Wavelength beam coupling device, direct diode laser device, and laser processing 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] This application relates to a wavelength beam combining device, a direct diode laser device, and a laser processing machine.

Background Art

[0002] Processing such as cutting, drilling, and marking on various types of materials, or welding of metal materials, is performed using a high-power and high-brightness laser beam. Conventionally, some of the carbon dioxide laser devices and YAG solid laser devices that have been used for such laser processing are being replaced by fiber laser devices with high energy conversion efficiency. A laser diode (hereinafter simply referred to as LD) is used as the pump light source of the fiber laser device. In recent years, with the increase in the output power of LD, a technology is being developed to use LD not as a pump light source but as a light source of a laser beam for directly irradiating a material for processing. Such a technology is called direct diode laser (DDL) technology.

[0003] Patent Document 1 discloses an example of a light source device that combines (combines) a plurality of laser beams having different wavelengths emitted from a plurality of LDs to increase the optical output. Combining a plurality of laser beams having different wavelengths coaxially is referred to as "wavelength beam combining (WBC)" or "spectral beam combining (SBC)", and can be used, for example, to increase the optical output and brightness of a DDL device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The wavelength beam coupling apparatus of the present disclosure is, in one embodiment, a wavelength beam coupling apparatus for coupling a plurality of laser beams having different peak wavelengths, comprising: a polarization beam splitter that separates the plurality of laser beams into a plurality of first polarization beams linearly polarized in a first polarization direction and a plurality of second polarization beams linearly polarized in a second polarization direction orthogonal to the first polarization direction; a first polarization conversion element that converts the plurality of second polarization beams into a plurality of third polarization beams linearly polarized in the first polarization direction; and a plurality of first polarization beams that diffract the plurality of first polarization beams. The device comprises one or more diffraction gratings that form a first wavelength coupled beam by coaxially superimposing three third polarized beams, and diffract the plurality of third polarized beams to form a second wavelength coupled beam by coaxially superimposing the plurality of third polarized beams; a second polarization conversion element that changes the polarization state of at least one of the first wavelength coupled beam and the second wavelength coupled beam to orthogonalize the polarization directions of the first wavelength coupled beam and the second wavelength coupled beam; and a polarization beam coupler that forms and emits a third wavelength coupled beam by coaxially superimposing the first wavelength coupled beam and the second wavelength coupled beam.

[0007] In one embodiment, the direct diode laser apparatus of the present disclosure comprises the above-described wavelength beam coupling apparatus, a plurality of semiconductor laser apparatuses, each emitting laser light with a different peak wavelength from each other, and an optical fiber array apparatus that forms the plurality of laser beams incident on the polarization beam splitter of the wavelength beam coupling apparatus from the laser light emitted from the plurality of semiconductor laser apparatuses.

[0008] In one embodiment, the laser processing machine of the present disclosure comprises at least one direct diode laser device, an optical transmission fiber coupled to the third wavelength coupled 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] Embodiments of this disclosure provide a wavelength beam coupling device, a direct diode laser device, and a laser processing machine that can further increase the output and power density of laser beams coupled by wavelength beam coupling. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows an example configuration of a first embodiment of the wavelength beam coupling apparatus according to this disclosure. [Figure 2] Figure 2 is a schematic perspective view illustrating an example configuration and function of a polarizing beam splitter. [Figure 3A] Figure 3A is a schematic perspective view showing how a light ray with a peak wavelength λn is incident on a diffraction grating, diffracted, and forms a diffracted light ray. [Figure 3B] Figure 3B is a schematic cross-sectional view showing the main diffracted rays formed when light rays are incident on a transmission-type diffraction grating. [Figure 4A] Figure 4A is a schematic graph showing the spectrum of the first wavelength-coupled beam, which is formed by wavelength coupling of three laser beams with peak wavelengths λ1, λ2, and λ3. [Figure 4B] Figure 4B is a schematic graph showing the spectrum of a second wavelength-coupled beam formed by wavelength coupling of three laser beams with peak wavelengths λ1, λ2, and λ3. [Figure 5] Figure 5 is a schematic graph showing the spectrum of a third-wavelength coupled beam when the number of coupled laser beams is K (where K is an integer greater than or equal to 4). [Figure 6]Figure 6 shows an example configuration of a second embodiment of the wavelength beam coupling apparatus according to this disclosure. [Figure 7] Figure 7 is a side view showing an example configuration of a polarizing beam splitter. [Figure 8] Figure 8 shows an example configuration of a third embodiment of the wavelength beam coupling apparatus according to this disclosure. [Figure 9] Figure 9 shows an example configuration of an embodiment of the direct diode laser apparatus according to the present disclosure. [Figure 10] Figure 10 shows an example configuration of an embodiment of the laser processing machine according to this disclosure. [Modes for carrying out the invention]

[0011] <First Embodiment of Wavelength Beam Coupling Device> A first embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figure 1. For reference, the accompanying drawings, including Figure 1, schematically show mutually orthogonal X, Y, and Z axes.

