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 reflective diffraction grating, an optical path compression component, and an external cavity mirror; the optical path compression component includes at least one waveguide structure; in the optical path along the spectral beam combining direction, the laser unit is distributed on both sides of the optical axis, and the reflective diffraction grating and the external cavity mirror are both located at the optical axis position; in the optical path outside the spectral beam combining direction, the position of the laser unit coincides with the position of the reflective diffraction grating; the reflective diffraction grating has a tilt angle Δθ with the direction of the optical axis, and the tilt angle Δθ does not exceed 5°; by introducing the optical path compression component, the reflective conversion mirror, and the reflective diffraction grating, multiplexing reflection and diffraction is achieved, and the light passes through the optical path compression component four times, greatly reducing the physical size of the entire spectral beam combining structure without changing the optical path length, providing a technical approach for realizing a compact, high-power, high-beam-quality laser.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and particularly relates to a compact spectral beam combining device. Background Technology

[0002] Spectral beam combining technology is one of the most feasible techniques for achieving high-power, high-beam-quality combined lasers. Since its initial report in 1999, this technology has been successfully applied to all-solid-state lasers, fiber lasers, and semiconductor lasers, significantly improving laser performance.

[0003] The basic principle of spectral beam combining is as follows: using optical elements with dispersive capabilities, such as gratings and prisms, multiple unit laser beams with different lasing wavelengths are arranged according to a certain pattern. Through the dispersive effect of the dispersive elements, these unit laser beams are output as a combined laser beam with both near-field and far-field overlap. The resulting combined laser beam has a power equal to the sum of the power of all unit beams and a beam quality similar to that of the unit beams, thus achieving high-power, high-beam-quality combined laser output.

[0004] The current basic structure of a spectral beam combiner consists of a laser unit, a transforming lens, a reflective 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 beam output from the laser unit is incident at different angles onto the reflective diffraction grating through the transforming lens, where it coincides with the grating. After further diffraction by the grating, it is incident perpendicularly onto the external cavity mirror. Only light perpendicular to the external cavity mirror that returns to the original laser unit can effectively resonate and output laser light; therefore, all beams are output with coincidence in both the near and far fields. To obtain high beam quality, the laser unit and the reflective diffraction grating are located on the front and rear focal planes of the transforming lens, respectively. Due to limitations in the spectral beam combining principle and the performance of the laser unit devices, the focal length of the transforming lens currently used is generally several hundred millimeters. Furthermore, with the increase in the number of beam combining units and the limitations of the combined spectrum, the focal length of the transforming lens further increases, resulting in a long optical path and large size for the entire spectral beam combining source, making it inconvenient for engineering applications.

[0005] To achieve high beam quality in the combined beam, the laser units and the reflective diffraction grating are located on the front and rear focal planes of the transform lens, respectively. To obtain high combined power, the more laser units in the combined beam within the rated spectral range, the better. Correspondingly, the spectral spacing between the units needs to be compressed. There are three main methods: 1) reducing the laser unit spacing, 2) increasing the focal length of the transform lens, and 3) increasing the grating dispersion. The physical spatial spacing of the laser units is mainly determined by the laser's packaging. Due to limitations in chip manufacturing processes and heat dissipation requirements, it is difficult to directly and significantly reduce the unit spatial spacing.

[0006] The paper "Hundred-watt diode laser source by spectral beam combining" proposes a relay imaging method to convert the laser into a reduced image, effectively reducing the spatial spacing of the laser chip. This method can also be seen as increasing the focal length of the transform lens while maintaining the physical spatial spacing of the laser units. Regarding methods to increase grating dispersion, according to the principle of grating dispersion, this is mainly achieved by increasing the number of lines per unit size of the grating; however, the dispersion capability of a single grating is limited.

[0007] The literature "Narrow-spectral-span spectral beam combining with a nonparallel double-grating structure" and the Chinese patent application with publication number CN114994933A, published on September 2, 2022, entitled "Spectral beam combining device and method" propose a method of multiplexing multiple gratings, which effectively improves the dispersion capability of the equivalent grating and achieves a narrower spectral interval. However, the spectral beam combining structure is still too large.

