Optical transmission systems and optical transmission devices

Abstract

The objective is to provide an optical transmission system and optical transmission device that improves the intensity of OSC (Optical Supervisory Channel) light. [Solution] The optical transmission system includes a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, wherein the first optical transmission device has a first optical output unit that outputs first OSC light, a first pseudo-light source that outputs first pseudo-light including the wavelength band of first signal light, and a first transmitting unit that transmits first combined light obtained by combining the first OSC light and the first pseudo-light toward the second optical transmission device, and the second optical transmission device has a second optical output unit that outputs second OSC light, a second pseudo-light source that outputs second pseudo-light including the wavelength band of second signal light, and a second transmitting unit that transmits second combined light obtained by combining the second OSC light and the second pseudo-light toward the first optical transmission device.

Description

Technical Field

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

Background Art

[0002] An optical transmission system for transmitting a WDM (Wavelength Division Multiplexing) signal light including a plurality of optical signals with different wavelengths is known. Also, an optical transmission system that amplifies and relays the 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 transmission device and an optical reception device. The optical transmission device and the optical reception device actually have the same functions as each other as a single optical transmission device. For example, the optical transmission device is provided with an optical amplifier that amplifies and outputs the signal light. In addition, in the optical transmission system, an optical monitoring signal called an OSC (Optical Supervisory Channel) is used for operation settings, status monitoring, etc. (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] Here, the output level of the optical amplifier installed in the optical transmission device is determined at startup based on the loss value of the optical transmission path interposed between the opposing optical transmission devices. The loss value of the optical transmission path is communicated from one optical transmission device to the other by the aforementioned optical monitoring signal (hereinafter referred to as OSC light). This allows the optical transmission device to determine the output level of the optical amplifier. For this reason, at least OSC light communication is required between the optical transmission devices at startup.

[0006] However, if the loss value of the optical transmission path is excessive, depending on the intensity of the OSC light, communication of OSC light between optical transmission devices may become difficult. In this case, the optical transmission devices may not be able to confirm the communication of OSC light.

[0007] Therefore, one objective is to provide an optical transmission system and optical transmission device that improve the intensity of OSC light. [Means for solving the problem]

[0008] In one embodiment, the optical transmission system includes a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, wherein the first optical transmission device includes a first optical output unit that outputs first OSC light, a first pseudo-light source that outputs first pseudo-light including the wavelength band of a first signal light, and a first transmitting unit that transmits first combined light obtained by combining the first OSC light and the first pseudo-light toward the second optical transmission device, and the second optical transmission device includes a second optical output unit that outputs second OSC light, a second pseudo-light source that outputs second pseudo-light including the wavelength band of a second signal light, and a second transmitting unit that transmits second combined light obtained by combining the second OSC light and the second pseudo-light toward the first optical transmission device. [Effects of the Invention]

[0009] The intensity of OSC light can be improved. [Brief explanation of the drawing]

[0010] [Figure 1]An example of an optical transmission system according to the first embodiment. [Figure 2] A flowchart showing an example of the operation of an optical transmission device according to the first embodiment. [Figure 3] A diagram for explaining an example of improving the intensity of OSC light. [Figure 4] A diagram for explaining an example of OSC link-up. [Figure 5] An example of an optical transmission system according to the second embodiment. [Figure 6] A flowchart showing an example of the operation of an optical transmission device according to the second embodiment. [Figure 7] A diagram for explaining another example of improving the intensity of OSC light. [Figure 8] An example of an optical transmission system according to the third embodiment. [Figure 9] A flowchart showing an example of the operation of an optical transmission device according to the third embodiment. [Figure 10] An example of an optical transmission system according to the fourth embodiment. [Figure 11] A flowchart showing an example of the operation of an optical transmission device according to the fourth embodiment. [Figure 12] A flowchart showing an example of the operation of an optical relay device according to the fourth embodiment. [Figure 13] (a) is a diagram for explaining a comparative example. (b) is a diagram for explaining an example. [Figure 14] An example of an optical transmission system according to the fifth embodiment. [Figure 15] A flowchart showing an example of the operation of an optical transmission device according to the fifth embodiment. [Figure 16] A flowchart showing an example of the operation of an optical relay device according to the fifth embodiment. [Figure 17] An example of an optical transmission system according to the sixth embodiment. [Figure 18] A flowchart showing an example of the operation of an optical transmission device according to the sixth embodiment. [Figure 19]It is a flowchart showing an example of the operation of the optical relay device according to the sixth embodiment.

Mode for Carrying Out the Invention

[0011] Hereinafter, the mode for carrying out the present case will be described 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. 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 OTDR (Optical Time Domain Reflectometer) 101, an OSC input / output unit 102, and optical amplifiers 103 and 104. The OTDR 101 is an example of a pulse transmission / reception unit. The OSC input / output unit 102 is an example of a first optical output unit.

[0015] Furthermore, the optical transmission device 100 includes an ASE (Amplified Spontaneous Emission) light source 105, WDM couplers 106, 107, 108, a branch coupler 109, and a control unit (labeled CTRL in Figure 1) 110. The ASE light source 105 is an example of a first pseudo-light source. In addition, the optical transmission device 100 includes a user interface (labeled USR I / F in Figure 1) 111, optical transmission units 112, 113, and optical reception units 114, 115. Optical transmission unit 112 is an example of a first transmission unit. Optical reception unit 114 is an example of a first optical reception unit. The optical transmission units 112, 113 and the optical reception units 114, 115 each include connectors.

[0016] The optical amplifier 103, WDM couplers 106 and 108, optical transmitter 112, and optical receiver 115 are located on the optical waveguide 116 of the optical transmission device 100. The optical amplifier 104, WDM coupler 107, branch coupler 109, optical transmitter 113, and optical receiver 114 are located on the optical waveguide 117 of the optical transmission device 100.

[0017] OTDR101 is optically connected to WDM couplers 106 and 107. OTDR101 transmits optical pulses OP to optical transmission lines T1 and T2 via optical waveguides 116 and 117 and receives reflected pulses of those optical pulses OP. By receiving reflected pulses, OTDR101 can generate optical power profiles for optical transmission lines T1 and T2. As will be described in detail later, based on the optical power profiles generated by OTDR101, the magnitude of the loss value of optical transmission line T1 (hereinafter referred to as span loss) and the span loss of optical transmission line T2 are measured, and the location of optical power loss is estimated. Furthermore, based on the span losses of optical transmission lines T1 and T2, the connection status of optical transmission lines T1 and T2, such as connector disconnection, is measured.

