Optical amplifier and control method

Abstract

This optical amplifier (1) comprises an EDFA (13) that amplifies and outputs light, an excitation light source (16) that excites the EDFA (13), PDs (15, 18) that detect the intensity of the light, and a control unit (17) that controls the excitation light source (16). The control unit (17) acquires a correction value corresponding to a change in the photoelectric conversion efficiency of the PDs (15, 18) due to radiation, and controls the excitation of the EDFA (13) by using the excitation light source (16) on the basis of the intensity of the light detected by the PDs (15, 18) and corrected using the correction value.

Description

Optical amplifier and control method

[0001] The present disclosure relates to optical amplifiers and control methods.

[0002] Optical amplifiers are widely used in optical fiber communications, such as metro networks, core networks, and submarine optical cable systems. Optical amplifiers used in optical fiber communications are controlled so that output light does not fluctuate even if input light fluctuates within a certain range. For example, Patent Document 1 describes an optical amplifier that branches a portion of the optical input or output, detects the intensity of the branched light with a photodiode (hereinafter referred to as PD), and controls a pump light source so that the intensity of the detected light is amplified to a desired level.

[0003] Japanese Patent Application Publication No. 7-307704

[0004] In the conventional optical amplifier described in Patent Document 1, when exposed to a radiation environment such as outer space, the photoelectric conversion efficiency of the PD may change due to radiation, which may result in the PD being unable to accurately detect the intensity of light. If the PD is unable to accurately detect the intensity of light, the conventional optical amplifier has the problem of being unable to amplify the intensity of light to a desired level.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide an optical amplifier that can amplify the intensity of light to a desired level even in a radiation environment.

[0006] The optical amplifier according to the present disclosure comprises an optical amplifier unit that amplifies and outputs light, an excitation light source that excites the optical amplifier unit, a PD that detects the intensity of the light, and a control unit that controls the excitation light source, wherein the control unit acquires a correction value according to a change in the photoelectric conversion efficiency of the PD due to radiation, and controls excitation of the optical amplifier unit by the excitation light source based on the intensity of light detected by the PD and corrected using the correction value.

[0007] According to the present disclosure, a correction value corresponding to a change in the photoelectric conversion efficiency of the PD due to radiation is acquired, and excitation of the optical amplifier unit by the excitation light source is controlled based on the intensity of light detected by the PD and corrected using the correction value, thereby enabling the optical amplifier according to the present disclosure to amplify the intensity of light to a desired level even in a radiation environment.

[0008] Fig. 7A is a block diagram showing an example of the configuration of an optical amplifier according to embodiment 1. Fig. 7B is a block diagram showing an example of a hardware configuration that realizes the functions of a control unit of the optical amplifier according to embodiment 1. Fig. 7C is a flowchart showing a method for controlling the optical amplifier according to embodiment 1. Fig. 7D is a block diagram showing an example of the configuration of an optical amplifier according to embodiment 2. Fig. 7E is a block diagram showing an example of a hardware configuration that realizes the functions of a control unit of the optical amplifier according to embodiment 2. Fig. 7F is a flowchart showing a method for controlling the optical amplifier according to embodiment 2. Figs. 7A and 7B are timing charts showing the process of performing optical input presence and optical input interruption.

[0009] First Embodiment Fig. 1 is a block diagram showing an example of the configuration of an optical amplifier 1 according to a first embodiment. In Fig. 1, the optical amplifier 1 is an optical device that amplifies input signal light to a desired level and outputs the amplified signal. As shown in Fig. 1, the optical amplifier 1 includes an optical coupler 10, an optical coupler 11, an optical isolator 12, an EDFA 13, an optical coupler 14, a PD 15, a pumping light source 16, a control unit 17, a PD 18, a holding circuit 19, a memory circuit 20, and a radiation detector 21.

[0010] The optical coupler 10 is an optical component that, when light is input, branches the input light to the optical coupler 11 and the PD 15 and outputs the branched light. The optical coupler 11 is an optical component that, when light branched from the optical coupler 10 is input, multiplexes the input light with pumping light input from the pumping light source 16 and outputs the combined light. The optical isolator 12 is an optical component that passes the light output from the optical coupler 11 through the EDFA 13 and blocks return light that propagates through the EDFA 13 and returns to the input side.

[0011] The EDFA (Erbium-Doped Fiber Amplifier) ​​13 is an optical amplifier that amplifies and outputs the light output from the optical isolator 12. The EDFA 13 is an optical fiber doped with a rare earth element such as erbium, and is capable of amplifying the intensity of the propagating light. When excitation light (pump light) output from the excitation light source 16 is incident on the EDFA 13, electrons of the rare earth element such as erbium in the EDFA 13 are excited, causing the EDFA 13 to emit light of the same wavelength as the input light. In the EDFA 13, the input light and the emitted light interfere with each other, amplifying the intensity of the input light.

[0012] Although the optical amplifier 1 is shown as including an EDFA, the present invention is not limited to this. For example, the optical amplifying section of the optical amplifier 1 may be an optical fiber doped with a rare earth element such as neodymium.

[0013] The optical coupler 14 is an optical component that, when the light whose intensity has been amplified by the EDFA 13 is input, outputs a part of the input light as output light and branches the remainder to be output to the PD 18 .

[0014] PD15 is a photodiode that detects the intensity of the light output from optical coupler 10. PD18 is a photodiode that detects the intensity of the light output from optical coupler 14. PD15 and PD18 are semiconductor devices that convert the detected light into an electrical signal corresponding to its intensity, and generally have a pn junction structure in which a p-type semiconductor and an n-type semiconductor are joined. When light is irradiated onto the pn junction, the optical energy generates electrons and holes in the semiconductor, and these charges are separated in the reverse-biased pn junction and detected as a current.

[0015] Photoelectric conversion efficiency is a parameter that indicates how efficiently a PD converts incident light energy into an electrical signal. A PD with high photoelectric conversion efficiency can output a large portion of the incident light energy as an electrical signal. For example, high-energy radiation such as gamma rays or X-rays can combine with electrons in the semiconductor of a PD to generate impurities, which can create crystal lattice defects. When crystal lattice defects are created, the photoelectric conversion efficiency of the PD decreases. The light intensity detected by a PD with reduced photoelectric conversion efficiency will be lower than the true level.

