JP2003258346A - Light amplifier and attenuation adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust light attenuation so that it becomes optimum NF a gain-sum constant control, and to improve transmission quality. <P>SOLUTION: An attenuation control part 40 controls the attenuation level of variable optical attenuators 12 and 22 so that the output levels of a previous step side gain control part 10 and a post step side gain control part 20 become constant. A gain target value setting part 50 distributes the attenuation level of a plurality of variable light attenuators 12 and 22 so that a noise potential becomes optimum when a device input level or an inter-step loss due to distributed compensation fluctuates. Thus, the gain target values are set in a second light amplification part 13 and a fourth light amplification part 23, and the gain-sum from a first light amplification part 11 to the fourth light amplification part 23 is controlled to be constant. <P>COPYRIGHT: (C)2003,JPO

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 and an attenuation amount adjusting method, and more particularly to an optical amplifying device for amplifying an optical signal and an optical amplifying section having a multi-stage structure by adjusting the amount of attenuation. The present invention relates to an attenuation amount adjusting method for controlling the constant.

[0002]

2. Description of the Related Art In recent years, wavelength division multiplexing (WDM) for multiplexing and transmitting optical signals of a plurality of different wavelengths.
Ision Multiplexing) has attracted attention and has come into practical use. An EDFA (Erbium-Doped Fiber Amplifier) is one of the devices used in the WDM system. EDFA is erbium (Er ³⁺⁾ doped fiber: a (EDF Erbium-Doped Fiber) optical amplifier with an amplification medium.

As a repeater for WDM transmission, ED is usually used.
The configuration is such that Fs are connected in multiple stages. Also, EDF
A has a gain wavelength characteristic. Therefore, the gain wavelength characteristic is flattened within the signal band by controlling the sum of EDF gains in each stage to a constant value and performing gain equalization.

FIG. 11 is a diagram showing a control image for gain equalization. To flatten the gain of the EDFA 101, E
The gain is flattened by providing the gain equalizer 102 having a loss characteristic that is contrary to the gain wavelength dependence of the DF.

On the other hand, the optical input level of the repeater fluctuates,
When the gain sum deviates from a certain value, flatness is not maintained and tilt occurs, which leads to a reduction in transmission distance and transmission band.

Therefore, as a conventional technique, Japanese Patent Laid-Open No. 2001-2001
In Japanese Patent No. 144352, a variable optical attenuator (VOA) is provided at the front stage and the rear stage inside the repeater.
Is provided, the increase of the input level is attenuated by the VOA in the preceding stage to make the gain sum constant, and the output of the VOA in the latter stage is variably controlled to make the output light level constant.

[0007]

However, in the prior art as described above, the entire input dynamic range is absorbed by the VOA in the preceding stage. Therefore, when a high input level occurs, the middle stage section is affected. However, there is a problem in that the input level of (2) is lowered (because the pumping light in the previous stage is limited), which causes deterioration of the noise figure (NF).

The present invention has been made in view of the above points, and is an optimum NF according to each level of the EDF input section.
It is an object of the present invention to provide an optical amplifying device that improves the transmission quality by adjusting the optical attenuation amount so that the EDF gain sum is controlled to be constant.

Another object of the present invention is to improve the transmission quality by adjusting the optical attenuation so as to obtain the optimum NF according to each level of the EDF input section and performing the EDF gain sum constant control. It is an object of the present invention to provide a method for adjusting an attenuation amount.

[0010]

In order to solve the above problems, the present invention provides a variable optical attenuator 12 and a variable optical attenuator in an optical amplifying device 1 for amplifying an optical signal as shown in FIG. A first optical amplifier 11 arranged before the optical amplifier 12 for gain control and optical amplification, and a second optical amplifier 1 arranged after the variable optical attenuator 12 for optical amplification by gain control.
And a variable optical attenuator 22 and a variable optical attenuator 22, which is disposed in a stage prior to the variable optical attenuator 22 and which performs gain control for optical amplification. A post-stage gain control unit 20 that is arranged at a post stage of the device and includes an amplification unit 21 and a fourth optical amplification unit 23 that is arranged at a post stage of the variable optical attenuator 22 and performs gain control to perform optical amplification.
And a dispersion compensating unit 30 located between the front-stage side gain control unit 10 and the rear-stage side gain control unit 20 for performing dispersion compensation of light.
An attenuation amount control unit 40 that controls the attenuation amounts of the variable optical attenuators 12 and 22 so that the output levels of the front-stage gain control unit 10 and the rear-stage gain control unit 20 become constant levels.
When the interstage loss amount changes due to the device input level or dispersion compensation, the second optical amplifying unit 13 distributes the attenuation amount to the plurality of variable optical attenuators 12 and 22 so that the noise figure becomes optimum. And a gain target value setting unit 50 that sets a gain target value to each of the fourth optical amplification units 23 and controls the sum of gains from the first optical amplification unit 11 to the fourth optical amplification unit 23 to be constant. An optical amplifying device 1 is provided having the following.

