Wavelength beam coupling device, direct diode laser device, and laser processing machine

Abstract

To improve the coupling efficiency when coupling a wavelength-coupled beam into an optical transmission fiber. [Solution] The wavelength beam coupling device couples multiple laser beams emitted from a laser light source, each having different peak wavelengths, and arranged in a second direction where the central axes of the beams emitted in a first direction intersect with respect to the first direction. The wavelength beam coupling device comprises first and second diffraction gratings, the first diffraction grating being positioned to receive multiple laser beams and diffracting the multiple laser beams in different directions according to their wavelengths and causing them to be incident on the second diffraction grating, the second diffraction grating further diffracting the multiple laser beams diffracted by the first diffraction grating to form a wavelength-coupled beam, and emitting the wavelength-coupled beam in the first direction, and an optical coupling unit for coupling the wavelength-coupled beam into an optical transmission fiber, the optical coupling unit being configured to be movable in the second direction.

Description

Technical Field

[0001] The present disclosure 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 various types of materials, or welding 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 a pump light source for 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 for a laser beam that directly irradiates a material for processing. Such a technology is called direct diode laser (DDL) technology.

[0003] Patent Document 1 describes a multi-wavelength beam combiner including a laser stack having a plurality of laser arrays that emit light beams having respective unique wavelengths, a cylindrical telescope, a conversion lens that blocks the light beams from each of the plurality of laser arrays and combines the light beams along the stacking dimension of the laser stack to form a multi-wavelength light beam, and a diffraction element located in the overlapping region of the light beams. 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.

[0004] Patent Document 2 describes a laser oscillator comprising multiple laser modules that emit laser light. The laser oscillator has a Peltier control unit that individually controls the temperature of each of the multiple laser modules. The temperature control by the Peltier control unit shifts the wavelength of the laser light emitted from the laser modules. This matches the lock wavelength with the gain wavelength, and as a result, the maximum gain at the lock wavelength of the laser module can be obtained, making it possible to increase the laser output. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2012-508453 [Patent Document 2] Japanese Patent Publication No. 2021-158302 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention provides a wavelength beam coupling device, a direct diode laser device, and a laser processing machine capable of improving the coupling efficiency when coupling a wavelength-coupled beam into an optical transmission fiber. [Means for solving the problem]

[0007] The wavelength beam coupling apparatus of the present disclosure, in one embodiment, couples a plurality of laser beams emitted from a laser light source, having different peak wavelengths, and arranged in a second direction such that the central axes of the beams emitted in a first direction intersect the first direction, comprising a first diffraction grating and a second diffraction grating, wherein the first diffraction grating is positioned to receive the plurality of laser beams, and diffracts the plurality of laser beams in different directions according to their wavelengths and causes them to be incident on the second diffraction grating, and the second diffraction grating is in the same position as the first diffraction grating The device comprises a first diffraction grating and a second diffraction grating that further diffract the plurality of diffracted laser beams to form a wavelength-coupled beam and emit the wavelength-coupled beam in the first direction, and an optical coupling unit that couples the wavelength-coupled beam into an optical transmission fiber, the optical coupling unit being configured to be movable in the second direction.

[0008] 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 beams with different peak wavelengths, and an optical fiber array that forms the plurality of laser beams incident on the collimator of the wavelength beam coupling apparatus from the plurality of laser beams emitted from the plurality of semiconductor laser apparatuses.

[0009] The laser processing machine of this disclosure comprises at least one direct diode laser device, an optical transmission fiber coupled to the 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]

[0010] According to embodiments of this disclosure, a wavelength beam coupling device, a direct diode laser device, and a laser processing machine are provided that can improve the coupling efficiency when coupling a wavelength-coupled beam to an optical transmission fiber. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic plan view, seen from a direction perpendicular to the XZ plane, illustrating an example of a device configuration that coaxially couples multiple laser beams with different peak wavelengths. [Figure 2] Figure 2 is a schematic diagram showing the incident angle α of the laser beam incident on the diffraction grating shown in Figure 1 and the diffraction angle β of the reflected diffracted light. [Figure 3A]Figure 3A is a graph illustrating the gain spectrum and output spectrum of an external resonant LD in a state where the lock wavelength and gain peak are matched. [Figure 3B] Figure 3B is a graph illustrating the gain spectrum and output spectrum of an external resonant LD, showing a state where the gain spectrum is shifted to the longer wavelength side and the lock wavelength and gain peak are not matched. [Figure 3C] Figure 3C is a graph illustrating the gain spectrum and output spectrum of an external resonant LD, showing a state where the gain spectrum is shifted to the shorter wavelength side and the lock wavelength and gain peak are not matched. [Figure 3D] Figure 3D is a graph illustrating the output spectrum of a distributed feedback type LD or a distributed reflection type LD. [Figure 4] Figure 4 is a schematic diagram illustrating the decrease in coupling efficiency due to the occurrence of wavelength shift. [Figure 5] Figure 5 is a graph illustrating the relationship between wavelength shift and coupling efficiency. [Figure 6] Figure 6 is a schematic plan view of the configuration of a wavelength beam coupling apparatus according to the first embodiment of the present disclosure, as seen from a direction perpendicular to the XZ plane. [Figure 7] Figure 7 is a schematic diagram showing a first implementation example of the optical coupling unit. [Figure 8] Figure 8 is a schematic plan view, taken from a direction perpendicular to the XZ plane, illustrating another configuration in the first embodiment of the wavelength beam coupling apparatus according to this disclosure. [Figure 9] Figure 9 is a schematic diagram showing a second implementation example of the optical coupling unit. [Figure 10] Figure 10 is a plan view, viewed from a direction perpendicular to the XZ plane, schematically showing further other configurations in the first embodiment of the wavelength beam coupling apparatus according to the present disclosure. [Figure 11] Figure 11 is a schematic plan view of the configuration of a second embodiment of the wavelength beam coupling apparatus according to this disclosure, as seen from a direction perpendicular to the XZ plane. [Figure 12] Figure 12 is a schematic diagram showing a third implementation example of the optical coupling unit. [Figure 13] FIG. 13 is a plan view seen from a direction perpendicular to the XZ plane, schematically showing the configuration in the third embodiment of the wavelength beam combining device according to the present disclosure. [Figure 14] FIG. 14 is a plan view seen from a direction perpendicular to the YZ plane, schematically showing the configuration in the third embodiment of the wavelength beam combining device according to the present disclosure. [Figure 15] FIG. 15 is a diagram schematically showing a configuration example of a beam reducer having a Galilean lens configuration. [Figure 16] FIG. 16 is a diagram schematically showing another configuration example of a beam reducer having a Galilean lens configuration. [Figure 17A] FIG. 17A is a schematic diagram for explaining the divergence angle of the laser beam in the XZ plane. [Figure 17B] FIG. 17B is a schematic diagram for explaining the divergence angle of the laser beam in the YZ plane. [Figure 18] FIG. 18 is a plan view seen from a direction perpendicular to the XZ plane, schematically showing another configuration in the third embodiment of the wavelength beam combining device according to the present disclosure. [Figure 19] FIG. 19 is a plan view seen from a direction perpendicular to the YZ plane, schematically showing another configuration in the third embodiment of the wavelength beam combining device according to the present disclosure. [Figure 20] FIG. 20 is a plan view seen from a direction perpendicular to the XZ plane, schematically showing the configuration in the fourth embodiment of the wavelength beam combining device according to the present disclosure. [Figure 21A] FIG. 21A is a graph showing the measurement results of the optical output when the optical coupling unit is moved in a predetermined direction. [Figure 21B] FIG. 21B is a graph showing the measurement results of the multiplexing efficiency when the optical coupling unit is moved in a predetermined direction. [Figure 22A] FIG. 22A is a graph showing the measurement results of the optical output when the moving unit is moved in a predetermined direction. [Figure 22B] FIG. 22B is a graph showing the measurement results of the multiplexing efficiency when the moving unit is moved in a predetermined direction. [Figure 23] Figure 23 is a schematic plan view, taken from a direction perpendicular to the XZ plane, showing the configuration of an embodiment of the direct diode laser apparatus according to this disclosure. [Figure 24] Figure 24 is a schematic plan view, taken from a direction perpendicular to the XZ plane, illustrating another configuration in an embodiment of the direct diode laser apparatus according to this disclosure. [Figure 25] Figure 25 shows an example configuration of an embodiment of the processing machine according to this disclosure. [Modes for carrying out the invention]

[0012] Before describing embodiments of this disclosure, an overview of wavelength beam coupling using two diffraction gratings will be given with reference to Figures 1 to 5. For reference, the accompanying drawings show mutually orthogonal X, Y, and Z axes.

[0013] Figure 1 is a schematic plan view, viewed from a direction perpendicular to the XZ plane, illustrating an example of the configuration of a device that coaxially couples multiple laser beams with different peak wavelengths. Figure 1 shows an example of couplening three laser beams 10 with peak wavelengths λ1, λ2, and λ3. In this specification, a device that coaxially couples multiple laser beams with different peak wavelengths is called a "wavelength beam coupler." Hereinafter, the peak wavelengths 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).

[0014] In Figure 1, each of the multiple laser beams 10 is shown as a simple straight line. An actual laser beam 10 is a light beam with 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 a plane perpendicular to the direction of propagation of the light beam. The diameter of the light beam is, for example, 1 / e of the intensity at the beam center. 2 It is defined by the size of the cross-sectional area having more than twice the intensity. In the diagram, the central axis of each light beam is represented by a straight line to schematically show the direction of propagation of light beams such as laser beams or wavelength-coupled beams. These straight lines can be thought of as representing the rays passing through the center of each light beam.

[0015] The wavelength beam coupling device 700 shown in Figure 1 comprises a pair of parallel-arranged diffraction gratings G1 and G2, and a focusing lens 710. The first diffraction grating G1 is positioned to receive multiple laser beams 10 emitted from a laser light source 750, and diffracts the multiple laser beams 10 in different directions according to their wavelengths, causing them to be incident on the second diffraction grating G2. The second diffraction grating G2 further diffracts the multiple laser beams 10 diffracted by the first diffraction grating G1 to form a wavelength-coupled beam 19, and causes the wavelength-coupled beam 19 to be incident on the focusing lens 710. The focusing lens 710 focuses the wavelength-coupled beam 19 and couples it into an optical transmission fiber 760. The wavelength beam coupling device makes it possible to increase the laser beam output while maintaining beam quality. Beam quality can be expressed by BPP [mm·mrad], which is the product of the beam waist radius (ω0) and the half-angle of the beam divergence angle (θ). A smaller BPP indicates higher beam quality.

[0016] The principle of wavelength beam coupling using two diffraction gratings, and various configuration examples of wavelength beam coupling devices, are described in detail, for example, in the Japanese Patent Application Publication No. 2023-088438 or No. 2024-172262, both domestic applications filed by the present applicant. All disclosures of No. 2023-088438 and No. 2024-172262 are incorporated herein by reference.