[0018] 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 light Lo1, which has an intensity (specifically, optical power) of several dBm, toward the optical transmission device 200. OSC light Lo1 is an example of the first OSC light. By having an intensity of several dBm in OSC light Lo1, the adverse effects on the WDM signal light Lw1 due to nonlinear effects in the optical transmission path T1 are suppressed. OSC light Lo1 may or may not include the span loss of the optical transmission path T1. In addition, OSC light Lo2 output from the optical transmission device 200 is input to the OSC input / output unit 102. OSC light Lo2 may or may not include the span loss of the optical transmission path T2.

[0019] 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. 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. The post-amplifier is an amplifier located after or downstream of a WSS (Wavelength Selective Switch) (not shown) provided 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 transmitter 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 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.

[0021] The ASE light source 105 is 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 1530nm to 1565nm. The L-band is, for example, a wavelength band of 1565nm to 1625nm.

[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 combined optical light Mx1 is an example of the first combined optical light. 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.

[0023] The control unit 110 is electrically connected to the OTDR 101, the OSC input / output unit 102, the optical amplifiers 103 and 104, 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). The control unit 110 controls the operation of the OTDR 101, the OSC input / output unit 102, the optical amplifiers 103 and 104, and the ASE light source 105.

[0024] For example, the control unit 110 can request the OTDR 101 to transmit an optical pulse. The control unit 110 can request the OSC input / output unit 102 to output OSC optical Lo1. The control unit 110 can request 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. In addition, as a measurement unit, the control unit 110 can measure the connection status of the optical transmission lines T1 and T2 and the optical transmission device 100 based on the reflected optical pulses. The control unit 110 can also measure the span loss of the optical transmission line T1 and the optical transmission line T2, the location of optical power loss, etc., based on the optical power profile generated by the OTDR 101.

[0025] Furthermore, the control unit 110 acquires configuration information, including the span loss of the optical transmission path T1, from the user interface 111 when the optical transmission device 100 is started up, before the optical transmission system ST is put into operation. In other words, the control unit 110 acquires the configuration information before the communication of WDM signal optical 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. 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 the normal mode, which does not output pseudo-optical light Pw1, to the extended mode, which outputs pseudo-optical light Pw1. In this way, the control unit 110 checks the configuration information and selects either the normal mode or the extended mode based on the configuration information. Note that the normal mode is an example of the first mode, and the extended mode is an example of the second mode.

[0026] When the control unit 110 switches the startup mode to extended mode, it measures the connection status between the optical transmission paths T1 and T2 and the optical transmission device 100 based on the reflected pulses received by the OTDR 101. Specifically, the control unit 110 measures whether the optical transmission paths T1 and T2 are connected to the optical transmission device 100, and whether the span loss is excessive and the transmission path length is greater than or equal to a specified distance. Since the optical power of OSC optical Lo1 is low, around a few dBm, and it is difficult to measure the connection status using OSC optical Lo1, the control unit 110 measures the connection status between the optical transmission device 100 and the optical transmission paths T1 and T2 based on the reflected pulses.

[0027] Next, the optical transmission device 200 will be described. The optical transmission device 200 includes an OTDR 201, an OSC input / output unit 202, and optical amplifiers 203 and 204. The OTDR 201 is an example of a pulse transmitting and receiving unit. The OSC input / output unit 202 is an example of a second optical output unit. The optical transmission device 200 also includes an ASE light source 205, WDM couplers 206, 207, and 208, a branch coupler 209, and a control unit 210. The ASE light source 205 is an example of a second pseudo-light source. Furthermore, the optical transmission device 200 includes a user interface 211, optical transmitting units 212 and 213, and optical receiving units 214 and 215. The optical transmitting unit 212 is an example of a second transmitting unit. The optical receiving unit 214 is an example of a second optical receiving unit.

[0028] The optical amplifier 203, WDM couplers 206 and 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, WDM coupler 207, branch coupler 209, optical transmitter 213, and optical receiver 214 are located on the optical waveguide 217 of the optical transmission device 200.

[0029] 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 will be omitted. For example, the OSC input / output unit 202 outputs OSC light Lo2 to the optical transmission device 100. OSC light Lo2 is an example of second OSC light. 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. Pseudo-light Pw2 is an example of second pseudo-light. The optical transmission unit 212 transmits combined light Mx2, which is obtained by combining OSC light Lo2 and pseudo-light Pw2, to the optical transmission device 100. Combined light Mx2 is an example of second combined light. As a result, the combined light Mx2 propagates through the optical transmission path T2. As mentioned above, the control unit 110 measures the connection status of optical transmission lines T1 and T2 using OTDR 101, but the control unit 210 may also measure the connection status of optical transmission lines T1 and T2 using OTDR 201.

[0030] The operation of the optical transmission device 100 according to the first embodiment will be described with reference to Figures 2 to 4. Note that the operation of the optical transmission device 200 according to the first embodiment is basically the same as that of the optical transmission device 100 according to the first embodiment, so a detailed explanation will be omitted.

[0031] 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, the control unit 110 may measure the span loss of the optical transmission path T1 based on the optical power profile, as described above. 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).

[0032] 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). As a result, the OSC input / output unit 102 outputs OSC optical Lo1.

[0033] When OSC optical Lo1 is output, the control unit 110 performs an OTDR measurement (step S5). That is, the control unit 110 requests the OTDR 101 to transmit an optical pulse OP. As a result, the OTDR 101 transmits the optical pulse OP, receives the reflected pulse, and generates optical power profiles for the optical transmission paths T1 and T2. Based on the optical power profiles generated by the OTDR 101, the control unit 110 measures whether the optical transmission paths T1 and T2 corresponding to the span loss excess section are connected to the optical transmission device 100. That is, the control unit 110 performs an OTDR measurement separately from the setting information to measure the connection status of the optical transmission paths T1 and T2. Note that the processing order of steps S4 and S5 may be reversed.

[0034] When an OTDR measurement is performed, the control unit 110 requests the ASE light source 105 to output pseudo-light Pw1. As a result, the ASE light source 105 outputs pseudo-light Pw1 (step S6). When the ASE light source 105 outputs pseudo-light Pw1, the optical amplifier 103 amplifies the pseudo-light Pw1 (see Figure 1). The pseudo-light Pw1 amplified by the optical amplifier 103 propagates through the optical waveguide 116 and is combined with the OSC light Lo1 by the WDM coupler 108. This generates combined light Mx1. The combined light Mx1 is transmitted from the optical transmitter 112 to the optical transmission path T1.

