JP2010166000A - Optical amplifier and control method, and control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier reliably detecting the interruption of input light, and to provide a control method and a control program. <P>SOLUTION: When an input light level is less than a predetermined level, a high-speed response measure is unnecessary and the improvement of detection accuracy is required, since a reverse bias voltage of a photodiode 3 is lowered, a dark current is reduced and also a minimum response frequency required for monitoring a low input is allowed to be a low frequency, so that the monitoring accuracy of input light can be improved while suppressing a reduction in a response speed, and the interruption of input light can be reliably detected. When the input light level is not less than the predetermined level and the high-speed response measure is required, since the reverse bias voltage is increased, the inter-terminal capacitance of the photodiode 3 is reduced and a minimum response frequency required for a high-speed response is also increased, so that the response speed can be improved while suppressing the reduction in the monitoring accuracy of the input light and also the interruption of the input light can be reliably detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical amplifying device used for optical fiber communication, and in particular, an optical amplifying device, a control method, and a control program provided with control means for controlling a reverse bias voltage of a photoelectric conversion element for detecting an input light level. It is about.

  Optical fiber communication is one of the indispensable technologies for point-to-point transmission that connects a computer to a network through a telephone line and for ultra-high-speed and large-capacity communication in a metro / access network. Has been developed.

  Currently, as a technology that supports optical fiber communication, a wavelength division multiplexing (WDM) method is known in which optical pulse spectra are transmitted orthogonally on the frequency axis. With this method, the transmission capacity has been dramatically increased, and improvement in frequency utilization efficiency can be expected. In addition, an erbium-doped fiber amplifier (EDFA) has been put into practical use to compensate for the loss of the optical fiber that transmits the optical signal, and the transmission distance has been greatly increased.

  FIG. 6 is a block diagram showing a configuration of a conventional optical amplifying device. This optical amplifying device includes an input port 1 for inputting an optical signal, an optical branching device 2 for branching an input optical signal transmitted from the input port 1, and an optical signal partially branched by the optical branching device 2 A photodiode 3 as a photoelectric conversion element that converts the signal into a reverse bias circuit 4 that applies a reverse bias voltage to the photodiode 3, and a log amplifier 5 that logarithmically converts the electrical signal output from the photodiode 3 are provided.

  The optical amplifying apparatus includes an EDFA 6 as an optical amplifying means for optically amplifying the input optical signal transmitted from the optical splitter 2, an optical splitter 7 for splitting the optical signal amplified by the EDFA 6, and an optical splitter. 7 is an output port 8 that outputs an optical signal transmitted from 7, a photodiode 9 as a photoelectric conversion element that converts an optical signal partially branched by the optical splitter 7 into an electrical signal, and a reverse bias voltage across the photodiode 9. The reverse bias circuit 10 for providing the log signal, the log amplifier 11 for logarithmically converting the electric signal output from the photodiode 9, and the electric signal output from the log amplifier 5 and the electric signal output from the log amplifier 11 increase the gain of the EDFA 6. A DSP (Digital Signal Processor) 12 is provided as control means for controlling.

  Next, the operation of this conventional optical amplifying device will be described. In FIG. 6, an input port 1 inputs an optical signal from the outside of the optical amplification device. The optical branching device 2 branches the input optical signal transmitted from the input port 1 to the EDFA 6 and the photodiode 3 on the optical input monitor side with a predetermined branching ratio. The reverse bias circuit 4 applies a predetermined reverse bias voltage to the photodiode 3. The photodiode 3 converts a part of the input optical signal transmitted from the optical branching device 2 into an electric signal according to the applied reverse bias voltage. The log amplifier 5 performs logarithmic conversion on the electrical signal transmitted from the photodiode 3 and transmits a logarithmic conversion signal to the DSP 12. The DSP 12 controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5. The EDFA 6 directly optically amplifies the input optical signal transmitted from the optical branching device 2 in accordance with an electric signal with a gain controlled by the DSP 12.

