JP2002204209A - Optical branching and inserting multiple node device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical ADM node device which can effectively reduce the influence of noise caused by ASE of an optical amplifier. SOLUTION: The optical ADM node devices has an optical amplifier 11 which amplifies a wavelength-multiplex signal light transmitted through an optical transmission line 10, an optical demultiplexer 12 which demultiplexes the amplified wavelength-multiplex signal into signal lights of respective wavelengths and also branches a signal light of a desired wavelength, an optical receiver 16 which receives the branched signal light of the desired wavelength, an optical transmitter 19 which outputs the signal light of the desired wavelength, and an optical multiplexer 13 which multiplexes and sends out of the signal light of the respective wavelengths demultiplexed by the optical demultiplexer 12 and the signal light from the optical transmitter 19 to the optical transmission line 10; and optical filters 32-1 to 32-3 which are tuned to the respective wavelengths of the signal light demultiplexed by the optical demultiplexer 12 are inserted into optical paths 31-1 to 31-2 between the optical demultiplexer 12 and optical multiplexer 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an add-drop multiplexing (ADM) node device using a length division multiplexing (WDM) technique.

[0002]

2. Description of the Related Art In recent years, with the progress of optical fiber amplifiers, long-distance, large-capacity optical transmission systems have been actively studied. Wavelength Division Multiplexing (W)
DM) transmission method is to multiplex optical signals in the wavelength region without increasing the transmission capacity per channel,
Since the total transmission capacity can be dramatically increased and a highly flexible network can be constructed, it has attracted much attention as an effective method for realizing a long-distance, large-capacity optical transmission system.

[0003] As a lightwave network using the WDM transmission method, an add-drop multiplexing (ADM) having a function of dropping / adding signal light of a specific wavelength.
Is mentioned. Optical ADM is one of the implementations of a transparent lightwave network in which no electric signal is interposed at nodes in the network.

FIG. 11 shows a basic configuration of an optical ADM node. The wavelength-division multiplexed signal light transmitted via the optical transmission line 10 is amplified by an optical amplifier 11 and then demultiplexed into an optical signal of each wavelength by an optical demultiplexer 12. Of the split signal light,
The signal light of the specific wavelength (λ _j ) assigned to the node is split and received by the optical receiver 16. The signal lights of other wavelengths are multiplexed by the optical multiplexer 13, amplified by the optical amplifier 14, and transmitted to the optical transmission line 10. In the node, a signal light having a wavelength (λ _j ) equal to the wavelength of the branched signal light is output from the optical transmitter 19 and transmitted to the optical transmission line 10 via the optical multiplexer 13.

In such an optical ADM node, the wavelength of the signal light to be split by the optical splitter 12 and the optical splitter 1
It is inevitable that the transmission wavelength characteristics of No. 2 will be shifted to some extent. When such a wavelength shift occurs, the spontaneous emission light (Amplified Spond light) of the optical amplifier 11 is transmitted to the optical receiver 16.
Since not only the same wavelength component as the signal light of the ASE (ASE), but also other wavelength components are mixed, beat noise occurs between the ASEs. Due to the influence of the beat noise, the signal to noise ratio of the optical receiver 16 (Signal to Noise Rat)
io: SNR), and the receiving sensitivity is significantly degraded.

In the above-described optical ADM node, when a wavelength shift occurs, the signal spectrum becomes asymmetric due to the transmission wavelength characteristics of the optical demultiplexer 12 and the optical multiplexer 13, so that the signal waveform is distorted. This waveform distortion causes a large sensitivity degradation even with a slight wavelength shift as the number of nodes increases.

Further, in the above-described conventional optical ADM node, it is desirable that only one signal light of one wavelength λ _i be output from one port of the optical demultiplexer 12. Due to the imperfect demultiplexing characteristics, the signal light of the wavelength λ _i leaks to other ports to some extent. The leakage of the signal light to the other port is caused when the optical signal split by the optical splitter 12 is multiplexed again by the optical multiplexer 13.
This causes coherent crosstalk called coherent crosstalk, and deteriorates optical transmission characteristics.

