WO2013132596A1

WO2013132596A1 - Wavelength multiplexed photo-transmission system, photo-relay device, and light intensity control method

Info

Publication number: WO2013132596A1
Application number: PCT/JP2012/055691
Authority: WO
Inventors: 十倉　俊之; 杉原　隆嗣; 和行石田
Original assignee: 三菱電機株式会社
Priority date: 2012-03-06
Filing date: 2012-03-06
Publication date: 2013-09-12

Abstract

Provided is a wavelength multiplexed photo-transmission system comprising a receiving node (1) which receives, amplifies, and outputs wavelength multiplexed light. The receiving node (1) further comprises: a photo-amplifier (16) which amplifies wavelength multiplexed light; a variable attenuator (15) which attenuates the intensity of the wavelength multiplexed light; a target value setting unit (13) which sets a target value of the post-amplification wavelength multiplexed light intensity; a control circuit (14) which controls the variable attenuator (15) such that the wavelength multiplexed light intensity reaches a target value after passing through the photo-amplifier (16) and the variable attenuator (15); a PD (8) which detects the total power of the wavelength multiplexed light; a photo-extraction filter (7) which extracts a signal of a portion of a waveband of the wavelength multiplexed light; and a PD (9) which detects the intensity of the extracted signal which is extracted by the photo-extraction filter (7). A determination is made, on the basis of whether the ratio of change of the total power and the ratio of change of the intensity of the extracted signal approximately match, whether to preserve or reset the target value.

Description

Wavelength multiplexing optical transmission system, optical repeater, and light intensity control method

The present invention relates to a wavelength division multiplexing optical transmission system, an optical repeater, and an optical intensity control method.

Conventionally, in an optical repeater transmission system, even if the optical fiber between repeater stations or the optical fiber in each station of the transmitter station, repeater station, and receiver station is subject to fluctuations due to environmental temperature, vibration, bending, etc. In order to maintain good transmission characteristics, control is performed to absorb variations and fluctuations in the loss of the optical fiber and maintain the signal light power in the optical fiber at a predetermined value.

Furthermore, when the optical repeater transmission system is a wavelength division multiplexing transmission system, it is necessary to control the signal light power of each wavelength to a predetermined value regardless of the number of wavelengths of the multiplexed signal light. For example, Patent Document 1 below discloses a method for controlling the signal light power of each wavelength to a predetermined value even when the number of multiplexed wavelengths is intentionally or suddenly changed. .

Japanese Patent No. 4724226

However, according to the above conventional technique, it is necessary to monitor the signal light powers of all wavelengths that are wavelength-multiplexed at high speed. For this reason, there is a problem that the monitor circuit that performs power and the circuit that counts the number of wavelengths from the monitored power value and reflects them in power control are complicated and large-scale. In particular, in a large-scale optical transmission system in which the number of wavelength multiplexing exceeds 100, there is a large problem that it is not realistic in terms of mounting volume of circuit components, speeding up of arithmetic processing circuits, and cost.

The present invention has been made in view of the above, and a wavelength division multiplexing optical transmission system capable of controlling optical power to a predetermined value while suppressing an increase in circuit scale even when the number of multiplexed wavelengths is large. An object of the present invention is to obtain an optical repeater and a light intensity control method.

In order to solve the above-described problems and achieve the object, the present invention provides an upstream device that transmits wavelength-multiplexed light in which a plurality of optical signals having different wavelengths are wavelength-multiplexed, receives the wavelength-multiplexed light, and receives the wavelength-multiplexed light. An optical repeater that amplifies and outputs multiplexed light, the optical repeater comprising: an optical amplifier that amplifies the wavelength-multiplexed light; A variable attenuator for attenuating the intensity of the wavelength multiplexed light after amplification by an amplifier; a target value setting unit for setting a target value of the intensity of the wavelength multiplexed light after amplification; passing through the optical amplifier and the variable attenuator A control unit that controls the variable attenuator so that the intensity of the later wavelength multiplexed light becomes the target value; a total intensity detecting unit that detects the total intensity of the received wavelength multiplexed light; and the received wavelength multiplexed light of A light extraction filter that extracts a signal in a part of the wavelength band, and an extraction signal intensity detection unit that detects the intensity of the extraction signal extracted by the light extraction filter, and the target value setting unit includes the total value Whether to maintain or reset the target value is determined based on whether or not the intensity change ratio and the intensity change ratio of the extracted signal are substantially the same.

The wavelength division multiplexing optical transmission apparatus according to the present invention has an effect that the optical power can be controlled to a predetermined value while suppressing an increase in circuit scale even when the number of multiplexed wavelengths is large.

FIG. 1 is a diagram illustrating a configuration example of the wavelength division multiplexing optical transmission system according to the first embodiment. FIG. 2 is a diagram illustrating an example of an optical spectrum of wavelength multiplexed light. FIG. 3 is a diagram illustrating an optical signal after extraction by the light extraction filter. FIG. 4 is a diagram illustrating a configuration example of a wavelength division multiplexing optical transmission system according to the fourth embodiment. FIG. 5 is a diagram illustrating a configuration example of a reception node in the case where a duplexer is arranged upstream of the optical amplifier. FIG. 6 is a diagram illustrating a configuration example of the wavelength division multiplexing optical transmission system according to the fifth embodiment. FIG. 7 is a diagram illustrating a configuration example of a wavelength division multiplexing optical transmission system according to the sixth embodiment.

