Wavelength beam binding device, direct diode laser device, and laser cutting machine

Abstract

To further heighten output and power density of a laser beam having been bound by wavelength beam binding.SOLUTION: A wavelength beam binding device comprises: a polarized beam splitter for separating a plurality of laser beams into a plurality of first polarized beams that is linearly polarized in a first polarization direction and a plurality of second polarized beams that is linearly polarized in a second polarization direction; a first polarized beam conversion element for converting the second polarized beams into a plurality of third polarized beams that is linearly polarized in the first polarization direction; and a diffraction lattice for diffracting the plurality of first polarized beams to form a first coaxially superimposed wavelength bound beam, and diffracting the plurality of third polarized beams to form a second coaxially superimposed wavelength bound beam; and a polarized beam coupler for forming and emitting a third wavelength bound beam in which the first and second wavelength bound beams are coaxially superimposed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to a wavelength beam combining device, a direct diode laser device, and a laser processing machine. [Background technology]

[0002] High-power, high-brightness laser beams are used to process a wide variety of materials, including cutting, drilling, and marking, as well as to weld metal materials. Some of the carbon dioxide gas lasers and YAG solid-state lasers that have traditionally been used for such laser processing are being replaced by fiber lasers with high energy conversion efficiency. Laser diodes (hereafter simply referred to as LDs) are used as pump light sources for fiber laser devices. In recent years, with the increasing power output of LDs, technology is being developed that uses LDs not as pump light sources but as light sources for laser beams that directly irradiate materials for processing. This technology is called direct diode laser (DDL) technology.

[0003] Patent Document 1 discloses an example of a light source device that increases optical output by combining a plurality of laser beams with different wavelengths emitted from a plurality of LDs. Coaxially combining multiple laser beams with different wavelengths is called wavelength beam combining (WBC) or spectral beam combining (SBC) and can be used to increase the light output and brightness of, for example, DDL devices. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent No. 6,192,062 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need to further increase the power output and power density of laser beams combined by wavelength beam combining. [Means for solving the problem]

[0006] In one embodiment, the wavelength beam combining device of the present disclosure is a wavelength beam combining device that combines a plurality of laser beams having different peak wavelengths, and includes a polarizing beam splitter that separates the plurality of laser beams into a plurality of first polarized beams that are linearly polarized in a first polarization direction and a plurality of second polarized beams that are linearly polarized in a second polarization direction orthogonal to the first polarization direction, a first polarization conversion element that converts the plurality of second polarized beams into a plurality of third polarized beams that are linearly polarized in the first polarization direction, and a polarization conversion element that diffracts the plurality of first polarized beams to separate the plurality of first polarized beams. the first wavelength combined beam and the second wavelength combined beam are orthogonal to each other by changing the polarization state of at least one of the first wavelength combined beam and the second wavelength combined beam; and a polarization beam combiner that forms and outputs a third wavelength combined beam by coaxially superimposing the first wavelength combined beam and the second wavelength combined beam.

[0007] In one embodiment, the direct diode laser device of the present disclosure comprises the above-mentioned wavelength beam combining device, a plurality of semiconductor laser devices each emitting laser light of a different peak wavelength, and an optical fiber array device that forms the plurality of laser beams from the laser light emitted from the plurality of semiconductor laser devices, which are incident on the polarizing beam splitter of the wavelength beam combining device.

[0008] In one embodiment, the laser processing machine of the present disclosure includes at least one direct diode laser device described above, an optical transmission fiber coupled to the third wavelength combined beam emitted from the at least one direct diode laser device, and a processing head connected to the optical transmission fiber. [Effects of the Invention]

[0009] According to the embodiments of the present disclosure, a wavelength beam combining device, a direct diode laser device, and a laser processing machine are provided that can further increase the output and power density of laser beams combined by wavelength beam combining. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a first embodiment of a wavelength beam combining device according to the present disclosure. [Figure 2] FIG. 2 is a perspective view schematically showing an example of the configuration and function of a polarizing beam splitter. [Figure 3A] FIG. 3A is a perspective view schematically showing how a light beam with a peak wavelength λn is incident on a diffraction grating and diffracted to form a diffracted light beam. [Figure 3B] FIG. 3B is a cross-sectional view schematically showing main diffracted light beams formed when a light beam is incident on a transmission type diffraction grating. [Figure 4A] FIG. 4A is a graph schematically showing the spectrum of a first wavelength combined beam obtained by wavelength-combining three laser beams having peak wavelengths λ1, λ2, and λ3. [Figure 4B] FIG. 4B is a graph schematically showing the spectrum of a second wavelength combined beam obtained by wavelength combining three laser beams having peak wavelengths λ1, λ2, and λ3. [Figure 5] FIG. 5 is a graph schematically showing the spectrum of the third-wavelength combined beam when the number of laser beams to be combined is K (K is an integer of 4 or more). [Figure 6]FIG. 6 is a diagram showing a configuration example of a second embodiment of a wavelength beam combining device according to the present disclosure. [Figure 7] FIG. 7 is a side view showing an example of the configuration of a polarizing beam splitter. [Figure 8] FIG. 8 is a diagram showing a configuration example of a third embodiment of a wavelength beam combining device according to the present disclosure. [Figure 9] FIG. 9 is a diagram illustrating a configuration example of an embodiment of a direct diode laser device according to the present disclosure. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of an embodiment of a laser processing machine according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] <First embodiment of wavelength beam combining device> A first embodiment of a wavelength beam combining device according to the present disclosure will be described with reference to Figure 1. In the accompanying drawings including Figure 1, mutually orthogonal X-axis, Y-axis and Z-axis are schematically shown for reference.

[0012] The wavelength beam combining device 100 of this embodiment shown in FIG. 1 can combine multiple laser beams 10 with different peak wavelengths. For simplicity, FIG. 1 illustrates an example of the configuration of a device that coaxially combines three laser beams 10 with peak wavelengths λ1, λ2, and λ3. The number of laser beams 10 to be combined is not limited to three; two or four or more laser beams 10 with different peak wavelengths may be combined. Hereinafter, the peak wavelength of the multiple laser beams 10 to be combined may be referred to as λn. Here, "n" is an integer greater than or equal to 1 and is used as a numerical value to distinguish (identify) each of the multiple laser beams 10. In the illustrated example, the relationship λ1<λ2<λ3 holds. The peak wavelength λn may be measured in any unit, such as nanometers (nm).

