Fiber laser device

Abstract

To provide a fiber laser device capable of reducing light having a wavelength different from that of light that is originally desired to be amplified.SOLUTION: A fiber laser device 1 includes a seed light source 10 capable of generating seed light S1, a first amplification optical fiber 30 capable of amplifying the seed light S1 to generate signal light S2, a plurality of excitation optical fiber lasers 20 capable of generating excitation light P1, a plurality of photodetectors 26 capable of detecting different wavelength light having a wavelength different from that of the excitation light P1, and a control unit 60. Each excitation optical fiber laser 20 includes an excitation light source 24 capable of generating excitation light P2, a second amplification optical fiber 40 that generates excitation light P1 with excitation caused by the excitation light P2, and a high reflection section 51 and a low reflection section 52 that reflect the excitation light P1. The control unit 60 is configured to control the excitation light source 24 of the excitation optical fiber laser 20 such that the light intensity of the different wavelength light detected by the plurality of photodetectors 26 is equal to or lower than a threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fiber laser device.

Background Art

[0002] In a fiber laser, the quantum conversion efficiency is determined by the ratio of the wavelength of the pump light to the wavelength of the signal light. As the difference between the wavelength of the pump light and the wavelength of the signal light increases, the heat due to quantum deficiency increases. When the heat load on the optical fiber increases, a phenomenon called transverse mode instability (TMI) is likely to occur. This TMI is a phenomenon in which the laser output becomes unstable due to a thermal grating generated in the optical fiber.

[0003] In order to suppress such TMI, it is considered to reduce the heat load in the optical fiber by bringing the wavelength of the pump light closer to the wavelength of the signal light. For example, a tandem excitation fiber laser system has been developed in which pump light having a wavelength close to the wavelength of the signal light is generated by a fiber laser in the previous stage and this pump light is introduced into an optical fiber for amplification (see, for example, Patent Document 1).

[0004] However, light close to the wavelength of the signal light generated by the fiber laser in the previous stage is more difficult to amplify than light having a wavelength in the range of 1060 to 1080 nm, which is commonly used as the oscillation wavelength of the fiber laser. When attempting to amplify light of this wavelength, light having a wavelength different from the pump light that is originally intended to be amplified is more likely to be emitted than the pump light. When the power of the light having a wavelength different from the pump light increases, it may cause damage to optical components such as the pump light source and the optical combiner.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a fiber laser device capable of reducing light having a wavelength different from that of light to be originally amplified.

Means for Solving the Problems

[0007] Aspect 1 of the present invention is a seed light source capable of generating seed light, a first amplifying optical fiber including a first core doped with a first active element, and capable of amplifying the seed light supplied from the seed light source to generate signal light having a first wavelength, a plurality of excitation fiber lasers capable of generating first excitation light having a second wavelength shorter than the first wavelength and exciting the first active element, each an excitation light source capable of generating second excitation light, a second amplifying optical fiber including a second core doped with a second active element excited by the second excitation light supplied from the excitation light source, and generating the first excitation light by excitation with the second excitation light, a high reflection portion connected to the upstream side of the second amplifying optical fiber and reflecting the first excitation light at a first reflectivity, a low reflection portion connected to the downstream side of the second amplifying optical fiber and reflecting the first excitation light at a second reflectivity lower than the first reflectivity and a plurality of excitation fiber lasers including, a plurality of photodetectors provided corresponding to the plurality of excitation fiber lasers, the plurality of photodetectors being capable of detecting different wavelength light having a wavelength different from the second wavelength, and a control unit configured to control the excitation light source of the plurality of excitation fiber lasers so that the light intensity of the different wavelength light detected by the plurality of photodetectors becomes equal to or less than a threshold value A fiber laser device comprising.

[0008] Aspect 2 of the present invention is the fiber laser device according to Aspect 1, wherein the wavelength of the different-wavelength light is longer than the second wavelength.

[0009] Aspect 3 of the present invention further includes an optical combiner that introduces the seed light generated by the seed light source and the first excitation light that has passed through the low-reflection portion of the plurality of excitation light fiber lasers into the first amplification optical fiber, and the plurality of photodetectors are arranged on the upstream side of the optical combiner, and is the fiber laser device according to Aspect 1 or 2.

