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

Technical Field

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[0001] The present disclosure relates to an optical amplifier and a control method thereof.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0007] According to this disclosure, a correction value is obtained in response to the change in the photoelectric conversion efficiency of the PD due to radiation, and the excitation of the optical amplification unit by the excitation light source is controlled based on the intensity of light detected by the PD and corrected using the correction value. As a result, the optical amplifier according to this disclosure can amplify the intensity of light to a desired level even in a radiation environment. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram showing an example configuration of the optical amplifier according to Embodiment 1. [Figure 2] This is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit of the optical amplifier according to Embodiment 1. [Figure 3] This is a flowchart showing a control method for an optical amplifier according to Embodiment 1. [Figure 4] This is a block diagram showing an example configuration of the optical amplifier according to Embodiment 2. [Figure 5] This is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit of the optical amplifier according to Embodiment 2. [Figure 6] This is a flowchart showing a control method for an optical amplifier according to Embodiment 2. [Figure 7] Figures 7A and 7B are timing charts showing the implementation process with and without optical input. [Modes for carrying out the invention]

[0009] Embodiment 1. Figure 1 is a block diagram showing an example configuration of an optical amplifier 1 according to Embodiment 1. In Figure 1, the optical amplifier 1 is an optical device that amplifies an input signal light to a desired level and outputs it. As shown in Figure 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, an excitation light source 16, a control unit 17, a PD 18, a holding circuit 19, a memory circuit 20, and a radiation detector 21.

[0010] Optical coupler 10 is an optical component that, upon receiving light, splits the input light into optical coupler 11 and PD 15 for output. Optical coupler 11 is an optical component that, upon receiving light branched from optical coupler 10, combines the input light with the excitation light input from excitation light source 16 and outputs the result. Optical isolator 12 is an optical component that passes the light output from optical coupler 11 through EDFA 13 and blocks the return light that propagates through EDFA 13 and returns to the input side.

[0011] The EDFA (Erbium-Doped Fiber Amplifier) ​​13 is an optical amplification unit that amplifies and outputs the light output from the optical isolator 12. The EDFA 13 is an optical fiber doped with rare earth elements such as erbium, and can amplify the intensity of propagating light. When excitation light (pump light) output from the excitation light source 16 is incident on the EDFA 13, electrons of rare earth elements 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, thereby amplifying the intensity of the input light.

[0012] Although the optical amplifier 1 equipped with EDFA is shown, it is not limited to this. For example, the optical amplification section of the optical amplifier 1 may be a rare-earth doped optical fiber such as neodymium.

[0013] 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 PD 18 for output.

[0014] PD15 is a photodiode that detects the intensity of light output from the optical coupler 10. PD18 is a photodiode that detects the intensity of light output from the 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 together. When light is shone on a pn junction, electrons and holes are generated within the semiconductor by the light energy. These charges are then separated within the reverse-biased pn junction and detected as an electric current.

[0015] Photoelectric conversion efficiency is a parameter that indicates how efficiently a photodiode (PD) can convert incident light energy into an electrical signal. A PD with high photoelectric conversion efficiency can output most of the incident light energy as an electrical signal. For example, high-energy radiation such as gamma rays or X-rays can generate impurities by combining with electrons within the semiconductor of the PD, potentially creating defects in the crystal lattice. When defects are generated in the crystal lattice, the photoelectric conversion efficiency of the PD decreases. The intensity of light detected by a PD with reduced photoelectric conversion efficiency will be lower than the true level.

[0016] The excitation light source 16 excites the EDFA 13. The excitation light source 16 outputs excitation light to the optical coupler 11 to control the optical amplification factor of the EDFA 13, under control from the control unit 17. The optical coupler 11 combines the input light and the excitation light from the excitation light source 16 and outputs it to the optical isolator 12. For example, the excitation light source 16 is a laser diode that generates high-energy light with a wavelength close to the wavelength absorbed by erbium, and generally generates excitation light with a wavelength of about 980 nm or 1550 nm. Furthermore, the excitation level of erbium can be adjusted by adjusting the intensity of the excitation light output from the excitation light source 16. That is, when the intensity of the excitation light from the excitation light source 16 increases, the excitation of erbium also increases, and the amplification effect of the EDFA 13 is strengthened. Conversely, when the intensity of the excitation light decreases, the excitation of erbium also decreases, and the amplification effect of the EDFA 13 decreases.

