Optical transmission device and optical transmission method

Abstract

To prevent a malfunction in APSD caused by noise included in OSC light in an optical transmission device that performs Raman excitation.SOLUTION: An optical transmission device 100A performs Raman amplification on WDM light in a transmission path 101a with Raman excitation light. A control unit of the optical transmission device 100A measures, at the start-up, a reflection monitor value A reflected and input from the transmission path 101a when only OSC light is transmitted to the transmission path 101a, measures a reflection monitor value B reflected and input from the transmission path 101a when the WDM light, Raman excitation light, and OSC light are transmitted to the transmission path 101a, and subtracts the reflection monitor value A from the reflection monitor value B to calculate a correction value corresponding to noise light at a reflected light level. The control unit monitors the reflected light level to be input during operation, and performs APSD control based on the reflected light level corrected with the correction value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical transmission device and an optical transmission method.

Background Art

[0002] In an optical transmission device, there is one that optically amplifies WDM light in a transmission path such as an optical fiber based on Raman excitation light. This optical transmission device has a safety control function for blocking the optical output by APSD (Auto Power Shut Down), and prevents the laser light of the optical power from being radiated to the outside and harming the human body. APSD stops the output of the optical amplifier when detecting a link down using OSC (Optical Supervisory Channel) light.

[0003] As a prior art for monitoring the transmission state of WDM light, for example, there is one that includes a filter for removing the reflected light of Raman excitation light, and removes the residual Raman excitation light mixed in the reflected light by filtering, thereby preventing the malfunction of the cutoff circuit of the optical amplifier by the Raman excitation light. Also, there is a monitoring method for determining the position of the backscattering and the signal loss of the optical fiber link based on a monitoring signal for monitoring the optical fiber link and a data signal to be transmitted (see, for example, Patent Documents 1 and 2 below).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, in WDM transmission systems, the bandwidth has been expanded. For example, a multi-band (C+L band) WDM transmission system that transmits WDM light using the C band and the L band simultaneously has been proposed. When performing multi-band transmission as it is with the conventional technology, the number of wavelengths of WDM light (main signal) having gain increases. In this case, due to factors such as noise light in the OSC band becoming high level along with stimulated Raman scattering (SRS) being reflected and input to the transmission node, the monitor value of the OSC may be erroneously detected as a high reflection. In this case, the APSD function of the transmission node is activated, and the WDM light in operation is shut down. WDM is the abbreviation for Wavelength Division Multiplexing, and SRS is the abbreviation for Stimulated Raman Scattering.

[0006] In one aspect, an object of the present invention is to prevent malfunction of APSD caused by noise included in OSC light in an optical transmission device that performs Raman excitation.

Means for Solving the Problems

[0007] According to one aspect of the present invention, in an optical transmission device that Raman-amplifies WDM light in a transmission line with Raman excitation light, when the device is started up, the first reflected light level reflected and input from the transmission line when only OSC (Optical Supervisory Channel) light is transmitted to the transmission line is measured, and the second reflected light level reflected and input from the transmission line when the WDM light, the Raman excitation light, and the OSC light are transmitted to the transmission line is measured. Based on the first reflected light level and the second reflected light level, a correction value corresponding to the noise light of the reflected light level reflected and input from the transmission line is calculated. During operation of the device itself, the input reflected light level is monitored, and APSD (Auto Power Shut Down) control based on the reflected light level corrected by the correction value is performed, and it is required to be provided with a control unit.

Effects of the Invention

[0008] According to one aspect of the present invention, there is an effect that malfunction of the APSD due to noise included in the OSC light can be prevented in an optical transmission device that performs Raman excitation.

Brief Description of Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8A

Figure 8B

Figure 8C

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the disclosed optical transmission device will be described in detail with reference to the drawings.

[0011] (Configuration example of the optical transmission device according to the embodiment) FIG. 1 is an explanatory diagram of the optical transmission device according to the embodiment. In the example shown in FIG. 1, the optical transmission devices 100 are arranged with the same configuration at the upstream Node A and the downstream Node B, respectively, and transmit WDM optical (main signal) through a transmission line 101 such as an SMF.

[0012] SMF is an abbreviation for Single Mode optical Fiber. The WDM optical has, for example, a multi-band wavelength band of the C band and the L band (C + L) for the main signal.

[0013] The transmission line 101 has a downstream transmission line 101a from the optical transmission device 100A of the upstream (Node A) to the optical transmission device 100B of the downstream (Node B). Further, it has an upstream transmission line 101b from the optical transmission device 100B of the downstream (Node B) to the optical transmission device 100A of the upstream (Node A).

[0014] Hereinafter, a configuration example will be described when the optical transmission device 100A of the upstream (Node A) of the downstream transmission line 101a is the local station (transmitting node). The optical transmission device 100A includes a Raman amplifier 111 and a ROADM 112. ROADM is an abbreviation for Reconfigurable Optical Add / Drop Multiplexer.

[0015] The optical transmission device 100A includes a Raman amplifier 111. The Raman amplifier 111 has a Raman excitation light source inside and performs backward Raman excitation on the transmission line 101a with backward Raman excitation light. The ROADM 112 includes a multiplexer / demultiplexer 121, a WDM amplifier (optical amplifier) 123, a wavelength selective switch (WSS) 124, a multiplexer (MUX / DEMUX) 125, and an OSC processing unit 126. WSS is the abbreviation of Wavelength Selective Switch. The OSC processing unit 126 includes the function of transmitting and receiving OSC light.