Reference: IEEE Photon.Technol.Lett., Vol. 6,
According to pp. 657-660, 1994, the reception sensitivity degradation P due to coherent crosstalk is expressed as in equation (1). P = −5 log (1−4Q ² Nε) (1) N: Number of paths causing coherent crosstalk ε: Crosstalk amount per path Q: SNR (signal pair required to obtain a predetermined error rate) Noise ratio) Here, considering a lightwave network in which a unique wavelength is assigned to each node, N is approximately proportional to the square of the number of wavelengths (= the number of nodes). Therefore, as the number of wavelengths and the number of nodes of the wavelength multiplexed signal light increase, the requirements for the crosstalk characteristics of the optical demultiplexer 12 and the optical multiplexer 13 become strict, but these crosstalk characteristics should be about 25 dB. Considering that, when the number of wavelengths is about 16, about 1 dB
, The reception sensitivity is deteriorated. For this reason, coherent crosstalk becomes a problem as the number of wavelengths and the number of nodes of the wavelength multiplexed signal light increase. Also, if there is a difference between the wavelength of the signal light output from the transmitter 19 and the transmission wavelength characteristic of the optical demultiplexer 12, the crosstalk characteristics of the optical demultiplexer 12 and the optical multiplexer 13 are deteriorated. Degradation of transmission characteristics due to crosstalk becomes a more serious problem.

[0009]

As described above, in the conventional optical ADM node, when a difference occurs between the wavelength of the signal light to be split by the optical demultiplexer and the transmission wavelength characteristic of the optical demultiplexer,
In the optical receiver, there is a problem that the reception SNR is reduced due to the influence of beat noise between ASEs of the optical amplifier, and the reception sensitivity is significantly deteriorated.

In addition, when the wavelength of the signal light deviates from the transmission wavelength characteristic of the optical multiplexer / demultiplexer, there is a problem that a signal waveform is distorted and the receiving sensitivity is deteriorated.

Further, as the number of wavelengths and the number of nodes of the wavelength division multiplexed signal light increase, there is a problem that optical transmission characteristics are deteriorated due to coherent crosstalk due to imperfect demultiplexing characteristics of the optical demultiplexer. In particular, the problem has been remarkable when there is a deviation between the wavelength of the signal light and the transmission wavelength characteristic of the optical demultiplexer.

An object of the present invention is to provide an optical ADM node device that can effectively reduce the influence of noise caused by ASE of an optical amplifier.

Another object of the present invention is to reduce the influence of noise caused by ASE of an optical amplifier, and to reduce the influence of noise on the wavelength of signal light and the transmission wavelength characteristics of an optical multiplexer / demultiplexer. It is an object of the present invention to provide an optical ADM node device capable of suppressing degradation of the optical ADM node device.

Still another object of the present invention is to provide an optical amplifier having an A
Light A capable of reducing the influence of noise caused by SE and suppressing deterioration of optical transmission characteristics due to coherent crosstalk
A DM node device is provided.

[0015]

In order to solve the above problems, a first optical ADM node device according to the present invention comprises: an optical amplifier for amplifying a wavelength multiplexed signal light transmitted via an optical transmission line; An optical demultiplexing means for demultiplexing the wavelength multiplexed signal output from the optical amplifier into signal light of each wavelength and branching the signal light of a desired wavelength; and a signal light of a desired wavelength split by the optical demultiplexing means. An optical receiver for receiving, an optical transmitter for outputting signal light of a desired wavelength, and a signal light for multiplexing the signal light of each wavelength demultiplexed by the optical demultiplexing means and the signal light output from the optical transmitter. An optical multiplexing means for transmitting to a transmission path, and a plurality of optical filters provided on an optical path between the optical demultiplexing means and the optical multiplexing means, and tuned to each wavelength of the signal light demultiplexed by the optical demultiplexing means. It is characterized by having.

