JP4757938B2 - Pre-emphasis method, optical communication system, and control apparatus - Google Patents

Description

The present invention provides an optical signal-to-noise ratio for measuring an optical signal-to-noise ratio of a wavelength-division multiplexing optical signal obtained by multiplexing optical signals at high density in measuring an optical signal-to-noise ratio of a wavelength-division multiplexing optical signal. The present invention relates to a measuring method and an optical signal-to-noise ratio measuring apparatus using the measuring method. Furthermore, the present invention relates to a pre-emphasis method, an optical communication system, a measurement circuit, and a control device using the optical signal-to-noise ratio measurement method.
Aiming at the construction of a future multimedia network, an ultra-long-distance and large-capacity optical communication system is required. For this reason, research and development of a wavelength-division multiplexing (hereinafter abbreviated as “WDM”) system is underway from the advantage of being able to effectively use the broadband and large capacity of optical fibers. In particular, in recent years, there is a tendency to increase the density by narrowing the wavelength interval of wavelength-division multiplexed optical signals in order to meet the demand for higher capacity. Even when such a WDM optical signal is transmitted, in order to maintain the signal quality, the optical signal-to-noise ratio (hereinafter, “optical SNR”) of the WDM optical signal that is wavelength-multiplexed with high density is abbreviated. ) Is required.

  In general, when an optical signal is transmitted over a long distance, the optical signal is amplified by an optical repeater station including an optical amplifier between the optical transmission station and the optical reception station in order to compensate for transmission loss of the optical transmission path. The optical signal is superimposed with amplified spontaneous emission (hereinafter abbreviated as “ASE”) generated by the optical amplifier when amplified, and the ASE is cumulative every time it is amplified by the optical amplifier. Is superimposed on. Since this cumulatively superimposed ASE is noise for the optical signal, it is necessary to measure the optical SNR of the optical signal in order to maintain a predetermined signal quality.

FIG. 20 is a diagram for explaining a conventional optical SNR measurement method.
FIG. 20 shows a case where a WDM optical signal is amplified by several optical amplifiers and ASE is superimposed. In this WDM optical signal, four-wave optical signals of channel 1 to channel 4 are wavelength-multiplexed. Then, as shown in FIG. 20, the optical signals are arranged with a sufficient wavelength interval so as not to overlap each other in the low light level portion of the optical signal. Hereinafter, the channel is abbreviated as “ch.”.

  In such a WDM optical signal, each ch. The light level at a substantially intermediate wavelength (marked with x in FIG. 20) is the light level of ASE. For this reason, a certain ch. In the optical SNR, the spectrum of the WDM optical signal is measured by a spectrum analyzer, and from the measurement result, a certain ch. And the optical level of the wavelength (marked with ● in FIG. 20) and a certain ch. And the adjacent ch. Can be measured by taking a ratio with the light level of a wavelength approximately in the middle of the wavelength where X is arranged (marked with x in FIG. 20).

  In general, the level diagram of an optical communication system is designed for light at a predetermined wavelength. When a WDM optical signal is transmitted to such an optical communication system, the WDM optical signal is transmitted to each channel due to non-uniform gain wavelength characteristics and gain saturation characteristics in an optical amplifier in the optical repeater station. Are amplified with different gains. Furthermore, due to the non-uniform loss wavelength characteristics of the optical transmission line, each ch. Loses optical power with different losses. Therefore, the level diagram in the optical signal having a wavelength far from the predetermined wavelength is far from the designed level diagram. For this reason, the low optical power ch. In addition, an error rate (bit error rate) higher than that required by the optical communication system is generated.

Therefore, pre-emphasis is applied to the WDM optical signal so as to be lower than the required error rate.
FIG. 21 is a diagram illustrating a configuration of an optical communication system that performs conventional pre-emphasis.
In FIG. 21, the WDM optical signal generated by the optical transmitter 911 in the optical transmission station 901 is transmitted to the optical transmission line 902 by a plurality of optical repeaters 903 provided between the optical transmission lines 902 and the optical signal. The signal is amplified to compensate for the loss of the relay station 903 and transmitted to the optical receiving station 904 for reception and processing. The loss of the optical repeater station 903 is caused by each optical component such as a dispersion compensating fiber (hereinafter abbreviated as “DC”) in the station.

  The WDM optical signal is pre-emphasized by the pre-emphasis control circuit 912 in the optical transmission station 901 when it is emitted from the optical transmission station 901 to the optical transmission line 902.

  The pre-emphasis control circuit 912 receives each channel from the optical receiving station 904. Of each ch. Generated by the optical transmitter 911 based on the optical SNR of each channel. The WDM optical signal is pre-emphasized by adjusting the optical level of the optical signal corresponding to. The optical SNR of each optical signal is measured by an optical SNR measuring circuit 922 provided in the optical receiving station 904, for example, a spectrum analyzer, and transmitted through a line 931.

Here, the pre-emphasis control circuit 912 adjusts the optical level of each optical signal as follows, for example. That is,
As a first step, all ch. The average value of the optical SNR is obtained for.
As the second step, the average value and the ch. The difference from the optical SNR of 1 is obtained.

As a third step, the optical transmission station 901 changes the optical level to compensate for this difference to ch. 1 and ch. 1 light level is adjusted.
As the fourth step, the second step and the third step described above are performed for each channel of the WDM optical signal. It carries out for each optical signal corresponding to.
In this way, each ch. In the optical transmission station 901, the optical level of each optical signal may be adjusted so that the optical SNRs of the optical signals become equal to each other.

Adjusting the optical level of each optical signal corresponds to adjusting the level diagram for each optical signal. For this reason, the optical SNR of each optical signal in the WDM optical signal is optimized by applying pre-emphasis.
Pre-emphasis in a point-to-point optical communication system is disclosed in, for example, Patent Literature 1, Patent Literature 2, and Patent Literature 3.

  Furthermore, in recent years, not only an optical communication system that transmits and receives a WDM optical signal between two end stations, but also a station provided in the middle of an optical transmission line has a specific wavelength among optical signals that are wavelength-multiplexed. An add-drop multiplexer that selectively passes only an optical signal and branches an optical signal of a wavelength other than that optical signal at that station, or inserts another optical signal from this station and transmits it to another station. ) Realization of an optical communication system having a function is demanded. This ADM function tends to be performed by an optical branching / inserting device (hereinafter abbreviated as “OADM”) that branches and inserts a WDM optical signal as it is without optical / electrical conversion.

  This OADM has a certain ch. When branching / inserting, for example, the branching ch. Is removed by an optical filter, and then the optical signal to be inserted is changed to the ch. Insert into. In this case, the optical filter is divided into ch. As well as its optical power. ASE in a narrow range centering on the wavelength of is also removed. FIG. 22 shows the OADM ch. 3 is a diagram illustrating a spectrum of a WDM optical signal obtained by branching and inserting 3;

For example, from a four-wave WDM optical signal as shown in FIG. In the case of branching / inserting 3, OADM includes ch. 3 is removed, and then the optical signal to be inserted is changed to ch. Insert at 3 wavelengths. For this reason, ch. WDM optical signal after branching / inserting 3 shows a spectrum as shown in FIG. Ch. The light level of ASE in between changes rapidly.
Furthermore, the ASE for the optical signal that has not been branched / added and the ASE for the optical signal that has been dropped / added differ in the number of optical amplifiers to be relay-amplified, so that the optical level of the ASE is different.

Japanese Patent Application Laid-Open No. 06-068991 JP 09-261205 A JP-A-11-103287

  By the way, WDM optical signals tend to have a higher density that makes wavelength intervals of wavelength-division multiplexed optical signals closer due to the recent demand for larger capacity. The optical signal has a narrow wavelength width in the high light level portion and gradually widens as the light level decreases, and in particular, has a wide wavelength width in the low light level portion. Is normal. For this reason, as shown in FIG. 23, the optical signals in the high-density WDM optical signal have the low light level portions of the optical signals overlapping each other. As a result, in order to measure the optical SNR, each ch. Even if the optical level at the approximate center wavelength is measured, the optical level of the light in which a part of the optical signal is superimposed on the ASE is measured, and therefore the optical level of the ASE cannot be measured. Therefore, the conventional method has a problem that the optical SNR cannot be measured.

Further, in the WDM optical signal after branching / inserting, as shown in FIG. The ASE before and after changes rapidly. For this reason, this ch. However, the optical SNR cannot be measured because ASE cannot be measured.
In an optical communication system that performs control based on the measurement result of the optical SNR, there is a problem that optimal control is difficult because the optical SNR cannot be measured in this way.

Therefore, an object of the present invention is to provide a method, an apparatus, and a measurement circuit for measuring an optical SNR without directly measuring ASE in an optical signal.
An object of the present invention is to provide a pre-emphasis method, an optical communication system, and a control apparatus using an optical SNR measured without directly measuring ASE in a WDM optical signal.

  The above-described object is to provide an optical SNR measurement method for measuring the optical SNR of an optical signal on the emission side of the optical transmission line including a plurality of stations including an optical amplification unit that amplifies the optical signal between the optical transmission lines. A first step for obtaining predetermined physical quantities using measuring means provided in at least two of the stations, and an arithmetic circuit for obtaining a partial optical SNR for each of the plurality of stations based on the measured predetermined physical quantities This is achieved by comprising a second step and a third step for obtaining the reciprocal sum of the partial light SNR and further obtaining the optical SNR which is the reciprocal of the reciprocal sum.

  The above object is to provide a plurality of optical SNR devices for measuring the optical SNR of the optical signal on the emission side of the optical transmission path, including a plurality of stations including optical amplification means for amplifying the optical signal between the optical transmission paths. The measurement means for measuring a predetermined physical quantity in the station, the predetermined physical quantity in a plurality of stations is obtained from the measurement results of the measurement means, and the predetermined physical quantity obtained from the measurement means is provided. An arithmetic circuit that obtains a partial optical signal-to-noise ratio for each of a plurality of stations based on a physical quantity, obtains an inverse number of the partial optical signal-to-noise ratio, and further obtains an optical SNR that is an inverse number of the inverse number sum; This is achieved by configuring.

Another object of the present invention is to provide an optical signal to be wavelength-multiplexed in this optical transmission line including a plurality of stations provided with optical amplification means for amplifying a WDM optical signal obtained by wavelength-multiplexing a plurality of optical signals between the optical transmission lines. A pre-emphasis method for adjusting the optical level of the optical signal when the light is first incident, a first step of obtaining predetermined physical quantities using measurement means provided in at least two of the plurality of stations, and Based on the measured predetermined physical quantity, the arithmetic circuit calculates the partial light SNR for each of the plurality of optical signals for each of the plurality of stations, and calculates the reciprocal sum of the partial light SNR for each of the plurality of optical signals. calculated over the section station the signal is amplified overlap, as divided light SNR is the inverse of the respective inverse sum of a plurality of optical signals are equal to each other, are wavelength-multiplexed A plurality of optical signals and a third step of obtaining a light level adjusting means provided with an optical signal to be wavelength-multiplexed in the first station entering the optical transmission path when entering the first optical transmission path an optical signal can And a fourth step of adjusting the light levels of the plurality of optical signals so as to obtain the obtained light level .

  Further, the above object is to provide an optical communication system including a plurality of stations including an optical amplifying unit that amplifies a WDM optical signal obtained by wavelength multiplexing a plurality of optical signals between optical transmission lines. An optical signal that is provided in two or more stations and that is to be wavelength-multiplexed by a pre-emphasis method configured as described above based on a measurement unit that measures a predetermined physical quantity in the station and a measurement result of the measurement unit Is provided in an arithmetic circuit for determining the optical levels of a plurality of optical signals when first incident on the optical transmission line, and an optical signal to be wavelength-multiplexed is first provided in the optical transmission line and obtained by the arithmetic circuit. This is achieved by comprising adjusting means for adjusting the optical level of the optical signal so that the optical level becomes the specified optical level.

で定義し、光信号を増幅する局に亘ってこの逆数の和を求めてさらに逆数を求めることによって、ＡＳＥを用いないで光ＳＮＲを求めることができる。このため、ＡＳＥを直接測定することができない場合においても光ＳＮＲを測定することができる。そして、測定した光ＳＮＲを利用してプリエンファシスをＷＤＭ方式光信号に施すことができる。 In such an optical SNR measurement method, an optical SNR measurement device, a pre-emphasis method, and an optical communication system, for example, a predetermined physical quantity is an output optical level Pout, a noise figure NF, and a gain G, and a partial optical SNR is set to a Planck constant h, Under the frequency ν corresponding to the wavelength of the optical signal and the frequency Δf corresponding to the resolution of the desired optical SNR,

The optical SNR can be obtained without using ASE by calculating the sum of the reciprocals over the stations that amplify the optical signal and further calculating the reciprocal. For this reason, the optical SNR can be measured even when the ASE cannot be directly measured. Then, pre-emphasis can be applied to the WDM optical signal using the measured optical SNR.

  As described above, according to the present invention, the optical SNR of a WDM optical signal can be measured. By using the measured optical SNR, it is possible to perform appropriate pre-emphasis on the WDM optical signal in the optical communication system having the branching / inserting device.

It is a figure which shows the basic composition of this invention. P. G. It is a figure for demonstrating an example of the pre-emphasis in the inside. The overall configuration of the optical communication system according to the first embodiment G. FIG. It is a figure which shows the structure of the optical transmission station in the optical communication system of 1st Embodiment. It is a figure which shows the structure of the optical receiving station in the optical communication system of 1st Embodiment. It is a figure which shows the structure of the relay amplification apparatus in the optical communication system of 1st Embodiment. It is a figure which shows the structure of OADM in the optical communication system of 1st Embodiment. It is a figure which shows the flowchart of the system control circuit in the optical communication system of 1st Embodiment. It is a figure which shows the flowchart of the OADM control circuit in the optical communication system of 1st Embodiment. In the optical communication system of the first embodiment, the average value of all optical signals of each station and the P.P. G. It is a figure which shows partial light SNR. ch. It is a figure which shows the flowchart of the system control circuit in the case of resetting of pre-emphasis by increase / decrease of a number. ch. It is a figure which shows the flowchart of an OADM control circuit in the case of resetting of pre-emphasis by increase / decrease of a number. The overall configuration of the optical communication system in the second embodiment G. FIG. It is a figure which shows the structure of OADM in the optical communication system of 2nd Embodiment. It is a figure which shows the flowchart of the system control circuit in the optical communication system of 2nd Embodiment. It is a figure which shows the flowchart of the OADM control circuit in the optical communication system of 2nd Embodiment. It is a figure which shows the whole structure of the optical SNR measuring apparatus in 3rd Embodiment, and the detailed structure of a station. It is a figure which shows the flowchart of the arithmetic circuit in 3rd Embodiment. It is a figure showing other composition of a station in a 3rd embodiment. It is a figure explaining the conventional optical SNR measuring method. It is a figure which shows the structure of the optical communication system which performs the conventional pre-emphasis. OADM ch. 3 is a diagram illustrating a spectrum of a WDM optical signal obtained by branching and inserting 3; It is a figure which shows the spectrum of the WDM system optical signal which wavelength-multiplexed the optical signal with high density.

First, the principle of the present invention will be described.
FIG. 1 is a diagram showing a basic configuration of the present invention.
FIG. 1A shows the basic configuration of the present invention, and FIG. 1B shows the concept of a path group.
First, an optical SNR measurement method and an optical SNR measurement apparatus will be described below.
In FIG. 1A, the optical communication system includes a plurality of stations 12 including an optical amplifying means 21 for amplifying a WDM optical signal obtained by wavelength-multiplexing a plurality of optical signals between the optical transmission lines 11, and an optical transmission line 11. The optical transmission station 10 is connected to one end of the optical transmission line 11, and the optical reception station 14 is connected to the other end of the optical transmission line 11. In addition, the optical signal is not only transmitted from the optical transmission station 10 to the optical reception station 14, but may be dropped and inserted in the station 12 by an OADM (not shown) provided in the station 12.

