Long-wave mid-infrared fiber laser and laser system
By using an all-fiber structure and tilted fiber grating technology, the problems of complex structure and low beam quality of existing 3.8μm wavelength lasers have been solved, achieving high output power and strong stability laser output.
Patent Information
- Application Number
- CN202511126818.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-12
- Publication Date
- 2025-11-18
AI Technical Summary
Existing methods for generating 3.8μm wavelength lasers have complex structures, low beam quality, and limited output power.
A long-wavelength mid-infrared fiber laser with an all-fiber structure is used. The 3.5μm laser is filtered out by a tilted fiber grating to avoid gain competition with the 3.8μm laser. The erbium-doped fluoride fiber is excited by 976nm and 2000nm pump light to generate a high-output-power 3.8μm laser.
The output power of the 3.8μm laser was increased, the stability and beam quality of the laser were enhanced, the structure was simplified, and it is suitable for practical applications.
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Figure CN120978508A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of long-wavelength laser technology, and more particularly to a long-wavelength mid-infrared fiber laser and laser system. Background Technology
[0002] Lasers with a wavelength of 3.8 μm are located in the mid-infrared band. This wavelength has a very crucial characteristic: it exhibits low transmission loss within the atmospheric window of 3-5 μm. This characteristic determines that its primary applications are related to applications propagating through the atmosphere, such as free-space optical communication, infrared countermeasures, and gas detection.
[0003] Currently, the main technologies used to generate 3.8μm wavelength lasers are solid-state lasers using iron-doped zinc selenide laser crystals and nonlinear frequency conversion. Both of these technologies involve free-space optical paths, resulting in complex structures, relatively low beam quality, and limited output power. Summary of the Invention
[0004] This application provides a long-wavelength mid-infrared fiber laser and laser system, which aims to effectively solve the technical problems of complex structure, low beam quality and limited output power in the prior art for generating 3.8μm wavelength lasers.
[0005] According to a first aspect of this application, a long-wavelength mid-infrared fiber laser is provided, comprising: a first pump laser for generating 976nm pump light; a second pump laser for generating 2000nm pump light; a fiber combiner connected to the first pump laser and the second pump laser; a high-reflectivity fiber grating connected to the fiber combiner; an erbium-doped fluoride fiber connected to the high-reflectivity fiber grating; a tilted fiber grating connected to the erbium-doped fluoride fiber for filtering 3.5μm laser light into the cladding of the erbium-doped fluoride fiber; and a low-reflectivity fiber grating connected to the tilted fiber grating.
[0006] Furthermore, the long-wavelength mid-infrared fiber laser also includes a cladding power stripper connected to the low-reflection fiber grating.
[0007] Furthermore, the long-wavelength mid-infrared fiber laser also includes: an optical fiber end cap, connected to the cladding power stripper.
[0008] Furthermore, the tilted fiber grating has a preset tilt angle θ.
[0009] Furthermore, the period of the tilted fiber grating is Λ, and the tilt angle and the period have the following relationship:
[0010]
[0011] Where, λbragg n represents the center wavelength that is filtered out. eff Represents the refractive index of optical fiber.
[0012] Furthermore, the tilt angle and period of the tilted fiber grating can be controlled and adjusted to filter out laser light in the range of 3.4μm to 3.7μm by controlling the tilt angle and the period.
[0013] Furthermore, the tilted fiber grating is inscribed on the erbium-doped fluoride fiber.
[0014] Furthermore, both the high-reflectivity fiber grating and the low-reflectivity fiber grating are inscribed on the erbium-doped fluoride fiber.
[0015] Furthermore, the 976nm pump light generated by the first pump laser first enters the erbium-doped fluoride fiber to propel the particles from... 4 I 15 / 2 stimulated 4 I 11 / 2 The 2000nm pump light generated by the second pump laser then enters the erbium-doped fluoride fiber to propel particles from... 4 I 11 / 2 stimulated 4 F 9 / 2 .
[0016] According to another aspect of this application, this application also provides a long-wavelength mid-infrared fiber laser system, including the long-wavelength mid-infrared fiber laser described in any of the above claims.
[0017] Through one or more embodiments of the above embodiments in this application, at least the following technical effects can be achieved:
[0018] In the technical solution disclosed in this application, the long-wavelength mid-infrared fiber laser can utilize a tilted fiber grating to suppress gain competition between the 3.5μm and 3.8μm lasers, thereby increasing the output power of the 3.8μm laser. Furthermore, the long-wavelength mid-infrared fiber laser of this application is an all-fiber structure. All-fiber lasers exhibit strong stability, good beam quality, and a relatively simple structure, making them suitable for practical applications. Attached Figure Description
[0019] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.
