Optical combiner and laser device

Abstract

To provide an optical combiner that can easily bring the divergence angle of output light closer to an ideal value.SOLUTION: An optical combiner 1 includes a plurality of input optical fibers 10 each having a core 11 through which light propagates, a first bridge fiber 20 having a tapered portion 22 in which an outer shape of the bundled plurality of input optical fibers 10 decreases toward the downstream side, a second bridge fiber 30 having a core 31 into which light propagating through the core 11 of the first bridge fiber 20 is incident, and an output optical fiber 40 having a core 41 into which light propagating through the core 31 of the second bridge fiber 30 is incident. The core 31 at the upstream end of the second bridge fiber 30 has a diameter equal to or greater than a diameter of a circumscribed circle of the cores 11 of the plurality of input optical fibers 10 at the downstream end of the first bridge fiber 20. The core 31 of the second bridge fiber 30 has a reduced-diameter core portion 34 whose diameter decreases toward the downstream side.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an optical combiner and a laser device.

Background Art

[0002] An optical combiner is widely used to combine laser light from a plurality of light sources to obtain high-power laser light. As such an optical combiner, there is known one in which a plurality of optical fibers on the input side are bundled and melt-stretched to reduce the diameter, and the bundled optical fiber bundle with the reduced diameter is connected to an optical fiber on the output side (see, for example, Patent Document 1). In such an optical combiner, when light propagates through the diameter-reduced portion, the divergence angle of the light (the angle in the direction in which the light spreads with respect to the optical axis of the core) becomes large. Therefore, it is necessary to adjust the diameter reduction ratio of the optical fiber bundle (the ratio of the outer diameter or outer shape of the optical fiber bundle before diameter reduction to the outer diameter or outer shape of the optical fiber bundle after diameter reduction) so that the divergence angle of the light emitted from the optical combiner is within an appropriate range.

[0003] However, the higher the diameter reduction ratio of the optical fiber bundle, the more difficult it is to stabilize the melt-stretching conditions, and the variation due to dimensional tolerances of the core and cladding diameters of each optical fiber and dimensional errors in the state where a plurality of optical fibers are bundled becomes larger. Therefore, it becomes difficult to make the divergence angle of the output light approach an ideal value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an optical combiner that can easily bring the divergence angle of the output light closer to an ideal value and a laser device including such an optical combiner.

Means for Solving the Problems

[0006] Aspect 1 of the present invention is a first bridge fiber including a plurality of input optical fibers each having a first core through which light propagates, the outer shape of the bundled plurality of input optical fibers having a tapered portion that becomes smaller toward the downstream; a second bridge fiber having a second core into which the light propagating through the first core of the first bridge fiber is incident; an output optical fiber having a third core into which the light propagating through the second core of the second bridge fiber is incident and comprising the second core at the upstream end of the second bridge fiber has a diameter equal to or larger than the diameter of the circumscribed circle of the first cores of the plurality of input optical fibers at the downstream end of the first bridge fiber; the second core of the second bridge fiber has a reduced-diameter core portion whose diameter decreases toward the downstream; the third core of the output optical fiber has a diameter equal to or larger than the diameter of the second core at the downstream end of the second bridge fiber at the upstream end of the output optical fiber, which is an optical combiner.

[0007] Aspect 2 of the present invention is the optical combiner according to Aspect 1, wherein the cross-sectional area of each of the first cores of the plurality of input optical fibers in the tapered portion of the first bridge fiber is the same from the upstream end to the downstream end of the tapered portion. is.

[0008] Aspect 3 of the present invention is a ratio of a diameter at an upstream end of the reduced core section of the second bridge fiber to a diameter at a downstream end of the reduced core section is greater than a ratio of an outer dimension at an upstream end of the tapered section of the first bridge fiber to an outer dimension at a downstream end of the tapered section of the first bridge fiber; The optical combiner according to the first or second aspect is.