In order to measure the optical SNR of an optical signal between any two stations 12 or between the optical transmitting station 10 and the optical receiving station 14 in such an optical communication system, the optical SNR measuring apparatus includes measuring means 22 and And an arithmetic circuit 16.
The measuring means 22 is provided in at least two or more stations 12 out of the plurality of stations 12 and measures a predetermined physical quantity in the stations 12. Further, the measuring means 22 is also provided in the optical receiving station 14. The arithmetic circuit 16 obtains the optical SNR by the optical SNR measurement method described below based on the measurement result of the measuring means 22.

That is, as a first step, the arithmetic circuit 16 receives a predetermined physical quantity from the measuring means 22 and obtains a predetermined physical quantity in all stations 12.
Here, when the measuring means 22 is provided in all the stations 12, the predetermined physical quantity from each measuring means 22 is the predetermined physical quantity in each station 12 as it is. On the other hand, the predetermined physical quantity in the station 12 that does not include the measuring unit 22 as in the third station 12-3 is based on the predetermined physical quantity measured by the station 12 that includes the measuring unit 22 before and after the station 12. The predetermined physical quantity at 12 may be obtained.

For example, the difference between a predetermined physical quantity in the preceding and following stations 12 is proportionally distributed based on the distance between the front optical transmission path 11 and the distance between the rear optical transmission paths 11 with respect to this station 12, and the predetermined physical quantity in the previous station 12 is distributed. It can be obtained by adding. Alternatively, an optical transmission line equivalent to the front and rear optical transmission lines 11 may be prepared, and the value of this proportional distribution may be measured in advance.
As a second step, the arithmetic circuit 16 obtains a partial light SNR for each of the stations 12 based on a predetermined physical quantity obtained for all the stations 12.
As a third step, the arithmetic circuit 16 obtains the reciprocal sum of the obtained partial light SNR and further obtains the reciprocal of the reciprocal sum. This is the optical SNR.

とすれば、所定の物理量は、出力光レベルＰout、雑音指数ＮＦおよび利得Ｇである。なお、ｈは、プランク定数、νは、光信号の波長に対応する周波数、Δｆは、光ＳＮＲの分解能に相当する周波数である。
したがって、光信号を複数の光信号を波長多重したＷＤＭ方式光信号とすれば、一般に、各光信号の光ＳＮＲj、k は、上述の第１ないし第３ステップより、

で与えられる。なお、ｊは、ＷＤＭ方式光信号における複数の光信号にそれぞれ割り振られたｃｈ．番号、ｋは、局番号である。よって、光ＳＮＲj,k は、ｃｈ．ｊの第ｋ局１２-kにおける光ＳＮＲである。Ｐoutj、k は、ｃｈ．ｊが第ｋ局１２-kから射出される場合のｃｈ．ｊの光信号の光レベルである。ＮＦj、k は、ｃｈ．ｊの第ｋ局１２-kにおける雑音指数である。Ｇj、k は、ｃｈ．ｊの第ｋ局１２-kにおける利得である。 Here, the partial light SNR is

If so, the predetermined physical quantities are the output light level Pout, the noise figure NF, and the gain G. Here, h is a Planck constant, ν is a frequency corresponding to the wavelength of the optical signal, and Δf is a frequency corresponding to the resolution of the optical SNR.
Therefore, if the optical signal is a WDM optical signal obtained by wavelength-multiplexing a plurality of optical signals, generally, the optical SNRj, k of each optical signal is obtained from the first to third steps described above.

Given in. Note that j is the ch. Assigned to each of the plurality of optical signals in the WDM optical signal. Number, k is a station number. Therefore, the optical SNRj, k is ch. This is the optical SNR of the j-th station 12-k. Poutj, k is ch. ch. where j is emitted from the k-th station 12-k. j is the optical level of the optical signal. NFj, k is ch. j is the noise figure at the k-th station 12-k. Gj, k is ch. j is the gain at the k-th station 12-k.

とすれば、所定の物理量は、入力光レベルＰinおよび雑音指数ＮＦである。そして、各光信号の光ＳＮＲj、k は、（式２）で与えられる。なお、Ｐinj、k は、ｃｈ．ｊが第ｋ局１２-kに入射される場合のｃｈ．ｊの光信号の光レベルである。 Since Poutj, k = Gj, k · Pinj, k, the partial light SNR is

If so, the predetermined physical quantities are the input light level Pin and the noise figure NF. The optical SNRj, k of each optical signal is given by (Equation 2). Pinj, k is ch. ch. when j is incident on the k-th station 12-k. j is the optical level of the optical signal.

とおけば、所定の物理量は、出力光レベルＰout および利得Ｇである。そして、各光信号の光ＳＮＲj、k は、（式２）で与えられる。
また、部分光ＳＮＲを

とおけば、所定の物理量は、出力光レベルＰout である。そして、各光信号の光ＳＮＲj、k は、（式２）で与えられる。 Furthermore, the partial light SNR

Then, the predetermined physical quantities are the output light level Pout and the gain G. The optical SNRj, k of each optical signal is given by (Equation 2).
Also, the partial light SNR

Then, the predetermined physical quantity is the output light level Pout. The optical SNRj, k of each optical signal is given by (Equation 2).

とおけば、所定の物理量は、出力光レベルＰinである。そして、各光信号の光ＳＮＲj,k は、（式２）で与えられる。
以上の（式１）、および、（式３）ないし（式６）のいずれの数式を部分光ＳＮＲの定義として用いるかは、光ＳＮＲ測定方法および光ＳＮＲ測定装置に要求される精度によって決定される。 Furthermore, the partial light SNR

Then, the predetermined physical quantity is the output light level Pin. The optical SNRj, k of each optical signal is given by (Equation 2).
Which of the equations (Equation 1) and (Equation 3) to (Equation 6) is used as the definition of the partial optical SNR is determined by the accuracy required for the optical SNR measurement method and the optical SNR measurement apparatus. The

Thus, the optical SNR measurement method and the optical SNR measurement apparatus according to the present invention can measure the optical SNR without directly measuring the ASE, and thus measure the optical SNR of a high-density WDM optical signal. be able to. Of course, it is also possible to measure the optical SNR of one optical signal.
Next, the pre-emphasis method and the optical communication system will be described below.

In FIG. 1A, the optical communication system further includes adjustment means 23. Then, the arithmetic circuit 16 uses the pre-emphasis method to be described later on the basis of the measurement result of the measuring means 22, and the optical level when the optical signal to be wavelength-multiplexed on the optical transmission line 11 is first incident on the optical transmission line 11. Ask for.
The adjustment means 23 is provided in the station 12 that first enters the optical transmission line 11 with the optical signal to be wavelength-multiplexed in the optical transmission line 11, and adjusts the optical signal so that the optical level obtained by the arithmetic circuit 16 is obtained. Adjust the light level. Further, the adjusting means 23 is also provided in the optical transmission station 10.

A pre-emphasis method in such an optical communication system will be described below.
First, as a first step, the arithmetic circuit 16 receives a predetermined physical quantity from the measuring means 22 and obtains a predetermined physical quantity in all stations 12.

As a second step, the arithmetic circuit 16 obtains a partial light SNR for each of the stations 12 based on a predetermined physical quantity obtained for all the stations 12.
As a third step, the arithmetic circuit 16 obtains the reciprocal sum of the partial optical SNRs for each of the plurality of optical signals over a section where the stations 12 where the optical signals are amplified overlaps, and is the reciprocal of the reciprocal sum. The section light SNR is obtained.

As a fourth step, the optical levels of the plurality of optical signals are adjusted so that the section optical SNRs are equal to each other.
Here, (Expression 2) is an expression for obtaining the optical SNR from when a certain optical signal is first incident on the optical transmission line 11 until it is finally emitted. The optical SNR between any two stations can also be obtained. This optical SNR between any two stations 12 will be referred to as section optical SNR. In this case, if any two stations are a station 12 or an optical transmitting station 10 to which a certain optical signal is first incident and a station 12 or an optical receiving station 14 to be finally emitted, the section The optical SNR matches the optical SNR.

  For example, ch. Incident from the optical transmission station 10 and emitted (branched) at the fourth station. In the case of 7, the section optical SNR is a value obtained by (Expression 2) from the optical transmission station 10 to the third station 12-3, or (Expression 2) from the first station 12-1 to the third station 12-3. ) And the value obtained by (Equation 2) from the optical transmission station 10 to the fourth station 12-4. Then, the value obtained by (Expression 2) from the optical transmission station 10 to the fourth station 12-4 coincides with the optical SNR.

The case where the above-described pre-emphasis method is made more specific will be described below.
First, as a first step, the arithmetic circuit 16 receives a predetermined physical quantity from the measuring means 22 and obtains a predetermined physical quantity in all stations 12.

As a second step, the arithmetic circuit 16 obtains a partial light SNR for each of the stations 12 based on a predetermined physical quantity obtained for all the stations 12.
As a third step, the arithmetic circuit 16 obtains the reciprocal sum of the partial optical SNRs for each of the plurality of optical signals over a section where the stations 12 where the optical signals are amplified overlaps, and is the reciprocal of the reciprocal sum. The section light SNR is obtained.

As a third step, the arithmetic circuit 16 obtains the sum of the partial optical SNRs for all the optical signals amplified in this station for each of the plurality of stations 12, and further obtains an average value thereof.
As a fourth step, the arithmetic circuit 16 obtains a difference value between the average value in each of the plurality of stations 12 and the partial light SNR of this optical signal for each of the plurality of optical signals.

となるように複数の光信号について光レベルを調整すればよい。 As a fifth step, the arithmetic circuit 16 obtains the sum of these difference values for each of the plurality of optical signals over the station where the optical signal is amplified.
As a sixth step, the light levels of the plurality of optical signals are adjusted so that the sum of the difference values obtained for each of the plurality of optical signals is all zero.
When the above first to sixth steps are combined into one expression, the arithmetic circuit 16

What is necessary is just to adjust an optical level about a some optical signal so that it may become.

  Here, the all-optical signal average value j, k is expressed as ch. In the case where j is amplified in the k-th station 12-k, the partial optical SNR is obtained over all the optical signals amplified in the k-th station 12-k, and the average value thereof is obtained. ch. In the case where j is not amplified at the k-th station 12-k, it is zero. Therefore, ch. When j is not amplified in the k-th station 12-k, (partial light SNRj, k−all-optical signal average value j, k) = 0.

  According to such a pre-emphasis method, pre-emphasis can be performed on a high-density WDM optical signal. According to this method, even when there is a station 12 having an OADM between the optical transmitting station 10 and the optical receiving station 14 and a certain optical signal is dropped / added, pre-emphasis is applied to the WDM optical signal. Can be applied. Further, even if the optical levels of the ASE for the optical signal that has not been branched / added and the ASE for the optical signal that has been dropped / added are different, pre-emphasis can be applied to the WDM optical signal. Furthermore, according to this method, since the level diagram is adjusted for each optical signal in the WDM optical signal, the optical SNR of each optical signal is optimized.

On the other hand, when the station 12 includes a station having an OADM, the following pre-emphasis method is preferable.
Each channel of a WDM optical signal. Are inserted into the optical transmission line 11 from the same optical transmitting station 10 or station 12 and branched from the same optical receiving station 14 or station 12. There is. The same route ch. Together, a path group (hereinafter abbreviated as “PG”) is created.

And first, P.I. G. Pre-emphasis is performed between them, and then the P.P. G. Further pre-emphasis can be performed within the system, and final pre-emphasis can be performed.
For example, FIG. For the case where the number is 8, each ch. , Ch. 1 and ch. 2 is transmitted from the 0th station of the optical transmission station 10 to the optical transmission line 11 and branches from the second station. ch. 3 and ch. 5 is inserted into the optical transmission line 11 from the second station 2 and branches from the fourth station. ch. 4 and ch. 7 is transmitted from the 0th station of the optical transmission station 10 to the optical transmission line 11 and branches from the fourth station. ch. 6 and ch. 8 is transmitted from the 0th station of the optical transmission station 10 to the optical transmission line 11, and is received and processed by the nth station of the optical reception station 14.

  In this case, ch. 1 and ch. 2 to P.P. G. 1 can be grouped together. ch. 3 and ch. 5 to P.A. G. 2 can be grouped together. ch. 4 and ch. 7 to P.A. G. 3 can be grouped together. ch. 6 and ch. 8 for P.M. G. 4 can be grouped together.

  In this way, G. When P. is introduced. G. Pre-emphasis between P.P. and P.P. G. All ch. Using the partial PG average light SNRm, k, which is the average value of the partial light SNRj, k, in the same manner as in the first to sixth steps described above, the P.P. G. The partial light SNR is adjusted.

That is, first, as a first step, the arithmetic circuit 16 receives a predetermined physical quantity from the measuring means 22 and obtains a predetermined physical quantity in all stations 12.
As a second step, the arithmetic circuit 16 obtains a partial light SNR for each of the stations 12 based on a predetermined physical quantity obtained for all the stations 12.
As a third step, the arithmetic circuit 16 obtains the sum of the partial optical SNRs for all the optical signals amplified in this station for each of the plurality of stations 12, and further calculates the average value of all the optical signals that is the average value thereof. Ask for.

As a fourth step, the arithmetic circuit 16 combines the optical signals having the same interval from the first incident on the optical transmission line 11 to the final emission among the plurality of optical signals. P. G. Create
As a fifth step, the arithmetic circuit 16 calculates the sum of the partial optical SNRs for each of the plurality of stations 12 at the P.A. G. P., which is an average value thereof, is obtained over the optical signal in the signal. G. The partial light SNR is obtained.

As a sixth step, the arithmetic circuit 16 includes a plurality of P.P. G. For each of the plurality of stations 12 and the average value of all optical signals and P.I. G. A difference value from the partial light SNR is obtained.
As a seventh step, the arithmetic circuit 16 includes a plurality of P.P. G. For each of these, the sum of the difference values is obtained.

As an eighth step, the arithmetic circuit 16 includes a plurality of P.P. G. P. so that the sum of the difference values obtained for each of the two becomes zero. G. The partial light SNR is adjusted.
As a ninth step, the arithmetic circuit 16 adjusts the adjusted P.P. G. The light level is adjusted for a plurality of optical signals based on the partial light SNR.
In the ninth step, P.P. G. The pre-emphasis can be obtained using (Equation 1) and (Equation 2). G. Inside, the method of pre-emphasis between two terminal stations can be used. That is,
As a first step, P.I. G. All ch. Are all ch. In the station 12 (optical receiving station 14) from which the signal is branched. The average value of the optical SNR is obtained for.

As a second step, this average value and the ch. The difference from the optical SNR of 1 is obtained.
As a third step, P.I. G. All ch. Is inserted into the channel 12 (optical transmission station 10) with an optical level sufficient to compensate for this difference. 1 and ch. 1 light level is adjusted.

As the fourth step, the second step and the third step described above are performed on the P.P. G. All ch. Do about.
In addition, P. G. Pre-emphasis may be performed.
FIG. G. It is a figure for demonstrating an example of pre-emphasis in the inside.

FIG. 2 (a) shows a transmission P.A. with no pre-emphasis. G. Spectrum and received P.P. G. FIG. 2 (b) shows a transmission P.A. when pre-emphasis is performed based on FIG. 2 (a). G. FIG. In each of these figures, the vertical axis represents the light level, and the horizontal axis represents ch. (Wavelength).
Note that FIG. G. But ch. 1, ch. 4, ch. 5, ch. 7, ch. 9, ch. 10, ch. 15 and ch. 16 shows a case of 16; G. What ch. Similarly, the combination of P.I. G. Pre-emphasis can be performed.

P. G. Pre-emphasis in order to easily perform pre-emphasis. G. The deviation from the average value of the light level is halved, and the deviation that has been halved is transmitted after the magnitude relationship between the spectra is reversed. G. The amount of pre-emphasis is adjusted.
That is, as a first step, as shown in FIG. 2 (a), P is performed in a state where pre-emphasis is not performed (a state where the optical level of each ch. Matches the average value of the optical levels of the transmission PG). . G. To the target optical communication system, G. Measure the spectrum of.