[0035] When the combined wave light Mx1 is transmitted to the optical transmission path T1, stimulated Raman scattering occurs in the optical transmission path T1, as shown in Figure 3. When stimulated Raman scattering occurs, the optical power of the pseudo-light Pw1 belonging to the combined wave light Mx1 is transitioned to OSC light Lo1 with a wavelength λ8, which is longer than the longest wavelength λ7 in the wavelength band of the pseudo-light Pw1, due to the effect of stimulated Raman scattering. As a result, the optical power of OSC light Lo1 increases, that is, the intensity of OSC light Lo1 improves. In this way, by improving the intensity of OSC light Lo1, communication of OSC light Lo1 between optical transmission devices 100 and 200 is ensured even when the optical transmission path T1 corresponds to a section with excessive span loss.

[0036] As shown in Figure 3, the wavelength λ8 of OSC light Lo1 is shorter than the wavelength λ9 of the optical pulse OP of OTDR101 transmitted from the downstream optical transmission device 100 to the upstream optical transmission device 200. On the other hand, the shortest wavelength λ4 of the wavelength band of pseudo-light Pw1 is longer than the wavelength λ1 of the optical pulse OP of OTDR101 transmitted from the upstream optical transmission device 100 to the downstream optical transmission device 200.

[0037] When pseudo-optical light Pw1 is output, the control unit 110 determines that the OSC link is up (step S7). OSC link up indicates the establishment of a communication link between the optical transmission device 100 and the optical transmission device 200 based on the communication of OSC optical Lo1. More specifically, as shown in Figure 4, the optical transmission device 200 performs the same processing as the optical transmission device 100 asynchronously. Therefore, the OSC input / output unit 202 outputs OSC optical Lo2 and the ASE light source 205 outputs pseudo-optical light Pw2, causing the optical transmission device 200 to transmit combined wave optical light Mx2.

[0038] The optical transmission device 100 receives the multiplexed light Mx2 transmitted from the optical transmission device 200. The multiplexed light Mx2 propagates through the optical waveguide 117, and the branch coupler 109 separates the OSC light Lo2 from the multiplexed light Mx2. As a result, the OSC light Lo2 is input to the OSC input / output unit 102. Similarly, the optical transmission device 200 receives the multiplexed light Mx1 transmitted from the optical transmission device 100. The multiplexed light Mx1 propagates through the optical waveguide 217, and the branch coupler 209 separates the OSC light Lo1 from the multiplexed light Mx1. As a result, the OSC light Lo1 is input to the OSC input / output unit 202. When the OSC light Lo2 is input to the OSC input / output unit 102 and the OSC light Lo1 is input to the OSC input / output unit 202 in this way, the control units 110 and 210 simultaneously determine that the OSC link up.

[0039] When the OSC link-up is determined, the control unit 110 adjusts the gain of the optical amplifiers 103 and 104 (step S8) and terminates the startup process in extended mode. As described above, OSC link-up ensures communication between OSC optical Lo1 and Lo2. Therefore, the span loss of the optical transmission lines T1 and T2 is communicated to each other between the optical transmission devices 100 and 200 using OSC optical Lo1 and Lo2.

[0040] The control unit 110 adjusts the gain of the optical amplifier 103 and determines the output level of the optical amplifier 103 based on the span loss of the optical transmission path T1. Similarly, the control unit 110 adjusts the gain of the optical amplifier 104 and determines the output level of the optical amplifier 104 based on the span loss of the optical transmission path T2. Likewise, the control unit 210 adjusts the gain of the optical amplifier 203 and determines the output level of the optical amplifier 203 based on the span loss of the optical transmission path T2. Furthermore, the control unit 210 adjusts the gain of the optical amplifier 204 and determines the output level of the optical amplifier 204 based on the span loss of the optical transmission path T1. This ensures safe communication of the WDM signals Lw1 and Lw2 when the optical transmission system ST is put into operation.

[0041] In step S2 shown in Figure 2, if the optical transmission path T1 is not in a span loss excessive section (step S2: NO), the control unit 110 maintains the normal mode without switching the startup mode to the extended mode. In this case, the control unit 110 requests the OSC input / output unit 102 to output OSC optical Lo1. As a result, the OSC input / output unit 102 outputs OSC optical Lo1 (step S9).

[0042] When OSC optical Lo1 is output, the control unit 110 determines that the OSC link is up (step S10). Since the optical transmission path T1 is not in a section with excessive span loss, communication between OSC optical Lo1 and Lo2 is ensured. Once the OSC link is up, the control unit 110 uses OSC optical Lo1 and Lo2 to measure the span loss of the optical transmission paths T1 and T2 (step S11). After measuring the span loss, the control unit 110 adjusts the gain of the optical amplifier 103 based on the span loss of the optical transmission path T1 (step S12). After adjusting the gain of the optical amplifier 103 and determining the output level of the optical amplifier 103, the control unit 110 terminates the startup process in normal mode. Note that the control unit 210 performs the same processing as the control unit 110, so a detailed explanation is omitted.

[0043] As described above, according to the first embodiment, the intensity of OSC light Lo1 is improved by stimulated Raman scattering caused by pseudo-light Pw1. Similarly, the intensity of OSC light Lo2 is improved by stimulated Raman scattering caused by pseudo-light Pw2. As a result, even if the optical transmission lines T1 and T2 correspond to sections with excessive span loss, communication between OSC light Lo1 and OSC light Lo2 between the optical transmission devices 100 and 200 is ensured.

[0044] (Second Embodiment) The second embodiment of this invention will be described with reference to Figures 5 to 7. 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.

[0045] First, as shown in Figure 5, the optical transmission device 100 includes a back-excited Raman amplifier (indicated as BWD Raman in Figure 5) 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.

[0046] 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 intensity of the OSC light Lo2 belonging to the combined light Mx2 is further improved compared to when the pseudo-light Pw2 is used alone.

[0047] 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 intensity of the OSC light Lo1 belonging to the combined light Mx1 is further improved compared to when the pseudo-light Pw1 is used alone.

[0048] 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 6, the control unit 110 requests the output of the back-excitation light Pb1 from the back-excitation Raman amplifier 120 after the processing of step S5 described in the first embodiment, and before the processing of step S6 (step S21). As a result, the back-excitation Raman amplifier 120 outputs the back-excitation light Pb1.

[0049] Furthermore, the control unit 110 adjusts the gain of the back-pumped Raman amplifier 120 after the processing of step S7 described in the first embodiment and before the processing of step S8 (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 notified by utilizing OSC optical Lo2 after the OSC link-up. 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 notified by utilizing OSC optical Lo1 after the OSC link-up.

