19I controls the tilt compensation section 12B of the optical amplifier 102 based on the primary tilt compensation amount according to the power of the wavelength belonging to the C band. Under the control of the tilt control section 19I, the tilt compensation sections 12B and 14B each compensate for the primary tilt.

Further, the tilt control unit 19I controls the heater to compensate for the secondary tilt based on the power of the wavelength belonging to the S band acquired by the power calculation unit 19F and the temperature of the wavelength conversion medium 113 detected by the temperature sensor 116. 117 temperature. For example, the tilt control unit 19I may include the configuration shown in FIG. 9, FIG. 14, or FIG. 19(a).

The power control unit 19J controls the VOAs 142 and 143 based on the power compensation amount calculated by the fifth calculation unit 19H. Specifically, the power control unit 19J controls the VOA 142 based on the power compensation amount according to the power of the wavelength belonging to the S band. The power control unit 19J controls the VOA 143 based on the power compensation amount according to the power of the wavelength belonging to the C band. Under the control of the power control unit 19J, the VOAs 142 and 143 attenuate the power of the wavelength multiplexed lights λ1S and λ1C, respectively.

Next, with reference to FIG. 27, tilt compensation of the optical transmission system ST having the wavelength conversion devices 100, 200 according to the fifth embodiment will be described. In the optical transmission system ST according to the fifth embodiment, the wavelength conversion device 100 independently compensates for the primary tilt and the secondary tilt.

First, the power calculation unit 19F acquires the power of each of the wavelength multiplexed lights λ1S and λ1C (step S51). As described above, the power calculation unit 19F acquires the power of the wavelength belonging to the S band from the PD162. The power calculation unit 19F also acquires the power of the wavelength belonging to the C band from the PD163. After acquiring the power of each of the wavelength multiplexed lights λ1S and λ1C, the power calculation unit 19F estimates the average power and the primary tilt.

Next, the fourth calculation unit 19G calculates the primary tilt compensation amount (step S52). More specifically, the fourth calculation unit 19G calculates the primary tilt compensation amount according to the average power of the wavelength belonging to the S band, based on the average power of the wavelength belonging to the S band acquired by the power calculation unit 19F. Further, the fourth calculation unit 19G calculates the primary tilt compensation amount according to the power of the wavelength belonging to the C band, based on the average power of the wavelength belonging to the C band acquired by the power calculation unit 19F. When the fourth calculation section 19G calculates the first-order tilt compensation amount, the tilt control section 19I controls the tilt compensation section 14B of the optical amplifier 104 based on the first-order tilt compensation amount according to the average power of the wavelength belonging to the S band. Control. Further, the tilt control section 19I controls the tilt compensation section 12B of the optical amplifier 102 based on the primary tilt compensation amount according to the average power of the wavelength belonging to the C band.

Next, the fifth calculation unit 19H calculates the power compensation amount (step S53). More specifically, the fifth calculation unit 19H calculates a power compensation amount according to the average power of the wavelength belonging to the S band, based on the average power of the wavelength belonging to the S band estimated by the power calculation unit 19F. Similarly, the fifth calculation unit 19H calculates a power compensation amount according to the average power of the wavelength belonging to the C band, based on the average power of the wavelength belonging to the C band estimated by the power calculation unit 19F. When the fifth calculation unit 19H calculates the power compensation amount, the power control unit 19J controls the VOA 142 based on the power compensation amount according to the average power of the wavelength belonging to the S band. The power control unit 19J controls the VOA 143 based on the power compensation amount according to the average power of wavelengths belonging to the C band.

Next, the power calculation unit 19F determines whether the powers and primary tilts of the wavelength multiplexed lights λ1S and λ1C have decreased (step S54). For example, the power calculation unit 19F determines whether the average power of the wavelength multiplexed light λ1S and the average power of the wavelength multiplexed light λ1C before passing through the optical transmission line 300 are both within a predetermined first threshold range. Furthermore, the power calculation unit 19F determines whether the first-order tilt of the wavelength-multiplexed light λ1S and the first-order tilt of the wavelength-multiplexed light λ1C before passing through the optical transmission line 300 are both within a predetermined second threshold range. do. Note that when increasing the number of wavelengths, the power calculation unit 19F may determine whether or not the power has improved.

If the power and the primary tilt of the wavelength-multiplexed light λ1S and λ1C have not decreased (step S54: NO), the processes of steps S51 to S54 are repeated. That is, the processes of steps S51 to S54 are repeated until the power and the primary tilt of the wavelength-multiplexed light λ1S and λ1C have decreased.

When the power and primary tilt of the wavelength multiplexed lights λ1S and λ1C decrease (step S54: YES), the tilt control unit 19I controls the temperature (step S55). More specifically, the tilt control unit 19I controls the temperature of the heater 117 based on the read temperature of the wavelength conversion medium 113 read from the temperature sensor 116.

Next, the power calculation unit 19F estimates the secondary tilt (step S56). As described above, the power calculation unit 19F obtains the power of a wavelength belonging to the S band from the PD 162, and estimates the secondary tilt of the wavelength-multiplexed light λ1S based on the obtained power. Similarly, the power calculation unit 19F obtains the power of a wavelength belonging to the C band from the PD 163, and estimates the secondary tilt of the wavelength-multiplexed light λ1C based on the obtained power.

Next, the power calculation unit 19F determines whether the secondary tilt has decreased (step S57). For example, the power calculation unit 19F determines whether both the secondary tilt of the wavelength multiplexed light λ1S before passing through the optical transmission path 300 and the secondary tilt of the wavelength multiplexed light λ1C are minimum. If the secondary tilt has not decreased (step S57: NO), the processes of steps S55 to S57 are repeated. That is, the processes of steps S55 to S57 are repeated until the secondary tilts of the wavelength multiplexed light λ1S and λ1C decrease. Then, when the secondary tilt has decreased (step S57: YES), the tilt compensation according to the fifth embodiment is terminated.

