Optical amplification component and fiber laser device

Abstract

This optical amplification component (1) comprises an optical fiber (10) for amplification, wherein the optical fiber (1) has a core (11) to which an active element is added, and can propagate light of a predetermined wavelength through the core (11) in a multimode. The optical fiber (10) for amplification has: a first section (SC1) including a reference position (RP) which is between one end (E1) and the other end (E2) and not located alongside other portions of the optical fiber (10) for amplification, wherein a first fiber portion (10A) extending from the reference position (RP) toward the one end (E1) and a second fiber portion (10B) extending from the reference position (RP) toward the other end (E2) are not disposed alongside each other; and a second section (SC2) in which the first fiber portion (10A) and the second fiber portion (10B) surround the outside of the first section (SC1) alongside each other. The first section (SC1) is provided with a winding part (R1) in which the optical fiber (10) for amplification is wound one or more turns in a smaller radius than in other portions.

Description

Optical amplification components and fiber laser devices

[0001] The present invention relates to optical amplification components and fiber laser devices.

[0002] When light propagates through an amplification optical fiber, heat is generated due to light transmission loss. Additionally, heat is generated when an active element added to the core of the amplification optical fiber is excited by excitation light and emits light from that active element. This heat generated from the amplification optical fiber is dissipated, for example, by a cooling plate to which the amplification optical fiber is fixed. Patent Document 1 describes an optical amplification component in which the amplification optical fiber is fixed to a cooling plate. This optical amplification component allows for improved heat dissipation, thereby increasing the lifespan of the amplification optical fiber.

[0003] Patent No. 6034708

[0004] Light propagating through an optical fiber tends to leak more from the core the higher the order of the light mode. Therefore, if the optical fiber has a bend, higher-order mode light is more likely to leak from the fiber. This characteristic can be used to construct a higher-order mode filter using the bend of the optical fiber. By using such a higher-order mode filter, light with improved beam quality can propagate through the optical fiber. In the optical amplification component of Patent Document 1, the amplification optical fiber is bent on a cooling plate. Therefore, at least a portion of the higher-order mode light can leak even in this optical amplification component.

[0005] Incidentally, in the bent portion of an optical fiber, a refractive index unevenness occurs, with the refractive index becoming higher towards the outside of the bend. When such a refractive index unevenness occurs, the displacement of the electric field distribution of light is greater for light closer to the fundamental mode than for higher-order modes, and the light tends to be biased towards the outside of the bend. If this optical fiber is an amplification optical fiber with an active element added to the core, the intensity of light close to the fundamental mode will be lower on the inside of the bend. Therefore, on the inside of the bend in the core, it becomes more difficult for light close to the fundamental mode to strike the excited active element. In contrast, the higher-order mode light strikes the excited active element in the bend because the displacement of the electric field distribution is smaller than that of the fundamental mode. Consequently, the higher-order mode light is amplified in the bend, even though it leaks as described above. For this reason, in amplification optical fibers with bends, the amplification of the fundamental mode light may be smaller, while the amplification of the higher-order mode light may not be significantly smaller, compared to amplification optical fibers without bends. In particular, in the case of partially doped optical fibers where the concentration of active elements is higher towards the center of the core, the peak of the fundamental mode light is shifted from the center, so the amplification of the fundamental mode light may be smaller than the amplification of the higher-order modes. This raises concerns about a deterioration in beam quality.

[0006] Therefore, the present invention aims to provide an optical amplification component and a fiber laser apparatus that can amplify light while improving beam quality.

[0007] One aspect of the present invention for solving the above problems is an optical amplification component having a core to which an active element is added, and an amplification optical fiber capable of propagating light of a predetermined wavelength in multimode through the core, wherein the amplification optical fiber includes a reference position between one end and the other end of the amplification optical fiber and is not aligned with other parts of the amplification optical fiber, and has a first fiber portion extending from the reference position toward the one end and a second fiber portion extending from the reference position toward the other end, which are arranged not to be aligned with each other, and a second section in which the first fiber portion and the second fiber portion circumferentially surround the outside of the first section while being aligned with each other, and the first section is provided with a winding portion in which the amplification optical fiber is wound one or more times with a smaller radius than other parts.

[0008] In the optical amplification component described above, the second section is located on one end and the other end of the amplification optical fiber, respectively, compared to the first section. Therefore, in such an optical amplification component, when excitation light is incident from one end and the other, at least a portion of each excitation light is absorbed by the active element in the second section. As a result, the intensity of the excitation light propagating through the first section is smaller than the intensity of the excitation light propagating through the second section. Consequently, the amplification factor of the light propagating through the core is smaller in the first section compared to the second section and the sections closer to the ends of the second section. Because the winding section is wound one or more times with a smaller radius than other parts, more higher-order mode light may leak from the winding section than from other parts. Also, because the winding section is located in the first section, the amplification factor of light is small in the winding section as described above. Therefore, even if higher-order mode light is amplified at a higher amplification factor than the fundamental mode in the winding section, the overall amplification factor of the amplification optical fiber is small. Thus, in the winding section, a large amount of higher-order mode light leaks out, and the amplification factor of the light is small. Therefore, the beam quality of the light propagating through the core can be improved in the winding section. For this reason, the optical amplification component of this embodiment can amplify light while improving beam quality.

[0009] Aspect 2 of the present invention is an optical amplification component of aspect 1 in which the midpoint of the amplification optical fiber is located in the first section.

