Wavelength-coupled laser device and wavelength-coupled laser system

Abstract

This wavelength-coupled laser device includes n angle-dispersive wavelength coupling optical systems (11), n or more beam expansion optical systems (12), and (n-1) beam splitter type wavelength coupling optical systems (13), wherein: the angle-dispersive wavelength coupling optical systems (11) include a plurality of laser light sources (111) that output laser beams having mutually different wavelengths, and an angle-dispersive wavelength coupling optical element that outputs one wavelength-coupled beam having the wavelengths of each of the laser beams output by the plurality of laser light sources (111); the power density of the wavelength-coupled beams output by the angle-dispersive wavelength coupling optical systems (11) is the same as the power density of the wavelength-coupled beams finally obtained by the (n-1) beam splitter type wavelength coupling optical systems (13); and one wavelength-coupled beam having the wavelengths of the wavelength-coupled beams output by the n angle-dispersive wavelength coupling optical systems (11) is finally obtained by means of the (n-1) beam splitter type wavelength coupling optical systems (13).

Description

Wavelength-combined laser device and wavelength-combined laser system

[0001] The present disclosure relates to a wavelength-combined laser device and a wavelength-combined laser system that combine laser beams having different wavelengths into a single beam.

[0002] Wavelength combining is one of the methods to realize high-power lasers that cannot be achieved with a single laser. Wavelength combining can increase the laser power without compromising the beam quality or complex phase control. Therefore, wavelength combining is expected to be particularly useful in applications that require focusing.

[0003] When attempting to obtain a high-power laser with good beam quality through this wavelength combining, the power that can be obtained is, simply put, the power of one laser multiplied by the number of combined lasers. Therefore, in order to achieve high output, it is important to use a laser with a high power and to combine as many lasers as possible.

[0004] Fiber lasers are one example of lasers that have shown remarkable progress in increasing power output in recent years. By selecting an appropriate configuration, fiber lasers can achieve average powers of kW to over 10 kW in the 1 μm wavelength band. Furthermore, because the gain wavelength of the Yb ions used as the gain medium is broad, high-power lasers can potentially be obtained over a wide wavelength range of approximately 1000 nm to 1100 nm. Therefore, fiber lasers are suitable as lasers for wavelength combining.

[0005] On the other hand, the wavelength linewidth of these high-power fiber lasers is not necessarily narrow, but rather extends from several hundred MHz to several nm. This is the result of suppressing power limitations due to nonlinear effects within the fiber, and there is a trade-off between wavelength linewidth and laser power. For wavelength combining lasers, the power level of a single laser is important, so the wavelength linewidth is inevitably expected to be on the order of several hundred MHz to several nm.

[0006] In response to this, for example, Patent Document 1 discloses a wavelength-combined laser device that uses a diffraction grating as a wavelength-combining element. In this wavelength-combined laser device, two diffraction gratings with the same groove density are arranged opposite each other to suppress deterioration of beam quality caused by the wavelength linewidth of each laser. As a result, in this wavelength-combined laser device, the spread angle corresponding to the wavelength linewidth generated by the first diffraction grating is parallelized by the second diffraction grating, thereby converting the spread corresponding to the wavelength linewidth into a position shift.

[0007] Furthermore, with high-power lasers, even slight absorption by the substrate of the optical component or the optical thin film can generate a large amount of heat, causing adverse effects such as thermal lensing and thermal birefringence, and even damage. To suppress these effects, the power density of the beam is controlled below a certain level when passing through an optical component.

[0008] If the design concept is to maintain the power density at a certain value or less, increasing the power after wavelength combining by a factor of 10 (for example, increasing the number of combined fibers from 4 to 40) will increase the beam diameter after wavelength combining by a factor of √10, and the beam diameter will need to be expanded as the power increases.

[0009] The beam diameter (ω) has a relationship with the beam divergence angle (θ) as shown in the following formula (1) due to the law of luminance constancy. ２ is the beam quality and λ is the wavelength. From this formula (1), as the beam diameter increases with increasing power, the divergence angle becomes smaller. ω×θ=M ２ λ / π (1)

[0010] Furthermore, when a diffraction grating is used as the wavelength coupling element, the effect of the wavelength line width on the beam quality can be estimated by the following formula (2). In formula (2), g is the groove density of the diffraction grating, Δλ is the wavelength line width, and α is the diffraction angle from the diffraction grating. From formula (2), it can be seen that in wavelength coupling, if the number of coupled beams is simply increased or the power per beam is increased to scale the power, the accompanying need to expand the beam diameter poses the problem of degrading the beam quality. M ２=√(1+(πgΔλω / 2λcosα)) (2)

[0011] U.S. Patent No. 7,199,924

[0012] As described above, the conventional technology is unable to suppress the expansion of the beam diameter while maintaining the power density at a certain level or less.

