JP6691827B2 - Combiner and laser system - Google Patents

Description

  The present invention relates to a combiner including an entrance fiber, an exit fiber, and a reduced diameter portion. It also relates to a laser system provided with such a combiner and a method for manufacturing such a combiner.

  There is known a combiner that combines laser light emitted from each of a plurality of laser devices into one emitted light. For example, in Patent Document 1, a plurality of optical fibers forming an incident fiber (“optical fiber for input” in Patent Document 1), a reduced diameter portion having a tapered portion (“bridge fiber” in Patent Document 1), a plurality of optical fibers A GI fiber (“divergence angle reducing member” in Patent Document 1) interposed between the (seven) optical fibers and the reduced diameter portion, and an output fiber (“optical fiber for output” in Patent Document 1). A combiner provided (“optical fiber combiner” in Patent Document 1) is described (FIG. 1 of Patent Document 1).

  Such a combiner can be suitably used for a laser processing machine (laser system), for example. A laser processing machine combines laser light emitted from each of a plurality of laser devices into one emitted light by using such a combiner, so that a high output power which cannot be obtained by one laser device is obtained. You are getting the light. The laser processing machine is used for processing applications that require a high output by using the emitted light thus obtained, for example, cutting and welding.

JP, 2013-190714, A (published on September 26, 2013)

  In the conventional combiner, the plurality of lights propagating through each of the plurality of optical fibers are incident on the incident end face of the reduced diameter portion via each GI fiber. The plurality of lights incident on the incident end face are combined into one light in the process of propagating through the reduced diameter portion. One light collected by the reduced diameter portion, that is, output light, is emitted from the emission end face of the reduced diameter portion to the emission fiber. The combiner can obtain high-power output light by emitting the plurality of lights thus entered as one light.

  However, the combiner configured as described above has a problem that the distribution width of the numerical aperture of the emitted light is wide or the beam quality of the emitted light is non-uniform. The reason will be described below.

  The diameter-reduced portion increases the numerical aperture of light incident on the incident end face in the process of propagating the light to the emission end face. The amount of increase in the numerical aperture due to this propagation depends on the degree of deviation between the light incident region and the emission end face of the incident end face. The increase amount of the numerical aperture due to the propagation becomes larger as the above-mentioned deviation is larger.

  In the conventional combiner, one of the GI fibers is arranged in a central region including the center of the incident end face of the diameter-reduced portion. Therefore, the degree of deviation between the light incident region and the emission end face is zero. On the other hand, the remaining six GI fibers of each GI fiber are arranged in the outer region surrounding the central region. Therefore, the deviation degree in the light incident on the outer region is larger than the deviation degree in the light incident on the central region.

  From the above, the increase amount of the numerical aperture in the light incident on the outer region is larger than the increase amount of the numerical aperture in the light incident on the central region. Therefore, the light emitted from the combiner includes light from the central region having a small numerical aperture and light from the outer region having a large numerical aperture, and the distribution width of the numerical aperture becomes wide.

  The GI fiber can reduce the divergence angle of the light incident on the incident end face of the reduced diameter portion. Therefore, the numerical aperture of the emitted light can be suppressed by interposing the GI fiber between the plurality of incident fibers and the incident end surface of the reduced diameter portion. However, even when the GI fiber is interposed, the problem that the numerical aperture distribution in the emitted light is wide cannot be solved.

  The present invention has been made in view of the above problems, and an object thereof is to make the beam quality of outgoing light uniform in a combiner including a plurality of incoming fibers, outgoing fibers, and a reduced diameter portion. is there.

  In order to solve the above problems, a combiner according to an aspect of the present invention includes (1) a plurality of incident fibers, and (2) a GI fiber joined to each of the emission end faces of the plurality of incident fibers. And (3) an exit fiber, (4) an entrance end surface, and an exit end surface having an area smaller than that of the entrance end surface, each of the GI fibers is coupled to the entrance end surface, and the exit end surface is connected to the exit end surface. A combiner comprising a diameter-reduced portion to which the emission fiber is coupled, which is obtained when the incidence end face of the diameter-reduced portion is viewed in a plan view, in a region to which the GI fiber is coupled. The numerical aperture as a lens of each GI fiber is smaller for a GI fiber coupled in a region where the distance Ddif is larger, with the distance in plan view between the center and the center of the emission end face being the distance Ddif.

  The numerical aperture of light incident on the reduced diameter portion increases in the process of propagating through the reduced diameter portion. The amount of increase is smaller for the light incident on the region where the distance Ddif is smaller, and is larger for the light incident on the region where the distance Ddif is larger.

  According to the above configuration, the GI fiber having a large numerical aperture as a lens is connected to the region where the distance Ddif is small, that is, the region where the increase amount of the numerical aperture is small, and the region where the distance Ddif is large, that is, the above-mentioned. The GI fiber having a small numerical aperture as a lens is connected to the region where the increase in the numerical aperture is large. Therefore, compared with the case where the numerical aperture of each GI fiber as a lens is constant, the numerical aperture of the light emitted from the reduced diameter portion can be made uniform. That is, the beam quality of the emitted light can be made uniform.

  Further, in the combiner according to the aspect of the present invention, each of the GI fibers has the same refractive index distribution within a manufacturing tolerance range, and the length of each of the GI fibers is coupled to a region having a large distance Ddif. It is preferable that the GI fiber has a length closer to the optimum length which is a length for emitting the collimated light.

  The GI fiber has a characteristic that the numerical aperture of emitted light changes periodically according to its length. Therefore, the numerical aperture of the GI fiber has a minimum value when the length of the GI fiber is the optimum length, and has a maximum value at a length intermediate the optimum length. The GI fiber emits collimated light when the length of the GI fiber is optimal.

  According to the above configuration, it is possible to prepare GI fibers having different numerical apertures by using GI fibers having the same refractive index distribution within the manufacturing tolerance range. Therefore, as compared with the case of using GI fibers having different refractive index distributions, the present combiner can easily make the beam quality of outgoing light uniform.

