Optical transmission systems and optical transmission devices

Abstract

The objective is to provide optical transmission systems and devices that improve safety before optical communication via OSC (Optical Supervisory Channel). [Solution] The optical transmission system includes a first optical transmission device that transmits OSC light to an optical transmission path and a second optical transmission device that receives the OSC light from the optical transmission path, wherein the first optical transmission device has a first control unit that detects a transmission path interruption before the OSC light is transmitted in the optical transmission path based on a first detection method, and the second optical transmission device has a second control unit that detects a transmission path interruption after the OSC light is transmitted in the optical transmission path based on a second detection method different from the first detection method.

Description

Technical Field

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

Background Art

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

[0003] An optical transmission system includes an optical transmitter and an optical receiver. The optical transmitter and the optical receiver actually have the same functions as each other as a single optical transmission device. For example, an optical amplifier that amplifies and outputs signal light is provided in the optical transmitter. In addition, in an 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, if the span loss of the optical transmission path interposed between opposing optical transmission devices is excessive, depending on the optical power of the aforementioned optical monitoring signal (hereinafter referred to as OSC light), communication of OSC light between optical transmission devices may become difficult. In this case, when the optical transmission devices start up, they may not be able to confirm the communication of OSC light. If the optical transmission devices cannot confirm the communication of OSC light, one possible method to achieve this is to increase the optical power of the OSC light using pseudo-light called a Pseudo Wave.

[0006] However, when using pseudo-light, if a transmission line break occurs in the optical transmission line, a large amount of pseudo-light with high optical power will be emitted from the optical transmission line, making safe restoration work on the optical transmission line difficult. In other words, if a transmission line break occurs in the optical transmission line before OSC light is transmitted, it may not be possible to ensure the safety of the restoration work on the optical transmission line.

[0007] Therefore, one objective is to provide an optical transmission system and optical transmission device that improves safety before OSC optical communication. [Means for solving the problem]

[0008] In one embodiment, the optical transmission system includes a first optical transmission device that transmits OSC light to an optical transmission path and a second optical transmission device that receives the OSC light from the optical transmission path, wherein the first optical transmission device has a first control unit that detects a transmission path interruption before the OSC light is transmitted in the optical transmission path based on a first detection method, and the second optical transmission device has a second control unit that detects a transmission path interruption after the OSC light is transmitted in the optical transmission path based on a second detection method different from the first detection method. [Effects of the Invention]

[0009] This can improve safety before OSC optical communication. [Brief explanation of the drawing]

[0010] [Figure 1]This is an example of an optical transmission system according to the first embodiment. [Figure 2] This is a flowchart showing an example of the operation of the optical transmission system according to the first embodiment. [Figure 3] (a) through (f) are diagrams illustrating an example of the operation of an optical transmission system. [Figure 4] (a) through (d) are diagrams illustrating another example of the operation of an optical transmission system. [Figure 5] This figure illustrates an example of the optical operation of a comparative example of the optical transmission system according to the first embodiment. [Figure 6] This figure illustrates an example of the optical operation of an embodiment of the optical transmission system according to the first embodiment. [Figure 7] This is an example of an optical transmission system according to the second embodiment. [Figure 8] This flowchart shows an example of the operation of the optical transmission system according to the second embodiment. [Figure 9] This figure illustrates an example of the optical operation of a comparative example of the optical transmission system according to the second embodiment. [Figure 10] This figure illustrates an example of the optical operation according to an embodiment of the optical transmission system according to the second embodiment. [Figure 11] This is an example of an optical transmission system according to the third embodiment. [Figure 12] This is a flowchart showing an example of the operation of the optical transmission system according to the third embodiment. [Modes for carrying out the invention]

[0011] The following will explain the implementation of this project with reference to the drawings.

[0012] (First Embodiment) As shown in FIG. 1, the optical transmission system ST includes two opposing optical transmission devices 100 and 200. The optical transmission device 100 is an example of a first optical transmission device. The optical transmission device 200 is an example of a second optical transmission device. The optical transmission devices 100 and 200 include, for example, a ROADM (Reconfigurable Optical Add / Drop Multiplexer).

[0013] The optical transmission devices 100 and 200 are connected via two parallel optical transmission paths T1 and T2. One end of each of the optical transmission paths T1 and T2 is connected to the optical transmission device 100. The other end of each of the optical transmission paths T1 and T2 is connected to the optical transmission device 200. Both the optical transmission paths T1 and T2 include optical fibers. The type of the optical fiber is not particularly limited. The optical fiber may be a SMF (Single Mode Fiber) or a DSF (Dispersion Shifted Fiber).

[0014] First, the optical transmission device 100 will be described. The optical transmission device 100 includes an OSC input / output unit 102, optical amplifiers 103 and 104, and an ASE (Amplified Spontaneous Emission) light source 105. The optical transmission device 100 also includes a WDM coupler 108, a branching coupler 109, and a control unit (denoted as CTRL in FIG. 1) 110. The control unit 110 is an example of a first control unit. The ASE light source 105 is an example of a pseudo light source.

[0015] Furthermore, the optical transmission 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 transmission 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 transmission device 100.