[0013] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wavelength-combined laser device that can suppress the expansion of the beam diameter while maintaining the power density below a certain level.

[0014] A wavelength-combining laser device according to the present disclosure includes n angle-dispersive wavelength-combining optical systems that output wavelength-combined beams having a plurality of wavelengths different from each other; n or more beam expansion optical systems that expand the wavelength-combined beams output by the angle-dispersive wavelength-combining optical systems to have the same beam diameter, and (n-1) beam splitter-type wavelength-combining optical systems that receive as input two different wavelength-combined beams and output one wavelength-combined beam having the wavelength of the two wavelength-combined beams, wherein the angle-dispersive wavelength-combining optical system includes a plurality of laser light sources that output laser beams having different wavelengths from each other, and angle-dispersive wavelength-combining elements that receive as input the laser beams output by the plurality of laser light sources and output one wavelength-combined beam having the wavelengths of the plurality of laser beams, and the power density of the wavelength-combined beam output by the angle-dispersive wavelength-combining optical system is the same as the power density of the wavelength-combined beam finally obtained by the (n-1) beam splitter-type wavelength-combining optical systems, and wherein a single wavelength-combined beam having the wavelength of the wavelength-combined beams output by the n angle-dispersive wavelength-combining optical systems is finally obtained by the (n-1) beam splitter-type wavelength-combining optical systems.

[0015] According to the present disclosure, with the above-described configuration, it is possible to suppress the expansion of the beam diameter on the plane of the angle dispersive wavelength coupling element while maintaining the power density at or below a certain level.

[0016] Fig. 1 is a schematic diagram showing a configuration example of a wavelength-coupled laser device according to a first embodiment. Fig. 2 is a diagram showing a configuration example of a wavelength-coupled laser device according to a first embodiment. Fig. 3 is a diagram showing an example of the spectrum of a wavelength-coupled beam finally obtained by the wavelength-coupled laser device according to the first embodiment. Fig. 4 is a schematic diagram showing another configuration example of a wavelength-coupled laser device according to the first embodiment. Fig. 5 is a schematic diagram showing a configuration example of a wavelength-coupled laser system according to a second embodiment.

[0017] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1. Fig. 1 is a schematic diagram showing an example of the configuration of a wavelength-combining laser device 1 according to embodiment 1, and Fig. 2 is a diagram showing a more specific example of the configuration of the wavelength-combining laser device 1 according to embodiment 1. As shown in Figs. 1 and 2, for example, the wavelength-combining laser device 1 includes n angle-dispersive wavelength-combining optical systems (WD) 11, n or more beam expansion optical systems 12, and (n-1) beam splitter wavelength-combining optical systems (BS) 13.

[0018] 1 and 2 show a case where four angle-dispersive wavelength combining optical systems 11 (angle-dispersive wavelength combining optical system 11-1, angle-dispersive wavelength combining optical system 11-2, angle-dispersive wavelength combining optical system 11-3, and angle-dispersive wavelength combining optical system 11-4) are provided as the n angle-dispersive wavelength combining optical systems 11. Also, the example of FIGS. 1 and 2 shows a case where four beam expanding optical systems 12 (beam expanding optical system 12-1, beam expanding optical system 12-2, beam expanding optical system 12-3, and beam expanding optical system 12-4) are provided as the n or more beam expanding optical systems 12. Also, the example of FIGS. 1 and 2 shows a case where three beam splitter wavelength combining optical systems 13 (beam splitter wavelength combining optical system 13-1, beam splitter wavelength combining optical system 13-2, and beam splitter wavelength combining optical system 13-3) are provided as the (n-1) beam splitter wavelength combining optical systems 13.

[0019] Each of the angle-dispersive wavelength combining optical systems 11 outputs a wavelength-combined beam having a plurality of different wavelengths. As shown in FIG. 2 , the angle-dispersive wavelength combining optical system 11 includes a plurality of laser light sources 111 and a diffraction grating (angle-dispersive wavelength combining element) 112.

[0020] The laser light sources 111 output laser light. Note that the laser light sources 111 output laser light of wavelengths different from one another and different from the wavelengths used in the other angle-dispersive wavelength combining optical systems 11. The diffraction grating 112 receives the laser light output from each laser light source 111 and outputs a single wavelength-combined beam having the wavelength of each laser light. That is, the laser light output from each laser light source 111 is incident on the diffraction grating 112 at a plurality of different angles, and due to the characteristic that the propagation angle changes for each wavelength, the diffraction grating 112 outputs each laser light at the same (including the meaning of approximately the same) angle, thereby generating a single wavelength-combined beam.

