JP4829996B2 - Optical transmission equipment - Google Patents

Description

  The present invention relates to an optical transmission apparatus, and more particularly to an optical transmission apparatus for an optical transmission system that transmits a plurality of signal lights by wavelength multiplexing and a control method thereof.

  In an optical communication system, in order to increase communication capacity and reduce system cost, a wavelength division multiplexing optical transmission technique is generally applied in which a plurality of signal lights having different wavelengths are bundled and communicated with one optical fiber. In an actual system, an optical fiber amplifier is installed on the transmission path to compensate for the loss of the optical signal that occurs in the optical fiber that is the transmission path between two distant points. A plurality of signal lights having different wavelengths are collectively amplified without being converted into.

  An optical fiber amplifier has a wavelength dependency on an amplification factor (gain) for signal light. For example, in the case of an optical fiber amplifier that amplifies an optical signal having a wavelength range of 1530 nm to 1560 nm, the amplification gain for signal light near 1530 nm is larger than the amplification gain of signal light near 1560 nm. For this reason, when a plurality of multiplexed signal lights having different wavelengths are amplified together, it is necessary to flatten the gain corresponding to the wavelength. In order to flatten the gain, a gain equalizing filter such as a dielectric multilayer filter or a fiber Bragg grating is mounted inside the optical fiber amplifier.

  The wavelength dependence of the amplification gain described above varies depending on the input light intensity of the optical fiber amplifier. In other words, if the gain of the optical fiber amplifier changes, the wavelength dependence of the gain also changes. Therefore, even with an optical amplifier equipped with a gain equalization filter, gain equalization is realized by the optical fiber amplifier. Only the period during which the gain is held at the design value. For this reason, in an optical fiber amplifier, in order to obtain gain flatness of multiplexed signal light with multiple wavelengths, the intensity of input / output light is monitored and constant gain control is performed to keep the gain constant. ing.

  In addition, in order to cope with restrictions on the input dynamic range of the receiver and nonlinear effects of the optical fiber in the optical transmission system, in addition to the above-described constant gain control, the output signal light intensity at each wavelength is kept constant. Output intensity constant control (hereinafter simply referred to as output constant control) is performed. In an optical transmission system without a constant output control function, when the transmission line loss changes, the input optical signal strength of the signal relay optical amplifier changes and the output optical signal strength of the optical amplifier changes. There is a possibility that the input optical signal intensity of the side optical transmission device changes and the input signal level of the receiver is out of the dynamic range.

  In order to keep the intensity of the input optical signal at the receiver constant, for example, an optical attenuator is inserted in the signal path of the optical fiber amplifier, and the optical attenuation is determined according to the loss generated in the transmission path on the signal input side. What is necessary is just to adjust the amount of attenuation of a vessel. Since the wavelength dependency of the attenuation amount in the optical attenuator is not affected by the input light intensity, both constant gain control and constant output control are possible by combining an optical fiber amplifier and an optical attenuator.

  The gain constant control in the optical fiber amplifier is, for example, that the intensity of the wavelength multiplexed signal light is observed on the input side and output side of the optical fiber amplifier, and the intensity ratio (gain) of the input signal light and the output signal light is always constant. This can be realized by controlling the excitation light of the amplifier. The output constant control for each wavelength is obtained by, for example, obtaining the total output light intensity of the optical fiber amplifier from the number of multiplexed signal lights (the number of multiplexed wavelengths) specified in advance and the output light intensity for each wavelength. The attenuation amount of the optical attenuator may be controlled so that the total output light intensity becomes a desired intensity.

  However, in the above output constant control method, when there is a difference between the number of multiplexed wavelengths that is a condition for calculating the total output light intensity and the number of wavelengths of multiplexed signal light that is actually input to the optical fiber amplifier Problems arise. In an optical transmission system, for example, when a part of a plurality of transmitters accommodated in an optical fiber fails or an optical fiber that connects the transmitter and the wavelength multiplexing unit is disconnected, wavelength multiplexing is performed on the optical fiber. A change occurs in the number of signal lights (number of wavelengths).

  In this case, at the moment when the failure occurs, each optical fiber amplifier cannot grasp the state of the number of wavelengths actually multiplexed. It becomes impossible to match the number of multiplexed wavelengths on the optical fiber. Therefore, when an optical signal of a certain wavelength is lost due to maintenance work or failure, the total output light intensity calculated with the number of signal lights larger than the number of signal lights actually multiplexed is set as the target value, and the fiber amplifier When the constant output control is executed, the output light intensity per signal light becomes larger than a predetermined value, and as a result, there arises a problem that each signal light reaches the receiver with an excessive input signal level.

  In order to deal with such a problem, for example, in the 1996 IEICE Communication Society Conference, lecture number B1096 (Non-Patent Document 1), the total signal light intensity output from the optical amplifier and the wavelength accommodated in the system A "WDM optical amplifier output level control method" has been proposed in which the output light intensity per signal light becomes a desired intensity by detecting the number of signals. Further, in Japanese Patent Laid-Open No. 2001-257646 (Patent Document 1), monitor light for monitoring control called pilot light (probe light) is extracted by a branch element provided on the output side of an optical amplifier, and light of probe light is extracted. A method of controlling the optical amplifier so that the intensity is constant has been proposed.

Yoshida et al., 1996 IEICE Communication Society Conference, Lecture Number B1096

JP 2001-257646 A

  Conventionally, in optical amplifiers, the speed of loss variation in the transmission line is sufficiently slow compared to the control speed of the optical amplifier, while the transient response characteristic of the signal strength change accompanying the change in the number of multiplexed wavelengths is the optical amplifier. The above two types of fluctuation factors are discriminated from the difference in the change speed of the optical signal intensity observed in the optical transmission device. The change in the number of wavelengths is, for example, an event that occurs in the operation of changing the communication path connecting the transmission point and the reception point, and the change rate of the wavelength number is assumed to be several hundred μs or less. On the other hand, the loss fluctuation is an abnormal event that occurs when, for example, an optical transmission system maintainer pulls or hooks an optical fiber, and the change speed of the transmission line loss fluctuation is assumed to be several ms or more.

