JP2001156369A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier capable of realizing a wider input dynamic range and low noises. SOLUTION: The optical amplifier has a wavelength-band division section dividing light from a transmission line into a plurality of bands, a plurality of the first optical amplifying sections changing the command of an optical amplifying output when the alteration of divided light set in response to each divided light reaches a fixed value, a plurality of attenuating sections attenuating outputs from a plurality of the first optical amplifying sections respectively, a plurality of the second optical amplifying sections amplifying outputs from a plurality of the attenuating sections respectively, a mixing section mixing outputs from a plurality of the second optical amplifying sections, and a plurality of control sections changing the quantity of the attenuation of a plurality of the attenuating sections, respectively. The control sections alter the quantity of the attenuation of the attenuating sections in response to the difference of the commands of optical amplifying outputs before and after the change when the commands of the optical amplifying outputs of the first optical amplifying sections are changed. Accordingly, the deterioration of a noise index can be inhibited without altering the output-light levels of the attenuating sections before and after the variation of input-light levels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying device used in an optical repeater station or the like of an optical communication system, which realizes a wider input dynamic range and lower noise. With the aim of constructing a multimedia network in the future, an ultra-long distance and large-capacity optical communication device is required. As a method for realizing this large capacity, wavelength-division multiplexing (hereinafter, referred to as “wavelength-division multiplexing”)
Abbreviated as "WDM". Research and development are proceeding from the point of advantage that the method can effectively utilize the broadband and large capacity of the optical fiber. In particular, in an ultra-long distance optical communication system, an optical amplifying device for amplifying a WDM optical signal is necessary because the WDM optical signal is attenuated during transmission over an extremely long distance. In such an optical amplifying device, a wide input dynamic range is required due to a difference in distance or transmission loss between optical relay stations, and at the same time, low noise is required to transmit an ultra-long distance.

[0002]

2. Description of the Related Art In an optical communication system for transmitting a WDM optical signal, when an optical amplifier is inserted into an optical transmission line,
The transmission distance is limited by a gain tilt (gain tilt) based on the gain wavelength characteristic of the optical amplifier. This is because, when optical amplifiers are connected in cascade in order to increase the transmission distance, gain tilts generated in the respective optical amplifiers accumulate.
In a low optical level channel of a DM optical signal, an optical signal to noise ratio is used.
o, hereinafter abbreviated as “optical SNR”. ) Is deteriorated, and the waveform is deteriorated by a nonlinear optical effect or the like in a channel of a high optical level in the WDM optical signal.

Therefore, an optical amplifying device for making the gain wavelength characteristic substantially flat has been proposed by the same applicant as the present patent application in the specification of Japanese Patent Application No. 11-074371, which has not been disclosed. FIG. 23 is a diagram showing a configuration and a level diagram of a preceding optical amplifying device. This FIG.
This is an optical amplifying device proposed in the specification of No. 74371.

[0004] In FIG.
000 is input to an optical branching coupler.
upler, hereinafter abbreviated as "CPL". ) The light enters the optical amplifier 1013 via the 1011 and the CPL 1012, and is amplified by the gain G1. The amplified light is CPL1
014 via an optical variable attenuator
uator, hereinafter abbreviated as “VAT”. ) And is attenuated. The attenuated light enters the optical amplifier 1017 via the CPL 1016 and is amplified with a gain G2. The amplified light is output as output light of the optical amplifier 1000 via the CPL 1018.

CPL 1011, 1012, 1014, 1
016 and 1018 distribute incident light into two.
The light distributed by the CPL 1011 is a photodiode (hereinafter referred to as “P”) that generates a current according to the light level of the received light.
D ". ) 1026 and photoelectrically converted. An anode terminal of the PD 1026 is connected to a power supply of a voltage Vcc, and a cathode terminal is connected to a resistor 102 having a resistance value R1.
5 is grounded. The voltage between the terminals of the resistor 1025 is input to the control circuit 1027 as the output of the PD 1026, and the control circuit 1027 outputs the VAT based on this output.
The attenuation of 1015 is adjusted. Further, the control circuit 102
7 is an automatic gain control circuit (automa
Tic gain controller, hereinafter abbreviated as “AGC”. ) Optical amplifier 1013 via 1019, 1020,
Adjust the gain of 1017. The PD 1026 and the resistor 1025 constitute a monitor circuit that detects the light level of the input light.

Light and CP distributed by CPL 1012
The light distributed by L1014 is incident on the AGC 1019, which determines the gain of the optical amplifier 1013 based on the optical power of these lights, and
Is adjusted to the gain G1. The light distributed by the CPL 1016 and the light distributed by the CPL 1018
0, the AGC 1020 judges the gain of the optical amplifier 1017 based on the optical power of these lights, and adjusts the optical amplifier 1017 to the gain G2.

FIG. 23 (b) is a level diagram showing light levels at respective points a, b, c and d of the optical amplifying apparatus 1000 shown in FIG. 23 (a). The horizontal axis of FIG.
The vertical axis represents the light level. In FIG. 23B, the light input to the optical amplifying apparatus 1000 is amplified by the optical amplifier 1013 between a and b, and VAT is applied between bc.
Attenuated at 1015 and the optical amplifier 101 between cd
The signal is amplified again at 7 and output.

In such an optical amplifier 1000, FIG.
When the optical level of the input light fluctuates by Δ as shown in FIG. 3B, by changing the attenuation of the VAT 1015 by −Δ, the sum of the gain G1 of the optical amplifier 1013 and the gain G2 of the optical amplifier 1017 is obtained. Operates to maintain a constant.

That is, the gain G1 of the optical amplifier 1013 before and after the fluctuation of the optical level of the input light is G1x, G1x #
When the gain G2 of the optical amplifier 1017 is G2x, G2x #, the operation is performed such that G1x + G2x = G1x # + G2x # (Equation 1). By operating in this way, such an optical amplifier 1000 can amplify input light to a desired optical level and make the gain wavelength characteristic substantially flat.

This is because the following phenomenon is observed in the optical amplifier. FIG. 24 is a diagram illustrating a relationship between the gain of the optical amplifier and the gain wavelength characteristic. In FIG. 24, as shown by the center curve, when the gain Ga of the optical amplifier is a certain gain Gaf, the gain wavelength characteristic is flat (dGa / dλ) in the amplification wavelength band for amplifying the WDM optical signal.
= 0). When the gain Ga of the optical amplifier is larger than the gain Gaf as shown in the upper curve, the gain wavelength band has a negative slope (dGa / dλ <0) in the amplification wavelength band for amplifying the WDM optical signal. . On the other hand, when the gain Ga of the optical amplifier is smaller than the gain Gaf, as shown in the lower curve, the gain wavelength band has a positive slope (dGa / dλ) in the amplification wavelength band for amplifying the WDM optical signal.
> 0).

Due to such a phenomenon, the optical amplifying device 100
0 means that the optical amplifiers 1013 and 1017 operate so that one gain is increased and the other gain is decreased according to the change in the optical level of the input light, so that the gains are opposite to each other, and the optical amplification is performed. The gain wavelength characteristic of the device 1000 can be made substantially flat. The noise figure of such an optical amplifier 1000 is given by 10 ^{(NF / 10)} = 10 ^{(NF1 / 10)} +10 ^{((NF2-Pout + Lvat + Pin) / 10)} (Equation 2). Here, NF (dB) is the optical amplification device 1
NF1 (dB) is the optical amplifier 101
NF2 (dB) is the total noise figure obtained by adding the loss of the CPL1016 to the noise figure of the optical amplifier 1017, and Pout (dB / channel). Is
The output light level of the optical amplifier 1013, Lvat (dB), is
VAT1015 attenuation, Pin (dB / channel) is:
The noise figure of the optical amplifier 1013.

On the other hand, the system gain of the optical communication system differs for each optical relay station because the distance between the optical relay stations is different. The system gain is the maximum loss value that can be taken between the optical repeaters due to the difference in transmission / reception level between the optical repeaters,
More specifically, it is a value obtained by adding a margin to the transmission loss between optical relay stations. The transmission loss depends not only on the distance between the optical repeaters, but also on the temperature fluctuation and aging of the optical transmission line.

When an optical amplifier is used for an optical repeater station or the like, a wide input dynamic range is required to cope with various system gains. In order to cope with these various system gains, there is a method of lowering the input light level by an optical attenuator and then inputting the same to an optical amplifier. In this method, the fluctuation of the system gain is absorbed by the optical attenuator. When such an optical attenuator is not used, the input dynamic range of the optical amplifier is required to be wider than the difference between the minimum system gain and the maximum system gain in the optical communication system.

Further, it is known that the signal waveform of an optical signal transmitted through an optical transmission line such as an optical fiber is distorted by nonlinear optical effects such as self-phase modulation, four-wave mixing, and cross-phase modulation. The nonlinear optical effect increases when the optical level of the optical signal incident on the optical transmission line is increased, and thus the optical level of the optical signal incident on the optical transmission line is limited. The degree of the nonlinear optical effect is determined by a dispersion-shifted fiber (hereinafter, referred to as “DS”).
F ”. ) Or non-zero dispersion shifted fiber (no
n-zero-dispersion-shifted fiber, hereinafter referred to as “NZ-D
SF ”. ) Or single mode optical fiber (single
mode fiber, hereinafter abbreviated as “SMF”. ), The upper limit of the optical level of the optical signal is also different. For example, among SMF, NZ-DSF and DSF, the upper limit of SMF is the largest and the upper limit of DSF is the smallest. The difference between the upper limits can be several dB. In order to cope with such an optical fiber type with one optical amplifying device, conventionally, an optical attenuator is connected to an output terminal of the optical amplifying device.

The optical amplifier has an output end open detection function in order to ensure the safety of a worker who handles the optical amplifier. This output end open detection function detects whether the output end of the optical amplifier is open or not by detecting the reflected light from the open end, and when the output end is open, detects the optical level of the output light in the optical amplifier. It is a function to reduce.

[0016]

By the way, FIG.
In the optical amplifying apparatus 1000 shown in FIG. 23A, to cope with a wider input dynamic range, FIG.
Δ in becomes large. Since the output light level of the optical amplifier 1013 has an upper limit similarly to a general optical amplifier, the optical amplifier 1000 uses the attenuation amount Lvat of the VAT 1015.
Becomes larger. Therefore, such an optical amplification device 100
At 0, there is a problem that the output light level of the VAT 1015 decreases, and as can be seen from (Equation 2), the noise figure deteriorates significantly.

On the other hand, when the optical attenuator is used as described above to cope with a wider input dynamic range, the optical amplifying device is designed according to the maximum system gain, and the optical attenuator lowers the input light level. Therefore, the optical amplifier degrades its optical SNR before use. For this reason, there is a problem that the transmission distance is reduced.

There is a problem that a monitor circuit for detecting a light level needs to have a wider dynamic range in order to support a wider input dynamic range. Further, there is a problem that it is necessary to diversify the output light level of the optical amplifying device in order to be able to connect to various kinds of optical fibers already laid.

In order to cope with the need to be able to connect to various kinds of optical fibers already laid, an optical attenuator is used to determine whether the output end of the optical amplifier is open or not. It must be detected at both the output end of the amplifier and the output end of the optical attenuator, and it is necessary to detect weak reflected light, which makes it difficult to detect that the output end is open.

Accordingly, an object of the present invention is to provide an optical amplifier having a wider input dynamic range without deteriorating the noise figure. It is another object of the present invention to provide an optical amplifying device that can be connected to various types of optical fibers without impairing the output end opening function, in addition to the above-described objects. Still another object of the present invention is to provide an optical amplifier capable of amplifying light in a wide wavelength band.

It is another object of the present invention to provide an optical communication system in which an optical amplifier having a wider input dynamic range without deterioration of a noise figure is used for an optical repeater station or the like.

[0022]

SUMMARY OF THE INVENTION The above-mentioned object is achieved by providing a wavelength band dividing section for dividing light from a transmission line into a plurality of bands, and a plurality of wavelength bands. A plurality of first optical amplifiers for changing a target value of the optical amplification output when the change of the divided light reaches a predetermined value; a plurality of attenuators for attenuating the outputs of the plurality of first optical amplifiers; A plurality of second amplifiers each amplifying the output of the attenuation unit
An optical amplification unit, a multiplexing unit that multiplexes the outputs of the plurality of second optical amplification units, and a plurality of control units that change the amounts of attenuation of the plurality of attenuating units, respectively, are provided. When changing the target value of the optical amplification output of the amplification unit, the attenuation unit according to the difference between the target value of the optical amplification output of the first optical amplification unit and the target value of the optical amplification output of the first optical amplification unit after the change. Is achieved by changing the amount of attenuation.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a basic configuration of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a basic configuration of the present invention. 2 and 3 are diagrams showing a level diagram of the present invention. FIG. 2 shows a level diagram when the number of input light modes described later is, for example, three. In FIG. 3, (a) shows a level diagram when the level of the input light is within the range a,
(B) shows a level diagram when the level of the input light is within the range b. 2 and 3, the vertical axis represents the light level (dBm), and the horizontal axis represents the position.
B, C, and D correspond to the points A, B, C, and D shown in FIG. That is, the location A is the first optical amplification unit 11
, The point B is between the first optical amplifier 11 and the optical attenuator 12, the point C is between the optical attenuator 12 and the second optical amplifier 13, and the point D Is the emission side of the second optical amplifier. In FIG. 1, input light input to an optical amplifier 10 enters a first optical amplifier 11. The first optical amplifying unit 11 is an optical amplifying unit that changes the output light target value when the change of the input light becomes a predetermined value.
Injected to The optical attenuator 12 attenuates the output light of the first optical amplifier 11, and the output light is emitted to the second optical amplifier 13. The second optical amplifier 13 amplifies the output light of the optical attenuator, and the output light is emitted as output light of the optical amplifier 10.

The optical amplifying device 10 includes an optical attenuator 12
And a control unit 14 for changing the amount of attenuation of the
4 is based on the difference between the output light target value of the first optical amplification unit 11 and the changed output light target value of the first optical amplification unit 11 when the output light target value of the first optical amplification unit 11 is changed. Light attenuator 12
Change the amount of attenuation. The predetermined value of the input light is a plurality of values obtained by dividing the level of the input light into predetermined ranges, and the output light target value of the first optical amplifier 11 is provided corresponding to each of the divided values. . For example, as shown in FIG. 2, three modes of the input light are set at the light level,
The first target value a is defined as the first target value for the in-mode a in the range a, and the first target value a is defined as the first target value for the in-mode b in the range b.
The target value b is defined as the first target value, and the first target value c is defined as the first target value for the in-mode c in the range c.

Here, each of the ranges may partially overlap with each other, such as ranges a and b, and ranges b and c
, The boundaries of the ranges may be in contact. In such an optical amplifying device 10, when a certain in-mode is selected, the output optical level of the first optical amplifying unit 11 is not dependent on the input optical level within that range, and the first optical amplifying unit 11 has the first optical level corresponding to the in-mode.
It is almost fixed to the target value.

For example, as shown by a solid line in FIG.
When the in-mode a is selected as the mode of the input light, the output of the first optical amplifying unit 11 (point B in FIG. 2) becomes the first target value a even if the input light level changes within the range a. Almost fixed. In FIG. 2, the level diagram of the in-mode b is indicated by a broken line, and the level diagram of the in-mode c is indicated by a chain line. In addition, since the level diagrams from the location C to the location D are the same for the in-mode a, the in-mode b, and the in-mode c, they are apparently shown only by solid lines.

When the mode of the input light is changed, the attenuation of the light attenuator 12 is smaller in absolute value than the value X obtained by subtracting the changed first target value from the first target value before the change. It is adjusted by the amount of attenuation of the same sign. Therefore, the light attenuating unit 1
The output light level No. 2 (point C in FIG. 2) does not become lower even after the change of the mode of the input light than before the change of the mode of the input light.

In particular, in the above configuration, the output light of the optical attenuator 12 has a constant value irrespective of the output light target value of the first optical amplifier. For example, when the mode of the input light is changed, the amount of attenuation of the light attenuator 12 is equal to the absolute value equal to the value X obtained by subtracting the changed first target value from the first target value before the change, and has the same sign. When the attenuation is adjusted by the amount of attenuation, the output light level of the optical attenuation unit 12 becomes equal to that before the change of the mode of the input light even after the change of the mode of the input light as shown in FIG.
0).

Therefore, according to the present invention, the optical amplifier 10
Before and after this change, the degradation of the noise figure can be suppressed. Therefore, in the present invention, the input dynamic range can be expanded by setting a plurality of input light modes according to the input light level. Since the first target value is set in accordance with the mode of each input light and the attenuation of the optical attenuator 12 is adjusted, the noise figure is not deteriorated even if the input dynamic range is expanded.

In the above description, the case where the input dynamic range is divided into three in-modes has been described. However, the present invention can be similarly applied to any number of input light modes. The in mode refers to each mode of the input light mode, and the out mode described below refers to each mode of the output light mode.

Here, in FIG. 1, in the optical amplifying device 10, the second optical amplifying unit 13 amplifies the output light of the optical attenuating unit 12 to a predetermined output light target value.
When the output light target value of the second optical amplifier 13 is changed, the difference between the output light target value of the first optical amplifier 11 and the changed output light target value of the first optical amplifier 11 A configuration in which the amount of attenuation of the optical attenuator 12 is changed according to a value obtained by adding the difference between the output light target value of the two-light amplifier 13 and the changed output light target value of the second light amplifier 13. May be.

In FIG. 1, the optical amplifier 10
Is a first optical amplifying unit 11, an optical attenuating unit 12 for attenuating the output light of the first optical amplifying unit 11, and a second optical amplifying unit for amplifying the output light of the optical attenuating unit 12 to a predetermined output light target value. 13 and a control unit 14 for changing the amount of attenuation of the light attenuating unit 12.
When changing the target output light value of the second optical amplifier 13, the controller 14 determines the difference between the target output light value of the second optical amplifier 13 and the target output light value of the second optical amplifier 13 after the change. May be configured by changing the amount of attenuation of the light attenuating unit 12 according to.

In such an optical amplifier 10, for example,
As shown in FIG. 3A, when the in mode a is selected as the input light mode, three output light modes are set at the light level, and the second mode is set for the out mode Sa.
The target value Sa is defined as a second target value, the second target value Ta is defined as a second target value for the out mode Ta, and the second target value Ua is defined as a second target value for the out mode Ua. Is done. Further, as shown in FIG. 3B, when the in mode b is selected as the mode of the input light, three out modes are set in the light level,
The second target value Sa is defined as a second target value for the out mode Sa, the second target value Ta is defined as a second target value for the out mode Ta, and the second target value is defined for the out mode Ua. Ua is defined as the second target value.
Then, although not shown, the second target value is similarly defined when the in-mode c is selected as the mode of the input light.