Hereinafter, embodiments of a wavelength division multiplexing optical transmission system, an optical repeater, and a light intensity control method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of Embodiment 1 of a wavelength division multiplexing optical transmission system according to the present invention. As shown in FIG. 1, the wavelength division multiplexing optical transmission system of the present embodiment receives an upstream transmission node 2 (upstream apparatus) that transmits wavelength division multiplexed light to a transmission line optical fiber 3, and receives wavelength division multiplexed light to be transmitted. And a receiving node 1 that controls the power (intensity) to a predetermined value. In the present embodiment, the receiving node 1 will be described as an example of the optical repeater according to the present invention. The receiving node 1 amplifies and repeats the wavelength multiplexed light transmitted from the upstream transmitting node 2.

The upstream transmission node 2 includes an optical amplifier 4 that amplifies wavelength multiplexed light. The reception node 1 includes

branching filters

5 and 6, a light extraction filter 7, photodiodes (PD) 8 and 9, log amplifiers (Log) 10 and 11, a subtraction circuit 12, a target value setting circuit (target A value setting unit) 13, a control circuit (control unit) 14, a variable attenuator (VOA) 15, and an optical amplifier 16.

The demultiplexer 5 is a demultiplexer that branches a part of power in order to monitor wavelength multiplexed light. For example, an optical coupler that demultiplexes at a ratio of 10: 1, 20: 1, or the like can be applied. The demultiplexer 6 is a demultiplexer 6 that further demultiplexes the wavelength multiplexed light demultiplexed by the demultiplexer 5.

The light extraction filter 7 blocks light in some wavelength bands from the wavelength multiplexed light demultiplexed by the demultiplexer 6 and extracts only light in other wavelength bands. The light extraction filter 7 extracts supervisory control light for transmitting a low-speed signal in order to extract signal light of a part of the wavelength of multiplexed signal light, or to monitor or control a wavelength division multiplexing optical transmission system. For example, the case of extracting only the wavelength of the noise, or the case of extracting only the noise light that does not include any of the signal light and the monitoring control light is conceivable.

The photodiode 8 (total intensity detection unit) detects the total light power not passing through the light extraction filter 7. That is, the photodiode 8 monitors the total power including signal light, supervisory control light, noise light, etc. without extracting only a part of the wavelength band, and outputs an electric signal corresponding to the total power. The photodiode 9 (extracted signal intensity detection unit) is a detection unit for monitoring the power of the light in the wavelength band extracted by the light extraction filter 7 and determines the optical power of the light in the wavelength band extracted by the light extraction filter 7. A corresponding electrical signal is output.

The log amplifiers 10 and 11 (first log amplifier and second log amplifier) respectively convert the electrical signals output from the

photodiodes

8 and 9 into electrical signals proportional to the logarithm (when the input is X). log amplifier for outputting a signal proportional to logX). Although the

log amplifiers

10 and 11 are not essential, an example in which the

log amplifiers

10 and 11 are used will be described here.

The subtraction circuit 12 subtracts signals output from the

log amplifiers

10 and 11. The subtracting circuit 12 obtains a signal proportional to the logarithm of the ratio between the total power and the power obtained by extracting some wavelengths. The target value setting circuit 13 is a circuit that sets a target value for controlling the total power. The control circuit 14 is a circuit that controls the total power of the wavelength multiplexed light to approach the target value by changing the attenuation amount of the variable attenuator 15. The optical amplifier 16 is an optical amplifier that amplifies the wavelength-division multiplexed light whose power is adjusted, and gain constant control is performed so as to amplify with a constant gain.

Next, the operation of this embodiment will be described. FIG. 2 is a diagram illustrating an example of an optical spectrum of wavelength multiplexed light. FIG. 2 In this example, signal light of 10 wavelengths and monitoring control light (OSC light) for transmitting a low-speed signal for monitoring or controlling the wavelength multiplexing optical transmission system are multiplexed. Note that FIG. 2 is an example, and the number of wavelengths multiplexed in the wavelength division multiplexed light is not limited to this, and the monitoring control light may not be multiplexed.

FIG. 2 (a) shows a state in which the noise light generated in the optical amplifier 4 or the like exists in the same wavelength band as the signal light. FIG. 2B shows a case where the loss of the transmission line optical fiber 3 is increased by 10 dB from the state of FIG. 2A (the state before change) for some reason. The rate of change with time of all powers of signal light, supervisory control light, and noise light is the same, and the power is reduced to 1/10 due to an increase in loss. In this case, the loss amount of the variable attenuator 15 is quickly reduced so that the monitor value of the total power that is lower than the control target value is recovered, and the power of the signal light becomes a predetermined value before the loss increase. Need to be controlled.

FIG. 2 (c) shows a case where the number of wavelengths transmitted from the upstream has decreased from 10 waves to 1 wave for some reason from the state of FIG. 2 (a). In this case, the monitor value of the total power is reduced to 1/10. However, since the power (channel power) per wave does not change and the predetermined power is maintained, the loss amount of the variable attenuator 15 is There is no need to change. Therefore, it is necessary to control the variable attenuator 15 after changing the total power control target value to a value corresponding to the number of wavelengths of one wave.

In this way, when the total power changes, it is determined whether the change is due to the loss fluctuation as shown in FIG. 2B or the change due to the wavelength number fluctuation as shown in FIG. It is necessary to change the loss amount of the filter immediately to keep the total power constant, or to change the control target value quickly before changing the loss amount of the variable attenuator. For this purpose, in the prior art as described in Patent Document 1, the wavelength-multiplexed signal light is demultiplexed into one wavelength, the power of each wavelength is monitored, and the number of multiplexed wavelengths is counted at high speed. By doing so, the variable attenuator was controlled.