  When paying attention to the difference in the change speed described above, a frequency threshold is set in advance for a change in the total signal intensity detected from the multiplexed input light of the optical amplifier, and the change speed of the total signal intensity accompanying the occurrence of a certain event. It is possible to determine whether the cause of the signal intensity fluctuation is a loss change in the transmission path or a change in the number of wavelengths depending on whether or not the frequency threshold is exceeded. Further, the control mode to be executed by the optical amplifier can be determined in accordance with the determined cause of the change in the total signal intensity. Here, as the control mode of the optical amplifier, it is necessary to adopt constant output control when loss variation occurs, and constant gain control when the number of wavelengths changes. The relationship between and should not be reversed.

  However, in the method of determining an event based on the frequency threshold described above, for example, when a change in the number of wavelengths occurs at a low speed of ms or more, it is not recognized that the change in the total signal strength is caused by the change in the number of wavelengths. It is misrecognized as being caused by a loss change in the transmission line. In this case, the constant output control for holding the output light intensity of the optical amplifier at the target value is selected, and an erroneous control operation of increasing the signal light intensity of each wavelength more than necessary is executed. In addition, in an optical amplifier, two control modes of a constant output control that compensates for a signal intensity change caused by a loss variation and a constant gain control that compensates for a signal intensity change caused by a wavelength number change coexist, When it becomes difficult to identify the above-mentioned variation factors, two control modes are executed at the same time even though one of the variation factors actually occurs, resulting in an adverse effect on the signal quality. Sometimes.

  However, the method of controlling the optical amplifier by detecting the number of multiplexed wavelengths proposed in Non-Patent Document 1 can handle only the loss fluctuation of the transmission line that changes relatively slowly or the fluctuation of the wavelength number that changes relatively quickly. There is a problem that it is not possible. In Non-Patent Document 1, since constant output control is always operating, the optical amplifier may malfunction not only when an abnormal event occurs but also during normal operation by a system administrator.

  In Patent Document 1, focusing on only the intensity change of the probe light, constant output control and constant gain control of the optical amplifier are performed. Therefore, as in Non-Patent Document 1, it is necessary to distinguish the cause of the intensity change of the signal light. There is no. Further, since there is no special limitation on the response time constant of the optical amplifier, it is possible to cope with a high-speed transmission line loss fluctuation of several ms or less and a low-speed wavelength change of several ms or more. However, in Patent Document 1, since the optical amplifier control depends on the probe light which is the specific light, the optical amplifier becomes uncontrollable when an abnormality occurs in the probe light for some reason, such as a failure of the light source. There is a problem that the transmission of signal light is hindered.

The object of the present invention is to appropriately adjust the intensity of each signal light even in a steady state where there is no change in the loss of the transmission line or a change in the number of multiplexed wavelengths or in an abnormal state where a change in the loss of the transmission line or a change in the number of multiplexed wavelengths occurs. It is an object of the present invention to provide an optical transmission apparatus and a control method thereof that can ensure communication quality by controlling the above.
Another object of the present invention is to provide an optical transmission apparatus capable of controlling the output of an optical amplifier in an appropriate control mode corresponding to the variation factor of the light intensity regardless of the speed of change of the light intensity due to the occurrence of an abnormal event, and the control thereof. It is to provide a method.

In order to achieve the above object, the optical transmission apparatus of the present invention separates the monitoring light from the received wavelength multiplexed signal light and detects the intensity of the monitoring light, and the intensity of the wavelength multiplexed signal light after the monitoring light separation. A second means for detecting; a gain-controlled optical amplifier for amplifying the wavelength-multiplexed signal light; and an attenuation variable optical attenuator for adjusting the intensity of the wavelength-multiplexed signal light output from the optical amplifier; The optical amplifier is controlled so as to always have a constant gain, and includes a monitoring control unit that controls the attenuation amount of the optical attenuator so that the output intensity of the wavelength multiplexed signal light becomes a predetermined target value.
The monitoring control unit monitors the monitoring light intensity and the signal light intensity output from the first and second means, the fluctuation of the monitoring light intensity is within an allowable range, and the fluctuation of the signal light intensity is within an allowable range. When the value is off, constant control of the output light intensity by the optical attenuator is suppressed.

  One feature of the present invention is that the monitoring control unit intermittently executes constant control of the output light intensity by the optical attenuator for a period of Δt during the Δt period while the monitoring light intensity varies within an allowable range. It is in.

  Another feature of the present invention is that the monitoring control unit intermittently executes constant control of the output light intensity by the optical attenuator at a predetermined period during a period in which the fluctuation of the monitoring light intensity is within an allowable range. When the monitoring light intensity fluctuates outside the allowable range, the constant control of the output light intensity by the optical attenuator is forcibly executed over a predetermined period Δτ.

  According to still another aspect of the present invention, when the monitoring light intensity fluctuates outside the allowable range and the monitoring light intensity is within a preset output control range, the monitoring control unit outputs an optical attenuator. When the constant control of the light intensity is performed over a predetermined period Δτ and the monitoring light intensity fluctuates outside the output control range, the constant control of the output light intensity by the optical attenuator is terminated.

  According to one embodiment of the present invention, when the signal light intensity falls outside the allowable range during the constant control of the output light intensity, the constant control of the output light intensity is stopped. In addition, the monitoring control unit updates the threshold value for defining the above-described allowable range every fixed period T0 using the observed monitoring light intensity and the signal light intensity as reference values, and the monitoring light intensity with the variable threshold value. Changes in signal light intensity are monitored.

