JP2007005704A - Optical amplifier, control method thereof, and optical amplification indirect communications equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier which can amplify output light power without distortions, even when the input light power changes, while keeping the output light power level of the optical amplifier to be constant, and to provide control method thereof. <P>SOLUTION: The optical amplifier 1 performs constant gain control to a fiber 3 for amplification, by inputting both an input optical power signal 106 and an output optical power signal 107 to a computing unit 12. A gain target value setting circuit 13 calculates the newest gain target value 110, by inputting the input optical power signal 106 from a current/voltage converter 10, and outputs this to the computing unit 12 to update the gain target value. While making the control periods of the constant gain target control to be shorter than the gain moderation time (several μsecs) of the fiber for amplification, the updating periods of the gain target value is set longer than the gain moderation time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an optical amplifier that adjusts an output of an optical amplifier to a predetermined value, a control method thereof, and an optical amplification repeater communication apparatus using the optical amplifier.

In an optical amplifier used for a repeater of an optical communication device, as a method of amplifying input light and adjusting the optical power of output light to a constant level, conventionally, only output light power is detected, and based on this, the excitation light is detected. A method of controlling the optical power has been adopted.

In the control of the optical amplifier, it is necessary to consider the transient characteristics of the erbium-doped optical fiber (EDF) used for the amplification fiber (Non-Patent Documents 1, 2, and 3). That is, when the input light input to the EDF fluctuates, the gain fluctuates transiently, and the transient response time (hereinafter referred to as gain relaxation time) at that time is about 2 to 10 μsec. Therefore, in designing an optical amplifier, how to set the control period of the optical amplifier compared to the gain relaxation time is an important issue.

A conventional optical amplifier control method includes a method (hereinafter referred to as Conventional Technology A) in which a control cycle is set longer than the gain relaxation time to perform constant output level control (ALC (Automatic Level Control) control). The method can be broadly classified into a method (hereinafter referred to as Conventional Technology B) in which the output level constant control (ALC control) is performed with a time shorter than the gain relaxation time.

In either of the conventional techniques A or B, conventionally, only the optical power output from the optical amplifier is monitored, and the output optical power of the pumping laser is controlled so that the output optical power is constant. Level constant control was performed.
Yan Sun, et al., “Fast power transient in WDM optical networks with cascaded EDFAs”, IEEE Electronics Letters, 13th 1997, Vol. 3 No. 4. Alberto Bononi, et al., “Doped-Fiber Amplifier Dynamics: A System Perspective”, Journal of Lightwave Technology, May 1998, Vol.16 No.5

However, both of the above-described prior art A and prior art B have the following problems.

In the prior art A or the prior art B, the average output optical power of the optical amplifier is kept constant by ALC control. However, when the input light is a signal that turns “1” (on) / “0” (off) in a predetermined cycle, the operation to make the output power constant by ALC control and the on / off signal are distorted. It has been extremely difficult to achieve both an amplifying operation and an amplifying operation.

In the case where the input light is momentarily interrupted or becomes a zero signal for a time longer than the gain relaxation time of the EDF, for example, several tens of μsec, according to the conventional technique A, the output optical power immediately after the input light recovers from zero is There was a problem of distortion due to the transient response.

FIG. 7 schematically shows the response of the output optical power when the input light of the optical amplifier becomes zero for several tens of microseconds and then returns to the original power level again. In the figure, the optical power 601 has a input light power indicates the, from time t ₀ between t ₁ (being the number 10 .mu.sec) instantaneous interruption or zero signal to the optical amplifier. An optical power 602 indicates a response of the output optical power when ALC control based on the prior art A is performed. Here, the control cycle of the conventional technique A is assumed to be longer than the time during which the input light power 601 is momentarily interrupted or a zero signal.

As can be seen from the response of the output light 602, in the prior art A, immediately after the input optical power 601 returns to the original optical power level again, an overshoot occurs in the output optical power 602 due to the transient response of the amplification fiber. Resulting in. In the prior art A, since the control cycle of ALC control is longer than the transient response time of the amplification fiber, it is extremely difficult to suppress the overshoot of the output optical power 602.

