A cross-band wide-spectrum beam combining system and method based on a thin film and micro-nano structure

Abstract

This invention discloses a cross-band broadband beam combining system and method based on thin films and micro / nano structures, relating to the field of laser technology. It includes a mid-to-far infrared QCL module and thin film and micro / nano structure devices, comprising a first device, a second device, and a third device. The output beams from the first and second modules are incident on the first device, and after beam combining by the first device, a first combined beam is output. The output beams from the third and fourth modules are incident on the second device, and after beam combining by the second device, a second combined beam is output. The first and second combined beams are incident on the third device, and after beam combining by the third device, a common-aperture output beam is generated. This invention, employing the aforementioned cross-band broadband beam combining system and method based on thin films and micro / nano structures, can simultaneously achieve multi-band, cross-band high-power beam combining of mid-to-far infrared lasers, solving the problems of low output power, small bandwidth, and poor stability in existing beam combining methods. It offers a wide beam combining bandwidth range, high efficiency, and is easy to implement.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a cross-band broadband beam combining system and method based on thin films and micro / nano structures. Background Technology

[0002] Mid- and far-infrared lasers have broad application prospects in fields such as directed infrared countermeasures, trace gas monitoring, medical diagnosis, and optical communication. Currently, the main technological approaches to realizing mid- and far-infrared lasers typically include: optically pumped semiconductor lasers, quantum cascade lasers, carbon dioxide lasers, and laser-pumped optical parametric oscillators. Among these, quantum cascade lasers, due to their small size, low cost, and low power consumption, show the best application prospects.

[0003] Quantum cascade lasers (QCLs) possess excellent beam quality and power, tunable wavelength, small size, and low power consumption, making them promising candidates for applications in the aforementioned fields. Regarding the output power of QCLs, based on current domestic and international reports on the output power of various wavelengths, it has been concluded that a maximum continuous output power of approximately 5 watts at room temperature can currently be achieved within the 3.5-10.7 μm wavelength range. To further improve the output power of mid-infrared lasers, domestic and international researchers have proposed using laser beam combining methods to achieve high-power mid-infrared laser output through multi-path laser combination. Specific methods include thin-film beam combining, polarization beam combining, spatial beam combining, spectral beam combining, and coherent beam combining. Among these methods, thin-film filters, due to the bandwidth limitations of QCLs and the steepness limitations (100 nm), cannot combine QCLs of the same wavelength, resulting in a limited number of combined paths, typically only 3-5. Polarization beam combining has high efficiency and simple structure, while ensuring high beam quality. However, it can only combine two mid-infrared lasers with different polarization states, making it difficult to obtain high-power lasers that meet the requirements. Spatial beam combining schemes can combine multiple lasers and have a simple structure with high beam combining efficiency, but the beam quality is poor. Grating beam combining has many limitations on the spectral width, polarization, or wavelength characteristics of the QCL (Quadrant-Cellular Combined Laser), cannot combine different types of QCLs, and is limited by the beam combining device, resulting in low combining efficiency (~60%). Coherent beam combining can combine multiple lasers and obtain a high-quality combined laser beam. However, achieving laser coherence requires strict requirements on beam phase, frequency, and other parameters, as well as suitable phase modulation devices. As the number of optical paths increases, the coherent combining control system becomes increasingly complex.

[0004] Grating beam combining methods face numerous challenges. Currently, mid-infrared gratings struggle to meet requirements such as wide wavelength range, high diffraction efficiency, and high thermal load capacity, severely limiting the number of laser beam combiners and their output power. Furthermore, as the number of beam combining paths increases, system stability decreases, and excessive optical components introduce surface shape errors that significantly reduce beam quality. Summary of the Invention

[0005] The purpose of this invention is to provide a cross-band broadband spectral beam combining system and method based on thin films and micro / nano structures, thereby solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides a cross-band broadband spectral beam combining system based on thin films and micro / nano structures, comprising: The mid- and far-infrared QCL module includes a first module, a second module, a third module, and a fourth module; Thin film and micro / nano structure device, including a first device, a second device and a third device, wherein the first device, the second device and the third device are all optical elements combining thin film and micro / nano structure; The output beams of the first module and the second module are incident on the first device, and after being combined by the first device, the first composite beam is output. The output beams of the third and fourth modules are incident on the second device, and after being combined by the second device, a second composite beam is output. The first and second combined beams are incident on the third device, and after being combined by the third device, they are output with the same aperture.