Here, the first optical amplification section 11 is arranged in front of the variable optical attenuator 12 and performs gain control to perform optical amplification. The second optical amplification unit 13 is arranged in the subsequent stage of the variable optical attenuator 12 and performs gain control to perform optical amplification. The third optical amplification unit 21 is arranged in front of the variable optical attenuator 22 and performs gain control to perform optical amplification. The fourth optical amplification unit 23 is arranged in the subsequent stage of the variable optical attenuator 22 and performs gain control to perform optical amplification. The dispersion compensating unit 30 is located between the front-stage gain control unit 10 and the rear-stage gain control unit 20, and performs dispersion compensation of light. The attenuation amount control unit 40 controls the attenuation amounts of the variable optical attenuators 12 and 22 so that the output levels of the front-stage gain control unit 10 and the rear-stage gain control unit 20 become constant levels. The gain target value setting unit 50 distributes the attenuation amount to the plurality of variable optical attenuators 12 and 22 so that the noise figure becomes optimum when the interstage loss amount changes due to the device input level or dispersion compensation. , The second optical amplifier 13 and the fourth
The gain target value is set for each of the optical amplification units 23 of
The gain sum from the optical amplification section 11 to the fourth optical amplification section 23 is controlled to be constant.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a principle diagram of an optical amplifier of the present invention. The optical amplifying device 1 has a dispersion compensating unit 30, and a front-stage gain control unit 10 and a rear-stage gain control unit 20 are provided before and after the dispersion compensating unit 30 also for compensating for the loss generated in the dispersion compensating unit 30. To be Further, it has an attenuation amount control unit 40 and a target gain value setting unit 50. This optical amplification device 1 has a W
It is applied to optical repeaters in DM communication.

The pre-stage gain control section 10 comprises a first optical amplification section 11, a variable optical attenuator (VOA) 12 and a second optical amplification section 13. The first optical amplification unit 11 uses the VO
It is arranged in front of A12, and performs gain control on the input light to the device for optical amplification. The second optical amplification unit 13 uses the VOA1
The output light from the VOA 12 is arranged in the latter stage of the second optical amplifier 12, and gain control is performed on the output light to amplify the light.

The post-stage gain control section 20 comprises a third optical amplification section 21, a VOA 22, and a fourth optical amplification section 23. The third optical amplification unit 21 is arranged in front of the VOA 22 and performs gain control on the output light from the dispersion compensation unit 30 to perform optical amplification. The fourth optical amplification unit 23 is arranged in the subsequent stage of the VOA 22, performs gain control on the output light from the VOA 22, performs optical amplification, and outputs the output light from the device.

In the case of gain control, the gain of optical amplification is controlled by exciting the EDF with a semiconductor laser. The dispersion compensating unit 30 is located between the front-stage gain control unit 10 and the rear-stage gain control unit 20, and performs dispersion compensation of light. The dispersion compensator 30 actually uses the dispersion compensating fiber (D
CF: Dispersion Compensating Fiber).
The DCF 30 is a fiber for canceling chromatic dispersion (a phenomenon in which a waveform propagating in the fiber spreads along the time axis).

The attenuation amount control unit 40 is a gain control unit 1 on the front stage side.
0 and the output level of each of the rear gain control units 20 are
The attenuation amounts of the VOAs 12 and 22 are controlled so that the levels become constant.

The target gain setting unit 50 changes the VOA 1 when the device input level (the level of the optical signal input to the optical amplifier 1) or the interstage loss amount (attenuation amount due to dispersion compensation) changes.
The noise figure of the optical amplification section (hereinafter, NF) for 2 and 22
In order to distribute the amount of attenuation so as to be optimum, the gain target values are set in the second optical amplification unit 13 and the fourth optical amplification unit 23, respectively, and the first optical amplification unit 11 to the fourth optical amplification unit 23 are set. The sum of the gains of the amplifiers 23 is controlled to be constant. Details of the specific configuration and operation of the optical amplification device 1 will be described with reference to FIG. 6 and subsequent figures.

Next, the problems to be solved by the present invention will be described in detail. FIG. 2 is a diagram showing the configuration of a conventional optical amplifier. The optical amplifier 60 has a DCF 66 inside,
A gain control unit is provided in the front stage and the rear stage of the DCF 66. The gain control unit in the previous stage includes EDF units 61 and 62,
A VOA 65 is installed in the middle of this. The gain control section at the latter stage includes EDF sections 63 and 64, and VOA
67 is installed.

On the front side, the EDF section 61 includes photodiodes (hereinafter, PD) 61a and 61b, pumping semiconductor lasers (hereinafter, LD) 61c, demultiplexing optical splitter 61d,
61e, a wavelength division multiplexing optical coupler 61f, and an EDF 61g. Further, the EDF unit 62 includes PDs 62a, 62
b, LD 62c, demultiplexing optical splitters 62d and 62e, wavelength division multiplexing optical coupler 62f, and EDF 62g.

The EDF section 63 is connected to the PD 63 on the rear side.
a, 63b, LD 63c, demultiplexing optical splitters 63d, 63
e, a wavelength division multiplexing optical coupler 63f, and an EDF 63g. The EDF unit 64 includes PDs 64a, 64b, L
D64c, demultiplexing optical splitters 64d and 64e, wavelength multiplexing optical coupler 64f, and EDF 64g.

The operation will be described. The demultiplexing optical splitter 61d of the EDF unit 61 splits the input light, and one of the split lights goes to the PD 61a and the other goes to the wavelength multiplexing optical coupler 61f. The PD 61a converts the branched light into an electric signal and transmits the electric signal to an optical monitor unit (which performs optical level detection and the like) not shown.

