A special Tm / Ho:YAG-SiO2 optical fiber, a 2μm single-frequency fiber laser based on this fiber, and its fabrication method.

Abstract

The application relates to a Tm / Ho:YAG-SiO2 special optical fiber, a 2-micron single-frequency fiber laser based on the optical fiber and a preparation method, and belongs to the fiber laser field. The core of the special optical fiber is Tm / Ho:YAG, and the outer cladding is SiO2. The laser comprises a pump source, a fiber wavelength division multiplexer A and a laser resonant cavity arranged along an optical path. The pump source adopts a semiconductor LD. The laser resonant cavity is composed of a pair of fiber Bragg gratings, including a low-reflectivity Bragg grating and a high-reflectivity Bragg grating. The special optical fiber is arranged between the low-reflectivity Bragg grating and the high-reflectivity Bragg grating. The special optical fiber is prepared by a melting core method. The doping of Ho improves the absorption capacity of the gain optical fiber to the pump and the gain at the 2-micron waveband. The Tm / Ho:YAG-SiO2 special optical fiber is used to output a 2-micron waveband single-frequency fiber laser with higher output power and higher slope efficiency. 3+ ​

Description

Technical Field

[0001] This invention provides a Tm / Ho:YAG-SiO2 special optical fiber, a 2μm single-frequency fiber laser based on the optical fiber, and a fabrication method thereof, belonging to the field of fiber laser technology. Background Technology

[0002] Currently, 2μm lasers are mainly used in fields such as medicine, laser detection, laser remote sensing, and materials processing. For example, in medicine, since human tissue is 70% water, and water's absorption spectrum is at 2.5-4.0μm and 5.6-10μm, the output of a 2μm laser falls within the strong absorption spectrum of water. Therefore, human tissue exhibits strong absorption of 2μm lasers. When using 2μm lasers for treatment, the strong absorption of lasers by human tissue results in a shallow penetration depth. This allows 2μm lasers to precisely cut human tissue in most soft and hard tissue surgeries. Therefore, using 2μm lasers can achieve shallow penetration depth, high surgical precision, and better coagulation effects.

[0003] On the other hand, within the 2μm wavelength range, there are many absorption lines of atmospheric gases that can be detected and analyzed in this spectral region. Using a 2μm laser system, the concentration of carbon dioxide in the atmosphere can be directly detected, which is of great significance for studying the greenhouse effect. Furthermore, 2μm lasers can directly detect wind speed, which is crucial for weather forecasting, typhoon warnings, and aerospace safety. In addition, the narrow linewidth and good coherence of single-frequency lasers meet the requirements of coherent Doppler wind radar, making the 2μm single-frequency laser an ideal laser system for wind speed detection.

[0004] The 2μm wavelength laser output also offers advantages in processing transparent plastics. Since most plastics have sufficient absorption in the 2μm band, 2μm lasers can be used directly for cutting, welding, and marking plastic materials. In contrast, plastics absorb 1μm lasers much weaker, requiring the addition of additives to enhance absorption. Therefore, when plastics are used in medical and biosafety fields where material safety is paramount, using a reliable 2μm single-frequency laser with high continuous output power and good beam quality is essential. Furthermore, 2μm lasers have applications in laser-driven particle acceleration, high harmonic generation, and mid-infrared spectroscopy.

[0005] Currently, 2μm band fiber lasers mainly use Tm. 3+Ion-doped optical fibers are used as gain media, with core materials including Tm:YAG crystals, Tm₂O₃, and other substances. Due to the presence of Tm in silicate optical fibers... 3+ Due to low ion doping concentrations, current 2μm lasers exhibit low output power and poor slope efficiency. Researchers are working to improve Tm by fabricating germanate and phosphate glasses. 3+ Increasing the doping concentration of ions improves the output power of the laser, but due to the poor mechanical strength of germanate glass and phosphate glass fibers, the splicing loss is high when fused with optical fibers, resulting in poor laser stability. This patent uses the fused core method to prepare Tm / Ho:YAG-SiO2 special optical fiber, through Ho... 3+ Ion doping can enhance the pump absorption capability of gain fibers and provide stronger gain at the 2μm band, thereby increasing the output power of lasers. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a Tm / Ho:YAG-SiO2 special optical fiber, a 2μm single-frequency fiber laser based on this fiber, and a fabrication method. The Tm / Ho:YAG-SiO2 special optical fiber of this invention serves as the gain fiber, and through Ho… 3 + Ion doping enhances the fiber's ability to absorb pump energy and increases the gain at the 2μm band, resulting in a 2μm band single-frequency fiber laser with higher output power and slope efficiency.