However, in such a conventional method, it is necessary to monitor the signal light power of all wavelengths that are wavelength-multiplexed at high speed, and the number of wavelengths is counted from the monitored power value and the monitored power value. There is a problem that the circuit reflected in power control becomes complicated and large-scale. In particular, as in recent years, when the optical transmission system becomes larger as the number of wavelength divisions exceeds 100, it is not realistic in terms of mounting volume of circuit components, speeding up of an arithmetic processing circuit, and cost.

On the other hand, in the present embodiment, the total power P (output from the demultiplexer 6) including all the wavelength multiplexed signal light and the power P _filter (light that extracts light in a part of the wavelength band of the transmitted light) The output from the extraction filter 7) is monitored. Then, by comparing the change ratios of the two monitor values, it is determined whether the change is due to loss fluctuation as shown in FIG. 2B or the change due to wavelength number fluctuation as shown in FIG.

Hereinafter, in both cases of FIGS. 2B and 2C, the total power P decreases to 1/10. FIG. 3A shows an example of an extracted optical signal when signal light having a part of the wavelength is extracted from the signal light wavelength-multiplexed by the light extraction filter 7. Of these 10 wavelengths, filters are extracted so that 5 waves in the long wavelength band pass. Note that the number of wavelengths to be extracted is not limited to five waves. Further, the wavelength to be extracted is not limited to the long wavelength band, but may be near the center or in the low wavelength band.

When the loss increases by 10 dB as shown in FIG. 2B, the total power P and the light power P _filter after extraction by the light extraction filter 7 are both 1/10, and the change ratio is the same. is there. On the other hand, when the number of wavelengths is reduced from 10 waves to 1 wave as shown in FIG. 2C, the total power P is reduced to 1/10, but the light power P after being extracted by the light extraction filter 7 is reduced. _{The filter} is monitored for power for five wavelengths before the change, but only for one wavelength after the change, and is reduced to one fifth. Therefore, the change ratio differs between the total power P and the light power P _filter after being extracted by the light extraction filter 7. That is, the change ratio P / P ′ of the total power P when the monitor value of the total power P a predetermined time before is P ′, and the power P _filter of the light after being extracted by the light extraction filter 7 a predetermined time before. The change ratio P _filter / P _filter ′ of P _filter when the monitor value is P _filter ′ is compared. If they are the same, the power fluctuation caused by the loss fluctuation, and if they are different, the fluctuation in the number of wavelengths It can be determined that the power fluctuation is caused, and the variable attenuator can be appropriately controlled in each case. In determining whether P / P ′ and P _filter / P _filter ′ are the same, a certain amount of margin caused by an error or the like is taken in, and the difference between P / P ′ and P _filter / P _filter ′ is constant. When the value is equal to or greater than the value, it may be determined that P / P ′ and P _filter / P _filter ′ are different.

In the present embodiment, the target value setting circuit 13 uses the total power P, the power P _filter extracted by the light extraction filter 7, and the monitor values P ′ and P _filter ′ respectively before a predetermined time to generate P / P ′ And P _filter / P _filter ′ are obtained, and based on whether or not P / P ′ and P _filter / P _filter ′ are substantially the same value, the power fluctuation caused by the loss fluctuation or the wavelength number fluctuation is determined. . The target value setting circuit 13 does not change the target value Pt when it is determined that the fluctuation is a loss fluctuation. On the other hand, if it is determined that the power fluctuation is caused by the fluctuation in the number of wavelengths, the target value setting circuit 13 resets the target value Pt. . The value after the resetting is a value corresponding to the number of wavelengths of one wave (number of wavelengths) when it is assumed that the power including all of the wavelength multiplexed signal light becomes the target value Pt. The value after resetting can be obtained based on, for example, the difference or ratio between P / P ′ and P _filter / P _filter ′. The control circuit 14 can control the wavelength multiplexed light to a predetermined power by controlling the loss amount of the variable attenuator 15 according to these target values.

In FIG. 1, log

amplifiers

10 and 11 that convert the total power P and the power P _filter extracted by the light extraction filter 7 into signals proportional to the logarithm are used. In this case, P / P ′ and P _filter / P _filter ′ are compared by comparing (logP−logP ′) and (logP _filter −logP _filter ′). If they are different, it is determined that the number of wavelengths varies. Of course, instead of comparing P / P ′ and P _filter / P _filter ′ to determine whether they are substantially the same, is (logP−logP ′) − (logP _filter −logP _filter ′) zero? You may determine whether. Use of the log amplifier eliminates the need for a division circuit, so that circuit mounting is facilitated and the dynamic range can be widened. The method for obtaining P / P ′ and P _filter / P _filter ′ is not limited to such a configuration using a log amplifier.

As described above, in the present embodiment, P / P is obtained by using the total power P, the power P _filter extracted by the light extraction filter 7, and the monitor values P ′ and P _filter ′ before each predetermined time. 'And P _filter / P _filter ' are obtained, and based on whether P / P 'and P _filter / P _filter ' are substantially the same value, the power fluctuation caused by the loss fluctuation or the wavelength number fluctuation is determined. And according to the judgment result, the value of the target value Pt for controlling the optical attenuator 15 was set. For this reason, even when the number of multiplexed wavelengths is large, the optical power can be controlled to a predetermined value while suppressing an increase in circuit scale.

