High-power all-fiber intermediate infrared laser

Abstract

The invention provides a high-power all-fiber intermediate infrared laser, which relates to the technical field of fiber laser, and comprises a Raman fiber laser pumping source, a fiber laser system, a fiber coupling type pumping power stripper, a fiber coupling type isolator and an all-fiber laser amplification system. According to the Raman fiber laser pumping source, 1.5-micron laser is subjected to Raman effect frequency shift to generate 1.7-micron pump light, the fiber laser system absorbs the 1.7-micron pump light to generate 2.8-micron laser, and the 2.8-micron laser is injected into the laser amplification stage system through the pumping power stripper and the isolator to be amplified to generate high-power laser. According to the laser provided by the embodiment of the invention, quantum efficiency can be remarkably improved and system heating can be reduced by using 1.7 mu m pumping, different systems are connected through optical fiber coupling devices to form an all-optical-fiber system, high-power, high-efficiency and stable laser output is realized, and meanwhile, the influence of environmental factors on system performance can also be avoided.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber laser technology, and in particular to a 2.8 μm high-power and high-efficiency all-fiber mid-infrared laser. Background Art

[0002] So far, obtaining mid-infrared high-power fiber lasers mainly relies on two mainstream technical solutions. Among them, the first solution is to achieve high-power laser output directly through the resonant cavity. Aydin et al. used this solution to obtain a 41.6W high-output power 2.8μm mid-infrared fluoride fiber laser, but this solution is limited by the pump wavelength, resulting in high quantum loss. In addition, due to the use of highly doped fluoride fiber as the gain medium, significant heat is generated during the operation of the laser. These factors together lead to the output power efficiency of a single laser oscillator approaching the limit, and the laser performance can no longer be effectively improved further.

[0003] Another solution is to use the MOPA (Master Oscillator Power Amplifier) ​​structure. Uehara et al. used this structure to achieve a laser output power of 33W in the 2.8μm band. However, due to the lack of corresponding commercial mid-infrared all-fiber devices (such as mid-infrared isolators, etc.), this solution uses a spatial optical coupling system. Due to the small diameter of the optical fiber, the optical coupling system based on spatial elements is extremely sensitive to environmental factors (such as temperature, humidity, vibration, etc.). Slight changes in these environmental factors may have an adverse effect on system performance and even cause failures. The above two solutions can achieve high-power output, but due to the presence of partial spatial structures in the laser system, these two solutions have certain limitations in terms of practicality and integration. Summary of the invention

[0004] In view of this, the purpose of the present invention is to propose an all-fiber high-power mid-infrared fiber laser, which uses a Raman fiber laser pump source with a frequency shift of 1.5μm to 1.7μm for the first time, builds an all-fiber system through self-developed mid-infrared fiber devices, and combines pump power beam combining technology or power amplification technology to significantly improve the laser output performance and the overall stability of the system. Raman fiber laser pumping low-doped fiber reduces system heating, improves laser robustness through all-fiber architecture design, and improves power output through pump power beam combining technology and power amplification technology, effectively improving laser output performance and the overall stability of the system, breaking through the power output limit of a single oscillator in the prior art, achieving high-power, high-efficiency, and stable laser output, and avoiding the impact of environmental factors on system performance.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] Based on the above purpose, the present invention provides a high-power all-fiber mid-infrared laser, including a Raman fiber laser pump source, a fiber laser system, a fiber-coupled pump power stripper and an isolator, and a laser amplification system; the Raman fiber laser pump source provides 1.7μm pump light; the fiber laser system generates 2.8μm mid-infrared laser; the all-fiber laser amplification system amplifies the 2.8μm laser to generate high-power mid-infrared laser; the mid-infrared fiber device includes a fiber-coupled pump power stripper and an isolator, etc., and an all-fiber high-power mid-infrared laser is constructed by connecting the above systems.

[0007] As a further solution of the present invention, the laser pump source includes multiple 1.7μm fiber lasers, which are input into the fiber gain medium through a single-mode fluorosilicon pump combiner. The pump source is a 1.5μm laser that is frequency-shifted to 1.7μm by the Raman effect.

[0008] As a further solution of the present invention, 1.7 μm pump light is absorbed by the fiber gain medium to generate 2.8 μm spontaneous radiation light, and the spontaneous radiation light is continuously reflected by the fiber Bragg grating to achieve laser output in the 2.8 μm band through stimulated emission amplification.