[0010] Aspect 4 of the present invention is the fiber laser device according to any one of Aspects 1 to 3, wherein the different-wavelength light is a part of the amplified spontaneous emission light generated when generating the first excitation light.

[0011] Aspect 5 of the present invention is the fiber laser device according to any one of Aspects 1 to 4, wherein the control unit decreases the current supplied to the excitation light source of the excitation light fiber laser corresponding to the photodetector that has detected the different-wavelength light with an optical intensity exceeding the threshold value, and increases the current supplied to the excitation light source of the excitation light fiber laser corresponding to the photodetector that has detected the different-wavelength light with an optical intensity below the threshold value.

[0012] Aspect 6 of the present invention Each of the plurality of excitation light fiber lasers further includes an excitation light measurement unit capable of measuring the optical intensity of the first excitation light, and the control unit controls the excitation light sources of the plurality of excitation light fiber lasers so that the total optical intensity of the first excitation light measured by the excitation light measurement units of the plurality of excitation light fiber lasers becomes constant. It is the fiber laser device according to any one of Aspects 1 to 5.

[0013] Aspect 7 of the present invention further includes a signal light measurement unit capable of measuring the optical intensity of the signal light, The control unit controls the excitation light sources of the plurality of excitation fiber lasers so that the light intensity of the signal light measured by the signal light measurement unit becomes constant. The fiber laser device according to any one of Aspects 1 to 5.

[0014] Aspect 8 of the present invention is The signal light measurement unit is disposed on the downstream side of the first amplification optical fiber, and is the fiber laser device according to Aspect 7.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of a fiber laser device according to the present invention will be described in detail with reference to FIGS. 1 to 5. In FIGS. 1 to 5, the same or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted. Further, in FIGS. 1 to 5, there are cases where the scales and dimensions of each component are exaggeratedly shown or some components are omitted. In the following description, unless otherwise specified, terms such as "first" and "second" are used only to distinguish components from each other, and do not represent a specific order or sequence.

[0017] FIG. 1 is a schematic block diagram showing the configuration of a fiber laser device 1 according to a first embodiment of the present invention. As shown in FIG. 1, the fiber laser device 1 in the present embodiment includes a seed light source 10 capable of generating a seed light S1, a plurality of pump light fiber lasers 20 capable of generating a pump light P1 (first pump light), a first amplification optical fiber 30 capable of amplifying the seed light S1 supplied from the seed light source 10 using the pump light P1 to generate a signal light S2, a delivery fiber 14 connected to the first amplification optical fiber 30 via a fusion point 12, a laser output unit 16 provided at the downstream end of the delivery fiber 14, and an optical combiner 18 that introduces the seed light S1 generated by the seed light source 10 and the pump light P1 generated by the plurality of pump light fiber lasers 20 into the first amplification optical fiber 30. In this specification, unless otherwise specified, the direction from the seed light source 10 and the pump light fiber laser 20 (more specifically, the pump light source 24 of the pump light fiber laser 20 described later) toward the laser output unit 16 is referred to as the "downstream side", and the opposite direction is referred to as the "upstream side".

[0018] FIG. 2 is a cross-sectional view schematically showing the structure of the first amplification optical fiber 30. As shown in FIG. 2, the first amplification optical fiber 30 has a core 31 (first core), an inner cladding layer 32 covering the periphery of the core 31, and an outer cladding layer 33 covering the periphery of the inner cladding layer 32. The core 31 is formed by adding an element such as aluminum that increases the refractive index to quartz, and further adding an active element (first active element) to at least a part thereof. Examples of the active element added to the core 31 include rare earth elements such as ytterbium (Yb), erbium (Er), thulium (Tm), neodymium (Nd), and bismuth (Bi), chromium (Cr), and the like. In the present embodiment, an example in which Yb is added to the core 31 of the first amplification optical fiber 30 will be described, but the present invention is not limited thereto.