[0013] In FIG. 1, multiple laser beams 10 are each shown as a simple straight line. An actual laser beam 10 is a light beam that has an intensity distribution in a plane perpendicular to the direction of propagation. This intensity distribution can be approximated by a distribution function such as a Gaussian distribution in the plane perpendicular to the direction of propagation of the light beam. The diameter of the light beam is, for example, 1 / e with respect to the intensity at the center of the beam. 2 It is defined as the size of a cross-sectional area having an intensity equal to or greater than 1 / 100th of the incident light. In this disclosure, the laser beam 10 is collimated by an optical system such as a collimator lens. In the drawings, the central axis of each light beam is represented by a straight line to schematically show the direction of travel of a collimated light beam such as the laser beam 10. These straight lines may be considered to represent a ray passing through the center of each light beam.

[0014] The wavelength beam combining device 100 includes a polarizing beam splitter 20 onto which multiple laser beams 10 are incident. The polarizing beam splitter 20 has a reflection / transmission surface 20R whose transmittance and reflectance vary depending on the polarization state of the incident laser beams 10. Light is an electromagnetic wave, and the electromagnetic field of light is a transverse wave that oscillates perpendicular to the propagation direction. The polarization state of a laser beam can vary depending on the gain medium, resonator, oscillation method, etc. of the laser light source. Furthermore, even a laser beam that is in a specific polarization state when emitted from a laser light source may change its polarization state or become depolarized while passing through a transmission medium such as an optical fiber. The reflection / transmission surface 20R of the polarizing beam splitter 20 selectively reflects polarization components linearly polarized in a predetermined direction and transmits polarization components linearly polarized in a direction perpendicular to the predetermined direction. The reflection / transmission surface 20R is provided with, for example, a polarization-dependent dielectric multilayer film. In the example of FIG. 1, the polarizing beam splitter 20 splits a laser beam 10 traveling in the Z-axis direction into a plurality of first polarized beams 11 linearly polarized in a first polarization direction (Y-axis direction) and a plurality of second polarized beams 12 linearly polarized in a second polarization direction (X-axis direction) orthogonal to the first polarization direction. Note that the plurality of laser beams 10 do not need to be parallel to each other when they enter the polarizing beam splitter 20. In the example of FIG. 1, the traveling directions of the three laser beams 10 are adjusted to form a predetermined angle. Details of this "predetermined angle" will be described later.

[0015] Generally, when a light ray is incident on an object surface, the plane containing the normal to the object surface at the point of incidence and the propagation vector (wave vector) of the light ray is defined as the "plane of incidence." Light linearly polarized in a direction perpendicular to the plane of incidence is called S-polarized light, and light linearly polarized in a direction parallel to the plane of incidence is called P-polarized light. In the example of FIG. 1, the reflection / transmission surface 20R of the polarizing beam splitter 20 is perpendicular to the XZ plane, and the normal to the reflection / transmission surface 20R is in a plane parallel to the XZ plane. The propagation direction of the laser beam 10 is parallel to the XZ plane. Therefore, the "plane of incidence" when the laser beam 10 is incident on the reflection / transmission surface 20R is parallel to the XZ plane. In this disclosure, light linearly polarized in a first polarization direction, which is perpendicular to the XZ plane, is referred to as "S-polarized light." Light linearly polarized in a direction parallel to the XZ plane (a second polarization direction orthogonal to the first polarization direction) is referred to as "P-polarized light." In the accompanying drawings, a symbol consisting of a small circle with a cross symbol surrounding it indicates "S-polarized light," and a symbol consisting of a double-headed arrow indicates "P-polarized light." The polarization direction of "P-polarized light" is parallel to the XZ plane but perpendicular to the direction of propagation of the laser beam. Therefore, when the direction of propagation of the laser beam rotates due to reflection or diffraction while remaining parallel to the XZ plane, the polarization direction of "P-polarized light" also rotates within a plane parallel to the XZ plane. For this reason, the "second polarization direction" in this disclosure is defined as a direction perpendicular to the direction of propagation of the laser beam and perpendicular to the first polarization direction.

[0016] FIG. 2 is a perspective view schematically illustrating an example of the configuration and function of the polarizing beam splitter 20. In the example of FIG. 2, a laser beam 10 containing S-polarized and P-polarized light travels in the positive direction of the Z axis and enters the polarizing beam splitter 20. The polarization state of the laser beam 10 containing S-polarized and P-polarized light is, for example, an "unpolarized" state in which S-polarized and P-polarized light are randomly mixed. In this disclosure, "unpolarized" refers to light that is not linearly polarized in a specific direction. Therefore, in this broad sense, "unpolarized" can also include circularly polarized light and elliptically polarized light. Furthermore, "unpolarized" also includes a mixed state of linearly polarized light in which the polarization direction changes randomly or regularly with time or location.

[0017] 2, reflection / transmission surface 20R of polarizing beam splitter 20 reflects the S-polarized light and transmits the P-polarized light contained in laser beam 10. As a result, laser beam 10 is split into a first polarized (S-polarized) beam 11 that is linearly polarized in a first polarization direction (Y-axis direction) and a second polarized (P-polarized) beam 12 that is linearly polarized in a second polarization direction (X-axis direction).

[0018] An important point in this disclosure is that the reflection / transmission surface 20R of the polarizing beam splitter 20 separates reflected light and transmitted light, the polarization directions of which are orthogonal to each other (polarization separation). If the laser beam 10 is composed of only S-polarized light, the first polarized (S-polarized) beam 11 will be formed from the laser beam 10, but the second polarized (P-polarized) beam 12 will not be formed. Conversely, if the laser beam 10 is composed of only P-polarized light, the first polarized (S-polarized) beam 11 will not be formed from the laser beam 10, and only the second polarized (P-polarized) beam 12 will be formed.