[0050] Furthermore, the control unit 110 adjusts the gain of the back-excited Raman amplifier 120 after the processing of step S11 described in the first embodiment and before the processing of step S12 (step S23). Similarly, the control unit 210 can adjust the gain of the back-excited Raman amplifier 220.

[0051] Thus, according to the second embodiment, the optical transmission device 100 is equipped with a back-excited Raman amplifier 120. As a result, the intensity of the OSC light Lo2 is further improved compared to when the 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 intensity of the OSC light Lo1 is further improved compared to when the pseudo-light Pw1 is used alone. That is, as shown in Figure 7, the OSC lights Lo1 and Lo2 can enjoy not only the effect of stimulated Raman scattering from the pseudo-lights Pw1 and Pw2, but also the effect of stimulated Raman scattering from the back-excited lights Pb1 and Pb2, which include a wavelength band from the lowest wavelength λ2 to the longest wavelength λ3.

[0052] (Third embodiment) A third embodiment of this invention will be described with reference to Figures 8 and 9. First, as shown in Figure 8, 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 8) 130. The forward-excited Raman amplifier 130 is connected to the optical waveguide 116 via a WDM coupler 131.

[0053] 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.

[0054] 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 belonging to the multiplexed light Mx1 is further improved compared to when pseudo-light Pw1 and back-excited light Pb2 are used in combination.

[0055] 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.

[0056] 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 9, the control unit 110 requests the output of the forward excitation light Pf1 from the forward excitation Raman amplifier 130 after the processing of step S21 described in the second embodiment, and before the processing of step S6 (step S31). As a result, the forward excitation Raman amplifier 130 outputs the forward excitation light Pf1.

[0057] 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 S8 (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 notified using OSC optical Lo2 after the OSC link-up. Similarly, the control unit 210 can adjust the gain of the forward-excited Raman amplifier 230 based on the span loss of the optical transmission path T2, which is notified using OSC optical Lo1 after the OSC link-up.

[0058] 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 S12 (step S33). Similarly, the control unit 210 can adjust the gain of the forward-excited Raman amplifier 230.

[0059] Thus, according to the third embodiment, the optical transmission device 100 is equipped with a forward-excited Raman amplifier 130. As a result, the intensity of the OSC light Lo1 is further improved compared to when the pseudo-light Pw1 and the 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 intensity of the OSC light Lo2 is further improved compared to when the pseudo-light Pw2 and the back-excited light Pb1 are used in combination. In other words, the OSC lights Lo1 and Lo2 can enjoy not only the effect of stimulated Raman scattering from the pseudo-light Pw1 and Pw2 and the back-excited lights Pb1 and Pb2, but also the effect of stimulated Raman scattering from the forward-excited lights Pf1 and Pf2, which include a wavelength band from the lowest wavelength λ2 to the longest wavelength λ3.

[0060] (Fourth Embodiment) The fourth embodiment of this invention will be described with reference to Figures 10 to 13. As shown in Figure 10, the optical transmission system ST according to the fourth embodiment differs from the optical transmission system ST according to the first to third embodiments described above. Specifically, the optical transmission system ST according to the fourth embodiment includes optical relay devices 300, 400, and 500. Optical relay devices 300, 400, and 500 are examples of third optical transmission devices. Optical relay devices 300, 400, and 500 include, for example, an ILA (In-Line Amplifier).

[0061] Optical relay devices 300 and 400 are connected via two parallel optical transmission lines T12 and T22. Optical relay device 400 is connected to optical transmission device 100 via two parallel optical transmission lines T11 and T21. Optical relay devices 300 and 500 are connected via two parallel optical transmission lines T13 and T23. Optical relay device 500 is connected to optical transmission device 200 via two parallel optical transmission lines T14 and T24.

[0062] Optical transmission paths T11, T12, T13, T14, T21, T22, T23, and T24 all contain optical fibers. The type of optical fiber is not particularly limited. Optical transmission paths T11, T21, T14, and T24 correspond to the span loss excessive sections described in the first embodiment. On the other hand, optical transmission paths T12, T22, T13, and T23 correspond to non-span loss excessive sections. Non-span loss excessive sections represent normal sections where span loss is not excessive. Thus, in the fourth embodiment, multiple span loss excessive sections and non-span loss sections coexist.

[0063] The optical repeater 300 includes an OTDR 301, an OSC input / output unit 302, and optical amplifiers 303 and 304. The optical repeater 300 also includes an OSC input / output unit 305, WDM couplers 306, 307, and 308, a branch coupler 309, and a control unit 310.

[0064] Furthermore, the optical relay device 300 includes a user interface 311, optical transmitting units 312 and 313, optical receiving units 314 and 315, a branching coupler 318, a WDM coupler 319, and VOAs (Variable Optical Attenuators) 341 and 342. Optical receiving units 314 and 315 are examples of receiving units. Thus, the optical relay device 300 does not include the ASE light source mentioned above. In other words, the optical relay device 300 cannot output pseudo-light. For this reason, the optical relay device 300 cannot improve the intensity of the OSC light Lo3, which will be described later, by pseudo-light. Note that the optical relay devices 400 and 500 have basically the same configuration as the optical relay device 300, so a detailed explanation is omitted.

[0065] The optical amplifier 303, WDM couplers 306 and 308, optical transmitter 312, optical receiver 315, and branch coupler 318 are located on the optical waveguide 316 of the optical repeater 300. The optical amplifier 304, WDM couplers 307 and 319, branch coupler 309, optical transmitter 313, and optical receiver 314 are located on the optical waveguide 317 of the optical repeater 300.

[0066] OTDR301 is optically connected to WDM couplers 306 and 307. OTDR301 transmits optical pulses OP to optical transmission lines T12 and T22 via optical waveguides 316 and 317 and receives reflected pulses of those optical pulses OP. By receiving reflected pulses, OTDR301 can generate optical power profiles of optical transmission lines T12 and T22. Based on the optical power profiles generated by OTDR301, the span loss of optical transmission line T12, the span loss of optical transmission line T22, and the location of optical power loss are measured. Furthermore, based on the span losses of optical transmission lines T12 and T22, the connection status of optical transmission lines T12 and T22, such as connector disconnection, is measured.

[0067] 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 relay device 400. OSC optical Lo3 may or may not include the span loss of the optical transmission path T12. In addition, OSC optical Lo4 output from the optical relay device 400 is input to the OSC input / output unit 302. OSC optical Lo4 may or may not include the span loss of the optical transmission path T22.