[0016] 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 towards the optical transmission device 200. OSC optical Lo1 may or may not include the loss value of the optical transmission path T1 (hereinafter referred to as span loss). In addition, OSC optical Lo2 output from the optical transmission device 200 is input to the OSC input / output unit 102. OSC optical Lo2 may or may not include the span loss of the optical transmission path T2. Furthermore, if a transmission path break occurs in the optical transmission path T1, the OSC input / output unit 102 may also receive the reflected light from the OSC optical Lo1. Examples of transmission path breaks include connector disconnection and fiber breakage.

[0017] The optical amplifier 103 amplifies and outputs the WDM signal light Lw1 and the pseudo-light Pw1 (described later) received by the optical transmission device 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 realized by, for example, an EDFA (Erbium Doped Fiber Amplifier) ​​and a circuit board that controls the gain of the EDFA.

[0018] 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 T1 via the optical transmission unit 112.

[0019] The optical amplifier 104 amplifies and outputs the WDM signal light Lw2 and the pseudo-light Pw2 (described later) received by the optical transmission device 100 via the optical receiver 114. The optical amplifier 104 is a preamplifier realized by, for example, an EDFA and a circuit board that controls the gain of the EDFA. The preamplifier is an amplifier located before or upstream of the WSS (not shown) which is provided 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.

[0020] 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.

[0021] 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 transmission device 200. As a result, the combined optical light Mx1 propagates through the optical transmission path T1.

[0022] The control unit 110 is electrically connected to the OSC input / output unit 102, optical amplifiers 103 and 104, ASE light source 105, and 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).

[0023] 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 input / output unit 102 to output OSC optical Lo1. The control unit 110 can instruct the ASE light source 105 to output pseudo-optical Pw1. The control unit 110 can adjust the gain of the optical amplifiers 103 and 104.

[0024] Furthermore, the control unit 110 can measure the span loss of the optical transmission path T1 based on the optical power of the optical pulse output from the optical transmission device 100 to the optical transmission path T1 and the optical power of the reflected pulse of that optical pulse. Alternatively, the span loss of the optical transmission path T1 may be pre-configured without measurement. The control unit 110 then acquires configuration information, including the span loss of the optical transmission path T1, from the user interface 111 at the start of the optical transmission device 100, which is before the operation of the optical transmission system ST begins. In other words, the control unit 110 acquires the configuration information before communication of the WDM signal optical signals Lw1 and Lw2 begins. If the control unit 110 determines that the span loss is excessive based on the configuration information, it switches the startup mode based on the startup mode setting from the user via the user interface 111. Specifically, the control unit 110 determines that the span loss is excessive if the span loss 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.

[0025] Next, the optical transmission device 200 will be described. The optical transmission device 200 includes an OSC input / output unit 202 and optical amplifiers 203 and 204. The optical transmission device 200 also includes an ASE light source 205, a WDM coupler 208, a branch coupler 209, and a control unit 210. Furthermore, the optical transmission device 200 includes a user interface 211, optical transmission units 212 and 213, and optical reception units 214 and 215.

[0026] The optical amplifier 203, WDM coupler 208, optical transmitter 212, and optical receiver 215 are located on the optical waveguide 216 of the optical transmission device 200. The optical amplifier 204, branch coupler 209, optical transmitter 213, and optical receiver 214 are located on the optical waveguide 217 of the optical transmission device 200.

[0027] Thus, the optical transmission device 200 has basically the same configuration as the optical transmission device 100. For this reason, the details of the optical transmission device 200 are omitted. For example, the OSC input / output unit 202 outputs OSC light Lo2 directed to the optical transmission device 100. The ASE light source 205 outputs pseudo-light Pw2 that includes wavelength bands of the WDM signal light Lw2, such as the C-band and L-band. The optical transmission unit 212 transmits combined light Mx2, obtained by combining the OSC light Lo2 and the pseudo-light Pw2, toward the optical transmission device 100. As a result, the combined light Mx2 propagates through the optical transmission path T2.

[0028] The operation of the optical transmission system ST according to the first embodiment will be described with reference to Figures 2 to 6. 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 described as necessary.

[0029] When the user provides predetermined setting information to the optical transmission device 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 T1 and the transmission path length of the optical transmission path T1. Before processing in step S1, as described above, 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 transmission device 100 to the optical transmission path T1 and the optical power of the reflected pulse of that optical pulse. After verifying the setting information, the control unit 110 determines, based on the setting information, whether the optical transmission path T1 is in a span loss excess section (indicated as SL excess section in Figure 2) or not (step S2).

[0030] If the optical transmission path T1 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).

[0031] As a result, the OSC input / output unit 102 outputs OSC optical Lo1 at maximum optical power (specifically, around a few dBm). Therefore, as shown in Figure 3(a), the optical transmission device 100 including the OSC input / output unit 102 outputs OSC optical Lo1 at maximum optical power. Similarly, the OSC input / output unit 202 outputs OSC optical Lo2 at maximum optical power. Therefore, as shown in Figure 3(a), the optical transmission device 200 including the OSC input / output unit 202 outputs OSC optical Lo2 at maximum optical power.