[0009] A fourth aspect of the present invention is The output optical fiber is a first inner portion including the third core; a first covering portion covering the periphery of the first inner portion downstream of the connection portion with the second bridge fiber, the first covering portion including a first layer having a refractive index lower than that of an outermost layer of the first inner portion, and a second layer having a refractive index higher than that of the first layer; Including, the optical combiner further includes a first resin having a refractive index lower than the refractive index of the outermost layer of the first inner portion of the output optical fiber and equal to or higher than the refractive index of the first layer, the first resin covering the first inner portion from the upstream end of the first coating portion toward the upstream side; The optical combiner according to any one of aspects 1 to 3. is.

[0010] A fifth aspect of the present invention is Each of the plurality of input optical fibers of the first bridge fiber comprises: a second inner portion including the first core; a second covering portion covering the second inner portion upstream of the tapered portion, the second covering portion including a third layer having a refractive index lower than that of an outermost layer of the second inner portion, and a fourth layer having a refractive index higher than that of the third layer; Including, The optical combiner further includes a second resin having a refractive index lower than the refractive index of the outermost layer of the second inner portion of the first bridge fiber and equal to or higher than the refractive index of the third layer, the second resin covering the second inner portion from the downstream end of the second coating portion toward the downstream side. The optical combiner according to any one of Aspects 1 to 4 is as follows.

[0011] Aspect 6 of the present invention is a plurality of laser light sources that generate laser light, the optical combiner according to any one of Aspects 1 to 5, and is provided with wherein the first cores of the plurality of input optical fibers of the optical combiner are optically coupled to the plurality of laser light sources. Laser device is as follows.

[0012] Aspect 7 of the present invention is a plurality of excitation light sources that generate excitation light, the optical combiner according to any one of Aspects 1 to 5, and an amplification optical fiber that amplifies laser light using the excitation light from the plurality of excitation light sources coupled by the optical combiner, and is provided with wherein the first cores of the plurality of input optical fibers of the optical combiner are optically coupled to the plurality of excitation light sources. Laser device is as follows.

Brief Description of the Drawings

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the optical combiner according to the present invention and a laser device using the same will be described in detail with reference to FIGS. 1 to 8. In FIGS. 1 to 8, the same or corresponding components are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in FIGS. 1 to 8, the scales and dimensions of each component may be exaggerated or some components may be omitted. In the following description, unless otherwise specified, terms such as "first" and "second" are used only to distinguish components from each other and do not represent a specific order or sequence.

[0015] FIG. 1 is a perspective view showing an optical combiner 1 in an embodiment of the present invention, FIG. 2 is an exploded perspective view, and FIG. 3 is a cross-sectional view taken along the optical axis direction. In this specification, unless otherwise specified, the direction in which light propagates from a light source such as a laser light source described later is referred to as the "downstream side", and the opposite direction is referred to as the "upstream side". In FIG. 3, the left side is the upstream side and the right side is the downstream side. As shown in FIGS. 1 to 3, the optical combiner 1 includes a first bridge fiber 20 including a plurality of input optical fibers 10, a second bridge fiber 30 connected to the downstream end of the first bridge fiber 20, and an output optical fiber 40 connected to the downstream end of the second bridge fiber 30.

[0016] The first bridge fiber 20 is formed by bundling a plurality of input optical fibers 10. Each input optical fiber 10 has a core 11, a glass cladding 12 covering the periphery of the core 11, and a coating portion 13 covering the periphery of the glass cladding 12. The coating portion 13 includes a resin cladding covering the periphery of the glass cladding 12 and a resin coating covering the periphery of the resin cladding. As shown in FIGS. 1 to 3, the coating portion 13 on the downstream side of the input optical fiber 10 is removed, and the glass cladding 12 is exposed to the outside.

[0017] The refractive index of the glass cladding 12 is lower than that of the core 11, the refractive index of the resin cladding of the coating portion 13 is lower than that of the glass cladding 12, and the refractive index of the resin coating of the coating portion 13 is higher than that of the resin cladding. For example, the core 11 may be formed of quartz glass (SiO2), and the glass cladding 12 may be formed by adding a dopant (such as fluorine (F) or boron (B)) having the property of reducing the refractive index to the quartz glass. Alternatively, the glass cladding 12 may be formed of quartz glass (SiO2), and the core 11 may be formed by adding a dopant (such as germanium (Ge)) having the property of increasing the refractive index. Thereby, an optical waveguide through which light propagates is formed inside the core 11 of the input optical fiber 10.