[0016] The pumping light source 16 pumps the EDFA 13. Under the control of the control unit 17, the pumping light source 16 outputs pumping light to the optical coupler 11 for controlling the optical amplification factor of the EDFA 13. The optical coupler 11 combines the input light with the pumping light from the pumping light source 16 and outputs the combined light to the optical isolator 12. For example, the pumping light source 16 is a laser diode that generates high-energy light with a wavelength close to that absorbed by erbium, and typically generates pumping light with a wavelength of approximately 980 nm or 1550 nm. The pumping level of erbium can be adjusted by adjusting the intensity of the pumping light output from the pumping light source 16. That is, when the intensity of the pumping light from the pumping light source 16 increases, the pumping of erbium also increases, thereby enhancing the amplification effect of the EDFA 13. Conversely, when the intensity of the pumping light decreases, the pumping of erbium also decreases, thereby reducing the amplification effect of the EDFA 13.

[0017] The control unit 17 controls the pumping light source 16. For example, the control unit 17 controls the PD 15 to detect the intensity of the light branched from the input light by the optical coupler 10, and controls the pumping of the EDFA 13 by the pumping light source 16 so that the intensity of the light detected by the PD 15 is amplified to a desired level. Alternatively, the control unit 17 may control the PD 18 to detect the intensity of the light branched by the optical coupler 14 and amplified by the EDFA 13, and controls the pumping of the EDFA 13 by the pumping light source 16 so that the intensity of the light detected by the PD 18 is amplified to a desired level. Alternatively, the control unit 17 may control the PD 15 to detect the intensity of the light branched from the input light by the optical coupler 10, and the PD 18 to detect the intensity of the light branched by the optical coupler 14 and amplified by the EDFA 13, and controls the pumping of the EDFA 13 by the pumping light source 16 so that the intensities of the light detected by the PD 15 and the PD 18 are each amplified to a desired level.

[0018] The control unit 17 acquires a radiation correction value corresponding to a change in the photoelectric conversion efficiency of the PD 15 due to radiation, and controls the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by the PD 15 and corrected using the radiation correction value. The control unit 17 may also acquire a radiation correction value corresponding to a change in the photoelectric conversion efficiency of the PD 18 due to radiation, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by the PD 18 and corrected using the radiation correction value. The control unit 17 may also acquire radiation correction values ​​corresponding to changes in the photoelectric conversion efficiency of each of the PD 15 and PD 18 due to radiation, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by the PD 15 and PD 18 and corrected using the respective radiation correction values.

[0019] The radiation correction value is a correction value for the intensity of light detected by a PD whose photoelectric conversion efficiency has changed due to radiation. For example, the radiation correction value is a value corrected for a decrease in the intensity of light detected by a PD whose photoelectric conversion efficiency has decreased due to radiation. By replacing the intensity of light detected by the PD with the radiation correction value, a true level of intensity can be obtained in which the change in photoelectric conversion efficiency due to radiation has been corrected. Below, a case will be described in which the intensity of light detected by PD 15 is corrected using the radiation correction value for PD 15. Note that in the optical amplifier 1, the intensity of light detected by PD 18 may also be corrected using the radiation correction value for PD 18.

[0020] The holding circuit 19 is a holding unit that holds a radiation correction value calculated based on the change trend of photoelectric conversion efficiency due to radiation. The holding circuit 19 is a memory that can be read and written by the control unit 17, and holds a radiation correction value for each PD linked to a radiation dose. That is, the holding circuit 19 holds a radiation correction value corresponding to each radiation dose for PD 15 and PD 18. The radiation correction value is calculated by the control unit 17 or an external device.

[0021] The memory circuit 20 is a memory unit that accumulates the radiation dose detected by the radiation detector 21. For example, if the previous radiation dose detected by the radiation detector 21 is stored in the memory circuit 20, the current radiation dose detected by the radiation detector 21 is added to the previous radiation dose and accumulated in the memory circuit 20. The control unit 17 acquires the radiation dose accumulated in the memory circuit 20 and acquires the radiation correction value of the PD 15 or PD 18 that corresponds to the acquired radiation dose.

[0022] The radiation detector 21 is a circuit that detects the amount of radiation. The amount of radiation detected by the radiation detector 21 is acquired by the control unit 17. This allows the control unit 17 to acquire a radiation correction value corresponding to the amount of radiation detected by the radiation detector 21.

[0023] The control unit 17 stores the amount of radiation detected by the radiation detector 21 in the memory circuit 20. For example, the radiation detector 21 may be a semiconductor detector or a scintillation detector. A semiconductor detector detects electron-hole pairs generated when radiation interacts with a semiconductor material. An electrical signal is generated by the charge generated when radiation passes through the semiconductor. This signal is amplified and measured as the energy of the detected radiation. A scintillation detector utilizes the phenomenon that a substance called a scintillator emits light when radiation interacts with a substance, and the amount of light emitted is proportional to the energy of the radiation.

[0024] Next, a hardware configuration for realizing the functions of the control unit 17 will be described. The functions of the control unit 17 are realized by a processing circuit. That is, the control unit 17 includes a processing circuit for executing the processes from step ST1 to step ST9 shown in FIG. 3, which will be described later. The processing circuit may be dedicated hardware, or may be a CPU (Central Processing Unit) that executes a program stored in memory.

[0025] Fig. 2 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 17. In Fig. 2, the control unit 17 includes a processor 101, a memory 102, a PDIF 103, an excitation light source IF 104, a holding circuit IF 105, a storage circuit IF 106, and a radiation detector IF 107. The processor 101 reads and executes a program stored in the memory 102, thereby realizing the functions of the control unit 17. The PDIF 103 is an interface between the control unit 17 and the PD 15 and PD 18. The excitation light source IF 104 is an interface between the control unit 17 and the excitation light source 16. The holding circuit IF 105 is an interface between the control unit 17 and the holding circuit 19. The storage circuit IF 106 is an interface between the control unit 17 and the storage circuit 20. The radiation detector IF 107 is an interface between the control unit 17 and the radiation detector 21.

[0026] For example, the control unit 17 includes a memory 102 for storing a program that, when executed by the processor 101, results in the execution of steps ST1 to ST9 shown in Fig. 3 (described later). These programs cause a computer to execute the procedures or methods of each process of the control unit 17. The memory 102 may be a computer-readable storage medium that stores a program for causing a computer to function as the control unit 17.