[0007] The technical solution of this invention is as follows:

[0008] A special Tm / Ho:YAG-SiO2 optical fiber includes a core and an outer cladding, wherein the core is Tm / Ho:YAG and the outer cladding is SiO2.

[0009] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber includes a pump source, an optical fiber wavelength division multiplexer A, and a laser resonator arranged along the optical path;

[0010] The pump source is a semiconductor LD with a center wavelength of 1550-1650nm. The laser resonant cavity is composed of a pair of fiber Bragg gratings, which include a low-reflectivity Bragg grating and a high-reflectivity Bragg grating. The aforementioned Tm / Ho:YAG-SiO2 special optical fiber is disposed between the low-reflectivity Bragg grating and the high-reflectivity Bragg grating.

[0011] Preferably, the low-reflectivity Bragg grating has a reflectivity of 60%-85%, and the high-reflectivity Bragg grating has a reflectivity of not less than 95%. The low-reflectivity Bragg grating and the high-reflectivity Bragg grating form a resonant cavity, so that the gain fiber absorbs the pump energy and forms laser oscillation in the resonant cavity.

[0012] Preferably, the center wavelengths of both the low-reflectivity Bragg grating and the high-reflectivity Bragg grating are 1800nm-2300nm.

[0013] Preferably, the length of the Tm / Ho:YAG-SiO2 special optical fiber is 1-3 cm.

[0014] Preferably, an optical fiber isolator A (with a center wavelength of 1610 nm), a first-stage amplification system, and a second-stage amplification system are provided between the pump source and the optical fiber wavelength division multiplexer A. The first-stage amplification system includes an optical fiber wavelength division multiplexer B, an Er-doped single-clad fiber, an optical fiber wavelength division multiplexer C, and an optical fiber isolator B. One port of the optical fiber wavelength division multiplexer C is connected to an LD.

[0015] Preferably, the secondary amplification system includes a filter A, a pump combiner, Er / Yb co-doped double-clad fiber, an optical fiber wavelength division multiplexer D, a pump stripper, an optical fiber isolator C, and a filter B, with the pump combiner connected to a multimode LD.

[0016] The pump source of this invention uses a semiconductor LD with a central operating wavelength of 1550nm-1650nm. To prevent backlight damage to the LD, a fusion splice fiber isolator A is used. The first-stage amplification system uses forward pumping of the LD, with Er-doped single-clad fiber as the gain fiber, connected through a fiber wavelength division multiplexer C. Another fiber wavelength division multiplexer B separates the signal light from the remaining pump light. Finally, a fusion splice fiber isolator B is used for protection. To further optimize the signal-to-noise ratio of the signal light, a fusion filter is used. The second-stage amplification system uses a (2+1)×1 pump combiner connected to the multimode LD, with the gain fiber being Er / Yb co-doped double-clad fiber. A pump stripper is connected to the end of the pump combiner to remove the remaining pump light. Because Yb... 3+ Ion doping can lead to spontaneous emission noise of about 1 μm, so a fiber wavelength division multiplexer (WDM) is used to remove Yb. 3+ Noise generated by ions due to spontaneous emission; finally, the fusion filter B removes Er. 3+ Noise generated by ions at around 1.5μm; finally, the pump source output is fused to the reflector of fiber wavelength division multiplexer A, the low reflectivity fiber Bragg grating is fused to the common end, and the signal end is used as the output end.

[0017] Preferably, the wavelength of the single-frequency laser output by the 2μm single-frequency fiber laser is adjustable within the range of 1800nm-2300nm;

[0018] Preferably, the output power of the single-frequency laser output by the 2μm single-frequency fiber laser is adjustable within the range of 1mW-1W.

[0019] Preferably, the wavelengths of the LD and multimode LD in the 2μm single-frequency fiber laser are around 970nm (970-990nm) and around 808nm (805-815nm), respectively.

[0020] Preferably, the fiber wavelength division multiplexer A includes three ports, with the common port connected to the laser resonant cavity, and the other two ports connected to the pump source and serving as the output port, respectively.

