JP2019029421A - Fiber laser equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber laser device capable of emitting light with high beam quality and high power. A fiber laser device 1 includes an amplifying optical fiber 20 having a core in which an active element is added and propagating light of a plurality of modes, and a predetermined reflection less than 100% of light amplified by the amplifying optical fiber. The first FBG 31 that reflects at a rate, the second FBG 32 that reflects light reflected by the first FBG with a lower reflectance than the first FBG, and the light at least partially reflecting the wavelength band of light reflected by the first FBG. And an optical component 40. The optical component 40 propagates through the amplification optical fiber 20 and transmits light up to a predetermined mode including the fundamental mode out of a plurality of modes transmitted through the first FBG 31 higher than light in a higher-order mode than the predetermined mode. Reflect with reflectivity. [Selection] Figure 1

Description

  The present invention relates to a laser device having excellent reliability, and is particularly suitable for a laser device that emits light with high power.

  The fiber laser device is used in various fields such as a laser processing field and a medical field because it has excellent light condensing performance, has a high power density, and can obtain light as a small beam spot.

In such a fiber laser device, when the power of the emitted light increases, the power density of the light in the amplification optical fiber increases and a nonlinear optical effect may occur. In order to suppress this nonlinear optical effect, it is conceivable to increase the effective area (A _eff ) of the light propagating through the amplification optical fiber. However, when the effective area is increased, higher-order light other than the light in the fundamental mode (LP ₀₁ mode) is easily excited, and light is easily oscillated in the multimode. When multi-mode light is emitted, there is a demand for emitting light in which the power of high-order mode light is suppressed because the light collecting property of the light emitted from the fiber laser device tends to deteriorate.

  Patent Document 1 listed below describes a fiber laser device having an amplification double clad fiber capable of propagating multimode light. In this fiber laser device, an amplification double that propagates multimode light by arranging a mode converter that excites only the fundamental mode light so that only the fundamental mode light is included in the light incident on the core. It is said that it is possible to amplify light of a fundamental mode in a clad fiber.

US Pat. No. 5,818,630

  If only the fundamental mode light can be amplified using an amplification double clad fiber capable of propagating multimode light as in Patent Document 1, light with high beam quality and high power can be emitted. However, even when light having only fundamental mode light is incident on an optical fiber capable of propagating light in multimodes, higher-order mode light other than fundamental mode light tends to be excited. If the higher-order mode light is excited in the amplification optical fiber described in Patent Document 1, the higher-order mode light is amplified and light with poor beam quality is emitted. Therefore, there is a need for a fiber laser device that can emit light with high beam quality and high power.

  Even when multimode light propagates through the amplification optical fiber as described above, beam quality can be improved if the fundamental mode is amplified more than other modes. In addition, if the light up to a predetermined mode including the basic mode among the multimodes propagating through the amplification optical fiber as well as the basic mode can be amplified more than the light of the higher order mode than the predetermined mode, the beam quality Can be improved.

  Therefore, an object of the present invention is to provide a fiber laser device that can emit light with high beam quality and high power.

  In order to solve the above problems, a fiber laser device according to the present invention includes an excitation light source that emits excitation light, and an amplification light that includes an active element that is excited by the excitation light and has a core that propagates light of a plurality of modes. A first mirror that is provided on one side of the amplification optical fiber and reflects light amplified by the amplification optical fiber with a predetermined reflectance of less than 100%; and on the other side of the amplification optical fiber. A second mirror that reflects light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first mirror with a lower reflectance than the first mirror, and the amplification with reference to the first mirror An optical component that is provided on the side opposite to the optical fiber side and that reflects light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first mirror, wherein the optical component is the first optical component. Mi The light up to a predetermined mode including the fundamental mode is reflected with a higher reflectance than the light of a higher order mode than the predetermined mode among the light of the plurality of modes that transmits the light. .