[0010] When increasing the amplification factor of light using an optical amplification component, it is preferable that excitation light of the same power is incident from one end and the other end of the amplification optical fiber. When excitation light is incident in this manner, the power of the excitation light is lowest at the midpoint of the amplification optical fiber. Therefore, since the power of the excitation light is low in the first section where the winding is provided, the amplification factor of higher-order modes of light in the winding section can be suppressed compared to when the midpoint of the amplification optical fiber is located outside the first section, and the beam quality can be further improved.

[0011] Embodiment 3 of the present invention is an optical amplification component of Embodiment 1 or 2, wherein the first section is provided with a plurality of the winding portions.

[0012] In this configuration, higher-order modes of light can be leaked more easily, thereby improving beam quality.

[0013] Aspect 4 of the present invention is an optical amplification component of aspect 1, characterized in that the first section is provided with a pair of winding sections, and the midpoint of the amplification optical fiber is located between the pair of winding sections.

[0014] In this embodiment, the power of the excitation light in each winding can be reduced compared to the case where the midpoint of the amplification optical fiber is located anywhere other than between the pair of windings in the first section. Furthermore, this embodiment allows for a highly symmetrical layout.

[0015] Aspect 5 of the present invention is an optical amplification component in any of aspects 1 to 4, wherein the amplification optical fiber further comprises a third section consisting of the outermost end of the second section in the first fiber portion to the first end, and the outermost end of the second section in the second fiber portion to the other end, and in the third section, the first fiber portion and the second fiber portion extend outward from the second section.

[0016] The ends of the amplification optical fiber are connection points where it connects to other optical fibers. At such connection points, heat generation tends to be high due to light leakage and other factors. With this configuration, one end and the other end of the amplification optical fiber can be kept away from the second section. Therefore, the heat generated at both ends of the amplification optical fiber can suppress the degradation of the amplification optical fiber in the circulating second section and the first section surrounded by the second section. Thus, an optical amplification component that improves the lifespan of the amplification optical fiber can be realized.

[0017] Embodiment 6 of the present invention is an optical amplification component of Embodiment 5, characterized in that, in the third section, the first fiber portion and the second fiber portion extend in different directions from each other.

[0018] In this embodiment, in the third section, the first fiber portion and the second fiber portion can be separated from each other by their respective ends, compared to the case where they extend in the same direction. Therefore, the effects of heat generated at both ends of the amplifying optical fiber can be dispersed. For this reason, this embodiment makes it possible to realize an optical amplification component that further improves the lifespan of the amplifying optical fiber.

[0019] Aspect 7 of the present invention is characterized in that, in the winding portion, light of a higher order than the LP11 mode among the light of the predetermined wavelength is cut off, and the LP11 mode light at the predetermined wavelength has an electric field distribution perpendicular to each other in the cross-section of the amplification optical fiber. ｏｄｄ Mode light and LP11 ｅｖｅｎ The optical amplification component is characterized in that the loss of the light of the mode with the greater loss among the modes of light is 1.0 dB / turn or more, and the loss of the light of the LP01 mode at the predetermined wavelength is 1.0 dB / turn or less, as described in any of embodiments 1 to 6.

[0020] In this configuration, the light can be brought sufficiently close to single mode. However, in the winding section, the light of LP11 mode is more prone to leakage than the light of LP01 mode, so the light of LP01 mode and LP11 ｏｄｄ Mode light and LP11 ｅｖｅｎ The light from the mode with the greater loss will not have the same loss as the light from the mode with the greater loss.

[0021] Embodiment 8 of the present invention is an optical amplification component of any embodiment 1 to 7, characterized in that, in the second section, the intensity of the LP01 mode light at the center of the core at the predetermined wavelength is 80% or more of the peak intensity of the LP01 mode light.

[0022] In this case, compared to the case where the intensity at the center of the core of the LP01 mode light in the second section is less than 80% of the peak intensity of the light, the amount of shift of the LP01 mode light is smaller, and the amplification factor of the LP01 mode light can be increased.

[0023] Aspect 9 of the present invention is a fiber laser device characterized by comprising an optical amplification component from any of aspects 1 to 8, a first excitation light source that injects excitation light to excite the active element into the amplification optical fiber from one end, and a second excitation light source that injects excitation light to excite the active element into the amplification optical fiber from the other end.

[0024] This configuration makes it possible to realize a fiber laser device that can emit highly amplified light with high beam quality.

[0025] Aspect 10 of the present invention is a fiber laser apparatus according to aspect 9, further comprising: a first mirror which is optically coupled to the core of the first amplifying optical fiber at one end of the amplifying optical fiber and reflects light of a predetermined wavelength among the light emitted by the excited active element; and a second mirror which is optically coupled to the core of the first amplifying optical fiber at the other end of the first amplifying optical fiber and reflects light of the predetermined wavelength among the light reflected by the first mirror with a lower reflectivity than the first mirror.

[0026] This configuration makes it possible to realize a resonator-type fiber laser device that can emit amplified light with high beam quality.

[0027] As described above, the present invention provides an optical amplification component and a fiber laser apparatus that can amplify light while improving beam quality.

