Beam combining device with wide bandwidth and high beam quality and beam combining method thereof

Abstract

The invention discloses a beam combining device with wide bandwidth and high beam quality and a beam combining method thereof, relates to the technical field of spectral beam combining, and solves the technical problems of extremely narrow light width of combined sub-beams, complex debugging process, increased beam quality of combined light and the like in the prior art. The laser assembly is used for outputting a plurality of sub-beam lasers; the grating pair is used for separating different wavelengths in each wide-line-width sub-beam laser and combining each sub-beam laser emitted by the steering optical element to generate combined light; the steering optical element is used for adjusting the steering of the sub-beam laser emitted by the different rows of lasers and adjusting the laser emitting height or the emitting height of the laser after passing through the steering optical element according to the position arrangement condition of the laser assembly and the height position condition of the combined beam light outlet; the technical scheme provided by the invention can effectively overcome the defects of narrow sub-beam line width, complex debugging, reduced beam quality, low grating surface utilization rate and the like in the grating beam combination in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of spectral beam combining, and in particular to a wide-bandwidth, high-beam-quality beam combining device and a beam combining method thereof. Background Art

[0002] In the military field, laser weapons usually refer to weapons that can destroy enemy incoming targets or important optoelectronic systems of incoming targets. Their main characteristics include fast attack speed, high hit rate, flexible fire switching, and low collateral damage. The power demand for military high-energy lasers has reached the order of tens of thousands of W to hundreds of thousands of W, while the theoretical limit output power of single-mode wide-spectrum fiber lasers is only tens of kW. It can be seen that the solution of using a single fiber laser to develop high-energy laser equipment is currently unfeasible. Therefore, the key direction of the development of high-energy laser equipment is to use laser beam combining technology to effectively synthesize the output lasers of multiple fiber lasers to achieve higher laser power at the target while maintaining the quality of the laser beam.

[0003] Currently, spectral beam combining using conventional gratings typically requires the combined sub-beams to have extremely narrow spectral widths (e.g., 0.5 nm). However, the spectral width of commercially available lasers is generally around 6 nm. This characteristic necessitates customization of combined sub-beams, resulting in high costs, especially for high-power, narrow-linewidth beams. Furthermore, if a beamlet is damaged, the position must be left vacant if a beamlet with the same wavelength is unavailable. Re-ordering a beamlet with the same wavelength also requires a long process, impacting usability.

[0004] Secondly, the spectral beam combining scheme using an ordinary grating requires that the position of the sub-beams be fixed. This is determined by the spectral beam combining formula: once the position of the grating and the wavelength difference between adjacent sub-beams are determined, the position distance between adjacent sub-beams is also determined. This makes the debugging process more complicated.

[0005] Finally, in the scheme of using ordinary grating for spectral beam combining, due to the splitting effect of the grating, the light spot will be widened to a certain extent after the sub-beam passes through the grating for the first time, and the increase in the beam quality of the combined light is inevitable.

[0006] In summary, laser beam combining technology is currently a high-energy laser solution for achieving higher laser power at the target. However, existing solutions require extremely narrow laser linewidths, which increases the cost of combining and limits the usability of the combining device. The one-to-one correspondence between the wavelength difference of adjacent sub-beams and the spacing between adjacent beams complicates the debugging process and significantly limits its practical application. While conventional grating combining greatly improves the combined light's beam quality, it inevitably increases the quality of the combined light. Summary of the Invention

[0007] The purpose of the present invention is to provide a wide bandwidth, high beam quality beam combining device to solve the following technical problems: overcoming the problems existing in the prior art such as extremely narrow width of combined sub-beams, complex debugging process and increased beam quality of combined light.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] A wide-bandwidth, high-beam-quality beam combining device, comprising:

[0010] A laser assembly, used for outputting multiple sub-beam lasers;

[0011] The grating pair separates different wavelengths in each wide-linewidth sub-beam laser and combines the sub-beam lasers emitted by the steering optical element to generate a combined beam;

[0012] The steering optical element is used to adjust the direction of the sub-beams emitted by different rows of lasers, and adjust the laser emission height or the laser emission height after passing through the steering optical element according to the position arrangement of the laser assembly and the height position of the combined light outlet.