[0017] Figure 2 is a schematic diagram showing the incident angle α and the diffraction angle β of the reflected diffracted light of a laser beam incident on the diffraction grating G1 shown in Figure 1. The incident angle α is the angle formed by the central axis of the laser beam with respect to the normal direction of the diffraction grating G1, shown by the dashed line. The diffraction angle β is the diffraction angle of the reflected diffracted light formed when a laser beam of wavelength λ is incident on the diffraction grating G1. The relationship between the incident angle α and the diffraction angle β is given by the following equation 1. [Mathematics 1] sinα + sinβ = N·m·λ Here, N is the number of grooves per unit length (e.g., 1 mm) of the diffraction grating G1, and m is the diffraction order. The number of grooves per unit length N is the reciprocal of the grating groove period. As can be seen from equation 1, when the incident angle α is constant, the diffraction angle β changes when the wavelength λ of the laser beam incident on the diffraction grating G1 changes.

[0018] Wavelength beam coupling utilizes wavelength-controlled light sources. Examples of wavelength-controlled light sources include external cavity laser diodes (EC-LDs), distributed feedback laser diodes (DFB-LDs), and distributed Bragg reflector laser diodes (DBR-LDs).

[0019] Referring to Figures 3A to 3D, the relationship between the design wavelength and the actual wavelength of a wavelength-controlled light source will be explained.

[0020] First, we will explain the gain spectrum and output spectrum of the external resonant LD.

[0021] External resonant LDs, as the name suggests, have an external resonant mirror placed outside the LD, making them less susceptible to the ambient or operating temperature of the LD, resulting in smaller fluctuations in the lock wavelength. However, the gain spectrum is affected by the ambient or operating temperature of the LD, leading to larger increases or decreases in output power.

[0022] Figure 3A is a graph illustrating the gain spectrum and output spectrum when the lock wavelength and gain peak are matched. Figure 3B is a graph illustrating the gain spectrum and output spectrum when the gain spectrum is shifted to the longer wavelength side and the lock wavelength and gain peak are not matched. Figure 3C is a graph illustrating the gain spectrum and output spectrum when the gain spectrum is shifted to the shorter wavelength side and the lock wavelength and gain peak are not matched.

[0023] The gain peak is the peak wavelength of the gain spectrum. The lock wavelength can be said to be the design wavelength of the laser beam. Due to the characteristics of LDs, for example, when the ambient temperature or operating temperature of the LD increases due to heating, the gain spectrum shifts to the longer wavelength side, while when the ambient temperature or operating temperature of the LD decreases due to cooling, the gain spectrum shifts to the shorter wavelength side.

[0024] In this specification, a shift in the output spectrum or gain peak towards longer or shorter wavelengths is referred to as a "wavelength shift." Various factors can cause a wavelength shift. These factors will be described in detail later.

[0025] In the case of an externally resonant laser diode (LD), when the lock wavelength and the gain peak are matched, in other words, when the lock wavelength and the gain peak coincide, a relatively high-power laser beam is emitted from the LD. On the other hand, when the lock wavelength and the gain peak are not matched due to wavelength shift, a relatively low-power laser beam is emitted from the LD. In Patent Document 2, the gain spectrum of multiple laser modules is individually controlled, and the gain peak is brought closer to the lock wavelength to achieve high laser output. However, because each of the multiple laser modules needs to be controlled individually, multiple cooling devices are required, resulting in an unavoidable increase in system size, complexity, and cost.

[0026] Next, we will describe the output spectra of distributed feedback LDs or distributed reflection LDs.

[0027] In contrast to externally resonant LDs, distributed feedback LDs or distributed reflection LDs have the diffraction grating inside the LD, making them susceptible to ambient or operating temperature fluctuations, resulting in large variations in the lock wavelength. However, like LDs, distributed feedback LDs or distributed reflection LDs are affected by ambient or operating temperature, so the increase or decrease in output is small.

[0028] Figure 3D is a graph illustrating the output spectrum of a distributed feedback type LD or a distributed reflection type LD. For example, when the ambient temperature or operating temperature of the LD increases due to heating, the output spectrum shifts to the longer wavelength side, while when the ambient temperature or operating temperature of the LD decreases due to cooling, the output spectrum shifts to the shorter wavelength side. The increase or decrease in laser beam output due to wavelength shift is smaller compared to an external resonance type LD.

[0029] Figure 4 is a schematic diagram illustrating the decrease in coupling efficiency due to wavelength shift in this embodiment. In Figure 4, the laser beam traveling at the design wavelength is shown by a solid line, and the laser beam when the wavelength is shifted to the longer wavelength side is shown by a dotted line. Figure 1 shows how the laser beam travels at the design wavelength. As mentioned above, when the wavelength λ of the laser beam incident on the diffraction grating changes, the diffraction angle changes. Therefore, when a wavelength shift occurs, the diffraction angle changes, and as a result, as shown in Figure 4, the spot on the diffraction grating G2 to which the reflected diffracted light is incident (the intersection of the central axes of each laser beam) changes. On the other hand, the wavelength-coupled beam 19 formed by the diffraction grating G2 due to the wavelength shift is emitted in the same direction as the wavelength-coupled beam 19 when no wavelength shift has occurred. In other words, even when a wavelength shift occurs, the diffraction angle of the reflected diffracted light from the diffraction grating G2 does not change, so the central axis of the wavelength-coupled beam 19 shown by a straight line and the central axis of the wavelength-coupled beam 19 shown by a dotted line are parallel. However, the central axis of the wavelength-coupled beam 19, shown by the dotted line, shifts in the X-axis direction relative to the central axis of the wavelength-coupled beam 19, shown by the straight line. Specifically, when the output spectrum shifts to the longer wavelength side, the central axis of the wavelength-coupled beam 19, shown by the dotted line, shifts in the negative X-axis direction from the central axis of the wavelength-coupled beam 19, shown by the straight line. On the other hand, when the output spectrum shifts to the shorter wavelength side, the central axis of the wavelength-coupled beam 19, shown by the dotted line, shifts parallel to the positive X-axis direction from the central axis of the wavelength-coupled beam 19, shown by the straight line.

[0030] Figure 5 is a graph illustrating the relationship between wavelength shift and coupling efficiency. The horizontal axis represents the wavelength shift [nm], and the vertical axis represents the coupling efficiency [%]. If we consider the coupling efficiency to be 100% when no wavelength shift occurs, i.e., when the wavelength shift, which represents the change in the output spectrum Δλ, is zero, then the coupling efficiency decreases as the wavelength shift increases.

[0031] The amount of shift in the central axis of a wavelength-coupled beam in the X-axis direction depends on the optical system of the wavelength-coupled beam. Specifically, the amount of shift changes depending on the spacing between the pair of diffraction gratings, the number of grooves N in the diffraction grating, or the incident angle of the laser beam incident on the diffraction grating. For example, a 0.1 nm change in the output spectrum can result in a shift of several tens of micrometers in the central axis of the wavelength-coupled beam in the X-axis direction. In this case, the coupling efficiency can decrease by more than 50% compared to when no wavelength shift occurs. A large shift in the central axis of a wavelength-coupled beam can lead to damage to optical components. For example, the wavelength-coupled beam, which should be incident on the core of the optical transmission fiber, may be incident on the cladding instead, potentially damaging the coating or jacket layer on the outer periphery of the cladding.

[0032] A wavelength beam coupling device according to an embodiment of the present disclosure includes an optical coupling unit that couples a wavelength-coupled beam to an optical transmission fiber. The optical coupling unit is configured to be movable in the direction of the shift of the central axis of the wavelength-coupled beam. For example, even if the ambient temperature or operating temperature of the laser light source rises and the central axis of the wavelength-coupled beam shifts, it is possible to suppress a decrease in the coupling efficiency of the optical transmission fiber by moving the optical coupling unit in the direction of that shift.

[0033] Hereinafter, with reference to the drawings, the wavelength beam coupling apparatus, direct diode laser apparatus, and laser processing machine according to embodiments of this disclosure will be described in detail. Parts with the same reference numerals appearing in multiple drawings indicate the same or equivalent parts. The descriptions of the dimensions, materials, shapes, and relative arrangements of the components are intended to be illustrative and not to limit the scope of the present invention. The size and positional relationships of the components shown in each drawing may be exaggerated to facilitate understanding.

[0034] <1. First Embodiment of a Wavelength Beam Coupling Device> Figure 6 is a schematic plan view of the configuration of a wavelength beam coupling apparatus according to the first embodiment of the present disclosure, as seen from a direction perpendicular to the XZ plane. In Figure 6, the propagation of the laser beam without wavelength shift and the propagation of the laser beam with wavelength shift are shown by solid and dotted lines, respectively.

[0035] The wavelength beam coupling device 100 shown in Figure 6 can couple multiple laser beams 10 with different peak wavelengths emitted from a laser light source 500. For simplicity, Figure 6 shows an example configuration of a device 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. As will be described later, the laser beams 10 can be collimated by an optical system such as a collimator lens (hereinafter simply referred to as "collimator"). 2 The beam diameter is, for example, 1 mm to 30 mm, which is smaller than the adjacent spacing between collimators.

[0036] In the example shown in Figure 6, the laser light source 500 has a plurality of semiconductor laser devices 510, each emitting laser light with a different peak wavelength. The laser light source 500 may have a laser bar, as will be described later. Laser beams with peak wavelengths λ1, λ2, and λ3 are emitted from the plurality of semiconductor laser devices 510. Each of the plurality of semiconductor laser devices 510 may be 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.

[0037] The laser light source 500 is controlled so that the amount of current input to each of the multiple semiconductor laser devices 510 is the same. Examples of semiconductor laser devices 510 include external resonant LDs, distributed feedback LDs, and distributed reflection LDs. An external resonant LD includes, for example, a surface relief grating (SRG) or a volume holographic grating (VHG) as a component necessary for external resonance. This type of semiconductor laser device allows for narrowing, or wavelength control, of the output spectrum of the laser beam by adjusting the laser light source 500, as shown in Figures 3A to 3D.

[0038] The wavelength beam coupling device 100 shown in Figure 6 comprises a pair of parallel-arranged diffraction gratings 30 and an optical coupling unit 40. The wavelength beam coupling device 100 couples multiple laser beams having different peak wavelengths and whose central axes, emitted in a first direction, are aligned in a second direction intersecting the first direction. In the example shown in Figure 6, the first direction is parallel to the Z-axis direction, and the second direction is parallel to the X-axis direction. In the illustrated example, the second direction is orthogonal to the first direction. In this disclosure, unless otherwise specified, the first direction is parallel to the Z-axis direction, and the second direction is parallel to the X-axis direction.

[0039] The wavelength beam coupling device 100 illustrated in Figure 6 further comprises a collimator 20 that converts multiple laser beams 10 into multiple collimated beams 11. Three laser beams 10, whose central axes are parallel to each other, are incident on the collimator 20. The collimator 20 is configured to convert multiple laser beams 10, each with a different peak wavelength, into multiple collimated beams 11. The collimator 20 is an assembly of collimator lenses. The collimator 20 may be a lens array in which a number of lenses equal to the number of laser beams 10 are formed from a single optical material, or it may be an optical component assembly in which multiple lenses are arranged. The collimated beams 11 that have passed through the collimator 20 and whose divergence angle has become small are not strictly parallel light, but are approximated as Gaussian beams in which the product of the divergence angle and beam diameter has a finite value. The optical material of the collimator 20 may be synthetic quartz or optical glass such as BK7. Optical glass is a glass material that has high transmittance in visible light.

