Excitation light generation circuit, method for redundancy of excitation light generation circuit, and optical amplifier

Abstract

To provide an excitation light generation circuit that ensures robustness against failure of the constant current circuit, a redundancy method for the excitation light generation circuit, and an optical amplifier. [Solution] The excitation light generation circuit according to the present disclosure includes an excitation light source that outputs excitation light, a constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, and a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, wherein if current stops flowing through the constant current circuit, current flows through the current maintenance circuit to maintain the output of excitation light from the excitation light source.

Description

【Technical Field】 【0001】 The present disclosure relates to an excitation light generation circuit, a redundancy method for an excitation light generation circuit, and an optical amplifier. 【Background Art】 【0002】 Patent Document 1 discloses an optical amplifier capable of maintaining the level of excitation light without increasing the supply current amount when the active excitation laser diode deteriorates. 【0003】 The optical amplifier disclosed in Patent Document 1 includes a main excitation light source and a standby excitation light source. Therefore, even when the main excitation light source deteriorates or fails, the level of excitation light can be maintained by operating the standby excitation light source. It is an optical amplifier that can do this. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 International Publication No. 2014-141684 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, since all the excitation light sources disclosed in Patent Document 1 are controlled by the same control circuit, when the control circuit that controls the excitation light sources fails, both the main excitation light source and the standby excitation light source stop operating, and optical amplification of the excitation light cannot be maintained. 【0006】 The present disclosure has been made in view of the above circumstances, and provides an excitation light generation circuit, a redundancy method for an excitation light generation circuit, and an optical amplifier that ensure robustness against failures of a constant current circuit. 【Means for Solving the Problems】 【0007】 The excitation light generation circuit according to one aspect of the present disclosure is An excitation light source that outputs excitation light in response to the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An excitation light generation circuit, comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, current flows through the current maintenance circuit to maintain the output of excitation light from the excitation light source. 【0008】 A redundancy method for an excitation light generation circuit according to one aspect of this disclosure is: A redundant method for an excitation light generation circuit, comprising an excitation light source that outputs excitation light in accordance with the flowing current, and a constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, A current maintenance circuit is provided, which is connected in series with the excitation light source and in parallel with the constant current circuit. If current stops flowing through the constant current circuit, the output of the excitation light from the excitation light source is maintained by supplying current to the current maintenance circuit. 【0009】 An optical amplifier according to one aspect of this disclosure is An excitation light generation circuit that generates excitation light, An optical amplifier comprising an optical amplification fiber connected to an excitation light generation circuit for amplifying the excitation light, The excitation light generation circuit is, An excitation light source that outputs the excitation light in accordance with the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An optical amplifier comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, current flows through the current maintenance circuit to maintain the output of excitation light from the excitation light source. [Effects of the Invention] 【0010】 According to the present disclosure, it is possible to provide an excitation light generation circuit having high robustness against failures of a constant current circuit, a redundancy method for the excitation light generation circuit, and an optical amplifier. 【Brief Description of Drawings】 【0011】 [Figure 1] It is a block diagram showing a configuration example of an excitation light generation circuit according to the present disclosure. [Figure 2] It is a circuit diagram showing a configuration example of an excitation light generation circuit according to the present disclosure. [Figure 3] It is a circuit diagram showing a configuration example of an excitation light generation circuit according to the present disclosure. [Figure 4] It is a circuit diagram showing a configuration example of an excitation light generation circuit according to the present disclosure. [Figure 5] It is a block diagram showing a configuration example of an optical amplifier according to the present disclosure. 【Embodiments for Carrying Out the Invention】 【0012】 Hereinafter, referring to the drawings, details of an excitation light generation circuit according to an embodiment of the present disclosure will be described. In the description of the drawings, the same reference numerals are assigned to the same elements, and redundant descriptions will be omitted as appropriate. 