[0028] Figure 1 shows a fiber laser apparatus in an embodiment. Figure 2 shows the cross-sectional configuration of the amplification optical fiber. Figure 3 shows the optical amplification component of Figure 1. Figure 4 shows the electric field distribution of light propagating through the core of the amplification optical fiber. Figure 5 shows the relationship between the bending diameter of the amplification optical fiber and the bending loss of light. Figure 6 shows a modified example of the optical amplification component.

[0029] Hereinafter, a preferred embodiment of an optical amplification component and a fiber laser device according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. Therefore, the present invention can be changed and improved from the embodiments within the scope of the claims. For ease of understanding, the scale of each figure may be different from the scale described in the following description.

[0030] FIG. 1 is a diagram showing a fiber laser device in the present embodiment. As shown in FIG. 1, the fiber laser device 100 in the present embodiment mainly includes an optical amplification component 1 including an amplification optical fiber 10, a first excitation light source 21 and a second excitation light source 22, a first FBG (Fiber Bragg Grating) 51 as a first mirror, and a second FBG 52 as a second mirror.

[0031] The first excitation light source 21 is composed of a plurality of laser diodes 21d and emits excitation light having a wavelength that excites an active element added to the amplification optical fiber 10 described later. When the active element added to the amplification optical fiber 10 is ytterbium (Yb) as described later, the wavelength of this excitation light is, for example, 976 nm. The first excitation light source 21 is connected to a predetermined power source and emits excitation light having a power corresponding to the current from the power source. It is preferable that this power source can vary the output current. Each laser diode 21d of the first excitation light source 21 is connected to one end of an excitation light optical fiber 23. The excitation light optical fiber 23 is, for example, an optical fiber having a core with a diameter of 125 μm. The other end of each excitation light optical fiber 23 is connected to a combiner 31.

[0032] One end of an optical fiber 41 described later is connected to the combiner 31, and one end E1 of the amplification optical fiber 10 is connected to the other end of the optical fiber 41.

[0033] Figure 2 shows a cross-section of the amplification optical fiber 10 shown in Figure 1. As shown in Figure 2, the amplification optical fiber 10 mainly comprises a core 11, an inner cladding 12 that completely surrounds the outer surface of the core 11, an outer cladding 13 that completely surrounds the outer surface of the inner cladding 12, and a coating layer 14 that covers the outer cladding 13. In other words, the amplification optical fiber 10 is a double-cladded optical fiber from a structural standpoint. The refractive index of the inner cladding 12 is lower than that of the core 11, and the refractive index of the outer cladding 13 is lower than that of the inner cladding 12. The diameter of the core 11 is, for example, 28 μm, and the outer diameter of the inner cladding 12 is, for example, 400 μm. In this embodiment, the amplification optical fiber 10 is a multimode optical fiber that propagates light of a predetermined wavelength in multiple modes, and the light of the predetermined wavelength propagates through the core 11 in, for example, 6LP mode. The predetermined wavelength is, for example, 1070 nm. The core 11 may be configured to allow light of a predetermined wavelength to propagate in, for example, 2LP mode to 20LP mode. The length of the amplification optical fiber 10 is, for example, 20 m. Excitation light propagates through the inner cladding 12, as will be described later, and such inner cladding through which excitation light propagates is sometimes simply called cladding.

[0034] The core 11 is doped with an active element that is excited by the excitation light emitted from the first excitation light source 21. In this embodiment, ytterbium is added as the active element. It is preferable that aluminum and phosphorus are further added to the core 11 in order to enhance the resistance to photodarkening. Further, dopants such as fluorine (F), boron (B), and germanium may be added to at least a part of the core 11 in order to adjust the refractive index. Further, although different from this embodiment, the active element added to the core 11 may be an active element other than ytterbium. Examples of such active elements include, in addition to ytterbium, for example, thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er), and the like. Further, examples of the active element include, in addition to rare earth elements, bismuth (Bi) and the like. Further, the active element may be added to the core 11 at a higher concentration as it is closer to the central portion, or the active element may be added to the central portion and not added to the outer peripheral portion.

[0035] Further, the inner cladding 12 is made of, for example, pure quartz to which no dopant is added, or quartz to which a dopant such as fluorine that decreases the refractive index is added. Further, the outer cladding 13 is made of, for example, a resin having a lower refractive index than the inner cladding 12, or quartz to which an element such as fluorine that decreases the refractive index is added. The coating layer 14 is made of, for example, a thermosetting resin or an ultraviolet curable resin, and when the outer cladding 13 is made of a resin, it is made of a resin different from the resin of the outer cladding 13.

[0036] The optical fiber 41 connected to one end E1 of the optical amplification fiber 10 has the same configuration as the optical amplification fiber 10 except that no active element is added to the core. Therefore, the optical fiber 41 is a double-clad optical fiber from a structural viewpoint and a multimode optical fiber from an optical viewpoint. The core 11 of the optical amplification fiber 10 and the core of the optical fiber 41 are optically coupled, and the inner cladding 12 of the optical amplification fiber 10 and the inner cladding of the optical fiber 41 are optically coupled.

[0037] A first mirror, the first FBG 51, is provided in the core of the optical fiber 41. Thus, the first FBG 51 is provided on one end E1 of the amplification optical fiber 10 and is optically coupled to the core 11 at the one end E1. The first FBG 51 is constructed such that a portion with a high refractive index is repeated at a constant period along the longitudinal direction of the optical fiber 41. By adjusting this period, the first FBG 51 reflects light with wavelengths including the predetermined wavelength among the light emitted by the active element of the amplification optical fiber 10 when it is in an excited state. As described above, if the active element added to the amplification optical fiber 10 is ytterbium and the predetermined wavelength is 1070 nm, the first FBG 51 reflects light with a wavelength of 1070 nm ± 3 nm, for example, with a reflectivity of 99% or more.