  In another embodiment of the present invention, the optical transmission device includes a monitoring light transmitter that generates monitoring light to be transmitted to the optical transmission path of the next section, and the monitoring control unit outputs the monitoring light from the first means. By changing the intensity of the monitoring light output from the monitoring light transmitter according to the intensity, the occurrence of the loss change in the previous section is transmitted to the subsequent optical transmission apparatus. Transmission of the loss change in the previous section to the subsequent optical transmission apparatus can also be achieved by changing the intensity of the monitoring light output from the monitoring optical transmitter according to the intensity of the signal light output from the optical amplifier. In this way, by transmitting the loss change in the previous section according to the intensity change of the monitoring light, for example, when wavelength multiplexed signal light is output to the next section in a state where the intensity compensation accompanying the loss change is incomplete However, the next optical transmission apparatus can be prevented from erroneously recognizing the cause of the change in the signal light intensity as the change in the number of multiplexed wavelengths.

The control method of the optical transmission apparatus of the present invention includes a step of detecting the light intensity of the monitoring light separated from the reception wavelength multiplexed signal light, a step of detecting the intensity of the wavelength multiplexed signal light after the monitoring light separation,
Amplifying the wavelength-multiplexed signal light with a constant gain; controlling the output light intensity so that the output light intensity of the amplified wavelength-multiplexed signal light becomes a target value; and the monitoring light intensity and the signal light intensity. And when the fluctuation of the monitoring light intensity is within the allowable range and the fluctuation of the signal light intensity is outside the allowable range, the constant control of the output light intensity by the optical attenuator is suppressed. Features.

  When loss fluctuations occur on the optical transmission path in which the monitoring light and the signal light are multiplexed and transported, the optical intensities of both the monitoring light and the signal light change, whereas the multiplexed signal light on the upstream side changes. When the number (number of wavelengths) changes, only the intensity of the signal light changes. The optical transmission device of the present invention utilizes the above-mentioned properties in the optical transmission system, and when the fluctuation of the monitoring light intensity is within the allowable range and the fluctuation of the signal light intensity is outside the allowable range, the fluctuation factor of the signal light intensity Therefore, the constant control of the output light intensity by the optical attenuator is suppressed.

  Therefore, according to the present invention, it is possible to avoid erroneous adjustment of the signal light intensity due to execution of constant control of the output intensity of the optical amplifier when the number of multiplexed wavelengths is changed. Further, according to the present invention, when the fluctuation of the monitoring light intensity is within the allowable range, the periodic light intensity output constant control is executed, and the monitoring light intensity is allowed due to the change in the loss of the transmission line. When the value is out of range, forced light intensity output constant control for a predetermined period is executed. Therefore, target value control of signal light output intensity is possible regardless of the change rate of loss fluctuation, and communication quality is improved. An optical transmission system that guarantees

  In the embodiment of the present invention, the constant gain control of the optical amplifier is always executed, and the constant output control is intermittently performed for a short time while the fluctuation of the monitoring light intensity is within the allowable range. The parallel execution period of constant control and constant gain control is made as short as possible. In this case, since the probability that the number of multiplexed wavelengths will change during the constant output control is reduced, it is possible to reduce the occurrence of the above-mentioned erroneous adjustment of the signal light intensity when the number of multiplexed wavelengths changes.

  In addition, if the monitoring light intensity is outside the allowable range, forced light intensity output constant control for a predetermined period is executed, and if the fluctuation of the signal light intensity is outside the allowable range during the output control, the light intensity is Since the constant output control is stopped, it is possible to reduce the occurrence of the erroneous adjustment of the signal light intensity when the number of multiplexed wavelengths is changed even during the constant light intensity output control.

The figure for demonstrating the schematic structure of the wavelength division multiplexing optical transmission system to which this invention is applied. The figure which shows one Example of the optical amplifier 30 mounted in the optical transmission apparatus 1 (1A-1C) of FIG. FIG. 6 is a diagram showing another embodiment of the optical amplifier 30 mounted on the optical transmission device 1 of FIG. 1. The figure for demonstrating the relationship between the gain fixed control (A) of the optical amplifier 30 in this invention, and periodic output fixed control (B). The figure for demonstrating the relationship between the execution conditions of the periodic output constant control and the forced output constant control which the monitoring control part 20 performs, and the signal light output intensity of the optical amplifier 30. FIG. The figure for demonstrating the output fixed control suppression operation | movement which the monitoring control part 20 performs. The flowchart of the threshold value update process routine which the monitoring control part 20 performs periodically. The flowchart of the fixed output control routine which the monitoring control part 20 performs. The figure which shows further another Example of the optical amplifier 30 mounted in the optical transmission apparatus of FIG. The figure which shows the principal part of the monitoring optical transmitter in the optical amplifier 30 of FIG.

Hereinafter, a wavelength division multiplexing optical transmission system and a control method thereof according to the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a wavelength division multiplexing optical transmission system to which the present invention is applied.
The optical transmission system includes a plurality of optical transmission apparatuses 1 (1A, 1B, 1C) connected by optical fibers 2 (2-1, 2-2) serving as transmission paths. The signal light output from the transmitter 10 mounted on the optical transmission device 1A is amplified by the transmission optical amplifier 30-1, and then the optical fiber 2-1, the relay optical transmission device 1B, and the optical fiber 2-2. Then, it reaches the opposite optical transmission device 1C and is received by the receiver 11 of the optical transmission device 1C. While the transmission signal light from the optical transmission device 1 </ b> A passes through the optical fiber 2, the light intensity decreases due to propagation loss. In order to compensate for this, the optical transmission device 1B is equipped with a repeater optical amplifier 30-2, and the optical transmission device 1C is equipped with a reception optical amplifier 30-3.

  Each of the optical transmission devices 1 (1A to 1C) includes a monitoring control unit 20 (20-1 to 20-3), and, as indicated by a broken line, the optical fiber is transmitted from the monitoring control unit 20-1 of the optical transmission device 1A. The monitoring light transmitted to 2-1 is received and processed by the monitoring control unit 20-2 of the adjacent relay optical transmission apparatus 1B, and the monitoring light transmitted from the monitoring control unit 20-2 to the optical fiber 2-2 is received. Reception processing is performed by the monitoring control unit 20 of the optical transmission device 1C. The monitoring light carries control information necessary for the optical transmission apparatus such as alarm information, apparatus status information, and the number of multiplexed signal lights.