As a second step, the measured reception P.P. G. Using the spectrum of each ch. Received P. G. The deviation from the average value of the light level is calculated (Pdf), and 1/2 of each is calculated (Pdf / 2).
As a third step, the received P.P. G. The optical level of the received P.P. G. Smaller than the average light level of ch. , Add Pdf / 2 and receive P.2 G. The optical level of the received P.P. G. Larger than the average light level of ch. For, subtract Pdf / 2. That is, in the case of FIG. 1 indicates that the optical level of the received P.I. G. Is smaller than the average value of the light levels of G. Add to the average light level. ch. 16 indicates that the optical level of the received P.P. G. Is greater than the average value of the light level of G. Subtract from the average light level.

In this way, P.I. G. Pre-emphasis can be performed.
As described above, the optical communication system shown in FIG. 1 can perform pre-emphasis on a WDM optical signal. Here, which equation (Equation 1) and (Equation 3) to (Equation 6) is used as the partial light SNRj, k depends on the error rate required for the optical communication system.

Embodiments of the present invention will be described below with reference to the drawings.
(Configuration of the first embodiment)
The first embodiment is an embodiment of an optical communication system.
FIG. 3 shows the overall configuration of the optical communication system according to the first embodiment and the P.264. G. FIG.
FIG. 4 is a diagram illustrating a configuration of an optical transmission station in the optical communication system according to the first embodiment.
FIG. 5 is a diagram illustrating a configuration of an optical receiving station in the optical communication system according to the first embodiment.
FIG. 6 is a diagram illustrating a configuration of the relay amplifying apparatus in the optical communication system according to the first embodiment.
FIG. 7 is a diagram illustrating the configuration of the OADM in the optical communication system according to the first embodiment.

  First, the overall configuration of the optical communication system according to the first embodiment will be described, and then the configurations of an optical transmission station, a relay amplification device, an OADM, and an optical reception station used in the optical communication system will be described in detail.

The overall configuration of the optical communication system in the first embodiment will be described.
3A, an optical communication system according to the first embodiment includes an optical transmission station 51, a relay amplification device 53, an OADM 54, an optical reception station 55, an optical transmission line 52 that connects these stations, and transmits an optical signal. The system control circuit 56 is configured.
The optical transmission station 51 has 32 ch. , And based on the control signal from the system controller 56, each ch. After pre-emphasis is performed, the optical signal is transmitted to the optical transmission line 52 as a WDM optical signal.

The relay amplifier 53 amplifies the WDM optical signal transmitted through the optical transmission line 52.
The OADM 54 receives a predetermined ch. From the WDM optical signal transmitted through the optical transmission line 52. Branch, insert and pass through. The OADM 54 outputs the spectrum of the WDM optical signal incident on the OADM 54 and the spectrum of the WDM optical signal emitted from the OADM 54 to the system control circuit 56, and inserts it based on the control signal from the system control circuit 56. Each ch. After pre-emphasis, the optical signal is inserted into the optical transmission line 52.

The optical receiving station 55 receives and processes the WDM optical signal and outputs the spectrum of the WDM optical signal incident on the optical receiving station 55 to the system control circuit 56.
The relay amplifier 53 and the OADM 54 are provided between the optical transmission station 51 and the optical reception station 55. The OADM 54 receives the ch. The repeater amplifying device 53 includes a transmission loss between the optical transmission station 51 and the OADM 54, a transmission loss between the OADMs 54 and an OADM 54 in an optical communication system provided with a plurality of OADMs 54. The required number is provided between them according to the transmission loss between the optical receiver 55 and the optical receiving station 55.

Next, the configuration of the optical transmission station used in the optical communication system according to the first embodiment will be described in detail.
In FIG. 4, an optical transmission station 51 includes a laser diode (hereinafter abbreviated as “LD”) 101, a modulator (hereinafter abbreviated as “MOD”) 102, an optical variable attenuator (hereinafter referred to as “VAT”). 103, a WDM coupler 104, an optical amplifier 108, a coupler 105, a spectrum analyzer (hereinafter abbreviated as “SPA”) 106, and an optical transmission station control circuit 107.

The LD 101 oscillates laser light having a predetermined wavelength, and the oscillated laser light is emitted to the corresponding MODs 102-1 to 102-32. For example, various lasers such as a Fabry-Perot laser, a distributed feedback laser, and a distributed Bragg reflection laser can be used as the LD 101.
The MOD 102 modulates the laser beam from the LD 101 with information to be transmitted and generates an optical signal. The generated optical signal is emitted to the VAT 103. As the MOD 102, for example, an external modulation type modulator such as a Mach-Zehnder type optical modulator or a semiconductor electroabsorption type optical modulator can be used.

Note that the MOD 102 can be omitted in the case of performing direct modulation for changing the light level of the laser beam to be oscillated by superimposing a modulation signal based on information to be transmitted on the drive current of the LD 101.
The VAT 103 attenuates the optical level of the optical signal from the MOD 102 and emits it to the WDM coupler 104. This attenuation amount is controlled by a control signal from the optical transmission station control circuit 107.

  The configuration comprising these LD 101, MOD 102, and VAT 103 is the WDM optical signal ch. 32 sets are prepared according to the number, and each of the LDs 101-1 to 101-32 has a corresponding ch. Oscillates a laser beam having a wavelength matched to the wavelength. For example, LD 101-1 has ch. 1 oscillates at a wavelength corresponding to the wavelength of 1. Oscillates at a wavelength corresponding to the second wavelength.

Note that the drive current / element temperature of the LD 101 may be controlled from the viewpoint of further stabilizing the oscillation wavelength of the LD 101. Further, a wavelength locker composed of a periodic filter or the like may be used between the LD 101 and the MOD 102.
The WDM coupler 104 wavelength-multiplexes each optical signal from each VAT to generate a WDM optical signal. The generated WDM optical signal is emitted to the coupler 105 via the optical amplifier 108 that amplifies the light.

The coupler 105 is an optical branching coupler that branches the WDM optical signal from the optical amplifier 108 into two. One of the branched WDM optical signals is emitted to the optical transmission line 52-1 and transmitted to the next station, and the other branched WDM optical signal is emitted to the SPA 106.
The SPA 106 is a spectrum analyzer that measures the wavelength of incident light and the light level at this wavelength. The SPA 106 measures the spectrum of the WDM optical signal transmitted from the optical transmission station 51 and outputs the measurement result to the optical transmission station control circuit 107.

  The optical transmission station control circuit 107 outputs the measurement result from the SPA 106 to the system control circuit 56. Then, the optical transmission station control circuit 107 performs pre-emphasis on the WDM optical signal by adjusting the attenuation amounts of the VATs 103-1 to 103-32 based on the control signal from the system control circuit 56. Further, the optical transmission station control circuit 107 determines whether or not the above-described pre-emphasis is applied to the WDM optical signal based on the measurement result from the SPA 106, and each VAT 103-1 to 103-32 based on the determination result. Control each attenuation amount.

Next, the configuration of the optical receiving station used in the optical communication system according to the first embodiment will be described in detail.
In FIG. 5, an optical receiving station 55 includes an optical amplifier 118, a coupler 111, an SPA 112, an optical receiving station control circuit 113, a WDM coupler 114, a filter (hereinafter abbreviated as “FIL”) 115, an optical amplifier 116, and It is composed of a demodulator (hereinafter abbreviated as “DEM”) 117.

The optical amplifier 118 amplifies the WDM optical signal from the optical transmission line 52-n connected to the optical receiving station 55, and compensates for the loss generated in the optical transmission line 52-n.
The coupler 111 is an optical branching coupler that branches the WDM optical signal from the optical amplifier 118 into two. One branched WDM optical signal is emitted to the WDM coupler 114, and the other branched WDM optical signal is emitted to the SPA 112.

The WDM coupler 114 transmits the WDM optical signal from the coupler 111 to each ch. Demultiplexes each wavelength corresponding to. Each demultiplexed ch. Are emitted to the FILs 115-1 to 115-32, respectively.
The FIL 115 is a band pass filter that transmits light of a predetermined wavelength band. As the FIL 115, for example, a fiber grating filter (hereinafter abbreviated as “FBG”), a dielectric multilayer filter, or the like can be used. Further, the FIL 115 can be omitted if the WDM coupler 114 can accurately separate light in a predetermined wavelength band.

The optical amplifier 116 amplifies the optical signal from the FIL 115 with a predetermined gain and emits it to the DEM 117 in order to compensate for the loss caused by the coupler 111, the WDM coupler 114, the FIL 115, and the like.
The DEM 117 demodulates the optical signal from the optical amplifier 116.
The configuration comprising these FIL 115, optical amplifier 116, and DEM 117 is the WDM optical signal ch. According to the number, 32 sets are prepared, and each FIL 115-1 to 115-32 has a corresponding ch. The transmission wavelength band is set according to the wavelength. For example, FIL115-1 is ch. The center wavelength of the transmission wavelength band is adjusted to the wavelength corresponding to the wavelength of 1, and the FIL 115-2 is ch. The center wavelength of the transmission wavelength band is adjusted to the wavelength corresponding to the second wavelength.

The SPA 112 measures the spectrum of the WDM optical signal incident on the optical receiving station 55 and outputs the measurement result to the optical receiving station control circuit 113.
The optical receiving station control circuit 113 outputs the measurement result from the SPA 112 to the system control circuit 56.
Next, the configuration of the relay amplifying apparatus used in the optical communication system according to the first embodiment will be described in detail.

In FIG. 6, the relay amplifier 53 includes optical amplifiers 121 and 124, an optical attenuator (hereinafter abbreviated as “ATT”) 122, and a dispersion compensator (hereinafter abbreviated as “DC”) 123. The
The optical amplifier 121 is a preamplifier that raises the received light level. The optical amplifier 121 amplifies the WDM optical signal from the optical transmission line 52 connected to the relay amplifier 53 and outputs the amplified signal to the ATT 122.

  The ATT 122 is an optical attenuator that emits incident light at a predetermined attenuation rate, and a WDM optical signal attenuated to a certain optical level is emitted to the DC 123. The reason why the WDM optical signal is attenuated to a certain optical level in this manner is that when an excessively high WDM optical signal is incident on the DC 123, nonlinear optical phenomena such as self-phase modulation and cross-phase modulation occur. It is.

The DC 123 is a dispersion compensator that compensates for chromatic dispersion generated mainly in the optical transmission line 52 in the WDM optical signal. The WDM optical signal compensated for chromatic dispersion is emitted to the optical amplifier 124.
The optical amplifier 124 is a postamplifier that amplifies the output light of the relay amplification device 53 to a predetermined optical level. The amplified WDM optical signal is emitted to the optical transmission line 52 for transmission to the next-stage station.

  When the optical amplifier 124 is an optical fiber amplifier, the WDM optical signal ch. May increase the gain of the optical amplifier 124. Therefore, in such a case, a booster excitation light source that is a light source for compensating the output light level of the excitation light source may be provided in the optical amplifier 124.

Next, the configuration of the OADM used in the optical communication system according to the first embodiment will be described in detail.
In FIG. 7, an OADM 54 is an optical amplifier 130, 132, 149, 151, 161, 166, ATT 131, 150, a coupler 133, 134, 146, 148, 155, 168, 171, an isolator (hereinafter abbreviated as “ISO”). 135), VAT136, 169, FBG141, FIL142, 172, DC145, 152, 153, monitor (hereinafter abbreviated as “MO”) 147, 167, 170, switch (hereinafter abbreviated as “SW”). 156, SPA 157, DEM 162, transmitter 165, and OADM control circuit 175.

The optical amplifier 130 is a preamplifier that raises the received light level. The optical amplifier 130 amplifies the WDM optical signal from the optical transmission line 52 connected to the OADM 54 and outputs the amplified signal to the ATT 131.
The ATT 131 is an optical attenuator that emits incident light at a predetermined attenuation rate, and a WDM optical signal attenuated to a certain optical level is emitted to the optical amplifier 132.

The optical amplifier 132 is a post amplifier that amplifies to a predetermined light level. The amplified WDM optical signal is emitted to the coupler 133.
The optical amplifier 130, the ATT 131, and the optical amplifier 132 constitute a preamplifier in the OADM 54.
The coupler 133 is an optical branching coupler that branches the WDM optical signal from the optical amplifier 132 into two. One branched WDM optical signal is emitted to the coupler 134, and the other branched WDM optical signal is emitted to the SW 156.

The coupler 134 is an optical branching coupler that branches the WDM optical signal from the coupler 133 into two. One of the branched WDM optical signals is emitted to ISO 135, and the other branched WDM optical signal is emitted to DC 152.
The WDM optical signal emitted to the ISO 135 becomes a WDM optical signal that passes through the OADM 54 by being processed by each optical component described later. On the other hand, the WDM optical signal emitted to the DC 152 is processed by each optical component to be described later and branched by the OADM 54. Is taken out.

DC152 is a ch. On the other hand, it is a dispersion compensator that mainly compensates for chromatic dispersion that occurs in the optical transmission line 52, and the WDM optical signal that has been compensated for chromatic dispersion is emitted to the rejection filter unit 140.
The ISO 135 is an isolator that transmits light only in a predetermined direction, and transmits light only in one direction from the coupler 134 to the VAT 136. For this reason, since the light reflected by the optical component in the OADM connected after ISO 135 can be blocked, multiple reflection of light in the OADM can be prevented. The ISO 135 can be configured, for example, by disposing a Faraday rotator between two polarizers that are shifted by 45 degrees.

The VAT 136 attenuates the optical level of the WDM optical signal from the ISO 135 and emits it to the rejection filter unit 140. This attenuation amount is controlled by a control signal from the OADM control circuit 175.
The rejection filter unit 140 is used for the optical signal ch. FBG units are prepared according to the number. In this embodiment, ch. 1 to ch. Eight FBG units are connected in cascade so that 8 can be branched and inserted.

The FBG unit includes an FBG 141 and an FIL 142. The FBG 141 is an FBG that reflects only a predetermined wavelength band, and the FIL 142 is an optical filter that transmits only the predetermined wavelength band. Then, the reflection center wavelength of the FBG 141 and the transmission center wavelength of the FIL 142 are branched. Is set equal to the wavelength of.
The rejection filter unit 140 of FIG. 1 to ch. 8 shows a case in which 8 FBG units are cascaded. As a result, the FBGs 141-1 to 141-8 are cascaded sequentially, and the FILs 142-1 to 142-8 are also cascaded sequentially.

  As shown in this figure, a 32-wave WDM optical signal whose chromatic dispersion is compensated by the DC 152 is incident on the FIL 142-1. The incident WDM optical signal is transmitted to ch. 1 and transmitted to the optical amplifier 161-1, ch. 2 to ch. 32 is reflected by the FIL 142-1 and emitted to the FIL 142-2. The WDM optical signal incident on the FIL 142-2 is ch. 2 and transmitted to the optical amplifier 161-2, ch. 3 to ch. 32 is reflected by the FIL 142-2 and emitted to the FIL 142-3. Similarly, ch. 3 to ch. 8 is ch. For each FIL142-3 to 142-8. And are emitted to optical amplifiers 161-3 to 161-8 connected to the respective FILs 142-3 to 142-8.

The optical amplifier 161 is a preamplifier that raises the received light level, amplifies the optical signals from the FILs 142-1 to 142-8, and emits them to the DEMs 162-1 to 162-8.
The DEM 162 demodulates the optical signals from the optical amplifiers 161-1 to 161-8, respectively. Extract information.