[0009] As a further solution of the present invention, the reflection peak of the fiber Bragg grating is located at 2.8μm, and the reflectivity is respectively >99% and 15%, which is used to ensure efficient output of 2.8μm wavelength; the fiber Bragg grating is engraved on the gain fiber core by femtosecond laser direct writing method to ensure high precision and high stability of the grating.

[0010] As a further solution of the present invention, a 20 mm area around the 2.8 μm fiber Bragg grating is actively cooled by a thermoelectric cooler (TEC) to prevent the grating from overheating and affecting system performance.

[0011] As a further solution of the present invention, a fiber power stripper (CPS) is provided at the output end of the high-power all-fiber mid-infrared laser to remove residual pump power and ensure the purity of the output laser; the fiber cap at the output end of the high-power all-fiber mid-infrared laser is cut at an angle to avoid damage to the laser due to Fresnel reflection.

[0012] As a further solution of the present invention, the heat dissipation system of the high-power all-fiber mid-infrared laser is to dissipate heat through an aluminum water-cooling plate, and the water cooling temperature is set to 15°C to ensure that the system works stably under high power output; the heat dissipation system design of the optical fiber gain medium ensures that the fluoride optical fiber will not be damaged due to overheating.

[0013] As a further solution of the present invention, the high-power all-fiber mid-infrared laser adopts a MOPA system, and the low-power laser output by the seed laser source is transmitted through a fiber-coupled pump power stripper and a fiber-coupled isolator. After the low-power laser is output by the seed laser source, it is amplified step by step by a pre-amplifier and a main amplifier to finally achieve high-power laser output; the seed laser source adopts a fiber-coupled pump power stripper to filter the 1.7μm laser to ensure that only the target 2.8μm mid-infrared laser is output.

[0014] As a further solution of the present invention, the fiber-coupled isolator in the MOPA system uses a mid-infrared fiber-coupled isolator to collimate the light beam and isolate the reflected light through the Faraday effect to avoid interference of amplified spontaneous emission (ASE) on the laser and amplifier.

[0015] As a further solution of the present invention, the high-power all-fiber mid-infrared laser avoids the use of spatial optical elements through an all-fiber architecture design, thereby improving the overall stability and robustness of the system; the all-fiber structure enhances the system's adaptability to environmental factors (such as temperature, humidity, vibration, etc.) and reduces the impact of external interference on laser output.

[0016] As a further solution of the present invention, the output power of the high-power all-fiber mid-infrared laser can reach 100W or higher, and has the ability to operate stably for a long time, which is suitable for high-power mid-infrared laser needs.

[0017] As a further solution of the present invention, the output wavelength of the high-power all-fiber mid-infrared laser is 2.8 μm, which is suitable for mid-infrared laser needs in the fields of environmental monitoring, remote sensing, spectral analysis, military applications, etc.

[0018] The invention has various technical innovations for high-power all-fiber 2.8μm mid-infrared lasers, including the selection of pump sources, the development and use of mid-infrared fiber devices, and the application of all-fiber architecture, to ensure that the laser system has high efficiency, stability, and high-power output characteristics. At the same time, all designs take into account system integration, environmental adaptability, and system maintenance convenience, and have significant engineering application value.

[0019] The all-fiber high-power 2.8μm mid-infrared laser provided by the present invention successfully breaks through the limitations of the existing technology through Raman fiber laser pumping and innovative all-fiber architecture design, achieves high-power and stable laser output, and has excellent environmental adaptability and reliability, and has broad application prospects.

[0020] Compared with the prior art, the high-power all-fiber mid-infrared laser proposed in the present invention has the following beneficial effects:

[0021] 1. The present invention uses a Raman fiber laser pump source with a frequency shift from 1.5μm to 1.7μm, and uses 1.7μm to pump low-doping concentration optical fiber, which can greatly reduce system heating and reduce system thermal load; using 1.7μm wavelength pumping greatly improves the upper limit of quantum efficiency compared to semiconductor pumping. Through pump power beam combining technology or power amplification technology, the output power of the laser is greatly improved. This solution effectively breaks through the power output limit of a traditional single oscillator and has a power output capacity of hundreds of watts.

[0022] 2. The present invention provides the application of the design of optical fiber devices, so that the entire laser system can be constructed with an all-fiber structure, which significantly enhances the overall stability and robustness of the system. Compared with traditional free-space optical systems, all-fiber systems are less susceptible to environmental changes (such as temperature, humidity, vibration, etc.), and are therefore more stable and reliable under dynamic working conditions. Fiber lasers perform well in terms of beam quality, power output, and long-term stability, greatly reducing the system failure rate.