[0012] The wavelength beam coupling apparatus 100 of this embodiment, shown in Figure 1, can couple multiple laser beams 10 with different peak wavelengths. For simplicity, Figure 1 shows an example configuration of an apparatus that coaxially couples three laser beams 10 with peak wavelengths λ1, λ2, and λ3. The number of laser beams 10 to be coupled is not limited to three; two or four or more laser beams 10 with different peak wavelengths may be coupled. Hereinafter, the peak wavelength of the multiple laser beams 10 to be coupled may be denoted as λn. Here, "n" is an integer of 1 or more and is used as a numerical value to distinguish (specify) each of the multiple laser beams 10. In the illustrated example, the relationship λ1 < λ2 < λ3 holds. The unit of the peak wavelength λn is arbitrary, but for example, it is nanometers (nm).

[0013] In FIG. 1, a plurality of laser beams 10 are each shown as simple straight lines. The actual laser beam 10 is an optical beam having an intensity distribution in a plane orthogonal to the traveling direction. This intensity distribution can be approximated by a distribution function such as a Gaussian distribution in a plane orthogonal to the traveling direction of the optical beam. The diameter of the optical beam is defined, for example, by the size of a cross-sectional area having an intensity of 1 / e 2 times or more with respect to the intensity at the beam center. In the present disclosure, the laser beam 10 is collimated by an optical system such as a collimator lens. In the drawings, in order to schematically show the traveling direction of the collimated optical beam such as the laser beam 10, the central axis of each optical beam is represented by a straight line. These straight lines may be considered to indicate the rays passing through the center of each optical beam.

[0014] The wavelength beam coupling device 100 includes a polarizing beam splitter 20 into which multiple laser beams 10 are incident. The polarizing beam splitter 20 has a reflective / transmitting surface 20R with different transmittance and reflectance 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 vibrates in a direction perpendicular to the direction of propagation. 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 experience changes in polarization state or depolarization while passing through a transmission medium such as an optical fiber. The reflective / transmitting surface 20R of the polarizing beam splitter 20 can selectively reflect polarization components linearly polarized in a predetermined direction and transmit polarization components linearly polarized in a direction perpendicular to that predetermined direction. For example, a dielectric multilayer film having polarization dependence is provided on the reflective / transmitting surface 20R. In the example shown in Figure 1, the polarization beam splitter 20 separates the laser beam 10 traveling in the Z-axis direction into multiple first polarization beams 11 linearly polarized in a first polarization direction (Y-axis direction) and multiple second polarization beams 12 linearly polarized in a second polarization direction (X-axis direction) perpendicular to the first polarization direction. Note that the multiple laser beams 10 do not need to be parallel to each other when incident on the polarization beam splitter 20. In the example shown in Figure 1, the directions of travel 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 beam is incident on the surface of an object, the plane containing the normal to the object surface at the point of incidence and the propagation direction vector (wave vector) of the light beam is defined as the "plane of incidence". Also, 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 polarization beam splitter 20 is perpendicular to the XZ plane, and the normal to the reflection / transmission surface 20R is within a plane parallel to the XZ plane. Also, 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 the present disclosure, light linearly polarized in the first polarization direction, which is a direction perpendicular to the XZ plane, is referred to as "S-polarized light". And light linearly polarized in a direction parallel to the XZ plane (second polarization direction orthogonal to the first polarization direction) is called "P-polarized light". In the accompanying drawings, "S-polarized light" is indicated by a symbol in which a small circle encloses a cross symbol, and "P-polarized light" is indicated by a symbol with arrowheads at both ends. The polarization direction of "P-polarized light" is parallel to the XZ plane, but since it is perpendicular to the propagation direction of the laser beam, when the propagation direction of the laser beam remains parallel to the XZ plane and rotates due to reflection or diffraction, the polarization direction of "P-polarized light" also rotates within a plane parallel to the XZ plane. Therefore, in the present disclosure, the "second polarization direction" is defined as a direction perpendicular to the propagation direction of the laser beam and perpendicular to the first polarization direction.

[0016] FIG. 2 is a perspective view schematically showing a configuration example and functions of the polarization beam splitter 20. In the example of FIG. 2, a laser beam 10 including S-polarized light and P-polarized light travels in the positive direction of the Z axis and is incident on the polarization beam splitter 20. The polarization state of the laser beam 10 including S-polarized light and P-polarized light is, for example, in a state of "unpolarized light" in which S-polarized light and P-polarized light are randomly mixed. In the present disclosure, "unpolarized light" means light that is not linearly polarized in a predetermined direction. Therefore, in this broad sense of "unpolarized light", circularly polarized light and elliptically polarized light may also be included. Also, a mixed state of linearly polarized light in which the polarization direction changes randomly or regularly depending on time or location is also included in "unpolarized light".