  On the other hand, the 32-wave WDM optical signal whose optical level is attenuated by the VAT 136 is incident on the FBG 141-1. The incident WDM optical signal is sent to ch. 1 is blocked, ch. 2 to ch. 32 is injected into the FBG 141-2. The WDM optical signal incident on the FBG 141-2 is transmitted to the ch. 2 is blocked, ch. 3 to ch. 32 is injected to the FBG 141-3. Similarly, ch. 3 to ch. 8 is ch .. in each of the FBGs 141-3 to 141-8. The WDM optical signal that is interrupted every time and emitted from the FBG 141-8 is ch. 9 to ch. 32.

The WDM optical signal emitted from the final stage FBG 141 in the rejection filter unit 140 is incident on the DC 145.
The DC 145 passes through the OADM 54 for ch. On the other hand, the dispersion compensator mainly compensates the chromatic dispersion generated in the optical transmission line 52, and the WDM optical signal compensated for the chromatic dispersion is emitted to the coupler 146.

  The coupler 146 is an optical branching coupler that branches the WDM optical signal from the DC 145 into two. One branched WDM optical signal is emitted to the MO 147, and the other branched WDM optical signal is emitted to the WDM coupler 148.

The MO 147 is a monitor that detects the optical level of the WDM optical signal, and the detection result is output to the OADM control circuit 175.
As one function of the OADM control circuit 175, the OADM control circuit 175 adjusts the attenuation amount of the VAT 136 based on the detection result from the MO 147 so that the detection result does not exceed a predetermined threshold value. By adjusting the attenuation in this way, the optical level of the WDM optical signal incident on the DC 145 can be limited, so that a nonlinear optical phenomenon in the DC 145 can be prevented.

On the other hand, ch. The optical signal is generated by the configuration described later.
The transmitter 165 includes an LD and a MOD, and generates an optical signal having a predetermined wavelength. The generated optical signal is emitted to the optical amplifier 166.
The optical amplifier 166 is a post amplifier that amplifies to a predetermined light level. The amplified optical signal is emitted to the coupler 168.

The coupler 168 is an optical branching coupler that branches the optical signal from the optical amplifier 166 into two. One branched optical signal is emitted to the MO 167, and the other branched optical signal is emitted to the VAT 169.
The MO 167 is a monitor that detects the optical level of the optical signal, and the detection result is output to the OADM control circuit 175.
The VAT 169 attenuates the optical level of the optical signal from the coupler 168 and emits it to the coupler 171. This attenuation amount is controlled by a control signal from the OADM control circuit 175.
The coupler 171 is an optical branching coupler that branches the optical signal from the VAT 169 into two. One branched optical signal is emitted to the MO 170, and the other branched optical signal is emitted to the FIL 172.

The MO 170 is a monitor that detects the optical level of the optical signal, and the detection result is output to the OADM control circuit 175.
As another function of the OADM control circuit 175, the OADM control circuit 175 adjusts the attenuation level of the VAT 136 based on the detection results of the MO 167 and the MO 170, thereby adjusting the optical level of the optical signal to a desired optical level. Since the optical level of the optical signal inserted in the OADM 54 can be adjusted by adjusting the attenuation amount in this way, optimal pre-emphasis can be performed.

  Such a configuration including the transmitter 165, the coupler 168, the MO 167, the VAT 169, the coupler 171 and the MO 170 is the channel to be inserted by the OADM 54. Prepared for each. In this embodiment, ch. 1 to ch. 8 to be able to insert these ch. A configuration for generating the optical signal is prepared. For example, the configuration including the transmitter 165-1, coupler 168-1, MO 167-1, VAT 169-1, coupler 171-1 and MO 170-1 shown in FIG. 1 optical signal is generated.

The FIL 172 includes the number of optical signals to be inserted by the OADM 54 and ch. Are prepared according to the above, and cascaded sequentially. The transmission center wavelength of the FIL 172 is the ch. It is set according to the wavelength.
In FIG. 7, ch. 1 to ch. 8 is inserted, and eight FILs 172-1 to 172-8 are connected in cascade.
As shown in this figure, ch. 1 is incident on the FIL 172-2, reflected by the FIL 172-2, and transmitted through the FIL 172-2. 2 and incident on FIL 172-3. Incident ch. 1 and ch. 2 is reflected by FIL 172-3 and transmitted through FIL 172-3. 3 is incident on the FIL 172-4. Similarly, ch. 4 to ch. 8 are respectively combined at each of the FILs 172-4 to 172-8, and the ch. 1 to ch. A WDM optical signal obtained by wavelength multiplexing 8 is emitted and incident on the DC 153.

DC153 is the channel ch. Inserted in the OADM 54. On the other hand, it is a dispersion compensator that mainly compensates the chromatic dispersion generated in the optical transmission line 52, and the WDM optical signal compensated for the chromatic dispersion is emitted to the WDM coupler 148.
The WDM coupler 148 wavelength-multiplexes the WDM optical signal passing through the OADM 54 from the coupler 146 and the WDM optical signal inserted by the OADM 54 from the DC 153. The wavelength-multiplexed WDM optical signal is output to the optical amplifier 149. The optical amplifier 149 is a preamplifier that raises the received light level. The optical amplifier 149 amplifies the WDM optical signal from the WDM coupler 148 and emits it to the ATT 150 in order to compensate for the loss caused by the optical components in the OADM 54.

The ATT 150 is an optical attenuator that emits incident light at a predetermined attenuation rate. A WDM optical signal attenuated to a certain optical level is emitted to the optical amplifier 151.
The optical amplifier 151 is a post-amplifier that amplifies to a predetermined light level. The amplified WDM optical signal is emitted to the coupler 155.
The optical amplifier 149, the ATT 150, and the optical amplifier 151 constitute a rear stage amplification unit in the OADM 54.

The coupler 155 is an optical branching coupler that branches the WDM optical signal from the optical amplifier 151 into two. One of the branched WDM optical signals is emitted to the optical transmission line 52 to be transmitted to the next-stage station, and the other branched WDM optical signal is emitted to the SW 156.
The SW 156 is a 2 × 1 optical switch, and emits either a WDM optical signal from the coupler 133 or a WDM optical signal from the coupler 155 to the SPA 157 according to a control signal from the OADM control circuit 175.
The SPA 157 is a spectrum analyzer that measures the wavelength of incident light and the light level at this wavelength. The SPA 157 measures the spectrum of the WDM optical signal emitted from the previous amplification unit or the spectrum of the WDM optical signal emitted from the subsequent amplification unit according to the selection of the SW 156, and outputs the measurement result to the OADM control circuit 175. .

  As another function of the OADM control circuit 175, the OADM control circuit 175 emits either a WDM optical signal from the coupler 133 or a WDM optical signal from the coupler 155 to the SPA 157 according to a control signal from the system control circuit 56. A control signal for controlling this is output to SW156. Then, the OADM control circuit 175 outputs the measurement result from the SPA 157 to the system control circuit 56. Further, the OADM control circuit 175 adjusts the attenuation amount of each of the VATs 169-1 to 169-32 and the VAT 136 based on the control signal from the system control circuit 56, so that the ch. Pre-emphasis is performed.

Here, as the VAT 103, 136, 169, for example, a metal attenuation film in which an attenuation disk is inserted between incident light and emission light, and the thickness is continuously changed in the rotation direction on the surface of the attenuation disk. A variable optical attenuator that adjusts the amount of attenuation by rotating the attenuation disk and a magneto-optic crystal between the incident light and the emitted light and a polarizer inserted on the exit side of the magneto-optic crystal. An optical variable attenuator that adjusts the amount of attenuation by applying a magnetic field to the magneto-optical crystal and changing the strength of the magnetic field can be used.
As the WDM couplers 104, 114, and 148, for example, a dielectric multilayer filter, an arrayed waveguide grating type optical multiplexer / demultiplexer (arrayed waveguide grating), or the like can be used.
Examples of the couplers 105, 111, 133, 134, 146, 155, 168, 171 include a micro optical element type optical branching coupler such as a half mirror, an optical fiber type optical branching coupler of a molten fiber, and an optical waveguide type optical branching. A coupler or the like can be used.

As the optical amplifiers 116, 121, 124, 130, 132, 149, 151, 161, 166, for example, a semiconductor laser amplifier or an optical fiber amplifier can be used.
As the DEMs 117 and 162, light receiving elements such as photodiodes that convert optical signals into electrical signals can be used.
As the DCs 123, 145, 152, and 153, dispersion compensating fibers having dispersions of opposite signs so as to cancel the dispersion generated in the WDM optical signal can be used.
As described above, the optical transmission station applied to the optical communication system according to the first embodiment has a function of generating a WDM optical signal, as well as each channel of the WDM optical signal. What is necessary is just to have a function to adjust the light level.

The optical receiving station applied to the optical communication system of the first embodiment has a function of receiving and processing a WDM optical signal, as well as each channel of the WDM optical signal incident on the optical receiving station. It is only necessary to have a function of measuring the light level of the.
In addition, the relay amplifying apparatus applied to the optical communication system of the first embodiment only needs to have a function of compensating for transmission loss received in an optical fiber that is an optical transmission path and a function of shaping a waveform deteriorated due to chromatic dispersion. .

  Further, the OADM applied to the optical communication system of the first embodiment is a predetermined ch. In addition to the function of branching, inserting, and passing through, each channel of the WDM optical signal incident on the OADM. A function for measuring the optical level of each channel of each WDM optical signal emitted from the OADM. Function for measuring the light level of the ch and ch. And passing ch. What is necessary is just to have a function to adjust the light level.

(Correspondence between the present invention and the first embodiment)
The correspondence relationship between the present invention and the first embodiment will be described below.
The optical transmission path corresponds to the optical transmission path 52, and the station corresponds to the relay amplification device 53, the OADM 54, and the optical reception station 55. In particular, the measuring means corresponds to the SPA 157 in the OADM 54 and the SPA 112 in the optical receiving station 55, the arithmetic circuit corresponds to the system control circuit 56, and the adjusting means corresponds to the VATs 136 and 169 in the OADM 54 and the VAT 103 in the optical transmitting station 51. Correspond.

The pre-emphasis control device corresponds to the system control circuit 56.
Here, the couplers 133 and 155 may be connected immediately before the optical amplifiers 130 and 149, respectively, and the spectrum of the WDM optical signal incident on the optical amplifiers 130 and 149 may be measured. Further, instead of the SPAs 112 and 157, the incident light is changed to ch. A coupler that branches in several minutes, and each of the ch. Each detector is configured by a detector configured by an FBG in which the center wavelength of the transmission band is set to a wavelength corresponding to each of the FBGs and a photodiode that is connected to each of the FBGs and measures a light level of light emitted from the FBG. The light level may be measured.

(Operational effects of the first embodiment)
Next, pre-emphasis in the optical communication system according to the first embodiment will be described.
FIG. 8 is a diagram illustrating a flowchart of the system control circuit in the optical communication system according to the first embodiment.
FIG. 9 is a diagram illustrating a flowchart of the OADM control circuit in the optical communication system according to the first embodiment.
FIG. 10 shows all channels of each station in the optical communication system according to the first embodiment. The average output light level and the P.P. G. It is a figure which shows an output light level average value.

First, when the optical communication system according to the first embodiment shown in FIG. 3 to FIG. 7 is started, each device is sequentially arranged upstream of the optical communication system, that is, from the optical transmission station 51 to the optical reception station 55. Launch.
Then, for each device, confirmation of signal arrival, ASE correction, confirmation of DC input light level limitation, slope compensation for compensating wavelength dependence of transmission line loss, and the like are performed.
Further, in the optical transmission station 51 and the OADM 54, all ch. Send. Then, the optical transmission station 51 transmits each ch. Are set to be approximately equal. In the OADM 54, each inserted ch. , So that the light levels of the channels ch. The average light level is set.

In the OADM 54, the total light level incident on the amplifier 149, the ASE correction amount of the pre-amplifier, ch. From the number, it is confirmed that the average light level incident on the subsequent amplification unit is equal to or higher than a predetermined value.
After performing such initial settings for each device, pre-emphasis of the optical communication system according to the first embodiment is performed according to the following procedure.

  The outline of pre-emphasis in the first embodiment is described in P.E. G. And P. G. Pre-emphasis, and G. Pre-emphasis within. P. G. The pre-emphasis is performed by setting the sum of the differences between the average value of all optical signals and the PG partial light SNRj, k within an allowable value at each station, and preferably by setting the sum to approximately “0”. P. G. As shown in FIG. 2, the pre-emphasis in FIG. G. Ch. P. G. A deviation from the average value of the light level of the light is obtained, and the amount obtained by halving the deviation is reversed in the magnitude relationship between the spectra. G. Is inserted as a pre-emphasis amount for each ch. It is done by adjusting to.

Hereinafter, the pre-emphasis in the first embodiment will be described in detail with reference to FIGS.
In S1 of FIG. From the path. G. Create
For example, in the present embodiment, as shown in FIG. 3B, the channel ch. Transmitted from the optical transmission station 51 and received by the optical reception station 55 is received. 1 to ch. 16 for P.I. G. Set to 1. Ch. Transmitted from the optical transmission station 51 and branched at the station 2 of the OADM 54-1. 17 to ch. 32. G. 2. Ch. Inserted from the station 2 of the OADM 54-1 and received by the optical receiving station 55. 17 to ch. 24 for P.M. G. 3. Inserted from station 2 of OADM 54-1 and branched at station 5 of OADM 54-2. 25 to ch. 32. G. 4 Ch. Inserted from the station 5 of the OADM 54-2 and received by the optical receiving station 55. 25 to ch. 32. G. 5

In S <b> 2 of FIG. 8, the system control circuit 56 instructs each OADM control circuit 175 to output the output spectrum of the subsequent amplification unit in each OADM 54. Further, the system control circuit 56 instructs the optical transmission station control circuit 107 to output the output spectrum.
9, the OADM control circuit 175 in each OADM 54 station receives an instruction from the system control circuit 56 and switches the SW 156 so that the light from the coupler 155 enters the SPA 157. Then, each OADM control circuit 175 outputs the output of SPA 157 (the output spectrum of the subsequent amplification unit) to the system control circuit 56.

The optical transmission station control circuit 107 outputs the output (output spectrum) of the SPA 106 to the system control circuit 56.
In S <b> 3 of FIG. 8, the system control circuit 56 acquires the output spectrum of the subsequent amplification unit in each OADM 54 from each OADM control circuit 175. Further, the system control circuit 56 acquires an output spectrum from the optical transmission station control circuit 107.

In S4 of FIG. 8, the system control circuit 56 instructs each OADM control circuit 175 to output the output spectrum of the pre-amplifier in each OADM 54. Further, the system control circuit 56 instructs the optical receiving station control circuit 113 to output the input spectrum.
In S21 of FIG. 9, the OADM control circuit 175 in each OADM station switches the SW 156 so that the light from the coupler 133 enters the SPA 157 in response to an instruction from the system control circuit 56. Each OADM control circuit 175 outputs the output of SPA 157 (the output spectrum of the pre-amplifier) to the system control circuit 56.

The optical receiving station control circuit 113 outputs the output (input spectrum) of the SPA 112 to the system control circuit 56.
In S5 of FIG. 8, the system control circuit 56 acquires the output spectrum of the pre-amplifier in each OADM from each OADM control circuit 175. Further, the system control circuit 56 acquires an input spectrum from the optical receiving station control circuit 113.
Here, in the optical amplifier in the OADM 54, when slope compensation is performed to compensate for the loss wavelength dependency of the transmission line, the gain and the like are determined from the output spectrum of the subsequent amplification unit and the output spectrum of the previous amplification unit in S3 and S5. When the gain equalization is not performed, the output spectrum of the post-amplifier and the output spectrum of the pre-amplifier when the gain equalization is not performed are obtained, and these are newly added to the output spectrum of the post-amplifier and the pre-stage, respectively. The output spectrum of the amplification unit.

