JP4615438B2 - Optical amplification method and optical amplification device - Google Patents

Description

  The present invention relates to an optical amplification method and an optical amplification device, and more particularly to an optical amplification method using automatic gain control and an optical amplification device using an automatic gain control circuit.

  In a wavelength division multiplexing (WDM) system in which a plurality of optical signals having different wavelengths are multiplexed and transmitted simultaneously to a single optical transmission line, the optical amplification device shown in FIG. 13 is mounted in the optical transmission line. Thus, after the power of the optical signal is adjusted, a configuration is adopted in which the optical signal is transmitted to an optical transmission line composed of a single mode optical fiber (SMF) or a dispersion shifted optical fiber (DSF).

  The optical amplifying device includes an erbium-doped fiber (EDF) 101 connected as an optical amplifier in the middle of an optical transmission line, and a pump laser diode (LD) that excites the EDF 101 via an optical coupler 102. 103, a first photodiode (PD) 105 that converts an optical signal input to the optical coupler 104 attached to the input side of the EDF 101 into an electrical signal, and an optical coupler 106 attached to the output side of the EDF 101. The second photodiode (PD) 107 that converts the optical signal input to the first and second photodiodes (PD) 107 and the first and second monitors that separately detect the output signals of the first and second photodiodes 105 and 107, respectively. The output of the excitation LD 103 is controlled based on the outputs of the circuits 108 and 109 and the first and second monitor circuits 108 and 109. And an LD control circuit 110.

The first monitor circuit 108 outputs a voltage value corresponding to the optical input power of the first photodiode 105 based on the electrical signal output from the first photodiode 105, and the second monitor circuit 109 is the same. In addition, a voltage value corresponding to the optical input power of the second photodiode 107 is output.
The LD control circuit 110 controls the excitation LD 103 based on the voltage values output from the first and second monitor circuits 108 and 109, thereby performing constant gain control (AGC (automatic gain control)) of the EDF 101. The gain of the EDF 101 is controlled to be a desired value.

In an optical amplifying apparatus that performs such AGC control, the pumping LD power is changed so as to keep the gain (gain) constant with a change in the number of wavelengths of the wavelength-multiplexed optical signal.
However, when the transient characteristics of the optical amplifier when the optical input power fluctuates are insufficient, the change in optical input power to the optical amplifier as shown in FIG. As shown, the change in the optical output power from the amplifier is delayed by Δt. As a result, when the optical input power fluctuates, the optical output power per wave greatly fluctuates as shown in FIG. 14C, which may deteriorate the transmission quality of the optical signal.

As a technique for controlling such deterioration in transmission quality, a circuit shown in FIG.
In FIG. 15, an optical amplifier 111 is composed of an EDF and an optical coupler. A first photodiode 105 is connected to an optical signal input portion of the optical amplifier 111 via an optical coupler 104, and an optical signal output of the optical amplifier 111 is provided. A second photodiode 107 is connected to this portion via an optical coupler 106. The electrical signal output terminals of the first and second photodiodes 105 and 107 are connected to the first and second logarithmic conversion circuits 112 and 113, respectively. Furthermore, the optical amplifier 111 is optically connected to a pumping LD 103 for irradiating pumping energy.

The AGC control circuit 120 that controls the output of the excitation LD includes a differential circuit 121 that calculates a deviation ΔG between the monitor gain and the target gain G ₀ obtained based on the outputs of the first and second logarithmic conversion circuits 112 and 113. A proportional circuit 122 that multiplies the deviation ΔG by a proportional multiple k, an integration circuit 123 that integrates the deviation ΔG by a predetermined formula, an addition circuit 124 that adds the calculation results of the integration circuit 123 and the proportional circuit 122, and an addition An LD current control circuit 125 that controls the drive current of the excitation LD 103 based on the circuit 124, and a proportional multiple adjustment circuit 126 that adjusts the proportional magnification k of the proportional circuit 122 based on the output value of the first logarithmic conversion circuit 112. Have.
The AGC control circuit 120 controls the gain of the optical amplifier 111, thereby suppressing the fluctuation of the optical output power per wave to be small and reducing the influence on the transmission quality.

  In this method, the optical input / output power of the optical amplifier 111 is monitored by the PDs 105 and 107 and the logarithmic conversion circuits 112 and 113, and the proportional multiple adjustment circuit 126 further integrates the proportional circuit 122 and the integration according to the optical input / output power of the optical amplifier 111. Since the control constant of the circuit 123 is adjusted, it is possible to adjust the control constant corresponding to a change in the optical input power to the optical amplifier 111 in operation, thereby increasing the response speed and improving the transient characteristics of the AGC control circuit 120. This is advantageous in that stable optical signal transmission can be performed.