[0068] 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 relay device 500. OSC optical Lo3 may or may not include the span loss of the optical transmission path T23. In addition, OSC optical Lo5 output from the optical relay device 500 is input to the OSC input / output unit 305. OSC optical Lo5 may or may not include the span loss of the optical transmission path T13.

[0069] The optical amplifier 303 amplifies and outputs the WDM signal light Lw2 and the pseudo-light Pw2 belonging to the combined light Mx5, which are received by the optical relay device 300 via the optical receiver 315. The optical amplifier 303 is an amplifier realized by, for example, an EDFA and a circuit board that controls the gain of the EDFA. The WDM signal light Lw2 output by the optical amplifier 303 is transmitted to the optical transmission path T22 via the optical transmitter 312.

[0070] The optical amplifier 304 amplifies and outputs the WDM signal light Lw1 and the pseudo-light Pw1 belonging to the combined light Mx4, which are received by the optical relay device 300 via the optical receiver 314. The optical amplifier 304 is an amplifier realized by, for example, an EDFA and a circuit board that controls the gain of the EDFA. The WDM signal light Lw1 output by the optical amplifier 304 is transmitted via the optical transmitter 313.

[0071] The control unit 310 is electrically connected to the OTDR 301, OSC input / output units 302 and 305, optical amplifiers 303 and 304, and user interface 311. Although not shown in the diagram, the control unit 310 is also electrically connected to the VOA 341 and 342. 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 OTDR 301, OSC input / output units 302 and 305, optical amplifiers 303 and 304, and VOA 341 and 342.

[0072] For example, the control unit 310 can request the OTDR 301 to transmit an optical pulse. The control unit 310 can request the OSC input / output units 302 and 305 to output OSC optical Lo3. The control unit 310 can adjust the gain of the optical amplifiers 303 and 304. The control unit 310 can adjust the attenuation of the VOAs 341 and 342. In addition, based on the optical power profile generated by the OTDR 301, the control unit 310 can measure the span loss of optical transmission lines T12 and T22, the span loss of optical transmission line T2, the location of optical power loss, and so on.

[0073] Furthermore, the control unit 310 acquires configuration information, including span losses of optical transmission paths T12, T13, T22, and T23, from the user interface 311 when the optical relay device 300 is started up, before the optical transmission system ST is put into operation. In other words, the control unit 310 acquires configuration information before communication of WDM signal optical Lw1 and Lw2 begins. Based on the configuration information, if the control unit 310 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 311. Specifically, the control unit 310 determines that the span loss is excessive if it is greater than or equal to a predetermined comparison value.

[0074] The control unit 310 switches from a normal mode that does not output predetermined section information to an extended mode that transfers predetermined section information from downstream to upstream if the span loss is excessive. Also, if the control unit 310 receives predetermined section information from downstream, it switches from a normal mode that does not output predetermined section information to an extended mode that transfers predetermined section information to upstream. The predetermined section information is, for example, information indicating that there is a section with excessive span loss downstream of the optical relay device 300. When the control unit 310 switches the startup mode to the extended mode, it measures the connection status between the optical transmission lines T12, T22 and the optical relay device 300 based on the reflected pulses received by the OTDR 301.

[0075] Referring to Figure 11, the operation of the optical transmission device 100 according to the fourth embodiment will be described. Note that the operation of the optical transmission device 200 according to the fourth embodiment is basically the same as that of the optical transmission device 100 according to the fourth embodiment, so a detailed explanation will be omitted. Also, the same reference numerals are used for processes similar to those described in the optical transmission device 100 in the first embodiment, and their detailed explanations will be omitted.

[0076] The control unit 110 performs a first decision process (step S41) after the processing of step S6 described in the first embodiment and before the processing of step S7. The first decision process is to wait until communication between OSC optical Lo1, ..., Lo5 is ensured in the entire section from optical transmission device 100 to optical transmission device 200. The control unit 110 also performs a second decision process (step S42) after the processing of step S7 described in the first embodiment and before the processing of step S8. The second decision process is to wait until its own path is established.

[0077] In other words, when pseudo-optical light Pw1 is output, the intensity of OSC optical Lo1 increases, so even if the optical transmission path T11 is in a span loss excessive section (see Figure 10), communication of OSC optical Lo1 between the optical transmission device 100 and the optical relay device 400 is ensured. On the other hand, since the optical transmission path T12 is in a non-span loss excessive section, communication of OSC optical Lo4 between the optical relay device 400 and the optical relay device 300 is ensured regardless of the presence or absence of pseudo-optical light. Also, since the optical transmission path T13 is in a non-span loss excessive section, communication of OSC optical Lo3 between the optical relay device 300 and the optical relay device 500 is ensured regardless of the presence or absence of pseudo-optical light.

[0078] However, if the optical transmission path T14 is in a section with excessive span loss, the optical relay device 500 cannot output pseudo-light, so the intensity of OSC optical Lo5 is not improved, and communication of OSC optical Lo5 between the optical relay device 500 and the optical transmission device 200 is not ensured and is hindered. For this reason, the control unit 110 waits in the first decision process until communication of OSC optical Lo1,...,Lo5 is ensured in the entire section from the optical transmission device 100 to the optical transmission device 200 (step S41: NO).

[0079] Furthermore, once communication between OSC optical Lo1, ..., Lo5 is ensured throughout the entire section (step S41: YES), the control unit 110 waits until its own path comes up (step S42: NO) according to the second decision process. That is, the control unit 110 waits until its own path, the optical transmission line T11, comes up. Once its own path comes up (step S42: YES), the control unit 110 executes the process in step S8 and terminates the process.

[0080] The operation of the optical relay device 300 will be explained with reference to Figure 12. Note that the operation of the optical relay devices 400 and 500 according to the fourth embodiment is basically the same as that of the optical relay device 300 according to the fourth embodiment, so a detailed explanation will be omitted.

[0081] 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 relay device 300 if the optical transmission paths T11, T12, T21, and T22 are not span loss excessive sections (step S51). For example, the control unit 310 can determine whether there is a span loss excessive section downstream of the optical relay device 300 based on the section information transmitted from the optical relay device 500.

[0082] If there is no section with excessive span loss (step S51: NO), the control unit 310 determines whether or not there is a section with excessive span loss upstream of the optical relay device 300 (step S52). For example, the control unit 310 can determine whether or not there is a section with excessive span loss upstream of the optical relay device 300 based on the section information transmitted from the optical relay device 400. If there is no section with excessive span loss (step S52: NO), the control unit 310 executes the processing in steps S9 to S12 and terminates the process.