[0027] The memory 102 may be, for example, a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), an electrically programmable programmable read-only memory (EEPROM), or an electrically programmable programmable read-only memory (EEPROM) (registered trademark). In addition to the above programs, the memory 102 stores various data used in the processing of the control unit 17 and various data obtained as a result of the processing of the control unit 17.

[0028] The processor 101 acquires data indicating the intensities of light detected by the PD15 and PD18 via the PDIF 103. The processor 101 also outputs a control signal to the excitation light source 16 via the excitation light source IF 104. The control signal is, for example, a signal that specifies the intensity of the excitation light output by the excitation light source 16. The processor 101 also stores a radiation correction value in the storage circuit 19 via the storage circuit IF 105 and reads out the radiation correction value from the storage circuit 19. The processor 101 accumulates a radiation dose in the storage circuit 20 via the storage circuit IF 106 and reads out the radiation dose from the storage circuit 20. The processor 101 acquires the radiation dose detected by the radiation detector 21 via the radiation detector IF 107.

[0029] Next, a control method for the optical amplifier 1 according to the first embodiment will be described. FIG. 3 is a flowchart showing the control method for the optical amplifier 1. Below, a process for correcting a change in the detected value of light intensity due to a change in the photoelectric conversion efficiency of the PD 15 caused by radiation will be described. The control unit 17 acquires information indicating the change trend in the photoelectric conversion efficiency of the PD 15 irradiated with radiation, and calculates a radiation correction value for the PD 15 based on the change trend in the photoelectric conversion efficiency indicated by the acquired information (step ST1). This makes it possible to correct the intensity of light detected by the PD 15 using the radiation correction value calculated based on the change trend in the photoelectric conversion efficiency of the PD 15 caused by radiation.

[0030] For example, the control unit 17 acquires the past radiation dose detected in the radiation environment in which the optical amplifier 1 is used, and acquires the photoelectric conversion efficiency of the PD 15 corresponding to the acquired radiation dose, thereby identifying the change trend of the photoelectric conversion efficiency of the PD 15. Next, the control unit 17 calculates a correction curve indicating the correspondence relationship between the radiation dose and the detection value of the PD 15 based on the identified change trend, and calculates a radiation correction value, which is a correction value for the light intensity for each radiation dose, using the calculated correction curve.

[0031] The control unit 17 stores the radiation correction value calculated in step ST1 in the storage circuit 19 (step ST2). For example, the control unit 17 stores the radiation correction value calculated for each radiation dose in the storage circuit 19.

[0032] The control unit 17 acquires the current radiation dose detected by the radiation detector 21 (step ST3). For example, in a radiation environment in which the optical amplifier 1 is used, the radiation detector 21 detects the radiation dose periodically or constantly. The radiation detector 21 sequentially outputs the detected radiation dose to the control unit 17.

[0033] The control unit 17 stores the current radiation dose detected by the radiation detector 21 in the memory circuitry 20 (step ST4). For example, if the previous radiation dose detected by the radiation detector 21 is stored in the memory circuitry 20, the control unit 17 adds the current radiation dose detected by the radiation detector 21 to the previous radiation dose and stores the result.

[0034] Next, the control unit 17 acquires the radiation dose accumulated up to now from the storage circuitry 20 (step ST5). Next, the control unit 17 acquires the radiation correction value of the PD 15 corresponding to the acquired radiation dose from the holding circuitry 19 (step ST6). For example, the control unit 17 acquires the radiation correction value corresponding to the PD 15 from the holding circuitry 19. This allows the control unit 17 to acquire the radiation correction value corresponding to the radiation dose accumulated up to now.

[0035] The control unit 17 acquires the current light intensity detected by the PD 15 or the PD 18 (step ST7). For example, the control unit 17 acquires the current light intensity detected by the PD 15. Note that since the photoelectric conversion efficiency of the PD 15 changes due to radiation, the light intensity detected by the PD 15 changes from the true level that is not affected by radiation.

[0036] Next, the control unit 17 calculates the true level from the current light intensity detected by the PD 15 using the acquired radiation correction value (step ST8). For example, the control unit 17 replaces the current light intensity detected by the PD 15 with the acquired radiation correction value. This allows the current light intensity detected by the PD 15 to be the true level intensity corrected for changes in photoelectric conversion efficiency due to radiation.

[0037] The control unit 17 controls the pump light source 16 so that the calculated true level is changed to a desired level (step ST9). For example, the control unit 17 controls the pumping of the EDFA 13 by the pump light source 16 based on the light intensity detected by the PD 15 and corrected using the radiation correction value. By having the control unit 17 execute the control method shown in Fig. 3 in this way, the light intensity can be amplified to a desired level even in a radiation environment. Note that the series of processes from step ST1 to step ST9 are repeatedly executed while the optical amplifier 1 is operating.

[0038] The control unit 17 may correct changes in the detected value of light intensity due to changes in the photoelectric conversion efficiency of the PD 18. For example, the control unit 17 acquires past radiation doses detected in the radiation environment in which the optical amplifier 1 is used, and acquires the photoelectric conversion efficiency of the PD 18 corresponding to the acquired radiation doses, thereby identifying a change trend in the photoelectric conversion efficiency of the PD 18. The control unit 17 calculates a correction curve indicating the correspondence between the radiation dose and the detection value of the PD 18 based on the identified change trend, and calculates a radiation correction value of the light intensity for each radiation dose using the calculated correction curve. The control unit 17 can correct the light intensity detected by the PD 18 to a true level by replacing the current light intensity detected by the PD 18 with the radiation correction value.

[0039] The control unit 17 may also correct changes in the detected light intensity due to changes in the photoelectric conversion efficiencies of both the PD 15 and the PD 18. For example, the control unit 17 acquires past radiation doses detected in the radiation environment in which the optical amplifier 1 is used and acquires the photoelectric conversion efficiencies of the PD 15 and PD 18 corresponding to the acquired radiation doses, thereby identifying a change trend in the photoelectric conversion efficiency. The control unit 17 calculates a correction curve indicating the correspondence between the radiation dose and the detection value of the PD 15 based on the identified change trend in the photoelectric conversion efficiency of the PD 15, and calculates a radiation correction value for the light intensity detected by the PD 15 for each radiation dose using the calculated correction curve. Similarly, the control unit 17 calculates a radiation correction value for the light intensity detected by the PD 18 for each radiation dose using the correction curve indicating the correspondence between the radiation dose and the detection value of the PD 18, calculated based on the identified change trend in the photoelectric conversion efficiency of the PD 18. The control unit 17 can correct the light intensity detected by the PD 15 to its true level by replacing the current light intensity detected by the PD 15 with the acquired radiation correction value of the PD 15. Similarly, the control unit 17 can correct the light intensity detected by PD18 to the true level by replacing the current light intensity detected by PD18 with the acquired radiation correction value of PD18.