Further, the response time of the gain of the EDF in the optical amplifier 111 depends on the optical input / output power of the EDF. For this reason, the optimum control constant of the AGC control circuit 120 differs depending on the optical input / output power. FIG. 16 shows the relationship between the proportional circuit 122 and the optical input power of the optical amplifier 111. When the optical input power increases or decreases, the proportional multiple adjustment circuit 126 increases or decreases the proportional coefficient k, and the transient characteristics are increased. Control is performed so as not to enter the insufficient region and the oscillation region.
JP 2004-266251 A

  However, according to the optical amplifying device as shown in FIG. 15, compared with the effect of suppressing fluctuation in the optical output power per wave immediately after the optical input power to the optical amplifier 111 is increased as shown in FIG. Thus, as shown in FIG. 17B, the effect of suppressing fluctuation in the optical output power per wave when the optical input power to the optical amplifier 111 decreases is insufficient, and further improvement is preferable. Note that the input light in FIG. 17A shows the change in optical power when the signal increases from 1 wave to 32 waves, and the input light in FIG. 17B decreases from 32 waves to 1 wave. The change in optical power is shown.

  An object of the present invention is to provide an optical amplification method and an optical amplification device that have an excellent effect in suppressing fluctuations in optical output power when the optical input power to the optical amplifier increases and decreases.

A first aspect of the present invention for solving the above problems is an optical amplifier that amplifies and outputs an input optical signal based on pumping light from a pumping light source, and input light input to the optical amplifier. Detecting means for detecting the optical power of each of the signal and the output optical signal output from the optical amplifier, and calculating the gain of the optical amplifier from the optical power of the input optical signal and the output optical signal detected by the detecting means And a control unit that feedback-controls the optical power of the pumping light output from the pumping light source so that the gain calculated by the calculating unit is equal to a target gain as a fixed value for constant gain control. a means, the said control means, said with the transient decrease of the optical power of the input optical signal, than the gain the target gain calculated by said calculating means If it becomes hear is an optical amplifying apparatus for causing a proportional coefficient of the feedback control is increased until the target gain and the gain is substantially equal.

According to a second aspect of the present invention, in the optical amplification device according to the first aspect, the proportionality factor is increased when a gain deviation obtained by subtracting the gain from the target gain is negative. Features.
According to a third aspect of the present invention, in the optical amplifying device according to the first or second aspect, the control means is a constant multiplication circuit provided in a feedback loop for adjusting the proportionality factor of the feedback control. The proportionality coefficient is increased by adjusting a constant value of the constant multiplication circuit .
According to a fourth aspect of the present invention, in the optical amplifying device according to the third aspect, the constant value of the constant multiplier circuit increases or decreases in proportion to the optical power of the input optical signal detected by the detecting means. It is set to a value .

According to a fifth aspect of the present invention, in the optical amplifying device according to the fourth aspect, the control means includes an integration circuit that integrates the target gain and a difference value between the gains, an output value of the integration circuit, and the constant. An adder circuit for adding the output value of the multiplier circuit, and the pumping light source is controlled according to the output value of the adder circuit, and along with a transient decrease in the optical power of the input optical signal When the gain calculated by the calculating means is larger than the target gain, the integration coefficient is adjusted until the gain and the target gain become substantially equal by adjusting the integration constant of the integration circuit. It is characterized by increasing .
According to a sixth aspect of the present invention, in the optical amplifying device according to any one of the first to fifth aspects, the control means has a difference value between the target gain and the gain larger than a predetermined value. Is characterized in that the proportionality coefficient is further increased .

According to a seventh aspect of the present invention, in the optical amplification device according to the sixth aspect, the control means temporarily sets the proportionality coefficient when a gain difference between the target gain and the gain is greater than 0.03 dB. The proportionality factor is temporarily quadrupled when the gain difference between the target gain and the gain is greater than 0.3 dB .

According to a ninth aspect of the present invention, there is provided an optical amplification method for an optical amplifier having an optical amplifier that amplifies an input optical signal based on pumping light from a pumping light source and outputs the amplified optical signal. A detection process for detecting the optical power of each of the optical signal and the output optical signal output from the optical amplifier, and the gain of the optical amplifier is calculated from the optical power of the input optical signal and the output optical signal detected by the detection process And a feedback control of the optical power of the excitation light output from the excitation light source so that the gain calculated by the calculation step is equal to a target gain as a fixed value for constant gain control. A control step, and the control step is configured such that the gain calculated by the calculation step is the target when the optical power of the input optical signal is transiently decreased. If it becomes larger than the resultant is an optical amplification method characterized by increasing during the proportional coefficient of the feedback control to the target gain and the gain is substantially equal.