[0019] If the multiple laser beams 10 incident on the polarizing beam splitter 20 are "unpolarized," the laser beams 10 are split into multiple first polarized (S-polarized) beams 11 linearly polarized in a first polarization direction (Y-axis direction) and multiple second polarized (P-polarized) beams 12 linearly polarized in a second polarization direction (X-axis direction). However, even if the laser beam 10 is linearly polarized in a state where S-polarized and P-polarized light are superimposed, the first polarized (S-polarized) beam 11 and the second polarized (P-polarized) beam 12 can be formed from such laser beam 10 as long as the polarization direction is not parallel to either the X-axis or the Y-axis in FIG. 2. Furthermore, even if the multiple laser beams 10 incident on the polarizing beam splitter 20 are linearly polarized in different directions, the multiple laser beams 10 can be split as a whole into multiple first polarized (S-polarized) beams 11 linearly polarized in the first polarization direction (Y-axis direction) and multiple second polarized (P-polarized) beams 12 linearly polarized in the second polarization direction (X-axis direction). Therefore, unless all of the "multiple" laser beams 10 incident on the polarizing beam splitter 20 are linearly polarized in the direction of one of the X-axis and Y-axis in FIG. 2, polarization separation by the polarizing beam splitter 20 is realized, and the multiple laser beams 10 as a whole are interpreted as being "unpolarized."

[0020] 2 shows a prism-type polarizing beam splitter 20, but the type of polarizing beam splitter 20 is not limited to this example and may be a cube-type, plate-type, or other type. In the example of FIG. 2, the first polarized (S-polarized) beam 11 reflected by the reflection / transmission surface 20R of the polarizing beam splitter 20 travels in a first propagation direction F indicated by a hollow arrow. On the other hand, the second polarized (P-polarized) beam 12 transmitted through the reflection / transmission surface 20R of the polarizing beam splitter 20 travels in the positive direction of the Z axis. However, the propagation directions of the first polarized (S-polarized) beam 11 and the second polarized (P-polarized) beam 12 can be changed by an optical element such as a mirror.

[0021] Referring again to FIG. 1, the wavelength beam combining device 100 includes a first polarization conversion element 30 that converts a plurality of second polarized (P polarized) beams 12 into a plurality of third polarized (S polarized) beams 13 that are linearly polarized in a first polarization direction (Y-axis direction). The first polarization conversion element 30 is, for example, a half-wave plate (a retardation plate). A half-wave plate has birefringence and changes the phase difference between two orthogonal components of an electromagnetic wave traveling in the thickness direction. By arranging the slow axis or fast axis of the half-wave plate so that it forms an angle of 45° with respect to the polarization direction of the second polarized (P polarized) beams 12, the half-wave plate can convert P polarized light into S polarized light.

[0022] In this way, the wavelength beam combining device 100 of this embodiment can form a plurality of first polarized beams 11 and a plurality of third polarized beams 13 that are linearly polarized in a specific direction from a plurality of laser beams 10 that are generally unpolarized. At this stage, the plurality of first polarized beams 11 are composed of a plurality of laser beams that have different peak wavelengths and are not coaxially coupled. Similarly, the plurality of third polarized beams 13 are also composed of a plurality of laser beams that have different peak wavelengths and are not coaxially coupled.

[0023] The phase difference formed by the half-wave plate depends on the wavelength of the incident light. Therefore, when three laser beams with peak wavelengths λ1, λ2, and λ3 pass through the half-wave plate, a phase difference of exactly half wavelength is not formed at all peak wavelengths, and a P-polarized component remains in the S-polarized light converted from P-polarized light. Therefore, the multiple third polarized (S-polarized) beams 13 output from the first polarization conversion element 30 contain a P-polarized component and, strictly speaking, may contain elliptically polarized light. However, if all of the multiple peak wavelengths λn fall within a relatively narrow range, for example, a range of 10 nm or less, the difference in phase difference (wavelength dispersion) caused by the half-wave plate is sufficiently small. Therefore, in the embodiment of the present disclosure, the third polarized beam 13 may contain mainly S-polarized components and partially P-polarized components.

[0024] 1 further includes two diffraction gratings 40 for respectively coaxially aligning the plurality of first polarized (S-polarized) beams 11 and the plurality of third polarized (S-polarized) beams 13. One of the two diffraction gratings 40 is configured to diffract the plurality of first polarized beams 11 to form a first wavelength combined beam 21 in which the plurality of first polarized beams 11 are coaxially superimposed, and the other is configured to diffract the plurality of third polarized beams 13 to form a second wavelength combined beam 22 in which the plurality of third polarized beams 13 are coaxially superimposed.

[0025] Next, with reference to Fig. 3A, a configuration example and function of the diffraction grating 40 will be described. The diffraction grating 40 shown in Fig. 3A is the diffraction grating 40 that diffracts the first polarized beam 11 in Fig. 1. The following description also applies to other diffraction gratings 40.

[0026] FIG. 3A is a perspective view schematically illustrating how a light beam 14A with a peak wavelength λn is incident on a diffraction grating 40, diffracted, and forms a diffracted light beam 14B. The incident angle of the light beam 14A is αn. The "n" in the incident angle αn is the same integer as the "n" in the peak wavelength λn. The incident angle αn is the angle formed between the normal direction N of the diffraction surface of the diffraction grating 40 and the light beam 14A with the peak wavelength λn. The surface of the diffraction grating 40 has a large number of diffraction grooves. FIG. 3A illustrates an imaginary plane 44. This plane 44 is a plane that includes the light beam 14A incident on the diffraction grating 40 and the diffracted light beam 14B emerging from the diffraction grating 40, and is perpendicular to the diffraction grooves. Because diffraction is a phenomenon in which the angle between the light beam 14A and the diffracted light beam 14B within the plane 40 changes depending on the wavelength (dispersion), the direction in which the plane 40 expands may be referred to as the "direction of dispersion."

[0027] If the diffraction angle of the diffracted light beam 14B is β, the relationship of the following formula 1 holds. sin(αn) + sin(β) = N·m·λn (Equation 1) where N is the number of diffraction grooves per mm of the diffraction grating 40, and m is the diffraction order.