[0020] Figure 1 A schematic diagram of a long-wavelength mid-infrared fiber laser provided in this application embodiment;
[0021] Figure 2A schematic diagram of the tilted fiber grating structure of a long-wavelength mid-infrared fiber laser provided in this application embodiment;
[0022] Figure 3 Laser emission cross-section spectra of erbium-doped fluoride fibers pumped by 976nm and 2μm lasers, provided for embodiments of this application;
[0023] Figure 4 This is a schematic diagram illustrating the operating principle of a long-wavelength mid-infrared fiber laser, provided as an embodiment of this application.
[0024] Figure label:
[0025] 1. First pump laser; 2. Second pump laser; 3. Fiber combiner; 4. High-reflectivity fiber grating; 5. Erbium-doped fluoride fiber; 6. Tilted fiber grating; 7. Low-reflectivity fiber grating; 8. Cladding power stripper; 9. Fiber end cap. Detailed Implementation
[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.
[0027] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the term "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Furthermore, the character " / " in this document, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.
[0028] Laser light with a wavelength of 3.8 μm is located in the mid-infrared band. This wavelength has a crucial characteristic: it exhibits low transmission loss within the atmospheric window of 3-5 μm. This is because 3.8 μm lies in the relatively transparent region between the absorption bands of water vapor (H2O) and carbon dioxide (CO2), resulting in less absorption by atmospheric molecules. Furthermore, the Mie scattering effect is weaker in the mid-infrared band, leading to more concentrated light intensity and higher photon transmittance, thus giving 3.8 μm laser light stronger penetration in fog. These characteristics determine its primary applications related to atmospheric propagation, such as:
[0029] 1) Free-space optical communication
[0030] Wireless transmission of optical signals is achieved using a 3.8μm laser as the carrier wave and the atmosphere as the channel. In the atmospheric channel, various gas molecules and aerosol particles absorb and scatter the light, leading to energy attenuation during laser transmission. Since the 3.8μm wavelength laser lies within the relatively transparent region between the absorption bands of water vapor (H2O) and carbon dioxide (CO2), and atmospheric molecules absorb less light, energy attenuation during 3.8μm laser transmission in the atmosphere can be reduced. Furthermore, atmospheric scattering has less impact on longer wavelength lasers, allowing the 3.8μm laser to maintain concentrated transmission energy and intensity even in relatively harsh environments, such as smoggy weather.
[0031] 2) Infrared countermeasures
[0032] In infrared countermeasures, laser-directed jamming is a technique that uses a laser to illuminate an infrared imaging seeker with a high-energy-density infrared laser, disrupting its guidance information or blinding the photoelectric sensor, rendering it unable to function properly or even completely losing its detection and tracking capabilities. Experimental results show that a 3.8μm laser, with a visibility of 5km, an interference distance of 1.8km, weak turbulence, and a laser output power of 0.5W, can create strong crosstalk on an InSb detector, causing the seeker to lose target.
[0033] 3) Gas detection
[0034] In gas detection, 3.8 μm lasers can be used to detect a variety of gases, such as methane (CH4) and acetylene (C2H2), which have high absorption peaks at this wavelength. NASA's Jet Propulsion Laboratory developed a 3.8 μm wavelength laser specifically for methane gas detection and used it as a core component of the tunable laser spectrometer on the Curiosity rover to explore the Martian atmosphere.
[0035] Currently, the main technologies used to generate 3.8μm wavelength lasers are solid-state lasers using zinc iron selenide laser crystals and nonlinear frequency conversion. Both of these technologies involve free-space optical paths, resulting in complex structures, relatively low beam quality, and limited output power.
[0036] To address the aforementioned issues, embodiments of this application provide a long-wavelength mid-infrared fiber laser and a laser system.
[0037] Figure 1The image shows a long-wavelength mid-infrared fiber laser provided in an embodiment of this application, comprising: a first pump laser 1, a second pump laser 2, a fiber combiner 3, a high-reflectivity fiber grating 4, an erbium-doped fluoride fiber 5, and a tilted fiber grating 6; the first pump laser 1 is used to generate 976nm pump light; the second pump laser 2 is used to generate 2000nm pump light; the fiber combiner 3 is connected to the first pump laser 1 and the second pump laser 2; the high-reflectivity fiber grating 4 is connected to the fiber combiner 3; the erbium-doped fluoride fiber 5 is connected to the high-reflectivity fiber grating 4; the tilted fiber grating 6 is connected to the erbium-doped fluoride fiber 5 and is used to filter out 3.5μm laser light into the cladding of the erbium-doped fluoride fiber 5; and the low-reflectivity fiber grating 7 is connected to the tilted fiber grating 6.