[0038] The combiner 31 is connected to the core of each excitation optical fiber 23, and optically couples the core of each excitation optical fiber 23 with the inner cladding of the optical fiber 41. Therefore, the excitation light emitted from the first excitation light source 21 can propagate to the inner cladding 12 of the amplification optical fiber 10 via the excitation optical fiber 23, the combiner 31, and the optical fiber 41. For this reason, the first excitation light source 21 is a light source that causes excitation light to be incident on the inner cladding 12 of the amplification optical fiber 10 from one end E1.

[0039] One end of optical fiber 42 is connected to the other end E2 of the amplification optical fiber 10. Optical fiber 42 has the same configuration as optical fiber 41. Therefore, from a structural standpoint, optical fiber 42 is a double-clad optical fiber, and from an optical standpoint, it is a multimode optical fiber. The core 11 of amplification optical fiber 10 and the core of optical fiber 42 are optically coupled, and the inner cladding 12 of amplification optical fiber 10 and the inner cladding of optical fiber 42 are optically coupled.

[0040] A second mirror, the second FBG 52, is provided in the core of the optical fiber 42. The second FBG 52 is thus provided on the other end E2 side of the amplification optical fiber 10 and is optically coupled to the core 11 and the other end E2. The second FBG 52 has a configuration that is generally the same as the first FBG 51, and is configured to reflect the light of the predetermined wavelength that the first FBG 51 reflects with a lower reflectivity than the first FBG 51. For example, the second FBG 52 is configured to reflect the light of the predetermined wavelength with a reflectivity of, for example, 10%. In this way, a resonator is formed by the first FBG 51, the amplification optical fiber 10, and the second FBG 52. A portion of the light that resonates in this resonator passes through the second FBG 52.

[0041] The second excitation light source 22 is a light source that introduces excitation light from the other end E2 into the inner cladding 12 of the amplification optical fiber 10. The second excitation light source 22 is composed of multiple laser diodes 22d with a configuration similar to that of the multiple laser diodes 21d of the first excitation light source 21, and emits light similar to that of the first excitation light source 21. Therefore, in this embodiment, the power of the excitation light emitted by the first excitation light source 21 and the power of the excitation light emitted by the second excitation light source 22 are approximately equal. Furthermore, the light emitted from the second excitation light source 22 has a wavelength approximately equal to that of the excitation light emitted by the first excitation light source 21, and excites the active element added to the amplification optical fiber 10. The second excitation light source 22 is connected to a power supply similar to that connected to the first excitation light source 21, for example. Each laser diode 22d of the second excitation light source 22 is connected to one end of an excitation optical fiber 24 with a configuration similar to that of the excitation optical fiber 23. The other end of each excitation optical fiber 24 is connected to a combiner 32.

[0042] The other end of the optical fiber 42 is connected to the combiner 32, optically coupling the core of each excitation optical fiber 24 with the inner cladding of the optical fiber 42. Therefore, the excitation light emitted from the second excitation light source 22 can propagate to the inner cladding 12 of the amplification optical fiber 10 via the excitation optical fiber 24, the combiner 32, and the optical fiber 42. In this way, excitation light from the first excitation light source 21 is incident on the amplification optical fiber 10 from one end E1, and excitation light from the second excitation light source 22 is incident on the other end E2.

[0043] One end of the delivery optical fiber 60 is connected to the combiner 32. The delivery optical fiber 60 has a core and a cladding, and the core and cladding are the same diameter as, for example, the core and inner cladding of the optical fiber 42. The core of the delivery optical fiber 60 is optically coupled with the core of the optical fiber 42 in the combiner 32. The other end of the delivery optical fiber 60 is connected to an output section 65. The output section 65 is made of, for example, a glass rod with a diameter larger than the core of the delivery optical fiber 60. Therefore, the light incident from the core of the delivery optical fiber 60 to the output section 65 has its diameter widened and is emitted from the output section 65.

[0044] Next, we will explain the optical amplification component 1 in detail.

[0045] Figure 3 shows the optical amplification component 1 of this embodiment. As shown in Figure 3, the optical amplification component 1 of this embodiment mainly comprises the amplification optical fiber 10 described above and the cooling plate 70.

[0046] The cooling plate 70 is a component that releases heat to lower the temperature. The cooling plate 70 is made of a metal or alloy such as copper, aluminum, or iron, and the shape of the main surface of the cooling plate 70 is, for example, rectangular. The amplification optical fiber 10 is arranged on the main surface of the cooling plate 70. In addition, heat dissipation fins may be provided on the main surface of the cooling plate 70 opposite to the main surface on which the amplification optical fiber 10 is arranged, and a water channel may be provided inside the cooling plate 70.

[0047] As shown in Figure 3, the amplification optical fiber 10 of this embodiment is composed of a first section SC1, a second section SC2, and a third section SC3.