[0021] A method for fabricating the above-mentioned 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber includes the following steps:

[0022] S1. Tm / Ho:YAG-SiO2 special optical fiber is fabricated using the fused core method;

[0023] S2. Fuse the semiconductor LD to phase A of the fiber optic isolator;

[0024] S3. The 1610nm laser output signal is amplified to 1000mW-1500mW through a first-stage amplification system;

[0025] S4. Fusion splice 1-3cm Tm / Ho:YAG-SiO2 special optical fiber between a pair of fiber Bragg gratings;

[0026] S5. Pump light is pumped into a laser resonant cavity composed of fiber Bragg gratings through fiber wavelength division multiplexer A, and then laser signal is output through the signal terminal.

[0027] This invention uses a semiconductor LD as the pump seed source and amplifies the 1610nm laser to 1200mW-1500mW using an optical fiber amplification system. A special Tm / Ho:YAG-SiO2 optical fiber is fused between a pair of gratings with a center wavelength of 1800nm-2300nm. The pump light is input into the resonant cavity through an optical fiber wavelength division multiplexer A to generate the laser output signal.

[0028] For any details not covered in this invention, please refer to the prior art.

[0029] The beneficial effects of this invention are as follows:

[0030] 1. This invention uses Tm / Ho:YAG-SiO2 special optical fiber as the gain medium. Since Tm ions can efficiently transfer energy to Ho ions, Tm-Ho co-doping can improve the absorption efficiency of the gain medium for pump energy, thereby increasing the output power of the laser. Secondly, the fluorescence intensity of Tm-Ho co-doped silicate glass is much greater than that of Tm-doped silicate glass and Ho-doped silicate glass. Therefore, using Tm / Ho:YAG-SiO2 special optical fiber as the gain medium can achieve a higher laser output power.

[0031] 2. The fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber proposed in this invention, due to Ho 3+ The emission spectrum of ions can reach 2.3 μm. Using Tm / Ho:YAG-SiO2 special optical fiber as the gain medium, the laser output near 2.3 μm can be explored.

[0032] 3. The fiber laser based on Tm / Ho:YAG-SiO2 special fiber proposed in this invention addresses the issue that traditionally, Tm-doped fiber is used as the gain medium to fabricate the laser as a pump source, providing pump energy to the Ho-doped fiber. This invention, by fabricating Tm / Ho:YAG-SiO2 special fiber as the gain fiber using the fused core method, avoids the need for a redundant laser as a pump source. This results in a more compact laser structure, higher output power, and wider applicability to various complex applications. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0034] Figure 1 This is a schematic diagram of the structure of the 2μm single-frequency fiber laser based on Tm / Ho:YAG crystal-derived fiber of the present invention;

[0035] In the diagram, 1. Pump source, 2. Fiber isolator A, 3. Fiber wavelength division multiplexer B, 4. Er-doped single-clad fiber, 5. Fiber wavelength division multiplexer C, 6. LD, 7. Fiber isolator B, 8. Filter A, 9. Pump combiner, 10. Multimode LD, 11. Er / Yb co-doped double-clad fiber, 12. Fiber wavelength division multiplexer D, 13. Pump stripper, 14. Tm / Ho:YAG-SiO2 special fiber, 15. Fiber isolator C, 16. Filter B, 17. Fiber wavelength division multiplexer A, 18. Low reflectivity Bragg grating, 19. High reflectivity Bragg grating. Detailed implementation method:

[0036] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0037] Example 1

[0038] A special Tm / Ho:YAG-SiO2 optical fiber includes a core and an outer cladding, wherein the core is Tm / Ho:YAG and the outer cladding is SiO2.

[0039] Example 2

[0040] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber, such as Figure 1 As shown, it includes a pump source 1, an optical fiber wavelength division multiplexer A17, and a laser resonant cavity arranged along the optical path;

[0041] Pump source 1 uses a semiconductor LD with a center wavelength of 1550-1650nm. The laser resonant cavity is composed of a pair of fiber Bragg gratings, which include a low-reflectivity Bragg grating 18 and a high-reflectivity Bragg grating 19. The Tm / Ho:YAG-SiO2 special optical fiber 14 described in Example 1 is disposed between the low-reflectivity Bragg grating 18 and the high-reflectivity Bragg grating 19.

[0042] The length of Tm / Ho:YAG-SiO2 special optical fiber 14 is 1-3cm.

