JP2003318831A - Optical amplifier and optical communication system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent degradation of transmission quality of an optical signal in accordance with increase/decrease of transmission channels and to simultaneously enhance safety. <P>SOLUTION: This optical amplifier is constituted so that the optical signal is outputted by control of an ALC (automatic level control) circuit by always setting the optical amplifier to the level Y2 of optical output power for two waves between X1 and X2 where only one wave is inputted. When optical input power is between X3 and X4, the ALC circuit is controlled so that the optical output power becomes a fixed value of Y1, when the optical input power is between X2 and X3 where the optical input power is in other case, an AGC (automatic gain control) circuit is made to perform control, an output level of optical power is prevented from exceeding a lower limit value Y2 or an upper limit value Y1 and optical output is made to be a stable state. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical amplifier having an automatic gain control (hereinafter referred to as "AGC") circuit or an automatic output level control (hereinafter referred to as "ALC") circuit and amplifying the power of an optical signal. And an optical communication system using the optical amplifier.

[0002]

2. Description of the Related Art In a conventional optical amplifier, for example, as shown in FIG. 10, the optical input power and the optical output power of an optical fiber amplifier (OFA) 11 provided on an optical fiber 10 are respectively converted by optical couplers 12 and 13. After branching, the photodiodes (PD) 14 and 15 are used for detection, and the AGC so that the ratio of the detected powers is always a desired value (gain).
By controlling the current of the pumping laser diode (LD) 17 by the circuit 16, the constant control of the gain of the OFA 11 is performed.

The gain control of this optical amplifier can be applied even when an OFA having no monitoring function for recognizing the number of wavelengths in operation is used, and other control circuits such as an ALC circuit and automatic current control. It is possible to reduce the flatness of the gain in the amplification band as compared with the one using a control circuit (hereinafter, referred to as “ACC”).

By this control, the OFA 11 shown in FIG.
As shown in the relationship diagram between the optical input power and the optical output power, the optical output power is proportional to the optical input power, and the optical input power is in the range of the input dynamic range of X1 to X4, and the optical output power is In the range of the output dynamic range from Y3 to Y4, a straight line that rises to the right in the figure is formed and stable gain control is performed.

This optical amplifier is a wavelength division multiplex (hereinafter referred to as "WD") that wavelength-multiplexes a plurality of optical signals having different wavelengths.
M)) system, for example, when changing the operating state of one wave of light to the operating state of newly adding a second wave of light and performing wavelength multiplexing, the OFA of the optical amplifier is It was necessary to output the optical output power Y2 for two waves from the output power Y3.

A semiconductor laser, for example, is used for the LD of this optical amplifier. As shown in the current-light output characteristics of FIG. 12, this semiconductor laser has an initial threshold value of a drive current required for driving the LD, and when the LD is driven near this initial threshold value, the light from the LD is emitted. It has the feature that the output fluctuates and is not stable. Usually, the LD of the conventional optical amplifier is operated at -20 dBm by a driving current slightly higher than the threshold current.

[0007]

However, in the optical amplifier of the above-mentioned conventional example, the optical level of the output of OFA (the output of Y3 shown in FIG. 11) when the channel of one wave is as shown in FIG. Since it is operated at -20 dBm, when the number of channels is increased to 2 waves, the optical level per channel cannot be tracked due to this increase, and the transient level is reduced by 3 dBm. Therefore, there is a problem that it falls below -20 dBm.

Therefore, in the above-mentioned conventional example, the optical output from the LD is due to the vicinity of the initial threshold value of the drive current, the optical output fluctuates and becomes unstable, and the transmitted optical signal. There was also a problem that the quality of the product deteriorates.

In addition, the optical level of the laser element has a safety standard (safety of laser product).
s: IEC-60825-1,2).
For example, when the wavelength used in the optical communication system is in the 1.55 μm band, when the optical level is 10 dBm or less, it is called class 1 and safety functions such as a shutdown function that temporarily stops the optical output when a failure occurs are specified. Although not described, the light level of 17 dBm or less is called class 3A and the addition of the above-mentioned safety function is stipulated.