  The optical branching device 7 branches the optical signal optically amplified by the EDFA 6 to the output port 8 and the photodiode 9 on the optical output monitor side at a predetermined branching ratio. Most of the branched optical signal is transmitted from the output port 8, and a part of the optical signal is transmitted to the photodiode 9. The reverse bias circuit 10 applies a predetermined reverse bias voltage to the photodiode 9. The photodiode 9 converts a part of the input optical signal transmitted from the optical branching device 7 into an electric signal according to the applied reverse bias voltage. The log amplifier 11 performs logarithmic conversion on the electrical signal transmitted from the photodiode 9 and transmits a logarithmic conversion signal to the DSP 12. The DSP 12 also controls the gain of the EDFA 6 with reference to the logarithmic conversion signal from the log amplifier 11. That is, the DSP 12 controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5 and the logarithmic conversion signal from the log amplifier 11. The EDFA 6 directly optically amplifies the input optical signal transmitted from the optical branching device 2 in accordance with an electric signal with a gain controlled by the DSP 12.

JP-A-9-260719 JP 2008-227411 A

  However, in the conventional optical amplifying device having the above-described configuration, when the input light level is less than a predetermined level, the input light monitoring accuracy of the photodiode 3 on the optical input monitor side is deteriorated, so that the input light monitoring accuracy is improved. However, the reverse bias voltage of the photodiode 3 needs to be lowered. However, if the reverse bias voltage is lowered, the capacitance between the terminals increases due to the characteristics of the photodiode 3 and the time constant of charge / discharge increases, and the response speed There arises a problem of lowering.

  Further, in the conventional optical amplifying device, when the input light level is equal to or higher than a predetermined level, the current flowing through the photodiode 3 is large, and the charge / discharge time constant is increased due to the inter-terminal capacitance, and the response speed is lowered. Therefore, in order to realize a high-speed response, it is necessary to increase the reverse bias voltage of the photodiode 3 and reduce the capacitance between the terminals. However, if the reverse bias voltage is increased, the characteristics of the photodiode 3 are increased due to the characteristics of the photodiode 3. Dark current increases, input light monitoring accuracy deteriorates, and there is a problem that normal input light break detection cannot be performed.

  By the way, in the prior art disclosed in Patent Document 1, an excessive photocurrent flows at the moment when an excessive optical signal is input, and the photoelectric conversion element is damaged, or because of a transient response due to a voltage drop resistor, In order to prevent a time delay from occurring until the reverse bias voltage required for the input signal is restored, detection means for detecting a reception signal corresponding to the level of the optical input signal, and the detection signal is the reception signal. Control means for applying the reverse bias voltage to the photoelectric conversion element without passing through the voltage drop resistor when the end of the signal is detected.

  However, this prior art relates to the characteristic deterioration of the photoelectric conversion element that occurs when an excessive optical signal is input to the photoelectric conversion element, and in order to improve the characteristic deterioration, a high reverse bias voltage is applied during a period when there is no optical input signal. Although it is applied to the photoelectric conversion element, it does not improve the characteristics of the photoelectric conversion element by continuously changing the reverse bias voltage. .

  In the prior art disclosed in Patent Document 2, in the multistage optical amplifier, the gain of the first-stage optical amplifier is made larger than the gain of the other-stage optical amplifier, thereby reducing the signal component reduced by the spontaneous emission light in the first-stage optical amplifier. The noise is increased by the amplifier to relatively reduce the noise, whereby the obtained signal with a high signal-to-noise ratio is maintained by an optical amplifier at another stage, and an optical output signal with a high signal-to-noise ratio is obtained. However, since the characteristics of the light receiving element (photoelectric conversion element) are not improved by continuously changing the reverse bias voltage, the above-described problems in the conventional optical amplifying apparatus cannot be solved.

  The present invention has been made to solve the above-described problems. When the input light level is low, the input light monitor accuracy is improved while suppressing a decrease in response speed, and when the input light level is high. An object of the present invention is to provide an optical amplifying device, a control method, and a control program capable of improving the response speed while suppressing the deterioration of the input light monitoring accuracy, and thereby reliably detecting the input light break.

  The present invention is an optical amplifying device having optical amplifying means for amplifying input light and outputting light of a desired level, wherein a reverse bias voltage of a photoelectric conversion element for detecting the input light level is applied to the input light. When the input light level is low by controlling the reverse bias voltage so as to achieve both improvement in input light monitoring accuracy when the input light level is low and high-speed response when the input light level is high An optical amplifying apparatus comprising control means for controlling the gain of the optical amplifying means based on an electric signal from the photoelectric conversion element.