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

[0018] A key aspect of this disclosure is the separation of reflected and transmitted light whose polarization directions are mutually orthogonal (polarization separation) by the reflective / transmitting surface 20R of the polarizing beam splitter 20. If the laser beam 10 consists only of S-polarized light, a first-polarized (S-polarized) beam 11 is formed from the laser beam 10, but a second-polarized (P-polarized) beam 12 is not formed. Conversely, if the laser beam 10 consists only of P-polarized light, a first-polarized (S-polarized) beam 11 is not formed from the laser beam 10, and only a second-polarized (P-polarized) beam 12 is formed.

[0019] If the multiple laser beams 10 incident on the polarization beam splitter 20 are "unpolarized," the laser beams 10 are separated 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). However, even if the laser beam 10 is linearly polarized in a superposition state of S-polarization and P-polarization, if its polarization direction is not parallel to either the X-axis or Y-axis in Figure 2, the first-polarized (S-polarized) beams 11 and the second-polarized (P-polarized) beams 12 can be formed from such a laser beam 10. Furthermore, even if each of the multiple laser beams 10 incident on the polarization beam splitter 20 is linearly polarized in a different direction, these multiple laser beams 10 can be separated 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, if all of the "multiple" laser beams 10 incident on the polarizing beam splitter 20 are not linearly polarized and aligned in the direction of one of the X and Y axes in Figure 2, polarization separation by the polarizing beam splitter 20 is achieved, and the multiple laser beams 10 as a whole are interpreted as "unpolarized".

[0020] Although Figure 2 shows a prism-type polarizing beam splitter 20, the type of polarizing beam splitter 20 is not limited to this example and may be cube-shaped, plate-shaped, or of other types. In the example in Figure 2, the first polarized (S-polarized) beam 11 reflected by the reflective / transmitting surface 20R of the polarizing beam splitter 20 travels in the first direction of propagation F indicated by the white arrow. On the other hand, the second polarized (P-polarized) beam 12 transmitted through the reflective / transmitting surface 20R of the polarizing beam splitter 20 travels in the positive direction of the Z axis. However, the respective directions of propagation of these first polarized (S-polarized) beam 11 and second polarized (P-polarized) beam 12 can be changed by optical elements such as mirrors.

[0021] Refer to Figure 1 again. The wavelength beam coupling device 100 includes a first polarization conversion element 30 that converts a plurality of second polarization (P-polarized) beams 12 into a plurality of third polarization (S-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 phase difference plate). A half-wave plate has birefringence and changes the phase difference in two orthogonal components of an electromagnetic wave propagating in the thickness direction. By arranging the slow-phase axis or fast-phase axis of the half-wave plate to form an angle of 45° with respect to the polarization direction of the second polarization (P-polarized) beam 12, the half-wave plate becomes capable of converting P-polarized to S-polarized.

[0022] Thus, the wavelength beam coupling device 100 in this embodiment can form a plurality of first polarized beams 11 and a plurality of third polarized beams 13 linearly polarized in a specific direction from a plurality of laser beams 10 that are, for example, unpolarized as a whole. At this stage, the plurality of first polarized beams 11 are composed of a plurality of laser beams with different peak wavelengths and that are not coaxially coupled. Similarly, the plurality of third polarized beams 13 are also composed of a plurality of laser beams with different peak wavelengths and that 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 a wavelength is not formed at all peak wavelengths, and the S-polarized light converted from P-polarized light retains a P-polarized component. For this reason, the multiple third-polarized (S-polarized) beams 13 emitted from the first polarization conversion element 30 retain a P-polarized component and may, strictly speaking, contain elliptic polarization. However, if all of the multiple peak wavelengths λn are within a relatively narrow range, for example, a range of 10 nm or less, the difference in phase difference due to the half-wave plate (wavelength dispersion) is sufficiently small. For this reason, in the embodiments of this disclosure, the third-polarized beam 13 may mainly contain an S-polarized component and partially contain a P-polarized component.

[0024] The wavelength beam coupling device 100 in Figure 1 further comprises two diffraction gratings 40 for coaxializing these multiple first-polarized (S-polarized) beams 11 and multiple third-polarized (S-polarized) beams 13, respectively. One of the two diffraction gratings 40 is configured to diffract the multiple first-polarized beams 11 to form a first wavelength coupled beam 21 by coaxially superimposing the multiple first-polarized beams 11, while the other is configured to diffract the multiple third-polarized beams 13 to form a second wavelength coupled beam 22 by coaxially superimposing the multiple third-polarized beams 13.