[0019] The inner cladding layer 32 is formed of, for example, quartz without a dopant added. The refractive index of the inner cladding layer 32 is lower than that of the core 31, and an optical waveguide is formed inside the core 31. The outer cladding layer 33 is formed of, for example, an ultraviolet curable resin. The refractive index of the outer cladding layer 33 is lower than that of the inner cladding layer 32, and an optical waveguide is also formed inside the inner cladding layer 32.

[0020] The seed light source 10 is constituted by, for example, a high-power semiconductor laser diode capable of emitting seed light S1 having a center wavelength of 1060 nm, and is connected to an optical combiner 18 by an optical fiber 15. The core (not shown) of the optical fiber 15 is optically coupled to the core 31 of the first amplification optical fiber 30 by the optical combiner 18, whereby the seed light S1 from the seed light source 10 propagates inside the core 31 of the first amplification optical fiber 30.

[0021] In FIG. 1, for ease of understanding, only the components in one excitation fiber laser 20A among the plurality of excitation fiber lasers 20 are shown, but the other excitation fiber lasers 20B and 20C also have the same components as those shown. As shown in FIG. 1, each excitation fiber laser 20 includes an optical resonator 21, a wavelength division multiplexing (WDM) coupler 22 disposed on one end side (upstream side) of the optical resonator 21, an excitation light source 24 fusion-connected to the WDM coupler 22 at a fusion point 23, a photodetector 26 fusion-connected to the WDM coupler 22 at a fusion point 25, and a delivery fiber 27 connected to the other end side (downstream side) of the optical resonator 21. The excitation light source 24 is, for example, a high-power semiconductor laser diode capable of emitting excitation light P2 (second excitation light) having a center wavelength of 976 nm.

[0022] The optical resonator 21 includes a second amplifying optical fiber 40 capable of amplifying laser light, a high-reflection portion 51 that reflects light in a predetermined wavelength band (for example, 1018 nm) with a high reflectivity (for example, a reflectivity close to 100%), and a low-reflection portion 52 that reflects light of this wavelength with a lower reflectivity than the high-reflection portion 51 (for example, a reflectivity of 10%). The high-reflection portion 51 and the low-reflection portion 52 are constituted by, for example, a fiber Bragg grating (FBG) formed by periodically changing the refractive index of the optical fiber along the light propagation direction or a mirror. In the example shown in FIG. 1, the high-reflection portion 51 and the low-reflection portion 52 are constituted by fiber Bragg gratings.

[0023] The high-reflection portion 51 and the second amplifying optical fiber 40 are fusion-connected to each other at a fusion point 53, and the high-reflection portion 51 and the WDM coupler 22 are fusion-connected to each other at a fusion point 54. Also, the low-reflection portion 52 and the second amplifying optical fiber 40 are fusion-connected to each other at a fusion point 55, and the low-reflection portion 52 and the delivery fiber 27 are fusion-connected to each other at a fusion point 56.

[0024] FIG. 3 is a cross-sectional view schematically showing the structure of the second amplifying optical fiber 40. As shown in FIG. 3, the second amplifying optical fiber 40 has a core 41 (second core), an inner cladding layer 42 that covers the periphery of the core 41, and an outer cladding layer 43 that covers the periphery of the inner cladding layer 42. The core 41 is formed by adding an element such as aluminum that increases the refractive index to quartz and further adding an active element (second active element) to at least a part thereof. Examples of the active element added to the core 41 include rare earth elements such as ytterbium (Yb), erbium (Er), thulium (Tm), neodymium (Nd), and bismuth (Bi), chromium (Cr), etc. The active element added to the core 41 of the second amplifying optical fiber 40 may be the same as or different from the active element added to the core 31 of the first amplifying optical fiber 30. In this embodiment, an example of adding Yb to the core 41 of the second amplifying optical fiber 40 will be described, but it is not limited thereto.

[0025] The inner cladding layer 42 is formed of, for example, quartz without a dopant added. The refractive index of the inner cladding layer 42 is lower than that of the core 41, and an optical waveguide is formed inside the core 41. The outer cladding layer 43 is formed of, for example, an ultraviolet curable resin. The refractive index of the outer cladding layer 43 is lower than that of the inner cladding layer 42, and an optical waveguide is also formed inside the inner cladding layer 42.

