Fiber laser, excitation light source unit, and method for controlling fiber amplifier

Abstract

To realize a fiber laser with generation of a giant pulse suppressed.SOLUTION: A fiber laser (1) includes an MO unit (11), a PA unit (12), a voltage detection unit (12b3), and a control unit (12b2). The PA unit (12) has an optical fiber (12a), an excitation light source (LD), a capacitor (C), and a switch (SW2). A voltage detection unit (12b3) detects a voltage of a DC power source (PS) for supply a current to the MO unit (11) and the excitation light source (LD). A control unit (12b2) controls the switch (SW2) in an open state with the transition of a voltage detected by the voltage detection unit (12b3) from being higher than a predetermined threshold value to being lower than the threshold value as a trigger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fiber laser including a MO section and a PA section. It also relates to an excitation light source unit used for such a fiber laser. It also relates to a control method for such a fiber laser.

Background Art

[0002] As a high-power fiber laser used for laser processing and the like, a MOPA type fiber laser is widely used. As a document that discloses a MOPA type fiber laser, for example, Patent Document 1 can be cited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a MOPA type fiber laser, high-intensity laser light is obtained by amplifying the laser light generated in the MO section in the PA section. As the PA section, a fiber amplifier including an optical fiber doped with a rare earth element and an excitation light source for generating excitation light for exciting the rare earth element is used. In the PA section, amplification of the laser light is realized by stimulated emission in the rare earth element excited by the excitation light.

[0005] When an MOPA-type fiber laser is shut down in an emergency, the cessation of the laser light supply from the MO section to the PA section may precede the cessation of the excitation light supply from the excitation source in the PA section to the rare earth element. In this case, the energy of the excitation light is not consumed for the amplification of the laser light but is stored in the rare earth element. When the excitation light energy is stored in the rare earth element, noise or other triggers can cause a chain reaction of stimulated emission in the rare earth element to proceed explosively. This results in the output of ultra-high intensity pulsed light from the PA section. This ultra-high intensity pulsed light output from the PA section is called a giant pulse and can cause damage to surrounding optical components.

[0006] One aspect of the present invention has been made in view of the above-mentioned problems, and its purpose is to realize a fiber laser or the like that suppresses the generation of giant pulses. [Means for solving the problem]

[0007] A fiber laser according to embodiment 1 of the present invention comprises: an MO (Master Oscillator) unit; a PA (Power Amplifier) ​​unit that amplifies the laser light generated in the MO unit using the optical fiber, and includes an optical fiber doped with rare earth elements, an excitation light source that generates excitation light for exciting the rare earth elements, a capacitor connected in parallel to the excitation light source, and a switch provided in a closed current path including the excitation light source and the capacitor; a voltage detection unit that detects the voltage of a DC power supply that supplies current to the MO unit and the excitation light source; and a control unit that controls the switch to an open state as a trigger when the voltage detected by the voltage detection unit transitions from a state above a predetermined threshold to a state below a predetermined threshold.

[0008] With the above configuration, the supply of excitation light from the excitation light source to the rare earth elements in the PA section can be stopped before the supply of laser light from the MO section to the PA section is stopped. As a result, the generation of giant pulses can be suppressed.

[0009] In the fiber laser according to embodiment 2 of the present invention, in addition to the configuration of embodiment 1, the MO section includes an optical fiber doped with rare earth elements, an excitation light source that generates excitation light to excite the rare earth elements, and a capacitor connected in parallel to the excitation light source, and the DC power supply is configured to supply current to both the excitation light source included in the MO section and the excitation light source included in the PA section.

[0010] With the above configuration, the cessation of the supply of excitation light from the excitation light source to the rare earth elements in the PA section can be more reliably preceded by the cessation of the supply of laser light from the MO section to the PA section. As a result, the generation of giant pulses can be suppressed more reliably.

[0011] In the fiber laser according to embodiment 3 of the present invention, in addition to the configuration of embodiment 2, the time from when the switch is controlled to the open state until the current supplied to the excitation light source included in the PA section becomes 0A is 100 μs or less, and the time from when the switch is controlled to the open state until the current supplied to the excitation light source included in the MO section becomes 0A is 1 ms or more.

