A multi-stage combined fiber-coupled semiconductor laser

Abstract

This invention provides a multi-stage fiber-coupled semiconductor laser, belonging to the field of fiber-coupled semiconductor technology. It includes: a fiber coupling module for outputting a wavelength-locked and tunable laser beam; a multi-stage spectral synthesis unit for performing step-by-step spectral synthesis on the laser beam to output a multi-path spectrally synthesized beam; and a fiber combining unit for combining the multi-path spectrally synthesized beam and outputting the synthesized laser beam from a single output fiber. This invention solves the technical problem in existing semiconductor lasers where it is difficult to balance beam quality and brightness when increasing power, achieving a balance between high power and high brightness, improving system synthesis efficiency and scalability, and enhancing output beam quality and availability.

Description

Technical Field

[0001] This invention relates to the field of fiber-coupled semiconductor technology, and more specifically to a fiber-coupled semiconductor laser assembled in multiple cascades. Background Technology

[0002] Semiconductor lasers possess advantages such as high electro-optical conversion efficiency, small size, long lifespan, and high reliability, and are widely used in industrial processing, medical aesthetics, laser lighting, and pump sources. As application scenarios increasingly demand higher laser power and beam quality, achieving high-power output without significantly degrading beam quality has become a critical problem that urgently needs to be solved in this field.

[0003] Currently, the main technical approaches to improving the output power of semiconductor lasers include spatial beamforming, polarization beam combining, spectral beam combining, and fiber beam combining. Among these, spatial beamforming, by arranging and focusing multiple light-emitting units in space, can increase power, but the beam quality decreases significantly with the increase in the number of units, making it difficult to meet the requirements of high-brightness applications. Polarization beam combining has limited power improvement. Spectral beam combining, by combining beams of different wavelengths into one, can maintain beam quality to some extent, but traditional single-stage spectral combining methods are limited by factors such as grating dispersion capability, device damage threshold, and thermal management, resulting in a limited number of beam paths and making it difficult to achieve high-power output.

[0004] Fiber optic beam combining technology achieves a linear power increase by combining multiple fiber laser outputs into a single beam. However, the brightness of the output beam is limited by the numerical aperture and core diameter of the input fiber, typically sacrificing brightness for power gains. While existing technologies have attempted to combine spectral beam combining with fiber beam combining, these are mostly simple cascades lacking system optimization of each stage of the combining process, resulting in low combining efficiency, severe beam quality degradation, and poor system scalability. Furthermore, existing semiconductor laser pump sources often employ single-chip or simple beam combining followed by direct coupling into the fiber, resulting in low output beam brightness that fails to meet the high beam quality requirements of long-distance laser illumination, laser power transfer, and high-brightness pumping of fiber lasers. Therefore, there is an urgent need for a high-brightness semiconductor laser output solution that can maintain or increase beam brightness while simultaneously improving power, and possesses good engineering feasibility.

[0005] Therefore, existing technologies still need further development. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a fiber-coupled semiconductor laser composed of multiple cascades to solve the problems existing in the prior art.

[0007] To achieve the above-mentioned technical objectives, according to a first aspect of the present invention, the present invention provides a fiber-coupled semiconductor laser assembled in multiple cascades, comprising: Fiber optic coupling module for outputting a wavelength-locked and tunable laser beam; A multi-stage spectral synthesis unit is used to perform step-by-step spectral synthesis on the laser beam to output a multi-path spectrally synthesized beam. The fiber optic beam combining unit is used to combine the multi-path spectrally synthesized beams and output the combined laser beam from a single output fiber.

[0008] Specifically, the fiber coupling module includes multiple chip units, and each chip unit has a fast-axis collimating mirror, a slow-axis collimating mirror, a beam rotator, a wavelength locking element, a first reflecting mirror, a half-wave plate, and a polarization combiner arranged sequentially on its outgoing optical path. The wavelength locking element is used for spectral locking and tuning, and the polarization combiner is used to combine multiple beams into one beam and couple it into the coupling fiber through the first focusing lens.

[0009] Specifically, the multi-level spectral synthesis unit includes: The first-stage spectral synthesis unit is used to synthesize the laser beams output from multiple fiber coupling modules, couple them into the optical fiber, and output a first laser beam. The second-stage spectral synthesis unit is used to synthesize the spectra of multiple first laser beams. The wavelength interval processed by the second-stage spectral synthesis unit is greater than the wavelength interval processed by the first-stage spectral synthesis unit. The second beam is coupled into the optical fiber and outputs a second laser beam. The third-level spectral synthesis unit is used to synthesize the spectra of multiple second laser beams. The wavelength interval processed by the third-level spectral synthesis unit is greater than the wavelength interval processed by the second-level spectral synthesis unit. The beams are coupled into an optical fiber and output as a third laser beam.

[0010] Specifically, the first-stage spectral synthesis unit includes multiple fiber coupling modules, a first collimating lens, a first grating, a second grating, a second focusing lens, a first input fiber, and a first output fiber; The output center wavelengths of the multiple fiber coupling modules are arranged at equal intervals from low to high. The laser beams output by each fiber coupling module are collimated by the collimating lens after being fed into the first input fiber, and then spectrally synthesized by the first grating and the second grating in sequence. The synthesized beam is coupled into the first output fiber by the second focusing lens.

[0011] Specifically, the first grating and the second grating constitute a dual-grating spectral synthesis structure, which is used to combine laser beams of different wavelengths output by multiple fiber coupling modules into a single beam.