[0028] For example, if the diffraction order m is 1, the diffraction angle β is 45.0 degrees, N=2500, and the wavelength λn is 450 nm, the incident angle αn is 24.7 degrees. When multiple laser beams with different peak wavelengths λn are incident on the same position on the diffraction grating 40, by appropriately selecting the wavelength λn and the incident angle αn, it is possible to diffract the multiple laser beams with different peak wavelengths λn in the direction of the same diffraction angle β.

[0029] FIG. 3B is a cross-sectional view schematically illustrating the main diffracted beams formed when a light beam I is incident on a transmission-type diffraction grating 40. FIG. 3B illustrates the reflected zeroth-order diffracted beam R-0, the reflected first-order diffracted beam R-1, the transmitted zeroth-order diffracted beam T-0, and the transmitted first-order diffracted beam T-1 formed by the diffraction grating 40. Even though the diffraction grating 40 is a transmission-type diffraction grating, the diffraction grating 40 used in this embodiment is configured to selectively generate a strong reflected first-order diffracted beam R-1. Therefore, the reflected zeroth-order diffracted beam R-0, the transmitted zeroth-order diffracted beam T-0, and the transmitted first-order diffracted beam T-1 generated by the transmission-type diffraction grating 40 are negligible. As a result, most of the laser beam incident on the diffraction grating is not absorbed by the material constituting the diffraction grating 40, thereby suppressing light loss. Unlike transmission-type diffraction gratings, reflection-type diffraction gratings have a reflective component (a dielectric multilayer film or a mirror), and light absorption by this component cannot be ignored. Therefore, with a reflective diffraction grating, if the intensity of the incident laser beam increases, heat generated by light absorption can degrade the performance of the diffraction grating. For this reason, in the present disclosure, it is desirable to use a transmission diffraction grating. The substrate of the diffraction grating 40 can be formed from a material with low absorption at the peak wavelength of the laser beam, such as quartz. The cross-sectional shape of the grating can be, for example, rectangular or trapezoidal.

[0030] A light absorbing member may be provided on the inner surface of the housing that houses the components of the wavelength beam combining device 100. The light absorbing member absorbs diffracted light beams other than the reflected first-order diffracted light beam R-1, thereby suppressing the generation of stray light.

[0031] Next, referring back to FIG. 1 , in an embodiment of the present disclosure, the angles of incidence (αn) of the multiple first polarized beams 11 incident on the left diffraction grating 40 are determined according to the wavelengths λn (=λ1, λ2, λ3) so as to satisfy Equation 1. Similarly, the angles of incidence (αn) of the multiple third polarized beams 13 incident on the right diffraction grating 40 are determined according to the wavelengths λn (=λ1, λ2, λ3) so as to satisfy Equation 1. In this manner, the first wavelength combined beam 21 and the second wavelength combined beam 22 can be generated, which are aligned so as to have the same diffraction angle (β). The diameters (beam diameters) of the first polarized beam 11 and the third polarized beam 13 on the surface of the diffraction grating 40 on which the diffraction grooves are formed are, for example, in the range of 0.5 mm to 10 mm.

[0032] In this embodiment, the laser beams incident on the diffraction grating 40 are the first polarized beam 11, which is S-polarized, and the third polarized beam 13, which is S-polarized. If the diffraction grating 40 has polarization dependency, when an unpolarized laser beam is incident, the diffraction efficiency will decrease depending on the polarization component. In this embodiment, the diffraction grating 40 has diffraction grooves parallel to the first polarization direction (Y-axis direction). In this embodiment, by using a diffraction grating 40 whose diffraction efficiency for S-polarized light is higher than that for P-polarized light, it is possible to suppress optical loss in the diffraction grating 40.

[0033] When the laser beam 10 has a spectral width Δλn approximately centered on the peak wavelength λn, the smaller the spectral width Δλn, the better. A wider spectral width Δλn results in a larger diffraction angle β. A larger diffraction angle β imparts a width to the propagation direction of the first wavelength combined beam 21 and the second wavelength combined beam 22. The spectral width Δλn is set to, for example, 0.3 nm or less. By combining multiple laser beams 10 with narrow spectral widths Δλn, a wavelength combined beam containing multiple peak wavelengths in a desired wavelength range can be generated, thereby efficiently increasing its optical output. In applications involving processing and welding metals such as Cu, the multiple peak wavelengths may be in the range of 430 nm to 480 nm, for example. The number of laser beams 10 may be 10 or more.

[0034] The wavelength beam combining device 100 further includes a second polarization conversion element 50 and a polarization beam combiner 60. The second polarization conversion element 50 is configured to change the polarization state of at least one of the first wavelength combined beam 21 and the second wavelength combined beam 22 to orthogonalize the polarization directions of the first wavelength combined beam 21 and the second wavelength combined beam 22. Like the first polarization conversion element 30, the second polarization conversion element 50 is, for example, a half-wave plate (half-wave retardation plate). In the example of FIG. 1 , the second polarization conversion element 50 is positioned to rotate the polarization direction of the second wavelength combined beam 22 by 90 degrees. The second wavelength combined beam 22 transmitted through the second polarization conversion element 50 is linearly polarized in the second polarization direction. Alternatively, the second polarization conversion element 50 may be positioned to rotate the polarization direction of the first wavelength combined beam 21 by 90 degrees.

[0035] The polarizing beam combiner 60 is configured to form and output a third wavelength combined beam 23 by coaxially superimposing the first wavelength combined beam 21 and the second wavelength combined beam 22. The polarizing beam combiner 60 may have a configuration similar to that of the polarizing beam splitter 20. In general, a polarizing beam splitter can also be used as a polarizing beam combiner. In the example of FIG. 1, the first wavelength combined beam 21 is S-polarized light, and the second wavelength combined beam 22 transmitted through the second polarization conversion element 50 is P-polarized light. The polarizing beam combiner 60 has a reflection / transmission surface 60R that reflects S-polarized light and transmits P-polarized light. As a result, the polarizing beam combiner 60 can output a third wavelength combined beam 23 by coaxially superimposing the first wavelength combined beam 21, which is S-polarized light, and the second wavelength combined beam 22, which is P-polarized light.