  According to the present invention, when performing proportional calculation and integral calculation based on the gain deviation for controlling the drive current of the pumping optical element that excites the optical amplifier, at least one of the absolute value and sign of the gain deviation is used. Thus, the calculation is performed using the coefficient to be changed. Since the gain deviation is obtained based on both the optical input power and the optical output power of the optical amplifier, according to the present invention, proportional calculation and integration calculation are performed in consideration of the change of the optical power in the optical amplifier. Fluctuation of the remaining light gain can be suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a configuration diagram illustrating an optical amplifying device according to an embodiment of the present invention.
In FIG. 1, an erbium-doped optical fiber (EDF) 1 connected to an optical transmission line through which an optical signal having a predetermined wavelength is changed and transmitted by wavelength multiplexing / demultiplexing means such as OADM (Optical Add-Drop Multiplexer) and the EDF 1 An optical amplifier 3 including a first optical coupler 2 connected to the laser, an excitation laser diode (LD) 4 that irradiates the EDF 1 with optical excitation energy via the first optical coupler 2, and an optical signal input to the EDF 1. A first photodiode (PD) 6 that receives light through the second optical coupler 5 and performs photoelectric conversion, and an optical signal output from the optical amplifier 3 through the third optical coupler 7 and photoelectrically converts the light signal. First and second logarithmic conversion circuits 9 and 10 connected to the second photodiode (PD) 8 and the electric signal output terminals of the first and second photodiodes 6 and 8, respectively, Second logarithmic transformation And an AGC control circuit 11 for inputting respective output signals of the circuits 9 and 10.

  The first logarithmic conversion circuit 9 is configured to output the optical input signal of the optical amplifier 3 as the input side voltage signal Vin by logarithmically converting the electrical signal output from the first photodiode 6 by a predetermined formula. ing. Further, the second logarithmic conversion circuit 10 outputs the optical output signal of the optical amplifier 3 as the output side voltage signal Vout by logarithmically converting the electrical output signal output from the second photodiode 8 by a predetermined formula. It has a configuration.

The AGC control circuit 11 includes a target gain setting circuit 12 that sets a target gain G ₀ , a difference between voltage signals Vin and Vout output from the first and second logarithmic conversion circuits 9 and 10, and a target gain G ₀ . A differential circuit 13 that outputs a gain deviation ΔG based on the above, a proportional circuit 14 that receives the gain deviation ΔG output from the differential circuit 13 and calculates a value obtained by multiplying the gain deviation ΔG by a variable proportional coefficient k; An integration circuit 15 for integrating and outputting the gain deviation ΔG output from the dynamic circuit 13 by a predetermined formula using an integration coefficient γ, and the output signals from the first and second logarithmic conversion circuits 9 and 10 and the differential. A PI coefficient adjusting circuit 16 that adjusts a proportional integration (PI) coefficient of the proportional circuit 14 and the integrating circuit 15 based on at least one of the gain deviations ΔG of the circuit 13 and an output signal of the proportional circuit 14 and the integrating circuit 15 are added. And an adder circuit 17 for outputting, And a LD current control circuit 18 is controlled on the basis of the current driving the electromotive LD4 on the output signal of the adder circuit 17. The control by the proportional circuit 14, the integrating circuit 15, and the adding circuit 17 is hereinafter referred to as PI control.

The differential circuit 13 in the AGC control circuit 11 calculates the gain deviation ΔG based on the following equation (1).
ΔG = G ₀ − (Vout−Vin) (1)

Further, the proportional circuit 14 calculates and outputs T1 by the calculation according to the following equation (2), the integrating circuit 15 calculates and outputs the value T2 by the calculation according to the equation (3), and the adding circuit 17 calculates the equation (2). The value T3 is calculated and output by the calculation in 3).
T1 = k · ΔG (2)
T2 = γ∫ΔGdt (3)
T3 = k · ΔG + γ∫ΔGdt (4)
Γ is an integral coefficient, k is a proportional coefficient, and both γ and k are changed based on the output of the PI coefficient adjustment circuit 16.

For example, as shown in FIG. 2, the proportional circuit 14 includes a comparator 14a, a fixed resistor 14b, and a variable resistor 14c. The variable resistor 14c has a digital control potentiometer (Digital Controlled Potentiometer: digital adjustment by a CPU, for example). DCP) makes it possible to change the resistance value R2 of the variable resistor 14c stepwise using the automatic adjustment function of the PI coefficient adjustment circuit 16 even during operation of the optical amplifying device according to the present embodiment. .
Proportional coefficient of the proportional circuit 14 k is determined by the ratio k = R2 / R1 of the resistance value R 2 of the resistance value R1 and the variable resistor 14c of the fixed resistor 14b in the circuit.