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

[0018] The control unit 17 obtains 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 the light detected by the PD 15 and corrected using the radiation correction value. Alternatively, the control unit 17 may obtain 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 the light detected by the PD 18 and corrected using the radiation correction value. The control unit 17 may obtain radiation correction values corresponding to changes in the photoelectric conversion efficiencies of the PD 15 and the PD 18 due to radiation respectively, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensities of the lights detected by the PD 15 and the PD 18 respectively 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 photovoltaic display (PD) whose photoelectric conversion efficiency has been altered by radiation. For example, the radiation correction value is a value that corrects for the decrease in light intensity detected by a PD whose photoelectric conversion efficiency has been reduced by radiation. By replacing the light intensity detected by the PD with the radiation correction value, the true level of intensity, corrected for the change in photoelectric conversion efficiency due to radiation, can be obtained. The following describes the case where the light intensity detected by PD15 is corrected using the radiation correction value for PD15. Note that in the optical amplifier 1, the light intensity detected by PD18 may also be corrected using the radiation correction value for PD18.

[0020] The holding circuit 19 is a holding unit that stores radiation correction values ​​calculated based on the trend of changes in photoelectric conversion efficiency due to radiation. The holding circuit 19 is a memory that can be read from and written by the control unit 17, and stores radiation correction values ​​for each PD linked to the radiation dose. In other words, the holding circuit 19 stores radiation correction values ​​corresponding to each radiation dose for PD15 and PD18. The radiation correction values ​​are calculated by the control unit 17 or an external device.

[0021] The memory circuit 20 is a memory unit that stores 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 stored in the memory circuit 20. The control unit 17 acquires the radiation dose stored in the memory circuit 20 and obtains the radiation correction value of PD15 or PD18 corresponding to the acquired radiation dose.

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

[0023] The control unit 17 stores the radiation dose detected by the radiation detector 21 in the memory circuit 20. For example, the radiation detector 21 can 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 produced when radiation passes through the semiconductor. This signal is amplified and measured as the energy of the detected radiation. A scintillation detector is a detector that utilizes the fact that when radiation interacts with a substance, a substance called a scintillator emits light, and the amount of light is proportional to the energy of the radiation.

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

[0025] Figure 2 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 17. In Figure 2, the control unit 17 comprises a processor 101, memory 102, PDIF 103, excitation light source IF 104, holding circuit IF 105, memory circuit IF 106, and radiation detector IF 107. The functions of the control unit 17 are realized when the processor 101 reads and executes a program stored in memory 102. PDIF 103 is an interface between the control unit 17 and PD 15 and PD 18. Excitation light source IF 104 is an interface between the control unit 17 and excitation light source 16. Holding circuit IF 105 is an interface between the control unit 17 and holding circuit 19. Memory circuit IF 106 is an interface between the control unit 17 and memory circuit 20. Radiation detector IF 107 is an interface between the control unit 17 and 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, will result in the execution of the processes from step ST1 to step ST9 shown in Figure 3, which will be described later. These programs cause the computer to execute the procedures or methods for each process of the control unit 17. The memory 102 may be a computer-readable storage medium that stores a program for causing the computer to function as the control unit 17.

[0027] Memory 102 includes, for example, non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically-EPROM) (registered trademark). In addition to the above program, 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 intensity of light detected by PD15 and PD18 via PDIF103. The processor 101 also outputs a control signal to the excitation light source 16 via the excitation light source IF104. 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 the radiation correction value in the holding circuit 19 via the holding circuit IF105 and reads the radiation correction value from the holding circuit 19. The processor 101 stores the radiation dose in the memory circuit 20 via the memory circuit IF106 and reads the radiation dose from the memory circuit 20. The processor 101 acquires the radiation dose detected by the radiation detector 21 via the radiation detector IF107.

[0029] Next, a control method for the optical amplifier 1 according to Embodiment 1 will be described. Figure 3 is a flowchart showing the control method for the optical amplifier 1. The following describes the process for correcting changes in the detected light intensity due to changes in the photoelectric conversion efficiency of PD15 caused by radiation. The control unit 17 acquires information showing the trend of change in the photoelectric conversion efficiency of PD15 irradiated with radiation, and calculates a radiation correction value for PD15 based on the trend of change in photoelectric conversion efficiency shown in the acquired information (step ST1). This makes it possible to correct the light intensity detected by PD15 using the radiation correction value calculated based on the trend of change in the photoelectric conversion efficiency of PD15 caused by radiation.

[0030] For example, the control unit 17 acquires past radiation doses detected in the radiation environment in which the optical amplifier 1 is used, and identifies the trend of change in the photoelectric conversion efficiency of PD15 by acquiring the photoelectric conversion efficiency of PD15 corresponding to the acquired radiation dose. Next, the control unit 17 calculates a correction curve that shows the correspondence between the radiation dose and the detected value of PD15 based on the identified trend of change, and uses the calculated correction curve to calculate a radiation correction value, which is a correction value for the light intensity for each radiation dose.