[0012] Specifically, the second-stage spectral synthesis unit includes multiple second input optical fibers, a second collimating lens, a second reflecting mirror, and a volume Bragg grating; Each of the second input optical fibers is used to receive the first laser beam, and each of the second collimating lenses is disposed at the output end of each of the second input optical fibers to collimate the beam. The second reflector is disposed in the output light path of the second collimating lens and is used to reflect the light beam to the volume Bragg grating; The volume Bragg grating is disposed on the reflected light path of the second reflector and is used to perform wavelength-interval spectral synthesis of multiple laser beams of different wavelengths.

[0013] Specifically, the second-stage spectral synthesis unit also includes a third focusing lens and a second output optical fiber; The third focusing lens is disposed on the output optical path of the volume Bragg grating and is used to couple the synthesized beam into the second output optical fiber.

[0014] Specifically, the third-level spectral synthesis unit includes a third input fiber, a third collimating lens, a third reflecting mirror, multiple dichroic mirrors, a fourth focusing lens, and a third output fiber; The third input optical fiber is used to receive the second laser beam, and the third collimating lens is respectively disposed at the output end of each of the third input optical fibers to collimate the beam. The third reflecting mirror is disposed in the output light path of the third collimating lens and is used to deflect the light beam horizontally. The dichroic mirror is disposed on the reflected light path of the third reflecting mirror and is used to perform spectral synthesis of multiple laser beams of different wavelengths; The fourth focusing lens is disposed on the outgoing light path of the dichroic mirror and is used to couple the combined light beam into the third output optical fiber.

[0015] Specifically, the laser beam output by the fiber coupling module is connected to the first-stage spectral synthesis unit via a fiber connector or a fiber pluggable device.

[0016] Specifically, the fiber optic bundle unit includes multiple fourth input fibers, a fiber optic bundler, and a fourth output fiber; Each of the fourth input optical fibers is an optical fiber with a first core diameter and a first numerical aperture, used to receive the laser beam output by the third-level spectral synthesis unit; The fiber optic combiner is used to combine the beams from multiple input fibers into a single beam. The fourth output fiber is a fiber with a second core diameter and a second numerical aperture, used to output the combined laser beam. Wherein, the second core diameter is larger than the first core diameter, and the second numerical aperture is larger than the first numerical aperture.

[0017] Beneficial effects: This invention provides a multi-stage cascaded fiber-coupled semiconductor laser that achieves a balance between high power and high brightness. By employing fiber coupling modules as the basic unit for high brightness and combining multi-stage heterogeneous spectral synthesis with final fiber beam combining, it can significantly increase output power without significantly degrading beam quality, while effectively maintaining laser brightness. This solves the technical problem of difficulty in balancing power and brightness in traditional solutions, improving system synthesis efficiency. Compared to single technologies or simple cascading, it significantly improves overall synthesis efficiency and the number of beams that can be combined. At the same time, the modular design makes the system easy to assemble, maintain, and expand power, improving output beam quality and availability. Finally, the synthesized laser beam is output through a single fiber, resulting in a well-symmetrical circular spot, which facilitates subsequent beam shaping and applications, greatly improving the availability and reliability of the beam. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the fiber-coupled semiconductor laser assembled in multiple cascades according to a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the composition of the optical fiber coupling module provided in a specific embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the first-stage spectral synthesis unit provided in a specific embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the second-level spectral synthesis unit provided in a specific embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the third-level spectral synthesis unit provided in a specific embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of the optical fiber combining unit provided in a specific embodiment of the present invention; The reference numerals in the above figures are as follows: 1. Chip unit; 2. Fast-axis collimating lens; 3. Slow-axis collimating lens; 4. Beam rotator; 5. Wavelength locking element; 6. First reflecting mirror; 7. Half-wave plate; 8. Polarization combiner; 9. First focusing lens; 10. Coupled fiber; 11. First input fiber; 12. Fiber optic connector; 13. First collimating lens; 14. First grating; 15. Second grating; 16. Second focusing lens; 17. First output fiber; 18. Second collimating lens; 19. Second reflecting mirror; 20. Volume Bragg grating; 23. 24. Third collimating lens; 25. Third reflecting mirror; 26. Dichroic mirror; 27. Fourth focusing lens; 28. Third input fiber; 29. ​​Third output fiber; 30. Fiber optic combiner; 31. Fourth input fiber; 32. Fiber optic fusion splice; 33. Fourth output fiber; 100. Fiber optic coupling module; 200. Multi-stage spectral synthesis unit; 300. Fiber optic combiner unit; 210. First-stage spectral synthesis unit; 220. Second-stage spectral synthesis unit; 230. Third-stage spectral synthesis unit. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0020] Before providing a further detailed description of the embodiments of this application, the nouns and terms involved in the embodiments of this application will be explained, and the nouns and terms involved in the embodiments of this application shall be interpreted as follows.

[0021] (1) Fiber coupling module: refers to a basic unit for outputting laser with locked wavelength and tunable spectrum. It can integrate multiple semiconductor laser chips and initially improve power and brightness through spatial beaming, polarization beam combining and other methods. Finally, the laser is coupled into a single fiber for output as the basic sub-beam for subsequent spectral synthesis.

[0022] (2) Multi-level spectral synthesis unit: refers to a system composed of multiple spectral synthesis stages with different wavelength intervals connected in series. Its feature is that, for the spectral beam combining requirements of different densities, the optimal synthesis scheme (such as double grating, volume Bragg grating, dichroic mirror, etc.) is adopted to realize the stepwise spectral synthesis from dense to sparse, so as to maximize the number of beam combining paths while ensuring high synthesis efficiency and beam quality.

[0023] (3) Fiber beam combiner: refers to a device used to combine multiple fiber laser beams into an output fiber with a larger core diameter and numerical aperture. It is usually referred to as a fiber beam combiner. Its main function is to further improve the total output power after spectral synthesis.