[0036] The third wavelength combined beam 23 is a laser beam obtained by wavelength-combining three laser beams 10 having peak wavelengths λ1, λ2, and λ3. Thus, the wavelength beam combining device 100 makes it possible to increase the output and power density of the wavelength-combined laser beam. If the number of laser beams 10 to be combined increases, the output and power density of the third wavelength combined beam 23 can increase proportionally.

[0037] Conversely to the above example, it is also possible to reflect second polarized (P polarized) beam 12 in first traveling direction F at reflection / transmission surface 20R of polarizing beam splitter 20, and transmit first polarized (S polarized) beam 11 in the positive direction of the Z axis. In this case, first polarization conversion element 30 is placed at a position that transmits the multiple second polarized (P polarized) beams 12, and converts the multiple second polarized (P polarized) beams 12 into multiple third polarized (S polarized) beams 13 that are linearly polarized in the first polarization direction (Y axis direction).

[0038] FIG. 4A is a graph schematically showing the spectrum of a first wavelength combined beam 21 obtained by wavelength-combining three laser beams 10 having peak wavelengths of λ1, λ2, and λ3. The vertical axis of the graph represents light intensity, and the horizontal axis represents wavelength. FIG. 4B is a graph schematically showing the spectrum of a second wavelength combined beam 22 obtained by wavelength-combining three laser beams 10 having peak wavelengths of λ1, λ2, and λ3. The vertical axis of the graph represents light intensity, and the horizontal axis represents wavelength. The light intensity of a third wavelength combined beam 23 obtained by coaxially superimposing the first wavelength combined beam 21 and the second wavelength combined beam 22 is equal to the sum of the light intensities shown in FIG. 4A and FIG. 4B, ignoring optical loss due to the polarization beam combiner 60.

[0039] FIG. 5 is a graph schematically showing the spectrum of the third-wavelength combined beam 23 when the number of combined laser beams 10 is K (K is an integer equal to or greater than 4). The vertical axis of the graph represents light intensity, and the horizontal axis represents wavelength. Increasing the number of combined laser beams 10 increases the light output and power density. Furthermore, to combine multiple laser beams 10 within a predetermined wavelength range, the interval between the peak wavelengths of the laser beams 10 can be narrowed.

[0040] According to the wavelength beam combining device of this embodiment, the diffraction efficiency is increased by using a diffraction grating suitable for the polarization state of the incident light, and the diffracted light generated by the diffraction grating is made coaxial, thereby making it possible to increase the output and power density.

[0041] <Second embodiment of wavelength beam combining device> A second embodiment of a wavelength beam combining device according to the present disclosure will now be described with reference to FIGS.

[0042] The wavelength beam combining device 200 of this embodiment shown in FIG. 6 can combine a plurality of laser beams 10 having different peak wavelengths, similar to the first embodiment.

[0043] The wavelength beam combining device 200 of Fig. 6 includes a polarizing beam splitter 20 that splits a plurality of laser beams 10 having different peak wavelengths into a plurality of first polarized beams 11 linearly polarized in a first polarization direction (Y-axis direction) and a plurality of second polarized beams 12 linearly polarized in a second polarization direction (direction in the XZ plane) orthogonal to the first polarization direction. As shown in detail in Fig. 7, the polarizing beam splitter 20 has a reflection / transmission surface 20R that splits the incident laser beam 10 into the first polarized (S-polarized) beam 11 and the second polarized (P-polarized) beam 12, and a mirror 26M that reflects the second polarized (P-polarized) beam 12 in the first traveling direction (F direction). In this example, a transparent member having a parallelogram cross section is fixed to a transparent prism having a triangular cross section via the reflection / transmission surface 20R. The mirror 26M is fixed to the slope of the transparent member having a parallelogram cross section.

[0044] The plurality of second polarized beams 12 reflected by mirror 26M are converted by first polarization conversion element 30 into a plurality of third polarized beams 13 that are linearly polarized in the first polarization direction (Y-axis direction).

[0045] In the wavelength beam combining device 200 of FIG. 6 , one diffraction grating 40 is arranged to diffract the multiple first polarized beams 11 to form a first wavelength combined beam 21 by coaxially superimposing the multiple first polarized beams 11, and to diffract the multiple third polarized beams 13 to form a second wavelength combined beam 22 by coaxially superimposing the multiple third polarized beams 13. The positions on the diffraction grating 40 at which the multiple first polarized beams 11 are incident are different from the positions on the diffraction grating 40 at which the multiple third polarized beams 13 are incident. Therefore, the diffraction grating 40 of FIG. 6 may be separated into a first diffraction grating on which the multiple first polarized beams 11 are incident and a second diffraction grating on which the multiple third polarized beams 13 are incident. When the collective power of the multiple laser beams 10 increases, the temperature of the diffraction grating 40 on which the multiple laser beams 10 are incident increases locally, which may result in deformation of the diffraction grating 40 due to thermal expansion. Such deformation may result in a decrease in diffraction efficiency and degrade the performance of the diffraction grating 40. In this embodiment, even in a configuration in which one diffraction grating 40 is used, each polarized beam is applied to a different region of the diffraction grating 40, so that even if the total output of the multiple laser beams 10 increases, the aforementioned performance degradation of the diffraction grating 40 can be suppressed.

[0046] The wavelength beam combining device 200 of FIG. 6 also includes a second polarization conversion element 50 that changes the polarization state of at least one of the first wavelength combined beam 21 and the second wavelength combined beam 22 to make the polarization directions of the first wavelength combined beam 21 and the second wavelength combined beam 22 orthogonal to each other, and a polarization beam combiner 60 that forms and outputs a third wavelength combined beam 23 by coaxially superimposing the first wavelength combined beam 21 and the second wavelength combined beam 22.

[0047] The polarized beam combiner 60 in this embodiment has the same configuration as the polarized beam splitter 20, but its orientation is rotated by 90 degrees around the Y axis. In this example, a mirror 60M fixed to the polarized beam combiner 60 reflects the second-wavelength combined beam 22, enabling the first-wavelength combined beam 21 and the second-wavelength combined beam 22 to be coaxially superimposed.