The LD 61c radiates pumping light, and pumps the EDF 61g through the wavelength multiplexing optical coupler 61f to perform optical amplification. Thereafter, the amplified optical signal is branched by the demultiplexing optical branching device 61e, one of which goes to the VOA 65 and the other of which goes to the PD 61b for optical monitoring.

The VOA 65 variably attenuates the light level to make the output constant. The light output from the VOA 65 is E
The DF unit 62 controls the gain in the same manner as the EDF unit 61.
Then, the output light of the EDF unit 62 is dispersion-compensated through the DCF 66, and the EDF unit 63, VOA 67, ED in the subsequent stage is compensated.
The F section 64 receives the same control as the preceding stage side and outputs from the relay transmission line.

The light levels detected through the PDs 61a and 61b are designated as PAin and PAout, and PDs 62a and 62b are used.
The light level detected through PCin, PCout, P
The light level detected through D63a and 63b is PEin,
Let PEout be the light levels detected through the PDs 64a and 64b be PGin and PGout. In the section shown in the figure, A
~ G is attached.

FIG. 3 is a diagram showing a level diagram in the optical amplifier 60. The sections A to G correspond to the sections A to G inside the optical amplifying device 60 shown in FIG.
The light levels detected through are shown.

The curved line W1 shown by the dotted line represents the level before the input level of the optical signal input to the optical amplifier 60 increases, and the curved line W1a shown by the solid line represents the level when the input level increases. . However, in the sections D to G, there is no change before and after the change of the input level, and therefore, both are shown by a solid line.

Both the curves W1 and W1a are EDF units 61 to 6
In sections A, C, E, and G of 4, since the level increases, the slope rises to the right, and section B with VOAs 65 and 67,
In the section D in which F and DCF 66 are present, the level decreases, and the slope decreases to the right.

The sum of the gains of the EDF units 61 to 64 is controlled to be constant. Therefore, with respect to the curve W1 before the level change, (PAout-PAin) + (PCout-PCin) + (PEout-PEi
n) + (PGout−PGin) = constant.

Next, the curve W1 when the input level increases
Think about a. In the EDF section 61 in the section A, since the LD 61c is used almost in the gain saturation region as a measure for noise reduction, the input level increases and PAin changes to PAin1.
Even if it becomes, the output only increases from PAout to PAout1.

If a large dynamic range is attempted in such a state, as can be seen from the figure, the input level extremely decreases in the section B (PAout1 → PCin1). Then, the input level of the EDF unit 62 in the section C changes from PCin to PCin.
It will decrease to 1.

As described above, conventionally, the increase in the input level is attenuated by using only the VOA 65 in the section B of the preceding stage, and the constant gain sum is controlled. Therefore, in the curve W1a after the level change, (PAout1-PAin1) + (PCo
ut-PCin1) + (PEout-PEin) + (PGout-PGin) = constant, and the sum of gains is constant, but there is a portion where the input level is fixed and concentrated, so NF There was a problem that it got worse (the NF,
It is an index showing the performance of the amplifier, and the lower the NF, the better.

FIG. 4 is a diagram showing a level diagram in the optical amplifier 60. Similar to FIG. 3, the sections A to G are shown in FIG.
It corresponds to the sections A to G inside the optical amplifying device 60 shown by (3), and the light level detected through the PD is shown in the figure.

A curved line W2 shown by a dotted line is DC in the section D.
The level before the reduction of the interstage loss amount by F66 is represented, and the curve W2a shown by the solid line represents the level when the interstage loss amount is reduced. However, in the sections A to C, there is no change before and after the fluctuation of the interstage loss amount, and therefore, both are represented by a solid line.

The gain sum constant control is performed on the curve W2 before the reduction of the interstage loss amount, and (PAout-PAin) + (PCout-PC
in) + (PEout−PEin) + (PGout−PGin) = constant. Next, consider the curve W2a when the amount of interstage loss decreases. When the amount of interstage loss in the section D decreases (when the level rises from PEin to PEin1), only the VOA 67 in the section F is conventionally attenuated (PEout → PGin1) and the constant gain sum control is performed.

Then, as in the case described above with reference to FIG. 3, the input level to the EDF section 64 in the section G section changes from PGin to PGin.
It will go down to in1. As described above, in the related art, the VOA 67 in the section F in the subsequent stage is related to the decrease in the amount of interstage loss.
It was attenuated by using only and the constant gain sum was controlled.
Therefore, the curve W2a after the level change is (PAout-PAi
n) + (PCout-PCin) + (PEout-PEin1) + (PGout-P
Gin1) = constant, and the sum of gains is constant, but there is a problem that NF deteriorates because there is a fixed concentration in one location where the input level decreases.

As explained above, if only one VOA absorbs all the increase in the level, NF deterioration will be caused. Therefore, according to the present invention, the attenuation amount is adaptively distributed so that the NF is optimized in a plurality of VOAs, and the gain sum of the EDF is controlled to be constant, and the NF is adjusted.
It is intended to suppress the deterioration and improve the transmission quality.

Next, the concept of the present invention for solving the problems will be described. The present invention has a function of adjusting the attenuation amounts of a plurality of VOAs so that the NF becomes optimum. Here, the total NF of the device having the optical amplifying section configured in multiple stages of n stages is expressed by the equation (1). However,
NF1 to NFn are NFs of the EDF alone, P1 to P
n is the input level of the EDF.