  The present invention also relates to a method for controlling an optical amplifying apparatus having an optical amplifying means for amplifying input light and outputting light of a desired level, wherein a reverse bias of a photoelectric conversion element for detecting the input light level is provided. Changing the voltage according to the input light level, controlling the reverse bias voltage so as to achieve both improvement of input light monitor accuracy when the input light level is low and high-speed response when the input light level is high, A control method for an optical amplifying device, wherein the gain of the optical amplifying means is controlled based on an electrical signal from a photoelectric conversion element.

  The present invention also provides a control program for controlling an optical amplifying device having an optical amplifying means for amplifying input light and outputting light of a desired level, and photoelectric conversion for detecting the input light level The reverse bias voltage of the element is changed according to the input light level, and the reverse bias voltage is set so as to achieve both improvement in input light monitoring accuracy when the input light level is low and high-speed response when the input light level is high. A control program for controlling and causing a computer to execute control in order to control the gain of the optical amplification means based on an electric signal from the photoelectric conversion element.

  According to the present invention, the input light is controlled by controlling the reverse bias voltage of the photoelectric conversion element so as to achieve both improvement in input light monitoring accuracy when the input light level is low and high-speed response when the input light level is high. When the level is low, the input light monitor accuracy can be improved while suppressing a decrease in response speed, and when the input light level is high, the response speed can be improved while suppressing a decrease in input light monitor accuracy. In this way, the effect of reliably detecting the input light break can be obtained.

It is a block diagram which shows the structure of the optical amplifier by one Embodiment of this invention. It is explanatory drawing which showed in a graph the relationship between the reverse bias voltage of a photodiode, dark current, and the capacity | capacitance between terminals. It is explanatory drawing which showed in a graph the relationship between the input light level for every reverse bias voltage of a photodiode, and an input light monitor. It is explanatory drawing which showed in a graph the relationship between the response frequency for every reverse bias of a photodiode, and a gain (photoelectric conversion current). It is a block diagram which shows the structure of the optical amplifier by other embodiment. It is a block diagram which shows the structure of the conventional optical amplifier.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the optical amplifying device according to the present embodiment. In FIG. 1, components corresponding to those shown in FIG. This optical amplifying device changes the reverse bias voltage of the photoelectric conversion element for detecting the input light level according to the input light level, and improves the input light monitoring accuracy when the input light level is low, and the input light level is Control means for controlling the reverse bias voltage so as to achieve both high-speed response when high and controlling the gain of the optical amplification means based on an electric signal from the photoelectric conversion element when the input light level is low It is characterized by having.

  In FIG. 1, this optical amplifying device includes an input port 1 for inputting an optical signal, an optical branching device 2 for branching an input optical signal transmitted from the input port 1, and light partially branched by an optical branching device 2. A photodiode 3 as a photoelectric conversion element that converts a signal into an electric signal, a reverse bias circuit 4a that applies a reverse bias voltage to the photodiode 3, and a log amplifier 5 that performs logarithmic conversion of the electric signal output from the photodiode 3 are provided. Yes.

  The optical amplifying apparatus includes an EDFA 6 as an optical amplifying means for optically amplifying the input optical signal transmitted from the optical splitter 2, an optical splitter 7 for splitting the optical signal amplified by the EDFA 6, and an optical splitter. 7 is an output port 8 that outputs an optical signal transmitted from 7, a photodiode 9 as a photoelectric conversion element that converts an optical signal partially branched by the optical splitter 7 into an electrical signal, and a reverse bias voltage across the photodiode 9. The reverse bias circuit 10 for providing the log signal, the log amplifier 11 for logarithmically converting the electric signal output from the photodiode 9, and the electric signal output from the log amplifier 5 and the electric signal output from the log amplifier 11 increase the gain of the EDFA 6. A DSP (Digital Signal Processor) 12a is provided as control means for controlling.

  The DSP 12a changes the reverse bias voltage of the photodiode 3 for detecting the input light level in accordance with the input light level, and controls the gain of the EDFA 6 based on the electrical signal from the photodiode 3 (not shown) Is stored in a memory (not shown), the input light level is less than a predetermined level, no fast response measures are required, and the detection accuracy needs to be improved, the reverse bias voltage If the input light level is equal to or higher than the predetermined light level and high-speed response measures are required, the computer is caused to execute control to increase the reverse bias voltage according to the input light level. Is.

