JP2010262993A - Fiber laser, and optical combiner and optical fiber used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress breakage of an excitation light source due to return light of a fiber laser. <P>SOLUTION: The fiber laser is constituted such that excitation lights from a plurality of excitation light sources are incident on an incident end surface 34 of an optical fiber 30 through a projection end surface 22a of an optical combiner 20, and laser light is propagated in a core 31a of the optical fiber 30 toward the incident end surface 34. At least on one of the projection end surface 22a of the optical combiner 20 and the incidence end surface 34 of the optical fiber 30, a concave portion 35 is formed so as to correspond to the core 31a of the optical fiber 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fiber laser, and an optical combiner and optical fiber used therefor.

  There is known a fiber laser configured such that excitation light from a plurality of excitation light sources is incident on an incident end face of an optical fiber via an emission end face of an optical combiner (for example, Patent Document 1).

JP 2007-163650 A

  By the way, in the fiber laser configured as described above, there is a problem that at least a part of the laser light that oscillates the core of the optical fiber is emitted from the incident end face as so-called return light, thereby destroying the excitation light source.

  The subject of this invention is suppressing generation | occurrence | production of the failure | damage of the excitation light source by the return light in a fiber laser.

  In the fiber laser of the present invention, pumping light from a plurality of pumping light sources is incident on the incident end face of the optical fiber via the exit end face of the optical combiner, and the laser light propagates through the core of the optical fiber toward the incident end face. A recess is formed on at least one of the output end face of the optical combiner and the incident end face of the optical fiber so as to correspond to the core of the optical fiber.

  The optical combiner of the present invention is for a fiber laser that makes excitation light from a plurality of excitation light sources incident on an incident end face of an optical fiber configured to propagate the laser beam toward the incident end face. A recess is formed on the exit end face of the optical combiner so as to correspond to the core of the optical fiber.

  The optical fiber of the present invention is for a fiber laser in which pumping light from a plurality of pumping light sources enters through the exit end face of the optical combiner and laser light propagates toward the entrance end face of the core. A recess is formed on the end surface so as to correspond to the core.

  According to the present invention, since at least one of the exit end face of the optical combiner and the entrance end face of the optical fiber is formed with a recess corresponding to the core of the optical fiber, the core of the optical fiber faces the entrance end face. Even if laser light, that is, so-called return light propagates, it is reflected by the concave surface and the like, so that incidence on the excitation light source is limited, and as a result, the occurrence of damage to the excitation light source due to return light can be suppressed. it can.

1 is a diagram illustrating a configuration of a fiber laser according to Embodiment 1. FIG. It is a figure which shows the structure by which the clearance gap was provided between the output end surface of the optical combiner, and the incident end surface of the double clad fiber, and the lens was arrange | positioned in the clearance gap. (A)-(c) is principal part sectional drawing which shows the structure which the optical combiner and double clad fiber in the fiber laser which concerns on Embodiment 1 were melt-connected or butt-connected. (A)-(c) is principal part sectional drawing which shows the structure which the optical combiner and double clad fiber in the fiber laser which concerns on Embodiment 2 were melt-connected or butt-connected. It is principal part sectional drawing which shows the structure which the optical combiner and double clad fiber in the fiber laser which concerns on Embodiment 3 were fusion-connected or butt-connected. It is a figure which shows the structure of the fiber laser of a modification.

  Hereinafter, embodiments will be described in detail based on the drawings.

(Embodiment 1)
FIG. 1 shows a fiber laser L according to the first embodiment.

  The fiber laser L according to the first embodiment includes a plurality of excitation light sources 10, an optical combiner 20, and a double clad fiber 30.

  Examples of the excitation light source 10 include an LD (laser diode) that emits light having a wavelength of 1.5 μm, 0.98 μm, 0.90 μm, 0.80 μm, 0.67 μm, and the like.

  The optical combiner 20 is composed of a plurality of optical fiber cores 21 for excitation. In each of the plurality of optical fiber cores 21 for excitation, the coating layer is peeled from the tip of the core wire by a predetermined length at one end portion to expose the optical fiber for excitation, and the optical combiner 20 includes a plurality of optical fibers for excitation. For example, one end portion of the optical fiber is bundled in a close-packed manner and is configured as an exit end portion 22 that is fused and integrated.

  Each of the plurality of excitation optical fiber cores 21 has an excitation optical fiber and a coating layer provided so as to cover the excitation optical fiber. The excitation optical fiber core wire 21 has, for example, a core wire length of 1 to 10 m (including the emission end 22) and a core wire diameter of 240 to 260 μm. The number of the excitation optical fiber core wires 21 is 3 to 10, for example.