[0038]

[Equation 1]

Here, when the pumping direction is fixed, the NF of the EDF simple substance at each stage is almost constant as long as the constant gain control is performed. FIG. 5 is a diagram showing the NF of the EDF alone. The horizontal axis is the input level (dBm / c) of the light input to the EDF unit.
h) and the vertical axis is NF (dB) of the EDF alone.

From the figure, it can be seen that the change in the NF of the EDF alone is smaller than the change in the input level of the EDF alone (range H). Therefore, from the equation (1), it can be seen that the fluctuation of the total NF is strongly controlled by the input level of the light input to the EDF alone (in the present invention, the NF of the EDF alone is fixed and the NF value is set in advance. Store it in memory).

On the other hand, when the change amounts of the light levels in the plurality of VOA1 to VOAm are X1 to Xm, the following equation (2) is obtained.

[0042]

[Expression 2] X1 + X2 + ... + Xm = 0 (2) If the gain sum is controlled by changing the attenuation amount and the gain sum is kept constant, no gain deviation occurs. That is, VOA1 to VOA are calculated based on the monitor value that monitors the input level to the EDF of each part and the NF of the EDF simplex of each part that is given as a fixed value so that the total NF expressed by the equation (1) is minimized.
By allocating the attenuation amount of m, it becomes possible to realize a device which has a wide dynamic range and always operates at the optimum NF.

Next, the specific structure and operation (attenuation amount adjusting method) of the optical amplifying device 1 of the present invention will be described. 6,
FIG. 7 is a diagram showing the configuration of the optical amplifying device 1. The optical amplification device 1 has a DCF 30 inside, and before and after the DCF 30,
A pre-stage gain control unit 10 and a post-stage gain control unit 20 are provided, and an ALC (Auto Level
Control) units 40a and 40b, and a gain target value setting unit 50 realized by a CPU.

The pre-stage gain control section 10 includes a first optical amplification section 11 (hereinafter, EDF section 11) and a second optical amplification section 13 (hereinafter, EDF section 13), and a VOA 12 is installed between them. It The latter-stage gain control unit 20 includes the third optical amplification unit 2
1 (hereinafter, EDF section 21) and fourth optical amplification section 23 (hereinafter, EDF section 23), and VOA 22 is installed in the middle.

The EDF section 11 includes PDs 11a, 11b, L
D11c, demultiplexing optical splitters 11d and 11e, wavelength division multiplexing optical coupler 11f, EDF 11g, analog / digital converters (hereinafter, AD) 11h and 11i, digital / analog converters (hereinafter, DA) 11j. . The EDF unit 13 includes PDs 13a, 13b, LD 13c, demultiplexing optical splitters 13d, 13e, wavelength division multiplexing optical coupler 13f, and EDF.
13g, AD13h, 13i, DA13j.

Further, the EDF section 21 includes PDs 21a, 21
b, LD 21c, demultiplexing optical splitters 21d and 21e, wavelength division multiplexing optical coupler 21f, EDF 21g, AD 21h and 21.
i, DA21j. The EDF unit 23 is a PD
23a, 23b, LD 23c, demultiplexing optical splitter 23d,
23e, WDM optical coupler 23f, EDF 23g, AD
23h, 23i and DA 23j.

The target gain value setting unit 50 is composed of optical level acquisition units 51a to 51h, gain setting units 52a to 52d, adders 53a and 53b, and a noise figure correction unit (NF correction unit) 54.

The operation will be described. First, the flow of processing of an optical signal in the front stage gain control unit 10, the rear stage gain control unit 20, and the DCF 30 will be described. The demultiplexing optical splitter 11d of the EDF unit 11 splits the input light, and one of the split lights is to the PD 11a and the other is the wavelength division multiplexing optical coupler 1
Head to 1f. The PD 11a converts the branched light into an analog electric signal, and the AD 11h converts the analog signal into a digital signal. This digital signal is transmitted to the target gain value setting unit 50.

The DA 11j converts the digital setting signal output from the target gain value setting section 50 into an analog signal, and transmits it as a drive signal to the LD 11c. LD11
Based on this drive signal, c radiates excitation light and excites the erbium-doped EDF 11g through the wavelength division multiplexing optical coupler 11f to perform optical amplification.

Thereafter, the amplified optical signal is branched by the demultiplexing optical branching device 11e, one of which goes to the VOA 12 and the other of which goes to the PD 11b for optical monitoring. AD11i is P
The output signal from D11b is converted into a digital signal. This digital signal is transmitted to the target gain value setting unit 50.

The DA 12a converts the digital setting signal output from the ALC unit 40a into an analog signal and transmits it to the VOA 12 as an attenuation amount setting signal. VOA12
On the basis of this attenuation amount setting signal, variably attenuates the light level to make the output constant.

The light output from the VOA 12 is subjected to the same gain control and monitor control as the EDF unit 11 in the EDF unit 13. The output light of the EDF unit 13 is DCF.
Dispersion compensation is performed through 30, and the EDF unit 21 and VO in the subsequent stage
The A22 and EDF unit 23 receives the same control as that of the preceding stage side and outputs from the relay transmission line.