In such an optical amplifier 10, for example,
When the in-mode a is selected as the mode of the input light, as described above, even if the input light level changes within the range a, the output light level of the first optical amplifier 11 (FIG. 3A) B) is substantially fixed to the first target value a,
Output light level of light attenuator 12 (location C in FIG. 3A)
Becomes a predetermined constant value V0. This situation is shown by a solid line in FIG.

When the mode of the output light is changed, the attenuation amount of the light attenuator 12 is smaller in absolute value than the value Y obtained by subtracting the changed second target value from the second target value before the change. It is further adjusted by the amount of attenuation of the opposite sign. Further, when the mode of the output light is changed, the amount of attenuation of the light attenuator 12 is equal to the value Y obtained by subtracting the second target value after the change from the second target value before the change, and the absolute value is equal to the opposite sign. You may make it further adjust only by the amount of attenuation.

When the mode of the input light and the mode of the output light are changed, the attenuation amount of the light attenuator 12 is a value X obtained by subtracting the first target value after the change from the first target value before the change.
Is obtained, a value Y obtained by subtracting the changed second target value from the second target value before the change is obtained, and the value obtained by subtracting the value Y from the value X is equal in absolute value to the attenuation amount of the opposite sign-(X− The adjustment may be made only for Y).

Therefore, in such an optical amplifying device 10, the degradation of the noise figure can be suppressed before and after the above-mentioned change in the input light level.
The output mode can be selected according to the output light level of the optical amplifying device 10, so that the output light of the optical level optimal for the type of the optical transmission line connected to the output side of the optical amplifier 10 can be emitted.
Therefore, the output light does not undergo significant waveform deterioration due to nonlinear optical effects such as self-phase modulation, cross-phase modulation, and four-wave mixing while propagating through the optical transmission line.

On the other hand, in FIG. 1, in the optical amplifying device 10, the input light input to the first optical amplifying unit 11 is a wavelength multiplexed optical signal, and the output light of the second optical amplifying unit 13 is
The output light level of a specific wavelength in the optical signal may be a constant value. In such an optical amplifying device 10, since the output of the second optical amplifying unit 13 is controlled to be constant, it is possible to absorb a variation in attenuation of the optical attenuator used in the optical attenuating unit 12 due to a product. For this reason, the optical amplification device 10
Is maintained substantially constant.

In FIG. 1, in the optical amplifying device 10, the input light input to the first optical amplifying unit 11 is a wavelength-multiplexed optical signal and the output light 13 of the second optical amplifying unit.
May have a constant gain. Further, FIG.
In the optical amplifying device 10, the first optical amplifying unit 11
Are a first optical amplifier 21 for amplifying the received light and a second
Optical amplifier 23, first optical amplifier 21, and second optical amplifier 23
And an optical attenuator 22 such that the sum of the gain of the first optical amplifier 21 and the gain of the second optical amplifier 23 and the output light level of the second optical amplifier 23 become constant.
And a controller 24 for adjusting the amount of attenuation of the control signal.

In FIG. 1, in the optical amplifying device 10, the first optical amplifying unit 11 and the second optical amplifying unit 13 include
A first optical amplifier 21 and a second optical amplifier 23 for amplifying received light, an attenuator 22 connected between the first optical amplifier 21 and the second optical amplifier 23, and a gain of the first optical amplifier 21; Sum of gain of second optical amplifier 23 and second optical amplifier 2
3 may be provided with a controller 24 for adjusting the attenuation of the optical attenuator 22 so that the output light level becomes constant.
In FIG. 1, the above-described detailed configuration of the second optical amplifying unit 13 is omitted.

Next, an embodiment of the present invention will be described. (Configuration of the First Embodiment) FIG. 4 is a diagram showing the overall configuration of the optical amplifying device according to the first to fourth embodiments. FIG. 4 is also a diagram showing an overall configuration of an optical amplifying device according to second to fourth embodiments described later.

FIG. 5 is a diagram showing a detailed configuration of the pre-stage optical amplifier, the pre-stage optical attenuator, and the middle-stage optical amplifier in the first to fourth embodiments. FIG. 5 shows a second embodiment to a fourth embodiment described below.
It is also a figure which shows the detailed structure of a front | stage optical amplification part, a front | stage optical attenuation part, and a middle stage optical amplification part. FIG. 6 is a diagram illustrating a detailed configuration of the rear-stage optical attenuator and the rear-stage optical amplifier in the first embodiment.

In FIG. 4A, the WDM optical signal input to the optical amplifier 301 in the first embodiment is input to the pre-stage optical amplifier 101 and amplified. The amplified WDM optical signal is input to the pre-stage optical attenuator 102 and attenuated. The attenuated WDM optical signal enters the middle optical amplifier 103 and is amplified. The amplified WDM optical signal is input to the post-stage optical attenuator 104,
Attenuated. The attenuated WDM optical signal is input to the subsequent optical amplifier 105 and amplified. Amplified WDM
The optical signal is output from the optical amplifying device 301 as
Be injected.

This WDM optical signal is an optical signal set in the wavelength band of C band (1530 to 1570 nm). The optical amplifying device 301 has two input light modes, i.e., in-mode 1 and in-mode 2. For example, in the in-mode 1, the input light level is -30 to -20.
(DBm / channel) of the input light. In the in-mode 2, the input light level is −25 to −15.
(DBm / channel) of the input light.

Next, the first-stage optical amplifier 101, the first-stage optical attenuator 102, the middle-stage optical amplifier 103, and the second-stage optical attenuator 10
4 and the configuration of the post-stage optical amplifier 105 will be described in order. First, the configuration of the pre-stage optical amplifier 101 will be described with reference to FIG. In FIG. 5, a WDM optical signal input to the optical amplifying device 301 in the first embodiment is input to the CPL 111 in the pre-amplifier 101. The CPL 111 is an optical component that splits incident light into two and emits the same, and the same applies to other CPLs described later.
As the CPL, for example, a micro optical element type optical splitter / coupler such as a half mirror, an optical fiber type optical splitter / coupler of a fused fiber, an optical waveguide type optical splitter / coupler, or the like can be used.

One WDM optical signal distributed by the CPL 111 enters the PD 121, and the other enters an optical isolator (hereinafter abbreviated as “ISO”) 112. The PD 121 is a photoelectric converter that generates a current according to the optical power of the received light, and the same applies to other PDs described later. In addition, ISO 112
It is an optical component that transmits light only in one direction, and the same applies to other ISOs described later. The ISO can be configured by, for example, disposing a Faraday rotator between two polarizers shifted by 45 degrees. ISO is
It plays a role in preventing the reflected light from the connection portion of each optical component in the device from propagating to any places. In particular, when the reflected light returns to the semiconductor laser, the semiconductor laser
Oscillation modes are changed or noise is generated due to reflected light having different phases and amplitudes. Therefore, I
This adverse effect is prevented by SO.

The output from the PD 121 is a variable gain amplifier 133 and a switch (hereinafter abbreviated as “SW”).
127. SW127 is a switch of one input and four outputs. Each of the four output terminals has a resistor 128 having a resistance R1, a resistor 129 having a resistance R2, a resistor 130 having a resistance R3 and a resistor 130 having a resistance R4. Resistor 131
Is connected, and each resistor 128,
129, 130, 131 are grounded. These resistance values R1 to R4 are determined according to the mode of the input light of the optical amplifier 301. Then, PD is performed by SW127.
When the voltage between the terminals of the resistor connected to the
Of the AGC 12 via the variable gain amplifier 133
2 and logarithmic conversion circuit (log amplifier)
G ”. ) 124.

The gain of the variable gain amplifier 133 is equal to SW12
7 is switched from the PD 121 to the variable gain amplifier 1
It is varied to keep the gain up to the output of 33 constant.
These PD 121, SW 127 and resistor 128, 1
The circuit consisting of 29, 130, 131 is an optical amplifier 30
This is a monitor circuit for detecting the optical level of the WDM optical signal input to the input unit 1.

The WDM optical signal from the ISO 112 is incident on the CPL 113. On the other hand, CPL113
A laser diode (hereinafter, referred to as a laser diode) is used as excitation light for the erbium-doped optical fiber 114 described later.
Abbreviated as "LD". ) 119 is also incident. As the LD 119, for example, various semiconductor lasers such as a Fabry-Perot laser, a distributed feedback laser, and a distributed Bragg reflection laser can be used. The same applies to other LDs described later.

The WDM optical signal from the ISO 112 and the laser light from the LD 119 are multiplexed to form an erbium doped fiber (hereinafter referred to as “Ebium doped fiber”).
DF ". ) 114. The erbium element is one of the rare earth elements of the lanthanoid and has an element symbol Er and an atomic number of 68. Elements belonging to lanthanoids have similar properties to each other.

The EDF 114 absorbs the excitation light from the LD 119 to excite the Er ions in the EDF 114 to form a population inversion. When a WDM optical signal is incident in a state where the population inversion is formed, the WDM optical signal is induced and stimulated radiation occurs, and the WDM optical signal is amplified. Other EDFs to be described later also amplify light similarly.

As described above, since the LD 119 is an excitation light source for the EDF 114, the oscillation wavelength of the LD 119
The excitation wavelength is set to 114, for example, 1480 nm. Alternatively, it may be 980 nm or the like. The WDM optical signal amplified by the EDF 114 is incident on a gain equalizer (hereinafter, abbreviated as “GEQ”) 116 via the ISO 115. GEQ116 is E
This is an optical component for compensating the gain wavelength characteristic of the DF 114 to a substantially flat gain wavelength characteristic in the wavelength band of the WDM optical signal. The same applies to other GEQs described later except that the EDF to be compensated is different. As GEQ, EDF to be compensated
An optical filter or the like in which the loss wavelength characteristic is matched to the same shape as the gain wavelength characteristic can be used.

The WDM optical signal from the GEQ 116 is
The light enters the CPL 117. One of the WDM optical signals distributed by the CPL 117 is
The other WDM optical signal input to the AT 141 is
D120. The output from the PD 120 is converted into a voltage between terminals by a resistor (not shown in FIG. 5) and input to the AGC 122 and the LOG 123. As for the PD described below, unless otherwise specified.
Similarly to the PD 120, the output of the PD is obtained by converting the current value of the PD into a terminal voltage by a resistor (not shown).

The AGC 122 determines the gain of the EDF 114 from the output from the PD 120 and the output from the PD 121 via the variable gain amplifier 133, and determines the drive current (injection current) of the LD 119 within the range where the injection current does not reach the limiter value. ) Is adjusted so that the gain of the EDF 114 becomes constant at a predetermined gain. This predetermined gain corresponds to the low optical level WDM input to the optical amplifier 301.
The system is set in consideration of reducing the noise figure of the optical signal.

The LOG 123 converts the output from the PD 120 into a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of a subtractor 125. The LOG 124 converts the output from the PD 121 via the variable gain amplifier 133 into a logarithmic value of the voltage level, and the converted logarithmic value is input to the other input terminal of the subtractor 125. The subtractor 125 is a LOG12
The value obtained by subtracting the output of LOG 124 from the output of 3 is output to the subtractor 126. From the output of this LOG123, L
The value obtained by subtracting the output of the OG 124 corresponds to the gain of the EDF 114.

The subtractor 126 outputs a value obtained by subtracting the output of the subtractor 125 from a predetermined reference voltage Vref 1 to an adder 161 in the middle-stage optical amplifier 103. The reference voltage Vref1 is a voltage value that is referenced to make the sum of the gains of the pre-stage optical amplifier 101 and the middle-stage optical amplifier 103 a predetermined constant value Gs1. Next, the pre-stage light attenuator 102
Will be described with reference to FIG.

The WDM optical signal from the CPL 117 in the pre-stage optical amplifier 101 enters the CPL 151 in the middle-stage optical amplifier 103 via the VAT 141. VAT1
Reference numeral 41 denotes an optical component capable of attenuating and emitting incident light and changing the amount of attenuation, and the same applies to other VATs described later. As the VAT, for example, an attenuation disk is inserted between incident light and emission light, and a metal attenuation film whose thickness is continuously changed in the rotation direction is deposited on the surface of the attenuation disk, and this attenuation is performed. A variable optical attenuator that adjusts the amount of attenuation by rotating the disk, and a magneto-optical crystal between the incident light and the emitted light, and a polarizer on the exit side of the magneto-optical crystal, and a magnetic field is applied to the magneto-optical crystal. An optical variable attenuator or the like that adjusts the amount of attenuation by changing the strength of the magnetic field by applying it can be used.

On the other hand, the output according to the output light level of the WDM optical signal output from the middle optical amplifier 103 to the second optical attenuator 104 is transmitted from the PD 159 in the middle optical amplifier 103 to the LOG 144 in the first optical attenuator 102. Is entered. L
The OG 144 converts this input into a logarithmic value of the voltage level, and converts the converted logarithmic value to an automatic output control circuit (automati
c Level controller, hereinafter abbreviated as “ALC”. )
143 is input to one input terminal.

The ALC 143 compares the predetermined reference voltage Vref2 with the value from the LOG 144 so that the optical level per channel of the WDM optical signal emitted from the middle optical amplifier 103 becomes constant. To
The amount of attenuation of the VAT 141 is adjusted. The reference voltage Vref2 is
The output light level (CPL 156) of the part composed of the pre-stage optical amplifier 101, the pre-stage optical attenuator 102, and the middle-stage optical amplifier 103
Is a voltage value that is referred to for setting the output light level output from the optical attenuator to the subsequent optical attenuation unit as the first target value, and is prepared to be equal to the number of modes of the input light. For example, in mode 1
, A reference voltage Vref2M1 for the in-mode 1 is prepared, and a reference voltage Vref2M2 for the in-mode 2 is prepared for the in-mode 2.

Next, the configuration of the middle optical amplifier 103 will be described with reference to FIG. The WDM optical signal from the VAT 141 in the upstream optical attenuator 102 is incident on the CPL 151 in the middle optical amplifier 103. CPL151
One WDM optical signal distributed by the above is input to the PD 157, and the other WDM optical signal is input to the GEQ 152. The GEQ 152 compensates a gain wavelength characteristic of the EDF 155 described later to be substantially flat.

The WDM optical signal from the GEQ 152 is
The light enters the CPL 154 via the ISO 153. On the other hand, laser light from the LD 158 is also incident on the CPL 154. The WDM optical signal from the ISO 153 and the laser light from the LD 158 are multiplexed by the CPL 154 and input to the EDF 155.

The EDF 155 amplifies the incident WDM optical signal and outputs the amplified signal to the CPL 156. CPL156
One of the WDM optical signals distributed by the above is an optical attenuator (hereinafter abbreviated as “ATT”) in the subsequent optical attenuator 104.
171 (FIG. 6) and the other WDM optical signal is incident on PD 159. The output from the PD 159 is input to the AGC 162 and the above-described LOG 144 in the pre-stage optical attenuator 102.

On the other hand, the output from the PD 157 is L
Input to OG160. LOG160 is the PD1
The output from 57 is converted to a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of adder 161. The other input terminal of the adder 161 receives an output from the above-described subtractor 126 in the pre-stage optical amplifier 101.

The adder 161 adds the output of the LOG 160 and the output of the subtractor 126, and outputs the added value to an antilog amplifier (hereinafter, referred to as "Anti-LOG").
". 163). Anti-LOG 1
63 performs an inverse logarithmic conversion of the added value, and outputs the converted value to the AGC 162. AGC 162 is the PD
The drive current (injection current) of the LD 158 is adjusted so that the sum of the gain of the pre-stage optical amplification unit 101 and the gain of the middle-stage optical amplification unit 103 is constant based on the output from the anti-LOG 159 and the output from the Anti-LOG. Thus, the gain of the EDF 155 is adjusted.

Next, the configuration of the post-stage light attenuator 104 will be described with reference to FIG. The WDM optical signal from the CPL 156 in the middle optical amplifier 103 is
, And is incident on the CPL 181 in the post-stage optical amplification unit 105. The ATT 171 is prepared for each mode of the input light, and the attenuation of the ATT 171 for the in-mode 1 is set in consideration of the output light level of the optical amplifier 301. The amount of light attenuation of the ATT 171 for the in-mode 2 is determined by subtracting the input light level in the case of the in-mode 1 from the input light level in the case of the in-mode 2 in the subsequent optical attenuator 104. It is set larger than the amount of attenuation.

Next, the configuration of the post-stage optical amplifier 105 will be described with reference to FIG. The WDM optical signal from the ATT 171 in the downstream optical attenuator 104 enters the CPL 181 in the downstream optical amplifier 105. One WDM optical signal distributed by the CPL 181 is input to the PD 187, and the other WDM optical signal is input to the CPL 184 via the GEQ 182 and the ISO 183.

The PD 187 is connected to a resistor 20 having a resistance value Rerf1.
1, and the voltage between the terminals of the resistor 201 is PD
The output from 187 is output to one terminal of AGC 190. The GEQ 182 compensates for the gain wavelength characteristic of the EDF 185 almost flat. The CPL 184 has L
The laser beam from D188 is also incident. These ISO1
The WDM optical signal from 83 and the laser light from LD 188 are multiplexed by CPL 184 and input to EDF 185.

The EDF 185 amplifies the input WDM optical signal and outputs the amplified signal to the CPL 186. CPL186
One WDM optical signal distributed by the above is emitted as output light of the optical amplifying device 301, and the other WDM optical signal is incident on the PD 189. The PD 189 is grounded via a resistor 202 having a resistance value Rerf2,
2 is the output of the PD 189 and the AGC 190
Is output to the other terminal.

The AGC 190 determines the gain of the EDF 185 from the output from the PD 187 and the output from the PD 189, and drives the LD 188 so that the gain becomes a predetermined constant value (injection current). Is adjusted, the gain of the EDF 185 is adjusted. Therefore, the setting of the gain of the post-stage optical amplifying unit 105 depends on the AGC 190
May be set so that the output ratio between the PD 189 and the PD 187 becomes a predetermined constant value.