That is, if the control cycle of the ALC control is longer than the gain relaxation time of the amplification fiber, the pumping light power is not controlled even if the input light 601 is momentarily interrupted or becomes a zero signal during the control cycle, and the amplification light Fiber excitation will continue. For this reason, when the input optical power 601 is restored next time, an extra optical power is output as much as it has been excited so far. As described above, the conventional technique A has a problem that the output light power 602 cannot be stably controlled with respect to an operation in which the input light 601 temporarily becomes zero.

Further, the conventional technique B has the following problems.
Similarly to the above, when the input optical power is momentarily interrupted or becomes a zero signal for several tens of μsec longer than the gain relaxation time of the EDF, in the related art B, the period of the input optical power is zero even during the period when the input optical power is zero. The output optical power does not become zero, and the original output optical power is maintained as it is. Therefore, there is a problem in that it is impossible to detect on / off information that the input light has from the amplified output light.

In the schematic diagram shown in FIG. 7, a response 603 of the output optical power when ALC control based on the prior art B is performed is indicated by 603. In the figure, the output optical power 603 from the optical amplifier according to the prior art B returns to the original optical power level immediately after the input optical power 601 is turned off.

This is because even when the input optical power 601 becomes zero, the ALC control operates immediately and works to return the output optical power 603 to the original optical power level again. As a result, the output optical power 603 is returned to the original optical power level before it becomes zero, and is maintained at the optical power level. As described above, the output light 603 amplified by the amplifier according to the conventional technique B has a problem that the on / off information that the input light 601 has cannot be detected.

As described above, with the conventional technology, it is extremely difficult to amplify the output light power without distortion even if the input light is momentarily interrupted or turned off while keeping the output light level of the optical amplifier constant. there were.

Accordingly, the present invention has been made to solve these problems, and can maintain the output light level of the optical amplifier constant and amplify the output light power without distortion even when the input light changes. An object of the present invention is to provide an optical amplifier, a control method therefor, and an optical amplification repeater communication apparatus using the optical amplifier.

A first aspect of the optical amplifier according to the present invention includes an amplification fiber, an excitation LD (laser diode) that supplies excitation light to the amplification fiber, and a drive current control circuit that controls the drive current of the excitation LD. A first light receiving circuit that receives a part of the input light to the amplification fiber and outputs the input light power as a first electric signal; and a part of the output light from the amplification fiber. The second light receiving circuit for outputting the output optical power as a second electric signal, and the driving current so as to maintain the predetermined control target value by inputting the first electric signal and the second electric signal. A first control circuit that outputs a control signal to the control circuit; and the first electric signal is input from the first light receiving circuit to calculate the control target value of the first control circuit and to calculate the first control signal. From the second control circuit that supplies the control circuit An optical amplifier characterized by Rukoto.

A second aspect includes two or more amplification fibers, each of the amplification fibers connected in series via an optical filter and an optical isolator, and the excitation LD and the drive current control for each amplification fiber. Each of the circuits is connected, and the first control circuit outputs the control signal to all of the drive current control circuits.

A third aspect is an optical amplifier characterized in that the amplification fiber is made of an erbium-doped optical fiber (EDF).

A fourth aspect is an optical amplifier control method according to any one of the first to third aspects, wherein the gain target value of the amplification fiber is the control target value, and the gain target value is The output optical power is increased or decreased based on the input optical power, and the first control circuit has a gain value calculated from the first electrical signal and the second electrical signal. A control method for an optical amplifier, characterized in that the control signal is generated so as to coincide with a target gain value and output to the drive current control circuit.

According to a fifth aspect, when the control target value output from the second control circuit to the first control circuit increases the power target level of the input optical power, the gain target value is decreased, and the input The optical amplifier control method is characterized in that when the power level of optical power decreases, the gain target value is increased.

A sixth aspect is an optical amplifier control method, wherein a control period of the drive current by the drive current control circuit is shorter than a gain relaxation time of the amplification fiber.

In a seventh aspect, the first control circuit outputs the optical output power target value or the drive current target value of the excitation LD as the control signal, and the control cycle of the first control circuit is the amplification The optical amplifier control method is characterized in that it is shorter than the gain relaxation time of the optical fiber.

An eighth aspect is a method of controlling an optical amplifier, wherein a control cycle of the first control circuit is shorter than 10 μsec.

A ninth aspect is an optical amplifier control method characterized in that the control cycle of the first control circuit is shorter than 1 μsec.

