Compact Spectral Beam Combiner

Abstract

This invention relates to the field of laser technology, and more particularly to a compact spectral beam combining device, comprising a laser unit, a reflective conversion mirror, a diffraction grating, and an optical path compression component disposed between the laser unit and the reflective conversion mirror; the optical path compression component includes at least one waveguide structure; the waveguide structure includes at least two reflective surfaces; the diffraction grating is arranged on the optical axis and overlaps with the laser unit in the non-spectral beam combining direction; the compact spectral beam combining device provided by this invention, by adjusting the layout of the laser unit and the diffraction grating, and introducing a reflective conversion mirror placed perpendicular to the optical axis, facilitates overall packaging and improves structural stability; at the same time, it reuses the same optical path compression component twice, folding the optical path twice, reducing the size of the spectral beam combining structure; it also reduces the number of components and the workload of assembly and adjustment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of laser technology, and particularly relates to a compact spectrum beam combining device. BACKGROUND

[0002] The spectrum beam combining technology is one of the most feasible technologies for realizing high-power and high-beam-quality combined laser beams. Since it was reported in 1999, the technology has been successfully applied to all-solid-state lasers, fiber lasers and semiconductor lasers, greatly improving the performance of the lasers.

[0003] The basic principle of spectrum beam combining is as follows: optical elements with dispersion capability, such as gratings and prisms, are used to arrange multiple unit laser beams with different wavelengths in a certain rule, and the dispersion effect of the dispersion elements is used to output the combined laser beams in a manner of near-field and far-field coincidence, so that the combined laser beams have a power being the sum of the powers of all the unit beams and a beam quality similar to that of the unit beams, thereby realizing high-power and high-beam-quality combined laser output.

[0004] The current spectrum beam combining structure basically consists of laser units, a transform lens, a diffraction grating and an external cavity mirror. The external cavity mirror and the rear cavity surface of the laser unit form a resonant cavity. The laser output by the laser unit is incident on the diffraction grating at different angles through the transform lens and is combined on the grating. After further diffraction by the grating, the light is vertically incident on the external cavity mirror. Only the light that is perpendicular to the external cavity mirror and can return to the original laser unit can effectively resonate and output laser, so all the beams are output in a manner of near-field and far-field coincidence. In order to obtain high combined beam quality, the laser unit and the diffraction grating are respectively located on the front and rear focal planes of the transform lens. Due to the limitations of the spectrum beam combining principle and the performance of the laser unit, the focal length of the transform lens used at present is generally hundreds of millimeters. With the increase in the number of combined units and the limitation of the combined spectrum, the focal length of the transform lens is further increased, resulting in a long optical path and a large size of the entire spectrum beam combining source, which is not convenient for engineering application.

[0005] In order to obtain high combined beam quality, the laser unit and the diffraction grating are respectively located on the front and rear focal planes of the transform lens. In order to obtain high combined power, the number of combined laser units within the rated spectral range should be as large as possible, and the spectral interval between the units should be compressed accordingly. There are three main methods: 1) reducing the interval between the laser units, 2) increasing the focal length of the transform lens, and 3) increasing the grating dispersion. The physical spatial interval of the laser units is mainly determined by the packaging of the laser. Due to the limitations of chip technology and heat dissipation requirements, it is difficult to directly reduce the unit spatial interval by a large margin.

[0006] The document "Hundred-watt diode laser source by spectral beam combining" proposes a method of relay imaging to convert it into a reduced image, effectively reducing the spatial interval of the laser chip. This method can also be regarded as equivalent to increasing the focal length of the conversion lens while maintaining the physical spatial interval of the laser unit. For the method of increasing grating dispersion, according to the principle of grating dispersion, it is mainly realized by increasing the number of ruling lines in the unit size of the grating, but the dispersion capacity of a single grating is limited.

[0007] The document "Narrow-spectral-span spectral beam combining with a non-parallel double-grating structure" and the invention patent application for "Spectral beam combining device and method" with the patent number CN114994933A and the publication date of September 2, 2022, propose a multi-grating multiplexing method, which effectively improves the dispersion capacity of the equivalent grating and realizes narrow spectral interval, but the spectral beam combining structure is still large.

[0008] Increasing the focal length of the conversion lens is one of the most direct methods to obtain narrow linewidth spectral interval. As reported in the document "Narrow linewidth operation of a spectral beam combined diode laser bar", a conversion lens with an equivalent focal length of 4.5m is used to compress the spectrum of a bar containing 19 laser units to 0.48nm, corresponding to a unit spectral interval of 0.0267nm, achieving good spectral interval compression effect. However, the length of the entire laser from the laser unit to the diffraction grating is several meters, making it difficult to implement engineering applications.