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

[0009] The structural size of spectral beam combining light sources can be reduced to some extent by using multiple gratings or laser unit relay imaging methods. However, compared with conventional laser beam combining structures, the size of spectral beam combining light sources is still very large, making it difficult to achieve miniaturization. Summary of the Invention

[0010] In view of this, and addressing the current challenge of miniaturizing spectral beam combining light sources, this invention aims to provide a compact spectral beam combining device. It introduces an optical path compression component, a reflective conversion lens, and a reflective diffraction grating. By setting a specific angle for the reflective diffraction grating, multiplexing of reflection and diffraction is achieved. The light passes through the optical path compression component four times, significantly reducing the physical size of the entire spectral beam combining structure without changing the optical path length. This provides a technical approach to realizing compact, high-power, high-beam-quality lasers, meeting the stringent requirements of applications demanding high power, beam quality, and light source size.

[0011] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0012] This invention provides a compact spectral beam combining device, comprising a laser unit, a reflective conversion mirror, a reflective diffraction grating, an optical path compression component, and an external cavity mirror; the optical path compression component includes at least one waveguide structure; the optical path compression component is disposed between the laser unit and the reflective conversion mirror; the laser unit outputs laser light; the compact spectral beam combining device includes an optical path in the spectral beam combining direction and an optical path in a non-spectral beam combining direction; the compact spectral beam combining device includes spectral beam combining... The optical path includes both a directional optical path and a non-spectral beam combining directional optical path. The optical path compression component compresses the optical path for both the spectral beam combining directional optical path and the non-spectral beam combining directional optical path without altering the spectral beam combining function of the spectral beam combining directional optical path. In the spectral beam combining directional optical path, the laser units are distributed on both sides of the optical axis, and the reflective diffraction grating and the external cavity mirror are both positioned along the optical axis. In the non-spectral beam combining directional optical path, the position of the laser units coincides with the position of the reflective diffraction grating. The reflective diffraction grating has a tilt angle Δθ relative to the optical axis, and the tilt angle Δθ does not exceed 5°.

[0013] Furthermore, the reflective diffraction grating is a positive first-order diffraction grating or a blazed grating, the first-order diffraction efficiency of the reflective diffraction grating is greater than 90%, and the high diffraction efficiency spectral width of the reflective diffraction grating is greater than or equal to 5 nm.

[0014] Furthermore, in the optical path of the spectral beam combining direction, the reflective diffraction grating is set at a littrow angle, and the central axis of the incident light direction coincides with the diffraction direction.

[0015] Furthermore, in the non-spectral beam combining direction optical path, the reflective conversion mirror is perpendicular to the direction of the optical axis.

[0016] Furthermore, the waveguide structure includes at least two reflecting surfaces, which are either planar or concave cylindrical surfaces; the bending direction of the concave cylindrical surface corresponds to the non-spectral beam combining direction.

[0017] Furthermore, the laser is reflected at least twice on a single reflecting surface; and the reflectivity of a single reflecting surface is greater than 99%.

[0018] Furthermore, the waveguide structure includes two parallel reflecting surfaces, both of which are planar. When the laser first incident on a single reflecting surface, the angle formed between the laser and the normal to the reflecting surface is the incident angle θ. The effective length of the single reflecting surface in the optical path compression direction is d, and the optical path length m within it is n. d / sinθ, where n is the refractive index within a single waveguide structure.

[0019] Furthermore, the incident angle θ is less than or equal to 30°.

[0020] Furthermore, the optical path compression component includes two or more waveguide structures; the waveguide structures are connected in series.

[0021] Furthermore, the laser unit includes a laser device and optical elements;

[0022] The optical element collimates or shapes the laser output from the laser device and adjusts its polarization direction.

[0023] The optical elements include at least a fast-axis collimating lens, a slow-axis collimating lens, a half-wave plate, and a narrow-band filter;

[0024] The laser device is selected from semiconductor lasers, fiber lasers, or all-solid-state lasers.