Here, AGC 122, 162, 190
More specifically, as shown in FIG. 5 (b), an arithmetic circuit 135 and an arithmetic circuit 137 are provided, and two inputs Pia,
Pib is input to a division circuit 135, and the division circuit 135 calculates the ratio Pia / Pib. This ratio is calculated by the arithmetic circuit 1
37 is input to one terminal, and a predetermined value is input to the other terminal. Then, the arithmetic circuit 137 compares the ratio with a predetermined value, and outputs an output value according to the result. The same applies to AGC described later.

(Operation and Effect of First Embodiment) When the optical amplifying apparatus 301 of the first embodiment is installed as an optical repeater station of an optical communication system, the optical transmission connected to the input side of the optical amplifying apparatus 301 The mode of the input light and the SW 127 are set in accordance with the light level output from the road. For example, when the light level is -30 to -20 (dBm / channel), the in-mode 1 is selected, and thus the reference voltage Vref2
Indicates that the reference voltage Vref2M1 for the in-mode 1 is set and A
As the TT 171, an ATT having an attenuation amount for the in-mode 1 is set. Then, the monitor circuit determines that the light level is -30.
A resistor corresponding to the case of ２０−20 (dBm / channel), for example, the resistor 128 is selected, and the SW 127 is selected.
Is switched to connect the PD 121 and the resistor 128. Therefore, AGC122 and LOG12
Reference numeral 4 denotes a voltage between terminals of the resistor 128.

If the monitor circuit is composed of one resistor irrespective of the input light level as shown in FIG. 23, if the input light level changes over a wide range, Since the ratio of the change of the voltage between the terminals of the resistor to the change becomes small, the detection of the input light level becomes difficult. However, in the optical amplifying device 301 of the first embodiment, since the resistor of the monitor circuit can be selected in accordance with the input light level, the input light level varies over the range of the selected input light mode. In this case, the ratio of the change in the voltage between the terminals of the resistor to the change in the input light level can be set optimally. Therefore, the optical amplifier 301 can easily and reliably detect the input light level.

The reason why the monitor circuit is composed of four resistors, which is larger than the number of input light modes, is to more finely correspond to the input light level in each input light mode. The number of resistors in the monitor circuit may be equal to the number of modes of the input light, or may be more than four. In mode 1 and resistor 1
In the optical amplifying device 301 set to 28, the AGC
Reference numeral 122 denotes the PD 12 based on the output from the PD 121.
By outputting to the LD 119 a signal according to the ratio with the output from 0, the EDF 11 is controlled so that the ratio becomes a predetermined value.
4 is controlled. For this reason, the EDF 114 is subjected to constant gain control, so that the W
The DM optical signal is amplified with a predetermined constant gain. This predetermined constant gain adjustment is performed by adjusting the resistance value R1 of the resistor 128 for converting the current value of the PD 121 to a voltage value and the PD 120
The ratio of the current value to the resistance value of the resistor that converts the current value to the voltage value may be adjusted.

The AGC 162 is an Anti-LOG 16
By outputting to the LD 158 a signal according to the ratio of the output from the PD 159 to the output from the PD 159, the gain of the EDF 155 is controlled so that the ratio becomes a predetermined value. For this reason, the EDF 155 is subjected to constant gain control. The output of the Anti-LOG 163 is a value obtained by adding the output from the subtractor 126 of the preceding optical amplifier to the optical level of the WDM optical signal input to the intermediate optical amplifier 103. The output from the subtractor 126 is a value obtained by subtracting the gain of the preceding optical amplifier 101 from the sum Gs1 of the gains of the former optical amplifier 101 and the middle optical amplifier 103. Therefore, AGC 162
Since the gain of the EFD 155 is adjusted based on the output from the Anti-LOG 163, the sum of the gain of the pre-stage optical amplifier 101 and the gain of the middle-stage optical amplifier 103 is almost maintained at Gs1. That is, the upstream optical amplifying section 101 and the upstream optical attenuating section 1
02 and the middle-stage optical amplifier 103 satisfy (Equation 1).

On the other hand, the ALC 143 is connected to the reference voltage Vref2M1.
By outputting a signal according to the difference from the output from PD 159 to VAT 141 with reference to
The attenuation of the VAT 141 is controlled so that Therefore, the output light level from the middle optical amplifier 103 is controlled to be constant. As described above, the pre-stage optical amplification unit 101, the pre-stage optical attenuation unit 102, and the middle-stage optical amplification unit 103 operate,
The output light level of the middle optical amplification unit 103 is
01, the first target value T1M corresponding to the in-mode 1 regardless of the fluctuation of the input light level within the range of the in-mode 1
Maintained at 1.

Then, since the rear-stage light attenuator 104 attenuates with a constant attenuation corresponding to the in-mode 1, the input light level of the rear-stage optical amplifier 105 is maintained substantially constant.
In the latter-stage optical amplifier 105, the AGC 190
By outputting a signal according to the ratio of the output from the PD 187 to the output from the PD 189 to the LD 188, the gain of the EDF 185 is controlled so that the ratio becomes a predetermined value. The predetermined value is separately given as a reference value in the AGC 190. Therefore, the EDF 185 is controlled with a constant gain,
The WDM optical signal input to the post-stage optical amplifier 105 is
The signal is amplified with a predetermined constant gain. Since the input light level of the rear-stage optical amplifier 105 is substantially constant, the output light level of the rear-stage optical amplifier 105 (the output light level of the optical amplifier 301) is maintained substantially constant.

On the other hand, when this optical amplifying device 301 is installed as another optical repeater, the optical level becomes -25 to -15 (d
Bm / channel), the in-mode 2 is selected. Therefore, the reference voltage Vref2 is set to the reference voltage Vref2M2 for the in-mode 2, and the ATT 171 is set to the ATT having the amount of attenuation for the in-mode 2. And
In the monitor circuit, a resistor corresponding to the case where the light level is −25 to −15 (dBm / channel), for example, the resistor 130 is selected, and the SW 127 is switched to connect the PD 121 and the resistor 130. Can be For this reason,
The voltage between the terminals of the resistor 130 is input to the AGC 122 and the LOG 124.

AGC 122, 162 and ALC143
Operates in the same manner as in the above-mentioned in-mode 1, except that the reference voltage Vref2 is set to the reference voltage Vref2M2 for the in-mode 2, so that the output light level of the middle-stage optical amplifier 103 becomes the It becomes 1 target value T1M2. And ATT
Since the ATT having the attenuation for the in-mode 2 is also set in the 171, the output light level of the downstream optical attenuator 104 is equal to that in the case of the in-mode 1.

Therefore, such an optical amplifier 301
By providing two input light modes, it is possible to cope with a wide input dynamic range. In the optical amplifying device 301, the output light level of the downstream optical attenuator 104 is maintained substantially constant, so that the noise figure is not degraded by switching the mode of the input light. Here, in order to more specifically show the above-described effects, a level diagram in the optical amplifier 301 was simulated.

FIG. 7 is a diagram showing a simulation result of a level diagram in the optical amplifying device of the first embodiment. In FIG. 7, from the left, the mode of the input light, the input, gain, and output of the pre-stage optical amplifying unit 101, the amount of attenuation of the pre-stage optical attenuator 102, the input, gain, and output of the middle-stage optical amplifying unit 103, These are the amount of attenuation, the input, gain, and output of the rear optical amplifier 105, the sum of the gain of the front optical amplifier 101 and the gain of the middle optical amplifier 103, and the total gain of the optical amplifier 301.

The upper part shows the simulation result in the case of the in-mode 1, and the lower part shows the simulation result in the case of the in-mode 2. And in in mode 1,
Pin + 10, Pin + 5 and Pin are connected to the pre-stage optical amplifier 101
Was calculated. In In mode 2, Pin
+15, Pin + 10 and Pin + 5 to the pre-amplifier 10
The case where 1 was input was calculated.

The first target value (the output light level of the middle-stage optical amplifier 103) was set to P0 in the in-mode 1 and set to P0 + 5 in the in-mode 2. The amount of attenuation of the rear light attenuator 104 was set to 2 in the in-mode 1 and to 7 in the in-mode 2. The difference between the attenuation amounts is a difference between the first target values between the in-mode 2 and the in-mode 1. The gain of the rear-stage optical amplifier 105 was set to 7 in each mode. Further, the gain of the pre-stage optical amplifier 101 and the mid-stage optical amplifier 1
The sum with the gain of 03 was set to Gr1 + 2.

Here, Gr1 and Gr2 in FIG. 7 are Gr1 = P0-Pin (Equation 3) and Gr2 = Gr1-10 (Equation 4), respectively. The result calculated under the above conditions is as shown in FIG.

Further, under the above conditions, Pin = −3
FIG. 8 shows a level diagram of each mode when 0 (dBm / channel) and P0 = 0 (dBm / channel). FIG. 8 is a diagram illustrating a level diagram in the optical amplifying device according to the first embodiment. FIG. 8A shows in mode 1
FIG. 8B is a diagram showing a level diagram in FIG.
It is a figure showing the level diagram in in mode 2. FIG. 8C is a diagram in which FIG. 4A is re-described in order to clarify the positional relationship between the level diagram and the optical amplifying device 301. 8A and 8B, the vertical axis represents the light level per channel, and the horizontal axis represents the position of the optical amplifier.
B, C, D, E, and F show respective portions of the optical amplifying device 301 shown in FIG. That is, the location A is on the input side of the pre-stage optical amplification unit 101, the location B is between the pre-stage optical amplification unit 101 and the pre-stage optical attenuation unit 102, and the location C is
The position D is between the front optical attenuator 102 and the middle optical amplifying unit 103,
4, the point E is between the downstream optical attenuator 104 and the downstream optical amplifier 105, and the location F is on the output side of the downstream optical amplifier 105.

As can be seen from FIGS. 7 and 8, by setting the first target value and the amount of attenuation of the ATT in each mode as described above, the output light level of the post-stage light attenuator 104 (the point E in FIG. 8). ) Is a constant value of -2 (dBm / channel) regardless of the selected in-mode. For this reason, the optical amplifying device 301 in the first embodiment
The switching of the mode of the input light does not degrade the noise figure.

In order to compare the effects of the first embodiment, the level diagram of the optical amplifier shown in FIG. 23 was calculated. FIG. 9 is a diagram showing a simulation result of a level diagram in the optical amplifying device according to the prior art. In FIG. 9, the input, gain, and output of the optical amplifier 1013, VAT 1015,
, Gain and output at 17, optical amplifier 1013
Is the sum of the gain of the optical amplifier 518 and the total gain of the optical amplifier 1000.

For comparison with the simulation result of FIG. 7, in FIG. 9, Pin + 15, Pin + 10, Pin + 5 and Pin are input to the optical amplifier 1013 and the optical amplifier 101
The case where P0 + 5 was output from 7 was calculated. As can be seen by comparing FIG. 9 with FIG. 7, the attenuation of the VAT 1015 needs to correspond to 17 to 2 (dB), and the gain of the optical amplifier 1017 needs to correspond to 17 to 2 (dB). . Fabricating such a VAT and optical amplifier is not easy.

On the other hand, the optical amplifying device 301 of the first embodiment
, The attenuation of the pre-stage light attenuator 102 is 12 to 2
(DB), and the amount of attenuation of the latter-stage optical attenuator 104 may correspond to 2, 7 (dB). The gain of the pre-stage optical amplifying unit 101 ranges from “Gr1-15” to “Gr1-5” (d
B), and the gain of the middle-stage optical amplifier 103 is
17 to 7 (dB).
The gain of 5 may correspond to 7 (dB). As described above, the optical amplifying device 301 according to the first embodiment is an easily manufactured device.

FIG. 10 shows the relationship between the input light level and the noise figure based on the above simulation results.
FIG. 10 shows the relationship between the input light level and the noise figure.
FIG. 4 is a diagram illustrating a comparison between the case of the optical amplifying device of the first embodiment and the case of the optical amplifying device of the prior art. The vertical axis in FIG. 10 is the noise figure (dB), and the horizontal axis is the input light level (dBm / channel). A broken line indicates a noise figure in the case of in-mode 1 in the optical amplifying apparatus 301 of the first embodiment, and a dashed line indicates a noise figure in the case of in-mode 2 in the optical amplifying apparatus 301 of the first embodiment. It is. The solid line is the noise figure for the optical amplifier according to the prior art.

As shown in FIG. 10, the input light level is -3.
The noise figure of the optical amplifying device 301 of the first embodiment is 5 to 7 (dB) when changing in the range of 0 to -15 (dBm / channel), but the optical amplifying device according to the prior art Has a noise figure of 5 to 12 (dB). In particular, when the input light level is in the range of −25 to −15 (dBm / channel), by switching to the in-mode 2, the optical amplifying device 301 in the first embodiment can be compared with the optical amplifying device according to the prior art. Thus, the noise figure can be significantly reduced.

Next, another embodiment will be described. (Configuration of the Second Embodiment) The second embodiment is directed to a post-stage optical attenuator 104 in the optical amplifier 301 of the first embodiment.
The optical amplifying device 302 uses a post-stage optical attenuator 106 in place of, and further uses a post-stage optical amplifier 107 in place of the post-stage optical amplifier 105.

In FIG. 4B, the WDM optical signal input to the optical amplifying device 302 in the second embodiment is input to the pre-amplifier 101 and amplified. The amplified WDM optical signal is input to the pre-stage optical attenuator 102 and attenuated. The attenuated WDM optical signal enters the middle optical amplifier 103 and is amplified. The amplified WDM optical signal is input to the subsequent optical attenuator 106,
Attenuated. The attenuated WDM optical signal is input to the post-amplifier 107 and amplified. Amplified WDM
The optical signal is output from the optical amplifying device 302 as
Be injected.

This WDM optical signal is an optical signal set in the wavelength band of C band (1530 to 1570 nm). The optical amplifying device 302 has two input light modes, i.e., in-mode 1 and in-mode 2. For example, in the in-mode 1, the input light level is -30 to -20.
(DBm / channel) of the input light. In the in-mode 2, the input light level is −25 to −15.
(DBm / channel) of the input light.

Here, the configurations of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102, and the middle-stage optical amplifying unit 103 are the same as those of the first embodiment, and the description thereof will be omitted. Hereinafter, configurations of the post-stage optical attenuator 106 and the post-stage optical amplifier 107 will be described. FIG. 11 is a diagram illustrating a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the second embodiment.

First, the configuration of the post-light attenuator 106 is shown in FIG.
It will be described based on. CPL1 in the middle optical amplifier 103
The WDM optical signal from 56 (FIG. 5) is CPL172
Is incident on. One WDM distributed by CPL172
The optical signal is transmitted via the VAT 173 to the second-stage optical amplifier 1.
07, and the other is PD174
Is incident on.

The attenuation of the VAT 173 is set to the attenuation for the in-mode 1 as an initial setting.
An attenuation control circuit that adjusts the attenuation of T173
Abbreviated as "ACC". ) In accordance with the output from 175, the attenuation is adjusted to the in-mode 2 attenuation. This in mode 2
Is set to be greater than the attenuation for in-mode 1 by a value obtained by subtracting the input light level for in-mode 1 from the input light level for in-mode 2 in the latter-stage light attenuator 106.

The output from PD 174 is input to one input terminal of ACC 175. A predetermined reference voltage Vref3 is input to the other input terminal of the ACC 175. This reference voltage Vref3 is the first voltage for in-mode 1
The voltage value is set to a voltage value equal to the output of the PD 174 when the WDM optical signal of the target value is incident on the downstream optical attenuator 106.

The ACC 175 compares the output from the PD 174 with the reference voltage Vref3, and outputs a signal corresponding to the difference to the VAT 173 to adjust the amount of attenuation of the VAT 173. That is, when an in-mode 1 WDM optical signal enters the optical amplifying device 302, the PD
174 becomes equal to the reference voltage Vref3.
C175 does not output a signal to VAT173. on the other hand,
When an in-mode 2 WDM optical signal enters the optical amplifying device 302, the output of the PD 174 becomes the reference voltage Vre.
Since a difference is generated from f3, the ACC 175 outputs a signal corresponding to the difference to the VAT 173.

Next, the configuration of the post-amplifier 107 is shown in FIG.
It will be described based on. In FIG. 11, W from the VAT 173 in the post-stage optical attenuator 106 of the second embodiment is shown.
The DM optical signal is transmitted to the CPL 21 in the post-amplifier 107.
1 is incident. One WD distributed by CPL211
The M-type optical signal is incident on the PD 225 and the other is IS
It is incident on O212. The output from PD 225 is AG
Input to C232 and LOG234. Also, IS
The WDM optical signal from O212 enters the CPL 213.

On the other hand, the laser beam from the LD 226 is also incident on the CPL 213. W from these ISO212
The DM optical signal and the laser light from the LD 226 are multiplexed and input to the EDF 214. EDF214 is L
A population inversion is formed by the laser beam from D226, and W
A DM optical signal is amplified by stimulated radiation.

The WDM optical signal amplified by the EDF 214 is transmitted to the CP through the ISO 215 and the GEQ 216.
The light is incident on L217. GEQ 216 is EDF 214
Is compensated to a substantially flat gain wavelength characteristic.
One WDM optical signal distributed by the CPL 217 is
The other WDM optical signal input to the VAT 218 is
The light enters the PD 227. The output from PD 227 is A
Input to GC232 and LOG233.

The AGC 232 determines the gain of the EDF 214 from the output from the PD 227 and the output from the PD 225, and adjusts the drive current (injection current) of the LD 226 so that the gain of the EDF 214 becomes a predetermined constant gain. adjust. The LOG 233 converts the output from the PD 227 into a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of the subtractor 235. And L
The OG 234 converts the output from the PD 225 into a logarithmic value of the voltage level, and converts the converted logarithmic value to the subtractor 23.
5 is input to the other input terminal. The subtractor 235 calculates L
The value obtained by subtracting the output of LOG 234 from the output of OG 233 is output to subtractor 236. The value obtained by subtracting the output of LOG 234 from the output of LOG 233 is EDF 21
4 corresponds to a gain of 4.

The subtractor 236 outputs a value obtained by subtracting the output of the subtractor 235 from a predetermined reference voltage Vref4 to an adder 239 described later. The reference voltage Vref4 is ED
The sum of the gains of F214 and EDF223 is set to a predetermined constant value G.
This is a voltage value referred to be s2. On the other hand, VAT
The WDM optical signal attenuated at 218 is input to the CPL 219. One WDM optical signal distributed by the CPL 219 is input to the PD 229, and the other WDM optical signal is transmitted to the PD 229 via the GEQ 220 and the ISO 221.
It is incident on PL222. The GEQ 220 is used for E
The gain wavelength characteristic of the DF223 is compensated almost flat. The laser light from the LD 230 is incident on the CPL 222, is multiplexed with the WDM optical signal from the ISO 221, and is incident on the EDF 223.