[0009] The multi-grating multiplexing or laser unit relay imaging method reduces the size of the spectral beam combining light source to some extent, but compared with the conventional laser beam combining structure, the size of the spectral beam combining light source is still very large, making it difficult to realize miniaturization. SUMMARY

[0010] Therefore, in view of the current difficulty of miniaturization of spectral beam combining light sources, the present invention aims to provide a compact spectral beam combining device. By adjusting the layout of the laser unit and the diffraction grating, introducing a reflective conversion mirror perpendicular to the optical axis, it is convenient for overall packaging and improves the structural stability. At the same time, the same optical path compression component is twice folded, reducing the size of the spectral beam combining structure, and also reducing the number of devices and the amount of adjustment work.

[0011] To achieve the above object, the technical scheme of the present application is implemented as follows:

[0012] The present application provides a compact spectrum beam combination device, which comprises a laser unit, a reflecting transform mirror, a diffraction grating and an optical path compression assembly; the optical path compression assembly comprises at least one waveguide structure; the optical path compression assembly is arranged between the laser unit and the reflecting transform mirror; the laser unit outputs laser; the compact spectrum beam combination device comprises an optical path in a spectrum beam combination direction and an optical path in a non-spectrum beam combination direction; the compact spectrum beam combination device comprises an optical path in a spectrum beam combination direction and an optical path in a non-spectrum beam combination direction; the optical path compression assembly realizes optical path compression for both the optical path in the spectrum beam combination direction and the optical path in the non-spectrum beam combination direction, and does not change the spectrum beam combination function of the optical path in the spectrum beam combination direction; in the optical path in the spectrum beam combination direction, the laser unit is arranged on both sides of an optical axis, and the diffraction grating is arranged at the position of the optical axis; in the optical path in the non-spectrum beam combination direction, the position of the laser unit coincides with the position of the diffraction grating.

[0013] Further, the reflecting transform mirror is perpendicular to the direction of the optical axis.

[0014] Further, the waveguide structure comprises at least two reflecting surfaces, and the reflecting surfaces are planes or concave cylindrical surfaces.

[0015] Further, the bending direction of the concave cylindrical surface corresponds to the direction of the optical path in the non-spectrum beam combination direction.

[0016] Further, the laser is reflected by a single reflecting surface for more than or equal to two times; the reflectivity of a single reflecting surface is greater than 99%.

[0017] Further, the waveguide structure comprises two reflecting surfaces arranged in parallel to each other, and the reflecting surfaces are both planes; when the laser is first incident to a single reflecting surface, an included angle formed between the laser and the normal line of the reflecting surface is an incident angle θ, the effective length of a single reflecting surface in the direction of optical path compression is d, and the internal transmission optical path m of the single reflecting surface is n d / sinθ, and n is the refractive index in a single waveguide structure.

[0018] Further, the incident angle θ is less than or equal to 30°.

[0019] Further, the optical path compression assembly comprises two or more waveguide structures; the waveguide structures are arranged in series.

[0020] Further, the laser unit comprises a laser device and an optical element.

[0021] The optical element collimates or shapes and adjusts a polarization direction of the laser output by the laser device;

[0022] The optical element at least includes a fast-axis collimation mirror, a slow-axis collimation mirror, a half-wave plate, and a narrow-band filter.

[0023] The laser device is selected from a semiconductor laser, a fiber laser, or a solid-state laser.

[0024] Further, the compact spectral beam combining device further comprises an external cavity mirror; the external cavity mirror is arranged in a diffraction direction of the laser after the laser passes through the diffraction grating.

[0025] Compared with the prior art, the present application can achieve the following beneficial effects:

[0026] 1) More compact spectral beam combining structure; under the premise of not reducing optical performance, secondary multiplexing the same optical path compression component, doubling the folded optical path, reducing the size of the spectral beam combining structure, and realizing the miniaturization of the spectral beam combining light source;

[0027] 2) Stronger power expansion; conventional spectral beam combining light sources are limited by the chip gain spectrum width and the high-efficiency diffraction spectrum width of the grating, and the number of beam combining units is limited, the present application increases the focal length of the reflective conversion mirror, reduces the unit spectral interval under the condition of not increasing the size of the light source, realizes more unit beam combining within the rated spectral width, and thus increases the beam combining power;

[0028] 3) More stable spectral beam combining structure; the stability of the laser is largely determined by the stability of the front and rear cavity surfaces, the present application compresses the optical path through the optical path compression component and the multiplexing optical path compression component, so that the distance between the front and rear cavity surfaces is greatly reduced, and the same mounting mechanism can be designed to stabilize the laser, so that a more stable structure is obtained; at the same time, the laser units and the diffraction grating completely overlap in the non-spectral beam combining direction, and the overall structural stability can be effectively improved through the common base design with better stability. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of this application, and their