[0040] Although the optical amplifier 1 has been described so far as including the PD 15 and the PD 18, the present invention is not limited to this. For example, the optical amplifier 1 may include either the PD 15 or the PD 18. The optical amplifier 1 may also include three or more PDs. In this case, the control unit 17 corrects changes in the detected value of the optical intensity due to changes in the photoelectric conversion efficiency of at least one of the three or more PDs.

[0041] As described above, the optical amplifier 1 according to the first embodiment includes the EDFA 13 that amplifies and outputs light, the pumping light source 16 that pumps the EDFA 13, the PDs 15 and 18 that detect the intensity of the light, and the control unit 17 that controls the pumping light source 16. The control unit 17 acquires a radiation correction value corresponding to changes in the photoelectric conversion efficiency of the PDs 15 and 18 due to radiation, and controls the pumping of the EDFA 13 by the pumping light source 16 based on the intensity of the light detected by the PDs 15 and 18 and corrected using the radiation correction value. This allows the optical amplifier 1 to amplify the intensity of the light to a desired level even in a radiation environment.

[0042] The optical amplifier 1 according to the first embodiment includes a radiation detector 21 that detects a radiation dose, and the control unit 17 acquires a radiation correction value corresponding to the radiation dose detected by the radiation detector 21. This allows the control unit 17 to acquire the radiation correction value corresponding to the radiation dose detected by the radiation detector 21.

[0043] In the optical amplifier 1 according to the first embodiment, the control unit 17 stores the radiation dose detected by the radiation detector 21 in the memory circuit 20, and acquires a radiation correction value corresponding to the radiation dose stored in the memory circuit 20. This allows the control unit 17 to acquire a radiation correction value corresponding to the radiation dose that has been stored up to the present time.

[0044] In the optical amplifier 1 according to the first embodiment, the control unit 17 holds, in the holding circuit 19, a radiation correction value calculated based on the change trend of the photoelectric conversion efficiency due to radiation, and corrects the intensity of light detected by the PD 15 or PD 18 using the radiation correction value held in the holding circuit 19. This makes it possible to correct the intensity of light detected by the PD 15 or PD 18 using the radiation correction value calculated based on the change trend of the photoelectric conversion efficiency of the PD 15 or PD 18 due to radiation.

[0045] A control method for optical amplifier 1 according to the first embodiment is a control method for optical amplifier 1 including EDFA 13 that amplifies and outputs light, a pumping light source that pumps EDFA 13, PDs 15 and 18 that detect the intensity of the light, and a control unit 17 that controls pumping light source 16, and includes the steps (ST1 to ST8) of control unit 17 acquiring a radiation correction value corresponding to a change in photoelectric conversion efficiency of PD 15 and 18 due to radiation, and a step (ST9) of controlling pumping of EDFA 13 by pumping light source 16 based on the light intensity detected by PD 15 and 18 and corrected using the radiation correction value. Control unit 17 that executes the control method according to the first embodiment can amplify the intensity of light to a desired level even in a radiation environment.

[0046] In the control method for the optical amplifier 1 according to the first embodiment, the optical amplifier 1 includes a radiation detector 21 that detects a radiation dose, and the control unit 17 acquires a radiation correction value corresponding to the radiation dose detected by the radiation detector 21. This allows the control unit 17 to correct the detection value of the PD 15 or the PD 18 using the radiation correction value corresponding to the radiation dose actually detected by the radiation detector 21.

[0047] Embodiment 2. In the first embodiment, an optical amplifier was shown that was equipped with a radiation detector that detects radiation doses and a memory circuit that stores the radiation doses. However, in the second embodiment, an optical amplifier that does not have a radiation detector or a memory circuit and that grasps changes in photoelectric conversion efficiency due to radiation based on the dark current and temperature of a PD will be described.

[0048] 4 is a block diagram showing an example of the configuration of an optical amplifier 1A according to the second embodiment. The optical amplifier 1A is an optical device that amplifies input signal light to a desired level and outputs the amplified signal. As shown in FIG. 4, the optical amplifier 1A includes an optical coupler 10, an optical coupler 11, an optical isolator 12, an EDFA 13, an optical coupler 14, a PD 15, a pumping light source 16, a control unit 17A, a PD 18, a holding circuit 19A, an optical disconnection circuit 22, an optical disconnection circuit 23, a temperature monitor 24, and a temperature monitor 25.

[0049] The optical coupler 10 is an optical component that, when light is input, branches the input light to the optical coupler 11 and the optical disconnection circuit 22 and outputs the branched light. The optical coupler 11 is an optical component that, when light branched from the optical coupler 10 is input, multiplexes the input light with pumping light input from the pumping light source 16 and outputs the combined light. The optical isolator 12 is an optical component that passes the light output from the optical coupler 11 through the EDFA 13 and blocks return light that propagates through the EDFA 13 and then returns to the input side.

[0050] The EDFA 13 is an optical amplifier that amplifies and outputs the light output from the optical isolator 12. The EDFA 13 is an optical fiber doped with a rare earth element such as erbium, and is capable of amplifying the intensity of the propagating light. When the pumping light output from the pumping light source 16 is incident on the EDFA 13, electrons of the rare earth element such as erbium in the EDFA 13 are excited, and light of the same wavelength as the input light is emitted. In the EDFA 13, the input light and the emitted light interfere with each other, amplifying the intensity of the input light. Note that although the optical amplifier 1A is shown as including an EDFA, the present invention is not limited thereto. For example, the optical amplifier included in the optical amplifier 1A may be an optical fiber doped with a rare earth element such as neodymium.

[0051] The optical coupler 14 is an optical component that, when light whose intensity has been amplified by the EDFA 13 is input, outputs a portion of the input light as output light and branches the remainder to the light disconnection circuit 23 for output.

[0052] PD15 is a photodiode that detects the intensity of light output from optical coupler 10 via optical disconnection circuit 22 in the OFF state. Note that light branched by optical coupler 10 and heading toward PD15 is blocked by optical disconnection circuit 22 in the ON state. PD18 is a photodiode that detects the intensity of light output from optical coupler 14 via optical disconnection circuit 23 in the OFF state. Light branched by optical coupler 14 and heading toward PD18 is blocked by optical disconnection circuit 23 in the ON state. PD15 and PD18 are semiconductor devices that convert the detected light into an electrical signal corresponding to its intensity.