[0024] (4) Wavelength locking element: refers to an optical element used to stabilize the output wavelength of a semiconductor laser and suppress wavelength drift. In this invention, its specific implementation can be an external cavity grating with a Littrow structure or a volume Bragg grating (VBG). By wavelength locking, the center wavelength of each laser can be precisely controlled, which is a prerequisite for high-efficiency spectral synthesis.

[0025] (5) Heterogeneous spectral synthesis: refers to the use of spectral synthesis elements with different physical principles or structures in different stages of multi-stage spectral synthesis. For example, the first stage uses dense spectral synthesis based on diffraction gratings, the second stage uses medium-interval spectral synthesis based on volume Bragg grating (VBG), and the third stage uses coarse-interval spectral synthesis based on dichroic mirror (thin film filter TFF). This strategy can make full use of the advantages of various technologies to achieve the overall performance optimization and solve the problem that single synthesis technology is difficult to balance efficiency and cost when combining high-number and large-bandwidth beams.

[0026] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0027] Please see Figures 1 to 6 This application provides a multi-stage synthesized fiber-coupled semiconductor laser, including a fiber coupling module 100, a multi-stage spectral synthesis unit 200, and a fiber combining unit 300 arranged sequentially along the laser beam propagation direction. The fiber coupling module 100 is used to output a wavelength-locked and tunable laser beam; the multi-stage spectral synthesis unit 200 is used to perform step-by-step spectral synthesis on the laser beam to output a multi-path spectrally synthesized beam; and the fiber combining unit 300 is used to synthesize the multi-path spectrally synthesized beam and output the synthesized laser beam from a single output fiber.

[0028] Understandably, this solution aims to address the technical problem in existing semiconductor lasers where it is difficult to maintain beam quality while increasing power, resulting in insufficient output brightness. In this embodiment, the laser generally includes one or more fiber coupling modules 100, a multi-level spectral synthesis unit 200, and a fiber combining unit 300. The fiber coupling module 100 serves as the basic light source unit, and its core function is to generate a laser beam with precisely locked wavelength and tunable performance, providing a high-quality laser beam for subsequent spectral synthesis. This solution achieves high-power, high-brightness laser output through a systematic, hierarchical synthesis architecture.

[0029] Specifically, the fiber coupling module 100 is responsible for generating the initial laser beam. Existing technologies typically use a single laser chip as the light source, which has limited power and beam quality, and the wavelength is easily affected by temperature and current, making it unsuitable for direct use in precise spectral synthesis. In this solution, the fiber coupling module 100, through internal integration and preliminary beam combining, outputs an optimized fiber laser with higher power, better beam quality, and stable wavelength. This lays a solid foundation for subsequent large-scale synthesis. By providing stable and high-quality sub-beams, it solves the problem of stringent requirements for the input light source in subsequent synthesis units, improving the stability and synthesis efficiency of the entire system.

[0030] Furthermore, the aforementioned multi-stage spectral synthesis unit 200 receives laser beams from multiple fiber-coupled modules 100 and performs spectral synthesis on these beams step by step. Its design aims to combine a large number of laser beams of different wavelengths into fewer optical paths, thereby significantly increasing the power density of the optical path without significantly increasing the beam spread angle and size (i.e., without degrading beam quality). Compared with the simple single-stage spectral synthesis or isomorphic synthesis in existing technologies, the multi-stage heterogeneous approach employs the most suitable technology according to the beam combining requirements of different wavelength intervals, resolving the contradiction that a single technical approach cannot simultaneously achieve beam combining density, efficiency, and bandwidth, and optimizing overall performance.

[0031] Furthermore, the aforementioned fiber combining unit 300 receives multiple spectrally synthesized beams output from the multi-stage spectral combining unit 200 and performs final power superposition. Spectral synthesis mainly increases the number of wavelengths within a single fiber, while fiber combining directly increases the total output power by merging the beams from multiple fibers into a thicker fiber. This design combines spectral synthesis that maintains brightness with fiber combining that increases power. In this way, the solution ultimately outputs a synthesized laser beam with both high power and excellent beam quality from a single output fiber, effectively overcoming the technical problem of not being able to balance power and beam quality in the prior art.

[0032] Furthermore, in a preferred embodiment, such as Figure 2 As shown, the fiber coupling module 100 includes multiple chip units 1. Each chip unit 1 has a fast-axis collimating lens 2, a slow-axis collimating lens 3, a beam rotator 4, a wavelength locking element 5, a first reflecting mirror 6, a half-wave plate 7, and a polarization combiner 8 arranged sequentially on its outgoing optical path. The wavelength locking element 5 is used for spectral locking and tuning, and the polarization combiner 8 is used to combine multiple beams into one beam and couple it into the coupling fiber 10 through the first focusing lens 9.

[0033] It should be noted that, in order to ensure the quality and controllability of the beam from the source, the internal structure of the fiber coupling module 100 has been optimized. The fiber coupling module 100 includes multiple chip units 1. By using multiple chip units 1 instead of a single one, preliminary power superposition can be achieved within the module. In the output optical path of each chip unit 1, a fast-axis collimating lens 2 and a slow-axis collimating lens 3 are arranged sequentially. The divergence angle of the beam emitted by the semiconductor laser chip in the fast-axis and slow-axis directions is very different. By collimating the beams of the fast-axis collimating lens 2 and the slow-axis collimating lens 3 respectively, the divergent beam can be shaped into a nearly parallel beam. This is the basis for all subsequent optical operations, which solves the problem of large divergence and strong asymmetry of the original chip beam and provides a prerequisite for high-quality beam synthesis.