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

[0026] Figure 3A is a schematic perspective view showing how a light ray 14A with a peak wavelength λn is incident on a diffraction grating 40 and diffracted to form a diffracted light ray 14B. Let αn be the angle of incidence of the light ray 14A. The "n" in the angle of incidence αn is the same integer as the "n" in the peak wavelength λn. The angle of incidence αn is the angle formed between the light ray 14A with a peak wavelength λn and the normal direction N of the diffraction plane of the diffraction grating 40. Numerous diffraction grooves are provided on the surface of the diffraction grating 40. A hypothetical plane 44 is shown in Figure 3A. This plane 44 is a plane that contains the light ray 14A incident on the diffraction grating 40 and the diffracted light ray 14B emitted from the diffraction grating 40, and is perpendicular to the diffraction grooves. Since diffraction is the change in the angle between the light ray 14A and the diffracted light ray 14B within the plane 40 according to the wavelength (dispersion), the direction in which the plane 40 expands may be called the "direction of dispersion".

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

[0028] For example, if the diffraction order m is 1 and the diffraction angle β is 45.0 degrees, then if 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 becomes possible to diffract multiple laser beams with different peak wavelengths λn in the same diffraction angle β direction.

[0029] Figure 3B is a schematic cross-sectional view showing the main diffracted rays formed when a light ray I is incident on a transmissive diffraction grating 40. Figure 3B shows the reflected zero-order diffracted ray R-0, the reflected first-order diffracted ray R-1, the transmitted zero-order diffracted ray T-0, and the transmitted first-order diffracted ray T-1 formed by the diffraction grating 40. Even though it is a transmissive diffraction grating, the diffraction grating 40 used in this embodiment is configured to selectively and strongly generate the reflected first-order diffracted ray R-1. Therefore, the reflected zero-order diffracted ray R-0, the transmitted zero-order diffracted ray T-0, and the transmitted first-order diffracted ray T-1 generated by the transmissive diffraction grating 40 can be ignored. As a result, most of the laser beam incident on the diffraction grating is not absorbed by the material constituting the diffraction grating 40, and light loss is suppressed. Unlike transmissive diffraction gratings, reflective diffraction gratings are equipped with reflective components (dielectric multilayer films or mirrors), and the light absorption by these components cannot be ignored. Therefore, with reflective diffraction gratings, if the intensity of the incident laser beam increases, the heat generated by light absorption may degrade the performance of the diffraction grating. For this reason, it is desirable to use a transmissive diffraction grating in the embodiments of this disclosure. The substrate of the diffraction grating 40 may be formed from a material with low absorptivity at the peak wavelength of the laser beam, such as quartz. The shape of the grating cross-section is, for example, rectangular or trapezoidal.

[0030] Furthermore, a light-absorbing member may be provided on the inner surface of the housing that accommodates the components of the wavelength beam coupling device 100. The light-absorbing member absorbs diffracted light rays other than the reflected first-order diffracted light ray R-1, thereby suppressing the generation of stray light.

[0031] Next, refer again to Figure 1. In the embodiments of this disclosure, the incident angles (αn) of a plurality of first polarized beams 11 incident on the left diffraction grating 40 are determined to satisfy Equation 1 according to the wavelengths λn (=λ1, λ2, λ3). Similarly, the incident angles (αn) of a plurality of third polarized beams 13 incident on the right diffraction grating 40 are determined to satisfy Equation 1 according to the wavelengths λn (=λ1, λ2, λ3). In this way, a first wavelength coupled beam 21 and a second wavelength coupled beam 22 can be generated that are coaxially aligned so that their diffraction angles (β) are equal. The respective diameters (beam diameters) of the first polarized beams 11 and the third polarized beams 13 on the surface of the diffraction grating 40 where the diffraction grooves are formed are, for example, in the range of 0.5 mm to 10 mm.

[0032] In this embodiment, the laser beam incident on the diffraction grating 40 is a first polarized beam 11 with S polarization and a third polarized beam 13 with S polarization. If the diffraction grating 40 is polarization-dependent, the diffraction efficiency will decrease depending on the polarization component when an unpolarized laser beam is incident on it. 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 in which the diffraction efficiency for S polarization is higher than the diffraction efficiency for P polarization, optical loss in the diffraction grating 40 can be suppressed.

[0033] Furthermore, when the laser beam 10 has a spectral width Δλn with the peak wavelength λn approximately centered, it is preferable that this spectral width Δλn be small. If the spectral width Δλn is wide, the diffraction angle β will have a large width. A large diffraction angle β gives width to the propagation direction of the first wavelength coupled beam 21 and the second wavelength coupled beam 22. The spectral width Δλn is set to, for example, 0.3 nm or less. By coupling multiple laser beams 10 with narrow spectral widths Δλn, it becomes possible to generate a wavelength-coupled beam that includes multiple peak wavelengths in a desired wavelength range, thereby efficiently increasing its optical output. In applications such as processing and welding metals such as Cu, for example, the multiple peak wavelengths may be included in the range from 430 nm to 480 nm. Also, the number of multiple laser beams 10 may be 10 or more.