[0032] However, the optical transmission path T1 corresponds to a section with excessive span loss. Therefore, even if OSC optical Lo1 is output at maximum optical power, the insufficient optical power prevents OSC optical Lo1 from reaching the optical transmission device 200 on its own. As a result, OSC optical Lo1 becomes inoperable. OSC optical Lo2 also becomes inoperable for the same reason as OSC optical Lo1.

[0033] When the OSC light Lo1 is output at maximum optical power, the control unit 110 monitors the return light (step S5), as shown in Figure 2. For example, as shown in Figure 3(b), when a transmission path break occurs in the optical transmission path T1, the return light Lr1 of the OSC light Lo1 is input to the optical transmission device 100 due to Fresnel reflection at the location of the transmission path break. More specifically, the return light Lr1 is input to the OSC input / output unit 102 included in the optical transmission device 100.

[0034] The control unit 110 monitors the OSC input / output unit 102 and determines whether or not the return light Lr1 is input to the OSC input / output unit 102. If the return light Lr1 is input to the OSC input / output unit 102, the control unit 110 measures the optical power of the return light Lr1 and determines that a transmission path break has occurred in the optical transmission path T1 if the optical power is above a threshold. When the control unit 110 determines that a transmission path break has occurred, it requests the optical amplifier 103 to cancel the shutdown release. As a result, the optical amplifier 103 remains in the shutdown state.

[0035] As a result, the optical amplifier 103 can block the transmission of the pseudo-light Pw1. Therefore, no combined light Mx1 containing the pseudo-light Pw1 is generated, and the OSC light Lo1 is output from the optical transmission device 100 alone. In this way, the control unit 110 detects a break in the optical transmission path T1 based on a first detection method that detects an optical power above a threshold of the return light Lr1 of the OSC light Lo1.

[0036] Here, the optical power of OSC optical Lo1 is smaller than the optical power of combined optical Mx1. This is because combined optical Mx1 includes not only OSC optical Lo1 but also pseudo-optical Pw1. Even if OSC optical Lo1 is output to the optical transmission path T1 at maximum optical power, its optical power is small, thus improving safety during the recovery operation of the optical transmission path T1 compared to when combined optical Mx1 is output from the optical transmission device 100. In this way, the recovery operation is carried out safely by blocking the output of pseudo-optical Pw1. The control unit 110 may also stop the output of OSC optical Lo1 from the optical transmission device 100 if it detects a transmission path break in the optical transmission path T1.

[0037] Meanwhile, the control unit 110 monitors the reflected light Lr1, and if the reflected light Lr1 is not input to the OSC input / output unit 102, it instructs the output of the pseudo-light Pw1 (step S6), as shown in Figure 2, and requests the release of the shutdown (indicated as SD in Figure 2) of the optical amplifier 103 (step S7). As a result, the ASE light source 105 outputs the pseudo-light Pw1, and the optical amplifier 103 allows the transmission of the pseudo-light Pw1.

[0038] As a result, a combined light Mx1 containing pseudo-light Pw1 is generated, and the combined light Mx1 is output from the optical transmission device 100. For example, as shown in Figure 3(b), if no transmission path break occurs in the optical transmission path T2, no return light is generated, and the combined light Mx2 is output from the optical transmission device 200.

[0039] Even if the optical transmission path T2 corresponds to a section with excessive span loss, the optical power of the combined light Mx2 is greater than the optical power of the OSC light Lo2 alone, so the combined light Mx2 propagates through the optical transmission path T2. As a result, the OSC light Lo2 included in the combined light Mx2 reaches the optical transmission device 100. In other words, communication of OSC light Lo1 is unavailable in the optical transmission path T1, while communication of OSC light Lo2 is available in the optical transmission path T2. To put it another way, one-way communication representing communication of either OSC light Lo1 or Lo2 is established.

[0040] Here, as shown in Figure 2, the control unit 101 waits until OSC optical Lo1 and Lo2 are in communication (step S8: NO). In other words, the control unit 101 waits until communication between OSC optical Lo1 and Lo2 is established on both optical transmission paths T1 and T2. To put it another way, the control unit 101 waits until communication representing bidirectional communication between OSC optical Lo1 and Lo2 is established.

[0041] For example, once the restoration of the optical transmission path T1 is complete, no return light Lr1 is generated, and as shown in Figure 3(c), the combined light Mx1 is output from the optical transmission device 100. Once the combined light Mx1 is output, it propagates along the optical transmission path T1. As a result, the OSC light Lo1 contained in the combined light Mx1 reaches the optical transmission device 200. When the OSC light Lo1 reaches the optical transmission device 200, the OSC lights Lo1 and Lo2 communicate (Step S8: YES).

[0042] As will be explained in more detail later, when the combined wave light Mx1 propagates through the optical transmission path T1, stimulated Raman scattering occurs, and the optical power of the pseudo-light Pw1 contained in the combined wave light Mx1 is transferred to the OSC light Lo1. This is because the wavelength of the OSC light Lo1 is longer than that of the pseudo-light Pw1. As a result, the optical power of the OSC light Lo1 increases, and even if the optical transmission path T1 corresponds to a section with excessive span loss, the OSC light Lo1 can reach the optical transmission device 200 from the optical transmission device 100.