A tenth aspect is a method of controlling an optical amplifier according to any one of the first to third aspects, wherein the control period of the second control circuit is greater than the gain relaxation time of the amplification fiber. This is a method of controlling an optical amplifier characterized by being long.

An eleventh aspect is an optical amplifier control method characterized in that a control cycle of the second control circuit is longer than 10 μsec.

In a twelfth aspect, the first control circuit performs proportional / integral control so that the gain value obtained from the first electric signal and the second electric signal matches the target gain value. An optical amplifier control method characterized by the following.

A thirteenth aspect is an optical amplifying relay communication apparatus characterized in that one or more optical amplifiers according to any one of the first to third aspects are provided between a transmission end and a reception end. .

As described above, according to the present invention, even when the input optical power to the amplifier fluctuates sharply while keeping the average output optical power of the optical amplifier constant, the transient fluctuation of the gain of the amplification fiber such as EDF Therefore, it is possible to provide an optical amplifier and a control method thereof that can suppress the occurrence of signal distortion.

In an optical communication system, the optical amplifier of the present invention is applied to an optical amplification repeater communication apparatus provided between a transmission end and a reception end, thereby transmitting an optical signal transmitted from the transmission end to the reception end without distortion. It becomes possible.

The optical amplifier according to the present invention realizes constant output light level control without distortion in output light by performing constant gain control and updating the target gain value of the constant gain control at an appropriate period. For this purpose, both the input optical power and the output optical power are monitored, and in the constant gain control, the control is performed based on both the input optical power and the output optical power. In updating the gain target value, the gain target value is dynamically changed using the input optical power.

Furthermore, in the optical amplifier of the present invention, the control period for the constant gain control is made shorter than the gain relaxation time (several μsec) of the EDF (erbium-doped optical fiber) that is an amplification fiber, while the gain target value is updated. Such an update cycle is set longer than the gain relaxation time.

Hereinafter, an optical amplifier according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, about each structural part which has the same function, the same code | symbol is attached | subjected and shown for simplification of illustration and description.

FIG. 1 is a block diagram showing a schematic configuration of an optical amplifier according to an embodiment of the present invention.
The optical amplifier 1 takes in the input light 101 from the input optical connector 2, amplifies it with the amplification fiber 3, and sends it out as output light 102 from the output optical connector 4. The optical amplifier 1 also includes a pumping laser diode (LD) 5 for amplifying the input light 101 with the amplification fiber 3, and the pumping light 103 output from the pumping LD 5 is supplied to the amplification fiber 3. It is configured to be incident. As the amplification fiber 3, for example, EDF (erbium-doped optical fiber) can be used.

Since the optical power level of the output light 102 is determined by the gain of the amplification fiber 3, the gain of the amplification fiber 3 is adjusted in order to adjust the optical power level to a desired magnitude. This gain adjustment can be performed by controlling the optical power of the pumping light 103 output from the pumping LD 5.

In the optical amplifier 1 of the present embodiment, not only the output light 102 but also the input light 101 is monitored in order to control the pumping light 103 output from the pumping LD 5. In order to monitor the input light 101, a part of the input light 101 taken from the input optical connector 2 is branched by the branch coupler 6 and sent to the photodiode 8 where it is converted into a current signal 104. Then, the current signal 104 is sent to the current-voltage conversion circuit 10, and is converted into an input optical power signal 106 as an electric signal by the current-voltage conversion circuit 10 and output.

In order to monitor the output light 102, a part of the output light 102 amplified by the amplification fiber 3 is branched by the branch coupler 7 and sent to the photodiode 9 where it is converted into a current signal 105. . Then, the current signal 105 is sent to the current-voltage conversion circuit 11, and is converted into an output optical power signal 107 as an electrical signal by the current-voltage conversion circuit 11 and output.

In the present embodiment, constant gain control for the amplification fiber 3 is performed by the arithmetic unit 12. In the arithmetic unit 12, both the input optical power signal 106 and the output optical power signal 107 are input and the constant gain control is performed. Is realized. The arithmetic unit 12 that performs constant gain control may be an analog circuit using an operational amplifier, or a digital signal processing circuit using a microprocessor or an FPGA (field programmable gate array).

