JP3306700B2 - Optical amplifier and wavelength division multiplexing optical transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for directly amplifying an optical signal.
Multiplexed optical amplifiers and optical signals of different wavelengths
The present invention relates to a wavelength division multiplexing optical transmission system for transmitting. 2. Description of the Related Art An optical fiber amplifier that directly amplifies an optical signal using an optical fiber doped with a rare earth such as erbium (Er) is known. There is also known a wavelength division multiplexing optical transmission system for multiplexing and transmitting optical signals of a plurality of wavelengths in order to perform large-capacity transmission. In such a wavelength division multiplexing optical transmission system,
When a rare-earth doped optical fiber amplifier is applied, it is necessary to solve problems such as a problem that the wavelength of an optical signal is not a single wavelength and a problem that an optical power input varies depending on the number of channels (the number of wavelengths). Becomes

[0002]

2. Description of the Related Art An optical amplifying device applied to a transmitting device and a relay device in a wavelength division multiplexing optical transmission system generally uses an optical fiber amplifier doped with a rare earth element, and combines optical signals of a plurality of wavelengths. The wavelength-division multiplexed optical signal and the pumping light from the pumping laser diode are input to an optical fiber amplifier, and a part of the output light is detected by a photodiode to control the pumping light power so that the amplified output light has a predetermined value. A configuration for performing constant optical gain control for controlling the amplification gain is known.

Also, an output wavelength multiplexed optical signal of the optical fiber amplifier is input to an optical variable attenuator, and the output light is detected to control the amount of optical attenuation, and an optical output in which the level of the wavelength multiplexed optical signal is within a predetermined value range. It is also known to provide constant control means.

[0004]

Since an optical fiber amplifier has wavelength dependence, the following problems arise when amplifying a wavelength-division multiplexed optical signal. . Changes in the number of channels. . Insertion loss of dispersion compensating optical fiber etc. . High output level light output constant control. However, these problems are not considered at all with respect to the above-mentioned conventional optical fiber amplifier.

That is, the number of channels increases or decreases depending on whether the number of channels corresponding to the wavelength is used or not used. In order to secure a desired S / N on the receiving side of the wavelength multiplexed optical signal,
A predetermined amplified light output power P is required corresponding to the wavelength. For example, if the number of channels is n, the total optical output Pc of the optical fiber amplifier is controlled to be n × P. In this case, if the number of channels n fluctuates by + α or −α, that is, if the number of channels increases or decreases, the total optical output is
The control is performed so as to be (n ± α) P. In this switching process, a change in the optical power corresponding to the wavelength occurs, and thus there is a problem that nonlinear deterioration and S / N deterioration occur.

Another dispersion compensating optical fiber is, for example,
In a long-distance, large-capacity optical transmission system, a repeater is provided together with an optical fiber amplifier to compensate for dispersion of a transmission optical fiber. In this case, there is a problem that there is an insertion loss of the dispersion compensating optical fiber, and the variation of the loss becomes a variation of the optical output level of the repeater including the optical fiber amplifier.

Further, the constant control of the light output at the high output level is as follows.
Even if the amplified light output level by the optical fiber amplifier exceeds a predetermined range, the optical output is kept constant by the optical variable attenuator, but the attenuation by the optical variable attenuator is considered in advance. It is necessary to amplify extra by an optical fiber amplifier. In this case, it is necessary to control the output power of the pumping laser diode for performing the optical gain constant control substantially exponentially with respect to the level fluctuation of the input optical signal. For this purpose, it is necessary to provide a relatively large-capacity pumping laser diode so as to be able to cope with exponential function control. Since a large-capacity laser diode is expensive, there is an economic problem. The present invention provides a wavelength multiplexed optical signal even when the number of channels changes.
Optical signal by suppressing the deterioration of the nonlinear characteristic and S / N of the signal
The purpose of the present invention is to amplify a signal and transmit the amplified wavelength-division multiplexed optical signal .

[0008]

An optical amplifying apparatus according to the present invention comprises:
(1) different have a plurality of channels corresponding to the optical signal of the wavelength, the number capable of changing wavelength-multiplexed optical signal of the channel
First optical amplification means for inputting and amplifying and outputting ;
First control for controlling the gain of the optical amplification means to be constant
Means and a variable light for attenuating the amplified output of the first optical amplifying means
An attenuator and a second optical amplifier for amplifying the output of the variable attenuator
The width means and the gain of the second optical amplifying means are constant.
Control means for controlling the number of channels before and after changing the number of channels.
The width of the output optical signal becomes a certain level corresponding to the number of channels.
Control the attenuation of the variable optical attenuator so that
When changing the number, keep the light transmittance of the variable optical attenuator constant.
And third control means for performing the following control.

[0009] (2) Multiple signals corresponding to optical signals of different wavelengths
Multiplexed wavelength-multiplexed optical signal is input and amplified
Optical amplifying means for outputting, and when the number of channels is changed,
The level of the wavelength multiplexed optical signal input to the amplification means
Level of WDM optical signal amplified and output from optical amplifier
The gain of the optical amplifying means based on
Gain control means to control and before and after changing the number of channels
Is the wavelength multiplexed optical signal amplified by the optical amplification means.
The optical amplifier is controlled so that the level becomes a predetermined value.
Level control means.

(3) Multiple signals corresponding to optical signals of different wavelengths
Multiplexed wavelength-multiplexed optical signal is input and amplified
Output optical amplification means, and
Attenuating means for attenuating a wavelength-multiplexed optical signal and the number of channels
At the time of change, the gain of the optical amplification means is controlled to be constant.
Gain control means and before and after changing the number of channels
The level of the wavelength multiplexed optical signal amplified by the optical amplifier
Is controlled to a predetermined value.
Level control means.

(4) Different wavelengths input from the input terminal
Multiplexed light with multiple channels corresponding to different optical signals
An optical amplification means for amplifying a signal and outputting from an output end;
The level of the wavelength multiplexed optical signal at the input end and the wavelength at the output end
Gain of the optical amplification means based on the level of the multiplexed optical signal
Gain control means for controlling so that is constant, said wavelength
Wavelength division multiplexing at the output end by optically attenuating the multiplexed optical signal
The amount of attenuation is controlled so that the level of the optical signal becomes a predetermined value.
Light attenuating means for controlling the gain when the number of channels is changed.
Means for controlling the gain of the optical amplification means to be constant.
And control means for controlling.

(5) The control means of the optical amplifier.
When the number of channels is changed, the amount of attenuation of the
There is a configuration for performing control so as to be constant.

A wavelength division multiplexing optical transmission system according to the present invention
(6) Multiple channels corresponding to optical signals of different wavelengths
Notify the wavelength multiplexed optical signal and the change in the number of channels
An optical device for transmitting a control optical signal to an optical transmission line;
Receiving the wavelength multiplexed optical signal transmitted through the transmission path
Optical amplification means for amplifying and transmitted through the optical transmission path
Receiving means for receiving and processing the control optical signal,
Channel notified by the control optical signal by means
Number change is detected, and the level of the received wavelength multiplexed optical signal is detected.
Multiplexed optical signal amplified and output by the optical amplifying means
The gain of the optical amplification means is constant based on the level of
An optical amplifying device including gain control means for controlling
It has.

(7) Multiple signals corresponding to optical signals of different wavelengths
Wavelength multiplexed optical signal having a number of channels and
Sends a control optical signal notifying the change completion to the optical transmission line
An optical device, and the wavelength multiplex transmitted through the optical transmission path.
Optical amplification means for amplifying the heavy optical signal,
Receiving means for receiving and transmitting the control optical signal transmitted by
Notified by the receiving means by the control light signal.
Detecting the completion notification of the change in the number of channels, and
Predetermines the level of the wavelength multiplexed optical signal amplified and output by the stage
Level control means for controlling the optical amplifying means so as to obtain a value.
And an optical amplifying device including a step.

[0015]

FIG . 1 is a block diagram of a wavelength division multiplexing optical transmission system.
FIG. 4 is an explanatory diagram showing a transmitting side and a receiving side of the wavelength division multiplexing optical transmission system
Outline with the side, for example, by one optical fiber
Four channels are multiplexed and transmitted. Transmission unit
20-1 to 20-4, the individual lights of wavelengths λ1 to λ4
Carrier is modulated by information and transmitted
Where wavelengths λ1 to λ4 represent individual channels. Different
The optical signals having different wavelengths are multiplexed by the optical multiplexer 22.
To become a wavelength multiplexed optical signal.

This wavelength multiplexed optical signal is transmitted to an optical fiber 24.
Is transmitted to the optical demultiplexer (optical demultiplexer) 26 on the receiving side . The optical multiplexing / demultiplexing device 26 separates a wavelength multiplexed optical signal into four optical signals having wavelengths λ1 to λ4.
You. The four separated optical signals are respectively received by the receiving units.
It is input to the knits 28-1 to 28-4.

In the above-mentioned optical fiber communication system, four carriers (wavelengths) are multiplexed. However, it is possible to multiplex more carriers.
By multiplexing a large number of channels (number of wavelengths),
Large amounts of data can be transmitted using optical fibers.

FIG. 2 is an explanatory diagram of an optical amplifying device of the wavelength division multiplexing optical transmission system .
(Here, referred to as “rare earth doped optical fiber amplifier section”) and the second portion 2000 (here,
"Electrically controlled optical device unit").