Embodiment 2. FIG.
Next, an optical power control method according to the second embodiment of the present invention will be described. The configuration of the wavelength division multiplexing optical transmission system of the present embodiment is the same as that of the first embodiment. In the first embodiment, the example in which the light extraction filter 7 extracts a part of the wavelength multiplexed light is described. However, in this embodiment, the light extraction filter 7 extracts the monitoring control light. Hereinafter, a different part from Embodiment 1 is demonstrated.

As shown in FIG. 3B, in this embodiment, the light extraction filter 7 extracts supervisory control light (OSC light) that transmits a low-speed signal for monitoring and control of the wavelength division multiplexing optical transmission system. When the loss increases by 10 dB as shown in FIG. 2B, the total power P and the power P _filter extracted by the light extraction filter 7 are both 1/10, and the change ratios of both are the same. On the other hand, when the number of wavelengths decreases from 10 waves to 1 wave as shown in FIG. 2C, the total power P decreases to 1/10, but the supervisory control light (OSC light) extracted by the light extraction filter. The power P _filter does not change, and the change ratios of the two are different.

Accordingly, as in the first embodiment, the total power P, the power P _filter extracted by the light extraction filter 7, and the monitor values P ′ and P _filter ′ before the predetermined time are used to obtain P / P ′. And P _filter / P _filter ′, and based on whether P / P ′ and P _filter / P _filter ′ are substantially the same value, it is possible to determine the power fluctuation caused by the loss fluctuation or the wavelength number fluctuation. it can. The operations of the present embodiment other than those described above are the same as those of the first embodiment.

As described above, in this embodiment, the monitoring control light is extracted by the light extraction filter 7, and the total power P, the power P _filter extracted by the light extraction filter 7, and the monitor values P ′ and P before each predetermined time are obtained. _filter P ′, and P / P ′ and P _filter / P _filter ′ are obtained. Based on whether P / P ′ and P _filter / P _filter ′ are substantially the same value or not, the loss variation Judgment was made on power fluctuations caused by wavelength fluctuations. For this reason, even when the number of multiplexed wavelengths is large, the optical power can be controlled to a predetermined value while suppressing an increase in circuit scale.

Embodiment 3 FIG.
Next, an optical power control method according to the third embodiment of the present invention will be described. The configuration of the wavelength division multiplexing optical transmission system of the present embodiment is the same as that of the first embodiment. In the first embodiment, the example in which the light extraction filter 7 extracts a part of the wavelength multiplexed light is described. However, in this embodiment, the light extraction filter 7 is either a signal light or a monitoring control light. Noise light is extracted. Hereinafter, a different part from Embodiment 1 is demonstrated.

As shown in FIG. 3C, in the present embodiment, the light extraction filter 7 extracts noise light that does not include either signal light or monitoring control light. That is, a signal in a wavelength band that is neither the wavelength of the signal light nor the wavelength of the monitoring control light is extracted. When the loss increases by 10 dB as shown in FIG. 2B, the total power P and the power P _filter extracted by the light extraction _filter are both 1/10, and the change ratios of both are the same. On the other hand, when the number of wavelengths decreases from 10 waves to 1 wave as shown in FIG. 2C, the total power P decreases to 1/10, but the supervisory control light (OSC light) extracted by the light extraction filter. The power P _filter does not change, and the change ratios of the two are different.

As described above, in this embodiment, noise light is extracted by the light extraction filter 7, and the total power P, the power P _filter extracted by the light extraction filter 7, and the monitor values P ′ and P _filter before each predetermined time are obtained. ′, P / P ′ and P _filter / P _filter ′ are obtained, and based on whether P / P ′ and P _filter / P _filter ′ are substantially the same value, the loss variation or the number of wavelengths The power fluctuation caused by the fluctuation was judged. For this reason, even when the number of multiplexed wavelengths is large, the optical power can be controlled to a predetermined value while suppressing an increase in circuit scale.

Embodiment 4 FIG.
FIG. 4 is a diagram showing a configuration example of a wavelength division multiplexing optical transmission system according to a fourth embodiment of the present invention. As shown in FIG. 4, the wavelength division multiplexing optical transmission system of the present embodiment includes an upstream transmission node 2 and a reception node 1a similar to those of the first embodiment. The wavelength multiplexed light transmitted from the upstream transmission node 2 is received by the reception node 1a via the transmission line optical fiber 3.

The configuration of the reception node 1a is the same as that of the reception node 1 of the first embodiment except that the arrangement of the optical amplifier 16 is changed and the optical amplifier 16 is arranged in front of the variable attenuator 15. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

As shown in FIG. 4, the optical power control method similar to that of the first to third embodiments can also be applied when the optical amplifier 16 is arranged in front of the variable attenuator 15.

Consider the operation when the loss in the transmission line optical fiber 3 greatly increases in the configuration example of FIG. When a loss increase of 20 dB occurs in the transmission line optical fiber 3, the power of the signal light and noise light input to the optical amplifier 16 both decreases by 20 dB. The signal light output from the optical amplifier 16 is also reduced by 20 dB, but the output amount of the noise light is smaller than 20 dB. This is because the power of the noise light generated by the optical amplifier 16 itself is a constant value regardless of the input signal power.

Also in this case, when a part of the signal light or the monitoring control light is extracted by the light extraction filter 7, the power fluctuation caused by the loss fluctuation or the wavelength number fluctuation is determined by the same method as in the first and second embodiments. Can do. On the other hand, when noise light is extracted by the light extraction filter 7 that does not include either signal light or supervisory control light as in the third embodiment, the total power P and the light are output when a large loss fluctuation occurs. The change ratio of the power P _filter extracted by the extraction filter 7 is different, and it may be erroneously determined that the number of wavelengths varies.