[0016] Looking at the path of the downstream transmission line 101a, the multiplexer 125 performs wavelength multiplexing / demultiplexing of the WDM light input to and output from the WSS 124a. The WSS 124a performs branching and insertion of WDM light of an arbitrary wavelength with respect to the transmission line 101a. The optical amplifier 123a optically amplifies the WDM light on the transmission line 101a.

[0017] The OSC processing unit 126 includes the failure information detected by the optical transmission device 100A in the OSC light. The OSC light is multiplexed with the WDM light on the downstream transmission line 101a via the multiplexer / demultiplexer 121a and transmitted to the optical transmission device 100B downstream (NodeB).

[0018] Looking at the path of the upstream transmission line 101b, the multiplexer / demultiplexer 121b separates the wavelength band of the monitoring OSC light from the WDM light on the transmission line 101b and outputs it to the OSC processing unit 126. The optical amplifier 123b optically amplifies the WDM light on the transmission line 101b. The WSS 124b performs branching and insertion of WDM light of an arbitrary wavelength with respect to the transmission line 101b. For example, an EDFA is used for the optical amplifiers 123a and 123b. EDFA is the abbreviation of Erbium Doped Fiber Amplifier.

[0019] The optical transmission device 100A performs APSD control based on the state of the OSC light. For example, when the downstream optical transmission device 100B detects an OSC outage on the downstream transmission line 101a, it transmits the OSC light to the optical transmission device 100A via the upstream transmission line 101b. When the OSC processing unit 126 of the optical transmission device 100A receives an OSC outage, it stops the output of the WDM light by the local APSD.

[0020] Further, when a failure (such as a transmission line break or an open circuit) occurs in the downstream transmission line 101a, the OSC processing unit 126 detects a state in which the reflected light generated in the OSC light becomes high reflection (high level), and applies APSD to stop the output of the WDM light.

[0021] The configuration of the optical transmission device 100B downstream (NodeB) is the same as that of the optical transmission device 100A upstream (NodeA) described above, and the same components are denoted by the same reference numerals.

[0022] FIG. 1 shows a configuration example of backward Raman excitation using the Raman amplifier 111, but a configuration example of forward Raman excitation or a configuration example of forward Raman excitation and backward Raman excitation may also be used.

[0023] The optical transmission device 100A according to the embodiment executes the following startup sequences 1 to 4 at startup (when the span between the pair of optical transmission devices 100A and 100B is started up).

[0024] 1. The optical transmission device 100A measures (detects) the level of the reflected light of the OSC (the first reflected light level, the reflection monitor value A) when only the OSC light is output as the signal light to the downstream transmission line 101a.

[0025] 2. Next, the optical transmission device 100A measures the level of the reflected light of the OSC (the second reflected light level, the reflection monitor value B) when the OSC light, the WDM light (C + L), and the Raman excitation light by the Raman amplifier 111 are output as the signal light to the downstream transmission line 101a. In the case of the configuration example of FIG. 1, the Raman excitation light is backward excitation by the Raman amplifier 111 of the optical transmission device 100B.

[0026] 3. Next, the optical transmission device 100A calculates a correction value of the reflection monitor value based on the measured reflection monitor value A and reflection monitor value B. The optical transmission device 100A calculates, for example, the difference in the reflection level when the correction value of the reflection monitor value = reflection monitor value B - reflection monitor value A. Although details will be described later, the correction value corresponds to noise at the time of reflected light detection.

[0027] 4. Thereafter, during operation, the optical transmission device 100A monitors the reflection monitor value. When monitoring this reflection monitor, the optical transmission device 100A corrects the reflection monitor value measured during operation with the calculated correction value. For example, the reflection monitor value is calculated as the reflection monitor value - correction value.

[0028] During the monitoring of the reflection monitor value, the optical transmission device 100A compares the corrected reflection monitor value with a predetermined reflection detection threshold, and based on the corrected reflection monitor value, determines the presence or absence of a failure (such as a transmission line break or an open circuit) in the downstream transmission line 101a. For example, when the corrected reflection monitor value is a high reflection (high level) exceeding the reflection detection threshold, it is determined that a failure has occurred in the downstream transmission line 101a, and APSD is applied to shut down the optical amplifier 123a and the Raman amplifier 111.

[0029] For example, when the characteristics (such as loss, fiber type, etc.) of the fiber of the transmission line 101a change, an optical fiber removal operation occurs. Due to the occurrence of this removal operation, APSD is applied, and the optical transmission device 100A shuts down the optical amplifier 123a. In this case, after reconnecting the optical fiber of the transmission line 101a, the optical transmission device 100A executes the above processes 1 to 4 again.

[0030] In the above description, it is described that the optical transmission device 100A executes the above processes 1 to 4. More specifically, the above processes 1 to 3 are executed by the OSC processing unit 126 at startup, and process 4 is monitored and executed by the APSD control unit 905 (see FIG. 9) described later during the operation of the optical transmission device 100A.

[0031] According to the optical transmission device of the embodiment, a correction value of the reflection monitor value is calculated at startup, and during operation, the calculated correction value is used to monitor the reflection monitor value. Thereby, it becomes possible to prevent misdetection of reflected light caused by noise light generated in the OCM wavelength band due to WDM transmission of broadband multi-band transmission.