As described above, in the first optical ADM node device, the optical filter tuned to the wavelength of the signal light passing through each path is inserted into the optical path between the optical demultiplexer and the optical multiplexer. ASE noise of the optical amplifier is reduced, and coherent crosstalk is suppressed. Therefore, even if the number of wavelengths or the number of nodes increases, deterioration of transmission characteristics due to ASE noise or coherent crosstalk is suppressed.

A second optical ADM node device according to the present invention includes an optical amplifier for amplifying a wavelength multiplexed signal light transmitted through an optical transmission line, and a wavelength multiplexed signal light output from the optical amplifier. An optical demultiplexing means for demultiplexing the signal light of the desired wavelength and branching the signal light of the desired wavelength, an optical receiver for receiving the signal light of the desired wavelength split by the light demultiplexing means, and a signal light of the desired wavelength An optical transmitter for outputting the signal light of each wavelength demultiplexed by the optical demultiplexer and the signal light output from the optical transmitter and transmitting the signal light to the optical transmission path; A plurality of optical filters provided in the optical path between the optical multiplexing means and the optical signal multiplexed to the respective wavelengths of the signal light demultiplexed by the optical demultiplexing means; and a signal of each wavelength output from the optical multiplexing means. Detects the output power of the light and adjusts the light so that this output power is maximized. Characterized in that a control means for controlling the wavelength characteristic of the filter.

As described above, the second optical ADM node device is inserted into the optical path between the optical demultiplexer and the optical multiplexer so that the signal light power of each wavelength is maximized at the output of the optical multiplexer. By controlling the wavelength characteristic of the optical filter, even if the wavelength of the signal light deviates from the wavelength characteristic of the optical demultiplexer, transmission characteristic deterioration due to coherent crosstalk is suppressed.

Further, the optical filter inserted between the optical demultiplexer and the optical multiplexer has a function of reducing a wavelength shift between the signal light at the node and the transmission wavelength characteristics of the optical demultiplexer and the optical multiplexer. Accordingly, distortion of the signal waveform due to the wavelength shift is reduced.

A third optical ADM node device according to the present invention comprises an optical amplifier for amplifying a wavelength multiplexed signal light transmitted via an optical transmission line, and a wavelength multiplexed signal light output from the optical amplifier. An optical demultiplexing means for demultiplexing the signal light of the desired wavelength and branching the signal light of the desired wavelength, an optical receiver for receiving the signal light of the desired wavelength split by the light demultiplexing means, and a signal light of the desired wavelength An optical transmitter for outputting the signal light of each wavelength demultiplexed by the optical demultiplexer and the signal light output from the optical transmitter and transmitting the signal light to the optical transmission path; A plurality of optical filters provided in the optical path between the multiplexing means and the optical multiplexing means, and detecting a wavelength shift between the transmission center wavelength of the optical demultiplexing means and the optical multiplexing means and the wavelength of the signal light; Detecting means for outputting a signal corresponding to the Characterized in that a control means for controlling the wavelength characteristic of the optical filter on the basis of the signal.

As described above, in the third optical ADM node device, the wavelength deviation between the transmission center wavelength of the optical demultiplexer and the optical multiplexer and the signal light wavelength is detected, and the optical demultiplexer is compensated for this wavelength deviation. By controlling the wavelength characteristics of the optical filter inserted in the optical path between the optical device and the optical multiplexer, even if there is a deviation between the wavelength of the signal light and the transmission wavelength characteristics of the optical demultiplexer and the optical multiplexer, Transmission characteristic degradation due to signal waveform distortion is suppressed.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. In FIG. 1, an optical transmission line 10 is an optical fiber transmission line, and wavelength multiplexed signal light (wavelengths λ ₁ ,..., Λ ₄ ) transmitted through the optical transmission line 10 is first amplified by an optical amplifier 11. You. The wavelength multiplexed signal light output from the optical amplifier 11 is
The optical demultiplexer 12 demultiplexes the signal light of each wavelength λ ₁ ,..., Λ ₄ .