[0013] As a further solution of the present invention: the laser assembly includes a plurality of lasers of different wavelengths and similar spot sizes;

[0014] The sub-beams of laser light emitted by all the lasers are located on the same vertical plane and are parallel to each other, and are incident on the grating pair at the same incident angle.

[0015] As a further embodiment of the present invention, the laser assembly is composed of M rows of laser mounting holes, M rows of lasers and combined light output holes arranged in order of position; each row of laser mounting holes is respectively denoted as K1, K2, ..., KM, and each row of lasers is respectively denoted as J1, J2, ..., JM;

[0016] The wavelength range corresponding to the laser mounting holes in the i-th row is λ Ki ±Δλ Ki , the wavelength of the laser in row i is λ Ji ±Δλ Ji ,have:

[0017] λ Ki -Δλ Ki ≤λ Ji ±Δλ Ji ≤λ Ki +Δλ Ki .

[0018] As a further solution of the present invention: the ridge line of the deflection optical element is perpendicular to the lines of the grating pair and perpendicular to the incident light.

[0019] As a further solution of the present invention: the deflection optical element is composed of M optical elements for deflecting laser light.

[0020] As a further solution of the present invention: the ridge line of the i-th optical element among the M optical elements is between the i-th row of laser mounting holes and the combined light output hole;

[0021] When the distance between the laser mounting holes in the i-th row and the combined light output hole is Hi, and the incident angle of the sub-beam is ∠i, the vertical distance Zi between the ridge line of the i-th optical element and the combined light output hole is:

[0022] Zi=Hi·cos 2 i.

[0023] As a further solution of the present invention: the optical element is one or more of a reflector, a right-angle mirror, and a Dove prism.

[0024] As a further solution of the present invention: the grating pair is one of a multi-grating, a double grating or a single grating.

[0025] As a further solution of the present invention: in the double grating, the vertical distance between the two double grating planes is D;

[0026] When the incident angle of the sub-beam laser is α, the length Li of the i-th right-angle mirror is:

[0027] L i ≥Dcosα(tanβ +Ki -tanβ -Ki ), i=1,2…,M;

[0028] Among them, β +Ki is the wavelength λ Ki +Δλ Ki The corresponding diffraction angle, β -Ki is λ Ki -Δλ Ki The corresponding diffraction angle.

[0029] As a further solution of the present invention: a beam combining method of a wide-bandwidth, high-beam-quality beam combining device comprises the following steps:

[0030] Step 1: Multiple lasers output wide-bandwidth sub-beams of laser light of different wavelengths, and the sub-beams are incident on the grating at a certain incident angle perpendicular to the grating lines;

[0031] Step 2: After multiple grating diffraction, each sub-beam of laser light emits a broadened sub-beam parallel to the incident light;

[0032] Step 3: The expanded sub-beams at different heights are reflected by optical elements at different positions in the steering optical element and then reach the same height;

[0033] Step 4: After being diffracted by the grating, each sub-beam of laser light is combined into a combined beam parallel to the incident light, completing the beam combining.

[0034] Beneficial effects of the present invention:

[0035] The present invention has a simple principle, reasonable configuration, and strong feasibility. By using a steering optical element, the lasers in the laser assembly can overcome many shortcomings of existing technical solutions without controlling the line width, and can also achieve higher beam quality and higher power laser beam combination. The details are as follows:

[0036] 1) High beam quality: The present invention can be viewed as two processes: splitting wide-linewidth beamlets and combining the split beams. Since the optical path is reversible, the beam quality of the combined beam and the beamlets is consistent and does not change.