In the AGC circuit, when the optical input power increases, the optical output power also increases accordingly.
The gain is constantly controlled. Therefore, for example, when a very high level of optical input power is input to the OFA,
In this OFA, a very high light output is emitted from the pump LD, and the above-mentioned safety standard may not be satisfied in some cases. In particular, if the condition of Class 1 defined by the safety standard is exceeded, a safety function has to be added, so that the device configuration becomes complicated and the manufacturing cost becomes high.

Further, in this optical amplifier, in order to speed up the transient response from the shutdown by the OFA, the initial current value of the LD is generally set. Then, when it is confirmed that there is an optical input in the PD, there has been a method in which an automatic recovery control (ARC) function is used to flow an initial current set in the LD to output an optical pulse for quick automatic recovery. .

For example, in the case of an AGC amplifier which has a large input dynamic range as in the conventional example, the initial current value is -20 dBm as shown in FIG. 14 so that overshoot does not occur. It must be kept low so that the light level will be. At this time,
When a high optical input power is input to the OFA, the initial current value is considerably lower than the level of the current value that outputs the target optical power, so it takes time to output the target optical power, and it is quick. However, there was a problem that it could not be restored properly.

Further, in the AGC circuit, when control is performed so as to have a large input dynamic range, the drive current of the LD is too small in a region where the optical input power of the OFA is low, so the optical output from the LD is generated. There is also a problem that the optical output is not stable because it is close to the initial threshold.

Further, there is a system for controlling an optical amplifier by using AGC and ALC, such as the system disclosed in Japanese Patent Laid-Open No. 11-121848, but the system disclosed in this publication has the above-mentioned problems. No condition setting or specific means for solving the above is described, and the object of the present invention described below cannot be achieved.

The present invention has been made in view of the above problems, and it is possible to prevent deterioration of the transmission quality of an optical signal due to an increase or decrease in the number of transmission channels and to improve safety, and an optical amplifier using the optical amplifier. An object is to provide a communication system.

[0016]

To achieve the above object, in claims 1 and 2 of the present invention, a gain control means for controlling a gain for an optical signal and a level control means for controlling an output level of the optical signal. In the optical amplifier for amplifying and outputting the optical power of the wavelength-multiplexed optical signal under the control of the gain control means and the level control means, detection means for detecting the optical power input to the optical amplifier, At least one threshold value is set to the input optical power, of the lower limit first threshold value or the upper limit value second threshold, and the optical power detected by the detection means is less than or equal to the first threshold value. And a control execution means for executing the control by the level control means at the time of or more than the second threshold value, and at the other time, the control by the gain control means. An optical amplifier is provided that.

According to the present invention, as shown in the diagram of the relation between the optical input power and the optical output power of the OFA for explaining the control of the OFA in FIG. 1, the optical input power is equal to or lower than the lower limit first threshold value X2. In (between X1 and X2), the optical output power is set to a constant value of Y2, or when the optical input power is equal to or higher than the upper second threshold value X3 (between X3 and X4),
The level control means (ALC) is controlled so that the optical output power becomes a constant value of Y1, and the gain control means (AGC) is controlled when the optical input power is between X2 and X3 other than that. The output level of power is prevented from exceeding the lower limit value Y2 or the upper limit value Y1 and the optical output is stabilized.

According to a third aspect of the present invention, in the above invention, the control executing means sets the input optical power when the optical signals of at least two waves are multiplexed as the first threshold value, and The level control means controls the level so that the optical power of the optical signal output from the optical amplifier becomes a constant output level for two waves, and the control execution means controls the second power based on a safety standard. Set the threshold,
The level control means may perform level control such that the optical power of the optical signal output from the optical amplifier has a constant output level equal to or lower than the upper limit of the optical power set by the safety standard.

