Optical transmission device and optical transmission system

Abstract

The objective is to provide an optical transmission device and optical transmission system that reduces the tilt amount of pseudo-light. [Solution] The optical transmission device is an optical transmission device that relays signal light and includes an optical output unit that outputs OSC (Optical Supervisory Channel) light, a calculation unit that calculates the amount of tilt generated in the pseudo-light in the optical transmission path connecting the optical transmission device and the other optical transmission device when establishing communication between the optical transmission device and the other optical transmission device based on the OSC light and pseudo-light including the wavelength band of the signal light, and a control unit that controls the output of the pseudo-light based on the amount of tilt.

Description

Technical Field

[0001] This invention relates to an optical transmission device and an optical transmission system.

Background Art

[0002] An optical transmission system for transmitting a WDM (Wavelength Division Multiplexing) signal light including a plurality of optical signals having different wavelengths is known. Also, an optical transmission system that amplifies and relays signal light by an optical repeater using an optical amplifier is known (see, for example, Patent Document 1).

[0003] The optical transmission system includes an optical transmitter and an optical receiver. The optical transmitter and the optical receiver actually have the same functions. For example, an optical amplifier for amplifying and outputting signal light is provided in the optical transmitter. In addition, in the optical transmission system, an optical monitoring signal called an OSC (Optical Supervisory Channel) is used for operation settings and status monitoring (see, for example, Patent Documents 2 to 4).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, multiple stages of optical transmission devices may be interposed between the optical transmitter and the optical receiver as optical repeaters. Depending on the optical transmission path between the optical transmission devices, if the span loss, which represents the loss value of the optical transmission path, is excessive, the optical power of the optical monitoring signal (hereinafter referred to as OSC light) may be insufficient to ensure that the OSC light can be transmitted between the optical transmission devices. In this case, when the optical transmission devices are started up, they may not be able to confirm the transmission of the OSC light.

[0006] If an optical transmission device cannot confirm OSC light connectivity, for example, an increase in the optical power of the OSC light using pseudo-waves is conceivable. Pseudo-waves are output from an optical transmitter and, via relays, reach the optical transmission device that cannot confirm OSC light connectivity. The pseudo-waves propagate through multiple optical transmission paths from the optical transmitter to the optical transmission device.

[0007] However, when pseudo-light propagates through the optical transmission path in multiple stages, tilt occurs in the pseudo-light each time it propagates through the optical transmission path. This tilt in the pseudo-light is caused by stimulated Raman scattering, wavelength-dependent losses, and other factors. As a result, the amount of tilt in the pseudo-light increases cumulatively by the time it reaches the optical transmission device. Consequently, the optical power becomes concentrated on the longer wavelength side of the pseudo-light. Since the wavelength of OSC light is close to the longest wavelength side of the pseudo-light, if the optical power is concentrated on the longer wavelength side of the pseudo-light, the gain from the pseudo-light to the OSC light may be insufficient, potentially leading to an insufficient increase in the optical power of the OSC light. If the optical power of the OSC light is insufficient, the optical transmission device may not be able to confirm the communication of the OSC light.

[0008] Therefore, one objective is to provide an optical transmission device and optical transmission system that reduces the amount of tilt of pseudo-light. [Means for solving the problem]

[0009] In one embodiment, the optical transmission device is an optical transmission device that relays signal light and includes an optical output unit that outputs OSC light, a calculation unit that calculates the amount of tilt generated in the pseudo-light in the optical transmission path connecting the optical transmission device and the other optical transmission device when establishing communication between the optical transmission device and the other optical transmission device based on the OSC light and pseudo-light including the wavelength band of the signal light, and a control unit that controls the output of the pseudo-light based on the amount of tilt. [Effects of the Invention]

[0010] The amount of tilt caused by the false light can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is an example of an optical transmission system according to the first embodiment. [Figure 2] This is another example of an optical transmission system according to the first embodiment. [Figure 3] This flowchart shows an example of the operation of the optical transceiver according to the first embodiment. [Figure 4] This flowchart shows an example of the operation of the optical transmission device according to the first embodiment. [Figure 5] (a) A diagram illustrating a comparative example according to the first embodiment. (b) A diagram illustrating an embodiment according to the first embodiment. [Figure 6] (a) A diagram illustrating another comparative example according to the first embodiment. (b) A diagram illustrating another embodiment according to the first embodiment. [Figure 7] (a) A diagram illustrating a comparative example according to the second embodiment. (b) A diagram illustrating an embodiment according to the second embodiment. [Figure 8] (a) A diagram illustrating a comparative example according to the third embodiment. (b) A diagram illustrating an embodiment according to the third embodiment. [Figure 9] This is an example of an optical transmission system according to the fourth embodiment. [Figure 10]It is a flowchart showing an example of the operation of the optical transmission device according to the fourth embodiment. [Figure 11] (a) It is a diagram for explaining a comparative example according to the fourth embodiment. (b) It is a diagram for explaining an example according to the fourth embodiment. [Figure 12] It is an example of an optical transmission system according to the fifth embodiment. [Figure 13] It is a flowchart showing an example of the operation of the optical transmission device according to the fifth embodiment.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present case will be described with reference to the drawings.

[0013] (First Embodiment) As shown in FIGS. 1 and 2, the optical transmission system ST includes two indirectly opposed optical transmission / reception devices 100 and 200. As shown in FIGS. 1 and 2, between the optical transmission / reception devices 100 and 200, a plurality of stages of directly opposed optical transmission devices 300, 400, and 500 are interposed. The optical transmission / reception devices 100 and 200 include, for example, a ROADM (Reconfigurable Optical Add / Drop Multiplexer). The optical transmission devices 300, 400, and 500 include, for example, an ILA (In-Line Amplifier). Any of the optical transmission devices 300, 400, and 500 can relay the WDM signal lights Lw1 and Lw2 transmitted from each of the optical transmission / reception devices 100 and 200. Thereby, the optical transmission / reception devices 100 and 200 can receive the WDM signal lights Lw1 and Lw2, respectively. In the first embodiment, the optical transmission device 300 will be described as an example of an optical transmission device, and the optical transmission / reception device 200 will be described as an example of another optical transmission device.

[0014] The optical transceiver device 100 is connected to the optical transmission device 400 via two parallel optical transmission lines T11 and T21. The optical transceiver device 200 is connected to the optical transmission device 300 via two parallel optical transmission lines T14 and T24. The optical transmission device 500 is connected to the optical transmission device 400 via two parallel optical transmission lines T12 and T22. The optical transmission device 500 is connected to the optical transmission device 300 via two parallel optical transmission lines T13 and T23. All of the optical transmission lines T11, T12, T13, T14, T21, T22, T23, and T24 include optical fibers. The type of the optical fiber is not particularly limited. For example, the optical fiber may be a SMF (Single Mode Fiber) or a DSF (Dispersion Shifted Fiber).

[0015] First, referring to FIG. 1, the optical transceiver device 100 will be described. The optical transceiver device 100 includes an OSC input / output unit 102, optical amplifiers 103 and 104, and an ASE (Amplified Spontaneous Emission) light source 105. Further, the optical transceiver device 100 includes a WDM coupler 108, a branching coupler 109, and a control unit (denoted as CTRL in FIG. 1) 110.

