JP2002374208A - Variable dispersion equalizer, optical transmission system using the same, optical receiver and dispersion control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable dispersion equalizer, having superior controllability and a widened dispersion controllable range that applies dispersion equalization control, even with respect to large residual dispersion values, with optimum conditions. SOLUTION: An optical filter circuit 17 captures part of an optical signal transmitted through an optical fiber transmission line 11 by branching the optical signal by an optical tap 13 and passes an optical signal with processing wavelength band in the distributed optical signal, a photoelectric conversion circuit 14 converts the optical signal into an electrical signal, a clock extract filter circuit 15 outputs a clock component with a specific frequency from the electric signal and a control circuit 16 applies wavelength distribution control to a variable dispersion equalizer 12, depending on the magnitude of the clock component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a variable dispersion equalizer that performs appropriate dispersion equalization according to chromatic dispersion fluctuation of a transmission line, an optical transmission system using the same, and a dispersion control method.

[0002]

2. Description of the Related Art In a conventional optical transmission system, chromatic dispersion occurs according to a wavelength difference of an optical signal transmitted in an optical fiber transmission line. This chromatic dispersion fluctuates due to changes over time such as temperature and stress in the external environment. In particular, in a high-speed optical transmission system for transmitting an optical signal at high speed, the chromatic dispersion tolerance of the optical signal significantly deteriorates, and The transmission signal quality of the optical signal is also degraded by the fluctuation of the dispersion. Therefore, in order to avoid the influence of chromatic dispersion accompanied by such fluctuation, there has been a method that realizes automatic dispersion equalization by a dispersion control method using a variable dispersion equalizer.

[0003] For example, JP-A-11-68657 and JP-A-11-8826 disclose this distributed control.
As described in Japanese Patent Laid-Open No. 2 (Kokai) No. 2, the magnitude of a clock component (bit rate frequency component) of an optical signal transmitted through an optical transmission line is detected, and a variable dispersion equalizer is controlled based on the magnitude. There is something to do.

FIG. 9 is a block diagram showing the configuration of a conventional example of a variable dispersion equalizer 10 for performing dispersion control. In FIG. 9, 11 is an optical fiber transmission line, 12 is a variable dispersion equalizer provided in the optical fiber transmission line 11, and 13 is an optical tap provided on the optical fiber transmission line 11 subsequent to the variable dispersion equalizer 12. The optical signal output from the tunable dispersion equalizer 12 is partially branched by the optical tap 13, and after the branched optical signal is input to the photoelectric conversion circuit 14 and converted into an electric signal, Input to the clock extraction filter circuit 15. The clock extraction filter circuit 15 extracts only a clock component of a frequency from the electric signal.

The clock component extracted by the clock extraction filter circuit 15 (hereinafter referred to as "extracted clock component") uses a frequency corresponding to the bit rate of the optical signal transmitted through the optical fiber transmission line. Any frequency may be used as long as it is a frequency component that characteristically changes according to the distortion of the optical signal waveform due to chromatic dispersion. The control circuit 16 detects the magnitude of the clock component and performs dispersion control of the variable dispersion equalizer such that the magnitude takes a maximum value or a minimum value, for example.

Next, as an example, in the case of an RZ (Return-to-Zero) optical signal having a signal bit rate of 40 Gbit / s and a pulse width of about half the signal bit rate, the signal after passing through the variable dispersion equalizer is used. , The change in the magnitude of the extracted clock component with respect to the residual variance is calculated, and the calculation result is shown in FIG. The solid line in FIG. 2 shows the magnitude of the extracted clock component when the optical signal output from the variable dispersion equalizer is directly photoelectrically converted, and the residual dispersion value after passing through the variable dispersion equalizer becomes zero. It can be seen that the extracted clock component has a maximum value when the time has elapsed. Therefore, in this example, by controlling the variable dispersion equalizer so that the extracted clock component has a maximum value, the residual dispersion value after passing through the variable dispersion equalizer is controlled toward zero.

In the above conventional example, the magnitude of the clock component is monitored when performing automatic distribution equalization, and this method has an advantage that the configuration of the monitoring unit is simplified.

[0008]

However, in the above conventional example, the degree of change of the clock component with respect to the residual dispersion value after passing through the variable dispersion equalizer is determined by the bit rate, coding format, signal waveform, etc. of the signal. Therefore, it is necessary to design a control circuit to cope with this degree of change. For this reason, there is a problem that the degree of freedom in designing the control circuit is limited.

In addition, since the clock component is reduced due to the generation of a small residual dispersion value, when a larger residual dispersion value is generated, the magnitude of the clock component changes rapidly and control becomes difficult. is there. For example, in the change shown by the solid line in FIG. 2, when performing control to search for the maximum value of the extracted clock component, the magnitude of the residual variance at which the extracted clock component first becomes the minimum value is indicated by the point C1 in the solid line. At this point C1, the control range in which distributed control is possible is limited. Here, if the residual dispersion value exceeds the C1 point, it is not easy to determine the control direction (the magnitude of the equalization amount) of the variable dispersion equalization amount for obtaining the maximum value of the extracted clock component. It is difficult to perform optimal dispersion control only by observing only the magnitude of the extracted clock component.
Furthermore, when transmitting an optical signal at an ultra-high speed,
When the bit rate of the modulation of the optical signal becomes very high, the chromatic dispersion tolerance of the optical signal decreases according to the speed, and the control range is greatly limited. This indicates that when the optical signal is transmitted at an ultra-high speed, the magnitude of the clock component changes abruptly even with a slight change in the residual dispersion value, and while high-precision control is possible, If the change of the clock component with respect to the fluctuation of the dispersion value is too rapid, the control range is greatly limited, and there is a problem that it is difficult to perform the dispersion control.

Further, the size of the extracted clock component is set to a maximum value or a minimum value in the dispersion control. However, the maximum or minimum value of the extracted clock component does not always match the optimum condition in the optical receiver. However, even when the distributed control is performed by monitoring the extracted clock component having a simple configuration, it is necessary to set a more flexible control operating point that meets the above conditions.

The present invention has been made in view of the above problems, has excellent controllability, widens a control range in which dispersion control can be performed, and performs dispersion equalization under optimum conditions even for a large residual dispersion value. It is an object to obtain a variable dispersion equalizer capable of performing control, an optical transmission system using the same, and a dispersion control method.