  In the present invention, as indicated by a broken line, the monitoring light transmitted from the monitoring control unit 20-1 of the optical transmission device 1A is transmitted from the signal light before being input to the optical amplifier 30-2 of the relay optical transmission device 1B. These are separated and input to the monitoring control unit 20-2. Also, the monitoring light output from the monitoring control unit 20-2 is multiplexed with the signal light on the output side of the optical amplifier 30-2, and from the signal light before being input to the optical amplifier 30-3 of the optical transmission device 1C. It is separated and input to the monitoring control unit 20-3.

  That is, in the present invention, only signal light is input to the optical amplifier 30. Therefore, for example, when a loss variation occurs in the section of the optical fiber 2-1, in the succeeding relay optical transmission device 1B, the monitoring light input to the monitoring control unit 20-2 and the optical amplifier 30-2 Both input and output intensities change, but when the number of signal lights (number of wavelengths) transmitted from the optical transmission device 1A to the optical fiber 2-1 increases or decreases, only the input light intensity of the optical amplifier 30-2 changes. However, there is no change in the intensity of the monitoring light input to the monitoring control unit 20-2.

  In the present invention, the monitoring control unit 20-2 monitors the intensity of the input / output signal light of the optical amplifier 30-2 and the intensity of the monitoring light, and the intensity change appears in both the input / output signal light and the monitoring light. The change factor of the signal light is identified depending on whether it appears only in the input / output signal light. During the period when at least one signal light is input to the optical amplifier 30-2, the supervisory control unit 20-2 is always capable of dealing with the fluctuation in the intensity of the signal light due to the change in the number of multiplexed wavelengths. A constant gain control of the optical amplifier 30-2 is performed.

  One feature of the present invention is that when the supervisory control unit 20-2 performs periodic constant output control of the optical amplifier 30-2 in parallel with the constant gain control, and detects a change in the supervisory light intensity. Thus, it is determined that the loss of the optical fiber 2-1 has changed, and instead of the periodic output constant control, the forced output constant control for a predetermined period is executed. The periodic output constant control is executed for a relatively short Δt period every fixed period T1, and the attenuation amount of the optical attenuator is adjusted so that the total output signal intensity of the optical amplifier 30-2 matches the target value. In the forced output constant control, the attenuation adjustment of the optical attenuator is performed over a period Δτ longer than the period Δt.

Another feature of the present invention is that when the supervisory control unit 20-2 detects a change in the number of multiplexed wavelengths, that is, the supervisory light has no intensity change that is outside the allowable range, but the optical amplifier 30-2. When it is detected that there has been a change in light intensity outside the allowable range of the input / output signal, the execution of the periodic or forced output constant control described above is suppressed.
That is, the fact that the number of multiplexed wavelengths has changed means that the number of multiplexed signal lights (number of wavelengths), which is a precondition for constant output control in the monitoring control unit 20-2, and the actual input / output to the optical amplifier 30-2. This means that the number of signal lights (number of wavelengths) is different, so that the correct total output light intensity that is the target value for constant output control is set in the monitoring controller 20-2. This is because the execution of the constant output control is meaningless during this period.

  When the number of multiplexed wavelengths changes, the supervisory control unit 20-2, for example, determines the total output based on the number of multiplexed signal lights indicated by the control information transmitted by the upstream optical transmission device of the optical transmission system by the supervisory light. Change the target value of light intensity. However, the supervisory control unit 20-2 itself may identify the input signal light of the optical amplifier for each wavelength and detect the current number of multiplexed signal lights. The monitoring control unit 20-3 of the opposite optical transmission device 1C performs the same control operation as that of the monitoring control unit 20-2 of the relay optical transmission device 1B described above for the received light.

FIG. 2 is a configuration diagram showing an embodiment of the optical amplifier 30 mounted on the optical transmission apparatus 1.
The optical amplifier 30 includes a demultiplexer 31 for demultiplexing the monitoring light from the input light of the optical fiber, a first optical coupler 32 for branching a part of the signal light that has passed through the demultiplexer 31, and an optical coupler. Optical fiber amplifier 33 that optically amplifies signal light within the signal light wavelength band that has passed through 32, second optical coupler 34 that branches a part of the output signal light of optical fiber amplifier 33, and optical coupler 34 A variable optical attenuator 35 that can freely adjust the passage loss of the output light, a third optical coupler 36 that branches a part of the output signal light of the optical attenuator 35, a monitoring optical transmitter 47, and a transmitter 47 Is provided with a multiplexer 37 for combining the monitoring light output from the signal light and the signal light passed through the optical coupler 36 and transmitting the resultant light to the optical fiber on the output side.

  The monitoring light separated from the signal light by the demultiplexer 31 is input to the monitoring light receiver 41, and the monitoring light intensity Em and the control information extracted from the monitoring light are input from the monitoring light receiver 41 to the monitoring control unit 20. D1 is output. The signal light branched by the first optical coupler 32 is input to the detector 42, and the output of the detector 42 is input to the monitoring controller 20 as the signal light input intensity Es. The signal light branched by the second optical coupler 34 is input to the detector 44, and the output of the detector 44 is input to the monitoring controller 20 as the amplified signal light intensity Ea. The signal light branched by the third optical coupler 36 is input to the detector 46, and the output of the detector 46 is input to the monitoring controller 20 as the signal light output intensity Eo.

  The monitoring control unit 20 monitors the light intensity output from the monitoring light receiver 41 and the detectors 42 to 46, performs the above-described constant gain control, constant output control, and suppression control of the constant output control, and also receives the monitoring light. The control information D1 received from the transmitter 41 is relayed to the monitoring light transmitter 47 as control information D2. In the constant gain control, the pump light of the optical fiber amplifier 33 is adjusted by the control signal S1 so that the ratio between the signal light input intensity Es and the amplified signal light intensity Ea is always constant. In the constant output control, the attenuation amount of the variable optical attenuator 35 is adjusted by the control signal S2 so that the signal light output intensity Eo becomes a predetermined target value.