Next, the flow of processing by the gain target value setting unit 50 and the ALC units 40a and 40b including the control of the present invention will be described. The light level acquisition unit 51a is AD11h.
The digital signal (voltage value) output from is log-converted to obtain the optical level PAin (unit: dBm) of the light monitored by the PD 11a. The light level acquisition unit 51b is AD
Log-convert the digital signal output from 11i,
The light level PAout of the light monitored by the PD 11b is acquired.

The same operation is performed, and as shown in the figure,
The light level acquisition units 51c and 51d are respectively light level PCs.
in, PCout are acquired, the optical level acquisition units 51e and 51f are respectively acquired optical levels PEin and PEout, and the optical level acquisition units 51g and 51h are respectively optical levels PGin and PGout.
To get.

On the other hand, the gain setting section 52a is equivalent to the EDF section 1
The difference between the levels of input light and output light for 1 (PAout-PAi
The LD 11c is operated via the DA 11j so that n) becomes the set gain value Gain (A).

The gain setting section 52b is a difference between the levels of the input light and the output light with respect to the EDF unit 13 (PCout-PCin).
However, the LD 13c is operated via the DA 13j so that the gain becomes the set gain value Gain (C).

Similarly, the gain setting section 52c detects the difference (PEout-P) between the levels of the input light and the output light with respect to the EDF section 21.
Ein) becomes the set gain value Gain (E) so that DA21j
The LD 21c is operated via the gain setting unit 52d
Operates the LD 13c via the DA 13j so that the difference (PGout-PGin) between the levels of the input light and the output light with respect to the EDF unit 23 becomes the set gain value Gain (G). Set gain values Gain (A), Gain (C), Gain (E), Gain (G)
Are stored in the memory in advance.

Further, in the front stage side gain control section 10 and the rear stage side gain control section 20, since the output light level is regulated by considering the influence on the DCF 30 and the transmission line on the nonlinear effect, the output It is necessary to perform constant control of the light level.

Therefore, in the ALC units 40a and 40b,
PCout and PGout are set to the set values Pout (F) and Pout (R), respectively, via the DAs 12a and 22a, the VOA 12,
22 is being driven. The set values Pout (F), Pout
(R) is previously stored in the memory.

The operation when the device input level and the amount of interstage loss vary will be described. First, the control for not producing the wavelength characteristic will be described. When the input level is low, the LD 11c has a set gain value for the EDF unit 11.
The excitation light of Gain (A) can be emitted. However,
Usually, from the viewpoint of low NF, the LD 11c is used at almost the maximum output. Therefore, because it is in the saturation region,
The higher the input level, the lower the gain of the EDF unit 11.

Therefore, in order to prevent wavelength characteristics,
The gain setting unit 52a transmits the insufficient gain amount Ga (= (PAout−PAin) −Gain (A)) that the LD 11c cannot output to the next stage, and the insufficient gain amount Ga is added to the gain of the next stage by the adder 53a. It is added to the set value Gain (C) of the setting unit 52b. The gain setting value G1 of the gain setting unit 52b in this case
Becomes the following expression (3).

[0062]

G1 = Gain (C) + Ga (3) As a result, the operation of the ALC unit 40a causes the EDF unit 13 to operate.
The input level PCin of is reduced (since the original Gain (C) is increased by Ga, the ALC unit 40a attenuates the increased amount, and therefore the VOA 12 is attenuated. Input level PCin of 13 drops).

When the interstage loss amount of the DCF 30 decreases, the input level to the EDF section 21 increases. Therefore, considering the same way as when the device input level is increased, the LD 21c is used at almost the maximum output, so that the gain of the EDF unit 21 decreases as the input level increases in the saturation region. become.

Therefore, in order to prevent the wavelength characteristic from being exhibited,
The gain setting unit 52c controls the amount of insufficient gain Ge (= (PEout−PEin)
-Gain (E)) is transmitted to the next stage, and the insufficient gain Ge is set by the adder 53b to the set value of the gain setting unit 52d of the next stage.
It is added to Gain (G). Gain setting section 52 in this case
The gain setting value G2 of d is given by the following equation (4).

[0065]

G2 = Gain (G) + Ge (4) As a result, the operation of the ALC unit 40b causes the EDF unit 23 to operate.
Input level PGin decreases (Because Ge increases with respect to the original Gain (G), the ALC unit 40b attenuates the increased amount, and therefore the VOA 22 is attenuated. Therefore, the EDF unit The input level PGin of 23 drops).

Next, in addition to the above control, the control when the attenuation amount is distributed to improve the NF will be described. The NF correction unit 54 in the target gain value setting unit 50 obtains a correction value X that optimizes NF by the following equation (5). However, Pc
Is the input level to the EDF unit 13, and NFc is the EDF1.
NF and Pg of a single unit of 3 g are input levels to the EDF unit 23, and NFg is a single NF of the EDF unit 23 g.

[0067]

## EQU00005 ## X = ((Pc-NFc)-(Pg-NFg)) / 2 (5) Then, the correction value X calculated in this way is used as the EDF unit 1
This is added to the gain control in 3 and 23. Specifically, EDF
The adder 53a adds the correction value X, the gain setting value Gain (C), and the insufficient gain amount Ga that the LD 11c cannot output to the unit 13, and the added value is the gain target value in the EDF unit 13. Set to AGC (C).