[0012] With the above configuration, the cessation of the supply of excitation light from the excitation light source to the rare earth elements in the PA section can be more reliably preceded by the cessation of the supply of laser light from the MO section to the PA section. As a result, the generation of giant pulses can be suppressed more reliably.

[0013] In the fiber laser according to aspect 4 of the present invention, in addition to the configuration of aspects 1 to 3, the switch is a negative-side switch provided on the current path between the negative electrode of the DC power supply and the excitation light source of the MO section, and the control unit controls the negative-side switch to an open state when the voltage detected by the voltage detection unit transitions from a state above the threshold to a state below the threshold.

[0014] With the above configuration, the negative electrode switch, which is used to drive the excitation light source during normal operation, can be used to prevent the charge stored in the capacitor from flowing into the excitation light source during an emergency stop.

[0015] In the fiber laser according to aspect 5 of the present invention, in addition to the configuration of aspects 1 to 3, the switches are a negative-side switch provided on the current path between the negative electrode of the DC power supply and the excitation light source of the MO unit, and a positive-side switch provided on the current path between the positive electrode of the DC power supply and the excitation light source of the MO unit, and the control unit controls both the negative-side switch and the positive-side switch to an open state when the voltage detected by the voltage detection unit transitions from a state above the threshold to a state below the threshold.

[0016] With the above configuration, even if the negative electrode switch fails or a ground fault occurs in the excitation light source, the charge stored in the capacitor can be prevented from flowing into the excitation light source by controlling the positive electrode switch to an open state.

[0017] In the fiber laser according to aspect 6 of the present invention, in addition to the configuration of any of aspects 1 to 5, the switch is a FET (Field Effect Transistor).

[0018] With the above configuration, the switch can be opened and closed at high speed.

[0019] An excitation light source unit according to embodiment 7 of the present invention is an excitation light source unit for use in a fiber amplifier including an optical fiber doped with a rare earth element, comprising: an excitation light source that generates excitation light for exciting the rare earth element; a capacitor connected in parallel with the excitation light source; a switch provided on the current path between the excitation light source and the capacitor; a voltage detection unit that detects the voltage of a DC power supply that supplies current to the excitation light source; and a control unit that controls the switch to an open state as a trigger when the voltage detected by the voltage detection unit transitions from a state above a predetermined threshold to a state below a predetermined threshold.

[0020] With the above configuration, the supply of excitation light from the excitation light source to the rare earth element in the fiber amplifier can be stopped before the supply of laser light to the fiber amplifier is stopped. As a result, the generation of giant pulses can be suppressed.

[0021] A control method for a fiber laser according to aspect 8 of the present invention is a control method for a fiber laser comprising: an MO (Master Oscillator) unit; a PA (Power Amplifier) ​​unit which includes an optical fiber doped with rare earth elements, an excitation light source that generates excitation light for exciting the rare earth elements, a capacitor connected in parallel to the excitation light source, and a switch provided on the current path between the excitation light source and the capacitor, and which amplifies the laser light generated in the MO unit using the optical fiber, the control method comprising: a voltage detection step of detecting the voltage of a DC power supply that supplies current to the MO unit and the excitation light source; and a control step of controlling the switch to an open state when the voltage detected by the voltage detection unit transitions from a state above a predetermined threshold to a state below a predetermined threshold.

[0022] With the above configuration, the supply of excitation light from the excitation light source to the rare earth elements in the PA section can be stopped before the supply of laser light from the MO section to the PA section is stopped. As a result, the generation of giant pulses can be suppressed. [Effects of the Invention]

[0023] According to one aspect of the present invention, generation of giant pulses can be suppressed.