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

[0026] 1) More compact spectral beam combining structure; by introducing optical path compression components, reflective conversion lenses and reflective diffraction gratings, and by setting the special angle of the reflective diffraction grating, multiplexing of reflection and diffraction is achieved. The light passes through the optical path compression components four times, greatly reducing the physical size of the entire spectral beam combining structure without changing the optical path, thus realizing the miniaturization of the spectral beam combining light source.

[0027] 2) Enhanced power scalability: Conventional spectral beam combining light sources are limited by the chip gain spectral width and the grating's high-efficiency diffraction spectral width, resulting in a limited number of beam combining units. This invention increases the focal length of the reflective conversion mirror, thereby reducing the spectral spacing of the units without increasing the size of the light source, and achieving more units within the rated spectral width, thus increasing the beam combining power.

[0028] 3) More stable spectral beam combining structure; the stability of a laser largely depends on the stability of the front and rear cavity surfaces. This invention reduces the distance between the front and rear cavity surfaces by compressing the optical path using an optical path compression component and by reusing the optical path compression component. Furthermore, the laser can be stabilized by designing the same mounting mechanism, resulting in a more stable structure. In addition, through a simple layout, the reflective grating is arranged on the optical axis and coincides with the unit in the non-spectral beam combining direction. The external cavity mirror is packaged close to the laser unit, which facilitates overall packaging and improves the overall structural stability. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 A schematic diagram of the optical path structure of the compact spectral beam combining device in the spectral beam combining direction according to an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the optical path structure of the compact spectral beam combining device in a non-spectral beam combining direction according to an embodiment of the present invention;

[0032] Figure 3 A schematic diagram showing the position of the reflective diffraction grating in a non-spectral beam combining direction in a compact spectral beam combining device according to an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of the optical path structure of a spectral beam combiner in the spectral beam combining direction, as a comparative example of existing technologies;

[0034] Figure 5 A schematic diagram of the optical path structure of a spectral beam combiner in a non-spectral beam combining direction, serving as a comparative example of existing technologies.

[0035] Figure 6 A schematic diagram of the compressed optical path of the optical path compression component in the compact spectral beam combining device of the present invention;

[0036] Figure 7 A schematic diagram of a compact spectral beam combiner in an embodiment of the present invention, showing multiple waveguide structures connected in series.

[0037] Figure 8 A schematic diagram of a waveguide structure in an optical path compression component of a compact spectral beam combiner according to an embodiment of the present invention;

[0038] Figure 9 This is another schematic diagram of the waveguide structure in the optical path compression component of the compact spectral beam combiner, which is an embodiment of the present invention.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1. Laser unit; 11. First laser unit; 12. Second laser unit; 13. Third laser unit; 14. Fourth laser unit; 101. Incident light; 102. Outgoing light; 21. Transformer lens; 22. Reflective transformer mirror; 31. Diffraction grating; 32. Reflective diffraction grating; 4. External cavity mirror; 5. Optical path compression assembly; 51. First reflecting surface; 52. Second reflecting surface. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0043] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] This invention provides a compact spectral beam combining device, comprising a laser unit, a reflective conversion mirror, a reflective diffraction grating, and an optical path compression component. The optical path compression component includes at least one waveguide structure and is disposed between the laser unit and the reflective conversion mirror. The laser unit outputs laser light. The compact spectral beam combining device includes an optical path along the spectral beam combining direction and an optical path along a non-spectral beam combining direction. The optical path comprises a beam-combining direction optical path and a non-spectral beam-combining direction optical path; the optical path compression component compresses the optical path for both the spectral beam-combining direction optical path and the non-spectral beam-combining direction optical path without altering the spectral beam-combining function of the spectral beam-combining direction optical path; in the spectral beam-combining direction optical path, the laser units are distributed on both sides of the optical axis, and the reflective diffraction grating and the external cavity mirror are both positioned on the optical axis; in the non-spectral beam-combining direction optical path, the position of the laser units coincides with the position of the reflective diffraction grating; the reflective diffraction grating has an inclination angle Δθ relative to the direction of the optical axis, and the inclination angle Δθ does not exceed 5°. The compact spectral beam combining device provided in this invention introduces an optical path compression component, a reflective conversion lens, and a reflective diffraction grating. By setting a special angle for the reflective diffraction grating, multiplexing of reflection and diffraction is achieved. The beam passes through the optical path compression component four times, greatly reducing the physical size of the entire spectral beam combining structure without changing the optical path. The interval between the laser unit, the reflective conversion lens, the reflective diffraction grating, the reflective conversion lens, and the external cavity mirror is f, where f is the focal length of the reflective conversion lens. The laser unit is directly imaged onto the external cavity mirror, facilitating effective feedback. The laser unit and the diffraction grating overlap in directions other than spectral beam combining.