The excitation LD 5 that adjusts the gain of the amplification fiber 3 is controlled by the excitation LD drive circuit 14 via the supplied drive current 108. The excitation LD drive circuit 14 controls the drive current 108 based on the optical power target value for the excitation light 103 output from the excitation LD 5 or the drive current target value for the drive current 108.

The constant gain control executed in the arithmetic unit 12 calculates the optical power target value for the pumping light 103 or the driving current target value for the driving current 108. The arithmetic unit 12 sends the calculated optical power target value or the driving current target value to the excitation LD driving circuit 14 as an electric signal 109 composed of the output voltage of the operational amplifier or the output voltage converted by the D / A converter. Output.

On the other hand, the target gain value used for the constant gain control executed by the arithmetic unit 12 is periodically updated by the target gain setting circuit 13. The gain target value setting circuit 13 receives the input optical power signal 106 from the current-voltage conversion circuit 10, calculates the latest gain target value 110 at a predetermined period based on this, and outputs this to the calculator 12. Like to do.

As described above, the target gain value is increased or decreased based on the input optical power so that the output optical power becomes constant. The relationship shown in FIG. 2 is provided between the optical power level of the input light 101 and the gain target value for the constant gain control. In FIG. 2, the horizontal axis represents the optical power level of the input light 101, the vertical axis represents the gain target value, and 201 represents the relationship of the gain target value to the input optical power. For the output light level constant control, it is necessary to decrease the gain target value when the optical power level of the input light 101 increases, and conversely, when the optical power level of the input light 101 decreases, the gain target value. Need to be increased. Therefore, the target gain value is set so as to monotonously decrease with respect to the optical power level of the input light 101.

The relationship 201 between the optical power level of the input light 101 and the gain target value for the constant gain control as shown in FIG. 2 can be expressed by the following equation.
Gset = Pouts-Pinm [dB] (Formula 1)
Gset: Target gain
Pinm: Input optical power level
Pouts: Optical power level of output light 102 (fixed value)
However, the input optical power signal 106 is used as the optical power level of the above input light 101.

The updating of the target gain value performed by the target gain setting circuit 13 may be performed by calculating and updating the target gain value 110 based on (Equation 1), or the relationship shown in FIG. The gain target value 110 may be stored in the storage unit of the gain target value setting circuit 13 and the gain target value 110 may be updated with reference to this.

Next, the control cycle of the constant gain control performed by the arithmetic unit 12 and the update cycle of the gain target value 110 performed by the gain target value setting circuit 13 will be described in detail below. The control period and the update period are determined based on the gain relaxation time that the amplification fiber 3 has.

The gain relaxation time is a time required for the gain of the output light 102 to reach a predetermined value when the optical power of the input light 101 input to the amplification fiber 3 changes. The graph 211 shown in FIG. 3 plots the gain relaxation time of the amplification fiber 3 when the optical power of the input light 101 changes by 6 dB (4 times) in a stepwise manner, with the horizontal axis as the optical power of the output light 102. Is. A graph 211 in FIG. 3 is obtained by experiments.

From the graph 211 in FIG. 3, it can be seen that the gain relaxation time decreases as the optical power of the output light 102 increases, and the gain relaxation time is whatever the optical power of the output light 102 is. It can be confirmed that the time is approximately 10 μsec or less.

Based on the experimental results of FIG. 3, in the optical amplifier 1 of the present invention, the execution period of the control executed by the arithmetic unit 12 and the gain target value setting circuit 13 is based on the gain relaxation time of the amplification fiber 3 of about 10 μsec. Is determined.

First, in the constant gain control executed by the arithmetic unit 12, the control period is set to the gain relaxation time of the amplification fiber 3 in order to accurately realize the constant gain control regardless of the magnitude of the optical power of the input light 101. Is about 10 μsec or less. That is, in the constant gain control, the optical power of the pumping light 103 or the driving current 108 is adjusted with a control period of approximately 10 μsec or less.

On the other hand, the update of the gain target value 110 executed by the gain target value setting circuit 13 is performed to correct this when the optical power of the input light 101 fluctuates due to drift or the like. Therefore, it is preferable to update the gain target value 110 at a cycle slower than the constant gain control, and the update cycle should be longer than about 10 μsec which is the gain relaxation time of the amplification fiber 3. That is, the gain target value setting circuit 13 is configured to update the gain target value 110 for the constant gain control at a period longer than approximately 10 μsec.