Brief Description of the Drawings

[0024] [Figure 1] (a) is a schematic diagram showing the configuration of a fiber laser according to an embodiment of the present invention. (b) is a circuit diagram showing the configuration of an excitation light source unit included in the MO section of the fiber laser. (c) is a circuit diagram showing the configuration of an excitation light source unit included in the PA section of the fiber laser. [Figure 2] The effects of the fiber laser shown in FIG. 1 are shown. (a) is a graph showing the time change of the power supply voltage of the DC power supply. (b) is a graph showing the time change of the drive current of the laser diode. [Figure 3] Modifications of the fiber laser shown in FIG. 1 are shown. (a) is a circuit diagram showing a first modification of the excitation light source unit of the PA section. (b) is a circuit diagram showing a second modification of the excitation light source unit of the PA section. (c) is a circuit diagram showing a third modification of the excitation light source unit of the PA section. [Figure 4] Modifications of the fiber laser shown in FIG. 1 are shown. (a) is a schematic diagram showing a first modification of the MO section. (b) is a schematic diagram showing a second modification of the MO section. [Figure 5] Modifications of the fiber laser shown in FIG. 1 are shown. (a) is a schematic diagram showing a first modification of the PA section. (b) is a schematic diagram showing a second modification of the PA section.

Modes for Carrying Out the Invention

[0025] (Configuration of Fiber Laser) The fiber laser 1 according to an embodiment of the present invention will be described with reference to (a) of FIG. 1. (a) of FIG. 1 is a schematic diagram showing the configuration of the fiber laser 1.

[0026] The fiber laser 1 is an MOPA-type processing fiber laser, and as shown in Figure 1(a), it comprises an MO (Master Oscillator) unit 11, a PA (Power Amplifier) ​​unit 12 that amplifies the laser light generated by the MO unit 11, and a processing head 13. The processing head 13 can be replaced depending on the application, and can also be omitted.

[0027] In this embodiment, a forward-excited fiber laser is used as the MO unit 11. The MO unit 11 is, for example, shown in Figure 1(a) to As shown, the system can be composed of an optical fiber 11a, an excitation light source unit 11b, a combiner 11c, and a pair of FBGs (Fiber Bragg Gratings) 11d1 and 11d2. The excitation light source unit 11b may be a plurality of units, as shown in Figure 1(a).

[0028] The optical fiber 11a is an optical fiber (for example, a double-clad fiber) in which rare earth elements are added to the core. The rare earth element added to the core of the optical fiber 11a is not particularly limited, but in this embodiment, Yb is used. An FBG11d1, which functions as a mirror, is connected to one end of the optical fiber 11a, and an FBG11d2, which functions as a half-mirror, is connected to the other end of the optical fiber 11a. As a result, the optical fiber 11a functions as a resonator that recursively amplifies the laser light emitted from the excited rare earth element.

[0029] The excitation light source unit 11b is configured to generate excitation light (forward excitation light) to excite the rare earth elements added to the core of the optical fiber 11a. The excitation light source that generates the excitation light is not particularly limited, but in this embodiment, an LD (Laser Diode) is used. The configuration of the excitation light source unit 11b will be described later with reference to Figure 1(b). The excitation light generated by the excitation light source unit 11b is introduced into the inner cladding of the optical fiber 11 by the combiner 11c.

[0030] Furthermore, in this embodiment, a back-excited fiber amplifier is used as the PA unit 12. The PA unit 12 can be composed of, for example, an optical fiber 12a, an excitation light source unit 12b, and a combiner 12c, as shown in Figure 1(a). There may be multiple excitation light source units 12b, as shown in Figure 1(a).

[0031] The optical fiber 12a is an optical fiber (for example, a double-clad fiber) with a rare earth element added to its core. The rare earth element added to the core of the optical fiber 12a is not particularly limited, but in this embodiment, Yb is used. The FBG11d2 of the MO section 11 is connected to one end of the optical fiber 12a. As a result, the optical fiber 12a functions as an amplifier that amplifies the laser light generated by the MO section 11. The processing head 13 is connected to the other end of the optical fiber 12a. As a result, the laser amplified by the optical fiber 12a is irradiated onto the workpiece via the processing head 13.

[0032] The excitation light source unit 12b is configured to generate excitation light (back-excitation light) to excite the rare earth elements added to the core of the optical fiber 12a. The excitation light source that generates the excitation light is not particularly limited, but in this embodiment, an LD is used. The configuration of the excitation light source unit 12b will be described later with reference to Figure 1(c). The excitation light generated by the excitation light source unit 12b is introduced into the inner cladding of the optical fiber 12 by the combiner 12c.