The first portion 1000 includes a rare earth doped optical fiber (EDF) 34 and an optical branching coupler 36 _1.
And 36 ₂ , optical isolators 38 ₁ and 38 ₂ , photodiodes (PD) 40 ₁ and 40 ₂ , optical wavelength multiplexing coupler 42, pump laser diode (LD) 44 and automatic optical gain control circuit (AGC) 46. .

The second part 2000 includes the optical branching coupler 36.
₃ , electrically controlled variable optical attenuator (ATT) 48,
It includes a photodiode (PD) 40 ₃ and an automatic level control circuit (ALC) 50. For example, the variable optical attenuator 48 is made of a magneto-optical material. However, various different types of variable optical attenuators can be used.

The wavelength division multiplexed optical signal is divided into optical branch couplers 36 ₁ ,
The light is sent to an optical fiber 34 doped with rare earth through an optical isolator 38 and an optical wavelength multiplexing coupler 42. The pumping light beam is sent from the pumping laser diode 44 to the rare earth-doped optical fiber 34 through the optical wavelength multiplexing coupler 42. Wavelength-multiplexed optical signal is amplified by an optical fiber 34 doped with rare earth, is input through the optical isolator 38 ₂ and optical branching coupler 36 ₂ to the variable optical attenuator 48.

The wavelength-multiplexed optical signal branched by optical branching coupler 36 ₁ is converted into an electrical signal by photodiode 40 ₁ is input to automatic optical gain control circuit 46. Portion of the amplified output WDM optical <br/> signal branched by optical branching coupler 36 ₂ is converted into an electric signal by the photodiode 40 ₂ is input to automatic optical gain control circuit 46. The pump laser diode 44 is controlled to maintain a ratio between the level of the input wavelength multiplexed optical signal and the level of the amplified wavelength multiplexed optical signal at a predetermined level.

More specifically, the optical gain control circuit 46 comprises:
By controlling the pump laser diode 44, the level of the photodiode 40 input wavelength-multiplexed optical signal <br/> signal converted to an electrical signal by _1, the amplified output WDM optical signal converted into an electric signal by the photodiode 40 ₂ maintaining the ratio between the level constant. In this way, the first portion 1000 maintains the wavelength dependence by controlling the optical gain to be constant.

The optical branching coupler 36 ₃ part of the branch output wavelength-multiplexed optical signal by the input to the automatic level control circuit 50. The variable optical attenuator 48 is controlled to maintain the wavelength multiplexed optical signal at a predetermined level.

More specifically, the automatic level control circuit 50
Controls the variable optical attenuator 48 using the electrical signals obtained from the wavelength-multiplexed optical signal by photodiode 40 _3, to maintain the output level of the wavelength-multiplexed optical signal at a constant level.

However, when the optical amplifying device shown in FIG. 2 is used, there is a problem as described above when changing the number of channels of a wavelength multiplexed optical signal. For example, in order to obtain a preferable S / N ratio of the receiver, it is generally necessary to set the optical output power of the amplifier to a predetermined value for each wavelength (channel). If total and N-channel, total light output Pc of the optical fiber amplifiers earth-doped for amplifying a wavelength-multiplexed optical signal <br/> No. is controlled to N × P. When the number of channels N is changed by + α or −α, the total optical power becomes (N ± α) P by the switching control. Since the optical power of each wavelength (channel) is changed by the switching control, the linearity is degraded or the signal-to-noise ratio (S /
N) will be degraded.

In FIG . 2, the light output by the first part 1000 is maintained at a constant level by the second part 2000. Thus, when the light output of the first portion 1000 exceeds a predetermined level, the second portion 2000 maintains the light output at a constant level. As a result, by using the variable optical attenuator 48, other means are required for amplification by the first portion 1000 , and the output power of the pump laser diode 44 to maintain a constant optical gain is It is necessary to control exponentially with respect to the level change of the input wavelength multiplexed optical signal. Therefore, it is necessary to prepare a pump laser diode 44 having a relatively large capacity.

FIG. 3 is an explanatory diagram of an optical amplifier according to an embodiment of the present invention. The optical amplification device includes a first part 1000 and a second part 2000. First part 100
0 is a rare earth doped optical fiber (EDF) 52
₁ , optical branching couplers 54 ₁ and 54 ₂ , optical isolators 55 ₁ and 55 ₂ , optical wavelength multiplexing coupler 56 ₁ , photodiodes (PD) 58 ₁ and 58 ₂ , pump laser diode (LD) 59 ₁ , and automatic optical gain control circuit (AGC) contains 60 _1. The first part 1000 amplifies the wavelength multiplexed optical signal while maintaining the wavelength dependency.

As an example, wavelength multiplexed optical signals are often
It is a 1.5 μm band. For amplification of an optical signal in the wavelength band is known an optical fiber doped with erbium, it is used as an optical fiber (EDF) 52 ₁ doped with rare earth. Furthermore, more optical fiber doped with erbium, in order to amplify the WDM optical signal of 1.5μm band, it is known to use pump light of 0.98μm or 1.48 .mu.m.
Therefore, pump laser diode (LD) 59 _1, an example
For example, an excitation light of 0.98 μm or 1.48 μm is output.
In other words, the configuration will be adopted.

[0030] The Figure 3 shows a forward pumping configuration, wherein the excitation light beams generated by the excitation laser diode 59 ₁ is transmitted through the optical fiber 52 ₁ doped with the rare earth in the wavelength-multiplexed optical signal in the same direction. However, a reverse excitation configuration can be used as well. In that case, the laser diode generates pump light beam, the excitation light beam is transmitted through the optical fiber 52 ₁ doped with the rare earth in the direction opposite to the wavelength-multiplexed optical signal. Further can be used as well bidirectional pumping configuration, in this case, two laser diode generates pump light beam, the excitation light beam is transmitted in both directions of the optical fiber 52 ₁ doped with rare earth . Thus, the invention is not limited to either form of directional excitation.

The second part 2000 includes an electrically controlled variable optical attenuator (ATT) 64 and an automatic level control circuit (A).
LC) 66, containing the optical branching coupler 54 ₃ and the photodiode (PD) 58 _3. The second part 2000 controls the total optical output of the wavelength multiplexed optical signal to a constant level without maintaining the wavelength dependency. More specifically, automatic level control circuit 66 by changing the amount of attenuation or light transmittance of the variable optical attenuator 64, the power of the wavelength-multiplexed optical signal output of the first portion 1000, corresponding to the number of channels Maintain a constant power level.

[0032] Also the number of channels in the wavelength-multiplexed optical signal is changed, the monitor signal processing circuit 70, the attenuation or light transmittance of the variable optical attenuator 64 is maintained constant. That is, the monitoring signal processing circuit 70 temporarily "freezes" (stops) the operation of the variable optical attenuator 64. After the number of channels is changed, the monitoring signal processing circuit 70 controls the attenuation or light transmittance of the variable optical attenuator 64, and maintains the power of the wavelength multiplexed optical signal at a constant level according to the new number of channels. Is done.

More specifically, wavelength multiplexing to an optical amplifier
Optical signal input is branched by optical branching coupler 68 _1.
Branched optical signal is provided to the photodiode (PD) 58 _4. Photodiode (PD) 58 ₄ converts the optical signal branched to an electrical signal and inputs the electrical signal to monitor signal processing circuit 70.

The control signal for notifying the change in the number of channels of the wavelength division multiplexing optical transmission system is superimposed on the wavelength division multiplexing optical signal by, for example, amplitude modulation processing, preferably as a low-speed signal. However, this control signal can be transmitted by other methods. The monitoring signal processing circuit 70 extracts and identifies this control signal. Then, the monitoring signal processing circuit 70
Controls the variable optical attenuator 64 or the automatic level control circuit 66 according to the extracted control signal. If the amplitude modulation being performed by demodulating the electrical signal obtained by the photodiode _{58. 4,} the control signal a relatively simple it can be extracted.

It is also possible to send a control signal to the monitoring signal processing circuit 70 using a dedicated control channel (wavelength). If using such a dedicated control channel, the light branching filter (not shown), the main light
A control signal multiplexed into a wavelength-multiplexed optical signal as a signal;
An optical signal with (as branched by optical branching coupler 68 ₁₎ is extracted. For example, the optical signal of the control channel extracted by the optical branching filter is
₄ and convert it to an electrical signal to
Can be extracted.

[0036] Thus, part of the wavelength-multiplexed optical signal branched by optical branching coupler 68 ₁ is added to the monitor signal processing circuit 70 is converted into an electrical signal by photodiode 58 _4. When the control signal notifying the change of the number of channels is extracted and identified in the monitoring signal processing circuit 70 ,
Monitor signal processing circuit 70, the operation of the variable optical attenuator 64 "frozen" causes (STOP).

To ensure that the power level of the attenuated wavelength-division multiplexed optical signal matches the number of channels, the monitor signal processing circuit 70 selects a set voltage (reference voltage). In response to this set voltage, the power level depends on the number of channels.
It is controlled to a certain level according to the situation .