[0031] The control unit 17 stores the radiation correction value calculated in step ST1 in the holding circuit 19 (step ST2). For example, the control unit 17 stores the radiation correction value calculated for each radiation dose in the holding 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 where the optical amplifier 1 is used, the radiation detector 21 detects the radiation dose at regular intervals or continuously. 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 circuit 20 (step ST4). For example, if the memory circuit 20 has the previous radiation dose detected by the radiation detector 21 stored in it, the control unit 17 adds the current radiation dose detected by the radiation detector 21 to the previous radiation dose and stores it.

[0034] Next, the control unit 17 retrieves the radiation dose accumulated to date from the memory circuit 20 (step ST5). Then, the control unit 17 retrieves the radiation correction value of PD15 corresponding to the retrieved radiation dose from the holding circuit 19 (step ST6). For example, the control unit 17 retrieves the radiation correction value corresponding to PD15 from the holding circuit 19. This allows the control unit 17 to retrieve the radiation correction value corresponding to the radiation dose accumulated to date.

[0035] The control unit 17 acquires the current light intensity detected by PD15 or PD18 (step ST7). For example, the control unit 17 acquires the current light intensity detected by PD15. Note that the photoelectric conversion efficiency of PD15 changes due to radiation, so the light intensity detected by PD15 is different from the true level unaffected by radiation.

[0036] Next, the control unit 17 calculates the true level using the acquired radiation correction value from the current light intensity detected by the PD 15 (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 makes the current light intensity detected by the PD 15 the intensity of the true level, corrected for the change in photoelectric conversion efficiency due to radiation.

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

[0038] The control unit 17 may also correct changes in the detected light intensity due to changes in the photoelectric conversion efficiency of the PD18. For example, the control unit 17 acquires past radiation doses detected in the radiation environment in which the optical amplifier 1 is used, and identifies the trend of changes in the photoelectric conversion efficiency of the PD18 by acquiring the photoelectric conversion efficiency of the PD18 corresponding to the acquired radiation dose. Based on the identified trend of changes, the control unit 17 calculates a correction curve showing the correspondence between the radiation dose and the detected value of the PD18, and uses the calculated correction curve to calculate a radiation correction value for the light intensity for each radiation dose. The control unit 17 can correct the light intensity detected by the PD18 to the true level by replacing the current light intensity detected by the PD18 with the radiation correction value.

[0039] Furthermore, the control unit 17 may compensate for changes in the detected light intensity due to changes in the photoelectric conversion efficiency of both PD15 and PD18. For example, the control unit 17 acquires past radiation doses detected in the radiation environment in which the optical amplifier 1 is used, and identifies the trend of change in photoelectric conversion efficiency by acquiring the photoelectric conversion efficiencies of PD15 and PD18 corresponding to the acquired radiation doses. Based on the identified trend of change in the photoelectric conversion efficiency of PD15, the control unit 17 calculates a correction curve showing the correspondence between the radiation dose and the detected value of PD15, and uses the calculated correction curve to calculate a radiation correction value for the intensity of light detected by PD15 for each radiation dose. Similarly, the control unit 17 uses a correction curve that shows the correspondence between the radiation dose calculated based on the trend of change in the photoelectric conversion efficiency of the identified PD18 and the detected value of the PD18 to calculate a radiation correction value for the intensity of light detected by the PD18 for each radiation dose. The control unit 17 can correct the light intensity detected by PD15 to the true level by replacing the current light intensity detected by PD15 with the acquired radiation correction value of PD15. 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] It should be noted that while the optical amplifier 1 has been shown to include PD15 and PD18, it is not limited to this configuration. For example, the optical amplifier 1 may include either PD15 or PD18. Furthermore, the optical amplifier 1 may include three or more PDs. In this case, the control unit 17 corrects for changes in the detected light intensity caused by 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 Embodiment 1 comprises an EDFA 13 that amplifies and outputs light, an excitation light source 16 that excites the EDFA 13, PD 15 and PD 18 that detect the intensity of light, and a control unit 17 that controls the excitation light source 16. The control unit 17 acquires a radiation correction value corresponding to the change in the photoelectric conversion efficiency of PD 15 and PD 18 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 PD 15 and PD 18 and corrected using the radiation correction value. As a result, the optical amplifier 1 can amplify the intensity of light to a desired level even in a radiation environment.

[0042] The optical amplifier 1 according to Embodiment 1 includes a radiation detector 21 for detecting radiation dose, and the control unit 17 acquires a radiation correction value corresponding to the radiation dose detected by the radiation detector 21. As a result, the control unit 17 can acquire a radiation correction value corresponding to the radiation dose detected by the radiation detector 21.