[0030] Figure 1 The compact spectral beam combining device of the embodiment of the present application is a schematic diagram of an optical path structure in the spectral beam combining direction;

[0031] Figure 2 The compact spectral beam combining device of the embodiment of the present application is a schematic diagram of an optical path structure in the non-spectral beam combining direction;

[0032] Figure 3 Schematic diagram of light path structure of prior art comparative example in spectral beam combining direction;

[0033] Figure 4 Schematic diagram of light path structure of prior art comparative example in non-spectral beam combining direction;

[0034] Figure 5 Schematic diagram of compressed light path of light path compression component in compact spectral beam combining device of the present application;

[0035] Figure 6 Schematic diagram of structure of multiple waveguide structures arranged in series in compact spectral beam combining device of the present application;

[0036] Figure 7 Schematic diagram of one structure of waveguide structure in light path compression component in compact spectral beam combining device of the present application;

[0037] Figure 8 Schematic diagram of another structure of waveguide structure in light path compression component in compact spectral beam combining device of the present application.

[0038] Explanation of reference signs:

[0039] 1, laser unit; 11, first laser unit; 12, second laser unit; 13, third laser unit; 14, fourth laser unit; 101, incident light; 102, emergent light; 21, transform lens; 22, reflective transform mirror; 3, diffraction grating; 4, external cavity mirror; 5, light path compression component; 51, first reflecting surface; 52, second reflecting surface. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application.

[0041] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0042] In the description of the present application, it is to be understood by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can be explicitly or implicitly included one or more. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0043] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0044] In the present application, a compact spectral beam combining device is provided, which comprises a laser unit, a reflective transform mirror, a diffraction grating and an optical path compression assembly; the optical path compression assembly comprises at least one waveguide structure; the optical path compression assembly is arranged between the laser unit and the reflective transform mirror; the laser unit outputs laser; the compact spectral beam combining device comprises an optical path in the spectral beam combining direction and an optical path in the non-spectral beam combining direction; the compact spectral beam combining device comprises an optical path in the spectral beam combining direction and an optical path in the non-spectral beam combining direction; the optical path compression assembly realizes optical path compression for both the optical path in the spectral beam combining direction and the optical path in the non-spectral beam combining direction, and does not change the spectral beam combining function of the optical path in the spectral beam combining direction; in the optical path in the spectral beam combining direction, the laser unit is arranged on both sides of the optical axis, and the diffraction grating is arranged at the position of the optical axis; in the optical path in the non-spectral beam combining direction, the position of the laser unit coincides with the position of the diffraction grating. The reflective transform mirror is perpendicular to the direction of the optical axis.

[0045] The compact spectrum beam combining device provided in the specific embodiment of the present application adjusts the layout of laser units, arranges the diffraction grating, a key device in the spectrum beam combining structure, on the optical axis, and overlaps the laser unit position in the non-spectrum beam combining direction; a reflective conversion mirror is arranged perpendicularly to the optical axis, the laser beam passing through the optical path compression component is incident to the reflective conversion mirror, the laser beam is focused and reflected by the reflective conversion mirror and then returned to the optical path compression component for the second time, and then is output to the diffraction grating and combined and output after diffraction; the optical path from the laser unit to the diffraction grating is symmetrical in the non-spectrum beam combining direction. Specifically, the layout of the laser unit and the diffraction grating is adjusted, the reflective conversion mirror is arranged perpendicularly to the optical axis, the whole is packaged, and the structural stability is improved; meanwhile, the same optical path compression component is reused, the folded optical path is doubled, the spectrum beam combining structure size is reduced, and the number of devices and the adjustment workload are also reduced.

[0046] In the specific embodiment of the present application, the waveguide structure includes at least two reflecting surfaces, and the reflecting surfaces are planes or concave cylindrical surfaces, that is, the waveguide structure is various combinations of planes and concave cylindrical surfaces; the bending direction of the concave cylindrical surface corresponds to the direction of the optical path in the non-spectrum beam combining direction, that is, the bending direction of the concave cylindrical surface is basically consistent with the non-spectrum beam combining direction. Specifically, when the waveguide structure includes two reflecting surfaces, the two reflecting surfaces through which the laser passes in sequence can be a combination of a plane and a plane (referred to as plane-plane), a combination of a plane and a concave cylindrical surface (referred to as plane-concave), a combination of a concave cylindrical surface and a plane (referred to as concave-plane), or a combination of a concave cylindrical surface and a concave cylindrical surface (referred to as concave-concave); when the waveguide structure includes three reflecting surfaces, the three reflecting surfaces through which the laser passes in sequence can be a combination of plane-plane-plane, a combination of plane-plane-plane, or a combination of plane-plane-concave, and the like; the waveguide structure can also be separate reflecting surfaces or realized by coating a high-reflection film or internal reflection in a single structure.