In S6 of FIG. 8, the system control circuit 56 calculates the output spectrum of each relay amplifier 53. This calculation is performed as follows.
As described with reference to FIG. 6, the relay amplifying device 53 does not include means for measuring the output spectrum. Therefore, the relay amplifying device 53 for which the output spectrum is to be obtained is connected to the relay amplifier 53 in the nearest front OADM 54. The difference between the average value of the output spectrum and the average value of the output spectrum of the front amplification unit in the nearest rear OADM 54 is obtained, and the output spectrum of the relay amplification device 53 is the output spectrum of the rear stage amplification unit in the nearest front OADM 54. It is assumed that 1/2 of the obtained difference is added.

If the nearest device is not the OADM 54 but the optical transmission station 51, the average value of the output spectrum of the optical transmission station 51 may be used. If the nearest rear apparatus is not the OADM 54 but the optical receiving station 55, the average value of the input spectrum of the optical receiving station 55 may be used.
In the present embodiment, for example, the output spectrum of the first station shown in FIG. 3A is an average of the output spectrum of the front optical transmission station 51 and the rear side because the first station is the relay amplification device 53-1. The difference from the average value of the output spectrum of the pre-amplifier in the OADM 54-1 is obtained, and the output spectrum of the first station is obtained by adding 1/2 of the obtained difference to the output spectrum of the optical transmission station 51 ahead. Shall.

  Here, when there are a plurality of relay amplifying devices 54 between the two OADMs 54, the output of the rear amplification unit in the nearest front OADM 54 is determined with respect to the plurality of relay amplifying devices 53 whose output spectrum is to be obtained. The difference between the average value of the spectrum and the average value of the output spectrum of the preceding amplification unit in the nearest rear OADM 54 is obtained. Divide the obtained difference by the number obtained by adding “1” to the number of repeater amplifiers existing between the two OADMs 54 (that is, the number of spans of the optical transmission line 52 existing between the two OADMs 54). The amount of change per relay amplifier is obtained. It is assumed that the output spectrum of the nth relay amplification device 53 between the two OADMs 54 is obtained by adding an amount obtained by multiplying the output spectrum of the subsequent amplification unit in the nearest front OADM 54 by n times. For example, in the case where there are five relay amplifying devices 53, the output spectrum of the first relay amplifying device 53 is obtained by adding the amount obtained by multiplying the output spectrum of the rear amplification unit in the nearest front OADM 54 by one. And Further, the output spectrum of the fourth relay amplifying device 53 is assumed to be obtained by adding an amount obtained by multiplying the amount of change by four to the output spectrum of the rear amplification unit in the nearest forward OADM 54.

  In the first embodiment, for example, the output spectrum of the third station and the fourth station shown in FIG. 3A includes two relay amplification devices 54 between the two OADMs 54-1 and 54-2. Therefore, the difference between the average value of the output spectrum of the rear amplification unit in the front OADM 54-1 and the average value of the output spectrum of the front amplification unit in the rear OADM 54-2 is obtained. The obtained difference is divided by 3 obtained by adding “1” to the number of relay amplifying devices, and the amount of change per one relay amplifying device is obtained. Since the output spectrum of the third station is the first relay amplifying apparatus, it is assumed that the amount obtained by multiplying the amount of change by 1 is added to the output spectrum of the subsequent amplification unit in the front OADM 54-1. Since the output spectrum of the fourth station is the second relay amplifying device, it is assumed that the amount obtained by doubling the amount of change is added to the output spectrum of the subsequent amplification unit in the front OADM 54-1.

In the first embodiment, since the output spectrum of the relay amplifying device 52 can be calculated in this way, the measuring means is omitted. The repeater amplifier further includes a spectrum analyzer that measures the output light of the optical amplifier 124 and a repeater amplifier control circuit that outputs the output of the spectrum analyzer to the system control circuit 56, and the output spectrum of the repeater amplifier 52 is obtained. You may make it measure.
In this way, the system control circuit 56 acquires the spectrum of the WDM optical signal in the optical transmission station 51, each station, and the optical reception station 55.
In S7 of FIG. 8, the system control circuit 56 obtains the partial light SNRj, the total optical signal average value, and the PG partial light SNR of each station. Here, in the first embodiment, the partial light SNRj, k is defined as Poutj, k, and Poutj, k is obtained from each spectrum acquired in S3, S5, and S6.

Therefore, the average value of all optical signals is obtained by setting Poutj, k to all ch. Are summed and the average value is obtained. The PG partial light SNR is transmitted at each station by P.I. G. Each time, Poutj, k is amplified by the corresponding station. G. The optical signals within are summed and the average value is obtained.
For example, the average value of all the optical signals in the third station is obtained as follows: Poutj, 3 is amplified by the third station. 1 to ch. 32 are totaled and the average value is obtained. The PG partial light SNR is obtained from the P.P. G. 1, Poutj, 3 is changed to ch. 1 to ch. 16 is summed and the average value is obtained. G. 2, Poutj, 3 is ch. 17 to ch. 24, and the average value is obtained, and Poutj, 3 is set to ch. 25 to ch. 32 are summed and the average value is obtained.

Also, because Poutj, k is used, SPA 157 is assigned to each ch. There is no need to measure the ASE between. Therefore, the SPA 157 can use an inexpensive spectrum analyzer with a simple structure.
In S8 of FIG. 8, the system control circuit 56 obtains the difference between the all-optical signal average value and the PG partial light SNR at each station. The system control circuit 56 is connected to the P.P. G. Add the differences for each station obtained for all the stations where.

In S9 of FIG. G. It is determined whether or not the addition result of S8 is within an allowable value.
This tolerance is P.I. G. It is an allowable value that determines the accuracy in pre-emphasis between and depends on an error rate required for the optical communication system. By setting this allowable value to approximately “0”, the optical communication system can be an optical communication system that transmits an extremely long distance with a low error rate.

の各式を同時に満たすようにすることである。 As shown in FIG. 10, in the first embodiment, assuming that the optical transmitting station 51 is the 0th station and the optical receiving station 55 is the (n + 1) th station, the average value of all the optical signals at each kth station is Poutav, k and when the PG partial light SNR is expressed as Poutgα, k, S9 becomes

It is to satisfy each of the equations simultaneously.

If the result of determination is that the value is not within the allowable value, the system control circuit 56 performs the process of S10 in FIG. If the result of determination is that the value is within the allowable value, the system control circuit 56 performs the process of S11 in FIG.
In S10 of FIG. G. In the OADM 54 in which P. is inserted, the result of S8 is a positive value. G. Is reduced by 0.5 dB, and the result of S8 is negative. G. Indicates an instruction to raise 0.5 dB. G. To the OADM control circuit 175 of the OADM 54 to insert. The accuracy of pre-emphasis increases as the adjustment step size decreases.

In S22 of FIG. 9, the OADM control circuit 175 uses the VAT 169 based on an instruction from the system control circuit 56 to set each ch. Adjust the light level. The OADM control circuit 175 confirms the adjusted result from the outputs of the MOs 167 and 170, and adjusts the VATs 136 and 169 so that the target light level is obtained. Then, the OADM control circuit 175 outputs the end of adjustment to the system control circuit 56.
When confirming the end of the adjustment, the system control circuit 56 returns the process to S2 of FIG. 8, and performs the processes of S2 to S9.
On the other hand, in S11 of FIG. G. It is determined whether or not the pre-emphasis within is complete. The system control circuit 56 performs the process of S12 of FIG. 8 when the determination is not completed, and ends the pre-emphasis process when the determination is completed.

In S12 of FIG. 8, the system control circuit 56 instructs each OADM control circuit 175 to output the output spectrum of the pre-amplifier in each OADM 54. Further, the system control circuit 56 instructs the optical receiving station control circuit 113 to output the input spectrum.
In S23 of FIG. 9, the OADM control circuit 175 in each OADM 54 station receives an instruction from the system control circuit 56 and switches the SW 156 so that the light from the coupler 133 enters the SPA 157. Each OADM control circuit 175 outputs the output of SPA 157 (the output spectrum of the pre-amplifier) to the system control circuit 56.

The optical receiving station control circuit 113 outputs the output (input spectrum) of the SPA 112 to the system control circuit 56.
In S13 of FIG. 8, the system control circuit 56 determines that the P.P. G. Branches at every ch. The average value of the light level of G. In ch. Every ch. The deviation between the light level and the average value is calculated.
In S14 of FIG. 8, the system control circuit 56 reverses the magnitude relationship between the spectra by inverting the magnitude of the deviation by ½. G. Each ch. As the amount of pre-emphasis in each ch. Add to or subtract from. Then, the system control circuit 56 receives each ch. The light level of P. G. Is instructed to the OADM control circuit 175 of each OADM.

In S24 of FIG. 9, the OADM control circuit 175 uses the VATs 136 and 169 for each ch. Adjust the light level. The OADM control circuit 175 confirms the adjusted result from the outputs of the MOs 167 and 170, and adjusts the VAT 169 so that the target light level is obtained. Then, the OADM control circuit 175 outputs the end of adjustment to the system control circuit 56.
When confirming the end of the adjustment, the system control circuit 56 ends the pre-emphasis process.
In this way, the system control circuit 56 and each OADM control circuit 175 are connected to each ch. By controlling the light level of the predetermined ch. In an optical communication system having an OADM 54 that branches, inserts, and passes between two end stations, optimal pre-emphasis can be performed.

Next, after setting such optimum pre-emphasis, the ch. The procedure for the case where the pre-emphasis needs to be reset as a result of the increase or decrease in the number will be described.
FIG. It is a figure which shows the flowchart of the system control circuit in the case of resetting of pre-emphasis by increase / decrease of a number.
FIG. It is a figure which shows the flowchart of an OADM control circuit in the case of resetting of pre-emphasis by increase / decrease of a number.
In S31 of FIG. P. G. Recreate.
In S32 of FIG. 11, the system control circuit 56 instructs to switch the optical amplifier of each station to the AGC mode. The AGC mode is a mode for controlling the gain of the optical amplifier.

In S50 of FIG. 12, the OADM control circuit 175 switches the optical amplifier in the OADM 54 to the AGC mode.
In S51 of FIG. The OADM control circuit 175 in the OADM 64 that increases / decreases the number is 1ch. Incorporating branching sections of FBG 141, optical amplifier 161 and DEM 162 for receiving and processing the minute Incorporates transmitters 165, optical amplifiers 166, couplers 168, 171, MOs 167, 170, VAT 169 and FIL 172 inserts for generating minutes. Then, the IS state is set.

The IS (in-service) state is to make the insertion unit usable. When the insertion section is added in the IS state, light is transmitted from the transmitter at the same time as the connection is completed, which is unfavorable for the operation of the optical communication system such as adversely affecting other optical signals, so the insertion section cannot be used. Add (OOS; out-of-service). For this reason, when the expansion is completed, the insertion portion is set to the IS state.
In S52 of FIG. 12, the OADM control circuit 175 sets the added ch. The insertion light level of is set to the initial value. The initial value is the existing ch. When the optical amplifier is returned from the AGC mode to the ALC mode. In order not to affect the optical signal of the existing ch. Or the average value of the optical level in the WDM optical signal output from the OADM 64.

In S33 of FIG. 11, the system control circuit 56 performs provisioning for initial setting of various optical components in the optical transmission station 51, the relay amplification device 53, the OADM 54, and the optical transmission station 55. In particular, ch. Since the number has increased or decreased, the setting of the optical amplifier is changed.
In S34 of FIG. 11, the system control circuit 56 instructs the optical amplifier of each station to switch to the ALC mode. The ALC mode is a mode for controlling the output of the optical amplifier.

In S35 of FIG. 11, the system control circuit 56 instructs each OADM control circuit 175 to output the output spectrum of the subsequent amplification unit in each OADM 54. Further, the system control circuit 56 instructs the optical transmission station control circuit 107 to output the output spectrum.
In S53 of FIG. 12, the OADM control circuit 175 in each OADM 54 station receives an instruction from the system control circuit 56 and switches the SW 156 so that light from the coupler 155 enters the SPA 157. Then, each OADM control circuit 175 outputs the output of SPA 157 (the output spectrum of the subsequent amplification unit) to the system control circuit 56.

The optical transmission station control circuit 107 outputs the output (output spectrum) of the SPA 106 to the system control circuit 56.
In S <b> 36 of FIG. 11, the system control circuit 56 acquires the output spectrum of the subsequent amplification unit in each OADM 54 from each OADM control circuit 175. Further, the system control circuit 56 acquires an output spectrum from the optical transmission station control circuit 107.

In S37 of FIG. 11, the system control circuit 56 instructs each OADM control circuit 175 to output the output spectrum of the pre-amplifier in each OADM 54. Further, the system control circuit 56 instructs the optical receiving station control circuit 113 to output the input spectrum.
In S54 of FIG. 12, the OADM control circuit 175 in each OADM station switches the SW 156 so that the light from the coupler 133 enters the SPA 157 in response to an instruction from the system control circuit 56. Each OADM control circuit 175 outputs the output of SPA 157 (the output spectrum of the pre-amplifier) to the system control circuit 56.

The optical receiving station control circuit 113 outputs the output (input spectrum) of the SPA 112 to the system control circuit 56.
In S38 of FIG. 11, the system control circuit 56 acquires the output spectrum of the pre-amplifier in each OADM from each OADM control circuit 175. Further, the system control circuit 56 acquires an input spectrum from the optical receiving station control circuit 113.
Here, in the optical amplifier in the OADM 54, when the gain equalization is performed by the optical amplifier, the slope compensation amount is taken into consideration, and the output spectrum of the subsequent amplification unit and the previous amplification unit when the gain equalization is not performed. An output spectrum is obtained, and these are newly set as the output spectrum of the rear amplification unit and the output spectrum of the front amplification unit, respectively.

In S39 of FIG. 11, the system control circuit 56 calculates the output spectrum of each relay amplifier 53. Since this calculation can be obtained in the same manner as S6 described above, the description thereof is omitted.
In S40 of FIG. 11, the system control circuit 56 obtains the partial light SNRj, the total optical signal average value, and the PG partial light SNR of each station. Here, in the first embodiment, the partial light SNRj, k is defined by Poutj, k, and Poutj, k is obtained from each spectrum acquired in S36, S38, and S39.

In S41 of FIG. 11, the system control circuit 56 obtains the difference between the all-optical signal average value and the PG partial light SNR at each station. Then, the system control circuit 56 performs ch. P. increased or decreased in number. G. P. G. Add the differences for each station obtained for all the stations where.
In S42 of FIG. P. increased or decreased in number. G. It is determined whether or not the addition result of S41 is within an allowable value.

If the result of determination is that it is not within the allowable value, the system control circuit 56 performs the process of S43 in FIG. If the result of determination is that the value is within the allowable value, the system control circuit 56 performs the process of S44 in FIG.
In S43 of FIG. 11, the system control circuit 56 determines that the result of S41 is a positive value. G. Is reduced by 0.5 dB, and the result of S41 is a negative value. G. Instructs the OADM control circuit 175 of the OADM 54 in which the branching section such as the DEM 162 and the insertion section such as the transmitter 165 are added in S51 of FIG. The accuracy of pre-emphasis increases as the adjustment step size decreases.

In S55 of FIG. 12, the OADM control circuit 175 uses the VAT 169 based on the instruction from the system control circuit 56 to set each ch. Adjust the light level. The OADM control circuit 175 confirms the adjusted result from the outputs of the MOs 167 and 170, and adjusts the VAT 169 so that the target light level is obtained. Then, the OADM control circuit 175 outputs the end of adjustment to the system control circuit 56.
When the completion of adjustment is confirmed, the system control circuit 56 returns the process to S35 of FIG. 11 and performs the processes of S35 to S42.
On the other hand, in S44 of FIG. P. increased or decreased in number. G. In each ch. Each time, the sum of the inserted light level and the branched light level is obtained.

In S45 of FIG. P. increased or decreased in number. G. In step S44, each ch. For each ch. So that the sum of The insertion light level of the G. Is instructed to the OADM control circuit 175 to insert.
In S56 of FIG. 12, the OADM control circuit 175 adjusts the insertion light level using the VATs 136 and 169 based on an instruction from the system control circuit 56. The OADM control circuit 175 confirms the adjusted result from the outputs of the MOs 167 and 170, and adjusts the VATs 136 and 169 so that the target light level is obtained. Then, the OADM control circuit 175 outputs the end of adjustment to the system control circuit 56.

