A three-wavelength mid-infrared fiber laser

Abstract

The application discloses a three-wavelength mid-infrared fiber laser, which is composed of a first pump source, a second pump source, a pump combiner, a first high-refractivity fiber grating, a second high-refractivity fiber grating, a third high-refractivity fiber grating, an erbium-doped fluoride fiber, a first low-refractivity fiber grating, a second low-refractivity fiber grating, a third low-refractivity fiber grating, a cladding light filter and a fiber end cap. The three-wavelength mid-infrared fiber laser is realized by a scheme of dual-wavelength pumping a single rare earth ion doped fiber and multi-energy level transition of the rare earth ion. The dual-wavelength pumping mode makes the rare earth ion jump to a high energy level to realize particle number accumulation of the 3.1-micron laser upper energy level, and effectively consumes the 2.8-micron laser lower energy level particle, thereby avoiding the self-termination problem of the 2.8-micron laser, improving the recycling ability of the particle in the multi-energy level transition process, and ensuring the efficient and stable operation of the three-wavelength mid-infrared laser.

Description

Technical Field

[0001] This invention relates to the field of lasers, and more particularly to a three-wavelength mid-infrared fiber laser. Background Technology

[0002] Mid-infrared laser sources have significant applications in spectral analysis, atmospheric remote sensing, and biomedicine. Among them, mid-infrared fiber lasers based on fiber waveguide structures exhibit significant advantages in wavelength tuning range, beam quality control, and system integration capabilities, and have received widespread attention and research in recent years. Dual-wavelength or even multi-wavelength operation of mid-infrared fiber lasers is crucial for improving their practical effects in the aforementioned applications. However, the technical approach of combining multiple single-wavelength mid-infrared fiber lasers to achieve multi-wavelength laser output often results in complex systems and poor stability in multi-wavelength laser operation.

[0003] To maintain the advantage of high system integration in fiber lasers, it is still necessary to explore technical pathways for achieving multi-wavelength mid-infrared laser output based on a single fiber laser. One technical solution involves using an active fiber doped with multiple rare-earth ions capable of emitting in the mid-infrared band, combined with the energy transfer process between these rare-earth ions, to achieve multi-wavelength mid-infrared laser output. For example, a 3μm and 3.9μm dual-wavelength laser can be obtained by pumping a holmium-praseodymium co-doped fluoride fiber with an 888nm semiconductor laser. [1] Dual-wavelength lasers at 3.3 μm and 3.5 μm were achieved by pumping erbium-dysprosium co-doped fluoride fiber with a 642 nm semiconductor laser. [2] One technical solution requires that different rare-earth ions have similar energies at specific energy levels, and the doping concentration ratio between rare-earth ions needs to be optimized to ensure the energy transfer rate between ions and achieve effective output of multi-wavelength lasers. Another technical solution is to use active optical fibers with a single rare-earth ion, utilizing multiple transitions of rare-earth ions between different energy levels to achieve multi-wavelength mid-infrared lasers. For example, using a 1.15μm fiber laser to pump a holmium fluoride-doped fiber to achieve dual-wavelength lasers of 3μm and 2μm. [3] A dual-wavelength laser at 3.5μm and 2.8μm was achieved by using 0.98μm and 1.15μm dual-wavelength pumped erbium-doped fibers. [4] This technical solution can obtain multi-wavelength mid-infrared laser output using only a single rare earth ion, but currently it can only achieve dual-wavelength mid-infrared laser. Further exploration of new paths is needed to enrich the multi-wavelength working capability of lasers.

[0004] References

[0005] [1] Shen Yanlong, Wan Yingchao, Chai Tongxing, Wang Yousheng, Zhu Feng, Huang Ke, A mid-infrared 4μm and 3μm dual-wavelength all-fiber laser, CN202310104556.4, 2023.02.13.

[0006] [2]Luo,H.,Wang,Y.,Chen,J.et al.Red-diode-clad-pumped Er 3+ / Dy 3+ codopedZrF4 fiber:Apromising mid-infrared laser platform. Opt Lett 47,5313-5316(2022).

[0007] [3]Li,J.,Luo,H.,Wang,L.et al.Mid-infrared passively switched pulseddual wavelength Ho3+-doped fluoride fiber laser at 3μm and 2μm.Sci Rep 5,10770(2015).