[0046] In a specific embodiment of the present invention, the reflective diffraction grating is a positive first-order diffraction grating or a blazed grating. The first-order diffraction efficiency of the reflective diffraction grating is greater than 90%, and the high-diffraction-efficiency spectral width of the reflective diffraction grating is greater than or equal to 5 nm. In the optical path of the spectral beam combining direction, the reflective diffraction grating is set at a littrow angle, and the central axis of the incident light direction coincides with the diffraction direction; this ensures that the optical path after diffraction can return to the optical path compression component in the same direction in the spectral beam combining direction. The incident light of the diffraction grating is a combination of multiple unit beams with different angles. After diffraction by the grating, all unit beams are diffracted and output in the same direction. By setting the reflective diffraction grating at a littrow angle, the central beam of this combined beam coincides with the diffraction direction of the diffraction grating. Specifically, in the spectral beam combining direction, the laser output from the laser unit passes through the optical path compression component once, then is incident on the reflective conversion mirror once. After being focused and reflected by the conversion mirror, it passes through the optical path compression component a second time and is then incident on the reflective diffraction grating. The reflective diffraction grating is tilted at a small angle in the non-spectral beam combining direction. Without affecting the diffraction performance in the spectral beam combining direction, the diffracted light is output and enters the optical path compression component three times, then is incident on the reflective conversion lens a second time. After being imaged and reflected by the conversion mirror, it passes through the optical path compression component a fourth time and finally enters the external cavity mirror. In the optical path in the non-spectral beam combining direction, the reflective conversion mirror is perpendicular to the optical axis, and the normal of the reflective diffraction grating deviates from the optical axis at an angle Δθ, which is no greater than 5°. In this direction, the reflective diffraction grating mainly plays a small-angle reflection role.

[0047] In a specific embodiment of the present invention, the waveguide structure includes at least two reflecting surfaces, which are either planar or concave cylindrical surfaces; that is, the waveguide structure is a combination of planar and concave cylindrical surfaces. The bending direction of the concave cylindrical surface corresponds to the non-spectral beam combining direction, meaning the bending direction of the concave cylindrical surface is substantially consistent with the non-spectral 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 planar and planar surfaces (referred to as planar-planar), a combination of planar and concave cylindrical surfaces (referred to as planar-concave), a combination of concave cylindrical and planar surfaces (referred to as concave-planar), or a combination of concave cylindrical and concave cylindrical surfaces (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 planar-planar-planar, planar-planar-planar, or planar-planar-concave, etc. The waveguide structure can also be a series of separate reflecting surfaces, or it can be implemented in a single structure by coating a high-reflectivity film or internal reflection.

[0048] In a specific embodiment of the present invention, when the waveguide structure includes two mutually parallel reflecting surfaces, both of which are planar (i.e., a planar-planar combination), the angle formed between the laser beam and the normal to a single reflecting surface when the laser first incident on one of the reflecting surfaces is the incident angle θ. The effective length of the single reflecting surface in the optical path compression direction is d, and the optical path length m transmitted within it is n. d / sinθ, where n is the refractive index within a single waveguide structure. The incident angle θ is less than or equal to 30°.

[0049] In a specific embodiment of the present invention, the optical path compression component may include two or more waveguide structures; the waveguide structures are connected in series to fold the optical path in the rated space.