[0034] After collimation, the beam passes through a beam rotator 4, which rearranges or rotates the beams from different chip units 1 in space. For example, multiple linearly arranged chip spots are rotated 90 degrees and then stacked tightly to improve the space fill factor, facilitating subsequent beam combining. Subsequently, a wavelength locking element 5 and a first reflector 6 are set in the beam path. The wavelength locking element 5, such as a planar grating with a Littrow structure, generates strong feedback for light of a specific wavelength, forcing the lasing wavelength of the chip unit 1 to stabilize at the feedback wavelength. By finely adjusting the angle of the wavelength locking element 5, precise tuning of the output laser wavelength can be achieved. The first reflector 6 cooperates with the wavelength locking element 5 to form an external cavity, stabilizing the locking effect. This ensures that the laser output by each fiber coupling module 100 has a precise and stable center wavelength, which is the fundamental guarantee for spectral synthesis.

[0035] Furthermore, to further enhance the module's output power, after the beam rotator 4, part of the optical path is reflected by a large mirror and then rotated 90 degrees by a half-wave plate 7, resulting in two sets of beams with mutually perpendicular polarization directions. These two sets of beams are then guided together to a polarization combiner 8, which can merge two orthogonally polarized beams into one beam with almost no impact on beam quality. In this way, the module's output power is doubled based on spatial beaming. Finally, the high-power beam combined by the polarization combiner 8 is efficiently coupled into a coupling fiber 10 through the first focusing lens 9 for output. This makes the single fiber coupling module 100 itself a small, efficient, and wavelength-controllable high-brightness laser source.

[0036] See Figure 1 In this embodiment, the multi-level spectral synthesis unit 200 includes: The first-stage spectral synthesis unit 210 is used to spectrally synthesize the laser beams output by the multiple fiber coupling modules 100, couple them into the optical fiber, and output a first laser beam. The second-stage spectral synthesis unit 220 is used to synthesize the spectra of multiple first laser beams. The wavelength interval processed by the second-stage spectral synthesis unit 220 is greater than the wavelength interval processed by the first-stage spectral synthesis unit 210. The second laser beam is coupled into the optical fiber and outputs the second laser beam. The third-level spectral synthesis unit 230 is used to synthesize the spectra of multiple second laser beams. The wavelength interval processed by the third-level spectral synthesis unit 230 is greater than the wavelength interval processed by the second-level spectral synthesis unit 220. The beams are coupled into an optical fiber and output as a third laser beam.

[0037] It should be noted that the multi-level spectral synthesis unit 200 described above employs the most efficient synthesis technology for wavelength spacing at different scales. Specifically, the multi-level spectral synthesis unit 200 includes a first-level spectral synthesis unit 210, a second-level spectral synthesis unit 220, and a third-level spectral synthesis unit 230. The first-level spectral synthesis unit 210 is used to spectrally synthesize the laser beams output from multiple fiber coupling modules 100 to output the first laser beam. This level processes the laser beam with the densest wavelength spacing, for example, the wavelengths of adjacent channels differ by only 1-2 nanometers. Its function is to merge as many channels as possible within the smallest possible spectral bandwidth to achieve dense synthesis.

[0038] Subsequently, the first laser beams output after the first stage of synthesis are sent to the second-stage spectral synthesis unit 220 for further spectral synthesis. The wavelength interval processed by the second-stage spectral synthesis unit 220 is larger than that processed by the first-stage spectral synthesis unit 210. For example, if the first stage synthesizes beams of 975nm, 976nm, 977nm, etc., then the second stage may synthesize beam clusters from different first-stage units with center wavelengths of 976nm, 986nm, 996nm, etc., respectively. The wavelength interval is expanded to about 10 nanometers. This design is because different optical elements have different working efficiencies at different wavelength intervals. By decomposing the synthesis task, each stage operates in its own optimal parameter range, thereby improving the overall synthesis efficiency and signal-to-noise ratio.

[0039] Similarly, the second laser beams output after the second-stage synthesis are sent to the third-stage spectral synthesis unit 230 for spectral synthesis over a wider range. The wavelength interval processed by the third-stage spectral synthesis unit 230 is further larger than that processed by the second-stage spectral synthesis unit 220, for example, reaching the 50-100 nanometer level. Finally, the third laser beams after the third-stage spectral synthesis are sent to the fiber combining unit 300 for final power superposition. This heterogeneous synthesis architecture with progressively increasing wavelength intervals can effectively avoid the limitations of single-element dispersion capability, damage threshold, and angle tolerance compared to the isomorphic scheme of synthesizing all wavelengths with a single grating. This allows for the synthesis of an extremely high number of beams over an extremely wide spectral range, which is the key to achieving high power output.

[0040] Further, see Figure 3 The first-stage spectral synthesis unit 210 includes multiple fiber coupling modules 100, a first collimating lens 13, a first grating 14, a second grating 15, a second focusing lens 16, a first input fiber 11, and a first output fiber 17. The output center wavelengths of the multiple fiber coupling modules 100 are arranged at equal intervals from low to high. The laser beams output by each fiber coupling module 100 are collimated by the first collimating lens 13 after being input through the first input fiber 11, and then spectrally synthesized by the first grating 14 and the second grating 15 in sequence. The synthesized beam is coupled into the first output fiber 17 through the second focusing lens 16.

[0041] It should be noted that the first-stage spectral synthesis unit 210 is the core of realizing dense spectral synthesis. It includes multiple fiber coupling modules 100 as input sources, a first collimating lens 13, a first grating 14, a second grating 15, a second focusing lens 16, and optical fibers. The output center wavelengths of the multiple fiber coupling modules 100 are precisely set to be arranged at equal intervals from low to high, such as 975.0 nm, 975.5 nm, 976.0 nm, etc. The laser beams output by these modules are transmitted through optical fibers and emitted from the side-by-side fiber array.