  Further, according to the above configuration, it is possible to suppress the numerical aperture of the emitted light having the largest numerical aperture among the emitted lights emitted by the combiner. Therefore, the present combiner can improve the beam quality of the emitted light while making the beam quality of the emitted light uniform.

  Further, in the combiner according to the aspect of the present invention, it is preferable that both the shape of the incident end surface and the shape of the output end surface of the reduced diameter portion are circular.

  According to the above configuration, the diameter-reduced portion can be manufactured by extending the existing cylindrical optical member, for example, the optical rod. Therefore, the reduced diameter portion can be manufactured from an easily available optical member, so that the manufacturing cost of the combiner can be suppressed.

  In the combiner according to an aspect of the present invention, a central axis connecting the center of the incident end face and the center of the emission end face may be inclined with respect to a normal line of the incident end face.

  When a cylindrical optical member is stretched to produce a reduced diameter portion, distortion may occur in the shape of the stretched optical member. In that case, the central axis connecting the center of the incident end face and the center of the exit end face of the manufactured reduced diameter portion has an inclination with respect to the normal line of the incident end face. Since this combiner determines the numerical aperture of the GI fiber according to the distance Ddif, even if the central axis of the diameter-reduced portion is inclined with respect to the incident end face, the beam quality of the emitted light is made uniform. be able to.

  Further, in the combiner according to the aspect of the present invention, it is preferable that the length of the GI fiber having the maximum distance Ddif among the GI fibers is the optimum length of the GI fiber.

  According to the above configuration, the beam quality of the light emitted from the emission end face of the diameter-reduced portion can be made uniform by using the range in which the numerical aperture of the GI fiber can be changed to the maximum. Therefore, the present combiner can further improve the beam quality of the emitted light.

  In order to solve the above-mentioned problems, a laser system according to one aspect of the present invention includes (1) a plurality of incident fibers, and (2) a GI that is joined to each emission end face of each of the plurality of incident fibers. A fiber, (3) an emitting fiber, (4) an incident end face, and an emitting end face having an area smaller than that of the incident end face, wherein each of the plurality of incident fibers is coupled to the incident end face, and A combiner comprising a diameter-reduced portion in which the emission fiber is coupled to an emission end surface, which is obtained when the incidence end surface of the diameter-reduced portion is viewed in a plan view, in which the GI fiber of the incidence end surface is coupled. With the distance Ddif in plan view between the center of the existing region and the center of the emission end face, the numerical aperture of each GI fiber as a lens is smaller as the GI fiber coupled to the region with a larger distance Ddif has a smaller numerical aperture. And a plurality of laser devices each having an emission fiber, each of the emission fibers being respectively connected to any of the incidence fibers of the combiner. ing.

  INDUSTRIAL APPLICABILITY The present invention can make the beam quality of outgoing light uniform in a combiner including a plurality of incoming fibers, outgoing fibers, and a reduced diameter portion.

(A) And (b) is a perspective view of the combiner concerning a 1st embodiment of the present invention. (C) is a plan view of the incident end face of the reduced diameter portion included in the combiner shown in (a) and (b). (A) And (b) is sectional drawing of the diameter reduction part with which the combiner shown in FIG. 1 is equipped. 3 is a graph showing the length dependence of the numerical aperture as a lens in the GI fiber that constitutes the GI fiber bundle included in the combiner shown in FIG. 1. (A) is a perspective view of the combiner concerning a 2nd embodiment of the present invention. (B) is a plan view of an incident end face of a reduced diameter portion included in the combiner shown in (a). (A) And (b) is sectional drawing of the diameter reduction part with which the combiner shown in FIG. 4 is equipped. It is a block diagram which shows the structure of the fiber laser system which concerns on the 3rd Embodiment of this invention.

[First Embodiment]
The combiner 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 3.

  1A and 1B are perspective views of the combiner 10. It should be noted that FIG. 1B shows the combiner 10 without the incident fiber bundle 12 included in the combiner 10. FIG. 1C is a plan view obtained when the incident end surface 11a of the diameter-reduced portion 11 included in the combiner 10 is viewed in a plan view. This plan view is obtained by observing the reduced diameter portion 11 from the z-axis negative direction side in the coordinate axes shown in FIG. FIG. 1C shows regions P1 to P7 to which the GI fibers 141 to 147 forming the GI fiber bundle 14 are coupled on the incident end face 11a. It should be noted that FIG. 1C shows the incident end face 11 a in a state where the incident fiber bundle 12 and the GI fiber bundle 14 included in the combiner 10 are omitted.

  2A and 2B are cross-sectional views of the reduced diameter portion 11, and are cross-sectional views along a plane (yz plane) taken along the line AA ′ shown in FIG. ..

  FIG. 3 is a graph showing the LGI dependency of the numerical aperture NA as a lens in the GI fibers 141 to 147.

(Structure of combiner 10)
As shown in FIG. 1A, the combiner 10 includes a reduced diameter portion 11, an incident fiber bundle 12, an output fiber 13, and a GI fiber bundle 14.

  The reduced diameter portion 11 is an optical member made of optical glass, and is made of, for example, quartz glass. The diameter-reduced portion 11 is a truncated cone optical member in which the entrance end surface 11a constitutes one bottom surface and the exit end surface 11b constitutes the other bottom surface. The area of the emission end face 11b is smaller than the area of the incidence end face 11a.

  In the present embodiment, the shape of the incident end surface 11a and the shape of the exit end surface 11b are both circular. According to this configuration, the diameter-reduced portion 11 can be manufactured by stretching a commercially available cylindrical optical member, for example, an optical rod. Therefore, the reduced diameter portion can be manufactured using an easily available optical member, so that the manufacturing cost of the combiner can be suppressed.

  When the cylindrical optical member is stretched to manufacture the reduced diameter portion 11, the center axis of the stretched optical member may be eccentric. When the diameter-reduced portion 11 is manufactured using such an eccentric optical member, the diameter-reduced portion 11 has a decentered truncated cone shape (a truncated cone whose central axis is inclined with respect to the incident end face 11a). As will be described later as a modified example of the combiner 10, the shape of the reduced diameter portion 11 may be a truncated cone having such an eccentricity.