Then, the PI coefficient adjusting circuit 16 that adjusts the proportional coefficient k of the proportional circuit 14 adjusts the proportional coefficient k so that it becomes the target value k ₀ of the following equation (5), for example.
k ₀ = A · Vin + B (5)

Here, Vin is an output voltage from the first logarithmic conversion circuit 9, and A and B are preset constants. Further, k ₀ is multiplied by N and M (M> 0, N> 0) under a predetermined condition according to the sign and absolute value of the gain deviation ΔG.
When the oscillation region and the region having insufficient transient characteristics in the EDF 1 are shown by the relationship between the proportional coefficient and the optical input power, the PI coefficient including the proportional coefficient k is shown in FIG. 4 by the PI coefficient adjustment circuit 16. Adjusted according to the flow.

First, the input side voltage value Vin corresponding to the optical input power Pin of the optical amplifier 3 is output from the first logarithmic conversion circuit 9 to the PI coefficient adjustment circuit 16 and the differential circuit 13, and the optical output power of the optical amplifier 3 is also output. The output side voltage value Vout corresponding to Pout is output from the second logarithmic conversion circuit 10 to the differential circuit 13 (S1 in FIG. 4). Further, the gain deviation ΔG calculated by the differential circuit 13 using the equation (1) is output to the PI coefficient adjustment circuit 16 (S1 in FIG. 4).

Subsequently, the PI coefficient adjustment circuit 16 calculates the target proportionality coefficient k ₀ based on the equation (5) (S2 in FIG. 4) and determines whether or not the gain deviation ΔG is negative (S3 in FIG. 4). When the gain deviation ΔG is negative and the absolute value of the gain deviation ΔG is smaller than the predetermined value α, a value obtained by multiplying the target proportional coefficient k ₀ by the predetermined value N is set as a new target proportional coefficient k ₀ ( On the other hand, when the gain deviation ΔG is negative and the absolute value of the gain deviation ΔG is larger than the predetermined value α, a value obtained by multiplying the target proportionality coefficient k ₀ by the predetermined value N × M is obtained. A new target proportionality coefficient k ₀ is set (S3, S4, S6 in FIG. 4). When the gain deviation ΔG is positive, the target proportionality coefficient k ₀ is not multiplied by M or N × M but is kept at the initial value. N and M are multiples, and N> 0 and M> 0.

Here, at the moment the optical input power of the optical amplifier 3 is increased as indicated by the broken line X ₁ in FIG. 5, normally gain deviation ΔG becomes positive, the optical amplifier 3 as indicated by a broken line X ₂ in FIG. 5 Usually, the gain deviation ΔG becomes negative at the moment when the optical input power decreases.
The process of adjusting the proportional coefficient k of the proportional circuit 14 so as to become the target proportional coefficient k ₀ is performed as follows.

That is, the PI coefficient adjustment circuit 16 reads the resistance value R2 of the variable resistor 14c connected to the DCP 14a of the proportional circuit 14 shown in FIG. 2 (S7 in FIG. 4), and divides this by the resistance value R1 of the fixed resistor 14b. Therefore, the proportional coefficient k = R1 / R2 is calculated (S8 in FIG. 4). Further, a value Δk obtained by subtracting the target proportionality coefficient k ₀ from the obtained proportionality coefficient k is obtained (S9 in FIG. 4), and if the condition of −δ <Δk is not satisfied, the PI coefficient adjustment circuit 16 determines that the proportional circuit 14 while causing the variable resistor 14 c of the resistance R2 an operation to increase one step DCP14a Te (S10 in FIG. 4, S11), PI coefficient adjustment circuit 16 in the case of not satisfied .DELTA.k <+ [delta] is to proportional circuit 14 the resistance value R2 of the variable resistor 14 c of DCP14a to perform operations to reduce one step Te (S12 in FIG. 4, S13). This operation is repeated until Δk becomes smaller than the absolute value of the predetermined range δ, whereby the proportional coefficient k is set to the target proportional coefficient k ₀ or within the predetermined range, and the proportional circuit 14 adds the calculated value ΔGk to the adder circuit. 17 (S14 in FIG. 4).

The above operation is continued while it is necessary to adjust the PI coefficient (S15 in FIG. 4).
The reason why the output signal of the first logarithmic conversion circuit 9 on the optical input side and the value of the gain deviation ΔG are input to the PI coefficient adjustment circuit 16 as described above is as follows.

The response time of the gain of the EDF 1 is faster as the optical power in the EDF 1 is larger. However, as described in Patent Document 1, the proportional coefficient k is increased as the optical power input to the EDF 1 is increased. When the proportional coefficient k is increased as the optical input power is increased, such that the proportional coefficient k is decreased as the optical power is decreased, the optical input power is changed from P _H to P _L as shown in the broken line X ₂ in FIG. 5 and FIG. when reduced to, transient response as shown in FIG. 17 (b) is deteriorated with the change. This is because the pumping state of the EDF 1 immediately after the optical input power decreases from P _H to P _L has a characteristic that the pumping state immediately before the input power decreases is substantially maintained, as shown in FIG. according proportional coefficient k ₁ to the conventional method of reducing the optical output power of the small to excite LD4 to k _2, for internal excited state of EDF1 remains substantially the P _H, the gain response of the by EDF1 A situation occurs in which the time is shortened and the transient characteristics in the EDF 1 become insufficient, and as a result, the fluctuation suppressing effect of the residual light in the EDF 1 becomes insufficient.