According to the present invention, even between X1 and X2 corresponding to the optical power when one wave is input, the optical output power when the optical signals of two waves are multiplexed is controlled to a constant value of Y2 which is the lower limit. However, the optical output power set by the safety standard is set to the upper limit of Y1 (see FIG. 1), and the output dynamic range of the OFA is narrowed from Y3 to Y4 of the conventional example to Y2 to Y1 to reduce the optical output. The light output is kept in a stable state by preventing it from approaching the initial threshold value Y3.

According to a fourth aspect of the present invention, the optical amplifier has level control means for controlling the output level of the optical signal, and amplifies and outputs the optical power of the wavelength-multiplexed optical signal under the control of the level control means. In, detecting means for detecting the optical power of the optical signal input to the optical amplifier, a plurality of thresholds are set according to the input optical power, based on the optical power detected by the detecting means, An optical amplifier is provided, which comprises a control execution means for executing control by the level control means so that the optical power of an optical signal output from the optical amplifier becomes a constant output power stepwise. It

According to the present invention, the control executing means sets a plurality of thresholds according to the optical input power input to the optical amplifier, and the ALC is determined based on the optical power detected by the detecting means.
Controls the optical power of the optical signal input to the optical amplifier in a stepwise manner so that a constant output power can be obtained and the stability of the optical output is improved.

According to a fifth aspect of the present invention, in the above invention, the control executing means sets the optical power input to the optical amplifier when the optical signals of at least two waves are multiplexed, as the first threshold value. However, the level control means performs level control so that the optical power of the optical signal output from the optical amplifier becomes a constant output level of two waves, or the control execution means performs the level control based on a safety standard. A second threshold is set, and the level control means controls the level so that the optical power of the optical signal output from the optical amplifier becomes a constant output level equal to or lower than the upper limit of the optical power set by the safety standard. It is characterized by performing.

According to the present invention, the lower limit first threshold value X2
By setting a stepwise threshold value including the following optical power or an upper limit second threshold value X3 or more, the optical output power level is prevented from exceeding the lower limit value or the upper limit value, and the optical output power is prevented. To a stable state.

According to a sixth aspect of the present invention, in the above invention, the control execution means executes the control in the output dynamic range of the optical amplifier when the optical signal has two waves and is set by a safety standard. It is characterized by

According to the present invention, by controlling the output dynamic range of the OFA to be narrow, the amount of change in the optical power output from the initial current value to the target value is reduced, and as a result, the time until the rise is increased. Get faster

According to claim 7 of the present invention, in an optical communication system for wavelength-multiplexing and transmitting a plurality of optical signals having different wavelengths, the power of the optical signal is amplified and output. An optical communication system is provided, which comprises two optical amplifiers.

According to the present invention, at least one of the optical amplifiers according to claims 1 to 6 is used in the optical communication system to prevent the deterioration of the transmission quality of the optical signal due to the increase or decrease of the transmission channel and to improve the safety. .

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical amplifier according to the present invention and an optical communication system using the optical amplifier will be described below with reference to the accompanying drawings. Note that, in the following drawings, the same reference numerals are given to the same components as those of FIG. 10 for convenience of description.

(Embodiment 1) FIG. 2 is a configuration diagram showing a configuration of Embodiment 1 of an optical amplifier according to the present invention. In the figure, in this embodiment, the OFA 11, the optical couplers 12 and 13, the PDs 14 and 15, the AGC circuit 16 of the conventional example of FIG.
In addition to the LD 17, it is composed of an ALC 18 that controls the level of the optical output power from the OFA 11 and a control execution unit 19.