FIG. 3 shows another embodiment of the optical amplifier 30 mounted on the optical transmission apparatus 1.
In the optical amplifier 30 shown here, the optical fiber amplifier has a two-stage configuration of a front-stage optical amplifying unit 33 whose gain is controlled by a control signal S1 and a rear-stage optical amplifying unit 38 whose gain is controlled by a control signal S11. In addition, ports P1 and P2 for connecting a dispersion compensation device for compensating the chromatic dispersion of the optical fiber are provided on the input side of the optical amplification unit 38 at the subsequent stage. In an optical transmission system in which chromatic dispersion in an optical fiber section is a problem, an optical amplifier that enables connection of a dispersion compensation device as in this embodiment is effective.

  The optical amplifier 30 shown in FIG. 2 and FIG. 3 particularly shows the configuration of the optical amplifier 30-2 mounted on the relay optical transmission device 1B. Since the optical amplifier 30-1 mounted on the optical transmission device 1A on the transmission side does not receive monitoring light, the structure of FIGS. 2 and 3 omits the duplexer 31 and the monitoring light receiver 41. Things can be applied. In addition, in the optical transmission device 1C on the receiving side, since there is no next transmission section, the optical amplifier 30-3 omits the multiplexer 37 and the monitoring optical transmitter 47 from the configuration of FIGS. The structure can be applied.

FIG. 4 shows the relationship between the constant gain control and the periodic constant output control of the optical amplifier in the present invention, with the horizontal axis taking time.
When the optical transmission apparatuses 1B and 1C are in an operating state and signal light is input to the optical amplifier 30, the supervisory control unit 20 continuously executes constant gain control as shown in FIG. In the present invention, the output constant control is stopped in principle in a steady state where there is no loss fluctuation in the optical fiber section, and as shown in FIG. (B), only a minute period Δt at a constant time interval T1. It is executed intermittently.

  Next, periodic output constant control and forced output constant control executed by the monitoring control unit 20 of the optical transmission apparatuses 1B and 1C will be described with reference to the signal waveform diagram shown in FIG. 5, (A) is the monitoring light intensity Em observed as the output of the monitoring light receiver 41, (F) is the signal light intensity Es observed as the output of the detector 42, and (G) is the detector 46. A change in signal light output intensity Eo observed as an output is shown.

  As shown in (B), the monitoring control unit 20 updates the threshold for detecting a change in the monitoring light intensity Em at a constant period T0. As will be described later with reference to FIG. 6, the threshold for detecting the change in the signal light intensity Es is also updated at the same period T0. As a threshold for detecting a change in the monitoring light intensity Em, in this embodiment, as shown in (A), the first value is based on the value (black circle) of the monitoring light intensity Em observed at the time of threshold update. An upper limit threshold value Mth (H1), a first lower limit threshold value Mth (L1), a second upper limit threshold value Mth (H2), and a second lower limit threshold value Mth (L2) are set.

  The first upper limit threshold value Mth (H1) and the first lower limit threshold value Mth (L1) are used to determine whether or not the fluctuation of the monitoring light intensity Em is within an allowable range. For example, the first upper limit threshold value Mth (H1) and the first lower limit threshold value Mth (H1) A value of ± 3 dB of the monitoring light intensity Em observed at t3, t4,. On the other hand, the second upper limit threshold value Mth (H2) and the second lower limit threshold value Mth (L2) are used to determine whether or not the change in the monitoring light intensity Em is within the output control range in which the forced output constant control is to be executed. For example, a value of ± 5 dB of the observed monitoring light intensity Em is applied.

  Here, the threshold update period T0 can be arbitrarily selected by the system administrator, and is set to a period sufficiently larger than the change rate of the monitoring light intensity to be observed. The monitoring control unit 20 applies these variable threshold values updated at the period T0 and constantly monitors changes in the monitoring light intensity Em and the signal light intensity Es output from the monitoring light receiver 41 and the detector 42.

  In this embodiment, the monitoring control unit 20 determines that the loss variation of the transmission line (optical fiber) is as long as the monitoring light intensity Em is between the first upper limit threshold Mth (H1) and the first lower limit threshold Mth (L1). It is determined that the value is within the allowable range, and as shown by 51, 52,... In FIG. When the monitoring light intensity Em fluctuates beyond the allowable range of the first upper limit threshold value Mth (H1) to the first lower limit threshold value Mth (L1) as indicated by 61 in FIG. It is determined that a large loss change that affects the communication quality has occurred in the transmission line, and forced output intensity constant control for a certain period Δτ shown in FIG. While the forced constant output control is being executed, as shown by the broken line 53, the periodic constant output control is suppressed, and the constant output control (54,. ) Is resumed.

  If the amount of fluctuation of the monitoring light intensity Em is large and the monitoring light intensity Em is outside the output control range defined by the second upper limit threshold value Mth (H2) to the second lower limit threshold value Mth (L2), the monitoring control unit 20 Then, it is determined that an abnormality in intensity has occurred in the monitoring light itself, and the constant output control operation is stopped.

  As described above, when the fluctuation of the monitoring light intensity Em is within the allowable range between the first upper limit threshold Mth (H1) and the first lower limit threshold Mth (L1), the constant output control is performed intermittently. Therefore, the output intensity Eo of the signal light changes in proportion to the intensity fluctuation of the input light during the suspension period of the constant output control, as shown in FIG. However, the threshold update cycle T0, the first upper limit threshold Mth (H1), and the first lower limit threshold Mth (L1) are appropriately set, and the constant output control is suspended while the variation of the monitoring light intensity Em is within the allowable range. By doing so, it is possible to suppress the fluctuation of the signal light output intensity Eo described above to an extent that does not affect the communication quality.