As described above, according to the fifth embodiment, not only compensation for residual tilt is omitted, but also tilt compensation is completed by the wavelength conversion device 100 alone. Therefore, the optical transmission system ST according to the fifth embodiment can perform tilt compensation faster than the tilt compensation of the optical transmission system ST by cooperation of the wavelength conversion devices 100 and 200 in the fourth embodiment. .

Sixth Embodiment
Next, the sixth embodiment of the present invention will be described with reference to Figures 28 to 32. In Figure 28, the same or corresponding reference numerals are used to designate the same components as those shown in Figure 22, and their description will be omitted. In Figure 29, the same or corresponding reference numerals are used to designate the same components as those shown in Figure 23, and their description will be omitted. In Figures 28 and 29, the configuration related to the L band is omitted. The configuration related to the L band is basically the same as the configuration related to the S band, as described with reference to Figure 16, for example.

As shown in FIG. 28, the OSC communication unit 231 optically transmits OSC light λx according to the control signal output from the control unit 209. Although omitted in FIG. 28, similarly to the third embodiment, the OSC communication unit 281 optically transmits the OSC light λy according to the control signal output from the control unit 209-1 (see FIG. 16). . Further, the OSC communication unit 291 optically transmits the OSC light λz according to the control signal output from the control unit 209-2. Note that the OSC light λz may pass through the optical transmission line 300 or may pass through another optical transmission line different from the optical transmission line 300.

As shown in FIG. 28, the wavelength conversion device 200 according to the sixth embodiment includes a WSS 233. The WSS 233 is disposed between the optical amplifier 205 and the second WDM receiver 50. The WSS 233 selects a route for the wavelength-multiplexed light λ2C output from the optical amplifier 205 and outputs it. For example, the WSS 233 outputs the wavelength-multiplexed light λ2C including some wavelengths to the second WDM receiver 50. The WSS 233 also outputs the wavelength-multiplexed light λ2C including the remaining wavelengths to another wavelength conversion device (not shown) disposed downstream of the wavelength conversion device 200.

Furthermore, the wavelength conversion device 200 according to the sixth embodiment includes an optical amplifier 25A, a TAP 25B, an OCM 207-1, and a control section 209-2. Optical amplifier 25A and TAP 25B are arranged between optical filter 21B and optical amplifier 205. TAP 25B is placed downstream of optical amplifier 25A. Note that the optical amplifier 25A may be excluded from the wavelength conversion device 200. OCM 207-1 is arranged between TAP 25B and control section 209-2.

As a result, the wavelength multiplexed light λ2C is branched by TAP25B and guided to OCM207-1. OCM207-1 observes the wavelength power of multiple single wavelength lights contained in the wavelength multiplexed light λ2C. OCM207-1 outputs the observation result (i.e., wavelength power) to the control unit 209-2 by an electrical control signal. Based on the control signal, the control unit 209-2 transmits power information including the observation result by OCM207-1 to the OSC communication unit 291. As a result, the OSC communication unit 291 transmits OSC light λz according to the power information.

On the other hand, as shown in FIG. 29, the OSC communication unit 191 optically receives the OSC light λz transmitted from the OSC communication unit 291, and transmits a control signal corresponding to the OSC light λz to the control unit 109-2. Although omitted in FIG. 29, similar to the third embodiment, the OSC communication unit 181 optically receives the OSC light λy corresponding to the control signal output from the control unit 209-1 (see FIG. 16).

Further, as shown in FIG. 29, the wavelength conversion device 100 according to the sixth embodiment includes a wavelength conversion section 11A and a WSS 133. The wavelength converter 11A has the same configuration as the wavelength converter 110 except for the TAP 115 (see FIG. 25). WSS 133 is placed between second WDM transmitter 20 and optical amplifier 102. The WSS 133 selects and outputs the path of the wavelength multiplexed light λ2C output from the second WDM transmitter 20. For example, the WSS 133 outputs wavelength multiplexed light λ2C including some wavelengths to the optical amplifier 102. Further, the WSS 133 outputs the wavelength multiplexed light λ2C including the remaining wavelengths to another wavelength converter (not shown) different from the wavelength converters 100 and 200.

Furthermore, the wavelength conversion device 100 according to the sixth embodiment includes PDs 162 and 163, a TAP 192, and a WDM filter 193. WDM filter 193 includes optical filters 194 and 195. Examples of the optical filters 194 and 195 include BPF (Band Pass Filter). TAP 192 is placed between optical coupler 106 and optical transmission line 300.

WDM filter 193 is optically connected to PDs 162 and 163, and TAP 192. More specifically, optical filter 194 is optically connected to PD 162 and TAP 192. Optical filter 194 is also optically connected to optical filter 195. Optical filter 195 is optically connected to PD 163.

Thereby, the multiband light λmb is branched by the TAP 192 and guided to the optical filter 194 of the WDM filter 193. Optical filter 194 separates wavelength multiplexed light λ1S from multiband light λmb, and outputs multiband afterglow λr to optical filter 195. The wavelength multiplexed light λ1S is input to the PD 162.

Since the wavelength multiplexed light λ1S is separated from the multiband light λmb, the multiband afterglow λr includes the wavelength multiplexed light λ2C and the wavelength multiplexed light λ3L. The optical filter 195 separates the multiband afterglow λr into a wavelength multiplexed light λ2C and a wavelength multiplexed light λ3L, and outputs the separated wavelength multiplexed light λ3L. The wavelength multiplexed light λ2C is input to the PD 163. The wavelength multiplexed light λ3L is input to a PD (not shown) connected to the control unit 109-1 (see FIG. 16). The PD 162 detects the wavelength multiplexed light λ1S and observes the power of each wavelength of the wavelength multiplexed light λ1S. The PD 163 detects the wavelength multiplexed light λ2C and observes the power of each wavelength of the wavelength multiplexed light λ2C.

Next, the control units 109 and 209 according to the sixth embodiment will be described in detail with reference to FIG. 30. Note that the control unit (not shown) for the L band basically has the same configuration as the control unit 109, and therefore detailed description thereof will be omitted.