[0008] [4] Fu Shijie, Shi Wei, Zhang Lu, Sheng Quan, Zhang Junxiang, Yao Jianquan, A dual-wavelength mid-infrared fiber laser with 2.8μm and 3.5μm wavelengths, CN2023100986607, 2023.02.10. Summary of the Invention

[0009] This invention provides a three-wavelength mid-infrared fiber laser. Addressing the limitations of single mid-infrared fiber lasers and the complexity of combining multiple mid-infrared fiber lasers, this invention proposes a scheme based on dual-wavelength pumping of a single rare-earth ion-doped fiber. The three-wavelength mid-infrared laser output is achieved through the multi-level transition process of erbium ions, as detailed below:

[0010] A three-wavelength mid-infrared fiber laser, the fiber laser comprising a first pump source, a second pump source, a pump combiner, a first high-reflectivity fiber grating, a second high-reflectivity fiber grating, a third high-reflectivity fiber grating, an erbium-doped fluoride fiber, a first low-reflectivity fiber grating, a second low-reflectivity fiber grating, a third low-reflectivity fiber grating, a cladding optical filter, and fiber end caps;

[0011] The first high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the first low-reflectivity fiber grating constitute the first wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the first high-reflectivity fiber grating and the first low-reflectivity fiber grating are the same, and the wavelength is located at the erbium ion concentration in the erbium-doped fluoride fiber. 2 H 11 / 2 / 4 S 3 / 2 energy level to 4 F9 / 2 The range of amplified spontaneous emission spectrum for energy level transitions;

[0012] The second high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the second low-reflectivity fiber grating constitute the second wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the second high-reflectivity fiber grating and the second low-reflectivity fiber grating are the same, and the wavelength is located in the erbium ion concentration range of the erbium-doped fluoride fiber. 4 F 9 / 2 energy level to 4 I 9 / 2 The range of amplified spontaneous emission spectrum for energy level transitions;

[0013] The third high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the third low-reflectivity fiber grating constitute the third wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the third high-reflectivity fiber grating and the third low-reflectivity fiber grating are the same, and the wavelength is located in the erbium ion concentration range of the erbium-doped fluoride fiber. 4 I 11 / 2 energy level to 4 I 13 / 2 The range of amplified spontaneous emission spectrum for energy level transitions;

[0014] The first and second pump sources pump the erbium-doped fluoride optical fiber via a pump combiner; the first pump source pumps the erbium ions in the erbium-doped fluoride optical fiber from the ground state. 4 I 15 / 2 Energy level pump to 4 I 11 / 2 Energy level; the second pump source transfers erbium ions from 4 I 13 / 2 Energy level pump to 2 H 11 / 2 The energy level enables the accumulation of particles in the upper energy level of the 3.1-micron laser and consumes particles in the lower energy level of the 2.8-micron laser, ensuring continuous population inversion between the upper and lower energy levels of the 2.8-micron laser.

[0015] The cladding light filter is used to remove cladding light, and the fiber end cap is used to reduce the power density of mid-infrared laser at the fiber output end and improve long-term working stability.

[0016] Among them, the reflectivity of the first, second and third high-reflectivity fiber gratings is greater than 90%, and the reflectivity of the first, second and third low-reflectivity fiber gratings is in the range of 4%-70%.

[0017] The high-reflectivity fiber grating and low-reflectivity fiber grating can be replaced with coated reflectors that operate at three mid-infrared laser wavelengths.

[0018] The first pump source and the second pump source pump the laser resonator in the same direction or in opposite directions.

[0019] The pumping directions of the first pump source and the second pump source are the same as or opposite to the mid-infrared laser output direction.

[0020] The beneficial effects of the technical solution provided by this invention are:

[0021] 1. This invention uses dual-wavelength pumping of a single rare-earth ion-doped fiber to realize a three-wavelength mid-infrared fiber laser. The second pumping wavelength pumps erbium ions to the upper energy level of the 3.1-micron laser, thereby generating the 3.1-micron laser, while effectively consuming particles in the lower energy level of the 2.8-micron laser. This avoids the laser self-termination problem caused by the long lifetime of the lower energy level of the 2.8-micron laser, and ensures the continuous and stable operation of the 2.8-micron laser.