[0021] The wavelength bandwidth of the laser light output by the laser light source 111 is, for example, 100 MHz or more. In the above description, the angle-dispersive wavelength coupling element is the diffraction grating 112. However, the angle-dispersive wavelength coupling element is not limited to this, and may be, for example, a prism. In the example of FIG. 2, the diffraction grating 112 is a transmission type diffraction grating, but it may also be a reflection type diffraction grating.

[0022] The multiple laser light sources 111 and the diffraction grating 112 are set at approximately blazed angles that provide good diffraction efficiency at the design wavelength, and the angles of incidence are selected so that the diffraction angles of the multiple laser beams are equal. As a result, the multiple laser beams after diffraction are combined into one beam, and wavelength combination is performed.

[0023] For example, if the design wavelength is 1050 nm and the groove density is 1700 lines / mm, the blazed angle is 63.2°. Furthermore, if the adjacent wavelength is 1070 nm, the incident angle is 67.9° and the diffraction angle is 63.2°. These can be calculated using a known diffraction grating equation.

[0024] Each laser beam is collimated and enters the diffraction grating 112 as parallel light. The angle-dispersive wavelength combining optical system 11 also includes an optical system (not shown) that shapes the beam into an ellipse according to the ratio between the angle of incidence and the angle of diffraction for wavelengths other than the blazed angle, so that the beam becomes a perfect circular beam after diffraction.

[0025] 1 and 2, the angle-dispersive wavelength combining optical system 11-1 outputs a wavelength-combined beam (SBC1). The angle-dispersive wavelength combining optical system 11-1 includes a plurality of laser light sources 111-1 and a diffraction grating 112-1, as shown in Fig. 2. In the example of Fig. 2, four laser light sources 111-1 are provided as the plurality of laser light sources 111-1.

[0026] The laser light source 111-1 outputs laser light. Note that the laser light sources 111-1 output laser light of wavelengths different from one another and different from the wavelengths used in the other angle-dispersive wavelength combining optical systems 11. In the example of FIG. 2 , the laser light sources 111-1 output laser light of wavelength λ11, laser light of wavelength λ12, laser light of wavelength λ13, and laser light of wavelength λ14, respectively. The diffraction grating 112-1 receives the laser light output from each laser light source 111-1 at a plurality of different angles and outputs a single wavelength-combined beam (SBC1) having the wavelengths of the laser light. That is, the diffraction grating 112-1 receives the laser light output from each laser light source 111-1 at a plurality of different angles, and due to the characteristic that the propagation angle changes for each wavelength, emits the laser light at the same (including the meaning of approximately the same) angle, thereby generating a single wavelength-combined beam (SBC1). In the example of FIG. 2, the diffraction grating 112-1 generates a wavelength combined beam (SBC1) with wavelengths λ11, λ12, λ13, and λ14.

[0027] 1 and 2, the angle-dispersive wavelength combining optical system 11-2 outputs a wavelength-combined beam (SBC2). The angle-dispersive wavelength combining optical system 11-2 includes a plurality of laser light sources 111-2 and a diffraction grating 112-2, as shown in Fig. 2. In the example of Fig. 2, four laser light sources 111-2 are provided as the plurality of laser light sources 111-2.

[0028] The laser light sources 111-2 output laser light. Note that the laser light sources 111-2 output laser light of wavelengths different from each other and different from the wavelengths used in the other angle dispersive wavelength combining optical systems 11. In the example of FIG. 2, the laser light sources 111-2 output laser light of wavelength λ21, laser light of wavelength λ22, laser light of wavelength λ23, and laser light of wavelength λ24, respectively. These wavelengths λ21, λ22, λ23, and λ24 are not identical to any of the wavelengths λ11, λ12, λ13, and λ14. The diffraction grating 112-2 receives the laser light output by each laser light source 111-2 and outputs a single wavelength combined beam (SBC2) having the wavelength of each laser light. That is, the diffraction grating 112-2 receives the laser beams output from the laser light sources 111-2 at different angles, and generates a single wavelength-combined beam (SBC2) by emitting the laser beams at the same (including the meaning of approximately the same) angle due to the characteristic that the propagation angle changes for each wavelength. In the example of Fig. 2, the diffraction grating 112-2 generates a wavelength-combined beam (SBC2) of wavelengths λ21, λ22, λ23, and λ24.

[0029] 1 and 2, the angle-dispersive wavelength combining optical system 11-3 outputs a wavelength-combined beam (SBC3). The angle-dispersive wavelength combining optical system 11-3 has, for example, a plurality of laser light sources 111-3 and a diffraction grating 112-3, as shown in Fig. 2. In the example of Fig. 2, four laser light sources 111-3 are provided as the plurality of laser light sources 111-3.