The EDF 223 amplifies the incident WDM optical signal and outputs the amplified signal to the CPL 224. CPL224
One WDM optical signal distributed by the above is emitted as output light of the optical amplifying device 302, and the other WDM optical signal is incident on the PD 231. The output from PD 231 is input to AGC 240 and ALC 228.

The ALC 228 compares the predetermined reference voltage Vref5 with the output from the PD 231 so that the light level per channel of the WDM optical signal emitted from the optical amplifier 302 becomes constant. Next, the attenuation of the VAT 218 is adjusted. Therefore, the reference voltage Vref5 is a voltage value that is referenced to make the output light level constant with respect to the input light level of the post-stage optical amplifier 107.

Further, the output from the PD 229 is
LOG238. LOG238 is this PD
The output from 229 is converted to a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of adder 239. The output from the aforementioned subtractor 236 is input to the other input terminal of the adder 239. Adder 239
Adds the output of the LOG 238 and the output of the subtractor 236, and outputs the added value to the Anti-LOG 241. The Anti-LOG 241 performs antilogarithmic conversion on the added value, and outputs the converted value to the AGC 240.

The AGC 240 calculates the EDF from the output from the PD 231 and the output from the Anti-LOG 241.
The gain of the EDF 223 is adjusted by adjusting the drive current (injection current) of the LD 230 so that the sum of the gain of the 214 and the gain of the WDF 223 is constant. (Operation and Effect of Second Embodiment) When the optical amplifying apparatus 302 of the second embodiment is installed as an optical repeater station of an optical communication system, an output from an optical transmission line connected to the input side of the optical amplifying apparatus 302 is performed. The mode of the input light and the SW 127 are set in accordance with the light level to be input.

For example, if the light level is -30 to -20 (dB)
m / channel), the in-mode 1 is selected, so that the reference voltage Vref2 is set to the reference voltage Vref2M1 for the in-mode 1. Then, the monitor circuit selects a resistor corresponding to the case where the light level is -30 to -20 (dBm / channel), for example, the resistor 128, and selects S
W127 is switched to connect the PD 121 and the resistor 128. Therefore, AGC 122 and L
The voltage between terminals of the resistor 128 is input to the OG 124.

In the optical amplifying device 302 set to the in-mode 1 and the resistor 128, the functions and effects of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102 and the middle-stage optical amplifying unit 103 are the same as in the first embodiment. Therefore, the description is omitted. As described in the first embodiment, the optical level of the WDM optical signal input to the rear-stage optical attenuator 106 is independent of the fluctuation of the input optical level within the range of the in-mode 1 of the front-stage optical amplifier 101. , The first target value T1M1 corresponding to the in-mode 1 is maintained. For this reason, PD1
Since the difference between the output from 74 and the reference voltage Vref3 is substantially “zero”, the ACC 175 does not output a signal to the VAT 173. Therefore, the attenuation of the VAT 173 is maintained at a constant attenuation for the in-mode 1, and the WDM optical signal is
It is attenuated by the amount of attenuation for the in-mode 1. Therefore, the input light level of the post-stage optical amplifier 107 is maintained substantially constant.

In the post-stage optical amplifier 107, the AGC 23
2 controls the gain of the EDF 214 so that the ratio becomes a predetermined value by outputting to the LD 226 a signal according to the ratio of the output from the PD 225 to the output from the PD 227. For this reason, the EDF 214 is subjected to constant gain control. In addition, AGC 240 uses Anti-LOG 241
By outputting to the LD 230 a signal according to the ratio of the output from the PD 231 to the output from the PD 231, the gain of the EDF 223 is controlled so that the ratio becomes a predetermined value.
Therefore, the EDF 223 is controlled at a constant gain.

The output of the Anti-LOG 241 is a value obtained by adding the output from the subtractor 236 to the optical level of the WDM optical signal input to the subsequent optical amplifier 107. The output from the subtractor 236 is a value obtained by subtracting the gain of the EDF 214 from the sum Gs2 of the gains of the EDF 214 and the EDF 223. Therefore, since AGC 240 adjusts the gain of EFD 223 with reference to the output from Anti-LOG 241, the sum of the gain of EDF 214 and the gain of EDF 223 is almost maintained at Gs2. That is, the portion including the EDF 214 and the EDF 223 satisfies (Equation 1).

On the other hand, the ALC 228 outputs a signal according to the difference between the reference voltage Vref5 and the output from the PD 231 as the reference voltage Vref5.
By outputting to the AT 218, the amount of attenuation of the VAT 218 is controlled so that this difference becomes “zero”. For this reason, the output light level from the post-stage optical amplifier 107 is controlled to be constant. On the other hand, when this optical amplifying device 302 is installed as another optical repeater, the optical level becomes -25 to -15 (d
Bm / channel), the in-mode 2 is selected. Therefore, the reference voltage Vref2 is set to the reference voltage Vref2M2 for the in-mode 2. Then, the monitor circuit selects a resistor corresponding to the case where the light level is −25 to −15 (dBm / channel), for example, the resistor 130, and the SW 127 connects the PD 121 and the resistor 130. Can be switched to Further, the gain of the variable gain amplifier 133 is switched so that a signal of the same level is output if the input power of the PD 121 is the same. For this reason, the AGC 122 and the LOG 124
A terminal voltage of 0 is input.

AGC 122, 162 and ALC 143
Operates in the same manner as in the above-mentioned in-mode 1, except that the reference voltage Vref2 is set to the reference voltage Vref2M2 for the in-mode 2, so that the output light level of the middle-stage optical amplifier 103 becomes the It becomes 1 target value T1M2.

Here, since the optical level of the WDM optical signal input to the post-stage optical attenuator 106 is maintained at the first target value T1M2, the output from the PD 174 and the reference voltage Vref3 are not changed. There is a difference. For this reason,
The ACC 175 outputs a signal corresponding to the difference to the VAT 173. Therefore, the attenuation of the VAT 173 is maintained at a constant attenuation for the in-mode 2, and the WDM optical signal is attenuated by the attenuation for the in-mode 2. Therefore, the output light level of the post-stage light attenuator 106 is equal to that in the case of the in-mode 1.

The post-amplifier 107 operates in the same manner as in the case of the in-mode 1. Therefore, such an optical amplification device 302 can support a wide input dynamic range by providing two input light modes. In the optical amplifying device 302, the output light level of the downstream optical attenuator 106 is maintained substantially constant, so that the noise figure is not deteriorated by switching the mode of the input light.

In the second embodiment, the first target value and the amount of attenuation of the VAT 173 in each mode are set in the same manner as in the first embodiment, and the output light level of the post-stage optical amplifier 107 is set to P0 + 5. By setting, a simulation result as shown in FIG. 7 can be obtained. Next, another embodiment will be described.

(Configuration of Third Embodiment) In the third embodiment, a rear-stage optical attenuator 108 is used instead of the rear-stage optical attenuator 104 in the optical amplifier 301 of the first embodiment. An optical amplifying device 303 using a post-amplifier 107 instead of the optical amplifying unit 107. In FIG. 4C, the WDM optical signal input to the optical amplifying device 303 in the third embodiment is input to the pre-amplifier 101 and amplified. The amplified WDM optical signal is supplied to a pre-stage optical attenuator 10.
2 and is attenuated. The attenuated WDM optical signal enters the middle optical amplifier 103 and is amplified. The amplified WDM optical signal is input to the post-stage optical attenuator 108 and is attenuated. The attenuated WDM optical signal is
The light enters the rear-stage optical amplifier 107 and is amplified. The amplified WDM optical signal is emitted as output light of the optical amplifier 303.

This WDM optical signal is an optical signal set in the wavelength band of C band (1530 to 1570 nm). The optical amplifying device 303 has two input light modes, i.e., in-mode 1 and in-mode 2. For example, in the in-mode 1, the input light level is -30 to -20.
(DBm / channel) of the input light. In the in-mode 2, the input light level is −25 to −15.
(DBm / channel) of the input light.

Further, the optical amplifying device 303 has two output light modes, out mode 1 and out mode 2. For example, in out mode 1, the output light level is 4 (dBm / channel). The corresponding output light mode, out mode 2 is an output light mode corresponding to an output light level of 8 (dBm / channel). Here, the configurations of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102, and the middle-stage optical amplifying unit 103 are the same as those of the first embodiment, and therefore the description thereof will be omitted. Also, the configuration of the post-amplifier 107 is such that the reference voltage V
The second embodiment is the same as the second embodiment except for the point that ref8 is changed, and a description thereof will be omitted.

The configuration of the post-stage light attenuator 108 will be described below with reference to FIG.
2 will be described. FIG. 12 is a diagram illustrating a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the third embodiment. The WDM optical signal from the CPL 156 (FIG. 5) in the middle optical amplifier 103 enters the CPL 251. One WDM optical signal distributed by the CPL 251 includes a VAT 252, an ATT 254, and a dispersion compensating fiber (hereinafter, referred to as “DC”).
F ”. ) 253 through the post-amplifier 10
7 is incident on the CPL 211, and the other is incident on the PD 255.

The attenuation of the VAT 252 is set to the attenuation for the in-mode 1 as an initial setting.
The attenuation is adjusted to the in-mode 2 attenuation according to the output from the ACC 256 that adjusts the attenuation of T252. The amount of attenuation for the in-mode 2 is set to be larger than the amount of attenuation for the in-mode 1 by a value obtained by subtracting the input light level in the case of the in-mode 1 from the input light level in the case of the in-mode 2 in the subsequent light attenuating unit 108. Is done.

The output from PD 255 is input to one input terminal of ACC 256. A predetermined reference voltage Vref6 is input to the other input terminal of the ACC 256. This reference voltage Vref6 is the first voltage for in-mode 1
The voltage value is set to a voltage value equal to the output of the PD 255 when the target value WDM optical signal is incident on the downstream optical attenuator 108.

The ACC 256 compares the output from the PD 255 with the reference voltage Vref6 and outputs a signal corresponding to the difference to the VAT 252 to adjust the amount of attenuation of the VAT 252. That is, when an in-mode 1 WDM optical signal enters the optical amplifying device 303, the PD
255 becomes equal to the reference voltage Vref6.
C256 does not output a signal to VAT252. on the other hand,
When an in-mode 2 WDM optical signal enters the optical amplifying device 303, the output of the PD 255 becomes the reference voltage Vre.
Since a difference occurs with f6, the ACC 256 outputs a signal corresponding to the difference to the VAT 252.

The DCF 253 is a dispersion compensator connected to the optical amplifying device 303 and compensating for chromatic dispersion generated in an optical transmission line for transmitting a WDM optical signal and chromatic dispersion generated in the optical amplifying device 303. This DCF25
Reference numeral 3 denotes an optical fiber having a chromatic dispersion characteristic having a sign opposite to that of the dispersion value of the WDM optical signal.
This is necessary to utilize the 3μ zero dispersion fiber in the 1.55μ wavelength band.

Note that instead of the DCF 253, a dispersion compensator such as a chirped grating or a phase conjugator may be used. The ATT 254 is prepared for each mode of the output light, and the attenuation of the ATT 254 for the out mode 1 is as follows.
The setting is made in consideration of the output light level of the optical amplifier 303. The attenuation of ATT 254 for out mode 2 is DC
Since transmission loss also occurs in F253, ATT25
4 and the attenuation of the DCF 253 are equal to the value obtained by subtracting the output light level in the out mode 1 from the output light level in the out mode 2 in the post-stage optical amplifying section 107. It is set smaller than the amount of attenuation. For example, when the output light level of the out mode 1 is 4 and the output light level of the out mode 2 is 8,
The attenuation of the ATT 254 for the out mode 2 is obtained by further subtracting the DCF 2 from the value 4 obtained by subtracting the output light level 4 in the out mode 1 from the output light level 8 in the out mode 2.
The value is set to a value obtained by subtracting the attenuation generated in 53.

In the post-stage optical amplifier 107, the ALC 22
The reference voltage Vref8 supplied to one input terminal of the output mode 8 is set corresponding to each out mode of the output light mode, and supplies the reference voltage Vref8M1 for the out mode 1 and the reference voltage Vref8M2 for the out mode 2. can do. (Operation and Effect of Third Embodiment) When the optical amplifying device 303 of the third embodiment is installed as an optical repeater station of an optical communication system, an output from an optical transmission line connected to the input side of the optical amplifying device 303 is performed. The mode of the input light and the SW 127 are set in accordance with the light level to be input.

For example, when the light level is -30 to -20 (dB)
m / channel), the in-mode 1 is selected, so that the reference voltage Vref2 is set to the reference voltage Vref2M1 for the in-mode 1. Then, the monitor circuit selects a resistor corresponding to the case where the light level is -30 to -20 (dBm / channel), for example, the resistor 128, and selects S
W127 is switched to connect the PD 121 and the resistor 128. Also, the variable gain amplifier 133 is
The gain is switched so that the gain from the PD 121 to the output of the variable gain amplifier 133 is constant. Therefore, the voltage between terminals of the resistor 128 is input to the variable gain amplifier 133.

In the optical amplifying device 303 set to the in-mode 1 and the resistor 128, the functions and effects of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102 and the middle-stage optical amplifying unit 103 are the same as those of the first embodiment. Therefore, the description is omitted. Then, the mode of the output light is set according to the type of the optical transmission line connected to the output side of the optical amplifier 303.

For example, when the type of the optical transmission line is NZ-DSF, the out mode 1 is selected and the ATT254
Is connected to an optical attenuator having an attenuation amount for out mode 1. Then, the reference voltage Vref8 is supplied to the rear-stage optical amplifier 107.
Is set to a voltage value Vref8M1 for setting the output light level of the reference signal to 4 (dBm / channel). As described in the first embodiment, the optical level of the WDM optical signal input to the downstream optical attenuator 108 is the first target value T1M1 corresponding to the output optical level from the middle optical amplifier 103 corresponding to the in-mode 1. Is maintained. Therefore, the output from the PD 172 and the reference voltage V
Since the difference from ref6 is almost “zero”, ACC256
No signal is output to VAT252. Therefore, VAT25
2 is maintained at a constant attenuation for the in-mode 1, and the WDM optical signal is attenuated by the in-mode 1 attenuation.

The WDM attenuated by VAT252
Since the system optical signal is attenuated by the ATT 254 and the DCF 253 with a constant attenuation corresponding to the out mode 1, the input optical level of the post-stage optical amplifier 107 is equal to the WDM optical signal input to the optical amplifier 303. It is kept almost constant regardless of the input light level. Rear optical amplifier 107
In AGC 232, the signal according to the ratio of the output from PD 225 to the output from PD 227 with reference to the output from PD 225 is
The output of the EDF 214 controls the gain of the EDF 214 so that the ratio becomes a predetermined value. For this reason, ED
F214 is subjected to constant gain control.

The AGC 240 is an Anti-LOG 24
The gain of the EDF 223 is controlled so that the ratio becomes a predetermined value by outputting to the LD 230 a signal according to the ratio of the output from the PD 1 to the output from the PD 231. Therefore, the EDF 223 is controlled at a constant gain. The output of the Anti-LOG 241 is subtracted by the subtractor 236 from the optical level of the WDM optical signal input to the subsequent optical amplifier 107.
This is the value obtained by adding the outputs from. The output from the subtractor 236 is a value obtained by subtracting the gain of the EDF 214 from the sum Gs2 of the gains of the EDF 214 and the EDF 223. Therefore, AGC 240 sets the gain of EFD 223 to Anti-LO
Since the output from the G 241 is adjusted, the ED
The sum of the gain of F214 and the gain of EDF223 is substantially maintained at Gs2. That is, EDF 214 and EDF 22
3 satisfies (Equation 1).

Further, the ALC 228 sets the PD 231 with reference to the reference voltage Vref8M1 set for the out mode 1.
By outputting to VAT 218 a signal according to the difference from the output from
8 is controlled. For this reason, the post-stage optical amplifier 107
Is controlled to be almost constant at the light level 4 in the out mode 1.

On the other hand, when this optical amplifier 303 is installed as another optical repeater, the input light level is the same as that described above, but if the type of the optical transmission line connected to the output side is SMF, Out mode 2 is selected and ATT254
Is connected to an optical attenuator having an attenuation amount for the out mode 2. Then, the reference voltage Vref8 is supplied to the rear-stage optical amplifier 107.
Is set to a voltage value Vref8M2 for setting the output light level of the reference numeral 8 to 8 (dBm / channel).

In the latter-stage optical attenuator 108, the optical level of the WDM optical signal that is input remains at in-mode 1, and is therefore maintained at the first target value T1M1 corresponding to in-mode 1. Therefore, the attenuation of the VAT 252 is maintained at a constant attenuation for the in-mode 1, and the WDM optical signal is attenuated by the attenuation for the in-mode 1.

On the other hand, the WDM optical signal attenuated by the VAT 252 is attenuated by the ATT 254 and the DCF 253 with a constant attenuation corresponding to the out mode 2. Then, in the post-stage optical amplifier 107, the ALC 228 outputs a signal according to the difference from the output from the PD 231 with respect to the reference voltage Vref8M2 set for the out mode 2 to VAT2.
18, the attenuation of the VAT 218 is controlled so that this difference becomes “zero”. For this reason, the output light level from the post-stage optical amplifier 107 is set to the out mode 2
The light level 8 is controlled almost constant.

Therefore, the optical amplifying device 303 can set the output light level according to the type of the optical transmission line in this way, and does not cause the nonlinear optical effect that occurs in the WDM optical signal in the optical transmission line. . Further, in the optical amplifying device 303, since the output of the subsequent-stage optical amplifying unit 107 is controlled to be constant, it is possible to absorb variations in the loss of the ATT 254 and the DCF 253.

Here, in order to more specifically show the above-described effects, a level diagram in the optical amplifier 303 was simulated. FIG. 13 is a diagram illustrating a simulation result of a level diagram in the optical amplifying device according to the third embodiment. In FIG. 13, the mode of the output light from the left,
System gain, pre-amplifier 101 and pre-attenuator 1
The input, gain, and output, and the input, gain, and type of the optical fiber in the second-stage optical attenuator 108 and the second-stage optical amplifier 107 are shown in FIG.