As shown in FIG. 30, the control unit 109 according to the sixth embodiment includes a non-linear SNR (Signal to Noise Ratio) calculation unit 19K, a GSNR (Generalized SNR) calculation unit 19M, and a power control unit 19N. On the other hand, the control unit 209 according to the sixth embodiment includes a linear SNR calculation unit 29K.

The nonlinear SNR calculation unit 19K acquires the power of the wavelength multiplexed light λ1S observed by the PD 162, and calculates the nonlinear SNR as SNR_NL based on the acquired power and the following calculation formula (5). Nonlinear SNR is an example of nonlinear second signal quality.
<Calculation formula (5)>

Here, the numerator P_CH(T) represents the power of the wavelength channel to be observed in the wavelength conversion device 100. That is, P_CH(T) represents the power of the wavelength multiplexed light λ1S in the C band observed by, for example, PD162. The numerator B_CH represents the bandwidth of the C band. Therefore, P_CH(T)/B_CH corresponds to the optical power per unit bandwidth of the wavelength channel to be observed.

＜算出式（７）＞

The denominator G_NLI represents the optical power of nonlinear noise per unit bandwidth. G_NLI is expressed by the following calculation formula (7) when P_NLI representing the optical power of nonlinear noise is expressed by the following calculation formula (6).
<Calculation formula (6)>

<Calculation formula (7)>

Here, η in calculation formula (6) represents a known proportionality coefficient for calculating the nonlinear SNR. Therefore, P_NLI is proportional to the cube of the power of the wavelength multiplexed light λ1S input to the optical coupler 106, for example. ηd in calculation formula (7) represents a known proportionality coefficient determined by the type of fiber of the optical transmission line 300 and the like. Since B_CH is known, when the power of the wavelength multiplexed light λ1S is notified to the nonlinear SNR calculation unit 19K, the nonlinear SNR calculation unit 19K can calculate the nonlinear SNR.

The linear SNR calculation unit 29K calculates the linear SNR as SNR_L based on the optical power of the wavelength multiplexed light λ1C observed by the OCM 207 and the following calculation formula (8). Linear SNR is an example of linear first signal quality.
<Calculation formula (8)>

Here, P_CH represents the power of the wavelength channel to be observed in the wavelength conversion device 200. That is, P_CH represents the power of wavelength-multiplexed light λ1C in the C band observed by, for example, the OCM 207. P_ASE represents the optical power of ASE (Amplified Spontaneous Emission) noise. In this way, the linear SNR is represented as the ratio of the power of wavelength-multiplexed light λ1C to the optical power of the ASE noise. After calculating the linear SNR, the linear SNR calculation unit 29K outputs linear SNR information including the linear SNR to the GSNR calculation unit 19M of the control unit 109.

The GSNR calculation unit 19M calculates the GSNR based on the non-linear SNR calculated by the non-linear SNR calculation unit 19K, the linear SNR of the linear SNR information calculated and output by the linear SNR calculation unit 29K, and the following calculation formula (9). The GSNR is an example of a third signal quality.
<Calculation formula (9)>

After calculating the GSNR, the GSNR calculation unit 19M notifies the power control unit 19N of the GSNR. Note that for the GSNR calculated using calculation formulas (5) to (9), the following documents 1 and 2 can be referred to, for example. In particular, P_NLI is calculated using the GN (Gaussian noise)/EGN (Enhanced GN) model described in Document 2.
Reference 1: P. Poggiolini, Analytical Modeling of Non-Linear Propagation in Coherent Systems, in Proc. OFC 2013, Anaheim, CA, USA, Mar. 2013.
Document 2: Pierluigi Poggiolini et al. “Closed Form Expressions of the Nonlinear Interference for UWB Systems,” ECOC 2022, paper Tu1D.1.

Based on the GSNR notified by the GSNR calculation unit 19M, the power control unit 19N executes slope control for the optical amplifier 104, temperature control for the wavelength conversion unit 11A, and power control for the WSS 132. The power control unit 19N executes slope control for the tilt compensation unit 14B of the optical amplifier 104, and executes temperature control for the heater 117 of the wavelength conversion unit 11A.

Slope control is a control that adds a slope to the wavelength characteristics while adjusting the wavelength characteristics of the wavelength multiplexed light λ1S in the wavelength conversion device 100 in the upstream stage so that the wavelength characteristics (spectrum) of the wavelength multiplexed light λ1S input to the wavelength conversion device 200 in the downstream stage is flat. By multiplexing and transmitting the wavelength multiplexed light λ1S with a slope in the wavelength characteristics, the primary tilt of the wavelength multiplexed light λ1S after passing through the optical transmission path 300 is compensated.

Temperature control is a control that adjusts the conversion characteristics of the wavelength conversion unit 11A by temperature. By adjusting the conversion characteristics of the wavelength conversion unit 11A, the secondary tilt of the wavelength multiplexed light λ1S after passing through the optical transmission path 300 is compensated for. Power control is a control that, for example, inserts dummy light into the wavelength multiplexed light λ1C to increase the power of the wavelength multiplexed light λ1C. This compensates for the residual tilt of the wavelength multiplexed light λ1S after passing through the optical transmission path 300.

As shown in FIG. 31, the control units 109-2 and 209-2 basically have the same configuration as the control units 109 and 209 described above. For this reason, detailed description of the control units 109-2 and 209-2 is omitted. For example, the power control unit 19N in the control unit 109-2 executes slope control for the optical amplifier 102 based on the GSNR notified by the GSNR calculation unit 19M. Specifically, the power control unit 19N executes slope control for the tilt compensation unit 12B of the optical amplifier 102. This compensates for the primary tilt of the wavelength-multiplexed light λ2C after passing through the optical transmission path 300.

Next, with reference to FIG. 32, tilt compensation of the optical transmission system ST having the wavelength conversion devices 100, 200 according to the sixth embodiment will be described. In the optical transmission system ST according to the sixth embodiment, the wavelength conversion devices 100 and 200 cooperate to compensate for the primary tilt, secondary tilt, and residual tilt.