The control execution unit 19 detects the level of the optical input power to the OFA 11 detected by the PD 14 (optical input level).
Is set as the threshold. In this embodiment, as shown in FIG. 1, for example, the light input level X2 is set to the first threshold value of the present invention and the light input level X3 is set to the second threshold value of the present invention. The control execution unit 19 determines that the light input level detected by the PD 14 is X2 or less (that is, the light input levels X1 to X2).
Interval) and the optical input level is X3 or more (that is, between the optical input levels X3 and X4), the ALC circuit 18 sets the optical output power to constant values Y2 and Y1.
The drive current of the excitation LD 17 is controlled.

Further, as shown in FIG. 1, the control executing section 19 determines that when the optical input level is other than the above optical input level (that is, between the optical input levels X2 and X3), the AG
The C circuit 16 controls the drive current of the excitation LD 17 so that the gain of the OFA 11 becomes a constant value.

Next, the control operation of this optical amplifier will be described with reference to the flowchart of FIG. In the figure, the control execution unit 19 monitors the optical input level detected by the PD 14 (step 101), and determines whether the monitored optical input level is less than or equal to the threshold level X2 (step 102).

Here, this optical input level is the threshold level X.
When it is 2 or less, the control execution unit 19 determines that the light input level is between X1 and X2 (step 103), and selects and drives the ALC circuit 18 (step 104). When the selected ALC circuit 18 is driven, it controls the drive current of the pumping LD 17 so that the optical output becomes the constant optical output power Y2 based on the monitor information of the PD 15 (step 105).

If the monitored optical output power is not X2 or less in step 102, then the control execution section 19 determines whether the monitored optical input level is X3 or more (step 106).

Here, this optical input level is the threshold level X.
When it is not 3 or more, it is judged that the monitored optical input level is between X2 and X3 (step 107), and the AGC circuit 16 is selected and driven (step 108). When the selected AGC circuit 16 is driven, the difference between the optical outputs is obtained from the monitor information of the PD 14 and the PD 15, and the excitation L is adjusted so that the gain of the OFA 11 becomes a constant value from the output difference.
The drive current of D17 is controlled (step 109).

In step 106, when the monitored optical output power is X3 or more, it is judged that the monitored optical input level is between X3 and X4 (step 11).
0), the ALC circuit 16 is selected and driven (step 111). When the selected ALC circuit 16 is driven, the drive current of the pumping LD 17 is controlled so that the optical output becomes the constant optical output power Y1 based on the monitor information of the PD 15 (step 112).

An example of using this optical amplifier in an optical communication system having a transmission wavelength band of 1.55 μm will now be described based on the relationship between the optical input power and the optical output power of the OFA 11 shown in FIG. . As described in the problem to be solved by the invention, when adding channels from 1 wave to 2 waves, the optical power per wave after amplification is temporarily 3 dB.
m becomes a factor that deteriorates the quality of the optical signal.

In the present invention, in order to prevent this, as shown in FIG. 4, X1 (-30 dB) in which only one wave is input.
m) to X2 (-27 dBm), the optical output power level Y2 for two waves is always set to -17DBm and ALC is set.
It is configured so that an optical signal can be output by control.
As a result, as shown in FIG. 5, channels are expanded from one wave to two waves, and the optical output power is temporarily -17d.
Even if it is reduced from Bm by 3 dBm, it has the lowest optical output Y3.
Since −20 dBm is secured, it is possible to sufficiently prevent the quality deterioration of the optical signal.

Further, an OF having a wide input dynamic range
In A, as shown in the conventional example of FIG. 14, the rise from shutdown is the lowest level optical output Y3 = −2.
Since the target light level rises from 0 dBm, the rising time B is delayed. On the other hand, in this embodiment, as shown in FIG. 4, the minimum level Y2 of the optical output power is set to -17 dBm and the maximum level Y1 is set to 10 dBm. The maximum level is 10 dBm
The reason is that it is applied to the optical output power of Class 1 of the safety standard in which the safety function is not defined.