Each wavelength λ ₁ , demultiplexed by the optical demultiplexer 12,
, Λ _4, the signal light of the specific wavelength λ _j assigned to the node is branched and input to the optical receiver 16 via the optical filter 18. The signal light that has not been split and the signal light (wavelength λ ₄ ) from the optical transmitter 19 are multiplexed by the optical multiplexer 13, amplified by the optical amplifier 14, and transmitted to the optical transmission line 10.

Part of the optical signal received by the optical receiver 16 is SN
It is input to the R detection unit 17. In the SNR detection unit 17, the signal-to-noise ratio (SN) of the received optical signal is
R), and outputs a signal corresponding to the received SNR to the control unit 1.
8 is output. The control unit 18 controls the optical filter 15 so that the reception SNR detected by the SNR detection unit 17 is maximized.
, Specifically, the transmission center wavelength.

FIG. 2 shows an input signal to the optical receiver 16 when there is a difference between the wavelength (λ ₄ ) of the signal light branched by the optical demultiplexer 12 and the transmission wavelength characteristic of the optical demultiplexer 12. FIG. FIG. 2A shows a case where the optical filter 15 is not provided.
FIG. 2B shows the case where the transmission center wavelength of the optical filter 15 is matched with the wavelength of the transmission light, and FIG. 2C shows the optical filter 1 so that the reception SNR becomes maximum due to the present embodiment only.
5 shows a case where the transmission center wavelength is controlled. From these, it is understood that the ASE noise of the optical amplifier 11 is reduced by the optical filter 15. That is, the optical filter 15 outputs the optical demultiplexer 1 of the ASE noise of the optical amplifier 11.
Since only the wavelength component of the signal light having the wavelength λ _j that is branched at 2 and received by the optical receiver 16 is transmitted, the ASE noise of the other wavelength components is not input to the optical receiver 16.

FIG. 3 shows the optical receiver 16 in various cases.
5 shows the error rate characteristics with respect to the average received light power in the case of FIG. FIG.
(A) to (c) correspond to (a) to (c) in FIG. 2, respectively, and (d) shows a case where there is no wavelength shift. As is apparent from this figure, when the optical filter 15 is controlled so that the reception SNR is maximized, the wavelength of the signal light branched by the optical demultiplexer 12 and the transmission wavelength characteristics of the optical demultiplexer 12 It can be seen that the deterioration of the receiving sensitivity due to the wavelength shift during the period can be suppressed to the minimum.

As described above, in the optical ADM node device according to the present embodiment, the signal light of a specific wavelength branched by the optical demultiplexer 12 is received by the optical receiver 16 via the optical filter 15, and the reception SNR is reduced. Optical filter 15 to be maximum
Of the optical receiver 16 by controlling the transmission wavelength characteristic of
In this case, the beat noise between the ASE noises can be reduced, and the deterioration of the receiving sensitivity due to the wavelength shift between the wavelength of the branched optical signal and the transmission wavelength characteristic of the optical demultiplexer 12 can be suppressed to a minimum.

In the present embodiment, the optical demultiplexer 12
And the optical multiplexer 13 to drop / add a signal light of a specific wavelength. However, as in an acousto-optic filter or an optical lattice filter, only a signal light of a specific wavelength is dropped / added, and other wavelengths of signal light are added. An optical circuit that can transmit signal light may be used.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description will focus on differences.

The output of the optical amplifier 11 for amplifying the wavelength multiplexed signal light transmitted via the optical transmission line 10 is input to the optical demultiplexer 12 via the optical resonator 21. The optical resonator 21 is an optical filter used in place of the optical filter 15 in FIG. 1, and is constituted by, for example, a fiber Fabry-Perot resonator, a ring resonator, or the like. The free spectrum range of the optical resonator 21 matches the wavelength interval of the wavelength multiplexed signal light.

The output signal from the SNR detector 17 for detecting the reception SNR of the optical receiver 16 is input to the optical resonator controller 22, and the optical resonator controller 22
Is controlled so as to maximize the transmission wavelength characteristic of the optical resonator 21.