[0053] Photoelectric conversion efficiency is a parameter that indicates how efficiently a PD can convert incident light energy into an electrical signal. A PD with high photoelectric conversion efficiency outputs a large portion of the incident light energy as an electrical signal. A PD's dark current is a current generated in a PD when light is blocked. A PD's dark current is mainly generated by heat generated inside the PD's semiconductor. For example, as the temperature of a PD rises, the carrier generation rate in the PD's semiconductor increases, so the PD's dark current tends to increase as the temperature rises. Furthermore, an increase in the PD's dark current increases the PD's noise and reduces its photoelectric conversion efficiency.

[0054] The pumping light source 16 pumps the EDFA 13. Under the control of the control unit 17A, the pumping light source 16 outputs pumping light to the optical coupler 11 for controlling the optical amplification factor of the EDFA 13. The optical coupler 11 combines the input light with the pumping light from the pumping light source 16 and outputs the combined light to the optical isolator 12. For example, the pumping light source 16 is a laser diode that generates high-energy light with a wavelength close to the wavelength absorbed by erbium. The pumping level of erbium can be adjusted by adjusting the intensity of the pumping light output from the pumping light source 16. That is, when the intensity of the pumping light from the pumping light source 16 increases, the pumping of erbium also increases, thereby enhancing the amplification effect of the EDFA 13. Conversely, when the intensity of the pumping light decreases, the pumping of erbium also decreases, thereby reducing the amplification effect of the EDFA 13.

[0055] The control unit 17A controls the pumping light source 16. For example, the control unit 17A controls the pumping of the EDFA 13 by the pumping light source 16 so that the intensity of the light detected by the PD 15 is amplified to a desired level. Alternatively, the control unit 17A may control the pumping of the EDFA 13 by the pumping light source 16 so that the intensity of the light detected by the PD 18 is amplified to a desired level. Alternatively, the control unit 17A may control the pumping of the EDFA 13 by the pumping light source 16 so that the intensities of the light detected by the PD 15 and the PD 18 are each amplified to a desired level.

[0056] The control unit 17A acquires a radiation correction value corresponding to the dark current and temperature of the PD 15, and controls the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by the PD 15 corrected using the acquired radiation correction value. The control unit 17A may also acquire a radiation correction value corresponding to the dark current and temperature of the PD 18, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by the PD 18 corrected using the acquired radiation correction value. The control unit 17A may also acquire a radiation correction value for the PD 15 based on the dark current and temperature of the PD 15, acquire a radiation correction value for the PD 18 based on the dark current and temperature of the PD 18, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensities of light detected by the PD 15 and PD 18 and corrected using the respective radiation correction values.

[0057] The control unit 17A may control the light-off circuit 22 and the light-off circuit 23 to alternately shut off light, acquire a radiation correction value for PD 15, of PD 15 and PD 18, whose light has been shut off by the light-off circuit 22, control excitation of EDFA 13 by the pump light source 16 based on the intensity of light detected by PD 15 and corrected using the acquired radiation correction value, acquire a radiation correction value for PD 18, whose light has been shut off by the light-off circuit 23, and control excitation of EDFA 13 by the pump light source 16 based on the intensity of light detected by PD 18 and corrected using the acquired radiation correction value. This allows the optical amplifier 1A to correct the intensity of light detected by PD 15 and PD 18 based on the dark currents and temperatures of PD 15 and PD 18, without using a radiation detector.

[0058] The radiation correction value is a correction value for the intensity of light detected by a PD whose photoelectric conversion efficiency has changed due to radiation. For example, the radiation correction value is a value corrected for a decrease in the intensity of light detected by a PD whose photoelectric conversion efficiency has decreased due to radiation. By replacing the intensity of light detected by the PD with the radiation correction value, a true level of intensity can be obtained in which the change in photoelectric conversion efficiency due to radiation has been corrected. Furthermore, the radiation correction value is linked to the dark current of the PD and the temperature around the PD and is held in the holding circuit 19A.

[0059] The holding circuit 19A is a holding unit that holds a radiation correction value calculated based on the change trend of photoelectric conversion efficiency due to radiation. The holding circuit 19A is a memory that can be read and written by the control unit 17A, and holds a radiation correction value for each PD linked to the dark current of the PD and the temperature around the PD. For example, in FIG. 4 , the holding circuit 19A holds a radiation correction value corresponding to the dark current and temperature of PD 15, or a radiation correction value corresponding to the dark current and temperature of PD 18. The radiation correction value is calculated by the control unit 17A or an external device.

[0060] In a radiation environment, the photoelectric conversion efficiency of a PD may change not only due to radiation but also due to an increase in the PD's dark current. The control unit 17A acquires a change trend in the photoelectric conversion efficiency due to radiation based on the PD's dark current and temperature, and calculates a radiation correction value based on the acquired change trend. For example, the control unit 17A acquires, under a certain temperature condition, measurement results of the PD's dark current and temperature in a reference state where no radiation is present, and measurement results of the dark current generated in the PD when irradiated with radiation and the temperature. The control unit 17A identifies a change trend in the photoelectric conversion efficiency corresponding to changes in the PD's dark current and temperature in the reference state based on a comparison result between the measured dark current and temperature and the dark current and temperature in the reference state. Next, the control unit 17A calculates a correction curve indicating the correspondence between the PD's dark current and temperature and the PD's detection value based on the identified change trend, and calculates the PD's radiation correction value using the calculated correction curve. The control unit 17A associates the calculated radiation correction value with the dark current and temperature and stores the calculated radiation correction value in the storage circuit 19A.

[0061] The light-off circuit 22 is a light-blocking unit that blocks light from reaching the PD 15. For example, the light-off circuit 22 switches between an on state and an off state in accordance with a control signal from the control unit 17A. When in the on state, the light-off circuit 22 blocks light from the optical coupler 10 toward the PD 15, and when in the off state, the light-off circuit 22 passes light from the optical coupler 10 toward the PD 15. The light-off circuit 22 is realized, for example, by an optical switch or the like.