For the EDF unit 23, the adder 5
3b is a correction value X, a gain setting value Gain (G), and LD2.
1c is added to the insufficient gain Ge that cannot be output, and the added value is the gain target value AGC (G) in the EDF unit 23.
So that

Here, when the device input level is increased, the target gain values AGC (C) and AGC (G) are expressed by equations (6a) and (6b).

[0070]

AGC (C) = − X + Gain (C) + Ga (6a) AGC (G) = X + Gain (G) + Ge (6b) Therefore, when the device input level is increased, the gain setting unit 52b outputs (PCout−PCin ) Becomes the gain target value AGC (C) of the equation (6a), and L is set via the DA 13j.
The D13c is driven, and the gain setting unit 52d changes the (PGout-P
The LD 23c is driven via the DA 23j so that Gin) becomes the target gain value AGC (G) of the equation (6b).

On the other hand, when the amount of interstage loss is reduced, the target gain values AGC (C) and AGC (G) are expressed by equation (7).
a) and (7b).

[0072]

## EQU00007 ## AGC (C) = X + Gain (C) + Ga (7a) AGC (G) =-X + Gain (G) + Ge (7b) Therefore, when the interstage loss amount decreases, the gain setting unit 5
2b uses LD1 via DA13j so that (PCout-PCin) becomes the target gain value AGC (C) of equation (7a).
3c is driven, and the gain setting unit 52d displays (PGout-PGi
The LD 23c is driven via the DA 23j so that n) becomes the target gain value AGC (G) of the equation (7b).

As described above, the plurality of VOAs 12,
22 by adaptively distributing the attenuation amount so that the NF becomes optimum (that is, when the device input level increases or the interstage loss amount decreases, the input level decreases only at one point (VOA attenuation control). The level of that part is raised so that the level of that part does not drop extremely, and the level of the raised part is lowered by other VOAs. It is possible to realize an optical amplification device in which the EDF gain sum is kept constant and the NF is improved.

Next, the level diagram when the control of the present invention is performed will be described. FIG. 8 is a diagram showing a level diagram in the optical amplifying device 1 of the present invention. Sections A to G correspond to the sections A to G inside the optical amplifier device 1 shown in FIGS. 6 and 7, and the light levels detected through the PD are shown in the figures.

The curved line W3 shown by the dotted line represents the level when the input level of the optical signal input to the optical amplifying device 1 increases, and the curved line W3a shown by the solid line represents the level when the control of the present invention is performed. ing. However, section A and sections D and E
Since there is no change before and after the control of the present invention, is represented by a solid line.

When the device input level is increased, conventionally, only the input level to the section C is lowered to PCin2, and thus NF
It was getting worse. On the other hand, in the present invention, the input level in the section C is increased by XdB from PCin2 to PCin3 (reduction in loss by -XdB), and the input level in the section G is PG.
The level of XdB is decreased from in2 to PGin3 (loss increase of XdB).

In this way, by distributing the attenuation amounts for the VOAs 12 and 22 so that the NF becomes optimum,
The level diamond of the present invention is not the conventional level diamond having a steep slope at one place, but NF is the optimum level diamond.

FIG. 9 is a diagram showing a level diagram in the optical amplifying device 1 of the present invention. Sections A to G correspond to the sections A to G inside the optical amplifier device 1 shown in FIGS. 6 and 7, and the light levels detected through the PD are shown in the figures.

The curved line W4 shown by the dotted line is the DCF3 of the section D.
A level when the interstage loss amount of 0 is reduced, and a curve W4a shown by a solid line represents a level when the control of the present invention is performed. However, since the section A and the sections D and E do not change before and after the control of the present invention, they are represented by solid lines.

When the amount of interstage loss is reduced, conventionally, only the input level to the section G is lowered to PGin2, which causes deterioration of NF. On the other hand, in the present invention, the input level to the section G is increased by X dB from PGin2 to PGin3 (-X
(dB loss reduction), the input level to the section C is designed to lower the XdB level from PCin2 to PCin3 (XdB loss increase).

Thus, by distributing the attenuation amounts for the VOAs 12 and 22 so that the NF becomes optimum,
The level diamond of the present invention is not the conventional level diamond having a steep slope at one place, but NF is the optimum level diamond.

FIG. 10 is a diagram showing an NF of the related art and the present invention. The horizontal axis is the device input level (dBm / ch), and the vertical axis is N
It is F (dB). The curve W6 of the present invention has a lower NF than the conventional curve W5 when the input level increases. Specifically, when the input level was increased by 12 dB, the NF was improved by 4 dB.

As described above, according to the present invention, by controlling the attenuation amount optimally for a plurality of VOAs, a good NF can be obtained even when there is a wide dynamic range and a large interstage loss allowance. Can be realized.

(Supplementary Note 1) In an optical amplifying device for amplifying an optical signal, a variable optical attenuator and a first optical amplifying section which is arranged in front of the variable optical attenuator and which performs gain control to perform optical amplification. A second optical amplifying section which is disposed in a subsequent stage of the variable optical attenuator and which performs gain control to perform optical amplification, and a variable gain attenuator, which is a pre-stage side gain control section located in a preceding stage of the device, A third optical amplifying unit arranged in the preceding stage of the variable optical attenuator and performing gain control for optical amplification, and a fourth optical amplifying unit arranged in the latter stage of the variable optical attenuator for performing gain control and optical amplification. A post-stage gain control section, which is composed of an amplifying section and is located at a post-stage of the device, and a dispersion compensating section which is located between the pre-stage side gain control section and the post-stage gain control section and performs dispersion compensation of light. And the output levels of the front stage gain control section and the rear stage gain control section are , An attenuation amount control unit that controls the attenuation amount of the variable optical attenuator so as to be a constant level, and when the interstage loss amount changes due to the device input level or dispersion compensation,
In order to distribute the attenuation amount to the plurality of variable optical attenuators so that the noise figure becomes optimum, the gain target value is set for each of the second optical amplification unit and the fourth optical amplification unit. , A gain target value setting unit that controls the gain sum from the first optical amplification unit to the fourth optical amplification unit to a constant value, and the optical amplification device.