[0018] The first bridge fiber 20 has a tapered portion 22 in which the outer shape of the bundled input optical fibers 10 becomes smaller toward the downstream, a large-diameter portion 24 located on the upstream side of the tapered portion 22, and a small-diameter portion 26 located on the downstream side of the tapered portion 22. The tapered portion 22 can be formed by heating and melt-stretching the bundle of the input optical fibers 10. Note that, by this melt-stretching, the bundled input optical fibers 10 are integrated into a cylindrical shape at the small-diameter portion 26.

[0019] The second bridge fiber 30 has a single core 31. The refractive index of the core 31 is higher than that of the air surrounding the core 31, and an optical waveguide through which light propagates is formed inside the core 31 of the second bridge fiber 30. The second bridge fiber 30 has a reduced-diameter core portion 34 in which the diameter of the core 31 decreases toward the downstream side, a large-diameter portion 36 located upstream of the reduced-diameter core portion 34, and a small-diameter portion 38 located downstream of the reduced-diameter core portion 34. The second bridge fiber 30 including such a reduced-diameter core portion 34 can be formed by heating and melt-stretching a large-diameter core.

[0020] The size (diameter) of the core 31 at the upstream end of the large-diameter portion 36 of the second bridge fiber 30 is such that it can internally contain all the cores 11 (shown by dotted lines in FIG. 2) of the input optical fiber 10 at the downstream end of the first bridge fiber 20, that is, the size (diameter) is larger than the circumscribed circle of the cores 11 of the plurality of input optical fibers 10 at the downstream end of the first bridge fiber 20. The first bridge fiber 20 and the second bridge fiber 30 are fusion-connected such that all the cores 11 of the input optical fiber 10 in the tapered portion 22 of the first bridge fiber 20 are located within the region of the core 31 at the upstream end of the second bridge fiber 30.

[0021] Since the reduced-diameter core portion 34 of the second bridge fiber 30 is not formed by fusing and stretching a bundle of a plurality of input optical fibers 10 like the tapered portion 22 of the first bridge fiber 20, it is easy to design so that the divergence angle of the output light approaches an ideal value, and it is easy to make the reduction ratio of the reduced-diameter core portion 34 of the second bridge fiber 30 larger than the reduction ratio of the tapered portion 22 of the first bridge fiber 20. Therefore, it is preferable that the ratio of the diameter of the upstream end portion to the diameter of the downstream end portion at the downstream end portion of the reduced-diameter core portion 34 of the second bridge fiber 30 is larger than the ratio of the outer dimension of the upstream end portion 22A to the outer dimension of the downstream end portion 22B of the tapered portion 22 of the first bridge fiber 20. With such a configuration, the reduction ratio of the tapered portion 22 in the first bridge fiber 20 can be suppressed, and as a result, it becomes easier to bring the divergence angle of the light output from the optical combiner 1 closer to an ideal value.

[0022] In the second bridge fiber 30 in the present embodiment, since air having a refractive index lower than that of the core 31 exists around the core 31, although no other member is formed outside the core 31, a member (for example, a cladding) having a refractive index lower than that of the core 31 may be formed outside the core 31.

[0023] The output optical fiber 40 has a core 41 and a coating portion 43 that covers the periphery of the core 41. The coating portion 43 includes a cladding (first layer) that covers the periphery of the core 41 and a resin coating (second layer) that covers the periphery of the cladding. The refractive index of the cladding of the coating portion 43 is lower than the refractive index of the core 41. Thereby, an optical waveguide through which light propagates is formed inside the core 41 of the output optical fiber 40. Further, the refractive index of the resin coating of the coating portion 43 is higher than the refractive index of the cladding. As shown in FIGS. 1 to 3, the coating portion 43 on the upstream side of the output optical fiber 40 is removed, and the core 41 is exposed to the outside. The diameter of the upstream end portion of the exposed core 41 is equal to or larger than the diameter of the small-diameter portion 38 of the second bridge fiber 30.