On the other hand, in this embodiment, in addition to changing the PI control coefficient according to the optical input power, the proportional coefficient which is the PI coefficient according to the sign of the gain deviation ΔG and the absolute value of ΔG k and the integration coefficient γ are changed so that the PI control coefficient when the gain deviation ΔG is negative is a predetermined multiple of the PI control coefficient when the gain deviation ΔG is positive with the same input power. input power as shown in becomes possible to increase the proportional coefficient of the PI control immediately after reduced to P _L sufficiently large to gain variation suppressing effect of k ₂ to k ₂ 'from P _H.

That is , in the above optical amplifying apparatus, when the optical input power Pin increases and the gain deviation ΔG becomes positive as shown by the broken line X ₁ in FIG. inputs the signal Vin from the first logarithmic converter 9, further calculates the target proportional coefficient k ₀ according to equation (5) (S1 in FIG. 4, S2). Then, PI coefficient adjustment circuit 16, as the difference between the proportional coefficient k and target proportional coefficient k ₀ by adjusting the resistance value R2 of the variable resistor 14c of DCP14a proportional circuit 14 falls below the absolute value of [delta], further adjustment Using the proportional coefficient k, the proportional circuit 14 outputs a calculated value of kΔG to the adder circuit 17 (S7 to S14 in FIG. 4).

On the other hand, when the optical input power Pin decreases and the gain deviation ΔG becomes negative as indicated by the broken line X ₂ in FIG. 5, the PI coefficient adjustment circuit 16 starts from the first logarithmic conversion circuit 9. inputs the signal Vin, further after calculating the target proportional coefficient k ₀ of the proportional coefficient based on the equation (5), as its target proportionality coefficient k ₀ a new a predetermined multiple value target proportional coefficient k ₀ (FIG. 4 of S1 to S6), further, the difference by adjusting the resistance value R2 of the new target proportional coefficient k ₀ and becomes as DCP14a of the variable resistor 14c of the proportional circuit 14 proportionality coefficient k and target proportional coefficient k ₀ is δ The proportional circuit 14 outputs the calculated value of kΔG to the adder circuit 17 using the adjusted proportionality coefficient k so as to be equal to or smaller than the absolute value (S7 to S14 in FIG. 4).

Next, the result of simulating the gain fluctuation of the residual light in the EDF 1 when the optical input power Pin input to the optical amplifier 3 is changed will be described in comparison with the prior art.
First, the function of the PI coefficient adjustment circuit 16 is stopped, and the conventional technique is used in which the proportionality coefficient k of the proportional circuit 14 and the integral coefficient γ of the integration circuit 15 are made constant regardless of changes in the optical input / output power. As shown in FIG. 5, the gain fluctuation of the residual light when the optical input power to the optical amplifier 3 is changed is as shown in FIG. In FIG. 6A, the transient change in the residual light gain when the optical input power increases is 0.50 dB, and the transient change in the residual light gain when the optical input power decreases is 0.56 dB. In both cases, the transient change was 0.5 dB or more.
Here, the target gain G ₀ is 27 dB, and the gain on the vertical axis in FIG. 6 represents (Vout−Vin) in the equation (1). Equation (1) is
(Vout−Vin) = G ₀ −ΔG = 27−ΔG
6 when the optical input in FIG . A 56 dB peak indicates that ΔG is negative. The display of the gain on the vertical axis is the same in FIGS. 7, 8, 10, and 12 described below.

In order to suppress the transient change, it is necessary to increase the PI coefficient, but the simulation result when the PI coefficient is quadrupled as in FIG. 6A is as shown in FIG. Although the change could be suppressed, since the PI coefficient is too large, vibration was observed even in a state where there was no change in the optical input power.
On the other hand, the PI coefficient adjusting circuit 16 is operated, and the proportional coefficient k of the proportional circuit 14 and the integral coefficient γ of the integrating circuit 15 are respectively changed according to the change of the optical input power without considering the absolute value and sign of the gain deviation ΔG. When the conventional technique shown in FIG. 14 is used, the change in the gain of the residual light when the optical input power to the optical amplifier 3 changes is as shown in FIG. In FIG. 7A, the transient change of the gain of the residual light when the optical input power is decreased is larger than that in FIG. 6A in which the PI coefficient is constant. This is because even if the optical input power in the EDF 1 decreases, the excitation state immediately before that hardly changes.