[0007] A method for a cross-band broadband spectral beam combining system based on thin films and micro / nano structures includes the following steps: S1. Thin film and micro / nano structure devices based on multilayer film etching microstructure are used as beam combiners. The beam combiners have high reflectivity and high transmittance in a specific wavelength band. S2. The beams output from the first module and the second module are incident on the first device to complete the initial beam combining and output the first combined beam; S3. The beams output from the third and fourth modules are incident on the second device to complete the initial beam combining and output the second combined beam; S4. The first and second combined beams are incident on the third device to complete the secondary beam combining and output cross-band broadband laser in a common aperture form.

[0008] Therefore, the present invention employs the above-mentioned cross-band broadband spectral beam combining system and method based on thin films and micro / nano structures, which has the following beneficial effects: (1) This invention proposes a novel cross-band broadband beam combining structure based on the combination of thin film and micro / nano structure. By using multilayer film to etch microstructures, broadband high reflectivity or high transmittance elements are realized. On this basis, mid-far infrared QCLs of different bands or cross-bands are combined to realize spectral beam combining of multiple mid-infrared QCLs or modules. The above synthesis is further combined by thin film microstructures with high reflectivity and high transmittance in specific bands to realize cross-band synthesis. It has the advantages of wide beam combining bandwidth, high efficiency and simple structure.

[0009] (2) This invention can not only achieve high-efficiency beam combining, but also multi-band (3.8μm-5μm or 8μm-12μm) beam combining or cross-band (mid-wave and long-wave bands) beam combining, thus achieving wide-band, high-efficiency beam combining of mid- and far-infrared QCL lasers. The method is simple in principle and easy to implement.

[0010] (3) The present invention adopts an integrated system, and the modules in the system can be freely combined and expanded. It can simultaneously realize multi-band and cross-band high-power beam combining of mid- and far-infrared lasers, solving the problems of low output power, small bandwidth and poor stability of existing beam combining methods.

[0011] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of an embodiment of a cross-band broadband beam combining system and method based on thin films and micro / nano structures according to the present invention. Figure 2 This is a schematic diagram of the first and second modules of an embodiment of a cross-band broadband beam combining system and method based on thin films and micro / nano structures according to the present invention. Reference numerals: 1. First module; 2. Second module; 3. Third module; 4. Fourth module; 5. First device; 6. Second device; 7. Third device. Detailed Implementation

[0013] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0014] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0015] Please see Figures 1-2The present invention provides a cross-band broadband beam combining system based on thin film and micro / nano structure, including a mid- and far-infrared QCL module and thin film and micro / nano structure devices. The mid- and far-infrared QCL module includes a first module 1, a second module 2, a third module 3 and a fourth module 4. The thin film and micro / nano structure devices include a first device 5, a second device 6 and a third device 7. The first device, the second device and the third device are all optical elements combining thin film and micro / nano structure.

[0016] The work process is as follows Figure 1 As shown: the first module 1 and the second module 2 achieve a single laser beam output with the same aperture through the first device 5; the third module 3 and the fourth module 4 achieve a single laser beam output with the same aperture through the second device 6; the two combined beams achieve a single laser beam output with the same aperture through the third device 7.

[0017] The above synthesis can be divided into two parts: first, the common-aperture laser output achieved by the first module 1 and the second module 2, which can be used as a separate synthesis output module; and second, the common-aperture laser output achieved by the third module 3 and the fourth module 4, which can also be used as a separate synthesis module. These two can be further synthesized to achieve a new common-aperture laser output module.

[0018] Among them, the first module 1, the second module 2, the third module 3 and the fourth module 4 can be used to implement the beam combining module for traditional beam combining technology, or they can represent the QCL of a single band.

[0019] The first device 5, the second device 6, and the third device 7 are designed as devices combining broadband high-efficiency thin films and micro / nano structures.

[0020] Thin-film and micro / nano-structure devices are proposed to achieve high bandwidth and high efficiency. The specific implementation is as follows: by etching microstructures on the surface of multilayer films, laser diffraction is modulated; phase modulation is achieved through the microstructures, suppressing zero-order reflections and allowing the incident laser to be output at a specific angle. Wavelength ( and A laser array (representing the wavelengths of the i-th to j-th lasers) is incident on the surface of a microstructure beam combiner at different incident angles and diffracted out at the same angle, thus realizing multi-channel laser combination.