  Next, the operation of this optical amplifying device will be described. In FIG. 1, an input port 1 inputs an optical signal from the outside of the optical amplification device. The optical branching device 2 branches the input optical signal transmitted from the input port 1 to the EDFA 6 and the photodiode 3 on the optical input monitor side with a predetermined branching ratio. The reverse bias circuit 4a applies a reverse bias voltage set based on the reverse bias control signal from the DSP 12a to the photodiode 3. The photodiode 3 converts a part of the input optical signal transmitted from the optical branching device 2 into an electric signal according to the applied reverse bias voltage. The log amplifier 5 performs logarithmic conversion on the electrical signal transmitted from the photodiode 3, and transmits a logarithmic conversion signal to the DSP 12a. The DSP 12 a controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5. The EDFA 6 directly amplifies the input optical signal transmitted from the optical branching device 2 in accordance with an electric signal having a gain controlled by the DSP 12a.

  The optical branching device 7 branches the optical signal optically amplified by the EDFA 6 to the output port 8 and the photodiode 9 on the optical output monitor side at a predetermined branching ratio. Most of the branched optical signal is transmitted from the output port 8, and a part of the optical signal is transmitted to the photodiode 9. The reverse bias circuit 10 applies a predetermined reverse bias voltage to the photodiode 9. The photodiode 9 converts a part of the input optical signal transmitted from the optical branching device 7 into an electric signal according to the applied reverse bias voltage. The log amplifier 11 performs logarithmic conversion on the electrical signal transmitted from the photodiode 9, and transmits a logarithmic conversion signal to the DSP 12a. The DSP 12 a controls the gain of the EDFA 6 with reference to the logarithmic conversion signal from the log amplifier 11. That is, the DSP 12 a controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5 and the logarithmic conversion signal from the log amplifier 11.

  Specifically, the DSP 12a monitors the input light level (input monitor level), and when the input light level is less than a predetermined level, the reverse bias voltage of the photodiode 3 is lowered according to the input light level at this time, and the input light When the level is equal to or higher than a predetermined level, a reverse bias control signal for increasing the reverse bias voltage of the photodiode 3 according to the input light level at this time is calculated and transmitted to the reverse bias circuit 4a, or obtained in advance and not shown. A reverse bias control signal determined by the correlation between the input light level stored in the memory and the reverse bias voltage is transmitted to the reverse bias circuit 4a. That is, the DSP 12a changes the reverse bias voltage of the photodiode 3 for detecting the input light level according to the input light level, and controls the gain of the EDFA 6 based on the electric signal from the photodiode 3. If the level is less than the specified level, fast response measures are not required, and detection accuracy needs to be improved (in the range where input light monitoring accuracy is important), the reverse bias voltage should be lowered according to the input light level. When the input light level is equal to or higher than a predetermined level and a high-speed response measure is necessary (in a range where high-speed response is important), the reverse bias voltage is increased according to the input light level.

  FIG. 2 is an explanatory diagram illustrating the relationship among the reverse bias voltage, dark current, and inter-terminal capacitance of the photodiode in the embodiment. In FIG. 2, the horizontal axis represents the reverse bias voltage of the photodiode, and the vertical axis represents the inter-terminal capacitance and dark current of the photodiode. According to FIG. 2, as the reverse bias voltage increases, the dark current increases as indicated by line L1, while the inter-terminal capacitance decreases as indicated by line L2. For example, the dark current increases when the reverse bias voltage Vrb is applied compared to when the reverse bias voltage Vra is applied, and the inter-terminal capacitance is greater when the reverse bias voltage Vrb is applied than when the reverse bias voltage Vra is applied. The direction is decreasing. As can be seen from the above, the photodiode has a characteristic that when the dark current increases, the input light monitoring accuracy deteriorates, and when the inter-terminal capacitance increases, the response frequency decreases.

  FIG. 3 is an explanatory diagram illustrating the relationship between the input light level and the input light monitor for each reverse bias voltage of the photodiode in the embodiment. In FIG. 3, a broken line L3 of necessary monitor accuracy indicates a limit of input light monitor accuracy necessary as an optical amplifying apparatus. For example, when the reverse bias voltage is fixed at Vrb, when the input light level decreases and reaches X1, the limit of the input light monitoring accuracy is reached.

  On the other hand, when the reverse bias voltage is set to Vra (<Vrb), the input light monitor range is extended to X2. Therefore, when the input light level is reduced to a range where the input monitor accuracy is important (a range where the input light level is less than X1), the reverse bias voltage is changed stepwise or continuously from Vrb to Vra, so that the input light The line L4 indicating the input light monitor with respect to the level changes from the vicinity of the input light level X0 from the line L5 to the line L6, and in the extended monitor range, the line L6 falls below the required monitor accuracy indicated by the line L3. The accuracy of the optical monitor can be improved.