[0016] Furthermore, the optical transceiver device 100 includes a user interface (denoted as USR I / F in FIG. 1) 111, optical transmission units 112 and 113, and optical reception units 114 and 115. Both the optical transmission units 112 and 113 and the optical reception units 114 and 115 include connectors. The optical amplifier 103, the WDM coupler 108, the optical transmission unit 112, and the optical reception unit 115 are provided on the optical waveguide 116 of the optical transceiver device 100. The optical amplifier 104, the branching coupler 109, the optical transmission unit 113, and the optical reception unit 114 are provided on the optical waveguide 117 of the optical transceiver device 100.

[0017] The OSC input / output unit 102 is optically connected to the WDM coupler 108 and the branch coupler 109. The OSC input / output unit 102 outputs OSC optical Lo1 directed to the optical transmission device 400. OSC optical Lo1 may or may not include the span loss of the optical transmission path T21. In addition, OSC optical Lo4 output from the optical transmission device 400 is input to the OSC input / output unit 102. OSC optical Lo4 may or may not include the span loss of the optical transmission path T11.

[0018] The optical amplifier 103 amplifies and outputs the WDM signal light Lw1 and the pseudo-light Pw1 (described later) received by the optical transceiver 100 via the optical receiver 115. In other words, the optical amplifier 103 increases the optical power of the WDM signal light Lw1 and the pseudo-light Pw1 and outputs it. The optical amplifier 103 is a post-amplifier, for example, an EDFA (Erbium Doped Fiber Amplifier). The optical amplifier 103 is provided with a circuit board 141 that controls the gain of the optical amplifier 103.

[0019] The post-amplifier is an amplifier located after or downstream of a WSS (Wavelength Selective Switch) (not shown) which is installed between the optical amplifier 103 and the ASE light source 105. The WDM signal light Lw1 output by the optical amplifier 103 is transmitted to the optical transmission path T11 via the optical transmission unit 112.

[0020] The optical amplifier 104 amplifies and outputs the WDM signal light Lw2 and the pseudo-light Pw2 (described later) received by the optical transceiver 100 via the optical receiver 114. The optical amplifier 104 is a preamplifier, for example, including an EDFA. The optical amplifier 104 is provided with a circuit board 142 that controls the gain of the optical amplifier 104. The preamplifier is an amplifier located before or upstream of the WSS (not shown), which is located between the optical amplifier 104 and the optical transmitter 113. The WDM signal light Lw2 output by the optical amplifier 104 is transmitted via the optical transmitter 113.

[0021] The ASE light source 105 is optically connected to the optical amplifier 103. More specifically, the ASE light source 105 is indirectly connected to the optical amplifier 103 via the WSS described above. The ASE light source 105 outputs a pseudo-light Pw1, for example, called a Pseudo Wave. The pseudo-light Pw1 includes wavelength bands of the WDM signal light Lw1, such as the C-band (Conventional-band) and L-band (Long-wavelength-band). The C-band is, for example, a wavelength band of 1530 nm to 1565 nm. The L-band is, for example, a wavelength band of 1565 nm to 1625 nm.

[0022] The pseudo-optical light Pw1 is amplified by the optical amplifier 103. After amplification, the pseudo-optical light Pw1 is combined with the OSC optical light Lo1 by the WDM coupler 108. This generates a combined optical light Mx1, which is the combined OSC optical light Lo1 and the pseudo-optical light Pw1. The optical transmitter 112 transmits this combined optical light Mx1 towards the optical transceiver 200. As a result, the combined optical light Mx1 propagates through the optical transmission path T11.

[0023] The control unit 110 is electrically connected to the OSC input / output unit 102, the optical amplifiers 103 and 104, their respective circuit boards 141 and 142, the ASE light source 105, and the user interface 111. The control unit 110 includes a processor such as a CPU (Central Processing Unit) and memory such as RAM (Random Access Memory) and ROM (Read Only Memory). The control unit 110 may also include an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0024] The control unit 110 controls the operation of the OSC input / output unit 102, the optical amplifiers 103 and 104, and the ASE light source 105. For example, the control unit 110 can request the OSC optical Lo1 output from the OSC input / output unit 102. The control unit 110 can request the pseudo-optical Pw1 output from the ASE light source 105. The control unit 110 can adjust the gain of the optical amplifiers 103 and 104 via the circuit boards 141 and 142.

[0025] Furthermore, the control unit 110 acquires configuration information, including the span loss of its own optical transmission path T11, from the user interface 111 when the optical transceiver 100 starts up, before the optical transmission system ST begins operation. In other words, the control unit 110 acquires the configuration information before the communication of the WDM signals Lw1 and Lw2 begins. Based on the configuration information, if the control unit 110 determines that the span loss is excessive, it switches the startup mode based on the startup mode setting from the user via the user interface 111.

[0026] Specifically, the control unit 110 determines that the span loss is excessive if it is greater than or equal to a predetermined comparison value. If the span loss is excessive, the control unit 110 switches from a normal mode that does not output pseudo-light Pw1 to an extended mode that outputs pseudo-light Pw1.

[0027] Next, the optical transceiver 200 will be described. The optical transceiver 200 includes an OSC input / output unit 202 and optical amplifiers 203 and 204. Circuit boards 241 and 242 are provided for the optical amplifiers 203 and 204, respectively. The optical transceiver 200 also includes an ASE light source 205, a WDM coupler 208, a branch coupler 209, and a control unit 210. Furthermore, the optical transceiver 200 includes a user interface 211, optical transmission units 213 and 214, and optical reception units 212 and 215.

[0028] The optical amplifier 203, WDM coupler 208, optical transmitter 214, and optical receiver 215 are located on the optical waveguide 216 of the optical transceiver 200. The optical amplifier 204, branch coupler 209, optical transmitter 213, and optical receiver 212 are located on the optical waveguide 217 of the optical transceiver 200.

[0029] Thus, the optical transceiver 200 has basically the same configuration as the optical transceiver 100. For this reason, the details of the optical transceiver 200 are omitted. For example, the OSC input / output unit 202 outputs OSC light Lo2 directed to the optical transmission device 300. The ASE light source 205 outputs pseudo-light Pw2, which includes wavelength bands of the WDM signal light Lw2, such as the C-band and L-band. The optical transmission unit 214 transmits combined light Mx2, obtained by combining the OSC light Lo2 and the pseudo-light Pw2, toward the optical transceiver 100. As a result, the combined light Mx2 propagates through the optical transmission path T24.

[0030] Next, the optical transmission device 300 will be described with reference to Figure 2. Note that the optical transmission devices 400 and 500 have essentially the same configuration as the optical transmission device 300, so a detailed explanation will be omitted.

[0031] The optical transmission device 300 includes an OSC input / output unit 302, optical amplifiers 303 and 304, and an OSC input / output unit 305. The OSC input / output units 302 and 305 are examples of optical output units. Circuit boards 341 and 342 are provided for the optical amplifiers 303 and 304, respectively. Circuit boards 341 and 342 are examples of control units that control the outputs of pseudo-optical signals Pw1 and Pw2. The optical amplifiers 303 and 304 may also be examples of control units.