Also in the present embodiment, as in the first embodiment, the transmission wavelength of the optical resonator 21 is set so that the reception SNR of the signal light branched to the optical receiver 16 by the optical demultiplexer 12 is maximized. By controlling the characteristics, the beat noise between the ASE noises in the optical receiver 16 is reduced, and the deterioration of the receiving sensitivity due to the wavelength shift between the wavelength of the branched optical signal and the transmission wavelength characteristic of the optical demultiplexer 12 is minimized. Can be suppressed.

In this embodiment, as in the first embodiment, instead of using the optical demultiplexer 12 and the optical multiplexer 13 to drop / add a signal light of a specific wavelength, an acousto-optic filter is used. An optical circuit, such as a filter or an optical lattice filter, capable of dropping / inserting only signal light of a specific wavelength and transmitting signal light of another wavelength may be used.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description will focus on differences.

The signal lights λ ₁ , λ ₂ , λ ₃ , and λ ₄ of the respective wavelengths demultiplexed by the optical demultiplexer 12 are respectively transmitted through optical paths 31-1, 31-1.
It is sent to 31-2, 31-3, 31-4. Wavelength λ ₄
Is split through an optical path 31-4, and the remaining signal lights of wavelengths λ ₁ , λ ₂ , λ ₃ are split into optical paths 31-1, 31-.
2, 31-3. Optical filters 32-
The signals are multiplexed by the optical multiplexer 13 via 1, 32-2 and 32-3.

Optical filters 32-1, 32-2, 32-3
Are the transmission center wavelengths of the signal light wavelengths λ ₁ , λ ₂ , λ ₃
Are in agreement with each other. Therefore, for example, the signal light components of the wavelengths λ ₂ , λ ₃ and λ ₄ leaking into the optical path 31-1 are suppressed by the optical filter 32-1 together with the ASE noise of the optical amplifier 11. Similarly, the signal light components of wavelengths λ ₁ , λ ₃ , λ ₄ leaking into the optical path 31-2 are suppressed by the optical filter 32-2 together with the ASE noise of the optical amplifier 11, and further leaked into the optical path 31-3. Wavelengths λ ₁ , λ ₂ ,
The signal light component of λ ₄ is suppressed by the optical filter 32-3 together with the ASE noise of the optical amplifier 11.

As a result, coherent crosstalk and ASE noise when multiplexed by the optical multiplexer 13 can be reduced. In particular, since the effect of suppressing signal light components having wavelengths apart from the desired wavelength is large, the number of optical paths that cause coherent crosstalk can be significantly reduced.

As described above, in the present embodiment, the wavelength division multiplexed signal light is demultiplexed by the optical demultiplexer 12, and then the optical filters 32-1, 32-2, and 32-3 tuned to the respective wavelengths.
Multiplexed by the optical multiplexer 13 via the optical communication device, coherent crosstalk and ASE noise of the optical amplifier can be reduced even if the number of wavelengths or the number of nodes increases, and good optical transmission characteristics can be achieved.

(Fourth Embodiment) FIG. 6 shows a fourth embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. The same parts as those in FIG. 5 are denoted by the same reference numerals, and the description will focus on the differences.

In this embodiment, an optical coupler 41 is provided on the output side of the optical multiplexer 13, and a part of the output light of the optical multiplexer 13 is extracted by the optical coupler 41 and input to the power detector 42. . The power detector 42 detects the power of the signal light of each wavelength and outputs a signal corresponding to the detected optical power to the optical filter controller 43.

The optical filter control section 43 controls the optical paths 31-1, 31-2, 3 so that the optical power of each wavelength is maximized.
Optical filters 32 respectively inserted in 1-3 and 31-4
-1, 32-2 and 32-3 are controlled.

If a shift occurs between the transmission wavelength characteristics of the optical demultiplexers 12 and the optical multiplexer 13 and the wavelength of the signal light, the crosstalk characteristics deteriorate, but the optical filters 32-1 and 32-
2, 32-3 are tuned to the wavelength of the signal light and suppress wavelength components other than the desired signal light, so that good crosstalk characteristics can be maintained.