[0040] The pair of diffraction gratings 30 illustrated in Figure 6 comprises first and second diffraction gratings 30A and 30B arranged in parallel between the collimator 20 and the optical coupling unit 40. Each of the first and second diffraction gratings 30A and 30B is a transmission type diffraction grating. However, the diffraction grating 30 may be a reflection type diffraction grating. In this embodiment, a diffraction grating of the type in which both reflected light reflected by the diffraction grating and transmitted light that passes through the diffraction grating exist is called a "transmission type diffraction grating," and a diffraction grating of the type in which no transmitted light exists is called a "reflection type diffraction grating."

[0041] Unlike transmission-type diffraction gratings, reflection-type diffraction gratings are equipped with reflective elements (e.g., metal mirrors), and the light absorption by these elements cannot be ignored. Therefore, with reflection-type 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 or even damage it. For this reason, it is desirable to use a transmission-type diffraction grating in this embodiment. The substrate of the diffraction grating 30 can be formed from a material with low absorption at the peak wavelength of the laser beam, such as synthetic quartz. The shape of the grating cross-section is, for example, rectangular or trapezoidal. As will be described later, it is also possible to use transmitted light instead of reflected light from a transmission-type diffraction grating.

[0042] The parallelism between the first diffraction grating 30A and the second diffraction grating 30B is evaluated by the angle between the first normal to the surface on which the diffraction grooves of the first diffraction grating 30A are formed and the second normal to the surface on which the diffraction grooves of the second diffraction grating 30B are formed. In this embodiment, it is desirable that the angle between these first and second normals be in the range of 180 degrees ± 1 degree.

[0043] The first diffraction grating 30A is positioned to receive multiple laser beams 10 and can diffract the multiple laser beams 10 in different directions according to their wavelengths and direct them onto the second diffraction grating 30B. The second diffraction grating 30B can further diffract the multiple laser beams 10 diffracted by the first diffraction grating 30A to form a wavelength-coupled beam 19 and emit the wavelength-coupled beam 19 in a first direction. In the example shown in Figure 6, the first diffraction grating 30A is positioned to receive multiple collimated beams 11 emitted from the collimator 20 and diffracts the multiple collimated beams 11 in different directions according to their wavelengths and directs them onto the same region 31 of the second diffraction grating 30B. The second diffraction grating 30B further diffracts the multiple collimated beams 11 diffracted by the first diffraction grating 30A in region 31 to form a wavelength-coupled beam 19 and emits the wavelength-coupled beam 19 in a first direction.

[0044] In this embodiment, the first diffraction grating 30A and the second diffraction grating 30B have the same structure. They are positioned so that the direction in which the diffraction grooves of the first diffraction grating 30A extend is parallel to the direction in which the diffraction grooves of the second diffraction grating 30B extend. More specifically, the normal of the first diffraction grating 30A and the normal of the second diffraction grating 30B are parallel, and the direction in which the diffraction grooves of the first diffraction grating 30A extend is parallel to the direction in which the diffraction grooves of the second diffraction grating 30B extend. In the example shown in Figure 6, the direction in which the diffraction grooves of the first diffraction grating 30A and the second diffraction grating 30B extend is parallel to the Y-axis direction. It can also be said that the dispersion directions (XZ planes) of the first diffraction grating 30A and the second diffraction grating 30B are the same. Furthermore, the diffraction groove period (center spacing of the diffraction grooves) of the first diffraction grating 30A and the diffraction groove period (center spacing of the diffraction grooves) of the second diffraction grating 30B are equal. By adopting this configuration, it becomes possible to emit the wavelength-coupled beam 19 in a first direction parallel to the emission direction of each collimated beam 11. In the example shown in Figure 6, the emission directions of the multiple laser beams 10, the emission directions of the multiple collimated beams 11, and the emission direction of the wavelength-coupled beam 19 are parallel.

[0045] The wavelength-coupled beam 19 can be a laser beam formed by wavelength-coupled n laser beams 10, each with peak wavelengths λ1, λ2, ..., λn. The beam quality of the wavelength-coupled beam 19, generated by coaxially superimposing multiple laser beams 10, is equivalent to that of each individual laser beam 10, and the light intensity of the wavelength-coupled beam 19 is equal to the sum of the light intensities of each individual laser beam 10. As the number of coupled laser beams 10 increases, the output and power density of the wavelength-coupled beam 19 can increase proportionally.

[0046] As mentioned earlier, there can be various factors causing the wavelength shift of the laser beam emitted from the laser light source 500. Typical factors include, for example, the input current (or applied current) supplied to the semiconductor laser device, the temperature of the semiconductor laser device, or degradation over time. The temperature of the semiconductor laser device can be controlled as a temperature parameter such as the ambient temperature or the operating temperature of the device. In this embodiment, the input current, ambient temperature, operating temperature, and degradation over time are defined as the "operating state of the laser light source."

[0047] Depending on the operating state of the laser light source, a wavelength shift may occur in the laser light source 500. For example, if the input current increases, the operating temperature of the semiconductor laser device rises, causing a wavelength shift towards longer wavelengths. Alternatively, if the ambient temperature rises, the operating temperature of the semiconductor laser device rises, causing a wavelength shift towards longer wavelengths. As the semiconductor laser device deteriorates over time, the threshold current increases, and the operating temperature of the semiconductor laser device rises, causing a wavelength shift towards longer wavelengths. As a result of this change in the operating state of the laser light source 500, a wavelength shift occurs, which changes the diffraction angle of the reflected diffracted light diffracted by the first diffraction grating 30A. When the diffraction angle of the reflected diffracted light changes, the spot on the second diffraction grating 30B into which the reflected diffracted light is incident moves from region 31 to region 32 in the XZ plane. As a result, the central axis of the wavelength-coupled beam 19 shifts in the second direction (parallel to the X-axis).

[0048] The optical coupling unit 40 optically couples the wavelength-coupled beam 19 to the optical transmission fiber 60. The optical coupling unit 40 is configured to be movable in a second direction. In this embodiment, when a wavelength shift occurs, the direction of the shift of the central axis of the wavelength-coupled beam 19 is constant and parallel to the X-axis. Furthermore, the direction and amount of the shift of the central axis of the laser beam can be predicted from the driving conditions of the semiconductor laser device. Therefore, when the central axis of the wavelength-coupled beam 19 shifts in a second direction according to the operating state of the laser light source 500, the decrease in the coupling efficiency of the optical transmission fiber 60 can be suppressed by moving the optical coupling unit 40 by the predicted amount of shift in the direction of the shift of the central axis of the laser beam.

[0049] The optical coupling unit 40 has a movable stage 41 that moves the optical coupling unit 40 by a shift amount in a second direction in response to a signal that defines a shift amount determined based on the operating state of the laser light source 500. An example of the movable stage 41 is an automatic stage having an electric motor. The movable stage 41 may be connected by wire or wireless to a dedicated controller for controlling the automatic stage. In this embodiment, the automatic stage alone, or a combination of the automatic stage and the controller, can function as the movable stage for moving the optical coupling unit 40. For example, by using a single-axis automatic stage, it is possible to move the optical coupling unit 40 in at least the second direction.

[0050] The control device 50 is connected to the movable stage 41 by wire or wireless. The control device 50 is configured or programmed to determine the shift amount of the optical coupling unit 40 based on the operating state of the laser light source 500 and to transmit a signal defining the shift amount to the movable stage 41. The control device 50 comprises at least one processor and at least one memory that stores a computer program (or software) that defines the control process performed by the processor. An example of the control device 50 is a computing device such as a personal computer (PC). In this embodiment, the control device 50 determines the shift amount of the central axis of the wavelength-coupled beam 19 in accordance with the input current input to the semiconductor laser device, which is set by the user. In another example, the control device 50 may measure the drive current from the output of the laser light measured by a power meter, based on an LI characteristic curve that shows the relationship between the output of the LD and the drive current. The control device 50 may determine the shift amount of the central axis of the wavelength-coupled beam 19 in accordance with the measured drive current. Because there is a correlation between the input current and the wavelength shift amount Δλ, a table defining the correspondence between the input current and the wavelength shift amount Δλ may be prepared in advance. The control device 50 can estimate the wavelength shift amount Δλ from the input current by referring to this table.

[0051] The control device 50 determines the amount of shift of the central axis of the wavelength-coupled beam 19 based on the estimated wavelength shift amount Δλ. The control device 50 may further determine the amount of shift of the central axis of the wavelength-coupled beam 19 based on pulse output conditions that define the pulse frequency, pulse width, and pulse waveform of the pulse signal, which is the control signal of the movable stage 41.

[0052] The control device 50 generates a control signal that defines the target movement position, target movement speed, target acceleration, etc., based on the determined shift amount, and transmits it to the movable stage 41. The movable stage 41 moves the optical coupling unit 40 according to the control signal. For example, the shift amount is determined each time the input current changes, and a control signal generated based on the shift amount is transmitted to the movable stage 41. In this example, the movable stage moves in synchronization with the change in the input current.

[0053] Figure 7 is a schematic diagram showing a first implementation example of the optical coupling unit 40. In Figure 7, the wavelength-coupled beam 19 before the shift of the central axis of the laser beam and the wavelength-coupled beam 19 after the shift are shown by solid and dotted lines, respectively.

[0054] The optical coupling unit 40A in the first implementation example comprises a movable stage 41, an optical focuser 42 for focusing the wavelength-coupled beam 19, and an optical coupling section 43 connected to the end face or termination of the optical transmission fiber 60. The movable stage 41 supports the optical focuser 42 and the optical coupling section 43. The movable stage 41 allows the optical focuser 42 and the optical coupling section 43 to move in the X-axis direction. In the example shown in Figure 7, the optical focuser 42 is a focusing lens for focusing the wavelength-coupled beam 19. However, the optical focuser 42 may include two or more lenses. The optical focuser 42 may include an aspherical lens for focusing the wavelength-coupled beam 19. By combining the movable stage 41 and the aspherical lens, it is possible to increase the coupling efficiency.

[0055] The optical coupling section 43 includes an end cap and is fixed at the position where the wavelength-coupled beam 19 emitted from the optical focuser 42 is incident, in other words, at the position where the wavelength-coupled beam 19 is coupled. The wavelength-coupled beam 19 is focused by the optical focuser 42 and incident at the optical coupling section 43.

[0056] In the examples shown in Figures 6 and 7, the directions of propagation of the multiple laser beams 10, the directions of propagation of the multiple collimated beams 11, and the direction of propagation of the wavelength-coupled beam 19 are parallel to the first direction. The wavelength-coupled beam 19 is focused by the optical focuser 42 and incident on the optical coupling unit 43. In this way, the optical coupling unit 40A can efficiently couple the wavelength-coupled beam 19 emitted from the wavelength beam coupling device 100 to the optical transmission fiber 60. Furthermore, the movable stage 41 supports the optical focuser 42 and the optical coupling unit 43 while maintaining the relative positional relationship between the optical focuser 42 and the optical coupling unit 43. Therefore, by moving the optical coupling unit 40 in the direction of the shift of the central axis of the wavelength-coupled beam 19 while maintaining the positional relationship between the optical focuser 42 and the optical coupling unit 43, the wavelength-coupled beam 19 can be efficiently focused by the optical focuser 42, and as a result, a decrease in the coupling efficiency of the optical transmission fiber 60 can be suppressed.