[0083] On the other hand, if there is a span loss overload section (step S51: YES, S52: YES), the control unit 310 performs the processing in steps S3 to S5 and then confirms the arrival of the pseudo-light (step S53). For example, the control unit 310 confirms the arrival of the pseudo-light Pw1 output from the optical relay device 400. Upon confirming the arrival of the pseudo-light, the control unit 310 forcibly activates the optical amplifier 304 (step S54) and performs the subsequent processing. As a result, the pseudo-light Pw1 is output from the optical relay device 400 to the optical relay device 500.

[0084] In other words, when the pseudo-optical light Pw1 output from the optical transmission device 100 reaches the optical relay device 400, the control unit (not shown) of the optical relay device 400 confirms the arrival of the pseudo-optical light Pw1 and forcibly activates the optical amplifier. As a result, the pseudo-optical light Pw1 is amplified and output from the optical relay device 400 to the optical relay device 300. The optical relay device 300 performs the same process. As a result, the pseudo-optical light Pw1 is amplified and output from the optical relay device 300 to the optical relay device 500. In this way, the intensity of the OSC optical Lo5 output by the optical relay device 500 is increased due to the pseudo-optical light Pw1. Therefore, even if the optical transmission path T14 is in a section with excessive span loss, communication of the OSC optical Lo5 between the optical relay device 500 and the optical transmission device 200 is ensured.

[0085] Therefore, even if the optical transmission system ST includes multiple optical relay devices 300, 400, and 500, and multiple sections with excessive span loss and sections with no span loss are mixed, communication of OSC optical Lo1, ..., Lo5, including span loss, is ensured throughout the entire section. This allows optical transmission devices 100 and 200 to adjust the gain of optical amplifiers 103 and 204 based on span loss. Similarly, optical relay device 300 can adjust the gain of optical amplifier 304 based on span loss. Optical relay devices 400 and 500 can also adjust the gain of their optical amplifiers in the same way as optical relay device 300.

[0086] The examples will be described in comparison with the comparative examples with reference to Figures 13(a) and (b).

[0087] First, in the comparative example, as shown in Figure 13(a), even if pseudo-optical Pw1 is output from the optical transmission device 100, the optical relay device 400 does not switch its startup mode to extended mode, and therefore the output of pseudo-optical Pw1 from the optical relay device 400 is interrupted. Similarly, the output of pseudo-optical Pw1 is interrupted for the optical relay devices 300 and 500 located downstream of the optical relay device 400. As a result, communication between the optical relay device 500 and the optical transmission device 200 via OSC optical Lo2 and Lo5 is hindered. Similarly, even if pseudo-optical Pw2 is output from the optical transmission device 200, communication between the optical relay device 400 and the optical transmission device 100 via OSC optical Lo1 and Lo4 is hindered.

[0088] However, in this embodiment, as shown in Figure 13(b), when a pseudo-optical signal Pw1 is output from the optical transmission device 100, the optical relay device 400 switches its startup mode to extended mode based on the section information transferred from the optical relay device 300. This allows the optical relay device 400 to output a pseudo-optical signal Pw1. Similarly, the optical relay device 300 switches its startup mode to extended mode based on the section information transferred from the optical relay device 500. This allows the optical relay device 300 to output a pseudo-optical signal Pw1.

[0089] The optical relay device 500 switches its startup mode to extended mode based on its own section information. This allows the optical relay device 500 to output pseudo-optical Pw1. As a result, communication between the optical relay device 500 and the optical transmission device 200 via OSC optical Lo2 and Lo5 is ensured. Similarly, communication between the optical relay device 400 and the optical transmission device 100 via OSC optical Lo1 and Lo4 is also ensured.

[0090] (Fifth embodiment) The fifth embodiment of this invention will be described with reference to Figures 14 to 16. Note that the same reference numerals are used for components and processes similar to those described in the fourth embodiment (optical relay device 300), and their detailed descriptions are omitted. Furthermore, since the optical relay devices 400 and 500 have the same configuration and processes as the optical relay device 300, their detailed descriptions are also omitted.

[0091] First, as shown in Figure 14, the optical relay device 300 includes a back-excited Raman amplifier 320. The back-excited Raman amplifier 320 is an example of a third optical output unit. The back-excited Raman amplifier 320 is connected to the optical waveguide 317 via a WDM coupler 321. The back-excited Raman amplifier 320 outputs back-excited light Pb3. The back-excited light Pb3 propagates along the optical transmission path T12 in the opposite direction to the direction in which the WDM signal light Lw1 propagates along the optical transmission path T12. In the optical transmission path T12, the back-excited light Pb3 uses stimulated Raman scattering to Raman-amplify the combined light Mx4 output from the optical relay device 400. As a result, the intensity of the OSC light Lo4 belonging to the combined light Mx4 is further improved compared to when the pseudo-light Pw1 is used alone.

[0092] Referring to Figure 15, the operation of the optical transmission device 100 according to the fifth embodiment will be described. Note that the operation of the optical transmission device 200 according to the fifth embodiment is basically the same as that of the optical transmission device 100 according to the fifth embodiment, so a detailed explanation will be omitted.

[0093] After the processing in step S5 described in the first embodiment, and before the processing in step S6, the control unit 110 requests the output of the back-excitation light Pb1 from the back-excitation Raman amplifier 120 (step S61). As a result, the back-excitation Raman amplifier 120 outputs the back-excitation light Pb1.

[0094] Furthermore, after the processing in step S42 described in the fourth embodiment, and before the processing in step S8, the control unit 110 adjusts the gain of the back-excited Raman amplifier 120 (step S62). After adjusting the gain of the back-excited Raman amplifier 120, the control unit 110 executes the subsequent processing and terminates the process.

[0095] Furthermore, after the processing of step S11 described in the first embodiment, and before the processing of step S12, the control unit 110 adjusts the gain of the back-excited Raman amplifier 120 (step S63). After adjusting the gain of the back-excited Raman amplifier 120, the control unit 110 executes the subsequent processing and terminates the process.

[0096] Referring to Figure 16, the operation of the optical relay device 300 according to the fifth embodiment will be described. Note that the operation of the optical relay devices 400 and 500 according to the fifth embodiment is basically the same as that of the optical relay device 300 according to the fifth embodiment, so a detailed explanation will be omitted.

[0097] The control unit 310, after the processing in step S53 described in the fourth embodiment and before the processing in step S54, requests the back-excited Raman amplifier 320 to output the back-excited light Pb3 (step S71). As a result, the back-excited Raman amplifier 320 outputs the back-excited light Pb3.