[0026] Although not shown in the figure, the high reflection portion 51 and the low reflection portion 52 each have a core, an inner cladding layer covering the periphery of the core, and an outer cladding layer covering the periphery of the inner cladding layer. The cores of the high reflection portion 51 and the low reflection portion 52 are optically coupled to the core 41 of the second amplifying optical fiber 40, respectively, and the inner cladding layers of the high reflection portion 51 and the low reflection portion 52 are optically coupled to the inner cladding layer 42 of the second amplifying optical fiber 40, respectively.

[0027] The core on the downstream side of the WDM coupler 22 is optically coupled to the inner cladding layer of the high reflection portion 51, whereby the excitation light P2 from the excitation light source 24 propagates inside the inner cladding layer 42 and the core 41 of the second amplifying optical fiber 40. The core of the delivery fiber 27 is optically coupled to the core of the low reflection portion 52. The delivery fiber 27 of each excitation optical fiber laser 20 is fusion-connected to the optical fiber 17 extending from the optical combiner 18 at the fusion point 19.

[0028] In the optical resonator 21, the excitation light P2 propagating through the inner cladding layer 42 of the second amplifying optical fiber 40 is absorbed by Yb when passing through the core 41, and this Yb is excited to generate spontaneous emission light. The spontaneous emission light generated by the excitation of Yb is recursively reflected between the high reflection portion 51 and the low reflection portion 52, and light of a specific wavelength (1018 nm in this embodiment) is amplified to cause laser oscillation. In this way, excitation light P1 (first excitation light) having a wavelength of 1018 nm is generated in the optical resonator 21.

[0029] Here, the optical combiner 18 optically couples the core (not shown) of the optical fiber 17 with the inner cladding layer 32 of the first amplifying optical fiber 30, whereby the excitation light P1 generated by the excitation fiber laser 20 propagates inside the inner cladding layer 32 and the core 31 of the first amplifying optical fiber 30.

[0030] As described above, the seed light S1 from the seed light source 10 propagates inside the core 31 of the first amplifying optical fiber 30. However, when the excitation light P1 propagating inside the inner cladding layer 32 and the core 31 of the first amplifying optical fiber 30 passes through the core 31, the active element added to the core 31 absorbs and is excited by the excitation light P1, and the seed light S1 propagating through the core 31 is amplified by stimulated emission to generate a high-power signal light S2 having a wavelength of 1060 nm (first wavelength). In the present embodiment, the excitation light P1 introduced into the first amplifying optical fiber 30 has a wavelength of 1018 nm (second wavelength) that is shorter than the wavelength of the signal light S2.

[0031] Here, in the second amplifying optical fiber 40 in the present embodiment, light having a wavelength (1030 nm) different from the wavelength (1018 nm) of the excitation light P1 (hereinafter referred to as "different-wavelength light") is more likely to be emitted than the excitation light P1 as amplified spontaneous emission (ASE) light. For this reason, it is conceivable that the power of the excitation light P1 introduced into the first amplifying optical fiber 30 decreases, making it difficult to stably introduce the excitation light P1 into the first amplifying optical fiber 30. Further, such different-wavelength light is hardly absorbed in the second amplifying optical fiber 40 and is not reflected by the high reflection portion 51 or the low reflection portion 52, so there is a possibility of causing damage to optical components such as the excitation light source 24 and the optical combiner 18. The fiber laser device 1 in the present embodiment has the following configuration in order to reduce the problems caused by such different-wavelength light.

[0032] Each excitation light fiber laser 20 includes a photodetector 26 capable of detecting the above-described different-wavelength light. The photodetector 26 in the present embodiment is configured to detect ASE light having a wavelength of 1030 nm, which is longer than the wavelength (1018 nm) of the excitation light P1, as the different-wavelength light. Further, the WDM coupler 22 is configured to separate the light having a wavelength of 1030 nm from the light propagating upstream and guide it to the photodetector 26. As this photodetector 26, any known photodetector can be used. For example, a photodiode can be used as the photodetector 26, but the present invention is not limited thereto, and any known photodetector can be used as the photodetector 26.