[0032] For example, when the reflection monitor value due to the noise light is erroneously detected, although there is no failure in the transmission path 101a, it becomes possible to prevent the situation where the APSD is applied and the WDM light (main signal) is blocked. Also, by preventing the erroneous detection of the reflected light, when a failure (such as a break or an open in the transmission path) occurs in the transmission path, the APSD can be appropriately applied, and the reliability of the safety control function for blocking the optical output can be improved.

[0033] Note that "applying (operating)" the APSD means controlling to "perform" the blocking of the output of the WDM light by the APSD. "Not applying" the APSD means controlling not to "perform" the blocking of the output of the WDM light by the APSD.

[0034] (Problems of the prior art) Here, the expected operation and problems of the APSD according to the prior art will be described with reference to FIGS. 2 to 7.

[0035] FIG. 2 is an explanatory diagram of the normal state according to the prior art. For convenience, the same reference numerals are given to the components of the existing optical transmission device 200 shown in FIG. 2 and the like as those of the optical transmission device 100 of the embodiment described in FIG. 1. As shown in FIG. 2, normally (in the normal state), the optical transmission device 200A outputs WDM light and OSC light by the rear excitation of the transmission path 101a. Also, the optical transmission device 200A outputs OSC light to the transmission path 101a.

[0036] Note that the optical transmission device 200B performs the output and APSD control of the WDM light and OSC light with respect to the transmission path 101b in the same manner as the optical transmission device 200A.

[0037] FIG. 3 is a start-up sequence diagram of the optical transmission device according to the prior art. When starting up, the optical transmission device 200A first outputs OSC light to the transmission path 101a by the OSC processing unit 126 (step S301) and checks the link-up of the OSC (step S302).

[0038] Next, the optical transmission device 200A measures the span loss of the transmission path 101a between it and the downstream optical transmission device 200B (step S303). Next, the optical transmission device 200A activates the WDM amplifier (optical amplifier) 123a (step S304) and activates the Raman amplifier 111 (step S305).

[0039] After that, the optical transmission device 200A monitors the reflection monitor value during operation (step S306). For example, the optical transmission device 200A determines the presence or absence of a failure (such as a transmission path break or opening) in the downstream transmission path 101a based on the reflection monitor value of the downstream transmission path 101a. For example, when the reflection monitor value exceeds a predetermined reflection detection threshold, it is determined that a failure (fiber break or opening) has occurred in the downstream transmission path 101a, and APSD is applied to shut down the optical amplifier 123a and the Raman amplifier 111.

[0040] FIG. 4 is an explanatory diagram of the APSD state expected when a failure occurs. As shown in FIG. 4, different from the normal time (see FIG. 2), assume that a fiber break failure has occurred in the transmission path 101a. In this case, based on the fiber break, 1. optical reflection occurs on the transmission path 101a, and 2. the OSC processing unit 126 of the optical transmission device 200A detects the reflection of the OSC light.

[0041] Then, when the reflection monitor value of the OSC light exceeds the reflection detection threshold, the optical transmission device 200A applies 3. APSD. As a result, the optical amplifier 123a shuts down, and the output of the WDM light to the transmission path 101a stops.

[0042] FIG. 5 is an explanatory diagram of problems during multi-band transmission according to the prior art. When attempting to perform optical transmission using multi-band WDM light such as the C+L band according to the prior art, even when there is no failure in the transmission path 101a, 1. noise light enters the transmission unit of the optical transmission device 200A at a high reflection level. In this case, 2. the OSC processing unit 126 erroneously detects the reflection monitor value, and 3. APSD is applied.

[0043] As a result, in the prior art, due to the noise light generated in the transmission line 101a, the optical transmission device 200A may apply APSD. In this case, even when there is no failure in the transmission line 101a, the optical amplifier 123a is shut down by APSD, and the output of the WDM light to the transmission line 101a stops (link down).

[0044] Thus, when attempting to perform recent multi-band transmission with the prior art optical transmission device 200A as it is, the optical power of the WDM light may generate noise in the OSC wavelength band, and the reflected light of the noise light may be erroneously detected.

[0045] For example, in multi-band transmission, the Raman amplifier 111 that performs the above-described backward Raman excitation or forward Raman excitation outputs excitation light of Raman wavelengths (primary excitation light and secondary excitation light) in a predetermined band corresponding to the C+L band to the transmission line 101a. This excitation light generates gain in the C+L WDM light band on the transmission line 101a. However, the broadband WDM light by C+L affects the OSC wavelength band.

[0046] Note that the optical transmission device 200A has an ASE light source for WDM transmission, and the number of wavelengths of the output WDM light is always kept constant. For example, the optical transmission device 200A automatically inserts ASE light into an unused wavelength. ASE is an abbreviation for Amplified Spontaneous Emission.

[0047] Next, with reference to FIGS. 6 and 7, the generation of noise light during multi-band transmission will be described. The horizontal axis in FIGS. 6(a) and 7(a) represents wavelength, and the horizontal axis in FIGS. 6(b) and 7(b) represents the length direction of the transmission line 101a.

[0048] FIG. 6 is an explanatory diagram of Factor 1 for the generation of noise light. As shown in FIG. 6(a), broadband C+L band WDM light with gain generates noise in the OSC wavelength band due to SRS amplification. Then, as shown in FIG. 6(b), the noise in the OSC wavelength band with high reflection (high level) is reflected and input from the transmission line 101a to the transmission node (optical transmission device 100A).