[0022] 2. This invention enables the output of three-wavelength mid-infrared fiber lasers based on active optical fibers doped with a single rare-earth ion. While ensuring the advantages of fiber laser system integration, it effectively improves the multi-wavelength working capability of mid-infrared lasers based on a single fiber laser. The solution proposed in this invention effectively avoids the stringent requirements on the energy level of rare-earth ions and the doping concentration ratio between different rare-earth ions in multi-wavelength mid-infrared fiber laser solutions based on multi-rare-earth ion doped fibers. The technical solution is simple and easy to implement. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a three-wavelength mid-infrared fiber laser.

[0024] Figure 2 This is a schematic diagram of the erbium ion energy level structure and erbium ion energy level transitions.

[0025] The attached diagram lists the components represented by each number as follows:

[0026] 1: First pump source; 2: Second pump source;

[0027] 3: Pump combiner; 4: First high-reflectivity fiber grating;

[0028] 5: Second high reflectivity fiber grating; 6: Third high reflectivity fiber grating;

[0029] 7: Erbium-doped fluoride fiber; 8: First low-reflectivity fiber grating;

[0030] 9: Second low-reflectivity fiber Bragg grating; 10: Third low-reflectivity fiber Bragg grating;

[0031] 11: Cladding optical filter; 12: Fiber end cap. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0033] A three-wavelength mid-infrared fiber laser, see [link / reference] Figure 1 The laser includes: a first pump source 1, a second pump source 2, a pump combiner 3, a first high reflectivity fiber grating 4, a second high reflectivity fiber grating 5, a third high reflectivity fiber grating 6, an erbium-doped fluoride fiber 7, a first low reflectivity fiber grating 8, a second low reflectivity fiber grating 9, a third low reflectivity fiber grating 10, a cladding optical filter 11, and an optical fiber end cap 12.

[0034] The first pump source 1 is a 980nm multimode semiconductor laser with a maximum output power of 50W, which can pump erbium ions in the erbium-doped fluoride fiber 7 from the ground state. 4 I 15 / 2 Energy level pump to 4 I 11 / 2 Energy levels, such as Figure 2 As shown; the second pump source 2 is a multimode semiconductor laser with a wavelength of 793nm and a maximum output power of 50W, which can convert erbium ions from... 4 I 13 / 2 Energy level pump to 2 H 11 / 2 Energy level. Two pump beams are cladding-pumped by a pump combiner 3 to the mid-infrared laser resonator.

[0035] The first high-reflectivity fiber grating 4, the erbium-doped fluoride fiber 7, and the first low-reflectivity fiber grating 8 constitute the first wavelength 3.1 μm laser resonant cavity of the three-wavelength mid-infrared fiber laser. The first high-reflectivity fiber grating 4 has a center wavelength of 3.1 μm, a reflectivity of 99%, and a reflection bandwidth of 1 nm; the first low-reflectivity fiber grating 8 has a center wavelength of 3.1 μm, a reflectivity of 60%, and a reflection bandwidth of 0.5 nm; the erbium-doped fluoride fiber 7 has an erbium ion doping concentration of 1 mol% and a fiber length of 10 m.

[0036] The second high-reflectivity fiber grating 5, the erbium-doped fluoride fiber 7, and the second low-reflectivity fiber grating 9 constitute the second wavelength 3.5μm laser resonant cavity of the three-wavelength mid-infrared fiber laser. The second high-reflectivity fiber grating 5 has a center wavelength of 3.5μm, a reflectivity of 99%, and a reflection bandwidth of 1nm; the second low-reflectivity fiber grating 9 has a center wavelength of 3.5μm, a reflectivity of 50%, and a reflection bandwidth of 0.5nm.

[0037] The third high-reflectivity fiber grating 6, the erbium-doped fluoride fiber 7, and the third low-reflectivity fiber grating 10 constitute the third wavelength 2.8 μm laser resonant cavity of the three-wavelength mid-infrared fiber laser. Among them, the center wavelength of the third high-reflectivity fiber grating 6 is 2.8 μm, the reflectivity is 99%, and the reflection bandwidth is 1 nm; the center wavelength of the third low-reflectivity fiber grating 10 is 2.8 μm, the reflectivity is 10%, and the reflection bandwidth is 0.5 nm.