[0024] In such a configuration, the light propagating downstream through the cores 11 of the plurality of input optical fibers 10 is incident on the core 31 of the second bridge fiber 30 through the large-diameter portion 24, the tapered portion 22, and the small-diameter portion 26 of the first bridge fiber 20. The light incident on the core 31 of the second bridge fiber 30 propagates through the large-diameter portion 36, the reduced-diameter core portion 34, and the small-diameter portion 38 and is incident on the core 41 of the output optical fiber 40. In this way, the light propagating through the cores 11 of the plurality of input optical fibers 10 is coupled to the core 41 of the single output optical fiber 40.

[0025] In the present embodiment, the output optical fiber 40 is connected to the downstream side of the second bridge fiber 30. However, in a case where light is emitted into space from the second bridge fiber 30, etc., it is not necessary to connect the output optical fiber 40 to the downstream side of the second bridge fiber 30.

[0026] FIG. 4 is a diagram showing the change in the cross-section of the tapered portion 22 of the first bridge fiber 20. The left side shows the cross-section of the upstream end 22A of the tapered portion 22 (the cross-section taken along line A-A in FIG. 3), and the right side shows the cross-section of the downstream end 22B of the tapered portion 22 (the cross-section taken along line B-B in FIG. 3). As described above, since the tapered portion 22 is formed by fusing and stretching a bundle of a plurality of input optical fibers 10, as shown in FIG. 4, the outer dimensions of the upstream end 22A are smaller than those of the downstream end 22B. Also, at the upstream end 22A of the tapered portion 22, the cross-section of each core 11 is circular, but at the downstream end 22B, the shape of the core 11 other than the central core 11 changes. Also, at the downstream end 22B, the glass claddings 12 of the plurality of input optical fibers 10 are joined to each other and integrated. In the present embodiment, although the shape of the core 11 at the downstream end 22B of the tapered portion 22 changes from the shape at the upstream end 22A, its cross-sectional area is the same as that of the circular cross-section core 11 at the upstream end 22A. Since the divergence angle of the propagating light does not theoretically deteriorate if the cross-sectional area of the core 11 is constant, by making the cross-sectional area of the core 11 the same from the upstream end 22A to the downstream end 22B of the tapered portion 22 in this way, even though the outer dimensions of the first bridge fiber 20 are reduced by the tapered portion 22, it becomes easier to bring the divergence angle of the light output from the optical combiner 1 closer to an ideal value. In this specification, the fact that the cross-sectional area of the core of the tapered portion 22 is the same means that it is in the range of 90% to 100% of the cross-sectional area of the core 11 at the upstream end 22A of the tapered portion 22.

[0027] Incidentally, it is conceivable that a part of the light incident from the core 31 of the second bridge fiber 30 into the core 41 of the output optical fiber 40 leaks to the upstream edge of the coating portion 43 and is absorbed by the coating portion 43, causing the coating portion 43 to generate heat. In order to suppress the heat generation in such a coating portion 43, a heat generation suppression mechanism as shown in FIG. 5 may be provided.

[0028] That is, when light propagates through the tapered portion 22 of the first bridge fiber 20 and the reduced-diameter core portion 34 of the second bridge fiber 30, the divergence angle of the light increases. The light with an increased divergence angle is reflected at the interface between the core 41 of the downstream output optical fiber 40 and the surrounding air and propagates downstream. However, since the refractive index of the cladding 44 that constitutes the coating portion 43 is higher than the refractive index of air, it is conceivable that a part of the light (for example, about 5% of the light) leaks from the core 41 through the cladding 44 to the resin coating 45, causing the resin coating 45 to generate heat. Therefore, in FIG. 5, a resin 50 (first resin) that covers the core 41 of the output optical fiber 40 is provided upstream from the upstream end of the coating portion 43. The refractive index of this resin 50 is lower than the refractive index of the core 41 and has a refractive index equal to or higher than the refractive index of the cladding 44 of the coating portion 43. For example, the resin 50 has the same refractive index as the cladding 44.