Further, in this embodiment, the output dynamic range of the OFA is narrower than the output dynamic range of the conventional OFA. The amount becomes smaller. Therefore, in this embodiment, as compared with the rising time B of the conventional example shown in FIG. 14, the time required for the change from the lowest light level to the target value light level becomes shorter as shown in FIG. As a result, rise time A
Has the effect of being short and rising quickly.

Further, in this embodiment, when the optical input power to the OFA is low, the optical output power is set high and the ALC is set.
By controlling by the circuit, a large amount of drive current for the excitation LD flows, which makes it possible to stabilize and output the optical output.

Further, in this embodiment, as shown in FIG. 4, even if the optical input power of the OFA exceeds 0 dBm, the control of the ALC circuit works so that the optical output power is less than the maximum optical output of 10 dBm. Therefore, the output is less than the output specified by Class 1 of the safety standard and the operational safety can be secured.

(Embodiment 2) FIG. 7 is a configuration diagram showing the configuration of Embodiment 2 of the optical amplifier according to the present invention. In the figure, the point different from the first embodiment is that the optical output power is controlled by using only the ALC circuit 18 without using the AGC circuit 16, and the control execution unit 19 depends on the optical input power input to the OFA 11. A plurality of thresholds are set, and the pump LD 17 is driven by the ALC circuit 18 so that the optical output power output from the OFA 11 becomes a constant output power stepwise based on the optical input power detected by the PD 14. The current is controlled.

That is, in this embodiment, the OFA shown in FIG.
As shown in the diagram of the relationship between the optical input power and the optical output power, the control execution unit 19 determines that the optical input power is equal to or less than the first threshold X2 (between X1 and X2), which is the first exemplary embodiment. Similarly, the ALC circuit 18 controls the drive current of the pumping LD 17 so that the optical output power becomes a constant value of Y2. Further, the control execution unit 19 determines whether the optical input power is equal to or less than the threshold value X5 (between X2 and X5), the ALC circuit 18
The drive current of the pumping LD 17 is controlled so that the optical output power becomes a constant value of Y5. Further, the control execution unit 19 determines that the optical input power is equal to or less than the threshold value X6 (X5 to X6.
In the case of (interval), the drive current of the pump LD 17 is controlled by the ALC circuit 18 so that the optical output power becomes a constant value of Y6. Further, when the optical input power is equal to or higher than the upper limit second threshold value X3 (between X3 and X4), the control execution unit 19 uses the ALC circuit 18 to set the optical output power to a constant value of Y1 as in the first embodiment. Excitation LD1
7 drive current is controlled.

As described above, in this embodiment, the control execution unit sets a plurality of threshold values according to the optical input power, and P
Based on the optical input power detected in D, the ALC circuit controls the optical output power in a stepwise manner so as to become a constant output power, so that the same effect as that of the first embodiment is obtained, and
Since the AGC circuit used in the first embodiment is unnecessary,
The number of parts of the optical amplifier is reduced, the circuit configuration is simplified, and the manufacturing cost can be reduced.

(Third Embodiment) FIG. 9 is a block diagram showing the arrangement of an embodiment of an optical communication system using the optical amplifier according to the present invention. In the figure, an optical communication system includes an optical fiber 10, a transmitting station 20 and a receiving station 30 connected to both ends of the optical fiber 10, and an optical fiber according to the present invention provided at an arbitrary position on the optical fiber 10. Amplifier 4
It is constructed from 0 and 41.

The transmitting station 20 is composed of optical transmitters 21 and 22 that output optical signals of different wavelengths, and a WDM device 23 that wavelength-multiplexes the optical signals and sends WDM signal light to the optical fiber 10. ing. The receiving station 30 includes a WDM device 31 that wavelength-divides WDM signal light input from the optical fiber 10 and outputs optical signals having different wavelengths, and optical receivers 32 and 33 that receive these optical signals. There is.