  The incident fiber bundle 12 is composed of a plurality of (seven in the present embodiment) incident fibers, which are fumode fibers (FMF) 121 to 127. The FMF 121 includes a core 121a and a clad 121b. Similarly, each of the FMFs 122 to 127 includes cores 122a to 127a and clads 122b to 127b. Each of the FMF 121 to FMF 127 is made of, for example, quartz glass.

  The emitting fiber 13 is composed of one multimode fiber. The emitting fiber 13 includes a core 13a and a clad 13b. The diameter of the core 13a is configured to be equal to the diameter Dout (see FIG. 2) of the emission end surface 11b of the reduced diameter portion 11. In the present embodiment, the end face of the core 13a of the emitting fiber 13 is fused to the emitting end face 11b. The emitting fiber 13 is made of, for example, quartz glass. The emitting fiber 13 is coupled to the emitting end surface 11b of the reduced diameter portion 11.

  A GI (Graded Index) fiber bundle 14 is interposed between the incident fiber bundle 12 and the incident end surface 11a of the reduced diameter portion 11. The GI fiber bundle 14 is composed of seven GI fibers 141 to 147, which is the same number as the FMFs 121 to 127.

  Each of the GI fibers 141 to 147 has a 1: 1 correspondence with each of the FMFs 121 to 127. For example, the entrance end surface of the GI fiber 141 is joined to the exit end surface of the FMF 121. The emission end face of the GI fiber 141 is coupled to the incident end face 11a of the reduced diameter portion 11. Similarly, each of the FMFs 122 to 127 is coupled to the incident end face 11a via each of the GI fibers 142 to 147.

  The diameter Din of the incident end face 11a is set to a size that includes all the emission end faces of the GI fibers 141 to 147 (see (c) of FIG. 1).

  Each of the GI fibers 141 to 147 is, for example, an optical member made of quartz, and has the highest refractive index at the central axis thereof, and the refractive index becomes lower as the distance from the central axis increases.

  The GI fibers 141 to 147 configured as described above can suppress the divergence angle of the light incident from the FMFs 121 to 127 in the process of propagating the light. As a result, the GI fibers 141 to 147 can emit light having a smaller divergence angle than the light incident from the FMFs 121 to 127. The degree of suppression of the divergence angle periodically changes according to the length of the GI fibers 141 to 147. The length of each of the GI fibers 141 to 147 will be described later.

  In this embodiment, the incident fiber bundle 12 and the GI fiber bundle 14 are joined by fusion. Further, the GI fiber bundle 14 and the incident end face 11a of the reduced diameter portion 11 are joined by fusion. Taking the FMF 121 and the GI fiber 141 as an example, (1) the emission end face of the FMF 121 is fused to the incident end face of the GI fiber 141, and (2) the emission end face of the GI fiber 141 is fused to the incident end face 11a. Has been done. The same applies to the FMFs 122 to 127 and the GI fibers 142 to 147.

  The GI fiber bundle 14 and the incident end face 11a may be optically coupled to each other. Therefore, for example, the connecting means for connecting the emission end faces of the GI fibers 141 to 147 forming the GI fiber bundle 14 and the incident end face 11a is not limited to fusion bonding. For example, the emission end faces of the GI fibers 141 to 147 and the incident end face 11a may be adhered to each other by using an adhesive made of a resin having a good transmittance in the wavelength region of light used in the combiner 10. The same applies to the coupling between the emitting fiber 13 and the emitting end face 11b of the reduced diameter portion 11.

(Area where each GI fiber is coupled)
As shown in (a) and (b) of FIG. 1, each of the FMFs 121 to 127 and the GI fibers 141 to 147 has the FMF 122 to 127 and the GI fibers 142 to 147 around the FMF 121 and the GI fiber 141, respectively. It is arranged so as to surround it. Regions on the incident end face 11a of the diameter-reduced portion 11 to which the GI fibers 141 to 147 are joined are referred to as regions P1 to P7, respectively.

  As shown in FIG. 1C, the region P1 includes the center C1 of the incident end face 11a. In the present embodiment, when the entrance end face 11a is viewed in a plan view, the center CP1 of the region P1, the center C1 of the entrance end face 11a, and the center C2 of the exit end face 11b coincide with each other. The center CP1 corresponds to the center of the GI fiber 141.

  Six areas (areas P2 to P7) surrounding the area P1 are arranged around the area P1. The centers of the regions P2 to P7 are referred to as centers CP2 to CP7, respectively. The area P2 is an area to which the GI fiber 142 is connected. The center CP2 corresponds to the center of the GI fiber 142 bonded to the incident end face 11a. Similarly, each of the regions P3 to P7 is a region to which the GI fibers 143 to 147 are connected, and each of the centers CP3 to CP7 is the center of the GI fibers 143 to 147 bonded to the incident end face 11a. Corresponding to. Each of the regions P2 to P7 is arranged around the region P1 so that the centers CP2 to CP7 form each vertex of a regular hexagon. In other words, each of the GI fibers 141 to 147 is arranged so as to have a close-packed structure within the incident end face 11a.

  A line A-A ′ shown in FIG. 1C is a straight line passing through the center CP1, the center CP2, and the center CP5. In each of the regions P1 to P7, the planar view distance between the center C2 and the centers CP1 to CP7 obtained when the incident end face 11a is viewed in plan is defined as a distance Ddif. In FIG. 1C, the distance Ddif in the region P2 is illustrated as an example of the distance Ddif.

  The distance Ddif represents the shift between the region where the incident light is coupled to the reduced diameter portion 11 and the region where the emitted light is coupled to the reduced diameter portion 11. The larger the distance Ddif, the larger the deviation between the region where the incident light is coupled and the region where the outgoing light is coupled. When distinguishing the distance Ddif in the areas P1 to P6, a code indicating the area, such as the distance Ddif (P1), is added to the end of the distance Ddif.