[0043] This invention uses a semiconductor LD as the pump source for a laser. Pump source 1 is a continuous pump source. A pair of fiber Bragg gratings form an ultrashort linear laser resonator. A 2μm single-frequency fiber laser is formed using Tm / Ho:YAG co-doped crystal-derived fiber as the gain medium. The Tm / Ho:YAG-SiO2 special fiber 14 is the gain medium that generates photons. Pump source 1 provides pump light, which acts as external energy to achieve population inversion in the gain medium. The laser resonator consists of a pair of fiber Bragg gratings, which provide feedback and amplify the photons in the working medium. After the pump light enters the Tm / Ho:YAG-SiO2 special fiber 14, it is absorbed, which causes population inversion in the gain medium. When the gain in the resonator is higher than the loss, laser oscillation is formed between the pair of fiber Bragg gratings, generating a laser signal output. This laser can provide high-power, high-quality 2μm laser light.

[0044] Example 3

[0045] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber has the structure described in Example 2. The difference is that the low-reflectivity Bragg grating 18 has a reflectivity of 60%-85%, and the high-reflectivity Bragg grating 19 has a reflectivity of not less than 95%. The low-reflectivity Bragg grating and the high-reflectivity Bragg grating form a resonant cavity, so that the gain fiber absorbs the pump energy and forms laser oscillation in the resonant cavity.

[0046] Example 4

[0047] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber is described in Example 3. The difference is that the center wavelengths of both the low-reflectivity Bragg grating and the high-reflectivity Bragg grating are 2015nm, resulting in 2015nm single-frequency laser output.

[0048] Example 5

[0049] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber has the structure described in Example 4. The difference is that an optical fiber isolator A2 (the center wavelength of the optical fiber isolator A2 is 1610nm), a first-stage amplification system, and a second-stage amplification system are arranged between the pump source 1 and the optical fiber wavelength division multiplexer A17. The first-stage amplification system includes an optical fiber wavelength division multiplexer B3, an Er-doped single-clad fiber 4, an optical fiber wavelength division multiplexer C5, and an optical fiber isolator B7. One port of the optical fiber wavelength division multiplexer C5 is connected to LD 6.

[0050] The secondary amplification system includes filter A8, pump combiner 9, Er / Yb co-doped double-clad fiber 11, fiber wavelength division multiplexer D12, pump stripper 13, fiber isolator C15, and filter B16. The pump combiner is connected to multimode LD 10.

[0051] The pump source 1 of this invention uses a semiconductor LD with a center operating wavelength of 1580nm. To prevent backlight damage to the LD, a fusion splice fiber isolator A2 is used. The first-stage amplification system uses forward pumping of the LD, with Er-doped single-clad fiber 4 as the gain fiber, connected through a fiber wavelength division multiplexer C5. Another fiber wavelength division multiplexer B3 separates the signal light from the remaining pump light. Finally, a fusion splice fiber isolator B7 is used for protection. To further optimize the signal-to-noise ratio of the signal light, a fusion filter A8 is used. The second-stage amplification system uses a (2+1)×1 pump combiner connected to a multimode LD 10, with the gain fiber being Er / Yb co-doped double-clad fiber. A pump stripper is connected to the end of the pump combiner to remove the remaining pump light. Because Yb... 3+ Ion doping can lead to spontaneous emission noise of about 1 μm, so a fiber wavelength division multiplexer (WDM) is used to remove Yb. 3+Noise generated by ions due to spontaneous emission; finally, the fusion filter B removes Er. 3+ Noise generated by ions at around 1.5μm; finally, the pump source output is fused to the reflector of fiber wavelength division multiplexer A, the low reflectivity fiber Bragg grating is fused to the common end, and the signal end is used as the output end.

[0052] Example 6

[0053] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber has the structure described in Example 5. The difference is that the wavelength of the single-frequency laser output by the 2μm single-frequency fiber laser is adjustable within the range of 1800nm-2300nm.

[0054] The output power of the single-frequency laser from the 2μm single-frequency fiber laser is adjustable from 1mW to 1W.

[0055] Example 7

[0056] A 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special fiber has the structure described in Example 5, except that the wavelengths of LD6 and multimode LD10 in the 2μm single-frequency fiber laser are around 970nm (970~990nm) and around 808nm (805~815nm), respectively.