From the monitoring signal processing circuit 70 to the variable optical attenuator 6
4 can be controlled in two ways. In one method, the variable optical attenuator 64 is directly controlled by the monitor signal processing circuit 70, as indicated by the control signal 69 in FIG. As another method, the variable optical attenuator 64 is indirectly controlled by the monitor signal processing circuit 70 via a control line 71 shown by a dotted line in FIG.

After the notification of the change in the number of channels, the number of channels is actually increased or decreased. In this example, the control signal indicating the completion of the change in the number of channels is transmitted while being superimposed on the wavelength multiplexed optical signal. The monitoring signal processing circuit 70 extracts this control signal. Alternatively, the control signal can be sent to the monitoring signal processing circuit 70 through a dedicated control channel (wavelength).
When the control signal is extracted and identified, the monitoring signal processing circuit 70 causes the variable optical attenuator 64 to perform a control operation again to change the power level of the wavelength multiplexed optical signal to a certain level corresponding to the number of channels. To maintain.

Also, instead of operating the monitor signal processing circuit 70 with a control signal indicating the completion of the change of the number of channels,
After the elapse of a predetermined time, the completion of the change in the number of channels can be assumed. Specifically, since the notification of the change in the number of channels is issued, the number of channels is actually increased or decreased after a predetermined time has elapsed. In this example, a control signal for notifying the change in the number of channels is extracted by the monitoring signal processing circuit 70,
After identification, a timer (not shown) is activated. After a lapse of a predetermined time, the variable optical attenuator 64 is restarted (“freeze” is released) to maintain the power level of the wavelength multiplexed optical signal at a constant level.

[0041] and determining the more the number of channels change completion to any of the control signal or a predetermined time has elapsed, the set voltage for controlling the power level (reference voltage) is applied, or channel
It is switched from one level to another depending on the information about the Le number. This information is preferably included in a control signal notifying the channel number change. Therefore, by restarting the control for maintaining the total optical output power at a constant level, the wavelength-multiplexed optical signal to be amplified and output is maintained at a predetermined level corresponding to the number of channels.

Therefore, the variable optical attenuator 64 can prevent a sudden change in the optical output power by fixing the amount of attenuation to a constant level in accordance with the change in the number of channels.
At this time, the second part 2000 does not perform an operation for maintaining the power of the wavelength multiplexed optical signal at a constant level.
When the number of channels is changed, the variable optical attenuator 64 is controlled again to maintain the power of the wavelength multiplexed optical signal at a constant level. Since the variable optical attenuator 64 is gradually driven, the total output power corresponding to the number of channels is maintained. With this configuration, it is possible to suppress a change in the optical output, and it is possible to avoid deterioration of the nonlinear characteristic and deterioration of the S / N ratio.

FIGS. 4A and 4B are graphs showing the operation of the optical amplifying apparatus when the number N of optical signal channels changes according to the embodiment of the present invention. This shows a case where the number N of optical signal channels is changed, for example, from 4 channels to 8 channels.
And a light transmittance or light attenuation controlled by the monitor signal processing circuit 70.

Before the time t1 at which the notification of the change in the number of channels is received, the light transmittance of the variable optical attenuator 64, which is electrically controlled, is changed by the automatic level control circuit 66 so that the variable optical attenuator 64 is controlled. The output is given a substantially constant light signal. Therefore, before time t1, the second part 2000 operates as automatic level control (ALC).

When the notification of the change in the number of channels is received at time t1, the light transmittance of the variable optical attenuator 64 electrically controlled by the automatic level control circuit 66 is maintained substantially constant.
I do . In this case, it appears as if the variable optical attenuator 64 has a constant gain, for example, to provide to the first portion 1000 or to a subsequent stage (not shown) for amplifying the optical signal. Therefore, after the time t1, the automatic level control (AL
Automatic gain control (AGC) is performed instead of C).

At time t2, as shown in FIG.
The optical power increases due to the increase in the number of channels. At time t3, after the change in the number of channels, the automatic level control circuit 66 changes the light transmittance of the electrically controlled variable optical attenuator 64. The output of the variable optical attenuator 64 is given a substantially constant optical signal power. Specifically, after the time t3, the second part 2000 again performs the automatic level control (AL
Perform C).

[0047] in FIG. 4 (A), the apparent by reference to (B)
In this way, the variable optical attenuator 64 controls the automatic level control (AL
Perform C). However, when the number of channels is changed, the automatic level control (ALC) is temporarily stopped. Thus, when the number of channels is changed, the variable optical attenuator 64 has a constant light transmittance or attenuation. The operation of the variable optical attenuator 64 is “frozen” (stopped) when the number of channels changes between times t1 and t3 as shown in FIGS.
I do.

As described above , between times t1 and t3, the output of the variable optical attenuator 64 is, for example, the first portion 1
000 or a later stage to amplify the optical signal (not shown)
Has a constant gain. Or, as disclosed in other embodiments of the invention described in detail below, the second portion 2000 is configurable, and
If the number of channels is changed, a constant gain (instead of automatic level control) can be provided. In this case, the second portion 2000 includes a controlled gain amplifier to provide a constant gain between times t1 and t3.

Therefore, as shown in FIGS. 4A and 4B, the optical amplifying device is an optical amplifier for amplifying a wavelength-division multiplexed optical signal whose number of channels can be changed (such as the first portion 1000). ). Before and after changing the number of channels of the wavelength division multiplexed optical signal, the control device (such as the second part 2000) passes the amplified output wavelength division multiplexed optical signal at a controlled light transmittance to correspond to the number of channels . A level that maintains the power level of the amplified output wavelength multiplexed optical signal at a nearly constant level.
Control means operates to change the number of channels of the wavelength multiplexed optical signal.
When changing, the controller controls the light transmittance to a certain
The level control means for passing the widened optical signal operates
Will be.

[0050] FIG. 5 is an explanatory diagram of an automatic gain control circuit 60 ₁ for controlling the optical gain at a constant level. Referring to FIG. 5, an automatic gain control circuit 60 ₁ divider (DVID
ER) 72, an operational amplifier 74, a transistor 76, and resistors R1 to R6. V _cc is a power supply voltage, V _ref is a reference voltage, and G is a ground or ground potential.

As shown in FIG. 5, the photodiode (P
D) 58 ₁ converts a portion of the wavelength-multiplexed optical signal into an electric signal, applied to the divider 72. Photodiode (PD) 58
₂ converts a part of the amplified wavelength multiplexed optical signal into an electric signal and adds it to the splitter 72. Thus, the divider 72
Obtains the ratio between the input and output of a rare earth doped optical fiber (EDF) 52 ₁ . The operational amplifier 74
Depending on the difference between the output signal indicative of the input and output optical signal level difference between the reference voltage V _ref and the divider 72 controls the transistor 76 to control the current supplied to the excitation laser diode 59 _1, the pump laser diode 59 ₁ The amplification gain of the wavelength multiplexed optical signal is kept constant by the generated pumping light beam. Configuration of the automatic gain control circuit 60 ₁ in Fig. 5 is only one of many configurations of the automatic gain control circuit.

FIG. 6 is an explanatory diagram of an automatic level control circuit 66 for controlling a constant level of light output. Referring to FIG. 6, an automatic level control circuit 66 includes a switching circuit (SWC) 82 for switching frequency characteristics using resistors R7 to R9, an operational amplifier 78, a transistor 80, a capacitor, and the like.
And a reference voltage circuit 84. V _cc is the power supply voltage,
V _ref is a reference voltage, G is ground or ground potential, C
S1 and CS2 are control signals provided from the monitoring signal processing circuit 70. The control element 86 is a control element of the variable optical attenuator 64 that controls the transmittance of the variable optical attenuator 64.

For example, when the variable optical attenuator 64 operates by the magneto-optical effect, the control element 86 applies, for example, a magnetic field.
It is composed of coils that are generated. The variable optical attenuator 64
Operates according to the electro-optic effect, the control element 86 is formed as an electrode and the voltage applied to this electrode is controlled. If a semiconductor optical amplifier is used instead of the variable optical attenuator 64, a bias voltage for controlling the gain of the semiconductor optical amplifier can be controlled.

[0054] Some of the optical signal output from the variable optical attenuator 64 (see FIG. 3) is branched by optical branching coupler 54 _3, converted into electrical signals by the photodiode (PD) 58 _3. In FIG. 6, an operational amplifier 78 compares an electric signal with a reference voltage (set voltage) _Vref supplied by a reference voltage circuit 84 according to a control signal CS1. The voltage difference resulting from the comparison is used to drive transistor 80. By controlling the current supplied to the control element 86, the amount of attenuation by the variable optical attenuator 64 is controlled, and the light output is maintained at a constant level.

FIG. 7 is an explanatory diagram of the switching circuit 82. Referring to FIG. 7, the switching circuit 82 includes a switch SW controlled by a control signal CS2 and capacitors C1 and C2 selected by the switch SW. Therefore, the switching circuit 82 is connected to the automatic level control circuit 66.
Control the frequency characteristics. Further, the switching circuit 82 controls the variable optical attenuator 64 by controlling the transistor 80 according to the level of the output wavelength multiplexed optical signal having a predetermined frequency characteristic. The control signal CS2 from the monitoring signal processing circuit 70 changes the frequency characteristics by switching the capacitors C1 and C2 of the switching circuit 82. The control signal CS1 switches between different levels of the reference voltage according to the number of channels.