[0049] FIG. 7 is an explanatory diagram of Factor 2 for the generation of noise light. As shown in FIG. 7(a), broadband C+L band WDM light with gain generates noise in the OSC wavelength band due to SRS amplification. As shown in FIG. 7(b), as the optical power of the OSC light increases due to SRS, Rayleigh backscattering itself occurs distributively and increases, and furthermore, the Rayleigh backscattering amplified by SRS is reflected and input from the transmission line 101a to the transmission node (optical transmission device 200A).

[0050] Regarding the problems described above, in the optical transmission device 100(100A) according to the embodiment, as described above, at startup, a correction value of the reflection monitor value is calculated, and during operation, the calculated correction value is used to monitor the reflection monitor value. Thereby, false detection of reflected light caused by noise light generated in the OCM wavelength band due to WDM transmission of broadband multi-band transmission is prevented. By preventing false detection of reflected light, when a failure (such as a transmission line break or open circuit) occurs in the transmission line, APSD is applied, and the reliability of the safety control function of optical output cutoff is improved.

[0051] (APSD Control by Correction of Reflection Monitor Value in Embodiment) FIGS. 8A and 8B are explanatory diagrams of the correction of the reflection monitor value in the optical transmission device according to the embodiment. The optical transmission device 100A executes the following startup sequence 1 to 4 at startup (when the span between the pair of optical transmission devices 100A and 100B is started).

[0052] 1. The optical transmission device 100A measures (detects) the level of the reflected light of the OSC (reflection monitor value A) when only the OSC light is output as the signal light to the transmission line 101a with the output of the Raman excitation (Raman amplifier 111) for the downstream transmission line 101a turned off (see FIG. 8A).

[0053] For example, with the output of the Raman amplifier 111 of the optical transmission device 100B turned off, the optical transmission device 100A has the OSC processing unit 126 output OSC light to the downstream transmission path 101a, and detects the reflection monitor value A of the OSC light from the downstream transmission path 101a.

[0054] 2. Next, the optical transmission device 100A measures the level (reflection monitor value B) of the reflected light of the OSC when outputting, as signal light to the downstream transmission path 101a, the OSC light, the WDM light (C+L), and the Raman excitation light by the Raman amplifier 111 (see FIG. 8B).

[0055] For example, the output of the Raman amplifier 111 of the optical transmission device 100B is turned on to perform backward excitation of the transmission path 101a. Not limited to this, the Raman excitation for the transmission path 101a can also be configured as forward Raman excitation provided at the output end of the transmission path 101a of the optical transmission device 100A, or a configuration combining forward Raman excitation and backward Raman excitation.

[0056] 3. Next, the optical transmission device 100A calculates a correction value for the reflection monitor value based on the measured reflection monitor value A and reflection monitor value B. The optical transmission device 100A calculates, for example, the correction value of the reflection monitor value = reflection monitor value B - reflection monitor value A (unit: dB). The correction value corresponds to the noise at the time of reflected light detection.

[0057] 4. After this, during operation, the optical transmission device 100A monitors the reflection monitor value. When monitoring this reflection monitor, the optical transmission device 100A corrects the reflection monitor value with the calculated correction value. For example, the reflection monitor value = reflected light measurement value - correction value (unit: dB) is used for correction.

[0058] During the monitoring of the reflection monitor value, the optical transmission device 100A compares the corrected reflection monitor value with a predetermined reflection detection threshold, and based on the corrected reflection monitor value, determines the presence or absence of a failure (such as a transmission line break or an open circuit) in the downstream transmission line 101a. For example, when the corrected reflection monitor value exceeds the reflection detection threshold, it is determined that a failure has occurred in the downstream transmission line 101a, and APSD is applied to shut down the optical amplifier 123a and the Raman amplifier 111.

[0059] For example, when the characteristics (such as loss and fiber type) of the fiber in the transmission line 101a change, an operation of removing the optical fiber occurs. Due to the occurrence of this removal operation, APSD is applied, and the optical transmission device 100A shuts down the optical amplifier 123a. In this case, after the optical fiber in the transmission line 101a is reconnected, the optical transmission device 100A executes the above processes 1 to 4 again.

[0060] FIG. 8C is a chart for explaining the correction of the reflection monitor value and the APSD control according to the embodiment. FIG. 8C(a) shows the reflection monitor value without reflection (without failure), and FIG. 8C(b) shows the reflection monitor value with reflection (with failure). The vertical axis represents the level of the reflected light.

[0061] As shown in FIG. 8C(a), the reflection monitor value A corresponds to the reflection monitor value of only the OSC light shown in FIG. 8A, and the reflection monitor value B corresponds to the reflection monitor value of the OSC light, the WDM light, and the Raman excitation light shown in FIG. 8B.

[0062] The reflection monitor value B - the reflection monitor value A (the difference D) is the level of the noise light and becomes the correction value of the reflection monitor value shown in FIG. 8C(a). Then, the optical transmission device 100A sets the reflection detection threshold Th, for example, to approximately the median value of the reflection monitor value B and the reflection monitor value A.

[0063] The optical transmission device 100A sets and holds the reflection detection threshold Th, monitors the level of the reflected light of the OSC light, and performs APSD control by comparing the level of the reflected light of the OSC light with the reflection detection threshold Th.