[0047] In the specific embodiment of the present application, when the waveguide structure includes two reflecting surfaces arranged in parallel to each other, and the reflecting surfaces are both planes, that is, a plane-plane combination; when the laser is incident to a single reflecting surface for the first time, an included angle formed between the laser and the normal line of the reflecting surface is an incident angle θ, the effective length of a single reflecting surface in the optical path compression direction is d, and the internal transmission optical path m of a single reflecting surface is n d / sinθ, and n is the refractive index in a single waveguide structure. The incident angle θ is less than or equal to 30°.

[0048] In the specific embodiment of the present application, the optical path compression component can include two or more waveguide structures; the waveguide structures are arranged in series, and the optical path is folded in a rated space.

[0049] In the embodiment of the present application, the number of reflections of the laser on a single reflection surface is greater than or equal to 2; the reflectivity of a single reflection surface is greater than 99%; the high reflectivity of a single reflection surface can be achieved by coating a dielectric film or a combination of "metal + dielectric film" on the optical surface, or by total reflection, specifically by selecting an appropriate refractive index and low absorption optical glass through the total reflection condition.

[0050] In the embodiment of the present application, the reflection type conversion mirror is a single mirror or a combination of multiple mirrors; the diffraction grating is a transmission type grating or a reflection type grating; the diffraction grating is a single grating or a combination of multiple gratings; the laser unit includes a laser device and an optical element; the optical element collimates or shapes the laser output by the laser device and adjusts the polarization direction; the optical element at least includes a fast-axis collimating mirror, a slow-axis collimating mirror, a half-wave plate, and a narrow-band filter, etc.; the laser device is coated with an anti-reflection film on the end face of the laser output, and the laser device is selected from a semiconductor laser, a fiber laser, or a solid-state laser.

[0051] In the embodiment of the present application, it can be an open-loop spectral beam combining structure without an external cavity mirror, or a closed-loop spectral beam combining structure with an external cavity mirror; when the compact spectral beam combining device further includes an external cavity mirror, the external cavity mirror is arranged in the diffraction direction of the laser after the diffraction grating.

[0052] The compact spectral beam combining device provided by the embodiment of the present application can achieve the following beneficial effects:

[0053] 1) More compact spectral beam combining structure; under the premise of not reducing the optical performance, the same optical path compression assembly is twice multiplexed, the folded optical path is doubled, the size of the spectral beam combining structure is reduced, and the miniaturization of the spectral beam combining light source can be realized;

[0054] 2) Stronger power scalability; conventional spectral beam combining light sources are limited by the chip gain spectrum width and the high-efficiency diffraction spectrum width of the grating, and the number of beam combining units is limited, the present application increases the focal length of the reflection type conversion mirror, reduces the unit spectral interval under the condition of not increasing the size of the light source, realizes more unit beam combining within the rated spectral width, and thus increases the beam combining power;

[0055] 3) More stable spectral beam combining structure; the stability of the laser is largely determined by the stability of the front and rear cavity surfaces, the present application compresses the optical path through the optical path compression assembly and the multiplexed optical path compression assembly, greatly reduces the distance between the front and rear cavity surfaces, and can stabilize the laser through the design of the same mounting mechanism to obtain a more stable structure; at the same time, the laser unit and the diffraction grating are completely overlapped in the non-spectral beam combining direction, and the overall structural stability can be effectively improved through the design of the common base with better stability.

[0056] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0057] Comparative Example 1

[0058] A schematic diagram of the light path in a conventional spectral beam combination structure is shown in FIG. 1. As shown in the figure, the basic components include laser units 1, a transform lens 21, a diffraction grating 3, and an external cavity mirror 4. The resonant cavity of the entire laser is formed by the rear cavity surface of the laser unit 1 and the external cavity mirror 4. The front cavity surface of each laser unit 1 is coated with a high-transmission film, and the rear cavity surface is coated with a high-reflection film. The lasing wavelength of each laser unit 1 is determined by the intracavity optical components and the position of the laser unit 1. The front cavity surface of the laser chip and the diffraction grating 3 are located on the front and rear focal planes of the transform lens 21, respectively. For ease of illustration, the combination of three laser units is shown. Figure 3 In the spectral beam combination direction ox, the laser units 1 include a first laser unit 11, a second laser unit 12, and a third laser unit 13, which output laser light along the same direction z. The light output by the second laser unit 12 in the center position is the main light, and the first laser unit 11 and the third laser unit 13 are distributed on both sides. In the spectral beam combination direction ox, the three laser units output laser light along the same direction z, which is incident on the transform lens 21, then is incident on the diffraction grating 3 at different angles, and the beams of all the laser units overlap on the diffraction grating 3, with their incident angles and diffraction angles both equal to or close to the Littrow angle. The light is then incident on the external cavity mirror 4, and only the light that is normally incident on the external cavity mirror 4 and can return to the original laser unit along the original path can effectively resonate.