【0013】 <First Embodiment> FIG. 1 is a block diagram showing a configuration example of an excitation light generation circuit according to the present disclosure. The excitation light generation circuit shown in FIG. 1 includes an excitation light source 1, a constant current circuit 2, and a current maintaining circuit 3. 【0014】 The excitation light source 1 outputs excitation light having a predetermined wavelength. The excitation light source 1 includes, for example, a laser diode, a photodiode, etc., but is not limited thereto. For example, when outputting excitation light incident on an erbium-doped fiber (EDF), the wavelength of the excitation light output by the excitation light source is in the 0.98 μm band or the 1.48 μm band. Also, the number of excitation light sources is not limited, and a plurality of excitation light sources may be connected in series or in parallel. 【0015】 The constant current circuit 2 is connected in series with the excitation light source 1 and controls the current flowing through the excitation light source 1 to a predetermined value. The constant current circuit 2 includes, for example, an integrated circuit (IC), a transistor, a resistor, etc., but is not limited thereto. 【0016】 The current maintaining circuit 3 is connected in series with the excitation light source 1 and also connected in parallel with the constant current circuit 2. Since the excitation light generation circuit shown in FIG. 1 includes the current maintaining circuit 3, for example, even when the current does not flow through the constant current circuit 2 due to a failure of the constant current circuit 2 or the like, the output of the excitation light by the excitation light source 1 can be maintained by the current flowing through the current maintaining circuit 3. The current maintaining circuit 3 includes, for example, a resistor, a switch, an integrated circuit, a transistor, etc., but is not limited thereto, and a plurality of these components may be included, and the plurality of components may be connected in series or in parallel. Also, the current maintaining circuit 3 may be a constant current circuit. 【0017】 In the excitation light generation circuit according to the present disclosure, even when the current does not flow through the constant current circuit, the output of the excitation light can be maintained by the current flowing through the current maintaining circuit. Therefore, robustness against failures of the constant current circuit can be ensured. 【0018】 <Second Embodiment> FIG. 2 is a circuit diagram showing a configuration example of the excitation light generation circuit according to the present disclosure. The excitation light generation circuit shown in FIG. 2 includes a Zener diode ZD, voltage dividing resistors R1, R2, and a current monitoring resistor Rmon in addition to the excitation light source 1, the constant current circuit 2, and the current maintaining circuit 3 shown in FIG. 1. That is, the excitation light generation circuit shown in FIG. 2 is an example in which the excitation light generation circuit shown in FIG. 1 is more具体化. As shown in FIG. 2, the excitation light source 1 includes laser diodes LD1, LD2. The constant current circuit 2 is, for example, an automatic current control (ACC) circuit and includes an integrated circuit IC1 and a bipolar transistor BT1. The current maintaining circuit 3 includes a current maintaining resistor Rmai. Note that a field effect transistor may be used instead of the bipolar transistor BT1. 【0019】 In the excitation light source 1, laser diodes LD1 and LD2 are connected in series. More specifically, the cathode of laser diode LD1 is connected to the anode of laser diode LD2. The anode of laser diode LD1 is connected to the second terminal of the current monitoring resistor Rmon. On the other hand, the cathode of laser diode LD2 is connected to the first terminal of the current maintenance resistor Rmai, and also to the collector of the bipolar transistor BT1 of the constant current circuit 2. Here, the current maintenance resistor Rmai and the bipolar transistor BT1 are connected in parallel. The excitation light source 1 may consist of one or three or more laser diodes. Furthermore, the laser diodes LD1 and LD2 in the excitation light source 1 may be connected in parallel. 【0020】 In constant current circuit 2, the collector of bipolar transistor BT1 is connected to the cathode of laser diode LD2 and the first terminal of current-maintaining resistor Rmai, as described above. On the other hand, the emitter of bipolar transistor BT1 is connected to the second terminal of current-maintaining resistor Rmai, the first terminal of voltage divider resistor R2, and the anode of Zener diode ZD. The base of bipolar transistor BT1 is connected to the output terminal of integrated circuit IC1. 【0021】 In the constant current circuit 2, the first input terminal of the integrated circuit IC1 is connected to the connection node between voltage divider resistors R2 and R1. The second input terminal of the integrated circuit IC1 is connected to the connection node between current monitoring resistor Rmon and laser diode LD1. 【0022】 In other words, the integrated circuit IC1 performs feedback control to ensure that the current I11 flowing through the bipolar transistor BT1 is at a predetermined value, based on the voltage at the connection node of the voltage divider resistors R1 and R2 (reference voltage Vref) and the voltage at the connection node of the current monitoring resistor Rmon and the laser diode LD1 (current monitoring voltage Vmon). As a result, the current I1 flowing through the laser diodes LD1 and LD2 is kept constant. 