  Each pumping optical fiber is made of, for example, quartz glass, and has a high refractive index core at the center of the fiber and a low refractive index clad provided so as to cover the periphery thereof. Each pumping optical fiber may have a core made of quartz doped with germanium (Ge) or the like to have a high refractive index and a cladding made of pure quartz, or a core made of pure quartz. The clad may be formed of quartz which is formed and doped with fluorine or the like to reduce the refractive index. Each excitation optical fiber is generally a multimode fiber. For example, the fiber length of the portion exposed by peeling off the coating layer is 0.5 to 5 mm, the fiber diameter is 123 to 127 μm, and the core diameter is 80-115 μm. The plurality of pumping optical fibers may be configured with a uniform fiber diameter, or may be configured differently. The plurality of pumping optical fibers may be configured to have a uniform core diameter, or may be configured to be different from each other.

  The coating layer is made of, for example, an ultraviolet curable resin, a silicon resin, a nylon resin, or the like, and may be composed of a single layer or may be composed of a plurality of layers. The layer thickness of the coating layer is, for example, 55 to 65 μm.

  The exit end 22 is formed by integrating a plurality of pumping optical fibers, in which the cores of the plurality of pumping optical fibers extend in the length direction. The core is exposed.

  The double clad fiber 30 has a fiber main body 31 and a coating layer 32 provided so as to cover it. The double clad fiber 30 has, for example, a fiber length of 3 to 40 m and a fiber diameter of 300 to 2000 μm.

  The fiber body 31 includes a core 31a at the center of the fiber, a first cladding 31b provided so as to cover the core 31a, and a second cladding 31c provided so as to further cover the core.

  The core 31a is made of, for example, quartz doped with a rare earth element as an optical amplification component. Examples of rare earth elements include ytterbium (Yb), erbium (Er), neodymium (Nd), and the like. The rare earth element may be doped with a single species or may be doped with a plurality of species. The doping amount of the rare earth element is, for example, 1000 to 20000 ppm. In addition, Pr (praseodymium) or the like may be doped into the core 31a. The core diameter is, for example, 20 to 60 μm. The relative refractive index of the core 31a with respect to the first cladding 31b is, for example, 0.03 to 0.3%. The core 31a is provided with an optical oscillation means 33 such as a fiber grating.

  The first cladding 31b has a lower refractive index than the core 31a, and is made of, for example, pure quartz. The outer diameter of the first cladding 31b is, for example, 125 to 600 μm.

  The second clad 31c has a lower refractive index than that of the first clad 31b, and may be formed of, for example, a low-refractive resin or the like, and pores extending along the core 31a are formed in the pure quartz in the core 31a. It may be a structure arranged so as to surround. The outer diameter of the second cladding 31c is, for example, 150 to 650 μm. The relative refractive index difference between the second cladding 31c and the first cladding 31b is, for example, 3 to 10%.

  The covering layer 32 is made of, for example, a low refractive silicone resin, a fluororesin, or the like. The coating layer 32 may be configured by a single layer or may be configured by stacking a plurality of layers. The thickness of the coating layer 32 is, for example, 60 to 600 μm.

  And in the fiber laser L which concerns on Embodiment 1, the excitation light source 10 is connected to each core wire end of the some optical fiber core wire 21 extended from the optical combiner 20, The optical combiner 20 and the double clad fiber 30 are as follows. The excitation light from the excitation light source 10 is arranged so as to enter the first cladding 31b of the latter incident end face 34 from the former emission end face 22a. In the optical combiner 20 and the double clad fiber 30, the former exit end face 22a and the latter entrance end face 34 may be fusion-connected, and the former exit end face 22a and the latter entrance end face 34 are mechanically connected. Further, as shown in FIG. 2, a gap is provided between the former emission end face 22a and the latter incident end face 34, and a lens 40 is disposed in the gap. Also good.

  The fiber laser L according to the first embodiment having the above configuration emits pumping light from each of the plurality of pumping light sources 10, and the pumping light is collected by the optical combiner 20 and surrounded by the second cladding 31 c of the double-clad fiber 30. It is incident on the core 31a and the first clad 31b which are the portions. At this time, a part of the excitation light incident on the core 31a oscillates in the core 31a by the optical oscillation means 33 such as a fiber grating, and changes the rare earth element of the light amplification component from the ground state to the excited state. Then, by the stimulated emission when the rare earth element returns from the excited state to the ground state, the light is apparently amplified to be laser light, and a part that passes through the light oscillation means 33 is emitted from the emission end face 22a of the double clad fiber 30. To do.

  3A to 3C show a structure in which the optical combiner 20 and the double clad fiber 30 in the fiber laser L according to the first embodiment are fusion-connected or butt-connected.