More specifically, the switching circuit 82 includes an operational amplifier 78 (see FIG. 6) and a resistor R7 (see FIG. 6).
And R9 (see FIG. 6) to form a first low frequency filter. Cut-off frequency f _c of the the first low-frequency filter is given by the following equation. f _c = 1 /
(2πR9 · C _swc ) where C _swc is the switch SW
Shows the capacitor C1 or C2 selected by. Therefore, by _increasing the value of C _swc , the control circuit of FIG. 6 operates at a low frequency. That is, the response characteristics are reduced.

The filter cutoff frequency in the high frequency band changes according to the capacitance of the selected capacitor C1 or C2 of the switching circuit 82. For example, a preferred configuration is that the cut-off frequency on the order of 10 to 100 kHz in normal ALC operation is used when the variable optical attenuator 64 is controlled to provide a constant attenuation (for example, when the number of channels is changed). To give a constant gain to 0.01 Hz). Ideally, the control of the switching circuit 82 is performed gradually, but for that purpose, the switching circuit 82 is configured using many capacitors instead of two simple capacitors .
Both are possible.

Referring to FIG. 6, before a change in the number of channels is notified, the cutoff frequency is high. When a control signal notifying of the change in the number of channels is received, the switching circuit 82 is controlled to lower the cutoff frequency.
Therefore, the attenuation provided by the variable optical attenuator 64 is fixed at the average level. When the change of the number of channels is completed, the switching circuit 82 is controlled, and the cutoff frequency increases again.

For example, in the monitoring signal processing circuit 70,
When the control signal notifying the change in the number of channels is extracted and identified, the control signal CS2 is supplied to the switching circuit 82, and the frequency characteristic of the automatic level control circuit 66 is switched to a low frequency range. As a result, the photodiode (P
D) The next operation is delayed according to the change in the signal detected by 58 ₃ . That is, the constant level control of the light output is temporarily frozen (stopped) (for example, the light transmittance of the variable light attenuator 64 is kept constant). Further, the control signal CS
1 corresponds to the number of channels included in the optical signal, and the monitoring signal processing circuit 70 supplies the control signal CS1 to the reference voltage circuit 84. Next, the reference voltage circuit 84 supplies a reference voltage _Vref corresponding to the number of channels. Therefore, the total optical output is at a level corresponding to the number of channels after the change in the number of channels . For example, since the reference voltage _Vref changes, when all the α channels are added to the first N channels, the final optical output of all the channels is (N + α) × P.

Referring to FIGS. 6 and 7, the value of the capacitance C _{swc is} a value sufficient to stop the operation of the variable optical attenuator 64. In general, the purpose is, for example,
Cut-off frequency f _c is reduced to 0.01Hz from 10 kHz. This is between 10,000 and 100,000
At a rate of shows the lowering the cutoff frequency f _c.

Normally, the amount of attenuation provided by the variable optical attenuator 64 changes instantaneously to perform an ALC operation to compensate for a change in polarization. Therefore, if the attenuation of the variable optical attenuator 64 is suddenly fixed to a certain level (for example, when the number of channels is changed), a problem occurs. Therefore, it is preferable to maintain the amount of attenuation at the average level.

FIGS. 8 and 9 are explanatory diagrams of an automatic level control circuit 66 according to another embodiment of the present invention. Referring to FIG. 8, a high frequency (f _c ~10kHz) filter 90 composed of a cutoff and capacitor C and the resistor R and the response speed of the automatic level control so provided between the switch 92 and the transistor 80 becomes appropriate. Reference numeral 94 denotes a latch circuit, 95 denotes an operational amplifier, and the same reference numerals as in FIG. 6 denote the same parts. For example, a typical time constant on the order of sub-milliseconds can be a time constant on the order of 10-100 milliseconds .

[0063] When the cut-off frequency f _c is switched to a high-frequency band, the response characteristic of the filter is faster,
Relatively fast changes such as changes in polarization are no longer performed,
The output of the variable optical attenuator 64 is kept constant.

[0064] More specifically, in FIG. 8 holds a voltage latch circuit 94 having a low pass filter (f _c ~0.01Hz) corresponds to the average level of the current control element 86, the operational amplifier 95 the positive terminal Is being entered.
During an ALC (automatic level control) operation, the control loop is switched to drive a control loop for controlling a constant level of drive current. That is, when the control loop is switched, the voltage corresponding to the average voltage of the current is latched by the latch circuit 94.
And become the reference voltage. Photodiode (P
D) bias current to maintain the level of the light beam which is input at a constant level to 58 ₃ have the word "average level" is used because the time-varying. Further, a voltage obtained in a time width determined by a time constant of a normal control loop is latched by the latch circuit 94.

The latch circuit 94 registers the read value,
Drive current (current flowing through transistor 80) through A / D converter that outputs a value registered through D / A converter
May be a circuit for reading the value of.

FIG. 9 corresponds to the configuration of the combination of FIGS. 6 and 8, and 96 is a time constant circuit (τ). Referring to FIG. 9, the capacitance C _swc since shifting switched to cut-off frequency f _c by the switching circuit 82 to the low frequency band, thereby delaying the response characteristics of the filter. The latch circuit 94 controls the amount of attenuation to an average value based on the monitored value.

Further, in FIG. 9, since the control loop is switched after the time constant of the normal control loop is increased in accordance with the control shown in FIG. 6, the effect of the ALC characteristic as a result of the control loop switching is obtained. Is reduced.

As described above, the monitoring signal processing circuit 70
After receiving the control signal notifying the change in the number of channels, the control signal notifying the completion of the change in the number of channels is received. Ah
Alternatively, the monitoring signal processing circuit 70 notifies the change of the number of channels.
After changing the number of channels after receiving the control signal
If the system does not receive a control signal that notifies
The control signal notifying the change in the number of channels is extracted and identified.
After that, a timer (not shown) is started and
Timeout signal is output at the scheduled time of channel number change completion
Control signal for notification of completion of channel number change
The same control can be performed as in the case where is received.

After receiving the control signal indicating the completion of the change in the number of channels, or after a predetermined time has elapsed, the control signal CS2 returns the switching circuit 82 to the initial frequency characteristic. Thus, the constant light output control is restarted according to the new reference voltage _Vref reset by the reference voltage circuit 84.

Control for maintaining the total optical output at a constant level corresponding to the number of channels is gradually restarted. For example,
The output of the photodiode (PD) 58 ₃ is a time constant circuit 96.
The reference voltage _Vref gradually changes to a level corresponding to the number of channels.

With the above configuration, the switching circuit 82
As a result of the control by the frequency characteristics can be switched reliably, and the control of the light output at a certain level can be stopped.
Therefore, when a control signal notifying the change in the number of channels is extracted and identified, a photodiode (PD) 58
₃ makes it possible to hold the signal. In this example, the held value is input to the operational amplifier 78, and the constant level control of the optical output is stopped. In order to stop the constant level control of the light output, another configuration can be adopted. If it is possible to configure an electrically controllable optical device using the variable optical attenuator 64, a semiconductor optical amplifier can be used instead of the variable optical attenuator 64. The wavelength dependency of the semiconductor optical amplifier is small. By controlling the semiconductor optical amplifier, the total optical output can be controlled to a constant level.

FIG. 10 shows an optical amplifying device according to another embodiment of the present invention. This optical amplifying device includes a first portion 1000, a second portion 2000, and a third portion 3000. The third portion 3000 includes a rare earth-doped optical fiber (EDF) 52 ₂ and an optical branching coupler 54.
₄ , optical wavelength multiplexing coupler 56 ₂ , optical isolator 5
5 _3, 55 _4, photodiode (PD) 58 _5, comprising an excitation laser diode (LD) 59 _2, and an automatic gain control circuit (AGC) 60 _2. Third part 3000
Is an optical branching coupler 54 ₃ and a photodiode (PD) 58
₃ is used in common with the second part 2000. The same reference numerals as those in FIG. 3 indicate the same parts.

First part 100 including first optical amplification means
0 and the third part 3000 including the second optical amplification means
Is an automatic gain control which constitutes the first control means and the second control means.
The gain is kept constant by the control circuits 60 ₁ and 60 _2.
You. Also, the first part 1000 and the third part 3000
In between, a second part 2000 including a variable optical attenuator 64 is provided.
The automatic level control circuit 66 constituting the third control means
Controlling a constant power level of the wavelength-multiplexed optical signal input to the from the third part 3000. As a result, the third part 3
000 of the optical output power level is also maintained similarly at a constant level. Therefore, even when the optical signal is attenuated by the variable optical attenuator 64 of the second part 2000, the third part 3
A preferable light output is obtained by the amplification action of 000.

[0074] Thus, the capacity of the pump laser diode 59 and _second excitation laser diode 59 ₁ and the third part 3000 of the first portion can be reduced, respectively,
The cost of the optical amplifier can be reduced.

In FIG. 10, the second portion 2000 and the third portion 3000 share the optical branching coupler 54 ₃ and the photodiode (PD) 58 ₃ . These can be provided with an optical branching coupler and a photodiode separately in the second portion 2000 and the third portion 3000, respectively.

[0076] The automatic gain control circuit 60 ₁ and 60 ₂ may be the same configuration. Furthermore, the first part 1
It is also possible to make the optical gains of 000 and the third part 3000 equal. Alternatively, the gain can be changed according to the characteristics of the transmission optical fiber used in the third portion 3000.