[0048] The first section SC1 includes the reference position RP. The reference position RP is located between one end E1 and the other end E2 of the amplification optical fiber 10 and is not aligned with other parts of the amplification optical fiber 10. The first section SC1 is the section in which the first fiber portion 10A extending from the reference position RP toward the one end E1 and the second fiber portion 10B extending from the reference position RP toward the other end E2 are arranged not to be aligned with each other. In other words, the first section SC1 is the section in which the first fiber portion 10A and the second fiber portion 10B are aligned with each other, and the reference position RP is located in this section. Therefore, the reference position RP is an arbitrary position in the amplification optical fiber 10 that is not aligned with other parts of the amplification optical fiber 10 and defines the first fiber portion 10A and the second fiber portion 10B. In Figure 3, a dashed line is shown along the first fiber portion 10A of the amplification optical fiber 10 and a dotted line is shown along the second fiber portion 10B.

[0049] A winding section R1 is provided in the first section SC1. The winding section R1 is a portion in which the amplification optical fiber 10 is wound one or more times with a radius smaller than that of the other portions of the amplification optical fiber 10. Since the reference position RP is an arbitrary position that does not align with other portions as described above, the reference position RP is not located in the winding section R1. Therefore, even if the winding section R1 is wound multiple times, the first fiber portion 10A and the second fiber portion 10B do not align with each other in the winding section R1. In this embodiment, the first fiber portion 10A is wound in the winding section R1. Although not specifically shown, the position of the winding section R1 may be provided in a position different from that shown in Figure 3 in the first section SC1, and the second fiber portion 10B may be wound in the winding section R1.

[0050] In the winding section R1, if the amplification optical fiber 10 is wound two or more times, from the second turn onward, it is wound spirally with the same diameter as the first turn, away from the main surface of the cooling plate 70 on which the amplification optical fiber 10 is placed. Alternatively, from the second turn onward, the outer circumference of the first turn may be wound spirally so that the diameter increases with each turn, and then placed on the main surface of the cooling plate 70.

[0051] In this embodiment, the midpoint C of the amplification optical fiber 10 is located in the first section SC1. In the example shown in Figure 3, the midpoint C is located outside the winding section R1 in the first section SC1, but the midpoint C may be located within the winding section R1. Also, for example, if the midpoint C is located at the position shown in Figure 3, it may be understood that the reference position RP is located on the midpoint C. However, the midpoint of the amplification optical fiber 10 may be located in the second section SC2, which will be described later.

[0052] The second section SC2 is a section in which the first fiber portion 10A and the second fiber portion 10B circle around the outside of the first section SC1 while running parallel to each other. In the second section SC2, the first fiber portion 10A and the second fiber portion 10B are arranged alternately. Furthermore, in the second section SC2, it is sufficient for the first fiber portion 10A and the second fiber portion 10B to circle around each other one or more times, and it is preferable for them to circle multiple times.

[0053] As shown in Figure 3, in the second section SC2, the first fiber portion 10A and the second fiber portion 10B are arranged on the main surface of the cooling plate 70, generally in a concentric circle, with the diameter increasing with each turn, from the first section SC1 toward one end E1 and the other end E2. However, in the second section SC2, the first fiber portion 10A and the second fiber portion 10B may be arranged in a shape other than a circle, for example, in an elliptical shape.

[0054] Furthermore, the first fiber portion 10A and the second fiber portion 10B in the second section SC2 may circle in contact with each other, or they may circle at a distance from each other. When the first fiber portion 10A and the second fiber portion 10B in the second section SC2 circle at a distance from each other, the distance between the first fiber portion 10A and the second fiber portion 10B in each lap may be the same, or they may be different.

[0055] The third section SC3 is a section composed of from the outermost peripheral end of the second section SC2 in the first fiber portion 10A to one end E1 and from the outermost peripheral end of the second section SC2 in the second fiber portion 10B to the other end E2. In the third section SC3, the first fiber portion 10A and the second fiber portion 10B extend outward from the second section SC2. In the example of FIG. 3, in the third section SC3, the first fiber portion 10A and the second fiber portion 10B extend in different directions from each other. Therefore, the one end E1 and the other end E2 are located apart from each other. However, in the third section SC3, the first fiber portion 10A and the second fiber portion 10B may extend in the same direction along each other.

[0056] Next, the winding portion R1 will be described in more detail.

[0057] FIG. 4 is a diagram showing the state of the electric field distribution of light propagating through the core 11 of the optical fiber 10 for amplification. In FIG. 4, the electric field distribution of light propagating through a portion where the optical fiber 10 for amplification is not bent and the electric field distribution of light propagating through the bent portion where the optical fiber 10 for amplification is bent are shown. In FIG. 4, each of the lights of the LP01 mode, LP11 ｅｖｅｎ mode, LP11 ｏｄｄ mode is shown.

[0058] As shown in FIG. 4, it can be seen that the light of the LP01 mode, which is the fundamental mode, is most displaced at the bent portion. Also, at the bent portion, it can be seen that the displacement of the light of the LP11 ｅｖｅｎ mode is larger than the displacement of the light of the LP11 ｏｄｄ mode. It can be seen that the light of the LP11 ｅｖｅｎ mode and the light of the LP11 ｏｄｄ mode have electric field distributions perpendicular to each other at a portion where the optical fiber 10 for amplification is not bent and constitute the light of the LP11 mode.