[0030] The laser light sources 111-3 output laser light. Note that the laser light sources 111-3 output laser light of wavelengths different from each other and different from the wavelengths used in the other angle dispersive wavelength combining optical systems 11. In the example of FIG. 2, the laser light sources 111-3 output laser light of wavelength λ31, laser light of wavelength λ32, laser light of wavelength λ33, and laser light of wavelength λ34, respectively. These wavelengths λ31, λ32, λ33, and λ34 are not identical to any of the wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, and λ24. The diffraction grating 112-3 receives the laser light output by each laser light source 111-3 and outputs a single wavelength combined beam (SBC3) having the wavelength of each laser light. That is, the diffraction grating 112-3 receives the laser beams output from the laser light sources 111-3 at different angles, and generates a single wavelength-combined beam (SBC3) by emitting the laser beams at the same (including the meaning of approximately the same) angle due to the characteristic that the propagation angle changes for each wavelength. In the example of Fig. 2, the diffraction grating 112-3 generates a wavelength-combined beam (SBC3) of wavelengths λ31, λ32, λ33, and λ34.

[0031] 1 and 2, the angle-dispersive wavelength combining optical system 11-4 outputs a wavelength-combined beam (SBC4). The angle-dispersive wavelength combining optical system 11-4 has a plurality of laser light sources 111-4 and a diffraction grating 112-4, as shown in Fig. 2. In the example of Fig. 2, four laser light sources 111-4 are provided as the plurality of laser light sources 111-4.

[0032] The laser light source 111-4 outputs laser light. Note that the laser light sources 111-4 output laser light of wavelengths different from each other and different from the wavelengths used in the other angle-dispersive wavelength combining optical systems 11. In the example of FIG. 2, the laser light sources 111-4 output laser light of wavelength λ41, laser light of wavelength λ42, laser light of wavelength λ43, and laser light of wavelength λ44, respectively. These wavelengths λ41, λ42, λ43, and λ44 are not identical to any of the wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, λ24, λ31, λ32, λ33, and λ34. The diffraction grating 112-4 receives the laser light output by each laser light source 111-4 and outputs a single wavelength-combined beam (SBC4) having the wavelength of each laser light. That is, the diffraction grating 112-4 receives the laser beams output from the laser light sources 111-4 at different angles, and generates a single wavelength-combined beam (SBC4) by emitting the laser beams at the same (including the meaning of approximately the same) angle due to the characteristic that the propagation angle changes for each wavelength. In the example of Fig. 2, the diffraction grating 112-4 generates a wavelength-combined beam (SBC4) of wavelengths λ41, λ42, λ43, and λ44.

[0033] Each beam expansion optical system 12 expands the beam diameter of the wavelength-combined beam output from each angle-dispersive wavelength combining optical system 11 (diffraction grating 112) to the same (including the meaning of approximately the same) beam diameter. As this beam expansion optical system 12, for example, a reflective optical system is used.

[0034] In the example of FIGS. 1 and 2, the beam expanding optical system 12-1 expands the beam diameter of the wavelength combined beam (SBC1) output by the angle dispersive wavelength combining optical system 11-1 (diffraction grating 112-1).

[0035] 1 and 2, the beam expansion optical system 12-2 expands the beam diameter of the wavelength combined beam (SBC2) output by the angle dispersive wavelength combining optical system 11-2 (diffraction grating 112-2). At this time, the beam expansion optical system 12-2 expands the beam diameter of the wavelength combined beam (SBC2) to the same (including the meaning of approximately the same) beam diameter as the wavelength combined beam (SBC1).

[0036] 1 and 2, the beam expansion optical system 12-3 expands the beam diameter of the wavelength combined beam (SBC3) output by the angle dispersive wavelength combining optical system 11-3 (diffraction grating 112-3). At this time, the beam expansion optical system 12-3 expands the beam diameter of the wavelength combined beam (SBC3) to the same (including the meaning of approximately the same) beam diameter as the wavelength combined beam (SBC1).

[0037] 1 and 2, the beam expansion optical system 12-4 expands the beam diameter of the wavelength combined beam (SBC4) output by the angle dispersive wavelength combining optical system 11-4 (diffraction grating 112-4). At this time, the beam expansion optical system 12-4 expands the beam diameter of the wavelength combined beam (SBC4) to the same (including the meaning of approximately the same) beam diameter as the wavelength combined beam (SBC1).

[0038] Each beam splitter-type wavelength combining optical system 13 is a beam splitter-type wavelength combining element that receives two different wavelength combined beams and outputs one wavelength combined beam having the wavelengths of the two wavelength combined beams. That is, the beam splitter-type wavelength combining optical system 13 transmits one of the two input wavelength combined beams and reflects the other wavelength combined beam in the same transmission direction to generate one wavelength combined beam. At least one of the wavelength combined beam expanded by the beam expansion optical system 12 or a wavelength combined beam output by another beam splitter-type wavelength combining optical system 13 is input to this beam splitter-type wavelength combining optical system 13.