[0034] The wavelength beam coupling device 100 further comprises a second polarization conversion element 50 and a polarization beam coupler 60. The second polarization conversion element 50 is configured to change the polarization state of at least one of the first wavelength coupled beam 21 and the second wavelength coupled beam 22 so that the polarization directions of the first wavelength coupled beam 21 and the second wavelength coupled beam 22 are orthogonal. The second polarization conversion element 50 is, like the first polarization conversion element 30, for example, a half-wave plate (half-wave phase difference plate). In the example in Figure 1, the second polarization conversion element 50 is positioned to rotate the polarization direction of the second wavelength coupled beam 22 by 90 degrees. The second wavelength coupled 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 coupled beam 21 by 90 degrees.

[0035] The polarization beam coupler 60 is configured to form and emit a third wavelength coupled beam 23 by coaxially superimposing a first wavelength coupled beam 21 and a second wavelength coupled beam 22. The polarization beam coupler 60 may have a configuration similar to that of the polarization beam splitter 20. In general, a polarization beam splitter can also be used as a polarization beam coupler. In the example in Figure 1, the first wavelength coupled beam 21 is S-polarized, and the second wavelength coupled beam 22 transmitted through the second polarization conversion element 50 is P-polarized. The polarization beam coupler 60 has a reflective / transmitting surface 60R that reflects S-polarized light and transmits P-polarized light. As a result, the polarization beam coupler 60 can emit a third wavelength coupled beam 23 in which the first wavelength coupled beam 21, which is S-polarized, and the second wavelength coupled beam 22, which is P-polarized, are coaxially superimposed.

[0036] The third wavelength coupled beam 23 is a laser beam formed by wavelength coupling of three laser beams 10, each with peak wavelengths λ1, λ2, and λ3. Thus, the wavelength beam coupling device 100 makes it possible to increase the output and power density of the wavelength-coupled laser beam. As the number of coupled laser beams 10 increases, the output and power density of the third wavelength coupled beam 23 can increase proportionally.

[0037] Conversely to the above example, it is also possible to reflect the second polarized (P-polarized) beam 12 in the first propagation direction F at the reflection / transmission surface 20R of the polarizing beam splitter 20, and transmit the first polarized (S-polarized) beam 11 in the positive direction of the Z axis. In this case, the first polarization conversion element 30 is positioned to transmit multiple second polarized (P-polarized) beams 12, and converts 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] Figure 4A is a schematic graph showing the spectrum of the first wavelength-coupled beam 21, which is formed by wavelength-coupled three laser beams 10 with peak wavelengths λ1, λ2, and λ3. The vertical axis of the graph represents light intensity, and the horizontal axis represents wavelength. Figure 4B is a schematic graph showing the spectrum of the second wavelength-coupled beam 22, which is formed by wavelength-coupled three laser beams 10 with peak wavelengths λ1, λ2, and λ3. The vertical axis of the graph represents light intensity, and the horizontal axis represents wavelength. The light intensity of the third wavelength-coupled beam 23, in which the first wavelength-coupled beam 21 and the second wavelength-coupled beam 22 are coaxially superimposed, is equal to the sum of the light intensities shown in Figure 4A and Figure 4B, provided that optical losses due to the polarizing beam coupler 60 are ignored.

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

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

[0041] <Second Embodiment of Wavelength Beam Coupling Device> Next, a second embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figures 6 and 7.

[0042] The wavelength beam coupling device 200 of this embodiment, shown in Figure 6, can couple multiple laser beams 10 having different peak wavelengths, similar to the first embodiment.

[0043] The wavelength beam coupling device 200 in Figure 6 includes a polarization beam splitter 20 that separates multiple laser beams 10 with different peak wavelengths into multiple first polarization beams 11 linearly polarized in a first polarization direction (Y-axis direction) and multiple second polarization beams 12 linearly polarized in a second polarization direction (direction in the XZ plane) perpendicular to the first polarization direction. As shown in detail in Figure 7, the polarization beam splitter 20 has a reflective / transmitting surface 20R that separates the incident laser beam 10 into a first polarization (S-polarized) beam 11 and a second polarization (P-polarized) beam 12, and a mirror 26M that reflects the second polarization (P-polarized) beam 12 in the first propagation direction (F direction). In this example, a transparent member with a parallelogram cross-section is fixed to a transparent prism with a triangular cross-section via the reflective / transmitting surface 20R. The mirror 26M is fixed to the slanted surface of the transparent member with a parallelogram cross-section.

[0044] Multiple second polarized beams 12 reflected by 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).