[0043] Here, with OSC optical Lo1 and Lo2 communicating, if a transmission break occurs in the optical transmission path T1, as shown in Figure 3(d), the combined optical wave Mx1 may be radiated from the optical transmission path T1 at the location where the transmission break occurred. In particular, if the transmission break occurs inside the station building where the optical transmission device 100 is installed, the optical power of the combined optical wave Mx1 may be greater than if the transmission break occurs outside the station building. This is because the optical power of the combined optical wave Mx1 attenuates as it moves away from the station building.

[0044] Thus, when a transmission break occurs in the optical transmission path T1 while the OSC optical signals Lo1 and Lo2 are communicating, the return light Lr2 of the combined optical signal Mx1 is input to the optical transmission device 100 due to Fresnel reflection at the location of the transmission break. More specifically, the return light Lr2 is input to the OSC input / output unit 102 included in the optical transmission device 100.

[0045] Here, the reflected light Lr2 includes not only the reflected light Lr1 of the OSC light Lo1, but also the noise light caused by the pseudo-light Pw1. As will be explained in more detail later, when the OSC light Lo1 is not output at its maximum optical power, the optical power of the reflected light Lr1 decreases compared to when the OSC light Lo1 is output at its maximum optical power. As a result, the optical power of the reflected light Lr1 becomes relatively smaller compared to the optical power of the noise light.

[0046] In this case, the control unit 110 may incorrectly determine whether a transmission line break has occurred based on the optical power of the noise light, even if the return light Lr1 does not have an optical power above the threshold. To avoid such an incorrect determination, the OSC light Lo1 is output at its maximum optical power. This allows the control unit 110 to detect the occurrence of a transmission line break based on the return light Lr1 having an optical power above the threshold. When the control unit 110 detects the occurrence of a transmission line break, it instructs the ASE light source 105 to stop outputting the pseudo-light Pw1 and requests the optical amplifier 103 to shut down. As a result, the ASE light source 105 stops outputting the pseudo-light Pw1 and the optical amplifier 103 shuts down.

[0047] As a result, although OSC optical Lo1 is output from the optical transmission device 100 alone, its optical power is small, thus ensuring greater safety during the restoration of the optical transmission path T1 compared to when combined optical Mx1 is output from the optical transmission device 100. In other words, the restoration work is carried out safely. As mentioned above, the control unit 110 may also stop the output of OSC optical Lo1.

[0048] Returning to Figure 2, once OSC optical Lo1 and Lo2 are in communication, the control unit 110 waits until its own path comes up (step S9: NO). That is, the control unit 110 waits until its own path, optical transmission path T1, comes up. Similarly, the control unit 210 waits until its own path, optical transmission path T2, comes up.

[0049] When the path starts up (step S9: YES), the control unit 110 adjusts the gain of the optical amplifiers 103 and 104 (step S10). More specifically, the control unit 110 adjusts the gain of the optical amplifiers 103 and 104 based on the span loss of the optical transmission paths T1 and T2. This adjusts the gain of the optical amplifiers 103 and 104 to a level suitable for transmitting WDM signal light Lw1 and Lw2. As described above, the control unit 110 can measure the span loss of the optical transmission path T1 based on the optical power of the optical pulse output from the optical transmission device 100 to the optical transmission path T1 and the optical power of the reflected pulse of that optical pulse.

[0050] When the gains of optical amplifiers 103 and 104 are adjusted, the control unit 110 switches the output from the optical transmission device 100 (step S11), and the control unit 210 monitors the OSC light, etc., until it detects a loss of light (LOL) (steps S12, S13: NO). Specifically, as shown in Figure 3(e), if no transmission path break occurs and the combined light Mx1 is output from the optical transmission device 100, the control unit 110 switches the output of the combined light Mx1 to the output of the WDM signal light Lw1, as shown in Figure 3(f). The control unit 210 also switches the output of the combined light Mx2 to the output of the WDM signal light Lw2, similar to the control unit 110.

[0051] When the control unit 110 switches the output of the combined wave light Mx1 to the output of the WDM signal light Lw1, it switches from the first detection method to the second detection method, as shown in Figure 4(a). Unlike the first detection method, the second detection method is a method in which the control unit 210 monitors the OSC light Lo1 and the WDM signal light Lw1, and detects a transmission break in the optical transmission path T1 when it detects an optical outage in either or both of the OSC light Lo1 and the WDM signal light Lw1. An optical outage corresponds to a state where the optical power is below a reference value, or a state in which neither the OSC light Lo1 nor the WDM signal light Lw1 is detected at all. The second detection method also includes a method in which the control unit 110 monitors the OSC light Lo2 and the WDM signal light Lw2, and detects a transmission break in the optical transmission path T2 when it detects an optical outage in either or both of the OSC light Lo2 and the WDM signal light Lw2.

[0052] When the control unit 110 switches from the first detection method to the second detection method, it reduces the optical power of OSC light Lo1 to an optical power level that suppresses the occurrence of XPM (Cross Phase Modulation) between OSC light Lo1 and WDM signal light Lw1. As a result, the optical power of OSC light Lo1 is reduced to an optical power level lower than the maximum optical power.

[0053] If the optical power of OSC optical Lo1 is maintained at its maximum optical power, and the optical power of OSC optical Lo1 is as high as, for example, its maximum optical power as shown in Figure 5, then XPM may occur between OSC optical Lo1 and WDM signal optical Lw1 due to power changes caused by the on and off states of OSC optical Lo1, potentially causing transmission errors in WDM signal optical Lw1.