[0048] According to the wavelength beam combining device of this embodiment, the diffraction efficiency is increased by using a diffraction grating suitable for the polarization state of the incident light, and the diffracted light generated by the diffraction grating is made coaxial, thereby making it possible to increase the output and power density.

[0049] <Third embodiment of wavelength beam combining device> Referring now to FIG. 8, a third embodiment of a wavelength beam combining device according to the present disclosure will be described.

[0050] A wavelength beam combining device 300 of this embodiment shown in FIG. 8 includes the polarizing beam splitter 20 of the second embodiment, but multiple laser beams 10 having different peak wavelengths are incident on the polarizing beam splitter 20 parallel to each other. A reflection / transmission surface 20R of the polarizing beam splitter 20 reflects the multiple first polarized beams 11 in a first traveling direction (F direction) and transmits the multiple second polarized beams 12. Like the wavelength beam combining device 200 of the second embodiment, the wavelength beam combining device 300 of this embodiment includes a mirror 26M that reflects the multiple second polarized beams 12 that have transmitted through the reflection / transmission surface 20R of the polarizing beam splitter 20 in the first traveling direction (F direction). The multiple second polarized beams 12 reflected by the mirror 26M are converted by the first polarization conversion element 30 into multiple third polarized beams 13 that are linearly polarized in the first polarization direction (Y-axis direction). The first polarization conversion element 30 is, for example, a half-wave plate (half-wave retardation plate) as in the other embodiments.

[0051] In this embodiment, unlike the second embodiment, the plurality of first polarized beams 11 and the plurality of third polarized beams 13 traveling in the first traveling direction (F direction) are parallel to each other.

[0052] The diffraction grating included in the wavelength beam combining device 300 of this embodiment includes a first diffraction grating 40A disposed at a position to receive the plurality of first polarized beams 11 reflected by the polarizing beam splitter 20 in the first traveling direction (F direction) and the plurality of third polarized beams 13 emitted from the first polarization conversion element 30 in the first traveling direction (F direction), and a second diffraction grating 40B disposed parallel to the first diffraction grating 40A. The second diffraction grating 40B includes a first region 41 that receives the reflected and diffracted light of the plurality of first polarized beams 11 by the first diffraction grating 40A and emits a first wavelength combined beam 21 in the first traveling direction (F direction), and a second region 42 that receives the reflected and diffracted light of the plurality of third polarized beams 13 by the first diffraction grating 40A and emits a second wavelength combined beam 22 in the first traveling direction (F direction).

[0053] The structures of the first diffraction grating 40A and the second diffraction grating 40B are designed based on the above-mentioned formula 1. More specifically, the first diffraction grating 40A and the second diffraction grating 40B have the same number N of diffraction grooves per mm and are arranged parallel to each other. The first diffraction grating 40A is arranged so that the multiple first polarized beams 11 and the multiple third polarized beams 13 are both incident at an incident angle α (e.g., 45 degrees). The first diffraction grating 40A is configured to diffract the multiple first polarized beams 11 and the multiple third polarized beams 13, which are incident parallel to each other at the same incident angle α, at different diffraction angles βn depending on their respective peak wavelengths λn, and cause the beams to be incident on predetermined positions of the opposing second diffraction grating 40B. The second diffraction grating 40B has the same structure as the first diffraction grating 40A and is configured to output the reflected diffracted light from the first diffraction grating 40A, which is incident at different incident angles βn depending on the peak wavelength λn, at the same diffraction angle α (e.g., 45 degrees). In this way, the pair of diffraction gratings 40A and 40B function to emit the coaxial first-wavelength combined beam 21 and the coaxial second-wavelength combined beam 22 in the first traveling direction (direction F).

[0054] As described above, the first diffraction grating 40A and the second diffraction grating 40B are parallel to each other with their respective dispersion directions contained within the same plane. In other words, the first diffraction grating 40A and the second diffraction grating 40B are arranged parallel to each other and share the plane 44 shown in FIG. 3A. In this case, the angle of incidence on the first diffraction grating 40A and the angle of diffraction from the second diffraction grating 40B are the same. This relationship is maintained regardless of wavelength, so even if the wavelengths of the multiple laser beams vary, the angle of diffraction from the second diffraction grating 40B can be kept constant, making it easier to focus the light into an optical fiber.

[0055] The parallelism between first diffraction grating 40A and second diffraction grating 40B is evaluated by the angle between a first normal to the surface on which the diffraction grooves of first diffraction grating 40A are formed and a second normal to the surface on which the diffraction grooves of second diffraction grating 40B are formed. In an embodiment of the present disclosure, the angle between the first normal and the second normal is preferably in the range of 180 degrees ± 1 degree.

[0056] 8 also includes a second polarization conversion element 50 that changes the polarization state of at least one of the first wavelength combined beam 21 and the second wavelength combined beam 22 to make the polarization directions of the first wavelength combined beam 21 and the second wavelength combined beam 22 orthogonal to each other, and a polarization beam combiner 60 that forms and outputs a third wavelength combined beam 23 by coaxially superimposing the first wavelength combined beam 21 and the second wavelength combined beam 22. In the example of Fig. 8, the polarization beam combiner 60 has the same configuration as the polarization beam splitter 20, but its orientation is rotated by 180 degrees around the Y axis.

[0057] According to the wavelength beam combining device of this embodiment, the diffraction efficiency is increased by using a diffraction grating suitable for the polarization state of the incident light, and the diffracted light generated by the diffraction grating is made coaxial, thereby making it possible to increase the output and power density.

[0058] <Embodiment of a direct diode laser device> Hereinafter, an embodiment of a direct diode laser device will be described with reference to FIG.

