A method of suppressing stimulated brillouin scattering in a single frequency fiber laser gain fiber

Abstract

The application discloses a method for inhibiting stimulated Brillouin scattering of a single-frequency fiber laser gain fiber, which comprises the following steps: stripping the coating layer of the gain fiber to obtain a bare fiber, wiping the bare fiber clean, and then positioning the two ends of the bare fiber by clamping the two ends of the bare fiber with a fiber clamp; heating the bare fiber by moving step by step according to a fixed length of moving interval from one end to the other end along the axial direction of the bare fiber; and increasing one or both of the temperature and the time of heating step by step after each movement, or decreasing one or both of the temperature and the time of heating step by step. The method for inhibiting stimulated Brillouin scattering of a single-frequency fiber laser gain fiber provided by the application can adjust the gradient distribution of the doped ions in the gain fiber by controlling the heating temperature, the heating time and the heating position direction parameters in a heat diffusion manner, and can broaden the Brillouin gain spectrum in the gain fiber while keeping the highest temperature of the gain fiber basically unchanged.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and specifically to a method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser. Background Technology

[0002] Continuous-frequency (CFF) lasers, due to their excellent coherence, stability, and monochromaticity, have broad application prospects in fields such as coherent combining, gravitational wave detection, lidar, imaging, and nonlinear frequency conversion. The maximum output power of a CFF fiber laser is primarily limited by the stimulated Brillouin scattering (SBS) effect in the fiber. The SBS effect leads to power instability, limiting the laser's output power and potentially causing mode hopping, thus affecting the laser's single-mode performance.

[0003] The maximum output power of continuous-frequency fiber lasers is primarily limited by the stimulated Brillouin scattering (SBS) effect in the fiber. Traditional methods for suppressing the SBS effect mainly include increasing the core diameter and reducing the effective fiber length. To obtain good beam quality, increasing the core diameter requires reducing the numerical aperture of the fiber, but traditional fiber manufacturing processes make it difficult to reduce the numerical aperture below 0.04. To ensure sufficient absorption of the pump light in the fiber, shortening the fiber length requires increasing the rare-earth ion doping concentration in the gain fiber. Increasing the doping concentration leads to a sharp increase in thermal effects in the gain fiber, hindering further increases in the fiber laser's output power. Phase and intensity modulation of the seed light can suppress the SBS effect in the fiber, but the modulated seed light spectrum exhibits significant broadening, which is detrimental to the output of single-frequency lasers. Photonic crystal fibers can reduce the numerical aperture of the fiber to below 0.03, but these fibers are particularly sensitive to bending, resulting in fiber lasers that are bulky, difficult to package, and susceptible to environmental interference.

[0004] To suppress stimulated Brillouin scattering (SBS) in the gain fiber of a single-frequency fiber laser, axially graded doped gain fiber is generally used. Existing methods typically involve first fabricating a graded-doped preform, followed by fiber drawing using a drawing tower. For example, Chinese Patent 202211717033.9 discloses a doped fiber fabrication system and method for increasing the SBS threshold. The system includes a fiber preform unit comprising a fiber preform and a heating furnace located circumferentially around the preform. However, this method suffers from time-consuming preform fabrication and drawing steps, resulting in a long production cycle. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser. This solves the technical problem that the existing gradient-doped gain fiber method has a long production cycle due to the time-consuming preform preparation and fiber drawing steps.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, comprising the following steps:

[0008] The coating layer of the gain fiber is stripped to obtain the bare fiber. The bare fiber is wiped clean and then positioned by clamping both ends of the bare fiber with a fiber clamp.

[0009] Heating is performed by moving the bare fiber gradually from one end to the other along the fiber axis at fixed intervals.

[0010] After each movement, gradually increase one or both of the heating temperature and time, or gradually decrease one or both of the heating temperature and time.

[0011] In some embodiments, the bare fiber heating employs a heating device with a heating temperature range of 1200-1650°C.

[0012] In some embodiments, the method further includes the step of setting a moving interval for each movement based on the width of the heating range of the heating device, wherein the moving interval is not less than half the width of the heating range and not greater than the width of the heating range.

[0013] In some embodiments, the heating device is an oxyhydrogen flame head.

[0014] In some embodiments, the heating width of the oxyhydrogen flame head is 15 mm, and the moving interval is set to 14 ± 0.5 mm.

[0015] In some embodiments, the heating device is a tungsten electrode heater.

[0016] In some embodiments, the heating width of the tungsten electrode heater is 8 mm, and the moving interval is set to 7.5 ± 0.1 mm.

[0017] In some embodiments, the heating device is a discharge electrode.

[0018] In some embodiments, the heating width of the discharge electrode is 0.1 mm, and the moving interval is set to 0.09 ± 0.01 mm.

[0019] In some embodiments, the fiber optic clamp includes two clamping ends, which respectively clamp the two ends of the bare fiber and form a void area for heating between the two clamping ends.