[0021] Thin film and micro / nano structure devices can be multilayer film grating devices. Taking multilayer film grating devices as an example, the principle of multilayer film gratings in controlling the polarization direction and diffraction bandwidth of laser diffraction is as follows: Duty cycle of grating structure f The equivalent refractive index of the grating structure is affected by adjusting the duty cycle parameter so that the equivalent refractive index in the TE and TM polarization directions satisfies the following condition: ; in, For TE polarization, the equivalent refractive index is... is the equivalent refractive index for TM polarization.

[0022] This allows for equal diffraction efficiencies in the TE and TM polarization directions, achieving grating depolarization diffraction.

[0023] The grating height of a multilayer grating primarily affects the propagation phase of the coupled wave. By adjusting the grating height parameter, the propagation phase can be made to satisfy the following conditions: ; This allows for the suppression of the 0th-order diffraction efficiency and the maximization of the -1st-order diffraction efficiency of the multilayer film grating.

[0024] The multilayer materials and thickness parameters of a multilayer grating primarily affect the interface phase of the coupled wave. Interface phase modulation is achieved by adjusting the thickness of the matching layer within the multilayer grating, ensuring that the interface phase satisfies the following conditions: ; in, For the interface phase difference, This represents the wavelength difference.

[0025] It can achieve wide-band phase stabilization, enabling multilayer film gratings to achieve broadband high-efficiency diffraction.

[0026] Multilayer gratings are fabricated by electron beam lithography (EBL). The EBL method has the advantages of ultra-high resolution (sub-10nm), no need for masks, and high flexibility, making it suitable for the fabrication of high-precision grating devices.

[0027] A thin-film beam combiner is a beam combiner that achieves high reflectivity or high transmittance for a specific wavelength by coating multiple layers of film. For example, by achieving wavelength... Laser with high reflectivity, wavelength High transmission is achieved by setting different incident angles to allow two laser beams of different wavelengths to be reflected and transmitted separately, and then emitted along the same optical path, thus achieving beam combining. A thin-film beam combiner is an extension element of this invention; its surface does not employ micro / nano structures, but rather achieves optical field manipulation solely through a multilayer film design. The thin-film beam combiner can be combined with multilayer film gratings to expand the number of beam combining paths in the entire cross-band broadband beam combining system. The thin-film beam combiner exhibits high transmittance and high reflectance within a specific wavelength band; by combining multiple thin-film beam combiners, the beam can be combined to achieve high transmittance and high reflectance. ( and The mid- and far-infrared lasers of wavelengths with high reflectivity and high transmittance are combined in a thin-film beam combiner and output in the same optical path direction.

[0028] The principle of polarizing filters is to achieve optical field modulation by depositing multiple layers of film, thereby achieving high reflection or high transmission of laser light with different polarization directions at specific wavelengths. For example, to achieve... The band has high transmission in the p-polarization direction. In the s-polarized band, high reflection occurs. By setting different incident angles, two laser beams with different polarization directions are reflected and transmitted separately, and then emitted along the same optical path, thus achieving beam combining. The polarization filter surface does not employ micro / nano structures; instead, optical field modulation is achieved solely through a multilayer film design. As an extension element, the polarization filter can be combined with thin-film beam combiners and multilayer film gratings to expand the number of beam combining paths in the entire cross-band broadband beam combining system.

[0029] Specifically, polarization filters form a periodic structure by alternately depositing high- and low-refractive-index dielectric layers, utilizing interference effects to enhance the transmission or reflection of specific polarization states. Polarization filters employ a dual-selectivity film structure: by optimizing the thickness and materials of multiple layers (such as Ge / ZnS), polarization filters can achieve specific polarization states at the target wavelength (e.g., [missing information]). Achieving high transmission (for p-polarization), in another band ( To achieve high reflectivity (for S-polarization), the polarization filter employs an inclined incidence design: by adjusting the installation angle of the thin-film beam combiner to near Brewster's angle, polarization selectivity is enhanced.