[0045] In the wavelength beam coupling apparatus 200 shown in Figure 6, one diffraction grating 40 is arranged to diffract multiple first polarized beams 11 to form a first wavelength coupled beam 21 by coaxially superimposing multiple first polarized beams 11, and to diffract multiple third polarized beams 13 to form a second wavelength coupled beam 22 by coaxially superimposing multiple third polarized beams 13. The positions on the diffraction grating 40 into which the multiple first polarized beams 11 are incident are different from the positions on the diffraction grating 40 into which the multiple third polarized beams 13 are incident. For this reason, the diffraction grating 40 in Figure 6 may be separated into a first diffraction grating into which the multiple first polarized beams 11 are incident and a second diffraction grating into which the multiple third polarized beams 13 are incident. When the overall output of the multiple laser beams 10 increases, the temperature of the diffraction grating 40 into which they are incident rises locally, which can result in deformation of the diffraction grating 40 due to thermal expansion. Such deformation can lead to a decrease in diffraction efficiency and degrade the performance of the diffraction grating 40. In this embodiment, even when using a single diffraction grating 40, the polarization beams are directed to different regions of the diffraction grating 40 separately. Therefore, even if the overall output of the multiple laser beams 10 increases, the aforementioned performance degradation of the diffraction grating 40 can be suppressed.

[0046] The wavelength beam coupling device 200 in Figure 6 also includes a second polarization conversion element 50 that changes the polarization state of at least one of the first wavelength coupled beam 21 and the second wavelength coupled beam 22 to orthogonalize the polarization directions of the first wavelength coupled beam 21 and the second wavelength coupled beam 22, and a polarization beam coupler 60 that forms and emits a third wavelength coupled beam 23 by coaxially superimposing the first wavelength coupled beam 21 and the second wavelength coupled beam 22.

[0047] In this embodiment, the polarizing beam coupler 60 has the same configuration as the polarizing beam splitter 20, but its orientation is rotated by 90 degrees around the Y-axis. In this example, a mirror 60M fixed to the polarizing beam coupler 60 reflects the second wavelength coupled beam 22, enabling the coaxial superposition of the first wavelength coupled beam 21 and the second wavelength coupled beam 22.

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

[0049] <Third Embodiment of Wavelength Beam Coupling Device> Next, a third embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figure 8.

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

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

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

[0053] The structures of the first diffraction grating 40A and the second diffraction grating 40B are designed based on the aforementioned Equation 1. More specifically, the first diffraction grating 40A and the second diffraction grating 40B have the same number of diffraction grooves N per 1 mm and are arranged parallel to each other. The first diffraction grating 40A is arranged so that multiple first polarized beams 11 and multiple third polarized beams 13 are all incident at an incident angle α (e.g., 45 degrees). The first diffraction grating 40A is configured to diffract multiple first polarized beams 11 and multiple third polarized beams 13 incident in parallel at the same incident angle α at different diffraction angles βn depending on their respective peak wavelengths λn, and to incident them at predetermined positions on the opposing second diffraction grating 40B. The second diffraction grating 40B, having the same structure as the first diffraction grating 40A, is configured to emit reflected diffracted light from the first diffraction grating 40A, which is incident at different incident angles βn depending on its peak wavelength λn, at the same diffraction angle α (e.g., 45 degrees). In this way, the pair of diffraction gratings 40A and 40B enable the coaxially coupled first wavelength beam 21 and the coaxially coupled second wavelength beam 22 to be emitted in the first propagation 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, sharing the plane 44 shown in Figure 3A. In this case, the angle of incidence to the first diffraction grating 40A and the diffraction angle from the second diffraction grating 40B are the same. Since this relationship is maintained regardless of wavelength, even if the wavelengths of multiple laser beams fluctuate, it is possible to keep the diffraction angle from the second diffraction grating 40B constant, making it easier to focus the beam onto the optical fiber.

[0055] The parallelism between the first diffraction grating 40A and the second diffraction grating 40B is evaluated by the angle between the first normal to the surface on which the diffraction grooves of the first diffraction grating 40A are formed and the second normal to the surface on which the diffraction grooves of the second diffraction grating 40B are formed. In the embodiments of this disclosure, it is desirable that the angle between these first and second normals be in the range of 180 degrees ± 1 degree.

[0056] The wavelength beam coupling device 300 in Figure 8 also includes a second polarization conversion element 50 that changes the polarization state of at least one of the first wavelength coupled beam 21 and the second wavelength coupled beam 22 to orthogonalize the polarization directions of the first wavelength coupled beam 21 and the second wavelength coupled beam 22, and a polarization beam coupler 60 that forms and emits a third wavelength coupled beam 23 by coaxially superimposing the first wavelength coupled beam 21 and the second wavelength coupled beam 22. In the example in Figure 8, the polarization beam coupler 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 coupling device of this embodiment, by using a diffraction grating suitable for the polarization state of the incident light to increase diffraction efficiency and by coaxializing the diffracted light generated by the diffraction grating, it is possible to increase output and power density.