[0059] FIG. 5 is a diagram showing the relationship between the bending diameter of the optical fiber 10 for amplification and the bending loss of light. LP01 mode, LP11 ｅｖｅｎ mode, LP11 ｏｄｄThe relationship is shown for each light of each mode. As described above, in the bent portion, LP11 ｅｖｅｎ The light of the mode, LP11 ｏｄｄ Because the position shifts compared to the light of the mode, as shown in Figure 5, LP11 ｅｖｅｎ The optical loss in mode is LP11 ｏｄｄ It is greater than the optical loss of the mode. As shown in Figure 5, the optical loss of the LP01 mode is 1.0 dB / turn or less, and LP11 ｏｄｄ Mode light and LP11 ｅｖｅｎ LP11 is the mode with the greater loss among the optical modes. ｅｖｅｎ There exists a bending diameter where the light loss of the mode is 1.0 dB / turn or more. Therefore, the winding portion R1 is configured to allow LP11 of the light of a predetermined wavelength propagating through the core 11 of the amplification optical fiber 10. ｏｄｄ Mode light and LP11 ｅｖｅｎ It is preferable to bend the light with a bending diameter such that the loss of the light of the mode with the greater loss among the modes is 1.0 dB / turn or more, and the loss of the light of the LP01 mode among those modes is 1.0 dB / turn or less.

[0060] Furthermore, as shown in Figure 5, the optical loss in LP01 mode is 1.0 dB / turn or less, and LP11 ｏｄｄ There are bending diameters where the light loss of the mode is 1.0 dB / turn or more. Therefore, the winding section R1 is configured to allow LP11 out of the light of a predetermined wavelength propagating through the core 11 of the amplification optical fiber 10. ｏｄｄ Mode light and LP11 ｅｖｅｎ The light may be bent to a bending diameter such that the loss of the light of the mode with the lower loss among the modes is 1.0 dB / turn or more, and the loss of the light of the LP01 mode among those modes is 1.0 dB / turn or less.

[0061] Furthermore, when the winding portion R1 of the amplification optical fiber 10 is bent to the above bending diameter, light of higher order modes than the LP11 mode among the light of a predetermined wavelength is cut off. Cut-off means that the loss of light of higher order modes than the LP11 mode is 10 dB / turn or more. By bending the winding portion R1 of the amplification optical fiber 10 in this way, the beam quality of the light passing through the winding portion R1 is improved.

[0062] Furthermore, the amplification optical fiber 10 is also bent in the second section SC2. As a result, the electric field distribution of the LP01 light, which is the basic mode, is shifted toward the outer circumference in the second section SC2 as well. However, since the bending diameter is larger in the second section SC2 compared to the winding section R1, etc., in this embodiment, when the light of a predetermined wavelength in the LP01 mode propagates through the second section SC2 of the amplification optical fiber 10, it is preferable that the intensity of the LP01 mode light at the center of the core 11 is 80% or more of the peak intensity of the LP01 mode light. In other words, the positional shift of the LP01 mode light does not occur to a great extent in the second section SC2. It is preferable that the second section SC2 be bent to this extent.

[0063] Next, the operation of the fiber laser device 100 will be described.

[0064] First, excitation light is emitted from each laser diode 21d of the first excitation light source 21 and each laser diode 22d of the second excitation light source 22. The excitation light emitted from the first excitation light source 21 enters the inner cladding 12 from one end E1 of the amplification optical fiber 10 in the optical amplification component 1 via the combiner 31 and optical fiber 41 from the excitation light optical fiber 23. The excitation light emitted from the second excitation light source 22 enters the inner cladding 12 from the other end E2 of the amplification optical fiber 10 in the optical amplification component 1 via the combiner 32 and optical fiber 42 from the excitation light optical fiber 24. Each excitation light incident on the inner cladding 12 mainly propagates through the inner cladding 12. A portion of the excitation light propagating through the inner cladding 12 is absorbed by the active element added to the core 11 as it passes through the core 11, exciting the active element. The excited active element emits spontaneous emission light in a wavelength band including a predetermined wavelength. Starting from this spontaneously emitted light, light containing a predetermined wavelength that is reflected in common by the first FBG 51 and the second FBG 52 resonates between the first FBG 51 and the second FBG 52. As the resonant light propagates through the core 11 of the amplifying optical fiber 10, excited active elements undergo stimulated emission, and the resonant light is amplified. Of the resonant light, some of it passes through the second FBG 52. Then, when the gain and loss in the resonator including the first FBG 51, the amplifying optical fiber 10, and the second FBG 52 become equal, the laser oscillation state is achieved. The light amplified by the amplifying optical fiber 10 is incident on the core of the delivery optical fiber 60 via the optical fiber 42 and the combiner 32 from the amplifying optical fiber 10. The light propagating through the core of the delivery optical fiber 60 propagates from the core to the output section 65, where its diameter is expanded and it is emitted from the output section 65.

[0065] As described above, when light propagates through the amplification optical fiber 10, the amplification optical fiber 10 generates heat. This heat is conducted to the cooling plate 70 and released from the cooling plate 70. Therefore, abnormal overheating of the amplification optical fiber 10 is suppressed.

[0066] Furthermore, the excitation light emitted from the first excitation light source 21 and the second excitation light source 22 is absorbed by the active element in the third section SC3 and the second section SC2, respectively. Therefore, the intensity of the excitation light in the first section SC1 is smaller than that in the third section SC3 and the second section SC2. Consequently, the amplification factor of the light propagating through the core 11 is small in the first section SC1. Consequently, the amplification factor of the higher-order mode light is also small in the first section SC1. In addition, when the light propagating through the core 11 passes through the winding section R1, the higher-order mode light leaks out. Therefore, the beam quality of the light propagating through the core 11 is improved in the winding section R1.