[0012]

In order to achieve the above object, a variable dispersion equalizer according to the present invention provides a variable dispersion equalizer for performing dispersion equalization at any time in accordance with a change in chromatic dispersion of an optical transmission line for transmitting an optical signal. In a variable dispersion equalizer having dispersion equalization means, a waveform shaping means for shaping a waveform of an optical signal transmitted to the optical transmission line, and an electric filter for outputting a clock component of a specific frequency from the waveform shaped optical signal Means, and control means for controlling the variable dispersion equalizing means according to the magnitude of the output clock component.

According to the present invention, the optical signal transmitted to the transmission path is branched and taken in, the waveform of the optical signal is shaped by the waveform shaping means, and the clock signal of a specific frequency is output from the optical signal by the electric filter means. Then, the control means controls the chromatic dispersion of the variable dispersion equalizing means according to the magnitude of the clock component, thereby adjusting the degree of fluctuation of the clock component with respect to the residual dispersion value.

[0014] A variable dispersion equalizer according to the next invention comprises:
In a variable dispersion equalizer having variable dispersion equalization means for performing dispersion equalization at any time in accordance with fluctuations in the chromatic dispersion of an optical transmission line for transmitting an optical signal, a predetermined wavelength of an optical signal transmitted to the optical transmission line Optical filter means for passing an optical signal in a band, electric filter means for outputting a clock component of a specific frequency from the passed optical signal, and the variable dispersion equalizing means according to the magnitude of the output clock component And control means for controlling

According to this invention, the optical signal transmitted to the transmission line is branched and taken in, and after the optical signal of a predetermined wavelength band among the optical signals is passed by the optical filter means, the optical signal is converted from the optical signal by the electric filter means. A clock component of a specific frequency is output, and the control unit controls the chromatic dispersion of the variable dispersion equalization unit according to the magnitude of the clock component, thereby adjusting the degree of fluctuation of the clock component with respect to the residual dispersion value.

[0016] The variable dispersion equalizer according to the next invention comprises:
The above invention is characterized in that the optical filter further comprises a dispersion imparting means connected to a preceding or subsequent stage of the optical filter means, and imparting chromatic dispersion of a predetermined characteristic to the input optical signal.

According to the present invention, the chromatic dispersion having a predetermined characteristic is given to the optical signal input by the dispersion giving means so that the operation control point of the variable dispersion equalizing means can be arbitrarily set.

The variable dispersion equalizer according to the next invention is as follows.
In the above invention, the optical filter means performs dispersion imparting for imparting chromatic dispersion having predetermined characteristics to the input optical signal.

According to the present invention, the optical filter means itself has a dispersion imparting function so that the operation control point of the variable dispersion equalizing means can be arbitrarily set with a smaller number of parts.

The variable dispersion equalizer according to the next invention is as follows.
In the above invention, the control means is further provided with a detecting means connected to the optical transmission line or the waveform shaping means or a preceding stage of the optical filter means for detecting a signal level of an optical signal transmitted to the optical transmission line. Controlling the variable dispersion equalizing means according to the magnitude of the output clock component and the signal level of the detected optical signal.

According to the present invention, the signal level of the optical signal fetched by branching is detected by the detecting means, and the control means controls the variable dispersion equalizing means in accordance with the magnitude of the input clock component and the signal level of the optical signal. , The control including both the fluctuation of the clock component of the specific frequency and the fluctuation of the signal level itself of the optical signal is performed.

A variable dispersion equalizer according to the next invention is as follows.
In the above invention, the optical filter means variably sets at least one of a center wavelength and a pass bandwidth to a desired value.

According to the present invention, in order to increase the degree of freedom in setting the control conditions, the center wavelength and / or the pass bandwidth of the optical filter means are variably set.

The variable dispersion equalizer according to the next invention is as follows.
In the above invention, the control means controls the variable dispersion equalization means so that the magnitude of the output clock component becomes a maximum value or a minimum value.

According to the present invention, the control means controls the variable dispersion equalization means so that the clock component output from the electric filter means has a maximum value or a minimum value.
Perform stable control.

The variable dispersion equalizer according to the next invention is as follows.
In the above invention, the control means calculates a ratio between the magnitude of the output clock component and the signal level of the detected optical signal, and the ratio is any one of a maximum value, a minimum value, and a predetermined value. And controlling the variable dispersion equalizing means.

According to the present invention, the ratio between the level of the clock component output from the electric filter means and the level of the optical signal detected by the detection means is variable so as to be one of a maximum value, a minimum value, and a predetermined value. By controlling the dispersion equalization unit, stable control is performed even on an optical signal that is an optimum condition when the output from the electric filter unit deviates from the maximum value or the minimum value.

The variable dispersion equalizer according to the next invention is as follows.
In a variable dispersion equalizer having a variable dispersion equalizer that performs dispersion equalization at any time according to a change in chromatic dispersion of an optical transmission line that transmits a wavelength-multiplexed optical signal, the wavelength-multiplexed optical signal is An optical wavelength demultiplexing unit for demultiplexing into an optical signal for each wavelength band, and at least one of the above-described variable dispersion equalizers connected to the optical wavelength demultiplexing unit and performing dispersion equalization for each of the wavelength bands; It is characterized by having.

According to the present invention, there is provided an optical wavelength demultiplexing means and a variable dispersion equalizing means, and the variable dispersion equalizing means applies an optical signal demultiplexed by the optical wavelength demultiplexing means to each wavelength band. Performs a distributed equalization process.

The variable dispersion equalizer according to the next invention is as follows.
In the above invention, an optical wavelength multiplexing means for multiplexing optical signals of a plurality of wavelength bands is further provided, and the optical signals output from each of the variable dispersion equalizers are multiplexed.

According to the present invention, there is provided the optical wavelength demultiplexing means, the respective variable dispersion equalizers, and the optical wavelength multiplexing means. By multiplexing the respective optical signals again, dispersion equalization processing for each wavelength band is performed even in the middle of the optical transmission line.

An optical transmission system according to the next invention is an optical transmission system in which an optical signal transmitted from at least one optical transmitter is received by an optical receiver via an optical transmission line. At least one variable dispersion equalizer described above is provided near a receiver.

According to the present invention, the reception characteristic of the optical receiver is optimized by disposing the variable dispersion equalizer in or near the optical receiver.

The optical transmission system according to the next invention is the above-mentioned invention, further comprising at least one optical amplification repeater for optically amplifying the optical signal transmitted from the optical transmitter, wherein At least one variable dispersion equalizer described above is provided on the optical transmission line.