[0043] In the optical amplifier 1 according to Embodiment 1, the control unit 17 stores the radiation amount detected by the radiation detector 21 in the memory circuit 20 and obtains a radiation correction value corresponding to the radiation amount stored in the memory circuit 20. As a result, the control unit 17 can obtain a radiation correction value corresponding to the radiation amount stored to date.

[0044] In the optical amplifier 1 according to Embodiment 1, the control unit 17 stores a radiation correction value calculated based on the trend of change in photoelectric conversion efficiency due to radiation in the holding circuit 19, and corrects the intensity of light detected by PD15 or PD18 using the radiation correction value stored in the holding circuit 19. This makes it possible to correct the intensity of light detected by PD15 or PD18 using a radiation correction value calculated based on the trend of change in photoelectric conversion efficiency of PD15 or PD18 due to radiation.

[0045] The control method for the optical amplifier 1 according to Embodiment 1 comprises an EDFA 13 that amplifies and outputs light, an excitation light source that excites the EDFA 13, PD 15 and PD 18 that detect the intensity of light, and a control unit 17 that controls the excitation light source 16. The control unit 17 includes the steps of: acquiring radiation correction values ​​corresponding to changes in the photoelectric conversion efficiency of PD 15 and PD 18 due to radiation (ST1 to ST8); and controlling the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by PD 15 and PD 18 and corrected using the radiation correction values ​​(ST9). The control unit 17 that executes the control method according to Embodiment 1 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 Embodiment 1, the optical amplifier 1 is equipped with a radiation detector 21 that detects radiation dose, and the control unit 17 acquires a radiation correction value corresponding to the radiation dose detected by the radiation detector 21. As a result, the control unit 17 can correct the detected value of PD15 or PD18 using the radiation correction value corresponding to the radiation dose actually detected by the radiation detector 21.

[0047] Embodiment 2. Embodiment 1 describes an optical amplifier equipped with a radiation detector for detecting radiation levels and a memory circuit for storing radiation levels. Embodiment 2 describes an optical amplifier that does not have a radiation detector or memory circuit, but instead grasps the change in photoelectric conversion efficiency due to radiation based on the dark current and temperature of the photodiode.

[0048] Figure 4 is a block diagram showing an example configuration of the optical amplifier 1A according to Embodiment 2. The optical amplifier 1A is an optical device that amplifies the input signal light to a desired level and outputs it. As shown in Figure 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, an excitation light source 16, a control unit 17A, a PD 18, a holding circuit 19A, an optical cutoff circuit 22, an optical cutoff circuit 23, a temperature monitor 24, and a temperature monitor 25.

[0049] The optical coupler 10 is an optical component that, upon receiving light, splits the input light into an optical coupler 11 and an optical blocking circuit 22 for output. The optical coupler 11 is an optical component that, upon receiving light branched from the optical coupler 10, combines the input light with the excitation light input from the excitation light source 16 and outputs the result. The optical isolator 12 is an optical component that passes the light output from the optical coupler 11 through the EDFA 13 and blocks the return light that propagates through the EDFA 13 and returns to the input side.

[0050] EDFA13 is an optical amplifier that amplifies and outputs the light output from the optical isolator 12. EDFA13 is an optical fiber doped with rare earth elements such as erbium, and can amplify the intensity of propagating light. When excitation light output from the excitation light source 16 is incident on EDFA13, electrons of rare earth elements such as erbium in EDFA13 are excited, and light of the same wavelength as the input light is emitted. In EDFA13, the input light and the emitted light interfere, thereby amplifying the intensity of the input light. Although optical amplifier 1A equipped with EDFA is shown, it is not limited to this. For example, the optical amplifier 1A may be a rare earth doped optical fiber 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 optical interruption circuit 23 for output.

[0052] PD15 is a photodiode that detects the intensity of light output from the optical coupler 10 via the off-state light-blocking circuit 22. Light branched by the optical coupler 10 and heading towards PD15 is blocked by the on-state light-blocking circuit 22. Similarly, PD18 is a photodiode that detects the intensity of light output from the optical coupler 14 via the off-state light-blocking circuit 23. Light branched by the optical coupler 14 and heading towards PD18 is blocked by the on-state light-blocking circuit 23. 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 photodiode (PD) can convert incident light energy into an electrical signal. A PD with high photoelectric conversion efficiency outputs most of the incident light energy as an electrical signal. The dark current of a PD is the current that occurs in a PD when light is blocked. The dark current of a PD is mainly caused by heat generated inside the semiconductor of the PD. For example, as the temperature of the PD rises, the rate of carrier generation in the semiconductor of the PD increases, so the dark current of the PD tends to increase with rising temperature. Furthermore, an increase in the dark current of the photodiode increases the noise of the photodiode, which reduces the photoelectric conversion efficiency.