[0067] As described above, the optical amplification component 1 of this embodiment has a core 11 to which an active element is added, and an amplification optical fiber 10 capable of propagating light of a predetermined wavelength in multimode through the core 11. The amplification optical fiber 10 includes a reference position RP located between one end E1 and the other end E2 of the amplification optical fiber 10 and not aligned with other parts of the amplification optical fiber 10. The first section SC1 has a first fiber portion 10A extending from the reference position RP toward the one end E1 and a second fiber portion 10B extending from the reference position RP toward the other end E2, which are arranged not aligned with each other. The second section SC2 has a winding portion R1 in the first section SC1 where the first fiber portion 10A and the second fiber portion 10B circumferentially surround the outside of the first section SC1 while aligning with each other.

[0068] Furthermore, in this embodiment, the midpoint C of the amplification optical fiber 10 is located in the first section SC1. Therefore, when excitation light of the same power is incident from one end E1 and the other end E2 of the amplification optical fiber 10, the power of the excitation light is lowest at the midpoint C. Consequently, since the power of the excitation light is low in the first section SC1 where the winding section R1 is provided, the amplification factor of higher-order mode light in the winding section R1 can be suppressed compared to the case where the midpoint C of the amplification optical fiber 10 is located outside the first section SC1, and the beam quality can be further improved.

[0069] Furthermore, in this embodiment, the amplification optical fiber 10 further has a third section SC3 consisting of the outermost end of the second section SC2 in the first fiber portion 10A to one end E1, and the outermost end of the second section SC2 in the second fiber portion 10B to the other end E2, and in the third section SC3, the first fiber portion 10A and the second fiber portion 10B extend outward from the second section SC2. The one end E1 and the other end E2 of the amplification optical fiber 10 are connection points where they are connected to other optical fibers 41 and 42. Such connection points tend to generate a lot of heat due to light leakage and the like. According to the optical amplification component 1 of this embodiment, the one end E1 and the other end E2 of the amplification optical fiber 10 can be kept away from the second section SC2. Therefore, the heat generated at one end E1 and the other end E2 of the amplification optical fiber 10 can suppress the deterioration of the amplification optical fiber 10 in the circulating second section SC2 and in the first section SC1 surrounded by the second section SC2. Consequently, the lifespan of the amplification optical fiber 10 can be improved.

[0070] Furthermore, in this embodiment, in the third section SC3, the first fiber portion 10A and the second fiber portion 10B extend in different directions from each other. This allows one end E1 and the other end E2 of the amplification optical fiber 10 to be separated. Consequently, the effects of heat generated at one end E1 and the other end E2 of the amplification optical fiber 10 can be dispersed. This allows for a further improvement in the lifespan of the amplification optical fiber 10.

[0071] While it is preferable for the optical amplification component 1 to include the third section SC3 as described above, the third section SC3 is not an essential component. For example, the outermost end of the second section SC2 of the first fiber portion 10A may be designated as one end E1, and this end E1 may be connected to the optical fiber 41, or the outermost end of the second section SC2 of the second fiber portion 10B may be designated as the other end E2, and this other end E2 may be connected to the optical fiber 42.

[0072] Furthermore, in the winding portion R1 of the optical amplification component 1 of this embodiment, light of higher-order modes than LP11 mode light among the light of a predetermined wavelength is cut off, and LP11 mode light at the predetermined wavelength is formed, having mutually perpendicular electric field distributions in the cross-section of the amplification optical fiber 10.ｏｄｄ Mode light and LP11 ｅｖｅｎ Preferably, the loss of the light of the mode with the greater loss among the modes of light is 1.0 dB / turn or more, and the loss of the light of the LP01 mode at the predetermined wavelength is 1.0 dB / turn or less. According to this embodiment, the light can be brought sufficiently close to a single mode. Note that in the winding section R1, the light of the LP11 mode is more likely to leak than the light of the LP01 mode, so the light of the LP01 mode and the LP11 ｏｄｄ Mode light and LP11 ｅｖｅｎ The light from the mode with the greater loss will not have the same loss as the light from the mode with the greater loss.

[0073] Furthermore, in the second section SC2 of the optical amplification component 1 of this embodiment, it is preferable that the intensity of the LP01 mode light at the center of the core 11 at a predetermined wavelength is 80% or more of the peak intensity of the LP01 mode light. In this case, compared to the case where the intensity of the LP01 mode light at the center of the core 11 in the second section SC2 is less than 80% of the peak intensity of the light, the amount of shift of the LP01 mode light is smaller, and the amplification rate of the LP01 mode light can be increased.

[0074] (Modifications) Next, modifications of the above embodiment will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of the same or equivalent configurations as those described in the above embodiment will be omitted.

[0075] Figure 6 shows a modified example of the optical amplification component 1. This modified example of the optical amplification component 1 differs from the optical amplification component 1 of the above embodiment in that it comprises a pair of winding sections R1 and R2. In this modified example, the winding sections R1 and R2 are wound with the same diameter and the same number of turns. However, the winding sections R1 and R2 may be wound with different diameters and with different numbers of turns.