In order to suppress the transient change, it is conceivable to increase the PI coefficient. However, when the PI coefficient is changed to four times the condition shown in FIG. 7A, as shown in FIG. 7B. Although a simulation result is obtained, since the PI coefficient is too large, vibration is observed in a state where there is no change in the optical input power.
On the other hand, as in this embodiment, the PI coefficient adjustment circuit 16 is operated, and the proportional coefficient k of the proportional circuit 14 and the integration of the integration circuit 15 are changed according to changes in the absolute value, sign, and optical input power of the gain deviation ΔG. When the coefficient γ was changed, simulation results as shown in FIGS. 8A and 8B were obtained.

FIG. 8A shows that when the gain deviation ΔG is negative, the PI coefficient is four times the condition of FIG. 7A, and the absolute value of the gain deviation ΔG is larger than 0.1 dB, the PI coefficient is further doubled. As a result, the transient change in the gain of the residual light is smaller than that in the prior art not only when the optical input power is increased but also when the optical input power is decreased.
FIG. 8B shows that the PI coefficient is further increased when the gain deviation ΔG is negative, the PI coefficient is four times the condition of FIG. 7A, and the absolute value of the gain deviation ΔG is greater than 0.1 dB. When the absolute value of the gain deviation ΔG is larger than 2 dB, the PI coefficient is further doubled to 16 times, and not only when the optical input power is increased but also decreased. The transient change of the residual light became even smaller than that in FIG. Accordingly, it is understood that the gain fluctuation of the residual light becomes smaller by setting a plurality of conditions for determining the absolute value of the gain deviation ΔG (S4 in FIG. 4) .

(Second Embodiment)
FIG. 9 is a flowchart showing adjustment of the PI coefficient in the optical amplification method according to the second embodiment of the present invention using the optical amplification device shown in FIG.
The flowchart shown in FIG. 9 shows a flow for adjusting the proportionality coefficient k of the proportional circuit 14 in the PI coefficient adjustment circuit 16 in FIG.
First, the gain deviation ΔG calculated by the differential circuit 13 based on the equation (1) is input to the PI coefficient adjustment circuit 16 (S21 in FIG. 9).

Subsequently, the PI coefficient adjustment circuit 16 sets the target proportionality coefficient k ₀ regardless of the optical input / output power (S22 in FIG. 9) and determines whether or not the absolute value of ΔG is larger than a certain value α. and, only the target proportionality coefficient k ₀ after resetting M times is greater (S23 in FIG. 9, S24), performs an operation to be smaller than matched or predetermined range proportionality factor k in the target proportional coefficient k ₀ ( (S7 to S14 in FIG. 9).
Operation for setting the proportional coefficient k in the match or a predetermined range to the target proportionality coefficient k ₀ is performed by the following process.

That is, the resistance value R2 of the variable resistor 14c connected to the DCP 14a shown in FIG. 2 constituting the proportional circuit 14 is read (S7 in FIG. 9), and divided by the resistance value R1 of the fixed resistor 14b to tentatively proportionally. The coefficient k = R1 / R2 is calculated (S8 in FIG. 9). Further, a value Δk obtained by subtracting the target proportionality coefficient k ₀ from the obtained proportionality coefficient k is obtained (S9 in FIG. 9), and it is determined whether Δk is larger than the absolute value of the predetermined range δ (S10 in FIG. 9). S12), if the condition −δ <Δk is not satisfied, the PI coefficient adjustment circuit 16 causes the proportional circuit 14 to increase the resistance value R2 of the variable resistor 14c by one step (S10 in FIG. 9). S11), if the condition of Δk <+ δ is not satisfied, the PI coefficient adjustment circuit 16 causes the proportional circuit 14 to perform an operation of decreasing the resistance value R2 of the variable resistor 14c by one step (S12 and S13 in FIG. 9). . This operation is repeated until Δk becomes smaller than the absolute value of the predetermined range δ.

When Δk becomes smaller than the absolute value of the predetermined range δ, the proportional circuit 14 outputs the calculated value kΔG to the adder circuit 17 (S14 in FIG. 9).
The above processing is continuously performed when the proportionality coefficient k needs to be adjusted (S15 in FIG. 9).
As described above, in this embodiment, in order to suppress the transient change and to ensure the stability at the normal time when the change of the input power is small, the PI control is performed only when the gain deviation ΔG is larger than a certain value α. The simulation was performed with a large coefficient. For example, when the absolute value of the gain deviation ΔG is larger than α = 0.03 dB, the change in the gain of the residual light in the EDF ₁ when M = 2 is multiplied by the target proportional coefficient k ₀ of the proportional coefficient is examined. The result as shown to a) is obtained and the transitional change is suppressed compared with Fig.6 (a). Further, when the absolute value of the gain deviation ΔG is larger than 0.3 dB, the transient change in the residual light gain when the PI coefficient is further doubled to M = 4 has a result as shown in FIG. Compared with the case where the PI coefficient is not changed according to the absolute value of the gain deviation ΔG, the transient change in the gain of the residual light when the optical input power is increased is 0.17 dB, and the optical input power is decreased. The transient change of the residual light at that time was suppressed to 0.25 dB, and the stability at the normal time when the input power did not change could be secured.