[0033] As shown in FIG. 1, the fiber laser device 1 in the present embodiment includes a control unit 60 connected to the excitation light source 24 and the photodetector 26 in each excitation light fiber laser 20. A signal indicating the light intensity of the different-wavelength light detected by each photodetector 26 is input to the control unit 60. The control unit 60 is configured to control the excitation light sources 24 of the excitation light fiber lasers 20A, 20B, and 20C so that the light intensity of the different-wavelength light detected by the photodetector 26 becomes equal to or less than a threshold value based on the signal input from the photodetector 26 in each excitation light fiber laser 20.

[0034] With such a configuration, even if different-wavelength light having a light intensity exceeding the threshold value is detected by the photodetector 26 in any one of the excitation light fiber lasers 20 (for example, the excitation light fiber laser 20A), the control unit 60 can control the excitation light source 24 of the excitation light fiber laser 20 (for example, the excitation light fiber laser 20A) in which such different-wavelength light is detected to make the light intensity of the different-wavelength light equal to or less than the above-described threshold value. Therefore, it becomes difficult for optical components such as the excitation light source 24 and the optical combiner 18 to be damaged by the different-wavelength light. For example, the control unit 60 can make the light intensity of the different-wavelength light equal to or less than the threshold value by controlling (decreasing) the current supplied to the excitation light sources 24 of the excitation light fiber lasers 20A, 20B, and 20C.

[0035] As an example, it is conceivable that the control unit 60 performs the following control. First, the control unit 60 determines whether the light intensity of the different-wavelength light generated by each excitation light fiber laser 20 exceeds a predetermined threshold value. When it is determined that the light intensity of the different-wavelength light exceeds the predetermined threshold value, the control unit 60 adjusts the current supplied to the excitation light source 24 of the excitation light fiber laser 20 (for example, the excitation light fiber laser 20A) that generates the different-wavelength light so that the light intensity of the different-wavelength light detected by the photodetector 26 (for example, the photodetector 26 of the excitation light fiber laser 20A) becomes equal to or lower than the threshold value. On the other hand, for the excitation light fiber lasers 20 (for example, the excitation light fiber lasers 20B and 20C) for which the control unit 60 determines that the light intensity of the different-wavelength light does not exceed the threshold value, the control unit 60 increases the current supplied to the excitation light source 24. When the current supplied to the excitation light source 24 is decreased, the light intensity of the excitation light P1 also decreases together with the light intensity of the different-wavelength light. Therefore, by the above-described control, the decrease in the light intensity of the excitation light P1 from the excitation light fiber laser 20 (for example, the excitation light fiber laser 20A) for which the current supplied to the excitation light source 24 is decreased is compensated for by increasing the intensity of the excitation light P1 from the excitation light fiber lasers 20 (for example, the excitation light fiber lasers 20B and 20C) for which the current supplied to the excitation light source 24 is increased, and the total light intensity of the excitation light P1 introduced into the first amplifying optical fiber 30 can be made constant, and the output of the signal light S2 from the laser output unit 16 of the fiber laser device 1 can be stabilized.

[0036] FIG. 4 is a schematic block diagram showing the configuration of the fiber laser device 101 in the second embodiment of the present invention. The fiber laser device 101 in the present embodiment is different from the above-described first embodiment in that an excitation light measurement unit 150 capable of measuring the light intensity of the excitation light P1 generated by the second amplification optical fiber 40 is provided in the delivery fiber 27 of each excitation optical fiber laser 20. The excitation light measurement unit 150 is connected to the control unit 60, and a signal indicating the light intensity of the excitation light P1 measured by the excitation light measurement unit 150 of each excitation optical fiber laser 20 is input to the control unit 60. As such an excitation light measurement unit 150, any known optical measurement unit can be used. For example, a photodiode capable of detecting Rayleigh scattered light can be used as the excitation light measurement unit 150.

[0037] Similar to the first embodiment, the control unit 60 controls the excitation light source 24 of each excitation optical fiber laser 20 so that the light intensity of the different wavelength light detected by the photodetector 26 becomes equal to or less than the threshold value. At this time, the control unit 60 controls the excitation light sources 24 of the excitation optical fiber lasers 20A, 20B, and 20C so that the sum of the light intensities of the excitation light P1 measured by the excitation light measurement units 150 of the excitation optical fiber lasers 20A, 20B, and 20C becomes constant. By doing so, since the sum of the light intensities of the excitation light P1 introduced into the first amplification optical fiber 30 becomes constant, the output of the signal light S2 from the laser output unit 16 of the fiber laser device 101 can be stabilized.