First, the linear SNR calculation unit 29K of each of the control units 209 and 209-2 acquires the power of each of the wavelength-multiplexed light λ1C and λ2C (step S61). The linear SNR calculation unit 29K of the control unit 209 can acquire the wavelength-multiplexed light λ1C from the OCM 207. The linear SNR calculation unit 29K of the control unit 209-2 can acquire the wavelength-multiplexed light λ2C from the OCM 207-1.

After acquiring the powers of the wavelength-multiplexed lights λ1C and λ2C, each linear SNR calculation unit 29K calculates the linear SNR (step S62). That is, the linear SNR calculation unit 29K of the control unit 209 calculates the linear SNR of the wavelength multiplexed light λ1C based on the power of the wavelength multiplexed light λ1C. The linear SNR calculation unit 29K of the control unit 209-2 calculates the linear SNR of the wavelength multiplexed light λ2C based on the power of the wavelength multiplexed light λ2C.

Next, each linear SNR calculation unit 29K outputs linear SNR information (step S63). More specifically, the linear SNR calculation unit 29K of the control unit 209 outputs linear SNR information including the linear SNR of the wavelength multiplexed light λ1C to the control unit 109. The linear SNR calculation unit 29K of the control unit 209-2 outputs linear SNR information including the linear SNR of the wavelength multiplexed light λ2C to the control unit 109-2.

Next, each of the nonlinear SNR calculation units 19K of the control units 109 and 109-2 obtains each power of the wavelength multiplexed lights λ1S and λ2C (step S64). The nonlinear SNR calculation unit 19K of the control unit 109 can obtain the power of the wavelength multiplexed light λ1S from the PD 162. The nonlinear SNR calculation unit 19K of the control unit 109 can acquire the power of the wavelength multiplexed light λ2C from the PD 163.

After acquiring the respective powers of the wavelength multiplexed lights λ1S and λ2C, each nonlinear SNR calculation unit 19K calculates the nonlinear SNR (step S65). That is, the nonlinear SNR calculation unit 19K of the control unit 109 calculates the nonlinear SNR of the wavelength multiplexed light λ1S based on the power of the wavelength multiplexed light λ1S. The nonlinear SNR calculation unit 19K of the control unit 109-2 calculates the nonlinear SNR of the wavelength multiplexed light λ2C based on the power of the wavelength multiplexed light λ2C.

Next, each GSNR calculation unit 19M of the control units 109 and 109-2 calculates the GSNR (step S66). That is, the GSNR calculation unit 19M of the control unit 109 calculates the GSNR of the wavelength multiplexed light λ1S based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ1S. The GSNR calculation unit 19M of the control unit 109-2 calculates the GSNR of the wavelength multiplexed light λ2C based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ2C.

Next, each power control section 19N of the control sections 109 and 109-2 controls the slope of the optical amplifiers 104 and 102 (step S67). More specifically, the power control unit 19N of the control unit 109 performs control to adjust the slope of the tilt compensation unit 14B of the optical amplifier 104 based on the GSNR of the wavelength multiplexed light λ1S. Furthermore, the power control unit 19N of the control unit 109-2 performs control to adjust the slope of the tilt compensation unit 12B of the optical amplifier 102 based on the GSNR of the wavelength multiplexed light λ2C. In this way, the tilt compensation units 14B and 12B compensate for the primary tilt under the control of the control units 109 and 109-2.

Next, the power control unit 19N of the control unit 109 controls the temperature of the wavelength conversion unit 11A (step S68). For example, the power control unit 19N controls the temperature of the heater 117 based on the GSNR of the wavelength multiplexed light λ1S and the temperature of the wavelength conversion medium 113 detected by the temperature sensor 116, and performs control to adjust the conversion characteristics of the wavelength conversion medium 113. In this way, the control unit 109 compensates for the secondary tilt.

Next, the power control unit 19N of the control unit 109 determines whether the GSNR has decreased (step S69). If the GSNR has not decreased (step S69: NO), the power control unit 19N of the control unit 109 executes the process of step S68. That is, the power control section 19N of the control section 109 repeats the processing of steps S68 and S69 until the GSNR decreases.

When the GSNR decreases (step S69: YES), the power control unit 19N of the control unit 109 controls the average power (step S70) and ends the process. More specifically, the power control unit 19N of the control unit 109 calculates the amount of compensation for the residual tilt based on the GSNR, and performs control to adjust the average power of the WSS 132 based on the calculated amount of compensation. In this way, the control unit 109 compensates for the residual tilt in the wavelength multiplexed light λ1S by performing control to adjust the average power of the WSS 132. As described above, according to the optical transmission system ST of the sixth embodiment, it is possible to compensate not only for the secondary tilt, but also for the primary tilt and the residual tilt, taking into account the nonlinear SNR and the linear SNR.

Seventh Embodiment
Next, the seventh embodiment of the present invention will be described with reference to Fig. 33 and Fig. 34. The wavelength conversion device 100 according to the seventh embodiment is basically the same as the wavelength conversion device 100 according to the fifth embodiment described with reference to Fig. 25, except for the configuration of the control unit 109. Therefore, in Fig. 33, the same or corresponding reference numerals are used in principle for configurations similar to those of the respective parts shown in Fig. 26, Fig. 30, and Fig. 31, and their description will be omitted. In Fig. 26, the configuration related to the L band is omitted. The configuration related to the L band is basically the same as the configuration related to the S band.

As shown in FIG. 33, the control unit 109 according to the seventh embodiment includes a linear SNR calculation unit 29K, a nonlinear SNR calculation unit 19K, a GSNR calculation unit 19M, a tilt control unit 19I, and a power control unit 19N. Contains.

The linear SNR calculation unit 29K acquires the power of the wavelength belonging to the S band from the PD 162, and calculates the linear SNR of the wavelength multiplexed light λ1S based on the acquired power. Similarly, the linear SNR calculation unit 29K acquires the power of the wavelength belonging to the C band from the PD 163, and calculates the linear SNR of the wavelength multiplexed light λ2C based on the acquired power.