According to the present invention, by disposing the variable dispersion equalizer in the optical amplifier repeater or on the optical transmission line,
A dispersion equalization process is performed at an arbitrary position in the optical transmission system.

An optical receiver according to the next invention is characterized in that the optical receiver for receiving an optical signal includes at least one variable dispersion equalizer as described above.

According to the present invention, the reception characteristics of the optical receiver are optimized by arranging the variable dispersion equalizer in the optical receiver.

[0038] The dispersion control method according to the present invention is a dispersion control method for controlling chromatic dispersion of an optical transmission line for transmitting an optical signal, the method comprising a waveform shaping step of waveform-shaping the optical signal transmitted to the optical transmission line. Extracting a clock component of a specific frequency from the waveform-shaped optical signal; and controlling the chromatic dispersion of the transmission path so that the magnitude of the extracted clock component becomes a maximum value or a minimum value. And a step.

According to the present invention, after shaping the waveform of the optical signal transmitted to the optical transmission line, a clock component of a specific frequency is extracted from the optical signal, and the magnitude of the clock component becomes a maximum value or a minimum value. By controlling the chromatic dispersion of the transmission line as described above, the degree of fluctuation with respect to the residual dispersion value of the clock component is adjusted.

A dispersion control method according to the present invention is a dispersion control method for controlling chromatic dispersion of an optical transmission line for transmitting an optical signal, wherein the optical signal of a predetermined wavelength band is included in the optical signal transmitted to the optical transmission line. Passing, a step of extracting a clock component of a specific frequency from the passed optical signal, and a wavelength of the transmission path such that the magnitude of the extracted clock component becomes a maximum value or a minimum value. And a control step of controlling dispersion.

According to the present invention, after the optical signal transmitted to the optical transmission line is band-limited to a specific frequency, a clock component is extracted from the optical signal, and the magnitude of the clock component becomes a maximum value or a minimum value. By controlling the chromatic dispersion of the transmission line as described above, the degree of fluctuation with respect to the residual dispersion value of the clock component is adjusted.

The dispersion control method according to the next invention is the above-mentioned invention, wherein the dispersion control method further includes a detection step of detecting a signal level of an optical signal transmitted to the optical transmission line. Taking the ratio between the magnitude of the extracted clock component and the signal level of the detected optical signal, and controlling the chromatic dispersion of the transmission line so that the ratio becomes one of a maximum value, a minimum value, and a predetermined value. It is characterized by doing.

According to the present invention, the transmission is performed such that the ratio between the respective levels of the clock component and the optical signal becomes a maximum value or a minimum value, or a predetermined value when the ratio deviates from the maximum value or the minimum value. Control the chromatic dispersion of the path.

The dispersion control method according to the present invention is the dispersion control method according to the above-mentioned invention, wherein the dispersion control method includes a step of imparting chromatic dispersion of a predetermined characteristic to an input optical signal before or after the execution of the passing step. Is further included.

According to the present invention, the wavelength dispersion having a predetermined characteristic is given to the optical signal, and the optimum control point of the dispersion is equivalently shifted.

A dispersion control method according to the next invention is characterized in that, in the above invention, in the passing step, at least one of a center wavelength and a pass bandwidth of the passing optical signal is variably set to a desired value. And

According to the present invention, the center wavelength and / or the pass bandwidth of the passing optical signal are variably set.

A dispersion control method according to the present invention is a dispersion control method for controlling dispersion equalization at any time according to a change in chromatic dispersion of an optical transmission line for transmitting a wavelength-multiplexed optical signal. Demultiplexing the split optical signal into optical signals for each wavelength band, and dispersing the split optical signal for each wavelength band by at least one of the control methods described above. Controlling the equalization.

According to the present invention, the dispersion equalization process is performed on the optical signal demultiplexed for each wavelength band.

A dispersion control method according to the next invention is characterized in that, in the above invention, the method further comprises an optical wavelength multiplexing step of multiplexing the optical signals of the respective wavelength bands on which the dispersion equalization control has been performed. .

According to the present invention, after the dispersion equalization processing for each wavelength band, the optical signals for each wavelength band are multiplexed again, so that the dispersion equalization processing for each wavelength band can be performed even in the middle of the optical transmission line. I do.

[0052]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a variable dispersion equalizer, an optical transmission system using the same, and a dispersion control method according to the present invention will be described below in detail with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 1 of the present invention. 1, the variable dispersion equalizer 10 further includes an optical filter circuit 17 in the variable dispersion equalizer shown in FIG. The optical filter circuit 17 includes the optical fiber transmission line 1
It is used for limiting a wavelength band that allows an optical signal in a predetermined wavelength band to pass through among the optical signals transmitted to the optical disk 1. For example, an optical bandpass filter such as a fiber grating type filter or a dielectric multilayer filter can be used. Other configurations are the same as those of the variable dispersion equalizer shown in FIG. Hereinafter, the same components are denoted by the same reference numerals.

In FIG. 1, a tunable dispersion equalizer 12 connected to an optical fiber transmission line 11 gives the optical signal a wavelength characteristic opposite to that of the chromatic dispersion received by the optical fiber transmission line. This equalizes the waveform distortion received by the optical signal due to the chromatic dispersion of the optical fiber transmission line 11. The chromatic dispersion created by the tunable dispersion equalizer 12 can be arbitrarily set in accordance with the chromatic dispersion of the optical fiber transmission line 11. Such a tunable dispersion equalizer 12 includes, for example, a thin film in a fiber grating. With a heater attached (for example, see Japanese Patent Application Laid-Open No. 2000-137)
197) can be used. Thereby, even when the chromatic dispersion of the optical fiber transmission line 11 changes due to, for example, a change in environmental temperature, the chromatic dispersion characteristic created by the tunable dispersion equalizer 12 is arbitrarily changed as needed to perform optimal control. Optimum distributed equalization processing can be performed.

The optical signal output from the tunable dispersion equalizer 12 is split by the optical tap 13 and a part is input to the optical filter circuit 17. The split optical signal is subjected to band limitation by an optical filter circuit 17 and then converted into an electric signal by an opto-electrical conversion circuit 14. Further, the clock extraction filter circuit 15 generates a clock component having a frequency corresponding to the bit rate of the optical signal. Is extracted. The extracted clock component is input to the control circuit 16 and the control circuit 16
Controls the variable dispersion equalizer 12 according to the magnitude of the extracted clock component obtained by a detecting means such as a peak detector (not shown). As a simple method of controlling such a variable dispersion equalizer, there is a method of monitoring a change in a frequency component corresponding to a modulation bit rate of an optical signal.