When such a misjudgment may occur, the misjudgment can be avoided by adopting the configuration shown in FIG. FIG. 5 is a diagram illustrating a configuration example of the reception node 1b when the duplexer 5 is arranged upstream of the optical amplifier 16. An erroneous determination can be avoided by using the receiving node 1b instead of the receiving node 1a. In the example of FIG. 5, the duplexer 5 is arranged upstream of the optical amplifier 16 to monitor the total power and the power extracted by the light extraction filter. In the example of FIG. 5, with respect to the configuration example of FIG. 4, the branching filter 5 and the subtraction circuit 12 are arranged in front of the optical amplifier 16, and the branching filter 19, the photodiode (PD) 17 and the log amplifier (Log) ) 18 is added.

In the example of FIG. 5, the monitor value by the

photodiodes

8 and 9 does not include the power of the noise light generated by the optical amplifier 16, so that even when the loss greatly increases, the total power P and the light extraction filter 7 are used for extraction. The change ratio of the power P _filter does not change, and the loss fluctuation and the wavelength number fluctuation can be accurately discriminated. The power of the output light of the variable attenuator 15 is demultiplexed by the demultiplexer 19, and the light demultiplexed by the demultiplexer 19 is monitored by the photodiode 17. Then, by inputting to the control circuit 14 via the log amplifier 18, the loss amount of the variable optical attenuator 15 is controlled according to the target value.

In the example of FIG. 5, a noise light removal filter 24 is added to the upstream transmission node 2a. Thus, by adding the noise light removal filter 24 to the upstream transmission node 2a, the change in the total power P and the power P _filter extracted by the light extraction filter due to the influence of the change in the noise light power from the upstream transmission node 2a. The ratio can reduce fluctuations. As a result, only the noise light generated by the optical amplifier 4 is monitored by the photodiode 9 of the reception node 1b, and the change ratio between the total power P and the power P _filter extracted by the light extraction filter 7 is accurately compared. be able to. The noise light removal filter 24 is an optical device having a characteristic of blocking a wavelength band for monitoring noise light. The noise light removal filter 24 may be an optical filter designed to cut off the corresponding wavelength, or may be a wavelength selective switch (WSS) having a characteristic to cut off other than the signal band, for example. . The upstream transmission node 2a can be used to compare the change ratio more accurately. However, when the influence of noise other than the optical amplifier 4 is small, the upstream transmission node 2 is used instead of the upstream transmission node 2a. Also good.

As described above, the optical power control method similar to that of the first to third embodiments can also be applied to the configuration example in which the optical amplifier 16 is arranged in the preceding stage of the variable attenuator 15. Further, by arranging the branching filter 5 and the subtracting circuit 12 upstream from the optical amplifier 16, even when noise light is extracted by the light extraction filter 7, it is more accurately caused by loss fluctuation or wavelength number fluctuation. It can be determined whether the power fluctuation. Further, by adding the noise light removal filter 24 to the upstream transmission node 2a, it is possible to more accurately determine whether the fluctuation is a loss fluctuation or a power fluctuation caused by a wavelength number fluctuation.

Embodiment 5. FIG.
FIG. 6 is a diagram showing a configuration example of the fifth embodiment of the wavelength division multiplexing optical transmission system according to the present invention. As shown in FIG. 6, the wavelength division multiplexing optical transmission system of the present embodiment includes an upstream transmission node 2a and a reception node 1c similar to those of the fourth embodiment. The wavelength multiplexed light transmitted from the upstream transmission node 2 a is received by the reception node 1 c via the transmission line fiber 3. Note that the upstream transmission node 2 of the first embodiment may be used instead of the upstream transmission node 2a.

In the present embodiment, the configuration and operation in the case of combining Raman amplification will be described. An excitation LD (Laser Diode) 21 is an excitation light source that outputs excitation light (Raman excitation light) for Raman amplification of signal light by the transmission line optical fiber 3. The pumping light is sent to the transmission line optical fiber 3 through the Raman pumping light multiplexer 20. The constant gain control circuit 22 is a circuit that controls the power of pumping light so as to keep the gain of Raman amplification constant. In this example, the total power monitored by the photodiode 8 is used for control. Any method may be used as a method for controlling the gain of Raman amplification to be constant. For example, the methods described in Japanese Patent No. 4040044 and Japanese Patent No. 4046602 can be used, and a monitor circuit is appropriately used. And control circuit.

In the present embodiment, the duplexer 6 inputs the demultiplexed light to the photodiode 8, the light extraction filter 7a, and the light extraction filter 7b. The light extraction filter 7a extracts noise light in the excitation light band, and the light extraction filter 7b generates noise light (in the signal light and monitoring control light bands) between the excitation light band and the signal light and monitoring control light bands. , Noise light not including the wavelengths of the signal light and the monitoring control light). The

photodiodes

9a and 9b convert the light extracted by the

light extraction filters

7a and 7b into electric signals, respectively. The

log amplifiers

11a and 11b convert the electrical signals output from the

photodiodes

9a and 9b into electrical signals proportional to the logarithm. The correction circuit 25 estimates noise light from the band of the signal light and the monitoring control light based on the output from the log amplifier 11a and the output from 11b. In the present embodiment, the change rate of the total power P and the power P _filter extracted by the light extraction filter is compared with the output of the correction circuit 25 as P _filter extracted by the light extraction filter.

Here, the

light extraction filters

7a and 7b extract the noise light. However, as in the first and second embodiments, a part of the signal light or the monitoring control light may be extracted. .