When the number of channels is changed, the optical attenuating function of the variable optical attenuator 64 controls the monitoring signal processing circuit 70 or the monitoring signal processing circuit 7 controlling the automatic level control circuit 66.
Stopped directly by 0. In the same manner as in the embodiment shown in FIG. 3, the change in the optical output according to the change in the number of channels is reliably limited, so that the deterioration of the nonlinear characteristic and the S / N ratio is reduced.

FIG. 11 is an explanatory view of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. 10 denote the same parts. Referring to FIG. 11, the optical amplifying device includes a first portion 1000, a second portion 2000, and a third portion 3000, as shown in FIG. However, the optical amplifier shown in FIG.
And an ALC correction circuit 98 for controlling and correcting the 000 automatic level control circuit 66.

[0079] More particularly, a portion of the wavelength-multiplexed optical signal output by the variable optical attenuator 64 is branched by optical branching coupler 54 _3, photodiode (PD) 58
₃ is converted into an electric signal by the automatic level control circuit 6
6 is input. The automatic level control circuit 66 controls the variable optical attenuator 64 to maintain the total optical output power of the wavelength multiplexed optical signal at a constant level. However, the optical output power of the wavelength division multiplexed optical signal of the third part 3000 is not controlled by the automatic level control circuit 6.
6 is not directly input.

[0080] Thus, a part of the wavelength-multiplexed optical <br/> signal of the third part 3000 is converted into an electrical signal by photodiode (PD) 58 _5, similarly to the automatic gain control circuit 60 ₂ AL
It is input to the C correction circuit 98. The ALC correction circuit 98 determines whether the total optical output power is maintained within a predetermined range. If the total optical output power is not within the predetermined range, the ALC correction circuit 98 controls the automatic level control circuit 66, thereby controlling the variable optical attenuator 64 to set the total optical output power to the predetermined level. Is maintained in the range. When a semiconductor optical amplifier is used instead of the variable optical attenuator 64, the automatic light level control circuit 66 controls the gain of the semiconductor optical amplifier, so that the total optical output of the third part 3000 falls within a predetermined range. Will be maintained.

FIG. 12 is an explanatory view of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as those in FIGS. 10 and 11 denote the same parts. The optical amplifier of FIG.
And the optical amplifying device of FIG. Referring to FIG. 12, when the number of channels changes, the monitor signal processing circuit 70 temporarily stops the control performed by the second part 2000 for controlling the optical output to a constant level. Decrease. Further, the ALC correction circuit 98 controls the automatic level control circuit 66 to maintain the total light output power of the third portion 3000 within a predetermined range.

FIG. 13 is an explanatory diagram of an optical amplifier according to still another embodiment of the present invention. 12 denote the same parts. The optical amplifying device of FIG. 13 operates in the same manner as the above-described embodiment of the present invention, except that the optical branching coupler 54 ₅ , the photodiode (PD) 58 ₆ , the dispersion compensating optical fiber (DCF) 100, and the dispersion compensating optical fiber (DCF) And) a loss correction circuit 102. Optical branching coupler 54 ₅ and the photodiode (PD) 58 ₆ is included in the third part 3000.

The dispersion compensating optical fiber 100 is connected between the second section 2000 and the third section 3000. The DCF loss correction circuit 102 is an automatic level control circuit 6.
6 is controlled. In a long-distance, large-capacity WDM optical transmission system, dispersion compensation is required for the dispersion level of the transmission optical fiber and the WDM optical signal. For this reason, the dispersion compensating optical fiber 100 is required.

However, a problem occurs due to the insertion loss of the dispersion compensating optical fiber. More specifically, when the loss due to the dispersion compensating optical fiber changes, the optical output of a repeater including a wavelength-multiplexed optical fiber amplifier changes. Therefore, by measuring the loss due to the dispersion compensating optical fiber 100 and setting the automatic level control circuit 66 so as to compensate for the loss, the variable optical attenuator 64 is controlled to give a constant optical output. The loss due to dispersion compensating optical fiber 100 appears to be highly dependent on the dispersion compensation level. Therefore, the level of the wavelength multiplexed optical signal input to the third part 3000 can be changed even by the constant optical output control by the automatic level control circuit 66.

[0085] Thus, the output from the dispersion compensation fiber 100, a portion of the branched wavelength-multiplexed optical signal output from the optical branching coupler 54 ₅ is converted into an electrical signal by photodiode (PD) 58 _6. The electrical signal is input together with an automatic gain control circuit 60 ₂ to DCF loss correction circuit 102. The DCF loss correction circuit 102 determines whether or not the level of the wavelength multiplexed optical signal output from the dispersion compensating optical fiber 100 is within a predetermined range. If the level is outside the predetermined range, the DCF loss correction circuit 102 supplies a correction signal to the automatic level control circuit 66. For example, by correcting a reference voltage (set voltage) for constant control of the optical output, the optical output power falls within a predetermined range. Accordingly, when the dispersion compensating optical fiber 100 is required to compensate for dispersion in the transmission optical fiber, the change in the insertion loss is corrected, and a predetermined output level of the amplified wavelength-division multiplexed optical signal is obtained.

FIG. 14 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. 13 denote the same parts. Referring to FIG. 14, monitor signal processing circuit 7
When 0 extracts and identifies a control signal notifying the change in the number of channels, the operation of the variable optical attenuator 64 is stopped (that is, the light transmittance or the amount of light attenuation is kept constant).
Abrupt changes in optical signal level are limited. The DCF loss correction circuit 102 controls the automatic level control circuit 66 to correct a loss that changes according to the level of dispersion compensation by the dispersion compensation optical fiber 100. Thus, the third part 3
The level of the wavelength-division multiplexed optical signal input to 000 is maintained within a predetermined range.

FIG. 15 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. 14 denote the same parts. Referring to FIG. 15, a dispersion compensating optical fiber 100 compensates for dispersion of a transmission optical fiber, and
The F loss correction circuit 102 corrects a change in loss according to the compensation level of the dispersion compensating optical fiber 100, and the ALC correction circuit 98 controls the automatic level control circuit 66 to control the level of the output wavelength multiplexed optical signal of the third part 3000. Is maintained in a predetermined range. Thus, the wavelength multiplexed optical signal of the wavelength multiplexed optical transmission system is amplified.

FIG. 16 is an explanatory view of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. 15 denote the same parts. Referring to FIG. 16, when the monitor signal processing circuit 70 extracts and identifies a control signal for notifying a change in the number of channels, the monitor signal processing circuit 70 controls the variable optical attenuator 64 or the automatic level control circuit 66 to control the optical output to a predetermined level. Stop control. In this method, the level of light output is limited from changing abruptly. Further, the DCF loss correction circuit 10
2 controls the automatic level circuit 66 to correct a loss change according to the dispersion level of the dispersion compensating optical fiber 100. The ALC correction circuit 98 controls the automatic level control circuit 66 to maintain the output wavelength multiplexed optical signal of the third part 3000 at a predetermined level.

FIG. 17 shows an embodiment of the present invention.
It is explanatory drawing of the modification of the optical amplifier of this. More specifically, in FIG. 17, a photodiode (PD) 58 ₂
Between the output of the optical isolator 55 ₂ and optical branching coupler 54 ₂ at the input of the optical filter A1 is provided. The optical filter A2 is a photodiode (PD).
It is provided between the output of the optical isolator 55 ₄ and optical branching coupler 54 ₄ at the input of 58 _5. The optical filters A1 and A2 are described, for example, in US Pat. 08 /
655,027 and referred to in the present invention to correct the wavelength dependence of gain.

FIG. 18A shows a rare earth-doped optical fiber (EDF) shown in FIG. 17 according to an embodiment of the present invention.
52 is a graph showing a gain of _two versus wavelength characteristics, (B) is a graph showing transmittance versus wavelength characteristics of an optical filter A2 in FIG. 17, (C) optical fiber doped with rare earth FIG 17 (EDF) 52 is a graph showing the overall gain of ₂ and optical filter A2.

[0091] For example, an optical fiber (EDF) 52 ₂ doped with rare earth has a wavelength dependence of the gain characteristic as shown in (A) of FIG. 18, also photodiode (P
D) 58 gain correction optical filter A2 input of ₅ 18
(B). This optical filter A
Some of the optical signal branched from 2 by an optical branching coupler 54 ₄ is converted into an electrical signal by photodiode 58 _5, is input to an automatic gain control circuit 60 ₂ and ALC correction circuit 98, shown in FIG. 18 (C) Can be obtained. The optical filters A1 and / or A2 are optical fibers (EDF) 52 ₁ and 52 ₂ doped with rare earth elements.
Can be used or omitted depending on the use of.

FIG. 19 is an explanatory view of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as those in the above-described embodiments denote the same parts. Referring to FIG. 19, the positions of the first portion 1000 and the second portion 2000 are interchanged with respect to the above-described embodiments. Therefore , the wavelength-division multiplexed optical signal is controlled so as to have a constant power level by the second stage 2000 at the front stage, and is controlled to have a constant gain by the first portion 1000 at the subsequent stage .