[0039] Then, by the (n−1) beam splitter type wavelength combining optical systems 13, one wavelength combined beam having the wavelength of the wavelength combined beams output by the n angle dispersive type wavelength combining optical systems 11 is finally obtained.

[0040] For example, a dielectric multilayer filter or the like is used as this beam splitter type wavelength combining optical system 13. When a dielectric multilayer filter is used as the beam splitter type wavelength combining optical system 13, stable operation cannot be achieved in the wavelength region where the transmission and reflection characteristics of the dielectric multilayer filter are switched, resulting in an unusable band for wavelength combining. Therefore, when a dielectric multilayer filter is used as the beam splitter type wavelength combining optical system 13, it is suitable to use a filter designed as an edge filter with steep transmission and reflection characteristics, but this is not limitative.

[0041] 1 and 2, the beam splitter type wavelength combining optical system 13-1 has spectral characteristics of transmitting the wavelength combined beam (SBC1) of wavelengths λ11, λ12, λ13, and λ14 and reflecting the wavelength combined beam (SBC2) of wavelengths λ21, λ22, λ23, and λ24 in the transmission direction, out of the wavelength combined beam (SBC1) after the beam diameter has been expanded by the beam expansion optical system 12-1 and the wavelength combined beam (SBC2) after the beam diameter has been expanded by the beam expansion optical system 12-2. That is, the wavelength combined beam (SBC1) and the wavelength combined beam (SBC2) are incident on the beam splitter type wavelength combining optical system 13-1 from different directions, and the beam splitter type wavelength combining optical system 13-1 transmits the wavelength combined beam (SBC1) and reflects the wavelength combined beam (SBC2) in the transmission direction, thereby generating a single wavelength combined beam (SBC12).

[0042] 1 and 2, the beam splitter type wavelength combining optical system 13-2 has spectral characteristics of transmitting the wavelength combined beam (SBC3) of wavelengths λ31, λ32, λ33, and λ34 out of the wavelength combined beam (SBC3) after the beam diameter has been expanded by the beam expansion optical system 12-3 and the wavelength combined beam (SBC12) output by the beam splitter type wavelength combining optical system 13-1, and reflecting the wavelength combined beam (SBC12) of wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, and λ24 in the transmission direction. That is, in the beam splitter type wavelength combining optical system 13-2, the wavelength combined beam (SBC3) and the wavelength combined beam (SBC12) are incident from different directions, the wavelength combined beam (SBC3) is transmitted, and the wavelength combined beam (SBC12) is reflected in the same transmission direction, thereby forming a single wavelength combined beam (SBC123).

[0043] 1 and 2, the beam splitter type wavelength combining optical system 13-3 has spectral characteristics of transmitting the wavelength combined beam (SBC4) of wavelengths λ41, λ42, λ43, and λ44 out of the wavelength combined beam (SBC4) after the beam diameter has been expanded by the beam expansion optical system 12-4 and the wavelength combined beam (SBC123) output by the beam splitter type wavelength combining optical system 13-2, and reflecting the wavelength combined beam (SBC123) of wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, λ24, λ31, λ32, λ33, and λ34 in the transmission direction. That is, in the beam splitter type wavelength combining optical system 13-3, the wavelength combined beam (SBC4) and the wavelength combined beam (SBC123) are incident from different directions, the wavelength combined beam (SBC4) is transmitted, and the wavelength combined beam (SBC123) is reflected in the transmission direction, thereby forming a single wavelength combined beam (SBC1234).

[0044] 1 and 2, the beam splitter type wavelength combining optical systems 13-1 to 13-3 finally obtain a single wavelength combined beam having the wavelengths of the wavelength combined beams output by the angle dispersive wavelength combining optical systems 11-1 to 11-4. That is, in the example of FIG. 1 and 2, wavelength combined beams of wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, λ24, λ31, λ32, λ33, λ34, λ41, λ42, λ43, and λ44 are finally obtained.

[0045] Furthermore, the power density of the wavelength-combined beam output by each angle-dispersive wavelength-combining optical system 11 is the same (including the meaning of approximately the same) as the power density of the wavelength-combined beam finally obtained by the beam splitter-type wavelength-combining optical system 13.