[0032] Furthermore, the optical transmission device 300 includes a WDM coupler 308, a branch coupler 309, a control unit 310, a branch coupler 318, and a WDM coupler 319. The control unit 310 is an example of a calculation unit that calculates the amount of tilt generated in the pseudo-optical Pw1 and Pw2.

[0033] Furthermore, the optical transmission device 300 includes a user interface 311, optical transmission units 312 and 313, optical reception units 314 and 315, and VOAs (Variable Optical Attenuators) 351 and 352. On the other hand, the optical transmission device 300 does not include an ASE light source. In other words, the ASE light source is excluded from the optical transmission device 300. Therefore, the optical transmission device 300 cannot emit pseudo-lights Pw1 and Pw2.

[0034] The optical amplifier 303, WDM coupler 308, optical transmitter 312, optical receiver 315, and branch coupler 318 are located on the optical waveguide 316 of the optical transmission device 300. The optical amplifier 304, WDM coupler 319, branch coupler 309, optical transmitter 313, and optical receiver 314 are located on the optical waveguide 317 of the optical transmission device 300.

[0035] The OSC input / output unit 302 is optically connected to the WDM coupler 308 and the branch coupler 309. The OSC input / output unit 302 outputs OSC optical Lo3 to the optical transmission device 500. OSC optical Lo3 may or may not include the span loss of the optical transmission path T13. In addition, OSC optical Lo5 output from the optical transmission device 500 is input to the OSC input / output unit 302. OSC optical Lo5 may or may not include the span loss of the optical transmission path T23.

[0036] The OSC input / output unit 305 is optically connected to the WDM coupler 319 and the branch coupler 318. The OSC input / output unit 305 outputs OSC optical Lo3 to the optical transceiver 200. OSC optical Lo3 may or may not include the span loss of the optical transmission line T24. In addition, OSC optical Lo2 output from the optical transceiver 200 is input to the OSC input / output unit 305. OSC optical Lo2 may or may not include the span loss of the optical transmission line T14.

[0037] The optical amplifier 303 amplifies and outputs the WDM signal light Lw2 and the pseudo-light Pw2 belonging to the combined light Mx2, which are received by the optical transmission device 300 via the optical receiver 315. In other words, the optical amplifier 303 increases the optical power of the WDM signal light Lw2 and the pseudo-light Pw2 and outputs it. The optical amplifier 303 is an amplifier that includes, for example, an EDFA. The optical amplifier 303 is provided with a circuit board 341 for controlling and adjusting the gain of the optical amplifier 303. The WDM signal light Lw2 output by the optical amplifier 303 is transmitted to the optical transmission path T23 via the optical transmitter 312.

[0038] The optical amplifier 304 amplifies and outputs the WDM signal light Lw1 and the pseudo-light Pw1 belonging to the combined wave light Mx5, which are received by the optical transmission device 300 via the optical receiver 314. In other words, the optical amplifier 304 increases the optical power of the WDM signal light Lw1 and the pseudo-light Pw1 and outputs them. The optical amplifier 304 is an amplifier that includes, for example, an EDFA. The optical amplifier 304 is provided with a circuit board 342 for controlling and adjusting the gain of the optical amplifier 304. The WDM signal light Lw1 output by the optical amplifier 304 is transmitted via the optical transmitter 313.

[0039] The control unit 310 is electrically connected to the OSC input / output units 302 and 305, the optical amplifiers 303 and 304, their respective circuit boards 341 and 342, and the user interface 311. Although not shown in the diagram, the control unit 310 is also electrically connected to the VOAs 351 and 352. The hardware configuration of the control unit 310 is basically the same as that of the control unit 110, so a detailed explanation is omitted. The control unit 310 controls the operation of the OSC input / output units 302 and 305, the optical amplifiers 303 and 304, their respective circuit boards 341 and 342, and the VOAs 351 and 352.

[0040] For example, the control unit 310 can individually request the output of OSC optical Lo3 from the OSC input / output units 302 and 305. The control unit 310 can adjust the gain of the optical amplifiers 303 and 304 via the circuit boards 341 and 342. The control unit 310 can adjust the attenuation of the VOAs 351 and 352.

[0041] Furthermore, the control unit 310 acquires configuration information, including span losses of optical transmission lines T13, T14, T23, and T24, from the user interface 311 when the optical transmission device 300 is started up, before the optical transmission system ST is put into operation. In other words, the control unit 310 acquires the configuration information before communication of WDM signals Lw1 and Lw2 begins. Based on the configuration information, if the control unit 310 determines that the span loss is excessive in any of the optical transmission lines T11, ..., T24, it switches the startup mode based on the startup mode setting from the user via the user interface 311.

[0042] Specifically, the control unit 310 determines that the span loss is excessive if it is greater than or equal to a predetermined comparison value. If the span loss is excessive, the control unit 310 switches from a normal mode in which tilt control is not performed for the pseudo-lights Pw1 and Pw2 to an extended mode in which tilt control is performed.

[0043] Referring to Figure 3, the operation of the optical transceiver 100 according to the first embodiment will be described. Note that the control units 110 and 210 perform essentially the same processing. Therefore, the processing performed by control unit 110 will be described as an example, and the processing performed by control unit 210 will be omitted.

[0044] When the user provides predetermined setting information to the optical transceiver 100, the control unit 110 acquires and verifies the setting information (step S1). The setting information includes, for example, the span loss of the optical transmission path T11 and the transmission path length of the optical transmission path T11. As will be described later, before processing in step S1, the control unit 110 may measure the span loss of the optical transmission path T1 based on the optical power of the optical pulse output from the optical transceiver 100 to the optical transmission path T1 and the optical power of the reflected pulse of that optical pulse. The span loss may also be prepared in advance. After verifying the setting information, the control unit 110 determines, based on the setting information, whether the optical transmission path T11 is in a span loss excess section (indicated as SL excess section in Figure 3) (step S2).

[0045] If the optical transmission path T11 is in a section with excessive span loss (step S2: YES), the control unit 110 switches the startup mode to extended mode based on the startup mode setting from the user (step S3). When switched to extended mode, the control unit 110 requests the OSC input / output unit 102 to output OSC optical Lo1 (step S4).

[0046] As a result, the OSC input / output unit 102 outputs OSC optical Lo1 with a predetermined optical power of several dBm (see Figure 1). However, the optical transmission path T11 corresponds to a section with excessive span loss. Therefore, even though OSC optical Lo1 is output, due to insufficient optical power, OSC optical Lo1 cannot reach the optical transmission device 400 on its own.

[0047] Therefore, when OSC light Lo1 is output, the control unit 110 requests the output of pseudo-light Pw1, as shown in Figure 3 (step S5). More specifically, the control unit 110 determines a constant optical power to be used for the output of pseudo-light Pw1 based on the type of optical transmission path T11, and requests the output of pseudo-light Pw1 based on this constant optical power. As a result, the ASE light source 105 outputs pseudo-light Pw1 with the constant optical power determined by the control unit 110 (see Figure 1).

[0048] When the pseudo-optical signal Pw1 is output, the control unit 110 performs tilt control (step S6). For example, the control unit 110 calculates the amount of tilt generated in the pseudo-optical signal Pw1 at the optical transmission path T11, which is the transmitting side of the optical transceiver 100 (hereinafter referred to as transmission path tilt). The method by which the control unit 110 calculates the amount of transmission path tilt will be described later.