[0098] Furthermore, after the processing in step S42 and before the processing in step S8, the control unit 310 adjusts the gain of the back-excited Raman amplifier 320 (step S72). 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 S11 and before the processing in step S12, the control unit 310 adjusts the gain of the back-excited Raman amplifier 320 (step S73). After adjusting the gain of the back-excited Raman amplifier 320, the control unit 310 executes the subsequent processing and terminates the process.

[0099] Thus, according to the fifth embodiment, the optical relay device 300 can improve the intensity of the combined light Mx4 by outputting the back-excited light Pb3. Similarly, the optical relay devices 400 and 500 can also improve the intensity of the combined light in the same way as the optical relay device 300. As a result, even if multiple span loss excess sections and span loss non-excess sections are mixed in the optical transmission system ST, communication of OSC light Lo1, ..., Lo5 including span loss is ensured in all sections.

[0100] (Sixth Embodiment) The sixth embodiment of this invention will be described with reference to Figures 17 to 19. Note that the same reference numerals are used for components and processes similar to those described in the fifth embodiment of the optical relay device 300, and their detailed descriptions are omitted. Furthermore, since the optical relay devices 400 and 500 have the same configuration as the optical relay device 300, their detailed descriptions are also omitted.

[0101] First, as shown in Figure 17, the optical relay device 300 includes a forward-excited Raman amplifier 330. The forward-excited Raman amplifier 330 is an example of a fourth optical output unit. The forward-excited Raman amplifier 330 is connected to the optical waveguide 316 via a WDM coupler 331. The forward-excited Raman amplifier 330 outputs forward-excited light Pf3. The forward-excited light Pf3 propagates along the optical transmission path T22 in the same direction as the WDM signal light Lw2 propagates along the optical transmission path T22. In the optical transmission path T22, the forward-excited light Pf3 uses stimulated Raman scattering to Raman-amplify the combined light Mx3 output from the optical relay device 300. As a result, the intensity of the OSC light Lo3 belonging to the combined light Mx3 is further improved compared to when pseudo-light Pw2 and back-excited light output from the optical relay device 400 are used in combination.

[0102] Referring to Figure 18, the operation of the optical transmission device 100 according to the sixth embodiment will be described. Note that the operation of the optical transmission device 200 according to the sixth embodiment is basically the same as that of the optical transmission device 100 according to the sixth embodiment, so a detailed explanation will be omitted.

[0103] The control unit 110, after the processing of step S61 described in the fifth embodiment and before the processing of step S6, requests the output of the forward excitation light Pf1 from the forward excitation Raman amplifier 130 (step S81). As a result, the forward excitation Raman amplifier 130 outputs the forward excitation light Pf1.

[0104] The control unit 110 adjusts the gain of the forward-excited Raman amplifier 130 after the processing in step S62 and before the processing in step S8 (step S82). After adjusting the gain of the forward-excited Raman amplifier 130, the control unit 110 executes the subsequent processing and terminates the process. Furthermore, the control unit 110 adjusts the gain of the forward-excited Raman amplifier 130 after the processing in step S63 and before the processing in step S12 (step S83). After adjusting the gain of the forward-excited Raman amplifier 130, the control unit 110 executes the subsequent processing and terminates the process.

[0105] Referring to Figure 19, the operation of the optical relay device 300 according to the sixth embodiment will be described. Note that the operation of the optical relay devices 400 and 500 according to the sixth embodiment is basically the same as that of the optical relay device 300 according to the sixth embodiment, so a detailed explanation will be omitted.

[0106] After the processing in step S71 and before the processing in step S54, the control unit 310 requests the output of the forward excitation light Pf3 from the forward excitation Raman amplifier 330 (step S91). As a result, the forward excitation Raman amplifier 330 outputs the forward excitation light Pf3.

[0107] Furthermore, after the processing in step S72 and before the processing in step S8, the control unit 310 adjusts the gain of the forward-excited Raman amplifier 330 (step S92). 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 S73 and before the processing in step S12, the control unit 310 adjusts the gain of the forward-excited Raman amplifier 330 (step S93). After adjusting the gain of the forward-excited Raman amplifier 330, the control unit 310 executes the subsequent processing and terminates the process.

[0108] Thus, according to the sixth embodiment, the optical relay device 300 can improve the intensity of the combined light Mx3 by outputting forward excitation light Pf3. Similarly, the optical relay devices 400 and 500 can also improve the intensity of the combined light in the same way as the optical relay device 300. As a result, even if multiple span loss excess sections and span loss non-excess sections are mixed in the optical transmission system ST, communication of OSC optical Lo1, ..., Lo5 including span loss is ensured in all sections.

[0109] 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. 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. Similarly, the use of back-excited Raman amplifier 320 alone and the use of back-excited Raman amplifier 320 and forward-excited Raman amplifier 330 in combination were described as examples, but the invention is not limited to such uses. For example, forward-excited Raman amplifier 330 may be used alone without using back-excited Raman amplifier 320.