FIG. 7 shows optical filters 32-1 and 32-
The ratio at which the wavelength shift at the node when 2, 32-3 is inserted is reduced. The horizontal axis is the optical filter 32-
The ratio m (= f2 / f1) of the transmission bandwidth (f2) of 1, 32-2, 32-3 to the transmission bandwidth (f1) of the optical demultiplexer 12 or the optical multiplexer 13 is shown. The vertical axis indicates the optical filter 32-
The ratio Δλ (= Δλ2 / Δλ1) of the wavelength shift amount (Δλ2) of the gas when 1, 32-2 and 32-3 are inserted and the wavelength shift amount (Δλ1) of the gas without the insertion are shown. Note that Gaussian filters are assumed as the optical filters 32-1, 32-2, and 32-3.

FIG. 7 shows that the optical filters 32-1 and 32-
By inserting 2,32-3, it can be seen that the wavelength shift amount is reduced to half when m = 1, and to one-fifth when m = 0.5.

As described above, in the present embodiment, each optical filter 3 inserted between the optical demultiplexer 12 and the optical multiplexer 13 is
Since 2-1, 32-2 and 32-3 are always tuned to each wavelength of the signal light, there is a deviation between the transmission wavelength characteristic of the optical demultiplexer 12 and the optical multiplexer 13 and the wavelength of the signal light. Even if it occurs, ASE noise of the optical amplifier 11 can be reduced, and deterioration of transmission characteristics due to coherent crosstalk and signal waveform distortion can be suppressed.

(Fifth Embodiment) FIG. 8 shows a fifth embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. The same parts as those in FIG. 6 are denoted by the same reference numerals, and the description will focus on the differences.

In the present embodiment, the position portion of the signal light output from the optical multiplexer 13 is extracted by the optical coupler 41 and input to the wavelength shift detector 45. Wavelength shift detector 4
5, the wavelength of the signal light and the optical demultiplexer 12 and the optical multiplexer 1
3 and outputs a signal corresponding to the detected shift amount to the optical filter control unit 44.

The optical filter controller 44 controls the optical filter 32
When -1, 32-2, and 32-3 are Gaussian filters,
The optical paths 31-1, 31-2, 31-3 according to equation (2)
, The optical filters 32-1, 32-2,
Control the transmission center wavelength of 32-3.

B = −2m ² a (2) a: deviation between the wavelength of the signal light and the transmission center wavelength of the optical demultiplexer 12 and the optical multiplexer 13 m: band of the optical demultiplexer 12 and the optical multiplexer 13 The ratio between the width and the bandwidth of the optical filters 32-1, 32-2, and 32-3. B: Control amount of the transmission center wavelength of the optical filters 32-1, 32-2, and 32-3 from the signal light wavelength. In the present embodiment, the optical filters 32-1 and 32 inserted between the optical demultiplexer 12 and the optical multiplexer 13 are provided.
−2 and 32-3 always cancel the transmission center wavelength of the optical demultiplexer 12 and the optical multiplexer 13, the wavelength of the signal light, and the wavelength shift. Therefore, even if the wavelength shift occurs, the ASE noise of the optical amplifier 11 is reduced. It is possible to more effectively reduce and suppress deterioration of transmission characteristics due to distortion of a signal waveform.

(Sixth Embodiment) FIG. 9 shows a sixth embodiment of the present invention.
1 shows a configuration of an optical ADM node device according to the embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description will focus on differences.

The signal light having the wavelength λ ₄ of the signal light split by the optical splitter 12 is split and received by the optical receiver 16. The optical receiver 16 outputs a signal corresponding to the optical power of the received signal light to the optical demultiplexer control unit 51. The optical demultiplexer controller 51 controls the optical demultiplexer 1 so that the received optical power is maximized.
2 is controlled.