[0054] Therefore, when the control unit 110 switches from the first detection method to the second detection method, it reduces the optical power of the OSC optical Lo1, as shown in Figure 6. This suppresses the generation of XPM and avoids signal errors in the WDM signal optical Lw1 caused by the OSC optical Lo1. In this way, adverse effects (such as transmission errors) caused by nonlinear effects such as XPM originating from the OSC optical Lo1 are suppressed.

[0055] As shown in Figures 5 and 6, the wavelength λ8 of OSC light Lo1 is longer than the longest wavelength λ7 of pseudo-light Pw1. Therefore, as described above, when the combined light Mx1 propagates through the optical transmission path T1, stimulated Raman scattering occurs, and the optical power of pseudo-light Pw1 contained in the combined light Mx1 is transferred to OSC light Lo1, increasing the optical power of OSC light Lo1.

[0056] Returning to Figure 2, when the control unit 210 detects an optical interruption such as OSC light (step S13: YES), the control unit 110 executes the process in step S5 again. For example, as shown in Figure 4(b), when a transmission path interruption occurs in the optical transmission path T1, the control unit 210 detects the transmission path interruption of the optical transmission path T1 by detecting an optical interruption of the WDM signal light Lw1.

[0057] More specifically, when a transmission path interruption occurs in the optical transmission path T1, the control unit 210 detects an optical interruption of the WDM signal light Lw1. The control unit 210 may also detect an optical interruption of the OSC light Lo1. Upon detecting an optical interruption, the control unit 210 requests the OSC input / output unit 202 to output OSC light Lo2, which includes an instruction to shut down the optical amplifier 103 of the optical transmission device 100. As a result, as shown in Figure 4(c), the OSC input / output unit 202 outputs OSC light Lo2, which includes an instruction to shut down the optical amplifier 103. Consequently, the optical amplifier 103 shuts down. After the OSC input / output unit 202 outputs OSC light Lo2, the control unit 210 waits for a predetermined time before shutting down the optical amplifier 203. The predetermined time is set to, for example, enough time for the instruction to shut down the optical amplifier 103 to be reliably transmitted to the optical transmission device 100.

[0058] Note that optical amplifiers 103 and 203 may be shut down using a method different from this one. For example, when the control unit 210 detects an optical failure in OSC optical Lo1, it notifies the optical transmission device 100 of the optical failure in OSC optical Lo1 based on FEFI (Far End Fault Indication). FEFI is a protocol that, when either OSC optical Lo1 or Lo2 experiences an optical failure, uses the other of OSC optical Lo1 or Lo2 to notify the opposing device of the optical failure. As shown in Figure 4(c), the control unit 210 notifies the optical failure of OSC optical Lo1 via OSC optical Lo2, and then shuts down optical amplifier 203. When the control unit 210 shuts down optical amplifier 203, the input of WDM signal light Lw2 to optical amplifier 104 stops. This allows the control unit 110 to detect an optical failure in WDM signal light Lw2. Based on the notification of the optical failure of OSC optical Lo1 and the detection of the optical failure of WDM signal light Lw2, the control unit 110 shuts down optical amplifier 103.

[0059] Subsequently, the control unit 110 executes the process of step S5 again, and as shown in Figure 4(d), the control unit 110 switches the second detection method back to the first detection method and returns the optical power of OSC optical Lo1 to its maximum optical power. Since the output of the WDM signal optical Lw1 was stopped while it was being output, the OSC optical Lo1 is output from the optical transmission device 100 on its own. Therefore, if a transmission break occurs in the optical transmission path T1, the return optical light Lr1 is input to the optical transmission device 100.

[0060] Returning to Figure 2, in the process of step S2, if the optical transmission path T1 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 S14). If it is not in a span loss excessive section, the OSC input / output unit 102 may output OSC optical Lo1 with maximum optical power, or it may output OSC optical Lo1 with optical power less than the maximum optical power. Since it is not in a span loss excessive section, OSC optical Lo1 can reach optical transmission device 200 from optical transmission device 100.

[0061] When OSC optical Lo1 is output, the control unit 210 monitors the OSC optical signal, etc. (step S15). That is, the control unit 210 monitors the OSC optical Lo1 and the WDM signal optical Lw1 and determines whether or not a transmission path break has occurred based on the second detection method described above. After monitoring the OSC optical signal, etc., the control unit 110 adjusts the gain of the optical amplifiers 103 and 104 (step S16). More specifically, the control unit 110 adjusts the gain of the optical amplifiers 103 and 104 based on the span loss of the optical transmission path T1.

[0062] 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 T1 based on the attenuation of the optical power of OSC optical Lo1 output from the optical transmission device 100 to the optical transmission path T1. The attenuation of the optical power of OSC optical Lo1 is communicated to the optical transmission device 100 via OSC optical Lo2 output from the optical transmission device 200.

[0063] When the gains of the optical amplifiers 103 and 104 are adjusted, the control unit 110 switches the output from the optical transmission device 100 (step S17), and the control unit 210 waits until it detects an optical interruption such as OSC light (step S18: NO). Then, when the control unit 210 detects an optical interruption such as OSC light (step S18: YES), the control unit 110 executes the process in step S16 again.