[0076] In this modified example, the midpoint C of the amplification optical fiber 10 is located between the winding section R1 and the winding section R2. However, even when a pair of winding sections R1 and R2 are provided in this way, the midpoint C does not have to be located between the winding section R1 and the winding section R2. Also, if we consider that the reference position RP is located between the winding section R1 and the winding section R2, then as shown in Figure 6, the winding section R1 is formed by winding the first fiber section 10A, and the winding section R2 is formed by winding the second fiber section 10B.

[0077] In this modified example, a pair of winding sections R1 and R2 are provided in the first section SC1, but three or more winding sections may be provided. By providing multiple winding sections in the first section SC1 in this way, more light of higher-order modes can be leaked compared to the case where only one winding section R1 is provided in the first section SC1, and thus the beam quality can be further improved.

[0078] Furthermore, as in this modified example, when a pair of winding sections R1 and R2 are provided in the first section SC1, and the midpoint C of the amplification optical fiber 10 is located between the pair of winding sections R1 and R2, the power of the excitation light in each winding section R1 and R2 can be reduced compared to when the midpoint C is located anywhere other than between the pair of winding sections R1 and R2 in the first section SC1. Also, this embodiment allows for a highly symmetrical layout. However, even when a pair of winding sections R1 and R2 are provided in the first section SC1, the midpoint C may be located anywhere other than between the pair of winding sections R1 and R2 in the first section SC1.

[0079] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments.

[0080] For example, the cooling plate 70 is not essential in the optical amplification component 1. However, it is preferable for the optical amplification component 1 to be equipped with the cooling plate 70 from the viewpoint of extending the lifespan of the amplification optical fiber 10.

[0081] Furthermore, although the above embodiment described an example of a resonator-type fiber laser device 100, an MO-PA (Master Oscillator - Power Amplifier) ​​type fiber laser device may also be used.

[0082] Furthermore, the optical amplification component 1 of the present invention is most effectively applied to a bi-excited fiber laser device 100 in which excitation light is incident from both ends E1 and E2 of the amplification optical fiber 10. However, the optical amplification component 1 may also be used in a fiber laser device in which excitation light is incident from either end E1 or E2 of the amplification optical fiber 10. Therefore, the fiber laser device 100 is not a bi-excited type and does not need to include one of the first excitation light source 21 and the second excitation light source 22.

[0083] According to the present invention, an optical amplification component and a fiber laser device are provided that can amplify light while improving beam quality, and these are expected to be used in laser devices for processing and the like.

Claims

1. An optical amplification component comprising a core to which an active element is added, and an amplifying optical fiber capable of propagating light of a predetermined wavelength in multimode through the core, wherein the amplifying optical fiber includes a reference position between one end and the other end of the amplifying optical fiber, which is not aligned with other parts of the amplifying optical fiber, and comprises a first fiber portion extending from the reference position toward the one end and a second fiber portion extending from the reference position toward the other end, which are arranged not to be aligned with each other, and a second section in which the first fiber portion and the second fiber portion circumferentially surround the outside of the first section while being aligned with each other, wherein the first section is provided with a winding portion in which the amplifying optical fiber is wound one or more times with a radius smaller than that of other parts.

2. The optical amplification component according to claim 1, characterized in that the midpoint of the amplification optical fiber is located in the first section.

3. The optical amplification component according to claim 1 or 2, characterized in that a plurality of winding portions are provided in the first section.

4. The optical amplification component according to claim 1, characterized in that a pair of winding portions are provided in the first section, and the midpoint of the amplification optical fiber is located between the pair of winding portions.

5. The optical amplification component according to any one of claims 1 to 4, wherein the amplification optical fiber further comprises a third section consisting of the outermost end of the second section in the first fiber portion to the first end, and the outermost end of the second section in the second fiber portion to the other end, and in the third section, the first fiber portion and the second fiber portion extend outward beyond the second section.

6. The optical amplification component according to claim 5, characterized in that, in the third section, the first fiber portion and the second fiber portion extend in different directions from each other.

7. In the winding section, light of higher-order modes than the LP11 mode light among the light of the predetermined wavelength is cut off, and the LP11 mode light at the predetermined wavelength has an electric field distribution perpendicular to each other in the cross-section of the amplification optical fiber. ｏｄｄ Mode light and LP11 ｅｖｅｎ The optical amplification component according to any one of claims 1 to 6, characterized in that the loss of the light of the mode with the greater loss among the modes of light is 1.0 dB / turn or more, and the loss of the light of the LP01 mode at the predetermined wavelength is 1.0 dB / turn or less.

8. The optical amplification component according to any one of claims 1 to 7, characterized in that, in the second section, the intensity of the LP01 mode light at the center of the core at the predetermined wavelength is 80% or more of the peak intensity of the LP01 mode light.

9. A fiber laser apparatus comprising: an optical amplification component according to any one of claims 1 to 8; a first excitation light source that incidents excitation light for exciting the active element into the amplification optical fiber from one end; and a second excitation light source that incidents excitation light for exciting the active element into the amplification optical fiber from the other end.

10. The fiber laser apparatus according to claim 9, further comprising: a first mirror optically coupled to the core of the amplifying optical fiber at one end of the amplifying optical fiber, which reflects light of a predetermined wavelength among the light emitted by the excited active element; and a second mirror optically coupled to the core of the amplifying optical fiber at the other end of the amplifying optical fiber, which reflects light of the predetermined wavelength among the light reflected by the first mirror with a lower reflectivity than the first mirror.

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