[0049] When the control unit 110 calculates the tilt amount, it generates an inverse tilt that flattens the tilt generated in the pseudo-optical Pw1 in the optical transmission path T11 based on the tilt amount, and requests the circuit board 141 of the optical amplifier 103 to apply the inverse tilt to the pseudo-optical Pw1 as tilt control.

[0050] When the control unit 110 performs tilt control, it requests the release of the shutdown (indicated as SD in Figure 3) of the optical amplifier 103 (step S7). That is, the control unit 110 forcibly starts up the optical amplifier 103. As a result, the optical amplifier 103 allows the transmission of the pseudo-light Pw1. Thus, the pseudo-light Pw1 is amplified by the optical amplifier 103, and the optical power of the pseudo-light Pw1 increases. At this point, the circuit board 141 of the optical amplifier 103 is requested to perform tilt control by the control unit 110. Therefore, the optical amplifier 103 applies a reverse tilt to the pseudo-light Pw1.

[0051] As a result, the optical amplifier 103 outputs a pseudo-optical light Pw1 with reverse tilt. This generates a combined optical light Mx1 by combining the OSC optical light Lo1 and the pseudo-optical light Pw1 with reverse tilt. The combined optical light Mx1 is output from the optical transceiver 100 toward the optical transmission device 400 and propagates through the optical transmission path T11 (see Figure 1).

[0052] When the shutdown of the optical amplifier 103 is released, the control unit 110 waits until communication between OSC optical Lo1,...,Lo5 is secured in the entire section from the optical transceiver 100 to the optical transceiver 200 (Step S8: NO). Once communication between OSC optical Lo1,...,Lo5 is secured (Step S8: YES), the control unit 110 waits until its own path is powered up (Step S9: NO).

[0053] In other words, when pseudo-light Pw1 is output, the optical power of OSC light Lo1 in the optical transmission path T11 increases. As will be explained in detail later, since the wavelength of OSC light Lo1 is longer than that of pseudo-light Pw1, stimulated Raman scattering occurs when the combined light Mx1 propagates through the optical transmission path T11, and the optical power of pseudo-light Pw1 contained in the combined light Mx1 is transferred to OSC light Lo1. As a result, the optical power of OSC light Lo1 increases. This ensures communication of OSC light Lo1 between the optical transceiver 100 and the optical transmission device 400, even if the optical transmission path T11 is in a section with excessive span loss, and OSC light Lo1 can reach the optical transmission device 400 from the optical transceiver 100.

[0054] However, for example, if the optical transmission path T14 is in a section with excessive span loss, and a large amount of tilt accumulates in the pseudo-optical Pw1 that reaches the optical transmission device 300 via relays such as the optical transmission device 400, the gain of the pseudo-optical Pw1 relative to the OSC optical Lo3 will be insufficient. This makes it difficult to increase the optical power of the OSC optical Lo3, and hinders communication of the OSC optical Lo3 between the optical transmission device 300 and the optical transceiver 200. For this reason, the control unit 110 waits until communication of the OSC optical Lo1, ..., Lo5 is ensured throughout the entire section from the optical transceiver 100 to the optical transceiver 200.

[0055] Furthermore, once communication between OSC optical Lo1, ..., Lo5 is ensured throughout the entire section, the control unit 110 waits until its own path comes up. That is, the control unit 110 waits until its own path, the optical transmission path T11, comes up. Once its own path comes up (step S9: YES), the control unit 110 adjusts the gains of the optical amplifiers 103 and 104 (step S10). More specifically, the control unit 110 adjusts the gains of the optical amplifiers 103 and 104 based on the span loss of the optical transmission paths T11 and T21.

[0056] As a result, the optical amplifiers 103 and 104 are adjusted to gains suitable for transmitting the WDM signals Lw1 and Lw2. The control unit 110 can measure the span loss of the optical transmission path T11 based on the optical power of the optical pulse output from the optical transceiver 100 to the optical transmission path T11 and the optical power of the reflected pulse of that optical pulse.

[0057] When the gains of the optical amplifiers 103 and 104 are adjusted, the control unit 110 switches the output from the optical transceiver 100 (step S11) and terminates the process. Specifically, the control unit 110 stops the output of the pseudo-optical light Pw1, switches the output of the combined optical light Mx1 to the output of the WDM signal light Lw1, and terminates the process.

[0058] On the other hand, in the processing of step S2, if the optical transmission path T11 is not in a span loss excessive section (step S2: NO), the control unit 110 requests the OSC input / output unit 102 to output OSC optical Lo1 (step S12). If it is not in a span loss excessive section, the OSC input / output unit 102 may output OSC optical Lo1 with the constant optical power described above, or it may output OSC optical Lo1 with an optical power less than the constant optical power. Since it is not in a span loss excessive section, OSC optical Lo1 can reach the optical transmission device 400 from the optical transceiver 100.

[0059] When OSC optical Lo1 is output, the control unit 110 adjusts the gain of optical amplifiers 103 and 104 (step S13). More specifically, the control unit 110 adjusts the gain of optical amplifiers 103 and 104 based on the span loss of optical transmission paths T11 and T12. This adjusts the gain of optical amplifiers 103 and 104 to a level suitable for transmitting WDM signal optical signals Lw1 and Lw2. The control unit 110 can also measure the span loss of optical transmission path T11 based on the attenuation of the optical power of OSC optical Lo1 output from the optical transceiver 100 to the optical transmission path T11. The attenuation of the optical power of OSC optical Lo1 is notified to the optical transceiver 100 via OSC optical Lo4 output from the optical transmission device 400.

[0060] When the gains of the optical amplifiers 103 and 104 are adjusted, the control unit 110 switches the output from the optical transceiver 100 (step S14) and terminates the process. Specifically, the control unit 110 switches the output of the OSC optical Lo1 to the output of the WDM signal optical Lw1 and terminates the process.

[0061] The operation of the optical transmission device 300 will be explained with reference to Figure 4. Note that the operation of optical transmission devices 400 and 500 is basically the same as that of optical transmission device 300, so a detailed explanation will be omitted. Furthermore, the same reference numerals are used for operations similar to those of the optical transceiver 100 described above, and their detailed explanations will also be omitted.

[0062] The control unit 310, similar to the process in step S2 described above, determines whether there is a span loss excessive section downstream of the optical transmission device 300 if the optical transmission paths T13, T14, T23, and T24 are not span loss excessive sections (step S21). If there is no span loss excessive section (step S21: NO), the control unit 310 determines whether there is a span loss excessive section upstream of the optical transmission device 300 (step S22). If there is no span loss excessive section (step S22: NO), the control unit 310 executes the processes in steps S12 and S13 and terminates the process. The control unit 310 can determine whether there is a span loss excessive section downstream or upstream of the optical transmission device 300 based on predetermined information transferred from the optical transceiver 200, the optical transmission device 400, etc.