[0062] The light-off circuit 23 is a light-blocking unit that blocks light from reaching the PD 18. For example, the light-off circuit 23 switches between an on state and an off state in accordance with a control signal from the control unit 17A. When in the on state, the light-off circuit 23 blocks light from the optical coupler 14 toward the PD 18, and when in the off state, the light-off circuit 23 passes light from the optical coupler 14 toward the PD 18. The light-off circuit 23 is realized, for example, by an optical switch or the like.

[0063] The temperature monitor 24 is a sensor that detects the temperature around the PD 15. The temperature monitor 25 is a sensor that detects the temperature around the PD 18. Monitor information on the temperatures detected by the temperature monitors 24 and 25 is output to the control unit 17A.

[0064] Next, a hardware configuration for realizing the functions of the control unit 17A will be described. The functions of the control unit 17A are realized by a processing circuit. That is, the control unit 17A includes a processing circuit for executing the processes from step ST1A to step ST20A shown in FIG. 6, which will be described later. The processing circuit may be dedicated hardware, or may be a CPU that executes a program stored in memory.

[0065] FIG. 5 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 17A. In FIG. 5, the control unit 17A includes a processor 101, a memory 102, a PDIF 103, an excitation light source IF 104, a holding circuit IF 105, an optical disconnection circuit IF 108, and a temperature monitor IF 109. The processor 101 reads and executes a program stored in the memory 102, thereby realizing the functions of the control unit 17A. The PDIF 103 is an interface between the control unit 17A and the PDs 15 and 18. The excitation light source IF 104 is an interface between the control unit 17A and the excitation light source 16. The holding circuit IF 105 is an interface between the control unit 17A and the holding circuit 19A. The optical disconnection circuit IF 108 is an interface between the control unit 17A and the optical disconnection circuits 22 and 23. The temperature monitor IF 107 is an interface between the control unit 17A and the temperature monitors 24 and 25.

[0066] For example, the control unit 17A includes a memory 102 for storing a program that, when executed by the processor 101, results in the execution of steps ST1A to ST20A shown in FIG. 5, which will be described later. These programs cause a computer to execute the procedures or methods of each process of the control unit 17A. The memory 102 may be a computer-readable storage medium that stores a program for causing a computer to function as the control unit 17A.

[0067] The memory 102 may be, for example, a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, an EEPROM (registered trademark), etc. In addition to the above programs, the memory 102 also stores various data used in the processing of the control unit 17A and various data obtained as a result of the processing of the control unit 17A.

[0068] The processor 101 acquires data indicating the intensities of the light detected by the PD 15 and PD 18 via the PDIF 103. The processor 101 also outputs a control signal to the excitation light source 16 via the excitation light source IF 104. The control signal is, for example, a signal that specifies the intensity of the excitation light output by the excitation light source 16. The processor 101 also stores a radiation correction value in the storage circuit 19A via the storage circuit IF 105, and reads out the radiation correction value from the storage circuit 19A. The processor 101 outputs a control signal for controlling light interruption to the light interruption circuit 22 or the light interruption circuit 23 via the light interruption circuit IF 108. The processor 101 acquires temperature information detected by the temperature monitor 24 and the temperature monitor 25 via the temperature monitor IF 109.

[0069] Next, a control method for the optical amplifier 1A according to the second embodiment will be described. Fig. 6 is a flowchart showing the control method for the optical amplifier 1A. The processes from step ST1A to step ST20A shown in Fig. 6 are repeatedly executed while the optical amplifier 1A is activated. The control unit 17A acquires information indicating the change trend of the photoelectric conversion efficiency of the PD 15 and PD 18 irradiated with radiation, and calculates radiation correction values ​​for the PD 15 and PD 18 based on the change trend of the photoelectric conversion efficiency indicated by the acquired information (step ST1A).

[0070] For example, the control unit 17A acquires the measurement results of the dark current and temperature of the PD in a reference state in which no radiation is present, and the measurement results of the dark current and temperature generated in the PD when irradiated with radiation, and identifies a change trend in the photoelectric conversion efficiency corresponding to changes in the dark current and temperature of the PD based on a comparison result between the measured dark current and temperature and the dark current and temperature in the reference state. Next, the control unit 17A calculates a correction curve showing the relationship between the dark current and temperature and the detection value of the PD based on the identified change trend, and calculates a radiation correction value using the calculated correction curve.

[0071] The control unit 17A stores the radiation correction value calculated in step ST1A in the storage circuit 19A (step ST2A). For example, the control unit 17A stores the radiation correction value associated with at least one of the dark current and the temperature of the PD 15 and the PD 18 in the storage circuit 19A.

[0072] Next, the control unit 17A turns on only the light-off circuit 22 to cut off light to the PD 15 (step ST3A). For example, the control unit 17A outputs a rectangular wave control signal to the light-off circuit 22. The light-off circuit 22 is in an off state when the control signal is at a high level, and in an on state when the control signal is at a low level.

[0073] When the light to the PD 15 is blocked by the light interruption circuit 22 (step ST3A; YES), the control unit 17A acquires the dark current from the PD 15 (step ST4A). Next, the control unit 17A acquires temperature information around the PD 15 from the temperature monitor 24 (step ST5A). The control unit 17A acquires the radiation correction value of the PD 15 from the holding circuit 19A based on the dark current of the PD 15 and the temperature around the PD 15 (step ST6A). The processing of steps ST4A, ST5A, and ST6A may be performed in reverse order or simultaneously.

[0074] With the light to the PD 15 blocked, the control unit 17A acquires the intensity of the light detected by the PD 18 (step ST7A). Note that, since the photoelectric conversion efficiency of the PD 18 changes due to radiation, the intensity of the light detected by the PD 18 changes from the true level without the influence of radiation.

[0075] Next, the control unit 17A calculates the true level of the current light intensity detected by the PD 18 using the radiation correction value of the PD 18 obtained in step ST13A by previously executing the series of processes shown in Fig. 6 (step ST8A). For example, the control unit 17A replaces the current light intensity detected by the PD 18 with the radiation correction value of the PD 18. This allows the current light intensity detected by the PD 18 to be the true level of intensity corrected for changes in photoelectric conversion efficiency due to radiation.

[0076] Next, the control unit 17A controls the pumping light source 16 so that the calculated true level becomes a desired level (step ST9A). For example, the control unit 17A controls the pumping of the EDFA 13 by the pumping light source 16 based on the light intensity detected by the PD 18 and corrected using the radiation correction value of the PD 15.