[0042] The diverging beams emitted from the fiber array are first converted into parallel beams by the first collimating lens 13. Subsequently, these parallel beams containing multiple wavelength components are incident on the first grating 14. The first grating 14 separates the beams of different wavelengths at different angles according to the different diffraction angles of different wavelengths. These dispersed beams are then incident on the second grating 15. The second grating 15 has the opposite function to the first grating 14. It readjusts the beams of different wavelengths incident at different angles into mutually parallel directions for emission. Finally, all the beams of different wavelengths overlap in space but propagate in the same direction, forming a composite beam containing all input wavelengths. This composite beam is finally coupled into the first output fiber 17 through the second focusing lens 16. Through this dual-grating structure, multiple spatially separated laser beams of different wavelengths are merged into the same fiber, greatly improving the power density of single fiber transmission.

[0043] In one optional embodiment, the first grating 14 and the second grating 15 together constitute a dual-grating spectral combining structure, used to combine laser beams of different wavelengths output from multiple fiber coupling modules 100 into a single beam. Compared to a single-grating structure, this structure has higher dispersion compensation capability and better beam quality. In single-grating combining, the wavelength of the combined beam varies at different positions on the beam cross-section, which affects subsequent focusing and coupling efficiency. The dual-grating structure effectively eliminates this phenomenon through a second diffraction, resulting in a uniform wavelength distribution on the cross-section of the combined beam and beam quality close to the diffraction limit. Therefore, by employing a dual-grating spectral combining structure, laser beams of different wavelengths output from multiple fiber coupling modules 100 can be efficiently combined into a high-quality collinear beam, providing an ideal light source for subsequent multi-stage combining and high-efficiency fiber coupling.

[0044] See Figure 4 In this embodiment, the second-stage spectral synthesis unit 220 includes multiple second input optical fibers 23, second collimating lenses 18, second reflecting mirrors 19, and a volume Bragg grating 20. Each second input optical fiber 23 receives the first laser beam, and each second collimating lens 18 is disposed at the exit end of each second input optical fiber 23 to collimate the beam. The second reflecting mirror 19 is disposed on the exit optical path of the second collimating lens 18 to reflect the beam to the volume Bragg grating 20. The volume Bragg grating 20 is disposed on the reflected optical path of the second reflecting mirror 19 to perform spectral synthesis of multiple laser beams of different wavelengths with medium wavelength intervals.

[0045] Furthermore, the second-stage spectral synthesis unit 220 also includes a third focusing lens and a second output optical fiber; the third focusing lens is disposed on the output optical path of the volume Bragg grating 20 and is used to couple the synthesized beam into the second output optical fiber.

[0046] It should be noted that the aforementioned second-stage spectral synthesis unit 220 is used to achieve spectral synthesis with medium wavelength intervals, such as... Figure 4 As shown, the second-stage spectral synthesis unit 220 includes multiple second input optical fibers 23, multiple corresponding second collimating lenses 18, second reflecting mirrors 19, and volume Bragg gratings 20 (VBG). Each second input optical fiber 23 is used to receive the first laser beam (i.e., dense wavelength cluster) output from the first-stage spectral synthesis unit 210. After the beam exits from the optical fiber, it is collimated by its corresponding second collimating lens 18 and becomes a parallel beam.

[0047] In this embodiment, after exiting the second collimating lens 18, part of the optical path (e.g., a beam with wavelength λ1) passes through a second reflecting mirror 19. The function of this reflecting mirror is to change the propagation direction of the beam, causing it to be incident on the volume Bragg grating 20 at a specific angle. Meanwhile, another beam (e.g., a beam with wavelength λ2) is directly incident on the volume Bragg grating 20. The volume Bragg grating 20 is a special type of volume grating that has extremely high reflectivity for light of specific wavelengths and angles that satisfy the Bragg diffraction conditions, while being almost completely transparent to light of other wavelengths or angles. Through precise design, the volume Bragg grating 20 can diffract the λ1 beam reflected from the second reflector 19 onto a path that is completely collinear with the transmitted λ2 beam. In this way, two beams of different wavelengths are combined into one beam. By cascading multiple volume Bragg gratings 20 with different reflection wavelengths, multiple laser beams of different wavelengths can be combined sequentially. The advantages of VBG technology are its extremely high angle and wavelength selectivity and low insertion loss. It is very suitable for processing spectral synthesis with medium wavelength intervals of about 10 nanometers, achieving high efficiency and high signal-to-noise ratio synthesis effect.

[0048] In a preferred embodiment, in order to output the beam synthesized by the second-stage spectral synthesis unit 220, the unit further includes a third focusing lens and a second output optical fiber, such as... Figure 4 As shown, after the multiple beams pass through the last volume Bragg grating 20 and are combined into a collinear composite wavelength beam, this beam is incident on the third focusing lens. The third focusing lens focuses this parallel composite beam and precisely couples it into the core of the second output fiber. In this way, the result of the second-stage spectral synthesis is stably encapsulated in the fiber, which is convenient for transmission to the next-stage synthesis unit. This ensures the modularity and robustness of the entire system and avoids the instability caused by excessively long free space optical paths.

[0049] In this embodiment, see Figure 5 The third-stage spectral synthesis unit 230 includes a third input fiber 28, a third collimating lens 24, a third reflecting mirror 25, multiple dichroic mirrors 26, a fourth focusing lens 27, and a third output fiber 29. The third input fiber 28 receives the second laser beam; the third collimating lens 24 is disposed at the exit end of each of the third input fibers 28 to collimate the beam; the third reflecting mirror 25 is disposed in the exit optical path of the third collimating lens 24 to horizontally deflect the beam; the dichroic mirror 26 is disposed in the reflected optical path of the third reflecting mirror 25 to perform spectral synthesis of multiple laser beams of different wavelengths; and the fourth focusing lens 27 is disposed in the exit optical path of the dichroic mirror 26 to couple the synthesized beam into the third output fiber 29.