[0057] Example 8

[0058] A method for fabricating a 2μm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber includes the following steps:

[0059] S1. Tm / Ho:YAG-SiO2 special optical fiber is fabricated using the fused core method;

[0060] S2. Fuse the semiconductor LD to phase A of the fiber optic isolator;

[0061] S3. The 1610nm laser output signal is amplified to 1000mW-1500mW through a first-stage amplification system;

[0062] S4. Fusion splice 1-3cm Tm / Ho:YAG-SiO2 special optical fiber between a pair of fiber Bragg gratings;

[0063] S5. Pump light is pumped into a laser resonant cavity composed of fiber Bragg gratings through fiber wavelength division multiplexer A, and then laser signal is output through the signal terminal.

[0064] This invention uses a semiconductor LD as a pump seed source and amplifies the laser to 1200mW-1500mW through an optical fiber amplification system. A special Tm / Ho:YAG-SiO2 optical fiber is fused between a pair of gratings with a center wavelength of 2μm. The pump light is input into the resonant cavity through an optical fiber wavelength division multiplexer A to generate a laser output signal.

[0065] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a 2 pm single-frequency fiber laser based on Tm / Ho:YAG-SiO2 special optical fiber, characterized in that, The laser comprises a pump source, a fiber wavelength division multiplexer A and a laser resonant cavity arranged along an optical path; The pump source is a semiconductor LD with a central wavelength of 1550-1650 nm, and the laser resonant cavity is composed of a pair of fiber Bragg gratings, including a low reflectivity Bragg grating and a high reflectivity Bragg grating, and a Tm / Ho:YAG-SiO2 special optical fiber is arranged between the low reflectivity Bragg grating and the high reflectivity Bragg grating, the special optical fiber comprises a core and an outer cladding, the core is Tm / Ho:YAG, and the outer cladding is SiO2. The reflectivity of the low reflectivity Bragg grating is 60%-85%, the reflectivity of the high reflectivity Bragg grating is not less than 95%, and the low reflectivity Bragg grating and the high reflectivity Bragg grating form a resonant cavity, so that the gain optical fiber absorbs pump energy to form laser oscillation in the resonant cavity. The length of the Tm / Ho:YAG-SiO2 special optical fiber is 1-3 cm. A fiber isolator A, a first-stage amplification system and a second-stage amplification system are arranged between the pump source and the fiber wavelength division multiplexer A, the first-stage amplification system comprises a fiber wavelength division multiplexer B, an Er-doped single-clad optical fiber, a fiber wavelength division multiplexer C and a fiber isolator B, and one port of the fiber wavelength division multiplexer C is connected with an LD; The second-stage amplification system comprises a filter A, a pump combiner, an Er / Yb co-doped double-clad optical fiber, a fiber wavelength division multiplexer D, a pump stripper, a fiber isolator C and a filter B, and the pump combiner is connected with a multimode LD. A preparation method comprises the following steps: S1. Drawing the Tm / Ho:YAG-SiO2 special optical fiber by using a fused core method; S2. Fusing the semiconductor LD with the fiber isolator A; S3. Amplifying the 1610 nm laser output signal to 1000 mW-1500 mW through the first-stage amplification system; S4. Fusing the 1-3 cm Tm / Ho:YAG-SiO2 special optical fiber between the pair of fiber Bragg gratings; S5. Pumping the pump light into the laser resonant cavity composed of the fiber Bragg gratings through the fiber wavelength division multiplexer A, and outputting the laser signal through a signal port.

2. The method of producing a 2 pm single-frequency fiber laser based on Tm / Ho:YAG-Si02 special optical fiber according to claim 1, characterized in that, The central wavelengths of the low reflectivity Bragg grating and the high reflectivity Bragg grating are both 1800 nm-2300 nm.

3. The method of producing a 2 pm single-frequency fiber laser based on Tm / Ho:YAG-Si02 special optical fiber according to claim 2, characterized in that, The wavelength of the single-frequency laser output by the 2μm single-frequency fiber laser is adjustable within 1800 nm-2300 nm. The output power of the single-frequency laser output by the 2μm single-frequency fiber laser is adjustable within 1 mW-1 W.

4. The method of producing a 2 pm single-frequency fiber laser based on Tm / Ho:YAG-Si02 special optical fiber according to claim 3, characterized in that, The wavelengths of the LD and the multimode LD in the 2μm single-frequency fiber laser are 970-990 nm and 805-815 nm.

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