  Since this fiber laser device uses an amplification optical fiber that propagates light of a plurality of modes, the diameter of the core can be made larger than that of an amplification optical fiber that propagates only light of the fundamental mode. Accordingly, it is possible to suppress the generation of nonlinear optical light even when light having high power propagates through the amplification optical fiber. However, the amplification optical fiber that propagates light of a plurality of modes as described above tends to excite light of a plurality of modes. Therefore, in the fiber laser device of the present invention, light up to a predetermined mode out of the light transmitted through the first mirror by the optical component is reflected with a higher reflectance than the light in the higher order mode. A part of the reflected light passes through the first mirror again and is amplified by the amplification optical fiber. Accordingly, the light incident on the amplification optical fiber from the first mirror has a light power up to a predetermined mode higher than that of the light in the higher-order mode as compared with the case where there is no optical component. The light up to the predetermined mode is a low-order mode light among a plurality of modes propagating through the amplification optical fiber. For this reason, in the amplification optical fiber, even if the amplification factor of the low-order mode light and the amplification factor of the high-order mode light are the same, as a result, the low-order mode light is higher than the high-order mode light. Will also be amplified. Therefore, it is possible to emit low-order mode light with higher power than high-order mode light. As described above, according to the fiber laser device of the present invention, light with good beam quality and high power can be emitted.

  The predetermined mode light is preferably fundamental mode light, and the higher order mode light is preferably second order LP mode light or higher.

  According to such a configuration, light in the fundamental mode can be emitted with higher power than light in a higher-order mode than in the case where there is no optical component. Therefore, light with better beam quality can be emitted.

  The optical component may include a filter and a third mirror that reflects light transmitted through the filter, and the filter may suppress transmission of light in the higher-order mode.

  In this case, it is preferable that the filter is an optical fiber that suppresses propagation of light in the higher-order mode and propagates light up to the predetermined mode.

  The optical component in this case can be composed of an optical fiber as a filter and a third mirror. This optical fiber is an optical fiber having a smaller number of propagation modes than the amplification optical fiber. Further, since an optical fiber is used as a filter, a mirror such as an FBG (Fiber Bragg Grating) can be used as the third mirror, and an optical component can be configured with a simple configuration.

  The optical fiber used as the filter is preferably a single mode fiber.

  By using a single mode fiber as a filter, light with better beam quality can be emitted with a simple configuration.

  Alternatively, it is preferable that the filter is an optical fiber in which the higher-order mode light is lost by being bent.

  In this case, the higher-order mode light to be lost can be determined by adjusting the bending diameter or the like of the optical fiber used as a filter, so that the light up to a desired mode can be propagated. Accordingly, it is possible to appropriately adjust the number of modes of light for which the power of emitted light is desired to be increased.

  The diameter of the core of the optical fiber used as the filter is preferably equal to the diameter of the core of the optical fiber for amplification.

  In this case, light loss can be suppressed when light propagates from the amplification optical fiber to the optical fiber as a filter, and the efficiency of the fiber laser device can be suppressed from decreasing.

  The light reflectance of the optical component is preferably higher than the reflectance of the first mirror.

  At least a part of the wavelength band of light reflected by the first mirror and the wavelength band of light reflected by the optical component overlap. Accordingly, part of the light reflected by the optical component and incident on the first mirror is reflected again by the first mirror toward the optical component. In this case, the light reciprocating between the first mirror and the optical component is mainly transmitted from the first mirror side because the light reflectance of the optical component is higher than the reflectance of the first mirror as described above. The light exits and enters the amplification optical fiber. Therefore, according to this configuration, it is possible to amplify light of a lower order mode more efficiently.

  As described above, according to the fiber laser device of the present invention, it is possible to emit light with high beam quality and high power.

It is a figure which shows the fiber laser apparatus in 1st Embodiment of this invention. It is a figure which shows the fiber laser apparatus in 2nd Embodiment of this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a fiber laser device according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a fiber laser device according to the present embodiment. As shown in FIG. 1, the fiber laser device 1 of the present embodiment includes an excitation light source 10 that emits excitation light, excitation light that is emitted from the excitation light source 10 is incident, and an active element that is excited by the excitation light is added. Amplifying optical fiber 20, an optical fiber 21 connected to one end of the amplifying optical fiber 20, a first FBG 31 as a first mirror provided in the optical fiber 21, and the other end of the amplifying optical fiber 20. Optical fiber 22, second FBG 32 as a second mirror provided in optical fiber 22, optical component 40 connected to optical fiber 21, and combiner 50 for making excitation light incident on optical component 40. Prepare as a simple configuration.