Further, the input wavelength multiplexed optical signal is sent to the variable optical attenuator 64. Wavelength multiplexing from variable optical attenuator 64
Optical signal output is sent to the optical fiber 52 ₁ doped with rare earth through the optical isolator 55 ₁ and the optical wavelength multiplexing coupler 56 _1. The amplified WDM optical signal is output through the optical isolator 55 ₂ and optical branching coupler 54 _2.

[0094] Some of the optical wavelength-multiplexed optical signal branched by the branching coupler 54 ₁ is converted into an electrical signal by photodiode 58 ₁ is sent to the automatic level control circuit 66 and automatic gain control circuit 60 _1. Since the automatic level control circuit 66 controls the attenuation of the optical signal by the variable optical attenuator 64, the wavelength multiplexed optical signal has a level controlled within a predetermined range and is sent to the first portion 1000.

[0095] Some of the branched WDM optical signal by the optical branching coupler 54 ₂ is converted into an electrical signal by photodiode 58 ₂ is sent to the automatic gain control circuit 60 _1.
Automatic gain control circuit 60 ₁ pump laser diode 59
Since the control _1, the ratio between the levels of the optical fibers 52 ₁ of the output wavelength-multiplexed optical signal which is doped with rare earth is kept constant.

Therefore, even if the optical signal input changes greatly through the transmission optical fiber, the second portion 2000
Thus, the level of the wavelength multiplexed optical signal can be made constant. As a result, a wavelength-multiplexed optical signal of a certain level can be input to the first portion 1000. Thus, the control range of the automatic gain control circuit 60 ₁ is reduced, structure is relatively simplified. Further, since the power level of the optical signal input optical fiber 52 ₁ doped with rare earth never exceeds a predetermined level, it is not necessary to raise the level of the excitation laser beam supplied by pump laser diode 59 _1. In other words, the capacity of the pump laser diode 59 ₁ would be reduced.

FIG. 20 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. 19 denote the same parts. The optical amplifying device shown in FIG. 20 is the same as the optical amplifying device shown in FIG. 19, except that the optical branching coupler 54 ₃ ,
A photodiode (PD) 58 ₃ and a monitor signal processing circuit 70 are included. Wavelength-multiplexed optical signal supplied via a transmission optical fiber is input to variable optical attenuator 64, a portion branched by optical branching coupler 54 ₃ is converted into an electrical signal by photodiode 58 _3, the monitor signal processing circuit 70 Is entered.

A control signal for notifying a change in the number of channels is superimposed on a wavelength-multiplexed optical signal by amplitude modulation or multiplexed by a dedicated control channel and transmitted. When the control signal notifying the change in the number of channels is extracted and identified, the monitor signal processing circuit 70 controls the automatic level control circuit 66 to reduce the amount of attenuation of the optical signal by the variable optical attenuator 64 to the value at the time. (Therefore, the variable optical attenuator 64)
The optical output power is no longer maintained at a constant level.

When the change of the number of channels is completed, the monitoring signal processing circuit 70 resumes the control of the variable optical attenuator 64 to maintain the optical output power at a constant level. With this configuration,
A sudden change in the power level of the optical signal can be reduced or avoided.

FIG. 21 is an explanatory view of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. The optical amplifier of FIG. 21 is similar to the optical amplifier of FIG. 19, but includes an ALC correction circuit 90. The ALC correction circuit 98 determines whether the power level of the output wavelength multiplexed optical signal is within a predetermined range. If the power level is not within the predetermined range, the ALC correction circuit 98
Controls the automatic level control circuit 66 so that the variable optical attenuator 6
The attenuation of the optical signal by 4 causes the output wavelength multiplexed optical signal to have a power level within a predetermined range.

FIG. 22 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention. The same reference numerals as in FIG. The optical amplifier shown in FIG. 22 is a combination of the optical amplifiers shown in FIGS. 20 and 21. FIG.
2, the ALC correction circuit 98 controls the automatic level control circuit 66 to maintain the power level of the output wavelength multiplexed optical signal within a predetermined range. When the control signal notifying the change in the number of channels is extracted and identified, the monitoring signal processing circuit 70 stops the automatic level control function, so that the optical output power is not maintained at a constant level. By restarting the automatic level control function upon completion of the change in the number of channels, the optical output power is stabilized in accordance with the changed number of channels.

FIG. 23 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention. Referring to FIG. 23, instead of controlling (stopping) the variable optical attenuator 64 to provide a constant attenuation when the number of channels is changed,
When the number of channels is changed, the entire optical amplifier is changed to the AGC mode. This change can be achieved by controlling the ratio between the input to the variable optical attenuator 64 or the output from the variable optical attenuator 64 to a constant level. This operation is the same as maintaining the gain G (0 <G <1) of the variable optical attenuator 64 or the light transmittance of the variable optical attenuator 64 at a constant level.

Therefore, in FIG.
Is controlled by the monitor signal processing circuit 70 and the automatic level control operation by the automatic level control circuit 66 and the automatic gain control circuit 6
0 ₃ switches the automatic gain control operation by. More specifically, for example, as shown in FIG. 4A, the monitor signal processing circuit 70 causes the switch 104 to select the automatic level control circuit 66 before and after the number of channels is changed. While the number of channels is being changed, monitor signal processing circuit 70 controls switch 104 to control automatic gain control circuit 6.
0 ₃ to select.

Referring to FIG.
And a laser diode (LD) 105 that is controlled to transmit control information to an optical device such as an optical repeater on the downstream side. For example, as described in detail below, this laser diode (LD) 105
Is controlled by the control information (the change of the number of channels described above).
, Or a control signal for notifying the completion of the change in the number of channels, etc.) to an optical device such as a repeater on the downstream side.

FIG. 24 is a detailed view of a part of the optical amplifying device shown in FIG. 23. The same reference numerals as those in the above-described embodiments denote the same parts, 60-1 and 60-2 indicate LOG, and 60-3 to 60-3. 60-
5 is an operational amplifier, Ri and Rf are resistors, 66-1, 66-
2, OPA indicates an operational amplifier. Referring to FIG.
The following operation is performed. (1). Normally (that is, when the number of channels has not been changed), the switch 104 operates the automatic level control circuit 66 (A
Because you selected LCP side), the power level of light output from the variable optical attenuator 64 is monitored through the photodiode 58 ₃ is maintained at a constant level corresponding to the reference voltage V _ALC. (2). When the monitoring signal processing circuit 70 receives a control signal to notify the change in the number of channels, the automatic gain control circuit 60 ₃
Monitor signal (GM) from the operational amplifier 60-3
107 is read and an average gain (attenuation) is determined according to a time constant on the order of 10 to 100 ms.

(3). Reference voltage V _AGC corresponding to the average gain determined in (2) is applied from the monitor signal processing circuit 70 to automatic gain control circuit 60 ₃ of the operational amplifier 60-5. (4). The switch 104 is connected to the automatic gain control circuit 60 ₃ (A
GCP). (5). The monitoring signal processing circuit 70 receives information indicating the new number of channels included in the wavelength division multiplexed optical signal. (6). The monitoring signal processing circuit 70 _applies the reference voltage _VALC corresponding to the new number of channels to the operational amplifier 66-2 of the automatic level control circuit 66. (7). The monitoring signal processing circuit 70 receives a signal indicating that the change in the number of channels has been completed. Alternatively, it is determined that a change in the number of channels has been completed after a predetermined time has elapsed from the reception of the signal notifying the change in the number of channels. (8). The switch 104 is connected to the automatic level control circuit 66 (A
LCP side) is selected.

The relationship between the attenuation by the variable optical attenuator 64 and the drive current of the control device 86 by the transistor 80 is determined by parameters such as the operating temperature, but they have a one-to-one relationship. Accordingly, item (2) above relates to the process of monitoring the drive current (with respect to a time constant on the order of 10-100 ms) to determine an average gain (attenuation) based on the monitored drive current (operational amplifier OPA). From the current monitor signal IM). Since the control current of the variable optical attenuator 64 is controlled, its average level is kept constant.

FIG. 25 is an explanatory diagram of a wavelength division multiplexing optical transmission system using an optical amplifying device according to an embodiment of the present invention.
108 is an optical transmitter (Tx or node), Tx
(SV) is a control signal transmitter, 110 is an optical receiver (Rx or node), 112 is an optical amplifier (O-AM)
P) and 114 are a main signal control unit and 116 is a monitoring signal processing unit. The optical amplifier (O-AMP) 112 is a main optical signal (wave)
(A long multiplexed optical signal) and a control optical signal superimposed thereon. Main signal control unit 114 and monitoring signal processing unit 116
Controls the optical amplifier 112 to amplify the main optical signal and the control optical signal to desired levels and send them to the receiving side. Soshi
To receive the main optical signal by the optical receiver 110 on the receiving side.
The control optical signal is received by the control signal receiver Rx (SV).
Processing.

FIG. 26 shows a configuration of an optical amplifier including the optical amplifier 112, the main signal control unit 114, and the monitor signal processing unit 116 of FIG. The optical amplifying device of FIG. 26 has the same configuration as that of FIG. 3, but includes a laser diode (LD) 105 for transmitting a control optical signal for monitoring to a downstream side from a transmitting side to a receiving side. More specifically, the monitoring signal processing circuit 70 supplies information indicating when the attenuation or light transmittance of the variable optical attenuator 64 is kept constant or "frozen" when the number of channels is changed. The light is converted into a control light signal by a laser diode (LD) 105 and
The signal is multiplexed and transmitted to a transmission line.