[0050] In a specific embodiment of the present invention, the laser is reflected more than or equal to 2 times on a single reflecting surface; the reflectivity of a single reflecting surface is greater than 99%; the high reflectivity of a single reflecting surface can be achieved by depositing a dielectric film or a combination of "metal + dielectric film" on the optical surface, or by total internal reflection, specifically by selecting optical glass with a suitable refractive index and low absorption rate under the conditions of total internal reflection.

[0051] In a specific embodiment of the present invention, the reflective conversion mirror is a single mirror or a combination of multiple mirrors; the reflective diffraction grating is a single grating or a combination of multiple gratings; the laser unit includes a laser device and optical elements; the optical elements collimate or shape the laser output by the laser device and adjust its polarization direction; the optical elements include at least a fast-axis collimating mirror, a slow-axis collimating mirror, a half-wave plate, and a narrow-band filter, etc.; the laser device has an anti-reflection coating deposited on the end face that outputs the laser, and the laser device is selected from semiconductor lasers, fiber lasers, or all-solid-state lasers.

[0052] The compact spectral beam combining device provided in the specific embodiments of the present invention can achieve the following beneficial effects:

[0053] 1) More compact spectral beam combining structure; by introducing optical path compression components, reflective conversion lenses and reflective diffraction gratings, and by setting the special angle of the reflective diffraction grating, multiplexing of reflection and diffraction is achieved. The light passes through the optical path compression components four times, greatly reducing the physical size of the entire spectral beam combining structure without changing the optical path, thus realizing the miniaturization of the spectral beam combining light source.

[0054] 2) Enhanced power scalability: Conventional spectral beam combining light sources are limited by the chip gain spectral width and the grating's high-efficiency diffraction spectral width, resulting in a limited number of beam combining units. This invention increases the focal length of the reflective conversion mirror, thereby reducing the spectral spacing of the units without increasing the size of the light source, and achieving more units within the rated spectral width, thus increasing the beam combining power.

[0055] 3) More stable spectral beam combining structure; the stability of a laser largely depends on the stability of the front and rear cavity surfaces. This invention reduces the distance between the front and rear cavity surfaces by compressing the optical path using an optical path compression component and by reusing the optical path compression component. Furthermore, the laser can be stabilized by designing the same mounting mechanism, resulting in a more stable structure. In addition, through a simple layout, the reflective grating is arranged on the optical axis and coincides with the unit in the non-spectral beam combining direction. The external cavity mirror is packaged close to the laser unit, which facilitates overall packaging and improves the overall structural stability.

[0056] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0057] Comparative Example 1

[0058] The optical path diagram of the spectral beam combining direction in a conventional spectral beam combining structure is shown below. Figure 4 As shown in the figure, the basic components include a laser unit 1, a transformation lens 21, a diffraction grating 31, 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-reflection 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 position of the intracavity optical components and the laser unit 1. The front cavity surface of the laser chip and the diffraction grating 31 are located on the front and rear focal planes of the transformation lens 21, respectively. For ease of explanation, the beam is illustrated by combining three laser units.

[0059] In the spectral beam combining direction ox, laser unit 1 includes a first laser unit 11, a second laser unit 12, and a third laser unit 13, all outputting laser light along the same direction z. The light output by the second laser unit 12, located at the center, is the main light, while the first laser unit 11 and the third laser unit 13 are distributed on both sides. In the spectral beam combining direction ox, the three laser units output laser light along the same direction z, which is incident on the transformation lens 21, and then incident on the diffraction grating 31 at different angles. The beams of all laser units overlap on the diffraction grating 31, with their incident angle and diffraction angle being equal to or close to the Littoral angle. The light is then incident on the external cavity mirror 4. Only the light that is perpendicularly incident on the external cavity mirror 4 and can return to the laser unit along the original path can resonate effectively.