[0059] The direct diode laser device 1000 of this embodiment includes a wavelength beam combiner 400, a plurality of semiconductor laser devices 72 each emitting laser light of a different peak wavelength, and an optical fiber array device 70 configured to form a laser beam 10 from the laser light emitted from the plurality of semiconductor laser devices 72, which is incident on the polarization beam splitter 20 of the wavelength beam combiner 400. The laser light emitted from each semiconductor laser device 72 is optically coupled to a corresponding optical fiber 74 of the optical fiber array device 70. Each of the plurality of semiconductor laser devices 72 is configured to oscillate in a single longitudinal mode with a different peak wavelength. Each peak wavelength is, for example, in the range of 430 nm to 480 nm. Even if the laser light emitted from each semiconductor laser device 72 is linearly polarized, if the optical fiber 74 is not a polarization-maintaining fiber, the polarization state of the laser light changes during passage through the optical fiber 74. Therefore, each of the plurality of laser beams 10 formed by the optical fiber array device 70 of this embodiment is unpolarized.

[0060] Examples of the semiconductor laser device 72 that oscillates in a single longitudinal mode include an external cavity laser (ECL) device, a distributed feedback (DFB) laser device, and a distributed Bragg reflector (DBR) laser device.

[0061] By using the optical fiber array device 70, the optical fibers 74 can be aligned, making it easy to adjust the emission angle of the laser beam 10. As a result, it becomes easy to emit, for example, multiple laser beams 10 in parallel with high accuracy from the optical fiber array device 70. The optical fiber array device 70 also makes it possible to connect optical fibers extending from a laser light source to the optical fibers 74 of the optical fiber array device 70 by fusion splicing. The optical fiber array device 70 includes a lens system that collimates the laser light emitted from the tip of each optical fiber 74.

[0062] The wavelength beam combining device 400 in this embodiment includes a polarizing beam splitter 20, similar to the third embodiment. However, the polarizing beam splitter 20 in this embodiment is a plate-type. A plurality of laser beams 10 with different peak wavelengths, which are emitted from the optical fiber array device 70 in a second propagation direction perpendicular to the first propagation direction (F direction), are incident parallel to each other on this plate-type polarizing beam splitter 20. A reflection / transmission surface 20R of the polarizing beam splitter 20 reflects the plurality of first polarized beams 11 in the first propagation direction (F direction) and transmits the plurality of second polarized beams 12. When the polarizing beam splitter 20 is a plate-type, the proportion of the second polarized beams 12 absorbed by the polarizing beam splitter 20 is reduced compared to the polarizing beam splitter 20 in the previous embodiment, thereby suppressing optical energy loss and temperature rise of the polarizing beam splitter 20. As the optical energy of each of the combined laser beams 10 increases, and as the number of combined laser beams 10 increases, it is desirable to minimize heating of optical elements within the device due to absorption of optical energy.

[0063] The wavelength beam combining device 400 includes a mirror 26M that reflects the multiple second polarized beams 12 that have passed through the reflection / transmission surface 20R of the polarization beam splitter 20 in a first traveling direction (F direction). This mirror 26M is also plate-shaped. The multiple second polarized beams 12 reflected by the plate-shaped mirror 26M are converted by a first polarization conversion element 30 into multiple third polarized beams 13 that are linearly polarized in the first polarization direction (Y-axis direction). As in the other embodiments, the first polarization conversion element 30 is, for example, a half-wave plate (half-wave retardation plate). In this embodiment, as in the third embodiment, the multiple first polarized beams 11 and the multiple third polarized beams 13 traveling in the first traveling direction (F direction) are parallel to each other.

[0064] The wavelength beam combining device 400 includes a first diffraction grating 40A disposed at a position to receive the plurality of first polarized beams 11 reflected in the first traveling direction (F direction) by the polarizing beam splitter 20 and the plurality of third polarized beams 13 emitted in the first traveling direction (F direction) from the first polarization conversion element 30, and a second diffraction grating 40B disposed parallel to the first diffraction grating 40A. In this embodiment, each of the first diffraction grating 40A and the second diffraction grating 40B is a transmissive diffraction grating.

[0065] The second diffraction grating 40B includes a first region 41 that receives the reflected and diffracted light of the multiple first polarized beams 11 by the first diffraction grating 40A and outputs a first-wavelength combined beam 21 in the first propagation direction (F direction), and a second region 42 that receives the reflected and diffracted light of the multiple third polarized beams 13 by the first diffraction grating 40A and outputs a second-wavelength combined beam 22 in the first propagation direction (F direction). In the second diffraction grating 40B, the first region 41 and the second region 42 are two elements separated by a gap. The diffraction grooves in each of the first region 41 and the second region 42 are parallel to the first polarization direction (Y-axis direction). The grating pitch of the diffraction grooves in each of the first region 41 and the second region 42 is, for example, not less than 200 nm and not more than 500 nm. When the number of diffraction grooves in each of the first region 41 and the second region 42 is set to, for example, 2,000 to 5,000, the size of each of the first region 41 and the second region 42 (the length in the direction perpendicular to the diffraction grooves) is limited to, for example, 15 mm or less. By reducing the area of ​​the second diffraction grating 40B where the reflected diffracted light from the first diffraction grating 40A converges, when the peak wavelength of the laser beam deviates from the set value, the reflected diffracted light from the first diffraction grating 40A does not hit the first region 41 or the second region 42, thereby suppressing degradation of beam quality. If the beam quality deteriorates, the wavelength-combined beam converged by the condenser lens 80 may irradiate portions other than the core of the optical transmission fiber 90, potentially damaging the optical transmission fiber 90. It is preferable that a light-absorbing member or the like be provided on the back side of the second diffraction grating 40B, and the reflected diffracted light that deviates from the first region 41 or the second region 42 be absorbed by the light-absorbing member.

[0066] The wavelength beam combining device 400 may further include an aperture (pinhole element) 95 for at least one of the first wavelength combined beam 21, the second wavelength combined beam 22, and the third wavelength combined beam 23. For example, by arranging the pinhole element 95 at the position shown in FIG. 9 , it is possible to prevent the third wavelength combined beam 23 converged by the condenser lens 80 from irradiating a portion other than the core of the optical transmission fiber 90 and damaging the optical transmission fiber 90. The pinhole diameter of the pinhole element 95 may be in the range of 1.0 mm to 5 mm, for example. The pinhole element 95 may be provided at a position where it functions as an aperture for the first wavelength combined beam 21, or may be provided at a position where it functions as an aperture for the second wavelength combined beam 22. The number of pinhole elements 95 is not limited to one.