[0059] Specifically, after the laser units 1 output laser light, the laser light is incident on the diffraction grating 3 at different angles through the transform lens 21 and overlaps on the diffraction grating 3. After further diffraction by the diffraction grating 3, the laser light is normally incident on the external cavity mirror 4. Only the laser light that is normally incident on the external cavity mirror 4 can return to the original laser unit 1 and effectively resonate to output laser light. Therefore, all the beams are output in a near-field and far-field overlapping manner. In order to obtain high beam quality of the combined light, the laser units 1 and the diffraction grating 3 are located on the front and rear focal planes of the transform lens 21, respectively.

[0060]

[0061] ​Further in combination with the actual situation, in the example of the 19-laser-unit standard 976 nm centimeter bar as the spectrum beam combining unit, the laser unit 1 has a light emitting area width of 100 μm, a period interval of 500 μm, a fast axis divergence angle of 45°, a slow axis direction of 8°, a front cavity surface coated with an anti-reflection film with a transmittance of >99.5%, most of the output laser being TE linearly polarized light with a linear polarization degree of 90%, and an output power of each laser unit being 5 W. The focal length of the transform lens 21 is selected to be 300 mm, the diffraction grating 3 is selected to be a transmission grating with a line number of 1600 lines / mm, a first-order diffraction efficiency of 96% for S-polarized light, and a first-order diffraction efficiency of 30% for P-polarized light. After the laser unit 1 is collimated in the fast axis, beam shaped, and collimated in the slow axis, it is arranged in one dimension in the spectrum beam combining direction for 19 laser units; among them, the output beam of the second laser unit 12 at the middle position coincides with the optical axis, and the first laser unit 11 and the third laser unit 13 on both sides each distribute 9 laser units, each laser unit has a spot size of 400 μm in the spectrum beam combining direction, a spatial period of 500 μm, a divergence angle of 6 mrad, a size of 2.4 mm in the non-spectrum beam combining direction, and a divergence angle of 6 mrad.

[0062] After the action of the transform lens 21, the spot size of the spectrum beam combining direction hitting the diffraction grating 3 is 1.8 mm, the divergence angle is 1.3 mrad, the spot size of the non-spectrum beam combining direction is 6 mm, and the divergence angle is 6 mrad. The external cavity mirror 4 is a partial reflector with a reflectivity of 10%, which is placed 100 mm away from the diffraction grating 3. After the feedback action of the external cavity mirror 4, each laser unit resonates to different wavelengths. The spot size hitting the external cavity mirror 4 is 2.06 mm (spectrum beam combining direction) x 7.2 mm (non-spectrum beam combining direction).

[0063] The resonant wavelength of each laser unit satisfies the grating equation with the same diffraction angle and different incident angles, and the wavelength distribution is shown in Table 1.

[0064] Table 1 Resonant central wavelength of conventional spectrum beam combining structure

[0065]

[0066] In this Example 1, the spectrum width of the 19-laser-unit spectrum beam combining is 12.3 nm, the focal length of the transform lens 21 is 300 mm, and according to the conventional spectrum beam combining structure, the laser unit 1 and the diffraction grating 3 are located on the front and rear focal planes of the transform lens 21, i.e. the distance between the laser unit and the diffraction grating 3 is 600 mm, the distance between the external cavity mirror 4 and the diffraction grating 3 is 100 mm, and without considering the laser packaging structure, etc., the physical size reaches 700 mm, which is large in volume and difficult to realize miniaturization.