[0033] The excitation light source unit 11b of the MO section 11 and the excitation light source unit 12b of the PA section 12 are operated by current supplied from a common DC power supply PS (for example, an AC / DC converter connected to an AC power supply such as a commercial power supply). A switch SW0 is provided in the current path between the DC power supply PS and the excitation light source units 11b and 12b. This switch SW0 is an emergency stop switch for, for example, to emergency stop the operation of the fiber laser 1 when some abnormality occurs in the fiber laser 1. In this embodiment, a relay switch is used as switch SW0.

[0034] When this switch SW0 is opened, the supply of current to the excitation light source units 11b and 12b is stopped, and as a result, the supply of excitation light to the optical fibers 11a and 12a is stopped. In this case, if the cessation of the supply of excitation light to the optical fiber 11a by the MO unit 11 precedes the cessation of the supply of excitation light to the optical fiber 12a by the PA unit 12, there is a risk of giant pulses occurring in the PA unit 12. For this reason, in the fiber laser 1 according to this embodiment, the configuration of the excitation light source unit 12b is modified so that the cessation of the supply of excitation light to the optical fiber 12a by the PA unit 12 precedes the cessation of the supply of excitation light to the optical fiber 11a by the MO unit 11.

[0035] (Configuration of the excitation light source unit in the MO section) The configuration of the excitation light source unit 11b of the MO section 11 will be explained with reference to Figure 1(b). Figure 1(b) is a circuit diagram showing the configuration of the excitation light source unit 11b of the MO section 11.

[0036] The excitation light source unit 11b consists of a laser diode LD that generates excitation light and a drive circuit that drives the laser diode LD. This drive circuit can consist of, for example, a diode D, a capacitor C, an inductor L, a switch SW1 (an example of a "positive-side switch" in the claims), a switch SW2 (an example of a "negative-side switch" in the claims), a current detection unit 11b1, and a control unit 11b2, as shown in Figure 1(b).

[0037] Diode D and capacitor C are connected in parallel to the laser diode LD. The laser diode LD is oriented so that its anode is connected to the positive terminal of the DC power supply PS and its cathode is connected to the negative terminal of the DC power supply PS. Similarly, diode D is oriented so that its cathode is connected to the positive terminal of the DC power supply PS and its anode is connected to the negative terminal of the DC power supply PS.

[0038] Switches SW1, SW2, and inductor L are each connected in series with the laser diode LD. Switch SW1 is located outside the closed current path γD containing the laser diode LD and diode D, and outside the closed current path γC containing the laser diode LD and capacitor C. Switch SW2 is located outside the closed current path γD containing the laser diode LD and diode D, and inside the closed current path γC containing the laser diode LD and capacitor C. Inductor L is located inside the closed current path γD containing the laser diode LD and diode D, and inside the closed current path γC containing the laser diode LD and capacitor C. In this embodiment, FETs (Field Effect Transistors) are used as switches SW1 and SW2.

[0039] The current detection unit 11b1 detects the current flowing into the laser diode LD (hereinafter also referred to as "drive current I1"). During normal operation, the control unit 11b2 maintains switch SW1 in the closed state and controls switch SW2 to open or close based on the magnitude of the drive current I1. More specifically, the control unit 11b2 (1) controls switch SW2 to the open state when the drive current I1 exceeds a predetermined threshold Th1, and (2) controls switch SW2 to the closed state when the drive current I1 falls below the threshold Th1. As a result, while switch SW0 shown in Figure 1(a) is controlled to the open state, the laser diode LD is continuously supplied with a drive current I1 having a magnitude approximately equal to the threshold Th1.

[0040] When switch SW0 is opened during an emergency stop, the supply of current to the excitation light source unit 11b is stopped. However, if switch SW2 is closed, the supply of drive current I1 to the laser diode LD continues. This is because the charge stored in capacitor C flows into the laser diode LD. Also, as shown in Figure 1(b), if the filter F inserted between the excitation light source unit 11b and the DC power supply PS includes a capacitor connected in parallel with the laser diode LD, then if switches SW1 and SW2 are closed, the charge stored in these capacitors will also flow into the laser diode LD. Note that filter F is not an essential component and may be omitted.