A part of the output light from the optical multiplexer 13 is input to the power detector 42 via the optical coupler 41 as in the fourth embodiment. The power detector 42 detects the optical power of the signal light of the wavelengths λ ₁ , λ ₂ , λ ₃ transmitted through the node, and outputs a signal corresponding to the detected optical power to the optical multiplexer controller 52. The optical multiplexer control unit 52 controls the transmission wavelength characteristic of the optical multiplexer 13 so that the signal light power of each wavelength of the output light of the optical multiplexer 13 is maximized.

In this embodiment, since the transmission wavelength characteristics of the optical demultiplexer 12 and the optical multiplexer 13 are controlled with reference to the wavelength of the signal light, the wavelength of the signal light and the wavelength of the optical demultiplexer 12 and the optical multiplexer are controlled. A due to the wavelength shift from the transmission wavelength characteristic of the detector 13
It is possible to suppress reception sensitivity deterioration in the optical receiver 16 due to beat noise between SEs, increase in coherent crosstalk, and signal waveform distortion.

(Seventh Embodiment) FIG. 10 shows a configuration of an optical ADM node device according to a seventh embodiment of the present invention.
The same parts as those in FIG.

The power detector 42 detects the optical power of the signal light of wavelengths λ ₁ , λ ₂ , λ ₃ passing through the node, and outputs a signal corresponding to the detected optical power to the optical multiplexer controller 5.
Output to 2. Further, the power detector 42 detects the optical power of the inserted signal light having the wavelength λ ₄ and outputs a signal corresponding to the detected optical power to the optical transmitter 19. Optical transmitter 19
In, the transmission wavelength is controlled based on the signal from the power detection unit so that the optical power transmitted through the optical multiplexer 13 is maximized.

In the present embodiment, the transmission wavelength characteristic of the optical multiplexer / demultiplexer 13 is stabilized with reference to the wavelength passing through the node, and the transmission wavelength characteristic of the optical multiplexer / demultiplexer 13 is further used by the optical transmitter 19. The wavelength of the signal light to be inserted is controlled. Therefore, a signal light having the same wavelength as the branched wavelength can be inserted, so that good optical transmission characteristics can be achieved without increasing coherent crosstalk in other optical ADM nodes.

[0058]

As described above, according to the present invention, the influence of noise due to the ASE of the optical amplifier can be effectively reduced, and furthermore, the deterioration of the optical transmission characteristics due to coherent crosstalk can be suppressed. .

That is, in the first optical ADM node device according to the present invention, an optical filter tuned to the wavelength of the signal light passing through each path is inserted into the optical path between the optical demultiplexer and the optical multiplexer. As a result, the ASE noise of the optical amplifier is reduced and the coherent crosstalk is suppressed. Therefore, even if the number of wavelengths and the number of nodes increase, it is possible to suppress the transmission characteristic deterioration due to the ASE noise and the coherent crosstalk. it can.

In the second optical ADM node device according to the present invention, the optical path between the optical demultiplexer and the optical multiplexer is set so that the signal light power of each wavelength becomes maximum at the output of the optical multiplexer. By controlling the wavelength characteristics of the inserted optical filter, even if the wavelength of the signal light deviates from the wavelength characteristics of the optical demultiplexer and the optical multiplexer, the optical transmission characteristics due to coherent crosstalk and distortion of the signal waveform can be improved. Deterioration can be suppressed.

In the third optical ADM node device according to the present invention, the optical demultiplexer and the optical multiplexer are combined so as to cancel the wavelength shift between the wavelength of the signal light and the wavelength of the optical demultiplexer and the optical multiplexer. By controlling the wavelength characteristics of the optical filter inserted between the optical filters, it is possible to suppress the deterioration of the optical transmission characteristics due to the distortion of the signal waveform even if such a wavelength shift occurs.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical ADM node according to a first embodiment.

FIG. 2 is a diagram showing an optical receiver input optical spectrum of signal light split in various optical ADM nodes.