[0063] On the other hand, if there is a span loss overload section (step S21: YES, S22: YES), the control unit 310 performs the processing in step S3 and then confirms the arrival of the pseudo-light (step S23). Specifically, the control unit 310 confirms the arrival of the pseudo-light Pw1 output from the optical transmission device 500. Once the control unit 310 confirms the arrival of the pseudo-light Pw1, it determines a constant optical power to be used for the output of the pseudo-light Pw1 based on the type of optical transmission path T14, and requests the circuit board 342 of the optical amplifier 304 to output the pseudo-light Pw1 based on the constant optical power. As a result, the circuit board 342 can control the optical power of the pseudo-light Pw1 to the constant optical power determined by the control unit 310. Once the optical power of the pseudo-light Pw1 is controlled, the control unit 310 performs tilt control (step S24).

[0064] For example, the control unit 310 calculates the amount of transmission path tilt generated in the pseudo-optical Pw1 at the optical transmission path T14, which is the transmitting side of the optical transmission device 300. More specifically, the control unit 310 individually calculates the amount of SRS (Stimulated Raman Scattering) tilt caused by stimulated Raman scattering and the amount of WDL (Wavelength Dependent Loss) tilt caused by wavelength-dependent loss, and calculates the sum of the two tilt amounts as the amount of transmission path tilt. Note that SRS tilt is an example of the first tilt, and WDL tilt is an example of the second tilt.

[0065] Here, the control unit 310 can calculate the tilt amount of the SRS tilt based on the type of optical transmission path T14 (specifically, an optical fiber), the output power of the pseudo-optical Pw1 output to the optical transmission path T14, the loss coefficient corresponding to the type of optical transmission path T14, at least one of the connection loss between the optical transmission path T14 and the optical transmission device 300, and a pre-specified known first calculation formula. The tilt amount of the SRS tilt is an example of the first tilt amount.

[0066] Furthermore, the control unit 310 can calculate the amount of WDL tilt based on the transmission path distance of the optical transmission path T14, the transmission path loss of the optical transmission path T14, and a loss coefficient corresponding to the type of optical transmission path T14, and then calculate the amount of WDL tilt based on the transmission path distance, the loss value per unit distance of the WDL, and a pre-specified known second calculation formula. The amount of WDL tilt is an example of the second tilt amount.

[0067] Furthermore, the control unit 110, like the control unit 310, can calculate the tilt amounts for SRS tilt and WDL tilt, and sum the two tilt amounts to calculate the tilt amount for the transmission path tilt. Once the control unit 310 has calculated the tilt amount for the transmission path tilt, it generates an inverse tilt that flattens the tilt generated in the pseudo-optical Pw1 in the optical transmission path T14 based on the tilt amount, and requests the circuit board 342 of the optical amplifier 304 to apply the inverse tilt to the pseudo-optical Pw1 as tilt control. Once the control unit 310 has executed the tilt control, it executes the subsequent steps S7 to S10 and terminates the process.

[0068] As a result, the pseudo-optical light Pw1 is amplified by the optical amplifier 103, increasing the optical power of the pseudo-optical light Pw1. At this point, the circuit board 342 of the optical amplifier 304 is requested to perform tilt control from the control unit 310. Therefore, the optical amplifier 304 applies a reverse tilt to the pseudo-optical light Pw1. As a result, the optical amplifier 304 outputs a pseudo-optical light Pw1 with a reverse tilt applied. This generates a combined light Mx3 by combining the OSC light Lo3 and the pseudo-optical light Pw1 with a reverse tilt applied. The combined light Mx3 is output from the optical transmission device 300 toward the optical transceiver 200 and propagates through the optical transmission path T14 (see Figure 2).

[0069] An example of the first embodiment will be described in comparison with a comparative example according to the first embodiment, with reference to Figures 5(a) and (b) and Figures 6(a) and (b).

[0070] First, in the comparative example where tilt control is not performed, as shown in Figure 5(a), the optical amplifier 304 can output pseudo-optical light Pw1 with flat optical power and no tilt. As a result, combined light Mx3 including pseudo-optical light Pw1 is output from the optical transmission device 300 and propagates through the optical transmission path T14.

[0071] However, a tilt occurs in the pseudo-optical Pw1 as it propagates through the optical transmission path T14. As a result, as shown in Figure 6(a), the gain from the pseudo-optical Pw1 to the OSC optical Lo3 included in the combined optical Mx3 becomes insufficient, making it difficult to increase the optical power of the OSC optical Lo3. Furthermore, because a tilt occurs in the pseudo-optical Pw1 in the optical transmission path T14, as shown in Figure 5(a), the pseudo-optical Pw1 branched from the combined optical Mx3 in the optical transceiver 200 is input to the optical amplifier 204 with the tilt still present. Therefore, even if the pseudo-optical Pw1 is amplified by the optical amplifier 204, the tilt remains in the pseudo-optical Pw1.

[0072] On the other hand, in the embodiment in which tilt control is performed, as shown in Figure 5(b), the optical amplifier 304 can output pseudo-optical light Pw1 with inverse tilt applied based on the transmission path tilt amount. The transmission path tilt amount represents the amount of tilt of the transmission path. As a result, combined light Mx3, which includes pseudo-optical light Pw1 with higher optical power on the short-wavelength side than on the long-wavelength side, is output from the optical transmission device 300 and propagates through the optical transmission path T14.

[0073] A tilt occurs in the pseudo-optical light Pw1 as it propagates through the optical transmission path T14. Since the pseudo-optical light Pw1 is given an inverse tilt, when a tilt occurs in the pseudo-optical light Pw1, the tilt is canceled out by the inverse tilt, resulting in a pseudo-optical light Pw1 with suppressed tilt and flat optical power, as shown in Figure 6(b). This ensures that the gain from the pseudo-optical light Pw1 for the OSC optical Lo3 included in the combined optical light Mx3 is secured, and the optical power of the OSC optical Lo3 is increased. Furthermore, because a tilt occurs in the pseudo-optical light Pw1 in the optical transmission path T14, as shown in Figure 5(b), the pseudo-optical light Pw1 branched from the combined optical light Mx3 in the optical transceiver 200 is input to the optical amplifier 204 in a flat state with improved tilt. Therefore, even if the pseudo-optical light Pw1 is amplified without tilt control being performed in the optical amplifier 204, the optical power of the pseudo-optical light Pw1 is maintained in a flat state.

[0074] As described above, according to the first embodiment, when establishing communication between the optical transmission device 300 and the optical transceiver 200 based on the OSC light and the pseudo-light Pw1 during OSC link-up, the control unit 310 calculates the amount of transmission path tilt generated in the pseudo-light Pw1 in the optical transmission path T14. The circuit board 342 of the optical amplifier 304 controls the output of the pseudo-light Pw1 based on this transmission path tilt amount. As a result, the optical transmission device 300 can reduce the amount of transmission path tilt of the pseudo-light Pw1. Note that the optical transceiver 200 can be another optical transmission device facing the optical transmission device 300. Similarly, for example, the optical transceiver 100 can also be another optical transmission device facing the optical transmission device 400.

[0075] (Second Embodiment) Referring to Figures 7(a) and (b), an embodiment of the second embodiment will be described in comparison with a comparative example of the second embodiment. In the second embodiment, the optical transmission device 300 will be described as an example of an optical transmission device, and the optical transmission device 500 will be described as an example of another optical transmission device.