[0064] Thus, according to the first embodiment, if a transmission outage occurs in the optical transmission path T1 before the OSC optical Lo1 and Lo2 communicate between the optical transmission devices 100 and 200, for example, the output of the pseudo-optical Pw1 from the optical transmission device 100 is stopped based on the return light Lr1 of the OSC optical Lo1. This ensures safety when restoring the optical transmission path T1. Furthermore, if a transmission outage occurs in the optical transmission path T2, the output of the pseudo-optical Pw2 from the optical transmission device 200 is stopped based on the return light (not shown) of the OSC optical Lo2. This ensures safety when restoring the optical transmission path T2.

[0065] (Second Embodiment) The second embodiment of this invention will be described with reference to Figures 7 to 10. Note that the same reference numerals are used for components and processes similar to those described in the optical transmission devices 100 and 200 in the first embodiment, and their detailed descriptions are omitted.

[0066] First, as shown in Figure 7, the optical transmission device 100 includes a back-excited Raman amplifier (indicated as BWD Raman in Figure 7) 120. The back-excited Raman amplifier 120 is connected to the optical waveguide 117 via a WDM coupler 121. The optical transmission device 200 also includes a back-excited Raman amplifier 220. The back-excited Raman amplifier 220 is connected to the optical waveguide 217 via a WDM coupler 221. Note that the back-excited Raman amplifiers 120 and 220 are examples of back-excited light sources.

[0067] The back-excited Raman amplifier 120 outputs back-excited light Pb1. The back-excited light Pb1 propagates along the optical transmission path T2 in the opposite direction to the direction in which the combined light Mx2 and WDM signal light Lw2 propagate along the optical transmission path T2. In the optical transmission path T2, the back-excited light Pb1 Raman-amplifies the combined light Mx2 using stimulated Raman scattering. As a result, the optical power of the OSC light Lo2 included in the combined light Mx2 is further increased compared to when the pseudo-light Pw2 is used alone.

[0068] Similarly, the back-excited Raman amplifier 220 outputs back-excited light Pb2. The back-excited light Pb2 propagates along the optical transmission path T1 in the opposite direction to the direction in which the combined light Mx1 and WDM signal light Lw1 propagate along the optical transmission path T1. In the optical transmission path T1, the back-excited light Pb2 Raman-amplifies the combined light Mx1 using stimulated Raman scattering. As a result, the optical power of the OSC light Lo1 included in the combined light Mx1 is further increased compared to when the pseudo-light Pw1 is used alone.

[0069] The operation of the optical transmission device 100 will now be described. Note that the operation of the optical transmission device 200 is basically the same as that of the optical transmission device 100, so a detailed explanation will be omitted. As shown in Figure 8, the control unit 110, after the processing of step S6 described in the first embodiment and before the processing of step S7, instructs the back-excited Raman amplifier 120 to output the back-excited light Pb1 (step S21). As a result, the back-excited Raman amplifier 120 outputs the back-excited light Pb1.

[0070] Furthermore, the control unit 110 adjusts the gain of the back-pumped Raman amplifier 120 after the processing of step S9 described in the first embodiment and before the processing of step S10 (step S22). For example, the control unit 110 adjusts the gain of the back-pumped Raman amplifier 120 based on the span loss of the optical transmission path T2, which is communicated using the OSC optical Lo2. Similarly, the control unit 210 can adjust the gain of the back-pumped Raman amplifier 220 based on the span loss of the optical transmission path T1, which is communicated using the OSC optical Lo1.

[0071] Furthermore, the control unit 110 adjusts the gain of the back-excited Raman amplifier 120 after the processing of step S15 described in the first embodiment and before the processing of step S16 (step S23). Similarly, the control unit 210 can adjust the gain of the back-excited Raman amplifier 220.

[0072] In the second embodiment, as shown in Figures 9 and 10, when the combined light Mx1 propagates through the optical transmission path T1, stimulated Raman scattering occurs, and the optical power of the pseudo-light Pw1 contained in the combined light Mx1 is transferred to the OSC light Lo1. This increases the optical power of the OSC light Lo1. In the second embodiment, stimulated Raman scattering based on the back-excited light Pb1 also occurs, increasing the optical power of the OSC light Lo1. When the control unit 110 switches the output of the combined light Mx1 to the output of the WDM signal light Lw1 and switches from the first detection method to the second detection method, the optical power of the OSC light Lo1 is reduced, as shown in Figures 9 and 10. This suppresses the generation of XPM, similar to the first embodiment.

[0073] Thus, according to the second embodiment, the optical transmission device 100 is equipped with a back-excited Raman amplifier 120. As a result, the optical power of OSC light Lo2 is further improved compared to when pseudo-light Pw2 is used alone. Similarly, the optical transmission device 200 is equipped with a back-excited Raman amplifier 220. As a result, the optical power of OSC light Lo1 is further improved compared to when pseudo-light Pw1 is used alone. In other words, OSC light Lo1 and Lo2 can enjoy not only the effect of stimulated Raman scattering from pseudo-light Pw1 and Pw2, but also the effect of stimulated Raman scattering from back-excited light Pb1 and Pb2, which includes a wavelength band from the lowest wavelength λ2 to the longest wavelength λ3.