[0077] When the light to the PD 15 is not blocked by the light-off circuit 22 (step ST3A; NO), the control unit 17A turns on only the light-off circuit 23 to block the light to the PD 18 (step ST10A). For example, the control unit 17A outputs a rectangular wave control signal to the light-off circuit 23. The light-off circuit 23 is in the off state when the control signal is at a high level, and in the on state when the control signal is at a low level.

[0078] When the light to the PD 18 is blocked by the light interruption circuit 23 (step ST10A; YES), the control unit 17A acquires a dark current from the PD 18 (step ST11A). Next, the control unit 17A acquires temperature information around the PD 18 from the temperature monitor 25 (step ST12A). The control unit 17A acquires a radiation correction value for the PD 18 from the holding circuit 19A based on at least one of the dark current of the PD 18 and the temperature around the PD 18 (step ST13A). The order of the processing of step ST11A, the processing of step ST12A, and the processing of step ST13A may be reversed or may be executed simultaneously.

[0079] With the light to the PD 18 blocked, the control unit 17A acquires the intensity of the light detected by the PD 15 (step ST14A). Note that since the photoelectric conversion efficiency of the PD 15 changes due to radiation, the intensity of the light detected by the PD 15 changes from the true level due to the influence of radiation.

[0080] Next, the control unit 17A calculates the true level of the current light intensity detected by the PD 15 using the radiation correction value of the PD 15 obtained in step ST7A by previously executing the process shown in Fig. 6 (step ST15A). For example, the control unit 17A replaces the current light intensity detected by the PD 15 with the radiation correction value of the PD 15. This makes it possible to set the current light intensity detected by the PD 15 to a true level of intensity corrected for changes in photoelectric conversion efficiency due to radiation.

[0081] Next, the control unit 17A controls the pumping light source 16 so that the calculated true level becomes a desired level (step ST16A). For example, the control unit 17A controls the pumping of the EDFA 13 by the pumping light source 16 based on the light intensity detected by the PD 15 and corrected using the radiation correction value of the PD 18.

[0082] When the light to PD15 is not blocked by the light-off circuit 22 and the light to PD18 is not blocked by the light-off circuit 23 (step ST10A; NO), the control unit 17A acquires the radiation correction value of PD15 or PD18 from the holding circuit 19A based on the dark current of PD15 or PD18 and the temperature around PD15 or PD18 (step ST17A).

[0083] In a state where light to PD 15 and PD 18 is not blocked, control unit 17A acquires the intensity of light detected by PD 15 or PD 18 (step ST18A). Note that, since the photoelectric conversion efficiency of PD 15 and PD 18 changes due to radiation, the intensity of light detected by PD 15 or PD 18 changes from the true level.

[0084] Next, the control unit 17A uses the acquired radiation correction value to calculate the true level of the current light intensity detected by PD 15 or PD 18 (step ST19A). For example, the control unit 17A replaces the current light intensity detected by PD 15 or PD 18 with the radiation correction value of PD 15 or PD 18. This allows the current light intensity detected by PD 15 or PD 18 to be the true level of intensity corrected for changes in photoelectric conversion efficiency due to radiation.

[0085] The control unit 17A controls the pumping light source 16 so that the calculated true level becomes a desired level (step ST20A). For example, the control unit 17A controls the pumping of the EDFA 13 by the pumping light source 16 based on the light intensity detected by the PD 15 or PD 18 and corrected using the radiation correction value.

[0086] The control of the light interruption circuit 22 in step ST3A and the control of the light interruption circuit 23 in step ST10A are performed by control signals output from the control unit 17A to the light interruption circuit 22 and the light interruption circuit 23. For example, Fig. 7A is a timing chart of the light interruption processing controlled by the control signal output from the control unit 17A to the light interruption circuit 22, and Fig. 7B is a timing chart of the light interruption processing controlled by the control signal output from the control unit 17A to the light interruption circuit 23.

[0087] 7A is a rectangular wave signal. When the control signal is at a high level, it indicates "optical input present," i.e., the light-off circuit 22 is turned off, and light from the optical coupler 10 is input to the PD 15 via the light-off circuit 22. On the other hand, when the control signal is at a low level, it indicates "optical input interruption," i.e., the light-off circuit 22 is turned on, and light from the optical coupler 10 to the PD 15 is blocked by the light-off circuit 22.

[0088] The control signal in Fig. 7B is a square wave signal. When the control signal is at a high level, "light input present" is indicated, i.e., the light interruption circuit 23 is turned off, and light from the optical coupler 14 is input to the PD 18 via the light interruption circuit 23. On the other hand, when the control signal is at a low level, "light input interruption" is indicated, i.e., the light interruption circuit 23 is turned on, and light from the optical coupler 14 to the PD 18 is blocked by the light interruption circuit 23. Note that the duty ratio of the control signal shown in Fig. 7A and the control signal shown in Fig. 7B may be any value as long as it does not generate a timing at which both the light interruption circuit 22 and the light interruption circuit 23 are turned off.

[0089] During period (1) shown in Figures 7A and 7B, the control signals shown in Figures 7A and 7B are both at high level, so that the light-disconnection circuits 22 and 23 are both in the off state. At this time, the light branched from the optical coupler 10 to the PD 15 is input to the PD 15 via the light-disconnection circuit 22, and the light branched from the optical coupler 14 to the PD 18 is input to the PD 18 via the light-disconnection circuit 23. The control unit 17A controls the excitation of the EDFA 13 by the pump light source 16 based on the intensity of the light detected by the PD 15 or the PD 18. This allows the optical amplifier 1A to output light amplified to a desired level. Note that the control unit 17A corrects for changes in the intensity of the light detected by the PD 15 or the PD 18 due to radiation using a radiation correction value.

[0090] During period (2) shown in Figures 7A and 7B, the control signal shown in Figure 7A is at a high level and the control signal shown in Figure 7B is at a low level, so the light-off circuit 22 is in an off state and the light-off circuit 23 is in an on state. At this time, the light branched from the optical coupler 10 to the PD 15 is input to the PD 15 via the light-off circuit 22, and the light branched from the optical coupler 14 to the PD 18 is blocked by the light-off circuit 23. The control unit 17A acquires the dark current and temperature of the PD 18 from which light is blocked, and controls the excitation of the EDFA 13 by the pump light source 16 based on the intensity of the light detected by the PD 15. This allows the optical amplifier 1A to output light amplified to a desired level. The control unit 17A corrects for changes in the intensity of the light detected by the PD 15 due to radiation using a radiation correction value.