[0076] First, in the comparative example where tilt control is not performed, as shown in Figure 7(a), the optical amplifier 504 can output pseudo-optical light Pw1 with flat optical power and no tilt. As a result, combined light Mx5 including pseudo-optical light Pw1 is output from the optical transmission device 500 and propagates through the optical transmission path T13.

[0077] However, a tilt occurs in the pseudo-optical signal Pw1 as it propagates through the optical transmission path T13. As a result, the pseudo-optical signal Pw1 branched from the combined optical signal Mx5 in the optical transmission device 300 is input to the optical amplifier 304 with the tilt still present. Therefore, even when the pseudo-optical signal Pw1 is amplified by the optical amplifier 304, the tilt remains in the pseudo-optical signal Pw1.

[0078] On the other hand, in the embodiment in which tilt control is performed, the optical amplifier 504 can output pseudo-optical light Pw1, as shown in Figure 7(b). Therefore, the combined optical light Mx5 including pseudo-optical light Pw1 is output from the optical transmission device 500 and propagates through the optical transmission path T13.

[0079] As the pseudo-optical light Pw1 propagates through the optical transmission path T13, a tilt occurs in the pseudo-optical light Pw1 branched from the multiplexed optical light Mx5 in the optical transmission device 300, and this tilt remains when it is input to the optical amplifier 304. Here, the circuit board 342 of the optical amplifier 304 is requested by the control unit 310 to perform tilt control. Therefore, the optical amplifier 304 applies an inverse tilt to the pseudo-optical light Pw1 based on the amount of transmission path tilt. The control unit 310 can calculate the amount of transmission path tilt that occurs in the pseudo-optical light Pw1 at the optical transmission path T13, which is the receiving side of the optical transmission device 300.

[0080] Therefore, when the pseudo-optical Pw1 is amplified by the optical amplifier 304, the tilt is canceled out by the inverse tilt, and a pseudo-optical Pw1 with flat optical power and suppressed tilt is output from the optical amplifier 304. In the first embodiment, the transmission path tilt was compensated in advance, but as described above, according to the second embodiment, the transmission path tilt of the pseudo-optical Pw1 can be compensated afterward.

[0081] (Third embodiment) Referring to Figures 8(a) and (b), an embodiment of the third embodiment will be described in comparison with a comparative example of the third embodiment. In the third embodiment, the optical transmission device 500 will be described as an example of an optical transmission device, and the optical transmission device 300 will be described as an example of another optical transmission device.

[0082] First, in the comparative example where tilt control is not performed, as shown in Figure 8(a), the optical amplifier 504 can output pseudo-optical light Pw1 with flat optical power and no tilt. As a result, the combined light Mx5, which includes pseudo-optical light Pw1, is output from the optical transmission device 500 and propagates through the optical transmission path T13. However, tilt occurs in the pseudo-optical light Pw1 as it propagates through the optical transmission path T13.

[0083] As a result, the pseudo-optical light Pw1 branched from the combined optical light Mx5 in the optical transmission device 300 is input to the optical amplifier 304 with a residual tilt. Furthermore, if the input power of the pseudo-optical light Pw1 to the optical amplifier 304 is small, the optical amplifier 304 may generate a tilt where the short-wavelength side is higher than the long-wavelength side. Therefore, when the pseudo-optical light Pw1 is amplified by the optical amplifier 304, there is a possibility that the pseudo-optical light Pw1 with a tilt where the short-wavelength side is higher than the long-wavelength side will be output from the optical amplifier 304.

[0084] On the other hand, in an embodiment in which tilt control is performed, as shown in Figure 8(b), the optical amplifier 504 applies an inverse tilt to the pseudo-optical Pw1 based on the transmission path tilt amount and the amplifier tilt amount by the circuit board 542 provided on the optical amplifier 504. The circuit board 542 is an example of a control unit, and the amplifier tilt amount is an example of a third tilt amount. The amplifier tilt amount is calculated by the control unit 310. The control unit 310 can calculate the amplifier tilt amount of the optical amplifier 304 located downstream of the optical amplifier 504 based, for example, on the input power of the pseudo-optical Pw1 to the optical amplifier 304 estimated based on the gain of stimulated Raman scattering, a typical set value of the amplifier tilt generated due to noise or fluctuations in the optical amplifier 304, and a known third calculation formula specified in advance.

[0085] When the control unit 310 calculates the amplifier tilt amount, it requests the OSC input / output unit 302 to output the OSC optical Lo3, which includes the amplifier tilt amount. This allows the OSC input / output unit 302 to output the OSC optical Lo3 directed towards the optical transmission device 500. The OSC optical Lo3 is output from the optical transmission device 300, passes through the optical transmission path T23, and is input to the optical transmission device 500. The circuit board 542 of the optical amplifier 504 adds the amplifier tilt amount and the transmission path tilt amount included in the OSC optical Lo3, and applies a reverse tilt to the pseudo-optical Pw1 according to the sum result.

[0086] As a result, pseudo-optical light Pw1, which has an inverse tilt based on the transmission path tilt amount and the amplifier tilt amount, is output from the optical amplifier 504. The combined light Mx5, including pseudo-optical light Pw1, is output from the optical transmission device 500 and propagates through the optical transmission path T13. Here, when propagating through the optical transmission path T13, a tilt occurs in the pseudo-optical light Pw1, which may result in pseudo-optical light Pw1 with a small optical power where the long wavelength side has a higher optical power than the short wavelength side being input to the optical amplifier 304. However, since the optical amplifier 304 generates a tilt where the short wavelength side has a higher tilt than the long wavelength side, the optical power of the pseudo-optical light Pw1 is canceled out by the optical amplifier 304. As a result, the optical amplifier 304 can output pseudo-optical light Pw1 with a flat optical power and suppressed tilt.

[0087] As described above, the first and second embodiments describe how to compensate for transmission line tilt, but according to the third embodiment, not only transmission line tilt but also amplifier tilt can be compensated in advance.

[0088] (Fourth Embodiment) The fourth embodiment of this invention will be described with reference to Figures 9 to 11. Components and processes similar to those described in the first embodiment (optical transmission device 300) are denoted by the same reference numerals, and their detailed descriptions are omitted. Furthermore, since the optical transmission devices 400 and 500 have the same configuration and processes as the optical transmission device 300, their detailed descriptions are also omitted.

[0089] First, as shown in Figure 9, the optical transmission device 300 includes a back-excited Raman amplifier (indicated as BWD Raman in Figure 9) 320. The back-excited Raman amplifier 320 is an example of a back-excited light source. The back-excited Raman amplifier 320 is connected to the optical waveguide 317 via a WDM coupler 321.

[0090] The back-excited Raman amplifier 320 outputs back-excited light Pb3. The back-excited light Pb3 propagates along the optical transmission path T13 in the opposite direction to the direction in which the WDM signal light Lw1 propagates. In the optical transmission path T13, the back-excited light Pb3 Raman amplifies the combined light Mx5 output from the optical transmission device 500 using stimulated Raman scattering. As a result, the optical power of the OSC light Lo5 belonging to the combined light Mx5 is further increased compared to when the pseudo-light Pw1 is used alone.