(Supplementary Note 2) The gain target value setting section sets the input level to the second optical amplification section to Pc, the noise figure of the EDF unit in the second optical amplification section to NFc, and the fourth optical level. When the input level to the amplification unit is Pg and the noise figure of the EDF alone in the fourth optical amplification unit is NFg, X = ((Pc-NFc)-(Pg-NFg)) / 2 correction value X 2. The optical amplification device according to appendix 1, further comprising a noise figure correction unit that supplies the second optical amplification unit and the fourth optical amplification unit.

(Supplementary Note 3) The target gain value setting unit sets the deficient gain of the first optical amplifier unit to Ga, the set gain of the second optical amplifier unit to Gain (C), and the third optical amplifier. The insufficient gain due to the amplifier is Ge, and the set gain of the fourth optical amplifier is Ga.
in (G), where the correction value is X, and the device input level increases, AGC (C) =-X + Gain (C) + Ga AGC (G) = X + Gain (G) + Ge C) is set in the second optical amplification section, and a target gain value AGC (G) is set in the fourth optical amplification section.

(Supplementary Note 4) The gain target value setting unit sets the shortage gain of the first optical amplification unit to Ga, the set gain of the second optical amplification unit to Gain (C), and the third optical gain. The insufficient gain due to the amplifier is Ge, and the set gain of the fourth optical amplifier is Ga.
in (G), where the correction value is X and the interstage loss amount is reduced, AGC (C) = X + Gain (C) + Ga AGC (G) = − X + Gain (G) + Ge (C) is set in the second optical amplification section, and a gain target value AGC (G) is set in the fourth optical amplification section.

(Supplementary Note 5) In the attenuation amount adjusting method in which the attenuation amount is adjusted and the sum of gains is controlled to be constant for the multi-stage optical amplification section, the amplification medium is excited to perform optical amplification.
In order to distribute the attenuation amount to the plurality of variable optical attenuators installed inside the device so that the noise figure becomes optimum when the device input level or the amount of interstage loss varies due to dispersion compensation, the optical amplification is performed. A gain adjustment method for setting a gain target value to each unit and controlling the gain sum of the plurality of optical amplification units to be constant.

(Supplementary Note 6) When there is a first optical amplification section and a second optical amplification section in the front stage and a third optical amplification section and a fourth optical amplification section in the rear stage centering on the dispersion compensation medium, The input level to the second optical amplification section is Pc, the noise figure of the amplification medium alone of the second optical amplification section is NFc, the input level to the fourth optical amplification section is Pg, and the fourth optical level is When the noise figure of the amplification medium alone of the amplification section is NFg, a correction value X such that X = ((Pc-NFc)-(Pg-NFg)) / 2 is set to the second optical amplification section and the fourth 6. The attenuation amount adjusting method according to appendix 5, wherein the attenuation amount adjusting method is applied to the optical amplifying unit.

(Supplementary Note 7) Ga is the shortage gain of the first optical amplifier and Gain is the set gain of the second optical amplifier.
(C), Ge is the deficient gain by the third optical amplifier, Gain (G) is the set gain of the fourth optical amplifier, and X is the correction value.
Then, when the device input level is increased, the gain target value AGC (C) which becomes AGC (C) = − X + Gain (C) + Ga AGC (G) = X + Gain (G) + Ge is set to the second optical amplification section. And the target gain value AGC (G) is set in the fourth optical amplification section.

(Supplementary Note 8) Ga is the insufficient gain due to the first optical amplifier, and Gain is the set gain of the second optical amplifier.
(C), Ge is the deficient gain by the third optical amplifier, Gain (G) is the set gain of the fourth optical amplifier, and X is the correction value.
Then, when the amount of interstage loss decreases, the gain target value AGC (C), which is AGC (C) = X + Gain (C) + Ga AGC (G) = − X + Gain (G) + Ge, is used for the second optical amplification. And a gain target value AGC (G) is set in the fourth optical amplification section.

[0092]

As described above, the optical amplifier of the present invention has the optimum noise figure for a plurality of variable optical attenuators when the interstage loss amount changes due to the device input level or dispersion compensation. As described above, in order to distribute the attenuation amount, a gain target value is set in the optical amplification unit to perform constant gain sum control. As a result, the optical sum of gains can be made constant by adjusting the amount of optical attenuation so as to obtain the optimum noise figure according to each input level of the optical amplification unit, so that it is possible to improve the transmission quality. .

Further, the attenuation amount adjusting method of the present invention, when the device input level or the interstage loss amount due to dispersion compensation changes,
In order to distribute the attenuation amount to the plurality of variable optical attenuators so that the noise figure becomes optimum, the gain target value is set in the optical amplification unit and the constant gain sum is controlled. As a result, the optical sum of gains can be made constant by adjusting the amount of optical attenuation so as to obtain the optimum noise figure according to each input level of the optical amplification unit, so that it is possible to improve the transmission quality. .