[0046] Fig. 3 is a schematic diagram showing an example of the spectrum of the wavelength combined beam (SBC1234) finally obtained in the wavelength combining laser device 1 shown in Fig. 1 and Fig. 2. As shown in Fig. 3, in the spectrum of the wavelength combined beam (SBC1234), there are unusable bands between the wavelengths λ11, λ12, λ13, and λ14 of the wavelength combined beam (SBC1), the wavelengths λ21, λ22, λ23, and λ24 of the wavelength combined beam (SBC2), the wavelengths λ31, λ32, λ33, and λ34 of the wavelength combined beam (SBC3), and the wavelengths λ41, λ42, λ43, and λ44 of the wavelength combined beam (SBC4).

[0047] Next, the effects of the wavelength-combined laser device 1 according to the first embodiment will be described. For example, consider a case where there are fiber lasers each having a power of 1 kW, and wavelength combining is performed on a total of 16 fibers as exemplified in the first embodiment to create a 16 kW system. In addition, to prevent the thermal effects and damage to optical components, a power density of 10 kW / cm is set. ２ The beam area (S) must be less than 1.6 cm ２ The above size is required.

[0048] In this case, we will compare it with the case of simple wavelength combining in which 16 wavelengths are combined with one diffraction grating. When wavelengths are combined with one diffraction grating, the beam diameter on the diffraction grating surface is corrected for the projection (cosθ) due to the diffraction angle, and when the diffraction angle (θ) is 63.2°, the beam radius (ω) is calculated to be 4.8 mm from the following formula (3). When the wavelength line width of the laser light source is 20 GHz, the beam quality (M ２ ) deteriorates to 2.2. ω = √(S × cosθ / π) (3)

[0049] In contrast, when the diffraction grating is divided into four, as in the wavelength combining laser device 1 according to the first embodiment, a single diffraction grating 112 wavelength combines a 4 kW beam. In this case, the beam radius (ω) is calculated to be 2.4 mm, and the beam quality (M ２ ) is calculated to be 1.4, which shows an improvement.

[0050] In addition, in the beam splitter type wavelength combining optical system 13, the beam quality (M ２ ) degradation does not occur, so in the same 16kW system, when 16 beams are coupled with one diffraction grating, M ２ 2.2, in the wavelength-coupled laser device 1 according to the first embodiment, M ２ This effect is due to the contribution of the beam diameter reduction on the angle dispersive wavelength coupling element, and therefore varies depending on various conditions such as the number of diffraction gratings 112 and the number of beams.

[0051] Furthermore, the wavelength combining laser device 1 according to the first embodiment is characterized in that it can be used with the power density increased to a set value to prevent damage to optical components, etc., in order to reduce the beam diameter on the diffraction grating 112 surface. Without this feature, if laser light is incident on the beam splitter-type wavelength combining optical system 13 with its original beam diameter (without the beam expansion optical system 12), two different wavelength combined beams will be incident, causing the power density to exceed the set value and easily damaging the optical components. Alternatively, it may be possible to increase the beam diameter at the angle-dispersive wavelength combining optical system 11 so that the power density after wavelength combining in the beam splitter-type wavelength combining optical system 13 is equal to or less than the set value, and not insert the beam expansion optical system 12. However, in this case, the beam diameter on the diffraction grating 112 surface is not reduced, and it is clear that no effect toward improving beam quality can be achieved. The configuration of embodiment 1, which consists of n diffraction gratings 112 and n beam expansion optical systems 12, is not conceived from the conventional design that aims to reduce the number of optical components and make them common, but its effect is important for improving the beam quality of the wavelength-combined laser device 1.

[0052] The configuration described in the first embodiment can be modified in various ways, and specifically, there is considerable flexibility in the combination types and order of the beam splitter wavelength combining optical systems 13. For example, Fig. 4 is a schematic diagram showing another configuration example of the wavelength combining laser device 1 according to the first embodiment. The example of Fig. 4 shows a case where three beam splitter wavelength combining optical systems 13 (beam splitter wavelength combining optical system 13-1, beam splitter wavelength combining optical system 13-4, and beam splitter wavelength combining optical system 13-5) are provided as the (n-1) beam splitter wavelength combining optical systems 13.

[0053] The beam splitter type wavelength combining optical system 13-4 has spectral characteristics of transmitting the wavelength combined beam (SBC3) of wavelengths λ31, λ32, λ33, and λ34 out of the wavelength combined beam (SBC3) after the beam diameter has been expanded by the beam expansion optical system 12-3 and the wavelength combined beam (SBC4) after the beam diameter has been expanded by the beam expansion optical system 12-4, and reflecting the wavelength combined beam (SBC4) of wavelengths λ41, λ42, λ43, and λ44 in the transmission direction. That is, the wavelength combined beam (SBC3) and the wavelength combined beam (SBC4) are incident on the beam splitter type wavelength combining optical system 13-4 from different directions, and the beam splitter type wavelength combining optical system 13-4 transmits the wavelength combined beam (SBC3) and reflects the wavelength combined beam (SBC4) in the transmission direction, thereby generating a single wavelength combined beam (SBC34).