In the optical amplifier 1 of the present invention configured as described above, control for making the optical power of the output light 102 constant on average by updating the gain target value 110 is realized, and constant gain control is performed in a short period. Therefore, even when the optical power of the input light 101 is momentarily interrupted, it is possible to control the output light 102 so as not to be distorted.

Next, a method for controlling the optical amplifier 1 of the present embodiment will be described in detail below with reference to FIG. FIG. 4 is a flowchart for explaining a control method of the optical amplifier 1 of the present embodiment. In the flowchart of FIG. 4, TAGC represents a control period of constant gain control by the arithmetic unit 12, TALC represents an update period of the gain target value 110 by the gain target value setting circuit 13, and t _n represents the gain target value 110. Represents a time counter for controlling the update cycle.

In step 301, first set the 0 time counter t _n used for the determination of the updating period of the gain target value, to initialize the control. Next, advancing the time counter by adding the TAGC the time counter _{t n} in step 302. That is, step 302 and subsequent is executed every cycle TAGC, advancing the time counter _{t n} accordingly.

In step 303 and step 304, the optical power level Pin of the input light 101 and the optical power level Pout of the output light 102 are measured. In step 305, a current gain value Gm (gain monitor value) is calculated from the Pin and Pout.
Gm = Pout−Pin [dB] (Formula 2)

Next, in step 306, it is determined whether or not the update cycle of the target gain value 110 has been reached, that is, whether or not the TALC that is the update cycle has elapsed since the previous update of the target gain value. If it is determined that TALC or more has elapsed since the previous update, the process proceeds to step 311 to step 313 to update the gain target value Gs.

In step 311, the current value of the optical power level Pin of the input light 101 is measured. In step 312, a gain target value corresponding to the measured optical power level Pin is obtained and set as Gs. The gain target value Gs can be obtained from the relationship 201 between the input optical power level and the gain target value shown in FIG. The relationship 201 between the input optical power level and the gain target value shown in FIG. 2 can be used in the form of a table, or can be used in the following mathematical formula.

Gs = Pouts−Pin [dB] (Formula 3)
Gs: target gain value Pin: input optical power Pouts: target value of output optical power (fixed value)
In the above equation, the target gain value Gs is obtained by substituting the power level of the input light 101 measured in Step 311 for Pin.

When the gain target value Gs is obtained, it is set as the gain target value for the constant gain control executed by the calculator 12. Thereafter, in step 313, and clears the time counter t _n to zero, initialization for the next updating of the target gain value.

When the time counter t _n has not reached the target gain update period, or when the target gain update is completed in steps 311 to 313, the gain constant control is performed in steps 307 and 308. First, at step 307, a control error E is calculated from the currently set gain target value Gs and the gain monitor value Gs calculated by (Equation 2).
E = Gs−Gm [dB] (Formula 4)

Based on the control error E obtained by (Expression 4), in step 308, the drive current 108 (referred to as Is) of the excitation LD 5 is calculated. As a control method for constant gain control, for example, proportional / integral control can be used. In step 308 of the present embodiment, the drive current Is is calculated using the proportional constant Kp and the integral constant Ki by the following equation.
Is = Kp × E + Σ (Ki × E) [mA] (Formula 5)

The drive current Is calculated by (Equation 5) is supplied as an electric signal 109 to the excitation laser drive circuit 14 and is used for controlling the drive current 108 as the drive current target value in the excitation LD drive circuit 14.

A second embodiment of the present invention is shown in FIG.
In the optical amplifier 401 of this embodiment, the pumping light 103 of the pumping LD 5 is multiplexed to the amplification fiber 3 via the wavelength multiplexer 404, as compared with the first embodiment shown in FIG. There is a feature that it is configured.

At the same time, in order to prevent optical oscillation from occurring in the input light 101 and the output light 102 of the optical amplifier 401, an optical isolator 405 is disposed at the rear stage of the input optical connector 2 and the rear stage of the amplification fiber 3, respectively. Yes. Further, in order to correct the wavelength dependency of the optical power of the output light 102, an optical correction filter 406 is disposed on the output side.