  According to this embodiment, the attenuation is periodically adjusted on the output side of the optical fiber amplifier so that the output intensity Eo of the signal light matches the target value every T1, and the constant output control is suspended. Even if the input intensity Es of the signal light fluctuates beyond the allowable range during the period, the monitoring control unit 20 performs the forced output constant control, and thus the output intensity Eo of the signal light. However, there is no fear that it will fluctuate so much as to affect the communication quality.

  Next, with reference to the signal waveform diagram shown in FIG. 6, a description will be given of the output constant control suppression operation required when the number of multiplexed wavelengths changes. 6A shows a change in the signal light intensity Es observed as the output of the detector 42, and FIG. 6C shows output constant control that is periodically executed at intervals of T1.

  As shown in FIG. (B), the monitoring controller 20 updates the upper limit threshold value Sth (H) and the lower limit threshold value Sth (L) for detecting a change in the signal light intensity Es at a constant period T0. As the upper limit threshold value Sth (H) and the lower limit threshold value Sth (L), for example, a value of ± 3 dB of the periodically observed signal light intensity Es is applied.

  The monitoring control unit 20 applies the variable threshold values Sth (H) and Sth (L) updated at the period T0 in parallel with the above-described variation detection of the monitoring light intensity Em to constantly change the variation in the signal light intensity Es. Monitoring. Although the monitoring light intensity Em varies within the allowable range between the first upper limit threshold value Mth (H1) and the first lower limit threshold value Mth (L1), the signal light intensity Es is shown in FIG. ), When the value falls outside the range of the threshold values Sth (H) to Sth (L), the monitoring control unit 20 determines that the number of multiplexed signal lights (number of wavelengths) has changed.

  When the number of multiplexed signal light changes, if the constant output control is executed by applying the previous target value (total signal light intensity), the light intensity per signal light is controlled to an incorrect value. Therefore, the monitoring control unit 20 turns on the constant output prohibition flag as shown in FIG. 4D at the time tn when it is detected that the number of multiplexed signal lights (number of wavelengths) has changed. During the period when the output constant control prohibition flag is on, the execution of the periodic output constant control is suppressed as indicated by a broken line in FIG. During this period, the forced output constant control is also suppressed.

  The suppression of the constant output control by the constant output control prohibition flag needs to be continued until the abnormal state of the target value of the constant output control in the monitoring controller 20 is resolved. When the monitoring control unit 20 turns on the constant output control prohibition flag, the control target value reset state shown in FIG. In this state, the output constant control is performed at timing tm when the number of multiplexed wavelengths physically input to the optical amplifier 30 is specified, and resetting of a new total signal light intensity that is the target value of the constant output control is completed. The prohibition flag is returned to the off state, and the constant output control is resumed.

  The number of multiplexed wavelengths is extracted from the monitoring light received from the upstream optical transmission apparatus, and the supervisory control unit 20 calculates a new total signal light intensity as a control target based on the number of multiplexed wavelengths. Since the change of the control target value for the constant output control is necessary for all the transmission apparatuses in the optical transmission system, each monitoring control unit 20 is configured to perform a predetermined time after the resetting of the control target value is completed. Then, the output constant control prohibition flag is returned to the off state. Even when the constant output control is suppressed by the prohibition flag, since the constant gain control is continuously executed, the influence of the change in the number of multiplexed wavelengths on the output intensity of the signal light is small.

FIG. 7 shows a flowchart of a threshold update processing routine 200 that the monitoring control unit 20 executes in response to a timer interrupt at the T0 interval.
In the threshold update processing routine 200, the input intensity Em of the monitoring light output from the monitoring light receiver 41 is read (step 202), and the input intensity Es of the signal light output from the detector 42 is read (204). Next, the first upper limit threshold value Mth (H1), the first lower limit threshold value Mth (L1), the second upper limit threshold value Mth (H2), and the second lower limit threshold value are determined by a predetermined calculation formula using the monitoring light input intensity Em as a reference value. Mth (L2) is calculated, and these values are stored as threshold values for determining the monitoring light fluctuation amount (206). Further, the upper limit threshold value Sth (H) and the lower limit threshold value Sth (L) are calculated by a predetermined calculation formula using the signal light input intensity Es as a reference value, and these values are stored as threshold values for determining the variation amount of the signal light. (208).

  Instead of calculating the threshold value, for example, conversion indicating values of Mth (H1), Mth (L1), Mth (H2), and Mth (L2) calculated in advance corresponding to the expected Em value. A table may be prepared, and each threshold value may be searched from the conversion table using the observed Em value as a search key each time the threshold value is updated. The same applies to the threshold values Sth (H) and Sth (L).

FIG. 8 shows a flowchart of a constant output control routine 300 executed by the monitoring control unit 20.
In the constant output control routine 300, the monitoring control unit 20 starts a T1 timer indicating the passage of time T1 (step 302), and checks the state of the constant output control prohibition flag (304). If the prohibition flag is in the on state (“1”), it is determined whether or not the resetting of the control target value has been completed (306). If not, the process returns to step 304. When the resetting of the control target value has been completed, the prohibition flag is returned to the off state (“0”) (308), the T1 timer is started (310), and the monitoring light intensity Em is determined (320). ).

  When the prohibition flag is in the OFF state in step 304, the monitoring controller 20 reads the signal light input intensity Es output from the detector 42, and the signal light input intensity Es is the upper limit threshold value Sth (H) and the lower limit threshold value Sth. It is determined whether or not it is within an allowable range between (L) (312). If the input intensity Es of the signal light is within the allowable range, step 320 for constant output control is executed. If the input intensity Es of the signal light is outside the allowable range, the prohibition flag is set to the on state. The process returns to step 304 (314). From these control sequences, it can be seen that the constant output control is suppressed during the period in which the prohibition flag is on.

  In step 320, the monitoring control unit 20 reads the input intensity Em of the monitoring light output from the monitoring light receiver 41, and the input intensity Em of the monitoring light is determined by the first upper limit threshold value Mth (H1) and the first lower limit threshold value Mth ( Check whether it is within the allowable range with L1). If the input intensity Em of the monitoring light is within the allowable range, it is determined whether or not the T1 timer has timed out (322). If not, the process returns to step 304.