The upper part shows the simulation result in the case of the out mode 1, and the lower part shows the simulation result in the case of the out mode 2. And out mode 1
Then, -21 to -11 and -26 to -16 (dBm /
(Channel) was input to the pre-stage optical amplifier 101. In out mode 2, -17 to -11 and-
26 to -16 (dBm / channel) is set to
The case where 1 was input was calculated.

The second target value (the output light level of the latter-stage optical amplifier 107) was set to 4 (dBm / channel) in the out mode 1, and was set to 8 (dBm / channel) in the out mode 2. The attenuation of the post-stage optical attenuator 108 is DC
The setting is made as shown in FIG. 13 in accordance with the fluctuation of the transmission loss of F253. The result calculated under the above conditions is shown in FIG.
As described above, the optical amplifier 303 can set the output light level according to the type of the optical transmission line.

In order to compare the effects of the third embodiment, the level diagram of the optical amplifier shown in FIG. 23 was calculated. FIG. 14 is a diagram showing a simulation result of a level diagram in the optical amplifying device according to the prior art. In FIG. 14, from the left, the system gain, input, gain and output of the optical amplifier 1013, VAT1
015, input, gain, and output of the optical amplifier 1017, total optical amplifier gain, and type of optical fiber.

For comparison with the simulation result of FIG. 13, in FIG. 14, −11 and −26 (dBm / channel) are input to the optical amplifier 1013 and the optical amplifier 101
A case where 7 to 4 (dB) is output was calculated. Also,
-11 and -22 (dBm / channel) are converted to the optical amplifier 1
013 was input and 8 (dB) was output from the optical amplifier 1017.

As can be seen by comparing Out mode 1 in FIG. 13 with FIG. 14, the gain of the optical amplifier 1017 needs to correspond to 23 and 38 (dB). And FIG.
As can be seen by comparing Out mode 2 of FIG.
The gain of the optical amplifier 1017 needs to correspond to 27 and 38 (dB). Fabricating such an optical amplifier is not easy.

On the other hand, the optical amplifying device 303 of the third embodiment
In the above, the post-stage optical amplifier 107 only has to correspond to 27 (dB). Thus, the optical amplifying device 3 of the third embodiment
01 is a range that is easy to manufacture. Next, another embodiment will be described. (Configuration of Fourth Embodiment) FIG. 15 is a diagram showing a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the fourth embodiment.

FIG. 16 is a diagram showing an example of the configuration of an OADM in a post-stage optical attenuator in the fourth embodiment. The fourth embodiment is an optical amplifying device 304 using a post-stage optical attenuator 109 instead of the post-stage optical attenuator 104 in the optical amplifier 301 of the first embodiment. In FIG. 4D, WDM incident on the optical amplifier 304 according to the fourth embodiment is shown.
The optical signal is input to the pre-stage optical amplifier 101 and amplified. The amplified WDM optical signal is supplied to a pre-stage optical attenuator 1.
02 and is attenuated. The attenuated WDM optical signal enters the middle optical amplifier 103 and is amplified.
The amplified WDM optical signal is input to the post-stage optical attenuator 109 and attenuated. The attenuated WDM optical signal is input to the subsequent optical amplifier 105 and amplified. The amplified WDM optical signal is emitted as output light of the optical amplifier 304.

The WDM optical signal is an optical signal set in the wavelength band of C band (1530 to 1570 nm). The optical amplifying device 304 has two input light modes, i.e., in-mode 1 and in-mode 2. For example, in the in-mode 1, the input light level is -30 to -20.
(DBm / channel) of the input light. In the in-mode 2, the input light level is −25 to −15.
(DBm / channel) of the input light.

Further, the optical amplifying device 304 has two output light modes of an out mode 1 and an out mode 2. For example, in the out mode 1, the output light level is 4 (dBm / channel). The corresponding output light mode, out mode 2 is an output light mode corresponding to an output light level of 8 (dBm / channel). Here, the configurations of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102, and the middle-stage optical amplifying unit 103 are the same as those of the first embodiment, and therefore the description thereof will be omitted. The configuration of the latter-stage optical amplifier 105 is the same as that of the first embodiment except that the predetermined value for setting the gain in the AGC 190 is changed according to the mode of the output light. Is omitted.

Hereinafter, the configuration of the post-stage light attenuator 109 will be described with reference to FIG.
5 and FIG. In FIG.
W from the CPL 156 (FIG. 5) in the middle optical amplifier 103
The DM optical signal is transmitted to the CPL 26
1 is incident. One WD distributed by CPL 261
The M-system optical signal is input to the CPL 181 in the post-stage optical amplification unit 105 via the VAT 262, the ATT 264, and an optical add / drop multiplexer (hereinafter, abbreviated as “OADM”) 263, and the other. Is
The light enters the PD 265.

The attenuation of VAT 262 is set to the attenuation for in-mode 1 as an initial setting.
The attenuation is adjusted to the in-mode 2 attenuation according to the output from the ACC 266 that adjusts the attenuation of T262. The amount of attenuation for the in-mode 2 is set to be larger than the amount of attenuation for the in-mode 1 by a value obtained by subtracting the input light level in the case of the in-mode 1 from the input light level in the case of the in-mode 2 in the subsequent light attenuating unit 109. Is done.

The output from PD 265 is input to one input terminal of ACC 266. A predetermined reference voltage Vref7 is input to the other input terminal of the ACC 266. This reference voltage Vref7 is the first voltage for in-mode 1
The voltage value is set to a voltage value equal to the output of the PD 265 when the target value WDM optical signal is incident on the post-stage optical attenuator 109.

The ACC 266 compares the output from the PD 265 with this reference voltage Vref7, and outputs a signal corresponding to the difference to the VAT 262 to adjust the amount of attenuation of the VAT 262. That is, when an in-mode 1 WDM optical signal enters the optical amplifying device 304, the PD
265 becomes equal to the reference voltage Vref7.
C266 does not output a signal to VAT262. on the other hand,
When an in-mode 2 WDM optical signal enters the optical amplifying device 304, the output of the PD 265 changes to the reference voltage Vre.
Since a difference is generated with f7, the ACC 266 outputs a signal corresponding to the difference to the VAT 262.

The ATT 264 is prepared for each output light mode, and the attenuation of the ATT 264 for the out mode 1 is as follows.
The setting is made in consideration of the output light level of the optical amplifier 304. The attenuation of the ATT 264 for the out mode 2 is OA
Since transmission loss also occurs in DM263, ATT2
The ATT 264 for the out mode 1 is equal to the sum of the attenuation of the OADM 263 and the attenuation of the OADM 263 by a value obtained by subtracting the output light level in the out mode 1 from the output light level in the out mode 2 in the post-stage optical amplifier 105. Is set to be smaller than the amount of attenuation. For example, when the output light level of the out mode 1 is 4 and the output light level of the out mode 2 is 8, the attenuation of the ATT 264 for the out mode 2 changes from the output light level 8 in the out mode 2 to the out mode 1 Is further subtracted from the value 4 obtained by subtracting the output light level 4 in the case of
The value is set to a value obtained by subtracting the attenuation generated in the ADM 263.

The OADM 263 transmits the W signal transmitted through the optical transmission line.
An optical signal (channel) is dropped / inserted from a DM optical signal.
A fixed wavelength type OADM which is an optical component that can transmit and drop a fixed wavelength optical signal, and an arbitrary wavelength type OA which can drop and insert an optical signal of an arbitrary wavelength.
There is DM. An example of the configuration of the OADM will be described with reference to FIG.

FIG. 16A is a diagram showing a configuration example of a fixed wavelength type OADM. In FIG. 15 and FIG. 16A, the WDM optical signal from the ATT 264 is OAD
The light is incident on the CPL 271 in M. One WDM optical signal distributed by the CPL 271 is output to the optical receiver 267, and the other WDM optical signal is input to the rejection filter 270.

The rejection filter 270 is a WDM
This is an optical component that blocks four optical signals (four channels) from the optical signal. The rejection filter 270
In order to cut off, four fiber bragggrating filters,
Abbreviated as "FBG". ) 272-1 to 272-4 are cascaded, and the FBG 272 is a band-elimination filter (band-elimination).
and the cutoff wavelength bandwidth of the FBG 272 is set to a wavelength bandwidth that does not cut off an optical signal adjacent to the optical signal to be cut off.
The center wavelength of the 2-4 cutoff wavelength band is set to the wavelength of the optical signal branched by the OADM.

For example, in the case where a WDM optical signal wavelength-multiplexes 32 channels, this OADM uses channel 2, channel 5, channel 10, and channel 1.
3, the center wavelength of the cutoff wavelength band in the FBG 272-1 is set to the wavelength of the channel 2, and
The center wavelength of the cutoff wavelength band in BG272-2 is set to the wavelength of channel 5, the center wavelength of the cutoff wavelength band in FBG272-3 is set to the wavelength of channel 10, and the cutoff wavelength band of FBG272-4 is set. The center wavelength may be set to the wavelength of the channel 13.

Although the case where four optical signals are split has been described, the number of FBGs 272 is determined according to the number of split optical signals. The light receiving unit 267
The optical signal branched by the ADM is received and processed.

The rejection filter 270 uses this OA
The WDM optical signal from which the optical signal branched by DM is removed is input to the CPL 273. Also, the optical transmission unit 268
Generates an optical signal to be inserted by the OADM. The optical signal from the optical transmission unit 268 enters the CPL 273,
The predetermined optical signal from the rejection filter 270 is wavelength-multiplexed with the WDM optical signal from which the signal has been removed. And
The WDM optical signal in which the optical signal to be inserted is wavelength-division multiplexed is output to the CPL 181 in the subsequent optical amplifier 107.

In such a fixed-wavelength OADM, the channel to be dropped / added by the optical amplifier 304 is determined when the optical amplifier 304 is installed in an optical communication system. (Operation and Effect of Fourth Embodiment) When the optical amplifying device 304 of the fourth embodiment is installed as an optical repeater station of an optical communication system, an output from an optical transmission line connected to the input side of the optical amplifying device 304 is performed. The mode of the input light and the SW 127 are set in accordance with the light level to be input.

For example, when the light level is -30 to -20 (dB)
m / channel), the in-mode 1 is selected, so that the reference voltage Vref2 is set to the reference voltage Vref2M1 for the in-mode 1. Then, the monitor circuit selects a resistor corresponding to the case where the light level is -30 to -20 (dBm / channel), for example, the resistor 128, and selects S
W127 is switched to connect the PD 121 and the resistor 128. Therefore, AGC 122 and L
The voltage between terminals of the resistor 128 is input to the OG 124. At this time, the gain of the variable gain amplifier 133 also
The gain is switched so that the gain from 21 to the output of the variable gain amplifier 133 becomes single.

In the optical amplifying device 304 set to the in-mode 1 and the resistor 128, the functions and effects of the pre-stage optical amplifying unit 101, the pre-stage optical attenuating unit 102, and the middle-stage optical amplifying unit 103 are the same as in the first embodiment. Therefore, the description is omitted.

The mode of the output light is set in accordance with the type of the optical transmission line connected to the output side of the optical amplifier 304. For example, when the type of the optical transmission line is NZ-DSF, since the out mode 1 is selected, the ATT
The H.264 is connected to an optical attenuator having an attenuation amount for the out mode 1, and the AGC 190 controls the output light level of the post-stage optical amplification unit 105 to be 4 (dBm / channel).

As described in the first embodiment, the optical level of the WDM optical signal input to the rear optical attenuating section 109 is the first optical level corresponding to the in-mode 1 output light level from the intermediate optical amplifying section 103. It is maintained at the target value T1M1. Therefore, since the difference between the output from the PD 265 and the reference voltage Vref7 is substantially “zero”, the ACC 266 sets the VAT 26
2 does not output a signal. Therefore, the attenuation of the VAT 262 is maintained at a constant attenuation for the in-mode 1, and the WDM
The system optical signal is attenuated by the in-mode 1 attenuation amount.

Then, the WDM attenuated by VAT262
The system control signal includes OADM 263 and ATT 264.
Therefore, the input light level of the post-stage optical amplifier 105 is substantially constant irrespective of the input optical level of the WDM optical signal incident on the optical amplifier 303 because the optical signal is attenuated by a constant attenuation corresponding to the out mode 1. Is maintained. Post-stage optical amplifier 10
5, the AGC 190 outputs a signal according to the ratio of the output from the PD 187 to the output from the PD 189 with reference to the output from the PD 187.
By outputting to D188, the gain of the EDF 185 is controlled so that this ratio becomes a predetermined value. Therefore, E
The DF 185 is controlled at a constant gain with a gain corresponding to the out mode 1. The WDM optical signal input to the post-stage optical amplifier 105 is amplified with a predetermined constant gain. And
Since the input light level of the rear optical amplifier 105 is almost constant, the output light level of the rear optical amplifier 105 (the optical amplifier 3
01 is the light level 4 of the out mode 1.
Is kept almost constant.

On the other hand, when this optical amplifying device 304 is installed as another optical repeater, the input light level is the same as that described above, but the type of the optical transmission line connected to the output side is SMF. , Because out mode 2 is selected, ATT
Reference numeral 264 denotes an optical attenuator having an attenuation amount for the out mode 2, and the ratio between the resistance value Rref1 and the resistance value Rref2 is such that the output light level of the post-stage optical amplification unit 105 is 8 (dBm / channel). Set to be value.

In the latter-stage optical attenuator 109, the optical level of the WDM optical signal that is input remains at in-mode 1, so that it is maintained at the first target value T1M1 corresponding to in-mode 1. Therefore, the attenuation of the VAT 262 is maintained at a constant attenuation for the in-mode 1, and the WDM optical signal is attenuated by the in-mode 1 attenuation. on the other hand,
The WDM optical signal attenuated by the VAT 262 is OA
DM 263 and ATT 264 attenuate at a constant attenuation corresponding to out mode 2.

Then, in the post-stage optical amplifier 105, A
The GC 190 determines the PD based on the output from the PD 187.
By outputting a signal to the LD 188 in accordance with the ratio with the output from the EDF 189, the EDF is adjusted so that the ratio becomes a predetermined value.
185 gain is controlled. For this reason, EDF185
Constant gain control is performed at a gain corresponding to the out mode 2. The WDM optical signal input to the post-stage optical amplifier 105 is amplified with a predetermined constant gain. Then, the latter-stage optical amplifier 1
Since the input light level of the optical amplifier 05 is almost constant, the output light level of the post-stage optical amplifier 105 (the output light level of the optical amplifier 301) is kept almost constant at the light level 8 of the out mode 2.

Therefore, the optical amplifying device 304 can set the output light level in accordance with the type of the optical transmission line as described above, so that the remarkable waveform due to the nonlinear optical effect generated in the WDM optical signal in the optical transmission line. Does not cause distortion. Note that the loss adjusted by ATT264 is VAT262.
May be realized only by the VAT 262 by giving an offset to the control voltage.

In the fourth embodiment, the OAD
Although the fixed wavelength type OADM is used for M, an arbitrary wavelength type OADM may be used. Next, another embodiment will be described. (Configuration of Fifth Embodiment) FIG. 17 is a diagram showing a configuration of an optical communication system of a fifth embodiment.

Referring to FIG. 17, an optical communication system includes an optical transmitting station 401 for generating a plurality of m-wave WDM optical signals,
The optical transmission path 402 transmits the WDM optical signal emitted from the optical transmitting station 401, and the optical receiving station 404 receives the transmitted WDM optical signal and receives and processes the WDM optical signal. . Further, an optical relay station 403 is connected between the optical transmission paths 402 in this optical communication system. The optical relay station 403 is connected to the optical transmission line 10.
It is not limited to the case where one is connected between the two, and a plurality may be provided as needed.

The optical transmitting station 401 includes, for example, a plurality of m optical transmitters (hereinafter abbreviated as “OS”) 411-1 to 411-m that generate optical signals of each channel of the WDM optical signal.
An optical multiplexer (hereinafter abbreviated as “MUX”) 412 that wavelength-multiplexes the optical signals from the OSs 411-1 to 411-m, and an optical amplifier 413 that amplifies the WDM optical signal from the MUX 412. It is comprised including. The number of OSs 111 is a number corresponding to the number of channels of the WDM optical signal. The same applies to the number of optical receivers 419 described later.

Further, the OS 411 includes, for example, a semiconductor laser that oscillates a laser beam at a predetermined wavelength, and an external modulator such as a Mach-Zehnder interferometric optical modulator that modulates the laser beam with information to be transmitted. be able to. M
As the UX 412, for example, a dielectric multilayer filter or an arrayed waveguide grating type optical multiplexer / demultiplexer, which is one of interference filters, can be used.

The optical transmission line 402 is an optical fiber,
1.3μm band zero dispersion single mode fiber or 1.5μm
Various optical fibers such as a band dispersion shift fiber can be used. The receiving device 404 includes, for example, an optical amplifying device 417 and an optical demultiplexer (hereinafter, “DEMUX”).
Abbreviated. ) 418 and optical receivers (hereinafter abbreviated as “OR”) 419-1 to 419-16. The WDM optical signal input from the optical transmission path 402 to the optical amplifier 417 is amplified and then DEMUX 418
And the wavelength is separated by the DEMUX 418 into an optical signal for each channel. The optical signal of each separated channel is
OR419-1 to 4 consisting of photodiodes and demodulators
Each of them is incident on 19-m and is received and processed.

The optical repeater station 403 is provided with a station equipped with an optical amplifying device 415 for compensating for the transmission loss in the optical transmission line 402, and for compensating for the transmission loss in the optical transmission line 402,
2 is a station equipped with an optical amplifying device 416 for dropping / adding a channel from a WDM optical signal transmitting T.2. As the optical amplifying device 413 in the optical transmitting station 401 and the optical amplifying device 417 in the optical receiving station 404, any one of the optical amplifying devices 301 to 303 in the first to third embodiments is used. The optical amplifying device 416 in the first to fourth
Any one of the optical amplifying devices 301 to 304 in the embodiment is used.

For example, as the optical amplifying device 413, the optical amplifying device 301 in the first embodiment is used, and as the optical amplifying device 417, the optical amplifying device 302 in the second embodiment is used. 1, the optical amplifying device 304 in the fourth embodiment is used, and the optical amplifying device 415-1 is used.
415-n are the optical amplifying devices 30 in the third embodiment.
3 is used. The optical relay station 403-1 has an ADM (add / dr
optical multiplexer). In addition,
The optical communication system may include a plurality of optical relay stations having such an ADM function.