[0041] (Configuration of the PA section's excitation light source unit) The configuration of the excitation light source unit 12b of the PA section 12 will be explained with reference to Figure 1(c). Figure 1(c) is a circuit diagram showing the configuration of the excitation light source unit 12b of the PA section 12.

[0042] The excitation light source unit 12b consists of a laser diode LD that generates excitation light and a drive circuit that drives the laser diode LD. The configuration of the drive circuit of the excitation light source unit 12b is the same as that of the drive circuit of the excitation light source unit 11b shown in Figure 1(b), except that a voltage detection unit 12b3 is added.

[0043] The current detection unit 12b1, like the current detection unit 11b1, detects the current flowing into the laser diode LD (hereinafter also referred to as "drive current I2"). The control unit 12b2, like the control unit 11b2, maintains switch SW1 in the closed state during normal operation and controls the opening and closing of switch SW2 based on the magnitude of the drive current I2. More specifically, the control unit 12b2 (1) controls switch SW2 to the open state when the drive current I2 exceeds a predetermined threshold Th2, and (2) controls switch SW2 to the closed state when the drive current I2 falls below the threshold Th2. As a result, while switch SW0 shown in Figure 1(a) is controlled to the open state, the laser diode LD is continuously supplied with a drive current I2 having a magnitude approximately equal to the threshold Th1.

[0044] The voltage detection unit 12b3 detects the voltage of the DC power supply PS (hereinafter also referred to as "power supply voltage V0"). The control unit 12b2 controls the switch SW2 based on the magnitude of the power supply voltage V0. More specifically, the control unit 12b2 controls the switch SW2 to the open state as a trigger when the power supply voltage V0 transitions from a state where it exceeds a predetermined threshold Th0 to a state where it falls below the threshold Th0.

[0045] Here, the threshold Th is set to a value smaller than the rated voltage of the DC power supply PS (for example, a value of about 85% of the rated voltage of the DC power supply PS). For example, if the rated voltage of the DC power supply PS is 270V, then the threshold Th is set to 230V. Therefore, when switch SW0 is opened during an emergency stop, switch SW2 is controlled to open immediately afterward. By opening switch SW2, the charge stored in capacitor C is prevented from flowing into the laser diode LD. Also, by opening switch SW2, the charge stored in the capacitor included in filter F is prevented from flowing into the laser diode LD. Consequently, the time from when the supply of current to the excitation light source unit 12b is stopped until the supply of the drive current I2 from the excitation light source unit 12b to the laser diode LD is stopped is shorter than the time from when the supply of current to the excitation light source unit 11b is stopped until the supply of the drive current I1 from the excitation light source unit 11b to the laser diode LD is stopped.

[0046] Furthermore, when the power supply voltage V0 transitions to a state below the threshold Th0, the control unit 12b2 may control not only switch SW2 but also both switches SW1 and SW2 to the open state. This makes it possible to prevent the charge stored in the capacitor included in the filter F from flowing into the laser diode LD even if a ground fault occurs in the laser diode LD or if switch SW2 fails. Switch SW1 can also be used for emergency shutdown when an alarm occurs.

[0047] In this embodiment, the voltage detection unit 12b3 is located inside the excitation light source unit 12b, but the present invention is not limited thereto. That is, a configuration in which the voltage detection unit 12b3 is located outside the excitation light source unit 12b may also be adopted. Furthermore, in this embodiment, the function of controlling switches SW1 and SW2 to the open state according to the power supply voltage V0 is handled by a control unit 12b2 located inside the excitation light source unit 12b, but the present invention is not limited thereto. That is, the function of controlling switches SW1 and SW2 to the open state according to the power supply voltage V0 may be handled by a control unit located outside the excitation light source unit 12b, for example, a control unit that controls the entire fiber laser.

[0048] (Effects of fiber lasers) The effects obtained by the fiber laser 1 will be explained with reference to Figure 2. In Figure 2, (a) is DC. power supply This shows the time variation of the PS power supply voltage V0. G (b) is a rough graph showing the time variation of the drive current I1 supplied to the laser diode LD of the MO section 11 and the drive current I2 supplied to the laser diode LD of the PA section 12.