[0023] 3. Due to the all-fiber architecture design, high integration, simplified maintenance and operation, the present invention avoids the complex spatial optical elements (such as reflectors, lenses, etc.) used in traditional optical lasers. The improvement of system integration not only simplifies the installation and operation of the laser, but also reduces the maintenance cost and difficulty, providing convenience for practical applications.

[0024] 4. Compared with traditional laser systems, the all-fiber laser of the present invention has enhanced anti-interference ability and environmental adaptability, avoiding multiple interference sources in the free space optical path, and reducing the errors and deviations of optical components. The anti-interference ability of the laser system is improved, and it can operate stably in more complex environments and adapt to a variety of application scenarios, including industrial detection, communications, medical treatment, and national defense.

[0025] 5. All-fiber lasers have high power output and stability and can be widely used in many fields, such as material processing, spectral analysis, laser radar, etc. Its integrated and modular characteristics make the system more adaptable in different applications, providing great potential for the popularization and innovation of laser technology. By avoiding the use of complex spatial optical components, the system can effectively reduce the impact of external environmental factors on laser performance. Due to the compactness and strong anti-interference ability of optical fiber, the laser system can still maintain high working stability in environments with changes in temperature, humidity, etc., which is particularly important for applications with high stability requirements such as industrial sites and scientific research experiments.

[0026] In summary, the all-fiber high-power mid-infrared laser of the present invention has a significant improvement in performance through innovative design, and has excellent performance in output performance, stability, integration and anti-interference ability. It is of great significance to promote the practical application, integration and application breadth of laser technology. It not only helps to improve the performance of existing technologies, but also paves the way for the commercialization of lasers, and has huge market application potential.

[0027] These and other aspects of the present application will be more concise and understandable in the following description of the embodiments. It should be understood that the above general description and the following detailed description are only exemplary and explanatory and cannot limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the exemplary embodiments or related technical descriptions. The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0029] Figure 1 Schematic diagram of the structure of the double-end pumped 2.8μm fluoride fiber laser in Example 1 of the present invention.

[0030] Figure 2 Schematic diagram of the structure of the 2.8 μm fluoride fiber MOPA laser in Example 2 of the present invention.

[0031] Figure 3 This is a schematic diagram of the single-mode fluorosilicone fiber pump combiner in the present invention.

[0032] Reference numerals:

[0033] 1-1.5μm fiber laser, 2-1.7μm high reflectivity grating, 3-Raman gain fiber, 4-1.7μm low reflectivity grating, 5-single-mode fluorine silica fiber pump combiner, 6-2.8μm high reflectivity grating, 7-doped fluoride fiber, 8-2.8μm low reflectivity grating, 9-1.7μm Raman fiber laser pump source, 10-mode stripper (CPS), 11-output end fiber cap (End-cap), 12-1.7μm pump power stripper, 13-fiber isolator (ISO), 14-amplifier section, 15-seed source section, 16-double-clad fluoride fiber, 17-single-mode silica fiber, 18-single-clad fluoride fiber. DETAILED DESCRIPTION

[0034] Below, the present application is further described in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0036] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are intended to distinguish two non-identical entities or non-identical parameters with the same name. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, other steps or units inherent to a process, method, system, product or device that includes a series of steps or units.

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] The flowcharts shown in the accompanying drawings are only examples and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may also be decomposed, combined or partially merged, so the actual execution order may change according to actual conditions.

[0039] The high-power all-fiber mid-infrared laser provided by the present invention is an all-fiber 2.8μm mid-infrared laser. It is pumped by Raman fiber laser and adopts an all-fiber architecture design. It combines pump power beam combining technology and power amplification technology to effectively improve the laser output performance and the overall stability of the system, break through the power output limit of a single oscillator in the prior art, achieve high-power, high-efficiency, and stable laser output, and avoid the influence of environmental factors on system performance.

[0040] In this mid-infrared laser, a Raman fiber laser pump source with a frequency shift from 1.5μm to 1.7μm is used. The pump source generates a 1.7μm laser by injecting it into a Raman gain fiber with a 1.7μm fiber Bragg grating (FBG). The pump light is injected into the fiber laser system to generate a 2.8μm laser, which is then amplified by the laser amplification system to generate a high-power laser. Among them, different systems are connected using optical fiber devices to form an all-fiber structure. This all-fiber system built with mid-infrared optical fiber devices ensures that the system can operate stably in various environments. Through optimized pump power combining technology and power amplification technology, the laser system can output high-power 2.8μm continuous wave laser, which can break through the power limit of a single laser oscillator and achieve a high-power output of hundreds of watts.