[0058] <Embodiment of a Direct Diode Laser Device> The following describes an embodiment of the direct diode laser apparatus with reference to Figure 9.

[0059] The direct diode laser apparatus 1000 in this embodiment comprises a wavelength beam coupling device 400, a plurality of semiconductor laser devices 72, each emitting laser light with a different peak wavelength, and an optical fiber array device 70 configured to form a laser beam 10 incident on a polarization beam splitter 20 of the wavelength beam coupling device 400 from the laser light emitted from the plurality of semiconductor laser devices 72. The laser light emitted from each semiconductor laser device 72 is optically coupled to the 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-retaining fiber, the polarization state of the laser light changes as it passes through the optical fiber 74. For this reason, each of the plurality of laser beams 10 formed by the optical fiber array device 70 in this embodiment is unpolarized.

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

[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 multiple laser beams 10 from the optical fiber array device 70 in parallel with high accuracy. With the optical fiber array device 70, optical fibers extending from the laser light source can also be fused and connected to the optical fibers 74 of the optical fiber array device 70. The optical fiber array device 70 is equipped with a lens system that collimates the laser light emitted from the tip of each optical fiber 74.

[0062] The wavelength beam coupling 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 of the plate type. Multiple laser beams 10 with different peak wavelengths, emitted from the optical fiber array device 70 parallel to a second propagation direction perpendicular to the first propagation direction (F direction), are incident on this plate-type polarizing beam splitter 20 in parallel with each other. The reflection / transmission surface 20R of the polarizing beam splitter 20 reflects the multiple first polarizing beams 11 in the first propagation direction (F direction) and transmits the multiple second polarizing beams 12. When the polarizing beam splitter 20 is of the plate type, the proportion of the second polarizing beams 12 absorbed by the polarizing beam splitter 20 is reduced compared to the polarizing beam splitter 20 in the above-described embodiment, thus suppressing the loss of optical energy and also suppressing the temperature rise of the polarizing beam splitter 20. As the light energy of each of the combined laser beams 10 increases, and as the number of combined laser beams 10 increases, it is desirable to suppress, as much as possible, the heating of optical elements due to the absorption of light energy within the device.

[0063] The wavelength beam coupling 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 polarized beam splitter 20 in the first propagation direction (F direction). This mirror 26M is also of plate type. The multiple second polarized beams 12 reflected by the plate-type 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, as in other embodiments, for example, a half-wave plate (half-wave phase difference plate). In this embodiment as in the third embodiment, the multiple first polarized beams 11 and the multiple third polarized beams 13 propagating in the first propagation direction (F direction) are parallel to each other.

[0064] The wavelength beam coupling device 400 includes a first diffraction grating 40A positioned to receive a plurality of first polarized beams 11 reflected in the first direction of propagation (direction F) by the polarizing beam splitter 20, and a plurality of third polarized beams 13 emitted from the first polarization conversion element 30 in the first direction of propagation (direction F), and a second diffraction grating 40B positioned 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 transmission type diffraction grating.

[0065] The second diffraction grating 40B includes a first region 41 that receives reflected diffracted light from the first diffraction grating 40A of multiple first polarized beams 11 and emits a first wavelength coupled beam 21 in the first propagation direction (F direction), and a second region 42 that receives reflected diffracted light from the first diffraction grating 40A of multiple third polarized beams 13 and emits a second wavelength coupled 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, 200 nm or more and 500 nm or less. If the number of diffraction grooves in the first region 41 and the second region 42 is set to, for example, 2000 to 5000, the size of the first region 41 and the second region 42 (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 reflected diffracted light from the first diffraction grating 40A converges, if the peak wavelength of the laser beam deviates from the set value, the reflected diffracted light from the first diffraction grating 40A will not hit the first region 41 and the second region 42, and as a result, the deterioration of beam quality is suppressed. If the beam quality deteriorates, the wavelength-coupled beam focused by the focusing lens 80 may irradiate parts of the optical transmission fiber 90 other than the core, potentially damaging the optical transmission fiber 90. It is desirable that a light-absorbing member or the like is provided on the back side of the second diffraction grating 40B to absorb the reflected diffracted light that deviates from the first region 41 and the second region 42.

[0066] The wavelength beam coupling device 400 may further include an aperture (pinhole element) 95 for at least one of the first wavelength coupled beam 21, the second wavelength coupled beam 22, and the third wavelength coupled beam 23. For example, by arranging the pinhole element 95 in the position shown in Figure 9, it is possible to suppress the third wavelength coupled beam 23, which has been focused by the focusing lens 80, from irradiating parts of the optical transmission fiber 90 other than the core and damaging the optical transmission fiber 90. The pinhole diameter of the pinhole element 95 may be, for example, in the range of 1.0 mm to 5 mm. The pinhole element 95 may be provided in a position that functions as an aperture for the first wavelength coupled beam 21, or in a position that functions as an aperture for the second wavelength coupled beam 22. The number of pinhole elements 95 is not limited to one.