FIG. 2 shows an RZ (return-to-to-turn) in which the pulse width is about half of the signal bit rate as described above.
(Zero) An example is shown in which the change in the magnitude of the extracted clock component with respect to the residual dispersion value in the case of an optical signal is calculated. Here, the signal bit rate is 40 Gbit / s, and the solid line in FIG. 2 represents the change in the magnitude of the clock component with respect to the residual dispersion value when the optical filter circuit 17 is not provided in the variable dispersion equalizer 10. The one-dot chain line indicates that the optical filter circuit 17 has a 3 dB pass band of 0.3 nm and 20 dB.
When having a trapezoidal pass characteristic with a pass band of 0.5 nm,
The dotted line indicates that the optical filter circuit 17 has a 3 dB pass band of 0.4 n.
m, a change in the magnitude of the clock component with respect to the residual dispersion value when the trapezoidal pass characteristic has a 20 dB pass band of 0.6 nm. Also, the magnitude of the clock component in FIG. 2 is normalized when the residual dispersion value is zero.

In FIG. 2, first, the variable dispersion equalizer 10
Considering the case where the optical filter circuit 17 is not provided, when the residual dispersion value is zero as shown by the solid line in the figure, the magnitude of the extracted clock component shows the maximum value (point A in the figure).
By controlling the variable dispersion equalizer 12 by the control circuit 16 so that the extracted clock component has a maximum value, it is possible to perform optimal equalization such that the residual dispersion value after the dispersion equalization processing becomes zero. Here, when performing control such that the magnitude of the extracted clock component is larger, the extracted clock component is
When the residual dispersion value is larger than a value that becomes zero, that is, when the residual dispersion value is ± 50 ps / nm or more in the case of the solid line in the drawing, the convex including another peak other than the convex-shaped waveform having the local maximum as the peak. Since the shape of the waveform exists, it is impossible to determine the direction of control of the equalization amount to obtain the maximum value of the extracted clock component, and it is difficult to perform the distributed control only by observing the magnitude of the extracted clock component. Become.

Therefore, as shown in FIG. 1, if the wavelength band is limited by the optical filter circuit before the photoelectric conversion of the optical signal, the signal is transmitted as shown by a dotted line or a dashed line in FIG. Even when the optical signals are the same (an RZ optical signal having a signal bit rate of 40 Gbit / s), the degree of change in the magnitude of the extracted clock component with respect to the residual dispersion value changes. For this reason, since the waveform has only a convex shape having a peak at the local maximum value, even when only the extracted clock component is observed, optimal control can be performed even for a larger residual dispersion value than when no optical filter is provided. It becomes possible. In the case of the dotted line and the alternate long and short dash line compared to the case of the solid line, the degree of change of the extracted clock component with respect to the residual dispersion value is small, so that the degree of change of the extracted clock component is sharp and controllability by the control circuit is difficult. However, the degree of change of the extracted clock component that is optimal for control can be determined by adjusting the band limiting width in the optical filter circuit, so that controllability and design flexibility are greatly improved.

In the first embodiment, a case has been described in which the extracted clock component is controlled to have a maximum value for the RZ optical signal. However, the present invention is not limited to this.
When control is performed so that the extracted clock component takes a value of zero or a minimum value, for example, NRZ (Non Return-to-
(Zero) In the case of using an optical signal, by controlling the extracted clock component to have a minimum value when the residual dispersion value is zero, it is possible to obtain the same effect as having the optical filter circuit 17. Become.

In the first embodiment, the case where the variable dispersion equalizer is controlled based on the clock frequency component corresponding to the modulation bit rate of the optical signal has been described. However, the present invention is not limited to this. A similar effect can be obtained regardless of which frequency component is used, as long as the effect of the distortion of the optical waveform caused by chromatic dispersion is remarkable.

Further, by using an optical filter circuit whose center wavelength or pass band width is variable as the optical filter circuit, it becomes possible to obtain a variable dispersion equalizer having a higher degree of freedom in setting control conditions.

According to the first embodiment, the optical filter circuit is provided in the variable dispersion equalizer, and the band is limited.
The control circuit adjusts the degree of fluctuation of the magnitude of the extracted clock component with respect to the residual dispersion value, thereby providing excellent controllability and widening the control range in which effective dispersion control is possible.
Appropriate dispersion equalization according to the chromatic dispersion fluctuation of the transmission path can be performed.

Embodiment 2 Also, as shown in FIG.
It is also possible to provide a waveform shaping circuit 21 for changing the waveform of the optical signal itself instead of the optical filter circuit 17. The waveform shaping circuit 21 shapes a part of the optical signal of the optical fiber transmission line 11 branched by the optical tap 13 into, for example, a waveform indicated by a dotted line or a dashed line in FIG. I do. The optical signal whose waveform has been shaped is converted into an electric signal by the photoelectric conversion circuit 14, and a clock component having a frequency corresponding to the bit rate of the optical signal is extracted in the clock extraction filter circuit 15. The extracted clock component is input to the control circuit 16, and the control circuit 16 controls the variable dispersion equalizer 12 according to the magnitude of the obtained extracted clock component, as in the first embodiment.
Control.

According to the present embodiment, the waveform shaping circuit is provided in the variable dispersion equalizer to shape the waveform of the optical signal, and the control circuit controls the degree of fluctuation of the magnitude of the extracted clock component with respect to the residual dispersion value. As in the first embodiment, the control range is excellent and the effective dispersion control can be performed in a wide control range to perform appropriate dispersion equalization according to the chromatic dispersion variation of the transmission line. Can be.

Embodiment 3 FIG. 4 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 3 of the present invention. The third embodiment is a modification of the variable dispersion equalizer shown in the first embodiment. 4, the variable dispersion equalizer 10 further includes a dispersion imparting circuit 18 in the variable dispersion equalizer shown in FIG. The dispersion providing circuit 18
It is connected to the subsequent stage of the optical filter circuit 17 and adds a predetermined chromatic dispersion to an input optical signal. As such a dispersion providing circuit 18, for example, an optical device such as a dispersion compensating fiber or a chirped fiber grating can be used.