  In the fiber laser L according to the first embodiment, a concave portion 35 is formed on the incident end face 34 of the double clad fiber 30 so as to correspond to the core 31a. As described above, a part of the laser light oscillating means 33 that passes through the light emitting means 33 is emitted from the exit end face 22a of the double clad fiber 30, but the other part of the laser light oscillating means 33 that passes through the core of the double clad fiber 30. 31a propagates toward the incident end face 34. When such laser light is incident on the excitation light source 10 via the optical combiner 20, the excitation light source 10 may be destroyed. However, according to the fiber laser L according to the first embodiment, the incident end face of the double clad fiber 30. 34, since the recess 35 is formed so as to correspond to the core 31a of the double clad fiber 30, laser light, that is, so-called return light propagates through the core 31a of the double clad fiber 30 toward the incident end face 34. However, it is reflected on the surface of the concave portion 35 and the incidence on the excitation light source 10 is limited, and as a result, the occurrence of damage to the excitation light source 10 due to the return light can be suppressed.

  The size of the recess 35 may be provided so as to correspond to a part of the core 31a, or may be provided so as to correspond to the entire core 31a. However, the latter is preferable from the viewpoint of more effectively restricting the incident return light to the excitation light source 10. The depth of the recess 35 is, for example, 5 to 60 μm.

  The shape of the recess 35 may be, for example, a wedge shape as shown in FIG. 3A, may be a conical shape as shown in FIG. A substantially semi-elliptical sphere as shown in FIG. However, since the light intensity at the center of the core 31a is the strongest, the surface corresponding to the core 31a of the double clad fiber 30 of the recess 35 is inclined with respect to the axial direction of the core 31a from the viewpoint of effectively reflecting it. It is preferably a surface, and specifically, a wedge shape as shown in FIG. In this case, the inclination angle θ of the surface inclined with respect to the axial direction of the core 31a is preferably 30 to 60 °. For example, if the refractive index of the core 31a is 1.46, since θ = 43.2 ° where sin θ = 1 / 1.46, if the inclination angle is larger than this, almost all the return light is doubled. The light is reflected on the clad fiber 30 side.

  The concave portion 35 can be formed by mirror-polishing the incident end face 34 of the double clad fiber 30 and then performing mechanical processing using a micro tool or the like or selective etching processing using a hydrofluoric acid solution.

The surface of the recess 35 is preferably covered with a reflective film 36. Thereby, return light can be reflected more effectively. Examples of the reflective film 36 include a dielectric film such as a titanium oxide (TiO) film, a zinc sulfide (ZnS) film, and a silicon oxide (SiO ₂ ) film, a metal film, and the like. The transmittance of the reflective film 36 is preferably 0 to 10%, and more preferably 0 to 1%. The film thickness of the reflective film 36 is, for example, 0.5 to 10 μm. The reflective film 36 can be formed on the surface of the recess 35 by, for example, removing unnecessary portions by polishing after film formation by sputtering or the like.

(Embodiment 2)
4A to 4C show a structure in which the optical combiner 20 and the double clad fiber 30 in the fiber laser L according to the second embodiment are fusion-connected or butt-connected. In addition, the part of the same name as Embodiment 1 is shown with the same code | symbol as Embodiment 1. FIG.

  In the fiber laser L according to the second embodiment, a recess 23 is formed on the emission end face 22a of the optical combiner 20 so as to correspond to the core 31a of the double clad fiber 30. As described in the first embodiment, a part of the laser light transmitting means 33 that passes through the light emitting means 33 is emitted from the emitting end face 22a of the double clad fiber 30, while the other part of the laser light transmitting means 33 that passes through the double light is used as the double light. It propagates through the core 31 a of the clad fiber 30 toward the incident end face 34. When such laser light is incident on the excitation light source 10 via the optical combiner 20, the excitation light source 10 may be destroyed. However, according to the fiber laser L according to the second embodiment, the emission end face 22 a of the optical combiner 20. In addition, since the recess 23 is formed so as to correspond to the core 31a of the double clad fiber 30, even if so-called return light propagates through the core 31a of the double clad fiber 30 and is emitted from the incident end face 34, it is not reflected in the light. Incidence to the excitation light source 10 is limited by reflection on the surface of the concave portion 23 of the combiner 20, and as a result, occurrence of damage to the excitation light source 10 due to return light can be suppressed.

  The size of the recess 23 may be provided so as to correspond to a part of the core 31a, or may be provided so as to correspond to the entire core 31a. However, the latter is preferable from the viewpoint of more effectively restricting the incident return light to the excitation light source 10. The depth of the recess 23 is, for example, 5 to 60 μm.