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

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

[0056] The control unit 17A acquires radiation correction values ​​corresponding to the dark current and temperature of the PD15, and controls the excitation of the EDFA13 by the excitation light source 16 based on the intensity of light detected by the PD15 corrected using the acquired radiation correction values. Furthermore, the control unit 17A may acquire radiation correction values ​​corresponding to the dark current and temperature of the PD18, and control the excitation of the EDFA13 by the excitation light source 16 based on the intensity of light detected by the PD18 corrected using the acquired radiation correction values. Furthermore, the control unit 17A may acquire a radiation correction value for PD15 based on the dark current and temperature of PD15, acquire a radiation correction value for PD18 based on the dark current and temperature of PD18, and control the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by PD15 and PD18 and corrected using their respective radiation correction values.

[0057] The control unit 17A may control the light blocking circuits 22 and 23 to alternately block light, obtain the radiation correction value for PD15, which has its light blocked by the light blocking circuit 22, and control the excitation of EDFA 13 by the excitation light source 16 based on the light intensity detected by PD15 and corrected using the obtained radiation correction value. Alternatively, it may obtain the radiation correction value for PD18, which has its light blocked by the light blocking circuit 23, and control the excitation of EDFA 13 by the excitation light source 16 based on the light intensity detected by PD18 and corrected using the obtained radiation correction value. In this way, the optical amplifier 1A can correct the light intensity detected by PD15 and PD18 based on the dark current and temperature of PD15 and PD18 without using a radiation detector.

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

[0059] The retention circuit 19A is a retention unit that stores radiation correction values ​​calculated based on the trend of changes in photoelectric conversion efficiency due to radiation. The retention circuit 19A is a memory that can be read from and written to by the control unit 17A, and the retention circuit 19A stores radiation correction values ​​for each PD, linked to the dark current of the PD and the temperature around the PD. For example, in Figure 4, the retention circuit 19A stores radiation correction values ​​corresponding to the dark current and temperature of PD15, or radiation correction values ​​corresponding to the dark current and temperature of PD18. The radiation correction values ​​are calculated by the control unit 17A or an external device.

[0060] In a radiation environment, the photoelectric conversion efficiency of a photodiode (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 the trend of change in the photoelectric conversion efficiency due to radiation based on the PD's dark current and temperature, and acquires a radiation correction value calculated based on the acquired trend. For example, the control unit 17A acquires the measurement results of the dark current and temperature of a PD in a reference state where no radiation is present, and the measurement results of the dark current and temperature generated in a PD irradiated with radiation, at a certain temperature. Based on the comparison results of the measured dark current and temperature with the dark current and temperature in the reference state, the control unit 17A identifies the trend of change in photoelectric conversion efficiency corresponding to the change in the dark current and temperature of the PD in the reference state. Subsequently, based on the identified trend of change, the control unit 17A calculates a correction curve showing the correspondence between the dark current and temperature of the PD and the detected value of the PD, and calculates a radiation correction value for the PD using the calculated correction curve. The control unit 17A stores the calculated radiation correction value in the holding circuit 19A, linked to the dark current and temperature.

[0061] The light blocking circuit 22 is a light blocking unit that blocks light from going to the PD15. For example, the light blocking circuit 22 switches between an on state and an off state according to a control signal from the control unit 17A. When the light blocking circuit 22 is on, it blocks the light going from the optical coupler 10 to the PD15, and when it is off, it allows the light going from the optical coupler 10 to the PD15 to pass through. The light blocking circuit 22 can be implemented, for example, by an optical switch.

[0062] The light blocking circuit 23 is a light blocking unit that blocks light from going to the PD18. For example, the light blocking circuit 23 switches between an on state and an off state according to a control signal from the control unit 17A. When the light blocking circuit 23 is on, it blocks the light going from the optical coupler 14 to the PD18, and when it is off, it allows the light going from the optical coupler 14 to the PD18 to pass through. The light blocking circuit 23 can be implemented, for example, by an optical switch.

[0063] Temperature monitor 24 is a sensor that detects the temperature around PD15. Temperature monitor 25 is a sensor that detects the temperature around PD18. The temperature monitoring information detected by temperature monitors 24 and 25 is output to the control unit 17A.