  As described above, the center C1, the center CP1, and the center C2 coincide with each other when the incident end face 11a is viewed in a plan view. Therefore, the distance Ddif (P1) in the area P1 is Ddif (P1) = 0. On the other hand, the centers CP2 to CP7 of the regions P2 to P7 are located at the vertices of a regular hexagon centered on the center CP1. Therefore, the distances Ddif (P2) to Ddif (P7) in the regions P2 to P7 are all equal and approximately match the diameters of the regions P2 to P7. Therefore, the distances Ddif (P1) to Ddif (P7) in the combiner 10 are divided into the distance Ddif (P1) having a small value and the distances Ddif (P2) to Ddif (P7) having a large value.

  In the present embodiment, the diameter-reduced portion 11 has a diameter (a length intersecting the central axis of the truncated cone and along the y-axis direction in the coordinate system shown in FIG. 1) with the central axis of the truncated cone. It has been explained as one that keeps changing. However, the diameter-reduced portion 11 has a section in which the diameter does not change along the central axis in at least one of a front stage and a rear stage of the section (conical section) in which the diameter keeps changing along the central axis of the truncated cone ( It may further include a columnar section). Such a cylindrical section is connected to the truncated cone section via one end face. The other end face of the cylindrical section forms the incident end face 11a or the output end face 11b of the reduced diameter portion 11.

(Numerical aperture of each GI fiber as a lens)
In the combiner 10, the numerical aperture NA (hereinafter, also simply referred to as numerical aperture NA) as a lens of each of the GI fibers 141 to 147 is set to be smaller as the GI fiber coupled in the region where the distance Ddif is larger. ing. In other words, the numerical apertures NA of the GI fibers coupled to the regions having the same distance Ddif are set to be equal. That is, the numerical aperture NA of the GI fibers 142 to 147 coupled to each of the regions P2 to P7, which is the region where the distance Ddif is large, is smaller than the numerical aperture NA of the region P1, which is the region where the distance Ddif is small.

  As will be described later with reference to FIG. 2, the numerical aperture of the light incident on the reduced diameter portion 11 increases in the process of propagating through the reduced diameter portion 11. The amount of increase is smaller for the light incident on the region P1 where the distance Ddif is smaller, and is larger for the light incident on the regions P2 to P7 where the distance Ddif is larger. In other words, the increase amount of the numerical aperture is equal in each of the lights coupled to the regions P2 to P7 having the same distance Ddif. Hereinafter, for example, the light that is coupled to the region P2 and that is emitted from the emission end face 11b of the reduced diameter portion 11 is referred to as the light that originates from the region P2. The light that is coupled to the other regions P1 and P3 to P7 and that is emitted from the emission end face 11b is also referred to as light that is derived from the regions P1 and P3 to P7, respectively.

  According to the above configuration, (1) light having a large numerical aperture can be made incident on the region P1 that is a region where the amount of increase in the numerical aperture of light is small, and (2) Light having a small numerical aperture can be made to enter regions P2 to P7 that are regions where the amount of increase is large. Therefore, as compared with the case where the numerical aperture of the GI fiber coupled to the incident end face 11a is constant, the combiner 10 has the numerical aperture of light originating in the region P1 and the light originating in each of the regions P2 to P7. The difference from the numerical aperture can be reduced. Therefore, the combiner 10 can emit outgoing light having a high output and having a uniform numerical aperture (in other words, beam quality).

  In this embodiment, the incident fiber bundle 12 is composed of seven incident fibers (FMF121 to FMF127). However, the number of incident fibers forming the incident fiber bundle 12 is arbitrary. Since the number of GI fibers forming the GI fiber bundle 14 is the same as the number of incident fibers forming the incident fiber bundle 12, it is uniquely determined. For example, the number of incident fibers forming the incident fiber bundle 12 may be two, three, or nineteen.

(Length of each GI fiber)
The GI fiber has a characteristic of periodically changing the numerical aperture of the emitted light according to the length LGI. When (1) LGI = Ls × (2n-1 / 4), where the length of this one cycle is the cycle length Ls, the numerical aperture of the light emitted from the GI fiber becomes the minimum value, and (2) LGI = When Ls × 2n / 4, the numerical aperture of the light emitted from the GI fiber becomes the maximum value (the same value as the NA of the light incident on the GI fiber) (see FIG. 3). Hereinafter, the length LGI (= Ls × (2n-1 / 4)) at which the numerical aperture of the emitted light is the minimum value is called the optimum length of the GI fiber. Here, n is a positive integer. The GI fiber having the optimum length LGI emits collimated light.

  In the combiner 10, it is preferable that each of the GI fibers 141 to 147 has a length closer to an optimum length which is a length for emitting collimated light, as the GI fiber connected to a region having a larger distance Ddif. With this configuration, it is possible to suppress the numerical aperture of the emitted light having the largest numerical aperture among the emitted lights emitted from the combiner 10. Therefore, the combiner 10 can improve the beam quality of the emitted light while making the numerical aperture of the emitted light uniform. Moreover, it is more preferable that the length of each of the GI fibers 142 to 147 having the largest distance Ddif among the GI fibers 141 to 147 is the optimum length. With this configuration, the combiner 10 can further improve its beam quality. In this embodiment, the optimum length (Ls / 4) is adopted as the length LGI of each of the GI fibers 142 to 147 (see (b) of FIG. 1).

  Further, in the combiner 10, the length LGI of the GI fiber 141 is shorter than the length LGI of the GI fibers 142 to 147, which is the optimum length. This is to make the numerical aperture NA of the GI fiber 141 larger than the numerical aperture NA of the GI fibers 142 to 147.

  Since the numerical aperture NA of the GI fiber changes periodically as described above, the numerical aperture NA can be increased by making it longer than the optimum length. Therefore, as the length LGI of the GI fiber 141, a length longer than the optimum length may be adopted.

  Further, each of the GI fibers 141 to 147 preferably has the same refractive index distribution within the range of manufacturing tolerance. The GI fibers 141 to 147 having the same refractive index distribution within the manufacturing tolerance can be manufactured by cutting a commercially available GI fiber into a predetermined length. Therefore, it is possible to easily manufacture the GI fibers 141 to 147 having different numerical apertures NA, as compared with the case where the GI fibers having different refractive indexes are used.