[0050] It should be noted that the aforementioned third-level spectral synthesis unit 230 is used to achieve spectral synthesis with coarse wavelength intervals, such as... Figure 5 As shown, the third-stage spectral synthesis unit 230 includes multiple third input optical fibers 28, multiple corresponding third collimating lenses 24, a third reflecting mirror 25, multiple series-connected dichroic mirrors 26, a fourth focusing lens 27, and a third output optical fiber 29. Each third input optical fiber 28 is used to receive the second laser beam output from the second-stage spectral synthesis unit 220, i.e., a beam cluster with medium wavelength intervals. After the beam exits from the optical fiber, it is collimated by its corresponding third collimating lens 24.

[0051] Similar to the second-order synthesis, part of the light path (such as wavelength cluster λa) is collimated and then horizontally deflected by, for example, 90 degrees by the third reflecting mirror 25 before being incident on the first dichroic mirror 26. The other light beam (such as wavelength cluster λb) is directly incident on the dichroic mirror 26. The dichroic mirror 26 is a thin-film optical element capable of efficiently reflecting light in one wavelength band while simultaneously efficiently transmitting light in another. Through design, the dichroic mirror 26 can precisely reflect the λa wavelength band beam while allowing the λb wavelength band beam to pass through. The two beams are combined by passing through the dichroic mirror, and the combined beam is then incident on the next dichroic mirror to be combined with the third beam (λc). This process is repeated. By connecting multiple dichroic mirrors 26 with different reflection / transmission bands in series, multiple beam clusters with large wavelength intervals can be spectrally combined. The dichroic mirror 26 can handle a very large wavelength interval and has extremely low insertion loss, making it very suitable as the last stage for wide-spectrum combination. Finally, the combined beam is coupled into the third output fiber 29 through the fourth focusing lens 27.

[0052] In an alternative implementation, to improve the modularity and maintainability of the system, the laser beam output from the fiber optic coupling module 100 can be connected to the first-stage spectral synthesis unit 210 via the fiber optic connector 12 or a fiber optic pluggable device. For example... Figure 3 As shown, an optical fiber connector 12 is installed between the output optical fiber of the optical fiber coupling module 100 and the input end of the first-stage spectral synthesis unit 210, completely decoupling the optical fiber coupling module 100 from the spectral synthesis system. When one of the optical fiber coupling modules 100 fails, maintenance personnel do not need to re-adjust the entire complex spectral synthesis optical path; they only need to replace the faulty module. Furthermore, this greatly facilitates system upgrades and expansions, allowing for flexible addition or removal of light source channels as needed. This significantly improves the system's reliability and maintainability.

[0053] In another preferred embodiment, see Figure 6 The fiber optic combining unit 300 includes multiple fourth input fibers 31, a fiber optic combiner 30, and a fourth output fiber 33. Each of the fourth input fibers 31 is an fiber with a first core diameter and a first numerical aperture. One end of each fourth input fiber 31 is provided with a fiber fusion splice 32. The fourth input fiber 31 is used to receive the laser beam output by the third-stage spectral synthesis unit 230. The fiber optic combiner 30 is used to combine the beams from the multiple input fibers into one beam. The fourth output fiber 33 is an fiber with a second core diameter and a second numerical aperture, and is used to output the combined laser beam. The second core diameter is larger than the first core diameter, and the second numerical aperture is larger than the first numerical aperture.

[0054] It should be noted that the multiple fourth input fibers 31 are used to receive the spectrally synthesized laser beam output from the third-stage spectral synthesis unit 230. These input fibers have a small first core diameter and a small first numerical aperture (NA). These fourth input fibers 31 are bundled together and fused with an fiber combiner 30, which is typically a tapered fiber structure that guides and combines the beams from the multiple input fibers into a single output fiber, namely the fourth output fiber 33. The fourth output fiber 33 has a second core diameter and a second numerical aperture, wherein the second core diameter is larger than the first core diameter. The second numerical aperture is larger than the first numerical aperture. According to the law of conservation of laser brightness, during the beam combining process, the beam parameter product of the output beam (the product of the core diameter and the numerical aperture) is approximately equal to the sum of the beam parameter products of all input beams. By selecting appropriate input and output fiber parameters, such as combining seven fibers with a core diameter of 50μm and an NA of 0.12 into a single fiber with a core diameter of 150μm and an NA of 0.22, the total power can be increased while maintaining the brightness of the output laser essentially unchanged. This solves the problem of traditional fiber beam combining sacrificing brightness for power, ensuring that the final output laser has both high power and high brightness.