FIG. 3 is a diagram illustrating error rate characteristics of signal light branched in various optical ADM nodes;

FIG. 4 is a diagram illustrating a configuration of an optical ADM node according to a second embodiment;

FIG. 5 is a diagram illustrating a configuration of an optical ADM node according to a third embodiment;

FIG. 6 is a diagram illustrating a configuration of an optical ADM node according to a fourth embodiment;

FIG. 7 is a diagram showing a rate at which a wavelength shift is reduced by inserting an optical filter.

FIG. 8 is a diagram showing a configuration of an optical ADM node according to a fifth embodiment.

FIG. 9 is a diagram showing a configuration of an optical ADM node according to a sixth embodiment.

FIG. 10 is a diagram showing a configuration of an optical ADM node according to a seventh embodiment.

FIG. 11 is a diagram showing a basic configuration of an optical ADM node;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Optical transmission line 11 ... Optical amplifier 12 ... Optical demultiplexer 13 ... Optical multiplexer 14 ... Optical amplifier 16 ... Optical receiver 17 ... SNR detection part 18 ... Optical filter control part 19 ... Optical transmitter 21 ... Optical resonator 22 optical resonator controller 31-1 to 31-4 optical path 32-1 to 32-3 optical filter 41 optical coupler 42 optical power detector 43 optical filter controller 44 optical filter controller 45 … Wavelength shift detecting section 51… optical demultiplexer control section 52… optical multiplexer control section

Claims (3)

[Claims] An optical amplifier for amplifying a wavelength-division multiplexed signal light transmitted via an optical transmission line, a wavelength-division multiplexed signal output from the optical amplifier is demultiplexed into signal lights of respective wavelengths, and a desired wavelength is multiplexed. An optical demultiplexing unit that splits the signal light; an optical receiver that receives the signal light of a desired wavelength split by the optical demultiplexing unit; an optical transmitter that outputs the signal light of the desired wavelength; Optical multiplexing means for multiplexing the signal light of each wavelength demultiplexed by the multiplexing means and the signal light output from the optical transmitter and sending the multiplexed signal light to an optical transmission line; the optical multiplexing means and the optical multiplexing means And a plurality of optical filters tuned to each wavelength of the signal light demultiplexed by the optical demultiplexing means. 2. An optical amplifier for amplifying a wavelength multiplexed signal light transmitted via an optical transmission line, a wavelength multiplexed signal light output from the optical amplifier being demultiplexed into signal lights of respective wavelengths, and a desired wavelength Optical demultiplexing means for splitting the signal light of the above, an optical receiver for receiving the signal light of a desired wavelength split by the optical demultiplexing means, an optical transmitter for outputting the signal light of the desired wavelength, and the light Optical multiplexing means for multiplexing the signal light of each wavelength demultiplexed by the demultiplexing means and the signal light output from the optical transmitter and sending the multiplexed signal light to an optical transmission line; the optical demultiplexing means and the optical multiplexing means A plurality of optical filters provided in an optical path between the optical filter, detecting the output power of the signal light of each wavelength output from the optical multiplexing means, the wavelength of the optical filter so that this output power is maximized And control means for controlling characteristics. That the optical add-drop multiplexing node device. 3. An optical amplifier for amplifying a wavelength-division multiplexed signal light transmitted via an optical transmission line; a wavelength-division multiplexed signal light output from the optical amplifier is demultiplexed into signal lights of respective wavelengths; Optical demultiplexing means for splitting the signal light of the above, an optical receiver for receiving the signal light of a desired wavelength split by the optical demultiplexing means, an optical transmitter for outputting the signal light of the desired wavelength, and the light Optical multiplexing means for multiplexing the signal light of each wavelength demultiplexed by the demultiplexing means and the signal light output from the optical transmitter and sending the multiplexed signal light to an optical transmission line; the optical demultiplexing means and the optical multiplexing means A plurality of optical filters provided in the optical path between the optical demultiplexing means and the optical demultiplexing means and the optical multiplexing means detect a wavelength shift between the transmission center wavelength and the wavelength of the signal light, and a signal corresponding to the wavelength shift. Detecting means for outputting a signal, and an output signal from the detecting means. Control means for controlling the wavelength characteristic of the optical filter based on the optical filter.