In this embodiment, log amplifiers having a logarithmic conversion function are used for the current-voltage conversion circuits 402 and 403. Further, a PLD (programmable logic device) is used for the arithmetic unit 407 so that arithmetic processing can be performed at high speed.

The control period of the constant gain control executed by the arithmetic unit 407 is preferably shorter than the gain relaxation time of the amplification fiber 3 and is preferably 10 μsec or less. More preferably, it is 1 μsec or less.

In addition, the gain target value setting circuit 408 for calculating the gain target value for the constant gain control executed by the arithmetic unit 407 is configured using an MPU (microprocessor) in this embodiment, and the gain target value is obtained by software processing. Is calculated.

In this embodiment, the update cycle of the gain target value by the gain target value setting circuit 408 is 4 msec. The update period of the target gain value is preferably longer than the gain relaxation time of the amplification fiber 3 and is preferably longer than 10 μsec.

The result of measuring how the optical power of the output light 102 is changed by the control method of the present invention when the optical power of the incident light 101 to the optical amplifier 401 of the present embodiment is instantaneously turned off. This will be described below.

FIG. 6 shows the result of measuring the optical powers of the input light 101 and the output light 102 with an oscilloscope through a photoelectric converter. In FIG. 6, 501 indicates the optical power of the input light 101 to the optical amplifier 401, and 502 indicates the optical power of the output light 102 from the optical amplifier 401.

In the example of FIG. 6, the optical power 501 of the input light 101 to the optical amplifier 401 is turned off for 8 μsec from the −10 dBm state, and then restored to the original state. Further, the target gain value of the optical amplifier 401 is set so that the optical power 502 of the output light 102 is maintained at +9 dBm.

From the measurement result of the optical power 502 of the output light 102 shown in FIG. 6, the optical power 502 of the output light 102 shows a waveform similar to the optical power 501 of the input light 101, and the input light 101 has returned to its original state. No peak is observed in the optical power 502 of the output light 102 later. It can be confirmed from the measurement result of FIG. 6 that the optical amplifier 401 of the present invention can sufficiently suppress the occurrence of distortion in the waveform of the output light 102 with respect to the instantaneous interruption of the optical power of the input light 101.

Still another embodiment of the present invention will be described below.
The optical amplifier of this embodiment includes two or more sets of amplification fibers 3 and pumping LDs 5. The amplification fiber 3 includes an optical isolator 405 and a gain correction filter 406 on the output side, and each amplification fiber 3 is connected in series via the optical isolator 405 and the gain correction filter 406.

In this embodiment, each of the excitation LDs 5 has the excitation LD drive circuit 14, and in the constant gain control executed by the computing unit 12, the electric signal 109 is sent to each of the excitation LD drive circuits 14. I am trying to output. With such a configuration, two or more sets of the amplification fiber 3 and the pumping LD 5 can be arranged as the optical amplifier of the present invention.

As described in detail above, the optical amplifier of the present invention performs constant gain control by monitoring the optical power of the input light and the optical power of the output light, and also performs the constant gain control based on the optical power of the input light. By making the gain target value dynamically variable, the output light level constant control is realized.

Also, the control period of the constant gain control is made shorter than the gain relaxation time of the amplification fiber, while the update period of the gain target value is made longer than the gain relaxation time of the amplification fiber. By adopting such a configuration for the optical amplifier of the present invention, it is possible to prevent waveform distortion, overshoot, etc. from occurring in the output light even when instantaneous interruption occurs in the input light. .

For example, the optical amplifier of the present invention amplifies the input light without distortion even during the period of 10 μsec to several 100 μsec (longer than the gain relaxation time of the EDF which is an amplification fiber) during the zero signal. can do. Alternatively, even when the input light repeats the “0” state and the “1” state in a relatively long time period, the output light can be amplified without causing waveform distortion.