The pumping light output fluctuation detecting circuit (pumping light output fluctuation detecting unit) 23 is a circuit that detects the fluctuation of the pumping light power that is controlled by the constant gain control circuit 22. When the fluctuation of loss in the transmission line optical fiber 3 increases, the Raman gain decreases as the attenuation of the pumping light increases. In this case, the constant gain control circuit 22 operates to increase the Raman pumping light power in order to suppress a decrease in the gain of Raman amplification. That is, the power of the Raman pumping light changes according to the fluctuation of loss.

Therefore, regardless of the comparison result of the change ratio between the total power P and the power P _filter extracted by the light extraction filter, it may be determined that a loss fluctuation has occurred when a change in Raman pumping light power is detected. Combined with the comparison of the change ratio of the total power P and the power P _filter extracted with light extraction filter, when detecting a change in the Raman pumping light power, and total power P and the change ratio of the power P _filter extracted with light extraction filter If the comparison results match, it is determined that loss fluctuation has occurred. On the other hand, when the change in the Raman pumping light power is not detected (the Raman pumping light power does not change) and the change ratio between the total power P and the power _Pfilter extracted by the light extraction filter is different, the number of wavelengths varies. It is determined that the power fluctuation is caused.

As described above, in this embodiment, when combined with Raman amplification, it is determined whether or not there is a loss variation based on the presence or absence of a change in Raman pumping light power. As a result, when combined with Raman amplification, the optical power can be controlled to a predetermined value while suppressing an increase in circuit scale even when the number of multiplexed wavelengths is large.

Embodiment 6 FIG.
FIG. 7 is a diagram showing a configuration example of the sixth embodiment of the wavelength division multiplexing optical transmission system according to the present invention. As shown in FIG. 7, the wavelength division multiplexing optical transmission system of the present embodiment includes an upstream transmission node 2a and a reception node 1d similar to those of the fourth embodiment. The receiving node 1d receives the optical amplifier 16 in the preceding stage of the variable attenuator 15 and adds the duplexer 19, the photodiode 17 and the log amplifier 18 similar to those in the fourth embodiment. The same as the node 1c.

In the present embodiment, an example in which the optical amplifier 16 is arranged on the input side of the variable attenuator 15 when combined with Raman amplification will be described. Also in this case, as in the example of FIG. 5, the demultiplexer 5 is arranged on the input side of the optical amplifier 16 in order to correctly determine the wavelength number variation and the loss variation even when the input level of the optical amplifier 16 is greatly reduced. is doing. In order to control the output power of the variable attenuator 15 to be constant, the total power is monitored by the photodiode 17 via the duplexer 19. The operations of the present embodiment other than those described above are the same as those of the fifth embodiment.

Embodiment 7 FIG.
Next, a method for resetting the control target value Pt of the seventh embodiment of the wavelength division multiplexing optical transmission system according to the present invention will be described. The configuration of the present embodiment is the same as that of any of the first to sixth embodiments.

In the example described in the first to sixth embodiments, the target value setting circuit 13 resets the control target value Pt of the total power P when detecting the change in the number of wavelengths. An example of the resetting method will be described.

The upstream transmission node 2 is monitoring the total power in its own node, and the upstream transmission node 2 transmits information on the monitor value of the total power in its own node to the reception node. The target value setting circuit 13 can reset the control target value in accordance with the received monitor value of the total power in the upstream transmission node 2. When the number of multiplexed wavelengths changes, the monitor value of the total power transmitted from the upstream transmission node 2 changes according to the number of wavelengths. Therefore, by setting a target value for controlling the total power according to the monitor value of the total power transmitted from the upstream transmitting node 2, the power per wavelength can be controlled to a predetermined value regardless of the number of wavelengths. it can.

Embodiment 8 FIG.
Next, a method for resetting the control target value Pt according to the eighth embodiment of the wavelength division multiplexing optical transmission system of the present invention will be described. The configuration of the present embodiment is the same as that of any of the first to sixth embodiments.

In the example described in the first to sixth embodiments, the target value setting circuit 13 resets the control target value Pt of the total power P when detecting the change in the number of wavelengths. A second example of the resetting method will be described.

The upstream transmission node 2 knows the information on the number of wavelengths multiplexed in the wavelength multiplexed light transmitted from the own node, and the upstream transmission node 2 sends the information on the number of multiplexed wavelengths to the reception node. Send. The target value setting circuit 13 can reset the control target value in accordance with the number of received wavelengths. By setting a target value for controlling the total power in accordance with the number of wavelengths transmitted from the upstream transmission node 2, the power per wavelength can be controlled to a predetermined value regardless of the number of wavelengths.

Embodiment 9 FIG.
Next, a method for resetting the control target value Pt of the ninth embodiment of the wavelength division multiplexing optical transmission system according to the present invention will be described. The configuration of the present embodiment is the same as that of any of the first to sixth embodiments.

In the example described in the first to sixth embodiments, the target value setting circuit 13 resets the control target value Pt of the total power P when detecting the change in the number of wavelengths. A third example of the resetting method will be described.

The target value setting circuit 13 detects the fluctuation in the number of wavelengths, and then sets the monitor value of the total power P including all of the wavelength multiplexed signal light as a new control target value Pt, thereby changing the number of wavelengths after the change. Control to maintain the signal light power is performed. As a result, the signal light power per wavelength can be kept at the same value as before the number of wavelengths is changed.

Embodiment 10 FIG.
Next, a method for resetting the control target value Pt according to the tenth embodiment of the wavelength division multiplexing optical transmission system of the present invention will be described. The configuration of the present embodiment is the same as that of any of the first to sixth embodiments.