[0057] As shown in Figure 7, when the central axis of the wavelength-coupled beam 19 shifts by Δx in the negative direction of the X-axis according to the operating state of the laser light source 500, the control device 50 moves the movable stage 41 by a shift amount Δx in the same direction as the shift of the central axis of the laser beam. In this way, automatic control is performed to move the optical focuser 42 and the optical coupling unit 43 in conjunction with the shift of the central axis of the laser beam.

[0058] Figure 8 is a schematic plan view taken perpendicular to the XZ plane, showing another configuration in the first embodiment of the wavelength beam coupling apparatus according to this disclosure. The wavelength beam coupling apparatus 101 shown in Figure 8 comprises a pair of parallel-arranged diffraction gratings 30. The first and second diffraction gratings 30A and 30B are, respectively, transmission diffraction gratings, similar to the wavelength beam coupling apparatus 100 shown in Figure 6. However, in this example, transmitted light is used instead of reflected light. Thus, it is also possible to use transmitted light from a transmission diffraction grating.

[0059] Figure 9 is a schematic diagram showing a second implementation example of the optical coupling unit. The optical coupling unit 40B in the second implementation example includes a movable stage 41 that operates under the control of a control device 50, and a first mirror 45A and a second mirror 45B arranged parallel to each other on the optical path between the second diffraction grating 30B and the optical transmission fiber 60. The first mirror 45A and the second mirror 45B each have a first reflecting surface 45AR and a second reflecting surface 45BR, respectively. The first reflecting surface 45AR and the second reflecting surface 45BR are perpendicular to a plane (the XZ plane in the figure) that includes the first and second directions. The first reflecting surface 45AR receives the wavelength-coupled beam 19 and reflects it toward the second reflecting surface 45BR, and the second reflecting surface 45BR reflects the wavelength-coupled beam 19 reflected by the first reflecting surface 45AR and directs it toward the optical coupling section 43 of the optical transmission fiber 60.

[0060] The movable stage 41 supports the first mirror 45A of the two mirrors 45B, and moves the first mirror 45A in the second direction by a shift amount determined based on the operating state of the laser light source 500. Figure 9 shows an example in which the first mirror 45A is supported and moved in the second direction, but a similar effect can be obtained by supporting the second mirror 45B and moving it in the first direction.

[0061] The wavelength beam coupling device 102 shown in Figure 9 includes an optical focuser 42 that focuses the wavelength-coupled beam 19 reflected by the second reflective surface 45BR of the second mirror 45B. The optical coupling section 43 includes an end cap and is fixed at the position into which the wavelength-coupled beam 19 emitted from the optical focuser 42 is incident. The wavelength-coupled beam 19 is focused by the optical focuser 42 and incident on the optical coupling section 43.

[0062] In the example shown in Figure 9, the central axis of the wavelength-coupled beam 19 when no wavelength shift occurs and the central axis of the wavelength-coupled beam 19 when a wavelength shift occurs are shown by a solid line and a dotted line, respectively. When the central axis of the wavelength-coupled beam 19 shifts by Δx in the negative direction of the X-axis according to the operating state of the laser light source 500, the movable stage 41 is moved by a shift amount Δx in the same direction as the shift of the central axis of the laser beam, thereby moving the first mirror 45A. In this way, by supporting one of a pair of parallel-arranged mirrors with the movable stage and moving the movable stage 41 in the same direction as the shift of the central axis of the laser beam, an optical coupling unit can be realized with a relatively simple optical system.

[0063] Figure 10 is a plan view, viewed from a direction perpendicular to the XZ plane, schematically showing further other configurations in the first embodiment of the wavelength beam coupling apparatus according to the present disclosure. The wavelength beam coupling apparatus 103 illustrated in Figure 10 may include a moving unit 46 that supports the second diffraction grating 30B so as to be movable in at least one of the first or second directions. The moving unit 46 illustrated in Figure 10 is a two-axis automatic stage that supports the second diffraction grating 30B so as to be movable in the X-axis and Z-axis directions. Thus, it is possible to move the second diffraction grating 30B on the XZ plane.

[0064] Compared to moving the second diffraction grating 30B in either the X-axis or Z-axis direction, moving the second diffraction grating 30B in both the X-axis and Z-axis directions offers the advantage of suppressing the expansion of the second diffraction grating 30B's size. For this reason, it is preferable to move the second diffraction grating 30B in both the X-axis and Z-axis directions.

[0065] When the position of the second diffraction grating 30B is fixed, as described above, the diffraction angle at the first diffraction grating 30A changes due to the wavelength shift, and the spot on the second diffraction grating 30B onto which the reflected diffracted light is incident moves Δx and Δz in the X-axis and Z-axis directions, respectively, as shown in Figure 10. In this case, by moving the second diffraction grating 30B by a shift amount Δx in the X-axis direction and a shift amount Δz in the Z-axis direction to follow this movement, it becomes possible to form a spot in a desired region on the surface of the second diffraction grating 30B where the diffraction grooves are formed. Furthermore, vignetting of the laser beam at the second diffraction grating 30B can be suppressed.

[0066] <2. Second Embodiment of Wavelength Beam Coupling Apparatus> A second embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figures 11 and 12.

[0067] A wavelength beam coupling device according to a second embodiment of the present disclosure further comprises a polarization separation and synthesis mechanism. Specifically, the wavelength beam coupling device may further comprise a polarization beam splitter, a first polarization conversion element, a polarization beam coupler, and a second polarization conversion element. Such a wavelength beam coupling device makes it possible to combine multiple laser beams having different peak wavelengths and further increase the output and power density of the wavelength-coupled beam.

[0068] Figure 11 is a schematic plan view of the configuration of a second embodiment of the wavelength beam coupling device according to the present disclosure, as seen from a direction perpendicular to the XZ plane. The wavelength beam coupling device 104 further comprises a polarizing beam splitter 81, a first polarization conversion element 91, a polarizing beam coupler 82, and a second polarization conversion element 92. The polarizing beam splitter 81 is positioned in the optical path between the laser light source 500 and the first diffraction grating 30A. The first polarization conversion element 91 is positioned in the optical path between the polarizing beam splitter 81 and the first diffraction grating 30A. The polarizing beam coupler 82 is positioned in the optical path between the second diffraction grating 30B and the optical focuser 42. The second polarization conversion element 92 is positioned in the optical path between the second diffraction grating 30B and the polarizing beam coupler 82.

[0069] The polarization beam splitter 81 separates the multiple collimated beams 11 emitted from the collimator 20 into multiple first polarization beams 13 linearly polarized in the first polarization direction (Y-axis direction) and multiple second polarization beams 14 linearly polarized in the second polarization direction (direction in the XZ plane) perpendicular to the first polarization direction. In Figure 11, for simplicity, the multiple laser beams 10 emitted from the laser light source 500 and the multiple collimated beams 11 emitted from the collimator 20 are represented together by a single straight line. However, in reality, the multiple laser beams 10 and the multiple collimated beams 11 travel in parallel.

[0070] In the example shown in Figure 11, the polarization beam splitter 81 has a reflective / transmitting surface 81R with different transmittance and reflectance depending on the polarization state of the incident collimated beam 11. The reflective / transmitting surface 81R functions as a reflective surface for the first polarization beam 13 and as a transmitting surface for the second polarization beam 14. The reflective / transmitting surface 81R separates the incident collimated beam 11 into the first polarization beam 13 and the second polarization beam 14. The polarization beam splitter 81 further has a mirror 81M that reflects the first polarization beam 13, which has been reflected in the second direction by the reflective / transmitting surface 81R, back in the first direction. The first polarization beam 13 and the second polarization beam 14 are emitted parallel to each other from the polarization beam splitter 81. Light is an electromagnetic wave, and the electromagnetic field of light is a transverse wave that oscillates in a direction perpendicular to the direction of propagation. The polarization state of the laser beam may vary depending on the gain medium, resonator, oscillation method, etc., of the laser light source 500. Furthermore, a laser beam that is in a specific polarization state when emitted from the laser light source 500 may experience changes in polarization state or depolarization while passing through a transmission medium such as an optical fiber. The reflective / transmitting surface 81R of the polarizing beam splitter 81 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. The reflective / transmitting surface 81R is provided with, for example, a dielectric multilayer film having polarization dependence.

[0071] Generally, when a light ray is incident on an object's surface, the plane containing the normal to the object's surface at the point of incidence and the direction vector (wave vector) of the light ray is defined as the "plane of incidence." Light linearly polarized perpendicular to the plane of incidence is called S-polarized light, and light linearly polarized parallel to the plane of incidence is called P-polarized light. In the example in Figure 11, the reflection / transmission surface 81R of the polarization beam splitter 81 is perpendicular to the XZ plane, and the normal to the reflection / transmission surface 81R lies in a plane parallel to the XZ plane. The direction of propagation of the collimated beam 11 is also parallel to the XZ plane. Therefore, the "plane of incidence" used to define the polarization direction when the collimated beam 11 is incident on the reflection / transmission surface 81R is parallel to the XZ plane. In this disclosure, light linearly polarized in the first polarization direction, which is perpendicular to the XZ plane, is called "S-polarized light." Light linearly polarized in the direction parallel to the XZ plane (the second polarization direction orthogonal to the first polarization direction) is called "P-polarized light." In the attached drawings, "S polarization" is indicated by a symbol with a cross enclosed in a small circle, and "P polarization" is indicated by a symbol with arrows at both ends. The polarization direction of "P polarization" is parallel to the XZ plane, but perpendicular to the direction of propagation of the laser beam. Therefore, if the direction of propagation of the laser beam remains parallel to the XZ plane and rotates due to reflection or diffraction, the polarization direction of "P polarization" 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.

[0072] In the example shown in Figure 11, a transparent member with a parallelogram cross-section is fixed to a transparent prism (or right-angle prism) with a triangular cross-section via a reflective / transmitting surface 81R. The mirror 81M is formed on the slanted surface of the transparent member with the parallelogram cross-section. When the total internal reflection condition is applied, it is not necessary to form a mirror surface. Instead of the transparent member with a parallelogram cross-section, it is possible to use two right-angle prisms bonded together. However, by using the transparent member with a parallelogram cross-section, adjustment of the right-angle prism becomes unnecessary, and reflection at the interface between the two right-angle prisms is further reduced.

[0073] The first polarization conversion element 91 converts multiple second polarization (P-polarized) beams 14 into multiple third polarization beams 15 that are linearly polarized in the first polarization (S-polarized) direction. Multiple second polarization beams 14 that have passed through the reflection / transmission surface 81R of the polarization beam splitter 81 are converted into third polarization beams 15 by the first polarization conversion element 91. The first polarization conversion element 91 is, for example, a half-wave plate (half-wave phase difference plate). A half-wave plate has birefringence and changes the phase difference between two orthogonal components of an electromagnetic wave propagating in the thickness direction. By arranging the slow or fast 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 14, the half-wave plate can convert P-polarized to S-polarized.