  The shape of the recess 23 may be, for example, a wedge shape as shown in FIG. 4A, may be a conical shape as shown in FIG. A substantially semi-elliptical sphere as shown in FIG. However, since the light intensity at the center of the core 31a is the strongest, the surface corresponding to the core 31a of the double clad fiber 30 of the recess 23 is inclined with respect to the axial direction of the core 31a from the viewpoint of effectively reflecting it. It is preferably a surface, and specifically, a wedge shape as shown in FIG. In this case, since the return light is incident on the surface of the recess 23 from the space, it does not totally reflect, but an inclination angle equal to or greater than the numerical aperture (NA) in the emission end face 22a of the optical combiner 20 is preferable, and the axis of the core 31a The inclination angle θ of the surface inclined with respect to the direction is preferably 10 to 30 °. For example, assuming that the numerical aperture (NA) at the exit end face 22a of the optical combiner 20 is 0.5 and the refractive index of the exit end face 22a portion of the optical combiner 20 is 1.456, 0.5 = 1.456 × sin θ. Since some θ = 20.1 °, if the inclination angle is larger than this, almost all the return light is emitted to the outside of the optical combiner 20.

  The concave portion 23 can be formed by mirror-polishing the incident end face 34 of the double clad fiber 30 and then performing mechanical processing using a micro tool or the like or selective etching processing using a hydrofluoric acid solution.

The surface of the recess 23 is preferably covered with a reflective film 24. As a result, it is possible to more effectively restrict the return light from entering the optical combiner 20. Examples of the reflective film 24 include a dielectric film such as a titanium oxide (TiO) film, a zinc sulfide (ZnS) film, and a silicon oxide (SiO ₂ ) film, a metal film, and the like. The transmittance of the reflective film 24 is preferably 0 to 10%, and more preferably 0 to 1%. The film thickness of the reflective film 24 is, for example, 0.2 to 10 μm. The reflective film 24 can be formed on the surface of the recess 23 by removing unnecessary portions by polishing after film formation by sputtering or the like, for example.

  Other configurations and operational effects are the same as those of the first embodiment.

(Embodiment 3)
FIG. 5 shows a structure in which the optical combiner 20 and the double clad fiber 30 in the fiber laser L according to the third embodiment are fusion-connected or butt-connected. In addition, the part of the same name as Embodiment 1 is shown with the same code | symbol as Embodiment 1. FIG.

  In the fiber laser L according to the third embodiment, since the concave portions 23 and 35 are provided in both the double clad fiber 30 and the optical combiner 20, the incident light is prevented from being incident on the excitation light source 10 by both the concave portions 23 and 35. An effect can be obtained.

  Other configurations and operational effects are the same as those of the first embodiment.

(Other embodiments)
In the first to third embodiments, the pump light is incident on the double clad fiber 30 from the optical combiner 20, but the present invention is not particularly limited thereto, and as shown in FIG. A configuration in which another optical fiber 50 such as a double clad fiber is interposed may be employed, and a concave portion may be formed on the incident end face 51 of the other optical fiber 50.

  The present invention is useful for fiber lasers and optical combiners and optical fibers used therefor.

L fiber laser 10 excitation light source 20 optical combiner 21 excitation optical fiber core wire 22 emission end 22a emission end 23, 35 recess 24, 36 reflective film 30 double clad fiber 31 fiber body 31a core 31b first clad 31c second clad 32 Covering layer 33 Optical oscillation means 34, 51 Incident end face 40 Lens 50 Other optical fiber

Claims (6)

A fiber laser configured such that pumping light from a plurality of pumping light sources is incident on an incident end surface of an optical fiber via an output end surface of an optical combiner, and laser light propagates through the core of the optical fiber toward the incident end surface. Because
A fiber laser in which a concave portion is formed on at least one of the emission end face of the optical combiner and the incident end face of the optical fiber so as to correspond to the core of the optical fiber. The fiber laser of claim 1, wherein
A fiber laser in which the surface of the recess is coated with a dielectric reflecting film. The fiber laser according to claim 1 or 2,
A fiber laser in which a surface of the recess corresponding to the core of the optical fiber is inclined with respect to the axial direction of the core. The fiber laser according to any one of claims 1 to 3,
The optical fiber includes a core, a first clad provided so as to cover the core, and a second clad provided so as to cover the first clad, and optical oscillation means is provided in the core. A fiber laser which is a double clad fiber provided with An optical combiner for a fiber laser that makes excitation light from a plurality of excitation light sources incident on an incident end face of an optical fiber configured to propagate a laser beam toward the incident end face of a core,
An optical combiner in which a concave portion is formed on the emission end face of the optical combiner so as to correspond to the core of the optical fiber. An optical fiber for a fiber laser in which pumping light from a plurality of pumping light sources is incident through the emission end face of the optical combiner and laser light propagates toward the incident end face of the core,
An optical fiber in which a concave portion is formed on the incident end surface so as to correspond to the core.

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