(Operation and Effect of Fifth Embodiment) In such an optical communication system, the optical amplifying device 41
3, the mode of the input light of the optical amplifying device 413 can be adjusted to the output light level of the MUX 412, and the mode of the output light of the optical amplifying device 413 can be adjusted to the input light level of the optical transmission line 402-1. Can be adjusted to

Then, the optical amplifying device 41 is connected to the optical repeater 403.
When the optical amplifiers 415 and 416 are provided,
16 can be adjusted to the output light level of the optical transmission line 402 on the input side, and the optical amplifier 41
5, 416 output light modes are set on the output side optical transmission path 402.
Can be adjusted to the input light level. Further, when the optical receiving station 404 is provided with the optical amplifying device 417, the mode of the input light of the optical amplifying device 417 can be adjusted to the output light level of the optical transmission line 402.
The mode of the 17 output light can be adjusted to the input light level of the DEMUX 418.

Accordingly, in such an optical communication system, various optical transmission lines 402 such as SMF and NZ-DSF are used.
Can be handled. Therefore, the existing optical transmission line can be effectively used. Further, in such an optical communication system, the optical amplifiers 413, 415,
Since the degradation of the noise figure caused in 416 and 417 is suppressed, long-distance transmission is possible and the number of optical repeaters can be reduced.

Next, another embodiment will be described. (Configuration of Sixth Embodiment) FIG. 18 is a diagram showing a configuration of an optical communication system of a sixth embodiment. FIG.
FIG. 13 is a diagram illustrating a detailed configuration of a pre-stage optical amplifying unit, a pre-stage optical attenuating unit, and a middle-stage optical amplifying unit for C band in the embodiment.

FIG. 20 is a diagram showing a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier for the C band in the sixth embodiment. FIG. 21 shows L in the sixth embodiment.
FIG. 4 is a diagram illustrating a detailed configuration of a pre-stage optical amplifier, a pre-stage optical attenuator, and a middle-stage optical amplifier for a band.

FIG. 22 is a diagram showing a detailed configuration of the post-stage optical attenuator and post-stage optical amplifier for the L band in the sixth embodiment. In FIG. 18, this optical communication system transmits 32 WDM optical signals to an optical transmitting station 501 in a C-band wavelength band (1530 to 1570 nm) and an L-band wavelength band (1570 nm to 1610 nm).
The optical signal is generated by the optical repeater station 503 and multi-stage relayed, and the optical receiving station 504 receives and processes the optical signal. Further, optical signals for control and monitoring for the C band and the L band are generated by the optical transmitting station 501. This signal for the C band is wavelength-multiplexed on the shorter wavelength side than the channel 1, and this signal for the L band is wavelength-multiplexed on the longer wavelength side than the channel 64 and transmitted together with 64 WDM optical signals. Each of the optical transmitting station 501, the optical relay station 503, and the optical receiving station 504 includes the composite optical amplifier according to the present invention.

Each control and monitoring optical signal contains information necessary for operating and maintaining this optical communication system. More specifically, WDM in each band
The number of wavelengths (number of channels) of the optical signal, and each EDF described later
The information includes information such as the operation status of the server and the failure status of the own station. The operation state of the EDF changes depending on control states such as constant gain control and constant output control of the EDF.

In FIG. 18, 64 OSs 521-1 through
32 OSs 521-1 to 521-32 of 521-64
Generates optical signals corresponding to C-band channels 1 to 32, respectively. Each generated optical signal is
The wavelength is multiplexed by being input to the MUX 522-1 to be a WDM optical signal of 32 waves in the C band. The WDM optical signal is input to the composite optical amplifier 513. Further, WDM optical signals obtained by wavelength multiplexing the channel 33 to the channel 64 of the L band are OS521-33 to 521-6.
4 and the MUX 522-2. This L-band WDM optical signal is
The light enters the composite optical amplifier 513.

The C-band WDM optical signal input to the composite optical amplifying device 513 is combined with the C-band optical amplifying device 52.
The light is incident on 3-1 and amplified, and is incident on the MUX 524 together with the optical signal for control and monitoring for the C band. Then, the L-band WDM optical signal input to the composite optical amplifying device 513 is input to the L-band optical amplifying device 523-2 and amplified, and together with the L-band control and monitoring optical signal, the MU.
It is incident on X524.

Each optical signal incident on the MUX 524 is wavelength-multiplexed by the MUX 524, and the W
It becomes a DM optical signal. The two-wavelength band WDM optical signal is emitted to the optical transmission line 502-1 and transmitted to the next-stage optical relay station 503-1. WD transmitted in two wavelength bands
The M-system optical signal is input to the DEMUX 532 in the composite optical amplifier 516-1 in the optical repeater 503-1.

The DEMUX 532 has the W
The DM optical signal is wavelength-separated into a C-band control and monitoring optical signal and a C-band WDM optical signal, an L-band control and monitoring optical signal, and an L-band WDM optical signal. The wavelength-separated C-band WDM optical signal is
MUX amplified by C-band optical amplifier 533-11
534-1. The wavelength-separated L-band WDM optical signal is supplied to the L-band optical amplifier 53.
The signal is amplified by 3-12 and is incident on the MUX 534-2.

The MUX 534-1 wavelength-multiplexes the WDM optical signal of each band together with the control / monitoring optical signal for each band. Then, the optical signal which has become the WDM optical signal in the two wavelength band again is emitted to the optical transmission line 502-2, and
The signal is transmitted to the next-stage optical relay station 503-2. W in two wavelength bands
The DM optical signal is sequentially amplified by the optical repeater 503 and is incident on the optical receiver 504.

The incident WDM optical signal in the two wavelength band is incident on the DEMUX 542 in the composite optical amplifier 517, and the control and monitoring optical signal for C band, the WDM optical signal for C band and the L band optical signal for L band. The wavelength is separated into a control monitoring optical signal and an L-band WDM optical signal.

The wavelength-separated C-band WDM optical signal is amplified by the optical amplifying device 543-1, and is amplified by the DEMUX5.
48-1. The C-band WDM optical signal is wavelength-separated by DEMUX 548-1 for each channel, and each channel has a corresponding OR
529-32 and received. The wavelength-separated L-band WDM optical signal is supplied to the optical amplifier 5.
43-2, DEMUX548-2 and OR549-33 ~ 5
29-64, amplified and received / processed.

Next, the composite optical amplifiers 513, 516, 5
17 will be described. First, the composite optical amplifying device 516 is described.
, And only the differences of the composite optical amplifiers 513 and 517 from the composite optical amplifier 516 will be described. The composite optical amplifying device 516 has the DE
The MUX 532 includes an optical amplifier 533-n1 capable of amplifying the C band, an optical amplifier 533-n2 capable of amplifying the L band, and a MUX 534. The C-band optical amplifying device 533-n1 includes the C-band pre-amplifier 6 shown in FIGS.
00, a first-stage optical attenuator 601, a middle-stage optical amplifier 602, a second-stage optical attenuator 603, and a second-stage optical amplifier 604. The optical amplifying device 533-n2 for L band is shown in FIG.
And L-band pre-amplifier 60 shown in FIG.
5, a first-stage optical attenuator 606, a middle-stage optical amplifier 607, a second-stage optical attenuator 608, and a second-stage optical amplifier 609.

Each optical amplifying device 533 has two input light modes, in-mode 1 and in-mode 2, and two output light modes, out-mode 1 and out-mode 2. First, the configuration of a C-band optical amplifier 533-1 that amplifies a C-band WDM optical signal will be described.

In FIGS. 18 and 19, the control / monitoring optical signal for the C band and the WD of the C band which are incident on the composite optical amplifier 516 and separated by the DEMUX 532 are separated.
The M-system optical signal is incident on the CPL 611 in the pre-stage optical amplifier 600 for the C band. CPL 611 is
The wavelengths are separated into a control and monitoring optical signal for the band and a WDM optical signal for the C band. For the CPL for wavelength separation, a dielectric multilayer filter is used.

The wavelength-separated control / monitoring optical signal is a band-pass optical filter (hereinafter abbreviated as “BPF”) 62.
1 is incident. In the BPF 621, the center wavelength of the wavelength band is set to the wavelength of the control and monitoring optical signal for the C band. The BPF 621 extracts an optical signal for control and monitoring for the C band, and emits the signal to the SV-Out1 terminal. On the other hand, the WDM optical signal of the wavelength-separated C band is
The signal is split into two by the PL 612, and one of the WDM optical signals is input to the monitoring PD 627 via the BPF 626, and the other is input to the ISO 613.

The BPF 626 has a property of blocking the L band light and transmitting the C band light so as not to be affected by the L band light that has not been completely removed by the DEMUX 548. The WDM optical signal input to the PD 627 is photoelectrically converted and input to the variable gain amplifier 628 and the SW 629. SW629 is a switch of one input and four outputs, and each of the four output terminals has a resistor 631 having a resistance value R1, a resistor 632 having a resistance value R2, a resistor 633 having a resistance value R3 and a resistor 633 having a resistance value R4. Any one of the resistors 634 is connected, and each of the resistors 631 to 634 is
Grounded. These resistance values R1 to R4 are determined according to the mode of the input light of the optical amplifier 533-n1 for the C band. The voltage between the terminals of the resistor connected to the PD 627 by the SW 629 is supplied to the AGC 623 and the gain output control circuit 668 via the variable gain amplifier 628 as the output of the PD 627.

The gain of the variable gain amplifier 628 is equal to
9 when switching, the gain variable amplifier 6
It is varied to keep the gain up to 28 outputs constant.
These PD627, SW629 and resistors 631-6
The circuit consisting of 34 is a monitor circuit for detecting the optical level of the C-band WDM optical signal input to the optical amplifier 533-n1.

[0195] The WDM optical signal from the ISO 613 is input to the CPL 614. On the other hand, CPL614
Has a fiber Bragg grating (hereinafter referred to as “FB”).
G ”. ) The laser beam from the LD 622 is also incident via 619. The LD 622 oscillates a laser beam that is an excitation light for the EDF 615, and the oscillation wavelength is 980.
Set to nm. EFD is 980 nm and 146 nm.
It is excited by light of a wavelength such as 0 nm,
When excited by light of m, noise can be reduced.

The FBG 619 is a reflection type optical filter provided for fixing the oscillation wavelength of the LD 619. In general, the oscillation wavelength of an LD fluctuates due to mode hopping (mode hopping).
By returning to D, the oscillation wavelength of the LD can be fixed. Therefore, the reflection center wavelength of the FBG619 is 9
It is set to 80 nm and the reflectivity is sufficient to fix the oscillation wavelength of the LD 622 to 980 nm.
Is set to a value sufficient to excite the EDF 615. More specifically, the reflectance of FBG619 is
It is set to 3 to 10%. FBG 701, 82 to be described later
1, 822 and 891 also stabilize the oscillation wavelength of the LD.

As described above, since the oscillation wavelength of the LD 622 is almost fixed, it is possible to prevent the gain variation of the EDF 615 caused by the variation of the oscillation wavelength of the LD 622. These WDM optical signals from ISO 613 and FB
The laser light from the LD 622 via the G 619 is multiplexed and incident on the EDF 615.

The EDF 615 absorbs the laser beam from the LD 622 to excite Er ions in the EDF 615 to form a population inversion. When a C-band WDM optical signal is incident in a state where the population inversion is formed, this W
Stimulated radiation is induced by the DM optical signal, resulting in WDM
The optical signal is amplified. C amplified by EDF615
Band WDM optical signals are ISO616 and GE
The light enters the CPL 618 via the Q 617. GEQ
A gain equalizer 617 equalizes the gain wavelength characteristics of the EDF 615 and the EDF 654.

One of the WDM optical signals distributed by the CPL 618 is a VA signal in the pre-stage optical attenuator 601 for the C band.
T641 and the other WDM optical signal is
The light is incident on the PD 625 via T620. ATT62
0 adjusts the optical level of the C-band WDM optical signal incident on the PD 625 so as not to damage the PD 625 with light having an excessive optical level. ATT665, 702, 704, 706, 82 described later
3,865,892,894,912,913 also protect the PD from damage.

The output of the PD 625 is converted into a terminal voltage by a resistor (not shown in FIG. 19).
It is input to AGC 623 and gain output control circuit 668. Unless otherwise specified, the output of other PDs is also converted into a terminal voltage by a resistor (not shown). A
The GC 623 is connected to the output of the PD 625 and the variable gain amplifier 62.
8 and the output of the PD 627 through the EDF 615
To determine the gain. The AGC 623 adjusts the drive current (injection current) of the LD 622 so that the injection current does not reach the limiter value based on the determination result, so that the gain of the EDF 615 becomes constant at a predetermined gain. I do. This predetermined gain is determined by the optical amplifier 533-n
This is set in consideration of reducing the noise figure of the low-level C-band WDM optical signal input to 1.

Next, the configuration of the pre-stage light attenuator 601 for the C band will be described with reference to FIG. The aforementioned CP
The C-band WDM optical signal from L618 is incident on VAT 641 in pre-stage optical attenuator 601. VAT6
Reference numeral 41 denotes an optical component capable of attenuating and emitting the incident light and changing the attenuation amount. VAT6
The WDM optical signal from 41 is incident on the CPL 651 in the middle-stage optical amplifier 602 for the C band.

Here, the output according to the output light level of the C-band WDM optical signal emitted from the middle optical amplifying section 602 to the second optical attenuating section 603 will be described later.
2 is input to the gain output control circuit 668 from the PD 669 in the second. The gain output control circuit 668 converts the output of the PD 669 into a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of the ALC 643.

The ALC 643 compares the predetermined reference voltage Vref 9 with the value from the gain output control circuit 668 to output the W output from the middle-stage optical amplifier 602.
The attenuation of the VAT 641 is adjusted so that the optical level per channel of the DM optical signal becomes constant. The reference voltage Vref9 is supplied to the pre-stage optical amplifier 600 and the pre-stage optical attenuator 601.
This is a voltage value referred to for setting the output light level (the output light level output from the CPL 659 to the subsequent light attenuating section) of the portion including the optical amplifier and the middle optical amplifying section 602 to the first target value. Are prepared equal to the number of For example, a reference voltage Vref9M1 for in-mode 1 is prepared for in-mode 1, and a reference voltage Vref9M2 for in-mode 2 is prepared for in-mode 2.

Next, the configuration of the middle-stage optical amplifier 602 for the C band will be described with reference to FIG. VA described above
The C-band WDM optical signal from T641 is incident on the CPL 651 in the middle-stage optical amplifier 602. CPL6
One of the WDM optical signals distributed at 51 is the PD 66
1 and the other WDM optical signal is
2. The light is incident on the CPL 657 via the CPL 653, the EDF 654, the CPL 655, and the ISO 656.

The PD 661 photoelectrically converts the received WDM optical signal, and the output is input to the gain output control circuit 668. Here, 1460 nm laser light from the LD 662 is also incident on the CPL 653. These IS
The WDM optical signal from the O652 and the laser light from the LD 662 are multiplexed by the CPL 653 and input to the EDF 654. Further, 1460 nm laser light from the LD 663 is also incident on the CPL 655, and this laser light is also incident on the EDF 654. Thus, EDF65
4 is forward-excited by LD662 and LD663
Is excited backward.

[0206] The EDF 654 is provided for these LDs 662 and 66.
WDM of C band excited by laser light from 3
Amplifies the optical signal. CPL657 is the amplified C
The band WDM optical signal is divided into two. One of the splits enters the CPL 658 and the other splits into the BPF 6
The light is incident on the PD 669 via the 64 and the ATT 665.

The transmission wavelength band of the BPF 664 is set to the wavelength band of the C band to block the residual pump light, and to accurately detect the optical level of the C band WDM optical signal. The WDM optical signal input to the PD 669 is subjected to photoelectric conversion, and the output thereof is supplied to the gain output control circuit 6.
68.

The gain output control circuit 668 is connected to the PD6
25 and 627, the gain of the pre-stage optical amplifying unit 600 is determined, and from the outputs of the PDs 669 and 661, the gain of the middle-stage optical amplifying unit 602 is determined.
A signal is output to the LD control circuit 666 so that the sum of the gain of 0 and the gain of the middle optical amplifier 602 becomes constant. LD
The control circuit 666 determines whether the LD 662,
By adjusting the drive current (injection current) of 663,
Adjust the gain of EDF654.

Then, W of C band from CPL657 is
The DM optical signal is transmitted through CPL658 to CPL659.
Is incident on. The CPL 658 makes the return light output from the C-band middle-stage optical amplifier 602 incident on the PD 667. P
D667 receives this return light and performs photoelectric conversion, and its output is input to the LD control circuit 666.

When the output from the PD 667 exceeds a predetermined threshold, the LD control circuit 666 determines that the output side of the middle-stage optical amplifier 602 is open. When an optical component such as an optical fiber is connected to the output side of the middle optical amplifier 602, the reflectance at the connection surface is small. Therefore, the amount of return light is small, and the output from the PD 667 is also small. On the other hand, when no optical component is connected to the output side of the middle-stage optical amplifying unit 602, the reflectance at the connection surface is larger than when the optical component is connected. Therefore, the amount of return light increases, and the output from the PD 667 also increases. More specifically, the light level of the return light is approximately −30 to −40 dB when connected, but is about −14 dB when not connected.
Therefore, the LD control circuit 666 can determine the connection state of the output side of the middle-stage optical amplifier 602 based on the magnitude of the output from the PD 667.

The LD control circuit 666 has the
When it is determined that nothing is connected to the output side of LD 2, LD
The drive currents 662 and 663 are reduced. Therefore, E
The gain of DF654 decreases. Therefore, the optical level of the C-band WDM optical signal emitted from the middle-stage optical amplifier 602 is significantly reduced.
Even if the output side of the middle-stage optical amplifying unit 602 is accidentally opened during the operation of 6, the safety of the operator handling the optical repeater station 503 can be ensured.

On the other hand, the LD control circuit 666
If the output of the LDs 662 and 663 does not exceed the predetermined threshold, the signals from the gain output control circuit 668 are used.
Control.

The CPL 659 distributes the incident C-band WDM optical signal into two. One of the divided light is output to the subsequent light attenuator 603 as an output of the middle light amplifier 602, and the other is output to the SA-Out1 terminal. Next, the configuration of the post-stage light attenuator 603 for the C band will be described with reference to FIG.