[0037] 2) Relaxation of beamlet parameter performance: In order to ensure the beam quality of the combined light, ordinary beam combining requires the beamlets to be extremely narrow, and the beam quality of the combined light is affected by wavelength drift; in the present invention, the beamlets participating in the beam combining are not restricted by line width, wavelength drift, etc.

[0038] 3) Cost reduction: The relaxation of the sub-beam linewidth reduces the manufacturing restrictions of lasers, and commercially available lasers can be directly used for beam combining, significantly reducing the cost of lasers in the beam combining module.

[0039] 4) Increased combined beam power: Narrow linewidth lasers limit the increase in laser power to a certain extent. The present invention widens the beamlet width, making it easier to increase the power of the beamlet lasers and thus increasing the combined beam power.

[0040] 5) Simple debugging and easy use: Since the one-to-one correspondence between beamlet wavelengths and beamlet positions in ordinary grating beam combining is avoided, the debugging process only requires inserting the corresponding wavelength beamlet into the input hole of the corresponding wavelength range to complete the beam combining debugging. The use process is plug-and-play, which is convenient and fast.

[0041] 6) High grating surface utilization: The grating surface is utilized multiple times during the beam combining process of the present invention, and the entire grating surface is utilized. Compared with ordinary grating beam combining in a laser linear arrangement mode, the grating utilization rate is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] Figure 1 It is a structural schematic diagram of the present invention;

[0044] Figure 2 This is a schematic diagram of the second structure of the present invention;

[0045] Figure 3This is a schematic diagram of the third structure of the present invention;

[0046] Figure 4 This is the principle diagram of reflective grating diffraction;

[0047] Figure 5 is a schematic diagram of a right-angle mirror;

[0048] Figure 6 Schematic diagram of adjusting the height of sub-beams for right-angle mirrors;

[0049] Figure 7 This is a schematic diagram of the placement of a common double-grating combined neutron beam;

[0050] Figure 8 Diffraction efficiency curves at different incident angles;

[0051] Figure 9 This is the equivalent optical path diagram of the Dove prism. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0053] Example 1

[0054] See also Figure 1 As shown, the present invention is a wide bandwidth, high beam quality beam combining device, comprising:

[0055] A laser assembly, used for outputting multiple sub-beam lasers;

[0056] The grating pair 2 separates the different wavelengths in each wide-linewidth sub-beam laser and combines the sub-beam lasers emitted by the steering optical element 3 to generate a combined beam;

[0057] The steering optical element 3 is used to adjust the steering of the sub-beams of laser emitted from different rows of lasers, and adjust the laser emission height or the laser emission height after passing through the steering optical element according to the position arrangement of the laser assembly and the height position of the combined light outlet.

[0058] The laser assembly includes a plurality of lasers of different wavelengths and similar spot sizes;

[0059] The sub-beams of laser light emitted by all the lasers are located on the same vertical plane and are parallel to each other, and are incident on the grating pair 2 at the same incident angle.

[0060] The spectral width of a single laser in the laser assembly only needs to be within the wavelength range limited by the corresponding laser mounting hole position.

[0061] In this embodiment, the grating pair 2 is a double grating, including a grating 1 201 and a grating 202 .

[0062] The principle is as follows: Broadband laser beams of different wavelengths are arranged vertically and initially incident on grating 1 201 at a specific angle of incidence, perpendicular to the grating lines. Due to the grating's dispersion, each laser beam diverges after a first diffraction. It then strikes grating 202, emitting broadened beams parallel to the incident light. The broadened beams at different heights are reflected by right-angle mirrors at different positions in the steering optical element 3 before reaching the same height. They strike grating 202 again, generating convergent diffracted light. These converge to a single point upon reaching grating 1 201 again. After four grating diffraction events, the laser beams are combined into a combined beam parallel to the incident light, completing the beam combining process.