The nonlinear SNR calculation unit 19K acquires the power of a wavelength belonging to the S band from the PD 162, and calculates the nonlinear SNR of the wavelength-multiplexed light λ1S based on the acquired power. Similarly, the nonlinear SNR calculation unit 19K acquires the power of a wavelength belonging to the C band from the PD 163, and calculates the nonlinear SNR of the wavelength-multiplexed light λ2C based on the acquired power.

The GSNR calculation unit 19M calculates the GSNR of the wavelength multiplexed light λ1S based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ1S. Similarly, the GSNR calculation unit 19M calculates the GSNR of the wavelength multiplexed light λ2C based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ2C.

The tilt control unit 19I controls the adjustment of the slope of the tilt compensation unit 14B of the optical amplifier 104 based on the GSNR of the wavelength multiplexed light λ1S. The tilt control unit 19I also controls the adjustment of the slope of the tilt compensation unit 12B of the optical amplifier 102 based on the GSNR of the wavelength multiplexed light λ2C. Furthermore, the tilt control unit 19I controls the temperature of the heater 117 based on the GSNR of the wavelength multiplexed light λ1S and the temperature of the wavelength conversion medium 113 detected by the temperature sensor 116, and controls the adjustment of the conversion characteristics of the wavelength conversion medium 113.

The power control unit 19N calculates a power compensation amount corresponding to the average power of the wavelengths belonging to the S band based on the GSNR of the wavelength multiplexed light λ1S, and performs control to adjust the average power of the VOA 142 based on the calculated power compensation amount. The power control unit 19N also calculates a power compensation amount corresponding to the average power of the wavelengths belonging to the C band based on the GSNR of the wavelength multiplexed light λ2C, and performs control to adjust the average power of the VOA 143 based on the calculated power compensation amount.

In this way, according to the seventh embodiment, compensation for residual tilt is omitted. Therefore, the optical transmission system ST according to the seventh embodiment can perform first-order and second-order tilt compensation that also takes into account the linear SNR and nonlinear SNR at high speed compared to the case where compensation for residual tilt is performed.

Next, tilt compensation of the optical transmission system ST having the wavelength conversion devices 100 and 200 according to the seventh embodiment will be described with reference to FIG. 34. In the optical transmission system ST according to the seventh embodiment, the wavelength conversion device 100 alone performs compensation for the primary tilt and the secondary tilt.

First, the linear SNR calculation section 29K and the nonlinear SNR calculation section 19K obtain the respective powers of the wavelength multiplexed lights λ1S and λ2C (step S71). The linear SNR calculation unit 29K can acquire the power of the wavelength multiplexed light λ1S from the PD 162. Furthermore, the linear SNR calculation unit 29K can obtain the power of the wavelength multiplexed light λ2C from the PD 163. On the other hand, the nonlinear SNR calculation unit 19K can acquire the power of the wavelength multiplexed light λ1S from the PD 162. Further, the nonlinear SNR calculation unit 19K can acquire the power of the wavelength multiplexed light λ2C from the PD 163.

When the powers of the wavelength-multiplexed light λ1S and λ2C are acquired, the linear SNR calculation unit 29K calculates the linear SNR (step S72). That is, the linear SNR calculation unit 29K calculates the linear SNR of the wavelength-multiplexed light λ1S based on the power of the wavelength-multiplexed light λ1S. The linear SNR calculation unit 29K also calculates the linear SNR of the wavelength-multiplexed light λ2C based on the power of the wavelength-multiplexed light λ2C.

Next, the nonlinear SNR calculation unit 19K calculates the nonlinear SNR (step S73). That is, the nonlinear SNR calculation unit 19K calculates the nonlinear SNR of the wavelength multiplexed light λ1S based on the power of the wavelength multiplexed light λ1S. Furthermore, the nonlinear SNR calculation unit 19K calculates the nonlinear SNR of the wavelength multiplexed light λ2C based on the power of the wavelength multiplexed light λ2C.

Next, the GSNR calculation unit 19M calculates the GSNR (step S74). That is, the GSNR calculation unit 19M calculates the GSNR of the wavelength multiplexed light λ1S based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ1S. Furthermore, the GSNR calculation unit 19M calculates the GSNR of the wavelength multiplexed light λ2C based on the linear SNR and nonlinear SNR of the wavelength multiplexed light λ2C.

Next, the tilt control section 19I controls the slopes of the optical amplifiers 104 and 102 (step S75). More specifically, the tilt control unit 19I performs control to adjust the slope of the tilt compensation unit 14B of the optical amplifier 104 based on the GSNR of the wavelength multiplexed light λ1S. Furthermore, the tilt control unit 19I performs control to adjust the slope of the tilt compensation unit 12B of the optical amplifier 102 based on the GSNR of the wavelength multiplexed light λ2C. In this way, under the control of the tilt control section 19I, the tilt compensation sections 14B and 12B compensate for the primary tilt.

Next, the power control unit 19N controls the average power of the VOAs 142 and 143 (step S76). More specifically, the power control unit 19N performs control to adjust the amount of attenuation of the VOA 142 based on the GSNR of the wavelength multiplexed light λ1S. Furthermore, the power control unit 19N performs control to adjust the amount of attenuation of the VOA 143 based on the GSNR of the wavelength multiplexed light λ2C. Under the control of the power control unit 19N, the VOAs 142 and 143 compensate for the average power.

Next, the tilt control section 19I controls the temperature of the wavelength conversion section 11A (step S77). For example, the tilt control unit 19I controls the temperature of the heater 117 based on the GSNR of the wavelength multiplexed light λ1S and the temperature of the wavelength conversion medium 113 detected by the temperature sensor 116, and controls to adjust the conversion characteristics of the wavelength conversion medium 113. I do. In this way, the wavelength converter 11A compensates for the secondary tilt under the control of the tilt controller 19I.

Next, the tilt control unit 19I determines whether the GSNR has decreased (step S78). If the GSNR has not decreased (step S78: NO), the tilt control unit 19I executes the process of step S77. That is, the tilt control unit 19I repeats the processes of steps S77 and S78 until the GSNR has decreased. If the GSNR has decreased (step S78: YES), the process ends.