[0030] Polarizing filters in In the band, p-polarized transmittance > 90%, s-polarized reflectance > 90%; In the band, s-polarized reflectivity > 90% and p-polarized transmittance < 10%.

[0031] The high reflectivity or high transmittance in specific bands and polarization directions mentioned above are just examples. The band, polarization direction, reflection or transmission characteristics are specifically achieved through filter design according to the specific beam combining requirements.

[0032] This invention presents an integrated system capable of achieving high-power beam combining of mid- and far-infrared lasers across multiple bands, overcoming the problems of low output power, narrow bandwidth, and poor stability in existing beam combining methods. The modules within the system can be freely combined and expanded, enabling simultaneous multi-band and cross-band mid- and far-infrared laser beam combining.

[0033] The present invention also provides a method for a cross-band broadband spectral beam combining system based on thin films and micro / nano structures, comprising the following steps: S1. Thin film and micro / nano structure devices based on multilayer film etching microstructure are used as beam combiners. The beam combiners have high reflectivity and high transmittance in a specific wavelength band. S2. The beams output from the first module and the second module are incident on the first device to complete the initial beam combining and output the first combined beam; S3. The beams output from the third and fourth modules are incident on the second device to complete the initial beam combining and output the second combined beam; S4. The first and second combined beams are incident on the third device to complete the secondary beam combining and output cross-band broadband laser in a common aperture form.

[0034] Example 1 S1. Module 1 is a traditional grating beam combiner module, which can only combine beams of the same type of QCL, such as a center wavelength of 3.9 μm and a bandwidth of 150 nm. Module 2 is also a traditional grating beam combiner module, which can only combine beams of the same type of QCL, such as a center wavelength of 8.5 μm and a bandwidth of 150 nm. Therefore, using the method of this invention, these two modules can achieve multi-band beam combining through the first device 5 in the thin film and micro / nano structure device. The wavelength and bandwidth of the same type of QCL can be selected arbitrarily; the above are just examples, and the same applies to the following cases.

[0035] The same applies to modules S2, 3 (third module), and 4 (fourth module). Therefore, using this method, these two modules can achieve broadband synthesis through the second device 6 in thin film and micro / nano structure devices.

[0036] S3. Then, the above two are further processed through the third device 7 in the thin film and micro / nano structure device to achieve multi-band, cross-band common aperture synthesis.

[0037] Example 2 S1. Module 1 is a mid-infrared band QCL, such as a center wavelength of 3.9 μm and a bandwidth of 150 nm. Module 2 is also a mid-infrared band QCL, such as a wavelength of 4.3 μm and a bandwidth of 150 nm. The two modules are combined using the first device 5 to achieve multi-band synthesis. Figure 2 As shown.

[0038] S2 and the third module 3 are mid-infrared band QCLs, such as 8.5μm with a bandwidth of 150nm. The fourth module 4 is a mid-infrared band QCL, such as 9.4μm with a bandwidth of 150nm. The two are combined into a multi-band composite through the second device 6.

[0039] S3. Then, the above two are further combined through the third device 7 to achieve multi-band and cross-band common aperture synthesis.

[0040] Example 3 S1. Module 1 is a traditional polarization beam combiner module, such as a center wavelength of 3.9 μm, a bandwidth of 150 nm, and QCLs for TE and TM polarization respectively. Module 2 is also a traditional polarization beam combiner module, such as a center wavelength of 4.5 μm, a bandwidth of 150 nm, and QCLs for TE and TM polarization respectively. These two modules can then achieve wide-band multi-band beam combining using the first device 5.

[0041] S2 and the third module 3 are mid-infrared band QCLs, such as 8μm with a bandwidth of 200nm, and the fourth module 4 is a mid-infrared band QCL, such as 8.5μm with a bandwidth of 200nm. The two can be combined in a wide band using the second device 6.

[0042] S3. Then, the above two are further combined through the third device 7 to achieve multi-band and cross-band common aperture synthesis.

[0043] Example 4 S1. Module 1 is a traditional polarization beam combiner module, such as a center wavelength of 3.9 μm, a bandwidth of 150 nm, and QCLs for TE and TM polarization respectively. Module 2 is a traditional polarization beam combiner module, such as a center wavelength of 4.3 μm, a bandwidth of 150 nm, and QCLs for TE and TM polarization respectively. Modules 1 and 2 are combined into a new module through the first device 5 to achieve common-aperture output.