(Virtual beam diameter)
Here, with reference to FIG. 2, the concept of the virtual beam diameter that greatly affects the numerical aperture of light will be described.

  2A shows a state in which the light L1 is incident on the region P1 on the incident end surface 11a of the reduced diameter portion 11. FIG. 2B shows a state in which the light L2 is incident on the region P5 on the incident end face 11a. In addition, here, each of the light L1 and the light L2 will be described as being collimated light.

  The cross-sectional shape of the reduced diameter portion 11 illustrated in FIG. 2 is an isosceles trapezoid having the entrance end surface 11a and the exit end surface 11b as the bases. The two hypotenuses of the isosceles trapezoid are referred to as hypotenuses 11c and 11d, respectively. The angle formed by the oblique side 11c and the normal line of the emission end surface 11b and the angle formed by the oblique side 11d and the normal line of the emission end surface 11b are both θ0.

  In the light L1, the central axis of the light L1 passes through the center C2 of the emission end face 11b. In this case, as shown in FIG. 2A, the virtual beam diameter DL1 of the light L1 is equal to the width of the light L1.

  The virtual beam diameter of the light L2 can be calculated as follows.

  (1) Of the extension lines of the light L2 extending inside the reduced diameter portion 11, the extension line on the side farther from the emission end face 11b (the y-axis negative direction side) is the extension line L2e.

  (2) The intersection of the extension line L2e and the hypotenuse 11d of the reduced diameter portion 11 is defined as an intersection I2a.

  (3) A straight line LI2 is drawn that passes through the intersection I2a and is parallel to the incident end face 11a and the outgoing end face 11b.

  (4) An intersection between the straight line I2b and the hypotenuse 11c of the reduced diameter portion 11 is defined as an intersection I2b.

  (5) The virtual beam diameter DL2 is the distance between the intersection I2a and the intersection I2b.

  As is clear from the above calculation method, the light having the minimum virtual beam diameter is the light L1 among the light coupled to the incident end face 11a. On the other hand, the farther the central axis of light is from the central axis of the diameter-reduced portion 11 (the axis connecting the centers C1 and C2), that is, the larger the distance Ddif is, the virtual beam diameter of the light becomes growing. The distances Ddif in each of the regions P2 to P7 are equal and larger than the distance Ddif in the region P1. Therefore, the virtual beam diameter of the light incident on each of the regions P2 to P7 is equal to the virtual beam diameter DL2.

(Reduction rate)
The diameter reduction ratio for the light incident on a certain region can be defined by using the diameter Dout of the emission end face 11b and the virtual beam diameter described above. The diameter reduction ratio is obtained by dividing the diameter Dout of the emission end face 11b by the virtual beam diameter. That is, the diameter reduction ratio of the light L1 incident on the region P1 is Dout / DL1, and the diameter reduction ratio of the light L2 incident on the region P5 is Dout / DL2 (regions P2 to P4 and regions P6 to The same applies to the light incident on P7).

  This diameter reduction ratio is an index indicating the degree to which the numerical aperture of light increases when propagating through the diameter reduced portion 11. When propagating through the diameter-reduced portion 11, light having a smaller diameter reduction ratio has a smaller degree of increase in the numerical aperture NA, and light having a larger diameter reduction ratio has a greater degree of increase in the numerical aperture NA.

  In the combiner 10, a GI fiber having a large numerical aperture NA is joined to a region where light having a small diameter reduction ratio is incident, and a GI fiber having a small numerical aperture NA is joined to a region where light having a large diameter reduction ratio is incident. .. Therefore, the combiner 10 can make the numerical aperture of the emitted light uniform.

(Example of numerical aperture NA of GI fiber)
FIG. 3 shows the dependence of the numerical aperture NA on the GI fibers 141 to 147 on the length LGI. In the GI fibers 141 to 147, the non-refractive index difference Δ is 0.055 and the effective lens diameter is 100 μm. The mode field diameter of the FMFs 121 to 127 fused to the GI fibers 141 to 147 is 20 μm.

  Referring to FIG. 3, it can be seen that the numerical aperture NA of the GI fibers 141 to 147 periodically changes according to the length LGI. The period length Ls of the GI fibers 141 to 147 is Ls = 10.4 mm.

  In the present embodiment, the length LGI of the GI fibers 142 to 147 is equal to the optimum length. That is, the length LGI of the GI fibers 142 to 147 is 2.6 mm. At this time, the numerical aperture NA of the GI fibers 142 to 147 is 0.010.

Table 1 shows the output obtained when light having a numerical aperture of 0.010 or more and 0.014 or less is incident on a region P1 where Ddif = 0 μm and a region P2 which is an example of a region where Ddif = 150 μm. The numerical aperture of the light is summarized. The numerical apertures of these emitted lights were obtained by simulating using a combiner 10 having a reduced diameter portion 11 configured as follows.
・ Diameter of incident end face 11a Din = 400 μm
・ Diameter Dout of the emitting end face 11b = 100 μm
・ Ddif (P1) = 0 μm
・ Ddif (P2) to Ddif (P7) = 150 μm
The length of the reduced diameter portion 11 (distance from the incident end face 11a to the outgoing end face 11b) = 40 mm
-The length of the output fiber 13 = 10 mm
Moreover, 20 μm was adopted as the mode field diameter of the FMFs 121 to 127 fused to the GI fibers 141 to 147.

  When the numerical aperture NA of the GI fiber 142 is 0.010, that is, when light having a numerical aperture of 0.010 is incident on the region P2, the numerical aperture of the light emitted from the combiner 10 is 0.111. It was

  On the other hand, when the numerical aperture NA of the GI fiber 141 was changed in the range of 0.010 or more and 0.014 or less, emitted light having a numerical aperture of 0.097 or more and 0.131 or less was obtained. In order to make the numerical aperture of the light emitted from the combiner 10 uniform, the numerical aperture NA of the GI fiber 141 is determined so as to minimize the difference from the numerical aperture (0.111) of the light emitted from the region P2. Just do it. According to Table 1, when the numerical aperture NA of the GI fiber 141 is set to 0.012, the difference between the numerical aperture of the emitted light originating in the region P2 and the numerical aperture of the outgoing light originating in the region P1 is minimized. It turns out that it can be transformed.