[0110] Furthermore, the following additional information is disclosed regarding the above explanation. (Note 1) An optical transmission system comprising a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, wherein the first optical transmission device comprises a first optical output unit that outputs first OSC light, a first pseudo-light source that outputs first pseudo-light including the wavelength band of a first signal light, and a first transmitting unit that transmits first combined light obtained by combining the first OSC light and the first pseudo-light toward the second optical transmission device, and the second optical transmission device comprises a second optical output unit that outputs second OSC light, a second pseudo-light source that outputs second pseudo-light including the wavelength band of a second signal light, and a second transmitting unit that transmits second combined light obtained by combining the second OSC light and the second pseudo-light toward the first optical transmission device. (Appendix 2) The optical transmission system according to Appendix 1, characterized in that the first optical transmission device has a first optical receiving unit that receives the second multiplexed light from the second optical transmission device, the second optical transmission device has a second optical receiving unit that receives the first multiplexed light from the first optical transmission device, the second optical receiving unit receives the first multiplexed light, the second optical output unit detects the first OSC light separated from the first multiplexed light by the second optical transmission device, the first optical receiving unit receives the second multiplexed light, and the first optical output unit detects the second OSC light separated from the second multiplexed light by the first optical transmission device, and so on, that a communication link between the first optical transmission device and the second optical transmission device is determined to have been established. (Note 3) The optical transmission system according to Note 1 or 2, characterized in that the first optical transmission device has a control unit that selects either a first mode in which the first pseudo-light is not output or a second mode in which the first pseudo-light is output, based on the setting information of the optical transmission path. (Note 4) The optical transmission system according to Note 1 or 2, characterized in that the first optical transmission device includes a pulse transmitting / receiving unit that transmits an optical pulse to the optical transmission path and receives a reflected pulse of the optical pulse, and a measuring unit that measures the connection state between the optical transmission path and the first optical transmission device based on the reflected pulse. (Note 5) The optical transmission system according to Note 1 or 2, characterized in that the second optical transmission device has 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 first signal light propagates in the optical transmission path. (Note 6) The optical transmission system according to Note 1 or 2, characterized in that the first optical transmission device has a forward excitation light source that outputs forward excitation light to the optical transmission path, which propagates in a first direction in which the first signal light propagates along the optical transmission path. (Note 7) The optical transmission system according to Note 1 or 2, characterized in that a third optical transmission device is provided between the first optical transmission device and the second optical transmission device for relaying the first pseudo-light and the second pseudo-light from upstream to downstream, and the third optical transmission device activates an optical amplifier provided in the third optical transmission device when it receives information about the optical transmission path and the first pseudo-light from the first optical transmission device. (Note 8) The optical transmission system according to Note 7, characterized in that the third optical transmission device has a third optical output unit that outputs back-excitation light to the optical transmission path, which propagates in a second direction opposite to the first direction in which the first signal light propagates in the optical transmission path. (Note 9) The optical transmission system according to Note 7, characterized in that the third optical transmission device has a fourth optical output unit that outputs forward excitation light to the optical transmission path, which propagates in the first direction in which the first multiplexed light propagates through the optical transmission path. (Note 10) The optical transmission system according to Note 1 or 2, characterized in that the wavelength of the first OSC light is longer than the wavelength of the first pseudo-light, and the wavelength of the second OSC light is longer than the wavelength of the second pseudo-light. (Note 11) 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 12) An optical transmission device connected to another optical transmission device facing it via an optical transmission path, comprising: an optical output unit that outputs OSC light; a pseudo-light source that outputs pseudo-light including the wavelength band of signal light; and a transmitting unit that transmits combined light obtained by combining the OSC light and the pseudo-light toward the other optical transmission device. (Note 13) An optical transmission device provided between a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, which relays signal light and pseudo-light output from the first optical transmission device and the second optical transmission device from upstream to downstream, comprising: a receiving unit that receives information relating to the optical transmission path and the pseudo-light; an optical amplifier that amplifies and outputs the signal light; and a control unit that controls the optical amplifier, wherein the control unit activates the optical amplifier according to the information and controls the optical amplifier to amplify and output the pseudo-light received by the receiving unit. [Explanation of Symbols]

[0111] ST Optical Transmission Systems 100,200 Optical transmission devices 300, 400, 500 Optical relay devices 102,202,302,305 OSC input / output section 105,205 ASE light source 110,210,310 Control Unit 112,113,212,213,312,313 Optical Transmitter 120, 220, 320 Back-Pumped Raman Amplifier 130,230,330 Forward-excited Raman amplifier

Claims

1. An optical transmission system including a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, The first optical transmission device is A first optical output section that outputs first OSC (Optical Supervisory Channel) light, A first pseudo-light source that outputs a first pseudo-light including the wavelength band of the first signal light, The system includes a first transmitting unit that transmits a first combined light, obtained by combining the first OSC light and the first pseudo-light, toward the second optical transmission device. The second optical transmission device is A second optical output unit that outputs a second OSC light, A second pseudo-light source that outputs a second pseudo-light including the wavelength band of the second signal light, The device includes a second transmitting unit that transmits a second combined light, obtained by combining the second OSC light and the second pseudo-light, toward the first optical transmission device. An optical transmission system characterized by the following:

2. The first optical transmission device has a first optical receiving unit that receives the second multiplexed light from the second optical transmission device, and the second optical transmission device has a second optical receiving unit that receives the first multiplexed light from the first optical transmission device. The second optical receiving unit receives the first multiplexed light, and the second optical output unit detects the first OSC light separated from the first multiplexed light by the second optical transmission device. When the first optical receiving unit receives the second combined light, and the first optical output unit detects the second OSC light separated from the second combined light by the first optical transmission device, It is determined that a communication link has been established between the first optical transmission device and the second optical transmission device. The optical transmission system according to feature 1.

3. The first optical transmission device is The control unit has a first mode in which the first pseudo-light is not output and a second mode in which the first pseudo-light is output, based on the setting information of the optical transmission path. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

4. The first optical transmission device is A pulse transmitting and receiving unit that transmits an optical pulse to the optical transmission path and receives a reflected pulse of the optical pulse, The system includes a measuring unit that measures the connection status between the optical transmission path and the first optical transmission device based on the reflected pulse. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

5. The second optical transmission device is The optical transmission path has 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 first signal light propagates through the optical transmission path. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

6. The first optical transmission device is The optical transmission path has a forward excitation light source that outputs forward excitation light to the optical transmission path, which propagates in a first direction in which the first signal light propagates along the optical transmission path. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

7. A third optical transmission device is provided between the first optical transmission device and the second optical transmission device, which relays the first pseudo-light and the second pseudo-light from upstream to downstream, respectively. The third optical transmission device is When information regarding the optical transmission path and the first pseudo-light are received from the first optical transmission device, the optical amplifier provided in the third optical transmission device is activated. The optical transmission system according to claim 1 or 2, characterized in that it is as described above.

8. The third optical transmission device is The device has a third optical output unit that outputs backward-excitation light to the optical transmission path, which propagates in a second direction opposite to the first direction in which the first combined light propagates through the optical transmission path. The optical transmission system according to feature 7.

9. The third optical transmission device is The device has a fourth optical output unit that outputs forward excitation light to the optical transmission path, which propagates in a first direction in which the first multiplexed light propagates through the optical transmission path. The optical transmission system according to feature 7.

10. An optical transmission device connected to another optical transmission device on the opposite side via an optical transmission path, An optical output section that outputs OSC (Optical Supervisory Channel) light, A pseudo-light source that outputs pseudo-light including the wavelength band of signal light, A transmitting unit that transmits combined light, obtained by combining the OSC light and the pseudo-light, toward the other optical transmission device, An optical transmission device having the following features.

11. An optical transmission device provided between a first optical transmission device and a second optical transmission device facing each other via an optical transmission path, which relays signal light and pseudo-light output from the first optical transmission device and the second optical transmission device from upstream to downstream, A receiving unit that receives information relating to the optical transmission path and the pseudo-light, An optical amplifier that amplifies and outputs the aforementioned signal light, The optical amplifier has a control unit, The control unit activates the optical amplifier according to the information and controls the optical amplifier to amplify and output the pseudo-light received by the receiving unit. An optical transmission device characterized by the following features.

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