(Third embodiment)
FIG. 11 is a flowchart showing the adjustment of the PI coefficient in the optical amplification method according to the third embodiment of the present invention using the optical amplification device shown in FIG.
The flowchart shown in FIG. 11 shows a flow for adjusting the proportional coefficient k of the proportional circuit 14 in the PI coefficient adjustment circuit 16 in FIG.
First, the input-side voltage value Vin corresponding to the optical input power Pin of the optical amplifier 3 are entered from the first logarithmic converter 9 into PI coefficient adjusting circuit 16 (S31 in FIG. 11). Further, the gain deviation ΔG calculated by the differential circuit 13 using the equation (1) is input to the PI coefficient adjustment circuit 16 (S31 in FIG. 11).
Subsequently, the PI coefficient adjustment circuit 16 calculates the target proportionality coefficient k ₀ based on the equation (1) (S32 in FIG. 11) and determines whether the gain deviation ΔG is negative (S33 in FIG. 11). When ΔG is positive, the proportional coefficient k is matched with the target proportional coefficient k ₀ or within a predetermined range (S7 to S14 in FIG. 11), while when ΔG is negative, the target proportional coefficient k After resetting ₀ to the initial M (M is a positive number) times (S34 in FIG. 11), the proportional coefficient k is matched with the target proportional coefficient k ₀ or set within a predetermined value range (FIG. 11). 11 S7 to S14).

Process of matching the proportionality factor k in the target proportional coefficient k ₀ is performed as follows.
That is, the resistance value R2 of the variable resistor 14c of the proportional circuit 14 shown in FIG. 2 is read (S7 in FIG. 11), and this is divided by the resistance value R1 of the fixed resistor 14b to temporarily calculate the proportional coefficient k = R1 / R2. Calculation is performed (S8 in FIG. 11). Further, a value Δk obtained by subtracting the target proportionality coefficient k ₀ from the obtained proportionality coefficient k is obtained (S9 in FIG. 11), and it is determined whether Δk is larger than the absolute value of the predetermined range δ (S10 in FIG. 11). S12), - δ <S10 of Δ one a non PI coefficient adjusting circuit 16 when satisfied k to perform an operation to increase in the resistance R2 a step variable resistor 14c relative to the proportional circuit 14 (FIG. 11, S11 ), When Δ k <+ δ is not satisfied, the PI coefficient adjustment circuit 16 causes the proportional circuit 14 to perform an operation of decreasing the resistance value R2 of the variable resistor 14c by one step (S12 and S13 in FIG. 11). This operation is repeated until Δk becomes smaller than the absolute value of the predetermined range δ.

When Δk becomes smaller than the absolute value of the predetermined range δ, the proportional circuit 14 outputs the calculated value k ΔG to the adder circuit 17 (S14 in FIG. 11).
The above processing is continuously performed in a state where the proportional coefficient k needs to be adjusted (S15 in FIG. 11).
When the gain deviation ΔG is negative, that is, in order to suppress only a transient change in the gain of the residual light when the optical input power is reduced under a predetermined condition, the gain deviation ΔG is negative compared to the positive case. When the PI coefficient was increased by 3 times, 4 times, and 5 times to simulate the gain of the residual light, the results shown in FIGS. 12 (a), 12 (b), and 12 (c) were obtained. 12 (a) to 12 (c), the transient of the gain of the residual light when the optical input power is reduced as compared with FIG. 7 (a) showing the simulation result when the sign of the gain deviation ΔG is not considered. The normal stability in which the change was suppressed and the change in the optical input power was small could be secured.
Note that at least one optical amplifying device according to each of the above embodiments may be connected to the optical transmission line.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the present invention, the embodiment in which the AGC control circuit is an analog circuit has been described. However, the present invention is not limited to this, and the AGC control circuit may be a digital circuit.