[0063] Figure 4 is the principle diagram of grating diffraction. The diffracted light after grating diffraction is determined by the following formula:

[0064] sinα+sinβ=mΛλ;

[0065] Where α is the incident angle, β is the diffraction angle, Λ is the double grating line density, λ is the wavelength of the incident light, and m is the diffraction order.

[0066] In this embodiment, the laser assembly consists of M rows of laser mounting holes, and M rows of lasers and combined light output holes are arranged in order of position; the laser mounting holes are used to fix the mechanical structure of the laser, and the provision of multiple precision positioning holes ensures the precise installation of the laser; the laser arrangement corresponds one-to-one to the mounting holes, and the layout is linear, with each row consisting of one laser, and the laser line width can be relatively large; the combined light output hole refers to a specially designed terminal optical interface for wavelength synthesis of the output light beams of each row of lasers; each row of the laser mounting holes is respectively recorded as K1, K2, ..., KM, and each row of the lasers is respectively recorded as J1, J2, ..., JM.

[0067] In this embodiment, the steering optical element 3 is composed of M right-angle mirrors 301. The schematic diagram of the right-angle mirror 301 is shown in FIG. Figure 5 shown.

[0068] The ridge line of the right-angle mirror 301 is perpendicular to the grating line 2 and the incident light. The ridge line of the i-th right-angle mirror (30i) is between the i-th row laser mounting holes and the combined light output hole.

[0069] 1) The wavelength range corresponding to the laser mounting hole position in row i is λ Ki ±Δλ Ki, the wavelength of the laser in row i is λ Ji ±Δλ Ji ,have:

[0070] λ Ki -Δλ Ki ≤λ Ji ±Δλ Ji ≤λ Ki +Δλ Ki ;

[0071] 2) If Figure 6 As shown in the figure, when the distance between the laser mounting holes in the i-th row and the combined light output hole is Hi, and the incident angle of the sub-beam is ∠i, the vertical distance Zi between the ridge line of the i-th optical element and the combined light output hole is:

[0072] Zi=Hi·cos 2 i.

[0073] 3) When the vertical distance between the two double grating surfaces is D and the incident angle of the beamlet is α, the length Li of the i-th right-angle mirror is:

[0074] L i ≥Dcosα(tanβ +Ki -tanβ -Ki ), i=1,2…,M;

[0075] Among them, β +Ki is the wavelength λ Ki +Δλ Ki The corresponding diffraction angle, β -Ki is the wavelength λ Ki -Δλ Ki The corresponding diffraction angle.

[0076] Specifically, the double grating spacing is 500 mm, the grating line density is 1740 lines / mm, the incident angle is 71.5°, and the position of the 1030-1090 nm beamlet is as follows: Figure 7 , from left to right are the sub-beam positions of 1090nm, 1089nm, 1088nm, ..., 1030nm.

[0077] Specifically, some laser parameters on the market are shown in Table 1:

[0078]

[0079] Table 1

[0080] The beam quality is 1.2 in the x-direction (perpendicular to the grating lines) with a central wavelength of 1080nm, a spot radius of 3mm, and a 3dB linewidth of 6nm. Without considering wavelength drift, after passing through the double grating, the x-direction spot size increases by 107mm, that is, the beam quality reaches 22.6, which is a serious deterioration of the beam quality.

[0081] By adopting the beam combining scheme of the present invention, the position of the beamlets is not limited by the wavelength difference of adjacent beamlets, and the wide beamlets are first widened and then compressed, and the spot sizes of the combined light and the beamlets remain unchanged, which significantly improves the effect compared with the original beam combining scheme.

[0082] Example 2

[0083] like Figure 2 As shown, compared with the above embodiment 1, there are mainly the following two differences:

[0084] I) The incident angle of all lasers is the littrow angle corresponding to a wavelength λ0 in the center of the combined beam bandwidth;

[0085] II) The beam combining grating is composed of three gratings (grating 1 201, grating 202, and grating 3 203). After the incident beamlets are incident on the first grating, they are diffracted toward the two gratings according to their wavelengths. Beamlets with wavelengths greater than λ0 are diffracted toward one side, while beamlets with wavelengths less than λ0 are diffracted toward the other side.