[0067] The number of beam combining units in the structure of the above-mentioned Comparative Example 1 is 19. Considering the beam combining loss, the output power is 76 W at a beam combining efficiency of 80%. Considering the need for high-power laser in industrial processing and other application scenarios, such as achieving kilowatt-level power output while maintaining high beam quality, 14 centimeter bars of laser units need to be stacked in the spectral beam combining direction according to the laser structure in this example, i.e., 266 laser units. If the same spectral beam combining structure is used, the spectral width is simply evaluated to be 12.3*14 nm, and the generated spectral width will reach 172.2 nm. The effective gain width of a conventional semiconductor laser chip is not more than 20 nm, and the gain width further decreases as the wavelength decreases. For example, the effective gain spectrum width of an 808 nm high-power semiconductor laser chip is only about 10 nm. In addition, as the lasing spectrum deviates from the center gain peak, the output power generated also decreases sharply, so it is difficult to achieve an effective gain spectrum of 172.2 nm with the current gain width of a high-power semiconductor laser chip. Even if a plurality of laser chips with different gain ranges are used to achieve such a large spectral width through gain spectrum splicing, it is difficult for the diffraction grating to achieve high diffraction efficiency in such a large gain range, which will also lead to a decrease in spectral beam combining power.

[0068] How to maintain a narrow spectrum in the premise of beam combining multiple laser units can be known from the principle of spectral beam combining. The simplest way is to increase the focal length of the transform lens 21. For example, in the above structure, if the focal length of the transform lens 21 is increased to 4.2 m (14 times the current focal length), kilowatt-level spectral beam combining power output can still be achieved in a relatively narrow spectral range. However, the size of the beam combining structure generated will be greatly increased. Simply considering the distance between the laser unit and the grating will reach 8.4 m, which is unacceptable for conventional laser devices.

[0069] Figure 4 A schematic diagram of a conventional spectral beam combining structure in a non-spectral beam combining direction can be seen from the figure. In the non-spectral beam combining direction y, the laser unit 1 outputs laser light along the oz direction, and then passes through the transform lens 21, the diffraction grating 3 and the external cavity mirror 4 for beam combining output. The optical axis does not deviate and return. The light path transformation in this direction is relatively simple, and the basic requirement is that the laser unit 1 has good collimation effect, so as to form an effective resonance between the laser unit 1 and the external cavity mirror 4.

[0070] Embodiment 1

[0071] The schematic diagram of the light path structure in the spectral beam combining direction and the schematic diagram of the light path structure in the non-spectral beam combining direction of the compact spectral beam combining device according to the specific embodiments of the present application are respectively as follows: Figure 1 and Figure 2As shown in the figure, Example 1 is the same as Comparative Example 1, both being closed-loop spectral beam combining structures, specifically including a laser unit 1, a reflective conversion mirror 22, a diffraction grating 3, an external cavity mirror 4, and an optical path compression component 5; the resonant cavity of the entire laser is composed of the rear cavity surface of the laser unit 1 and the external cavity mirror 4. The laser unit 1 can include multiple laser units, each with a high anti-reflection coating on its front cavity surface and a high reflectivity coating on its rear cavity surface; the lasing wavelength of each laser unit is determined by the position of the intracavity optical components and the laser unit; the front cavity surface of the laser chip and the diffraction grating 3 in the laser unit 1 are located on the front and rear focal planes of the reflective conversion mirror 22.

[0072] As shown in the figure, in the spectral beam combining direction ox, laser unit 1 specifically includes a first laser unit 11, a second laser unit 12, a third laser unit 13, and a fourth laser unit 14. A diffraction grating 3 is placed at the center of the optical axis, and the four laser units are distributed in pairs on both sides of the optical axis. The four laser units output laser light along the same direction z, which is incident on the optical path compression component 5. After multiple reflections, the output light is incident on the reflective conversion mirror 22, and after reflection, it returns to the optical path compression component 5. After multiple reflections again, it is output to the diffraction grating 3, and after diffraction by the diffraction grating 3, it is output to the external cavity mirror 4, finally achieving beam combining. Only one set of beam compression components and reflective conversion mirrors are used to achieve two compressions of the beam combining optical path, effectively reducing the volume of the compressed light source without changing the optical path. In the non-spectral beam combining direction, the laser light output from laser unit 1 completely coincides with the optical path that returns to the diffraction grating 3 after passing through the optical path compression component 5. The diffraction grating 3 and laser unit 1 spatially overlap in the non-spectral beam combining direction, which is beneficial for achieving a stable structural layout.

[0073] Specifically, Figure 1 This is a schematic diagram of the optical path in the spectral beam combining direction of the compact spectral beam combining device structure proposed in this embodiment. Compared with Comparative Example 1, this embodiment uses four 1976nm mini bars, each containing five laser units, as spectral beam combining units. After fast-axis collimation, beam shaping, and slow-axis collimation, the spectral beam combining direction is a one-dimensional arrangement of 20 laser units. There are no laser units at the central optical axis position. The first laser unit 11 and the second laser unit 12 each have five laser units distributed on one side of the optical axis, while the third laser unit 13 and the fourth laser unit 14 each have five laser units distributed on the other side. Each laser unit has a spot size of 400μm, a spatial period of 500μm, and a divergence angle of 6mrad in the spectral beam combining direction. In the non-spectral beam combining direction, the spot size is 2.4mm, and the divergence angle is 6mrad. The focal length of the reflective converter mirror 22 is 300mm, and the diffraction grating 3 has a line count of 1600 lines / mm.