As described above, according to the optical transmission system ST according to the seventh embodiment, tilt compensation for the primary tilt and the secondary tilt can be performed at high speed, taking into consideration the nonlinear SNR and the linear SNR.

The above describes in detail preferred embodiments of the present invention, but the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

In addition, the following supplementary notes are provided in relation to the above description.
(Supplementary Note 1) A wavelength conversion device comprising: an optical medium that converts a first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band into a second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band; a first monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band; a memory unit that holds control information for adjusting a conversion characteristic of the optical medium; and a control unit that performs control to adjust the conversion characteristic of the optical medium using the control information acquired from the memory unit in accordance with a first observation result by the first monitor.
(Supplementary Note 2) The wavelength conversion device described in Supplementary Note 1, characterized in that the control unit performs a first control to adjust the conversion characteristics of the optical medium using the control information so as to compensate for secondary tilt that occurs in a transmission path that transmits wideband wavelength-multiplexed light including the multiple first wavelengths, the multiple second wavelengths, and multiple third wavelengths belonging to a third wavelength band.
(Appendix 3) The wavelength conversion device described in Appendix 2, characterized in that the control unit performs a second control to adjust the conversion characteristics of the optical medium so as to compensate for variations in the zero dispersion wavelength, and performs the first control after recording the control information in the memory unit based on the results of the second control.
(Appendix 4) The wavelength conversion device described in Appendix 3, characterized in that the control unit resets the first control when the amount of decrease in conversion efficiency due to the adjustment of the conversion characteristics exceeds the power deviation of the multiple second wavelengths belonging to the second wavelength band before the adjustment of the conversion characteristics.
(Appendix 5) A wavelength conversion device as described in Appendix 1, further comprising a second monitor that observes the power of the multiple first wavelengths belonging to the first wavelength band, and the control unit performs control to adjust the conversion characteristics of the optical medium using the control information obtained from the memory unit in accordance with the first observation results and the second observation results by the second monitor.
(Supplementary Note 6) The wavelength conversion device according to Supplementary Note 1, characterized in that the control unit performs control to adjust the temperature of the optical medium to adjust the conversion characteristics of the optical medium.
(Appendix 7) A wavelength conversion device as described in Appendix 1, further comprising an excitation light source that outputs excitation light, and the control unit performs control to adjust the wavelength of the excitation light input from the excitation light source to the optical medium to adjust the conversion characteristics of the optical medium.
(Supplementary Note 8) The wavelength conversion device according to Supplementary Note 1 or 2, characterized in that the optical medium is a nonlinear optical medium including PPLN (Periodically Poled Lithium Niobate).
(Supplementary Note 9) The wavelength conversion device according to Supplementary Note 2, characterized in that the first wavelength band is an S band, the second wavelength band is a C band, and the third wavelength band is an L band.
(Supplementary Note 10) An optical transmission system including a receiving-side wavelength conversion device and a transmitting-side wavelength conversion device, wherein the receiving-side wavelength conversion device includes a receiving-side optical amplifier that amplifies a first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band, a first optical medium that converts the amplified first wavelength multiplexed light into a second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band, a receiving-side first monitor that observes power of the plurality of second wavelengths belonging to the second wavelength band, a first storage unit that holds first control information for adjusting a conversion characteristic of the first optical medium, and a first control information acquired from the first storage unit according to a first observation result by the receiving-side first monitor. and a receiving-side control unit that controls to adjust the conversion characteristics of an optical medium, wherein the wavelength conversion device on the transmitting side comprises: a second optical medium that converts the second wavelength multiplexed light output from a first transmitter into the first wavelength multiplexed light, a transmitting-side first optical amplifier that amplifies the first wavelength multiplexed light after the conversion, a transmitting-side second optical amplifier that amplifies the second wavelength multiplexed light output from a second transmitter, and an optical coupler that multiplexes the second wavelength multiplexed light output from the transmitting-side second optical amplifier and the first wavelength multiplexed light output from the transmitting-side first optical amplifier, and outputs the multiplexed light to a transmission path connecting the wavelength conversion device on the receiving side and the wavelength conversion device on the transmitting side.
(Supplementary Note 11) The optical transmission system described in Supplementary Note 10, characterized in that the transmitting-side wavelength conversion device further includes a transmitting-side first monitor that observes the power of the multiple first wavelengths belonging to the first wavelength band, a second memory unit that holds second control information for adjusting the conversion characteristics of the second optical medium, and a transmitting-side control unit that performs control to adjust the conversion characteristics of the second optical medium using the second control information obtained from the second memory unit in response to the first observation results output from the receiving-side control unit and the second observation results by the transmitting-side first monitor.