[0038] FIG. 5 is a schematic block diagram showing the configuration of the fiber laser device 201 in the third embodiment of the present invention. The fiber laser device 201 in the present embodiment is different from the above-described first embodiment in that a signal light measuring unit 250 capable of measuring the light intensity of the signal light S2 is provided in the delivery fiber 14. The signal light measuring unit 250 is connected to the control unit 60, and a signal indicating the light intensity of the signal light S2 measured by the signal light measuring unit 250 is input to the control unit 60. As such a signal light measuring unit 250, any known light measuring unit can be used. For example, a photodiode capable of detecting Rayleigh scattered light can be used as the signal light measuring unit 250.

[0039] Similar to the first embodiment, the control unit 60 controls the excitation light sources 24 of the respective excitation light fiber lasers 20 so that the light intensity of the different wavelength light detected by the photodetector 26 is equal to or less than the threshold value. At this time, the excitation light sources 24 of the excitation light fiber lasers 20A, 20B, and 20C are controlled so that the light intensity of the signal light S2 measured by the signal light measuring unit 250 becomes constant. By doing so, the output of the signal light S2 from the laser output unit 16 of the fiber laser device 201 can be stabilized.

[0040] Such a signal light measuring unit 250 can be disposed at any location where the signal light S2 propagates. However, in order to further stabilize the output of the signal light S2 from the laser output unit 16 of the fiber laser device 201, it is preferable to dispose the signal light measuring unit 250 on the downstream side of the first amplification optical fiber 30 and make the light intensity of the signal light S2 on the downstream side of the first amplification optical fiber 30 constant.

[0041] The excitation light fiber laser 20 in the above-described embodiment incorporates the photodetector 26. However, the photodetector 26 does not necessarily have to be incorporated in the excitation light fiber laser 20 and can be disposed at any position as long as it is provided corresponding to each excitation light fiber laser 20. In order to specify the light intensity of the different wavelength light generated in each excitation light fiber laser 20, it is preferably disposed upstream of the optical combiner 18.

[0042] Further, the fiber laser devices 1, 101, and 201 in the above-described embodiments have three excitation light fiber lasers 20, but the number of excitation light fiber lasers 20 is not limited to this, and can be any number of 2 or more.

[0043] The first amplifying optical fiber 30 in the above-described embodiments is not limited to the illustrated double-clad fiber, and may be, for example, a side-excitation type optical fiber. This side-excitation type optical fiber arranges cores of optical fibers extending from the excitation light fiber laser 20 along an optical fiber having a core (to which an active element is added) through which the seed light from the seed light source 10 propagates, and accommodates these in the inside of a common clad. In this configuration, the excitation light from the excitation light fiber laser 20 propagates inside the common clad, and stimulated emission occurs when the excitation light passes through the core through which the seed light propagates.

[0044] As described above, according to the embodiment of the present invention, even if light of a different wavelength having a light intensity exceeding the threshold is detected by the photodetector in any of the excitation light fiber lasers, the control unit controls the excitation light source of the excitation light fiber laser in which such light of a different wavelength is detected, so that the light intensity of the light of a different wavelength can be made equal to or less than the threshold. Therefore, optical components such as the excitation light source and the optical combiner are less likely to be damaged by light of a different wavelength.

[0045] Further, if the control unit decreases the current supplied to the excitation light source of the excitation light fiber laser corresponding to the detector that has detected light of a different wavelength having a light intensity exceeding the threshold, and increases the current supplied to the excitation light source of the excitation light fiber laser corresponding to the detector that has detected light of a different wavelength having a light intensity equal to or less than the threshold, the decrease in the light intensity of the first excitation light from the excitation light fiber laser for which the current supplied to the excitation light source has been decreased is compensated for by the first excitation light from the excitation light fiber laser for which the current supplied to the excitation light source has been increased, and the total light intensity of the first excitation light introduced into the first amplifying optical fiber can be made constant. Therefore, the output of the signal light from the fiber laser device can be stabilized.