In this system, the optical transmitter 22 and the optical receiver 33 are added devices, and this system configuration is used when a second light is newly added from the operating state of the first light. Is shown. 40 conventional optical amplifiers,
When used in the optical amplifier 41, the additional optical transmitter 2
When No. 2 is activated, the optical powers of the transmitted optical signals are the same, and the optical amplifiers 40 and 41 are driven by the drive current for one wave, so the optical output power is temporarily reduced by 3 dBm, and This leads to deterioration of signal transmission quality.

Therefore, when the optical amplifiers shown in Embodiments 1 and 2 of the present invention are used in this system, the optical output power is set in advance to the optical output power for two waves when operating one wave of light. Every other time, when the optical transmitter 22 of the second wave is added, the optical output power is reduced by 3 dBm, but the minimum level optical output of -20 dBm is secured, so that the quality deterioration of the optical signal can be sufficiently prevented. .

As described above, when the optical amplifier according to the present invention is used in the optical communication system, the optical output of the lowest level can be secured even if the number of optical transmitters is increased and the number of channels is increased. Deterioration is prevented, and good optical communication can be performed.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention.

[0052]

As described above, according to the first and second aspects of the present invention, when the optical power below the lower limit first threshold value or above the upper limit second threshold value is input to the optical amplifier. , The level control means controls the output level of the optical signal to a constant level, and when the optical power is between the first and second threshold values other than that, the gain control means controls the gain with respect to the optical power of the optical signal to obtain an optical output. Since the optical output is kept stable in the vicinity of the initial threshold value, it is possible to prevent the deterioration of the transmission quality of the optical signal due to the increase or decrease of the transmission channels and to improve the safety.

In the third aspect of the present invention, the optical input power when at least two optical signals are multiplexed is set as the first threshold value, and the level control means sets the optical input power in the lower limit control. The level control is performed so that the optical power of the optical signal output from the amplifier has a constant output level for two waves, so that the output is prevented from becoming close to the initial threshold, the optical output is stabilized, and the transmission channel The deterioration of the transmission quality of the optical signal due to the increase or decrease of In the upper limit control, the level control is performed so that the optical power of the optical signal output from the optical amplifier becomes a constant output level equal to or lower than the upper limit of the optical power set by the safety standard. Can improve the safety of.

Further, according to claim 4 of the present invention, a plurality of thresholds are set according to the optical input power, and the optical output power of the optical signal input to the optical amplifier by the ALC is set based on the detected optical input power. Since the constant output power is obtained by performing the stepwise control, it is possible to prevent the light output from becoming close to the initial threshold value Y3, and to secure and improve the stability of the light output.

According to a fifth aspect of the present invention, a stepwise threshold value including the optical power below the lower limit first threshold value or the optical power above the upper limit second threshold value is set, and the optical output power level is set. Is prevented from exceeding the lower limit value or the upper limit value, it is possible to prevent the deterioration of the transmission quality of the optical signal due to the increase / decrease of channels and improve the safety of the optical output.

According to the sixth aspect of the present invention, by controlling the output dynamic range of the optical amplifier to be narrow, the amount of change in the optical power output from the initial current value to the target value becomes small. As a result, The time until the rise of the optical power becomes faster at the time of shutdown.

Further, according to claim 7 of the present invention, since the optical communication system is provided with at least one optical amplifier according to claims 1 to 6, the deterioration of the transmission quality of the optical signal due to the increase or decrease of the transmission channel is prevented. , The safety of light output can be improved.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a relationship between an optical input power and an optical output power of an OFA for explaining OFA control.

FIG. 2 is a configuration diagram showing a configuration of a first embodiment of an optical amplifier according to the present invention.

3 is a flowchart for explaining a control operation of the optical amplifier shown in FIG.

FIG. 4 is a diagram showing a relationship between optical input power and optical output power of the OFA shown in FIG.

FIG. 5 is a state change diagram showing a state change of the optical level output from the optical amplifier of the embodiment when the number of channels is increased.

FIG. 6 is a diagram of an optical level showing a rising time from the time when the shutdown of the optical amplifier shown in FIG. 2 is released.