[0060] Specifically, after the laser unit 1 outputs laser light, it passes through the transformation lens 21 and is incident on the diffraction grating 31 at different angles, where they coincide. After further diffraction by the diffraction grating 31, the laser light is incident perpendicularly on the external cavity mirror 4. Only the laser light perpendicular to the external cavity mirror 4 can return to the original laser unit 1 and effectively resonate to output laser light. Therefore, all beams are output in a manner where the near field and far field coincide. In order to obtain high beam quality, the laser unit 1 and the diffraction grating 31 are located on the front and rear focal planes of the transformation lens 21, respectively.

[0061] To further illustrate this point with a practical example, in this comparative example, a standard 976nm centimeter bar with 19 built-in laser units is used as the spectral beam combining unit. Laser unit 1 has a 100μm emission area width, a period interval of 500μm, a fast axis divergence angle of 45°, a slow axis divergence angle of 8°, an anti-reflection coating on the front cavity surface with a transmittance >99.5%, and the output laser is mostly TE linearly polarized light with a degree of polarization of 90%. Each laser unit has an output power of 5W. The conversion lens 21 has a focal length of 300mm, and the diffraction grating 31 is a transmission grating with a line count of 1600 lines / mm, achieving a first-order diffraction efficiency of 96% for S-polarized light and 30% for P-polarized light. After fast-axis collimation, beam shaping, and slow-axis collimation, laser unit 1 consists of 19 laser units arranged in a one-dimensional manner along the spectral beam combining direction. Among them, the output beam of the second laser unit 12 in the middle position coincides with the optical axis, and the first laser unit 11 and the third laser unit 13 on both sides each have 9 laser units. The spot size of each laser unit in the spectral beam combining direction is 400μm, the spatial period is 500μm, and the divergence angle is 6mrad. The size in the non-spectral beam combining direction is 2.4mm, and the divergence angle is 6mrad.

[0062] After passing through the transforming lens 21, the spot size in the spectral beam combining direction on the diffraction grating 31 is 1.8 mm, with a divergence angle of 1.3 mrad. The spot size in the non-spectral beam combining direction is 6 mm, with a divergence angle of 6 mrad. The external cavity mirror 4 is a partial reflector with a reflectivity of 10%, placed 100 mm away from the diffraction grating. Through the feedback effect of the external cavity mirror 4, each laser unit resonates to a different wavelength. The spot size on the external cavity mirror 4 is 2.06 mm (spectral beam combining direction) × 7.2 mm (non-spectral 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 center wavelengths of conventional spectral beam combining structures

[0065]

[0066] In this comparative example 1, the spectral width of the combined beam of 19 laser units is 12.3 nm, and the focal length of the corresponding transformation lens 21 is 300 mm. According to the conventional spectral beam combining structure, the laser unit 1 and the diffraction grating 31 are located on the front and rear focal planes of the transformation lens 21, respectively. That is, the distance between the laser unit and the diffraction grating 31 is 600 mm, and the distance between the external cavity mirror 4 and the diffraction grating 31 is 100 mm. Without considering the laser packaging structure, etc., from the perspective of the beam combining optical path alone, the physical size reaches 700 mm, which is large and difficult to miniaturize.

[0067] In the structure of Comparative Example 1 above, there are 19 beam combining units. Considering beam combining loss and assuming an 80% beam combining efficiency, the output power is 76W. Considering the need for high-power lasers in industrial processing and other applications, to achieve kilowatt-level power output while maintaining high beam quality, according to this laser structure, 14 centimeter-bar strips, or 266 laser units, need to be superimposed in the spectral combining direction. Using the same spectral combining structure, a simple assessment of the spectral width is 12.3 × 14 nm, resulting in a spectral width of 172.2 nm. However, the effective gain width of conventional semiconductor laser chips does not exceed 20 nm, and it further decreases with decreasing wavelength; for example, the effective gain spectral width of an 808 nm high-power semiconductor laser chip is only about 10 nm. Furthermore, as the lasing spectrum deviates from the central gain peak, the output power decreases sharply. Therefore, achieving an effective gain spectral width of 172.2 nm is difficult to achieve with current high-power semiconductor laser chips. Even if such a large spectral width is achieved by using multiple laser chips with different gain ranges through gain spectral coupling, the diffraction gratings involved are still difficult to achieve high diffraction efficiency over such a large gain range, which will also lead to a reduction in spectral beam combining power.