[0074] (Third embodiment) A third embodiment of this invention will be described with reference to Figures 11 and 12. First, as shown in Figure 11, the optical transmission device 100 according to the third embodiment differs from the optical transmission device 100 according to the second embodiment. Specifically, the optical transmission device 100 according to the third embodiment further includes a forward-excited Raman amplifier (indicated as FWD Raman in Figure 11) 130. The forward-excited Raman amplifier 130 is connected to the optical waveguide 116 via a WDM coupler 131.

[0075] Furthermore, the optical transmission device 200 according to the third embodiment differs from the optical transmission device 200 according to the second embodiment. Specifically, the optical transmission device 200 according to the third embodiment further includes a forward-excited Raman amplifier 230. The forward-excited Raman amplifier 230 is connected to the optical waveguide 216 via a WDM coupler 231. Note that the forward-excited Raman amplifiers 130 and 230 are examples of forward-excited light sources.

[0076] The forward-excited Raman amplifier 130 outputs forward-excited light Pf1. The forward-excited light Pf1 propagates along the optical transmission path T1 in the same direction as the multiplexed light Mx1 and the WDM signal light Lw1 propagate along the optical transmission path T1. In the optical transmission path T1, the forward-excited light Pf1 Raman-amplifies the multiplexed light Mx1 using stimulated Raman scattering. As a result, the intensity of the OSC light Lo1 contained in the multiplexed light Mx1 is further improved compared to when pseudo-light Pw1 and back-excited light Pb2 are used in combination.

[0077] Similarly, the forward-excited Raman amplifier 230 outputs forward-excited light Pf2. The forward-excited light Pf2 propagates along the optical transmission path T2 in the same direction as the combined light Mx2 and the WDM signal light Lw2 propagate along the optical transmission path T2. In the optical transmission path T2, the forward-excited light Pf2 Raman-amplifies the combined light Mx2 using stimulated Raman scattering. As a result, the intensity of the OSC light Lo2 belonging to the combined light Mx2 is further improved compared to when pseudo-light Pw2 and back-excited light Pb1 are used in combination.

[0078] The operation of the optical transmission device 100 will now be described. Note that the operation of the optical transmission device 200 is basically the same as that of the optical transmission device 100, so a detailed explanation will be omitted. As shown in Figure 12, the control unit 110, after the processing of step S21 described in the second embodiment and before the processing of step S7, instructs the forward-excited Raman amplifier 130 to output the forward-excited light Pf1 (step S31). As a result, the forward-excited Raman amplifier 130 outputs the forward-excited light Pf1.

[0079] Furthermore, the control unit 110 adjusts the gain of the forward-excited Raman amplifier 130 after the processing of step S22 described in the second embodiment and before the processing of step S10 (step S32). For example, the control unit 110 adjusts the gain of the forward-excited Raman amplifier 130 based on the span loss of the optical transmission path T1, which is communicated using the OSC optical Lo2. Similarly, the control unit 210 adjusts the gain of the forward-excited Raman amplifier 230 based on the span loss of the optical transmission path T2, which is communicated using the OSC optical Lo1.

[0080] Furthermore, the control unit 110 adjusts the gain of the forward-excited Raman amplifier 130 after the processing of step S23 described in the second embodiment and before the processing of step S16 (step S33). Similarly, the control unit 210 adjusts the gain of the forward-excited Raman amplifier 230.

[0081] Thus, according to the third embodiment, the optical transmission device 100 is equipped with a forward-excited Raman amplifier 130. As a result, the optical power of OSC light Lo1 is further improved compared to when pseudo-light Pw1 and back-excited light Pb2 are used in combination. Similarly, the optical transmission device 200 is equipped with a forward-excited Raman amplifier 230. As a result, the optical power of OSC light Lo2 is further improved compared to when pseudo-light Pw2 and back-excited light Pb1 are used in combination. In other words, OSC light Lo1 and Lo2 can enjoy not only the effect of stimulated Raman scattering from pseudo-light Pw1 and Pw2 and back-excited light Pb1 and Pb2, but also the effect of stimulated Raman scattering from forward-excited light Pf1 and Pf2, which includes a wavelength band from the lowest wavelength λ2 to the longest wavelength λ3.

[0082] Although preferred embodiments of the present invention have been described in detail above, the 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. For example, the optical transmission devices 100 and 200 may include an ILA (In-Line Amplifier) ​​instead of a ROADM. Furthermore, in the embodiments described above, the use of both back-excited Raman amplifiers 120 and 220, and the use of all back-excited Raman amplifiers 120 and 220 and forward-excited Raman amplifiers 130 and 230 were described as examples, but the invention is not limited to such uses. For example, both forward-excited Raman amplifiers 130 and 230 may be used without using back-excited Raman amplifiers 120 and 220.