[0074] In the example shown in Figure 11, the spots on the first diffraction grating 30A into which multiple first polarized beams 13 are incident are different from the spots on the first diffraction grating 30A into which multiple third polarized beams 15 are incident. The first diffraction grating 30A diffracts the multiple first polarized beams 13 in different directions according to their wavelength and causes them to incident on the first region 35 of the second diffraction grating 30B, and diffracts the multiple third polarized beams 15 in different directions according to their wavelength and causes them to incident on a second region 36 of the second diffraction grating 30B that is different from the first region 35.

[0075] The second diffraction grating 30B further diffracts a plurality of first polarized beams 13 incident on the first region 35 to form a first wavelength coupled beam 16 by coaxially superimposing the plurality of first polarized beams, and further diffracts a plurality of third polarized beams 15 incident on the second region 36 to form a second wavelength coupled beam 17 by coaxially superimposing the plurality of third polarized beams 15.

[0076] In the second embodiment, when the aforementioned wavelength shift occurs, the central axes of the first wavelength-coupled beam 16 and the second wavelength-coupled beam 17 shift in the second direction (i.e., the X-axis direction) as a result of this shift. The direction of the shift of the central axis of the first wavelength-coupled beam 16 is the same as the direction of the shift of the central axis of the second wavelength-coupled beam 17, and the amount of the shift of the central axis of the first wavelength-coupled beam 16 is the same as the amount of the shift of the central axis of the second wavelength-coupled beam 17. When the central axes of the first wavelength-coupled beam 16 and the second wavelength-coupled beam 17 shift according to the operating state of the laser light source 500, the control device 50 controls the optical focuser 42, optical coupling unit 43, polarizing beam coupler 82, and second polarization conversion element 92 to move in the direction of the shift of the central axis of the wavelength-coupled beam by an amount determined based on the operating state of the laser light source 500. The wavelength beam coupling device 104 shown in Figure 11 includes an optical coupling unit 40C according to the third implementation example.

[0077] Figure 12 is a schematic diagram showing a third implementation example of the optical coupling unit. The optical coupling unit 40C has a movable stage 41, an optical focuser 42, and an optical coupling section 43, and further includes a polarizing beam coupler 82 and a second polarization conversion element 92. In the example shown in Figure 12, the movable stage 41 further supports the polarizing beam coupler 82 and the second polarization conversion element 92, and moves the optical focuser 42, optical coupling section 43, polarizing beam coupler 82, and second polarization conversion element 92 by a shift amount in the second direction.

[0078] The optical coupling unit 40C shown in Figure 12 has a mounting substrate 47 on which an optical focuser 42, an optical coupling section 43, a polarizing beam coupler 82, and a second polarization conversion element 92 are mounted. The movable stage 41 indirectly supports the optical focuser 42, optical coupling section 43, polarizing beam coupler 82, and second polarization conversion element 92 by supporting the mounting substrate 47. In this way, mounting the optical focuser 42, optical coupling section 43, polarizing beam coupler 82, and second polarization conversion element 92 on the same substrate makes it easier to control the movement of the optical coupling unit 40C. Furthermore, compared to the case where the polarizing beam coupler 82 and second polarization conversion element 92 are not moved by the movable stage 41, it is possible to suppress the enlargement of the polarizing beam coupler 82 and second polarization conversion element 92.

[0079] When the central axes of the first wavelength coupled beam 16 and the second wavelength coupled beam 17 are shifted by Δx in the negative direction of the X axis according to the operating state of the laser light source 500, an automatic control system is realized that moves the movable stage 41 by the shift amount Δx in the same direction as the shift of the beam's central axis, thereby moving the optical focuser 42, optical coupling unit 43, polarizing beam coupler 82, and second polarization conversion element 92.

[0080] Thus, according to this third implementation example of the optical coupling unit, it is possible to move the optical focuser 42, optical coupling section 43, polarizing beam coupler 82, and second polarization conversion element 92 in conjunction using the movable stage 41. By linking these four optical elements, vignetting of the laser beam caused by the polarizing beam coupler 82 or the second polarization conversion element 92 can be suppressed. Furthermore, it becomes possible to use a 1-axis automatic stage as the movable stage 41, which can facilitate the control or alignment of the movable stage 41.

[0081] Refer again to Figure 11. The second polarization conversion element 92 is configured to change the polarization state of at least one of the first wavelength coupled beam 16 and the second wavelength coupled beam 17 so that the polarization directions of the first wavelength coupled beam 16 and the second wavelength coupled beam 17 are orthogonal. The second polarization conversion element 92 is, like the first polarization conversion element 91, for example, a half-wave plate (half-wave phase difference plate). In the example shown in Figure 11, the second polarization conversion element 92 is positioned to rotate the polarization direction of the first wavelength coupled beam 16 by 90 degrees. The first wavelength coupled beam 16 that has passed through the second polarization conversion element 92 is linearly polarized in the second polarization direction. Alternatively, the second polarization conversion element 92 may be positioned to rotate the polarization direction of the second wavelength coupled beam 17 by 90 degrees.

[0082] The polarization beam coupler 82 is configured to form and emit a third wavelength coupled beam 18 by coaxially superimposing the first wavelength coupled beam 16 and the second wavelength coupled beam 17. In the example shown in Figure 11, the polarization beam coupler 82 has the same structure as the polarization beam splitter 81. Generally, a polarization beam splitter can also be used as a polarization beam coupler, except that its orientation is rotated 180 degrees around the Y axis. In the example in Figure 11, the first wavelength coupled beam 16 transmitted through the second polarization conversion element 92 is P-polarized, and the second wavelength coupled beam 17 is S-polarized. The polarization beam coupler 82 includes a mirror 82M that reflects the second wavelength coupled beam 17 propagating in the first direction in the second direction, and a reflective / transmitting surface 82R that reflects S-polarized light and transmits P-polarized light. As a result, the polarization beam coupler 82 can emit a third wavelength coupled beam 18 in which the first wavelength coupled beam (P-polarized) 16 and the second wavelength coupled beam (S-polarized) 17 that have passed through the second polarization conversion element 92 are coaxially superimposed.

[0083] The third wavelength coupled beam 18 is a laser beam formed by wavelength coupling of multiple laser beams 10 with different peak wavelengths. In this way, the wavelength beam coupling device 104 makes it possible to increase the output and power density of the wavelength coupled laser beam. If the number of laser beams 10 to be coupled increases, the output and power density of the third wavelength coupled beam 18 can increase in proportion to the number of laser beams while maintaining beam quality.

[0084] In the example shown in Figure 11, the laser beam incident on the pair of diffraction gratings 30 consists of multiple S-polarized first-polarized beams 13 and multiple S-polarized third-polarized beams 15. If the diffraction grating 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, each of the pair of diffraction gratings 30 has diffraction grooves parallel to the first polarization direction (Y-axis direction). In this embodiment, by using a diffraction grating 30 in which the diffraction efficiency for S-polarization is higher than the diffraction efficiency for P-polarization, optical loss in the diffraction grating can be suppressed.

[0085] According to the wavelength beam coupling apparatus of this embodiment, by combining a diffraction grating with a polarization separation and synthesis mechanism, it is possible to increase the diffraction efficiency by using a diffraction grating suitable for the polarization state of the incident light, and to further increase the output and power density by coaxializing the diffracted light generated by the diffraction grating.

[0086] Furthermore, Japanese Patent Publication No. 2023-088438 and Japanese Patent Publication No. 2024-172262 provide a more detailed description of a wavelength beam coupling apparatus comprising a diffraction grating and a mechanism for polarization separation and synthesis.

[0087] <3. Third Embodiment of Wavelength Beam Coupling Device> A third embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figures 13 to 19.

[0088] Figure 13 is a schematic plan view of the configuration of the third embodiment of the wavelength beam coupling apparatus according to this disclosure, viewed from a direction perpendicular to the XZ plane. In Figure 13, the laser beam propagates without wavelength shift and the laser beam propagates with wavelength shift, respectively, shown by solid and dotted lines. Figure 14 is a schematic plan view of the configuration of the third embodiment of the wavelength beam coupling apparatus according to this disclosure, viewed from a direction perpendicular to the YZ plane. However, in Figure 14, the second diffraction grating 30B, optical coupling unit 40, movable stage 41, and control device 50 shown in Figure 13 are omitted.

[0089] The wavelength beam coupling device 105 illustrated in Figure 13 further comprises an optical element 70 positioned in the optical path between the collimator 20 and the first diffraction grating 30A, configured to reduce the distance between the beam center axes of multiple collimated beams 11 before emission. For simplicity, Figure 13 illustrates how two laser beams 10 with peak wavelengths λ1 and λ2 are emitted with the distance between their beam center axes reduced.

[0090] The optical element 70 is configured to reduce the distance between the beam center axes of multiple collimated beams 11 and emit them. Multiple collimated beams 12, which have been affected by the optical element 70, are incident on the first diffraction grating 30A. The optical element 70 may include at least one lens that focuses the multiple collimated beams 11 in a first plane (XZ plane) that includes a first direction (Z axis direction) and a second direction (X axis direction). The lens constituting the optical element 70 is, for example, an axially symmetric lens such as a spherical lens or an aspherical lens, or a cylindrical lens. The material of the lens constituting the optical element 70 may be synthetic quartz or optical glass such as BK7. It is preferable to form it from synthetic quartz because multiple high-power laser beams are incident on it.

[0091] The optical element 70 is, for example, a beam reducer. In this embodiment, the optical element 70 is a beam reducer. For example, a Keplerian beam reducer or a Galilean beam reducer can be used as the beam reducer. Alternatively, an anamorphic lens may be used instead of a beam reducer as the optical element 70. The beam reducer in this embodiment can not only reduce the distance between the beam center axes of the multiple collimated beams 11, but also reduce the beam diameter of each individual collimated beam 11.

[0092] In the examples shown in Figures 13 and 14, the optical element (beam reducer) 70 is Galilean in type, but is not limited thereto. The optical element 70 includes two lenses 71 and 72, each focusing in the XZ plane. Each of the two lenses 71 and 72 is a cylindrical lens, having the function of focusing in the XZ plane but not the function of focusing in the YZ plane. The two lenses 71 and 72 are sometimes referred to as the incident lens 71 and the exit lens 72, respectively.

[0093] Figures 15 and 16 are schematic diagrams illustrating examples of beam reducer configurations with Galilean lens configurations. Figures 15 and 16 each show seven collimated beams with their central axes parallel to each other. The optical element 70 illustrated in Figure 15 is a beam reducer composed of two lenses 71 and 72. The incident lens 71 is an aspherical lens, and the exit lens 72 is a spherical lens. Using aspherical lenses allows for a design of the optical element 70 with a reduced number of lenses.

[0094] The optical element 70 illustrated in Figure 16 is a beam reducer composed of multiple lens groups. Each of the multiple lens groups is a spherical lens. The incident lens 71 is composed of four spherical lenses 71-1 to 71-4, and the exit lens 72 is composed of two spherical lenses 72-1 and 72-2. When spherical lenses are used in this way, spherical aberration is likely to occur. However, by configuring the optical element 70 from multiple lens groups, it is possible to gradually narrow the optical path and reduce spherical aberration. In this way, the optical element 70 can be composed of multiple axially symmetric lenses.