  The excitation light source 10 includes a plurality of laser diodes 11 and emits excitation light having a wavelength for exciting an active element added to the amplification optical fiber 20. Each laser diode 11 of the excitation light source 10 is connected to an optical fiber 12 for excitation light, and light emitted from the laser diode 11 is optically connected to each laser diode 11 for optical fiber 12 for excitation light. To propagate. Examples of the pumping light optical fiber 12 include a multimode fiber. In this case, the pumping light propagates through the pumping light optical fiber 12 as multimode light. As will be described later, when the active element added to the amplification optical fiber 20 is, for example, ytterbium, the wavelength of the excitation light is, for example, 915 nm.

  The amplifying optical fiber 20 includes a core, an inner cladding that surrounds the outer peripheral surface of the core without a gap, and an outer cladding that has a lower refractive index than the core, and an outer cladding that covers the outer peripheral surface of the inner cladding and has a lower refractive index than the inner cladding. It is comprised from the clad and the coating layer which coat | covers the outer peripheral surface of an outer clad. As a material constituting the core of the optical fiber 20 for amplification, for example, an element such as germanium for increasing the refractive index and an active element such as ytterbium (Yb) excited by light emitted from the excitation light source 10 are added. Quartz. Examples of such an active element include rare earth elements, and examples of rare earth elements include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er), and the like. Can be mentioned. Furthermore, bismuth (Bi) etc. other than rare earth elements are mentioned as an active element. Moreover, as a material which comprises the inner clad of the optical fiber 20 for amplification, the pure quartz to which no dopant is added is mentioned, for example. In the case where an element for increasing the refractive index is not added to the core, the inner cladding may be made of quartz to which an element for decreasing the refractive index such as fluorine is added. The material constituting the outer cladding of the amplification optical fiber 20 includes, for example, a resin having a refractive index lower than that of the inner cladding, and the material constituting the coating layer of the amplification optical fiber 20 is, for example, the outer cladding. UV curable resin that is different from the resin that constitutes the.

The amplification optical fiber 20 is an optical fiber capable of propagating light in a plurality of modes. For example, the amplification optical fiber 20 is a fu-mode fiber that propagates light having a wavelength of 1060 nm in several modes. For example, the amplification optical fiber 20 can propagate light of 4 LP modes of LP ₀₁ mode, LP ₁₁ mode, LP ₂₁ mode, and LP ₀₂ mode. Examples of such an amplification optical fiber that propagates a plurality of modes include an amplification optical fiber having a core diameter of 16 μm and a relative refractive index difference between the core and the inner cladding of 0.15%. Can do. Further, the amplification optical fiber 20 may be a multimode fiber that propagates light of a larger number of modes than several modes.

  The optical fiber 21 has the same configuration as that of the amplification optical fiber 20 except that no active element is added to the core. Therefore, in this embodiment, the diameter of the core of the optical fiber 21 and the diameter of the core of the amplification optical fiber 20 are equal to each other, and the outer diameter of the inner cladding of the optical fiber 21 and the outer cladding of the amplification optical fiber 20 are outside. The diameters are made equal to each other. The optical fiber 21 is connected to one end of the amplification optical fiber 20 with the center axis of the core aligned with the center axis of the core of the amplification optical fiber 20. Accordingly, the core of the amplification optical fiber 20 and the core of the optical fiber 21 are optically coupled, and the inner cladding of the amplification optical fiber 20 and the inner cladding of the optical fiber 21 are optically coupled.