[0054] The beam splitter type wavelength combining optical system 13-5 has spectral characteristics of transmitting the wavelength combined beam (SBC12) of wavelengths λ11, λ12, λ13, λ14, λ21, λ22, λ23, and λ24 out of the wavelength combined beam (SBC12) output by the beam splitter type wavelength combining optical system 13-2 and the wavelength combined beam (SBC34) output by the beam splitter type wavelength combining optical system 13-2, and reflecting the wavelength combined beam (SBC34) of wavelengths λ31, λ32, λ33, λ34, λ41, λ42, λ43, and λ44 in the transmission direction. That is, in the beam splitter type wavelength combining optical system 13-5, the wavelength combined beam (SBC12) and the wavelength combined beam (SBC34) are incident from different directions, the wavelength combined beam (SBC4) is transmitted, and the wavelength combined beam (SBC123) is reflected in the transmission direction, thereby forming a single wavelength combined beam (SBC1234).

[0055] In this way, even with the configuration shown in FIG. 4, the same wavelength combining results as with the configuration shown in FIG. 1 can be finally obtained.

[0056] Furthermore, in general, the beam splitter type wavelength combining optical systems 13 can be arranged in series, in parallel, or in a mixed arrangement. However, since one wavelength combined beam is newly wavelength combined in one beam splitter type wavelength combining optical system 13, when there are n angle dispersive wavelength combining optical systems 11, (n-1) beam splitter type wavelength combining optical systems 13 are necessary and sufficient.

[0057] It is desirable that the number of beams to be wavelength-combined in the angle-dispersive wavelength combining optical systems 11 is the same (including the meaning of approximately the same) in all n angle-dispersive wavelength combining optical systems 11. In this case, the effect of reducing the beam diameter on the diffraction grating surface is maximized.

[0058] The laser light output from the laser light source 111 may be linearly polarized. Of the two wavelength-combined beams input to the beam splitter-type wavelength combining optical system 13, one may be p-polarized and the other may be s-polarized.

[0059] As described above, according to the first embodiment, the wavelength combining laser device 1 includes n angle-dispersive wavelength combining optical systems 11 that output wavelength-combined beams having a plurality of wavelengths different from each other, n or more beam expanding optical systems 12 that expand the wavelength-combined beams output by the angle-dispersive wavelength combining optical systems 11 to have the same beam diameter, and (n-1) beam splitter type wavelength combining optical systems 13 that receive two wavelength-combined beams different from each other and output one wavelength-combined beam having the wavelengths of the two wavelength-combined beams. The angle-dispersive wavelength combining optical system 11 is configured to combine n laser beams outputting laser light of different wavelengths from each other. The optical fiber optics includes a light source 111 and an angle-dispersive wavelength combining element that receives laser beams output from the plurality of laser beams 111 and outputs a single wavelength-combined beam having the wavelengths of the plurality of laser beams, wherein the power density of the wavelength-combined beam output from the angle-dispersive wavelength combining optical system 11 is the same as the power density of the wavelength-combined beam finally obtained by the (n−1) beam splitter-type wavelength combining optical systems 13, and the (n−1) beam splitter-type wavelength combining optical systems 13 finally obtain a single wavelength-combined beam having the wavelengths of the wavelength-combined beams output from the n angle-dispersive wavelength combining optical systems 11. According to the first embodiment, the laser beam output from the laser light source 111 has a wavelength bandwidth of 100 MHz or more. According to the first embodiment, the laser beam output from the laser light source 111 is linearly polarized. According to the first embodiment, one of the two wavelength-combined beams input to the beam splitter-type wavelength combining optical system 13 is p-polarized and the other is s-polarized. According to the first embodiment, the beam expanding optical system 12 is a reflective optical system. As a result, in the wavelength-coupled laser device 1 according to the first embodiment, it is possible to suppress the expansion of the beam diameter while maintaining the power density at a certain level or less.

[0060] That is, in the wavelength-coupled laser device 1 according to the first embodiment, the total power of the constituent lasers is dispersed among a plurality of angle-dispersive wavelength coupling elements, and the beam diameter can be reduced by adjusting the power density on the surface of the angle-dispersive wavelength coupling element to the allowable upper limit. As a result, in the wavelength-coupled laser device 1 according to the first embodiment, the influence of the spread angle corresponding to the wavelength line width generated in the angle-dispersive wavelength coupling element is reduced, and power scaling with high beam quality can be achieved in wavelength coupling.