[0095] Refer again to Figure 13. The optical element 70 may include a lens with a positive focal length and a lens with a negative focal length. In the example shown in Figure 13, lens 71 of the optical element 70 is a cylindrical lens with a positive focal length, and lens 72 is a cylindrical lens with a negative focal length. By using a lens with a negative focal length, the distance between the two lenses can be reduced, and as a result, the optical path length of the laser beam can be reduced.

[0096] Let f1 be the focal length of the incident lens 71 and f2 be the focal length of the exit lens 72 shown in Figure 13. The beam reducer optical element 70 has a magnification M that reduces the incident light pitch to 1 / M. The magnification M of the beam reducer is determined by the ratio of the lens focal lengths and is given by the equation (Equation 1). Here, p1 is the incident light pitch incident on the optical element 70 (incident lens 71), and p2 is the pitch of the exit light emitted from the optical element 70 (exit lens 72), that is, the incident light pitch incident on the first diffraction grating 30A. The magnification M of the beam reducer can be, for example, between 2 and 20. M = f1 / -f2 = p1 / p2 (Equation 1) For example, when f1 is 100 mm and f2 is -10 mm, M becomes 10 times larger. In this case, if the incident light pitch p1 is 5 mm, the exit light pitch p2 becomes 0.5 mm. In this way, by using the optical element 70, it is possible to reduce the incident light pitch incident on the first diffraction grating 30A according to the magnification of the beam reducer. This contributes to reducing the interval Δλ of the peak wavelengths of the laser beam. However, the residual divergence angle, which indicates the angle of spreading from parallel light, becomes larger by the magnification, thereby preserving beam quality.

[0097] Furthermore, the principle by which the pitch of incident light on the diffraction grating can be reduced to decrease the interval Δλ between the peak wavelengths of the laser beams, and the reason why the number of laser beams that can be coupled is limited by the pitch of incident light on the diffraction grating, are described in detail in Japanese Patent Application Publication No. 2024-172262.

[0098] Figure 17A is a schematic diagram illustrating the divergence angle of a laser beam in the XZ plane. Figure 17B is a schematic diagram illustrating the divergence angle of a laser beam in the YZ plane. In Figure 17A, the divergence angle θy1 of the collimated beam emitted from the collimator 20 and the divergence angle θy2 of the collimated beam that passes through the incident lens 71 and is emitted from the exit lens 72 satisfy the relationship (Equation 2). θy2 = M·θy1 (Equation 2)

[0099] Thus, under the influence of the optical element 70, the distance between the beam center axes of the multiple collimated beams is reduced, while the residual divergence angle increases. However, by employing at least one cylindrical lens that focuses in the XZ plane but does not have the function of focusing in the YZ plane, as shown in Figure 17B, the distance between the beam center axes of the multiple collimated beams 11 in the second direction (X-axis direction) can be reduced, as shown in Figure 13, while maintaining the residual divergence angle θx in the third direction (Y-axis direction) which is orthogonal to the first and second directions. In this embodiment, since it is not necessary to reduce the incident light pitch in the Y-axis direction, a beam reducer in that direction is unnecessary.

[0100] In the example shown in Figure 13, the propagation directions of the multiple laser beams 10, the propagation directions of the multiple collimated beams 11 and 12, and the propagation direction of the wavelength-coupled beam 19 are parallel to the first direction. The wavelength-coupled beam 19 is focused by the optical coupling unit 40 and incident on the optical transmission fiber 60. In this way, for example, the optical coupling unit 40A in the first implementation example can efficiently couple the wavelength-coupled beam 19 emitted from the wavelength beam coupling device 105 to the optical transmission fiber 60.

[0101] Figure 18 is a plan view, viewed perpendicular to the XZ plane, schematically showing another configuration in the third embodiment of the wavelength beam coupling apparatus according to this disclosure. In Figure 18, the propagation of the laser beam without wavelength shift and the propagation of the laser beam with wavelength shift are shown by solid and dotted lines, respectively. Figure 19 is a plan view, viewed perpendicular to the YZ plane, schematically showing another configuration in the third embodiment of the wavelength beam coupling apparatus according to this disclosure.

[0102] In the examples shown in Figures 18 and 19, each of the two lenses 71 and 72 is an axially symmetric lens. However, as shown in Figure 19, each of the two lenses 71 and 72 has been processed by cutting the top and bottom in the Y-axis direction, leaving a central region through which the laser beam passes. For reference, the outline of the lens before the top and bottom were cut is shown by a dotted line in Figure 19. In this example, the size of each of the two lenses 71 and 72 in the X-axis direction is larger than the size in the Y-axis direction. By adopting such a lens structure, it is expected that lens costs, lens processing time, and the weight of the optical element 70 will be reduced. Furthermore, this lens structure may also contribute to saving space inside the wavelength beam coupling device 106 and miniaturizing the wavelength beam coupling device 106. Note that the two lenses 71 and 72 may be formed by injection molding or glass molding without the cutting process.

[0103] When wavelength beam coupling is performed, the optical element 70 reduces the distance between the beam center axes of the multiple collimated beams 11, thereby reducing the incident light pitch to the first diffraction grating 30A and decreasing the interval Δλ between the peak wavelengths of the laser beam. This increases the number of wavelengths that can be combined, and as a result, enables higher output of the wavelength beam coupling device. Thus, with the wavelength beam coupling device 105 or 106 according to this embodiment, it is possible to further increase the output and power density of the wavelength-coupled laser beam.

[0104] In the wavelength beam coupling device 104 shown in Figure 11, an optical element 70 can be placed in the optical path between the collimator 20 and the polarizing beam splitter 81. With a wavelength beam coupling device having such a configuration, it is possible to further increase the output and power density by combining an optical element that reduces the distance between the beam center axes, a diffraction grating, and a polarization separation and combination mechanism.

[0105] <4. Fourth Embodiment of a Wavelength Beam Coupling Apparatus> A fourth embodiment of the wavelength beam coupling apparatus according to this disclosure will be described with reference to Figure 20.

[0106] Figure 20 is a schematic plan view of the configuration of a fourth embodiment of the wavelength beam coupling apparatus according to the present disclosure, viewed from a direction perpendicular to the XZ plane. The wavelength beam coupling apparatus 110 illustrated in Figure 20 includes a moving unit 46A that supports the second diffraction grating 30B so as to be movable in at least a first direction, but does not include the aforementioned optical coupling unit configured to be movable in a second direction. The moving unit 46A illustrated in Figure 20 is a single-axis automatic stage that supports the second diffraction grating 30B so as to be movable in the Z-axis direction, which is the first direction. However, similar to the moving unit 46 shown in Figure 10, the moving unit 46A may be a two-axis automatic stage that supports the second diffraction grating 30B so as to be movable in the X-axis and Z-axis directions.

[0107] The moving unit 46A may be configured to move the second diffraction grating 30B in at least a first direction in response to a signal defining a shift amount determined based on the operating state of the laser light source 500. The control device 50 in the example shown in Figure 20 may be electrically connected to the moving unit 46A and configured or programmed to determine the shift amount based on the operating state of the laser light source 500 and transmit a signal defining the shift amount to the moving unit 46A.

[0108] When the position of the second diffraction grating 30B is fixed, as described above, the diffraction angle at the first diffraction grating 30A changes due to the wavelength shift, and the spot on the second diffraction grating 30B onto which the reflected diffracted light is incident moves. In this case, by moving the second diffraction grating 30B by a shift amount Δz in the Z-axis direction shown in Figure 20, it becomes possible to align the central axis of the wavelength-coupled beam 19 traveling at the design wavelength (solid line shown in Figure 20) with the central axis of the wavelength-coupled beam 19 when a wavelength shift occurs (dotted line shown in Figure 20), while forming a spot in a desired region on the surface of the second diffraction grating 30B where the diffraction grooves are formed.

[0109] The shift amount Δz, which defines the amount of movement in the Z-axis direction, can be predicted from the driving state of the laser light source 500. Therefore, the control device 50 can determine the shift amount Δz based on the driving state of the laser light source 500. The control device 50 transmits a signal defining the determined shift amount Δz to the moving unit 46A, and moves the second diffraction grating 30B by the shift amount Δz in the Z-axis direction. This suppresses the decrease in coupling efficiency of the optical transmission fiber 60. In this way, even when the moving unit 46A is moved in the Z-axis direction, the same suppression effect against the decrease in coupling efficiency as when the optical coupling unit described above is moved in the X-axis direction can be obtained.

[0110] The inventors verified the effect of suppressing the decrease in coupling efficiency of the optical transmission fiber when the optical coupling unit is moved in the second direction, the X-axis direction, and when the moving unit is moved in the first direction, the Z-axis direction, using optical output [W] and multiplexing efficiency [%] as indicators. Here, optical output is defined by the optical power (Pf [W]) output from the optical transmission fiber. Multiplexing efficiency is defined by the ratio (Pf / P0) of the optical power output from the optical transmission fiber (Pf [W]) to the optical power (P0 [W]) output from the laser light source. In other words, multiplexing efficiency is the overall efficiency of the wavelength beam coupling device, which is obtained by integrating the transmittance of the optical elements, the diffraction efficiency of the diffraction grating, the coupling efficiency to the optical transmission fiber, and the transmission efficiency of the optical transmission fiber. The optical power (P0 [W]) output from the laser light source and the optical power (Pf [W]) output from the optical transmission fiber were measured using the "Fan-Cooled Thermal Sensor (FL500A-LP1)" from Ophir Japan Co., Ltd. DBR-LDs with different wavelengths were used as the laser light source.

[0111] Figure 21A is a graph showing the measurement results of the optical output when the optical coupling unit is moved in the second direction. Figure 21B is a graph showing the measurement results of the multiplexing efficiency when the optical coupling unit is moved in the second direction. In the graph of Figure 21A, the vertical axis represents the optical output [W] and the horizontal axis represents the drive current of the laser light source [A]. In the graph of Figure 21B, the vertical axis represents the multiplexing efficiency [%] and the horizontal axis represents the drive current of the laser light source [A]. Figure 21A shows the measurement results of the optical output when the optical coupling unit is moved in the second direction, and the calculation results of the optical output when no measures are taken to correct the wavelength shift, as Example 1 and Comparative Example, respectively. Figure 21B shows the measurement results of the multiplexing efficiency when the optical coupling unit is moved in the second direction, and the calculation results of the multiplexing efficiency when no measures are taken to correct the wavelength shift, as Example 1 and Comparative Example, respectively.

[0112] In Example 1, the optical output [W] is the measured result of wavelength beam coupling of three laser beams with wavelengths of 457, 459, and 461 [nm], and the multiplexing efficiency [%] is the measured result of wavelength beam coupling of these three laser beams. On the other hand, in the Comparative Example, the optical output [W] is the calculated result of theoretical calculation of the optical output [W] estimated from the measured wavelength shift amount, and the multiplexing efficiency [%] is the calculated result of theoretical calculation of the multiplexing efficiency [%] estimated from the measured wavelength shift amount.