FIG. 1 is a configuration diagram illustrating an optical amplifying device according to an embodiment of the present invention. FIG. 2 is a circuit diagram of a proportional circuit constituting the AGC control circuit of the optical amplifying device according to the embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the proportional coefficient of the proportional circuit constituting the AGC control circuit of the optical amplifying device according to the embodiment of the present invention and the optical input power. FIG. 4 is a flowchart showing control of the proportional integration coefficient according to the first embodiment of the present invention. FIG. 5 is a waveform diagram showing a change in optical input power in the optical amplifying apparatus according to the embodiment of the present invention. FIG. 6 is a waveform diagram showing the gain fluctuation of the residual light when the optical input power changes in the conventional optical amplifying apparatus. FIG. 7 is a waveform diagram showing the gain fluctuation of the residual light when the optical input power changes in another conventional optical amplifying device. FIG. 8 is a waveform diagram showing the gain fluctuation of the residual light when the optical input power changes in the optical amplifying device according to the first embodiment of the present invention. FIG. 9 is a flowchart showing control of the proportional integration coefficient in the optical amplification method according to the second embodiment of the present invention. FIG. 10 is a waveform diagram showing the gain fluctuation of the residual light when the optical input power changes in the optical amplification method according to the second embodiment of the present invention. FIG. 11 is a flowchart showing control of the proportional integration coefficient according to the third embodiment of the present invention. FIG. 12 is a waveform diagram showing gain variation of residual light when the optical input power changes in the optical amplification method according to the third embodiment of the present invention. FIG. 13 is a block diagram showing a first conventional optical amplifying device. FIG. 14 is a waveform diagram of optical input power, optical output power, and optical output power per wave in the optical amplifying device shown in FIG. FIG. 15 is a block diagram showing a second conventional optical amplifying device. FIG. 16 is a diagram showing the relationship between the proportional coefficient of the proportional circuit constituting the AGC control circuit of the optical amplifying device shown in FIG. 15 and the optical input power. FIG. 17 is a waveform diagram showing changes in residual wavelength output when the optical input power changes in the optical amplifying apparatus shown in FIG.

1 EDF
2, 5, 7 Optical coupler 3 Amplifier 6, 8 Photodiode 4 Excitation laser diodes 9, 10 Logarithmic conversion circuit 11 AGC control circuit 12 Target gain setting circuit 13 Differential circuit 14 Proportional circuit 15 Integration circuit 16 PI coefficient adjustment circuit 17 Adder circuit 18 LD current control circuit

Claims (8)

An optical amplifier that amplifies and outputs an input optical signal based on pumping light from a pumping light source; and
Detecting means for detecting respective optical powers of an input optical signal input to the optical amplifier and an output optical signal output from the optical amplifier;
Calculating means for calculating the gain of the optical amplifier from the optical power of the input optical signal and the output optical signal detected by the detecting means;
Control means for feedback-controlling the optical power of the pumping light output from the pumping light source so that the gain calculated by the calculating means is equal to a target gain as a fixed value for constant gain control; Have
It said control means, along with the transient decrease of the optical power of the input optical signal, when the gain calculated by the calculating means is larger than the target gain is a proportional coefficient of the feedback control An optical amplifying device characterized in that the gain is increased until the target gain becomes substantially equal. The optical amplification apparatus according to claim 1, wherein the proportionality coefficient is increased when a gain deviation obtained by subtracting the gain from the target gain is negative. The control means includes a constant multiplier circuit provided in a feedback loop to adjust the proportional coefficient of the feedback control, and increases the proportional coefficient by adjusting a constant value of the constant multiplier circuit. The optical amplifying device according to claim 1 or 2, wherein 4. The optical amplifying apparatus according to claim 3, wherein the constant value of the constant multiplying circuit is set to a value that increases or decreases in proportion to the optical power of the input optical signal detected by the detecting means. The control means includes an integration circuit that integrates the target gain and a difference value between the gains, and an addition circuit that adds the output value of the integration circuit and the output value of the constant multiplication circuit,
The pumping light source is controlled according to the output value of the adding circuit, and the gain calculated by the calculating means is larger than the target gain with a transient decrease in the optical power of the input optical signal. 5. The optical amplification according to claim 3, wherein when the gain is reached, the integration coefficient is increased until the gain and the target gain are substantially equal by adjusting an integration constant of the integration circuit. apparatus. 6. The control unit according to claim 1, wherein the control means further increases the proportionality coefficient when a difference value between the target gain and the gain becomes larger than a predetermined value. The optical amplifying device described in 1. The control means temporarily doubles the proportionality factor when the gain difference between the target gain and the gain is greater than 0.03 dB, and the gain difference between the target gain and the gain is greater than 0.3 dB. 7. The optical amplifying apparatus according to claim 6, wherein the proportionality coefficient is temporarily quadrupled. In an optical amplification method of an optical amplification device having an optical amplifier that amplifies an input optical signal based on excitation light from an excitation light source and outputs the amplified optical signal,
A detection step of detecting respective optical powers of an input optical signal input to the optical amplifier and an output optical signal output from the optical amplifier;
A calculation step of calculating the gain of the optical amplifier from the optical power of the input optical signal and the output optical signal detected by the detection step;
A control step of feedback-controlling the optical power of the pumping light output from the pumping light source so that the gain calculated by the calculating step is equal to a target gain as a fixed value for constant gain control; Have
In the control step, when the gain calculated in the calculation step becomes larger than the target gain with a transient decrease in the optical power of the input optical signal, the proportional coefficient of the feedback control is set. An optical amplification method, wherein the gain is increased until the target gain becomes substantially equal.

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