[0029] By providing such a resin 50, the light that would have leaked from the core 41 of the output optical fiber 40 to the coating portion 43 in the absence of the resin 50 leaks into the resin 50 before reaching the coating portion 43. Therefore, the amount of light leaking into the coating portion 43 can be suppressed, and the amount of heat generated in the coating portion 43 can be reduced. In order to suppress the heat generation of the resin 50 itself, the resin 50 is preferably formed from a material with a high transmittance (transparent) to the light propagating through the core 41.

[0030] Also, in this embodiment, the portion (first inner portion) of the output optical fiber 40 connected to the second bridge fiber 30 is composed only of the core 41, and the core 41 is the outermost layer of this portion. However, the portion (first inner portion) of the output optical fiber 40 connected to the second bridge fiber 30 may be composed of the core 41 and a glass cladding that covers the periphery of the core 41, and the coating portion 43 may be composed of a resin cladding (first layer) that covers the periphery of the glass cladding and a resin coating (second layer) that covers the periphery of the resin cladding. In this case, the resin 50 only needs to have a refractive index lower than the refractive index of the glass cladding that is the outermost layer of the first inner portion and equal to or higher than the refractive index of the resin cladding that is the first layer.

[0031] Also, when the optical combiner 1 is used for applications that output high-power laser light, return light such as the reflected light of the output laser light may propagate from the downstream side to the upstream side. Since a similar phenomenon may occur in the coating portion 13 of the input optical fiber 10 for such return light, a heat generation suppression mechanism as shown in FIG. 6 may be provided.

[0032] That is, it is conceivable that a part of the return light leaks from the outermost layer of the second inner portion composed of the core 11 and the glass cladding 12 of the input optical fiber 10, that is, from the glass cladding 12 through the resin cladding 14 (third layer) of the coating portion 13 to the resin coating 15 (fourth layer), and the resin coating 15 generates heat. For this reason, in FIG. 6, a resin 60 (second resin) that covers the glass cladding 12 of the input optical fiber 10 is provided from the downstream end of the coating portion 13 toward the downstream side. The refractive index of this resin 60 is lower than the refractive index of the glass cladding 12 and has a refractive index equal to or higher than the refractive index of the resin cladding 14 of the coating portion 13. For example, the resin 60 has the same refractive index as the resin cladding 14.

[0033] By providing such a resin 60, the return light that would have leaked from the glass cladding 12 of the input optical fiber 10 to the coating portion 13 without the resin 60 will leak into the resin 60 before reaching the coating portion 13. Therefore, the amount of return light leaking into the coating portion 13 can be suppressed, and the amount of heat generation in the coating portion 13 can be reduced. In order to suppress the heat generation of the resin 60 itself, the resin 60 is preferably formed of a material with a high transmittance (transparent) with respect to the return light propagating through the glass cladding 12.

[0034] FIG. 7 is a diagram schematically showing a fiber laser device 401 as a laser device including the above-described optical combiner. As shown in FIG. 7, the fiber laser device 401 includes an optical resonator 412 including an amplifying optical fiber 410 capable of amplifying laser light, a plurality of pump light sources 420 that supply pump light to the optical resonator 412 from one end side of the optical resonator 412, an optical combiner 430 that combines the pump light output from the plurality of pump light sources 420 and introduces the combined pump light into the optical resonator 412, a delivery fiber 440 extending from the optical resonator 412, and a laser output unit 450 provided at the downstream end of the delivery fiber 440. Each pump light source 420 and the optical combiner 430 are connected by an optical fiber 460, and the optical combiner 430 and the optical resonator 412 are connected by an optical fiber 470.

[0035] The amplifying optical fiber 410 of the optical resonator 412 has a core doped with rare earth element ions such as ytterbium (Yb), erbium (Er), thulium (Tm), and neodymium (Nd), and is constituted by, for example, a double-clad fiber having an inner cladding formed around the core and an outer cladding formed around the inner cladding.