[0064] For example, when there is no reflection as shown in FIG. 8C(a), the reflection monitor value a detected is lowered by only the correction value (difference D) and becomes the corrected reflection monitor value L1. The corrected reflection monitor value L1 becomes a level corresponding to the reflection monitor value A and is lower than the reflection detection threshold Th. Thereby, the optical transmission device 100A can appropriately determine that there is no reflection (no failure) based on the corrected reflection monitor value L1.

[0065] Note that when operating without correction, since the reflection monitor value a exceeds the reflection detection threshold Th, it is erroneously determined that there is reflected light (there is a failure).

[0066] Also, when there is reflection as shown in FIG. 8C(b), it becomes the corrected reflection monitor value L2. The corrected reflection monitor value L2 becomes a level of the actually detected reflection monitor value b - correction value (difference D). The reflection monitor value L2 in the case of FIG. 8(b) exceeds the reflection detection threshold Th. In this case, the optical transmission device 100A can appropriately determine that there is reflection (there is a failure) based on the corrected reflection monitor value L2. Then, APSD control based on the presence or absence of a failure can be appropriately implemented.

[0067] (Functional configuration example of optical transmission device) FIG. 9 is a functional block diagram of the optical transmission device according to the embodiment. In FIG. 9, the same components as those of the optical transmission device 100 (100A) such as FIG. 1 described above are denoted by the same reference numerals. Also, solid lines in FIG. 9 indicate optical signals, and dotted lines indicate electrical signals.

[0068] FIG. 9 mainly describes a configuration in which, among the above-described optical transmission device 100, reflected light from the transmission line 101a is detected, and APSD control is performed based on the corrected reflection monitor value.

[0069] The optical transmission device 100 includes functions of a transmission port 901, a reception port 902, a Raman amplifier 111, a multiplexer / demultiplexer 121, an OSC processing unit 126, a WDM optical transmission unit 903, a WDM optical reception unit 904, and an APSD control unit 905.

[0070] The Raman amplifier 111 outputs the excitation light for backward pumping to the transmission line 101b via the multiplexer / demultiplexer 121c.

[0071] The WDM optical transmission unit 903 corresponds to the optical amplifier 123a, and transmits and outputs the transmission data output from the switch unit (WSS 124) in the apparatus as WDM light to the transmission line 101a using the ASE light source output by the ASE light source 903a.

[0072] The OSC processing unit 126 multiplexes the OSC light transmitted by the OSC optical transceiver unit 911 with the WDM light via the optical filter 912 and the multiplexer / demultiplexer 121a, and outputs it to the transmission line 101a. The multiplexer / demultiplexer 121a multiplexes the OSC light with the WDM light output by the WDM optical transmission unit 903. The optical filter 912 allows only the wavelength band of the OSC light to pass through.

[0073] The WDM light including the OSC light transmitted from the downstream node (optical transmission apparatus 100B) input via the transmission line 101b has the OSC light demultiplexed by the multiplexer / demultiplexer 121b and received by the OSC transceiver unit 911.

[0074] Among the WDM light including the OSC light output to the transmission line 101b, the optically reflected input component has the wavelength band of the OSC light extracted via the multiplexer / demultiplexer 121a to the optical filter 912, and is detected by the photodetector (PD) 913.

[0075] The reflected light processing unit 914 executes the processes related to 1. measurement of the reflection monitor value A, 2. measurement of the reflection monitor value B, and 3. calculation of the correction value of the reflection monitor value when executing the startup sequence of 1. to 4. described above.

[0076] The reflected light processing unit 914 measures the reflection level of the OSC light detected by the PD 913 as the reflection monitor value A via the transmission line 101a to the multiplexer / demultiplexer 121a to the optical filter 912 in a state where only the OSC light is output as the signal light to the downstream transmission line 101a for the reflection monitor value A.

[0077] Further, the reflected light processing unit 914 similarly measures the reflected monitor value B. In this case, with the OSC light, the WDM light (C+L), and the Raman excitation light being output as signal lights on the downstream transmission path 101a, the reflected level of the OSC light detected by the PD 913 is measured as the reflected monitor value B via the transmission path 101a ~ the multiplexer / demultiplexer 121a ~ the optical filter 912.

[0078] Then, as shown in FIG. 8C and the like, the reflected light processing unit 914 calculates 3. the correction value of the reflected monitor value based on the reflected monitor values A and B, and outputs the calculated correction value of the reflected monitor value to the APSD control unit 905.

[0079] Thereby, the APSD control unit 905 corrects the reflected monitor value with the calculated correction value and 4. monitors the reflected monitor value during operation. The APSD control unit 905, for example, when a failure occurs in the transmission path 101a or when applying APSD control, cuts off the optical output to the transmission path 101a by the WDM optical transmission unit 903 (optical amplifier 123a), and also cuts off the Raman excitation to the transmission path 101b by the Raman amplifier 111.

[0080] In addition, when a failure occurs in the transmission path 101a, the APSD control unit 905 notifies the OSC processing unit 126 and, using the OSC signal, notifies the downstream NodeB (100B) of the APSD request.

[0081] (Hardware Configuration Example of the Control Unit of the Optical Transmission Device) FIG. 10 is a diagram showing a hardware configuration example of the control unit of the optical transmission device according to the embodiment. For example, the functions of the reflected light processing unit 914 shown in FIG. 9 can be configured by the general-purpose hardware shown in FIG. 10.