[0068] How can spectral beam combining maintain a narrow spectrum while combining multiple laser units? According to the principle of spectral beam combining, the simplest way is to increase the focal length of the transformation lens 21. As shown in the structure above, if the focal length of the transformation lens 21 is increased to 4.2m (14 times the current focal length), kilowatt-level spectral beam combining power output can still be achieved within a relatively narrow spectral range. However, the resulting beam combining structure size will increase significantly. Considering only the distance between the laser unit and the grating, it will reach 8.4m, which is unacceptable for conventional laser devices.

[0069] Figure 5 The diagram shows the non-spectral beam combining direction of a conventional spectral beam combining structure. As can be seen from the diagram, in the non-spectral beam combining direction y, the laser unit 1 outputs laser light along the oz direction, which is then combined and output through the transformation lens 21, the diffraction grating 31, and the external cavity mirror 4 in sequence, without any deviation or return of the optical axis. The optical path transformation in this direction is relatively simple. The basic requirement is that the laser unit 1 has a good collimation effect, so that the laser unit 1 and the external cavity mirror 4 form an effective resonance.

[0070] Example 1

[0071] The specific embodiments of the compact spectral beam combining device proposed in this invention are illustrated in the optical path structure diagrams for the spectral beam combining direction and the non-spectral beam combining direction, respectively. 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 reflective diffraction grating 32, 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. Multiple laser units 1 may be included, each with a high anti-reflection coating on its front cavity surface and a high-reflection 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 itself. The front cavity surface of the laser chip and the reflective diffraction grating 32 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 reflective diffraction grating 32 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 transmitted along the D11 direction and incident on the optical path compression component 5. After multiple reflections, it is incident on the reflective conversion mirror 22 along the D12 direction. After reflection, it returns to the optical path compression component 5 along the D21 direction. After multiple reflections, it is output to the reflective diffraction grating 32 along the D22 direction. After diffraction, it is incident on the optical path compression component 5 along the D31 direction. After multiple reflections, it is incident on the reflective conversion mirror 22 along the D32 direction. After reflection, it returns to the optical path compression component 5 along the D41 direction. After multiple reflections, it is output to the external cavity mirror along the D42 direction, and finally, the beam is combined and output along the D43 direction. Using only one set of beam compression components, a reflective transformation mirror, and a reflective diffraction grating, the beam combining optical path is compressed four times, effectively reducing the volume of the compressed light source without changing the optical path.

[0073] Specifically, such as Figure 3 The image shows a schematic diagram of the position of the reflective diffraction grating 32 in a non-spectral beam combining direction; combined with... Figures 1-3 It can be seen that the reflective diffraction grating 32 is a positive first-order diffraction grating, and the first-order diffraction efficiency of the reflective diffraction grating 32 is greater than 90%. The reflective diffraction grating 32 is placed at a littrow angle in the spectral beam combining direction, and the central axis of the incident light direction coincides with the diffraction direction. This allows the light path after diffraction to return to the light path compression component 5 in the same direction in the spectral beam combining direction.

[0074] In the non-spectral beam combining direction, the reflective conversion mirror 22 is perpendicular to the optical axis, and the normal of the reflective diffraction grating deviates from the optical axis at an angle Δθ, where Δθ is no greater than 5°. In this direction, the reflective diffraction grating mainly plays a small-angle reflection role.

[0075] The laser output from laser unit 1 is completely overlapped with the optical path that returns to the reflective diffraction grating 32 after passing through optical path compression component 5. The diffraction grating and laser unit are spatially overlapped in the non-spectral beam combining direction, which is beneficial to achieving a stable structural layout.

[0076] 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. The spot size of each laser unit in the spectral beam combining direction is 400μm, the spatial period is 500μm, and the divergence angle is 6mrad. The size in the non-spectral beam combining direction is 2.4mm, and the divergence angle is 6mrad. The focal length of the reflective converter mirror 22 is 300mm, and the reflective diffraction grating 32 has a line count of 1600 lines / mm.