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

[0065] Figure 5 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 17A. In Figure 5, the control unit 17A includes a processor 101, memory 102, PDIF 103, excitation light source IF 104, holding circuit IF 105, light interruption circuit IF 108, and temperature monitor IF 109. The functions of the control unit 17A are realized when the processor 101 reads and executes a program stored in memory 102. PDIF 103 is the interface between the control unit 17A and PD15 and PD18. Excitation light source IF 104 is the interface between the control unit 17A and excitation light source 16. Holding circuit IF 105 is the interface between the control unit 17A and holding circuit 19A. Light interruption circuit IF 108 is the interface between the control unit 17A and light interruption circuits 22 and 23. Temperature monitor IF 107 is the interface between the control unit 17A and 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, will result in the execution of the processes from step ST1A to step ST20A shown in Figure 5, which will be described later. These programs cause the computer to execute the procedures or methods for each process of the control unit 17A. The memory 102 may be a computer-readable storage medium that stores a program for causing the computer to function as the control unit 17A.

[0067] Memory 102 includes, for example, non-volatile or volatile semiconductor memories such as RAM, ROM, flash memory, EPROM, and EEPROM (registered trademark). In addition to the above program, memory 102 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 intensity of light detected by PD15 and PD18 via PDIF103. The processor 101 also outputs a control signal to the excitation light source 16 via the excitation light source IF104. 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 the radiation correction value in the holding circuit 19A via the holding circuit IF105 and reads the radiation correction value from the holding circuit 19A. The processor 101 outputs a control signal to the light blocking circuit 22 or light blocking circuit 23 via the light blocking circuit IF108 to control light blocking. The processor 101 acquires temperature information detected by temperature monitors 24 and 25 via the temperature monitor IF109.

[0069] Next, a control method for the optical amplifier 1A according to Embodiment 2 will be described. Figure 6 is a flowchart showing the control method for the optical amplifier 1A. The processes from step ST1A to step ST20A shown in Figure 6 are repeatedly executed while the optical amplifier 1A is running. The control unit 17A acquires information showing the trend of change in the photoelectric conversion efficiency of PD15 and PD18 irradiated with radiation, and calculates radiation correction values ​​for PD15 and PD18 based on the trend of change in photoelectric conversion efficiency shown in the acquired information (step ST1A).

[0070] For example, the control unit 17A acquires the measurement results of the dark current and temperature of a PD in a reference state where no radiation is present, and the measurement results of the dark current and temperature generated in a PD irradiated with radiation. Based on the comparison results of the measured dark current and temperature with the dark current and temperature in the reference state, it identifies the trend of change in photoelectric conversion efficiency corresponding to the change in the dark current and temperature of the PD. Next, the control unit 17A calculates a correction curve showing the relationship between the dark current and temperature and the detected value of the PD based on the identified trend of change, 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 holding circuit 19A (step ST2A). For example, the control unit 17A stores in the holding circuit 19A a radiation correction value associated with at least one of the dark current or temperature of PD15 and PD18.

[0072] Next, the control unit 17A turns on only the light blocking circuit 22 to block the light to the PD15 (step ST3A). For example, the control unit 17A outputs a square wave control signal to the light blocking circuit 22. The light blocking circuit 22 is turned off when the control signal is at a high level and turned on when the control signal is at a low level.

[0073] When the light to PD15 is blocked by the light blocking circuit 22 (step ST3A; YES), the control unit 17A acquires the dark current from PD15 (step ST4A). Next, the control unit 17A acquires temperature information around PD15 from the temperature monitor 24 (step ST5A). Based on the dark current of PD15 and the temperature around PD15, the control unit 17A acquires the radiation correction value for PD15 from the holding circuit 19A (step ST6A). The processes in steps ST4A, ST5A, and ST6A may be performed in any order or simultaneously.

[0074] With light to PD15 blocked, the control unit 17A acquires the intensity of light detected by PD18 (step ST7A). Note that since the photoelectric conversion efficiency of PD18 changes due to radiation, the intensity of light detected by PD18 is different from the true level unaffected by radiation.

[0075] Next, the control unit 17A calculates the true level of the current light intensity detected by PD18 using the radiation correction value of PD18 obtained in step ST13A by performing the series of processes shown in Figure 6 in the previous step (step ST8A). For example, the control unit 17A replaces the current light intensity detected by PD18 with the radiation correction value of PD18. This makes it possible to set the current light intensity detected by PD18 to the true level of intensity corrected for the change in photoelectric conversion efficiency due to radiation.

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

[0077] When the light to PD15 is not blocked by the light blocking circuit 22 (step ST3A; NO), the control unit 17A turns on only the light blocking circuit 23 to block the light to PD18 (step ST10A). For example, the control unit 17A outputs a square wave control signal to the light blocking circuit 23. The light blocking circuit 23 is in the off state when the control signal is high level and in the on state when the control signal is low level.