[0082] Note that the APSD control unit 905 shown in FIG. 9 requires high-speed processing and is currently configured by hardware such as an FPGA (Field-Programmable Gate Array).

[0083] In the example shown in FIG. 10, it includes a processor 1001 such as a CPU (Central Processing Unit), a memory 1002, a network IF 1003, a recording medium IF 1004, and a recording medium 1005. Also, each component is connected by a bus 1000 respectively.

[0084] Here, the processor 1001 is a control unit mainly responsible for the functions related to the reflected light processing unit 914. The processor 1001 may have a plurality of cores. The memory 1002 has, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), and a flash ROM. Specifically, for example, the flash ROM stores a control program, the ROM stores an application program, and the RAM is used as a work area for the processor 1001. The program stored in the memory 1002 is loaded into the processor 1001 to cause the processor 1001 to execute the coded processing.

[0085] The network IF 1003 serves as an interface with the network NW and controls the input / output of information with the outside. The network NW can use, for example, not only wired or wireless electrical transmission lines but also an optical transmission line via the transmission line 101.

[0086] The recording medium IF 1004 controls the read / write of data to the recording medium 1005 according to the control of the processor 1001. The recording medium 1005 stores the data written under the control of the recording medium IF 1004.

[0087] In addition to the components described above, for example, an input device, a display, etc. may be connectable via an IF.

[0088] Also, the function of the control unit shown in FIG. 10 may be, for example, a control unit that overall controls the optical transmission device 100. In this case, the function of the reflected light processing unit 914 shown in FIG. 9 can be a partial function of the control unit (processor 1001) that overall controls the optical transmission device 100.

[0089] (Example of reflection light control processing) FIG. 11 is a startup sequence diagram of the optical transmission device according to the embodiment. FIG. 11 shows the startup sequence in normal times and the processing executed by the control unit of the optical transmission device 100 (100A), mainly the reflection light processing unit 914 (processor 1001 in FIG. 10).

[0090] At startup, the optical transmission device 100A (reflection light processing unit 914) first outputs OSC light to the transmission line 101a by the OSC processing unit 126 (step S1101) and checks the link-up of the OSC (step S1102).

[0091] Next, the optical transmission device 100A measures the reflection monitor value A of the OSC light (step S1103). Also, the optical transmission device 100A measures the span loss of the transmission line 101a between itself and the downstream optical transmission device 100B (step S1104).

[0092] Next, the optical transmission device 100A activates the WDM amplifier (optical amplifier) 123a (step S1105) and activates the Raman amplifier 111 (step S1106).

[0093] Next, the optical transmission device 100A measures the reflection monitor value B of the OSC light (step S1107). Next, the optical transmission device 100A calculates a correction value of the reflection monitor value based on the measured reflection monitor values A and B (step S1108). The calculated correction value of the reflection monitor value is held by the APSD control unit 905.

[0094] After that, the optical transmission device 100A monitors the reflection monitor value during operation (step S1109). For example, the optical transmission device 100A (APSD control unit 905) determines the presence or absence of a fault (such as a transmission line break or opening) in the downstream transmission line 101a based on the reflection monitor value of the downstream transmission line 101a.

[0095] For example, when the corrected reflection monitor values (L1, L2) exceed a predetermined reflection detection threshold Th, it is determined that a failure (fiber break or disconnection) has occurred in the downstream transmission path 101a, and APSD is applied to shut down the optical amplifier 123a and the Raman amplifier 111.

[0096] In the normal state shown in FIG. 11, in order to always keep the number of wavelengths of WDM constant, the optical transmission device 100A does not change the correction value of the reflection monitor value even when the operating wavelength by the ROADM function changes. For example, the optical transmission device 100A automatically inserts ASE light into an unused wavelength for service operation to always keep the number of wavelengths of WDM constant.

[0097] FIG. 12 is a startup sequence diagram of the optical transmission device according to the embodiment. FIG. 12 shows the processing mainly executed by the control unit of the optical transmission device 100 (100A), particularly the reflected light processing unit 914 (the processor 1001 in FIG. 10), when the characteristics of the fiber in the transmission path 101a change.

[0098] Due to the fiber removal operation, the characteristics (loss, fiber type, etc.) of the fiber in the transmission path 101a change. Due to this fiber removal operation, the optical transmission device 100A applies APSD to shut down the WDM amplifier (optical amplifier 123a) and executes the sequence again after reconnecting the fiber.

[0099] Specifically, as shown in FIG. 12, when starting up, the optical transmission device 100A (reflected light processing unit 914) first outputs OSC light to the transmission path 101a by the OSC processing unit 126 (step S1201) and checks for OSC link-up (step S1202).

[0100] Next, the optical transmission device 100A measures the reflection monitor value A of the OSC light (step S1203). Also, the optical transmission device 100A measures the span loss of the transmission path 101a between itself and the downstream optical transmission device 100B (step S1204).

[0101] Next, the optical transmission device 100A activates the WDM amplifier (optical amplifier) 123a (step S1205) and activates the Raman amplifier 111 (step S1206).

[0102] Next, the optical transmission device 100A measures the reflection monitor value B of the OSC light (step S1207). Next, the optical transmission device 100A calculates a correction value of the reflection monitor value based on the measured reflection monitor value A and the reflection monitor value B (step S1208). The calculated correction value of the reflection monitor value is held by the APSD control unit 905.