  The first FBG 31 is provided in the core of the optical fiber 21. Thus, the first FBG 31 is provided on one end side of the amplification optical fiber 20 and is optically coupled to the core of the amplification optical fiber 20. The FBG (Fiber Bragg Grating) is configured by repeating a high refractive index portion and a low refractive index portion at a constant period along the longitudinal direction of the optical fiber 21. By adjusting the repetition period of the high refractive index portion and the low refractive index portion, the number of repetitions of the high refractive index portion and the low refractive index portion, the refractive index difference between the high refractive index portion and the low refractive index portion, etc. , The reflection wavelength band of the FBG, the reflectance of the FBG, and the like are determined. The first FBG 31 reflects light in a specific wavelength band out of light emitted from the active element of the amplification optical fiber 20 in an excited state with a reflectance of less than 100%. As described above, when the active element added to the amplification optical fiber 20 is ytterbium, the first FBG 31 reflects light having a wavelength of, for example, 1060 nm with a reflectance of, for example, 80% to 90%.

  The optical fiber 22 has the same configuration as the core of the amplification optical fiber 20 except that no active element is added, and the same configuration as the inner cladding of the amplification optical fiber 20 surrounding the outer peripheral surface of the core without a gap. The inner cladding and a coating layer covering the outer peripheral surface of the inner cladding. The optical fiber 22 is connected to the other end of the amplification optical fiber 20, and the core of the amplification optical fiber 20 and the core of the optical fiber 22 are optically coupled.

  The second FBG 32 is provided in the core of the optical fiber 22. Thus, the second FBG 32 is provided on the other end side of the amplification optical fiber 20 and is optically coupled to the core of the amplification optical fiber 20. The second FBG 32 is configured to reflect light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first FBG 31 with a lower reflectance than the first FBG 31. For example, the second FBG 32 is configured to reflect light having the same wavelength band as that of the light reflected by the first FBG 31 with a reflectance of 50%.

  Thus, a resonator is formed by the amplification optical fiber 20, the first FBG 31, and the second FBG 32, and the fiber laser device 1 of the present embodiment is a resonator type.

  Although not particularly illustrated, a delivery fiber may be connected to the side of the optical fiber 22 opposite to the amplification optical fiber 20 side.

  An optical component 40 is connected to the end of the optical fiber 21 opposite to the amplification optical fiber 20 side. The optical component 40 of this embodiment includes an optical fiber 41 and a third FBG 43 as a third mirror.

  In the present embodiment, the optical fiber 41 has the same configuration as the optical fiber 21 except that the optical fiber 41 is a single mode fiber that propagates light in the wavelength band propagating through the amplification optical fiber 20 only in the fundamental mode. The Therefore, as described above, when light having a wavelength of 1060 nm propagates through the amplification optical fiber 20, the light having the wavelength propagates in the fundamental mode, and the light of the second order LP mode or higher which is a higher order mode than the fundamental mode. Propagation is suppressed. When light of a wavelength of 1060 nm propagates in a single mode, for example, an optical fiber having a core diameter of 10 μm and a relative refractive index difference between the core and the inner cladding of 0.15% is cited. be able to. The optical fiber 41, which is such a single mode fiber, can be understood as a filter that can suppress the transmission of light in the higher order mode and transmit the light in the fundamental mode. Further, in this embodiment, the diameter of the core of the optical fiber 41 and the diameter of the core of the amplification optical fiber 20 are equal to each other, and the outer diameter of the inner cladding of the optical fiber 41 and the outer cladding of the amplification optical fiber 20 are increased. The diameters are made equal to each other. Therefore, in this embodiment, the amplification optical fiber 20, the optical fiber 21, and the optical fiber 41 have the same core diameter, and the amplification optical fiber 20, the optical fiber 21, and the optical fiber 41 have the outer diameter of the inner cladding. Made equal to each other. The optical fiber 41 is connected to the optical fiber 21 with the central axis of the core aligned with the central axis of the core of the optical fiber 21. Therefore, the core of the amplification optical fiber 20 and the core of the optical fiber 41 are optically coupled via the core of the optical fiber 21, and the inner cladding of the amplification optical fiber 20 and the inner cladding of the optical fiber 41 are optical fibers. 21 is optically coupled through the inner cladding.

  A third FBG 43 is provided at the core of the optical fiber 41. Thus, the third FBG 43 is optically coupled to the first FBG 31. The third FBG 43 is configured to reflect light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first FBG 31. In the present embodiment, the third FBG 43 has the same reflection wavelength as the reflection wavelength band of the first FBG 31. The band light is configured to be reflected with a higher reflectance than the first FBG 31. For example, the third FBG 43 is configured to reflect light having the same wavelength band as that of the light reflected by the first FBG 31 with a reflectance of 99%.