[0061] Embodiment 2 Fig. 5 is a schematic diagram showing a configuration example of a wavelength-combined laser system according to embodiment 2. The wavelength-combined laser system includes two wavelength-combined laser devices 1 and a polarization combining element 2, as shown in Fig. 5, for example.

[0062] The wavelength-combined laser device 1 is the wavelength-combined laser device 1 shown in the first embodiment. The laser light output from the laser light source 111 of the wavelength-combined laser device 1 is linearly polarized. One of the laser lights output from the two wavelength-combined laser devices 1 is p-polarized and the other is s-polarized.

[0063] The polarization combining element 2 receives the wavelength combined beams output by the two wavelength combining laser devices 1 and outputs one polarization combined beam. That is, the polarization combining element 2 transmits one of the p-polarized wavelength combined beams and the s-polarized wavelength combined beam output by the two wavelength combining laser devices 1 and reflects the other wavelength combined beam in the transmission direction, thereby polarizing and combining the two wavelength combined beams to generate one polarization combined beam. A polarization beam splitter, for example, is used as the polarization combining element 2.

[0064] In this way, in the wavelength-combined laser system according to the second embodiment, by using linearly polarized light as the laser light, wavelength combining can be performed by each of the two sets of wavelength-combined laser devices 1, and then polarization combining can be performed by the polarization combining element 2, thereby easily doubling the power.

[0065] As described above, according to the second embodiment, the wavelength-combined laser system includes two wavelength-combined laser devices 1 according to claim 1 and a polarization combining element 2 that receives the wavelength-combined beams output from the two wavelength-combined laser devices 1 and outputs one polarization-combined beam, and the laser light output from the laser light source 111 of the wavelength-combined laser device 1 is linearly polarized light. This makes it possible for the wavelength-combined laser system according to the second embodiment to easily double its power.

[0066] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0067] The wavelength-combined laser device according to the present disclosure is capable of suppressing the expansion of the beam diameter on the surface of the angle-dispersive wavelength-combining element while maintaining the power density at or below a certain level, and is suitable for use in wavelength-combined laser devices that combine laser beams having different wavelengths into a single beam.

[0068] 1 wavelength combining laser device, 2 polarization combining element, 11 angle dispersive wavelength combining optical system, 12 beam expanding optical system, 13 beam splitter type wavelength combining optical system, 111 laser light source, 112 diffraction grating (angle dispersive wavelength combining element).

Claims

1. A system comprising: n angle-dispersive wavelength combining optical systems that output wavelength-combined beams having a plurality of wavelengths different from each other; n or more beam expansion optical systems that expand the wavelength-combined beams output by the angle-dispersive wavelength combining optical systems to have the same beam diameter; and (n-1) beam splitter-type wavelength combining optical systems that receive two different wavelength-combined beams as input and output one wavelength-combined beam having the wavelengths of the two wavelength-combined beams, wherein the angle-dispersive wavelength combining optical system comprises: a plurality of laser light sources that output laser beams having different wavelengths from each other; and angle-dispersive wavelength combining elements that receive the laser beams output by the plurality of laser light sources, respectively, and output one wavelength-combined beam having the wavelengths of the plurality of laser beams, wherein the power density of the wavelength-combined beam output by the angle-dispersive wavelength combining optical system is the same as the power density of the wavelength-combined beam finally obtained by the (n-1) beam splitter-type wavelength combining optical systems, and wherein a single wavelength-combined beam having the wavelength of the wavelength-combined beams output by the n angle-dispersive wavelength combining optical systems is finally obtained by the (n-1) beam splitter-type wavelength combining optical systems. A wavelength-combined laser device.

2. The wavelength-combined laser device according to claim 1, wherein the wavelength line width of the laser light output from said laser light source is 100 MHz or more.

3. A wavelength-combined laser device according to claim 1 or claim 2, characterized in that the laser light output from said laser light source is linearly polarized light.

4. The wavelength combining laser device according to claim 3, wherein one of the two wavelength combining beams input to said beam splitter type wavelength combining optical system is p-polarized light and the other is s-polarized light.

5. A wavelength-combined laser device according to any one of claims 1 to 4, characterized in that the beam expanding optical system is a reflective optical system.

6. A wavelength-combined laser system comprising: two sets of wavelength-combined laser devices according to any one of claims 1 to 5; and a polarization combining element which receives the wavelength-combined beams output by the two sets of wavelength-combined laser devices and outputs one polarization-combined beam, wherein the laser light output by the laser light source of the wavelength-combined laser devices is linearly polarized.

7. The wavelength-combined laser system according to claim 6, wherein the wavelength line width of the laser light output from said laser light source is 100 MHz or more.

8. A wavelength-combined laser system according to claim 6 or 7, characterized in that the beam expanding optical system is a reflective optical system.

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