The variable dispersion equalizer 10 is provided with a dispersion providing circuit 18
Is provided, it is possible to shift the optimal control point of dispersion equivalently, for example, A1 in FIG.
When the variable dispersion equalizer 12 is operating at the point (A2, A3), the dispersion extraction circuit 18 imparts a dispersion of about 25 ps / nm, and the clock extraction level becomes B1 (B2, B3
3) By giving a dispersion of about 50 ps / nm, the clock extraction level becomes the point C1 (C2, C3), and by equivalently changing the operating point in the control circuit 16,
It is possible to select an operation point that is easier to control.

In the case of an optical signal at a very high speed, a slight chromatic dispersion value of the optical filter circuit also affects the change in the magnitude of the extracted clock component. For example, the optical filter circuit 17
In a general dielectric multilayer optical filter, the dispersion value in the pass wavelength band is about several tens ps / nm, and considering the change in the residual dispersion value and the magnitude of the extracted clock component shown in FIG. The dispersion value of this optical filter cannot be ignored. Even in such a case, the variance of the characteristic opposite to the characteristic of the optical filter circuit 17 is added to the dispersion imparting circuit 18.
In this case, the influence of the chromatic dispersion of the optical filter circuit 17 can be canceled.

In the third embodiment, the dispersion imparting circuit 18 is arranged to be connected to the subsequent stage of the optical filter circuit 17. However, the dispersion imparting circuit 18 may be arranged before the optical filter circuit 17. .

In the third embodiment, the optical filter circuit 17 and the dispersion imparting circuit 18 are provided as separate optical elements. However, the optical filter itself can have a dispersion imparting function. By adopting such a configuration, the number of components can be reduced, and a simpler configuration can be achieved. As the optical filter circuit having such a configuration, for example, an optical device such as a chirped fiber grating can be used.

According to the third embodiment, a dispersion imparting circuit is provided to add a predetermined chromatic dispersion to an input optical signal to shift the optimum control point of dispersion equivalently, thereby obtaining the optical signal shown in FIG. A variable dispersion equalizer having a greater degree of freedom in setting control conditions than in the first embodiment can be realized.

Embodiment 4 FIG. 5 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 4 of the present invention. The fourth embodiment is a modification of the variable dispersion equalizer shown in the first embodiment. 5, the variable dispersion equalizer 10 further includes an optical tap 19 and an optical power monitor circuit 20 in the variable dispersion equalizer 10 shown in FIG. The optical tap 19 is connected to a stage preceding the optical filter circuit 17, branches a part of the optical signal from the optical tap 13, and inputs the branched optical signal to the optical power monitor circuit 20. The optical power monitor circuit 20 detects the signal level (power) of the optical signal input to the optical filter circuit 17 and outputs the detection result to the control circuit 16. For example, the optical power monitor circuit 20 uses a photoelectric converter such as a photodetector. Be composed. The control circuit 16 controls the variable dispersion equalizer 12 according to the detection result of the optical power monitor circuit 20 and the magnitude of the clock component extracted from the clock extraction filter circuit 15.

In the fourth embodiment, the optical filter circuit 1
7, the change in the magnitude of the clock component extracted by the clock extraction filter circuit 15 is a change in the residual dispersion value or a change in the optical signal power itself. Is determined. Therefore, the control circuit 16 determines, for example, the ratio between the optical signal power and the magnitude of the extracted clock component, and sets the variable dispersion equalizer 1 such that the ratio takes a maximum value, a minimum value, or an arbitrary constant value.
By controlling 2, the optimum dispersion equalization processing taking into account the fluctuation of the optical signal power itself is executed.

When a device whose passing amplitude characteristic changes when the dispersion is varied, for example, a device using a fiber grating, is used as the variable dispersion equalizer 12, the operating conditions of the variable dispersion equalizer 12 are changed. The optical signal power input to the optical filter circuit 17 also fluctuates due to a change (for example, a change in external temperature, stress, or the like). Even in such a case, by detecting the input optical signal power to the optical filter circuit 17, it is possible to control the variable dispersion equalizer 12 in consideration of the fluctuation of the optical signal power itself.

In the fourth embodiment, the input optical signal power to the optical filter circuit 17 is detected, but the optical power monitor circuit 20 is connected to the optical fiber transmission line 11 downstream of the variable dispersion equalizer 12. Then, the optical signal power here may be detected. Further, if the fluctuation of the optical signal power caused by passing through the variable dispersion equalizer 12 can be ignored,
The optical power monitor circuit 20 may be connected to the optical fiber transmission line 11 in front of the variable dispersion equalizer 12 to detect the optical signal power here. Further, it is also possible to use a plurality of optical power monitor circuits at each of the above locations to accurately detect fluctuations in the optical signal power itself.

According to the fourth embodiment, the signal power of the optical signal fetched by branching is detected, and the variable dispersion equalizer is controlled in accordance with the magnitude of the extracted clock component and the power of the optical signal, whereby the identification is performed. Controlling the variable dispersion equalizer stably even in a transmission system where the optical signal power itself fluctuates by adopting a configuration that performs control that includes both the fluctuation of the frequency clock component and the fluctuation of the optical signal power itself. It can be performed.

Embodiment 5 FIG. 6 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 5 of the present invention. The fifth embodiment is an application example of the variable dispersion equalizer shown in the first to fourth embodiments. In FIG. 6, variable dispersion equalizers 10a to 10n represent the variable dispersion equalizers described in the first to fourth embodiments, and the variable dispersion equalizer 30 according to the fifth embodiment includes a variable dispersion equalizer 30a. Device 10a-1
0n, optical fiber transmission lines 31, 32a to 32n, and an optical wavelength demultiplexer 33. Optical wavelength demultiplexer 3
For example, AWG (Arrayed Wave)
A device having periodicity and capable of collectively demultiplexing multiple wavelengths, such as a guide grating or an interleaver, can be used.

In FIG. 6, the wavelength multiplexed light is transmitted through the optical fiber transmission line 31 and is input to the optical wavelength demultiplexer 33. The optical wavelength demultiplexer 33 converts the input wavelength multiplexed light into light for each wavelength. The signal is split into signals and input to the respective variable dispersion equalizers 10a to 10n via the optical fiber transmission lines 32a to 32n. The variable dispersion equalizers 10a to 10n perform the optimum dispersion equalization processing on the input optical signals of the respective wavelengths as described in the first to fourth embodiments, and convert the equalized optical signals. Output.