  FIG. 4 is an explanatory diagram showing, in a graph, the relationship between the response frequency and gain (photoelectric conversion current) for each reverse bias of the photodiode in the embodiment. In FIG. 4, a line L7 shows the relationship between the response frequency and the gain when the reverse bias voltage of the photodiode is Vrb. Line L8 shows the relationship between the response frequency and the gain when the reverse bias voltage of the photodiode is Vra. fca is a minimum response frequency necessary for low input monitoring when the input light level is lower than the input light level X1, for example, as shown in FIG. fcb is a response frequency that is at least required as a high-speed response when the input light level is equal to or higher than the input light level X1 as shown in FIG. 3, for example.

  A cut-off frequency equal to or higher than fcb is required at an input light level where a high-speed response is important (see FIG. 3). Further, in the range where the input monitor accuracy is important (see FIG. 3), it is only necessary to have a cutoff frequency equal to or higher than fca. Therefore, when the input level rises to a range where a high-speed response is important, a high-speed response can be realized by changing the reverse bias stepwise or continuously from Vra to Vrb.

  Next, the operation of the optical amplifying device shown in FIG. 1 will be described with reference to FIGS. The input optical signal input from the input port 1 is branched by the optical branching device 2 into the direction of the EDFA 6 and the direction of the photodiode 3 at a predetermined branching ratio. The reverse bias circuit 4a applies a reverse bias voltage set based on the reverse bias control signal from the DSP 12a to the photodiode 3. For example, when the DSP 12a detects that the input light level is less than X1 (see FIG. 3) with the reverse bias voltage set to Vrb, the DSP 12a controls the reverse bias circuit 4a to control the photodiode 3 Is set to Vra, for example (see FIG. 2).

  As a result, when the input light level of the input optical signal to the input port 1 is low, that is, the input light level is less than a predetermined level, no high-speed response measure is required, and the input light detection accuracy needs to be improved. In some cases (in the range where input monitor accuracy is important (see Fig. 3)), the reverse bias voltage is lowered, so the dark current decreases (see Fig. 2), and the minimum response frequency required for low input monitoring Therefore, the input light monitoring accuracy can be improved while suppressing a decrease in the response speed, and therefore the input light breakage detection can be reliably performed. When the reverse bias voltage is lowered from Vrb to Vra, the capacitance between the terminals of the photodiode 3 increases (see FIG. 2), but the input light level is low and the photoelectric conversion current is small, so the charge / discharge time constant is As a result, a decrease in response speed is also suppressed, so that there is no problem in input light monitoring accuracy and responsiveness.

  Next, for example, when the DSP 12a detects that the input light level is X1 or more (see FIG. 3) with the reverse bias voltage set to Vra, the DSP 12a controls the reverse bias circuit 4a. The reverse bias voltage of the photodiode 3 is set to, for example, Vrb (see FIG. 2).

  As a result, when the input light level of the input optical signal to the input port 1 is high, that is, when the input light level is equal to or higher than a predetermined level and a high-speed response measure is required (high-speed response is important). In the range (see FIG. 3), since the reverse bias voltage is increased, the capacitance between the terminals of the photodiode 3 is reduced, and the minimum response frequency required for high-speed response is also increased (see FIG. 4). The response speed can be improved while suppressing the deterioration of the input light monitoring accuracy, and the input light break detection can be reliably performed. When the reverse bias voltage is increased from Vra to Vrb, the dark current of the photodiode 3 increases (see FIG. 2), but the input light level is high and the photoelectric conversion current is large, but the capacitance between the terminals is small. The charging / discharging time constant is greatly increased, thereby suppressing a decrease in response speed, so that there is no problem in input light monitoring accuracy and responsiveness.

  FIG. 5 is a block diagram showing a configuration of an optical amplifying device according to another embodiment. In FIG. 5, components corresponding to those shown in FIG.

  In FIG. 5, this optical amplifying device includes an input port 1 for inputting an optical signal, an optical branching device 2 for branching an input optical signal transmitted from the input port 1, and light partially branched by the optical branching device 2. A photodiode 3 as a photoelectric conversion element that converts a signal into an electric signal, a reverse bias circuit 4a that applies a reverse bias voltage to the photodiode 3, and a log amplifier 5 that performs logarithmic conversion of the electric signal output from the photodiode 3 are provided. Yes.