[0038] like Figure 2 As shown, in this embodiment, the tilted fiber grating 6 has a preset tilt angle θ.
[0039] Furthermore, the period of the tilted fiber grating 6 is Λ, and the tilt angle and period have the following relationship:
[0040]
[0041] Where, λ bragg n represents the center wavelength that is filtered out. eff Represents the refractive index of optical fiber.
[0042] The tilt angle and period of the tilted fiber grating can be controlled and adjusted to filter out laser light in the range of 3.4μm to 3.7μm by controlling the tilt angle and period.
[0043] Therefore, by controlling the angle of the tilted fiber grating 6 and the period of the grating, laser light in the 3.4-3.7μm range can be filtered out.
[0044] like Figure 3 The image shows the laser emission cross-section spectrum of erbium-doped fluoride fiber 5, pumped by a 976 nm laser and a 2 μm laser. The emission cross-section spectrum covers 3.2 μm to 3.9 μm, with the strongest gain peak at 3.5 μm. According to... Figure 1 Under the same population inversion conditions, the gain achievable by a 3.5μm laser is always higher than that of a 3.8μm laser, and this gain advantage actually increases with the increase in population inversion. Therefore, simply increasing the pump power cannot improve the output power of a 3.8μm laser; it will only make the 3.8μm laser increasingly disadvantaged in mode competition compared to the 3.5μm laser, until it is completely replaced by the latter. To generate a high-power 3.8μm laser, it is necessary to avoid gain competition with the 3.5μm laser. Figure 3 The dashed box in the image indicates that the wavelength range to be filtered is 3.4μm-3.7μm.
[0045] In this embodiment, the 3.5μm laser can be filtered out by tilted fiber grating 6, reducing the gain competition between the 3.5μm laser and the 3.8μm laser, and improving the output power of the 3.8μm laser.
[0046] In this process, the 976nm pump light generated by the first pump laser 1 first enters the erbium-doped fluoride fiber 5 to propel the particles from... 4 I 15 / 2 stimulated 4 I 11 / 2 The 2000nm pump light generated by the second pump laser 2 enters the erbium-doped fluoride fiber 5 to deflect particles from... 4 I 11 / 2 stimulated 4 F 9 / 2 .
[0047] The operating principle of the 3.8μm fiber laser provided in this embodiment is as follows: Figure 4 As shown, when the 976nm pump light enters the erbium-doped fluoride fiber 5, the particles move from... 4 I 15 / 2 stimulated 4 I 11 / 2 Subsequently, 2000nm pump light enters the erbium-doped fluoride fiber 5, and particles from... 4 I 11 / 2 Further stimulated to 4 F 9 / 2 The 3.8μm laser corresponds to the figure shown. 4 F 9 / 2 → 4 I 9 / 2 The transition process.
[0048] In this embodiment, the tilted fiber grating 6 is inscribed on the erbium-doped fluoride fiber 5.
[0049] Among them, femtosecond laser technology can be used to inscribe the tilted fiber grating 6 onto the erbium-doped fluoride fiber 5. The tilted fiber grating 6 is directly integrated with the fiber body, without the need for additional optical coupling elements.
[0050] Therefore, the long-wavelength mid-infrared fiber laser provided in this embodiment can suppress the gain competition between the 3.5μm and 3.8μm lasers by utilizing the tilted fiber grating 6, thereby improving the output power of the 3.8μm laser. Furthermore, the long-wavelength mid-infrared fiber laser of this application is an all-fiber structure. All-fiber lasers have strong stability, good beam quality, and a relatively simple structure, which is in line with practical application scenarios.
[0051] In some embodiments, the long-wavelength mid-infrared fiber laser further includes a cladding power stripper 8 connected to a low-reflection fiber grating 7.
[0052] In this embodiment, the 3.5μm laser is filtered out into the fiber cladding, which can be achieved by using the cladding power stripper 8.
[0053] In some embodiments, the long-wavelength mid-infrared fiber laser further includes: an optical fiber end cap 9, connected to a cladding power stripper 8.
[0054] In some embodiments, both the high-reflectivity fiber grating 4 and the low-reflectivity fiber grating 7 are inscribed on the erbium-doped fluoride fiber 5.
[0055] In the above embodiments, the high-reflectivity fiber grating 4 is a high-reflectivity Bragg fiber grating, and the low-reflectivity fiber grating 7 is a low-reflectivity Bragg fiber grating. The reflectivity of the high-reflectivity fiber grating 4 is 90% to 100%, and the reflectivity of the low-reflectivity fiber grating 7 is 10% to 50%.