[0086] Specifically, the diffraction efficiency curves at different incident angles are as follows: Figure 8 The grating diffraction efficiency decreases as the angle between the incident angle and the Littrow angle increases. When the incident angle is near the Littrow angle, the grating diffraction efficiency reaches its maximum. This embodiment brings the average Littrow angle corresponding to each beamlet closer to the incident angle, thereby improving the beam combining efficiency of the beam combining device.

[0087] For the purpose of improving beam combining efficiency, spectral beam combining achieved using multiple gratings is also within the scope of protection of the present invention.

[0088] Example 3

[0089] like Figure 3 As shown, unlike Example 1, the beamlet arrays are arranged horizontally. After the wide-spectrum beamlets are broadened by the dual grating, they form parallel, broadened beamlets. These broadened beamlets then pass through a deflection mirror and a Dove prism before being re-injected into the dual grating system for re-combining. Due to the reversibility of the optical path, assuming the influence of the Dove prism is not considered, the quality of the recombined output beam remains consistent with that of the beamlets.

[0090] In this embodiment, the laser array is composed of M laser mounting holes, M lasers and combined light output holes arranged in order of position; each of the laser mounting holes is respectively recorded as K1, K2, ..., KM, and each row of lasers is respectively recorded as J1, J2, ..., JM, and the distance between the i-th laser mounting hole and the combined light output hole is Di.

[0091] The steering optical element array 3 is one or more of a reflector, a right-angle mirror, and a Dove prism.

[0092] The ridges of the right-angle mirror are parallel to the grating lines.

[0093] 1) The wavelength range corresponding to the i-th laser installation hole is λ Ki ±Δλ Ki , the wavelength of the i-th laser is λ Ji ±Δλ Ji ,have:

[0094] λ Ki -Δλ Ki ≤λ Ji ±Δλ Ji ≤λ Ki +Δλ Ki ;

[0095] 2) When the double grating spacing is D and the beamlet incident angle is α, the distance Di between the i-th laser mounting hole and the first laser mounting hole is:

[0096] D i =2D c o sα(tanβ i -tanβ1), i=1,2…,M;

[0097] Among them, β i is the diffraction angle corresponding to the central wavelength of the i-th laser, and β1 is the diffraction angle corresponding to the central wavelength of the first laser.

[0098] 3) The distance between the i-th laser installation hole and the beam combining light output hole is Li, so:

[0099] Li=Zi-2Xi;

[0100] Where Xi is the distance between the center wavelength of the i-th laser and the centerline of the Dove prism, and Zi is the horizontal difference between the outgoing and incident light of the i-th laser after being refracted by the right-angle mirror. Xi and Zi are not fixed; they complement each other to adjust the laser position.

[0101] Furthermore, the influence of the Dove prism on the beam quality is considered.

[0102] Specifically, the equivalent optical path of parallel light incident on the Dove prism is as follows: Figure 9 As shown, a beam passing through a Dove prism is equivalent to passing through a glass sheet of thickness L. Assuming the spectral width of the beamlet spectrum is 10 nm, the central wavelength is 1065 nm, and the material of the Dove prism is K9. For a beam incident at a 45° angle, the corresponding refractive index and refraction angle are shown in Table 2:

[0103] Wavelength (nm) K9 refractive index Refraction angle 1060 1.50598 28.0067° 1070 1.50578 28.0098°

[0104] Table 2

[0105] The refraction angle difference is 0.0031°, or 0.054 mrad. Assuming L is 50 mm, the aberration caused by the dove prism is 2.7 μm, which means the spot size after beam combination increases by 2.7 μm, which is negligible. In other words, the use of the dove prism has no effect on the beam quality of the combined light.