  The optical amplifying apparatus includes an EDFA 6 as an optical amplifying means for optically amplifying the input optical signal transmitted from the optical splitter 2, an optical splitter 7 for splitting the optical signal amplified by the EDFA 6, and an optical splitter. 7 is an output port 8 that outputs an optical signal transmitted from 7, a photodiode 9 as a photoelectric conversion element that converts an optical signal partially branched by the optical splitter 7 into an electrical signal, and a reverse bias voltage across the photodiode 9. The reverse bias circuit 10 for supplying the signal, the log amplifier 11 for logarithmically converting the electrical signal output from the photodiode 9, the electrical signal output from the log amplifier 5 and the electrical signal output from the log amplifier 11 are used to control the gain of the EDFA 6. The control circuit 13 serving as the control means for performing the calculation and the electric signal output from the log amplifier 5 are calculated and transmitted to the reverse bias circuit 4a to transmit the reverse bias voltage. And a analog control circuit 14 for controlling.

  The analog control circuit 14 changes the reverse bias voltage of the photodiode 3 for detecting the input light level according to the input light level, the input light level is less than a predetermined level, and no fast response measures are required. When the detection accuracy needs to be improved, the reverse bias voltage is lowered according to the input light level. When the input light level is equal to or higher than the predetermined level and a fast response measure is required, the reverse bias voltage is reduced. Is controlled in accordance with the input light level.

  Next, the operation of this optical amplifying device will be described. In FIG. 5, an input port 1 inputs an optical signal from the outside of the optical amplification device. The optical branching device 2 branches the input optical signal transmitted from the input port 1 to the EDFA 6 and the photodiode 3 on the optical input monitor side with a predetermined branching ratio. The reverse bias circuit 4 a applies a reverse bias voltage set based on the reverse bias control signal from the analog control circuit 14 to the photodiode 3. The photodiode 3 converts a part of the input optical signal transmitted from the optical branching device 2 into an electric signal according to the applied reverse bias voltage. The log amplifier 5 logarithmically converts the electrical signal transmitted from the photodiode 3 and transmits the logarithmic conversion signal to the control circuit 13 and the analog control circuit 14. The control circuit 13 controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5. The EDFA 6 directly amplifies the input optical signal transmitted from the optical branching device 2 in accordance with an electric signal having a gain controlled by the DSP 12a. The analog control circuit 14 calculates a logarithmic conversion signal from the log amplifier 5 and transmits it to the reverse bias circuit 4 a to control the reverse bias voltage of the photodiode 3.

  The optical branching device 7 branches the optical signal optically amplified by the EDFA 6 to the output port 8 and the photodiode 9 on the optical output monitor side at a predetermined branching ratio. Most of the branched optical signal is transmitted from the output port 8, and a part of the optical signal is transmitted to the photodiode 9. The reverse bias circuit 10 applies a predetermined reverse bias voltage to the photodiode 9. The photodiode 9 converts a part of the input optical signal transmitted from the optical branching device 7 into an electric signal according to the applied reverse bias voltage. The log amplifier 11 performs logarithmic conversion on the electrical signal transmitted from the photodiode 9 and transmits a logarithmic conversion signal to the control circuit 13. The control circuit 13 also controls the gain of the EDFA 6 with reference to the logarithmic conversion signal from the log amplifier 11. That is, the control circuit 13 controls the gain of the EDFA 6 according to the logarithmic conversion signal from the log amplifier 5 and the logarithmic conversion signal from the log amplifier 11.

  Next, the operation of the optical amplifying device shown in FIG. 5 will be described with reference to FIGS. The input optical signal input from the input port 1 is branched by the optical branching device 2 into the direction of the EDFA 6 and the direction of the photodiode 3 at a predetermined branching ratio. The reverse bias circuit 4 a applies a reverse bias voltage set based on the reverse bias control signal from the analog control circuit 14 to the photodiode 3. For example, when the analog control circuit 14 detects that the input light level is less than X1 (see FIG. 3) while the reverse bias voltage is set to Vrb, the analog control circuit 14 causes the reverse bias circuit 4a to operate. By controlling, the reverse bias voltage of the photodiode 3 is set to Vra, for example (see FIG. 2).