[0055] To more clearly demonstrate the complete implementation and synergistic effects of the technical solution of this invention, the following specific embodiments illustrate the technical path of this invention from the basic light source to the final output: First, at the light source level, adopting, for example Figure 2 The fiber coupling module 100 shown integrates, for example, four 40μm wide semiconductor chip units 1. The emitted beam is shaped by a fast-axis collimating lens 2 and a slow-axis collimating lens 3, and then spatially stacked by a beam rotator 4. A two-in-one polarization beam combining is achieved using a half-wave plate 7 and a polarization combiner 8, combining the beams of the four chip units 1 into two high-power beams. These two beams are then spatially bundled and wavelength locked by an external cavity grating with a Littrow structure as a wavelength locking element 5. Finally, they are coupled into a coupling fiber 10 with a core diameter of 50μm and an NA of 0.12 through a first focusing lens 9. By adjusting the wavelength locking elements 5 of different modules, N fiber coupling modules 100 with center wavelengths of λ1, λ2, …, λN and a wavelength interval of 0.5nm are prepared. Next, the multi-level heterogeneous spectral synthesis stage begins. The first stage is the first-level dense spectral synthesis, such as... Figure 3 As shown, N fiber coupling modules 100 are connected to the first-stage synthesis unit through pluggable fiber connectors 12. N beams with a wavelength spacing of 0.5nm are collimated by the first collimating lens 13 and then incident on the dual-grating spectral synthesis structure composed of the first grating 14 and the second grating 15. The synthesized beam is coupled into a coupling fiber with the same specifications as the input fiber, i.e., the first output fiber 17, through the second focusing lens 16. Assuming N=20, this output fiber contains 20 wavelengths, and the total power is increased by about 20 times, while the spectral width is only about 10nm. M such first-stage synthesis units are prepared, and their center wavelength clusters are separated by 10nm, such as 970-980nm, 980-990nm, etc. Then, it proceeds to the second-stage medium-wavelength interval spectral synthesis, such as... Figure 4 As shown, the M-path output fiber from the first-stage combining unit serves as the second input fiber 23. Its beam is collimated by the second collimating lens 18. Using the second reflecting mirror 19 and multiple volume Bragg gratings 20 connected in series, these beam clusters spaced 10nm apart are combined. For example, one VBG reflects the 980-990nm band and transmits the 970-980nm band. The combined beam is coupled into the second output fiber through the third focusing lens. Assuming M=5, this output fiber contains 100 wavelengths, and the spectral width is extended to 50nm. Subsequently, the third-order coarse-wavelength interval spectral synthesis is performed, such as... Figure 5As shown, multiple output fibers from the second-stage combining unit are used as the third input fiber 28. The beams are collimated by the third collimating lens 24. Using the third reflecting mirror 25 and multiple dichroic mirrors 26 connected in series, these beam clusters spaced 50nm apart are combined. For example, one dichroic mirror 26 reflects the 950-1000nm band and transmits the 1050-1100nm band. The combined beam is coupled into the third output fiber 29 through the fourth focusing lens 27. Assuming there are 3 beams, i.e., P=3, the output fiber ultimately contains 300 wavelengths, with a total spectral width of over 150nm. Finally, the fiber bundling stage begins, such as... Figure 6 As shown, multiple (e.g., Q-channel) output fibers from the third-stage combining unit are used as the fourth input fiber 31 (core diameter 50μm, NA 0.12). Through a (Qx1) fiber combiner 30, they are bundled into a fourth output fiber 33 with a larger core diameter and a larger NA, for example, a core diameter of 200μm and NA of 0.22. In this way, the total output power is increased by Q times on the basis of spectral combining, while the brightness is basically maintained.

[0056] The complete workflow of this embodiment is as follows: the current-driven chip unit 1 emits light, and the beam undergoes collimation, rotation, polarization combining, and wavelength locking within the fiber coupling module 100 to form a high-quality single-wavelength fiber output; multiple single-wavelength fibers are connected to the first-stage dual-grating unit through connectors to achieve dense spectral synthesis; the outputs of multiple first-stage units are merged into the second-stage VBG unit to achieve medium-spaced spectral synthesis; the outputs of multiple second-stage units are merged into the third-stage dichroic mirror 26 unit to achieve coarse-spaced spectral synthesis; finally, the outputs of multiple third-stage units are sent to the fiber combiner 30 to achieve final power superposition, outputting kilowatt-level, high-brightness laser light from a single large-core fiber.

[0057] It should be noted that this embodiment adopts a three-level heterogeneous synthesis architecture, including a first-level dual grating, a second-level VBG, and a third-level dichroic mirror 26, to achieve ultra-high density synthesis of hundreds or thousands of lasers within an ultra-wide spectral bandwidth of hundreds of nanometers. It employs a technical solution of spectral synthesis to maintain brightness and fiber bundle combining to increase power. By controlling the core diameter and NA relationship of the input and output fibers, high power and high brightness output of the semiconductor laser are achieved.

[0058] Furthermore, the multi-stage synthesized fiber-coupled semiconductor laser provided by this invention has broad application prospects due to its high power, high brightness, and excellent beam quality. In industrial processing, such as laser cutting and welding, high brightness means that the laser can be focused to a smaller point, thereby achieving higher power density, faster cutting speed, narrower kerf, and smaller heat-affected zone, significantly improving processing quality and efficiency. In long-distance applications, such as laser lighting, laser communication, and lidar, high brightness is a core indicator. The laser beam output by this invention has a small divergence angle and concentrated energy, maintaining a sufficiently high power density even at a distance of several kilometers, for target indication, remote power supply, or high signal-to-noise ratio detection and communication, solving the problem of limited operating distance due to insufficient brightness in traditional semiconductor laser sources. In the field of medical aesthetics, high-brightness lasers can be precisely delivered and focused onto diseased tissue, achieving precise cutting, vaporization, or coagulation while minimizing damage to surrounding healthy tissue.

[0059] Furthermore, this invention is also an ideal pump source for high-power fiber lasers and solid-state lasers. Traditional pump sources have insufficient brightness, which limits the absorption efficiency of the gain medium for the pump light, thereby affecting the output power and efficiency of the final laser. The high-brightness pump light provided by this invention can be more effectively coupled into a thin-core gain fiber or crystal, thereby enabling the pumping of lasers with higher power and higher beam quality.

[0060] The modular design of this invention also gives it high flexibility and scalability. Users can customize the laser system by increasing or decreasing the number of fiber coupling modules 100 or replacing modules with different wavelengths according to their specific requirements for power and wavelength. This flexibility enables it to adapt to a variety of different application needs, reducing the development cost and cycle for specific applications. In summary, this invention provides a high-power, high-brightness semiconductor laser source through its unique technical architecture, which can be applied to fields such as industrial processing and long-distance detection where high power and brightness are required.