[0020] Compared with existing technologies, the method for suppressing stimulated Brillouin scattering (SBS) in the gain fiber of a single-frequency fiber laser provided by the present invention uses thermal diffusion to adjust the gradient distribution of doped ions in the gain fiber by controlling the heating temperature, heating time, and heating position and direction parameters. While keeping the maximum temperature of the gain fiber basically unchanged, it broadens the Brillouin gain spectrum in the gain fiber, increases the SBS threshold in the fiber, and reduces the SBS effect in the gain fiber. It eliminates the need for preform preparation and fiber drawing steps, simplifies the operation, and shortens the production cycle. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser provided in an embodiment of the present invention, using an oxyhydrogen flame head;

[0022] Figure 2 This is a schematic diagram of a method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, provided in an embodiment of the present invention, using a tungsten electrode heated element.

[0023] Figure 3 This is a schematic diagram of the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser provided in an embodiment of the present invention, using a discharge electrode;

[0024] Figure 4 This is a schematic diagram of the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser provided in an embodiment of the present invention, using the movement of an oxyhydrogen flame head.

[0025] Figure 5 This is a schematic diagram illustrating the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser provided in this embodiment of the invention, using a tungsten electrode heated to move a quantum.

[0026] Figure 6 This is a schematic diagram illustrating the movement of the discharge electrode in the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser provided in an embodiment of the present invention.

[0027] Figure 7 This is a schematic diagram showing the gradient distribution of doped ions in the bare fiber core of the method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, as provided in an embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1. Bare fiber; 2. Fiber optic clamp; 21. Clamping end; 22. Empty area; 3. Hydrogen-oxygen flame head; 4. Tungsten electrode heater; 5. Discharge electrode. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] To address the technical problem of long production cycles caused by the time-consuming preform preparation and fiber drawing steps in existing gradient doped gain fiber methods, this invention provides a method for suppressing stimulated Brillouin scattering in single-frequency fiber laser gain fibers. This method eliminates the need for preform preparation and fiber drawing steps, simplifies operations, and shortens the production cycle.

[0032] Please see Figure 1-7 This invention provides a method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, comprising the following steps:

[0033] The coating layer of the gain fiber is stripped to obtain bare fiber 1. The bare fiber 1 is wiped clean with lint-free paper, and then the two ends of the bare fiber 1 are clamped by fiber clamp 2 for positioning.

[0034] Start the heating device to heat bare fiber 1;

[0035] The heating device is moved gradually along the axis of the bare fiber 1 from one end to the other, according to a fixed length of moving interval;

[0036] After each movement, gradually increase one or both of the heating temperature and time, or gradually decrease one or both of the heating temperature and time.

[0037] In this process, the heating temperature or heating time is gradually increased after each movement. The higher the heating temperature, the faster the diffusion rate of doped ions from the fiber core to the cladding; the longer the heating time, the greater the number of doped ions diffusing from the fiber core to the cladding. As the heating process continues, the concentration of doped ions in the core of bare fiber 1 gradually decreases from right to left or from left to right, exhibiting a gradient distribution along the axis of bare fiber 1. The frequency shift of Stokes light in the SBS effect is directly related to the temperature in the optical fiber. The gradient doping achieved by this invention can make the temperature in the gain fiber periodically distributed along the fiber axis. While keeping the maximum temperature of the gain fiber basically unchanged, it can broaden the Brillouin gain spectrum in the gain fiber, increase the SBS threshold in the fiber, and reduce the SBS effect in the gain fiber.

[0038] Furthermore, in order to effectively form the dopant in the fiber core to diffuse radially during heating, the heating temperature range of the heating device is between 1200-1650℃. When the optical fiber is heated at a high temperature above 1200℃, the dopant in the fiber core will diffuse radially, that is, the dopant in the fiber core will diffuse into the cladding. In addition, the heating temperature is set below 1650℃ to avoid structural changes and performance degradation caused by excessively high temperatures.

[0039] Furthermore, in order to clamp the bare optical fiber 1 during heating and reserve an uninterrupted heating space, the optical fiber clamp 2 includes two clamping ends, which respectively clamp the two ends of the bare fiber 1 and form an empty area for heating between the two clamping ends, thus clamping both ends of the bare fiber 1 and reserving an empty area for heating and movement of the heating device.

[0040] Furthermore, in order to avoid excessive overlap during heating, which could affect the formation of the gradient, this method also includes the following steps: setting the movement interval for each movement according to the width of the heating range of the heating device, wherein the movement interval is not less than half the width of the heating range and not greater than the width of the heating range.

[0041] Understandably, the heating interval setting should match the heating width of the heating device. If the moving interval is set too large, exceeding the heating width, then adjacent heating zones will not be affected by heating, and the doped ions will not decrease in a gradient along the optical fiber. If the moving interval is too small, less than half the heating width, then the overlap between adjacent heating zones will be too large, and the overlapped portion will be affected by heating twice, resulting in the doped ions not decreasing in a gradient along the optical fiber.

[0042] Example 1

[0043] Based on this method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, please refer to [link / reference needed]. Figure 1 and Figure 4 The heating device employs an oxyhydrogen flame head 3 with a heating width of 15 mm and a moving interval of 14 ± 0.5 mm. The bare fiber 1 is heated to a temperature range of 1200-1650℃. Heating is performed at a fixed point, followed by moving the flame head a certain distance before resuming heating. Its relatively wide heating width is suitable for gradient diffusion of doped ions in longer gain optical fibers. (Appendix) Figure 4 The middle arrow indicates either a gradual movement from left to right or from left to right to left, one of two options. The heating temperature is gradually increased.