[Brief description of drawings]

FIG. 1 is a principle diagram of an optical amplifier according to the present invention.

FIG. 2 is a diagram showing a configuration of a conventional optical amplifier.

FIG. 3 is a diagram showing a level diagram in the optical amplifier.

FIG. 4 is a diagram showing a level diagram in the optical amplifier.

FIG. 5 is a diagram showing NF of a single EDF.

FIG. 6 is a diagram showing a configuration of an optical amplifier.

FIG. 7 is a diagram showing a configuration of an optical amplifier.

FIG. 8 is a diagram showing a level diagram in the optical amplifying device of the present invention.

FIG. 9 is a diagram showing a level diagram in the optical amplifier of the present invention.

FIG. 10 is a diagram showing NFs of the related art and the present invention.

FIG. 11 is a diagram showing a control image of gain equalization.

[Explanation of symbols]

1 Optical amplifier 10 Previous gain control section 11 First optical amplifier 12 Variable optical attenuator 13 Second optical amplifier 20 Rear gain control section 21 Third Optical Amplifier Section 22 Variable optical attenuator 23 Fourth Optical Amplifier Section 30 Dispersion compensator 40 Attenuation control unit 50 Gain target value setting section

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04B 10/16 10/17 F term (reference) 2H079 CA04 FA01 FA04 5F072 AB09 AK06 FF09 HH02 HH06 JJ01 JJ05 JJ08 KK30 MM01 PP07 RR01 YY17 5K002 AA06 BA02 CA01 CA10 CA13

Claims (5)

[Claims] 1. An optical amplifying device for amplifying an optical signal, comprising: a variable optical attenuator, and a variable optical attenuator arranged in front of the variable optical attenuator.
A first optical amplification section that performs gain control and optical amplification, and a second optical amplification section that is arranged at the rear stage of the variable optical attenuator and performs gain control and optical amplification, are provided at the front stage of the device. A pre-stage gain control unit located, a variable optical attenuator, and arranged in front of the variable optical attenuator,
A third optical amplification section that performs gain control and optical amplification, and a fourth optical amplification section that is arranged at the subsequent stage of the variable optical attenuator and performs gain control and optical amplification, are provided at the latter stage of the device. A post-stage gain control section located, a dispersion compensating section located between the pre-stage gain control section and the post-stage gain control section for performing dispersion compensation of light, the pre-stage gain control section and the post-stage An attenuation amount control unit that controls the attenuation amount of the variable optical attenuator so that the output level of each side gain control unit becomes a constant level, and a plurality of In order to distribute the attenuation amount to the variable optical attenuator so that the noise figure becomes optimum, a gain target value is set for each of the second optical amplification unit and the fourth optical amplification unit, and From the first optical amplification section to the fourth optical amplification section Optical amplifying apparatus comprising: the target gain value setting section for controlling the sum to be constant, the. 2. The gain target value setting unit, Pc is an input level to the second optical amplification unit, NFc is a noise figure of a single EDF in the second optical amplification unit, and the fourth optical amplification unit. When the input level to Pg is Pg and the noise figure of the EDF simple substance in the fourth optical amplification unit is NFg, a correction value X such that X = ((Pc-NFc)-(Pg-NFg)) / 2 is obtained. The optical amplification device according to claim 1, further comprising a noise figure correction unit that supplies the second optical amplification unit and the fourth optical amplification unit. 3. The gain target value setting unit is configured such that the insufficient gain component of the first optical amplification unit is Ga, the set gain of the second optical amplification unit is Gain (C), and the third optical amplification unit. In the case where the device input level is increased, AGC (C) = − X + Gain (C), where Ge is the shortage gain due to G, Gain (G) is the set gain of the fourth optical amplification unit, and X is the correction value. A gain target value AGC (C) that satisfies + Ga AGC (G) = X + Gain (G) + Ge is set in the second optical amplification unit, and a gain target value AGC (G) is set in the fourth optical amplification unit. The optical amplifying device according to claim 2, wherein 4. The gain target value setting unit is configured so that the shortage gain of the first optical amplification unit is Ga, the set gain of the second optical amplification unit is Gain (C), and the third optical amplification unit. In the case where the amount of loss between stages is reduced, AGC (C) = X + Gain (C), where Ge is the shortage gain due to the gain, Gain (G) is the set gain of the fourth optical amplification unit, and X is the correction value. + Ga AGC (G) = − X + Gain (G) + Ge is set in the second optical amplification unit, and the gain target value AGC (G) is set in the fourth optical amplification unit. The optical amplifying device according to claim 2, wherein 5. An attenuation amount adjusting method for adjusting an attenuation amount and controlling a gain sum to be constant with respect to a multi-stage optical amplification section, wherein an amplification medium is excited to perform optical amplification, and an apparatus input level or When the amount of interstage loss varies due to dispersion compensation, the gain to the optical amplifier unit is distributed to the plurality of variable optical attenuators installed in the device so that the amount of attenuation is distributed so that the noise figure becomes optimum. A method for adjusting an attenuation amount, wherein a target value is set and the sum of gains of the plurality of optical amplification units is controlled to be constant.