[0061] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0062] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0063] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A fiber-coupled semiconductor laser assembled in multiple cascades, characterized in that, include: Fiber optic coupling module (100) for outputting a wavelength-locked and tunable laser beam; A multi-stage spectral synthesis unit (200) is used to perform step-by-step spectral synthesis on the laser beam to output a multi-path spectrally synthesized beam; The fiber combining unit (300) is used to combine the multi-path spectrally synthesized beam and output the combined laser beam from a single output fiber.

2. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 1, characterized in that, The fiber coupling module (100) includes multiple chip units (1), and each chip unit (1) has a fast-axis collimating lens (2), a slow-axis collimating lens (3), a beam rotator (4), a wavelength locking element (5), a first reflecting mirror (6), a half-wave plate (7), and a polarization combiner (8) arranged sequentially on its outgoing optical path. The wavelength locking element (5) is used for spectral locking and tuning, and the polarization combiner (8) is used to combine multiple beams into one beam and couple it into the coupling fiber (10) through the first focusing lens (9).

3. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 1, characterized in that, The multi-level spectral synthesis unit (200) includes: The first-level spectral synthesis unit (210) is used to synthesize the laser beams output by the multiple fiber coupling modules (100) and couple them into the optical fiber to output the first laser beam. The second-stage spectral synthesis unit (220) is used to synthesize the spectra of multiple first laser beams. The wavelength interval processed by the second-stage spectral synthesis unit (220) is greater than the wavelength interval processed by the first-stage spectral synthesis unit (210), and is coupled into the optical fiber to output the second laser beam. The third-level spectral synthesis unit (230) is used to synthesize the spectra of multiple second laser beams. The wavelength interval processed by the third-level spectral synthesis unit (230) is greater than the wavelength interval processed by the second-level spectral synthesis unit (220), and is coupled into the optical fiber to output the third laser beam.

4. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 3, characterized in that, The first-stage spectral synthesis unit (210) includes multiple optical fiber coupling modules (100), a first collimating lens (13), a first grating (14), a second grating (15), a second focusing lens (16), a first input optical fiber (11), and a first output optical fiber (17). The output center wavelengths of the multiple fiber coupling modules (100) are arranged at equal intervals from low to high. The laser beams output by each fiber coupling module (100) are collimated by the first collimating lens (13) after being input through the first input fiber (11), and then spectrally synthesized by the first grating (14) and the second grating (15) in sequence. The synthesized beam is coupled into the first output fiber (17) through the second focusing lens (16).

5. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 4, characterized in that, The first grating (14) and the second grating (15) constitute a dual-grating spectral synthesis structure, which is used to synthesize laser beams of different wavelengths output by multiple fiber coupling modules (100) into one beam.

6. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 3, characterized in that, The second-stage spectral synthesis unit (220) includes multiple second input optical fibers (23), a second collimating lens (18), a second reflecting mirror (19), and a volume Bragg grating (20). Each of the second input optical fibers (23) is used to receive the first laser beam, and each of the second collimating lenses (18) is disposed at the output end of each of the second input optical fibers (23) to collimate the beam. The second reflector (19) is disposed on the outgoing light path of the second collimating lens (18) and is used to reflect the light beam to the volume Bragg grating (20). The volume Bragg grating (20) is disposed on the reflected light path of the second reflector (19) and is used to perform wavelength-interval spectral synthesis of multiple laser beams of different wavelengths.

7. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 6, characterized in that, The second-stage spectral synthesis unit (220) also includes a third focusing lens and a second output optical fiber; The third focusing lens is disposed on the output optical path of the volume Bragg grating (20) and is used to couple the synthesized beam into the second output optical fiber.

8. The fiber-coupled semiconductor laser assembled by multiple cascades according to claim 3, characterized in that, The third-level spectral synthesis unit (230) includes a third input fiber (28), a third collimating lens (24), a third reflecting mirror (25), multiple dichroic mirrors (26), a fourth focusing lens (27), and a third output fiber (29). The third input fiber (28) is used to receive the second laser beam, and the third collimating lens (24) is respectively disposed at the output end of each of the third input fibers (28) to collimate the beam. The third reflecting mirror (25) is disposed on the outgoing light path of the third collimating lens (24) and is used to deflect the light beam horizontally. The dichroic mirror (26) is disposed on the reflected light path of the third reflecting mirror (25) and is used to perform spectral synthesis of multiple laser beams of different wavelengths; The fourth focusing lens (27) is disposed on the outgoing light path of the dichroic mirror (26) and is used to couple the synthesized light beam into the third output optical fiber (29).

9. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 3, characterized in that, The laser beam output by the fiber optic coupling module (100) is connected to the first-stage spectral synthesis unit (210) via the fiber optic connector (12) or a fiber optic pluggable device.

10. The fiber-coupled semiconductor laser assembled in multiple cascades according to claim 3, characterized in that, The fiber optic bundle unit (300) includes multiple fourth input fibers (31), a fiber optic bundler (30), and a fourth output fiber (33). Among them, each of the fourth input optical fibers (31) is an optical fiber with a first core diameter and a first numerical aperture, used to receive the laser beam output by the third-level spectral synthesis unit (230); The fiber optic combiner (30) is used to combine the beams of multiple input fibers into one beam; The fourth output fiber (33) is a fiber with a second core diameter and a second numerical aperture, used to output the combined laser beam; Wherein, the second core diameter is larger than the first core diameter, and the second numerical aperture is larger than the first numerical aperture.

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