[0083] Furthermore, the following additional information is disclosed regarding the above explanation. (Note 1) An optical transmission system comprising a first optical transmission device that transmits OSC light to an optical transmission path and a second optical transmission device that receives the OSC light from the optical transmission path, wherein the first optical transmission device has a first control unit that detects a transmission path interruption before the OSC light is transmitted in the optical transmission path based on a first detection method, and the second optical transmission device has a second control unit that detects a transmission path interruption after the OSC light is transmitted in the optical transmission path based on a second detection method different from the first detection method. (Note 2) The optical transmission system according to Note 1, characterized in that the first detection method detects the transmission path disconnection before communication in accordance with the reflected light that returns due to the reflection of the OSC light. (Note 3) The optical transmission system according to Note 1 or 2, characterized in that the second detection method detects the transmission path break after communication in response to either the OSC light or the signal light transmitted from the first optical transmission device to the second optical transmission device. (Note 4) The optical transmission system according to Note 1 or 2, characterized in that the first control unit reduces the optical power of the OSC light after the OSC light has been transmitted. (Note 5) The optical transmission system according to Note 4, characterized in that the wavelength of the OSC light is longer than the wavelength of the signal light. (Note 6) The optical transmission system according to Note 1 or 2, wherein the first optical transmission device further comprises a pseudo-light source that outputs pseudo-light which increases the optical power of the OSC light based on the occurrence of stimulated Raman scattering in the optical transmission path, and the first control unit instructs the pseudo-light source to output the pseudo-light when it does not detect a transmission path break before communication. (Note 7) The optical transmission system according to Note 6, characterized in that the wavelength of the OSC light is longer than the wavelength of the pseudo-light. (Note 8) The optical transmission system according to Note 1 or 2, wherein the second optical transmission device 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, and the second control unit instructs the back excitation light source to output the back excitation light if it does not detect a transmission path disconnection before communication. (Note 9) The optical transmission system according to Note 1 or 2, wherein the first optical transmission device 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, and the first control unit instructs the forward excitation light source to output the forward excitation light if it does not detect a transmission path break before communication. (Note 10) The optical transmission system according to Note 1 or 2, characterized in that the first optical transmission device is connected to one end of the optical transmission path, and the second optical transmission device is connected to the other end of the optical transmission path. (Note 11) The optical transmission system according to Note 1 or 2, characterized in that the first control unit checks the setting information and, before the OSC light is transmitted, selects either a control to output the OSC light at a first optical power or a control to output the OSC light at a second optical power lower than the first optical power, based on the setting information. (Note 12) An optical transmission device comprising: an optical transmitting unit that transmits OSC light to a first optical transmission path; an optical receiving unit that receives light from the second optical transmission path that propagates in a second direction opposite to the first direction in which the OSC light propagates in the first optical transmission path; and a control unit that detects a transmission path break, wherein the control unit detects a transmission path break in accordance with the reflected light that returns due to the reflection of the OSC light before the OSC light is transmitted, and detects a transmission path break in accordance with the light received by the optical receiving unit after the OSC light is transmitted. [Explanation of Symbols]

[0084] ST Optical Transmission Systems 100,200 Optical transmission devices 102,202 OSC input / output section 105,205 ASE light source 110,210 Control Unit 112,113,212,213 Optical Transmitter 114,115,214,215 Optical receiving section 120,220 Back-Pumped Raman Amplifier 130,230 forward-excited Raman amplifier

Claims

1. An optical transmission system comprising a first optical transmission device that transmits OSC (Optical Supervisory Channel) light to an optical transmission path, and a second optical transmission device that receives the OSC light from the optical transmission path, The first optical transmission device is The optical transmission path has a first control unit that detects a transmission path break in the optical transmission path before the OSC light is transmitted, based on a first detection method. The second optical transmission device is The system has a second control unit that detects a transmission path break in the optical transmission path after the OSC light has been transmitted, based on a second detection method different from the first detection method. An optical transmission system characterized by the following:

2. The first detection method detects the transmission path disconnection before communication in accordance with the return light that comes back due to the reflection of the OSC light. The optical transmission system according to feature 1.

3. The second detection method detects the transmission path break after communication in response to either the OSC light or the signal light transmitted from the first optical transmission device to the second optical transmission device. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

4. The first control unit reduces the optical power of the OSC light after the OSC light has been transmitted. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

5. The first optical transmission device further includes a pseudo-light source that outputs pseudo-light that increases the optical power of the OSC light based on the occurrence of stimulated Raman scattering in the optical transmission path, If the first control unit does not detect a transmission path disconnection before communication, it instructs the pseudo-light source to output the pseudo-light. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

6. The second optical transmission device 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. If the second control unit does not detect a transmission path disconnection before communication, it instructs the rear excitation light source to output the rear excitation light. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

7. The first optical transmission device 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. If the first control unit does not detect a transmission path disconnection before communication, it instructs the forward excitation light source to output the forward excitation light. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

8. An optical transmission unit that transmits OSC (Optical Supervisory Channel) light to the first optical transmission path, An optical receiving unit that receives light from the second optical transmission path that propagates in the second optical transmission path in a second direction opposite to the first direction in which the OSC light propagates in the first optical transmission path, It has a control unit that detects transmission line breaks, The control unit, Before the OSC light is transmitted, the transmission path disconnection is detected in accordance with the return light that comes back due to the reflection of the OSC light. After the OSC light has been transmitted, the light receiving unit detects the transmission path break in accordance with the light it has received. An optical transmission device characterized by the following features.

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