[0103] Thereafter, the optical transmission device 100A monitors the reflection monitor value during operation (step S1209). For example, the optical transmission device 100A (APSD control unit 905) determines the presence or absence of a fault in the downstream transmission path 101a based on the reflection monitor value of the downstream transmission path 101a.

[0104] For example, due to a change in the characteristics of the fiber (such as loss, fiber type, etc.) described above, that is, the occurrence of a fiber removal operation, the corrected reflection monitor value (L2) exceeds a predetermined reflection detection threshold Th. As a result, the optical transmission device 100A (APSD control unit 905) determines that a fault has occurred in the downstream transmission path 101a and applies APSD (step S1210). Then, the optical transmission device 100A (APSD control unit 905) shuts down the optical amplifier 123a and the Raman amplifier 111 (step S1211). After the fiber is reconnected, the optical transmission device 100A returns to the process of step S1202 and executes the startup sequence again.

[0105] In the above embodiment, it is assumed that the optical transmission device 100A of the transmission node (NodeA) of one span executes the above processes 1 to 4. However, the present invention is not limited to this, and it can also be applied to an optical transmission system having a plurality of optical transmission devices 100A to 100N of a plurality of spans and a network management device (for example, a network controller).

[0106] For example, the optical transmission device 100 of a corresponding one-span transmission node (NodeA) performs the processes of 1. "Measurement of reflection monitor value A" and 2. "Measurement of reflection monitor value B". Then, the network controller acquires the information of 1 and 2 from the optical transmission device 100 of the transmission node (NodeA) of the corresponding span, calculates 3. "Corrected reflection monitor value", and transmits it to the optical transmission device 100 of the transmission node (NodeA) of the corresponding span. And the optical transmission device 100 of the transmission node (NodeA) of the corresponding span may perform 4. "Monitoring of reflection monitor value and APSD control" using the corrected reflection monitor value.

[0107] Also, in the above embodiment, the C band and the L band are taken as examples for the multi-band transmission of WDM light. However, it can be similarly applied to multi-band transmission including a plurality of other band ranges in which Raman excitation light generates noise in the wavelength band of OSC.

[0108] The optical transmission device of the embodiment described above Raman-amplifies the WDM light of the transmission line with Raman excitation light. When the device starts up, it measures the first reflected light level reflected from the transmission line when only OSC light is transmitted to the transmission line, and measures the second reflected light level reflected from the transmission line when WDM light, Raman excitation light, and OSC light are transmitted to the transmission line. After that, based on the first reflected light level and the second reflected light level, a correction value corresponding to the noise light of the reflected light level reflected from the transmission line is calculated. And during the operation of the device itself, it is provided with a control unit that monitors the input reflected light level and performs APSD (Auto Power Shut Down) control based on the reflected light level corrected by the correction value. Thereby, since the noise light equivalent included in the reflected light from the transmission line is corrected and the reflected light level is monitored, the malfunction of APSD caused by the noise included in the OSC light can be prevented, and the APSD control based on the presence or absence of a failure can be appropriately implemented.

[0109] In addition, in the embodiment, the WDM light of the optical transmission device includes a plurality of band regions where Raman excitation light generates noise in the wavelength band of the OSC. For example, the band regions are the C band and the L band. Thereby, even when high-level noise light is included in the reflected light due to multi-band transmission, an appropriate correction value can be calculated.

[0110] In addition, the optical transmission device of the embodiment has a Raman excitation amplifier that outputs Raman excitation light to the transmission line by backward excitation, forward excitation, or a combination thereof. Thereby, even when high-level noise light is included in the reflected light due to Raman excitation, an appropriate correction value can be calculated.

[0111] In addition, the optical transmission device of the embodiment has an optical filter that passes only the wavelength band of the OSC light among the signal lights reflected and input from the transmission line, and a photodetector that detects the reflected light level of the OSC light after passing through the optical filter, and the control unit monitors the reflected light level detected by the photodetector. Thereby, the level of the noise light included in the OSC light can be detected, the reflected light level can be monitored by correcting the equivalent of the noise light, and the APSD control can be appropriately performed in response to the presence or absence of a failure.

[0112] In addition, in the embodiment, the control unit of the optical transmission device calculates a correction value of the reflected light level based on the difference between the second reflected light level and the second reflected light level, sets a reflection detection threshold based on the correction value of the reflected light level, compares the input reflected light level with the reflection detection threshold during operation, and performs APSD control based on the comparison result. In this way, the optical transmission device can calculate the correction value of the reflected light level by a simple calculation process, and can perform APSD control simply and appropriately using the reflection detection threshold based on the correction value of the reflected light level during monitoring.

[0113] Regarding the above-described embodiment, the following additional remarks are further disclosed.

[0114] (Additional Remark 1) In an optical transmission device that Raman-amplifies the WDM light of a transmission line with Raman excitation light When starting up the device, measure the first reflected light level reflected and input from the transmission line when only OSC (Optical Supervisory Channel) light is transmitted to the transmission line. Measure the second reflected light level reflected and input from the transmission line when the WDM light, the Raman excitation light, and the OSC light are transmitted to the transmission line. Based on the first reflected light level and the second reflected light level, calculate a correction value corresponding to the noise light of the reflected light level reflected and input from the transmission line. During the operation of the device, monitor the input reflected light level and perform APSD (Auto Power Shut Down) control based on the reflected light level corrected by the correction value. An optical transmission device characterized by comprising a control unit.