[0036] The optical resonator 412 includes a high-reflection portion 414 that reflects light in a predetermined wavelength band (e.g., 1060 nm to 1100 nm) with a high reflectivity, and a low-reflection portion 416 that reflects light in this wavelength band with a lower reflectivity than the high-reflection portion 414. The high-reflection portion 414 and the low-reflection portion 416 are constituted by, for example, a fiber Bragg grating (FBG) or a mirror formed by periodically changing the refractive index of the optical fiber along the light propagation direction. In the example shown in FIG. 7, the high-reflection portion 414 and the low-reflection portion 416 are constituted by fiber Bragg gratings.

[0037] The optical fibers 460 connected to the excitation light source 420 each have a core and a cladding that covers the periphery of the core and has a refractive index lower than that of the core. Inside the cores of these optical fibers 460, an optical waveguide through which the excitation light generated by the excitation light source 420 propagates is formed. As the excitation light source 420, for example, a laser module including a high-power multimode semiconductor laser element capable of emitting laser light with a wavelength of 975 nm is used. The excitation light generated by each excitation light source 420 propagates through the core of the optical fiber 460 and travels toward the optical combiner 430, where it is combined and introduced into the optical resonator 412.

[0038] The excitation light introduced from the excitation light source 420 into the optical resonator 412 via the optical combiner 430 propagates through the inner cladding and the core of the amplifying optical fiber 410. This excitation light is absorbed by the rare-earth element ions added to the core when passing through the core, and these rare-earth element ions are excited to generate spontaneous emission light. This spontaneous emission light is recursively reflected between the high-reflection portion 414 and the low-reflection portion 416, and light with a specific wavelength (for example, 1070 nm) is amplified to cause laser oscillation. The laser light amplified by the optical resonator 412 in this way propagates through the core of the amplifying optical fiber 410, and a part of it passes through the low-reflection portion 416. The laser light that has passed through the low-reflection portion 416 propagates through the core of the delivery fiber 440 and is output from the laser output portion 450.

[0039] The optical combiner 1 of the above-described embodiment can be used as the optical combiner 430 in such a fiber laser device 401. In this case, a part of the optical fiber 460 extending from the excitation light source 420 constitutes the input optical fiber 10 of the above-described optical combiner 1, or the input optical fiber 10 of the optical combiner 1 is connected to the optical fiber 460, and the core 11 of the input optical fiber 10 is optically coupled to the excitation light source 420. Also, a part of the optical fiber 470 constitutes the output optical fiber 40 of the optical combiner 1, or the output optical fiber 40 of the optical combiner 1 is connected to the optical fiber 470.

[0040] In addition to the configuration shown in FIG. 7, as a fiber laser device, a MOPA fiber laser device that amplifies seed light from a seed light source using excitation light from an excitation light source is also known. Needless to say, the above-described optical combiner 1 can also be used in such a MOPA fiber laser device.

[0041] FIG. 8 is a diagram schematically showing a laser device 501 including an optical combiner according to the present invention. This laser device 501 includes a plurality of laser generation units 510 (laser light sources) that generate laser light, optical fibers 520 that propagate the laser light output from each laser generation unit 510, an optical combiner 530 that combines the laser light propagating through each optical fiber 520, a delivery fiber 540 that extends from the optical combiner 530, and a laser output unit 550 provided at the downstream end of the delivery fiber 540. As the laser generation unit 510, for example, a fiber laser device 401 as shown in FIG. 7 can be used, and the laser device 501 can output higher-power laser light by combining the outputs from such a plurality of fiber laser devices 401.

[0042] The optical combiner 1 of the above-described embodiment can be used as the optical combiner 530 in such a laser device 501. In this case, a part of the optical fiber 520 extending from the laser generation unit 510 constitutes the input optical fiber 10 of the above-described optical combiner 1, or the input optical fiber 10 of the optical combiner 1 is connected to the optical fiber 520, and the core 11 of the input optical fiber 10 is optically coupled to the laser generation unit 510. Also, a part of the delivery fiber 540 constitutes the output optical fiber 40 of the optical combiner 1, or the output optical fiber 40 of the optical combiner 1 is connected to the delivery fiber 540.