According to the fifth embodiment, the dispersion equalization process is performed after the wavelength division multiplexed light is demultiplexed into the optical signal of each wavelength. Therefore, the optimum dispersion equalization for each wavelength of the wavelength division multiplexed light is performed. Processing can be performed.

Embodiment 6 FIG. FIG. 7 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 6 of the present invention. The sixth embodiment is an application example of the variable dispersion equalizer shown in the first to fourth embodiments. 7, the variable dispersion equalizer 30 includes an optical wavelength multiplexer 34 connected to the variable dispersion equalizer shown in FIG. 6 via the optical fiber transmission lines 32a to 32n, and an optical wavelength multiplexer. An optical fiber transmission line 35 connected to the optical fiber 34 is further provided. As the optical wavelength demultiplexer 33, for example, AWG (Arrayed W)
It is possible to use a device that has periodicity and is capable of collectively demultiplexing multiple wavelengths, such as aveguide grating and interleaver.

In FIG. 7, the variable dispersion equalizers 10a to 10a
Similarly to the configuration described in the sixth embodiment, 10n corresponds to the optical signal demultiplexed for each wavelength by the optical wavelength demultiplexer 33 and input, as described in the first to fourth embodiments. An optimal dispersion equalization process is performed, and the equalized optical signal is output to the optical wavelength multiplexer 34. The optical wavelength multiplexer 34 combines the input optical signals for each wavelength again into one. Waves are output to the optical fiber transmission line 35.

According to the sixth embodiment, after the wavelength division multiplexed light is demultiplexed into optical signals for each wavelength, dispersion equalization processing is performed.
Since the optical signal of each wavelength is multiplexed and output again, the optimum dispersion equalization processing for each wavelength can be performed even in the middle of the optical fiber transmission line through which the wavelength multiplexed light is transmitted.

Seventh Embodiment FIG. 8 is a configuration diagram showing a configuration of an optical transmission system having a variable dispersion equalizer according to a seventh embodiment of the present invention. The seventh embodiment is an example in which the variable dispersion equalizer shown in the first to fifth embodiments is applied to an optical transmission system that performs optical amplification relay. 8, an optical transmission system 40 includes an optical transmitter 41 for transmitting an optical signal of a predetermined wavelength, optical fiber transmission lines 42a to 42c, optical amplification repeaters 43a and 43b,
The optical transmitter 41 via the variable dispersion equalizer 10 (or 30), the optical fiber transmission lines 42a to 42c, the optical amplifier repeaters 43a and 43b, and the variable dispersion equalizer 10 (30) in that order.
And an optical receiver 44 connected thereto.

The variable dispersion equalizer 10 (30) is the variable dispersion equalizer 10 or 30 described in the first to fifth embodiments. That is, when the optical transmission system 40 transmits a single-wavelength optical signal, the optimal dispersion equalization process is performed using the variable dispersion equalizer 10 described in Embodiments 1 to 4,
When the optical transmission system 40 transmits wavelength-division multiplexed light,
By performing optimal dispersion equalization processing for each wavelength using the variable dispersion equalizer 30 described in the fifth embodiment, the optical transmission performance of the system can be further improved.

The optical signal transmitted by the optical transmitter 41 is optically amplified by each of the optical amplifying repeaters 43a and 43b, and then the variable dispersion equalizer 10 (30) arranged near the optical receiver 44.
Is input to The tunable dispersion equalizer 10 (30) performs an optimum chromatic dispersion equalization process at the receiving end, and outputs the equalized optical signal to the optical receiver 44. The optical receiver 44 An optical signal that has undergone equalization processing can be received.

According to the seventh embodiment, by arranging the variable dispersion equalizer 10 (30) immediately before the optical receiver 44, the optimum chromatic dispersion equalization processing can be performed at the receiving end. .

In the seventh embodiment, the variable dispersion equalizer 10 (30) and the optical receiver 44 have different configurations. However, the configuration of the variable dispersion equalizer 10 (30) is different from that of the optical receiver 4.
4 may be included. Further, when the variable dispersion equalizer 10 (30) is connected to the receiving end and used, the signal receiving characteristics themselves (for example, error rate and eye opening) obtained from the optical receiver 44, and the optical receiver itself It may be used for controlling a variable dispersion equalizer by using the clock extraction function of.

In the seventh embodiment, the optical receiver 4
The variable dispersion equalizer 10 (30) is arranged in the vicinity of the variable dispersion equalizer 10 according to the sixth embodiment.
By arranging (30) in the middle of an optical transmission line or in an optical amplification repeater, it is possible to perform optimal chromatic dispersion equalization processing for each wavelength on wavelength multiplexed light in the middle of the transmission line.

[0088]

As described above, according to the present invention, when the control means performs chromatic dispersion control of the variable dispersion equalization means using the magnitude of the clock component extracted by the electric filter means, Since the optical signal transmitted to the path is branched and taken in, and the waveform of the optical signal is shaped by the waveform shaping means, a clock component of a specific frequency is extracted from the optical signal by the electric filter means. There is an effect that the controllable range of control can be widened and the dispersion equalization can be controlled under optimum conditions even for a large residual dispersion value.

According to the next invention, when the control means performs chromatic dispersion control of the variable dispersion equalization means using the magnitude of the clock component extracted by the electric filter means, the optical signal transmitted to the transmission line is controlled. The optical filter means extracts a clock component of a specific frequency from the optical signal after passing the optical signal of a predetermined wavelength band out of the optical signal by the optical filter means, thereby providing excellent controllability and dispersion control. Thus, there is an effect that the dispersion equalization can be controlled under optimum conditions even for a large residual dispersion value.

According to the next invention, the dispersion imparting means is connected before or after the optical filter means to impart chromatic dispersion having a predetermined characteristic to the input optical signal, so that the operation control point of the variable dispersion equalizing means can be set. This has the effect of being arbitrarily configurable.

According to the next invention, since the optical filter means itself has a dispersion imparting function of imparting a predetermined wavelength dispersion to the input optical signal, the operation control point of the variable dispersion equalizing means can be easily reduced with a smaller number of parts. Can be set arbitrarily.