[0078] When the light to PD18 is blocked by the light blocking circuit 23 (step ST10A; YES), the control unit 17A acquires the dark current from PD18 (step ST11A). Next, the control unit 17A acquires temperature information around the PD18 from the temperature monitor 25 (step ST12A). Based on at least one of the dark current of the PD18 or the temperature around the PD18, the control unit 17A acquires a radiation correction value for the PD18 from the holding circuit 19A (step ST13A). The processes in steps ST11A, ST12A, and ST13A may be performed in any order or simultaneously.

[0079] With light to PD18 blocked, the control unit 17A acquires the intensity of light detected by PD15 (step ST14A). Note that the photoelectric conversion efficiency of PD15 changes due to radiation, so the intensity of light detected by PD15 is different 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 PD15 using the radiation correction value of PD15 obtained in step ST7A by performing the process shown in Figure 6 in the previous step (step ST15A). For example, the control unit 17A replaces the current light intensity detected by PD15 with the radiation correction value of PD15. This makes the current light intensity detected by PD15 the true level of intensity corrected for the change in photoelectric conversion efficiency due to radiation.

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

[0082] When the light to PD15 is not blocked by the light blocking circuit 22 and the light to PD18 is not blocked by the light blocking circuit 23 (step ST10A; NO), the control unit 17A obtains a radiation correction value for 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] With light not blocked to PD15 and PD18, the control unit 17A acquires the intensity of the light detected by PD15 or PD18 (step ST18A). Note that the photoelectric conversion efficiency of PD15 and PD18 changes due to radiation, so the intensity of the light detected by PD15 or PD18 is different 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 PD15 or PD18 (step ST19A). For example, the control unit 17A replaces the current light intensity detected by PD15 or PD18 with the radiation correction value of PD15 or PD18. This makes the current light intensity detected by PD15 or PD18 the true level of intensity after correcting for changes in photoelectric conversion efficiency due to radiation.

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

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

[0087] In Figure 7A, the control signal is a square wave signal. When the control signal is at a high level, "optical input is present," meaning the optical interruption circuit 22 is in the off state, and light from the optical coupler 10 is input to PD15 via the optical interruption circuit 22. On the other hand, when the control signal is at a low level, "optical input is off," meaning the optical interruption circuit 22 is in the on state, and light from the optical coupler 10 to PD15 is blocked by the optical interruption circuit 22.

[0088] In Figure 7B, the control signal is a square wave signal. When the control signal is at a high level, "optical input is present," meaning the optical interruption circuit 23 is in the off state, and light from the optical coupler 14 is input to the PD 18 via the optical interruption circuit 23. On the other hand, when the control signal is at a low level, "optical input is off," meaning the optical interruption circuit 23 is in the on state, and light from the optical coupler 14 to the PD 18 is blocked by the optical interruption circuit 23. Note that the duty cycle of the control signals shown in Figure 7A and Figure 7B may be any value, as long as they do not generate a timing at which both the light interruption circuit 22 and the light interruption circuit 23 experience a light interruption.

[0089] During the period (1) shown in Figures 7A and 7B, both the control signals shown in Figure 7A and Figure 7B are at a high level, so both the optical cutoff circuit 22 and the optical cutoff circuit 23 are in the off state. At this time, the light branched from the optical coupler 10 to PD15 is input to PD15 via the optical cutoff circuit 22, and the light branched from the optical coupler 14 to PD18 is input to PD18 via the optical cutoff circuit 23. The control unit 17A controls the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of the light detected by PD15 or PD18. As a result, the optical amplifier 1A can output light amplified to the desired level. Changes in the intensity of the light detected by PD15 or PD18 due to radiation are corrected by the control unit 17A using a radiation correction value.

[0090] During the 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 blocking circuit 22 is in the off state and the light blocking circuit 23 is in the on state. At this time, the light branched from the optical coupler 10 to PD15 is input to PD15 via the light blocking circuit 22, and the light branched from the optical coupler 14 to PD18 is blocked by the light blocking circuit 23. The control unit 17A acquires the dark current and temperature of PD18, from which the light is blocked, and controls the excitation of EDFA 13 by the excitation light source 16 based on the light intensity detected by PD15. As a result, the optical amplifier 1A can output light amplified to the desired level. Changes in the light intensity detected by PD15 due to radiation are corrected by the control unit 17A using a radiation correction value.

[0091] During the 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 blocking circuit 22 is ON and the light blocking circuit 23 is OFF. At this time, the light branched from the optical coupler 10 to PD15 is blocked by the light blocking circuit 22, and the light branched from the optical coupler 14 to PD18 is input to PD18 via the light blocking circuit 23. The control unit 17A acquires the dark current and temperature of PD15, from which the light is blocked, and controls the excitation of EDFA13 by the excitation light source 16 based on the light intensity detected by PD18. As a result, the optical amplifier 1A can output light amplified to the desired level. Changes in the light intensity detected by PD18 due to radiation are corrected by the control unit 17A using a radiation correction value.