【0023】 In the current maintenance circuit 3, the first terminal of the current maintenance resistor Rmai is connected to the cathode of the laser diode LD2 and the collector of the bipolar transistor BT1. On the other hand, the second terminal of the current maintenance resistor Rmai is connected to the emitter of the bipolar transistor BT1, the first terminal of the voltage divider resistor R2, and the anode of the Zener diode ZD. 【0024】 The current-maintaining resistor Rmai is connected in parallel with the constant-current circuit 2. Therefore, even if the current I11 becomes 0 due to a failure of the constant-current circuit 2, the output of the excitation light from the laser diodes LD1 and LD2 can be maintained by the current I12 flowing through the current-maintaining resistor Rmai. 【0025】 Here, the current maintenance resistor Rmai has an upper resistance value such that when the current I11 becomes 0, the current I12 exceeds the oscillation threshold of the laser diodes LD1 and LD2. On the other hand, in the excitation light generation circuit shown in Figure 2, the current I12 continues to flow through the current maintenance resistor Rmai even while the constant current circuit 2 is operating normally. 【0026】 The anode of the Zener diode ZD is connected to the second terminal of the current-maintaining resistor Rmai, the emitter of the bipolar transistor BT1, and the voltage divider resistor R2. On the other hand, the cathode of the Zener diode ZD is connected to the second terminal of the voltage divider resistor R1 and the first terminal of the current-monitoring resistor Rmon. The Zener diode ZD generates the voltage necessary for the excitation light source 1 to output excitation light from the supplied current (not shown). 【0027】 The first terminal of voltage divider resistor R1 is connected to the second terminal of voltage divider resistor R2. The second terminal of voltage divider resistor R1 is also connected to the cathode of Zener diode ZD and the first terminal of current monitoring resistor Rmon. The first terminal of voltage divider resistor R2 is connected to the second terminal of current maintaining resistor Rmai, the emitter of bipolar transistor BT1, and the anode of Zener diode ZD. Furthermore, the second terminal of voltage divider resistor R2 is connected to the first terminal of voltage divider resistor R1. The voltage divider resistors R1 and R2 generate a reference voltage Vref, which is input to the first input terminal of the integrated circuit IC1, in order to provide feedback control to the current I1 flowing through the laser diodes LD1 and LD2. 【0028】 The first terminal of the current monitoring resistor Rmon is connected to the cathode of the Zener diode ZD and the second terminal of the voltage divider resistor R1. The second terminal of the current monitoring resistor Rmon is also connected to the anode of the laser diode LD1. The current monitoring resistor Rmon generates a current monitoring voltage Vmon, which is input to the second input terminal of the integrated circuit IC1, in order to provide feedback control of the current I1 flowing through the laser diodes LD1 and LD2. 【0029】 In the excitation light generation circuit described herein, even if current stops flowing through the constant current circuit, the output of the excitation light can be maintained by current flowing through the current maintenance circuit. Therefore, robustness against failure of the constant current circuit can be ensured. 【0030】 <Third Embodiment> Figure 3 is a circuit diagram showing one example configuration of an excitation light generation circuit according to this disclosure. The excitation light generation circuit shown in Figure 3 includes an excitation light source 1, a constant current circuit 2, a current maintenance circuit 3, a Zener diode ZD, voltage divider resistors R1 and R2, and a current monitoring resistor Rmon, similar to the excitation light generation circuit shown in Figure 2. Here, the current maintenance circuit 3 shown in Figure 3 includes a switch SW in addition to the current maintenance resistor Rmai shown in Figure 2. 【0031】 In the current maintenance circuit 3, the first terminal of switch SW is connected to the cathode of laser diode LD2 and the collector of bipolar transistor BT1. The second terminal of switch SW is connected to the first terminal of current maintenance resistor Rmai. In other words, the switch SW and current maintenance resistor Rmai, which are connected in series, are connected in parallel with the bipolar transistor BT1. 【0032】 In Figure 3, the switch SW is located upstream of the current-maintaining resistor Rmai, but the switch SW may also be located downstream of the current-maintaining resistor Rmai. Furthermore, a switch SW may be provided at the branch node of the constant current circuit 2 and the current maintenance circuit 3. That is, under normal conditions, the second terminal of the switch SW may be connected to the constant current circuit 2, and in the event of an abnormality such as a failure of the constant current circuit 2, the second terminal of the switch SW may be connected to the current maintenance resistor Rmai. 【0033】 Furthermore, the voltage at the connection node between the current monitoring resistor Rmon and the laser diode LD1, i.e., the current monitoring voltage Vmon, is input to the switch SW as a control signal. Based on the input current monitoring voltage Vmon, the switch SW determines whether or not current I1 is flowing through the laser diodes LD1 and LD2, thereby determining a failure in the constant current circuit 2. The switch SW is OFF while the constant current circuit 2 is operating normally and current I1 is flowing through the laser diodes LD1 and LD2. On the other hand, if the constant current circuit 2 fails and the switch SW detects that the current I11 has become 0, it switches from OFF to ON. With this configuration, if the constant current circuit 2 fails, current I12 is supplied to the current maintenance circuit 3 to maintain current I1. However, the control signal of the switch SW is not limited to the current monitoring voltage Vmon; for example, the excitation light output of the laser diodes LD1 and LD2 may also be used. 