[0115] (Appendix 2) The optical transmission device according to Appendix 1, characterized in that the WDM light includes a plurality of band bands in which the Raman excitation light generates noise in the wavelength band of the OSC.

[0116] (Appendix 3) The optical transmission device according to Appendix 2, characterized in that the band bands are the C band and the L band.

[0117] (Appendix 4) The optical transmission device according to Appendix 1, characterized by having a Raman excitation amplifier that outputs the Raman excitation light to the transmission line by backward excitation, forward excitation, or a combination thereof.

[0118] (Appendix 5) An optical filter that passes only the wavelength band of the OSC light among the signal lights reflected and input from the transmission line, An optical detector that detects the reflected light level of the OSC light after passing through the optical filter, and The control unit of the optical transmission device according to Appendix 1 is characterized by monitoring the reflected light level detected by the optical detector.

[0119] (Appendix 6) The control unit Calculate a correction value of the reflected light level based on the difference between the second reflected light level and the second reflected light level. Set a reflection detection threshold based on the correction value of the reflected light level. During the operation, compare the input reflected light level with the reflection detection threshold, and perform the APSD control based on the comparison result. The optical transmission device according to Addendum 1, characterized in that.

[0120] (Addendum 7) The control unit During the operation, when the WDM light to the transmission path stops due to the APSD control, re-execute the processing at startup. The optical transmission device according to Addendum 1, characterized in that.

[0121] (Addendum 8) In an optical transmission method of an optical transmission device that Raman-amplifies WDM light on a transmission path with Raman excitation light, When starting the own device, measure the first reflected light level reflected and input from the transmission path when only OSC (Optical Supervisory Channel) light is transmitted to the transmission path. Measure the second reflected light level reflected and input from the transmission path when the WDM light, the Raman excitation light, and the OSC light are transmitted to the transmission path. Based on the first reflected light level and the second reflected light level, calculate a correction value corresponding to the noise light of the reflected light level reflected and input from the transmission path. During the operation of the own device, monitor the input reflected light level, and perform APSD (Auto Power Shut Down) control based on the reflected light level corrected by the correction value. An optical transmission method, characterized in that.

Explanation of Signs

[0122] 100 (100A, 100B) Optical transmission device 101 (101a, 101b) Transmission path 111 Raman amplifier 121 (121a, 121b, 121c) Multiplexer / demultiplexer 123 (123a, 123b) Optical amplifier 125 Multiplexer 126 OSC Processing Unit 905 APSD Control Unit 911 OSC Optical Transceiver 912 Optical Filter 913 Photodetector (PD) 914 Reflected Light Processing Unit 1001 Processor 1002 Memory 1005 Recording Medium

Claims

1. In an optical transmission device that Raman-amplifies WDM light in a transmission line with Raman excitation light, when starting up the device itself, when only OSC (Optical Supervisory Channel) light is transmitted to the transmission line, the first reflected light level reflected and input from the transmission line is measured, when the WDM light, the Raman excitation light, and the OSC light are transmitted to the transmission line, the second reflected light level reflected and input from the transmission line is measured, based on the first reflected light level and the second reflected light level, a correction value corresponding to the noise light of the reflected light level reflected and input from the transmission line is calculated, during the operation of the device itself, the input reflected light level is monitored, and APSD (Auto Power Shut Down) control is performed based on the reflected light level corrected by the correction value, An optical transmission device characterized by comprising a control unit.

2. The optical transmission device according to claim 1, wherein the WDM light includes a plurality of band bands in which the Raman excitation light generates noise in the wavelength band of the OSC.

3. The optical transmission device according to claim 2, wherein the band bands are a C band and an L band.

4. The optical transmission device according to claim 1, further comprising a Raman excitation amplifier that outputs the Raman excitation light to the transmission line by backward excitation, forward excitation, or a combination thereof.

5. An optical filter that passes only the wavelength band of the OSC light among the signal lights reflected and input from the transmission line, and a photodetector that detects the reflected light level of the OSC light after passing through the optical filter, The optical transmission device according to claim 1, wherein the control unit monitors the reflected light level detected by the photodetector.

6. The control unit, calculates a correction value of the reflected light level based on the difference between the second reflected light level and the second reflected light level, sets a reflection detection threshold based on the correction value of the reflected light level, compares the input reflected light level with the reflection detection threshold during the operation, and performs the APSD control based on the comparison result. The optical transmission device according to claim 1.

7. In an optical transmission method of an optical transmission device that Raman-amplifies WDM light in a transmission line with Raman excitation light, When starting up the device, measure the first reflected light level that is reflected and input from the transmission line when only OS (Optical Supervisory Channel) light is transmitted to the transmission line. Measure the second reflected light level that is reflected and input from the transmission line when WDM light, Raman excitation light, and OS light are transmitted to the transmission line. Based on the first reflected light level and the second reflected light level, calculate a correction value corresponding to the noise light of the reflected light level that is reflected and input from the transmission line. During the operation of the device, monitor the input reflected light level, and perform APSD (Auto Power Shut Down) control based on the reflected light level corrected by the correction value. A optical transmission method characterized by the above.

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