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of an optical amplifier according to the present invention. FIG. 2 is a diagram illustrating the relationship between the power level of input light and the gain target value for constant gain control. FIG. 3 is a graph showing a result of experimentally measuring the gain relaxation time of the amplification fiber when the optical power of the input light is changed by 6 dB (4 times) stepwise. FIG. 4 is a flowchart for explaining a control method in the optical amplifier according to the first embodiment. FIG. 5 is a block diagram showing a schematic configuration of the optical amplifier according to the second embodiment of the present invention. FIG. 6 is a graph showing the result of measuring the optical power of the output light when there is a momentary interruption in the input light in the optical amplifier of the second embodiment. FIG. 7 is a schematic diagram showing the response of the output optical power when the input light of the conventional optical amplifier becomes zero for several tens of microseconds and then returns to the original power level again.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 401 ... Optical amplifier 2 ... Input optical connector 3 ... Amplifying fiber 4 ... Output optical connector 5 ... LD for excitation
6, 7 ... branch couplers 8, 9 ... photodiodes 10, 11, 402, 403 ... current-voltage conversion circuits 12, 407 ... arithmetic units 13, 408 ... gain target value setting circuit 14 ... Excitation LD drive circuit 101 ... Input light 102 ... Output light 103 ... Excitation light 104, 105 ... Current signal 106 ... Input optical power signal 107 ... Output optical power signal 108 ... Drive current 109 ... Electric signal 110 ... Target gain value 201 ... Relationship of target gain value with respect to input optical power 211 ... Amplification when input optical light power changes stepwise Fiber gain relaxation time 404 ... wavelength multiplexer 405 ... optical isolator 406 ... correction filter 601 ... input optical power 602, 603 ... output optical power

Claims (13)

An amplification fiber;
An excitation LD (laser diode) for supplying excitation light to the amplification fiber;
A drive current control circuit for controlling the drive current of the excitation LD;
A first light receiving circuit that receives a part of the input light to the amplification fiber and outputs the input light power as a first electric signal;
A second light receiving circuit that receives a part of the output light from the amplification fiber and outputs the output light power as a second electrical signal;
A first control circuit that inputs the first electric signal and the second electric signal and outputs a control signal to the drive current control circuit so as to maintain a predetermined control target value;
A second control circuit that receives the first electrical signal from the first light receiving circuit, calculates the control target value of the first control circuit, and supplies the control target value to the first control circuit. An optical amplifier characterized by. Comprising two or more amplification fibers;
Each of the amplification fibers is connected in series via an optical filter and an optical isolator,
The excitation LD and the drive current control circuit are connected to each of the amplification fibers,
The optical amplifier according to claim 1, wherein the first control circuit outputs the control signal to all of the drive current control circuits. The optical amplifier according to claim 1, wherein the amplification fiber is made of an erbium-doped optical fiber (EDF). An optical amplifier control method according to any one of claims 1 to 3, comprising:
The gain target value of the amplification fiber is the control target value,
The gain target value is increased or decreased based on the input optical power so that the output optical power is constant,
The first control circuit generates the control signal so that a gain value calculated from the first electric signal and the second electric signal matches the target gain value, and outputs the control signal to the drive current control circuit A method for controlling an optical amplifier. The control target value output from the second control circuit to the first control circuit decreases the gain target value when the power level of the input optical power increases, and the power level of the input optical power is 5. The method of controlling an optical amplifier according to claim 4, wherein when the value decreases, the target gain value is increased. 5. The method of controlling an optical amplifier according to claim 4, wherein a control period of the drive current by the drive current control circuit is shorter than a gain relaxation time of the amplification fiber. The first control circuit outputs an optical output power target value or a drive current target value of the excitation LD as the control signal,
7. The method of controlling an optical amplifier according to claim 4, wherein a control period of the first control circuit is shorter than a gain relaxation time of the amplification fiber. 8. The method of controlling an optical amplifier according to claim 7, wherein a control cycle of the first control circuit is shorter than 10 μsec. 8. The method of controlling an optical amplifier according to claim 7, wherein the control cycle of the first control circuit is shorter than 1 μsec. An optical amplifier control method according to any one of claims 1 to 3, comprising:
The control method of the optical amplifier, wherein a control period of the second control circuit is longer than a gain relaxation time of the amplification fiber. 11. The method of controlling an optical amplifier according to claim 10, wherein a control period of the second control circuit is longer than 10 μsec. The first control circuit performs proportional / integral control so that the gain value obtained from the first electric signal and the second electric signal matches the target gain value. 5. A method for controlling an optical amplifier according to 4. One or more optical amplifiers according to any one of claims 1 to 4 are provided between a transmission end and a reception end.
An optical amplification repeater communication device.

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