【0034】 In the current maintenance circuit 3, the first terminal of the current maintenance resistor Rmai is connected to the second terminal of the switch SW. The second terminal of the current maintenance resistor Rmai is connected to the emitter of the bipolar transistor BT1, the first terminal of the voltage divider resistor R2, and the anode of the Zener diode ZD. 【0035】 Here, the current-maintaining resistor Rmai has an upper resistance value such that when the current I11 becomes 0, the current I12 exceeds the oscillation threshold of the laser diodes LD1 and LD2. On the other hand, in the excitation light generation circuit shown in Figure 3, the current I12 is 0 while the constant current circuit 2 is operating normally, so no power loss occurs due to the current I12 flowing through the current-maintaining resistor Rmai. For this reason, the lower resistance value of the current-maintaining resistor Rmai is not particularly limited. For example, even if the current I11 becomes 0 due to a failure of the constant current circuit 2, the resistance value of the current-maintaining resistor Rmai can be adjusted so that the current I1 becomes the same as the current under normal conditions. 【0036】 In the excitation light generation circuit described herein, even if current stops flowing through the constant current circuit, the output of the excitation light is maintained by current flowing through the current maintenance circuit. Therefore, robustness against failure of the constant current circuit can be ensured. Furthermore, since current flows through the current maintenance circuit only when current stops flowing through the constant current circuit, power loss due to the current flowing through the current maintenance circuit under normal conditions can be suppressed. In addition, even if current stops flowing through the constant current circuit, it is possible to supply the same current to the excitation light source as under normal conditions. 【0037】 <Fourth Embodiment> Figure 4 is a circuit diagram showing one example configuration of an excitation light generation circuit according to this disclosure. The excitation light generation circuit shown in Figure 4 includes an excitation light source 1, a constant current circuit 2, a current maintenance circuit 3, a Zener diode ZD, voltage divider resistors R1 and R2, and a current monitoring resistor Rmon, similar to the excitation light generation circuit shown in Figure 3. Here, the current maintenance circuit 3 shown in Figure 4 includes a switch SW and a constant current circuit 2a instead of the current maintenance resistor Rmai shown in Figure 3. 【0038】 In the current maintenance circuit 3, the collector of the bipolar transistor BT2 of the constant current circuit 2a is connected to the second terminal of the switch SW. The emitter of the bipolar transistor BT2 is connected to the emitter of the bipolar transistor BT1 of the constant current circuit 2, the first terminal of the voltage divider resistor R2, and the anode of the Zener diode ZD. In addition, the base of the bipolar transistor BT2 is connected to the output terminal of the integrated circuit IC2. In other words, the switch SW and the constant current circuit 2a, which are connected in series, are connected in parallel with the bipolar transistor BT1. 【0039】 In the current maintenance circuit 3, the first input terminal of the integrated circuit IC2 is connected to the connection node between the voltage divider resistor R2 and the voltage divider resistor R1. Furthermore, the second input terminal of the integrated circuit IC2 is connected to the connection node between the current monitoring resistor Rmon and the laser diode LD1. 【0040】 When the switch SW is turned ON and current I12 flows through constant current circuit 2a, it performs feedback control of the current I1 flowing through laser diodes LD1 and LD2, similar to constant current circuit 2. Note that the number of constant current circuits 2a is not limited to one, and multiple constant current circuits 2a may be provided within the current maintenance circuit 3. 【0041】 In Figure 4, a switch SW is provided upstream of the constant current circuit 2a, but the switch SW may also be provided downstream of the constant current circuit 2a. Furthermore, a switch SW may be provided at the branch node of the constant current circuit 2 and the current maintenance circuit 3. That is, under normal conditions, the second terminal of the switch SW may be connected to the constant current circuit 2, and in the event of an abnormality such as a failure of the constant current circuit 2, the second terminal of the switch SW may be connected to the constant current circuit 2a. 【0042】 In the excitation light generation circuit described herein, even if current stops flowing through the constant current circuit, the output of the excitation light is maintained by current flowing through the current maintenance circuit. Therefore, robustness against failure of the constant current circuit is ensured. Furthermore, even if current stops flowing through the constant current circuit, the backup constant current circuit acts as a current maintenance circuit to control the current, making it possible to feedback control the current flowing to the excitation light source in the same way as under normal conditions. 