  Since the optical component 40 has the optical fiber 41 and the third FBG 43, the fundamental mode light among the light of the plurality of modes propagating through the amplification optical fiber 20 and transmitted through the first FBG 31 is higher-order mode light than the fundamental mode. It can be understood as a component that reflects with higher reflectivity.

  A combiner 50 is formed at the end of the optical fiber 41 opposite to the amplification optical fiber 20 side. In the combiner 50, the core of the optical fiber 12 for excitation light is connected to the inner cladding of the optical fiber 41. Thus, the pumping light optical fiber 12 connected to the pumping light source 10 and the inner cladding of the amplification optical fiber 20 are optically coupled via the optical fiber 41 and the inner cladding of the optical fiber 21.

  Next, the operation of the fiber laser device 1 will be described.

  First, excitation light is emitted from each laser diode 11 of the excitation light source 10. The pumping light emitted from the pumping light source 10 enters the inner cladding of the amplification optical fiber 20 from the pumping optical fiber 12 through the inner cladding of the optical fiber 41 and the inner cladding of the optical fiber 21. The excitation light incident on the inner cladding of the amplification optical fiber 20 mainly propagates through the inner cladding and excites the active element added to the core when passing through the core of the amplification optical fiber 20. The active element in the excited state emits spontaneous emission light. The spontaneous emission light propagates through the core of the amplification optical fiber 20, a part of the wavelength light is reflected by the first FBG 31, and the light of the reflected wavelength reflected by the second FBG 32 is reflected by the second FBG 32. Then, it reciprocates between the first FBG 31 and the second FBG 32, that is, inside the resonator. This light is amplified by stimulated emission when propagating through the core of the amplification optical fiber 20, and enters a laser oscillation state. By the way, as described above, the amplification optical fiber 20 can propagate a plurality of modes of light, so that the light amplified by the amplification optical fiber 20 is a plurality of modes of light. For example, when the amplification optical fiber 20 is a fu-mode fiber as described above, several modes of light are amplified.

  Further, since the first FBG 31 has a reflectance of less than 100% as described above, some of the light in the plurality of modes propagating through the amplification optical fiber 20 is transmitted through the first FBG 31. The light transmitted through the first FBG 31 is incident on the core of the optical fiber 41 of the optical component 40. As described above, since the optical fiber 41 of the present embodiment is a single mode fiber, the light of the fundamental mode propagates through the optical fiber 41 among the light of a plurality of modes that propagates through the optical fiber 21 through the first FBG 31. Propagation of the optical fiber 41 is suppressed for light of a higher order mode higher than the second order LP mode. At this time, as described above, since the amplification optical fiber 20, the optical fiber 21, and the optical fiber 41 have the same core diameter, it is possible to suppress light loss. The fundamental mode light propagating through the optical fiber 41 is reflected by the third FBG 43, propagates again through the optical fiber 41, and enters the core of the optical fiber 21. The optical fiber 21 can propagate light of a plurality of modes as described above. However, when the light of the fundamental mode is incident from the optical fiber 41, the light of the fundamental mode is mainly propagated. That is, when the light of the fundamental mode is incident on the core of the optical fiber 21, the light of a plurality of modes is incident on the optical fiber 21 even when light of a higher-order mode other than the fundamental mode is excited in the optical fiber 21. As compared with the above, light whose fundamental mode light power is larger than the light power of other modes propagates through the optical fiber 21.

  A part of the light having a large fundamental mode power propagating from the optical fiber 41 to the core of the optical fiber 21 is transmitted through the first FBG 31 and the other part is reflected by the first FBG 31. The light reflected by the first FBG 31 propagates through the optical fiber 41, is reflected again by the third FBG 43, and propagates again toward the first FBG 31. Thus, a part of the light reciprocates between the first FBG 31 and the third FBG 43. However, in the present embodiment, the reflectance of the light of the third FBG 43 is higher than the reflectance of the first FBG 31 as described above. And reciprocating between the first FBG 31 and the third FBG 43 are mainly emitted from the first FBG 31 side.