  The supervisory control unit 20 executes the constant output control when the T1 timer times out (324). That is, the output intensity Eo of the signal light output from the detector 46 is read, the intensity Eo is compared with a predetermined control target value, and the attenuation of the optical attenuator 35 is set so that the intensity Eo matches the control target value. A control signal S2 for adjusting the amount is output. The constant output control here is repeatedly executed until the time Δt elapses after the control is started. When the time Δt elapses (326), the monitoring control unit 20 stops the constant output control (328). Returning to step 302, the T1 timer is restarted.

  In step 320, if the input intensity Em of the monitoring light is outside the allowable range, the monitoring controller 20 determines that the input intensity Em of the monitoring light is between the second upper limit threshold value Mth (H2) and the second lower limit threshold value Mth (L2). It is checked whether it is within the output control range defined in (330). When the input intensity Em of the monitoring light is out of the output control range, the monitoring control unit 20 determines that the monitoring light is in an abnormal state, and ends the constant output control routine 200. When the input intensity Em of the monitoring light remains within the output control range, the monitoring control unit 20 executes the forced output constant control for the period Δτ (332). That is, similarly to the periodic output constant control executed in step 324, the attenuation amount of the optical attenuator 35 is adjusted by the control signal S2 so that the output intensity Eo of the signal light matches the control target value.

  Since the forced constant output control is performed over a period Δτ longer than the periodic constant output control time Δt, the number of multiplexed wavelengths may change during the constant output control. Therefore, during the execution of the forced output constant control, the monitoring control unit 20 determines whether or not the period Δτ has passed for each control cycle from the reading of the signal light output intensity Eo to the output of the control signal S1. If the period Δτ has not elapsed (334), it is determined whether or not the input intensity Es of the signal light output from the detector 42 is within the allowable range of the upper limit threshold value Sth (H) to the lower limit threshold value Sth (L). Determine (336). If the signal light input intensity Es is within the allowable range, the process returns to step 330 and the constant output control cycle is repeated. If the signal light input intensity Es is outside the allowable range, it is determined that the number of multiplexed wavelengths has changed, the output constant control is stopped (338), and the prohibition flag is set to the on state (340). Return to step 304.

  In the above flowchart, since the execution period Δt of the periodic output constant control is short, the output constant control in step 324 is repeated on the assumption that the probability that the number of multiplexed wavelengths will change during execution of the output constant control is extremely low. However, even in periodic output constant control, the control operation may be stopped immediately when a change in the number of multiplexed wavelengths is detected by performing the same determination as in step 336. .

  In the first embodiment described above, the monitoring controller 20 terminates the monitoring light for each section of the optical fiber, and for the next section, a new one is sent from the monitoring light transmitter 47 as shown in FIG. Since the monitoring light is transmitted, for example, the monitoring control unit 20-3 of the optical transmission device 1C illustrated in FIG. 1 grasps whether or not the loss change has occurred in the first optical fiber transmission section 2-1, and its degree. Can not do it. Therefore, when a loss change occurs in the transmission section 2-1, if for some reason, the compensation of the signal light output intensity Eo in the optical transmission device 1B is incomplete and the signal light output intensity Eo remains unchanged, As a result, there is a possibility that an optical signal showing an intensity change exceeding the allowable range is relayed to the transmission section 2-2. In this case, the monitoring control unit 20-3 of the downstream optical transmission device 1C can erroneously recognize the change in the input intensity of the received signal light as the change in the number of wavelengths because the intensity fluctuation of the monitoring light is within the allowable range. There is sex.

  In the optical amplifier of the second embodiment, in order to eliminate the above-described misrecognition in the optical transmission apparatus on the downstream side, as shown in FIG. The output intensity of the monitoring light output from is changed. In this case, the supervisory control unit 20 reflects the change in the supervisory light intensity Em detected by the supervisory light receiver 41 in the new supervisory light intensity output from the supervisory light transmitter 47, so that The generated loss fluctuation is relayed to the subsequent optical transmission apparatus.

  In order to change the light intensity of the monitoring light, for example, the drive bias current of the laser diode included in the monitoring light transmitter 47 may be controlled by the control signal S3. Also, as shown in FIG. 10, a variable optical attenuator 471 is inserted in the output optical path of the laser diode 470 driven by the modulation circuit 472, and the monitoring controller 20 controls the optical attenuator 35 as described above. The monitoring light intensity input to the multiplexer 37 may be changed by controlling the variable optical attenuator 471.

  In this embodiment, the monitoring control unit 20 generates a control signal S3 that changes in proportion to the monitoring light intensity Em of the previous transmission section read from the monitoring light receiver 41, and is output from the monitoring light receiver 41. The light intensity is changed in the same manner as the monitoring light intensity Em. The change in the intensity of the monitoring light is observed by the monitoring control unit 20-3 mounted on the downstream optical transmission apparatus 1C. The supervisory control unit 20-3 operates in the same manner as the supervisory control unit 20 described in the first embodiment, and the observed supervisory light intensity Em has a first upper limit threshold value Mth (H1) and a first lower limit threshold value Mth (L1). ), The periodic output constant control is executed. When the monitoring light intensity Em is out of the allowable range, the forced output constant control is executed.

  As described above, even if the compensation of the signal light output intensity Eo in the optical transmission apparatus 1B is incomplete and the signal light output intensity Eo from the preceding optical transmission apparatus remains fluctuated, this is a loss of the transmission path. As long as it is caused by the change, the observed monitoring light intensity Em also fluctuates, so that it is not erroneously detected as a change in the number of multiplexed wavelengths. Further, when the fluctuation of the signal light intensity Es observed by the monitoring control unit 20-3 is within the allowable range, and the fluctuation of the monitoring light intensity Em is out of the allowable range, the forced output constant control is executed. However, the output constant control can be freely executed except when the number of multiplexed wavelengths is changed, and there is no problem even if there is a partial difference in the fluctuation pattern of the signal light intensity Es and the monitoring light intensity Em.