According to the next invention, a detecting means is connected to the optical transmission line or the preceding stage of the waveform shaping means or the optical filter means, and the signal level of the branched optical signal is detected by the detecting means and inputted. The control means controls the variable dispersion equalization means according to the magnitude of the clock component and the signal level of the optical signal, so that the control includes both the variation of the clock component of a specific frequency and the variation of the signal level of the optical signal. Therefore, even when the signal level itself of the optical signal fluctuates, there is an effect that the control by the clock component of the specific frequency can be stably performed.

According to the next invention, since the center wavelength and / or the pass band width of the optical filter means are variably set, the degree of freedom in setting the control conditions is improved.

According to the next invention, the control means controls the variable dispersion equalization means so that the clock component output from the electric filter means has a maximum value or a minimum value.
There is an effect that stable control can be performed even when the signal level of the optical signal fluctuates.

According to the next invention, the variable dispersion equalizing means is controlled such that the ratio between the level of the clock component and the level of the optical signal becomes one of the maximum value, the minimum value, and the predetermined value. Thus, there is an effect that stable control can be performed even on an optical signal that becomes an optimum condition when the output from the optical amplifier deviates from the maximum value or the minimum value.

According to the next invention, there is provided an optical wavelength demultiplexing means and a variable dispersion equalizer connected to the optical wavelength demultiplexing means, and a dispersion is provided for each wavelength band demultiplexed by the optical wavelength demultiplexing means. Since the equalization processing is performed, an effect is obtained that the optimum dispersion equalization processing can be performed for each wavelength band.

According to the next invention, there is provided an optical wavelength demultiplexing means, a variable dispersion equalizer, and an optical wavelength multiplexing means. Since each optical signal is multiplexed again, it is possible to perform an optimal dispersion equalization process for each wavelength band even in the middle of the optical transmission line.

According to the next invention, by arranging the variable dispersion equalizer in or near the optical receiver, it is possible to obtain the effect that the optimum receiving characteristics of the optical receiver can be obtained.

According to the next invention, since the variable dispersion equalizer is disposed in the optical amplification repeater or on the optical transmission line,
There is an effect that the optimum dispersion equalization processing can be performed at an arbitrary place in the optical transmission system.

According to the next invention, by arranging the variable dispersion equalizer in the optical receiver, it is possible to obtain an optimum receiving characteristic of the optical receiver.

According to the next invention, after the optical signal transmitted to the optical transmission line is waveform-shaped in the waveform shaping step, a clock component of a specific frequency is extracted from the optical signal in the extraction step, and further, the clock component is extracted in the control step. By controlling the chromatic dispersion of the transmission line so that the magnitude of the clock signal becomes a maximum value or a minimum value, the degree of fluctuation with respect to the residual dispersion value of the clock component is adjusted. The effect is obtained that the range can be widened and the dispersion equalization can be controlled under optimum conditions even for a large residual dispersion value.

According to the next invention, after the optical signal transmitted to the optical transmission line in the passing step is band-limited to a specific frequency,
In the extraction step, a clock component is extracted from the optical signal, and further in the control step, the chromatic dispersion of the transmission line is controlled so that the magnitude of the clock component becomes a maximum value or a minimum value. Since the degree of fluctuation is adjusted, the controllability is excellent, the control range in which the dispersion control can be performed is widened, and the dispersion equalization can be controlled under optimal conditions even for a large residual dispersion value. .

According to the next invention, the ratio between the level of the clock component extracted in the extraction step and the level of the optical signal detected in the detection step becomes a maximum value or a minimum value, or the maximum value or the minimum value. Since the chromatic dispersion of the transmission line is controlled by the control step so as to be a predetermined value when deviated from the above, even when the signal level of the optical signal itself fluctuates, it is possible to stably control the clock component of the specific frequency. This has the effect that it can be performed.

According to the next invention, the chromatic dispersion having a predetermined characteristic is given to the optical signal in the dispersion giving step, and the optimum control point of the dispersion is equivalently shifted, so that the optimum control point can be set arbitrarily.

According to the next invention, since the center wavelength and / or the pass band width of the optical signal are variably set in the passing step, the effect of increasing the freedom of setting the control conditions is obtained.

According to the next invention, the dispersion equalization processing is performed on the optical signal demultiplexed for each wavelength band in the optical wavelength demultiplexing step, so that the optimum dispersion equalization is performed at an arbitrary position in the optical transmission system. There is an effect that processing can be performed.

According to the present invention, dispersion equalization processing for each wavelength band is performed on the optical signal demultiplexed in the optical wavelength demultiplexing step, and the optical signal for each wavelength band is again converted in the optical wavelength multiplexing step. Since the multiplexing is performed, an effect is obtained that the optimum dispersion equalization processing for each wavelength can be performed in the middle of the optical transmission line.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a variable dispersion equalizer according to Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating an example of a change in the magnitude of an extracted clock component with respect to a residual variance value.

FIG. 3 is a block diagram illustrating a configuration of a variable dispersion equalizer according to Embodiment 2 of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a variable dispersion equalizer according to Embodiment 3 of the present invention.

FIG. 5 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 4 of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a variable dispersion equalizer according to Embodiment 5 of the present invention.

FIG. 7 is a block diagram showing a configuration of a variable dispersion equalization apparatus according to Embodiment 6 of the present invention.

FIG. 8 is a configuration diagram showing a configuration of an optical transmission system having a variable dispersion equalization apparatus according to Embodiment 7 of the present invention.

FIG. 9 is a block diagram illustrating a configuration of a conventional variable dispersion equalizer that performs dispersion control.

[Explanation of symbols]

10, 10a to 10n, 30 Variable dispersion equalizer, 1
1, 31, 32a to 32n, 35, 42a to 42c Optical fiber transmission line, 12 Variable dispersion equalizer, 13, 19
Optical tap, 14 photoelectric conversion circuit, 15 clock extraction filter circuit, 16 control circuit, 17 optical filter circuit, 18 dispersion imparting circuit, 20 optical power monitor circuit,
21 Waveform shaping circuit, 33 Optical wavelength demultiplexer, 34 Optical wavelength multiplexer, 40 Optical transmission system, 41 Optical transmitter, 4
3a, 43b Optical amplification repeater, 44 optical receiver.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/00 H04B 9/00 E 10/18 B H04J 14/00 14/02 (72) Inventor Yukio Kobayashi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Minoru Hashimoto 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Mitsubishi Electric Corporation 2H048 GA01 GA04 GA13 GA62 2H049 AA02 AA33 AA45 AA59 AA62 2H079 AA06 AA13 BA01 CA04 EA09 FA01 HA11 KA07 KA11 KA19 5K002 AA03 AA06 BA04 BA05 CA01 DA02 DA05 FA01