WD of C band from the aforementioned CPL659
The M-type optical signal is output to the CPL 681 in the post-stage optical amplifier 604 for the C band via the ATT 671. A
The TT 671 is prepared for each mode of the input light, and the attenuation of the ATT 671 for the in-mode 1 is set in consideration of the output light level of the optical amplifier 533-n1 for the C band. The optical attenuation of the ATT 671 for the in-mode 2 is equal to the value obtained by subtracting the input light level for the in-mode 1 from the input light level for the in-mode 2 in the post-stage optical attenuator 603 for the C band. Is set to be larger than the optical attenuation of ATT671.

Here, the attenuation of the ATT 671 is adjusted together with the attenuation of the ATT 871, which will be described later, when the composite optical amplifier 516 is installed in the optical repeater station 503. Next, regarding the configuration of the post-stage optical amplifier 604 for the C band,
A description will be given based on FIG. The C-band WDM optical signal from the ATT 671 is incident on the CPL 681 in the post-amplifier 604.

One WDM optical signal distributed by the CPL 681 enters the PD 711, and the other WDM optical signal is transmitted to the ISO 682, CPL 683, and EDF 68.
4, CPL via ISO 685 and GEQ 686
687. The PD 711 photoelectrically converts the received optical power of the WDM optical signal and outputs the AGC signal.
713 and the gain output control circuit 723.

The CPL 683 supplies the laser light from the LD 712 incident via the FBG 701 to the EDF 684. The LD 712 oscillates a laser beam having a wavelength of 980 nm. The EDF 684 is excited by the laser light from the LD 712 and amplifies the incident C-band WDM optical signal.

The GEQ 686 compensates the gain wavelength characteristics of the EDFs 684 and 693 to almost flat gain wavelength characteristics. C
The PL687 splits the amplified C-band WDM optical signal into two. One of the divided light is incident on the VAT 688, and the other is incident on the PD 716 via the ATT 702.

PD 716 is the WDM of the received C band.
The optical signal is photoelectrically converted, and its output is input to the AGC 713 and the gain output control circuit 723. AGC71
Reference numeral 3 determines the gain of the EDF 684 from the output of the PD 716 and the output of the PD 711, and adjusts the drive current (injection current) of the LD 712 to adjust the gain of the EDF 684 to a predetermined constant gain.

The C-band WDM optical signal attenuated by the VAT 688 enters the CPL 689. CP
One WDM optical signal distributed by L689 is PD
717, and the other is incident on the CPL 691. The PD 717 performs photoelectric conversion of the received C-band WDM optical signal, and outputs the signal to a gain output control circuit 723.
Is input to

The C-band WDM optical signal from CPL 691 is transmitted via ISO 692 and EDF 693 to C
It is incident on PL694. Here, CPL694 has
Laser light obtained by polarization-combining the laser light from the LD 719 and the laser light from the LD 720 with the CPL 705 is incident. The polarization-combined laser light is supplied to the EDF 693 via the CPL 694. Therefore, EDF69
3 is backward pumped by the laser light and amplifies the C-band WDM optical signal. LD719, 720
Oscillates a laser beam having a wavelength of 1480 nm. A polarization beam splitter is used for the CPL 705 that performs polarization combining. A polarization maintaining optical fiber is used as an optical fiber between the LDs 719 and 720 and the CPL 705.

Further, the number of wavelengths increases, and the excitation light
If 19 or 720 is insufficient, pump light is further supplied from the BST-In1 terminal. This can reduce the cost when introducing a small number of wavelengths. The pumping light from the BST-In1 terminal enters the CPL 691 via the CPL 690. The CPL 691 combines the C-band WDM optical signal and the pump light from the CPL 689, and
This excitation light is supplied to the EDF 693 via the 692.
Therefore, the pumping light from the BST-In1 terminal is
The DF693 will be excited in the forward direction.

A part of the pumping light from the BST-In1 terminal is distributed by the CPL 690 and is incident on the PD 718 via the ATT 704. The PD 718 photoelectrically converts the received excitation light, and the output is output to the PD-Out1 terminal. The output from the PD-Out1 terminal is used to control the light level of the aforementioned excitation light, for example, to make the light level a predetermined constant value.

The amplified C-band WDM optical signal is transmitted from CPL 694 through ISO 695 to CPL 69
Injected to 6. One WD distributed by CPL696
The M-type optical signal is output through the CPLs 697, 698, and 699 as MUX5 as output light of the optical amplifier 533-n1.
34, the other being BPF 708 and ATT 706
And is output to the PD 724 through. BPF 708 is
This is for eliminating the residual excitation light. The PD 724 photoelectrically converts the received WDM optical signal, and the output is input to the gain output control circuit 723.

The CPL 697 wavelength-multiplexes the C-band control / monitoring optical signal input to the SV-In1 terminal with the C-band WDM optical signal from the CPL 696. The control / monitoring optical signal for the C band emitted from the SV-Out1 terminal (FIG. 19) is converted from an optical signal to an electric signal, and operation / maintenance information is extracted from the control / monitoring optical signal. The operation / maintenance information is stored in the optical relay station 503.
And is updated with operation / maintenance information to be transmitted in the optical relay station 503. The updated operation / maintenance information is converted from an electrical signal to an optical signal again, and is input to the SV-In1 terminal as a C-band control / monitoring optical signal.

The CPL 698 causes the return light from the CPL 699 to enter the PD 725. The PD 725 receives this return light and performs photoelectric conversion. The output of PD725 is LD
It is input to the control circuit 721. The LD control circuit 721 is
The connection state of the output side of the post-stage optical amplification unit 604 is determined based on the magnitude of the output of the PD 725. If the output from the PD 725 exceeds a predetermined threshold, nothing is connected to the output side of the post-stage optical amplification unit 604. Judge that there is no. On the other hand, when the output of the PD 725 does not exceed the predetermined threshold, the LD control circuit 721 controls the LDs 719 and 720 with a signal from the gain output control circuit 723.

The LD control circuit 721 is connected to the post-amplifier 60
When it is determined that nothing is connected to the output side of LD 4, LD
719 and 720 drive currents are reduced. Therefore, E
The gain of DF693 decreases. Therefore, the optical level of the C-band WDM optical signal emitted from the post-stage optical amplifier 604 is significantly reduced, so that the safety of the operator handling the optical relay station 503 can be ensured.

Then, the CPL 699 emits a part of the incident C-band WDM optical signal to the SA-Out2 terminal. In addition, the gain output control circuit 723 determines whether the P
The gain of EDF 684 is determined from the outputs of D716 and 711, and the EDF6 is determined from the outputs of PDs 724 and 717.
93 and the gain of these EDF 684 and ED
A signal is output to the LD control circuit 721 so that the sum with the gain of F693 becomes constant. The LD control circuit 721 adjusts the gain of the EDF 694 by adjusting the drive current (injection current) of the LDs 719 and 720 based on this signal.

Further, the gain output control circuit 723 includes a PD
A signal based on the output of 724 is output to ALC 703.
The ALC 703 compares the predetermined reference voltage Vref10 with the output from the gain output control circuit 723 to thereby determine the CDM band WDM optical signal per channel in the C-band WDM optical signal emitted from the optical amplifier 535-n1. The attenuation of the VAT 688 is adjusted so that the light level becomes constant. The reference voltage Vref10 is a voltage value that is referenced to make the output light level constant with respect to the input light level of the post-light amplification unit 604.

Second, the configuration of an L-band optical amplifier 533-2 for amplifying an L-band WDM optical signal will be described. The difference between the optical amplifier 533-2 for the L band and the optical amplifier 533-1 for the C band lies mainly in the configuration of the gain equalizer and the way of supplying the pump light for pumping the EDF. 18 and 21, in the composite optical amplifying device 51
The L-band control / monitor optical signal and the L-band WDM optical signal that have been input to the D.6 and demultiplexed by the DEMUX 532 are transmitted to the C-band in the L-band pre-stage optical amplifier 605.
It is incident on PL811.

The CPL 811 separates the wavelength into an L-band control and monitoring optical signal and an L-band WDM optical signal. The wavelength-separated control / monitoring optical signal is a BPF 621
SV-Ou via a BPF 824 that performs the same function as
Injected to terminal t2. The center wavelength of the wavelength band of the BPF 824 is set to the wavelength of the optical signal for control and monitoring for the L band.

On the other hand, the wavelength-separated L-band WDM optical signal is transmitted through CPL 812, ISO 813, CPL 81
4 and EDF 834 to be incident on CPL 839. The CPL 812 emits a part of the incident WDM optical signal to the PD 831 via the BPF 820. BP
The transmission wavelength band of F820 is set to the L band and set so that the C band signal is cut off.

The PD 831 photoelectrically converts the received WDM optical signal, and the output is input to the variable gain amplifier 832 and the SW 833. SW833 is a switch of one input and four outputs, and each of the four output terminals has:
A resistor 835 having a resistance value R6 and a resistor 83 having a resistance value R7
6. Any one of a resistor 837 having a resistance value R8 and a resistor 838 having a resistance value R9 is connected, and each of the resistors 835 to 838 is grounded. These resistance values R6 to R6
9 is determined according to the mode of the input light of the optical amplifier 533-n2 for the L band.

The gain of the variable gain amplifier 832 is
3 is switched from the PD 831 to the variable gain amplifier 8
It is varied to keep the gain up to 32 outputs constant.
The CPL 814 supplies the 980 nm laser light incident from the LD 825 via the FBG 821 to the EDF 834. Further, the CPL 839 supplies the 1460 nm laser light incident from the LD 826 to the EDF 834. Thus, the EDF 834 is excited forward by the LD 825 and backward excited by the LD 826.

[0235] EDF834 is used for these LD825, 82
LDM WDM pumped by laser light from 6
Amplifies the optical signal. Here, the EDF 834 has a longer optical fiber length than the EDFs 615, 654, 684, and 693 that amplify the wavelength band of the C band in order to amplify the wavelength band of the L band. The reason for lengthening the EDF 834 in this way is that the EDF originally has an amplification band in the C band wavelength band and the L band wavelength band, but the amplification factor of the L band wavelength band is the C band wavelength band. This is because it is smaller than the amplification factor. Therefore, the optical fiber length of the EDF 834 needs to be longer than that of the EDF in the C-band wavelength band in order to realize the optical amplification in the L-band wavelength band to the same degree as the optical amplification in the C-band wavelength band. There is. More specifically, the length is increased by about 10 times. EDF854 described later,
884 and 894 are also lengthened like EDF834.

The L-band WDM optical signal from the CPL 839 amplified by the EDF 834 is
The light enters the CPL 819 via the EQ 816, the ISO 817, and the GEQ 818. GEQ816, ISO
The pair of 817 and GEQ818 are EDF834, 85
4 is equalized.

Here, GEQ816 and GEQ818
Is composed of a fiber grating filter that transmits light of a specific wavelength and reflects other wavelengths. Therefore, when the reflection wavelengths of the GEQ 816 and the GEQ 818 are common, the light reflected by the GEQ 816 is reflected by the GEQ 818.
And is incident on the GEQ 816 again. Then, the re-entered light is reflected by the GEQ 816 and re-enters the GEQ 818. That is, GEQ816 and GEQ81
In some cases, multiple reflections are repeated between the light reflected from the light emitting device 8 and the light emitting device 8 to oscillate. Therefore, by providing ISO 817 between GEQs 816 and 818, this oscillation can be prevented.
If the gain wavelength characteristic of the EDF 834 can be equalized to the extent that the optical amplifier 533-2 is required by one GEQ, the number may be one.

[0238] The CPL 819 detects the incident W of the L band.
A DM optical signal is split into two, and one of the split signals is L
The light enters the VAT 841 in the pre-attenuation unit 606 for the band, and the other enters the PD 830 via the ATT 623. The PD 830 photoelectrically converts the received L-band WDM optical signal, and the output is input to the AGC 827 and the gain output control circuit 826.

The AGC 827 determines the gain of the EDF 834 from the output of the PD 830 and the output of the PD 831 via the variable gain amplifier 832. And AGC 82
7 adjusts the drive current (injection current) of the LDs 825 and 826 on the basis of the determination result, thereby obtaining the EDF 8.
The gain of 34 is adjusted to be constant at a predetermined gain.
The predetermined gain is set in consideration of reducing the noise figure of the L-band WDM optical signal of the low optical level input to the optical amplifier 533-n2.

Next, the configuration of the pre-stage light attenuator 606 for the L band will be described with reference to FIG. The aforementioned CP
The L-band WDM optical signal from L819 is incident on the VAT 841 in the pre-stage optical attenuator 606. VAT8
41 attenuates the incident WDM optical signal and outputs it to the CPL 851 in the L-band middle-stage optical amplifier 607.

Here, the output according to the output light level of the L-band WDM optical signal output from the middle-stage optical amplifier 607 to the latter-stage optical attenuator 608 is output to the later-described middle-stage optical amplifier 60.
7 is input to the gain output control circuit 868 from the PD 869 in the. Gain output control circuit 868 converts the output of PD 869 to a logarithmic value of the voltage level, and the converted logarithmic value is input to one input terminal of ALC843.

The ALC 843 compares the predetermined reference voltage Vref11 with the value from the gain output control circuit 868 to determine the L-band WDM optical signal output from the middle-stage optical amplifier 607 for one channel. The attenuation of the VAT 841 is adjusted so that the light level becomes constant. The reference voltage Vref11 is equal to the value of the pre-amplifier 605.
And the output light level of the portion consisting of the front light attenuator 606 and the middle light amplifier 607 (from the CPL 858 to the rear light attenuator 6).
This is a voltage value referred to for setting the output light level (output light level 08) to the first target value, and is prepared equal to the number of modes of the input light. For example, for the in-mode 1, a reference voltage Vref11M1 for the in-mode 1 is prepared, and for the in-mode 2, the reference voltage Vref11M2 for the in-mode 2 is provided.
Is prepared.

Next, the configuration of the middle-stage optical amplifier 607 for the L band will be described with reference to FIG. VA described above
The L-band WDM optical signal from T841 is incident on the CPL 851 in the middle-stage optical amplifier 607. CPL8
One of the WDM optical signals distributed at 51 is a PD 86
1 and the other is ISO 852, CPL 853,
CPL856 via EDF854 and ISO855
Is incident on.

The PD 861 receives the received L-band WDM.
The optical signal is photoelectrically converted, and the output is output to the gain output control circuit 868. In addition, CPL853 is LD8
The laser light of 1460 nm incident from
54. The EDF 834 is excited by the laser light and amplifies the L-band WDM optical signal.

[0245] The CPL 856 is the W of the incident L band.
A DM optical signal is split into two, and one of the split signals is B
The light enters the PD 869 via the PF 863 and the ATT 865. The transmission wavelength band of the BPF 863 is set to the wavelength band of the L band, and blocks the residual pump light. PD8
69 performs photoelectric conversion of the received WDM optical signal,
The output is input to the gain output control circuit 868.

The gain output control circuit 868 is the same as the PD8
30 and 831, the gain of the pre-stage optical amplifying unit 605 is determined, and from the outputs of the PDs 869 and 861, the gain of the middle-stage optical amplifying unit 607 is determined.
The signal is output to the LD control circuit 866 so that the sum of the gain of the gain 5 and the gain of the middle-stage optical amplifier 607 is constant. LD
The control circuit 866 adjusts the drive current (injection current) of the LD 862 based on this signal,
Adjust the gain of 54.

In addition, the other L distributed by CPL 856
The WDM optical signal of the band is incident on the ATT 871 in the L-band rear-stage optical attenuator 608 as an output of the middle-stage optical amplifier 607 via the CPLs 857 and 858.

The CPL 857 causes the return light from the CPL 858 to enter the PD 864. The PD 864 receives the return light and performs photoelectric conversion, and outputs the converted light to the LD control circuit 8.
66 is input. The LD control circuit 866 controls the PD8
The connection state of the output side of the middle-stage optical amplifying unit 607 is determined based on the magnitude of the output of 64. The LD control circuit 866 controls the PD8
When the ratio between the output of the PD 69 and the output of the PD 864 exceeds a predetermined threshold, it is determined that nothing is connected to the output side of the middle-stage optical amplifier 607. Then, the LD control circuit 666
Reduces the drive current of the LD 862 based on this determination. Therefore, the gain of the EDF 854 decreases. Therefore, the L-band W emitted from the middle-stage optical amplifier 607
Since the optical level of the DM optical signal is significantly reduced, the safety of the operator handling the optical relay station 503 can be ensured. On the other hand, when the output of PD 864 does not exceed the predetermined threshold, LD control circuit 866 controls LD 862 by a signal from gain output control circuit 868.

The CPL 858 emits a part of the L-band WDM optical signal to the SA-Out2 terminal. Next, L
FIG. 22 shows the configuration of the post-stage light attenuator 608 for the band
It will be described based on. The L-band WDM optical signal from the above-mentioned CPL 858 is incident on the CPL 881 in the L-band post-amplifier 609 via the ATT 871.

The ATT 871 is prepared for each mode of the input light, and the attenuation of the ATT 871 for the in-mode 1 is L
The setting is made in consideration of the output light level of the band optical amplifier 533-n2. The optical attenuation of the ATT 871 for the in-mode 2 is equal to the value obtained by subtracting the input light level for the in-mode 1 from the input light level for the in-mode 2 in the L-band post-stage optical attenuator 809. AT
It is set to be larger than the light attenuation amount of T871.

Next, the configuration of the latter-stage optical amplifier 609 for the L band will be described with reference to FIG. AT mentioned above
The L-band WDM optical signal from T871 is input to the CPL 881 in the post-amplifier 609. CPL8
One of the WDM optical signals distributed at 81 is a PD90
1 and the other is ISO882, CPL883,
The light enters the CPL 887 via the EDF 884, the ISO 885, and the GEQ 886.

The PD 901 photoelectrically converts the received optical power of the WDM optical signal, and outputs the output to the AGC 903 and the gain output control circuit 925. CPL88
Reference numeral 3 supplies the EDF 884 with laser light having a wavelength of 980 nm, which is incident from the LD 902 via the FBG 904.
The EDF 884 is excited by the laser light and amplifies the incident L-band WDM optical signal.

The GEQ 886 compensates the gain wavelength characteristics of the EDFs 884 and 894 to almost flat gain wavelength characteristics. C
The PL 887 divides the incident L-band WDM optical signal into two, one of which is incident on the VAT 888 and the other is incident on the PD 907 via the ATT 905.
The PD 907 photoelectrically converts the received L-band WDM optical signal, and the output is input to the AGC 903 and the gain output control circuit 925.