[0049] When switch SW0 is controlled to the open state at time t0, the power supply voltage V0 begins to decrease (see Figure 2(a)). Then, at time t1, when the power supply voltage V0 transitions from a state above the threshold Th0 to a state below the threshold Th0 (see Figure 2(a)), the control unit 12b2 of the PA unit 12 controls switch SW2 to the open state (see Figure 1(c)).

[0050] As a result, the drive current I2 supplied to the laser diode LD in the PA section 12 decreases sharply (see Figure 2(b)). On the other hand, the charge stored in the capacitor C continues to flow into the laser diode LD in the MO section 11 as the drive current I1. Therefore, the drive current I1 supplied to the laser diode LD in the MO section 11 decreases more slowly than the drive current I2 supplied to the laser diode LD in the PA section 12 (see Figure 2(b)).

[0051] The time Δt1 from when the control unit 12b2 of the PA unit 12 controls switch SW2 to the open state until the supply of drive current I1 to the laser diode LD of the MO unit 11 is stopped is the time required for the capacitor C to discharge, and is, for example, 1 millisecond or more. There is no particular upper limit to this time Δ1, but for example, it is 500 milliseconds. In contrast, the time Δt2 from when the control unit 12b2 of the PA unit 12 controls switch SW2 to the open state until the supply of drive current I2 to the laser diode LD of the PA unit 12 is stopped is the time required for the inductor L to discharge, and is, for example, 100 microseconds or less. There is no particular lower limit to this time Δt2, but for example, it is 1 nanosecond.

[0052] This allows the supply of excitation light from the excitation light source unit 12b of the PA unit 12 to the optical fiber 12a of the PA unit 12 to be stopped before the supply of laser light from the optical fiber 11a of the MO unit 11 to the optical fiber 12a of the PA unit 12 is stopped. Therefore, the possibility of giant pulses occurring in the optical fiber 12a of the PA unit 12 can be significantly reduced.

[0053] (Modified version of the excitation light source unit in the PA section) A modified example of the excitation light source unit 12b of the PA section 12 will be described with reference to Figure 3.

[0054] Figure 3(a) is a circuit diagram showing a first modified example of the excitation light source unit 12b.

[0055] The difference between the excitation light source unit 12b shown in Figure 1(c) and the excitation light source unit 12b shown in Figure 3(a) lies in the position of the switch SW1. Specifically, in the excitation light source unit 12b shown in Figure 1(c), the switch SW1 is located outside the closed current path γC which includes the laser diode LD and capacitor C. In contrast, in the excitation light source unit 12b shown in Figure 3(a), the switch SW1 is located inside the closed current path γC which includes the laser diode LD and capacitor C.

[0056] Therefore, in the excitation light source unit 12b shown in Figure 3(a), by controlling at least one of switches SW1 and SW2 to the open state, it is possible to prevent the charge stored in capacitor C from flowing into the laser diode LD. If a configuration is adopted in which both switches SW1 and SW2 are controlled to the open state, it becomes possible to prevent the charge stored in capacitor C and the capacitor included in filter F from flowing into the laser diode LD even if a ground fault occurs in the laser diode LD or if switch SW2 fails.

[0057] Figure 3(b) is a circuit diagram showing a second modified example of the excitation light source unit 12b.

[0058] The difference between the excitation light source unit 12b shown in Figure 1(c) and the excitation light source unit 12b shown in Figure 3(b) is that the former has a switching-type drive circuit, while the latter has a linear-type drive circuit. ,figure In the excitation light source unit 12b shown in 3(b), the diode D and inductor L are omitted. Furthermore, during normal operation, the control unit 12b2 sets the resistance value of the switch SW2(FET) by adjusting the gate voltage of the switch SW2(FET) so that the drive current I2 matches a predetermined value.

[0059] In the excitation light source unit 12b shown in Figure 3(b), similar to the excitation light source unit 12b shown in Figure 1(c), the charge stored in capacitor C can be prevented from flowing into the laser diode LD by controlling switch SW2 to the open state.