FIG. 27 shows a wavelength division multiplexing optical transmission system using a plurality of optical amplifiers according to an embodiment of the present invention.
Wavelength multiplexing optical transmission system comprises a transmitter (Tx) 120,
Wavelength multiplexing optical fiber amplifier / repeater (OAMP) 1
22 and a receiver (Rx) 124 . SVTx and SVRx denote a transmission unit and a reception unit of a control optical signal, and a configuration related to a monitoring signal processing circuit and the like is omitted in the drawing.
ing. Arrow UPS indicates the upstream direction, and DNS indicates the downstream direction. When the number of channels is changed, all OAMPs 122 on the upstream (or downstream) line in the system are set to a constant optical gain control operation.

The photomultiplier described in each of the above embodiments is described.
Wavelength multiplexed optical post-amplifier (not shown) and each receiver Rx provided in each transmitter Tx 120 with width device
Provided 124 wavelength-multiplexed optical preamplifier (not shown), are both set to a constant gain control operation, and before
All wavelength multiplexed optical fibers with the optical amplifier described above
Amplifier / repeater (OAMP) 122 in constant gain control state
, The optical signal power input to the optical receiving device in the receiver (Rx) 124 may change.

In the transmission line having the optical amplifying device shown in FIGS. 25 to 27, all the optical fiber amplifiers in the transmission line managed by the receiver (Rx) on the transmission line reduce the attenuation to a certain level. It is possible to determine whether to keep the optical gain fixed and at a constant level. Once all optical fiber amplifiers are determined to maintain their optical gain at a constant level, information indicating this is sent to the transmitter (Tx) through the reverse transmission path,
The change of the number of channels is started.

The following is an example of the operation flow in the transmission line having the optical amplifier shown in FIGS. 25 to 27 for the process of changing the number of channels. (1). A control signal notifying the change in the number of channels is transmitted from the upstream SV transmission unit (SVTx). (2). The monitoring signal processing circuit 70 of each OAMP receives a control signal notifying the change of the number of channels. (3). Each OAMP "freezes" its associated variable optical attenuator
Start operation. (4). Each OAMP "freezes" its associated variable optical attenuator
By completing the operation and transmitting the information with the monitor signal (identification numbers for identifying individual OAMPs are also inserted in the monitor signal), a certain optical gain control is started. Is transmitted to the downstream side.

(5). SV receiver on the upstream side (SVRx)
Recognizes that all upstream OAMPs are in a constant optical gain state. (6). The downstream SV transmitter (SVTx) notifies that all upstream OAMPs are in a constant optical gain state. (7). The downstream SV receiver (SVRx) recognizes that all upstream OAMPs are in a constant optical gain state. (8). The upstream transmitter (Tx) actually changes the number of channels. (9). The upstream SV transmitter (SVTx) generates information indicating that the change in the number of channels has been completed.

(10). The monitoring signal processing circuit 70 of each OAMP receives information indicating that the change of the number of channels has been completed. (11). Each OAMP stops the freezing operation for freezing the operation of the associated variable optical attenuator, and advances the control to keep the optical output constant. (12). Each OAMP sends, in the form of a monitor signal, information indicating that the transition to the control for keeping the optical output constant has been completed to the downstream side (identification signals for identifying individual OAMPs are also sent out). (13). The upstream SV receiver (SVRx) receives information indicating that all the OAMPs have performed the change processing of the number of channels. (14). Information indicating that all the OAMPs have performed the process of changing the number of channels is sent to the transmitter.

FIG. 28 is a timing chart showing the above operation flow. (A) Number of channels 2ch, 4ch, 8c
channel number information for notifying channel number change such as h,
(B) is information on the number of operating channels, (c) is an ALC reference signal, (d) is an ALC lock signal, (e) is a status signal,
(F) shows ON / OFF of the ALC correction operation, (g) shows the total optical power, (h) shows the optical power corresponding to the channel, and the optical power corresponding to the channel has a preset level (PR
ESET LEVEL is maintained.

Therefore, in the process of changing the number of channels, the optical amplifying device temporarily sets the automatic level control function (AL
The execution of C) is stopped (FREEZE), and the constant gain function is performed instead, or the constant gain function is executed in the entire optical amplifier. However, in an optical communication system, it is usually necessary to maintain the power of an optical signal supplied to an optical receiver at a constant level. The change in input power due to the change in polarization occurs under conventional circumstances, but by controlling the optical gain of the optical fiber amplifier to maintain a constant level, the power of the optical signal supplied to the optical receiver changes. .

This problem can be overcome by demultiplexing the wavelength-multiplexed optical signal into individual channels and controlling the optical power level of each of the demultiplexed channels. FIG. 29 shows a wavelength division multiplexing optical transmission system according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram of a main part of a system. Referring to FIG. 29, a demultiplexer (DEMUX) 125 demultiplexes a wavelength division multiplexed optical signal into individual channels received by individual receivers 126. Since the optical preamplifier 127 and the automatic level control unit 128 are provided for each individual channel, the associated receiver 126 can receive an optical signal at a constant power level.

According to the above embodiment of the present invention, the variable optical attenuator or the optical amplifier can be controlled so as to obtain a constant gain when the number of channels of the wavelength multiplexed optical signal is changed. In this case, the gain G is in the range of 0 <G <1. Thus, by maintaining the ratio between the input and output of the variable optical attenuator constant, the variable optical attenuator can be controlled to provide a constant gain.

Further, according to the embodiment of the present invention, an optical fiber doped with rare earth is used in the optical amplifier. In this case, the dopant is erbium (Er). However, the invention is not limited to erbium (Er) doped optical fibers. instead of,
Depending on the wavelength, other rare earth doped optical fiber,
For example, an optical fiber doped with neodymium (Nd) or an optical fiber doped with praseodymium (Pd) can be used. Further, for example, the various photodiodes disclosed herein can be replaced with phototransistors.

According to the above embodiments of the present invention, specific embodiments of the automatic gain control circuit and the automatic level control circuit are disclosed. However, the invention is not limited to the specific circuit arrangements of these or other circuits disclosed herein, and many other different circuit arrangements may be used. Further, according to the above-described embodiment of the present invention, the amount of attenuation with respect to the optical signal is made variable using the optical attenuation function. Many different variable optical attenuators have already been disclosed. Therefore, the embodiment of the present invention is not limited to the specific variable optical attenuator described above.

While several embodiments of the present invention have been shown and described, those skilled in the art would depart from the principles and spirit of the present invention as set forth in the appended claims. Obviously, various modifications are possible without doing so.

[0123]

As described above, the present invention provides a multi-wavelength
Optical amplification means such as an optical fiber amplifier for amplifying heavy optical signals
When changing the number of channels,
Based on the level of the heavy optical signal and the output wavelength multiplexed optical signal.
Use of an automatic gain control circuit that controls the gain to be constant
Change number of channels by providing
Can be amplified and transmitted to the corresponding optical signal level
You. Furthermore, before and after the channel change, the optical amplification means
Control so that the optical signal level amplified by
Equipped with level control means such as an automatic level control circuit
To amplify to the wavelength multiplexed optical signal level corresponding to the number of channels.
Can be transmitted. Thereby the number of channels
Of the nonlinear characteristics of the optical amplification means and the S / N
It has the advantage that degradation can be suppressed.
Stable transmission even when the number of channels in the transmission system changes
There are advantages that are possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a wavelength division multiplexing optical transmission system.

FIG. 2 is an explanatory diagram of an optical amplifying device of the wavelength division multiplexing optical transmission system .

FIG. 3 is an explanatory diagram of an optical amplifying device according to an embodiment of the present invention.

FIG. 4 is a graph showing an operation of the optical amplifying device when the number N of channels of the optical signal changes according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of an automatic gain control circuit according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram of an automatic level control circuit according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a switching circuit of the automatic level control circuit according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram of an automatic level control circuit according to another embodiment of the present invention.

FIG. 9 is an explanatory diagram of an automatic level control circuit according to another embodiment of the present invention.

FIG. 10 is an explanatory diagram of an optical amplifier according to another embodiment of the present invention.

FIG. 11 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 12 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 13 is an explanatory diagram of an optical amplification device according to still another embodiment of the present invention.

FIG. 14 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 15 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 16 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 17 is a diagram illustrating a modification of the optical amplifying device shown in FIG. 16 according to an embodiment of the present invention.

FIG. 18 shows a gain of an optical fiber (EDF) doped with a rare earth in the optical amplifying device according to the embodiment of the present invention.
FIG. 3 is an explanatory diagram of wavelength characteristics, light transmittance of an optical filter, and overall gain of the optical filter.

FIG. 19 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 20 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 21 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 22 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 23 is an explanatory diagram of an optical amplifying device according to still another embodiment of the present invention.

FIG. 24 is a detailed view of a part of the optical amplifying device shown in FIG. 23 according to an embodiment of the present invention.

FIG. 25 shows a case where the optical amplifying device according to the embodiment of the present invention is used.
FIG. 1 is an explanatory diagram of a wavelength division multiplexing optical transmission system.

FIG. 26 is a detailed diagram showing the optical amplifying device shown in FIG. 25 according to an embodiment of the present invention.