  The light emitted from the first FBG 31 enters the core of the amplification optical fiber 20 from the optical fiber 21 and is amplified again. The light incident on the amplification optical fiber 20 from the optical fiber 21 is light having a large fundamental mode power. Accordingly, light of a plurality of modes is propagated through the amplification optical fiber 20, but light having a large fundamental mode power is incident and amplified so that the light is not reflected by the optical component 40. In comparison, light having a large fundamental mode power propagates through the amplification optical fiber 20. A part of the light amplified by the amplification optical fiber 20 passes through the second FBG 32 and is emitted from the optical fiber 22. As described above, this light has a large power in the fundamental mode.

  Thus, the fiber laser device 1 emits light having a large fundamental mode power.

  In the above embodiment, an example in which the optical fiber 41 is a single mode fiber has been described. However, the optical fiber 41 is not limited to a single mode fiber as long as it is an optical fiber that propagates light of a mode number smaller than the number of modes of light that propagates through the amplification optical fiber 20. In other words, the optical fiber 41 propagates light up to a predetermined mode including the fundamental mode out of a plurality of modes propagating through the amplification optical fiber 20 and passing through the first FBG 31, and is higher than the predetermined mode. The optical fiber is configured to suppress the propagation of light in the next mode. In this case, the optical component 40 transmits light up to a predetermined mode including the fundamental mode among light of a plurality of modes propagating through the amplification optical fiber 20 and passing through the first FBG 31 from light of a higher mode than the predetermined mode. It becomes a part that reflects with high reflectivity. The light up to the predetermined mode is a low-order mode light among a plurality of modes propagating through the amplification optical fiber 20. In the fiber laser device 1 having such an optical component, when a part of light in a plurality of modes propagating through the amplification optical fiber 20 passes through the first FBG 31, light in a plurality of modes that can propagate through the amplification optical fiber 20 is obtained. Among them, the light in the lower order mode propagates through the optical fiber 41 and is reflected by the third FBG 43. Accordingly, a part of light having a large power of low-order mode light including the fundamental mode is transmitted through the first FBG 31, and the light is amplified by the amplification optical fiber 20. As described above, a plurality of modes of light are propagated through the amplification optical fiber 20, but light having a large power of a low-order mode is incident and amplified so that the optical component 40 can transmit the light. Compared with the case where the light does not reflect, light having a large power of light in the low-order mode propagates through the amplification optical fiber 20. Accordingly, the fiber laser device 1 emits light having a high power in a low-order mode.

  As described above, the fiber laser device 1 of the present embodiment includes the pumping light source 10 that emits pumping light and the amplification optical fiber 20 that propagates light of a plurality of modes by adding an active element pumped by the pumping light. A first FBG 31 that is provided on one side of the amplification optical fiber 20 and reflects light amplified by the amplification optical fiber 20 with a predetermined reflectance of less than 100%; and provided on the other side of the amplification optical fiber 20. Provided on the opposite side of the amplifying optical fiber 20 with respect to the first FBG 31 and the second FBG 32 that reflects light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first FBG 31 with a lower reflectance than the first FBG 31. And an optical component 40 that reflects light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first FBG 31. Then, the optical component 40 transmits light up to a predetermined mode including the fundamental mode among light of a plurality of modes propagating through the amplification optical fiber 20 and passing through the first FBG 31 from light of a higher mode than the predetermined mode. Also reflect with high reflectivity.

  Such a fiber laser device 1 uses an amplification optical fiber 20 that propagates light of a plurality of modes, and has a larger core diameter than an amplification optical fiber that propagates only light of a fundamental mode. Therefore, it is possible to suppress the generation of nonlinear optical light even when light having high power propagates through the amplification optical fiber 20. Further, in the fiber laser device 1, light up to a predetermined mode among the light transmitted through the first FBG 31 by the optical component 40 is reflected with a higher reflectance than the light in the higher order mode. A part of the reflected light passes through the first FBG 31 again and is amplified by the amplification optical fiber 20. Therefore, the light incident on the amplification optical fiber from the first FBG 31 has a light power up to a predetermined mode higher than the light power in the higher-order mode as compared with the case where the optical component 40 is not provided. As described above, the light up to the predetermined mode is the light of the lower order mode among the light of the plurality of modes propagating through the amplification optical fiber 20. Therefore, in the amplification optical fiber 20, even when the amplification factor of the low-order mode light and the amplification factor of the high-order mode light are the same, as a result, the light of the low-order mode is in the high-order mode. It will be amplified rather than light. Therefore, it is possible to emit low-order mode light with higher power than high-order mode light. Thus, according to the fiber laser device 1 of the present embodiment, light with good beam quality and high power can be emitted.