【0043】 <Fifth Embodiment> Figure 5 is a block diagram showing an example configuration of an optical amplifier according to this disclosure. The optical amplifier shown in Figure 5 includes an excitation light source 1, a constant current circuit 2, a current maintenance circuit 3, an optical coupler 4, and an optical amplification fiber 5. The optical amplifier according to this disclosure is not particularly limited, but is, for example, an optical amplifier in a long-distance transmission system such as an optical submarine cable system. An optical amplifier used in an optical submarine cable system can withstand long-term operation, for example, for several decades. 【0044】 The optical amplification fiber 5 amplifies the incident signal light with excitation light. The optical amplification fiber 5 is, for example, an optical fiber made of components such as SiO2, GeO2, TiO2, or Al2O3 with erbium added, but is not limited to this. Also, although the optical amplification fiber 5 is provided downstream of the optical coupler 4 in Figure 5, the optical amplification fiber 5 may also be provided upstream of the optical coupler 4. 【0045】 The signal light is incident on the optical amplification fiber 5 via the optical coupler 4. The excitation light output from the excitation light source 1 is also incident on the optical amplification fiber 5 via the optical coupler 4. The signal light incident on the optical amplification fiber 5 is amplified by the excitation light output from the excitation light source 1. 【0046】 Here, the optical amplifier shown in Figure 5 is equipped with a current maintenance circuit 3. Therefore, even if current stops flowing through the constant current circuit 2 due to a failure of the constant current circuit 2, for example, the output of the excitation light from the excitation light source 1 can be maintained by the current flowing through the current maintenance circuit 3. 【0047】 In the optical amplifier according to this disclosure, even if current stops flowing through the constant current circuit, current continues to flow through the current maintenance circuit, thereby maintaining the output of the excitation light incident on the optical amplification fiber. Therefore, an optical amplifier with robustness against failure of the constant current circuit can be provided. 【0048】 Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure are possible, as can be understood by those skilled in the art within the scope of the present disclosure. Each embodiment can be combined with other embodiments as appropriate. 【0049】 Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features described with reference to any one drawing can be combined with features shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features may be omitted. 【0050】 In summary, this disclosure provides an excitation light generation circuit that ensures robustness against failures of constant current circuits, a redundancy method for the excitation light generation circuit, and an optical amplifier. 【0051】 Some or all of the above embodiments may also be described as follows, but are not limited to the following: 【0052】 [Note 1] An excitation light source that outputs excitation light in response to the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An excitation light generation circuit, comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, the current maintenance circuit will maintain the output of the excitation light from the excitation light source by allowing current to flow through it. Excitation light generation circuit. 【0053】 [Note 2] The current maintenance circuit includes a resistor, The excitation light generation circuit described in Appendix 1. 【0054】 [Note 3] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The excitation light generation circuit described in Appendix 2. 【0055】 [Note 4] The current maintenance circuit includes a pre-constant current circuit and The said auxiliary constant current circuit includes a switch circuit connected in series with it, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The aforementioned pre-constant current circuit controls the current flowing to the excitation light source when current flows through the current maintenance circuit. The excitation light generation circuit described in Appendix 1. 【0056】 [Note 5] A redundant method for an excitation light generation circuit, comprising an excitation light source that outputs excitation light in accordance with the flowing current, and a constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, A current maintenance circuit is provided, which is connected in series with the excitation light source and in parallel with the constant current circuit. If current stops flowing through the constant current circuit, the output of the excitation light from the excitation light source is maintained by supplying current to the current maintenance circuit. A method for redundancy in the excitation light generation circuit. 【0057】 [Note 6] The current maintenance circuit includes a resistor, A method for redundancy of the excitation light generation circuit described in Appendix 5. 【0058】 [Note 7] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, thereby supplying current to the current maintenance circuit. A method for redundancy of the excitation light generation circuit described in Appendix 6. 【0059】 [Note 8] The current maintenance circuit includes a pre-constant current circuit and The said auxiliary constant current circuit includes a switch circuit connected in series with it, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The aforementioned pre-constant current circuit controls the current flowing to the excitation light source when current is supplied to the current maintenance circuit. A method for redundancy of the excitation light generation circuit described in Appendix 7. 