  From the dependence of the numerical aperture NA on the length LGI shown in FIG. 3, the length LGI at which the numerical aperture NA becomes 0.012 was found to be LGI = 2.41 mm and 2.79 mm (in the case of three significant figures. ).

  As described above, when the numerical aperture NA of the GI fiber 142 is 0.010, by setting the numerical aperture NA of the GI fiber 141 to 0.012, the numerical aperture of the outgoing light derived from the region P2 and the region It was found that the difference with the numerical aperture of the emitted light originating from P1 can be suppressed. In other words, it has been found that the combiner 10 configured as described above can make the numerical aperture of emitted light uniform.

  In this way, by obtaining the numerical aperture of the outgoing light obtained when light having various numerical apertures is made incident on each of the regions P1 to P7, the numerical aperture of the outgoing light can be made uniform. The numerical aperture NA of the preferable GI fibers 141 to 147 can be easily determined. Further, by previously obtaining the correlation between the numerical aperture NA and the length LGI in the GI fibers 141 to 147 shown in FIG. 3, the lengths of the GI fibers 141 to 147 for realizing the desired numerical aperture NA are obtained. The LGI can be easily determined.

[Second Embodiment]
A combiner 10A according to a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 4A is a perspective view of the combiner 10A. It should be noted that FIG. 4A shows the combiner 10A without the incident fiber bundle 12 included in the combiner 10A. FIG. 4B is a plan view obtained when the incident end surface 11Aa of the reduced diameter portion 11A included in the combiner 10A is viewed in a plan view. This plan view is obtained by viewing the reduced diameter portion 11A from the z-axis negative direction side in the coordinate axes shown in FIG. FIG. 4B shows the regions P1A to P7A to which the GI fibers 141A to 147A forming the GI fiber bundle 14 are coupled on the incident end face 11Aa. It should be noted that FIG. 4B shows the incident end face 11a without the incident fiber bundle 12 and the GI fiber bundle 14A included in the combiner 10A.

  5A and 5B are cross-sectional views of the reduced diameter portion 11A, which are cross-sectional views along a plane (yz plane) taken along the line BB 'shown in FIG. 4B. ..

(Structure of combiner 10A)
The combiner 10A can be obtained by replacing the reduced diameter portion 11 and the GI fiber bundle 14 included in the combiner 10 shown in FIG. 1 with the reduced diameter portion 11A and the GI fiber bundle 14A, respectively. The input fiber bundle 12 and the output fiber 13 included in the combiner 10A are configured similarly to those included in the combiner 10. Therefore, in this embodiment, the description of the incident fiber bundle 12 and the output fiber 13 is omitted.

  As shown in FIG. 4A, a line segment connecting the center C1A of the incident end face 11Aa and the center C2A of the exit end face 11Ab in the reduced diameter portion 11A is defined as a central axis 11AC. The central axis 11AC is inclined with respect to the incident end face 11Aa and the emitting end face 11Ab. Therefore, the shape of the reduced diameter portion 11A can be said to be an eccentric truncated cone.

  Therefore, when the incident end face 11Aa is viewed in a plan view, the center C1A and the center C2A are displaced from each other (see (b) of FIG. 4). The planar view distance between the center C1A and the center C2A, which is obtained when the incident end surface 11Aa is viewed in a plane, is an offset amount Doff (plane view distance Doff described in the claims). The offset amount Doff represents the degree of deviation between the center C1A and the center C2A. The larger the offset amount Doff, the greater the degree of deviation between the center C1A and the center C2A.

  As shown in FIG. 4B, a region including the center C1A and connected to the GI fiber 142A is referred to as a region P2A. Further, the center of the region P2A is called the center CP2A. The center CP2A corresponds to the center of the GI fiber 142A coupled to the entrance end face 11Aa. In the combiner 10A, the center C1A and the center CP2A coincide with each other.

  Six regions (region P1A and regions P3A to P7A) surrounding the region P2A are arranged around the region P2A. The centers of the area P1A and the areas P3A to P7A are referred to as centers CP1A and CP3A to CP7A, respectively. The area P1A is an area to which the GI fiber 141A is connected. The center CP1A corresponds to the center of the GI fiber 141A coupled to the incident end face. Similarly, each of the regions P3A to P7A is a region to which the GI fibers 143A to 147A are connected, and each of the centers CP3A to CP7A is the center of each of the GI fibers 143A to 147A coupled to the incident end face 11Aa. Corresponding to. Each of the region P1A and the regions P3A to P7A is isotropically arranged around the region P2A, that is, the centers CP1A and CP3 to CP7A form each vertex of a regular hexagon. In other words, each of the GI fibers 141A to 147A is arranged so as to have a close-packed structure within the incident end face 11Aa.

  The line B-B ′ shown in FIG. 4B is a straight line connecting the center C1A and the center C2A. In each of the areas P1A to P7A, the distance in plane view between the center C2A and the centers CP1A to CP7A obtained when the incident end surface 11Aa is viewed in plane is defined as the distance Ddif. In FIG. 4B, the distance Ddif for the region P1 is illustrated as an example of the distance Ddif. The distance Ddif represents the shift between the region where the incident light is coupled to the reduced diameter portion 11A and the region where the emitted light is coupled to the reduced diameter portion 11A. The larger the distance Ddif, the larger the deviation between the region where the incident light is coupled and the region where the outgoing light is coupled.