[0041] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0042] Example 1

[0043] See also Figure 1 As shown, the high-power all-fiber mid-infrared laser provided by the present invention is a high-power double-end pumped all-fiber 2.8μm continuous wave laser, in which the pump source of the Raman fiber laser pump source adopts a 1.5μm fiber laser 1, which is injected into a Raman gain fiber 3 with 1.7μm fiber Bragg gratings (including a 1.7μm high reflectivity grating 2 and a 1.7μm low reflectivity grating 4) engraved on both ends to generate 1.7μm laser. Using a double-end pumping method, the output light of multiple 1.7μm Raman fiber laser pump sources 9 is combined by a beam combiner and then injected into the resonant cavity of a 2.8μm fiber laser (including a 2.8μm high reflectivity grating 6 and a 2.8μm low reflectivity grating 8). The active gain fiber of the 2.8 μm fiber laser is a rare earth ion doped fluoride fiber 7, the output fiber of the Raman laser is a quartz fiber, and the combiner is a single-mode fluorine-silicon fiber pump combiner 5, see Figure 3 As shown, the single-mode fluorine-silicon fiber pump combiner 5 includes a double-clad fluoride fiber 16, a single-mode quartz fiber 17 and a single-clad fluoride fiber 18, and two strands of the single-mode quartz fiber 17 and the single-clad fluoride fiber 18 are wrapped in the double-clad fluoride fiber 16. The resonant cavity is composed of a fiber Bragg grating written by a femtosecond laser direct writing method, and its reflection peak is located at 2825nm, and the reflectivity is >99% and 15%, respectively.

[0044] The entire fiber laser system is placed in an aluminum water-cooled plate for heat dissipation, and the water-cooling temperature is set to 15°C. The 20mm area before and after the fiber Bragg grating is actively cooled by a thermoelectric cooler (TEC) to prevent overheating. A stripper 10 is installed at the output end of the laser to remove residual pump power, and the output fiber cap 11 is cut at an angle to avoid damage to the laser due to Fresnel reflection.

[0045] Example 2

[0046] See also Figure 2 As shown, the high-power all-fiber mid-infrared laser provided by the present invention is a high-power all-fiber 2.8μm continuous wave laser based on a MOPA system, wherein a MOPA system is used to build an all-fiber 2.8μm laser system. In order to ensure that a seed laser with good output characteristics such as narrow line width, high stability and high beam quality is obtained, the seed source outputs low power, and then a pre-amplifier and a main amplifier can be added according to the needs of the actual situation to achieve the desired high-power laser output. In this embodiment, the low-power laser pump power stripper 12 output by the seed laser source filters the 1.7μm laser and enters the optical fiber isolator 13 to collimate the beam and realize unidirectional transmission of light. Subsequently, the desired high-power output is achieved through a step-by-step amplification through the array of amplifier distribution 14.

[0047] The seed source part 15 and the amplifier part 14 are connected by a mid-infrared fiber isolator (ISO) 13 to replace the spatial optical coupling system. The fiber C-lens lens in the fiber isolator 13 (the lens is polished into a spherical surface by the fiber end face) is used for beam collimation, and the Faraday effect of the magneto-optical crystal is used to isolate the reflected light to ensure that the signal light is transmitted in one direction, avoiding the interference of the amplified spontaneous emission (ASE) in the rear amplifier to the seed laser and the pre-amplifier or damage to the components of the front system. Similarly, in order to effectively dissipate heat, the fiber laser system is placed in an aluminum water cooling plate for heat dissipation, and the water cooling temperature is set to 15°C.

[0048] The present invention uses Raman fiber laser pumping that frequency shifts from 1.5μm to 1.7μm. Compared with other 1.7μm Raman lasers, this solution only requires one-stage Raman to achieve frequency shift, and the structure is more compact and simple. In addition, although thulium-doped fiber lasers can directly emit 1.7μm lasers, due to the low 1.7μm emission cross-section of thulium ions and weak gain, it is difficult for 1.7μm tm-doped fiber lasers to output high power and the output band is limited.

[0049] The present invention adopts Raman laser pumping and combines mid-infrared all-fiber devices to construct an all-fiber high-power 2.8μm mid-infrared laser. Through Raman fiber laser pumping and innovative all-fiber architecture design, it successfully breaks through the limitations of existing technologies, achieves high-power and stable laser output, and has excellent environmental adaptability and reliability, and has broad application prospects.