[0060] Figure 3(c) is a circuit diagram showing a third modified example of the excitation light source unit 12b.

[0061] The difference between the excitation light source unit 12b shown in Figure 3(b) and the excitation light source unit 12b shown in Figure 3(c) lies in the position of the switch SW1. Specifically, in the excitation light source unit 12b shown in Figure 3(b), the switch SW1 is located outside the closed current path γC, which includes the laser diode LD and capacitor C. In contrast, in the excitation light source unit 12b shown in Figure 3(c), the switch SW1 is located inside the closed current path γC, which includes the laser diode LD and capacitor C.

[0062] Therefore, in the excitation light source unit 12b shown in Figure 3(c), by controlling at least one of switches SW1 and SW2 to the open state, it is possible to prevent the charge stored in capacitor C from flowing into the laser diode LD. If a configuration is adopted in which both switches SW1 and SW2 are controlled to the open state, it becomes possible to prevent the charge stored in capacitor C and the capacitor included in filter F from flowing into the laser diode LD even if a ground fault occurs in the laser diode LD or if switch SW2 fails.

[0063] In this document, we have described three modifications of the excitation light source unit 12b of the PA section 12, but similar modifications are also possible for the excitation light source unit 11b of the MO section 11.

[0064] (Modified version of MO section) A first modified example of the MO section 11 will be described with reference to Figure 4(a). Figure 4(a) is a schematic diagram showing the first modified example of the MO section 11.

[0065] The MO unit 11 shown in Figure 4(a) is a bidirectional excitation fiber laser, which is the MO unit 11 shown in Figure 1(a) with the addition of an excitation light source unit 11b' and a combiner 11c'. Here, the excitation light source unit 11b' is configured to generate excitation light (back-excitation light) to excite the rare earth elements added to the core of the optical fiber 11a. The combiner 11c' is configured to introduce the excitation light generated by the excitation light source unit 11b' into the inner cladding of the optical fiber 11a.

[0066] A second modified example of the MO section 11 will be described with reference to Figure 4(b). Figure 4(b) is a schematic diagram showing the second modified example of the MO section 11.

[0067] The MO unit 11 shown in Figure 4(b) is a back-excited fiber laser in which the excitation light source unit 11b and combiner 11c of the MO unit 11 shown in Figure 1(a) are replaced with an excitation light source unit 11b' and combiner 11c'. Here, the excitation light source unit 11b' is configured to generate excitation light (back-excited light) to excite the rare earth elements added to the core of the optical fiber 11a. The combiner 11c' is configured to introduce the excitation light generated by the excitation light source unit 11b' into the inner cladding of the optical fiber 11a.

[0068] Furthermore, the MO unit 11 can be any laser device that generates the laser light (seed light) supplied to the PA unit 12, and does not need to be a fiber laser. Any laser device that can be driven by a DC power supply PS, such as a solid-state laser, liquid laser, or gas laser, can be used as the MO unit 11.

[0069] (A variation of the PA section) A first modified example of the PA section 12 will be described with reference to Figure 5(a). Figure 5(a) is a schematic diagram showing the first modified example of the PA section 12.

[0070] The PA unit 12 shown in Figure 5(a) is a bidirectional excitation type fiber amplifier, which adds an excitation light source unit 12b' and a combiner 12c' to the PA unit 12 shown in Figure 1(a). Here, the excitation light source unit 12b' is configured to generate excitation light (forward excitation light) to excite the rare earth elements added to the core of the optical fiber 12a. The combiner 12c' is configured to introduce the excitation light generated by the excitation light source unit 12b' into the inner cladding of the optical fiber 12a.

[0071] A second modified example of the PA section 12 will be described with reference to Figure 5(b). Figure 5(b) is a schematic diagram showing the second modified example of the PA section 12.

[0072] The PA unit 12 shown in Figure 5(b) is a forward-excited fiber laser in which the excitation light source unit 12b and combiner 12c of the PA unit 12 shown in Figure 1(a) are replaced with an excitation light source unit 12b' and a combiner 12c'. Here, the excitation light source unit 12b' is configured to generate excitation light (forward excitation light) to excite the rare earth elements added to the core of the optical fiber 12a. The combiner 12c' is configured to introduce the excitation light generated by the excitation light source unit 12b' into the inner cladding of the optical fiber 12a.