[0106] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A wide bandwidth, high beam quality beam combining device, characterized in that: include; A laser assembly, used for outputting multiple sub-beam lasers; The grating pair (2) separates different wavelengths in each wide-linewidth sub-beam laser and combines each sub-beam laser emitted by the steering optical element (3) to generate combined beam light; The steering optical element (3) is used to adjust the steering of the sub-beams of laser light emitted from different rows of lasers, and to adjust the laser emission height or the laser emission height after passing through the steering optical element according to the position arrangement of the laser assembly and the height position of the combined light outlet.

2. A wide bandwidth, high beam quality beam combining device according to claim 1, characterized in that: The laser assembly includes a plurality of lasers of different wavelengths and similar spot sizes; The sub-beams of laser light emitted by all the lasers are located on the same vertical plane and are parallel to each other, and are incident on the grating pair (2) at the same incident angle.

3. A wide bandwidth, high beam quality beam combining device according to claim 1 or 2, characterized in that: The laser assembly is composed of M rows of laser mounting holes, M rows of lasers and combined light output holes arranged in order of position; each row of laser mounting holes is respectively denoted as K1, K2, ..., KM, and each row of lasers is respectively denoted as J1, J2, ..., JM; The wavelength range corresponding to the laser mounting holes in the i-th row is λ Ki ±Δλ Ki , the wavelength of the laser in row i is λ Ji ±Δλ Ji ,have: l Ki -Dl Ki ≤λ Ji ±Dλ Ji ≤λ Ki +Dl Ki 。 4. A wide bandwidth, high beam quality beam combining device according to claim 3, characterized in that: The ridge line of the deflection optical element (3) is perpendicular to the grating lines (2) and perpendicular to the incident light.

5. The wide bandwidth, high beam quality beam combining device according to claim 4, characterized in that: The deflection optical element (3) is composed of M optical elements for deflecting laser light.

6. The wide bandwidth, high beam quality beam combining device according to claim 5, characterized in that: The ridge line of the i-th optical element among the M optical elements is between the i-th row of laser mounting holes and the combined light output hole; When the distance between the laser mounting holes in the i-th row and the combined light output hole is Hi, and the incident angle of the sub-beam is ∠i, the vertical distance Zi between the ridge line of the i-th optical element and the combined light output hole is: Zi=Hi·cos 2 and.

7. The wide bandwidth, high beam quality beam combining device according to claim 5, characterized in that: The optical element is one or more of a reflector, a right-angle mirror, and a Dove prism.

8. The wide bandwidth, high beam quality beam combining device according to claim 7, characterized in that: The grating pair (2) is one of a multi-grating, a double grating or a single grating.

9. The wide bandwidth, high beam quality beam combining device according to claim 8, characterized in that: In the double grating, the vertical distance between the two double grating planes is D; When the incident angle of the sub-beam laser is α, the length Li of the i-th right-angle mirror is: L i ≥Dc o sα(tanβ +Ki -tanβ -Ki ),i=1,2…,M; Among them, β +Ki is the wavelength λ Ki +Δλ Ki The corresponding diffraction angle, β -Ki is λ Ki -Δλ Ki The corresponding diffraction angle.

10. A beam combining method for a wide bandwidth, high beam quality beam combining device, characterized in that: The wide-bandwidth, high-beam-quality beam combining device according to claim 1 comprises the following steps: Step 1: multiple lasers output wide-bandwidth sub-beam lasers of different wavelengths, and the sub-beams are incident on the grating pair (2) at a certain incident angle perpendicular to the grating lines; Step 2: After multiple grating diffraction, each sub-beam of laser light emits a broadened sub-beam parallel to the incident light; Step 3: The expanded sub-beams at different heights are reflected by the optical elements at different positions in the steering optical element (3) and then reach the same height; Step 4: After being diffracted by the grating pair (2), each sub-beam of laser light is combined into a combined beam parallel to the incident light, thus completing the beam combination.

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