[0091] Referring to Figure 10, the operation of the optical transmission device 300 according to the fourth embodiment will be described. Note that the operation of the optical transmission devices 400 and 500 according to the fourth embodiment is basically the same as that of the optical transmission device 300 according to the fourth embodiment, so a detailed explanation will be omitted. Furthermore, the same reference numerals are used for operations similar to those of the optical transmission device 300 described above, and their detailed explanations will also be omitted.

[0092] After the processing in step S23 described in the first embodiment, and before the processing in step S24, the control unit 310 instructs the back-excited Raman amplifier 320 to output the back-excited light Pb3 (step S31). As a result, the back-excited Raman amplifier 320 outputs the back-excited light Pb3.

[0093] Furthermore, after the processing in step S9 and before the processing in step S10, the control unit 310 adjusts the gain of the back-excited Raman amplifier 320 (step S32). After adjusting the gain of the back-excited Raman amplifier 320, the control unit 310 executes the subsequent processing and terminates the process. In addition, after the processing in step S12 and before the processing in step S13, the control unit 310 adjusts the gain of the back-excited Raman amplifier 320 (step S33). After adjusting the gain of the back-excited Raman amplifier 320, the control unit 310 executes the subsequent processing and terminates the process.

[0094] Thus, according to the fourth embodiment, the optical transmission device 300 is equipped with a back-excited Raman amplifier 320. As a result, the optical power of the OSC light Lo5 included in the combined light Mx5 is further increased compared to when the pseudo-light Pw1 is used alone. Also, as shown in Figure 11(a), if the gain from the pseudo-light Pw1 to the OSC light Lo5 included in the combined light Mx5 is insufficient due to the occurrence of tilt, it becomes difficult to increase the optical power of the OSC light Lo5. However, as shown in Figure 11(b), the OSC light Lo5 can enjoy not only the effect of stimulated Raman scattering from the pseudo-light Pw1 but also the effect of stimulated Raman scattering from the back-excited light Pb3, which includes a wavelength band from the lowest wavelength λ2 to the longest wavelength λ3.

[0095] (Fifth embodiment) The fifth embodiment of this invention will be described with reference to Figures 12 and 13. Components and processes similar to those described in the fourth embodiment (optical transmission device 300) are denoted by the same reference numerals, and their detailed descriptions are omitted. Furthermore, since the optical transmission devices 400 and 500 have the same configuration as the optical transmission device 300, their detailed descriptions are also omitted.

[0096] First, as shown in Figure 12, the optical transmission device 300 includes a forward-excited Raman amplifier (indicated as FWD Raman in Figure 12) 330. The forward-excited Raman amplifier 330 is an example of a forward-excited light source. The forward-excited Raman amplifier 330 is connected to the optical waveguide 316 via a WDM coupler 331.

[0097] The forward-excited Raman amplifier 330 outputs forward-excited light Pf3. The forward-excited light Pf3 propagates along the optical transmission path T23 in the same direction as the WDM signal light Lw2 propagates along the optical transmission path T23. In the optical transmission path T23, the forward-excited light Pf3 uses stimulated Raman scattering to Raman-amplify the combined light Mx3 output from the optical transmission device 300. As a result, the optical power of the OSC light Lo3 belonging to the combined light Mx3 is further increased compared to when the pseudo-light Pw2 output from the optical transceiver 200 and the back-excited light Pb5 output from the optical transmission device 500 are used in combination.

[0098] Referring to Figure 13, the operation of the optical transmission device 300 according to the fifth embodiment will be described. Note that the operation of the optical transmission devices 400 and 500 according to the fifth embodiment is basically the same as that of the optical transmission device 300 according to the fifth embodiment, so a detailed explanation will be omitted. Furthermore, the same reference numerals are used for operations similar to those of the optical transmission device 300 described above, and their detailed explanations will also be omitted.

[0099] The control unit 310, after the processing of step S31 as described in the fourth embodiment and before the processing of step S24, instructs the forward-excited Raman amplifier 330 to output the forward-excited light Pf3 (step S41). As a result, the forward-excited Raman amplifier 330 outputs the forward-excited light Pf3.

[0100] Furthermore, after the processing in step S32 and before the processing in step S10, the control unit 310 adjusts the gain of the forward-excited Raman amplifier 330 (step S42). After adjusting the gain of the forward-excited Raman amplifier 330, the control unit 310 executes the subsequent processing and terminates the process. In addition, after the processing in step S33 and before the processing in step S13, the control unit 310 adjusts the gain of the forward-excited Raman amplifier 330 (step S43). After adjusting the gain of the forward-excited Raman amplifier 330, the control unit 310 executes the subsequent processing and terminates the process.

[0101] Thus, according to the fifth embodiment, the optical transmission device 300 includes a forward-excited Raman amplifier 330. As a result, the optical power of the OSC light Lo3 included in the combined light Mx3 is further increased compared to when the pseudo-light Pw2 and the back-excited light Pb5 are used in combination.

[0102] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims.

[0103] For example, the control unit 310 may determine a constant optical power to be used for the output of the pseudo-optical light Pw1 based not only on the type of optical transmission path T14, but also on the configuration of the Raman amplifier, such as using the back-excited Raman amplifier 320 alone, using the forward-excited Raman amplifier 330 alone, or using the back-excited Raman amplifier 320 and the forward-excited Raman amplifier 330 in combination.

[0104] Furthermore, the control unit of the optical transmission device 500 may calculate the amount of amp tilt generated in the optical amplifier 504 (see Figure 8(b)) based on the input power of the pseudo-light Pw1 to the optical amplifier 504 estimated based on the gain of stimulated Raman scattering, a typical set value for the amp tilt of the optical amplifier 504, and a pre-specified known fourth calculation formula. If the control unit of the optical transmission device 500 cannot control the optical amplifier 504 based on this amount of amp tilt, it may send an OSC optical Lo5 to the optical transmission device 300 that includes an instruction to control the output of the pseudo-light Pw1 based on this amount of amp tilt.