[0038] The output pigtail of the third low-reflectivity fiber grating 10 is connected to the cladding light filter 11 to filter out the cladding light. The three wavelengths of mid-infrared laser light, namely 2.8μm, 3.1μm and 3.5μm, are output through a 500μm long aluminum fluoride end cap 12.

[0039] In summary, the three-wavelength mid-infrared fiber laser proposed in this invention achieves three-wavelength mid-infrared fiber laser output through a scheme of dual-wavelength pumping of a single rare-earth ion-doped fiber and multi-level transitions of rare-earth ions. The dual-wavelength pumping method achieves the accumulation of particles in the upper energy level of the 3.1-micron laser by transitioning rare-earth ions to higher energy levels, while effectively consuming particles in the lower energy level of the 2.8-micron laser. This avoids the self-termination problem of the 2.8-micron laser and improves the recycling ability of particles in the multi-level transition process, ensuring the efficient and stable operation of the three-wavelength mid-infrared laser.

[0040] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0041] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-wavelength mid-infrared fiber laser, characterized in that, The fiber laser comprises a first pump source, a second pump source, a pump combiner, a first high-reflectivity fiber grating, a second high-reflectivity fiber grating, a third high-reflectivity fiber grating, an erbium-doped fluoride fiber, a first low-reflectivity fiber grating, a second low-reflectivity fiber grating, a third low-reflectivity fiber grating, a cladding optical filter, and fiber end caps. The first high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the first low-reflectivity fiber grating constitute the first wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the first high-reflectivity fiber grating and the first low-reflectivity fiber grating are the same, and the wavelength is located at the erbium ion concentration in the erbium-doped fluoride fiber. 2 H 11 / 2 / 4 S 3 / 2 energy level to 4 F 9 / 2 The range of amplified spontaneous emission spectrum for energy level transitions; The second high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the second low-reflectivity fiber grating constitute the second wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the second high-reflectivity fiber grating and the second low-reflectivity fiber grating are the same, and the wavelength is located in the erbium ion concentration range of the erbium-doped fluoride fiber. 4 F 9 / 2 energy level to 4 I 9 / 2 The range of amplified spontaneous emission spectrum for energy level transitions; The third high-reflectivity fiber grating, the erbium-doped fluoride fiber, and the third low-reflectivity fiber grating constitute the third wavelength laser resonant cavity of the three-wavelength mid-infrared fiber laser; wherein, the center wavelengths of the third high-reflectivity fiber grating and the third low-reflectivity fiber grating are the same, and the wavelength is located in the erbium ion concentration range of the erbium-doped fluoride fiber. 4 I 11 / 2 energy level to 4 I 13 / 2 The range of amplified spontaneous emission spectrum for energy level transitions; The first and second pump sources pump the erbium-doped fluoride optical fiber via a pump combiner; the first pump source pumps the erbium ions in the erbium-doped fluoride optical fiber from the ground state. 4 I 15 / 2 Energy level pump to 4 I 11 / 2 Energy level; the second pump source transfers erbium ions from 4 I 13 / 2 Energy level pump to 2 H 11 / 2 The energy level enables the accumulation of particles in the upper energy level of the 3.1-micron laser and consumes particles in the lower energy level of the 2.8-micron laser, ensuring continuous population inversion between the upper and lower energy levels of the 2.8-micron laser. The cladding light filter is used to remove cladding light, and the fiber end cap is used to reduce the power density of mid-infrared laser at the fiber output end and improve long-term working stability. The reflectivity of the first, second, and third high-reflectivity fiber gratings is greater than 90%, while the reflectivity of the first, second, and third low-reflectivity fiber gratings is in the range of 4%-70%.

2. A three-wavelength mid-infrared fiber laser according to claim 1, characterized in that, The high-reflectivity fiber grating and low-reflectivity fiber grating can be replaced with coated reflectors operating at three mid-infrared laser wavelengths.

3. A three-wavelength mid-infrared fiber laser according to claim 1, characterized in that, The first pump source and the second pump source pump the laser resonator in the same direction or in opposite directions.

4. A three-wavelength mid-infrared fiber laser according to claim 1, characterized in that, The pumping directions of the first pump source and the second pump source are the same as or opposite to the mid-infrared laser output direction.

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