[0056] In summary, this embodiment provides a long-wavelength mid-infrared fiber laser, which uses a 976nm laser diode and a 2μm fiber laser to build a stable pumping system. Next, a high-reflectivity, low-loss fiber grating and a tilted fiber grating 6 are fabricated in an erbium-doped fluoride fiber 5 using femtosecond laser line-by-line writing technology. Then, the erbium-doped fluoride fiber 5 with the fabricated fiber grating is combined with the pumping system, fiber combiner 3, cladding power stripper 8, and fiber end cap 9 to build an all-fiber mid-infrared laser system, generating a 3.8μm laser. The tilted fiber grating is used to filter out the 3.5μm laser from the cladding of the erbium-doped fluoride fiber 5, avoiding gain competition with the 3.8μm laser.
[0057] Therefore, existing fiber lasers that generate 3.8μm laser light have a spatial structure, resulting in low integration and poor stability, making them unsuitable for practical applications. This invention proposes an all-fiber 3.8μm fiber laser, comprising a fiber combiner 3, a high- and low-reflection fiber grating 7, a tilted fiber grating 6, a cladding power stripper 8, and fiber end caps 9, all of which are fiber structures. The advantage of the all-fiber structure is that it avoids interference from the external environment, enhancing the laser's stability and improving the output beam quality. Furthermore, this invention innovatively uses a tilted fiber grating 6 to filter out 3.5μm laser light into the fiber cladding, avoiding gain competition between the 3.5μm and 3.8μm lasers and resulting in higher output power for the 3.8μm laser.
[0058] This application also provides a long-wavelength mid-infrared fiber laser system, including a long-wavelength mid-infrared fiber laser described in any of the above embodiments.
[0059] In summary, although the present application has disclosed the preferred embodiments as described above, the above preferred embodiments are not intended to limit the present application. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be determined by the scope defined in the claims.
Claims
1. A long-wavelength mid-infrared fiber laser, characterized in that, include: The first pump laser is used to generate 976nm pump light; A second pump laser is used to generate 2000nm pump light; An optical fiber combiner is connected to the first pump laser and the second pump laser; A high-reflectivity fiber optic grating is connected to the fiber combiner. Erbium-doped fluoride optical fiber is connected to the high-reflectivity fiber grating; A tilted fiber grating, connected to the erbium-doped fluoride fiber, is used to filter out 3.5 μm laser light from the cladding of the erbium-doped fluoride fiber. A low-reflection fiber grating is connected to the tilted fiber grating.
2. The long-wavelength mid-infrared fiber laser as described in claim 1, characterized in that, The long-wavelength mid-infrared fiber laser also includes a cladding power stripper connected to the low-reflection fiber grating.
3. The long-wavelength mid-infrared fiber laser as described in claim 2, characterized in that, The long-wavelength mid-infrared fiber laser also includes: an optical fiber end cap, which is connected to the cladding power stripper.
4. The long-wavelength mid-infrared fiber laser as described in claim 1, characterized in that, The tilted fiber grating has a preset tilt angle θ.
5. The long-wavelength mid-infrared fiber laser as described in claim 4, characterized in that, The period of the tilted fiber grating is Λ, and the tilt angle and the period have the following relationship: Where, λ bragg n represents the center wavelength that is filtered out. eff Represents the refractive index of optical fiber.
6. The long-wavelength mid-infrared fiber laser as described in claim 5, characterized in that, The tilt angle and period of the tilted fiber grating can be controlled and adjusted to filter out laser light in the range of 3.4μm to 3.7μm by controlling the tilt angle and the period.
7. The long-wavelength mid-infrared fiber laser as described in claim 1, characterized in that, The tilted fiber grating is inscribed on the erbium-doped fluoride fiber.
8. The long-wavelength mid-infrared fiber laser as described in claim 1, characterized in that, Both the high-reflectivity fiber grating and the low-reflectivity fiber grating are inscribed on the erbium-doped fluoride fiber.
9. The long-wavelength mid-infrared fiber laser as described in claim 1, characterized in that, The 976nm pump light generated by the first pump laser first enters the erbium-doped fluoride fiber to propel the particles from... 4 I 15 / 2 stimulated 4 I 11 / 2 ; The 2000nm pump light generated by the second pump laser then enters the erbium-doped fluoride fiber to propel the particles from... 4 I 11 / 2 stimulated 4 F 9 / 2 .
10. A long-wavelength mid-infrared fiber laser system, characterized in that, Includes the long-wavelength mid-infrared fiber laser as described in any one of claims 1-9.