(Supplementary Note 12) The optical transmission system described in Supplementary Note 10, characterized in that the receiving-side wavelength conversion device has an OSC transmitting unit that optically transmits the first observation result output from the receiving-side control unit, and the transmitting-side wavelength conversion device further has a second monitor that observes the power of the multiple first wavelengths belonging to the first wavelength band, a second memory unit that holds second control information for adjusting the conversion characteristics of the second optical medium, an OSC receiving unit that optically receives the first observation result transmitted from the OSC transmitting unit, and a transmitting-side control unit that controls adjustment of the conversion characteristics of the second optical medium using the second control information acquired from the second memory unit in accordance with the first observation result received by the OSC receiving unit and the second observation result by the second monitor.
(Supplementary Note 13) The optical transmission system according to Supplementary Note 10, characterized in that the receiving-side wavelength conversion device further includes a receiving-side second monitor that monitors the power of the plurality of first wavelengths belonging to the first wavelength band, and the receiving-side control unit acquires a second observation result by the receiving-side second monitor from the receiving-side second monitor and outputs it to the transmitting-side wavelength conversion device together with the first observation result, and the transmitting-side wavelength conversion device further includes a transmitting-side first monitor that monitors the power of the plurality of first wavelengths belonging to the first wavelength band, and a transmitting-side control unit that performs control to adjust a slope of the transmitting-side first optical amplifier so as to reduce a deviation in power of each wavelength of the first wavelength multiplexed signal light after passing through the transmission path, and control to adjust a conversion characteristic of the second optical medium by temperature, in accordance with the first observation result and the second observation result output from the receiving-side control unit and a third observation result by the transmitting-side first monitor.
(Supplementary Note 14) The optical transmission system according to Supplementary Note 10, wherein the wavelength conversion device on the transmitting side further comprises: a first variable optical attenuator that attenuates the power of the first wavelength multiplexed light output from the transmitting side first optical amplifier; a second variable optical attenuator that attenuates the power of the second wavelength multiplexed light output from the transmitting side second optical amplifier; a transmitting side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band; a transmitting side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band; and a transmitting side control unit that performs control to adjust each slope of the transmitting side first optical amplifier and the transmitting side second optical amplifier so as to reduce a deviation in power of each wavelength of the first wavelength multiplexed signal light before passing through the transmission path, control to adjust each attenuation amount of the first variable optical attenuator and the second variable optical attenuator, and control to adjust a conversion characteristic of the second optical medium by temperature, according to a third observation result by the transmitting side first monitor and a fourth observation result by the transmitting side second monitor.
(Supplementary Note 15) In the wavelength conversion device on the receiving side, the receiving side control unit acquires the first observation result for each wavelength band, and calculates a linear first signal quality for each wavelength band based on the first observation result and a predetermined first calculation method for calculating a linear signal quality, and outputs the linear first signal quality to the wavelength conversion device on the transmitting side. The wavelength conversion device on the transmitting side includes a transmitting side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band, a transmitting side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band, a predetermined second calculation method for calculating a nonlinear signal quality, a third observation result by the transmitting side first monitor, and a transmitting side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band. and a transmitting-side control unit that calculates a third signal quality different from both the first signal quality and the second signal quality for each wavelength band based on the first signal quality and the second signal quality output from the receiving-side control unit, and performs control to adjust the slopes of the transmitting-side first optical amplifier and the transmitting-side second optical amplifier so that the third signal quality is reduced, and control to adjust the conversion characteristic of the second optical medium by temperature.
(Supplementary Note 16) The wavelength conversion device on the transmitting side includes a first variable optical attenuator that attenuates the power of the first wavelength multiplexed light output from the transmitting side first optical amplifier, a second variable optical attenuator that attenuates the power of the second wavelength multiplexed light output from the transmitting side second optical amplifier, a transmitting side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band, a transmitting side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band, a predetermined first calculation method for calculating linear signal quality, a predetermined second calculation method for calculating nonlinear signal quality, a third observation result by the transmitting side first monitor, and a fourth observation result by the transmitting side second monitor, The optical transmission system described in Appendix 10, further comprising: a predetermined third calculation method for calculating a linear first signal quality and a nonlinear second signal quality for each wavelength band and calculating a generalized signal quality; and a transmitting side control unit for calculating a third signal quality different from both the first signal quality and the second signal quality for each wavelength band based on the first signal quality and the second signal quality, and performing control to adjust the slopes of the transmitting side first optical amplifier and the transmitting side second optical amplifier so that the third signal quality is reduced, control to adjust the attenuation amounts of the first variable optical attenuator and the second variable optical attenuator, and control to adjust the conversion characteristics of the second optical medium with temperature.