Claims (20)

[Claims] 1. A variable dispersion equalizer having variable dispersion equalization means for performing dispersion equalization at any time according to a change in chromatic dispersion of an optical transmission line for transmitting an optical signal, wherein the light transmitted to the optical transmission line is A waveform shaping unit for shaping a signal; an electric filter unit for outputting a clock component of a specific frequency from the waveform-shaped optical signal; and the variable dispersion equalizing unit according to the magnitude of the output clock component. A variable dispersion equalizer, comprising: control means for controlling. 2. A variable dispersion equalizer having variable dispersion equalization means for performing dispersion equalization at any time according to a change in chromatic dispersion of an optical transmission line for transmitting an optical signal, comprising: Optical filter means for passing an optical signal of a predetermined wavelength band out of signals, electric filter means for outputting a clock component of a specific frequency from the passed optical signal, and said filter element according to the magnitude of the output clock component. A variable dispersion equalizer, comprising: control means for controlling variable dispersion equalization means. 3. The tunable dispersion equalizer further includes a dispersion providing unit connected to a stage before or after the optical filter unit and providing wavelength dispersion having predetermined characteristics to the input optical signal. The variable dispersion equalizer according to claim 2. 4. The variable dispersion equalizer according to claim 2, wherein said optical filter means performs dispersion imparting for imparting chromatic dispersion having predetermined characteristics to said input optical signal. 5. The variable dispersion equalizer is connected to the optical transmission line or a stage preceding the waveform shaping unit or the optical filter unit, and detects a signal level of an optical signal transmitted to the optical transmission line. 2. The apparatus according to claim 1, further comprising a control unit, wherein the control unit controls the variable dispersion equalization unit according to a magnitude of the output clock component and a signal level of the detected optical signal.
The variable dispersion equalizer according to any one of Items 1 to 4. 6. The variable dispersion or the like according to claim 2, wherein said optical filter means variably sets at least one of a center wavelength and a pass bandwidth to a desired value. Device. 7. The variable dispersion equalization unit according to claim 1, wherein the control unit controls the variable dispersion equalization unit such that the magnitude of the output clock component becomes a maximum value or a minimum value.
7. The variable dispersion equalizer according to any one of items 6 to 6. 8. The control means calculates a ratio between the magnitude of the output clock component and the signal level of the detected optical signal, and sets the ratio to one of a maximum value, a minimum value, and a predetermined value. The variable dispersion equalizer according to claim 5, wherein the variable dispersion equalizer is controlled. 9. A variable dispersion equalizer having variable dispersion equalization means for performing dispersion equalization at any time in accordance with a change in chromatic dispersion of an optical transmission line for transmitting a wavelength-multiplexed optical signal, An optical wavelength demultiplexing unit that demultiplexes an optical signal into an optical signal for each wavelength band, and at least one of the at least one that is connected to the optical wavelength demultiplexing unit and performs dispersion equalization for each of the wavelength bands. A variable dispersion equalizer, comprising: a variable dispersion equalizer according to claim 8. 10. The variable dispersion equalizer further includes an optical wavelength multiplexing unit that multiplexes optical signals in a plurality of wavelength bands, and is output from each of the variable dispersion equalizers according to claim 1 to 8. The variable dispersion equalizer according to claim 9, wherein the optical signals are multiplexed. 11. An optical transmission system in which an optical signal transmitted from at least one optical transmitter is received by an optical receiver via an optical transmission path, wherein the optical signal is in the optical receiver or in the vicinity of the optical receiver. ~ 1
An optical transmission system comprising at least one variable dispersion equalizer. 12. The optical transmission system further comprises at least one optical amplification repeater for optically amplifying an optical signal transmitted from the optical transmitter, wherein the optical transmission repeater is in the optical amplification repeater or on the optical transmission line. An optical transmission system comprising at least one of the variable dispersion equalizers 1 to 10. 13. An optical receiver for receiving an optical signal, comprising: at least one variable dispersion equalizer according to claim 1. 14. A dispersion control method for controlling chromatic dispersion of an optical transmission line for transmitting an optical signal, wherein: a waveform shaping step of shaping the waveform of the optical signal transmitted to the optical transmission line; An extraction step of extracting a clock component of a specific frequency from the control signal, and a control step of controlling chromatic dispersion of the transmission line so that the magnitude of the extracted clock component becomes a maximum value or a minimum value. Distributed control method. 15. A dispersion control method for controlling chromatic dispersion of an optical transmission line for transmitting an optical signal, wherein: a passing step of passing an optical signal of a predetermined wavelength band among the optical signals transmitted to the optical transmission line; An extraction step of extracting a clock component of a specific frequency from the passed optical signal; anda control step of controlling chromatic dispersion of the transmission line such that the magnitude of the extracted clock component is a local maximum or a local minimum, A distributed control method comprising: 16. The dispersion control method further includes a detecting step of detecting a signal level of an optical signal transmitted to the optical transmission line, wherein in the controlling step, the magnitude of the extracted clock component and the detected level are detected. The chromatic dispersion of the transmission line is controlled such that a ratio of the signal levels of the optical signals obtained is obtained, and the ratio becomes any one of a maximum value, a minimum value, and a predetermined value. Distributed control method. 17. The dispersion control method according to claim 15, further comprising a dispersion imparting step of imparting chromatic dispersion having a predetermined characteristic to an input optical signal before or after execution of the passing step. 3. The distributed control method according to 1. 18. The method according to claim 15, wherein in the passing step, at least one of a center wavelength and a pass bandwidth of the passing optical signal is variably set to a desired value.
The distributed control method according to any one of the above. 19. A dispersion control method for controlling dispersion equalization at any time according to a change in chromatic dispersion of an optical transmission line for transmitting a wavelength-multiplexed optical signal, wherein the wavelength-multiplexed optical signal is transmitted to each wavelength band. A demultiplexing step of demultiplexing the demultiplexed optical signal into each of the wavelength bands;
Controlling distributed equalization by at least one of the distributed control methods of 4 to 18. A distributed control method, comprising: 20. The dispersion control method according to claim 19, wherein the dispersion control method further includes an optical wavelength multiplexing step of multiplexing the optical signals of each wavelength band on which the dispersion equalization control has been performed. Control method.