[0092] Furthermore, if the light branched to PD15 and the light branched to PD18 are blocked, it becomes impossible to control the optical output level of the optical amplifier 1A. For this reason, as shown in Figures 7A and 7B, the optical blocking process by optical blocking circuits 22 and 23 is controlled by the control unit 17A at a timing that does not block the light to at least one of PD15 or PD18.

[0093] As described above, in the optical amplifier 1A according to Embodiment 2, the control unit 17A acquires radiation correction values ​​corresponding to the dark current and temperature of PD15 or PD18. As a result, the optical amplifier 1A can amplify the intensity of light corrected based on the dark current and temperature of PD15 or PD18 to a desired level, even in a radiation environment.

[0094] In the optical amplifier 1A according to Embodiment 2, the control unit 17A acquires the trend of change in photoelectric conversion efficiency due to radiation based on the dark current and temperature of PD15 or PD18, and acquires a radiation correction value calculated based on the acquired trend of change. The optical amplifier 1A can acquire a radiation correction value based on the trend of change in photoelectric conversion efficiency acquired based on the dark current and temperature of PD15 or PD18, even without a radiation detector.

[0095] The optical amplifier 1A according to Embodiment 2 includes PD15 and PD18, and an optical blocking circuit 22 or optical blocking circuit 23 that blocks light to PD15 or PD18. The control unit 17A acquires the radiation correction value of PD15 or PD18 from which light is blocked by the optical blocking circuit 22 or optical blocking circuit 23, and controls the excitation of the EDFA 13 by the excitation light source 16 based on the intensity of light detected by PD15 or PD18 and corrected using the acquired radiation correction value. As a result, the optical amplifier 1A can 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 Embodiment 2, the control unit 17A acquires radiation correction values ​​corresponding to the dark current and temperature of PD15 or PD18. As a result, the control unit 17A can correct the detected value of PD15 or PD18 using the radiation correction values ​​corresponding to the dark current and temperature of PD15 or PD18.

[0097] Furthermore, it is possible to combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. [Industrial applicability]

[0098] The optical amplifier described herein can be used, for example, in optical fiber communications. [Explanation of Symbols]

[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. A light amplification unit that amplifies and outputs light, An excitation light source for exciting the aforementioned optical amplification unit, A photodiode for detecting the intensity of the aforementioned light, The system comprises a control unit for controlling the excitation light source, The control unit, A correction value is obtained corresponding to the change in the photoelectric conversion efficiency of the photodiode due to radiation. Based on the intensity of the light detected by the photodiode and corrected using the correction value, the excitation of the light amplification unit by the excitation light source is controlled. A light amplifier characterized by the following features.

2. Equipped with a radiation detector to detect radiation levels, The control unit acquires the correction value corresponding to the radiation dose detected by the radiation detector. The optical amplifier according to feature 1.

3. The control unit stores the radiation amount detected by the radiation detector in the storage unit and acquires the correction value corresponding to the radiation amount stored in the storage unit. The optical amplifier according to feature 2.

4. The control unit holds the correction value calculated based on the trend of change in the photoelectric conversion efficiency due to radiation in a holding unit, and corrects the intensity of the light detected by the photodiode using the correction value held in the holding unit. The optical amplifier according to any one of claims 1 to 3.

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

6. The control unit acquires the trend of change in the photoelectric conversion efficiency due to radiation based on the dark current and temperature of the photodiode, and acquires the correction value calculated based on the acquired trend. The optical amplifier according to feature 5.

7. Multiple photodiodes, The photodiode is provided with a light blocking section that blocks the light, The control unit acquires the correction value of the photodiode from which the light is blocked by the light blocking unit, and controls the excitation of the light amplification unit by the excitation light source based on the intensity of the light detected by the photodiode and corrected using the acquired correction value. The optical amplifier according to feature 6.

8. A light amplification unit that amplifies and outputs light, An excitation light source for exciting the aforementioned optical amplification unit, A photodiode for detecting the intensity of the aforementioned light, A method for controlling an optical amplifier comprising a control unit for controlling the excitation light source, The control unit, A step of obtaining a correction value corresponding to the change in the photoelectric conversion efficiency of the photodiode due to radiation, The method includes a step of controlling the excitation of the light amplification unit by the excitation light source based on the intensity of the light detected by the photodiode and corrected using the correction value. A control method characterized by the following:

9. The optical amplifier is equipped with a radiation detector for detecting radiation dose, The control unit acquires the correction value corresponding to the radiation dose detected by the radiation detector. The control method according to feature 8.

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

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