  As a result, when the input light level of the input optical signal to the input port 1 is low, that is, the input light level is less than a predetermined level, no high-speed response measures are required, and the optical signal detection accuracy needs to be improved. In some cases (in the range where input monitor accuracy is important (see Fig. 3)), the reverse bias voltage is lowered, so the dark current decreases (see Fig. 2), and the minimum response frequency required for low input monitoring Therefore, the input light monitoring accuracy can be improved while suppressing a decrease in the response speed, and therefore the input light breakage detection can be reliably performed.

  Next, for example, when the analog control circuit 14 detects that the input light level is X1 or more (see FIG. 3) in a state where the reverse bias voltage is set to Vra, the analog control circuit 14 The circuit 4a is controlled to set the reverse bias voltage of the photodiode 3 to, for example, Vrb (see FIG. 2).

  As a result, when the input light level of the input optical signal to the input port 1 is high, that is, when the input light level is equal to or higher than a predetermined level and a high-speed response measure is required (high-speed response is important). In the range (see FIG. 3), since the reverse bias voltage is increased, the capacitance between the terminals of the photodiode 3 is reduced, and the minimum response frequency required for high-speed response is also increased (see FIG. 4). The response speed can be improved while suppressing the deterioration of the input light monitoring accuracy, and the input light break detection can be reliably performed.

  The present invention can be applied to an optical amplifying apparatus that amplifies an optical signal in optical fiber communication.

3 Photodiode (photoelectric conversion element)
6 EDFA (light amplification means)
12a DSP (control means)
13 Control circuit (control means)
14 Anagro control circuit (control means)

Claims (8)

An optical amplifying device having optical amplifying means for amplifying input light and outputting light of a desired level,
The reverse bias voltage of the photoelectric conversion element for detecting the input light level is changed according to the input light level, the input light monitor accuracy is improved when the input light level is low, and the high-speed response when the input light level is high An optical amplifying apparatus comprising: control means for controlling the reverse bias voltage so as to satisfy both requirements and controlling the gain of the optical amplifying means based on an electric signal from the photoelectric conversion element.   The control means, when the input light level is less than a predetermined level, fast response measures are unnecessary, and when improvement in detection accuracy is required, the reverse bias voltage is lowered according to the input light level, 2. The optical amplifying apparatus according to claim 1, wherein the reverse bias voltage is increased according to the input light level when the input light level is equal to or higher than a predetermined level and high-speed response measures are required. .  2. The optical amplification device according to claim 1, wherein a rare earth-doped optical fiber amplifier is used as the optical amplification means.   4. The optical amplifying apparatus according to claim 3, wherein an erbium-doped optical fiber amplifier is used as the rare earth-doped optical fiber amplifier. A method for controlling an optical amplifying apparatus having optical amplifying means for amplifying input light and outputting light of a desired level,
The reverse bias voltage of the photoelectric conversion element for detecting the input light level is changed according to the input light level, the input light monitor accuracy is improved when the input light level is low, and the high-speed response when the input light level is high A control method of the optical amplifying device, wherein the reverse bias voltage is controlled so as to satisfy both requirements and the gain of the optical amplifying means is controlled based on an electric signal from the photoelectric conversion element.   When the input light level is less than a predetermined level, fast response measures are unnecessary, and improvement in detection accuracy is required, the reverse bias voltage is lowered according to the input light level, and the input light level is 6. The control of an optical amplifying apparatus according to claim 5, wherein when the response level is equal to or higher than a predetermined level and a high-speed response measure is required, the reverse bias voltage is controlled to be increased according to the input light level. Method. A control program for controlling an optical amplifying device having optical amplifying means for amplifying input light and outputting light of a desired level,
The reverse bias voltage of the photoelectric conversion element for detecting the input light level is changed according to the input light level, the input light monitor accuracy is improved when the input light level is low, and the high-speed response when the input light level is high A control program for causing a computer to execute the control so as to control the reverse bias voltage so as to satisfy both requirements and to control the gain of the optical amplifying means based on an electric signal from the photoelectric conversion element.   When the input light level is less than a predetermined level, fast response measures are unnecessary, and improvement in detection accuracy is required, the reverse bias voltage is lowered according to the input light level, and the input light level is 8. The control program according to claim 7, which causes a computer to execute control to increase the reverse bias voltage according to the input light level when a response level is higher than a predetermined level and a high-speed response measure is necessary.

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