[0077] Specifically, Figure 2 This diagram illustrates the optical path in the non-spectral beam combining direction of the compact spectral beam combining device structure proposed in this embodiment. As shown, 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 reflective diffraction grating 32, 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.

[0078] like Figure 6 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. For example, if the incident angle of the reflecting surface is designed to be 5° and the effective length of the reflecting surface in the compression direction is 25mm, then the corresponding optical path in 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 dimension between the reflective conversion mirror 22 and the reflective diffraction grating 32 is also compressed from 300mm to less than 50mm. Simultaneously, in this embodiment, a single optical path compression component 5 is used. Secondary optical path compression folds the optical paths before and after the reflective conversion mirror 22, sharing a single optical path compression component 5. The physical dimensions are reduced, thus the physical distance from the laser unit 1 to the reflective diffraction grating 32 is compressed from the conventional 600mm to less than 50mm, meaning the overall size of the device in the x-direction is further compressed. Compared to the conventional spectral beam combining structure in Example 1, this significantly shortens the physical size of the laser resonator cavity. Simultaneously, in the entire device, the optical paths of the diffraction grating and the external cavity mirror are introduced into the compressed structure through four compressions. By using a multiplexed reflective transform mirror, the external cavity mirror is imaged onto the diffraction grating and further onto the laser unit, improving the effective resonance between the laser unit and the external cavity mirror. The laser unit, diffraction grating, and external cavity mirror are positioned close together in the spectral beam combining direction, facilitating common base installation and effectively improving the overall stability of the device structure.

[0079] Example 2

[0080] Figure 7 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.

[0081] 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, reducing the structural size of each set to less than 100mm. Correspondingly, the optical axis offset in the y-direction is also 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.

[0082] Example 3

[0083] Figure 8 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.

[0084] Example 4

[0085] Figure 9 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.

[0086] 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.

[0087] 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 spectrum beam combination device comprises a laser unit, a reflective transform mirror, a reflective diffraction grating, an optical path compression assembly and an external cavity mirror; 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 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 reflective diffraction grating and the external cavity mirror are arranged at positions 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 reflective diffraction grating; the normal line of the reflective diffraction grating has an inclination angle Δθ with the direction of the optical axis, and the inclination angle Δθ is not more than 5°.

2. The compact spectral beam combining device of claim 1, wherein: The reflective diffraction grating is a positive first-order diffraction grating or a blazed grating, the first-order diffraction efficiency of the reflective diffraction grating is greater than 90%, and the high-efficiency diffraction spectral width of the reflective diffraction grating is greater than or equal to 5 nm.

3. The compact spectral beam combining device of claim 1, wherein: In the optical path in the spectrum beam combination direction, the reflective diffraction grating is arranged at a Littrow angle, and the central axis of the incident light direction coincides with the diffraction direction.

4. The compact spectral beam combining device of claim 1, wherein: In the optical path in the non-spectrum beam combination direction, the reflective transform mirror is perpendicular to the direction of the optical axis.

5. The compact spectral beam combining device of claim 1, wherein: The waveguide structure comprises at least two reflective surfaces, and the reflective surfaces are plane or concave cylindrical surfaces; the bending direction of the concave cylindrical surface corresponds to the non-spectrum beam combination direction.

6. The compact spectral beam combining device of claim 5, wherein: The number of reflections of the laser on a single reflective surface is greater than or equal to 2; the reflectivity of a single reflective surface is greater than 99%.

7. 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 incident to a single reflecting surface for the first time, 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.

8. The compact spectral beam combining device of claim 7, wherein: The incident angle θ is less than or equal to 30°.

9. 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.

10. The compact spectral beam combining device of claim 1, wherein: The laser unit comprises a laser device and an optical element; The optical element collimates or shapes and adjusts the polarization direction of the laser output by the laser device; The optical element at least comprises a fast-axis collimating mirror, a slow-axis collimating mirror, a half-wave plate and a narrow-band filter; The laser device is selected from a semiconductor laser, a fiber laser or a full-solid-state laser.

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