【0060】 [Note 9] An excitation light generation circuit that generates excitation light, An optical amplifier comprising: an optical amplification fiber connected to an excitation light generation circuit and which amplifies the input signal light with the excitation light, The excitation light generation circuit is, An excitation light source that outputs the excitation light in accordance with the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An optical amplifier comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, the current maintenance circuit will maintain the output of the excitation light from the excitation light source by allowing current to flow through it. Optical amplifier. 【0061】 [Note 10] The current maintenance circuit includes a resistor, The optical amplifier described in Appendix 9. 【0062】 [Note 11] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The optical amplifier described in Appendix 10. 【0063】 [Note 12] The current maintenance circuit includes a pre-constant current circuit and The said auxiliary constant current circuit includes a switch circuit connected in series with it, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The aforementioned pre-constant current circuit controls the current flowing to the excitation light source when current flows through the current maintenance circuit. The optical amplifier described in Appendix 9. [Explanation of Symbols] 【0064】 1. Excitation light source 2, 2a constant current circuit 3 Current maintenance circuit 4 Optical coupler 5. Optical amplification fiber BT1, BT2 bipolar transistors IC1, IC2 Integrated Circuit LD1, LD2 excitation light source R1, R2 voltage divider resistors Rmai current maintenance resistor Rmon current monitoring resistor SW Switch ZD Zener diode

Claims

[Claim 1] An excitation light source that outputs excitation light in response to the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An excitation light generation circuit, comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, the current maintenance circuit will maintain the output of the excitation light from the excitation light source by allowing current to flow through it. Excitation light generation circuit. [Claim 2] The current maintenance circuit includes a resistor, The excitation light generation circuit according to claim 1. [Claim 3] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, allowing current to flow through the current maintenance circuit. The excitation light generation circuit according to claim 2. [Claim 4] The current maintenance circuit includes a pre-constant current circuit and The said auxiliary constant current circuit includes a switch circuit connected in series with it, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, and current flows through the current maintenance circuit. The aforementioned pre-constant current circuit controls the current flowing to the excitation light source when current flows through the current maintenance circuit. The excitation light generation circuit according to claim 1. [Claim 5] A redundant method for an excitation light generation circuit, comprising an excitation light source that outputs excitation light in accordance with the flowing current, and a constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, A current maintenance circuit is provided, which is connected in series with the excitation light source and in parallel with the constant current circuit. If current stops flowing through the constant current circuit, the output of the excitation light from the excitation light source is maintained by supplying current to the current maintenance circuit. A method for redundancy in the excitation light generation circuit. [Claim 6] The current maintenance circuit includes a resistor, A method for redundancy of the excitation light generation circuit according to claim 5. [Claim 7] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, thereby supplying current to the current maintenance circuit. A method for redundancy of the excitation light generation circuit according to claim 6. [Claim 8] An excitation light generation circuit that generates excitation light, An optical amplifier comprising: an optical amplification fiber connected to an excitation light generation circuit and which amplifies the input signal light with the excitation light, The excitation light generation circuit is, An excitation light source that outputs the excitation light in accordance with the flowing current, A constant current circuit connected in series with the excitation light source and controlling the current flowing through the excitation light source, An optical amplifier comprising a current maintenance circuit connected in series with the excitation light source and in parallel with the constant current circuit, If current stops flowing through the constant current circuit, the current maintenance circuit will maintain the output of the excitation light from the excitation light source by allowing current to flow through it. Optical amplifier. [Claim 9] The current maintenance circuit includes a resistor, The optical amplifier according to claim 8. [Claim 10] The current maintenance circuit further includes a switch circuit connected in series with the resistor, The switch circuit switches from OFF to ON when current stops flowing through the constant current circuit, allowing current to flow through the current maintenance circuit. The optical amplifier according to claim 9.

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