[0044] If S2, the third module 3, and the fourth module 4 are traditional polarization beam combining modules, the same applies.

[0045] S3. The QCL wavelengths of the first, second, third, and fourth modules mentioned above can be QCLs with the same center wavelength but different polarization states, or QCLs with different polarization states in different bands.

[0046] It should be noted that the mid- and far-infrared QCL module can represent traditional beam combining modules, such as grating beam combining mode, polarization beam combining, thin film beam combining, etc., or it can represent different QCLs, and is not limited to these.

[0047] Therefore, the present invention employs the above-mentioned cross-band broadband beam combining system and method based on thin film and micro / nano structure, which can simultaneously realize multi-band and cross-band high-power beam combining of mid- and far-infrared lasers, solving the problems of low output power, small bandwidth, and poor stability of existing beam combining methods. It has a wide beam combining bandwidth range, high efficiency, simple body structure, and is easy to implement.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A cross-band broadband spectral beam combining system based on thin films and micro / nano structures, characterized in that, include: The mid- and far-infrared QCL module includes a first module, a second module, a third module, and a fourth module; Thin film and micro / nano structure device, including a first device, a second device and a third device, wherein the first device, the second device and the third device are all optical elements combining thin film and micro / nano structure; The output beams of the first module and the second module are incident on the first device, and after being combined by the first device, the first composite beam is output. The output beams of the third and fourth modules are incident on the second device, and after being combined by the second device, a second composite beam is output. The first and second combined beams are incident on the third device, and after being combined by the third device, they are output with the same aperture.

2. The cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 1, characterized in that: The mid- and far-infrared QCL module is a traditional beam combiner module or a QCL that outputs a single-band beam. Traditional beam combiners include grating beam combiners, polarization beam combiners, and thin-film beam combiners.

3. The cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 1, characterized in that: The thin film and micro / nano structure device is an optical element with microstructures etched on the surface of a multilayer film. The incident laser is diffracted and phase-controlled through the microstructure, suppressing the 0th order reflection and making the incident laser output at a specific angle.

4. The cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 3, characterized in that: The thin film and micro / nano structure devices operate in wavelengths of 3.8μm~5μm and 8μm~12μm, and are used to achieve cross-band beam combining of mid-wave and long-wave bands.

5. The cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 4, characterized in that: Laser arrays of different wavelengths are incident on the surface of the thin film and micro / nano structure device at different incident angles, and output at the same angle after diffraction modulation.

6. The cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 5, characterized in that: The combination of thin film and micro / nano structure devices with thin film beam combiners expands the number of beam combining paths in a cross-band broadband beam combining system. The combination of thin films and micro / nano structure devices, thin film beam combiners and polarizing filters expands the number of beam combining paths in a cross-band broadband beam combining system.

7. A method for applying the cross-band broadband spectral beam combining system based on thin films and micro / nano structures as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Thin film and micro / nano structure devices based on multilayer film etching microstructure are used as beam combiners. The beam combiners have high reflectivity and high transmittance in a specific wavelength band. S2. The beams output from the first module and the second module are incident on the first device to complete the initial beam combining and output the first combined beam; S3. The beams output from the third and fourth modules are incident on the second device to complete the initial beam combining and output the second combined beam; S4. The first and second combined beams are incident on the third device to complete the secondary beam combining and output cross-band broadband laser in a common aperture form.

8. The method for a cross-band broadband spectral beam combining system based on thin films and micro / nano structures according to claim 7, characterized in that, The thin film and micro / nano structure devices in S1 are multilayer film grating devices, and the control method is as follows: S11. By adjusting the duty cycle parameter of the grating structure, the equivalent refractive indices of the TE polarization direction and the TM polarization direction meet the preset conditions, so as to achieve equal diffraction efficiency of TE polarization and TM polarization, and complete the grating depolarization diffraction. S12. By adjusting the grating height parameter to make the transmission phase meet the preset conditions, the 0th order diffraction efficiency of the multilayer film grating is suppressed, and the -1st order diffraction efficiency is maximized. S13. By adjusting the thickness parameters of the multilayer matching layer, the interface phase meets the preset conditions, achieving wide-band phase stability and ensuring that the multilayer grating achieves broadband high-efficiency diffraction.

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