[0091] During period (3) shown in Figures 7A and 7B, the control signal shown in Figure 7A is at a low level and the control signal shown in Figure 7B is at a high level, so the light-off circuit 22 is in an on state and the light-off circuit 23 is in an off state. At this time, the light branched from the optical coupler 10 to the PD 15 is blocked by the light-off circuit 22, and the light branched from the optical coupler 14 to the PD 18 is input to the PD 18 via the light-off circuit 23. The control unit 17A acquires the dark current and temperature of the PD 15 from which light is blocked, and controls the excitation of the EDFA 13 by the pump light source 16 based on the intensity of the light detected by the PD 18. This allows the optical amplifier 1A to output light amplified to a desired level. The control unit 17A corrects for changes in the intensity of the light detected by the PD 18 due to radiation using a radiation correction value.

[0092] If the light branched to PD 15 and the light branched to PD 18 are blocked, it becomes impossible to control the optical output level of the optical amplifier 1 A. Therefore, as shown in Figures 7A and 7B, the light interruption processing by the light interruption circuit 22 and the light interruption circuit 23 is controlled by the control unit 17 A at a timing when the light to at least one of PD 15 and PD 18 is not interrupted.

[0093] As described above, in the optical amplifier 1A according to the second embodiment, the control unit 17A acquires a radiation correction value corresponding to the dark current and temperature of the PD 15 or 18. This allows the optical amplifier 1A to amplify the intensity of light corrected based on the dark current and temperature of the PD 15 or 18 to a desired level even in a radiation environment.

[0094] In the optical amplifier 1A according to the second embodiment, the control unit 17A acquires a change trend in the photoelectric conversion efficiency due to radiation based on the dark current and temperature of the PD 15 or 18, and acquires a radiation correction value calculated based on the acquired change trend. The optical amplifier 1A can acquire a radiation correction value based on the change trend in the photoelectric conversion efficiency acquired based on the dark current and temperature of the PD 15 or 18, even if it does not include a radiation detector.

[0095] The optical amplifier 1A according to the second embodiment includes PD15 and PD18, and a light-off circuit 22 or a light-off circuit 23 that cuts off light to PD15 or PD18, and the control unit 17A acquires a radiation correction value for PD15 or PD18 whose light has been cut off by the light-off circuit 22 or the light-off circuit 23, and controls excitation of the EDFA 13 by the pump light source 16 based on the intensity of light detected by PD15 or PD18 and corrected using the acquired radiation correction value. This allows the optical amplifier 1A to correct the intensity of light detected by PD15 and PD18 based on the dark current and temperature of PD15 and PD18, without using a radiation detector.

[0096] In the control method for the optical amplifier 1A according to the second embodiment, the control unit 17A acquires a radiation correction value corresponding to the dark current and temperature of the PD 15 or PD 18. This allows the control unit 17A to correct the detection value of the PD 15 or PD 18 using the radiation correction value corresponding to the dark current and temperature of the PD 15 or PD 18.

[0097] It is possible to combine the embodiments, modify any of the components of the embodiments, or omit any of the components of the embodiments.

[0098] The optical amplifier according to the present disclosure can be used, for example, in optical fiber communications.

[0099] 1, 1A Optical amplifier, 10, 11, 14 Optical coupler, 12 Optical isolator, 16 Excitation light source, 17, 17A Control unit, 19, 19A Holding circuit, 20 Memory circuit, 21 Radiation detector, 22, 23 Light interruption circuit, 24, 25 Temperature monitor, 101 Processor, 102 Memory, 109 Temperature monitor IF, 104 Excitation light source IF, 105 Holding circuit IF, 106 Memory circuit IF, 107 Radiation detector IF, 108 Light interruption circuit IF.

Claims

1. An optical amplifier comprising: an optical amplifier section that amplifies and outputs light; an excitation light source that excites the optical amplifier section; a photodiode that detects the intensity of the light; and a control section that controls the excitation light source, wherein the control section obtains a correction value corresponding to a change in photoelectric conversion efficiency of the photodiode due to radiation, and controls excitation of the optical amplifier section by the excitation light source based on the intensity of the light detected by the photodiode and corrected using the correction value.

2. The optical amplifier according to claim 1, further comprising a radiation detector for detecting a radiation dose, wherein the control unit acquires the correction value corresponding to the radiation dose detected by the radiation detector.

3. The optical amplifier according to claim 2, characterized in that the control unit stores the amount of radiation detected by the radiation detector in a memory unit and obtains the correction value corresponding to the amount of radiation stored in the memory unit.

4. An optical amplifier according to any one of claims 1 to 3, characterized in that the control unit stores the correction value calculated based on the change tendency of the photoelectric conversion efficiency due to radiation in a storage unit, and corrects the intensity of the light detected by the photodiode using the correction value stored in the storage unit.

5. The optical amplifier according to claim 1, wherein the control unit acquires the correction value corresponding to the dark current and temperature of the photodiode.

6. The optical amplifier according to claim 5, characterized in that the control unit obtains a change trend of the photoelectric conversion efficiency due to radiation based on the dark current and temperature of the photodiode, and obtains the correction value calculated based on the obtained change trend.

7. An optical amplifier according to claim 6, comprising: a plurality of said photodiodes; and a light blocking unit that blocks the light to said photodiodes, wherein said control unit acquires the correction value of a photodiode from among said plurality of photodiodes, the photodiode from which the light has been blocked by said light blocking unit, and controls excitation of said optical amplification unit by said excitation light source based on the intensity of the light detected by said photodiode and corrected using said acquired correction value.

8. A control method for an optical amplifier comprising: an optical amplifier section that amplifies and outputs light; an excitation light source that excites the optical amplifier section; a photodiode that detects the intensity of the light; and a control section that controls the excitation light source, characterized in that the control section comprises the steps of: acquiring a correction value according to a change in photoelectric conversion efficiency of the photodiode due to radiation; and controlling excitation of the optical amplifier section by the excitation light source based on the intensity of the light detected by the photodiode and corrected using the correction value.

9. The control method according to claim 8, wherein the optical amplifier is provided with a radiation detector that detects a radiation dose, and the control unit acquires the correction value corresponding to the radiation dose detected by the radiation detector.

10. The control method according to claim 8, wherein the control unit acquires the correction value corresponding to the dark current and temperature of the photodiode.

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