[0067] In this embodiment, 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-type. When the peak wavelength of the laser beam is included in the blue band, these optical elements can be formed from a material that does not easily absorb blue band light, such as quartz. Integrating these optical elements into a predetermined space by making them thin not only contributes to miniaturization of the device but also facilitates the overall temperature adjustment of multiple optical elements.

[0068] The third wavelength coupled beam 23 is coupled to the 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 a "high OH-pure silica" core with a high OH group content, coreless fibers, and photonic crystal fibers.

[0069] Furthermore, the direct diode laser apparatus according to this disclosure is not limited to the example comprising a wavelength beam coupling apparatus 400 having the configuration shown in Figure 9, but may also comprise wavelength beam coupling apparatuses 100, 200, 300 in other embodiments, or modified versions thereof.

[0070] According to the direct diode laser apparatus of this embodiment, even if the polarization state of laser light emitted from multiple semiconductor laser devices becomes unpolarized by the optical fiber array apparatus, it is converted to linear polarization by the polarization beam splitter. This makes it possible to increase diffraction efficiency by using diffraction gratings suitable for each polarization state. Furthermore, by coaxializing the diffracted light generated by such diffraction gratings, it becomes possible to increase output and power density.

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

[0072] The illustrated laser processing machine 2000 comprises 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 the object 1300 with a wavelength-coupled beam emitted from the optical transmission fiber 90. In the illustrated example, there is one light source device 1100. 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 coupling device having the configuration described above, and a plurality of semiconductor laser devices that emit a plurality of laser beams with different peak wavelengths. The wavelength beam coupling device included in the light source device 1100 may be one of the various embodiments described above, or a variation thereof. The number of semiconductor laser devices mounted on 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 coupling and 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] Furthermore, the laser beam emitted from the processing head 1200 may include laser beams other than the laser beam emitted from and coupled to the semiconductor laser device. For example, the peak wavelength of the laser beam emitted from and wavelength-coupled to the semiconductor laser device is in the range of 430 nm to 480 nm, but separately, a laser beam with a peak wavelength in the near-infrared region may be superimposed. Depending on the material to be processed, a laser beam with a wavelength that has a high absorption rate for that material may be superimposed as appropriate. [Industrial applicability]

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

[0077] 10... Laser beam, 20... Polarizing beam splitter, 11... First polarizing beam, 12... Second polarizing beam, 13... Third polarizing beam, 21... First wavelength coupled beam, 22... Second wavelength coupled beam, 23... Third wavelength coupled beam, 30... First polarization conversion element, 40... Diffraction grating, 50... Second polarization conversion element, 60... Polarizing beam coupler, 100... Wavelength beam coupling device, 200... Wavelength beam coupling device, 300... Wavelength beam coupling device, 400... Wavelength beam coupling device, 1000... Direct diode laser device, 2000... Laser processing machine

Claims

1. A wavelength beam coupling device that combines multiple laser beams with different peak wavelengths, The peak wavelength is in the range of 430 nm to 480 nm. A first diffraction grating is positioned to receive the plurality of laser beams, A second diffraction grating is positioned parallel to the first diffraction grating and emits a wavelength-coupled beam by receiving reflected diffracted light from the first diffraction grating of the plurality of laser beams, A wavelength beam coupling device equipped with the following features.

2. The wavelength beam coupling apparatus according to claim 1, wherein the first diffraction grating and the second diffraction grating have the same number of diffraction grooves N per 1 mm.

3. The wavelength beam coupling apparatus according to claim 1 or 2, wherein the number of the plurality of laser beams is 10 or more.

4. The wavelength beam coupling apparatus according to any one of claims 1 to 3, wherein each of the first diffraction grating and the second diffraction grating is a transmission type diffraction grating.

5. The wavelength beam coupling apparatus according to any one of claims 1 to 4, wherein the angle between the first normal to the surface on which the diffraction grooves of the first diffraction grating are formed and the 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 coupling apparatus according to any one of claims 1 to 5, Multiple semiconductor laser devices, each emitting laser light with 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 equipped with the following features.

7. The direct diode laser apparatus according to claim 6, wherein the optical fiber array apparatus is configured to emit the plurality of laser beams parallel to each other.

8. At least one direct diode laser apparatus according to claim 6 or 7, An optical transmission fiber coupled to the wavelength-coupled beam emitted from the at least one direct diode laser device, A processing head connected to the aforementioned optical transmission fiber, A laser processing machine equipped with the following features.

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