[0043] Although the preferred embodiments of the present invention have been described so far, it goes without saying that the present invention is not limited to the above-described embodiments and may be implemented in various different forms within the scope of its technical idea.

Explanation of Reference Numerals

[0044] 1 Optical combiner 10 Input optical fiber 11 Core (first core) 12 Glass cladding 13 Coating part (second coating part) 14 Resin cladding (third layer) 15 Resin coating (fourth layer) 20 First bridge fiber 22 Tapered part 22A Upstream end 22B Downstream end 30 Second bridge fiber 31 Core (second core) 34 Reduced-diameter core part 40 Output optical fiber 41 Core (third core) 43 Coating part (first coating part) 44 Resin cladding (first layer) 45 Resin coating (second layer) 401 Fiber laser device (laser device) 410 Amplifying optical fiber 420 Excitation light source (laser light source) 430 Optical combiner 501 Laser device 510 Laser generation unit (laser light source)

Claims

1. A first bridge fiber including a plurality of input optical fibers each having a first core through which light propagates, the first bridge fiber having a tapered portion in which the outer shape of the bundled plurality of input optical fibers becomes smaller toward the downstream; A second bridge fiber having a second core into which the light propagating through the first core of the first bridge fiber is incident; An output optical fiber having a third core into which the light propagating through the second core of the second bridge fiber is incident and comprising: The second core at the upstream end of the second bridge fiber has a diameter equal to or greater than the diameter of the circumscribed circle of the first cores of the plurality of input optical fibers at the downstream end of the first bridge fiber; The second core of the second bridge fiber has a reduced-diameter core portion in which the diameter decreases toward the downstream side; The third core of the output optical fiber has a diameter equal to or greater than the diameter of the second core at the downstream end of the second bridge fiber at the upstream end of the output optical fiber, An optical combiner.

2. The optical combiner according to claim 1, wherein the cross-sectional area of each of the first cores of the plurality of input optical fibers in the tapered portion of the first bridge fiber is the same from the upstream end to the downstream end of the tapered portion.

3. The ratio of the diameter at the upstream end to the diameter at the downstream end of the reduced-diameter core portion of the second bridge fiber is greater than the ratio of the outer dimension at the upstream end to the outer dimension at the downstream end of the tapered portion of the first bridge fiber. The optical combiner according to claim 1.

4. The output optical fiber includes a first inner portion including the third core, and a first coating portion that covers the periphery of the first inner portion downstream of the connection portion with the second bridge fiber, the first coating portion including a first layer having a refractive index lower than the refractive index of the outermost layer of the first inner portion and a second layer having a refractive index higher than the refractive index of the first layer. and comprising: The optical combiner further includes a first resin having a refractive index lower than the refractive index of the outermost layer of the first inner portion of the output optical fiber and equal to or higher than the refractive index of the first layer, the first resin covering the first inner portion from the upstream end of the first coating portion toward the upstream side. The optical combiner according to claim 1.

5. Each of the plurality of input optical fibers of the first bridge fiber is a second inner portion including the first core, a second coating portion that covers the second inner portion upstream of the tapered portion, the second coating portion including a third layer having a refractive index lower than the refractive index of the outermost layer of the second inner portion, and a fourth layer having a refractive index higher than the refractive index of the third layer and includes the optical combiner further includes a second resin having a refractive index lower than the refractive index of the outermost layer of the second inner portion of the first bridge fiber and equal to or higher than the refractive index of the third layer, the second resin covering the second inner portion toward the downstream side from the downstream end of the second coating portion The optical combiner according to claim 1. **Claim 6** A plurality of laser light sources that generate laser light, the optical combiner according to any one of claims 1 to 5 and includes the first core of the plurality of input optical fibers of the optical combiner is optically coupled to the plurality of laser light sources A laser device. **Claim 7** A plurality of excitation light sources that generate excitation light, the optical combiner according to any one of claims 1 to 5, and an amplification optical fiber that amplifies laser light using the excitation light from the plurality of excitation light sources coupled by the optical combiner and includes the first core of the plurality of input optical fibers of the optical combiner is optically coupled to the plurality of excitation light sources A laser device.

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