[0046] Although the preferred embodiments of the present invention have been described so far, it goes without saying that the present invention is not limited to the above-described embodiments and may be implemented in various different forms within the scope of its technical idea.

Explanation of Reference Numerals

[0047] 1,101,201 Fiber Laser Device 10 Seed Light Source 18 Optical Combiner 20 Pumped Fiber Laser 21 Optical Resonator 22 WDM Coupler 24 Pump Light Source 26 Photodetector 30 First Amplifying Optical Fiber 31 Core (First Core) 32 Inner Cladding Layer 33 Outer Cladding Layer 40 Second Amplifying Optical Fiber 41 Core (Second Core) 42 Inner Cladding Layer 43 Outer Cladding Layer 51 High Reflection Portion 52 Low Reflection Portion 60 Control Unit 150 Pump Light Measurement Unit 250 Signal Light Measurement Unit P1 Pump Light (First Pump Light) P2 Pump Light (Second Pump Light) S1 Seed Light S2 Signal Light

Claims

1. A seed light source capable of generating seed light, A first amplifying optical fiber including a first core doped with a first active element, capable of amplifying the seed light supplied from the seed light source to generate signal light having a first wavelength, A plurality of excitation fiber lasers capable of generating first excitation light having a second wavelength shorter than the first wavelength and exciting the first active element, each An excitation light source capable of generating second excitation light, A second amplifying optical fiber including a second core doped with a second active element excited by the second excitation light supplied from the excitation light source, and generating the first excitation light by excitation with the second excitation light, A high reflection part connected to the upstream side of the second amplifying optical fiber and reflecting the first excitation light at a first reflectivity, A low reflection part connected to the downstream side of the second amplifying optical fiber and reflecting the first excitation light at a second reflectivity lower than the first reflectivity And a plurality of excitation fiber lasers including, A plurality of photodetectors provided corresponding to the plurality of excitation fiber lasers, the plurality of photodetectors capable of detecting different-wavelength light having a wavelength different from the second wavelength, A control unit configured to control the excitation light source of the plurality of excitation fiber lasers such that the light intensity of the different-wavelength light detected by the plurality of photodetectors becomes equal to or lower than a threshold value A fiber laser device comprising.

2. The fiber laser device according to claim 1, wherein the wavelength of the different-wavelength light is longer than the second wavelength.

3. The fiber laser device further includes an optical combiner that introduces the seed light generated by the seed light source and the first excitation light transmitted through the low reflection part of the plurality of excitation fiber lasers into the first amplifying optical fiber, The fiber laser device according to claim 1, wherein the plurality of photodetectors are arranged upstream of the optical combiner.

4. The fiber laser device according to claim 1, wherein the different-wavelength light is part of amplified spontaneous emission light generated when generating the first excitation light.

5. The fiber laser device according to any one of claims 1 to 4, wherein the control unit decreases a current supplied to the excitation light source of the excitation light fiber laser corresponding to the photodetector that has detected the different-wavelength light having a light intensity exceeding the threshold value, and increases a current supplied to the excitation light source of the excitation light fiber laser corresponding to the photodetector that has detected the different-wavelength light having a light intensity equal to or lower than the threshold value.

6. Each of the plurality of excitation light fiber lasers further includes an excitation light measurement unit capable of measuring the light intensity of the first excitation light. The control unit controls the excitation light sources of the plurality of excitation light fiber lasers so that the total light intensity of the first excitation light measured by the excitation light measurement units of the plurality of excitation light fiber lasers becomes constant. The fiber laser device according to any one of claims 1 to 4.

7. The fiber laser device further includes a signal light measurement unit capable of measuring the light intensity of the signal light. The control unit controls the excitation light sources of the plurality of excitation light fiber lasers so that the light intensity of the signal light measured by the signal light measurement unit becomes constant. The fiber laser device according to any one of claims 1 to 4.

8. The fiber laser device according to claim 7, wherein the signal light measurement unit is disposed on a downstream side of the first amplification optical fiber.

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