The AGC 903 determines the gain of the EDF 884 from the output of the PD 907 and the output of the PD 901 and adjusts the drive current (injection current) of the LD 902 to adjust the gain of the EDF 884 to a predetermined constant gain. . Also, WDM of L band attenuated by VAT888
The system optical signal is incident on the CPL889. CPL88
9, one of the WDM optical signals is distributed to the PD 908.
And the other is incident on CPL 892. PD
908, photoelectrically converts the received L-band WDM optical signal, and the output is input to the gain output control circuit 925.

On the other hand, the LDs 910 and 911 have the wavelength 146.
A laser beam of 0 nm is oscillated, and the laser beams from each of the LDs 910 and 911 are polarization-synthesized by the CPL 895, and
The light is incident on CPL 892 via 891. A polarization beam splitter is used for the CPL 895 for polarization synthesis. A polarization maintaining optical fiber is used as an optical fiber between the LDs 910 and 911 and the CPL 895.

The CPL 892 is an L-band WDM optical signal from the CPL 889 and the CPL 895, 891
Are combined with the laser beams from the LDs 910 and 911 via the. The multiplexed light is ISO 893, EDF 894, C
The light enters the CPL 897 via the PL 895 and the ISO 896. Therefore, the EDF 894 has the LD 910, 911
Is pumped forward by the laser light from
Amplifies the DM optical signal.

Here, the laser light from the LDs 910 and 911 cannot excite the EDF 894 sufficiently.
When the WDM optical signal of the band cannot be sufficiently amplified by the EDF 894, one or both of the pump light from the BST-In2 terminal and the pump light from the BST-In3 terminal are further supplied. This BST-In
The excitation light from the two terminals is transmitted through the CPL890 via the CPL890.
It is incident on 91. The CPL 891 multiplexes the laser light and the pump light from the above-described LDs 910 and 911, which are incident via the CPL 895. This combined light is CPL
It is supplied to EDF 894 via 892 and ISO 893. Therefore, the pump light from the BST-In2 terminal pumps the EDF 894 forward. Also, part of the excitation light from the BST-In2 terminal is
890 and distributed via ATT894 to PD909.
Is incident on. The PD 909 photoelectrically converts the received excitation light, and the output is output to the PD-Out2 terminal.

On the other hand, the pump light from the BST-In3 terminal is supplied to the EDF 894 via the CPLs 917 and 895. Therefore, the pump light from the BST-In3 terminal pumps the EDF 894 backward. CP
The L917 distributes a part of the pump light from the BST-In3 terminal to the PD 915 via the ATT912. PD
915 photoelectrically converts the received excitation light, and the output is
It is output to the PD-Out3 terminal.

The CPL 897 is used to detect the incident W of the L band.
The DM optical signal is split into two. On the other hand,
The light is output to the MUX 534 (FIG. 18) as output light of the optical amplifying device 533-n2 via CPLs 898, 899, and 890, and the other light is output to the PD 916 via the BPF 918 and the ATT 913. The PD 916 photoelectrically converts the received WDM optical signal, and the output is input to the gain output control circuit 925.

The CPL 898 multiplexes the L-band control and monitoring optical signal incident on the SV-In2 terminal with the L-band WDM optical signal from the CPL 897. The control and monitoring optical signal for the L band is based on the SV-Out described above.
These are optical signals emitted from two terminals (FIG. 21), used / updated by the optical relay station 503, and incident on the SV-In2 terminal.

The CPL 899 and PD 914 are for detecting return light and detecting connection of an output connector, and perform the same operations as the CPL 698 and PD 725 in FIG. Then, the CPL 900 emits a part of the incident L-band WDM optical signal to the SA-Out4 terminal.

The gain output control circuit 925 determines the gain of the EDF 884 based on the outputs of the PDs 907 and 901 and determines the EDF 884 based on the outputs of the PDs 916 and 908.
The gain of EDF 884 and the gain of EDF 884 are determined.
A signal is output to LD control circuit 920 so that the sum with the gain of DF894 becomes constant. The LD control circuit 920 is
The drive current (injection current) of the LDs 910 and 911 is adjusted based on this signal, thereby adjusting the gain of the EDF 894.

Further, gain output control circuit 925 includes a PD
A signal based on the output of 916 is output to ALC 906.
The ALC 906 outputs this output and a predetermined reference voltage V
By comparing with ref12, this optical amplifier 535
Vn so that the optical level per channel in the L-band WDM optical signal emitted from -n2 is constant.
Adjust the amount of AT888 attenuation.

Next, the composite optical amplifier 513 will be described. The difference between the composite optical amplifier 513 and the composite optical amplifier 516 is that the composite optical amplifier 513 is a DEMUX 532
And the CPLs 611 and 811 and the BPFs 621 and 824 in the pre-stage optical amplifiers 600 and 605 are not provided. The composite optical amplifier 513 is a DEMUX5
The reason why the optical transmission station 501 does not include the OS 321 and the M
This is because the signals are individually generated by the UX 522, and there is no need to separate the wavelength from the WDM optical signal in the two wavelength bands into the WDM optical signal in each band. Then, the composite optical amplifier 513 includes the CPLs 611 and 811 and the BPF 621,
824 is not provided because the optical signal for control and monitoring for each band is generated for the first time in the optical transmitting station 501.
This is because there is no need to separate the wavelengths of the control monitoring optical signal and the WDM optical signal.

Therefore, the composite optical amplifier 513 includes the optical amplifier 523 and the MUX 524. And
The correspondence between the composite optical amplifier 513 and the composite optical amplifier 516 is such that the optical amplifier 523-1 corresponds to the optical amplifier 533-n1, and the optical amplifier 523-2 corresponds to the optical amplifier 533-n2. , MUX 524 correspond to the MUX 534. Next, the composite optical amplifier 517 will be described.

The composite optical amplifier 517 and the composite optical amplifier 5
The difference from the MUX 53 is that the composite optical amplifier 517
4 and the subsequent optical amplifiers 600 and 605
Is not provided with the CPLs 697 and 898. The reason why the composite optical amplifier 517 does not include the MUX 534 is that the optical receiving station 504 receives and processes each optical signal in the WDM optical signal by the OR 549 as described above. This is because it is not necessary to wavelength-multiplex a band WDM optical signal into a two-wavelength WDM optical signal. Then, the composite optical amplifying device 51
The reason why 7 does not include the CPLs 697 and 898 is that it is no longer necessary to transmit the control and monitoring optical signal for each band to the optical transmission line.

Therefore, the composite optical amplifying device 517
An EMUX 542 and an optical amplifier 543 are provided. The correspondence between the composite optical amplifier 517 and the composite optical amplifier 516 is such that the DEMUX 542 corresponds to the DEMUX 532, the optical amplifier 543-1 corresponds to the optical amplifier 533-n1, and the optical amplifier 543-2 corresponds to the optical amplifier 543-2. This corresponds to the device 533-n2.

(Operation and Effect of Sixth Embodiment) In such an optical communication system, the optical amplifying device 52 is
3-1, 523-2, the mode of the input light of the composite optical amplifier 513 can be adjusted to the output light level of the MUXs 522-1, 522-2, and the composite optical amplifier 51
The mode of the output light of No. 3 can be adjusted to the input light level of the optical transmission line 502-1.

Then, the optical amplifying device 53 is provided to the optical repeater 503.
Since 3-n1 and 533-n2 are provided, the composite optical amplifying device 51
6, the mode of the input light can be adjusted to the output light level of the optical transmission line 502 on the input side, and the composite optical amplifier 5
The mode of the 16 output lights can be adjusted to the input light level of the optical transmission line 502 on the output side. Further, the optical receiving station 5
Since optical amplifiers 543-1 and 543-2 are provided in the optical transmission line 502, the mode of the input light of the composite optical amplifier 517 is changed to the optical transmission line 502.
And the mode of the output light of the composite optical amplifying device 517 is DEMUX 548-1,
548-2 input light level.

Here, the optical amplifying devices 523, 533, and 543 in the sixth embodiment have the same operation and effect in each in-mode and each out-mode as those of the first to fourth embodiments. Description is omitted. Therefore, in such an optical communication system, SMF or NZ-D
It can correspond to various optical transmission paths 502 such as SF. Therefore, the existing optical transmission line can be effectively used. Further, in such an optical communication system, since the deterioration of the noise figure caused in the composite optical amplifiers 513, 516, and 517 is suppressed, long-distance transmission is possible and the number of optical relay stations can be reduced. .

Further, when transmitting a WDM optical signal in a wide wavelength band, such as a WDM optical signal in a two-wavelength band, the optical level of the short-wavelength channel decreases due to stimulated Raman scattering and the long-wavelength optical signal is transmitted. The light level of the channel increases. Therefore, an optical amplifier that amplifies a WDM optical signal in a wide wavelength band is required to have a wide input dynamic range. The composite optical amplifying device according to the sixth embodiment has a wide input dynamic range, and thus is suitable for amplifying a WDM optical signal in a wide wavelength band.

In the sixth embodiment, the WDM optical signal arranged in the C band and the WDM optical signal arranged in the L band are transmitted in the same direction. It may be. For example, a C-band WDM optical signal is transmitted in the upstream direction and an L-band WD
The M-type optical signal is transmitted in the downstream direction. In the sixth embodiment, the change in the amount of attenuation in the post-stage optical attenuators 603 and 608 is changed when the composite optical amplifier is installed in the optical communication system.
As shown at 109, the VATs 173, 252, and 262 may be automatically changed by an optical variable attenuator.

Further, in the case of using such a VAT, the function of automatically lowering the light level of the emitted laser light by detecting the opening of the output side provided in the middle-stage optical amplifier is omitted. Can be. In the sixth embodiment,
A case has been described in which the downstream light attenuators 603 and 608 have only the function of attenuating light.
A function of compensating for chromatic dispersion may be added by further providing a CF. Further, by further providing the OADM as in the post-stage optical attenuator 109, an optical repeater having a function of dropping / adding a channel from a WDM optical signal transmitted through the optical repeater can be provided.

Then, the first to fourth embodiments
In the embodiment, the WDM optical signal is a wavelength band of the C band.
Range, but is not limited to this. Departure
Can be applied to any wavelength band.
it can. And an EDF for amplifying the WDM optical signal.
Is appropriately selected according to the wavelength band of the WDM optical signal.
You. For example, if the WDM optical signal is in the L-band wavelength band,
(1570nm-1610nm)
In other words, the gain shift error amplifies the L-band wavelength band.
Rubidium-doped optical fibers can be used. WD
If the M optical signal is S⁺Band wavelength band (1450 to 14
90 nm), S ⁺Of the band
Thulium-doped optical fiber (thulium-
doped fiberamplifier) can be used. Ma
Also, the oscillation wavelength of the LD which is the excitation light source is appropriately selected.
You.

In the first embodiment, the ATT 171 is replaced according to the mode of the input light when the optical amplifying device 301 is installed. Post-stage light attenuation unit 1 in form
As in 06, the attenuation may be changed using VAT instead of ATT171. Conversely, in the second embodiment, the amount of attenuation of the post-stage optical attenuator 106 is determined by using the ATT instead of the VAT 173 and using the input light when installing the optical amplifying device 302 as in the first embodiment. The ATT may be replaced according to the mode.

Further, in the first to fourth embodiments, the post-stage optical attenuators 104, 106, 108,
The adjustment of the amount of attenuation in 109 is performed by adjusting the amount of attenuation of the semi-fixed optical attenuator in accordance with the mode of the input light when installing the optical amplifiers 301, 302, 303, 304 using the semi-fixed optical attenuator. You may do so. Further, the attenuation may be adjusted by applying a predetermined voltage to the VAT alone.

In the first to fourth embodiments, the output light level of the middle optical amplifier 103 is adjusted to the mode of the input light when the optical amplifiers 301, 302, 303, 304 are installed. The reference voltage Vref2 is changed by changing the reference voltage Vref2 according to the mode of each input light.
ref2 may be prepared in advance, and a control circuit for switching the prepared reference voltage Vref2 by detecting the input light level of the pre-stage optical amplifier 101 may be provided. Such an optical amplifying device can automatically switch the mode of the input light by the control circuit.

[0278]

According to the present invention, the input dynamic range can be expanded with one optical amplifier without deteriorating the noise figure. Further, according to the present invention, it is possible to connect to various types of optical fibers without impairing the output end opening function. Furthermore, according to the present invention, since a plurality of wavelength bands can be amplified, light having a wide wavelength band can be amplified.

Further, the present invention can cope with various types of optical transmission lines. Therefore, the existing optical transmission line can be effectively used. Furthermore, longer distance transmission is possible, and the number of optical repeaters can be reduced. Further, since the present invention has a wide input dynamic range, it is suitable for amplifying a WDM optical signal in a wide wavelength band.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a level diagram of the present invention.

FIG. 3 is a diagram showing a level diagram of the present invention.

FIG. 4 is a diagram illustrating an overall configuration of an optical amplifying device according to the first to fourth embodiments.

FIG. 5 is a diagram showing a detailed configuration of a pre-stage optical amplifier, a pre-stage optical attenuator, and a middle-stage optical amplifier in the first to fourth embodiments.

FIG. 6 is a diagram showing a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the first embodiment.

FIG. 7 is a diagram illustrating a simulation result of a level diagram in the optical amplifying device of the first embodiment.

FIG. 8 is a diagram illustrating a level diagram in the optical amplifying device according to the first embodiment.

FIG. 9 is a diagram showing a simulation result of a level diagram in the optical amplifying device according to the prior art.

FIG. 10 shows a relationship between an input light level and a noise figure.
FIG. 4 is a diagram illustrating a comparison between the case of the optical amplifying device of the first embodiment and the case of the optical amplifying device of the prior art.

FIG. 11 is a diagram illustrating a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the second embodiment.

FIG. 12 is a diagram illustrating a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the third embodiment.

FIG. 13 is a diagram illustrating a simulation result of a level diagram in the optical amplifying device according to the third embodiment.

FIG. 14 is a diagram showing a simulation result of a level diagram in the optical amplifying device according to the prior art.

FIG. 15 is a diagram illustrating a detailed configuration of a post-stage optical attenuator and a post-stage optical amplifier in the fourth embodiment.

FIG. 16 is a diagram illustrating an OA in a post-stage optical attenuation unit according to the fourth embodiment;
It is a figure showing the example of composition of DM.

FIG. 17 is a diagram illustrating a configuration of an optical communication system according to a fifth embodiment.

FIG. 18 is a diagram illustrating a configuration of an optical communication system according to a sixth embodiment.

FIG. 19 is a diagram illustrating a detailed configuration of a pre-stage optical amplifying unit, a pre-stage optical attenuating unit, and a middle-stage optical amplifying unit for the C band in the sixth embodiment.

FIG. 20 is a diagram illustrating a detailed configuration of a rear-stage optical attenuator and a rear-stage optical amplifier for the C band in the sixth embodiment.

FIG. 21 is a diagram illustrating a detailed configuration of a pre-stage optical amplifying unit, a pre-stage optical attenuating unit, and a middle-stage optical amplifying unit for an L band according to a sixth embodiment.

FIG. 22 is a diagram illustrating a detailed configuration of an L-band rear-stage optical attenuator and a rear-stage optical amplifier in the sixth embodiment.

FIG. 23 is a diagram showing a configuration and a level diagram of a preceding optical amplifying device.

FIG. 24 is a diagram illustrating a relationship between gain of an optical amplifier and gain wavelength characteristics.

[Explanation of symbols]

10, 301 to 304, 413, 415, 417 Optical amplifier 11 First optical amplifier 12 Optical attenuator 13 Second optical amplifier 21 First optical amplifier 22 Optical attenuator 23 Second optical amplifier 101, 600, 605 Pre-stage Optical amplification units 102, 601, 606 Pre-stage optical attenuation units 103, 602, 607 Middle-stage optical amplification units 104, 106, 108, 109, 603, 608 Rear-stage optical attenuation units 105, 107, 604, 609 Rear-stage optical amplification units 114, 155 , 185, 214, 223, 615, 6
54, 684, 693, 834, 854, 884, 89
4 Erbium-doped optical fiber 121, 255, 627, 667, 831, 864 Photodiode 122, 162, 190, 232, 240, 623, 7
13, 827, 903 Automatic gain control circuit 123, 124, 144, 160, 233, 234, 2
38 Logarithmic conversion circuit 125, 126, 235, 236 Subtractor 127 Switch 128-131, 201, 202, 613-634, 8
35-838 Resistor 143, 228, 643, 843 Automatic output control circuit 161, 239 Adder 163, 241 Antilogarithmic conversion circuit 171, 254, 264, 671, 871 Optical attenuator 173, 218, 252, 262 Optical variable attenuation 175, 256, 266 Attenuation control circuit 253 Dispersion compensating fiber 263 Optical dropping / inserting device 401, 501 Optical transmitting station 403, 503 Optical relay station 404, 504 Optical receiving station 666, 721, 866, 920 LD control circuit 668, 723, 868, 925 Gain output control circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/06 10/04 (72) Inventor Go Sakamoto 4-1-1 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture No. Within Fujitsu Limited (72) Inventor Makoto Murakami 1-4-3 Kita-Nanajo-Nishi 4-chome, Kita-ku, Sapporo-shi, Hokkaido Within Fujitsu Hokkaido Digital Technology Co., Ltd. (72) Inventor Chihiro Oshima 4 Kamikadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture 1-1-1 Fujitsu Limited (72) Inventor Yoshito Onoda 4-1-1 1-1 Kamidadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa F-term within Fujitsu Limited 5F072 AB09 AK06 JJ20 KK15 KK30 PP07 YY17 5K002 AA06 CA02 CA10 CA13

Claims (1)

[Claims] 1. A wavelength band splitter for splitting light from a transmission line into a plurality of bands, and a change in the split light provided corresponding to each light split by the wavelength band splitter. A plurality of first optical amplifying units for changing a target value of the optical amplification output when a predetermined value is reached; a plurality of attenuating units for respectively attenuating the outputs of the plurality of first optical amplifying units; A plurality of second optical amplifiers for amplifying, a multiplexing unit for multiplexing the outputs of the plurality of second optical amplifiers, and a plurality of control units for respectively changing the amounts of attenuation of the plurality of attenuators, The control unit, when changing the target value of the optical amplification output of the first optical amplification unit, sets the target value of the optical amplification output of the first optical amplification unit and the optical amplification output of the first optical amplification unit after the change. An optical amplifying device, wherein the amount of attenuation of the attenuator is changed in accordance with a difference from the target value.