In the example described in the first to sixth embodiments, the target value setting circuit 13 resets the control target value Pt of the total power P when detecting the change in the number of wavelengths. A fourth example of the resetting method will be described.

Based on the power P including all the wavelength multiplexed signal light, the power P _filter obtained by extracting light in a part of the wavelength band, and the monitor values P ′ and P _filter ′ before the predetermined time, the target after resetting It is conceivable to set the value Pt. For example, it sets so that the following formula | equation (1) may be satisfy | filled.
Pt = Pt ′ × (P / P _filter ) / (P ′ / P _filter ′) (1)
That is, it sets so that the following formula | equation (2) may be satisfy | filled.
logPt =
logPt ′ + (logP−logP _filter ) − (logP′−logP _filter ′) (2)

As a result, the target value Pt can be changed by the ratio at which the total power P has changed with reference to the power P _{filter from} which light in a part of the wavelength band is extracted, and the signal light power per wavelength can be changed by the number of wavelengths. Can keep the same as before.

In the embodiment described above, a part of examples are described, but the present invention is not limited to this example.

In the above embodiment, the total power P including all the wavelength multiplexed signal light includes the power of all the wavelength multiplexed signal lights and the power of the noise light existing in the same band. . When supervisory control light for supervisory control of the optical transmission system is multiplexed and transmitted, the total power P may or may not include the power of the supervisory control light. Either case is within the scope of the present invention.

As described above, the wavelength division multiplexing optical transmission system, the optical repeater, and the light intensity control method according to the present invention are useful for an optical repeater transmission system, and are particularly suitable for a system having a large number of multiplexed wavelengths. .

1, 1a, 1b, 1c,

1d Reception node

2, 2a Upstream transmission node 3 Transmission path

optical fiber

4, 16

Optical amplifier

5, 6, 19

Demultiplexer

7, 7a, 7b

Light extraction filter

8, 8a, 8b, 9 , 9a, 9b, 17 Photodiode (PD)
10, 11, 11a, 11b, 18 Log amplifier (Log)
12 Subtraction circuit 13 Target value setting circuit 14 Control circuit 15 Variable attenuator (VOA)
20 Raman excitation light multiplexer 21 Excitation LD
22 constant gain control circuit 23 excitation light output fluctuation detection circuit 24 noise light removal filter 25 correction circuit