[0044] As the heating process continues, the concentration of doped ions in the core of bare fiber 1 gradually decreases or increases from right to left, such as Figure 7 As shown, a gradient distribution is observed along the axis of bare fiber 1.

[0045] Example 2

[0046] Based on this method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, please refer to [link / reference needed]. Figure 2 and Figure 5 The heating device employs a tungsten electrode heater 4 with a heating width of 8 mm and a moving interval of 7.5 ± 0.1 mm. The bare fiber 1 is heated to a temperature range of 1200-1650℃. Heating is performed at a fixed point, followed by moving the element a certain distance before resuming heating. Its relatively wide heating width is suitable for gradient diffusion of doped ions in medium-length gain optical fibers. (Appendix) Figure 5 The middle arrow indicates either moving gradually from left to right or from left to right to left, choose one. The heating time will be gradually increased.

[0047] As the heating process continues, the concentration of doped ions in the core of bare fiber 1 gradually decreases or increases from right to left, such as Figure 7 As shown, a gradient distribution is observed along the axis of bare fiber 1.

[0048] Example 3

[0049] Based on this method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, please refer to [link / reference needed]. Figure 3 and Figure 6 The heating device employs a discharge electrode 5 with a heating width of 0.1 mm and a moving interval of 0.09 ± 0.01 mm. The bare fiber 1 is heated to a temperature range of 1200-1650℃. Heating is performed at a fixed point, followed by moving the electrode a certain distance before resuming heating. Its relatively wide heating width makes it suitable for gradient diffusion of doped ions in shorter gain fibers. (Appendix) Figure 6 The middle arrow indicates either a gradual movement from left to right or from left to right to left, one of two options. The heating temperature will gradually decrease.

[0050] As the heating process continues, the concentration of doped ions in the core of bare fiber 1 gradually decreases or increases from right to left, such as Figure 7 As shown, a gradient distribution is observed along the axis of bare fiber 1.

[0051] Example 4

[0052] Based on this method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, please refer to [link / reference needed]. Figure 3 and Figure 6The heating device employs a discharge electrode 5 with a heating width of 0.1 mm and a moving interval of 0.09 ± 0.01 mm. The bare fiber 1 is heated to a temperature range of 1200-1650℃. Heating is performed at a fixed point, followed by moving the electrode a certain distance before resuming heating. Its relatively wide heating width makes it suitable for gradient diffusion of doped ions in shorter gain fibers. (Appendix) Figure 6 The middle arrow indicates either a gradual movement from left to right or from left to right to left, one of two options, and a gradual increase in heating temperature.

[0053] As the heating process continues, the concentration of doped ions in the core of bare fiber 1 gradually decreases or increases from right to left, such as Figure 7 As shown, a gradient distribution is observed along the axis of bare fiber 1.

[0054] In the above embodiments, the heating precision discharge electrode 5 > tungsten electrode heater 4 > oxyhydrogen flame head 3. By selecting heating methods with different precision, a gradual distribution of doped ion gradients can be achieved in gain fibers of different lengths. By controlling parameters such as heating temperature, heating time, and heating position and direction, the gradual distribution of doped ion gradients in the gain fiber can be adjusted, either rapidly decreasing or increasing, or gradually decreasing or increasing, along the gain fiber axis.

[0055] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser, characterized in that, Includes the following steps: The coating layer of the gain fiber is stripped to obtain the bare fiber. The bare fiber is wiped clean and then positioned by clamping both ends of the bare fiber with a fiber clamp. Heating is performed by moving the bare fiber gradually from one end to the other along the fiber axis at fixed intervals. After each movement, gradually increase one or both of the heating temperature and time, or gradually decrease one or both of the heating temperature and time. It also includes the following steps: setting the movement interval for each movement according to the width of the heating range of the heating device, wherein the movement interval is not less than half the width of the heating range and not greater than the width of the heating range; The bare fiber heating is performed using a heating device with a heating temperature range of 1200-1650℃.

2. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 1, characterized in that, The heating device is an oxyhydrogen flame head.

3. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 2, characterized in that, The heating width of the hydrogen-oxygen flame head is 15mm, and the moving interval is set to 14±0.5mm.

4. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 1, characterized in that, The heating device is a tungsten electrode heater.

5. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 4, characterized in that, The heating width of the tungsten electrode heater is 8 mm, and the moving interval is set to 7.5 ± 0.1 mm.

6. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 1, characterized in that, The heating device is a discharge electrode.

7. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 6, characterized in that, The heating width of the discharge electrode is 0.1 mm, and the moving interval is set to 0.09 ± 0.01 mm.

8. The method for suppressing stimulated Brillouin scattering in the gain fiber of a single-frequency fiber laser according to claim 1, characterized in that, The fiber optic clamp includes two clamping ends, which respectively clamp the two ends of the bare fiber, and form an empty area for heating between the two clamping ends.

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