[0113] In the optical output graph shown in Figure 21A, in the comparative example, the optical output decreases as the drive current of the laser light source increases, whereas in Example 1, the optical output increases in proportion to the increase in drive current. In the multiplexing efficiency graph shown in Figure 21B, in the comparative example, the multiplexing efficiency decreases as the drive current of the laser light source increases, whereas in Example 1, the multiplexing efficiency remains almost constant even as the drive current increases.

[0114] Thus, it was confirmed that the decrease in coupling efficiency of the optical transmission fiber can be suppressed by moving the optical coupling unit in a second direction as a countermeasure against wavelength shift.

[0115] Figure 22A is a graph showing the measurement results of the optical output when the mobile unit is moved in the first direction. Figure 22B is a graph showing the measurement results of the multiplexing efficiency when the mobile unit is moved in the first direction. In the graph of Figure 22A, the vertical axis represents the optical output [W] and the horizontal axis represents the drive current of the laser light source [A]. In the graph of Figure 22B, the vertical axis represents the multiplexing efficiency [%] and the horizontal axis represents the drive current of the laser light source [A]. Figure 22A shows the measurement results of the optical output when the mobile unit is moved in the first direction, and the calculation results of the optical output when no measures are taken to correct the wavelength shift, as Example 2 and Comparative Example, respectively. Figure 22B shows the measurement results of the multiplexing efficiency when the mobile unit is moved in the first direction, and the calculation results of the multiplexing efficiency when no measures are taken to correct the wavelength shift, as Example 2 and Comparative Example, respectively.

[0116] In Example 2, the optical output [W] is the measured result of wavelength beam coupling of three laser beams of wavelengths 457, 459, and 461 [nm], similar to Example 1 in Figure 21A, and the multiplexing efficiency [%] is the measured result of wavelength beam coupling of these three laser beams, similar to Example 1 in Figure 21B. On the other hand, in the comparative example, the optical output [W] is the calculated result of theoretical calculation of the optical output [W] estimated from the measured wavelength shift amount, similar to the comparative example in Figure 21A, and the multiplexing efficiency [%] is the calculated result of theoretical calculation of the multiplexing efficiency [%] estimated from the measured wavelength shift amount, similar to the comparative example in Figure 21B.

[0117] In the optical output graph shown in Figure 22A, in the comparative example, the optical output decreases as the drive current of the laser light source increases, whereas in Example 2, the optical output increases in proportion to the increase in drive current. In the multiplexing efficiency graph shown in Figure 22B, in the comparative example, the multiplexing efficiency decreases as the drive current of the laser light source increases, whereas in Example 2, the multiplexing efficiency remains almost constant even as the drive current increases.

[0118] Thus, it was confirmed that moving the mobile unit in the first direction as a countermeasure against wavelength shift can suppress the decrease in coupling efficiency of the optical transmission fiber. Furthermore, from the measurement results of Example 1 and Example 2, it was confirmed that whether the optical coupling unit is moved in the second direction or the mobile unit is moved in the first direction as a countermeasure against wavelength shift, substantially equivalent suppression effects on the decrease in coupling efficiency of the optical transmission fiber can be obtained. In other words, it was confirmed that both moving the optical coupling unit and moving the mobile unit are effective as countermeasures against wavelength shift.

[0119] <5. Embodiment of a Direct Diode Laser Apparatus> Hereinafter, embodiments of the direct diode laser apparatus according to this disclosure will be described with reference to Figures 23 and 24.

[0120] Figure 23 is a schematic plan view of an embodiment of the direct diode laser apparatus according to the present disclosure, viewed from a direction perpendicular to the XZ plane. The direct diode laser apparatus 1000 in this embodiment includes a wavelength beam coupling device 400, a laser light source 500 comprising a plurality of semiconductor laser devices 510, each emitting laser light with different peak wavelengths, and an optical fiber array 530 configured to form a laser beam 10 incident on the collimator 20 of the wavelength beam coupling device 400 from the laser light emitted from the plurality of semiconductor laser devices 510. In the example shown in Figure 23, laser light with peak wavelengths λ1, λ2, λ3, λ4, and λ5 is emitted from the plurality of semiconductor laser devices 510. The laser light emitted from each semiconductor laser device 510 is optically coupled to the corresponding optical fiber 520 of the optical fiber array 530. Even if the laser light emitted from each semiconductor laser device 510 is linearly polarized, if the optical fiber 520 is not a polarization-retaining fiber, the polarization state of the laser light changes as it passes through the optical fiber 520. Therefore, each of the multiple laser beams 10 formed by the optical fiber array 530 in this embodiment is unpolarized.

[0121] By using the optical fiber array 530, the optical fibers 520 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 530 in parallel with high accuracy. With the optical fiber array 530, the optical fiber extending from the laser light source 500 can also be fused and connected to the optical fiber 520 of the optical fiber array 530.

[0122] Figure 23 illustrates a direct diode laser apparatus 1000 comprising a wavelength beam coupling device 400 having the structure shown in Figure 18. However, the direct diode laser apparatus according to the embodiments of this disclosure is not limited to the example shown in Figure 23, and may include various embodiments described above, or modifications thereof. Multiple laser beams 10 with different peak wavelengths, emitted parallel to each other from an optical fiber array 530 in a first direction, are incident parallel to each other on the collimator 20 of the wavelength beam coupling device 400.

[0123] In this embodiment, the optical elements such as diffraction gratings and polarization conversion elements in the wavelength beam coupling device 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 materials that do not easily absorb blue band light, such as synthetic 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.

[0124] The wavelength-coupled beam 19 is coupled to the optical transmission fiber 60 by the optical coupling unit 40. Examples of optical transmission fibers 60 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.

[0125] Figure 24 is a plan view, viewed from a direction perpendicular to the XZ plane, schematically showing another configuration in an embodiment of the direct diode laser apparatus according to the present disclosure. The direct diode laser apparatus 1000 shown in Figure 24 includes a semiconductor laser element 540 as a laser light source 500. The semiconductor laser element 540 is a single light source with controlled wavelength. In the example shown in Figure 24, the semiconductor laser element 540 is a laser bar having five laser oscillation regions 540X. Each of the five laser oscillation regions 540X is a distributed feedback type LD or a distributed reflection type LD, which performs laser oscillation at peak wavelengths λ1, λ2, λ3, λ4, and λ5, and emits laser light with peak wavelengths λ1, λ2, λ3, λ4, and λ5. The number of laser oscillation regions 540X contained in one laser bar is not limited to 5, but may be 2, 3, or 4, or 6 or more, for example, 10 or more. The semiconductor laser element 540 may have multiple ridges or multiple stripe electrodes that define multiple laser oscillation regions 540X. The semiconductor laser element 540 does not have to be a single laser bar, but may be a collection of multiple laser bars.

[0126] According to the direct diode laser apparatus of this embodiment, the output and power density can be increased by coaxializing the diffracted light generated by the diffraction grating. In particular, by using the wavelength beam coupling apparatus according to the second embodiment, even if the polarization state of the laser light emitted from multiple semiconductor laser apparatuses or semiconductor laser elements becomes unpolarized by the optical fiber array apparatus, it is converted to linear polarization by the polarization beam splitter, making it possible to increase the diffraction efficiency by using a diffraction grating suitable for each polarization state. Furthermore, by coaxializing the reflected diffracted light generated by such a diffraction grating, the output and power density can be increased.

[0127] <6. Embodiment of a laser processing machine> Next, an embodiment of the laser processing machine 2000 according to the present disclosure will be described with reference to Figure 25. Figure 25 is a diagram showing an example of the configuration in an embodiment of the processing machine according to the present disclosure.

[0128] The illustrated laser processing machine 2000 comprises a light source device 1100 and a processing head 1200 connected to an optical transmission fiber 60 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 60. In the illustrated example, there is one light source device 1100. The processing head 1200 can be connected to multiple light source devices 1100 via the optical transmission fiber 60.

[0129] 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 or semiconductor laser elements 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.

[0130] 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.

[0131] Furthermore, the laser beam emitted from the processing head 1200 may include laser beams other than those emitted and coupled from a semiconductor laser device or semiconductor laser element. For example, the peak wavelength of the laser beam emitted from a semiconductor laser device and wavelength-coupled 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.

[0132] This disclosure includes wavelength beam coupling devices, direct diode laser devices, and laser processing machines as described in the following items.

[0133] [Item 1] A wavelength beam coupling device for coupling multiple laser beams emitted from a laser light source, each having different peak wavelengths, and whose central axes are aligned in a second direction intersecting the first direction, wherein the central axes of the beams emitted in a first direction intersect the first direction, A first diffraction grating and a second diffraction grating, wherein the first diffraction grating is positioned to receive the plurality of laser beams and diffracts the plurality of laser beams in different directions according to their wavelengths and causes them to be incident on the second diffraction grating, and the second diffraction grating further diffracts the plurality of laser beams diffracted by the first diffraction grating to form a wavelength-coupled beam and emits the wavelength-coupled beam in the first direction, An optical coupling unit for coupling the wavelength-coupled beam into an optical transmission fiber, comprising an optical coupling unit configured to be movable in the second direction, A wavelength beam coupling device equipped with the following features.

[0134] [Item 2] The wavelength beam coupling apparatus according to item 1, wherein the optical coupling unit has a movable stage that moves the optical coupling unit in the second direction by the shift amount in response to a signal that defines a shift amount determined based on the operating state of the laser light source.

[0135] [Item 3] The aforementioned photo-coupled unit is An optical focuser for focusing the wavelength-coupled beam, An optical coupling portion connected to the end face (termination) of the optical transmission fiber, the optical coupling portion being fixed at the position into which the wavelength-coupled beam emitted from the optical converger is incident, It has, The movable stage supports the optical focuser and the optical coupling unit, and is a wavelength beam coupling apparatus as described in item 2.

[0136] [Item 4] A polarizing beam splitter is disposed between the laser light source and the first diffraction grating, The system comprises a first polarization conversion element disposed between the polarization beam splitter and the first diffraction grating, The aforementioned photo-coupled unit is A polarizing beam coupler is disposed between the second diffraction grating and the optical focuser, A second polarization conversion element is disposed between the second diffraction grating and the polarization beam coupler, It has, The wavelength beam coupling apparatus according to item 3, wherein the movable stage further supports the polarizing beam coupler and the second polarization conversion element, and moves the optical focuser, the optical coupling section, the polarizing beam coupler and the second polarization conversion element by the shift amount in the second direction.

[0137] [Item 5] The optical coupling unit has a mounting substrate on which the optical converger, the optical coupling section, the polarizing beam coupler, and the second polarization conversion element are mounted. The movable stage supports the mounting substrate, and the wavelength beam coupling apparatus is as described in item 4.

[0138] [Item 6] The optical coupling unit has a first mirror and a second mirror arranged parallel to each other between the second diffraction grating and the optical transmission fiber. The first reflective surface of the first mirror and the second reflective surface of the second mirror are perpendicular to a plane including the first and second directions. The wavelength beam coupling apparatus according to item 1, wherein the first reflecting surface receives the wavelength-coupled beam and reflects it toward the second reflecting surface, and the second reflecting surface reflects the wavelength-coupled beam reflected by the first reflecting surface and directs it toward the optical transmission fiber.