Claims

Wavelength multiplexed light comprising: an upstream device that transmits wavelength multiplexed light in which a plurality of optical signals having different wavelengths are wavelength multiplexed; and an optical repeater that receives the wavelength multiplexed light and amplifies and outputs the wavelength multiplexed light A transmission system,
The optical repeater is
An optical amplifier for amplifying the wavelength multiplexed light;
A variable attenuator for attenuating the intensity of the wavelength multiplexed light before amplification by the optical amplifier or after amplification by the optical amplifier;
A target value setting unit for setting a target value of the intensity of the wavelength multiplexed light after amplification;
A control unit that controls the variable attenuator so that the intensity of the wavelength multiplexed light after passing through the optical amplifier and the variable attenuator becomes the target value;
A total intensity detector that detects the total intensity of the received wavelength multiplexed light;
A light extraction filter for extracting a signal in a part of the wavelength band of the received wavelength multiplexed light;
An extracted signal intensity detector for detecting the intensity of the extracted signal extracted by the light extraction filter;
With
The target value setting unit determines whether to maintain or reset the target value based on whether or not the change ratio of the total intensity and the intensity change ratio of the extracted signal are substantially the same. A wavelength division multiplexing optical transmission system.
The detected value of the total intensity is P, the detected value of the total intensity before a predetermined time is P ′, the detected value of the intensity of the extracted signal is P filter, and the intensity of the extracted signal before the predetermined time is detected. Let the value be P filter ′,
The target value setting unit does not change the target value when P / P ′ and P filter / P filter ′ are substantially the same, and when P / P ′ and P filter / P filter ′ are different, 2. The wavelength division multiplexing optical transmission system according to claim 1, wherein the target value is reset by judging that the number of wavelengths multiplexed in the multiplexed light has changed.
The detected value of the total intensity is P, the detected value of the total intensity before a predetermined time is P ′, the detected value of the intensity of the extracted signal is P filter, and the intensity of the extracted signal before the predetermined time is detected. Let the value be P filter ′,
a first log amplifier that outputs a signal proportional to log P;
a second log amplifier that outputs a signal proportional to the logP filter ;
With
The target value setting unit does not change the target value when (logP−logP ′) and (logP filter −logP filter ′) are substantially the same, and (logP−logP ′) and (logP filter −logP filter). 2), the target value is reset to a target value corresponding to the number of wavelengths after the change by determining that the number of wavelengths multiplexed in the wavelength multiplexed light has changed. 2. The wavelength division multiplexing optical transmission system according to 1.
4. The wavelength division multiplexing optical transmission according to claim 1, wherein the light extraction filter extracts a signal in a wavelength band including a part of the signal light multiplexed on the wavelength division multiplexed light. system.
The wavelength multiplexed light is multiplexed with signal light and supervisory control light that transmits a low-speed signal for monitoring or control,
4. The wavelength division multiplexing optical transmission system according to claim 1, wherein the light extraction filter extracts a signal in a wavelength band including the supervisory control light multiplexed on the wavelength division multiplexed light.
4. The wavelength division multiplexing optical transmission system according to claim 1, wherein the light extraction filter extracts a signal in a wavelength band not including signal light and including noise light.
The wavelength multiplexed light is multiplexed with signal light and supervisory control light that transmits a low-speed signal for monitoring or control,
4. The wavelength division multiplexing optical transmission according to claim 1, wherein the light extraction filter extracts a signal in a wavelength band not including both the signal light and the supervisory control light and including noise light. system.
The wavelength division multiplexing optical transmission system according to claim 7, wherein the upstream device includes a noise light removal filter that removes noise light in a band in which no signal light exists.
The variable attenuator is disposed before the optical amplifier,
9. The wavelength-multiplexed light after passing through the variable attenuator and before being input to the optical amplifier is input to the total intensity detector and the light extraction filter. The wavelength division multiplexing optical transmission system according to one.
The variable attenuator is disposed downstream of the optical amplifier,
The wavelength division multiplexing optical transmission according to any one of claims 1 to 8, wherein the total intensity detection unit and the light extraction filter receive the wavelength division multiplexed light before being input to the optical amplifier. system.
A pumping light source for sending Raman pumping light in a direction opposite to the transmission direction of the wavelength multiplexed light;
A constant gain Raman amplifier that controls the intensity of the Raman pumping light so as to keep the Raman amplification gain obtained by the Raman pumping light constant;
An excitation light output fluctuation detector for detecting fluctuations in the intensity of the excitation light;
On the input side of the optical amplifier,
In the target value setting unit, the change rate of the total intensity and the change rate of the intensity of the extracted signal are substantially the same, or a change in the intensity of the excitation light is detected by the excitation light output fluctuation detection unit. If the target value is not changed, the change ratio of the total intensity is different from the change ratio of the intensity of the extraction signal, and the excitation light output fluctuation detector does not detect the fluctuation of the intensity of the excitation light, The wavelength division multiplexing optical transmission system according to any one of claims 1 to 10, wherein the target value is reset by judging that the number of wavelengths multiplexed in the wavelength division multiplexed light has changed.
The wavelength division multiplexing optical transmission system according to any one of claims 1 to 11, wherein the optical amplifier is subjected to constant gain control.
The target value setting unit determines the target value after resetting based on intensity information of the wavelength multiplexed light transmitted from the upstream device. The wavelength division multiplexing optical transmission system described.
The target value setting unit determines the target value after resetting based on information on the number of wavelengths multiplexed in the wavelength multiplexed light transmitted from the upstream device. The wavelength division multiplexing optical transmission system according to any one of the above.
The wavelength division multiplexing optical transmission system according to any one of claims 1 to 12, wherein the target value setting unit sets the target value after resetting as the detected value of the total intensity.
The detected value of the total intensity is P, the detected value of the total intensity before a predetermined time is P ′, the detected value of the intensity of the extracted signal is P filter, and the intensity of the extracted signal before the predetermined time is detected. Let the value be P filter ′,
The wavelength according to any one of claims 1 to 12, wherein the target value setting unit determines a target value after resetting based on P, P ', P filter and P filter '. Multiplex optical transmission system.
When the target value before resetting is Pt ′ and the target value after resetting is Pt, the target value setting unit Pt = Pt ′ × (P / P filter ) / (P ′ / P filter ′) 17. The wavelength division multiplexing optical transmission system according to claim 16, wherein Pt is determined so as to satisfy logPt = logPt ′ + (logP−logP filter ) − (logP′−logP filter ′).
An optical repeater that receives wavelength-multiplexed light in which a plurality of optical signals having different wavelengths are wavelength-multiplexed, amplifies the wavelength-multiplexed light, and outputs the amplified light.
An optical amplifier for amplifying the wavelength multiplexed light;
A variable attenuator for attenuating the intensity of the wavelength multiplexed light before amplification by the optical amplifier or after amplification by the optical amplifier;
A target value setting unit for setting a target value of the intensity of the wavelength multiplexed light after amplification;
A control unit that controls the variable attenuator so that the intensity of the wavelength multiplexed light after passing through the optical amplifier and the variable attenuator becomes the target value;
A total intensity detector that detects the total intensity of the received wavelength multiplexed light;
A light extraction filter for extracting a signal in a part of the wavelength band of the received wavelength multiplexed light;
An extracted signal intensity detector for detecting the intensity of the extracted signal extracted by the light extraction filter;
With
The target value setting unit determines whether to maintain or reset the target value based on whether or not the change ratio of the total intensity and the intensity change ratio of the extracted signal are substantially the same. An optical repeater characterized by.
A light intensity control method in an optical repeater that receives wavelength multiplexed light in which a plurality of optical signals having different wavelengths are wavelength multiplexed and amplifies and outputs the wavelength multiplexed light,
The optical repeater is
An optical amplifier for amplifying the wavelength multiplexed light;
A variable attenuator for attenuating the intensity of the wavelength multiplexed light before amplification by the optical amplifier or after amplification by the optical amplifier;
With
A target value setting step for setting a target value of the intensity of the wavelength multiplexed light after amplification;
A control step for controlling the variable attenuator so that the intensity of the wavelength multiplexed light after passing through the optical amplifier and the variable attenuator becomes the target value;
A total intensity detecting step for detecting the total intensity of the received wavelength multiplexed light;
A light extraction step of extracting a signal in a part of the wavelength band of the received wavelength multiplexed light;
An extraction signal intensity detection step for detecting the intensity of the extraction signal extracted by the light extraction step;
A determination step for determining whether to maintain or reset the target value based on whether the change ratio of the total intensity and the change ratio of the intensity of the extracted signal are substantially the same;
The light intensity control method characterized by including.