In the combiner 10A, the center C1A and the center C2A are separated from each other by the offset amount Doff when the incident end face 11Aa is viewed in a plan view, and the separating direction is a direction approaching the center CP1A (away from the center CP7A). Direction). Therefore, the magnitude relationship of the distance Ddif is as follows (see (b) of FIG. 2).
Ddif (P1A) <Ddif (P2A) <Ddif (P4A), Ddif (P5A) <Ddif (P6A), Ddif (P7A) <Ddif (P3A)
The amount of increase in the numerical aperture of the light due to the light propagating through the reduced diameter portion 11A changes according to the distance Ddif. This increase amount is smaller for light originating from a region where the distance Ddif is smaller, and is larger for light originating from a region where the distance Ddif is larger. That is, the amount of increase in the numerical aperture of light is such that the light incident on the (1) region P1A is the smallest, and (2) region P2A, (3) region P4A, P5A, (4) region P6A, P7A, (5) region. It becomes larger in the order of P3A.

  Based on the magnitude relation of the increase amount of the numerical aperture, the GI fiber coupled to the region where the distance Ddif is large has a smaller numerical aperture NA. That is, the numerical aperture NA of the GI fibers 141A to 147A is (1) GI fiber 141A, (2) GI fiber 142A, (3) GI fiber 144A, 145A, (4) GI fiber 146A, 147A, (5) GI fiber. It is configured to become smaller in the order of 143A.

  For example, when a cylindrical optical member is stretched to manufacture a reduced diameter portion, distortion may occur in the shape of the stretched optical member. According to the combiner 10A, the numerical aperture of emitted light can be made uniform even if the diameter-reduced portion 11A having the shape of an eccentric truncated cone is used.

  In this embodiment, the length LGI of the GI fiber 143A having the smallest numerical aperture NA is set to Ls / 4 which is the optimum length of the GI fiber. Therefore, the GI fiber 143A couples the collimated light to the incident end surface 11Aa of the reduced diameter portion 11A (see (a) of FIG. 4).

  In addition, the lengths LGI of the GI fibers 141A to 147A are (1) GI fiber 141A, (2) GI fiber 142A, (3) GI fibers 144A, 145A, (4) based on the size relation of the numerical aperture NA. ) GI fibers 146A and 147A, and (5) GI fiber 143A are configured to become shorter in this order.

  Even when the shape of the diameter-reduced portion 11A is an eccentric truncated cone, each of the GI fibers 141A to 141A through the method described in (Example of numerical aperture NA of GI fiber) of the first embodiment. A length of 147A can be defined.

(Virtual beam diameter)
A method of calculating the virtual beam diameter will be described with reference to FIG. The reduced diameter portion 11A has an eccentric truncated cone shape, but the same calculation method as that for the reduced diameter portion 11 shown in FIG. 2B can be used.

  FIG. 5A shows a state in which the light L1A is incident on the region P1A on the incident end face 11Aa of the reduced diameter portion 11A. FIG. 5B shows a state in which the light L2A is incident on the region P3A on the incident end face 11Aa. Note that, here, each of the light L1A and the light L2A will be described as being collimated light.

  The cross-sectional shape of the reduced diameter portion 11A illustrated in FIG. 5 is a trapezoid having the entrance end surface 11Aa and the exit end surface 11Ab as the bases. The two hypotenuses of the trapezoid are referred to as hypotenuses 11Ac and 11Ad, respectively. The size of the angle formed by the hypotenuse 11Ac and the normal to the emission end face 11Ab is θ1. Further, the angle formed by the hypotenuse 11Ad and the normal line of the emitting end face 11Ab is θ2.

  The virtual beam diameter in the light L1A can be calculated as follows (see (a) in FIG. 5). A straight line that passes through the lower end of the emission end face 11Ab and forms an angle θ1 with the emission end face 11Ab is a straight line 11Ae.

  (1) Of the extension lines of the light L1A extending inside the reduced diameter portion 11A, the extension line on the side farther from the emission end face 11Ab (the y-axis positive direction side) is the extension line L1Ae.

  (2) The intersection between the extension line L1Ae and the hypotenuse 11Ac of the reduced diameter portion 11A is defined as an intersection I1Aa.

  (3) A straight line LI1A passing through the intersection I1Aa and parallel to the incident end face 11Aa and the outgoing end face 11Ab is drawn.

  (4) The intersection of the straight line LI1A and the straight line 11Ae is defined as the intersection point I1Ab.

  (5) The virtual beam diameter DL1A is defined as the distance between the intersection I1Aa and the intersection I1Ab.

  Similarly, the virtual beam diameter of the light L2A can be calculated as follows (see (b) of FIG. 5). A straight line that passes through the upper end of the emission end face 11Ab and forms an angle θ2 with the emission end face 11Ab is a straight line 11Af.

  (1) Of the extension lines of the light L2A extending inside the reduced diameter portion 11A, the extension line on the side farther from the emission end face 11Ab (the y-axis negative direction side) is the extension line L2Ae.

  (2) An intersection point between the extension line L2Ae and the oblique side 11Ad of the reduced diameter portion 11A is defined as an intersection point I2Aa.

  (3) A straight line LI2A passing through the intersection I2Aa and parallel to the incident end face 11Aa and the outgoing end face 11Ab is drawn.

  (4) The intersection of the straight line LI2A and the straight line 11Af is defined as the intersection I2Ab.

  (5) The virtual beam diameter DL2A is the distance between the intersection I2Aa and the intersection I2Ab.

  When the reduced-diameter portion 11A is eccentric, the size of the angle formed between the hypotenuse 11Ac and the normal to the emission end face 11Ab (= θ1) and the size of the angle formed between the hypotenuse 11Ad and the normal to the emission end face 11Ab (= It is different from θ2). Therefore, as compared with the case of the reduced diameter portion 11, the virtual beam diameter of each light incident on each area (areas P1A to P7A) of the incident end surface 11Aa has a wider distribution. However, the numerical aperture NA of the GI fiber can be changed over a wide range (0.01 or more and 0.04 or less) as shown in FIG. Therefore, although the combiner 10A includes the eccentric diameter reducing portion 11A, the numerical aperture of the emitted light can be made uniform.

[Third Embodiment]
A fiber laser system 1 according to a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of the fiber laser system 1. As shown in FIG. 6, a fiber laser system 1 (laser system described in claims) includes a combiner 10 described in the first embodiment, seven fiber laser devices 50a to 50g, and a laser head 60. Is equipped with.