[0067] In this embodiment, the optical elements, such as the polarizing beam splitter 20, mirror 26M, diffraction gratings 40A and 40B, and polarization conversion elements 30 and 50, are all plate-shaped. When the peak wavelength of the laser beam is in the blue band, these optical elements may be formed from a material that does not easily absorb light in the blue band, such as quartz. Making these optical elements thin and integrating them into a predetermined space not only contributes to the miniaturization of the device, but also makes it easier to adjust the temperature of multiple optical elements as a whole.

[0068] The third wavelength combined beam 23 is coupled into an optical transmission fiber 90 by a focusing lens 80. Examples of optical transmission fibers 90 suitable for high-power optical transmission in the blue band include optical fibers with "high-OH-pure silica" cores with a high OH group content, coreless fibers, and photonic crystal fibers.

[0069] It should be noted that the direct diode laser device according to the present disclosure is not limited to the example including the wavelength beam combining device 400 having the configuration shown in FIG. 9, but may include the wavelength beam combining devices 100, 200, 300 in other embodiments, or variations thereof.

[0070] According to the direct diode laser device of this embodiment, even if the polarization state of the laser light emitted from the multiple semiconductor laser devices is depolarized by the optical fiber array device, it is converted to linear polarization by the polarizing beam splitter, so that it is possible to improve the diffraction efficiency by using a diffraction grating suitable for each polarization state. Then, by coaxially aligning the diffracted light generated by such a diffraction grating, it is possible to increase the output and power density.

[0071] <Embodiment of laser processing machine> Next, an embodiment of a laser processing machine 2000 according to the present disclosure will be described with reference to Fig. 10. Fig. 10 is a diagram showing an example of the configuration of the laser processing machine 2000 according to this embodiment.

[0072] The illustrated laser processing machine 2000 includes a light source device 1100 and a processing head 1200 connected to an optical transmission fiber 90 extending from the light source device 1100. The processing head 1200 irradiates an object 1300 with the wavelength-combined beam emitted from the optical transmission fiber 90. In the illustrated example, the number of light source devices 1100 is one. The processing head 1200 may be connected to multiple light source devices 1100 via the optical transmission fiber 90.

[0073] The light source device 1100 is a direct diode laser device having a wavelength beam combining device having the above-described configuration and a plurality of semiconductor laser devices that emit a plurality of laser beams with different peak wavelengths. The wavelength beam combining device included in the light source device 1100 may be any of the various embodiments described above and modified examples of those embodiments. The number of semiconductor laser devices mounted in the light source device 1100 is not particularly limited and is determined according to the required optical output or irradiance. The wavelength of the laser light emitted from the semiconductor laser devices may also be selected according to the material to be processed.

[0074] According to this embodiment, a high-power laser beam is generated by wavelength beam combining and is efficiently coupled to an optical fiber, making it possible to obtain a high-power density laser beam with excellent beam quality and high energy conversion efficiency.

[0075] The laser beam emitted from the processing head 1200 may include laser beams other than the laser beams emitted from the semiconductor laser devices and combined. For example, the peak wavelength of the laser beams emitted from the semiconductor laser devices and combined may be in the range of 430 nm to 480 nm, but a laser beam with a peak wavelength of, for example, near-infrared may be superimposed separately. Depending on the material to be processed, a laser beam with a wavelength that is highly absorbed by the material may be superimposed as appropriate. [Industrial Applicability]

[0076] The wavelength beam combining device, direct diode laser device, and laser processing machine disclosed herein can be widely used in applications requiring high-output, high-power density laser light with high beam quality, such as cutting various materials, drilling, localized heat treatment, surface treatment, metal welding, and 3D printing. [Explanation of symbols]

[0077] 10...laser beam, 20...polarizing beam splitter, 11...first polarized beam, 12...second polarized beam, 13...third polarized beam, 21...first wavelength combined beam, 22...second wavelength combined beam, 23...third wavelength combined beam, 30...first polarization conversion element, 40...diffraction grating, 50...second polarization conversion element, 60...polarized beam combiner, 100...wavelength beam combining device, 200...wavelength beam combining device, 300...wavelength beam combining device, 400...wavelength beam combining device, 1000...direct diode laser device, 2000...laser processing machine

Claims

1. A wavelength beam combining device that combines a plurality of laser beams having different peak wavelengths, the peak wavelength is in the range of 430 nm to 480 nm; a first diffraction grating positioned to receive the plurality of laser beams; a second diffraction grating arranged parallel to the first diffraction grating, receiving reflected and diffracted light of the plurality of laser beams by the first diffraction grating and emitting a wavelength-combined beam; 1. A wavelength beam combining device comprising:

2. A wavelength beam combining device as described in claim 1, wherein the first diffraction grating and the second diffraction grating have the same number N of diffraction grooves per mm.

3. A wavelength beam combining device as described in claim 1 or 2, wherein the number of the multiple laser beams is 10 or more.

4. A wavelength beam combining device described in any one of claims 1 to 3, wherein each of the first diffraction grating and the second diffraction grating is a transmissive diffraction grating.

5. A wavelength beam combining device described in any one of claims 1 to 4, wherein the angle between a first normal to the surface on which the diffraction grooves of the first diffraction grating are formed and a second normal to the surface on which the diffraction grooves of the second diffraction grating are formed is in the range of 180 degrees ± 1 degree.

6. A wavelength beam combining device according to any one of claims 1 to 5; a plurality of semiconductor laser devices each emitting laser light having a different peak wavelength; an optical fiber array device that forms the plurality of laser beams incident on the first diffraction grating from the laser light emitted from the plurality of semiconductor laser devices; A direct diode laser device comprising:

7. A direct diode laser device as described in Claim 6, wherein the optical fiber array device is configured to emit the multiple laser beams parallel to each other.

8. At least one direct diode laser device according to claim 6 or 7; an optical transmission fiber coupled to the wavelength-combined beam emitted from the at least one direct diode laser device; a processing head connected to the optical transmission fiber; A laser processing machine comprising:

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