[0105] Furthermore, the following additional information is disclosed regarding the above explanation. (Note 1) An optical transmission device for relaying signal light, comprising: an optical output unit that outputs OSC light; a calculation unit that calculates the amount of tilt generated in the pseudo-light in the optical transmission path connecting the optical transmission device and the other optical transmission device when establishing communication between the optical transmission device and the other optical transmission device based on the OSC light and pseudo-light including the wavelength band of the signal light; and a control unit that controls the output of the pseudo-light based on the amount of tilt. (Note 2) The optical transmission device according to Note 1, characterized in that the calculation unit calculates the amount of tilt occurring in either the first optical transmission path connected to the transmitting side of the optical transmission device within the optical transmission path or the second optical transmission path connected to the receiving side of the optical transmission device within the optical transmission path. (Note 3) The optical transmission apparatus according to Note 1 or 2, characterized in that the calculation unit determines a constant optical power to be used for the output of the pseudo-light based on the type of optical transmission path, and the control unit controls the output power of the pseudo-light to the constant optical power. (Note 4) The optical transmission device according to Note 1 or 2, wherein the tilt includes a first tilt generated in the pseudolight in the optical transmission path based on stimulated Raman scattering, and the calculation unit calculates the first tilt amount of the first tilt based on any of the following: the type of optical transmission path, the output power for outputting the pseudolight to the optical transmission path, a loss coefficient corresponding to the type of optical transmission path, and the connection loss between the optical transmission path and the optical transmission device. (Note 5) The optical transmission apparatus according to Note 1 or 2, characterized in that the tilt includes a second tilt generated in the pseudolight in the optical transmission path based on wavelength-dependent loss, the calculation unit calculates the distance of the optical transmission path based on the transmission path loss of the optical transmission path and a loss coefficient corresponding to the type of optical transmission path, and calculates the amount of the second tilt of the second tilt based on either the distance or the loss value per unit distance of the wavelength-dependent loss. (Note 6) The optical transmission device according to Note 1 or 2, characterized in that either the optical transmission device or the other optical transmission device is equipped with a downstream optical amplifier, and the other of the optical transmission device or the other optical transmission device is equipped with an upstream optical amplifier, and the calculation unit calculates the third tilt amount of the amplifier tilt generated in the downstream optical amplifier based on either the optical power of the pseudo-light input to the downstream optical amplifier or a set value of the third tilt amount. (Note 7) The optical transmission device according to Note 1 or 2, wherein either the optical transmission device or the other optical transmission device comprises a downstream optical amplifier, and the other optical transmission device comprises an upstream optical amplifier, the calculation unit calculates a fourth tilt amount of the amplifier tilt generated by the upstream optical amplifier based on either the optical power of the pseudo-light input to the upstream optical amplifier or a set value of the fourth tilt amount, and transmits the OSC light, which includes an instruction to control the output of the pseudo-light based on the fourth tilt amount, to either the optical transmission device or the other optical transmission device. (Note 8) The optical transmission device according to Note 1 or 2, further comprising a back-excitation light source that outputs back-excitation light to the optical transmission path, which propagates in a second direction opposite to the first direction in which the OSC light propagates through the optical transmission path, wherein the calculation unit instructs the back-excitation light source to output the back-excitation light. (Note 9) The optical transmission device according to Note 1 or 2, further comprising a forward excitation light source that outputs forward excitation light to the optical transmission path, wherein the OSC light propagates in a first direction along the optical transmission path, and the calculation unit instructs the forward excitation light source to output the forward excitation light. (Note 10) The optical transmission device according to Note 1 or 2, characterized in that the wavelength of the OSC light is longer than the wavelength of the signal light. (Note 11) The optical transmission device according to Note 1 or 2, characterized in that the wavelength of the OSC light is longer than the wavelength of the pseudo-light. (Appendix 12) An optical transmission system including a first optical transmission device and a second optical transmission device that are opposite each other via an optical transmission path and both relay signal light, wherein at least one of the first optical transmission device and the second optical transmission device has an optical output unit that outputs OSC light, a calculation unit that calculates the amount of tilt generated in the pseudo-light in the optical transmission path when establishing communication between the first optical transmission device and the second optical transmission device based on the OSC light and pseudo-light including the wavelength band of the signal light, and a control unit that controls the output of the pseudo-light based on the amount of tilt. [Explanation of symbols]

[0106] ST Optical Transmission Systems 100,200 Optical Transceiver 300, 400, 500 Optical transmission equipment 102,202,302,305 OSC input / output section 303,304 Optical Amplifier 341,342 Circuit boards 110,210,310 Control Unit 320 Back-excited Raman amplifier 330 Forward-excited Raman amplifier

Claims

1. An optical transmission device that relays signal light, An optical output section that outputs OSC (Optical Supervisory Channel) light, A calculation unit calculates the amount of tilt generated in the pseudo-light in the optical transmission path connecting the optical transmission device and the other optical transmission device when establishing communication between the optical transmission device and another optical transmission device facing the optical transmission device, based on the OSC light and pseudo-light including the wavelength band of the signal light. A control unit that controls the output of the pseudo-light based on the tilt amount, An optical transmission device having the following features.

2. The calculation unit calculates the amount of tilt occurring in either the first optical transmission path connected to the transmitting side of the optical transmission device within the optical transmission path, or the second optical transmission path connected to the receiving side of the optical transmission device within the optical transmission path. The optical transmission device according to feature 1.

3. The calculation unit determines a certain optical power to be used for the output of the pseudo-light based on the type of optical transmission path. The control unit controls the output power of the pseudo-light to the constant light power. The optical transmission device according to claim 1 or 2.

4. The tilt includes a first tilt generated in the pseudolight in the optical transmission path based on stimulated Raman scattering. The calculation unit calculates the first tilt amount of the first tilt based on any of the following: the type of optical transmission path, the output power for outputting the pseudo-light to the optical transmission path, the loss coefficient corresponding to the type of optical transmission path, and the connection loss between the optical transmission path and the optical transmission device. The optical transmission device according to claim 1 or 2.

5. The tilt includes a second tilt generated in the pseudolight in the optical transmission path based on wavelength-dependent loss. The calculation unit calculates the distance of the optical transmission path based on the transmission path loss of the optical transmission path and a loss coefficient corresponding to the type of optical transmission path, and calculates the second tilt amount of the second tilt based on either the distance or the loss value per unit distance of the wavelength-dependent loss. The optical transmission device according to claim 1 or 2.

6. Either the optical transmission device or the other optical transmission device is equipped with a downstream optical amplifier, and the other optical transmission device is equipped with an upstream optical amplifier. The calculation unit calculates the third tilt amount of the amplifier tilt generated by the downstream optical amplifier based on either the optical power of the pseudo-light input to the downstream optical amplifier or a set value of the third tilt amount. The optical transmission device according to claim 1 or 2.

7. Either the optical transmission device or the other optical transmission device is equipped with a downstream optical amplifier, and the other optical transmission device is equipped with an upstream optical amplifier. The calculation unit calculates the fourth tilt amount of the amplifier tilt generated by the upstream optical amplifier based on either the optical power of the pseudo-light input to the upstream optical amplifier or a set value of the fourth tilt amount, and transmits the OSC light, which includes an instruction to control the output of the pseudo-light based on the fourth tilt amount, to either the optical transmission device or the other optical transmission device. The optical transmission device according to claim 1 or 2.

8. The system further includes a back-excitation light source that outputs back-excitation light to the optical transmission path, which propagates in a second direction opposite to the first direction in which the OSC light propagates through the optical transmission path. The calculation unit instructs the rear excitation light source to output the rear excitation light. The optical transmission device according to claim 1 or 2.

9. The system further includes a forward excitation light source that outputs forward excitation light to the optical transmission path, which propagates in a first direction in which the OSC light propagates along the optical transmission path. The calculation unit instructs the forward excitation light source to output the forward excitation light. The optical transmission device according to claim 1 or 2.

10. An optical transmission system comprising a first optical transmission device and a second optical transmission device that are opposite each other via an optical transmission path and both relay signal light, At least one of the first optical transmission device and the second optical transmission device is An optical output section that outputs OSC (Optical Supervisory Channel) light, A calculation unit calculates the amount of tilt generated in the pseudo-light in the optical transmission path when establishing communication between the first optical transmission device and the second optical transmission device based on the OSC light and pseudo-light including the wavelength band of the signal light, A control unit that controls the output of the pseudo-light based on the tilt amount, An optical transmission system.

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