ST Optical transmission system 10 1st WDM transmitter 20 2nd WDM transmitter 30 3rd WDM transmitter 40 1st WDM receiver 50 2nd WDM receiver 60 3rd WDM receiver 100,200 Wavelength conversion device 107, 207, 207-1, 208, 221,271 OCM
109,109-1,109-2,209,209-1,209-2 Control section 113,213 Wavelength conversion medium 131,181,191,231,281,291 OSC communication section 142,143 VOA
162,163 PD
300 Optical transmission line

Claims (13)

an optical medium that converts a first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band into a second wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band;
a first monitor configured to monitor the power of the plurality of second wavelengths belonging to the second wavelength band;
A storage unit that stores control information for adjusting the conversion characteristics of the optical medium;
a control unit that performs control to adjust the conversion characteristics of the optical medium using the control information acquired from the storage unit in response to a first observation result by the first monitor;
A wavelength conversion device comprising: The control unit compensates for a secondary tilt occurring in a transmission path that transmits broadband wavelength multiplexed light including the plurality of first wavelengths, the plurality of second wavelengths, and the plurality of third wavelengths belonging to a third wavelength band. performing first control to adjust the conversion characteristics of the optical medium using the control information,
The wavelength conversion device according to claim 1, characterized in that: The control unit performs a second control to adjust the conversion characteristics of the optical medium so as to compensate for the variation in the zero dispersion wavelength, and performs the first control after recording the control information in the storage unit based on the result of the second control.
3. The wavelength conversion device according to claim 2. The control unit resets the first control when a decrease in conversion efficiency due to the adjustment of the conversion characteristics exceeds a deviation in power of the plurality of second wavelengths belonging to the second wavelength band before the adjustment of the conversion characteristics.
4. The wavelength conversion device according to claim 3. further comprising a second monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band,
The control unit performs control to adjust the conversion characteristic of the optical medium using the control information acquired from the storage unit according to the first observation result and the second observation result by the second monitor.
The wavelength conversion device according to claim 1, characterized in that: The control unit performs control to adjust the temperature of the optical medium to adjust the conversion characteristics of the optical medium.
2. The wavelength conversion device according to claim 1 . Further comprising an excitation light source that outputs excitation light,
The control unit adjusts the wavelength of the excitation light input from the excitation light source to the optical medium to adjust the conversion characteristics of the optical medium.
2. The wavelength conversion device according to claim 1 . An optical transmission system including a receiving side wavelength converting device and a transmitting side wavelength converting device,
The wavelength conversion device on the receiving side includes:
a receiving side optical amplifier that amplifies first wavelength multiplexed light including a plurality of first wavelengths belonging to a first wavelength band; and a receiving side optical amplifier that amplifies the first wavelength multiplexed light including a plurality of second wavelengths belonging to a second wavelength band. a first optical medium that converts into second wavelength multiplexed light; a first monitor on the receiving side that observes the power of the plurality of second wavelengths belonging to the second wavelength band; and adjusting conversion characteristics of the first optical medium. a first storage section that stores first control information for controlling the first optical medium according to the first control information acquired from the first storage section according to a first observation result by the receiving first monitor; a receiving side control unit that performs control to adjust conversion characteristics;
The wavelength conversion device on the transmitting side is
a second optical medium that converts the second wavelength multiplexed light outputted from a first transmitter into the first wavelength multiplexed light; and a transmitting-side first optical amplifier that amplifies the first wavelength multiplexed light after conversion; a transmitting-side second optical amplifier that amplifies the second wavelength-multiplexed light output from the second transmitter; a transmitting-side second optical amplifier that amplifies the second wavelength-multiplexed light output from the transmitting-side second optical amplifier; and a transmitting-side first optical amplifier. an optical coupler that multiplexes the first wavelength multiplexed light output from the amplifier and outputs the multiplexed light to a transmission line connecting the wavelength conversion device on the reception side and the wavelength conversion device on the transmission side;
An optical transmission system characterized by: The wavelength conversion device on the transmitting side is
a transmitter-side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band;
a second storage unit that holds second control information for adjusting conversion characteristics of the second optical medium;
of the second optical medium based on the second control information acquired from the second storage unit in accordance with the first observation result output from the reception side control unit and the second observation result by the transmission side first monitor. a transmitting side control unit that performs control to adjust conversion characteristics;
The optical transmission system according to claim 8, further comprising: The wavelength conversion device on the reception side includes:
The receiver further includes a second receiver monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band, and the receiver control unit controls the power of the plurality of first wavelengths belonging to the first wavelength band. Obtaining the observation results and outputting them together with the first observation results to the wavelength conversion device on the transmitting side;
The wavelength conversion device on the transmitting side is
a transmitter-side first monitor that observes the powers of the plurality of first wavelengths belonging to the first wavelength band; and a transmitter-side first monitor that observes the powers of the plurality of first wavelengths belonging to the first wavelength band; The slope of the transmitting side first optical amplifier is adjusted according to the third observation result by one monitor so that the deviation in the power of each wavelength of the first wavelength multiplexed light after passing through the transmission path is reduced. and a transmission side control unit that performs control to adjust the conversion characteristics of the second optical medium by temperature,
The optical transmission system according to claim 8, characterized in that: The wavelength conversion device on the transmitting side is
a first variable optical attenuator that attenuates the power of the first wavelength multiplexed light output from the transmitting first optical amplifier;
a second variable optical attenuator that attenuates the power of the second wavelength multiplexed light output from the second optical amplifier on the transmission side;
a transmitter-side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band;
a transmitter-side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band;
The deviation of the power of each wavelength of the first wavelength multiplexed light before passing through the transmission path is determined according to the third observation result by the first monitor on the transmitting side and the fourth observation result by the second monitor on the transmitting side. control for adjusting each slope of the first optical amplifier on the transmitting side and the second optical amplifier on the transmitting side, and adjusting each attenuation amount of the first variable optical attenuator and the second variable optical attenuator so as to reduce and a transmission side control unit that performs control to adjust the conversion characteristics of the second optical medium by temperature;
The optical transmission system according to claim 8, further comprising: The wavelength conversion device on the receiving side includes:
The receiving side control unit acquires the first observation results for each wavelength band, and calculates the linear first signal quality based on the first observation result and a predetermined first calculation method for calculating the linear signal quality. is calculated for each wavelength band and outputted to the wavelength conversion device on the transmitting side,
The wavelength conversion device on the transmitting side is
a transmitter-side first monitor that observes the power of the plurality of first wavelengths belonging to the first wavelength band;
a transmitter-side second monitor that observes the power of the plurality of second wavelengths belonging to the second wavelength band;
Nonlinear second signal quality is calculated based on a predetermined second calculation method for calculating nonlinear signal quality, a third observation result by the first transmitter monitor, and a fourth observation result by the second transmitter monitor. is calculated for each wavelength band,
The first signal quality and the second signal quality are determined based on a predetermined third calculation method for calculating generalized signal quality, the first signal quality output from the receiving side control unit, and the second signal quality. Calculating a third signal quality different from any of the second signal qualities for each wavelength band,
control for adjusting each slope of the first optical amplifier on the transmitting side and the second optical amplifier on the transmitting side so that the third signal quality is reduced; and control for adjusting the conversion characteristic of the second optical medium by temperature. a transmitting side control unit that performs
The optical transmission system according to claim 8, further comprising: The wavelength conversion device on the transmitting side
a first variable optical attenuator that attenuates the power of the first wavelength multiplexed light output from the transmitting side first optical amplifier;
a second variable optical attenuator that attenuates the power of the second wavelength multiplexed light output from the transmitting side second optical amplifier;
a transmitting side first monitor that observes the power of the plurality of first wavelengths that belong to the first wavelength band;
a transmitting side second monitor that observes the power of the plurality of second wavelengths that belong to the second wavelength band;
calculating a first linear signal quality and a second nonlinear signal quality for each wavelength band based on a first predetermined calculation method for calculating a linear signal quality, a second predetermined calculation method for calculating a nonlinear signal quality, a third observation result by the first transmitting monitor, and a fourth observation result by the second transmitting monitor;
calculating a third signal quality, which is different from both the first signal quality and the second signal quality, for each wavelength band based on a predetermined third calculation method for calculating a generalized signal quality, the first signal quality, and the second signal quality;
a transmission-side control unit that performs control to adjust the slopes of the first transmission-side optical amplifier and the second transmission-side optical amplifier, control to adjust the attenuation amounts of the first variable optical attenuator and the second variable optical attenuator, and control to adjust the conversion characteristic of the second optical medium by temperature so that the third signal quality is reduced;
9. The optical transmission system according to claim 8, further comprising:

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