In S46 of FIG. 11, pre-emphasis is performed by the procedure of S1 to S14 shown in FIG. 8, and the system control circuit 56 ends the process.
WDM optical signal ch. When the number increases or decreases, pre-emphasis is reset as described above.
In the first embodiment, each ch. In the above description, the optical level is adjusted by the VATs 103, 136, and 169. However, instead of the VATs 103, 136, and 169, each ch. The light level may be adjusted.

Next, another embodiment will be described.
(Configuration of Second Embodiment)
The second embodiment is an embodiment of an optical communication system.
FIG. 13 shows the overall configuration of the optical communication system in the second embodiment. G. FIG.
FIG. 14 is a diagram illustrating the configuration of the OADM in the optical communication system according to the second embodiment.
First, the overall configuration of the optical communication system according to the second embodiment will be described, and then the configuration of the OADM used in the optical communication system will be described in detail. The configuration of the relay amplifying device used in the optical communication system of the second embodiment is the same as that of the relay amplifying device shown in FIG.

The overall configuration of the optical communication system according to the second embodiment will be described.
In FIG. 13A, the optical communication system in the second embodiment forms a ring-shaped network from an OADM 64 and an optical transmission line 62 connecting these OADMs 64, and between the OADMs 64, In order to compensate for the transmission loss, a relay amplifying device 63 for amplifying the WDM optical signal transmitted through the optical transmission path 62 is provided.
The OADM 64 receives a predetermined ch. From the WDM optical signal transmitted through the optical transmission line 62. Branch, insert and pass through. The OADM 64 outputs the spectrum of the WDM optical signal incident on the OADM 64 and the spectrum of the WDM optical signal emitted from the OADM 64 to the system control circuit 65, and inserts it based on the control signal from the system control circuit 65. Each ch. Then, after pre-emphasis, it is inserted into the optical transmission line 62.

Next, the configuration of the OADM used in the optical communication system according to the second embodiment will be described in detail.
In FIG. 14, the WDM optical signal transmitted through the optical transmission line 62 is incident on the optical amplifier 201 of the OADM 64 and amplified. The optical amplifier 201 is a preamplifier that compensates for transmission loss mainly generated in the optical transmission path 62. The amplified WDM optical signal is incident on the coupler 202.

The WDM optical signal incident on the coupler 202 is branched into two. One branched WDM optical signal is incident on the SW 280, and the other branched WDM optical signal is incident on the coupler 203.
The WDM optical signal incident on the coupler 203 is branched into two. One branched WDM optical signal is incident on the MO 227, and the other branched WDM optical signal is incident on the coupler 204.

  The MO 227 is a monitor that detects the optical level of the WDM optical signal, and the detection result is output to the OADM control circuit 285. Based on the output from the MO 227, the OADM control circuit 285 can detect the optical level of the WDM optical signal incident on the OADM 64, signal interruption, and the like. If the signal is interrupted, a warning is issued as necessary. This signal loss is caused by a failure between the optical amplifier 201 and the coupler 203.

The WDM optical signal incident on the coupler 204 is branched into two. One branched WDM optical signal enters the ATT 205, and the other branched WDM optical signal enters the DC 231.
The WDM optical signal emitted to the ATT 205 is processed by each optical component to be described later to become a WDM optical signal that passes through the OADM 64. On the other hand, the WDM optical signal emitted to the DC 231 is processed by each optical component described later and branched by the OADM 64. Is taken out.

The optical level of the WDM optical signal incident on the ATT 205 is attenuated and emitted to the DC 206. The attenuation amount of the ATT 205 is adjusted so that a nonlinear optical phenomenon occurring in the DC 206 can be prevented.
The DC 206 passes through the OADM 64 for ch. On the other hand, it is a dispersion compensator that mainly compensates the chromatic dispersion generated in the optical transmission line 62, and the WDM optical signal compensated for the chromatic dispersion is emitted to the optical amplifier 207. The optical amplifier 207 is a preamplifier that compensates for transmission loss caused by the couplers 202, 203, 204, ATT 205, DC 206, and the like.

The WDM optical signal amplified by the optical amplifier 207 enters the coupler 208. The WDM optical signal incident on the coupler 208 is branched into two. One branched WDM optical signal is incident on a cyclic filter (hereinafter abbreviated as “CFIL”) 210, and the other branched WDM optical signal is incident on MO 209.
The MO 209 is a monitor that detects the optical level of the WDM optical signal, and the detection result is output to the OADM control circuit 285. Based on the output from the MO 209, the OADM control circuit 285 detects the presence or absence of a WDM optical signal incident on the CFIL 210. As a result, the OADM control circuit 285 can detect a failure of the ATT 205, DC 206, optical amplifier 207, etc. or a dropout of each optical component connected by a connector or the like, and warns as necessary. To emit.

The WDM optical signal incident on the CFIL 210 is an even ch. And odd ch. And are incident on acousto-optic tunable filters (hereinafter abbreviated as “AOTF”) 211 and 212, respectively.
The AOTFs 211 and 212 are acousto-optic filters that separate and select incident light using a diffraction effect based on a change in refractive index induced by the acousto-optic effect. The ultrasonic waves that generate the acousto-optic effect use surface acoustic waves. The surface acoustic waves are generated by forming an electrode on a substrate exhibiting a piezoelectric action and applying a voltage of an RF frequency to the electrode. For this reason, by controlling the RF frequency, ch. Can be changed.

The AOTFs 211 and 212 are blocked by the control signal from the OADM control circuit 285. Is controlled and blocked. Ch. Branches at this OADM64. Is selected.
Here, even number ch. And odd ch. And then shut off by AOTFs 211 and 212 respectively. Shuts off even-numbered ch. And odd ch. And separated into ch. The ch. Of the WDM optical signal is spaced. Since it is twice the interval, ch. Should be cut off more easily and reliably than when it is cut off by a single AOTF. It is because it can block.

Predetermined ch. The WDM optical signal from the AOTF 211 that is blocked is input to the VAT 213. And predetermined ch. The WDM optical signal from the AOTF 212 that has been blocked is input to the VAT 214.
The VATs 213 and 214 are variable attenuators that attenuate and emit the light level of incident light. This amount of attenuation is controlled by a control signal from the OADM control circuit 285, and the VATs 213 and 214 are blocked by the AOTFs 211 and 212, respectively. The optical levels generated by the difference in the numbers are adjusted, and the optical levels of the WDM optical signals emitted from the AOTFs 211 and 212 are made substantially equal and emitted to the CFIL 215.

The WDM optical signals incident on the CFIL 215 from the VATs 213 and 214 are the even ch. And odd ch. Are wavelength-multiplexed and incident on the SW 216.
The SW 216 is a switch whose cutoff / transmission is controlled by the OADM control circuit 285. The SW 216 can prevent light from leaking to the optical transmission line 62 when setting each optical component in the OADM 64 or when a failure occurs in the OADM 64 by setting the cutoff state. Therefore, in such a case, the WDM optical signal transmitted between the other OADMs 64 is not affected by crosstalk or the like.

In particular, AOTF is effective during such setting because it is generally necessary to correct the relationship between the RF frequency and the cutoff wavelength at an appropriate interval due to temperature dependence of the cutoff wavelength and aging.
The WDM optical signal from the SW 216 is incident on the optical amplifier 217. The optical amplifier 217 is a preamplifier that compensates for transmission loss that occurs in each optical component between the optical amplifier 207 and the optical amplifier 217.
The WDM optical signal amplified by the optical amplifier 217 enters the coupler 218. The WDM optical signal incident on the coupler 218 is branched into two. One branched WDM optical signal is incident on the VAT 220, and the other branched WDM optical signal is incident on the MO 219.

  The VAT 220 is a variable attenuator that attenuates and emits the light level of incident light. The attenuated WDM optical signal is incident on the coupler 221. The WDM optical signal incident on the coupler 221 is branched into two. One branched WDM optical signal is incident on the WDM coupler 223, and the other branched WDM optical signal is incident on the MO 222.

  MOs 219 and 222 are monitors that detect the optical level of the WDM optical signal, and the detection result is output to the OADM control circuit 285. The OADM control circuit 285 adjusts the optical level of the WDM optical signal by adjusting the attenuation amount of the VAT 220 based on the detection results of the MO 219 and the MO 222. The attenuation is adjusted so that the average optical level of the WDM optical signal passed through the OADM 64 and the average optical level of the inserted WDM optical signal are substantially equal. The OADM control circuit 285 determines the average optical level of the inserted WDM optical signal based on the output of the MO 270 described later.

The coupler 223 wavelength-multiplexes the WDM optical signal passing through the OADM 64 from the coupler 221 and the WDM optical signal inserted by the OADM 64 generated by the configuration described later. The wavelength-multiplexed WDM optical signal is emitted to the optical amplifier 224.
The optical amplifier 224 is a post amplifier that amplifies to a predetermined light level. The amplified WDM optical signal is emitted to the coupler 225.
The WDM optical signal incident on the coupler 225 is branched into two. One of the branched WDM optical signals is emitted to the optical transmission path 62 to be transmitted to the next-stage station, and the other branched WDM optical signal is emitted to the SW 280.

The SW 280 is a 2 × 1 optical switch, and emits either a WDM optical signal from the coupler 202 or a WDM optical signal from the coupler 225 to the SPA 281 according to a control signal from the OADM control circuit 285.
The SPA 281 is a spectrum analyzer that measures the wavelength of incident light and the light level at this wavelength. The SPA 281 measures the spectrum of the WDM optical signal incident on the OADM 64 and amplified by the optical amplifier 201 or the spectrum of the WDM optical signal emitted from the OADM 64 to the optical transmission line 62 by selecting the SW 280, and displays the measurement result. Output to the OADM control circuit 285.

On the other hand, the WDM optical signal branched by the coupler 204 is incident on the DC 231 and ch. Is received and processed.
DC231 is a ch. On the other hand, it is a dispersion compensator that compensates for chromatic dispersion mainly occurring in the optical transmission line 62, and the WDM optical signal compensated for chromatic dispersion is emitted to the coupler 232.

The WDM optical signal incident on the coupler 232 is branched into two. One branched WDM optical signal is incident on the coupler 234, and the other branched WDM optical signal is incident on the MO 233.
The MO 233 is a monitor that detects the optical level of the WDM optical signal, and the detection result is output to the OADM control circuit 285. The OADM control circuit 285 can detect signal interruption of the WDM optical signal branched by the OADM 64 based on the output from the MO 233, and issues a warning if necessary.

  The WDM optical signal incident on the coupler 234 is branched into four and respectively incident on tributaries (hereinafter abbreviated as “TRB”) 290-1 to 290-4. One TRB 290 has 8 ch. Minute optical signal, 8 ch. Minute optical signal can be generated. 1 to ch. 8 optical signals are received and generated. TRB290-2 is ch. 9 to ch. 16 optical signals are received and generated. TRB290-3 is ch. 17 to ch. 24 optical signals are received and generated. And TRB290-4 is ch. 25 to ch. 32 optical signals are received and generated.

Here, since each TRB 290-1 to 290-4 has the same configuration, the TRB 290-1 will be described, and the description of the TRB 290-2 to 290-4 will be omitted.
One of the WDM optical signals branched into four by the coupler 234 is incident on the optical amplifier 235 of the TRB 290-1. The optical amplifier 235 is a preamplifier that compensates for transmission loss that occurs in each optical component between the optical amplifier 201 and the optical amplifier 235.

The WDM optical signal amplified by the optical amplifier 235 enters the coupler 236. The WDM optical signal incident on the coupler 236 is branched into two. The branched WDM optical signals are incident on the couplers 237-1 and 237-2, respectively.
The WDM optical signal incident on the coupler 237-1 is further branched into four and respectively incident on TFs 241-1 to 241-4. TF is an abbreviation for tunable filter.

The TF 241-1 is a band-pass filter that transmits light in a predetermined wavelength band. The center wavelength of the transmission wavelength band is ch. A wavelength corresponding to one wavelength is set. For this reason, TF 241-1 selects ch. Only one optical signal is transmitted.
Ch. From TF241-1. The optical signal 1 enters the coupler 242-1. The ch. One optical signal is branched into two. One of the branched ch. 1 is incident on the optical amplifier 244-1 and branched into the other ch. The optical signal 1 is incident on the MO 243-1.

MO243-1 is ch. The detection result is output to the OADM control circuit 285. The OADM control circuit 285 uses the output from the MO 243-1 to perform ch. The presence or absence of the 1 optical signal is confirmed.
The optical amplifier 244-1 is a preamplifier that increases the light reception level. The optical signal 1 is amplified and emitted to the DEM 245-1.

The DEM 245-1 is connected to the ch. 1 optical signal, ch. Information is extracted from one optical signal. As the DEM 245-1, a light receiving element such as a photodiode that converts an optical signal into an electric signal can be used.
The same configuration as the TF 241-1, coupler 242-1, MO 243-1, optical amplifier 244-1, and DEM 245-1 is applied to each WDM optical signal branched by the couplers 237-1 and 237-2. The center wavelengths of the transmission wavelength bands of the TFs 241-2 to 241-8 are ch. 2 to ch. A wavelength corresponding to 8 wavelengths is set.

In this way, ch. 1 to ch. Eight optical signals are received and processed.
Also, ch. 1 to ch. Eight optical signals are generated as follows.
The transmitter 251-1 in the TRB 290-1 is composed of LD and MOD and ch. An optical signal having a wavelength of 1 is generated. Generated ch. 1 optical signal is emitted to the optical amplifier 252-1.
The optical amplifier 252-1 is a post-amplifier that amplifies to a predetermined light level. Amplified ch. The optical signal 1 is incident on the TF 253-1.
The TF 253-1 is a band-pass filter that transmits light in a predetermined wavelength band, and the center wavelength of the transmission wavelength band is ch. A wavelength corresponding to one wavelength is set. For this reason, TF253-1- Only one optical signal can be transmitted, and the ASE generated in the optical amplifier 252-1 can be removed.

Ch. From TF253-1. 1 optical signal is emitted to the coupler 255-1. The coupler 255-1 is connected to the ch. This is an optical branching coupler for branching one optical signal into two. One of the branched ch. One optical signal is emitted to MO254-1, and the other branched optical signal is emitted to VAT256-1.
The MO254-1 is a monitor that detects the optical level of the optical signal, and the detection result is output to the OADM control circuit 285.

The VAT 256-1 attenuates the optical level of the optical signal from the coupler 255-1 and emits it to the coupler 257-1. This attenuation amount is controlled by a control signal from the OADM control circuit 285.
The coupler 257-1 is an optical branching coupler that branches the optical signal from the VAT256-1 into two. One branched optical signal is emitted to the MO 258-1, and the other branched optical signal is emitted to the coupler 260-1.
The MO 258-1 is a monitor that detects the optical level of the optical signal, and the detection result is output to the OADM control circuit 285.
The coupler 260-1 is an optical branching coupler that branches the optical signal from the VAT 256-1 into two. One branched optical signal is emitted to the coupler 261-1, and the other branched optical signal is emitted to the MO 259-1.

The MO 259-1 is a monitor that detects the optical level of the optical signal, and the detection result is output to the OADM control circuit 285. The OADM control circuit 285 detects ch. The presence or absence of the 1 optical signal is confirmed.
The OADM control circuit 285 adjusts the attenuation amount of the VAT 256-1 based on the detection results of the MO 254-1 and the MO 258-1. The optical level of one optical signal is adjusted to a desired optical level. Since the optical level of the optical signal inserted in the OADM 64 can be adjusted by adjusting the attenuation amount in this way, optimal pre-emphasis can be performed.