FIG. 7 is a configuration diagram showing a configuration of a second embodiment of the optical amplifier according to the present invention.

8 is a diagram showing the relationship between the optical input power and the optical output power of the OFA shown in FIG.

FIG. 9 is a configuration diagram showing a configuration of an embodiment of an optical communication system using the optical amplifier according to the present invention.

FIG. 10 is a configuration diagram showing a configuration of a conventional optical amplifier.

11 is a diagram showing a relationship between optical output power and optical input power of the OFA shown in FIG.

FIG. 12 is a characteristic diagram showing current-light output characteristics of a semiconductor laser.

FIG. 13 is a state change diagram showing a state change of the optical level output from the conventional optical amplifier when the number of channels is increased.

14 is a diagram of an optical level showing a rising time from the time when the shutdown of the optical amplifier shown in FIG. 10 is released.

[Explanation of symbols]

10 optical fibers 12, 13 Optical coupler 14,15 PD 16 AGC circuit 17 LD 18 ALC circuit 19 Control execution unit 20 transmitting stations 21,22 Optical transmitter 23,31 WDM device 30 receiving stations 32,33 Optical receiver 40,41 Optical amplifier

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Claims (7)

[Claims] 1. A light having a gain control means for controlling a gain for an optical signal and a level control means for controlling an output level of the optical signal, wherein the wavelength-multiplexed light is controlled by the gain control means and the level control means. In an optical amplifier that amplifies and outputs the optical power of a signal, at least one of a detection unit that detects the optical power input to the optical amplifier, and a first or second threshold value for the input optical power. When the threshold value is set and the optical power detected by the detection means is equal to or lower than the first threshold value or equal to or higher than the second threshold value, control by the level control means is executed; otherwise, the gain control is performed. An optical amplifier comprising control execution means for executing control by means. 2. The control executing means sets a lower limit value of the optical power as the first threshold value and an upper limit value of the optical power as the second threshold value. The optical amplifier according to. 3. The control execution means sets the input optical power when the optical signals of at least two waves are multiplexed as the first threshold value, and the level control means outputs the optical power from the optical amplifier. Level control is performed so that the optical power of the optical signal to be output becomes a constant output level of two waves, and the control execution means sets the second threshold value based on a safety standard, and the level control means 3. The level control is performed so that the optical power of the optical signal output from the optical amplifier becomes a constant output level equal to or lower than the upper limit value of the optical power set by the safety standard. The optical amplifier described. 4. An optical amplifier having level control means for controlling an output level of an optical signal, wherein the optical amplifier amplifies and outputs the optical power of the wavelength-multiplexed optical signal under the control of the level control means. Detection means for detecting the optical power of the input optical signal, a plurality of thresholds are set according to the optical power of the optical signal input to the optical amplifier, based on the optical power detected by the detection means An optical amplifier comprising: a control execution unit that executes control by the level control unit so that the optical power of the optical signal output from the optical amplifier becomes a constant output power stepwise. 5. The control execution means sets the optical power input to the optical amplifier when the optical signals of at least two waves are multiplexed as the first threshold value, and the level control means sets the optical power. The level control is performed so that the optical power of the optical signal output from the amplifier becomes a constant output level for two waves, or the control execution means sets the second threshold value based on a safety standard, and the level is set. The optical amplifier according to claim 4, wherein the control means performs level control so that the output power of the optical signal becomes a constant output level equal to or lower than an upper limit value of the output power set by the safety standard. 6. The control execution means executes the control in the output dynamic range of the optical amplifier when the optical signal has two waves and is set by a safety standard. An optical amplifier according to any one of 1. 7. An optical communication system for wavelength-multiplexing and transmitting a plurality of optical signals having different wavelengths, comprising at least one optical amplifier according to claim 1, which amplifies and outputs the power of the optical signal. An optical communication system characterized by the above.