[0050] The all-fiber architecture design of the present invention has successfully achieved high-power and high-efficiency laser output in the 2.8μm band, and is expected to break through the power output limit of a single oscillator and reach a hundred-watt output. The use of an all-fiber system avoids spatial optical components, reduces the impact of environmental factors (such as temperature, humidity, vibration, etc.) on the laser system, and improves the stability and robustness of the system. The design of the all-fiber structure greatly improves the integration of the system and reduces the difficulty of maintenance and debugging, which is of great significance to the practicality and integration of lasers.

[0051] The above are exemplary embodiments disclosed in the present invention, but it should be noted that various changes and modifications may be made without departing from the scope disclosed in the embodiments of the present invention as defined in the claims. The functions, steps and / or actions of the method claims according to the disclosed embodiments described herein do not need to be performed in any particular order. In addition, although the elements disclosed in the embodiments of the present invention may be described or required in individual form, they may also be understood as multiple unless explicitly limited to the singular.

[0052] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A high-power all-fiber mid-infrared laser, characterized in that: The invention comprises a Raman fiber laser pump source, a fiber laser system, a fiber-coupled pump power stripper, a fiber-coupled isolator and an all-fiber laser amplification system. The Raman fiber laser pump source generates 1.7μm pump light from 1.5μm laser through Raman effect frequency shift; the fiber laser system absorbs 1.7μm pump light to generate 2.8μm mid-infrared laser; the laser amplification system amplifies 2.8μm laser to generate high-power mid-infrared laser; a 2.8μm fiber-coupled pump power stripper and isolator are realized based on fluoride fiber lens, and a mid-infrared single-mode fiber pump combiner with multi-channel pumping is realized based on quartz / fluoride fiber; the above systems are connected by optical fiber devices to construct an all-fiber high-power mid-infrared laser.

2. The high-power all-fiber mid-infrared laser according to claim 1, characterized in that: The Raman fiber laser pump source includes multiple 1.7μm fiber lasers, which are input into the gain fiber cladding through a beam combiner; the pump source is a Raman fiber laser pump source, which is frequency-shifted from 1.5μm to 1.7μm through the Raman effect, and the beam combiner is a single-mode fluoride / quartz fiber single-mode pump combiner.

3. The high-power all-fiber mid-infrared laser according to claim 2, characterized in that: The 1.7μm pump light is absorbed by the fiber gain medium to generate 2.8μm spontaneous radiation light. The spontaneous radiation light is continuously reflected by the fiber Bragg grating, and the laser output in the 2.8μm band is achieved through stimulated emission amplification.

4. The high-power all-fiber mid-infrared laser according to claim 3, characterized in that: The optical fiber gain medium is composed of a rare earth ion-doped fluoride optical fiber gain material and has high transmittance to mid-infrared band lasers.

5. The high-power all-fiber mid-infrared laser according to claim 4, characterized in that: The reflection peak of the fiber Bragg grating is located at 2.8 μm; the fiber Bragg grating is inscribed on the gain optical fiber core by using a femtosecond laser direct writing method.

6. The high-power all-fiber mid-infrared laser according to claim 5, characterized in that: The 20 mm area around the 2.8 μm fiber Bragg grating is actively cooled by a thermoelectric cooler.

7. The high-power all-fiber mid-infrared laser according to claim 6, characterized in that: The output end of the high-power all-fiber mid-infrared laser is provided with a fiber power stripper; the fiber cap at the output end of the high-power all-fiber mid-infrared laser is cut at an angle.

8. The high-power all-fiber mid-infrared laser according to claim 1, characterized in that: The heat dissipation system of the high-power all-fiber mid-infrared laser is to dissipate heat through an aluminum water-cooling plate, and the water cooling temperature is set to 15°C.

9. The high-power all-fiber mid-infrared laser according to claim 8, characterized in that: The high-power all-fiber mid-infrared laser adopts a MOPA system. The low-power laser output by the seed laser source is transmitted through a pump power stripper and a fiber isolator, and is amplified step by step by a pre-amplifier and a main amplifier. The seed laser source uses a pump power stripper to filter 1.7μm laser. The pump power stripper is composed of a fluoride fiber lens and a dichroic mirror. The fiber lens is formed by polishing the fiber end face into a spherical surface.

10. The high-power all-fiber mid-infrared laser according to claim 9, characterized in that: The optical fiber isolator in the MOPA system uses a mid-infrared optical fiber isolator, which provides beam collimation and isolates reflected light through the Faraday effect. The isolator is composed of a fluoride optical fiber lens and a magneto-optical crystal. The optical fiber lens is formed by polishing the optical fiber end face into a spherical surface.

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