[0074] Specifically, Figure 2This diagram illustrates the optical path in the non-spectral combining direction of the compact spectral beam combining device structure proposed in this embodiment. The laser output from laser unit 1, after collimation, is incident on the optical path compression assembly 5, which consists of two mirrors. After being reflected back and forth by the two reflective surfaces, it is further output to the reflective transform mirror 22, and then re-enters the optical path compression assembly 5. After further optical path compression, it is output to the diffraction grating 3, and finally output by the external cavity mirror 4. Without changing the optical path length, the overall physical size of the structure is greatly reduced, with only a displacement ΔH in the y-direction.

[0075] like Figure 5 The diagram above illustrates the compressed optical path of the optical path compression component 5 in the compact spectral beam combining device of Embodiment 1, showing the implementation process of the compressed optical path. Here, 101 is the incident light, 102 is the outgoing light; 51 is the first reflecting surface, 52 is the second reflecting surface, both being high-reflectivity surfaces with a reflectivity greater than 99%, and their materials can be the same or different; θ is the incident angle of the incident light 101 onto the reflecting surface, a is the interval between the two reflecting surfaces, d is the effective length of the reflecting surface in the compression direction, and ΔH is the optical axis deviation. According to geometric relationships, the optical path m traversed within the optical path compression component is d / sinθ, and the optical axis deviation ΔH is d. From cosθ, it can be seen that the longer the effective length d of the reflecting surface and the smaller the incident angle θ, the longer the optical path travels within the optical path compression component, and the more obvious the optical path compression effect. If the incident angle of the reflective surface is designed to be 5° and the effective length of the reflective surface in the compression direction is 25mm, then the optical path length of the optical path compression component 5 reaches 287mm. Therefore, the distance between the laser unit 1 and the reflective conversion mirror 22 in the optical axis direction can be compressed from 300mm to less than 50mm, and the optical axis shifts by 24.9mm in the y direction. After passing through the reflective conversion mirror 22, it is again incident into the same optical path compression component 5. Then, the physical size between the reflective conversion mirror 22 and the diffraction grating 3 is also compressed from 300mm to less than 50mm. At the same time, the technical solution of this embodiment uses a shared optical path compression component 5. The optical path is compressed twice, and the optical paths before and after the reflective conversion mirror 22 can be folded to share a single physical size. Therefore, the physical distance from the laser unit 1 to the diffraction grating 3 is compressed from the conventional 600mm to less than 50mm, that is, the size of the entire device in the x direction is further compressed. Compared with the conventional spectral beam combining structure in Example 1, the physical size of the laser resonator cavity is greatly shortened. Meanwhile, the laser unit 1 and the diffraction grating 3 coincide in the non-spectral beam combining direction. The diffraction grating 3 is located on the optical axis in the spectral beam combining direction. The laser unit 1 is symmetrically distributed on both sides of the optical axis. The outgoing light of the laser unit 1 and the incident light of the diffraction grating 3 are parallel and overlap in position in the non-spectral beam combining direction. The laser unit 1 and the diffraction grating 3 can be installed with a common reference plane to obtain a more stable structure and simpler assembly and adjustment.

[0076] Example 2

[0077] Figure 6 This is a schematic diagram of a single optical path compression component with multiple waveguide structures connected in series, as shown in another embodiment. When the spectral beam combiner cavity is several meters long, although a single waveguide structure can achieve the same function in the optical path compression component, the optical device has a large structural size, is difficult to manufacture, and its surface accuracy is hard to guarantee. Therefore, large-size optical path compression can be achieved by superimposing multiple waveguide structures in series in a single optical path compression component.

[0078] As mentioned in Example 1, when the focal length of the reflective converter 22 is as long as 4.2m, if a single waveguide structure is used in a single compression component, assuming the incident angle θ is 5°, the effective length L of the compression direction of the reflecting surface is 360mm. The size in the x-direction can be compressed to within 100mm, and the optical axis offset ΔH in the y-direction is close to 360mm, achieving a size compression of tens of times compared to the original 4.2m. However, the overall structure is not coordinated, and the individual components of the optical path compression component reach more than 380mm, making actual processing difficult and assembly challenging, and the reflective surface shape cannot be guaranteed. Therefore, in this embodiment, multiple waveguide structures are directly connected in series to form an optical path compression component, balancing the structural dimensions in both directions and reducing the processing difficulty of the reflecting surface. Here, the optical path compression component incorporates 4 sets of waveguide structures connected in series, with the structural size of each set reduced to less than 100mm. Correspondingly, the optical axis offset in the y-direction is significantly reduced, and it can even be decomposed into 8 sets, with the structural size of each set reduced to less than 50mm, which is beneficial for processing and assembly.