Such a configuration including the transmitter 251-1, the optical amplifier 252-1, the coupler 255-1, the MO254-1, the VAT256-1, the coupler 257-1, the MO258-1, the coupler 260-1, and the MO259-1, ch. 1 to ch. Prepared every 8th. The center wavelengths of the transmission wavelength bands of the TFs 253-2 to 253-8 are respectively ch. 2 to ch. A wavelength corresponding to 8 wavelengths is set.
Ch. From each coupler 260-1 to 260-4. 1 to ch. 4 enters the coupler 261-1 and is wavelength-multiplexed. Wavelength multiplexed ch. 1 to ch. 4 WDM optical signals are emitted to the coupler 262. Further, ch. From each coupler 260-5 to 260-8. 5 to ch. 8 enters the coupler 261-2 and is wavelength-multiplexed. Wavelength multiplexed ch. 5 to ch. Eight WDM optical signals are emitted to the coupler 262.

The coupler 262 wavelength-multiplexes the WDM optical signal from the coupler 261-1 and the WDM optical signal from the coupler 261-2. 1 to ch. 8 WDM optical signals are generated.
In this way, ch. 1 to ch. Eight optical signals are generated.
Here, any of the ch. Is received and processed by this OADM 64, and which ch. Are generated and inserted by the OADM control circuit 285 by the DEMs 245-1 to 245-32, the transmitters 251-1 to 251-32, the TFs 241-1 to 241-32, and the TFs 253-1 to 253-32. Is done by controlling.

  The WDM optical signals from the TRBs 290-1 to 290-4 are incident on the couplers 264-1 to 264-4, respectively. Each coupler 264-1 is an optical branching coupler that branches a WDM optical signal into two. One branched WDM optical signal is emitted to the coupler 265, and the other branched WDM optical signal is emitted to the corresponding MO 263-1 to 263-4.

Each of the MOs 263-1 to 263-4 is a monitor that detects the optical level of the optical signal, and each detection result is output to the OADM control circuit 285. The OADM control circuit 285 confirms the presence / absence of WDM optical signals of the corresponding TRBs 290-1 to 290-4 from the outputs of the MOs 263-1 to 263-4.
The coupler 265 wavelength-multiplexes the WDM optical signals from the TRBs 290-1 to 290-4 that are incident through the corresponding couplers 264-1 to 264-4 and outputs the multiplexed signals to the optical amplifier 266.

The optical amplifier 266 is a preamplifier that compensates for transmission loss caused by optical components in the TRB 290. The WDM optical signal amplified by the optical amplifier 266 is emitted to the DC 267.
DC267 is the ch. Inserted in OADM64. On the other hand, the dispersion compensator mainly compensates the chromatic dispersion generated in the optical transmission line 52, and the WDM optical signal compensated for the chromatic dispersion is emitted to the coupler 269.
The coupler 269 is an optical branching coupler that branches a WDM optical signal into two. One of the branched WDM optical signals is emitted to the WDM coupler 223, and the other branched WDM optical signal is emitted to the MO 270.
The MO 270 is a monitor that detects the optical level of the optical signal, and each detection result is output to the OADM control circuit 285. The OADM control circuit 285 reads the channel to be inserted by the OADM 64 from the output of the MO 270. Check whether there is any optical signal.

Here, the optical amplifiers 201, 207, 217, 224, 244, 252 form an inversion distribution by supplying energy to the amplification medium from the outside, and in this state, the light to be amplified is incident to cause stimulated radiation. Thus, the light is amplified with a predetermined gain. As the optical amplifier, for example, a semiconductor laser amplifier or an optical fiber amplifier can be used.
Couplers 202, 203, 204, 208, 218, 221, 223, 232, 242, 255, 257, 260, 261, 262, 264, 265, and 269 are optical branching couplers that split incident light into two. is there. As the coupler, for example, a micro optical element type optical branching coupler such as a half mirror, an optical fiber type optical branching coupler of a molten fiber, an optical waveguide type optical branching coupler, or the like can be used.

As the DCs 206, 231, and 267, dispersion compensating fibers having dispersions of opposite signs so as to cancel dispersion generated in the WDM optical signal can be used.
As described above, the OADM 64 applied to the optical communication system according to the second embodiment has a predetermined ch. In addition to the function of branching, inserting, and passing through, each channel of the WDM optical signal incident on the OADM. A function for measuring the optical level of each channel of each WDM optical signal emitted from the OADM. Function for measuring the light level of the ch and ch. It has a function to adjust the light level.

(Correspondence between the present invention and the second embodiment)
The correspondence relationship between the present invention and the second embodiment will be described below.
The optical transmission path corresponds to the optical transmission path 62, and the station corresponds to the relay amplification device 63 and the OADM 64. In particular, the measuring means corresponds to the SPA 281 in the OADM 64, the arithmetic circuit corresponds to the system control circuit 65, and the adjusting means corresponds to the VAT 256 in the OADM 64.

The pre-emphasis control device corresponds to the system control circuit 65.
Here, the coupler 202 may be connected immediately before the optical amplifier 201, and the spectrum of the WDM optical signal incident on the optical amplifier 201 may be measured.

(Operational effects of the second embodiment)
Next, pre-emphasis in the optical communication system according to the second embodiment will be described.
FIG. 15 is a diagram illustrating a flowchart of the system control circuit in the optical communication system according to the second embodiment.
FIG. 16 is a diagram illustrating a flowchart of the OADM control circuit in the optical communication system according to the second embodiment.

First, when the optical communication system according to the second embodiment shown in FIGS. 13 and 14 is started up, each device is started up sequentially from a certain OADM 64 clockwise or counterclockwise.
Then, for each device, confirmation of signal arrival, ASE correction, confirmation of DC input light level restriction, and the like are performed.
Further, each ch. , So that the light levels of ch. The average light level is set.

In the OADM 64, the total optical level incident on the optical amplifier 224, the ASE correction amount of the optical amplifiers 201 and 207, and ch. From the number, it is confirmed that the average light level incident on the optical amplifier 217 is equal to or higher than a predetermined value.
After performing such initial setting for each device, pre-emphasis of the optical communication system is performed according to the following procedure. This pre-emphasis will be described with reference to FIGS. 15 and 16.

In S71 of FIG. From the path. G. Create
For example, in the present embodiment, as shown in FIG. 13B, the channel ch. Inserted from the station 2 of the OADM 64-1 and branched at the station 7 of the OADM 64-3. 1 to ch. 16 for P.I. G. Set to 1. Inserted from station 7 of OADM64-3 and branched at station 9 of OADM64-4. 1 to ch. 8 for P.M. G. 2. Inserted from station 4 of OADM 64-2 and branched at station 9 of OADM 64-4. 17 to ch. 32. G. 3. Inserted from station 9 of OADM64-4 and branched at station 2 of OADM64-1. 17 to ch. 24 for P.M. G. 4 Inserted from station 7 of OADM64-3 and branched at station 2 of OADM64-1. 9 to ch. 16 for P.I. G. 5

In S72 of FIG. 15, the system control circuit 65 instructs each OADM control circuit 285 to output the output spectrum of the optical amplifier 201 in each OADM 64.
In S90 of FIG. 16, the OADM control circuit 285 in each OADM 64 station switches the SW 280 so that the light from the coupler 202 enters the SPA 281 in response to an instruction from the system control circuit 65. Each OADM control circuit 285 outputs the output of the SPA 281 (the output spectrum of the optical amplifier 201) to the system control circuit 65.

In S73 of FIG. 15, the system control circuit 65 acquires the output spectrum of the optical amplifier 201 in each OADM 64 from each OADM control circuit 285.
In S74 of FIG. 15, the system control circuit 65 calculates the input spectrum of each OADM 64.
Since the output spectrum of the optical amplifier 201 acquired in S73 is a spectrum in which the ASE of the optical amplifier and the slope compensation amount for equalizing the gain wavelength characteristic of the optical amplifier 201 are superimposed, the input spectrum of each OADM 64 is the optical spectrum. It can be obtained by subtracting these ASE and slope compensation amounts from the output spectrum of the amplifier 201.

In S75 of FIG. 15, the system control circuit 65 instructs each OADM control circuit 285 to output the output spectrum of each OADM 64.
In S91 of FIG. 16, the OADM control circuit 285 in each OADM station switches the SW 280 so that the light from the coupler 225 enters the SPA 281 in response to an instruction from the system control circuit 65. Each OADM control circuit 285 outputs the output of SPA 280 (the output spectrum of OADM 64) to the system control circuit 65.

In S76 of FIG. 15, the system control circuit 65 acquires the output spectrum of each OADM from each OADM control circuit 285.
Here, in the optical amplifier in the OADM 64, when gain equalization is performed to equalize the gain wavelength characteristic of the optical amplifier generated by ASE, this gain equalization is compensated from the output spectrum of the optical amplifier 201 in S73. The slope compensation amount is subtracted to obtain the output spectrum of the optical amplifier 201 when gain equalization is not performed, and these are newly set as the output spectrum of the optical amplifier 201.

In S77 of FIG. 15, the system control circuit 65 calculates the input spectrum of each relay amplification device 63. Since the input spectrum of each relay amplifying device 63 is calculated in the same manner as S6 of FIG. 8 in the first embodiment, the description thereof is omitted.
In this way, the system control circuit 65 acquires the input spectrum of the WDM optical signal at each station.

（式９）は、（式３）をデシベル単位に変換した式である。また、ｈνΔｆは、定数であり、１０ｌｏｇ（ｈνΔｆ）＝５７．９である。
図１５のＳ７９において、システム制御回路６５は、各局において、全光信号平均値とＰＧ部分光ＳＮＲとの差分を求める。そして、システム制御回路６５は、Ｐ．Ｇ．が入射されるすべての局について求めた局ごとの差分を加算する。 In S78 of FIG. 15, the system control circuit 65 obtains the partial light SNRj, the total optical signal average value, and the PG partial light SNR of each station. In this embodiment, (Equation 3) is used as the partial light SNRj, k, but the light SNRj, k is calculated by (Equation 9) below using the values of S74, S76, and S77.

(Expression 9) is an expression obtained by converting (Expression 3) into a decibel unit. HνΔf is a constant, and 10 log (hνΔf) = 57.9.
In S79 of FIG. 15, the system control circuit 65 obtains the difference between the all-optical signal average value and the PG partial light SNR at each station. The system control circuit 65 is connected to the P.P. G. Add the differences for each station obtained for all the stations where.

In S80 of FIG. G. It is determined whether or not the addition result of S8 is within an allowable value. If the result of determination is that the value is not within the allowable value, the system control circuit 65 performs the process of S81 in FIG. If the result of determination is that the value is within the allowable value, the system control circuit 65 performs the processing of S82 in FIG.
In S81 of FIG. G. In the OADM 64 in which P. is inserted, the result of S79 is a positive value. G. Is reduced by 0.5 dB, and the result of S79 is negative. G. Indicates an instruction to raise 0.5 dB. G. Is inserted into the OADM control circuit 285 of the OADM 64.
In S92 of FIG. 16, the OADM control circuit 285 uses each VAT 220, 256 based on the instruction from the system control circuit 65. Adjust the light level. The OADM control circuit 285 confirms the adjusted result from the outputs of the MOs 254 and 258, and adjusts the VAT 256 so that the target light level is obtained. Then, the OADM control circuit 285 outputs the end of adjustment to the system control circuit 65.

When confirming the end of the adjustment, the system control circuit 65 returns the process to S72 of FIG. 15, and performs the processes of S72 to S80.
On the other hand, in S82 of FIG. G. It is determined whether or not the pre-emphasis within is complete. As a result of the determination, the system control circuit 65 performs the process of S83 in FIG. 15 if not completed, and ends the pre-emphasis process if completed.

In S83 of FIG. 15, the system control circuit 65 instructs each OADM control circuit 285 to output the output spectrum of the optical amplifier 201 of each OADM 64.
In S93 of FIG. 16, the OADM control circuit 285 of each OADM 64 receives an instruction from the system control circuit 65 and switches the SW 280 so that the light from the coupler 202 enters the SPA 281. Each OADM control circuit 285 outputs the output of the SPA 281 (the output spectrum of the optical amplifier 201) to the system control circuit 65.

  In S94 of FIG. 15, the system control circuit 65 obtains the input spectrum of each OADM 64 by subtracting the ASE and slope compensation amount of the optical amplifier 201 from the result of S73. The system control circuit 65 uses the equation (9) to calculate the P.P. G. Branches at every ch. The average value of only the partial light SNRj is obtained. The system control circuit 65 is connected to each P.D. G. In ch. Every time, the deviation between the partial light SNRj and its average value is calculated.

In S85 of FIG. G. Each ch. The amount obtained by inverting the sign of this deviation as the pre-emphasis amount in each ch. Add to. Then, the system control circuit 65 is connected to each ch. The partial light SNRj of P. G. To the OADM control circuit 285 of each OADM 64 to be inserted.
In S94 of FIG. 16, the OADM control circuit 285 determines each channel from the partial light SNRj based on an instruction from the system control circuit 65. Pinj of each channel is calculated using VAT256. Adjust the light level. The OADM control circuit 285 confirms the adjusted result from the outputs of the MOs 254 and 258, and adjusts the VAT 256 so that the target light level is obtained. Then, the OADM control circuit 285 outputs the end of adjustment to the system control circuit 65.

When confirming the end of the adjustment, the system control circuit 65 ends the pre-emphasis process.
In this way, the system control circuit 65 and each OADM control circuit 285 are connected to each ch. By controlling the light level of the predetermined ch. In a ring network having an OADM 64 that branches, inserts, and passes through, it is possible to perform optimum pre-emphasis.

Next, another embodiment will be described.
(Third embodiment)
The third embodiment is an embodiment of an optical SNR measurement apparatus.
FIG. 17 is a diagram illustrating an overall configuration of an optical SNR measurement apparatus and a detailed configuration of a station according to the third embodiment.
FIG. 18 is a diagram illustrating a flowchart of the arithmetic circuit according to the third embodiment.

  In FIG. 17A, a WDM optical signal is transmitted through an optical transmission line 72. Between the optical transmission lines 72, a plurality of stations 73 for amplifying light to compensate for transmission loss are connected. The station 73 transmits a signal from the supervisory control circuit 316 to the arithmetic circuit 76 as described later. The arithmetic circuit 76 measures the optical SNR based on this signal. An input device 77 and a display device 78 are connected to the arithmetic circuit 76. The input device 77 is a device for inputting an instruction to start measurement, such as a switch or a keyboard. The display device 78 is a device that displays measurement results such as a CRT or a liquid crystal display. FIG. 17A shows the case where the optical SNR in the section from the first station 73-1 to the fifth station 73-5 is measured.

In FIG. 17B, the WDM optical signal incident on the station 73 is optically amplified and emitted from the station 73 via the couplers 301, 302, and 303, the rare earth element-doped optical fiber 304, the coupler 305, and the ISO 306. The
The coupler 301 distributes a part of the incident WDM optical signal and makes it incident on the SPA 311. The SPA 311 outputs a signal corresponding to the spectrum of the received WDM optical signal to the monitoring control circuit 316.
The coupler 302 distributes a part of the incident WDM optical signal and makes it incident on a photodiode (hereinafter abbreviated as “PD”) 312. The PD 312 outputs a signal corresponding to the light level of the received light to the monitoring control circuit 316.

  The LDs 313 and 314 emit excitation light for exciting the rare earth element-doped optical fiber. The pump light from the LD 313 is combined with the WDM optical signal from the coupler 302 by the coupler 303 and supplied to the rare earth element-doped optical fiber 304. Excitation light from the LD 314 is supplied to the rare earth element-doped optical fiber 304 via the coupler 305. In this way, the LD 313 pumps the rare earth element-doped optical fiber forward, and the LD 314 pumps backward.