  Further, in the fiber laser device 1 of the present embodiment, the optical component 40 includes the optical fiber 41 that serves as a filter and the third FBG 43 that reflects the light transmitted through the optical fiber 41. Can be configured.

  Further, in the fiber laser device 1 of the present embodiment, since the optical fiber 41 is a single mode fiber, the fundamental mode light can be further amplified in the amplification optical fiber 20, and light with better beam quality is emitted. can do.

  In the fiber laser device 1 of the present embodiment, the light reflectance of the third FBG 43 is set higher than the light reflectance of the first FBG 31. That is, the light reflectance of the optical component 40 is made higher than the light reflectance of the first FBG 31. Accordingly, light reciprocating between the first FBG 31 and the optical component 40 is mainly emitted from the first FBG 31 side and enters the amplification optical fiber 20. For this reason, light up to a predetermined mode can be amplified more efficiently.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 2 is a diagram showing a fiber laser device according to the present invention. As shown in FIG. 2, the fiber laser device 1 of the present embodiment differs from the fiber laser device 1 of the first embodiment in that the optical fiber 41 used for the optical component 40 is a multimode fiber.

  The optical fiber 41 of the present embodiment can propagate the light in the same plurality of modes as the amplification optical fiber 20. However, the optical fiber 41 is bent with a predetermined diameter, and light of the second order LP mode or higher, which is a higher order mode than the fundamental mode, is lost due to the bending. For example, as described in the first embodiment, the amplification optical fiber 20 propagates light having a wavelength of 1060 nm in the 4LP mode, the core diameter is 16 μm, and the relative refractive index difference between the core and the inner cladding is 0.1. When the core diameter of the optical fiber 41 and the relative refractive index difference between the core and the inner cladding are made the same as the diameter of the core of the amplification optical fiber 20 and the relative refractive index difference between the core and the inner cladding. To do. In this case, for example, the bending diameter is set to 4 cm so that the light of the second order LP mode or more is lost due to the bending of the optical fiber 41.

  In such a fiber laser device 1, light that propagates through the amplification optical fiber 20 and passes through the first FBG 31 enters the optical fiber 41. In the optical fiber 41, light of the fundamental mode and light of higher order than the fundamental mode propagate, but light other than the fundamental mode is lost due to bending. Therefore, the light reflected by the third FBG 43 and incident again on the first FBG 31 is mainly the fundamental mode light in the same manner as in the first embodiment. For this reason, in the same manner as in the first embodiment, the fiber laser device 1 emits light having a large fundamental mode power.

  In the present embodiment, as described above, the optical fiber 41 propagates light of a higher mode than the fundamental mode and the fundamental mode, and the light of the higher mode is lost due to bending. However, light up to a predetermined mode including the fundamental mode and light of a higher order mode than the predetermined mode may be propagated, and the light of the higher order mode may be lost due to bending. In this case, the light propagating through the optical fiber 41, reflected by the third FBG 43 and incident on the first FBG 31 again is the light up to the predetermined mode. The light up to the predetermined mode is light of a lower order mode than the light of the higher order mode. Therefore, in this case, the fiber laser device 1 emits light having a large power in the low-order mode.

  According to the fiber laser device 1 of the present embodiment, it is possible to determine the high-order mode light to be lost by adjusting the bending diameter or the like of the optical fiber used as a filter. Light can be propagated. The low-order mode light may be the fundamental mode light as described above. Accordingly, it is possible to appropriately adjust the number of modes of light to be increased in the emitted light.