[0073] (Additional notes) The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means included in the embodiments described above are also included within the technical scope of the present invention. [Explanation of Symbols]

[0074] 1. Fiber laser 11 MO section 11a optical fiber 11b Excitation light source unit 11b1 Current detection unit 11b2 Control Unit 11c Combiner 12 PA section 12a optical fiber 12b Excitation light source unit 12b1 Current detection unit 12b2 Control Unit 12b3 Voltage detection unit 12c combiner

Claims

1. MO (Master Oscillator) section, A Power Amplifier (PA) unit that amplifies the laser light generated in the MO unit using the optical fiber, includes an optical fiber doped with rare earth elements, an excitation light source that generates excitation light to excite the rare earth elements, a capacitor connected in parallel to the excitation light source, and a switch provided in a closed current path including the excitation light source and the capacitor. A voltage detection unit for detecting the voltage of a DC power supply that supplies current to the MO unit and the excitation light source, The system includes a control unit that controls the switch to an open state when the voltage detected by the voltage detection unit transitions from a state above a predetermined threshold to a state below a predetermined threshold, which is used as a trigger. A fiber laser characterized by the following features.

2. The MO section includes an optical fiber doped with rare earth elements, an excitation light source that generates excitation light to excite the rare earth elements, and a capacitor connected in parallel to the excitation light source. The DC power supply supplies current to both the excitation light source included in the MO section and the excitation light source included in the PA section. The fiber laser according to feature 1.

3. The time from when the switch is controlled to the open state until the current supplied to the excitation light source included in the PA unit becomes 0 A is 100 μs or less. The time from when the switch is controlled to the open state until the current supplied to the excitation light source included in the MO unit becomes 0 A is 1 millisecond or more. The fiber laser according to feature 2.

4. The switch is a negative-side switch provided on the current path between the negative electrode of the DC power supply and the excitation light source of the MO section. The control unit controls the negative electrode switch to an open state when the voltage detected by the voltage detection unit transitions from a state above the threshold to a state below the threshold. A fiber laser according to any one of claims 1 to 3.

5. The switches are a negative-side switch provided on the current path between the negative electrode of the DC power supply and the excitation light source of the MO unit, and a positive-side switch provided on the current path between the positive electrode of the DC power supply and the excitation light source of the MO unit. The control unit controls one or both of the negative-side switch and the positive-side switch to an open state when the voltage detected by the voltage detection unit transitions from a state above the threshold to a state below the threshold. A fiber laser according to any one of claims 1 to 3.

6. The aforementioned switch is a FET (Field Effect Transistor). A fiber laser according to any one of claims 1 to 3.

7. An excitation light source unit for use in a fiber amplifier containing an optical fiber doped with rare earth elements, An excitation light source that generates excitation light for exciting the aforementioned rare earth element, A capacitor connected in parallel to the excitation light source, A switch provided in the current path between the excitation light source and the capacitor, A voltage detection unit that detects the voltage of a DC power supply that supplies current to the excitation light source, The system includes a control unit that controls the switch to an open state when the voltage detected by the voltage detection unit transitions from a state above a predetermined threshold to a state below a predetermined threshold, which is used as a trigger. An excitation light source unit characterized by the following features.

8. A control method for a fiber laser comprising: an MO (Master Oscillator) section; an optical fiber doped with rare earth elements; an excitation light source that generates excitation light to excite the rare earth elements; a capacitor connected in parallel to the excitation light source; and a PA (Power Amplifier) ​​section that amplifies the laser light generated in the MO section using the optical fiber, wherein the PA section includes a switch provided on the current path between the excitation light source and the capacitor. A voltage detection step for detecting the voltage of a DC power supply that supplies current to the MO section and the excitation light source, The control step includes controlling the switch to an open state when the voltage detected in the voltage detection step transitions from a state above a predetermined threshold to a state below a predetermined threshold. A method for controlling a fiber laser, characterized by the following features.

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