[0079] Example 3

[0080] Figure 7 This is a schematic diagram of the waveguide structure in the optical path compression component 5 in another embodiment. Specifically, the waveguide structure includes three reflecting surfaces, specifically adopting a flat-flat-flat combination structure, that is, an optical path compression component composed of a single plane mirror and two plane mirrors. As can be seen from the figure, the input laser is reflected back and forth in the structure and the optical path is folded before being output, thereby achieving optical path folding in non-spectral beam combining directions.

[0081] Example 4

[0082] Figure 8 This is a schematic diagram of another waveguide structure in the optical path compression component 5, as shown in another embodiment. Specifically, the waveguide structure includes two reflecting surfaces, specifically adopting a flat-concave combination structure, that is, an optical path compression component composed of a single planar reflector and two planar reflectors. As can be seen from the figure, the input laser is reflected back and forth in the waveguide and folded before being output, thereby achieving optical path folding in non-spectral beam combining directions.

[0083] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0084] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A compact spectral beam combining device, characterized by: The compact spectral beam combining device comprises a plurality of laser units, a reflective transform mirror, a diffraction grating and an optical path compression assembly; the optical path compression assembly comprises at least one waveguide structure, the waveguide structure comprises at least two reflecting surfaces, and the reflecting surfaces are planes or concave cylindrical surfaces; the optical path compression assembly is arranged between the laser units and the reflective transform mirror; the laser units output laser beams; The compact spectral beam combining device comprises an optical path in a spectral beam combining direction and an optical path in a non-spectral beam combining direction; the optical path compression assembly realizes optical path compression for both the optical path in the spectral beam combining direction and the optical path in the non-spectral beam combining direction, and does not change the spectral beam combining function of the optical path in the spectral beam combining direction; In the optical path in the spectral beam combining direction, the laser units are arranged on both sides of an optical axis, and the diffraction grating is arranged at a position of the optical axis; in the optical path in the non-spectral beam combining direction, the positions of the laser units coincide with the position of the diffraction grating; The laser units output laser beams in the same direction, the laser beams are incident into the optical path compression assembly, are output to the reflective transform mirror after multiple reflections, are returned to the optical path compression assembly again after reflection, are output to the diffraction grating again after multiple reflections, are diffracted by the diffraction grating and are output to an external cavity mirror, and are finally combined and output.

2. The compact spectral beam combining device of claim 1, wherein: The reflective transform mirror is perpendicular to the direction of the optical axis.

3. The compact spectral beam combining device of claim 1, wherein: The bending direction of the concave cylindrical surface corresponds to the direction of the optical path in the non-spectral beam combining direction.

4. The compact spectral beam combining device of claim 1, wherein: The number of reflections of the laser on a single reflecting surface is greater than or equal to 2, and the reflectivity of a single reflecting surface is greater than 99%.

5. The compact spectral beam combining device of claim 1, wherein: The waveguide structure comprises two mutually parallel arranged reflecting surfaces, and the reflecting surfaces are both planes; when the laser light is first incident to a single reflecting surface, the included angle between the laser light and the normal line of the reflecting surface is the incident angle θ, the effective length of a single reflecting surface in the optical path compression direction is d, and the internal transmission optical path m is n d / sinθ, and n is the refractive index in a single waveguide structure.

6. The compact spectral beam combining device of claim 5, wherein: The incident angle θ is less than or equal to 30°.

7. The compact spectral beam combining device of claim 1, wherein: The optical path compression assembly comprises two or more waveguide structures; the waveguide structures are arranged in series.

8. The compact spectral beam combining device of claim 1, wherein: The laser units comprise laser devices and optical elements; The optical elements collimate or shape and adjust the polarization direction of the laser beams output by the laser devices; The optical elements at least comprise fast-axis collimation mirrors, slow-axis collimation mirrors, half-wave plates and narrow-band optical filters; The laser devices are selected from semiconductor lasers, fiber lasers or all-solid-state lasers.

9. The compact spectral beam combining device of claim 1, wherein: The compact spectral beam combining device further comprises an external cavity mirror arranged in the diffraction direction of the laser after the diffraction grating.

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