In the third embodiment, in the optical amplifier of FIG. 9, the intensity of the new monitoring light output from the monitoring optical transmitter 47 is changed in proportion to the signal light output intensity Ea output from the optical fiber amplifier 33. Features.
That is, in the present embodiment, the monitoring control unit 20 changes the control signal S3 according to the signal light output intensity Ea output from the detector 44, and the control signal S3 causes the laser diode 470 of the monitoring light transmitter 47 to change. The drive bias current or the attenuation amount of the optical attenuator 471 is controlled. According to this embodiment, since the signal light intensity and the monitoring light intensity change in conjunction with each other at the time of output from the relay optical transmission apparatus, the signal light intensity fluctuation is multiplexed in the subsequent optical transmission apparatus. There is no possibility of being mistakenly recognized as a change in the number of wavelengths.

  As is clear from the above embodiments, according to the present invention, two types of events are identified: a change in transmission line loss that occurs in an optical transmission system and a change in the number of multiplexed wavelengths that occurs in normal maintenance work. By selectively executing the constant output control of the optical amplifier, it is possible to ensure the communication quality of the signal light in the optical transmission system. Further, according to the second and third embodiments, in the constant output control accompanying the change in the loss of the transmission line, even if the compensation of the signal light output intensity is incomplete, the subsequent malfunction of the optical transmission apparatus is prevented. It becomes possible to do.

1: optical transmission device, 2: optical fiber, 10: transmitter, 11: receiver, 20: monitoring control unit,
30: optical amplifier, 31: duplexer, 33, 38: optical fiber amplifier, 32, 34, 36: optical coupler, 35: variable optical attenuator, 37: multiplexer
41: monitoring light receiver, 42, 44, 46: detector, 47: monitoring light transmitter.

Claims (8)

An optical transmission device that outputs wavelength multiplexed signal light received together with monitoring light to an optical transmission path in the next section with a predetermined light intensity,
A first detector for separating the monitoring light from the received wavelength multiplexed signal light and detecting the monitoring light intensity;
A second detector for detecting the intensity of the wavelength multiplexed signal light after the separation of the monitoring light;
A gain control type optical amplifier for amplifying the wavelength-multiplexed signal light;
A variable attenuation optical attenuator for adjusting the intensity of the wavelength multiplexed signal light output from the optical amplifier;
The optical amplifier is controlled so as to always have a constant gain, and includes a monitoring control unit that controls the attenuation amount of the optical attenuator so that the output intensity of the wavelength multiplexed signal light becomes a predetermined target value.
The monitoring control unit compares the intensity of the monitoring light output from the first detection unit with a first allowable upper limit value and a first allowable lower limit value of the fluctuation of the monitoring light set in advance, and the second detection unit An optical transmission apparatus that monitors fluctuations in the intensity of the signal light output from the optical attenuator and controls execution of constant control of the output light intensity by the optical attenuator based on the comparison result and the monitoring result .   The optical transmission device according to claim 1, wherein the first allowable upper limit value and the first allowable lower limit value are values that are periodically updated.   The monitoring control unit periodically performs constant control of the output light intensity by the optical attenuator when the intensity of the monitoring light is between the first allowable upper limit value and the first allowable lower limit value. The optical transmission device according to claim 1, wherein:   When the intensity of the monitoring light is within an allowable range determined by the first allowable upper limit value and the first allowable lower limit value, the monitoring control unit controls the output light intensity to be constant during the first period by the optical attenuator. Are periodically performed, and when the intensity of the monitoring light exceeds the allowable range, the intensity of the monitoring light is greater than a second allowable upper limit value and a first allowable lower limit value that are greater than the first allowable upper limit value. If the intensity of the monitoring light is within an output control range determined by the second allowable upper limit value and the second allowable lower limit value as compared with a smaller second allowable lower limit value, the second allowable lower limit value is longer than the first period. The output light intensity constant control for two periods is performed, and when the intensity of the monitoring light exceeds the output control range, the constant control of the output light intensity by the optical attenuator is stopped. The optical transmission device described. An optical transmission device that outputs wavelength multiplexed signal light received together with monitoring light to an optical transmission path in the next section with a predetermined light intensity,
A first detector for separating the monitoring light from the received wavelength multiplexed signal light and detecting the monitoring light intensity;
A second detector for detecting the intensity of the wavelength multiplexed signal light after the separation of the monitoring light;
A gain control type optical amplifier for amplifying the wavelength-multiplexed signal light;
A variable attenuation optical attenuator for adjusting the intensity of the wavelength multiplexed signal light output from the optical amplifier;
The optical amplifier is controlled so as to always have a constant gain, and includes a monitoring control unit that controls the attenuation amount of the optical attenuator so that the output intensity of the wavelength multiplexed signal light becomes a predetermined target value.
The monitoring control unit compares the signal light intensity output from the second detection unit with a first allowable upper limit value and a first allowable lower limit value of the fluctuation of the signal light, and from the first detection unit. An optical transmission apparatus characterized by monitoring intensity fluctuation of output monitoring light and controlling execution of constant control of output light intensity by the optical attenuator based on the comparison result and the monitoring result.   The optical transmission device according to claim 5, wherein the first allowable upper limit value and the first allowable lower limit value are values that are periodically updated.   The monitoring control unit compares the intensity of the monitoring light with a predetermined allowable range, the intensity of the monitoring light is within the predetermined allowable range, and the intensity of the signal light is the first allowable upper limit value and the The optical transmission device according to claim 5, wherein when the range with the first allowable lower limit is exceeded, a change in the number of wavelengths of the wavelength multiplexed signal light is detected.   The optical transmission device according to claim 7, wherein the monitoring control unit suppresses constant control of the output light intensity when detecting a change in the number of wavelengths of the wavelength multiplexed signal light.

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