  Each of the fiber laser devices 50a to 50g is a configuration for generating laser light, and is one aspect of the laser device. The laser device in this embodiment is not limited to the fiber laser device. Each of the fiber laser devices 50a-50g is similarly configured. Here, the configuration of the fiber laser device 50a will be described as an example. The laser light generated by the fiber laser device 50a is input to the combiner 10 and combined with the laser light generated by the other fiber laser devices 50b to 50g. The laser light combined by the combiner 10 is applied to a workpiece (workpiece) (not shown) via the laser head 60.

  The fiber laser device 50a includes a current source (not shown), ten laser diodes LD1 to LD10, a pump combiner 51, a high reflection fiber Bragg grating (FBG) 54, a double clad fiber (DCF) 52, and a low reflection fiber Bragg grating. (FBG) 55 and delivery fiber 53a (emission fiber described in claims). Note that the number of laser diodes is not limited to ten and may be any number.

  Each of the laser diodes LD1 to LD10 is configured to generate pump light. The laser diodes LD1 to LD10 are connected to the input ports of the pump combiner 51, and the pump light generated by the laser diodes LD1 to LD10 is input to the pump combiner 51.

  The pump combiner 51 is configured to obtain combined pump light by multiplexing the pump lights generated by the laser diodes LD1 to LD10. The output port of the pump combiner 51 is connected to the DCF 52 via the high reflection FBG 54. The combined pump light obtained by the pump combiner 51 passes through the high reflection FBG 54, and then is input to the inner clad of the DCF 52.

  The DCF 52 has a configuration for converting the pump light multiplexed by the pump combiner 51 into laser light. A rare earth element such as Yb is added to the core of the DCF 52, and the synthetic pump light obtained by the pump combiner 51 is used to maintain the rare earth element in a population inversion state. The DCF 52 constitutes a resonator together with a high reflection FBG 54 connected to the input end and a low reflection FBG 55 connected to the output end. In the core of the DCF 52, the rare earth element maintained in the population inversion state repeats stimulated emission to generate laser light. The output end of the DCF 52 is connected to the FMF 121 that constitutes the incident fiber bundle 12 of the combiner 10 via the low reflection FBG 55. Of the laser light generated by the DCF 52, the laser light that has passed through the low reflection FBG 55 is input to the delivery fiber 53a connected to the fiber laser device 50a, and in turn input to the FMF 121.

  Similarly, each of the delivery fibers 53b to 53g included in each of the fiber laser devices 50b to 50g is connected to each of the FMF 122 to FMF 127 forming the incident fiber bundle 12.

  The combiner 10 combines the laser beams incident from the respective fiber laser devices 50a to 50g into one to generate output light. The output light emitted from the emission fiber 13 of the combiner 10 is input to the laser head 60.

  The laser head 60 is configured to prevent the output light input from the emitting fiber 13 from being reflected by the work piece and re-entering the emitting fiber 13. The laser head 60 is composed of, for example, a glass block and a housing that houses the glass block. The output light emitted from the laser head 60 is applied to the workpiece.

  As described in the first embodiment, the combiner 10 can emit the emitted light having a uniform numerical aperture (in other words, beam quality). Therefore, the fiber laser system 1 including the combiner 10 as the output combiner can emit the emitted light having a uniform numerical aperture.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

1 Fiber laser system (laser system)
10, 10A Combiner 11, 11A Reduced diameter portion 11a, 11Aa Incident end face 11b, 11Ab Emitting end face 12, 12A Incident fiber bundle 121-127 Fuse mode fiber (incident fiber)
121a to 127a core 121b to 127b clad 13 output fiber 13a core 13b clad 14,14A GI fiber bundle 141 to 147, 141A to 147A GI fiber 50a to 50g fiber laser device 53a to 53g output fiber LD1 to LD10 laser diode

Claims (6)

Multiple input fibers,
A GI fiber joined to each of the output end faces of each of the plurality of input fibers,
Output fiber,
An incident end face, and an emission end face having an area smaller than that of the incident end face, each of the GI fibers is coupled to the incident end face, and a reduced diameter portion in which the emission fiber is coupled to the emission end face, Is a combiner with
As a distance Ddif, a planar view distance between the center of the region of the entrance end face where the GI fiber is coupled and the center of the exit end face, which is obtained when the entrance end face of the reduced diameter portion is viewed in plan,
The numerical aperture of each GI fiber as a lens is smaller in a GI fiber coupled to a region having a larger distance Ddif,
A combiner characterized by that. Each of the GI fibers has the same refractive index profile within manufacturing tolerances,
The length of each GI fiber has a length closer to an optimum length which is a length for emitting collimated light, as the GI fiber coupled to a region having a larger distance Ddif is,
The combiner according to claim 1, wherein: The shape of the entrance end face and the shape of the exit end face of the reduced diameter portion are both circular,
The combiner according to claim 2, wherein: A central axis connecting the center of the incident end face and the center of the exit end face is inclined with respect to the normal line of the incident end face,
The combiner according to claim 3, wherein: The length of the GI fiber having the maximum distance Ddif among the GI fibers is the optimum length of the GI fiber,
The combiner according to any one of claims 2 to 4, characterized in that: (1) a plurality of incident fibers, (2) a GI fiber joined to each of the emission end faces of the plurality of incident fibers one by one, (3) a first emission fiber, (4) an incidence end face, and A reduced diameter portion having an exit end surface having an area smaller than that of the entrance end surface, each of the plurality of entrance fibers being coupled to the entrance end surface, and the first exit fiber being coupled to the exit end surface. A combiner comprising,
Each GI fiber is defined as a distance Ddif, which is a plan view distance between the center of the region of the incident end surface where the GI fiber is coupled and the center of the exit end surface, which is obtained when the incident end surface of the reduced diameter portion is viewed in a plan view. The numerical aperture as a lens of is a combiner that is smaller for a GI fiber coupled to a region where the distance Ddif is larger,
A respectively plurality laser device having a second emission fiber, each of the second emission fiber, respectively, and a laser device of the plurality being connected to one of the incident fiber of said combiner ,,
A laser system characterized by the above.

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