[0139] [Item 7] The wavelength beam coupling apparatus according to item 6, wherein the optical coupling unit has a movable stage that supports the first mirror and moves the first mirror in the second direction by a shift amount determined based on the operating state of the laser light source.

[0140] [Item 8] A wavelength beam coupling apparatus according to item 6 or 7, comprising an optical focuser for focusing the wavelength-coupled beam reflected by the second reflecting surface.

[0141] [Item 9] The wavelength beam coupling apparatus according to item 3 or 8, wherein the optical focuser includes an aspherical lens for focusing the wavelength-coupled beam.

[0142] [Item 10] A wavelength beam coupling apparatus according to any one of items 1 to 9, comprising a moving unit that supports the second diffraction grating so as to be movable in at least one of the first or second directions.

[0143] [Item 11] A collimator that converts the aforementioned multiple laser beams into multiple collimated beams, An optical element is positioned between the collimator and the first diffraction grating and configured to reduce the distance between the beam center axes of the plurality of collimated beams and cause them to be emitted. A wavelength beam coupling apparatus comprising any one of items 1 to 10.

[0144] [Item 12] The optical element is a beam reducer, The wavelength beam coupling apparatus according to item 11, wherein the beam reducer is configured to emit the plurality of laser beams parallel to each other.

[0145] [Item 13] A wavelength beam coupling apparatus according to any one of items 2 to 5 and 7, comprising a control device configured or programmed to determine the shift amount based on the operating state of the laser light source and to transmit the signal defining the shift amount to the movable stage.

[0146] [Item 14] Wavelength beam coupling apparatus as described in item 11 or 12, Multiple semiconductor laser devices, each emitting laser beams with different peak wavelengths, A fiber optic array that forms the plurality of laser beams incident on the collimator of the wavelength beam coupling device from the plurality of laser beams emitted from the plurality of semiconductor laser devices, A direct diode laser device equipped with the following features.

[0147] [Item 15] The direct diode laser apparatus according to item 14, wherein each of the plurality of semiconductor laser apparatuses comprises a distributed feedback laser diode or a distributed reflection laser diode.

[0148] [Item 16] The direct diode laser apparatus according to item 14, wherein each of the plurality of semiconductor laser apparatuses is configured to oscillate in a single longitudinal mode.

[0149] [Item 17] The direct diode laser apparatus according to any one of items 14 to 17, wherein the aforementioned distinct peak wavelengths are in the range of 430 nm to 480 nm.

[0150] [Item 18] The direct diode laser apparatus according to any one of items 14 to 17, wherein the optical fiber array is configured to emit the plurality of laser beams parallel to each other.

[0151] [Item 19] A direct diode laser apparatus as described in any one of items 14 to 18, 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.

[0152] [Item 20] A wavelength beam coupling device for coupling multiple laser beams emitted from a laser light source, each having different peak wavelengths, and whose central axes are aligned in a second direction intersecting the first direction, wherein the central axes of the beams emitted in a first direction intersect the first direction, A first diffraction grating and a second diffraction grating, wherein the first diffraction grating is positioned to receive the plurality of laser beams and diffracts the plurality of laser beams in different directions according to their wavelengths and causes them to be incident on the second diffraction grating, and the second diffraction grating further diffracts the plurality of laser beams diffracted by the first diffraction grating to form a wavelength-coupled beam and emits the wavelength-coupled beam in the first direction, A moving unit that supports the second diffraction grating so as to be movable in at least the first direction, A wavelength beam coupling device equipped with the following features.

[0153] [Item 21] The wavelength coupling apparatus according to item 20, wherein the moving unit is configured to move the second diffraction grating in the first direction in response to a signal defining a shift amount determined based on the operating state of the laser light source.

[0154] [Item 22] The wavelength beam coupling apparatus according to item 21, comprising a control device configured or programmed to determine the shift amount based on the operating state of the laser light source and to transmit the signal defining the shift amount to the moving unit. [Industrial applicability]

[0155] 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]

[0156] 20...Collimator, 30...Diffraction grating, 30A...First diffraction grating, 30B...Second diffraction grating, 40, 40A, 40B, 40C...Optical coupling unit, 41...Movable stage, 42...Optical focuser, 43...Optical coupling section, 45A, 45B...First and second mirrors, 46...Movement unit, 47...Mounting board, 50...Control device, 50...Optical transmission fiber, 70...Optical element, 71, 72...Lens, 81...Polarizing beam splitter, 8 2...Polarizing beam coupler, 91...First polarization conversion element, 92...Second polarization conversion element, 100-106, 400...Wavelength beam coupling device, 500...Laser light source, 510...Semiconductor laser device, 520...Optical fiber, 530...Optical fiber array, 540...Semiconductor laser element, 1000...Direct diode laser device, 1100...Light source device, 1200...Processing head, 1300...Object, 2000...Laser processing machine

Claims

1. A wavelength beam coupling device for coupling multiple laser beams emitted from a laser light source, each having different peak wavelengths, and whose central axes are aligned in a second direction intersecting the first direction, wherein the central axes of the beams emitted in a first direction intersect the first direction. A first diffraction grating and a second diffraction grating, wherein the first diffraction grating is positioned to receive the plurality of laser beams and diffracts the plurality of laser beams in different directions according to their wavelengths and causes them to be incident on the second diffraction grating, and the second diffraction grating further diffracts the plurality of laser beams diffracted by the first diffraction grating to form a wavelength-coupled beam and emits the wavelength-coupled beam in the first direction, An optical coupling unit for coupling the wavelength-coupled beam into an optical transmission fiber, comprising an optical coupling unit configured to be movable in the second direction, A wavelength beam coupling device equipped with the following features.

2. The wavelength beam coupling apparatus according to claim 1, wherein the optical coupling unit has a movable stage that moves the optical coupling unit in the second direction by the shift amount in response to a signal that defines a shift amount determined based on the operating state of the laser light source.

3. The aforementioned photo-coupled unit is An optical focuser for focusing the wavelength-coupled beam, An optical coupling portion connected to the end face of the optical transmission fiber, the optical coupling portion being fixed at a position into which the wavelength-coupled beam emitted from the optical converger is incident, It has, The wavelength beam coupling apparatus according to claim 2, wherein the movable stage supports the optical focuser and the optical coupling section.

4. A polarizing beam splitter is disposed between the laser light source and the first diffraction grating, The system comprises a first polarization conversion element disposed between the polarization beam splitter and the first diffraction grating, The aforementioned photo-coupled unit is A polarizing beam coupler is disposed between the second diffraction grating and the optical focuser, A second polarization conversion element is disposed between the second diffraction grating and the polarization beam coupler, It has, The wavelength beam coupling apparatus according to claim 3, wherein the movable stage further supports the polarizing beam coupler and the second polarization conversion element, and moves the optical focuser, the optical coupling section, the polarizing beam coupler and the second polarization conversion element by the shift amount in the second direction.

5. The optical coupling unit has a mounting substrate on which the optical focuser, the optical coupling section, the polarizing beam coupler, and the second polarization conversion element are mounted. The wavelength beam coupling apparatus according to claim 4, wherein the movable stage supports the mounting substrate.

6. The optical coupling unit has a first mirror and a second mirror arranged parallel to each other between the second diffraction grating and the optical transmission fiber. The first reflective surface of the first mirror and the second reflective surface of the second mirror are perpendicular to a plane including the first and second directions. The wavelength beam coupling apparatus according to claim 1, wherein the first reflecting surface receives the wavelength-coupled beam and reflects it toward the second reflecting surface, and the second reflecting surface reflects the wavelength-coupled beam reflected by the first reflecting surface and directs it toward the optical transmission fiber.

7. The wavelength beam coupling apparatus according to claim 6, wherein the optical coupling unit has a movable stage that supports the first mirror and moves the first mirror in the second direction by a shift amount determined based on the operating state of the laser light source.

8. The wavelength beam coupling apparatus according to claim 6 or 7, further comprising an optical focuser for focusing the wavelength-coupled beam reflected by the second reflective surface.

9. The wavelength beam coupling apparatus according to claim 3, wherein the optical focuser includes an aspherical lens for focusing the wavelength-coupled beam.

10. The wavelength beam coupling apparatus according to claim 1 or 2, comprising a moving unit that supports the second diffraction grating so as to be movable in at least one of the first or second directions.

11. A collimator that converts the aforementioned multiple laser beams into multiple collimated beams, An optical element is positioned between the collimator and the first diffraction grating and configured to reduce the distance between the beam center axes of the plurality of collimated beams and cause them to be emitted. A wavelength beam coupling apparatus according to claim 1 or 2, comprising:

12. The optical element is a beam reducer, The wavelength beam coupling apparatus according to claim 11, wherein the beam reducer is configured to emit the plurality of laser beams parallel to each other.

13. The wavelength beam coupling apparatus according to claim 2, comprising a control device configured or programmed to determine the shift amount based on the operating state of the laser light source and to transmit the signal defining the shift amount to the movable stage.

14. A wavelength beam coupling device for coupling multiple laser beams emitted from a laser light source, each having different peak wavelengths, and whose central axes are aligned in a second direction intersecting the first direction, wherein the central axes of the beams emitted in a first direction intersect the first direction. A first diffraction grating and a second diffraction grating, wherein the first diffraction grating is positioned to receive the plurality of laser beams and diffracts the plurality of laser beams in different directions according to their wavelengths and causes them to be incident on the second diffraction grating, and the second diffraction grating further diffracts the plurality of laser beams diffracted by the first diffraction grating to form a wavelength-coupled beam and emits the wavelength-coupled beam in the first direction, A moving unit that supports the second diffraction grating so that it can move in at least the first direction, A wavelength beam coupling device equipped with the following features.

15. The wavelength coupling apparatus according to claim 14, wherein the moving unit is configured to move the second diffraction grating in the first direction in response to a signal that defines a shift amount determined based on the operating state of the laser light source.

16. The wavelength beam coupling apparatus according to claim 15, comprising a control device configured or programmed to determine the shift amount based on the operating state of the laser light source and to transmit the signal defining the shift amount to the moving unit.

17. A wavelength beam coupling apparatus according to claim 11, Multiple semiconductor laser devices, each emitting laser beams with different peak wavelengths, A fiber optic array that forms the plurality of laser beams incident on the collimator of the wavelength beam coupling device from the plurality of laser beams emitted from the plurality of semiconductor laser devices, A direct diode laser device equipped with the following features.

18. The direct diode laser apparatus according to claim 17, wherein each of the plurality of semiconductor laser apparatuses comprises a distributed feedback laser diode or a distributed reflection laser diode.

19. The direct diode laser apparatus according to claim 17, wherein each of the plurality of semiconductor laser apparatuses is configured to oscillate in a single longitudinal mode.

20. The direct diode laser apparatus according to claim 17, wherein the aforementioned distinct peak wavelengths are included in the range of 430 nm to 480 nm.

21. The direct diode laser apparatus according to claim 17, wherein the optical fiber array is configured to emit the plurality of laser beams parallel to each other.

22. The at least one direct diode laser apparatus according to claim 17, 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 [specific features / equipment].

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