If the rare earth element-doped optical fiber can be excited with a single LD so that the WDM optical signal to be amplified can be sufficiently amplified, either one of the LDs 313 and 314 may be used.
The rare earth element added to the optical fiber is selected according to the wavelength of the WDM optical signal to be amplified. The wavelength of light that can excite the selected rare earth element is selected as the oscillation wavelength of the LD. For example, when the WDM optical signal is in the 1550 nm band, erbium element (Er) is selected as the rare earth element, and when the WDM optical signal is in the 1450 band, thulium element (Tm) is selected as the rare earth element. Is done. The erbium element and thulium element are both lanthanoid rare earth elements, and elements belonging to the lanthanoid have similar properties.

The rare earth element-doped optical fiber 304 absorbs the excitation light, thereby exciting the rare earth element in the fiber to form an inversion distribution. When a WDM optical signal is incident in a state where this inversion distribution is formed, the WDM optical signal is guided to the WDM optical signal to induce stimulated emission, and the WDM optical signal is amplified.
The ISO 306 is an optical component that transmits light only in one direction, and plays a role of preventing the reflected light from the connection portion of each optical component in the station 73 from being propagated anywhere. In particular, when the reflected light returns to the LDs 313 and 314, the LDs 313 and 314 are induced by the reflected light with various phases and amplitudes, and the oscillation mode is changed and noise is generated. Therefore, this adverse effect is prevented by ISO 306.

On the other hand, the supervisory control circuit 316 transmits both the SPA 311 and PD outputs and the noise figure stored in the memory 315 to the arithmetic circuit 76. This noise figure is a noise figure of the optical fiber amplifier in the station 73 composed of the LDs 313 and 314, the couplers 303 and 304, and the rare earth element-doped optical fiber.
(Correspondence relationship between the present invention and the third embodiment)
The correspondence relationship between the present invention and the third embodiment will be described below.

The optical transmission path corresponds to the optical transmission path 72, and the station corresponds to the station 73. In particular, the measuring means corresponds to SPA 311 and PD 312, and the arithmetic circuit corresponds to arithmetic circuit 76.
The optical amplification means corresponds to the station 73, the measurement means corresponds to the SAP 311 and the PD 312, and the arithmetic circuit corresponds to the arithmetic circuit 76.
The measurement circuit corresponds to the arithmetic circuit 76.
(Operational effect of the third embodiment)
Next, optical SNR measurement in the third embodiment will be described.

In FIG. 18, the arithmetic circuit 76 is instructed to start measurement by the input device 77. Then, the arithmetic circuit 76 instructs each station 73 to transmit the output of the SPA 311, the output of the PD 312 and the noise figure (S101).
In response to this instruction, the supervisory control circuit 316 of each station 73 transmits the above-described information content signal to the arithmetic circuit 76.

Based on the received information, the arithmetic circuit 76 makes each ch. Determine the input light level. That is, for each station 73, the arithmetic circuit 76 converts the output of the PD into the ch. One ch. Divided by the number. The light level per hit is obtained, and the ch. The deviation between is added to the light level. In this way, the arithmetic circuit 76 is connected to each ch. Determine the input light level.
The arithmetic circuit 76 calculates each ch. The partial light SNR of each station 73 is obtained by (Equation 3), that is, (Equation 9) based on the input light level for each (S103).
The arithmetic circuit 76 is connected to each ch. Each time, the reciprocal sum of the partial light SNR obtained is added from the first station 73-1 to the fifth station 73-5 (S104).

The arithmetic circuit 76 is connected to each ch. For each ch., By obtaining the reciprocal of the obtained reciprocal sum. Is obtained (S105). Then, the obtained optical SNR is displayed outside by the display device 78.
In this way, each ch. In the section from the first station 73-1 to the fifth station 73-5. Can be obtained.

In S104, the optical SNR of an arbitrary section can be obtained by changing the range in which the sum is taken. For example, in the case of obtaining the optical SNR from the second station 73-2 to the fourth station 73-4, in S104, the arithmetic circuit 76 determines each ch. Each time, the reciprocal of the obtained partial light SNR may be added from the second station 73-2 to the fourth station 73-4.
In the third embodiment, the partial light SNR is defined by (Expression 3), but may be defined by (Expression 5). Further, by configuring the station 73 as shown in FIG. 19, it can be defined by (Expression 1), (Expression 2), (Expression 4) and (Expression 6).
FIG. 19 is a diagram illustrating another configuration of a station in the third embodiment.

  In FIG. 19A, the station 74 is configured to include SPA 318 and PD 317 corresponding to the SPA 311 and PD 312 in the station 73 shown in FIG. 17B on the emission side of the ISO 306 in order to measure the output light level. . Therefore, the WDM optical signal incident on the station 74 is emitted from the station 74 via the coupler 303, the rare earth element-doped optical fiber 304, the coupler 305, the ISO 306, the coupler 307, and the coupler 308.

The coupler 307 distributes a part of the incident WDM optical signal and makes it incident on the PD 317. The PD 317 outputs a signal corresponding to the light level of the received light to the monitoring control circuit 316.
The coupler 308 distributes a part of the incident WDM optical signal and makes it incident on the SPA 318. The SPA 318 outputs a signal corresponding to the spectrum of the received WDM optical signal to the monitoring control circuit 316.

The other configuration is the same as that of the station 73 shown in FIG.
When the station 74 having such a configuration is used instead of the station 73 in FIG. 17A, the partial optical SNR is defined by (Equation 6), and the optical SNR can be measured.
Also, in FIG. 19B, the station 75 measures the input light level and the output light level by using the SPA 311 and PD 312 shown in FIG. 17B and the SPA 318 and PD 317 shown in FIG. Configured with both. Therefore, the WDM optical signal incident on the station 75 is emitted from the station 75 via the couplers 301, 302, 303, the rare earth element-doped optical fiber 304, the coupler 305, ISO 306, the coupler 307, and the coupler 308.

When the station 75 having such a configuration is used in place of the station 73 in FIG. 17A, the partial optical SNR is defined by any one of the formulas (1) to (6), and the optical SNR is measured. can do.
In the case of the station 75, each ch. May be obtained from the outputs of the PDs 312 and 317, or may be stored in the memory 315 in advance.

On the other hand, in the second embodiment, each ch. In the above description, the optical level is adjusted by the VAT 256. However, instead of the VAT 256, each ch. The light level may be adjusted.
In the first embodiment and the second embodiment, ch. Although the case of a WDM optical signal having a number of 32 has been described, the present invention is not limited to this. Any ch. The present invention can be applied to several WDM optical signals.

In the first embodiment, each ch. As shown in FIG. 3B, and in the second embodiment, each ch. Although the path has been specifically shown and described as shown in FIG. 13B, it is not limited to this. Each ch. The path of can be set arbitrarily.
Furthermore, in the first embodiment, the optical transmission station control circuit 107, the optical reception station control circuit 113, the OADM control circuit 175, and the system control circuit 56, and in the second embodiment, the OADM control circuit 285, In the third embodiment, the configuration in which communication is performed between each station 73 and the arithmetic circuit 76 using a dedicated line has been described in the third embodiment, but the present invention is not limited to this. For example, 1ch. You may communicate using minutes. Or in SDH (synchronous digital hierarchy), you may use the undefined area | region of the section overhead (section over head) etc. which accommodate the information on optical communication system operations, such as maintenance information and a status monitor, between transmission apparatuses.

10, 72 Stations 16, 76 Arithmetic circuit 22 Measuring means 23 Adjustment means 56, 65 System control circuits 103, 169, 256 Variable attenuators 106, 112, 157, 281, 311, 318 Spectrum analyzer 107 Optical transmission station control circuit 113 Light Receiving station control circuit 147, 167, 170, 219, 222, 254, 258 Monitor 175, 285 OADM control circuit 312, 314 Photodiode

Claims (6)

An optical signal to be wavelength multiplexed is first incident on the optical transmission line provided with a plurality of stations provided with optical amplification means for amplifying a wavelength division multiplexing optical signal obtained by wavelength multiplexing a plurality of optical signals between the optical transmission lines. In a pre-emphasis method for adjusting the optical level of the optical signal when
A first step of respectively obtaining predetermined physical quantities using measurement means provided in at least two of the plurality of stations;
A second step in which an arithmetic circuit calculates a partial optical signal-to-noise ratio for each of the plurality of optical signals for each of the plurality of stations based on the measured predetermined physical quantity;
The reciprocal sum of the partial optical signal-to-noise ratio for each of the plurality of optical signals is obtained over a section where the stations where the optical signals are amplified overlap, and the reciprocal of the reciprocal sum of each of the plurality of optical signals. A third step of obtaining optical levels of the plurality of optical signals when the optical signals to be wavelength-multiplexed are first incident on the optical transmission line so that the divided optical signal-to-noise ratios are equal to each other ;
4 to adjust the light level of the by using the adjustment means provided to the station that enters the optical transmission path an optical signal to be wavelength-multiplexed first, the plurality of optical signals such that the light level obtained With steps,
The measured predetermined physical quantity is
(A) When the output light level Pout, the noise figure NF, and the gain G,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(B) When the input light level Pin and the noise figure NF,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(C) When the output light level Pout and the gain G,
The partial optical signal to noise ratio is:

Defined in
(D) When the output light level is Pout,
The partial optical signal to noise ratio is defined by Pout, or
(E) When the input light level is Pin,
The pre-emphasis method, wherein the partial optical signal-to-noise ratio is defined by Pin. An optical signal to be wavelength multiplexed is first incident on the optical transmission line provided with a plurality of stations provided with optical amplification means for amplifying a wavelength division multiplexing optical signal obtained by wavelength multiplexing a plurality of optical signals between the optical transmission lines. In a pre-emphasis method for adjusting the optical level of the optical signal when
A first step of respectively obtaining predetermined physical quantities using measurement means provided in at least two of the plurality of stations;
A second step in which an arithmetic circuit calculates a partial optical signal-to-noise ratio for each of the plurality of optical signals for each of the plurality of stations based on the measured predetermined physical quantity;
For each of the plurality of stations, a third step of obtaining a sum of the partial optical signal-to-noise ratios over all the optical signals amplified by the station, and further obtaining an average value thereof;
A fourth step of determining, for each of the plurality of optical signals, a difference value between the average value in each of the plurality of stations and a partial optical signal-to-noise ratio of the optical signal;
For each of the plurality of optical signals, a sum of the difference values is obtained over a station where the optical signal is amplified, and the optical signals to be wavelength-multiplexed are set so that the sum of the difference values is all zero. a fifth step asking you to light levels of the plurality of optical signals at the time of initially entering the optical transmission path,
6 for adjusting the light level of the by using the adjustment means provided to the station that enters the optical transmission path an optical signal to be wavelength-multiplexed first, the plurality of optical signals such that the light level obtained With steps,
The measured predetermined physical quantity is
(A) When the output light level Pout, the noise figure NF, and the gain G,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(B) When the input light level Pin and the noise figure NF,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(C) When the output light level Pout and the gain G,
The partial optical signal to noise ratio is:

Defined in
(D) When the output light level is Pout,
The partial optical signal to noise ratio is defined by Pout, or
(E) When the input light level is Pin,
The pre-emphasis method, wherein the partial optical signal-to-noise ratio is defined by Pin. An optical signal to be wavelength multiplexed is first incident on the optical transmission line provided with a plurality of stations provided with optical amplification means for amplifying a wavelength division multiplexing optical signal obtained by wavelength multiplexing a plurality of optical signals between the optical transmission lines. In a pre-emphasis method for adjusting the optical level of the optical signal when
A first step of respectively obtaining predetermined physical quantities using measurement means provided in at least two of the plurality of stations;
A second step in which an arithmetic circuit calculates a partial optical signal-to-noise ratio for each of the plurality of optical signals for each of the plurality of stations based on the measured predetermined physical quantity;
A third step of obtaining, for each of the plurality of stations, a sum of the partial optical signal-to-noise ratios over all the optical signals amplified by the station, and further obtaining an average value of all optical signals, which is an average value thereof; ,
A fourth step of creating a path group in which optical signals having the same section from the first incident on the optical transmission line to the final emission among the plurality of optical signals are grouped together; ,
For each of the plurality of stations, the sum of the partial optical signal-to-noise ratios is obtained over the optical signals in the path group amplified by the stations, and the average value of the path group partial optical signal-to-noise ratios is obtained. A fifth step to find,
A sixth step of determining, for each of the plurality of path groups, a difference value between the all-optical signal average value and the path group partial optical signal-to-noise ratio in each of the plurality of stations;
A seventh step of obtaining a sum of the difference values for each of the plurality of path groups;
An eighth step of adjusting the path group partial optical signal-to-noise ratio so that the sum of the difference values obtained for each of the plurality of path groups is all zero;
Using the adjusting means provided in a station that enters the optical transmission path an optical signal to be the wavelength-multiplexed first, based on the adjusted the path group moiety optical signal-to-noise ratio of the plurality of optical signals light A ninth step of adjusting the level,
The measured predetermined physical quantity is
(A) When the output light level Pout, the noise figure NF, and the gain G,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(B) When the input light level Pin and the noise figure NF,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(C) When the output light level Pout and the gain G,
The partial optical signal to noise ratio is:

Defined in
(D) When the output light level is Pout,
The partial optical signal to noise ratio is defined by Pout, or
(E) When the input light level is Pin,
The pre-emphasis method, wherein the partial optical signal-to-noise ratio is defined by Pin. In an optical communication system comprising a plurality of stations comprising optical amplification means for amplifying a wavelength division multiplexing optical signal obtained by wavelength multiplexing a plurality of optical signals between optical transmission lines,
A measuring unit provided in at least two or more of the plurality of stations and measuring a predetermined physical quantity in the station;
4. The pre-emphasis method according to claim 1, wherein an optical signal to be wavelength-multiplexed is first incident on the optical transmission line based on a predetermined physical quantity measured by the measuring unit . An arithmetic circuit for obtaining optical levels of the plurality of optical signals when
Adjusting means for adjusting the optical level of the optical signal so that the optical signal to be wavelength-multiplexed is firstly incident on the optical transmission line and is adjusted to the optical level obtained by the arithmetic circuit; optical communication system according to claim Rukoto provided. An optical transmission station connected to one end of the optical transmission line and provided with the adjusting means;
Examples one of the at least two or more stations, optical communication system of claim 4, further comprising an optical receiving station that will be connected to the other end of the optical transmission line comprising the measuring means . Receive a predetermined physical quantity from at least two or more stations out of a plurality of stations provided with an optical amplification means for amplifying a wavelength division multiplexing optical signal obtained by wavelength multiplexing a plurality of optical signals between optical transmission lines, obtains the predetermined physical quantity of the plurality of stations on the basis of the predetermined physical quantity is, for each of said plurality of stations based on the predetermined physical quantity obtained partial light signal pair for each of the plurality of optical signals A noise ratio is obtained, and a reciprocal sum of the partial optical signal-to-noise ratio is obtained for each of the plurality of optical signals over a section in which stations where the optical signal is amplified overlap, and each of the plurality of optical signals is obtained. Obtaining the optical level of the plurality of optical signals when the optical signal to be wavelength multiplexed is first incident on the optical transmission line so that the divided optical signal-to-noise ratio which is the reciprocal of the reciprocal sum is equal to each other. , The optical signal to be serial wavelength multiplexing the first station that enters the optical transmission path, and outputs a control signal for adjusting the light level of the plurality of optical signals such that the light level determined,
Predetermined physical quantity, wherein the determined is,
(A) When the output light level Pout, the noise figure NF, and the gain G,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(B) When the input light level Pin and the noise figure NF,
The partial optical signal-to-noise ratio is based on a Planck constant h, a frequency ν corresponding to the wavelength of the optical signal, and a frequency Δf corresponding to the resolution of the desired optical signal-to-noise ratio.

Defined in
(C) When the output light level Pout and the gain G,
The partial optical signal to noise ratio is:

Defined in
(D) When the output light level is Pout,
The partial optical signal to noise ratio is defined by Pout, or
(E) When the input light level is Pin,
The control device for pre-emphasis characterized in that the partial optical signal-to-noise ratio is defined by Pin.

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