FIG. 27 is an explanatory diagram of a wavelength division multiplexing optical transmission system using a plurality of optical amplifying devices according to an embodiment of the present invention.

FIG. 28 is a timing chart showing an operation of the optical amplifying device according to the embodiment of the present invention.

FIG. 29 shows a wavelength division multiplexing optical transmission system according to an embodiment of the present invention.
It is explanatory drawing of the principal part of a stem .

[Explanation of symbols]

1000 First part 2000 Second part 52 ₁ Rare earth doped optical fiber 54 _{1 to} 54 ₃ Optical branching coupler 55 ₁ , 55 ₂ Optical isolator 56 ₁ Optical wavelength multiplexing coupler 58 _{1 to} 58 ₄ Photodiode (PD) 59 ₁ Excitation laser Diode (LD) 60 ₁ Automatic optical gain control circuit (AGC) 64 Variable optical attenuator (ATT) 66 Automatic level control circuit (ALC) 70 Monitoring signal processing circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-195733 (JP, A) JP-A-2000-174710 (JP, A) JP-A-8-95097 (JP, A) JP-A-6-152526 (JP, A) JP-A-5-37472 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H01S 3 /Ten

Claims (15)

(57) [Claims] 1. A different have a plurality of channels corresponding to the optical signal of the wavelength, the number capable of changing the wavelength-multiplexed light of the channel
A first optical amplifier for inputting, amplifying and outputting a signal, and controlling the gain of the first optical amplifier to be constant.
First control means, and a variable optical attenuator for attenuating the amplified output of the first optical amplification means
A second optical amplifier for amplifying the output of the variable attenuator, and controlling the gain of the second optical amplifier to be constant.
With the second control means, before and after the change in the number of channels, the amplified output optical signal corresponds to the number of channels.
The variable optical attenuator so that the level becomes
The attenuation is controlled, and when the number of channels is changed, the variable optical attenuator is used.
An optical amplifying device comprising: third control means for performing control for maintaining light transmittance constant . 2. The variable optical attenuator according to claim 2 , wherein
The optical signal at the subsequent stage is detected, and the optical signal output of the optical amplifying device is detected.
Before the force is at a certain level corresponding to the number of channels
Having a configuration for controlling the attenuation of the variable optical attenuator.
The optical amplifying device according to claim 1, wherein: 3. The method according to claim 2, wherein the third control means changes the number of channels.
A monitoring signal processing circuit that receives the control light signal to be notified is set up.
The variable based on a signal from the monitoring signal processing circuit.
Claims having a configuration for controlling an optical attenuator
Item 2. The optical amplifying device according to Item 1 . 4. The variable optical attenuator according to claim 3, wherein:
And the optical signal output of the second optical amplifying means.
After detecting, the output of the optical signal at the last stage corresponds to the number of channels.
The attenuation of the variable optical attenuator is controlled so as to be a constant level.
2. The optical amplifying device according to claim 1, wherein said optical amplifying device has a configuration for controlling said optical amplifying device. 5. A plurality of channels corresponding to optical signals of different wavelengths.
Wavelength multiplexed light having a channel and a variable number of the channels
An optical amplifier for inputting, amplifying and outputting a signal; and a first control unit for controlling the gain of the optical amplifier to be constant.
Control means, a variable optical attenuator for attenuating the amplified output of the optical amplifying means, and an amplified output optical signal corresponding to the number of channels before and after changing the number of channels.
The variable optical attenuator so that the level becomes
The attenuation is controlled, and when the number of channels is changed, the variable optical attenuator is used.
And a third control means for performing control for maintaining the light transmittance at a constant
An optical amplifying device comprising: 6. Different have a plurality of channels corresponding to the optical signal of the wavelength, the number capable of changing the wavelength-multiplexed light of the channel
A variable optical attenuator for inputting and attenuating a signal, optical amplifying means for amplifying the output of the variable optical attenuator, and a first control for controlling the gain of the optical amplifying means to be constant.
And control means, amplifies the output optical signal before and after the number of channels changes versus the number of channels
The variable optical attenuator so that the level becomes
The attenuation is controlled, and when the number of channels is changed, the variable optical attenuator is used.
And a third control means for performing control for maintaining the light transmittance at a constant
An optical amplifying device comprising: 7. The variable optical attenuator according to claim 3, wherein:
And the optical signal output of the optical amplification means are detected.
The final stage optical signal output has a certain level corresponding to the number of channels.
Control the attenuation of the variable optical attenuator so that the level
7. The optical amplifying device according to claim 6, having a configuration.
Place. 8. The method according to claim 1, wherein the third control means changes a number of channels.
A monitoring signal processing circuit to receive a control optical signal
The variable based on a signal from the monitoring signal processing circuit.
Characterized by having a configuration to control the attenuation of the optical attenuator
The optical amplifying device according to claim 6. 9. The third control means outputs the last optical signal.
After the level of the
A means for feeding in a flow direction.
2. The optical amplifying device according to 1. 10. A plurality of optical signals corresponding to optical signals of different wavelengths.
Input and amplify WDM optical signals with variable number of channels
A first optical amplifying means for outputting the same, and controlling the gain of the first optical amplifying means to be constant.
First control means, and a variable optical attenuator for attenuating the amplified output of the first optical amplification means
And second optical amplifying means for amplifying the output of the variable optical attenuator, and controlling the gain of the second optical amplifying means to be constant.
With the second control means, before and after the change in the number of channels, the amplified output optical signal corresponds to the number of channels.
The variable optical attenuator so that the level becomes
The attenuation is controlled, and when the number of channels is changed, the variable optical attenuator is used.
JP, further comprising a third control means for freezing or stopping the control
Optical amplification equipment 11. A plurality of optical signals corresponding to optical signals of different wavelengths.
Wavelength multiplexing having channels and changing the number of channels
A first optical amplifier for inputting, amplifying and outputting an optical signal; and controlling the gain of the first optical amplifier to be constant.
First control means, and a variable optical attenuator for attenuating the amplified output of the first optical amplification means
And second optical amplifying means for amplifying the output of the variable optical attenuator, and controlling the gain of the second optical amplifying means to be constant.
With the second control means, before and after the change in the number of channels, the amplified output optical signal corresponds to the number of channels.
The variable optical attenuator so that the level becomes
The attenuation is controlled, and when the number of channels is changed, the variable optical attenuator is used.
Further comprising a second control means for changing the control time constant
Characteristic optical amplifier. 12. A plurality of optical signals corresponding to optical signals of different wavelengths.
Wavelength multiplexing having channels and changing the number of channels
A first optical amplifier for inputting, amplifying and outputting an optical signal; and controlling the gain of the first optical amplifier to be constant.
A first control unit, and a variable optical attenuator for attenuating an amplified output of the first optical amplifying unit.
, A second optical amplifier for amplifying the output of the variable optical attenuator, and controlling the gain of the second optical amplifier to be constant.
With the second control means, before and after the change in the number of channels, the amplified output optical signal corresponds to the number of channels.
The variable optical attenuator so that the level becomes
When the number of channels is changed, the variable optical attenuator is
And a third control means for controlling so that the gain is constant
An optical amplifying device characterized in that: 13. A plurality of optical signals corresponding to optical signals of different wavelengths.
Wavelength multiplexing having channels and changing the number of channels
An optical signal and a control optical signal for notifying a change in the number of channels
An optical device for transmitting to a transmission line, and a first light for inputting, amplifying, and outputting the wavelength multiplexed optical signal
The gain of the amplifying means and the gain of the first optical amplifying means are constant.
Control means for controlling the first optical amplifying means,
A variable optical attenuator for attenuating the amplification output;
Second optical amplifying means for amplifying the output, and the second optical amplifying means
Second control means for controlling the gain of the stage to be constant;
The amplified output signal corresponds to the number of channels before and after changing the number of channels
Attenuation of the variable optical attenuator so that
The variable optical attenuator when the number of channels changes.
Optical amplifier comprising a third control means for freezing or stopping control
And a wavelength division multiplexing optical transmission system. 14. A plurality of optical signals having different wavelengths.
Wavelength multiplexing having channels and changing the number of channels
An optical device for transmitting an optical signal to the optical transmission path, the multi-wavelength light
First optical amplification means for inputting, amplifying, and outputting a signal;
The second optical amplifier is controlled so that the gain of the first optical amplifier is constant.
1 control means and attenuate the amplified output of said first optical amplifying means
Variable optical attenuator, and amplifying the output of the variable optical attenuator
The second optical amplifying means, and the gain of the second optical amplifying means is constant.
Control means for controlling the number of channels and changing the number of channels
Before and after, the amplified output signal has a fixed level corresponding to the number of channels.
Control the amount of attenuation of the variable optical attenuator so that
When changing the number of channels, freeze or stop the control of the variable optical attenuator.
Further comprising an optical amplifier comprising a Mel third control means
A wavelength division multiplexing optical transmission system characterized by the above. 15. The optical device has completed changing the number of channels.
Is transmitted to the optical transmission line, and the optical amplification is performed.
The second control means of the device sends a notification of completion of the change in the number of channels.
Detected and amplified by the optical amplification means
The variable attenuator so that the level of the heavy light signal becomes a predetermined value.
15. The apparatus according to claim 14, further comprising:
WDM optical transmission system.