  As mentioned above, although the said embodiment was demonstrated to the example about this invention, this invention is not limited to these, It can change suitably.

  For example, in the above embodiment, the optical component 40 includes the optical fiber 41 as a filter and the third FBG 43 as a third mirror. However, the optical component of the present invention reflects light up to a predetermined mode including the fundamental mode out of a plurality of modes transmitted through the first FBG 31 with a higher reflectance than light of a mode higher than the predetermined mode. As long as it does, it is not limited to the optical component 40 of the said embodiment. For example, the optical fiber 41 may not function as a filter, and the third mirror may reflect light up to a predetermined mode including the fundamental mode with a higher reflectance than light of a higher mode than the predetermined mode. good. For example, the third mirror is configured by FBG, and the FBG is configured such that the refractive index of the high refractive index portion is high at the center of the core and lower at the outer periphery of the core than at the center of the core. The light power in the fundamental mode is higher at the center of the core and lower at the core periphery. In addition, the power of the higher-order mode light is increased beyond the center of the core. Therefore, by using the FBG as described above, it is possible to reflect the light in the fundamental mode with a higher reflectance than the light in the higher order mode. By adjusting a region having a high reflectance in the high refractive index portion, light up to a predetermined mode can be reflected with a higher reflectance than light in a higher order mode.

  In the above embodiment, the optical fiber 41 is used as a filter. However, the filter is a filter that transmits light up to a predetermined mode including the fundamental mode and suppresses transmission of light in a higher-order mode than the predetermined mode. For example, the optical fiber is not limited.

  In the above embodiment, the first FBG 31, the second FBG 32, and the third FBG 43 have been described as examples of the first mirror, the second mirror, and the third mirror. However, the first mirror, the second mirror, and the third mirror have other configurations. It may be.

  According to the present invention, the fiber laser device of the present invention can emit light with high beam quality and high power, and can be used in various industries such as the laser processing field and the medical field.

DESCRIPTION OF SYMBOLS 1 ... Fiber laser apparatus 10 ... Excitation light source 20 ... Amplifying optical fiber 31 ... 1st FBG (1st mirror)
32 ... 2nd FBG (2nd mirror)
40 ... Optical component 41 ... Optical fiber 43 ... 3rd FBG (3rd mirror)

Claims (8)

An excitation light source that emits excitation light;
An optical fiber for amplification that propagates light of a plurality of modes by adding an active element excited by the excitation light; and
A first mirror that is provided on one side of the amplification optical fiber and reflects light amplified by the amplification optical fiber with a reflectance of less than 100%;
A second mirror that is provided on the other side of the optical fiber for amplification and reflects light having a wavelength band that is at least partially the same as the wavelength band of light reflected by the first mirror with a lower reflectance than the first mirror;
An optical component that is provided on the side opposite to the amplification optical fiber side with respect to the first mirror, and that reflects at least part of the wavelength band of the light reflected by the first mirror;
With
The optical component reflects light up to a predetermined mode including a fundamental mode among the light of the plurality of modes transmitted through the first mirror with a higher reflectance than light of a higher-order mode than the predetermined mode. And a fiber laser device. 2. The fiber laser device according to claim 1, wherein the light of the predetermined mode is light of a fundamental mode, and the light of the higher order mode is light of a second order LP mode or higher. The optical component includes a filter and a third mirror that reflects light transmitted through the filter,
The fiber laser device according to claim 1, wherein the filter suppresses transmission of light in the higher-order mode. 4. The fiber laser device according to claim 3, wherein the filter is an optical fiber that suppresses propagation of light in the higher-order mode and propagates light up to the predetermined mode. 5. The fiber laser device according to claim 4, wherein the optical fiber used as the filter is a single mode fiber. 4. The fiber laser device according to claim 3, wherein the filter is an optical fiber in which light of the higher-order mode is lost by being bent. The fiber laser device according to any one of claims 4 to 6, wherein a diameter of a core of the optical fiber used as the filter is equal to a diameter of a core of the optical fiber for amplification. 8. The fiber laser device according to claim 1, wherein the optical component has a light reflectance higher than that of the first mirror. 9.

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